Skoltech researchers have designed a software-based algorithm for synchronizing time between smartphones that can be used in practical tasks that require simultaneous measurements. This algorithm can essentially help turn different devices into a full-fledged network of sensors. The article was published in the journal Sensors
If you want a network of intelligent devices – say, a series of cameras capturing a dynamic scene or some other kind of network of sensors – to work properly, clock synchronization is one of the fundamental tasks to solve: all devices must be the same. timeline, often down to less than a millisecond for the more challenging tasks. Modern smartphones can easily be used as multi-functional sensors connected in a network, but they lack the hardware clock synchronization interface, especially in environments where GPS, which can also be used as a global clock, is not available. And because all non-atomic clocks float slowly but inevitably, they must be periodically resynchronized.
"Smartphone networks can act as microphone arrays to capture sound waves and collect more information about not only sound, but also direction. This is useful for noise reduction techniques: noise reduction algorithms only transmit the signal from a certain direction, such as a a person's voice amid office or city noise, "Marsel Faizullin, Skoltech Ph.D. student and a co-author of the paper, says.
Microphone arrays can also be used for so-called sound-based trilateration: a user's smartphone produces ultrasound and a series of other smartphones receive this signal. The delay between received signals allows the position of a user to be determined.
"You can also use this technique for soft synchronization of mobile phones with hardware-based systems. An example is a flash in cameras; our method allows any mobile phone to become part of a professional photography system," said Skoltech assistant. professor Gonzalo Ferrer adds.
Faizullin, Ferrer and their colleagues from Skoltech and St. Petersburg State University developed a clock synchronization method based on micro-electromechanical systems (MEMS) gyroscopes, which are now installed in every smartphone. They were able to design an algorithm that, in experiments with two smartphones capturing photos at the same time, showed better performance than existing sync software, with an accuracy of a few microseconds.
“This accuracy is enough to take a panoramic photo of a football or hockey game with a smartphone rig. An ice hockey puck can reach speeds of up to 100 miles per hour, traveling about four centimeters in one millisecond and in 20 microseconds it is 0.9 mm. This is much less than the field of view of one pixel of a professional camera. This means that it is also sufficient for capturing a hockey game with multiple cameras. An accuracy of microseconds is certainly more than sufficient for all tasks with consumer quality photo or video cameras, ”says Marsel Faizullin.
To use the algorithm, you have to grab the smartphones in one hand, turn them a bit and let the software do the rest in terms of all the clock sync operations and calculations – it's literally a "twist and sync" approach.
For future research, the team decided to apply their method to systems that include not only smartphones, but also other sensors such as lidars, depth cameras and so on. "This task is more complicated because of very different software and hardware compared to just a few identical smartphones. We are developing our method in this direction to be more practical," says Faizullin.
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Marsel Faizullin et al. Twist-n-Sync: software clock synchronization with microsecond accuracy using MEMS gyroscopes, Sensors (2020). DOI: 10.3390 / s21010068
QuoteScientists Use Smartphone Gyroscopes to Sync Time Across Devices (2021, Feb 19)
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