Due to the absence of spectrum regulation and limited bandwidth, underwater acoustic (UA) systems are prone to interfere with each other. In this paper, a decentralized power allocation strategy is proposed for multiple OFDM UA links sharing the same physical resource. These links are supposed to be noncooperative and aim at selfishly maximize their own information rate. Each link is assumed to only know the statistics of its channel and the overall noise plus interference power spectral density. A game-theoretic formulation, which explicitly takes into account the random time-varying nature of the underwater acoustic channel as well as the low speed of sound, is derived. Numerical simulations show the strong benefit of proposed approach in highly interfering channels.

The objective of this paper is to provide a multiuser transmission technique for underwater acoustic communication in the framework of an Autonomous Underwater Vehicle (AUV) fleet. By using a variant of a Hyperbolically Frequency-Modulated (HFM) signal, we describe a new family of transmission techniques called MultiUser Chirp Spread Spectrum (MU-CSS), which allows a very simple matched-filter-based decoding. These techniques are expected to provide good resilience against multiuser interference while keeping good robustness to Underwater Acoustic (UWA) channel impairments like Doppler shift. Their implementation for the UWA scenario is described, and the performance results over a simulated shallow-water UWA channel are analyzed and compared against conventional Code-Division Multiple Access (CDMA) and Time-Division Multiple Access (TDMA) transmission. Finally, the feasibility and robustness of the proposed methods are verified over the underWater AcousTic channEl Replay benchMARK (Watermark), fed by several channel responses from sounding experiments performed in a lake.

International audienceThis paper focuses on underwater acoustic (UA) communications and proposes a decentralized spectrum sharing method for noncooperative orthogonal frequency-division multiplexing systems in interference channels. The problem is formulated as a noncooperative game where the players are UA communication systems aiming at finding the power allocation on subcarriers that maximizes a utility function related to their information rate. Realistic assumptions regarding the UA context are formulated. Frequency-selective and randomly time-varying channels are considered. Each system is constrained in average power and adapts its power allocation strategy only with local knowledge of its channel statistics and noise plus interference power spectral density. This knowledge is obtained through a feedback link from the receiver. Estimation errors on the channel statistics are taken into account, thanks to a robust reformulation of the game. We show that an efficient decentralized spectrum sharing can be achieved when all players use a water-filling strategy against each other iteratively. Simulations results are obtained on synthetic but realistic channels. In configurations where the UA communication systems are in close areas, significant increases of spectral efficiencies can be expected compared to the conventional uniform power allocation. Results on channels sounded at sea support our conclusions