• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2A
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• pp.99-106
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• 2009

In this paper, we propose UCA algorithms that are applied to the unified inter-cell interference mitigation through frequency plannings in OFDMA cellular systems. Under three frequency plannings, UCA algorithms allocate frequency channels to UEs(User Equipments). Proposed UCA algorithms require the information of received signal power from home sector and neighbor sectors respectively. We compare all possible combinations of UCA algorithms and frequency plannings through compute simulation. A primary performance measure is the low 5th percentile of SINR at UEs. The proposed UCA algorithms can avoid the interference to neighbor cells by allocating relatively low transmit power to centrally-located UEs and cancel inter-cell interference at cell-edge UEs by a coordinated symbol repetition. We show that UCA algorithm 2 applied in frequency planning 1 is promising among other combinations of UCA algorithms and frequency palnnings in terms of the low 5th percentile of SINR at UEs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11A
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• pp.1038-1044
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• 2010

Interference may severely deteriorate performance in wireless communication. Han-Kobayashi scheme splits each user's signal into private and common information so that the receiver removes the other's common signal for partial interference cancellation. This paper proposes an optimal power allocation to private and common signals for Han-Kobayashi scheme by using required SNR in a private information only system. Numerical results show that the proposed power allocation is quite close to the optimal power allocation based on exhaustive searches.

• The Transactions of the Korea Information Processing Society
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• v.4 no.10
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• pp.2562-2570
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• 1997

This paper deals with the design and performance of the adaptive equalizer using high order statistics in order to improve the transmission characteristics of multipath fading channel. The multipath propagational phenomenon occurred in digital radio transmission causes the distortion and ISI of receiving signal. These are main reasons to increase the bit error rate and degrade the performance of receivers. In this paper, the adaptive equalization algorithm using high order statistics of received signal is used instead of CMA algorithm, Bussgang and Godard which are known widely. The performance of this algorithm (residualisi, recovered constellation, calculation) is presented varing SNR. As the result of the computer simulation, equalizer algorithm using high order statistics is better than CMA in the range of low SNR, $10{\sim}20dB$. Therefore, considering the actual communication systems which use the range of $14{\sim}20$ SNR, the adaptive equalizer using high order statistics can be used in the real multipath fading environment.

• Journal of Sensor Science and Technology
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• v.6 no.6
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• pp.458-465
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• 1997

In this paper, a theory of the geological magnetic filter for the improvements of the signal to noise ratio of the magnetic detection system has been developed. The geological magnetic filter takes two sequences of magnetic fields measured from the reference sensor and the detector sensor and calculate the correlations between them in the frequency domain. Using the filter, we can remove the coherent noises in the time domain and improve the signal to noise ratio of the magnetic detection system. With the recent developments of the DSP hardware technology the geological magnetic filter can be easily implemented using the digital signal processor. We show the ability of the geological magnetic filter under various circumstances through computer simulations. Numerical simulation results show that geological magnetic filter can excellently remove the sensor misalignment effects and the regular short range local noise as well as it delete the coherent noises.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.1
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• pp.59-64
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• 2005

To achieve a goal of minimum output power, the beamformer tends to cancel the desired signal if there exists correlated interference sources such as multipaths of the desired signal. In this paper, we propose a new method which overcomes the signal cancellation problem for correlated interferences. Instead of decorrelating the correlated interferences, the proposed bramformer regards them as replicas of the desired signal and coherently combines them with desired signal. This method uses an eigenvector constraint that suppresses a noise and uncorrelated interferences but keeps the desired signal and correlated interferences. Indisputably, the beamformer does not require any preliminary information on correlated interferences. Simulation results show that the proposed beamformer overcomes the signal cancellation problem and improves signal-to-noise ratio (SNR) of the array output when the correlated interferences exist.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.4
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• pp.519-529
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• 1998

In this paper, we analyze the effects of interference canceller on the performance of multitone DS/CDMA system. Although there are various kinds of interference cancellers suggested by different researchers, we adopt a canceller used by Yoon et at.［9］. We consider three kinds of inteferences, that is, multiPath interference(MPI), interchannel interference(ICI) and multiple access interference(MPI). The equations for variances ate derived for the inteferences and thermal noise used for signal to noise ratio calculation. We also consider RAKE reception over multipath channel and three stage interference canceller used for performance improvement. We draw some conclusions that interference canceller is effective in multitone DS/CDMA system and the performance is further improved with the higer order of diversity and larger number of PN chips.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.1025-1031
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• 2001

In this paper, we derive the outage probability of cellular mobile system with STTB(Space Time Transmitter Diversity) scheme where the received radio signals and interferers experience Rayleigh fading and AWGN. The new probability density function of L independent identically distributed interferers is derived using Laplace transforms. We express the probability of outage as a function of the average-signal to average-interference power ratio and the signal to noise ratio. In addition, the frequency reuse distance which is one of the key parameters in the design of cellular systems is analyzed.

• The Journal of the Acoustical Society of Korea
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• v.38 no.4
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• pp.406-413
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• 2019

This paper proposes a speech enhancement method through the process of combining the gain function with spectrum subtraction method in the two microphone array with close spacing. A speech enhancement method that uses a gain function estimated by the SNR (Signal-to Noise Ratio) based on the multi frequency band coherence function causes the performance degradation in high correlation between input noises of two channels. A new speech enhancement method is proposed where the weighted gain function is used by combining the gain function from the spectral subtraction. The performance evaluation of the proposed method was shown by comparison with PESQ (Perceptual Evaluation of Speech Quality) value which is an objective quality evaluation test provided by the ITU-T (International Telecommunications Union Telecommunication). In the PESQ tests, the maximum 0.217 of PESQ value is improved in the various background noise environments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.12
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• pp.2151-2156
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• 2006

Beamforming for underwater acoustic communication (UAC) is affected by the broadband feature of UAC signal, which has relatively low currier frequency as compared to the signal bandwidth. The narrow-band assumption does not hold good in UAC. In this paper, we discuss a broadband FIR beamformer for UAC using the baseband equivalent way signal model. We consider the broadband FIR beamformer for QPSK UAC with carrier frequency 25kHz and symbol rate 5kHz. Array geometry is a uniform linear way with 8 omni-directional elements and sensor spacing is the half of the carrier wavelength. The simulation results show that the broadband n beamformer achieves nearly optimum signal to interference and noise ratio (SINR) and outperforms the conventional narrowband beamformer by SINR 0.5dB when two-tap FIR filter is employed at each sensor and the inter-tap delay is a quarter of the symbol interval. The broadband FIR beamformer performance is more degraded as the FIR filter length is increased above a certain value. If the inter-tap delay is not greater than half of the symbol period, SINR performance does not depend on the inter-tap delay. More training period is required when the inter-tap delay is same as the symbol period.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.4B
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• pp.447-456
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• 2001

본 논문에서는 DS-확산대역 시스템에서 격자형 IIR 노치필터를 이용하여 협대역 간섭신호를 제거한다. 이를 위하여 우선 갑섭신호의 주파수와 파워가 격자형 IIR 노치필터에 의ㅏ형 추정된다. 그리고 또 다른 IIR 노치필터를 수긴기 닾에 위치시키고 노치의 위치가 추정된 갑섭신호의 주파수에 있도록 한다. 그러나 단워원 위에 영점이 존재하는 IIR 노치필터는 간섭신호 뿐만 아니라 노치부분의 신호 성분도 제거하므로 데이터의 왜곡이 발생하게 된다. 따라서 이러한 데이터의 왜곡을 줄이기 위해서 필터의 노치 깊이를 조절하는 알고리듬을 개발하였다. 이를 위해 노치필터 출력의 신호 대 잡음비를 필터 파라미터에 대한 식으로 유도하고 이를 최대로 하는 최적의 노치 깊이를 구하였다. 시뮬레이션 결과 제안한 알고리듬이 기존의 FIR 노치필터나 FIR LMS 알고리듬에 비해 좋은 성능을 갖는다는 것을 확인할 수 있다.