What are the channel encoding techniques like LDPC in Digital communication?
what are the improvements and what are the tradeoffs ?
Sanket Nawale
Low-Density Parity-Check (LDPC) codes are a type of channel encoding technique used in digital communication systems to improve the error correction capability of the transmission.
LDPC codes work by adding redundant information, in the form of parity bits, to the data being transmitted. The receiver then uses the parity bits to check for errors and to correct errors that are detected. LDPC codes are called "low-density" because they have a relatively low number of parity bits compared to other error correction codes, such as Reed-Solomon codes.
Improvements:
Trade-offs:
In summary, LDPC codes provide a trade-off between error correction capability, bandwidth efficiency, encoding complexity, and decoding latency. The choice of channel encoding technique will depend on the specific requirements of the application and the trade-off between these different factors.
In some textbooks, channel coding is also referred to as error control coding, in which two parts are included: error detection (ED), and error correction (EC) respectively. For ED, the data is coded with relatively fewer redundant bits inserted so that a certain number of errors can be detected (but not corrected) in the receiver. When errors are detected, the receiver sends a repeat-request message back to the transmitter asking for retransmissions. This is therefore called automatic-repeat-request (ARQ) scheme. Obviously, this is possible only if a reliable feed-back channel is available. Oppositely, for EC, the data is coded with relatively more redundant bits inserted so that a certain number of errors can be corrected in the receiver. ED does not need a feed-back channel, thus is called forward error correction (FCC) coding, or simply error-correction coding, and can be used on simplex channels (i.e. channels in which the information flow is in only one direction).
In terms of the code structures, the error correction codes can be classified mainly into two types, the block code and the convolutional code. For instance, the LDPC and the turbo code belong to these two types respectively, tough both can achieve almost the maximum channel capacity limit indicated by the information theory. Furthermore, the convolutional code and the block code can be jointly used in a concatenated way (e.g., a convolutional code concatenated with a Reed-Solomon code) to provide additional coding gain.
The main cost to pay in using error control coding is the wideness of the signal spectrum (i.e., lower the spectrum efficiency), since more bits (or symbols) need to be transmitted within the same time duration. This can be viewed as a trade off between the signal-to-noise ratio and the bandwidth efficiency as indicated by the information theory. A solution to avoid this cost is the technique called trellis code modulation (TCM), in which the encoder and the modulator are jointly designed and optimized with expanded signal constellations.
It is a big topic, and too many things can be added further.
Thank You very much all!! Aparna Sathya Murthy Shouxing Qu Shujat Ali Janak Trivedi
methods used to transform a stream of data bits into a sequence of symbols that can be transmitted over a communication channel. The purpose of channel encoding is to increase the reliability of the communication by introducing redundancy into the transmitted signal, allowing the receiver to correct errors that may occur during transmission.
There are several types of channel encoding techniques, including:
Block Codes: In block coding, data is divided into blocks of fixed length, and each block is encoded independently. Popular examples include Hamming codes, Reed-Solomon codes, and convolutional codes.
Convolutional Codes: In convolutional coding, the encoding process is performed by sliding a small window over the input data stream and generating an output symbol for each window position. This creates a continuous stream of symbols that can be transmitted over the channel.
Turbo Codes: Turbo coding is a type of iterative coding where the output of one encoder is fed back into another encoder. The encoding process is repeated several times, improving the reliability of the transmission.
Low-Density Parity-Check (LDPC) Codes: LDPC coding is a type of linear error-correcting code that uses sparse parity-check matrices to encode the data. LDPC codes have been widely adopted in modern communication systems, including wireless networks and satellite communications.
Polar Codes: Polar coding is a relatively new coding technique that has gained popularity in recent years. It is based on a mathematical transformation of the input data, which converts the original data stream into two streams with different levels of reliability. The more reliable stream is used to transmit the most critical information, while the less reliable stream is used to transmit the remaining information.
These techniques are used in various communication systems, including wireless networks, satellite communications, and storage devices. The choice of encoding technique depends on the specific requirements of the communication system, such as the available bandwidth, the desired error correction capability, and the computational complexity of the encoder and decoder.
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