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Re: [Discuss-gnuradio] Channel measurements?
From: |
Johnathan Corgan |
Subject: |
Re: [Discuss-gnuradio] Channel measurements? |
Date: |
Thu, 24 Jul 2008 13:37:11 -0700 |
On Thu, Jul 24, 2008 at 12:30 PM, Nikhil <address@hidden> wrote:
> Are you trying to measure the impulse response of the channel? If so, then
> one technique would be to transmit a known pseudo-random bit sequence (an
> m-sequence) using BPSK modulation at the carrier frequency of interest. The
> chip rate of the sequence determines the measurement system bandwidth, while
> the sequence length determines the 'dynamic range' of the measurement.
>
> At the receiver set the LO to the same carrier frequency as that at the
> transmitter. Here you need to cross-correlate the equivalent low-pass
> received signal with the known m-sequence to give the (complex) impulse
> response of the channel. Any 'peaks' that exceed your definition of a
> threshold noise level would be your channel coefficients in the time domain.
This is actually implemented in gr-sounder.
Unfortunately, the cross-correlation done on the very limited space
FPGA has no frequency offset compensation, so the resulting impulse
response vectors "roll" in the time domain.
--
Johnathan Corgan
Corgan Enterprises LLC
http://corganenterprises.com/