Performance of selective Rake (SRake) receiver is evaluated for direct sequence ultra wideband (DS-UWB) communications considering an independent Rayleigh channel having exponentially decaying power delay profile (PDP). BEP performances are shown. The results obtained are compared with similar results in a channel having flat PDP. Assumption of a flat PDP (as was previously made in DS-SS) is found to predict the optimum spreading bandwidth to be lower and suboptimum operating performance beyond optimum spreading bandwidth to be severely worse than that is achievable in a real channel with an SRake receiver having fixed number of combined paths. Optimum spreading bandwidth for SRake in a channel having exponentially decaying PDP is shown to be much larger than the one in a channel having flat PDP. This is specifically a good-news for UWB communication. Effects of partial band interference have also been considered. Interference is found to be less effective in case of exponentially decaying PDP.