Slashdot Mirror
BBC White Paper Claims HD Over Low Bandwidth Signal
Kelten Miynos writes "According to CNet, the BBC has written a white paper in which they claim it's possible to double the available Freeview TV bandwidth by using some clever technologies. 'Doubling the space would mean we could easily have HD channels on Freeview, although everyone would need to buy a new receiver and aerial to pick them up. The key to all this is something called MIMO, which stands for multiple-input multiple-output. MIMO works using two transmitters, and two receivers. The two transmitters mean the two sets of data — sent on the same frequency — will arrive at the receivers at different times. Different arrival times are what allow the receiver to differentiate between the two separate signals and subsequently decode them.' These procedures could then be transplanted abroad to other countries with similar services."
Even with two transmitters, it doesn't sound too prone to break downs, this could be a not-too-costly winner.
MIMO isn't exactly news though, but it's of course interesting to see it being used in this context.
I wonder how long this new found bandwidth will be enough, as we tend to expand usage right along side available resources at a disturbingly linear rate.
This wouldn't just require new equipment to view the new transmissions, it would also require throwing out all the freeview kit that the BBC and the digital alliance have spent years convincing the public to buy. This idea could only really be implemented in an unused frequency band - the space vacated by the analogue switch-off seems ideal for it to me, if only the UK government can be prevented from selling it for some other use.
As the article says, a far simpler solution to the badwidth issues of freeview would be to ditch the huge number of junk channels and use the bandwidth to provide a HD signal for the ones that people actually watch.
A pizza of radius z and thickness a has a volume of pi z z a
In the UK, we are moving over to digital TV region by region, starting next year. Already, people have had to go out and buy Freeview boxes, and in many cases new ariels (I needed one). Somehow, I doubt anyone will go for buying a new box and ariel just for the lucky minority to have HDTV.
Anyway, if you are going to have a new box, why not move to MPEG4 as well? That would double the number of available channels again.
const int one = 65536; (Silvermoon, Texture.cs)
SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
The BBC announced the world premier broadcast of Finding MIMO
MIMO is an intriguing technology but unfortunately the acronym is used loosely to refer to many unrelated things.
The most exciting MIMO technology is also known as "space multiplexing," which lets a system with N transmit and N receive antennas transfer data at N times the rate of a system with just 1 transmit and receive antenna. The marketing departments like to use MIMO to refer to any old system with multiple antennas, because technically the definition is correct. However, most of the time those systems can't get this kind of performance gain. I believe most of the pre-n hardware out there just does fancy antenna selection; the language is usually careful to say that "802.11n supports space multiplexing," even though it is optional, and there are no performance numbers yet. Someone please correct me if I'm wrong, which I'd love to be!
The way space multiplexing works is counterintuitive: each transmit antenna sends an independent stream of data on the same frequency. The "magic" that makes it work is the fact that multiple receiving antennas observe the combined signal at different times (the article summary got it surprisingly right here); specifically, the phase offsets observed at different RX antennas should be random. This can happen when the signals bounce off a lot of objects like walls indoors, or buildings etc. outdoors.
Here is a simplified example that illustrates how this can work. Suppose we have 2 transmit antennas. Suppose at a given time we send two signals a and b. If we only had one receive antenna, we would observe (a+b), and there would be no way to extract the individual signals. However, if we have a second antenna, AND the phase offset happens to be such that the other antenna gets (a-b), we can clearly extract the original signals.
There are environments such as open outdoor fields with line-of-sight, where the received phase offsets are not random and don't happen to be "nice" like in the above example; in that case MIMO performance falls back to 1x1, or a little better if the phase offsets have some degree of randomness.
Tsunami -- You can't bring a good wave down!
Digital TV via an aerial.
Previously there'd been two competing digital TV providers: Sky, selling digital via satellite, and ITV Digital, selling digital via aerial. Although both carried the same basic menu of free-to-air channels, they were basically pay-TV providers trying to push subscription services, and didn't really achieve much. Sky Digital inherited the viewers from Murdoch's existing satellite operation, but didn't really expand the market AFAIK, and ITV Digital did very poorly, being a second-best offering as a pay-TV platform, and again failing to win over the majority who aren't really interested in pay-TV. ITV Digital folded after a while.
At this point a BBC-led group established the Freeview standard, which is based around a set-top box made as cheap and simple as possible, and which provides a comparatively small number of free-to-air channels. There's an expansion that allows encrypted pay-TV channels, but few exist and hardly anyone bothers. Because the box was very cheap and it was a one-off expense - no subscriptions, no registration - it became the standard very quickly. These days it's being built in to most new TV sets as standard, and supposedly we're on course to be able to switch off the old analogue broadcasts on schedule.
Real Daleks don't climb stairs - they level the building.
Lets take a very trivial example of a two-antenna setup doubling bandwidth. If you have one transmission tower to your south and one to your north and you have directional antennas pointed at both you have multiplexed your signal spatially and nearly doubled your transmission rate in the same bandwidth. Multipath makes this harder too tease out, but that's what signal processing is for. Are you really telling me someone with two directional antennas can't tease out two different stations in two different directions? And that is with NO signal processing.
I'm pretty sure the people that made the BLAST demo system back in 2002 know more about this than you do. Yes there is a higher noise to signal ratio, but as long as our multiplexing multiples rise faster than this ratio then we are getting more information. Shannon's laws only apply to single channels, spatial multiplexing adds more channels as would polarization.
Letter To Iran
The BBC paper isn't rubbish. The Slashdot summary mangles things as usual so you need to go to the original source (dated December 2006 incidently). Even the paper itself says that this isn't news. The same frequency is used for two transmissions at but at different polarizations. So the noise floor is not raised to the levels that you might suggest (although originally orthogonal, reflections and refraction will cause some problems). Theoretically there are two independent channels and experimentally it works.
No, they use the same old MPEG2, only at far too low a bitrate, which is why it looks like shit regardless of what display you use.
The "2 to 5 seconds" to change the channels on Freeview is nothing to do with decoding times or slow processors in the Freeview set-top boxes. Nope, it's simply because there's more than 9 channels and the channels can indeed be numbered up to 999, which means that up to 3 digits have to be pressed to change channel.
As anyone with a cable or satellite remote control already knows, multi-digit channel numbering means that if you want to hop non-sequentially between channels and the channel numbers are only one or two digits, then the set-top box will pause for a second or so to see if you are adding the second or third digit. If you don't, then it assume that the digits entered so far are the complete channel number and then jump to it.
This is why many Freeview remotes have a "channel plus" and "channel minus" button to get around this problem for channel surfers - just press that to cycle sequentially through the Freeview channels with no digit-delays. I find channel changing to be about one second on the Freeview and IDTV sets using the +/- buttons on the remote, which is OK (but I could believe slower boxes might take 2 seconds, but certainly not 5).
Channels not nicely numbered to allow such +/- surfing? Again, many Freeview boxes/sets allow you to reorder the channel numbering to your preference (e.g. I can only get Welsh Freeview, which insists on putting S4C on channel 4 and English Channel 4 on channel 8, so I swap those over!) and, even better, let you delete channels completely, which I do for all the pay channels, shopping channels etc.
Almost ALL indie makers are using divx on standard DVD for Hd content distribution. Hell they even MAKE set top dvd players that play DivxHD DVD's and they look fan-fricking-tastic. People like to toute you need insane bitrates for clean HD yet I see every day incredible looking HD content at DVD bitrates played off of DVD discs onto a 1080i projector to a 102 inch screen for customer demos in shop. WE demo HDDVD as well but the custom cant tell the difference.
You can get HD content on standard HD discs. a dual layer standard DVD can hold incredible 1080i content that looks fantastic on all HD displays available, but then it does not have DRM up the wazoo and is not making several companies morbidly rich with royalties.
Do not look at laser with remaining good eye.
Although there's been a relatively high take-up of Digital TV in the UK (about 19 million homes roughly split 45%/45%/10% DVB-S/DVB-T/DVB-C depending on whose figures you believe) there have been two distinct driving factors for this - one is consumer demand for a wider choice of channels and the other is government determination to shut down analogue terrestrial TV in order to make money from the spectrum space by auctioning it.
To a first approximation, the technologies are each presently operated by a separate single supplier: DVB-S by Murdoch's Sky TV, DVB-C by Virgin Media (formerly NTL/Telewest) and DVB-T by Freeview (a consortium in which the BBC is a main player).
The principle advantage of "Freeview" is that it provides a very simple marketing message: you buy a £30 box which plugs into your existing aerial (mostly) and TV and that's it. In exchange you get both a wider range of channels and protection against the "analogue switch-off".
That message is getting progressively less simple, though. Freeview has subscription channels (entertainment and sport) as a result of the legacy of the collapsed On-Digital/ITV Digital service that preceded it (needs box with a card slot). There is also some limited PPV (mainly porn) which interestingly requires no card but an access code obtained by telephone.
Furthermore, there is a significant demand from broadcasters for additional Freeview slots - recently there have been auctions for broadcast rights which have reached millions of pounds per channel. In order to prevent interference to analogue signals, the number and power of DVB-T channels is artificially limited at present leading to a seriously-constrained supply of channels. Partly this has been addressed by improving the encoding and stat-muxing process, partly by compromising on quality (some services average below 2MBit/sec video rate) but basically the available spectrum is full. Sky TV (which is also a content provider as well as operating a DVB-S platform) has 3 channels on Freeview which it has contemplated pulling and replacing with 4 MPEG-4 channels which existing Freeview hardware cannot receive in order to increase the number of channels it can provide on DVB-T.
So, despite the current constraints, DVB-T has been a success. The danger is that the capacity constraints will cause the platform to fragment as different content-providers try to deal with this and the consequent increasing costs by invoking a range of incompatible technical solutions and payment mechanisms.
It was originally believed that the closure of analogue TV would enable a significant increase in the coverage and capacity of Freeview, but the government has since made it very clear that it intends to auction off the spectrum space rather than simply re-allocate it to Freeview as it becomes available. Consequently, the future expansion of Freeview is in doubt and the BBC in particular is concerned that it might only be able to provide HD programmes on DVB-T by sacrificing other channels.
This technical research by the BBC is very much a desperate bid to retain the future viability of DVB-T, in which it now has a significant stake, in the face of current government policy. So don't assume it's the BBC's preferred option: the recent DVB-T HD trials used rather more mundane and easily-deployable technology.
At the same time, there are consultations on switching off FM radio (about which there is a serious outcry as the DAB alternative is also seriously constrained by limited spectrum space meaning that the audio quality of FM is actually better; one possible consequence of which is that FM is switched off and DAB is enhanced incompatibly with current receivers) and trials replacing AM radio with DRM (that's Digital Radio Mondiale in this context!).
In almost 90 years of public broadcasting there has historically been only one major technology shift in Europe that has obsoleted consumer equipment - the move to colour TV (which led, after a decent interval, to the shutting down