• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.601-608
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• 2011

In OFDMA(Orthogonal Frequency Division Multiple Access) based multi-hop networks, the subcarrier-pairing scheme using the SNR(Signal-to-Noise Ratio) has been proposed as the best solution. But, this scheme is not optimal in cognitive radio system, because of the power control due to the interference to the primary user. In this paper, we propose two subcarrier-pairing schemes for OFDMA based 2-hop cognitive radio systems. One is the IT(Interference channel gain) scheme considering only the interference channel gain, and the other is the CI(Channel SNR over interference channel gain) scheme considering the ratio of channel SNR to interference channel gain. The results show that the CI scheme has the best performance in which throughput is improved more than 10% in comparison with other schemes.

• Journal of information and communication convergence engineering
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• v.7 no.3
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• pp.286-291
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• 2009

In this paper, the performance of ultra-wideband (UWB) single input multiple output (SIMO) systems to achieve high data rate communications is studied in dense multipath environments. The effects of spatial and temporal diversities on the performance of multi-user time-hopping UWB systems using binary pulse position modulation (2PPM) are analyzed. The reduced-complexity Rake receivers based on the selective combining (called SRake) and partial combining (called PRake) are considered. The theoretical and simulation results show that the BER performance of the UWB system can be enhanced as the number of array elements and/or Rake fingers increases. Moreover, we observe that SRake is more effective for the IR-UWB systems to achieve a good BER performance, as compared with PRake.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.8B
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• pp.745-751
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• 2002

The performance of existing CDMA-type multiple access data transmission systems is limited by interferences due to adverse mobile communication channel characteristics. Among them, the multi-user interference becomes one of the major performance degradation factors because the signal-to-signal orthogonality can be easily perturbed when numerous user signals are distorted by multipath fading channels and mixed together. In order to enhance the performance of CDMA-type systems by suppressing the multi-user interference, we have adopted chip-based cyclic prefix insertion along with adaptive one-tap DFE equalization into MC-DS-CDMA, which is known for its robustness in the frequency selective multipath fading channel environment. In order to assess the performance of the proposed system, a set of computer simulations is performed in the reverse link in which each user signal undergoes different multipath Rayleigh fading. The results show us a superior performance of our system over other CDMA systems in terms of SNR to BER measurements.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.9
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• pp.1-8
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• 2007

In this paper, the new beamforming is proposed for an orthogonal frequency division multiplexing(OFDM) system with multi-input multi-output(MIMO). Through the proposed Pre-FFT beamforming technique for MIMO-OFDM, the multibeams are formed toward each multi-transmitter antenna of the desired user. The proposed beamforming for MIMO-OFDM can reduce cochannel interference and get diversity gain in the multi-user environment. Therefore, the performance of MIMO-OFDM system is very improved. BER performance improvement of the proposed approach is investigated through computer simulation by applying it to MIMO-OFDM system in the multi-user environment.

• IEIE Transactions on Smart Processing and Computing
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• v.5 no.5
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• pp.346-348
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• 2016

Coordinated multi-point transmission is a candidate technique for next-generation cellular communications systems. We consider a system with multiple cells in which base stations coordinate with each other by sharing user channel state information, which mitigates inter-cell interference (ICI), especially for users located at the cell edge. We introduce a new user scheduling method that considers both ICI and intra-cell orthogonality. Due to the influence of ICI cancellation and the loss reduction of effective channel gain during the beamforming process, the proposed method improves the system sum rate, when compared to the conventional method, by an average of 0.55bps/Hz for different numbers of total users per cell.

• Journal of Korea Society of Digital Industry and Information Management
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• v.8 no.4
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• pp.129-133
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• 2012

Coordinated multi-point transmission (CoMP) is a candidate technique for next generation cellular communications systems. One of the primary elements discussed in LTE-Advanced technology is CoMP, which can improve cell edge user data rate as well as spectral efficiency due to multiple input multiple output - orthogonal frequency division multiplex (MIMO-OFDM). We consider a system with multiple cells in which base stations coordinate with each other by sharing user channel state information (CSI), which mitigates inter cell interference (ICI), especially for users located at the cell edge. We introduce a new user scheduling method of ICI cancellation and the loss reduction of effective channel gain during the beamforming process, the proposed method improves the system sum rate, when compared to the conventional method by an average of 0.55bps/Hz in different number of total users per cell. It also outperforms the conventional method by approximately 0.38bps/Hz using different SNRs.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.8
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• pp.1656-1662
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• 2005

This paper introduces M-PPAM(M-ary Pulse Position and Amplitude Modulation) architecture, combined PPM(Pulse Position Modulation) with PAM(Pulse Amplitude Modulation). Since M-PPAM can transmit several bits using one pulse, it is mon effective than PPM or PAM. Also, to obtain the same data transmission rate with PPM or PAM, M-PPAM can use a long pulse repetition period. This method will be able to use in the multi-path fading environment such as indoor condition. To accomodate multiple users, direct sequence technique is used. This paper has provided the modeling method of the M-PPAM DS-UWB receiver covering multi-user interference(MUI) with the Standard Gaussian Approximation under Gaussian channel. The performance of the receiver is simulated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1639-1644
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• 2016

In this paper, we consider the performance improvement that can be obtained with interference alignment (IA) technique applied to 802.11ac based multi-BSS WiFi service. To this end, we developed a system simulator consisting of a link-level PHY simulator, based on 802.11ac specification, and multi-BSS proportional-fair scheduler. Specifically, assuming perfect channel side information and synchronization of signals from multiple APs, we used a SLNR based interference alignment algorithm proposed in [13] and compared its performance with that of multiuser beamforming based time-sharing system. The performance was evaluated in terms of average throughput per BSS and 5% worst user throughput. The results show that 70 to 100% throughput gain can be obtained in this ideal scenario.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.53 no.3
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• pp.129-133
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• 2004

As In DS/CDMA(direct sequence code division multiple access) system, the system capacity is limited by multiple access interference(MAI), and self-interference(SI) resulting from the multi-path propagation of the desired user signal. This paper, which the approximated analytic chip waveforms are nearly the same as the computer generated chip waveforms are shown. And then, the BER(Bit Error Rate) performances in CDMA system using the approximated analytic chip waveforms are shown.

• Journal of Internet Computing and Services
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• v.12 no.1
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• pp.27-38
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• 2011

In this paper, we propose a multiple access scheme using MHP(Modified Hermite Polynomial) pulse and ternary code for high-data and low-data rate for Out-body WBAN(Wireless Body Area Network). To satisfy the requirement of WBAN system, UWB-IR has been considered as a promising candidate for Out-body WBAN. The proposed multiple access scheme, using orthogonal MHP pulse and ternary code sets, reduces multi-user interference and distinguishes user signal from multi-user signals. We propose two algorithms for synchronous and asynchronous WBAN system. The symbol is constructed by MHP pulses and time hopping duration to reduce multi-user interference in the synchronous WBAN system. The symbol also is constructed by ternary code to avoid collision between pulse trains in the asynchronous WBAN system. The results of the proposed multiple access scheme show a clear improvement of BER.