基于波束成形天线的分簇时间同步算法

波束成形天线相比较定向天线具有波束集中,抗干扰能力强等特点,配备波束成形天线的节点间通信复杂,造成网络同步困难。文中提出一种分簇网络时间算法解决基于波束成形天线网络同步问题,算法分为选举,分簇,同步三个阶段,选举阶段选举网络根节点,分簇阶段工作于定向天线且网络时间异步场景下,利用网络根节点作为分簇的初始节点完成网络分簇,同步阶段利用簇间同步与簇内迭代完成全网节点同步。仿真分析了算法的开销并能够促使网络时间收敛。     

Inexpensive upgrade of base-station dumb antennas by two magnetic loops for "blind" adaptive downlink beamforming

A simple scheme is herein proposed to upgrade an older base-station's "dumb" antennas for use in an adaptive space-division frequency-reuse downlink, with no expensive retrofitting of each "dumb" antenna with its own rake receiver. This scheme adds only two horizontally oriented loops (plus an optional vertically oriented dipole) to a base station's 120/spl deg/-azimuth sector, each with a temporal (not space-time) rake receiver. Such a pair (or triad) of diversely polarized but collocated antennas can estimate an incident mobile-source's uplink direction of arrival, based on which the existing "dumb" antennas can beam-form towards the mobile in downlink transmission.     

Opportunistic beamforming based on multiple weighting vectors

In order to improve the throughput of the opportunistic beamforming, the authors generalize the opportunistic beamforming by using multiple random weighting vectors at each time slot. The base station chooses the best weighting vector and performs the opportunistic beamforming with this optimum vector. For the case of equally strong independent fast Rayleigh fading channels, the throughput of the proposed scheme is analytically approximated and the optimum number of random weighting vectors per time slot is obtained. Numerical results demonstrate that the proposed scheme considerably improves the throughput compared to the conventional opportunistic beamforming for a low/realistic number of users.     

Directional random access scheme for mobile ad hoc networking using beamforming antennas

It has been proposed to upgrade the performance of medium access control (MAC) schemes through the use of beamforming directional antennas, to achieve better power and bandwidth utilization. In this paper, we consider a shared wireless medium as employed in a mobile ad hoc wireless network. We present and analyze a random access MAC algorithm that is combined with the use of directional beamforming formed by each transmitting mobile entity. Mathematical equations are derived to characterize the throughput performance of such a directional-ALOHA (D-ALOHA) algorithm. We describe the interferences occurring at each receiving node by considering both distance based and SINR based interference models. The D-ALOHA protocol includes the establishment of a (in-band or out-of-band) control sub-channel that is used for the transmission of location update messages. The latter is used for allowing mobile nodes to track the location of their intended destination mobiles. We present a separation property result that allows us to express the network throughput performance as a product of two factors: (1) a stationary factor that represents the system throughput performance under a perfect receiver location update process, and (2) a mobility factor that embeds the user mobility and location update processes in expressing the level of throughput degradation caused due to location update errors. We employ our derived mathematical equations, as well as carry out simulation evaluations, to present an extensive set of performance results. The throughput performance of such a beamforming based MAC protocol is characterized in terms of the system’s traffic loading conditions, the selected beamwidths of the antennas at the transmitting mobiles, the mobility levels of the nodal entities and the bandwidth capacity allocated to the control channel used for location update purposes. We show that the D-ALOHA protocol can provide a significant upgrade of network performance when the transmitting nodes adapt their beamwidth levels in accordance with our presented control scheme. The latter incorporates the involved tradeoff between the attained higher potential spatial reuse factors and the realized higher destination pointing process errors, and consequently uses nodal mobility levels and channel loading conditions as key parameters.     

互耦效应对波束赋形天线的影响分析

波束赋形天线技术可以通过基带调零等手段降低干扰信号影响,提升系统抗干扰性能,通过数字信号处理还可以在空间上形成多个波束,从而形成空分多址,大幅度提升系统的容量。但是波束赋形天线技术要求天线间隔尽可能小,一般约为工作频率的半波长,而较小的天线间隔在实际工程实现时会引起严重互相耦合。由于对互耦效应进行有效的数学描述非常困难,一般通过计算量极大的专业天线仿真软件进行仿真验证,严重制约了互耦效应解决方案的提出和论证。文中针对上述问题,提出了互耦效应的数学模型,并利用MATLAB和ANSYS-HFSS工具对相关模型进行了交叉验证。不同平台的对比仿真结果显示了相关模型的正确性和有效性。     

皮智能天线中的LMS自适应波束形成研究

自适应波束形成是智能天线的核心技术,其主要思想是利用自适应算法调整阵列权向量,使天线主瓣指向有用信号,干扰方向对准零陷,尽可能地提高阵列输出所需信号的强度,同时减小干扰信号的强度,从而提高阵列输出的信噪比.运用MATLAB仿真对LMS算法收敛性能进行常规研究,但重点研究了收敛因子、阵元个数、阵元间距等阵列系统因素,以及阵列接收信号过程中两波束夹角对LMS自适应波束形成性能的影响,为进一步优化自适应波束形成的性能奠定了基础.     

A deformable mirror-based optical beamforming system for phasedarray antennas

Microwave carrier generation along with the signal processing required for dynamic beamsteering of a high-resolution phased array antenna with an arbitrary radiation pattern is accomplished using optical components. It is shown that a deformable mirror type spatial light modulator can establish a truly arbitrary continuous optical phasefront which is directly converted to spatial RF phase information by an optical heterodyne system. Experimental results simulating the performance of the actual system are presented. A spatially integrated optical implementation providing mechanical stability and essentially eliminating the drift problems usually encountered in free space systems is presented     

Adaptive beamforming algorithm based on eigen-space method for smart antennas

This paper presents an adaptive beamforming technique based on the eigen-space method for computing the optimal weight vector that does not degrade the receiving performance even in wide angle spread circumstances. By exploiting the diversity gain, which is available in the signal environments of the wide angle spread, the proposed technique rather enhances the performance as the angle spread increases. It is also confirmed in this paper that performance of the proposed technique is almost identical to that of which has been obtained through the exact solution of the eigen-space method.     

Smart antennas in wireless communications: base-station diversity and handset beamforming

We review diversity and smart antenna research applied to both base-stations and terminals. To illustrate the performance gains possible, the paper describes research being conducted by the Smart Antenna Group at Virginia Tech, in both smart base-stations and smart handheld terminals.     

Power control and beamforming for systems with multiple transmit and receive antennas

This paper investigates the performance of narrowband, slowly fading, and delay-limited multiple-antenna systems where channel state information (CSI) is available at the transmission end. This situation can arise in time-division duplex (TDD) based two-way systems where channel state estimation can be performed using the signal received from the opposite link. Power control methods which attempt to keep the transmission rate constant at the expense of randomizing the transmit power are considered. It is shown that significant savings in average transmit power (sometimes on the order of tens of decibels) can be expected compared to systems which keep the total transmit power constant. Several practical channel coding examples using are illustrated and their bit and frame error rate performance are discussed.     

Fast beamforming of electronically steerable parasitic array radiator antennas: theory and experiment

A low-power consumption, small-size smart antenna, named electronically steerable parasitic array radiator (ESPAR), has been designed. Beamforming is achieved by tuning the load reactances at parasitic elements surrounding the active central element. A fast beamforming algorithm based on simultaneous perturbation stochastic approximation with a maximum cross correlation coefficient criterion is proposed. The simulation and experimental results validate the algorithm. In an environment where the signal-to-interference-ratio is 0 dB, the algorithm converges within 50 iterations and achieves an output signal-to-interference-plus-noise-ratio of 10 dB. With the fast beamforming ability and its low-power consumption attribute, the ESPAR antenna makes the mass deployment of smart antenna technologies practical.     

Modified constant modulus algorithm for digital signal processingadaptive antennas with microwave analog beamforming

This paper proposes a novel algorithm, called modified constant modulus algorithm (M-CMA), which is able to give adaptability to microwave beamforming phased array antennas. Since microwave analog beamformers basically require much fewer RF devices than digital beamformers, microwave analog beamformers based on M-CMA, that is, adaptive microwave beamformers, can be cheaply fabricated. Therefore, they are very suitable for mobile communication systems where both miniaturization and low cost are required for the mobile terminals. M-CMA obtains a gradient vector by a combination of analytical calculation and perturbation of the microwave beamforming control voltage. Though M-CMA is implemented with a digital signal processor, M-CMA controls the microwave analog beamformer by utilizing the gradient vector. The microwave analog beamformer based on M-CMA is analyzed to have the following characteristics: (1) the beamformer can point its main beam to the desired direction in additive white Gaussian noise (AWGN) channels; (2) although the beamformer may possibly fail in ill solutions in cochannel interference (CCI) channels, M-CMA can converge to the optimum solution when the desired direction is roughly a priori known     

SVM自适应波束成形算法

在天线阵列过载,以及强干扰与期望用户信号夹角过近的情况下,传统的线性阵列信号处理算法,如MMSE(minimum mean-squareerror)、NLMS(Normalized Least Mean Squares)等表现并不理想。SVM(SupportVectorMachine)是机器学习领域的最新成果,有较强的泛化能力,收敛快以及低复杂度等优点。本文提出了在上行波束成形中使用SVM算法,提高空域滤波的分辨率,与其他相关算法相比较,系统性能有了明显的改进。     

Ultrasound beamforming using compressed data

The rapid advancements in electronics technologies have made software-based beamformers for ultrasound array imaging feasible, thus facilitating the rapid development of high-performance and potentially low-cost systems. However, one challenge to realizing a fully software-based system is transferring data from the analog front end to the software back end at rates of up to a few gigabits per second. This study investigated the use of data compression to reduce the data transfer requirements and optimize the associated trade-off with beamforming quality. JPEG and JPEG2000 compression techniques were adopted. The acoustic data of a line phantom were acquired with a 128-channel array transducer at a center frequency of 3.5 MHz, and the acoustic data of a cyst phantom were acquired with a 64-channel array transducer at a center frequency of 3.33 MHz. The receive-channel data associated with each transmit event are separated into 8 × 8 blocks and several tiles before JPEG and JPEG2000 data compression is applied, respectively. In one scheme, the compression was applied to raw RF data, while in another only the amplitude of baseband data was compressed. The maximum compression ratio of RF data compression to produce an average error of lower than 5 dB was 15 with JPEG compression and 20 with JPEG2000 compression. The image quality is higher with baseband amplitude data compression than with RF data compression; although the maximum overall compression ratio (compared with the original RF data size), which was limited by the data size of uncompressed phase data, was lower than 12, the average error in this case was lower than 1 dB when the compression ratio was lower than 8.     

Broadband beamforming using Laguerre filters

Space-time processing is a well-substantiated method for designing broadband beamformers. In the conventional Frost space-time beamformer, tapped delay line (TDL) filters are used in each branch of the array to create a wideband response for interference suppression. In this article a new space-time beamforming method is introduced in which Laguerre filters replace the traditional TDL filters in the Frost beamformer. The Laguerre filters are fundamentally IIR filters but with only one pole in their structure. Unlike other IIR-based space-time beamforming methods, the proposed method does not need an adaptive procedure for the pole adjustment and is inherently stable. Simulation results show superior performance of the proposed method compared to the Frost beamformer and comparable results against other IIR-based beamformers with much less computational complexity and guaranteed stability.     

基于神经网络的盲波束形成

利用径向基函数神经网络来实现无线通信中智能天线的波束形成. 利用了信号相关阵的对称性质,仅考虑相关阵中的上三角(或下三角)的部分元素作为网络的输入量,计算量较小.进一步提高了运算速度,具有收敛快且准确的优点.计算机模拟实例证明结果与理论相吻合,表明了该方案的有效性.     

Nearfield beamforming using radial reciprocity

We establish the asymptotic equivalence, up to complex conjugation, of two problems: 1) determining the near-field performance of a far-field beam pattern specification and 2) determining the equivalent far-field beam pattern corresponding to a near-field beam pattern specification. Using this reciprocity relationship, we develop a computationally simple procedure to design a beamforming array to achieve a desired near-field beam pattern response. The superiority of this approach to existing methods, both in ease of design implementation and performance obtained, is analyzed and then illustrated by a design example     

Retro-transceiver array using monopole antennas

In this paper, we show how a self-tracking antenna array constructed using λ/4 monopoles can be constructed, which is capable of receiving with gain over an entire 360° azimuthal cut. It is also shown how the self-tracking receive unit can be used in conjunction with a self-phased transmitter so that self-steered spatially selective receive and transmit functions can be formed simultaneously. The resulting array is capable of maintaining spatially selective receive and transmit functions to a roaming target without prior knowledge of its physical location     

基于EIRP最优的智能天线阵赋型算法研究

在实际天线阵列中,由于互耦的影响会使得单天线阵元辐射方向图畸变,导致传统的波束赋形算法性能恶化甚至失效。针对这个问题,文中提出了基于等效全向功率约束条件的粒子群算法,避免了传统的波束赋形算法的失效,提升了系统的等效全向功率。同时,为了减弱干扰方向的影响,文中进一步提出了零陷生成方案。仿真结果显示本文提出的算法不仅能够提升波束的等效全向功率,而且可以有效地生成干扰方向的零陷。     

Adaptive beamforming using the constrained Kalman filter

From the viewpoint of achieving rapid convergence, application of a Kalman filter to an adaptive array is considered. Compared with the Frost's (1972) constrained least-mean-square algorithm, the constrained Kalman algorithm for adaptive beamforming is proposed to overcome the problem of signal distortion along the look direction which occurs in the unconstrained Kalman beamformer of Baird (1974). A constraint on the array response along the look direction is added to the measurement equation of the Kalman filter. The weight vector of the constrained Kalman beamformer is derived and shown to converge to that of the minimum-variance distortionless-response beamformer. The convergence rate of the proposed algorithm is also analyzed. Compared to Baird's algorithm and the sidelobe canceller with one-step Kalman predictor, simulation results show the effectiveness of the proposed algorithm