Multiple-burst correction techniques for slowly fading channels

Slowly fading channels, such as a troposcatter communication link, are characterized by multiple error bursts which may last for many thousand channel digits, as well as by random errors. It is shown that even the best random error-correcting codes cannot be effective on this type of channel unless some time delay between code letters is introduced to reduce the correlation between channel errors within the code. In addition to the conventional approach of interleaving code letters to obtain error independence, two alternative coding approaches are considered which correct random errors as well as detect and correct multiple bursts, i.e., multiple channel fades. A concatenated coding approach, based on interleaving inner code blocks but not interleaving digits within an inner block, and a new multiple-burst correction code based on generalized burst trapping codes, are shown to represent attractive alternatives to the conventional interleaver approach.