• Journal of information and communication convergence engineering
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• v.15 no.1
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• pp.28-36
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• 2017

The medium access control (MAC) protocol based on dynamic time division multiple access/time division duplex (TDMA/TDD) is responsible for random access control and radio resource allocation in dynamic traffic environments. These functions of random access and resource allocation are very important to prevent wastage of resources and improve MAC performance according to various network conditions. In this paper, we propose new random access and resource allocation schemes to guarantee quality of service (QoS) and provide priority services in a dynamic TDMA/TDD system. First, for the QoS guarantee, we propose an adaptive random access and resource allocation scheme by introducing an access probability. Second, for providing priority service, we propose a priority-based random access and resource allocation scheme by extending the first adaptive scheme in both a centralized and a distributed manner. The analysis and simulation results show that the proposed MAC protocol outperforms the legacy MAC protocol using a simple binary exponential backoff algorithm, and provides good differential performance according to priorities with respect to the throughput and delay.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.28 no.1
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• pp.129-133
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• 2005

Slotted ALOHA(S-ALOHA) is widely used in local wireless network. We analyze the performance of contention-based model in wireless LAN using S-ALOHA protocol. We analyze the performance of binary exponential backoff (BEB) algorithm under the slotted ALOHA protocol: whenever a node's message which tries to reserve a channel is involved in a collision for the ith time, it chooses one of the next $2^i$ frames with equal probability and attempts the reservation again. We derive the expected access delay and throughput which is defined as the expected number of messages that reserve a channel in a frame. A simulation study is performed to verify our method.

• Journal of Communications and Networks
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• v.14 no.5
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• pp.524-532
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• 2012

In this paper, we present the performance evaluation of the reliable cooperative media access control (RCO-MAC) protocol, which has been proposed in [1] by us in order to enhance system throughput in bad wireless channel environments. The performance of this protocol is evaluated with computer simulation as well as mathematical analysis in this paper. The system throughput, two types of average delays, average channel access delay, and average system delay, which includes the queuing delay in the buffer, are used as performance metrics. In addition, two different traffic models are used for performance evaluation: The saturated traffic model for computing system throughput and average channel access delay, and the exponential data generation model for calculating average system delay. The numerical results show that the RCO-MAC protocol proposed by us provides over 20% more system throughput than the relay distributed coordination function (rDCF) scheme. The numerical results show that the RCO-MAC protocol provides a slightly higher average channel access delay over a greater number of source nodes than the rDCF. This is because a greater number of source nodes provide more opportunities for cooperative request to send (CRTS) frame collisions and because the value of the related retransmission timer is greater in the RCO-MAC protocol than in the rDCF protocol. The numerical results also confirm that the RCO-MAC protocol provides better average system delay over the whole gamut of the number of source nodes than the rDCF protocol.

• Proceedings of the IEEK Conference
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• summer
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• pp.317-320
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• 2004

The exponential back-off algorithm doubles the back-off size after each collision without considering network traffic status, which causes degradation of system performance. In this paper, we propose a linear random back-off mechanism which dynamically selects the back-off window size based on the channel status which includes the number of active stations and collisions to significantly increase the protocol capacity. We present an analytical model for the saturated throughput of our linear random back-off algorithm. Simulation results show that performance can be substantially enhanced if binary exponential back-off algorithm is replaced by a linear back- off algorithm.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.5
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• pp.30-39
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• 2008

This paper proposes a secure and efficient handover authentication protocol in VANET supporting fast mobility. Although the existing schemes commonly use the hash function or XOR operation to be suitable for a light-weight mobile, it does not support the security feature such as PBS. To solve this security problem, another protocol utilizing the CGA technology is proposed but it is vulnerable to the DoS attack due to a number of exponent operations. The proposed protocol using a light-weight Diffie-Hellman provides security features and performs a reduced number of exponential operation at the MN than the existing scheme.

• Journal of Communications and Networks
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• v.14 no.1
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• pp.51-62
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• 2012

The exponential growth in wireless services has resulted in an overly crowded spectrum. The current state of spectrum allocation indicates that most usable frequencies have already been occupied. This makes one pessimistic about the feasibility of integrating emerging wireless services such as large-scale sensor networks into the existing communication infrastructure. Cognitive radio is an emerging dynamic spectrum access technology that can be used for flexibly and efficiently achieving open spectrum sharing. Cognitive radio is an intelligent wireless communication system that is aware of its radio environment and that is capable of adapting its operation to statistical variations of the radio frequency. In ad hoc cognitive radio networks, a common control channel (CCC) is usually used for supporting transmission coordination and spectrum-related information exchange. Determining a CCC in distributed networks is a challenging research issue because the spectrum availability at each ad hoc node is quite different and dynamic due to the interference between and coexistence of primary users. In this paper, we propose a novel CCC selection protocol that is implemented in a distributed way according to the appearance patterns of primary systems and connectivity among nodes. The proposed protocol minimizes the possibility of CCC disruption by primary user activities and maximizes node connectivity when the control channel is set up. It also facilitates adaptive recovery of the control channel when the primary user is detected on that channel.

• Journal of the Korea Society of Computer and Information
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• v.8 no.3
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• pp.130-137
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• 2003

This paper proposes protocol design that can do user authentication efficiently in current systems that client-server environment is developed. And proposes a password-based authentication protocol suitable to certification through trustless network or key exchange. While the existing password-base protocols certify users through certification authority (CA) between client and server, the proposed protocol in this paper, users and server exchange keys and perform authentication without help of CA. To ameliorate the drawback of password-based protocols causing by the short length and randomness of password, the proposed protocol uses the signature techniques of ECDSA and the SRP protocol based on Diffie-Hellman key exchange method. Also, by with compare to round number and Hash function number and exponential operation of existing protocols, we explained efficiency of proposed protocol.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.3
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• pp.91-99
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• 2009

Development of high-speed Internet services and the increased supply of mobile devices have become the key factor for the acceleration of ubiquitous technology. WiBro system, formed with lP backbone network, is a MBWA technology which provides high-speed multimedia service in a possibly broader coverage than Wireless LAN can offer. Wireless telecommunication environment needs not only mobility support in Layer 2 but also mobility management protocol in Layer 3 and has to minimize handover latency to provide seamless mobile services. In this paper, we propose a fast cross-layer handover scheme based on signal strength prediction in WiBro environment. The signal strength is measured at regular intervals and future value of the strength is predicted by Exponential Smoothing Method. With the help of the prediction, layer-3 handover activities are able to occur prior to layer-2 handover, and therefore, total handover latency is reduced. Simulation results demonstrate that the proposed scheme predicts that future signal level accurately and reduces the total handover latency.

• Journal of Korean Institute of Industrial Engineers
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• v.41 no.2
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• pp.220-224
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• 2015

The DCF (Dcistributed Coordination Function) and PCF (Point Coordination Function) are the basic MAC (Medium Access Control) protocols of IEEE 802.11 wireless LANs. According to the DCF, each node performs the exponential backoff algorithm before the transmission of its data frame. Each node doubles the backoff waiting time before the transmission of its data frame whenever it detects the transmission collision with other nodes. Therefore, as the number of the active nodes having the data frames to transmit increases, the overall MAC performance of the DCF decreases. On the other hand, according to the PCF, each node is granted the transmission opportunity by which the PCF transmission is possible without the collision with other nodes. Therefore, as the number of the active nodes increases, the MAC performance of the PCF increases, In this paper, considering the tradeoff of MAC performance between the DCF and PCF, a hybrid MAC protocol is proposed to enhance the performance of IEEE 802.11 wireless LANs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1851-1859
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• 1998

We summarize the password-based authetication protocol K1P which was introduced in our easlier papers [1,2] and then propose three more extended protocols. These protocols preserve a design concept of K1P, i.e., security and efficiency, and canbe used for various purposes. They are a One-time key K1P, a Client public key K1P, and an Exponential key exchange K1P.