Load balancing using cell range expansion in LTE advanced heterogeneous networks

The use of heterogeneous networks is on the increase, fueled by consumer demand for more data. The main objective of heterogeneous networks is to increase capacity. They offer solutions for efficient use of spectrum, load balancing and improvement of cell edge coverage amongst others. However, these solutions have inherent challenges such as inter-cell interference and poor mobility management. In heterogeneous networks there is transmit power disparity between macro cell and pico cell tiers, which causes load imbalance between the tiers. Due to the conventional user-cell association strategy, whereby users associate to a base station with the strongest received signal strength, few users associate to small cells compared to macro cells. To counter the effects of transmit power disparity, cell range expansion is used instead of the conventional strategy. The focus of our work is on load balancing using cell range expansion (CRE) and network utility optimization techniques to ensure fair sharing of load in a macro and pico cell LTE Advanced heterogeneous network. The aim is to investigate how to use an adaptive cell range expansion bias to optimize Pico cell coverage for load balancing. Reviewed literature points out several approaches to solve the load balancing problem in heterogeneous networks, which include, cell range expansion and utility function optimization. Then, we use cell range expansion, and logarithmic utility functions to design a load balancing algorithm. In the algorithm, user and base station associations are optimized by adapting CRE bias to pico base station load status. A price update mechanism based on a suboptimal solution of a network utility optimization problem is used to adapt the CRE bias. The price is derived from the load status of each pico base station. The performance of the algorithm was evaluated by means of an LTE MATLAB toolbox. Simulations were conducted according to 3GPP and ITU guidelines for modelling heterogeneous networks and propagation environment respectively. Compared to a static CRE configuration, the algorithm achieved more fairness in load distribution. Further, it achieved a better trade-off between cell edge and cell centre user throughputs. [Please note: this thesis file has been deferred until December 2016

Body bias generator design for ultra-low voltage applications in FDSOI technology

This thesis presents the derivation and validation processes of analytical models describing the dynamic and steady-state behaviors of CC-CP switched capacitor converters. The effects of FDSOI components in the implementation of such circuits is also addressed, studying their impact as compared to ideal models. Finally, the layout of a CMOS CC-CP in 28-nm UTBB-FDSOI technology is designed and tested against predicted functionality

Network Management and Decision Making for 5G Heterogeneous Networks

Heterogeneous networks (HetNets) will form an integral part of future cellular communications. With the proper management of network resources and decisions, the coexistence of small cells with macro base stations will improve coverage, data rate and quality of service for users. This thesis investigates critical issues that will arise in HetNets. The first half of this thesis studies major consequences of the disparity between HetNet tier transmit powers, namely that of interference and load balancing. To reduce the effects of harmful interference to small cell users arising from powerful macro transmissions, we first design a precoding matrix in the form of a generalized inverse, which, unlike conventional precoding methods, allows the base station to target a user specifically to reduce its own interference to that user. Even with a transmit power constraint, the affected user can achieve significant improvement in its interference reduction at the slightly compromise of existing macro users. Next, we study load balancing by showing the benefits of a dynamic biasing function for cell range expansion over a static bias value. Our findings indicate that a dynamic bias is a more intuitive way to prevent small cell overloading, and that associating closest users first is a preferred association order. We conclude our study into load balancing by proposing a new notion of network balance. We describe how network balance is different to user fairness, and subsequently define a new metric called the network balance index which measures the deviation of the actual base station load distribution with the expected load distribution. We show using an algorithm that the network balance index is more useful than fairness in improving sum rate for clustered networks. The second half of this thesis explores more advanced user-centric issues for HetNets. Chapter 5 proposes a user association scheme that achieves high fairness, and considers user association behaviour with network dynamics. In order to reduce the computation needed to re-associate a large network, we study the probabilities that each user will have to switch associations when a user or base station enters or leaves. In the process, we find that a shrinking network has more effect on user association than a growing one. Finally, Chapter 6 extends the conventional idea of HetNets to include device-to-device (D2D) communications. We propose a D2D decision making framework that more suitably selects D2D modes for potential D2D pairs by using a two-stage criteria that leads to fewer incorrect D2D mode selections. Once a suitable D2D mode is selected, we demonstrate how to determine optimal or near-optimal power and resource parameters for each mode in order to maximize sum rate. We present a geometric approach to solving the co-channel power control problem, and closed form expressions where possible for orthogonal frequency allocation. Our comprehensive study validates the potential for D2D integration in future cellular communications. The proposed techniques and insights gained from this thesis aims to illustrate how networks can be better managed and improve their decision making processes in order to successfully serve future users

Stochastic Geometric Analysis of Energy-Efficient Dense Cellular Networks

Dense cellular networks (DenseNets) are fast becoming a reality with the large scale deployment of base stations aimed at meeting the explosive data traffic demand. In legacy systems, however, this comes at the cost of higher network interference and energy consumption. In order to support network densification in a sustainable manner, the system behavior should be made “load-proportional” thus allowing certain portions of the network to activate on-demand. In this paper, we develop an analytical framework using tools from stochastic geometry theory for the performance analysis of DenseNets where load-awareness is explicitly embedded in the design. The proposed model leverages on a flexible cellular network architecture where there is a complete separation of the data and signaling communications functionalities. Using this stochastic geometric framework, we identify the most energy-efficient deployment solution for meeting certain minimum service criteria and analyze the corresponding power savings through dynamic sleep modes. According to state-of-the-art system parameters, a homogeneous pico deployment for the data plane with a separate layer of signaling macro-cells is revealed to be the most energy-efficient solution in future dense urban environments

Interrelations between advanced processing techniques, integrated circuits, materials development and analysis

Interrelations between advanced processing techniques, integrated circuits, laser radiation, and microcircuit interconnection

Power-efficient current-mode analog circuits for highly integrated ultra low power wireless transceivers

In this thesis, current-mode low-voltage and low-power techniques have been applied to implement novel analog circuits for zero-IF receiver backend design, focusing on amplification, filtering and detection stages. The structure of the thesis follows a bottom-up scheme: basic techniques at device level for low voltage low power operation are proposed in the first place, followed by novel circuit topologies at cell level, and finally the achievement of new designs at system level. At device level the main contribution of this work is the employment of Floating-Gate (FG) and Quasi-Floating-Gate (QFG) transistors in order to reduce the power consumption. New current-mode basic topologies are proposed at cell level: current mirrors and current conveyors. Different topologies for low-power or high performance operation are shown, being these circuits the base for the system level designs. At system level, novel current-mode amplification, filtering and detection stages using the former mentioned basic cells are proposed. The presented current-mode filter makes use of companding techniques to achieve high dynamic range and very low power consumption with for a very wide tuning range. The amplification stage avoids gain bandwidth product achieving a constant bandwidth for different gain configurations using a non-linear active feedback network, which also makes possible to tune the bandwidth. Finally, the proposed current zero-crossing detector represents a very power efficient mixed signal detector for phase modulations. All these designs contribute to the design of very low power compact Zero-IF wireless receivers. The proposed circuits have been fabricated using a 0.5μm double-poly n-well CMOS technology, and the corresponding measurement results are provided and analyzed to validate their operation. On top of that, theoretical analysis has been done to fully explore the potential of the resulting circuits and systems in the scenario of low-power low-voltage applications.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007

The ArgoNeuT Detector in the NuMI Low-Energy beam line at Fermilab

The ArgoNeuT liquid argon time projection chamber has collected thousands of neutrino and antineutrino events during an extended run period in the NuMI beam-line at Fermilab. This paper focuses on the main aspects of the detector layout and related technical features, including the cryogenic equipment, time projection chamber, read-out electronics, and off-line data treatment. The detector commissioning phase, physics run, and first neutrino event displays are also reported. The characterization of the main working parameters of the detector during data-taking, the ionization electron drift velocity and lifetime in liquid argon, as obtained from through-going muon data complete the present report.Comment: 43 pages, 27 figures, 5 tables - update referenc