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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."
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)
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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.
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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.
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