GPS-Assist (L6)

Introduction

GPS-assist is a cloud-assisted GNSS mechanism. Rather than compute a full autonomous GNSS fix on-device, the device works with aiding from Amazon Sidewalk: Amazon Sidewalk sends assistance data, the device uses it to acquire satellites quickly and produce pseudoranges, and it uplinks those pseudoranges for Amazon Sidewalk to solve into a position. This trades a cloud round-trip for much faster, lower-power acquisition than an unaided GNSS scan.

How the Cloud Resolves the Fix

GPS-assist is a two-phase exchange.

Build aiding

Amazon Sidewalk first establishes an approximate starting position for the device (for example, from a gateway or LoRa fix). Using that starting position, together with what it has learned about which satellites the device has locked before, it builds aiding (a satellite selection and an assistance payload) and sends it to the device as a downlink so the device can acquire satellites quickly.

Solve pseudoranges

The device acquires satellites using the aiding and uplinks its pseudorange measurement. Amazon Sidewalk combines that measurement with the starting position and the aiding to compute a GNSS position and publishes it with an accuracy estimate.

A position is not always produced. If the device locked too few satellites, or the pseudoranges are not consistent with the aiding (for example, the signal environment was poor or the device had moved too far since the aiding was built), the exchange produces no position. Locking more satellites with a clear view of the sky improves the chance of a fix and its accuracy.

A pseudorange measurement is solved only while the device has an active GPS-assist exchange in progress; the same measurement arriving from more than one gateway is solved once.

Accuracy and Constraints

Requires a GNSS-capable device and network timesync.
A pseudorange measurement is resolved only within an active GPS-assist exchange (aiding sent, measurement returned).
Accuracy depends on the number of satellites locked and sky visibility; a good starting position improves acquisition.