Erasure tagging in a slow Rayleigh-fading environment

Our proposed digital audio broadcast system uses a Reed-Solomon code with hard decoding. If a system can identify codeword symbols that have a high-likelihood of errors and tag them as erasures, the probability of error can be decreased significantly. We introduce a method for tagging erasures in a slow Rayleigh-fading environment. This method combines 4 PSK with multitone modulation using differential detection. To decrease probability of bit error, an erasure-tagging scheme augments a Reed-Solomon code. In this scheme, the 4 PSK constellation, which would normally have 4 decision regions, is divided into 8 decision regions; 4 of these decision regions are considered bad. The scheme takes advantage of the slowly-varying nature of the channel by tagging an erasure when a majority of received tone symbols in a given block of multicarrier symbols fall into 'bad' regions. This method deduces when there is a large SNR loss due to fading and can be used when it is difficult to measure the signal SNR directly.