The real-time kinematic precise point positioning (PPP-RTK) technique enables integer ambiguity resolution by providing singlereceiver users with information on the satellite phase biases next to the standard PPP corrections. Using undifferenced and uncombined observations, rank deficiencies existing in the design matrix need to be eliminated to formestimable parameters. In this contribution, the estimability of the parameters was studied in single-frequency ionosphere-weighted scenario, given a dynamic satellite-clock model in the network Kalman filter. In case of latency of the network corrections, the estimable satellite clocks, satellite phase biases, and ionospheric delays need to be predicted over short time spans. With and without satellite-clock models incorporated in the network Kalman filter, different approaches were used to predict the network corrections. This contribution shows how the predicted network corrections responded to the presence and absence of satellite-clock models. These differences in the predicted network corrections were also reflected in the user positioning results. Using three different 1-Hz global positioning system (GPS) single-frequency data sets, two user stations in one small-scale network were used to compute the positioning results, applying predicted network corrections. The latency of the network products ranges from 3 to 10 s. It was observed that applying strong satellite-clock constraints in the network Kalman filter (i.e., with the process noise of 1 or 0.5mm per square root of second) reduced the root-mean squares (RMS) of the user positioning results to centimeters in the horizontal directions and decimeters in the vertical direction for latencies larger than 6 s, compared to the cases without a satellite-clock model.@en

Precise point positioning (PPP) and its integer ambiguity resolution-enabled variant, PPP-RTK (real-time kinematic), can benefit enormously from the integration of multiple global navigation satellite systems (GNSS). In such a multi-GNSS landscape, the positioning convergence time is expected to be reduced considerably as compared to the one obtained by a single-GNSS setup. It is therefore the goal of the present contribution to provide numerical insights into the role taken by the multi-GNSS integration in delivering fast and high-precision positioning solutions (sub-decimeter and centimeter levels) using PPP-RTK. To that end, we employ the Curtin PPP-RTK platform and process data-sets of GPS, BeiDou Navigation Satellite System (BDS) and Galileo in stand-alone and combined forms. The data-sets are collected by various receiver types, ranging from high-end multi-frequency geodetic receivers to low-cost single-frequency mass-market receivers. The corresponding stations form a large-scale (Australia-wide) network as well as a small-scale network with inter-station distances less than 30 km. In case of the Australia-wide GPS-only ambiguity-float setup, 90% of the horizontal positioning errors (kinematic mode) are shown to become less than five centimeters after 103 min. The stated required time is reduced to 66 min for the corresponding GPS + BDS + Galieo setup. The time is further reduced to 15 min by applying single-receiver ambiguity resolution. The outcomes are supported by the positioning results of the small-scale network.

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The Indian Regional Navigation Satellite System (IRNSS) has recently (as of May 2016) become operational. The system has been developed with the objective of offering positioning, navigation, and timing (PNT) to users in its two service areas, covering the Indian landmass and the Indian Ocean, respectively. It is the goal of this contribution to provide further insight into the full-constellation L5 pseudorange single-point positioning (SPP) capabilities of the system. A detailed dilution of precision (DOP) analysis of its two service areas, including the identification, in location and time, of poor receiver-satellite geometries is provided. It is hereby demonstrated how the impact of some of these poor receiver-satellite geometries can be mitigated by means of height-constraining. An overview and analysis of the SPP precision is also provided including easy-to-use representative day-averaged values for a grid of locations covering the two service areas.

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The Indian Regional Navigation Satellite System (IRNSS) has recently (May 2016) reached its full operational capability. In this contribution, we provide the very first L5 attitude determination analyses of the fully operational IRNSS as a standalone system and also in combination with the fully operational GPS Block IIF along with the corresponding ambiguity resolution results. Our analyses are carried out for both a linear array of two antennas and a planar array of three antennas at Curtin University, Perth, Australia. We study the noise characteristics (carrier-to-noise density, measurement precision, time correlation), the integer ambiguity resolution performance (LAMBDA, MC-LAMBDA) and the attitude determination performance (ambiguity float and ambiguity fixed). A prerequisite for precise and fast IRNSS attitude determination is the successful resolution of the double-differenced integer carrier-phase ambiguities. In this contribution, we will compare the performance of the unconstrained and the multivariate-constrained LAMBDA method. It is therefore also shown what improvements are achieved when the known body geometry of the antenna array is rigorously incorporated into the ambiguity objective function. As our ambiguity-fixed outcomes show consistency between empirical and formal results, we also formally assess the precise attitude determination performance for several locations within the IRNSS service area.

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The Indian Regional Navigation Satellite System (IRNSS) has recently (May 2016) become fully operational. In this contribution, for the fully operational IRNSS as a stand-alone system and also in combination with GPS, we provide a first assessment of L5 integer ambiguity resolution and positioning performance. While our empirical analyses are based on the data collected by two JAVAD receivers at Curtin University, Perth, Australia, our formal analyses are carried out for various onshore locations within the IRNSS service area. We study the noise characteristics (carrier-to-noise density, measurement precision, time correlation), the integer ambiguity resolution performance (success rates and ambiguity dilution of precision), and the positioning performance (ambiguity float and ambiguity fixed). The results show that our empirical outcomes are consistent with their formal counterparts and that the GPS L5-data have a lower noise level than that of IRNSS L5-data, particularly in case of the code data. The underlying model in our assessments varies from stand-alone IRNSS (L5) to IRNSS (Formula presented.) GPS (L5), from unconstrained to height-constrained and from kinematic to static. Significant improvements in ambiguity resolution and positioning performance are achievable upon integrating L5-data of IRNSS with GPS.@en

The Indian Regional Navigation Satellite System (IRNSS) has recently (May 2016) become fully-operational and has been provided with the operational name of NavIC (Navigation with Indian Constellation). It has been developed by the Indian Space Research Organization (ISRO) with the objective of offering positioning, navigation and timing (PNT) to the users in its service area. This contribution provides for the first time an assessment of the IRNSS L5-signal capability to achieve instantaneous attitude determination on the basis of data collected in Perth, Australia. Our evaluations are conducted for both a linear array of two antennas and a planar array of three antennas. A pre-requisite for precise and fast IRNSS attitude determination is the successful resolution of the double-differenced (DD) integer carrier-phase ambiguities. In this contribution, we will compare the performances of different such methods, amongst which the unconstrained and the multivariate-constrained LAMBDA method for both linear and planar arrays. It is demonstrated that the instantaneous ambiguity success rates increase from 15% to 90% for the linear array and from 5% to close to 100% for the planar array, thus showing that standalone IRNSS can realize 24-h almost instantaneous precise attitude determination with heading and elevation standard deviations of 0.05 and 0.10 degrees, respectively.

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The concept of real-time kinematic precise point positioning (PPP-RTK) is to achieve integer ambiguity resolution (IAR) at a single global navigation satellite system (GNSS) user by providing network-derived satellite phase biases (SPBs) in addition to the standard PPP corrections. The integerness of the user ambiguities gets recovered and resolved, obtaining high-precision position solutions with the aid of the precise carrier-phase observables. Most of current PPP-RTK methods focus on processing dual-frequency or multifrequency GNSS network observations. The new developing Indian regional navigation satellite system (IRNSS), however, provides only a single-frequency signal in L-band, and shares the L5 frequency with the American global positioning system (GPS), the European Galileo, and the Japanese quasi-zenith satellite system (QZSS). This contribution proposes a new array-aided state-space RTK (SS-RTK) method following the concept of PPP-RTK, which is applicable to the single-frequency network data processing. A small array of multi-GNSS stations, separated by a few meters, takes the role of reference station to provide a batch of single-frequency RTK corrections. Similar to PPP-RTK, the single-frequency stand-alone user ambiguities are a double-differenced (DD) form after applying the SS-RTK corrections. Based on the proposed array-aided SS-RTK concept, the authors analyze the capability of the single-receiver positioning with IAR using L5/E5a frequency observations from IRNSS, as well as GPS, Galileo, and QZSS. Results from real-data experiments demonstrate that even though stand-alone RTK using current IRNSS satellites is not yet possible, they effectively contribute to the tightly integrated multisystem RTK. By increasing the number of antennas in the array used for SS-RTK corrections, the user would achieve more precise and reliable positions. After increasing the dimension of the array to four antennas, a 4-10% improvement in the IAR success rate is experienced. Moreover, the convergence time of the float solutions, reaching a subdecimeter precision level, reduces from 30 to 40 min (single-antenna array) to about 20 min (four-antenna array).

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The development of an Australian PPP-RTK processing platform is an important component of a multi-GNSS (global navigation satellite system) enabled national positioning infrastructure. The PPP-RTK concept extends the precise point positioning (PPP) concept by providing single-receiver users with information enabling integer ambiguity resolution, thereby reducing convergence times as compared to that of PPP. In this contribution we present and discuss the underlying principles of the PPP-RTK platform for both network and user. We demonstrate its GPS-based performance and provide an outlook for when multi-GNSS constellations, such as BDS, Galileo and QZSS, become fully operational.

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A first assessment of GLONASS CDMA L3 ambiguity resolution and positioning performance is provided. Our analyses are based on GLONASS L3 data from the satellite pair SVNs 755-801, received by two JAVAD receivers at Curtin University, Perth, Australia. In our analyses, four different versions of the two-satellite model are applied: the geometry-free model, the geometry-based model , the height-constrained geometry-based model, and the geometry-fixed model. We study the noise characteristics (carrier-to-noise density, measurement precision), the integer ambiguity resolution performance (success rates and distribution of the ambiguity residuals), and the positioning performance (ambiguity float and ambiguity fixed). The results show that our empirical outcomes are consistent with their formal counterparts and that the GLONASS data have a lower noise level than that of GPS, particularly in case of the code data. This difference is not only seen in the noise levels but also in their onward propagation to the ambiguity time series and ambiguity residuals distribution.

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Knowledge of inter-system biases (ISBs) is essential to combine observations of multiple global and regional navigation satellite systems (GNSS/RNSS) in an optimal way. Earlier studies based on GPS, Galileo, BDS and QZSS have demonstrated that the performance of multi-GNSS real-time kinematic positioning is improved when the differential ISBs (DISBs) corresponding to signals of different constellations but transmitted at identical frequencies can be calibrated, such that only one common pivot satellite is sufficient for inter-system ambiguity resolution at that particular frequency. Recently, many new GNSS satellites have been launched. At the beginning of 2016, there were 12 Galileo IOV/FOC satellites and 12 GPS Block IIF satellites in orbit, while the Indian Regional Navigation Satellite System (IRNSS) had five satellites launched of which four are operational. More launches are scheduled for the coming years. As a continuation of the earlier studies, we analyze the magnitude and stability of the DISBs corresponding to these new satellites. For IRNSS this article presents for the first time DISBs with respect to the L5/E5a signals of GPS, Galileo and QZSS for a mixed-receiver baseline. It is furthermore demonstrated that single-frequency (L5/E5a) ambiguity resolution is tremendously improved when the multi-GNSS observations are all differenced with respect to a common pivot satellite, compared to classical differencing for which a pivot satellite is selected for each constellation.

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Global Navigation Satellite Systems (GNSS) have become ubiquitous in positioning, guidance and navigation. GNSS-based attitude determination and relative navigation are the important and promising applications. In this contribution we explore the potential of Low Earth Orbiting (LEO) satellite navigation in formation using arrays of GNSS sensors. We consider multiple LEO platforms in close formation, each equipped with multiple GNSS antennas/receivers. Platform processing involves precise attitude determination using the Multivariate Constrained Least-squares AM Biguity Decorrelation Adjustment (MCLAMBDA) method effectively utilizing known antenna geometry in local body frame. Between-platform processing involves estimation of unconstrained baselines between platforms using array-aided relative positioning effectively exploiting the platform antenna geometry in improving between-platform ambiguity resolution and baseline estimates. Finally, we use nonlinear recursive filtering to further improve the attitude angular estimates and between-platform baseline estimates. Our hardware-in-the-loop experiment with space enabled Namuru GNSS receivers shows the potential of stand-alone, unaided, single-frequency attitude determination and relative positioning of LEO satellites.

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The concept of PPP-RTK is to achieve integer ambiguity resolution (IAR) at a single GNSS user by providing network-derived satellite phase biases (SPBs) in addition to the standard precise point positioning (PPP) corrections. These corrections enable recovering integerness of user ambiguities, thereby recovering the full capability of the precise carrier-phase observations. This contribution analyzes the capability of single-receiver positioning with IAR using new L5/E5a-frequency observations from GPS, the European Galileo, the Japanese quasi-zenith satellite system (QZSS) and the Indian regional navigation satellite system (IRNSS). In the absence of network products for new systems, especially for IRNSS, we use a small array of multi-GNSS stations to provide a batch of network-derived corrections. These array-aided corrections, comprising estimable combinations of the satellite clocks, first-order slant ionospheric delays as well as the satellite phase biases, are applied to the multi-system single-frequency L5/E5a-observations of the user station. Results from real-data experiments demonstrate that even though standalone PPP-RTK using current L5/E5a-enabled satellite sets of each single system is not possible yet, they effectively contribute to the tightly integrated multi-system PPR-RTK.@en