• Current Optics and Photonics
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• v.2 no.6
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• pp.532-539
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• 2018

Multiple LED arrays can be utilized in visible-light communication (VLC) to improve communication efficiency, while maintaining smart illumination functionality through dimming control. This paper proposes a modulation scheme called "Spatial Intensity Modulation" (SIM), where the effective number of turned-on LEDs is employed for data modulation and dimming control in VLC systems. Unlike the conventional pulse-amplitude modulation (PAM), symbol intensity levels are not determined by the amplitude levels of a VLC signal from each LED, but by counting the number of turned-on LEDs, illuminating with a single amplitude level. Because the intensity of a SIM symbol and the target dimming level are determined solely in the spatial domain, the problems of conventional PAM-based VLC and related MIMO VLC schemes, such as unstable dimming control, non uniform illumination functionality, and burdens of channel prediction, can be solved. By varying the number and formation of turned-on LEDs around the target dimming level in time, the proposed SIM scheme guarantees homogeneous illumination over a target area. An analysis of the dimming capacity, which is the achievable communication rate under the target dimming level in VLC, is provided by deriving the turn-on probability to maximize the entropy of the SIM-based VLC system. In addition, a practical design of dimmable SIM scheme applying the multilevel inverse source coding (MISC) method is proposed. The simulation results under a range of parameters provide baseline data to verify the performance of the proposed dimmable SIM scheme and applications in real systems.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.5
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• pp.379-388
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• 2019

Recently, a technique for acquiring spatial information data using UAV (Unmanned Aerial Vehicle) has been greatly developed. It is a very crucial issue of the GIS (Geographic Information System) mapping system that passes way point in the unmanned airframe and finally measures the accurate image and stable localization to the desired destination. Though positioning using DGPS (Differential Global Navigation System) or RTK-GPS (Real Time Kinematic-GPS) guarantee highly accurate, they are more expensive than the construction of a single positioning system using a single GPS. In the case of a low-priced single GPS system, the stability of the positioning data deteriorates. Therefore, it is necessary to supplement the uncertainty of the absolute position data of the UAV and to improve the accuracy of the current position data economically in the operating state of the UAV. The aim of this study was to present an algorithm enhancing the stability of position data in a single GPS mode of UAV with multiple GPS. First, the arrangement of multiple GPS receivers through the center of gravity of the UAV were examined. Next, MD (Mahalanobis Distance) is applied to detect instantaneous errors of GPS data in advance and eliminate outliers to increase the accuracy of previously collected multiple GPS data. Processing procedure for multiple GPS reception data by applying the center of the triangular method were presented to improve the position accuracy. Second, UAV navigation systems integrated multiple GPS through configuration of the UAV specifications were implemented. Using the unmanned airframe equipped with multiple GPS receivers, GPS data is measured with the TCM (Triangular Center Method). In addition, UAV equipped with multiple GPS were operated in study area and locational accuracy of multiple GPS of UAV with VRS (Virtual Reference Station) GNSS surveying were compared. The result showed that the error factors are compensated, and the error range are reduced, resulting in the reliability of the corrected value. In conclusion, the result in this paper is expected to realize high-precision position estimation at low cost in UAV using multiple low-cost GPS receivers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.7
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• pp.2365-2382
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• 2014

While single-user spatial multiplexing multiple-input multiple-output (SU-MIMO) allows spatially multiplexed data streams to be transmitted to one node at a time, multi-user spatial multiplexing MIMO (MU-MIMO) enables the simultaneous transmission to multiple nodes. However, if the transmission time required to send packets to each node varies considerably, MU-MIMO may fail to utilize the available MIMO capacity to its full potential. The transmission time typically depends upon two factors: the link quality of the selected channel and the data length (packet size). To utilize the cumulative capacity of multiple channels in MIMO applications, the assignment of channels to each node should be controlled according to the measured channel quality or the transmission queue status of the node.A MAC protocol design that can switch between MU-MIMO and multiple SU-MIMO transmissions by considering the channel quality and queue status information prior to the actual data transmission (i.e., by exchanging control packets between transmitter and receiver pairs) could address such issues in a simple but in attractive way. In this study, we propose a new MAC protocol that is capable of performing such switching and thereby improve the system performance of very high throughput WLANs. The detailed performance analysis demonstrates that greater benefits can be obtained using the proposed scheme, as compared to conventional MU-MIMO transmission schemes.

• Journal of KIISE:Software and Applications
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• v.34 no.12
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• pp.1075-1082
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• 2007

In this paper, we propose the method of multiple human action recognition on video clip. For being invariant to the change of speed or size of actions, Spatial-Temporal Pyramid method is applied. Proposed method can minimize the complexity of the procedures owing to select Motion Gradient Histogram (MGH) based on statistical approach for action representation feature. For multiple action detection, Motion Energy Image (MEI) of binary frame difference accumulations is adapted and then we detect each action of which area is represented by MGH. The action MGH should be compared with pre-learning MGH having pyramid method. As a result, recognition can be done by the analyze between action MGH and pre-learning MGH. Ten video clips are used for evaluating the proposed method. We have various experiments such as mono action, multiple action, speed and site scale-changes, comparison with previous method. As a result, we can see that proposed method is simple and efficient to recognize multiple human action with stale variations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.321-324
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• 2007

In this paper, the performance improvement of ultra-wideband (UWB) communications system to achieve high-data-rate using spatial diversity provided by multiple receive antennas is investigated. We derive the expression for the received SINR after spatially combining through multiple receive antennas and evaluate the bit error rate (BER) performance by numerical simulation. We also compare the performance results in the case of 2PPM systems with the theoretical performance results in the case of 2PAM THMA UWB systems. The impacts of spatial diversity on the performance of 2PPM and 2PAM THMA UWB systems are analyzed. It is shown that the BER performance is improved as the number of receive antennas increases. Also, it is observed that in the presence of multiple user interference signals, the performance of 2PAM THMA UWB systems is considerably superior to that of 2PPM THMA UWB systems.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.11
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• pp.2121-2126
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• 2007

In this paper, the performance improvement of ultra-wideband(UWB) communications system to achieve high-data-rate using spatial diversity provided by multiple receive antennas is investigated. We derive the expression for the received SINR after spatially combining through multiple receive antennas and evaluate the bit error rate(BER) performance by numerical simulation. We also compare the performance results in the case of 2PPM systems with the theoretical performance results in the case of 2PAM THMA UWB systems. The impacts of spatial diversity on the performance of 2PPM and 2PAM THMA UWB systems are analyzed. It is shown that the BER performance is improved as the number of receive antennas increases. Also, it is observed that in the presence of multiple user interference signals, the performance of 2PAM THMA UWB systems is considerably superior to that of 2PPM THMA UWB systems.

• ETRI Journal
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• v.30 no.3
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• pp.355-364
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• 2008

Multiple-input multiple-output (MIMO) systems can provide significant increments in capacity; however, the capacity of MIMO systems degrades severely when spatial correlation among multipath channels is present. This paper demonstrates that the influence of shadowing on the channel capacity is more substantial than that of multipath fading; therefore, the shadowing effect is actually the dominant impairment. To overcome the composite fading effects, we propose combining macroscopic selection diversity (MSD) schemes with MIMO technology. To analyze the system performance, the capacity outage expression of MIMO-based MSD (MSD-MIMO) systems using a characteristic function is applied. The analytic results show that there are significant improvements when MSD schemes are applied, even for the two-base-station diversity case. It is also observed that the effect of spatial correlation due to multipath fading is almost negligible when multiple base stations cooperatively participate in the mobile communication topology.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.3-6
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• 1988

The UCERSS algorithm is an extended MUSIC which is used to estimate incident angles of multiple wide band signals. The purpose of this paper is to extend the UCERSS in order to estimate the direction of arrivals of multiple wide band signals in multipath environment. The modifications of the UCERSS result in the wide band spatial smoothing and the UNSS approaches. Computer simulation results indicate that the performances of the UNSS are superior to those of the UCERSS and the wide band spatial smoothing method.

• Journal of Korean Association for Spatial Structures
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• v.24 no.1
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• pp.65-72
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• 2024

This paper aims to advance our understanding of extensible beams with multiple cracks by presenting a crack energy and motion equation, and mathematically justifying the energy functions of axial and bending deformations caused by cracks. Utilizing an extended form of Hamilton's principle, we derive a normalized governing equation for the motion of the extensible beam, taking into account crack energy. To achieve a closed-form solution of the beam equation, we employ a simple approach that incorporates the crack's patching condition into the eigenvalue problem associated with the linear part of the governing equation. This methodology not only yields a valuable eigenmode function but also significantly enhances our understanding of the dynamics of cracked extensible beams. Furthermore, we derive a governing equation that is an ordinary differential equation concerning time, based on orthogonal eigenmodes. This research lays the foundation for further studies, including experimental validations, applications, and the study of damage estimation and detection in the presence of cracks.

• Journal of the Korea Society of Computer and Information
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• v.3 no.4
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• pp.126-131
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• 1998

Spatial data warehouse, whose importance is being increased, is composed of huge amounts of historical spatial data for organizational decision making and it also allows users to obtain useful geospatial information through analyzing and summmarizing spatial data. In this paper, we survey effective spatial multidimensional model which is based on virtual scenario for spatial data warehouse modelling. Therefore, we describe spatial multidimensional analytical query which provide multiple analytical functions according tom user's requests.