Research Of Encode And Decode Algorithm For Adaptive QOSTBC In DF Cooperative System

With the rapid development and popularization of wireless communication technology, the requirements for communication quality and transmission rate have been increasing. The technology of MIMO can save frequency resources, improve system capacity, and ensure the quality of signal. But due to objective factors, like volume, complexity and power consumption, MIMO can’t meet the demand of the high rate services in future wireless communication. To overcome the above problems, scholars have put forward cooperative communication based on virtual MIMO. In addition, the adaptive quasi-orthogonal space-time block codes(A-QOSTBC) can achieve interference cancellation, and have linear decoding complexity through the channel feedback, so as to improve the system BER performance. In this paper, we have research on low complexity decoding algorithm for quasi orthogonal space-time block codes(QOSTBC) in decode and forward(DF) cooperative communication system. Meanwhile, the A-QOSTBC scheme with lower complexity and better performance has been proposed through the combination of A-QOSTBC and cooperative communication.Firstly, we discuss the encoding and low complexity decoding for traditional QOSTBC. We also analyze the code construction, adaptive factor and the low complexity decoding algorithm of A-QOSTBC. The simulation verifies the bit error rate(BER) performance of A-QOSTBC is superior to that of traditional QOSTBC.Secondly, we derive and simulate the traditional linear and nonlinear decoding algorithm respectively. On the basis of the traditional decoding algorithm, we combine Zero Forcing(ZF) detection algorithm and Minimum Mean Square Error(MMSE) detection algorithm with pairwise decoding algorithm to achieve ZF-Pairwise algorithm and MMSE-Pairwise algorithm respectively. Simulation results demonstrate that these two algorithms are suboptimal algorithms having the trade-off of performance and complexity. And they can be applied the suboptimal algorithms into collaborative system, thus we can get the corresponding QOSTBC schemes.Then, on the basis of the QOSTBC schemes, the A-QOSTBC scheme has been proposed in cooperative system. And the performance influence of the adaptive factor on QOSTBC scheme is verified by simulation. We also verify the signal rotation affecting the performance of the whole system with simulation. In addition, the traditional and modified low complexity decoding algorithms are applied to the A-QOSTBC scheme. The proposed schemes have lower complexity, and simulation results show that the A-QOSTBC scheme on the basis of MMSE-Pairwise algorithm can achieve 1.8d B gain at low SNR.Lastly, in order to make the transmission scheme more practical and achieve full diversity gain, this paper also considers the information exchange(IE) among source nodes. For the four antenna QOSTBC code matrix, we consider all 16 signal error cases. Moreover, we discuss the A-QOSTBC code matrix in every error case, and calculate its adaptive factor and eliminate the interference caused by equivalent channel matrix. The simulation results show that, compared with A-QOSTBC scheme neglecting information exchange(traditional A-QOSTBC) and that considering the information exchange, the A-QOSTBC scheme considering IE can achieve BER performance improvement.