| UWB systems employing sub-nanosecond waveforms benefit from large path diversity, resulting in an extremely high number of resolvable multipaths. The complexity arising from the use of an optimal matched-filter receiver (i.e., a RAKE receiver) can be overcome by so-called transmitted reference (TR) systems, where a sub-optimal receiving strategy correlates the received waveform with a dirty template. For this reason, TR systems do not need to perform channel estimation, but suffer from sub-optimal performance. On the other hand, both optimal 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. Furthermore, we show how the same scheme can be employed by an optimal receiver in order to jointly estimate the channel and acquire synchronization. The estimation and acquisition in the presence of additive white Gaussian noise and a narrow-band jammer are based on an approximate solution to the maximum-likelihood equation.
Several performance measures and means of comparison are presented. First, the probability of correct synchronization in different scenarios is presented. Second, the quality of the channel estimates to be used by an optimal RAKE receiver is addressed in terms of mean-square-error. Third, in order to compare the performance of RAKE and TR systems, the bit-error-rate is addressed. Results show that, while the same strategy can be employed by both TR and RAKE systems to acquire synchronization, RAKE reception with channel estimation always outperforms TR systems in the presence of narrow-band interference, at the price of increased complexity.
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