• Journal of IKEEE
• /
• v.23 no.1
• /
• pp.91-98
• /
• 2019

LTE's extension for unlicensed spectrum called Licensed Assisted Access (LAA) is equipped with Listen-Before-Talk (LBT) designed similar with the backoff mechanism of Wi-Fi for coexistence. However, Wi-Fi's backoff mechanism has not evolved from its old design for compatibility with legacy devices, thus LAA's LBT is not efficient either in utilizing spectrum. If LAA operates with no Wi-Fi systems in proximity, it can run more efficient LBT. In this paper, we propose Narrowband Clear Channel Assessment (NCCA) for narrowband transmission. In NCCA, an LAA node performs LBT in either wide or each narrow bandwidth segment. This allows multiple LAA nodes to perform simultaneous transmissions in orthogonal bandwidth segments in the same time slot. We design four variants of NCCA implementation and model their performance using a mathematical model. The coexistence performance of NCCA with conventional wideband nodes and the accuracy of the model are shown via simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.40 no.11
• /
• pp.10-16
• /
• 2003

In this paper, a dynamic contention periods based on the collision group(DCCG) algorithm is proposed for collision resolution in the IEEE 802.16 broadband wireless access network. The DCCG algorithm determines the contention periods according to the a number of collided slot and collided requests to the base station(BS). The DCCG algorithm is useful to improve the performance of throughput and system delay characteristic than binary backoff algorithm.

• Proceedings of the IEEK Conference
• /
• 2005.11a
• /
• pp.7-10
• /
• 2005

Ad hoc MAC protocols using directional antennas can be used to improve the network capacity. Directional antennas have a Deafness problem and decrease throughput of the network caused by increasing backoff duration. Dual channel protocols have been proposed to mitigate the Deafness and hidden node problems. In this paper, we propose a dual channel MAC protocol using a directional antenna to mitigate the Deafness problem and increase the network capacity. The performance of the proposed Ad hoc MAC protocol is confirmed by computer simulations using Qualnet ver. 3.8 simulator.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.9 no.6
• /
• pp.353-360
• /
• 2014

In cognitive radio networks (CRNs), SU (secondary user)'s transmissions are frequently disrupted by PU (primary user)'s transmission. Therefore SU expereiences consecutive retransmission timeout and its exponential backoff, and subsequently, the TCP of SU does not proceed with the transmission even after the disruption is over or the SU succeeds to hold an idle channel. In order to solve this problem, we propose a cross-layer approach called TCP-Freeze-CR. Moreover we consider a practical scenario where either secondary transmitter (ST) or secondary receiver (SR) detects PU's transmission, which results in the need of spectrum synchronization mechanism. All of our proposals are implemented and verified with a real CRN testbed consisting of 6 software radios called USRP. The experimental results illustrate that standard TCP suffers from significant performance degradation and show that TCP-Freeze-CR greatly mitigates the degradation.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.7 no.5
• /
• pp.1108-1130
• /
• 2013

Wireless Body Area Networks (WBANs) are becoming increasingly important to solve the issue of health care. IEEE 802.15.6 is a wireless communication standard for WBANs, aiming to provide a real-time and continuous monitoring. In this paper, we present our development of a modified Markov Chain model and a backoff model, in which most features such as user priorities, contention windows, modulation and coding schemes (MCSs), and frozen states are taken into account. Then we calculate the normalized throughput and average access delay of IEEE 802.15.6 networks under saturation and ideal channel conditions. We make an evaluation of network performances by comparing with IEEE 802.15.4 and the results validate that IEEE 802.15.6 networks can provide high quality of service (QoS) for nodes with high priorities.

• Proceedings of the Korea Society of Information Technology Applications Conference
• /
• 2005.11a
• /
• pp.179-182
• /
• 2005

The Home Phoneline Networking Alliance (HomePNA) 2.0 technology can establish a home network using existing in-home phone lines, which provides a channel rate of 4 - 32 Mbps. HomePNA 2.0 Medium Access Control (MAC) protocol adopts an IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method, a Quality of Service (QoS) algorithm, and a Distributed Fair Priority Queuing (DFPQ) collision resolution algorithm. In this paper, we analyze the HomePNA 2.0 MAC protocol and propose the architecture of HomePNA 2.0 MAC controller circuit. Then, we present the simulation result of each block included in the HomePNA 2.0 MAC controller.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 2007.11a
• /
• pp.330-340
• /
• 2007

IEEE 802.11 wireless LANs employ the backoff algorithm to avoid contentions among STAs when two or more STAs attempt to transmit their data frames simultaneously. The MAC efficiency can be improved if the CW values are adaptively changed according to the channel state of IEEE 802.11 wireless LANs. In this paper, we propose a dynamic contention window control algorithm using the genetic algorithm to improve the MAC throughput of IEEE 802.11 wireless LANs.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.34 no.3
• /
• pp.137-153
• /
• 2009

In this paper, we present an analytic model that evaluates the performance of B-MAC protocol under contention transmission conditions of two senders in a single-hop wireless sensor network. Our model considers the impact of several important factors such as sleep cycle, the backoff mechanism and incoming traffic loads. After obtaining the service delay distribution of a sending node and expected delay of a receiving node, an iterative algorithm is presented for calculating the performance measures such as expected energy consumption usage per packet and latency. Simulation results show that the proposed analytic model can accurately estimate the performance measures under different traffic conditions.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 2005.10a
• /
• pp.365-368
• /
• 2005

이동중인 단말에게 인터넷 서비스를 제공하고자 하는 WiBro 시스템은, 무선자원의 효율적인 사용을 위해서 전송할 데이터가 있는 단말들에게만 대역폭을 할당하는 demand-based 대역폭 할당 방식을 사용한다. 이때 여러 단말들이 동시에 데이터를 전송하고자할 경우 충돌이 발생하므로 이들의 전송순서를 정해주는 것이 필요하다. 기존의 WiBro 시스템에서는 binary exponential backoff algorithm 에 기초한 random access 기법을 사용하는데, 본 연구에서는 conflict resolution 기법에 기초한 새로운 random access 기법을 제안하고, 새로운 기법의 성능이 보다 우수함을 시뮬레이션을 통해 보였다.

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