Showing papers on "Antenna array published in 1996"

Closed-form 2-D angle estimation with rectangular arrays in element space or beamspace via unitary ESPRIT

Abstract: The UCA-ESPRIT is a closed-form algorithm developed for use in conjunction with a uniform circular array (UCA) that provides automatically paired source azimuth and elevation angle estimates. The 2-D unitary ESPRIT is presented as an algorithm providing the same capabilities for a uniform rectangular array (URA). In the final stage of the algorithm, the real and imaginary parts of the ith eigenvalue of a matrix are one-to-one related to the respective direction cosines of the ith source relative to the two major array axes. The 2-D unitary ESPRIT offers a number of advantages over other proposed ESPRIT based closed-form 2-D angle estimation techniques. First, except for the final eigenvalue decomposition of a dimension equal to the number of sources, it is efficiently formulated in terms of real-valued computation throughout. Second, it is amenable to efficient beamspace implementations that are presented. Third, it is applicable to array configurations that do not exhibit identical subarrays, e.g., two orthogonal linear arrays. Finally, the 2-D unitary ESPRIT easily handles sources having one member of the spatial frequency coordinate pair in common. Simulation results are presented verifying the efficacy of the method.

An analytical constant modulus algorithm

Abstract: Iterative constant modulus algorithms such as Godard (1980) and CMA have been used to blindly separate a superposition of cochannel constant modulus (CM) signals impinging on an antenna array. These algorithms have certain deficiencies in the context of convergence to local minima and the retrieval of all individual CM signals that are present in the channel. We show that the underlying constant modulus factorization problem is, in fact, a generalized eigenvalue problem, and may be solved via a simultaneous diagonalization of a set of matrices. With this new analytical approach, it is possible to detect the number of CM signals present in the channel, and to retrieve all of them exactly, rejecting other, non-CM signals. Only a modest amount of samples is required. The algorithm is robust in the presence of noise and is tested on measured data collected from an experimental set-up.

Blind separation of synchronous co-channel digital signals using an antenna array. I. Algorithms

Abstract: We propose a maximum-likelihood (ML) approach for separating and estimating multiple synchronous digital signals arriving at an antenna array at a cell site. The spatial response of the array is assumed to be known imprecisely or unknown. We exploit the finite alphabet property of digital signals to simultaneously estimate the array response and the symbol sequence for each signal. Uniqueness of the estimates is established for BPSK signals. We introduce a signal detection technique based on the finite alphabet property that is different from a standard linear combiner. Computationally efficient algorithms for both block and recursive estimation of the signals are presented. This new approach is applicable to an unknown array geometry and propagation environment, which is particularly useful In wireless communication systems. Simulation results demonstrate its promising performance.

Synthesis of unequally spaced arrays by simulated annealing

Abstract: Simulated annealing is applied to the synthesis of arrays in order to reduce the peaks of side lobes by acting on the elements' positions and weight coefficients. In the case considered, the number of array elements and the spatial aperture of an unequally spaced array are a priori fixed. Thanks to the high flexibility of simulated annealing, the results obtained for a 25-element array over an aperture of 50/spl lambda/ improve those reported in the literature.

Communication system and methods utilizing a reactively controlled directive array

Abstract: A reactively controlled directive antenna array that has a single central monopole or dipole as a radiating element excited directly by a feed system. A plurality of parasitic elements surround the radiating element and through changing the state of the parasitic impedance causing the antenna to be in an omni directional or beam pointing mode according to whether the parasitic elements are open circuited or short circuited. A computer modem and memory including stored programs control the antenna array in an omnidirectional or directive mode to locate, identify and communicate with nodes in a wireless communication network. A stored table is created in the memory indicating the antenna direction for communicating with each node in the network. Using the stored table, the computer initiates a communication sequence with a selected node, the sequence having the advantages of improved signal sensitivity and angular discrimination for wireless communication systems.

Efficient apparatus for simultaneous modulation and digital beamforming for an antenna array

Abstract: A digital beamforming network for transmitting a first number of digital information signal using a second number of antenna array elements is disclosed. Assemblers are used for assembling one information bit selected from each of the information signals into a bit vector. Digital processors have an input for the bit vector and a number of outputs equal to the second number of antenna elements and process the bit vector. Finally, modulation waveform generators coupled to each of the second number of outputs generate a signal for transmission by each antenna element.

Smart antenna arrays for CDMA systems

Abstract: There are a diverse range of products and services currently on the market, but cellular or personal communications services (PCS) radio networks probably have the highest public profile. These services provide highly mobile, widely accessible two-way voice and data communications links. In general, the most complex and expensive part of the radio path for these systems is the base station. As a result, manufacturers have been designing networks that have high efficiency in terms of the bandwidth occupied and the number of users per base station. Base station antenna arrays are a promising method for providing large capacity increases in cellular mobile radio systems. This article considers channel-modeling issues, receiver structures, and algorithms, and looks at the potential capacity gains that can be achieved. It considers antenna arrays for the mobile-to-base-station or reverse link of a CDMA cellular system. It begins with an introduction to CDMA communications systems and also addresses the general topic of antenna array receivers.

The constant modulus array for cochannel signal copy and direction finding

Abstract: The constant modulus (CM) array is a blind adaptive beamformer capable of recovering a narrowband signal among several cochannel sources without using a pilot or training signal. It is a conventional weight-and-sum adaptive beamformer whose weights are updated by the constant modulus algorithm. An adaptive signal canceller follows the beamformer to remove the captured signal from the array input and to provide an estimate of its direction vector. Based on a Wiener model, we investigate the steady-state properties of the CM array and the signal canceller. For mutually uncorrelated sources and noise, it is shown that the signal canceller exactly removes the source captured by the array. Thus, identical stages of the CM array and signal canceller may be used in a multistage system to recover several cochannel sources. Computer simulations are presented to verify the analytical results and to illustrate the transient behavior of the system.

Performance of wireless CDMA with M-ary orthogonal modulation and cell site antenna arrays

Abstract: An antenna array-based base station receiver structure for wireless direct-sequence code-division multiple-access (DS/CDMA) with M-ary orthogonal modulation is proposed. The base station uses an antenna array beamformer-RAKE structure with noncoherent equal gain combining. The receiver consists of a "front end" beamsteering processor feeding a conventional noncoherent RAKE combiner. The performance of the proposed receiver with closed loop power control in multipath fading channels is evaluated. Expressions for the system uncoded bit-error probability (BEP) as a function of the number of users, number of antennas, and the angle spread are derived for different power control scenarios. The system capacity in terms of number of users that can be supported for a given uncoded BEP is also evaluated. Analysis results show a performance improvement in terms of the system capacity due to the use of antenna arrays and the associated signal processing at the base station. In particular, analysis results show an increase in system capacity that is proportional to the number of antennas. They also show an additional performance improvement due to space diversity gain provided by the array for nonzero angle spreads.

Antenna array in an RFID system

Abstract: In accordance with the present invention, a general antenna system is disclosed suitable for applications in which an RFID Tag passes by an Interrogator. We then disclose a specific antenna design that uses a single planar antenna for transmit and a multi-element planar antenna array for receive. The multi-element planar antenna array is spaced such that each of the planar elements is four inches apart, center-to-center, thus defining a narrow 30° receive beamwidth in the horizontal plane. The vertical receive bandwidth is much greater than 30°, facilitating the Interrogator receiving signals at a variety of elevations. Furthermore, a multi-way microstrip combiner is used to sum the signals received from each of the planar antennas. To block interference from the transmit antenna and to improve receive sensitivity, this multi-way microstrip combiner is shielded using, in one embodiment, copper tape along its edges. In a specific embodiment, a four element receive antenna design is disclosed.

Base station equipment, and a method for steering an antenna beam

Abstract: The invention relates to a method for steering an antenna beam, and a base station equipment (100) comprising one or more antenna arrays (500, 700-704, 772-776), one or more channel units (504-508, 738-742) which channel unit comprises means (600-606, 706, 770) for phasing the signal to be transmitted and received by the antenna array (500, 700-704, 772-776) in such a way that the gain from the antenna array is the greatest in the desired direction, and means (616) for distinguishing the connection quality information from the information received from the mobile station (102). In order to improve the spectral efficiency and the connection quality, the channel unit (504-508, 738-742) comprises means (604, 732, 802) for searching for the incoming directions and delays of the received signal components, and means (604, 744, 802) for controlling the phasing means (606, 770) of the opposite transmission direction on the basis of said information and the connection quality information received from the mobile station.

Array processing for wireless communications

Abstract: By equipping the base stations of a wireless network with antenna arrays, it is possible to more fully exploit the spatial dimension in a wireless communication system. Multiple antennas can provide a processing gain to increase the base station range and improve coverage. Also, by exploiting the spatial selectivity of an antenna array, interference may be reduced which in turn can be traded for increased capacity of the system. A wide range of wireless communication systems may benefit from spatial processing including high mobility cellular systems, low mobility short range systems, wireless local loop applications, satellite communications and wireless LAN. By employing an array of antennas, it is possible to multiplex channels in the spatial dimension just as in the frequency and time dimension. This is often referred to as spatial division multiple access (SDMA). To increase system capacity, spatially selective reception as well as spatially selective transmission must be achieved. Herein, we present some different approaches and techniques for spatial/temporal processing. Critical aspects of SDMA for both high mobility cellular systems and low mobility or movable systems are reviewed and the potential benefits examined.

Directive beam selectivity for high speed wireless communication networks

Abstract: The present invention provides a wireless communication system which employs Butler matrix combiners and circuit switching at transmitter and receiver antenna arrays to provide directive beamwidth capabilities. Such narrow beamwidths permit the communication system to determine and select the transmission path having an optimum signal quality. The antenna arrays are integrated in a multilayer construction which reduces power consumption, increases the coverage range, improves the efficiency of the antenna array, and which has lower fabrication costs.

Method and device for space division multiplexing of radio signals transmitted in cellular radio communications

Abstract: A method and apparatus for spatial multiplexing and demultiplexing of radio signals. A multichannel transmitter and receiver is integrated in a base station and coupled to an antenna array. Using digital radio signals containing previously known or non-Gaussian sequences and arranged in frames, the spatial information about each mobile unit is estimated on the basis of the signal received by the receiver for the reception and transmission frequencies. This is done by known sequences or by blind source separation methods. The respective paths of each mobile unit with the power above a predetermined threshold is isolated by spatial filtering in the presence of multiple channel paths in order to provide spatial demultiplexing. Simultaneously, the intended signal is transmitted in the direction of the main path of each mobile unit while protecting each mobile unit from signals transmitted in the direction of other mobile units by spatial filtering with cancelling constraints in order to provide spatial multiplexing.

Explicit Ziv-Zakai lower bound for bearing estimation

Abstract: The extended Ziv-Zakai bound for vector parameters is used to develop a lower bound on the mean square error in estimating the 2-D bearing of a narrowband planewave signal using planar arrays of arbitrary geometry. The bound has a simple closed-form expression that is a function of the signal wavelength, the signal-to-noise ratio (SNR), the number of data snapshots, the number of sensors in the array, and the array configuration. Analysis of the bound suggests that there are several regions of operation, and expressions for the thresholds separating the regions are provided. In the asymptotic region where the number of snapshots and/or SNR are large, estimation errors are small, and the bound approaches the inverse Fisher information. This is the same as the asymptotic performance predicted by the local Cramer-Rao bound for each value of bearing. In the a priori performance region where the number of snapshots or SNR is small, estimation errors are distributed throughout the a priori parameter space and the bound approaches the a priori covariance. In the transition region, both small and large errors occur, and the bound varies smoothly between the two extremes. Simulations of the maximum likelihood estimator (MLE) demonstrate that the bound closely predicts the performance of the MLE in all regions.

A study of the rank-ambiguity issues in direction-of-arrival estimation

Abstract: We first extend a theorem on linear independence of steering vectors proposed by Godara and Cantoni to include more array-sensor scenarios. We then show that an array can have pairwise linearly independent steering vectors even when all its intersensor spacings are more than /spl lambda//2 where /spl lambda/ is the wavelength of the signals. We next propose a theorem for characterizing rank-2 ambiguity, which is applicable to direction-of-arrival estimation applications where the array sensor locations are fixed and known. Subsequently, we identify a class of three-sensor arrays and a class of uniform circular arrays that have pairwise linearly independent steering vectors and are free of rank-2 ambiguity. We also show that collinearity of sensors, uniformity in intersensor spacings, the dimensions of intersensor spacings, or a combination of some or all of these may give rise to linearly dependent steering vectors. In particular, we demonstrate that for a m-sensor array, m linearly dependent steering vectors exist if the aperture is greater than [(m-1)/2]/spl lambda//2, or when at least ([(m+1)/2]+1) sensors are collinear.

Uniqueness study of measurements obtainable with arrays of electromagnetic vector sensors

Abstract: In this correspondence, we investigate linear dependence of steering vectors for arrays comprising multiple electromagnetic vector sensors. We derive upper and lower bounds for the number of linearly independent steering vectors associated with such arrays. These bounds are potentially useful for determining the number of signals whose directions-of-arrival can be uniquely identified.

Joint angle and delay estimation (JADE) for signals in multipath environments

Abstract: We propose a subspace-based approach to estimate the angles-of-arrival (AOAs) and delays of multipath signals from one or more digitally modulated sources arriving at an antenna array. Our approach uses a collection of estimates of a consistent space-time vector channel. The channel estimates from different time slots in TDMA systems have constant path AOA and delay over the observed periods, but variable fade amplitudes between the slots. With this approach, we are able to estimate more parameters than the number of antennas. The Cramer-Rao bound for the parameter estimates is also provided.

Array redundancy for active line arrays

Abstract: Active imaging arrays are used to image scenes composed of reflectors of transmitted radiation, and in many such applications, line arrays are employed. In this paper, we discuss scanned active line arrays for imaging based on image synthesis. We define the novel concept of array redundancy for active arrays, analogous to the well-known concept of redundancy applied to passive arrays, and we define and give examples of minimum redundancy and reduced redundancy line arrays composed of transmit/receive elements. Such arrays differ from their passive imaging counterparts both in geometry and in element count.

Application of genetic algorithms and simulated annealing technique in optimising the aperture distributions of antenna array patterns

Abstract: Simulated annealing and genetic algorithms are used for finding optimum excitations for patterns with null-filling. These methods have the advantage that the optimum aperture distribution with a minimal variation between excitations of adjacent elements is found without searching the entire solution space. A comparison between the performance of both methods shows that genetic algorithms are faster than simulated annealing, for this problem.

Beacon signal receiving system

Abstract: A method and apparatus for locating and tracking a portable transmitter that may be deposited with currency or other items desired to be tracked, comprising a doppler antenna array, analog antenna switching, radio frequency and intermediate frequency circuitry and a digital signal processor, exhibiting increasing sensitivity, accuracy, and range.

Optimal compromise among sum and difference patterns

Abstract: Three methods to obtain compromised sets of excitations in monopulse antenna arrays are investigated. The techniques involve minimizing a scalar-valued performance measure, called cost function, via the use of simulated annealing method. The unknowns in the cost function are the weight factors of each sub-array or the relative amplitudes and the phases of the excitations of the array elements. Several examples are presented to illustrate the optimal results obtained.

Novel low-loss delay line for broadband phased antenna array applications

Abstract: The microwave propagation velocity along a nonlinear transmission line is a function of dc bias, hence, a nonlinear transmission line (NLTL) can be utilized as a broadband delay line. A hybrid NLTL has been fabricated in a proof-of-principle experimental concept test where a 1.1-ns true time delay with <4-dB insertion loss has been measured in good agreement with theory. A 2/spl times/2 NLTL-based antenna array has been utilized to demonstrate beam steering at 5 GHz. Using parameters appropriate to varactors tested by our group at 60 GHz, a monolithic NLTL is predicted to exhibit <3.4-dB insertion loss and 200 ps delay at 20 GHz.

An antenna downlink beamsteering arrangement

Abstract: A base station arrangement including an antenna array is disclosed, wherein the uplink signals are weighted with complex array weights and the downlink signals are steered, wherein the downlink signals are steered using data from directional information derived from the uplink signals. A method of operation is also disclosed.

Adaptive antenna system and method for cellular and personal communication systems

Abstract: A signal processing system and method for improving reception of plural signals received at an antenna array in a wireless communication system by increasing the carrier-to-interference plus noise ratio and by decreasing signal envelope variance of each of the plural signals using single or multiple stage subspace projection and a constant modulus beamformer Each of the stages separate and optimize one of the signals and projects the remaining signals (if present) to the subspace of the next stage In the method and system the plural signals received at each antenna are converted to baseband in a wideband RF downconverter Received signals are thereafter provided in digital form to the constant modulus beamformer where each stage of the beamformer separates one of the plural signals from a stage input so that a stage output has the remaining ones of the plural signals, and projects the stage output onto a subspace of the remaining signals in the next stage The subspace basis is given by the set of eigenvectors associated with the N largest eigenvalues of the spatial covariance matrix R This basis is preferably found iteratively using a linearized stochastic gradient ascent (SGA) algorithm

Adaptive array sensor processing applications for mobile telephone communications

Abstract: The mobile telephone cellular communication system is rapidly being saturated with an increase in subscribers. Although advanced coding and modulation techniques as well as different cell cluster architectures have been implemented, a great increase in the channel capacity is needed, especially in large markets. Adaptive sensor processing has been introduced as a possible remedy to increase the channel capacity by using the directional sensitivity, which leads to a reduction of the interference. Some high-resolution algorithms are evaluated for the direction of arrival (DOA) estimation for a cellular mobile radio environment whose cluster size is varied from K=7, K=4, and K=3; more signals and scattering scenarios that typically arise in urban areas are taken into account. This information is used to beamform toward the signal of interest, resulting in a decrease of the interference. Several signal estimation procedures are evaluated and compared, and it is observed that the DOAs, among other benefits, leads to even higher performance compared with the reference signal method. The computational aspects for the different signal processing, detection and estimation schemes are also discussed.

Electronic beam steering in wire and patch antenna systems using switched parasitic elements

Abstract: We explore the application of two alternative methods of electronically controlling the radiation pattern from an antenna array which has a single feed line. Type (a) involves switching one of the parasitic elements to become active. Type (b) requires switching the parasitic elements located in the vicinity of the active element between short circuit (i.e. continuous conduction in the element) and open circuit at a point where the induced current is minimised. Both techniques offer a reduced radiation loss in the feed network and relatively simple control circuitry and tracking software.

Dual polarization common aperture array formed by a waveguide-fed, planar slot array and a linear short backfire array

Abstract: A common aperture dual polarization array that comprises a vertical polarization antenna array that provides for vertical polarization, and horizontal polarization antenna array that provides for horizontal polarization. The vertical polarization antenna array is comprised of a flat plate shunt slot standing wave array that includes a plurality of sets of radiating slots configured in a staggered pattern that are laterally separated by an air gap. The horizontal polarization antenna array is comprised of a collinear array of radiating slots, a strip reflector, and a plurality of baffles that form a short backfire antenna array. The collinear slots are disposed orthogonal to the radiating slots of the vertical polarization antenna array. A feed network is coupled to the vertical polarization and horizontal polarization antenna arrays that comprises a centered collinear standing wave array of longitudinally aligned feed slots coupled to the vertical polarization antenna array, and the collinear array of feed slots coupled to the horizontal polarization antenna array. The plurality of baffles may be disposed adjacent to the horizontal polarization antenna array for increasing the effective aperture thereof. The feed network may comprise an offset resonant iris disposed in a rectangular waveguide, or a boxed stripline that comprises a meandered stripline. The vertical polarization antenna array may further comprise a plurality of waveguide shorts disposed in the gap between the sets of radiating slots of the vertical polarization antenna array.

Low profile antenna array for land-based, mobile radio frequency communication system

Abstract: An antenna for a land-based, mobile radio communication system, having a reduced size and shape, includes three, flat antenna dielectric panels (32a, 32b, 32c), each covering one hundred twenty degrees of azimuth. On each dielectric panel are formed two, interleaved microstrip antenna arrays having narrow vertical beam width. One of the antenna arrays (36) receives signals and the other antenna array (34) transmits signals. The receive array is circularly polarized. The panels are mounted in a triangular configuration about a central mast and a cylindrically shaped radome encloses the dielectric panels.