• Journal of KIISE:Computing Practices and Letters
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• v.6 no.1
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• pp.36-44
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• 2000

In this paper, we describe the developing of a tool which supports both multimedia presentation with user's participation through a high speed network and authoring of various media using a single authoring tool. To support real-time synchronous multimedia presentation, we adopt dynamic synchronization method and adaptive transmission algorithm for synchronizing data transfer rate between sender and receiver using buffer management algorithm based on QoS parameters. And we also allow user's participation in the presentation using TRSG(Temporal Relationship Specification Graph) model. Finally, the proposed tool supports the minimal level of QoS and its continuous play-out using event auditing threads which control the current state of a multimedia presentation continuously by monitoring of negative factors effecting on QoS, and synchronization.

• Journal of Information Processing Systems
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• v.10 no.2
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• pp.176-192
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• 2014

The realization of Wireless Multimedia Sensor Networks (WMSNs) has been fostered by the availability of low cost and low power CMOS devices. However, the transmission of bulk video data requires adequate bandwidth, which cannot be promised by single path communication on an intrinsically low resourced sensor network. Moreover, the distortion or artifacts in the video data and the adherence to delay threshold adds to the challenge. In this paper, we propose a two stage Quality of Service (QoS) guaranteeing scheme called Prioritized Multipath WMSN (PMW) for transmitting H.264 encoded video. Multipath selection based on QoS metrics is done in the first stage, while the second stage further prioritizes the paths for sending H.264 encoded video frames on the best available path. PMW uses two composite metrics that are comprised of hop-count, path energy, BER, and end-to-end delay. A color-coded assisted network maintenance and failure recovery scheme has also been proposed using (a) smart greedy mode, (b) walking back mode, and (c) path switchover. Moreover, feedback controlled adaptive video encoding can smartly tune the encoding parameters based on the perceived video quality. Computer simulation using OPNET validates that the proposed scheme significantly outperforms the conventional approaches on human eye perception and delay.

• Journal of the Korea Society of Computer and Information
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• v.6 no.3
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• pp.50-55
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• 2001

We review error resilience techniques for real-time video transport over unreliable networks. For error control on the source coding level, each decoder has to make provisions for error detection, resynchronization. and error concealment. and we review techniques suitable for that purpose. Further, techniques are discussed for intelligent processing of acknowledgment information by the coding control to adapt the source coder to the channel. We review and compare error tracking, error confinement. and reference picture selection techniques for channel-adaptive source coding. We review how feedback-based source codings are related with the precompressed video stored on a media server

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.6
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• pp.3165-3181
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• 2019

Spherical videos, which are also called 360-degree videos, have become increasingly popular due to the rapid development of virtual reality technology. However, the large amount of data in such videos is a huge challenge for existing transmission system. To use the existing encode framework, it should be converted into a 2D image plane by using a specific projection format, e.g. the equi-rectangular projection (ERP) format. The existing high-efficiency video coding standard (HEVC) can effectively compress video content, but its enormous computational complexity makes the time spent on compressing high-frame-rate and high-resolution 360-degree videos disproportionate to the benefits of compression. Focusing on the ERP format characteristics of 360-degree videos, this work develops a fast decision algorithm for predicting the coding unit depth interval and adaptive mode decision for intra prediction mode. The algorithm makes full use of the video characteristics of the ERP format by dealing with pole and equatorial areas separately. It sets different reference blocks and determination conditions according to the degree of stretching, which can reduce the coding time while ensuring the quality. Compared with the original reference software HM-16.16, the proposed algorithm can reduce time consumption by 39.3% in the all-intra configuration, and the BD-rate increases by only 0.84%.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.6
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• pp.3000-3022
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• 2019

Full-duplex (FD) technologies enable wireless nodes to simultaneously transmit and receive signal using the same frequency-band. The FD modes could improve their physical layer throughputs. However, in the wireless ad hoc networks, the FD communications also produce new interference risks. On the one hand, the interference ranges (IRs) of the nodes are enlarged when they work in the FD mode. On the other hand, for each FD pair, the FD communication may cause the potential hidden terminal problems to appear around the both sides. In this paper, to avoid the interference risks, we first model the IR of each node when it works in the FD mode, and then analyze the conditions to be satisfied among the transmission ranges (TRs), carrier-sensing ranges (CSRs), and IRs of the FD pair. Furthermore, in the media access control (MAC) layer, we propose a specific method and protocol for collision avoidance. Based on the modified Omnet++ simulator, we conduct the simulations to validate and evaluate the proposed FD MAC protocol, showing that it can reduce the collisions effectively. When the hidden terminal problem is serious, compared with the existing typical FD MAC protocol, our protocol can increase the system throughput by 80%~90%.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.8
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• pp.112-119
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• 1996

Among the various type of accelerometer, the servo rebalancing type accelermoter can be suitable for Inertial Navigation System, because of its high sensitivity and good response in low frequency. In this paper, we proposed a new technology to control inductive tuype accelerometer utilizing digital PWM method. The new developed digital PWM control has special design scheme for transmitting measurement value to outer device in its servo ollp. So it has no quantized error of transforming outputs of sensors to digital domain. The quantized error may make serious problem in INS system, because outputs of sensor are integrated once or twice by digital computer and it happens every sensor reading times. Therefore, in order to get the accurate information such as displacement, it is necessary to measure accurately the input current. In addition, Digital Signal Processing needs digital data transmission, digital PWM method is adaptive for this purpose. We realized a practical circuit for digital PWM control, analyzed the stability of the circuit, and designed the controller etc. In this study, we solved many practical problem for this application, and got out good results.

• Journal of Astronomy and Space Sciences
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• v.40 no.4
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• pp.237-245
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• 2023

Laser communication has been considered as a novel method for earth observation satellites with generation of high data volume. It offers faster data transmission speeds compared to conventional radio frequency (RF) communication due to the short wavelength and narrow beam divergence. However, laser beams are refracted due to atmospheric turbulence between the ground and the satellite. Refracted laser beams, upon reaching the receiver, result in angle-of-arrival (AoA) fluctuation, inducing image dancing and wavefront distortion. These phenomena hinder signal acquisition and lead to signal loss in the course of laser communication. So, precise alignment between the transmitter and receiver is essential to guarantee effective and reliable laser communication, which is achieved by pointing, acquisition, and tracking (PAT) system. In this study, we simulate the effectiveness of tip/tilt compensation for more efficient laser communication in the satellite-ground downlink. By compensating for low-order terms using tip/tilt mirror, we verify the alleviation of AoA fluctuations under both weak and strong atmospheric turbulence conditions. And the performance of tip/tilt correction is analyzed in terms of the AoA fluctuation and collected power on the detector.

• Journal of Internet Computing and Services
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• v.9 no.3
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• pp.141-158
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• 2008

In this paper, we developed the GML Map Server which visualized the map based on GML as international standard for exchanging the common format map and for interoperability of GIS information. And also, it should transmit effectively GML map into the mobile device by using dynamic map partition and caching. It manages a partition based on the visualization area of a mobile device in order to visualize the map to a mobile device in real time, and transmits the partition area by serializing it for the benefit of transmission. Also, the received partition area is compounded in a mobile device and is visualized by being partitioned again as four visible areas based on the display of a mobile device. Then, the area is managed by applying a caching algorithm in consideration of repetitiveness for a received map for the efficient operation of resources. Also, in order to prevent the delay in transmission time as regards the instance density area of the map, an adaptive map partition mechanism is proposed for maintaining the regularity of transmission time. GML Map Server can trace the position of mobile device with WIPI environment in this paper. The field emulator can be created mobile devices and mobile devices be moved and traced it's position instead of real-world. And we developed POIM(POI Management) for management hierarchically POI information and for the efficiency POI search by using the individual tagging technology with visual interface.

• Journal of KIISE:Information Networking
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• v.28 no.3
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• pp.389-405
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• 2001

In these days, we have increasing demands on the real-time services, especially for the multimedia data transmission in both of wired and wireless environments and thus efficient and stable ways of transmitting realtime data are needs. Although RTP is widely used for internet-based realtime applications, it cannot avoid packet losses, due to the use of UDP stack and its underlying layers. In the case of mobile computing applications, the packet losses are more frequent and consecutive because of the limited bandwidth. In this paper, we first statistically analyze the characteristics of packet losses in the wired and wireless communications, based on Gilbert model, and a new packet recovery scheme for realtime data transmission is presented. To reflect the transmission characteristics of the present network environment, our scheme makes the sender to dynamically adjust the amount of redundant information, using the current packet loss characteristic parameters reported by the receiver. Additionally, we use relatively large and discontinuous offset values, which enables us to recover from both of the random and consecutive packet losses. Due to these characteristics, our scheme is suitable for the mobile computing environment where packet loss rates are relatively high and varies rapidly in a wide range. Since our scheme is based on the analytic model form statistics, it can also be used for other network environments. We have implemented the scheme with Mobile IP and RTP/RTCP protocols to experimentally verify its efficiency.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.7
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• pp.1639-1645
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• 2015

In UHD high-speed video transmission system, when a signal within certain frequency region coincides electrically and structurally, the system becomes unstable because the energy is concentrated, and signal flux is interfered and distorted. For the instability, power integrity analysis should be conducted. To remove the signal distortion for MLB, using a high-frequency design technique for EMI phenomenon, EMI which radiates electromagnetic energy fluxed into power layer was analyzed considering system stabilization. In this paper, we proposed an adaptive MLB design method which minimizes high-frequency noise in MLB structure, enhances signal integrity and power integrity, and suppresses EMI. The characteristic impedance for multi-layer circuit board proposed in this study were High-Speed Video Differential Signaling(HSVDS) line width w = 0.203, line gap d = 0.203, beta layer height h = 0.145, line thickness t = 0.0175, dielectric constant ε_r = 4.3, and characteristic impedance Zdiff = 100.186Ω. When high-speed video differential signal interface board was tested with optimized parameters, the magnitude of Eye diagram output was 672mV, jittering was 6.593ps, transmission frequency was 1.322GHz, signal to noise was 29.62dB showing transmission quality improvement of 10dB compared to previous system.