Optimal power allocation and doppler compensation in cooperative underwater networks using OFDM

We consider a Decode-and-Forward and Amplify-and-Forward cooperative diversity network where a source communicates with a destination with the help of multiple relays. Relay selection among the set of multiple relays has been proposed as a diversity achieving communication protocol in wireless radio networks. The application of cooperative communication protocols to underwater networks using OFDM is considered and a lower bound on the data detection error at the destination is derived using the Hammersley Chapman Robbins Bound. This lower bound is optimized to jointly determine the optimal power allocation for the relay nodes and Doppler compensation factor at the destination. Numerical results suggest that while relay selection and subsequent Doppler compensation is optimal in most cases, jointly optimizing the power allocation to the relays and the Doppler compensation factor at the destination is the best strategy when several relays have links of comparable strength to the destination.