Limited Feedback Techniques in Multiple Antenna Wireless Communication Systems

Multiple antenna systems provide spatial multiplexing and diversity benefits.These systems also offer beamforming and interference mitigation capabilities in single-user (SU) and multi-user (MU) scenarios, respectively. Although diversity can be achieved without channel state information (CSI) at the transmitter using space-time codes, the knowledge of instantaneous CSI at the transmitter is essential to the above mentioned gains. In frequency division duplexing (FDD) systems, limited feedback techniques are employed to obtain CSI at the transmitter from the receiver using a low-rate link. As a consequence, CSI acquired by the transmitter in such manner have errors due to channel estimation and codebook quantization at the receiver, resulting in performance degradation of multi-antenna systems. In this thesis, we examine CSI inaccuracies due to codebook quantization errors and investigate several other aspects of limited feedback in SU, MU and multicell wireless communication systems with various channel models. For SU multiple-input multiple-output (MIMO) systems, we examine the capacity loss using standard codebooks. In particular, we consider single-stream and two-stream MIMO transmissions and derive capacity loss expressions in terms of minimum squared chordal distance for various MIMO receivers. Through simulations, we investigate the impact of codebook quantization errors on the capacity performance in uncorrelated Rayleigh, spatially correlated Rayleigh and standardized MIMO channels. This work motivates the need of effective codebook design to reduce the codebook quantization errors in correlated channels. Subsequently, we explore the improvements in the design of codebooks in temporally and spatially correlated channels for MU multiple-input single-output (MISO) systems, by employing scaling and rotation techniques. These codebooks quantize instantaneous channel direction information (CDI) and are referred as differential codebooks in the thesis. We also propose various adaptive scaling techniques for differential codebooks where packing density of codewords in the differential codebook are altered according to the channel condition, in order to reduce the quantization errors. The proposed differential codebooks improve the spectral efficiency of the system by minimizing the codebook quantization errors in spatially and temporally correlated channels. Later, we broaden the scope to massive MISO systems and propose trellis coded quantization (TCQ) schemes to quantize CDI. Unlike conventional codebook approach, the TCQ scheme does not require exhaustive search to select an appropriate codeword, thus reducing computational complexity and memory requirement at the receiver. The proposed TCQ schemes yield significant performance improvements compared to the existing TCQ based limited feedback schemes in both temporally and spatially correlated channels. Finally, we investigate interference coordination for multicell MU MISO systems using regularized zero-forcing (RZF) precoding. We consider random vector quantization (RVQ) codebooks and uncorrelated Rayleigh channels. We derive expected SINR approximations for perfect CDI and RVQ codebook-based CDI. We also propose an adaptive bit allocation scheme which aims to minimize the network interference and moreover, improves the spectral efficiency compared to equal bit allocation and coordinated zero-forcing (ZF) based adaptive bit allocation schemes

Near-Field Communications: A Tutorial Review

Extremely large-scale antenna arrays, tremendously high frequencies, and new types of antennas are three clear trends in multi-antenna technology for supporting the sixth-generation (6G) networks. To properly account for the new characteristics introduced by these three trends in communication system design, the near-field spherical-wave propagation model needs to be used, which differs from the classical far-field planar-wave one. As such, near-field communication (NFC) will become essential in 6G networks. In this tutorial, we cover three key aspects of NFC. 1) Channel Modelling: We commence by reviewing near-field spherical-wave-based channel models for spatially-discrete (SPD) antennas. Then, uniform spherical wave (USW) and non-uniform spherical wave (NUSW) models are discussed. Subsequently, we introduce a general near-field channel model for SPD antennas and a Green's function-based channel model for continuous-aperture (CAP) antennas. 2) Beamfocusing and Antenna Architectures: We highlight the properties of near-field beamfocusing and discuss NFC antenna architectures for both SPD and CAP antennas. Moreover, the basic principles of near-field beam training are introduced. 3) Performance Analysis: Finally, we provide a comprehensive performance analysis framework for NFC. For near-field line-of-sight channels, the received signal-to-noise ratio and power-scaling law are derived. For statistical near-field multipath channels, a general analytical framework is proposed, based on which analytical expression for the outage probability, ergodic channel capacity, and ergodic mutual information are derived. Finally, for each aspect, the topics for future research are discussed.Comment: 45 pages, 35 figures; submitted to possible IEEE journa

Joint Beamforming and Power Optimization for D2D Underlaying Cellular Networks

This paper studies the optimal joint beamforming and power control strategy for device-to-device (D2D) communication underlaying multiuser multiple-input multiple-output cellular networks. We consider multiple antennas at the base station (BS) and a single antenna at each cellular user (CU), D2D transmitter (DT) and D2D receiver (DR). We aim to minimize the total transmission power of the system by jointly designing the transmit beamforming at the BS and the transmit powers for both BS and DTs, while satisfying the signal-to-interference-plus-noise ratio based quality-of-service constraints for both CUs and DRs. Due to the non-convex nature of the problem, we apply the semidefinite relaxation technique to find the optimal solution, which always satisfies the rank-one constraint. We also investigate three sub-optimal fixed beamforming schemes: zero-forcing (ZF), regularized ZF and hybrid maximum ratio transmission-ZF, where the focus is to minimize the total transmission power while reducing complexity. When perfect channel information is not available, we propose a robust transmit power minimization strategy with ZF beamforming which only requires limited feedback based channel direction information at the BS. Finally, computer simulation results are presented to demonstrate the effectiveness of the proposed schemes

Lens antenna arrays: an efficient framework for sparse-aware large-MIMO communications

The recent increase in the demand for higher data transmission rates in wireless communications has entailed many implementation issues that can only be resolved by going through a full paradigm shift. Making use of the millimetric spectrum bands is a very attractive solution to the shortage of radio resources but, to garner all their potential, new techniques must be developed. Most of them are contained in the Massive Multiple Input Multiple Output (M-MIMO) framework: the idea of using very large antenna arrays for cellular communications. In this thesis, we propose the usage of Lens Antenna Arrays (LAA) to avoid the unbearable power and infrastructure costs posed by traditional M-MIMO architectures. This novel communication system exploits the angular-dependent power focusing capabilities of an electromagnetic lens to discern between waves with different angles of arrival and departure, without explicit signal processing. The work presented in this document motivates the use of LAAs in mmWave communications, studies some of their mathematical properties and proposes their application in noncoherent schemes. Numerical results validate the performance of this novel kind of systems and confirm their strengths in both multi-user and block fading settings. LAAs that use noncoherent methods appear to be very suitable for vehicular communications and densely populated cellular networks.En los últimos tiempos, el incremento en la demanda de mayor velocidad de transmisión de datos en redes de comunicación inalámbricas ha conllevado varios problemas de implementación que solo se podrán resolver a través de un cambio total de paradigma. Utilizar bandas milimétricas del espectro es una solución muy atractiva a la escasez de recursos de radio pero, para poder extraer todo su potencial, es necesario desarrollar nuevas técnicas. La mayor parte de éstas pasa por la infraestructura Massive Multiple Input Multiple Output (M-MIMO): la idea de usar matrices de antenas muy grandes para comunicaciones celulares. En esta tesis, proponemos el uso de matrices de antenas con lente, o Lens Antenna Arrays (LAA), para evitar los inasumibles costes energéticos y de instalación propios de las arquitecturas M-MIMO tradicionales. Este novedoso sistema de comunicaciones explota las capacidades de concentración de energía con dependencia angular de las lentes electromagnéticas para distinguir entre ondas con distintas direcciones de llegada y de salida, sin procesado de la señal explícito. El trabajo presentado en este documento motiva el uso de los LAAs en comunicaciones en bandas milimétricas (mmWave), estudia varias propiedades matemáticas y propone su aplicación en esquemas no coherentes. Resultados numéricos validan su ejecución y confirman sus fortalezas en entornos multiusuario y con desvanecimiento en bloque. Los LAAs que utilizan métodos no coherentes parecen ser idóneos para comunicaciones vehiculares y para redes celulares altamente pobladas.En els darrers temps, l'increment en la demanda de major velocitat de transmissió de dades en xarxes de comunicació inalàmbriques ha comportat diversos problemes d'implementació que tan sols es podran resoldre a través d'un canvi total de paradigma. Utilitzar les bandes mil·limètriques de l'espectre és una solució molt atractiva a l'escassetat de recursos de ràdio però, per tal d'extreure'n tot el seu potencial, és necessari desenvolupar noves tècniques. La majoria d'aquestes passa per la infraestructura Massive Multiple Input Multiple Output (M-MIMO): la idea d'utilitzar matrius d'antenes molt grans per a comunicacions cel·lulars. En aquesta tesi, proposem l'ús de matrius d'antenes amb lent, o Lens Antenna Arrays (LAA), per tal d'evitar els inassumibles costos energètics i d'instal·lació propis d'arquitectures M-MIMO tradicionals. Aquest innovador sistema de comunicacions explota les capacitats de concentració d'energia amb dependència angular de les lents electromagnètiques per tal de distingir entre ones amb diferents direccions d'arribada i de sortida, sense processament de senyal explícit. El treball presentat en aquest document motiva l'ús dels LAAs per comunicacions en bandes mil·limètriques (mmWave), n'estudia diverses propietats matemàtiques i proposa la seva aplicació en esquemes no coherents. Resultats numèrics en validen l'execució i confirmen les seves fortaleses en entorns multi-usuari i amb esvaïment en bloc. Els LAAs que utilitzen mètodes no coherents semblen ser idonis per a comunicacions vehiculars i per a xarxes cel·lulars altament poblades

Advanced Trends in Wireless Communications

Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics

MIMO Systems

In recent years, it was realized that the MIMO communication systems seems to be inevitable in accelerated evolution of high data rates applications due to their potential to dramatically increase the spectral efficiency and simultaneously sending individual information to the corresponding users in wireless systems. This book, intends to provide highlights of the current research topics in the field of MIMO system, to offer a snapshot of the recent advances and major issues faced today by the researchers in the MIMO related areas. The book is written by specialists working in universities and research centers all over the world to cover the fundamental principles and main advanced topics on high data rates wireless communications systems over MIMO channels. Moreover, the book has the advantage of providing a collection of applications that are completely independent and self-contained; thus, the interested reader can choose any chapter and skip to another without losing continuity

Advanced index modulation techniques for future wireless networks

In the research study proposed in this Ph.D Thesis, we consider Index Modulation as a novel tool to enhance energy and spectral efficiencies for upcoming 5G networks, including wireless sensor networks and internet of things. In this vein, spatial modulation was proposed to enhance the capacity of wireless systems to partially achieve the capacity of MIMO systems but at lower cost, making it a technique that has attracted significant attention over the past few years. As such, SM schemes have been regarded as possible candidates for spectrum- and energy-efficient next generation MIMO systems. However, the implementation of the SM is also challenging because of its heavy dependence on channel characteristics, channel correlation, corrupted CSI and the need to have adequate spacing between antennas. Moreover, the SM requires multiple antennas at the transmitter which adds cost to the hardware implementation. In addition, the number of mapped bits in SM is limited by the physical size of the wireless device where only small number of antennas can be used. The switching time wasted by RF antenna switches adds to the complexity of the issue. In this Thesis, we study the drawbacks of SM in the articles indicated, namely Performance Comparison of Spatial Modulation Detectors Under Channel Impairments that is placed in the Appendix at the end of Thesis as it is a conference paper, and The Impact of Antenna Switching Time on Spatial Modulation that is put in Chapter 1. In the first article, we have shown that channel impairments have serious impacts on the BER performance and on the capacity of the SM system and that the SM is too sensitive to both imperfect and correlated channels. In the second article, we have demonstrated that the switching time defined as the time needed by the system to turn off an antenna and turn on another one, which is an inherent property of RF industrial switches used in SM systems, is in the order of nanoseconds and naturally influences the transmission rate of SM systems because of introducing systematic transmission gaps or pauses. Given the speed limitation of practical RF switches in performing transitions, antenna transition-based technologies like SM schemes are capped in terms of data rate performance. In fact, the effective data rate of SM will remain hostage to developments in industrial RF switches. This brings restrictions to the implementation and operation issues when extremely high data rates become a necessity. It is shown by the assemblage of our results that the switching time Tsw which is a requirement for transitions between antennas to happen, dictates restrictions on data rate, capacity and spectral efficiency of SM systems. Furthermore, we propose baseband non-hardware-based indexing modulation schemes based on frequency-index modulation, coherent chaotic modulation and non-coherent differential chaotic modulation schemes as potential alternatives to SM, that would also fit wireless sensor networks and internet of things applications. In this regard, we have proposed three articles. The first article which represents frequency index modulation is called Frequency Index Modulation for Low Complexity Low Energy Communication Networks and is placed in Chapter 2 of this Thesis. In this article, we explore a low complexity multi-user communication system based on frequency index modulation that suits Internet of Things (IoT) applications and we show that such a system would constitute an excellent candidate for wireless sensor applications, where it represents a simpler substitution for frequency-hopping (FH) based architectures, in which the hops carry extra bits. The third article which concerns coherent chaotic modulation is called Design of an Initial-Condition Index Chaos Shift Keying Modulation and is located in Chapter 3. In this article, an initial condition index chaos shift keying modulation is proposed. This design aims to increase the spectral and energy efficiencies to unprecedented levels. The proposed scheme exploits the initial conditions to generate different chaotic sequences to convey extra bits per transmission. In comparison to rival modulation schemes, the results obtained in the proposed work show a promising data rate boost and a competitive performance. The last article employs a non-coherent differential chaotic shift-key system named Permutation Index DCSK Modulation Technique for Secure Multi-User High-Data-Rate Communication Systems that is found in the Appendix. In this original design, where each data frame is divided into two time slots in which the reference chaotic signal is sent in the first time slot and a permuted replica of the reference signal multiplied by the modulating bit is sent in the second time slot, we target enhancing data security, energy and spectral efficiencies. Overall, in light of the high demands for bandwidth and energy efficiencies of futuristic systems, the suggested soft indexing mechanisms are successful candidates with promising results