In the process of digital signal processing, it is often necessary to sample, quantize and code analog signals and finally convert them into digital signals for computer processing.The coding rate is the proportion of useful information in the data stream after the sampling, quantization and coding of analog signals are completed.
The coding rate (also called coding rate or coding efficiency) is the proportion of useful parts (non redundant) in the data stream.That is, if the coding rate isk/n, for everykBit useful information, generated by encodernBit data, wheren-kIt is redundant.
IfRyesTotal bit rateorData signaling rate(including redundant error codes),Net bit rate(excluding useful bit rate of error correction code) ≤R·k/n。This means that excluding error correction codes, the coding rate is 1, and the total bit rate or data signaling rate is equal to the net bit rate or useful bit rate.
give an example
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For example:Convolutional codeThe typical coding rate of can be 1/2, 2/3, 3/4, etc. One redundant bit is inserted after each, two, and three bits.RS Reed-Solomon Block codeThe coding rate of RS (204188) is 188/204, and 204-188=16 redundant bytes are added to the useful information of each 188 bytes.
Some error correction codes have no fixed code rate——Rate free erasure code。
In many demodulation chips, the decoder mostly uses LDPC decoder.In the datasheet, it will be marked with the supported code rate, that is, the coding rate. For example, the m88ds3103 of Montage supports 1/4, 1/3, 2/5, 3/5, 1/2, 2/3, 3/4, 4/5, 5/6, 8/9, and 9/10 code rates.
The higher the coding rate, the higher the efficiency.When the channel quality is poor, more redundant information needs to be added to ensure that the receiver can demodulate the signal correctly. More redundant information means a low coding rate. The minimum coding rate is that one code needs to add three redundant codes, that is, 1/4 coding.When the channel quality is good, it can be demodulated with few redundant parity bits, and the coding rate can be improved.The system can select the appropriate coding rate according to the channel change, so that users with good channel quality can obtain higher rate and improve the average throughput.
Sampling rate and coding rate
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In short, the quality and volume of the signal depend on two aspects:sampling rateAnd coding rate.Sampling rate: the natural signal is continuous, but the computer cannot process it directly, so it should be "discretized".Take a simple example: the sine curve is continuous. After entering the computer, the computer divides the continuous curve into several points at a fixed time interval, so that it can be processed. This process is called sampling.Obviously, the greater the density of points, the more realistic the curve will be. This density is the sampling rate in signal processing.Each point takes up storage space, so the higher the sampling rate, the larger the volume.Coding rate: sampling is only the first step of processing.After sampling, the collected data should be stored.Storage requires space. How much space is used to store one second of sampling data is called coding rate.It can be seen that under the same sampling rate, the lower the coding rate, the smaller the volume.However, both sampling and coding steps will cause signal distortion.The signal distortion caused by sampling is unavoidable, and the analog signal must be sampled if it is processed by computer.Coding is actually compression. For example, algorithms such as mp3 are lossy compression, which discards most of the acoustic data that the human ear does not detect, so the volume is very small.
Difference between coding rate and code rate
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In the field of signal coding, the coding rate is a unitless ratio.It represents the proportion of useful (non redundant) data in the total encoded data in the encoded data stream.In the fields of video and digital communication systems,Code rateIt is often called bit rate or information rate.The bit rate is defined as the amount of information transmitted per second.The coding rate can measure the proportion of the net bit rate in the total bit rate. The two nouns have different meanings.
Related nouns
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Bit rate
Bit rateIt refers to the number of bits transmitted per second.Unit:bps(Bit Per Second), the higher the bit rate, the faster the data transmission speed.The bit rate in sound refers to the amount of binary data per unit time after the analog sound signal is converted into a digital sound signal. It is an indirect indicator of audio quality.Bit rate in video（Code rate）The same principle as in sound means thatanalog signalConvert todigital signalThe amount of binary data per unit time.
chip rate
chip rate [1], also known asSymbol transmission rateOr code transfer rate.The symbol rate is also calledBaud rate, refers to the number of signal changes per second.The unit is "baud", which is usually represented by the symbol "Baud", abbreviated as "B".
