Tuesday, August 02, 2011

DIDO Wireless Broadband for NBN

Interest has been sparked in Distributed-Input-Distributed-Output (DIDO) Wireless Technology with claims it breaks Shannon's Law and a comment from shadow communications minister Malcolm Turnbull, that it could challenge the National Broadband Network's choice of fiber optic cable. However, some claims made for DIDO are not credible and it has yet to be proved commercially viable.

Essentially DIDO aims to provide full channel capacity to each user on a shared radio channel. Under current systems, each user has a proportion of the capacity, so if there are 10 users, they get one tenth each. DIDO aims to be able to provide each of the 100 users with all the capacity each. The method for doing this seemingly impossible task is to coordinate the output of multiple transmitters so that the signal received by each user is different and contains the information they want. This gets around Shannon's law, by effectively creating a separate channel for each user.

DIDO will require very sophisticated processing to create the waveforms needed for each transmitter. It will also likely require cooperation from the receiving units in order to model the transmission paths, so that the shape of the received signal can be estimated. As the number of users increases, the calculations will increase far more rapidly. Also if the users are moving, this will complicate the calculations, as will other objects moving in the environment (such as vehicles) which will; change propagation.

One use of this technology of particular reliance to Australia is “DIDO Rural”, which would use HF frequencies (3-7 MHz), bounced off the ionosphere, allowing 500 mile coverage. This would allow access in remote parts of Australia. The use of HF and even longer range radio (such as the Defence Department's JORN over-the-horizon radar), is not new to Australia.

Assuming DIDO works in practice, it will take five to ten years to come into commercial use. This may well replace some other forms of wireless broadband, or more likely be added to them to supplement capacity (much as how current mobile systems are being upgraded). DIDO may also prove useful in regional Australia. However, it is not likely to render fiber optic cable redundant in urban areas.

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