• Journal of information and communication convergence engineering
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• v.13 no.3
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• pp.167-171
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• 2015

A radio over fiber (RoF) system is a kind of analog optical transmission system and considered as a strong candidate for the next-generation fronthaul link in the future mobile network. In RoF systems, nonlinearity compensation is essential to increase the link capacity. In this paper, we propose a nonlinearity detection and compensation scheme using a monitoring channel in RoF systems. A monitoring channel is added at the transmitter site and used for transmitting a reference signal in an RoF transmission. The nonlinearity in the RoF transmission is detected by comparing the received monitoring signal and the original reference signal at the receiver site. Finally, the nonlinearity is compensated at the receiver by giving the reverse function of the detected nonlinearity. Our results show that the proposed scheme can almost remove the error vector magnitude degradation induced by the nonlinearity in the RoF system.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.2
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• pp.238-245
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• 2003

To overcome the weakness in the load capacity of conventional robot manipulators actuated by motors with the speed reducer such as the harmonic driver, we proposed a new closed-chain type of the robot actuator which is composed of the four-bar-link mechanism driven by the ball screw. The robot manipulator is revolute-jointed and composed of four axes. The base axis is actuated by the lineal actuator such as the ball screw, and the others are actuated by the proposed actuator. We analyzed the mechanism of the actuators of the robot joints, and developed the dynamics model. The dynamics are expressed in the joint coordinates and then they are mapped into the sliding coordinates of the ball screw. We performed fundamental tests on the structure of the robot.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10b
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• pp.599-606
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• 1992

A manipulator system that needs significantly large workspace volume and high payload capacity has greater link flexibility than typical industrial robots and teleoperators. If link flexibility is significant, position control of the manipulator's end-effector exhibits the nonminimum phase, noncollocated, and flexible structure system control problems. This paper addresses inverse dynamic trajectory planning issues of a flexible manipulator. The inverse dynamic equation of a flexible manipulator was solved in the time domain. By dividing the inverse system equation into the causal part and the anticausal part, the inverse dynamic method calculates the feedforward torque and the trajectories of all state variables that do not excite structural vibrations for a given end-point trajectory. Through simulation and experiment with a single-Unk flexible manipulator, the effectiveness of the inverse dynamic method has been demonstrated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.67-68
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• 2006

In this paper, a new revolute cooperating robot arms with 12 d.o.f was developed for autonomous moving robots. The robot ann was designed to have the load capacity of 10 Kg. For this, a new joint actuator based on the fourbar link mechanism was employed. As a control system for the robot arm, a distributed control system was developed composed of the main controller and five motor controller for the ann joints. The main controller and the motor controller were developed using the ARM microprocessor and the TMS320c2407 processor, respectively. To validate the performance of the robot system, an experiment to support 10 Kg payload was performed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.540-543
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• 2002

Conventional robot manipulators actuated by motors with the speed reducer such as the harmonic drive have weakness in the load capacity, since the speed reducer does not have enough strength. To overcome this, we proposed and constructed a new type of the robot actuator which is four-bar-link mechanism driven by the ball screw. We developed a new type of a revolute-jointed robot manipulator composed of four axes. The base axis is actuated with conventional speed reducer, but the others are actuated by the proposed actuators. We analyzed the mechanism of the actuators of the robot joints, and developed the dynamics model. The dynamics are expressed in the joint coordinates, and then they are mapped into the sliding coordinates of the ball screw. The structure specifications of the manipulator shown.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.464-472
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• 2009

In this paper, we propose a packet scheduling algorithm for cellular relay networks by considering relay selection, variation of channel quality, and packet delay. In the networks, mobile users are equipped with not only cellular but also user relaying radio interfaces, where base station exploits adaptive high speed downlink channel. Our proposed algorithm selects a user with good cellular channel condition as a relay station for other users with bad cellular channel condition but can get access to relay link with good quality. This can achieve flexible packet scheduling by adjusting transmission rates of cellular link. Packets are scheduled for transmission depending on scheduling indexes which are calculated based on user's achieved transmission rate, packet utility, and proportional fairness of their throughput. The performance results obtained by using computer simulation show that the proposed scheduling algorithm is able to achieve high network capacity, low packet loss, and good fairness in terms of received throughput of mobile users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.39-41
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• 2017

In this letter, we propose a power control mechanism in order to improve secrecy rate defined as the difference between capacity of main link and wiretap link in a wireless multi-cell multiuser network. Through simulations, we verify that the proposed power control mechanism with threshold based user scheduling can significantly increase secrecy rate in a multi-cell environment.

• ETRI Journal
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• v.19 no.3
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• pp.116-140
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• 1997

The base station transceiver subsystem (BTS) of the CDMA Mobile System is interfaced to mobile stations over the air and to the wired network through a packet switched interconnection network. The potential benefits of CDMA technology are achieved when the transmitter and the receiver are properly designed and implemented. The physical layer of the interface at the base station is implemented with the CDMA ASICs and control circuits in channel card of the BTS. We present the design perspectives and structural illustration of the BTS. Base station modem ASICs and their control to implement the CDMA receiver, Baseband and RF signal processing blocks, and BTS controller are described. Elaborate power control is essential to ensure the high capacity which is one of advantages of the CDMA technology. The closed loop reverse link power control and the forward link power control operated in the BTS are described.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1956-1959
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• 2002

Power control (PC) on the reverse link of CDMA cellular system is important to increase system capacity. PC eliminates fluctuations in the received signal level and hence reduces the required signal-to-interference ratio. However, both perfect PC and imperfect PC depend on number of interferences as number of users, which by using smart antenna system can decrease number of interferences in any directions except interferences from the main beam direction. In this paper , number of elements in smart antenna system, which directly relates to the main beam pattern, is studied to find the effects on the outage probability , bit energy-to-interference density ratio (Eb/Io) and the capacities of both perfect and imperfect PC.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1960-1963
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• 2002

Transmit diversity schemes we an effective capacity improvement method for down link of wideband code division multiple access (W-CDMA) systems. In this paper, we propose to use transmit antenna subset selection scheme in conjunction with closed loop transmit adaptive array (TxAA). The proposed scheme selects N$\_$s/ optimum antennas among N$\_$${\gamma}$/(>N$\_$s/) transmit antennas in order to maximize diversity gain from selected antennas, and also reduces the cost of RE chains by employing two different types of RF modules fur the selected and the unselected antenna group, respectively. Computer simulation results show performance improvement by the proposed scheme over the conventional TxAA when considering up link control information feedback.