Massive MIMO (Multiple-Input Multiple-Output) base stations have proven, both in theory and in practice, to possess many of the qualities that future wireless communication systems will require.  They can provide equally high data rates throughout their coverage area and can concurrently serve multiple low-end handsets without requiring wider spectrum, denser base station deployment or significantly more power than current base stations.  The main challenge of massive MIMO is the immense hardware complexity and cost of the base station—each element in the large antenna array needs to be individually controllable and therefore requires its own radio chain.  To make massive MIMO commercially viable, the base station has to be built from inexpensive simple hardware.  In this thesis, it is investigated how the use of low-end power amplifiers and analog-to-digital converters (ADCs) affects the performance of massive MIMO.  In the study of the signal distortion from low-end amplifiers, it is shown that in-band distortion is negligible in massive MIMO and that out-of-band radiation is the limiting factor that decides what power efficiency the amplifiers can be operated at.  A precoder that produces transmit signals for the downlink with constant envelope in continuous time is presented to allow for highly power efficient low-end amplifiers.  Further, it is found that the out-of-band radiation is isotropic when the channel is frequency selective and when multiple users are served; and that it can be beamformed when the channel is frequency flat and when few users are served.  Since a massive MIMO base station radiates less power than today's base stations, isotropic out-of-band radiation means that low-end hardware with poorer linearity than required today can be used in massive MIMO.  It is also shown that using one-bit ADCs—the simplest and least power-hungry ADCs—at the base station only degrades the signal-to-interference-and-noise ratio of the system by approximately 4 dB when proper power allocation among users is done, which indicates that massive MIMO is resistant against coarse quantization and that low-end ADCs can be used. / Massiv-MIMO-basstationer (eng: Multiple-Input Multiple-Output) har visats, både i teori och praktik, besitta många av de egenskaper som framtida trådlösa kommunikationssystem kommer att behöva.  De kan tillhandahålla enhetligt höga datatakter i hela täckningsområdet och simultant betjäna flera enkla mobilenheter utan att använda bredare spektrum, tätare basstationsplacering eller betydligt mer effekt än dagens basstationer.  Huvudutmaningen med massiv MIMO är basstationens enorma hårdvarukomplexitet och -kostnad – varje element i den stora gruppantennen skall kunna kontrolleras individuellt och kräver sålunda sin egen radiokedja.  För att massiv MIMO skall bli kommersiellt attraktiv, måste basstationen byggas av billig, enkel hårdvara.  I denna avhandling undersöks hur enkla effektförstärkare och analog-till-digital-omvandlare (AD-omvandlare) påverkar massiv-MIMO-systemets prestanda.  I studien av signaldistorsionen från enkla förstärkare visas det att inband-distorsionen är försumbar i massiv MIMO och att utombandsstrålningen är den begränsande faktorn som bestämmer vid vilken verkningsgrad förstärkarna kan arbeta.  En förkodare som åstadkommer nerlänks-sändsignaler som har konstant envelopp i kontinuerlig tid presenteras för att möjliggöra användandet av enkla förstärkare med hög verkningsgrad.  Vidare konstateras det att utombandsstrålningen är isotrop när kanalen är frekvensselektiv och när flera användare betjänas; och att den kan lobformas när kanalen är frekvensflat och när få användare betjänas.  Eftersom en massiv-MIMO-basstation utstrålar mindre effekt än dagens basstationer, betyder isotrop utombandsstrålning att enkel hårdvara med sämre linearitet än vad som krävs idag kan användas i massiv MIMO.  Det visas även att användandet av enbits-AD-omvandlare – de enklaste och mest strömsnåla AD-omvandlarna – i basstationen endast minskar signal-till-interferens-och-brus-förhållandet med 4 dB när tillbörlig effektallokering mellan användarna utförs, vilket indikerar att massiv MIMO är motståndskraftig mot grov kvantisering och att enkla AD-omvandlare kan användas. / 大規模多輸入多輸出基站，無論從理論上或實際上，皆已經證明具有許多未來無線通訊系統所需的特質。比如：在其整個覆蓋區域均一地提供高數據傳輸速率、在同一時間頻率資源上服務多個簡單的終端設備，而無需佔用更多頻譜資源或更密集地部署基站，亦無需提高基站的功耗。實現大規模多入多出系统的主要挑戰在於硬件複雜度及基站成本——大規模天線陣列中的每一個天線元必須單獨可控，因此需要其自身的射頻鏈路。爲使大規模多入多出基站有商業吸引力，基站必須以簡單低成本的硬件來建造。本論文探討簡單的功率放大器與模擬數字轉換器對大規模多入多出性能的影響。對低端功放信號失真的研究表明，帶內失真對大規模多入多出的性能影響幾乎可以忽略，而帶外泄露是限制功放效率的決定因素。爲使用高功率效率低端功放，本文提出能產生具有恆定包絡連續時間信號的預編碼。本文指出，在頻率選擇性衰落信道上服務多個用戶時，帶外泄露呈現各向同性；而在平坦衰落信道上服務少數用戶時，帶外泄露可呈現波束賦形。由於大規模多入多出基站比現用基站輻射較少功率，帶外泄露各向同性意味著大規模多入多出基站可使用低端硬件，其線性要求不比現有基站的高。另外表明，如果進行合理的多用戶功率分配，基站使用單比特模擬數字轉換器——最簡單低耗的轉換器——僅使系統的信干噪比降低約４分貝。以此可見，大規模多入多出系統對非精確量比較穩定，低端模擬數字轉換器可於此類系統中使用。

This thesis examines the high peak-to-average-power ratio (PAPR) problem of OFDM and other spectrally-efficient multicarrier modulation schemes, specifically their stringent requirements for highly linear, power-inefficient amplification. The thesis then presents a most intriguing answer to the PAPR-problem in the form of a constant-envelope OFDM (CE-OFDM) waveform, a waveform which employs phase modulation to transform the high-PAPR OFDM signal into a constant envelope signal, like FSK or GMSK, which can be amplified with non-linear power amplifiers at near saturation levels of efficiency. A brief analytical description of CE-OFDM and its suboptimal receiver architecture is provided in order to define and analyze the key parameters of the waveform and their performance impacts. The primary contribution of this thesis is a highly tunable software-defined radio (SDR) implementation of the waveform which enables rapid-prototyping and testing of CE-OFDM systems. The digital baseband processing of the waveform is executed on a general purpose processor (GPP) in the Linux Ubuntu 14.04 operating system, and programmed using the GNU Radio SDR software framework with a mixture of Python and C++ routines. A detailed description of the software implementation is provided, and baseband simulations of the SDR CE-OFDM receiver in additive white Gaussian noise (AWGN) validate the performance of the implemented signal processing. A fully-functional CE-OFDM radio system is proposed in which GPPs executing the software defined transmitter and receiver routines are interfaced with Ettus Universal Software Radio Peripheral (USRP) transceiver front ends. A software testbench is created to enable rapid configuration and testing of the CE-OFDM waveform over all permutations of its parameters, over both simulated and physical RF channels, to draw deeper insights into the characteristics of the waveform and the necessary design considerations and improvements for further development and deployment of CE-OFDM systems. / Master of Science

L’évolution des systèmes de télécommunications, liée à une demande sans cesse croissante en termes de débit et de volume de données, se concrétise par le développement de systèmes proposant des bandes passantes très larges, des modulations à très hautes efficacités spectrales, de la flexibilité en puissance et en fréquence d’émission. Par ailleurs, la mise en œuvre de ces dispositifs doit se faire avec un souci permanent d’économie d’énergie d’où la problématique récurrente de l’amplification de puissance RF qui consiste à allier au mieux rendement, linéarité et bande passante. L’architecture conventionnelle d’une chaine d’émission RF consiste dans une première étape à réaliser l’opération de modulation-conversion de fréquence (Modulateur IQ) puis dans une deuxième étape l’opération de conversion d’énergie DC-RF (Amplificateur de Puissance), ces deux étapes étant traditionnellement traitées de manière indépendante. L’objectif de ces travaux de thèse est de proposer une approche alternative qui consiste à combiner ces deux opérations dans une seule et même fonction : le modulateur vectoriel de puissance à haute efficacité énergétique. Le cœur du dispositif, conçu en technologie GaN, repose sur un circuit à deux étages de transistors HEMT permettant d’obtenir un gain en puissance variable en régime de saturation. Il est associé à un modulateur de polarisation multi-niveaux spécifique également en technologie GaN. Le dispositif réalisé a permis de générer directement, à une fréquence de 2.5 GHz, une modulation vectorielle 16QAM (100Msymb/s) de puissance moyenne 13 W, de puissance crête 25W avec un rendement global de 40% et une linéarité mesurée par un EVM à 5%. / The evolution of telecommunications systems, linked to a constantly increasing demand in terms of data rate and volume, leads to the development of systems offering very wide bandwidths, modulations with very high spectral efficiencies, increased power and frequency flexibilities in transmitters. Moreover, the implementation of such systems must be done with a permanent concern for energy saving, hence the recurring goal of the RF power amplification which is to combine the best efficiency, linearity and bandwidth. Conventional architectures of RF emitter front-ends consist in a first step in performing the frequency modulation-conversion operation (IQ Modulator) and then in a second step the DC-RF energy conversion operation (Power Amplifier), these two steps being usually managed independently. The aim of this thesis is to propose an alternative approach that consists in combining these two operations in only one function: a high efficiency vector power modulator. The core of the proposed system is based on a two-stage GaN HEMT circuit to obtain a variable power gain operating at saturation. It is associated with a specific multi-level bias modulator also design using GaN technology. The fabricated device generates, at a frequency of 2.5 GHz, a 16QAM modulation (100Msymb/s) with 13W average power, 25W peak power, with an overall efficiency of 40% and 5% EVM.

<p>DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content. </p><p>The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers. </p><p>This thesis talks about the improvement of the PAPR problem using the soft compression method. </p><p>The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.</p>

DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content. The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers. This thesis talks about the improvement of the PAPR problem using the soft compression method. The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.

In order to improve the drawback of the high peak-to-average power ratio (PAPR) on the multi-carrier systems, in this paper we derive a statistical characterization approach of the time domain signal power variance metric by means of every user¡¦s spreading code combination and subcarrier scrambling. We obviously reduce the PAPR on the multi-carrier code division multiple access (MC-CDMA) systems by resorting the combination of spreading codes and scrambling the polarities of subcarriers. Due to the large calculative number of exhaustive search, we use a low complexity Replacement Search Method (RSM) to reduce the calculation times of searching, and obtain a good result. Moreover, we can get a better PAPR reduction performance by increasing the number of iteration.

This thesis considers the use of the tone reservation (TR) technique in orthogonal frequency division multiplexing (OFDM) systems. The nonlinear distortion is usually introduces by the high power amplifiers (HPA) used in wireless communications systems. It orders to reduce the inter-modulation distortion (IMD) in OFDM systems. In addition to the original peak-to-average power ratio (PAPR)-reduction criterion, we propose signal-to-distortion plus noise power ratio (SDNR) criterion and distortion power plus inverse of signal power (DIS) criterion. Based on these criteria, the cross-entropy (CE) algorithm is introduced to determine desired values of the peak reduction carriers (PRCs) to improve the bit error rate (BER) of nonlinearly distorted. Computational complexity is always the major concern of PAPR technique. Therefore, the real-valued PRCs and the modified transform decomposition (MTD) method are introduced here to dramatically decrease complexity of inverse fast Fourier transform (IFFT) operation with slightly performance loss. The simulation results show that the proposed criteria provide a better BER performance and a lower computational complexity.

Orthogonal frequency division multiplexing (OFDM) system is the standard of next generation mobile communication, one of the major drawbacks of OFDM systems is the peak-to-average power ratio (PAPR). In this paper, we proposed a low complexity Selected mapping (SLM) scheme to reduce PAPR. In [27], Wang proposed a low complexity SLM scheme by utilizing conversion vectors having the form of a perfect sequence to solve the problem that phase rotation vectors of the conversion vectors do not usually have an equal magnitude in frequency domain. This paper proposed a low complexity SLM scheme based on perfect sequence and consider the symbol interleaving to reduce the correlation between signals in time domain. It is shown that the (Complementary Cumulative Distribution Function, CCDF) of our proposed scheme are closer to the traditional SLM scheme than Wang¡¦s in [27] but with additional complexity. And the computational complexity is much lower than traditional SLM.

For channel estimation without data-induced interference in data-dependent superimposed training (DDST) scheme, the data sequence is shifted by subtracting a data-dependent sequence before added to training sequence at transmitter. The distorted term causes the data identification problem (DIP) at the receiver. In this thesis, we propose two precoding schemes based on previous work. To maintain low peak-to-average power ratio (PAPR), the precoding matrix is restricted to a diagonal matrix. The first scheme is proposed to enlarge the minimum distance between the closest codewords, termed as efficient diagonal scheme. Conditions to make sure the precoding matrix is efficient for M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) modulation are listed in this paper. The second scheme pursues a lowest complexity at receiver which means the amount of searching set is reduced. It is a trade-off between the better bit error rate (BER) performance and a lower complexity at receiver. The simulation results show that PAPR have been improved and the DIP is solved in both schemes.

In this thesis we introduce a two-way Doherty amplifier architecture with multiple feedbacks for digital predistortion based on impedance-inverting directional coupler (transcoupler). The tunable two-way Doherty amplifier with a tuned circulator-based impedance inverter is presented. Compact N-way Doherty architectures that subsume impedance inverter and offset line functionality into output matching networks are derived. Comprehensive N-way Doherty amplifier design and analysis techniques based on load-pull characterization of active devices and impedance modulation effects are developed. These techniques were then applied to the design of a two-way Doherty amplifier and a three-way Doherty amplifier which were manufactured and their performance measured and compared to the amplifier performance specifications and simulated results.