Research On Optimization Technologies Of Coded Coordination Transmission In Wireless Communications

Currently,due to the transmission efficiency and reliability,wireless cooperative communications become a hot research spot.The main problem to be solved is to reduce the energy consumption and thus improve the systematic performance.This thesis mainly researches the optimization of wireless transmission and coded cooperation.First,the background and development of cooperative communications,and the current status of the relay protocol,power allocation and coded cooperation are briefly introduced.Then,the fundamental model and diversity combining technology of cooperative communication networks are summarized,and an improved cooperative relay forwarding scheme is introduced according to the existing simple relay scheme.Finally,innovative works are developed to the node power allocation,the relay location and the soft metric based coded cooperation.The contents and main contributions are concluded as follows:1.An optimized power allocation algorithm（OPA）is proposed for the relay network resource loss caused by the equal power allocation（EPA）.First,an incremental selective hybrid decoding and amplifying（ISHDAF）in a single relay cooperation scheme,and a hybrid decoding and amplifying and forwarding（HDAF）multiple relay selection cooperation are introduced.Then,the outage probability expression under high signal-to-noise ratio（SNR）is derived for these two networks.Finally,under the overall system power constraints,the transmission power of the distribution source and the relay nodes is optimized to minimize the outage probability.The simulation results show that,when the relay is far away from the source node and the outage probability is 10^-1,in the ISHDAF single-relay cooperative network,the OPA has a total system power gain of about 3W compared with that of the EPA.Under the same OPA,the single-relay ISHDAF scheme has a power gain of approximately 1W compared with that of the HDAF scheme.When the outage probability is 10^-2 and the number of relays is 4,the OPA in the HDAF multi-relay selection network has a total power gain of 2.5W than that of the EPA.2.To solve the problem that the node position affects the effectiveness of the proposed scheme under the optimized power,a method to determine the optimal relay position is proposed.In an OPA relay network,the path loss factor is introduced,and the outage probability optimization equation is established under the node distance constraint.The optimal relay position is determined by local optimization,and the effectiveness of the OPA is maximized under the required link condition.To optimize systematic outage performance,the proposed optimal relay position model is suited to all power allocations related to difference node distance.Theoretical analyses and related simulations show that the total power is fixed at 10 W.For the ISHDAF and HDAF cooperation schemes,when the relay node is much closer to the destination node,the proposed OPA obtains a larger outage probability gain,and when the relay is in the middle among the source and the destination nodes,our algorithm obtains the maximum outage gain.3.Aiming at the error propagation of decode-and-forward under the existing channel coding scheme,the soft metric forwarding（SMF）scheme is proposed.First,by using the structural features of a LDPC channel coding and its decoding effective statistic log likelihood ratio（LLR）,the relay node decides to forward the LDPC re-encoding parity bit or forward the received codeword LLR according to the decoding situation.So the error message propagation caused by false decoding is avoided.Then,in the multi-relay cooperative networks,the destination node uses the external information exchange of multiple signals to perform jointly iterative decoding BP algorithm to improve the decoding accuracy.Simulation results show that,at BER of 10^-2,the SMF scheme obtains 2d B and 5d B SNR gains,when compared with those of the LDPC decoding and uncoded HDAF schemes,respectively.Compared with a 4-relay network,the SMF scheme in 10 relays can obtain about 3d B SNR gains at BER of 10^-2.By the optimization of node power allocation and coding soft metric forwarding,the performance of the cooperative communication system is significantly improved.Moreover,high performance and low complexity in the proposed scheme enable it convenient for future practical applications,especially in 5G communications and so on.