摘要：With 5 billion mobile phone subscribers already in the world today and the projected rapid increase in wireless data consumption, the energy efficiency of cellular networks has now become an urgent issue –in terms of both a network operator’s energy cost (hence profit margin) and the perspective of environmental impacts. This is particularly the case for base stations, which can account for more than half of a network’s energy consumption. While much research in this area is already under way, many significant challenges at all levels still remain to be investigated. These issues range from fair metrics and the corresponding fundamental trade-offs to traffic patterns and user behaviours, and from circuit design and baseband processing to network deployment and dynamic reconfiguration.While base station design (e.g. power amplifier and remote radio head) still plays a key role in increasing the energy efficiency at a link level, the ultimate improvement of energy efficiency in cellular networks is likely to require a network approach based on dynamic cell reconfiguration and inter-level joint optimisation.One powerful network approach to improving the energy efficiency is heterogeneous networking. This can be achieved either by densification of cells overlaid by a macro-cell network or by deployment of relay stations at the boundary of macro cells. A critical question is: which structure is better in network performance and energy efficiency? This is studied in the 1st paper of this special issue: “Small-net vs. relays in a heterogeneous low energy LTE architecture” by W. Guo and T. O’Farrel. By using a multi-cell multi-user dynamic LTE simulator, the paper shows that a key parameter in deciding which structure to employ is the percentage of high-mobility users.Another network oriented strategy to increase the energy efficiency, which has lately received much attention, is to impose a sleep mode on certain base stations or sectors under certain traffic loads. While this makes obvious sense from the view point of energy consumption, many outstanding issues still exist. One challenge is: under which traffic condition(s) a base station should be “switched off”(i.e. entering sleep mode) while avoiding over-frequent mode switching. This is the topic of the 2nd paper: “Two teletraffic-based schemes for energy saving in cellular networks with micro-cells” by Z. Haq and F.Y. Li. By using a simplified 3-cell network, the authors propose both a deterministic switching scheme based on a channel occupancy threshold and a probabilistic scheme based on a finite Markov decision process, while suggesting the possibilities for future extension.The sleep mode strategy also faces some practical challenges, and these have not been addressed in great detail in the existing literature. The 3rd paper of this special issue, “Realistic energy saving potential of sleep mode for existing and future mobile networks” by G. Micallef, L. Saker, S. E. Elayoubi, and H.-O. Scheck, deals with exactly some of these practical factors, and shows how much gain in energy efficiency can potentially be realised when some realistic conditions or limitations are taken into account (such as user experience and the type of equipment and networks).The three papers included here are the results of a rigorous peer review and selection process, but we would like to express our gratitude to all the authors who have responded to our call for papers as well as all the reviewers for their constructive comments. Finally, we must also thank Dr. Haohong Wang, the Editor-in-Chief of Journal of Communications, for giving us the opportunity to guest edit this special issue.
