DQPSK Transmitter and Receiver

GNU Radio
1

Hello Everyone,

I’ve made a basic DBPSK transmitter and receiver. I can receive ASCII
strings fine and the spectrum looks exactly as it should.

However, if I swap the DBPSK modulator/demodulator for the DQPSK
modulator/demodulator, my system breaks. I can no longer receive the
same
strings and the spectrum looks very strange. It’s much wider and
triangular
shaped.

Same goes for the D8PSK system and the D16PSK system I recently was
asking
about.

I believe marcin_w asked a similar question a few days ago and I haven’t
seen a reply yet (am I wrong?) My question is, should I be doing
something
different? Do I need to add in some extra block when I switch from
DBPSK to
DQPSK? While searching old posts, I found some people talking about
DQPSK
not working correctly, but that was about a year ago.

Any help would be greatly appreciated.
Devin

2

On Mon, Apr 26, 2010 at 1:30 AM, devin kelly [email protected] wrote:

seen a reply yet (am I wrong?) My question is, should I be doing something
different? Do I need to add in some extra block when I switch from DBPSK to
DQPSK? While searching old posts, I found some people talking about DQPSK
not working correctly, but that was about a year ago.
Any help would be greatly appreciated.
Devin

Well, you haven’t really told us what you are doing (code-wise), so
it’s hard to tell…

Have you compared your code to the dbpsk/dbpsk2 and dqpsk/dqpsk2
blocks in the source code? That might give you a hint.

My best (blind) guess is that you are feeding the modulator the wrong
number of bits per sample. You have to send a dbspk a chunk size of 1
bit / byte while the dqpsk takes 2 bits/byte chunks.

Tom

3

Hello everyone,

Tom, thanks for that, that was a good start for me, but I’m still am
having
the problems.

This is how I make my modulator for dqpsk, the way I make the modulator
for
dbpsk is mostly the same. Tom, at first I thought you meant I might
need to
change the samples_per_symbol paramter. I did this, on the transmitter
and
receiver, with no results. I’m pretty sure you were talking about
something
else,

Here are my modulators. All I’m doing is switching between them.

modulator = gnuradio.blks2impl.dbpsk.dbpsk_mod(

samples_per_symbol=2,

excess_bw=0.35,

gray_code=True,

verbose=False,

log=False)

modulator = gnuradio.blks2impl.dqpsk.dqpsk_mod(

samples_per_symbol=4,

 excess_bw=0.35,

 gray_code=True,

 verbose=False,

 log=False)

Here is my transmitter.

class tx_top_block(gr.top_block):

def __init__(self, mod):
    gr.top_block.__init__(self)

    modulator=mod

    self.packet_modulator = blks2.mod_pkts(
        modulator,
        access_code=None,
        msgq_limit=4,
        pad_for_usrp=True,
        use_whitener_offset=False
        )

    usrp2_sink = usrp2.sink_32fc(network_interface)
    usrp2_sink.set_interp(interpolation)
    usrp2_sink.set_center_freq(center_freq)
    usrp2_sink.set_gain(usrp2_sink.gain_max())

    self.connect(self.packet_modulator, usrp2_sink)


def main_loop(self):
    packet_size        = 1000
    max_num_packets    = 100000
    repeat_packets     = True

    try:
        data = "Hello, World!\n"
        data = data + (packet_size-len(data))*' '  # pad rest of

packet

        self.start()
print "Started Transmitter"
        while True:
            for pkt_num in xrange(0,max_num_packets):
                self.packet_modulator.send_pkt(data, False)
            if not repeat_packets:
                break
        self.packet_modulator.send_pkt('', True)  # Tell the source

to
block if it is done transmitting
self.wait() # Wait for radio
to
finish.

    except KeyboardInterrupt:
        pass

    print "\n\nExiting."

Thanks For Any Help,
Devin