We present a vision for 4G cellular networks based on the concept of autonomous infrastructure deployment. Cellular base stations, or femtocell access points, are deployed by network users without being constrained by the conventional cell planning process from the network operator. Autonomous deployment allows the network to grow in an organic manner which requires new methods for spectrum management. We study a framework for autonomous network optimization based on the method of cognitive interference management. In our model, a number of femtocells are co-channel deployed in an underlay macrocellular network. Instead of fully reusing 100% of the macrocellular resource, partial reuse is cognitively determined in femtocells based on their individual network environment. According to an interference signature perceived from the environment, a femtocell autonomously determines the appropriate channel allocation and minimizes the network interference. Upon the cognitive acquisition of the random infrastructure topology, base station pilot power is autonomously configured in order to maximize the cellular coverage. A series of network self-configuration procedures are discussed for automatic cell size adaptation and resource management. Our results show that the new approaches based on cognitive radio configuration facilitate the network optimization in terms of interference management, mobile handoff, pilot power control and network resource allocation. The proposed framework offers a 4G vision for spectrum management in an autonomous self-managed cellular architecture.

We present a vision for 4G cellular networks based on the concept of autonomous infrastructure deployment. Cellular base stations, or femtocell access points, are deployed by network users without being constrained by the conventional cell planning process from the network operator. Autonomous deployment allows the network to grow in an organic manner which requires new methods for spectrum management. We study a framework for autonomous network optimization based on the method of cognitive interference management. In our model, a number of femtocells are co-channel deployed in an underlay macrocellular network. Instead of fully reusing 100% of the macrocellular resource, partial reuse is cognitively determined in femtocells based on their individual network environment. According to an interference signature perceived from the environment, a femtocell autonomously determines the appropriate channel allocation and minimizes the network interference. Upon the cognitive acquisition of the random infrastructure topology, base station pilot power is autonomously configured in order to maximize the cellular coverage. A series of network self-configuration procedures are discussed for automatic cell size adaptation and resource management. Our results show that the new approaches based on cognitive radio configuration facilitate the network optimization in terms of interference management, mobile handoff, pilot power control and network resource allocation. The proposed framework offers a 4G vision for spectrum management in an autonomous self-managed cellular architecture.

The rapid evolution of current and upcoming high speed and complex communications networks often necessitates flawless time synchronization among the network nodes in order to guarantee performance. GPS based synchronizers have long been used for synchronizing telecommunications equipment, currently providing an accuracy of up to 10ns. Such high accuracy demands excellent operation from GPS timing receivers. Interference is an important threat to GPS performance. Any degradation in performance, due to the introduction of interference, can cause these receivers to provide a low quality timing solution, or to lose lock with incoming GPS signals altogether. This consideration motivates the study of the performance of GPS timing receivers in the presence of harmful interference. This work is devoted to the theoretical and practical investigations of the effects of RF interference on GPS-based synchronizers and their impacts on communications networks. Contributions made during this work include: a) Identification of the processes and the parameters involved in producing a timing solution which are vulnerable to interference; b) experimentbased confirmation of a hypothesis about the effects of interference on GPS timing receivers; c) identification of the effects of degraded synchronization on the performance of communications networks, especially CDMA and GSM cellular networks, which rely upon GPS based synchronizers; and d) proposal of a method to predict and avoid communications network performance degradation.

Spectral efficiency (SE), energy efficiency (EE), and transmission reliability are basic parameters to measure the performance of a cellular network. In this paper, spectral efficiency and energy efficiency tradeoff is considered keeping in mind the transmission reliability, where all the three are function of signal to noise ratio (SNR). SNR, in turn is a function of constellation size (or the number of bits per symbol) and data rate. Then, we propose a new power model which is as function of this SNR. Based on the power model, SE-EE trade-off function is evaluated taking transmission reliability in to consideration. Results confirmed that increasing constellation size results an increase in SNR and leads to a significant increase in energy efficiency without changing the transmit power. To demonstrate the validity of our analysis, channel gain and constellation size are varied keeping transmit power constant. The results also indicate that securing transmission reliability, the EE-SE trade-off is optimized by increasing the constellation size.

L'hétérogénéité et l’irrégularité croissante des déploiements des réseaux sans fil de nouvelles générations soulèvent des défis importants dans l’évaluation de performances de ces réseaux. Les modèles classiques s’appuyant sur des modèles hexagonaux pour décrire les emplacements géographiques des nœuds de transmission sont difficilement adaptables à ces réseaux. Dans ce contexte, il a été proposé un nouveau paradigme de modélisation des réseaux sans fil qui s’appuie sur les processus ponctuels de Poisson (PPP), et de manière générale sur la géométrie stochastique. L'analyse, au travers de ces outils mathématiques, présente une complexité indépendante de la taille du réseau, et permet d’estimer avec précision des quantités pratiques liées aux performances des réseaux cellulaires. Cette thèse a porté sur la faisabilité mathématique de l'approche fondée sur les PPP en proposant de nouvelles méthodes mathématiques d’approximations justes incorporant des modèles de propagation du canal radio. Dans un premier temps, un nouveau cadre mathématique, considéré comme une approche Equivalent-in-Distribution (EiD), a été proposée pour le calcul exact de la probabilité d'erreur dans les réseaux cellulaires. L'approche proposée, s’appuyant donc sur la géométrie aléatoire et des modèles spatiaux, montre une complexité faible en terme d’évaluation numérique et est applicable à un grand nombre de configurations MIMO pour lesquelles nous considérons différentes techniques de modulation et techniques de récupération du signal. Dans un deuxième temps, nous étudions les performances des réseaux cellulaires en présence de relais, où trois processus ponctuels de Poisson modélisent respectivement les nœuds relais, les stations de base, et les terminaux mobiles. Pour ce modèle, nous avons considéré des critères souples d'association. Le cadre mathématique proposé et les résultats associés ont montré que les performances dépendent fortement des exposants des fonctions d’atténuation sur les deux premiers sauts sans fil. Nous montrons aussi qu’une mauvaise configuration du réseau peut amener à des gains négligeables de l’utilisation de cette technique. Enfin, nous considérons la modélisation des réseaux cellulaires au travers d’un PPP et d’un modèle unifié d'atténuation de signal généralisée qui prend en compte deux types de liaisons physiques : line-of-sight (LOS) et non-line-of-sight (NLOS). Un modèle de complexité réduite décrivant les propriétés de la liaison radio a aussi été proposée et permet de prendre en compte dans nos calculs un grand nombre de modèle radio proposés dans la littérature. Les résultats montrent, entre autres, qu’une densité optimale pour le déploiement des BS existe lorsque les liens LOS/NLOS sont classés en fonction de leur charge. Nous comparons nos résultats, s’appuyant donc sur un PPP pour modéliser la position des stations de bases et notre modèle de canal radio, avec des simulations de Monte Carlo décrivant des déploiements réels de stations de bases et un modèle de type blocages de construction empiriques. Une bonne correspondance est observée. / The increasing heterogeneity and irregular deployment of the emerging wireless networks give enormous challenges to the conventional hexagonal model for abstracting the geographical locations of wireless transmission nodes. Against this backdrop, a new network paradigm by modeling the wireless nodes as a Poisson Point Process (PPP), leveraging on the mathematical tools of stochastic geometry for tractable mathematical analysis, has been proposed with the capability of fairly accurately estimating the performance of practical cellular networks. This dissertation investigated the mathematical tractability of the PPP-based approach by proposing new mathematical methodologies, fair approximations incorporating practical channel propagation models. First, a new mathematical framework, which is referred to as an Equivalent-in-Distribution (EiD)-based approach, has been proposed for computing exact error probability of cellular networks based on random spatial networks. The proposed approach is easy to compute and is shown to be applicable to a bunch of MIMO setups where the modulation techniques and signal recovery techniques are explicitly considered. Second, the performance of relay-aided cooperative cellular networks, where the relay nodes, the base stations, and the mobile terminals are modeled according to three independent PPPs, has been analyzed by assuming flexible cell association criteria. It is shown from the mathematical framework that the performance highly depends on the path-loss exponents of one-hop and two-hop links, and the relays provide negligible gains on the performance if the system is not adequately designed. Third, the PPP modeling of cellular networks with unified signal attenuation model is generalized by taking into account the effect of line-of-sight (LOS) and non-line-of-sight (NLOS) channel propagation. A tractable yet accurate link state model has been proposed to estimate other models available in the literature. It is shown that an optimal density for the BSs deployment exists when the LOS/NLOS links are classified in saturate load cellular networks. In addition, the Monte Carlo simulation results of the real BSs deployments with empirical building blockages are compared with those with PPP distributed BSs with the proposed link state approximation at the end of this dissertation as supplementary material. In general, a good matching is observed.

Last decade witnessed the explosive growth in mobile devices and their traffic demand, and hence the significant increase in the energy cost of the cellular service providers. One major component of energy expenditure comes from the operation of base stations. How to reduce energy cost of base stations while satisfying users’ soaring demands has become an imperative yet challenging problem. In this dissertation, we investigate the minimization of the long-term time-averaged expected energy cost while guaranteeing network strong stability. Specifically, considering flow routing, link scheduling, and energy constraints, we formulate a time-coupling stochastic Mixed-Integer Non-Linear Programming (MINLP) problem, which is prohibitively expensive to solve. We reformulate the problem by employing Lyapunov optimization theory and develop a decomposition based algorithm which ensures network strong stability. We obtain the bounds on the optimal result of the original problem and demonstrate the tightness of the bounds and the efficacy of the proposed scheme.

The availability of location estimates of mobile devices (MDs) is vital for several important applications such as law enforcement, disaster management, battlefield operations, vehicular communication, traffic safety, emergency response, and preemption. While global positioning system (GPS) is usually sufficient in outdoor clear sky conditions, its functionality is limited in urban canyons and indoor locations due to the absence of clear line-of-sight between the MD to be localized and a sufficient number of navigation satellites. In such scenarios, the ubiquitous nature of cellular networks makes them a natural choice for localization of MDs. Traditionally, localization in cellular networks has been studied using system level simulations by fixing base station (BS) geometries. However, with the increasing irregularity of the BS locations (especially due to capacity-driven small cell deployments), the system insights obtained by considering simple BS geometries may not carry over to real-world deployments. This necessitates the need to study localization performance under statistical (random) spatial models, which is the main theme of this work. In this thesis, we use powerful tools from stochastic geometry and point process theory to develop a tractable analytical model to study the localizability (ability to get a location fix) of an MD in single-tier and heterogeneous cellular networks (HetNets). More importantly, we study how availability of information about the location of proximate BSs at the MD impacts localizability. To this end, we derive tractable expressions, bounds, and approximations for the localizability probability of an MD. These expressions depend on several key system parameters, and can be used to infer valuable system insights. Using these expressions, we quantify the gains achieved in localizability of an MD when information about the location of proximate BSs is incorporated in the model. As expected, our results demonstrate that localizability improves with the increase in density of BS deployments. / Master of Science / Location based services form an integral part of vital day-to-day applications such as traffic control, emergency response, and navigation. Traditionally, users have relied on the global positioning system system (GPS) for localizing a device. GPS systems rely on the availability of clear line-of-sight between the devices to be localized and a sufficient number of navigation satellites. Since it is not possible to have these line-of-sight links, especially in urban canyons and indoor locations, the ubiquity of cellular networks makes them a natural choice for localization. Typically, localization using cellular networks is studied using simulations, which are carried out by fixing the network configuration including the geometry of the base stations (BSs) as well as the number of BSs that participate in localization. This limits the scope of the results obtained since a change in the network configuration would mean that one must do another set of time consuming simulations with the new network parameters. This motivates the need to develop an analytical model to study the impact of fundamental system-design factors such as BS geometries, number of participating BSs, propagation effects, and channel conditions on localization in cellular networks. Such analysis would make it convenient to infer how changing these system parameters affects localization. In this thesis, we develop a general analytical model to study the localizability (ability of get a location fix) of a device in a cellular network. In particular, we study how information about the location of BSs in the proximity of the device to be localized affects localizability. We derive expressions for metrics such as the localizability probability of a device. Our results help quantify the gains achieved in localizability performance when information about the location of BSs in the vicinity of the device to be localized is available at the device. Our results concretely demonstrate that including this additional information significantly improves the localizability performance, especially in regions with dense BS deployments.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / This paper presents a method for the optimization of mixed networks that incorporates a mixed layer optimization of performance features. The expanded integrated Network Enhanced Telemetry (iNET) system envisioned telemetering for large and complex networks which will require core telemetry networks with ad hoc extensions for coverage. Organizing such a network has been successfully accomplished in simulations using a K-mean clustering algorithm. This paper shows how the features of these network elements will be captured and disseminated in a real system. This management of network elements across multiple layers is characterized as cross-layer optimization. This paper will also show how such cross layer features can be combined for a globally optimum solution. It shows by example how the iNET system comprising multiple ground stations, gateways, frequency, nodes, and three performance measures can be optimized to achieve overall optimal system performance.

Today, the radio spectrum is rarely fully utilized. This problem is valid in more domains, e.g., time, frequency and geographical location. To provide an efficient utilization of the radio spectrum, the Cognitive Radio Networks (CRNs) have been advanced. The key idea is to open up the licensed spectrum to unlicensed users, thus allowing them to use the so-called spectrum opportunities as long as they do not harmfully interfere with licensed users. An important focus is laid on the limitation of previously reported research efforts, which is due to the limited consideration of the problem of competition among unlicensed users for spectrum access in heterogeneous CRNs. A software framework is introduced, which is called PRioritized Opportunistic spectrum Access System (PROAS). In PROAS, the heterogeneity aspects of CRNs are specifically expressed in terms of cross-layer design and various wireless technologies. By considering factors like ease of implementation and efficiency of control, PROAS provides priority scheduling based solutions to alleviate the competition problem of unlicensed users in heterogenous CRNs. The advanced solutions include theoretical models, numerical analysis and experimental simulations for performance evaluation. By using PROAS, three particular CRN models are studied, which are based on ad-hoc, mesh-network and cellular-network technologies. The reported results show that PROAS has the ability to bridge the gap between research results and the practical implementation of CRNs.

The surest way to increase the capacity of a wireless system is by getting the transmitters and receivers closer to each other, which creates the dual bene¯ts of higher quality links and more spatial reuse. In a network with nomadic users, this inevitably involves deploying more infrastructure, typically in the form of microcells, hotspots, distributed antennas, or relays. Compared to these deployments, a less expensive alternative for cellular operators is the recent concept of femtocells { also called home base-stations { which are end consumer installed data access points in the desire to get better indoor voice and data coverage. A two-tier network consisting of a conventional macrocell overlaid with shorter range wireless hotspots o®ers poten- tial capacity bene¯ts with low upfront costs to cellular operators. This dissertation addresses the key technical challenges inherent to a femtocell-aided cellular network, speci¯cally managing radio interference and providing reliable coverage at either tier, for di®erent physical layer technologies. Speci¯c contributions include 1) an uplink capacity analysis and interference avoidance in two-tier networks employing Code Di- vision Multiple Access (CDMA), 2) a decentralized power control scheme in two-tier networks with universal frequency reuse, 3) a coverage analysis of multi-antenna two- tier networks, and 4) spectrum allocation in two-tier networks employing Orthogonal Frequency Division Multiple Access (OFDMA). The goal of this research is to inspire and motivate the use of decentralized interference management techniques requir- ing minimal network overhead in ongoing and future deployments of tiered cellular architectures. / text