Modified RTK-GNSS for Challenging Environments.

Real-Time Kinematic Global Navigation Satellite System (RTK-GNSS) is currently the premier technique for achieving centimeter-level accuracy quickly and easily. However, the robustness of RTK-GNSS diminishes in challenging environments due to severe multipath effects and a limited number of available GNSS signals. This is a pressing issue, especially for GNSS users in the navigation industry. This paper proposes and evaluates several methodologies designed to overcome these issues by enhancing the availability and reliability of RTK-GNSS solutions in urban environments. Our novel approach involves the integration of conventional methods with a new technique that leverages surplus satellites-those not initially used for positioning-to more reliably detect incorrect fix solutions. We conducted three tests in densely built-up areas within the Tokyo region. The results demonstrate that our approach not only surpasses the fix rate of the latest commercial receivers and a popular open-source RTK-GNSS program but also improves positional reliability to levels comparable to or exceeding those of the aforementioned commercial technology.

Application of Initial Bias Estimation Method for Inertial Navigation System (INS)/Doppler Velocity Log (DVL) and INS/DVL/Gyrocompass Using Micro-Electro-Mechanical System Sensors.

This article proposes a novel initial bias estimation method using a trajectory generator (TG). The accuracy of attitude and position estimation in navigation after using the inertial navigation system/Doppler velocity log (INS/DVL) and INS/DVL/gyrocompass (IDG) for 1 h were evaluated, and the results were compared to those obtained using the conventional Kalman filter (KF) estimation method. The probability of a horizontal position error < 1852 m (1 nautical mile) with a bias interval > 400 s was 100% and 9% for the TG and KF, respectively. In addition, the IDG average horizontal position errors over 1 h were 493 m and 507 m for the TG and KF, respectively. Moreover, the amount of variation was 2 m and 27 m for the TG and the KF, respectively. Thus, the proposed method is effective for initial bias estimation of INS/DVL and IDG using micro-electro-mechanical system sensors on a constantly moving vessel.

GNSS NLOS Signal Classification Based on Machine Learning and Pseudorange Residual Check.

Global navigation satellite system (GNSS) positioning has recently garnered attention for autonomous driving, machine control, and construction sites. With the development of low-cost multi-GNSS receivers and the advent of new types of GNSS, such as Japan's Quasi-Zenith Satellite System, the potential of GNSS positioning has increased. New types of GNSS directly increase the number of line-of-sight (LOS) signals in dense urban areas and improve positioning accuracy. However, GNSS receivers can observe both LOS and non-line-of-sight (NLOS) signals in dense urban areas, and more NLOS signals are observed under static conditions than under dynamic conditions. The classification of LOS and NLOS signals is important, and various methods have been proposed, such as C/N0, using three-dimensional maps, fish-eye view, and GNSS/inertial navigation system integration. Multipath detection based on machine learning has also been reported in recent years. In this study, we propose a method for detecting NLOS signals using a support vector machine (SVM) classifier modeled with unique features that are calculated by receiver independent exchange format-based information and GNSS pseudorange residual check. We found that using both the SVM classifier and GNSS pseudorange residual check effectively reduced the error due to NLOS signals. Several static tests were conducted near high-rise buildings that are likely to receive some NLOS signals in downtown Tokyo. For all static tests, the percentage of positioning errors within 10 m in the horizontal positioning error was improved by >80% by detecting and eliminating satellites receiving NLOS signals.

Performance Evaluation of IMU and DVL Integration in Marine Navigation.

Global navigation satellite system (GNSS) spoofing poses a significant threat to maritime logistics. Many maritime electronic devices rely on GNSS time, positioning, and speed for safe vessel operation. In this study, inertial measurement unit (IMU) and Doppler velocity log (DVL) devices, which are important in the event of GNSS spoofing or outage, are considered in conventional navigation. A velocity integration method using IMU and DVL in terms of dead-reckoning is investigated in this study. GNSS has been widely used for ship navigation, but IMU, DVL, or combined IMU and DVL navigation have received little attention. Military-grade sensors are very expensive and generally cannot be utilized in smaller vessels. Therefore, this study focuses on the use of consumer-grade sensors. First, the performance of a micro electromechanical system (MEMS)-based yaw rate angle with DVL was evaluated using 60 min of raw data for a 50 m-long ship located in Tokyo Bay. Second, the performance of an IMU-MEMS using three gyroscopes and three accelerometers with DVL was evaluated using the same dataset. A gyrocompass, which is equipped on the ship, is used as a heading reference. The results proved that both methods could achieve less than 1 km horizontal error in 60 min.

GNSS Multipath Detection Using Continuous Time-Series C/N0.

The reduction of multipath errors is a significant challenge in the Global Navigation Satellite System (GNSS), especially when receiving non-line-of-sight (NLOS) signals. However, selecting line-of-sight (LOS) satellites correctly is still a difficult task in dense urban areas, even with the latest GNSS receivers. This study demonstrates a new method of utilization of C/N0 of the GNSS to detect NLOS signals. The elevation-dependent threshold of the C/N0 setting may be effective in mitigating multipath errors. However, the C/N0 fluctuation affected by NLOS signals is quite large. If the C/N0 is over the threshold, the satellite is used for positioning even if it is still affected by the NLOS signal, which causes the positioning error to jump easily. To overcome this issue, we focused on the value of continuous time-series C/N0 for a certain period. If the C/N0 of the satellite was less than the determined threshold, the satellite was not used for positioning for a certain period, even if the C/N0 recovered over the threshold. Three static tests were conducted at challenging locations near high-rise buildings in Tokyo. The results proved that our method could substantially mitigate multipath errors in differential GNSS by appropriately removing the NLOS signals. Therefore, the performance of real-time kinematic GNSS was significantly improved.

Vehicle teleoperation using 3D maps and GPS time synchronization.

In conventional vehicle teleoperation systems, using low-bandwidth, high-delay transmission links causes a serious problem for remote control of the vehicles. To solve this problem, a proposed teleoperation system employs 3D maps and GPS time synchronization. Two GPS receivers measure the transmission delay, which the system uses to estimate the vehicle's location and orientation. Field experiments show that the 3D-map-based interface lets users easily comprehend the remote environment while navigating a vehicle. The experiments also show that taking communication delays into account improves maneuverability.

Characteristics of lifestyle and health status of workers in small-scale enterprises in Japan.

This study was conducted to clarify the characteristics of small-scale enterprises (SSEs) with fewer than 50 workers, which employ 62.2% of all Japanese workers. Subjects were 71,183 workers employed at 1,761 workplaces in Tochigi, Japan, in 2002. Frequencies of abnormal lifestyle and health check-up data were described according to the category of the enterprise. Adjusted odds ratios (ORs) of the abnormal findings were calculated by logistic regression analysis. Dose-response relationships were calculated by trend tests. The frequency of abnormal findings was higher in SSEs than in other categories of enterprises. The ORs of work intensity, alcohol consumption, current smoker, and the Brinkmann index were higher in SSEs than in large-scale enterprises (LSEs) and were also significant in trend tests. The ORs of audiometry, hypertension, glucose in urine and ECG in males and females, BMI, liver function, lipid metabolism, and blood sugar in females, chest X-ray, and anemia in males were higher in SSEs. Audiometry, hypertension, anemia, ECG in both males and females; chest X-ray, and glucose in urine in males, and liver function, lipid metabolism and blood sugar in females showed significant results in trend tests. Overall health and healthy lifestyle in SSEs were worse than in LSEs.

Feasibility and effect on blood pressure of 6-week trial of low sodium soy sauce and miso (fermented soybean paste).

A double-blind, randomized placebo-controlled study was conducted to evaluate the feasibility of the long-term use of low-sodium soy sauce and miso in the general Japanese population and its effect on blood pressure (BP). Forty men and 24 women were randomly allocated to a low-sodium group (n=32) or a control group (n=32). Low-sodium soy sauce and miso, which were approximately 25% and 20% lower in salt content than common soy sauce and miso, were used in the study. The change in BP after a 6-week intervention was evaluated. There were no significant differences in age, sex, body mass index, BP or hypertension between the 2 groups before intervention. After the 6-week intervention, no significant change in BP was observed in the entire cohort. However, in those aged 40 years and older, 6.4 mmHg net reduction in diastolic BP with no significant change in systolic BP was noted in the low-sodium group. Taste evaluation for the low-sodium seasoning was considerably good. Replacing soy sauce and miso of the common type with the low-sodium alternative is feasible in the general population and could be the basis for a salt reduction strategy in the Japanese diet.