Adaptive OFDM Modulation for Underwater Acoustic Communications: Design Considerations and Experimental Results
In this paper the authors explore design aspects of adaptive modulation based on Orthogonal Frequency Division Multiplexing (OFDM) for UnderWater Acoustic (UWA) communications, and study its performance using real-time at-sea experiments. Their design criterion is to maximize the system throughput under a target average Bit Error Rate (BER). They consider two different schemes based on the level of adaptivity: in the first scheme only the modulation levels are adjusted while the power is allocated uniformly across the sub-carriers, whereas in the second scheme, both the modulation levels and the power are adjusted adaptively. For both schemes they linearly predict the channel one travel time ahead so as to improve the performance in the presence of a long propagation delay.