Energy Efficiency In Wireless Networks Research Articles

A robust optimisation model and cutting planes for the planning of energy-efficient wireless networks

In this paper, we present an optimisation model for the energy-efficient planning of future wireless networks. By applying robust optimisation, we extend this model to a robust formulation which considers demand uncertainties. The computability of the resulting model is moderate. Hence, we apply three different cutting plane approaches for an improvement. Furthermore, an extensive case study is performed to examine the price of robustness, to compare the robust solution to conventional planning, and to explore the performance of the cutting planes.

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.

User cooperation in wireless networks

As the wireless communication channel is shared in nature, user cooperation is a key enabling tool to exploit the spatial multiplexing and diversity gains to improve spectrum and energy efficiency of wireless networks. User cooperation can take many forms, including the physical-layer cooperative communications, the link-layer cooperative and cognitive medium access, the network-layer cooperative routing and load balancing, the collaborative end-to-end congestion control in the transport layer, and the cooperative peer-to-peer services. The development and optimization of cooperation technologies requires interdisciplinary efforts, from advanced signal processing and communication to network protocol design and optimization. It also sparks theoretical breakthroughs in topology control, nonlinear optimization, signal processing and complex networks, and stimulates practical advances in mobile communications and networking technologies, devices and platforms.

A game theoretic study of energy efficient cooperative wireless networks

In wireless networks, it is well-known that intermediate nodes can be used as cooperative relays to reduce the transmission energy required to reliably deliver a message to an intended destination. When the network is under a central authority, energy allocations and cooperative pairings can be assigned to optimize the overall energy efficiency of the network. In networks with autonomous selfish nodes, however, nodes may not be willing to expend energy to relay messages for others. This problem has been previously addressed through the development of extrinsic incentive mechanisms, e.g., virtual currency, or the insertion of altruistic nodes in the network to enforce cooperative behavior. This paper considers the problem of how selfish nodes can decide on an efficient energy allocation and endogenously form cooperative partnerships in wireless networks without extrinsic incentive mechanisms or altruistic nodes. Using tools from both cooperative and non-cooperative game theory, the three main contributions of this paper are (i) the development of Pareto-efficient cooperative energy allocations that can be agreed upon by selfish nodes, based on axiomatic bargaining techniques, (ii) the development of necessary and sufficient conditions under which "natural" cooperation is possible in systems with fading and non-fading channels with- out extrinsic incentive mechanisms or altruistic nodes, and (iii) the development of techniques to endogenously form cooperative partnerships without central control. Numerical results with orthogonal amplify-and-forward cooperation are also provided to quantify the energy efficiency of a wireless network with sources selfishly allocating transmission/relaying energy and endogenously forming cooperative partnerships with respect to a network with centrally optimized energy allocations and pairing assignments.

Energy Efficient Wireless Networks Towards Green Communications

Wireless networks have become an essential part of the modern life. However, currently, 3% of the world-wide energy is consumed by the ICT infrastructures which causes about 2% of the world-wide CO2 emissions. The transmitted data-volume increases rapidly and wireless communications are used extensively while network design rules have practically ignored the energy efficient network design approach to limit CO2 emissions. This approach is currently named Green Communications. Significant energy savings in mobile networks can be expected by defining and standardizing energy efficiency metrics and combining energy aware flexible radios and networks. This paper discusses several techniques such as cross layer approach, multiple antennas, cell size reduction and cognitive radio, from the system-wide energy efficiency point of view, outlining challenges and open issues.

A cooperative differential game model based on network throughput and energy efficiency in wireless networks

Network throughout and energy efficiency are of paramount importance for network performance in an energy-constrained wireless network. However, it is difficult to achieve optimal network throughout and energy efficiency simultaneously. So it is very necessary to find a solution based on tradeoff between network throughput and energy efficiency, which have not yet been well studied in existing works. In this paper, we present a cooperative differential game model and find a time-consistency solution by Shapley value which determines a fair distribution of the total cooperative cost among players.

Power assignment problems in wireless communication: Covering points by disks, reaching few receivers quickly, and energy-efficient travelling salesman tours

In this paper, we present approximation algorithms for a variety of problems occurring in the design of energy-efficient wireless communication networks. We first study the k-station network problem, where for a set S of stations and some constant k, one wants to assign transmission powers to at most k senders such that every station in S can receive a signal from at least one sender. We give a (1 + ϵ)-approximation algorithm for this problem. The second problem deals with energy-efficient networks, allowing bounded hop multicast operations, that is given a subset C of the stations S and a designated source node s ∈ S, we want to assign powers to the sending stations, such that every node in C can be reached by a transmission from s within k hops. For this problem, we provide an algorithm which runs in time linear in ∣ S∣. The last problem deals with a variant of the non-metric TSP problem where the edge costs correspond to the Euclidean distances to the power of some α ⩾ 1; this problem is motivated by data aggregation schemes in wireless sensor networks. We provide a simple constant approximation algorithm, which improves upon previous results when 2 ⩽ α ⩽ 2.7.

Green radio: Energy efficiency in wireless networks

Rarely have technical innovations changed everyday life as fast and profoundly as the massive use of personal mobile communications. In the past two decades mobile wireless services grew from niche market applications to globally available components of daily life: The first GSM phone call took place in 1991 in Finland and only 15 years later there were over two billion GSM users. Today there are already more than 4 billion mobile phone subscribers in the world, more than half the population of the planet, and there are expected to be more than 1.2 billion mobile broadband subscribers by 2012. For the first time in history, worldwide mobile data traffic exceeded voice traffic in December 2009, a point which had already been reached in WCDMA networks in 2007.

Building blocks of cooperative relaying in wireless systems

The concept of cooperative relaying promises gains in robustness and energy efficiency in wireless networks. This survey gives an introduction and overview of promising methods that can be used for cooperative relaying: relay selection protocols, cooperative channel and network coding, and physical layer aspects such as cooperative modulation. The particular methods can be seen as building blocks that can be configured and optionally used for designing a system. They offer a large number of design options for relaying systems. Based on available hardware features, expected environment, and required services an efficient system needs to be tailored using the right subset of available methods.

On cooperation in energy efficient wireless networks: the role of altruistic nodes

In wireless networks with energy limited nodes, user cooperation is usually exploited to reduce the network energy consumption. In many practical scenarios, however, nodes' selfishness raises doubts on whether each node will be willing to spend its valuable energy in forwarding packets for other users. To analyze this problem, a non-cooperative game theoretic framework is adopted in our work. Using this framework, the critical role of altruistic nodes in encouraging cooperation is established, both for small and large scale networks. In a small network, where nodes utilize the Decode-Forward scheme to cooperate, we show that a relay node, with appropriate strategy and location, successfully turns the Nash Equilibrium from no- cooperation to full-cooperation. In the large scale network, we show that it is sufficient to have a vanishingly small fraction of the nodes to be altruistic, i.e., relay nodes, in order to ensure full cooperation from all the nodes in the network. This result hinges on using the appropriate forwarding policies by the altruistic nodes, as detailed in the sequel. Our work also establishes the sub-optimality of traditional relaying strategies, which ignore the game-theoretic aspect of the problem. An important aspect of our work is that only reward/punishment policies that can be realized on the physical layer are used, and hence, our results establish the achievability of full cooperation without requiring additional incentive mechanisms at the application layer.

A Game-Theoretic Approach to Energy-Efficient Modulation in CDMA Networks with Delay QoS Constraints

A game-theoretic framework is used to study the effect of constellation size on the energy efficiency of wireless networks for M-QAM modulation. A non-cooperative game is proposed in which each user seeks to choose its transmit power (and possibly transmit symbol rate) as well as the constellation size in order to maximize its own utility while satisfying its delay quality-of-service (QoS) constraint. The utility function used here measures the number of reliable bits transmitted per joule of energy consumed, and is particularly suitable for energy-constrained networks. The best-response strategies and Nash equilibrium solution for the proposed game are derived. It is shown that in order to maximize its utility (in bits per joule), a user must choose the lowest constellation size that can accommodate the user's delay constraint. This strategy is different from one that would maximize spectral efficiency. Using this framework, the tradeoffs among energy efficiency, delay, throughput and constellation size are also studied and quantified. In addition, the effect of trellis-coded modulation on energy efficiency is discussed.

An energy-efficient architecture of wireless home network based on MAC broadcast and transmission power control

To construct an energy-efficient wireless home network based on IEEE 802.15.4, a novel architecture is proposed. In this architecture, all nodes are classified into stationary nodes and mobile nodes according to the functionality of each node. Mobile nodes are usually battery-powered, and therefore need low-power operation. In order to improve power consumption of mobile nodes, effective handover sequence based on MAC broadcast and transmission power control based on LQ (link quality) are employed. Experimental results demonstrate that by using the proposed architecture, communication time and power consumption of mobile nodes can be reduced by 1.2 seconds and 42.8%, respectively.

Improving Communication Energy Efficiency in Wireless Networks Powered by Renewable Energy Sources

Energy efficiency is an important issue in wireless networks where the nodes are powered by batteries. In this work, we analyze the energy consumption in one-transmitter-multiple-receiver communication and develop scheduling schemes to improve energy efficiency at the transmitter. Our focus is on systems powered by a renewable energy source such as solar power. We consider an environment where both energy and time to access the wireless channel and transmit data are limited, and data destined for different receivers have different values and incur different energy costs. We present optimal scheduling algorithms that selectively transmit data at calculated rates so that the throughput or the total transmission value is maximized under given time limits and energy constraints.

Topology control of ad hoc wireless networks for energy efficiency

In ad hoc wireless networks, to compute the transmission power of each wireless node such that the resulting network is connected and the total energy consumption is minimized is defined as a Minimum Energy Network Connectivity (MENC) problem, which is an NP-complete problem. In this paper, we consider the approximated solutions for the MENC problem in ad hoc wireless networks. We present a theorem that reveals the relation between the energy consumption of an optimal solution and that of a spanning tree and propose an optimization algorithm that can improve the result of any spanning tree-based topology. Two polynomial time approximation heuristics are provided in the paper that can be used to compute the power assignment of wireless nodes in both static and low mobility ad hoc wireless networks. The two heuristics are implemented and the numerical results verify the theoretical analysis.

Distributed Algorithms in Wireless Sensor Networks

Wireless sensor networks (WSNs) are an emerging field of research which combines many challenges in distributed computing and network optimization. One important goal is to improve the functional lifetime of the sensor network using energy-efficient distributed algorithms, networking and routing techniques, and dynamic power management techniques. The energy consumption represents the major cost metric in almost all algorithms that are to be run in and on top of the WSN. Resulting from these constraints, various optimization criteria emerge. In our talk, we present some of the differences between energy-efficient wireless networking and network optimization usually considered by explaining key design features needed in the envisioned setting of wireless sensor networks.

Low-energy wireless communication network design

Energy-efficient wireless communication network design is an important and challenging problem. Its difficulty lies in the fact that the overall performance depends, in a coupled way, on the following subsystems: antenna, power amplifier, modulation, error control coding, and network protocols. In addition, given an energy constraint, improved operation of one of the aforementioned subsystems may not yield better overall performance. Thus, to optimize performance one must account for the coupling among the above subsystems and simultaneously optimize their operation under an energy constraint. In this article we present a generic integrated design methodology that is suitable for many kinds of mobile systems and achieves global optimization under an energy constraint. By pointing out some important connections among different layers in the design procedure, we explain why our integrated design methodology is better than traditional design methodologies. We present numerical results of the application of our design methodology to a situational awareness scenario in a mobile wireless network with different mobility models. These results illustrate the improvement in performance that our integrated design methodology achieves over traditional design methodologies, and the tradeoff between energy consumption and performance.