Partially adaptive beamforming for correlated interferencerejection

Conventional linearly constrained adaptive beamformers often suffer from severe signal cancellation in the presence of interferers correlated with the signal. We propose a partially adaptive beamforming technique for correlated interference rejection in broadband signal environments. The beamformer output mean squared error is decomposed into an interference mean squared error term and an additional signal cancellation term that is due to the presence of correlated interference. Both mean squared errors depend on the adaptation space. The partially adaptive beamforming technique proposed here chooses an adaptation space which results in little signal cancellation while maintaining satisfactory interference cancellation. It is shown that, for a given interference scenario, a partially adaptive beamformer can be designed such that maximum interference cancellation is achieved without any signal cancellation. In practice, an approximate design procedure is provided to accommodate a set of likely interference scenarios. Analysis of the feasibility of this approach is presented. The effectiveness of the technique is demonstrated through examples     

基于相关性的杂波环境自适应对消方法

旁瓣对消技术是应对旁瓣有源压制干扰的有效手段。实际应用发现,对于工作在具有强杂波环境的中近程雷达,指向杂波区域的回波数据中会存在大量乃至全距离的杂波数据,对干扰样本的选取带来了极大困难。错误选取强杂波数据作为干扰样本不仅难以有效对消干扰,还可能对检测目标的回波造成恶劣影响。本文提出一种基于相关性的杂波环境自适应旁瓣对消方法,首先统计辅助波束与主波束之间的干扰相关性,然后根据相关性统计结果采取不同的对消处理措施,仿真试验平台的试验数据表明本文方法不仅可以在强杂波环境下有效提取样本进行对消处理,而且保障了弱杂波环境下的对消性能,较大地提高了旁瓣对消方法在杂波环境下的适用性。     

基于离散余弦变换的旁瓣对消技术研究

自适应旁瓣对消是一种有效抑制有源干扰的措施。研究了自适应旁瓣对消和合成孔径雷达（SAR）有源遮盖式干扰的基本原理,详细推导了基于离散余弦变换的DCT-LMS频域自适应方法,并将其应用于SAR的旁瓣对消系统中。通过与其他自适应算法的对比实验,证明了DCT-LMS算法兼有收敛速度快,计算量小的优点。最终模拟实际环境中的干扰源,利用SAR的实际数据进行了仿真实验。实验结果表明,DCT-LMS算法能有效地抑制有源干扰噪声,确保SAR接收机正常工作,具有较高的干扰对消比。     

Fuzzy adaptive partial parallel multistage detection for MIMO systems

Vertical Bell Laboratories Layered Space-Time (V-BLAST) detection followed by a full parallel interference cancellation (full PIC) or a constant-weight partial parallel interference cancellation (CW-PPIC) scheme has been proposed. However, its performance degrades when the received power of the antenna is unbalanced and/or the system is heavily loaded. Therefore, V-BLAST is proposed, followed by fuzzy adaptive partial parallel multistage detection for MIMO systems. The simulation results show that the error probability of this proposed method is better than that of V-BLAST followed by full PIC or CW-PPIC schemes     

Maximizing jammer effectiveness for evaluating the performance of adaptive nulling array antennas

A theory is developed which is used to find interference source distributions which maximize consumption of the degrees of freedom forN-channel adaptive nulling arrays with arbitrary element positions. For a given number of interference sources, after proper positioning, these sources represent a maximally stressed environment for the adaptive array degrees of freedom. The interference covariance matrix eigenvalues are shown to have a direct bearing on the number of degrees of freedom consumed as well on the adaptive cancellation. Numerical examples are given showing that certain source geometries produce the situation where little or no adaptive cancellation is possible due to the available degrees of freedom being severely taxed.     

New aspects to event-synchronous cancellation of ECG interference: an application of the method in diaphragmatic EMG signals

An "event-synchronous interference canceller" (ESC) for cancellation of electrocardiographic (ECG) interference in diaphragmatic electromyographic (EMGdi) signals is addressed in this paper. ESC pursues the concept of the "event synchronous adaptive interference canceller" (ESAIC), which was proposed in [1] as a specific application of the well known "adaptive noise canceller" (ANC) paradigm, but ESC uses a simple adaptive gain control (AGC) instead of the complex adaptive filter of the ANC. The proposed ESC method is evaluated using both computer simulations and real EMGdi data, and its efficiency in interference cancellation is compared to that of ESAIC. Of particular interest is the result that the ESC can replace the ESAIC providing better performance as well as a considerable reduction of computational costs.     

一种自适应通道均衡技术及其实现

自适应天线接收通道间的幅相不一致会其以抑制干扰的零点深度变浅、方向图副瓣电平升高,严重影响自适应天线的抗干扰性能,因此在其工作之前必须对其各通道的幅度和相位特性进行均衡。提出了一种基于变步长最小均方算法（LMS）的自适应通道均衡技术,并给出了其现场可编程门阵列（FPGA）实现方案,仿真结果表明,该方案可以在很宽的频率范围内获得高均衡精度,可以为提高宽带自适应天线系统的抗干扰性能提供参考和借鉴。     

FMCW车载雷达自适应干扰抑制方法

车载雷达间相互干扰可能会导致传感器灵敏度降低,某些情况下会产生虚警.针对这个问题,本文提出了一种基于粒子群优化和自适应对消的干扰抑制方法.该方法将发射端波形优化及接收端自适应滤波相结合,进一步提高雷达的干扰抑制能力.首先采用粒子群算法进行波形参数优化,在参数约束范围内最小化波形相关性,缓解虚警问题,然后基于正交接收机内...     

Successive blind multi-target adaptive antenna array and interference cancellation for DS-CDMA

An effective design of successive joint blind multi-target (MT) adaptive antenna array (AAA) and interference cancellation is presented for multi-user detection of DS-CDMA. The MT-AAA employs the adaptive block size least square-constant modulus algorithm (LS-CMA) with pre-despreading at each antenna element combined with a simple weight adaptive canceller. The combined process is repeated successively for the detection of all users without any knowledge of the channel or training sequences. It is shown to utilise the advantages of both techniques and provides improved performance in fading channel for the near-far problem, in-beam interference, and a high number of users     

Robust blind PIC with adaptive despreader and improved interference estimator

An effective design of multistage parallel interference cancellation (PIC) receiver using blind adaptive (BA) despreader and pre‐respreader interference estimator for uplink CDMA is proposed and analysed. A novel algorithm is designed, which exploits constant modulus (CM) property of the users' transmitted signals and inherent channel condition to perform adaptive despreading based on minimum error variance criteria. This is carried out by BA weighting of each chip signal for accurate tracking of the desired user's signal power and hence for more improved data detection at the output of each stage of PIC. Furthermore, the despreader weights are used within the adaptive pre‐respreader interference estimation and cancellation to obtain online scaling factors during every symbol period, without any knowledge of users' channels or the use of training sequences. It is found that this way of estimation is optimal in minimum mean squared error sense, and hence, significant reduction in interference and noise variance is observed in detection and estimation of the desired users' signals compared with conventional PIC. Bit error probability of the proposed PIC is obtained using Gaussian Approximation method. Extensive simulation results are shown, which demonstrate impressive performance advantage in fading environments, high system loading, and severe near far conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

电离层返回散射探测中干扰抑制方法研究

电离层返回散射工作在高频频段,密集的外部干扰如短波通信、广播电台及大气噪声等污染了接收数据,严重影响返回散射电离图的判读。利用外部干扰的空时特性,提出了一种自适应波束形成-干扰对消级联去干扰的方法。对实测数据的处理结果表明这种方法的有效性和实用性。     

Adaptive parallel interference cancellation for CDMA systems—A weight selection and filtering scheme

Parallel interference cancellation (PIC) is a well-known multiuser detection algorithm in direct-sequence code-division multiple-access (DS-CDMA) systems. It is typically implemented with a multi-stage architecture. One problem associated with the PIC is that unreliable interference cancellation may occur in the early stages and the system performance may be degraded. Thus, the partial PIC detector was developed to control the cancellation level by use of interference cancellation factors. Partial PIC can be implemented with an adaptive form, in which optimal weights are derived using the least mean square (LMS) algorithm. In this paper, we propose an algorithm improving the conventional adaptive partial PIC. The main idea is to reduce the number of active weights in the LMS algorithm, and to perform weight post-filtering such that the resultant excess mean square error can be reduced. We also analyze the performance of the proposed algorithm and derive the bit error rate of the second stage output. Simulation results verify that the proposed algorithm outperforms the conventional partial PIC, and derived analytical results are accurate.     

基于CLEAN算法的自适应旁瓣对消技术

自适应旁瓣对消技术能够很好地抑制旁瓣干扰,但在应用中发现, 自适应旁瓣对消对跟踪的高信噪比目标带来的信噪比损失较大,导致单脉冲和差测角精度下降。本文提出了一种基于CLEAN算法的自适应旁瓣对消方法,首先通过观测目标的先验信息构建目标回波模型,再利用该回波模型剔除对消通道中的目标信息,然后基于剔除目标信息后的对消通道数据,重新计算最优加权值进行主通道的干扰对消,最后仿真和实测结果验证了该方法不仅可以减少主通道中目标对消后的信噪比损失,同时也降低了对消后对目标测角精度的影响。     

一种低副瓣稳健自适应波束算法

本文提出一种新型低副瓣自适应波束形成算法,解决了传统自适应波束形成器在干扰和高信噪环境下算法性能急剧下降的问题,并降低了快拍数对算法稳健性的影响。该算法基于标准Capon波束形成器,利用消除空域噪声的方法提高期望矢量的重估精度,并结合功率估计算法重构出干扰噪声协方差矩阵;然后使用特征干扰相消算法二次重构噪声协方差矩阵得到最优权值,增强算法在低样拍下的稳定性;最后对最优权值进行切比雪夫加权和二次约束实现了零陷加宽。仿真实验结果表明：新算法计算量小,旁瓣电平低,降低了在干扰运动和导向矢量失配时快拍数和信噪比对性能的影响。     

Adaptive multistage parallel interference cancellation for CDMA

Although the multistage interference cancellation detector is simple in structure, its performance degrades when the number of active users becomes large. In some cases, the performance is even worse than that without cancellation, due to the lack of the exact knowledge of the interfering signal in cancellation. Partial interference cancellation suggested by Divsalar and Simon (see IEEE Trans. Commun., vol.46, p.258-68, 1998) tries to remedy this weakness by reducing the cost of a wrong interference estimation through a weight in each stage. This paper presents an adaptive multistage structure based on the partial interference cancellation approach. In this structure, the weights are obtained by minimizing the mean-square error between the received signal and its estimate through a least mean square (LMS) algorithm. The resulting weights contain reliability information for the hard decisions made in the previous stage. Neither a training sequence nor a pilot signal is needed in the proposed scheme, and its complexity is much lower than that of linear multiuser detectors. Simulation results show that the proposed scheme can outperform some of the existing interference cancellation methods in both the additive white Gaussian noise (AWGN) and the multipath fading channels     

Parallel Interference Cancellation in Multiuser CDMA Channel Estimation

Parallel interference cancellation (PIC) based channel parameter estimators for frequency selective fading channels are proposed for the uplink in code-division multiple-access (CDMA) mobile communication systems. The performance of PIC based algorithms depends heavily on the quality of the multiple-access interference estimates, which can be improved by using adaptive channel estimation filters. The performance of two adaptive complex channel coefficient estimation filters has been verified in a fading channel by computer simulations. According to the results, the PIC based adaptive channel estimators outperform clearly conventional, successive interference cancellation, and decorrelation based adaptive channel estimators. The PIC method is also used in delay tracking. By using the principles of sample-correlate-choose-largest (SCCL) delay trackers, a robust algorithm for multiuser delay tracking in fading channels is obtained.     

自适应波束形成算法工程应用中的关键技术研究

对自适应波束形成算法工程应用中的一些关键技术进行了讨论。着重讨论了基于广义旁瓣对消结构的自适应波束形成器设计中的关键问题。给出了一种基于广义旁瓣对消结构的自适应波束形成算法应用方案,以及试验结果。     

WCDMA系统上行链路空时干扰抑制技术

该文提出一种将自适应并行干扰对消技术简化为利用软判决变量在一个比特周期内的平均作为再生信号幅度估计的并行干扰对消方法,这种简化大大降低了原方法的运算量,而且具有很好的稳定性。仿真实验表明在单阵元接收情况下,简化方法的对消效果较原方法有些下降,但在阵列接收然后进行并行干扰对消的情况下,二者的性能基本没有差别。因而该文针对WCDMA系统上行链路的帧结构特征,进一步提出了导频位辅助LMS-DRMTA算法加上软判决变量平均幅度估计法的空时联合WCDMA系统的干扰对消方案。     

An orthogonalized blind algorithm for hybrid of adaptive array and equalizer

The problems generated by the interference will be more complicated in the future. A combination of adaptive array and equalizer has been employed to solve the problems of interference when an adaptive array alone cannot suppress all the interferences. A constant modules algorithm (CMA) of the combination system was proposed to solve the problems of insufficient degrees of freedom and main‐beam multipath interference when no training signal is transmitted. The limitation of the CMA for combination systems is due to its slow rate of convergence. In this paper, an orthogonalized blind algorithm for hybrid of array and equalizer (OBHAE) is proposed to combat the problems of the interference. Because the modified input vector of the adaptive array is orthogonalized by the OBHAE in advance, the convergent rate of the CMA system can be improved by the OBHAE. When the coherent interference presents, the performance of the system will be degraded. In this paper, an orthogonalized spatial smoothing blind (OSSB) algorithm is proposed to further enhance the cancellation of the coherent interference. In the OSSB, we combine the OBHAE with the spatial smoothing method to combat the coherent interference problem. Simulation results are presented to demonstrate the merits of the OBHAE and the OSSB. Copyright © 2012 John Wiley & Sons, Ltd.