Hybrid Beamforming via the Kronecker Decomposition for the Millimeter-Wave Massive MIMO Systems

Despite its promising performance gain, the realization of mmWave massive MIMO still faces several practical challenges. In particular, implementing massive MIMO in the digital domain requires hundreds of RF chains matching the number of antennas. Furthermore, designing these components to operate at the mmWave frequencies is challenging and costly. These motivated the recent development of hybrid-beamforming where MIMO processing is divided for separate implementation in the analog and digital domains, called the analog and digital beamforming, respectively. Analog beamforming using a phase array introduces uni-modulus constraints on the beamforming coefficients, rendering the conventional MIMO techniques unsuitable and call for new designs. In this paper, we present a systematic design framework for hybrid beamforming for multi-cell multiuser massive MIMO systems over mmWave channels characterized by sparse propagation paths. The framework relies on the decomposition of analog beamforming vectors and path observation vectors into Kronecker products of factors being uni-modulus vectors. Exploiting properties of Kronecker mixed products, different factors of the analog beamformer are designed for either nulling interference paths or coherently combining data paths. Furthermore, a channel estimation scheme is designed for enabling the proposed hybrid beamforming. The scheme estimates the AoA of data and interference paths by analog beam scanning and data-path gains by analog beam steering. The performance of the channel estimation scheme is analyzed. In particular, the AoA spectrum resulting from beam scanning, which displays the magnitude distribution of paths over the AoA range, is derived in closed-form. It is shown that the inter-cell interference level diminishes inversely with the array size, the square root of pilot sequence length and the spatial separation between paths.Comment: Submitted to IEEE JSAC Special Issue on Millimeter Wave Communications for Future Mobile Networks, minor revisio

Review on the Design of the Isolation Techniques for UWB-MIMO Antennas

Ultra wide band - Multiple Input Multiple Output antenna technology provides higher data rates and the combination of the ultra wide band (UWB) and the multiple input multiple output (MIMO) technologies provides a solution for the demand of still higher data rates i.e. in excess of 3 Gb/sec in the future.  As the antenna technologies are improving, the size of the MIMO antenna is growing smaller and smaller. Placing the antenna elements in such close proximity increases the coupling between them. Various isolation techniques have to be introduced between the antenna elements to decrease the coupling and to improve the isolation. A study of the various isolation enhancement techniques have been made in this review. It analyses the various isolation enhancement methods such as using orthogonal polarization, parasitic elements, varied decoupling structures, defected ground structures (DGS), neutralization line (NL) and finally by using metamaterials. Metamaterials is a technology to perk up the isolation between the antenna elements. Split ring resonator (SRR) behaves as a metamaterial and it is used as an isolation mechanism in this study. The antennas are simulated and the results are compared. The method using parasitic elements gives the highest isolation of 35 dB and it is 5 dB better than the methods using orthogonal polarization and using the decoupling structure. The performance of all the antennas satisfies the conditions for minimum isolation. The envelope correlation coefficient is nearly zero in all the antennas and it implies good diversity performance. The diversity gain is also calculated for the various antennas and it satisfies good diversity performance. The bandwidth of the antennas is in the UWB frequency range and they have a fractional bandwidth above the required value of 1.09. The capacity loss for all the antennas is very low and the antennas using defected ground structure and the decoupling structure gives very low capacity loss

In-Band Full-Duplex 통신용 고격리도 이중편파 송수신기 안테나 어레이에 관한 연구

학위논문(석사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2023. 2. 오정석.In this thesis, we focused on realizing the propagation domain of transmitter and receiver system composed of the antennas and isolators. Firstly, a logical design procedure based on a new perspective of the common mode (CM) and differential mode (DM) theory for a dual-polarized antenna in sub-6 GHz N78 band (3.3-3.8 GHz) has been proposed. Next, novel illumination topologies and decoupling methodologies enabling dual-polarized multi-path coupling suppression for 5G sub-6 GHz transmit/receive (TRx) antenna arrays have been presented. For the antenna design, a novel elaborate design method using field concentration has been established via the mode segmentation of S-parameters. Interestingly, an improvement in the port isolation between two different polarizations is achieved by using an independently controllable Smith chart trace for each mode using simple methodologies. To provide a deep physical insight into the mechanism of realizing the dual-polarized antenna, the corresponding field distributions based on the CM and DM analysis have been proposed for the first time, and the proposed antenna has been simulated, fabricated, and measured. The simulation as well as experimentally measured results show that the antenna can offer peak isolations of 40 dB, a gain of 8 dBi, cross-polarization discrimination of 20 dB, an efficiency of 92% with stable radiation patterns, and a profile of 0.14λ across 3.3-3.8 GHz, using FR-4 substrates for low-cost. Furthermore, this study not only offers knowledge on cross-polarization but also provides the active S-parameters for all possible amplitude and phase sequences to reflect realistic scenarios. For the isolator design, the isolator composite consists of the proposed planar inverted-L isolator (PILI) and electromagnetic band-gap (EBG). To consider dual-polarized multi-path isolations in reliable 5G integration scenarios, a low profile (0.13λ at 3.5 GHz) antenna with dual (±45° slant) polarization, impedance bandwidth of 40%, and port isolation of 25 dB is proposed. It was demonstrated that the proposed PILI could significantly suppress the direct coupling and ground coupling between TRx. Their composite combined with EBGs can further improve their dual-polarized decoupling. Two sets of 3.5GHz 1×4 antenna arrays with 45° - slant polarization and the proposed PILI/EBG composite were designed, manufactured, and measured for simultaneous decoupling of eight paths among the TRx antenna elements. Finally, the measured results reveal that the overall isolation level of the dual-polarized array configuration is approximately 70 dB with a low profile (0.14λ), maintaining the matching and port isolation conditions.본 논문은 안테나와 아이솔레이터로 구성된 송신기와 수신기의 전파영역 구현에 집중하였다. 첫 째로, 단순 파라미터 스터디가 아닌 새로운 관점의 논리적인 Common Mode and Differential Mode (CMDM)에 기반 설계 절차를 sub-6 GHz N78 밴드 (3.3-3.8 GHz)에 대하여 제시하였다. 다음으로, 이중편파 다중경로 커플링 억제를 위한 5G sub-6 GHz 대역 송수신기 안테나 어레이의 획기적인 구조와 디커플링 방법을 제시하였다. 안테나 설계에 대하여, S파라미터 모드 분할을 통한 필드 집중 방법을 이용하여 섬세한 설계법을 제시하였다. 흥미롭게도, 앞서 제시한 간단한 방법을 이용해서 각 모드에 독립적인 조절이 가능한 스미스 차트를 통해 각기 다른 편파 사이의 포트 격리도를 개선하였다. 이중편파 안테나의 동작원리에 대한 깊은 물리적 통찰력을 제공하기 위하여, CMDM 분석에 기반한 대응하는 필드 분포를 최초로 제시하였고 제안된 안테나는 시뮬레이션, 제작, 측정되었다. 시뮬레이션뿐만 아니라 실험을 통한 측정 결과는 안테나가 FR-4기판을 사용하여 저비용 제작을 하였고 40 dB의 포트 격리도, 8 dBi의 이득, 20 dB의 XPD, 92 %의 효율과 안정적인 빔패턴을 저자세로 얻었다. 게다가, 본 연구는 실제 동작 상황을 반영하기 위하여 Cross 편파에 대한 지식뿐만 아니라 active S파라미터를 가능한 모든 진폭과 위상조합에 대하여 제공했다. 아이솔레이터 설계에 대하여, 아이솔레이터 복합체는 평면 역-L 모양 (PILI)과 전자기파 밴드갭 (EBG)로 구성되어있다. 5G 실제 상황을 위하여 이중편파 다중격로를 고려하였다. 안테나는 40%의 임피던스 대역폭, 25 dB의 포트 격리도를 갖는다. 제안된 PILI는 송신기와 수신기 사이에 주요하게 직접적인 커플링과 그라운드를 통한 커플링을 억제할 수 있음이 증명되었다. EBG와 결합된 복합체는 추가로 이중편파 디커플링을 수행할 수 있다. 송신기 수신기를 반영하여, 1×4 어레이 안테나의 두 세트와 PILI/EBG 복합체가 8개의 결과를 동시에 만족하기 위하여 설계, 제작, 측정 되었다. 최종적으로, 측정된 결과는 임피던스와 포트 격리도는 유지하면서 전체적인 이중편파 어레이의 격리도는 대략 70 dB의 결과를 얻었다.1. Study Background 1 2. Antenna Design 4 2.1 Introduction 4 2.2 Principle of the CM and DM Theory 8 2.3 Design of the Dual-Polarized Antennas 11 2.3.1 Design Procedure 14 2.3.2 Experimental Results 17 2.4 Intensive Interpretation 20 2.4.1 Active S-parameters 20 2.4.2 Cross-Polarization Discrimination 24 3. Isolator Design 26 3.1 Introduction 28 3.2 Design of Decoupling Structure 30 3.2.1 Wall Analysis 30 3.2.2 Transmission Line-Based Analysis 33 3.2.3 Isolator with EBG 40 3.3 Measurement and Analysis 45 4. Conclusion 48 References 50 Abstract in Korean 55석

Tunable decoupling and matching concepts for compact mobile terminal antennas

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A Comprehensive Survey on 'Various Decoupling Mechanisms with Focus on Metamaterial and Metasurface Principles Applicable to SAR and MIMO Antenna Systems'

Nowadays synthetic aperture radar (SAR) and multiple-input-multiple-output (MIMO) antenna systems with the capability to radiate waves in more than one pattern and polarization are playing a key role in modern telecommunication and radar systems. This is possible with the use of antenna arrays as they offer advantages of high gain and beamforming capability, which can be utilized for controlling radiation pattern for electromagnetic (EM) interference immunity in wireless systems. However, with the growing demand for compact array antennas, the physical footprint of the arrays needs to be smaller and the consequent of this is severe degradation in the performance of the array resulting from strong mutual-coupling and crosstalk effects between adjacent radiating elements. This review presents a detailed systematic and theoretical study of various mutual-coupling suppression (decoupling) techniques with a strong focus on metamaterial (MTM) and metasurface (MTS) approaches. While the performance of systems employing antenna arrays can be enhanced by calibrating out the interferences digitally, however it is more efficient to apply decoupling techniques at the antenna itself. Previously various simple and cost-effective approaches have been demonstrated to effectively suppress unwanted mutual-coupling in arrays. Such techniques include the use of defected ground structure (DGS), parasitic or slot element, dielectric resonator antenna (DRA), complementary split-ring resonators (CSRR), decoupling networks, P.I.N or varactor diodes, electromagnetic bandgap (EBG) structures, etc. In this review, it is shown that the mutual-coupling reduction methods inspired By MTM and MTS concepts can provide a higher level of isolation between neighbouring radiating elements using easily realizable and cost-effective decoupling configurations that have negligible consequence on the arrays characteristics such as bandwidth, gain and radiation efficiency, and physical footprint

Hybrid MIMO Architectures for Millimeter Wave Communications: Phase Shifters or Switches?

Hybrid analog/digital MIMO architectures were recently proposed as an alternative for fully-digitalprecoding in millimeter wave (mmWave) wireless communication systems. This is motivated by the possible reduction in the number of RF chains and analog-to-digital converters. In these architectures, the analog processing network is usually based on variable phase shifters. In this paper, we propose hybrid architectures based on switching networks to reduce the complexity and the power consumption of the structures based on phase shifters. We define a power consumption model and use it to evaluate the energy efficiency of both structures. To estimate the complete MIMO channel, we propose an open loop compressive channel estimation technique which is independent of the hardware used in the analog processing stage. We analyze the performance of the new estimation algorithm for hybrid architectures based on phase shifters and switches. Using the estimated, we develop two algorithms for the design of the hybrid combiner based on switches and analyze the achieved spectral efficiency. Finally, we study the trade-offs between power consumption, hardware complexity, and spectral efficiency for hybrid architectures based on phase shifting networks and switching networks. Numerical results show that architectures based on switches obtain equal or better channel estimation performance to that obtained using phase shifters, while reducing hardware complexity and power consumption. For equal power consumption, all the hybrid architectures provide similar spectral efficiencies.Comment: Submitted to IEEE Acces

Agregados de antenas para sistemas massive MIMO 5G e satélite

Wireless telecommunications systems are growing and improving at a breakneck pace, and its demands must be ful lled with hardware modi cations. The fth-generation will demand a revolution since antennas are going to be designed for high frequency, millimeter wave bands, where there is a lot of unexploited spectrum worldwide. However, these frequencies get absorbed quite easily, for example, they su er high attenuation due to rain. This implies a decrease of radiated power. To solve some of the issues, antenna arrays have been studied due to their high versatility. This dissertation has the goal of designing and testing several solutions based on microstrip patch antennas. Initially, an analysis of the coupling between elements is performed as well as some proposed techniques to reduce it, through more compact spaces, without any gain decreasing. Finally, considering the space limitations, series antenna arrays are developed for satellite communications and presented an indepth study of antennas effciently employed for both transmission and reception simultaneously.Os sistemas de telecomunicações sem fios continuam a crescer e a melhorar a um ritmo frenetico, por isso, novos requisitos tem de ser cumpridos com modificações ao nível do hardware. A quinta geração exigirá uma revolução, uma vez que as antenas serão projetadas para alta frequência, banda de ondas milimétricas, onde o espetro ainda não foi muito explorado. No entanto, estas frequências são absorvidas com facilidade como, por exemplo, na atmosfera devido á atenuação originada pela chuva. Para resolver estas limitações, os agregados de antenas têm sido estudados devido á sua versatilidade. Esta dissertação tem o objetivo de desenhar e testar várias soluções baseadas em antenas microstrip (patch). Inicialmente, é realizada uma avaliação do acoplamento entre elementos e propostas algumas técnicas de redução do mesmo, utilizando espaços mais compactos que o usual, mas prevenindo quaisquer diminuições de ganho. Por fim, tendo em vista a mesma limitação espacial, são desenvolvidos agregados de antenas em série direcionados para comunicações via satélite e apresentado um estudo detalhado de antenas para transmissão e recepção em simultâneo.Mestrado em Engenharia Eletrónica e Telecomunicaçõe