# Native Smartphone Single- and Dual-Frequency GNSS-PPP/IMU Solution in Real-World Driving Scenarios
## 5 Conclusions and Future Work  
This paper presents several noteworthy contributions by integrating single- and dual-frequency GNSS observations with inertial measurements from native smartphone sensors. A total of five datasets were collected from three days of road tests in suburban driving environments were analyzed and based on these investigations, this paper addresses the posed questions:  
Figure 16: Correlation of the horizontal errors on the number of satellites. Figure 15: Time series of estimated GPS clock offset and corresponding clock difference. (**a**) Estimated GPS clock offset. (**b**) Estimated GPS clock difference of adjacent epochs. _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?_ Verified by kinematic experiments, single- and dual-frequency PPP (SFDF-PPP) processing captures the essence of single-frequency and dual-frequency PPP processing strategies as all single-frequency signals (GREC), as well as dual-frequency signals including GPS L5 and Galileo E5a are utilized. SFDF-PPP processing with an average of 43.6 observations from all GREC constellations lead to an overall 6.8 m horizontal rms and 3.2 m of 95 th percentile horizontal error, which outperforms other PPP strategies. 2. _How does smartphone IMU dead-reckoning perform compared to other low-cost MEMS IMU? And how does the inclusion of the smartphone inertial sensor affect PPP solutions?_ Through the dead-reckoning experiments, it was found that the smartphone IMU is capable of providing metre-level positioning accuracy for an outage of less than 10 s with good bias estimation, which is comparable to that of the more capable Xsens IMU. Furthermore, the inclusion of the smartphone inertial sensor can reduce GNSS outliers and provide continuous and accurate navigation solutions in GNSS challenged environments. In addition, significant levels of 59%, 66%, and 72% improvement in overall horizontal rms can be observed from single-frequency PPP, dual-frequency PPP, as well as single- and dual-frequency PPP, respectively. 3. _What is the \"best\" positioning performance that smartphones can achieve with multi-GNSS PPP/IMU integration in real-world driving environments?_ Based on these investigations, single- and dual-frequency PPP/IMU integration is an optimal solution among other strategies for smartphone positioning. The general suburban performance statistics show that smartphones can achieve 1.9 m overall horizontal rms with 1.0 m standard deviation in real-world driving scenarios with the consideration of multiple multipath profiles, which have not been seen in previous studies. Future work will utilize additional holonomic and non-holonomic constraints for vehicle motion and explore the impacts of vehicle-smartphone relative motion when drivers move the phone. Furthermore, this work will be extended to more complex and obstructed environments with an adaptive EKF and fusion with additional sensors. Conceptualization, D.Y., S.Y. and S.B. ; Methodology, D.Y. and S.Y. ; Software, D.Y. ; Validation, D.Y. and S.Y. ; Writing--Original Draft Preparation, D.Y. and S.Y. ; Writing--Review and Editing, S.B. ; Supervision, S.B. All authors have read and agreed to the published version of the manuscript. Funding was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC). Data Availability Statement: The data presented in this study are available from the corresponding author on reasonable request. Acknowledgments: The authors would like to thank their colleagues at the GNSS Laboratory for support in collecting field data and discussing technical aspects of this work. In addition, the authors would like to acknowledge the data contribution from the International GNSS Service (IGS), German Research Centre for Geosciences (GFZ), and Centre National d'Etudes Spatiales (CNES).