Ad Hoc Networks for Cooperative Mobile Positioning

Abstract

Wireless ad-hoc networks have received huge attention during recent years due to the potential applications in different fields such as emergency, disaster relief, battle-fields, automotive, social networks and entertainment. They are rapidly deployable, selforganizing, and require no fixed infrastructure for communications. (Huang et al., 2008) At the same time, localization in wireless networks is becoming a hot topic for society, industry and research. The needs of location information has driven companies to build mobile handsets with embedded GPS receivers (which is nowadays the most popular mass market solution for positioning), causing huge increase in costs, size, battery consumption, and a long time for a full market penetration (Sayed et al., 2005). However, it is also known that the GPS is not always the most suitable solution for localization. In adverse environments, such as outdoor urban canyons and indoor, it is not an easy task to obtain location information, due to the signal blocking, multipath conditions and the infeasibility to have a continuous tracking of at least four satellites (Mayorga et al., 2007). The Fourth generation (4G) communication systems also stimulate the need of providing alternative ubiquitous localization solutions, regardless the environment (i.e., outdoors and indoors), which should overcome, or at least complement, the drawbacks of GPS-based and GPS-free systems (Della Rosa, 2007). Traditional alternative technologies make use of time difference of arrival (TDOA) measurements from the serving cellular system where the Base Stations (BSs) are considered as fixed reference points (Sayed et al., 2005). Different type of measurements, such as received signal strength (RSS), are widely used in local area scenarios, where Wi-Fi Hot Spots deployed in big cities allow user terminals to predict their locations by means of known fixed positions (Sayed et al., 2005). Unfortunately, when localization is performed in indoor environments the accuracy is highly dependent on the wireless channel conditions since several error sources cause huge signal fluctuations detected at terminal level, severely decreasing the final location estimation accuracy (Della Rosa et al., 2010). Recently, in alternative to traditional methods, a new branch of positioning techniques has been developed: the Cooperative Mobile Positioning (Figueiras & Frattasi, 2010), which makes use of hybrid schemes and exploits the benefits in terms of accuracy of short-range measurements provided by the ad-hoc networks (Della Rosa, 2007).