Underwater communication method

In an underwater communication network comprising a central node in operative communication with a terrestrial network and a plurality of underwater sensor nodes, a method for the transmission of underwater information in the underwater communication network, comprising the steps of:

• determining an entire useable frequency band suitable for the underwater propagation of sound between any of said plurality of sensor nodes and said central node, said frequency band extending between a lowest frequency and a highest frequency;
• assigning a forward direction frequency band inclusive of said lowest frequency for signal transmission from said central node to the plurality of sensor nodes;
• subtracting said forward direction frequency band from said entire frequency band and assigning the remainder as a backward direction frequency band for signal transmission from the plurality of underwater sensor nodes to said central node;
• subdividing said backward direction frequency band into a number M of smaller discrete frequency bands each for signal transmission from one of said plurality of sensor nodes to the central node, including a lowest backward frequency band comprising the lowest backwards direction frequency;
• performing an initial setting process comprising setting a data reception part of said central node to said lowest backwards direction frequency;
• estimating distance between the central node and each one of the plurality of sensor nodes;
• assigning one of said smaller discrete frequency bands to each of said plurality of sensor nodes based on the estimated distance from said central node thereto;
• wherein the central node uses the forward direction frequency band to transmit a signal from the central node to the plurality of sensor nodes,
• wherein each of the plurality of sensor nodes uses the allocated smaller discrete frequency band to transmit a signal to the central node;
• wherein said lowest backward frequency band is allocated to the sensor node disposed at the farthest distance away from said central node;
• and
• wherein each of the plurality of sensor nodes variably controls the frequency for transmission in response to a current position;
• wherein said data reception part of said central node is set with all backward direction frequency bands existent in the frequency band allocated to an arbitrary sensor node where the underwater communication is to be performed.