Re: [Discuss-gnuradio] header_payload_demux_impl.cc - problem when using random bit stream (variable trigger location)

[Martin Braun]

On 01/21/2014 07:16 PM, Aditya Dhananjay wrote:
> On Tue, Jan 21, 2014 at 1:03 PM, David Halls
> <address@hidden <mailto:address@hidden>> wrote:
> 
>     Ah, I see. You want to isolate the effect of the channel. I believe
>     it will be difficult, if not impossible, to remove the slight jitter
>     of the trigger, even in very high SNR - perhaps others can comment/help?
> 
> 
> Yes, that is correct. It is impossible to *eliminate* the jitter in
> triggers from Schmidl-Cox. But I want to minimize it, and have edited
> the plaueau/peak detector code to do just that. (all in a hackish manner!)

Hm, this will be hard to get right. After all, the Schmidl & Cox is an
estimator and operates on noisy values. Unless your SNR is crazy good,
there is always a chance of getting it wrong. And technically, even then.

Two ideas:
- You could remove the sync block and sync your rx/tx paths with other
means (e.g. MIMO connector, it depends on your hardware). This makes the
sync influence independent of the noise.

- Reconsider if the phase rotation really makes your measurements
invalid. You'll have a phase rotation in any case (due to channel,
propagation time etc.). The timing-related phase offset is constant,
after all, and the phase difference between sub-carriers depends on the
sub-carrier distance, too. Perhaps it doesn't matter all that much?

MB