A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Performance comparison <s> Accuracy criteria for wireless location systems have been the subject of much discussion due to the different interpretations and assumptions regarding the requirements that were stated in the FCC's wireless E-911 ruling. Indeed, these requirements cover only the expected accuracy/error percentage in location measurements, which is insufficient because it allows potentially misleading information from and about location systems. This article draws analogies with well-known performance criteria for wireless communications systems toward setting a comprehensive suite of benchmarks for wireless location systems. <s> BIB001 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Performance comparison <s> Wireless indoor positioning systems have become very popular in recent years. These systems have been successfully used in many applications such as asset tracking and inventory management. This paper provides an overview of the existing wireless indoor positioning solutions and attempts to classify different techniques and systems. Three typical location estimation schemes of triangulation, scene analysis, and proximity are analyzed. We also discuss location fingerprinting in detail since it is used in most current system or solutions. We then examine a set of properties by which location systems are evaluated, and apply this evaluation method to survey a number of existing systems. Comprehensive performance comparisons including accuracy, precision, complexity, scalability, robustness, and cost are presented. <s> BIB002
First of all we must state that an absolute, objective evaluation of the presented methods, based on the reported experimental results, is not possible. Too different are the applications and objectives of the studies, and too different are the development stages and the scenarios of many of the approaches. Some approaches are already quite mature, are tested and improved several times, whereas others are solely analysed on simulated data. If tests in real environments were con-ducted, the scenarios differ significantly. Not all considered their system as ubiquitous and performed indoor and outdoor tests. Several approaches are constrained to vehicle motions, others are more specific for pedestrians. Hence, it can only be tried to compare the approaches qualitatively. Accuracy, precision, robustness, complexity and costs will be evaluated. Resting on the depth of the data fusion, each category is surveyed towards its potential performance. To have a common understanding of these criteria, we follow the remarks of BIB002 and BIB001 on performance of positioning systems. Accuracy describes how good a location system performs, the metric representing the accuracy is mostly the average euclidean distance. The better the accuracy, the smaller is the deviation from the ground truth. A bias or a systematic influence are considered within the location error. The precision in contrast, represents the consistence of a positioning system. It contains information about the variation in its performance over several trials. A measure to capture the precision is the cumulative distribution function (CDF) or percentiles. With robustness it is referred to how likely a positioning system keeps functioning under harsh radio frequency signal conditions, for example when signals are totally or partially blocked, or have low power. It depends strongly on the environment and the variation and modifications of the environment. Robustness is also linked to coverage, continuity and availability. In fact in the context of GNSS and WPS fusion, these criteria are determined in first place by the deployment of WPS enabled areas. Meaning the arrangements of target areas to localise with WLAN location fingerprinting or WLAN ranging; which is not covered herein. The concept of complexity can be applied at many stages, such as hardware, firmware and computational complexity. Here, primarily computational/algorithmic complexity is considered, even though for some WLAN ranging methods hardware, or firmware modifications are necessary. Last but not least costs are examined. Costs are understood very broad. Certainly, costs are also closely connected with complexity. For example, monetary costs increase with modifications of hardware, and battery consumption increases with computational complexity. This paper focuses mainly on battery drainage, because the majority of algorithms aim for mobile devices and energy consumption is always a critical issue. Costs of infrastructure are not further considered in this comparison, because GNSS and a WPS enabled environment is required for all approaches.