Re: [Discuss-gnuradio] Channel measurements?

[Mohammad Hamed Firooz]

  Hi
 Johnathan is right, If you fulfill the channel measurement in 
software your temporal resolution is not sufficient and you may not be 
able to resolve lots of paths specially for indoor applications. For 
more information I can refer you to Rappaport's book "Wireless 
Communications: Principles and Practice (2nd Edition)". If you want to 
have a channel sounder you have to implement the correlation part 
inside the FPGA.
Actually we are working on that. I have implement a channel sounder 
which works using 802.11b packets. As you may know 802.11b use DSSS in 
its physical layer. We implement the de-spreading part inside the FPGA. 
(you can find the 802.11b receiver here: 
http://span.ece.utah.edu/pmwiki/pmwiki.php?n=Main.80211bReceiver)

Thanks to that now we have a channel sounder with the resolution of 
30ns which is fine for indoor measurements. We plan to published it on 
the web in the next two weeks after doing the last testing and 
debuging. But if anyone is interested s/he can contact me to send 
her/him the code.

regards,
hamed
http://span.ece.utah.edu/pmwiki/pmwiki.php

Quoting Johnathan Corgan <address@hidden>:

> On Fri, Jul 25, 2008 at 6:12 PM, Nikhil <address@hidden> wrote:
>
> > I'm curious -- in a channel sounder application what benefit, if any is
> > there to performing the cross-correlation on the FPGA?  This is  assuming
> > you are continuously transmitting the PRBS and computing the impulse
> > response at the receive end at a rate that is consistent with variations in
> > the channel (i.e. not continuously).
>
> The channel sounder transmitter is sending the PRNG modulated BPSK at
> 32 Mchips/sec.  You need to do the correlation at this speed; it's not
> possible to send that much data over the USB to the host.
>
> A channel sounder in software would work for chip rates less than 4
> Mchip/sec.  But that limits the resolution of your impulse response to
> about 250 ns per bin, or 75 meters per bin in the spatial domain.
>
> --
> Johnathan Corgan
> Corgan Enterprises LLC
> http://corganenterprises.com/
>
>
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--
Mohammad Hamed Firooz
ECE Department, U of Utah
Salt Lake City
UT, 48112