This chapter deals with mobile positioning in wireless heterogeneous next generation networks. Positioning process is analyzed and the chapter gives an overview of the basic positioning principles and methods that can be used in various NGN platforms. The main focus is given on cellular, ad hoc and sensor networks. Fundamental positioning methods are similar regardless of network platform. The difference usually lies in positioning accuracy. This is caused by technical parameters of the particular application platform. The end of the chapter deals with positioning experiments. The main purpose of authors is simple explanation of fundamental positioning principles for various NGN network platforms.
Positioning In Wireless Networks
The concept of positioning is not limited just to the geographic representation of physical location with sets of coordinates (latitude, longitude, and altitude). It is also applicable to symbolic location in a non-geographic sense, such as location in time or in a virtual information space, such as a data structure or the graph of a network.
Common to all notions of location is the concept that the individual locations are all relative to each other, meaning that they depend on a predefined frame of reference. This leads to a differentiation of the relative and absolute positioning (Tseng, Huang & Kuo, 2005).
If position information is used in reference to a geographic map or a global time reference, the context information can be extended. An absolute position is given with respect to an inertial system and a reference point in the inertial system. On the other side, a relative position can only be given with respect to other points resolving the distances and the geometric configuration, e.g., the topology.
When talking about physical location in the traditional way, points are usually viewed as three-dimensional coordinates [x; y; z] in a Cartesian reference coordinate system.
Usually, [x; y; z] coordinates by themselves are not meaningful for context-aware system services and the other information needs to be associated with this position information. In these cases, it is important to introduce the fourth dimension – time. If a time dimension is introduced, we are able to specify where and when a certain event took place resulting in sets of [x; y; z; t] for each position information. The four-dimensional fix can be used to put subsequent events into a context frame.
Key Terms in this Chapter
Weighted Proximity Positioning (WEP): This modified positioning method increases proximity accuracy by means of weighting data entering centroid proximity. The fundamental of WEP is increased influence of closer reference nodes at the expense of further nodes. WEP belongs to the group of range free positioning. Positioning using proximity measurements is popular, when low cost takes precedence in priority over accuracy.
Range Free Positioning: Category of positioning methods, which estimate the location of mobile devices (sensors, nodes or mobile stations) either by exploiting the radio connectivity information among neighboring mobile devices, or by exploiting the sensing capabilities of the mobile devices. The range free positioning methods are cost-effective solutions.
Geometric Algorithm (GA): The function of Geometric Algorithm (GA) is mobile device location estimation (with the highest probability) by means of calculation of lines of position intersection. The triangulation is used for calculation of the intersection.
Ad Hoc Network Positioning: Localization of mobile device (node) in ad hoc networks. Position estimation of mobile device is result of ad hoc networks positioning.
Network Based Positioning: Reference devices at one or more locations measure a signal originating from the localized device. These measurements are communicated to a central site where they are combined to give an estimate of the mobile device location. This position information can be used at the central site or sent to another system (application), which requires the location of given mobile device.
Range Based Positioning: The form of positioning it is based on the indirect measurements of distance or angle between sensors. The important thing to note is that the indirect measurements always have errors and individual measurements are not independent of each other. These measurements are strongly influenced by the surrounding environment and transmission system.
Mobile Based Positioning: A localized mobile device makes the appropriate signal measurements from geographically distributed reference devices, (e.g., base stations, reference nodes). These measurements are used to determine mobile device location. Computing operations are done in mobile device, e.g. Mobile Station (MS).
Adaptive Geometric Algorithm (AGA): The function of AGA is mobile device location estimation. The AGA is improvement of basic geometric algorithm. The AGA provides more accurate results compare with geometric algorithm.
Cellular Positioning: Localization of mobile devices in cellular networks. Position estimation of mobile device is result of cellular positioning.
Positioning Requirements: Basic requirements of a positioning system. These should be fulfilled for satisfied positioning. For example, the requirements include: maximum possible accuracy of the system; privacy protection, possibility to disable positioning in a case of assault.