Lens Antenna Array Research Articles

Channel Feedback Codebook Design for Millimeter-Wave Massive MIMO Systems Relying on Lens Antenna Array

The recently proposed millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) system relying on a lens antenna array (LAA) significantly reduces the number of radio frequency chains using beam selection. A high data rate can be achieved based on the reduced-dimensional equivalent channel after beam selection. In frequency division duplexing systems, the equivalent channel has to be fed back to the base station (BS) via a feedback channel based on a codebook. However, no dedicated codebook has been proposed for LAA-aided mmWave systems. To fill this gap, in this letter, we propose a reduced-dimensional subspace codebook (RDSC) for such systems. Specifically, under the recently proposed concept of angle coherence time , we first generate the large-dimensional vectors in the channel subspace , which is determined by the angles-of-departure of the dominant paths. Then, based on these vectors in the channel subspace, we create the RDSC by considering both the lens and the beam selector. Finally, the equivalent channel is quantized using the proposed RDSC and fed back to the BS. Finally, we carry out mathematical performance analysis of the proposed RDSC and show that its feedback overhead is rendered proportional to the relatively small number of dominant paths per user. The analytical results are verified by our simulations.

Four-element lens array antenna for advanced point-to-(multi)point high-bandwidth wireless communication

The aim of this work is to propose a wideband high-gain four-element (2 × 2) lens array antenna with operating frequency in an important region of the electromagnetic spectrum which is key for next-generation high-rate communication. Frequency- and time-domain methods were used to analyze the antenna, with time-domain simulations being preferred. The antenna design started from a basic wideband microstrip antenna on Rogers RO 4350 substrate. Next, to increase the basic antenna gain, a dielectric half-sphere lens was used. Subsequently, the lens antenna was utilized as an array element to form the proposed four-element array antenna. The proposed array antenna exhibited fractional bandwidth of 98.8 % from 34.4 to 101.6 GHz with maximum gain of 16.9 dB at 101.5 GHz. Interesting computational results are presented and discussed in terms of run time, maximum utilized memory, and number of mesh cells for each development step of the antenna. Finally, the antenna was mounted on top of a 24-pin integrated circuit (IC); its three-dimensional (3D) radiation pattern at 60 GHz is presented and discussed.

Joint Design of Beam Selection and Precoding Matrices for mmWave MU-MIMO Systems Relying on Lens Antenna Arrays

Wireless transmission relying on lens antenna arrays is becoming more and more attractive for millimeter wave (mmWave) multiple-input multiple-output (MIMO) systems using a limited number of radio frequency chains due to the lens' energy-focusing capability. In this paper, we consider the joint design of the beam selection and precoding matrices in order to maximize the sum-rate of a downlink single-sided lens MU-MIMO mmWave system under transmit power constraints. We first formulate the optimization problem into a tractable form using the popular weighted minimum mean squared error (WMMSE) approach. To solve this problem, we then propose an efficient joint beam selection and precoding design algorithm based on the innovative penalty dual decomposition method. To reduce the design complexity, we also propose a simplified algorithm by combining the interference-aware beam selection scheme with the WMMSE approach. Simulation results demonstrate that our proposed algorithms can converge in a few iterations and achieve near-optimal performance when compared to the fully digital precoding scheme, thus enabling them to outperform the competing methods.

Multi-User Millimeter Wave MIMO With Full-Dimensional Lens Antenna Array

Millimeter wave (mmWave) communication by utilizing lens antenna arrays is a promising technique for realizing cost-effective 5G wireless systems with large MIMO (multiple-input multiple-output) but only limited radio frequency (RF) chains. This paper studies an uplink multi-user mmWave single-sided lens MIMO system, where only the base station (BS) is equipped with a full-dimensional (FD) lens antenna array with both elevation and azimuth angle resolution capabilities, and each mobile station (MS) employs the conventional uniform planar array (UPA) without the lens. By exploiting the angle-dependent energy focusing property of the lens antenna array at the BS as well as the multi-path sparsity of mmWave channels, we propose a low-complexity path division multiple access (PDMA) scheme, which enables virtually interference-free multi-user communications when the angle of arrivals (AoAs) of all MS multi-path signals are sufficiently separable at the BS. To this end, a new technique called path delay compensation is proposed at the BS to effectively transform the multi-user frequency-selective MIMO channels to parallel frequency-flat small-size MIMO channels for different MSs, for each of which the low-complexity single-carrier(SC) transmission is applied. For general scenarios with insufficient AoA separations, analog beamforming at the MSs and digital combining at the BS are jointly designed to maximize the achievable sum-rate of the MSs based on their effective MIMO channels resulting from path delay compensation. In addition, we propose a new and efficient channel estimation scheme tailored for PDMA, which requires negligible training overhead in practical mmWave systems and yet leads to comparable performance as that based on perfect channel state information (CSI).

Channel Estimation for Millimeter-Wave MIMO Communications With Lens Antenna Arrays

Millimeter-wave (mmWave) communication is a promising technology for future wireless communication systems. By utilizing the advanced lens antenna arrays, a mmWave lens multiple-input multiple-output (MIMO) system significantly reduces the number of radio-frequency (RF) chains required, and thus, achieves cost-effective implementation. In this paper, we propose a novel channel estimation scheme for the mmWave lens MIMO system with limited RF chains. The proposed scheme is applicable for the general mmWave MIMO communications, regardless of narrow-band or wide-band, time-division-duplexing or frequency-division-duplexing operations. By exploiting the energy-focusing property of lens arrays, jointly with the multipath sparsity of mmWave channels, the proposed channel estimation scheme requires only low-complexity two-way energy-based antenna selections and reduced-size MIMO channel estimation. Numerical results show that under limited RF chains and taking the channel training overhead and imperfect estimation into account, the proposed lens MIMO system achieves significantly higher throughput compared to the more complex benchmark system with the conventional uniform planar array and MIMO-orthogonal-frequency-division-multiplexing-based transmissions.

Uplink Channel Estimation and Data Transmission in Millimeter-Wave CRAN With Lens Antenna Arrays

Millimeter-wave (mmWave) communication and network densification hold great promise for achieving high-rate communication in next-generation wireless networks. Cloud radio access network (CRAN), in which low-complexity remote radio heads (RRHs) coordinated by a central unit (CU) are deployed to serve users in a distributed manner, is a cost-effective solution to achieve network densification. However, when operating over a large bandwidth in the mmWave frequencies, the digital fronthaul links in a CRAN would be easily saturated by the large amount of sampled and quantized signals to be transferred between RRHs and the CU. To tackle this challenge, we propose in this paper a new architecture for mmWave-based CRAN with advanced lens antenna arrays at the RRHs. Due to the energy focusing property, lens antenna arrays are effective in exploiting the angular sparsity of mmWave channels, and thus help in substantially reducing the fronthaul rate and simplifying the signal processing at the multi-antenna RRHs and the CU, even when the channels are frequency-selective. We consider the uplink transmission in a mmWave CRAN with lens antenna arrays and propose a low-complexity quantization bit allocation scheme for multiple antennas at each RRH to meet the given fronthaul rate constraint. Further, we propose a channel estimation technique that exploits the energy focusing property of the lens array and can be implemented at the CU with low complexity. Finally, we compare the proposed mmWave CRAN using lens antenna arrays with a conventional CRAN using uniform planar arrays at the RRHs, and show that the proposed design achieves significant throughput gains, yet with much lower complexity.

Beamspace Channel Estimation in mmWave Systems via Cosparse Image Reconstruction Technique

This paper considers the beamspace channel estimation problem in 3D lens antenna array under a millimeter-wave communication system. We analyze the focusing capability of the 3D lens antenna array and the sparsity of the beamspace channel response matrix. Considering the analysis, we observe that the channel matrix can be treated as a 2D natural image; that is, the channel is sparse, and the changes between adjacent elements are subtle. Thus, for the channel estimation, we incorporate an image reconstruction technique called sparse non-informative parameter estimator-based cosparse analysis AMP for imaging (SCAMPI) algorithm. The SCAMPI algorithm is faster and more accurate than earlier algorithms such as orthogonal matching pursuit and support detection algorithms. To further improve the SCAMPI algorithm, we model the channel distribution as a generic Gaussian mixture (GM) probability and embed the expectation maximization learning algorithm into the SCAMPI algorithm to learn the parameters in the GM probability. We show that the GM probability outperforms the common uniform distribution used in image reconstruction. We also propose a phase-shifter-reduced selection network structure to decrease the power consumption of the system and prove that the SCAMPI algorithm is robust even if the number of phase shifters is reduced by 10%.

Reliable Beamspace Channel Estimation for Millimeter-Wave Massive MIMO Systems with Lens Antenna Array

Millimeter-wave massive MIMO with lens antenna array can considerably reduce the number of required radio-frequency (RF) chains by beam selection. However, beam selection requires the base station to acquire the accurate information of beamspace channel. This is a challenging task, as the size of beamspace channel is large while the number of RF chains is limited. In this paper, we investigate the beamspace channel estimation problem in mmWave massive MIMO systems with lens antenna array. Specifically, we first design an adaptive selecting network for mmWave massive MIMO systems with lens antenna array, and based on this network, we further formulate the beamspace channel estimation problem as a sparse signal recovery problem. Then, by fully utilizing the structural characteristics of mmWave beamspace channel, we propose a support detection (SD)-based channel estimation scheme with reliable performance and low pilot overhead. Finally, the performance and complexity analyses are provided to prove that the proposed SD-based channel estimation scheme can estimate the support of sparse beamspace channel with comparable or higher accuracy than conventional schemes. Simulation results verify that the proposed SD-based channel estimation scheme outperforms conventional schemes and enjoys satisfying accuracy, even in the low SNR region as the structural characteristics of beamspace channel can be exploited.

Cost-Effective Millimeter-Wave Communications with Lens Antenna Array

MmWave communication is a promising technology for 5G wireless systems. However, the large number of antennas used and the wide signal bandwidth in mmWave systems render the conventional multi-antenna techniques increasingly costly in terms of signal processing complexity, hardware implementation, and power consumption. In this article, we investigate cost-effective mmWave communications by first providing an overview of the main existing techniques that offer different trade-offs between performance and cost, and then focusing our discussion on a promising new technique based on the advanced lens antenna array. It is revealed that by exploiting the angle-dependent energy focusing property of lens arrays, together with the angular sparsity of the mmWave channels, mmWave lens antenna system is able to achieve capacity-optimal performance with very few RF chains and using low-complexity single-carrier transmission, even for wideband frequency-selective channels. Numerical results show that the lens-based system outperforms the benchmark schemes for mmWave communications in both spectrum efficiency and energy efficiency.

The Maximal SINR Selection Mode for 5G Millimeter-Wave MIMO: Model Systems and Analysis

<span>In mmWave massive MIMO systems, the lens antenna array and beam selection by beamspace MIMO are employed to target the number of required RF chains reduced without obvious performance loss. For cost – effective, the number of RF chain is an allowable limitation, however, to obtain the near-optimal capacity efficiently, beam selection must require the exact information of the wide size of beamspace channel. Solution to this problem, in this paper we suggest analyzing whole beamspace based on maximal SINR. </span><span class="fontstyle01"><span>More specicfically, it is confirmed that the proposed beam selection algorithms achieve higher power efficiencies than a full system where all beams are employed.</span></span>

In-Band Wireless Information and Power Transfer With Lens Antenna Array

This letter studies a new wireless information and power transfer coexisting system, where two uncoordinated energy and information sources simultaneously transmit to the same receiver for energy harvesting and information reception, respectively. In such a setup, the information decoder could suffer from severe signal distortion due to the simultaneously received energy signal that is usually orders-of-magnitude stronger than the desired information signal. To tackle this practical issue, we propose a novel lens antenna array-enabled receiver, which exploits the angle-of-arrival-dependent energy focusing capability of lens array for the spatial separation of energy and information signals. In addition, an optimal power splitting-based scheme is proposed by taking into account the signal distortion effect at the receiver, which is applicable for both lens and conventional antenna arrays. Numerical results show that the proposed lens array receiver significantly outperforms that with the conventional uniform planar array in terms of an achievable rate-energy tradeoff.

Integrated lens antenna array with full azimuth plane beam scanning capability at 60 GHz

ABSTRACTAn antenna array operating at 60 GHz is proposed. The proposed array covers impedance bandwidth of 5 GHz (57.5–62.5 GHz) with maximum gain of 16.25 dBi at 61. 5 GHz. With the proposed array 15 distinct radiation patterns in azimuth plane can be achieved, each having 3‐dB beamwidth of 24° and 3‐dB cross over. The beam scanning capability can be achieved by activating each array element one by one. Each array element consists of a conventional microstrip patch antenna (MPA) integrated with extended hemispherical Teflon lens. The Teflon lens is utilized to enhance the gain of conventional MPA as well as to achieve the desired elementary radiation pattern of array to cover full azimuth plane. A very good agreement between the measured and simulated results is observed. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:116–120, 2017

Millimeter Wave MIMO With Lens Antenna Array: A New Path Division Multiplexing Paradigm

Millimeter wave (mmWave) communication is a promising technology for future wireless systems, while one practical challenge is to achieve its large-antenna gains with only limited radio frequency (RF) chains for cost-effective implementation. To this end, we study in this paper a new lens antenna array enabled mmWave multiple-input multiple-output (MIMO) communication system. We first show that the array response of lens antenna arrays follows a “sinc” function, where the antenna element with the peak response is determined by the angle of arrival (AoA)/departure (AoD) of the received/transmitted signal. By exploiting this unique property along with the multi-path sparsity of mmWave channels, we propose a novel low-cost and capacity-achieving spatial multiplexing scheme for both narrow-band and wide-band mmWave communications, termed path division multiplexing (PDM) , where parallel data streams are transmitted over different propagation paths with simple per-path processing. We further propose a simple path grouping technique with group-based small-scale MIMO processing to effectively mitigate the inter-stream interference due to similar AoAs/AoDs. Numerical results are provided to compare the performance of the proposed mmWave lens MIMO against the conventional MIMO with uniform planar arrays (UPAs) and hybrid analog/digital processing. It is shown that the proposed design achieves significant throughput gains as well as complexity and cost reductions, thus leading to a promising new paradigm for mmWave MIMO communications.

Highly Directional Steerable Antennas: High-Gain Antennas Supporting User Mobility or Beam Switching for Reconfigurable Backhauling

Modern millimeter-wave (mmWave) communication systems for large indoor areas and most outdoor scenarios require high-gain antennas with beam-steering ability to support user mobility or beam switching for reconfigurable backhauling. In this article, two new concepts for the development of highly directional steerable mmWave antennas are proposed and analyzed. The first one is modular antenna array (MAA) technology, which allows the creation of large-aperture, high-gain adaptive antenna arrays in a cost-effective and scalable manner. Two MAA configurations based on the existing phased subarray module are considered and analyzed for mmWave small-cell access and backhauling. The second prospective technology that fulfills the required antenna parameters for mmWave smallcell flexible backhauling is the lens-array antenna (LAA). The combination of the dielectric lens for aperture increasing with only one subarray module with beam-steering capabilities may provide 25?30-dBi total antenna gain with azimuth sector sweeping !45?.

A Programmable Lens-Array Antenna With Monolithically Integrated MEMS Switches

This paper describes a reconfigurable millimeter-wave lens-array antenna based on monolithically integrated microelectromechanical systems (MEMS) switches. This device is constructed as a planar array of 2-bit programmable MEMS antenna-filter-antenna (AFA) unit cells that are used to provide a 1-D programmable ldquoaperture transfer functionrdquo between the input and output wavefronts. The fully integrated device consists of 484 (22 times 22) AFA elements and 2420 switches. Switches, bias lines, antennas, and the rest of the RF structure are fabricated on two quartz wafers (epsiv <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> = 3.8, tandelta = 0.002) that are subsequently stacked using adhesive bonding to form the tri-layer metal structure of the AFA array. The bonded structure also forms a package for the MEMS switches. This paper investigates the design and fabrication issues and presents the measured data related to yield and frequency response of this lens-array. It also characterizes the performance of this device as a steerable antenna. Measured results show that this lens-array can be used to steer the beam of a low gain horn antenna to plusmn40deg in either the E- or the H-plane. For the fabricated prototype, the yield is estimated to be 50% for the best region of the array, resulting in a relatively high insertion loss and sidelobe level.

Q‐band to V‐band 1D and 2D elliptical lens antenna arrays

AbstractAn investigation of the receiving properties of both 1D 13‐element and 2D 8 × 4‐element dual dipole antenna arrays on an elliptical MACOR lens from Q‐ to V‐band is reported. Theoretical and measurement results agree well. The intended application is for millimeter wave plasma radar reflectometric imaging, although the results have broader applicability (Munsat et al., Rev Sci Instrum 74 (2003) 1426–1432). © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1798–1801, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22620

Virtual channel space-time processing with dual-polarization discrete lens antenna arrays

This paper discusses channel capacity improvements with optimal multiantenna wireless communications using a discrete lens array (DLA) at the analog front end. It is first shown that optimal signaling over multiantenna channels via virtual spatial models (VSMs) has a direct hardware correspondence in a multibeam spatially fed antenna architecture. A multibeam dual-polarized DLA is designed and characterized, and the effects of measured antenna radiation patterns on calculated capacity are quantified. In particular, the paper examines: 1) effects of cross-polarization for a dual-polarized multibeam array; 2) effects of beam overlap in a multibeam array; and 3) effects of gain variations for different scan angles. It is demonstrated that adding an ideal dual-polarized array achieves a capacity improvement of up to 88% compared to the single-polarization case. In practice, the two polarizations are weakly coupled, and the measured cross-polarization level of -14 dB decreases the capacity of the system by less than 2%. Furthermore, it is shown that a dual-polarized multibeam DLA is nearly insensitive to polarization rotation in a rich scattering environment, whereas single-polarized antennas incur a capacity degradation of up to 24%. Finally, capacity decrease due to measured nonuniform amplitudes on the antenna aperture is shown to be less than 10%.

A lens antenna array with adaptive optical processing

This paper presents an X band smart antenna array in which adaptive processing of the received signals is performed by dynamic holographic optical circuitry. The optical circuitry adaptively extracts the principal component of the received signal space, that is the strongest first-order independent temporal component of the ensemble of received signals. The adaptive receiver system can be used, for example, to mitigate multipath interference effects and can separate one received signal from another even though their power spectra may entirely overlap. A prototype two-channel system is designed to fit in a standard-size briefcase and consume less than 50 W of power. The input to the system are modulated waves with a carrier in X band and the output is an electronic demodulated signal. Three major components of this system are described in detail: (1) the quasi-optical lens antenna array front end with angle-of-arrival preprocessing and downconversion, (2) the two-channel electrooptic modulation and optical carrier suppression stage, and (3) the smart optical processor (auto-tuning filter). Component and end-to-end system measurements give quantitative indicators for the usefulness of optical processing in wireless communications.

A satellite data transmission antenna

A retrodirective satellite antenna for a broad bandwidth, satellite-to-ground data transmission link, is described. An information-collecting satellite which transmits its data in the direction of the ground receiver upon command, is considered. The satellite antenna described for this system is an active retrodirective antenna which utilizes the beam-forming characteristics of a phasing matrix. A signal from the ground station is received on a particular beam port of the matrix which corresponds to a particular beam-pointing direction. Control circuitry in the satellite activates a switching matrix and a transmitter so that the data-carrying signal is transmitted in the same direction from which the satellite is interrogated. Other retrodirective techniques in addition to the phasing-matrix antenna are evaluated in terms of their relative merit. The systems considered include the active Van Atta array, the automatic three-dimensional electronic scanning, antenna (ATHESA), the Luneberg lens and various other antenna array techniques.