Showing papers on "Antenna array published in 2000"

Telemetry system for implantable medical devices

Abstract: A device for use in communication with an implantable medical device. The device is provided with a spatial diversity antenna array mounted to a housing and an RF transceiver operating at defined frequency, coupled to the antenna array. The antenna array comprises two antennas spaced a fraction of the wavelength of the defined frequency from one another, each antenna including two antenna elements mounted to the housing and located orthogonal to one another. Selection of which of the antennas is employed is accomplished by a device controller, responsive to the quality of the signals received by the antennas.

Identification of time-variant directional mobile radio channels

Abstract: For the identification of the time-variant, directional structure of the mobile radio channel impulse response (CIR), a broadband vector channel sounder is described. The measurement procedure relies on periodic multifrequency excitation signals, correlation processing, and joint delay-azimuth super-resolution based on the two-dimensional (2-D) unitary ESPRIT algorithm. Problems of imperfect receiver and antenna performance as well as antenna array calibration methods are discussed. Correlation analysis of the directional impulse response records is performed in the time-frequency-spatial domain and the corresponding Doppler-delay-angular domain. Results from measurements in the 5.2 GHz frequency range in an industrial environment are presented.

A neural network-based smart antenna for multiple source tracking

Abstract: This paper considers the problem of multiple-source tracking with neural network-based smart antennas for wireless terrestrial and satellite mobile communications. The neural multiple-source tracking (N-MUST) algorithm is based on an architecture of a family of radial basis function neural networks (RBFNN) to perform both detection and direction of arrival (DOA) estimation. The field of view of the antenna array is divided into spatial angular sectors, which are in turn assigned to a different pair of RBFNNs. When a network detects one or more sources in the first stage, the corresponding second stage network(s) are activated to perform the DOA estimation. Simulation results are performed to investigate the performance of the algorithm for various angular separations, with sources of random relative signal-to-noise ratio and when the system suffers from Doppler spread.

Antenna array calibration

Abstract: A method and a system for calibrating the reception and transmission of an antenna array for use in a cellular communication system is disclosed. The calibration of the reception of the antenna array is performed by injecting a single calibration signal into each of a number of receiving antenna sections, in parallel. The signals are collected after having passed receiving components that might have distorted the phase and amplitude. Correction factors are generated and applied to received signals. The calibration of the transmission of the antenna array is performed in a similar way. A single calibration signal is generated and injected into each of a number of transmitting antenna sections, one at a time. The signals are collected, one at a time, after having passed transmitting components that might have distorted the phase and amplitude. Correction factors are generated and applied to signals that are to be transmitted.

Synthesis of antenna arrays using genetic algorithms

Abstract: In this article, two particular methods for the synthesis of the complex radiation pattern of a linear and a planar array, based on genetic algorithms (GAs), are discussed. First, we present a combination of Schelkunoff's method and GAs for linear arrays with arbitrary radiation patterns; then, we consider the synthesis of planar arrays with rectangular cells. The results show the flexibility of GAs to solve complex problems related to antenna synthesis, subject to many restrictions which are difficult to treat by classical optimization techniques. There is good agreement between the desired and calculated radiation patterns.

Antenna arrays in mobile communications: gain, diversity, and channel capacity

Abstract: Are antenna arrays in mobile communications different from arrays in other applications? The answer is yes, sometimes, and it is the purpose of this paper to explain, in a tutorial fashion, when this is the case, and what this means for path loss in link calculations One aspect is the classical gain of an antenna, which we have to understand in a new way Another aspect is the possibility for two arrays, in a scattering environment, to create parallel channels, and thus, in effect, act as many independent antennas at the same time, carrying much more traffic over the same bandwidth

Decoupled estimation of DOA and angular spread for a spatially distributed source

Abstract: In mobile communications, local scattering in the vicinity of the mobile results in angular spreading as seen from a base station antenna array. In this paper, we consider the problem of estimating the parameters [direction-of-arrival (DOA) and angular spread] of a spatially distributed source, using a uniform linear array (ULA). A two-step procedure enabling decoupling the estimation of DOA from that of the angular spread is proposed. This method combines a covariance matching algorithm with the use of the extended invariance principle (EXIP). More exactly, the first step makes use of an unstructured model for the part of the covariance matrix that depends on the angular spread. Then, the solution is refined by invoking EXIP. Instead of a 2-D search, the proposed scheme requires two successive 1-D searches. Additionally, the DOA estimate is robust to mismodeling the spatial distribution of the scatterers. A statistical analysis is carried out, and a formula for the asymptotic variance of the estimates is derived. Numerical examples illustrate the performance of the method.

Closed-form eigenstructure-based direction finding using arbitrary but identical subarrays on a sparse uniform Cartesian array grid

Abstract: A sparse uniform Cartesian-grid array suffers cyclic ambiguity in its Cartesian direction-cosine estimates due to the spatial Nyquist sampling theorem. The proposed MUSIC-based or MODE-based algorithm improves and generalizes previous disambiguation schemes that populate the thin array grid with identical subarrays-such as electromagnetic vector sensors, underwater acoustic vector hydrophones, or half-wavelength spaced subarrays.

Low-complexity estimators for distributed sources

Abstract: In antenna array applications, the propagation environment is often more complicated than the ordinarily assumed model of plane wavefronts. Here, a low-complexity algorithm is suggested for estimating both the DOA and the spread angle of a source subject to local scattering, using a uniform linear array. The parameters are calculated from the estimates obtained using a standard algorithm such as root-MUSIC to fit a two-ray model to the data. The algorithm is shown to give consistent estimates, and the statistical performance is studied analytically and through simulations.

Phased array antenna system

Abstract: A miniature phased array antenna system is described which employs a substrate having a high dielectric constant. A plurality of antenna elements is located on a surface of the substrate, and a superstrate having a high dielectric constant covers the antenna elements. The dielectric constant, thickness, and shape of the superstrate enable it to act as a dielectric lens for controlling the phase relationship of a signal received by the antenna elements. The design of the superstrate dielectric lens permits a reduction in the physical spacing between the antenna elements while maintaining spatial diversity in phase between signals arriving from different directions. Thus, the antenna array may be significantly smaller than previously proposed phased array antennas while maintaining a similar phase relationship to that achieved using previously proposed phased array antennas. Electronic circuitry coupled to each of the plurality of antenna elements applies complex weights to received signals prior to a summation thereof in order to reconstruct a desired signal and to deconstruct an undesired signal. SAW filters employed in the electronic circuitry are temperature controlled to maintain group-delay and phase-offset stability.

Transmission antenna array system with predistortion

Abstract: A predistortion system comprises a digital compensation signal processing component (DCSP) (52) which predistorts a wideband input transmission signal to compensate for the frequency and time dependent AM-AM and AM-PM distortion characteristics of a non-linear amplifier (64). The DCSP (52) comprises a data structure (52H) in which each element stores a set of compensation parameters (preferably including FIR filter coefficients) for predistorting the input transmission signal. The parameter sets are preferably indexed within the data structure (52H) according to multiple signal characteristics, such as instantaneous amplitude and integrated signal envelope, each of which corresponds to a respective dimension of the data structure (52H). To predistort the input transmission signal, an addressing circuit (52C-52G) digitally generates a set of data structure indices from the input transmission signal, and the indexed set of compensation parameters is loaded into a compensation circuit (52A, 52B) which digitally predistorts the input transmission signal. This process of loading new compensation parameters into the compensation circuit (52A, 52B) is preferably repeated every sample instant, so that the predistortion function varies from sample-to-sample. The sets of compensation parameters are generated periodically and written to the data structure (52H) by an adaptive control processing and compensation estimator (ACPCE) (70) that performs a non-real-time analysis of amplifier input and output signals. The ACPCE (70) also implements various system identification processes for measuring the characteristics of the power amplifier (64) and generating initial sets of filter coefficients. In an antenna array embodiment (Figures 33 and 34), a single ACPCE (70) generates the compensation parameters sets for each of multiple amplification chains (64) on a time-shared basis. In an embodiment (Figure 32) in which the amplification chain (64) includes multiple nonlinear amplifiers (60A) that can be individually controlled (e.g., turned ON and OFF) to conserve power, the data structure (52H) separately stores compensation parameter sets for each operating state of the amplification chain (64).

Single-user and multiuser adaptive maximal ratio transmission for Rayleigh channels

Abstract: In maximal ratio transmission, the base station adjusts the complex weights of its transmit antennas to compensate for downlink channel gains in order to produce signal reinforcement-diversity-at a desired mobile that may have only a single antenna. To make the method adaptive, the complex weights are obtained from the instantaneous complex gains in the uplink; however, delay and frequency offset between uplink measurements and downlink transmission reduce the correlation between the gains in the two directions. This paper provides an analysis of the effects of gain decorrelation and of the number of antennas, and an assessment of the effect of fading when the method supports multiple users. It demonstrates that large reductions in downlink transmit power are achievable, and it examines simple transmission models to see how well they support the technique.

Stacked carrier discrete multiple tone communication system

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.

Multi-antenna transmission method and system

Abstract: The present invention relates to a method and system for transmitting a transmission signal from an antenna array (19) to a receiving means (20) of a wireless communication system, wherein a signal quality measurement is performed at the receiving means (20) for predetermined antennas or beams of said antenna array (19). Based on a feedback information derived from the signal quality measurement, at least two of the predetermined antennas or beams of the antenna array (19) are selected. The selected antennas or beams are used for transmitting said transmission signal according to a transmit diversity or beamforming scheme. Thus, spectral efficiency and diversity gain can be enhanced by using only selected ones of the predetermined antennas or beams.

Real-time 3-D spatial-temporal dual-polarized measurement of wideband radio channel at mobile station

Abstract: This paper describes a measurement system enabling the complete real-time characterization of the wideband radio channel. The system is based on a wideband radio channel sounder and a spherical antenna array, and it aims to describe the three-dimensional (3-D) spatial radio channel seen by the mobile terminal, including polarization. This information is highly valuable in designing antennas for mobile terminals. The spatial properties of the measurement system are analyzed through test measurements in an anechoic chamber. The system has a 40/spl deg/ spatial resolution and a 17 dB cross polarization discrimination. The values are well above those of a small mobile terminal antenna. The dynamic range in the spatial domain is 12 dB. The measurement is very fast, which makes real-time channel acquisition practical at normal mobile speeds.

Mitigating ghost signal interference in adaptive array systems

Abstract: A method and apparatus for mitigating co-channel and inter-channel interference in an antenna array system. It is determined by a base station or other transmitter employing an antenna array that transmission of at least a first downlink signal will generate a co-channel or inter-channel ghost signal at at least one location that may be susceptible to such ghost signal (e.g., as interference). As such, a weight to be applied to the at least first downlink signal is adjusted to reduce mitigate the undesirable effect of the ghost signal at the location before transmission of the at least first downlink signal.

Wideband beamspace adaptive array utilizing FIR fan filters for multibeam forming

Abstract: We propose a a wideband beamspace adaptive array that uses FIR fan filters to construct a multibeam forming network. We also describe a method for designing such FIR fan filters. Approximation is achieved by combining spectral transformation and the window method such that the beam patterns including the sidelobe characteristics of the resulting fan filters are virtually frequency independent. This is a requirement of beamforming networks used in multibeam forming. Fan filters designed with the proposed method are used to demonstrate that the beam-space adaptive array can suppress interference signals having a wide fractional bandwidth and that the array has fast convergence.

Millimeter-wave broad-band fiber-wireless system incorporating baseband data transmission over fiber and remote LO delivery

Abstract: We present the first demonstration of a millimeter-wave (mm-wave) broadband fiber-wireless system which incorporates baseband data transmission in both the downstream (622 Mb/s) and upstream (155 Mb/s) directions. The local oscillator (LO) required at the remote antenna base station for up- and downconversion to/from the mm-wave radio frequency (RF) is delivered remotely via a modulation scheme that is tolerant to the effects of fiber chromatic dispersion on the detected LO carrier power. The technique employs a single dual electrode modulator located at the central office (CO) and the data and an RF signal at a frequency equal to half the LO frequency, are applied simultaneously to the device. The modulation scheme was optimized as a function of the modulator operating conditions. Simultaneous bidirectional radio transmission in the mm-wave fiber-wireless network was implemented using specially designed mm-wave diplexers located at the base station (BS) and customer unit, and a single Ka-band printed antenna array at the BS operating simultaneously in transmit and receive mode. Error-free data transmission was demonstrated for both down(34.8 GHz) and uplinks (37.5 GHz) after 20 km of single-mode optical fiber and a bit error rate (BER) of 10/sup -6/ was achieved after the inclusion of a 2-m radio link.

Method permitting increased frequency re-use in a communication network, by recovery of transmitted information from multiple cochannel signals

Abstract: A method for use in a communication network having multiple users and limited bandwidth, wherein up to N users are allocated to the same frequency band at the same time, and the method provides for processing signals received at an M-element antenna array, using a cumulant-based signal recovery system to separate and recover the signals transmitted by the respective users.

Priority messaging method for a discrete multitone spread spectrum communications system

Abstract: A discrete multitone stacked-carrier spread spectrum communication method is based on frequency domain spreading including multiplication of a baseband signal by a set of superimposed, or stacked, complex sinusoid carrier waves. In a preferred embodiment, the spreading involves energizing 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 method may be extended to include multielement antenna array nulling methods 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 adaptation algorithms. In a specific embodiment the spectral and spatial components of the adaptive weights are calculated in a unified operation based on the mathematical analogy between the spectral and spatial descriptions of the airlink.

Beam forming and switching architecture

Abstract: Disclosed is a system and method providing beam forming and selection to provide desired signals to/from signal processing devices such as cell site modems. Systems of the present invention are operable with multi-beam antenna arrays to utilize antenna beams provided by the multi-beam antenna array and to form antenna beams which supplement the antenna beams formed by the multi-beam antenna array. Additionally, systems of the present invention are operable with adaptive array antennas to form antenna beams having desired characteristics. Preferably, predefined sets of beam forming weighting characteristics are utilized to provide a hybrid adaptive beam forming technique wherein antenna beams having predetermined characteristics may be rapidly selected and formed. Additionally, dynamically determined sets of beam forming weighting characteristics may be utilized to provide additional antenna beams having other desired characteristics.

Power transmission system

Abstract: PROBLEM TO BE SOLVED: To provide a power transmission system for operating an apparatus, eg a radio capsule, held in a living body for a long time SOLUTION: The power transmission system comprises a plurality of antennas 29 for transmitting power toward a radio capsule 28 held in a living body in order to detect information thereof and transmitting it by radio to the outside of a body, an antenna array 12 for receiving a signal transmitted from the radio capsule 28, means 19 for locating the radio capsule 28 in the body from the receiving state of the receiving antenna array 12, and a circuit 33 for selecting a power transmission antenna 29 closest to a position located by the locating means 19, wherein power is transmitted to the radio capsule 28 from a power transmission antenna 29 selected by the selecting circuit 33 COPYRIGHT: (C)2001,JPO

Downlink beamforming method

Abstract: A method for downlink capacity enhancement in a wireless communications system that has a base station with antenna array and terminals that are physically remote from the base station comprises the steps of receiving at the base station antenna array combinations of arriving signals from the plurality of remote terminals, estimating an uplink channel covariance matrix (UCCM) for each of the terminals from the combinations of arriving signals, constructing from each UCCM a downlink channel covariance matrix (DCCM), calculating from the DCCM a downlink weight vector for each of the terminals, transmitting a set of information signals from the base station antenna array according to the downlink weight vectors.

An aperture-coupled linear microstrip leaky-wave antenna array with two-dimensional dual-beam scanning capability

Abstract: This paper describes an X-band 4/spl times/1 aperture-coupled series-fed electronically steerable microstrip leaky-wave antenna (LWA) array design, which has dual-beam radiation pattern and two-dimensional (2-D) beam-scanning capability. The LWA array is operated in the first higher order mode and excited by center-fed aperture coupled for dual-beam operation. The varactor-tuned phase shifters are placed between the antenna elements. The measured half-power beamwidth of the H-plane and quasi-E-plane radiation patterns are less than 30/spl deg/. By tuning the reverse dc bias of the varactor diodes, the main beam can be scanned in azimuth plane from -13/spl deg/ to +13/spl deg/ off broadside. In the elevation plane, the beam-scanning angle is close to 20/spl deg/ as the operating frequency tuned from 11.58-12.5 GHz. Taking into account each phase-shifter insertion loss and phase progression, the measured results compared closely with the theoretical prediction. The proposed antenna array is suitable for wireless communication and collision warning radar systems.

Application of simulated annealing to design of serial feed sequentially rotated 2 × 2 antenna array

Abstract: A 5.8 GHz circularly polarised 2/spl times/2 patch antenna array is presented, employing sequential rotation of dual-feed circularly polarised elements; appropriate phase-shifting and power splitting are achieved via a serial feed arrangement. The feed has been optimised using simulated annealing; the resulting structure has a voltage standing wave ratio 2:1 bandwidth of 9.8%. Results obtained by full wave simulation and practical measurement confirm the integrity of the design.

Two-dimensional computer analysis of a microwave flat antenna array for breast cancer tomography

Abstract: In this paper, we report a two-dimensional computer simulation of a microwave flat antenna array for breast cancer tomography. This new technology promises reduction of X-ray exposure and easier access to peripheral areas of the breast. Using our version of the Newton algorithm, we studied two simple mathematical objects and a more sophisticated two-dimensional model of the breast that takes into account dielectric properties of different human tissues and malignant tumors. Our calculations show that, operating at 2 GHz, this device may give very reasonable images of tissues located up to 3-4 cm beneath the surface.

Array calibration in the presence of multipath

Abstract: We present an algorithm for the calibration of sensor arrays in the presence of multipath. The algorithm is based on two sets of calibration data obtained from two angularly separated transmitting points. We show the similarity between the calibration problem and blind identification of SIMO systems and analyze the identifiability of the problem. Simulation results demonstrating the performance of the algorithm are included.

Method and system for adaptive signal processing for an antenna array

Abstract: A method and system for adaptive signal processing for an antenna array reduces the requisite computations for executing an adaptive algorithm that combines or digitally filters baseband receive signals. The system receives uplink electromagnetic signals from a phased array and uplink electromagnetic signals from a diversity array during the reception of a desired electromagnetic signal transmitted by a desired mobile station. The uplink signals are converted into baseband signals for digital signal processing. The baseband signals are observable as a series of successive time slots. The system determines uplink coarse combining weights associated with the uplink baseband signals of the phased array and downlink coarse combining weights associated with the downlink baseband signals of the phased array. The baseband uplink signals are summed into as few as one resultant baseband signal during or after application of the coarse combining weights to the baseband uplink signals. The system determines fine combining weights for one or more resultant baseband signals and the baseband uplink signals on a symbol-by-symbol basis, or on any durational basis less than a time slot, to combine the signals into a single enhanced baseband signal for symbol detection.

Experimental performance of adaptive beamforming in a sonar environment with a towed array and moving interfering sources

Abstract: The performances of adaptive array algorithms are known to suffer from a strong degradation in scenarios with moving interfering sources. In this article, basic adaptive beamforming techniques are compared using shallow sea sonar data recorded in a towed horizontal array environment with moving interfering sources originated from shipping noise. Our experimental results show the relationship between the practical performances of adaptive and conventional beamforming techniques compared in terms of output SINR or a related measure given by the noncompensated postbeamforming interference power. These results demonstrate noticeable performance improvements that can be achieved using several robust algorithms relative to traditional adaptive beamforming schemes.