Showing papers on "Antenna array published in 1997"

Application of antenna arrays to mobile communications. II. Beam-forming and direction-of-arrival considerations

Abstract: Array processing involves manipulation of signals induced on various antenna elements. Its capabilities of steering nulls to reduce cochannel interferences and pointing independent beams toward various mobiles, as well as its ability to provide estimates of directions of radiating sources, make it attractive to a mobile communications system designer. Array processing is expected to play an important role in fulfilling the increased demands of various mobile communications services. Part I of this paper showed how an array could be utilized in different configurations to improve the performance of mobile communications systems, with references to various studies where feasibility of apt array system for mobile communications is considered. This paper provides a comprehensive and detailed treatment of different beam-forming schemes, adaptive algorithms to adjust the required weighting on antennas, direction-of-arrival estimation methods-including their performance comparison-and effects of errors on the performance of an array system, as well as schemes to alleviate them. This paper brings together almost all aspects of array signal processing.

Space-time processing for wireless communications

Abstract: This paper reviews space-time signal processing in mobile wireless communications. Space-time processing refers to the signal processing performed in the spatial and temporal domain on signals received at or transmitted from an antenna array, in order to improve performance of wireless networks. We focus on antenna arrays deployed at the base stations since such applications are of current practical interest.

Sidelobe reduction in array-pattern synthesis using genetic algorithm

Abstract: A simple and flexible genetic algorithm (GA) for pattern synthesis of antenna array with arbitrary geometric configuration is presented. Unlike conventional GA using binary coding and binary crossover, this approach directly represents the array excitation weighting vectors as complex number chromosomes and uses decimal linear crossover without a crossover site. Compared with conventional GAs, this approach has a few advantages: giving a clearer and simpler representation of the problem, simplifying chromosome construction, and totally avoiding binary encoding and decoding so as to simplify software programming and to reduce CPU time. This method also allows us to impose constraints on phases and magnitudes of complex excitation coefficients for preferable implementation in practice using digital phase shifters and digital attenuators. Successful applications show that the approach can be used as a general tool for pattern synthesis of arbitrary arrays.

Antenna array pattern synthesis via convex optimization

Abstract: We show that a variety of antenna array pattern synthesis problems can be expressed as convex optimization problems, which can be (numerically) solved with great efficiency by recently developed interior-point methods. The synthesis problems involve arrays with arbitrary geometry and element directivity, constraints on far- and near-field patterns over narrow or broad frequency bandwidth, and some important robustness constraints. We show several numerical simulations for the particular problem of constraining the beampattern level of a simple array for adaptive and broadband arrays.

Devices for transmitter path weights and methods therefor

Abstract: A receiving communication device (101) receives a reference signal transmitted through at least one of the antennas (106, 110, 112) of an antenna array of a transmitting communication device (102). The receiving communication device determines a weight to be associated with the at least one of the antennas, and transmits weight information to the transmitting communication device. The transmitting communication device adjusts the weight associated with the at least one of the antennas according to weight information received from the receiving communication device.

Joint angle and delay estimation (JADE) for multipath signals arriving at an antenna array

Abstract: In wireless communications, mobiles emit signals that arrive at a base station via multiple paths. Estimating each path's angle-of-arrival (AOA) and propagation delay is necessary for several applications, such as mobile localization for emergency services. We propose a novel subspace approach to estimate the AOA and delays of multipath signals from digitally modulated sources arriving at an antenna array. Our method uses a collection of estimates of a space-time vector channel. The Cramer-Rao bound (CRB) and simulations are provided.

Radio transmitter location finding for wireless communication network services and management

Abstract: A method and apparatus for location finding in a wireless communication system uses multipath signals in order to accurately determine a transmitter's location. Direct path and multipath signals from a mobile transmitter [74] arrive at an antenna array [80, 82, 84] of a base station receiver [76]. The base station determines signal signature from a subspace of an array covariance matrix. The signature is compared to a database of calibrated signal signatures and corresponding locations, and a location whose calibrated signature best matches the measured signature is selected as the most likely transmitter location. The database of calibrated signal signatures and corresponding locations is generated by a calibration procedure in which a phone [74] transmits location data derived from a GPS receiver [88] and GPS satellites [90, 92, 94] to the base station [76] which records the location information together with the signal signature of the transmitter [74]. The location information can be used to increase the performance of a cellular telephone network and provide useful services to cellular telephone customers.

Stacked-carrier discrete multiple tone communication technology and combinations with code nulling, interference cancellation, retrodirective communication and adaptive antenna arrays

Abstract: A "stacked-carrier" spread spectrum communication system based on frequency domain spreading that multiplies a time-domain representation of a baseband signal by a set of superimposed, or stacked, complex sinusoid carrier waves. In a preferred embodiment, the spreading energizes the bins of a large fast Fourier transform (FFT). This provides a considerable savings in computational complexity for moderate output FFT sizes. Point-to-multipoint and multipoint-to-multipoint (nodeless) network topologies are possible. A code-nulling method is included for interference cancellation and enhanced signal separation by exploiting the spectral diversity of the various sources. The basic system may be extended to include multi-element antenna array nulling methods also for interference cancellation and enhanced signal separation using spatial separation. Such methods permit directive and retrodirective transmission systems that adapt or can be adapted to the radio environment. Such systems are compatible with bandwidth-on-demand and higher-order modulation formats and use advanced (maximum-SINR) despreader adaptation algorithms.

Blind equalization in antenna array CDMA systems

Abstract: Multipath induced interchip-interference (ICI) alters waveforms of transmitted signals and presents a major obstacle to direct-sequence (DS) code-division-multiple-access (CDMA) communications. For systems with aperiodic pseudorandom (PN) spreading sequences, the primary way to counter fading is through employing RAKE receivers that enhance the signal-to-interference ratio (SIR) by combining multipath signals from the desired user. In this paper, we formulate a discrete-time model for antenna array CDMA systems and study the 2-D RAKE receiver problem by casting it into an optimum vector FIR equalizer design and estimation framework. A novel aspect of the present work is the full exploitation of the potential of 2-D RAKE receivers without requiring any detailed knowledge of the multipath channels.

Smart antenna CDMA wireless communication system

Abstract: A TDD antenna array S-CDMA system for increasing the capacity and quality of a wireless communications is disclosed. By simultaneous exploiting the spatial and code diversities, high performance communications between a plurality of remote terminals and a base station is achieved without sacrificing system flexibility and robustness. The time-division-duplex mode together with the inherent interference immunity of S-CDMA signals allow the spatial diversity to be exploited using simple and robust beamforming rather than demanding nulling. Measurements from an array of receiving antennas at the base station are utilized to estimate spatial signatures, timing offsets, transmission powers and other propagation parameters associated with a plurality of S-CDMA terminals. Such information is then used for system synchronization, downlink beamforming, as well as handoff management. In an examplary embodiment, the aforementioned processing is accomplished with minimum computations, thereby allowing the disclosed system to be applicable to a rapidly varying environment. Among many other inherent benefits of the present invention are large capacity and power efficiency, strong interference/fading resistance, robustness power control, and easy hand-off.

Method and apparatus for calibrating radio frequency base stations using antenna arrays

Abstract: A method operating in a communications station for calibrating the communications station, the communications station including an antenna array of antenna elements, each having associated with it and included in a transmit apparatus chain and a receiver apparatus chain. The method comprises transmitting a prescribed signal from each antenna element using the transmit apparatus chain associated with the antenna element while receiving the transmitted signal in receiver apparatus chains not associated with the antenna. Calibration factors for each antenna element are determined as dependent on the associated transmit apparatus chain and receiver apparatus chain transfer functions using the prescribed signal and each of the signals received during transmissions. A communications station also is described which includes: an antenna array of a plurality of elements, each antenna element having associated with it and included in a transmit apparatus chain and a receiver apparatus chain; transmitting means configured to transmit a prescribed signal from each antenna element while receiving the transmitted signal in at least one receiver apparatus chain not associated with the transmitting antenna element; a memory coupled to the receiver apparatus chains for storing the signals received during the transmissions of the prescribed signals; and a signal processor coupled to the memory and configured to determine calibration factors for each antenna element, the calibration factors for a particular antenna element based on the transmit apparatus chain and receiver apparatus chain transfer functions of the transmit and receiver apparatus chains, respectively, that are associated with the particular antenna element.

Method of making antenna array panel structure

Abstract: A tapered notch antenna structural panel array that can serve both as a structural member and an antenna is made from an injection molded monolithic three dimensional grid of thermoplastic material. The notch and feed line is in the form of microstrip or stripline circuitry formed to the sidewalls of adjacent cells. Dielectric sheets of material are bonded to the upper and lower edges of the grid. Interconnect circuitry on the antenna ground plane is supported by the sheet bonded to the lower edge and connected to the antenna circuitry of the sidewalls.

Wireless communication network using time-varying vector channel equalization for adaptive spatial equalization

Abstract: An adaptive reception and transmission technique according to one embodiment of the invention offers the advantages of adaptive reception transmission using feedback without the associated mobile radio complexity increase and information capacity penalty. The technique has been developed to exploit structured variation which occurs in the multipath fading present in the wireless antenna array channel. Thus, multipath propagation effects are explicitly accounted for in the problem approach. The technique is blind in that the antenna beam is formed in the absence of explicit knowledge of the array geometry, and without the necessity of array calibration or mobile feedback. The basic approach is to estimate the optimum receive and transmit antenna beam pattern based on certain statistical properties of the received antenna array signals. The optimum receive and transmit beam pattern is found by solving an optimization equation. The adaptive transceiver system is suitable for use in conjunction with either a diplexed transmit/receive antenna array, or with separate transmit and receive arrays.

Angle and waveform estimation via RELAX

Abstract: Describes how the RELAX algorithm, recently proposed for temporal spectral analysis, can be extended to the spatial problem of angle and waveform estimation for both narrowband and wideband plane waves arriving at a uniform linear array (ULA). Both numerical and experimental examples are used to demonstrate the performance of the RELAX algorithm and compare the performance of RELAX with that of other well-known algorithms including ESPRIT with forward/backward spatial smoothing, MODE/WSF, and AP/ANPA for narrowband signals, and CSM-ESPRIT for wideband signals.

Applications of cumulants to array processing. IV. Direction finding in coherent signals case

Abstract: For pt.III see ibid., vol.45, no.9, p.2253-64, 1997. We present a subspace-based direction finding method for coherent signal environments using an antenna array. Our method, which uses fourth-order statistics, is capable of resolving more signals than a comparable second-order statistics-based subspace method and is applicable to a larger class of arrays. The maximum number of signals resolvable with our method may exceed the number of sensors in the array. Only a uniform linear subarray is needed; the rest of the array may have arbitrary and unknown response and does not require calibration. On the other hand, the comparable second-order statistics-based method is limited to uniform linear arrays only. No search procedure is needed in our method. Simulation experiments supporting our conclusions are provided.

Analytical method for blind binary signal separation

Abstract: The blind separation of multiple co-channel binary digital signals using an antenna array involves finding a factorization of a data matrix X into X=AS, where all entries of S are +1 or -1. It is shown that this problem can be solved exactly and noniteratively, via a certain generalized eigenvalue decomposition. As indicated by simulations, the algorithm is robust in the presence of noise. An interesting implication is that certain cluster segmentation problems can be solved using eigenvalue techniques.

Comparative study of high-performance GPS receiving antenna designs

Abstract: The FAA decision allowing the use of the global positioning system (GPS) as a radio navigation and landing help system in the United States commercial airports boosts the need for a high-performance GPS receiver which provides the demanded precision. The design of the receiving antenna is one of the most important parts in the design process, as it has to face significant challenges including uniform coverage of all satellites and the rejection of the multipath signals. The rejection of the multipath signals is accomplished by specifying restrictive criteria to the GPS antenna. This includes a high rejection of the cross-polarized signals and a radiation pattern with a sharp slope for low-elevation angles; that is, near the horizon. The feasibility of using different types of antennas to satisfy restrictive criteria such as dual-frequency coverage (L1 and L2 frequencies), -15 dB cross-polarization rejection, and a beamwidth of more than 130/spl deg/ is discussed. The antenna designs examined in this study include patch antennas, helical antennas, and conical spiral antennas. Two different receiver designs were also examined including a single-antenna system with a hemispherical coverage and an antenna array which may provide independent sectoral coverage or the desired beamwidth. It is shown that a design based on a conical spiral antenna backed with absorbing material may be used to satisfy all the desired specifications. This result was confirmed experimentally.

Dividable transmit antenna array for a cellular base station and associated method

Abstract: A time division multiple access base station communicates with a plurality of mobile stations in a cellular communications system using a plurality of time division multiple access (TDMA) time slots. The base station includes an antenna, a modulator, and a radio frequency switch. The antenna includes an array of transmit antenna elements. The modulator generates a first cellular radio signal for transmission during a first time division multiple access (TDMA) time slot, as well as second and third cellular radio signals for simultaneous transmission during a second time division multiple access (TDMA) time slot. In addition, the second and third cellular radio signals are generated on different frequencies. The radio frequency switch couples the first cellular radio signal to a first plurality of the transmit antenna elements during the first time division multiple access (TDMA) time slot, while coupling the second and third cellular radio signals to respective second and third pluralities of the transmit antenna elements during the second time division multiple access (TDMA) time slot.

A monofilar spiral antenna and its array above a ground plane-formation of a circularly polarized tilted fan beam

Abstract: A monofilar spiral antenna is analyzed in the presence of a conducting plane reflector, using the method of moments. The circumference of the spiral antenna is chosen to be 2.3 wavelengths. A tilted beam of circular polarization is realized by superposing the fields from two active regions. The gain of the tilted beam is approximately 8 dB. The frequency bandwidths for 1-dB gain drop and 3-dB axial ratio criterions are 12% and 23%, respectively. An array consisting of the four monofilar spiral antennas is also analyzed, where the array element spacing is chosen to be 0.8 wavelength at a design frequency f/sub 0/. The input impedances of the four spirals are almost the same as the impedance of the single monofilar spiral antenna at f/sub 0/. The array radiates a tilted fan beam with a gain increase of approximately 6 dB from the gain of the single spiral antenna at f/sub 0/. The frequency bandwidth for a 3-dB axial ratio criterion is almost the same as that of the single spiral antenna.

Method and apparatus for detecting an RFID tag signal

Abstract: An antenna array for detecting a coded radio frequency identification (RFID) tag signal generated by a tag during passage of the tag through a detection volume, or portal. The array comprises at least first and second antennas disposed at different positions around the periphery of the detection volume, and circuitry, having inputs connected to receive the respective output signals from the first and second antennas and an output connected to a signal receiver for decoding the detected signal. The circuitry provides an output signal including the respective output signals of the first and second antennas, and the sum of the output signals of the first and second antennas. Preferably, the output signal of the circuitry additionally includes the inverse of the output signal of the second antenna, and the sum of the output signal of the first antenna and the inverse of the output signal of the second antenna.

Combined multi-beam and sector coverage antenna array

Abstract: A beam forming apparatus and method for forming a plurality of directional beams within a sector, as well as a full sector coverage beam is disclosed, wherein uplink reception diversity is maintained, through provision of a either a single facet antenna or a pair of single facet antennas. Two implementations are disclosed: a first implementation employs orthogonal polarization diversity from a single antenna facet, whereas a second implementation employs space diversity from a pair of spaced apart antenna facets. A first implementation employing polarization diversity comprises an antenna having an array of dipole pairs, dipoles of each pair being positioned orthogonally from each other. The dipole pairs are driven on a downlink, to form a plurality of directional beams having first polarization, and a full sector coverage beam having second polarization. On an uplink, a first plurality of directional beams have first polarity and a second cospatially overlapping set of directional beams have second polarity are formed. A first full sector coverage beam having first polarity spatially overlaps a second full sector beam having second polarity.

Performance evaluation of a cellular base station multibeam antenna

Abstract: Experimental test results are used to determine the performance that can be achieved from a multibeam antenna array, with fixed-beam azimuths, relative to a traditional dual-diversity three-sector antenna configuration. The performance tradeoffs between the hysterisis level, switching time, and gain improvement for a multibeam antenna are also examined. The multibeam antenna uses selection combining to switch the signals from the two strongest directional beams to the base station's main and diversity receivers. To assess the impact of beamwidth on overall system performance, the following two multibeam antennas were tested: a 12-beam 30/spl deg/ beamwidth array and a 24-beam 15/spl deg/ beamwidth array. Both multibeam antennas were field-tested in typical cellular base station sites located in heavy urban and light urban environments. Altogether, the system performance is evaluated by investigating three fundamental aspects of multibeam antenna behavior. First, the relative powers of the signals measured in each directional beam of the multibeam antenna are characterized. Then, beam separation statistics for the strongest two signals are examined. Gain improvements achievable with a multibeam antenna compared to the traditional sector configuration are determined in the second phase of the analysis. Results indicate that in excess of 5 dB of gain enhancement can be achieved with a 24-beam base station antenna in a cellular mobile radio environment. Finally, the effects of hysterisis level and switching time are characterized based on gain reductions relative to a reference case with no hysterisis and a 0.5-s switching decision time. Useful approximations are developed for the gain effects associated with varying hysterisis levels and switching times. The resulting design curves and empirical rules allow engineers to quantify multibeam antenna performance while making appropriate tradeoffs for parameter selection.

Blind separation of synchronous co-channel digital signals using an antenna array. II. Performance analysis

Abstract: We have recently proposed a blind maximum likelihood approach for demodulating multiple co-channel digital signals received synchronously at an antenna array. This approach exploits the finite alphabet (FA) property of digital signals to simultaneously estimate the array response and symbol sequence for each signal. We have presented two computationally efficient block algorithms for computing the array response and signal estimates: iterative least-squares with projection (ILSP) and iterative least-squares with enumeration (ILSE). In this paper, we study the performance of these algorithms using both analysis and simulation. We derive the probability of error in detecting the signals under the assumption that the array responses are known. We use this probability to estimate the probability of error in the algorithms. Simulation results confirm that the detection error probability yields a good approximation to the performance of the blind algorithms.

A physical spatio-temporal model of multipath propagation channels

Abstract: This paper presents a spatio-temporal model of multipath propagation channels based on a physically defined propagation process for testing and validation of the antenna array systems operating in multipath propagation environments. The idea behind the model is to generate a set of spatially distributed reflectors or scatterers which will act as sources for the signals arriving at the receiver in accordance with the distribution of excess delay times. The large scale and small scale signal fadings are incorporated into the model, which allows an easy and flexible simulation of multipath vector channels.

Space-time signal processing for wireless communications: a survey

Abstract: This survey paper reviews space-time signal processing (STP) in mobile wireless communications. Space-time processing refers to manipulating signals that are received at or transmitted from an antenna array so as to improve performance. We focus on antenna arrays deployed at the base stations since such applications are of current practical interest. We first introduce channel and signal models for base station antennas, and present the different structures present in the channel model after sampling and stacking the received signals. We then present single user (SU) and multiple user (MU) space-time processing techniques for the reverse link. Our focus is on blind signal separation, and intersymbol/co-channel interference cancellation. We consider a number of recent advances in batch and adaptive blind space-time processing that show promise in solving these problems.

Comparison of the ultimate direction-finding capabilities of a number of planar array geometries

Abstract: Although the properties of direction-finding (DF) algorithms have heen investigated extensively, the fundamental effects of the array configuration on the performance of DF systems remain unknown. Furthermore, it is often overlooked that there are some theoretical lower limits on the DF performance which are imposed by the array geometry itself. In the paper eight diverse array geometries of elevated feed monopoles, which are used in a number of experimental sites in the UK, are investigated and compared using the ultimate detection, resolution and accuracy thresholds as figures of merit.

Antenna system for controlling and redirecting communication beams

Abstract: An antenna system 10 for a communications satellite which transmits and receives communications from ground based devices. The system includes an antenna array 16 containing a plurality of feed elements 18 which cooperate to receive or transmit coverage beams arranged in a circular layout at a coverage area in a far-field region proximate the surface of the earth. The feed elements 18 are arranged in a non-circular layout within the antenna array 16. This system further includes a beam forming network 14 for mapping coverage beam signals onto feed signals which drive the antenna array 16. The beam forming network 14 includes a beam forming matrix 28 and a beam connecting network 30. The beam connecting network 30 separates each coverage beam signal into a plurality of component signals weighted to have differing amplitudes from one another. The component signals are delivered to the beam forming matrix 28 which in turn produces corresponding feed signals to drive the antenna array 16 in such a manner as to form feed beams which cooperate to define the coverage beams at the far-field region. The beam connecting network 30 weights the component signals unevenly in order to shift corresponding resultant coverage beams inward or outward until aligned within the coverage area in a circular layout along concentric circles.

Wireless geolocation system

Abstract: A wireless system for locating a signal emitter includes at least three base stations for receiving the emitter signal, and a central processing site for converting information from the received signals into range estimates. Specifically, an antenna array at each base station for receives the emitter signal, and a beamformer isolates the direct path component of this received signal from interference and multi-path signals using cyclic phase minimizer techniques. In operation, an extractor is used to separate a cyclostationary feature from the direct path component of the emitter signal, and the cyclostationary feature is identified in an absolute time reference. The identified cyclostationary feature is then passed to the central processing site. At the central processing site, phase delay characteristics of the cyclostationary features from all participating base stations are compared with each other to obtain phase difference measurements. These phase difference measurements are then converted into differential range estimates for locating the emitter.

Microstrip leaky-mode antenna array

Abstract: The first-pass design of a linear eight-element microstrip leaky-mode antenna array is proposed, built, and tested, showing a gain of 18.5 dB, directivity of 23.5 dB, and pencil beam with 3-dB beamwidth (Az/El) of 10.2/spl deg//14.3/spl deg/. Excellent agreement between the theoretical prediction and measured results for the array antenna performance is obtained.

Downlink beamforming for cellular mobile communications

Abstract: A new technique for downlink transmission beamformer design in cellular mobile communications systems using an antenna array at the base station is presented. The method is based on estimation of an underlying spatial distribution associated with each source's spatial downlink channel. The algorithm is "blind" in the sense that it depends only on uplink spatial channel statistics, requiring no mobile-to-base station feedback in the design procedure. The assumed underlying spatial distribution models are general enough to be used in a wide variety of mobile communications scenarios (e.g., rural, urban, sub-urban, indoor). Simulation results verify the effectiveness of the new approach.