Optimal LTE-A pilot patterns and numbers of MIMO transmission streams under high mobility scenarios

Under the high mobility scenario, some factors have a strong influence on LTE system performance such as the velocity of mobile user, pilot patterns, multiple-input-multiple-output (MIMO) transmission strategies, wireless channel characteristics, etc. The doppler shift or spread due to the user velocity will not only cause the inter-carrier-interference (ICI) for orthogonal frequency division multiplexing (OFDM) transmission but also increase the channel estimation error in time-varying channels, which further deteriorates the efficiency of precoding and symbol detection. Smaller pilot spacing in time domain provides better channel estimation accuracy however results in larger system overhead, thus lower transmission efficiency. Similarly, larger number of MIMO transmission streams definitely enables more data symbols to be transmitted simultaneously however requires more pilot symbols for channel estimation, also leading to larger system overhead. In this paper, the effects of user velocity, pilot patterns and the number of MIMO transmission streams on system throughput are investigated. The analysis and simulation results show that under certain user velocity and channel condition, there always exists an optimal pilot spacing and an optimal number of MIMO transmission streams in terms of the system throughput.