Re: [Discuss-gnuradio] DQPSK Transmitter and Receiver

[devin kelly]

>
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 = "" World!\n"

            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

On Mon, Apr 26, 2010 at 10:35 AM, Tom Rondeau <address@hidden> wrote:

On Mon, Apr 26, 2010 at 1:30 AM, devin kelly <address@hidden> wrote:
> 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

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

--
http://users.wpi.edu/~dkelly/