• Journal of information and communication convergence engineering
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• 제4권4호
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• pp.162-165
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• 2006

This paper presents a bandwidth efficient self-cancellation scheme for interchannel interference (ICI) in OFDM transmission systems. Conventional self-cancellation schemes provide an excellent cancellation capability of ICI for relatively low frequency offsets. However, this capability is achieved at the expense of bandwidth efficiency and thus a higher modulation level is often used to compensate for desired throughput. By applying a partial differential coding (PDC) to the transmit data prior to the ICI self-cancellation, bandwidth efficiency is greatly improved by a factor of 2, while maintaining a string of data (+1, -1) alternately for the ICI. self-cancellation in OFDM systems. Computer simulations show that the performance of the proposed scheme is comparable to the conventional self-cancellation scheme with slight performance degradation for relatively lower frequency offsets.

• ETRI Journal
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• 제34권4호
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• pp.613-616
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• 2012

A multi-spot-beam satellite is an attractive technique for future satellite communications since it can support high data rates by projecting high power density to each spot beam and can reuse a frequency in different cells to increase the total system capacity. In this letter, we propose a resource management technique adjusting the bandwidth of each beam to minimize the difference between the traffic demand and allocated capacity. This represents a reasonable solution for dynamic bandwidth allocation, considering a trade-off between the maximum total capacity and fairness among the spot beams with different traffic demands.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2013년도 춘계학술대회
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• pp.747-748
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• 2013

본 논문에서는 XGPON1 (10-Gbps-capable passive optical network stage 1) 시스템에 사용 가능한 새로운 동적 polling 방법을 제안한다. XGPON1 시스템은 상향 2.5 Gbps, 하향 10 Gbps 속도를 지원한다. XGPON1 시스템에서는 polling 빈도가 높으면 동적대역할당의 효율이 증가하지만 상향대역폭이 낭비되는 문제가 발생된다. 제안된 polling 방법은 polling에 사용되는 상향 대역폭 낭비를 줄이고 동시에 polling 횟수를 효율적으로 향상시킨다.

• 한국통신학회논문지
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• 제21권2호
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• pp.526-533
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• 1996

In this paper, the 800 MHz band N fractional frquency synthesizer having 677 channel with 30 kHz channel bandwidth is designed on the based on the theory which is dervied in terms of the relation between reference freqiency and the number of channels, loop bandwidth and acquistion time. The experimental resuls show 10 Hz deviation from the bandwidth and acquisition time. The experimental results show 10 Hz deviation from the bandwidth, the spurious suppression of aroud -45 dBc and the acqusition time of 1.44 ms. The results satisfy the given specification, but don't achieve thebesired spurious -60 dBc suppression. It is found that 500 hop per second will be possible over the range from 800 to 820 MHz.

• ETRI Journal
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• 제26권1호
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• pp.57-60
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• 2004

We propose an inductive compensation method for a surface-mountable 10 Gbps photoreceiver module. Since many typical 10 Gbps photoreceiver modules consist of a photodetector and low-noise pre-amplifier, the impedance mismatch between the photodetector and pre-amplifier, as well as package parasitics, may reduce the frequency bandwidth. In this paper, we inserted an inductive component between the photodetector and pre-amplifier in order to create frequency bandwidth expansion. From the measurement results, we have found that the proposed technique can increase the -3 dB bandwidth about 4.2 GHz wider compared with an uncompensated module. And, from a bit-error rate (BER) test, we observed -15.7 dB sensitivity at $10^{-12}$ BER. This inductive compensation can be implemented easily and is compatible with common manufacturing processes of photoreceiver modules.

• ETRI Journal
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• 제27권5호
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• pp.643-646
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• 2005

This letter proposes a band-pass filter (BPF) with two transmission zeros based on a combination of parallel coupling and end coupling of half-wave transmission lines. The fabricated BPF exhibited a narrow bandwidth and two transmission zeros near the pass-band due to the end-coupled and shielding waveguide. At the center operation frequency of 60 GHz, the 20 dB bandwidth of the BPF is 1.0 GHz, which is almost 2% of the center operation frequency, and the insertion loss is 3.12 dB. Two transmission zeros reach approximately 40 dB at 58.5 and 62.5 GHz. The simulation results almost agree with the measured results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.171-174
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• 1991

Among the various PWM methods, the hysteresis-band current control PWM method is popularly used because of its simplicity of implementation, fast response characteristics and inherent peak current limiting capability. However, the current control PWM method with a fixed hysteresis-band has the disadvantage that switching frequency decreases and current ripple is high as the increasing of back-EMF. As a result, load current contains excess harmonics. This paper describes a adaptive hysteresis-bandwidth control algorithm so as to maintain the average switching frequency constant and decrease the current ripple where the hysteresis bandwidth is derived as a relation with the switching frequency. This control algorithm is applied to the surface-type brushless DC motor with separated winding and using the computer simulation, the validity of its algorithm is proved.

• 대한전자공학회논문지TC
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• 제38권6호
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• pp.18-27
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• 2001

본 논문에서는 변형된 MSA에 전기력선의 제한이 없도록 용량을 장하한 MSA를 제안했다. 제안된 안테나는 1.9 GHz의 중심 주파수에서 7.76%의 대역폭을 갖고, 임의의 급전점 변화에 따라 대역폭과 공진주파수의 변화를 보였다. 용량을 장하한 MSA는 변형된 MSA보다 개선된 대역폭을 얻었다. 전송 선로 모델의 안테나 등가 회로는 정확한 공진 주파수를 찾기 위해 설계되었고, return loss 값을 계산했다. 계산된 값은 실험값과 양호하게 일치되었다.

• Smart Structures and Systems
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• 제25권4호
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• pp.393-399
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• 2020

In this paper, the design method and experimental validation for the two-degree-of-freedom (2DOF) electromagnetic energy harvester are presented. The harvester consists of the rigid body suspended by four tension springs and electromagnetic transducers. Once the two resonant frequencies and the mass properties are specified, both the constant and the positions for the springs can be determined in the closed form. The designed harvester can locate two resonant peaks close to each other and forms the extended frequency bandwidth for power harvesting. Halbach magnet array is also introduced to enhance the output power. In the experiment, two resonant frequencies are measured at 34.9 and 37.6 Hz and the frequency bandwidth improves to 5 Hz at the voltage level of 207.9 mV. The normalized peak power of 4.587 mW/G² is obtained at the optimal load resistor of 367 Ω.

• 음성과학
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• 제12권2호
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• pp.153-170
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• 2005

The sub-Nyquist nonuniform sampling (SNNS) and the perfect reconstruction (PR) formula are proposed for the development of a systematic method to obtain minimal representation of a speech signal. In the proposed method, the instantaneous sampling frequency (ISF) varies, depending on the least upper boundary of spectral support of a speech signal in time-frequency domain (TFD). The definition of the instantaneous bandwidth (IB), which determines the ISF and is used for generating the set of samples that represent continuous-time signals perfectly, is given. Also, the spectral characteristics of the sampled data generated by the sub-Nyquist nonuniform sampling method is analyzed. The proposed method doesn't generate the redundant samples due to the time-varying property of the instantaneous bandwidth of a speech signal.