| With the mobile internet developing and intellcectual terminal popular among the public,the number of users increased substantially,as well as the business requirement.The existing 4th Generation Mobile Communication System(4G)can’t offer sound services for consumers.So scientific institutions and companies around the word are devoted to develop the 5th Generation Mobile Communication System(5G),in which ultra-high speed is the most outstanding feature.Polar codes are the first ever provably capacity achieving codes,which becomes the alternative codes for ultra-high speed transmission in 5G.However,there are still some bottlenecks for the application of Polar codes.For the single link transmission,Polar codes with excellent performance are all long codes,but the decoding of which is with large delay and high complexity.For the multiple link transmission,Polar coded cooperation could bring the diversity of cooperation and the error correction of capacity-achieving codes,which shows essential significance for the ultra-high speed transmission,while there are few researches on Polar coded cooperation methods with good performance.In order to make the Polar codes more applicable in 5G high-speed transmission,this paper carries out researches on Polar codes for 5G from low-complexity decoding and coded cooperation.On the aspect of decoding complexity reduction,the decoding algorithms of Polar codes consist of serial decoding and parallel decoding,of which Sccessive Cancellation(SC)and Belief Propagation(BP)are the typical representatives.However,SC is with large decoding delay and the complexity of BP is high.In order to reduce the decoding delay and complexity of Polar codes,SC with low complexity is carried out,based on the subtree puncturing.Further more,subtree cutting、simplification of the iterative node calculation and root node decoding are combined to put forward BP decoding with low complexity,which has better performance than the original BP in high Signal Noise Ratio(SNR).On the aspect of coded cooperation,sub-code word design is the key step in Polar coded cooperation,on which the researches almost remain blank.Only Ejaz S proposes the sub-code word construction method,which is applicable in Additive White Gaussian Noise(AWGN)channel but doesn’t attain obvious benefits in the fading channel.In order to obtain the coded cooperation with diversity benefits,the required sub-code word construction and Polar coded cooperation method is put forward,based on Plotkin construction and information refreezing.Further more,the proposed method is extended to systematic Polar codes with better Bit Error Rate(BER)performance.In order to attain the coded cooperation with flexible cooperation levels,non-systematic Polar coded cooperation based on puncturing is implemented.Besides,this paper proves that puncturing algorithms of non-systematic Polar codes are applicable to systematic Polar codes,based on which systematic Polar coded cooperation with different cooperation levels is put forward.At last,extended coded cooperation is researched.In fast fading scenarios,the fading in each bit is likely to be independent,and traditional coded cooperation no longer get diversity benefits,so space time coded cooperation based on Alamouti coding is implemented,which gains benefits in fast fading channels.In order to get full use of diversity in multi-antenna terminal scenarios,Polar coded cooperation combined with Multi-Input Multi-Output(MIMO)is carried out.In the intensive user scenarios,multi-user cooperation can bring higher diversity order,so Polar coded cooperation with multi-user is proposed based on distributed space-time coding.The simulation results show that the proposed low-complexity BP decoding scheme,compared with the original BP,not only reduces the computation complexity but also improves the performance in high SNR,and the proposed coded cooperation schemes make the performance of Polar codes improved significantly in fading channels. |
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