A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> The proliferation of mobile computing devices and local-area wireless networks has fostered a growing interest in location-aware systems and services. In this paper we present RADAR, a radio-frequency (RF)-based system for locating and tracking users inside buildings. RADAR operates by recording and processing signal strength information at multiple base stations positioned to provide overlapping coverage in the area of interest. It combines empirical measurements with signal propagation modeling to determine user location and thereby enable location-aware services and applications. We present experimental results that demonstrate the ability of RADAR to estimate user location with a high degree of accuracy. <s> BIB001 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> Geolocation methods for HIPERLAN/2 OFDM systems were reported previously. This paper continues to study the possibility of overlaying geolocation functions in 802.11 DSSS wireless LANs. In this paper, a delay measurement-based TDOA measuring method is proposed for 802.11 wireless LANs, which eliminate the requirement of initial synchronization in the conventional methods. The performance of the potential overlaid geolocation systems for DSSS and OFDM wireless LANs are analyzed and compared in terms of symbol synchronization performance. <s> BIB002 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> In this paper, techniques and algorithms developed in the framework of Statistical Learning Theory are applied to the problem of determining the location of a wireless device by measuring the signal strength values from a set of access points (location fingerprinting). Statistical Learning Theory provides a rich theoretical basis for the development of models starting from a set of examples. Signal strength measurement is part of the normal operating mode of wireless equipment, in particular Wi-Fi, so that no special-purpose hardware is required.The proposed techniques, based on the Support Vector Machine paradigm, have been implemented and compared, on the same data set, with other approaches considered in scientific literature. Tests performed in a real-world environment show that results are comparable, with the advantage of a low algorithmic complexity in the normal operating phase. Moreover, the algorithm is particularly suitable for classification, where it outperforms the other techniques. <s> BIB003 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> Local positioning will be one of the most exciting features of the next generation of wireless systems. Completely new concepts and features for wireless data transmission and transponder systems will emerge. Self-organizing sensor networks, ubiquitous computing, location sensitive billing, context dependent information services, tracking and guiding are only some of the numerous possible application areas. This article introduces different concepts of several existing and emerging systems and applications. <s> BIB004 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> This publication explores the degree of accuracy to which the propagation delay of WLAN packets can be measured using today's commercial, inexpensive equipment. The aim is to determine the distance between two wireless nodes for location sensing applications. We conducted experiments in which we measured the time difference between sending a data packet and receiving the corresponding immediate acknowledgement. We found the propagation delays correlate closely with distance, having only a measurement error of a few meters. Furthermore, they are more precise than received signal strength indications. ::: ::: To overcome the low time resolution of the given hardware timers, various statistical methods are applied, developed and analyzed. For example, we take advantage of drifting clocks to determine propagation delays that are forty times smaller than the clocks' quantization resolution. Our approach also determines the frequency offset between remote and local crystal clocks. <s> BIB005 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> General wireless local area network (WLAN) based location systems use the received signal strength (RSS) as location fingerprint without any additional changes to the WLAN infrastructure. However, in real environment RSS are impacted by many factors, such as multiple path transmission (multi-path), temperature, body, etc, which harm the accuracy of location. This paper presents a method which uses both the angle of arrival (AOA) and RSS as location fingerprints based on AP scanning. Compared to other WLAN based location systems, this method takes advantages of fewer AP, less suffering from the influence of signal and higher accuracy. Furthermore, in some "clean" outdoor/indoor environments, the method can even used to locate WLAN clients without the radio map which is the basic infrastructure of general WLAN based location systems. Finally, this paper analyzes the characteristics of the AP scanning based location systems, and makes a further discussion on client-side location system using the same method <s> BIB006 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> Wireless location refers to the geographic coordinates of a mobile subscriber in cellular or wireless local area network (WLAN) environments. Wireless location finding has emerged as an essential public safety feature of cellular systems in response to an order issued by the Federal Communications Commission (FCC) in 1996. The FCC mandate aims to solve a serious public safety problem caused by the fact that, at present, a large proportion of all 911 calls originate from mobile phones, the location of which cannot be determined with the existing technology. However, many difficulties intrinsic to the wireless environment make meeting the FCC objective challenging. These challenges include channel fading, low signal-to-noise ratios (SNRs), multiuser interference, and multipath conditions. In addition to emergency services, there are many other applications for wireless location technology, including monitoring and tracking for security reasons, location sensitive billing, fraud protection, asset tracking, fleet management, intelligent transportation systems, mobile yellow pages, and even cellular system design and management. This article provides an overview of wireless location challenges and techniques with a special focus on network-based technologies and applications. <s> BIB007 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> Wireless positioning has attracted much research attention and has become increasingly important in recent years. Wireless positioning has been found very useful for other applications besides E911 service, ranging from vehicle navigation and network optimization to resource management and automated billing. Although many positioning devices and services are currently available, it is necessary to develop an integrated and seamless positioning platform to provide a uniform solution for different network configurations. This article surveys the state-of-the-art positioning designs, focusing specifically on signal processing techniques in network-aided positioning. It serves as a tutorial for researchers and engineers interested in this rapidly growing field. It also provides new directions for future research for those who have been working in this field for many years. <s> BIB008 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> In this paper we compare the capabilities of Wireless LAN and Ultra-Wideband to enable advanced localization systems. The two technologies are compared regarding their suitability towards time-delay-estimation by theoretical bounds as well as by means of practical time-of-flight range estimation in LOS and NLOS conditions in an industrial environment. <s> BIB009 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> Indoor geolocation using maximum likelihood algorithms applied to the measured reference radio map of the received signal strength (RSS) in indoor areas has attracted tremendous attention in the recent published literature. In this paper we examine generation of reference radio maps using two different radio propagation models to replace on site measurements for calibration of these indoor geolocation systems. The first model used for radio propagation is a statistical model recommended by the IEEE 802.11 standardization committee and the second model is a simple building-specific two dimensional ray tracing algorithm. The empirical reference radio map of the RSS from seven access points in 257 locations is collected in the first floor of the Atwater Kent Laboratory, Worcester Polytechnic Institute which represents a typical indoor office area. Using the empirical radio map and the radio map generated from the results of radio propagation modeling, the performance of the nearest neighbor and maximum likelihood location estimation techniques are compared. <s> BIB010 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> SUMMARY Location-Based Services (LBS) cover a wide spectrum of applications including fleet management, travel aids, location identification, emergency services and vehicle navigation. Applications of this service can be further extended if reliable and reasonably accurate 3dimensional positional information of a mobile device can be determined seamlessly in both indoor and outdoor environments. Current geolocation methods for LBS may be classified as GNSS-based, cellular network-based, or their combinations. GNSS-based methods rely very much on the satellite visibility and the receiver-satellite geometry. This can be very problematic in dense high rise urban environments and when transferring to indoor environment. Especially in Hong Kong the urban canyon will affect very much the reception of the GNSS signals. Moreover positioning in the indoor/outdoor transition area would experience signal quality and signal reception problems, if GNSS alone systems are employed. The authors have proposed the integration of GNSS with wireless positioning techniques (Mok and Xia, 2006; Xia et al., 2006), and a fingerprinting positioning method based on WiFi signal strength observations has been tested with results analyzed (Retscher et al., 2006). Further developments have been made on signal strength to distance conversion of WiFi data for integration with GNSS and other range data sources. Recent test results in the outdoor area are presented in this paper. <s> BIB011 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <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> BIB012 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> Indoor localisation technologies have received considerable attention in recent years and they are applicable in many fields. As with outdoor systems, they both suffer a degradation in performance when multi-path errors are present. Applications include locating essential equipment in hospitals and specific items in warehouses, tracking people with special needs, who are away from visual supervision, and navigating fire-fighters inside buildings. In this article, we study issues associated with the implementation of a real-time Wireless Fidelity (WiFi) localisation system for an indoor environment. In particular, we present robust techniques to mitigate the effects of the multi-path errors. This system utilises smart antennas to determine the signal strength information from a mobile target (MT) (access point) and send the information to a data processing station. This information is combined to find the direction of arrival of the signal and triangulate the MT position. No prior finger-printing is required, as this system avoids the use of an off-line training phase, which is computationally intensive and requires a big database. This approach is more computationally efficient and non-data intensive. Experimental results show an improvement in the accuracy of the localisation system over conventional techniques. <s> BIB013 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> This paper presents the implementation of a novel seamless indoor/outdoor positioning service for mobile users.The service is being made available in the Streamspin system(www.streamspin.com), an open platform for the creation and delivery of location-based services. Streamspin seeks to enable the delivery of truly ubiquitous location-based services by integrating GPS and Wi-Fi location fingerprinting. The paper puts focus on key aspects of the seamless handover between outdoor to indoor positioning. Several different handover solutions are presented,and their applicability is evaluated with respect to positioning accuracy and battery consumption of the mobile device. <s> BIB014 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> WiFi-based positioning has been widely used because it does not require any additional sensors for existing WiFi mobile devices. However, positioning accuracy based on radio signal strength is often influenced by noises, reflections, and obstacles. The Time-of-Arrival (TOA) or Angle-of-Arrival (AOA) methods may be used, but both require additional sensing mechanisms and cannot be applied to existing WiFi mobile devices. In this paper, we propose a new WiFi-based positioning method called directional beaconing. This method uses the Angle-of-Emission (AOE) method instead of the AOA. Using this method, access points (APs) emit beacon signals through rotating directional antennas with angle information encoded in beacons. WiFi devices estimate the direction and distance to the AP by receiving and decoding these beacons. This method integrates the advantages of the AOA and signal strength methods without requiring additional sensors. We constructed revolving directional APs and verified positioning accuracy is improved using the proposed method. <s> BIB015 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> The term “location fingerprinting” covers a wide variety of methods for determining receiver position using databases of radio signal strength measurements from different sources. In this work we present a survey of location fingerprinting methods, including deterministic and probabilistic methods for static estimation, as well as filtering methods based on Bayesian filter and Kalman filter. We present a unified mathematical formulation of radio map database and location estimation, point out the equivalence of some methods from the literature, and present some new variants. A set of tests in an indoor positioning scenario using WLAN signal strengths is performed to determine the influence of different calibration and location method parameters. In the tests, the probabilistic method with the kernel function approximation of signal strength histograms was the best static positioning method. Moreover, all filters improved the results significantly over the static methods. <s> BIB016 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> We present a hybrid indoor positioning solution combining angle-based localization, pedestrian dead reckoning, and map filtering. The angle-based localization system provides absolute location estimates, whereas pedestrian dead reckoning (PDR) results in accurate shape and length of the traversed route without absolute location and heading information. PDR movement and angle-based location estimates are fused together with a building vector map in a fusion filter, which in this study is implemented through a particle filter. When the fusion filter has been initialized with absolute position data and has converged, it can run also on PDR and map filtering, independently of the angle-based localization system, in areas that are not illuminated by multi-antenna arrays. In principle the same fusion design could accommodate location estimates also from other positioning sources, for example WiFi, or GPS in outdoor-to-indoor transitions. By combining information from various positioning modalities, different types of indoor environments can be provided with seamless positioning coverage with reasonable accuracy and infrastructural investments. <s> BIB017 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> WLAN <s> It is known that satellite radiolocalization was born in the military environment and was originally conceived for defense purposes. Nevertheless, the commercial explosion (dated to 20 years ago) of global positioning system (GPS) in the civil market (automotive, tourism, etc.) significantly changed the original perspectives of this technology. Another big change is expected when other global navigation satellite systems (GNSSs) such as the European Galileo or the Chinese COMPASS become operational and commercial. In fact, modern GNSSs are conceived principally for the civil market (at the opposite of GPS, whose civil employment is given as a sort of “kind gift,” with lower performance than that one granted to military users). The scope of this paper is to provide readers with a clear focus about the potentialities of current and forthcoming GNSSs and associated technologies in a renewed mass-market perspective. The paper also opens a window to the future of radiolocalization technology beyond GPS and GNSS, dealing with the role of digital signal processing and software-defined radio (SDR) in next-generation navigation systems and with the seamless integration of satellite-based navigation with other technologies in order to provide reliable position information also in hostile environments. <s> BIB018
As mentioned, GNSSs are studied and improved since thirty years BIB018 , whereas localisation with help of WLAN signals is a relatively recent field BIB001 BIB014 . In the last years several techniques have been investigated. Different localisation techniques lead to different advantages and drawbacks. For lateration, the positions of the transmittersthe WLAN access points (APs) -must be known, which they are not in usual, and precise time measurements are essential. Determining the APs positions may be difficult and moreover the APs must stay fix at known positions. These requirements are hard to fulfil in uncontrolled areas. Furthermore, one has to deal with non-line-of-site conditions and with severe multipath effects, especially indoors BIB009 . Various time delay measurement methods, for an overlaid positioning system based on WLAN, were investigated in  BIB005 BIB002  . A second geometrical method is angulation. Instead of time delays, angles are measured and used to derive a position. Angulation suffers from similar drawbacks as lateration. These are mainly the unknown and possibly variable positions of the APs and non-line-of-sight conditions. Triangulation with IEEE 802.11 signals was studied in BIB015 BIB006 BIB013 , and might become important again with further deployment of the IEEE 802.11n standard and antenna arrays in mobile devices. BIB017 proposed a WPS relying on beamforming, that estimates the mobile device position from WLAN signals received from a transmitting beamformer, whose location and calibration pattern is known. The stated problems of the geometrical methods are still not satisfactory solved. Some of these approaches need hardware and/or software modifications of the Wi-Fi ™ equipment to work, other diverge from the IEEE 802.11 standard  . Besides the timing issue, the unresolved problem of multipath propagation, diminishes the accuracy of these systems further. Therefore, most WPSs use received signal strength measure-ments (RSS) to estimate a position. Based on RSS, either i) lateration or ii) pattern recognition of RSS is employed. In i) a distance between the WLAN transceiver and an AP is deduced from the RSS via modified free space propagation models. This was also already suggested in BIB001 and then further adapted to different scenarios by many other researchers. The position can be estimated via trilateration with at least three distances. In realistic urban and indoor environments the IEEE 802.11 radio channel is influenced by several independent causes and varies in time BIB010 . Resulting in a complex signal propagation, which makes signal strength measurements at a certain point in space hardly predictable BIB003 BIB011 . Although the modelling of that IEEE 802.11 channel characteristics makes progress, these models still lack of precision to be universally applied for positioning in urban canyons and indoors. The second technique to employ RSSs in ii), is to use location fingerprinting. Location fingerprinting is performed in two phases: an off-line and an on-line phase. First, RSS measurements of all receivable APs are recorded at known reference positions of the target area. These signal strength measurements and their according reference positions are stored as fingerprints in a data base, often referred to as radio map. 1 During the on-line phase RSS observed at a certain location are compared against the data base entries from the off-line phase. For this comparison various pattern recognition techniques with many variants are available, see BIB016 BIB012 . The best matches of that comparison indicate the most likely locations. The alluded problems with WLAN ranges, either obtained from time measurements or from signal strength measurements, lead to a lack of robustness against variations of the environment, which in comparison WLAN RSS fingerprinting does not show. A general overview of positioning in wireless networks can be found in BIB007 BIB008 BIB004 . Above all, a WPS may compute its position estimate on the mobile device such as a GNSS receiver. So, by combining these to positioning techniques appropriately, as well privacy concerns are almost without cause. Disadvantageous and costly is the recording of the radio map. For large areas it is a very time consuming process. In addition it must be 1 In WLAN fingerprinting the radio maps can be stored directly on the mobile device, but due to the size of target areas the radio maps are often downloaded via a data connection when the user comes in the vicinity of the building or the target area. maintained and updated from time to time to adapt for changes in the WLAN infrastructure and environment.