Nuzzer: A Large-Scale Device-Free Passive Localization System for Wireless Environments (0908.0893v1)

Abstract: The widespread usage of wireless local area networks and mobile devices has fostered the interest in localization systems for wireless environments. The majority of research in the context of wireless-based localization systems has focused on device-based active localization, in which a device is attached to tracked entities. Recently, device-free passive localization (DfP) has been proposed where the tracked entity is neither required to carry devices nor participate actively in the localization process. DfP systems are based on the fact that RF signals are affected by the presence of people and objects in the environment. The DfP concept enables a wide range of applications including intrusion detection and tracking, border protection, and smart buildings automation. Previous studies have focused on small areas with direct line of sight and/or controlled environments. In this paper, we present the design, implementation and analysis of Nuzzer, a large-scale device-free passive localization system for real environments. Without any additional hardware, it makes use of the already installed wireless data networks to monitor and process changes in the received signal strength (RSS) transmitted from access points at one or more monitoring points. We present probabilistic techniques for DfP localization and evaluate their performance in a typical office building, rich in multipath, with an area of 1500 square meters. Our results show that the Nuzzer system gives device-free location estimates with less than 2 meters median distance error using only two monitoring laptops and three access points. This indicates the suitability of Nuzzer to a large number of application domains.

• The paper introduces a novel device-free localization system that uses probabilistic analysis of RSS fluctuations to track entities without devices.
• It employs an offline radio map and real-time signal analysis, achieving a median localization error of less than 2 meters in large indoor environments.
• The system leverages existing wireless hardware, ensuring scalability and improved handling of multipath and non-line-of-sight challenges compared to traditional methods.

Overview of Nuzzer: A Large-Scale Device-Free Passive Localization System for Wireless Environments

The paper, "Nuzzer: A Large-Scale Device-Free Passive Localization System for Wireless Environments," authored by Moustafa Seifeldin and Moustafa Youssef, presents a novel approach to localization in wireless environments without the need for tracked entities to carry any devices. This innovative system leverages existing wireless infrastructure to provide location estimates based on the changes in received signal strength (RSS) caused by entities affecting the radio frequency (RF) environment.

Probabilistic Approach and System Components

Nuzzer exploits device-free passive (DfP) localization, diverging from conventional systems that require device-based active participation. It leverages probabilistic techniques to interpret signal strength fluctuations, using the data from access points (APs) and monitoring points (MPs) within typical wireless networks such as WiFi and WiMax. A major contribution of the paper is the employment of a passive radio map created during an offline phase, which serves as a baseline for comparing future signal strength inferences.

The Nuzzer system operates in two phases: an offline phase to construct the radio map and an online phase for real-time localization. The offline phase involves capturing RSS data in a locale grid, forming the passive radio map. The online phase uses this data alongside probabilistic analyses to compute the probable location of an entity, employing algorithms to maximize conditional probability given observed signals.

Evaluation and Results

The results of the system evaluation reveal striking performance metrics, achieving a median localization error less than 2 meters. This was accomplished using only two monitoring laptops and three APs in a typical office setting of about 1500 square meters. This level of accuracy is maintained even in complex indoor environments characterized by multipath and non-line-of-sight (NLOS) challenges. The utility is evident in domains requiring large-scale coverage and scalability, like intrusion detection or smart building systems.

Comparison with Existing Systems

Nuzzer exhibits several advantages over traditional localization systems:

• Hardware Utilization: It operates using existing infrastructure, requiring no additional hardware investment.
• Scalability and Coverage: Designed to cover extensive areas without line-of-sight restrictions, offering seamless scalability.
• Total Device-Free: Unlike earlier systems such as RADAR or WLAN-based systems that require active signal input from the tracked device, Nuzzer operates without any entity-carried devices.

When compared with advanced techniques such as MIMO radar or Radio Tomographic Imaging, Nuzzer simplifies the hardware requirements and handles complex multipath better in typical environments while demonstrating comparable accuracy.

Future Directions

The introduction of Nuzzer enriches the landscape of passive localization systems by offering a robust, cost-effective alternative to traditional, device-dependent methodologies. Future work anticipated by the authors involves expanding the system to handle multiple entities, enhancing map generation automation, and refining system resilience against environmental dynamics. The pursuit of optimizing AP and MP placement to improve localization accuracy also presents a promising area for continued investigation.

In summary, the Nuzzer system marks a substantial advancement in device-free passive localization, showing how ubiquitous wireless networks can be repurposed for sophisticated tracking applications. Its design principles and demonstrated effectiveness open avenues for pervasive, non-invasive monitoring solutions across broad application spectrums.