Wireless positioning using the Signal Strength Difference on Arrival

Location Based Services (LBS) are continuously gaining popularity enabling a new area of innovative applications. The basic functionality needed in order to provide LBS is the user position location. Many localization systems and techniques are already available, but most of the positioning systems used indoors require proprietary hardware and software, or the user´s equipment active involvement. The objective of our work is to investigate analytically and by simulations a novel approach for the development of a positioning system, without the above restrictions. Therefore we consider an IEEE 802.11-based infrastructure network for our positioning system, thus enabling the location positioning for the majority of contemporary mobile computing devices. Most of the localization solutions using 802.11 are based on the generation of signal strength maps, a time consuming and labor intensive process. We introduce and evaluate a position location technique, the Signal Strength Difference on Arrival (SSDoA). We use the differences of the received signal strength in three or more observation points, which are in known positions, to generate a set of equations that provide an estimation of the transmitter´s position. These equations define the hyperbolic curves where the transmitter may lie. In parallel, the use of fixed and known observation points assists the calculation of the radio propagation path loss exponent. The knowledge of the propagation characteristics substitutes the need of signal strength mapping. The primary contribution of our approach is that it does not require any time consuming calibration or specific/proprietary hardware. Furthermore the user position is accurately located within a few meters without requiring any interaction from the user equipment, other than its ordinary data transmissions.