Underwater Communication Networks - Exploiting Absorption in Wireless Networks
Monday, June 11th 2007, 13:00, Turing Lecture Hall
Professor Michael FraterSchool of Electrical Engineering |
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It is a great pleasure for us to announce a talk from Prof. Michael Frater from the University College Canberra, Australia.
Description
Underwater acoustic data communications have attracted signicant research efforts over the past few decades. This is due to the fact that radio-frequency networks designed for surface environments usually deliver very poor propagation performance when used in underwater applications. Work by Zhang et al (Adaptive sampling for marine microorganism monitoring) show that 433MHz radios transmitting at full Mica-2 transmitting power delivered a communication range of less than 1 meter. ULF radio waves are therefore used by marine communications but the devices require very high transmitting power and large antennas.
Alternatively, acoustic communication devices can be employed since sound waves propagates well underwater although at a fairly low speed (approx. 1500m/s) and hence suffers from long propagation delays. Moreover, the velocity of sound waves varies with the temperature, density and salinity of seawater. Because the channel bandwidth is limited, the capacity of these acoustic communications systems tends to be much lower than modern RF systems, often providing data rates less than 10 kbps.
Underwater acoustic sensors can be used to form networks providing similar functionalities in much the same way as terrestrial sensor networks. For example, an underwater acoustic sensor network can be employed to monitor compass, pitch, roll, depth, temperature in the water and send data back to the observer. Similar to a terrestrial sensor network, a number of underwater sensors are deployed in the water of interest. There is at least one sink located on the water surface, which is in charge of collecting data from the sensors and dispatching commands of the network operator.
To be suitable for use in the underwater environment, therefore, a communications system must be able to cope with low channel capacities and long propagation delays. These form the focus of this research.
