IEEE Wireless Communications • June 2008 48 1536-1284/08/$25.00 © 2008 IEEE 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 W IRELESS T ECHNOLOGIES A DVANCES FOR E MERGENCY AND R URAL C OMMUNICATIONS INTRODUCTION The deployment of wired communication infras- tructures in rural areas is not convenient from an economical point of view. As a consequence, even in the most developed countries, large countryside areas are not equipped with any communication facilities. On the contrary, sever- al reasons exist for supporting a certain degree of network connectivity even in remote areas. For example: • Users driving in the countryside might be interested in accessing or delivering data for both entertainment and professional reasons. • Sensor and actor networks might be deployed in plantations to improve quantity and quality of the products of a farm; in this case, net- work connectivity is needed to allow remote users to access the data collected by the sen- sors and/or control the actors. If the application is delay-tolerant, mobility of some network elements involved in the sce- nario can be exploited, and a good trade-off between economic investment and the require- ment for connectivity in such areas can be achieved by using infostation systems [1]. In this system model wireless ports — simply called infostations — are deployed along highways and/or placed in selected hot spots, acting as gateways to the network infrastructure and pro- viding access to mobile wireless nodes when they are in radio coverage. An infostation requires a connection to the network infrastructure and a source of power supply. The former can be achieved thanks to wireless mesh networking technology [2], which makes communication capacities avail- able even in the most remote rural areas. Con- cerning the power supply, several methods can be used. For example, photovoltaic cells or eolic generators generate electric energy on site. Furthermore, new technologies to trans- mit energy wirelessly are emerging, which can be used to deliver energy in rural areas with low infrastructure investments [3]. Note, how- ever, that in any case energy will be a scarce resource. In fact, to increase production of energy, both size and cost of photovoltaic and eolic generators must increase as well. More- over, wireless energy transmission has very low efficiency; thus, an increase in the energy requirement results in a significantly higher increase in the energy that must be transmit- ted. It follows that energy must be used in the most efficient way by infostations. This aspect is even more critical when mobile wireless nodes also cannot rely on energy recharging power generators. Note that the problem highlighted above is typical of rural communications. On the con- trary, in urban environments the constraint is represented by the available bandwidth, which is a scarce resource to be shared among several mobile users, usually pedestrians, exhibiting strong energy constraints. In these scenarios, dif- LAURA GALLUCCIO, ALESSANDRO LEONARDI, GIACOMO MORABITO, AND SERGIO P ALAZZO, UNIVERSITY OF CATANIA ABSTRACT The infostation communication paradigm rep- resents a good trade-off between the size of investments in infrastructure and the connectivi- ty needs in rural areas. In fact, exploiting the emerging mesh networking technologies, infosta- tions can be deployed with low cost. In infosta- tion systems, mobile nodes achieve network connectivity when they are in the radio coverage of the infostation. Nevertheless, preliminary to the communication, there is a phase in which discovery must be achieved between mobile nodes and the infostation. This is an energy con- suming phase that has significant impact on the performance experienced by mobile nodes. In this article the trade-off between energy efficien- cy and performance experienced by mobile users is discussed. This is an important problem in rural areas since infostations will often be sup- plied by photovoltaic or eolic generators, which have a cost that increases as the need for energy increases. To carry the study, analytical results previously obtained for general mobile wireless networks are tailored to infostation systems deployed in rural areas. Such derivations have been utilized to gain insight into the design of energy-efficient protocols for the above applica- tion scenario. T IMELY AND E NERGY -E FFICIENT C OMMUNICATIONS IN R URAL I NFOSTATION S YSTEMS The authors discuss the trade-off between energy efficiency and performance experienced by mobile users. This is an important problem in rural areas since infostations will be often supplied by photovoltaic or eolic generators that have a cost that increases as the need of energy increases.