Joint Acquisition/Channel Estimation for UWB Communications in the Presence of Narrow-band Interference

In recent years, UWB has become a candidate for future high-speed indoor communications. Its wide bandwidth, on the order of a few gigahertz, and its very low power spectral density, can achieve high data rates as well as good coexistence capabilities with other commercial systems. UWB systems employing sub-nanosecond waveforms benefit from a large frequency diversity, resulting in an extremely high number of resolvable multipaths. The complexity arising from the use of an optimal matched-filter receiver (i.e. RAKE receiver) can be overcome by so-called transmitted reference (TR) systems, where the receiver strategy correlates the received waveform with a dirty template. For this reason, TR systems do not need channel estimation, but are sub-optimal. On the other hand, both RAKE and TR systems need to acquire code and/or symbol synchronization. This paper presents a general code acquisition strategy that can be applied to both schemes. The estimation and acquisition in the presence of additive colored Gaussian noise are based on an approximate maximum-likelihood criterion. Several performance measures and means of comparison are presented. The probability of correct synchronization in different scenarios is presented. Moreover, the quality of the channel estimates to be used by a RAKE receiver is addressed in terms of mean-square-error. Finally, in order to compare the performance of different receiving strategies, the performance in terms of bit-error-rate is addressed