Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions

Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio (NR) and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing of 8 terminals). Coarse and even error-prone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.Comment: submitted to IEEE transactions on signal processin

Eigenvector prediction-based precoding for massive MIMO with mobility

Eigenvector decomposition (EVD) is an inevitable operation to obtain the precoders in practical massive multiple-input multiple-output (MIMO) systems. Due to the large antenna size and at finite computation resources at the base station (BS), the overwhelming computation complexity of EVD is one of the key limiting factors of the system performance. To address this problem, we propose an eigenvector prediction (EGVP) method by interpolating the precoding matrix with predicted eigenvectors. The basic idea is to exploit a few historical precoders to interpolate the rest of them without EVD of the channel state information (CSI). We transform the nonlinear EVD into a linear prediction problem and prove that the prediction of the eigenvectors can be achieved with a complex exponential model. Furthermore, a channel prediction method called fast matrix pencil prediction (FMPP) is proposed to cope with the CSI delay when applying the EGVP method in mobility environments. The asymptotic analysis demonstrates how many samples are needed to achieve asymptotically error-free eigenvector predictions and channel predictions. Finally, the simulation results demonstrate the spectral efficiency improvement of our scheme over the benchmarks and the robustness to different mobility scenarios.Comment: 13pages, 7 figures, 1 table, journa

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

A survey on reconfigurable intelligent surfaces: wireless communication perspective

Using reconfigurable intelligent surfaces (RISs) to improve the coverage and the data rate of future wireless networks is a viable option. These surfaces are constituted of a significant number of passive and nearly passive components that interact with incident signals in a smart way, such as by reflecting them, to increase the wireless system's performance as a result of which the notion of a smart radio environment comes to fruition. In this survey, a study review of RIS-assisted wireless communication is supplied starting with the principles of RIS which include the hardware architecture, the control mechanisms, and the discussions of previously held views about the channel model and pathloss; then the performance analysis considering different performance parameters, analytical approaches and metrics are presented to describe the RIS-assisted wireless network performance improvements. Despite its enormous promise, RIS confronts new hurdles in integrating into wireless networks efficiently due to its passive nature. Consequently, the channel estimation for, both full and nearly passive RIS and the RIS deployments are compared under various wireless communication models and for single and multi-users. Lastly, the challenges and potential future study areas for the RIS aided wireless communication systems are proposed

Geringer RF-Komplexität Massive MIMO Systemen: Antennenselektion und Hybrid Analog-Digital Strahlformung

Wireless data traffic has been increased dramatically in the last decades, and will continue to increase in the future. As a consequence, the infrastructure of wireless communication systems needs to advance on the data capacity. Massive Multiple-Input Multiple-Output (MIMO) is a promising candidate technology to meet the demand. By scaling up the conventional MIMO by orders of magnitude number of \emph{active} antennas, a massive MIMO system can harvest considerable channel degrees of freedom to increase the spectral efficiency. However, increasing the number of \emph{active} antennas needs to increase both the numbers of Radio Frequency (RF) transceivers and antenna elements \emph{at the same rate}, which will increase the RF complexity and cost dramatically. It is known that the complexity and cost of antenna elements are usually much lower than that of RF transceivers, which motivates us to scale up MIMO by a lower increasing rate of the number of RF transceivers than that of antenna elements, resulting in so-called low RF-complexity massive MIMO systems. In this thesis, we study two types of low RF-complexity massive MIMO systems, i.e., massive MIMO antenna selection systems and massive MIMO hybrid analog-digital beamforming systems. Both systems use specific RF networks to bridge a massive number of antennas and a small number of RF transceivers, leading to signal dimension reduction from antennas to RF transceivers. The RF network used in antenna selection is referred to as RF switching network; while the RF network used in hybrid beamforming is referred to as Phase Shifting Network (PSN). Both RF networks have two types of architectures, i.e., full-array architecture and sub-array architecture. The latter has lower insertion loss, lower complexity and better scalability than the former, but at the price of performance degradation caused by connection constraint, which will be studied for both low RF-complexity systems in this thesis. In addition, a low RF-complexity PSN for the hybrid analog-digital beamforming system needs also to be studied to replace the conventional high-complexity-and-cost phase-shifter-based PSN. In the antenna selection system, the upper bounds on the channel capacity using asymptotic theory on order statistics are derived at the large-scale limit. The optimal antenna selection algorithms are also developed, which are based on Branch And Bound (BAB) search algorithm. Through the theoretical and algorithm studies, it is found that the sub-array antenna selection has close performance to the full-array antenna selection. In the hybrid beamforming system, we propose to use Rotman lens as PSN, which is of lower complexity and cost than the conventional phase-shifter-based PSN. Two beam selection algorithms, i.e., sub-optimal greedy search and optimal BAB search, are also proposed. In addition, the Rotman lenses are designed, fabricated and measured. The measurement results together with the beam selection algorithms are used to perform Monte Carlo simulation. Simulation results show that the proposed Rotman-lens-based system with the sub-array architecture suffers noticeable performance degradation compared to the system with the full-array architecture when ideal Rotman lenses are used. But when practical non-ideal Rotman lens are used, the former outperforms the latter when the number of antennas is large enough. Most interestingly, with non-ideal hardware, the sub-array Rotman-lens-based system has close performance to the sub-array phase-shifter-based system, and also exhibits a wideband capability. To prove the advantage of the low RF-complexity massive MIMO, two testbeds are built up for the antenna selection and hybrid beamforming systems, respectively. The measurement results show the low RF-complexity massive MIMO systems have superior performance over the small-scale MIMO systems under the condition of the same number of RF transceivers. The results in this thesis show that the low RF-complexity massive MIMO systems proposed in this thesis are feasible in technology and promising in performance, validating its potential usage for the future 5G wireless communication systems.Der drahtlose Datenverkehr ist in den letzten Jahrzehnten dramatisch gestiegen und wird auch in Zukunft weiter zunehmen. Infolgedessen muss die Datenkapazität der drahtlosen Infrastruktur erhöht werden. Mehrantennen Systeme mit einer sehr großen Anzahl an Antennen (engl. Massive Multiple-Input Multiple-Output (MIMO)) sind vielversprechende Technologiekandidaten, um diese Nachfrage zu erfüllen. Durch die Hochskalierung der Antennenanzahl eines konventionellen MIMO um mehrere Größenordnungen kann ein Massive MIMO-System erhebliche Kanalfreiheitsgrade erlangen, um die spektrale Effizienz zu verbessern. Allerdings muss mit der Anzahl der \emph{aktiven} Antennen sowohl die Anzahl der Hochfrequenz (engl. Radio Frequency (RF)) Transceiver als auch die der Antennenelemente \emph{im gleichen Maße} vergrössert werden, was die RF-Komplexität und Kosten dramatisch erhöht. Dabei ist bekannt, dass die Komplexität und die Kosten von Antennenelementen in der Regel viel niedriger sind als die von RF-Transceivern. Dies führt uns dazu dass wir das MIMO-System um eine im Verhältnis zur Antennenzahl geringere Anzahl von RF-Transceivern erweitern wollen, den so genannten Massive MIMO-Systemen mit geringer RF-Komplexität. In dieser Arbeit untersuchen wir zwei Arten von Massive MIMO-Systemen mit geringer RF-Komplexität, nämlich Massive MIMO-Antennenselektionssysteme und Massive MIMO-Hybrid-Analog-Digital-Strahlformungssysteme. Beide Systeme verwenden spezielle RF-Netzwerke, um eine größere Anzahl von Antennen von einer kleineren Anzahl von RF-Transceivern zu versorgen, was zu einer Signalraumreduktion von den Antennen zu den RF-Transceivern führt. Das bei der Antennenselektions verwendete RF-Netzwerk wird als RF-Koppelfeld bezeichnet, während das RF-Netzwerk, das bei der Hybrid-Strahlformung verwendet wird, als Phasenverschiebungsnetzwerk (engl. Phase Shifting Network, PSN) bezeichnet wird. Beide RF-Netzwerke können als Voll-Array-Architektur oder als Sub-Array-Architektur realisiert werden. Letztere hat eine geringere Einfügedämpfung, eine geringere Komplexität und eine bessere Skalierbarkeit als die erstere, aber zum Preis der Leistungsverschlechterung, die durch eine eingeschränkung Anzahl von Antennen-Transceiver-Verbindungen verursacht wird. Die vorliegende Arbeit untersucht dies für beide Systeme mit niedriger RF-Komplexität. Darüber hinaus wird auch ein PSN mit niedriger RF-Komplexität für das Hybride-Analog-Digital- Strahlformungssystem untersucht, das das herkömmliche hochkomplexe und kostenintensive PSN ersetzen soll. Im Antennenselektionssystem werden die Obergrenzen der Kanalkapazität unter Verwendung der Asymptoten Theorie der Ordnungsstatistik im Grenzverhalten abgeleitet. Die optimalen Antennenselektions-Algorithmen, die auf dem Branch and Bound (BAB) Suchalgorithmus basieren, werden ebenfalls entwickelt. Die theoretischen und algorithmischen Untersuchungen zeigen, dass die Leistung der Sub-Array-Antennenauswahl dicht bei der der Voll-Array-Antennenselektions liegt. Im Hybrid-Strahlformungssystem schlagen wir vor, eine Rotman-Linse als PSN zu verwenden, die von geringerer Komplexität und Kosten ist als das herkömmliche auf Phasenverschiebung basierende PSN. Es werden zwei Strahlauswahlalgorithmen vorgeschlagen, eine suboptimale Greedy-Suche und eine optimale BAB-Suche. Darüber hinaus wird die Rotman-Linse entworfen, gefertigt und vermessen. Die Messergebnisse werden zusammen mit den Strahlselektionsalgorithmen zur Durchführung einer Monte-Carlo-Simulation verwendet. Simulationsergebnisse zeigen, dass das vorgeschlagene Rotman-Linsen-basierte System mit der Sub-Array-Architektur eine spürbare Leistungsverschlechterung im Vergleich zum System mit der Full-Array-Architektur erleidet, wenn ideale Rotman-Linsen verwendet werden. Aber wenn reale nicht-ideale Rotman-Linsen verwendet werden, übertrifft erstere die zweite, wenn die Anzahl der Antennen groß genug ist. Noch interessanter, mit nicht-idealer Hardware, zeigt das Sub-Array Rotman-Linsen-basierte System in etwa die gleiche Leistung wie das Sub-Array Phasenschieber-basierte System und weist auch Breitbandfähigkeiten auf. Um den Vorteil der Massive MIMO-Systeme mit geringer RF-Komplexität zu beweisen, werden zwei Testumgebungen für die Antennenauswahl- und Hybrid-Strahlformungssysteme aufgebaut. Die Messergebnisse zeigen, dass, unter der Bedingung einer gleichen Anzahl von RF-Transceivern, die Massive MIMO-Systeme mit geringer RF-Komplexität in der Leistung den normalen MIMO-Systemen überlegen sind. Die Ergebnisse meiner Arbeit zeigen, dass die von mir vorgeschlagenen Massive MIMO-Systeme mit geringer RF-Komplexität technisch machbar und vielversprechend in der Leistung sind und bestätigen damit deren potentielle Nutzung für die zukünftigen 5G-Funkkommunikationssysteme

Keilaavan millimetriaaltoradiolinkin suuntaaminen ja seuraaminen

In order to provide high-throughput mobile broadband in a dense urban information society, upcoming cellular networks will finally employ the under-utilized millimeter-wave (mmW) frequencies. The challenging mmW radio environment, however, necessitates massive cell densification with wireless backhauling using very directional links. This thesis investigates how these links between access points may be aligned efficiently, and how alignment reflects the network organization. The work provides a thorough presentation of different high-level aspects and background information required when designing a mmW small cell system. In terms of alignment functionality, both automatic link establishment and proactive tracking are considered. Additionally, the presentation includes an overview of beam steerable antennas, mmW propagation in urban environments, and network organization. The thesis further specifies requirements, proposes possible approaches and compares those with existing implementations. Most of existing mmW beam alignment solutions are intended for short-range indoor communications and do not address the issues in cellular systems. While existing functionality considers only a single link between two devices, efficient design should consider both the entire network and the underlying phenomena. The devices should further exploit the existing network infrastructure, location and orientation information, and the concepts of machine learning. Even though the world has recently seen advancements in the related fields, there is still much work to be done before commercial deployment is possible.Seuraavan sukupolven matkaviestinjärjestelmien erittäin nopeissa datayhteyksissä tullaan hyödyntämään millimetriaaltoteknologiaa. Näillä taajuuksilla radioympäristö on kuitenkin hyvin haastava, mikä edellyttää verkon solutiheyden moninkertaistamista, täysin langattomia tukiasemia ja erittäin suuntaavia antenneja. Tässä diplomityössä tutkitaan eri keinoja kuinka tukiasemien väliset linkit kohdistetaan tehokkaasti, ja miten se vaikuttaa verkon rakenteeseen ja hallintaan. Työ tarjoaa kattavan taustaselvityksen mm-aaltosoluverkon toteuttamiseen tarvittavista asioista. Keilanohjausta tarkastellaan sekä verkon automaattisen laajentamisen että kohteen aktiivisen seurauksen kannalta. Tämän lisäksi työssä tutkitaan keilattavia antenneja, mm-aaltojen etenemistä kaupunkiympäristöissä ja verkkorakennetta. Näiden lisäksi työssä rajataan edellytykset, esitetään mahdollisia ratkaisuja, ja vertaillaan näitä olemassa oleviin toteutuksiin. Nykyiset keilaustoteutukset ovat pääasiassa suunniteltu lyhyen kantaman sisäyhteyksille, eivätkä siten vastaa ongelman asettelua. Aikaisempi toiminnallisuus keskittyy yhteen ainoaan linkkiin vaikka tehokas toteutus huomioisi koko järjestelmän kohdistusongelman fysikaalista perustaa unohtamatta. Verkkolaitteiden tulisi hyödyntää olemassa olevaa radioverkkoa, sekä paikka- että suuntatietoja, ja koneoppimisen keinoja. Vaikka aiheeseen liittyvä teknologia on kehittynyt viime vuosina harppauksin, mm-aaltosoluverkot ovat kaikkea muuta kuin valmiita markkinoille

Adaptive Coded Modulation Classification and Spectrum Sensing for Cognitive Radio Systems. Adaptive Coded Modulation Techniques for Cognitive Radio Using Kalman Filter and Interacting Multiple Model Methods

The current and future trends of modern wireless communication systems place heavy demands on fast data transmissions in order to satisfy end users’ requirements anytime, anywhere. Such demands are obvious in recent applications such as smart phones, long term evolution (LTE), 4 & 5 Generations (4G & 5G), and worldwide interoperability for microwave access (WiMAX) platforms, where robust coding and modulations are essential especially in streaming on-line video material, social media and gaming. This eventually resulted in extreme exhaustion imposed on the frequency spectrum as a rare natural resource due to stagnation in current spectrum management policies. Since its advent in the late 1990s, cognitive radio (CR) has been conceived as an enabling technology aiming at the efficient utilisation of frequency spectrum that can lead to potential direct spectrum access (DSA) management. This is mainly attributed to its internal capabilities inherited from the concept of software defined radio (SDR) to sniff its surroundings, learn and adapt its operational parameters accordingly. CR systems (CRs) may commonly comprise one or all of the following core engines that characterise their architectures; namely, adaptive coded modulation (ACM), automatic modulation classification (AMC) and spectrum sensing (SS). Motivated by the above challenges, this programme of research is primarily aimed at the design and development of new paradigms to help improve the adaptability of CRs and thereby achieve the desirable signal processing tasks at the physical layer of the above core engines. Approximate modelling of Rayleigh and finite state Markov channels (FSMC) with a new concept borrowed from econometric studies have been approached. Then insightful channel estimation by using Kalman filter (KF) augmented with interacting multiple model (IMM) has been examined for the purpose of robust adaptability, which is applied for the first time in wireless communication systems. Such new IMM-KF combination has been facilitated in the feedback channel between wireless transmitter and receiver to adjust the transmitted power, by using a water-filling (WF) technique, and constellation pattern and rate in the ACM algorithm. The AMC has also benefited from such IMM-KF integration to boost the performance against conventional parametric estimation methods such as maximum likelihood estimate (MLE) for channel interrogation and the estimated parameters of both inserted into the ML classification algorithm. Expectation-maximisation (EM) has been applied to examine unknown transmitted modulation sequences and channel parameters in tandem. Finally, the non-parametric multitaper method (MTM) has been thoroughly examined for spectrum estimation (SE) and SS, by relying on Neyman-Pearson (NP) detection principle for hypothesis test, to allow licensed primary users (PUs) to coexist with opportunistic unlicensed secondary users (SUs) in the same frequency bands of interest without harmful effects. The performance of the above newly suggested paradigms have been simulated and assessed under various transmission settings and revealed substantial improvements

Spatial Multizone Soundfield Reproduction Design

It is desirable for people sharing a physical space to access different multimedia information streams simultaneously. For a good user experience, the interference of the different streams should be held to a minimum. This is straightforward for the video component but currently difficult for the audio sound component. Spatial multizone soundfield reproduction, which aims to provide an individual sound environment to each of a set of listeners without the use of physical isolation or headphones, has drawn significant attention of researchers in recent years. The realization of multizone soundfield reproduction is a conceptually challenging problem as currently most of the soundfield reproduction techniques concentrate on a single zone. This thesis considers the theory and design of a multizone soundfield reproduction system using arrays of loudspeakers in given complex environments. We first introduce a novel method for spatial multizone soundfield reproduction based on describing the desired multizone soundfield as an orthogonal expansion of formulated basis functions over the desired reproduction region. This provides the theoretical basis of both 2-D (height invariant) and 3-D soundfield reproduction for this work. We then extend the reproduction of the multizone soundfield over the desired region to reverberant environments, which is based on the identification of the acoustic transfer function (ATF) from the loudspeaker over the desired reproduction region using sparse methods. The simulation results confirm that the method leads to a significantly reduced number of required microphones for an accurate multizone sound reproduction compared with the state of the art, while it also facilitates the reproduction over a wide frequency range. In addition, we focus on the improvements of the proposed multizone reproduction system with regard to practical implementation. The so-called 2.5D multizone oundfield reproduction is considered to accurately reproduce the desired multizone soundfield over a selected 2-D plane at the height approximately level with the listener’s ears using a single array of loudspeakers with 3-D reverberant settings. Then, we propose an adaptive reverberation cancelation method for the multizone soundfield reproduction within the desired region and simplify the prior soundfield measurement process. Simulation results suggest that the proposed method provides a faster convergence rate than the comparative approaches under the same hardware provision. Finally, we conduct the real-world implementation based on the proposed theoretical work. The experimental results show that we can achieve a very noticeable acoustic energy contrast between the signals recorded in the bright zone and the quiet zone, especially for the system implementation with reverberation equalization

Tri-Orthogonal Polarisation Diverse Communications

This thesis investigates improving communication link coverage through triorthogonal polarisation diversity. Tri-orthogonal polarisation diversity exploits radiated electromagnetic energy transmission and reception in three orthogonal spatial directions with an aim to provide enhanced communication link performance. Original contributions to this branch of diversity are presented in areas of both software and hardware design. First, simulations are presented highlighting the benefit of tri-orthogonal polarisation diversity at both the transmitter and receiver over a range of terrestrial channel conditions. The results are presented in an easily understandable graphical format that results from a novel model design considering all antenna orientations. Orientation robustness at the antenna is demonstrated as a consequence of a tri-orthgonal polarisation diverse approach. Second, additional research is performed in order to extend the model into the field of satellite systems. The ionosphere is required to be modelled, and this is performed according to a novel vectorised approach using realtime ionospheric data and terrestrial magnetic field appreciation. Third, ionospheric modelling is incorporated into a non-geosynchronous satellite orbit channel model that provides an insight into the benefit of applying a tri-orthogonal polarisation diverse approach uniquely at the receiver. Novelty is provided in the form of a vectorised approach to simulation covering all antenna orientations in a field-ofview as observed from a satellite transmitter. This is extended over the orbits of three distinct satellite systems. Output is provided in graphical format and conclusions are drawn form the data which suggest that a tri-orthogonal polarisation diverse approach applied at the receiver provides an increase in reception performance. Fourth, an antenna is designed, simulated, constructed and tested that provides three orthogonal polarisations in a phase-centred differentially-fed package. Novelty is provided in the design being planar in nature, with three orthogonal modes being able to be transmitted from a single slot. Results emanating from the testing procedure demonstrate the benefits of the design in terms of diversity and extension to beamforming applications. Fifth, as an extension to the antenna design, a circularly polarised feeding arrangement is used together with an omnidirectional vertically polarised mode feed in an antenna and feed combination. This provides the possibility of a direct comparison with conventional circularly polarised techniques, such as those used in both terrestrial and satellite receive antennas. Sixth, the operational bandwidth of the omnidirectional vertically polarised mode is extended by adapting the design of the cavity wall resonating slots in a substrateintegrated monopole antenna while maintaining a planar structure. The electric monopole design demonstrates an increase in operating bandwidth from 2.5% to 56%. In the thesis, a tri-orthogonal polarisation diverse approach is shown to be beneficial to signal reception over a range of channels, both in the areas of terrestrial and satellite communications. The concept is demonstrated to be feasible in a planar structure. Triorthogonal polarisation diversity is likely to play an increasing role in the future as systems look to cope with an ever increasing data flow. The demand for content on mobile devices has forced massive growth in mobile data over the past two decades. This growth has recently reached saturation point, and so new avenues for extending growth have to be considered. A search for available bandwidth has lead research to focus on the mmWave section of the electromagnetic spectrum. The advent of the next generation of wireless connectivity, dubbed fifth generation or 5G, is now upon us (Rappaport et al. 2013b). With data traffic set to multiply by up to one thousand fold by 2020 (Qualcomm Inc. Accessed: 2014b, Qualcomm Inc. Accessed: 2014a, Li et al. 2014, Chin et al. 2014), as The Internet of Things (Ashton 2009, Cisco Inc. Accessed: 2014, Gubbi et al. 2013) enters into the fray, an overhaul of wireless design is somewhat overdue. For static point-to-point, or LoS systems, challenges exist according to the channel environment and temporal changes that may occur within. For any network that has a mobile component built in, where spatial position and alignment of transmitter and receiver change over time, signal propagation is additionally influenced by link geometry. In an increasingly mobile world, this presents challenges as increased coverage, one of the main focus points of the 5G system, will require efficient use of radiated electromagnetic energy. Conventional techniques for improving data rate have typically aimed at increasing performance at the transmitter. For terrestrial networks, a transmitter is typically stationary. Performance outweighs size constraints and so power amplification and combination may be used to excite antennas that flood a network cell with a strong linearly polarised transmitted signal. For commercial providers, this has proved a very successful technique, mainly as a result of the majority of wireless subscribers living in dense urban environments. For a linearly polarised wave, operating at conventional operating frequencies around 2 GHz, and transmitted with relatively high power, the urban environment typically provides assistance for signal reception at the receiver through diversity brought about by reflection, refraction and scattering or multipath due to the presence of buildings. Small misalignments in transmit and receive antennas are mitigated as the propagating signal wavelength is large and a relatively high transmit power establishes a relatively high signal-to-noise ratio, providing useful multipath effects over the channel. At certain receive positions, channel fading may occur when superposition of received multipath components effectively cancel each other. This may be mitigated through additional transmitters that are spaced appropriately; a concept known as spatial diversity that has been cited at mmWave frequencies (Smulders 2002, Park and Pan 2012). Diversity of signal is important in that it offers a greater possibility of a signal being received due to individuality of uncorrelated channel propagation for each diverse signal component. As more content is demanded by subscribers within an ever shrinking timeframe, a higher frequency of operation is typically required for a carrier wave capable of providing this service. Add in the context of mobility, and issues quickly appear. Beneficial effects on a linearly polarised signal operating at conventional low gigahertz frequencies arising from reflection, refraction, and scattering or multipath effects, assist signal reception. Relatively long wavelengths are subjected to many scatterers, and due to the relatively high transmit power involved, scattering effects provide diversity at the receiver in the form of many smaller receivable diverse signal components. These signal components are superpositioned either constructively or destructively, after diverse individual propagation through the channel, at the receiver to provide signal reception. At mmWave frequencies, due to a shrinking wavelength, the following issues arise: • increased path loss over a defined range due to spreading loss (Pozar 2011), and increased atmospheric absorption (Liebe et al. 1989). An obvious solution is to provide more transmit power at the transmitter. At higher frequencies, miniaturisation of devices limits this possibility as heat sinking becomes problematic. Amplifier non-linearity and unwanted third order intermodulation impact on system performance (Niknejad and Hashemi 2008, Hashemi and Raman 2016) • the beneficial effect of multipath fading may not exist in a mmWave terrestrial channel (Pi and Khan 2011), as a smaller wavelength typically implies a reduced beamwidth and less scatterers available for the LoS signal to scatter into useful smaller diverse signal components. Due to a relatively low transmit power involved, any scattering of a LoS signal into smaller, weaker diverse signal components may result in no received signal. As a result, cell range is reduced and more transmitters are required to provide coverage over a network • with a shrinking wavelength, relatively lower transmit power, and increased mobility, antenna misalignment becomes problematic. A drive for radiated power efficiency is paramount in providing the next generation of wireless networks. An ability to transmit signals into and receive signals from all angles is necessary (Rappaport et al. 2013b). The terahertz range, for example, offers extremely high transfer rates, although any small misalignment greatly affects rate. The use of dielectric mirrors is required to effectively steer the transmitted signal to its destination. Mitigation of misalignment becomes important in maintaining system performance. For the next generation of mobile wireless systems to operate within the mmWave section of the electromagnetic spectrum, a solution to extend range is to increase radiated energy in a direction of propagation, through beam steering techniques. Within a mobile context, this poses challenges, not least as the link geometry is variable. For terrestrial networks, conventional transmitted waveforms are mainly vertically polarised, or circularly polarised, and as such are mainly one dimensional, or two dimensional at best, in performance. To provide the next generation of wireless networks, a third dimension needs to be considered to provide efficient use of radiated electromagnetic energy. Frequency bands of interest for 5G systems differ from country to country. According to the US Federal Communications Commission (FCC), the mmWave region that will be studied ranges from 24–80 GHz (Rappaport et al. 2013b, Rappaport Accessed: 2014, Above Ground Level Media Group Accessed: 2015). One of the aims of 5G is to improve coverage (Rappaport et al. 2013b). One method that is being considered is the joining of terrestrial and satellite services into one seamless network that may be readily accessed by the subscriber at the receiver (Evans et al. 2005, Evans et al. 2015, Federal Communications Commission Accessed: 2016). Satellite networks provide their own specific challenges, as transmit power is limited to payload specifications, and coverage typically requires a satellite that is moving relative to the Earth’s surface. Once again we find ourselves facing the same three issues that we encountered within the terrestrial context of a mmWave channel. If we are to increase link performance in a satellite channel to complement any improvement in terrestrial channels then the following points need to be considered: • propagation using higher operating frequencies typically suffers from higher path losses (Liebe et al. 1989, Pozar 2011). In some circumstances this can be mitigated by higher transmit power, but not all. A satellite payload is subject to a strict payload capacity and this restricts the size of transmit power devices and hence available transmit power that can be launched into orbit • a lack of beneficial reflectors, refractors, and scatterers is observed during channel propagation as the signal is typically LoS, narrow in beamwidth, and weak due to higher path loss and lower transmit power (Pi and Khan 2011). Multipath effects may degrade system performance as signals are weak • an evolving link geometry that affects antenna alignment. Linear and circular polarised signals are only two dimensional in nature. Three dimensions need to be considered, and beam steering of radiated power to provide the required range is a requirement (Evans et al. 2005, Hong et al. 2014b). To ensure that the next generation of mobile systems are fully mobile, while providing increased data rate, we need to consider diversity in three dimensions. Beam steering of a transmitted signal with high gain in the direction of a receiver is one viable option, and in the context of full mobility, three dimensional signal transmission and reception appears a logical step to achieving this (Hong et al. 2014a). While at a terrestrial transmitter, it is suggested that size is not a constraint, it remains so for a satellite transmitter, as it is at a mobile receiver. This rules out spatial diversity as an approach to increasing system performance. One approach of increasing diversity within a confined volume is through polarisation techniques (Vaughan 1990). In this thesis, we investigate the benefit of a subset of this approach—tri-orthogonal polarisation diversity (Andrews et al. 2001). In effect, the concept provides at least one additional degree of freedom or layer of diversity over conventional techniques such as circular polarisation. Due to orthogonality in three directions, this approach has a wide field of view, and potentially offers diversity and improved system performance through beam steering in any unit direction. Tri-orthogonal polarisation diversity may be applied either at the transmitter, at the receiver, or at both. In Chapter 1 of the thesis, both novel software and hardware aspects of the research are highlighted. Overall, the research outcomes of this thesis from both simulation and measured results suggest that the concept of tri-orthogonal polarisation diversity is: • beneficial to wireless performance over a majority of antenna orientations • plausible for implementation within typical antenna volume constraints.Thesis (Ph.D.) -- University of Adelaide, School of School of Electrical and Electronic Engineering, 201