Re: [Discuss-gnuradio] Channel Response in OFDM with MIMO USRP

[Marcus D. Leech]

> I see.
> Well, I'm running the regular OFDM rx-chain which includes preamble 
> detection->sampler->fft->so on. On the transmitter, each frame 
> (preamble[1 OFDM symbol] + data[multiple OFDM symbols]) acts as a 
> burst which includes the required timestamps and the burst tags.
>
> I was just somehow hoping to get a flat channel for some analysis 
> which otherwise is a pain, since I have to do it without channel 
> equalization. This phase change results in symbols rotating in the I/Q 
> domain. :)
>
> -jack
I've only been half paying attention to this thread.

But two frac-N synthesizers, even when fed with a phase-coherent 
reference clock, will have some random phase-offset between them every
  time they're tuned.  With newer UHD versions on the N2XX series 
machines and the SBX daughtercard, you can get around this with
  the special phase-alignment mode using timed commands for tuning. 
 But that isn't a particularly realistic scenario for real-world 
communications
  apps.

In the real world, the TX and RX will not be phase coherent in any way.



--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org