Showing papers on "Antenna array published in 2006"
TL;DR: The optimal detector in the Neyman–Pearson sense is developed and analyzed for the statistical MIMO radar and it is shown that the optimal detector consists of noncoherent processing of the receiver sensors' outputs and that for cases of practical interest, detection performance is superior to that obtained through coherent processing.
Abstract: Inspired by recent advances in multiple-input multiple-output (MIMO) communications, this proposal introduces the statistical MIMO radar concept To the authors' knowledge, this is the first time that the statistical MIMO is being proposed for radar The fundamental difference between statistical MIMO and other radar array systems is that the latter seek to maximize the coherent processing gain, while statistical MIMO radar capitalizes on the diversity of target scattering to improve radar performance Coherent processing is made possible by highly correlated signals at the receiver array, whereas in statistical MIMO radar, the signals received by the array elements are uncorrelated Radar targets generally consist of many small elemental scatterers that are fused by the radar waveform and the processing at the receiver, to result in echoes with fluctuating amplitude and phase It is well known that in conventional radar, slow fluctuations of the target radar cross section (RCS) result in target fades that degrade radar performance By spacing the antenna elements at the transmitter and at the receiver such that the target angular spread is manifested, the MIMO radar can exploit the spatial diversity of target scatterers opening the way to a variety of new techniques that can improve radar performance This paper focuses on the application of the target spatial diversity to improve detection performance The optimal detector in the Neyman–Pearson sense is developed and analyzed for the statistical MIMO radar It is shown that the optimal detector consists of noncoherent processing of the receiver sensors' outputs and that for cases of practical interest, detection performance is superior to that obtained through coherent processing An optimal detector invariant to the signal and noise levels is also developed and analyzed In this case as well, statistical MIMO radar provides great improvements over other types of array radars
1,652 citations
TL;DR: This paper considers the problem of downlink transmit beamforming for wireless transmission and downstream precoding for digital subscriber wireline transmission, in the context of common information broadcasting or multicasting applications wherein channel state information (CSI) is available at the transmitter.
Abstract: This paper considers the problem of downlink transmit beamforming for wireless transmission and downstream precoding for digital subscriber wireline transmission, in the context of common information broadcasting or multicasting applications wherein channel state information (CSI) is available at the transmitter. Unlike the usual "blind" isotropic broadcasting scenario, the availability of CSI allows transmit optimization. A minimum transmission power criterion is adopted, subject to prescribed minimum received signal-to-noise ratios (SNRs) at each of the intended receivers. A related max-min SNR "fair" problem formulation is also considered subject to a transmitted power constraint. It is proven that both problems are NP-hard; however, suitable reformulation allows the successful application of semidefinite relaxation (SDR) techniques. SDR yields an approximate solution plus a bound on the optimum value of the associated cost/reward. SDR is motivated from a Lagrangian duality perspective, and its performance is assessed via pertinent simulations for the case of Rayleigh fading wireless channels. We find that SDR typically yields solutions that are within 3-4 dB of the optimum, which is often good enough in practice. In several scenarios, SDR generates exact solutions that meet the associated bound on the optimum value. This is illustrated using measured very-high-bit-rate Digital Subscriber line (VDSL) channel data, and far-field beamforming for a uniform linear transmit antenna array.
1,511 citations
TL;DR: This paper shows that the configuration with spatially orthogonal signal transmission is equivalent to additional virtual sensors which extend the array aperture with virtual spatial tapering and provides higher performance in target detection, angular estimation accuracy, and angular resolution.
Abstract: In this paper, we propose a new space-time coding configuration for target detection and localization by radar or sonar systems. In common active array systems, the transmitted signal is usually coherent between the different elements of the array. This configuration does not allow array processing in the transmit mode. However, space-time coding of the transmitted signals allows to digitally steer the beam pattern in the transmit in addition to the received signal. The ability to steer the transmitted beam pattern, helps to avoid beam shape loss. We show that the configuration with spatially orthogonal signal transmission is equivalent to additional virtual sensors which extend the array aperture with virtual spatial tapering. These virtual sensors can be used to form narrower beams with lower sidelobes and, therefore, provide higher performance in target detection, angular estimation accuracy, and angular resolution. The generalized likelihood ratio test for target detection and the maximum likelihood and Cramer-Rao bound for target direction estimation are derived for an arbitrary signal coherence matrix. It is shown that the optimal performance is achieved for orthogonal transmitted signals. Target detection and localization performances are evaluated and studied theoretically and via simulations
1,243 citations
TL;DR: This article considers network coordination as a means to provide spectrally efficient communications in cellular downlink systems and describes how the antenna outputs are chosen in ways to minimize the out-of-cell interference, and hence to increase the downlink system capacity.
Abstract: In this article we consider network coordination as a means to provide spectrally efficient communications in cellular downlink systems. When network coordination is employed, all base antennas act together as a single network antenna array, and each mobile may receive useful signals from nearby base stations. Furthermore, the antenna outputs are chosen in ways to minimize the out-of-cell interference, and hence to increase the downlink system capacity. When the out-of-cell interference is mitigated, the links can operate in the high signal-to-noise ratio regime. This enables the cellular network to enjoy the great spectral efficiency improvement associated with using multiple antennas
1,124 citations
TL;DR: The proposed stochastic channel model for multiple-input multiple-output (MIMO) wireless radio channels is validated by means of measured data obtained from two completely different measurement campaigns and reveals its ability to better predict capacity and spatial channel structure than other popular stochastically channel models.
Abstract: -This paper presents a novel stochastic channel model for multiple-input multiple-output (MIMO) wireless radio channels. In contrast to state-of-the-art stochastic MIMO channel models, the spatial correlation properties of the channel are not divided into separate contributions from transmitter and receiver. Instead, the joint correlation properties are modeled by describing the average coupling between the eigenmodes of the two link ends. The necessary and sufficient condition for the proposed model to hold is that the eigenbasis at the receiver is independent of the transmit weights, and vice versa. The authors discuss the mathematical elements of the model, which can be easily extracted from measurements, from a radio propagation point of view and explain the underlying assumption of the model in physical terms. The validation of the proposed model by means of measured data obtained from two completely different measurement campaigns reveals its ability to better predict capacity and spatial channel structure than other popular stochastic channel models.
638 citations
TL;DR: In this article, the authors proposed a planar monopole antenna with dual band-notched characteristics, which is suitable for creating ultra-wideband antenna with narrow frequency notches or for creating multiband antennas.
Abstract: Wideband planar monopole antennas with dual band-notched characteristics are presented. The proposed antenna consists of a wideband planar monopole antenna and the multiple cup-, cap-, and inverted L-shaped slots, producing band-notched characteristics. In order to generate dual band-notched characteristic, we propose nine types of planar monopole antennas, which have two or three cap (cup or inverted L)-shaped slots in the radiator. This technique is suitable for creating ultra-wideband antenna with narrow frequency notches or for creating multiband antennas
322 citations
TL;DR: In this article, a dual-polarized antenna with two interleaved 2 x 2 arrays placed in a 2-layer Fabry-Perot cavity is presented. But the performance of the antenna is not as good as that of the conventional patch antennas, which have a 19 dBi gain and 30 dB of isolation between the two ports.
Abstract: A Fabry–Perot cavity (FPC) between a ground plane and a partially reflective surface (PRS) is used here to design array antennas with large distance between the radiating elements. This configuration provides some advantages: i) a reduction of the number of array elements to achieve high directivity; ii) large space between contiguous elements that may host a bulky feeding network as required for dual polarization or active antennas; iii) small coupling and easy feeding network designs because of the smaller number of elements with larger inter-element distance. We show that when designing the FPC antenna a frequency shift of the gain maximum may occur, especially in this sparse array configuration. We also show the existence of preferred distances between elements that controls both the directivity and the side lobe level, and how the presence of the FPC and the relaxed requirement of the interelement distance result in a lower interelement coupling. The presented dual polarized antenna comprises two interleaved 2 x 2 arrays placed in a 2-layer FPC, and exhibits a 19 dBi gain and 30 dB of isolation between the two ports over an operating bandwidth of approximately 5.7%, i.e., typical for patch antennas.
314 citations
TL;DR: In this article, a dual-diode rectenna with two diodes was proposed to achieve an RF-to-dc conversion efficiency of 76% at 5.8 GHz.
Abstract: This paper reports a new circularly polarized rectenna whose rectifying circuit includes two diodes. The rectenna consists of a coplanar stripline (CPS) truncated patch antenna and CPS bandpass filter, which can block harmonic signals up to the third order reradiating from the rectifying circuit. The rectenna is printed on Rogers Duroid 5880 substrate with /spl epsiv//sub r/=2.2 and a thickness of 20 mil. The new dual-diode rectenna can provide at least twice the dc output voltage than the traditional rectenna with only a single diode, which has the same layout dimension as the single-diode rectenna. The dual-diode rectenna achieves an RF-to-dc conversion efficiency of 76% at 5.8 GHz. The proposed rectennas can be interconnected to form the rectenna arrays by series, parallel, and cascaded connections. It is found that a cascade connected rectenna array can provide the highest output voltage. The antenna element can be easily extended to become a traveling-wave antenna or array suitable for high output voltage or current in wireless power transmission applications.
307 citations
TL;DR: The wide-band performance of four different matching networks for multiple dipole antennas is investigated and it is found that the efficiency advantage of multiport matching over individual-port matching diminishes with decreasing angular spread.
Abstract: We analyze the impact of the matching network on compact multiple-input multiple-output systems. Existing studies have found that the matching network has a significant influence on the performance of multiple antenna systems when the antennas are in close proximity. However, none has examined the wide-band case. In this paper, we investigate the wide-band performance of four different matching networks for multiple dipole antennas. The performance of the matching networks is given in terms of the bandwidths of correlation and matching efficiency, which are extensions of the single-antenna concept of bandwidth to multiple antenna systems. We also investigate the impact of the propagation conditions on the matching and bandwidth. For a uniform two-dimensional (2-D) angular power spectrum, we find that while individual-port matching can achieve in excess of 3% fractional correlation bandwidth for envelope correlation of 0.5 at an antenna separation of 0.01lambda, multiport matching is required for efficiency bandwidth to exist for a return loss of -6 dB. Moreover, even with multiport matching, both correlation and efficiency bandwidths decrease drastically at small antenna separations. At 0.01lambda, the correlation and efficiency bandwidths are 0.4% and 0.2%, respectively. Similar evaluations were performed for measured outdoor-to-indoor channels with moderate to small 2-D angular spreads. We find that the efficiency advantage of multiport matching over individual-port matching diminishes with decreasing angular spread
253 citations
9 Jul 2006
TL;DR: The primary focus of the paper is on the scaling of the capacity and achievable rates as the number of antennas and/or users is taken to infinity.
Abstract: The multiple antenna multicast channel is considered, in which the transmitter, equipped with an antenna array, sends a common message to multiple receivers, each of which are assumed to have only a single antenna. The information theoretic capacity of this channel is studied, along with the rates achievable using lower complexity transmission schemes. The primary focus of the paper is on the scaling of the capacity and achievable rates as the number of antennas and/or users is taken to infinity.
250 citations
TL;DR: In this article, the authors compared the performance of two cases of central element feeding and showed that the reduction in the sidelobe level to more than 20 dB was achieved without extra signal processing especially for small-sized arrays that have smaller number of elements and rings.
Abstract: Concentric circular antenna array (CCAA) has interesting features over other array configurations.A uniform arrangement of elements is assumed where the interelement spacing is kept almost half of the wavelength and the array parameters such as the steering matrix and gain are determined.The array performance such as beam power pattern, sidelobe level and beamwidth are discussed in two cases of central element feeding.The two cases are compared showing the reduction in the sidelobe level to more than 20 dB in the case of central element feeding without extra signal processing especially for small- sized arrays that have smaller number of elements and rings.
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19 Jan 2006TL;DR: In this paper, an apparatus and method for using ambient RF power in a portable terminal is described. But the authors focus on the charging apparatus and do not consider the use of RF signals.
Abstract: An apparatus and method for using ambient RF power in a portable terminal are provided. In the charging apparatus, an antenna array receives RF signals left derelict in the air, a rectifier rectifies the RF signals to DC voltages, and a power storage stores the DC voltages as power.
TL;DR: A new particle swarm optimization (PSO) technique for electromagnetic applications is proposed in this article, which is based on quantum mechanics rather than the Newtonian rules assumed in all previous versions of PSO, referred to as classical PSO.
Abstract: A new particle swarm optimization (PSO) technique for electromagnetic applications is proposed. The method is based on quantum mechanics rather than the Newtonian rules assumed in all previous versions of PSO, which we refer to as classical PSO. A general procedure is suggested to derive many different versions of the quantum PSO algorithm (QPSO). The QPSO is applied first to linear array antenna synthesis, which is one of the standard problems used by antenna engineers. The performance of the QPSO is compared against an improved version of the classical PSO. The new algorithm outperforms the classical one most of the time in convergence speed and achieves better levels for the cost function. As another application, the algorithm is used to find a set of infinitesimal dipoles that produces the same near and far fields of a circular dielectric resonator antenna (DRA). In addition, the QPSO method is employed to find an equivalent circuit model for the DRA that can be used to predict some interesting parameters like the Q-factor. The QPSO contains only one control parameter that can be tuned easily by trial and error or by suggested simple linear variation. Based on our understanding of the physical background of the method, various explanations of the theoretical aspects of the algorithm are presented
TL;DR: An efficient method for the pattern synthesis of the linear antenna arrays with the prescribed null and multi-lobe Beamforming is presented and several illustrative examples of uniform excited array patterns with the main beam placed in the direction of the useful signal.
Abstract: In this article, an efficient method for the pattern synthesis of the linear antenna arrays with the prescribed null and multi-lobe Beamforming is presented. Multi-lobe pattern and adaptive nulling of the pattern is achieved by controlling only the phase of each array element. The proposed method is based on the Sequential Quadratic Programming (SQP) algorithm and the linear antenna array synthesis was modelled as a multi-objective optimization problem. Multi-objective optimization is concerned with the maximization (or minimization) of a vector of objectives functions in the directions of desired signal that can be subject of a number of constraints (in our case, the constraints can be imposed as the null in the direction of interfering signal). To verify the validity of the technique, several illustrative examples of uniform excited array patterns with the main beam is placed in the direction of the useful signal and null is placed in the direction of potential interferers, and multi-beam patterns are demonstrated.
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6 Jun 2006TL;DR: In this paper, the rotary traveling wave oscillators are arranged in a pattern over an area and coupled so as to make them coherent, and the array also includes a plurality of phase shifters each of which is connected to one of the oscillators to provide a phase shifted local oscillator.
Abstract: Local oscillator circuitry for an antenna array is disclosed The circuitry includes an array of rotary traveling wave oscillators which are arranged in a pattern over an area and coupled so as to make them coherent This provides for a set of phase synchronous local oscillators distributed over a large area The array also includes a plurality of phase shifters each of which is connected to one of the rotary oscillators to provide a phase shifted local oscillator for the array The phase shifter optionally includes a cycle counter that is configured to count cycles of the rotary oscillator to which it is connected and control circuitry that is then operative to provide a shifted rotary oscillator output based on the count from the cycle counter A system and method for operating a true-time delay phased array antenna system The system includes a plurality of antenna element circuits for driving or receiving an rf signal from the elements of the array Each element circuit has a transmit and a receive path and a local multiphase oscillator, such as a rotary traveling wave oscillator Each path has an analog delay line for providing a true-time delay for the antenna element Preferably, the analog delay line is a charge coupled device whose control nodes are connected to phases of the local multiphase oscillator to implement a delay that is an integer number local multiphase oscillator periods A fractional delay is also included in the path by using a sample and hold circuit connected to a particular phase of the oscillator By delaying each antenna element by a true time delay, broadband operation of the array is possible
Patent•
18 Dec 2006
TL;DR: In this paper, the authors present systems and methods that may be employed to visually locate and/or track objects equipped with active RFID tags. And they employ an articulated camera, such as closed circuit television (CCTV) or other suitable type of articulated camera/s that is equipped with an antenna array.
Abstract: Systems and methods that may be employed to visually locate and/or track objects equipped with active RFID tags. The disclosed systems and methods may employ an articulated camera/s, such as closed circuit television (“CCTV”) or other suitable type of articulated camera/s, that is equipped with an antenna array.
Patent•
2 May 2006
TL;DR: In this paper, an antenna array structure which includes multiple array elements, and the array array structure is used for the application of the WLAN (wireless local area network) or WMAN (wirewireless metro area network).
Abstract: The present invention provides an antenna array structure which includes multiple array elements, and the antenna array structure is using for the application of the WLAN (wireless local area network) or WMAN (wireless metro area network.) Furthermore, the array elements of the present invention are phased arrays or attenuated arrays, and when configuration with different type of the array element is used, the corresponding BFN (beam forming network) can also be implemented in various possibilities. With all the configuration of the present invention, the manufacturers can have a stable array structure for their applications.
TL;DR: This paper analytically derives the spatial correlation coefficients of this array as a function of the mode excited, for realistic clustered MIMO channel models, and compares the performance of the circular patch array (CPA) against an array of two spaced dipoles.
Abstract: In this paper, we analyze a multiple-input multiple-output (MIMO) array consisting of two circular microstrip antennas, designed to exploit pattern diversity. We analytically derive the spatial correlation coefficients of this array as a function of the mode excited, for realistic clustered MIMO channel models. We compare the performance of the circular patch array (CPA) against an array of two spaced dipoles. In particular, we compute a theoretical tradeoff to predict when the pattern diversity provided by the CPA is more effective than space diversity from the uniform linear array (ULA), based on the eigenvalues of the spatial correlation matrix. Through simulations, we show that CPAs yield better performance or satisfy more restrictive size constraints than ULAs in clustered MIMO channels, depending on the element spacing of the ULA. These results make the CPA an attractive solution for miniaturized MIMO arrays for portable devices or access points.
TL;DR: A unified capacity formula is derived for the multiuser scheduling system with different multiple-input multiple-output antenna schemes, including: 1) selective transmission/selective combining (ST/SC); 2) maximum ratio transmission/maximum ratio combining (MRT/MRC); 3) ST/M RC; and 4) space-time block codes (STBC).
Abstract: In this paper, we present a cross-layer analytical framework to jointly investigate antenna diversity and multiuser scheduling under the generalized Nakagami fading channels. We derive a unified capacity formula for the multiuser scheduling system with different multiple-input multiple-output antenna schemes, including: 1) selective transmission/selective combining (ST/SC); 2) maximum ratio transmission/maximum ratio combining (MRT/MRC); 3) ST/MRC; and 4) space-time block codes (STBC). Our analytical results lead to the following four observations regarding the interplay of multiuser scheduling and antenna diversity. First, the higher the Nakagami fading parameter, the lower the multiuser diversity gain for all the considered antenna schemes. Second, from the standpoint of multiuser scheduling, the multiple antennas with the ST/SC method can be viewed as virtual users to amplify multiuser diversity order. Third, the boosted array gain of the MRT/MRC scheme can compensate the detrimental impact of the reduced amount of fading gain on multiuser scheduling, thereby resulting in greater capacity than the ST/SC method. Last, employing the STBC scheme together with multiuser diversity may cause capacity loss due to the reduced amount of fading gain, but without the supplement of array gain.
TL;DR: This paper demonstrates a MEMS-switched parasitic antenna array at 5.6 GHz providing two radiation patterns with beams at /spl plusmn/25/spl deg/.
Abstract: A micro-electro-mechanical series (MEMS)-switched parasitic antenna array providing radiation pattern diversity is described. A new modeling method is introduced in order to allow a fast and accurate optimization of the antenna. This method is demonstrated with the design of both passive and active prototypes at 5.6 GHz. The active prototype makes use of stand-alone packaged MEMS switches. Measured return loss and radiation patterns are in good agreement with the design, demonstrating a beam-switching at plusmn25deg
TL;DR: In this article, a 4 times 4 two-layer Butler matrix based on a broadband broadband 2-layer slot-coupled directional coupler is presented and implemented at 58 GHz using coplanar waveguide technology.
Abstract: In this paper, a novel 4 times 4 two-layer Butler matrix based on a broad-band two-layer slot-coupled directional coupler is presented and implemented at 58 GHz using coplanar waveguide technology With the slot-coupled directional coupler, the proposed matrix was designed without using any crossovers as used in conventional Butler matrices, which leads to significant size reduction and loss minimization To examine the performance of the proposed matrix, experimental prototypes of the multilayer directional coupler and the Butler matrix were fabricated and measured Furthermore, a four-antenna array was also designed and fabricated at 58 GHz and then connected to the matrix to form a beamforming antenna system As a result, four orthogonal beams at -45deg, -15deg, 15deg, and 45deg are produced Measured results on the entire system agree well with the theoretical predictions, validating the proposed design
TL;DR: Two novel joint radio-frequency (RF)-baseband designs for receivers in a MIMO system with Nt transmit antennas, N r receive antennas, but only L < Nr RF chains at the receiver are introduced, achieving superior performance by exploiting the spatial correlation of the received signals.
Abstract: We introduce two novel joint radio-frequency (RF)-baseband designs for receivers in a MIMO system with Nt transmit antennas, N r receive antennas, but only L < Nr RF chains at the receiver. The joint design introduces an RF pre-processing matrix that processes the signals from the different antennas, and is followed by selection (if necessary), down-conversion, and further processing in the baseband. The schemes are similar to conventional antenna selection in that they use fewer RF chains than antenna elements, but achieve superior performance by exploiting the spatial correlation of the received signals. The first of our proposed designs uses an L times N r RF pre-processing matrix that outputs only L streams followed by baseband signal processing, and, thus, eliminates the need for a selection switch. The second one uses an Nr times N r RF pre-processing matrix that outputs Nr streams and is followed by a switch that selects L streams for baseband signal processing. Both spatial diversity and spatial multiplexing systems are considered and the optimum pre-processing matrices are derived for all cases. To accommodate practical RF design constraints, which prefer a variable phase-shifter-based implementation, a sub-optimal phase approximation is also introduced. Performance better than conventional antenna selection and close to the full complexity receiver is observed in both single cluster and multi-cluster wireless channels. A beam-pattern-based geometric intuition is also developed to illustrate the effectiveness of the optimal solutions
Patent•
21 Dec 2006
TL;DR: The Backbone Connection Facilitator (BCF) as mentioned in this paper dynamically creates concurrent data pipelines to meet the data bandwidth demand to transfer packets from one short-range wired/wireless network to another.
Abstract: In accordance with the present invention, there is provided a high-speed wireless backbone connection, Backbone Connection Facilitator (BCF), to create a wireless home network, which may consist of many short-range wired/wireless networks. BCF dynamically creates concurrent data pipelines to meet the data bandwidth demand to transfer packets from one short-range wired/wireless network to another. BCF employs the newly developed antenna technologies (ex. MIMO, SDMA) to minimize the transmit power, to reduce the interferences, and to support the real time communication. BCF contains the BCF-PHY layer, the BCF-Data-Link-Layer, and the BCF-Network-Layer. The BCF-PHY layer consists of antenna array, a PHY Base Band controller, and a digital beam former. The BCF-Data-Link-Layer provides the MAC functionality. The BCF-Network-Layer assembles the packet, provides the source and destination address, and provides the BCF-PHY beam forming information. The BCF-Network-Layer is also responsible for parsing and assembling the packet payloads for the high-speed backbone connection.
TL;DR: In this paper, a longitudinally-slotted ridge waveguide antenna array with a compact transverse dimension is presented to broaden the bandwidth of the array, it is separated into two subarrays fed by a novel compact convex waveguide divider.
Abstract: A longitudinally-slotted ridge waveguide antenna array with a compact transverse dimension is presented. To broaden the bandwidth of the array, it is separated into two subarrays fed by a novel compact convex waveguide divider. A 16-element uniform linear array at X-band was fabricated and measured to verify the validity of the design. The measured bandwidth of S11les-15 dB is 14.9% and the measured cross- polarization level is less than -36 dB over the entire bandwidth. This array can be combined with the edge-slotted waveguide array to build a two-dimensional dual-polarization antenna array for the synthetic aperture radar (SAR) application
TL;DR: In this paper, two reconfigurable reflectarrays with patch elements which can vary the reflected phase by varying the height of the patches have been designed using a periodic method of moments simulation.
Abstract: Reconfigurable reflectarrays have been designed with patch elements which can vary the reflected phase by varying the height of the patches. These patches have been designed using a periodic method of moments simulation. Reflectarrays incorporating elements of varying heights have been built and tested. The first design is a 33 element array comprised of stacked patches which operates at 7.31 GHz. The second design is a 120-element dipole array over a ground plane which operates at 5.2 GHz. Microelectrical, mechanical systems actuation technology could be used to implement these designs and a potential concept is suggested
2 Jul 2006
TL;DR: Motivated to study simpler transmission techniques, a linear precoding technique based on the zero-forcing (ZF) algorithm is focused on, and numerical results show ZF with PAPC achieves a significant fraction of the optimum DPC sum-rate capacity in practical cases where K is bounded.
Abstract: We consider the downlink transmission of a wireless communication system where M antennas transmit independent information to a subset of K users, each equipped with a single antenna. The Shannon capacity of this MIMO broadcast channel (MIMO-BC) can be achieved using a non-linear preceding technique known as dirty paper coding (DPC) which is difficult to implement in practice. Motivated to study simpler transmission techniques, we focus on a linear precoding technique based on the zero-forcing (ZF) algorithm. In contrast to the typical sum power constraint (SPC), we consider a per-antenna power constraint (PAPC) motivated both by current antenna array designs where each antenna is powered by a separate amplifier and by future wireless networks where spatially separated antennas transmit cooperatively to users. We show that the problem of power allocation for maximizing the weighted sum rate under ZF with PAPC is a constrained convex optimization problem that can be solved using conventional numerical optimization techniques. For the special case of two users, we find an analytic solution based on waterfilling techniques. For the case where the number of users increases without bound, we show that ZF with PAPC is asymptotically optimal in the sense that the ratio of the expected sum-rate capacities between ZF with PAPC and DPC with SPC approaches one. We also show how the results can be generalized for multiple frequency bands and for a hybrid power constraint. Finally, we provide numerical results that show ZF with PAPC achieves a significant fraction of the optimum DPC sum-rate capacity in practical cases where K is bounded
TL;DR: In this paper, a reflectarray antenna composed of double crossed loops of variable lengths printed on a conductor backed substrate is introduced, which demonstrates a radiation efficiency close to 55% and 1'dB gain.
Abstract: A reflectarray antenna composed of double crossed loops of variable lengths printed on a conductor backed substrate is introduced. Using this technique, a single-layer reflectarray with wider bandwidth compared to conventional single-layer reflectarrays is fabricated and measured. Measured results demonstrate a radiation efficiency close to 55% and 1 dB gain–bandwidth of 10%, centred at 22 GHz.
TL;DR: In this paper, a method for partial discharge (PD) source location in power transformers based on detecting electromagnetic (EM) radiation emitted from PD is presented. But the problem of partial discharge location by EM waves is the difficulty in getting the accurate time arrivals of the signals from the source to multiple sensors.
Abstract: This paper presents a method for partial discharge (PD) source location in power transformers based on detecting electromagnetic (EM) radiation emitted from PD. The key problem of PD location by EM waves is the difficulty in getting the accurate time arrivals of the signals from the source to multiple sensors. Several measures are taken to improve the time arrival resolution. Firstly, a measuring frequency band (1 GHz-5 GHz) within RF band is proposed to accurately pick up the fast rise time of the signals. Secondly, an antenna array with diamond-shaped configuration is designed to improve the correlation coefficient of the waveforms from multiple sensors. Thirdly, two antenna arrays are proposed to eliminate the influences of the EM wave scattering caused by the iron core. Fourthly, an algorithm is proposed to increase the signal to noise ratio and to measure the time arrivals automatically through cross-correlation and averaging operation. Lastly, a hyperboloid-genetic algorithm is developed to search the PD source. Experiments on a single-phase transformer model were conducted in the laboratory. The tested results proved the validity of the proposed method and showed that the location error in 16 cm, mostly is about several cm
TL;DR: The array design problem is simplified by limiting the array search within a family of V-shaped arrays that are advantageously characterized by a single parameter, the angle between the two branches.
Abstract: We study the impact of the geometry of the (planar) antenna array on the accuracy of the estimated direction(s) of arrivals of an emitting source. We develop explicit Cramer-Rao bounds (CRBs) of the azimuth and elevation angles that show a simple structure. In particular, for a fixed elevation angle, the CRBs are cosine functions of the source azimuth, and so, regardless of the array geometry. The amplitude and extremes of these functions depend on the array geometry. Hence, the array configuration can be chosen in order to ensure a desired (an)isotropic behavior. To do so, we propose a pragmatic methodology that also takes into account the array ambiguity problem. The array design problem is simplified by limiting the array search within a family of V-shaped arrays that are advantageously characterized by a single parameter, the angle between the two branches. A performance measure is proposed, then analytically expressed, to assess the array directivity and gain with respect to the more standardly used uniform circular array.
Patent•
26 Dec 2006
TL;DR: In this paper, the antenna systems disclosed in a multiple-input, multiple-output (MIMO) wireless environment are utilized in a preferred embodiment, in which the antenna system disclosed herein are used in a MIMO wireless environment.
Abstract: A horizontally polarized antenna array allows for the efficient distribution of RF energy into a communications environment through selectable antenna elements and redirectors that create a particular radiation pattern such as a substantially omnidirectional radiation pattern. In conjunction with a vertically polarized array, a particular high-gain wireless environment may be created such that one environment does not interfere with other nearby wireless environments and avoids interference created by those other environments. Lower gain patterns may also be created by using particular configurations of a horizontal and/or vertical antenna array. In a preferred embodiment, the antenna systems disclosed herein are utilized in a multiple-input, multiple-output (MIMO) wireless environment.