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Ofcom moves to protect Freeview interference from 4G mobile devices

Don't worry - Ofcom will ensure that everyone effected by 4G interference will still be able to watch digital television, and at no cost to the affected viewers.

Don't worry - Ofcom will ensure that everyone effected by 4G in
published on UK Free TV

Ofcom has estimated it will cost £100m to deal with Freeview users who are located near to the transmitters for the next generation of mobile broadband services, which will use the frequencies (791 to 862 MHz) previously used for analogue television.

Once switchover is complete, over 10 million homes in the UK will use Freeview for their only television reception, and almost all of the remaining 17 million homes will use the terrestrial digital television service on their secondary TV sets.

The signals are provided from two types of transmitter. First there are around 80 high power transmitters located on hills that serve very large areas, such as the Crystal Palace transmitter (4.5 million homes in London), Winter Hill (2.7 million homes in the North West of England) and Sutton Coldfield (1.8 million homes in Birmingham). In addition there will be over 1,000 fill-in Freeview light transmitters, such as Boddam, which serves just 600 homes.

In contrast, the new 4G mobile services will use around 9,000 smaller transmitters located near where the services are required, which follows the current model for mobile phone networks.

4G transmitter interference location

In places where the 4G transmitter is located close to homes receiving Freeview, it is likely that Freeview viewers will experience to forms of interference:

Signal overload - when a Freeview receiver is overloaded because the total input signal level is more than a certain level, the whole receiver will stop working and all television services will be lost.

Signal-Interference Noise Ratio degradation: this is where reception breaks down because the receiver can no longer decode the digital information in the transmission. This could affect a single multiplex or could take out all services.

The "overload zone" will occur for Freeview viewers located close to the 4G transmitter, with the "degradation zone" will affect those slightly further from the 4G transmitter:

Interference factors

Not all 4G transmitters will cause problems for Freeview reception, the other factors are:

The types of Freeview installation, with single unamplified aerials to a single set have the best resilience, with communal and systems with amplifiers more likely to suffer. The 4G transmissions are capable of overloading most types of TV amplifier.

The frequencies used for the DTT services being received, with those on the adjacent C60 being worst, C52 to C59 second worst and those on lower frequencies having the best chance of avoiding interference.

The strength of the Freeview signal received is another factor, with those with weaker signals due to being distant from the Freeview transmitter, having the most potential for 4G interference.

Not all 4G transmitters will use the same frequency, those that happen to use the lower frequency allocation having the most potential to cause Freeview interference, and those that transmit at higher power levels having more effect than low power 4G transmitters.

Homes affected by 4G interference without intervention

Ofcom calculate that:

Of the 16.3 million UK homes with a standard (unamplified, unshared) Freeview reception, 110,000 (0.67%) would be effected.

Of the 5.2 million homes using communal aerials systems, 550,000 (10.6%) will have problems.

Of the 5.6 million homes using amplified Freeview reception, 100,000 (1.8%) will experience problems.

Prevention and mitigation

There are several ways to deal with these 760,000 homes that will have problems.

Signal filters

Use of signal filters for the Freeview reception combined with Fitting of filters at 4G transmitters.

Ofcom's modelling finds that this is the most effective way of dealing with the 4G interference problems. Of the 110,000 standard Freeview installation homes, 87,000 will have their reception restored this way, almost 100% of the 550,000 homes with communal systems will be mitigated with filtering and 93% of the 100,000 domestic installations with amplifiers.

The total cost will be £20m for the Freeview filters and £33m for fitting of the filters in homes. Also, for the domestic filtering to be effective, the 4G providers will also have to spend around £11 fitting filters at the 4G transmitters when they are being installed.

Freeview equipment adjustment

After the provision of filters, there will still be 23,000 homes with unamplified and 7,000 homes with amplified Freeview reception equipment that are unable to receive their services.

Some of these homes will simply need a new Freeview box for each TV set. Whilst these boxes cost around £15, the requirement to fit these and provide for each set could come to as much as £200.

Another option, for at least 20% of homes, is to receive the Freeview services from an alternative transmitter. However, this could lead to the provision of the 'wrong' version of BBC One, BBC Two, ITV1 and Channel 4/S4C to the home. Ofcom is unsure if this will be an effective mitigation.

On Channel Repeaters

The use of On Channel Repeters (OCR) to rebroadcast the Freeview signals at higher power levels in the interference area was considered by Ofcom, but the high cost and unknown effectiveness has caused them to be distrgarded as a viable option.

Ensure 4G polarization is opposite to Freeview polarization

Because of several factors, Ofcom does not consider that this will help prevent 4G interference of Freeview reception.

4G transmitter power reduction

Ofcom have concluded that causing service reception problems for the new 4G mobile services is undesirable for the services to be successful.

Provision of Freesat or free Virgin Media services for affected homes

This leaves providing a replacement Freesat installation (including multiple sets and Freesat+ boxes) for the 30,000 homes with their Freeview reception disabled, or the funding of a basic Virgin Media package. The total cost for this is £10m.

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Friday, 10 June 2011

7:33 AM

Richard Taylor: Yes, it will be the 4G licence holders.

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Briantist's 38,908 posts GB flag
Saturday, 18 June 2011
12:02 PM

Yet again we see the Ofcom answer as being related to set top boxes. They are an add on, a fudge and far from ideal. What about people who want tv's with intergrated FV receivers to reduce the clutter and number of remotes. I fine the quality of set tops to be poor compared with FV recorders and intergrateds.
How much extra CO2 is emitted by all the additional set top boxes across the UK?
I appreciate all the arguments about 4g revenues etc. and the small number of people affceted. This is all fine unless you are one of those affected. No doubt we will see a hoo-har at the time but some poor sod who moves house near one of these 4g base stations a few years down the line may well end up spending a fortune on new equipment, aerial installers etc. before someone says "oh it's 4G mate" with little or no chance of compensation. Persoanlly I would prefer in more investment in mobile phones was dedicated to ensure I can make uninterrupted calls on my moble on my drive home, walk before run!

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Andrew's 5 posts GB flag
Monday, 20 June 2011
Mark Aberfan Aerials

11:22 PM

Hi Brian,

At least one of our local tv relay masts also transmits mobile phone signals from the same mast, will the 4g masts all be new ones or will they use existing ones ? if so would that reduce the effective range of the tv transmissions.

Mark Aberfan Aerials

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Mark Aberfan Aerials's 1,059 posts GB flag
Wednesday, 22 June 2011
12:46 PM

I absolutely agree with Andrew above. I have a Sony integrated Freeview tv (standard definition), the picture quality of which I've always thought was very good, particularly as regards image sharpness. I recently plugged a neighbour's Freeview set-top box into a scart plug on the back of my tv and couldn't believe how poor the picture looked by comparison. The lack of picture sharpness was incredible, as was the "blocky" looking nature of the picture particularly in the darker tones. Maybe cheap Freeview boxes just produce all the required channels without regard to the quality of the signal processing. I tried 3 different scart cables, one of which was an expensive "high-quality" one, but the picture always looked massively inferior compared with my integrated Freeview receiver.

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Tony's 4 posts GB flag
Mike Dimmick

2:01 PM

Mark Aberfan Aerials: I assume the phone companies will want to site-share as much as possible, just as they do now.

The danger is that the combined signal level from the TV transmissions (wanted) and the 4G signals (unwanted) pushes equipment outside its linear region, causing distortion, resulting in intermodulation. That intermodulation creates frequency-shifted products, potentially splatting the 4G phone signal - an OFDM signal just like digital TV - onto one or more multiplexes. That will at least reduce the tolerance of interference and noise from other sources.

However, the 4G power is likely to be lower than digital TV power. If you make the coverage area too big, the bandwidth is shared between too many subscribers. Cells have to be fairly small. 800 MHz spectrum is in demand because of its penetration into buildings and the relatively lower power needed for the same coverage, not providing wider coverage (though some wide-area transmitters are needed for base coverage of relatively unpopulated areas).

I do think Ofcom are seriously underestimating the extent of the problem. It seems to be normal practice for newer aerial installations to have excess gain and often the owner has added amplification as well, thinking that this will correct any reception problems. Sometimes it might appear to have done so as by the time the amplifier is fitted, the root cause of the issue has gone away.

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Mike Dimmick's 2,486 posts GB flag
Mark Aberfan Aerials

4:18 PM

Hi Mike,

Thanks for your thoughts,I totally agree & am concerned as I think you are that the interferance problems are being intentionally downplayed or innocently underestimated.

Mark Aberfan Aerials

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Mark Aberfan Aerials's 1,059 posts GB flag
Sunday, 3 July 2011
Margaret Schneider
7:09 PM

I have a Humex Freeview box I am receiving BBC chanels with some disruptions but ITV recently has got worse and this weekend have lost all ITV Chanels

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Margaret Schneider's 1 post GB flag
Margaret's: mapM's Freeview map terrainM's terrain plot wavesM's frequency data M's Freeview Detailed Coverage
Friday, 15 July 2011
Tuesday, 4 October 2011
W Huggard
10:03 PM

Can a link be provided to the original Ofcom report, please. It would be useful to be able to cite this for further research.

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W Huggard's 1 post NZ flag
Friday, 7 October 2011

3:13 PM

W Huggard: I've read the Ofcom papers regards to the selling off of the UHF frequency spectrum channels 62 - 68. 4G or forth generation as it's called with operate mobile broadband services on these frequency channels nationwide. However, i'm not sure whether they are going to be allowed to have their antennas on the tv transmission masts, or on the same site, or adjacent to the tv transmitters.whatever is eventually decided upon, the risk of interference must be an issue here. Ofcom think that interference is most likely if 4G are allowed to place their antennas on the tv masts themselves, or off site in line with the direction of a multiplexed beam. The inteference is most likey in areas where the local mast uses frequency channels 59 or 60, closest to the 4G frequencies.
The solution, will be either situating the 4G masts out line of site of the mux beams, or will be the using of some sort of on site filteration at the transmission site, plus a filter for the population effected. Ofcom have stated that 4G must pay for the filters themselves, and viewers who experience interference can have a filter free of charge to install in line with the co-axial lead into the tv. However, they don't state where viewers can get these filters from etc. It's all abit unresolved issues at the moment. I'm sure an update on this issue will be published soon.

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KEVIN GARDINER's 68 posts GB flag
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