Re: [Discuss-gnuradio] Channel measurements?

[Nikhil]

On Fri, Jul 25, 2008 at 9:57 PM, Johnathan Corgan <address@hidden> wrote:

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.

I was thinking that since you don't need to probe the channel at the Rx continuously as it does not change that fast,  one solution would be to buffer a sequence length (~2kB for a 511 bit m-seq) and then transfer it over the USB link at a slower rate.


 

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/