Intercarrier Interference Self-cancellation Scheme Research Articles

Performance analysis of ICI self-cancellation schemes in OFDM systems

Abstract Orthogonal frequency division multiplexing (OFDM) is a promising technique in modern high data rate wireless communication system. However, the serious problem in OFDM system is the inter-carrier-interference (ICI) that is produced by the carrier frequency offset (CFO). CFO destroys the orthogonal properties among the sub-carriers and introduces ICI. ICI is a major impairment in OFDM system as it can degrade the bit error rate (BER) performance of the system. In this paper we have proposed an optimal ICI self-cancellation scheme that can maximize the carrier-to-interference-ratio (CIR) of the system. This scheme is based on optimizing the data allocation and combining parameters where, for estimated CFO, the optimized values of these parameters are calculated using Nelder Mead simplex algorithm. An approach to calculate the sub-optimized values of data allocation and combining parameters is also proposed, where the knowledge of CFO estimation can be avoided. In this paper, we have carried out the complete performance analysis of ICI self-cancellation schemes. We have also derived the mathematical expressions for ICI coefficients and presented a comparative analysis of standard OFDM system with different ICI cancellation schemes. The mathematical expressions for CIR and BER performance are further derived. To confirm the validity of the results Monte Carlo simulations using Matlab are also performed. We have also done the comparison of peak-to-average power ratio (PAPR) of conventional ICI self-cancellation scheme and proposed scheme.

Performance evaluation of ICI self-cancellation schemes in fractional wavelet-based OFDM system

The widely used multi carrier modulation technique in the current wireless scenario is orthogonal frequency division multiplexing (OFDM). It is severely affected by frequency offsets and leads to inter carrier interference (ICI). Fractional wavelet transforms (FrWT)-based OFDM model is proposed to mitigate the effect of ICI by its orthogonal fractional wavelets. The performance of FrWT involved OFDM model is comparatively analysed through various mapping schemes of ICI self-cancellation in order to mitigate frequency offsets. This system overcomes the drawback of ICI self-cancellation and shows improved bandwidth efficiency without any cyclic prefix. Simulation results are carried out for the proposed model and compared with exiting Fourier transform and wavelet transform-based OFDM system. The analysis is performed for a range of normalised frequency offsets values. The proposed model performance is tested with various mapping schemes against a frequency offset of 0.05. It is proved that FrWT-based OFDM with ICI self-cancellation gives reduced bit error rate (BER) of 10–5 at 8 dB signal to noise ratio (SNR). From various graphs, it states that weighted conjugated transformation results in effective mitigation of ICI with BER achievement of 10-4.4 at frequency offset of 0.1.

A Novel ICI Triple Cancellation Scheme in Fast Time-varying Environment for OFDM Systems

In fast time-varying environment, orthogonal frequency division multiplexing (OFDM) systems lose the orthogonality between subcarriers due to the Doppler effect, resulting in inter-carrier interference (ICI), which greatly affects the performance of the communication system. Based on the analysis of the principle of ICI generation in time-varying environment, an ICI triple cancellation scheme is proposed to reduce the ICI of the OFDM systems in fast time-varying environment. In the scheme, the ICI self-cancellation modulation is performed at the transmitter of the OFDM system. Then, the time-varying channel is modeled as a linearly time-varying (LTV) model for ICI dual cancellation. Finally, the ICI self-cancellation demodulation is executed at the receiver of the system. Simulation experiment results show that the proposed ICI triple cancellation scheme can achieve a better effect of ICI cancellation than ICI self-cancellation scheme and ICI dual cancellation scheme, improving the performance of the communication system.

Linear Processing for Intercarrier Interference in OFDM Index Modulation Based on Capacity Maximization

In this letter, we study the linear processing method to alleviate the intercarrier interference (ICI) for the orthogonal frequency division multiplexing (OFDM) index modulation (IM) in the rapidly time-varying (RTV) channel. Concretely, the proposed linear processing scheme is implemented by the joint design of the transmit precoding and receive postprocessing matrices. First, a lower bound of the capacity of OFDM-IM in the RTV channel is derived. Then, the precoding and postprocessing matrices are designed to maximize this capacity lower bound through utilizing the particle swarm optimization algorithm. Computer simulations show that the proposed scheme can alleviate the ICI effectively and has better performance than the conventional ICI self-cancellation scheme.

Efficient ICI Self-Cancellation Scheme for OFDM Systems

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.

ICI Cancellation in OFDM Systems by Frequency Offset Reduction

The rapid growth within the field of digital communication during the recent years expanded the need for high-speed data transmission to support a wide range of services such as: video, data and voice in wireless communication systems, etc. Orthogonal frequency division multiplexing (OFDM) and a multicarrier modulation scheme are employed to achieve the high data rates. Since OFDM is very much sensitive to carrier frequency offsets, which cause the Inter-carrier Interference (ICI) leads to mitigation of this ICI is necessary. The objectives of this paper are to, proposed an efficient ICI self-cancellation scheme to mitigate the effect of ICI on OFDM systems. For this purpose, a redundant data is transmitted onto adjacent sub-carriers such that the ICI between adjacent sub-carriers cancels out at the receiver side. One data symbol is modulated into a group of adjacent sub carriers with a group of weighting coefficients. At the receiver side, the received signals are linearly combined on these sub carriers with proposed coefficients. The residual ICI contained in the received signals can then be further reduced. This study provides significant carrier-to-interference power ratio (CIR) improvement, which has been studied theoretically and supported by simulations. Since no channel equalization is required to reduce ICI, so the proposed scheme doesnt increase the system complexity.

On the CFO estimation of the OFDM: A frequency domain approach

This paper presents a simple yet effective carrier-frequency-offset (CFO) estimation algorithm for orthogonal-frequency-division-multiplexing (OFDM) system using a general inter-carrier interference (ICI) self-cancellation scheme. The key feature of the proposed algorithm is that it has a significantly wider CFO estimation range than the maximum-likelihood (ML) algorithm. The proposed algorithm first constructs the snapshot vectors through stacking the signals in each subcarrier group of the precoded OFDM symbol. Because the ICI self-cancellation scheme can suppress the inter-group ICIs, the snapshot vectors can be expressed in a form having a CFO-directed response structure. This enables the proposed approach to estimate the CFO by using the multiple signal classification (MUSIC) algorithm in the frequency domain.

A Subspace-Based CFO Estimation Algorithm for General ICI Self-Cancellation Precoded OFDM Systems

This paper presents a carrier-frequency-offset (CFO) estimation algorithm for time-dispersive orthogonal frequency division multiplexing (OFDM) system using a general inter-carrier interference (ICI) self-cancellation scheme. This study uses the time shift invariant property in the precoded signal to estimate the CFO. To achieve this, the proposed algorithm first collects the highly correlated receive time samples into snapshot vectors. The snapshot vectors can be expressed in a form having a CFO-directed response structure, which enables the proposed approach to estimate the CFO by using the multiple signal classfication (MUSIC) algorithm in the time domian. This study also develops a time sample selection scheme to mitigate the noise enhancement caused in the equalization process before the MUSIC algorithm. As compared to conventional algorithms, in addition to having an estimation error approaching to the Cramer-Rao lower bound (CRLB), the proposed algorithm has an adjustable CFO estimation range linearly proportional to the order of the ICI self-cancellation scheme.

The Research of An Algorithm Based on Symmetric Symbols for ICI Self-Cancellation in OFDM System

The intercarrier interference (ICI) will occur when the orthogonality between subcarriers is destroyed in orthogonal frequency division multiplexing (OFDM) communication system. ICI caused by frequency offsets is analyzed, and an algorithm based on symmetric symbols is proposed after researching on the typical ICI self-cancellation scheme. The simulation results show that, compared with the self-cancellation scheme, this algorithm not only reduces the intercarrier interference (ICI) coefficient, but also greatly improves the carrier-to-interference power ratio (CIR) and the performance of the system.

A Spectrally Efficient Intercarrier Interference Reduction Scheme for Orthogonal Frequency Division Multiplexing Systems in Low Signal-to-noise Ratio Environment

The inherent sensitivity of orthogonal frequency division multiplexing (OFDM) systems to any frequency shift in the signal makes their design very challenging. In OFDM systems, the frequency shift may be due to instability of transmitter/ receiver oscillators or because of fading channel. The frequency shift in the signal destroys the orthogonality among subcarriers and results in intercarrier interference (ICI), which affects the system performance severely. A number of solutions are available to mitigate the effect of ICI. The existing ICI mitigation techniques include frequency equalization, time domain windowing, ICI self-cancellation, coding, etc., Among several ICI reduction methods, ICI self-cancellation scheme has received much attention due to its simplicity. The ICI mitigation schemes that depend on carrier frequency offset (CFO) correction at the transmitter are effective under high signal-to-noise ratio (SNR) scenario and those that depend on CFO estimation and correction at the receiver have additional computational complexity and some sort of data symbol redundancy. In this paper, a bandwidth-efficient ICI reduction method for M-ary QAM signals is proposed. The present method is effective in low SNR environment. This method reduces the effect of ICI and improves the performance of the system in terms of bit error rate. It is shown that the proposed ICI cancellation method considerably outperforms the existing ICI self-cancellation schemes in the presence of small CFO while maintaining the throughput level.

Repeated correlative coding scheme for mitigation of inter-carrier interference in an orthogonal frequency division multiplexing system

In this study, a repeated correlative coding scheme is proposed to combat the inter-carrier interference (ICI) caused by the frequency offset in orthogonal frequency division multiplexing (OFDM) communication systems. This proposed scheme combine two ideas of the well-known methods, which are the coding of adjacent subcarriers with antipodal of the same data symbol (ICI self-cancellation) and correlative coding. A mathematical expression for the carrier-to-interference ratio (CIR) by using this proposed repeated correlative coding scheme is derived. The simulated result of CIR for the proposed scheme is significantly improved compared to the correlative coding as well as a self-cancellation scheme. The bit-error-rate (BER) of the proposed scheme is also compared with the ICI self-cancellation scheme and correlative coding scheme, which is comparable to that of the ICI self-cancellation scheme and better than the correlative coding scheme.

A novel ICI self-cancellation scheme for OFDM systems

We propose a novel intercarrier interference (ICI) self-cancellation scheme for orthogonal frequency division multiplexing (OFDM) systems. The symmetric scheme is the best among all ICI self-cancellation scheme in the literature. Its coefficient pair is (1, − 1), and the loading subcarriers are the kth and N−k − 1th subcarriers, where N is the number of subcarriers. We propose to modify the symmetric scheme and change the coefficient pair from (1, − 1) to (1, −µ) where µis between 0 and 1. The proposed modified symmetric scheme has better carrier-to-interference-ratio (CIR) than all previous ICI self-cancellation schemes by at least 1.7 dB when the normalized frequency offset is 0.5. Copyright © 2011 John Wiley & Sons, Ltd.

Optimum weighting-coefficient-pair in inter-carrier interference self-cancellation scheme of OFDM system

As one of the most important components of the wideband wireless access technique, orthogonal frequency division multiplexing (OFDM) has a high usage rate of spectrum and combats inter-symbol interference (ISI) in multi-path fading channel. However, when there are frequency offsets during the signal transmission, the inter-carrier interference (ICI) is introduced, which significantly degrades the performance. The existing ICI self-cancellation schemes such as PCC-OFDM are not optimum to minimize the interference considering both noise and ICI. In this paper, a new metric named SINR (signal-to-interference-and-noise ratio) is proposed. We discuss the optimization issue when a constant frequency offset exists and in time-varying channels. The optimum weighting-coefficient-pair (OWCP) is obtained, which maximizes SINR theoretically through the alternant iteration algorithm. Simulations show that the performance of OWCP-OFDM is better than that of PCC-OFDM, especially when the frequency offset is large. Although the ICI self-cancellation scheme suffers bandwidth inefficiency, from the simulation results we can also see that the performance of OWCP-OFDM is much better than that of the standard OFDM systems with the same bandwidth efficiency when a frequency offset exists. Moreover, since the redundant modulation provides the capability to suppress ICI as well as a receiving SNR gain, it can be considered as exchanging the bandwidth for SNR.

Performance evaluation for PCC-OFDM systems impaired by carrier frequency offset over AWGN channels

Orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO), which destroys the orthogonality and causes inter-carrier interference (ICI). ICI self-cancellation schemes based on polynomial cancellation coding (PCC-OFDM) can evidently reduce the sensitivity to CFO. In this paper, we analyze the performance of PCC-OFDM systems impaired by CFO over additive white gaussian noise (AWGN) channels. Two criteria are used to evaluate the effect of CFO on performance degradations. Firstly, the closed-form expressions of the average carrier-to-interference power ratio (CIR) and the statistical average ICI power, both of which reflect the desired power loss, are presented. Simulation and analytical results show that the theoretical expressions depend crucially on the normalized frequency offset and are hardly relevant to the number of subcarriers. Secondly, by exploiting the properties of the Beaulieu series, the effect of CFO on symbol error rate (SER) and bit error rate (BER) performance for PCC-OFDM systems are exactly expressed as the sum of an infinite series in terms of the characteristic function (CHF) of ICI. We consider the systems modulated with binary phase shift keying (BPSK), quadrature PSK (QPSK), 8-ary PSK (8-PSK), and 16-ary quadrature amplitude modulation (16-QAM), and all above modulation schemes are mapped with Gray codes for the evaluations of BER.

An Improved ICI Self-Cancellation Scheme for Multi-Carrier Communication Systems

For broadband wireless mobile communication systems the orthogonal frequency division multiplexing (OFDM) is a suitable modulation scheme. The frequency offset between transmitter and receiver local oscillator is main drawback of OFDM systems, which causes intercarrier interference (ICI) in the subcarriers of the OFDM system. This ICI degrades the bit error rate (BER) performance of the system. In this paper an improved self-ICI cancellation scheme is proposed to improve the system performance. The proposed scheme is based on discrete Fourier transform-inverse discrete Fourier transform (DFT-IDFT). The simulation results show that there is satisfactory improvement in the bit error rate (BER) performance of the present scheme. Keywords—OFDM, Intercarrier Interference, Interference Coefficients, DFT based Self-ICI Cancellation. I. INTRODUCTION FDM is an emerging modulation scheme in the current broadband wireless mobile communication system due to the high spectral efficiency and robustness to multi-path interference (1). A well-known disadvantage of the OFDM system is its sensitivity to frequency offset between transmitted and received signals, which may be caused by Doppler shift in the channel (2), or by the difference between the transmitter and receiver local oscillator frequencies. The carrier frequency offset causes loss of orthogonality and then the signals transmitted on each carrier are not independent of each other, thus leading to ICI (3). All the methods, available in the literature, that have been developed to reduce the effect of frequency offset can be divided into two groups. In first group, the frequency offset in OFDM systems is estimated and corrected at the receiver side and in the second group the frequency offset is reduced at the transmitter side. The first group is termed as the frequency offset estimation and correction, not considered in this paper. Here the second group, called frequency-offset reduction, is considered. In the frequency offset reduction approaches (2, 4-6), available in the literature, either a guard interval or redundant modulation is necessary in order to achieve a trade-

Decision Feedback Frequency Offset Estimation and Tracking for General ICI Self-Cancellation Based OFDM Systems

Inter-carrier interference (ICI) self-cancellation schemes were often employed in many OFDM systems as a simple and effective approach to suppress ICI caused by carrier frequency errors. The same procedure, however, can not perform very well at high frequency offsets. We propose a simple decision feedback scheme based on the general ICI self-cancellation scheme to perform estimation and tracking of the carrier frequency offsets. A system with the scheme does not consume additional bandwidth since it used the same data symbols employed for ICI cancellation for the estimation. After an initial estimation is completed, the scheme switches to the tracking mode to carry out the estimation of deviations in the frequency offsets. Finally this fine-tuned estimate is applied to the ICI self-cancellation scheme concurrently for frequency offset correction and hence improved the system performance greatly. Simulation results showed that our scheme allowed up to 9% of random variations in the frequency offset. The effectiveness of our scheme is further verified by calculating the bit error rate performance of various OFDM receivers.

ML Estimation of Frequency Offset for General ICI Self-Cancellation Based OFDM Systems

We develop a maximum likelihood estimation scheme for correcting the carrier frequency offsets prior to the general intercarrier interference (ICI) self-cancellation in the OFDM systems. Since the same data symbols employed for ICI self-cancellation are also used for frequency offset estimation, the proposed scheme does not consume additional bandwidth. The combined use of the estimation algorithm and ICI self-cancellation scheme provides both frequency offset compensation and ICI reduction hence improves the system performance greatly. The effectiveness of the proposed estimation-cancellation scheme is further verified by calculating the bit error rates of various OFDM receivers, and substantial improvements are found.

Pilot-Aided ICI Self-Cancellation Scheme for OFDM Systems

In this letter, a novel pilot-aided inter-carrier interference (ICI) self-cancellation scheme is proposed for use in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme maps both modulated data symbols and pre-defined pilot symbols onto non-neighboring sub-carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols, a more accurate estimation of frequency offsets can be obtained, and the ICI self-cancellation demodulation can be operated properly.

Performance evaluation of an ICI self-cancellation coded transceiver for mobile DVB-T applications

Digital video broadcasting-terrestrial (DVB-T) is an important multimedia technology capable of high data-rate transmission. Orthogonal frequency division multiplexing (OFDM) has been the backbone technique in the current DVB-T systems adopted by Europe and Japan. However, since the OFDM system is very sensitive to the frequency synchronization and phase errors, which induces the intercarrier interference (ICI), the ongoing research has been dedicated to this ICI problem in the presence of the Doppler frequency drift and the fading channels. A means to deal with the ICI problem is called the ICI self-cancellation or polynomial cancellation coding scheme. In this paper, we establish the complete simulation environment for the physical layer of the DVB-T system and then evaluate the effectiveness of the ICI self-cancellation coding scheme compared with the existing convolutional coding scheme for different fading channels and different Doppler frequencies. According to our simulation results, we conclude that the ICI self-cancellation scheme significantly outperforms the convolutional coding scheme which is adopted by the existing DVB-T standard for the AWGN and the frequency non-selective fading channels, but both schemes have the similar performance in the frequency-selective fading channels.

Robust ICI Self-cancellation OFDM Receiver with Dynamic Phase and Amplitude Estimations

Orthogonal frequency division multiplexing (OFDM) has been applied in the current wireless local-area networks and digital video broadcasting since it is robust against the frequency-selective channels. However, there is still a crucial intercarrier-interference (ICI) problem due to Doppler effect, local frequency drift and sampling clock offset, associated with OFDM systems. Recently ICI self-cancellation schemes have been proposed to significantly reduce the ICI and empirically they greatly outperform the convolutional coding schemes adopted by the IEEE 802.11 standard. However, all existing ICI self-cancellation receivers are still sensitive to the phase and amplitude ambiguities due to the phase offset, the local oscillator frequency drift and the multipath reflections. Therefore, in this paper, a novel receiver design integrating the ICI self-cancellation with a proposed dynamic phase and amplitude estimation mechanism is introduced, which can well solve the ambiguity problem. The Monte Carlo simulation results show that our phase and amplitude estimators can greatly decrease the error probability for the final symbol detection in the ICI self-cancellation OFDM receivers.