A rate-adaptive coded OFDM (RA-OFDM) spread spectrum system for tactical radio networks

This paper investigates the use of spread spectrum OFDM modulation to provide a variable rate communications link that is tolerant of multipath fading and interference. The system adaptively varies to changing channel conditions in a way that optimizes throughput while maintaining acceptable error rate performance. System performance for a variety of channel conditions including AWGN, static multipath, time-varying frequency selective and frequency non-selective Rayleigh fading shows that a desired BER can be maintained through adjustment of the processing gain. A trade-off analysis between forward error correction (FEC) coding and spreading shows that a coding rate of approximately 1/2 is best, with the remainder of the bandwidth expansion used for spreading. An overall system adaptation strategy in a broad range of channel conditions is presented.