A reduced complexity MAP receiver for digital ISI channels, with application to HF radio links

A reduced-complexity MAP equalizer (RMAP) is proposed, together with an associate channel estimator, where only H channel states having largest probability are adaptively retained over the total of N states, with H≪N. For a channel length L, RMAP reduces the complexity from LN to LH. Channel estimator complexity is LH² + HL² instead of LN². Performance analysis shows that P-MAP allows practical applications using state-of-art low-cost DSP devices: this is the case of a HF digital modem recently developed at Marconi Mobile laboratories.