Powered by Project Soli, Motion Sense is one of the highlight features of the Pixel 4 and Pixel 4 XL, enabling users to perform various tasks with gestures. The chip that enables the feature is said to be the first integrated short-range radar sensor in a consumer smartphone. While Google engineers had earlier detailed some of the key aspects of the Soli chip and how it works, they’ve now revealed some more details about the technology, including its radar sensing principles, design of the signal processing and machine learning (ML) algorithms used to recognize human activity.

According to Google, Soli differs from traditional radar designs insofar as its sensing paradigm is based on motion rather than fine spatial resolutions. For that, the Soli team developed “a new, small-scale radar system, novel sensing paradigms, and algorithms from the ground up specifically for fine-grained perception of human interactions”. Those human interactions include gesture recognition in the form of tapping or swiping above the Pixel 4 to control music, receive calls, turn-off alarms and more. It can also detect people approaching the phone to pick it up and unlock it via face detection.

The Google researchers also shared some animations on how the radar ‘sees’ motions and gestures, saying that different actions exhibit distinctive motion features in the processed Soli signal. According to them, “distribution and trajectory of energy within these range-velocity mappings show clear differences for a person walking, reaching, and swiping over the device”, enabling the technology to differentiate between different gestures. The Google ATAP team goes into technical details about the inner workings of the complex technology, and you can read all of that on the official Google AI blog.

Left: Person walking towards the device. Middle: Person reaching towards the device. Right: Person swiping over the device.

Unfortunately for Indian residents, though, the Pixel 4 never made it way to the country because the radar technology that that powers its Motion Sense feature operates in the 57 to 64GHz (V band) frequency range that’s reserved for the Defense forces in the country, and hence, is zealously regulated by the government. The device, however, is still available in dozens of countries around the world, including the US, the UK, France, Germany and more.

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