• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.267-277
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• 2011

Like other wireless network protocols, IEEE 802.15.4 adopts CA (Collision Avoidance)algorithm to avoid the early collision of a new packet by randomizing its first transmission time rather than its immediate delivery. The traditional CA scheme of IEEE 802.15.4, however, selects the random access time from the predetermined range without considering the degree of current congestion. It probably causes either a long delay to settle in the suitable range for the current network load or frequent clashes especially during the long lasting heavy traffic period. This paper proposes an ACA(Adaptive Collision Avoidance) algorithm adapting the initial backoff range to the undergoing collision variations. It also introduces a mathematical model to predict the performance of ACA algorithm added to IEEE 802.15.4. With only small deviations from corresponding simulations, our analytical model shows that ACA technique can improve the throughput of IEEE 802.15.4 by up-to 41% maximally in addition to shortening the packet delays.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.74-84
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• 2008

UWB radio systems have drawn attention during the last few years. These systems are the core technique for ubiquitous home and enable to co-exist with other narrow band systems over the same frequency without interfering them. But UWB signals have a very low power per pulse, so they are affected by strong narrow band interferences. Specially, IEEE 802.11a systems which operate around 5GHz overlap the band of UWB signals and they will interfere with UWB systems significantly. In this paper, we propose a novel narrow band interference suppression method based on singular value decomposition(SVD) algorithm for DS-UWB in IEEE 802.15.4a channel model. The proposed method is very effective and robust for both a single user DS-UWB system and a multiuser DS-UWB system to reduce the narrow band interference.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.7
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• pp.572-580
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• 2013

IEEE 802.15.4e is a prospective standard for low latency control application in industries. This paper proposes a framework to evaluate the closed loop IEEE 802.15.4e based WNCS performance. The framework consists of two models: closed loop control system model and network model. The network model focuses on the PHY parameters of wireless link and takes the channel parameters into consideration. The PHY model combining with MAC model gives the control system model the probability of packet loss in a super-frame. In addition, redundancy mechanism is considered in IEEE 802.15.4e to reduce to data frame loss probability. The simulation is implemented in Matlab, PHY model takes the channel parameters from empirical results. Hence our evaluation gives insight into behavior of WNCS in different environments and it provides us a tool to design wireless network to achieve a good performance for control system.

• Journal of Advanced Navigation Technology
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• v.23 no.1
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• pp.36-43
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• 2019

In this paper, a novel channel access scheme for the next-generation vehicle to anything (V2X) system based on IEEE 802.11p standard which is applied to recent connected car technologies is suggested and analyzed. The proposed scheme proposes a channel access method utilizing OFDMA multi-user transmission for IEEE 802.11p based system. In this paper, the authors examine geographical distance and network area performance of IEEE 802.11p system and the proposed scheme. Results of this research show that the proposed scheme is quite suitable for improving conventional V2X standards and systems. This paper also provides mathematical analysis and simulation results of the conventional IEEE 802.11p system and the proposed scheme.

• Journal of Internet Computing and Services
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• v.7 no.1
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• pp.151-164
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• 2006

The DCF of IEEE 802.11 standard coordinates transmissions onto the shared communication channel based on CSMA/CA protocol. Currently, 802,11 is the most widely deployed wireless LAN standard. In this paper, for 802.11-based wireless LAN we propose a service differentiation scheme adopting different contention window sizes and retransmission schemes for two different types of data packets and we present a Markov model for the state of a given station under a finite load traffic condition. We then derive an algorithm to find the transmission probability and the throughput. The proposed model is validated through simulation under various system settings.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.456-458
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• 2010

VoIP services are growing fast and WLAN VoIP phones are being used in widespread. Emergency services are very critical in WLAN VoIP as in other traditional networks. This paper summarize recent standards of IEEE 802.11 supporting emergency services in WLANs. Two standards are discussed. The 11u deals with the aspect of access in WLAN emergency services, and the 11v deals with the location services.

• Journal of the Korea Society of Computer and Information
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• v.13 no.6
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• pp.225-232
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• 2008

When a single source of multimedia contents is distributed to multiple reproduction devices, the audio and video contents require synchronous play for multi-channel stereo sound and lip-synchronization. The multimedia system in vehicle, especially, has researched to move to wireless environments from legacy wired environments. This paper proposes the advanced algorithm for providing synchronized services of real-time multimedia traffic in IEEE 802.11 WLANs [1]. For these, we implement the advanced IEEE 1588 Precision Time Protocol [2] and the environments for simulation. Also, we estimate and analysis performance of the algorithm, then we experiment and analysis after the porting of algorithm in wireless LAN devices (Linksys wrt-350n AP network device) to characterize timing synchronization accuracy.

• Journal of KIISE:Information Networking
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• v.37 no.2
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• pp.142-149
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• 2010

In this paper, we propose to modify the IEEE 802.16 MAC protocol in order to allow the coexistence of IEEE 802.11 and IEEE 802.16 wireless networks in shared bands. Our suggested protocol enables 802.16 WMAN to control WLAN devices for the coexistence. That is, in the downlink subframes(BS to SS), SS(Subscriber Station) prohibits WLAN to transmit by using CTS(Clear to Send) in order to protect it's burst. In the uplink subframes(SS to BS), on the other hand, BS(Base Station) sends CTS to block WLAN's communications. Our proposals enables the coexistence between WLAN and WMAN, and simulation results show that our protocols enhance the throughput of the entire system.

• 한국ITS학회:학술대회논문집
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• 2008.11a
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• pp.376-379
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• 2008

• 한국ITS학회:학술대회논문집
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• v.2006 no.10
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• pp.108-112
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• 2006