Precise Point Positioning (PPP)

Being able to determine a device’s position anywhere in the world is crucial to many applications. From products that will be sold in a range of geographical markets to portable devices operating across large distances, the ability to achieve fast, high-precision positioning data globally, without the need to select local infrastructure, is essential.

Positioning signals from global navigation satellite system (GNSS) satellites alone cannot enable the level of accuracy required in certain use cases. This is where correction data is needed. PPP correction services are one option to consistently achieve sub-20 cm-level accuracy  in real-world use. Applications for which PPP correction services are well-suited include industrial automation, smart construction, precision agriculture, rail, maritime, and robotics.

Why do we need correction data?

GNSS signals enable devices to calculate their position in the world. GNSS receivers work out their location by multiplying the speed of light by the time taken for the satellite signal to reach them. However, various factors impact these signals and, by extension, the accuracy of the calculated position .    

Factors that influence GNSS signals include:

• Satellite orbit errors: Differences between a satellite’s predicted orbit and its actual orbit.
• Satellite clock errors: Differences between a satellite’s onboard clock time and the GNSS system time of the constellation.
• Code and carrier phase biases: Variations between the GNSS signals transmitted by a satellite, e.g., GPS L1 vs L2C vs L5. These introduce errors in pseudo-range (code biases) and carrier-phase (phase biases) measurements.
• Atmospheric conditions: Ionospheric and tropospheric delays impact signals as they pass through the atmosphere.      

While the factors above can be mitigated using PPP correction services, other variables are environment or hardware-dependent:

• Multipath interference: Significant in urban or obstructed environments, where signals reflect off surfaces before reaching the antenna.
• Receiver clock errors: Internal timing variations within the device itself. While correction services cannot "fix" local hardware drift, u-blox modules utilize high-quality TCXOs to minimize these effects, providing the stable timing foundation necessary for high-precision convergence.

As a result of these factors, the position accuracy of a GNSS receiver varies significantly depending on the receiver's capabilities and the environment.

For a standard single-band, multi-constellation receiver, horizontal accuracy typically sits within the 1.5m to 2.0m (CEP 50%) range under open-sky conditions. While multi-band (L1/L2/L5) receivers can improve this by internally mitigating ionospheric errors, they still lack the correction data for satellite orbit and clock biases necessary to break the meter barrier reliably.

To obtain the consistent decimeter, or even centimeter-level, accuracy required by many real-time applications, each end device requires access to high-fidelity correction data. By addressing the space-segment and atmospheric errors discussed above, these services allow the navigation filter to achieve high-confidence convergence, transforming a meter-level estimate into a precise, actionable position.

What are PPP correction services, and how do they work? 

PPP services are one option for obtaining greater levels of positional accuracy when using GNSS. PPP correction data is broadcast as a one-way stream from the service provider to end devices, which enables these services to scale and support very large deployments cost-effectively. Data can be delivered via GNSS satellites, dedicated satellites (typically in geostationary orbit) using the L-band, or over the internet.

When PPP correction data reaches the receiver, it is applied to the measurements the receiver has collected from multiple GNSS satellites.

This takes place in a navigation filter such as an Extended Kalman Filter (EKF) or similar estimation algorithm. The result is an estimation of the position, clock error, and other parameters of the receiver.  

The result is a much more precise global position estimation for the receiver. The corrected position data can be fused with other sensors to control the movement of a machine or as an instantaneous reference point for a construction monitoring report. 

What GNSS errors do PPP services correct?

Different variants of PPP service exist. Most of them provide clock, orbit, and code bias corrections, but the presence of additional corrections varies. This has a significant impact on the position accuracy and convergence time a receiver can achieve.

The table below compares different correction service types and illustrates these differences. 

PointPerfect Flex (PPP-RTK) provides regional atmospheric corrections, enabling fast convergence when used with a suitable receiver, such as a multi-band model from the u-blox F9, F20 or X20 family. It offers excellent performance, reaching accuracy of 3-6 cm, in its coverage areas. Products that sell or operate all around the world may require global coverage.

By contrast, classical global PPP services don’t include atmospheric correction data and suffer from long convergence times to achieve full accuracy. Convergency times can lasts as long as 20-30 minutes. However, advancements in GNSS receiver technology blend more powerful processors with all-band reception, which can make PPP a viable option or even optimal solution for some high-precision applications. To achieve the best convergence times of between 1-5 minutes, signals are selected to maximize the separation between different GNSS signal frequencies. For this reason, the all-band capability and specifically L6/E6 signal support have a major impact.

To achieve cm-level precision, the receiver must be able to resolve carrier-phase ambiguities. In addition to the highest-quality clock, orbit and code bias corrections, this requires phase bias corrections to be included. PPP-AR and PPP-RTK services include these phase bias corrections, enabling significantly improved accuracy compared to classical PPP solutions, as shown in the table above.

Lastly, in a PPP-RTK service, regional ionospheric corrections account for the vast majority of the data payload, whereas PPP services by design omit these bandwidth-intensive atmospheric corrections to enable global scalability and significantly reduced data transmission requirements. This streamlined data footprint allows for consistent, high-precision positioning even over communication links with minimal transmission capabilities, such as constrained L-band satellite channels or low-power wide-area networks (LPWAN), offering OEMs a cost-effective and operationally efficient path to deploying decimeter-level accuracy worldwide while avoiding an asset-heavy approach requiring both tightly spaced reference stations and expensive communications infrastructure.

What PPP services exist today?

Product designers can choose from a number of free and commercial PPP correction services.

u-blox PointPerfect Global

u-blox PointPerfect portfolio of correction data services is expanding to include PointPerfect Global (PPP-AR) alongside the existing PointPerfect Flex (PPP-RTK) and PointPerfect Live (network RTK)  service. This comprehensive offering ensures that users can achieve the highest possible positioning accuracy by automatically leveraging the best available infrastructure for their specific location. By providing a consistent, high-accuracy alternative in regions where local RTK networks or SBAS coverage are unavailable, these services allow OEMs to deploy a single, scalable solution that maintains decimeter-level performance across diverse geographical markets.

Galileo High Accuracy Service (HAS)

While still evolving, the Galileo High Accuracy Service (HAS) is arguably the most significant development in free-to-use PPP corrections. Its value proposition lies in its unique delivery mechanism and global accessibility, offering an "out-of-the-box" high-precision experience that removes traditional barriers to entry.

The standout feature of Galileo HAS is its distribution. Correction data is transmitted directly from the Galileo satellite constellation on the E6 signal (within the L6 band).

• Infrastructure-free: Unlike L-band services delivered via a few geostationary satellites, which can be low on the horizon and prone to "radio shadows" or obstructions, Galileo HAS signals come from every satellite in the constellation.
• Operational Simplicity: For OEMs, this eliminates the need for cellular modems, SIM cards, or third-party service and data   subscriptions. Furthermore, because the corrections are embedded in the GNSS signal, there is no requirement for a separate, dedicated L-band receiver. A compatible all-band receiver and antenna, such as the u-blox ZED-X20P or ZED-X20D, are the only requirements to unlock decimeter-level accuracy.

Galileo HAS is designed to scale in performance. While currently in its initial phase, the roadmap committed by the European Union Agency for the Space Programme (EUSPA) outlines a clear path to "Full Service" by Q4 2026:

• Service Level 1 (Global): Provides corrections for orbit and clock errors, as well as code and phase biases. This level targets an accuracy of better than 20 cm under favorable conditions, with a convergence time of less than 300 seconds.

Technical Note: While phase bias transmission is key to reaching these accuracies, users should monitor the phased rollout as EUSPA optimizes these streams toward the 2026 full-service milestone.

• Service Level 2 (Regional - Europe): By including atmospheric (ionospheric) corrections, Service Level 2 will significantly accelerate performance, bringing convergence times below 100 seconds across the European continent.

Galileo HAS offers a compelling "global SKU" strategy. Because the reach is global and the delivery is embedded in the GNSS signal itself, manufacturers can develop a single hardware solution that works worldwide without managing region-specific contracts or local hardware variances.
This creates a simplified integration path where high-precision positioning is no longer a complex add-on, but a standard, embedded feature.

Regional PPP Alternatives: 

Alternatives to Galileo HAS include China’s BeiDou PPP-B2b, Japan’s MADOCA-PPP, and SouthPAN PPP, a joint initiative of the Australian and New Zealand governments.   They present a "fragmentation tax" for global OEMs. These services rely on regional reference stations and the corrections are only valid within a specific region. The OEM is left to stitch together many regional services throughout the development process. By contrast, Galileo HAS and u-blox PointPerfect Global provide true global platforms.

What capabilities does your product need to use PPP services?

For PPP to be a viable option in dynamic applications, several key criteria need to be met. As discussed, the receiver must be all-band, including L6/E6/B3, and powerful enough to handle the complex calculations required for PPP processing. Products built on the u-blox X20 platform are capable of this.

In addition, the correction service itself plays a crucial role. It must include carrier-phase bias corrections and support as many constellations and frequency bands as possible. Ideally, all global GNSS systems. 

Careful antenna design is also essential for any high-precision solution because multipath remains a significant challenge when trying to obtain the highest levels of accuracy.  As the market evolves, we expect a growing range of all-band antennas to become available, catering to diverse budgets and form-factor requirements. One option for designers is the u-blox all-band ANN-MB2 antennas, which can provide a highly cost-effective way of achieving the required performance for many applications.

PPP: A global solution for OEMs

Together, these advancements enable a uniform, globally scalable, high-precision solution that doesn’t rely on local infrastructure. This unlocks new possibilities for OEMs to seamlessly integrate high-precision positioning into their products and services. With this, cm-level navigation can be deployed at scale, eliminating the burden on end users to source and integrate correction services themselves, or negotiate region-specific contracts, licensing, and hardware. Rather than presenting a fragmented and complex challenge, these new technologies allow high-precision GNSS to be seamlessly integrated as an embedded feature, fully operational upon deployment.