Digital Radio: DAB vs DVB-T2A

[Note: this article has nothing to do with my employer, they are my own musings and may not represent company policy.]

Recently I have been asked many times about Digital Radio in the UK, specifically about implementing DAB. This has required me to revisit the situation and fully understand the commercial/technical issues around the deployment of digital radio. The UK Government has asked the industry to work towards a switch-off of the current FM radio services, it was originally suggested that a decision about when to switch off would be made in 2015 but in the past year the government stepped back from any fixed dates for a decision and a lesser progress review will be done in 2013 instead. Once a review has been done they will know when they can start thinking about a more formal switch-off programme for analogue services. In this post I want to talk about what DAB means to me and what I would like seen done over the long-term.

To give some rough background: In the 1980s the DAB system was designed and in 1995 it was implemented by the BBC in the UK. It uses OFDM or DQPSK modulation and with error correction has a usable payload of 1,184kbit/sec. The audio codec is MPEG 1 Layer 2, which produces acceptable audio at about 192kbps.

According to the Guardian newspaper the first 5 million DAB radios were sold prior to 2007 and the next 5 million were sold between 2007 and 2009. Thus between launch and 2009 10m DAB radios were sold. If 5m radios are over 4 years old that means that by attrition quite a few of those will have been 'retired'.

I am told that the UK needs 60 million new digital radios to satisfy the current market, this is for cars, kitchens, portable radios, bathrooms, bedrooms, etc. This means that while a portion of the market has been addressed only between 10-20% of radios have been functionally replaced and most importantly there has been very little take up in cars. The SMMT (the trade body which represents car manufacturers) has committed to ensuring that by 2013 all cars are fitted with WorldDMB radios which can be used all over Europe, but currently it costs up-to £2000 to have a digital radio fitted at manufacture.

Reception is currently quite limited (85-90%) and the system is prone to interference from impulsive noise sources.

So, as you might guess I am really not a fan of DAB.

I would like to propose an alternative, I don't want to kill the millions of radios that are currently out there as that would make me wildly unpopular, what I want to achieve is a next generation system that can replace DAB in the long term. I know governments aren't prone to long-term thinking but I think there should be a replacement to DAB which we can quickly work toward but not eliminate the current system entirely. It should be a system which is compatible with some current technology and which provides a substantial benefit to both consumers and broadcasters.

Some people talk about upgrading to DAB+, which uses AAC audio coding instead of MPEG 1 Layer 2, this provides a nominal 50% advantage and doesn't address coverage issues. The current DAB system gives six channels per 1.7MHz channel in VHF Band III. Adding DAB+ would double the number of channels, but that isn't a big advantage compared to the losses.

My proposal is to launch a new mux with DVB-T2A as the transmission system, this is the same transmission system as is used in Freeview HD but with much smaller bandwidth of 1.7MHz, this could be broadcast either at Band III, or in UHF along with the TV services even at full 8MHz bandwidth. For the purposes of this I will assume it should be broadcast at Band III VHF, to mimic the DAB licenses of 1.7MHz. I believe the DAB system could be held as it is, or rationalised to fewer channels. If one multiplex license was given to DVB-T2A then a single multiplex could broadcast fifty six services at an equivalent to DAB's six services! This is a dramatic improvement with the same coverage and would also improve noise immunity. With less services the coverage could be increased at no extra cost!

Using DVB-T2A would allow the use of Multiple PLPs, this is a technology which allows different services to have their own specific space/time in a broadcast stream. Each PLP may have different transmission properties such as error correction, which would allow different services to pay for different levels of protection. A commercial service could have less protection, paying less money and get less reliable coverage. Also other services could be delivered in the payload, thus a low-data rate video service could be delivered to provide mobile TV. Current TV broadcasts are not very suitable to mobile reception (such as in car) and this proposal would allow TV channels to be received on the move with high reliability. They would be MPEG4 at relatively low quality. Also, because of PLPs, when the receiver is looking at one service it can ignore the other services and it can even not decode the other services it doesn't need. Not decoding unwanted broadcast data would reduce the power demands of the product and would improve battery life.

Using a relatively cheap T2A Bluetooth device any smartphone could receive radio and mobile TV services. These would not demand a great deal of power and would be highly portable. The same system could also deliver IP data packets for other content related (or unrelated) to the broadcast. There could be regional and local information transmitted about network changes and devices could even be location aware for easy tuning. Just set your location in the product and it would be aware of what services to offer you. Channels could have service text which defined now/next and optionally broadcast a full week guide. Programme content could have series link information which allows for the consumer to be notified when a programme is being broadcast and even record that content to local storage.

A DVB-T2A radio would contain components which are commodity to a number of countries for their HDTV system, this provides an advantage because the volume of production for the components drives the price down competitively. Currently there are very few manufacturers of DAB radio silicon for manufacturers to use, but many large companies are producing large volumes of T2 silicon for the TV market. I believe the price of DVB-T2A radios could be highly commoditised, even more so than current models and many existing Freeview HD TV models could receive services without hardware changes (software updates may be needed to recognise them).

Because of the large number of services that can be carried in a single multiplex local radio could economically be transmitted nationally, which might be popular with consumers. Local multiplexes could be transmitted in existing DAB white space until DAB is ready to be retired in a further 10-14 years.

Brand-wise it would make sense to brand this as "Freeview HD Radio", so that consumers don't have to worry about "Digital" confusion, consumers can see the value of the quality increase in terms of the "HD" brand and the compatibility with TV could be established quickly.

Products could be quickly developed and the standardisation process would be simple if based on existing core DVB and DTG standards. A Danish broadcaster is already running tests with T2A, thus the UK could not be alone. Finland and other Nordic markets use Band III for TV services on T2, so there is room for expansion.

I believe this is a cost-effective and economical way of delivering a high quality digital radio service, this is in contrast to the existing system which is limited and ageing quickly. Before we are stuck with a legacy of poor products I think we should introduce a system which is fit for the next two decades and keeps the UK competitive in the world. Once one country sets the standard many others will follow and the market could be commercially vibrant.

What is the migration path for DVB-T2A? Transmission technology has a thing called the Shannon Limit, which was determined to be a physical constraint of transmission capacity in 1948. This states that for any given transmission spectrum there is a fininte quantity of information that can be put through it. DVB-T2 is described as being really very, very 'close to Shannon'. Thus as a transmission technology there is unlikely to be much that can match it within the same spectrum conditions. The error correction technique that is used is really intensive as well, previous systems where more limited by the chip processing abilities but T2 really pushed designers to implement everything but the kitchen sink. I am not saying T2 is all that can be done, but it is very, very fit for purpose.

The Fraunhoffer Institute recently started demonstrating a new audio codec, this is where I see the next advancement coming from, if more than a 30% improvement in efficiency could be shown then there might be a migration path for such products. The DVB model includes support for broadcasting software updates to receivers, with a system called DVB-SSU, while this can't change the hardware it can be used to keep products in line with new software standards. Increasingly products are moving away from hardware media decoders towards DSPs and software codecs. It makes sense that in the future roadmap a design could be defined which allows for codecs could be upgraded (within resource limits). It is possible now to plan for a post 2020 design which implemented upgradable profiles for decoding of content. Also, as processing power increases and efficiency improves, not only codecs are being implemented in software but also the radio reception function using a "Software Defined Radio" and this *may* be standardised later but this presents a bigger risk. If you upgrade the radio receiver function incorrectly you will make the product non-functional and possibly not upgradable again.

I welcome comments, no doubt some will be harsh, bit I believe it is better to cut it off now before it gets much worse. Lets not be stuck with the digital equivalent of AM radio when the rest of the world is moving forward without a legacy.

References: http://bit.ly/qSP254

LinkedIn discussion: http://linkd.in/pu0O2G