Area coverage adaptive nulling from geosynchronous satellites: Phased arrays versus multiple-beam antennas

Antenna design trade-offs associated with providing an area coverage communication link via a geosynchronous satellite, where the geographical area to be serviced by the associated adaptive antenna system is characterized by a narrow-cone angle directed at an a priori known region on the earth's surface, are considered. Interference sources within and just surrounding the coverage area are adaptively nulled; interference sources located far from the coverage area are minimized by designing the antenna system to have low sidelobes outside the coverage area. This minimizes the number of adaptive channels which must be processed, with subsequent decrease in satellite weight and power requirements. The antenna design trade-off is between the phased array (PA) and the multiple-beam antenna (MBA). Three specific performance factors are considered in the MBA/PA design trade-off: susceptibility to out-of-coverage-area interference sources which use up the adaptive degrees of freedom allocated to the desired coverage area; effects of reduced link margin for low-gain thinned arrays; and nulling bandwidth restrictions imposed on spread spectrum communication systems. Three classes of PA's are considered: filled arrays, high gain thinned arrays, and low-gain thinned arrays.     

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。     

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     

Using spectral estimation techniques in adaptive processing antenna systems

Improved spectral estimation techniques hold promise for becoming a valuable asset in adaptive processing array antenna systems. Their value lies in the considerable amount of additional useful information which they can provide about the interference environment, utilizing a relatively small number of degrees of freedom (DOF). The "superresolution" capabilities, estimation of coherence, and relative power level determination serve to complement and refine the data from faster conventional estimation techniques. Two conceptual application area examples for using such techniques are discussed; partially adaptive low-sidelobe arrays, and fully adaptive tracking arrays. For the partially adaptive area the information is utilized for efficient assignment of a limited number of DOF in a beamspace constrained adaptive system in order to obtain a stable main beam, retention of low sidelobes, considerably faster response, and reduction in overall cost. These benefits are demonstrated via simulation examples computed for a 16-element linear array. For the fully adaptive tracking array area the information is utilized in an all-digital processing system concept to permit stable hulling of coherent interference sources in the main beam region, efficient assignment/control of the available DOF, and greater flexibility in time-domain adaptive filtering strategy.     

基于自适应对消的单通道相位编码同频异步干扰抑制

针对相位编码脉冲压缩雷达,利用多部雷达发射信号调相码间较好的正交性,结合自适应干扰对消原理,提出了一种基于自适应对消的单通道相位编码同频异步干扰抑制算法,在单通道情况下较好地抑制了同频异步干扰。并提出了同频异步干扰对消的结构,从统计特性与维纳霍夫方程两方面对算法进行性能分析。仿真表明,该算法在干信比38dB时脉压处理后主副比可达到20dB。     

Adaptive array with global weighted spatial smoothing

Global weighted spatial smoothing is utilised in adaptive arrays for coherent interference suppression. With the prior knowledge of the directions of coherent sources, signal cancellation is eliminated and the smoothing index can be reduced to the number of sources even for small spatial separation.     

Wide-band nulling performance versus number of pattern constraints for an array antenna

The problem of wide-band pattern hulling for an array antenna is addressed, in particular the relation between the number of constraints imposed and the sidelobe suppression achieved. The two constraint methods considered are multiple nulling over a narrow angular sector and hulling of the pattern and its derivatives at a single point. To first order the sidelobe cancellation is shown to be independent of the actual pattern type and is determined by only two parameters: the number of null constraintsMand the number of sidelobesvto be cancelled. The latter parameter directly translates into a desired hulling bandwidthDelta f. A numerical solution to the problem is offered in the form of curves, from which the number of nulls required to suppress a jammer over a given bandwidth can be conveniently estimated. This number is indicative of how many degrees of freedom a conventional adaptive antenna system must allocate to attain a specific hulling performance.     

Source-oriented adaptive beamforming

A system concept expected to improve sonar multiple target detection and classification performance in severe directional interference environments is presented. Adaptive nulling of undesired strong interference sources and detection of desired weak sources are achieved by utilizing constrained adaptive processing techniquestogether with conventional processing techniques. The adaptive processing functions are incorporated in the overall system architecture in a manner which maintains the computational complexity and storage requirementslinearly proportional to the product of the number of interference sources and the number of adaptive weights per interference source. In addition, a detailed discussion is provided concerning the importance of certaina priori assumptions on constrained adaptive algorithm performance.This research was supported by NSERC Grant A0912 and Raytheon Company Independent Research and Development Programs.     

Adaptive detection for DS-CDMA

A review of adaptive detection techniques for direct-sequence code division multiple access (CDMA) signals is given. The goal is to improve CDMA system performance and capacity by reducing interference between users. The techniques considered are implementations of multiuser receivers, for which background material is given. Adaptive algorithms improve the feasibility of such receivers. Three main forms of receivers are considered. The minimum mean square error (MMSE) receiver is described and its performance illustrated. Numerous adaptive algorithms can be used to implement the MMSE receiver, including blind techniques, which eliminate the need for training sequences. The adaptive decorrelator can be used to eliminate interference from known interferers, though it is prone to noise enhancement. Multistage and successive interference cancellation techniques reduce interference by cancellation of one detected signal from another. Practical problems and some open research topics are mentioned. These typically relate to the convergence rate and tracking performance of the adaptive algorithm     

互信息量最大化和低复杂度的全双工中继网络自干扰消除和干扰对齐算法

该文针对多用户全双工中继干扰信道,同时考虑全双工中继自干扰消除及用户端干扰消除问题。首先,提出了基于最大化全局互信息量的自干扰消除和干扰对齐算法,并具体给出了自干扰消除矩阵的具体求解算法和方案。进一步,给出了信号对齐和干扰抑制的可行性条件,并分析了系统的互信息量和所受干扰噪声功率,以及系统的自由度。理论分析和仿真结果显示,与现有的典型全双工中继方案相比,该文算法可以提高系统互信息量和自由度,并有较低误码率;另外,该文算法的中继只需进行简单的功率约束,不需做复杂的信号处理,降低了整个系统的信号处理复杂度。     

基于干扰抵消的卫星异常信号检测应用

首先提出了需要区分两类不同来源的卫星干扰信号的问题，然后提出了采用自适应干扰消除技术来抵消一种干扰信号，从而将两类干扰信号分离的解决方法，最后对该方法的可行性进行了仿真，仿真结果表明该方法可以较好地解决上述问题。     

Interference Cancellation for High-Frequency Surface Wave Radar

The performance of high-frequency surface wave radar (HFSWR) is known to suffer from external environmental interference and noise, such as cochannel radio-frequency interference from other radiating source, ionospheric clutter, lightning impulsive noise, etc. This paper experimentally evaluates the interference cancellation performance of various adaptive beamforming schemes with respect to the aforementioned three types of interferences in an attempt to find the most promising adaptive cancellation scheme in practical HFSWR environment.     

船舶航行辐射噪声的主动控制方法研究

船舶航行辐射噪声控制对于环境保护和军事应用均具有重要意义。根据船舶的航行轨迹和接收点建立了自适应噪声抵消模型,从船舶外部对其产生的特定低频线谱进行主动控制,实现局部自由声场静区。针对低频线谱信号,在船舶上布设自适应次级声源,进行了不同信号频率的仿真,研究其在特定空间内产生的降噪效果。仿真显示当船舶在特定区域内航行时,次级声源的开启能够在接收点处实现特定低频线谱信号的有效抵消。针对仿真结果,理论推导了有效声抵消区域半径的计算公式。由此得到了一种可能的船舶航行辐射噪声低频线谱主动控制方法:首先计算有效声抵消区域半径,当船舶进入或离开该区域时,动态开启或关闭次级声源,从而实现噪声的有源控制。      

WCDMA无线直放站中自适应干扰抵消单元的设计方案

WCDMA数字无线直放站由于架设方便,外形美观等优点受到市场的追捧。它采用自适应干扰抵消技术,可以消除由于自身收发天线隔离度小而产生的自激问题。文章针对WCDMA系统中的自适应干扰抵消技术展开了研究。重点对时域的三种干扰抵消算法:LMS、NLMS和RLS算法,进行了研究和性能分析,并在原有的NLMS算法的基础上,为降低复杂度和节省资源,提出一种新的H-NLMS算法。最后在MATLAB仿真环境中建立WCDMA干扰抵消直放站系统链路级仿真模型,验证改进的算法和干扰抵消单元的性能。     

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.     

Representation of electromagnetic fields over arbitrary surfaces bya finite and nonredundant number of samples

It is shown that the electromagnetic (EM) field, radiated or scattered by bounded sources, can be accurately represented over a substantially arbitrary surface by a finite number of samples even when the observation domain is unbounded. The number of required samples is nonredundant and essentially coincident with the number of degrees of freedom of the field. This result relies on the extraction of a proper phase factor from the field expression and on the use of appropriate coordinates to parameterize the domain. It is demonstrated that the number of degrees of freedom is independent of the observation domain and depends only on the source geometry. The case of spheroidal sources and observation domains with rotational symmetry is analyzed in detail and the particular cases of spherical and planar sources are explicitly considered. For these geometries, precise and fast sampling algorithms of central type are presented, which allow an efficient recovery of EM fields from a nonredundant finite number of samples. Such algorithms are stable with respect to random errors affecting the data     

Sparse LCMV beamformer design for suppression of ground clutter inairborne radar

Cancellation of the ground clutter received at an airborne phased array radar is an inherently two dimensional problem. Clutter returns are Doppler shifted due to platform motion forcing the use of processors that can resolve targets in both velocity (Doppler) and azimuth. Fully adaptive processors that operate in both dimensions require prohibitively large computation so that reduced adaptive dimension, or partially adaptive processors must be considered. In conventional partially adaptive linearly constrained minimum variance (LCMV) beamformer design the approach taken has been to represent the interference subspace with some reduced set of vectors, typically the eigenvectors associated with the largest eigenvalues of the interference covariance matrix. This technique does yield good performance but will not give the optimum performance for a given partially adaptive dimension. In this paper, an off-line method for selecting the “best” degrees of freedom to be retained in a partially adaptive design is presented. The sequential algorithm described selects those degrees of freedom that best minimize the beamformer output mean square error. This approach leads to a sparse structure for the transformation matrix, which when implemented in a generalized sidelobe canceller (GSC) structure results in a reduction in the computational load. This approach also allows a reduction in the required adaptive dimension as compared to the eigenvector based approach. Illustrative examples demonstrate the effectiveness of this method     

Interference suppression with adaptive multipath control technique for broadband private wireless access systems

Proposed is an adaptive multipath control technique to suppress interference radiation from a transmitter to the non-target receivers for broadband private wireless access systems. In the proposed scheme, deep and wide creation techniques are employed in the adaptive array antenna to effectively use a limited number of antenna degrees of freedom under rich scattering indoor channel conditions. Computer simulation confirms that the proposed scheme is very effective in control of the transmit antenna directivity to suppress interference radiation, thereby the interference to the non-target receivers is largely reduced, and BER performance is greatly improved with low outage probability.     

A multiple time scale modularized adaptive beamformer

This paper analyzes the cascaded equivalent form of the minimum variance distortionless response (MVDR) beamformer. A unique feature of the modularized MVDR (M²VDR) beamformer is the ability to distribute adaptive degrees of freedom (DOF) among beamformer stages. This property of the M²VDR beamformer allows DOF to be adapted over different time scales. As a consequence of the multiple stage decomposition adaptive beamformer weights appear in a form which suggest an apparent increase in the number of DOF. To properly analyze this ease an alternative interpretation of adaptive DOF is introduced to establish the equivalence between the MVDR beamformer and its cascaded realization. In the second part of this paper the distribution for the output power estimate of a P stage M²VDR beamformer is derived. Analysis reveals the necessity of placing constraints on the adaptation time assigned to each beamformer stage. Simulation experiments are presented that demonstrate the applicability of the M ²VDR beamformer in resolving closely spaced sources under impulsive interference conditions