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[FAQ] AWR1843: Detecting Static Objects at Same Range, Distance

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Part Number: AWR1843

Recently, we have received questions related to detecting static objects at near range (~ 40 cm). This thread will discuss some of the specific details related to this type of detection.

Readers are invited to ask more questions if some of the explanations are not clear.

Let's assume that we are trying to detect  static objects such as cones, pipes, 2x4 posts...

Following need to be considered

  • Antenna, Angular Resolution
  • Chirp/Profile Configuration
  • Processing Chain

Antenna, Angular Resolution

Angular Resolution has been discussed in this thread:

https://e2e.ti.com/support/sensors/f/1023/t/681263

It is important to understand that angular resolution is different from angular accuracy. Angular resolution comes into play only when more than one objects have to be detected.

It is also important to notice that angular resolution is a function of the angle and is highest at angle θ = 0.

For example for an antenna that has an array of 4 Rx antennae, the angular resolution at angle θ = 0 would be 2/4 radian, i.e.  28.6 degrees. If MIMO is used with 2 TX, the virtual antennae array can be increased to 8 Rx antennae and the angular resolution at angle θ = 0 would be 2/8 radian, i.e 14.33 degrees.

This would mean that two static objects at same range can only be separated if the angle between the objects is higher than the angular resolution.

Chirp/Profile Configuration

The Chirp/Profile Configuration will define the maximum range and the range resolution

See

https://e2e.ti.com/support/sensors/f/1023/t/633560?

Processing Chain

A Processing Chain will usually process raw data to extract range, velocity, angle information. For static objects there is no velocity information, so all the information contained in the data is part of range and angle domains.

A processing chain may be optimized for static object detection and generate a heatmap only in range/angle domain. This is what the Obstacle Detection Processing Chain described in this TI design implements:

http://www.ti.com/tool/TIDEP-0104

However if velocity detection is also desired, a processing chain similar to the USRR can be used (see in automotive toolbox mmwave_automotive_toolbox\labs\lab0007_medium_range_radar)

Both of the processing chains will detect only onestatic object at a specific range (distance) The reason for this is that both processing chains detect only a single peak in the angular spectrum. In order to detect multiple objects at same distance the angular detection would have to be updated.

Also, we need to keep in mind that the angular resolution will limit the separation of two objects. So, if two static objects are at the same distance at an angle smaller than the angular resolution it will not be able to separate them in detection.

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