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#1 2018-Nov-16 16:54:22

lu
Member
Registered: 2018-Sep-21
Posts: 5

Full duplex relay RX-TX latency

Hi,

I am trying to implement full duplex relay with warp v3 by modifying latest warplab. While it seems to work, I observe a pretty large RX-TX delay (~45 samples).

Even without full duplex, if I just transmit from one antenna to the other antenna on the same node, I observe a latency of >40 samples.

Do you have any idea where the latency mainly comes from? I am using manual tx rx gain. Will the AGC module introduce any delay?

I know the state-of-the-art full duplex relay design (FastForward, Sigcomm 14, also used Warp) claimed they have only 4 samples delay.

Sorry for such a vague question. Any suggestion is highly appreciated.


Thank you in advance,
Lu

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#2 2018-Nov-19 10:14:53

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 5159

Re: Full duplex relay RX-TX latency

I've never measured it directly, but 40 sample periods (1 usec @ 40MSps) seems about right for the Rx -> Tx latency. There are many stages in that path:

Code:

Rx antenna -> LNA -> Mixer -> Buffer amp -> ADC -> FPGA Rx buffers -> FPGA Tx buffers -> DAC -> Mixer -> PA -> Tx antenna

I know the state-of-the-art full duplex relay design (FastForward, Sigcomm 14, also used Warp) claimed they have only 4 samples delay.

I'm not familiar with this work, but the Rx to Tx latency will definitely be >4 sample periods. I think the ADC itself has that much latency from analog input to digital output. I suspect these authors are describing the latency of some other path, maybe their cancellation signal generation logic?

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