29 th NATIONAL RADIO SCIENCE CONFERENCE (NRSC 2012) April 10 Ǧ 12, 2012, Faculty of Engineering/Cairo University, Egypt C5. Time Difference of Arrival by IEEE 802.11a, g Based on Practical Estimation S. A. Napoleon 1 , A. S. Omar 2 , S. H. Elramly 3 , S. A. Khamis 1 , M. E. Nasr 1 1 Faculty of Engineering, Tanta University, Tanta, Egypt, e-mail: s.napoleon@tu.edu.eg 2 Faculty of Engineering, Magdeburg University, Magdeburg, Germany, e-mail: a.omar@ieee.org 3 Faculty of Engineering, Ain Shams University, Cairo, Egypt, e-mail: sramlye@netscape.net ABSTRACT Localization and tracking have recently gained a special importance. A common system for positioning in outdoor environment as e.g. the Global Positioning System (GPS) exists already. GPS is useless for indoor positioning because its signals are weakened or even blocked. This motivated the use of another wireless system to accomplish positioning. Wireless Local Area Network (WLAN) Access Points (APs) are already installed inside buildings, making them a suitable replacement for GPS. Many techniques exist for extracting and calculating location information form the WLAN signals. Among them are super resolution algorithms such as Root Multiple Signal Classification (Root-MUSIC), Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT), and Matrix Pencil (MP). Many researchers applied these techniques on a specially designed WLAN signals. To apply these techniques in real applications, they should be tested on true wireless signals. In this paper, the performance of super resolution techniques is practically tested on a WLAN transceiver using the communication signals without any modifications. Keywords: WLAN, TDoA, Super Resolution, Root-MUSIC, ESPRIT, Matrix Pencil I. INTRODUCTION Localization and tracking have recently gained a special importance. Existing outdoor positioning systems like GPS are for indoor applications because their signals are weakened or even blocked by walls and other obstacles inside buildings. This fact motivated the use of another wireless system to accomplish positioning. WLAN APs are already installed inside buildings, making them the suitable indoor replacement of GPS. Many techniques exist for extracting and calculating location information form WLAN signals. Among them are super resolution algorithms such as Root-MUSIC [1], ESPRIT [2], and MP [3]. The previous studies used a specially designed WLAN frames as in [3] and [1] to test these algorithms. A WLAN Orthogonal-Frequency-Division-Multiplexing (OFDM) frame in the WLAN standards IEEE 802.11a and g includes two synchronization characters which are the Short Training Symbols (STS) and the Long Training Symbols (LTS). They are important in frame synchronization and channel estimation and fully discribed in [4]. In this paper, both LTS and STS are used for Time Difference of Arrival (TDoA) calculation to find which super resolution technique will be more accurate with each character. The paper is organized as follows: Section II describes OFDM in the physical layer for the WLAN IEEE 802.11a and g. Section III gives a short description of super resolution algorithms. In section IV, the equipment setup is descried. Section V is dedicated to results and discussions. Section VI concludes the paper. II. PHYSICAL LAYER FOR WIRELESS LAN IEEE 802.11 The IEEE 802.11 sets the specifications for a series of WLAN technologies. Table 1 shows some of these specifications for both the a and g amendments of the IEEE 802.11 standards. As it is clear, they support the Table 1: The IEEE 802.11 a, g Specifications IEEE 802.11a IEEE 802.11g Frequency band 5 GHz 2.4 GHz Channel separation 20 MHz 25 MHz Max. data rate 54 Mbps 54 Mbps Carrier type OFDM OFDM & DSSS OFDM for transmitting data through the air interface while Direct Sequence Spread Spectrum (DSSS) is only supported in the IEEE 802.11g for back compatibility with the IEEE 802.11b standard which employs DSSS only. OFDM can provide data rates up to 54 Mbps while DSSS cannot provide more than 11 Mbps [4], which makes OFDM the most important and usable transmission technique in both a and g standards. The transmitted OFDM 185 978-1-4673-1887-7/12/$31.00 ©2012 IEEE