Maximizing spectral efficiency with imperfect channel information in high mobility systems

This paper studies the optimum system design that can maximize the spectral efficiency of a high mobility wireless communication system with imperfect channel state information (CSI). In a high mobility system, the percentage of pilot symbols in the transmitted symbols plays a critical role on system performance: a higher pilot percentage yields a more accurate channel estimation at the cost of more overhead. The channel estimation mean square error is quantified as a closed-form expression of the pilot percentage through asymptotic analysis. The effects of both estimation at pilot locations and channel interpolation at non-pilot locations are studied. The results are then used to derive an analytical spectral efficiency lower bound for systems operating with imperfect CSI. The spectral efficiency lower bound is expressed as an explicit function of a number of parameters, such as pilot percentage, maximum Doppler spread, and the signal-to-noise ratio, etc. The optimum pilot percentage that can maximize the spectral efficiency lower bound is analytically identified, and the impacts of imperfect CSI on system performance are studied through both analytical and simulation results.