[Discuss-gnuradio] USRP: is performance degradation of PSK OK?

[Alick Zhao]

Hi list,

I am experimenting with narrowband benchmark_tx/rx in real indoor air
interface. The software is GNU Radio 3.5.3.2 and the hardware available
is USRP with RFX2400 daughter boards.

When I use gmsk modulation to transmit and receive, the performance is
quite good - very few packets are lost or received wrongly. However,
with dbpsk, I find the performance is quite degraded. I have not seen
better results than the case with (ok, rx, total) is about (407, 470,
666), which means no more than 2/3 of the packets can be received.
Besides, I got some OOO in the receiver side and this tell me overrun
happens. This is also not the case with gmsk. The current bitrate is
125kHz and samples per symbol is set to 2, and I find this results in
the lowest sample rate for USRP. So it is impossible to lower down the
sample rate :(

Is the performance degradation with psk normal? Does anyone experience
the same issue? Can it be improved in some way? One labmate told me that
he once worked with GNU Radio 3.2 and the same hardware but he didn't
see such performance with psk. So is the new UHD interface/driver
related?

alick