Research On Outage Probability Performance Analysis And Optimization For Multihop Relay Communication Networks

With the rapid development of wireless communication technology,the access scale of wireless terminals in the communication network increases sharply.In the future,a wireless communication network that can achieve full coverage,no blind spots,and high rate is required to support a large number of wireless terminals accessing highly reliable wireless communication.Multi-hop relay communication technology divides long-distance direct links into multiple short-distance and lowfading transmission paths by means of relay nodes,which has the advantages of reducing transmission power,extending network coverage and increasing system capacity.Therefore,it can effectively meet the coverage requirements of future wireless communication systems for high data rate services in a large range,and is considered to be one of the key technologies of future wireless communication.However,complex network topology and multiple forwarding of signals will affect the reliability of multi-hop transmission.How to deploy relay node and efficiently use network resources to improve the reliability of multi-hop relay network is the key issue.In this regard,this thesis studies the outage probability performance analysis and optimization of multi-hop relay networks.The main research contributions of this thesis are listed as follows:Firstly,aiming at the transmission reliability problem of multi-hop relay network,an optimization method of relay node deployment that minimizes outage probability is proposed.We consider a multihop relay network consisting of one source,one destination and multiple relays,where the source transmits to the destination with the assistance of multiple relays.Under the condition that the position of source and destination are given,a closed-form end-to-end outage probability expression of the multi-hop relay network is derived.We then formulate an optimization problem to minimize the outage probability by taking outage probability as the objective function.The Lagrange multiplier method is used to obtain the closed form solution of the optimal relay position.And we use the search algorithm to get the number of relays to minimize the outage probability.Simulation results show that the proposed optimal relay deployment scheme is significantly better than the traditional isometric relay deployment scheme in terms of outage probability performance.Secondly,aiming at the power resource allocation problem of cognitive multi-hop relay network in overlay spectrum sharing mode,a power allocation scheme is proposed to minimize the outage probability.The closed-form expression of outage probability for the secondary transmission under imperfect spectrum sensing is derived.We then formulate an optimization problem to minimize the outage probability of the cognitive multi-hop relay network with a constraint on the total transit power of the secondary transmitter and secondary relays,and propose a power allocation scheme based on particle swarm optimization(PSO)algorithm to obtain the numerical solution of optimal power allocation.Moreover,when the fading coefficients of multi-hop relay channels are independent and identically distributed(i.i.d.),the outage probability expression is greatly simplified,for which a closed-form solution of optimal power allocation is obtained.Simulation results show that the proposed PSO-based power allocation scheme significantly outperforms the traditional equal power allocation in terms of the outage probability.Finally,aiming at the routing problem of cluster-based multi-hop cognitive radio networks,an improved hop-by-hop routing method based on local channel state information is proposed.Compared with the traditional hop-by-hop single relay routing method,the proposed improved hopby-hop routing method selects multiple relay nodes in the last hop for signal forwarding,and maximizes channel capacity by optimizing the power resource allocation of the last hop under the restriction of the total transmitted power of each hop.Considering the existence of spectrum sensing error and channel estimation error,the outage probability expression of cluster-based multi-hop cognitive radio network using improved hop-by-hop routing method is derived.Simulation results show that the improved hop-by-hop routing scheme can significantly reduce the outage probability compared with the traditional hop-by-hop single relay routing method.