M-ary PPM for Transmitted Reference Ultra-Wideband Communications

In this paper, we investigate the multiple-access (MA) performance of transmitted reference (TR) ultra-wideband (UWB) systems employing M-ary PPM in multipath environments. Because we assume there is no power control in the network, interfering power levels from users can vary over many 10´s of dB. We categorize the interfering users into two groups with respect to power levels. A new method for deriving the variance of the Gaussian random variable resulting from multiple-access interference (MAI) is developed using the power delay profile (PDP) of the channel. This makes the theoretical analysis tractable and enables us to predict the system-level performance such as the supported number of users, the achievable data rate, and the required bit-energy-to-noise ratio. Chip discrimination is applied and shown to mitigate the effect of high-power users. Performance is quantified due to the combined effects of equal-power and high-power users.