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Apple Invents an Accurate Radionavigation System for Swimmers wearing an Apple Watch



Today the US Patent & Trademark Office published a patent application from Apple that relates to methods, systems and computer program products for radionavigation for swimmers using an Apple Watch.


A radionavigation receiver measures observables (e.g., pseudorange and Doppler shift) from RF signals which are used to compute an estimate of position, velocity and time (PVT). Because these observables are a function of antenna motion, if the radionavigation receiver embedded in a smartwatch or other wearable computer is worn on a wrist of a swimmer the PVT estimate could be inaccurate due to the inclusion of the velocity of the wrist in the PVT estimate. Additionally, because the radionavigation receiver could receive RF signals only when above water, the PVT estimate may be inaccurate due to the radionavigation receiver being periodically submerged under water.


Apple's latest Apple Watch invention solves this problem. Apple notes that the Apple Watch could be configured to estimate a location using radio frequency signals that could estimate a position of the swimmer when worn on a limb of the swimmer and periodically submerged. The Apple Watch could supply auxiliary information to a radionavigation subsystem to correct a navigation solution affected by limb motion of the swimmer and affected by the periodic submersion of the mobile device.


2 apple watch patent figure

Apple's patent FIG. 1 noted above is a diagram illustrating example techniques of radionavigation by an Apple Watch worn by a swimmer. Apple Watch #102 could be configured to estimate PVT using radionavigation technologies.


In particular, the Apple Watch could estimate PVT using RF signals from one or more signal sources #104 that could be transmitters on satellites of a global navigation satellite system (GNSS).


In various implementations, signal sources could be wireless access points (APs) of one or more wireless local area networks (WLANs), cellular towers, or other beacons that emit RF signals. The latter could be used for indoor swimming where such APs may exist.

A swimmer could wear their Apple Watch on a limb while swimming. The swimmer could swim in various styles where the limb (and thus the mobile device) is above water periodically.


For example, the swimmer could perform a crawl stroke, butterfly stroke, or backstroke, while the Apple Watch on their wrist. At some portions of the stroke, e.g., at position #105 (of FIG. 1), the Apple Watch is above water and could receive RF signals.


At some other time in the stroke cycle, e.g., at position #106, the Apple Watch is submerged and cannot receive RF signals. Moreover, when the Apple Watch is above water it tends to have higher linear velocity than the torso velocity of the swimmer, because a wrist tends to move from behind the torso to in front of the torso in the direction of travel. Accordingly, the Apple Watch may provide a PVT estimate that includes an incorrect velocity of the swimmer due to inclusion of the velocity of the wrist.


Apple's patent then explains how to correct the velocity component of the PVT estimate with a mathematical solution, too complicated for this report.


Apple's patent FIG. 4 below is a block diagram illustrating components of an example location subsystem configured to estimate a velocity of a swimmer; FIG. 2 is a diagram illustrating determining a relative velocity of a mobile device worn on a limb of a swimmer; FIGS. 3A/B/C are diagrams illustrating example techniques of selecting limb length scalars in determining the relative velocity.



For more details on this invention, see Apple's patent application #20170357007 which was filed back in Q2 2016. Considering that this is a patent application, the timing of such a product to market is unknown at this time.


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