[show abstract][hide abstract] ABSTRACT: In this paper we study base station sleep modes that, by reducing power consumption in periods of low traffic, improve the energy efficiency of cellular access networks. We assume that when some base stations enter sleep mode, radio coverage and service provisioning are provided by the base stations that remain active, so as to guarantee that service is available over the whole area at all times. This may be an optimistic assumption in the case of the sparse base station layouts typical of rural areas, but is, on the contrary, a realistic hypothesis for the dense layouts of urban areas, which consume most of the network energy.
We consider the possibility of either just one sleep mode scheme per day (bringing the network from a high-power, fully-operational configuration, to a low-power reduced configuration), or several sleep mode schemes per day, with progressively fewer active base stations. For both contexts, we develop a simple analytical framework to identify optimal base station sleep times as a function of the daily traffic pattern.
We start by considering homogeneous networks, in which all cells carry the same amount of traffic and cover areas of equal size. Considering both synthetic traffic patterns and real traffic traces, collected from cells of an operational network, we show that the energy saving achieved with base station sleep modes can be quite significant, the actual value strongly depending on the traffic pattern. Our results also show that most of the energy saving is already achieved with one sleep mode scheme per day. Some additional saving can be achieved with multiple sleep mode schemes, at the price of a significant increase in complexity.
We then consider heterogeneous networks in which cells with different coverage areas and different amounts of traffic coexist. In particular, we focus on the common case in which some micro-cells provide additional capacity in a region covered by an umbrella macro-cell, and we prove that the optimal scheduling of micro-cell sleep times is in increasing order of load, from the least loaded to the most loaded. This provides a valuable guideline for the scheduling of sleep modes (i.e., of low-power configurations) in complex heterogeneous networks.
[show abstract][hide abstract] ABSTRACT: The increasing concern about the energy consumption of communication networks is driving the research community to identify approaches to save energy in the networks of today. For instance, considering wireless local area networks (WLANs), the activation of network resources can be driven by the user demand, avoiding having to always power on all Access Points (APs). In this paper, we consider a portion of a dense WLAN system, where many APs are deployed to provide sufficient capacity to serve a large number of active users during peak traffic hours. To provide large capacity, a number of APs are colocated in the same position and provide identical coverage; we say that these APs belong to the same group, and they serve users in the same area. The areas covered by different groups only partially overlap, so that some active users can only be served by a group of APs, but a fraction of active users can be served by several groups. Due to daily variations of the number of active users accessing the WLAN, some APs can be switched off to save energy when not all the capacity is needed. The main focus of our study is the investigation of the type of algorithm that should be used for the association of active users with APs in order to increase the amount of saved energy in dense WLANs. Results show that when some system state information is available, such as the number of users associated with each AP, the energy consumption can decrease up to 20%. Furthermore, our study gives comprehensive insights on the trade-off between the opposite needs to save energy and provide quality of service to the users.
[show abstract][hide abstract] ABSTRACT: Recent works advocate the possibility of improving energy efficiency of network devices by modulating switching and transmission capacity according to traffic load. However, addressing the trade-off between energy saving and Quality of Service (QoS) under these approaches is not a trivial task, specially because most of the traffic in the Internet of today is carried by TCP, and is hence adaptive to the available resources. In this paper we present a preliminary investigation of the possible intertwining between capacity scaling approaches and TCP congestion control, and we show how this interaction can affect performance in terms of both energy saving and QoS.
[show abstract][hide abstract] ABSTRACT: In this short note we briefly discuss three issues related to the relevance and the possible impact of research in the field of green networking, with special attention to the wireless case, since this is the context where energy efficiency is needed most.
Ad Hoc Networking Workshop (Med-Hoc-Net), 2011 The 10th IFIP Annual Mediterranean; 07/2011
[show abstract][hide abstract] ABSTRACT: In this paper we study the energy-aware cooperative management of the cellular access networks of the operators that offer service over the same area. In particular, we evaluate the amount of energy that can be saved by using all networks in high traffic conditions, but progressively switching off networks during the periods when traffic decreases, and eventually becomes so low that the desired quality of service can be obtained with just one network. When a network is switched off, its customers are allowed to roam over those networks that remain powered on. Several alternatives are studied, as regards the traffic profile, the switch-off pattern, the energy cost model, and the roaming policy. Numerical results indicate that a huge amount of energy can be saved with an energy-aware cooperative management of the networks, and suggest that, to reduce energy consumption, and thus the cost to operate the networks, new cooperative attitudes of the operators should be encouraged with appropriate incentives, or even enforced by regulation authorities.
[show abstract][hide abstract] ABSTRACT: In this article, we consider the adoption of sleep modes for the base stations of a cellular access network, focusing on the design of base station sleep and wake-up transients.. We discuss the main issues arising with this approach, and we focus on the design of base station sleep and wake-up transients, also known as cell wilting and blossoming. The performance of the proposed procedures is evaluated in a realistic test scenario, and the results show that sleep and wake-up transients are short, lasting at most 30 seconds.
[show abstract][hide abstract] ABSTRACT: The introduction of sleep modes in the operations of base stations is today considered one of the most promising approaches to reduce the energy consumption of cellular access networks. Several papers have considered this option, assuming that the switch-on and switch-off transients are of negligible duration. In this paper we study the switch-off transients for one cell, investigating the amount of time necessary to implement the switch-off, while allowing terminals to handover to a new BS without overloading the signaling channels, and we show that the switch-off durations have a marginal impact on the energy savings achievable with the sleep mode scheme. I. INTRODUCTION
[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: Sleep modes are emerging as a promising technique for energy-efficient networking: by adequately putting to sleep and waking up network resources according to traffic demands, a proportionality between energy consumption and network uti-lization can be approached, with important reductions in energy consumption. Previous studies have investigated and evaluated sleep modes for wireless access networks, computing variable percentages of energy savings. In this paper we characterize the maximum energy saving that can be achieved in a cellular wireless access network under a given performance constraint. In partic-ular, our approach allows the derivation of realistic estimates of the energy-optimal density of base stations corresponding to a given user density, under a fixed performance constraint. Our results allow different proposals to be measured against the maximum theoretically achievable improvement. We show, through numerical evaluation and simulation, the possible energy savings in today's networks, and we further demonstrate that even with the development of highly energy-efficient hardware, a holistic approach incorporating system level techniques is essential to achieving maximum energy efficiency.
[show abstract][hide abstract] ABSTRACT: Energy efficient networks are becoming a hot research topic, and the networking community is increasingly devoting its attention to the identification of approaches to save energy in the networks of today. However, the networks of tomorrow will require built-in energy efficiency capabilities, so that new design techniques based on network models that account for energy efficiency are called for. One of the simplest approaches to obtain energy efficiency is based on the activation of network resources on demand, thus avoiding to always power on all the resources that are necessary to serve users during peak traffic periods. In this paper we both present a simple analytical model to determine the effectiveness of policies that activate APs (Access Points) in dense WLANs (Wireless LANs) according to the actual user demands, and quantify the performance that is achieved by such policies in terms of energy savings and QoS (Quality of Service). Numerical results show that, in the configurations that we studied, energy savings up to 87% are possible during low traffic periods, with hardly any sacrifice in QoS.
Proceedings of the 1st International Conference on Energy-Efficient Computing and Networking, e-Energy 2010, Passau, Germany, April 13-15, 2010; 01/2010
[show abstract][hide abstract] ABSTRACT: In this paper we evaluate the energy saving that can be achieved with the energy-aware cooperative management of the cellular access networks of two operators offering service over the same area. We evaluate the amount of energy that can be saved by using both networks in high traffic conditions, but switching off one of the two during the periods when traffic is so low that the desired quality of service can be obtained with just one network. When one of the two networks is off, its customers are allowed to roam over the one that is on. Several alternatives are studied, as regards the switch-off pattern: the one that balances the switch-off frequencies, the one that balances roaming costs, the one that balances energy savings, and the one that maximizes the amount of saved energy. Our results indicate that a huge amount of energy can be saved, and suggest that, to reduce energy consumption, new cooperative attitudes of the operators should be encouraged with appropriate incentives, or even enforced by regulation authorities.
[show abstract][hide abstract] ABSTRACT: The increasing concern about the energy consumption of telecommunication networks is driving operators to manage their equipments so as to optimize energy utilization without sacrificing the user experience. In this paper, we focus on UMTS access networks, since access devices are the main energy consumers in UMTS networks. We propose a novel approach for the energy-aware management of UMTS access networks, consisting in a dynamic network planning, that, based on the instantaneous traffic intensity, reduces the number of active access devices when they are underutilized (typically at night). When some access devices are switched off, radio coverage and service provisioning are taken care of by the devices that remain active, possibly with some small increase in the emitted power, so as to guarantee that service is available over the whole area, with the desired quality.
[show abstract][hide abstract] ABSTRACT: This paper is about design methodologies for packet networks, under the constraints of end-to-end quality of service (QoS) metrics. The network modeling also considers the dynamics of today's packet networks. We are particularly considering the problem of capacity and flow assignment where the routing assignments and capacities are considered to be decision variables. An efficient Lagrangean relaxation-based heuristic procedure is developed to find bounds and solutions for a corporate virtual private network (VPN), where the traffic is mostly based on TCP connections. Numerical results for a variety of problem instances are reported.
AEU - International Journal of Electronics and Communications. 01/2009;
[show abstract][hide abstract] ABSTRACT: In this paper we study with simple analytical models the energy-aware management of cellular access networks, trying to characterize the amount of energy that can be saved by reducing the number of active cells during the periods when they are not necessary because traffic is low. When some cells are switched off, radio coverage and service provisioning are taken care of by the cells that remain active, so as to guarantee that service is available over the whole area. We show how to optimize the energy saving, first assuming that any fraction of cells can be turned off, and then accounting for the constraints resulting from the cell layout.
[show abstract][hide abstract] ABSTRACT: In this paper, we consider packet networks loaded by admissible traffic patterns, i.e., by traffic patterns that, if optimally routed, do not overload network resources. We prove that simple distributed dynamic routing and scheduling algorithms based upon link state information can achieve the same network throughput as optimal centralized routing and scheduling algorithms with complete traffic information. Our proofs apply the stochastic Lyapunov function methodology to a flow-level abstract model of the network, and consider elastic traffic, i.e., we assume that flows can adapt their transmission rates to network conditions, thus resembling traffic engineering and quality-of-service approaches being currently proposed for IP networks. Although the paper mainly brings a theoretical contribution, such dynamic routing and scheduling algorithms can be implemented in a distributed way. Moreover we prove that maximum throughput is achieved also in case of temporary mismatches between the actual links state and the link state information used by the routing algorithm. This is a particularly relevant aspect, since any distributed implementation of a routing algorithm requires a periodic exchange of link state information among nodes, and this implies delays, and thus time periods in which the current link costs are not known.
IEEE/ACM Transactions on Networking 01/2008; · 2.01 Impact Factor