Employing Spatial Analysis in Indoor Positioning and Tracking Using Wi-Fi Access Points Song Gao Sathya Prasad Department of Geography Applications Prototype Lab University of California, Santa Barbara Esri Inc., Redlands CA 93106, USA CA 92373, USA [email protected] [email protected] ABSTRACT Bluetooth sensors [29, 33]. Positioning is the key compo- A practical WiFi-based positioning system has to be adapt- nent to support smart mobility studies, trajectory data min- able to the variations of indoor environmental dynamic fac- ing and travel related applications [43, 36, 40]. It is well tors. In this work, we propose a novel Wi-Fi indoor posi- known that GPS-enabled devices work well for positioning tioning and tracking framework which employs the spatial in outdoor environments but not in indoor environments be- analysis and image processing techniques. The Wi-Fi sur- cause of the signal obstructions and attenuation[26]. How- faces can be dynamically constructed and updated and thus ever, as reported in a national human activity pattern survey help to address the challenges of signal spatial heterogene- (NHAPS), people spend an average of 87% of their time in ity and environmental variations. A mobile app for indoor enclosed buildings and about 6% of their time in enclosed positioning application has been developed as a proof of con- vehicles [19]. There is a high-demand for indoor positioning cept. Based on the experiments we conducted at the Esri technologies. In [44] the researcher systematically compare campus, this method can achieve about 2-meter positioning three dominant positioning technologies: Assisted-GPS, Wi- accuracy. The proposed methodology and theoretical frame- Fi, and Cellular positioning. Their pros and cons are dis- work can guide engineers to implement cost-effective indoor cussed in terms of coverage, accuracy and reliability. It re- positioning infrastructure, and thus offer insights on future ports that Assisted-GPS obtains an average median error of smart campus applications. The introduced spatial analy- 8m outdoors while Wi-Fi positioning only gets 74m of that sis and geoprocessing workflow may also bring the attention and cellular positioning has about 600m median error in av- of GIScientists to make more efforts to conquer the indoor erage and is least accurate. However, high-resolution GPS or positioning and tracking challenges. Assisted-GPS positioning chipsets don't work well in indoor environments due to limited satellite visibility; and thus a variety of indoor positioning technologies and systems have CCS Concepts been designed and developed to increase the indoor posi- •Information systems ! Mobile information pro- tioning accuracy. cessing systems; Spatial-temporal systems; Loca- The widely use of Wi-Fi access points for Internet connec- tion based services; Geographic information sys- tion in hotels, offices, coffee shops, airports and many other tems; Global positioning systems; fixed places makes Wi-Fi become an attractive technology for the positioning purpose. Location positioning systems Keywords using wireless area local network (WLAN) infrastructure are considered as cost-effective and practical solutions for Indoor positioning; Spatial analysis; WiFi fingerprinting indoor location estimation and tracking [7]. There is almost no extra hardware or other infrastructure investment, which 1. INTRODUCTION is different from other indoor positioning technologies such In the era of mobile age, location-based systems and ser- as low-energy Bluetooth sensor networks or radio-frequency vices become more and more popular in people's daily life, identification (RFID) systems. Conventional methods for such as searching nearby points of interest (POI), way find- indoor positioning are based on time of arrival, time differ- ing and navigation. There has been growing interest among ence of arrival and angle of arrival of radio signals transmit- researchers in studying human mobility patterns based on ted by mobile stations [30]. Another type of WLAN posi- the data collected from location-awareness devices, e.g., tioning method unitizes the fingerprinting idea to determine GPS-enabled devices [45, 39], cellular phones [13, 18], and a receiver's location via clustering and probabilistic distri- butions [42]. The accuracy of localization is dependent on Permission to make digital or hard copies of all or part of this work for personal or the separation distance between two-adjacent Wi-Fi refer- classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation ence points and the transmission range of these reference on the first page. Copyrights for components of this work owned by others than the points [5]. One challenge that WLAN indoor positioning author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or techniques face is the spatial heterogeneity of Wi-Fi signal republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]. surfaces caused by the signal path loss because of absorp- ISA 16, October 31-November 03 2016, Burlingame, CA, USA tion, reflection and refraction by the surrounding environ- c 2016 Copyright held by the owner/author(s). Publication rights licensed to ACM. ment. Thus the physical radiation models need complex ISBN 978-1-4503-4585-9/16/10. $15.00 parameter estimation and empirical fitting. Spatial analysis DOI: http://dx.doi.org/10.1145/3005422.3005425 techniques can be employed in dealing with geometric, topo- In an indoor environment equipped with equal to or large logical, and geographic properties which can help to capture than three Bluetooth low energy (BLE) beacons, the loca- better indoor environment and to construct more accurate tion of a target mobile device with Bluetooth can be de- Wi-Fi surfaces for indoor positioning and tracking purpose. termined using classic positioning approaches (see Section In this research, we propose a novel geoprocessing-based 2.2 in detail). In this way, location-dependent triggers, no- framework and develop a mobile application for real-time tifications and tracking activities can be enabled by em- indoor positioning and tracking using Wi-Fi access points. ploying multiple BLE beacons. There are several popular The goal of this study is to explore how accurate Wi-Fi in- BLE beacon-positioning protocols and technology available door positioning with the support of spatial analysis can online, including Apple iBeacon1, Google Eddystone2 and achieve. The following of this paper is organized as follows. Gualcomm Gimbal3, which guide developers to implement In Section 2, we review some related work and discuss the up-to-date indoor positioning and tracking applications. state of the art in indoor positioning technologies. Our pro- Radio-frequency Identification (RFID): is a general posed theoretical framework towards indoor positioning and term used for a system that communicates using radio waves tracking, and detailed methods are introduced in Section 3. between a reader and an electronic tag attached to an ob- The system implementation and experiments are described ject. Comparing with Bluetooth technology, RFID systems in Section 4, which is followed by discussions in Section 5. usually comprise of readers and tags that store relatively We conclude and give a vision for future work in Section 6. limited information about the object such as location and attribute information. Those tags can be activated and send 2. LITERATURE REVIEW out stored information if they receive the signal from RFID readers within certain distance thresholds, which can be 2.1 Indoor Positioning Technologies used to estimate the reader's location and to show relevant information. Currently RFID positioning and tracking sys- In general, indoor positioning technologies can be classi- tems are widely used for asset tracking, shipments tracking fied into two broad categories: radio-frequency-based (RF) in supply chains, and object positioning in retailing places and non-radio-frequency-based (NRF) technologies. The RF and shopping malls. group includes but not limited to WLAN, Bluetooth, and Because of sensor diversity and positioning challenges in RFID systems, while the NRF group contains ultrasound, various indoor environments, there is also an increasing magnetic fields, and vision-based systems. Researchers have trend towards combining and integrating different sensor made great efforts in the field of indoor positioning using networks to get a better spatial coverage and position ac- these sensors and technologies [17, 11, 23, 15, 21, 24, 20]. curacy than using single data source. In [9] researchers in- The spatial coverage area and positioning accuracy of those tegrate Wi-Fi and inertial navigation systems to get perfor- different technologies have been reviewed by [26]. Here, we mance close to meter by fusing pedestrian dead reckoning only briefly discuss the RF technologies that are most popu- and Wi-Fi signal strength measurements. lar in the current market share and face several challenging issues to investigate. 2.2 Indoor Positioning Methods Wi-Fi: The Institute of Electrical and Electronics Engi- neers (IEEE) 802.11 work group [14] documents the stan- The following methods usually work for both outdoor and dard use of Wi-Fi technology to enable wireless network indoor environments, but we emphasize the indoor case here. connections in five distinct frequency ranges: 2.4 GHz, 3.6 Note that those methods can be applied in most radio- GHz, 4.9 GHz, 5 GHz, and 5.9 GHz bands. The wireless frequency-based sensors, such as Wi-Fi and Bluetooth. networks are widely implemented in many types of indoor 2.2.1 Geometric Approaches buildings in which wireless access points are usually fixed at certain positions. Those access points allow wireless de- In geometry, trilateration is a method to determine the vices (e.g., mobile phones, laptops and tablets) to connect target location of a point by measurement of distances to to a wired network using Wi-Fi technology.