SpyLoc: a light weight localization system for smartphones

In this paper, we propose and addresses the challenge of designing a light-weight high-accuracy indoor/outdoor localization system (SpyLoc) for off-the-shelf smartphones. In SpyLoc, we want to leverages both the acoustic interface (microphone/speaker) and the Wi-Fi interface at the kernel-level of the smartphones as well as the inertial sensors in the smartphones to achieve high localization accuracy. In the ranging-based approach, we utilizes the RF-Beep ranging scheme[?], and in dead reckoning-based approach, we fuses the inertial sensors of the smartphone to estimate the direction and the distance of user's movements. In RF-Beep [?], we develope a ranging scheme that utilizes the Time-Difference-of-Arrival (TDoA) between the acoustic and the radio-frequency (RF) signal. The RF-Beep basically leverages the slow propagation speed of the acoustic signal with respect to the RF signal to estimate the relative range. The well known acoustic range based localization scheme, Cricket [?] also utilizes the same concept of using the difference in arrival times of concurrent transmissions of radio and ultrasound signals at the target device to infer the distance. Unlike the Cricket, which was designed with special hardware, our localization scheme is applicable to the smartphones. In RF-Beep, we address the different challenges of implementing such ranging scheme in smartphones by leveraging the existing functionalities of the audio driver and the WiFi driver. Further details on RF-Beep scheme could be found in~\cite{Uddin:RF}. The ranging based localization scheme typically requires at least three reference points (e.g., anchor points), in order to calculate the location. However all these three reference points must be in Line of Sight(LoS) to the target device. In \textit{SpyLoc} localization system, we use the combination of both ranging-based and dead reckoning approaches to reduce the constraint of having three LoS anchor/reference points all the time. The basic idea of the SpyLoc is to leverage the benefits of both the dead-reckoning and the ranging scheme to build a practical localization system. Given the high errors of the inertial sensors, SpyLoc uses a novel ranging scheme based on both the acoustic and WiFi interfaces to mitigate this error in order to improve the localization accuracy. Unlike the ranging-based or RF-based localization schemes that require multiple reference points (e.g., achor points), using the dead reckoning in SpyLoc reduces the required number of reference points to only one reference to locate and track users accurately. This low dependency on ranging scheme make SpyLoc practically applicable to high mobility environment. Finally, In the SpyLoc system, user's device (i.e. smartphone) works autonomously to determine its location. This system does not require any coordination from the nearby smartphones or from a central controller. Furthermore, this localization system does not require user's device to transmit any acoustic signal or RF messages to nearby smartphones. Therefore increasing the number of user's devices have no impact on the complexity of the SpyLoc system, which make SpyLoc a light-weight localization system. In addition, such characteristics make the localization system privacy preserving and energy efficient for the user's smartphone.