On Thu, Jul 24, 2008 at 4:37 PM, Johnathan Corgan < [EMAIL PROTECTED]> wrote:
> On Thu, Jul 24, 2008 at 12:30 PM, Nikhil <[EMAIL PROTECTED]> 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 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). Thanks. Nikhil > has no frequency offset compensation, so the resulting impulse > response vectors "roll" in the time domain. > > -- > Johnathan Corgan > Corgan Enterprises LLC > http://corganenterprises.com/ >
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