A novel spatially shared TDMA protocol and quality measure for ad-hoc underwater acoustic network

Underwater acoustic communication networking is an innovative area, which faces difficult medium problems, such as long propagation time and dynamic network topology. Our challenge is to develop a MAC protocol which provides a stable and efficient underwater acoustic network for a system with high message rate. In previous work, a TDMA based algorithm was implemented and tested in various sea trials [1]. The result was a reliable but inefficient network since the TDMA protocol does not utilize the network resources providing reuse in the code domain (using the CDMA concept) or in the frequency domain (using the FDMA concept). In this paper we introduce a quality measure taking into account both the reliability and efficiency requirements of the network. From this measure a novel MAC protocol, combining the TDMA scheme and multiple access techniques, was derived. The suggested MAC protocol confronts the acoustic underwater network challenges, such as the "near-far" problem and fast time varying topology. Results from network simulations, demonstrating the efficacy of the proposed networking scheme, are presented showing a significant efficiency increase with respect to the TDMA protocol without deteriorating the network stability and reliability.