Research On Hybrid ARO Transmission Schemes Using Polar Codes Over Time-vatiant Channels

Polar codes are a class of capacity-achieving codes.Within the ongoing 5th generation wireless systems standardization process,polar codes have been adopted as channel coding for uplink and downlink control information for the enhanced mobile broadband(eMBB)communication service.Polar codes are channel-specific,when transmitting over time-varying channels,degradation of eiror correction performance which caused by the mismatching between channel state and code construction takes place.To resolve the problem,we hope that the transmission system can adaptively adjust the code construction according to the channel state,where hybrid automatic repeat request(HARQ),as a common technique of self-adaption link control,is feasible.In this paper,we study the polar codes based HARQ scheme over compound charnels.For degraded compound channels,the existing incremental freezing(IF)HARQ scheme based on the nesting property of polar codes is capacity-achieving,but it adopts a successive joint decoding structure,which results in the problem of error propagation.To resolve the error propagation problem,we propose two improved IF HARQ schemes with polar codes,namely the cyclic redundancy check(CRC)aided IF HARQ scheme and the cumulative-path-metrics-based IF HARQ scheme.In the CRC-aided IF HARQ scheme,several CRC bits are added to each transmitted block including the original transmitted block and the retransmitted block(s)to get rid of the error propagation.Using these CRC bits,the IF HARQ scheme and the Chase Combining(CC)HARQ scheme can be combined to obtain a better error correction performance.In the cumulative-path-metrics-based IF HARQ scheme,we take the thought of successive cancellation list(SCL)decoding algorithm for reference,the successive joint decoder maintains multiple possible paths at the same time,and the cumulative path metrics is introduced to represent the reliability of each surviving path in decoding procedure.Moreover,a modified path splittin.cg reduced successive cancellation list decoding algorithm is presented to reduce the time complexity and space complexity ot the cumulative-path-1etrics-based IF HARQ scheme.Simulation results show that both proposed scheles have better error correction perfor1ances and system throughputs than the traditional IF HARQ.IF HARQ schele can not apply to non-degraded compound channels for capacity-achieving transmissions,because the nesting property of polar codes no longer exists.We adjust the construction of universal polar codes by changing the polarized channels participated in each recursive transformation and adding extra channel permutations,so that the nesting property of polar codes is preserved under non-degraded compound channels.Using universal polar codes based IF HARQ,transmission over non-degraded compound channels can be capacity-achieving theoretically.Simulation results show that universal polar codes based IF HARQ has a good system throughput under non-degraded compound channels.