Underwater acoustic modem configured for use in a local area network (LAN)

The U.S. Navy Telesonar RDTandE effort is developing a low cost, non-coherent acoustic modem capable of data transmission under adverse channel conditions at data rates up to 2400 bits per second (bps). This modem was described by Scussel et al. (1997) at Oceans '97. A substantial number of modems have been constructed by Datasonics Inc., including some intended for deployment in the SEAWEB '98 series of acoustic experiments in September, 1998 in Buzzards Bay, Massachusetts, in the USA. The purpose is to demonstrate an acoustic network capability supporting approximately 10 modems deployed in very shallow water. The network consists of two groups of modems, each using frequency partitioning of the approximately 5 kHz of available bandwidth, to communicate independently with a master modem. The master modem then acoustically communicates with a gateway containing both cellular and RF communications capabilities to reach distant users. Communications amongst the modems involves message transfer ("hops") across several modems, thus requiring careful attention to the development and implementation of network protocols. This is the first in a planned series of network experiments involving increasingly sophisticated modems and protocols, with autonomous handshaking and adaptive modulation offering both much lower and much higher data rates than are now available.