Geometric precision evaluation methodology of multiple reference station network algorithms

High accuracy acceleration determination by using multiple GNSS reference stations

Reusable launch vehicles (RLV) in a vertical take-off vertical landing configuration require accurate measurements of the height above the ground during the final descent just before landing. It is proposed to use real-time kinematic positioning (RTK), which is a differential GNSS navigation method requiring a nearby reference GNSS antenna and receiver, to measure the rover's position with centimetre accuracy. The effects of the engine plume, vibration and multipath are challenging when using this carrier-phase based positioning method on an RLV. Especially the residual differential tropospheric error due to the rover and reference GNSS antennas being at different heights, primarily caused by humidity in the air, may hinder the successful fixing of the carrier phase ambiguities. To gain a better understanding of the RTK performance to be expected on a landing RLV, a skydiver experiment was conducted in April 2022. The skydiver was equipped with a rover GNSS receiver and a helmet with a GNSS antenna on top and an independent integrated navigation system serving as reference. The skydiver reached free fall velocities of up to 385 km/h, which is seen representative of the vertical velocity of an RLV. The paper describes the experiment procedure and the results of the experiment.

Reliable real-time kinematic (RTK) is crucially important for emerging global navigation satellite systems (GNSSs) applications, such as drones and unmanned vehicles. The performance of conventional single baseline RTK (SBRTK) with one reference station degrades greatly in dense, urban environments, due to signal blockage and multipath error. The increasing use of multiple reference stations for kinematic positioning can improve RTK positioning accuracy and availability in urban areas. This paper proposes a new algorithm for multi-baseline RTK (MBRTK) positioning based on the equivalence principle. The advantages of the solution are to keep observation independent and increase the redundancy to estimate the unknown parameters. The equivalent double-differenced (DD) observation equations for multiple reference stations are firstly developed through the equivalent transform. A modified Kalman filter with parameter constraints is proposed, as well as a partial ambiguity resolution (PAR) strategy is developed to determine an ambiguity subset. Finally, the static and kinematic experiments are carried out to validate the proposed algorithm. The results demonstrate that, compared with single global positioning system (GPS) and Beidou navigation system (BDS) RTK positioning, the GPS/BDS positioning for MBRTK can enhance the positioning accuracy with improvement by approximately (45%, 35%, and 27%) and (12%, 6%, and 19%) in the North (N), East (E), and Up (U) components, as well as the availability with improvement by about 33% and 10%, respectively. Moreover, the MBRTK model with two and three reference receivers can significantly increase the redundancy and provide smaller ambiguity dilution of precision (ADOP) values. Compared with the scheme-one and scheme-two for SBRTK, the MBRTK with multiple reference receivers have a positioning accuracy improvement by about (9%, 0%, and 6%) and (9%, 16%, and 16%) in N, E, and U components, as well as the availability improvement by approximately 10%. Therefore, compared with the conventional SBRTK, the MBRTK can enhance the strength of the kinematic positioning model as well as improve the positioning accuracy and availability.

A method of time difference of arrival (TDOA) location for shortwave signal source by four receiving stations is introduced. The precision of time difference and the Geometric Dilution of Precision (GDOP) of TDOA location are analyzed and simulated. The results show that TDOA estimation performance is positively correlated with signal bandwidth, signal cumulative time and signal-to-noise ratio (SNR), while TDOA location precision is positively correlated with TDOA estimation precision and distance between the receiving stations. At the same time, the simulation analysis of station arrangement among multiple stations is carried out, and the results show that Y-shaped station mode gets the best location effect.

Influence of the input layer signals of ANNs on wind power estimation for a target site: A case study

기선장에 따른 GPS 위치 정도 및 분포를 측정하기 위하여 2002년 5월 29일부터 6월 2일까지 2대의 GPS수신기 (L1, 12채널)를 이용하여 고정점에서 30분에서 24시간동안 관측하는 실험을 수행하였다. 기준국(PKNU)과 이동, 국립지리원의 GPS 상시관측소에서 수신한 GPS 데이터는 동적 및 정적 후처리방식으로 처리하였으며, 그 결과를 요약하면 다음과 같다. 1. 2002년 5월 31일 차단각 (cut-off angle) <TEX>$15^{\circ}$</TEX>에서 6시간 이상 관측 가능한 위성은 16개였고, 위성은 주로 동서방향으로 배치되어 있었다. 10분마다 평균한위성 수와 GDOP는 각각 8개, 3.89이었다. 2. 후처리 전후의 GPS 평균위치는 모두 기준점에서 남서쪽으로 편위 (단독 측위 : 1.17m, 후처리 : 평균 0.43m)되었다. 확율원 오차는 단독 측위가 6.65m이었고 이를 동적 후처리하면 단독 측위의 약 33.8%(표준편차 0=17.2), 정적 후처리하면 단독 측위의 약 5.3% (0=2.2)로 감소시 킬 수 있었다. 3. 정적 후처리방식으로 구한 기선장 x(Km)와 확률원 오차 y(m) 의 관계식은 y = 0.0016x + 0006 <TEX>$(R^2=0.87)$</TEX>이었다. 본 연구에서 사용한 1주파용 GPS 수신기를 이용하여 정적 후처리방식으로 위치를 측정하는 경우, 기선장을 100Km 이내로 하고 GPS 수신시간을 30분 이상으로 하면 확율원 오차 20 Cm 이내의 측위가 가능함을 알 수 있었다. To measure the GPS position accuracy and its distribution according to the length of the baseline, 30 minutes to 24 hours observations at the fixed location were conducted with two GPS receivers (Ll, 12 channels) on May 29 to June 2, 2002. The GPS data received at the reference station, the rover station and the ordinary times GPS observation station operated by the National Geography Institute in Korea were processed in kinematic and static post-processing methods with a post -processing software. The results obtained are summarized as follows: 1. The number of the satellite that could be observed continuously more than six hours was 16 and most of these satellites were positioned at east-west direction on May 31, 2002. The number of the satellite observed and the geometric dilution of precision (GDOP) determined by the average of every 10 minute for the day were 8 and 3.89, respectively. 2. Both the average GPS positions before and after post-processing were shifted (standalone: 1.17 m, post -processing: 0.43m) to the south and west. The twice distance root mean square (2drms) measured with standalone was 6.65m. The 2drms could be reduced to 33.8% (standard deviation 0=17.2) and 5.3% (0=2.2) of standalone by the kinematic and the static post-processing methods, respectively. 3. The relationship between the length of the baseline x (km) and the 2drms y (m) obtained by the static post-processing method was y=0.00l6x+0.006 <TEX>$(R^2=0.87)$</TEX>. In the case of the positioning with the static post-processing method using the GPS receiver, it was found that a positioning within 20cm 2drms was possible when the length of the baseline was less than 100km and the receiving time of the GPS is more than 30 minutes.

: This paper evaluates the performance of real-time kinematic (RTK) algorithms designed for highway environments. The experiments were performed over a number of years in a variety of environments ranging from a racetrack with a completely clear view of the sky to a busy suburban freeway with overpasses, trucks, and other obscurations. A description of a single-epoch RTK algorithm, which performs well in the freeway environment, is given. A number of the experiments used two antennas and two receivers on the vehicle for error detection. This configuration is capable of providing high confidence in correct RTK solutions. Some of the experiments used map-based altitude aiding to improve RTK performance. Possible racetrack and highway applications are discussed.

By using multiple reference stations, we have developed a method to get reliable ULF global geomagnetic variations. This background is extremely useful for detecting local anomalous behaviors. This paper demonstrates developed variable tools to identify the anomalies in two frequency ranges; daily variation and 10-1000 seconds. For estimating background daily variations, the periodical model has been applied for data observed at 3 reference stations and a study station. Comparison between the first principal component of the periodical data from the reference stations and the periodical data derived from the target station provides high correlation in general. For data with 100 sec periods after wavelet filtering, the nighttime energy variations have been investigated among 3 reference stations and a study station. The similar principal component analysis as the diurnal variation has been performed and results also show high correlation between the variation at the target and the global background. These tendency suggest that the developed two methods are effective to identify the anomalies in automatic. Examining the original data, we can know details of waveform and distinguish whether the anomalies is related to underground activities or just some artificial noises.

There is a trend for the establishment of regional-scale GPS permanent receiver networks, for a variety of applications including to support high accuracy, carrier phase-based positioning for surveying and precise navigation. When implemented in real-time, GPS users located within the region enclosed by multiple GPS reference stations can precisely position by using, for example, the ‘correction terms’ generated and transmitted by the reference station network. For such a configuration one of the major challenges is that the integer ambiguities have to be resolved during the real-time processing of the reference network data in order to ensure the generation of the carrier phase corrections, even when the reference receivers are many tens of kilometres apart. Due to the presence of distance dependent errors in the double-differenced data (principally the ionospheric and tropospheric delays) reliable instantaneous (single epoch) ambiguity resolution is difficult in the case of medium-scale reference networks (defined here as where the reference stations are typically in the range 50–100km apart).In practice, the ambiguities among the reference stations can be correctly resolved during an initialization procedure, but the main challenge is to continuously resolve the new ambiguities that result when the tracked satellite experiences cycle slips, or after any long data gap, or when a new satellite rises. In this paper a three-step methodology is proposed which can be implemented in realtime. Firstly, the high correlation of the atmospheric delay between adjacent epochs is used to assist cycle-slip recovery and ambiguity resolution. Then these atmospheric biases are predicted for double-differenced observations on an epoch-by-epoch and satellite-by-satellite basis. Finally these predicted atmospheric biases are applied to an algorithm that can fix the new ambiguities after a long data gap or when a new satellite rises.Data from a set of reference stations spaced 80 km apart were used to test the effectiveness of the algorithm. The results indicate that the proposed methodology can provide reliable integer ambiguities for reference stations spaced many tens of kilometres apart.

A novel key frames matching approach for human locomotion interpolation is proposed in this paper. Firstly, locomotion data is transformed from body coordinate system to world coordinate system based on recursive algorithm; secondly, features of two feet and step distance are extracted; thirdly, key frames are extracted based on feature curve and the locomotion sequence is segmented; fourthly, a new approach for key frames matching is put forward; finally, transition frames are interpolated between the matched key frames using quaternion Slerp (Spherical linear interpolation) algorithm and linear interpolation algorithm. The main contributions of this paper are: i) different locomotion sequences can be synthesized in a controllable manner with good effect; ii) to extract locomotion features conveniently, locomotion data in body coordinate system is transformed to world coordinate system; iii) to analyze locomotion sequences intuitively and accurately, key frames are extracted and locomotion sequences are segmented based on feature curve analysis; iv) to avoid illogical jump of traditional interpolation between key frames, a new key frames matching strategy is put forward and only the key frames between two continuous segments can be chosen as matching frames. Experimental results based on the CMU MoCap database show that the proposed method can confirm the logical correctness and naturalness in the junction of two locomotion sequences.

This paper introduces data broadcasting technology and cm-level precision positioning technology, which are contributing to taking one step further into the era of autonomous driving. How ‘broadcasting’ and ‘positioning’ can be the best combination will be explained. Furthermore, the performance of RTK (Real-Time Kinematic) correction data for cm-level accuracy will be verified through ATSC 3.0 test-service in South Korea.

With the rapid development of V2X (Vehicle to Everything), high-accuracy positioning technology has drawn the attention of operators and manufactures. In consideration of automation levels, operated condition or other factors, different V2X application scenarios are required different position accuracy. In general, the quality of positioning has a significant impact on the accuracy of service triggering. The vehicle can adopt different positioning technologies according to its own application scenarios' requirements. As the essential component of C-V2X equipment, GNSS (Global Navigation Satellite System) and RTK (Real-time Kinematic) are most basic positioning technology. However, this technology is not suitable for whole conditions, such as dense urban areas, tunnels or underground parking. The location service providers always provide the highest value of position accuracy in open environment, but positioning quality of the special environments is unknown. Therefore, this paper proposes a test method to evaluate the performance of GNSS and RTK in actual environments. This method can evaluate multiple vehicle terminals' positioning quality from different location service providers simultaneously. Finally, according to the actual test results, this paper estimates whether key performance indicators of GNSS and RTK can meet the application requirements and analyses the influence of positioning for V2X applications scenarios.

Differential GPS (DGPS) and Real-Time- Kinematic (RTK) solutions are widely accepted meth- ods for accurate positioning and navigation. Initially these methods were based on single reference stations. A big breakthrough in performance and accuracy was achieved by the introduction of network solutions. To- day, the use of the Virtual Reference Station method is a standard technology applied in a large number of regional RTK networks all over the world, to pro- vide a positioning service with centimetre accuracy. DGPS techniques are used for marine, airborne and land applications and provide accuracies in the sev- eral decimetre range. The DGPS and RTK methods are based on regional reference station networks or nearby single stations. In contrast, the Precise Point Position- ing (PPP) method is providing position accuracy of several centimetres to decimetres based on a globally distributed tracking network. Precise satellite orbit and clock information is derived from the network process- ing. The achievable accuracy with PPP is impressive, but this method suffers from long convergence times of the order of more than 20-30 min to achieve acceptable

Performance evaluation of a real-time high-precision landslide displacement detection algorithm based on GNSS virtual reference station technology

Virtual Reference Station (VRS) is a kind of network RTK technology. For solving the limitations of real-time standard dynamic (RTK) system, a new method for high-precision RTK positioning VRS is proposed. At the same time, aiming at the real-time solution of the ambiguity of VRS network, a new method based on the non-ionospheric combination equation to solve the ambiguity is proposed. The linear interpolation model is used to generate the comprehensive error correction number, and the virtual observation value is proposed. The method was generated and tested in Nanchang University and Poyang Lake area. The test was conducted at different locations around Poyang Lake to assess the accuracy of VRS RTK positioning; the results show that the use of multiple reference station networks increases the coverage of location service areas and enhances robustness over a single reference station system, got higher positioning accuracy. The VRS RTK is positioned in the experimental network with a horizontal accuracy of 1–2 cm and a vertical accuracy of 3–5 cm.