Abstract

Communication systems of high-speed railway have inherent disadvantages and advantages. The estimation error of direction-of-arrival (DOA) of desired users caused by channel feedback delay and high moving speed make the common beamforming technique of smart antennas work abnormally. Instead, the opportunistic beamforming (OBF) with dumb antennas which does not need channel feedback is proper for high-speed railway. As the system has linear topology, regular movement as well as predictable location and speed information, the OBF can be improved to adapt to this scenario. In this article, conventional OBF is first introduced to the communication systems of high-speed railway. By multiplying random complex on each transmit antenna, the channel fluctuation dynamic range is extended so that multiuser diversity can be exploited. And then location information is employed to assist the conventional one. Communication systems in high-speed railway have the advantage of predictable location and speed information. The improved OBF can perform closer to the performance of coherent beamforming. Numerical analysis and simulation results show that both two algorithms can improve the system performance significantly.