Design Of Polar-HARQ Transmission Schemes

With the development of communication technology,the fifth generation mobile communication technology(5G)has become a global research hotspot.Three important scenarios in 5G,namely Enhanced Mobile Broadband(eMBB),Massive Machine Type Communication(mMTC),Ultra-reliable and Low Latency Communication(URLLC),all put forward higher requirement to channel coding.Hybrid Automatic Repeat Request(HARQ)is a technology that combines forward error correction(FEC)with ARQ protocol to achieve reliable communication.It is a common method applied in link adaptive transmission to improve the system throughput.Compared with the fixed rate polar codes,HARQ transmission system requires rate-compatible polar codes.That is,the code rate can be flexibly configured by changing the code length,and the transmitted code bits can be flexibly selected.Professor Arikan proposed that the code length of polar codes should be the integer power of two,which exactly poses a severe challenge to realize the rate-compatible polar codes.However,if polar codes want to be the coding scheme of 5G data channel,we must solve this problem.Therefore,it is of great significance to study how to make better use of the characteristics of polar codes to design HARQ transmission system.In this paper,we mainly research on how to design Polar-HARQ transmission system.The relevant research contents are summarized as follows.First,a HARQ scheme based on equivalent puncturing patterns of polar codes is proposed.As we all know,HARQ-CC has been widely used in wireless communication systems.However,when HARQ-CC system uses punctured polar codes to transmit information bits,it can't make up for the vacancies of the Log Likelihood Ratios(LLR)of the punctured code bits which are never transmitted at all,thus degrading the system efficiency.To address this issue,we propose a new HARQ scheme based on the equivalent puncturing patterns of punctured polar codes.It successfully complements the LLRs of punctured code bits,and therefore improves the system throughput.Moreover,we show that the proposed scheme can be implemented efficiently with the same complexity as HARQ-CC.Numerical results indicate that,for punctured polar codes with 21.875%puncturing proportion,the proposed HARQ can achieve 7.5%improvement at the SNR of-2.5dB on the normalized system throughput compared with HARQ-CC.A new Polar-HARQ scheme by polarizing matrix extension is developed.The existing Polar-HARQ scheme by polarizing matrix extension only transmits the original information bits in the former transmissions,but does not transmit new information bits.When the SNR of the physical channel is relatively high,the code rate of polar codes designed by the existing HARQ scheme descends too fast to result in transmitting overmuch redundant bits and decreases the system throughput.Compared with the existing scheme,the new proposed HARQ scheme will transmit a few of new information bits during retransmission by designing the code rate of polar codes properly.At high SNRs,the designed code rate is more closed to the channel capacity,thus a higher system throughput is realized.The simulation results show that the normalized system throughput of the new HARQ scheme is superior to the existing scheme at high SNRs.Especially,it has a 17%throughput gain at the SNR of 1 dB.Finally,we put forward a method of Polar-LT packet coding scheme in order to satisfy the latency and reliability requirements of the scenario of URLLC in 5G which requires ultra-reliable and low latency communication.Although long-length codewords can achieve a better coding gain and low block error rate,they have larger transmission latency and decoding complexity.While short-length codewords have advantages in small latency and low decoding complexity but higher block error rate.In view of the above phenomena,we propose a polar-LT packet coding scheme,which uses LT code as an outer code to introduce a certain parity relationship between different short-length polar codes.We expect that transmission errors in multiple packets can be corrected by sending one redundant packet.It can improve the coding gain and reduce transmission delay in the meanwhile.