Effects of spreading bandwidth on the performance of UWB rake receivers

We consider an ultra-wide bandwidth system using reduced-complexity Rake receivers, which are based on either selective (called SRake) or partial (called PRake) combining of a subset of the available resolved multipath components. We investigate the influence of the spreading bandwidth on the system performance using the two considered types of Rake receivers. We show that, for a fix number of Rake fingers and a fix transmit power, there is an optimum bandwidth. This optimal bandwidth increases with the number of Rake fingers, and is higher for an SRake than for a PRake. We also investigate the effects of the fading statistics (Rayleigh or Nakagami) on the optimal spreading bandwidth. We find that the optimal spreading bandwidth is approximately the same for both types of fading, but that the actual performance of an SRake can be better or worse in Rayleigh fading (compared to Nakagami), depending on the spreading bandwidth and the number of fingers.