Evaluation of an Acoustic Charge Transport (ACT) Device for Adaptive Interference Suppression in Spread Spectrum Communications Systems.

摘要

Analytical results have shown that adaptive filtering can be a powerful tool for the rejection of narrowband interference in a direct sequence spread spectrum receiver. However, the complexity of adaptive filtering hardware has hindered the experimental validation of these results. This thesis describes a unique adaptive filter architecture for implementing the Widrow-Hoff Least-Mean-Square (LMS) algorithm using two state-of-the-art Acoustic Charge Transport (ACT) Programmable Transversal Filters (PTFs). Signal-to-noise ratio improvement measurements demonstrate the effectiveness of the adaptive filter for suppressing single- and dual-tone jammers at jammer-to-signal ratios (JSRs) of up to 30 dB. It is shown that the ACT adaptive interference rejection system can consistently produce 55 dB notch depths with 3-dB bandwidths as low as 300 kHz with minimal degradation to the spread spectrum signal. It is also shown that the adaptive system can eliminate single tone jammers at any frequency within the spread spectrum bandwidth at any of 10, 20, or 30 dB JSRs within 10-15 iterations of the adaptive algorithm. The only drawback with the adaptive system as tested is the amount of time taken to perform an iteration because of the requirement to update the PTF tap weights sequentially. Suggestions are given as to how this particular parameter of the adaptive interference system could be optimized. Adaptive interference suppression, Adaptive interference rejection, Least-Mean-Square(LMS) algorithm, Acoustic Charge Transport(ACT), Direct sequence spread spectrum, Narrowband jammers, CW Jammers.