Originally featured on BroadcastEngineering.com
UK extends 4G DTT interference tests after promising early results
The UK is extending testing of 4G interference to digital terrestrial TV services after a small-scale trial indicated that the problem may be much less serious than had been expected.
The enlarged trial, now taking place, covers 170,000 household and businesses in SE London and is being run by at800, an organization funded by telcos to alleviate potential mutual interference problems between DTT and 4G mobile broadband services. Viewers in this area are being asked to report any interference to their TV over a week while 4G services in the 800MHz range are being trialed.
This follows a smaller trial of 22,000 households in the West Midlands region close to the UK’s second city Birmingham, where a dummy 4G mast was switched on during the last two weeks of March. Computer models forecasted 120 homes would be affected in this area but only 15 reported problems.
In July 2012, UK regulator last year Ofcom issued the dire prediction that 2.3 million households would lose some or all of their DTT reception when the 4G networks are rolled out in the 800 MHZ spectrum. This was made on the basis of theoretical models indicating that the powerful 4G emissions in the band neighboring the 700 MHz used by DTT would cause significant interference. That forecast now looks wildly exaggerated, although it is still likely a number of homes very near 4G base stations will be affected. Ofcom was also right to highlight the issue of RF overload, which affects signal amplifiers when there are strong emissions in a frequency band adjacent to the one they are tuned to, causing loss of both picture and sound.
For the UK, these trials are crucial because the country has just auctioned off the spectrum in the 800MHz band freed up by analogue switch off. The one existing 4G service in the UK from Everything Everywhere operates in the higher 1800MHz and so does not affect digital television. But mobile service providers want to operate in the 800MHz because range is increased at the lower frequencies so that they achieve better coverage per base station, reducing deployment costs in more sparsely populated areas.