• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.228-231
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• 2006

Mobile ad hoc 환경에서의 TDMA(time division multiple access)는 contention 없이 node 간에 충돌(collision) 없는 전송을 제공하며 동일 주파수대를 시간으로 분할하여 신호가 겹치지 않도록 상호통신을 하는 시분할다중접속 방식이다. TDMA는 충돌 없이 전송할 수 있다는 이점 때문에 Mobile 환경에서 많이 응용하여 사용되어 지고 있다. 하지만 할당 되어진 time slot을 사용하지 않을 경우 대역폭의 낭비가 발생할 수 있다는 문제 점도 가지고 있다. 본 논문에서는 사용하지 않는 time slot의 재사용을 통해서 성능을 향상시키는 방법을 제안하고 그 것을 Mobile ad hoc 환경에 적용하는 방법에 대해 연구한다.

• Current Optics and Photonics
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• v.4 no.3
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• pp.186-192
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• 2020

This paper describes a real-time monitoring system in Ethernet passive optical networks (EPON) that uses burst-mode fiber Bragg grating (FBG) optical sensors. The FBG interrogation unit in the optical line terminal (OLT) transmits the monitoring wavelength to optical network units (ONUs). The FBG sensor unit in each ONU returns a burst-mode monitoring signal to the OLT. As the system applies time division multiple access (TDMA), a uniform Bragg wavelength can be used to monitor the EPON system. The FBG interrogation unit analyzes the received burst-mode monitoring signals and outputs fault information on the ONU branches in EPON. The simulation results show the effectiveness of the proposed monitoring system based on TDMA. In addition, we compared the proposed TDMA-based monitoring system with a WDMA-based monitoring system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.952-958
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• 1994

In this paper a method calculates the time offset between a binary sequence and its shifted sequence based on the number theoretic approach is presented. Using this method the time offset between a binary sequence and its shifted sequence can be calculated. It has been recongnized that the defining the reference (zero-offset) sequence is important in synchronous code division multiple access(CDMA) system since the same spreading sequence are used by the all base station. The time offset of the sequence with respect to the zero offset sequence are used to distinguish signal received at a mobile station from different base stations. This paper also discusses a method that defines the reference sequence.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.323-335
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• 2015

Mobile healthcare is a fusion of information technology and biotechnology and is a new type of health management service to keep people's health at anytime and anywhere without regard to time and space. The WBAN(Wireless Body Area Network) technology that collects bio signals and the data analysis and monitoring technology using mobile devices are essential for serving mobile healthcare. WBAN consisting of users with mobile devices meet another WBAN during movement, WBANs transmit data to the other media. Because of WBAN conflict, several nodes transmit data in same time slot so a collision will occur, resulting in the data transmission being failed and need more energy for re-transmission. In this thesis, we proposed a MAC protocol for WBAN with mobility to solve these problems. First, we proposed a superframe structure for WBAN. The proposed superframe consists of a TDMA(Time Division Muliple Access) based contention access phase with which a node can transmit data in its own time slot and a contention phase using CSMA/CA algorithm. Second, we proposed a network merging algorithm for conflicting WBAN based on the proposed MAC protocol. When a WBAN with mobility conflicts with other WBAN, data frame collision is reduced through network reestablishment. Simulations are performed using a Castalia based on the OMNeT++ network simulation framework to estimate the performance of the proposed superframe and algorithms. We estimated the performance of WBAN based on the proposed MAC protocol by comparing the performance of the WBAN based on IEEE 802.15.6. Performance evaluation results show that the packet transmission success rate and energy efficiency are improved by reducing the probability of collision using the proposed MAC protocol.

• Journal of Advanced Navigation Technology
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• v.15 no.5
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• pp.764-773
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• 2011

IEEE 802.15.4 is a standard for LWPAN based on TDMA. IEEE 802.15.4 has not been used widely because of restrictions on the QoS, scalability, and reliability. IEEE 802.15.4 utilizes GTS for one-hop QoS transmission. However GTS is not an effective method to satisfy QoS in multi-hop environments. Currently IEEE 802.15.4e, an extended version of IEEE 802.15.4 MAC sub-layer, is being developed to satisfy more diverse performance requirements than IEEE 802.15.4. IEEE 802.15.4e provides muti-hop QoS transmission functionality and uses multiple frequency channels. In this paper, a multi-channel TDMA scheduling scheme is proposed to satisfy end-to-end transmission delay in IEEE 802.15.4e. The performance of the proposed scheme is evaluated using simulation.

• ETRI Journal
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• v.40 no.4
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• pp.537-545
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• 2018

In this paper, we present a comprehensive analytical study of the symbol error rate (SER) of single-carrier frequency-division multiple access (SC-FDMA) with zero-forcing frequency domain equalization (ZF-FDE) over a Rayleigh fading channel. SC-FDMA is considered as a potential waveform candidate for fifth-generation (5G) radio access networks (RANs). First, the $N_C$ fold convolution of the noise distribution of an orthogonal frequency-division multiplexing (OFDM) system is computed for each value of the signal-to-noise ratio (SNR) in order to determine the noise distribution of the SC-FDMA system. $N_C$ is the number of subcarriers assigned to a user or the size of the discrete Fourier transform (DFT) precoding. Here, we present a simple alternative method of calculating the SER by simplifying the $N_C$ fold convolution using time and amplitude scaling properties. The effects of the $N_C$ fold convolution and SNR over the computation of the SER of the SC-FDMA system has been separated out. As a result, the proposed approach only requires the computation of the $N_C$ fold convolution once, and it is used for different values of SNR to calculate the SER of SC-FDMA systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.1
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• pp.168-186
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• 2016

In this paper, we investigate the degrees of freedom (DoF) of a two-cluster multiple-input multiple-output (MIMO) multiway relay interference channel (mRIC), where there are two relays and two users per cluster. In this channel, users within the same cluster exchange messages among themselves with the help of two relays.We first obtain the DoF upper bound of the considered MIMO mRIC based on cut-set bound. Then, we propose a novel transmission strategy, blind interference neutralization (BIN), to approach the DoF upper bound. This new method utilizes the overheard information at two relays and focuses on the beamforming matrix designs at two relays so that the channel state information (CSI) at users is not required. Through theoretical analysis and numerical simulations, we show that the DoF upper bound can be obtained by using the BIN scheme. From simulation results, we show that the proposed BIN scheme can provide significant performance gain over the conventional time division multiple access (TDMA) scheme in terms of DoF. In addition, we show that the BIN scheme is a superior approach to the existing signal space alignment (SSA) schemes for the considered mRIC.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.29-32
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• 2000

In this paper, we present an extension of the multi-code CDMA (code division multiple access) systems based on bi-orthogonal modulation by employing a convolutional encoder and an interleaver before serial-to-parallel conversion in the modulator. Bandwidth expansion by the convolutional encoder can be compensated for by the bi-orthogonal modulation, and the interleaver in the system scrambles the convolutionally encoded data bits so that, after serial-to-parallel conversion, each code channel conveys those bits far apart in time. The result is that the proposed system with several order of magnitude less implementational complexity, achieves quite close performance of the conventional systems comprised of Walsh modulation and multiple convolutional encoders and interleavers in all the code channels.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06d
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• pp.445-446
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• 2012

본 논문에서는 MF-TDMA(Multiple Frequency - Time Division Multiple Access) 방식을 이용하는 위성 시스템의 위성 자원 효율을 높이기 위한 동적 MF-TDMA 프레이밍 기법을 제안한다. DVB-RCS (Digital Video Broadcasting - Return Channel via Satellite)은 감우감쇠를 극복하기 위해 ACM (Adaptive Coding and Modulation) 기법을 사용한다. MF-TDMA에서는 하나의 채널이 동일한 ACM 모드를 지원하기 때문에 사용자의 채널 상태와 요청량을 고려하여 실제로 요구되는 ACM 모드를 지원하는 채널의 수를 계산한다. 모의실험을 통해 채널 상태 변화를 고려하지 않은 정적인 방식에 비해 제안하는 동적인 방식의 위성 자원 효율이 증가한 것을 확인할 수 있었다.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.1310-1312
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• 2007

Throughput improvement problem in wireless mesh network can be alleviated by equipped mesh router with multiple radios tuned into orthogonal channels. However, some links on the same channel also can be activated concurrently if the Signal-to-Noise and Interference Ratio (SNIR) at their receiver endpoints is not lower than the threshold. We propose a greedy algorithm to investigate the problem of how to schedule a set of feasible transmission under physical interference model by using the spatial time-division multiple-access (STDMA) scheme. We also consider the fairness in scheduling to prevent some border nodes from starvation. We evaluate our algorithms through extensive simulation and the results show that our algorithms can achieve better aggregate throughput and fairness performance than 802.11 standard.