• 한국ITS학회:학술대회논문집
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• 2005.11a
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• pp.177-179
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• 2005

• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.180-189
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• 2005

This paper describes a transmission power control method for power saving in 802.11b wireless LANs. We have first explored how much effects reducing transmission power has on communication performance. Then we propose a power control algorithm, whose approach is similar to that of TCP congestion control, determining an appropriate transmission power level by monitoring the retransmission rate. We have implemented an utility software on a Linux-based system and made several experiments to validate the proposed method. The results show that it is possible to save energy consumption by controlling transmission power without sacrificing communication performance.

• Journal of Information Processing Systems
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• v.2 no.3 s.4
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• pp.159-162
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• 2006

Wireless LANs are becoming more widespread because of the rapid advance of wireless technologies and mobile computers. In this paper, we present the design and implementation of a system to help mobile users to select the most competent AP. By monitoring the network traffic of APs within the local LAN in real time, this system offers the mobile user the network utilizations, locations, and signal strengths of APs online. Based on the information, the user can select a competent AP with a high wireless bandwidth. Finally, we verified the accuracy of monitoring and calculating with regard to the utilizations of APs through real experiments.

• IEIE Transactions on Smart Processing and Computing
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• v.2 no.3
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• pp.176-187
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• 2013

Message replay, malicious Access Point (AP) associations and Denial of Service (DoS) attacks are the major threats in Wireless LANs. These threats are possible due to a lack of proper authentication and insecure message communications between wireless devices. Current wireless authentication & key exchange (AKE) schemes and security protocols (WEP, WPA and IEEE 802.11i) are not sufficient against these threats. This paper presents a novel Secure WLAN Authentication Scheme (SWAS). The scheme introduces the delegation concept of mobile authentication in WLANs, and provides mutual authentication to all parties (Wireless Station, Access Point and Authentication Server). The messages involved in the process serve both authentication and key refreshing purposes. The scheme enhances the security by protecting the messages through cryptographic techniques and reduces the DoS impact. The results showed that cryptographic techniques do not result in extra latencies in authentication. The scheme also reduces the communication cost and network overhead.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.113-118
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• 2006

Recently, wireless LANs are often applied in home or office because of its various of convenience. Frequency rage of wireless LANs specified by IEEE 802.11b is at 2.4 GHz. The bluetooth, the microwave oven, and the PDA(Personal Digital Assistants) uses ,however, the same frequency band. So problems will be produced in these environments, such as multi-pass interference and system-to-system interference. These problems can be eliminated by using EM wave absorber. In this paper, we designed and fabricated EM wave absorber using Sendust, $Al(OH)_3$, and CPE. The double-layered EM wave absorber with thickness of 1.5 mm has absorption ability more than 10 dB at 2.4 GHz.

• The KIPS Transactions:PartC
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• v.18C no.3
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• pp.187-194
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• 2011

IEEE 802.11 wireless LAN has become the center of attention for one of the most dominant wireless networking technologies nowadays. In densely deployed wireless LANs, mobile stations are exposed to a number of AP, thus it is needed to select the best AP to associate with. The most common approach is to select the AP with the highest received signal strength. However it does not consider traffic load imposed to each AP so that it may cause the poor network performance. Therefore, in this paper, we propose a throughput estimation scheme for neighboring APs by sniffing the traffic within 802.11 networks. We devise a tool, named "VirtFrame", which is to estimate the station's capable throughput from neighbor APs based on the channel access time by virtually combining the sniffed frames. Simulation results show that our proposed scheme well matches that there exists correlation between the channel access time and the actual throughput of the APs.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.3
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• pp.381-392
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• 2007

In this paper, we present an analytical method for estimating the saturation throughput of an 802.11 ad hoc LAN in the presence of noise distorting transmitted frames. This is the first method that allows studying analytically the 802.11 network performance with consideration of correlated channel failures usually inherent to realistic wireless channels. With the study, we consider the possible packet fragmentation that can be adopted to reduce the performance degradation caused by noise-induced distortions. In addition to the throughput, our method allows estimating the probability of a packet rejection occurring when the number of packet transmission retries attains its limit. The obtained numerical results of investigating 802.11 LANs by the developed method are validated by simulation and show high estimation accuracy as well as the method efficiency in determining the optimal fragmentation threshold.

• Journal of Communications and Networks
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• v.16 no.3
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• pp.311-321
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• 2014

This paper focuses on contention-based medium access control (MAC) protocols used in wireless local area networks. We propose a novel MAC protocol called adaptive backoff tuning MAC (ABTMAC) based on IEEE 802.11 distributed coordination function (DCF). In our proposed MAC protocol, we utilize a fixed transmission attempt rate and each node dynamically adjusts its backoff window size considering the current network status. We determined the appropriate transmission attempt rate for both cases where the request-to-send/clear-to-send mechanism was and was not employed. Robustness against performance degradation caused by the difference between desired and actual values of the attempt rate parameter is considered when setting it. The performance of the protocol is evaluated analytically and through simulations. These results indicate that a wireless network utilizing ABTMAC performs better than one using IEEE 802.11 DCF.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.965-972
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• 2005

We propose a new resource management scheme, Distributed Channel Allocation Protocol (DCAP), for multimedia Ad Hoc Wireless LANs (AWLANS). This scheme implements a Qualify-of-Service (QoS) providing distributed resource management on the Orthogonal Frequency Division Multiplexing-Code Division Multiple Access (OFDM-CDMA) channel architecture. According to the performance evaluation results for MPEG traffic sources, DCAP can be a good choice of resource management scheme for AWLANs supporting multimedia services on the Broadband Wireless Access(BWA)-type physical layer.

• The KIPS Transactions:PartA
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• v.11A no.6
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• pp.451-458
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• 2004

The previous studies focussed on the security problem and the fast re-authentication mechanism during handoffs in a single wireless LAN system. When the multiple wireless LAN systems share their network infrastructure one another, we propose an authentication mechanism allowing the subscriber to Perform the authentication procedure with the authentication server of its own wireless LAN system even in areas of other wireless LAN systems as well as in areas of its own wireless LAN system. In the proposed mechanism, the access point or the authentication server of other wireless LAN systems plays a role of the authentication agent between the subscriber and the authentication server of the subscriber's wireless LAN system. The proposed authentication mechanism is designed on the basis of the 802.1X and EAP-MD5 protocols.