The Research On Power Allocation For Cooperative Communications

The multi-input multi-output (MIMO) system can utilize fully space resources toimprove the system capacity and reliability multiply without increasing spectrumresources and transmit power. However, because some wireless terminals are limitedby size, cost or hardware, multi-antenna cannot be sued. Fortunately, the problems canbe solved by cooperative communications, where many adjacent single-antenna usersshare antenna to cooperate each other to form a virtual MIMO system. Source andrelay nodes transmit together information to the destination. However, thetransmission of information will consume power, how to allocate power rationallybetween nodes has become a critical issue. According to the number of relays, thechannel link and the relay position, the relationship of power allocation and systemperformance are discussed respectively in this paper.First, amplify and forward protocol and decode and forward protocol areintroduced. Simultaneously, based on outage probability and bit error rate for twoprotocols, the impact of different channel quality on the two protocols is verified.Then, to study the impact of different topologies on system performance, systemsymbol error rate is compared for equilateral triangle, isosceles triangle and lineartopology. The study find that symbol error rate under the optimal power allocation isalways less than the case of the equal power allocation in any topologies. Underdifferent allocations, symbol error rate is minimum for linear topology.Finally, the cooperative system is studied to select variable number of relay.Based on the feasible single-relay region, the feasible two-relay region is researchedand an adaptive relay selection strategy is presented for equal power allocation. Then,the optimal power allocation is investigated using geometric programming and anadaptive relay selection strategy is designed by traversal search. Due to a largeamount of computation, an approximation strategy is proposed. The proposedadaptive strategies can reduce the power consumption at a given outage probability.Moreover, power consumption can further be reduced by optimizing power allocation.