• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12A
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• pp.1177-1184
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• 2008

Non-line-of-sight (NLOS) propagation can severely weaken the accuracy of ranging and localization in wireless location systems. NLOS bias mitigation techniques have recently been proposed to relieve the NLOS effects, but positively rely on the capability to accurately distinguish between LOS and NLOS propagation scenarios. This paper proposes an energy-capture-based NLOS identification method for LDR-UWB systems, based on the analysis of the characteristics of the channel impulse response (CIR). With this proposed energy capture method, the probability of successfully identifying NLOS is much improved than the existing methods, such as the kurtosis method, the strongest path compare method, etc. This NLOS identification method can be employed in adaptive modulation scheme to decrease bit error ratio (BER) level for certain signal-to-noise ratio (SNR). The BER performance with the adaptive modulation can be significantly enhanced by selecting proper modulation method with the knowledge of channel information from the proposed NLOS identification method.

• Journal of IKEEE
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• v.20 no.1
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• pp.1-8
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• 2016

In this paper, we propose an effective time-of-arrival (TOA)-based localization method with adaptive bias computation in indoor environments. The goal of the localization is to estimate an accurate target's location in wireless localization system. However, in indoor environments, non-line-of-sight (NLOS) errors block the signal propagation between target device and base station. The NLOS errors have significant effects on ranging between two devices for wireless localization. In TOA-based localization, finding the target's location inside the overlapped area in the TOA-circles is difficult. We present an effective localization method using compensated distance with adaptive bias computation. The proposed method is possible for the target's location to estimate an accurate location in the overlapped area using the measured distances with subtracted adaptive bias. Through localization experiments in indoor environments, estimation error is reduced comparing to the conventional localization methods.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.4
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• pp.747-752
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• 2009

In this paper, the MIMO(Multi-Input Multi-Output) channel characteristics for Rx antenna spacing are described in the real environment, which has LOS(Ling of Sight) and NLOS (Won-Line of Sight). We developed $2\times2$ MIMO channel measurement system at 2.3GHz Wibro Band. MIMO antenna evaluation parameters such as received power, channel capacity and spatial correlation are evaluated for standard dipole antenna with 0.25, 0.5, 0.75 and 1.0 wavelength spacing at 2-position for LOS and 4-position for NLOS. The spatial correlation is distributed more than 0.9 in most LOS case which might be intricate to operate MIMO communication. MIMO antenna design need to be focused on getting spatial diversity and reducing spatial correlation in LOS case.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4B
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• pp.300-308
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• 2012

Many indoor location tracking technologies have been proposed. Generally indoor location tracking using TOA signal is used, there is a weak point that it's difficult to track the location due to obstacles like a refraction, reflection and dispersion of radio wave. In this paper, we apply ETOA(Estimated-TOA) algorithm in NLOS(Non-Line-Of-Sight) environment to solve above problem. In NLOS environment, TOA value between Beacon and Mobile node is predicted by ETOA algorithm and the tracking of indoor location is also possible to identify using two NLOS beacons of three beacons by this algorithm. We show that the proposed algorithm is accurate location tracking is accomplished using the applying the proposed algorithm to indoor moving robot and the inertia sensor of robot and Kalman filter algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.10
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• pp.1004-1010
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• 2012

In this paper, we propose the algorithm which considers applying recently proposed clock synchronization techniques with quite high accuracy in a few wireless sensor networks researches to time synchronization algorithm for multi-static radar system and especially overcomes the limitation of previous theory, cannot be applied between nodes in non-line of sight (NLOS). Proposed scheme estimates clock skew and clock offset using recursive robust least M-estimator with information of time stamp observations. And we improve the performance of algorithm by tracking and suppressing the time delays difference caused by NLOS system. Futhermore, this paper derive the mean square error (MSE) to present the performance of the proposed estimator and comparative analysis with previous methods.

• Journal of the Korean Institute of Intelligent Systems
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• v.20 no.3
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• pp.413-421
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• 2010

In the study, self-organization by color detection is proposed to overcome required constraints for existing self-organization by an external ceiling camera and communication. In the proposed self-organization, each swarm robot can follow its colleague robot and all swarm robots can follow a target by LOS(Line of Sight). The swarm robots follow the moving target by the proposed potential field, avoiding confliction with neighboring robots and obstacles. Finally, all swarm robots are reached by a sight among swarm robots. In this paper, for unicycle robots with non-holonomic constraints instead of point robot with holonomic constraints self-organization is presented, it enhances the possibility of H/W realization.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.11
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• pp.1-8
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• 1997

A prediction model is proposed to describe the path loss in propagation environment of indoor microcell. This model includes the lineal corridor for line--of-sight(LOS) and T-shaped corridor for non-line-of-sight(NLOS). In computation of receiving power the ray tracing technique based on image method is utilized and also reflected waves bounced on the walls and ceilings are considered. To check validity of the computed resuls cross checks between the predicted and measured are being made, which shows a close agreement for LOS case whereas somewhat disagreement for NLOS case. UTD technique is incorporated with propagation path determination algorithm in the treatment of NLOS case.

• Journal of electromagnetic engineering and science
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• v.9 no.4
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• pp.202-210
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• 2009

In this paper, we have analyzed the effect of interference between ultra-wideband(UWB) and intelligent transport systems(ITS). The maximum possible UWB emission power and minimum possible distance between UWB devices and ITS are found. In order to analyze the interference, we employ the Monte-Carlo(MC) method. We consider six situations, which are indoor office line-of-sight(LOS), indoor office non-line-of-sight(NLOS), indoor residential LOS, indoor residential NLOS, outdoor rural LOS, and outdoor rural NLOS environments. From the simulation results, it is confirmed that coexistence between UWB and ITS devices can be realized in accordance with the emission mask of 19.3 dB for indoor application or 19.3 dB for an image system. And in the outdoors, coexistence between UWB and ITS devices can be realized if the emission mask is at least 1.6 dB for vehicles' radar systems.

• Journal of the Korean institute of surface engineering
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• v.23 no.1
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• pp.1-7
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• 1990

Ion implantation is a well established superior superior surface modification technique for the improvement of wear resistance, hardenece, hardness, corrosion resistance, biocompaibity, surface friction, as well as for the modification of surface electric conductance. Conventional ion implantaion is a line-of-sight process witch ues the ion beam accelerator techniques. Plasma sheath ion implantation (PSII), as a new technique, is described in this paper. In PSII high voltage pulse is applied to a target material placed directly in a plasma, forming a think ion-matrix sheath around the target. Ions accelerate through the sheath drop and bombard the traget from all sides simultaneosuslyregardless of the target shape. This paper describes the principle of PSII, which has non-line-of sight characteristics, as well as the experimental appratus.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.58-58
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• 2001

This paper shows a practical approach that is robust to the errors causing path-delay in mobile wireless location, and analyzes its performance by comparing with other methods. NLOS(non-line-of-sight) error and multipath are two big sources of positioning error in wireless location. Contrary to GPS(global positioning system), they result from the terrestrial propagation of a signal. Especially, since LOS(line-of-sight) path between a transceiver and a receiver is blocked by intermediate buildings and topography, NLOS causes a signal to be reflected and diffracted. This path-delay error is very localized, and so, it is not easy to be estimated and mitigated. To treat such localized error, therefore ...