MULTI-MODE ADAPTIVE MAC PROTOCOL SUITE AND STANDARDIZATION PROPOSAL FOR HETEROGENEOUS UNDERWATER ACOUSTIC NETWORKS

This paper investigates a multi-mode MAC protocol suite for use in a heterogeneous underwater network. Modems from different manufacturers may employ different physical layers and MAC protocols. If multiple modems operating in the same or overlapping frequency bands are deployed in the same geographic area, they cannot function correctly due to interference. We propose a mechanism to achieve co-existence and communication among such heterogeneous assets. Co-existence is defined as the state where modems of the same type can communicate with each other while minimizing interference with other types. The Communications state is when all modems in one area can communicate with each other. Alien signals are defined as non-decipherable communication signals for any one modem type. The Co-existence mode requires all modems to implement an alien signal detection feature. In this mode, a CSMA based scheme will be used to communicate among modems of the same type, if alien signals are detected, and to allow non-interfering co-existence among different modem types. In order to achieve Communications mode, modems will be required to implement a standardized Physical Layer (along with their proprietary Physical Layer or as the only system and on top of the alien signal detector). Such suitable Physical Layer standards are currently being addressed under the JANUS initiative at NURC. For this mode, we propose using a MACA based protocol suite for the MAC layer. It has a distributed MACA-based mode and a centrally controlled polled mode that nodes dynamically adapt to, depending on deployment and node configurations. Features include autonomous selection of distributed or controlled MAC modes, inter-cell interference mitigation strategies, and provisions for both reliable and unreliable modes. This paper presents some simulation results and mathematical analysis for the two MAC protocol modes.