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A new approach to the deconvolution of acoustic sources has been developed and is presented in this work. The goal of this postprocessing is to simplify the beamforming output by suppressing the side lobes and reducing the sources' main lobes to single (or a small number of) points that accurately identify the noise sources' positions and their actual levels. In this work, a new modeling technique for the beamforming output is proposed. The idea is to use an image-processing-like approach to identify the noise sources from the beamforming maps: that is, recognizing lobe patterns in the beamformed output and relating them to the noise sources that would produce that map. For incoherent sources, the beamforming output is modeled as a superposition of point-spread functions and a linear system is posted. For coherent sources, the beamforming output is modeled as a superposition of complex point-spread functions and a nonlinear system of equations in terms of the sources' amplitudes is posted. As a first approach to solving this difficult problem, the system is solved using a new two-step procedure. In the first step, an approximated linear problem is solved. In the second step, an optimization is performed over the nonzero values obtained in the previous step. The solution to this system of equations renders the sources' positions and amplitudes. In the case of coherent sources, their relative phase can also be recovered. The technique is referred as noise source localization and optimization of phased-array results. A detailed analytical formulation, numerical simulations, and sample experimental results are shown for the proposed postprocessing. DOI: 10.2514/1.38073

An adaptive wideband beamforming structure is proposed with combined spatial/temporal subband decomposition. The received signals are first processed by a transformation matrix, and then split into a series of subbands, where independent beamformers can be operated. A special property is that some of the lower subbands can be discarded without affecting its performance, which leads to a system with a lower computational complexity and higher convergence speed. Index Terms--Adaptive arrays, array signal processing, linear arrays.

We propose a framework based on the use of a set of beampattern shaping constraints. The proposed beamformer possesses not only adaptive interference-rejection ability and robustness against large steering direction errors, but also direct sidelobe control. It contains a new weighing ratio that can automatically control the relative proportions of interference-rejection and sidelobe suppression in different scenarios, without ambiguity. Unlike other beamformers, the proposed beamformer is robust against strong moving interferences, requiring only a coarse estimation of their directions-of-arrival. The generic framework encompasses different optimization strategies for specific application problems. Index Terms--Adaptive arrays, array signal processing, robustness.

A calibration technique is proposed in this paper for an arbitrary array. This technique estimates the array sensor gain/ phase and geometry with a set of simultaneous equations formed by using the MUSIC null spectrum property. Note that the technique does not use iterative calculation in estimating the array parameters and hence it has no convergent problem; however, it requires that n directions of arrival (DOAs) of signal sources to be known to calibrate the array which is perturbed n-dimensionally. The efficacy of the method is demonstrated by means of simulations and on experimental data collected with an antenna array operating in high-frequency radio band. Index Terms--Array calibration, beamforming, direction-of-arrival (DOA) estimation.

The opportunistic beamforming system (OBS) is currently receiving much attention in the field of downlink beamforming due to its simple random beamforming, low feedback complexity, and same throughput scaling obtained with perfect channel-state information using dirty paper coding at the transmitter. In this paper, we focus on its closed-form throughput evaluation over Rayleigh fading channels, based on the asymptotic theory of extreme order statistics. First, the throughput of a single-beam OBS is investigated, and an analytical solution tighter than the previously reported one is derived. Then, the asymptotic throughput bounds on a multibeam OBS are presented, and also, our analytical expression is shown to be very tight with the simulation results even with fewer users. After that, we argue that the reported conclusion that the single-beam OBS is much preferable to the multibeam OBS in the high-signal-to-noise-ratio (SNR) regime is inaccurate, but that, instead, it is satisfied only when the number of users is very small, due to its limited multiuser diversity gain. Finally, we show that four transmit beams is the most preferable in the multibeam OBS with a large number of users and moderate SNR, which arrives at the tradeoff between increasing spatial multiplexing gain and disappearing multiuser diversity gain. Index Terms--Multiple-input single-output (MISO), multiuser diversity, opportunistic beamforming system (OBS), spatial multiplexing, throughput.

In this paper, we consider an adaptive modulation system with multiple-input-multiple-output (MIMO) antennas in conjunction with orthogonal frequency-division multiplexing (OFDM) operating over frequency-selective Rayleigh fading environments. In particular, we consider a type of beamforming with a maximum ratio transmission/maximum ratio combining (MRT-MRC) transceiver structure. For this system, we derive a central limit theorem for various block-based performance metrics. This motivates an accurate Gaussian approximation to the system data rate and the number of outages per OFDM block. In addition to the data rate and outage distributions, we also consider the subcarrier signal-to-noise ratio (SNR) as a process in the frequency domain and compute level crossing rates (LCRs) and average fade bandwidths (AFBs). Hence, we provide fundamental but novel results for the MIMO OFDM channel. The accuracy of these results is verified by Monte Carlo simulations, and applications to performance analysis and system design are discussed. Index Terms--Adaptive modulation, average fade bandwidth (AFB), beamforming, eigenvalues, level crossing rate (LCR), multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO OFDM), Rayleigh fading channels.

A 24-beams slot array antenna, which achieves 360-degrees coverage over azimuth direction, based on substrate integrated waveguide (SIW) technology is designed, fabricated and measured for supporting the concept of triangle cell, beam diversity and multiple input multiple output (MIMO) wireless communications. Constructed by six 4-beams single layer SIW antennas which integrate the 4 x 8 modified Butler matrix with a low side lobe level (SLL) amplitude distribution, measured SLLs are reduced as low as -14.5 dB for all beams in E-plane. The size of the SIW single layer multibeam antenna is 385 mm x 110 mm including feeding network. The usable bandwidth of the proposed antenna is 3.75% at 16 GHz. Index Terms--Beam-forming, Butler matrix, substrate integrated waveguide (SIW).

A Nolen matrix design method is proposed as an asymptotic singular case of a recent Blass matrix design algorithm. The procedure is illustrated by a 4 x 4 Nolen matrix, which design is centred at 2.2 GHz, with the amplitude and phase output excitation laws of a Butler matrix using 90[degrees] hybrids. Simulation and measurement results are presented in this paper. Such a matrix may find applications on multiport amplifiers as well as multiple beam antennas required on satellite digital multimedia broadcasting systems. This is illustrated by the use of such a matrix to feed a four-element multiple beam linear array antenna. Beam squint effects are investigated. Index Terms--Beam forming network, multiple beam antenna, Nolen matrix.

We report on the design and measurement of an eight-by-eight modular phased array that uses analog quadrature baseband phase shifters. The array is designed for 2.4 GHz and has a few MHz of bandwidth. Though for such frequency, bandwidth and number of elements, digital beam forming is still feasible with contemporary analog-to-digital converters (ADC), the design is a proof of concept for analog baseband beam forming and shows that this technique will work at frequencies and bandwidths beyond ADCs capabilities. Besides covering the architecture, implementation and the measurement of the array, the calibration is discussed extensively, as this is an inevitable step in activating the antenna. Index Terms--Active arrays, array signal processing, phase shifters, printed circuits.

Two approaches towards beamforming based on constrained particle swarm optimization (PSO) are presented. One approach relies on the penalty function method, for which a new mathematical expression to select the penalty factors is derived. The other method uses a new PSO strategy for solving constrained optimization problems. To maximize performance of the beamforming procedure, the optimal system parameters for the PSO algorithm are derived. Mutual coupling and platform effects are fully accounted for by using the measured active element radiation patterns. The new PSO strategy is compared with a standard genetic algorithm. Using the measured radiation patterns of a seven-element antenna array, a real-life example is presented that demonstrates the possibilities of the new approach. Index Terms--Beamforming, constrained optimization, mutual coupling, particle swarm optimization (PSO), smart antenna system.

The purpose of this paper is to present a robust and fast beamforming algorithm for the low-cost mobile phased array antennas. The proposed beamforming algorithm uses a sequentially perturbation gradient estimation method to update the control voltages of the phase shifters, with the objective of maximizing the received power by the array. This algorithm does not require either the knowledge of phase shifter characteristics or signal Direction-of-Arrival. Moreover, in this paper, the algorithm parameters are derived for the stationary and mobile platform configurations. For the stationary array, it is shown how the proper selection of the beamforming parameters limits the noise effects and increases the array output power. For the mobile array, a condition for the fast convergence is derived and the advantage of using nonuniform step size to update the control voltages is illustrated. When phase shifters suffer from the imbalanced insertion loss the proposed beamforming technique perturbs the phase-conjugate condition to increase the total received power. This algorithm has been implemented with the low-cost microwave components and applied to a Ku-band phased array antenna with 34 sub-arrays. The experimental results verify the broadband performance, and the fast convergence of the algorithm for different platform maneuvers. Index Terms--Adaptive array, beamforming, mobile phased array antenna, satellite communications, smart antenna.

A detector of targets behind walls and in enclosed structures is presented. The detector is applied to through-the-wall radar images obtained by wideband delay and sum beamforming. We consider the detection problem using single- and multiple-view imaging. The statistics of noise, clutter, and target images are examined and formulated using sample scenes. The effects of wall parameter errors on the image statistics are shown. An iterative detection scheme, which adapts itself to the image statistics, is presented. The proposed detection schemes are evaluated using real data. Index Terms--Detection theory, radar imaging, through the wall (TTW).

Synthetic Aperture Radar (SAR) is a well-proven imaging technique for remote sensing of the Earth. However, conventional SAR systems are not capable of fulfilling the increasing demands for improved spatial resolution and wider swath coverage. To overcome these inherent limitations, several innovative techniques have been suggested which employ multiple receive-apertures to gather additional information along the synthetic aperture. These digital beamforming (DBF) on receive techniques are reviewed with particular emphasis on the multi-aperture signal processing in azimuth and a multi-aperture reconstruction algorithm is presented that allows for the unambiguous recovery of the Doppler spectrum. The impact of Doppler aliasing is investigated and an analytic expression for the residual azimuth ambiguities is derived. Further, the influence of the processing on the signal-to-noise ratio (SNR) is analyzed, resulting in a pulse repetition frequency (PRF) dependent factor describing the SNR scaling of the multi-aperture beamforming network. The focus is then turned to a complete high-resolution wide-swath SAR system design example which demonstrates the intricate connection between multi-aperture azimuth processing and the system architecture. In this regard, alternative processing approaches are compared with the multi-aperture reconstruction algorithm. In a next step, optimization strategies are discussed as pattern tapering, prebeamshaping-on-receive, and modified processing algorithms. In this context, the analytic expressions for both the residual ambiguities and the SNR scaling factor are generalized to cascaded beamforming networks. The suggested techniques can moreover be extended in many ways. Examples discussed are a combination with ScanSAR burst mode operation and the transfer to multistatic sparse array configurations.

Spatial filtering (SF) constitutes an integral part of building EEG-based brain-computer interfaces (BCIs). Algorithms frequently used for SF, such as common spatial patterns (CSPs) and independent component analysis, require labeled training data for identifying filters that provide information on a subject's intention, which renders these algorithms susceptible to over-fitting on artifactual EEG components. In this study, beamforming is employed to construct spatial filters that extract EEG sources originating within predefined regions of interest within the brain. In this way, neurophysiological knowledge on which brain regions are relevant for a certain experimental paradigm can be utilized to construct unsupervised spatial filters that are robust against artifactual EEG components. Beamforming is experimentally compared with CSP and Laplacian spatial filtering (LP) in a two-class motor-imagery paradigm. It is demonstrated that beamforming outperforms CSP and LP on noisy datasets, while CSP and beamforming perform almost equally well on datasets with few artifactual trials. It is concluded that beamforming constitutes an alternative method for SF that might be particularly useful for BCIs used in clinical settings, i.e., in an environment where artifact-free datasets are difficult to obtain. Index Terms--Beamforming, brain-computer interfaces, common spatial patterns, electroencephalography, motor imagery, spatial filtering.

Introducing mobile sinks into wireless sensor networks improves energy efficiency and prolongs network lifetime. Mobile sinks are also in demand in many sensor network applications. However, sink mobility causes frequent topology changes, resulting in high packet loss rate and poor energy efficiency. A directional-antenna-assisted reactive routing protocol, namely, interest dissemination with directional antennas (IDDA), is proposed to solve this problem. Different from traditional interest diffusion routing protocols, IDDA exploits the directional antenna on the mobile sink to prearrange interest dissemination along the direction of motion. The antenna directionality and the transmission power can indicate the motion of the mobile sink. An analytical model is established to calculate the optimal width of the antenna beam pattern and the optimal transmitting power. The multiple IDDA scheme, which is an enhancement to IDDA that can further improve network performance, is also presented. Extensive simulation results show that IDDA outperforms the traditional directed diffusion protocol, which guarantees that IDDA can be applied to sensor networks with highly mobile data sinks. Index Terms--Beam pattern, directional antenna, mobile sink, wireless sensor network (WSN).

In this paper, we analyze spatial multiplexing techniques for the downlink of a multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system. Our study is focused on outdoor environments characterized by a moderate angular spread. We consider two techniques that are able to separate the downlink data streams associated with different users and to guarantee a fixed error probability by exploiting limited feedback from each user. The grid of beams (GoBs) and the proposed adaptive GoB (AGoB) differ in the way the precoders are designed (by adaptive or fixed processing) and in their scheduling policy. The new AGoB is able to harness partial knowledge of the downlink channel spatial structure to better select the users and adjust their precoders for downlink transmission. The performances of GoB and AGoB are compared in this paper in terms of throughput and cell coverage capability. The radio interface is adapted to fit the requirements for the adaptive modulation and coding with advanced antenna system (AMC-AAS) mode of the IEEE 802.16-2005 standard. Numerical results show that, as long as the channel exhibits a limited angular spread at the base station, the AGoB technique is able to provide significant throughput gains compared with the fixed GoB approach. On the other hand, large angular spreads are proved to have a substantial impact on system performance as the benefits of adaptation are significantly reduced. Index Terms--MIMO-OFDM systems, multiuser diversity, spatial multiplexing, zero-forcing beamforming.

We consider the uplink of collaborative wireless communication systems, where multiple relay terminals decode the signal of a nearby user and forward it to a distant single-antenna base station. We present a collaborative uplink transmit beamforming strategy that can be employed at the relay terminals to provide robustness against uncertainties in the channel state information. The proposed beamforming scheme is obtained using the available knowledge about the second-order statistics of the channel and the possibly erroneous channel state information. The beamforming weight vector is derived by minimizing the total transmitted power subject to a constraint that preserves the received signal at the base station for all the channel realizations within a prescribed uncertainty set. We present two beamforming algorithms based on different mathematical descriptions of the uncertainty set. Both algorithms can be applied to fine-of-sight (LOS) propagation and fiat-fading channels. In the first algorithm, the robust beamforming vector is computed at the base station using the uplink data and fed back to the cooperating relay terminals. This centralized processing scheme allows any additional convex constraint to be easily incorporated into the beamforming strategy. In the second algorithm, the beamforming vector of each terminal is locally computed using the available knowledge about the terminal's channel and a single parameter (Lagrange multiplier) that is broadcast from the base station to all the cooperating terminals. Simulation results are presented, showing the superior performance of our proposed algorithms compared with classical transmit beamforming techniques in both LOS propagation and fiat-fading channels. Index Terms--Array signal processing, convex optimization, cooperative systems, distributed beamforming.

On the multiantenna broadcast channel, the spatial degrees of freedom support simultaneous transmission to multiple users. The optimal multiuser transmission, which is known as dirty paper coding, is not directly realizable. Moreover, close-to-optimal solutions such as Tomlinson-Harashima precoding are sensitive to channel state information (CSI) inaccuracy. This paper considers a more practical design called per user unitary and rate control (PU2RC), which has been proposed for emerging cellular standards. PU2RC supports multiuser simultaneous transmission, enables limited feedback, and is capable of exploiting multiuser diversity. Its key feature is an orthogonal beamforming (or precoding) constraint, where each user selects a beamformer (or precoder) from a codebook of multiple orthonormal bases. In this paper, the asymptotic throughput scaling laws for PU2RC with a large user pool are derived for different regimes of the signal-to-noise ratio (SNR). In the multiuser interference-limited regime, the throughput of PU2RC is shown to logarithmically scale with the number of users. In the normal SNR and noise-limited regimes, the throughput is found to scale double logarithmically with the number of users and linearly with the number of antennas at the base station. In addition, numerical results show that PU2RC achieves higher throughput and is more robust against CSI quantization errors than the popular alternative of zero-forcing beamforming if the number of users is sufficiently large. Index Terms--Broadcast channels, feedback communication, multiuser channels, space division multiplexing.

In this study, a four-element prototype of the microwave sampling beamformer structure is constructed and tested. The prototype is composed of the microwave hardware and control hardware. A new compact switch is designed and utilized in the structure. The control circuitry is a four-branch time delay and pulse width control circuits along with p-i-n diode drivers. The beamforming structure is designed to have 8-bit phase shifter resolution and 12-bit attenuation resolution. For each antenna element the phase shift and attenuation are controlled through the time delay and pulse width of the corresponding pulse train. Different beamforming examples such as beam steering, sidelobe level (SLL) control and null forming are examined with the prototype. It is observed that the structure scans the beams to the proper steering angles. SLL close to--30 dB and nulls deeper than--30 dB are measured. Index Terms--Amplitude-phase control, beam steering, microwave beamforming (MBF), microwave sampling beamformer (MSBF).

In this paper, a new and practical mode-based array concept is proposed. The key principle of this mode-based approach is the use of orthogonal radiation modes existing in highly coupled arrays as individual information channels so as to avoid mutual coupling and correlation. Consequently, mode-based arrays can be very compact in size but without suffering undesired effects such as impedance mismatch or pattern distortion. While providing a general theoretical discussion for this mode-based approach, a practical application example, namely, a compact electronically scanning array module is developed. With a suitable signal combining algorithm, the module is capable of forming and full 360[degrees] scanning of a high-gain radiation pattern in the azimuth plane. An experimental prototype has been fabricated on a traditional printed circuit board to validate the practicability of the proposed concept. Measurement results obtained are in good agreement with theoretical simulations, showing promising potential of mode-based array modules for modern miniaturized wireless devices. Index Terms--Antenna arrays, array signal processing, beamforming systems, mutual coupling.

A modified microwave sampling beamformer (MSBF) for fast weight control and image replica rejection is presented. In the MSBF, each element weight is modified by controlling the corresponding switch using a pulse train with adjusted pulse width and time delay. A new limit for the sampling frequency is obtained as a function of the signal bandwidth and the pulse train duration. The image replica is introduced and techniques to lower its effect or to reject it are proposed. The relation between the sampling frequency and the pulse train duration, the effect of the image replica, and the effectiveness of the rejection technique are verified by simulating the new structure in the time domain. Index Terms--Adaptive beamforming, amplitude and phase weighting, microwave beamforming, microwave sampling beamformer.

In this paper, a stair-planar phased array antenna system for mobile broadcast satellite reception in Ku-band will be introduced. The height of the antenna is only 6 cm and the system has two-dimensional electronic scanning capability. The design procedures of low profile high gain microstrip sub-array antennas, low noise amplifiers, hybrid analog phase shifters, along with a novel fast electronic beamforming algorithm will be discussed in this paper. The mobile phased array antenna receives LHCP and RHCP signals simultaneously. For each polarization 496 microstrip elements have been used to provide a radiation gain of 31.5 dBi. This phased array system scans [+ or -]2.8[degrees] in azimuth and [+ or -]20[degrees] in elevation with less than 3 dB scanning loss. The main objective of this design is to develop a Ku-band phased array system with very low cost components anda minimum number of tracking sensors. A novel beamforming algorithm compensates for the fabrication inaccuracies of the microwave components and variations in their characteristics due to ambient changes. Neither a priori knowledge of the satellite's direction, nor the phase-voltage characteristic of the phase shifters are required in this algorithm which results in eliminating an expensive laborious calibration procedure. The real time field tests verify that the developed mobile antenna system can nullify the base vehicle yaw disturbances up to 60 deg/s and 85 deg/[s.sup.2]. Index Terms--Beamforming, mobile reception, phased array antenna, satellite antenna, satellite communications system, tracking system.

We propose to combine directional antennas in a conformal array configuration with a matching two-stage receiver architecture to improve performance of code-division multiple-access (CDMA) communication systems in time-varying channels. We propose a reduced-dimension space-time (ST) RAKE architecture that matches the ST correlation structure of the data received by a circular array. In time-varying channels, this reduced-dimension architecture outperforms the full-dimension architecture due to improved convergence of its adaptive processor. Index Terms--Multipath, multiuser detection, RAKE receiver, space-time beamforming.

The theory of the inverse source problem is employed to compute a class of continuously distributed and compactly supported three-dimensional (volume) sources that radiate the scalar wavelets investigated by Kaiser as well as certain electromagnetic generalizations of these scalar fields. These efforts have shown that the scalar wavelet fields can be radiated by a distributional source (generalized function) supported on a circular disk of radius a or an oblate spheroid surrounding that disk. Our main goal here is to replace this distributional source by a more conventional volume source that radiates the same wavelet field outside its support volume. The equivalent volume sources computed in this paper are supported on (three-dimensional) spherical shells whose outer radius [a.sub.+] > a and inner radius [a.sub.-] < [a.sub.+] are arbitrary. These sources are analytic functions of position within their support volumes for any finite, but arbitrarily large temporal frequency [omega], and possess minimum [L.sup.2] norm among all possible solutions to the inverse source problem with the given support volume constraint. Electromagnetic versions of the wavelet sources and fields are shown to be easily derived from their scalar wave counterparts. Index Terms--Inverse source problem, pulsed beam, reliability, wavelet field.

A shaped-beam reflectarray based on patches, aperture-coupled to delay lines is demonstrated for local multipoint distribution system (LMDS) central station antennas, in the 10.10-10.70 GHz band. The antenna must cover a 60[degrees]-sector in azimuth with a squared cosecant pattern in elevation. The design process consists of two steps. First, a phase-only pattern synthesis technique is applied to obtain the required phase-shift distribution on the reflectarray surface which generates the shaped pattern. The second stage consists of determining the length of the delay lines, aperture-coupled to the square patches, in order to achieve the phase distribution synthesized in the previous step. Two reflectarray antennas have been designed, one for vertical (V) and the other for horizontal (H) polarization. A breadboard for V-polarization has been manufactured and tested in an anechoic chamber, showing a good agreement between theoretical and measured radiation patterns. Index Terms--Aperture coupling, local multipoint distribution system (LMDS), reflectarray, shaped beam antennas.

Beamforming is a key technology in smart antenna systems that can increase capacity and coverage and mitigate multipath propagation in mobile radio communication systems. The most popular criterion for linear beamforming is the minimum mean square error (MMSE). However, the mean square error (MSE) cost function is not optimal in terms of the bit error probability performance of the system. A class of adaptive beamforming algorithms has been proposed based on minimizing the bit error rate (BER) cost function directly. Unfortunately, the popular least minimum BER (LMBER) stochastic beamforming algorithm suffers from low convergence speed. Gradient Newton algorithms have been proposed to speed up the convergence rate and enhance performance but at the expense of complexity. In this paper, a block processing objective function for the minimum BER (MBER) is formulated, and a nonlinear optimization strategy, which produces the so-called block-Shanno MBER (BSMBER), is developed. A complete discussion for the complexity calculations of the proposed algorithm is demonstrated. Simulation scenarios are carried out in a multipath Rayleigh-fading direct-sequence code-division multiple access (DS-CDMA) system to explore the performance of the proposed algorithm. Simulation results show that the proposed algorithm offers good performance in terms of convergence speed, steady-state performance, and even system capacity compared to other MBER- and MSE-based algorithms. Index Terms--Antennas, array signal processing, communication system performance, fading channels, mean square error (MSE) methods.

We consider the problem of estimating the nominal direction of arrival (DOA) of an incoherently distributed source. This problem is encountered due to the presence of local scatterers in the vicinity of a transmitter or due to signals propagating through a random inhomogeneous medium. Since the spatial covariance matrix has full rank for an incoherently distributed source, the performance of most high-resolution DOA estimation algorithms conceived under coherently distributed sources, as well as point source models, degrades when scattering is present. In addition, several DOA estimation techniques devised under a distributed source model require a high-dimensional nonlinear optimization problem. In this paper, we propose a novel method based on the conventional beamforming approach, which estimates the nominal DOA from a spatial maximum peak of the output power. The proposed method is computationally more attractive than the maximum likelihood (ML) estimator, although the performance degrades in comparison with the ML estimator, whose asymptotic performance is equivalent to the Cramer--Rao bound (CRB). We derive and compare the asymptotic performances of the proposed method and the redundancy-averaged covariance matching (RACM) method in the single-source case. The simulation results illustrate that the asymptotic performance of the proposed method is better than that of the RACM method. Index Terms--Beamforming, direction of arrival (DOA), distributed source, redundancy-averaged covariance matching (RACM).

A novel substrate integrated waveguide (SIW) multibeam antenna based on the parabolic reflector principle is proposed and implemented at 37.5 GHz, which takes the advantages of low loss, low profile, high gain, and mass producible. A prototype of the proposed antenna with seven input ports generating a corresponding number of output beams is fabricated in a standard PCB process. The measurements are in good agreement with the simulations, and the results demonstrate that this type of printed multibeam antenna is a good choice for communications applications where mobility and high gain are simultaneously required. Index Terms--Beamforming network, multibeam antenna, parabolic reflector, substrate integrated waveguide (SIW).

With the introduction of the unlicensed spectrum at the 60 GHz range, the development of communication systems with data rates in Gb/s range has become feasible. However, there are quite significant challenges at this frequency range such as high propagation loss, oxygen absorption, antenna alignment and unavailability of high-gain, high power circuit elements. In this paper we present a novel 2-channel hybrid smart-antenna system operating at 60 GHz band which can be used with an antenna switching system to improve the signal power performance and to serve as an automated alignment system. The critical system parameters for a smart-antenna system at this frequency are the transmitter to receiver distance, element spacing, and antenna beamwidth. As the widely known beamforming assumptions may not hold for some configurations, a more general beamforming formulation is given in the paper to serve as a guideline for system designers. The twist angle of array elements is introduced as a new array design parameter. By selecting the optimal twist angle to help overlap radiation patterns, the fine alignment of the transmit and receive beams is established electronically using beamforming, thus reducing the cost of deployment and maintenance of the 60 GHz indoor communication systems. Index Terms--60 GHz, antenna arrays, beamforming, hybrid smart-antenna, smart-antennas, switched antenna.

A nonlinear beamforming assisted detector is proposed for multiple-antenna-aided wireless systems employing complex-valued quadrature phase shift-keying modulation. By exploiting the inherent symmetry of the optimal Bayesian detection solution, a novel complex-valued symmetric radial basis function (SRBF)-network-based detector is developed, which is capable of approaching the optimal Bayesian performance using channel-impaired training data. in the uplink case, adaptive nonlinear beamforming can be efficiently implemented by estimating the system's channel matrix based on the least squares channel estimate. Adaptive implementation of nonlinear beamforming in the downlink case by contrast is much more challenging, and we adopt a cluster-variation enhanced clustering algorithm to directly identify the SRBF center vectors required for realizing the optimal Bayesian detector. A simulation example is included to demonstrate the achievable performance improvement by the proposed adaptive nonlinear beamforming solution over the theoretical linear minimum bit error rate beamforming benchmark. Index Terms--Beamforming, complex-valued radial basis function (RBF) network, multiple-antenna wireless system, symmetry, unsupervised clustering.

We propose a closed-loop multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO--OFDM) transmission scheme appropriate for the IEEE 802.22 wireless regional area network (WRAN) channel environments. The proposed scheme utilizes the Grassmannian beamforming and an antenna selection algorithm to maintain bit-error-rate (BER) performance and to reduce feedback information. To further reduce the feedback information considering the channel property of the IEEE 802.22 WRAN, the proposed scheme employs an extension of the feedback period and subcarrier grouping. Simulation results in the IEEE 802.22 WRAN reference channel models indicate that the proposed MIMO--OFDM transmission scheme achieves superior BER performance and spectral efficiency than open-loop MIMO--OFDM system even considering the feedback overhead of the system. Index Terms--Antenna selection, cognitive radio, Grassmannian beamforming, IEEE 802.22, multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO--OFDM), wireless regional area network (WRAN).

In a separate paper, the authors show that a nonlinear active core with a fourth-order resonator can generate two stable independent frequencies simultaneously. In this paper, the effect of injecting two frequencies into such a concurrent dual-frequency oscillator is analyzed and experimentally verified. It is shown that, for weak injection, the effect of injection at one frequency is decoupled from the effect of injection at the other frequency. The differential equation describing the effect of injection at either of the two frequencies is similar to the Adler's injection-locking equation for single-frequency oscillators. A theoretical analysis for a linear array of coupled concurrent dual-frequency oscillators is provided. It is shown that a linear phase progression at both frequencies can be achieved independently by detuning the array's end elements. Dual-frequency quadrature signal generation using two coupled concurrent dual-frequency oscillators is also demonstrated. To verify the theoretical derivations, an integrated circuit in a 0.18-[micro]m SiGe BiCMOS process is designed and fabricated. Measurement results closely match the theoretical predictions. The application of concurrent coupled oscillator array in dual-frequency beam forming with steering capability is also demonstrated. Index Terms--Injection-locked oscillators, nonlinear systems, oscillators.

This paper presents a novel design of monolithic 2.5-GHz 4 x 4 Buffer matrix in 0.18- Sheng- [micro]m CMOS technology. To achieve a full integration of smart antenna system monolithically, the proposed Buffer matrix is designed with the phase-compensated transformer-based quadrature couplers and reflection-type phase shifters. The measurements show an accurate phase distribution of 454 [+ or -] 3[degrees], 135 d= 4[degrees], -45 [+ or -] 3[degrees], and -135 [+ or -] 4[degrees] with amplitude imbalance less than 1.5 dB. The antenna beamforming capability is also demonstrated by integrating the Butler matrix with a 1 x 4 monopole antenna array. The generated beams are pointing to -45[degrees], -15[degrees], 15[degrees], and 45[degrees], respectively, with less than 1[degrees] error, which agree very well with the predictions. This Buffer matrix consumes no dc power and only occupies the chip area of 1.36 x 1.47 [mm.sup.2]. To our knowledge, this is the first demonstration of the single-chip Buffer matrix in CMOS technology. Index Terms--Antenna array, beamforming, Buffer matrix, quadrature coupler, reflection-type phase shifter (RTPS), transformer.

A new type of substrate integrated waveguide (SIW) multibeam antenna is proposed for mobile satellite communications using beam switching and diversity techniques. It employs an SIW Rotman lens as the beamforming network. The prototype of a single multibeam antenna is implemented at 28.5 GHz with seven input ports and an antenna array constructed by nine SIW linear slot arrays, which can generate a corresponding number of beams along one dimension. Several such antennas are grouped in two different ways to cover a 2-D solid angle with multiple beams. Experiment results show that the 2-D solid angle around (-40[degrees], 40[degrees]) x (-35[degrees], 35[degrees]) or (-25[degrees], 25[degrees]) x (-35[degrees], 35[degrees]) are covered with 20 or 25 beams with 5-dB beamwidth, respectively. It is demonstrated that this type of printed multibeam antenna is a good choice for communication applications where mobility and high gain are simultaneonsly required. Index Terms--Beamforming network (BFN), multibeam antenna, Rotman lens, substrate integrated waveguide (SIW).

We study the diversity performance of multiple-inputmultiple-output (MIMO) transmit beamforming when perfect channel state information is available at the transmitter side. In particular, we derive the achievable diversity order on each eigenmode in closed form. As an application, the diversity result is applied in average bit error rate (BER) approximation for IEEE 802.11n systems, where approximate BER performance bounds are obtained and further validated by numerical results. Index Terms--Beamforming, diversity analysis, multiple-inputmultiple-output (MIMO) eigenmode.

The arrival of new data services for wireless mobile communications requires an efficient use of the available bandwidth. Interference-limited cellular systems based on codedivision multiple access (CDMA) can benefit from multiuser detection (MUD) and beamforming with antenna array to reduce multiple-access interference. Group-based techniques have been proposed to reduce the complexity of space--time MUD and have been shown to provide a performance--complexity tradeoff between matched filtering and full MUD. In this paper, the intergroup interference, which is a limiting factor in group-based systems, is reduced using multistage parallel interference cancellation after group-based minimum mean square error (MMSE) linear filtering. In addition, the extra resources that are available at the receiver are exploited by sharing users among groups. The proposed receiver is shown to converge, as the number of stages increases, to the full space--time MMSE linear MUD filter. The results show that the new approach provides bit error rate (BER) performance close to the full MUD receiver at a fraction of the complexity. Index Terms--Code-division multiple access (CDMA), group-based detection, multiuser detection (MUD), space--time systems.

The performance of high-frequency surface wave radar (HFSWR) is known to suffer from external environmental interference and noise, such as cochannel radio-frequency interference from other radiating source, ionospheric clutter, lightning impulsive noise, etc. This paper experimentally evaluates the interference cancellation performance of various adaptive beamforming schemes with respect to the aforementioned three types of interferences in an attempt to find the most promising adaptive cancellation scheme in practical HFSWR environment. Index Terms--Adaptive beamforming, high-frequency surface wave radar (HFSWR), interference cancellation.

In this paper, we study the problem of maximizing the throughput of a multiuser multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system in the downlink with a total power constraint using a beamforming approach. An iterative algorithm that takes turns to optimize, jointly among users, the power allocation in the downlink, the transmit and the receive beamforming antenna vectors, and the power allocation in the virtual uplink is proposed. The algorithm is proved to converge, and the throughput increases from one iteration to the next. In addition to the total power constraint, the proposed algorithm is also capable of handling individual users' rate constraints. To reduce complexity, a geometric-programming-based power control in the high signal-to-interference-plus-noise ratio (SINR) region and an orthogonal frequency-division multiple-access scheme in the low SINR region are proposed. Numerical results illustrate that the proposed algorithm significantly outperforms the generalized zero-forcing (GZF) approach. Index Terms--Beamforming, multiple-input multiple-output (MIMO), multiuser communication, orthogonal frequency-division multiplexing (OFDM), throughput.