Effect of the VLF Propagation Channel on Spread-Spectrum Communication Systems

摘要

The effect of propagation on the performance of a differentially coherent, MSK communication system having a demodulator not matched to the channel is determined. The system performance level is found to be dependent on the dispersion characteristics of the channel transfer function. Near deep interference minima, performance increased as the bandwidth increased. For the particular sharp null studied, improvement of up to 20 dB above the level expected by a cw system operating at the center frequency was obtained. Up to 4-dB further improvement can be gained at wide bandwidths for sharp, deep nulls by implementation of a demodulator which matches the channel. The extreme phase dispersion at interference minima, which was expected to cause severe degradation, in fact caused only 2-to-3-dB degradation. (Author)