Forum: GNU Radio BPSK modulatio

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9bf620728a30576ba2245d117c7cb8fb?d=identicon&s=25 mehdimolu (Guest)
on 2008-11-17 01:25
(Received via mailing list)
hey,
I am triying to implement a BPSK link between two USRPs. I had a look to
the
bench mark code and I tried to implement such a modulator and
demodulator
except removing differential blocks in both RX and TX. the tx and rx
chains
are as below :

TX
:message_from_string->bytes2chunks->symbol_mapper->chunks2symbols->rrc_filter->amlifier->USRP
RX  :
USRP->pre_scaler->AGC->rrc_filter->rec_clock_recovery->Channel_estimator&equaliser->slicer->symbol_mapper->unpack->access_code_correlator->framer_sink


I have written a signal processing block which estimates the channel(by
correlating the received signal points by access code and estimating
based
on access code).
my problem is I can not receive properly, so, I don't have data in
sink_file.
first I thought it can be due to SPB, so,
I modified the RX above into a two parallel receivers which get the
input
signal from the same USRP, I mean, I removed the SPB that I had written
and

1-in the first chain I multiplied output of USRP_source by ( 1 )
2- in the second chain I multiplied output of USRP_source by ( -1 )

and the rest of receivers for both paths are the same as mentioned
above(again, I have removed SPBs in both receiving paths)
 I was thinking no matter what is the channel effect(BPSK modulation
works
based on sign of real part of signal) one of the chains will detect the
data
but still nothing in the output.
now i am really confused what can be the problem of the communication
chain
I am trying to implement.

any hint is appreciated,
Mehdi
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