Design and Evaluation of Compact Multi-antennas for Efficient MIMO Communications

The use of multi-antenna systems with multiple-input multiple-output (MIMO) technology will play a key role in providing high spectrum efficiency for next generation mobile communication systems. This thesis offers valuable insights on the design of compact multi-antennas for efficient MIMO communications. In the course of the thesis work, several novel six-port antenna designs have been proposed to simultaneously exploit all six possible degrees-of-freedom (DOFs) by means of various antenna diversity mechanisms (Paper I & II). Moreover, the thesis also examines the potential of using uncoupled matching networks to adaptively optimize compact multi-antenna systems to their dynamic usage environments (Paper III). Furthermore, a simple and intuitive metric is proposed for evaluating the performance of MIMO antennas when operating in the spatial multiplexing mode (Paper IV). Last but not least, cooperation among multi-antenna systems at all three sectors of a given cellular base station is shown to deliver significant benefit at sector edges (Paper V). The thesis with five included research papers extend the understanding of MIMO systems from an antenna and propagation perspective. It provides important guidelines in designing compact and efficient MIMO antennas in their usage environments. In Paper I, a fundamental question on the number of effective DOFs in a wireless channel is explored using two co-located six-port antenna arrays. The antenna elements of both arrays closely reproduce the desired characteristics of fundamental electric and magnetic dipoles, which can efficiently extract angle and polarization diversities from the wireless channel. In particular, one of the two array designs is by far the most electrically compact six-port antenna structure in the literature. Analysis of measured channel eigenvalues in a rich multi-path scattering environment shows that six eigenchannels are successfully attained for the purpose of spatial multiplexing. To study the potential of implementing different diversity mechanisms on a practical multi-port antenna, Paper II builds on an existing dielectric resonator antenna (DRA) to provide a compact six-port DRA array that jointly utilizes space, polarization and angle diversities. In order to fully substantiate the practicality of the DRA array for indoor MIMO applications, the compact DRA array together with two reference but much larger arrays were evaluated in an office scenario. The use of the compact DRA array at the receiver is shown to achieve comparable performance to that of the reference monopole array due to the DRA array's rich diversity characteristics. In Paper III, the study of uncoupled matching networks to counteract mutual coupling effects in multi-antenna systems is extended by allowing for unbalanced matching impedances. Numerical studies suggest that the unbalanced matching is especially effective for array topologies whose effective apertures can vary significantly with respect to the propagation channel. Moreover, it is also demonstrated that the unbalanced matching is capable of adapting the radiation patterns of the array elements to the dynamic propagation environment. Paper IV introduces multiplexing efficiency as a performance metric which defines the loss of efficiency in decibel when using a multi-antenna prototype under test to achieve the same multiplexing performance as that of an ideal array in the same propagation environment. Its unique features are both its simplicity and the valuable insights it offers with respect to the performance impacts of different antenna impairments in multi-antenna systems. In Paper V, intrasite cooperation among three 120°-sector, each with a cross-polarized antenna pair, is investigated in a measured urban macrocellular environment. The single-user capacity improvement is found to exceed 40% at the sector edges, where improvements are most needed. In addition, a simple simulation model is developed to analyze the respective impact of antennas and specific propagation mechanisms on the measured cooperative gain

Space-time-frequency methods for interference-limited communication systems

textTraditionally, noise in communication systems has been modeled as an additive, white Gaussian noise process with independent, identically distributed samples. Although this model accurately reflects thermal noise present in communication system electronics, it fails to capture the statistics of interference and other sources of noise, e.g. in unlicensed communication bands. Modern communication system designers must take into account interference and non-Gaussian noise to maximize efficiencies and capacities of current and future communication networks. In this work, I develop new multi-dimensional signal processing methods to improve performance of communication systems in three applications areas: (i) underwater acoustic, (ii) powerline, and (iii) multi-antenna cellular. In underwater acoustic communications, I address impairments caused by strong, time-varying and Doppler-spread reverberations (self-interference) using adaptive space-time signal processing methods. I apply these methods to array receivers with a large number of elements. In powerline communications, I address impairments caused by non-Gaussian noise arising from devices sharing the powerline. I develop and apply a cyclic adaptive modulation and coding scheme and a factor-graph-based impulsive noise mitigation method to improve signal quality and boost link throughput and robustness. In cellular communications, I develop a low-latency, high-throughput space-time-frequency processing framework used for large scale (up to 128 antenna) MIMO. This framework is used in the world's first 100-antenna MIMO system and processes up to 492 Gbps raw baseband samples in the uplink and downlink directions. My methods prove that multi-dimensional processing methods can be applied to increase communication system performance without sacrificing real-time requirements.Electrical and Computer Engineerin

D3.2 First performance results for multi -node/multi -antenna transmission technologies

This deliverable describes the current results of the multi-node/multi-antenna technologies investigated within METIS and analyses the interactions within and outside Work Package 3. Furthermore, it identifies the most promising technologies based on the current state of obtained results. This document provides a brief overview of the results in its first part. The second part, namely the Appendix, further details the results, describes the simulation alignment efforts conducted in the Work Package and the interaction of the Test Cases. The results described here show that the investigations conducted in Work Package 3 are maturing resulting in valuable innovative solutions for future 5G systems.Fantini. R.; Santos, A.; De Carvalho, E.; Rajatheva, N.; Popovski, P.; Baracca, P.; Aziz, D.... (2014). D3.2 First performance results for multi -node/multi -antenna transmission technologies. http://hdl.handle.net/10251/7675

D 3. 3 Final performance results and consolidated view on the most promising multi -node/multi -antenna transmission technologies

This document provides the most recent updates on the technical contributions and research challenges focused in WP3. Each Technology Component (TeC) has been evaluated under possible uniform assessment framework of WP3 which is based on the simulation guidelines of WP6. The performance assessment is supported by the simulation results which are in their mature and stable state. An update on the Most Promising Technology Approaches (MPTAs) and their associated TeCs is the main focus of this document. Based on the input of all the TeCs in WP3, a consolidated view of WP3 on the role of multinode/multi-antenna transmission technologies in 5G systems has also been provided. This consolidated view is further supported in this document by the presentation of the impact of MPTAs on METIS scenarios and the addressed METIS goals.Aziz, D.; Baracca, P.; De Carvalho, E.; Fantini, R.; Rajatheva, N.; Popovski, P.; Sørensen, JH.... (2015). D 3. 3 Final performance results and consolidated view on the most promising multi -node/multi -antenna transmission technologies. http://hdl.handle.net/10251/7675

User Effect Mitigation in MIMO Terminal Antennas

The rapid growth of cellular technology over the past decade transformed our lives, enabling billions of people to enjoy interactive multimedia content and ubiquitous connectivity through a device that can fit into the palm of a hand. In part the explosive growth of the smartphone market is enabled by innovative antenna system technologies, such as multiple-input multiple-output (MIMO) systems, facilitating high data rates and reliable connections. Even though future deployment of Long Term Evolution Advanced (LTE-A) is expected to provide seamless internet connectivity at even higher speeds over a wide range of devices with different form factors, fundamental terminal antenna limitations can severely impact the actual performance of the terminal. One of the key challenges in terminal antenna design are user-induced losses. It has been shown that electromagnetic absorption in body tissues as well as antenna impedance mismatch due to user proximity significantly degrade terminal antenna performance. Moreover, user interactions are non-static, which further complicates terminal design by leading to the requirement of evaluating a wide range of hand grips and usage scenarios. This doctoral thesis explores these challenges and offers useful insight on effective user interaction mitigation. In particular, state-of-the-art multiple antenna designs have been investigated in an attempt to formulate guidelines on efficient terminal antenna design in the presence of a user (Paper I). Moreover, the major part of the thesis considers the method of adaptive impedance matching (AIM) for performance enhancements of MIMO terminals. Both ideal and very practical and realistic AIM systems have been studied in order to extend the knowledge in the area by determining achievable performance gains and providing insights on AIM gain mechanisms for different terminal antenna designs, propagation environments and user scenarios. In Paper I, five different MIMO terminal antenna designs were evaluated in 11 representative user scenarios. Two of the prototypes were optimized with the Theory of Characteristic Modes (TCM), whereas the remaining three were based on more conventional antenna types. Multiplexing efficiency (ME) was used as the MIMO system performance metric, assuming an ideal uniform 3D propagation environment. The paper focuses on performance at frequency bands below 1 GHz due to the more stringent size limitations. Paper II presents a simulation model of the complete physical channel link based on ideal lossless AIM and evaluates the potential of AIM to mitigate user effects for three terminal antennas in four user scenarios. The prototypes studied have different performances in terms of bandwidth and isolation. MIMO capacity was used as the main performance metric. In order to gain insight on the impact of terminal bandwidth, as well as system bandwidth on AIM performance, capacity calculations were performed both for the center frequency and over the full LTE Band 13. In Paper III, a practical AIM system was set up and measured in both indoor and outdoor propagation scenarios for a one-hand and a two-hand grip, including a torso phantom. The AIM system consisted of two Maury mechanical tuners controlled with LabView. MIMO capacity was used to determine performance in the different user and channel cases. The impact of different propagation environments and user cases was discussed in detail. Moreover, tuner loss estimation was done to enable the calculation of AIM net gains. In Paper IV, the simulation model from Paper II was extended to include real antenna parameters as well as simulated environments with non-uniform angular power spectra. Two fundamentally different antenna designs were measured in three user scenarios involving phantom hands, whereas non-uniform environments of different angular spreads were simulated in post-processing. The study presents results and analysis on the impact of user scenarios and environment on the AIM gains for the terminals with different antenna designs. Finally, Paper V describes a realistic AIM system with custom-designed CMOS-SOI impedance tuners on a MIMO terminal antenna. Measurement setup control, as well as MIMO system evaluation, was achieved through a custom-developed LabView software. Detailed propagation measurements in three different environments with both phantom users and real test subjects were performed. The analysis and discussions provided insights on the practical implementation of AIM as well as on its performance in realistic conditions

A survey on hybrid beamforming techniques in 5G : architecture and system model perspectives

The increasing wireless data traffic demands have driven the need to explore suitable spectrum regions for meeting the projected requirements. In the light of this, millimeter wave (mmWave) communication has received considerable attention from the research community. Typically, in fifth generation (5G) wireless networks, mmWave massive multiple-input multiple-output (MIMO) communications is realized by the hybrid transceivers which combine high dimensional analog phase shifters and power amplifiers with lower-dimensional digital signal processing units. This hybrid beamforming design reduces the cost and power consumption which is aligned with an energy-efficient design vision of 5G. In this paper, we track the progress in hybrid beamforming for massive MIMO communications in the context of system models of the hybrid transceivers' structures, the digital and analog beamforming matrices with the possible antenna configuration scenarios and the hybrid beamforming in heterogeneous wireless networks. We extend the scope of the discussion by including resource management issues in hybrid beamforming. We explore the suitability of hybrid beamforming methods, both, existing and proposed till first quarter of 2017, and identify the exciting future challenges in this domain