2015 Fiscal Year Annual Research Report
| Project/Area Number |
15F15047
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| Research Institution | The University of Tokyo |
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Principal Investigator |
上條 俊介 東京大学, 大学院情報学環, 准教授 (70334357)
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| Co-Investigator(Kenkyū-buntansha) |
HSU LI-TA 東京大学, 大学院情報学環, 外国人特別研究員
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| Project Period (FY) |
2015-04-24 – 2017-03-31
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| Keywords | GPS / GNSS / 3D maps / 3D building model / Urban Canyon / Multipath / RAIM / Autonomous driving |
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| Outline of Annual Research Achievements |
Autonomous driving requires lane-level positioning accuracy, in the other word, 1.5 meters accuracy. We focused on urban canyon environments such as Hitotsubashi and Shinjuku. The GNSS performance in these areas are strongly affected by multipath effects and NLOS receptions. To solve these difficulties, we used 3D building model and ray-tracing simulation to estimate the reflection effects caused by buildings. A position hypothesis positioning is proposed to apply the estimated reflection effects. We called it 3D-GNSS. This 3D-GNSS positioning achieves 5.1 meters of positioning accuracy using GPS, GLONASS and QZSS signals. An accuracy estimation method is proposed to calculate the reliability of 3D-GNSS result. By selecting the reliable result, we achieve 4.4 meters in 1-sigma positioning error. To exclude the abnormal NLOS reflection, a consistency-check that similar to RAIM FDE algorithm is developed to be used in 3D-GNSS, hence, the positioning accuracy is further improved to approximately 3 meters. In very deep urban canyon that covered by buildings and foliage, only a few GNSS signals can be received even if using high sensitivity receivers. To bridge the navigation service while the termination of GNSS signal, INS is a promising candidate. We implemented a pocket-based smartphone PDR to combine with 3D-GNSS. The result shows the proposed integration system achieves 4.3 meters positioning accuracy while the commercial GNSS receiver achieves about 39.8 meters in Shinjuku area.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The 3D-GNSS positioning algorithm is successfully developed and validated. Its integration with inertial sensor is also first evaluated with a pocket-based pedestrian dead reckoning. The current evaluation is mostly based on pedestrian tests because of the ease of conducting experiments. The pedestrian usually experiences more difficult signal reception scenarios because of walking on the sidewalk instead of the middle of the streets. It is reasonable to assume the vehicle performance is better or similar to pedestrian test.
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| Strategy for Future Research Activity |
Currently, the 3D-GNSS algorithm uses only code measurements (well-known as pseudorange). The carrier phase provided by GNSS receiver has potential to provide even more accurate measurements because its resolution is in centimeter level. However, the carrier phase measurement contains a troublesome shift error, which is called carrier ambiguity. The general approach is real time kinematic (RTK), which requires a reference station (base station) to provide code/carrier corrections. We plan to develop the algorithm step by steps. Before developing the 3D map aided RTK positioning algorithm, the code-level relative positioning, namely differential GNSS (DGNSS), should be developed first. The 3D-DGNSS expects to enjoy two features of DGNSS correction, the atmospheric correction and satellite clock corrections. Moreover, the DGNSS correction also provides the clock-offset between different satellite constellation systems. This correction could benefit the previous developed consistency-check algorithm in 3D-GNSS. The second step is to implement the RTK positioning. The RTK algorithm applied double-difference measurements to retrieve the ambiguity. However, commercial GNSS receivers usually one receive measurements from single-frequency signal, which reduced the number of measurements. The insufficient number of measurements make the estimation of ambiguity even tougher. Our focus of future work will be studying how to take advantage of 3D building model and inertial navigation system to facilitate the resolution of integer ambiguity of carrier phase.
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[Presentation] GNSS positioning using WLS, DGNSS and RAIM in Tokyo City2015
Author(s)
Hsu, Li-Ta, Tokura, H., Kubo, N., Kamijo, S.
Organizer
International Symposium on GNSS 2015
Place of Presentation
Miyakomesse, Kyoto city, Kyoto fu, Japan
Year and Date
2015-11-16 – 2015-11-19
Int'l Joint Research
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