Yong Seon Moon

DSSS-Based Channel Access Technique DS-CDMA for Underwater Acoustic Transmission

This paper proposes a novel method for acoustically and wirelessly transmitting data underwater with a high transmission rate. The method uses the most promising physical layer and multiple access technique (i.e., the code division multiple channel access technique) to divide the channel into subchannels. Data is transmitted through these subchannels. The codes are PN (pseudo random) sequences. In the spread-spectrum technique, a signal such as electrical, electromagnetic, acoustic signal generated in a particular bandwidth is deliberately spread in the frequency domain, which results in a signal with a wider bandwidth. This paper reviews the possibility of application of the DS-CDMA (direct sequence-code division multiple access) technique in an underwater system using MATLAB. As the result of our review, we recognize that the DS-CDMA technique can be applied to underwater environments.

Attitude estimation using depth measurement and AHRS data for underwater vehicle navigation

This paper proposes a method for attitude estimation that utilizes the depth measurement as well as the MEMS-AHRS (Micro-electromechanical systems Attitude Heading Reference System). Estimating attitude in real-time is crucial for navigation of an unmanned underwater vehicle since path planning, trajectory tracking, and collision-avoidance is based on the attitude information. Many of the attitude estimation methods usually use the measurements from IMU(Inertial Measurement Unit) and three axis magnetic field measurements. However, the IMU measurement leads accumulated drift in attitude estimation and the magnetic field measurements are affected by bias and disturbance by electromagnetic field sources around the sensor. The method that makes use of the depth measurement whose accuracy and robustness is superior to the measurements by IMU and magnetic field sensors, can improve the performance of the attitude estimation. The method uses quaternion to explicitly relate the depth to the attitude including the yaw. The method is tested and evaluated using simulated data and the data from test tank and sea trial experiment. The results show explicit improvement especially when the depth changes with time.

Measurement of DS-CDMA Propagation Distance in Underwater Acoustic Communication Considering Attenuation and Noise

It is very difficult to design an underwater communication system because of multipath, Doppler effects, noise, and attenuation. These factors lead to errors in the communication performance and maximum propagation distance. In this study, we calculate the distance that can be realized using the direct-sequence code division multiple access (DS-CDMA) technique with direct-sequence spread spectrum (DSSS) in an underwater communication system considering only the attenuation and noise. We also compare the estimated and calculated propagation distances obtained for several different scenarios.

Implementation of motor controller using Zynq EPP

In this paper, in order to control motor, we apply latest All Programmable SoC technologies that fuse FPGA technologies and embedded processor technologies. We also propose to apply method that the structure of motor controller decentralizes into FPGA and level of embedded processor. We verify the possibility of application of motor controllers through design, implementation and experiment for multi-axis motor controller using Zynq EPP(Extensible Processing Platform) which is one of All Programmable SoC by made Xilinx.

Implementing indoor navigation of a mobile robot

This paper describes an implementation of autonomous navigation of a mobile robot indoors. The implementation includes map building, path planning, localization, local path planning and obstacle avoidance, and path tracking. ICP(Iterative closest point) is employed to build grid based map using scanned range data. Dijkstra algorithm plans path from an initial location to a goal position. Particle filter estimates the robot position and orientation using the scanned range data. Elastic force is used for local path planning and obstacle avoidance towards a goal position. The algorithms are combined for autonomous navigation in a work area of 100m×40m, which comprises rooms, corridors, obstacles like passers-by, and many furniture and exhibition area. The robot ran at the maximum speed of 1.0 m/sec, and passed all the way points and reached to goal location through the path of the length 165m in 255 seconds, with the average speed of 0.65m/sec.

A method for object detection using point cloud measurement in the sea environment

This paper describes a method for detection of object using 3D point cloud measurement in the sea environment. The method employs RBNN clustering method and using a 3D Lidar, mono-vision and stereo-vision cameras, and radar vision system. A radially based nearest neighbors (RBNN) clustering technique is adopted to perform object detection on 3D point cloud clustering. RBNN is constructing clusters based on the radius or distance parameter. In RBNN, each 3D point searches its nearest neighbor (NN) under some radius threshold value and combines all the neighboring points as a group or cluster. The experimental results verify the performance of RBNN to detect objects from 3D point cloud measurements in sea environment.

Navigation of unmanned surface vehicle and detection of GPS abnormality by fusing multiple sensor measurements

This paper proposes a method for fused navigation of an unmanned surface vehicle (USV). The method also detects the outlier and interference of global positioning system (GPS) simultaneously. The method fuses available sensor measurements through extended Kalman filter (EKF) to find the location and attitude of the USV. The method uses error covariance of estimated location for detection of GPS outlier and interference. When outlier and interference of the GPS is detected, the method excludes GPS data from navigation process. The measurements to be fused for the navigation are position by GPS, acceleration, angular rate, magnetic field, linear velocity, and range and bearing to acoustic beacons. The method is tested using simulated measurement data and measurement data provided by experiment. The results show that the method detects GPS outlier and interference as well as the GPS recovery, which frees the USV navigation from the problem of GPS abnormality.

Fusion of multiple sensor measurements for navigation of an unmanned marine surface vehicle

This paper proposes a method for fused navigation of an unmanned marine surface vehicle (UMSV). The method also detects the outlier and interference of global positioning system (GPS) simultaneously. The method fuses available sensor measurements through extended Kalman filter (EKF) to find the location and attitude of the vehicle. The method uses error covariance of estimated location for detection of GPS outlier and interference. When outlier and interference of the GPS is detected, the method excludes GPS data from navigation process. The measurements to be fused for the navigation are position by GPS, acceleration, angular rate, magnetic field, linear velocity, and range and bearing to acoustic beacons. The method is tested through simulated data and measurement data produced through navigation of a vehicle. The results show that the method detects GPS outlier and interference as well as the GPS recovery, which frees the UMSV navigation from the problem of GPS abnormality. The method is applicable to the vehicle navigation where the UMSV is out of reach from the GPS jamming detection network such as GAARDIAN (GNSS Availability Accuracy Reliability and Integrity Assessment for Timing and Navigation) or jammer detection and location (JLOC) system.

Visual tracking of objects for unmanned surface vehicle navigation

This paper presents a method which detects and tracks objects for navigation of a maritime surface vehicle. The method uses stereo vision system which finds saliency map, calculates disparity and distance from the stereo vision image. The method adopts frequency-tuned saliency map and finds dissimilar area in the image with the template which is found by the salient region detection. It is possible to find the absolute distance using the information of baseline, characteristics of the camera such as focal length, and the disparity which is affected by the difference of viewpoints between the cameras. The algorithm works in real time and the performance is tested through experiments surface of maritime environment.

Direct drive thruster: Reduction of magnetic field distortion for navigation of an underwater robot

This paper reports development of a direct drive thruster for underwater vehicles. The direct drive thruster does not use mechanical gear and magnetic coupling for torque transmission to propeller. Therefore it generates less magnetic distortion than usual electrical thrusters which use magnetic coupling. Many underwater robots use magnetic field for determining the heading of an underwater robot. The use of direct drive thruster contributes reducing the disturbance on magnetic field, and thus, reduces the uncertainty in measured heading direction. The thruster consists of motor, propeller, electrical driver, and water resistant housing. It has 1 kW power rating with brushless DC direct drive motor. It is designed to provide the maximum speed of 7 nautical miles and maximum thrust force of 25 Kg force. Since it uses direct drive motor, gear system, which is needed to reduce revolution speed and increase torque, is no longer needed. With no gear system, reduction of weight, power loss, and maintenance effort is possible. Also, it does not use magnetic coupling, and does not generate magnetic interference. The test results show power efficiency and robust drive.