Context-aware Self-Optimization in Small-Cell Networks

Most mobile communications take place at indoor environments, especially in commercial and corporate scenarios. These places normally present coverage and capacity issues due to the poor signal quality, which degrade the end-user Quality of Experience (QoE). In these cases, mobile operators are offering small cells to overcome the indoor issues, being femtocells the main deployed base stations. Femtocell networks provide significant benefits to mobile operators and their clients. However, the massive integration and the particularities of femtocells, make the maintenance of these infrastructures a challenge for engineers. In this sense, Self-Organizing Networks (SON) techniques play an important role. These techniques are a key feature to intelligently automate network operation, administration and management procedures. SON mechanisms are based on the analysis of the mobile network alarms, counters and indicators. In parallel, electronics, sensors and software applications evolve rapidly and are everywhere. Thanks to this, valuable context information can be gathered, which properly managed can improve SON techniques performance. Within possible context data, one of the most active topics is the indoor positioning due to the immediate interest on indoor location-based services (LBS). At indoor commercial and corporate environments, user densities and traffic vary in spatial and temporal domain. These situations lead to degrade cellular network performance, being temporary traffic fluctuations and focused congestions one of the most common issues. Load balancing techniques, which have been identified as a use case in self-optimization paradigm for Long Term Evolution (LTE), can alleviate these congestion problems. This use case has been widely studied in macrocellular networks and outdoor scenarios. However, the particularities of femtocells, the characteristics of indoor scenarios and the influence of users’ mobility pattern justify the development of new solutions. The goal of this PhD thesis is to design and develop novel and automatic solutions for temporary traffic fluctuations and focused network congestion issues in commercial and corporate femtocell environments. For that purpose, the implementation of an efficient management architecture to integrate context data into the mobile network and SON mechanisms is required. Afterwards, an accurate indoor positioning system is developed, as a possible inexpensive solution for context-aware SON. Finally, advanced self-optimization methods to shift users from overloaded cells to other cells with spare resources are designed. These methods tune femtocell configuration parameters based on network information, such as ratio of active users, and context information, such as users’ position. All these methods are evaluated in both a dynamic LTE system-level simulator and in a field-trial

Spectrum access and handover strategy in femtocell network

The femtocell concept is a modern approach in solving the ever increasing demand of mobile communication all over the world. The spectrum Access algorithm used in this project is based on dynamic spectrum allocation approach. This minimizes the interference suffered by Primary and secondary users by allocating proper channel. In this project , a handover algorithm is used including the different access modes of femtocell. Since the femtocell may be operated in various setups ,hence different modes. The algorithm is analyzed for increasing number of users with the handover decision taken and how the algorithm is effective in minimization of unnecessary handover

Handoffs in hierarchical macro/femto networks and an algorithm for efficient handoffs

The surest way to increase the system capacity of a wireless link is by getting the transmitter and receiver closer to each other, which creates the dual benefits 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, hot spots, distributed antennas, or relays. A less expensive alternative is the recent concept of femtocells also called home base stations which are data access points installed by home users to get better indoor voice and data coverage. In macro/femto hierarchical networks, one of the biggest challenges is ensuring efficient handoffs. Here in this thesis, we first evaluated received signal strength at mobile user using different path loss models (indoor and outdoor) which is the main criterion for performing handoff. We also obtained the interference and SINR scenarios for handoff performance. Then we derived some basic handoff parameters like handoff probability, radio link failure rate, ping-pong handoff for macro/femto environment. Finally we proposed an algorithm for efficient handoff. The main idea of the proposed algorithm is to combine the values of received signal strength from a serving macro BS and a target femto BS in the consideration of large asymmetry in their transmit powers. Numerical results show that there is a significant gain in view of the probability that the user will be assigned to the femtocell while keeping the same level of the number of handoffs

AN INVESTIGATION OF THE INFLUENCE OF FEMTOCELLS NETWORK ON A SMALL SIZE INDOOR ENVIRONMENT USING ITU-R AND WINNER II PATH LOSS MODELS

The rapid integrations of wireless controls in mechatronics, the broadening applications of wireless radio communications in aviation, and the exponential increase in the growth of mobile phone users in the last decade have made it necessary to expand the capacity of GSM users and ultimately increase the system performance. It has also become imperative for service providers to ensure adequate coverage is provided for all mobile users in areas with poor or no service. Even though many solutions such as distributed antenna system, relays, macrocells, and picocells were developed but they could not proffer the needed solution to indoor users. In this perspective, researchers were of the opinion that femtocells have a gifted technology to enhance indoor coverage because of properties such as short power, short coverage area, reduced distance between device and user and being a plug and play device. It was however discovered that research findings on large deployment of femtocells does not corroborate when a handful is deployed. This study therefore examines the influence of femtocells network on a small size indoor environment using ITU-R and WINNER II path loss models. To accomplish this, femtocells were modeled in six apartments of a building and parameters such as path loss, received power and signal to interference plus noise ratio were determined to ascertain the performance of a particular femtocell under the influence of co-tier interference. Results show that the ITU-R model was found to experience lower path losses which produced higher received powers than WINNER II (-57.0445dBm on the average)

5G and beyond networks

This chapter investigates the Network Layer aspects that will characterize the merger of the cellular paradigm and the IoT architectures, in the context of the evolution towards 5G-and-beyond, including some promising emerging services as Unmanned Aerial Vehicles or Base Stations, and V2X communications

A Spatial Estimation-based Handover Management For Challenging Femtocell Deployments

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2015Thesis (M.Sc.) -- İstanbul Technical University, Instıtute of Science and Technology, 2015Bu çalışmada, femtocell tabanlı ağlarda gereksiz aktarım sayısını düşürmeye yönelik, mobil kullanıcıların sinyal kaybı raporlarını kullanarak yeni bir aktarım yönetim mekanizması tasarlanmıştır. Tasarlanan mekanizmada sinyal kaybı değerlerini uzaysal olarak kestirebilmek için semivariogram analizi yapan Ordinary Kriging yöntemleri kullanmaktadır. Bu yöntem iki kısımdan oluşmaktadır. İlk olarak yeni tanımlanan sinyal kaybı değişkeni hesaplanır ve sonrasında bu değer önceden tanımlanan eşik değeri ile kıyaslanarak aktarım kararı alınır. Yeni tanımlanan sinyal kaybı değişkeni mobil kullanıcının gelecekte bulunacağı noktaların sinyal kaybı değişkenine dayanmaktadır. Sayısal veriler önerilen yöntemin geleneksel yönteme göre gereksiz aktarım sayısı ve ping-pong aktarım oranı anlamında daha iyi sonuçlar verdiği görülmüştür.In this study, a new path loss-based handover management mechanism is introduced in order to minimize the number of unnecessary handovers in femtocell-based networks by using path loss measurement reports from mobile stations. The proposed mechanism includes a spatial estimation of path loss step that depends on ordinary Kriging using Semivariogram Analysis. This method is composed of two parts. First calculate mobile station's newly defined path loss and then compare this value with the predefined threshold to make a handover decision. The newly defined path loss is calculated by considering the path loss of future locations which are the locations that the mobile station will most likely reach in the future. Numerical results demonstrate that the proposed handover scheme is superior to conventional handover scheme from the viewpoints of both unnecessary handover number and ping-pong handover rate.Yüksek LisansM.Sc

Cooperation strategies for inter-cell interference mitigation in OFDMA systems

Recently the use of modern cellular networks has drastically changed with the emerging Long Term Evolution Advanced (LTE-A) technology. Homogeneous networks which were initially designed for voice-centric and low data rates face unprecedented challenges for meeting the increasing traffic demands of high data-driven applications and their important quality of service requirements. Therefore, these networks are moving towards the so called Heterogeneous Networks (HetNets). HetNets represent a new paradigm for cellular networks as their nodes have different characteristics such as transmission power and radio frequency coverage area. Consequently, a HetNet shows completely different interference characteristics compared to homogeneous deployment and attention must be paid to these disparities when different tiers are collocated together. This is mostly due to the potential spectrum frequency reuse by the involved tiers in the HetNets. Hence, efficient inter-cell interference mitigation solutions in co-channel deployments of HetNets remain a challenge for both industry and academic researchers. This thesis focuses on LTE-A HetNet systems which are based on Orthogonal Frequency Division Multiplexing Access (OFDMA) modulation. Our aim is to investigate the aggressive interference issue that appears when different types of base stations are jointly deployed together and especially in two cases, namely Macro-Femtocells and Macro-Picocells co-existence. We propose new practical power adjustment solutions for managing inter-cell interference dynamically for both cases. In the first part dedicated to Femtocells and Macrocell coexistence, we design a MBS-assisted femtocell power adjustment strategy which takes into account femtocells users performance while mitigating the inter-cell interference on victim macrocell users. Further, we propose a new cooperative and context-aware interference mitigation method which is derived for realistic scenarios involving mobility of users and their varying locations. We proved numerically that the Femtocells are able to maintain their interference under a desirable threshold by adjusting their transmission power. Our strategies provide an efficient means for achieving the desired level of macrocell/femtocell throughput trade-off. In the second part of the studies where Picocells are deployed under the umbrella of the Macrocell, we paid a special attention and efforts to the interference management in the situation where Picocells are configured to set up a cell range expansion. We suggest a MBS-assisted collaborative scheme powered by an analytical model to predict the mobility of Macrocell users passing through the cell range expansion area of the picocell. Our goal is to adapt the muting ratio ruling the frequency resource partitioning between both tiers according to the mobility behavior of the range-expanded users, thereby providing an efficient trade-off between Macrocell and Picocell achievable throughputs.Récemment, l'utilisation des réseaux cellulaires a radicalement changé avec l’émergence de la quatrième génération (4G) de systèmes de télécommunications mobiles LTE/LTE-A (Long Term Evolution-Advanced). Les réseaux de générations précédentes (3G), initialement conçus pour le transport de la voix et les données à faible et moyen débits, ont du mal à faire face à l’augmentation accrue du trafic de données multimédia tout en répondant à leurs fortes exigences et contraintes en termes de qualité de service (QdS). Pour mieux répondre à ces besoins, les réseaux 4G ont introduit le paradigme des Réseaux Hétérogènes (HetNet).Les réseaux HetNet introduisent une nouvelle notion d’hétérogénéité pour les réseaux cellulaires en introduisant le concept des smalls cells (petites cellules) qui met en place des antennes à faible puissance d’émission. Ainsi, le réseau est composé de plusieurs couches (tiers) qui se chevauchent incluant la couverture traditionnelle macro-cellulaire, les pico-cellules, les femto-cellules, et les relais. Outre les améliorations des couvertures radio en environnements intérieurs, les smalls cells permettent d’augmenter la capacité du système par une meilleure utilisation du spectre et en rapprochant l’utilisateur de son point d’accès au réseau. Une des conséquences directes de cette densification cellulaire est l’interférence générée entre les différentes cellules des diverses couches quand ces dernières réutilisent les mêmes fréquences. Aussi, la définition de solutions efficaces de gestion des interférences dans ce type de systèmes constitue un de leurs défis majeurs. Cette thèse s’intéresse au problème de gestion des interférences dans les systèmes hétérogènes LTE-A. Notre objectif est d’apporter des solutions efficaces et originales au problème d’interférence dans ce contexte via des mécanismes d’ajustement de puissance des petites cellules. Nous avons pour cela distingués deux cas d’étude à savoir un déploiement à deux couches macro-femtocellules et macro-picocellules. Dans la première partie dédiée à un déploiement femtocellule et macrocellule, nous concevons une stratégie d'ajustement de puissance des femtocellules assisté par la macrocellule et qui prend en compte les performances des utilisateurs des femtocells tout en atténuant l'interférence causée aux utilisateurs des macrocellules sur leurs liens montants. Cette solution offre l’avantage de la prise en compte de paramètres contextuels locaux aux femtocellules (tels que le nombre d’utilisateurs en situation de outage) tout en considérant des scénarios de mobilité réalistes. Nous avons montré par simulation que les interférences sur les utilisateurs des macrocellules sont sensiblement réduites et que les femtocellules sont en mesure de dynamiquement ajuster leur puissance d'émission pour atteindre les objectifs fixés en termes d’équilibre entre performance des utilisateurs des macrocellules et celle de leurs propres utilisateurs. Dans la seconde partie de la thèse, nous considérons le déploiement de picocellules sous l'égide de la macrocellule. Nous nous sommes intéressés ici aux solutions d’extension de l’aire picocellulaire qui permettent une meilleure association utilisateur/cellule permettant de réduire l’interférence mais aussi offrir une meilleure efficacité spectrale. Nous proposons donc une approche basée sur un modèle de prédiction de la mobilité des utilisateurs qui permet de mieux ajuster la proportion de bande passante à partager entre la macrocellule et la picocellule en fonction de la durée de séjour estimée de ces utilisateurs ainsi que de leur demandes en bande passante. Notre solution a permis d’offrir un bon compromis entre les débits réalisables de la Macro et des picocellules