Researches And Simulations Of Unitary-Space Time Modulation In High-speed Train-ground Communication Systems

Shannon theory illustrates that the multiple input multiple output (MIMO) channels can improve the channel capacity compared with the single antenna systems, which offers the theory foundation of space-time coding. According to the fact whether receiver possesses the full knowledge of the channel state information (CSI). the detection method of space-time coding can be divided into coherent detection and non-coherent detection. Unitary space-time modulation has been widely discussed by many scholars, which features for its no need for CSI at the receiver for detection.Firstly, the thesis introduces the MIMO system models under the quasi-static and continuous time-varying channel, and the basic principle of unitary space-time modulation is also discussed, including a method of designing of constellations which is based on the Fourier matrix. Further, the paper conducts the study on the effect of the number of the constellations to the unitary space-time system on the basis of the optimal constellation when T<8.Secondly, the detailed analysis of the non-coherent detection of unitary space-time modulation is applied over the quasi-static channels and sample-to-sample time variant fading channels, different factors effects to the system are displayed, such as the number of the transmit antennas,the existence of the time variation of channel,etc. Research of Chernoff bound of the pair-wise error probability is presented, at the same time the theory formula is compared with the simulation results, the coincidence of the two cures illustrates the correctness of theory formulation derivation. Over the continuous time-varying channel, we take the channel correlation including the impact of the spatial correlation and time correlation in to account, the conclusion that the greater correlation the worse bit error rate is obtained. Moreover, a sub-solution is also presented which ignores the channel correlation in the quasi-static channels and it has no difference with the optimal one almost except for the1-2db gap in SNR when they have the same error performance.At last, a coherent detection algorithm is proposed over the continuous time-varying channel. The simulation result reveals that even the CSI is unreliable, in low SNR the proposed coherent detection has the lower bit error probability than the existing non-coherent detection, while the inaccurate channel state information may deteriorate the performance seriously in the high SNR. At the same time, this thesis simply introduces how the train can complete the exchange its location and speed information with the ground under the guidance of the CTCS train control system. Combined with the dynamic speed curves, simulation results also show that the bit error rate will not be affected obviously even the Doppler frequency shift estimation error exists within some certain limits in the high speed train-ground communications. The conclusion achieved above certifies the application of the unitary space-time modulation in high speed train-ground communication systems.