0.2.3.1 Use-Case Geometry and Sensor Considerations
The IWR6843 is a radar-based sensor that integrates a fast, FMCW, radar front end, with both an integrated Arm Cortex-R4F MCU and a TI C674x DSP for advanced signal processing. The configuration of the IWR6843 radar front end depends on the configuration of the transmit signal and the configuration and performance of the RF transceiver, the design of the antenna array, and the available memory and processing power. This configuration influences key performance parameters of the system.
The key performance parameters at issue follow with brief descriptions:
- Maximum Range - maximum range at which a human can be detected
- Range Resolution - minumum distance required between two objects for the radar to detect them as separate objects
- Maximum Velocity - the maximum unambiguous velocity that can be detected. Objects moving faster than this may have incorrect velocity measurements
- Velocity resolution - minimum velocity difference between two objects for the radar to detect them as separate objects
When designing the frame and chirp configuration for a people-counting use case, start by considering the geometry of the scene specifically the range of interest. Table 2 lists example chirp configurations with good range and Doppler resolution and memory for a 8m indoor people counting application.
Table 2. Performance Parameters of Two Example Chirp Designs on the IWR6843
| KEY INPUT PARAMETERS |
| PERFORMANCE PARAMETER |
6-METER RANGE |
| Starting frequency (GHz) |
60.75 |
| Maximum range, Rmax (m) |
8.1 |
| Range resolution (cm) |
8.4 |
| Maximum velocity (km/h) |
16.2 |
| Velocity resolution (km/h) |
0.324 |
| Idle time (µs) |
30 |
| ADC valid start time (µs) |
25 |
| Periodicity (ms) |
55 |
| Valid sweep bandwidth (MHz) |
1780 |
| Ramp slope (MHz/µs) |
57 |
| Sampling frequency (Msps) |
2.95 |
| Number of samples per chirp |
96 |
| Ramp end time (µs) |
62 |
| Chirp repetition period (µs) |
184.0 |
| Number of chirps |
288 |
| Active frame time (ms) |
25.5 |