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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

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