Luis Suarez

An overview and classification of research approaches in green wireless networks

Energy consumption of wireless networks is now a very important research topic and several research teams worldwide are proposing solutions for the so-called green wireless networks, i.e. energy-efficient wireless networks. Although the increase of this research activity is rather recent, a great number of research papers and collaborative projects exist nowadays. We first summarise the metrics used in the related literature for performance evaluation. Then, we focus on describing the current approaches proposed by reviewing a good number of references from literature. The main research directions are presented: the component level research, where the efforts are mainly concentrated on the power amplifier section; the cell layout adaptation including the cell-breathing technique and coverage extension methods like femtocells and relays; in addition, we also include the radio resource management and the cognitive radio into the studied approaches. These methods are analysed, compared, classified and then a framework of classification and integration is proposed. We finally describe some major collaborative projects dedicated to this topic.

Energy-efficient BS switching-off and cell topology management for macro/femto environments

In the context of ever-increasing wireless data rates, energy consumption could increase fast, with severe consequences on the operators energy bill, in addition to environmental considerations. Energy-efficient cell breathing and BS switching-off algorithms are an important tool for energy reduction in cellular networks. In this paper, an energy-efficient cell breathing and offloading mechanism in both macrocellular and heterogeneous networks is studied. First, the need for limiting the number of Macro-BSs switched off and the control of cell sizes are analyzed. An approach based on the use of a traffic threshold from a technique previously proposed by our team is applied in order to control the BS switching-off aggressiveness. One reason for limiting this aggressiveness is the trade-off we point out between the existing RAN power consumption and the transmission power in uplink for mobile devices. Then, in the context of macro/femto deployments, the BS switching-off possibilities are extended by means of the extra capacity from an added femtolayer under regulated control access. We explore the impact of access policies from 3GPP CSGs (Closed Subscriber Groups) on the network performance and how CSG features may be used by operators to set aspects such as pricing policies and QoS provision levels. In this article, our goal is to provide a combined approach of both techniques in a single framework for macro/femto environments. The obtained results are analyzed showing the importance of proper tuning of energy-efficient algorithms in order to guarantee convenient energy savings and maintaining good QoS levels.

Energy performance of a distributed BS based green cell breathing algorithm

In this article a novel distributed cell-breathing algorithm based on a clustered architecture is proposed for energy-efficient cellular networks. Firstly, a brief state of the art of current cell-breathing techniques is provided. Afterwards a description of the system model is given followed by the algorithm description. The algorithm is executed in each BS of each cluster following a sequence, which is synchronized into the set of clusters. When a BS attempts to go to sleep mode, it tries to redistribute the traffic to its neighbors if it is not more loaded than any one of them. When the BS redistributes this traffic, it will prefer to send the traffic to the highest loaded neighbors first. The presented algorithm avoids a centralized coordination and initial setup load thresholds. Therefore single point failure problems are not a risk and a robust self-organized approach is provided. We compare the results of state-of-the-art algorithms with the ones of our algorithm and point out the drawbacks of the other algorithms.

Analysis of a green-cell breathing technique in a hybrid access network environment

Energy efficiency in cellular networks is a major issue for current and future mobile networks. Several approaches have been proposed for this purpose: the component approach, the radio resource management (RRM) algorithms, the cell topology adaptation mechanisms, the hybrid network architectures, the cognitive radio approach and others. However, it is rare to find proposals where two or more of these approaches are combined in order to obtain a better energy efficiency. In this paper we combine the cell breathing technique, a cell topology adaptation mechanism, with a hybrid network approach composed of small and large cell layers. Our scenario includes the possibility of users being blocked by the femto-layer due to Closed-Subscriber Groups (CSG) access policies, a concept defined in 3GPP standards but not very discussed so far in the literature. By adding the cell breathing to the macro layer, we have two ways of traffic redistribution in order to offload and deactivate a larger number of Macro-BSs achieving to take the most of benefits from the hybrid cellular infrastructure. The described proposal is compared with other related mechanisms found in the literature. Our results lead to interesting conclusions for shortterm practical implementations.

Energy efficiency and cost issues in backhaul architectures for high data-rate green mobile heterogeneous networks

Small cells and heterogeneous network approaches in mobile networks are very promising as they provide an enhancement of capacity without a significant impact on the energy consumption when properly designed. Yet, recent studies have pointed out that the backhaul energy consumption cannot be neglected when a small cell deployment is introduced. In this paper, we provide a comprehensive study on energy efficiency, cost issues and trade-offs for backhaul infrastructure when the influence of Radio Access Network (RAN) design and growth strategies are considered. For the case study, we use two well-known backhaul architectures, one supported on fiber-to-the-building (FTTB)+ 10Gbps passive optical Network (10GPON) and a second which consists of FTTB+ Microwave backhauling. The numerical results and analysis performed provide significant insights of the potential energy savings, CAPEX, OPEX and challenges for backhaul and RAN architecture design.

A cross-layer MAC and routing protocol based on slotted aloha for wireless sensor networks

Wireless Sensor Networks (WSN) consist of a large number of sensors which have limited battery power. One of the major issues in WSN is the need to improve the overall network lifetime. Hence, WSN necessitate energy-efficient routing protocols. In this paper, a cross-layer routing protocol (PLOSA) is designed to offer a high delivery rate, a low end-to-end delay, and a low energy consumption. To achieve these goals, the transmission channel is divided into different slots, and a sensor has access to a slot related to its distance from the collector. The transmissions are then ordered within the frame from the farthest nodes to the closest ones which is a key point in order to ease forwarding and to conserve energy. We have conducted simulation-based evaluations to compare the performance of the proposed protocol against the framed aloha protocol. The performance results show that our protocol is a good candidate for WSN.

Electromagnetic radiation compliance under the use of green cell breathing and hybrid network approaches in LTE

The purpose of this paper is to study the effects on electromagnetic field levels of the green cell breathing technique in mobile networks. Although a great number of papers dedicated to QoS, radio issues and energy savings of the cell breathing algorithms have already been proposed, to the best of our knowledge, none has analyzed the effect on electromagnetic radiation. Yet, when cell sizes are changed (and specifically increase), it is evident that in some cases, the transmitted or received powers increase. We analyze the problem taking into account the different electromagnetic fields legal requirements and then estimate the received electric field for different cellular scenarios for LTE: a macro-only scenario, a macro scenario with cell-breathing and then a hybrid approach (femto/macro) combined with cell-breathing. Our simulation results show that given a number of radiation measurement sample points in a coverage zone, the percentage of threshold violations is exceeded by the use of cell breathing. This occurs when more exigent levels to those given in the ICNIRP recommendations are taken.

Impact of energy-efficient cell-breathing on the electromagnetic radiation levels of mobile phone devices

Energy-efficient cell breathing is a mechanism that consists of adapting cell sizes and number of active Base Stations (BS) to the distribution and current levels of traffic. In this article, our goal is to analyse the effect of such a technique on the electromagnetic (EM) radiation levels for mobile phone devices. Although there exist large details in the literature of cell-breathing on energy-efficiency related to the Radio Resource Management (RRM) aspects, to the best of our knowledge, there is still a lack of work on analysing the consequences of cell-breathing and BS switching-off schemes on the EM exposure issues related to the mobile terminal. In such approaches during low-traffic, whereas there are some BSs being switched-off, there are some other BSs that must remain active expanding their cell sizes to guarantee coverage. This requires a transmission power increase for both downlink and uplink side, that for mobile devices implies an increase of the specific absorption rate (SAR) [W/kg] on the mobile user. To conduct our study, we use one of our previously proposed techniques on cell-breathing to analyse the impact of uplink transmission power increase on resulting SAR levels. Here, different BS switching-off aggressiveness levels are considered to observe the resulting exposure levels using a 3G/CDMA scenario. The results show how SAR maximum levels increase as more aggressive switching-off schemes take place as well as the uplink interference rises due to a progressive increase of network load.

Energy-efficient scheduling for cloud mobile gaming

In this paper, we study the problem of wireless schedulers for cloud-based wireless gaming systems, with focus on energy efficiency issues. While green communications and networks have been widely studied in recent years, the rise of gaming based on wireless clouds introduces many specific aspects allowing important savings and improvements. We try to minimize the power consumption of this type of networks in a hybrid WiFi/LTE radio access network (RAN) by proposing a novel Wireless Cloud Scheduler (WCS) mechanism and applying different utility functions. We find that it is possible to reduce the power consumption, increase the maximum attainable capacity of the network in terms of number of served UEs and minimize the costs of cloud resources usage, while maintaining a good level of QoS.