Scheduling multicast and unicast transmissions in an infostation environment

An infostation is a wireless data disseminator that provides data to mobile terminals within its limited range at high transmission speeds. Users of an infostation subscribe to information categories and receive relevant data from the infostation automatically as they pass through the infostation's transmission range. Data from an infostation is meant to be transmitted quickly to the mobile terminal and consumed later in an offline setting. Due to the limited amount of time that a terminal is within range of an infostation, an important goal is to minimize the delivery time for a data item in order to maximize the likelihood that the item will be transferred successfully to the mobile terminal before its departure. This dissertation uses mathematical analysis and simulation to investigate how to schedule data transmissions using multicast and unicast transmission techniques.; A single-channel model of an infostation environment is analyzed mathematically using M/D/1 queueing principles, and simulations are performed on this model to verify the analysis. In addition, an alternate broadcast model for the infostation is presented and analyzed through simulation, and a simulation of the effect of packet errors on the standard model using a basic IEEE 802.11b packet error model is presented. We show that for light terminal traffic in the infostation range, unicast transmission is adequate to handle all requests, but as the traffic increases, the system should begin to use multicast, however all of the data items should not be multicast. Typically, only a small number of the most popular items should be multicast in order to achieve optimal performance of the infostation.; By analyzing the arrival rate of terminals into the infostation area and the distribution of items downloaded, the infostation designer can use these results to determine the specific number of multicast items to transmit per cycle to maximize the likelihood that a terminal will receive its desired item before it leaves the infostation's transmission range.