Abstract: A method of determining the position of an underwater node. The positions of three or more transmitters are determined. Each transmitter transmits at least four pulses, wherein a time difference between each pulse and a previous one of the pulses is proportional to a respective co-ordinate of the position of the transmitter. The pulses are received at the underwater node and decoded by measuring the delays between them, thereby determining the co-ordinates of the transmitters. The range of each transmitter relative to the underwater node is also determined. Finally the position of the underwater node is determined in accordance with the co-ordinates and ranges. Any errors in the measurements of the delays between the pulses only translate into small errors in the determined position because of the proportionality between the delays and the coordinates. Therefore if there is a gradual decrease of signal-to-noise ratio then the accuracy of the position estimate also degrades gradually.

Abstract: A method of determining the position of an underwater node. The positions of three or more transmitters are determined. Each transmitter transmits at least four pulses, wherein a time difference between each pulse and a previous one of the pulses is proportional to a respective co-ordinate of the position of the transmitter. The pulses are received at the underwater node and decoded by measuring the delays between them, thereby determining the co-ordinates of the transmitters. The range of each transmitter relative to the underwater node is also determined. Finally the position of the underwater node is determined in accordance with the co-ordinates and ranges. Any errors in the measurements of the delays between the pulses only translate into small errors in the determined position because of the proportionality between the delays and the coordinates. Therefore if there is a gradual decrease of signal-to-noise ratio then the accuracy of the position estimate also degrades gradually.