# A Real-Time GNSS/PDR Navigation System for Mobile Devices
## 4 Conclusions  
This article provides an overview of the design and the development of a pedestrian navigation systems using information from different sensors present in smartphones. In particular, it has been highlighted the importance of an accurate technique to determine the individual steps and how crucial a proper implementation of a PLL can be for this goal. To determine the direction of motion at each detected step, an algorithm that evaluates the second harmonic component of the planar acceleration has been developed. From the knowledge of this signal, through analytical and geometric considerations, the direction of motion was calculated using a closed-form mathematical solution. This innovative approach allows to calculate the direction of motion in real time and to use this information in a dead reckoning method for estimating the current position with respect to a North-East local reference frame. It is important to underline that this system has been designed to work with the mobile device in a pocket, being independent of its orientation during the motion activity.  
Moreover, a Kalman Filter for the integration of a pedestrian dead reckoning navigation system with a global navigation satellite system has been developed. A multi-rate filter was developed according to the size varying approach as the satellite system information is not always available. Finally, the algorithm provides the positioning values in real time by updating the latitude and longitude angles in order to show the current estimated position on the map. In order to validate the performance of the system, tests were carried out both in an urban environment, where the accuracy of the GNSS is lost due to the passage between tall buildings, and in an open environment where the visibility of the satellite is clear. Where the GNSS accuracy is high, the best performance filter that continuously uses the GNSS data has the best results, whereas in several situations where the GNSS signal is particularly degraded, the energy saving filter with an appropriate update interval brings some advantages.  
Our current activity is aimed at estimating the saved energy amounts and the update interval: to this aim different time intervals are taken into account by analyzing the battery drain and the energy impact of the processor when processing the GNSS/PDR algorithm. These results will be dealt with in future publications.  
Figure 13: Comparison between the reconstructions performed by the PDR navigation, the GNSS data and the energy saving fusion algorithm with 60 s as interval between two consecutive GNSS activations in an open space environment.  
**Author Contributions:** Conceptualization, M.B., A.M., S.M. and F.S.; methodology, M.B., A.M., S.M. and F.S.; software, M.B., A.M., S.M. and F.S.; validation, M.B., A.M., S.M. and F.S.; formal analysis, M.B., A.M., S.M. and F.S.; investigation, M.B., A.M., S.M. and F.S.; resources, M.B., A.M., S.M. and F.S.; data curation, M.B., A.M., S.M. and F.S.; writing--original draft preparation, M.B., A.M., S.M. and F.S.; writing--review and editing, M.B., A.M., S.M. and F.S.; visualization, M.B., A.M., S.M. and F.S.; supervision, M.B., A.M., S.M. and F.S.; project administration, M.B., A.M., S.M. and F.S. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.