Guard Time Optimization for Capacity Maximization of BPSK Impulse UWB Communications

—Usually, for the design of UWB systems, the symbol duration is chosen larger than the delay of the channel impulse response, in order to avoid the ISI (inter symbol interference). However, this approach does not maximize the system capacity. An adaptation of the guard time (GT) is a flexible mean of exploiting system resources efficiently in a multi-path fading environment. The optimal guard time length in BPSK impulse UWB communications is obtained by exhaustively searching for the guard time that maximizes capacity. This approach is complex since it has to be implemented for each channel realization. To reduce this complexity, in this paper we present new optimization methods. The first method assumes the fading channel to be partitioned into classes. Then, a given GT length for each channel class is used. The second optimization method provides a guard time for each channel realization. However, the GT is obtained by looking at simplified metrics which are based on the channel delay spread, the received signal energy, or on an approximation of the capacity formula. Simulation results are performed for UWB communications over WiMedia channels and they show that significant gains are achievable with the proposed guard time adaptation w.r.t. to the use of a constant guard time.