Single-relay And Multiple-relay Selection And Power Allocation Method Based On Outdated Channel State Information

In recent years,along with the popularity of 4G and the proposed scheme of 5G,wireless communication networks become a key research.Cooperative diversity is an effective method against multi-path fading in wireless communication,since it can improve the reliability of information transmission and reduce the system power loss.Among cooperative communication,relay nodes assist source node to communicate with destination node,thus form a virtual MIMO system,and use the relay selection techniques to select the best relay node(single or multiple)to transmit the information.At the destination node,we use the maximum ratio combing technique to process the diversity signals.Most of the relay selection strategies use the outdated channel state information(OCSI)for the relay decision,which will bring serious performance for communication system,however,channel prediction can greatly improve the effects of delay.For this,we introduce cooperative relay selection and power allocation method based on the OCSI,and make the following progress:Firstly,the existing relay selection and power allocation method considering the OCSI only consider the Link of source-to-relay or relay-to-destination.In fact,both the link of source-to-relay and relay-to-destination are existing outdated channel state information.The paper considering the complete effects of OCSI on the source-to-relay link and the relay-to-destination link,through the Bayesian estimation criterion of minimum mean square error(MMSE)estimation method,forecast the channel gain of data transmission time,and through the Max-min predicted channel gain to select relay nodes.Meanwhile,under the condition of the system total power,according to the predicted channel gain,propose a simple and effective optimal power allocation method,and compared with the average power allocation method by the outage probability.Through the simulation,the proposed Max-min predicted channel gain relay selection and the optimal power allocation method has a certain advantage of improving the performance of outage probability.Secondly,in the case of poor channel conditions,only selecting one relay node is not good at the implementation of communication effect,we need to select multiple relay nodes to cooperate.At the same time,under the condition of the system total power,we optimize the power between the relay nodes and the source node.On the basis of the study,by setting the predict channel gain threshold,expand the single relay to multiple relay selection,and optimize the power allocation between the source nodes and the relay nodes.The simulation results show that,under the condition of the system power allocation,multiple relay selection is better than single relay selection at the performance of outage probability,optimized power allocation is better than equal power allocation at the performance of outage probability.