A survey of self organisation in future cellular networks

This article surveys the literature over the period of the last decade on the emerging field of self organisation as applied to wireless cellular communication networks. Self organisation has been extensively studied and applied in adhoc networks, wireless sensor networks and autonomic computer networks; however in the context of wireless cellular networks, this is the first attempt to put in perspective the various efforts in form of a tutorial/survey. We provide a comprehensive survey of the existing literature, projects and standards in self organising cellular networks. Additionally, we also aim to present a clear understanding of this active research area, identifying a clear taxonomy and guidelines for design of self organising mechanisms. We compare strength and weakness of existing solutions and highlight the key research areas for further development. This paper serves as a guide and a starting point for anyone willing to delve into research on self organisation in wireless cellular communication networks

Deployment of Femtocells in 3rd Generation Networks

Femtosolulla tarkoitetaan pientä matkapuhelinverkon solua, jonka liitäntäyhteytenä operaattorin verkkoon käytetään kuluttajan omaa laajakaistaliittymää. Femtosolut ovat itsestään asentuvia eli niiden käyttöönottoon ei tarvita ammattitaitoisen asentajan erillistä käyntiä. Kooltaan femtosolut ovat nykyisten langattomien lähiverkkojen tukiasemien kokoisia. Kova kilpailu ja kuluttajien jatkuvat odotukset entistä nopeammista datayhteyksistä saavat laitevalmistajat jatkuvasti kehittelemään uusia, entistä edullisempia, ratkaisuja. 2100 MHz taajuudella toimiville 3G UMTS verkoille on ollut ongelmallista saavuttaa niin hyvää peittoa sisätiloissa ja haja-asutusalueilla, mihin asiakkaat ovat tottuneet toisen sukupolven matkapuhelinverkoissa. Femtosolut tarjoavat edullisen ja nopean tavan kapasiteetin ja peiton parantamiseen sekä koti että yritysympäristöissä. Ensimmäisiä laajamittaisia UMTS femtosolu verkkojan odotetaan toteutuvaksi jo vuoden 2009 aikana. Femtosoluja on aiemmin tutkittu lähinnä liiketoimintamallina sekä niiden tuomaa etua on simuloitu yksinkertaisina hyvin teoreettisina hahmotelmina. Tämän diplomityön tarkoituksena on tutkia femtosolujen käyttöönottoa nykyisten 3G verkkojen rinnalla ja siihen liittyviä mahdollisia ongelmia. Työssä tullaan esittelemään femtosolut tekniikkana ja 3GPP:n standardisoima femtosoluratkaisu Home NodeB. Lisäksi esitellään verkkoon tarvittavat lisäelementit ja femtosoluverkon erilaiset mahdolliset toteutustavat. Femtosolujen tehokkuutta tutkittiin simuloimalla olemassa olevaa ympäristöä kuvaavaa verkkoa. Simulointityökaluna käytettiin laajamittaisessa tuotantokäytössä olevaa kaupallista radioverkkosuunnittelutyökalua. Simulaatioiden tuloksina nähtiin peiton parantuvan femtosolujen ansioista kaikissa tilanteissa, sekä verkon kokonaiskapasiteetin jopa viisinkertaistuvan, femtosolujen ollessa omalla kanavallaan. Femtosolujen käyttöönotto ei merkittävästi huononna makroverkon suorituskykyä. Päinvastoin, huolellisesti suunniteltuna makroverkon suorituskyky voi jopa parantua. Simulaatiot eivät voi antaa vastausta kaikkiin mahdollisiin femtosolujen ongelmiin ja kokeiluprojektit ovat tarpeen.Femtocells are small mobile telecommunication network basestations using the customers' DSL or cable modem connections as backhaul. In addition, femtocells are self-configuring and do not require a professional for installation. The devices themselves are approximately of the same size as the current Wi-Fi access points. The growing capacity expectations and intensive competition between operators is constantly driving vendors to come up with new solutions. In 2100 MHz 3G UMTS networks, indoor and rural coverage are not at the level customers are used to with 2G networks. Femtocells are a cheap and fast way to offer capacity and coverage to homes and offices. First large scale UMTS femtocell implementations are predicted to happen during the year 2009. Many researchers have studied the femtocell business model, and simulated the performance and co-operation with the macro layer network. These studies, however, have been often done in a very theoretical honeyconb simulating environment. This thesis will study the possible problems in femtocell rollouts and evaluate the status of current standardization and available devices. The femtocell specified in 3GPP standards, known as the Home NodeB, and other new components needed to integrate the solution with the current networks are presented together with the different possible deployment configurations. Performance of femtocells was examined by simulations with a widely used radio network planning tool and simulator. The simulations studied service coverage and throughput. This thesis shows how the coverage is improved by femtocells and how the total network capacity gains can be up to 5 times, compared to the current macro layer network. This can be achieved with femtocells implemented on a dedicated carrier. Furthermore, it is shown how the femtocells do not cause serious problems to the macro network, on the contrary, by careful planning macro layer performance can even be enhanced. Nevertheless, everything can not be evaluated by simulations. Piloting is the next natural step to learn more about femtocell functionality

Open vs Closed Access Femtocells in the Uplink

Femtocells are assuming an increasingly important role in the coverage and capacity of cellular networks. In contrast to existing cellular systems, femtocells are end-user deployed and controlled, randomly located, and rely on third party backhaul (e.g. DSL or cable modem). Femtocells can be configured to be either open access or closed access. Open access allows an arbitrary nearby cellular user to use the femtocell, whereas closed access restricts the use of the femtocell to users explicitly approved by the owner. Seemingly, the network operator would prefer an open access deployment since this provides an inexpensive way to expand their network capabilities, whereas the femtocell owner would prefer closed access, in order to keep the femtocell's capacity and backhaul to himself. We show mathematically and through simulations that the reality is more complicated for both parties, and that the best approach depends heavily on whether the multiple access scheme is orthogonal (TDMA or OFDMA, per subband) or non-orthogonal (CDMA). In a TDMA/OFDMA network, closed-access is typically preferable at high user densities, whereas in CDMA, open access can provide gains of more than 200% for the home user by reducing the near-far problem experienced by the femtocell. The results of this paper suggest that the interests of the femtocell owner and the network operator are more compatible than typically believed, and that CDMA femtocells should be configured for open access whereas OFDMA or TDMA femtocells should adapt to the cellular user density.Comment: 21 pages, 8 figures, 2 tables, submitted to IEEE Trans. on Wireless Communication

Interference mitigation in cognitive femtocell networks

“A thesis submitted to the University of Bedfordshire, in partial fulfilment of the requirements for the degree of Doctor of Philosophy”.Femtocells have been introduced as a solution to poor indoor coverage in cellular communication which has hugely attracted network operators and stakeholders. However, femtocells are designed to co-exist alongside macrocells providing improved spatial frequency reuse and higher spectrum efficiency to name a few. Therefore, when deployed in the two-tier architecture with macrocells, it is necessary to mitigate the inherent co-tier and cross-tier interference. The integration of cognitive radio (CR) in femtocells introduces the ability of femtocells to dynamically adapt to varying network conditions through learning and reasoning. This research work focuses on the exploitation of cognitive radio in femtocells to mitigate the mutual interference caused in the two-tier architecture. The research work presents original contributions in mitigating interference in femtocells by introducing practical approaches which comprises a power control scheme where femtocells adaptively controls its transmit power levels to reduce the interference it causes in a network. This is especially useful since femtocells are user deployed as this seeks to mitigate interference based on their blind placement in an indoor environment. Hybrid interference mitigation schemes which combine power control and resource/scheduling are also implemented. In a joint threshold power based admittance and contention free resource allocation scheme, the mutual interference between a Femtocell Access Point (FAP) and close-by User Equipments (UE) is mitigated based on admittance. Also, a hybrid scheme where FAPs opportunistically use Resource Blocks (RB) of Macrocell User Equipments (MUE) based on its traffic load use is also employed. Simulation analysis present improvements when these schemes are applied with emphasis in Long Term Evolution (LTE) networks especially in terms of Signal to Interference plus Noise Ratio (SINR)

Business models for deployment and operation of femtocell networks; - Are new cooperation strategies needed for mobile operators?

In this paper we discuss different business models for deployment and operation of femtocell networks intended for provisioning of public mobile broad band access services. In these types of business cases the operators use femtocells in order to reduce investments in "more costly" macro networks since the traffic can be "offloaded" to "less costly" femtocell networks. This is in contrast to the many business cases presented in Femtoforum where femtocells mainly are discussed as a solution to improve indoor coverage for voice services in homes and small offices, usually for closed user groups The main question discussed in this paper is if "operators need to consider new forms of cooperation strategies in order to enable large scale deployment of femtocells for public access?" By looking into existing solutions for indoor wireless access services we claim that the answer is both "Yes" and "No". No, since many types of cooperation are already in place for indoor deployment. Yes, because mobile operators need to re-think the femtocell specific business models, from approaches based on singe operator networks to different forms of cooperation involving multi-operator solutions, e.g. roaming and network sharing. --

Optimization of Mobility Parameters using Fuzzy Logic and Reinforcement Learning in Self-Organizing Networks

In this thesis, several optimization techniques for next-generation wireless networks are proposed to solve different problems in the field of Self-Organizing Networks and heterogeneous networks. The common basis of these problems is that network parameters are automatically tuned to deal with the specific problem. As the set of network parameters is extremely large, this work mainly focuses on parameters involved in mobility management. In addition, the proposed self-tuning schemes are based on Fuzzy Logic Controllers (FLC), whose potential lies in the capability to express the knowledge in a similar way to the human perception and reasoning. In addition, in those cases in which a mathematical approach has been required to optimize the behavior of the FLC, the selected solution has been Reinforcement Learning, since this methodology is especially appropriate for learning from interaction, which becomes essential in complex systems such as wireless networks. Taking this into account, firstly, a new Mobility Load Balancing (MLB) scheme is proposed to solve persistent congestion problems in next-generation wireless networks, in particular, due to an uneven spatial traffic distribution, which typically leads to an inefficient usage of resources. A key feature of the proposed algorithm is that not only the parameters are optimized, but also the parameter tuning strategy. Secondly, a novel MLB algorithm for enterprise femtocells scenarios is proposed. Such scenarios are characterized by the lack of a thorough deployment of these low-cost nodes, meaning that a more efficient use of radio resources can be achieved by applying effective MLB schemes. As in the previous problem, the optimization of the self-tuning process is also studied in this case. Thirdly, a new self-tuning algorithm for Mobility Robustness Optimization (MRO) is proposed. This study includes the impact of context factors such as the system load and user speed, as well as a proposal for coordination between the designed MLB and MRO functions. Fourthly, a novel self-tuning algorithm for Traffic Steering (TS) in heterogeneous networks is proposed. The main features of the proposed algorithm are the flexibility to support different operator policies and the adaptation capability to network variations. Finally, with the aim of validating the proposed techniques, a dynamic system-level simulator for Long-Term Evolution (LTE) networks has been designed

Client-based and Cross-layer Optimized Flow Mobility for Android Devices in Heterogeneous Femtocell/Wi-Fi Networks*

AbstractThe number of subscribers accessing Internet resources from mobile and wireless devices has been increasing continually since i-mode, the first mobile Internet service launched in 1999. The handling and support of dramatic growth of mobile data traffic create serious challenges for the network operators. Due to the spreading of WLAN networks and the proliferation of multi-access devices, offloading from 3G to Wi-Fi seems to be a promising step towards the solution. To solve the bandwidth limitation and coverage issues in 3G/4G environments, femtocells became key players. These facts motivate the design and development of femtocell/Wi-Fi offloading schemes. Aiming to support advanced offloading in heterogeneous networks, in this paper we propose a client-based, cross-layer optimized flow mobility architecture for Android devices in femtocell/Wi-Fi access environments. The paper presents the design, implementation and evaluation details of the aforementioned mechanisms

Femtocell Performance Over Non-SLA xDSL Access Network

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