Pcm encoding and decoding

This module generates a pulse code modulated PCM- output signal from an analog input message. Introduction Pulse Code Modulation is a method of converting an analog signal into digital signals.

Information in analog form cannot be processed by digital computers so it's necessary to convert them into digital form. PCM is a term which was formed during the development of digital audio transmission standards.

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Digital data can be transported robustly over long distances unlike the analog data and can be interleaved with other digital data so various combinations of transmission channels can be used. In the text which follows this term will apply to encoding technique which means digitalization of analog information in general. The range of values which the signal can achieve quantization range is divided into segments, each segment has a segment representative of the quantization level which lies in the middle of the segment.

To every quantization segment and quantization level one and unique code word stream of bits is assigned. The value that a signal has in certain time is called a sample.

pcm encoding and decoding

The process of taking samples is called quantization by time. After quantization by time, it is necessary to conduct quantization by amplitude. Quantization by amplitude means that according to the amplitude of sample one quantization segment is chosen every quantization segment contains an interval of amplitudes and then record segments code word.

A PCM encoded signal is nothing more than stream of bits. The input analog message is sampled periodically. The sample rate is a sub-multiple of the external clock. The sampling is a sampleand-hold operation. It is internal to the module, and cannot be viewed by the user. What is held is the amplitude of the analog message at the sampling instant.

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Each sample amplitude is compared with a finite set of amplitude levels. These are the system quantizing levels of the signal. Each quantizing level is assigned a number, starting from zero for the lowest most negative level, with the highest number being L-1where L is the available number of levels.

Each sample is assigned a digital binary code word representing the number associated with the quantizing level which is closest to the sample amplitude. The number of digits n in the digital code word will depend upon the number of quantizing levels.

The code word is assembled into a time frame together with other bits as may be required.Login Now. This technique is the breakthrough for moving from analog to digital communication. This must be constrained to a defined bandwidth and amplitude range. The Nyquist criterion must be observed.

Pcm Encoding and Decoding Lab Report

This is in keeping with the input amplitude limits set for all analog modules. The input analog message is sampled periodically. The sample rate is determined by the external clock. The sampling is a sample-and-hold operation. It is internal to the module, and cannot be viewed by the user.

What is held is the amplitude of the analog message at the sampling instant. Each sample amplitude is compared with a finite set of amplitude levels. These are the system quantizing levels. Each quantizing level is assigned a number, starting from zero for the lowest most negative level, with the highest number being L-1where L is the available number of levels.

Each sample is assigned a digital binary code word representing the number associated with the quantizing level which is closest to the sample amplitude. This is alternately a one or a zero. These bits are used by subsequent decoders for frame synchronization. The frames are transmitted serially.

encoding and decoding

They are transmitted at the same rate as the samples are taken. The serial bit stream appears at the output of the module. This clock signal is synchronized to that of the transmitter. Extracts a frame synchronization signal FS from the data itself from the embedded alternate ones and zeros in the LSB positionor uses an FS signal stolen from the transmitter.

Extracts the binary number, which is the coded and quantized amplitude of the sample from which it was derived, from the frame.

Presents this voltage to the output Vout. The voltage appears at Vout for the duration of the frame under examination. Message reconstruction can be achieved, albeit with some distortion, by lowpass filtering. A built-in reconstruction filter is provided in the module. Find answer to specific questions by searching them here. It's the best way to discover useful content.

Download our mobile app and study on-the-go.Modulation is the process of varying one or more parameters of a carrier signal in accordance with the instantaneous values of the message signal. The message signal is the signal which is being transmitted for communication and the carrier signal is a high frequency signal which has no data, but is used for long distance transmission. There are many modulation techniques, which are classified according to the type of modulation employed.

A signal is pulse code modulated to convert its analog information into a binary sequence, i. The output of a PCM will resemble a binary sequence. The following figure shows an example of PCM output with respect to instantaneous values of a given sine wave.

Instead of a pulse train, PCM produces a series of numbers or digits, and hence this process is called as digital. Each one of these digits, though in binary code, represent the approximate amplitude of the signal sample at that instant.

In Pulse Code Modulation, the message signal is represented by a sequence of coded pulses. This message signal is achieved by representing the signal in discrete form in both time and amplitude. The transmitter section of a Pulse Code Modulator circuit consists of Sampling, Quantizing and Encodingwhich are performed in the analog-to-digital converter section.

The low pass filter prior to sampling prevents aliasing of the message signal. The basic operations in the receiver section are regeneration of impaired signals, decoding, and reconstruction of the quantized pulse train. Following is the block diagram of PCM which represents the basic elements of both the transmitter and the receiver sections.

This filter eliminates the high frequency components present in the input analog signal which is greater than the highest frequency of the message signal, to avoid aliasing of the message signal. This is the technique which helps to collect the sample data at instantaneous values of message signal, so as to reconstruct the original signal.

The sampling rate must be greater than twice the highest frequency component W of the message signal, in accordance with the sampling theorem. Quantizing is a process of reducing the excessive bits and confining the data.

pcm encoding and decoding

The sampled output when given to Quantizer, reduces the redundant bits and compresses the value. The digitization of analog signal is done by the encoder.

It designates each quantized level by a binary code. The sampling done here is the sample-and-hold process. Encoding minimizes the bandwidth used. This section increases the signal strength. The output of the channel also has one regenerative repeater circuit, to compensate the signal loss and reconstruct the signal, and also to increase its strength.

The decoder circuit decodes the pulse coded waveform to reproduce the original signal. This circuit acts as the demodulator.

pcm encoding and decoding

After the digital-to-analog conversion is done by the regenerative circuit and the decoder, a low-pass filter is employed, called as the reconstruction filter to get back the original signal. Hence, the Pulse Code Modulator circuit digitizes the given analog signal, codes it and samples it, and then transmits it in an analog form. This whole process is repeated in a reverse pattern to obtain the original signal. Pulse Code Modulation Advertisements.

Previous Page.Your email address will not be published. Website :. Save my name, email, and website in this browser for the next time I comment. There are some important advantages of PCM pulse code modulation which are given below, The PCM pulse code modulation convenient for long distance communication. It has a higher transmitter efficiency. It has a higher noise immunity.

There are some disadvantages of PCM pulse code modulation which are given below, The PCM pulse code modulation requires large bandwidth as compared to analog system. Encoding, decoding and quantizing circuit of PCM is very complex. It is used in space communication.

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It is used in telephony. Like 80 Dislike Related Articles: Basic block diagram of communication system What is modulation? Explain the frequency stability of an oscillator Advantages, disadvantages and applications of direct… Advantages and applications of spread spectrum Types of communication channels.

Tags: PCM. Leave a Reply Cancel reply Your email address will not be published.In computers, encoding is the process of putting a sequence of character s letters, numbers, punctuation, and certain symbols into a specialized format for efficient transmission or storage.

Decoding is the opposite process -- the conversion of an encoded format back into the original sequence of characters. Encoding and decoding are used in data communications, networking, and storage. The term is especially applicable to radio wireless communications systems. ASCII can depict uppercase and lowercase alphabetic characters, numerals, punctuation marks, and common symbols.

In data communications, Manchester encoding is a special form of encoding in which the binary digits bits represent the transitions between high and low logic states. In radio communications, numerous encoding and decoding methods exist, some of which are used only by specialized groups of people amateur radio operators, for example. The oldest code of all, originally employed in the landline telegraph during the 19th century, is the Morse code.

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The terms encoding and decoding are often used in reference to the processes of analog-to-digital conversion and digital-to-analog conversion.

In this sense, these terms can apply to any form of data, including text, images, audio, video, multimedia, computer programs, or signals in sensors, telemetry, and control systems.

Encoding should not be confused with encryptiona process in which data is deliberately altered so as to conceal its content. Encryption can be done without changing the particular code that the content is in, and encoding can be done without deliberately concealing the content.

Slack plans to launch the new messaging feature next year. New capabilities set for this year include audio and video messagingEncoding process converts the quantized samples into codewords. In a binary code, each symbol may have either a 0 value or a 1 value.

There are various formats i. They are known as line codes.

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Figure 4. With increase in number of independent message sources, the time interval allotted to each source has to be reduced to accommodate all the sources. This reduces the duration of each binary hit in PCM codeword. This increases the bandwidth requirement of the system. If the pulses become, very short then the impairments in the transmission medium start to interfere with the proper operation of the system.

Therefore, in practice, it is essential to restrict the number of message sources. For synchronization, it is essential to synchronize the clocks at the transmitter and receiver.

It is also known as decoding noise.

Pulse-code modulation

Both of them are present simultaneously but we shall consider them one by one to find their effect on the PCM system. The major effect of channel noise is introduction of transmission errors at the receiver when the PCM signal is being reconstructed. Due to such errors, the receiver will make mistake in making the decision about whether a 0 was received or a 1 was received.

A 0 may be mistaken as 1 and al may be mistaken as 0. Such errors must be minimized so as to improve the fidelity of PCM system.

The fidelity of a PCM system in presence of channel noise is measured in terms of error or probability of error. The probability of error or error rate is the probability that the symbol at the receiver output differs from that transmitted.

From figure 4. A very small increase in transmitted signal energy or power will make the reception of binary pulses almost error free. Table 4. Whereas below this threshold, the probability of error is high and hence the effect of noise is quite significant. The effect of channel noise may be reduced by using the regenerative repeaters. Another important characteristics of PCM system is its raggedness to interference. As discussed earlier, for on off signaling, there is no effect of noise unless the peak amplitude is greater than half the pulse height.

Thus, if adequate margin over the error threshold is provided, then the system can successfully withstand large amount of noise and interference. Hence we can say that PCM is a noise resistant or rugged system. The property is that, these systems tend to reduce the wideband noise above the threshold levels.

All the curves in figure 4.

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The dots indicate the threshold points.Pulse-code modulation PCM is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discsdigital telephony and other digital audio applications. In a PCM streamthe amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps.

Matlab Code for Pulse Code Modulation by u9fnfsmw.site Babu, VIT University

A PCM stream has two basic properties that determine the stream's fidelity to the original analog signal: the sampling ratewhich is the number of times per second that samples are taken; and the bit depthwhich determines the number of possible digital values that can be used to represent each sample. Early electrical communications started to sample signals in order to multiplex samples from multiple telegraphy sources and to convey them over a single telegraph cable.

The American inventor Moses G. Farmer conveyed telegraph time-division multiplexing TDM as early as Electrical engineer W. Miner, inused an electro-mechanical commutator for time-division multiplexing multiple telegraph signals; he also applied this technology to telephony. Inthe Bartlane cable picture transmission system used telegraph signaling of characters punched in paper tape to send samples of images quantized to 5 levels. Rainey of Western Electric patented a facsimile machine which transmitted its signal using 5-bit PCM, encoded by an opto-mechanical analog-to-digital converter.

Advantages, disadvantages and application of PCM (pulse code modulation)

British engineer Alec Reevesunaware of previous work, conceived the use of PCM for voice communication in while working for International Telephone and Telegraph in France. He described the theory and advantages, but no practical application resulted.

Reeves filed for a French patent inand his US patent was granted in PCM in the late s and early s used a cathode-ray coding tube with a plate electrode having encoding perforations. The plate collected or passed the beam, producing current variations in binary code, one bit at a time.

Rather than natural binary, the grid of Goodall's later tube was perforated to produce a glitch-free Gray codeand produced all bits simultaneously by using a fan beam instead of a scanning beam. Patent 2, filed in andgranted in Another patent by the same title was filed by John R.

Pierce inand issued in U. Patent 2, This development improved capacity and call quality compared to the previous frequency-division multiplexing schemes. Cummiskey, Nikil Jayant and James L.