Minimum Error Transmissions with Imperfect Channel Information in High Mobility Systems

Abstract

One of the main challenges faced by communications in high mobility systems, such as unmanned aerial vehicle (UAV), is the fast time-varying fading. This paper studies the optimum system design that can minimize the error probability of a high mobility wireless communication system with imperfect channel state information (CSI). We consider a system that employs pilot-assisted minimum mean square error (MMSE) channel estimation. The channel estimation error is usually non-negligible in high mobility systems and might have significant impacts on system performance. With asymptotic analysis, the channel estimation mean square error (MSE) is expressed as a closed-form expression of the percentage of pilot symbols in the transmitted symbols. An optimum receiver for systems with imperfect CSI and the corresponding symbol error rate (SER) are then derived by analyzing the statistical properties of the channel estimation error. The SER is expressed as an explicit function of a number of parameters, such as pilot percentage, maximum Doppler spread, and the signal-to-noise ratio (SNR), etc. The optimum pilot percentage that can minimize the SER is analytically identified, and the impacts of the imperfects CSI on the system performance are studied through both theoretical analysis and simulations.