Re: [Discuss-gnuradio] RSSI measurement / questions

[Christoph Thein]

Hi,


> Hello
> 
> I would like to be able to measure the received signal power by the
> USRP2's antenna at any compatible frequency. My idea is store the value
> of the received signal power in a variable, which I'll use to determine
> if the channel is busy or not (based on a configurable threshold).
> 
> I've taken a look at USRP2_fft example and I've thought this:
> 
> [USRP2 source] --> [Complex to Mag ^2]--> [FFT sink]
> 
> When I run this graph (using grc) in a computer, I obtain the USRP2's
> measurement modulus. On another computer I run a program which generates
> 802.11 a/g/p frames. The result is: there's a big difference between
> received signals (when I'm sending 802.11 frames and when I'm not
> sending).
> 
> My questions are:
> 
> - Is it a good way to test the 'RSSI' by the USRP2's antenna? Is it
> accurate?
> 
> - How could I store some resultant samples in a file (instead of
> graphical sink)? If I could do this, I'll be able to estimate whether
> the channel is busy or not.
> 
> - Does it exist another method to do the RSSI measurement "easily"?
> 

I assume you are using the XCVR2450 when dealing with 802.11. 
If so,you can access the rssi output from the maxim chip directly with the aux 
adc (ad7922) on the USRP2. You can add the lsadc_read_rx() command in the 
firmware to get the adc output and then pass the 12 bits through the 
metadata.word0 to the host. The rest of the adc output to dBm estimation can 
be done on the host side. That works for us with version 3.2.2 as an 
indication of the received signal strength but I am not sure if it will affect 
other functionalities. We are still testing this way. Any comments are 
welcome!   

BR Christoph

> - I've been reading and googling before posting, and I found this post
> http://lists.gnu.org/archive/html/discuss-gnuradio/2007-08/msg00088.html
> but it's from 08/2007. Is it possible to check the value of "rssi
> registers" directly? Are they deprecated because they're related to
> USRP1 & inband signaling?
> 
> Regards,
> 
> J. Gutierrez
> 
> 
> 
> 
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>