Applying Precise-Point Positioning

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GNSS researchers presented hundreds of papers at the 2023 Institute of Navigation (ION) GNSS+ conference, which took place Sept. 11-15, 2023, in Denver, Colorado, and virtually. The following four papers focused on the use of precise-point positioning for various applications. The papers are available here.

Smartphone Positioning Resiliency

Ultra-low-cost GNSS receivers used in smartphones have several drawbacks that include insufficient observations and poor signal reception quality compared to higher-cost receivers. The authors of this article proposed that using native sensors and precise-point positioning (PPP) augmentation can offer resilient smartphone positioning.

During their research, the authors deployed only inertial measurement unit (IMU) and GNSS sensors native to existing smartphones. They were able to achieve a standalone solution using PPP and IMU integration that performed better than standard techniques.

In vehicle experiments with unobstructed sky, the sensor integration algorithm achieved 1.6 m horizontal RMS. This reduced 80% of horizontal errors in GNSS-challenged environments through a tightly coupled GNSS-PPP solution that has not appeared in any other publications according to the authors.

To address resilient smartphone positioning, the authors stated that sensor fusion is also being explored by using smartphone sensors, including IMUs, cameras, and other fusion techniques.

Yang, Yi, Vana, and Bisnath, “Resilient Smartphone Positioning Using Native Sensors and PPP Augmentation.”

Multi-GNSS PPP and MEMS IMU Integration for Navigation in Urban Environments

This paper addressed the issue of accurate, precise and continuous navigation in obstructed environments for vehicles. To provide a low-cost lane-level navigation solution for automotive applications, the authors proposed an integrated solution featuring low-cost GNSS PPP and MEMS-based IMUs.

During the authors’ research, they introduced a low-cost, triple-frequency GNSS, a MEMS-based IMU and a patch antenna to achieve decimeter-level accuracy in suburban and urban environments. Low-cost hardware and software were used to bridge GNSS gaps in urban environments to provide a continuous, accurate, and reliable position solution that is novel and has not been previously published, according to the authors.

The low-cost navigation system demonstrated an accuracy of less than a decimeter in the presence of a sufficient number of satellites. During half a minute of introduced GNSS signal loss, the overall RMS of the algorithm was 10% to 40% better than dual-frequency PPP with IMU as the satellite availability was reduced.

The results obtained during partial GNSS availability indicated a step forward in the low-cost navigation area for applications such as low-cost autonomous vehicles, intelligent transportation systems, and more that demand a decimeter level of accuracy.

Vana and Bisnath, “Low-Cost, Triple-Frequency, Multi-GNSS PPP and MEMS IMU Integration for Continuous Navigation in Simulated Urban Environments.”

Message Authentication for PPP/PPP-RTK Data

This paper analyzed candidate schemes for PPP/PPP-real-time kinematic (RTK) data authentication. As current PPP/PPP-RTK services are not authenticated, the motivations behind the authors’ research were the new availability of GNSS authentication services such as the Galileo Open Service Navigation Message Authentication (OSNMA), new PPP/PPP-RTK services such as QZSS Centimeter Level Augmentation Service (CLAS) and Galileo High Accuracy Service (HAS), and more.

In this paper, asymmetric schemes were proposed based on existing standards and compatibility with GNSS messages. Post-quantum cryptographic signatures were also reviewed and discussed. Two of the schemes were selected for analysis: digital signature based on ECDSA, and delayed disclosure based on a hybrid scheme using the TESLA protocol.

Each of the schemes was described in detail for both Galileo HAS and QZSS CLAS. The performance of the schemes in terms of time to receive the corrections message and the increase in the age of the data was analyzed. The analysis was complemented by a review of the CPU consumption at receiver level.

Fernandez-Hernandez, Hirokawa, Rijmen, and Aikawa, “PPP/PPP-RTK Message Authentication.”

Creating Consistent RVIM By Estimating Receiver Biases

Ionospheric augmentation is one of the most important dependences of PPP-RTK. Due to the dispersive features of the ionosphere, the ionospheric information is usually coupled with satellite- and receiver-related biases. This could result in inconsistent ionospheric corrections if a different number of reference stations are involved in the calculation.

In this paper, the authors aimed to introduce a consistent regional vertical ionospheric model (RVIM) by estimating receiver biases. First, they presented the inconsistent ionospheric corrections under sparse networks. Then the RVIM was compared with the International GNSS Service (IGS) final global ionospheric map (GIM) product, and the average of differences between them is 1.13 TECU.

The slant ionospheric corrections were then employed as a reference to evaluate both RVIM and GIM. The RMS values were 1.48 and 2.23 TECU for the RVIM and GIM. Finally, the authors applied the RVIM into PPP-RTK.

The results showed that the PPP-RTK with RVIM constraints improved horizontal errors, vertical errors, and convergence time by 43.45%, 29.3%, and 22.6% under the 68% confidence level, compared with conventional PPP-AR.

Lyu, Xiang, Tang, Pei, Yu, and Truong, “A Consistent Regional Vertical Ionospheric Model and Application in PPP-RTK Under Sparse Networks.”