Research On Key Technologies Of Polar Coded Random Access

Polar codes are the first constructive code family achieving channel capacity,which is one of frontier research directions in the coding theory.In the 2015 IEEE Symposium on Information Theory(IEEE ISIT),Prof.Ankan,the inventor of polar codes,has pointed out that for the future development of polar coding,the whole communication system optimization based on the channel polarization idea and the polar code application will become the mainstream directions.However,the design and optimization of wireless transmission systems guided by polarization transform theory is still lacking of the well-established framework,especially for the analysis of erasure channel capacity and the design and optimization of polar codes for slot erasure within random access transmission,as well as high-performance decoding methods for multi-user random access codes based on PUPE(Per-User Probability of Error)constraints are far from adequate.In view of this,this dissertation starts with the generalized polarization phenomena commonly exists in wireless random access communication systems so that we extend the core design idea of polar codes to the non-collaborative random access transmission,and oriented to the next-generation non-collaborative giant-access wireless IoT random access transmission scenario,the theoretical framework and technical solutions of polar slotted ALOHA transmission are established with the generalized polarization transform as the guiding theory,and the study of PUPE-constrained polar coded multi-user codes is carried out.The innovative works of this dissertation consists of the following four aspects:1)The dissertation derives the upper bounds on throughput threshold of the coded slot ALOHA(CSA)over erasure channel,and investigation of the upper bound on the throughput threshold of the T-fold CS A and the scaling properties of the CSA in the short and medium frame lengths regions.First,the average probabilities of packet recovery failure in SIC is analyzed by Gaussian elimination method and density evolution method for the successive interference cancellation(SIC)process,and by using them the upper bound of the load threshold of CSA over the slot erasure channel(SEC)and packet erasure channel(PEC)are derived respectively.Then,the upper bound on the achievable throughput performance of the T-fold CSA scheme is investigated.Finally,the scaling property of the CSA for the finite frame length is given.2)On the basis of above work,this dissertation constructs a slot polarization theoretical analysis framework,and further proposes the polar slotted ALOHA(PSA)method over SEC channel.First,we demonstrates the existence of slot polarization of SEC(∈)channels,and further introduces the theoretical framework of slot polarization transform for symmetric SEC channels.Accordingly,packet-level SC(pSC)and packet-level pSC list(pSCL)decoding algorithms are proposed.Secondly,with the guidance of time slot polarization theory,the PSA method is proposed,where the random access process is divided into two stages:in the first stage,under the guidance of slot polarization theory,the identical slot subset is constructed at each active user side and the base station(BS)side.According to the optimized irregularity distribution,the active user transmits multiple packet copies over slots selected from the slot subset.Then,in the second stage,the packet vector of the slot subset is encoded using packet-level polar codes based on packet-level polarization transform and transmitted over SEC to the BS side.Accordingly,the decoding recovery process of PSA is divided into two steps,i.e.,before executing the SIC to recover the packets on the slot subset,the pSC or pSCL decoding algorithm is executed first to recover the lost packets caused for the slot erasure by SEC.Finally,the degree distributions of PSA are optimized by using two linear equations about the degree distribution,and the upper bound of the packet-level polar code rate in the PSA scheme is derived.3)Guide by the polarization transform theory,this dissertation investigates an improved T-fold aided list decoding approach for the concatenated polar random access codes.In recent years,the design of PUPE-constrained multi-user codes for the grant-free random access has been attracted much attention.The T-fold concatenated codes are the first family of random access code designed under this framework.The T-fold code,which is constructed by using the check matrix of BCH code,is acted as the outer code,followed by the inner encoding,and then the T-fold concatenated code is obtained.In this dissertation,we propose a performance-enhanced decoding algorithm for the T-fold coded concatenated polar codes where the polar code is used as inner code.To providing useful decoding information for the list decoding algorithm of polar(inner)codes by the Berlekamp-Massey(BM)decoding algorithm of T-fold(outer)codes,we make an insight analysis of the BM algorithm for T-fold codes,which shows the BM decoding algorithm can output a number of indicator variables that reflect its decoding status.We feed these indicator variables back to the SCL decoding of the inter polar code to assent for the selection of the last surviving path.Result in introducing information transfer between inner/outer code decoders,the improved decoding organically integrates the inner/outer code decoding.Comparedto the conventional method,the proposed method can significantly improve the performance of this grain-free random access system.4)This dissertation investigates a PUPE-constrained polar coded irregular repetition slotted ALOHA(IRSA)scheme.First,a pointer-free IRSA scheme is proposed for the grant-free short packet random access within the wireless IoT communications scenario,where the number of copies of each user’s packet is determined by the degree distribution and the messages contained in the transmitted packet itself,as well as the selection method of the slot-subset used to send these copies.The short packets of each active user are encoded by CRC concatenated polar codes,then the multiple copies of each encoded packet are transmitted simultaneously over the constructed slot-subset.Second,the CRCaided list decoding algorithm for polar codes is extended to the Gaussian multiple access channel model by using the linearity property of CRC codes and polar codes.Finally,guided by the scaling law of packet loss rate of IRSA with finite slot frame length,the performance of the proposed scheme is evaluated:without providing additional multi-user detection in the SIC of IRSA,the performance of the proposed CRC-based polar coded IRSA has a comparable performance with the 4-fold coded IRSA.In summary,based on the polarization transmission theory and modern coded random access theory,this dissertation derives the performance upper bounds of coded random access over erasure channels,proposes a slot polarization theoretical analysis framework,and investigates a PSA scheme to resists the slot erasure of SEC.A performance-enhanced T-fold aided list decoding approach for the concatenated polar random access codes,and the design and performance evaluation of polar-coded IRSA random access schemes are presented.The innovative work ensure the efficient and reliable transmission of the polar-coded random access scheme.