Beacon-based short message exchange in an inner city environment

In this paper, we proposes a method to utilize the huge number of IEEE 802.11 access points in an inner city environment to distribute information such as local sensor values, votes or short text messages. Due to the overlapping channels on IEEE 802.11b/g it is possible to receive packets from neighboring channels by overhearing. This fact allows every access point to monitor a part of the frequency band without switching the current radio channel. Our novel idea is to add user data to network layer beacon packets which every access point continuously send on a user-selected radio channel. This method allows transferring small size messages between access points or an access point and a mobile device without any reconfiguration like disabling the WLAN encryption. We conduct a measurement in the inner city of Mannheim, Germany to evaluate the typical density and distribution of access points in such an environment. We then use the measured data to calculate for every access point the expected reception probability on the street segments around. Based on these statistics, we appraise the reception probabilities of the access points among each other and perform a simulation study to estimate the size of the dissemination area that can be reached. Additionally, we analyze the required time to distribute the information to all reachable access points. Based on the measurement and simulation results, we can conclude that the estimated connectivity of an ad-hoc network based on access points is sufficient to disseminate information in the proximity.