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Re: [Discuss-gnuradio] Received Signal Power ?

From: bjoernm
Subject: Re: [Discuss-gnuradio] Received Signal Power ?
Date: Fri, 02 Sep 2011 11:55:58 +0200
User-agent: Internet Messaging Program (IMP) H3 (4.2)

Hi all,

Thanks for the answer! But isn't there a functionality in the XCVR2450 daughterboard, which already measures the RSSI value?

Isn't there like a function which could output this value?

Secondly. Capturing the samples right at the output of the USRP, meaning within "gr.fft_filter_ccc" or maybe within the "gr.probe_avg_mag_sqrd_c"?

It's strange, the mailing list archive is full of RSSI related posts, but none of which are able to deliver answers to this issue, or am I missing something here?

best regards, and thanks again for helping

Quoting "Kresimir Dabcevic" <address@hidden>:

-----Original Message-----
From: address@hidden on
behalf of address@hidden
Sent: Fri 9/2/2011 10:26 AM
To: address@hidden
Subject: [Discuss-gnuradio]  Received Signal Power ?

I'm using the UCLA ZigBee PHY by Thomas Schmid, with the benchmark
example from gnuradio.

Now I need the signal power of each received packet (at the receiver).
For the signal
power computation:

P_S = sum ( all samples squared ) divided by number of samples

but the problem is where to fetch these samples, and how to make sure,
that only samples
of the received packet are considered, and no noise...

Distinguishing "useful" samples from noise was a problem when I was playing around with UCLA as well. It wasn't an issue when RSS was good, because with power_squelch block, you could filter out the noise. Thus, try setting different TX amplitude / RX gain values in order to get more distinguishable samples.

1. is there a gnuradio block/function which would already perform this
task of received
signal power computation, or RSSI determination, which I could
use/edit for my task?

There isn't (or at least wasn't until few months ago, I haven't looked into gnu radio since), so you'll have to extract that yourself. Try searching forum archives for "RSSI measurement", someone (Josh Blum?) explained it to me quite nicely there...

2. If not, where would be the best spot to capture the received
samples? As the
clock_recovery looks to be too late, and capturing the packets earlier
makes it hard to
distinguish between noise and received signal, as no clock recovery
nor packet detection
is performed, yet.

It seems that you'll have to capture the samples right at the exit from USRP, no way around that...


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