Next generation mobile broadband (LTE) could interfere with Digital TV
Ofcom have warned that next-generation mobile broadband services using LTE (Long Term Evolution) could interfere with digital terrestrial TV (DTT), affecting around 3% of users in the UK (760,000 households). The problem exists as the DTT frequencies are so close to those which will be used by the mobile networks and some DTT receivers were designed to receive the whole of the frequency band including that which has been assigned for use for LTE.
Testing carried out by Ofcom found that households which use an amplifier are more prone to this problem as they get overloaded by the mobile signal more easily than a standard TV receiver. Ofcom have various proposals for ways to deal with this interference and that includes deploying satellite or cable services where restoring digital terrestrial TV is not possible. Other mitigation techniques include:
- Filtering at the DTT receiver - A filter can be installed (between aerial and amplifier if an amplifier is being used) to stop the unwanted signals being received. This may include more advanced filters for communal aerial systems.
- Filtering at the base station - Additional filtering would result in less interference to DTT services
- Improvements and alterations to DTT equipment - The quality of DTT receiving equipment could be improved by using, for example, directional antennas and receivers with better immunity to channel interference.
- Re-orienting DTT aerials
- - Where more than one DTT signal can be received, re-orienting the aerial to an alternate receiver could decrease the level of interference.
- Opposite polarisation to DTT
- - Mobile networks could polarise the signal using vertical polarisation (or horizontal in regions where vertical is used by DTT)
- Base station power reductions - Reducing the amount of power of the signal transmitted by mobile base stations could reduce interference but could also lead to degradation of mobile services.
Ofcom believe filtering should form a large portion of preferred mitigation options and modelling proposes that the use of receiver filters could decrease the affected households by around 90% and when combined with transmitter filters, this would reduce the amount affected to only 30,000 (down by 95%). Funding for this will be through the mobile network licensees (with receiver filters costing in the region of £10 for homes, but more where a communal aerial system is employed). One could perhaps argue that this should be funded by the digital switchover process which had an underspend of around £250m, but this money has already been appropriated for use for by BDUK (Broadband Delivery UK) for next-generation broadband services (which could include LTE).
The consultation is open for responses until the 11th August and the full document can be found here.