The Research On Optimize Spectral Efficiency In A Cooperative Diversity System

Cooperative diversity is to use the source node and the surrounding one or moreadjacent nodes of the distributed virtual multi-antenna system, it can overcome theinfluence of the wireless communication system in multipath fading channel.Adaptive modulation and coding (AMC) technology is one of the best balancesbetween data transmission rate and bit error rate for the guidelines to meet therequirements of transmission quality, according to the instantaneous channel qualit ycondition, choose to match the signal to noise ratio the best modulation codingscheme. In order to decrease the error probability, automatic repeat request (ARQ)protocols by means of retransmit the packet error data to guarantee the transmissionof data reliability. This paper considers a cross-layer approach to jointly design AMCat the physical layer and the ARQ protocols at the data-link layer for adaptive controlthe signal modulation method and the parameters, it can effectively improve thesystem spectral efficiency, and improve the overall performance of the nextgeneration of wireless network. The main work of this article as follows:This paper presents an overview of the principles classification of cooperativediversity and link adaptation techniques, channel fading of wireless channel model isanalyzed, and the signal diversity reception technology in wireless co mmunicationsystem, discusses the combination of technology and investigate the mode ofcooperative diversity, and determine the diversity technology used in this paper.The paper first adopts a three-node cooperative diversity system which is source-relay-destination of as the research model, the Nakagami-m fading channelconditions, analyzes the relay coordination and no relay coordination under thecondition of each mode of packet error rate affects the spectral efficiency of thesystem. The main innovation of this article consists in the destination node uses themaximum ratio combining signals in the cross layer design system, which canimprove the system spectral efficiency.In multiple relays cooperative diversity system, this paper studies the way ofreceiving signals in the system and total signal noise ratio expression, then analyseschannel model and strategy of relays in the best relay system, and the relay nodes useamplify-and-forward technology and decoding-and-forward technology have differentperformances. And the paper compares the different influence in the number of relays in multiple relays and best relay systems on system outage probability and spectralefficiency. Through experiment and numerical analysis show that the destination nodeuses the best relay to retransmission is better than using all of the relay nodes toforward the signal, and also have lower system outage probability. And furthermore,when the number of relays is different, it will cause the change of spectral efficiencyin the best relay system.