DVB-T reception problems

[Ralf Gorholt]

Dear all,

after a pause of two years I have started to work again on my DVB-T RX
project for GNU Radio.

I have tried to port Federico La Rocca's ISDB-T blocks "OFDM
Synchronization" and "TMCC Decoder" to DVB-T and in principle they seem
to work. When the received signal is stable, I have a stable reception,
i.e. frequency and sampling rate are corrected, the constellation is
stable and as far as I can see, the OFDM symbols are correctly
recognized (at least it seems to me). I have added a TPS decoder that
decodes the TPS pilots and delivers the data to the following blocks.

The TPS decoder performs some checks to assure that the forwarded data
are correct and prints error messages on the console when a problem is
detected. In detail, I check the following things:

- frame index sequence
- symbol index sequence
- superframe start

However, it still happens from time to time that reception "freezes",
i.e. the video pauses and does not start again automatically, despite
the fact that there isn't any error message from the TPS decoder.
Therefore I assume that there is still at least one error somewhere that
I have not found yet.

I have got two questions to the DVB-T experts:

1) How should I handle the following cases:
- symbol out of sequence / lost symbols
- incorrect decoded or incomplete frames

In such cases, should I always wait for the next superframe or is there
a possibility for a different (and faster) error recovery?

2) When OFDM reception and TPS decoding is OK, what could cause the
reception "freeze"? Any idea?

As far as GNU Radio and DSP is concerned, I consider myself still as a
beginner, so please don't assume too much knowledge on my part :-)

Thank you very much for your help!

Kind regards,

Ralf, DL5EU