Indiscriminate use is threatening the viability of Wi-Fi wireless broadband technology.
The ease of installation and potential speed of Wi-Fi, also known as IEEE standard 802.11b, is attracting more companies into providing broadband internet services but, because it operates at the unlicensed 2.4GHz frequency, interference becomes a problem when gear isn’t properly configured.
Warren Harding, an engineer with Auckland company Johnstone Dick and Associates, which manages the telecommunications facilities on the Sky Tower — including a Walker Wireless installation operating in the 2.4GHz range — says the spectrum in which Wi-Fi operates is capable of supporting multiple users. However, interference can occur when users on other sites “turn their data rates up to the max”.
There have been apparent cases of interference in Rotorua and Christchurch, referred to in postings to the nznog network operators’ mailing list, but the network providers and users concerned are saying little about it. In both instances existing networks are reported to have been disrupted when TelstraClear began deploying its Tempest wireless broadband internet service.
According to a posting to the list last year, several networks in Rotorua were disrupted by the arrival of Tempest, but TelstraClear spokesman Ralph Little says things have been resolved.
“As soon as we identified that there was a problem we made a point of taking every step to correct it. Very infrequently, we’ll find we share the same frequency and [if there is interference] will take every step to resolve it.” Tempest is deployed in some instances in the 2.4GHz range.
“There are a number of operators who do that. When we plan [to introduce Tempest] we see check to see what other operators are using it.”
Harding says the technology is such that it allows multiple users within range of each other, recognising data collisions. But even if an area of spectrum is quiet when a data burst is sent, there’s no guarantee it will be quiet as the burst travels through the airwaves.
“The problem is that people don’t keep their data rates down and it busies up the band, increasing the chances of a particular channel being in use. You end up with data colliding and the system becomes unusable.”
Matthew Brown, chief executive of wireless consultancy B&R Holdings, says when wireless networks collide, it’s usually because of poor installation.
“If wireless equipment isn’t installed properly, there’ll be interference and you’ll end up hearing stuff you’re not part of.”
The easy availability of cheap Wi-Fi gear, and the ease with which it can be erected — as opposed to properly installed — contribute to the proliferation of poorly configured wireless networks in New Zealand, Brown says.
“A common problem in New Zealand is over-powering; an ISP will put up a central access point and say ‘I want to go to the other side of town’, and go there at full power.”
In 99% of interference cases, the problem can be corrected with education about how to install the gear, he says. “Wireless isn’t a matter of putting up the antennas and turning it on; for me to do a link between two offices 5km apart, I’d spend two hours doing the maths to engineer it correctly.”
Interference often occurs when a wireless LAN that uses the DSSS (direct sequence spread spectrum) method comes into contact with one operating on FHSS (frequency hopping spread spectrum), Brown says. “Every second, FHSS does a hopping pattern over everything that’s there and people say ‘we’ve got interference’.” Although initially more expensive than DSSS, FHSS is very scalable, Brown says.
Richard Naylor, technical director of Wellington metro ethernet provider CityLink, says in his experience, wireless networks can co-exist if the radio engineering has been done properly.
He says there is a site in Wellington where CityLink and another operator’s gear is 2m apart, “but because we both have been careful we co-exist and there is enough space in the spectrum for others to use. We tend to avoid amplifiers, because it makes it harder for other people.”