• Journal of KIISE:Information Networking
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• v.35 no.3
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• pp.173-182
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• 2008

Promoting quality of streaming service in wireless networks has attracted intensive research over the years. Instable wireless channel condition causes high transmission delay and packet loss, due to fading and interference. Therefore, they lead to degrade quality of video streaming service. The IEEE 802.11 Working Group is currently working on a new standard called IEEE 802.11e to support quality of service in WLANs. And several schemes were proposed in order to guarantee QoS. However, they are not adaptable to network condition. Accordingly, they suffered video quality degradation, due to buffer overflow or packet loss. In this paper, to promote quality of video streaming service in WLANs, we propose a cross-layer architecture based on IEEE 802.11e EDCA model. Our cross-layer architecture provides differentiated transmission mechanism of IEEE 802.11e EDCA based on priority of MPEG-4 video frames and adaptively controls the transmission rate by dropping video frames through the efficient bandwidth estimation based on distinction of each AC. Through the simulation, proposed scheme is shown to be able to improve end-to-end qualify for video streaming service in WLANs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.18-25
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• 2020

With the development of water internet technology, data communication between objects is expanding. Research related to data communication technology between vehicles that incorporates related technologies into vehicles has been actively conducted. For data communication between mobile terminals, data stability, reliability, and real-time performance must be guaranteed. The 5 GHz Wi-Fi band, which is advantageous in bandwidth, communications speed, and wireless saturation of the wireless network, was selected as the data communications network between vehicles. This study analyzes how to design and implement a 5 GHz Wi-Fi network in a vehicle network. Considering the characteristics of the mobile communication terminal device, a continuous variable communications structure is proposed to enable high-speed data switching. We simplify the access point access procedure to reduce the latency between wireless terminals. By limiting the Transmission Control Protocol Internet Protocol (TCP/IP)-based Dynamic Host Configuration Protocol (DHCP) server function and implementing it in a broadcast transmission protocol method, communication delay between terminal devices is improved. Compared to the general commercial Wi-Fi communication method, the connection operation and response speed have been improved by five seconds or more. Utilizing this method can be applied to various types of event data communication between vehicles. It can also be extended to wireless data-based intelligent road networks and systems for autonomous driving.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.10
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• pp.1-9
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• 2004

User-Perceived application-level performance is a key to the adoption and success of CDMA 2000. To predict this performance in advance, a detailed end-to-end simulation model of a CDMA network was built to include application traffic characteristics, network architecture, network element details, and protocol features. We assess the user application performance when a Radio Access Network (RAN) and a Core Network (CN) adopt different transport architectures such as ATM and If. For voice Performance, we found that the vocoder bypass scenario shows 8% performance improvement over the others. For data packet performance, we found that HTTP v.1.1 shows better performance than that of HTTP v.1.0 due to the pipelining and TCP persistent connection. We also found that If transport technology is better solution for higher FER environment since the IP packet overhead is smaller than that of ATM for web browsing data traffic, while it shows opposite effect to small size voice packet in RAN architecture. Though simulation results we showed that the 3G-lX EV system gives much better packet delay performance than 3G-lX RTT, the main conclusion is that end-to-end application-level performance is affected by various elements and layers of the network and thus it must be considered in all phases of the technology evolution process.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.12 no.1
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• pp.43-50
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• 2013

This paper aims to determine the optimal location of expressway patrol vehicle stations that minimizes additional troubles caused by the delay of crash treatments. To do this, we formulate a maximum covering problem and a p-center problem weighted by crash frequency, using the shortest distance as the criteria for allocating service district, and we employ the Lagrangian relaxation algorithm to solve the former and Daskin's heuristic algorithm to solve the latter, respectively. Based on crash data of Korean expressways, the results from the proposed models are compared with the current location of patrol vehicle stations by using several indices as the level of service for crash treatment, such as maximum crash-weighted distance, average crash-weighted distance, and average access distance. The results show that the proposed models improve average access distance and time by about 10km and 10min, respectively. When allocation for service district is changed only with the fixed current location, the level of service can be also improved. The models and results proposed in this paper can contribute to improving the level of service for crash treatment on expressways. They can also provide the theoretical basis on the location decision for other various emergency facilities, and the allocation decision for floating service districts according to time-period crash data.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.6
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• pp.88-96
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• 2011

Underwater acoustic communication is applicable in various areas, such as ocean data collection, undersea exploration and development, tactical surveillance, etc. Thus, robot control system construction used for underwater-robot like AUV or ROV is essential in these areas. In this paper, we propose the Message Merging MAC($M^2$-MAC) protocol, which is suitable for real time robot control system, considering energy efficiency in important parts of underwater acoustic sensor network constitution. In this proposed MAC protocol, gateway node receives the data from robot nodes according to the time slots that were allotted previously. And messages delivered from base-station are generated to one MAC frame by buffering process. Finally, generated MAC frames are broadcasted to all robot nodes in the cluster. Our suggested MAC protocol can also be hybrid MAC protocol, which is successful blend of contention based and contention-free based protocol through relevant procedure with Maintenance&Sleep (M&S) period, when new nodes join and leave as an orphan. We propose mathematical analysis model concerned about End-to-End delay and energy consumption, which is important factor in constructing real-time robot control system. We also verify the excellence of performance according to comparison of existing MAC protocols with our scheme.

• Journal of Broadcast Engineering
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• v.14 no.6
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• pp.796-806
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• 2009

SVC (Scalable Video Coding) is a new video coding standard to provide convergence media service in heterogeneous environments with different networks and diverse terminals through spatial-temporal-quality combined flexible scalabilities. This paper presents the performance analysis on packet loss in the delivery of SVC over IP networks and an efficient adaptation method to packet loss caused by buffer overflow. In particular, SVC with MGS (Medium Grained Scalability) as well as spatial and temporal scalabilities is addressed in the consideration of packet-based adaptation since finer adaptation is possible with a sufficient numbers of quality layers in MGS. The effect on spatio-temporal quality due to the packet loss of SVC with MGS is evaluated. In order to minimize quality degradation resulted by packet loss, the proposed adaptation of MGS based SVC first sets adaptation unit of AU (Access Unit) or GOP corresponding to allowed delay and then selectively discards packets in order of importance in terms of layer dependency. In the experiment, the effects of packet loss on quantitative qualities are analyzed and the effectiveness of the proposed adaptation to packet loss is shown.

• The Journal of the Korea Contents Association
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• v.11 no.1
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• pp.34-41
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• 2011

At present wireless internet access service is available through the 3G network, mobile WiMAX and WiFi anytime and anywhere. In this environment where there are various networks, users should be able to select specific networks depending on different situations. And it is necessary to provide mobility support between homogeneous and between heterogenous networks. Given this situation, the many proposals have been presented to link 3G, which has the largest service area among various networks, with mobile WiMAX(IEEE 802.16e), or with WiFi(IEEE 802.11). But, recently, with the increasing volume of wireless internet use and wireless internet data, due to the advents of net-book, e-book and smart phone, the service area of WiFi and mobile WiMAX has rapidly expanded. Especially, the availability of real-time application such as internet phone has led to the relative shrinking of the proportion of 3G mobile communication network giving conventional voice service, and enlargement of those of wireless internet access networks like WiFi and mobile WiMAX. This paper suggests a handover scheme based on PMIPv6, whitch support mobility between WiFi and mobile WiMAX, and minimizes handover delay. In this scheme, the mobile node has a dual stack structure composed of two interfaces-WiFi and mobile WiMAX. Since WiFi dose not support mobility, it is suggested that the mobile node have the capacity to deal with handover signaling between gateway in case of handover between homogeneous networks. This handover scheme, suggested comparing with current handovers between homogeneous networks, has proved, in its analytic evaluation, to be able to reduce handover, transmission, and signaling overhead.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6604-6610
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• 2015

In this paper, an efficient Wireless Access in Vehicular Environment (WAVE) packet transmission scheme for railroad communication is proposed. WAVE communication is a wireless local area network (WLAN) based communication and it is developed to be suitable for vehicular communication. There has been a lot of study on WAVE's applicability to Intelligent Transport System (ITS). As one of main transportation methods, by using WAVE, quality of railroad communication including WLAN based Communication Based Train Control (CBTC) can be enhanced and variety of railroad communication systems can be integrated into WAVE. However, there are technical challenges to adopt WAVE in railroad communications. For the simplest single-PHY WAVE, time division alternation of 50ms between Control Channel (CCH) and Service Channel (SCH) is required. Since there are delay sensitive railroad traffic types, alternation operation of CCH and SCH may cause performance degradation. In this paper, after identifying a couple of problems based on detailed analysis, a novel packet transmission scheme under railroad environment is proposed. In order to verify if the proposed scheme meets the requirement of railroad communication, WAVE transmission is mathematically modeled.

• Journal of KIISE:Computing Practices and Letters
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• v.9 no.6
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• pp.623-634
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• 2003

In this paper, we propose a collaborative multimedia authoring system. Our authoring system represents a multimedia presentation in a 3D coordinate system. One axis represents the traditional timeline information (T-zone), and the other two axes represent spatial coordinates (XY-zone). Our system represents a visual media objects as a 3D parallelepipeds and audio media objects as cylinders. This interface allows for simultaneous authoring and manipulation of both the temporal and the spatial aspects of a presentation. Using our system, users can design multimedia presentations collaboratively in the unified spatio-temporal space while freely traversing the spatial domain and the temporal domain without changing the context of authoring. In addition, we suggest an efficient mechanism of concurrency control for shared objects generated by our collaborative writing system. The mechanism is mainly based on the user awareness, the multiple versions, and the access permission of shared objects. Our concurrency control mechanism is designed to keep data consistency by minimizing the collision due to the delay or the failure of network communication and to allow maximum responsiveness for users using optimistic concurrency control. Also, the mechanism maximize the responsiveness by refining the locking granularity and applying different concurrency control mechanisms to each.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2B
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• pp.98-106
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• 2006

In order to provide a realtime transmission over a wireless LAM, we here present a new jamming based retransmission mechanism. In a legacy wireless LAN system, all stations use the binary exponential backoff algorithm to avoid collisions among frames. It is well known that the backoff algorithm causes more collisions as the numbers of active stations increases. This makes transmission of real time traffic hard. In the proposed scheme, when each station senses collisions, it promptly allows to send a jamming signal during a unique jamming window period which is determined by its own channel access count database(CACDB). This jamming windows is chosen not to be overlapped each other by using of CACDB, and thus channel access of another station is prevented. Hereafter the station gets the ownership of the medium when the wireless medium becomes idle after sending the jamming signal and sensing carrier, and then sends frame in medium. In our proposal, repeating collisions is never happened. We here assume that real time traffic use a frame of fixed length in order to make the time for receiving its ACK frame same. Comparing the proposed jamming-based retransmission scheme with the the 802.11 and 802.11e MAC by simulation. one can find that the proposed scheme have advantages in terms of delay, average backoff time, and average number of collisions per frame. One can find that the proposed scheme might be practically applicable to several applications of realtime traffic transmission in wireless LAN systems.