Adaptive processing at the subarray level

This paper describes a class of partially adaptive arrays with adaptive processing applied to the outputs of steered subarrays. The problem is to detect a signal or estimate its direction of arrival in the presence of jammers. The advantage of applying adaptive processing to subarrays is that it requires much less CPU time than the corresponding fully adaptive processing. The subarray processing equations for the two kinds of problem are described. In this paper, we compare partially adaptive processing performance with fully adaptive processing performance in the case of the following antenna and signal sources:

• •- array with regularly spaced sensors ;
• •- between 20 and 100 elements ;
• •- between 3 and 20 subarrays ;
• •- a single jammer ;
• •- desired signal from the antenna zenith.

We suggest a method for determining the optimal subarray configurations in this case. An example is given to show that the performance of an antenna with five subarrays is comparable to that of a fully adaptive thirty-element array for eliminating a single jammer with a target at the zenith.     

Coordinated adaptive beamformer over distributed antenna network

The spatial diversity of distributed network demands the individual filter to accommodate the topology of interference environment. In this paper, a type of distributed adaptive beamformer is proposed to mitigate interference over coordinated antenna arrays network. The proposed approach is formulated as generalized sidelobe canceller (GSC) structure to facilitate the convex combination of neighboring nodes’ weights, and then it is solved by unconstrained least mean square (LMS) algorithm due to simplicity. Numerical results show that the robustness and convergence rate of antenna arrays network can be significantly improved in strong interference scenario. And they also clearly illustrate that mixing vector is optimized adaptively and adjusted according to the spatial diversity of the distributed nodes which are placed in different power of received signals to interference ratio (SIR) environments.     

Blind GPS receiver with a modified despreader for interference suppression

The global positioning system (GPS) was designed to provide location estimates for various civilian and military applications using at least four satellites. Since GPS signals have a low signal-to-noise ratio (SNR), they also have a low signal-to-jammer ratio so that the accuracy of location estimates is influenced by cochannel interference and intentional jammers. We propose a low-complexity blind adaptive receiver that is based on a novel modified despreader and the constant modulus (CM) array. This system is capable of ing directional interference and capturing the GPS signal of interest without requiring explicit angle-of-arrival (AOA) information. We also consider the multiple satellite problem and extend the proposed receiver to capture several GPS signals of interest. Representative computer simulation examples are presented to illustrate the performance of the multicomponent system for the suppression of different jammer types.     

An Lms Adaptive Array Using a Pilot Signal

A least mean square (LMS) adaptive array requires a reference signal. When the desired signal contains a pilot signal, it may be used as the reference signal. In this paper the steady-state performance of an LMS adaptive array in which the pilot signal is used as the reference signal is examined. It is shown that the LMS adaptive array occasionally suppresses the desired signal. The loop gain, which is an important parameter, is also considered.     

阵列旋转对功率倒置算法性能的影响分析

针对卫星导航抗干扰中,功率倒置算法下导航信号载噪比受干扰来波方向的影响,通过理论推导和数值计算的方法研究了天线阵列旋转与功率倒置算法抗干扰性能的关系。分析结果表明:天线阵列旋转会使功率倒置算法下的阵列增益在最大值和最小值之间呈现连续的、周期性的变化。相比固定天线阵不变的载噪比,阵列旋转能够使信号在一段时间内获得更大的载噪比,对于四阵元Y型阵列,阵列旋转理论上对载噪比的最大提升程度可以达到14dB左右。仿真结果验证了理论推导的正确性。     

Application of the Normalized LMS Algorithm to MSLC

For some conditions, the convergence time of the conventional LMS algorithm is longer than the radar dwell time so that the MSLC technique does not cancel jammers. The convergence time depends upon the power and angular locations of the jammers. The normalized LMS technique can decrease convergence times by several orders of magnitude. It causes the convergence time to be essentially independent of the jammer powers and decreases the convergence time dependence upon location. The derivation of an exact first moment analysis of the weights for the normalized LMS algorithm is given. Simulation results are also given. There is excellent agreement between the two.     

深空组阵迭代FX相关合成算法及性能分析

针对火星距离下大规模天线组阵中极微弱接收信号的高效合成问题,在VLBI(Very Long Baseline Interferometry,甚长基线干涉测量)的FX相关器开环处理架构基础上提出了一种新的迭代FX相关合成算法,对算法原理进行了详细理论推导,对数据处理流程、算法合成性能等进行深入分析,与FSC(Full-Spectrum Combining,全频谱合成)、BC(Baseband Combining,基带合成)、SSC(Symbol-Stream Combining,符号流合成)等组阵方案进行性能仿真对比,并给出该算法在36接收天线组阵的实测试验结果。仿真和试验结果表明,迭代FX相关合成算法相比于FSC、BC、SSC等组阵方案具有较好的合成性能,在输入带内信噪比不低于-20d B时,合成效率达到了95%以上,非常适用于火星天线组阵微弱接收信号的组阵合成。     

Convergence Rate of the Extended SMI Algorithm for Narrowband Adaptive Arrays

An extended sample matrix inversion (SMI) algorithm can be used for minimizing the mse (mean-squared error) between the output of an N-element adaptive array and a desired reference signal. This algorithm is shown to yield mse within 3 dB of minimum (on the average) after (2N - 1) observations of the antenna element outputs.     

卫星导航接收机空间自适应调零抗干扰技术研究

比较了两种自适应调零抗干扰天线系统方案的优缺点,根据实际应用场合,确定抗干扰天线方案设计为中频输出的数字调零系统.对自适应调零的信号处理进行了理论研究,建立了阵列信号的模型,根据导航卫星信号远小于干扰信号等因素,选用了基于线性约束的功率倒置算法,通过调整权值系数使得天线阵的方向图零点对准干扰信号方向,实现干扰零陷.仿真结果表明:通过零陷处理可达到干信比为77dB的抗干扰能力,验证了算法的有效性.     

Design and Application of a DSP Controller for Giant Magnetostrictive Smart Structure

It is proposed a digital signal processing (DSP) controller used in the control system of six degree-of-freedom (DOF) giant mag-netostrictive smart structure (GMSS). Also are presented the controller design and its implementation, the embedded adaptive least mean-square (LMS) control algorithm and the real-time experiments of GMSS. Three programs are embedded in this controller. Of them are the adaptive LMS control algorithm and the other two which are used to search for the optimal values for the initial weight vectors. Moreover, the work flow and the control approach of the GMSS with the DSP controller are introduced. The experimental results indi-cate that the DSP controller has better control precision and real-time property, and the damping effect is up to 20 dB-30 dB.     

Adaptive digital beamforming for angle estimation in jamming

A radar digital beamforming (DBF) architecture and processing algorithm is described for nulling the signal from a mainlobe electronic jammer and multiple sidelobe electronic jammers while maintaining monopulse angle estimation accuracy on the target. The architecture consists of a sidelobe jamming (SLJ) cancelling adaptive array (AA) followed by a mainlobe jamming (MLJ) canceller. A mainlobe maintenance (MLM) technique or constrained adaptation during the sidelobe cancellation process is imposed so that the results of the SLJ cancellation process do not distort the subsequent mainlobe cancellation process. The SLJ signals and the MLJ signals are thus cancelled sequentially in separate processes. This technique was developed for improving radar processing in determining the angular location of a target, and specifically for improving the monopulse technique by maintaining the accuracy of the target echo monopulse ratio in the presence of electronic jamming by adaptive suppression of the jamming signals before forming the monopulse sum and difference beams     

Adaptive Array Behavior with Periodic Phase Modulated Interference

We consider a least mean square (LMS) adaptive array [1] receiving a phase modulated interference signal. The phase modulation is assumed to be periodic and to have finite bandwidth. Under these assumptions, we determine the time-varying array weights, the modulation on the array output desired signal, and the time-varying output interference-to-noise ratio (INR) and SINR (signal-to-interference-plus-noise ratio). We present numerical results describing the behavior of a 2-element adaptive array that receives an interference signal with sinusoidal phase modulation. We show how each signal parameter (arrival angle, power, modulation index, and modulation frequency) affects the performance of the array.     

The Steady-State Antenna Patterns of Adaptive Arrays

The antenna pattern of a receiving adaptive array of arbitrary three-dimensional geometry operating in an environment of K sources, one desired signal and (K - 1) jammers, is considered. It is shown that the adapted (voltage) antenna pattern of the array is a linear combination of K (or less) basis patterns, each of which is a function of one source only. We find that these basis patterns have a simple physical meaning, namely, the kth basis pattern is the pattern realized by the array when the transmission of source k is considered a desired signal and all other sources are turned off. When the array elements are isotropic, these basis patterns are retrodirective (that is, the mainlobe of the kth basis pattern points at source k). It had been shown that this property is also exhibited by a different decomposition of the adapted pattern in the special case of a single jammer (K = 2). In contrast, our decomposition which is simpler than the earlier one, yields retrodirective beams for all K. The simple, physically meaningful, pattern decomposition developed here is quite significant in the insight it provides regarding the basic underlying principles of adaptive arrays. It is also instrumental in elucidating their capabilities and limitations.     

Robust algorithm for combating look direction error problems

A simple and fast zero tracking algorithm for adaptive arrays with large look direction errors is presented and investigated. Basically, the algorithm is based on adjusting the complex zeroes of a power inversion array in a time-multiplexed manner to track all the sources in the environment. To preserve the desired signal which is supposed to be closest to the look direction of 0°, the algorithm removes the zero with the shortest distance to e^j0 so that the directional response consists of only nulls steered at the jammers. When compared with the least mean square (LMS) algorithm employing zeroth and first-order look direction constraints, the new algorithm has about the same implementation complexity, is considerably faster, and possesses a much better signal-to-noise ratio (SNR) performance when the look direction is erroneous     

Adaptive array transient sidelobe levels and remedies

The transient sidelobe level of a sidelobe canceler (SLC) is a function of the external noise environment, the number of adaptive auxiliary antennas, the adaptive algorithm used, auxiliary antenna gain margins, and the number of samples used to calculate the adaptive weights. An analytical result for the adaptive sidelobe level is formulated for the case when the adaptive algorithm is the open-loop, sampled matrix inversion (SMI) algorithm. The result is independent of whether concurrent or nonconcurrent data processing is used in the SMI algorithm's implementation. It is shown that the transient sidelobe level is eigenvalue dependent and increases proportionally to the gain margin of the auxiliary antenna elements with respect to the quiescent main antenna sidelobe level. Techniques that reduce this transient sidelobe level are discussed, and it is theoretically shown that injection independent noise into the auxiliary channels significantly reduces the transient sidelobe level. It is demonstrated that using this same technique reduces the SMI noise power residue settling time     

Adaptive Maximum Likelihood Receiver for Direct-Ranging Applications

Recent interest in direct-ranging navigation methods has prompted new research into practical receiver structures which provide improved signal processing. Maximum likelihood receivers are compared with conventional phase-locked receivers by theoretical and simulation methods as phase estimators based on signal measurements only. Signal-to-noise ratio (SNR) enhancement is examined and filter recommendations made. An adaptive maximum likelihood receiver is then developed which uses both signal measurements and a priori data to improve phase estimation accuracy. Simulation results indicate a 33.3 dB processing gain yielding a ranging error standard deviation of ±15 feet for zero dB received SNR. Nonadaptive and adaptive receivers are fabricated, flight tested, and experimental results reported.     

Application of Adaptive Arrays to Suppress Strong Jammers in the Presence of Weak Signals

The purpose of this paper is to demonstrate that an adaptive array can be used to acquire weak signals, whose direction and timing are unknown, in an environment of stronger jammers. Specifically, it is shown that in an environment of one weak signal and one strong jammer, the adaptive array output suppresses the strong jammer below the weak signal by roughly the same amount that the jammer exceeded the signal before adaptation.     

Electronically Tracking Antenna System for Satellite Reception

This correspondence describes a novel electronically tracking antenna system for satellite reception in the VHF range. The "hedgehog" antenna consists of several antennas directed in different directions to cover the whole sky. An electronic switch, controlled by the satellite receiver, connects the receiver to the antenna from which the desired satellite signal is obtained. This system is especially suitable for unmanned reliable receiving stations if an antenna gain of the order of 10 dB is enough.     

Median cascaded canceller for robust adaptive array processing

A median cascaded canceller (MCC) is introduced as a robust multichannel adaptive array processor. Compared with sample matrix inversion (SMI) methods, it is shown to significantly reduce the deleterious effects of impulsive noise spikes (outliers) on convergence performance of metrics; such as (normalized) output residue power and signal to interference-plus-noise ratio (SINR). For the case of no outliers, the MCC convergence performance remains commensurate with SMI methods for several practical interference scenarios. It is shown that the MCC offers natural protection against desired signal (target) cancellation when weight training data contains strong target components. In addition, results are shown for a high-fidelity, simulated, barrage jamming and nonhomogenous clutter environment. Here the MCC is used in a space-time adaptive processing (STAP) configuration for airborne radar interference mitigation. Results indicate the MCC produces a marked SINR performance improvement over SMI methods.     

GPS多径信号的自适应滤波估计方法

 研究全球定位系统(GPS)多径信号估计的问题。通过分析自适应滤波器的原理,建立了数字中频信号处理的数学模型,提出一种用自适应滤波实现GPS多径幅度、码相位和载波相位估计的方法。该方法采用不同延迟的伪随机序列对信号进行解扩、解调和累加,得到了作为期望信号的系列自适应滤波相关值。对该方法与其他3种方法进行了理论上的分析比较,得出本方法具有信噪比高、自适应滤波性能好、带有码相位信息和不存在载波模糊度问题等优点。根据各种滤波器算法的特点和本应用的需求,给出了选用递归最小二乘算法实现的方法。通过计算机仿真,验证了提出的方法能够在14 dB的信噪比下,以1个采样间隔的时间延迟分辨率和0.005周的载波相位估计精度估计出GPS L1的多径信号。