Researches On The Optimal Power Allocation Algorithm For Multiple Users AF Cooperative Diversity Systems

To wireless communication channels, signal fading includes large-scale fading andsmall-scale fading, especially, the rayleigh small-scale fading affects the communicationperformance seriously. With the MIMO(multiple-input multiple-output) system as a typicalapplication, the spatial diversity technique can achieve the diversity gain with no additionalbandwidth consumption , and mitigate the effect of small-scale fading effectively. However, atypical MIMO system, it has to equip with multiple antennas in both the receiving andtransmitting terminals, for there should have some spatial separation among these antennas toreduce the correlation among the space signals from the antennas. But it's almost impractical toequip with multiple antennas on some smaller wireless terminals for the constraint of size, suchas cellular phones in cellular network and sensor notes in the sensor network. Consequently, itconfines the application of MIMO technique in these areas. The VMIMO(Visual MIMO)technique is giving a new technical solution to the above problem. Specially, the Cooperativediversity extends the traditional conception of MIMO, it forms a VMIMO structure by lettingother wireless terminals with single antenna in the system cooperate to transmit signals, also canrealize the spatial diversity processing. Theoretically speaking, the cooperative diversitytechnique can achieve the equivalent performance as the traditional MIMO technique.Firstly, the concept and the principle of the cooperative diversity are introduced in the paper.Then the realization process of the multiple users AF (Amplify-and-Forward) cooperativediversity system is introduced, and the corresponding theoretic analysis and the simulationresults are also given. It implied that the cooperative diversity processing has better performanceof average bit-error-ratio (ABER) and capacity-outage-probability compared with thenon-cooperative processing.There exists the problem: the total power in traditional multiple users AF cooperativediversity system may be too high. In this paper, under the constraint of the total power, with theminimal ABER as the objective function, an optimal power allocation algorithm for the multipleusers in AF cooperative diversity system is proposed. Simulation results imply that the proposedalgorithm improves both of the system ABER and capacity-outage-probability performance compared with the uniformpower allocation algorithm remarkably.In the end of the paper, an idea of the optimal transmitting strategy is discussed, expectingto achieve the coding gain as well as achieve the diversity gain to improve the systemperformance further. These problems still need research deeply.