Maximizing Spectral Efficiency for High Mobility Systems with Imperfect Channel State Information

This paper studies the optimum system design that can maximize the spectral efficiency of high mobility wireless communication systems with imperfect channel state information (CSI). The fast time-varying fading in high mobility systems can be tracked with pilot-assisted channel estimation. The percentage of pilot symbols in the transmitted symbols plays a critical role on the system performance: a higher pilot percentage yields a more accurate channel estimation, but also more overhead. The effects of pilot percentage are quantified through the derivation of the channel estimation mean squared error (MSE), which is expressed as a closed-form expression of various system parameters through asymptotic analysis. It is discovered that, if the pilots sample the channel above its Nyquist rate, then the estimation of the channel coefficients of data symbols through temporal interpolation yields the same asymptotic MSE as the direct estimation of the channel coefficients of the pilot symbols. Based on the statistical properties of the channel estimation error, we quantify the impacts of the imperfect CSI on the system performance by developing the analytical symbol error rate (SER) and a spectral efficiency lower bound of the communication system. The optimum pilot percentage that can maximize the spectral efficiency lower bound is identified through both analytical and simulation results.