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DVB-T

Started by javi September 5, 2005
Hi everybody, 

I have a question related to the OFDM frame structure in a DVT-T system.
The standard specifies that the input MUX packet is composed of 188 bytes:
1 synchronization byte and 187 data bytes. Along the transmision chain, the
bit stream undergoes some interleaving and coding (Reed-Solomon and
Convolutional). My question is: should this stages be also applied to the
synchronization word? As I see it, there's no problem in applying RS
coding because the synchro word won't be changed, but if we apply the
bit-wise interleaving or the convolutional coding, the synchro word is not
anymore at the beginning of the frame.    

I've gone through the standard but this point is not very clear to me. At
some points I understand that the OFDM frame should have this synchro word
at the beginning of the frame even after the aforementioned stages and
sometimes I understand that the sychro word will not anymore be there
(since it was changed by the previous stages).

I would be greatful if somebody could throw some light to me in this
matter. Thank you in advance, 

J.
		
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On Mon, 05 Sep 2005 09:12:57 -0500, "javi" <javiarrospide@yahoo.es>
wrote:

> >Hi everybody, > >I have a question related to the OFDM frame structure in a DVT-T system. >The standard specifies that the input MUX packet is composed of 188 bytes: >1 synchronization byte and 187 data bytes. Along the transmision chain, the >bit stream undergoes some interleaving and coding (Reed-Solomon and >Convolutional). My question is: should this stages be also applied to the >synchronization word? As I see it, there's no problem in applying RS >coding because the synchro word won't be changed, but if we apply the >bit-wise interleaving or the convolutional coding, the synchro word is not >anymore at the beginning of the frame. > >I've gone through the standard but this point is not very clear to me. At >some points I understand that the OFDM frame should have this synchro word >at the beginning of the frame even after the aforementioned stages and >sometimes I understand that the sychro word will not anymore be there >(since it was changed by the previous stages). > >I would be greatful if somebody could throw some light to me in this >matter. Thank you in advance, > >J.
This is typical of a lot of systems that use concatenated convolutional and RS coding. Since the inner code and interleaving are deterministic, finding the synch word in the demod after decoding and de-interleaving is not problematic. If the interleaving/deinterleaving and the encoders and decoders are working properly, the output of the inner code and deinterleaver will be the RS codewords with the synch word intact. Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org