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

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)

Efficient radio resource management for future generation heterogeneous wireless networks

The heterogeneous deployment of small cells (e.g., femtocells) in the coverage area of the traditional macrocells is a cost-efficient solution to provide network capacity, indoor coverage and green communications towards sustainable environments in the future fifth generation (5G) wireless networks. However, the unplanned and ultra-dense deployment of femtocells with their uncoordinated operations will result in technical challenges such as severe interference, a significant increase in total energy consumption, unfairness in radio resource sharing and inadequate quality of service provisioning. Therefore, there is a need to develop efficient radio resource management algorithms that will address the above-mentioned technical challenges. The aim of this thesis is to develop and evaluate new efficient radio resource management algorithms that will be implemented in cognitive radio enabled femtocells to guarantee the economical sustainability of broadband wireless communications and users' quality of service in terms of throughput and fairness. Cognitive Radio (CR) technology with the Dynamic Spectrum Access (DSA) and stochastic process are the key technologies utilized in this research to increase the spectrum efficiency and energy efficiency at limited interference. This thesis essentially investigates three research issues relating to the efficient radio resource management: Firstly, a self-organizing radio resource management algorithm for radio resource allocation and interference management is proposed. The algorithm considers the effect of imperfect spectrum sensing in detecting the available transmission opportunities to maximize the throughput of femtocell users while keeping interference below pre-determined thresholds and ensuring fairness in radio resource sharing among users. Secondly, the effect of maximizing the energy efficiency and the spectrum efficiency individually on radio resource management is investigated. Then, an energy-efficient radio resource management algorithm and a spectrum-efficient radio resource management algorithm are proposed for green communication, to improve the probabilities of spectrum access and further increase the network capacity for sustainable environments. Also, a joint maximization of the energy efficiency and spectrum efficiency of the overall networks is considered since joint optimization of energy efficiency and spectrum efficiency is one of the goals of 5G wireless networks. Unfortunately, maximizing the energy efficiency results in low performance of the spectrum efficiency and vice versa. Therefore, there is an investigation on how to balance the trade-off that arises when maximizing both the energy efficiency and the spectrum efficiency simultaneously. Hence, a joint energy efficiency and spectrum efficiency trade-off algorithm is proposed for radio resource allocation in ultra-dense heterogeneous networks based on orthogonal frequency division multiple access. Lastly, a joint radio resource allocation with adaptive modulation and coding scheme is proposed to minimize the total transmit power across femtocells by considering the location and the service requirements of each user in the network. The performance of the proposed algorithms is evaluated by simulation and numerical analysis to demonstrate the impact of ultra-dense deployment of femtocells on the macrocell networks. The results show that the proposed algorithms offer improved performance in terms of throughput, fairness, power control, spectrum efficiency and energy efficiency. Also, the proposed algorithms display excellent performance in dynamic wireless environments

A Novel Handover Decision Policy for Reducing Power Transmissions in the two-tier LTE network

Femtocells are attracting a fast increasing interest nowadays, as a promising solution to improve indoor coverage, enhance system capacity, and lower transmit power. Technical challenges still remain, however, mainly including interference, security and mobility management, intercepting wide deployment and adoption from mobile operators and end users. This paper describes a novel handover decision policy for the two-tier LTE network, towards reducing power transmissions at the mobile terminal side. The proposed policy is LTE backward-compatible, as it can be employed by suitably adapting the handover hysteresis margin with respect to a prescribed SINR target and standard LTE measurements. Simulation results reveal that compared to the widely-adopted strongest cell policy, the proposed policy can greatly reduce the power consumption at the LTE mobile terminals, and lower the interference network-wide

Efficient resource allocation algorithm for dense femtocell networks

La couverture d'intérieur pauvre et la basse capacité d'utilisateur représentent deux défis importants pour les opérateurs cellulaires. Plusieurs solutions (telles que les antennes distribuées) ont été proposées pour résoudre ces problèmes. Cependant, aucune de ces solutions ne fournit le niveau désiré de l'évolutivité et elles manquent l'aspect pratique. Pour ces raisons, une solution attrayante caractérisée par sa faible puissance et son prix faible connue sous le nom de femto-cellule a été introduite pour offrir une meilleure capacité et couverture d'utilisateur. Malgré tous les avantages provoqués par l'intégration de cette nouvelle technologie femto-cellule, plusieurs nouveaux défis ont émergé. Ces défis sont principalement présentés dans deux genres d'interférences ; connu comme interférence cross-tier et interférence co-tier. Tandis que l'impact d'interférence cross-tier (provoqué en partageant le spectre de fréquence) peut être réduit en mettant en application des algorithmes efficaces de réutilisation de fréquence, l'interférence co-tier continue à présenter un défi difficile pour les opérateurs et les chercheurs dans le domaine de réseaux cellulaires. Le déploiement non planifié et mal organisé des stations de base femto-cellule a comme conséquence une réduction radicale de la capacité d'utilisateur qui peut mener à une déconnexion des utilisateurs. L'impact de l'interférence co-tier devient plus provocant dans un déploiement dense des femto-cellule où les utilisateurs demandent des services en temps réel (par exemple, taux de données constant). Afin de réduire l'interférence co-tier, plusieurs solutions ont été proposées dans la littérature comprenant des algorithmes de contrôle de puissance, des techniques de détection avancées et des schémas d'allocation de ressources intelligentes. Dans ce projet, nous proposons une stratégie intelligente d'attribution des fréquences avec une stratégie avancée d'association de station de base femto-cellule pour les réseaux femto-cellule basés sur LTE. L'objectif des deux stratégies proposées est d'atténuer l'interférence co-tier et de réduire la probabilité de panne des utilisateurs en augmentant le nombre d'utilisateurs actifs par station de base femto-cellule. Nous montrons par simulations l'efficacité de notre solution proposée.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : femtocell base station, interference management, resource block assignment, base station assignment, outage probability

Measurement-based coverage function for green femtocell networks

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Energy Efficient Mobility Management for the Macrocell – Femtocell LTE Network

Femtocells will play a key role in future deployments of the 3rd Generation Partnership Project (3GPP) the Long Term Evolution (LTE) system, as they are expected to enhance system capacity, and greatly improve the energy-efficiency in a cost-effective manner. Due to the short transmit-receive distance, femtocells prolong handset battery life and enhance the Quality of Service (QoS) perceived by the end users. However, large-scale femtocell deployment comprises many technical challenges, mainly including security, interference and mobility management. Under the viewpoint of energy-efficient mobility management, this chapter discusses the key features of the femtocell technology and presents a novel energy-efficient handover decision policy for the macrocell – femtocell LTE network. The proposed HO decision policy aims at reducing the transmit power of the LTE mobile terminals in a backwards compatible with the standard LTE handover decision procedure. Simulation results show that significantly lower energy and power consumption can be attained if the proposed approach is employed, at the cost of a moderately increased number of handover executions events