Research On Polar-Coded HARQ Schemes And Rate-Compatible Techniques

Polar codes are the first class of error-correction codes that have been proved theoretically to achieve the channel capacity,which have attracted a lot of attention.Recently,polar codes have been adopted in the control channel of the enhanced mobile broadband(e MBB)scenario for the fifth-generation(5G)mobile communications and they will still be one of the most competitive coding schemes in other scenarios,as well as the future mobile communication systems.Hybrid automatic repeat request(HARQ)is a widely used link-adaptation technique.The polar-coded HARQ transmission schemes can effectively improve the throughput and performance,which has been widely studied in recent years.For polar-coded chase combining(CC)HARQ scheme,it has very low complexity and is easy to be combined with other techniques(e.g.,the codedmodulation and space-time coding).However,the CC-HARQ scheme usually suffers from error-correction and throughput performance degradation,and this inevitably limits its practical applications.Furthermore,the length of polar codes is limited to powers of 2 due to the original binary Kronecker construction,which restricts their flexible applications in practice.Although polar codes with arbitrary code length can be constructed by rate-compatible techniques,the performance of existing rate-compatible techniques is unsatisfied.This thesis focuses on the above problems,and the main work and innovations are sumarized as follows:1)To improve the performance and throughput of CC-HARQ scheme,a retransmission scheme based on multiple decoding(MD)is proposed,called MDCC-HARQ scheme.Instead of requesting retransmission or stopping decoding,the presented MDCC-HARQ scheme can provide extra decoding chances when chase combining decoding fails by constructing new LLR sequences.Four methods to construct new LLR sequences from the received signals are further presented.Simulation results show that the proposed MDCC-HARQ scheme can achieve 0.35-0.4d B gain compared with the original CC-HARQ scheme.Moreover,the proposed scheme has higher throughput efficiency and needs less retransmissions,especially at low-to-moderate signal noise ratio(SNR)region;2)A two-stage construction method for the rate-compatible shortened polar(RCSP)codes is proposed to achieve flexible code length and excellent performance.For the stage-I construction,it is required that the shortened bits are completely known by the receiver.To this end,a strategy is jointly designed with the shortening pattern and the frozen set,such that the shortened bits are a linear combination of the frozen bits.Besides,a RM code-aided distance-greedy algorithm is proposed to maximize the minimum Hamming distance of the codes.For the presented algorithm,the rows having the minimum weight in generator matrix are first deleted by using the row weight constraint of RM codes.In this way,it is ensured that the constructed RCSP code has the maximum Hamming distance;3)In practical applications,the flexibility of code rate is needed.After the jointly design of shortening pattern and frozen bits in stage-I,the remaining frozen sets are needed to be further designed,called the stage-II construction.Three different construction schemes are presented,called the RM construction,the GA construction and the RM-GA construction.The RM construction is completely designed by the distance constraint and has the simplest structure,while the RM-GA construction considers both distance and channel reliability and has the best performance.The GA construction is a simplified version of the RM-GA construction that the RM constraint is omitted in this case.The row weight distribution numerical results of the generator matrix show that the proposed constructions can efficiently improve the minimum Hamming distance.Simulation results show that the proposed RCSP codes have excellent performance at different code lengths and code rates.More specifically,compared to the Wang14 and the QUP schemes,the RM-GA construction performs best and can achieve at most 0.7-0.8 d B gain.The RM construction has the simplest structure,while it still performs better than the Wang14 and the QUP schemes,especially at high SNR region.The GA construction has similar performance compared to the Wang14 and the QUP schemes.