[USRP-users] Trouble on loopback for square waves

Soumen Banerjee soumen08 at gmail.com
Tue Apr 7 00:16:01 EDT 2015


Hi Neel,

Thanks for your reply.

I have looked at the tx_waveforms example earlier and I guess it is a SISO
program. I wanted this to work in MIMO. Also, I have borrowed several
concepts for my code from that one.

In response to your other questions, Im using a USRP B210. The sample rate
is 1e5 = 100KHz.

I was wondering if you (or someone else on the list) could help clear up
some doubts I've been having for a while. When we send data using the USRP,
does it work like this:

1) The data(both the I and Q channels) is broken into bits - this gives us
2 bitstreams (I and Q).
2) The bitstream modulates the intermediate carrier using QPSK(Or, is the
modulation scheme something else?)
3) We upconvert the intermediate carrier to the transmit frequency and this
is the signal that the USRP finally transmits.

If the above were to be true, since all the data is finally modulated onto
the carrier as bits, then it shouldn't matter what we are transmitting
right? It should all work the same way - square or sine or anything else
for that matter.

Regards,
Soumen

On Mon, Apr 6, 2015 at 9:25 PM, Neel Pandeya <neel.pandeya at ettus.com> wrote:

> Hello Soumen:
>
> At first glance, I don't immediately see any problem with your code. It
> might be helpful to look at the "tx_waveforms" utility in the
> "uhd/host/examples" folder. It also generates square waves.
>
> Which USRP and which daughterboard are you using? What sample rate?
>
> --Neel
>
>
>
> On 1 April 2015 at 04:52, Soumen Banerjee via USRP-users <
> usrp-users at lists.ettus.com> wrote:
>
>> Hi,
>>
>> I am having some trouble sending and receiving square waves using uhd
>> programs. I have the receiver and transmitter connected using rf cable. On
>> the exact same program, I am able to send and receive sine waves properly
>> though. I have attached the code I'm using to transmit and receive the data
>> into the file. All the parameters are hardcoded in the code file itself.
>>
>> Simply exchanging line 230 with line 231 causes it to work just fine(for
>> sine waves).
>>
>> Also attached is a  snapshot of what I get instead of square waves.
>>
>> Can someone please help? Im totally stuck on this one!
>>
>> Regards,
>> Soumen
>>
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users at lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>
>>
>
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