Differential Global Navigation Satellite System

Description

DGANSS is a network-assisted positioning technology standardized in 3GPP that delivers differential correction data to mobile devices to improve the accuracy of Global Navigation Satellite System (GNSS) measurements. The system operates by having reference stations at precisely known locations continuously monitor GNSS signals from multiple satellite constellations (GPS, GLONASS, Galileo, BeiDou). These reference stations calculate the differences between the measured satellite positions and their known theoretical positions, generating correction data that accounts for various error sources including ionospheric and tropospheric delays, satellite clock errors, and ephemeris inaccuracies.

The architecture involves several key components: Location Measurement Units (LMUs) or DGANSS reference stations that collect raw GNSS measurements, a DGANSS server that processes these measurements to generate differential corrections, and the cellular network infrastructure that delivers these corrections to User Equipment (UE). The corrections are transmitted over standardized interfaces between network elements, typically using protocols defined in the 3GPP specifications. The UE receives both the raw GNSS satellite signals and the differential corrections via the cellular network, then applies these corrections to its position calculations to achieve significantly improved accuracy.

The differential corrections can be delivered in different formats depending on the implementation and requirements. Real-time kinematic (RTK) corrections provide centimeter-level accuracy for specialized applications, while standard differential corrections typically achieve sub-meter to meter-level accuracy. The system supports various delivery methods including point-to-point connections for individual UEs and broadcast methods where corrections are transmitted to multiple devices simultaneously. DGANSS integrates with existing 3GPP positioning architectures, working alongside other positioning methods like Observed Time Difference of Arrival (OTDOA) and Assisted GNSS (A-GNSS) to provide comprehensive location services.

In operation, the DGANSS server continuously computes correction parameters based on inputs from multiple reference stations to ensure coverage and reliability. These corrections are then formatted according to standardized message structures (such as RTCM SC-104 or proprietary formats) and delivered through the cellular network's control or user plane. The UE's positioning engine combines the satellite measurements with the received corrections using algorithms that typically involve weighted least squares or Kalman filtering techniques to compute the final position fix. This hybrid approach leverages both satellite signals and terrestrial network infrastructure to overcome the limitations of standalone GNSS, particularly in challenging environments like urban canyons or indoors where satellite visibility is limited.

Purpose & Motivation

DGANSS was developed to address the accuracy limitations of conventional GNSS positioning, which typically provides 5-10 meter accuracy under ideal conditions but degrades significantly due to atmospheric effects, satellite clock errors, and multipath interference. These limitations were particularly problematic for applications requiring precise location information, such as emergency services (E911/E112), autonomous vehicle navigation, precision agriculture, and surveying. The differential approach had been successfully used in specialized terrestrial systems but required dedicated infrastructure; integrating it with cellular networks made high-accuracy positioning widely accessible.

Before DGANSS, cellular networks primarily offered network-based positioning methods like Cell-ID and OTDOA, or assisted GNSS (A-GNSS) which helped with faster acquisition but didn't significantly improve accuracy. Standalone differential GNSS systems existed but required separate receivers and subscription services, limiting their adoption. DGANSS leveraged the existing cellular infrastructure to deliver corrections efficiently, creating a standardized approach that could be implemented across different network operators and device manufacturers. This integration was particularly important as location-based services became more demanding and regulatory requirements for emergency caller location became stricter.

The creation of DGANSS was motivated by the growing need for reliable, high-accuracy positioning that could work in various environments without requiring additional user equipment. By utilizing the cellular network's broadcast capabilities or dedicated data channels, DGANSS made centimeter-to-meter level accuracy feasible for mass-market devices. This enabled new applications and services while improving existing ones, creating business opportunities for network operators and enhancing public safety through more precise emergency location capabilities.

Key Features

• Provides differential corrections for multiple GNSS constellations (GPS, GLONASS, Galileo, BeiDou)
• Delivers corrections via cellular network control or user plane
• Supports both real-time kinematic (RTK) and standard differential positioning
• Integrates with existing 3GPP positioning architecture and protocols
• Enables centimeter to meter-level accuracy depending on implementation
• Utilizes network of reference stations for correction calculation

Evolution Across Releases

Defining Specifications