Research On Cooperative Transmission Technology Of Multi-relay Polarization Coding In Satellite Sensor Network

At present,satellite sensor network（SSN）technology has made great progress,including wireless sensor network（WSN）and satellite communication network（SCN）.In the SSN application scenario,reducing the outage probability of long-distance signal transmission and solving the error propagation of the signal are the primary problems.For this reason,this thesis mainly focuses on the researches of the cooperative transmission technology of multi-relay polarization coding in SSN.Firstly,the background and research status of polarization coding and multi-relay cooperation technology at home and abroad are briefly introduced.Secondly,the principle of polarization coding and decoding is summarized,and the higher order polarization weight（HPW）construction algorithm and the cyclic redundancy check assisted fast successive cancellation list（CA-FSCL）decoding algorithm are proposed respectively for the polarization coding and decoding algorithm.Thirdly,in the energy-efficiency oriented SSN,the transmission scheme of the communication system is optimized,and an optimized higher-order polarization weight incremental selection decoding and forwarding relay cooperation scheme is proposed.Finally,reinforcement learning is applied to relay selection system,and a relay selection scheme of rein-Q network（RQN）is proposed.The research contents and contributions of the thesis are as follows.1.Aiming at the problems of low coding efficiency and high BER caused by the high delay and complexity of current polarization coding and decoding,HPW construction algorithm and CA-FSCL decoding algorithm are proposed respectively.The construction algorithm estimates the channel reliability through the reliability estimation function,and only needs to consider the channel index,which simplifies the mathematical calculation.At the same time,the introduction of higher-order basis reduces the difference between the contributions of different binary bits to the base integral,and enhances the anti-interference performance of the coding.Therefore,its channel index can be located by reliability estimation function,which can effectively improve coding efficiency and reduce coding complexity.CA-FSCL decoding algorithm sets rate zero code（R0）,repeat code（Rep）,parity check code（SPC）and rate one code（R1）as four special frame structures on the basis of SCL decoding algorithm,and adds CRC assistance at the same time.In the SCL decoding process,once the system recognizes the special frame structure,it can directly perform fast decoding according to the established decoding method,which greatly improves the decoding efficiency and reduces the decoding complexity.The simulation results show that the HPW algorithm retains the mathematical simplicity of PW method and the robustness of polar codes without losing the coding performance;CA-FSCL can perform CRC after fast decoding to reduce error propagation of information.When the block error rate（BLER）is 10^-3,this decoding algorithm has 0.6,0.3 and 0.1d B performance improvement over SC,SCL and CA-SCL,respectively.2.Aiming at the problems of serious error propagation and low transmission reliability caused by the complexity and variability of SSN relay cooperation channel,a high order polarization weight incremental selection decoding and forwarding（HPWISDF）scheme is proposed.Based on switching between non-cooperative transmission and cooperative transmission according to channel state information（CSI）,this scheme adds incremental retransmission mode in source node.The signal source is encoded by HPW,and the destination node can complete the ideal channel estimation according to the HPW coding weight,and quickly obtain the mutual information of each transmission scheme.When the amount of mutual information between direct transmission and relay transmission is less than the threshold,the error information will not be transmitted,the system will automatically retransmit.This scheme effectively improves the error propagation problem of traditional decoding and forwarding,and reduces the outage probability.Simulation results show that the scheme can dynamically adjust the system transmission scheme and improve the information transmission efficiency when the channel quality is poor.When BER is 10^-6,this scheme has about 1 d B performance gain compared with the traditional polarization selective decoding and forwarding scheme.3.In view of the large number of relay nodes in the large-scale relay cooperation SSN scenario,as well as the huge system overhead and high BER of information transmission caused by the inaccuracy and dynamic variability of CSI,a polarization selective decoding and forwarding relay cooperation（RQ-SDF）scheme based on reinforcement learning is proposed.In this scheme,the relay selection is modeled as a Markov decision process（MDP）,and the RQN algorithm combining reinforcement learning and Q-learning is used for reinforcement learning training to finally select the best relay.The simulation results show that under the condition of large number of candidate relays and unstable CSI,compared with the original Q-learning scheme,when the SNR is 40d B,the outage probability is reduced by 30%and the calculation speed is increased by about 3 times.The polarization encoding and decoding algorithm studied in this paper improves the overall performance of polarization encoding and decoding.The proposed higher-order polarization weight incremental selection decoding and forwarding can enhance the reliability of cooperative transmission and improve the transmission efficiency of the system.The proposed polarization selection decoding and forwarding relay cooperation based on reinforcement learning solves the problems of slow computation speed and low efficiency of relay selection in large-scale relay selection scenarios to some extent.Therefore,this study is very suitable for 5G SSN.