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Re: [Discuss-gnuradio] Is RFX900 simultaneous transmit and receive funti

From: Rushikesh Khasgiwale
Subject: Re: [Discuss-gnuradio] Is RFX900 simultaneous transmit and receive funtion possible?
Date: Sun, 22 Nov 2009 12:19:35 -0600

Hi all,
I used the usrp1 for implementing a UHF gen2 reader(not the entire functionality though). I have used a single board at the same frequency without any problem. RFX900 has 2 antenna ports TX/RX and rx2 so tx and rx antennas can be connected simultaneously.
However I found a major problem with latency. transmitting was not a problem but recd signal was delayed quite a bit.
@Michael -  did you use usrp1 or usrp2? since usrp2 has ethernet interface, it should give lower latency than mine.

Sent: Friday, November 20, 2009 1:04 PM
Subject: Re: [Discuss-gnuradio] Is RFX900 simultaneous transmit and receive funtion possible?

> Hi to all,
> I need to implement a RFID reader using GNURadio RFX900.
> I wanted to know urgently that is it possible to use a single
> RFX900 for simultaneously transmitting and receiving.
> I am in a hurry to purchase the stuff so I can receive it before holidays.
> Prompt responses are highly appreciated.
> Thanks in advance.

> Regards,
> Subodh

I have developed a GNU Radio based Gen 2 RFID reader that can communicate with standard tags from a few feet away.  The code has been uploaded to George Nychis' Comprehensive GNU Radio Archive (https://www.cgran.org/wiki/Gen2).  As RFID needs to transmit and receive on the same frequency, my setup uses two RFX900 boards, one for transmit and one for receive. As long as the antennas are a few inches apart the transmit signal doesn't entirely swamp the receive chain and you can pick up the backscattered tag responses. The main difficulty in getting the system to work was reducing system latency to < 500 us.  The modifications involved some tweaks to the way GNU Radio interfaces with the USB driver. This means that it should also help other applications that want low latency.

If the code I have developed is useful to you, it would be great if you wanted to spend your energy improving the system instead of starting from scratch.  There have been posts before on this list by other people interested in RFID with the USRP, and this way everyone else could benefit from your work.  The reader code could definitely use some more work.


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