Underwater Acoustic Carrier Aggregation: Achievable Rate and Energy-Efficiency Evaluation

In this work, carrier aggregation in orthogonal frequency division multiplexing (OFDM)-based underwater acoustic cellular networks is proposed, and its achievable communication rate and energy efficiency are evaluated. This technique improves the total throughput of OFDM using an expanded bandwidth, where multiple carriers are aggregated for data transmission from one transmitter. In this paper, a study is presented for a practical communication system consisting of a surface buoy station mounting single transducer and an autonomous underwater vehicle also with single transducer. The results are evaluated in a simulation environment as well as by field experiments. The simulation is first performed on a wide bandwidth up to ${\text{500}}\;{\text{kHz}}$, where the results indicate that carrier aggregation can greatly improve the achievable underwater communication rate for distances up to ${\text{5}}\;{\text{km}}$. It is further found by simulation that the maximum bandwidth configuration does not achieve the optimal energy efficiency; instead, there is an optimal bandwidth that can lead to such optimal energy efficiency. Further measurement results obtained in sea trials with a specifically designed sounding sequence are then presented. The achievable rate and energy efficiency are evaluated by the field measurement data. The measurement results provide insights into the performance of the system under narrow bandwidth settings.