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IWR6843ISK: Waveform for multiple TX antennas

Kai Yang1
Expert 1400 points
Part Number: IWR6843ISK

Hi

In the mmwave SDK user guide, the chirp waveform is defined as follows. I believe this is the chirp for a single TX antenna, e.g., TX1. When you use two TX antennas in some applications, how does the waveform look like? Specifically, are TX1 and TX3 on and off simultaneously or interleaved? What will be the waveform when all three TX antennas are required?   

Thanks!

Kai

  • Former Member
    0 Former Member

    Hello,

    Your image does not appear to attach correctly. However I assume you're asking about how the chirp order/diagram appears?

    This is dependent on how you set the chirpCfg commands. The last parameter dictates which transmitter is enabled for that chirp cfg. (Refer to the SDK user's guide for more details).

    For each frame each chirpCfg command is issued, then the chirpcfgs are looped over depending on the number of loops set in frameCfg.

    For example if we look at the profile_3d.cfg in the SDK

    profileCfg 0 60 7 3 24 0 0 166 1 256 12500 0 0 30
    chirpCfg 0 0 0 0 0 0 0 1
    chirpCfg 1 1 0 0 0 0 0 4
    chirpCfg 2 2 0 0 0 0 0 2
    frameCfg 0 2 32 0 100 1 0

    This means we will chirp the profile defined as profile 0 on TX1 then TX3 then TX2 then we will loop over it 32 time giving 96 total chirps for this frame of data.

    Now if we modify and add another  

    profileCfg 0 60 7 3 24 0 0 166 1 256 12500 0 0 30
    chirpCfg 0 0 0 0 0 0 0 1
    chirpCfg 1 1 0 0 0 0 0 4
    chirpCfg 2 2 0 0 0 0 0 2

    chirpCfg 3 3 0 0 0 0 0 7

    frameCfg 0 3 32 0 100 1 0

    We've now defined four chirps. The first three as above and the fourth has all 3 transmitters enabled at the same time. So we would have a total of 128 chirps per frame. (Note this is just an illustrative example. This kind of chirping would not make sense with the processing chain)

    Amanda

  • 0 in reply to Former Member
    Expert 1400 points

    Hi Amanda

    Thanks for your quick reply.

    Now, it is clear to me how to set the waveform. Basically, profileCfg defines the parameters for a single ramp; chirpCfg assigns profileCfg to different TXs or a combination of TXs, and frameCfg defines a single frame that is composed of those chirpCfg.

    A follow-up question is if TX1+TX3 or TX1-TX3 (both azimuth TXs are on and off at the same time) is a valid chirping for the processing chain.

    Thanks!

    Kai 

  • Former Member
    0 Former Member in reply to Kai Yang1

    Hello Kai,

    I'm not sure I understand your follow up question perhaps if you could describe your objective or the context I could better answer to how to use different TX/RX schemes.

    Generally the reason why you see the chirping scheme as I showed from the profile_3d is because this enables TDM MIMO for better angular resolution.

    There are more details on MIMO radar here: http://www.ti.com/lit/pdf/swra554

    If you are using the simultaneous azimuth  TX then the advantage is you can have higher TX power enabling better SNR/max detectable range at the cost of angular resolution.

    Amanda 

  • 0 in reply to Former Member
    Expert 1400 points

    Hi Amanda

    My question is that if the signal process chain is still applicable when we turn on 2 TXs in a single ramp.Or, can we turn on 2 TXs in a single ramp. For example, TX1+TX3 means both TXs are in phase while TX1-TX3 means they are out of phase by 180 degrees.

    Thanks!

    Kai

  • Former Member
    0 Former Member in reply to Kai Yang1

    Hello Kai,

    Please refer to the MIMO application previously linked to understand how the processing occurs when TX1-TX3 is enabled for TDM MIMO. This processing is supported in the SDK out of box demo. For simultaneous TX1 and TX3 you will effectively improve SNR/transmit power at the cost of angular resolution. Either is valid.

    Amanda

  • 0 in reply to Former Member
    Expert 1400 points

    Hi Amanda

    I am not able to open the reference on MIMO Radar http://www.ti.com/lit/pdf/swra554. Would you please check if the link is correct?

    Thanks!

    Kai

  • Former Member
    0 Former Member in reply to Kai Yang1

    Hello Kai,

    The link works without issue for me. Perhaps there's an issue with your network configuration since the link redirects to a pdf download. Please try just searching for "mimo radar application note texas instruments" and the link to the document should come up.

    Amanda

  • 0 in reply to Former Member
    Expert 1400 points

    Thanks Amanda. It works for me now.