• Journal of information and communication convergence engineering
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• v.4 no.4
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• pp.162-165
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• 2006

This paper presents a bandwidth efficient self-cancellation scheme for interchannel interference (ICI) in OFDM transmission systems. Conventional self-cancellation schemes provide an excellent cancellation capability of ICI for relatively low frequency offsets. However, this capability is achieved at the expense of bandwidth efficiency and thus a higher modulation level is often used to compensate for desired throughput. By applying a partial differential coding (PDC) to the transmit data prior to the ICI self-cancellation, bandwidth efficiency is greatly improved by a factor of 2, while maintaining a string of data (+1, -1) alternately for the ICI. self-cancellation in OFDM systems. Computer simulations show that the performance of the proposed scheme is comparable to the conventional self-cancellation scheme with slight performance degradation for relatively lower frequency offsets.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9C
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• pp.896-905
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• 2009

In this paper, we propose an enhanced iterative ICI (Inter Carrier Interference) cancellation method for cooperative STBC-OFDM (Space Time Block Coded-Orthogonal Frequency Division Multiplexing) system. In cooperative STBC-OFDM system, ICI cancellation is necessary because ICI due to the independent local oscillators always exits. The conventional iterative ICI cancellation method has severe performance degradation due to the initial estimation error. Also the performance degradation increases as CFOs (Carrier Frequency Offsets) and modulation order increases. Therefore, in this paper, we propose an enhanced iterative ICI cancellation method which can reduce the initial estimation error by giving a priority to initial estimation and cancellation process. Through the complexity and performance comparisons, we verwey that the proposed method has better performance with approximately same complexity compared with the conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.950-957
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• 2007

In this paper, a recursive intercarrier interference (ICI) cancellation technique for cooperative space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) with different carrier frequency offsets (CFOs) is proposed. Also, different CFOs existing in a cooperative STBC-OFDM system is shown to produce phase difference in the received signal, causing noise enhancement effect in the STBC decoding process. The performance degradation caused by the noise enhancement effect can be effectively reduced by a proposed ML-based recursive ICI cancellation technique. It is shown by computer simulation that the proposed recursive ICI cancellation technique is effective in reducing ICI, especially for STBC-OFDM systems with a large FFT size and large CFOs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.3 s.94
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• pp.319-326
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• 2005

In the multi-carrier OFDM communication system for the high data rate transmission, the ICI caused by phase noise of transceiver local oscillator may degrade the system performance seriously. In this paper, a new ICI self-cancellation scheme using data-conjugate method is proposed to reduce the ICI caused by phase noise effectively. Then, the CPE, ICI and CIR are derived by the phase noise linear approximation method. Besides, to analyze the efficiency of system performance improvement, the proposed method is compared with the original OFDM and the conventional ICI self-cancellation scheme using data-conversion method. As results, the performance degradation caused by ICI can be mitigated effectively in the OFDM system with ICI self-cancellation scheme, and more performance improvement can be achieved by the proposed ICI self-cancellation scheme using data-conjugate method than the conventional ICI self-cancellation scheme using data-conversion method when phase noise exists.

• ETRI Journal
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• v.36 no.4
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• pp.537-544
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• 2014

In this paper, we present a new inter-carrier interference (ICI) self-cancellation scheme - namely, ISC scheme - for orthogonal frequency-division multiplexing systems to reduce the ICI generated from phase noise (PHN) and residual frequency offset (RFO). The proposed scheme comprises a new ICI cancellation mapping (ICM) scheme at the transmitter and an appropriate method of combining the received signals at the receiver. In the proposed scheme, the transmitted signal is transformed into a real signal through the new ICM using the real property of the transmitted signal; the fast-varying PHN and RFO are estimated and compensated. Therefore, the ICI caused by fast-varying PHN and RFO is significantly suppressed. We also derive the carrier-to-interference power ratio (CIR) of the proposed scheme by using the symmetric conjugate property of the ICI weighting function and then compare it with those of conventional schemes. Through simulation results, we show that the proposed ISC scheme has a higher CIR and better bit error rate performance than the conventional schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.8
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• pp.3704-3724
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• 2018

This paper proposes an advanced turbo receiver with joint inter-carrier interference (ICI) self cancellation and channel equalization for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over rapidly time-varying channel environment. The ICI caused by impairment of local oscillators and carrier frequency offset (CFO) is the major problem for MIMO-OFDM communication systems. The existing schemes (conjugate cancellation (CC) and phase rotated conjugate cancellation (PRCC)) that deal with the ICI cancellation and channel equalization can't provide satisfactory performance over time-varying channels. In term of error rate performance and low computational complexity, ICI self cancellation is the best choice. So, this paper proposes a turbo receiver to deal with the problem of joint ICI self cancellation and channel equalization. We employ the adaptive phase rotations in the receiver to effectively track the CFO variations without feeding back the CFO estimate to the transmitter as required in traditional existing scheme. We also give some simulations to verify the proposed scheme. The proposed schene outperforms the existing schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2A
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• pp.155-163
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• 2009

OFDM System is a promising transmission technique due to its spectral efficiency But, a major disadvantage of the OFDM system is its sensitivity to frequency offset and phase noise that makes intercarrier interference (ICI), which degrades the system performance severely The ICI self-cancellation method has a good performance with frequency offset or phase noise. This paper proposed the N/2 spacing data-conjugate method that works well in large frequency offset and phase noise (normalized frequency offset=0.2-0.4, phase noise standard deviation=about lodes). Also, an efficiency ICI cancellation method using pilot was proposed. Simulation results confirm that performance of the proposed scheme is better than conventional schemes.

• Journal of Broadcast Engineering
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• v.15 no.2
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• pp.217-223
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• 2010

In this paper, an interchannel interference (ICI) cancellation method is proposed for multiple frequency offsets in orthogonal frequency division multiplexing (OFDM) systems. When several same signals are received from different transmitters simultaneously, multiple frequency offsets may occur at the receiver because of the frequency difference of the oscillators of the two transmitters and the receiver. This causes degradation of system performance because OFDM systems are very sensitive to the frequency offsets. In this paper, we propose a method to eliminate the effect of the multiple frequency offsets for OFDM systems. The method is accomplished in two steps: compensation of the frequency offset in the time domain and subsequent cancellation of the ICI in the frequency domain. Through computer simulations, we verify the effectiveness of the proposed ICI cancellation method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.6
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• pp.1150-1155
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• 2007

Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier modulation scheme, which has been adopted for several wireless standards such as IEEE 802.11a and HiperLAN2. A well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. This frequency offset introduces inter-carrier interference (ICI) in the OFDM symbol. This paper investigates three methods for combating the effects of ICI: ICI self-cancellation (SC), maximum likelihood (ML) estimation, and extended Kalman filter (EKF) method. These three methods are compared in terms of bit error rate performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.7 s.110
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• pp.638-647
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• 2006

Recently, the DFT-Spread OFDM has been studied for the PAPR reduction. However, the DFT-Spread OFDM produces more ICI and SCI problems than OFDM because phase offset mismatch of the DFT spreading code results from the random phase noise in the oscillator. In this paper, at first, phase noise influence on the DFT-Spread OFDM system is theoretically analyzed in terms of the BER performance. Then, the conventional ICI self-cancellation methods are discussed and two kinds of ICI self-cancellation methods are newly proposed. Lastly, a new DFT-Spread OFDM system which selectively adopts the ICI self-cancellation technique is proposed to resolve the interference problem and PAPR reduction simultaneously. Proposednew DFT-Spread OFDM system can minimize performance degradation caused by phase noise, and still maintain the low PAPR property. Among the studied methods, DFT-Spread OFDM with data-conjugate method or newly proposed symmetric data-conjugate method show the significant performance improvements, compared with the DFT-Spread OFDM without ICI self-cancellation schemes. The data-conjugate method is slightly better than symmetric data-conjugate method.