A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <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> Switching between GNSS and WPS positions <s> A new concept called Always Best Located (ABL) is introduced to achieve a pervasive indoor- outdoor positioning system. Designed as a combination of WLAN and GPS, this hybrid positioning system is shown to yield ubiquitous coverage and best-effort accuracy in any environment. An original mapping algorithm has been conceived to enable the system to discover the location of nearby WLAN access points on the fly, without requiring human intervention or connection to an existing database. Following an outline of positioning algorithms and location based application requirements, a comparative study of positioning technologies based on GPS, GSM, WLAN, and Bluetooth is presented. As revealed by this benchmark, none of the existing technologies suffice to provide ubiquitous coverage; however a combination GPS and WLAN is shown to provide excellent coverage and accuracy indoors as well as outdoors. New algorithms are then presented to illustrate how these two technologies can be combined to provide a continuous service by switching from one technology to another, to accurately locate the user indoors, and to automatically discover location of nearby WLAN access points. Finally the ABL system is validated over time by several users and is shown to yield 97% availability – the equivalent of more than 23 hours of service a day. <s> BIB002 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <s> New services in wireless communications are enforcing needs for accurate indoor and outdoor location technologies. Existing technologies are offering different coverage and accuracy, but none a pervasive location service. This paper first assesses the coverage and accuracy of the fundamental positioning technologies - GPS, WLAN-based, and GSM-based (Cell-ID and Trilateration) - by systematic measurements in various environments both indoor and outdoor. Then, an Always Best Located (ABL) algorithm is introduced and experimental performance results obtained in real situations are presented. <s> BIB003 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <s> The 3G iPhone was the first consumer device to provide a seamless integration of three positioning technologies: Assisted GPS (A-GPS), WiFi positioning and cellular network positioning. This study presents an evaluation of the accuracy of locations obtained using these three positioning modes on the 3G iPhone. A-GPS locations were validated using surveyed benchmarks and compared to a traditional low-cost GPS receiver running simultaneously. WiFi and cellular positions for indoor locations were validated using high resolution orthophotography. Results indicate that A-GPS locations obtained using the 3G iPhone are much less accurate than those from regular autonomous GPS units (average median error of 8 m for ten 20-minute field tests) but appear sufficient for most Location Based Services (LBS). WiFi locations using the 3G iPhone are much less accurate (median error of 74 m for 58 observations) and fail to meet the published accuracy specifications. Positional errors in WiFi also reveal erratic spatial patterns resulting from the design of the calibration effort underlying the WiFi positioning system. Cellular positioning using the 3G iPhone is the least accurate positioning method (median error of 600 m for 64 observations), consistent with previous studies. Pros and cons of the three positioning technologies are presented in terms of coverage, accuracy and reliability, followed by a discussion of the implications for LBS using the 3G iPhone and similar mobile devices. <s> BIB004 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <s> As mobile computing has become more popular over the past decade, experts have touted the future of location-based services. LBS systems could determine mobile users' locations. Proponents say they could thus enable applications that would not only tell people where they are and how best to get to their destinations, but also whether friends are nearby, what the local weather forecast is, and where businesses of interest in the area are located. The technology could also help companies track packages or vehicles. <s> BIB005 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <s> This paper presents a flexible approach to ubiquitous positioning technologies on smart phone. It deploys three optional indoor/outdoor locating solutions based on Multi-sensor, Satellite, and Terrestrial positioning techniques. The solutions cover six locators including Integrated GPS (Global Positioning System), Bluetooth GPS, AGPS (Assisted GPS), Network based, Multi-sensors, and Wireless LAN (WLAN). In order to merge multi positioning techniques on smart phone, a five-layer software architecture is developed on Symbian S60 platform. Moreover, the implementations of the solutions are described in the paper. Finally, we evaluate the performances of time consumption and positioning accuracy of the solutions according to the experiments on Nokia N95. <s> BIB006 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <s> Localization is a key support service for all users of mobile devices. We envision a lightweight localization service for Smartphones that overcomes the limitations of existing GPS-based approaches, namely their high energy cost and their issues with coverage. Our localization service uses GPS only if available and necessary, and employs other methods, such as WiFi and GSM, to achieve its goal of ubiquitous and energy-efficient operation. In this paper, we discuss our preliminary results as well as our future research directions. <s> BIB007 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <s> Location-aware is becoming an important aspect of mobile computing. A core problem in location-aware service is the determination of physical location. For applications in open, outdoor areas, the Global Positioning System is a common choice. Although GPS offers near-worldwide coverage, its performance degrades indoors and in high-rise urban areas. By using signal strength, it is possible to locate Wi-Fi-enabled devices with accuracies from several meters to tens of meters indoor areas. We design a solution named ULGW (Ubiquitous Locating based on GPS and Wi-Fi) system. ULGW can be used for ubiquitous location by using the existing 802.11 wireless assists GPS for indoor areas. In order to providing position continuously even if the device client travels from outdoor to indoor, ULGW utilizes a kind of map service to help switching from outdoor-location to indoor location. <s> BIB008 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <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> BIB009 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <s> This paper describes the design and implementation of a multi sensor, collaborative localization system for diverse environments. Many different approaches and systems are utilized depending on the requirements and settings of a particular environment, such as indoor, outdoor or urban environments. Location-based services could benefit from a localization system that is suitable for changing environments. We propose an architecture that facilitates multiple localization systems, such as GPS for outdoor as well as RFID-based and optical systems for indoor purposes. Due to the fact that access to respectively integration of localization systems in mobile handheld devices is limited, we introduce the Location Exchange protocol to share ascertained location information among nearby devices using Bluetooth and Wi-Fi communication. This information can be used to improve the accuracy of obtained positions and enables devices to benefit from localization systems and sensors incorporated by nearby devices. <s> BIB010 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Switching between GNSS and WPS positions <s> The high potential of new generation smartphones in terms of resources capability as well as availability of embedded sensors and radio interfaces has opened new perspectives to developers, which came out with a massive number of applications for mobile phones. Most of them are location based, where location data is used either as main or as auxiliary information. However, the location service is power hungry. Thus, a major challenge is the optimization of the trade-off between resources usage of the location service and its accuracy. We introduce the architecture of the Enhanced Localization Solution (ELS), an efficient localization strategy for smartphones which smartly combines the standard location tracking techniques (e.g., GPS, GSM and WiFi localization), the newly built-in technologies, as well as Human Mobility Modelling and Machine Learning techniques. This solution aims to provide a continuous and ubiquitous service while reducing the impact on the device's resources usage. <s> BIB011
The most common and most intuitive procedure to combine measurements from a GNSS receiver and measurements from a WLAN transceiver, is to use the position derived by each system independently. It can be distinguished between methods which only switch between the positioning systems, and methods which actually fuse positions to one position, see Section 3.3. Usually it is switched from one positioning system to another positioning system, because the former system is not able anymore to derive a position or a more accurate position is available from the second system. Also the last smart phone generations are able to provide a somehow derived position BIB001 as an alternative to a GPS position and can switch between these positioning modes, see application programming interfaces (APIs) of modern cellular phone operating systems. Notice, modern mobile devices may also be able to integrate GNSS and WLAN positioning techniques deeper with help of the Skyhook Wireless hybrid positioning system called XPS. Skyhook Wireless cooperates with global players GNSS/Wi-Fi ™ chip producers, whose chips can be found in the majority of mobile devices and likely enable this hybrid positioning system for many users  . Further details about the XPS hybridisation method are not disclosed. Different information about the localisation method can be found in the literature. That the Skyhook WPS relies on fingerprinting is stated by  BIB004 , that it is based on multilateration can be found in  BIB005 . The fact that Skyhook's web site notes a "massive reference data base of Wi-Fi ™ access points" suggests the use of lateration. The most general procedure to switch between different positioning sources is obtaining a GNSS position if the user is outdoors (GNSS detectable), and obtaining a WPS position when no GNSS position is available, usually indoors. If none of these two systems is available and the device is equipped with a modem for cellular networks, a position is obtained from that. Unfortunately it is not clear to all details how a position in mobile devices is finally deduced. The GNSS receiver is in most cases a consumer grade A-GPS receiver. About the WPS is less disclosed and it is probably carried out differently in each mobile device operating system (OS). Building up on one of the mentioned APIs and their location frameworks, various location aware applications have been proposed. A few of them deal in particular with a seamless indoor/outdoor positioning. In BIB006 , for example, the Symbian Mobile Location Framework makes use of positions from an inter-nal and an external GPS receiver, and from positions derived from a WPS and the cellular network. The authors of BIB010 presented a multisensor positioning system suitable as well for collaborative localisation. Different position sources, amongst others A-GPS and WPS, are all requested in parallel and for each an accuracy is deduced. All position estimates, which achieve a specific accuracy threshold are stored, and the position with the highest accuracy is chosen as the current device's position. Moreover, a devaluation function based on the position accuracy is defined to diminish the accuracy of the stored positions over time. A new position with an accuracy lying within the mentioned accuracy threshold, is then compared against the (devalued) accuracy of the current position. Only if the new position has higher accuracy, the current position of the mobile device is updated. The position switching strategy described in  decides mainly on the availability of GNSS, WPS and cell-ID. The OS executes that task. In addition historical location information of the user and clustering of this data is incorporated into the algorithm. K-means clustering is used on the historical location data to condense the data sets and to compensate for outliers (different thresholds for WPS and GPS are applied). This data is then clustered to generate a personal mobility map, which helps to save energy and to refine the tracking accuracy of the mobile device. Likewise the approach presented in BIB007 BIB011 , where the location API of the OS is also used to switch between positions, and a mobility model is also employed to refine position accuracy. Besides, to decrease the energy consumption, additional sensors and algorithms are added. The radio frequency based positioning systems (GPS, Wi-Fi ™ , GSM pos. system) of the OS are considered as expensive with respect to their energy needs. A personalised mobility model of the user, derived from former user positions, and an inertial sensor based positioning algorithm are augmenting the system. For each position providing system a position accuracy measure is derived, or obtained from the OS respectively. On the basis of this data the trade-off between energy consumption and position accuracy is made. In both of the last presented approaches the localisation improvement is achieved by applying transition probabilities to the mobility models. The majority of applications relying upon a location framework of an OS, aim towards LBS and use these frameworks unmodified, so that we not further consider these approaches. A position mode switching by solely checking the availability of GPS was presented in BIB008 . GPS is the main position provider. The system switches to the WPS if the GPS fix is lost, and switches back if the fix is available again. A bit more advanced approach of integrating WLAN and GPS into one system is presented in BIB002 BIB003 . Between three different localisation methods is switched automatically, dependent on the availability of these methods. One is called "place detection" and is a WLAN fingerprinting reduced to a set of common places. WLAN RSSs are used to recognise the current location among common known places. If the "place detection" does not recognise the user's location the system switches to GPS. Only when GPS can neither provide a position estimate it is switched to an other WLAN based method. A WLAN localisation algorithm based on a previously created data base of WLAN access points and their positions. This algorithm estimates the position as weighted mean of the positions of receivable APs. The weights are determined in terms of the RSS, the AP coverage and the total number of detection of the AP, which has been recorded while creating the data base. Based on GPS and WPS, BIB009 discusses four different position switching strategies to deal with indoor/outdoor transitions. The GPS and WPS run continuously and keep sensing for signals to reestablish the position estimation. The finding of the paper is that the best handover strategy would be to prefer GPS until the position fix is lost for five seconds; then the WPS position is used until a GPS position can be obtained. A similar method was published in  , which additionally uses information of the radio map. In the radio map, certain indoor transition zones are marked where entrances are located. GPS is used outdoors. Is a transition zone is detected, the system switches to the WPS. It stays in WPS mode until no WPS derived position is reported for a few seconds, then it switches to GPS to acquire satellites. If indoors, the systems also switches from WPS to GPS when a user position is within a transition zone for a given time. If a change of positioning mode is initiated, but signals of the other positioning system are not detected, the algorithm switches back to the previous mode.