Problem with USRP PSK modulation

GNU Radio
1

I think my problem has something to do with the parameters of the USRP.

I try to send a file modulated with BPSK. So I build a graph like this
:

File source -> Packet Encoder -> PBSK MOD -> PBSK DEMOD -> Packet
Decoder -> File sink

and i really get the correct output file with thee right constellation.

If I put a USRP source and USRP sink into graph, I don’t receive
anything.
I hope anyone can help me. Thanks

2

Hi Vivian,

give us details about your set up, like what USRP you are using,
daughterboads and frequency of transmission,

Edmar

2012/4/18 Vivian Paola Triana G. [email protected]:

and i really get the correct output file with thee right constellation.

If I put a USRP source and USRP sink into graph, I don’t receive anything.
I hope anyone can help me. Thanks

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3

I’m working with USRP1 daughterboard RFX 2400 MHz.
The configuration of the parameter in UHD_USRP block is sample rate=
1MHz
Center freq=2.4GHz.

2012/4/18 Edmar Candeia G. [email protected]

4

Are you using GRC?

Sam

On Wed, Apr 18, 2012 at 8:32 AM, Vivian Paola Triana G. <

5

Yes! I’m using GRC.

2012/4/18 Samuel I. [email protected]

6

On Wed, Apr 18, 2012 at 11:32 AM, Vivian Paola Triana G.
[email protected] wrote:

I’m working with USRP1 daughterboard RFX 2400 MHz.
The configuration of the parameter in UHD_USRP block is sample rate= 1MHz
Center freq=2.4GHz.

Vivian,
Are you using differential or non-differential modulation? Over the
air, the phase ambiguity at the receiver does not get worked out, so
it will only work if you use differentially encoded symbols.

Tom

7

I’m using non-differential modulation. But I used differential before
and
it didn’t work neither. I think my problem is with the sample rate that
I
have to set in UHD_USRP Sink and Source Blocks. I try to send a wav file
that has maximum frequency of 12kHz so I set the sample rate at 28kHz,
however it didn’t. I need understand what the sample rate refers to.

Thansks in advance for helping me!

2012/4/19 Tom R. [email protected]

8

Hello Vivian,

I have also had this problem, but I haven’t being able to solve it.
Could
you please let me know if your able to solve it? I would greatly
appreciate
your help.

Sam

On Thu, Apr 19, 2012 at 7:41 AM, Vivian Paola Triana G. <

9

Hi Samuel!

I haven’t solved it yet. I tried to set center frequency with a slider
to
vary a little bit the frequency of the receiver, but it didn’t work.
Have you solved the problem?

Thanks!

Vivian Triana

2012/4/19 Samuel I. [email protected]

10

On Thu, Apr 19, 2012 at 10:41 AM, Vivian Paola Triana G.
[email protected] wrote:

I’m using non-differential modulation. But I used differential before and it
didn’t work neither. I think my problem is with the sample rate that I have
to set in UHD_USRP Sink and Source Blocks. I try to send a wav file that has
maximum frequency of 12kHz so I set the sample rate at 28kHz, however it
didn’t. I need understand what the sample rate refers to.

Thansks in advance for helping me!

Vivian,

You definitely need to use differential, so make sure you start there
(on both ends of the chain).

Have you just tried using the benchmark_tx/rx examples and got those
working first? Best to understand that and get it working before
trying to do your own thing. At least at that point, you know that
your setup will work and if something goes wrong it’s in the new code.

Often, people have problems because the frequency of the transmitter
and receiver radios are too far apart and the receiver cannot lock to
the signal. Make sure you’ve corrected for any major frequency offsets
(this is a common problem that people bring up on the list, so google
for it if you need more information).

Tom

11

Hey Samuel,
Could you kindly tell me what other modulation schemes has it worked
for .
When i use GMSK it did work but with DBPSK it did not . What Sample
rates have you chosen ?

I would be awfully obliged if you were to let me know.

Thanks,
Josh.

12

Samuel I. wrote in post #1058562:

Hello Vivian,

I was able to solve the problem. The encoder and decoder blocks seem to
only work with certain modulation blocks. You should try changing your
modulation type to GMSK. We have being able to transmit text and picture
files with this set up.

Sam

On Wed, Apr 25, 2012 at 7:14 AM, Vivian Paola Triana G. <

The test and picture files what type of formats are you using in order
to send them across the USRP’s?

13

Hello Samuel I.

I was able to solve the problem. The encoder and decoder blocks seem to
only work with certain modulation blocks. You should try changing your
modulation type to GMSK. We have being able to transmit text and picture
files with this set up.

Sam

On Wed, Apr 25, 2012 at 7:14 AM, Vivian Paola Triana G. <

I am also working on the examples of benchmark and trying to build my
own graph like that. But there was a problem troubled me .
My graph is like this:
file_source–>PSK modulation -->multiply–>usrp_source
But various kinds of errors always torment me,and I wonder maybe it is
because of the connection between the file_source and PSK modulation .DO
I have to packet the numbers from the file and send to the
moudlator?since I don’t want to use the module’pkt.py’,I really
appreciate your advise to me.

I am a beginner with the GNU Radio. Thanks very very much for your help.

14

Hello Vivian,

I was able to solve the problem. The encoder and decoder blocks seem to
only work with certain modulation blocks. You should try changing your
modulation type to GMSK. We have being able to transmit text and picture
files with this set up.

Sam

On Wed, Apr 25, 2012 at 7:14 AM, Vivian Paola Triana G. <