Adaptive narrowband interference rejection in DS-CDMA systems: ascheme of parallel interference cancellers

In the presence of narrowband interference (NBI), the performance of the direct-sequence code-division multiple access communication system can be improved by using various interference cancellation schemes. In this paper, a scheme of parallel interference cancellers (PICs), which includes a set of NBI cancellation filters and a set of multiple access interference (MAI) cancellation filters, is developed to improve the signal-to-interference ratio (SIR) and handle the MAI effect. In order to avoid performance deterioration due to unreliable initial detection, a robust coefficient γ is introduced in our proposed design criterion. A recursive least-square algorithm is employed to update the tap coefficients of the PICs. In other words, no training or retraining period is needed in our proposed PICs. Finally, the SIR performance of the proposed detector is analyzed and compared to that of the conventional linear detector     

DSSS系统中线性调频干扰抑制技术研究

扩频通信系统中宽带干扰的抑制技术越来越引起人们的重视。本文以典型的宽带干扰信号线性调频干扰(Linear Frequency—Modulated，LFM)为例，综述了目前直接序列扩频(Direct Sequence Spread Spectrum，DSSS)系统中宽带干扰抑制的研究热点和成果。     

HOS AND GA BASED INTERFERENCE REJECTION IN DS SS COMMUNICATION SYSTEMS

A new interference rejection filter based on Higher Order Statistics (HOS)and Genetic Algorithm(GA) is introduced.The advantages over the adaptive filters based on second-order statistics or gradient algorithm are shown throrgh computer simulation.     

直接序列扩频通信中窄带干扰抑制的奇异值分解方法

在很强的单音干扰存在时,传统的线性预测滤波方法不能达到很好的抗干扰性能.该文提出了一种用奇异值分解方法(SVD)来抑制扩频通信中的单音干扰的问题,建立了利用SVD技术抑制直接序列扩频通信(DSSS)中的窄带干扰的系统模型.并与传统的双边LMS滤波器进行了误码率比较.仿真表明,SVD方法对干扰有很强的抑制能力,当BER=10-2时,SVD方法的增益要高于LMS方法3dB.而且同传统的LMS算法相比,SVD方法避免了算法收敛的问题.     

Closed-form analytical results for interference rejection ofnonlinear prediction filters in DS-SS systems

Closed-form analytical expressions for narrow-band interference rejection of nonlinear prediction filters in direct-sequence spread-spectrum (DS-SS) systems are established. It is shown that nonlinear prediction filters outperform linear ones     

MIMO-OFDM系统中的子空间半盲信道估计

本文主要讨论了MIMO-OFDM系统中的一种半盲信道估计算法.该算法基于子空间分解技术,利用信号子空间和噪声子空间的正交性将两者分离.针对盲信道估计存在计算量大及收敛速度慢等缺点,本文充分利用少量的导频,给出了一种基于子空间跟踪技术的半盲MIMO-OFDM信道估计算法.仿真结果表明,该算法在保持盲信道估计算法性能的基础上,明显加快了收敛速度、降低了计算量.     

HOS AND GA BASED INTERFERENCE REJECTION IN DIRECT SEQUENCE SPREAD SPECTRUM COMMUNICATION SYSTEMS

A new Higher Order Statistics (OHS) and Genetic Algorithm (GA)-based inter-ference rejection filter is introduced.Compared with the adaptive filters based on second-order statistics and gradient algorithm,the HOS and GA-based filter can reject the interference more efficiently,is independent of uncorrelated Gaussian noise,tende to converge to the optimum solution and is much less sensitive to the choice of the step size parameter.Computer simulations show that the method can reject narrowband interference efficiently.     

Error probabilities for DS spread-spectrum systems using an ALE fornarrow-band interference rejection

The effects of the least-mean-squares adaptive line enhancer (ALE) weight misadjustment errors on the bit error rate are investigated for a direct-sequence spread-spectrum binary communication system in the presence of strong narrowband interference. The converged ALE weights are modeled as the parallel connection of a deterministic FIR (finite impulse response) filter and a random FIR filter. The statistics of the random filter are derived, assuming the output of the random filter to be primarily due to the jammer convolved with random filter weights. This output is shown to be nonGaussian and to cause significant error rate degradation in comparison to a Gaussian model. Error probability expressions are derived for the bit error rate, evaluated numerically, and compared to the corresponding error probabilities for a Gaussian model for the random filter output. For some typical system parameter values and error probabilities it is shown that the Gaussian model yields performance results that are too optimistic by several decibels     

Time-varying narrow-band interference rejection in asynchronousmultiuser DS/CDMA systems over frequency-selective fading channels

In this paper, we handle the problem of joint suppression of multiple-access interference (MAI) and narrowband interference (NBI) in fading, dispersive channels. The detectors we consider are linear, one-shot structures, which allow for possible window enlargement and signal-space oversampling to improve performance. We focus on both zero-forcing and minimum-mean square-error design strategies, showing that the presence of NBI generally requires a time-varying processing of the observables, no matter what the optimization criterion. A thorough performance assessment of the proposed detectors is also presented, either through analytical formulas or through computer simulations. We finally deal with the problem of blind suppression of both MAI and NBI, introducing batch-estimation procedures to be implemented offline, which require very little and sometimes no prior knowledge as to the interference structure     

Novel semi-blind ICI equalization algorithm for wireless OFDM systems

Intercarrier interference is deemed as one of the crucial problems in the wireless orthogonal frequency division multiplexing (OFDM) systems. The conventional ICI mitigation schemes involve the frequency-domain channel estimation or the additional coding, both of which require the spectral overhead and hence lead to the significant throughput reduction. Besides, the OFDM receivers using the ICI estimation rely on a large-dimensional matrix inverter with high computational complexity especially for many subcarriers such as digital video broadcasting (DVB) systems and wireless metropolitan-area networks (WMAN). To the best of our knowledge, no semi-blind ICI equalization has been addressed in the existing literature. Thus, in this paper, we propose a novel semi-blind ICI equalization scheme using the joint multiple matrix diagonalization (JMMD) algorithm to greatly reduce the intercarrier interference in OFDM. However, the well-known phase and permutation indeterminacies emerge in all blind equalization schemes. Hence we also design a few OFDM pilot blocks and propose an iterative identification method to determine the corresponding phase and permutation variants in our semi-blind scheme. Our semi-blind ICI equalization algorithm integrating the JMMD with the additional pilot-based iterative identification is very promising for the future high-throughput OFDM systems. Through Monte Carlo simulations, the QPSK-OFDM system with our proposed semi-blind ICI equalizer can achieve significantly better performance with symbol error rate reduction in several orders-of-magnitude. For the 16QAM-OFDM system, our scheme can also improve the performance over the plain OFDM system to some extent.     

Iterative receiver for OFDM systems based on semi-blind channel estimation

In this paper we propose two iterative algorithms of joint channel estimation and symbol detection for Orthogonal Frequency Division Multiplexing （OFDM） systems. In which, superimposed pilot scheme is adopted and an initial Channel State Information （CSI） is obtained by employing a first-order statistic. In each subsequent iteration, we propose two algorithms to update the CSI. The Mean Square Error （MSE） of channel estimation and Bit Error Rate （BER） performance are given and simulation results demonstrate that the iterative algorithm using method B has good performance approaching the ideal condition.     

5G系统中基于相位补偿的半盲检测算法

由于物理上行控制信道格式2发送的解调参考信号所占发送信号比例较小,精确检测发送数据具有一定难度。针对现有半盲检测算法在有相位干扰情况下性能较差的问题,通过加入相位补偿过程,利用信号的相关性最小化损失函数,结合现有算法提出了基于相位补偿的半盲检测算法。仿真结果表明,所提算法在信噪比为-10 dB的情况下信号检测误码率相比传统算法下降了48.49%,并且所提算法的适用性相较基于信道复用的半盲检测算法得到了提升,适合实际工程应用。     

Blind FSR-LPTV equalization and interference rejection

We address the problem of synthesizing blind channel identification and equalization methods for digital communications systems, aimed at counteracting the presence of cochannel or adjacent-channel interference. Owing to the presence of the interfering signal, the minimum mean-square error equalizer turns out to be linear periodically time-varying, which is implemented by resorting to its Fourier series representation. Moreover, by exploiting the cyclic conjugate second-order statistics of the channel output, we propose a new weighted subspace-based channel identification method, which is asymptotically immune to the presence of high-level interference. Computer simulation results confirm the effectiveness of the proposed identification/equalization technique.     

Narrow-band interference rejection using real-time Fouriertransforms

An analysis is presented of a BPSK-PN (binary phase shift-keyed with pseudonoise) demodulator when present narrowband interference is attenuated using transform domain filtering. The signal of interest is a wideband direct-sequence spread-spectrum signal (DS-SS). The interference is a narrowband signal which may be of high power and which is either intentionally or unintentionally collocated in frequency and interfering with the signal of interest. The effect of windowing the input signal by a rectangular or Hamming windows as well as the use of an overlap and save scheme is presented. It is shown that the Hamming window far outperforms the rectangular window, and that the interference is for all purposes completely eliminated when the Hamming window is used in conjunction with the overlap and save scheme. The criterion used to evaluate the effectiveness of the different interference rejection techniques is the bit error rate (BER) as measured at the output of the demodulator     

An adaptive array for interference rejection

An adaptive array that rejects undesired or interfering signals is presented. The array pattern is controlled by an adaptive feedback system based on a steepest descent minimization of mean-square error. Error is defined as the difference between the array output and a locally generated reference signal. Minimization of mean-square error is closely related to maximization of signal-to-noise ratio (SNR). A two-element adaptive array has been built, and its experimental performance is discussed. Typical patterns for various desired and interfering signals are shown, as well as measured transient response. Finally, some experiments showing the array behavior with modulated signals are described. The results show that such an antenna system is capable of automatically rejecting interfering signals, subject only to certain basic constraints. No a priori information about the angles of arrival of the signals is required, Detailed knowledge of the waveforms of the desired and interfering signals is also not needed, although the spectral characteristics of the desired signal must be known.     

基于信号子空间的改进OFDM系统信道半盲估计

本文改进了一种基于信号子空间的OFDM系统半盲信道估计算法.该算法利用基于梯度变化的变遗忘因子递归最小二乘算法(GVFF-RLS)计算接收信号的自相关矩阵.通过同时对角化接收信号中的信息信号和噪声信号的全局协方差矩阵,推导出噪声信号子空间,无需对噪声信号的统计特性进行任何先验假定.本算法弥补了原始算法在慢衰落信道下收敛慢以及只限于加性白噪声的不足,实现了色噪声背景下高效半盲信道估计.仿真结果表明本文提出的算法具有良好的性能.     

干扰链路计算中频率相关抑制算法研究*

本文对WLAN与雷达系统之间干扰链路计算中的频率相关抑制算法（FDR）进行研究,通过使用OoB域内频点序列,采用离散方法得到频率相关抑制FDR,得出两系统共存时FDR与干扰限值和干扰隔离之间的关系,为WLAN和雷达系统间共存提供必要的理论支持。     

Narrow-band interference rejection in DS/CDMA systems using adaptive (QRD-LSL)-based nonlinear ACM interpolators

An Mth order adaptive lattice filter automatically generates all M of the outputs that would be provided by M separate transversal filters. This feature may effectively suppress narrow-band interference (NBI) of either unknown or time-varying bandwidth (or number of frequency bands) in direct-sequence code-division multiple access systems for which the order of the interference rejection filter that achieves the optimal performance is unknown or constantly changing. Moreover, a lattice filter may significantly outperform its transversal counterpart in complex jamming environments in which the adaptive lattice filter must suppress multiple jammers, since each stage of a lattice filter adapts to suppress an orthogonal component of the NBI. The paper develops a computationally efficient and numerically stable adaptive QR-decomposition-based least squares lattice (QRD-LSL)-based nonlinear approximate conditional mean interpolator to suppress NBI effectively. Simulation results demonstrate that both the signal-to-noise ratio improvement and the convergence rate achieved by the proposed interpolators outperform those of other existing prediction-based techniques.     

Simple adaptive algorithm for rejection of interference

A simple algorithm is presented which does not require inversion of the covariance matrix of received signals. Besides computational simplicity, it has the advantage of reducing the sensitivity to beam pointing error.     

An adaptive parallel algorithm for interference rejection

A new algorithm is suggested for fast approximate calculation of the dominating eigenvector and eigenvalues of the correlation matrix. The algorithm was used for synthesis of an adaptive rejection filter with parallel structure. Comparative analysis of the filter effectiveness is performed.