Enabling Energy-Efficient and Backhaul-aware Next Generation Heterogeneous Networks

Heterogeneous networks have been firmly established as the direction in which next-generation cellular networks are evolving. We consider the dense deployment of small cells to provide enhanced capacity, while the macro cells provide wide area coverage. With the development of dual connectivity technology, deploying small cells on dedicated carriers has become an attractive option, with enhanced flexibility for splitting traffic within the network. The power consumption and latency requirements of the backhaul link are also gaining increasing prominence due to these factors. Backhaul link quality itself is expected to play an important role in influencing the deployment costs of next-generation 5G systems.  Energy efficiency as a network design paradigm is also gaining relevance due to the increasing impact cellular networks are having on the global carbon emission footprint. For operators, improving energy efficiency has the added advantage of reducing network operation expenditures. For the end-users, avoiding unnecessary draining of device battery power would improve the user experience.  In this work, we study energy efficient mechanisms for inter-frequency small cell discovery, based on mobility awareness and proximity estimation. Further, we apply generalized small cell discovery concepts in a device-to-device communication environment in order to optimize the energy consumption for device discovery. We also look at energy efficient small cell operations based on traffic characteristics and load constraints-based offloading in relation to the radio access and backhaul power consumption. In addition we study intelligent means of dist-ributing delay-critical functionalities such as Hybrid ARQ, while centralizing the computationally-intense processes in a 5G, cloud-based, centralized radio access network. Numerical evaluations done using a LTE-Advanced heterogeneous network and analytical settings indicate that significant UE and network power consumption reductions could be achieved with the considered enhancements. Using the optimized small cell operation schemes investigated in this work, reductions in network power consumption and consequent improvements in the overall energy efficiency of the network were observed. The performance of the distributed opportunistic HARQ mechanism for a centralized radio access network is compared to the optimal and static retransmission mechanisms, and the evaluated scheme is shown to perform close to the optimal mechanism, while operating with a non-ideal backhaul link

On the performance of multi-tier Heterogeneous networks under LoS and NLoS transmissions

Heterogeneous networks (HetNets) with a multi-tier structure have been considered as a promising method to provide high quality of service to mobile users. The dense deployment of small-cell base stations (BSs) implies short distances between BSs and users. It is therefore likely that users will see line-of-sight (LoS) links from its serving BS and even nearby interfering BSs, which has not been considered in performance analysis for multi-tier HetNets yet. In this paper, we study a dense multi-tier HetNet with LoS and non-line-of-sight (NLoS) transmissions based on a multislope path loss model. The spatial locations of BSs of any given network tier and those of mobile users are modeled as independent spatial Poisson point processes (SPPPs). We derive the expression of downlink coverage probability for the multi-tier HetNet, based on which we calculate the area spectral efficiency (ASE) and energy efficiency (EE) of the HetNet. Our analytical results demonstrate that in an extremely dense HetNet, both the ASE and EE of the HetNet will drop quickly with further increase of the small-cell density due to the dominance of LoS interfering small-cell links

On the performance of multi-tier Heterogeneous networks under LoS and NLoS transmissions

Heterogeneous networks (HetNets) with a multi-tier structure have been considered as a promising method to provide high quality of service to mobile users. The dense deployment of small-cell base stations (BSs) implies short distances between BSs and users. It is therefore likely that users will see line-of-sight (LoS) links from its serving BS and even nearby interfering BSs, which has not been considered in performance analysis for multi-tier HetNets yet. In this paper, we study a dense multi-tier HetNet with LoS and non-line-of-sight (NLoS) transmissions based on a multislope path loss model. The spatial locations of BSs of any given network tier and those of mobile users are modeled as independent spatial Poisson point processes (SPPPs). We derive the expression of downlink coverage probability for the multi-tier HetNet, based on which we calculate the area spectral efficiency (ASE) and energy efficiency (EE) of the HetNet. Our analytical results demonstrate that in an extremely dense HetNet, both the ASE and EE of the HetNet will drop quickly with further increase of the small-cell density due to the dominance of LoS interfering small-cell links

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

Expanding cellular coverage via cell-edge deployment in heterogeneous networks: spectral efficiency and backhaul power consumption perspectives

Heterogeneous small-cell networks (HetNets) are considered to be a standard part of future mobile networks where operator/consumer deployed small-cells, such as femtocells, relays, and distributed antennas (DAs), complement the existing macrocell infrastructure. This article proposes the need-oriented deployment of smallcells and device-to-device (D2D) communication around the edge of the macrocell such that the small-cell base stations (SBSs) and D2D communication serve the cell-edge mobile users, thereby expanding the network coverage and capacity. In this context, we present competitive network configurations, namely, femto-on-edge, DA-onedge, relay-on-edge, and D2D-communication on- edge, where femto base stations, DA elements, relay base stations, and D2D communication, respectively, are deployed around the edge of the macrocell. The proposed deployments ensure performance gains in the network in terms of spectral efficiency and power consumption by facilitating the cell-edge mobile users with small-cells and D2D communication. In order to calibrate the impact of power consumption on system performance and network topology, this article discusses the detailed breakdown of the end-to-end power consumption, which includes backhaul, access, and aggregation network power consumptions. Several comparative simulation results quantify the improvements in spectral efficiency and power consumption of the D2D-communication-onedge configuration to establish a greener network over the other competitive configurations

Self organising cloud cells: a resource efficient network densification strategy

Network densification is envisioned as the key enabler for 2020 vision that requires cellular systems to grow in capacity by hundreds of times to cope with unprecedented traffic growth trends being witnessed since advent of broadband on the move. However, increased energy consumption and complex mobility management associated with network densifications remain as the two main challenges to be addressed before further network densification can be exploited on a wide scale. In the wake of these challenges, this paper proposes and evaluates a novel dense network deployment strategy for increasing the capacity of future cellular systems without sacrificing energy efficiency and compromising mobility performance. Our deployment architecture consists of smart small cells, called cloud nodes, which provide data coverage to individual users on a demand bases while taking into account the spatial and temporal dynamics of user mobility and traffic. The decision to activate the cloud nodes, such that certain performance objectives at system level are targeted, is carried out by the overlaying macrocell based on a fuzzy-logic framework. We also compare the proposed architecture with conventional macrocell only deployment and pure microcell-based dense deployment in terms of blocking probability, handover probability and energy efficiency and discuss and quantify the trade-offs therein

On Energy Efficient Inter-Frequency Small Cell Discovery in Heterogeneous Networks

In this paper, we investigate the optimal inter-frequency small cell discovery (ISCD) periodicity for small cells deployed on carrier frequency other than that of the serving macro cell. We consider that the small cells and user terminals (UTs) positions are modelled according to a homogeneous Poisson Point Process (PPP). We utilize polynomial curve fitting to approximate the percentage of time the typical UT missed small cell offloading opportunity, for a fixed small cell density and fixed UT speed. We then derive analytically, the optimal ISCD periodicity that minimizes the average UT energy consumption (EC). Furthermore, we also derive the optimal ISCD periodicity that maximizes the average energy efficiency (EE), i.e. bit-per-joule capacity. Results show that the EC optimal ISCD periodicity always exceeds the EE optimal ISCD periodicity, with the exception of when the average ergodic rates in both tiers are equal, in which the optimal ISCD periodicity in both cases also becomes equal