LTE vs broadcasters: let the spectrum wars begin

ACMA scratches head over 4G interference

As mobile carriers prepare to upgrade to 4G/LTE networks, Australia’s free to air broadcasters and Foxtel are bracing for potentially significant and costly interference to their transmissions.

Earlier this month UK regulator Ofcom estimated that it would cost £100m to deal with the disruption caused by 4G transmitters to over 760,000 households with digital Freeview.

However the technical issues at stake for Australian broadcasters differ from the UK and Europe 4G deployments, involving interference caused by LTE/4G downlinks to handsets in the home.

According to industry analysts, recent closed technical trials have revealed that if an LTE handset is in active use near a Foxtel set-top box, it will disrupt the signal. Interference issues also pose threats to Foxtel services in multi-dwelling premises such as apartment blocks, where an LTE phone can interfere with a service next door.

Free-to-air broadcasters are becoming concerned at the risk that remote and regional viewers will suffer, particularly where multiple LTE devices are in use. As well as Australians' appetite for multiple handsets, many households add mobile wireless USB devices, tablets, and smart meters.

An engineering spokesperson from the Australian Communications and Media Authority told The Register the issue is now under investigation. It is understood that concerned broadcasters and Foxtel are also actively in discussions with tha ACMA and the government to ensure that these technical hurdles are sorted before the government’s new spectrum allocation plan is finalized.

The ACMA spokesperson said that while the situation is similar, there are a number of differences between Australia's spectrum proposals and UK/European arrangements. The UK/European arrangement uses reverse duplex with only a 1MHz guard band between the top of the Digital Terrestrial Television (DTT) band and the bottom of the band to be used for IMT(4G/LTE).

“In Australia we intend to adopt the AWG plan. This plan provides two 45MHz blocks of spectrum separated by a 10MHz midband gap, uses conventional duplex, and there will be a 9MHz guard band,” the spokesperson explained.

However, industry sources say that this approach may not stop the “handset splatter” caused by the LTE emissions.

The ACMA is currently working on the reallocation of spectrum channel plans and deciding what level of guard band will be sufficient to stop interference. Sources close to ACMA admit that there is a “great deal of uncertainty over how big the problem is going to be in regional areas and apartment blocks.”

A study released last year by European trade association, Cable Europe and analysts Excentis, claims that LTE handsets operating in the 800MHz band could cause interference to set-top boxes and cable modems. It found that the majority of LTE devices, when used indoors, would be operating at maximum transmit power and at these levels would cause interference if the user came within 3 meters of consumer equipment.

“At distances of 1 metre the chance of the LTE handset causing interference becomes very high, although Cable Europe accepts that the exact level of disruption for all distances depends on the type and position within the home of the cable modem or set-top,” the report said. ®

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