Adaptive Spread Spectrum Systems Using Filterbanks and the Discrete Wavelet Transform

摘要

This report discusses the development of new approaches for providing anti-jam, multipath resistant, multi-user communications based on filterbank and wavelet techniques. The first portion considers the synthesis of spreading waveforms using full binary tree multi-rate filterbank design techniques. Non- binary spreading waveforms are produced that are optimized for multi-user, multipath and interference channels and shown to out-perform some conventional spreading sequences. The second part of the report describes and evaluates a spread spectrum version of Orthogonal Frequency Division Multiplexing (OFDM) wherein the same information is transmitted on multiple orthogonal carriers, creating both time and frequency diversity. In the receiver, time domain and transform domain excision are used to improve performance in pulsed wideband or narrowband jamming, respectively. In addition, the report considers replacing the inverse and forward FFT's commonly used in OFDM systems with inverse and forward Modulated Lapped Transforms (MLT's). Performance results demonstrate the effectiveness of the techniques. For both the spreading waveform design and OFDM work, simulations were performed using the Signal Processing WorkSystem (SPW) from AltaGroup of Cadence Design Systems, Inc.