1 Cooperative Positioning Techniques for Mobile Localization in 4G Cellular Networks Carlos Leonel Flores Mayorga, Francescantonio Della Rosa, Satya Ardhy Wardana, Gianluca Simone, Marie Claire Naima Raynal, Jo˜ ao Figueiras, Simone Frattasi Institute of Electronic Systems, Aalborg University, Aalborg, DK-9220, Denmark E-mail: sf@es.aau.dk * Abstract—In this paper, we exploit the concept of cooperative localization by utilizing the additional information obtained from short-range links to enhance the location estimation ac- curacy in forthcoming cellular systems. Simulations for a hybrid WiMAX/Wi-Fi system are carried out considering an outdoor en- vironment, where time difference of arrival (TDOA) and received signal strength (RSS) measurements are combined thanks to advanced data fusion techniques. Results show that the proposed system allows to meet the Federal Communications Commission (FCC) requirements and overcome the ever changing channel conditions. Index Terms— 4G, Cooperation, Data Fusion, Localization, Wi-Fi, WiMAX. I. I NTRODUCTION Nowadays an integration process has started, and the traditional fields of computer industry, telecommunications, and multimedia services are merging. Contrarily to the second generation (2G) and the third generation (3G), which achieve low data rates and are respectively designed for voice and video communications, the fourth generation (4G) is expected to provide a unified solution in terms of data rate, coverage, energy consumption, and spectral efficiency [1]. As the trend towards convergence, globalization and mobility increases, new developments and services are beginning to emerge. Originally, localization was thought to be used only to assist Emergency-911 (E-911) calls, but now in the form of location- based services is considered as one of the potential market drivers in the telecommunications industry. Promising applications are [2]: vehicle navigation, fraud detection, resource management, automated billing, etc. Specifically, location information may be requested by and reported to a client (application) associated with its personal device, or by a client within or attached to the core network, or utilized internally by the operators for location-assisted handover, for example. The use of the Global Positioning System (GPS) for mobile localization has been applied in 3G. However, the introduction of handsets with built-in GPS receivers leads to an increased cost, size, battery consumption, and a long time for a full market penetration. Furthermore, it is sometimes unfeasible in dense urban and indoor environments – which actually represent the greatest interest of cellular network providers and service providers in general – to obtain any sort of location information [3]. Hence, investigations started in connection with 4G in order to define a localization system able to provide location information with a high level of accuracy anywhere and anytime. Toward this end, in addition to novel air- interface technologies and collocated antenna technologies, some major modifications in the wireless network architecture itself are required. The most promising architectural upgrade relies on the use *This work is supported by the Cooperative Mobile Positioning (COMET) project. COMET has been funded by Det Obelske Familiefond (DOF) and Center for TeleInFrastruktur (CTIF) Denmark. of a combination of the cellular network model with the peer-to-peer (P2P) one, which is usually used only in a special class of wireless networks called ad-hoc networks. Whereas in conventional cellular networks mobile hosts operate in a purely peer-agnostic fashion, in ad-hoc networks, they act cooperatively as routers or relays for other hosts, where the communication is enabled through multi-hopping without the need for a centralized base station. By using transmission powers that are just large enough to ensure network connectivity, the ad-hoc network model achieves several performance benefits over the cellular one, including better spatial reuse characteristics and lower energy consumption [4]. It is straightforward to realize that a hybrid network model, such as the cellular ad-hoc one, is the most natural type of environment in which cooperation not only between users or terminals, but also between networks can be established and best flourish. Cooperation is a raising alchemic paradigm in wireless communications, which gives the designers the potentials to achieve enhancements in terms of data rate, coverage, energy consumption and spectral efficiency [5]. However, there is little research that studies the impact of cooperation on geo-localization, i.e., location estimation in terms of geographic coordinates of a mobile with respect to a fixed reference system. Cooperative mobile positioning is raising up as a new branch of wireless location, in which several research directions are being explored (e.g., positioning, tracking, clustering, etc.). Its underlying concept is based on the exploitation of reliable short-range mobile- to-mobile measurements to increase the location estimation accuracy of a wireless system, which is usually provided only with unreliable long-range fixed-to-mobile measurements. The major contribution of this paper is the development of a cooperative mobile positioning system supported by a hybrid WiMAX/Wi-Fi network, where we assume that none of the involved mobiles is GPS-equipped. The simulation results in Section VI will show that thanks to the spatial proximity and spatial diversity within a group of cooperative mobiles, our proposal has the potential to enhance the location estimation accuracy with respect to conventional terrestrial positioning systems in stand-alone cellular networks. It is also worth mentioning that the concept of cooperative mobile positioning can be easily applied in case of (i) indoor environments, where the cellular and ad-hoc segments may be replaced by wireless local area network (WLAN) communications in infrastructure and ad-hoc mode, respectively; and (ii) GPS-equipped mobiles, where the location estimation accuracy can be reinforced and assured even in areas where the GPS alone might not be sufficient. As a consequence, our proposal might rep- resent a possible global solution to the mobile localization problem. Finally, it can also stimulate the creation of a new range of services: cooperative location-based services. The rest of the paper is organized as follows: Section II introduces the existing positioning techniques; Section III shows the proposed system architecture; Section IV describes the system models used to carry out the simulation results; Section V presents the proposed data fusion technique; and Section VI discusses the performance of the proposed positioning system evaluated via computer simulations. Finally, our concluding remarks are given in Section VII.