The performance of an adaptive least squares lattice decision-feedback equalizer on a fading multipath HF channel

The performance of an adaptive lattice decision-feedback equalizer, originally proposed by F. Ling and J.G. Proakis (IEEE Trans. on Comm., vol.COM-33, no.4, p.348-56, 1985) is compared with that of transversal equalizer that uses a gradient tap adaptation algorithm operating in a periodic-channel estimation-mode. Results obtained over a simulated two-path HF channel model with a 1-ms differential multipath delay and 0.5-Hz fading rate show an approximately 5-dB advantage for the lattice equalizer for low signal-to-noise ratios (SNR), but only marginal improvement for high SNR. This phenomenon is primarily attributed to the occurrence of a significant number of flat fades during typical test runs over the two-path channel model, which accounts for the total lack of any form of diversity during these periods. Since diversity enhances modem performance in the presence of flat fades, the error rate plateau was significantly reduced by exploiting dual-polarization diversity without reducing the nominal bit speed of 2400 b/s