Re: [Discuss-gnuradio] Phase shift correction in Bpsk!!

[Tom Rondeau]

On Thu, May 10, 2012 at 3:55 AM, sreenath kambala
<address@hidden> wrote:
>
> Hello All,
>
> I have designed BPSK transmitter and receiver in grc.
> But Costas loop can able to correct frequency offset, not phase offset.
>
> Here, I attached both transmitter and receiver files.
>
> Transmitter :
>
> 1). File sink contains Bpsk symbols {-1,1}  (repeat = yes)
> 2). Samples per symbol : 20
> 3). RRC pulse lasts for 2 symbol periods
>
> Receiver   :
>
> 1). Matched filtering
> 2). Costas loop & Timing recovery
> 3). saving samples in File sink
>
> and final Symbols are recovered from the samples in matlab.
>
>
> I'm using uhd + gnuradio + USRP1 + RFX 2400 daughter boards.
>
> Can somebody suggest me how to deal with Phase offset ?
> (especially when the gain of Rx is low phase shifts are happening
> frequently)
>
> One more Question : Is Rms value sufficient in SNR Calculation ?


There is a Costas loop in GRC that will handle the phase and small
frequency offsets properly. But make sure that you use the timing
recovery loop BEFORE the Costas loop. The output of the timing loop
will output 1 sample/symbol at the right timing location, which will
aid the Costas loop in its recovery.

Look at the code in gr-digital/python/generic_mod_demod.py for how
we've done this.

Tom