Automated Estimation and Mitigation of Wireless Time-Delays in Smartphones for a Robust Integrated Navigation Solution

Y. Zhuang, Z. Syed, C. Goodall, U. Iqbal, N. El-Sheimy

Abstract:	The last decade has witnessed a growing demand for low cost navigation systems. Many of these systems provide accurate positioning for outdoor scenarios by making range measurements to at least four Global Navigation Satellite System (GNSS) satellites. Advanced technologies have empowered the manufacturing of compact, inexpensive, and low power consumption receivers; therefore, providing incentives for innovative applications in numerous domains. One area with potential for exponential growth is the advancement of navigation applications on cell phones. Smartphones, specifically, create limitless possibilities for navigation and positioning applications due to their sophisticated microprocessors, powerful operating systems, and built-in Assisted Global Positioning System (A-GPS) chipset with high-sensitivity capabilities. A smartphone with an A-GPS chipset challenges the basic assumption associated with GNSS positioning: a clear-line-of-sight to at least four satellites with good geometry. Additionally, the smartphones also incorporate cell phone positioning solutions and WiFi-based positioning when available. Unfortunately, the limitations of these technologies become apparent in challenging environments, and for that reason the navigation and positioning of smart-phones cannot be considered continuous and accurate. The gaps in navigation information caused by the limitations of wireless signal updates, such as Global Positioning Systems (GPS) and Wi-Fi, can be filled by using information from inertial sensors. Tri-axial gyroscopes, tri-axial accelerometers, tri-axial magnetometers, and a barometer are the sensors commonly found in smartphones. Due to space and cost requirements of mobile devices, mostly micro-electro-mechanical-system (MEMS) sensors are used. These sensors are self-contained and generally immune to external interference, but their accuracy declines over the long-term. Deterioration in the performance of these sensors is due to various factors that may include sensor biases, drifts, scale factor instability, and misalignment. To achieve continuous, accurate, and affordable navigation and positioning for indoor and urban outdoor environments, integrating wireless signal updates, such as GPS and Wi-Fi, with inertial navigation and multi-sensor systems is crucial. Trusted Positioning Inc., a technology company based in Calgary, Alberta, Canada, turns sensors signals from the smart-phone into seamless navigators that work with any wireless signal update, such as GPS and Wi-Fi. In order to achieve the objective of continuous and accurate navigation and positioning, the signals from wireless sensors are integrated with the self-contained sensor solution. For this to be possible, wireless signals must be time synchronized without any delay to depict current system dynamics. The time delay and synchronization error of wireless signals decreases the accuracy of real-time integrated navigation systems. The time delay of each receiver is independent and affected by a number of factors. Two of the most important factors are (1) the type of the platform used for processing on the smartphone, and (2) the operating system (OS) running on the smartphone. Some A-GPS receivers used in smartphones may also apply modeling techniques on their navigation solution, which can also adversely affect the performance of the integrated navigation solution. It is observed that the application of some GPS measurement modeling techniques in smartphones can cause substantial delays. These delays in GPS measurement can even cause the navigation solution to diverge in specific situations. The objective of this paper is to present an automatic tool that can detect and estimate the time delay experienced by GPS receivers of smartphones and tablets. This estimated time delay is then used to provide a robust navigation solution for all scenarios that mitigates the time delay effect of receivers and provides 3D positioning even when satellite signals are degraded. The delay in the measurement may be caused by intermission between actual information and projected information on the smartphone due to the OS limitations or it may be due to the underlying model within the GPS receiver that is used to produce the GPS PVT solution. Initially, detailed analysis of these time delays along with their estimation will be discussed. Subsequently, the focus will be shifted towards the algorithms developed to diminish the time delay effect and to enhance the performance of the integrated navigation system. The delay analysis takes into consideration the multitasking aspect of the smartphone, and imperative steps, such as integration of multiple measurements to provide the navigation solution. The delay estimation and mitigation tool shows improvement in the real-time integrated navigation solution for the specific situations that are usually affected by such delays, thus providing a more robust, reliable and improved overall solution. The effectiveness of the proposed algorithm is verified on the commercially available Windows 8, Android, and QNX operating systems in smartphones and tablets, in different real-life tests in walking and driving modes, and in both challenging and open sky GPS scenarios. The effects of delay on the navigation solution in straight-line portions and on turns will be discussed and presented in both walking and driving modes. The effect of time delay on different scenarios such as texting mode, on the ear, in the pocket, in a backpack, and on the belt will also be briefly discussed. Real-time results for these scenarios will be compared to the real time results when the techniques were disabled to evaluate the performance. The comparison demonstrates the advantage of using the proposed techniques to estimate and diminish the time delay experienced by signals from wireless sources, such as GPS. Ultimately, this comparison will advocate the use of these techniques to enhance the performance of real-time systems for continuous and accurate navigation and positioning.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	667 - 676
Cite this article:	Zhuang, Y., Syed, Z., Goodall, C., Iqbal, U., El-Sheimy, N., "Automated Estimation and Mitigation of Wireless Time-Delays in Smartphones for a Robust Integrated Navigation Solution," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 667-676.
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