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MMWCAS-RF-EVM: MMWCAS-RF-EVM Height Discrimination

Gabriel Gan
Prodigy 85 points
Part Number: MMWCAS-RF-EVM
Other Parts Discussed in Thread: AWR2243, , MMWCAS-DSP-EVM, TIDEP-01012

Hi TI,  

I am currently using a system, MMWCAS-RF-EVM (AWR2243) with the MMWCAS-DSP-EVM. I conducted an experiment whereby I wanted to test the accuracy of the height (vertical) discrimination of the system with the MIMO mode. 

Here is the setup:

The configuration settings were taken from Design Guide: TIDEP-01012: Imaging Radar Using Cascaded mmWave Sensor Reference Design.

Both the MRR and SRR MIMO settings were used as shown in table 2: (All the parameters were followed and the only exception was that I did not program in the frame length, as I was not sure on how to do that, maybe you could provide some insight on this?)

Both Master and Slave have 10 frames each. 

MRR

The distance to the target was approximately 20m.  In order to test the vertical discrimination of the target, 2 tests were done. The first is shown below. The distance between CRs (lengthwise) is approx 2.5m.

(setup 1)

The second test (setup 2) is by adding a 2nd CR at the bottom of the cart as shown below: The CRs have approximately a distance of 1m (height-wise) between them.

I've run Matlab sample code cascade-MIMO_signalProcessing (note that I am using the default calibration file, i.e. no calibration was done). Although the range profile did show a return for both test setups at the correct distance,  it seems that the height discrimination was not effective (by viewing the 3dpoint cloud) whatsoever. (Note that the Axis of the 3d point cloud were limited in order to filter out any unwanted dots)

By using the 3d point cloud, I was not able to really decern any height discrimination. (note that the background capture in MRR-Results Comparison was taken without any CRs present. just the cart itself)

The second test (SRR Parameters), was performed in the exact same way with only 2 differences.

1. The CRs were at a much closer distance to the system (approx 9m.) i.e distance from the system to target was approx 9m.

2. The CRs were placed closer together (lengthwise), approx 1.5m

However this time, there was some height discrimination.

As the System was placed inverted,  (something like this)

I've noticed that the 3D point cloud has to be read by flipping it along the x-axis.

Hence,

With regards, to the system, I noticed that it has good azimuth discrimination, however,

1. what are the factors that lead to height discrimination. Do the system parameters (start freq, stop freq, chirp rate) play a part in this? 

2. Would it be possible to get any height discrimination at mid-range i.e. 50 to 100m?. If so, how can this be done and what can I expect the height discrimination to be?

3. What about Tx beamforming, will that help with height discrimination?

Your help is much appreciated. Thank You!

  • 0
    TI__Genius 13805 points

    Hi,

          Please find the responses below.

    1. what are the factors that lead to height discrimination. Do the system parameters (start freq, stop freq, chirp rate) play a part in this? 

    Height discrimination is basically an elevation angle estimation and angle resolution problem. TI has some training material in the link below that explains the angle estimation in mmWave sensors

    Intro to mmWave Sensing : FMCW Radars - Module 5 : Angle Estimation | TI.com Video

     If the two objects are in the same range-Doppler-azimuth bin then the height discrimination capability of the system is dependent on the virtual array aperture in the elevation direction and is not dependent on the chirp parameters such as sampling rate, chirp slope, start frequency etc. If all the TX channels along the elevation direction in the cascade board EVM are used then theoretical elevation angle resolution is ~ 18 degrees. This angle resolution in degrees is independent of the radial distance of the object from the sensor.

    In the experimental setup that you have described i.e. 20 m radial distance and separation of 1 m between the corner reflectors, the angle separation of the two corner reflectors is roughly ~  2.9 degrees (based on basic geometry). Note that this is less than the elevation angle resolution of the system (i.e. 18 deg), hence you would not be able to discriminate between the two corner reflectors. This is consistent with what you are observing in your experiments

    2. Would it be possible to get any height discrimination at mid-range i.e. 50 to 100m?. If so, how can this be done and what can I expect the height discrimination to be?

    Given that the theoretical elevation angle resolution is ~ 18 degrees, you would need to calculate the physical separation needed between two corner reflectors to resolve the height at these particular distances.

    Also note that the elevation angle resolution only comes into play if the two objects occupy the same range-Doppler-azimuth bin.  For example, if object 1 is at 100 range-bin and object 2 is at 102 range-bin then the heights of the two objects can be distinguished as these objects are already separated in the range dimension. However, if the objects are static (zero Doppler) and are at the same radial distance and azimuth angle (meaning they occupy the same range-Doppler-azimuth bin) then they need to have a separation of at least 18 degrees for them to be resolved as two separate objects.

    Also note that there are several super-resolution algorithms (MUSIC, ESPIRIT) proposed in the literature that attempt to break the theoretical aperture limited angle resolution. You can investigate these algorithms if a higher angular resolution is desired.

    3. What about Tx beamforming, will that help with height discrimination?

    No, TX beamforming will not help in height discrimination

    Regards