• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.1
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• pp.76-82
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• 2014

In order for heterogeneous unlicensed devices to co-exist on the same frequency band, the frequency interference avoidance mechanism is necessary. In this paper, a frequency interference between WLAN and WPAN systems that operate at 2.4 GHz ISM band was analyzed in the MAC layer. We observed that WPAN systems suffer from severe interference from WLAN systems. To avoid this interference problem, we propose a new channel shift algorithm for WPAN systems. We showed that the proposed channel shift algorithm is better than the traditional WPAN system which uses a fixed channel in terms of throughput.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.392-399
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• 2014

The underwater acoustic communication is characterized by doubly spread channels, which are the delay spread due to multiple paths and the doppler spread due to environmental fluctuations or a moving platform. An equalizer is used to remove the inter-symbol interferences that the delay spread causes, but an equalizer doesn't use an acoustic environment such as a multipath. However, a passive time-reversal mirror is simpler than an equalizer because a matched filter is implemented numerically at the receiver structure along with one-way propagation. In this paper, a passive time-reversal mirror is applied to remove interferences due to a multipath in sea-going experimental data in East Sea in Oct. 2010 and improved communication performance is confirmed. The performance is verified by comparing the signal-to-interference plus noise ratio before/after passive time-reversal mirror. It is also performed independently of the passive time-reversal mirror and adaptive equalizer and the bit error rate is compared to verify the performance of underwater acoustic communication.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.3
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• pp.3-10
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• 2016

To establish a network environment where multiple wireless personal area networks(WPAN) are simultaneously operating in the same area, we need to consider the effects of inter-device interference. The extent of interference effect from neighboring frequency channel interferer may be different depending on the modulation types that are used for constructing the wireless network. If a modulation scheme with high spectral side lobes is used, the spatial separation between devices plays a major role in determining the amount of interference from neighboring frequency channel interferer. In this paper, we investigate the effect of inter-device interference in the overlapped raised cosine offset quadrature-quadrature phase shift keying (ORC-$OQ^2PSK$) modulation based WPAN. By comparing the results with those of GFSK modulation based WPAN, we verify the feasibility of ORC-$OQ^2PSK$ based WPAN.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.10
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• pp.7-12
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• 2011

The effect of frequency interference situation between WiBro and WLAN in TV White Space band was taken into account in this paper. We assumed the using frequency in each system is applied in co-channel. When it comes to co-channel interference case, the minimum distance between WiBro ME and WLAN UE should be at least 210m if the maximum transmitter power of WiBro UE of 25dBm is limited. Analysis results of this paper can provide efficient reference and guideline to make spectrum plan for deploying WiBro and WLAN in TVWS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.72-78
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• 2006

It is impossible to provide full diversity and full rate simultaneously using more than two transmit antennas in transmit diversity system. To do this, simple interference cancellation scheme and transmit power allocation scheme have been proposed, recently. But the former has increased noise power and the latter has increased interference which is induced by other channel in fading channel. In this paper, we propose an adaptive transmit power allocation algorithm to minimize the estimation error in the channel environments which have different fading levels each other and to improve the system performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9B
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• pp.1608-1615
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• 1999

In this study, we investigate the inter cell interference of LMDS(Local multipoint Distribution Service) system cell in LMDS system design process. There are several interference sources in LMDS system but we consider co-channel adjacent interference, cross-polarization interference, tx/rx interworking interference as three major factors. As the summation of each interference, C/N is keep 19 dB in 2km range but decreased gradually over 2km. Based on theoretical results, we process the experimental test and get results that C/I=20 dB have to be maintained to transmit the data successfully under rain fall attenuation condition. This experiential results are similar to the theoretical analysis results we examined.

• The Magazine of Kiice
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• v.6 no.1
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• pp.70-75
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• 2005

• The Journal of Korean Institute of Communications and Information Sciences
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• v.7 no.4
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• pp.167-172
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• 1982

We have studied and discussed the error rate performance of Quadrature Amplitude Modulation(QAM) in an environment of cochannel QAM interference and impulsive noise. A general equation of error probability for L-level QAM signal has been derived and the error rate of the 16-QAM signal, as an example, has been calculated as functions of carrier-to-noise power ratio(CNR), carrier-to-interferer power ratio(CIR), impulsive indes, and the phase difference between signal and interferer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.5B
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• pp.545-553
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• 2001

다중 사용자 DS-CDMA 시스템에서 더 나은 성능을 얻고자 컨볼루션 코드와 차등 코드의 직렬 연쇄 구조를 제안한다. 시스템은 접속 간섭 (MAI: Multiple-access Interference)를 억제하기 위해 다른 사용자의 확산 코드, 동기, 그리고 전력 정보 등을 필요로 하지 않는 단일 사용자 검파기(SUD: Single User Detection)로 이루어진다. 채널 부호로 사용된 부호화율 1과 메모리 수 1을 가지는 차등 부호는 부호화로 인한 효율 저하를 가져오지 않으며 최소 상태수를 가지게 된다. 이러한 차등 부호와 컨볼루션 부호를 복호함에 있어서 서로간의 정보를 교환하는 반복 복호 처리를 이용한다. AWGN 채널에서의 분석 결과로부터 본 연쇄 부호 기법이 DS-CDMA 시스템에서 기존의 컨볼루션 코드보다 유사한 복잡도에서 더 나은 성능과 유연성을 제공함을 알 수 있다. 또한 제안한 기법이 SUD를 하는 DS-CDMA 시스템에 적용될 때, 처리 이득(Processing Gain)이나 간섭 억제 여파기의 탭 개수를 증가시킴으로써 성능 향상이 일어나며, 원근 간섭 전력 문제가 심한 경우에 성능 저하가 일어남을 알 수 있다.

• The KIPS Transactions:PartC
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• v.11C no.2
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• pp.203-212
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• 2004

There is a rapidly growing demand for wireless telecommunication. The restricted number of channels is a significant bottleneck for the capacity of mobile communication systems. Consequently, when assigning the channels to the different base stations, it is desirable to reuse the same channel af much as possible. It is then important to avoid any possible interference between different mobile users, while satisfying the given demand. The objective of this thesis is to develop a hybrid heuristic algorithm to find the channel assignment method for allocating the channels in an efficient way, which does not violate the compatibility constraints. We also show several benchmarking channel assignment problems using proposed channel assignment method for validation in this thesis.