Impact of MAI and channel estimation errors on the performance of Rake receivers in UWB communications

The performance of Rake receivers for ultrawide-bandwidth communications is discussed, taking into account the effects of multiple access interference (MAI) and channel estimation errors. Two alternative signaling formats are considered: time-hopping pulse-position modulation (TH-PPM) and TH pulse-amplitude modulation (TH-PAM). The channel exhibits multipath propagation and its impulse response is either assumed known or is estimated with least squares methods. Computer simulations show that, even with perfect channel knowledge (PCK), TH-PAM is superior to TH-PPM. The superiority increases with the number of users and becomes substantial in the presence of channel estimation errors. An intuitive explanation of this fact is provided.