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The challenge of stand-alone GNSS
GNSS users expect instant position information. With standard positioning this is often not possible because at least four satellites must be identified, and their complete orbital position data (called Ephemeris) received. Under adverse signal conditions, data downloads from the satellites to the receiver can take minutes, hours or even fail altogether. Assisted GNSS (A-GNSS) accelerates calculation of position by delivering satellite data such as Ephemeris, Almanac, accurate time and satellite status to the GNSS receiver via wireless networks or the Internet. This aiding data enables a GNSS receiver to compute a position within seconds, even under poor signal conditions.
AssistNow A-GPS services
AssistNow Online and AssistNow Offline are u-blox’ end-to-end A-GNSS services for OEM customers and their end users. These services boost GNSS acquisition performance for devices with or without network connectivity. AssistNow Online and AssistNow Offline can either be used alone or in combination. AssistNow A-GNSS services require no additional hardware and generate virtually no CPU load. The system is very easy to implement and can be installed and operational within a day. u-blox wireless modules feature an embedded AssistNow client making integration simple.
With AssistNow Online, an internet-connected GNSS device downloads assistance data from u-blox’ AssistNow Online Service at system start-up. The service works on all standard mobile communication networks that support Internet access, including GPRS, UMTS and Wireless LAN. No special arrangements with mobile network operators are needed to enable AssistNow Online, making this solution network operator independent and globally available. u-blox only sends ephemeris data for those satellites currently visible to the mobile device requesting the data, thus minimizing the amount of data transferred.
With AssistNow Offline, users download u-blox’ Differential Almanac Correction Data from the Internet at their convenience. The correction data is then transferred to the mobile terminal via TCP/IP, serial port, memory card, etc, and can either be stored in the GNSS receiver’s memory or in the memory of the application processor. Therefore, the service requires no connectivity at system start-up and enables a position fix within seconds, even when no network is available.
u-blox provides correction data valid from 1 to 35 days. The size of these files increases with the length of the prediction period, from as little as 3 kB to 90 kB. Positioning accuracy decreases with the length of the correction data duration, with 1–3 day data providing relatively high accuracy and 10–35 day data progressively less accuracy. Regular updates help to ensure a high level of position accuracy.
AssistNow Autonomous is an embedded feature available free-of-charge that accelerates GNSS positioning by capitalizing on the periodic nature of GNSS satellite orbits. GNSS orbit predictions are directly calculated by the GNSS receiver and no external aiding data or connectivity is required. AssistNow Autonomous can be used alone, or together with AssistNow Online or AssistNow Offline for increased positioning speed and accuracy.
Benefits of AssistNow
AssistNow data is collected by u-blox’ global array of satellite receivers, and maintained in real-time on u-blox AssistNow servers accessible via the Internet. For best effort applications, u-blox provides AssistNow free-of-charge to its customers. For applications requiring a guaranteed minimum Quality of Service (QoS), u-blox provides AssistNow Premium which provides guaranteed availability based on a service level agreement and 24/7 support.
u-blox products compatible with AssistNow: