This reference design highlights the IWRL6432AOP's ability to detect motion and presence for outdoor surveillance systems, such as home cameras, video doorbells and automatic controls. IWRL6432AOP detects people and objects at long ranges and high angles through efficient antenna design, consumes very little power by cycling into deep sleep modes, and filters out nearly all false alarms through advanced algorithms. A multi-stage architecture allows the radar to achieve all three attributes (long detection range, low power consumption, low false alarm rate) at the same time. Devices with the IWRL6432AOP can benefit from faraway detections, long battery life, and fewer false alarms.
TIDEP-01035 | Design Folder |
IWRL6432AOP | Product Folder |
IWRL6432AOPEVM | Tool Folder |
As consumer technology becomes smaller and lower-power, video doorbells and video cameras are increasingly being powered by batteries instead of direct line-power. While this shift has made the process easier to put more surveillance devices in different places, the process has created a challenge to increase battery life of these devices. The most power-hungry event in typical operation for surveillance devices is recording and streaming video. Recording and streaming require the device to capture data over the camera, run image signal processing algorithms, and stream over WiFi to the cloud. To reduce the amount of time a device spends streaming data, smart surveillance systems have presence detection devices built onto them, which decrease the number of false alarms detected by the system, extending battery life without missing any true detection events.
Nearly all presence detection technologies face a tradeoff between low-power consumption, long detection range and low-false alarm rate. TI’s IWRL6432AOP mmWave radar balances these factors effectively through the high transmission power, multiple detection modes and seamless programmability on the M4F core and hardware accelerator (HWA).
The radar equation found in Programming Chirp Parameters in TI Radar Devices, application note describes the tradeoff between long detection range, low power consumption, and low false alarm rate mathematically.
Pt and Tr are functions of power consumption - as the functions increase, power consumption increases. SNRdet is a function of false alarm rate - as SNRdet increases, false alarm rate decreases. Keeping all the other terms constant, this yields the following relation, that detection range is proportionate to the product of power consumption and false positive rate.
This can also be understood through a broader lens through statistics. A known fact is that the noise of a radar system can be modeled as the magnitude of a complex Gaussian, which is known as a Rayleigh Distribution. If the received signal of a target of interest is modeled as a Gaussian, centered around some non-zero returned power, then the detection threshold for the amount of power returned to the radar system needs to be set somewhere between the two distributions. Detecting whether an object is present or not reduces simply to a hypothesis test of two distributions.
If the detection threshold is set lower, then there can be more false positive alarms (radar wakes up unnecessarily), but fewer false negatives (radar misses a real detection). Conversely, if the detection threshold is set higher, then there can be fewer false positive alarms, but the radar can experience some false negatives. Since the cost of missing a real detection can be quite high for surveillance systems, often the strategy is to make the detection threshold lower, and absorb some of the false alarms in exchange for the reduced likelihood of a missed real detection.
While a good detection system has all three of these qualities (low power, long range, low false alarm rate), the recommendation is to prioritize some over others in specific scenarios to extract the best overall system performance. The IWRL6432AOP navigates this balance by using multiple detection modes. This design guide assumes that three modes are used, but the logic can apply for two modes, or even more than three modes if necessary.
First pass mode is the default option for the radar. In first pass mode, the IWRL6432AOP operates in the lowest possible power configuration while still maintaining the ability to detect at long ranges. IWRL6432AOP does have some false alarms, even in low-noise conditions to achieve long range at the lowest possible power. For best results, the first pass mode need to be as low-power as possible, even at the expense of some false alarms.
When detections occur in first pass mode, the radar switches to second pass mode, which uses a higher-power chirp that reduces the false alarm rate of the radar, and achieves the same detection range as the first pass mode. There is no advantage for the second pass mode to detect objects at further ranges than the first pass mode, since the first pass mode is what triggers the second pass mode. The second pass mode do not have nearly as many false alarms as the first pass mode, but is acceptable to still wake up sometimes from winds, bushes and trees.
Finally, a third pass mode can be used to eliminate any false positives still detected in second pass mode. The third pass mode cannot have any false alarms if possible, since the third pass mode can be used to awaken the camera, which can draw 10-100 times more power than the radar.
By cycling between the three power modes, the IWRL6432AOP is able to take advantage of the lowest-power consumption of the first pass mode when there is very little ambient motion, while also benefiting from the minimal false alarm rate of the third pass mode. The second pass mode serves to make sure that in times of high ambient movement in the scene, when first pass mode can be too sensitive to be effective, the radar still has a reasonably low power mode.
First Pass Mode | Second Pass Mode | Third Pass Mode | |
---|---|---|---|
Power Consumption | Low | Medium | High |
False Alarm Rate | High, even in low-movement scenarios | Moderate, only when there is wind, trees, or bushes | Low |
Detection Range | Equal | Equal | Equal |
Percent of Time Spent in Mode | High | Medium | Small |