Weaving a wireless mesh

Wireless local loops could be costly and controversial to build. But a mesh of co-operating sites could shift the balance, creating a real rival for DSL, says Bill Pechey

Last November, the Radiocommunications Agency awarded licences for Broadband Fixed Wireless Access using frequencies in the 28GHz radio band, often called the wireless local loop. Not all the licences were taken up and the auction brought in an average of just over £2m per licence ­ not much above the reserve price.

This represents quite a bargain for the six companies that bought the licences. Each is based on geographical boundaries and large swathes of the country ­ mainly the south, with the exception of London ­ attracted no interest. The government wants to sell more licences so services can be provided everywhere, and recently announced a second auction to be held in October.

Any operator buying one of these licences will have to buy equipment to set up the network and provide services to customers. Several technologies are available, the most obvious being a point-to-multipoint arrangement that combines a network of base stations. These stations will probably require tall masts to ensure an unobstructed signal path to each customer's site. Sites must be found for the masts, which have to be connected to the provider's backbone network ­ not an easy task, particularly with current environmental concerns.

However, Radiant Networks, based near Cambridge, has developed a system called mesh radio that has considerable benefits. The equipment installed at each customer's site does not necessarily link directly to the central site, but may connect via other customers' sites. Each node effectively acts as a relay for up to four others in the vicinity, thus creating a mesh network structure.

Once there is a reasonable number of customers, the length of the typical radio link will be quite short and there are likely to be fewer obstructions. This means transmitters can be low-power and antennas can always be directional, reducing power and interference even further. Clearly, there is a potential chicken-and-egg problem if the first customer is not within range of the first base station. Radiant solves this by installing temporary 'seed' nodes on strategic buildings; these only need a power supply and are autonomous.

But what services can mesh radio provide to the customer? The mesh uses Asynchronous Transfer Mode to carry traffic and can provide circuit- or packet-switched services at rates of up to about 25Mbit/s. This includes E1 (2.048Mbit/s) and various Internet Protocol services. Nobody is talking openly about tariffs yet, but it appears as though mesh radio should provide serious competition to current and future xDSL services.

The relatively low prices paid for 28GHz licences and the use of technologies like mesh radio should make these new networks successful, and open up a new avenue of competition in the broadband wired-access market.

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