Performance enhancement of differential UWB autocorrelation receivers under ISI

The autocorrelation receiver (AcR) is a suboptimum, low-complexity receiver architecture particularly suited to ultra-wideband (UWB) communication systems. As the bit rate increases, interference among pulses due to multipath propagation causes serious impairments of the AcR´s performance. To mitigate this effect, we propose an appropriate design of the chip code and of the delay hopping (DH) code. We provide conditions to be satisfied by the DH code in order to reduce the nonlinear intersymbol interference (ISI) and the bias term, which are peculiar nuisance parameters of autocorrelation receivers. By extending the length of the chip code, we show that N_p transmitted pulses per symbol can be employed to suppress the average linear ISI of N_p-1 previous symbols. Simulated results confirm the performance improvement in terms of bit-error rate. However, in previous work it has been shown that the noise power linearly increases with N_p. Although a large number of pulses per symbol is favorable for ISI mitigation, we show that the transmission of a single pulse minimizes the probability of error, for bit rates lower than an upper bound depending on the channel root mean-square delay spread and on the noise power.