Hi,
I am trying to send a stream of bits using On Off keying and am having
some issues.
At this stage, I just want to check if 1's and 0's are getting received with
a high and low amplitude respectively. I have modified dbpsk.py setting the
constellation to 0+0i and 1+0i in psk.py and invoke the tx/rx as in
benchmark_tx,benchmark_rx ..
My flowgraph is
Bytes2symbols ->RRCFilter->USRP
USRP->filesink
I have a Bytes2symbols file which just writes the complex symbols for a
given set of bytes as in gr_chunks2symbols_bc.cc.
I have also checked that the complex symbols entering the USRP at the
transmitter are as expected.
However, at the receiver (USRP baseband samples without any processing) when
I measure the power, I do not see the power going low for the 0 bits.
Specifically, when I send a 101010... bit stream of 128 samples (just these
bits without any headers/trailers). The transmitted baseband complex
symbols are as expected with the real part going between 1 and 0
alternatively. *At the receiver, the received power stays almost the same
high value throughout the packet duration, whereas I would have expected it
to alternatively go high and low*.
Adding or removing the RRC filter doesn't affect the observation. The
following observations are true for the power and the real part of the
baseband samples.
1. For a tx. stream of all 1's, i can see the beat frequency or the
frequency offset for the duration of the packet (as expected).
2. For a tx. stream of all 0's , i see a low received value. (almost close
to the noise levels) as expected.
3. However, for a tx. stream of 1's and 0's mixed, I still see the received
amplitude (real part) showing the beat frequency continuously and not going
to 0 for the 0 bits.
I am using the latest stable version i.e gnuradio-3.1.3 on Ubuntu laptops.
Could this be Inter Symbol Interference or a setting which makes the
(carrier) power coming out of the USRP constant for the packet duration
irrespective of the tx.data?
Any help is greatly appreciated.
Thanks,
Sri.
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