Rapid Dynamic Power Rail Switching of OFDM Signal Amplifiers

Global resource usage and allocation is becoming an increasingly critical topic. Efficiency is at the heart of a plethora of current research fields from reducing energy consumption in the manufacturing industry, to increasing energy generation from renewable sources, or reusing waste materials for alternative applications. The telecommunications industry is no different, OFDM as a modulation format is ubiquitous and popular due to its spectral efficiency and robustness to interference but its major drawback is its high peak-to-average power ratio (PAPR) meaning that its efficiency is compromised. A review of existing methods for improving OFDM signal amplifier efficiency showed a lack of innovative techniques for power supply control for such amplifiers. This thesis proposes two unique solutions to innovate efficiency for a range of applications. Firstly, a novel power supply control technique to improve the efficiency of OFDM signal amplifiers based on probabilistic analyses. The probability density function of an OFDM signal was analysed and optimum switching thresholds were determined to maximise the efficiency of the power supply. The proposed mechanism considers the theory of Golomb rulers and perfect difference sets, specifically the conversion from linear rulers to modular to achieve a much greater system implementation efficiency. The result is a dynamic fast-switching multi-level power supply which achieves the main benefits of Doherty and Chireix amplifiers but without requiring multiple amplifiers. This class A-G amplifier topology can achieve a 63% efficiency increase compared to amplifiers with single-level voltage supplies. Secondly, a generalised resource management technique known as Total Resource Utilisation Shuffling Technique (TRUST) to tackle the wider issue of resource utilisation and management. The focus for TRUST in this work is on batteries but it could be applied to a wide range of resources, not necessarily in the technology sector. Keywords: Chireix, Class A-G, Doherty, Golomb, OFDM, PAPR, PD

Analysis and Design of a Transmitter for Wireless Communications in CMOS Technology

The number of wireless devices has grown tremendously over the last decade. Great technology improvements and novel transceiver architectures and circuits have enabled an astonishingly expanding set of radio-frequency applications. CMOS technology played a key role in enabling a large-scale diffusion of wireless devices due to its unique advantages in cost and integration. Novel digital-intensive transceivers have taken full advantage of CMOS technology scaling predicted by Moore's law. Die-shrinking has enabled ubiquitous diffusion of low-cost, small form factor and low power wireless devices. However, Radio Frequency (RF) Power Amplifiers (PA) transceiver functionality is historically implemented in a module which is separated from the CMOS core of the transceiver. The PA is traditionally dictating power and battery life of the transceiver, thus justifying its implementation in a tailored technology. By contrast, a fully integrated CMOS transceiver with no external PA would hugely benefit in terms of reduced area and system complexity. In this work, a fully integrated prototype of a Switched-Capacitor Power Amplifier (SCPA) has been implemented in a 28nm CMOS technology. The SCPA provides the functionalities of a PA and of a Radio-Frequency Digital-to-Analog Converter (RF-DAC) in a monolithic CMOS device. The switching output stage of the SCPA enables this circuital topology to reach high efficiencies and offers excellent power handling capabilities. In this work, the properties of the SCPA are analyzed in an extensive and detailed dissertation. Nowadays Wireless Communications operate in a very crowded spectrum, with strict coexistence requirements, thus demanding a strong linearity to the RF-DAC section of the SCPA. A great part of the work of designing a good SCPA is in fact designing a good RF-DAC. To enhance RF-DAC linearity, a precision of the timing of the elements up to the ps range is required. The use of a single core-supply voltage in the whole circuit including the CMOS inverter of the switching output stage enables the use of minimum size devices, improving accuracy and speed in the timing of the elements. The whole circuit operates therefore on low core-supply voltage. Throughout this work, a detailed analysis carefully describes the electromagnetic structures which maximize power and efficiency of low-voltage SCPAs. Due to layout issues subsequent to limited available voltages, however, there is a practical limitation in the maximum achievable power of low-voltage SCPAs. In this work, a Multi-Port Monolithic Power Combiner (PC) is introduced to overcome this limitation and further enhance total achieved system power. The PC sums the power of a collection of SCPAs to a single output, allowing higher output powers at a high efficiency. Benefits, drawbacks and design of SCPA PCs are discussed in this work. The implemented circuit features the combination of four differential SCPAs through a four-way monolithic PC and is simulated to obtain a maximum drain efficiency of 44% at a peak output power of 29dBm on 1.1V supply voltage. Extensive spectrum analysis offers full evaluation of system performances. After exploring state-of-the-art possibilities offered by an advanced 28nm CMOS technology, this work predicts through rigorous theoretical analysis the expected evolution of SCPA performances with the scaling of CMOS Technologies. The encouraging forecast further emphasizes the importance of SCPA circuits for the future of high-performance Wireless Communications

Radio Communications

In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks

Enhancing the energy efficiency of radio base stations

This thesis is concerned with the energy efficiency of cellular networks. It studies the dominant power consumer in future cellular networks, the Long Term Evolution (LTE) radio Base Station (BS), and proposes mechanisms that enhance the BS energy efficiency by reducing its power consumption under target rate constraints. These mechanisms trade spare capacity for power saving. First, the thesis describes how much power individual components of a BS consume and what parameters affect this consumption based on third party experimental data. These individual models are joined into a component power model for an entire BS. The component model is an essential step in analysis but is too complex for many applications. It is therefore abstracted into a much simpler parameterized model to reduce its complexity. The parameterized model is further simplified into an affine model which can be applied in power minimization. Second, Power Control (PC) and Discontinuous Transmission (DTX) are identified as promising power-saving Radio Resource Management (RRM) mechanisms and applied to multi-user downlink transmission. PC reduces the power consumption of the Power Amplifier (PA) and is found to be most effective at high traffic loads. DTX mostly reduces the power consumption of the Baseband (BB) unit while interrupting transmission and is better applied in low traffic loads. Joint optimization of these two techniques is found to enable additional power-saving at medium traffic loads and to be a convex problem which can be solved efficiently. The convex problem is extended to provide a comprehensive power-saving Orthogonal Frequency Division Multiple Access (OFDMA) frame resource scheduler. The proposed scheduler is shown to reduce power consumption by 25-40% in computer simulations, depending on the traffic load. Finally, the thesis investigates the influence of interference on power consumption in a network of multiple power-saving BSs. It discusses three popular alternative distributed uncoordinated methods which align DTX mode between neighbouring BSs. To address drawbacks of these three, a fourth memory-based DTX alignment method is proposed. It decreases power consumption by up to 40% and retransmission probability by around 20%, depending on the traffic load

Satellite Communications

This study is motivated by the need to give the reader a broad view of the developments, key concepts, and technologies related to information society evolution, with a focus on the wireless communications and geoinformation technologies and their role in the environment. Giving perspective, it aims at assisting people active in the industry, the public sector, and Earth science fields as well, by providing a base for their continued work and thinking

Modelling, Dimensioning and Optimization of 5G Communication Networks, Resources and Services

This reprint aims to collect state-of-the-art research contributions that address challenges in the emerging 5G networks design, dimensioning and optimization. Designing, dimensioning and optimization of communication networks resources and services have been an inseparable part of telecom network development. The latter must convey a large volume of traffic, providing service to traffic streams with highly differentiated requirements in terms of bit-rate and service time, required quality of service and quality of experience parameters. Such a communication infrastructure presents many important challenges, such as the study of necessary multi-layer cooperation, new protocols, performance evaluation of different network parts, low layer network design, network management and security issues, and new technologies in general, which will be discussed in this book

Journal of Telecommunications and Information Technology, 2017, nr 4

kwartalni

Signal optimization for Galileo evolution

Global Navigation Satellite System (GNSS) are present in our daily lives. Moreover, new users areemerging with further operation needs involving a constant evolution of the current navigationsystems. In the current framework of Galileo (GNSS European system) and especially within theGalileo E1 Open Service (OS), adding a new acquisition aiding signal could contribute to providehigher resilience at the acquisition phase, as well as to reduce the time to first fix (TTFF).Designing a new GNSS signal is always a trade-off between several performance figures of merit.The most relevant are the position accuracy, the sensitivity and the TTFF. However, if oneconsiders that the signal acquisition phase is the goal to design, the sensitivity and the TTFF havea higher relevance. Considering that, in this thesis it is presented the joint design of a GNSS signaland the message structure to propose a new Galileo 2nd generation signal, which provides ahigher sensitivity in the receiver and reduce the TTFF. Several aspects have been addressed inorder to design a new signal component. Firstly, the spreading modulation definition must considerthe radio frequency compatibility in order to cause acceptable level of interference inside the band.Moreover, the spreading modulation should provide good correlation properties and goodresistance against the multipath in order to enhance the receiver sensitivity and to reduce theTTFF. Secondly, the choice of the new PRN code is also crucial in order to ease the acquisitionphase. A simple model criterion based on a weighted cost function is used to evaluate the PRNcodes performance. This weighted cost function takes into account different figures of merit suchas the autocorrelation, the cross-correlation and the power spectral density. Thirdly, the design ofthe channel coding scheme is always connected with the structure of the message. A joint designbetween the message structure and the channel coding scheme can provide both, reducing theTTFF and an enhancement of the resilience of the decoded data. In this this, a new method to codesign the message structure and the channel coding scheme for the new G2G signal isproposed. This method provides the guideline to design a message structure whose the channelcoding scheme is characterized by the full diversity, the Maximum Distance Separable (MDS) andthe rate compatible properties. The channel coding is essential in order to enhance the datademodulation performance, especially in harsh environments. However, this process can be verysensitive to the correct computation of the decoder input. Significant improvements were obtainedby considering soft inputs channel decoders, through the Log Likelihood Ratio LLRs computation.However, the complete knowledge of the channel state information (CSI) was usually considered,which it is infrequently in real scenarios. In this thesis, we provide new methods to compute LLRlinear approximations, under the jamming and the block fading channels, considering somestatistical CSI. Finally, to transmit a new signal in the same carrier frequency and using the sameHigh Power Amplifier (HPA) generates constraints in the multiplexing design, since a constant orquasi constant envelope is needed in order to decrease the non-linear distortions. Moreover, themultiplexing design should provide high power efficiency to not waste the transmitted satellitepower. Considering the precedent, in this thesis, we evaluate different multiplexing methods,which search to integrate a new binary signal in the Galileo E1 band while enhancing thetransmitted power efficiency. Besides that, even if the work is focused on the Galileo E1, many ofthe concepts and methodologies can be easily extended to any GNSS signa