• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1191-1197
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• 2003

In the multi-carrier OFDM communication system, the inter-carrier-interference(ICI) produced by phase noise in the transceiver local oscillator makes a severe influence on the system performance. In this paper, a new ICI self-cancellation scheme in the data-conversion type is proposed to reduce effectively the ICI. Also, the common phase error(CPE), ICI and carrier to interference power ratio(CIR) are found by the linear approximation of the phase noise. Then, the proposed method is compared with the conventional OFDM to analyze the efficiency of system performance improvement. When the number of subcarriers is 64, there are respectively the SNR gain of 0.6 ㏈ in the phase noise variance of 0.3 with QPSK and 1.5 ㏈ in the phase noise variance of 0.1 with 16 QAM at BER=10$\^$-3/. As a result, the performance degradation by ICI can be effectively lowered in the proposed system with ICI self. cancellation scheme, compared with the conventional OFDM system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.9
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• pp.4334-4356
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• 2017

In orthogonal frequency-division multiplexing (OFDM) systems, phase noise introduced by the local oscillators can cause bit error rate (BER) performance degradation. To solve the phase noise problem, a novel orthogonal-polarization-based phase noise self-cancellation (OP-PNSC) scheme is proposed. First, the efficiency of canceling the phase noise of the OP-PNSC scheme in the AWGN channel is investigated. Then, the OP-PNSC scheme in the polarization-dependent loss (PDL) channel is investigated due to power imbalance caused by PDL, and a PDL pre-compensated OP-PNSC (PPC -OP-PNSC) scheme is proposed to mitigate the power imbalance caused by PDL. In addition, the performance of the PPC-OP-PNSC scheme is investigated, where the signal-to-interference-plus-noise ratio (SINR) and spectral efficiency (SE) performances are analyzed. Finally, a comparison between the OP-PNSC and polarization diversity scheme is discussed. The numerical results show that the BER and SINR performances of the OP-PNSC scheme outperform the case with the phase noise compensation and phase noise self-cancellation scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.23-36
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• 2016

We propose a new type of OFDM-CDMA scheme which allows large inter-user timing offset using zero correlation zone(ZCZ) code in conjunction with block spreading technique. Moreover to maximize spectral efficiency, the proposed OFDMA does not have guard time(GT). This is opposite to the trends in the conventional schemes where GT are supposed to be larger to allow larger inter-user timing offset. It is remarkable that the proposed GT-free OFDM-CDMA scheme completely cancels inter-user interference in the multipath fading simply by despreading process. This inter-user interference-free feature still remains even there exist inter-user timing offsets as large as multiple OFDM symbols. Although the self-user interference exists due to no GT, it can be effectively suppressed by simple successive interference cancellation(SIC) from the first symbol in spread block as it is free from inter symbol interference(ISI).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.11
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• pp.2131-2141
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• 2015

In this paper, we analyze ADC effect in IBFD system. Also, we design IBFD system with ADC effect, and evaluate BER performance of the system according to power of self-interference. Firstly, we describe a fundamentals of general IBFD system. And then we calculate and analyze characteristics of desired signal before and after ADC when residual self-interference is added to desired signal after RF cancellation. In this calculation, we have confirm some conditions for selection of # of ADC bit. Finally, we design IBFD system with ADC effect, and evaluate BER performance of the system by using Simulink simulation tool. As simulation results, we have confirmed that when power of residual self-interference is high before ADC, IBFD system must use high-bit ADC for decreasing quantization step. Also, we have confirmed that quantization step should be lower than one-third of amplitude of desired signal for effective communication with good performance.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.5
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• pp.396-401
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• 2017

In this paper, we propose a solution for interference with Bluetooth when connecting Bluetooth and other devices. The random frequency hopping technique is a technique of generating a hopping pattern using the entire Bluetooth channel without considering the interference of the wireless LAN. The proposed adaptive frequency hopping technique is a technique for generating a hopping pattern of Bluetooth channel considering periodic carrier sensing of Bluetooth and considering WLAN interference. Simulation results show that the use of adaptive frequency hopping reduces the packet error rate as the Bluetooth carrier sensing interval decreases even in the congestion of WLAN interference. Especially, the frequency hopping technique improves the average packet error rate by about 13% compared to the adaptive frequency hopping technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.25-33
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• 2018

In this paper, we propose an iterative self-interference (SI) channel estimation method for in-band full-duplex cellular systems that employ orthogonal frequency division multiple access (OFDMA) on downlink (DL) and single-carrier frequency division multiple access (SC-FDMA) on uplink (UL), as in Long Term Evolution (LTE) systems. The proposed method first acquires coarse estimates of SI channels using DL signals and UL pilots, which are known to the base stations, and then refines the estimates by consecutively exploiting averaging in the frequency domain and channel truncation in the time domain. In addition, the method enhances the estimates further by iteratively executing this estimation procedure, and does not require any radio resources dedicated to SI channel estimation. Simulation results demonstrate that by significantly improving the SI channel estimation performance without requiring exact knowledge of the SI channel length, the proposed method achieves UL channel estimation performance and signal-to-interference-plus-noise ratio (SINR) performance very close to those in perfect SI cancellation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1276-1285
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• 2015

Full-duplex communications have emerged as a key technology for next-generation wireless local area networks (WLANs). Although the key enabling technology for full-duplex communications is the self-interference cancellation (SIC) technique in the physical layer, the employment of full-duplex communications has huge potentials to substantially increase the throughput at the medium access control (MAC) layer. At the same time, full-duplex communications pose non-trivial challenges to the MAC protocol design. In this article, we first identify salient problems in supporting full-duplex communications in WLAN MAC protocols. After that, we survey the state-of-the art to address those problems and analyze their pros and cons. Finally, we present open research challenges to improve the effectiveness of full-duplex communications in WLANs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.5
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• pp.531-538
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• 2016

In this paper, we have proposed MIMO-IBFD system that can transmit and receive multiple data stream at the same time in the single band, and analyze the system. We have confirmed that MIMO-IBFD system requires multiple RF cancellation and multiple Digital cancellation techniques. In simulation, we have analyzed characteristic of received signal on MIMO-IBFD system, and evaluate system performance of conventional $2{\times}2$ MIMO system and MIMO-IBFD system. As simulation results, we have confirmed that MIMO-IBFD system can transmit and receive multiple data stream at the same time in the single band by using multiple RF and digital cancellation techniques. Additionally, we have confirmed that BER performance of $2{\times}2$ MIMO-IBFD system with low-level QAM modulation is similar to performance of $2{\times}2$ MIMO system, and BER performance of $2{\times}2$ MIMO-IBFD system with high-level QAM modulation is degraded in comparison with $2{\times}2$ MIMO system with high-level QAM modulation. We can confirm that MIMO-IBFD system requires high level self-interference cancellation technique in order to use high level modulation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.853-864
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• 2001

In this paper, system model is based on proposed standardization by 3GPP(Asynchronous IMT-2070 system), and we have analyzed the performance of the DS-CDMA/QPSK which cancelled self-interference, so that occurs when the received signal time is delay by multipath fading. We proposed the new scheme that designed for self-interference cancellation and the system performance is calculated in Rician fading and Rayleigh fading channel. The proposed rake receiver can be achieved a gain of about 1 [dB]∼6 [dB] more than generally rake receiver, and will be a very effective method to improve the performance of IMT-2000, and these data can be available for modem design of DS-CDMA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.4
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• pp.378-386
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• 2013

In this paper, we propose a multi-way relaying system, in which N communicating nodes interchange their information one another by the help of a multiple-antenna non-regenerative relay station (RS). While the conventional multi-way relaying requires 2N transmission phases to complete the data exchange, the proposed system completes the mission with N phases composed of one multiple access phase and N-1 broadcast phases. For effective broadcast transmission, the proposed system pairs users for signal transmission with a new RS beamforming matrix not to interfere with the nodes of different pairs and a self-interference canceler at each node. The performance evaluation in terms of the average sum rate shows that the proposed system outperforms the conventional one with more significant gain when the number of RS antennas is comparable to the number of communicating nodes. The proposed schemes can be applicable to marine communications where the ships need to share their information with extended coverage.