Philip Hunter /
Originally featured on BroadcastEngineering.com
EBU acts to protect DTT from uplink mobile interference
Digital terrestrial operators in Europe face not just losing capacity to mobile through re-allocation of some of their spectrum, but also interference as the bands will be adjacent. This prospect has provoked strong lobbying from European terrestrial operators, leading to joint proposals from four groups, the Digital Terrestrial Action Group (DigiTAG), the European Broadcasting Union (EBU), Broadcast Networks Europe (BNE) and the Association of Commercial Television in Europe (ACT), to ensure technical safeguards are in place to protect the TV services from interference.
The first proposals made in November 2010 addressed only downlink interference caused by signals transmitted from fixed base station towers to users' handsets, but the four groups followed up at IBC2011with recommendations to deal with the trickier issue of uplink interference. The latter, emanating from mobile handsets, is harder to trace as a source of interference because the devices are by definition in no fixed position and also generate signals at random times.
This interference arises because most European countries have decided to clear the so called 800MHz band between 790MHz and 862MHz and reallocate it to mobile or sometimes even fixed communications networks, following the switch off of analogue terrestrial television services. Terrestrial services are then transmitted on the band just below, with potential for interference. Uplink interference can be particularly annoying for users of services because of its intermittent nature, resulting in temporary break up or complete loss of TV pictures. Until now, viewers had no way of knowing that the problem was not with their own TVs or with the service. The new proposals tackle the problem in various ways, with an acknowledgement that technical measures may be needed as well as steps to ensure operators do their bit to avoid interference. Therefore, one of the recommendations is that consumers experiencing degradation of DTT service due to interference from mobile terminals should be promptly provided with filters connected between the receiving antenna and the DTT receiver, or other equipment, to eliminate harmful interference stemming from emissions in the 790-862MHz band. Furthermore, the four groups insist the cost of such measures should be borne by governments or the mobile operators themselves and not broadcasters.
Should these measures prove ineffective, regulators should have the power to act against mobile operators, the four groups add.
The earlier proposals covering downlink interference were in addition to European Union rules governing use of the 800MHz frequency band set out in its decision 2010/267/EC. While advocating the highest level of protection defined in these rules, the recommendations from EBU and co go further by urging that that mobile operators should have to undertake careful network planning to avoid situations where interference might result. They should also adopt measures that might include reducing the power output of their transmitters and adjusting antennae conditions to take account of local topographical features that might trigger interference.
At present, these are just recommendations that have yet to be adopted by the European Union or member states, but is a fair bet that at least some of them will be implemented given the strength of the lobbying.