• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.4
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• pp.29-38
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• 2005

Because IEEE 802.11 has several security vulnerabilities, IEEE 802.11i was proposed and accepted. But IEEE 802.11i has much overhead for most of users for the web surfing. Besides not only node the authentication but also the packet authentication is needed to communicate. Although IEEE 802.11i uses TKIP(Temporal Key integrity Protocol) and CCMP(CTR with CBC-MAC Protocol), they have a lot of overheads. In this paper, Lightweight Packet Authentication(LIPA) is proposed. LIPA has less overhead and short delay so that it can be affordable for simple web-surfing which does not need stronger security. After comparing performances of LIPA with those of TKIP and CCMP, LIPA is more efficient than other schemes for transmitting packets.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.11
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• pp.1001-1011
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• 2012

In this paper, the effects to system performance are evaluated in IEEE 802.11 system when the number of competing terminals are estimated and reflected to the system. The IEEE 802.11 system uses DCF (Distributed Coordination Function) for the multiple access method, and the system throughput performance depends on the accuracy of the estimated number of competing terminals. We propose extended H infinity filter (EHIF) approach which does not require the noise information for estimating the number of competing terminals. Simulation results show that EHIF outperforms the extended Kalman filter in both saturated and non-saturated network conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1A
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• pp.73-81
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• 2011

IEEE 802.11 PHY and MAC layer provide multiple channels and data rates. To improve the performance of IEEE 802.11 multi-radio ad hoc networks, it is required to utilize available channels and data rates efficiently. However, in IEEE 802.11 multi-rate networks, the rate anomaly (RA) problem occurs that the network performance is severely degraded as low-rate links affect high-rate links. Hence, in this paper, we propose a model-based rate separation (MRS) algorithm that uses multiple channels to separate different data rate links so that the RA problem is mitigated. MRS algorithm utilizes an existing throughput model that estimates the throughput of IEEE 802.11 single-hop networks to separate low-rate links and high-rate links. Through simulations, we demonstrate that the MRS algorithm shows improved network performance compared with existing algorithms in multi-radio ad hoc networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.65-71
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• 2006

In IEEE 802.11b wireless network, the access point(AP) sends beacons periodically to manage stations when they are running in low power mode. Stations contend for the transmission medium after they receive a beacon and continuously check its state until it becomes available. Thus the energy consumption of each station increases as the load of wireless network. In this paper, we propose a method to reduce energy consumption controlling virtual bitmap in wireless network with multiple stations. The problems of low power mode in IEEE 802.11b wireless interface are described and a new method to reduce energy consumption is proposed. The proposed method is simulated with the network simulator, ns2, and compared with the low power mode of the IEEE 802.11b. The result measured in terms of station's wakeup time shows some enhancement in energy consumption when multiple stations are communicating through the AP in wireless network.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4A
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• pp.205-213
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• 2012

In this paper, we propose a new channel hopping scheme based on IEEE 802.11h as a good countermeasure against jamming attacks in IEEE 802.11 wireless networks. 802.11h Dynamic Frequency Selection (DFS) is a mechanism which enables hopping to a best channel with full channel measurement, not a randomly chosen channel, when the current link quality degradation occurs due to interferers such as military radars. However, under jammer attacks, this needs a time for full channel measurement before a new channel hopping and due to link disconnection during the time network performance degradation is inevitable. In contrast, our proposed schemes make an immediate response right after a jammer detection since every device is aware of next hopping channel in advance. To do this, a next hopping channel is announced by Beacon frames and the channel is selected by full channel measurement within Beacon intervals. Simulation results show that proposed scheme minimizes throughput degradation and keeps the advantages of DFS.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.5
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• pp.733-738
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• 2013

Orthogonal Frequency Division Multiplexing (OFDM) based IEEE 802.11 a/g systems which are widely used in wireless LAN carry out channel estimation in one time per packet since the systems use only preamble. Whereas, midamble based channel estimation supports continuous channel estimation by tracking the channel state information periodically. Using IEEE 802.11p Wireless Access in Vehicular Environments (WAVE) system, we analyze the performance of the proposed system via practical measurements. Based on these results, practical issues on midamble based channel estimation are investigated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.4
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• pp.837-846
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• 2013

Recently, new technologies based on wireless LAN is being studied because utilization on smart phone using Wi-Fi is increased. 802.11 b/g/a is universalized wireless LAN technologies based on ISM, the standard developed in 11's working group of IEEE 802. standardization about IEEE 802.11ac that overcame limitation on Blue-ray of IEEE 802.11n or uncompressed video transmission and IEEE 802.af's technologies using TVWS is being actively studied. In this paper, ability of transmission considering the security on AP operated by these technologies have measured and done a comparative analysis with existing wireless LAN environment ability of transmission measured when appling security is more stable than existing ability of transmission in an environment with obstacles and shorten of transmission time is confirmed as a result of analysis.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2007.11a
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• pp.330-340
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• 2007

IEEE 802.11 wireless LANs employ the backoff algorithm to avoid contentions among STAs when two or more STAs attempt to transmit their data frames simultaneously. The MAC efficiency can be improved if the CW values are adaptively changed according to the channel state of IEEE 802.11 wireless LANs. In this paper, we propose a dynamic contention window control algorithm using the genetic algorithm to improve the MAC throughput of IEEE 802.11 wireless LANs.

• Journal of applied mathematics & informatics
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• v.22 no.1_2
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• pp.501-515
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• 2006

The IEEE 802.11 protocol is the most mature technology for WLANs(Wireless Local Area Networks). However, as the number of stations increases, the delay and throughput performance of IEEE 802.11 MAC(Medium Access Control) degrades severely. In this paper, we present the comprehensive performance analysis of IEEE 802.11 MAC protocol by investigating the MAC layer packet service time when arrival packet sizes have a general probability distribution. We obtain the discrete probability distribution of the MAC layer service time. By using this, we analyze the system throughput and the MAC layer packet service time of IEEE 802.11 MAC protocol in wireless LAN environment. We take some numerical examples for the system throughput and the mean packet service time for several special distributions of arrival packet sizes.

• Journal of Korea Society of Industrial Information Systems
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• v.16 no.2
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• pp.1-11
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• 2011

A lot of works on the throughput analysis of the IEEE 802.11 DCF have been studied since last few years. However, we should predict the throughput of the IEEE 802.11g that we mostly use today because the existing numerical results do not consider exactly the IEEE 802.11g with the physical layer ERP-OFDM parameters. In particular, we might have different results in the working WLAN s compared with the simple predictions of the throughput using the previous results. In this paper, we directly monitor the ERP-OFDM physical layer parameters on the operating WLANs, and then analyze the saturated DCF throughput with the well-known analytic model. Moreover, we measure the bandwidth utilization on the real WLANs working with FTP services, and then compare them with the analytic results. According to the experiment results, we confirm the usefulness of the analytic models which assume the saturated traffic sources.