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 <[EMAIL PROTECTED]>:
On Fri, Jul 25, 2008 at 6:12 PM, Nikhil <[EMAIL PROTECTED]> 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
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