Research On Channel Coding Techniques In GNSS

The Global Navigation Satellite System(GNSS)provides services such as navigation,positioning and timing,and it is an integral part of modern life.GNSS is often interfered by factors such as fading and noise during high-altitude communications.Therefore,high-performance channel coding techniques are required to ensure the reliability of satellite communication.Polar code is the first kind of channel coding that has been proved to be able to reach the Shannon limit,and it has a low complexity of coding and decoding.The proposal of polar code has attracted widespread attention from scholars at home and abroad.However,the application of polar code is not mature enough.Therefore,after studying the principle of polar code and the algorithms of coding and decoding,two improved decoding algorithms are designed.Then,the polar code is applied to the GPS-L1 C signal,and the possibility of applying the polar code to GNSS is initially explored.The main researches of this article are as follows:First,aiming at the problem of high delay of Successive Cancellation List(SCL)decoding algorithm for polar code,a multi-bit SCL(MSCL)decoding algorithm based on log-likelihood ratio is proposed in this paper.The algorithm uses the metric of a path with length M×(i-1)to directly calculate the metric of a path with length M×i,where i?[1,N/ M],N and M are the code length and multi-bit numbers of the polar code,respectively.The MSCL decoding algorithm simultaneously decodes multiple codeword bits by judging the path metrics.Under the premise of ensuring the decoding performance,the decoding delay is reduced from 3N-2 clocks to 4N/ M-2 clocks.Since the MSCL decoding algorithm deletes the paths that incorrectly determine frozen bits when performing candidate path extension,compared with the existing multi-bit SCL decoding algorithm,when M(28)8 and the polar code rate is 0.1 to 0.9,the MSCL decoding algorithm can reduce the number of path metric calculation by 94% to 58%.Then,aiming at the problems of high latency and much space storage of Cyclic Redundancy Check(CRC)assisted SCL(CA-SCL)decoding algorithm for polar code,a segmented CRC assisted MSCL(SCA-MSCL)decoding algorithm is proposed in this paper,and it requires corresponding segmentation of information bits during encoding.By using multiple CRC decisions,the SCA-MSCL decoding algorithm can select one path which best meets the conditions in each segment to output.At the same time,only the estimated value of the path is saved for the latter decoding.Compared to the CA-SCL decoding algorithm,the SCA-MSCL decoding algorithm can reduce at least 21% of the storage space and 84% of the decoding delay.Finally,aiming at the problem that GNSS is susceptible to interference in high-altitude communication,a satellite navigation channel coding method based on punctured polar code in Rician channel is proposed.Take the GPS-L1 C signal as an example,by analyzing the frame format of GPS-L1 C signal,it is found that the subframe of GPS-L1 C signal has a CRC code,and there are erroneous inequalities in subframe 2 and subframe 3.Without the increase of redundancy,the CRC aided MSCL(CA-MSCL)decoding algorithm is adopted,and the rate-adaptive unequal error protection is applied to the different pages existing in the subframe 3.The simulation result shows that the error probability of subframe 3 is close to subframe 2.And in terms of signal error rate,compared to the Low Density Parity Check(LDPC)code used in the GPS-L1 C signal,the punctured polar code can achieve a gain of 1.1 to 1.5 dB.