Research Of BP Decoding Algorithm For Polar Code Based On Bit Flipping

With the rapid development of wireless communication systems,higher demands are required on their corresponding supporting technologies.The fifth generation mobile communication system(5G)and the future B5G/6G,etc.,focus on providing high transmission rate,extremely low latency,high throughput,and high quality of service.The polar code proposed by Professor Arikan is one of the competitive candidates for future channel coding schemes,which is the first coding scheme mathematically proven to reach the Shannon limit.The Belief Propagation(BP)decoding algorithm for the polar code can meet the requirements of future communication systems for high throughput and low latency applications due to its parallel decoding feature,which has attracted much attention among many polar code decoding algorithms.However,the original BP decoding algorithm does not perform well.In this thesis,our research work is focused on the two performance-improved methods,namely the noise perturbation and bit flipping,for BP decoding algorithm and the main contents and innovations are summarized as follows:1)To handling the error-oscillation phenomenon caused by the short loops in BP factor graphs,a majority-logic-based selecting-scheme is proposed,which can effectively distinguish the error-oscillation bits with low complexity.Based on this scheme,we propose a Received-sequence BitFlip BP(RF-BP)decoding algorithm,which can achieve better performance,compared with the existing BP Correction(BPC)decoding algorithm and the Enhanced BP Bit-Flip(EBPF)decoding algorithm.Besides,with the flipping set size of 30,the performance of the proposed algorithm is close to that of the classical CRC-aided Successive Cancelation List(CA-SCL)decoding algorithm with path number L=4;2)An effective way to improve the performance of BP decoding is to inject artificial noise into the received signal,i.e.,the random scrambling method.In this paper,we investigate the characteristics of the artificial noise added by the algorithm and design a construction scheme in which the noise power can vary with the signal-to-noise ratio(SNR)of the system.Compared with the original algorithm,the scheme constructed in this paper is more effective in perturbing the bits where error-oscillations occur,while can also alleviate the influence of the regular bits;3)Based on the above optimized artificial noise construction scheme,this thesis introduces the idea of bit-flip into the noise-aided BP decoding algorithm and we further propose a Noise-aided BP Bit-Flip decoding algorithm(Na-BPF).Experimental results show that the proposed algorithm can achieve better error performance while require less iteration number in average,compared with the existing algorihtms at the same SNR region.For example,when the code length of 1024 and frame error rate(FER)= 310-,the proposed algorithm can achieve a performance gain of about 0.14 d B with a list size of 30 and a flipping set size of 20,compared with the classical Nosie-aided BP List(Na-BPL)decoding algorithm with a list size of 50.