Traffic modelling and cost optimization for transmitting traffic messages over a hybrid broadcast and cellular network

Broadcast networks are typically used for distributing common information (music, data) to many users within a given service area, while cellular networks provide point-to-point voice or data delivery to individual users. The fundamental difference from an economic point of view is that cellular networks follow a ´pay-per-use´ paradigm with ´per minute´ or ´per kbyte´ charges, whereas commercial broadcast services (e.g. pay-TV) are charged for by long-term (months or years) subscriptions. In this paper, we investigate a hybrid system for carrying traffic information services. It comprises a data broadcast network for providing the base capacity and a cellular network for carrying the peak traffic exceeding this base capacity. Cellular capacity for the excess data traffic can be purchased whenever needed. However, capacity in broadcast networks is typically leased for long periods of time (potentially several years) at a fixed price. The key problem is how to choose depending on the statistic properties of the input data traffic - the fixed broadcast capacity such that the overall operation cost for the hybrid network is minimized. Results for a telematics service delivering traffic information show that indeed considerable cost savings can be achieved by carefully balancing the capacity allocated in the broadcast network against the peak traffic redirected through the cellular network. The simple analytical model proposed to aid in this tradeoff is validated by simulations.