Coding schemes for M-QAM digital radio with frequency selective fading

The dispersive effects of frequency selective fading in digital radio systems can result in significant degradation of bit error rates and system outage. This paper discusses bandwidth efficient applications of error correction codes to reduce the outage probability of high capacity digital radio systems. One approach uses interleaving combined with a linear code. The parity bits generated by encoding the binary information on one or more radio bearers are transmitted over a common standby bearer. The performance of this scheme with either block or convolutional codes is considered. Attention is focussed on decoding techniques appropriate to bit rates as high as 140 Mbit/s. An alternative approach using trellis coding with an expanded signal set is also examined. It is shown that coding techniques can be an effective supplement to the conventional use of equalizers and space diversity.