Hisham Elshaer

Load & backhaul aware decoupled downlink/uplink access in 5G systems

Until the 4th Generation (4G) cellular 3GPP systems, a user equipments (UE) cell association has been based on the downlink received power from the strongest base station. Recent work has shown that - with an increasing degree of heterogeneity in emerging 5G systems - such an approach is dramatically suboptimal, advocating for an independent association of the downlink and uplink where the downlink is served by the macro cell and the uplink by the nearest small cell. In this paper, we advance prior art by explicitly considering the cell-load as well as the available backhaul capacity during the association process. We introduce a novel association algorithm and prove its superiority w.r.t. prior art by means of simulations that are based on Vodafones small cell trial network and employing a high resolution pathloss prediction and realistic user distributions. We also study the effect that different power control settings have on the performance of our algorithm.

Downlink and Uplink Decoupling: A disruptive architectural design for 5G networks

Cell association in cellular networks has traditionally been based on the downlink received signal power only, despite the fact that uplink and downlink transmission powers and interference levels differed significantly. This approach was adequate in homogeneous networks with macro base stations all having similar transmission power levels. However, with the growth of heterogeneous networks where there is a big disparity in the transmit power of the different base station types, this approach is highly inefficient. In this paper, we study the notion of Downlink and Uplink Decoupling (DUDe) where the downlink cell association is based on the downlink received power while the uplink is based on the pathloss. We present the motivation and assess the gains of this 5G design approach with simulations that are based on Vodafones LTE field trial network in a dense urban area, employing a high resolution ray-tracing pathloss prediction and realistic traffic maps based on live network measurements.

Why to decouple the uplink and downlink in cellular networks and how to do it

Ever since the inception of mobile telephony, the downlink and uplink of cellular networks have been coupled, that is, mobile terminals have been constrained to associate with the same base station in both the downlink and uplink directions. New trends in network densification and mobile data usage increase the drawbacks of this constraint, and suggest that it should be revisited. In this article we identify and explain five key arguments in favor of downlink/uplink decoupling based on a blend of theoretical, experimental, and architectural insights. We then overview the changes needed in current LTE-A mobile systems to enable this decoupling, and then look ahead to fifth generation cellular standards. We demonstrate that decoupling can lead to significant gains in network throughput, outage, and power consumption at a much lower cost compared to other solutions that provide comparable or lower gains.

Downlink and Uplink Cell Association With Traditional Macrocells and Millimeter Wave Small Cells

Millimeter wave (mmWave) links will offer high capacity but are poor at penetrating into or diffracting around solid objects. Thus, we consider a hybrid cellular network with traditional sub-6 GHz macrocells coexisting with denser mmWave small cells, where a mobile user can connect to either opportunistically. We develop a general analytical model to characterize and derive the uplink and downlink cell association in the view of the signal-to-interference-and-noise-ratio and rate coverage probabilities in such a mixed deployment. We offer extensive validation of these analytical results (which rely on several simplifying assumptions) with simulation results. Using the analytical results, different decoupled uplink and downlink cell association strategies are investigated and their superiority is shown compared with the traditional coupled approach. Finally, small cell biasing in mmWave is studied, and we show that unprecedented biasing values are desirable due to the wide bandwidth.

Shaping QoE in the 5G ecosystem

5G is rapidly moving from vision to reality and there is already some consensus regarding the technical requirements of 5G. Traditionally, performance monitoring based on existing standards has been focusing on technical Key Performance Indicators (KPIs). However, it is actually more important to focus on Quality of Experience (QoE) directly. Service delivery in 5G should account for the sheer diversity of existing and emerging use cases as well as for the vast variety of demands per service type. These requirements would only be addressed by a shift from system-centric to user-centric architectures. Given this background, this paper aims to push towards integrating QoE requirements in the 5G ecosystem, and to highlight the importance of network designs that have the enduser at their epicenter. To this end, we identify and analyze the essential must-have attributes that can shape QoE-centric networks and discuss how they fit in the 5G big picture. Then we describe current and emerging technological enablers of QoE in 5G, as well as important challenges towards achieving this goal.

Interference-Aware Decoupled Cell Association in Device-to-Device Based 5G Networks

Cell association in cellular networks is an important aspect that impacts network capacity and eventually quality of experience. The scope of this work is to investigate the different and generalized cell association (CAS) strategies for Device-to-Device (D2D) communications in a cellular network infrastructure. To realize this, we optimize D2D-based cell association by using the notion of uplink and downlink decoupling that was proven to offer significant performance gains. We propose an integer linear programming (ILP) optimization framework to achieve efficient D2D cell association that minimizes the interference caused by D2D devices onto cellular communications in the uplink as well as improve the D2D resource utilization efficiency. Simulation results based on Vodafones LTE field trial network in a dense urban scenario highlight the performance gains and render this proposal a candidate design approach for future 5G networks.

Bio-Inspired Resource Allocation for Relay-Aided Device-to-Device Communications

The Device-to-Device (D2D) communication principle is a key enabler of direct localized communication between mobile nodes and is expected to propel a plethora of novel multimedia services. However, even though it offers a wide set of capabilities mainly due to the proximity and resource reuse gains, interference must be carefully controlled to maximize the achievable rate for coexisting cellular and D2D users. The scope of this work is to provide an interference- aware real- time resource allocation (RA) framework for relay- aided D2D communications that underlay cellular networks. The main objective is to maximize the overall network throughput by guaranteeing a minimum rate threshold for cellular and D2D links. To this direction, genetic algorithms (GAs) are proven to be powerful and versatile methodologies that account for not only enhanced performance but also reduced computational complexity in emerging wireless networks. Numerical investigations highlight the performance gains compared to baseline RA methods and especially in highly dense scenarios which will be the case in future 5G networks.

Downlink and Uplink Cell Association in Sub-6GHz and Millimeter Wave 5G Heterogeneous Networks

Millimeter wave (mmWave) frequencies promise much higher capacities than conventional sub-6GHz networks thanks to the much wider bandwidth. However, mmWaves suffer from poor penetration and diffraction characteristics and are therefore expected to be deployed as an overlay to existing sub- 6GHz networks. We develop a general analytical framework where we derive the biased uplink and downlink cell association as well as the SINR and rate coverage probabilities in such a hybrid system. Simulation results are presented to validate the analytical model. Using the analytical results, we show that decoupled uplink and downlink association plays a key role in this mixed deployment. We then show the effect of small cell biasing on the SINR and rate trends where very high biasing values are desirable to harness the gains from the wide bandwidths at mmWaves. In addition, robust modulation and coding schemes are needed to operate under very low SINR resulting from the aggressive bias values.