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Original question:

AWR1642BOOST: Signal Transmission: Can two distinct frequency bands be transmitted simultaneously?

AWR1642BOOST: Code Division Multiplexing? // MIMO Network where transmitters are not colocated.

George Denove
Expert 1435 points
Part Number: AWR1642BOOST
Other Parts Discussed in Thread: AWR1642

Hi,

I have two AWR1642 sensors located in two different places throughout the environment. I am trying to figure out a way to have them both transmit at the same time and allow each of the other radars in the network collect their transmissions as well. With the hardware provided in the AWR, how do you recommend completing this? Is a code division multiplexing strategy feasible?

Here are the avenues I have tried out so far:

  1. Shift the frequency bands for each node/AWR transmitter, but an AWR can only transmit one band of frequency at once. (Therefore, it cannot transit a second band for the IF signal to be realized.)
  2. Do a Binary Phase Shift Keying, but there is not a phase changer (per the block diagram below from your website) before the signal is transmitted. Also, how would one differentiate node 1's BPM signal on node 2 if the distance (therefore, phase of the incoming received wave) is not known.

Therefore, I am wondering if there is another way to do this with the hardware provided on an AWR1642. CDM?

Thank you!

George

  • 0
    TI__Guru 69960 points

    Hello George,

    If both of AWR1642 are at a reachable distance then frame can be trigger using hardware trigger mode. In this case, one device can drive GPIO pulse which is connected to itself on AR_SYNC_IN line and on the same line of other AWR1642. This way both devices transmit frames at the same time (considering other device get GPIO pulse at same time as first device).

    Regards,

    Jitendra

  • 0 in reply to Jitendra Gupta
    Expert 1435 points

    Hi Jitendra,

    Thank you so much for getting back to me with all your answers.

    As of right now, I have implemented what you described above. My question, though, is about interference avoidance in this hardware (or even one day hopefully, software) synchronized setting. Say I have 3 radars in a network. Right now, only Radar 1 transmits, while Radar 2 and Radar 3 receive the reflected Radar 1 signal. Now I want to implement a system where two radars transmit and receive all signals. So Radar 1 and Radar 2 transmit, and all three Radars collect their transmitted signal, mix, process, etc. I am doing the processing offline so no need to consider the onboard DSP chain.

    Here is the issue I am running into. If two hardware triggered AWR1642's trigger at once and we want to use their spatial differences in a multistatic mode (mode described above), we need a way to do interference avoidance. As described in more detail in original post, I tried BPM (Radar 1 transmits at 0 degrees and Radar 2 transmits at 180 degrees) and shifting the frequency bands (radar 1 transmits a band of 77GHz-79 GHz and radar 2 transmits at 79-81GHz), but because there is only one synthesizer and no phase changers on the AWR, I am unsure these two avenues will work (since each radar will need to mix the differing received signals on their device to get an IF signal).

    Do you have any other recommendations on how to accomplish interference avoidance while also being able to receive the bistatic signal from the other radars in the network? 

    Thank you very much Jitendra, and I look forward to hearing back from you!

    George

  • 0 in reply to George Denove
    TI__Expert 4720 points

    Hi George, 

    There is no way to acheive proper bi-static operation with AWR1642.  If one AWR1642 receives reflected signals generated from another AWR1642, the 'phase noise/chirp linearity' performance of the radar is degraded drastically.

    The one caveat to the above statement is the method of cascading radars where one chip (called the master) provides the rest of the devices (called slaves) with the 20 Ghz synthesizer signal. In this mode, both master and slave are generating near identical chirps, and so every radar in a cascaded setup will be able to recieve and 'mix down correctly' signals transmitted by other radars.   

    That being said, the only available solution to solving the problem of interference for your problem is BPM. BPM is simply a phase change on the RF signal (not a frequency change) so the mixers will be able to down convert the signal without issue. Then using the ADC data, you should be able to separate the signals from different devices. 

    In fact, note that AWR1642 has itself 2 transmitters with independent BPM controls, so you should be able to do the BPM test using one device with two transmitters transmitting simultaneously. 

    Regards

    Anil