Enhanced Inter-Cell Interference Coordination Challenges in Heterogeneous Networks

3GPP LTE-Advanced has started a new study item to investigate Heterogeneous Network (HetNet) deployments as a cost effective way to deal with the unrelenting traffic demand. HetNets consist of a mix of macrocells, remote radio heads, and low-power nodes such as picocells, femtocells, and relays. Leveraging network topology, increasing the proximity between the access network and the end-users, has the potential to provide the next significant performance leap in wireless networks, improving spatial spectrum reuse and enhancing indoor coverage. Nevertheless, deployment of a large number of small cells overlaying the macrocells is not without new technical challenges. In this article, we present the concept of heterogeneous networks and also describe the major technical challenges associated with such network architecture. We focus in particular on the standardization activities within the 3GPP related to enhanced inter-cell interference coordination.Comment: 12 pages, 4 figures, 2 table

Resource and power management in next generation networks

The limits of today’s cellular communication systems are constantly being tested by the exponential increase in mobile data traffic, a trend which is poised to continue well into the next decade. Densification of cellular networks, by overlaying smaller cells, i.e., micro, pico and femtocells, over the traditional macrocell, is seen as an inevitable step in enabling future networks to support the expected increases in data rate demand. Next generation networks will most certainly be more heterogeneous as services will be offered via various types of points of access (PoAs). Indeed, besides the traditional macro base station, it is expected that users will also be able to access the network through a wide range of other PoAs: WiFi access points, remote radio-heads (RRHs), small cell (i.e., micro, pico and femto) base stations or even other users, when device-to-device (D2D) communications are supported, creating thus a multi-tiered network architecture. This approach is expected to enhance the capacity of current cellular networks, while patching up potential coverage gaps. However, since available radio resources will be fully shared, the inter-cell interference as well as the interference between the different tiers will pose a significant challenge. To avoid severe degradation of network performance, properly managing the interference is essential. In particular, techniques that mitigate interference such Inter Cell Interference Coordination (ICIC) and enhanced ICIC (eICIC) have been proposed in the literature to address the issue. In this thesis, we argue that interference may be also addressed during radio resource scheduling tasks, by enabling the network to make interference-aware resource allocation decisions. Carrier aggregation technology, which allows the simultaneous use of several component carriers, on the other hand, targets the lack of sufficiently large portions of frequency spectrum; a problem that severely limits the capacity of wireless networks. The aggregated carriers may, in general, belong to different frequency bands, and have different bandwidths, thus they also may have very different signal propagation characteristics. Integration of carrier aggregation in the network introduces additional tasks and further complicates interference management, but also opens up a range of possibilities for improving spectrum efficiency in addition to enhancing capacity, which we aim to exploit. In this thesis, we first look at the resource allocation in problem in dense multitiered networks with support for advanced features such as carrier aggregation and device-to-device communications. For two-tiered networks with D2D support, we propose a centralised, near optimal algorithm, based on dynamic programming principles, that allows a central scheduler to make interference and traffic-aware scheduling decisions, while taking into consideration the short-lived nature of D2D links. As the complexity of the central scheduler increases exponentially with the number of component carriers, we further propose a distributed heuristic algorithm to tackle the resource allocation problem in carrier aggregation enabled dense networks. We show that the solutions we propose perform significantly better than standard solutions adopted in cellular networks such as eICIC coupled with Proportional Fair scheduling, in several key metrics such as user throughput, timely delivery of content and spectrum and energy efficiency, while ensuring fairness for backward compatible devices. Next, we investigate the potentiality to enhance network performance by enabling the different nodes of the network to reduce and dynamically adjust the transmit power of the different carriers to mitigate interference. Considering that the different carriers may have different coverage areas, we propose to leverage this diversity, to obtain high-performing network configurations. Thus, we model the problem of carrier downlink transmit power setting, as a competitive game between teams of PoAs, which enables us to derive distributed dynamic power setting algorithms. Using these algorithms we reach stable configurations in the network, known as Nash equilibria, which we show perform significantly better than fixed power strategies coupled with eICIC

Radio resource management strategies for interference mitigation in 4G heterogeneous wireless networks

The new era of mobile communications is dictated by the user demand for robust and high speed connections, data hungry applications and seamless connectivity. Operators and researchers all over the world are challenged to fulfill these requirements by providing enhanced coverage, increased capacity and efficient usage of the scarce spectrum. The introduction of the fourth generation systems (4G), LTE and LTE-A, have set the initiative for a technology evolution that offers new possibilities and is able to satisfy the user requirements and overcome the imposed challenges. However, and despite the improvements brought by the LTE and LTE-A systems, there are certain constraints that still need to be surpassed. LTE for example adopts innovating technologies, such as Orthogonal Frequency Division Multiplexing Access (OFDMA) that improves the spectral efficiency and reduces the Intra-Cell Interference. Nevertheless, Inter-Cell Interference (ICI) remains a constraining factor that can degrade the system capacity and limit the overall performance of the network. On that respect, Inter-Cell Interference Coordination (ICIC) techniques are adopted with target the interference mitigation. One of the limitations of these techniques is that follow static configurations lacking of flexibility and adaptation on network changes. Moreover, LTE-A employs enhanced and new techniques and involves alternative strategies. A promising solution lies on the introduction of Heterogeneous Networks (HetNets), which are networks that include low power small cells under the already existing macro cellular network and exploit several other technologies, such as WiFi. HetNets can further improve the network capacity, enhance the coverage and provide higher speed data transfer. However, due to the heterogeneous nature of the network, traditional methods for the user association, resource allocation and interference mitigation may not always be suitable since their design was based on homogeneous deployments. As such, new and enhanced methods are introduced, such as enhanced ICIC (eICIC), with their accompanied requirements and challenges. Motivated by the abovementioned aspects, this thesis has been focused on the study of ICIC and eICIC schemes, the identification of the related challenges, the enhancement of existing schemes and the proposal of novel solutions. In particular in the initial stages of the work, ICIC techniques have been studied and analyzed. A distributed algorithm that performs dynamic channel allocation has been developed for homogeneous deployments and extended later on to include heterogeneous networks. The solution has been optimized with the use of the Gibbs Sampler, while the setting of algorithm related parameters has been addressed through a detailed analysis. Moreover, a possible implementation of the solution has been presented in detail. The efficiency of the proposed schemes has been demonstrated through simulations and comparisons with benchmark schemes. In the next steps, the work has targeted eICIC techniques with purpose the investigation and analysis of the main constraining issues related to the user association, resource management and interference mitigation. Novel eICIC schemes that aim a better resource management and the overall capacity improvement have been developed and presented in detail, while the performance of the solutions has been shown through simulations and comparisons with reference schemes. Moreover, an optimized eICIC solution has been implemented based on genetic algorithms. Simulation results and comparisons with reference schemes have demonstrated the efficiency of the solution, while the selected configurations are discussed and analyzed.La nueva era de las comunicaciones móviles viene marcada por la demanda de los usuarios por conseguir conexiones robustas de alta velocidad que permitan soportar aplicaciones de datos de elevados requerimientos. El cumplimiento de estos requisitos conlleva la necesidad de mejorar la cobertura, incrementar la capacidad y utilizar el espectro eficientemente. La introducción de los sistemas de cuarta generación (4G), LTE y LTE-A, ha dado lugar a una tecnología que ofrece nuevas posibilidades y es capaz de satisfacer las necesidades de los usuarios y superar los retos impuestos. Sin embargo, y a pesar de las mejoras introducidas por estos sistemas, hay ciertas limitaciones que todavía tienen que ser superadas. LTE, por ejemplo, adopta tecnologías tales como OFDMA que mejora la eficiencia espectral y reduce la interferencia intracelular. Sin embargo, la interferencia intercelular (ICI) sigue siendo un factor limitante que puede degradar la capacidad del sistema y limitar el rendimiento global de la red. En ese sentido, se requieren técnicas de coordinación de interferencias intercelulares (ICIC) con el objetivo de mitigar dicha interferencia. Una de las limitaciones de estas técnicas es que siguen configuraciones estáticas que carecen de flexibilidad y capacidad de adaptación a los cambios de la red. Por otra parte, LTE-A introduce nuevas mejoras, como las redes heterogéneas (HetNets), que son redes que incluyen pequeñas células de baja potencia conjuntamente con la red macrocellular y también pueden explotar diferentes tecnologías, como WiFi. Las HetNets pueden mejorar aún más la capacidad de la red, mejorar la cobertura y facilitar la transferencia de datos de mayor velocidad. Sin embargo, debido a la naturaleza heterogénea de la red, los métodos tradicionales para la asociación de usuarios, asignación de recursos y reducción de la interferencia pueden no ser siempre adecuados, ya que su diseño se basó en despliegues homogéneos. En este sentido, es preciso introducir técnicas mejoradas de ICIC, denominadas en inglés eICIC (enhanced-ICIC), que involucran nuevos requerimientos y retos. En base a todos estos aspectos, esta tesis se ha centrado en el estudio de los sistemas de ICIC y eICIC en redes celulares, incluyendo la identificación de los retos relacionados con la mejora de los sistemas existentes y la propuesta de soluciones novedosas. En particular, en las etapas iniciales de la tesis se han estudiado y analizado las técnicas ICIC, y se ha desarrollado un algoritmo distribuido que realiza la asignación dinámica de canales para despliegues homogéneos, ampliándose posteriormente para su utilización en redes heterogéneas. La solución opera de forma optimizada mediante el uso de la técnica denominada Gibbs Sampler, mientras que el ajuste de parámetros relacionado con el algoritmo se ha abordado a través de un análisis detallado basado en simulaciones. Por otra parte, una posible implementación de la solución se ha presentado en detalle. La eficiencia de los esquemas propuestos se ha demostrado a través de simulaciones y comparaciones con sistemas de referencia. En los siguientes pasos, el trabajo se ha centrado en las técnicas eICIC con el propósito de investigar y analizar los principales problemas relacionadas con la asociación de usuarios, gestión de recursos y mitigación de la interferencia. A partir de aquí se han desarrollado nuevos esquemas de eICIC que tienen como objetivo una mejor gestión de los recursos y la mejora general de la capacidad. El rendimiento de las soluciones se ha demostrado a través de simulaciones y comparaciones con sistemas de referencia. Por otra parte, se ha propuesto una solución eICIC optimizada basada en algoritmos genéticos. La eficacia de dicha solución se ha demostrado mediante simulaciones, a la vez que se han analizado las diferentes configuraciones seleccionadas por el proceso de optimización.Postprint (published version

Optimisation de la gestion des interférences inter-cellulaires et de l'attachement des mobiles dans les réseaux cellulaires LTE

Driven by an exponential growth in mobile broadband-enabled devices and a continue dincrease in individual data consumption, mobile data traffic has grown 4000-fold over the past 10 years and almost 400-million-fold over the past 15 years. Homogeneouscellular networks have been facing limitations to handle soaring mobile data traffic and to meet the growing end-user demand for more bandwidth and betterquality of experience. These limitations are mainly related to the available spectrumand the capacity of the network. Telecommunication industry has to address these challenges and meet exploding demand. At the same time, it has to guarantee a healthy economic model to reduce the carbon footprint which is caused by mobile communications.Heterogeneous Networks (HetNets), composed of macro base stations and low powerbase stations of different types, are seen as the key solution to improve spectral efficiency per unit area and to eliminate coverage holes. In such networks, intelligent user association and interference management schemes are needed to achieve gains in performance. Due to the large imbalance in transmission power between macroand small cells, user association based on strongest signal received is not adapted inHetNets as only few users would attach to low power nodes. A technique based onCell Individual Offset (CIO) is therefore required to perform load balancing and to favor some Small Cell (SC) attraction against Macro Cell (MC). This offset is addedto users’ Reference Signal Received Power (RSRP) measurements and hence inducing handover towards different eNodeBs. As Long Term Evolution (LTE) cellular networks use the same frequency sub-bands, mobile users may experience strong inter-cellxv interference, especially at cell edge. Therefore, there is a need to coordinate resource allocation among the cells and minimize inter-cell interference. To mitigate stronginter-cell interference, the resource, in time, frequency and power domain, should be allocated efficiently. A pattern for each dimension is computed to permit especially for cell edge users to benefit of higher throughput and quality of experience. The optimization of all these parameters can also offer gain in energy use. In this thesis,we propose a concrete versatile dynamic solution performing an optimization of user association and resource allocation in LTE cellular networks maximizing a certainnet work utility function that can be adequately chosen. Our solution, based on gametheory, permits to compute Cell Individual Offset and a pattern of power transmission over frequency and time domain for each cell. We present numerical simulations toillustrate the important performance gain brought by this optimization. We obtain significant benefits in the average throughput and also cell edge user through put of40% and 55% gains respectively. Furthermore, we also obtain a meaningful improvement in energy efficiency. This work addresses industrial research challenges and assuch, a prototype acting on emulated HetNets traffic has been implemented.Conduit par une croissance exponentielle dans les appareils mobiles et une augmentation continue de la consommation individuelle des données, le trafic de données mobiles a augmenté de 4000 fois au cours des 10 dernières années et près de 400millions fois au cours des 15 dernières années. Les réseaux cellulaires homogènes rencontrent de plus en plus de difficultés à gérer l’énorme trafic de données mobiles et à assurer un débit plus élevé et une meilleure qualité d’expérience pour les utilisateurs.Ces difficultés sont essentiellement liées au spectre disponible et à la capacité du réseau.L’industrie de télécommunication doit relever ces défis et en même temps doit garantir un modèle économique pour les opérateurs qui leur permettra de continuer à investir pour répondre à la demande croissante et réduire l’empreinte carbone due aux communications mobiles. Les réseaux cellulaires hétérogènes (HetNets), composés de stations de base macro et de différentes stations de base de faible puissance,sont considérés comme la solution clé pour améliorer l’efficacité spectrale par unité de surface et pour éliminer les trous de couverture. Dans de tels réseaux, il est primordial d’attacher intelligemment les utilisateurs aux stations de base et de bien gérer les interférences afin de gagner en performance. Comme la différence de puissance d’émission est importante entre les grandes et petites cellules, l’association habituelle des mobiles aux stations de bases en se basant sur le signal le plus fort, n’est plus adaptée dans les HetNets. Une technique basée sur des offsets individuelles par cellule Offset(CIO) est donc nécessaire afin d’équilibrer la charge entre les cellules et d’augmenter l’attraction des petites cellules (SC) par rapport aux cellules macro (MC). Cette offset est ajoutée à la valeur moyenne de la puissance reçue du signal de référence(RSRP) mesurée par le mobile et peut donc induire à un changement d’attachement vers différents eNodeB. Comme les stations de bases dans les réseaux cellulaires LTE utilisent les mêmes sous-bandes de fréquences, les mobiles peuvent connaître une forte interférence intercellulaire, en particulier en bordure de cellules. Par conséquent, il est primordial de coordonner l’allocation des ressources entre les cellules et de minimiser l’interférence entre les cellules. Pour atténuer la forte interférence intercellulaire, les ressources, en termes de temps, fréquence et puissance d’émission, devraient être alloués efficacement. Un modèle pour chaque dimension est calculé pour permettre en particulier aux utilisateurs en bordure de cellule de bénéficier d’un débit plus élevé et d’une meilleure qualité de l’expérience. L’optimisation de tous ces paramètres peut également offrir un gain en consommation d’énergie. Dans cette thèse, nous proposons une solution dynamique polyvalente effectuant une optimisation de l’attachement des mobiles aux stations de base et de l’allocation des ressources dans les réseaux cellulaires LTE maximisant une fonction d’utilité du réseau qui peut être choisie de manière adéquate.Notre solution, basée sur la théorie des jeux, permet de calculer les meilleures valeurs pour l’offset individuelle par cellule (CIO) et pour les niveaux de puissance à appliquer au niveau temporel et fréquentiel pour chaque cellule. Nous présentons des résultats des simulations effectuées pour illustrer le gain de performance important apporté par cette optimisation. Nous obtenons une significative hausse dans le débit moyen et le débit des utilisateurs en bordure de cellule avec 40 % et 55 % de gains respectivement. En outre, on obtient un gain important en énergie. Ce travail aborde des défis pour l’industrie des télécoms et en tant que tel, un prototype de l’optimiseur a été implémenté en se basant sur un trafic HetNets émulé

An energy saving small cell sleeping mechanism with cell range expansion in heterogeneous networks

In recent years, the explosion of wireless data traffic has resulted in a trend of large scale dense deployment of small cells, with which the rising cost of energy has attracted a lot of research interest. In this paper, we present a novel sleeping mechanism for small cells to decrease the energy consumption of heterogeneous networks. Specifically, in the cell-edge area of a macrocell, the small cells will be put into sleep where possible and their service areas will be covered by the range-expanded small cells nearby and the macrocell; in areas close to the macrocell, the user equipments associated with a sleeping small cell will be handed over to the macrocell. Furthermore, we use enhanced inter-cell interference coordination techniques to support the range expanded small cells to avoid QoS degradation. Using a stochastic geometry-based network model, we provide the numerical analysis of the proposed approach, and the results indicate that the proposed sleeping mechanism can significantly reduce the power consumption of the network compared with the existing sleeping methods while guaranteeing the QoS requirement

A distributed power-saving framework for LTE Het-Nets exploiting Almost Blank Subframes

Almost Blank Subframes (ABS) have been defined in LTE as a means to coordinate transmissions in heterogeneous networks (HetNets), composed of macro and micro eNodeBs: the macro issues ABS periods, and refrains from transmitting during ABSs, thus creating interference-free subframes for the micros. Micros report their capacity demands to the macro via the X2 interface, and the latter provisions the ABS period accordingly. Existing algorithms for ABS provisioning usually share resources proportionally among HetNet nodes in a long-term perspective (e.g., based on traffic forecast). We argue instead that this mechanism can be exploited to save power in the HetNet: in fact, during ABSs, the macro consumes less power, since it only transmits pilot signals. Dually, the micros may inhibit data transmission themselves in some subframes, and optimally decide when to do this based on knowledge of the ABS period. This allows us to define a power saving framework that works in the short term, modifying the ABS pattern at the fastest possible pace, serving the HetNet traffic at reduced power cost. Our framework is designed using only standard signaling. Simulations show that the algorithm consumes less power than its competitors, especially at low loads, and improves the UE QoS

D13.2 Techniques and performance analysis on energy- and bandwidth-efficient communications and networking

Deliverable D13.2 del projecte europeu NEWCOM#The report presents the status of the research work of the various Joint Research Activities (JRA) in WP1.3 and the results that were developed up to the second year of the project. For each activity there is a description, an illustration of the adherence to and relevance with the identified fundamental open issues, a short presentation of the main results, and a roadmap for the future joint research. In the Annex, for each JRA, the main technical details on specific scientific activities are described in detail.Peer ReviewedPostprint (published version