channel coding 信道编码英文知识

1、Wireless Mobile Communication and Transmission Lab.1 Error Control Strategies, Performance MeasuresError Control StrategiesnForward Error Correction (FEC)nAutomatic Repeat Request (ARQ)nHybrid ARQPerformance MeasuresProbability of decoding error (error probability)nCoding gainnShannon Limit 2Forward

2、 Error Correction(FEC)nOne-way system, even not strictly one-waynDigital storage systems, deep-space communication systems and most of the coded systems in use today Automatic Repeat Request(ARQ)nTwo-way systemnsome data networks and satellite communication systems3Employ error-correcting codesAutom

3、atically correct errors detected at receiverThis book is devoted mostly to the analysis and design of FEC system4Stop-and-wait ARQContinuous ARQnGo back NnSelective reject (selective retransmission)5Continuous ARQ is more efficientContinuous ARQ is more expensiveStop-and-wait ARQ designed for half-d

4、uplex channelsContinuous ARQ designed for full-duplex channels6ARQ requires much simpler decoding equipment (Actually only detecting no correcting) ARQ is adaptive in the sense that information is retransmitted only when errors occurWhen error rate is high, the system throughput is lowered by using

5、ARQA hybrid combination of FEC is more efficient than ARQ alone7How to measure the performance of a coded system? (A curve of BER vs ) nProbability of decoding error (error probability) - Y directionnCoding gain - X direction8Error probability (WER and BER)nProbability of word (or block) error-WER-W

6、ord error ratenProbability of bit error-BER-Bit error rateThese two error probabilities should be kept as low as possible9The energy-per-information bitn : energy per transmitted symbolnR: code rate, R=k/n commonly used to express error probabilityn : one-sided PSD (Power Spectrum Density) of the ch

7、annel noise1011 3.7dB3.7dBThe reduction in the Eb/No required to achieve a specific error probability (BER or WER)Coding gain is important in communication applications Coding threshold is the SNR at which the coding gain actually becomes negativeAsymptotic coding gain the coding gain for large SNR1

8、213Coding thresholdCoding thresholdCoding gainCoding gainWireless Mobile Communication and Transmission Lab.14Definition: the minimum SNR required - error-free - coded system - code rate RMeaning: SNR should exceeds Shannon limitUse : measure the maximum achievable coding gain15error-freeAWGNBPSKcod

9、ed system R=0.5 0.188dB0.188dB0.188dBR=0.5R=0.5Wireless Mobile Communication and Transmission Lab.16R: 00.99Eb/No: Shannon limitExample:AWGN channel BPSK -10-5 9.65dB 0.188dB9.462dB(So you can compare different coding schemes to see which one is better)17Coding gain:Coding gain: 4.15dB4.15dB(Coding gain)max:(Coding gain)max: 9.462dB9.462dBImprovement gap:3.962dB Improvement gap:3.962dB Shannon limit: 0.188dBShannon limit: 0.188dB4.15dB4.15dB9.65dB9.65dBSoft-decision MLD, R=0.5