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AWR1642: Will the wave deconstruct themselves by using 180 deg phase coding?

Peter010
Genius 4165 points
Part Number: AWR1642

Hello everyone

By using the phase coding, we could use the two Tx on the AWR1642 simultaneously by phase shifting one TX by 180 degree. My question is: since one channel is 180 degree off from another one, when the receiver received those two waves, will the waves deconstruct themselves totally (I mean I would receive nothing)?

Thanks

Xining

  • 0
    TI__Mastermind 37500 points

    Hello,

    If you are transmitting on Tx1 (not using BPM delay), and transmitting on Tx3 (using BPM delay), in most cases there is not destructive cancellation.

    The transmitter radar FMCW is reflecting off of the target.   The radial distance from Transmitter to Target and Target to Receivers would have to be exactly the same distance.   Since there are 4 receivers, at least one of the 2 of the receivers, from each Tx are needed for angle of arrival measurement.

    If you have an EVM, you can place an .5 RCS target (or tin can) centered between the 2 Tx antenna patches at a distance of 5 to 10 meters.   Using a modified Out of Box capture demo, I think you will find that at least 2 Receivers have a signal level.   

    Note: the BPM removal for xWR1642 is done in the DSP software. If you are doing the BPM receiver processing, you can send the post DSP memory to a location in L3 memory, then capture that in CCS to a file.   If you are not doing the BPM receiver processing, we would expect the delayed signal (from BPM) to be decoded as later in time.

    Regards,

    Joe Quintal

     

  • 0 in reply to Radio-Joe
    Genius 4165 points

    Thanks for yoru reply.

    Radio-Joe said:
     If you are not doing the BPM receiver processing, we would expect the delayed signal (from BPM) to be decoded as later in time.

    I do not quite understand what the "delayed signal" means.

    Regards

    Xining

  • 0 in reply to Peter010
    TI__Mastermind 37500 points
    Hello,

    The Tx1 (non delayed reference) and Tx3 (delayed by 180 degrees) are both transmitted, So the target sees two different frequency waves, because the two signals they are not in phase or not exactly 180 degrees out of phase. There is some intereference but not total cancellation. In order for us to transmit multiple phase references, we must process the receiver data 2 times, one for the standard reference (BPM1), and a different complex filter for the BPM(-1) case,

    In most cases we use non concurrent MIMO, so we don't have to extract Matched Filter values for each Tx. The BPM is 0 or 180 degrees. If we are using concurrent MIMO to increase velocity processing (reducing chirp period), BPM makes sense. In most cases we should initially try non concurrent MIMO for Tx1, all Rx; then Tx2(3), all Rx.

    You can try to setup the 1443 with non coherent MIMO and using the data capture portion of the out of box demo, you can collect the raw IQ data to compare a frame of data. You can then change to coherent MIMO, and capture the same data. You should be able to place a phase shift of 180 degrees by applying a separate filter for I and Q for the receiver with BPM activated, You can see the amount of interference in the signal (I have not done this test yet).

    Regards,
    Joe Quintal