Cíl disertační práce leží v oblasti modelování a vyhodnocení bezdrátových komunikačních systémů s dvojrozměrným rozprostíráním signálu a jejich klíčových parametrů v závislosti na vybraných vlastnostech moderního bezdrátového komunikačního řetězce. Výzkumné metody použité v této práci spočívají především ve vývoji softwarového simulátoru pro prostředí Matlab, s jehož pomocí, a s využitím statistického přístupu, jsou navržené algoritmy ověřeny. Dále je použit simulátor fyzické vrstvy dle 3rd Generation Partnership Project Long Term Evolution (3GPP LTE), vyvinutý na Technické univerzitě ve Vídni. Tento představuje ideální platformu pro implementaci metody dvojrozměrného (2D) rozprostírání a její vyhodnocení s přihlédnutím k současným bezdrátovým komunikačním systémům. Zjištění prezentovaná v této práci představují především ověření účinnosti systému nazvaného jako Variable Spreading Factor - Orthogonal Code Frequency Division Multiplex (VSF-OFCDM), který využívá principu 2D rozprostírání signálu a zjištění, že VSF-OFCDM systém překonává systémy využívající Orthogonal Division Frequency Multiplex (OFDM), nebo Code Division Multiple Access (CDMA). Dále byla navržena metoda 2D rozprostírání signálu v systému LTE, kde se též potvrdila její účinnost. Díky účinnějšímu potlačení vlivu rychlé variace přenosového kanálu v závislosti na frekvenci a čase, dosahuje systém VSF-OFCDM znatelně vyšší datové prostupnosti.

This work deals with high-frequency power amplifiers. In the theoretical part are briefly summarized the general characteristics and properties of particular working classes of amplifiers focusing on their efficiency. The next section is aimed on design of high-frequency power amplifier for 1296MHz band and its individual components. In this part is desribed design of hybrid combiners - splitters, directional couplers of the coupled lines, amplifiers with RA18H1213G module and power amplifier with transistor BLV958. The work also includes the results of simulations of designed circuit, realization procedure and the measured parameters of manufactured components. In conclusion of this work the theoretical and measured values are compared.

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。

abstract: This dissertation focuses on three different efficiency enhancement methods that are applicable to handset applications. These proposed designs are based on three critical requirements for handset application: 1) Small form factor, 2) CMOS compatibility and 3) high power handling. The three presented methodologies are listed below: 1) A transformer-based power combiner architecture for out-phasing transmitters 2) A current steering DAC-based average power tracking circuit for on-chip power amplifiers (PA) 3) A CMOS-based driver stage for GaN-based switched-mode power amplifiers applicable to fully digital transmitters This thesis highlights the trends in wireless handsets, the motivates the need for fully-integrated CMOS power amplifier solutions and presents the three novel techniques for reconfigurable and digital CMOS-based PAs. Chapter 3, presents the transformer-based power combiner for out-phasing transmitters. The simulation results reveal that this technique is able to shrink the power combiner area, which is one of the largest parts of the transmitter, by about 50% and as a result, enhances the output power density by 3dB. The average power tracking technique (APT) integrated with an on-chip CMOS-based power amplifier is explained in Chapter 4. This system is able to achieve up to 32dBm saturated output power with a linear power gain of 20dB in a 45nm CMOS SOI process. The maximum efficiency improvement is about ∆η=15% compared to the same PA without APT. Measurement results show that the proposed method is able to amplify an enhanced-EDGE modulated input signal with a data rate of 70.83kb/sec and generate more than 27dBm of average output power with EVM<5%. Although small form factor, high battery lifetime, and high volume integration motivate the need for fully digital CMOS transmitters, the output power generated by this type of transmitter is not high enough to satisfy the communication standards. As a result, compound materials such as GaN or GaAs are usually being used in handset applications to increase the output power. Chapter 5 focuses on the analysis and design of two CMOS based driver architectures (cascode and house of cards) for driving a GaN power amplifier. The presented results show that the drivers are able to generate ∆Vout=5V, which is required by the compound transistor, and operate up to 2GHz. Since the CMOS driver is expected to drive an off-chip capacitive load, the interface components, such as bond wires, and decoupling and pad capacitors, play a critical role in the output transient response. Therefore, extensive analysis and simulation results have been done on the interface circuits to investigate their effects on RF transmitter performance. The presented results show that the maximum operating frequency when the driver is connected to a 4pF capacitive load is about 2GHz, which is perfectly matched with the reported values in prior literature. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019

The emphasis on higher data rates, spectral efficiency and cost reduction has driven the field towards linear modulation techniques such as quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM), wideband code division multiple access (WCDMA), and orthogonal frequency division multiplexing (OFDM). The result is a complex signal with a non-constant envelope and a high peak-to-average power ratio. This characteristic makes these signals particularly sensitive to the intrinsic nonlinearity of the RF power amplifier (PA) in the transmitter. The nonlinearity will generate intermodulation (IMD) components, also referred to as out-of-band emission or spectral re-growth, which interfere with adjacent channels. Such distortion, or so called Adjacent Channel Interference (ACI), is strictly limited by FCC and ETSI regulations. Meanwhile, the nonlinearity also causes in-band distortion which degrades the bit error rate performance. Typically, the required linearity can be achieved either by reducing power efficiency or by using linearization techniques. For a Class-A PA, simply “backing off” the input power level can improve linearity; however, for high peak to average power ration (PAPR) signals, this normally reduces the power efficiency down to 10% while increasing heat dissipation up to 90%.When considering the vast number of base stations that wireless operators need to account for, increasing power consumption, or in other words, power back-off is not a viable tradeoff. Therefore, amplifier linearization has become an important technology and a desirable alternative to backing-off an amplifier in modern communications systems. In this work, a novel adaptive algorithm is presented for predistorter linearization of power amplifiers. This algorithm uses Pade-Chebyshev polynomials and a QR decomposition followed by back substitution to find the pre-distorter coefficients.This algorithm is implemented on a Field Programmable Gate Array (Stratix 1S80).The implementation provides improved linearization and also runs the algorithm fast enough so that the adaptive part can be done quickly. Yet another challenge was the integration of a transmitter, receiver and this adaptive algorithm into a single FPGA chip and its communication with a base station. The work thus presents a novel pre-distortion implementation technique using an FPGA and a soft processor (Nios 2) which provides significant intermodulation distortion suppression.

The need for high spectral efficiency and data rate drives the modulation schemes like OFDM and QAM. The resulting signal is a complex signal with high peak to average power ratio. This property causes signal sensitivity to the non-linearity of power amplifiers. Power amplifiers create out-of-band distortion, in band distortion and spectral re-growth. The spectral re-growth affects the adjacent channels and cause Adjacent Channel Interference (ACI). So linearization techniques should be used to remove the skirts produced by the amplifier in the adjacent frequencies. The objective of this thesis is to figure out a pre distortion method that is simple enough to implement with an analog circuit. We are proposing a novel method to model the non linearity and use the same model as post-distorter and pre-distorter to invert non linearity so linear gain is maintained. The implementation is generic to all the non linear systems and can be implemented to invert the non linearity of any such system.

Thulium based fiber lasers represent a promising alternative for pulse energy scaling and high peak power generation with ytterbium based systems at 1µm. Advantages of thulium arise from the operation at longer wavelengths and a large gain bandwidth (1.8-2.1µm). Nonlinear effects, such as self phase modulation, stimulated Raman scattering and stimulated Brillouin scattering generally limit peak power scaling in fiber lasers. The longer wavelength of thulium fiber lasers and large mode field areas can significantly increase the nonlinear thresholds. Compared to 1µm systems, thulium fiber lasers enable single mode guidance for two times larger mode field diameter in step index fibers. Similar behavior is expected for index guiding thulium doped photonic crystal fibers. In this work a novel thulium doped rod type photonic crystal fiber design with large mode field diameter ( > 50µm) was first characterized in CW-lasing configuration and then utilized as final amplifier in a two stage master oscillator power amplifier. The system generated MW-level peak power at 6.5ns pulse duration and 1kHz repetition rate. This world record performance exemplifies the potential of thulium fiber lasers to supersede ytterbium based systems for very high peak power generation in the future. As part of this work a computer model for the transient simulation of pulsed amplification in thulium based fiber lasers was developed. The simulations are in good agreement with the experimental results. The computer model can be used for efficient optimization of future thulium based fiber amplifier designs.

Universal Mobile Telecommunications Systems (UMTS) is the preferred third generation (3G) communication standard for mobile communications and will provide worldwide coverage, a convenient software technology and very high data rate. The high data rate, especially, requires the use of bandwidth-efficient modulation schemes such as Quadrature Phase Shift Keying (QPSK). But modulation schemes such as QPSK need, in turn, a very linear power from the output of the transmitter power amplifier in order to meet the spectral requirements. A linear power amplifier, traditionally, has very low energy efficiency. Poor energy efficiency directly affects operational costs and causes thermal heating issues in base station transmitters. Thus the power amplifier designer is forced to trade-off between linearity and efficiency. As a result of this trade-off a Class-AB power amplifier is most often used in QPSK based systems. Class-AB power amplifiers provide acceptable linearity at efficiency values around 45-50% typically. This compromise is not a satisfactory solution but is inevitable while using traditional power amplifier design techniques. This thesis details the use of a Class-F amplifier with carefully chosen bias points and harmonic traps to overcome this problem. Class-F amplifiers are usually considered as very high efficiency (80% or more power-added efficiency) amplifiers where the high efficiency is obtained through the use of harmonic traps (L-C filters or quarter-wavelength transmission lines), which provide suitable terminations (either open or short) for the harmonics generated. By doing this, a square wave drain voltage and a peaked half-sinusoidal drain current out-of-phase by 180 are produced. Since only a drain voltage or a drain current exists at any given time, the power dissipation is ideally zero resulting in 100% theoretical efficiency. These very high efficiency values are usually associated with poor linearity. However the linearity can be improved to meet the design standards but compromising on efficiency. Even after this is done, efficiencies are usually 10 to 15% greater than a traditional Class AB power amplifier with similar linearity performance. Thus efficiency can be improved without affecting linearity by the use of Class-F power amplifiers. In order to verify this theory, a Class-AB and a Class-F power amplifier are designed using Motorola's high voltage laterally diffused metal oxide semiconductor (LDMOS) transistor. The choice of bias points and the design of the harmonic traps are very critical for the Class-F performance and hence were designed after careful consideration. The designs were simulated on Agilent's Advanced Design System (ADS) and the simulated results were compared for three different power levels namely, the peak power, 3 dB below peak power and 6 dB below peak power. At all of these power levels it was noted that the Class-F and Class-AB power amplifiers have very similar linearity performance whereas the Class-F power amplifiers show about 10% improvement in efficiency in comparison to the Class-AB power amplifiers. / Master of Science

No description available.

Modern wireless communication systems use spectrally efficient modulation schemes to reach high data rate transmission. These schemes are generally involved with signals with high peak-to-average power ratio (PAPR). Moreover, the development of next generation wireless communication systems requires the power amplifiers to operate over a wide frequency band or multiple frequency bands to support different applications. These wide-band and multi-band solutions will lead to reductions in both the size and cost of the whole system. This dissertation presents several advanced power amplifier solutions to provide wide-band and multi-band operations with efficiency improvement at power back-offs.