• Journal of Korea Multimedia Society
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• v.12 no.11
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• pp.1521-1529
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• 2009

There is a serious unfairness problem between upstream and downstream flows of AP in IEEE 802.11 Wireless LAN. This problem is because Wireless LAN's DCF MAC protocol provides AP with equal channel access priority to mobile noded. Also, it makes this problem worse that the TCP's Data segment loss is more effective on throughput than the TCP's ACK segment. In this paper, we first make several simulations to analysis the unfairness in the various point of view and to find reasons of the unfairness. Also, this paper presents AP's scheduling scheme to alleviate the unfairness problem and evaluate the scheme through ns2 simulator.

• Journal of Satellite, Information and Communications
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• v.12 no.2
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• pp.51-55
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• 2017

This paper aims to maximize the energy harvesting rate and channel capacity in RF-energy harvesting networks (RF-EHNs) under the constraints of maximum transmit power and minimum quality of service (QoS) in terms of rate capacity for each user. We study a multi-user RF-EHN with frequency division multiple access (FDMA) in a Rayleigh channel. An access point (AP) simultaneously transmitting wireless information and power in the RF-EHN serves a subset of active users which have a power-splitting antenna. To gauge the network performance, we define energy efficiency (EE) and propose an optimization solution for maximizing EE with Lagrangian dual decomposition theory. In simulation results, we confirm that the EE is effectively maximized by the proposed solution with satisfying the given constraints.

• Journal of Information Processing Systems
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• v.16 no.3
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• pp.541-556
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• 2020

Wireless networks have become integral to society as they provide mobility and scalability advantages. However, their disadvantage is that they cannot control the media, which makes them vulnerable to various types of attacks. One example of such attacks is the evil twin access point (AP) attack, in which an authorized AP is impersonated by mimicking its service set identifier (SSID) and media access control (MAC) address. Evil twin APs are a major source of deception in wireless networks, facilitating message forgery and eavesdropping. Hence, it is necessary to detect them rapidly. To this end, numerous methods using clock skew have been proposed for evil twin AP detection. However, clock skew is difficult to calculate precisely because wireless networks are vulnerable to noise. This paper proposes an evil twin AP detection method that uses a multiple-feature-based machine learning classification algorithm. The features used in the proposed method are clock skew, channel, received signal strength, and duration. The results of experiments conducted indicate that the proposed method has an evil twin AP detection accuracy of 100% using the random forest algorithm.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.1
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• pp.145-148
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• 2020

Wearable computing is growing rapidly as research on body area communication network using wireless sensor network technology is actively conducted. In particular, there is an increasing interest in smart clothing measuring unrestrained and insensitive bio signals, and research is being actively conducted. However, research on smart clothing is mainly based on 1: 1 wireless communication. In this paper, we propose a multi-access monitoring system that can measure bio-signals by multiple users wearing smart clothing. The proposed system consists of wireless access device, multiple access control server and monitoring system. It also provides a service that allows multiple users to monitor and measure bio signals at the same time.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9A
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• pp.717-727
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• 2003

The HIPERLAN/2(HIgh PERformance Local Area Network Type2) is one of the wireless LAN standards for providing raw data rates of up to 54 Mbps. The MAC protocol of HIPERLAN/2 is based on TDMA/TDD, and resources in one MAC frame can be allocated dynamically by Access Point(AP). The random channel(RCH) is defined for the purpose of giving a mobile terminal the opportunity to request transmission resources in the uplink MAC frames. It is desirable that the number of RCHs is dynamically adapted by the AP depending on the current traffic situation. Allocation of excessive RCHs may waste radio resources and insufficient RCHs compared to traffic loads may result in many collisions in access attempts. We propose an RCH allocation scheme based on split algorithm in HIPERLAN/2. The simulation and analytic results show that the proposed scheme achieves a higher channel throughput, lower access delay and delay jitter than previously proposed RCH allocation schemes.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.413-420
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• 2020

The Tactical Information and Communication Network system provides real-time multimedia services such as voice and data by utilizing the Mobile Subscriber Access Point. At this time, an external transmission path is constructed through the Low Capacity Trunk Radio and the High Capacity Trunk Radio system. The communication devices of each wireless transmission system are mounted on a tactical vehicle and a secondary battery is used to prevent a power interruption when the supply power to the tactical vehicle is transferred to the integrated power control device. In this paper, the basic design of the Wireless Power Transfer device for charging the battery of the integrated power control system of the mobile base station system using the Loading Distribution Method and checking the number of primary windings and the core material selection by the air gap through the Finite Elements Method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.5 s.347
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• pp.84-93
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• 2006

Ethernet-PON is an emerging access network technology that provides a low-cost method of deploying optical access lines between OLT and ONUs. It has a point-to-multipoint and multipoint-to-point architecture in downstream and upstream direction, respectively. Therefore, downstream packets are broadcast from an OLT toward all ONUs sithout collision. On the other hand, since alt ONUs share a common channel, the collision may be occurred for the upstream transmission. Therefore, earlier efforts on Ethernet-PON have been concentrated on an upstream MAC protocol to avoid collision. But it is needed to control downstream traffic in practical access network, where the network provider limits available bandwidth according to the number of users. In this paper, we propose a traffic control scheme for supporting the fairness of the downstream bandwidth. The objective of this algorithm is to guarantee the fairness of ONUs while maintaining good performance. In order to do this, we define the service probability that considers the past traffic information for downstream, the number of tokens and the relative size of negotiated bandwidth. We develop the simulation model for Ethernet-PON to evaluate the rate-limiting algorithm by using AWESIM. Some results are evaluated and analyzed in terms of defined fairness factor, delay and dropping rate under various scenario.

• Journal of Internet Computing and Services
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• v.20 no.5
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• pp.95-104
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• 2019

Various kinds of devices are used for the Internet of Things (IoT) service, and IoT devices mainly use communication technology that uses the frequency of the unlicensed band. There are several types of communication technology in the unlicensed band, but WiFi is most commonly used. Devices used for IoT services vary in computing resources from devices with limited capabilities to smartphones and provide services over wireless networks such as WiFi. Most IoT devices can't perform complex operations for network control, thus they choose a WiFi access point (AP) based on signal strength. This causes a decrease in IoT service efficiency. In this paper, an intelligent AP system that can efficiently control the WiFi connection of the IoT devices is implemented. Based on the network information measured by the IoT device, the access point learns using a feed forward neural network algorithm, and predicts a network connection state to control the WiFi connection. By controlling the WiFi connection at the AP, the service efficiency of the IoT device can be improved.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.922-925
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• 2004

Bluetooth technology is essentially a method for wireless connection of a diverse set of devices ranging from PDAs, mobile phone, notebook computers, to another equipments. The bluetooth system supports both point-to-point connection and point-to-multipoint connections. In point-to-multipoint connection, the channel is shared among several bluetooth devices. Two or more devices sharing the same channel form a piconet. There is one master device and up to seven active slave devices in a piconet. The radio operates in the unlicensed 2.45GHz ISM band. This allows users who travel world-wide to use bluetooth equipments anywhere. Since the link is based on frequency-hop spread spectrum, multiple channels can exist at the same time. The Bluetooth standard has been suggested that Bluetooth equipments can be used in the short-range, maximum 100 meters . It has been defined that the time takes to setup and establish a bluetooth connection among devices is 10 seconds. It is a long time and may be a cause to lose a chance of finding other non-fixed devices. We propose a routing protocols for scatternets which can be used to control a mobile units(MUs) in this network. The proposed routing protocol is composed of two kinds of bluetooth information, access point(AP) and MU.

• Journal of Communications and Networks
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• v.13 no.5
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• pp.463-471
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• 2011

Cooperative communications using relays in wireless networks have similar effects of multiple-input and multiple-output without the need of multiple antennas at each node. To implement cooperation into a system, efficient protocols are desired. In IEEE 802.11 families such as a/b/g, mobile stations can automatically adjust transmission rates according to channel conditions. However throughput performance degradation is observed by low-rate stations in multi-rate circumstances resulting in so-called performance anomaly. In this paper, we propose active relay-based cooperative medium access control (AR-CMAC) protocol, in which active relays desiring to transmit their own data for cooperation participate in relaying, and it is designed to increase throughput as a solution to performance anomaly. We have analyzed the performance of the simplified AR-CMAC using an embedded Markov chain model to demonstrate the gain of AR-CMAC and to verify it with our simulations. Simulations in an infrastructure network with an IEEE 802.11b/g access point show noticeable improvement than the legacy schemes.