SMI adaptive antenna arrays for weak interfering signals

The performance of adaptive antenna arrays in the presence of weak interfering signals (below thermal noise) is studied. It is shown that conventional adaptive antenna arrays sample matrix inversion (SMI) algorithm is used are unable to suppress such interfering signals. To overcome this problem, the SMI algorithm is modified. In the modified algorithm, the covariance matrix is redefined such that the effect of thermal noise on the weights of adaptive arrays is reduced. Thus, the weights are dictated by relatively weak signals. It is shown that the modified algorithm provides the desired interference protection.     

An experimental adaptive array to suppress weak interfering signals

An experimental adaptive antenna system to suppress weak interfering signals is described. It is a sidelobe canceller with two auxiliary elements. Modified feedback loops are used to control the array weights. The received signals are simulated in hardware for parameter control. Digital processing is used for algorithm implementation and performance evaluation. The experimental results are presented. They show that interfering signals as much as 10 dB below the thermal noise level in the main channel are suppressed by 20-30 dB. Such a system has potential application in suppressing the interference encountered in direct broadcast satellite communication systems     

An adaptive antenna array under directional constraint

The concept of the adaptive system working on the principle of minimizing the output power under the constrained response to specified directions is introduced. Theoretical analysis and computer simulation experiments on this directional constraint system are also presented. By comparison with the computer experiment, the differential equation approach is shown to be useful to predict the behavior of the system. The effect of error in setting the constraint direction is investigated, and it is demonstrated that the system is not very sensitive to such error. This margin can be made even greater by adopting the double directional constraints system. This system is also analyzed theoretically and experimented by computer simulation. History of output power components during adaptation is shown, which enables the comprehension of the behavior of the system.     

An experimental four-element adaptive array

The experimental pattern behavior of a four-element adaptive array based on a steepest-descent feedback algorithm is described. The array uses four multiturn loop elements on an aircraft fuselage mock-up. Operational patterns have been measured as a function of various parameters: frequency, element placement, desired signal and interference angles of arrival, signal powers, etc. Typical patterns are presented and the performance characteristics of the array are described.     

Analysis of modified SMI method for adaptive array weight control

The authors characterize the performance of the diagonally loaded sample matrix inverse (SMI) algorithm versus the number K of snapshots used in the covariance matrix estimate by providing O(1/K) statistics (bias and variance) of the array weights, output powers, and output power ratios such as signal to interference noise ratio (SINR) and INR. The approach accommodates wideband signals. Monte Carlo simulations verify the theoretical analysis     

Microstrip adaptive array antenna

A planar adaptive array of three microstrip patch antennas consisting of a central active microstrip antenna and two symmetrical lateral passive antennas is used to steer the beam. An electronic beam scanning of ±20° can be achieved with the control of reactive loads located into the lateral patches     

Tamed adaptive antenna array

The adaptive array under directionaily constrained minimization of power (DCMP) algorithm is improved by adding a "pseudonoise." It is effective to protect the desired signal from cancellation or distortion in such cases as 1) where a coherent interference is incident, or 2) where the desired signal direction for the constraint contains some pointing error, or 3) when the desired signal is broad band, The optimum amount of pseudonoise to be added is also discussed and its formula is given. This system is named "tamed adaptive antenna" since its killing capability is somewhat moderated so as not to hurt the desired signal.     

An adaptive wideband antenna array receiver of low complexity

A low complexity wideband antenna array receiver is proposed for wideband wireless communication systems. With the proposed algorithm, the array beampattern remains almost the same within a wide frequency range of interest. In comparison to the conventional algorithm, the new algorithm offers a faster convergence rate with a lower computational complexity. Simulation results are presented to demonstrate the proposed algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

Weight-convergence analysis of adaptive antenna arrays based on SMI algorithm

Weight-convergence analysis of adaptive antenna arrays based on the sample matrix inversion (SMI) algorithm is presented. First, we derive a required number of samples for weight computation to achieve an output signal-to-interference-plus-noise ratio -10 log/sub 10/ r dB (r /spl les/ 1) below an optimum value. Next, we evaluate weight convergence of code-division multiple-access adaptive antenna arrays based on the SMI algorithm, where two types of weight computational methods are compared between "chip-level computation" and "symbol-level computation". Analytical and simulation results reveal that "chip-level computation", before despreading process, enables faster convergence than "symbol-level computation", after the despreading process.     

An adaptive algorithm for antenna array low-rank processing incellular TDMA base stations

A new adaptive algorithm for blind interference rejection and multipath mitigation is studied and applied to antenna array processing in the reverse channel of a time-division multiple-access (TDMA) cellular communication system. The method is based on higher order statistics (HOS) processing of the baseband vector samples at the antenna array output. The similarity between the cumulant-based solution and the standard multivariable least-squares solution is exploited to derive an efficient adaptive algorithm based on a low-rank processing architecture. The algorithm exhibits good tracking and enhanced identification capability with respect to traditional least-squares methods     

Optimum beamforming for pre-FFT OFDM adaptive antenna array

It is well known that orthogonal frequency-division multiplexing (OFDM) is robust to frequency-selective fading in wireless channels due to the exploitation of a guard interval that is inserted at the beginning of each OFDM symbol. However, once delayed signals beyond the guard interval are introduced in a channel with a large delay spread, intersymbol interference causes a severe degradation in the transmission performance. In this paper, we propose a novel pre-fast Fourier transform (FFT) OFDM adaptive antenna array, which requires only one FFT processor at a receiver, for suppressing such delayed signals. We derive the optimum weight set for beamformers based on the maximum signal-to-noise-and-interference power ratio (Max-SNIR) and the minimum mean square error (mmse) criteria, respectively. In addition, we propose a novel mmse-criterion-based commutative optimization scheme, which is more robust to the estimation error of the channel state information. Furthermore, we show the equivalence between the Max-SNIR-criterion-based scheme and the proposed commutative optimization scheme. Computer simulation results show its good performance even in channels where directions of arrival of arriving waves are randomly determined.     

Convergence of the SMI and the diagonally loaded SMI algorithmswith weak interference [adaptive array]

Approximations for the power levels at the output of an adaptive array that uses the diagonally loaded sample matrix inversion (SMI) algorithm are derived. Diagonal loading is a technique where the diagonal of the covariance matrix is augmented with a positive or negative constant prior to inversion. The authors examine how the signal-to-interference-plus-noise ratio (SINR) and signal-to-interference ratio (SIR) at the array output vary with the number of samples taken when the input signals are continuous wave. It is shown that positive loading produces more rapid convergence with a reduction in output SIR. Negative loading provides an improved SIR level, but it is shown that positive loading produces more rapid convergence with a reduction in output SIR. Negative loading provides an improved SIR level, but it is shown that the output power levels are erratic and slow to converge. Simulation results which verify the theoretical procedure are given     

Multiple-access phased array antenna simulator for A digital beam-forming system investigation

Future versions of data relay satellite systems are currently being planned by NASA. Being given consideration for implementation are on-board digital beam-forming techniques which will allow multiple users to simultaneously access a single S-band phased array antenna system. To investigate the potential performance of such a system, a laboratory simulator has been developed at NASA's Lewis Research Center. This paper describes the system simulator, and in particular, the requirements, design and performance of a key subsystem, the phased array antenna simulator, which provides realistic inputs to the digital processor including multiple signals, noise and non-linearities.     

The tripole antenna: An adaptive array with full polarization flexibility

The performance of an adaptive array using three mutually perpendicular dipoles (a "tripole") is studied. A desired signal and an interference signal, each with arbitrary angle of arrival and polarization, are assumed incident on the array. Uncorrelated thermal noise is also assumed present on each element signal. The output desired signal-to-interference-plus-noise ratio (SINR) is computed as a function of the signal arrival angles and polarizations. It is shown that for most angles of arrival and polarizations, the array has an excellent ability to protect a desired signal from interference. Certain special cases where the performance is not good are discussed in detail.     

一种基于无偏协方差估计RLS的自适应阵列天线抗干扰算法

RLS是自适应阵列天线抗干扰的主要算法之一。为提高RLS算法对遗忘因子选择健壮性,避免因遗忘因子选择不当所造成的算法不收敛问题,本文针对自适应阵列天线的多路接收信号,基于其无偏协方差矩阵模型,推导设计出了一种新的RLS算法,相比于常规RLS,在该算法中遗忘因子可以更加精确地控制RLS迭代过程项,降低因遗忘因子设置不当而造成的算法不收敛风险。通过仿真验证了算法的有效性。     

An adaptive antenna array formed from an E3M3 radiator

It is shown that a miniature E3M3 radiator can be used as an adaptive antenna array forming a prescribed level of the radiation pattern of the sum electric field in a specified angular direction and nulls in two arbitrarily chosen angular directions. A technique for calculation of weighting coefficients ensuring formation of the radiation pattern satisfying these constraints is developed.     

一种自适应阵列天线波束赋形合成算法

自适应阵列天线中的波束赋形技术是智能天线数字信号处理部分的核心,在介绍和比较常用波束赋形算法以及RLS算法的基础上,提出了-种改进的RLS算法以提高系统的性能。对于用自适应阵列天线改善GPRS基站系统,提高其容量、减少干扰信号、提高信噪比、提高系统频谱利用率有很大的现实意义。     

Experiment on coherent adaptive antenna array for wideband DS-CDMAmobile radio

A four-element pilot symbol-assisted coherent adaptive antenna array diversity receiver for 4.096 Mchip/s wideband direct sequence code division multiple access mobile radio is implemented and its performance in a multipath fading environment is evaluated by a laboratory experiment using hardware fading simulators. The receiver comprises an adaptive antenna array using the normalised least mean square algorithm and Rake combiner. It is demonstrated that, for the three-user case, the required average signal-to-interference ratio obtaining average BER of 10^-3 can be reduced by ~8 dB compared to four-branch antenna diversity