• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.10
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• pp.2272-2281
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• 1997

This paepr proposes a shared medium access control protocol for hgih-speed multimedia services of distributed subscriber home and small-sized business ATM networks. This protocol offers not only global fairness for the whole network at the same time, but also local fairness for different prioritytraffics on each node. Considering that the future B-ISDN service si a mixture of real and non-real time traffic data, this protocol is designed to accommodate the real time service, by controlling the priority of the real and non-real time data. The simulation results show that the proposed protocol has better performance than the other protocols.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.9
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• pp.1633-1637
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• 2008

A protocol is proposed to control the rate of each subcarrier in OFDM-based wireless network systems. The proposed protocol adds an OFDM symbol in CTS frame defined in IEEE 802.11 standard. A receiver determines the rate of its subcarrier after it receives the RTS frame. The determined rate is added to OFDM symbol in CTS frame. In order to synchronize the rate information between the sender and the receiver, error recovery process is proposed. The performance improvement of the proposed method is shown by numerical results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.4
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• pp.759-764
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• 2009

A new backoff scheme for infrastructure mode in IEEE 802.11 wireless LANs is proposed to improve a performance. Each station generates a unique backoff number using total number of stations, fairness parameter included in beacon frame and an user's ID that is assigned by AP. The station sends a packet after its own backoff number of idle slots, which makes a collision free access among stations within AP's coverage. The proposed method shows better performance in the view of channel utilization and packet delay than an original IEEE 802.11 CSMA/CA backoff scheme.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.4
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• pp.9-16
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• 2015

Quick and safe message transmission is an important research topic of vehicular ad hoc networks (VANET). Most studies assume that the periodic broadcast of beacon-frames between vehicles increases the safety of the driver. In this paper, we propose a medium access control (MAC) protocol and location-based clustering for the VANET to support reliable data transfer. In our proposal, the cluster heade (CH) manage the access and allocate the resources of the node. Our proposal uses simulation to confirm the reduction of the transmission delay and the collision rate of the signal.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.6 s.324
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• pp.33-39
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• 2004

Design of efficient Medium Access Control (MAC) protocols with both high throughput performances is a major focus in distributed contention based MAC protocol research. In this paper, we propose an efficient contention based MAC protocol for wireless Local Area Networks, namely, the Developed Collision Resolution (DCR) algorithm. This algorithm is developed based on the following innovative ideas: to speed up the collision resolution, we actively redistribute the backoff timers for all active nodes; to reduce the average number of idle slots, we use smaller contention window sizes for nodes with successful packet transmissions and reduce the backoff timers exponentially fast when a fixed number of consecutive idle slots are detected. We show that the proposed DCR algorithm provides high throughput performance and low latency in wireless LANs.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.3
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• pp.534-541
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• 2018

The number of stations existing in the same wireless channel is increasing due to the spread of the wireless LAN devices. CSMA/CA, a conventional wireless LAN protocol, uses a random backoff method. In the random backoff scheme, collision between stations is frequent in a dense region where the number of stations existing in the same channel is several tens or more, and the performance of the performance degradation of such a protocol, the IEEE 802.11ah standard proposed a Restricted Access Window(RAW) wireless access method. RAW improves performance by limiting the number of concurrent access stations by dividing the stations into several groups. In this paper, we propose a method to improve the performance of channel connection by using new group creation, group removal and group relocation algorithm according to traffic change by improving existing RAW method.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.6
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• pp.151-158
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• 2010

In line with the requirement of appropriate protocol support for such mission-critical wireless sensor network (WSN) applications as patient monitoring, we investigate the framework for designing medium access control (MAC) schemes. The data traffic in medical systems comes with inherent traffic heterogeneity as well as strict requirement of reliability according to the varied extents of devise-wise criticality in separate cases. This implies that the quality-of-Service (QoS) issues are very distinctly delicate requiring specialized consideration. Besides, there are features in such systems that can be exploited during the design of a MAC scheme. In a monitoring or routine surveillance application, there are degrees of regularity or predictability in traffic as coordinated from a node of central control. The coordinator thus takes on the role of marshaling the resources in a neighborhood of nodes deployed mostly for upstream traffic; in a collision-free scheme, it schedules the time slots for each superframe based on the QoS specifications. In this preliminary study, we identify the key artifacts of such a MAC scheme. We also present basic performance issues like the impact of superframe length on delay incurred, energy efficiency achieved in the network operation as obtained in a typical simulation setup based on this framework.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.945-947
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• 1999

첨단의 자동화 시스템을 구축하기 위해서는 각 필드기기에서 생산되는 정보들을 적절한 형태로 가공하여 적시에 필요한 공정으로 제공하여 줄 수 있는 지능형 센서 및 필드기기의 도입이 필요하다. 이러한 필드기기들이 유기적으로 정보를 교환하고 공유하기 위해서는 통신망 시스템을 구축할 필요가 있다. 필드버스는 자동화 및 분산 제어 시스템의 컴퓨터 통신망 계층구조에서 최하위 계층 기기들 간에 실시간 통신을 제공하는 산업용 통신망이다. 본 연구에서는 통신용 프로세서인 Mc68360을 기반으로 하여 필드버스의 일종인 Profibus의 물리계층과 데이터링크계층 프로토콜을 구현하였다. 물리계층은 프로세서의 UART 통신 기능과 RS-485칩을 사용하여 구현하고, 데이터링크계층 프로토콜은 프레임 분석과 송수신, 에러처리, 흐름제어, 매체접속권한 관리 등의 기능을 소프트웨어로 구현하였다. 또한 지능형 센서 본래의 목적중의 하나인 원격관리 기능을 위하여 각 필드기기의 노드 주소, 타이머 값 등의 통신 파라미터를 원격 마스터에서 설정할 수 있도록 관리계층의 기능을 추가하였다. 본 연구에서는 각각 하나의 노드기능을 담당하는 여러 개의 보드들로 구성된 testbed를 구축하고, 다양한 통신환경에서 초기화, 정상, 비정상 상태 등의 동작을 실험하였으며, 이를 통하여 지능형 센서용 필드버스의 데이터링크계층 프로토콜이 정상적으로 동작됨을 확인하였다.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.189-192
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• 2000

This paper proposes a fuzzy-based random access controller with a superimposed frame structure (F$^2$RAC) fur voice/data-integrated wireless networks. F$^2$RAC adopts mini-slot technique for reducing contention cost, and these mini-slots of which number may dynamically vary from one frame to the next as a function of the traffic load are further partitioned into two regions for access requests coming from voice and data traffic with their respective QoS requirements. And F$^2$RAC is designed to properly determine the access regions and permission probabilities for enhancing the data packet delay while ensuring the voice packet dropping probability constraint. It mainly consists of the estimator with Pseudo-Bayesian algorithm and fuzzy logic controller with Sugeno-type of fuzzy rules. Simulation results prove that F$^2$RAC can guarantee QoS requirement of voice and provide the highest throughput efficiency and the smallest data packet delay amongst the different alternatives including PRMA［1］, IPRMA［2］, and SIR［3］.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.2
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• pp.261-266
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• 2009

We analyze the performances of the DCF, which is the medium access control protocol of IEEE 802.11 WLAN, assuming normal traffic condition. There have been much less research efforts under the normal condition than those under the saturated one. This paper proposes an analytical method of approximating the transmission attempt rate under normal condition as proportional to that under saturated condition. In result, we show that we can obtain the transmission attempt rate and the packet collision probability which quickly converge using iterative computations of relatively simple equations, and using these results we derive the network throughput and medium access delay. Numerical results show that our method is much less complex than those based on the Markov Chain while it can predict the performances quite accurately.