Home opinion-and-analysis Cornered! Claims of NBN's death by DIDO greatly exaggerated


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Claims of NBN's death by DIDO greatly exaggerated

  • 31 July 2011
  • Written by 
  • Published in Cornered!

News emanating out of the US of a new and "revolutionary" wireless technology have, predictably, been seized on by opponents of the NBN that the Government should not be putting $36b worth of eggs in one technology basket, namely FTTH. Before they shoot off at the mouth the Cassandras of the NBN should read the claims for the technology more closely.

The Australian reported "The new technology, called DIDO, allows Internet users to access download speeds up to 1000 times faster than possible on conventional wireless networks, without any fall in speed as more users get on to the network.

It quoted Opposition communications spokesman, Malcolm Turnbull, saying that the wireless breakthrough underlined the importance of being "technology agnostic" when it came to choosing broadband solutions to meet the nation's needs.

Details of the DIDO technology have been published in a white paper from which the Australian quoted as follows.

"The potential of DIDO is to have unlimited numbers of simultaneous users, all streaming high-definition video, utilising the same spectrum that a single user would use with conventional wireless technology, with no degradation in performance, no dead zones, no interference between users and no reduction in data rate as more users are added."

That's the equivalent of the perpetual motion machine - impossible according to the laws of physics. Something to which far too many writers, including my own colleague Stan Beer, are inclined to give short shrift: despite the fact that they have been shown to apply throughout the known universe, that there are no proven exceptions to them and that it is the understanding and application of these laws that has made possible all the technologies we enjoy today.

As Beer wrote in his iTWire article "claims to offer all the advantages of wireless Internet connectivity without the disadvantages of latency and bandwidth limitations caused by the pesky laws of physics that NBN devotees love to cite."


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Not so. The authors of the white paper are not cranks and whatever the claims they make breaking the laws of physics is not one of them. And yes, they did make that quote. So what exactly are they claiming?

Essentially it is this. Radio Waves have an tendency to propagate in all directions - which is very useful but very inconvenient because it means all users have to share the same band of frequencies and that limits the rate at which a given band of frequencies can deliver a different data stream to each individual user in the same area. The coverage areas of adjacent transmitters overlap, there is interference between the signals carrying data to different users and this limits the rate at which information can be carried.

The more users in a given area, the greater the interference. But imagine if the radio waves could be constrained into a narrow flexible corridor linking each user to the base station and that followed each user as they moved. In such a situation the entire frequency range would be available to deliver data to every user and the number of users that could be supported by each base station would be, to all practical purposes, limitless.

Remember a fibre network delivers information using exactly the same electromagnetic energy as a radio network, but because that energy is constrained with the fibre there is no interference between different channels using the same spectrum and the capacity of an FTTH network is, to all practical purposes, limitless. You could run a fibre cable containing hundreds fibres each carrying several terabits per second to every home.

This is the essence of the DIDO technology: It claims to enable the entire spectrum available to be dedicated to each and every user in the coverage area, even when transmissions from nearby base stations interfere with each other. Here is how it is claimed to work.

In all wireless systems today - WiFi or cellular - the base stations simply take whatever data is destined for each user, modulate it onto the wireless carrier and transmit it.


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In the DIDO system a central processor looks at each user device and at all the signals destined for other nearby users that the device is able to receive. It then combines all these signals to modulate the radio carriers from all the base stations such that these combine at each unit to create a signal that contains just the information intended for that device.

As the white paper puts it: "DIDO communication begins with the DIDO access points exchanging brief test signals with the DIDO user devices. By analysing what happened to these test signals as they propagate through the wireless links, the DIDO data centre determines precisely what will happen when it transmits data signals from the APs to users, and how the simultaneously transmitted signals will sum together when received by each user device. Then, the DIDO data centre uses this analysis, along with the data each user is requesting (eg video from a website), to create precise waveforms for all of the APs that, when transmitted at once will sum together at each user device to create a clean, independent waveform carrying the data requested by that user.

"So, if there are 10 APs and 10 users all within range of each other, then 10 radio signals will sum together at each antenna of each user's device to produce an independent waveform for each device with only that device's data."

The practicalities of this seem significantly daunting - especially if the receivers are mobile. The white paper does not discuss in detail what limitations might be possible given current and future projections in processing power, but says: "We do not know of a theoretical limitation to how many users we can add to a DIDO system without a degradation in data rate per user.

"There certainly will be practical limitations with each era of technology evolution, but we have not yet come close to them. So far, as we've increased the number of simultaneous users in the same area to 10 (limited just by the number of hand-built radios we have) we have not seen any degradation in performance'¦Until we start to see some degradation in performance as we add more users, we will not be able to predict how far it can go."


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The white paper claims that: "DIDO was designed to be a mass-market product, not a lab experiment. As a result, many of design decisions were specifically made to enable DIDO to be built practically and inexpensively, and to scale to any size. For example, much of the work has been focused on making sure the DIDO data centre computing requirements scale linearly, not exponentially, as more users are added. DIDO also uses very advanced mathematics, not switching, to enable users to move among adjacent DIDO clusters (the DIDO APs controlled by each data centre make up a DIDO Cluster) seamlessly without requiring any 'handoff', allowing adjacent Clusters to share the same frequency. However it seems inevitable that processing requirements increase exponentially with the number of users in a given area.

The corollary of the claims for the DIDO technology is that if you have few users and few overlapping base stations (ie as in rural Australia) the technology will offer little gain over today's technologies. And to serve many users in a small areas is likely to need a large number of access points each with limited coverage area to limit the processing load.

The white paper does not go into any details that would answer the question: "If the are x users in an area of y square kilometres how many base stations wil be needed to deliver bandwidth of zMbps to each user, given the central processor's ability to handle the processing load involved?"

What it does say is: "You can think of the DIDO access points as a vast random array of antennas extending out from the DIDO data centre for miles, but instead of running long wires from the data centre to the antennas, DIDO uses the Internet to connect to each DIDO AP, allowing each DIDO AP to be placed anywhere there is an Internet connection, whether indoor or outdoor, much like a WiFi AP could be placed anywhere there is an Internet connection."

Which sounds remarkably like the topology of WiFi, or a cellular network with lots of picocells and femtocells. And the more bandwidth this technology can deliver the more backhaul will be needed.

I've no expectations that DIDO will make a Dodo of the NBN any time soon.

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