Greetings Estefania.
04-09-2018 01:41 PM
Good Evening
I am currently trying to make an FMCW Radar for my senior project.
I am using two 2922 USRP's to transmit and receive a chirp which increase frequency and decrease linearly (Triangular Pattern) .
To measure the Doppler shift I am using peak detectors to measure the time difference between a peak and another This method was successfully done for the transmitter part. However, for the received part, the signal wasn't the same using a wire,the higher frequency part can be in another location in the 0-10000 samples scale.
The transmitted and received chirps screenshots are attached with the blocks of both the transmitter and receiver.
04-10-2018 10:47 AM
Hello,
Could you tell us more about the physical setup? Are you using one USRP to transmit and another to receive the signal? Are you currently just trying to verify that you can receive what you are sending?
The screenshots are a bit low-resolution for me to see exactly what is going on. How are you synchronizing the transmit/receive portions of the code?
04-10-2018 10:51 AM
I am using two USRP’s
one for transmitting and another for recieving
they are connected using a MIMO cable, which i think they must be synchronized. One is master and one is slave
04-11-2018 10:48 AM
The MIMO cable will allow you to share a ref clock and PPS signal, but does not synchronize the start of the acquisition and generation. I can see some sort of trigger in your receive code, but as I mentioned before the resolution of the screenshot is too low for me to see exactly how you are attempting to do this.
04-14-2018 07:23 AM
Thanks for your replay
I just took clearer screenshots for the configuration part in both transmitter and receiver USRP's
Do I have to make a trigger for the transmitter also? and how to do it?
Thanks you very much
04-16-2018 10:33 AM
Thanks for this.
So you are setting up a time for the USRP to start Rx and get samples, but only controlling the start of Tx by when you run the code. I would suggest setting up a very similar start trigger for Tx as Rx in order to ensure that you're generating and capturing the waveform at the right time. The tricky part will be ensuring that you set the time to 0 on both USRPs at approximately the same time.
04-21-2018 04:27 AM
Sorry for late replay
I just did set time 0 on both the devices, and I put trigger time equal in both Tx and Rx USRP's. However, I still get different received waveform (Delayed) .
The reason I want them to be same is because I take the values to measure frequencies and I need them to be exactly the same when using a wire.
Snapshot is attached I hope you look at it and help me to know what is wrong
Thanks
04-23-2018 12:31 PM
Try to change your structure to ensure that the calls to set the time to zero on the USRPs are occurring at the same time (use a sequence structure or something similar). Because this process is software timed, there will also be variability in the difference between the times on the two different devices. This could result in differences between runs.
After doing this, you can also try experimenting with different start times for the Tx and Rx portions (i.e. delaying one compared to the other) in order to get the signal you want to see.
10-16-2019 11:12 AM