Energy efficiency perspectives of femtocells in internet of things : recent advances and challenges

Energy efficiency is a growing concern in every aspect of the technology. Apart from maintaining profitability, energy efficiency means a decrease in the overall environmental effects, which is a serious concern in today's world. Using a femtocell in Internet of Things (IoT) can boost energy efficiency. To illustrate, femtocells can be used in smart homes, which is a subpart of the smart grid, as a communication mechanism in order to manage energy efficiency. Moreover, femtocells can be used in many IoT applications in order to provide communication. However, it is important to evaluate the energy efficiency of femtocells. This paper investigates recent advances and challenges in the energy efficiency of the femtocell in IoT. First, we introduce the idea of femtocells in the context of IoT and their role in IoT applications. Next, we describe prominent performance metrics in order to understand how the energy efficiency is evaluated. Then, we elucidate how energy can be modeled in terms of femtocell and provide some models from the literature. Since femtocells are used in heterogeneous networks to manage energy efficiency, we also express some energy efficiency schemes for deployment. The factors that affect the energy usage of a femtocell base station are discussed and then the power consumption of user equipment under femtocell coverage is mentioned. Finally, we highlight prominent open research issues and challenges. © 2013 IEEE

Learning and Reasoning Strategies for User Association in Ultra-dense Small Cell Vehicular Networks

Recent vehicular ad hoc networks research has been focusing on providing intelligent transportation services by employing information and communication technologies on road transport. It has been understood that advanced demands such as reliable connectivity, high user throughput, and ultra-low latency required by these services cannot be met using traditional communication technologies. Consequently, this thesis reports on the application of artificial intelligence to user association as a technology enabler in ultra-dense small cell vehicular networks. In particular, the work focuses on mitigating mobility-related concerns and networking issues at different mobility levels by employing diverse heuristic as well as reinforcement learning (RL) methods. Firstly, driven by rapid fluctuations in the network topology and the radio environment, a conventional, three-step sequence user association policy is designed to highlight and explore the impact of vehicle speed and different performance indicators on network quality of service (QoS) and user experience. Secondly, inspired by control-theoretic models and dynamic programming, a real-time controlled feedback user association approach is proposed. The algorithm adapts to the changing vehicular environment by employing derived network performance information as a heuristic, resulting in improved network performance. Thirdly, a sequence of novel RL based user association algorithms are developed that employ variable learning rate, variable rewards function and adaptation of the control feedback framework to improve the initial and steady-state learning performance. Furthermore, to accelerate the learning process and enhance the adaptability and robustness of the developed RL algorithms, heuristically accelerated RL and case-based transfer learning methods are employed. A comprehensive, two-tier, event-based, system level simulator which is an integration of a dynamic vehicular network, a highway, and an ultra-dense small cell network is developed. The model has enabled the analysis of user mobility effects on the network performance across different mobility levels as well as served as a firm foundation for the evaluation of the empirical properties of the investigated approaches

Spectral and Energy Efficiency in Cellular Mobile Radio Access Networks

Driven by the widespread use of smartphones and the release of a wide range of online packet data services, an unprecedented growth in the mobile data usage has been observed over the last decade. Network operators recently realised that the traditional approach of deploying more macrocells could not cope with this continuous growth in mobile data traffic and if no actions are taken, the energy demand to run the networks, which are able to support such traffic volumes risks to become unmanageable. In this context, comprehensive investigations of different cellular network deployments, and various algorithms have been evaluated and compared against each other in this thesis, to determine the best deployment options which are able to deliver the required capacity at a minimum level of energy consumption. A new scalable base station power consumption model was proposed and a joint evaluation framework for the relative improvements in throughput, energy consumption,and energy efficiency is adopted to avoid the inherent ambiguity of using only the bit/J energy efficiency metric. This framework was applied to many cellular network cases studies including macro only, small cell only and heterogeneous networks to show that pure small cell deployments outperform the macro and heterogeneous networks in terms of the energy consumption even if the backhaul power consumption is included in the analysis. Interestingly, picocell only deployments can attain up to 3 times increase in the throughput and 2.27 times reduction in the energy consumed when compared with macro only RANs at high target capacities, while it offers 2 times more throughput and reduces the energy consumption by 12% when compared with the macro/pico HetNet deployments. Further investigations have focused on improving the macrocell RAN by adding more sectors and more antennas. Importantly, the results have shown that adding small cells to the macrocell RAN is more energy efficient than adding more sectors even if adaptive sectorisation techniques are employed. While dimensioning the network by using MIMO base stations results in less consumed energy than using SISO base stations. The impact of traffic offloading to small cell, sleep mode, and inter-cell interference coordination techniques on the throughput and energy consumption in dense heterogeneous network deployments have been investigated. Significant improvements in the throughput and energy efficiency in bit/J were observed. However, a decrease in the energy consumption is obtained only in heterogeneous networks with small cells deployed to service clusters of users. Finally, the same framework is used to evaluate the throughput and energy consumption of massive MIMO deployments to show the superiority of massive MIMOs versus macrocell RANs, small cell deployments and heterogeneous networks in terms of achieving the target capacity with a minimum level of energy consumption. 1.6 times reduction in the energy consumption is achieved by massive MIMOs when compared with picocell only RAN at the same target capacity and when the backhaul power consumption is included in the analysis

Contributing to Second Harmonic Manipulated Continuum Mode Power Amplifiers and On-Chip Flux Concentrators

The current cellular network consumes a staggering 100 TWh of energy every year. In the coming years, millions of devices will be added to the existing network to realize the Internet of Things (IoT), further increasing its power consumption. An RF power amplifier typically consumes a large proportion of the DC power in a wireless transceiver, improving its efficiency has the largest impact on the overall system. Additionally, amplifiers need to demonstrate high linearity and bandwidth to adhere to constraints imposed by wireless standards and to reduce the number of amplifiers required as an amplifier with a broader bandwidth can potentially replace several narrowband amplifiers. A typical approach to improve efficiency is to present an appropriate load at the harmonics generated by the transistor. Recently proposed continuous modes based on harmonic manipulation, such as class B/J continuum, continuous class F (CCF) and continuous class F-1 (CCF-1), have shown the capability of achieving counteracting requirements viz., high efficiency, high linearity, and broad bandwidth (with a fractional bandwidth greater than 30%). In these classes of amplifiers, the second harmonic is manipulated by placing a reactive second harmonic load and the reactive component of the fundamental load is adjusted while keeping a fixed resistive component of the fundamental load. The first contribution of this work is to investigate the reason for amplifiers designed in classes B/J continuum and CCF to achieve high efficiency at back-off and 1dB compression. In this thesis, we demonstrate that the variation of the phase of the current through the non-linear intrinsic capacitances due to the variation of the phase in the continuum of drain voltage waveforms in Class B/J/J* continuum leads to either a reduction or enhancement of intrinsic drain current. Consequently, a subset of voltage waveforms of the class B/J/J* continuum can be used to design amplifiers with higher P1dB, and efficiency at P1dB than in Class B. A simple choice of this subset is demonstrated with a 2.6GHz Class B/J/J* amplifier, achieving a P1dB of 38.1dBm and PAE at P1dB of 54.7%, the highest output power and efficiency at P1dB amongst narrowband linear amplifiers using the CGH40010 reported to date, at a comparable peak PAE of 72%. Secondly, we propose a new formulation for high-efficiency modes of power amplifiers in which both the in-phase and out-of-phase components of the second harmonic of the current are varied, in addition to the second harmonic component of the voltage. A reduction of the in-phase component of the second harmonic of current allows reduction of the phase difference between the voltage and current waveforms, thereby increasing the power factor and efficiency. Our proposed waveforms offer a continuous design space between class B/J continuum and continuous F-1 achieving an efficiency of up to 91% in theory, but over a wider set of load impedances than continuous class F-1. These waveforms require a short at third and higher harmonic impedances, which are easier to achieve at a higher frequency. The load impedances at the second harmonic are reactive and can be of any value between -j∞ and j∞, easing the amplifier design. A trade-off between linearity and efficiency exists in the newly proposed broadband design space, but we demonstrate inherent broadband capability. The fabricated narrowband amplifier using a GaN HEMT CGH40010F demonstrates 75.9% PAE and 42.2 dBm output power at 2.6 GHz, demonstrating a comparable frequency weighted efficiency for this device to that reported in the literature. IoT devices may be deployed in critical applications such as radar or 5G transceivers of an autonomous vehicle and hence need to operate free of failure. Monitoring the drain current of the RF GaN MMIC would allow to optimize the device performance and protect it from surges in its supply current. Galvanic current sensors rely on the magnetic field generated by the current as a non-invasive method of current sensing. In this thesis, our third major contribution is a planar on-chip magnetic flux concentrator, is enhance the magnetic field at the current sensor, thereby improving the current detection capability of a current sensor. Our layout utilizes a discontinuity in a magnetic via, resulting in penetration of the magnetic field into the substrate. The proposed concentrator has a magnetic gain x1.8 in comparison to air. The permeability of the magnetic core required is 500, much lower than that reported in off-chip concentrators, resulting in a significant easing of the specifications of the material properties of the core. Additionally, we explore a novel three-dimensional spiral-shaped magnetic flux concentrator. It is predicted via simulations that this geometry becomes a necessity to enhance the magnetic field for increased form factor as the magnetic field from a single planar concentrator deteriorates as its size increases

Techniques for nonlinear distortion suppression in radio over fiber communication systems

Radio over fiber (RoF) is a promising technology that will indisputably compete as a viable solution for future wireless, cellular and broadband networks. RoF, when combined with dense wavelength division multiplexing (DWDM), such as SONET/SDH, it can become a complete flexible and cost effective solution to the global telecommunication network, where asynchronous and synchronous communications may be efficiently supported. Subcarrier modulation (SCM) is utilized to modulate a RF signal on light, which in turn will be transmitted by fiber. Unfortunately, the transmission in most cases may become corrupted by nonlinear distortion that is induced by the nonlinear response of the optical transmitter, optical receiver and chromatic dispersion of the single mode fiber (SMF). The nonlinear distortion degrades the receiver sensitivity, which leads to a poor bit error rate (BER) and spurious free dynamic range (SFDR). Ultimately, this will increase RoF system costs and render it impractical. The objective of this thesis is to develop linearization methods that reduce the nonlinear distortion, increase receiver sensitivity and increase SFDR. The designs should also address the entire RoF system by combating the optical power fading issue that will be discussed in Chapter 2 without significantly adding great expense and complexity to the RoF system. Four optical linearization methods are proposed and shown through extensive simulation and/or experimentation to outperform similar existing linearization systems described in literature. The proposed single wavelength balanced system is shown to improve the suppression of 2nd order distortion over the dual wavelength balanced system, thereby leading to greater improvement in receiver sensitivity and BER. Furthermore, the design also suppresses relative intensity noise (RIN). The proposed tunable fiber Bragg grating (FBG) balanced system is capable of suppressing both 2 nd and 3 rd order distortions despite which RF carrier that is used. Furthermore, it was shown to outperform the conventional RoF system in terms of receiver sensitivity and BER. The proposed asymmetric Mach-Zehnder modulator (MZM) has been shown to generate optical single sideband (OSSB) transmissions and outperform the dual-parallel modulator, by improving 3rd order intermodulation distortion (3IMD) suppression and increasing SFDR. The final proposed linearization method is the mixed-polarization MZM, where OSSB is also generated and outperforms the conventional OSSB RoF system in terms of 3IMD suppression and SFDR. Furthermore, close form expressions for SFDR are developed for the final two designs, which is crucial in study of their stability and performance

Energy efficiency heterogeneous wireless communication network with QoS support

The overarching goal of this thesis is to investigate network architectures, and find the trade-off between low overall energy use and maintaining the level of quality of service (QoS), or even improve it. The ubiquitous wireless communications environment supports the exploration of different network architectures and techniques, the so-called heterogeneous network. Two kinds of heterogeneous architectures are considered: a combined cellular and femtocell network and a combined cellular, femtocell and Wireless Local Area Network(WLAN) network. This thesis concludes that the investigated heterogeneous networks can significantly reduce the overall power consumption, depending on the uptake of femtocells and WLANs. Also, QoS remains high when the power consumption drops. The main energy saving is from reducing the macrocell base station embodied and operational energy. When QoS is evaluated based on the combined cellular and femtocell architecture, it is suggested that use of resource scheduling for femtocells within the macrocell is crucial since femtocell performance is affected significantly by interference when installed in a co-channel system. Additionally, the femtocell transmission power mode is investigated using either variable power level or a fixed power level. To achieve both energy efficiency and QoS, the choice of system configurations should change according to the density of the femtocell deployment. When combining deployment of femtocells with WLANs, more users are able to experience a higher QoS. Due to increasing of data traffic and smartphone usage in the future, WLANs are more important for offloading data from the macrocell, reducing power consumption and also increasing the bandwidth. The localised heterogeneous network is a promising technique for achieving power efficiency and a high QoS system

Impulse radio ultra wideband over fiber techniques for broadband in-building network applications

In recent years, the demand for high bandwidth and mobility from the end users has been continuously growing. To satisfy this demand, broadband communication technologies that combined the benefit of both wired and wireless are considered as vital solutions. These hybrid optical wireless solutions enable multi-Gbit/s transmission as well as adequate flexibility in terms of mobility. Optical fiber is the ideal medium for such hybrid solution due its signal transparency and wide bandwidth. On the other hand, ultra wideband(UWB) radio over optical fiber technology is considered to be one of the key promising technologies for broadband communication and sensor network applications. The growing interest for UWB is mainly due to its numerous attractive features, such as low power spectral density, tolerance to multipath fading, low probability of interception, coexistence with other wireless services and capability of providing cost-effective > 1 Gb/s transmission. The main idea of UWB over fiber is to deliver UWB radio signals over optical channels, where the optical part serves as a backbone communication infrastructure to carry the UWB signal with a bandwidth of several GHz. This enables multiple novel applications such as: range extension of high speed wireless personal area networks (WPANs), low cost distributed antenna systems, secure and intelligent networks, or delivering broadband services to remote areas. In particular, this thesis deals with novel concepts on shaping and generation of IR-UWB pulses, theoretical and experimental demonstrations over different fiber types, routing of integrated wired/wireless IR-UWB services and effect of fiber types on ranging/localization of IR-UWB-over-fiber systems. Accordingly, this thesis investigates techniques for delivery of high data rate wireless services using impulse radio ultra wideband (IR-UWB) over fiber technology for both access and in-building network applications. To effectively utilize the emission mask imposed for UWB technologies by the Federal Communications Commission(FCC), novel pulse shaping techniques have been investigated and experimentally demonstrated. Comparison of the proposed pulses with conventional ones in terms of the compliance to the FCC-mask requirements, spectral power efficiencies and wireless coverage has been theoretically studied. Simple and efficient optical generation of the new pulse has been experimentally demonstrated. Furthermore, performance evaluation of 2 Gb/s transmission of IR-UWB over different types of fiber such as 25 km silica single-mode, 4.4 km silica multi-mode and 100 m plastic heavily-multi-mode fiber have been performed. To improve the functionalities of in-building networks for the delivery of wireless services; techniques that provide flexibility in terms of dynamic capacity allocation have been investigated. By employing wavelength conversion based on cross-gain modulation in optical semiconductor amplifiers(SOA), routing of three optical channels of IR-UWB over fiber system has been experimentally realized. To reduce the cost of the overall system and share the optical infrastructure, an integrated testbed for wired baseband data and wireless IR-UWB over 1 km SMF-28 fiber has been developed. Accordingly, 1.25 Gb/s wired baseband and 2 Gb/s wireless IR-UWB data have been successfully transmitted over the testbed. Furthermore, to improve the network flexibility, routing of both wired baseband and wireless signals has been demonstrated. Additionally, the ranging and localization capability of IR-UWB over fiber for in-door wireless picocells have been investigated. The effect of different fiber types (4 km SMF, 4.4 km GI-MMF and 100 m PF GI-POF) on the accuracy of the range estimation using time-of-arrival (ToA) ranging technique has been studied. A high accuracy in terms of cm level was achieved due to the combined effect of high bandwidth IR-UWB pulses, short reach fiber and low chromatic dispersion at 1300nm wavelength. Furthermore, ranging/ localization using IR-UWB over fiber system provides additional benefit of centralizing complex processing algorithms, simplifying radio access points, relaxing synchronization requirement, enabling energy-efficient and efficient traffic management networks. All the concepts, design and system experiments presented in this thesis underline the strong potential of IR-UWB for over optical fiber(silica and plastic) techniques for future smart, capacity and energy-efficient broadband in-building network applications

Towards UAV Assisted 5G Public Safety Network

Ensuring ubiquitous mission-critical public safety communications (PSC) to all the first responders in the public safety network is crucial at an emergency site. The first responders heavily rely on mission-critical PSC to save lives, property, and national infrastructure during a natural or human-made emergency. The recent advancements in LTE/LTE-Advanced/5G mobile technologies supported by unmanned aerial vehicles (UAV) have great potential to revolutionize PSC. However, limited spectrum allocation for LTE-based PSC demands improved channel capacity and spectral efficiency. An additional challenge in designing an LTE-based PSC network is achieving at least 95% coverage of the geographical area and human population with broadband rates. The coverage requirement and efficient spectrum use in the PSC network can be realized through the dense deployment of small cells (both terrestrial and aerial). However, there are several challenges with the dense deployment of small cells in an air-ground heterogeneous network (AG-HetNet). The main challenges which are addressed in this research work are integrating UAVs as both aerial user and aerial base-stations, mitigating inter-cell interference, capacity and coverage enhancements, and optimizing deployment locations of aerial base-stations. First, LTE signals were investigated using NS-3 simulation and software-defined radio experiment to gain knowledge on the quality of service experienced by the user equipment (UE). Using this understanding, a two-tier LTE-Advanced AG-HetNet with macro base-stations and unmanned aerial base-stations (UABS) is designed, while considering time-domain inter-cell interference coordination techniques. We maximize the capacity of this AG-HetNet in case of a damaged PSC infrastructure by jointly optimizing the inter-cell interference parameters and UABS locations using a meta-heuristic genetic algorithm (GA) and the brute-force technique. Finally, considering the latest specifications in 3GPP, a more realistic three-tier LTE-Advanced AG-HetNet is proposed with macro base-stations, pico base-stations, and ground UEs as terrestrial nodes and UABS and aerial UEs as aerial nodes. Using meta-heuristic techniques such as GA and elitist harmony search algorithm based on the GA, the critical network elements such as energy efficiency, inter-cell interference parameters, and UABS locations are all jointly optimized to maximize the capacity and coverage of the AG-HetNet