Hi,
I need to help, I’m doing a transmitter and receiver BPSK, using USRP2
and a 20dB cable that link both 2 devices,
In TX
sps=8
interpolation=16
IF=100MHz/interpolation
Sample_rate=IF/sps
GLFSR source
(gr_glfsr_source)[degree:12,repeat:yes,mask:0,seed:1]–>chunks to
symbols(gr_chunks_to_symbols)[psk.costellation[2],dimension:1]–>Interpolating
FIR
Filter(gr_interp_fir_filter)[Interpolation:8,Taps:gr_firdes_root_raised_cosine(sps2000,sps,1,0.3,sps11)]–>USRP2_sink[interpolation:16,frequency:2.45Ghz,gain(dB):45]
In RX:
sps=8
interpolation=16
IF=100MHz/interpolation
Sample_rate=IF/sps
USRP_sink[interpolation:16,frequency:2.45Ghz,gain(dB):45]–>Feed Forward
AGC(gr_feedforward_agc_cc)[num samples:256,reference:1]–>costas
loop(gr_costas_loop)[alfa:0.8,beta:0.0025,max_freq:1,min_freq:-1,order:2]–>M&M
clock recovery(gr_clock_recovery_mm)[omega:sps,gain
omega:0.0025,mu:0.5,gain mu:0.1,omega relative
limit:0.005]–>costellation
decoder(gr_costellation_decoder)[symbolPosition:psk.costellation(2)],symbol
value out:range(2)]–>Unpack K bits(gr_unpack_K_bits)[K:1]
I have some questions:
- I want to send a 5MHz signal How can I do, which parameters do I have
to change?
2)If I see the costellation after M&M clock recovery I see the typical
BPSK costellation but I don’t have 2 little point in -1,1 but a large
smear in these 2 points, why?
3)what do you thing about my project?is it good?
Thank you I’m sorry but I’m not a good gnuradio programmer
best regards
Claudio
Johnathan C. wrote in post #905054:
On Wed, Apr 14, 2010 at 06:48, Tom R. [email protected]
wrote:
Another point of clarification for the way benchmark_rx works. We use
differential modulation to account for the phase ambiguity. For BPSK,
there would indeed be a 180 degree ambiguity, but we use DBPSK, which
is insensitive to that. For anyone wanting to use non-differential
BPSK, you would have to use information in the preamble to account for
that.
There seems to be confusion about which script the original poster is
referring to. Both the digital packet modem (“digital”) and the
digital bit error rate tester (“digital-bert”) have scripts called
benchmark_rx.py. The original question was how the digital-bert
example was avoiding phase ambiguity while using straight BPSK and not
differential BPSK. This is due to the use of a self-synchronizing
digital scrambler prior to modulation.
As you point out above, the receive chain in the digital packet modem
is indeed using DBPSK to avoid the phase lock ambiguity, but that’s
not what the OP was referring to, unless I am mistaken. Either way
it’s important to distinguish between these two applications, as they
work differently.
Johnathan