LIKE VEHICLES LIKE PEDESTRIANS, IN AN INTERCONNECTED WORLD Alessandro Amoroso, Marco Roccetti Department of Computer Science and Engineering Mura Anteo Zamboni 7, 40127 Bologna {roccetti, amoroso}@cs.unibo.it Gustavo Marfia Department of Life Quality Studies Corso D’Augusto 237, 47921 Rimini gustavo.marfia@unibo.it ABSTRACT We present some scenarios where a group of people walking around and linked together by a common intent could take advantage by communicating each other by means of their smartphones and tablets implementing an ad–hoc network. We show the results of a study for extending to walk- ing pedestrian of an optimal broadcast for platoon of vehicles traveling on a road. The extension has the scope of porting the original broadcast from a mono–dimensional space to a bi– dimensional one. The pedestrians could walk in open spaces and are not constrained to move along roads or walkway. We could consider that each person brings its own smart- phone or tablet. The current models of these devices offer enough computational power to run both a communication mechanism and an overlying application. We started from an optimal and lightweight P2P communication system for vehi- cles. Smartphones and a tablets are devices fully equipped to implement such a broadcast service by means of GPS receiver and WiFi capabilities. We show several examples and scenarios to proof the im- possibility of extend the optimal broadcast from one to two dimensions. The mono–dimensional case takes strong advan- tages form the underlying geometry and its key concepts be- came unusable in a bi–dimensional case. Index Terms— ad-hoc networks, mobility, full 2D sce- nario, interactivity, smartphones 1. INTRODUCTION Nowadays we are witnessing a growing diffusion of smart- phones worldwide. A large portion of currently used cellular phones is capable to run specialized applications, to connect to WiFi network and to receive GPS signals. Smartphones could be connected to the Internet either by means of Wifi or cellular data networks. Both of these means of communica- tion could be not available, or properly viable, while those devices could always implement ad–hoc networks. We consider a group of people walking around, each person equipped with its own smartphone running a specific This work was supported by the Italian PRIN Project ALTERNET. application to communicate each other in a P2P fashion by means of ad–hoc network. We can sketch three scenarios, that differ each other with respect to GPS and WiFi availability and pattern of mobil- ity. We consider as cellular data any kind of data transmis- sion over the cellular phone signal, without differentiating be- tween the generations of mobile data standards. This simplifi- cation does not affect the scenarios. Note that in the classifica- tion below we could ignore WiFi networks while our proposal does not require such an infrastructure and it is somewhat al- ternative to it. Open air in this case, we can suppose that the pedestrians could walk in a large space either without constraints, such as in the countryside, or with some limitation, such as in an archeological site. We could characterize this scenario with fickle cellular data signals and ro- bust GPS reception. WiFi networks are almost absent or sporadically available. Urban or inside buildings pedestrians could walk either on the streets and squares or inside a building, such as mu- seums or public edifices. In this scenario, we could suppose that GPS reception is inconstant, and could be negligible, while cellular data are reliable. WiFi net- works are generally private and overlapping, each one distinct from its neighborhood. Transportation facilities a group of persons is sitting in a train or in a bus; they are almost immobile each other but they are moving as a whole with respect to the sur- rounding environment. GPS reception is inconstant and cellular signals could be varying. Onboard WiFi net- works are rarely available, while external ones are al- most unaccessible. It is worth mentioning that some train companies are start- ing to offer WiFi connections on selected trains, usually their top class ones, and that some airline companies are announc- ing the imminent introduction of some WiFi capabilities is selected fights and aircrafts. As an example, consider that in Italy some high speed trains, that largely travels at 300Km/h,