J. Syrjarinne’s research while affiliated with Nokia and other places

The invention relates to a navigation systems and elements. A network element (M) includes a receiver (M.2.2) for forming assistance data relating to at least one navigation system. The network element (M) inserts indication of the navigation system and a selected mode into the assistance data and constructs the assistance data according to the selected mode. The network element (M) has a transmitting element (M.3.1) for transmitting the assistance data via a communications network (P) to a device (R). The device (R) includes a positioning receiver (R.3) for performing positioning on the basis of one or more signals of the at least one satellite navigation system; a receiver (R.2.2) for receiving the assistance data from the network element (M); and an examining element (R.1.1) adapted to examine the received assistance data. The assistance data is adapted to be used by the positioning receiver for performing positioning of the device (R).

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 Bluetooth^TMGPS -receivers and one antenna was Trimble Bullet^TMIII 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.

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.

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.