Performance evaluation of impulse radio UWB systems with pulse-based polarity randomization in asynchronous multiuser environments

The performance of a binary phase shift keyed random time-hopping impulse radio system with pulse-based polarity randomization is analyzed. The effects of multiple access interference are investigated for both chip-synchronous and asynchronous systems. It is shown that the performance of a chip-synchronous system is the same as that for the symbol-synchronous case studied in E. Fisher and H. V. Poor (Oct. 2-4, 2002). The asynchronous system is modelled as a chip-synchronous system with uniformly distributed timing jitter on the transmitted pulses of interfering users. This extends the analytical technique developed for the chip-synchronous case to the asynchronous case. An approximate closed-form expression for the probability of error, expressed in terms of the autocorrelation function of the transmitted pulse, is derived for the asynchronous case. The analysis shows that the chip-synchronous assumption can result in over-estimating the error probability, and hence that the system design based on this approximation will he on the safe side. The degree of over-estimation mainly depends on the autocorrelation function of the UWB pulse and signal-to-interference-plus-noise-ratio (SIR) of the system. Simulations studies support this approximate analysis.