OFDM for Underwater Acoustic Communications

Chapter 16OFDM in Relay Channels

Cooperative communication through the use of relay nodes has been extensively studied in recent years for wireless radio systems. Some example relay strategies include:

• Amplify and forward (AF): A relay node simply amplifies the signal received from the source and sends it to the destination [57];
• Decode and forward (DF): A relay node tries to decode the signal received from the source, and sends the re-encoded message to the destination [89];
• Compress and forward (CF): A relay node transmits a quantized and compressed version of the received signal to the destination [7, 89, 237];
• Quantize, map and forward (QMF): A relay quantizes the received signal at the distortion of the noise power, then randomly maps these bits to a transmit Gaussian codeword [13].

This chapter presents two scenarios of relay networks in underwater acoustic channels, where OFDM is used as the underlying modulation. The first scenario considers a dynamic coded cooperation (DCC) scheme in a three-node network, where the half-duplex relay listens until it can decode the message correctly and then switches to the transmission mode. When transmitting, the relay superimposes its transmission on the ongoing transmissions from the source. The second scenario considers a dynamic block cycling (DBC) protocol in a line network with multiple relays. As in DCC, each relay starts the transmission once it successfully decodes the incoming packet. This helps to reduce the end-to-end ...