PPP-RTK GNSS correction services

What is PPP-RTK? Overcoming GNSS Errors with PPP-RTK Technology

PPP-RTK is a GNSS correction technique that combines PPP's global broadcast coverage with RTK's fast convergence, delivering centimeter-level accuracy within seconds using one-way communication.

A GNSS RTK receiver needs corrections data, because its raw satellite measurements carry errors that limit achievable precision to several meters. These errors are caused by satellite clock drift, atmospheric interference, and slight deviations from the predicted orbits. The receiver itself measures raw satellite signals, but it has no way of knowing how much error is present in those measurements at its specific location. To overcome these issues, GNSS correction services use a variety of techniques, delivery mechanisms, and core technologies to achieve decimeter or even centimeter-level positioning accuracy. 

RTK vs PPP: Traditional GNSS Correction Methods

Conventional real-time kinematic (RTK) GNSS correction services, technically known as observation state representation (OSR), work by measuring GNSS errors from one or several fixed reference stations and transmitting the correction data via IP-based communication to users within a 30-kilometer radius. This method achieves localized, sub 2 cm accuracy in under 10 seconds but requires higher bandwidth and continuous two-way communication between the receiver and the correction provider. This can result in high data costs, limiting support of mass market applications.

RTK correction services typically use a standardized data format like RTCM over IP and focus on a single geographic region targeting high precision applications requiring the highest accuracy and lowest convergence time, such as surveying, agriculture and construction.

Precise point positioning (PPP) GNSS correction services, the foundation of state space representation (SSR), model individual GNSS error "states" (clock, orbit, atmospheric, and bias errors) across large geographical regions, then transmitting that model to the user.  

PPP correction services broadcast at lower bandwidth over large geographic regions using satellite L-band or IP-based communication. Because performance depends on which error states are included in the broadcast, PPP services vary significantly in accuracy and coverage. Unlike RTK, PPP does not require a nearby reference station and supports an unlimited number of users, because it only requires one-directional communication. However, it takes several minutes to achieve decimeter-level accuracy, making it less suitable for dynamic applications such as robotics and autonomous navigation.  

PPP-RTK: High Precision GNSS Corrections with Fast Convergence

PPP-RTK GNSS corrections services combine near RTK-level accuracy and initialization times with the broad coverage of PPP. This hybrid approach delivers 3-6 cm positioning accuracy with rapid initialization times of less than 30 seconds, while maintaining the wide coverage and one-way broadcast advantages of PPP.

PPP-RTK correction services transmit a model of GNSS errors over large geographic areas, including satellite clock and orbit errors, atmospheric delays, and signal biases. The GNSS RTK receiver processes this data and applies corrections to achieve high-precision positioning. Additional statistical data further refines accuracy, enabling precise and reliable navigation for mission-critical applications.

The u-blox PointPerfect Flex PPP-RTK correction service supports both SSR (SPARTN) and OSR (RTCM)-based representation models.  

End-user benefits of PPP-RTK GNSS correction services include: 

	RTK Networks	PPP-RTK Networks  PointPerfect Flex	PPP Networks
Technology	RTK  OSR corrections format	PPP-RTK  SSR and  OSR corrections format	PPP  SSR corrections format  (Some with regional PPP-RTK)
Performance	Sub 2 cm in under 20 sec	3-6 cm in 10-30 sec	<10 cm in 1-30 min
Data Format	RTCM	SPARTN (SSR) / RTCM (OSR)	SSR-compatible correction formats (e.g., SPARTN)
Required Bandwidth	~6 kbit/s	SPARTN: ~0.5 kbit/s  RTCM: ~6 kbit/s	~0.5 - 5 kbit/s
Coverage	Regional / National	Continental   Seamless Performance	Global  Some areas with localized PPP-RTK  Not seamless
Data Stream	Bi-directional	Uni-directional	Uni-directional
Communication	IP-based	IP-based  Satellite L-band	IP-based  Satellite L-band

Error types corrected by various PPP and PPP-RTK techniques

Because performance depends on exactly which error states are included in the broadcast, SSR-based services vary significantly in accuracy, bandwidth, and coverage:

Service Type	Sat.clocks & orbits	Global Iono	Biases	Regional Iono / Tropo	Coverage	Performance
SBAS	█	Regional			Continent	meter in sec
PPP	█	□*			Global	meter in sec
PPP-AR	█	□*	█		Global	decimeter in min
PPP-RTK	█	█	█	█	Continent	centimeters in sec

*service-dependent

Applications for PPP-RTK GNSS Correction Services

As demand for high-precision positioning grows, PPP-RTK technology is becoming a preferred solution for various industries, including:

Autonomous robotic lawn mowers and outdoor ground robots 

They often follow the same precise routes on recurring schedules. They need fast initialization and must work in broad coverage areas without the close ground station coverage required by RTK solutions. The low bandwidth SPARTN data format offered by u-blox PointPerfect Flex reduces transmission costs and power for budget-conscious use cases.  

Drones and unmanned aerial vehicles (UAV) 

UAVs require accurate waypoint tracking, quick convergence of location data, and accurate geo-tagging. Assignments such as delivery or dock station landing must be precise and within centimeters of the intended target.

Precision agriculture

Tractors, sprayers, and other agricultural vehicles that need to improve pass-to-pass accuracy, improve yield or minimize damage to the environment. Farmers can save costs by reducing the volume of seeds planted, as well as limit water pollution and protect land through more efficient use of pesticides, herbicides, and fertilizer.