Researches On Simulation And Dsp Implementation Of Unitary-Space Time Modulation System In Fast Fading Channel

In2000, Hochwald proposed a new space-time coding scheme named as unitary space-time coding or unitary space-time modulation (USTM) that maps bit sequences to unitary space-time matrices. Hochwald’s study has shown that even if the transmitter and receiver do not know the instantaneous channel state information(CSI), MIMO system can still achieve high channel capacity in Rayleigh fast fading channel, which is very attractive for high-speed mobile communication environment.This thesis introduces the basic principle of the unitary space-time coding firstly, including the design of constellations and decoding algorithm of unitary space-time. Further, analysis of Chernoff bound of the pairwise error probability is presented and the constellation construction factors are obtained through search under different parameters, based on which, the impacts exerted by constellation construction parameters over USTM performance are evaluated. Through simulation, analysis of the advantages and disadvantages of the traditional coherent detection and noncoherent detection of unitary space-time coding are compared. When noncoherent detection is employed, instantaneous channel state information is not required which worse error performance is exhibits in low signal-to-nosie region. When coherent detection is applied, the performance shows a significant performance gain compared with noncoherent detection, while the inaccurate channel state information may deteriortate the performance seriously.Considering the fact that the channel state information may not be estimated and fed back correctly, we propose an improved coherent detection algorithm. The simulation results show that the performance of the proposed detection algorithm is better than that of noncoherent detection while a little worse than that of traditional coherent detection in the low signal-to-noise region. In high SNR region, the proposed algorithm can improve the performance of coherent detection in the presence of channel estimation error. Based on the proposed detection algorithm, we can choose the coherent and noncoherent algorithms adaptively according to the SNR, which can improve the performance of the unitary space-time coding significantly when accurate channel state information is not available.Finally, the thesis discuss the implementation of unitary space-time modulation in digital signal processing (DSP) system. Based on the system design, the bit error rate results obtained in CCS environment are provided and compared with Matlab simulation results, which show1dB performance loss caused by quantizing error. The fixed-point results also verify the feasibility of the DSP implementation of unitary space-time modulation in the thesis.