Emmanouil Pateromichelakis

On the Evolution of Multi-Cell Scheduling in 3GPP LTE / LTE-A

This paper provides a holistic overview of multi-cell scheduling strategies in emerging wireless systems. Towards this objective, the evolution of interference management techniques is thoroughly investigated from simple inter-cell interference coordination (ICIC) techniques towards more advanced coordinated multipoint transmissions (CoMP), while comparing and contrasting their common features and differences. Finally CoMP is explored in detail as an advanced and challenging mechanism to fully cooperate between adjacent cells in order to have an efficient resource allocation and inter-cell interference mitigation in multi-cell environments.

Dynamic Clustering Framework for Multi-Cell Scheduling in Dense Small Cell Networks

This letter proposes a novel graph-based multi-cell scheduling framework to efficiently mitigate downlink inter-cell interference in small cell OFDMA networks. This framework incorporates dynamic clustering combined with channel-aware resource allocation to provide tunable quality of service measures at different levels. Our extensive evaluation study shows that a significant improvement in users spectral efficiency is achievable, while also maintaining relatively high cell spectral efficiency via empirical tuning of re-use factor across the cells according to the required QoS constraints.

Towards a flexible functional split for cloud-RAN networks

Very dense deployments of small cells are one of the key enablers to tackle the ever-growing demand on mobile bandwidth. In such deployments, centralization of RAN functions on cloud resources is envisioned to overcome severe inter-cell interference and to keep costs acceptable. However, RAN back-haul constraints need to be considered when designing the functional split between RAN front-ends and centralized equipment. In this paper we analyse constraints and outline applications of flexible RAN centralization.

Joint TDD Backhaul and Access Optimization in Dense Small-Cell Networks

This paper addresses the problem of joint backhaul (BH) and access link optimization in dense small-cell networks with a special focus on time-division duplexing (TDD) mode of operation in BH and access link transmission. Here, we propose a framework for joint radio resource management, where we systematically decompose the problem in BH and access links. To simplify the analysis, the procedure is tackled in two stages. At the first stage, the joint optimization problem is formulated for a point-to-point scenario where each small cell is simply associated with a single user. It is shown that the optimization can be decomposed into separate power and subchannel allocation in both BH and access links, where a set of rate-balancing parameters in conjunction with duration of transmission governs the coupling across both links. Moreover, a novel algorithm is proposed based on grouping the cells to achieve rate balancing in different small cells. Next, in the second stage, the problem is generalized for multiaccess small cells. Here, each small cell is associated with multiple users to provide the service. The optimization is similarly decomposed into separate subchannel and power allocation by employing auxiliary slicing variables. It is shown that similar algorithms, as in the previous stage, are applicable by a slight change with the aid of slicing variables. Additionally, for the special case of line-of-sight BH links, simplified expressions for subchannel and power allocation are presented. The developed concepts are evaluated by extensive simulations in different case studies from full orthogonalization to dynamic clustering and full reuse in the downlink, and it is shown that the proposed framework provides significant improvement over the benchmark cases.

On the analysis of co-tier interference in femtocells

This paper quantifies the impact of co-tier interference in femtocells (i.e. inter-cell interference arising from other neighbouring femtocells) through a semi-analytical approach concluding that without interference mitigation techniques, QoS in the form of acceptable outage probability is not achievable in scenarios representing medium to worst cases of interference. Results obtained from semi-analytical approach are also compared against Monte Carlo simulations for evaluation purposes. Subsequently, some important radio access parameters and deployment configurations, such as path loss model, shadowing, wall penetration loss, location of femtocells and user distribution are further examined as key elements that can potentially affect, positively or negatively, the femtocell-to-femtocell interference in a multi-femtocell deployment. The results can be used as guidelines in the deployments of femtocells.

Graph-Based Multicell Scheduling in OFDMA-Based Small Cell Networks

This paper proposes a novel graph-based multicell scheduling framework to efficiently mitigate downlink intercell interference in OFDMA-based small cell networks. We define a graph-based optimization framework based on interference condition between any two users in the network assuming they are served on similar resources. Furthermore, we prove that the proposed framework obtains a tight lower bound for conventional weighted sum-rate maximization problem in practical scenarios. Thereafter, we decompose the optimization problem into dynamic graph-partitioning-based subproblems across different subchannels and provide an optimal solution using branch-and-cut approach. Subsequently, due to high complexity of the solution, we propose heuristic algorithms that display near optimal performance. At the final stage, we apply cluster-based resource allocation per subchannel to find candidate users with maximum total weighted sum-rate. A case study on networked small cells is also presented with simulation results showing a significant improvement over the state-of-the-art multicell scheduling benchmarks in terms of outage probability as well as average cell throughput.

Dynamic graph-based multi-cell scheduling for femtocell networks

This paper proposes a dynamic semi-centralized resource partitioning algorithm to mitigate the problem of co-tier interference in dense femtocell deployments. This algorithm incorporates graph-colouring and network utility concepts to address inter-cell interference in femtocell networks. The aforementioned scheme acts as a multi-cell coordination mechanism on top of intra-cell scheduling by applying a low complexity graph-based algorithm. The objective of the coordination mechanism is the efficient management of resource conflicts due to interference in a multi-cell environment consisting of femtocells. This coordination mechanism defines a novel category of graph-based ICIC algorithms that uses bipartite graph colouring to avoid resource conflicts by randomizing them in time domain.

Agile resource management for 5G: A METIS-II perspective

An explosive growth in the demand for higher data rates and capacity along with diverse requirements set by massive and ultra-reliable machine-type communications are the main drivers behind the development on new access technologies as part of the fifth generation (5G) networks. Currently, different air interface (AIF) and/or AIF variants, optimized based on the frequency band of operation and use case, are envisioned for such a network. Developing an agile resource management framework for 5G networks is one of the main goals of the METIS-II project. The METIS-II project builds strongly upon the EU flagship project METIS, which has laid the foundation of 5G. This framework will take into account the multi-link and multi-layer constraints currently envisioned for 5G. In this paper, we provide our first insights into agile resource management and the associated synchronous control functions. We will discuss the essential building blocks in terms of technology enablers and their mapping to 5G services and deployments. The introduced agile resource management framework for 5G is expected to enable enhanced interference management, dynamic traffic steering, fast radio access network (RAN) moderation, efficient context management, and optimized integration with legacy networks.

Wireless-Optical Network Convergence: Enabling the 5G Architecture to Support Operational and End-User Services

This article presents a converged 5G network infrastructure and an overarching architecture to jointly support operational network and end-user services, proposed by the EU 5G PPP project 5G-XHaul. The 5G-XHaul infrastructure adopts a common fronthaul/backhaul network solution, deploying a wealth of wireless technologies and a hybrid active/passive optical transport, supporting flexible fronthaul split options. This infrastructure is evaluated through a novel modeling. Numerical results indicate significant energy savings at the expense of increased end-user service delay.

5G infrastructures supporting end-user and operational services: The 5G-XHaul architectural perspective

We propose an optical-wireless 5G infrastructure offering converged fronthauling/backhauling functions to support both operational and end-user cloud services. A layered architectural structure required to efficiently support these services is shown. The data plane performance of the proposed infrastructure is evaluated in terms of energy consumption and service delay through a novel modelling framework. Our modelling results show that the proposed architecture can offer significant energy savings but there is a clear trade-off between overall energy consumption and service delay.