Diversity Combining for Frequency-Hop Spread-Spectrum Communications With Partial-Band Interference and Fading (anti-Jam)

114 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.This thesis presents results on the evaluation of several diversity combining techniques that are suggested for frequency-hop (FH) communications with partial-band interference and fading. The analysis covers systems with M -ary orthogonal signaling and noncoherent demodulation. The partial-band interference is modeled as a Gaussian process, although some of the results also apply to general (non-Gaussian) partial-band interference. The performance measures we use to evaluate the diversity combining techniques are the narrowband interference rejection capability and the signal to noise ratio requirement over the entire range of interference duty factors. We evaluate the exact probability of error for each of the diversity combining techniques studied.The performance of the optimum combining technique for receivers with perfect side information is established. It is shown that for receivers with perfect side information, the system performance does not change significantly with the choice of the diversity combining technique. However, the same schemes that work well in receivers with perfect side information perform poorly in receivers without side information. The goal of this work is to find and analyze diversity combining schemes that do not use side information, but that perform nearly as well as the optimum combining technique.Clipped linear combining is proposed as a diversity combining technique for receivers without side information. The numerical results demonstrate that clipped linear combining can perform nearly as well as the optimum combining technique in terms of both narrowband interference rejection and signal to noise ratio requirement. However, knowledge of the signal output voltage is required to set the clipping level. We analyze two alternative diversity combining techniques that do not have this requirement. These diversity combining schemes use ratio statistics in a ratio threshold test to determine the quality of each diversity reception. It is shown that the ratio threshold test with diversity combining provides good narrowband interference rejection, but at the expense of an increased signal to noise ratio requirement near full-band interference. Although the ratio threshold test with diversity combining does not achieve the optimum performance, it is an effective, as well as practical, scheme for use in FH communication systems with partial-band interference and fading.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD