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.     

Polarization-based optimal detection scheme for digital self-interference cancellation in full-duplex system

In order to detect and cancel the self-interference (SI) signal from desired binary phase-shift keying (BPSK) signal, the polarization-based optimal detection (POD) scheme for cancellation of digital SI in a full-duplex (FD) system is proposed. The POD scheme exploits the polarization domain to isolate the desired signal from the SI signal and then cancel the SI to obtain the interference-free desired signal at the receiver. In FD communication, after antenna and analog cancellation, the receiver still contains residual SI due to non-linearities of hardware imperfections. In POD scheme, a likelihood ratio expression is obtained, which isolates and detects SI bits from the desired bits. After isolation of these signal points, the POD scheme cancels the residual SI. As compared to the conventional schemes, the proposed POD scheme gives significantly low bit error rate (BER), a clear constellation diagram to obtain the boundary between desired and SI signal points, and increases the receiver's SI cancellation performance in low signal to interference ratio (SIR) environment.     

Blind Signal Separation Using Steepest Descent Method

A method that significantly improves the convergence rate of the gradient-based blind signal separation (BSS) algorithm for convolutive mixtures is proposed. The proposed approach is based on the steepest descent algorithm suitable for constrained BSS problems, where the constraints are included to ease the permutation effects associated with the convolutive mixtures. In addition, the method is realized using a modified golden search method plus parabolic interpolation, and this allows the optimum step size to be determined with only a few calculations of the cost function. Evaluation of the proposed procedure in simulated environments and in a real room environment shows that the proposed method results in significantly faster convergence for the BSS when compared with a fixed step-size gradient-based algorithm. In addition, for blind signal extraction where only a main speech source is desired, a combined scheme consisting of the proposed BSS and a postprocessor, such as an adaptive noise canceller, offers impressive noise suppression levels while maintaining low-target signal distortion levels.     

Online identification of induction machine electrical parameters for vector control loop tuning

In a vector-controlled induction machine drive, accurate knowledge of the machine electrical parameters is required to ensure correct alignment of the stator current vector relative to the rotor flux vector, to decouple the fluxand torque-producing currents and to tune the current control loops. This paper presents a new method for online identification of the induction machine parameters required to tune a rotor-flux-oriented (RFO) vector control scheme. Accuracy of the slip frequency estimation required for RFO vector control is achieved by utilizing the parameter independent "flux pulse" rotor time constant estimation scheme, which utilizes short-duration pulses injected into the flux-producing current. The parameters required to tune the synchronous frame current control loops with a decoupling circuit are estimated using a recursive estimation scheme derived from the synchronous frame voltage equations. As the "flux pulse" scheme requires signal injection into the flux-producing current a new rotor time constant estimation scheme is presented, based on the sensitivity analysis of the recursive parameter estimation scheme. Simulation and experimental results are presented which demonstrate the effectiveness of the online parameter identification and control loop tuning technique.     

噪声环境下信号相位获取的快速算法

提出一种基于快速傅立叶变换(FFT)的算法来计算噪声环境中的有用信号相位,可用于无线通信中双传声器应用系统中的自适应定向。通过理论推导和仿真结果给出有效计算有用信号相位,进而提供有效减小来自目标信号不同方向噪声的方法。与其他一些可用的方法相比,此方法实现简单,可以消除处理单元的附加时延,有效解决传声器适配问题,并可排除目标信号必须严格的在正前方的假设。     

Inter-Frame, Fine Frequency/Phase Synchronization forSimple Space-Time-Coded OFDM Receivers

This paper proposes an enhanced receiver (Rx) configuration for multiple-input, multiple-output (MIMO) OFDM systems, operating under the composite effect of phase noise (PHN), residual frequency offset (RFO) and the transmission channel, herein modeled as quasi-static but unknown. The proposed Rx identifies the different impairments by exploiting their different time constants and compensates for each one accordingly. It includes a novel inter-frame fine frequency synchronization (FFS) scheme, which is closely coupled to an intra-frame adaptive phase synchronizer/channel estimator. The proposed scheme is evaluated for a 2 times 2, Alamouti space-time code (STC), and is shown to provide significant performance gain. The theory can be employed with any other STC scheme.     

基于多信道的干扰消除信号接收方法

提出一种多信道条件下带有Low-IF接收机的新型模数信号接收处理方法,一般Low-IF接收机中,镜频信号会对期望信号造成干扰。在该文方案下,由模拟复带通滤波器完成信道选择,干扰信号通过采用DLMS算法的FIR自适应滤波器消除。仿真分析表明,该方案对AD转换器复杂度要求低,有利于工程实现,而且能很好抑制邻近信道信号干扰,提高系统性能。     

Noise cancellation with improved residuals

An effective adaptive scheme for noise cancellation when the signal to be recovered has known autocorrelation is presented. Two algorithms that exploit a special form of prior information are investigated. In this approach the desired signal is removed from the output feedback by linear prediction: the prior information used is the desired signal's autocorrelation. Knowing this, one can find a filter that whitens the desired signal. Screening the error feedback through this filter removes most of the desired signal energy, reducing its interference with the coefficient update. This is the basis for the first algorithm discussed, namely, the least-mean-square algorithm with augmented predictor (LMS-AP) proposed by Orgren et al. (1986). In many applications the whitening filter may not be strictly positive real (SPR). In such cases a different algorithm is needed; one which is assuredly convergent regardless of the satisfaction of the SPR condition. A modified LMS algorithm with augmented predictor (MLMS-AP) which provides such an alternative is proposed     

Cramér-Rao Bound for SAGE-based Residual Frequency Offset Estimation Algorithm in OFDM Systems

The Cramér-Rao bound (CRB) is a powerful tool in estimation theory as it gives a performance lower bound for parameter estimation problems. In this paper, a much tighter CRB for Lee’s residual frequency offset (RFO) estimation method (IEEE Transactions on Communications 54:765, 2006) is first given. The tighter low bound is obtained by considering the ICI that affects the performance of space-alternating generalized expectation-maximization (SAGE) based RFO estimator. It can be concluded that the performance of SAGE based RFO estimation method decreases as the normalized RFO increases and increases with the increasing of signal-to-noise (SNR). Simulation results show that the proposed CRB of SAGE based RFO estimator is extremely tight. It approximates closely the MSE performance obtained by Monte Carlo simulation.     

Parallel genetic algorithm based unsupervised scheme for extractionof power frequency signals in the steel industry

A steel industry has different types of loads, and so the incoming supply voltage of some units becomes distorted thus affecting those systems that depend on a distortionless supply. A novel unsupervised scheme named the recursive hybrid parallel genetic algorithm based line enhancer (RHPGABLE) scheme is proposed, to track the desired power frequency signal from the corrupted one. The RHPGABLE scheme is based on a proposed new crossover operator known as the generalised crossover (GC) operator. The delay and the filter coefficients are estimated recursively to yield optimal solutions. In the recursion of the proposed RHPGABLE algorithm, a parallel genetic algorithm (PGA) based on a coarse-grained approach is employed to estimate the delay, while the filter coefficients are estimated by PGA and a least mean squares (LMS) algorithm. RHPGABLE is an unsupervised scheme in the sense that no a priori knowledge of delay or filter coefficients and the associated training signal component is assumed to be available. The proposed scheme has been tested successfully on both synthetic data and data obtained from the Steel Melting Shop of Rourkela Steel Plant, Orissa, India     

Partially blind extraction of continuous chaotic signals from a linear mixture

In this paper, we address the problem of blind extraction and separation of a continuous chaotic signal from a linear mixture consisting of some chaotic signal and/or random signals. The problem of blind extraction is firstly formulated as a problem of the synchronization-based parameter estimation. Then an efficient least square based parameter estimation method is introduced to de-termine the desired extracting vector. The proposed blind signal extraction scheme is applicable to blind separation of chaotic signals by formulating the separation problem as the extraction of each chaotic source. Numerical simulation shows that the proposed approach can blindly extract and separate the desired chaotic signals and it is also robust to measurement noise.     

一种天波雷达多径扩展多普勒杂波抑制方法

该文分析了天波超视距雷达(Over The Horizon Radar, OTHR)多径扩展多普勒杂波(Spread Doppler Clutter, SDC)的产生机理。由于阵列存在幅相误差且期望信号的功率大于SDC功率,自适应数字波束形成(Adaptive Digital Beam Forming, ADBF)将降低SDC抑制能力,同时还会导致信号对消,严重降低信噪比。针对以上问题,该文提出一种自适应抑制SDC的方法。该方法首先采用改进噪声子空间拟合自校正法消除阵列幅相误差,得到期望信号和SDC准确的到达仰角,然后采用正交投影权矢量进行ADBF处理,避免了强期望信号条件下ADBF权矢量估计不准的问题。理论分析和仿真实验表明该方法能够较彻底地抑制多径SDC。     

Pilot-Assisted Fine Frequency Synchronization for OFDM-Based DVB Receivers

After coarse synchronization in orthogonal frequency division multiplexing (OFDM) systems, there might still be a residual frequency offset (RFO) and a sampling clock frequency offset (SFO), which seriously degrade the performance of the systems. This paper proposes a simple way of jointly estimating the RFO and SFO by using a continual pilot (CP) defined in an OFDM-based digital video broadcasting (DVB) system. For deriving an unbiased joint RFO and SFO estimator in the current DVB system, a CP subset is selected to simultaneously remove the effect of RFO and SFO. We can observe by simulation that the proposed frequency estimator endowed with a properly selected CP subset is unbiased and performs robustly.      

Performance of Efficient Signal Detection for LED-ID Systems

In this paper, effects of reader-to-reader interference are investigated for LED identification (LED-ID) system in a multi-reader environment. The LED-ID readers typically use different channels to avoid collision between readers. However, in-channel collision usually happens in terms of interrogation range. A reader-to-reader interference scenario is proposed, and nominal interrogation range of a desired reader is derived from this model. In order to evaluate the LED-ID reader-to-reader interference quantitatively, an efficient detection scheme is proposed and simulated by employing spreading sequence. The spreading sequence is inserted between each user’s frame formats. In the receiver, the desired signal is detected by using correlation among inserted spreading sequences. From simulation results, it is confirmed that the proposed scheme is very effective to enhance reliability of LED-ID communication systems.     

New fractional-order LADRC scheme based on a novel filtered-Bode’s ideal transfer function for integer-order systems

In this paper, a new Fractional-Order Linear Active Disturbance Rejection Control scheme (FO-LADRC) is proposed to enhance the robustness against loop gain variations of the standard Active Disturbance Rejection Control (ADRC) in the case of uncertain integer-order systems. A new filtered Bode’s ideal transfer function (F-BITF) is proposed to be used as a reference model in the design approach of the proposed control scheme to ensure the dynamic behavior of the closed-loop BITF to the controlled system. A Fractional-order Extended State Observer (F-ESO) is used in the proposed FO-LADRC structure to approximate the system to be controlled by a filtered fractional-order integrator. The fractional order of the F-ESO is a design parameter to tune to achieve the desired overshoot of the closed-loop step response. For the tuning of FO-LADRC structure, an analytical method is proposed. The performance of the proposed FO-LADRC and the Chen’s et al. FO-ADRC structures are evaluated thorough numerical simulation, and then validated in practice in the case of a Cart-Pendulum. Both the simulation and the experimental results show that the proposed FO-LADRC is able to achieve the desired dynamics of the F-BITF and guarantee the robustness with respect to the controller gain variation and the system parameter uncertainties. The comparative study conducted also reveals that the proposed control scheme is more robust than that of Chen.     

Beamforming for Downlink Multiuser MIMO Time‐Varying Channels Based on Generalized Eigenvector Perturbation

A beam design method based on signal‐to‐leakage‐plus‐noise ratio (SLNR) has been recently proposed as an effective scheme for multiuser multiple‐input multiple‐output downlink channels. It is shown that its solution, which maximizes the SLNR at a transmitter, can be simply obtained by the generalized eigenvectors corresponding to the dominant generalized eigenvalues of a pair of covariance matrices of a desired signal and interference leakage plus noise. Under time‐varying channels, however, generalized eigendecomposition is required at each time step to design the optimal beam, and its level of complexity is too high to implement in practical systems. To overcome this problem, a predictive beam design method updating the beams according to channel variation is proposed. To this end, the perturbed generalized eigenvectors, which can be obtained by a perturbation theory without any iteration, are used. The performance of the method in terms of SLNR is analyzed and verified using numerical results.     

基于BP神经网络的IRFPA改进型非均匀性校正算法

提出了一种基于神经网络的红外焦平面阵列（Infrared Focal Plane Array,IRFPA）非均匀性自适应校正算法。首先,利用归一化思想对图像进行处理以利于选取迭代步长;其次,优化隐含层结构以获得更接近于真实信号的期望信号。实验结果表明,该方法在校正精毖、收敛速度和稳定性方面均优于传统的神经网络校正算法。     

基于人工噪声辅助的D2D异构蜂窝安全通信方法

A secure communication scheme based on artificial noise assisted from base station(BS)was proposed to improve the system secrecy rate of the D2D underlaying cellular.Firstly,the system secrecy rate was modeled.Then the BS with multi-antennas added artificial noise(AN)in cellular user’s signal as well as designed beam vectors of the desired signal and artificial noise to maximize system secrecy rate.In the end,a joint optimization scheme based on the fairness constraint was introduced to optimize beam vectors of the desired signal,the power allocation for BS’s information signal and AN and the D2D power control.Simulation results show that the system ergodic secrecy rate can be improved 2.7 bit·s^?1·Hz^?1more than the schemes based on SVD and zero-forcing at most.     

Simple Amplitude and Phase Predistortion for PAPR Reduction in OFDM Systems

One of the drawbacks in an OFDM system is the high peak‐to‐average power ratio (PAPR). Among a number of techniques to reduce the high PAPR, simple amplitude predistortion (SAP), a form of active constellation extension, has been proposed to effectively achieve the desired PAPR. In this letter, a novel scheme, simple amplitude and phase predistortion (SAPP), is proposed. In SAP the carriers' amplitude is utilized to combat the peak signal. Each amplitude is amplified according to its degree of contribution as a metric. In addition to amplitude, SAPP also utilizes the phase. Simulation results indicate that the proposed scheme provides better PAPR reduction than SAP.     

Efficient wireless transmission scheme based on the recent DST-MC-CDMA

The capacity of a multicarrier code-division multiple access (MC-CDMA) system is limited by a multiple access interference (MAI) from other users. In this paper, we propose a MAI cancellation scheme to transmit images over a recent discrete sine transform (DST) based MC-CDMA (DST-MC-CDMA) system. In the proposed scheme the minimum mean square error (MMSE) equalizer is used to provide the initial estimate of users’ data and the parallel interference cancellation (PIC) scheme is then used to regenerate and cancel the MAI from the desired user. The proposed scheme is called MMSE-PIC. Simulation results in multi-path fading channel confirm the excellent performance of the proposed scheme as compared to MMSE equalization method. It is also found that the best suitable tentative decision for the proposed scheme is the null zone decision or the clipper decision. We also conduct experiments to show the performance of the proposed scheme with a real image transmission over the DST-MC-CDMA system. Results show that the proposed scheme provides significant image quality improvement as compared to the existing schemes. The average peak signal to noise ratio improvement achieved by the proposed scheme over the conventional MMSE equalizer at a SNR = 30 dB is about 6.5 dB for different number of users.