• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.778-798
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• 2014

This paper proposes a novel exposed-terminal-eliminated medium access control (ETE-MAC) protocol by combining channel reservation, collision avoidance and concurrent transmissions to improve multi-access performance of the multihop wireless networks. Based on the proposed slot scheduling scheme, each node senses the control channel (CCH) or the data channel (DCH) to accurately determine whether it can send or receive the corresponding packets without collisions. Slot reservation on the CCH can be simultaneously executed with data packet transmissions on the DCH. Therefore, it resolves the hidden-terminal type and the exposed-terminal type problems efficiently, and obtains more spatial reuse of channel resources. Concurrent packet transmissions without extra network overheads are maximized. An analytical model combining Markov model and M/G/1 queuing theory is proposed to analyze its performance. The performance comparison between analysis and simulation shows that the analytical model is highly accurate. Finally, simulation results show that, the proposed protocol obviously outperforms the link-directionality-based dual-channel MAC protocol (DCP) and WiFlex in terms of the network throughput and the average packet delay.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제42권2호
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• pp.23-38
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• 2005

The state of channel between two or more wireless terminals is changed frequently due to noise or multiple environmental conditions in wireless network. In this paper, we analyze packet transmission time and queue length in a time-varying channel of packet based Wireless Networks. To reflect the feature of the time-varying channel, we model the channel as two-state Markov model and three-state Markov model Which are transformed to SFG(Signal Flow Graph) model, and then the distribution of the packet transmission can be modeled as Gaussian distribution. If the packet is arrived with Poisson distribution, then the packet transmission system is modeled as M/G/1. The average transmission time and the average queue length are analyzed in the time-varying channel, and are verified with some simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4240-4258
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• 2016

A practical iterative channel estimation technique is proposed for the multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system in the high-speed mobile environment, such as high speed railway scenario. In the iterative algorithm, the Kalman filter and data detection are jointed to estimate the time-varying channel, where the detection error is considered as part of the noise in the Kalman recursion in each iteration to reduce the effect of the detection error propagation. Moreover, the employed Kalman filter is from the canonical state space model, which does not include the parameters of the autoregressive (AR) model, so the proposed method does not need to estimate the parameters of AR model, whose accuracy affects the convergence speed. Simulation results show that the proposed method is robust to the fast time-varying channel, and it can obtain more gains compared with the available methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제27권11C호
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• pp.1158-1163
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• 2002

In this paper it is focused on the relation between CLR (Cell Loss Ratio) and blocking probability, GoS(Grade of Services) parameters in the wireless ATM (Asynchronous Transfer Mode) access network which consists of access node and wireless channel. Traffic model of wireless ATM access network is based on the cell scale, burst scale and call connection level. The CLR equation due to buffer overflow for wireless access node is derived for CBR (Constant Bit Rate) traffic. The CLR equation due to random bit errors and burst errors for wireless channel is derived. Using the CLR equation for both access node and wireless channel, the CLR equation of wireless ATM access network is derived. The relation between access network CLR and blocking probability is analyzed for CBR traffic.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 한국전산구조공학회 2011년도 정기 학술대회
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• pp.36-39
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• 2011

In this paper, performance of EMI interface and multi-channel wireless impedance sensor node is evaluated for SHM on bolted connection. To achieve the objective, following approaches are implemented. Firstly, an interface washer is designed to monitor loosened bolt through the variation in EMI of interface washer due to change in preload in bolt. Secondly, a multi-channel wireless impedance sensor node based on Imote2 platform is designed for automated and cost-efficient impedance-based SHM on bolted connections. Finally, performance of the multi-channel wireless impedance sensor node and the interface washer are experimentally validated for a lab-scale bolted connection model. A damage monitoring method using RMSD index of EMI signatures is utilized to examine the strength of each individual bolted connection.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제22권9호
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• pp.1843-1853
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• 1997

The channel throughput and packet delay of wireless media control (MAC) protocols with Rayleigh fading, log-normal shoadowing and near-far effects are analyzed. We consider CSMA/CA protocols as the wireless MAC protocols, since CSMA/CA protocols are based on the standard for wireless Local Area Networks (LANs) IEEE 802. 11. We have found that the performance of CSMA/CA in radion channel model is reduced above 50% than those of error free channel model in low traffic load. We also found that 4-Way Handshake CSMA/CA protocol is supterior to the other CSMA/CA protocols in high traffic load.

• International Journal of Contents
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• 제4권3호
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• pp.20-28
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• 2008

To obtain realistic performance measures for wireless networks, one should consider changes in performance due to failure related behavior. In performability analysis, simultaneous consideration is given to both pure performance and performance with failure measures. SRN is an extension of stochastic Petri nets and provides compact modeling facilities for system analysis. In this paper, a new methodology to model and analyze performability based on stochastic reward nets (SRN) is presented. Composite performance and availability SRN models for wireless handoff schemes are developed and then these models are decomposed hierarchically. The SRN models can yield measures of interest such as blocking and dropping probabilities. These measures are expressed in terms of the expected values of reward rate functions for SRNs. Numerical results show the accuracy of the hierarchical model. The key contribution of this paper constitutes the Petri nets modeling techniques instead of complicate numerical analysis of Markov chains and easy way of performance analysis for channel allocation under SRN reward concepts.

• Journal of Satellite, Information and Communications
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• 제10권1호
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• pp.17-21
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• 2015

In this paper, we introduce satellite communication for new wireless disaster network to be built on the basis of amateur radio HR (HAM Radio) as a wireless package system, and channel environments of a D2D terminal that tries to connect and communicate with the wireless disaster network. In this disaster network, we propose a LOS component ratio based adaptive channel modeling approach to accurately estimate a variety of channels whose the D2D terminal could have and smoothly transfer to the level of multimedia data based on the Okumura-Hata channel model. As a result of computer simulation, performance of the proposed method was compared with the that of Okumura-Hata model of open area and urban area model and we were confirmed that there is a gain of BER performance from the results of the computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제28권8B호
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• pp.674-682
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• 2003

This paper presents the studies on wireless channel modeling and reverse link synchronization of CATV. This paper analyzes multi-path fading channel to the cause of signal distortion in the wireless communication environment. We represent the microwave link characteristics according to the channel model. Multi-path channel can affect fading.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권6호
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• pp.2893-2907
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• 2019

Wireless mobile communication systems in subway tunnels have been widely researched these years, due to increased demand for the communication applications. As a result, an accurate model is essential to effectively evaluate the communication system performance. Thus, a neoteric three-dimensional (3D) geometry-based stochastic model (GBSM) is proposed for the massive multiple-input multiple-output (MIMO) fading channels in tunnel environment. Furthermore, the statistical properties of the channel such as space-time correlation, amplitude and phase probability density are analyzed and compared with those of the traditional two-dimensional (2D) model by numerical simulations. Finally, the ergodic capacity is investigated based on the proposed model. Numerical results show that the proposed model can describe the channel in tunnels more practically.