Development and implementation of multi-user detection (MUD) strategies for shallow water acoustic network (SWAN) telemetry

Abstract

This thesis describes the development and implementation multi-user detection strategies for phase coherent Shallow Water Acoustic Network (SWAN) communication. Sea-trial experiments were carried out in the North Sea, 8 km near Noordwijk, Netherlands. The present demand for shallow water acoustic networks (SWAN) is driven by the need for environmental and other data acquisition from fixed and mobile measuring platforms located in the continental sea. Such networks require new, reliable and bandwidth-efficient data communication systems. Which maximises the use of the underwater channel for simultaneous transmissions. However, horizontal-link digital acoustic communication is limited by both environmental and system factors. Underwater acoustic channels are characterised by multipath propagation, which is due to signal reflection from the sea surface and the sea bottom. Due to wave motion, the multipath components undergo time-varying propagation delays, which result in signal fading and phase fluctuations in the received signal. Another problem with horizontal-link communication is that of the Doppler effect that arises as a result of relative motion between the transmitter and receiver. Receivers employing array processing with adaptive decision feedback equalisation schemes have been shown to be effective to tackle these problems. However, in a phase coherent SWAN, the base-station receiver has the added task of mitigating the effect of co-channel interference from users in the network. Although various multiple access protocols can be implemented to help ease the co-channel interferences, they usually utilises a significant amount of the limited channel resources. The constraints of SWAN communication lead to the need for multi-user detection strategies. The thesis proposes a number of novel multi-user detection strategies and presents the software architecture and practical implementation of these phase coherent multi-user receiver structures. Both simulation data and experimental real data were used to compare the performances of the proposed receiver structures. Successful implementation of the receiver system was demonstrated by field trail results for ranges up to 5km.