• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.143-146
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• 1989

Narrowband bandpass waveguide filters using inducive post obstacles are designed and constructed to have an equal-ripple bandwidth of 50MHz at a center frequency of 9GHz. Both the triple-post and the single-post configurations are realized and compared. The measured results for both filters show good agreement with the theoretical calculations. When the two filters are compared, the performance of the triple-post filter is better than that of the single-post filter.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.6 s.97
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• pp.603-614
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• 2005

In this paper, digital ultra-narrowband Walky-Talky using direct conversion method for CQPSK modulation scheme is implemented with satisfying the requirements of APCO P25. RF transceiver design and implementation scheme that minimize the influence of DC-offset and AC-coupling at ultra-narrowband is proposed. This scheme also minimizes the influence of nonlinear characteristic at power amplifier fir CQPSK modulation method. Test results of full system including DSP module and direct conversion RF transceiver show that FCC emission mask at 36.8 dBm PEP meets the standard requirements. The characteristic of receiver AGC by PWM control signal is linear at 40 dB dynamic range and voice communication at input power level of -116 dBm is successful. Also it is verified that the performance of BER versus frequency offset and versus SNR meets the standard requirements.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.3
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• pp.1-7
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• 2012

In this paper, we consider a channel selection method for the coexistence of heterogeneous systems in the TV white space (TVWS). First, we define the target heterogeneous system structure. Then, under the defined system structure, we discuss how the heterogeneous systems share the TVWS channels. Specifically, the heterogeneous systems having different bandwidths cannot use the TVWS channels due to the lack of wideband channels when only narrowband channels are remained. Hence, in order to minimize the blocking from the different bandwidth problem, we propose a channel selection method for the narrowband systems to firstly occupy the narrowband channels rather than the wideband channels. The proposed narrowband-first channel selection is shown to enhance the spectral efficiency of the TVWS, especially in the IEEE 802.19.1 wireless coexistence system.

• The Journal of the Acoustical Society of Korea
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• v.21 no.5
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• pp.462-470
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• 2002

Wideband speech, characterized by a bandwidth of 50∼7000 ㎐, sounds more natural and intelligible, and is less tiring to listen to when compared to narrowband speech characterized by a bandwidth of 300∼3400 ㎐. Wideband speech coders, however, have not been as successful as the narrowband speech coders because of their higher bit rate. In this paper, we propose a new wideband speech coder which combines the European standard of a narrowband speech coder, i.e., GSM-EFR, and a transform coder using the discrete wavelet transform. The proposed wideband speech coder operates as follows input speech is first split into two subbands with equal bandwidth and the two subband signals are coded and decoded by each subband coder. A GSM-EFR is adopted as a lower subband coder and a subband coder with wavelet transformed speech is designed for a upper subband coder. The total bit rate of the proposed coder is 18.9kbps (12.2 kbps for lower band coder and 6.7 kbps for upper band coder), and informal listening test results have shown that the proposed coder has comparable speech quality to that of G.722 with 56 kbps.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.359-364
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• 2006

Interference can seriously degrade the performance of GPS receiver because GPS signal has extremely low power at earth surface. This paper presents a Narrowband Interference Excision Filter (NIEF) in frequency domain that removes narrowband interferences with small signal loss. A NIEF transforms the received GPS signals with interferences into the frequency domain with FFT and then compute statistics such as mean and standard deviation to determine an excision threshold. All spectrums exceeding the threshold are removed and the remaining spectrums are restored by IFFT. A NIEF effectively can remove various and strong interferences with a simple structure. However, the signal power loss is unavoidable during FFT and IFFT. Besides the hamming window and overlap technique, a threshold-whitening technique and an adaptive detection threshold are adopted to effectively reduce the signal power loss. The performance of implemented NIEF is evaluated using real signals obtained by 12 bit GPS signal acquisition board. The output of NIEF is fed into the Software Defined Receiver to evaluate the acquisition and tracking performance. Experimental results shows that many types of interference such as single-tone CWI, AM, FM, swept CWI and multi-tones CWI are effectively mitigated with small signal power loss.

• Journal of IKEEE
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• v.23 no.1
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• pp.91-98
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• 2019

LTE's extension for unlicensed spectrum called Licensed Assisted Access (LAA) is equipped with Listen-Before-Talk (LBT) designed similar with the backoff mechanism of Wi-Fi for coexistence. However, Wi-Fi's backoff mechanism has not evolved from its old design for compatibility with legacy devices, thus LAA's LBT is not efficient either in utilizing spectrum. If LAA operates with no Wi-Fi systems in proximity, it can run more efficient LBT. In this paper, we propose Narrowband Clear Channel Assessment (NCCA) for narrowband transmission. In NCCA, an LAA node performs LBT in either wide or each narrow bandwidth segment. This allows multiple LAA nodes to perform simultaneous transmissions in orthogonal bandwidth segments in the same time slot. We design four variants of NCCA implementation and model their performance using a mathematical model. The coexistence performance of NCCA with conventional wideband nodes and the accuracy of the model are shown via simulation.

• The Journal of the Korea Contents Association
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• v.8 no.4
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• pp.79-85
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• 2008

These days, orthogonal frequency division multiplexing (OFDM) transmission method is widely used for broadband communication systems. The OFDM, which uses sine waves as orthogonal basis functions, is one of the orthogonal waveform modulation techniques. In this paper, we investigate a wavelet packet modulation method which uses wavelet packets instead of sine waves as the basis functions. The wavelet packets may have different patterns in two dimensional time-frequency domain, and we can design the packets appropriate for the channel environments with much flexibility. In this paper, we investigate the characteristics of the wavelet packet modulation as one of the multicarrier modulation methods, And we illustrate by simulations that narrowband interference can be reduced effectively by control the bandwidth of the wavelet packets.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.42 no.4
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• pp.53-62
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• 2005

In this paper, we implement a 40kbps narrowband powerline communication modem which is able to high transfer rate than conventional powerline communication technology by using the chirp technique that is one of the spread spectrum techniques. A modem that implement in this paper used the CEBus standard and a symbol that the linear variable frequency signal of 100$\sim$380kHz is kept for 25us. Experimental results, we verified the possibility that communication technology with the Chirp technique can make transfer rate more than 40kbps at narrowband communication.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.21-24
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• 2001

본 논문은 신경 회로망을 이용하여, 전화망 대역의 음성, 즉, narrowband 음성에서 wideband 음성을 복원하고자 했다. BP 알고리즘을 사용하는 기존의 신경 회로망의 경우에는 음성과 같이 복잡하고 크기가 큰 훈련데이터에 대해서는 훈련이 제대로 되지 않는 단점이 있다. 그러므로 븐 논문에서는 이를 해결하기 위해 입력으로 들어온 LPC 켑스트럼 벡터를 k-means 알고리즘을 이용하여 미리 정한 개수의 cluster로 나눈 다음, 각각의 cluster에 대해 독립적인 신경 회로망을 적용했다 이로 인해 각각의 신경 회로망은 제한되고 서로 상관관계가 많은 음성들만 훈련하면 되므로, 기존의 신경 회로망에서 생기는 훈련의 정체를 개선할 수 있었다. 또 clustering 과정에서 생기는 오류를 보완하기 위해 후보신경 로망들의 출력에 fuzzy 개념을 적용해서 최종 출력을 내도록 했다 실험 결과에서, 제안한 알고리즘은 기존의 codebook mapping 알고리즘보다 스펙트럼 거리척도에 의한 비교 및 주관적인 음질 평가 양쪽에서 개선된 성능을 보였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6C
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• pp.577-584
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• 2005

Optimal methods for designing multiplierless minimal complexity FIR filters with cascaded prefilter-equalizer structures are proposed for narrowband communication systems. Assuming that an FIR filter consists of a cyclotomic polynomial(CP) prefilter and an interpolated second order polynomial(ISOP) equalizer, in the proposed method the prefilter and equalizer are simultaneously designed using mixed integer linear programming(MILP). The resulting filter is a cascaded filter with minimal complexity. Design examples demonstrate that the proposed methods produce a more computationally efficient cascaded prefilter-equalizer than other existing filters.