Channel estimation for Ultra-Wide Bandwidth Time-Hopping Impulse Radio

We address the problem of channel parameter estimation for time-hopping impulse radio signals received in a multipath environment and in the presence of multi-access interference. The parameters of interest are the attenuations and the delays incurred by the signal echoes in the multipath propagation. A maximum likelihood approach is adopted under the assumption that the symbol data are either known (DA estimation) or unknown (NDA estimation). The effects of the estimation errors on the performance of a Rake receiver are assessed by simulation. The results show that, as the number of users increases, so does the degradation in receiver performance as compared with ideal operation with perfectly known channel parameters. As expected the DA method has an edge over the NDA in that, for a fixed degradation, it can handle a larger number of users. The number of users that can be accommodated is found for some values of the system parameters.