Broadcast Technology Jammed Tomorrow (Part 1)

4/16/2013 9:25:13 AM

Jim L. investigates the impact the new 4G mobile networks will have on Freeview reception, and who will be paying the price

The government has been boasting for years about a ‘digital dividend’ and part of the bright vision for a high-tech future are 4G mobile networks. With the Everything Everywhere (aka EE) 4G network already up and running and others set to follow later in 2013, the current plans may be offering a ‘jammed tomorrow’ for millions of Freeview TV viewers…

In the period from October 2012 to October 2013 the channels will be re-allocated in many parts of the UK to ‘clear’ two parts of the spectrum. What have been UHF TV channels 61 - 69 will be handed over to 4G mobile service providers. In principle, this is fine, but the devil is in the details.

4G network transmitting from antenna farms like this could block your TV reception

4G network transmitting from antenna farms like this could block your TV reception

It is worth nothing that the final details are still under discussion, but something like the arrangements described look like being the settled outcome after some years of argument… erm negotiation.

The plan provides a 1 MHz ‘guard gap’ which no-one should use. The 4G allocation just above this – i.e. nearest TV channel 60 are for 4G base stations to send information out to 4G mobile devices (i.e. downlinks). These will occupy the band space from 791 MHz upwards.

The 1MHz gap will ring loud alarm bells in the minds of experienced radio engineers. It puts the 4G transmissions very close to DTTV reception. The power levels for 4G base station transmissions will also be high compared to older generations of mobiles and the combination represents a serious threat to DTTV reception.

Spectrum by the end of 2013

Spectrum by the end of 2013

4G WRC07 changes

4G WRC07 changes

The effects of 4G interference

Mark Waddell is a lead research engineer at the BBC who has made a great number of measurements on domestic DTTV equipment subjected to 4G-like interference. He kindly gave permission for us to use the published details to help explain the likely consequences. For clarity we have picked out one receiver as an example.

The graph below shows how large a 4G ‘challenge’ could be tolerated for various input levels. The blue line represents when the base station is sending as much data as it can to as many users as it can handle. The red line shows what happened when the base station was idle (i.e. no actual 4G use). The broken red line indicates where the 4G voltage would be 50 times the DTTV signal voltage.

Impact of 4G interference on a DDTV receiver

Impact of 4G interference on a DDTV receiver

The most obvious point is that changes in 4G activity can have a dramatic effect on how much it will degrade DTTV reception. This complicates the situation because reception may come and go as the demand on the local 4G base station fluctuates and could result in an engineer call out to investigate the problem of a set that doesn’t work only to face the classic behavior where the problem has evaporated by the time the engineer arrives! The result is a call-out charge, the tradesman leaves…and the problem comes back again once he has gone. The details will vary from house to house, making it frustrating for those affected.

Focusing on when the 4G base station is working 1100 percent – i.e. the ‘best’ situation at low 4G interference voltages levels the receiver can reject the interference fairly effectively. However, at higher levels of interference, the ability of the receiver to cope collapses. If the 4G interference is as high as 100 mV we find that the receiver needs around 20 mV of DTTV signal.

This behavior is a classic response for a system being driven into nonlinearity be excessive input signal levels. It shows that we can’t rely on the RF filtering implemented in existing domestic equipment, and those living near a 4G base station may be unable to watch even a strong DTTV signal. The situation becomes worse when the 4G usage is less than 100 percent and in this situation 4G can become a very effective ‘jammer’ for DTTV reception!

The bulk of TV reception equipment in UK homes has been designed and sold during a time when interference like this was not expected to be widespread. So it will hardly be a surprise if it cannot cope.

The magician’s wand?

The proposals include a ‘mitigation’ strategy, mainly based on handing out filters to households that are affected. This seems an odd take on the ‘polluter pays’ principle. The idea being that the 4G companies will pay for the filters. Yet the ‘pollution’ is actually their transmissions being so powerful and so near to established TV services.

You might think it would be more appropriate for the 4G transmission powers and channel allocations to be restricted to ensure that far fewer people are adversely affected. This seems much like someone being allowed to make a bit of a mess provided they also hand out a few brooms.

Even assuming that filters are handed out, there is an additional problem that seems not to have had much consideration. What about those who move into an affected area particularly into newly built houses in the future? Should we expect the 4G providers to have a perpetual obligation to hand out ‘free’ filters to such people who may find that none are in place when they set up home? Or is the assumption that all new DTTV sets and boxes from the end of 2012 onwards will have 4G filters incorporated by the set-makers? If the latter is the presumption, then it seems prudent to wonder how quickly such designs will come to market, and what impact this may have on the cost of new DTTV sets/boxes. How quickly will they replace all earlier designs? Another hidden ‘cost’ is also the impact on the second-hand value of existing sets and boxes because they are not ‘4G hardened’.

Snags and desirable changes

Having ‘ch59’ and ‘ch60’ filter designs has clearly been driven by allocating a tiny guard gap between DTTV and 4G. The failure to make a single filter design adequate is nature’s way of telling us that 1 MHz is impractically small for the intended 4G powers.

It seems to me that it would be more sensible to have a wider frequency gap between DTTV and 4G. This could be done by either changing the DTTV allocations to leave ch60/60- unused, or increase the guard gap to at least 5MHz.

Either option would reduce the costs and improve the performance of the required filtering. Given the ‘polluter pays’ principle, it would seem that the onus should be the latter option unless the former is easily feasible and does not pose a difficulty for TV coverage.

As it stands, though, the current 4G plans look uncomfortably like a ‘cunning plan’ to use 4G as a stealth jamming system in order to push people into abandoning DTTV and pay for costly alternatives.

Top 10
Extending LINQ to Objects : Writing a Single Element Operator (part 2) - Building the RandomElement Operator
Extending LINQ to Objects : Writing a Single Element Operator (part 1) - Building Our Own Last Operator
3 Tips for Maintaining Your Cell Phone Battery (part 2) - Discharge Smart, Use Smart
3 Tips for Maintaining Your Cell Phone Battery (part 1) - Charge Smart
OPEL MERIVA : Making a grand entrance
FORD MONDEO 2.0 ECOBOOST : Modern Mondeo
BMW 650i COUPE : Sexy retooling of BMW's 6-series
BMW 120d; M135i - Finely tuned
PHP Tutorials : Storing Images in MySQL with PHP (part 2) - Creating the HTML, Inserting the Image into MySQL
PHP Tutorials : Storing Images in MySQL with PHP (part 1) - Why store binary files in MySQL using PHP?
- First look: Apple Watch

- 3 Tips for Maintaining Your Cell Phone Battery (part 1)

- 3 Tips for Maintaining Your Cell Phone Battery (part 2)
- How to create your first Swimlane Diagram or Cross-Functional Flowchart Diagram by using Microsoft Visio 2010 (Part 1)

- How to create your first Swimlane Diagram or Cross-Functional Flowchart Diagram by using Microsoft Visio 2010 (Part 2)

- How to create your first Swimlane Diagram or Cross-Functional Flowchart Diagram by using Microsoft Visio 2010 (Part 3)
Popular Tags
Microsoft Access Microsoft Excel Microsoft OneNote Microsoft PowerPoint Microsoft Project Microsoft Visio Microsoft Word Active Directory Biztalk Exchange Server Microsoft LynC Server Microsoft Dynamic Sharepoint Sql Server Windows Server 2008 Windows Server 2012 Windows 7 Windows 8 Adobe Indesign Adobe Flash Professional Dreamweaver Adobe Illustrator Adobe After Effects Adobe Photoshop Adobe Fireworks Adobe Flash Catalyst Corel Painter X CorelDRAW X5 CorelDraw 10 QuarkXPress 8 windows Phone 7 windows Phone 8 BlackBerry Android Ipad Iphone iOS