Interference Management In Heterogeneous Networks With Fractional Frequency Reuse

Modern day cellular networks are facing unprecedented data surge due to advanced intelligence in hardware and software systems,ranging from smartphones/handheld devices,to machine type communications and services.Network architectures are transforming from homogeneous macro-only deployments to heterogeneous-like networks with macrocells overlaid with dense small cells such as microcells,picocells,femtocells and distributed antenna systems.These are referred to as Heterogeneous Networks(Hetnets)and have been found to be more cost-effective in capacity and coverage improvements than traditional physical layer improvements and spectrum increase.However,the heterogeneity of the various network tiers in terms of transmit power,coverage and other technical parameters,introduces new challenges in design and modeling of such networks,with serious implications on interference distribution and mobility management among others.Understanding network topology is critical in managing scarce resources and mitigating interference even in single-macro networks,let alone in Hetnets with complex interference distribution and coverage patterns.Fractional Frequency Reuse is an efficient intercell interference coordination(ICIC)mechanism intended to address the co-channel interference problem in homogeneous deployments,but could also minimize cross-tier interference in multi-tier networks with strategic allocation of resources between the different tiers.This thesis provides a comprehensive guide on appropriate modeling and design of Hetnets using sectored Fractional Frequency Reuse for effective interference mitigation and resource allocation in the downlink.The contributions provided encompass both simulation-based and analytical models,thereby providing researchers and operators with adequate tools for evaluating emerging Hetnets in future networks under various practical deployment scenarios.Firstly,an improved architecture based on the hexagonal grid-based topology is proposed with an intermediary region for higher resistance to cross-tier interference,especially for user equipments(UE)at the transition area of center and edge regions of the cell.Strategically increasing the resource share to macro UEs(MUEs)in this new intermediary region,and allocating sub-bands with least received interference from the set of usable sub-bands,the overall performance of UEs is improved in terms of throughput and coverage.In order to better capture the irregularity of femtocells overlaid on planned macrocell infrastructure in the two-tier Hetnet topology,a hybrid deterministic-random model is then proposed for evaluating performance of UEs employing six-sectored antennas with FFR.A theoretical SINR distribution framework is then derived for all the different kinds of UEs in the network,which enables the derivation of per-tier coverage probability and average user throughputs provided by both macrocell and femtocell networks.The derived SINR framework is then used to define the minimum distance for co-channel operation of the edge femtocells with the underlaying FFR macrocells without violating outage constraints,referred to as the co-channel prohibition zone.Subsequently,the FFR-related parameters are optimized so as to maximize total network throughput and a new metric called the harmonic mean for ensuring fairness amongst all UEs.The proposed analytical framework provides practical design guidelines for effective and interference-reduced femtocell deployments.Finally,a completely irregular cell architecture is proposed whereby both macro and femto access points are assumed to be distributed based on independent spatial Poisson Point Processes(PPPs)and employing sectored antennas with FFR.Although macrocells are usually deployed with network planning and consideration to economics,coverage and aesthetics,modeling their locations with PPP has been found to be as accurate to actual 4G deployments as the idealistic hexagonal-grid assumptions.An analytical framework is then proposed for performance evaluation of the described network topology for co-tier and cross-tier interference management under both closed and open access operation mode by leveraging tools of stochastic geometry.The derived SINR distribution framework is verified by numerical simulation and then results compared with other FFR schemes and the No-FFR system.Lastly,average network spectral efficiency is computed for the case of both 3-sectored and 6-sectored FFR deployments to identify the effects of interference reduction via use of directional antennas under the analytical model.This is arguably the first contribution in the literature that provides insights into FFR-aided OFDMA heterogeneous networks employing directional antennas using real analytical tools from stochastic geometry for modeling all the tiers as well as evaluate the performance metrics.