Showing papers on "Smart antenna published in 2003"

MIMO capacity with interference

Abstract: System capacity is considered for a group of interfering users employing single-user detection and multiple transmit and receive antennas for flat Rayleigh-fading channels with independent fading coefficients for each path. The focus is on the case where there is no channel state information at the transmitter, but channel state information is assumed at the receiver. It is shown that the optimum signaling is sometimes different from cases where the users do not interfere with each other. In particular, the optimum signaling will sometimes put all power into a single transmitting antenna, rather than divide power equally between independent streams from the different antennas. If the interference is either sufficiently weak or sufficiently strong, we show that either the optimum interference-free approach, which puts equal power into each antenna, or the approach that puts all power into a single antenna is optimum and we show how to find the regions where each approach is best.

Antenna Arrays: A Computational Approach

Abstract: A comprehensive tutorial on the design and practical applications of antenna arrays An antenna array is an assembly of antenna elements that maximizes a received or transmitted signal in a desired direction. This practical book covers a wide range of antenna array topics that are becoming increasingly important in wireless applications, with emphasis on array design, applications, and computer modeling. Each chapter in Antenna Arrays builds upon the previous chapter, progressively addressing more difficult material. Beginning with basic electromagnetics/antennas/antenna systems information, the book then deals with the analysis and synthesis of arrays of point sources and their associated array factors. It presents a sampling of different antenna elements that replace these point sources, then presents element configurations that do not have to lie along a line or in a plane. The complex and difficult-to-predict interactions of elements and electromagnetic waves are introduced, along with computer modeling and experiments that are necessary for predicting the performance of arrays where mutual coupling is important. Then, various approaches to getting signals to and from the array elements to a computer where the signal detection takes place are explored, as are the numerical techniques behind smart antennas. The book emphasizes the computational methods used in the design and analysis of array antennas. Also featured are signal processing and numerical modeling algorithms, as well as pictures of antenna arrays and components provided by industry and government sources, with explanations of how they operate. Fully course-tested, Antenna Arrays serves as a complete text in phased array design and theory for advanced undergraduate- and graduate-level courses in electronics and communications, as well as a reference for practicing engineers and scientists in wireless communications, radar, and remote sensing.

Receive antenna selection for MIMO flat-fading channels: theory and algorithms

Abstract: This correspondence discusses the problem of the receive antenna subset selection in multiple-element antenna (MEA) transmission systems. The antennas are selected so as to maximize the channel capacity. A set of near-optimal selection algorithms is presented. The first algorithm in particular allows statistical analysis of selection gains. We present tight analytic lower bounds on the outage capacity achievable through antenna selection. Extensive simulations validating analysis and illustrating performance of the selection algorithms are also presented.

Wide band four-port butler matrix for switched multibeam antenna arrays

Abstract: This paper presents the design and realization of a wide band four-port microstrip matrix to feed a switched-beam antenna array for wireless applications at 1.9 GHz. The objective of this investigation is to develop an antenna-array feeding network based on Butler with a large bandwidth in order to cover the PCS band: 1900 MHZ to 2200 MHZ. In order to meet these requirements, wide band microwave components such as hybrids and crossovers were designed and used to Butler proposed matrix. The Butler matrix is used as a beamforming network that allows to produce orthogonal beams that can be steered in different directions. To examine the performance of the proposed matrix, simulated and experimental results is presented and discussed.

Selecting a set of antennas for use in a wireless communication system

Abstract: Mechanisms for selecting a set of antennas for use in a wireless communication system are disclosed. The selected set of antennas is for use in communicating data in a wireless local area network (WLAN) comprising an access point and a plurality of mobile stations. The access point includes a baseband chip capable of adapting various radio frequency (RF) units. Each RF unit in turns includes a plurality of RF sub units, each of which connects to a plurality of antennas. The access point thus includes a number of antennas that, together with the RF units and the baseband chip, form a smart antenna. To identify the selected set of antennas to communicate with a particular mobile station, the access point initially uses a first set of antennas each in a RF sub unit. From this first set of antennas, the access point identifies a first set of winner antennas and a first set of non-winner antennas. From the first set of winner antennas, the access point identifies a first set of winner RF sub units each connecting to a winner antenna in the first set of winner antennas. From each winner RF sub unit, the access point identifies a final winner. The access point then uses the final winner antenna in the selected set of antennas. The access point also uses the first set of non-winner antennas in the selected set of antennas.

Fast algorithms for antenna selection in MIMO systems

Abstract: We consider the capacity of multiple-input-multiple-output (MIMO) systems with reduced complexity. One link end uses all available antennas, while the other chooses the "best" L out of N antennas. The selection of the optimum antenna subset requires an exhaustive search of all possible combinations, involving (/sub L//sup N/) computations of determinants of size L /spl times/ L, which can become prohibitively complex. In this paper, we suggest a class of fast antenna selection algorithm that are based on the correlation or mutual information between the signals at the different antenna elements. It requires less than N/sup 2/ vector multiplications and thus leads to dramatic savings on the computation time. Its performance is very close to the optimum selection procedure: the capacity penalty is less than l bit/s/Hz for the analyzed examples. The algorithm thus offers the possibility of almost-optimum selection even in fast-changing environments.

Performance analysis of cellular mobile systems with successive co-channel interference cancellation

Abstract: This paper presents an analytical framework for the performance evaluation of cellular mobile radio systems equipped with smart antenna systems. In particular, the paper focuses on low-complexity systems which are able to successively suppress the strongest active interferers. The desired user fading statistics is assumed to be flat Rayleigh, Rician, or Nakagami, whereas the interfering signals are assumed to be independent and subject to slow flat Rayleigh fading. The paper starts by presenting generic closed-form expressions for the the carrier-to-interference ratio probability density function after interference cancellation. Based on that, exact closed-form expressions for the outage probability and average error rate formulas are derived. Finally, a comparison with a practical cancellation scheme and the impact of some practical considerations on the performance of successive interference cancellation are investigated. More specifically, the effect of traffic loading, the overall spectral efficiency gain, and the impact of time delay are studied.

Compact internal quad‐band antenna for mobile phones

Abstract: A novel compact internal quad-band handset antenna for covering GSM900, DCS1800, PCS1900, and ISM2450 bands is presented. Details of the antenna are discussed along with measured and simulated results. The simulation is based on the FDTD method. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 217–223, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11019

Robust adaptive beamforming using worst-case performance optimization

Abstract: In recent decades, adaptive arrays have been widely used in sonar, radar, wireless communications, microphone array speech processing, medical imaging and other fields. In practical array systems, traditional adaptive beamforming algorithms are known to degrade if some of exploited assumptions on the environment, sources, or antenna array become wrong or imprecise. Therefore, the robustness of adaptive beamforming techniques against environmental and array imperfections and uncertainties remains one of the key issues. In this paper, we overview a recently emerged approach to robust adaptive beamforming using worst-case performance optimization.

Application and performance of downlink beamforming techniques in UMTS

Abstract: The opportunities and constraints for application of beamforming techniques in UMTS are reviewed and compared by means of extensive dynamic network-level simulations. We start by reviewing the physical layer specifications for UMTS in order to clarify which channels are allowed to use beamforming. Second, radio resource management for cells with beamforming capabilities are addressed from a standardization and algorithmic point of view. The exchange of beamforming specific measurement reports between the base station (Node-B) and the radio network controller is discussed as well as beam switching mechanisms, directional power-based admission control, and more. In addition to implementation of beamforming within logical cells, options for exploiting the antenna array to synthesize independent sector beams are also investigated (i.e., higher order sectorization via beamforming). The presented results show that beamforming within logical cells is an effective enabler for higher system capacity, while the use of beamforming for creation of many logical cells is less attractive due to significantly larger soft handover overhead and somewhat reduced capacity gain.

Adaptive Beamforming for Audio Signal Acquisition

Abstract: This chapter provides an overview of adaptive beamforming techniques for speech and audio signal acquisition. We review basic concepts of optimum adaptive antenna arrays and show how these methods may be applied to meet the requirements of audio signal processing. In particular, we derive optimum beamformers using time-domain least-squares instead of frequency-domain minimum mean-squares criteria, and, thereby, are not constrained by the commonly used narrow-band and stationarity assumptions. We thus obtain a more general representation of various beamforming aspects relevant to our application. From this, a robust generalized sidelobe canceller (GSC) [1] results as an attractive solution for practical audio acquisition systems. Moreover, the general theoretical framework leads to new insights for the GSC behavior in complex practical situations.

Smart Antenna Systems for Mobile Communications

Abstract: Note: 110 pages Reference LEMA-REPORT-2009-001 Record created on 2009-09-11, modified on 2016-08-08

Apparatus and method for forming a forward link transmission beam of a smart antenna in a mobile communication system

Abstract: A method and apparatus for a base station including an antenna array calculates a direction of a weight vector of a transmission beam to maximize in-phase component power for a common channel signal in a transmission channel signal for transmission to a mobile station and to minimize a sum of quadrature-phase power component and interference power for other mobile stations inside and outside a cell due to a transmission channel signal for the mobile station.

Apparatus and method for calibrating and compensating for distortion of an output signal in a smart antenna

Abstract: Disclosed is an apparatus and method for calibrating and compensating for distortion of an output signal to an antenna in a mobile communication system with a smart antenna array (1). A calibration signal generator (200) generates an extended Walsh code by extending a Walsh code used in the mobile communication system, and generates a calibration signal in synchronism with a Walsh code synchronization signal of the mobile communication system. A mobile communication signal generator (100) generates a traffic signal for forming a beam pattern to a position of a mobile terminal in communication. A multiplier multiplies an error compensation value by an output signal of the mobile communication signal generator. An adder (140) adds an output of the multiplier (120) to an output signal of the calibration signal generator (200) . An RF block for up-converting an output signal of the adder into an RF band signal, provides the up-converted RF band signal to the antenna array, extracts part of the signal provided to the antenna array, and feeds back the extracted signal component. An error calibration and compensation value calculator (180) calibrates an error of the antenna array from the feedback signal, calculates a compensation value for compensating for the error, and provides the compensation value to the multiplier. (120)

Complementary Beamforming Methods and Apparatuses

Abstract: Improved methods and apparatuses are provided to address a potential “hidden beam problem” in wireless communication systems employing smart antennas. The improved methods and apparatuses utilize complementary beamforming (CBF) techniques, such as, for example, Subspace Complementary Beamforming (SCBF), Complementary Superposition Beamforming (CSBF) and/or Single Beam Complementary Beamforming (SBCBF) techniques.

Asympotic capacity bounds for ad-hoc networks revisited: the directional and smart antenna cases

Abstract: Directional and smart antennas can be useful in increasing the capacity of wireless ad hoc networks. A number of media access and routing protocols have been recently proposed for use with such antennas, and have shown significant performance improvements over the omni-directional case. However, it is important to explore if and how different directional and smart antenna designs affect the asymptotic capacity bounds, derived by Kumar and Gupta (2000). These bounds are inherent to specific ad-hoc network characteristics, like the shared nature of the wireless media and multihop connectivity, and may pose major scalability limitations for such networks. In this paper, we look into how directional and smart antennas can affect the asymptotic behavior of an ad-hoc network's capacity. Specifically, we perform a capacity analysis for an ideal flat-topped antenna, a linear phased-array antenna, and a fully adaptive array antenna model. Finally, we explain how an ad-hoc network designer can manipulate different antenna parameters to mitigate the scalability problem of ad-hoc networks.

Antenna saturation effects on MIMO capacity

Abstract: A theoretically derived antenna saturation point is shown to exist for MIMO systems, at which the system suffers a capacity growth decrease from linear to logarithmic with increasing antenna numbers. We show this saturation point increases linearly with the radius of the region containing the receiver antennas and is independent of the number of antennas. Using an alternative formulation of capacity for MIMO systems we derive a closed form capacity expression, which uses the physics of signal propagation combined with statistics of the scattering environment. This expression gives the capacity of a MIMO system in terms of antenna placement and scattering environment and show that the saturation effect is due to spatial correlation between receiver antennas.

Angular resolution antenna system

Abstract: For an angle-resolving antenna system, only two radar sensors are provided including separate transmitting and receiving antennas. The receiving antennas of the two radar sensors are switchable with reference to their main beam direction as well as to their beam width.

Capacity of antenna arrays with space, polarization and pattern diversity

Abstract: We present an analytical characterization of multi-antenna capacity in the limit of a large number of antennas. In contrast to previous studies, the entries of the channel matrix are not restricted to be identically distributed, thus incorporating diversity mechanisms that are otherwise excluded, such as those based on the use of antennas with distinct polarizations and radiation patterns. In addition to the capacity, first-order expressions in the low- and high-power regimes are also evaluated both asymptotically and non-asymptotically.

Mobile communications system and method for providing common channel coverage using beamforming antennas

Abstract: Wireless mobile unit communication initiation is provided in a radio network that has a plurality of base stations, each providing wireless communication services in a respective geographic coverage. The wireless communication is established by first transmitting an omnidirectional sounding pulse from a wireless mobile unit. Information related to the detected sounding pulse is communicated to an interface by each base station detecting the sounding pulse. One of the base stations that detected the sounding pulse is selected for mobile unit communication based on the communicated information and directs a communication beam to the mobile unit to establish wireless communication. Alternatively, one or more of the base stations that detected the sounding pulse direct a communication beam to the mobile unit and the mobile unit selects unit the base station with which it is to establish wireless communication. Preferably, smart antennas, including directional beamforming capability, are employed by the base stations.

Impulse detection and rejection methods for radio systems

Abstract: Impulses that exist in the nature or are artificial may severely decrease the performance of any radio system including communication and interception receivers and radars This paper investigates impulse detection in receivers that can have either a single antenna or an antenna array The proposed detector uses either a backward or forward outlier search strategy and assumes zero mean signals and spatially and temporally white background noise Signal need not to be weak, ie, signal-to-noise ratio may be large and the methods still works The backward method uses all the data in an initial step whereas the forward method uses smaller, (hopefully) clean set in an initial step The forward method is expected to perform better Simulations confirm this expectation Indeed, the used forward method can detect outliers even if their contamination exceeds 90% of all the samples

Robust adaptive beamforming: an overview of recent trends and advances in the field

Abstract: In recent decades, adaptive arrays have been widely used in sonar, radar, wireless communications, microphone array speech processing, medical imaging and other fields. In practical array systems, traditional adaptive beamforming algorithms are known to degrade if some of exploited assumptions on the environment, sources, or antenna array become wrong or imprecise. Therefore, the robustness of adaptive beamforming techniques against environmental and array imperfections and uncertainties is one of the key issues. In this paper, we present an overview of recent trends and advances in the field of robust adaptive beamforming.

Forced beam switching in wireless communication systems having smart antennas

Abstract: Methods and apparatuses are proved which allow a wireless communication system using a smart antenna(s) to selectively cause a receiving device to switch its operative association from one transmitted beam to another available transmitted beam.

Adaptive MIMO antenna selection

Abstract: The performance of multiple-input multiple-output (MIMO) systems can be improved by employing a larger number of antennas than actually used and selecting the optimal subset based on the channel state information. Existing antenna selection algorithms assume perfect channel knowledge and optimize criteria such as Shannon capacity or various bounds on error rate. This paper examines MIMO antenna selection algorithms when the set of possible solutions is large and only a noisy estimate of the channel is available. We propose discrete stochastic approximation algorithms to adoptively select a better antenna subset using criteria such as maximum channel capacity, minimum error rate, etc. We also consider scenarios of time-varying channels for which the antenna selection algorithms can track the time-varying optimal antenna configuration. We present numerical examples to show the convergence of these algorithms and the excellent tracking capabilities.

Performance enhancement of smart antennas with reduced element spacing

Abstract: This paper addresses the problem of degradations in adaptive digital beam-forming (DBF) systems caused by mutual coupling between array elements. The focus is on compact arrays with reduced element spacing and, hence, strongly coupled elements. Deviations in the radiation patterns of coupled and (theoretically) uncoupled elements can be compensated for by weight-adjustments in DBF, but SNR degradation due to impedance mismatches cannot be compensated for via signal processing techniques. It is shown that this problem can be overcome via the implementation of a RF-decoupling-network. SNR enhancement is achieved at the cost of a reduced frequency bandwidth and an increased sensitivity to dissipative losses in the antenna and matching network structure.

The square kilometer array (SKA) antenna

Abstract: One of the major approaches to satisfying future goals for radio astronomy is a wide bandwidth receiving array that forms a radio telescope with one square kilometer of collecting area The array will operate over a decade of frequency, approximately 200 MHz to 2000 MHz, it will provide polarimetric information for at least 100 simultaneous beams, and it will form interferometric images with 01 arcsec angular resolution at 14 GHz Such an array will be comprised of approximately 10/sup 8/ wide bandwidth elements and will require calibration, digital beamforming, and adaptive nulling This paper describes the radiating aperture design that is currently employed for the demonstration system It is likely that the final array design will resemble this demonstration aperture, which utilizes wide bandwidth Vivaldi tapered slot antennas for the individual elements Design information and results for prototypes and the demonstrator are presented

A calibration technique for active phased array antennas

Abstract: In active phased array antennas, transmit and receive functions are distributed at the aperture using transmit and receive (T/R) modules. Active phased arrays are typically calibrated in a near-field antenna range at the factory. The performance of active phased array antennas would degrade over time due to changes in the characteristics of active devices and would require recalibration in the field. In this paper, we present a calibration technique for active phased array antennas that uses a small number of passive array elements dedicated to calibration. The dedicated calibration elements are passive in that they do not have T/R modules behind them. The measured mutual coupling data in the field are compared with the measured data at the factory.

MIMO channel estimation in correlated fading environments

Abstract: Pilot aided channel estimation is considered for wireless MIMO systems in the presence of fading correlation. Assuming a linear minimum mean squared error based channel estimator, we study statistical shaping of the training sequence via a matrix prefilter depending on the correlation properties of the channel. The new scheme is a general concept that can readily be applied to smart antenna multiple-input single-output systems. Furthermore, in a quasi-stationary environment with limited mobility, it requires only a long-term update interval of the prefilter, thus admitting its use in FDD systems with a low-rate feedback link for the correlation matrices. Simulation results of a MIMO system with maximum eigenmode transmission, including realistic channel estimation, demonstrate the effectiveness of the proposed scheme with a significant SNR gain.

Using airborne vehicle-based antenna arrays to improve communications with UAV clusters

Abstract: Recently, there have been many proposed applications for clusters of small Unmanned Aerial Vehicles (UAVs). Some of these applications, such as Synthetic Aperture Radar and video surveillance, can generate large quantities of data which must be transmitted to a base station quickly. UAV size limitations often prevent the use of large, highly directive antennas in this link with the base station. This paper proposes the solution of forming an antenna array from several UAVs and applies antenna array theory to analyze its performance. An example is given where phase compensation is used to achieve high directivity even in the presence of element position errors.