Hi all,

I am currently trying to get plot the received bpsk samples and look

at the constellations as received by the USRP, but all I get a big

'ole blob of points in the middle.

I think the main issue probably has to do with the interpolation and

decimation rates so I included that code at the bottom, the whole

source is attached along with a symbol plot. I

In the symbol plot you can clearly see the received bits on the ‘unit’

circle, I was wondering why there are so many bits clustered at the

crossing point; I was expecting a big clump above/below 0 (which I

have) and almost no points at 0.

My questions are:

1. Is this the right way to find the decimation and interpolation

rates for a given bit rate (I tried to base it off of pick_bitrate.py)

2. Using only one USRP, will there be significant (any?)

constellation rotation?

3. Why are there so many ambiguous bits (maybe same as #1)

data_rate = 250000

bits_per_symbol = 1 # 1:bpsk 2:qpsk 3:8psk, etc

#Calculated generic parameters

bit_rate = 8 * data_rate

symbol_rate = bit_rate / bits_per_symbol

arity = pow(2,bits_per_symbol)

#User defined transmit parameters

tx_samples_per_symbol = 1

tx_converter_rate = 128e6 #Default DA converter rate

tx_interp_rate = int(math.ceil( tx_converter_rate /

tx_samples_per_symbol / symbol_rate ))

rx_samples_per_symbol = 1 #How many rx samples are devoted to one

symbol?

rx_converter_rate = 64e6 #Default AD converter rate

rx_decim_rate = int(math.ceil( rx_converter_rate /

rx_samples_per_symbol / symbol_rate ))