IOSR Journal of Engineering (IOSRJEN) www.iosrjen.org ISSN (e): 2250-3021, ISSN (p): 2278-8719 Vol. 09, Issue 2 (February. 2019), ||V (I) || PP 41-51 International organization of Scientific Research 41 | P a g e IoT Scanning Through Walls Using Wi-Fi C. M. S. Ferreira 1 , J. S. Pereira 1,2,3 , S. P. Mendes 1,2 1 Polytechnic Institute of Leiria, School of Technology and Management, Leiria, Portugal 2 Center for research in Informatics and Communications, Polytechnic Institute of Leiria, Portugal 3 Instituto de Telecomunicações, Leiria Branch, Portugal Corresponding Author: C. M. S. Ferreira Abstract: Earthquakes are one of the most devastating and frightening natural disasters that can be experienced. After such occurrences, it may be vital to identify objects or (living) beings within buildings that have collapsed. In this context the usage of scanning techniques employing Wi-Fi allow an innovative approach to facilitate referred identification. By using wireless technology, this work presents a proposal for the detection and identification of object contours or silhouettes through walls. This goal was achieved by reading the radio signal strength (RSS) variations with an array of affordable IoT (Internet of Things) Wi-Fi antennas. Keywords: Antenna, Emitter, Path loss, Radio Signal Strength (RSS), and Wi-Fi. --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 21-01-2019 Date of acceptance: 05-02-2019 --------------------------------------------------------------------------------------------------------------------------------------- I. INTRODUCTION In recent years there has been a growing interest in IoT (Internet of Things) technologies. The evolution of technology has favored usage of Wi-Fi (Wireless Fidelity) devices that as they become more sophisticated are also smaller, more energy-efficient, and cheaper. The gathering of these factors has attracted not only the research departments of the universities but also the industry in general and the result is the appearance of numerous academic and commercial projects on this subject which in itself is very broad. The work "Holography of Wi-Fi Radiation" [1] is a good example of the use of a coherent light (electromagnetic waves with precisely known amplitude and phase) emitted by Wi-Fi systems. In this work, the radiation that results from the propagation in the space of electromagnetic waves, forms a hologram that allows to identify objects located between the emitter and the receiver. At the same time, there are commercial solutions about the TWI (Through-the-Wall Imaging) subject using RF (Radio-frequency) in security and rescue applications. The majority are Ultra-Wide Band like Cambridge Consultants’ system Prism200 [2]. This is a commercial Through Wall Radar that provides a 3D view through brick or concrete walls over a range of up to 20 meters. This technology provides comprehensive coverage of indoor spaces and has well known advantages over conventional narrow band solutions, but its high cost and the susceptibility to receive interference from signals in overlapping spectral bands and low resolution are major disadvantages that must be considered. On the other hand, as Wi-Fi signals are present in a growing number of buildings all over the world, there are some TWI projects that use Wi-Fi sources to try to detect the position of people or objects inside of buildings. Nevertheless, if it is necessary to detect such targets in a building without a Wi-Fi source this TWI project doesn’t offer an adequate solution. Thus, the purpose of this work is to present a low cost project which can contribute to the detection of objects and living beings within buildings that do not have Wi-Fi Networks. This way, in free space, RF power varies inversely with the square of the distance between the receiver and transmitter. The stronger the power, the higher the signal strength [3] [4]. It is well known that RF signals are influenced by the environment and by other factors [5]. This means that fog, objects, human beings or walls, attenuate signal power between the transmitters and receivers. In addition, it is important to note that the attenuation also depends on the frequency used [3]. RSSI (Received Signal Strength Indicator), describes the total signal power received and is usually expressed in dBm. Additionally, free space path loss model of propagation and Shadowing model are common methods of RSSI signal propagation for WSN (Wireless Sensor Network) [4] [5]. In this work a Raspberry PI 3 was used as a low cost Wi-Fi emitter. The receiver, a directional array composed by sixteen antennas (fig. 1) was prepared to measure RSSI values trough the wall and transmit it to the Raspberry PI. After that, images were computed showing the attenuation of objects like a book shelf or a metal- coated wooden cross, both near a real wall. The number of antennas on the array is related to the resolution, since each antenna will represent a pixel in the image of the TWI system.