Narrow bands hamper WiMAX future

Commercial arrangements encouraged for broader spectrum bands

WiMAX, the fixed-wireless data technology of choice, may not be able to deliver the promised high speeds in New Zealand as the frequency bands in the licensed spectrum it operates in are too narrrow.

Jonathan Brewer, technical director of Wellington wireless provider Araneo, says a WiMAX operator using unlicensed spectrum such as 5.8GHz has four 20MHz channels for transmission and another four for reception. This provides 50Mbit/s per sector of full-duplex (transmit/receive simultaneously) bandwidth, according to Brewer.

However, unlicensed spectrum raises the issue of interference, so many operators are looking at Crown-allocated 3.5GHz spectrum instead. Apart from not having to share the allocated spectrum, 3.5GHz also works better for near line-of-sight installations thanks to the lower frequency, and it also penetrates buildings better.

However, Brewer says that as the 3.5GHz band is split into 7MHz pairs, a four-sector transmission site will only have 1.75MHz per sector, providing less than 5Mbit/s. This, Brewer says, is not sufficient for anything apart from “a pile of 2Mbit/s symmetric links that no one wants, as they can get better from DSL.”

Unless WiMAX operators manage to acquire wider pairs of frequency blocks, like 21MHz ones, Brewer says those using Crown-allocated spectrum won’t be able to offer a competitive service.

Brian Miller, manager of radio spectrum policy and planning at the Ministry of Economic Development (MED), says that at the time when the 3.4 to 3.6GHz spectrum was configured, WiMAX had not been conceived.

The MED released an engineering consideration document in September 2000, asking for commercial and public views on its draft plan for the spectrum. Originally, Miller says International Telecommunications Union-RadioCommunications (ITU-R) studies, as well as international trends at the time were based on the aggregation of 250kHz channels. The band itself was aimed for wireless local loop (WLL) and broadband wireless access (BWA) multipoint distribution service.

Miller says that the MED initially proposed the band should be subdivided into 2.5, 5 and 10MHz sub-blocks, aggregated to form 25MHz blocks where possible in accordance with ITU-R recommendations.

The current legislation allows providers to reach commercial agreements with each other to widen existing spectrum bands if needed, says Miller. Management rights can be carved up he says for this purpose.

The 2.3GHz band that Woosh recently reached an agreement with Telecom to use was configured for 8MHz channels, as this was deemed likely to be the most appropriate when it was originally allocated in 1990, Miller says.

Although 2.3GHz isn’t officially part of the WiMAX standard, Intel and South Korean operators are promoting it for mobile wireless broadband or WiBro, as it is dubbed.

Samsung has developed WiBro handsets that are currently being trialled by Korean telcos, but it’s not known if this is what Woosh intends to use its spectrum allocation for in New Zealand.

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