Vincenzo Mancuso

A Survey on Device-to-Device Communication in Cellular Networks

Device-to-device (D2D) communications was initially proposed in cellular networks as a new paradigm for enhancing network performance. The emergence of new applications such as content distribution and location-aware advertisement introduced new user cases for D2D communications in cellular networks. The initial studies showed that D2D communications has advantages such as increased spectral efficiency and reduced communication delay. However, this communication mode introduces complications in terms of interference control overhead and protocols that are still open research problems. The feasibility of D2D communications in Long-Term Evolution Advanced is being studied by academia, industry, and standardization bodies. To date, there are more than 100 papers available on D2D communications in cellular networks, but there is no survey on this field. In this paper, we provide a taxonomy based on the D2D communicating spectrum and review the available literature extensively under the proposed taxonomy. Moreover, we provide new insights into the over-explored and under-explored areas that lead us to identify open research problems of D2D communications in cellular networks.

Reducing costs and pollution in cellular networks

Cellular wireless networks are expected to provide high-quality audio and video services while enabling fast and low-cost Internet access to mobile users. The need for green cost-efficient networks is twofold: reduce the service price and preserve the environment. In this work, we discuss the various strategies that help reduce infrastructure costs, power costs, and greenhouse gas (GHG) emissions with no impairments on the quality of network services. These strategies range over a wide area from enhancing the electronics, to developing new energy-aware radio access protocols, to deploying enhanced base stations with tunable capacity. To reduce both capital and operational expenditures, and the GHG footprint, manufacturers propose new compact installation with lightweight antenna systems, very efficient power amplifiers, and efficient hardware and software. The resulting economy can be up to 50 percent or more by reducing the electricity bill, sparing the use of air conditioning, and deploying compact sites that would seldom require maintenance. Recent scientific publications confirm that a very high gain could be achieved by optimizing the use of base stations proactively, and huge additional improvements could be obtained by optimizing power saving mechanisms by leveraging traffic statistics.

A Survey on Opportunistic Scheduling in Wireless Communications

Wireless technology advancements made opportunistic scheduling a popular topic in recent times. However, opportunistic schedulers for wireless systems have been studied since nearly twenty years, but not implemented in real systems due to their high complexity and hardly achievable requirements. In contrast, todays popularity of opportunistic schedulers extends to implementation proposals for next generation cellular technologies. Motivated by such a novel interest towards opportunistic scheduling, we provide a taxonomy for opportunistic schedulers, which is based on scheduling designs objectives; accordingly, we provide an extensive review of opportunistic scheduling proposals which have appeared in the literature during nearly two decades. The huge number of papers available in the literature propose different techniques to perform opportunistic scheduling, ranging from simple heuristic algorithms to complex mathematical models. Some proposals are only designed to increase the total network capacity, while others enhance QoS objectives such as throughput and fairness. Interestingly, our survey helps to unveil two major issues: (i) the research in opportunistic is mature enough to jump from pure theory to implementation, and (ii) there are still under-explored and interesting research areas in opportunistic scheduling, e.g., opportunistic offloading of cellular traffic to 802.11-like networks, or cooperative/distributed opportunistic scheduling.

An SDN-Based Network Architecture for Extremely Dense Wireless Networks

Telecommunications networks are undergoing major changes so as to meet the requirements of the next generation of users and services, which create a need for a general revised architectural approach rather than a series of local and incremental technology updates. This is especially manifest in mobile broadband wireless access, where a major traffic increase is expected, mostly because of video transmission and cloud-based applications. The installation of a high number of very small cells is foreseen as the only practical way to achieve the demands. However, this would create a struggle on the mobile network operators because of the limited backhaul capacity, the increased energy consumption, and the explosion of signalling. In the FP7 project CROWD, Software Defined Networking (SDN) has been identified as a solution to tame extreme density of wireless networks. Following this paradigm, a novel network architecture accounting for MAC control and Mobility Management has been proposed, being the subject of this paper.

WiFi Direct and LTE D2D in action

With the evolution of high-performance multi-radio smartphones, Device-to-Device (D2D) communications became an attractive solution for enhancing the performance of cellular networks. Although D2D communications have been widely studied within past few years, the majority of the literature is confined to new theoretical proposals and did not consider implementation challenges. In fact, the implementation feasibility of D2D communications and its challenges are still a relevant research question. In this paper, we introduce a protocol that focuses on D2D communications using LTE and WiFi Direct technologies. We also show that currently available WiFi Direct features permits to deploy the D2D paradigm on top of the LTE cellular infrastructure, without requiring any fundamental change in LTE protocols.

Measurement and Modeling of the Origins of Starvation in Congestion Controlled Mesh Networks

Significant progress has been made in understanding the behavior of TCP and congestion-controlled traffic over multi- hop wireless networks. Despite these advances, however, no prior work identified severe throughput imbalances in the basic scenario of mesh networks, in which one-hop flows contend with two-hop flows for gateway access. In this paper, we demonstrate via real network measurements, test-bed experiments, and an analytical model that starvation exists in such a scenario, i.e., the one-hop flow receives most of the bandwidth while the two- hop flow starves. Our analytical model yields a solution consisting of a simple contention window policy that can be implemented via mechanisms in IEEE 802.11e. Despite its simplicity, we demonstrate through analysis, experiments, and simulations, that the policy has a powerful effect on network-wide behavior, shifting the networks queuing points, mitigating problematic MAC behavior, and ensuring that TCP flows obtain a fair share of the gateway bandwidth, irrespective of their spatial locations.

CROWD: An SDN Approach for DenseNets

Traffic demands in mobile networks are expected to grow substantially in the next years, both in terms of total traffic volume and of bit-rate required by individual users. It is generally agreed that the only possible solution to overcome the current limitations is to deploy very dense and heterogeneous wireless networks, which we call DenseNets. However, simply scaling down existing networks by orders of magnitude, as required to fulfill traffic forecasts, is not possible because of the following constraints: i) the bottleneck would shift from the Radio Access Network (RAN) to the backhaul, ii) control overhead, especially related to mobility management, would make the network collapse, iii) operational costs of the network would be unbearable due to energy consumption and maintenance/optimisation. In this paper, Software Defined Network (SDN) for mobile networks is claimed as the paradigm shift necessary to tackle adequately the above challenges. A novel architecture is proposed, which supports DenseNets made of overlapping LTE and WLAN cells connected to the core network via a reconfigurable backhaul.

On the minimization of power consumption in base stations using on/off power amplifiers

Using energy generated with fossil fuel causes global warming due to the greenhouse effect, which threatens our environment. One of the challenges for New Generation Networks (NGN) is then the reduction of energy consumption, in particular at the BSs (Base Stations) which use about 85% of the total network energy. We contribute to the research with a mathematical model that calculates the total power consumption of a BS and enlightens the way to minimize it. First, we analyze the power consumed at every different component of the BS. Second, based on the cost incurred in turning off the BSs power amplifiers, we show how to decide whether it is convenient to keep the BS idle during those intervals in which no traffic has to be sent, or to turn off the amplifiers. Our model is evaluated by means of numerical examples, and shows that interesting power gain can be obtained under a large spectrum of load conditions.

A Simple Analytical Model for Energy Efficient Ethernet

The recently approved Energy Efficient Ethernet standard IEEE 802.3az achieves energy savings by using a low power mode when the link is idle. However, those savings heavily depend on the traffic patterns, due to the overhead inherent in transitions between active and low power modes. This makes it impractical to estimate energy savings through measurements or simulations in all relevant scenarios. In this letter we present an analytical model to estimate the energy consumption of an Energy Efficient Ethernet link, based on simple traffic parameters. The model is validated through simulation and experimental data.

On the compound impact of opportunistic scheduling and D2D communications in cellular networks

Opportunistic scheduling was initially proposed to exploit user channel diversity for network capacity enhancement. However, the achievable gain of opportunistic schedulers is generally restrained due to fairness considerations which impose a tradeoff between fairness and throughput. In this paper, we show via analysis and numerical simulations that opportunistic scheduling not only increases network throughput dramatically, but also increases energy efficiency and can be fair to the users when they cooperate, in particular by using D2D communications. We propose to leverage smartphones dual-radio interface capabilities to form clusters among mobile users. We design simple, scalable and energy-efficient D2D-assisted opportunistic strategies, which would incentivize mobile users to form clusters. We use a coalitional game theory approach to analyze the cluster formation mechanism, and show that proportional fair-based intra-cluster payoff distribution brings significant incentive to all mobile users regardless of their channel quality.