Radio Resource Management in Heterogeneous Cellular Networks

Heterogeneous cellular networks (HetNets) have been considered as one of enabling technologies not only to increase the cell coverage and capacity, but to improve the user experience. In this dissertation, we address two research challenges in HetNets: one is the cross-tier interference problem where cell range expansion (CRE) is applied for user offloading in cell association so that pico mobile stations located in expanded range (ER-PMSs), which are connected to macrocells unless CRE is enabled, are severely interfered. The other is the load-aware cell association which tries to overcome the drawback of the received signal strength-based cell association including CRE, i.e., the degradation of network performance by user load imbalance. In the first part, we present the frequency-domain transmit power reduction scheme for the cross-tier interference mitigation. Inspired by the fact that a macrocell accommodates more users than its underlaid picocells, we focus on minimizing the macrocell's performance degradation while improving the throughput of ER-PMSs by the transmit power reduction. Due to the discreteness of frequency resource block scheduling, we also propose a greedy-based heuristic algorithm to solve the binary integer programming problem. In the following part, we present a different approach for the cross-tier interference mitigation, which is the time-domain transmit power nulling scheme utilizing the almost blank subframes (ABSs) in 3GPP standards. We turn our attention to a network-wide performance enhancement through configuring a certain number of ABSs while improving the performance of ER-PMSs as in the first part. A new scheduling policy for pico mobile stations is proposed and the optimal ER-PMS scheduling onto ABSs/non-ABSs is solved by decomposing the problem into multiple independent problems for pico base stations. In the last part, we study the load-aware cell association problem. Due to the combinatorial nature of the cell association problem and the cross-tier interference between macrocells and picocells, we propose an online heuristic algorithm where the cell association and the number of ABSs for cross-tier interference mitigation are jointly optimized. Through approximation of the required condition for load balancing and ABS control from the network-wide utility point of view, the proposed online algorithm not only requires simple feedback messages, but also be applicable to any state of cell association/ABSs in HetNets

Millimeter wave picocellular networks: capacity analysis and system design

The explosive growth in demand for wireless mobile data, driven by the proliferationof ever more sophisticated handhelds creating and consuming rich multimedia, calls fororders of magnitude increase in the capacity of cellular data networks. Millimeter wavecommunication from picocellular base stations to mobile devices is a particularly promisingapproach for meeting this challenge because of two reasons. First, there is a largeamount of available spectrum, enabling channel bandwidths of the order of Gigahertz(GHz) which are 1-2 orders of magnitude higher than those in existing WiFi and cellularsystems at lower carrier frequencies. Second, the small carrier wavelength enables therealization of highly directive steerable arrays with a large number of antenna elements,in compact form factors, thus significantly enhancing spatial reuse. Hence, we propose toemploy the 60 GHz unlicensed band for basestation to mobile communication in outdoorpicocells.We first investigate the basic feasibility of such networks, showing that 60GHz linksare indeed viable for outdoor applications. For this purpose, we provided link budgetcalculations along with preliminary simulations which show that despite the commonconcerns about higher oxygen absorption and sensitivity to movement and blockage,picocloud architecture provides availability rate of more than 99%.Next, we explore the idea of increasing spatial reuse by shrinking picocells hopingthat interference is no longer the bottleneck given the highly directive antenna arrays atthis band. Our goal is to estimate the achievable capacity for small picocells along an urban canyon. We consider basestations with multiple faces or sectors, each with one or more antenna arrays. Each such array, termed subarray can employ Radio Frequency(RF) beamforming to communicate with one mobile user at a time. We first focus oncharacterization and modeling the inter-cell interference for one subarray on each face.Our analysis provides a strong indication of very large capacity (in the order of Tbps/km)with a few GHz of bandwidth.Following this, we explore the impact of adding multiple subarrays per face. This leadsto intra-cell interference as well as additional inter-cell interference. While the effect ofadditional inter-cell interference can be quantified within our previous framework, intracellinterference has inherently different features that call for new approaches for analysisand design. We propose a cross-layer approach to suppress the intra-cell interference intwo stages: (a) Physical layer (PHY-layer) method which mitigates interference by jointprecoding and power adaptation and (b) Medium Access Control layer (MAC-layer)method which manages the residual interference by optimizing resource allocation. Wethen estimate the capacity gain over conventional LTE cellular networks and establishthat 1000-fold capacity increase is indeed feasible via mm-wave picocellular networks.Lastly, we examine fundamental signal processing challenges associated with channelestimation and tracking for large arrays, placed within the context of system designfor a mm-wave picocellular network. Maintainance of highly directive links in the faceof blockage and mobility requires accurate estimation of the spatial channels betweenbasestation and mobile users. Here we develop the analytical framework for compressivechannel estimation and tracking. We also address the system level design discussinglink budget, overhead, and inter-cell beacon interference. Simulation results demonstratethat our compressive scheme is able to resolve mm-wave spatial channels with a relativelysmall number of compressive measurements

Stochastic Geometry Based Analysis of Capacity, Mobility and Energy Efficiency for Dense Heterogeneous Networks

In recent years, the increase in the population of mobile users and the advances in computational capabilities of mobile devices have led to an exponentially increasing traffic load on the wireless networks. This trend is foreseen to continue in the future due to the emerging applications such as cellular Internet of things (IoT) and machine type communications (MTC). Since the spectrum resources are limited, the only promising way to keep pace with the future demand is through aggressive spatial reuse of the available spectrum which can be realized in the networks through dense deployment of small cells. There are many challenges associated with such densely deployed heterogeneous networks (HetNets). The main challenges which are considered in this research work are capacity enhancement, velocity estimation of mobile users, and energy efficiency enhancement. We consider different approaches for capacity enhancement of the network. In the first approach, using stochastic geometry we theoretically analyze time domain inter-cell interference coordination techniques in a two-tier HetNet and optimize the parameters to maximize the capacity of the network. In the second approach, we consider optimization of the locations of aerial bases stations carried by the unmanned aerial vehicles (UAVs) to enhance the capacity of the network for public safety and emergency communications, in case of damaged network infrastructure. In the third approach, we introduce a subsidization scheme for the service providers through which the network capacity can be improved by using regulatory power of the government. Finally, we consider the approach of device-to-device communications and multi-hop transmissions for enhancing the capacity of a network. Velocity estimation of high speed mobile users is important for effective mobility management in densely deployed small cell networks. In this research, we introduce two novel methods for the velocity estimation of mobile users: handover-count based velocity estimation, and sojourn time based velocity estimation. Using the tools from stochastic geometry and estimation theory, we theoretically analyze the accuracy of the two velocity estimation methods through Cramer-Rao lower bounds (CRLBs). With the dense deployment of small cells, energy efficiency becomes crucial for the sustained operation of wireless networks. In this research, we jointly study the energy efficiency and the spectral efficiency in a two-tier HetNet. We optimize the parameters of inter-cell interference coordination technique and study the trade-offs between the energy efficiency and spectral efficiency of the HetNet

Resource allocation in future green wireless networks : applications and challenges

Over the past few years, green radio communication has been an emerging topic since the footprint from the Information and Communication Technologies (ICT) is predicted to increase 7.3% annually and then exceed 14% of the global footprint by 2040. Moreover, the explosive progress of ICT, e.g., the fifth generation (5G) networks, has resulted in expectations of achieving 10-fold longer device battery lifetime, and 1000-fold higher global mobile data traffic over the fourth generation (4G) networks. Therefore, the demands for increasing the data rate and the lifetime while reducing the footprint in the next-generation wireless networks call for more efficient utilization of energy and other resources. To overcome this challenge, the concepts of small-cell, energy harvesting, and wireless information and power transfer networks can be evaluated as promising solutions for re-greening the world. In this dissertation, the technical contributions in terms of saving economical cost, protecting the environment, and guaranteeing human health are provided. More specifically, novel communication scenarios are proposed to minimize energy consumption and hence save economic costs. Further, energy harvesting (EH) techniques are applied to exploit available green resources in order to reduce carbon footprint and then protect the environment. In locations where implemented user devices might not harvest energy directly from natural resources, base stations could harvest-and-store green energy and then use such energy to power the devices wirelessly. However, wireless power transfer (WPT) techniques should be used in a wise manner to avoid electromagnetic pollution and then guarantee human health. To achieve all these aspects simultaneously, this thesis proposes promising schemes to optimally manage and allocate resources in future networks. Given this direction, in the first part, Chapter 2 mainly studies a transmission power minimization scheme for a two-tier heterogeneous network (HetNet) over frequency selective fading channels. In addition, the HetNet backhaul connection is unable to support a sufficient throughput for signaling an information exchange between two tiers. A novel idea is introduced in which the time reversal (TR) beamforming technique is used at a femtocell while zero-forcing-based beamforming is deployed at a macrocell. Thus, a downlink power minimizationscheme is proposed, and optimal closed-form solutions are provided. In the second part, Chapters 3, 4, and 5 concentrate on EH and wireless information and power transfer (WIPT) using RF signals. More specifically, Chapter 3 presents an overview of the recent progress in green radio communications and discusses potential technologies for some emerging topics on the platforms of EH and WPT. Chapter 4 develops a new integrated information and energy receiver architecture based on the direct use of alternating current (AC) for computation. It is shown that the proposed approach enhances not only the computational ability but also the energy efficiency over the conventional one. Furthermore, Chapter 5 proposes a novel resource allocation scheme in simultaneous wireless information and power transfer (SWIPT) networks where three crucial issues: power-efficient improvement, user-fairness guarantee, and non-ideal channel reciprocity effect mitigation, are jointly addressed. Hence, novel methods to derive optimal and suboptimal solutions are provided. In the third part, Chapters 6, 7, and 8 focus on simultaneous lightwave information and power transfer (SLIPT) for indoor applications, as a complementary technology to RF SWIPT. In this research, Chapter 6 investigates a hybrid RF/visible light communication (VLC) ultrasmall cell network where optical transmitters deliver information and power using the visible light, whereas an RF access point works as a complementary power transfer system. Thus, a novel resource allocation scheme exploiting RF and visible light for power transfer is devised. Chapter 7 proposes the use of lightwave power transfer to enable future sustainable Federated Learning (FL)-based wireless networks. FL is a new data privacy protection technique for training shared machine learning models in a distributed approach. However, the involvement of energy-constrained mobile devices in the construction of the shared learning models may significantly reduce their lifetime. The proposed approach can support the FL-based wireless network to overcome the issue of limited energy at mobile devices. Chapter 8 introduces a novel framework for collaborative RF and lightwave power transfer for wireless communication networks. The constraints on the transmission power set by safety regulations result in significant challenges to enhance the power transfer performance. Thus, the study of technologies complementary to conventional RF SWIPT is essential. To cope with this isue, this chapter proposes a novel collaborative RF and lightwave power transfer technology for next-generation wireless networks

Radio over fiber enabling PON fronthaul in a two-tiered cloud

Avec l’avènement des objets connectés, la bande passante nécessaire dépasse la capacité des interconnections électriques et interface sans fils dans les réseaux d’accès mais aussi dans les réseaux coeurs. Des systèmes photoniques haute capacité situés dans les réseaux d’accès utilisant la technologie radio sur fibre systèmes ont été proposés comme solution dans les réseaux sans fil de 5e générations. Afin de maximiser l’utilisation des ressources des serveurs et des ressources réseau, le cloud computing et des services de stockage sont en cours de déploiement. De cette manière, les ressources centralisées pourraient être diffusées de façon dynamique comme l’utilisateur final le souhaite. Chaque échange nécessitant une synchronisation entre le serveur et son infrastructure, une couche physique optique permet au cloud de supporter la virtualisation des réseaux et de les définir de façon logicielle. Les amplificateurs à semi-conducteurs réflectifs (RSOA) sont une technologie clé au niveau des ONU(unité de communications optiques) dans les réseaux d’accès passif (PON) à fibres. Nous examinons ici la possibilité d’utiliser un RSOA et la technologie radio sur fibre pour transporter des signaux sans fil ainsi qu’un signal numérique sur un PON. La radio sur fibres peut être facilement réalisée grâce à l’insensibilité a la longueur d’onde du RSOA. Le choix de la longueur d’onde pour la couche physique est cependant choisi dans les couches 2/3 du modèle OSI. Les interactions entre la couche physique et la commutation de réseaux peuvent être faites par l’ajout d’un contrôleur SDN pour inclure des gestionnaires de couches optiques. La virtualisation réseau pourrait ainsi bénéficier d’une couche optique flexible grâce des ressources réseau dynamique et adaptée. Dans ce mémoire, nous étudions un système disposant d’une couche physique optique basé sur un RSOA. Celle-ci nous permet de façon simultanée un envoi de signaux sans fil et le transport de signaux numérique au format modulation tout ou rien (OOK) dans un système WDM(multiplexage en longueur d’onde)-PON. Le RSOA a été caractérisé pour montrer sa capacité à gérer une plage dynamique élevée du signal sans fil analogique. Ensuite, les signaux RF et IF du système de fibres sont comparés avec ses avantages et ses inconvénients. Finalement, nous réalisons de façon expérimentale une liaison point à point WDM utilisant la transmission en duplex intégral d’un signal wifi analogique ainsi qu’un signal descendant au format OOK. En introduisant deux mélangeurs RF dans la liaison montante, nous avons résolu le problème d’incompatibilité avec le système sans fil basé sur le TDD (multiplexage en temps duplexé).With the advent of IoT (internet of things) bandwidth requirements triggered by aggregated wireless connections have exceeded the fundamental limitation of copper and microwave based wireless backhaul and fronthaul networks. High capacity photonic fronthaul systems employing radio over fiber technology has been proposed as the ultimate solution for 5G wireless system. To maximize utilization of server and network resources, cloud computing and storage based services are being deployed. In this manner, centralized resources could be dynamically streamed to the end user as requested. Since on demand resource provision requires the orchestration between the server and network infrastructure, a smart photonic (physical layer)PHY enabled cloud is foreseen to support network virtualization and software defined network. RSOAs (Reflective Semiconductor Optical Amplifier) are being investigated as key enablers of the colorless ONU(Optical Network Unit) solution in PON (Passive Optical Network). We examine the use of an RSOA in radio over fiber systems to transport wireless signals over a PON simultaneously with digital data. Radio over fiber systems with flexible wavelength allocation could be achieved thanks to the colorless operation of the RSOA and wavelength reuse technique. The wavelength flexibility in optical PHY are inline with the paradigm of software defined network (SDN) in OSI layer 2/3. The orchestration between optical PHY and network switching fabric could be realized by extending the SDN controller to include optical layer handlers. Network virtualization could also benefit from the flexible optical PHY through dynamic and tailored optical network resource provision. In this thesis, we investigate an optical PHY system based on RSOA enabling both analog wireless signal and digital On-Off Keying (OOK) transportation within WDM (Wavelength Division Multiplexing) PON architecture. The RSOA has been characterized to show its potential ability to handle high dynamic range analog wireless signal. Then the RF and IF radio over fiber scheme is compared with its pros and cons. Finally we perform the experiment to shown a point to point WDM link with full duplex transmission of analog WiFi signal with downlink OOK signal. By introducing two RF mixer in the uplink, we have solved the incompatible problem with TDD (Time Division Duplex) based wireless system

Evaluation of Alternative Telecommunication Technologies for the Karoo Central Astronomy Advantage Area

Cite: Academy of Science of South Africa (ASSAf), (2021). Evaluation of Alternative Telecommunication Technologies for the Karoo Central Astronomy Advantage Area. [Online] Available at: DOI http://dx.doi.org/10.17159/assaf.2021/0073The National Research Foundation (NRF) requested the Academy of Science of South Africa (ASSAf), on behalf of South African Radio Astronomy Observatory (SARAO) and the Square Kilometre Array (SKA), to undertake an independent and objective evaluation of potential alternative telecommunication technologies for the areas of the Karoo Central Astronomy Advantage Areas (KCAAA). The study encompasses regulatory, public sphere, and technical dimensions to explore options for maintaining the functionality of the telescope while, at the same time, delivering appropriate connectivity solutions for local communities.The objectives of this study are as follows:1) Assess the technologies currently being, or planning to be, deployed through existing alternative communications programs managed by SARAO, including whether these technologies are comparable with market available technologies that could feasibly be deployed in the KCAAA; and2) Assessment of current and future telecommunication technologies that may act as suitable replacement and/or improvement (functional and feasible) for existing detrimental technologies, utilised in the KCAAA.This report provides a critical background into the relationship between the SKA and local communities as it relates to ICTs in the area. Based on this understanding, potential technology solutions are proposed to ensure residents of the KCAAA are still afforded valuable access to information and communication technologies (ICTs) within the parameters of affordability, desirability and feasibility.National Research Foundation (NRF