• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.343-345
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• 2003

최근 무선랜의 발전으로 공공의 사용자 밀집 지역에서 무선랜의 이용이 가능해졌다. 이러한 사용자 밀집 지역에서는 엑세스 과밀 현상이 발생하므로 기존의 무선랜 방식보다 차별화된 엑세스 관리 방법이 요구된다. 본 논문에서는 무선랜의 표준인 IEEE 802.11 에서 제안된 DCF(Distributed Coordination Function)와 PCF(Point Coordination Function) 두가지 전송 방식의 데이터 전송과 폴링 방법을 핫스팟 환경에 맞추어 효과적으로 개선하는 방법으로 노드에 의해서 폴링을 관리하는 스킴을 제안한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.12
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• pp.2259-2266
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• 2016

Recently dense wireless local area networks (WLANs) emerge as the number of WLAN cells and stations increases. In such dense WLAN environment, this paper proposes a new distributed medium access control (MAC) protocol. The proposed MAC protocol extends the previous CSMA with collision resolution (CSMA/CR) that uses a single collision detection (CD) phase and employs multiple CD phases to resolve more collisions. It checks the collision detection in each CD phase and stops the CD phase if consecutive non-detected CD phases occur more than the threshold. Therefore, the proposed protocol can control the number of CD phases adaptively according to the number of accessing stations and increase the probability of collision resolution while decreasing the packet overhead. The simulation results show that the proposed adaptive CSMA/CR protocol employs a variable number of CD phases according to the number of stations and achieves a greater throughput than the previous CSMA/CR protocol using the fixed number of CD phases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.3
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• pp.441-450
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• 2015

Nowadays, many WLAN access points (APs) are deployed in hotspot areas such as shopping malls and stations. As the number of WLAN APs deployed increases, how to manage densely deployed APs in an efficient manner becomes one of the most important issues in WLANs. In this environment, uncoordinated multicast services can lead to frequent collisions due to simultaneous transmissions among APs. In this paper, we propose a multicast scheduling algorithm that can exploit simultaneous transmissions in multiple sectors and avoid redundant transmissions in dense networks. Simulation results demonstrate that the proposed scheme can reduce the multicast transmission latency compared to comparison scheduling schemes.

• 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 Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.646-651
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• 2012

This paper is about the experiment which is throughput of WLANs based on 802.11 due to interference each other. Recently, WLAN has been increased due to generalization of smart-phone and potable notebook. Therefore, the decrease of throughput because of interference between WLANs is expected. In regard of this, the throughput of WLANs according to channelling is measured in order to figure out efficient channelling and the throughput of WLANs according to the number of AP was measured in order to get relation between number of AP and throughput. Then, more efficient channelling of 1, 5, 9, 13 is suggested and the throughput of WLAN is decreased as increasing of number of AP.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.3
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• pp.451-458
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• 2015

The deployment density of AP increases as well as the density WLAN stations due to increase of WLAN use and the real performance of WLAN is degraded. To improve the performance, there are many PHY/MAC technologies and OFDMA and full duplex are promising technologies among them. In conventional OFDMA WLAN MAC relate works, there are some limitations in terms of channel utilization and collision probability. Thus, it need to research for effective channel allocation protocol. Full duplex can transmit data on the same time and same frequency resource so it can allocate channel more flexible than half duplex. In this paper, we prose the OFDMA FD-MAC(Full Duplex MAC) protocol that it allocates the sub-channels based on the idle channel information for full duplex pair. In addition, it shows the throughput improvement by performance analysis.

• Journal of Digital Contents Society
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• v.19 no.8
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• pp.1545-1554
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• 2018

In order to support the mobility of the wireless devices, at least two APs (Access Points) must be arranged in a single AP area to maintain communication area. In the WLAN (Wireless LAN) environment, seamless handover is one of the most important issues in terms of effective utilization of wireless networks and maximization of services for users. On the other hand, SDN (Software-Defined Networking), which is emerging rapidly in recent years, is revolutionizing network management in terms of flexibility, fine control, and convenience. SDN originally reduces latency time or increases network robustness by real-time flow table control reducing or bypassing paths between switches in LAN-based data centers. In this study, we apply OpenFlow, a SDN platform focused on wired LAN, to a dense WLAN environment using legacy APs to implement and evaluate seamless handover for streaming services of digital contents.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.3
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• pp.469-477
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• 2015

In this paper, joint spatial division and reuse (JSDR) scheme is proposed for maximizing network throughput in densely-deployed wireless local area networks equipped with massive antenna array. The proposed JSDR scheme divides the massive spatial space into two subspaces: one is for suppressing the interference from the neighboring access points and another is for sensing the carrier sensing and transmitting the information-bearing signals to intended stations. By using computer simulation, the proposed JSDR can provide 133% higher network throughput, compared to the carrier sensing technique defined in the IEEE 802.11 standard so that the proposed JSDR is suitable for the next generation WLAN systems.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.1
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• pp.12-21
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• 2012

IEEE 802.11 MAC protocol standard, DCF(CSMA/CA), is originally designed to ensure the fair channel access between mobile nodes sharing the local wireless channel. It has been, however, revealed that some misbehavior nodes transmit more data than other nodes through artificial means in hot spot area spreaded rapidly. The misbehavior nodes may modify the internal process of their MAC protocol or interrupt the MAC procedure of normal nodes to achieve more data transmission. This problem has been referred to as a selfish node problem and almost literatures has proposed methods of analyzing the MAC procedures of all mobile nodes to detect the selfish nodes. However, these kinds of protocol analysis methods is not effective at detecting all kinds of selfish nodes enough. This paper address this problem of detecting selfish node using Tsallis-Entropy which is a kind of statistical method. Tsallis-Entropy is a criteria which can show how much is the density or deviation of a probability distribution. The proposed algorithm which operates at a AP node of wireless LAN extracts the probability distribution of data interval time for each node, then compares the one with a threshold value to detect the selfish nodes. To evaluate the performance of proposed algorithm, simulation experiments are performed in various wireless LAN environments (congestion level, how selfish node behaviors, threshold level) using ns2. The simulation results show that the proposed algorithm achieves higher successful detection rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12C
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• pp.1248-1255
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• 2005

We investigate the OFDM-based wireless LAN systems operating in the 60 GHz frequency band as part of the fourth-generation (4G) systems. The 60 GHz band is of much interest since this is the band in which a massive amount of spectral space has been allocated worldwide for dense wireless local communications. This paper gives an overview of 60 GHz bandchannel characteristics and an effect on phase noise. The performance of OFDM system is severely degraded by the local oscillator phase noise, which causes both common phase error and inter-carrier interference. In this paper, we apply phase noise suppression (PNS) algorithm that is easy for implementation to OFDM based 60 GHz wireless LAM system and analyze the SER performance. In case of using the PNS algorithm, SER performance is improved about 6dB, 7.5dB, respectively in 16, 64-QAM.