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.

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