• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.9
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• pp.841-851
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• 2014

Wireless technologies sharing the same frequency band and operating in the same environment often interfere with each other, causing severe decrease in performance. In this paper, we propose a algorithm based on traffic scheduling techniques that mitigate interference between different wireless systems operating in the 2.4-GHz industrial, medical, and scientific band. In particular, we consider IEEE 802.11 wireless local area networks (WLANs) and Bluetooth data transfer, showing that the proposed algorithms can work when the two systems are able to exchange information as well as when they operate independently of one another. Results indicate that the proposed algorithm remarkably mitigate the interference between the WLAN and Bluetooth technologies at the expense of a small additional delay in the data transfer.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.10
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• pp.2121-2128
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• 2009

The application range of IEEE 802.11 wireless LAN has rapidly expanding from campus, enterprise to the public network of Hot Spot area due to the advantages of easiness of construction, mobility of wireless client station, convenience of usage and so on. However the security of WLAN(Wireless LAN) is vulnerable inherently because of using RF as a medium, and so the dangers of infringement of personal information and inside data of enterprises have increased and wardriving attack searching for security vulnerability in wireless LAN has become more serious especially. In this paper, we find out the overview of various procedures and preparatory stages for wardriving attack against wireless LAN, and propose complementary methods to prevent information infringement accidents from wardriving attack in wireless LAN. For this purpose, we make an equipment which is suitable for wardriving in wireless LAN and show security vulnerability of AP(Access Point) operation in WLAN around Yangjae-Dong in Seoul as a result of using the equipment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1492-1512
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• 2011

Due to multiple hops, mobility and time-varying channel, supporting delay sensitive real-time traffic in wireless local area network-based (WLAN) mesh networks is a challenging task. In particular for real-time traffic subject to medium access control (MAC) layer control overhead, such as preamble, carrier sense waiting time and the random backoff period, the performance of real-time flows will be degraded greatly. In order to support real-time traffic, an efficient adaptive packet scheduling (APS) scheme is proposed, which aims to improve the system performance by guaranteeing inter-class, intra-class service differentiation and adaptively adjusting the packet length. APS classifies incoming packets by the IEEE 802.11e access class and then queued into a suitable buffer queue. APS employs strict priority service discipline for resource allocation among different service classes to achieve inter-class fairness. By estimating the received signal to interference plus noise ratio (SINR) per bit and current link condition, APS is able to calculate the optimized packet length with bi-dimensional markov MAC model to improve system performance. To achieve the fairness of intra-class, APS also takes maximum tolerable packet delay, transmission requests, and average allocation transmission into consideration to allocate transmission opportunity to the corresponding traffic. Detailed simulation results and comparison with IEEE 802.11e enhanced distributed channel access (EDCA) scheme show that the proposed APS scheme is able to effectively provide inter-class and intra-class differentiate services and improve QoS for real-time traffic in terms of throughput, end-to-end delay, packet loss rate and fairness.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.4
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• pp.378-384
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• 2015

Indoor localization is becoming one of the most important technologies for smart mobile applications with different requirements from conventional outdoor location estimation algorithms. Fingerprinting location estimation techniques based on neural networks have gained increasing attention from academia due to their good generalization properties. In this paper, we propose a novel location estimation algorithm based on an ensemble of multiple neural networks. The neural network ensemble has drawn much attention in various areas where one neural network fails to resolve and classify the given data due to its' inaccuracy, incompleteness, and ambiguity. To the best of our knowledge, this work is the first to enhance the location estimation accuracy in indoor wireless environments based on a neural network ensemble using fingerprinting training data. To evaluate the effectiveness of our proposed location estimation method, we conduct the numerical experiments using the TGn channel model that was developed by the 802.11n task group for evaluating high capacity WLAN technologies in indoor environments with multiple transmit and multiple receive antennas. The numerical results show that the proposed method based on the NNE technique outperforms the conventional methods and achieves very accurate estimation results even in environments with a low number of APs.

• Journal of information and communication convergence engineering
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• v.18 no.1
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• pp.1-7
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• 2020

This paper proposes a fast-processing and low-cost hardware multiple input multiple output (MIMO) channel emulator. The channel emulator is an important component of hardware-based simulation systems. The novelty of this work is the use of sharing and pipelining functions to reduce hardware resource utilization while maintaining a high sample rate. In our proposed emulator, the samples are created sequentially and interpolated to ensure the sample rate is equal to the base band rate. The proposed 4 × 4 MIMO requires low-cost hardware resource so that it can be implemented on a single field-programmable gate array (FPGA) chip. An implementation on Xilinx Virtex-7 VX980T was found to occupy 10.47% of the available configurable slice registers and 12.58% of the FPGA's slice lookup tables. The maximum frequency of the proposed emulator is 758.064 MHz, so up to 560 different paths can be processed simultaneously to generate 560 × 758 million × 2 × 32 bit complex-valued fading samples per second.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.11
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• pp.1996-2001
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• 2006

Open System Authentication Method, Shared Key Method, Mac Based Authentication Method are very hard to use in wireless network that needs security. So now, many researches have been performed about 802.1x and user authentication method applying PKI. but certificate verification protocol has been used abolished list called CRL since it's first usage of PKI, there were still has a problem about distribution point. This paper applied CVS to use CA direct not to use CRL and OSCP server in order to improve this problems. Also It suggested the system that can make authentication steps more shorter using authentication server and Mutual authentication system by public certificate(small size/low speed wireless terminal can access to wireless network fast and safely)

• 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.

• Journal of Advanced Navigation Technology
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• v.20 no.4
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• pp.352-360
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• 2016

In this paper, a novel multiple multicast feed-back scheme for improving multimedia multicast and broadcast system based on IEEE 802.11. The proposed scheme improves multicast PPDU delivery ratio of next generation wireless LAN by utilizing multicast feed-back information. By using the proposed scheme, regardless of its size of multicast group, an AP STA could collect transmission failure information by receiving simultaneous NAK frame. The proposed scheme shows large performance enhancement in broadcast or multicast system of Intelligent Transport System and Passenger Entertainment Service. According to the analysis results, the proposed scheme could enhance wireless LAN multicast and broadcast performance significantly.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.1
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• pp.161-169
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• 2009

Multicast-based data communication is an efficient communication scheme in wireless networks where the Media Access Control (MAC) layer is based on one-hop broadcast from one source to multiple receivers. Compared with unicast, multicast over wireless channel should handle varying channel conditions of multiple users and user mobility to achieve good quality for all users. However, IEEE 802.11 does not support reliable multicast due to its inability to exchange RTS/CTS and ACK with multiple recipients. Thus, several MAC layer protocols have been proposed to provide reliable multicast. For the reliable multicast, an additional overhead is introduced and it degrades the system performance. In this paper, we propose a cross-layer design to reduce the control overhead for reliable multicast in OFDMA systems. We present an analytical formulation of the system throughput associated with the overhead.

• Journal of IKEEE
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• v.12 no.2
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• pp.95-101
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• 2008

In this paper, we study an optimum design of search synchronization structure for Baseband Modem to support ISO/IEC 18185-5 and 24730-2 Standard. For DSSS Modem, we design the code acquisition and tracking structure which are important in receiver operation, and examine the parameters to be considered. The data and PN chip transmission rates and processing gain of the proposed modem are 59.7 kbps, 30.521875 Mcps, and 27 dB, respectively. This indicates that the noise immunity of the proposed modem is 17dB better than IEEE 802.11b (Processing gain : 10dB). Therefore, we design the optimum structure for the modem search synchronization which is compatible to the proposed modem standard.