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soukacatv · 5 years ago

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Digital Modulation and Demodulation Formats -- Managing Modulation and Demodulation | Soukacatv.com

Digital modulation/demodulation formats provide options in terms of bandwidth efficiency, power efficiency, and complexity/cost when meeting a modern communications system’s data-transfer needs.

Modulation and demodulation provide the means to transfer information over great distances. As noted in the first part of this article (see “Basics of Modulation and Demodulation”), analog forms of modulation and demodulation have been around since the early days of radio. Analog approaches directly encode information from changes in a transmitted signal’s amplitude, phase, or frequency. Digital modulation and demodulation methods, on the other hand, use the changes in amplitude, phase, and frequency to convey digital bits representing the information to be communicated.

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With growing demands for voice, video, and data over communications networks of all kinds, digital modulation and demodulation have recently replaced analog modulation and demodulation methods in wireless networks to make the most efficient use of a limited resource: bandwidth. In this second part, we explore how some higher-order modulation and demodulation formats are created, and how software and test equipment can help to keep different forms of modulation and demodulation working as planned.

Enhancing Efficiency

Efficiency is a common goal of all modulation/demodulation methods, whether they involve conserving bandwidth, power, or cost. Digital modulation/demodulation formats, in particular, have been found able to transfer large amounts of information with minimal bandwidth and power. While increased data capacity tends toward increased complexity in digital modulation/demodulation, high levels of integration in modern ICs have made possible communications systems capable of reliable, cost-effective operation with even the most advanced digital modulation/demodulation formats.

Reasonable bandwidth efficiency is possible with standard digital modulation formats, such as amplitude-shift keying (ASK), frequency-shift keying (FSK), and phase-shift keying (PSK). By executing additional variations, more complex digital modulation formats can be created with improved data capacity and bandwidth efficiency, as measured in the number of digital bits that can be transferred in a given amount of time per unit amount of bandwidth (b/s/Hz).

For example, with minimum-shift keying (MSK), essentially a form of FSK, peak-to-peak frequency deviation is equal to one-half the bit rate. A further variation of MSK is Gaussian MSK (GMSK), in which the modulated signal passes through a Gaussian filter to minimize instantaneous frequency variations over time and reduce the amount of bandwidth occupied by the transmitted waveforms. GMSK maintains a constant envelope and provides good bit-error-rate (BER) performance in addition to its good spectral efficiency.

By applying some small changes, it is also possible to improve power efficiency. Quadrature PSK (QPSK) is basically a four-state variation of simple PSK. It can be modified in different ways—e.g., offset QPSK (OQPSK)—to boost efficiency. In QPSK, the in-phase (I) and quadrature (Q) bit streams are switched at the same time, using synchronized digital signal clocks for precise timing. A given amount of power is required to maintain the timing alignment.

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In OQPSK, the I and Q bit streams are offset by one bit period. Unlike QPSK, only one of the two bit streams can change value at any one time in OQPSK, which also provides benefits in terms of power consumption during the bit switching process. The spectral efficiency, using two bit streams, is the same as in standard QPSK, but power efficiency is enhanced due to reduced amplitude variations (by not having the amplitudes of both bit streams passing at the same time). OQPSK does not have the same stringent demands for linear amplification as QPSK, and can be transmitted with a less-linear, more-power-efficient amplifier than required for QPSK.

The Role of Filtering

The bandwidth efficiency of a modulation/demodulation format can be improved by means of filtering, removing signal artifacts that can cause interference with other communications systems. Various types of filters are used to improve the spectral efficiency of different modulation formats, including Gaussian filters (with perfect symmetry of the rolloff around the center frequency); Chebyshev equiripple, finite-impulse-response (FIR) filters; and lowpass Nyquist filters (also known as raised-cosine filters, since they pass nonzero bits through the frequency spectrum as basic cosine functions).

The goal of filtering is to improve spectral efficiency and reduce interference with other systems, but without degrading modulation waveform quality. Excessive filtering can result in increased BER due to a blurring of transmitted symbols that comprise the data stream of a digital modulation format. Known as intersymbol interference (ISI), this loss in integrity of the symbol states (phase, amplitude, frequency) make it difficult to decode the symbols at the demodulator and receiver in a digitally modulated communications system.

An ideal filter is often referred to as a “brickwall” filter for its instant changeover from a passband to a stopband. In reality, filters do not provide an ideal reduction in signal bandwidth due to the need for some amount of transition between a filter passband and its stopband; longer transitions require more bandwidth.

Filters for digital modulation/demodulation applications are regularly characterized by a parameter known as “alpha,” which provides a measure of the amount of occupied bandwidth by a filter. For example, a “brickwall” filter, with instant transition from stopband to passband, would have an alpha value of zero. Filters with longer transitions will maintain larger values of alpha. Smaller values of filter alpha result in increased ISI, because more symbols can contribute to the interference.

Modeling and Measuring

A wide range of suppliers offer modulators and demodulators in various formats, from highly integrated ICs to discrete components. A number of those highly integrated transceiver ICs can be used for both functions—as transmitters/modulators and receivers/demodulators. Some are even based on software-defined-radio (SDR) architectures with sufficient bandwidths to serve multiple wireless communications standards and modulation/demodulation requirements.

Modeling software helps simplify the determination of requirements for a communications system’s modulation/demodulation scheme. Some software programs provide general-purpose modulation/demodulation analysis capabilities, allowing users to predict the results of using different analog and digital modulation schemes. For example, the Modulation Toolkit (Fig. 1) from National Instruments works with the firm’s popular LabVIEW design software to simulate communications systems based on different analog and digital modulation/demodulation formats. The software makes it possible to experiment with different variables, such as carrier frequency, signal strength, and interference; and predict different performance parameters, such as BER, bandwidth efficiency, and power efficiency, under different operating conditions.

In contrast, S1220 software from RIGOL Technologies USA simulates ASK and FSK demodulation, in particular for Internet of Things (IoT) applications (Fig. 2). The software teams with the company’s spectrum analyzers to study modulation/demodulation over a carrier frequency range of 9 kHz to 3.2 GHz (and to 7.5 GHz with options). It provides an ASK symbol rate measurement range of 1 to 100 kHz and FSK deviation measurement range of 1 to 400 kHz.

Test instruments are an important part of achieving good modulation/demodulation performance. Numerous test-equipment suppliers offer programmable signal generators, such as arbitrary waveform generators, that can create different modulation formats to be used with or without a carrier signal generator for emulating modulated test signals. Spectrum analyzers provide windows to the modulation characteristics of waveforms within their frequency ranges. And some specialized measurement instruments have been developed for the purpose of testing modulation and demodulation and associated components, such as modulation domain analyzers (MDAs).

A number of different display formats provide ways to visualize modulated signals—with both signal analyzers and software—including constellation diagrams, eye diagrams, polar diagrams, and trellis diagrams (for trellis modulation). For example, separate eye diagrams can be used to show the magnitude versus time characteristics of two separate I and Q data channels, with I and Q transitions appearing as “eyes” on a computer or instrument display screen. Different modulation formats will show as different types of displays; for instance, QPSK will appear as four distinct I/Q states, one in each quadrant of the display screen. A high-quality signal creates eyes that are open at each symbol.

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Company: Dingshengwei Electronics Co., Ltd

Address: Bldg A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Mobile: 13410066011

Email: [email protected]

Source: mwrf

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Pulse Width Modulation (PWM) Controllers Market 2019 Global Demand and Scope – Analog Devices | Soukacatv.com

Global Pulse Width Modulation (PWM) Controllers Market 2018 by Manufacturers, Regions, Type and Application, Forecast to 2023 details the summary and describes the Product/Industry scope within the market. The report also discusses the market review and forecast to 2023. As per several market studies being conducted by Fior Markets, it is evident that the Pulse Width Modulation (PWM) Controllers Market is growing at a very fast pace. The rising industrial advancements market is expected to flourish the growth of the market over the forecast period.

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The report aims to change the dynamics of the Market Research industry by providing quality intelligence backed by data. Readers’ requirement for market forecasting is fulfilled by our exclusive quantitative and analytics driven intelligence. Decision makers can now rely on our distinct data gathering methods to get factual market forecasting and detailed analysis.

In addition to the charts and analysis, marketing decision makers from companies and retailers offer their individual candid advice, as the words of wisdom from their peers all designed to help readers marketing efforts.

The report helps its clients to address their evolving business needs with personalized solutions. These valuable insights can additionally help the clients form revenue generating business policies and build a sustainable growth model.

Geographically, the global big data market report has been segmented in key regions involving North America (United States, Canada and Mexico), Europe (Germany, France, UK, Russia and Italy), Asia-Pacific (China, Japan, Korea, India and Southeast Asia), South America (Brazil, Argentina, and Colombia etc.), Middle East and Africa (Saudi Arabia, UAE, Egypt, Nigeria and South Africa). These regions held the largest market revenue share for Pulse Width Modulation (PWM) Controllers market in 2016 and is expected to dominate during forecast period due to high adoption of analytics across the countries. However, the few countries are expected to register highest growth rate during forecast period due to increasing amount of demands as well as high availability of supply in the regions.

Readers can benefit:

· Market Overview.

· Market Competition by Manufacturers.

· Supply (Production), Consumption, Export, Import by Region.

· Capacity, Production, Revenue (Value) by Region.

· Industry Effect Factors Analysis.

· Manufacturers Profiles/Analysis.

· Manufacturing Cost Analysis.

· Market Forecast 2018-2022.

· Industrial Chain, Sourcing Strategy and Downstream Buyers.

The report also focuses on the importance of the industry chain analysis and all variables, both upstream and downstream. These include equipment and raw materials, industry trends, client surveys, propels, marketing channels, major and most demanding types and applications Consumer Electronics, Telecommunication, Automotive, Industrial, Other. Some of the other critical data covering consumption, raw material suppliers, and key regions and distributors and suppliers are also mentioned in this report.

The Global Pulse Width Modulation (PWM) Controllers Market consists of data accumulated from numerous primary and secondary sources. This information has been verified and validated by the industry analysts, thus providing significant insights to the researchers, analysts, managers, other industry professionals and key players Analog Devices (Linear Technology), Texas Instruments, STMicroelectronics, ON Semiconductor, Microchip Technology, Maxim Integrated, Infineon Technology, Vishay, Diodes Incorporated, Renesas Electronics, Semtech, Active-Semi.

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Nonetheless, the surplus amount invested is then employed for making investments which are helpful for earning a higher profit for the policyholders. It is gaining prominence in the major countries and endeavoring to meet the growing need to impart quality deployment.

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Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source: bizztribune

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soukacatv · 5 years ago

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What’s Amplitude Modulation (AM)? Amplitude Modulation History and Its Applications | Soukacatv.com

Amplitude Modulation or AM as it is often called is an electronic communication systems technique wherein the baseband signal is superimposed with the amplitude of the carrier wave i.e. the amplitude of the carrier wave varies with proportion to the base waveform that is being transmitted. Amplitude Modulation has been in use since the earliest days of radio technology. One of the main reasons for the use of amplitude modulation was its ease of use. The system mainly required the carrier amplitude to be modulated, additionally; the detector required in the receiver could be a simple diode-based circuit. This meant that complicated demodulators weren’t required and as a result, the costs were reduced – a key requirement for the use of radio technology in the early days when ICs weren’t available.

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What is Amplitude Modulation (AM)?

When an amplitude modulated signal is created, the amplitude of the created signal represents the original baseband signal to be transmitted. This amplitude forms an envelope over the underlying high-frequency carrier wave. Here, the overall envelope of the carrier is modulated to carry the audio signal. AM is the simplest way of modulating a signal. In short, amplitude modulation is defined as the modulation in which the amplitude of the carrier wave is varied in accordance with some characteristic of the modulating signal.

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Amplitude Modulation History

The first recorded instance of amplitude modulation of the baseband wave harks back to 1901 when a Canadian man Reginald Fessenden used a continuous spark transmission to create the first amplitude modulation ever. Into this continuous spark transmission, he puts a carbon microphone in the antenna lead. The sound waves impacting on the microphone varied its resistances and this, in turn, varied the intensity of the transmission.

Though the accuracy and the signal-to-noise ratio in this earlier method of transmission were very low, with the advent of a continuous sine wave generator, the audio quality was greatly improved. This led to Amplitude modulated waves becoming the standard for voice transmission.

Amplitude Modulation Formula

Amplitude Modulation expression is given by:

s(t)=[Ac+Amcos(2πfmt)]cos(2πfct)

Where,

Am is the amplitude of the modulating signal

Ac is the amplitude of the carrier signal

fm is the frequency of the modulating signal

fc is the frequency of the carrier signal

Amplitude Demodulation

Demodulation or detection is a process where the signal that is a mixture of the amplitude of the baseband signal and the frequency of the carrier signal, is deconstructed to yield the original signal that is to be transmitted. Simply, it is the recovery of the modulating signal from the modulated wave.

Detection of Amplitude Modulated Wave (Demodulation)

The amplitude modulation and demodulation are equally simple to perform. The amplitude modulated signal needs just a simple diode detector circuit to demodulate. The diode rectifies the incoming signal, allowing only one-half of the signal waveform to pass through. The capacitor then is used to remove the radio frequency parts of the signal, leaving just the original waveform. As you see, the equipment for demodulation is very cheap, and this enables the cost of the receivers to be kept low.

Thus, amplitude modulated wave can be demodulated in two steps:

Rectification of modulated wave

Elimination of the RF component of the modulated wave

Advantages and Disadvantages of Amplitude Modulation

Given below in a tabular column are the various advantages and disadvantages of amplitude modulation.

Advantages

It can be demodulated using a circuit with fewer components.

It is easy to implement.

AM receivers are cheap and there is no requirement of specialized components.

Disadvantages

It is not efficient in terms of its use of bandwidth, requiring a bandwidth equal to twice of the highest audio frequency.

Not efficient in terms of power usage.

Prone to high levels of noise as most noise is amplitude based and AM detectors are sensitive to it.

Applications of Amplitude Modulation

With the improvement of the technology, the uses of amplitude modulation waves has become somewhat less prevalent, nevertheless it can still be found playing an important role in;

Broadcast Transmission: AM is still widely used for broadcasting either long or medium or short wave bands. The received signal is simple to break down into the baseband signal and hence the equipment cost to the user is very little and it is easy to manufacture

Air band Radio: The use of AM in the aerospace industry is widespread. The VHF (Very High Frequency) transmissions made by the airborne equipment still use AM. The radio contact between ground to air and also ground to ground use AM signals.

Quadrature Amplitude Modulation: Believe it or not, AM is used in the transmission of data of pretty much everything, from short range transmissions such as Wi-Fi to cellular communications and etc. Quadrature amplitude modulation is formed by mixing two carriers that are out of phase by 90o.

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The need for modulation was sky high and the invention of Amplitude modulation has changed the way in which we communicate.

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Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source: byjus

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soukacatv · 5 years ago

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Pulse Width Modulation (PWM) Controllers Market: 2019 Worldwide Opportunities | Soukacatv.com

The Pulse Width Modulation (PWM) Controllers market report analysis series and provides a comprehensive insight into the global Pulse Width Modulation (PWM) Controllers channel. It analyses the market, the major players, and the main trends, strategies for success and consumer attitudes. It also provides forecasts to 2024.

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About Pulse Width Modulation (PWM) Controllers Industry

The overviews, SWOT analysis and strategies of each vendor in the Pulse Width Modulation (PWM) Controllers market provide understanding about the market forces and how those can be exploited to create future opportunities.

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Key Players in this Pulse Width Modulation (PWM) Controllers market are:

Analog Devices (Linear Technology)

Texas Instruments

STMicroelectronics

ON Semiconductor

Microchip Technology

Maxim Integrated

Infineon Technology

Vishay

Diodes Incorporated

Renesas Electronics

Semtech

Active-Semi

Production Analysis: SWOT analysis of major key players of Pulse Width Modulation (PWM) Controllers industry based on Strengths, Weaknesses, company’s internal & external environments. Opportunities and threats. It also includes Production, Revenue, and average product price and market shares of key players. Those data are further drilled down with Manufacturing Base Distribution, Production Area and Product Type. Major points like Competitive Situation and Trends, Concentration Rate Mergers & Acquisitions, Expansion which are vital information to grow/establish a business is also provided.

Product Segment Analysis of the Pulse Width Modulation (PWM) Controllers Market is:

Product Type Segmentation

Current Mode PWM Controllers

Voltage Mode PWM Controllers

Industry Segmentation

Consumer Electronics

Telecommunication

Automotive

Industrial

Channel (Direct Sales, Distributor) Segmentation

The scope of Pulse Width Modulation (PWM) Controllers Market report:

Global market size, supply, demand, consumption, price, import, export, macroeconomic analysis, type and application segment information by region, including:

Global (Asia-Pacific [China, Southeast Asia, India, Japan, Korea, Western Asia]

Europe [Germany, UK, France, Italy, Russia, Spain, Netherlands, Turkey, Switzerland]

North America [United States, Canada, Mexico]

Middle East & Africa [GCC, North Africa, South Africa],

South America [Brazil, Argentina, Columbia, Chile, Peru])

Industry chain analysis, raw material and end users information

Global key players’ information including SWOT analysis, company’s financial figures, Laser Marking Machine figures of each company are covered.

Powerful market analysis tools used in the report include: Porter’s five forces analysis, PEST analysis, drivers and restraints, opportunities and threatens.

Based year in this report is 2019; the historical data is from 2014 to 2018 and forecast year is from 2020 to 2024.

Table Content of Pulse Width Modulation (PWM) Controllers Market Research Report

This report covers definition, development, market status, geographical analysis of Pulse Width Modulation (PWM) Controllers market.

Competitor analysis including all the key parameters of Pulse Width Modulation (PWM) Controllers market

Market estimates for at least 7 years

Market Trends (Drivers, Constraints, Opportunities, Threats, Challenges, Investment Opportunities, and proposals)

Strategic proposals in key business portions dependent available estimations

Company profiling with point by point systems, financials, and ongoing improvements

Mapping of the most recent innovative headways and Supply chain patterns

In this study, the years considered to estimate the market size of Pulse Width Modulation (PWM) Controllers Market are as follows:-

History Year: 2013-2017

Base Year: 2018

Estimated Year: 2019

Forecast Year 2019 to 2024

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Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source: thescrippsvoice

#Digital modulatorDigital modulator manufacturerDigital modulator supplierChina Digital modulator manufactureranalog modulator16in1 digital h

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Modulating 5G -- 5G are Hybrids of QAM and OFDM Modulation Principles | Soukacatv.com

The IoT will make heavy use of fifth-generation mobile networks that use a yet-to-be-determined modulation scheme. Here are the major contenders.

Fifth-generation mobile networks, abbreviated 5G, will form the telecommunications standards for the internet of things. Planners say 5G will have a higher capacity than the current 4G equipment partly to support the device-to-device, ultra reliable, and massive machine communications expected to help define the IoT of the future. Among the goals of 5G: lower latency than 4G equipment and lower battery consumption, data rates of tens of megabits per second for tens of thousands of users, several hundreds of thousands of simultaneous connections available for wireless sensors, along with better spectral signaling efficiency.

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The better spectral efficiency will partly be a function of the modulation schemes used in 5G. However, those modulation schemes have yet to be standardized. There are several contenders, and derivatives of the same quadrature-style schemes in use by mobile networks today haven’t been ruled out for 5G. So it is interesting to review the major modulation techniques now up for consideration as part of 5G.

Techniques discussed for 5G tend to use multiple carriers as a means of obtaining spectral efficiency. At present, 4G LTE uses QAM (quadrature amplitude modulation) with OFDM (orthogonal frequency division multiplexing) as modulation and OFDMA (OFDM multiple access) as access scheme. 5G will provide a high bit rate so it will need to make efficient use of the spectrum. Several of the ideas proposed for 5G are hybrids of QAM and OFDM principles.

Firstly, Quadrature techniques represent a transmitted symbol as a complex number and modulate a cosine and sine carrier signal with the real and imaginary parts. This lets the symbol be sent with two carriers. The two carriers are generally referred to as quadrature carriers. A coherent detector can independently demodulate these carriers. This principle of using two independently modulated carriers is the foundation of quadrature modulation.

Quadrature amplitude modulation conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme o+r amplitude modulation (AM) analog modulation scheme. The two carrier waves of the same frequency are out of phase with each other by 90° and are thus called quadrature carriers. The modulated waves are summed, and the final waveform is a combination of both phase-shift keying (PSK) and amplitude-shift keying (ASK), or, in the analog case, of phase modulation (PM) and amplitude modulation.

QAM conveys information by modulating the amplitudes of the two carrier waves, using either amplitude-shift keying (ASK) for digital data or straight amplitude modulation for analog. The two carrier waves of the same frequency, usually sinusoids, are out of phase with each other by 90°. The modulated waves are summed, and the final waveform is a combination of both phase-shift keying (PSK) and amplitude-shift keying (ASK).

QAM is said to be spectrally efficient, and the reason becomes clear by comparing a QAM signal with that of an ordinary AM’ed carrier. A straight amplitude-modulated signal has two sidebands. The carrier plus the sidebands occupy twice the bandwidth of the modulating signal. In contrast, QAM places two independent double-sideband suppressed-carrier signals in the same spectrum as one ordinary double-sideband suppressed-carrier signal.

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QAM can give arbitrarily high spectral efficiencies by setting a suitable constellation size. As a quick review, a constellation diagram represents the signal as a scatter diagram in the Q and I axes and represents the possible symbols as points on the plane. The more symbols defined in the modulation scheme, the more points on the constellation diagram. The number of points at which the signal can rest, i.e. the number of symbols, is indicated in the modulation format description: 16QAM uses a 16-point constellation, and so forth.

Constellation points are normally arranged in a square grid with equal vertical and horizontal spacing. Use of higher-order modulation formats, i.e. more points on the constellation, makes it possible to transmit more bits per symbol. However, use of higher-order symbols positions constellation points closer together, making the link more susceptible to noise. Specifically, it takes less noise to move the signal to a different decision point on the constellation diagram.

A point to note about QAM is that it is considered a single-carrier system. The two digital bit streams come from one source that is split into two independent signals.

QAM signals are often sent via multi-carrier modulation schemes that transmit one QAM signal over one of several subcarriers. The point of doing this is to simplify the task of compensating for distortions arising in the communication channel. Each of the subcarriers has a small bandwidth. The communication channel has a relatively flat frequency response over each of these small bands. So it is relatively easy to compensate for distortions over each of the small subcarrier bands.

In OFDM, many closely spaced orthogonal sub-carriers carry data on several parallel data streams or channels. Each sub-carrier is modulated with a conventional modulation scheme such as QAM at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.

The primary advantage of OFDM over using a single carrier is its ability to cope with severe interference as caused by RF sources at nearly the same frequency or frequency-selective fading from multipath. OFDM may be viewed as using many slowly modulated narrowband signals rather than one rapidly modulated wideband signal. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to eliminate inter-symbol interference (ISI) and use echoes and time-spreading to improve signal-to-noise.

The orthogonality of OFDM comes from the selection of the sub-carrier frequencies so they are orthogonal to each other. This basically means the spectrum space between sub-carriers obeys a mathematical relationship where it is inversely proportional to the symbol duration. Sub-carriers spaced this way don’t experience any cross-talk and thus eliminate the need for inter-carrier guard bands, simplifying the design of both the transmitter and the receiver.

There are a few inherent difficulties with OFDM. One is that an OFDM signal can have a high instantaneous peak compared to its average level. There can also be a large signal amplitude swing when the signal traverses from a low to a high instantaneous power. The power amp used must be linear over a wide bandwidth to prevent a high out-of-band harmonic distortion. This phenomenon can potentially interfere with adjacent channels.

Other difficulties arise with the time and frequency synchronization between the OFDM transmitter and receiver. Numerous techniques have been proposed for estimating and correcting both timing and carrier frequency offsets at the OFDM receiver. For example, one idea is to embed pilot tones into OFDM symbols, then use timing and frequency acquisition algorithms to sync on them.

HYBRID SCHEMES FOR 5G

Several of the modulation schemes under review for 5G are hybrids employing elements found in QAM and OFDM. One is called F-QAM or FSK-QAM. F-QAM is a combination of QAM and frequency shift keying (FSK). It has been proposed in conjunction with OFDMA, the multi-user version of OFDM where individual users are assigned subsets of subcarriers.

F-QAM combines MF-FSK (multiple frequency FSK) and MQ-QAM (multiple QAM modulation levels). F-QAM has many similarities with OFDM-IM (OFDM with index modulation). In both cases the information is not only conveyed through the modulated symbols but also via the indices of the active subcarriers. At the receiver side, the detection process is similar to that of the OFDM-IM. The receiver employs what’s called a log-likelihood-ratio (LLR) detector to determine the active subcarrier in each sub-block and, afterwards, estimates the received symbols using a maximum likelihood (ML) detector.

One drawback of current OFDMA schemes is that they require accurate synchronization of the user signals at the base station. Such synchronization is not straightforward and demands a lot of resources. So a lot of the work on 5G aims at a way around this base station syncing. One idea from AlcatelLucent Bell Labs is a modified OFDM waveform dubbed universal filtered multicarrier (UFMC). UFMC passes each bundle of adjacent subcarriers that belong to a user through a filter to minimize multi-user interference. Bandwidth efficiency is kept at the same level as OFDM, but UFMC uses no cyclic prefix (CP). The interval the CP normally occupies instead absorbs the transient of the underlying filters, making the filtering more effective.

Generalized frequency division multiplexing (GFDM) is another candidate waveform. GFDM may be thought of as a modified OFDM, where each subcarrier is shaped by a high-quality filter. To allow the addition of the CP, the subcarrier filtering operation in GFDM is based on a circular convolution.

Another 5G contender is based on filter bank multicarrier with offset QAM (FBMC-OQAM). FBMCs employ two sets of band pass filters called analysis and synthesis filters, one at the transmitter and the other at the receiver, to filter the collection of subcarriers being transmitted simultaneously in parallel frequencies. FBMC filter bandwidth, and therefore selectivity, is a parameter that can be varied during design. FBMC also offers better bandwidth efficiency when compared to OFDM. FBMC eliminates the need for CP processing while efficiently attenuating interferences within and close to the frequency band. FBMC systems are also comparatively more resistant to narrowband noise.

OTHER IDEAS

Though multi-carrier systems seem to be getting most of the attention for 5G, experts say single-carrier modulation could still be part of the spec. There is also what might be termed odd-ball techniques still in the mix. One is called faster than Nyquist (FTN) modulation. It is a non-orthogonal subcarrier system that actually makes use of intersymbol interference to pack more data into a communication channel.

Another non-orthogonal idea is called time-frequency packing. The carriers are close together, and a super-sophisticated detector in the receiver decodes the closely packed signals. TFS is implemented either with QAM or OQAM.

Finally, a couple of ideas from independent companies have been floated as 5G specs. One is called wave modulation (WAM) which comes from MagnaCom, an Israeli startup acquired by Broadcom. Here a set of algorithms implement a form of spectral compression. Details about WAM are sparse, but the spectral compression is said to enable a higher signaling rate thereby affording the use of lower-order symbol alphabet, which reduces complexity. It is also said to give an overall 10% system gain advantage, up to 4x increase in range, a 50% spectrum savings, improved noise tolerance, and increase in data speed.

Another company called Cohere Technologies patented a modulation technology called Orthogonal Time Frequency and Space (OTFS). Again, details about OTFS are sparse, but press releases put out by Cohere speak highly of it.

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Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source: microcontrollertips

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What is H.264 (AVC) Format? A popular Compression for HD Video | Soukacatv.com

H.264 is a new video codec standard which can achieve high quality video in relatively low bitrates. You can think it as the "successor" of the existing formats (MPEG2, MPEG-4, DivX, XviD, etc.) as it aims in offering similar video quality in half the size of the formats mentioned before.

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Also known as AVC (Advanced Video Coding, MPEG-4 Part 10), H.264 is actually defined in an identical pair of standards maintained by different organizations, together known as the Joint Video Team (JVT). While MPEG-4 Part 10 is an ISO/IEC standard, it was developed in cooperation with the ITU, an organization heavily involved in broadcast television standards. Since the ITU designation for the standard is H.264, you may see MPEG-4 Part 10 video referred to as either AVC or H.264. Both are valid, and refer to the same standard.

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The latest version of ffdshow supports H.264 playback. Please remember, ffdshow is a DirectShow filter so after you install it you'll be able to play H.264 in most video players you already have installed, including Windows Media Player. Alternatively you can download 5KPlayer and VLC player. Both can play H.264 without need of any codec or DirectShow filter. Apple QuickTime players support H.264 too, but their support is not so great for all formats, so don't use them for general H.264 playback. Generally most players or codec packs nowadays include H264 support so you shouldn't have any problems. You may also watch your H.264 files on your Xbox 360 and PSP with smooth playback.

You may come across all kinds of file extensions and still the codec can be H.264:

*.avi - People also use .avi for H.264 videos too!

*.mp4 - QuickTime use this format. Better than AVI as you can store AAC audio as well.

*.m4v - The standard file format for videos for iOS devices developed by Apple.

*.mkv - (Matroska container) - can support many video and audio formats.

*.h264 - Not commonly used, but you may download some video files with this extension name from Internet.

*MPEG-4 - One of the latest (audio and video) compression method standardized by MPEG group, designed especially for low-bandwidth video/audio encoding purposes.

Definition of Both MP4 and H.264

MP4 - a container format, full name is MPEG-4 Part 14, written as .mp4

MP4 is undoubtedly the most popular video format at present, because it allows a combination of audio, video, subtitles and images to be held in the one single file. Moreover, it can be played on nearly all devices, leaving other formats like AVI, WMV, MOV far behind; it can be shared on many online video sites like YouTube. It is usually encoded with H.264/HEVC/MPEG-4 video codec and AAC audio codec.

H.264 - a video codec

H.264, currently one of the frequently-used video codecs, is a popular compression for HD video. Since H.264 can achieve high quality video relatively low bitrates, it's commonly used in AVCHD camcorders, HDTV, Blu-ray, and HD DVD. MP4 (.mp4) is one of the H.264 encoded video formats.

The Difference between MP4 and H.264

From the respective definition above, we can easily see that MP4 is a file container format, while H.264 is actually a video compression codec that requires a video container to host the encoded video. They are different things, not even with the same property. In most cases, H.264 encoded files are MP4 files and they can also be AVI or MKV ones.

Compare MP4 with H.264 formats

File Extension

File Type of MP4: MPEG-4 Video File, developed by Moving Picture Experts Group.

MP4 is currently the most popular video format, commonly used for sharing video files on the Internet and can be played on most devices. The MPEG-4 video is compressed with MPEG-4 video encoding. Audio is compressed using AAC compression.

File Type of H.264: H.264 Encoded Video File

Video file encoded with H.264 compression, which is a popular format for high definition video; often used as the video format for AVCHD camcorders, HDTV, Blu-ray, and HD DVD; generally refers to a video file that is actually an .MP4 file.

MP4 is a file container format, while H.264 is actually a video compression codec that requires a video container to host the encoded video. Most of the time, H.264 refers to MP4 file encoded with H.264 codec, and a file with the ".h264" extension is generally a misnamed .MP4 file (or another supporting container file format such as .AVI or .MKV).

For more, please access to https://www.soukacatv.com.

Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source: winxdvd

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Global and Regional Frequency Modulation Broadcast Transmitter Market Report | Soukacatv.com

The Frequency Modulation Broadcast Transmitter market report analysis series and provides a comprehensive insight into the global Frequency Modulation Broadcast Transmitter channel. It analyses the market, the major players, and the main trends, strategies for success and consumer attitudes. It also provides forecasts to 2024.

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About Frequency Modulation Broadcast Transmitter Industry

The overviews, SWOT analysis and strategies of each vendor in the Frequency Modulation Broadcast Transmitter market provide understanding about the market forces and how those can be exploited to create future opportunities.

Key Players in this Frequency Modulation Broadcast Transmitter market are:–

RVR Nautel Elenos Worldcast Ecreso DB Electtrronica Eddystone Broadcast Broadcast Electronics, Inc. GatesAir BBEF ZHC(China)Digital Equipment Electrolink S.r.l

Important application areas of Frequency Modulation Broadcast Transmitter are also assessed on the basis of their performance. Market predictions along with the statistical nuances presented in the report render an insightful view of the Frequency Modulation Broadcast Transmitter market. The market study on Global Frequency Modulation Broadcast Transmitter Market 2018 report studies present as well as future aspects of the Frequency Modulation Broadcast Transmitter Market primarily based upon factors on which the companies participate in the market growth, key trends and segmentation analysis.

Application of Frequency Modulation Broadcast Transmitter Market are:

Radio Station(National, Provincial, City, County) Rural and Other Radio Stations

Product Segment Analysis of the Frequency Modulation Broadcast Transmitter Market is:

300W 300W~1KW(Include 1KW) 1KW~5KW(Include 5KW) >5KW

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Geographically this report covers all the major manufacturers from India, China, USA, UK, and Japan. The present, past and forecast overview of Frequency Modulation Broadcast Transmitter market is represented in this report.

The report offers the market growth rate, size, and forecasts at the global level in addition as for the geographic areas: Latin America, Europe, Asia Pacific, North America, and Middle East & Africa. Also it analyses, roadways and provides the global market size of the main players in each region. Moreover, the report provides knowledge of the leading market players within the Frequency Modulation Broadcast Transmitter market. The industry changing factors for the market segments are explored in this report. This analysis report covers the growth factors of the worldwide market based on end-users.

Also it analyses, roadways and provides the global market size of the main players in each region. Moreover, the report provides knowledge of the leading market players within the Frequency Modulation Broadcast Transmitter market. The industry changing factors for the market segments are explored in this report. This analysis report covers the growth factors of the worldwide market based on end-users.

For more, please access to https://www.soukacatv.com.

Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source：thestatetime

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The Difference between Digital and Analog Cable TV Channels | Soukacatv.com

When the first television broadcasts hit the airwaves in the 1920’s, television shows were transmitted using an analog signal. But in 1996, a new technology was invented that would change the way TV signals were transmitted through the air, with a digital signal. Today, the FCC requires all TVs to contain a digital tuner and for most TV stations to broadcast their channels in digital format.

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The big difference between Analog and Digital is how the signal is transmitted from the source to the TV in your home. Analog TV’s transmit audio and video signals over the airwaves in a manner similar to a radio signal. Each station has a single frequency over which to broadcast its analog television signal. You know these frequencies as channel numbers on your TV. Like radio signals, an analog TV signal can experience interference with their frequencies. This can cause static, snow, or ghosting on a channel. It can also cause fluctuations in color, brightness, and sound quality. And like a radio signals, analog transmission declines the further away you are from the source.

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A Digital TV signal, on the other hand, transmits in “packets” of compressed data. The data uses a combination of 1’s and 0’s, similar to your computer, DVD player, and Internet. Because it uses this code, digital signals do not experience the same interference, or signal loss, that analog TV signals do. That means you enjoy a consistently clear picture, high-quality audio, and no static or snow.

A Digital TV signal is also a more efficient technology. A digital transmission requires less bandwidth when compared to a similar Analog signal. In fact, four or more digital channels use the same bandwidth as a single analog channel. This allows a television station to broadcast more channels and more HD channels over the same airwaves, giving you more variety of programming with better quality.

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Another difference between Digital and Analog is the ability for digital signals to broadcast programming in a true HD widescreen (16:9) format. This allows you to experience movie quality programming at home. Analog signals on the other hand are transmitted in 4:3 aspect ratio. Meaning the picture is 4 units wide for every 3 units of height. So on a HDTV, you will see black bars on the sides of your TV picture when analog programming is broadcast.

Unfortunately, digital TV transmissions cannot be received by older analog TVs. To receive digital TV signals, you must have a newer TV with a digital tuner built-in it or a digital-to-analog converter box. The set-top converter box will automatically convert the digital signal into something your older TV can display.

Established in 2000, the Soukacatv.com main products are modulators both in analog and digital ones, amplifier and combiner. For more, please access to https://www.soukacatv.com.

Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source: http://blog.imon.net/2017/06/14/the-difference-between-digital-and-analog-cable-tv-channels

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Fundamentals of Digital Communications Systems: Pulse amplitude modulation (PAM) | Soukacatv.com

Learn some of the basic building blocks that make digital systems work. This chapter starts with a discussion of a basic digital communications link, covers the most commonly used clocking architectures, discusses line-coding methods, and concludes with special techniques for high-speed serial transmission systems.

During the last ten years, most major communications and broadcast systems and many other systems were converted from analog to digital. Examples of digital systems that we use every day include mobile phones, television, radio, and of course the Internet. CDs and MP3s are replacing records and tapes, and the number of digital cameras sold this year exceeded the number of analog cameras by a factor of three. In this chapter, you will see some of the basic building blocks that make all of these digital systems work.

The material in this chapter is intended to provide a background that will be useful when studying digital communications test and measurement techniques described in later chapters. We start with a discussion of a basic digital communications link, cover the most commonly used clocking architectures, discuss line-coding methods, and conclude with special techniques for high-speed serial transmission systems.

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1.1 Introduction

The most important aspect of any digital communications system is the required transmission speed. Just how much data needs to be transmitted, and how fast? The variability is huge, even within a single system: The keyboard interface of a typical PC, for example, runs at several kilobits per second, which is still significantly faster than anyone can type. However, the fastest interface available for graphics adapters is not nearly fast enough for the newest games, even at 40 Gbit/s (which is the accumulated bandwidth of a PCIe x16 link, the current standard for graphics adapters).

The second, equally important aspect is the link distance. How far apart are sender and receiver? Again, there is huge variability: The main processor of a computer communicates with its main memory over a distance that's usually less than 10 cm. But when you type a URL into a Web browser, you communicate with a server that's potentially on a different continent.

Generally, digital transmission becomes harder when the transmission speed and link distance increase. A measure for the effort required to make a digital communications link work is the bandwidth-distance product. An old telegraph, for example, transmitted about 100 bit/s, over a maximum distance of 20 km. The radio downlink from the Voyager spacecraft transmits data slightly faster, at 160 bit/s, but over an incredible distance of 14.821 billion km. The much larger bandwidth-distance product of the spacecraft link can be achieved only with incredible effort.

Every digital link consists of three components: a sender, a transport medium, and a receiver. Usually, the medium is defined first, depending on the required link bandwidth, the distance between transmitter and receiver, and economic considerations. Electrical links are still the most common type; they come in a great variety, ranging from bond wires within an integrated circuit package to printed circuit board traces on a motherboard to Ethernet cables connecting office computers. Fiber-optic cables are used for very high bandwidth connections in network and storage environments, but it seems as if "fiber to the home" might be replaced by wireless links in the near future.

1.2 Line Coding of Digital Signals

When binary data is sent through a link, it is represented by a physical quantity in the transport medium. In electrical links, that's usually a voltage or current; optical systems use the intensity of light; and wireless radio links often use the phase and frequency of a signal carrier. Line coding determines how the binary data is represented on the link.

Numerous coding schemes are available, and which one is best for any given application depends on many factors. Coding can influence the frequency spectrum, the direct current content, and the transition density of the resulting data stream. Coding efficiency determines the required link bandwidth, and the cost of implementation depends on the complexity of the code.

1.2.1 Properties of Binary Data

1.2.1.1 Mark Density

The mark density (MD) of a binary data pattern is defined as the number of one bits in the pattern, divided by the length of the pattern:

where NOne is the number of ones in the pattern, and NZero is the number of zeros. The mark density ranges from 0.0 to 1.0, where the extremes are marked by all-zeros (NOne equals 0) and all-ones data (NZero equals 0). Random data is exactly at the middle of the range: It contains as many one bits as zero bits, and its long-term mark density is therefore 0.5. If we look only at a subsection of the random data pattern, however, its mark density can be very different.

If we represent a zero bit by 0.0 and a one bit by 1.0, the mark density is equal to the time average over the pattern. It is therefore a direct measure for the DC content of the signal. A pattern with a mark density of 0.5 is therefore also called a DC-balanced pattern. DC balance is an important property in some applications; if it is required to maintain a DC level in the link, then amplifiers and other system components need to be DC coupled, often leading to a more complicated and problematic design.

1.2.1.2 Transition Density

The transition density (TD) of a data pattern is defined as the number of transitions in the pattern, divided by the length of the pattern:

where NT is the number of transitions in the pattern, NOne is the number of ones, and NZero is the number of zeros. The transition density ranges from 0.0 to 1.0, where the extremes are marked by static patterns (all-zeros or all-ones) and toggle patterns. Random data is again exactly at the middle of the range: Because the probability that two consecutive bits are identical is 0.5, the transition density is 0.5, too.

1.2.1.3 Run Length Distribution

The run length distribution of a data pattern gives the relative probabilities for runs of identical consecutive bits. Longer runs create stress in many applications, because of either excessive intersymbol interference (ISI) or baseline wander due to local disparity.

1.2.2 Binary Line Codes

1.2.2.1 Non-Return-to-Zero Code

The non-return-to-zero (NRZ) format is the prototypical representation of binary data: A logical zero state is transmitted as one signal level, and a logical one state as another level. Levels change at bit boundaries only if the bit value changes and remain stable for the entire duration of the bit period. If the level representing the zero logical bit state is lower than the level for the one state, we call this positive logic, and the respective levels are then called low level and high level. NRZ coding is essentially free because binary data is already stored in this format in CPUs and other digital devices. It is therefore the most commonly used coding scheme and the reference for all other coding schemes in terms of signal properties, efficiency, and implementation effort.

NRZ signals always have a clock signal associated with them, even if it is not transmitted along with the data. Figure 1-15 shows the NRZ representation of a short data sequence, together with a clock signal. Note how the data signal changes on the falling edge of the clock; the receiver samples it on the rising edge. There are also systems that work with an inverted clock. The data then changes on the rising edge, and the receiver samples at the falling clock edge. The clock signal for NRZ transmission usually runs at the base frequency of the data: for a 10 Gbit/s signal, the clock rate is 10 GHz (single data rate, SDR). A variant of NRZ transmission uses a clock signal at half rate (5 GHz for 10 Gbit/s), and the receiver samples the data both at the rising and falling edges of the clock. This is called double data rate (DDR) transmission.

Figure 1-15 NRZ coding of a short data sequence (PRBS 24-1). Top: single data rate clock. Bottom: double data rate clock.

The properties of NRZ-formatted data depend entirely on the data itself. The drawback of NRZ coding is that the DC content, frequency spectrum, and transition density depend on the data sequence. Long runs of zeros or ones cause problems in some applications because of effects such as baseline wander and ISI or because there are not enough transitions for clock data recovery.

Figure 1-16 shows the power spectral densities of two short NRZ-formatted data sequences. Note how both spectra have zero power at multiples of the signal base rate (e.g., 1 GHz, 2 GHz, 3 GHz). The PRBS spectrum follows the typical sinc envelope, with nulls at multiples of the data rate. Because of the very fast rise times that we used to create the spectrum, there is significant spectral content at very high frequencies. The spectrum for the toggle pattern equals that of a 500 MHz square wave. The spectra of all-zeros or all-ones patterns are zero, with the exception of a DC value.

Figure 1-16 Power spectral density for NRZ-formatted data at 1 Gbit/s. Left: PRBS 24-1. Right: Toggle pattern (101010 . . .). Power density is normalized to a maximum power of 1.0.

1.2.2.2 Return-to-Zero Code

The return-to-zero (RZ) code represents the zero logical state as a static low level and the one state as a short high-level pulse. The signal always returns to the level representing a zero state immediately after the high level, hence the name. RZ signals can be easily created from NRZ signals, by a binary AND of the NRZ and a clock. The width of the pulses depends on the duty cycle of the clock. Figure 1-17 shows the RZ representation of a short data sequence, with 50% and 25% duty cycles.

Figure 1-17 RZ coding of a short data sequence (PRBS 24-1). Top: 50% duty cycle. Bottom: 25% duty cycle.

RZ coding is used primarily in optical transmission systems because it minimizes power consumption and the effects of system dispersion on optical signal distortion. Consecutive one bits carry one transition each, so that clock data recovery is fairly easy with this coding, provided the signal doesn't consist of all zeros. The signals also carry significant DC content, which is not a factor in optics, though.

The signal bandwidth of RZ-coded data is significantly higher than that of NRZ data, by at least a factor of two (for a 50% duty cycle). The spectral densities for the RZ-coded signals from Figure 1-17 are shown in Figure 1-18. The signal with a 50% duty cycle has significantly less energy at lower frequencies than the NRZ signal and very distinct spikes at the data rate and its even harmonics. The 25% duty cycle signal has even less low-frequency content but distinct spikes at all integer multiples of the data rate.

Figure 1-18 Power spectral density for a short RZ-formatted data sequence (PRBS 24-1), at 1 Gbit/s. Left: 50% duty cycle. Right: 25% duty cycle. Power density is normalized for comparison with NRZ format (dotted line).

1.2.2.3 Return-to-One Code

Return-to-one (R1) code uses a static high level for the logical one state and a short low-level pulse for a zero. Creating an R1-formatted signal from NRZ data is a bit more complicated than using the RZ format: It's a binary AND of the inverted NRZ data with the clock, and the result inverted again. Figure 1-19 shows an example. The properties of R1-coded data are very similar to those of RZ-coded data, with the exception of the DC content, which is significantly higher than for RZ-coded signals.

Figure 1-19 R1 coding of a short data sequence (PRBS 24-1)

1.2.2.4 Manchester Code

Manchester code is generated from NRZ data by a binary XOR with a clock signal. Since there are two possible clock phases, there are also two variants of Manchester code. The coded data has a transition in the middle of every bit, and the direction of this transition indicates a binary zero or one. The original Manchester variant uses a falling edge for a one and a rising edge for a zero; the other variant (which is used in IEEE 802.3 10Base-T Ethernet, for example) is the exact inverse. Figure 1-20 shows both variants.

Figure 1-20 Manchester code representation of a short data sequence (PRBS 24-1). Top: "10" variant. Bottom: "01" variant.

Manchester code is very attractive for embedded clock applications because it forces at least one transition per bit, even if the data is a constant zero or one. It is also a DC-balanced code. However, the price for this is a significantly higher bandwidth relative to NRZ data. Figure 1-21 shows the spectral densities for two short data sequences. Compared to the NRZ spectrum (dotted line), the PRBS spectrum has significantly less spectral content at low frequencies but more at higher frequencies. Spectral nulls are at even harmonics. The spectrum for the constant one pattern is equal to a 1 GHz square wave.

Figure 1-21 Power spectral density for Manchester-coded data at 1 Gbit/s. Left: PRBS 24-1. Right: Constant one (111111 . . .). Power density is normalized for comparison with NRZ format (dotted line, left plot only).

1.2.2.5 Non-Return-to-Zero Inverted Code

Non-return-to-zero inverted (NRZI) code is not, as the name suggests, the mere inversion of an NRZ-coded signal; it is an example of a differential code, where the state of the signal depends on both the current and the previous bit. An NRZI-coded signal changes its state when the current bit is a logic one bit but stays constant if the current bit is a logic zero (Figure 1-22). Using transitions rather than levels makes detection less error-prone in noise environments, and the signal polarity is insignificant. NRZI coding is used, for example, in USB.

Figure 1-22 NRZI coding of a short data sequence (PRBS 24-1)

The signal properties of NRZI-coded data are similar to those of NRZ data: The transition density can be between 0.0 (for a constant zero pattern) and 1.0 (for a constant one pattern), and the spectral content for random data is exactly the same as for NRZ. The NRZI code is therefore not sufficient to enable data transmission with clock recovery, or to limit the amount of ISI.

1.2.2.6 Differential Manchester Code

Differential Manchester code (DMC) is a combination of Manchester and NRZI: It uses transitions in the middle of the bit, but the transition direction changes with everyone in the data stream (Figure 1-23). This coding can be generated by an XOR function of NRZI-coded data and a clock signal. DMC is also known as conditional de-phase (CDP) code and used in token ring LANs (IEEE 802.5).

Figure 1-23 Differential Manchester coding of a short data sequence (PRBS 24-1)

The properties of data that is coded with DMC are very similar to those of pure Manchester code: The signal is DC balanced, there is at least one transition per bit, and the spectrum has low content at lower frequencies but significantly more high-frequency content than NRZ data has.

1.2.3 Multilevel Line Codes

1.2.3.1 Bipolar Return-to-Zero Code

A variant of the RZ code is bipolar return-to-zero (BPRZ) coding, where the signal returns to an intermediate zero level after both zero and one bits (Figure 1-24). There are two transitions per bit, which makes synchronization of the receiver fairly easy. The drawback is the fairly complicated circuitry and an even higher bandwidth requirement than for RZ and R1 data. Figure 1-25 shows the power spectral density for a BPRZ-formatted data sequence.

Figure 1-24 BPRZ coding of a short data sequence (PRBS 24-1)

Figure 1-25 Power spectral density for a short BPRZ-formatted data sequence (PRBS 24-1), at 1 Gbit/s. Left: 50% duty cycle. Right: 25% duty cycle. Power density is normalized for comparison with NRZ format (dotted line).

1.2.3.2 Pulse Amplitude Modulation

Pulse amplitude modulation (PAM) is a class of multilevel codes that encodes several consecutive bits into one of several levels. PAM-4, for example, encodes two bits into one out of four levels (Figure 1-26). Demodulation is performed by detecting the signal level once per symbol period. PAM-4-encoded data has much less high-frequency content than, for example, NRZ data because the signal level changes only for every other bit. However, the cost is increased transmitter and especially receiver complexity, and a lower signal-to-noise ratio if the same levels are used. PAM-4 alone is not sufficient for embedded clock systems, as it does not guarantee transition density: Constant zero or one patterns are encoded as DC levels. Figure 1-27 shows the power spectral density for a PAM-4-coded data sequence.

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Figure 1-26 PAM-4 coding of a short data sequence (PRBS 24-1)

Figure 1-27 Power spectral density for PAM-4-coded data at 1 Gbit/s. Left: PRBS 24-1. Right: Half-rate toggle (11001100 . . .). Power density is normalized for comparison with NRZ format (dotted line).

1.2.4 Block Codes

1.2.4.1 mBnB Block Codes

Block codes of type mBnB take m bits of the original data and encode them into n bits, following very specific rules. Several of the coding schemes from the previous sections can be expressed as 1B2B codes; RZ coding, for example, encodes every one bit as a one, followed by a zero, and every zero bit as two zeros. Widely used in serial high-speed applications are 4B5B and in particular 8B10B coding. The dominant encoding scheme in computing applications, 8B10B seems to hit a sweet spot with relatively low overhead (25%), ease of implementation, coding properties such as maximum run length, and so on. Chapter 3 describes 4B5B and 8B10B coding in greater detail.

1.2.4.2 Error Detection and Forward Error Correction

Some of the block codes from Section 1.3.4.1 enable the receiver to detect some transmission errors, either from calculating disparity or by detecting invalid code words. A system that is based on such coding techniques can issue a packet resend command and transmit the packet again, this time hopefully without an error. Ideally, however, the receiver would be able to not only detect errors (all errors, not just a few) but also correct them.

The process of adding redundancy to the data stream and analyzing and correcting errors in real time is called forward error correction (FEC). Systems that use FEC can operate with less margin in transmission than non-FEC systems. In practical applications, this means a longer range between sender and receiver or reduced transmission power. Especially under difficult transmission conditions, FEC systems are more effective than non-FEC systems because fewer packets need to be retransmitted.

1.3 Summary

In this chapter, we've introduced the basic concepts of high-speed serial transmission systems: clock architectures, line coding, and differential electrical signaling with preemphasis or receiver equalization.

The remainder of this book describes how we can characterize such a system, either as a whole or individually for its components. Transmitter tests verify the electrical performance of the signal before it enters the channel, while receiver tests verify that the worst-case realistic signals can be understood by the receiver. Channel tests finally determine the quality of the transmission medium.

For more, please access to https://www.soukacatv.com.

Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source：http://www.informit.com/articles/article.aspx?p=1157195&seqNum=3

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soukacatv · 5 years ago

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THE DIGITAL REVOLUTION: ITS ADVANTAGES AND DISADVANTAGES | SOUKACATV.COM

The Digital Revolution is the newest economic revolution. Like the Industrial Revolution, the Digital Revolution marks a complete shift in our society, signals a new era, and alters many aspects of our lives. While not everyone is familiar with the term, the Digital Revolution refers to the shift from technology based on analog and mechanical electronics to digital technology.

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Digital technology allows information to be copied and replicated precisely. It is due to digital technology that our society is now so defined by computers, smart phones, internet access, and cell phone communication. The Digital Revolution, in fact, marks the beginning of a new age: the Information Age.

Advantages

It isn’t hard to see the advantages of the Digital Revolution. You probably benefit from it every day. In fact, if you are reading this article, then you are experiencing one of the benefits of the Revolution – it vastly increases the knowledge at our fingertips, expanding our understanding of the world, and compiling entire encyclopedias of knowledge in online databases. Consider some other advantages of this Revolution:

· The Digital Revolution links individuals and groups together. Never before have we been able to communicate real-time with others in distant corners of the world. And this advantage is not limited to international communication – we now have instant access to our friends and family members a few miles away. Unlike traditional telephones, cell phones have brought this ‘communication power’ into our hands in the most remote locations.

· The Digital Revolution has created tools that are catalysts for sharing ideas. No longer do you need to be the executive of a wealthy business in order to share your thoughts with others on a broad scale – using social media and common technologies, ideas can be shared and innovation can be accelerated.

· Similarly, we now have a world of online opportunity. Start-up companies can begin in a bedroom with a single laptop. Jobs can be obtained – and worked – in the back of a truck deep in the forest. You can find and purchase rare books through online services without getting out of bed.

· While not all may appreciate it, the Digital Revolution forces competitiveness on a global scale. Prior to the revolution, stores only needed to compete with other stores in their region. A book may not have been the best book on the subject, but only needed to be the best book that the library had. Now, the level of competition is global. If this competitiveness hurts smaller, less efficient and lower-quality entities, it allows us, the consumers, access to a far wider marketplace of goods and knowledge.

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Disadvantages

While we can all recognize and appreciate the powerful advantages that the Digital Revolution brings to our fingertips, I write this article primarily so that we would recognize the disadvantages that tag along. The Digital Revolution has become such an ubiquitous part of our lives that we may hardly notice the damaging effects that it brings along. My point is not to focus on those clear and obvious evils such as hackers and organized crime that are so obvious – you probably already understand those problems. Rather, consider how the Digital Revolution can bring about such disadvantages on a personal and societal level:

· You and I are gifted beyond measure to live in an age when so much knowledge is available, but as I have previously described, people abuse this wealth of knowledge in three ways: (1) by only wishing to be acquainted with many things, (2) by turning its blessing into a curse, and (3) by wishing to know only for the sake of knowing. (You can read more about the abuse of knowledge here).

· By opening up so much knowledge to us – and presenting it at our fingertips – the Information Age allows evil to spawn and grow at an alarming rate. From the questionable to the perverted, from the dubious to the depraved, the same information can be presented to us instantly and transit the globe in moments, without allowing society time to sit back and consider the information or ideas that are offered to us.

· A whole family can now live in a single house and yet live like single people, because this Revolution breaks down many relationships and our sense of community. While we can maintain friendships in distant states and countries, it breaks down all those friendships which are not actively fostered in the digital realm. When you get on a bus or train full of people on their smartphones, it reveals this sad truth: that everyone is connected, but only to those whom they chose to connect with.

· Similarly, digital technology breaks apart our sense of political and regional community. This has been in decay for some time now, but the Information Age is tearing it apart faster than ever. The idea that we can choose our friends through social media, and stay connected with only those – without spending time with those who live and interact around us – tears down the idea that we live in a community, in a special place in the world. It tears down the idea that we need our neighbors on a political level, which prepares for the abuse of democracy.

· Finally, the digital realm encourages passivism, rather than discernment. Having information presented on a screen (as it constantly is in the Information Age) welcomes viewers to sit back, accept the message that is presented, and move on without time for reflection. While movies and media all communicate messages, digital electronics have a strange way of obscuring that fact and encouraging passive consumerism. Television has been around for some time, but only multiply the problem.

Like fire, electronics make a handy servant but a dangerous master. Or, as we could alter the phrase, ‘Electronics make a stultifying master but an astonishing servant.’ When they dominate our lives, they encourage us to sit back, stop thinking, and grow ignorant and disconnected. When we harness them as a servant, then electronics are some of the most beneficial tools ever known to man.

For more, please access to https://www.soukacatv.com.

Company: Dingshengwei Electronics Co., Ltd

Address: Bldg A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Mobile: 13410066011

Email: [email protected]

Source: fromdanielsdesk

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soukacatv · 5 years ago

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Difference between Amplitude Modulation and Frequency Modulation | Soukacatv.com

Amplitude Modulation and frequency modulation, both are the type of transmission techniques for transmitting information from sender to receiver. But the similarity between the two ends here. Amplitude modulation involves the modulation of the carrier signal according to the amplitude of the baseband signal. The frequency and phase of the carrier signal remain constant.

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On the contrary, frequency modulation involves the modulation of the carrier signal according to the frequency of the baseband or information signal. Thus, the major difference between the amplitude modulation and frequency modulation is that the amplitude modulation is the process of modulating the amplitude of the carrier signal, while frequency modulation is the modulation of the frequency of the carrier signal.

Another significant term which creates the difference between these two modulation techniques is the bandwidth requirement. The bandwidth requirement in case of amplitude modulation is very less as compared to frequency modulation.

We will discuss some other crucial differences between amplitude modulation and frequency modulation like frequency range, quality of transmission etc. with the help of comparison chart. But before discussing the comparison chart, let’s put light on the crucial cornerstone of this article.

Content: Amplitude Modulation and Frequency Modulation

1. Comparison Chart

2. Definition

3. Key Differences

4. Conclusion

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Comparison Chart

PARAMETERS

AMPLITUDE MODULATION

FREQUENCY MODULATION

Definition

The amplitude of the carrier wave is modulated according to the value of the amplitude of the information signal.

The frequency of the carrier wave is modulated according to the value of the frequency of the information signal.

Circuit designing

Simple

Complex

Cost of the circuit

It is less costly.

It is more costly than amplitude modulation technique.

Bandwidth requirement

The bandwidth requirement is low in the range of 10 kHz.

The bandwidth requirement is high in the range of 200 kHz.

Area of reception

The area of reception is large.

The area of reception is limited in comparison to that of amplitude modulation system.

Constant terms

The frequency and phase is constant.

The amplitude and phase is constant.

Power

The wastage of power is more in amplitude modulation because the significant part of the power is carried by the carrier signals which do not contain any information.

The power is utilized properly, because all transmitted power is carried by the information signal.

Noise Immunity

The amplitude modulation system is not immune from noise distortion as frequency deviation technique and amplitude delimiters cannot be utilized in amplitude modulation system.

The frequency modulation is more immune to noise distortion because we can use frequency deviation technique and amplitude delimiters.

Quality of reception

Low quality signal is obtained.

The received signal is of high quality.

Definition of Amplitude Modulation

The amplitude modulation is the process of transmitting the information signal by superimposing it on the high-frequency wave called carrier wave. The information signal can be of any type based on the type of information it is carrying such as voice, data etc.

The frequency of the information signal which is also known as the baseband signal is extremely low. The frequency of the signal is directly related to the energy of the signal. Thus, if signal frequency is very low then the signal will get attenuate after travelling a certain distance. In order to avoid the attenuation of the signal, it is superimposed on the high-frequency carrier wave.

In case of amplitude modulation, the amplitude of the carrier wave modulates, i.e. it varies with the amplitude of the information signal. Thus, the modulation is called amplitude modulation. It is to be noted that the frequency and the phase of the carrier remain constant during amplitude modulation.

The main drawback of the using amplitude modulation technique is the lower efficiency and poor quality. The modulated signal obtained from amplitude modulator does not resemble the transmitted signal as its quality gets degraded. Besides, the noise immunity of amplitude modulators is also poor.

The advantage of using amplitude modulation technique is that it requires low bandwidth which makes it less costly.

Frequency Modulation

The frequency modulation is the technique of modulation in which the frequency of the carrier signal is varied in accordance with the frequency of the information or baseband signal keeping the amplitude of carrier signal constant.

The frequency modulator performs the modulation task, in this carrier signal from radio frequency generator and the information signal from the information source is introduced. The modulated signal is then passed to RF amplifier which ameliorates the necessary attenuations.

The main advantage of using the frequency modulation technique for transmission is that quality of the transmitted signal does not deteriorate. But the frequency modulation system is complex to design thus, the cost of such system are quite high.

The frequency modulation system is immune to noise distortion. Thus, the effect of noise on the frequency modulated signal is extremely low that it can be neglected.

Key Differences between Amplitude Modulation and Frequency Modulation

1. The operation mechanism of amplitude modulation and frequency modulation creates the key difference between these transmission technologies. Amplitude modulation deals with the carrier which is modulated by the amplitude of the signal, while frequency modulation technique deals with the carrier which is modulated by the frequency of the modulated signal.

2. The quality of the received signal varies in both the techniques. The amplitude limiters can be fitted with frequency modulation system. Thus, the distortions due to noise signal can be minimized in frequency modulation system. On the contrary, the amplitude modulators cannot be equipped with amplitude limiters.

3. The frequency deviation technique also reduces the noise and can exponentially increase the quality of the signal, but the technique of frequency deviation is not possible in amplitude modulation. This makes the frequency modulation better in comparison to amplitude modulation.

4. The bandwidth requirement also plays a pivotal role in differentiating amplitude modulation and frequency modulation. The frequency modulation system requires high bandwidth in the range of 200 kHz. While the amplitude modulation system requires bandwidth in the range of 10kHz for the broadcasting information signals.

5. The circuit architecture of frequency modulation system is very complex in comparison to amplitude modulation system.

6. The amplitude modulation and frequency modulation also differs in the cost of the system. The complex design of the frequency modulation system makes it costly in comparison to amplitude modulation system.

Conclusion

The amplitude modulation and frequency modulation, both are the crucial technologies of the communication system. Our requirements and specification of applications decide which of the above-mentioned modulation technique should be used. If we are dealing with such an application in which we cannot compromise with the quality of reception, then we should opt for frequency modulation system.

However, if we are dealing with such an application that we needn’t maintain the quality of the reception and looking for the cheap and simple technique then we should go for amplitude modulation technique.

For more, please access to https://www.soukacatv.com.

Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source: electronicscoach

#Digital modulatorDigital modulator manufacturerDigital modulator supplierChina Digital modulator manufactureranalog modulator16in1 digital h

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soukacatv · 5 years ago

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Digital Modulation Techniques (ASK, FSK, PSK, BPSK) / Amplitude, Frequency and Phase Shift Keying | Soukacatv.com

In this post we will discuss three kinds of digital modulation techniques, Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) and Phase Shift Keying (PSK).

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So first of all let's understand, what is modulation?

What is Modulation?

Modulation is a process, where some characteristic of the carrier wave (amplitude, frequency or phase) is varied in accordance with the instantaneous value of the modulating (message or baseband) signal.

So if amplitude of the carrier wave is varied, then it is called as amplitude modulation, but if frequency or phase of the carrier wave is varied, according to the instantaneous value of the modulating signal, then it is known as frequency modulation or phase modulation respectively.

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So now let's understand the basic difference between continuous wave modulation and digital modulation-

Difference between Continuous Wave Modulation and Digital Modulation:

Amplitude Modulation (AM), Frequency Modulation (FM) and Phase Modulation (PM) are the examples of Continuous Wave (CW) modulation, while Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) and Phase Shift Keying (PSK) are examples of Digital Modulation Techniques. The basic difference between continuous wave Modulation and digital modulation techniques is based on the nature of message signal (modulating signal).

In continuous wave modulation, the message signal is of analog nature but in digital modulation, the message signal is of digital nature (Binary or M-ary encoded version).

In both of these modulation techniques, the carrier wave is of analog form.

Here it is interesting to note that, the three forms of digital modulation techniques that is ASK, FSK and PSK are analogous to AM, FM and PM of continuous wave modulation respectively.

So now let's discuss each digital modulation technique (ASK, FSK and PSK) in detail.

Amplitude shift keying (ASK)

In ASK, the amplitude of the carrier wave is changed (switched) according to the digital input signal (modulating signal). Therefore amplitude shift keying is analogous to Amplitude Modulation (analog modulation).

ASK is analogous to AM, because in Amplitude Modulation (AM), amplitude of the carrier wave is changed according to the instantaneous value of the modulating (message) signal, in the same way in ASK also, the amplitude of the carrier wave is switched (varied) according to the instantaneous value of the modulating signal (digital input signal). The difference is only of the nature of the modulating signal. In amplitude modulation, the modulating signal is of analog kind but in digital modulation, it is a stream of digital bits.

Now let’s understand the concept of amplitude shift keying (ASK) with the help of an example.

Look carefully the image shown below.

Amplitude Shift Keying (ASK) Waveform

Here in this image observe that we are going to modulate a sinusoidal carrier wave (shown in green color), with the digital input signal (0 1 1 0 0 1).

This image also shows the ASK waveform (modulated signal).

So now it's time to understand, how this amplitude shift keying takes place.

In amplitude shift keying, we change the amplitude of this sinusoidal carrier wave according to the digital input signal which is acting as modulating signal (message signal) here.

So the basic concept is, we do not transmit the carrier wave when the digital input signal is '0', and transmit the sinusoidal carrier as it is, for digital input signal '1'.

You can observe this phenomena in the image carefully, that in this example, we have digital input signal '0', at three places, so for these three digital '0', no carrier signal has been transmitted. But for binary '1' at three places, the full carrier wave has been transmitted without any change.

Here the amplitude of the sinusoidal carrier wave is switched, as per the digital input signal. The carrier wave is either not transmitted or transmitted for digital input signal '0' or '1' respectively. That is why amplitude shift keying (ASK) is also called as "ON - OFF Keying (OOK)".

Now we will discuss the Frequency Shift Keying (FSK)

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Frequency Shift Keying (FSK)

If the frequency of sinusoidal carrier wave is varied (switched) as per the digital input signal, then it is known as the frequency shift keying (FSK). It is analogous to frequency modulation (analog modulation).

The reason behind why FSK is analogous to FM is....

In Frequency Modulation (FM), the frequency of the carrier wave is varied according to the instantaneous value of the modulating signal, in the same way in frequency shift keying also, the frequency of the sinusoidal carrier wave is varied (switched) as per the digital input signal. The difference is only of the nature of the modulating signal. In FM the modulating signal is of analogue nature while in FSK modulating signal is digital.

Now to understand the concept of frequency shift keying; look at the image shown below carefully

Frequency Shift Keying (FSK) Waveform

This image shows three parts

Digital Input signal (0 1 1 0 0 1)

Sinusoidal carrier wave and

FSK waveform

So here the basic purpose of Frequency Shift Keying (FSK) is to modulate (change/switch) the frequency of the carrier wave, according to the digital input signal.

Now observe the image, the places where digital input '0' is to be transmitted; the frequency of the sinusoidal carrier is decreased but when we transmit '1'; the frequency of the carrier wave is increased.

(Frequency is the number of cycles passed per second or 1/Time period).

So in Frequency Shift Keying (FSK), we have two types of frequencies of the carrier wave, low frequency for the transmission of '0' and high frequency for the transmission of '1'.

In this way, in Frequency Shift Keying (FSK), the information of the digital input signal is present in the frequency variations of the carrier wave. That is why it is known as frequency shift keying.

Now let's discuss the Phase Shift Keying (PSK)

Phase Shift Keying (PSK)

In phase shift keying, phase of the carrier wave (analog) is varied as per the digital input signal. Phase shift keying is analogous to Phase Modulation (analogue phase modulation).

The phase shift keying is very much similar to Phase Modulation (PM), because in both of these modulation techniques, the phase of the carrier wave is changed, according to the instantaneous value of the modulating signal. The difference is only of the nature of the modulating signal. In phase modulation, the modulating signal is analog but in case of phase shift keying, modulating signal is of digital nature.

The carrier wave is of analogue kind in both of these modulation techniques.

Now we will understand the basic concept of Phase Shift Keying (PSK), with the help of an example shown in the image given below.

Phase Shift Keying (PSK) Waveform

The Image contains three parts

The digital input signal (011001)

The sinusoidal carrier wave (analog)

PSK waveform

Now let's understand the basic concept, how the phase shift keying takes place.

In Phase Shift Keying (PSK), the phase of the carrier wave is changed (switched) according to the digital input signal. Therefore the information of this digital input signal is present in the phase shift variations of the carrier wave.

Here we will try to understand the concept of PSK with the help of an example given in this image.

Notice here that, whenever the digital input changes the bit (either from '0' to '1' or from '1' to '0'), a phase shift of 180 degrees (π) takes place in the carrier wave. But no phase change occurs when there is no change in the digital bit.

In this image, observe; the phase shift of 180 degrees takes place in the carrier wave at three places. At all these three places, the digital input bit has either change from '0' to '1' or from '1' to '0'. No phase shift takes place when two successive (back to back) 1's or two successive 0's are to be transmitted (as per the image). Hence we get the PSK waveform in this way.

This was all about three kinds of digital modulation techniques, amplitude shift keying, frequency shift keying and phase shift keying.

For more, please access to https://www.soukacatv.com.

Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

Skype: soukaken

Source：engineeringmadeeasypro

#Digital modulatorDigital modulator manufacturerDigital modulator supplierChina Digital modulator manufactureranalog modulator16in1 digital h

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soukacatv · 5 years ago

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Modulation Schemes: Moving Digital Data with Analog Signals | Soukacatv.com

Modulations are the techniques to carry digital data over analog waveforms. This rather arcane subject has been brought to the forefront of the DSP, EE, and telecommunications worlds by the ongoing interest in broadband communications, specifically, the great opportunity represented by bringing low cost broadband communications to the home. Think what it would be like to log on to the Internet or to the corporate LAN at speeds of over a megabit per second. The potential is enormous. The phone companies are approaching this opportunity with a grab bag of technologies known as DSL, digital subscriber loops. Many articles have appeared recently on ADSL, RDSL, SDSL, HDSL, MDSL, and VDSL. These will be covered in more depth in future newsletters. The cable companies are offering broadband services with cable modems. In either case, modulations are one of the fundamental technologies.

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The modulation process places (analog or digital) signal information onto sinewave carriers while demodulation reverses the process at the receiving end. Modulation schemes are very much in the news today because newer algorithms that take advantage of newer and more powerful DSP architectures make possible faster and more reliable communications than was possible before. However, modulation changes, with few exceptions, are incompatible with previous schemes, making the economic cost of improvements very high if there is an installed base of users or equipment to worry about.

As you will see below, there are many types of modulation schemes available today. In the xDSL marketplace, there is an active marketing war going on between those in the CAP camp and those vendors in the DMT camp. A companion article in this newsletter from Rupert Baines of Analog Devices goes a long way towards explaining the CAP vs. DMT debates. Another technology camp where modulations are very much in the news is the cable modem camp. The cable operator companies have banded together to sort out these issues in order to bring a measure of standardization to their industry. These standardization issues are outside the scope of this newsletter. The information below is an overview to help you sort through the issues.

Modulation Schemes: Moving Digital Data with Analog Signals

Analog modulation processes perform their magic by changing one or more of the three characteristics of a sine wave: amplitude, frequency, and phase.

Digital modulation applies a digital data stream to the carrier and makes the data stream compatible with the RF communications channel. Each wave state generated in this way represents one symbol of data (each symbol is an N-bit word where N is a power of two from 1 to 8, depending on the technology used). The resulting modulations schemes are called amplitude shift keying, frequency shift keying, and phase shift keying. In RF communications however, the two main approaches are phase shift (constant amplitude) and amplitude shift. The number of symbols per second transmitted is known as the baud rate. The number of bits per second equals (symbols per second) multiplied by (bits per symbol).

When it comes to modulations, the lack of standards becomes quite evident. A hodgepodge of modulation techniques with a range of price/performance features are in use today, although the cable modem industry seems to be settling on a de-facto turn to a 64-QAM (N=6) or 256-QAM (N=8) delivery model for downstream data, and QPSK for a moderate bit-rate return path.

All modulation schemes can be judged by their spectral efficiency and by their error rates. Spectral efficiency is the input digital rate divided by the allocated RF channel bandwidth. The unit of measure is "bits/Hz." The error rate (usually failed bits per million or bits per billion of "good" bits) is a function of several factors, including susceptibility to noise and interference, susceptibility to fading, and non-linearity, which can arise due to dependencies on signal frequency and amplitude. In general, as spectral efficiency increases, so unfortunately does the error rate, which means a higher signal-to-noise ratio might be needed to achieve acceptable error rates.

There are several ways to achieve more than one bit/Hz of throughput. Instead of simple binary encoding, the system can define four different voltages or phases for a single wave cycle, allowing one cycle to represent a two-bit symbol. If both phase and amplitude can vary simultaneously over four values, then one cycle can represent one of 16 discrete logical states. This squeezes 4 bits of data into a single wave cycle, or 4 bits/Hz. Much of the work on modulation techniques currently benefiting the cable modem industry stems from interest in digital video and from technology developed for telephony. While MPEG-2 is becoming the digital video standard for the broadcast industry, digital modulation techniques allow vendors to squeeze 6 or more digital channels into the 6 MHz space normally used for a single analog channel. This is one of digital video's major benefits (and is the basis for much of the talk about 500 cable channels in the future).

The set of available transmission symbols in a particular modulation scheme is known as its alphabet while a graph of the alphabet on a complex plane is known as the constellation (see examples below). After symbols have been formed and converted to complex numbers, the constellation diagram is drawn by plotting the real part, I, and complex (or imaginary) part, Q, on a 2-D map.

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Carrierless Amplitude Modulation/Phase Modulation (CAP) CAP is a bandwidth-efficient two-dimensional pass band line code derived from QAM by AT&T Bell Labs as part of an effort to produce a variant of QAM that could be efficiently implemented on a digital signal processor. 16-CAP has been adopted by DAVIC, the Digital Audio-Visual Interoperability Council, for interactive TV and video-on-demand applications and is proposed for SVD systems. In 16-CAP, blocks of four bits are mapped into one of 16 possible 2-D symbols in each symbol period. Two bits represent the quadrant, two bits identify a symbol within the quadrant. Increasing the number of bits per symbol increases bandwidth efficiency. But the modulation scheme also becomes more sensitive to noise. This is the basis of any modulation tradeoff. In Switched Digital Video systems, 16-CAP squeezes 51.84 Mbps into a downstream signal occupying approximately 20 MHz of bandwidth.

Code Division Multiple Access (CDMA) CDMA is a form of spread spectrum transmission which works by coding and spreading the information to be transmitted over a wide band. CDMA is asynchronous, and typically uses a 30 MHz bandwidth. CDMA used by some vendors, like Zenith and Cisco, who believe the spread spectrum approach to be superior in noisy upstream environments. Maximum digital bandwidth is approximately 10 Mbps over cable.

Coded Orthogonal Frequency Division Multiplexing (COFDM) COFDM is an experimental approach, intended for broadcast TV, which works by taking the transmitted data and spreading it over a large number of carriers, rather than modulating it all onto a single carrier. Hence, COFDM creates a large number of parallel paths, each of which carries data at a slower rate than the overall signal. The longer symbol times are more resistant to system noise. The data on the carriers can be modulated using one of the standard digital modulation schemes such as QPSK, 16-QAM, 64-QAM, or 256-QAM. Data is spread redundantly over many carriers so that a loss of some carriers leads only to loss of an occasional bit, a problem which can be corrected for at the receiving (forward-error correction) end. ADC Telecom uses orthogonal frequency division multiplexing for its cable-based telephony product to modulate 240 individual DS0 channels into a 5MHz spectrum with 0.5 MHz guardband on either side. This is very attractive to a cable operator with only 18 MHz usable upstream bandwidth. While OFDM has many advantages, it requires more signal processing horsepower at the headend than do some of the other modulation techniques.

Figure 1: OFDM breaks the channel into many subchannels and shifts traffic to a clear channel when needed.

Quadrature Amplitude Modulation (QAM) QAM systems combine PSK and ASK to increase the number of states per symbol. QAM is a proven technique for the transmission of digital data over a wide range of channels from voice band modems at 9600 bps to microwave links transmitting hundreds of Mbps. QAM is also the modulation technique used by V.34 modems. Each symbol value represents multiple bits. 16-QAM carries 4 bits per symbol while 256-QAM carries 8 bits per symbol. The signal-to-noise ratio at the receiver determines the QAM level that can be used reliably on a given transmission channel. Typical terrestrial and cable channels allow 16-QAM and 256-QAM, leading to digital data rates of approximately 20 and 40 Mbps, respectively.

In a typical cable TV application, 64-QAM can squeeze a 30 Mbps data stream into a 6 MHz (bandwidth) TV channel. QAM is also of use for digital video broadcast. Note that for video-on-demand or MPEG-based broadcast video delivery, 64-QAM allows five channels of 6 Mbps video for each analog channel allocation. For telephony, which uses 64 kbps data streams, a single "video channel" could handle over 450 downstream phone calls, which would be time-division multiplexed within the DataStream. Hence, in 750 MHz cable systems, the upper 240 MHz can contain up to 1000 3-Mbps DataStream, each carrying a unique digital address that directs it to a particular set-top box or cable modem (used for video on demand, or VOD). QAM is used in some upstream traffic designs, but is less noise resistant, though more bit-efficient, than QPSK.

It is easier to visualize QAM by looking at 16-QAM. QAM separates points widely and is hence fairly noise immune. The system for 16-QAM combines 4 input bits to produce 1 signal burst. Both phase and amplitude are modulated. Odd-numbered bits in the input stream are combined in pairs to form one of 4 levels which modulate the sine term. Even-numbered bits are similarly combined to modify the cosine term. Sine and cosine terms are then combined.

V(t) = x(t) cos1/2t + y(t)sin1/2t

Figure 2: I-Q diagram or constellation for 16-QAM scheme.

16-QAM has better spectral efficiency than 8-PSK and is less sensitive to noise than 16-PSK because the spacing between symbols are larger (see diagrams below). This is true because the symbols are not all on the same circle; the resultant signals are not all of the same amplitude.

Figure 3: Digital multiplexing of data, video, and voice services in the cable headend.

Quadrature Phase Shift Keying (QPSK) QPSK (which is QAM without an amplitude component) has become the preferred modulation format for the upstream. QPSK is inherently robust and economical. While other modulation techniques have been proposed with efficiencies higher than the 1.5 bits/Hz of QPSK, these formats have yet to be tested as thoroughly. QPSK has been selected by DAVIC as the upstream modulation format, and is the current front-runner for selection by the IEEE 802.14 committee. QPSK is also used in many satellite systems.

QPSK involves channel hopping until a clear path is found. QPSK is sometimes called four-phase PSK; the phase of the carrier can take on one of 4 values. Each transmitted symbol represents two bits.

00 01 10 11

Acos(wt) Acos(wt+90) Acos(wt+180) Acos(wt+270)

Figure 4: Constellations for QPSK (4-PSK) and 8-PSK

The system is less bit-efficient, but more noise-resistant and has advantages in its ability to operate over long distances with many interfering sources such as those found in a neighborhood cable network. For this reason, QPSK is favored for upstream traffic in cable modem applications. QPSK delivers about 1.5 bits per Hertz of bandwidth used. QPSK can go up to 10 Mbps in cable systems, but uses up a large portion of the available upstream bandwidth. Hence, most symmetrical cable modem products are expected to be limited to 10 Mbps. QPSK is also used for cable-based telephony applications (as well as some set-top box designs). Approximately 50 kHz of bandwidth is required for one DS0 channel (64 kbps). Individual channels are assigned to callers on a per-call basis anywhere within the 6-to-42 MHz band (downstream telephony modulations are different. Up to 72-64 kbps DS0 channels are packaged within a single 3 MHz slot in the 50-to-750 MHz region).

Figure 5: Block diagram of cable modem with QPSK modulation. Source: Hewlett Packard

Synchronous Code Division Multiple Access (S-CDMA) S-CDMA is a modulation scheme introduced by Terayon Corporation. With ordinary time division multiple access (TDMA) modulations, users share data channels by taking turns accessing the network in different time slots; with ordinary frequency division multiple access (FDMA) modulations, all the time is used but the available frequencies are divided up into multiple channels. With S-CDMA technology, the information is a spread over a wide band of the spectrum and all the frequencies are used all the time. S-CDMA allows for 10 Mbps throughput over each 6 MHz channel, upstream and downstream. The spread spectrum results in 10 Mbps by sending multiple streams of data, each comprised of 64 kbps. These are interleaved within a 6 MHz bandwidth. Individual 64 kbps streams may be allotted to telephony, while multiples of these may be used for videoconferencing, Internet access, etc. S-CDMA, according to Terayon, addresses the cable modem noise ingress problem better than a frequency-hopping scheme because it eliminates the process of searching for clean frequencies. S-CDMA spreads the information over the entire 6 MHz channel and uses encoding to make the transmission noise immune. Also, according to Terayon, the 10 Mbps upstream bandwidth addresses the capacity issues presented by the limited 5-42MHz spectrum.

Vestigal Side Band (VSB) VSB is the major competing modulation technique (to QAM) for downstream transmission on HFC networks. 32-VSB is one of the modulations used by Zenith for downstream delivery. 2-, 4-, and 8-VSB is also used by Hybrid Networks for upstream data. Using VSB, operators can offer reverse-band channels at 512 kbps using a 300 kHz channel, or they can range speeds between 128 kbps and 2.048 Mbps. Data traveling upstream can be rapidly moved to cleaner areas of the 5-40 MHz spectrum during adverse conditions posed by electrical noise and signal ingress. VSB is the modulation scheme selected by the Grand Alliance for digital television.

QAM and VSB Comparison The March 1995 issue of the IEEE Transactions on Broadcasting carried a paper written by K. Kerpez of Bellcore which compares QAM and VSB for HFC networks. The paper notes that both modulations are bandwidth efficient and use multiple signal levels to send multiple bits/Hz. VSB conserves bandwidth by only transmitting a single sideband of the modulated RF spectrum while QAM conserves bandwidth by sending two orthogonal sine and cosine carriers in the same frequency band. The paper concludes that the two approaches have practically the same overall performance and costs on an HFC network, although they are incompatible and have many differences.

16-VSB

64, 256-QAM

Proponents

Zenith, Grand Alliance

Broadcom, AT&T, Scientific-Atlanta, General Instruments

Prior Use

Modems

Receiver

Analog front-end demodulator

All digital

Symbol Rate

10.76 Mbaud

5 Mbaud

Information Bit Rate

38.6 Mbps

27 Mbps (64-QAM) 36 Mbps (256-QAM)

Table 1: Comparison of VSSB and QAM. Source: IEEE Transactions on Broadcasting, Vol. 41, No. 1, March, 1995, page 9

Modulation and Testing In a paper presented on Testing of Digital Video on Cable TV Systems, engineers from Hewlett Packard noted that a cable system will probably have to manage program material transported in different digital video formats. This presents a myriad of electronics testing issues to the headend system operator, a subject outside the scope of this study. However, the paper did present the following comparison of cable modulation techniques.

Modulation

Advantage

Disadvantage

QAM

High spectral efficiency

Sensitive to signal-to-noise ratio

VSB

Robust carrier and symbol clock recovery

High peak-to-average power ratio

QPSK

Robust in low signal-to-noise environment

Not spectral efficient

COFDM

Robust in high multipath environments

Complex to implement and requires more expensive modulation hardware

Table 2: Comparison of modulation techniques. Source: Hewlett Packard

Modulation and Filtering While an FCC channel is defined as having a 6 MHz bandwidth, the edges of this are often not used in order to provide "space" between channels and to avoid interference. While an ideal pulse can be used to transmit signals, an ideal pulse is impractical. Waveforms in reality are never perfect in shape. Practical systems use pulses with more bandwidth than the ideal. The bandwidth above the minimum is called excessive bandwidth, usually expressed as a per cent, and involves the use of roll off filters. Using the Nyquist principle, 100% excess bandwidth is twice (2x) the minimum needed. Practical systems typically have excess numbers between 10% and 100%.

Figure 6: Bandwidth and rolloff.

Increasing the excess bandwidth simplifies implementation of the communications system, but reduces spectral efficiency. The type of rolloff filter used is a network design consideration, and affects the throughput possible in a data delivery system. This also explains why there is variation in cable modem specifications from different vendors using the same modulation techniques.

Bits/Hz

Mbps

Rolloff Filter

20%

100%

20%

100%

QPSK

1.67

16-QAM

3.33

64-QAM

256-QAM

6.67

Table 3: Effect of filtering on modulation techniques and bandwidth.

Figure 7: Block diagram of cable modem with QAM/QPSK modulation

Jumping quickly from the cable side to the telephone side of the coin, ADSL is still in its formative stages. The CAP-based ADSL implementations have enabled 1.5 Mbps MPEG-1 video over common two-wire subscriber telephone connections with 64kbps upstream. CAP uses a single QAM signal instead of dividing the channel into multiple tones, and is thus more susceptible to interference. A newer version of the CAP ADSL technology is being marketed under the GlobeSpan label with one-way speeds of over 6 Mbps.

The CAP vs. DMT debate has taken on the nature of a religious holy war within the ADSL community and has stolen much attention and, perhaps, momentum. The CAP crowd has been pushing to make CAP a standard, pointing out that their technology is less complex, cheaper, easier to implement, and meets the large majority of user needs. The DMT team argues that their solution is technologically superior from speed and noise immunity considerations. The two are totally incompatible. Several "box vendors" have announced that they will have products which support both flavors, so they are "modulation neutral" and one vendor, 3Com/US Robotics, has even announced the intention to use a very powerful DSP inside their DSL modem which would be capable of running both modulations (only one at a time, however) depending on the software code which is downloaded to the chip.

According to an opinion expressed by Analog Devices (see companion newsletter article), resolving "the bitter dispute over ADSL line code modulation is crucial in order to expedite system development, speed deployment, and ultimately abate the growing traffic congestion on the nation's telephone infrastructure."

CAP is closely related to QAM; in fact the two are compatible. QAM is well understood. It is a single carrier signal where the data rate is divided into two and modulated onto two orthogonal carriers I and Q using sine and cosine mixers, before being combined and transmitted. CAP operates in the frequency domain, whereas DMT operates in the time domain.

DMT is a multi-carrier modulation system that resembles OFDM. DMT divides signal frequency into many discrete bands or sub-channels. These are independently modulated with a carrier frequency corresponding to the center frequency of the bin and then processed in parallel. DMT's ANSI T1.413 standard specifies 255 sub-carriers, each with a 4 kHz bandwidth. Each channel can be independently modulated from zero to a maximum of 15 bits/Hz (32-QAM on each channel). This allows up to 60 kbps per tone. (DMT-based ADSL uses 249 channels for downstream data, leading to a theoretical maximum of (249 * 60) 14.94 Mbps. At low frequencies, where copper wire attenuation is low and SNR is good, 10 bits/Hz is typical. In unfavorable line conditions modulation can be relaxed to accommodate lower SNR, and 4 bits/Hz is common. The whole process is analogous to simultaneously running 256 modems on a chip. The result is 6 Mbps performance on a 4 kHz phone line.

Figure 8: CAP and DMT Concepts.

Conceptually, CAP symbols last a short time (0.001 sec) but have sizable bandwidth. DMT symbols last a long time (0.250 ms) but occupy a narrow frequency band. The long time period makes them less susceptible to wideband noise spikes.

DMT

CAP

Directs information to subcarriers which are modulated independently

Single-carrier system

More complex to initialize

Faster start-up time

Rate adaptive, steps of 32 kbps

Supports rate adaption by varying the constellation and the bandwidth in steps of 320 kbps

High latency

Low latency

More adept at coping with multiple RFI sources

More resistant to RFI, which is averaged across the wideband of a single carrier

Greater immunity to impulse noise because its symbols are longer

More difficult for echo cancellation

Lower power needs, simpler analog design stages needed

More versatile, flexible, but more complex

Easier to implement

More field experience and test equipment available for QAM/CAP technology

Patented technique with serious intellectual property rights questions

Few chip sets available

1.5 Mbps chip sets available in volume

Table 4: Comparison of DMT and CAP

It should be pointed out that DMT won a major victory when the ADSL Joint Procurement Consortium, a collection of four RBOCs (Regional Bell Operating Companies), elected to go with a system using both ADSL-DMT and ATM.

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Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

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Source：edn https://www.edn.com/electronics-news/4196988/Modulation-Schemes-Moving-Digital-Data-With-Analog-Signals

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Basic Introduction about Digital Communication: How Digital Signal Process Works and Advantages | Soukacatv.com

Today’s world is heavily dependent on Digital Communication. Whatever we use for any sort of communication, it has a niche touch of Digitization. This post will discuss about various aspects of Digital Communication such as Introduction, Basic components, How Digital Signal Communication Process works and its various advantages over Analog Signal Communication.

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Introduction to Digital Communication

Digital Communication is defined as the process by which Digital devices communicate information digitally. The communication that occurs in our daily life is in the form of signals such as sound signals. These sound/ audio signals are normally analog in nature. For such communication via sound signals, we must be near the source of sound signal, at least within our hearing range. But what if the source and receiver are at a long distance? In case if the communication needs to be established over a distance, the analog signals are sent through wire, using different techniques for effective and efficient transmission.

Why Digitization is needed for Communication?

The traditional methods of communication were using analog signals for long distance communications. Due to the long distance, the analog signal has to go through many losses such as distortion, intervention or interference and even security breach too.

To minimize and overcome these types of losses, the signals are now digitized using different techniques. With the use of digitized signals, the communication becomes more clear and accurate with minimum or no losses.

Fig. 2 – Representation of Digital and Analog Signals

The Fig. 2 above represents analog and digital signals. The digital signals consist of 1s and 0s which indicate High and Low values respectively.

Basic Components of a Digital Communication System

Broadly, every digital Communication system consists of these basic components.

· Source

· Input Transducer

· Analog to Digital Converter

· Source Encoder

· Channel Encoder

· Digital Modulator

· Communication Channel

· Digital Demodulator

· Digital to Analog Converter

· Channel Decoder

· Source Decoder

· Output Transducer

· Output Signal

Fig. 3 – Basic Components of Digital Communication System

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How Digital Communication Process Works?

1. Source

The source consists of an analog signal.

For example: A Sound signal

2. Input Transducer

This block consists of input transducer which takes a physical input and converts it to an electrical signal For example: Microphone

3. Analog to Digital Converter

This electrical signal from Input Transducer is further processed and converted into Digital Signal by Analog to Digital Converter.

Fig. 4 – Analog to Digital Conversion

4. Source Encoder

The source encoder compresses the data into lowest number of bits. This procedure helps in efficient operation of the bandwidth. It removes the unnecessary bits.

5. Channel Encoder

The channel encoder, here the coding is done for error correction. During the transmission of the signal, due to the sound in the channel, the signal may get distorted. To avoid this, the channel encoder adds some unnecessary bits to the transmitted data. These bits are the error correcting bits.

6. Digital Modulator

Here the signal which is to be transmitted is modulated by a carrier. The carrier is used for effective long distance transmission of data.

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7. Digital to Analog Converter

The digital signal extracted from the carrier is then converted again into analog so that the signal can be passed effectively through the channel or medium.

8. Channel

The channel provides a path for the signal and permits the analog signal to transmit from the transmitter end to the receiver end.

9. Digital Demodulator

This is the place from where the data retrieving process is started at the receiver end. The received signal is demodulated and again converted from analog to digital. The signal gets rebuild here.

10. Channel Decoder

The channel decoder does the error corrections post sequence detection. The distortions which might take place during the transmission are corrected by adding some additional bits. Addition of these bits help in the complete recovery of the original signal.

11. Source Decoder

The resulting signal is again digitized by sampling and quantizing. This is done to obtain the unadulterated digital output without any loss of information. The source decoder creates again the source output.

12. Output Transducer

This is the final block which converts the signal into its original form (which was at the input of the transmitter). It converts the electrical signal into physical output.

For example: Speaker

13. Output Signal

This is the output for which the whole process is done.

For example: The sound signal received

Fig. 5 – Advantage of Digital Signal

Advantages of Digital Communication over Analog Communication

Digital Communication has many advantages over Analog Communication. Some of them are listed below:

· The specific signal level of the digital signal is not very important. Due to this, digital signals are quite unaffected by the flaws of electronic systems that may spoil analog signals.

· The configuration process of digital signals is easier than analog signals.

· Encryption works better in Digital Signals (using codes).

· Digital circuits are more consistent and reliable.

· Digital circuits are easy to design (normally).

· The cost of manufacturing Digital Circuits is lesser than Analog Circuits.

· Digitals Signals do not get corrupted by noise, interference, and distortions.

· Cross-talking is very rare in Digital Communication.

· Long distance data transmission is more easy and cheap with Digital Signals.

· The hardware implementation in digital circuits is much more flexible if compared to analog circuits.

· The method of combining digital signals using Time Division Multiplexing (TDM) is easier than the method of combining analog signals using Frequency Division Multiplexing (FDM).

· Digital signals can be saved and extracted more easily than analog signals.

· Most of the digital circuits have almost common encoding techniques and therefore similar devices can be used for a number of purposes.

· Digital Communication supports multi-dimensional transmissions simultaneously.

· The capability of the channel is efficiently utilized by digital signals.

· The signal is unchanged as the pulse needs a high interruption to change its properties, which is very complex.

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Source：electricalfundablog

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What is Phase Modulation: Advantages, Disadvantages, and Applications? | Soukacatv.com

In our day by day life, we can see many entertainment media sources for communication such as radio, TV, newspaper, mobile phone, internet, and with a lot of people. Communication can be defined as; it is the procedure of two ways or one-way communication of information from one place to another or one person to another person. For example, if we take a basic communication system it comprises of three components namely transmitter (Tx), receiver (Rx), and a communication channel in between them. The designing of a transmitter and a receiver in a communication system can be built with a set of electronic circuits. A transmitter converts the data into a signal to transmit over a communication medium. A receiver is used to change the signal reverse to the original data. The channel is the medium that transmits the signal from one place to another. If we want to transmit a signal from one place to another, then we need to make the signal stronger. Once the signal strengthening process is done then the signal can transmit to a long distance. This is known as the modulation process.

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What is Phase Modulation?

The term PM or phase modulation definition is a type of modulation intended for transmitting communication signals. It changes message signal in accordance with the carrier signal due to differences in the immediate phase. This modulation is the combination of two principal forms such as frequency modulation and angle modulation.

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The carrier signal’s phase is modulated to follow the amplitude of the message signal. Both pinnacle amplitude, as well as the carrier signal’s frequency, is maintained stable, although when the message signal’s amplitude changes, then the carrier signals phase also changes. Phase Modulation can be defined as the Phase of the carrier (Ø) signal is varied proportional to (in accordance with) the Amplitude of the input modulating signal.

Phase Modulation Waveforms

PM Equation:

V = A sin [ wct + Ø ]

V = A sin [ wct + mp sin wmt ]

A = Amplitude of PM signal

mp = Modulation Index of PM

wm = 2π fm wc = 2π fc

V = A sin [2π fct + mp sin2π fmt]

The phase modulation diagram is shown above. The carrier phase deviation will be more if the input signal amplitude increases and vice versa. When the input amplitude increases (+ve slope) the carrier undergoes phase lead. When the input amplitude decreases (-ve slope) the carrier undergoes phase lag.

Therefore as the input amplitude increases, the magnitude of the phase lead also goes on increasing from instant to instant. For example, if the phase lead was 30 degrees at t =1 sec, the phase lead increases to 35 degrees at t = 1.1 sec and so on. Increase in phase lead is equivalent to an increase in frequency.

Similarly, as the input amplitude decreases, the magnitude of the phase lag also goes on increasing from instant to instant. For example, if the phase lag was 30 degrees at t =1 sec, the phase lag increases to 35 degrees at t = 1.1 sec and so on. Increase in phase lag is equivalent to decrease frequency. Therefore phase modulation waveform will be similar to FM waveform in all aspects.

Forms of Phase Modulation

Even though PM is used in analog transmissions, it is widely used as a digital type of modulation wherever it controls among dissimilar phases, which is known as PSK (phase shift keying), and there are several forms are available in this.

It is still possible to merge PSK (phase shift keying) & AK (amplitude keying) in a type of modulation is also called as QAM (quadrature amplitude modulation). Some of the forms of FM that are used are listed below.

· Phase Modulation (PM)

· Phase Shift Keying (PSK)

· Binary Phase Shift Keying (BPSK)

· Quadrature Phase Shift Keying (QPSK)

· 8-Point Phase Shift Keying (8 PSK)

· 16-Point Phase Shift Keying (16 PSK)

· Offset Phase Shift Keying (OPSK)

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The above showed list is some of the forms of PM which are frequently used in the applications of radio.

Advantages and Disadvantages of Phase Modulation

The advantages of phase modulation include the following.

· Phase modulation (PM) is a simple contrasted to Frequency modulation (FM).

· It is used to find out the velocity of a target by removing Doppler data. This needs constant carrier which is achievable during phase modulation however not in FM (frequency modulation).

· The main benefit of this modulation is signal modulation because it permits computer for communicating on high-speed using a telephone system.

· When the information is being transmitted without intrusion then the speed rates can be observed.

· And one more advantage of PM (phase modulation) is improved immunity toward the noise.

The disadvantages of phase modulation include the following.

· Phase modulation needs two signals by a phase variation among them. Through this, both the two patterns are required like a reference as well as a signal.

· This type of modulation requires hardware which obtains more complex due to its conversion technique.

· Phase ambiguity arrives if we exceed index pi radian of modulation (1800).

· Phase modulation index can be enhanced by employing frequency multiplier.

Phase Modulation Applications

The applications of phase modulation include the following.

· This modulation is very useful in radio waves transmission, and it is an essential element in several digital transmission coding schemes.

· Phase modulation is widely used for transmitting radio waves and is an integral element of many digital transmission coding schemes that support an ample range of wireless technologies such as GSM, Satellite television, and Wi-Fi.

· Phase modulation is used in digital synthesizers for generating waveform and signal

· PM is used for signal and waveform generation in digital synthesizers like Yamaha DX7 for phase modulation synthesis implementation, and Casio CZ for sound synthesis which is known as phase distortion.

Thus, this is all about what is phase modulation, PM equation, a phase modulation graph. From the above information finally, we can conclude that PM is a type of modulation which denotes data as differences in the immediate phase of a carrier wave. Variation in phase based on the low-frequency will provide phase modulation. Here is a question for you, what is a self-phase modulation?

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Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

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Source: elprocus

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Digital Communication: Advantages of Digital Modulation | Soukacatv.com

OBJECTIVES:

To explain digital modulation To identify the different digital modulation schemes To discuss the operations and features of the different modules

KEY TERMS:

Digital Transmission is the transmittal of digital pulses between two or more points in a communication system Digital Radio is the transmittal of digitally modulated analog carrier between two or more points in a communication system. Bit Rate is the rate of change in the input of modulator. Baud Rate is the rate of change in the output of modulator.

Before anything else, let us first recall or understand the difference between Analog Signals and Digital Signals; and the difference between Analog Radio and Digital Radio.

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The Comparison between Analog Signals and Digital Signals:

ADVANTAGES of Digital Signals

Ease of Processing. Rather than being sinusoidal or having a continuous value of signals, the digital signal has a sequence of two discrete values. It can either be 1 or 0 but cannot be in between. These look like square waves. Ease of Multiplexing. Multiplexing is a method of combining signals so it is easier to combine discrete data than continuous. Noise Immunity. In [Digital Communication #1: Information Capacity] I explained noise. They are the unwanted signals that interfere with our signals. Because of the type of wave the digital signal possess, it is hard for the noise to penetrate the signal.

DISADVANTAGES of Digital Signals Circuit Complexity. Higher Cost.

The Comparison between Analog Radio and Digital Radio:

In digital radio, the modulating and demodulating signals are digital pulses rather than analog waveforms. Digital Radios used Digital Modulation Schemes.

What is Digital Modulation?

Digital Modulation is the transmittal of digitally modulated analog signals (carrier) between two or more points in a communication system. It is sometimes called as Digital Radio – Tomasi.

Have you ever wonder how is it even possible to send information without physical contact? Just like what I did, I typed this information and sent it here but how? Is it a magic that the messages we send and post online just appear from nowhere? Of course not! And everything we believe as magic can be explained through science. So to correct you and make you understand how things in our electronic communication been possible keep on reading and let us untangle the curiosity in ourselves.

Whenever we send a message from a transmitter, there is what we call carriers. These are the high-frequency signals that carry our information. They undergo a process called modulation. Modulation is where the carrier signal is changed and serves as the envelope or capsule of the information. Why is it that the carrier must be changed? Well that is the nature of modulation because if ever the information is the one being changed then the text you sent will also be changed. For instance you texted your partner the words’ LOVE YOU” but because of the unwanted changes of information occurred, then he/she may receive” YOU ARE NOT THE ONLY ONE” instead. It is impractical to use analog modulation so nowadays, we use digital modulation. In the type of modulation we are currently using, the information signal is also digital, which could be encoded or computer-generated but still uses an analog carrier. An Analog-to-Digital Converter is use resulting to a more complex circuit than an Analog Modulation Technique. Digital Modulation uses bit rate frequency or bf, which is basically the rate of change to the input of the modulator. It is represented by bits per second or bps.

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What are the Kinds of Digital Modulation?

1. Amplitude Shift Keying

It is simply a double sideband, full carrier amplitude modulation where the input modulating signal is in binary waveform. The output signal is always dependent on its input signal. It is basically an equivalent of an A.M. (Amplitude Modulation) wherein the amplitude of the signal is what being change. It is sometimes called as continuous wave modulation or on-off keying since because it is in binary form, it can only be shifted as on or off.

ASK Operation

If the INPUT logic is HIGH then the OUTPUT is the maximum peak amplitude of the carrier. While if the INPUT is LOW then the OUTPUT is ZERO. It only follows multiplication.

2. Frequency Shift Keying

It is a form of constant amplitude angle modulation that was proved by Emily Baudot, it similar to conventional FM or Frequency Modulation except that the modulating signal is a binary signal. This signal varies between two discrete levels. These levels can either be logic 1 known as Mark Frequency or logic 0 known as * Space Frequency*.

FSK Operation

If the INPUT logic is HIGH then the OUTPUT is the Mark Frequency. While if the INPUT is LOW then the OUTPUT is the Space Frequency.

3. Phase Shift Keying

This is another form of angle modulated, constant amplitude digital modulation --Tomasi

This is basically an equivalent of PM or Phase Modulation but the difference is that its input signal is in the form of binary.

Types of PSK

Binary PSK There are two possible output phases for a single carrier frequency which is either logic 1 or logic 0. When the digital signal changes it state then the phase of the output carrier shifts between two angles that are 180 degrees out of phase of the carrier. It is a form of suppressed carrier, square wave modulation of a continuous wave signal. It is sometimes called as Phase Reversal Keying or Biphase Modulation

Quaternary PSK The angle is being modulated while there is constant amplitude. From the its name “Quaternary”, it basically means that there are 4 possible output phases in a single carrier frequency with different input conditions

8-PSK The incoming bits are considered in groups of 3 or known as tribits The incoming serial bit stream enters in the bit splitter The I (in- phase) or Q (quadrature) bit determines the polarity while the C (control channels) bit provides the magnitude.

16-PSK The incoming bits are considered in groups of 4 or known as quad bits The output does not change until 4 bits have been inputted into the modulator.

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Dingshengwei Electronics Co., Ltd

Company Address: Building A, the first industry park of Guanlong, Xili Town, Nanshan, Shenzhen, Guangdong, China

Tel: +86 0755 26909863

Fax: +86 0755 26984949

Phone: +86 13410066011

Email:[email protected]

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Source: https://steemit.com/steemiteducation/@sissyjill/digital-communication-2-digital-modulation

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