A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Integration of GNSS pseudo ranges with WPS features <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> BIB001 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Integration of GNSS pseudo ranges with WPS features <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> BIB002 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Integration of GNSS pseudo ranges with WPS features <s> If nowadays, positioning becomes more and more accurate, and covers better and better a territory (indoor and outdoor), it remains territories where traditional (and basic) positioning system (GPS, gsm or WiFi) and hybrid ones (GPS- gsm, GPS-WiFi, GPS-WiFi-gsm, …) are insufficient and requires research investment treating combined positioning. In this paper we propose a GPS-WiFi combined positioning algorithm, based on trilateration technique. Real experiments and other simulation are conduced and demonstrate accuracy gains, even where various criteria dilution of precision (GPS dop's criteria, or ours WiFi geometrical and signal attenuation's dop proposal, or hybrid dop one's) indicate all the disruption of positioning service. A testbed scenario issued from a real urban campus environment validates not only our GPS-WiFi combined positioning algorithm but also an implementation of pertinent positioning techniques and dop's criteria. This work constitutes a further step to better position everywhere and to ensure continuity of a positioning service. <s> BIB003 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Integration of GNSS pseudo ranges with WPS features <s> This paper proposes a positioning method that combines GPS pseudoranges and WLAN ranges when less than four GPS satellites are within sight. To enhance the positioning availability, a tight hybridization approach with both technologies is considered. Although the work has been performed considering WLAN and GPS, most of the presented ideas, procedures and results are also valid for generic tight non-synchronized fusion of GNSS with terrestrial signals [1]. Special emphasis is placed on the phenomenon of positioning ambiguity that appears due to the combination of measurements with different characteristics. To solve this ambiguity, a method is proposed and studied. The availability and accuracy of the system are tested considering different satellite and terrestrial geometries. The results show that the proposed system is able to improve the availability while maintaining the accuracy of GPS as a standalone. <s> BIB004 </s> A survey of hybridisation methods of GNSS and wireless LAN based positioning system <s> Integration of GNSS pseudo ranges with WPS features <s> Wireless Local Area Network (WLAN) is a new information access platform which can be used to achieve positioning, monitoring and tracking in wide area. Self-positioned of the network node is the basis and prerequisite for most applications, although the current popular WiFi positioning technology is a position solution for WLAN series standard (IEEE802.11). In this paper, based on the principle of satellite navigation and positioning with wireless sensor networks, the new method of combining GPS and WiFi networks is put forward to achieve seamless positioning and navigation. And the potential problems of existed technology are conducted in-depth discussion by summing up the seamlessly, current location and navigation technology, as well as analyzing existed problems and trends. Finally, the WiFi network assisted GPS positioning algorithm is analyzed in detail. <s> BIB005
In contrast to the former section, now data fusion architectures are considered, which may not provide positions independently to the application, but deduce a common position from features derived from sensory data. To provide robust systems, able to cope with signal outages and so on, a single subsystem ought to be able to compute a position on its own. The majority of the approaches, presented in the following, make use of lateration. GNSS pseudo ranges and ranges from WLAN signals are combined in a way that WLAN ranges complement the GNSS PVT equations. It is worth noting, that WPSs are in most cases software solutions, more or less easy to modify to obtain the desired sensory data. Whereas the GNSS chip in the systems, described in the following, must be able to deliver pseudo ranges. Due to imprecise timing of WLAN chips and missing synchronisation of the network, accurate WLAN ranges are not easily obtained directly by measuring time delays BIB002 BIB001 . An other difficulty when measuring transmission times, is that the positions of the WLAN APs must be known, which are usually not. As well problematic in unknown, uncontrolled environments is that APs can easily be moved, vanish, reappear, etc. Multipath propagation is another drawback, which has to be overcome for an accurate positioning based upon time measurements. Many of these problems have not been solved yet or could only be solved by modifying hardware or firmware. No development is known to the authors which has solved all, for its approach specific, problems. WPSs RSS fingerprinting solutions on the other hand are much more widespread. The authors of BIB003 addressed hybrid localisation in rural and suburban environments. In their approach pseudo ranges from GNSS satellites are complemented with ranges deduced from WLAN RSS. The position is estimated by lateration. They employ three subsystems: first a GNSS receiver estimating a stand-alone position, when more than 4 satellites are detectable; second a WPS, estimating a stand-alone positions from WLAN RSS deduced ranges, if more than four APs are detectable. A third module, fuses range measurements of both subsystems. In that third module pseudo ranges and WLAN ranges solve the localisation problem, when both systems together provide at least 4 ranges. The system may have three positions from the three modules available. One from the GNSS receiver, one from the WPS and one from the fusion module. The final position estimate is a combination of the possibly three positions based on the combined GDOP derived from all (pseudo) ranges. In BIB004 as well the combination of pseudo ranges and WLAN ranges is investigated, but focused on the case of less than four satellites in view. The work concentrates on the issue, which exists more likely when ranges of very different magnitudes are fused: ambiguous position solution. The position solution of lateration may be ambiguous, due to coplanar transmitters. In GNSS this is usually not a problem, because the ranges to the satellites are huge and one of the solutions does not lie on the earth's surface. Thus, the solution far away from the earth can be excluded. The problem of ambiguous solutions occurs more likely when much smaller WLAN ranges and pseudo ranges are in a common set of lateration equations. Two valid position solutions are almost always derived in the common case of combining three pseudo ranges and one WLAN range. In BIB004 a method is developed to solve that ambiguity by exploiting information about the GNSS and WPS positions gathered over time. The algorithm relies on the key idea that in a static receiver scenario the false position must move due to the movement of the satellites and the true position solution must not; but since the measurements contain errors, both move. So, the two possible solutions are derived with the Bancroft algorithm. Furthermore, the evolution over time of these two initial positions is stored for four minutes and compared against the initial positions. The evolution of true initial position is supposed to have a smaller slope, hence it deviates less over time than the wrong position. A combination of almost all so far presented ideas to fuse GNSS and WPS can be found in BIB005 . The algorithm of BIB005 first switches between four modes dependent on the availability of GNSS and WPS, and the number of receivable GNSS signals. Then it uses, according to the chosen mode, an adaptive filter to fuse features of the two systems. In accordance with the four conditions, the following mode and positioning algorithm are chosen: a) WPS but no GPS, WPS standalone and least square method; b) WPS and GNSS but with less than four satellites, KF to fuse GPS and WPS ranges; c) WPS and GNSS with more than four satellites, federal KF to fuse positions derived by each subsystem; and d) GPS but no WPS, least square or KF (as usual for GNSS). Details about the design of the filters or how the different filters are used in particular is not revealed. A last approach fusing GNSS pseudo ranges and WPS features is a probabilistic algorithm proposed in  . A particle filter is applied to merge likelihood functions, obtained from GNSS pseudo ranges and WLAN RSS pattern recognition. The pseudo range likelihood function is modelled as a Gaussian distribution and is derived from available pseudo ranges. The derivation of the likelihood of the RSS measurements is not that straight forward. Recall the RSS pattern matching of the on-line phase, where a current RSS observation is compared with the RSS data base entries (recorded during the off-line at known reference points). The outcomes of the RSS comparisons usually weight the according positions to obtain the final estimate. To fuse the likelihoods, in  the RSS comparisons are not done with the fingerprint positions in the data base but with the particles. An approximation is carried out to map RSS data base entries from fingerprint reference points to particles. By normalising the weights obtained from the data base comparison, such that the weights sum up to one, a pseudo-likelihood over the target area is established. The GNSS likelihood is represented by particles and corresponding weights and the WPS pseudo-likelihood is represented by the same particles and weights derived from the data base comparison. Multiplication of the likelihood functions accomplishes the data fusion.