Multiple Antenna Elements Research Articles

Propeller-Shaped Antenna: A Steerable Ultrawideband Planar Antenna

We propose an ultrawideband planar antenna having a controllable radiation pattern for coarse steering to avoid fading in indoor communications. In the antenna, multiple tapered-slot antenna (TSA) elements are connected to a feeding part through p-i-n diode switches. The TSA elements have such wide aperture and round shape that the mutual coupling among them is effectively suppressed, resulting in sufficient steering ability. Simulation and experiments demonstrate that the radiation is switched to intended directions. Reflection S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> is below or around -10 dB in the frequency range of 3.1-10.6 GHz independent of the switching condition. Basic characteristics are investigated and discussed.

Comparative Analysis of Feeding Techniques for Micro strip Patch Antenna and Smart Antenna Applications in Mobile Communication

This paper describes two folds. First it describes comparative analysis of different feeding techniques for microstrip patch antenna wireless applications. Where it covers two broad categories of feeding approach - contracting (coaxial and microstrip feeds) and non-contracting (aperture coupling and proximity coupling feeds). Today as smart antenna has emerged as an auspicious technique to improve the performance of cellular mobile system. In second section authors propose a MIMO structure ,consist of multiple antenna elements and its application in mobile communication with the key characteristics features, benefits, drawbacks, types of smart antennas and their working mechanism..

A Markov Decision Theoretic Approach to Pilot Allocation and Receive Antenna Selection

This paper considers antenna selection (AS) at a receiver equipped with multiple antenna elements but only a single radio frequency chain for packet reception. As information about the channel state is acquired using training symbols (pilots), the receiver makes its AS decisions based on noisy channel estimates. Additional information that can be exploited for AS includes the time-correlation of the wireless channel and the results of the link-layer error checks upon receiving the data packets. In this scenario, the task of the receiver is to sequentially select (a) the pilot symbol allocation, i.e., how to distribute the available pilot symbols among the antenna elements, for channel estimation on each of the receive antennas; and (b) the antenna to be used for data packet reception. The goal is to maximize the expected throughput, based on the past history of allocation and selection decisions, and the corresponding noisy channel estimates and error check results. Since the channel state is only partially observed through the noisy pilots and the error checks, the joint problem of pilot allocation and AS is modeled as a partially observed Markov decision process (POMDP). The solution to the POMDP yields the policy that maximizes the long-term expected throughput. Using the Finite State Markov Chain (FSMC) model for the wireless channel, the performance of the POMDP solution is compared with that of other existing schemes, and it is illustrated through numerical evaluation that the POMDP solution significantly outperforms them.

Beam tilting of single microstrip antenna using high permittivity superstrate

AbstractAntenna beam tilting or steering requires multiple antenna elements to be phase shifted and arranged in the form of an array. This article presents a novel method to tilt the main beam of a microstrip patch by partially covering it with a high dielectric‐constant superstrate. The beam tilting is possible because of the dual‐slot radiation mechanism of the microstrip antenna. In effect, the electromagnetic radiation from the covered radiating slot reaches the far‐field with an additional phase with respect to the uncovered slot, resulting in an inclined beam whose angle depends on the superstrate's refractive index. Experimentally and numerically, a beam deflection of 25° is achieved when a microstrip patch is partially covered with a superstrate having a dielectric constant of 10. Moreover, the proposed structure provides gain enhancement of about 3 dB. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1657–1661, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27659

A Novel GPS Receiver Algorithm for Continuous Tracking on Spinning Cylindrical Platforms

Recently, there has been increased interest in GPS navigation for spinning cylindrical platforms (60-160 mm diameter). As expected, a single antenna element does not provide spherical coverage which is needed for continuous satellite tracking. To provide the desired coverage, one can use antenna diversity with multiple antenna elements. Previously, different antenna diversity techniques were compared, and it was shown that the maximum gain method (i.e., choosing the element with the highest gain) provides the spherical coverage. However, it is a challenge to implement this method because of the unknown time-varying platform attitude. In this paper, a novel tracking algorithm is derived that implements the maximum gain method by modifying the receiver itself. Example results are shown for the delay lock loop (DLL) and demonstrate that the proposed approach is able to provide continuous satellite tracking as the platform rotates and eliminate the need for knowledge of the time-varying platform attitude. Copyright © 2013 Institute of Navigation.

Implementation of Alamouti 2X3 Code on FPGA Board

MIMO systems with multiple antenna elements at both Transmitter and Receiver ends are an efficient solution for future wireless communication systems. They provide high data rates by exploiting the spatial domain under the constraints of limited bandwidth and transmit power. SpaceTime Block Coding is a MIMO transmit strategy which exploits transmit diversity and high reliability. In the present paper performance analysis and a comparative study is reported for Alamouti code using transmit-receive diversity ( 2x1, 2X2, 2x3) with maximum likelihood detection technique. The channel is assumed to be flat Rayleigh fading channel and noise samples are independent with zero mean complex Gaussian random variable. The Alamouti Space Time Block codes with modulation techniques BPSK, QPSK and 16-QAM are used to obtain the bit error rate performance under different SNR scenarios. The results reported in this paper suggest substantial improvement in the system performance by incorporating multiple input multiple output techniques in order to improve the link quality.

Effects of Channel Estimation on Spatial Modulation

In this letter, we investigate the effects of training-based channel estimation on the achievable performance of the recent spatial modulation (SM) based multiple-input multiple-output (MIMO) scheme. This is motivated by the fact that the SM transmitter is constituted by a single radio-frequency (RF) branch and multiple antenna elements (AEs), hence simultaneous pilot transmissions from the AEs are impossible, unlike in the classic multiple-RF MIMO transmitters. Our simulation results demonstrate that the SM scheme's BER curve exhibits a performance penalty, while relying on realistic imperfect channel-estimation. In order to combat these limitations, we propose two single-RF arrangements, namely a reduced-complexity joint channel estimation and data detection aided SM scheme as well as a non-coherently detected single-RF space-time shift keying scheme dispensing with channel estimation.

Multilayer Antenna Package for IEEE 802.11ad Employing Ultralow-Cost FR4

This paper demonstrates the possibility and feasibility of an ultralow-cost antenna-in-package (AiP) solution for the upcoming generation of wireless local area networks (WLANs) denoted as IEEE802.11ad. The iterative design procedure focuses on maximally alleviating the inherent disadvantages of high-volume FR4 process at 60 GHz such as its relatively high material loss and fabrication restrictions. Within the planar antenna package, the antenna element, vertical transition, antenna feedline, and low- and high-speed interfaces are allocated in a vertical schematic. A circular stacked patch antenna renders the antenna package to exhibit 10-dB return loss bandwidth from 57-66 GHz. An embedded coplanar waveguide (CPW) topology is adopted for the antenna feedline and features less than 0.24 dB/mm in unit loss, which is extracted from measured parametric studies. The fabricated single antenna package is 9 mm × 6 mm × 0.404 mm in dimension. A multiple-element antenna package is fabricated, and its feasibility for future phase array applications is studied. Far-field radiation measurement using an inhouse radio-frequency (RF) probe station validates the single-antenna package to exhibit more than 4.1-dBi gain and 76% radiation efficiency.

Cross-Layer Optimization of Multichannel Multiantenna WMNs

Use of multiple channels can significantly improve the throughput of wireless mesh networks (WMNs). Additionally, recent advances in radio technology have made it possible to realize software-defined radio (SDR), which is capable of switching from one channel to another dynamically. On the other hand, equipping wireless nodes with multiple antennas creates great potential for throughput improvement via interference suppression, spatial multiplexing, and spatial division multiple access techniques. In this paper, we investigate the joint optimization of routing and scheduling in multichannel WMNs, where nodes are equipped with a single SDR and multiple antenna elements. We analyze achievable throughput of these networks under four different multiantenna modes: single user single stream, single user multi stream, multi user single stream, and multi user multi stream, each mode integrates different combinations of multiantenna techniques. We mathematically model scheduling and interference constraints and formulate joint routing and scheduling optimization problem with the objective of maximizing the throughput by minimizing network schedule time such that traffic demands for a set of sessions are satisfied. A column generation-based decomposition approach is proposed to solve the problem. Simulation results are presented to evaluate the impact of number of antennas, number of channels, and number of sessions on the schedule time for the four proposed modes.

Performance Analysis of Correlated Multiple Antenna Spectrum Sensing Cognitive Radio

We derive probability of detection Pd and false alarm Pf for spectrum sensing cognitive devices, employing correlated multiple antenna elements using linear test statistic. Detection performance of such sensors is severely degraded due to the correlation among antennas, in addition to that fading channel conditions may further deteriorate the performance. We propose a simple hard decision fusion strategy at the secondary Base Station to improve the performance by exploiting collaborative gain. Region of Convergence (ROC) is also evaluated under OR based fusion strategy. Numerical results certify the proposed proposal.

On the applicability of steerable beams in LTE-Advanced networks with high user mobility

This article deals with the problem of applying scanning narrow beams to long-term evolution (LTE)-advanced networks that include in their coverage areas fast moving mobiles. The system scenario is assumed to include eNodeBs that can form multiple beams which can steer (rotate) their respective coverage areas. Additionally, the user downlink transmissions are supposed to be dynamically scheduled based on signal-to-noise plus interference ratio reports for physical resource blocks. The mobile user equipments (UEs) have multiple antenna elements which allow maximal ratio combining of the received signals. By applying coordinated transmission of steerable beams at neighboring eNodeBs, we could mitigate inter-cell interference in a multi-cell interference deployment. The coverage area and total throughput may significantly be enhanced, compared to the current LTE standard where inter-cell interference coordination technique is adopted for low-speed UEs. Furthermore, the proposed schemes involve low-complexity hardware implementation and low power consumption.

Space Efficiency of Multiple Element Antennas

Multiple element antennas (MEAs) support multiple-input multiple-output (MIMO) communications and other antenna diversity techniques, resulting in better communications performance than available from single antenna systems. The space occupied by MEAs becomes important when the antennas are integrated into small or portable devices, and a metric would be helpful for the design of compact MEAs. A figure of merit for the spatial efficiency is presented here for evaluating the MEA compactness with respect to the MEA bandwidth and the potential communications performance. A spherical volume is used and different propagation scenario models can be incorporated. The impact of element efficiencies, mutual coupling, correlation, diversity scheme, and propagation scenario are included.

Radiation Characteristics of a Multimode Concentric Circular Microstrip Patch Antenna by Controlling Amplitude and Phase of Modes

Conventional method of beam scanning such as phased array antenna is costly by using multiple antenna elements and phase shifters. In this communication, a different method is investigated to achieve beam scanning. A multimode concentric circular microstrip patch antenna on a single substrate layer backed by a finite ground plane is presented where radiation patterns are reconfigurable. Pattern reconfiguration is achieved by exciting higher order TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n1</sub> modes in addition to the dominant TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode. Next, limited beam scan performance for linear polarization by employing mode combination and control of the amplitude and phase values is demonstrated. A prototype multimode patch antenna was fabricated and experimentally verified for the individual modes impedance matching and radiation patterns which showed acceptable agreement. The beam scan performance for a selected combination of modes of the patch was also measured.

Multiple Element Antenna Efficiency and its Impact on Diversity and Capacity

A desirable characteristic of a multiple element antenna (MEA) is to be compact, but a smaller size tends to lead to higher ohmic and mutual coupling losses. A metric for the efficiency of the MEA would help clarify the tradeoffs between compactness and performance. In a MIMO/diversity antenna, the total efficiency seen at each port directly affects the signal-to-noise ratio (SNR) in the diversity branch. The SNR after diversity combining governs the performance of the diversity antenna system. In this paper, MEA efficiencies is therefore discussed and formulated in the context of mutual coupling and diversity combining. The impact of MEA efficiency on the diversity gain and the information theoretical capacity is also formulated and demonstrated using measurements of example MEAs. With these formulations, an equivalent number of idealized (lossless, uncorrelated, uncoupled, equal power) branches can be found for an MEA, and this defines the diversity order and the capacity order of the MEA. With this metric, the performance of different MEAs can be compared.

Analysis of Optimal Weighted Cooperative Spectrum Sensing with Multiple Antenna Elements

This paper investigates the use of cooperative spectrum sensing (CSS) to detect primary user (PU) signals during spectrum sharing between the PU and the secondary user (SU). In particular, we employ a variant of CSS (which achieves space diversity), called weighted gain combining CSS (W-CSS), which has the potential to achieve increased diversity gain and enhance detection performance. In a typical W-CSS system, the SU needs to obtain the PU signal power information in order to set the proper weight value. However, as it is hard for the SU to ascertain whether the PU is present or absent, this is difficult to obtain. To address this problem, a PU signal power estimation algorithm is introduced. In addition, we also analyze the statistics of the estimator and derive the detection probability of the W-CSS when the PU signal power estimation algorithm is applied. The analysis and related simulation results reveal that the detection probability of the proposed W-CSS under time-variant Rayleigh fading asymptotically approaches the detection probability in an additive white Gaussian noise channel as the number of antennas is increased. This also follows results from our Monte Carlo simulations, showing that multiple antenna elements could suppress the effect of Rayleigh fading. In short, the accuracy of the estimation algorithm is affected by channel variation (especially in the case of fast Rayleigh fading). Hence, to address this problem, we employ multiple antenna elements with a square-law combining energy detector in the W-CSS. key words: cognitive radio, cooperative spectrum sensing, NeymanPearson theorem, multiple antenna elements

Downlink System Throughput Statistics for Various MEA Configurations

The advent of applications that need higher throughputs motivates wireless service providers and cellular operators to embrace newer technologies that can meet these demands. Multiple-input-multiple-output (MIMO) systems have shown promise in their ability to deliver high throughput per bandwidth with reasonable constellation sizes. Adding antennas at the base station (BS) is practical due to reasons of size and cost amortization over users. However, adding antennas at the mobile station (MS), which does not have similar advantages, needs to be carefully evaluated. We therefore consider the more general class of techniques involving a multiple-element antenna (MEA) at one or both ends of the link (MIMO corresponding to the case of both). From a commercial standpoint, one needs to address the following questions: (i) What is the benefit of a second antenna at the BS or the MS relative to the single-input-single-output (SISO) case? (ii) What is the added value of a second antenna at both ends? (iii) If a second antenna is indeed used at both ends, which mode of operation --- spatial multiplexing (SM) or diversity (Div) --- is the preferred one? Using $(n, m)$ to denote a link with $n$ BS transmit elements and $m$ MS receive elements, we compare the downlink throughput performance of the SISO link with that of four MEA configurations: $(1, 2)$, \mbox{$(2, 1)$}, $(2, 2)$ with Div and $(2, 2)$ with SM. Our results indicate that, in the context of adaptive modulation with practical limits on constellation size, $(1, 2)$ is the preferred configuration. We also show this finding to be robust to assumptions used in the study.

Multiple-input multiple-output radar search strategies for high-velocity targets

The radar detection of high-velocity targets with a multiple-element antenna array is considered. The detection performance of multiple-input multiple-output (MIMO) radar with orthogonal waveforms is compared with that of a radar using a directed beam. An analytical expression for the probability of detection for a radar with a multiple-element array is derived. For high-velocity targets, the decrease in probability of detection because of the longer integration time required for MIMO radar is quantified. It is shown that for lower-velocity targets, sector search using orthogonal waveforms results has similar detection range performance to that of scanning directed beams. For higher-velocity targets, the use of scanning directed beams yields larger detection range.

A reconfigurable plasma antenna

An experiment aimed at investigating the antenna properties of different plasma structures of a plasma column as a reconfigurable plasma antenna, is reported. A 30 cm long plasma column is excited by surface wave, which acts as a plasma antenna. By changing the operating parameters, e.g., working pressure, drive frequency, input power, radius of glass tube, length of plasma column, and argon gas, single plasma antenna (plasma column) can be transformed to multiple small antenna elements (plasma blobs). It is also reported that number, length, and separation between two antenna elements can be controlled by operating parameters. Moreover, experiments are also carried out to study current profile, potential profile, conductivity profile, phase relations, radiation power patterns, etc. of the antenna elements. The effect on directivity with the number of antenna elements is also studied. Findings of the study indicate that entire structure of antenna elements can be treated as a phased array broadside vertical plasma antenna, which produces more directive radiation pattern than the single plasma antenna as well as physical properties and directivity of such antenna can be controlled by operating parameters. The study reveals the advantages of a plasma antenna over the conventional antenna in the sense that different antennas can be formed by tuning the operating parameters.

Moment-based SNR estimation over linearly-modulated wireless SIMO channels

In this paper, we develop a new method for signal-to-noise ratio (SNR) estimation when multiple antenna elements receive linearly-modulated signals in complex additive white Gaussian noise (AWGN) spatially uncorrelated between the antenna elements. We also derive extensions of other existing moment-based SNR estimators to the single-input multiple-output (SIMO) configuration. The new SIMO SNR estimation technique is non-data-aided (NDA) since it is a moment-based method and does not rely, therefore, on the a priori knowledge or detection of the transmitted symbols; it does not require the a priori knowledge of the modulation type or order. The new method is shown by Monte Carlo simulations to clearly outperform the best NDA moment-based SNR estimation methods in terms of normalized root mean square error (NRMSE) over QAM-modulated transmissions, namely the M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> method and the estimators referred to, in this paper, as the GT and the M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> methods, even when we extend them to the SIMO configuration.

Combined diversity and multiplexing for multiple-input multiple-output system with cochannel interference

A multiple-input multiple-output (MIMO) system that combines diversity and multiplexing is proposed for multi-cellular networks with cochannel interference. In the proposed MIMO system, the data stream is divided into multiple substreams, and each substream is transmitted and received over multiple antenna elements. Because of having both the advantages provided by diversity and multiplexing, the proposed MIMO system can gain larger throughput than the scheme with either diversity or multiplexing solely being employed. We propose an algorithm to find the optimum antenna configuration that maximises the throughput of the proposed MIMO system. We also propose a power control algorithm for the proposed MIMO system such that the interference is decreased and the throughput can be increased. In addition, the time division multiple access scheme and a scheduling algorithm are proposed to mitigate the interference in one time slot so that the throughput of the proposed MIMO system can be further increased.