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[Discuss-gnuradio] Channel Response in OFDM with MIMO USRP
From: |
Unforgiven11 dreams |
Subject: |
[Discuss-gnuradio] Channel Response in OFDM with MIMO USRP |
Date: |
Sun, 13 Jan 2013 01:04:39 -0600 |
Hello -
I've created a MIMO setup connecting 2 USRPs using an external clock reference (10MHz) and 1-PPS input. However, when I transmit packets between them, I see a phase rotation experienced by the subcarriers. I've attached an image highlighting the same.
The x-axis is the subcarrier index (80 subcarriers = 1 OFDM symbol) and the y-axis is the unwrapped channel phase.
I'm trying to understand why this would happen. As far as I know only sampling offset should be the reason for the same, but since these 2 USRPs now share the external clock, can this still be a problem? Or could there be another reason why I see this happening. The slope of this channel phase remains seemingly consistent for all the packets. I'm trying to achieve a scenario where I see a constant phase for all the subcarriers.
Using USRP N200's rev 4.
Thanks.
phase.png
Description: PNG image
- [Discuss-gnuradio] Channel Response in OFDM with MIMO USRP,
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