09 Jan 2022

辅助 GNSS (AssistNow)

通过更快的 GNSS 卫星数据下载,全面提升定位性能。

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Signal acquisition is one of the main bottlenecks of satellite-based positioning technologies. It is a power-hungry process that involves detecting signals from orbiting GNSS satellites, downloading the almanac of their constellation, and each individual satellite’s ephemeris data, which are transmitted via the GNSS signal.


A cold start (in which the GNSS receiver does not have valid ephemeris data stored in memory) typically takes around 30 seconds in perfect conditions. In more challenging conditions, it can take considerably longer or fail altogether.


Assisted GNSS (A-GNSS) speeds up the signal acquisition process and shortens the time needed to achieve a first position fix. It does so by retrieving satellite data, accurate time, and satellite status using a faster data connection – typically wireless networks or the internet. With A-GNSS, GNSS receivers can determine their position in seconds, even under poor signal conditions.

Description how Assisted GNSS (A-GNSS) works

End-user benefits of A-GNSS

A-GNSS improves the performance of GNSS receivers beyond shorting the time required to determine their position when switched on, their time to first fix (TTFF). Eliminating lengthy or repeated data download attempts reduces the duration of the signal acquisition phase, increasing the battery life of GNSS devices.

Energy needed for fix position

A-GNSS increases satellite availability, particularly in challenging scenarios such as urban canyons and when exiting buildings or tunnels. By providing the ephemerides and signals for all satellites, even those beyond line of sight or when signal levels are low (below -148 dBm), GNSS receivers can immediately track new satellites that enter their field of view. By tracking more satellites, this can substantially improve the accuracy of the position output.

What is AssistNow?

AssistNow is u-blox’s A-GNSS location service. AssistNow supports GNSS receivers by providing satellite data required to determine their position either in real-time or ahead of time as predictions.


Designed for devices with cellular connectivity, AssistNow Online delivers satellite data to the device every time it is switched on. The 1-3 kilobyte data packet shortens the time to first fix to around three seconds and remains valid for roughly 2-4 hours.


Devices without access to wireless connectivity can use AssistNow Offline. With AssistNow Offline, predicted GNSS assistance data is loaded onto the device when internet access is available, for example via a paired smartphone. The 125-kilobyte dataset, which remains valid for up to 35 days (28 days for GPS and GLONAS), reduces the time to first fix to between 5 and 20 seconds.


Infographic that presents how AssistNow works

u-blox differentiators

Assured availability, warranty, and support

AssistNow Online is the only real-time, globally available GNSS assistance service that is backed by a full warranty and support. It is network operator independent and works on all standard mobile communication networks that support internet access, including GPRS, UMTS, and wireless LAN.


Ease of integration

AssistNow is available in all u-blox positioning solutions and can be easily integrated into third-party GNSS receivers. It requires no additional hardware, generates negligable CPU load, and can be installed and operational within a day. It is the only A-GNSS service that extends to modems that are not SUPL (secure user plane location) compliant.  


Delivery through the Thingstream service platform

AssistNow is delivered through the Thingstream IoT service delivery platform, a cloud-based e platform and administration interface for enterprise IoT services. Pressure tested and proven to support the delivery of billions of messages, the platform provides a self-service user interface for users to manage IoT device fleets, optimize service plans, manage billing, monitor events, and control functionality.


Use cases that benefit from CellLocate



With AssistNow Online, automotive solutions such as in-vehicle navigation systems precisely determine their location within seconds when they are switched on and immediately reestablish a position fix when they regain GNSS coverage, for example, upon exiting a parking garage.

Logistics trackers

Logistics trackers

AssistNow extends the battery life of power constrained industrial tracking solutions such as logistics trackers that spend most of their time in power save mode or asleep. With access to real-time satellite data, the logistics trackers shorten the signal acquisition phase and minimize wake time.

women with smart watch


By storing ephemeris predictions transferred from a paired smartphone in their device memory with AssistNow Offline, smart watches, medical wearables, pet and people trackers, and other connected consumer wearables and ehealth solutions considerably reduce the time they need to acquire a first position fix, prolonging battery life and improving end-user experience.

AssistNow is available on all u‑blox GNSS receiver modules and chips including: