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Hello, I would like to enquire a time delay issue.
Say we have two WARP boards running WARPLab, board A and B. What I want to do is
(1) A sends a packet to B, B measures the received power
(2) B sends a packet to A, A measures the received power
A and B repeat the above process. I don't have a requirement on the length of the packet payload, as long as the receiver can measure the received power.
I would like to know what is the minimum time delay between the above step (1) and step (2). Many thanks.
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Junqing Zhang wrote:
I would like to know what is the minimum time delay between the above step (1) and step (2). Many thanks.
If the two measurements are made with two separate WARPLab commands, the delay will probably be dominated by the processing time through your host computer running MATLAB. I'm not sure what that number is. You'd have to run an experiment to measure that time.
Alternatively, you might be able to rig up something vaguely full-duplex to achieve the measurements with arbitrary small delay between them. From a high-level, you could use both RFA and RFB on both nodes where one interface is used for Tx and the other is used for Rx. Both nodes could transmit simultaneously but orthogonalized over time (i.e. one node is transmitting zero-valued IQ samples while the other is transmitting the waveform and vice versa). So it's not really full-duplex... it's still TDD. It's just that the structure of the experiment looks a lot like a full duplex experiment. One major challenge with this approach is that you'd have to make sure that the Tx interface one one node to the Rx interface on the same node is sufficiently attenuated (>30dB) so that you don't damage the receiver.
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Thanks for the reply Chris.
the Tx interface one one node to the Rx interface on the same node is sufficiently attenuated (>30dB) so that you don't damage the receiver.
I am not an expert in this area. Do you have any working solution in mind? Probably we need some special hardware?
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We use attenuators from Crystek (search Digikey for CATTEN), Minicircuits (search for "VAT-" parts), and Pasternak. Pay attention to the connectors (you probably want SMA for use with WARP v3) and frequency range (i.e. Crystek attenuators are only specified up to 3GHz).
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Many thanks. BTW, are you aware of any published work using the above setup mimicking ''full duplex''?
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Not for this exactly, but a lot of the full-duplex papers that use WARP have a similar configuration. You can search through the paper list for "full duplex" and find some, but they aren't very constructive for building the WARPLab experiment you need. They largely focus on the self interference cancellation problem, which isn't relevant for you since your waveforms will be TDD by design.
A circulator like this could be something useful. From that datasheet:
PE83CR1004 wrote:
These unique devices enable two signals to use one channel. The classic use of this three port device is for the line/coax between an antenna and a transceiver, allowing the receive signal to come from the antenna (port 1) to the receiver (port 2) while the transmit signal goes from the transmitter (port 3) to the antenna (port 1)
That's pretty close to what you want, except 20dB of isolation between the Tx and Rx interfaces isn't enough to avoid damage. You'd need to either lower the Tx power or add at least another 10dB of external attenuation on the output of your Tx interface.
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