# Native Smartphone Single- and Dual-Frequency GNSS-PPP/IMU Solution in Real-World Driving Scenarios
## 1 Introduction
For smartphone navigation, there is a stronger need due to poor GNSS measurement quality, as well as a tendency from users to acquire positioning solutions in obstructed environments such as urban canyons. Traditionally, it has been shown that during GNSS outages, low-cost MEMS (Micro-ElectroMechanical System) IMUs have the potential to achieve decimetre-level accuracy over 60 s when coupled with geodetic-grade GNSS receivers in PPP mode [29], or at the metre-level for a few seconds with low-cost, single-frequency GNSS receivers [30]. Fusing more recently available low-cost, dual-frequency GNSS receivers in PPP with MEMS-IMU produces decimetre-to-metre-level accuracy during 30 s of outages with four visible satellites, and dual-frequency processing gives a significant edge of 10 times improvement over single-frequency processing [31]. The emergence of the latest smartphone-grade, or ultra-low-cost GNSS chipsets has led to studies investigating a native sensor fusion scheme using the onboard inertial sensors of smartphones [32; 33; 34]. However, in smartphone PPP processing, there is little literature which investigates GNSS-PPP/IMU fusion specific to the ultra-low-cost GNSS receivers and IMUs. An earlier study by the authors, has shown the potential of bridging solution gaps produced from GNSS outages, while maintaining a metre-level solution [35] using smartphones wrapped on top of vehicles. It has yet to been seen if a feasible GNSS-PPP/IMU processing scheme that brings the performance to a similar level in real-world driving environments where complex obstruction and multipath profiles are involved. In spite of this remarkable progress, the major limitations restricting the use of smartphones for precise navigation applications are their low-quality noisy measurements and positioning degradation during GNSS outages. Thus, utilizing single- and dual-frequency (SFDF) observations, as well as IMU information are vital for smartphone navigation. Ref. [36] proposed to use the single-frequency ionosphere-corrected code measurements with dual-frequency ionospheric-free code and phase measurements for low-cost GNSS device position determination, and in this context, ref. [37] proved that this approach would benefit smartphone positioning through walking experiments. While single- and dual-frequency PPP is not a novel concept and there are some studies focusing on SFDF scheme for low-cost and smartphone devices, it should be noted that this paper uniquely explores the benefits of SFDF strategy for smartphone not only in benign environments, but also in realistic (automotive) suburban areas where smartphone GNSS signals tend to be blocked or affected by multipath effects. For this research, this paper also employed the native inertial sensor from smartphones and developed a single- and dual-frequency PPP engine enhanced with ionospheric constraints (PPP-IC). Therefore, the main significant novelties and contributions of this work aim to answer the following research questions:  
1. How does single- and dual-frequency PPP processing improve smartphone GNSS positioning performance and how does it compare with other PPP processing strategies (single-frequency PPP and dual-frequency PPP) in GNSS challenged environments? 2. How does smartphone IMU dead-reckoning perform compared to other low-cost MEMS IMU? How does the inclusion of the smartphone inertial sensor affect PPP solutions? 3. What is the \"best\" positioning performance that smartphones can achieve with multi-GNSS PPP/IMU integration in real-world driving environments?