• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12B
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• pp.1050-1057
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• 2008

Wireless Mesh Networks (WMNs) have recently become a hot issue to support high link capacity in wireless access networks. The IEEE 802. I 1 standard which is mainly used for the network interface technology in WMNs supports up to 3 or 12 multiple channels according to the IEEE 802.11 specification. However, two important problems must be addressed when we design a channel assigmnent algorithm: channel dependency problem and channel scanning delay. The former occurs when the dynamic channel switching of an interface leads to the channel switching of other interfaces to maintain node connectivity. The latter happens per channel switching of the interface, and affects the network performance. Therefore, in this paper, we propose the Distance-Based Channel Assigmnent (DB-CA) scheme for multi-channel WMNs to solve such problems. In DB-CA, nodes just perform channel switching without channel scanning to communicate with neighboring nodes that operate on different channels. Furthermore, DB-CA minimizes the interference of channels being used by nodes near the gateway in WMNs. Our simulation results show that DB-CA achieves improved performance in WMNs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.1
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• pp.17-28
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• 2014

The increase of smartphone users have made mobile carriers offload increasingly congested traffic of 3/4G by providing Wi-Fi hot-spots in the public places such as coffee shops and subway stations. In the traditional authentication in WLAN, the users should convince the service providers that they are valid customers before they use WLAN services. Since the authentication protocol is designed for service providers. Even with the mutual authentication based on the IEEE 802.1X, which is supported by IEEE 802.11 standard, it is difficult to be convinced of that the service providers really have installed the WLAN APs, which users are confronted with. An attacker can install rogue APs that masquerade as legitimate APs by copying the SSID, MAC address, etc. in order to obtain users' private information. In this paper, we introduce a method of authenticating legitimate APs for smartphone users. And we show our proposal can be well utilized for the current Wi-Fi hot-spots as a security plug-in and prove it through our experiments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.3
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• pp.547-551
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• 2010

In this paper, Double rectangular patch with 4-bridges is investigated for solution of IEEE 802.11b/g(2.4GHz) and 802.11a(5.7GHz). Rectangular patch for 5.7GHz frequency band is printed on the PCB substrate and connected to another rectangular patch for 2.4GHz frequency band with 4-bridges to obtain dual band operation in a antenna element. The proposed antenna has a low profile and is fed by $50{\Omega}$ coaxial line. The dielectric constant of the designed antenna substrate is 3.27. Two rectangular patches have each resonance frequencies that are 2.4GHz and 5.7GHz. A dual-band characteristic is shown as connecting two rectangular patch using four bridges. Also, the proposed antenna is shown input return loss that is below -10dB at 2.4GHz and 5.7GHz of WLAN(Wireless LAN).

• Journal of Korea Multimedia Society
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• v.10 no.11
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• pp.1483-1495
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• 2007

Thanks to IEEE 802.11 technique, accessing Internet through a wireless LAN(Local Area Network) is possible in the most of the places including university campuses, shopping malls, offices, hospitals, stations, and so on. Most of the APs(access points) for wireless LAN are supporting 2.4 GHz band 802.11b and 802.11g protocols. This paper is introducing a C# library function which can be used to read RSSIs(Received Signal Strength Indicator) from APs. An LBS(Location Based Service) estimates the current location of the user and provides useful user's location-based services such as navigation, points of interest, and so on. Therefore, indoor, LBS is very desirable. However, an indoor LBS cannot be realized unless indoor position ing is possible. For indoor positioning, techniques of using infrared, ultrasound, signal strength of UDP packet have been proposed. One of the disadvantages of these techniques is that they require special equipments dedicated for positioning. On the other hand, wireless LAN-based indoor positioning does not require any special equipments and more economical. A wireless LAN-based positioning cannot be realized without reading RSSIs from APs. Therefore, our C# library function will be widely used in the field of indoor positioning. In addition to providing a C# library function of reading RSSI, this paper introduces implementation of indoor positioning modules making use of the library function. The methods used in the implementation are K-NN(K Nearest Neighbors), Bayesian and trilateration. K-NN and Bayesian are kind of fingerprinting method. A fingerprint method consists of off-line phase and realtime phase. The process time of realtime phase must be fast. This paper proposes a decision tree method in order to improve the process time of realtime phase. Experimental results of comparing performances of these methods are also discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.8
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• pp.865-871
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• 2010

A compact dual-band(IEEE 802.11b: 2.4~2.5 GHz, 11a: 5.15~5.825 GHz) 2-channel MIMO antenna for PMP applications is presented. The proposed antenna is composed of a planar inverted F-shape antenna(PIFA) operating at 2 GHz band and a loop antenna operating at 5 GHz band. The proposed antenna is orthogonally arranged at the edge of the ground plane for polarization and pattern diversities with excellent isolation characteristics. The two PIFA antennas operating 2 GHz have connecting line($\lambda_g$/4) face to the feed point for high isolation and low correlation at 2 GHz band. The two loop antennas connected each other in the bottom side to improve the isolation at 5 GHz band. The proposed antenna has a sufficient gain in WLAN service band and is compact sized for the portable media player (PMP) applications.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.10
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• pp.2615-2618
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• 2009

Double rectangular patch with 4-bridges is investigated for solution of IEEE 802.11b/g (2.4 GHz) and 802.11a (5.5 GHz). Rectangular patch for 5.5 GHz frequency band is printed on the PCB substrate and connected to another rectangular patch for 2.4 GHz frequency band with 4-bridges to obtain dual band operation in an antenna element. 4-bridges can modify the desired frequency band from its original frequency band by changing its width. Gain of 2.4 GHz patch is 5 dBi and 5.5 GHz patch is 3.7 dBi at ${\theta}=0^{\circ}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.11
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• pp.1133-1136
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• 2011

In this paper, we proposed a collinear antenna with a stripline structure for IEEE 802.11b/g applications in ISM (Industrial, Scientific, Medical) band of 2.4~2.5 GHz, which supplements disadvantages of COCO(Coaxial Collinear) antenna and OMA(Omnidirectional planar Microstrip Antenna). By using the proposed 4-layer substrate, we obtained improved performances and advantages in production compared with the existing antenna. In order to get antenna arrays, the same phase structure is designed by alternatively connecting outer conductor to inner conductor with ${\lambda}$/2 antenna element, and the substrate of FR4 epoxy (${\epsilon}_r$=4.4, tan${\delta}$=0.02) was used for the actual implementation. The maximum gain of about 4.93 dBi was measured, which leaded to a little improved gain of 0.33 dBi in comparison to the existing OMA structure.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.4
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• pp.309-317
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• 2011

This paper describes a baseband analog (BBA) chain for wireless local area network (WLAN) applications. For the given specifications of the receiver BBA chain, the optimum allocation of the gain and filter rejection of each block in a BBA chain is achieved to maximize the SFDR. The fully integrated BBA chain is fabricated in 0.13 ${\mu}m$ CMOS technology. An input-referred third-order intercept point (IIP3) of 22.9 dBm at a gain of 0.5 dB and an input-referred noise voltage (IRN) of 32.2 nV/${\surd}$Hz at a gain of 63.3 dB are obtained. By optimizing the allocation of the gain and filter rejection using the proposed design methodology, an excellent SFDR performance of 63.9 dB is achieved with a power consumption of 12 mW.

• 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.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.3 s.118
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• pp.257-264
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• 2007

In this paper, we have designed and fabricated a wide-band and high gain antenna which can integrate a standard of IEEE 802.1la$(5.15\sim5.25\;GHz,\;5.25\sim5.35\;GHz,\;5.725\sim5.825\;GHz)$. We inserted a parallel dual slot into a rectangular patch to have wide-band, and we offset an element of capacitance from the slot by using coaxial probe feeding method. We also designed a converter of $\lambda_g/4$ impedance with taper type line so that wide-band impedance can be matched easily. We finally designed structure with $2\times2$ array in order to improve the antenna gain, and the final fabricated antenna could have a good return loss(Return loss$\leq$-10 dB) and a high gain(over 13 dBi) at the range of $5.01\sim5.95\;GHz(B/W\doteqdot940\;MHz)$.