Research On Channel Estimation And Resource Allocation Algorithm For Multi-relay Cooperative Networks

With high channel capacity and spatial diversity gain,MIMO has become one of the key technologies of next generation mobile communication networks.However,the limitation of size and weight of the mobile terminals makes it difficult to realize MIMO technology.By considering distributed single antenna terminals as a virtual antenna array,multi-relay cooperative communication system takes the key technology of MIMO into reality so that the signal distortion caused by multipath effect and path loss are mitigated,communication reliability is enhanced and signal coverage is expanded as well.In order to further improve communication reliability,this paper studies the channel estimation and wireless resource allocation problems for multi-relay cooperative communication network in slow fading channel.Firstly,the forwarding schemes and the principle of cooperative diversity are reviewed.Two forwarding schemes used in cooperative relaying system are introduced,and the signal processing in the single relay cooperative scenario is briefly analyzed.This paper introduces two kinds of diversity techniques used in MIMO system: space-time coding and spacefrequency coding,which lay the theoretical foundation for the following chapters.A novel channel estimation algorithm based on statistical channel state information is proposed for multi-relay cooperative communication network.The training sequence sending scheme of multi-relay network is introduced.The received training sequences is modeled and the ISI and ICI are analyzed.A decision-feedback equalizer is proposed for received data frame signals.The optimization problem,which takes minimization of the mean square error of the frequency response between destinat ion node and relay nodes as objective function,is proposed.Power allocation algorithm of the training sequences based on distance among nodes is proposed under the premise of constant total transmit power.A novel decision-feedback estimation algorithm based on multipath delay is proposed in the slow fading channel.Simulation results reveal that the power allocation algorithm of training sequences based on distance effectively reduces the mean square error of the estimation of frequency response.Compared with the decision-feedback algorithm based on LS criterion,multipath delay based decisionfeedback algorithm improves the accuracy of the channel estimation and reduces BER of the data frame,so that each node obtains more accurate global CSI.Power allocation scheme based on distributed space-time coding is studied,and a novel power allocation scheme based on water-filling algorithm is proposed.Firstly,distributed GABBA coding is applied to the multi-relay AF cooperative communication network,signal processing of the source node and the relay node is analyzed,the received signal in the destination node is modeled and the received SNR is deduced.According to quasi-orthogonality of distributed GABBA encoding matrix,an improved relay-node mapping algorithm is proposed.The optimization problem is established by minimizing the outage probability of cooperative network.Then the problem is decomposed into the joint relay selection and power allocation problem according to the feasible domain of the variable.A novel power allocation scheme based on water-filling algorithm is proposed.Simulation results reveal that the relay-node mapping algorithm effectively improves the performance of distributed GABBA cod ing.Compared with other power allocation algorithms,the power allocation scheme proposed in this paper reduces the outage probability and the BER of the distributed GABBA cod ing.Wireless resource allocation problem based on distributed space-frequency coding is studied,a joint power allocation,subcarrier pairing and relay selection algorithm is proposed.Firstly,the optimization criterion of distributed space-frequency encoding matrix is deduced by minimizing the pairwise error probability.Then,an improved power allocation scheme of DSFBC is proposed,which is proved to make the DSFBC obtain the full diversity order.Applying the subcarrier interleaving algorithm to DSFBC,the separation factor is deduced.According to the optimization criterion of encoding matrix,a joint subcarrier pairing and relay selection algorithm is proposed.Simulation results reveal that DSFBC can obtain the full diversity order using the power allocation scheme proposed in this paper,subcarrier interleaving algorithm effectively improves the performance of DSFBC.Based on the optimization criterion for encoding matrix of DSFBC,performance of cooperative relaying system is further improved.Extending the scenario from two-hop network to mult i-hop network,a novel relay selection algorithm based on DSFBC is proposed.Firstly,the mult i-path routing protocol is analyzed and the structure of relay-nodes in each hop is modeled into VMIMO system,in which a physical layer transmission scheme based on DSFBC is proposed.Then,an optimization model is established to minimize the lower bound of pairwise error probability in each hop,and a relay selection algorithm is proposed based on the optimization criterion for encoding matrix of DSFBC.Simulation results reveal that the lower bound of the BER performance in each hop achieves full diversity order,the relay selection algorithm proposed in this paper can effectively improve the lower bound of the BER performance.