Jari Syrjärinne

Mass-market requirements for indoor positioning and indoor navigation

The next step in location services will be repeating the success of location services in outdoor use for navigation and local search in the indoor environment. In order to make indoor positioning and navigation reality in large scale not only compelling business opportunities must be present, but also the technology must be low-cost, low-power, have low maintenance expenses and require minimal amount of new infrastructure. This paper reviews the challenges and solution models for indoor positioning starting from the service level aspects, reflecting them to the architectural considerations and finally discusses selected technical implementation issues.

A Fast Positioning Method Without Navigation Data Decoding for Assisted GPS Receivers

This paper describes an assisted positioning approach for Global Positioning System (GPS) receivers without navigation data extraction from the received signals. In the presented approach, pseudorange values are reconstructed from partially available measurements, as opposed to conventional techniques, and five or more satellites are used for position computation. The technique is based on iterative estimations of satellite times of transmissions, receiver time, and position using a least-squares method. It is computationally similar to conventional GPS positioning algorithms, but the time to first fix is reduced as there is no need to recover the time of week from navigation data.

A network aided iterated LS method for GPS positioning and time recovery without navigation message decoding

The paper suggests a network aided iterated least squares (LS) method for GPS positioning and time recovery when a navigation message from satellite vehicles (SV) is not available. Using an additional variable which defines the satellite positions, the estimates of time of transmissions and pseudoranges are obtained from measurements available from the tracking side of the receiver. LS iterations are modified to account for adjustment of SV positions on orbits, adjustment of pseudoranges, etc. As a result, the positioning is performed without time-of-week (TOW) information from the navigation message.

Investigating effective methods for integration of building's map with low cost inertial sensors and wifi-based positioning

In this paper a study has been made to investigate effective methods for utilizing building map information to complement indoor positioning using wifi positioning and inertial sensors. Two solutions have been developed which utilize Particle filter to integrate wifi positioning, inertial sensors and two different representations of the building map information. The first representation of the map information is a Computer Aided Drawing (CAD) that provides information of the walls inside a building. The information of the walls can be utilized for removing particles with impossible movements i.e. crossing walls. The second representation is a graph that provides information of the walkable areas inside a building. The motion of the user is constrained to the walkable areas only helping to remove the particles on the wrong trajectory. The performances of the developed solutions have been evaluated for the accuracy, consistency, number of particles and processing time needed for the calculation of the position estimate. Both of the developed solutions provide satisfactory performance. They run in real time on a tablet with dual core processor with mean error being less than 3m and consistency more than 90%. The analysis of the results indicates that the use of graphs in constraining the position estimate is an accurate and compact method for providing position aiding to the indoor positioning system based on wifi-positioning and inertial sensors.

Bringing RTK to Cellular Terminals Using a LowCost Single-Frequency AGPS Receiver and Inertial Sensors

Today an ever-increasing number of handsets come equipped with a GPS receiver and some even with inertial sensors. Moreover, an even higher number of terminals are already capable of connecting to an add-on device with such capabilities. However, the full potential of these devices is not yet exploited. This paper introduces the mobile RTK (mRTK) solution, which can be included in the wireless standards to enable high-precision double-difference carrier phase positioning in handsets at no extra hardware cost. mRTK differs from the current OTF/RTK solutions in that it is a software-only solution using the hardware and wireless connections already existing in handsets. Moreover, the mRTK solution can utilize information from on-board inertial sensors. These are the key differentiating factors compared to the previous solutions. The paper shows that the sensors supplying information on baseline changes during the ambiguity initialization significantly assist the ambiguity resolution. A new communication protocol and messaging was defined in order to be able to exchange information between mRTK-capable handsets. The protocol includes reservations for additional GPS frequencies as well as for other Global Navigation Satellite Systems (GNSSs), such as Galileo. This protocol can be directly included in the wireless standards. Challenges in the current implementation include using only the L1 frequency for ambiguity resolution. Utilizing an L1-only receiver necessarily leads to penalties in the baseline accuracy due to inherent problems in the ambiguity resolution and validation. However, this paper shows that the baseline obtained is still better than the plain difference of positions. This paper shows that the mRTK solution significantly improves A-GPS performance. The mRTK solution also brings near-professional-quality positioning performance to the mass market. It would, therefore, be beneficial to include mRTK in wireless standards in order to expand A-GPS use cases in the short term and A-GNSS use cases in the long term.

Inertial Sensor Enhanced Mobile RTK Solution Using Low-Cost Assisted GPS Receivers and Internet-Enabled Cellular Phones

Location-based services are one of the biggest drivers for integrating positioning capability into mobile phones. The accuracy requirements are constantly tightening. In particular, location-based games and features such as “friend finder” sometimes require better accuracy than that which is achievable with state-of-the-art A-GPS. The concept of Real-Time Kinematics (RTK) with GPS receivers is well known. Until now, RTK receivers have been very expensive and have been mainly used in geodesy and surveying applications. This paper describes a solution, called Mobile RTK (mRTK), which utilizes single-band low-cost assisted-GPS receivers, inertial sensors and cellular link for high-accuracy positioning. The protocol used in mRTK is designed to be suitable for cellular use and for various positioning applications such as relative positioning between two or more GPS-enabled cellular terminals and absolute positioning of GPS-enabled cellular terminals using surveyed position information. The paper will describe the mRTK solution in greater depth focusing on the aspects of terminal software implementation and especially on the aspects of server implementation including the proposed protocol and the special requirements and features in the protocol design. The paper will also describe some testing results from the demonstration devices and the test network.

The effect of the antenna phase response on the ambiguity resolution

In order to get the best performance from carrier phase -based GNSS positioning methods in terms of accuracy and reliability the factors affecting the signal propagation must be characterized accurately. These carrier phase -based methods include precise point positioning (PPP) as well as real-time kinematic (RTK). While much focus has been put on atmospheric effects, the antenna effects are either ignored (low-end solutions) or handled by utilizing phase center offset and phase center variation (high-end solutions). The latter approach is typical in modern RTK equipment. Survey-grade antennas are designed to have such fine az-imuthal symmetry in the phase response that only elevation- dependent correction must be applied to the observations. This is referred to as the phase center variation. Moreover, the final baseline solution is corrected with the phase center offset in order to map the solution to a physical point in the antenna structure. The approach typically assumes that antennas of the same type have similar spatial response characteristics so that the same correction data can be applied to all the antennas of the same make. However, carrier phase -based techniques have been proposed for consumer-grade devices, in which the antennas are typically cheap, small and unoptimally positioned in the devices. In such cases the phase response may have high asymmetry both in azimuth and elevation and, hence, the current practices may no longer be sufficient. The unmodelled biases, amongst other, have impact on the probability of successful integer ambiguity fixing in RTK. This paper characterizes three antennas designed for GPS LI reception in terms of their magnitude and phase responses as a function of azimuth and elevation of the signal source. Two of the measured antennas were patches mounted in BluetoothTMGPS -receivers and one antenna was Trimble BulletTMIII that was measured for reference purposes. The phase responses are analyzed in the context of phase center offset and variation. The phase responses are then utilized in estimating the statistics of ambiguity fixing success rates. The measured antennas show varying performance in terms of phase response symmetry. The patches mounted in Bluetooth devices show approximately 70- and 49-degree variation in the phase response depending upon the direction of the signal. The lack of azimuthal symmetry prohibits the use of only elevation- dependent phase center variation tables and suggests the need for a full 3D table. The two antennas also show such differing responses that the use of a single PCV table for the antennas is not feasible. The bullet, however, shows only 4-degree variation and, hence, fine symmetry. Finally, even though the absolute variations in the phase responses are quite significant in antennas mounted in a Bluetooth GPS, the simulations show that these variations do not have a significant effect on the success rates for ambiguity resolution. This is because the probability of having a significant double difference bias turns out to be practically negligible.