Technology

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24 Nov 2021

High precision positioning

Achieving cm-level accuracy by combining RTK technology and deep expertise in GNSS.

High precision positioning can be achieved by combining global navigation satellite systems (GNSS), such as GPS, GLONASS, Galileo and BeiDou, with real time kinematic (RTK) technology. RTK is a technique that uses the receiver’s measurements of the phase of the satellite signal’s carrier wave. These measurements combined with corrections from a local or virtual base station allow the receiver to solve carrier ambiguities and provide centimeter-level accurate position information to the end user, typically a moving device referred to as the rover.

The demand for scalable high precision technology is growing rapidly, as evident in the automotive world with next generation ADAS and V2X applications, and in robotics with applications such as UAVs and robotic lawnmowers.

However, due to the complexity, size, power, and cost restrictions, existing high precision solutions have been unable to meet the demands of these markets.

Building on the success of our NEO-M8P high precision GNSS module series and drawing on our extensive experience in GNSS positioning technologies, including dead reckoning, multi-band, RTK, and GNSS correction services, we created the u-blox F9 platform. The platform delivers the next level of scalable GNSS high precision technology, which is paving the path for new navigation applications such as unmanned vehicle navigation, automated driving and various machine automation applications.

 

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High precision GNSS solutions are made up of several key components:

  • GNSS satellite signals from multiple constellations
  • A high quality GNSS antenna
  • The RTK algorithm
  • GNSS correction data

HPG solutions enable centimeter to sub-meter accuracy in seconds to minutes, depending on the selection of components, configuration options, and correction data inputs.

 

HPG-solutions-enable-centimeter-to-sub-meter-accuracy

High Precision GNSS with u-blox receiver modules

Our highly integrated high precision GNSS modules are in essence a positioning system - the core of the high precision GNSS solution. Combining satellite signal receivers featuring embedded RTK algorithms, various value adding features, and open interfaces, they allow for easy and efficient integration with communication and correction services.

  • Having all hardware components, critical for the operation in the receiver module, allows for simplified and scalable solution integration.
  • The integrated RTK algorithms and features, verified in thousands of hours in various operation modes, present a significant time saving and performance assurance for the solution integrator.
  • The high freedom in functional configurability of the module, combined with carefully selected default settings, allow integration in software-defined platforms and a wide number of applications, as well as reliable out-of-the-box operation.

In addition, the open hardware and software interfaces, following industry standards, provide unmatched useability and flexibility in implementing various high precision GNSS navigation solution types.

A device with an integrated u-blox high precision GNSS receiver module can be flexibly re-configured also in the field, to operate in the desired solution type, according to the available correction data or service.

By implementing module firmware upgrade functionality on the device, system integrators can allow for upgrades and feature enhancements of the GNSS module even for devices in the field.

High precision GNSS solution types

There are a variety of high precision solution types, based on the correction data input they rely on:

1. Local base: for small area coverage

 

Local_base_for_small_area_coverage

2. Network RTK: for the most demanding needs, regional coverage

 

Network-RTK-for-the-most-demanding-needs

3. PPP-RTK: for widest applicability, continental/global coverage

 

PPP-RTK-for-widest-applicability-continental-global-coverage

Key benefits of u-blox High Precision GNSS technology:

  • Delivers accuracy down to the centimeter-level in seconds
  • Paves the way for high precision navigation, augmented reality, and unmanned vehicles
  • Easy access to RTK, multi-band, and multi-constellation technology for fast time-to-market
  • Compatible with leading correction services for global coverage and flexibility
  • Dead Reckoning option for reliable performance in urban environments
  • Advanced jamming and spoofing detection for highest security

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GNSS Correction Services

The accuracy and integrity of GNSS can be greatly improved by using high quality GNSS corrections. These data streams, wirelessly transmitted to the rover, contain real-time information on GNSS signal errors to GNSS receivers, enhancing their performance and precision, and enabling positioning accuracies down to and below the centimeter level.

GNSS correction services generally fall into two categories, based either on the observation state representation (OSR) or a state space representation (SSR) of the errors. These groups use different techniques, delivery mechanisms, and core technologies to solve the same problem – the mitigation of key GNSS errors (e.g. clocks, orbits, biases, ionosphere, troposphere) in order to enable high precision GNSS performance.

Observation state representation (OSR)

Observation space representation (OSR) correction services are supplied by the legacy GNSS correction services providers. The term observation is used as the core techniques are centered on transferring corrected GNSS observations from the nearest reference station to the rover.

OSR services typically use a standardized format in RTCM v 3.x over IP and the offerings are mainly B2C models focusing on a single geographic region (i.e., a country or state) targeting existing low-volume, niche high precision markets (such as surveying, agriculture, machine control).

While OSR services deliver centimeter-level accuracy provided the rover is within approximately 30 kilometers of the nearest reference station, they require two-way communication with a higher bandwidth, making them difficult to scale up to serve mass market applications.

 

Schematics-of-Observation-state-representation
Benefits:Downsides:
  • Centimeter-level accuracy
  • Local / regional coverage
  • Established standard format
  • Two-way communication
 
  • Higher bandwidth need
 
  • Correction data tailored to each location or vicinity

 

State space representation (SSR)

State space representation (SSR) correction services are the latest generation of GNSS correction services provided by new entrants and the larger legacy providers. The term state is used as the core techniques are centered on using the reference station network to model the key errors over large geographical regions and transferring them to the rover. The rover uses the incoming data to create a local model of the GNSS errors, which it applies directly to the GNSS observations. The performance of SSR correction services depends on which errors are transmitted to the rover device, as detailed in the table below.

 

performance-of-SSR-correction-services

Furthermore, the broadcast nature of SSR corrections enables the service to be more easily distributed over IP and even L-Band satellite communication channels. In addition, providers of SSR services are focusing on scalable B2B models to meet the demands of high precision mass market applications such as in the automotive field.

SSR services achieve centimeter-level positioning accuracies over large geographic areas requiring low bandwidth. Because all roving GNSS receivers rely on the same GNSS correction data stream, SSR services are a good fit for mass market applications.

 

Schematics-of-State-Space-Representation
Benefits:Downsides:
  • Centimeter-level accuracy 
  • Often proprietary formats
  • Global coverage
 
  • One-way communication
 
  • Lower bandwidth need
 
  • Performance levels differentiation
 

 

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