Hi-def over Freeview? The BBC has a cunning plan

AnonymousSun 29 April, 2007 5:59am

Who confirmed this nonsense? Since when does the BBC do the inventing? Don't we have engineers at high-tech companies doing that?
The BBC's claim to be able to seperate 2 streams because of a temporal shift is AFAIK impossible. Think water ripples. 2 kids making waves the same wave length in a pool. They collide and eather cancel each other out or become twice as high or anything in between. In either case, it becomes impossible to figure out who made which waves, even if you know exactly the timing difference between the waves.
But, of course, if you polarize the 2 signals differently, you can simply block the unwanted signal at the receiver, and only receive the correct signal.
Which has nothing to do with timing at all.
A small problem might arise, however. That problem is: in the real world, signals do a whole lot of bouncing around, and both the polarity, and the timing of an incoming signal cannot be guaranteed to be in the same relation to the other signal as it was when it left the transmitter.
That's what causes ghosting.

I'm not an engineer, but I'm sure gonna be laughing when the BBC comes out with... well... nothing!

AnonymousSun 29 April, 2007 9:50am

Look at wifi, 802.11N uses this exact same technology so it is not "nonsense" it is something that does work in the real world.

The BBC has a long history of doing R&D work. They have defined numerous international standards based on their R&D work.

Other technologies that have multiple people on the same frequency include CDMA which is used for mobile phone communcations (CDMA2000 - US mobile networks Verizon and Sprint use this technology and UMTS (W-CDMA) which is used by the UK 3G networks including Three, Vodafone, T-Mobile, Orange and O2).

AnonymousSun 29 April, 2007 5:26pm

On the pond example. Instead of thinking of one horizontal pond with ripples think of two ponds at right angles to each other, one verticle to the horizontal one. Forget about gravity with TV spectrum.

With a vertical and horizontal pond you can have two different non interferring patterns. The problem is in transmitting and receiving those signals and using them. That is doable.

The fact that those signals can change polarity when they bounce off an object for instance does not change the fact that they are two distinct signals and a properly designed receiver can still tell them apart. That is all the receiver would have to do.

Doable IMO.

I don't care who engineers it. Go BBC!!

AnonymousThu 24 May, 2007 11:43am

'I'm not an Engineer' yet I comment on engineering subjects with unwaranted distain

so the BBC who have produced many tecnologies that are in use all over the world are not inventors?? Are you going to say the same about BT? T*wat

AnonymousWed 29 August, 2007 4:50pm

The BBC has a world renowned technical R&D facility in Surrey. The vast majority of early BBC kit was designed and built in-house. Nicam, Teletext, etc. were all invented there. They built the world's first DVB-T modem and the earlier chip designs for set top boxes were done there. Have a look at www.bbc.co.uk/rd

AnonymousSun 29 April, 2007 10:38am

The BBC has "done inventing" for years - Teletext was invented by the BBC way back in the 1970s and subsequently was championed by the EBU, the BBC has a long track record of technical innovation especially in the technicalities of broadcasting.

AnonymousSun 29 April, 2007 1:19pm

The BBC also helped to develop NICAM digital stereo as well as Teletext, so technical innovation from them is clearly nothing new.

AnonymousSun 29 April, 2007 5:18pm

I don't think that the article is right about this being a time based system. By transmitting two different signals at different times will get you no more bits. In fact it should cost you some bits.

I am not an engineer but this seems to be only MIMO or the use of vertical and horizontal polarization and the ability to seperate the two signals at the receiver.

AnonymousSun 29 April, 2007 5:37pm

can anyone tell me if the bbc will sho the 2007 f a cupfinal in HD on sky

Brian KorsedalSun 29 April, 2007 8:39pm

Hi,

I design communications ASIC/FPGA based systems. From what I know of MIMO it has to do with the spacing of the antennas. Imagine that each path between a transmitter and receiver is a different equation. Two transmitters and two receivers equals four separate paths. Therefore we have four separate equations. Then we solve the equations so that the two receivers can see each transmitter separately. I'm sure it's a bit more involved than this but it's been the buzz for about six or seven years.

AnonymousMon 30 April, 2007 12:25am

"It works by sending the signals at different times. "

This is incorrect. In MIMO spatial multiplexing, multiple independent signals are sent at the same time. Due to reflections and scattering of the radio waves in the environment, multiple copies of each signal arrive at the receiver antennas with varying delays and attenuations. These delays and attenuations are measured by sending training signals known to the receiver. This is used to create a digital filter which is effectively the inverse of the channel. The received signals are passed thorugh this filter to separate them out again.

802.11N gear uses MIMO, which is widely available. The digital filter in this case includes a Fast Fourier Transform since OFDM is used.

crispyThu 24 May, 2007 11:39am

storm Bid-Up TV... on my way!!!!!

HoraceTue 12 June, 2007 5:36pm

If this is possible, than maybe it's also possible to send unlimited signals?