Research On Link Adaptation Technology In Cooperative Communication

Cooperative technology can obviously increase the channel capacity of wirelessmobile communication system, improve system performance effectively. Thereappear more and more uncertain factors in complex high-speed wireless mobilecommunication environment, multi-path fading and time-varying characteristics ofwireless mobile channel have become the obstacles of spectral efficiency and systemoutage performance improvement.In cooperative networks, only choose relays with good channel conditions andadopt reasonable resource allocation, the diversified communication requirements ofhuman can be satisfied. Now more and more wireless application demands andcomplicated communication environment, more and more researchers are turning tolink adaptive technology in cooperative system to ensure the reliability and stabilityof wireless mobile communication.In this paper, cooperative diversity technology is briefly summarized, thedevelopment situation of adaptive technology is systematically described, and themain contents of research are given. And then link adaptive technologies are studied,which mainly include principles and applications of ARQ (Automatic RepeatRequest) protocol and AM (Adaptive Modulation), the common classification ofrelay selection and basic application of power control technology as well.To solve the problem that spectral utilization rate is not high due to strictconstraint on packet error rate in cooperative system combining AM and ARQ, athree-node cooperative amplify-and-forward source adaptive transmission model isanalyzed, probability density function at destination node is derived, the dynamicadjustment SNR threshold algorithm is proposed. Simulation and theoretical resultsshow that the system average spectral efficiency is improved under the proposeddynamic threshold algorithm.As the resource inefficiency in the default multi-relay system and defects ofcommon relay selection algorithms, an improved relay selection algorithm isproposed to minimize outage probability. According to composite average channelgain of relays, eligible and symmetric relays are removed at the same time to realizerelay adaptive selection and avoid conflict. Compared with classical scheme withpower optimization distribution under the limited total power and the sub-optimal power relay selection method, numerical and simulation results show that outageprobability has greatly reduced. Further combine power optimization and theimproved relay selection algorithm to minimize outage probability. Theoreticalresults show that the outage probability has further reduced; the simulation resultsalso confirm effectiveness of the joint algorithm.