Induce Inter-carrier Interference Research Articles

Joint Doppler shift and channel estimation for UAV mmWave system with massive ULA

A joint Doppler shift and channel estimation method for the millimeter-wave communication system of an unmanned aerial vehicle (UAV) equipped with a large-scale uniform linear antenna (ULA) array has been proposed. Since Doppler shift induces intercarrier interference, the parameters of the channel paths have been decomposed into the Doppler shift and the channel information. In order to obtain the Doppler shift, a new estimation algorithm based on a combination of discrete Fourier transform and phase rotation has been proposed, which can determine the appropriate number of antennas. In addition to estimating the channel information, a low-complexity joint Doppler shift and channel estimation method has been designed that can quickly obtain accurate estimates. Furthermore, the achievable sum rate, the theoretical bounds of the mean squared errors, and the Cramér-Rao lower bounds of the estimation method have been derived. The analysis and simulation results prove that the performance of the proposed approach is close to the theoretical inference.

Non-Orthogonal Discrete Multi-Tone: Toward Higher Spectral Efficiency for Optical Networks

Achieving higher spectral efficiency is an efficient approach to address the bandwidth crisis of optical networks, but it faces significant technical challenges. High-spectral-efficiency non-orthogonal frequency-division multiplexing (NOFDM) has been proposed for meeting the requirement of optical networks' capacity upgrade. Compared to orthogonal frequency-division multiplexing, NOFDM can achieve higher spectral efficiency by compressing the subcarrier spacing narrower than the Nyquist orthogonal spacing, but this inevitably induces inter-carrier interference (ICI). ICI cancellation algorithms are crucial in NOFDM for correctly recovering the transmitted signal at the expense of extra processing power. Nowadays, processing power is no longer the obstacle to eliminate ICI due to the rapid development of application-specific integrated circuits for efficient implementation of digital signal processing. In this article, fast multiplexing and demultiplexing for NOFDM are implemented based on inverse fast Fourier transform and fast Fourier transform, respectively. Meanwhile, three representative ICI cancellation algorithms are discussed, and one of them is experimentally implemented. Furthermore, we propose non-orthogonal discrete multitone (NODMT) by integrating the advantages of NOFDM and DMT, which has the potential to achieve improved spectral efficiency for future optical networks.

Particle Filter Based Nonlinear Data Detection in Presence of CFO for Frequency Selective mmWave MIMO-OFDM Systems

The nonlinear distortions attributed by the radio frequency (RF) power amplifier (PA) and other RF circuits from the enormous bandwidth of millimeter wave (mmWave) and high frequency design limitations of the integrated circuits involved, degrade the performance of the hybrid mmWave multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. This nonlinear distortions in the hybrid mmWave systems cause nonlinear coupling of the hybrid precoder with the data signals. Further, it induces intercarrier interference (ICI) in the OFDM systems, which also involves the interference from the precoders of other subcarriers. These difficulties in collusion with frequency selective channel and carrier frequency offset (CFO) may pose great challenges to the estimation accuracy of these parameters (channel gains and CFO) and signal detection. The nonlinearity causes the target posterior distribution for data detection as non-Gaussian and analytically intractable. In this work, we present a novel pilot assisted maximum likelihood (ML) based framework for estimating the CFO with PA impairment in the time domain by formulating a low dimensional equivalent channel matrix. The low dimensional equivalent channel matrix is composed of hybrid precoders-combiners, high dimensional MIMO channel, and the nonlinearly distorted components from PA. We further propose a group-sparse Bayesian learning (G-SBL) based semi-blind channel estimator in the time domain, which incorporates the CFO and nonlinearity of PA in its estimation process. With the estimated channel, a procedure to obtain the hybrid precoder and combiner matrices for data transmission is developed next. An iterative algorithm based on particle filter (PF) that effectively handles the nonlinear coupling of precoder matrix with data, and ICI is also proposed for data detection. The performance of the algorithms are evaluated on two different channel models: (a) synthetic geometric based mmWave channel (b) realistic mmWave channel for an urban microcell (UMi) environment. To validate the efficacy of the CFO and channel estimator, the Cramer-Rao bound (CRB) and Bayesian CRB (BCRB) are derived respectively.

Tensor-Based Receiver for Joint Channel, Data, and Phase-Noise Estimation in MIMO-OFDM Systems

Phase-noise is a system impairment caused by the mismatch between the oscillators at the transmitter and the receiver. In OFDM systems, this induces inter-carrier-interference (ICI) by rotating the transmitted symbols. Thus it can cause severe system performance degradation. To reduce its effects, the phase-noise must be estimated or compensated. In this work, we propose a two-stage tensor-based receiver for a joint channel, phase-noise (PN), and data estimation in MIMO-OFDM systems. In the first stage, we show that the received signal at the pilot subcarriers can be modeled as a third-order PARAFAC tensor. Based on this model, we propose two algorithms for channel and phase-noise estimation at the pilot subcarriers. The first algorithm, based on the BALS (Bilinear Alternating Least Squares), is an iterative algorithm that estimates the channel gains and the phase-noise impairments. The second is a closed-form algorithm based on the LS-KRF (Least Squares - Khatri-Rao Factorization) that estimates the channel gains and the phase-noise terms through multiple rank-one factorizations. Both algorithms achieve similar performance, but in terms of computational complexity, we show that the LS-KRF becomes more attractive than the BALS as the number of receive antennas is increased. The second stage consists of data estimation, for which we propose a ZF (Zero-Forcing) receiver that capitalizes on the PARATuck tensor structure of the received signal at the data subcarriers using the Selective Kronecker Product (SKP) operator. Our numerical simulations show that the proposed receiver achieves an improved performance compared to the state-of-art receivers in terms of symbol error rate (SER) and normalized mean square error (NMSE) of the estimated channel and phase-noise matrices.

Interference avoidance and cancellation in automotive OFDM radar networks

With increasing use of millimeter-wave radars in driving safety applications, interference between vehicles becomes a significant issue. Moreover, oscillator imperfections and relative velocity effects induce inter-carrier interference (ICI) owing to frequency offset, leading to degradation of target detection. In this paper, time-frequency resources are divided into several orthogonal logical channels according to the time-frequency division (TFD) scheme. We propose a two-stage interference mitigation method. First, an interference avoidance technique is designed for each piece of radar equipment (RE) to select logical channels with the least ICI. Then, each RE reconstructs and cancels interference according to estimated parameters based on the proposed interference cancellation technique. Computer simulations reveal that the proposed interference avoidance technique can approximately achieve the performance of ground truth, especially when the number of interferers is small. In addition, noise enhancement effects can be effectively mitigated through the proposed cancellation technique.

Location-Aided mMIMO Channel Tracking and Hybrid Beamforming for High-Speed Railway Communications: An Angle-Domain Approach

Wireless communication for high-speed railways (HSRs) has received considerable attention in recent years. The fast time-varying and doubly selective fading properties of channels pose a substantial threat to the link performance. Meanwhile, the nonnegligible Doppler frequency offset (DFO) resulting from the high-speed motion induces intercarrier interference. In this paper, we propose an angle-domain channel tracking and hybrid beamforming scheme for HSR by investigating the time and spatial properties of channels. A large-scale uniform linear antenna array is applied at the base station to provide high spatial resolution. The DFO is compensated through beam alignment and capturing the precise angular information from signals. Then, the spatial beam gain is tracked during the angle-of-arrival time, which can be used to reconstruct the full-dimensional channel state information. Finally, the hybrid beamforming is used to realize data transmission. The key idea of tracking is, applying a linear Kalman filter to modify the time-varying beam gain, while the main idea of hybrid beamforming is utilizing nonorthogonal beams to compress the channel dimension and decrease the computational complexity. The superiority of the proposed scheme is evaluated through simulations.

Fractional wavelet transform based OFDM system with cancellation of ICI

The future of wireless communication systems stimulate researchers to improve bandwidth efficiency and data rate by carrying out several analyses. The reliability of multiple input multiple output (MIMO) combined with orthogonal frequency division multiplexing (OFDM) in wireless communication is reduced by frequency error. This leads to damage of orthogonality between sub-carriers and induces inter carrier interference (ICI). To overcome this problem in conventional OFDM system, cyclic prefix is used. In this work, a novel technique named fractional wavelet transform (FrWT) is proposed. The FrWT reduces the effect of ICI in conventional system without any usage of cyclic prefix. Also, the bandwidth efficiency is improved due to its orthogonal wavelets and absence of cyclic prefix. The proposed work investigates the performance of FrWT-OFDM model and tested against carrier frequency offsets. The efficiency of ICI self cancellation technique in mitigating the effect of frequency offsets is analysed. The efficiency of proposed model is highlighted by comparing with existing FFT and wavelet based OFDM system by means of bit error rate (BER). Simulation results show reduced BER of 10−4.8 at 8 dB SNR for the proposed model with a normalized carrier frequency offset value of 0.1. Thus the effect of ICI is reduced efficiently for proposed transform in OFDM.

A Diversity Enhanced-Particle Filter based Multiple Carrier Frequency Offset Estimation Using Hadamard Matching in CA-OFDM Based LTE-A System

Carrier aggregation (CA) is a promising bandwidth extension technique which in turn increases the data rate. A scalable and flexible Orthogonal frequency-division multiplexing (OFDM) can be considered as a key element in 5G wireless communications. The combination of CA and OFDM is a prominent factor in LTE-A system followed by strict synchronicity. So, carrier frequency offset (CFO) is an important parameter to be considered and corrected. In carrier-aggregated OFDM (CA-OFDM) systems, multiple carrier frequency offsets (MCFOs) are a non linear synchronization error that induces inter carrier interference (ICI) to the system. To solve this problem, our self proposed Diversity Enhanced Particle Filter (DE-PF) with a novel resampling algorithm is used in downlink CA-OFDM receiver structure with Hadamard sequence based prominent matching algorithm to match the estimated MCFO to its corresponding Component Carrier (CC). Simulations prove that with DE-PF algorithm and proposed Hadamard matching algorithm improves MCFO estimation accuracy to a greater extent than the existing linear and non linear algorithms.

Channel-Coded Physical-Layer Network Coding With OFDM Modulation

This paper addresses the carrier frequency offset (CFO) problem in OFDM modulated physical-layer network coding (PNC) operated in a two-way relay channel (TWRC). CFO, caused by node-motion induced Doppler shifts and/or asynchronous oscillators, induces inter-carrier interference (ICI) between OFDM subcarriers and hence, degrades PNC performance. To mitigate the CFO/ICI effect in PNC, this paper considers channel-coded PNC and focuses on the receiver design at the relay. CFO compensation, signal detection, and channel decoding are the three basic signal processing blocks at the relay node. For the latter two, we consider both a joint and a separate design. For the joint design, we construct a factor graph to integrate channel coding with ICI, and then, propose a scheme based on belief propagation. For the separate design, two low-complexity schemes differing in channel decoding are proposed. Our simulation results, using repeat-accumulate channel codes, reveal that (1) a CFO compensation approach that amounts to positioning the relay’s oscillator frequency at the middle of the received frequencies from the two end nodes is bit error rate (BER)-optimal for all the three schemes; (2) the joint design is superior at low SNR and/or high CFO levels; and (3) more importantly, with the joint design, for low-to-medium CFO levels, the BER of the channel-coded PNC is comparable with that of traditional point-to-point communications without CFO, thus manifesting itself as a promising technique in OFDM modulated TWRC with practical CFO constraints.

Stability Proof of Iterative Interference Cancellation for OFDM Signals With Blanking Nonlinearity in Impulsive Noise Channels

Blanking nonlinearity is a widely applied technique for suppressing impulsive noise. However, for orthogonal frequency-division multiplexing signals, the blanking nonlinearity induces intercarrier interference, which must be removed in order to fully exploit the advantage of the blanking nonlinearity and to avoid performance degradation. For this purpose, interference cancellation techniques are attracting a considerable attention. Particularly, the nonlinear iterative ones show a good complexity-performance behavior. Nevertheless, one of the most important features of nonlinear iterative methods in the context of interference cancellation often remains disregarded: The stability. In this correspondence, we prove the asymptotical stability in the sense of Lyapunov of a nonlinear iterative interference cancellation technique for OFDM signals with blanking nonlinearity in impulsive noise channels. This is achieved by reformulating the considered technique as a multithreshold recurrent neural network and by taking advantage of the extensive research on the Lyapunov stability of recurrent neural networks. We show that the considered nonlinear iterative interference cancellation technique either reaches a fixed point or a limit cycle of length two. The obtained results can be utilized to find an upper bound on the required number of iterations to settle on a fixed point.

The Feasibility of Mobile Physical-Layer Network Coding with BPSK Modulation

This paper considers applying physical-layer network coding (PNC) to orthogonal frequency division multiplexing (OFDM) modulated mobile ad-hoc networks (MANETs) to resolve the outstanding issue of short contact time between nodes due to their mobility. Ideally, PNC enables data exchange twice as fast as the traditional scheduling, and thus, it is a potential performance booster in MANETs. However, the application of PNC in MANETs is challenged by the carrier frequency offset (CFO) problem inherently caused by node-motion-induced Doppler shifts and asynchronous oscillators. CFO induces intercarrier interference (ICI) that degrades PNC performance. In this paper, we investigate the CFO/ICI impact on the signal-to-interference-and-noise ratio (SINR) and bit error rate (BER) in the signal detection of PNC in a two-way relay channel (TWRC) based on binary phase-shift keying (BPSK) modulation. We find that PNC with power control suffers, at most, a 3 dB SINR penalty compared with generic point-to-point communications in both the flat-fading and the frequency-selective channels. We also find that a belief propagation (BP) algorithm could be employed in the signal detection of PNC to effectively tackle ICI and reduce its impact on the BER of PNC. For CFO compensation in PNC, we propose a method that amounts to positioning the relay's local oscillator frequency at the middle of the received frequencies from the two end nodes in the TWRC. Importantly, we show that 1) this compensation method can theoretically maximize the worst SINR in PNC and that 2) in the case of similar CFO of the two uplinks in TWRC, it allows PNC to achieve a BER at the relay close to that in the ideal case, i.e., in point-to-point communications without CFO. Overall, this paper demonstrates that mobile PNC is feasible in general, laying the foundation for future studies.

Investigation of PMD in direct-detection optical OFDM with zero padding

We investigate the polarization-mode dispersion (PMD) effect of zero padding OFDM (ZP-OFDM) in direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems. We first study the conventional equalization method for ZP-OFDM. Then an equalization method based on sorted QR decomposition is proposed to further improve the performance. It is found that the performance improvement of ZP-OFDM is due to the frequency domain oversampling (FDO) induced inter-carrier interference (ICI). Numerical simulation results show that compared with cyclic prefix OFDM (CP-OFDM), ZP-OFDM has a significantly higher tolerance to PMD in DDO-OFDM systems when the channel spectral nulls occur at certain differential group delay (DGD) values.

Efficient Joint Carrier Frequency Offset and Phase Noise Compensation Scheme for High-Speed Coherent Optical OFDM Systems

The vulnerable sensitivity to laser linewidth induced inter-carrier interference (ICI) has long been recognized as a major problem to coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems. Among the existing phase noise compensation algorithms, the RF-pilot aided phase recovery (RAPR) method shows a better compensation capability to laser linewidth. However, RAPR may fail to extract the pre-inserted RF-pilot at the receiver due to the influence of carrier frequency offset (CFO). An effective frequency offset estimation (FOE) is thus required to implement before performing RAPR. In consideration of the fact that the conventional FOE algorithm not only has high computational complexity, but more importantly cannot work in coordination with RAPR, a new RF-pilot aided frequency offset estimation (RAFOE) algorithm is proposed, in which CFO can be easily estimated by searching the peak of spectral samples. Furthermore, in order to obtain the optimum compensation performance with lower computing cost at combining RAFOE and RAPR, a joint frequency offset and phase noise compensation scheme is also proposed, and its performance is numerically verified in a 475 Gbit/s polarization multiplexed 16-ary quadrature amplitude modulation coherent optical orthogonal frequency-division multiplexing (PM-16QAM- CO-OFDM) system.

Novel Finite Summation Expressions for Total Interference Power due to Carrier Frequency Offset in Uplink Multiuser OFDM Systems

Carrier Frequency Offset which poses adverse threats in uplink Multiuser OFDM systems induces Inter-Carrier Interference (ICI) and Multiuser Interference (MUI). It is very essential that the power of ICI and MUI is calculated precisely. In previous work, the total interference power was presented in an indefinite integral form or as an infinite series. Further, an ideal channel was the scenario under consideration in earlier work. In this paper, novel finite summation expressions for power of ICI and MUI are derived over slowly fading channels which make the calculation of total interference simpler for any number of users by just specifying the total number of users and the number of subcarriers allotted for each user. Based on the mean of the dominant signal and the total interference power experienced in the system, closed-form expressions for mean and variance of the desired signal in uplink multiuser OFDM system are obtained which provide an idea of the strength of the desired signal. Finite-sum expressions for the total interference power, and closed-form expressions for mean and variance of the desired signal under Rayleigh, Weibull and Nakagami fading channels are derived and plotted from which the response of the system can be understood perfectly.

Experimental demonstration of non-iterative interpolation-based partial ICI compensation in100G RGI-DP-CO-OFDM transport systems

We experimentally investigate the performance of a low-complexity non-iterative phase noise induced inter-carrier interference (ICI) compensation algorithm in reduced-guard-interval dual-polarization coherent-optical orthogonal-frequency-division-multiplexing (RGI-DP-CO-OFDM) transport systems. This interpolation-based ICI compensator estimates the time-domain phase noise samples by a linear interpolation between the CPE estimates of the consecutive OFDM symbols. We experimentally study the performance of this scheme for a 28 Gbaud QPSK RGI-DP-CO-OFDM employing a low cost distributed feedback (DFB) laser. Experimental results using a DFB laser with the linewidth of 2.6 MHz demonstrate 24% and 13% improvement in transmission reach with respect to the conventional equalizer (CE) in presence of weak and strong dispersion-enhanced-phase-noise (DEPN), respectively. A brief analysis of the computational complexity of this scheme in terms of the number of required complex multiplications is provided. This practical approach does not suffer from error propagation while enjoying low computational complexity.

Noniterative Interpolation-Based Partial Phase Noise ICI Mitigation for CO-OFDM Transport Systems

We introduce and investigate the feasibility of a noniterative phase noise induced intercarrier interference (ICI) compensation scheme based on linear interpolation for coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) transport systems. The study of bit-error-rate (BER) performance for a 40-Gb/s 16-quadrature amplitude modulation (QAM) CO-OFDM signal demonstrates a significant improvement versus the conventional equalizer (CE) in the optical signal-to-noise ratio (OSNR) requirement. Moreover, the capability of this equalizer in conjunction with the back-propagation (BP) nonlinearity compensation scheme is investigated and a brief analysis of the computational complexity, in terms of the number of required complex multiplications, is provided. This practical approach does not suffer from error propagation while enjoying low computational complexity.

Uplink Timing Misalignment in Open and Closed Access OFDMA Femtocell Networks

We focus on an uplink network composing of femtocell access points (FAPs), macrocell users (MUs) and a macrocell base station (MBS) employing orthogonal frequency division multiple access (OFDMA) signaling. Synchronization of MUs at the MBS results in asynchronous signal arrivals at the FAPs which may induce intercarrier interference (ICI). Given a fixed distance between an FAP and the MBS, we derive a closed-form expression for the probability of an MU causing ICI to the FAP. Then, we extend this to obtain the probability of an open and closed access FAP experiencing ICI in the presence of a fixed number of MUs, and the average number of open and closed access FAPs experiencing ICI.

Optimum Second Order Polynomial Nyquist Windows for Reduction of ICI in OFDM Systems

A new class of time domain second order polynomial Nyquist window functions is proposed and applied to orthogonal frequency division multiplexing (OFDM) systems for reducing frequency offset induced inter-carrier interference (ICI) at the receiver. The signal to ICI plus noise ratio (SINR) of the receiver is analyzed in this paper. We also propose a method to select the window parameters to maximize the SINR of the receiver thus providing optimal performance. The receiving method with optimal second order polynomial window is shown to provide performance better than raised cosine and "better than" Nyquist window.

Carrier frequency offset estimation and correction for OFDMA uplink

The paper develops a new method for estimating and correcting the carrier frequency offsets (CFO) of orthogonal frequency division multiple access (OFDMA) systems at the uplink receiver. Multiple CFO of the different users in the OFDMA system may violate the orthogonality among subcarriers and induce inter-carrier interference (ICI) and inter-user interference (IUI). The IUI provides some extra challenges to CFO estimation not addressed in OFDM systems with only a single CFO. By significantly reducing the IUI, the paper presents an improved CFO estimator which can provide a higher accuracy than the existing approaches. After having estimated the CFO, the author also proposes a new method for CFO correction or compensation at the uplink receiver. Through simulations, it is shown that the new CFO estimator and the correction method outperform the existing approaches.

IQ-Imbalance Compensation for OFDM in the Presence of IBI and Carrier-Frequency Offset

In this paper, we propose a frequency-domain equalization technique for orthogonal frequency division multiplexing (OFDM) transmission over frequency-selective channels. We consider the case where the receiver analog front-end suffers from IQ-imbalance and the local oscillator suffers from carrier-frequency offset (CFO). While the IQ-imbalance results in a mirroring effect, the CFO induces inter-carrier interference (ICI). In addition to ICI, we consider the channel delay spread is larger than the cyclic prefix (CP). This means that inter-block interference (IBI) is present. The frequency-domain equalizer is obtained by transferring a time-domain equalizer (TEQ) to the frequency-domain resulting in a per-tone equalizer (PTEQ). Due to the presence of IQ-imbalance the conventional TEQ (where only one TEQ is applied to the received sequence) is not sufficient to cope with the mirroring effect. A sufficient TEQ consists of two time-domain filters; one applied to the received sequence and another applied to a conjugated version of the received sequence. For the case of IQ-imbalance and CFO, the TEQs are designed according the basis expansion model (BEM) which showed to be able to cope with the ICI problem. Finally, in addition to the frequency-domain PTEQ design procedure, a training-based RLS type initialization scheme for direct per-tone equalization is also proposed