Performance of Four Rake Modems Over the Non-Disturbed Wideband HF (High Frequency) Channel

摘要

The Rake Modem technique was proposed some thirty years ago by R. Price and P. Green as a means for combating multipath when direct sequence spread spectrum signals are transmitted. This report presents performance evaluations for four Rake modems used to communicate over the wide band (e.g., 1-MHz) HF channel. Attention is confined in this paper to performance for the non-disturbed HF channel. Consideration is given to the impact of mode Doppler shift and multipath spread due to dispersion. The effects of additive noise, self noise and imperfect channel measurements are included. Results are presented for decision-directed, parallel-probe, serial-probe, and DPSK Rake modems. With a suitable codec, performance to within 1-3 dB of the additive white Gaussian noise channel at 0.00001 error rate is predicted, depending upon the modem and the channel dispersion, if Doppler shifts of modes can be tracked to within 0.1 Hz. (RH)