Fundamentals of coding for broadcast OFDM

The same information is often broadcast to many receivers over different frequency selective channels. Digital audio signals and digital video signals are commonly distributed by such broadcasts. A coded modulation technique for orthogonal frequency division multiplexing (OFDM) is presented that provides consistent performance over a variety of frequency selective channels. The range of performance for an example of the new scheme over three different frequency selective channels is 0.75 dB at P/sub e/=3/spl times/10/sup -6/ as compared to 4 dB for a currently used scheme. The new technique employs relatively dense constellations combined with low rate codes designed to allow the receiver to take advantage of reliable symbols to compensate for unreliable symbols. Frequency hopped systems and flat fading systems with interleaving can also benefit from the new technique.