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Re: [Discuss-gnuradio] Duplex daughter
From: |
Marcus Leech |
Subject: |
Re: [Discuss-gnuradio] Duplex daughter |
Date: |
Fri, 26 Jul 2013 15:45:19 +0000 (UTC) |
If your processing delay is 1 second, that has nothing to do with the daughtercard. It has to do with the way you've implemented your code.
The delay through the USRP is a few sample-times at the input sample rate, and then the latency of to-host
link buffering, which is negligible, and then the link latency to host, which is again negligible--none of that adds up
to 1 second of processing delay.
Now, on the duplex issue:
Imagine for a moment that there's someone shining a bright light in your eyes, and there's another person, several hundred meters away, trying to signal you in morse-code, using a candle and their hand. It's unlikely you'll be able to see the remote person signalling you with a candle, unless you do some clever things. Like move the candle spectrum outside the spectrum of the flashlight...
Now, there are things you can do, like subtracting-out your transmitted signal from your RX signal by phase-shifting it by 180 degrees and mixing it with the RX signal. This is essentially how circulators work. The results aren't that great, and when you have a wide-band, noise-like signal, it's rather hard to shift it by exactly 180 degrees, because it has more than one frequency component.
Which is why for same-frequency operation, many systems use half-duplex architectures like TDD.
on Jul 26, 2013,
Dong Wang <address@hidden> wrote:
Hi Marcus,
Thank you for your help.
I tried to implement the TDD on my USRP with a half-duplex daughterboard XCVR2450 using same frequency.
But because of the processing time delay, the receiver can not receive the packet until maybe 1 second after the transmitter send it.
that means I can hardly do real-time communication between two USRPs.
So I want to try some duplex daughterboard. It seems that these duplex daughterboard can only implement dul-band.