• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• 제3권2호
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• pp.30-38
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• 1992

In this paper, in order to apply the $\pi$/4 shift QPSK to TCM, we propose the $\pi$/8 shift 8PSK modulation technique and the trellis-coded $\pi$/8 shift 8PSK performing signal set expansion and set partition by phase difference. In addition, the Viterbi decoder with branch metrics of the squared Euclidean distance of the first phase difference as well as the Lth phase difference is introduced in order to improve the bit error rate(BER) performance in differential detection of the trellis-coded $\pi$/8 shift 8 PSK. The proposed Viterbi decoder is conceptually the same as the sliding multiple de- tection by using the branch metric with first and Lth order phase difference. We investigate the performance of the uncoded .pi. /4 shift QPSK and the trellis-coded $\pi$/8 shift 8PSK with or without the Lth phase difference metric in an additive white Gaussian noise (AWGN) and Rayleigh fading channel using the Monte Carlo simulation. The study shows that the $\pi$/4 shift QPSK with the Trellis-code i. e. the trellis-coded $\pi$/8 shift 8PSK is an attractive scheme for power and bandlimited systems and especially, the Viterbi decoder with first and Lth phase difference metrics improves BER performance. Also, the next proposed algorithm can be used in the TC $\pi$/8 shift 8PSK as well as TC MDPSK.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제31권4B호
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• pp.323-332
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• 2006

In this paper, we consider a WDM based metro ring connecting broadband access networks by using FT-TR (Fixed Transmitter-Tunable Receiver) type access nodes and a new MAC protocol for fair transmission is proposed. The basic channel access scheme is CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) and the transferred optical slot is changed to be empty slot by SS(Source-Stripping) which drops a packet from ring-rotated slot. This empty slot can be either used to send head-of-line packet in buffer or transmitted to next access node. In former cases, there is the improvement of network throughput, but latter case leads unfairness problem of transmission. Thus the proposed MAC protocol exploits the advantages form tow cases. It gives downstream access nodes chance to use empty slots and limits the unconditional usage of empty slots at upstream access nodes with probability as called p-Persistent MAC protocol. We use a numerical analysis to evaluate bandwidth efficiency and maximum node throughput and compares simulation results in terms of node throughput, fairness factor, transfer delay depending on probability. Under two different FT-TR type architectures for metro ring network the proposed MAC protocol is evaluated and compared.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• 제8권2호
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• pp.83-90
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• 2009

White LEDs(Light Emitting Diode) offer advantageous properties such as high brightness, improved reliability, lower power consumption, and long lifetimes. An LED is an electronic device that converts an electrical signal into a tight signal and is used not only in Optical Communication Indoor wireless optical illuminating rooms, but also for wireless optical communication systems. Currently, studies about these white LEDs have been being progressed, and in this raper, we discuss the multiplex and the multiple access method of VLC(Visible Light Communication) systems using white LEDs. In proposed system, CDMA(Code Division Multiple Access) apples to VLC system to reduce interference of VLC system, and improve capacity. The superiority of OOK modulation is presented in analysis of results by comparing VLC-CDMA communication system using OOK(On-off keying) modulation and BPSK modulation in AWGN(Additive White Gaussian Noise) channel and Diffuse channel. And we investigate the significance of a solution of interference by multipath by comparing BER in multipath channel and AWGN channel. In the proposed system, we assume Directed LOS(Line Of Sight) and Diffuse Link, and suppose VLC-CDMA using OOC(Optical Orthogonal Code) as methods to increase efficiency of system by removing ISI(Inter Symbol Interference) caused by multiple access, optical spreading code, and also present an analysis of its performance.

• Journal of IKEEE
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• 제24권3호
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• pp.859-866
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• 2020

This paper proposes a 2-ch DC-DC converter with a wide-input voltage range from 2.9V~5.6V for wearable AMOLED displays. For positive voltage V_POS, a boost converter is designed using an over-charged voltage permissible circuit (OPC) which generates a normal output voltage even if over-input voltage is applied, and a SPWM-PWM dual mode with 3-segmented power transistors to improve efficiency at light load. For negative voltage V_NEG, a 0.5x regulated inverting charge pump is designed to increase power efficiency. The proposed DC-DC converter was designed using a 0.18-㎛ BCDMOS process. Simulation results show that the proposed DC-DC converter generates V_POS voltages of 4.6 V and V_NEG voltage of -0.6V~-2.3V for input voltage of 2.9V to 5.6V. In addition, it has power efficiency of 49%~92%, output ripple voltage has less than 20 mV for load current range of 1 mA~70 mA.

• Journal of Energy Engineering
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• 제17권2호
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• pp.116-123
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• 2008

In order to study the heat transfer, effectiveness and pressure drop of an internal heat exchanger (IHX) for $CO_2$, heat pump under heating condition, the experiment and numerical analysis were performed. Four kinds of IHXs were used. The section-by-section method and Hardy-Cross method were used for the numerical analysis. The effects of IHX on the flow rate of refrigerant, the IHX length, the operating condition of a gas-cooler and an evaporator and the type of IHXs were investigated. With increasing the flow rate, the heat transfer rate increased about 25%. The heat transfer of the micro-channel tube was larger about 100% than that of the coaxial tube. With increasing the IHX length, the heat transfer rate decreased. The low-side pressure drop was larger compared with that of the high-side. And the pressure drop of the microchannel tube was larger about 100% than that of the coaxial tube. With increasing the high-side temperature and decreasing the low-side temperature, the heat transfer rate increased about 3%. From this study, we can see that new correlation on $CO_2$ heat transfer characteristics and tube type is necessary.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제21권8호
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• pp.1480-1485
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• 2017

A conventional max SNR scheme, which allocates uplink resources to the user with the highest gain of desired signal channel with a serving base station (BS), exhibits excellent performance in low interference environments. On the other hand, max SGIR scheme, which allocates resources by considering both the desired signal chanel gain and users' interference generating to neighboring BSs, outperforms the max SNR in high interference environments. The conventional two scheduling schemes exhibit optimal performance in different interference environments. Thus, we propose an adaptive scheduling scheme in order to overcome disadvantages of the conventional schemes. In the proposed scheme, a user is selected by max SNR and then the user's generating interference is compared with a pre-determined threshold value. If the generating interference is larger than a pre-determined threshold, then a user is re-selected by max SGIR policy. Monte-Carlo simulation results reveals that the proposed scheme outperforms the conventional schemes in various interference environments.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제18권5호
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• pp.1028-1033
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• 2014

We investigate the OFDM-based wireless LAN systems operating in the 60 GHz frequency band as part of the fourth-generation (4G) systems. The 60 GHz band is of much interest since this is the band in which a massive amount of spectral space has been allocated worldwide for dense wireless local communications. This paper gives an overview of 60 GHz band channel characteristics and an effect on phase noise. The performance of OFDM system is severely degraded by the local oscillator phase noise, which causes both common phase error and inter-carrier interference. In this paper, we apply phase noise suppression (PNS) algorithm that is easy for implementation to OFDM based 60 GHz wireless LAN system and analyze the SER performance. In case of using the PNS algorithm, SER performance is improved about 6 dB, 7.5 dB, respectively in 16, 64-QAM.

• Convergence Security Journal
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• 제12권1호
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• pp.35-42
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• 2012

Increase of data traffic and the advent of new real-time services require to change from the traditional TDM-based (Time Division Multiplexing) networks to the optical networks that soft and dynamic configuration. Voice and lease line services are main service area of the traditional TDM-based networks. This optical network became main infrastructure that offer many channel that can convey data, video, and voice. To provide high resilience against failures, Packet-optical networks must have an ability to maintain an acceptable level of service during network failures. Fast and resource optimized lightpath restoration strategies are urgent requirements for the near future Packet-optical networks with a Generalized Multi-Protocol Label Switching(GMPLS) control plane. The goal of this paper is to provide packet-optical network with a hierarchical multi-layer recovery in order to fast and coordinated restoration in packet-optical network/GMPLS, focusing on new implementation information. The proposed schemes do not need an extension of optical network signaling (routing) protocols for support.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제44권2호
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• pp.37-45
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• 2007

A lot of conventional algorithms has tried to cancel the Residual Frame Synchronization Error (RFSE), which causes the performance degradation of channel estimation when using interpolation in lattice-type pilot-aided Time Division Duplex (TDD) OFDM systems. Among them, a pre- and post-compensation method has been attractive to eliminate the effects of RFSE, providing good performance but requiring high computational complexity. In this paper we propose a new method which lowers computational costs by adjusting the starting point of TDD OFDM systems' FFT window in order to compensate for the RFSE. For the performance verification, we apply the proposed method to IEEE 802.16e standard and also estimate additionally required computational power of it compared to the pre- and post-compensation method. Simulation and implementation results show that the proposed algorithm has performance similar to the conventional method and is very efficient with low power implementation, requiring only 4.9 % of the power which the conventional method needs additionally.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제45권11호
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• pp.1-8
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• 2008

In this paper, we analyze the symbol error rate (SER) performance of maximum likelihood (ML) joint detection in downlink multiple-input multiple-output (MIMO) multicarrier code division multiple access (MC-CDMA) systems by deriving a tight union bound on the symbol error rate (SER). The union bound for ML joint detection is utilized to demonstrate the performance of MIMO MC-CDMA systems quantitatively in multiuser and frequency selective Rayleigh fading environments. An analysis of the diversity order of the systems shows the effects of multiple users, spread subcarriers, and multiple antennas on the ML joint detection performance. Furthermore, the analysis shows that MIMO MC-CDMA systems without full loading can achieve more diversify than MIMO orthogonal frequency division multiplexing (OFDM) systems.