Evaluation of diversity combining methods for underwater acoustic OFDM communication

Underwater acoustic communication has been widely used in remotely operated vehicle (ROV) and wireless video and image transmission systems. Orthogonal frequency division multiplexing (OFDM) is effective to cope with multipath interference. However, OFDM in acoustic communication requires a very long guard interval (GI) in accordance with long delay reflected waves, which decreases an effective transmission speed and delays a received response. We study various diversity techniques to obtain sufficient communication quality even for a short GI. In general, maximum ratio combining (MRC) is superior to selective combining (SC) in terms of improvement of signal-to-noise ratio (SNR). We present that SC provides better communication performance than MRC in the condition that a multipath delay exceeds GI and OFDM symbol duration.