Packet Length Optimization for MIMO Mobile Systems with Estimated CSI

The reliability of mobile packet data transmission in multi-input multi-output (MIMO) communication systems is degraded by time-varying multi-path channel fading. This so-called Doppler-effect can be mitigated by using a shorter packet length and/or inserting more pilot training symbols and frequently tracking the channel at the receiver at the cost of additional rate overhead. A judicious choice of the packet length according to channel conditions aims at achieving a tradeoff between reliability and overhead to maximize the achievable throughput. We present an analytical framework for optimizing the packet length in mobile MIMO systems to maximize throughput taking into account channel estimation and Doppler effects. As a case study, we consider the Alamouti space-time block code (STBC) for 2 transmit antennas over Rayleigh flat-fading channels and determine the optimum packet length as a function of input SNR and Doppler rate. Furthermore, we investigate the effect of various system design parameters on the optimum packet length and achievable throughput such as signal constellation size, number of receive antennas, and receiver detection algorithm.