[USRP-users] Rx performance degraded in TDD using X310+SBX, ATR setting or what else?

Marcus D. Leech mleech at ripnet.com
Thu Mar 31 17:51:05 EDT 2016

On 03/31/2016 05:27 PM, hanwen via USRP-users wrote:
> Dear USRP users and experts,
> Using X310+SBX, I'm building a TDD system with predefined pattern of 
> Tx and Rx time slots:
> Tx: using tx_metadata_t to specify the transmitting time and end of 
> transmitting
> Rx: always streaming, discarding the i/q samples in the Tx slots
> Observations:
> 1. When the Tx is completely off, the Rx demodulation performance is 
> very good. The noise figure of 3~5dB can achieved with maximum 37.5dB 
> Rx gain, which is indicated by the estimated SNR in my demodulation 
> algorithm as well as the simple PSD observation.
> 2. When the Tx is on according to the TDD pattern. The receiver 
> sensitivity becomes tens of dB poorer, although in the Rx slots I'm 
> sure there is no Tx signal scheduled.
> I tried the ATR settings in my earlier post: 
> http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2015-August/015436.html
> BUT it seems doesn't help.
> I'd eager to know how to make the optimal configuration for 
> interference-free TDD operation. Thanks.
> Bests, Hanwen
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> USRP-users at lists.ettus.com
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Try using offset-tuning on TX, to move the TX LO leakage out of your 
passband.   It may still desense during TX schedule, but that doesn't
   matter.  I think you're complaining that even when your TDD schedule 
isn't using the TX, but with the TX chain turned on, you're getting
   de-sense on the RX side?   You could also decrease the TX gain 
whenever your TDD schedule needs to TX, but that may take too much time
   depending on the size of your timeslots.

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