• Journal of Communications and Networks
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• 제7권4호
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• pp.462-470
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• 2005

We propose a multi-rate and multi-BEP transmission scheme using adaptive overlapping pulse-position modulator (OPPM) and optical power controller in optical code division multiple access (CDMA) networks. The proposed system achieves the multi-rate and multi-BEP transmission by accommodating users with different values of OPPM parameter and transmitted power in the same network. The proposed scheme has advantages that the system is not required to change the code length and number of weight depending on the required bit rate of a user and the difference of bit rates does not have so much effect on the bit error probabilities (BEPs). Moreover, the difference of transmitted powers does not cause the change of bit rate. We analyze the BEPs of the four multimedia service classes corresponding to the com­binations of high/low-rates and low/high-BEPs and show that the proposed scheme can easily achieve distinct differentiation of the service classes with the simple system configuration.

• Journal of Communications and Networks
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• 제6권2호
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• pp.123-132
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• 2004

The various challenges to realize a fixed wireless ATM network are discussed and some solutions for these challenges are presented. In this paper, the capacity allocation in wireless ATM, the wireless link impact on ATM traffic, and the optimum utilization of the wireless network resonrces for a line of sight (LOS) winless ATM link are studied. An adaptive MQAM modulator is introduced to provide a suitable solution to these issues. The modulator level is adjusted using a unique QoS metric in a wireless network. The metric, termed modified effective bandwidth, takes into account the bandwidth demand, QoS requirements, and outage conditions of the wireless ATM link. A performance study using VBR MPEG-l video traffic in a fixed wireless channel (Ricean channel) demonstrates the advantages of the proposed system.

• International journal of advanced smart convergence
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• 제8권3호
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• pp.61-68
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• 2019

Spatial modulation (SM) is the first proposed space modulation technique. By further utilizing the quadrature spatial dimension, quadrature spatial modulation (QSM) has been developed as an amendment to SM system to enhance the overall spectral efficiency. Both techniques are capable of entirely eliminating interchannel interference (ICI) at the receiver. In this paper, we propose a simple adaptive hybrid switching transmission scheme to obtain better system performance than SM and QSM systems under a fixed transmission date rate. The presented modulator selection criterion for switching between spatial modulator and quadrature spatial modulator is based on the larger received minimum distance of spatial modulator and quadrature spatial modulator to exploit the spatial channel freedom. It is shown through Monte Carlo simulations that the proposed hybrid SM and QSM switching system yields lower error performance than the conventional SM and QSM systems under the same fixed data rate and thus can provide signal to noise ratio (SNR) gain.

• 대한전자공학회논문지SD
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• 제44권11호
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• pp.1-8
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• 2007

본 논문에서는, 무선 통신 응용을 위한 광대역 연속시간 시그마-델타 모듈레이터를 130nm CMOS공정으로 구현하였다. 제안된 양자화 레벨을 효율적으로 조절할 수 있는 적응성 양자화기를 사용하여, 작은 크기의 입력에 대해서 SNR의 이득을 볼 수 있었다. 모듈레이터는 전력 소모를 줄이기 위해 2차 루프 필터로 구성되어 있고, 지터에 의한 영향을 줄이고 높은 선형성을 보장하기 위해 4 비트 양자화기, DAC를 사용하였다. 설계된 회로는 320MHz 샘플링 주파수에서 동작하며 10MHz 입력 대역에서 30mW의 전력을 소모하고 최대 SNR 51.36dB를 얻었다.

• 한국정보통신학회논문지
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• 제11권8호
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• pp.1558-1563
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• 2007

논문은 fractional-N 방식의 주파수 합성기(PLL)를 낮은 차수의 ${\Delta}{\Sigma}$변조기로 더욱 높은 성능의 PLL로 설계하기 위하여 대역폭 가변 방식의 PLL과 ${\Delta}{\Sigma}$방식의 fractional-N PLL의 구조를 합성한 새로운 방식의 PLL을 제안한다. Matla으로 대역폭 가변을 이용한 ${\Delta}{\Sigma}$방식의 fractional-N PLL의 시뮬레이션을 수행하여 제안된 구조의 특성을 관찰하였다. 본 논문의 대역폭 가변 PLL은 HSPICE 0.35um CMOS 공정을 이용하여 시뮬레이션 하였고, 그 결과 제안된 PLL은 빠른 록이 가능하고 fractional spur를 20dB 정도 낮출 수 있었다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권2호
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• pp.140-148
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• 2000

In this paper, using surface micromachining technology with thick photoresist and aluminum, an SLM(Spatial Light Modulator), which is applied to the fields of adaptive optics and pattern recognition system, was fabricated and the electromechanical properties of the fabricated micro SLM are measured. In order to maximize fill-factor and remove mechanical coupling between micro SLM actuators, the micro SLM is composed of three aluminum layers so that spring structure and upper electrode are placed beneath the mirror plate, and $10\times10$ each mirror plate is individually actuated. Also, the micro SLM was designed to be able to modulate phase and amplitude of incoming light in order to have a continuity of phase modulation of incoming light. In the case of amplitude and phase modulation, maximum vertical displacement is 4$\mum$, and maximum angular displacement is $\pm4.6^{\corc}$ respectively. The height difference of the fabricated mirror plate was able to be reduced to 1100A with mirror plate planarization method using negative photoresist(AZ5214). The electromechanical properties of the fabricated micro SLM were measured with the optical measurement system using He-Ne laser and PSD(position sensitive device).

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 B
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• pp.715-717
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• 1999

본 논문에서는 feedforward 선형 증폭기에서의 지연 불일치에 의한 효과를 최소화하기 위한 등화기의 차수 결정에 관하여 수학적 접근과 모의실험을 하였다. 현재 feedforward 선형 증폭기에서 주로 사용하는 vector modulator는 지연 불일치에 확실한 개선을 이루지 못하고 있다. 이것을 극복하고자 vector modulator를 등화기로 대체하고 증폭기와 시지연선의 최대시간불일치와 sampling frequency와의 관계로 등화기의 차수를 결정하여 지연 불일치에 의한 오류 제거능력을 향상시켰다.

• 한국자동차공학회논문집
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• 제9권4호
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• pp.157-165
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• 2001

In the brake systems, it is important to reduce the rear brake pressure in order to secure the safety of the vehicle in braking. So, there was some research that reduced and controlled the rear brake pressure exactly like a LSPV and a ELSPV. However, the previous research has some weaknesses: the LSPV is a mechanical system and its brake efficiency is lower than the efficiency of ELSPV, But, the cost of ELSPV is very higher so its application to the vehicle is very difficult. Additionally, when a fail appears in the circuit which controls the valves, the fail results in some wrong operation of the valves. But, the previous researchers didn't take the effect of fail into account. Hence, the efficiency of them is low and the safety of the vehicle is not confirmed. So, in this paper we develop a new economical pressure modulator that exactly controls brake pressure and confirms the safety of the vehicle in any case using a direct adaptive fuzzy controller.

• 대한전기학회논문지
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• 제36권4호
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• pp.259-266
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• 1987

In order to drive motor control system precisely, the motor is to be controlled by mmfs and current with sinusoidal waveforms. In this paper the Delta Modulation (DM) Technique is used for generating PWM pulse with sinusoidal waveform. However the motor currents yet contain odd harmonics due to leakage inductances, speed and exitation. To reduce harmonics, the parameter adaptive control method is introduced. That is, Req.C parameter of Delta Modulator is controlled adaptively by parameter adaptor. The adaptive signal is achieved by the difference between motor current and reference waveform, and this signal is converted to the voltage commend signal by adaptive mechanism. The test reslts show that this system is operated smoothly over a wide range of motor speed and motor current is controlled to be sinusoidal waveform adaptively.

• 전자공학회논문지A
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• 제31A권12호
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• pp.9-15
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• 1994

In this paper, the linearized power amplifier using digital adaptive predistorter is implemented in order to restrict spectral spreading and adjacent channel interference. The linearized systems is composed of a DSP56001 processor that executes predistortion in baseband. 90.deg. phase shifter, power splitter/combiner, quadrature modulator/demodulator of 360MHz band, and nonlinear amplifier. A ${\pi}$/4-shift QPSK is used to modulate digital random signals. As the quantized power of baseband signal and the output of amplifier are fed to the predistorter, and predistorting values are calculated using an adaptive algorithm. In the experiment, a peak to sidelobe ratio of the linearized amplifier is improved up to 15dB in comparison with conventional nonlinear amplifier, which means that the distortion of transmitted signal is decreased and adjacent channel interference was reduced.