Mistakes in the DVB-T standard?

Started by lanbaba October 4, 2005
Hi,

Are there any DVB-T experts around? I found something weired in ETSI EN
300744 v.1.5.1 (2004-11) and want to have verifications for my suspect.

I implemented a DVB-T receiver according to the DVB-T physical layer
standard ETSI EN 300744 v.1.5.1 (2004-11) but it does not work with real
signals in the air. It turns out that R'i and Ri in the bit permutation in
the symbol interleaver is exchanged, i.e., the standard does not describe
what is implemented!!!!

In the standard:
Table 3a: Bit permutations for the 2K mode
___________________________________________________________
R'i bit positions | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
___________________________________________________________
Ri bit positions  | 0 | 7 | 5 | 1 | 8 | 2 | 6 | 9 | 3 | 4 |
___________________________________________________________

My observation: (it works)
___________________________________________________________
Ri bit positions | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
___________________________________________________________
R'i bit positions| 0 | 7 | 5 | 1 | 8 | 2 | 6 | 9 | 3 | 4 |
___________________________________________________________


Can anyone share my view?

Cheers, Lanbaba


		
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lanbaba wrote:
> Hi, > > Are there any DVB-T experts around? I found something weired in ETSI EN > 300744 v.1.5.1 (2004-11) and want to have verifications for my suspect. > > I implemented a DVB-T receiver according to the DVB-T physical layer > standard ETSI EN 300744 v.1.5.1 (2004-11) but it does not work with real > signals in the air. It turns out that R'i and Ri in the bit permutation in > the symbol interleaver is exchanged, i.e., the standard does not describe > what is implemented!!!! > > In the standard: > Table 3a: Bit permutations for the 2K mode > ___________________________________________________________ > R'i bit positions | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | > ___________________________________________________________ > Ri bit positions | 0 | 7 | 5 | 1 | 8 | 2 | 6 | 9 | 3 | 4 | > ___________________________________________________________ > > My observation: (it works) > ___________________________________________________________ > Ri bit positions | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | > ___________________________________________________________ > R'i bit positions| 0 | 7 | 5 | 1 | 8 | 2 | 6 | 9 | 3 | 4 | > ___________________________________________________________ > > > Can anyone share my view? > > Cheers, Lanbaba > > > > This message was sent using the Comp.DSP web interface on > www.DSPRelated.com
The standard defines the transmitter, not the receiver. The receiver has to reverse the operation, is this not what you are seeing?
Dal wrote:
> lanbaba wrote: > > Hi, > > > > Are there any DVB-T experts around? I found something weired in ETSI EN > > 300744 v.1.5.1 (2004-11) and want to have verifications for my suspect. > > > > I implemented a DVB-T receiver according to the DVB-T physical layer > > standard ETSI EN 300744 v.1.5.1 (2004-11) but it does not work with real > > signals in the air. It turns out that R'i and Ri in the bit permutation in > > the symbol interleaver is exchanged, i.e., the standard does not describe > > what is implemented!!!! > > > > In the standard: > > Table 3a: Bit permutations for the 2K mode > > ___________________________________________________________ > > R'i bit positions | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | > > ___________________________________________________________ > > Ri bit positions | 0 | 7 | 5 | 1 | 8 | 2 | 6 | 9 | 3 | 4 | > > ___________________________________________________________ > > > > My observation: (it works) > > ___________________________________________________________ > > Ri bit positions | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | > > ___________________________________________________________ > > R'i bit positions| 0 | 7 | 5 | 1 | 8 | 2 | 6 | 9 | 3 | 4 | > > ___________________________________________________________ > > > > > > Can anyone share my view? > > > > Cheers, Lanbaba > > > > > > > > This message was sent using the Comp.DSP web interface on > > www.DSPRelated.com > > The standard defines the transmitter, not the receiver. > > The receiver has to reverse the operation, is this not what you are seeing?
another possibility is that the "off air" signal you have is out of a TV tuner at IF frequency in which case the original RF signal was translated in frequency by an LO ad a "mixer". If so, the signal may have undergone a "spectral inversion" which will have the same effect as reversing the I and Q components and reversing the sense of the differentiual encoding. Mark
Thank you for all answers. The bug was still in my Rx implementation, and
the standard is correct. The origianl post was a false alarm...
		
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Mark wrote:
> Dal wrote: > >>lanbaba wrote: >> >>>Hi, >>> >>>Are there any DVB-T experts around? I found something weired in ETSI EN >>>300744 v.1.5.1 (2004-11) and want to have verifications for my suspect. >>> >>>I implemented a DVB-T receiver according to the DVB-T physical layer >>>standard ETSI EN 300744 v.1.5.1 (2004-11) but it does not work with real >>>signals in the air. It turns out that R'i and Ri in the bit permutation in >>>the symbol interleaver is exchanged, i.e., the standard does not describe >>>what is implemented!!!! >>> >>>In the standard: >>>Table 3a: Bit permutations for the 2K mode >>>___________________________________________________________ >>>R'i bit positions | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | >>>___________________________________________________________ >>>Ri bit positions | 0 | 7 | 5 | 1 | 8 | 2 | 6 | 9 | 3 | 4 | >>>___________________________________________________________ >>> >>>My observation: (it works) >>>___________________________________________________________ >>>Ri bit positions | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | >>>___________________________________________________________ >>>R'i bit positions| 0 | 7 | 5 | 1 | 8 | 2 | 6 | 9 | 3 | 4 | >>>___________________________________________________________ >>> >>> >>>Can anyone share my view? >>> >>>Cheers, Lanbaba >>> >>> >>> >>>This message was sent using the Comp.DSP web interface on >>>www.DSPRelated.com >> >>The standard defines the transmitter, not the receiver. >> >>The receiver has to reverse the operation, is this not what you are seeing? > > > > another possibility is that the "off air" signal you have is out of a > TV tuner at IF frequency in which case the original RF signal was > translated in frequency by an LO ad a "mixer". If so, the signal may > have undergone a "spectral inversion" which will have the same effect > as reversing the I and Q components and reversing the sense of the > differentiual encoding. > > Mark >
I think you will struggle to explain any further how this could result in the observed problem!
I'm not going to try  :-)
Mark