Performance of an optimally spaced PPM ultra-wideband system with direct sequence spreading for multiple access

We analyze the error performance of an ultra-wideband (UWB) system with pulse position modulation (PPM) for data modulation and direct sequence (DS) spreading for multiple access in indoor lognormal fading channels. A RAKE receiver is used to combine a subset of the resolvable multipath components using the maximal ratio combining technique. Inter-path and multiple-access interferences are modeled and incorporated into the BER expressions. As two special cases, the performances of the optimally-spaced and orthogonal signaling schemes are compared. The presented results allow comprehensive evaluation of system performances with any combination of parameters.