Coding Technology Of Rateless Codes And Their Applications In Wireless Communication

With the rapid development of wireless communication technologies,the demand for improving error correction capability and transmission efficiency of communication system gets higher.Channel coding,as a key technology of error detection and error correction,can significantly improve the reliability and efficiency of communication system.Therefore,it has become one of the key researches of communication technologies.However,since the complexity of wireless communication environment,it is difficult for the transmitting side to accurately predict the channel state information(CSI),which deteriorates the performance of the traditional channel coding technologies whose coding rate is determined by CSI.Rateless codes,a way of adaptive transmission without obtaining CSI,have become a feasible method to improve the reliability and efficiency of communication system.In this thesis,the rateless coding technology and its applications in wireless communications are intensively investigated in the aspects of improving reliability,efficiency and robustness.The main innovations and contributions are listed as follows:1.Based on the parity check matrix,a physical layer rateless coding technology with a reverse systematic transmission method is proposed.By employing ball-into-bin algorithm and inverse systematic transmission method,this technology can decrease the error floor significantly.Based on this coding technology,an optimization method for designing fixed degree distribution is proposed,which improves the robustness of physical layer rateless coding.The error floor of traditional rateless codes over AWGN channel is firstly investigated.The expressions of error floor are derived.After that,a physical layer rateless coding technology with a reverse systematic transmission method is proposed.The proposed technology averages the degree of all variable nodes,which decreases the error floor.In addition,a degree optimization method is proposed.By using this method,a fixed degree distribution that fits for a wide range of SNR is designed,which ensures the robustness of the proposed coding technology.2.Based on the two way relay channel(TWRC),a hybrid estimate and forward(EF)/decoding and forward(DF)scheme is proposed.The proposed physical layer rateless coding technology is employed in this scheme and a continuous degree distribution optimization method is employed to design the degree distribution.To further improve the reliability of this scheme,a joint optimization method of forwarding scheme and coding technology is investigated.Classical forwarding schemes are firstly investigated,e.g.amplify and forward,demodulation and forward and estimate and forward.A joint belief propagation(BP)decoding method is employed at the relay and a hybrid EF/DF scheme is proposed.Based on the relay forwarding scheme,three different kinds of network coding signals are generated,and the expressions of their received SNR at the destination are derived.After that,physical layer rateless coding is employed in this scheme and a continuous degree distribution optimization method is proposed.A joint optimization method of forwarding scheme and coding technology is investigated.In this method,the degree distributions of two source nodes are firstly optimized.Then the degree distributions of relay node for re-encoding are optimized based on the optimal degree distribution of two source nodes.3.A joint modulation and coding scheme is investigated.The expression of error floor is derived,based on which an average sum of square weight selection method is proposed.This method realizes the fusion of coding and modulation,and further improves the transmission efficiency.Traditional rateless coding scheme is separated from modulation scheme,which causes the problem that the modulation scheme has to use CSI to choose suitable modulation level.To solve this problem,a rateless coded modulation scheme is proposed,which is called weighted rate compatible modulation(WRCM).This scheme uses a fixed constellation,which avoids the constellation switchover due to different CSI and avoids the system unstable caused by constellation switchover.The expression of error floor performance is derived,and an average sum of square weight selection method is proposed to further improve the efficiency.4.The ideas of designing rateless codes are introduced into the multiple access scheme.The successive interference cancellation(SIC)is employed in the slotted ALOHA(SA)system to improve the system throughput.Markov analysis is employed to derive the relationship between transmission probability and throughput.After that,a feedback-aided coded slotted ALOHA(CSA)is proposed,which decreases the invalid retransmission and saves the transmission resources.Finally,a distributed decoding algorithm for CSA system is proposed.Rather than start decoding process from the clean packet,the proposed decoding algorithm distributes the decoding operations over the whole frame to achieve a high throughput.Traditional SA system discards the collided packets,which leads to the deterioration of system throughput.In order to make full use of the information contained in collided packets,an SIC receiver is employed.The relationship between the transmission probability and the throughput is studied by using Markov analysis,and the transmission probability parameters are optimized to maximize the throughput.It is proved that the SIC algorithm can effectively improve the system throughput.Note that the SA system with SIC algorithm is similar to the decoding process of rateless codes,the ideas of designing rateless codes are introduced into SA system.Then,a feedback-aided CSA system is proposed,which decreases the invalid retransmission and saves the transmission resources.Finally,a distributed decoding algorithm is proposed.Unlike SIC algorithm which needs to wait for a clean packet to start the decoding process,the proposed algorithm can distribute the decoding operations over the whole frame and effectively improve the system throughput.The decoding performance is analyzed and the lower bound of the error probability is derived.This lower bound provides guidance for practical application of CSA.