The picture is transmitted as 4 HD segments, top left, top right, bottom left, bottom right, each on its own PID.
I have received the stream, decoded it, displayed it, now I need 4 seemless HD monitors.
See my postings in alt.satellite.tv.europe.
I hope that format is just for testing... Modulation and coding technology has advanced to the point that if they make a new system it should be such that the resolution you get depends on the signal quality. If you have a good signal, you get the best resolution, if your signal is marginal due to noise or multi- path, instead of getting nothing, the resolution should gracefully degrade, at least you still get a usable picture. No reason we can't make that work in this day and age.
Mark
That's what we had, with analog TV! These days, with modern digital technology, if there's the slightest degradation of the signal, you get nothing. Ah, progress!
Jeroen Belleman
On a sunny day (Wed, 9 Jan 2013 16:46:51 -0800 (PST)) it happened Mark wrote in :
That is not how digital TV works. Look up mpeg compression.
This is known as Hierarchical Coding (usually with hierarchical modulation)
For instance the lower DCT coefficients can be coded with a robust modulation method and strong ECC. Thus the lower resolution pictures can be decoded in weak signal conditions.
The higher DCT coefficients are coded with less robust coding and modulation and can only be decoded in good signal conditions. The high DCT coefficients are added to the low resolution well protected lower details, inserting finer details into the picture.
Alternatively, if the (IP-TV) bandwidth is limited for some users, the higher coefficients are simply dropped.
One advantage of the hierarchical coding is that you do not have to simulcast the same program at different resolutions.
Some of the DVB standard have some options for hierarchical modulation. In a simple 64QAM constellation, the states are in an equal spaced 8x8 grid.
In a hierarchical modulation a cluster of e.g. 2x2 states are clustered closer to each other, which will increase the distance between the 16 cluster, which are then decodable as 16QAM. No matter, which of the 4 states are sent, this will produce the same 16QAM results (e.g. usable for sending important low order coefficient) even in weak signal conditions.
In a strong signal case, the 2x2 cluster can also be decoded and hence extract some "extra" data, such as high order DCT coefficients for high resolution stationary displays.
However, I have never heard anyone using this DVB feature.
Maybe we need to recode or redo the error correction approach. Better still redo both to coordinate degradation gracefully.
?-)
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