Signal Processing

Produce a heat map and/or IQ Data with the same algorithms that FMCW signal processing equipment would use, to visualize the effects of limitations in such algorithms and/or optimize the parameters in such algorithms.

FMCW Signal Processing

To obtain such a heat map and/or IQ Data, do the following:

In the results tree, select Power (MS) or Power. These are the power received by the receiver antenna and the power received by a hypothetical isotropic antenna, respectively.
Click Display > FMCW Radar.
Click on the radar result pixel.
On the FMCW Radar Postprocessing dialog, specify the parameters.

You can specify the radar parameters using two modes, either with Set Radar Parameters or Design Radar Parameters.

In case uncorrelated superposition of rays is specified in the simulation setup, the power values are summed. As a consequence, in the FMCW heatmap, the peaks are higher and the ghost targets are lower than in the case of coherent superposition.

Figure 1. If uncorrelated superposition of rays is specified in the simulation setup, the power values are summed. The peaks are higher and the ghost targets are lower (top image) than in comparison to the case of coherent superposition (bottom image).

Set Radar Parameters

You can specify the following radar parameters:

Chirp duration

The sawtooth chirp sweep period in μs. It has an impact on the maximum measurable velocity and on the velocity resolution¹ of the radar.
Sweep Bandwidth

The difference between starting and final frequency of a chirp. It has an impact on the maximum measurable range and on the range resolution² of the radar.
Number of Chirps

The number of chirps in one frame. It has an impact on the velocity resolution.
Frequency Bins

The number of FFT samples in one chirp. It has an impact on the maximum detectable range.

Design Radar Parameters

You can specify performance quantities like the desired range, range resolution, maximum velocity, and velocity resolution. It will calculate/design the radar parameters (for example, chirp duration, sweep bandwidth, number of chirps, and FFT samples) that can satisfy the required performance quantities.

Output

You can specify the desired output and optionally the type of windowing function. Windowing functions are applied in the time domain to suppress the side lobes in the frequency domain. They are also used to detect low signals that could be hidden beneath the side lobe of another target.

The output options are:

Doppler-Range Heat Map
Angle-Range Heat Map
IQ Data.

The Doppler-Range Heat Map shows the processed signal as a function of range and relative velocity.

The Angle-Range Heat Map shows the processed signal as a function of range and angle of arrival.

For the angle of arrival estimation plots, the following requirements need to be satisfied:

The receiver antenna type must be a Uniform Linear Array with number of receiving elements > 1.
The array azimuth angle needs to be set correctly, for example, in case of simulating an automotive radar, the antenna array must be aligned horizontally with radar car's bumper.
The horizontal spacing between the Rx elements must be $\geq \frac{λ}{2}$ ( $\frac{λ}{2}$ corresponds to maximum angular field of view ±90° where $λ$ represents the wavelength).

To obtain an accurate angle estimation, the following recommendations apply:

Use a large number Rx elements. For N receiving elements (with antenna spacing of $d = \frac{λ}{2}$ ), the angular resolution can be calculated as follows: $θ_{r e s} = \frac{2}{N} [rad]$ .
Apply a window function to reduce the ripples caused by zero padding in the angle-FFT. The angle-FFT was processed using zero-padding to improve the angle estimation accuracy.
Use a project based on Standard Polarimetric Analysis rather than Full Polarimetric Analysis, see Set Up a New Project.

If a heat map is chosen, it will be plotted. If IQ Data is selected, it is written to disk in ASCII format for external signal processing.

Figure 2. A snapshot in a time-variant simulation and an example of a heat map produced by FMCW processing. This heat map shows not only the range and relative velocities, but also the artifacts produced by the signal-processing algorithm with user-defined parameters.

¹ Velocity resolution is the ability to resolve two objects having close velocities (they show up as two peaks in the heat map).

² Range resolution is the ability to resolve two closely spaced objects (they show up as two peaks in the heat map).