A Research On Joint Power Allocation And Relay Selection For Cooperative Communication

The cooperative communication can achieve spatial diversity by generating a virtual multiple input multiple output(MIMO)system,and enhance the capacity,coverage and robustness of the wireless communication network.The common relay protocols in the cooperative communication include amplify-and-forward(AF),decode-and-forward(DF)and coded cooperation(CC),besides network models include one-way relay network(OWRN)and two-way relay network(TWRN).Compare to OWRN system,TWRN has higher spectral efficiency,however it's easily affected by the channel estimation error because of the self-interference.Relay selection(RS)and power allocation(PA)are the two main ways to improve system performance of the cooperative communication.RS means to choose the most suitable relay point by channel situations to forward signals.Power allocation means to distribute the total transmit power appropriately to achieve maximal system performance.In this paper,we focus on the joint RS and PA method for TWRN system.On the one hand,several joint RS and PA methods are proposed to improve system performance both for conventional TWRN and energy harvesting(EH)TWRN;on the other hand,we analyze the influence of the channel estimation error on the power assumption,transmit rate and bit error ratio.The main work of this paper is organized as follows:(1)In traditional AF-TWRN system,a joint RS and PA method to maximize the sum transmission rate will be proposed.Utilizing the instantaneous channel information to formulate the end-to-end signal-to-noise ratio expressions,optimal PA for each relay point will get,compare all relays and the point achieving the max transmission rate will be chosen.Then,we will propose the joint RS and PA method with a relay power constraint to decrease the relay power assumption.(2)In conventional AF-TWRN system,a joint RS and PA method aiming at minimizing total power consumption with channel estimation error will be given.Utilizing Karush-Kuhn-Tucker(KKT)optimization conditions,the optimal PA will get and the relay point consuming least power will forward signal in the second phase.Then,power consumption satisfying the business requirements with different channel estimation error will be compared.(3)In EH-TWRN system,an energy-efficient joint RS and PA method based on power-splitting relaying protocol will be proposed whenever the system has perfect CSI or imperfect CSI,optimal PA of the two sources and the optimal energy harvesting proportion at relays are formulated.Analysis results show that that channel estimation error would increase the total transmit power consumption,and energy harvesting twoway relay network could achieve less power consumption compared to conventional twoway relay network.(4)In EH-TWRN system,an optimal joint RS and PA method based on the signalnoise-ratios balancing criterion will be given.Analysis results validate the method could achieve the highest transmission rate among other conventional methods and the channel estimation error has a significant impact on the performance of the EH-TWRN.