• Journal of the Korean Society for Aviation and Aeronautics
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• v.17 no.1
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• pp.52-57
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• 2009

One of the error sources for microwave ranging is the instability of the oscillator that drives the microwave signals. Dual one-way ranging (DOWR) minimizes the oscillator effect by combining two one-way carrier phase signals from two transmitter/receiver instrument. The DOWR is first implemented in the GRACE (Gravity Recovery and Climate Experiment) satellites. Direct evaluation of the DOWR is not possible due to its extremely high accuracy. The flight performance of the GRACE DOWR is analyzed by applying several indirect methods. Comparison with the design noise level is discussed.

• IEMEK Journal of Embedded Systems and Applications
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• v.5 no.4
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• pp.234-242
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• 2010

Two-way ranging methods such as TWR and SDS-TWR have been considered for many ranging systems because these methods are useful in the absence of synchronization. To estimate the location of a mobile node, complicated ranging procedures consisting of ranging frames between an anchor node and the mobile node are performed. Supporting multiple mobile nodes such as a few hundreds or thousands and several anchor nodes, the ranging procedures have the fatal disadvantage of processing delay and inefficient traffic bandwidth. On the other hand, the one-way ranging method is simple and fast, but susceptible to network synchronization. In this paper, we propose a method to modify asynchronous ranging equations to establish exact frequency or frequency offset, a method to estimate frequencies or frequency offsets, and a method to establish post-facto synchronization with anchor nodes. The synchronization for a node pair is adapted using instantaneous time information and corresponding difference of distances can be determined. We evaluate the performance of TWR, SDS-TWR and proposed ranging algorithms.

• ETRI Journal
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• v.31 no.4
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• pp.466-468
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• 2009

In this letter, we propose a one-way ranging algorithm that is based on wireless synchronization with measured timestamps and clock frequency offsets. In our proposed algorithm, an active mobile node initiates a ranging procedure by transmitting a ranging frame, and the anchor nodes report their timestamps for the received ranging frame to a reference anchor node. The synchronization of a pair of nodes is provided with instantaneous time information, and the corresponding difference of distances can be calculated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1136-1143
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• 2010

One-way laser ranging technology is applied for the precise orbit determination of LRO, which is the first trial for supporting the missions of lunar or planetary spacecraft. In this paper, LRO payload and ground system are discussed for LRO laser ranging, and some errors effecting on time of flight and tracking mount accuracy are analyzed. Additionally several technologies are also analyzed to make laser pulses shot from ground stations to arrive in the LRO earth window. Measurement data of LRO laser ranging verified that these technologies could be implemented for one-way laser ranging of lunar spacecraft.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.350-355
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• 2017

UWB (Ultra Wide Band) refers to a system with a bandwidth of over 500 MHz or a bandwidth of 20% of the center frequency. It is robust against channel fading and has a wide signal bandwidth. Using the IR-UWB based ranging system, it is possible to obtain decimeter-level ranging accuracy. Furthermore, IR-UWB system enables acquisition over glass or cement with high resolution. In recent years, IR-UWB-based ranging chipsets have become cheap and popular, and it has become possible to implement positioning systems of several tens of centimeters. The system can be configured as one-way ranging (OWR) positioning system for fast ranging and TWR (two-way ranging) positioning system for cheap and robust ranging. On the other hand, the ranging based positioning system has a limitation on the number of terminals for localization because it takes time to perform a communication procedure to perform ranging. To overcome this problem, code multiplexing and channel multiplexing are performed. However, errors occur in measurement due to interference between channels and code, multipath, and so on. The measurement filtering is used to reduce the measurement error, but more fundamentally, techniques for removing these measurements should be studied. First, the TWR based positioning was analyzed from a stochastic point of view and the effects of outlier measurements were summarized. The positioning algorithm for analytically identifying and removing single outlier is summarized and extended to three dimensions. Through the simulation, we have verified the algorithm to detect and remove single outliers.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.2
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• pp.125-130
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• 2013

Compared to OWR (One-Way Ranging) method that requires precise network time synchronization, TWR (Two-Way Ranging) method has advantages in building an indoor WPAN (Wireless Personal Area Network) location system with lower cost. However, clock offsets of nodes in WPAN system should be eliminated or compensated to improve location accuracy of the TWR method. Because conventional clock offset elimination methods requires multiple TWR transactions to reduce clock offset, they produce network traffic burden instead. This paper presents a clock offset estimation method that can reduce clock offset error with a single TWR transaction. After relative clock offsets of sensor nodes are estimated, clock offsets of mobile tags are estimated using a single TWR communication. Simulation results show that location accuracy of the proposed method is almost similar to the conventional clock offset elimination method, while its network traffic is about a half of the conventional method.

• 한국ITS학회:학술대회논문집
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• 2010.05a
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• pp.180-183
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• 2010

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.9
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• pp.898-902
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• 2015

Alternative radio-navigation technologies aim at providing continuous navigation solution even if one cannot use GNSS (Global Navigation Satellite System). In shadowing region such as indoor environment, GNSS signal is no longer available and the alternative navigation system should be used together with GNSS to provide seamless positioning. For soldiers in battlefield where GNSS signal is jammed or in street battle, the alternative navigation system should work without positioning infrastructure. Moreover, the radio-navigation system should have scalability as well as high accuracy performance. This paper presents a TWR (Two-Way-Ranging)-based cooperative positioning system (CPS) that does not require location infrastructure. It is assumed that some members of CPS can obtain GNSS-based position and they are called mobile anchors. Other members unable to receive GNSS signal compute their position using TWR measurements with mobile anchors and neighboring members. Error propagation in CPS is analytically studied in this paper. Error budget for TWR measurements is modeled first. Next, location error propagation in CPS is derived in terms of range errors. To represent the location error propagation in the CPS, Location Error Propagation Indicator (LEPI) is proposed in this paper. Simulation results show that location error of tags in CPS is mainly influenced by the number of hops from anchors to the tag to be positioned as well as the network geometry of CPS.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.75-83
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• 2005

NASA/DLR Gravity Recovery and Climate Experiment (GRACE) mission, which consists of two co-orbiting low altitude satellites, is to measure the Earth gravity field with unprecedented accuracy. Its key instruments include inter-satellite ranging systems and three-axis accelerometers. For the preliminary design and requirements analysis, extensive instrument simulation models are developed. These modeling techniques and orbit-gravity field estimation techniques are described.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.608-615
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• 2007

Generally time of arrival (TOA) information via two way communications can be derived by accurate round trip time (RTT) between two devices. However, response time demanded in RTT measurement is long, a serious TOA error is caused by each different clock drift between two devices. In order to solve this problem, we propose the TOA and time difference of arrival (TDOA) estimation scheme with mitigating clock drift effect. To verify the performance of proposed method, we compared the proposed scheme with one way based TDOA acquisition method introduced by IEEE 802.15.4a Task Group and then we could conclude that the proposed method has better performance over other methods.