Hi Mauro,
On Thu, 23 Apr 2015 07:40:46 -0300 Mauro Carvalho Chehab mchehab@osg.samsung.com wrote:
What about demod-diversity: demods of some manufacturers can be used to combine their demodulated symbols and, due to their different antennas and RF-paths, improve the overall reception quality.
If we ever have someone contributing in this area with hardware-drivers, it would be nice to have the user-space possible to select demod-combinations. It should be possible to add and remove a demod to a diversity-chain when and when not being tuned to a channel.
It makes sense to map demod diversity via the media controller.
Not sure what would be the best way to map it though, as I don't have a clear understanding about how the hardware pipelines are set for demod diversity.
The way the media controller currently is is that it maps only the data flow. There are discussions about how the control flow should happen.
The data flow for a normal demod is:
IF (or baseband) ---> [demod] ---> MPEG-TS
From dib0700 demod drivers, I remember that several of the demods have a concept of a "slave demod". Are those full demods that can get an IF/baseband input and produce a MPEG-TS output, or are those just IP blocks that have the IF/baseband input but doesn't produce an MPEG-TS output, but, instead, sends some sort of data into the "master demod"?
In other words, would the dataflow be something like
IF TS[tuner] ---> [master demod] ----->[ ] | IF TS [ combiner ] ---> [demux] |--------> [slave demod] ----->[ ]
or: IF TS [tuner] -----------> [master demod] ---> [demux] | IF ^ | | (what sort of data?) |----> [slave demod] ----|
Or is it something else?
Let's define a demodulation object:
+---------------------------------------------------+ |RF tuner --> IF|baseband --> demod --> FEC-decoder | +---------------------------------------------------+
RF-tuner: RF downconverter (to a low or zero-IF) IF|baseband: ADC and digital filters demod: synchonization and symbol extraction FEC-decoder: viterbi/ldpc/turbo-code forward error correction
Let's call this object a frontend.
Now imagine a board which has 4 frontends:
high-speed-data-bus --------------------- | | | | FE3 FE2 FE1 FE0
To create a diversity-chain, for simplicity, we can say we connect at least 2 frontends in any order. Both frontends are tuned to the same physical channel and then a combiner will combine symbols decoded at demod-stage.
Any FE can be connected with any FE in any order. Per board different standards can be demodulated at the same time. For example: FE3 and FE2 are doing DVB-T and FE1 and FE0 DVB-T2 .
-- Patrick.