Tag: channels

Digital Radio: DAB vs DVB-T2A

Posted on by bobdvb

[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

 

UK Broadcasting and Local Multiplexes

Posted on by bobdvb

 

If you’ve ever seen full frame uncompress 625line SD with component 10-bit colour then you will know that sometimes resolution doesn’t matter. At a previous employer of mine we could show normal people pictures on a Barco Grade 1 monitor and they would swear it was HD. Freeview just has poor quality because the cost of carriage is so high, especially when there are a dozen versions of BBC One or ITV1 and they have to compress everything down to the n-th degree. The reason that regionalisation costs money is that we must have a cellular transmitter design, each region has it’s own frequency (or more than one because of relays), adjacent regions can’t use these frequencies because otherwise that would affect coverage. The UK design has many “guard” frequencies to protect adjacent transmitters in this way. If every region had the same channels they we could uses a system called an “SFN”, or Single Frequency Network, in this configuration the transmitters all transmit exactly the same thing at exactly the same time at exactly the same frequency. When transmitting in an SFN if you are between two transmitters you get the signal from both transmitters, but instead of causing a problem for you it actually helps because the two transmitters actually re-enforce each other.

 

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PSBs in Free To Air Environments

Posted on by bobdvb

The Synopsis

This document aims to describe the current movements in PSB’s (Public Service Broadcasters) and how their circumstances are affecting changes in technology. This is an incomplete document so far and I have posted it here for discussion, I could easily be wrong about so many things, but I have been working on all sides for enough time to have made some observations that need to be discussed.
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DVB-T2 implications

Posted on by bobdvb

Introduction:

The coming launch of ‘Freeview HD‘ will doubtless have implications for retailers as well as consumers and in this note I hope to help address some of the questions. There are several new features which are implemented in ‘Freeview HD‘ which might impact consumer and some less obvious features you might not know about.

New features:

  • DVB-T2

This is a new type of transmission technology which has evolved from the existing DTT standards and next generation communications theory.

  • H.264 HD video

Using the more recent developments from MPEG using the H.264 compression method the video can be transmitted in as little as 25% of the bandwidth that would be required for the same type of transmission in MPEG2. This allows HD which would consumer substantially more bandwidth to be transmitted efficiently.

  • MHEG HD

MHEG is the standard for interactive services in the UK and is a very light weight system. It failed to impress some people in it’s original form but substantial progress has been made in the last few years to delivery a much more powerful user experience. The speed and graphics quality has been enhanced and the implementation on Freesat has already proven popular with consumers. As time passes the developers are able to demonstrate further enhancements in graphics performance and quality. The most significant step is in being able to render graphics to the screen with HD resolutions.

  • MHEG Interaction Channel

This allows MHEG applications to communicate back to the broadcasters over the consumers broadband package. This potentially gives consumers access to interactive voting, a wider range of content than can be broadcast and even streaming catch-up television. Broadcasters will decide what services they will implement but the connection is available to consumers on their product for those future services.

  • Audio Description

All products are now expected to be capable of audio description, this system allows people with visual impairments to have a description of the programme they are watching. TV is popular with a wide range of people and we are looking to include as many groups as possible. It will even work on HD channels, so the whole family can enjoy the latest releases. Some products may not support mixing multi-channel surround sound with AD tracks to produce surround out, but AD will still work with surround but produce a stereo output.

  • HD Subtitles

In addition to supporting existing Teletext format subtitles and standard DVB format subtitles the new boxes should now support HD format DVB subtitles which provides decent subtitles for HD video broadcasts.

Less obvious features:

  • HD Simulcast

The broadcaster can signal that a programme is also available in HD so that a viewer can get the best quality version even when watching the SD channel.

  • Content Management

Broadcasters have difficulties obtaining rights for some programmes to be broadcast in HD on free television. So in order to be licensed by ‘freeview’ the manufacturer must agree to record the broadcasts subject to rules that are transmitted by the broadcaster for each programme. It is possible for the broadcaster to signal that they will not permit the programme to be copied or that it may only be copied once. They may also indicate that the programme can be streamed or copied to DVD. The ability to archive and copy programme content is not a requirement but where it is implemented it must follow the broadcast rules.

  • Network Change Notification

The transmitter network can signal when changes are going to happen, this way when a re-tune is needed the receiving device can react more intelligently than they currently do.

  • Guidance Descriptor

A broadcaster can use new signaling on both programs and channels to indicate that their broadcasts contain content which may might not be appropriate for certain viewers. It is not intended just as an “Adult” genre but it is designed to show a wide range of sensitive issues, possibly including photosensitive epilepsy and violence.

Questions:

  • What type of antenna does Freeview HD device need?

Freeview HD uses a traditional UHF antenna as used by existing terrestrial television.

  • Will I need a new antenna for DVB-T2?

No, not unless you don’t get a good signal level currently. The T2 transmissions are being designed to perform under equal conditions as the existing digital transmissions but with more bandwidth to put more information in.

  • What does DVB-T2 provide to broadcasters/consumers?

The development of DVB-T2 was not just about the steady march of time but has been done to provide more data in the available bandwidth. This means that the broadcasters can send more information per transmitter. DVB-T already allows many channels to exist in the same equivalent

  • I have a High Definition ready TV, will it support Freeview HD?

Freeview HD requires the product to support the DVB-T2 transmission standard, only products made on/after winter 2009 and which say they support “Freeview HD” will work with the new service. All current IDTVs will need an external set-top box device to be able to receive Freeview HD. The current definition of “HD TV Ready” does not cover the new UK standard for HDTV.

  • Can I upgrade my receiver to support T2?

It is not possible to software upgrade any existing products to support DVB-T2 due to the significant differences between the platforms. In theory certain IDTV displays from certain manufacturers may be upgraded by replacing certain parts of the hardware, but no manufacturer has yet stated their intention to do this.

  • When will broadcasts of HD services start?

No dates have yet been confirmed, but it is expected that in preparation for product being available broadcasts are expected to begin during Winter of 2009. This schedule may change in response to changes in conditions and consumers should not expect to have reception before 2010. The service will have limited coverage to begin with and only certain areas will have availability to begin with. Consumers should check their coverage to determine what services are available in their area. It may be that a product like the Foxsat-HD or Foxsat-HDR (using the Freesat service) is the best way to get access to free HD channels.

  • When will product be available for Freeview HD?

While the technology of HD has been available for some time the variations required for the Freeview HD, particularly DVB-T2, will require significant work. Because new silicon chips must be designed for this service there needs to be careful work on this investment.

  • How many HD channels will be available?

There will be an HD service from the BBC and other services are expected from ITV-HD and Channel4 HD. Eventually a fourth and perhaps fifth HD provider are expected to join the platform. The platform operators are aiming to upgrade the video encoders to improve their efficiency in order to maximise the volume of content available on the platform for the available capacity.

Further definition:

  • DVB-T2:

A working group of the European DVB organisation has evolved this new standard for transmission. This has allowed more data to be broadcast in the same terrestrial spectrum. This is achieved by using powerful error correction technology as well as learning quite a number of lessons from the work on DVB-T. It has been many years since Digital Terrestrial Television was first launched in the UK and in this time the engineers/scientists have studied the different parameters available to engineers then this time has highlighted areas for improvement. The change in error correction is based on some mathematics which was first used in DVB-S2 and has now been refined further for DVB-T2. Overall the system is exploiting the next generation of technology and the latest innovations in transmission/communications theory.

  • Multiplex:

A multiplex is the container which is used to broadcast digital services. The UHF radio frequency ‘channel’ in which a single analogue service was broadcast in can now be occupied by a multiplex which can contain many digital television services. There are currently six multiplexes in the UK which carry all of our digital television viewing. Each multiplex can carry services of differing quality averaging between eight and fourteen video services.

  • Bandwidth:

Bandwidth is the measure of size of the information carried, the term can be used in analogue or digital environments. In analogue it is the number of Hz and in digital it is the number of bits per second (the rate at which data is carried through a system).

  • High Definition (HD) video:

Currently used to define any superior resolution of video over 720×576 in pixels.