HF modem test and evaluation

The objective of this program was to evaluate a recently developed, bandwidth efficient, Decision-Feedback Equalizer "Fast DFE' serial modem for radio communications in the High Frequency (3-30 MHz) radio band. The experimental model of the modem is realized on an AP-120B array processor. Tests of nonfading, flat and frequency selective fading were performed using a separate AP-120B array processor as the channel simulator. Successful performance of the modem operating at 2900 bps in a 2.7 KHz bandwidth was demonstrated on channels with 2 sigma fade rates up to 1 Hz and multipath delay values up to 5 milliseconds. Under slow fading conditions a significant implicit gain due to the multipath is realized. In a comparison with parallel tone modems, the Fast DFE modem significantly outperformed the USC-10, ACQ-6, and MX-190 modems in all test cases. Results reported here show considerable promise of the Fast DFE configuration and there is every indication that the preliminary design implementation which was tested can be further optimized for superior performance.