Inter-carrier Interference Cancellation 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.

Joint fast time-varying channel estimation with noise elimination and ICI cancellation for LTE-V2X systems

Vehicle-to-everything (V2X) communication is essential for intelligent transportation systems (ITS) and critical technology to ensure traffic safety. Aiming at the problems of noise interference, time-varying, and inter-carrier interference (ICI) in the LTE-V2X channel, a joint fast time-varying channel estimation with noise elimination and ICI cancellation is proposed in this paper. Firstly, using the autocorrelation characteristics of the Zadoff Chu (ZC) pilot sequence, a modified discrete Fourier transform (M-DFT) channel estimation algorithm is proposed to eliminate the noise in cyclic prefix (CP). Secondly, a joint iterative direct decision (IDD) and time-varying channel fitting (CF), called IDD-CF channel estimation algorithm, is proposed to track the rapid changes of channels on different symbols and eliminate ICI. The system simulation results show that the proposed joint fast time-varying channel estimation algorithm can effectively eliminate the noise and ICI, improve the performance of channel estimation, and have better robustness under different Doppler frequency shifts than the representative channel estimation algorithm.

Non-Orthogonal DMT Enabled by Iterative ICI Cancellation Algorithm for Bandwidth-Limited IM/DD Optical Systems

In this paper, non-orthogonal discrete multi-tone (NO-DMT) is proposed for improving the performance of bandwidth-limited intensity-modulation and direct-detection (IM/DD) optical systems. The bandwidth of NO-DMT signal can be compressed to alleviate high-frequency distortions. Meanwhile, the adaptive bit and power loading in the NO-DMT can make full use of the SNR on each subcarrier. However, inter-carrier interference (ICI) is induced by the bandwidth compression, which significantly degrades the performance of NO-DMT. Therefore, we propose an iterative ICI cancellation algorithm for the NO-DMT, which is applicable to the large number of subcarrier and high-order modulation. For verifying the feasibility of the proposed scheme, a 50 Gbit/s NO-DMT system is experimentally demonstrated using 10 G-class optics at center wavelength of 1370 nm. Due to the limited bandwidth of the devices and the large chromatic dispersion at the wavelength of 1370 nm, the overall 10 dB bandwidth of the system is only approximately 10 GHz. Owing to the robustness to high-frequency distortions, the NO-DMT has 3 dB higher receiver sensitivity compared to DMT at the BER of <inline-formula><tex-math notation="LaTeX">$1.0\times 10^{-2}$</tex-math></inline-formula>. Thanks to the full use of SNR, the adaptive bit and power loading in NO-DMT improves approximately 6 dB receiver sensitivity. In conclusion, NO-DMT has the potential for application in bandwidth-limited IM/DD optical systems.

An Efficient ICI Cancellation Scheme to Mitigate the Effect of ICI on OFDM Systems.

Inter-carrier interference (ICI) emerges in orthogonal frequency division multiplexing (OFDM) systems used for mobile communication as a consequence of the Doppler Effect's loss of orthogonality among subcarriers. Inter-Carrier Interference (ICI), which affects every subcarrier, drastically lowers performance. The performance of OFDM systems may be enhanced using a variety of ICI mitigation strategies. Comparable subcarrier frequency offsets are guaranteed by the premise that the OFDM transmission bandwidth is suitably modest in the majority of ICI mitigation strategies, on the other hand. The frequency offsets between each subcarrier might change, hence a wideband OFDM system in a situation with high mobility is investigated. Furthermore, the suggested ICI cancellation approach, Total ICI Cancellation, does not reduce bandwidth efficiency or transmission rate. As an example, the Total ICI Cancellation approach uses the ICI matrix's orthogonality to provide perfect ICI cancellation and a significant boost in BER at a linearly increasing cost. The suggested technique, which matches the BER performance of a wideband OFDM system without ICI, offers the best BER performance possible in the presence of frequency offset and time shifts in the channel, according to simulation findings in the AWGN and multipath fading channels.

Multilevel Redundant Discrete Wavelet Transform (ML-RDWT) and Optimal Red Deer Algorithm (ORDA) Centred Approach to Mitigate the Effect of ICI, BER and CIR in a MIMO-OFDM System

Nowadays, there is a great demand for ultra-high data rate (UHDR) transmission on most 5th generation wireless networks. In this concern, the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) scheme is used on a large scale to achieve UHDR transmission with reduced inter-symbol interference (ISI) and inter-carrier interference (ICI). Discrete wavelet transform-based OFDM (DWT-OFDM) provides better orthogonality due to presence of orthogonal wavelets, which mitigates the effects caused by ISI and ICI. Also, it has extended bandwidth than the traditional OFDM systems. But a major drawback in this system is that it suffers from down sampling. The down-sampling effect reduces the actual size of the input bit streams. As a result, the system performance is degraded. For solving this problem, a multilevel redundant discrete wavelet transform (ML-RDWT) is used instead of DWT to achieve improved spectral performance. Here, complex down-sampling operation is eliminated. From the simulation outcomes, it is clearly viewed that effects caused by ICI, ISI and BER are mitigated by improving the performance of CIR. The proposed method employs optimal red deer algorithm (ORDA) to locate the optimized weights for the ICI cancellation system. This algorithm enhances the spectral efficiency by achieving high CIR with reduced BER, ISI and ICI. The BER in the proposed MIMO-ML-RDWT-OFDM-ORDA method is 68%, 76%, 38% and 75%, which is very low when compared to the BER in the existing techniques like MIMO-DWT-OFDM-RDA, MIMO-RNS-OFDM-PNMA, MIMO-OFDM-BMA and MIMO-OFDM-ICIMA. The ISI in the proposed method is 94%, 91%, 95% low when compared to the ISI in the existing techniques. The ICI in the proposed work is 71%, 57%, 73% and 86% low when compared to the ICI in the existing techniques. Therefore, the general performance of the proposed MIMO-ML-RDWT-OFDM-ORDA method is improved in an efficient way with less complexity, error rate and processing delay.

Joint fast time domain channel estimation with ICI cancellation for LTE-R systems

In this paper, we consider the high-speed railway (HSR) communication bases on the long-term evolution for railway (LTE-R) platform. Since the large Doppler spread is introduced due to the movement of the train, the orthogonality of subcarriers is destroyed resulting in the inter-carrier interference (ICI). Moreover, the critical speed of transceivers moving leads to a very fast-time varying channel within an OFDM symbol, hence the existing frequency domain channel estimation (FDCE) method cannot reliably estimate the channel state information (CSI). To better track the fast-time varying channel, we propose a new framework for LTE-R systems. First, we modify the WINNER II channel model and the D2a propagation scenario to approximate the multipath fading and high Doppler spread in high mobility scenarios. Second, we use a novel pilot structure-based time domain channel estimation (TDCE), helping to track the channel variations for each channel path separately. The CSI at data subcarriers is estimated by using different conventional interpolation methods to reconstruct the ICI channel matrix in the frequency domain. Different from the linear channel model, the channel time-variations of current OFDM data symbol are predicted from the third-order polynomial function, which is reconstructed base on CIR at the pilot position by using several constitutive OFDM symbols. The cubic Hermite function is chosen by considering its simplicity and efficiency. Lastly, we propose the deep neural network (DNN) based CE in LTE-R systems, which helps to further improve the accuracy of estimated channel information in the previous state, especially at low signal-to-noise (SNR) level. The simulation results show that our proposed CE method for each channel path agrees well with the theoretical derivation and the simulation. The system performance with the proposed framework is significantly improved in comparison with state-of-the-art methods.

A novel inter-carrier interference cancellation scheme in highly mobile environments

In the current multi-carrier communications, Orthogonal Frequency Division Multiplexing (OFDM) is widely considered as a leading technology. For mobile applications, however, the orthogonality between subcarriers is deteriorated by Doppler frequency shift, which will introduce serious subcarrier phase rotation in the received signals and degrade the system performance. Thus, a method of differential grouping weighted symmetry data-conjugate (DWSCC) have been previously presented to obtain a better inter-carrier interference (ICI) suppressing effect and Bit Error Rate (BER) performance with no loss of spectral efficiency. In this paper, a novel scheme applying a completely different method of subcarrier interactive mapping is put forward. By mapping two different symbols which are both conjugated or multiplied by a complex weighting factor onto a pair of symmetric subcarriers, the presented scheme can greatly reduce the influence of subcarriers phase rotation caused by Doppler frequency shift in highly mobile environments. Analysis and simulation results indicate that comparing with the DWSCC method, our formulated scheme can not only maintain the spectrum utilization with no loss, but also have the advantages of an improvement on reduction effect and BER performance as well as a lower computational complexity in highly mobile environments.

56 Gbit/s OOK Signal in C-band Over 20 km Dispersion-Uncompensated Link Transmission With Receiver-Side EDC Algorithm

In this paper, we propose and experimentally demonstrate a receiver-side electronic dispersion compensation (EDC) algorithm for direct-detection 56 Gbit/s on-off keying signal in C-band over 20 km dispersion-uncompensated standard single-mode fiber transmission. The proposed receiver-side EDC algorithm includes the feed-forward equalizer, post noise-whitening filter and modified iterative detection algorithm, which is originally used in spectrally efficient frequency division multiplexing systems for inter-carrier interference cancellation. Only with the aid of the proposed EDC algorithm for the compensation of power fading effect caused by bandwidth limit and chromatic dispersion, bit-error ratio below the 7% hard-decision forward error correction limit is achieved. This scheme can keep the system cost-effective and flexible, showing potentials for optical interconnects.

Intercarrier interference analysis for massive MIMO fractional Fourier transform‐OFDM systems over time‐varying channels

SummaryMassive multiple‐input multiple‐output orthogonal frequency division multiplexing (MIMO‐OFDM) system is an approach to increase data rate and spectral efficiency of 5G wireless communication systems. It's easy to analyze the performance of any system with the assumption of immobile users, but if the user is moving with varying velocity, then the communication between user and base station (BS) is very difficult to maintain. Under high mobility, rapidly fading, doubly dispersive, and nonstationary environment, the conventional system fails to respond and leads to the problem of intercarrier interference (ICI). To overcome these problems, fractional Fourier transform (FrFT) has been used in place of Fourier transform (FT) to increase the correlation coefficient, to mitigate effect of ICI, and to improve bit error rate. In this paper, novel formulae for correlation coefficient, average power of ICI, and closed form bit error expression have been derived for the proposed system by considering fast‐fading model and imperfect channel state information. Finally, the comparison of both the systems conventional and proposed proved that the proposed system has improved bit error rate by 40% and intercarrier interference cancelation by 70%.

Nonlinear-frequency-packing nonlinear frequency division multiplexing transmission.

A nonlinear frequency division multiplexing (NFDM) transmission system, designed specifically for nonlinear fiber channel, has the potential to overcome the nonlinear Shannon capacity limit. However, the spectral efficiency (SE) of the current proven NFDM transmission systems is still lower than that of the analogous orthogonal frequency division multiplexing system. It is extremely necessary to explore effective modulation scheme for the aim of increasing the SE of NFDM system. In this study, we first propose the nonlinear-frequency-packing nonlinear frequency division multiplexing (NFP-NFDM) transmission system. In NFP-NFDM, the spacing of nonlinear subcarriers is squeezed and more nonlinear subcarriers can be packed, but the inter carrier interference (ICI) is introduced. The method of NFP in nonlinear Fourier domain is carefully designed to reduce the complexity of ICI cancellation. Through numerical simulation, we illustrate the feasibility of NFP-NFDM transmission, and higher SE in NFP-NFDM than that of NFDM system is also demonstrated. The upper bound of the normalized SE for NFP-NFDM is estimated, which is higher than that of current NFDM system. Besides, we find out that the NFP scheme may have the advantage of reducing the signal-noise interaction in fiber transmission scenario, which indicates there may be a better way to load the data into the nonlinear Fourier domain.

BER Performance of Space–Time Parallel ICI Cancellation of OFDM in MIMO Power Line Communications

Most of the studies on power line communication (PLC) are focused on single-input-single output (SISO)-PLC. There have been recent empirical and/or theoretical research with the focus on multiple-input-multiple-output (MIMO)-PLC. This article analyzes the effects of correlation between different paths in MIMO-PLC on the performance of bit error rate (BER) and the channel capacity in the PLC system. Orthogonal frequency division multiplexing (OFDM) is an effective method to mitigate the effect of the frequency selective multipath fading channel in the PLC system. However, OFDM is susceptible to the imperfect orthogonality among its subcarriers caused by the frequency offset at the receiver. Intercarrier interference cancellation technique such as parallel cancellation (PC) scheme is implemented in MIMO-PLC scenario to study the effect of correlation based on the latest research in MIMO-PLC. 2 × 1 and 2 × 2 space-time (ST)-OFDM and 2 × 2 STPC-OFDM channel models are investigated for the performance of the BER and channel capacity in additive impulsive Gaussian noise via computer simulations. It shows that the BER and channel capacity of both 2 × 1 and 2 × 2 STPC-OFDM outperforms 2 × 1 and 2 × 2 ST-OFDM, respectively, regardless of the correlation between different paths in MIMO-PLC.

Iterative Multiuser Detection and Decoding for Sparse Code Multiple Access Combined With Spectrally Efficient Frequency Division Multiplexing

Sparse code multiple access (SCMA) combined with spectrally efficient frequency division multiplexing (SEFDM) is a wireless air-interface technology with dual non-orthogonal characteristic which can meet the high spectral efficiency requirement of the future Internet of Things (IoT). In this paper, an iterative multiuser detection/decoder (IMUDD) method for SCMA-SEFDM is proposed, which performs soft information iteration in a turbo style. IMUDD can effectively achieve the multiple-access interference (MAI), inter-symbol interference (ISI) and inter-carrier interference (ICI) cancellation through an external iteration and three internal iterative processes. At each iteration, extrinsic information is extracted from detection and decoding stages, then it is used as a priori information in the next iteration. Furthermore, to reduce the computational complexity of IMUDD scheme, a logarithm domain IMUDD is adopted and analyzed. The simulation results show that IMUDD has a noticeable performance improvement compared to the traditional turbo structured receivers over the multipath fading channel or the additive white Gaussian noise (AWGN) channel.

Efficient CFO Estimation and Compensation Approach in OFDMA for Uplink Mobile WiMax

Synchronization is a complex task in uplink Orthogonal Frequency Division Multiple Access (OFDMA) for Mobile WiMax as each user presents different Carrier Frequency Offsets (CFO). Synchronization begins with the CFO estimation and followed by the compensation of residual CFO present in the received signal. This paper deals with various techniques in time and frequency domains to compensate the effect of CFO on the received signal for different estimation techniques. SImple time domain MultiUser Interference Cancellation (SIMUIC) performs in time domain. It employs delays in the compensation of CFO while synchronizing the last user. Decorrelation Successive Interference Cancellation (DC-SC) and Integrated Estimation and Compensation (IEC) perform in frequency domain for the compensation of CFO. These approaches are more complex for Inter-Carrier Interference (ICI) cancellation. In this paper, we propose a new efficient CFO compensation technique in frequency domain for different estimation methods. This technique is a modified version of IEC for reducing the CFO effect on the received signal with lesser computations. Simulation results show that the modified IEC performs better than SIMUIC, DC-SC and IEC for different estimation methods.

Radius-aided QRM-MLD for faster-than-Nyquist non-orthogonal FDM systems

In this paper, a radius-aided maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD) is proposed for inter-carrier interference (ICI) cancellation in a faster-than-Nyquist non-orthogonal frequency-division multiplexing (FTN-NOFDM) system. With almost the same ICI cancellation performance, the radius-aided QRM-MLD has lower computational complexity than the conventional QRM-MLD by predicting the search radius with the radius-predicted symbol. There is not any redundancy induced by radius-predicted symbol because the transmitted data also can be obtained from it. In order to validate the proposed algorithm in the experiment, the 28-Gb/s FTN-NOFDM signal was transmitted through a bandwidth-limited experimental system, and the radius-aided QRM-MLD is applied for ICI cancellation. In this bandwidth-limited system, the 3-dB equivalent bandwidth is only approximately 5.5 GHz. The experimental results reveal that the bandwidth-compressed FTN-NOFDM with radius-aided QRM-MLD has better bit error rate performance than orthogonal frequency-division multiplexing, which shows the superiority of the proposed scheme in bandwidth-limited systems.

Partial ML Detection for Frequency-Asynchronous Distributed Alamouti-Coded (FADAC) OFDM

To further enhance frequency-asynchronous distributed Alamouti-coded (FADAC) orthogonal frequency division multiplexing (OFDM), we propose a new scheme which combines the partial maximum likelihood detection (PMLD) to the residual intercarrier interference cancellation (RIC). In order to decrease the performance gap from intercarrier interference- (ICI-) free level after single time iteration of the RIC, the final stage of the proposed scheme performs the PMLD limited to the symbols of less-reliable decision variables. We show that with the practically acceptable candidate symbol set size, a single iteration for RIC is enough to achieve the ICI-free performance. Moreover, the proposed scheme substantially expands the allowable ranges of the three undesirable terms, i.e., the timing and frequency offsets between the transmit antennas and the multipath delay spreads.

Performance analysis of MIMO-RDWT-OFDM system with optimal genetic algorithm

Multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) is required to achieve ultra-high data rate (UHDR) due to the increasing demand of 5th generation wireless networks with reduced inter symbol interference (ISI) and inter carrier interference (ICI) for the efficient transmission of data. Discrete wavelet transform-based OFDM (DWT-OFDM) presents itself as a key solution since it provides good orthogonality by employing orthogonal wavelets, which enclose further possibilities of ISI and ICI impacts mitigation because of multipath attenuation environs and extends the efficacy of further bandwidth which equate to the traditional OFDM systems. However, DWT-OFDM systems suffer from down sampling, which mitigates the actual size of input bit streams and thereby degrading the system efficiency. To resolve this, redundant discrete wavelet transform (R-DWT) is utilized in place of DWT for enhanced spectral efficiency. Further, mitigation of jitter noise with enhancement in the performance of CIR results in reduction of inter carrier interference (ICI) in MIMO-RDWT-OFDM system and is presented in this article. Proposed methodology utilizes optimal genetic algorithm (OGA) to find the optimized weights of proposed ICI cancellation scheme. This algorithm reduces complexity and processing delay, improves bit error rate (BER) performance and enhances the performance of CIR in MIMO-RDWT-OFDM system.

Positioning and Location-Aware Communications for Modern Railways with 5G New Radio

Providing high-capacity radio connectivity for high-speed trains (HSTs) is one of the most important use cases of emerging fifth generation (5G) New Radio (NR) networks. In this article, we show that 5G NR technology can also facilitate high-accuracy continuous localization and tracking of HSTs. Furthermore, we describe and demonstrate how the NR network can utilize the continuous location information for efficient beam management and beamforming, as well as for downlink Doppler precompensation in the single-frequency network context. Additionally, with particular focus on millimeter-wave networks, novel concepts for low-latency inter-carrier interference (ICI) estimation and compensation, due to residual Doppler and oscillator phase noise, are described and demonstrated. The provided numerical results at 30 GHz operating band show that sub-meter positioning and sub-degree beam direction accuracies can be obtained with very high probabilities on the order of 95-99 percent. The results also show that the described Doppler precompensation and ICI estimation and cancellation methods substantially improve the throughput of the single-frequency HST network.

Iterative channel estimation and pilot design rules for high‐mobility comb‐pilot OFDM system

SummaryWith wireless communications in high‐mobility environment becoming popular, this poses a big challenge for communication systems based on the comb‐pilot OFDM, such as IEEE 802.11p, since it has not the enough pilots to estimate the time‐ and frequency‐selective channel accurately. In this paper, several comb‐pilot schemes and three comb‐pilot design rules are proposed to meet the Nyquist criterion for sampling the vehicle‐to‐vehicle (V2V) channel and the requirements of second‐order statistic of V2V channel. Based on the proposed pilot schemes, an iterative channel estimation method from the CE‐BEM model is proposed, together with three ICI cancellation methods. After thorough simulation, the effectiveness of the comb‐pilot design rules, the proposed channel estimation method, and intercarrier interference (ICI) cancellation methods is verified. Compared with other channel estimation methods, the proposed method performs better. The simulation results also reveal that the channel order L+1 has a great impact on the performance of the comb‐pilot OFDM system.

ID Insertion and Data Tracking with Frequency Offset for Physical Wireless Parameter Conversion Sensor Networks.

As the applications of the internet of things are becoming widely diversified, wireless sensor networks require real-time data reception, accommodation of access from several sensors, and low power consumption. In physical wireless parameter conversion sensor networks (PhyC-SN), all the sensors use frequency shift keying as the modulation scheme and then access the channel to the fusion center, simultaneously. As a result, the fusion center can recognize the statistical tendency of all the sensing results at a time from the frequency spectrum of the received signal. However, the information source, i.e., the sensor, cannot be specified from the received signal because no ID-indicating sensor is inserted to the signal. The data-tracking technique for tracing the time continuity of the sensing results is available for decomposing the sequence of the sensing results per sensor but the error tracking, which is a wrong recognition between the sensing results and the sensor, occurs owing to the similarity of the sensing results. This paper proposes the sensing result separation technique using a fractional carrier frequency offset (CFO) for PhyC-SN. In the proposed scheme, the particular fractional CFO is assigned to each user and it is useful for the ID specifying sensor. The fractional CFO causes inter-carrier interference (ICI). The ICI cancellation of the narrowband wireless communications is proposed. The two types of data-tracking techniques are proposed and are selectively used by the fusion center. Since the proposed data-tracking technique is multi-dimensional, high accuracy of data tracking is achieved even under the similar tendency of the sensing results. Based on computer simulation, we elucidate the advantage of the proposed sensing results separation.

ICI Cancellation Based on MIMO Decoding for FTN Non-Orthogonal FDM Systems

In this paper, we investigate multiple-input multiple-output (MIMO) decoding in faster-than-Nyquist non-orthogonal frequency-division multiplexing (FTN-NOFDM) for inter-carrier interference (ICI) cancellation. The MIMO decoding is based on depth-first tree search or breadth-first tree search. The sphere decoder (SD) is a commonly used decoding algorithm based on the depth-first tree search. Maximum-likelihood detection with QR decomposition and M-algorithm (QRM-MLD) is a commonly used decoding algorithm based on the breadth-first tree search. By adding the initial radius to both SD and QRM-MLD, the computational complexity of these can be further decreased without the loss of the ICI cancellation performance. In the experiment, SD, QRM-MLD, and their corresponding simplified versions are used for the ICI cancellation in a 28-Gb/s FTN-NOFDM system with transmission over a 10-km standard single-mode fiber. The 3-dB equivalent bandwidth of this system is only approximately 5.5 GHz. Under serious high-frequency distortion caused by limited bandwidth, the bit error rate performance of the FTN-NOFDM can still reach the forward error correction limit due to the bandwidth compression and effective ICI cancellation. FTN-NOFDM with 20% and 30% bandwidth savings has approximately 1.3- and 1.1-dB improvements in receiver sensitivity compared to FTN-NOFDM with 10% bandwidth savings, respectively. To the best of our knowledge, this paper is the first experimental demonstration of the depth-first tree search and breadth-first tree search for FTN-NOFDM in a bandwidth-limited optical transmission system. The experimental results show that FTN-NOFDM is a promising scheme for bandwidth-limited systems.