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Abstract-This paper introduces the underwater acoustic modem as implemented within the UAN -Underwater Acoustic Network project. The low power modem has implemented turbo equalization algorithms in addition to variable spread rate direct sequence spread spectrum signaling. The network layer implemented on the modem support automatic network discovery, multi hop routing and support for mobile nodes, and when expanded with a single board computer via serial line it supports IP connectivity end-to-end. Experimental results from sea trials are presented.

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Different methods for network-based mobile positioning were compared experimentally. The Cell-id and TA method provided limited accuracy, the uncertainty ranging from 500 m to 3000 m for the median, dependant on area type. This could be reduced up to 25% by using alternative radii based on observations in the "doughnut" shaped prediction area. The Planning tool method improved the accuracy by approximately 30-50 % compared to this in urban area. The Forced handover method provided the best overall performance. In rural area the improvement was approximately 40-55 % compared to Cell-id and TA.