Comparison of DFE and MLSE equalisation in a HF serial tone modem and implications for frequency selection

Optimum frequency selection for a HF serial tone modem should be made with prior knowledge of the performance constraints of the available channel coding and equalisation techniques. Two popular channel equalising schemes are considered using the international NATO high frequency (HF) modem standard STANAG 4285. The performance of decision feedback equalisation (DFE) and equalisation using maximum likelihood sequence estimation (MLSE) are compared and their computational complexity explored. Channel state convergence algorithms are assessed for DFE performance with the STANAG 4285 standard using CCIR channel states. The MLSE equaliser employs a Viterbi algorithm trellis and is trained using the pseudo-periodic auto-correlation of the STANAG 4285 frame preamble. The capabilities of the MLSE receiver have been enhanced for a fading channel by the mid-frame interpolation of channel impulse response estimates. Simulation results are presented that compare the performances of the DFE and MLSE receivers over the CCIR HF channel standards. The delay spread limitations of the DFE and MLSE receivers are given and the influence they have on frequency selection discussed