Effect Of Inter-carrier Interference Research Articles

Index modulation-based efficient technique for underwater wireless optical communications

This paper presents and experimentally demonstrates energy and spectral efficient index modulation (IM) scheme for underwater wireless optical communications (UWOC). The proposed scheme utilizes IM with direct-current optical orthogonal frequency division multiplexing which is based on discrete Hartley transform (DHT-OFDM) instead of conventional discrete Fourier transform-based OFDM (DFT-OFDM). Although DHT-OFDM has been previously studied in various applications such as optical and wireless communications, this is the first work that practically investigates it with the UWOC system. In this paper, we first demonstrate that DHT-OFDM can inherit all advantages of conventional DFT-OFDM with less computational complexity and higher robustness to the inter-carrier interference (ICI). Therefore, the DFT process is employed at receiving end instead of DHT to guarantee low-complexity frequency-domain estimation and equalization processing and ensure that shorter required pilot overheads are required to track the UWOC channel effects. Furthermore, IM-DHT-OFDM has been presented to provide better flexibility of spectral and energy efficiency (SE/EE) to UWOC and offers higher robustness to the ICI effect as the transmitted data is modulated and physically transmitted via some active subcarriers while others must be kept idle. For instance, IM-DHT-OFDM provides up to 50% spectral efficiency improvement compared to DFT-OFDM and DHT-OFDM with better performance over the UWOC system. Simulation and experimental tests, performed over 2-meter UWOC, are provided to demonstrate the outperformance of the proposed schemes against the existing benchmarks in terms of bit error rate (BER), achieved SE, peak-to-average ratio (PAPR), and computational complexity.

Outage Analysis of Sparse Vector Coding-Based Downlink Multicarrier NOMA for URLLC

Ultra-reliable and low latency communication (uRLLC) is a promising use case in the fifth generation and beyond systems for critical and delay-sensitive applications with aid of short packet transmission. Nevertheless, multi-carrier non-orthogonal multiple access (MCNOMA) is a promising technique to achieve spectral efficiency and massive connectivity, however, inter-carrier interference (ICI) stands out to be a major downside. Recently, sparse vector coding (SVC) is proposed to fulfill the trade-off between reliability and latency, thereby achieving the benchmarks of uRLLC. In this paper, SVC based downlink MCNOMA (SVC-MCNOMA) system is considered and first it is shown that SVC-MCNOMA is free from ICI due to the sparse nature of the information. Further, compressed sensing-based recovery at the receiver end helps in reducing the latency as well as enhances reliability. Moreover, to study the system performance, this paper derives the closed form outage expressions of the SVC-MCNOMA system over the Rician fading channel and through Monte-Carlo simulation, the analytical results are validated. The analyses demonstrate that SVC-MCNOMA outperforms conventional MCNOMA (C-MCNOMA), thereby achieving spectral efficacy, ultra-reliability with low latency and eradicates the effect of ICI.

Doubly selective channel estimation and equalization based on ICI/ISI mitigation for OQAM-FBMC systems

Over a doubly selective channel, broadband transmission systems face challenges in channel estimation and equalization. High mobility causes inter-carrier interference (ICI), while multipath transmission induces inter-symbol interference (ISI). In this paper, we present a mitigation method of ICI/ISI for the offset quadrature amplitude-modulated filter bank multi-carrier (OQAM-FBMC) system. It features low inherent imaginary interference (IMI) sensitivity and high efficiency. Specifically, a pilot indices optimization algorithm and a sparse adaptive orthogonal subspace pursuit (SAOSP) algorithm are presented based on the 2-D channel modeling scheme. The guard pilots are first added to mitigate the effect of ICI. Then the index optimization and SAOSP algorithms are applied to achieve a high-accuracy estimation of sparse channel coefficients. In addition, a threshold judgment suboptimal minimum mean square error (MMSE) equalization method is presented based on the variability of the interference power. The method uses normalized interference power thresholds to estimate the ISI dimension and reduce the equalization data, thus mitigating the effect of ISI and achieving efficient equalization. To verify the above methods, single-input-single-output (SISO) and multiple-input-multiple-output (MIMO) models are built. Simulation results indicate a 3-5 dB improvement in channel estimation accuracy. The suboptimal MMSE equalization results are close to the optimal MMSE with about four orders of magnitude reduction in complexity.

Precoded Filterbank Multicarrier Index Modulation With Non-Orthogonal Subcarrier Spacing

In this paper, we propose a novel precoded non-orthogonal frequency division multiplexing (NOFDM) with subcarrier index modulation (SIM) to increase spectral efficiency for multicarrier systems. The proposed NOFDM-SIM scheme is constituted by a filterbank multicarrier system under reduced subcarrier spacing, where precoded index modulated symbols are mapped onto the subcarriers. The detrimental effects of inter-carrier interference (ICI) resulting from the non-orthogonality between subcarriers are efficiently mitigated with the aid of eigenvalue-decomposition-based precoding. Our simulation results demonstrate that the proposed precoded NOFDM-SIM system exhibits a similar peak-to-average power ratio to OFDM and OFDM-SIM counterparts while achieving the bit error rate limit of zero-ICI OFDM in a channel-uncoded setting. We analyze the power spectral density of the proposed scheme to demonstrate that the proposed scheme is strictly bandlimited, unlike its orthogonal counterpart. Furthermore, we present detailed investigations of the effects on ICI in the proposed scheme with and without precoding as well as power allocation. Finally, we introduce a three-stage iterative decoding architecture for our proposed scheme and show near-capacity error performance.

SDFnT-Based Parameter Estimation for OFDM Radar Systems with Intercarrier Interference

The orthogonal frequency division multiplexing (OFDM) radar suffers from severe performance degradation in range-velocity estimation in high mobility scenarios. In this paper, a novel intercarrier interference (ICI)-free parameter estimation method for OFDM radar is proposed. By employing a scale discrete Fresnel transform (SDFnT), the OFDM radar signals are converted to the scale Fresnel domain, and the orthogonality of subcarriers can be recovered with the optimal scale factor. Furthermore, due to the compatibility of the SDFnT and the discrete Fourier Transform (DFT), the proposed method has low computational complexity and high feasibility for OFDM radar implementation. Simulation results show that the proposed SDFnT-based scheme effectively eliminates the ICI effect for single and multiple targets and achieves high accuracy delay-Doppler estimation for OFDM radar systems in circumstances of high velocity and low SNR with consistency and robustness.

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.

MIMO-OFDM Joint Radar-Communications: Is ICI Friend or Foe?

Intercarrier interference (ICI) poses a significant challenge for OFDM joint radar-communications (JRC) systems in high-mobility scenarios. In this paper, we propose a novel ICI-aware sensing algorithm for MIMO-OFDM JRC systems to detect the presence of multiple targets and estimate their delay-Doppler-angle parameters. First, leveraging the observation that spatial covariance matrix is independent of target delays and Dopplers, we perform angle estimation via the MUSIC algorithm. For each estimated angle, we next formulate the radar delay-Doppler estimation as a joint carrier frequency offset (CFO) and channel estimation problem via an APES (amplitude and phase estimation) spatial filtering approach by transforming the delay-Doppler parameterized radar channel into an unstructured form. To account for the presence of multiple targets at a given angle, we devise an iterative interference cancellation based orthogonal matching pursuit (OMP) procedure, where at each iteration the generalized likelihood ratio test (GLRT) detector is employed to form decision statistics, providing as by-products the maximum likelihood estimates (MLEs) of radar channels and CFOs. In the final step, target detection is performed in delay-Doppler domain using target-specific, ICI-decontaminated channel estimates over time and frequency, where CFO estimates are utilized to resolve Doppler ambiguities, thereby turning ICI from foe to friend. The proposed algorithm can further exploit the ICI effect to introduce an additional dimension (namely, CFO) for target resolvability, which enables resolving targets located at the same delay-Doppler-angle cell. Simulation results illustrate the ICI exploitation capability of the proposed approach and showcase its superior detection and estimation performance in high-mobility scenarios over conventional methods.

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.

Performance Analysis of Improved Self Cancellation Technique for Wavelet Based OFDM Through Simulink Model

As per the most recent literature, Orthogonal Frequency Division Multiplexing (OFDM), a multi access technique, is considered most suitable for the 3G, 4G and 5G techniques in high speed wireless communication. What made OFDM most popular is its ability to deliver high bandwidth efficiency and superior data rate. Besides it, high value of peak to average power ratio (PAPR) and Inter Carrier Interference (ICI) are the challenges to tackle down via appropriate mitigation scheme. As a research contribution in the present work, an improved self-cancellation (SC) technique is designed and simulated through Simulink to mitigate the effect of ICI. This novel proposed technique (Improved SC) is designed over discrete wavelet transform (DWT) based OFDM and compared with conventional SC scheme over different channel conditions i.e. AWGN and Rayleigh fading environments. It is found that proposed DWT-OFDM with Improved SC scheme outperforms conventional SC technique significantly, under both AWGN and Rayleigh channel conditions. Further, in order to justify the novelty in the research contribution, a Split-DWT based Simulink model for Improved SC scheme is investigated to analyse the BER performance. This Split-DWT based Simulink model presented here foretells the future research potential in wavelet hybridization of OFDM to side-line ICI effects more efficiently.

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%.

Generalized OFDM-IM With Noncoherent Detection

This paper generalizes the conventional noncoherent OFDM-IM systems by allowing selection of different numbers of active subcarriers for message representation. We then present the maximum-likelihood (ML) detection rule for frequency-selective block fading channels. The performance of the ML receiver is analyzed in terms of pairwise-error probability as well as diversity order. Asymptotic analysis of the proposed system reveals the role of partial Hamming distance in designing diversity-exploiting activation patterns. Practical issues including low-complexity receiver, and code (activation pattern) design techniques are discussed. Furthermore, the effect of inter-carrier interference in fast fading scenarios, and generalization of the technique to multiple-antenna scenarios are studied. Finally, we present simulation results to illustrate performance benefits of the generalized OFDM-IM systems over the conventional noncoherent OFDM-IM systems.

An Efficient Carrier Frequency Offset Tracking for OFDMA Systems Using Normalized Least-Mean-Square Algorithm

In orthogonal frequency-division multiple access (OFDMA), carrier frequency offset (CFO) destroys the orthogonality between subcarriers due to Doppler effect of the channel and also causes inter-carrier interference (ICI) as well as multiple access interference (MAI). In this paper, CFO tracking algorithm for OFDMA system is presented to overcome the effect of ICI as well as MAI. The proposed algorithm employs normalized least-mean-square (NLMS) algorithm which tracks the residual carrier frequency offset in OFDMA system. The proposed NLMS-based tracking algorithm uses average of all residual carrier frequency offset (RCFO) for improving the mean square error (MSE) performance. The proposed NLMS-based frequency tracking along with frequency offset compensator improves the error performance by reducing the effect of ICI and MAI. Simulation results indicate that the proposed algorithm achieves better tracking performance in the presence of frequency offset. From the results, it is observed that the MSE of the proposed estimator is improved about 3.8 dB at SNR = 20 dB with the frequency offset.

Analytical method of parameter determination for OFDM system over measurement-based underwater acoustic channel modeling

In underwater acoustic (UWA)-OFDM systems, the major problem in implementation of complex equalization algorithms at receiver can be avoided by finding appropriate system parameters. This paper proposes an analytical method for determining the UWA-OFDM system parameters in order to maximize the achievable system capacity and to limit interference power. Unlike most existing research studies that analyzed the system performance without consideration of the inter-carrier interference (ICI), we focus on evaluating the UWA-OFDM system performance under both the ambient noise and ICI effect. The signal-to-interference-plus-noise ratio and the achievable system capacity are formulated by using the simulation UWA channel model, which is derived from the measurement data of the real UWA channel from a very shallow water environment in West Lake, Hanoi, Vietnam. Using the proposed method, the UWA-OFDM system parameters including the symbol duration, the number of subcarriers, the system bandwidth, and the transmit power are determined to achieve the maximal spectral efficiency of 3.2bits/sec/Hz. The proposed analytical method can be used as a practical guideline to determine appropriate transmission parameters for the design of UWA-OFDM systems.

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.

Spectrally Efficient Frequency Division Multiplexing With Index-Modulated Non-Orthogonal Subcarriers

In this letter, we propose a novel index-modulated non-orthogonal spectrally efficient frequency-division multiplexing (SEFDM) scheme, in order to attain a higher bandwidth efficiency than the conventional orthogonal frequency-division multiplexing (OFDM) and SEFDM counterparts. More specifically, the recent index modulation concept is amalgamated with SEFDM, for the sake of reducing the effects of intercarrier interference while benefiting from SEFDM's increased spectral efficiency. We also formulate a low-complexity log-likelihood ratio-based detection algorithm, which allows the proposed SEFDM to operate in the configuration of an arbitrarily high number of subcarriers. Our simulation results demonstrate that the proposed SEFDM scheme outperforms the conventional SEFDM and OFDM, especially in a low-rate scenario.

OFDM Modulated PNC in V2X Communications: An ICI-Aware Approach Against CFOs and Time-Frequency-Selective Channels

This paper studies the application of physical-layer network coding (PNC) in vehicle-to-everything communications to accommodate the time-critical nature of vehicular ad-hoc networks (VANETs). The idea can theoretically reduce the transmission latency by 50%, thus alleviating the short contact time issues caused by high-speed vehicle motion. Conventional studies of PNC primarily considered static networks. In highly mobile networks like VANETs, the carrier frequency offsets (CFOs) due to high-speed motion will lead to inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems. Moreover, the vehicular environment with time–frequency-selective channels further undermines accurate channel estimation for multiple users. It is also worth noting that the CFO that exists in OFDM modulated PNC cannot be completely eliminated through CFO tracking and equalization as in conventional point-to-point transmissions. These critical issues can significantly increase the bit error rate at the receiver. To address these challenges, this paper proposes an ICI-aware approach that jointly achieves accurate channel estimation, signal detection, and channel decoding. We express the channel estimation and detection and decoding as two optimization problems and resolve them with the expectation–maximization algorithm and the belief propagation algorithm, respectively. The proposed approach can efficiently mitigate the negative effect of ICI by exploiting both pilot and data tones in channel estimation, detection, and decoding. Both simulation and experiment are conducted to evaluate the proposed approach, and the results reveal that the proposed algorithm outperforms the benchmark that simply treats ICI as Gaussian noise.

Sub-Band Filter in Universal Filtered Multi-Carrier Transceiver for Cognitive Radio Network

Modern wireless mobile communication system concentrates on effective utilization of frequency band and efficient modulation technique for side lobe elimination. Frequency bands are effectively utilized by using Cognitive radio networks. Cognitive radio network (CRN) is one of the intelligent technologies to solve spectrum scarcity. Universal Filtered Multi-Carrier (UFMC) is the potential multi-carrier modulation technique for the fifth generation (5G) wireless communication networks, as it detains the side lobes of spectral component and also reduces the effect of inter-carrier interference. In this paper, we design the UFMC transceiver whose parameters are adjusted in response to the challenge of side lobe removal. To this end, we first estimate the Peak-to-Average power Ratio (PAR), optimum sub-band filter length at the transmission and the bit error rate (BER) at the reception. The proposed UFMC transceiver can be applicable for the detection of unused spectrum by exploiting the autocorrelation properties of received signal. Finally we verify the performance of proposed UFMC transceiver for the application of CRN by computer simulation.

Hybrid Micro Genetic Algorithm Assisted Optimum Detector for Multi-Carrier Systems

<p>A low-complexity detection scheme, which consists of a Hybrid Micro Genetic Algorithm (Hybrid- µGA), is proposed for Orthogonal Frequency Division Multiplexing (OFDM) systems. In the absence of orthogonality, intercarrier-interference (ICI) occurs because a signal from one subcarrier causes interference to others. In several environment, the OFDM signal reflections from a far obstacle generate inter-block-interference (IBI) due to long time delays. To avoid these unpleasant effects of IBI and ICI in OFDM system, a Hybrid-µGA detection algorithm is proposed. The proposed detector combines the conventional one-Tap equalizer and the Micro Genetic Algorithm (µGA) search engine. The output of one-Tap equalizer is considered as the input to µGA search engine. Therefore, the µGA starts with some knowledge rather than blindly to speed up the search. Theoretical analysis and simulation results show that the proposed detection Hybrid- µGA scheme substantially improves the performance of OFDM systems. Moreover, its complexity is 10 times lower than the conventional GA.</p>

Closed-Form Expressions for ICI/ISI in Filtered OFDM Systems for Asynchronous 5G Uplink

One of the major purposes for fifth generation (5G) communications waveform design is to relax the synchronization requirements for supporting efficient massive machine type communications (MTCs). Polynomial cancellation coded orthogonal frequency-division multiplexing (PCC-OFDM) and universal filtered multi-carrier (UFMC) are designed to reduce the sidelobes of the OFDM waveform to protect against intercarrier interference (ICI) in the 5G uplink. To the best of our knowledge, there is no analysis of the effect of ICI for the UFMC system with time offset transmissions that many arise in MTC scenarios. Furthermore, there is no study on reducing the computational complexity of the UFMC system. This paper provides closed-form expressions for time offsets interference in such a case for OFDM, PCC-OFDM, and UFMC. This paper also presents theoretical analysis for the signal-to-interference-plus-noise ratio, achievable rate, and bit error ratio performance. The results show that PCC-OFDM significantly protects against ICI at the cost of halving the spectral efficiency. UFMC improves the ICI and intersymbol interference protection performance, especially when the length of time offset is very small, at the cost of significantly increasing the computational complexity. Finally, this paper proposes the overlap and adds UFMC and a variant of UFMC using infinite impulse response prototype filter banks to reduce the processing complexity.

White LED-based optical wireless link with improved transmission capacity using nonorthogonal multiamplitude phase frequency modulation

A nonorthogonal amplitude, phase, and frequency modulation (APFM) technique that can increase the transmission capacity of an optical wireless link based on white light-emitting diode (LED) is proposed. It is implemented by the simultaneous use of nonorthogonal frequency shift keying (FSK) and quadrature amplitude modulation (QAM). A white LED-based wireless link using a 64-APFM scheme is constructed to experimentally verify the proposed technique, where the 64-APFM scheme is implemented by the combination of nonorthogonal 4-FSK and 16-QAM. Two more bits per symbol are transmitted using the proposed scheme with the same bandwidth of QAM. No intercarrier interference effect is observed at the 0.02-% frequency spacing (0.001 MHz) for the used RF carrier (5 MHz) because the correlation between the received 64-APFM signal and only one carrier at a time is accomplished with the help of digital signal processing. 6 - Mbit / s ( 1 - Msymbol / s ) data are successfully transmitted through an optical wireless channel with a limited bandwidth of 1 MHz. This indicates that six bits per symbol can be transmitted using the proposed APFM technique at the same physical bandwidth as 16-QAM.