Energy efficiency in heterogeneous wireless access networks

In this article, we bring forward the important aspect of energy savings in wireless access networks. We specifically focus on the energy saving opportunities in the recently evolving heterogeneous networks (HetNets), both Single- RAT and Multi-RAT. Issues such as sleep/wakeup cycles and interference management are discussed for co-channel Single-RAT HetNets. In addition to that, a simulation based study for LTE macro-femto HetNets is presented, indicating the need for dynamic energy efficient resource management schemes. Multi-RAT HetNets also come with challenges such as network integration, combined resource management and network selection. Along with a discussion on these challenges, we also investigate the performance of the conventional WLAN-first network selection mechanism in terms of energy efficiency (EE) and suggest that EE can be improved by the application of intelligent call admission control policies

Self-Organizing Radio Resource Management and Backhaul Dimensioning for Cellular Networks

The huge appetite for mobile broadband has resulted to continuous and complementary improvement in both radio access technology and mobile backhaul of cellular networks, along with network densification. Femtocells are foreseen to complement traditional macro base stations (BSs) in Long Term Evolution (LTE) and future cellular networks.  Deployment of femtocells, introduce new requirements for distributing phase synchronization and interference management in heterogeneous network. Achieving phase synchronization for indoor femtocells will be beneficial for time division duplexing (TDD) operation and inter-cell interference cancellation and management techniques, but challenging to achieve as global positioning system does not work indoors. In this thesis, we propose coordinated transmission and reception algorithms to reduce interference across BSs, and thereby achieve better network-wide phase synchronization over the air. We also cover the problem of selecting component carriers for dense small cell network, by improving the throughput of cell-edge user equipment's (UEs). We propose three strategies: Selfish, Altruistic and Symmetric for primary carrier selection and remove the outage of the macro UEs near the closed subscriber group (CSG) femtocells. Further, we propose dynamic frequency selection algorithm for component carrier selection, where decisions to select or drop a carrier are based on gain/loss predictions made from UE handover measurements. Thereby, we maximize the sum utility of the dense femtocell network, which includes mean-rate, weighted fair-rate, proportional fair-rate and max-min utility.  Mobile backhaul dimensioning is studied to improve the handover and provide the cost-effective backhaul opportunity for femtocells deployed in emerging markets. In a packet-switched wireless system e.g. LTE, data packets are needed to be efficiently forwarded between BSs during handover over the backhaul. We improve the packet forwarding handover mechanism by reducing the amount of forwarded data between BSs. Another challenge lies in equipping the femtocells with backhaul, where copper cable, optical fiber or microwave radio links are expensive options for unplanned emerging market case. We consider leveraging macro LTE networks to backhaul High Speed Packet Access femtocells, thereby highlight the possibilities for cost-effective capacity upgrades of dense settlements

Self-organising network management for heterogeneous LTE-advanced networks

This thesis was submitted for the award of Doctor of Philosophy and awarded by Brunel University LondonSince 2004, when the Long Term Evolution (LTE) was first proposed to be publicly available in the year 2009, a plethora of new characteristics, techniques and applications have been constantly enhancing it since its first release, over the past decade. As a result, the research aims for LTE-Advanced (LTE-A) have been released to create a ubiquitous and supportive network for mobile users. The incorporation of heterogeneous networks (HetNets) has been proposed as one of the main enhancements of LTE-A systems over the existing LTE releases, by proposing the deployment of small-cell applications, such as femtocells, to provide more coverage and quality of service (QoS) within the network, whilst also reducing capital expenditure. These principal advantages can be obtained at the cost of new challenges such as inter-cell interference, which occurs when different network applications share the same frequency channel in the network. In this thesis, the main challenges of HetNets in LTE-A platform have been addressed and novel solutions are proposed by using self-organising network (SON) management approaches, which allows the cooperative cellular systems to observe, decide and amend their ongoing operation based on network conditions. The novel SON algorithms are modelled and simulated in OPNET modeler simulation software for the three processes of resource allocation, mobility management and interference coordination in multi-tier macro-femto networks. Different channel allocation methods based on cooperative transmission, frequency reuse and dynamic spectrum access are investigated and a novel SON sub-channel allocation method is proposed based on hybrid fractional frequency reuse (HFFR) scheme to provide dynamic resource allocation between macrocells and femtocells, while avoiding co-tier and cross-tier interference. Mobility management is also addressed as another important issue in HetNets, especially in hand-ins from macrocell to femtocell base stations. The existing research considers a limited number of methods for handover optimisation, such as signal strength and call admission control (CAC) to avoid unnecessary handovers, while our novel SON handover management method implements a comprehensive algorithm that performs sensing process, as well as resource availability and user residence checks to initiate the handover process at the optimal time. In addition to this, the novel femto over macro priority (FoMP) check in this process also gives the femtocell target nodes priority over the congested macrocells in order to improve the QoS at both the network tiers. Inter-cell interference, as the key challenge of HetNets, is also investigated by research on the existing time-domain, frequency-domain and power control methods. A novel SON interference mitigation algorithm is proposed, which is based on enhanced inter-cell interference coordination (eICIC) with power control process. The 3-phase power control algorithm contains signal to interference plus noise ratio (SINR) measurements, channel quality indicator (CQI) mapping and transmission power amendments to avoid the occurrence of interference due to the effects of high transmission power. The results of this research confirm that if heterogeneous systems are backed-up with SON management strategies, not only can improve the network capacity and QoS, but also the new network challenges such as inter-cell interference can also be mitigated in new releases of LTE-A network