Re: [Discuss-gnuradio] Channel Model omits first 3 samples

[Gregory Warnes]

On Jul 10, 2013, at 4:47 AM, Tom Rondeau <address@hidden> wrote:

> On Tue, Jul 9, 2013 at 8:38 PM, Gregory Warnes <address@hidden> wrote:
>> Hi All,
>> 
>> I've been working on calculating BER for simulated transmitter/recieved pair
>> and have noticed that the channel_model eats the first 3 samples.  Thus to
>> correctly align the data input and output from channel_model (e.g. for
>> calculating BER), it is necessary to account for the 3-sample offset.
>> 
>> Perhaps it would be worth adding a note to this effect to the channel_model
>> documentation.
>> 
>> -Greg
> 
> It's not that the channel model 'eat's 3 samples. This is group delay
> of your filters that you're seeing. The transmitter, receiver, and
> channel model may all have filters in them and each has a group delay.
> You always have to adjust for this. Not sure we can put it into the
> documentation except to say that you need to calculate the total group
> delay of your system if you want to align the data.

Thanks Tom,

Is there a straightforward way to calculate group delay for a flow graph?

Alternatively, would it be straightforward to create a block that annotates the 
data stream with a time index and another block that uses this information to 
align streams?

-Greg