Exploiting locality of demand to improve the performance of wireless data broadcasting

With the increasing popularity of wireless networks and mobile computing, data broadcasting has emerged as an efficient way of delivering data to mobile clients having a high degree of commonality in their demand patterns. In many applications, clients are grouped into several groups, each one located in a different region, with the members of each group having similar demands. In fixed-bit-rate wireless broadcast systems, transmission power is set at such a level that guarantees the necessary level of received energy per bit for all clients in the service area so that they can operate under a predefined bit error rate level. However, as in wireless cellular environments, the path loss of wireless signals is typically inverse to the fourth power of the transmitter/receiver distance, there exists an increasing redundancy in the level of received energy per bit for decreasing distances from the server´s antenna. This paper proposes a mechanism that exploits locality of demand in order to increase the performance of wireless data dissemination systems. Specifically, it trades the received energy per bit redundancy at distances smaller than the radius of the service area for an increased bit rate for transmission of items demanded by clients at such distances. This results in an increased transmission speed for many items. The bit rate for an item transmission is dynamically determined from the distance between the server´s antenna to the group of clients that demand this item. Knowledge of clients´ positions is conveyed to the server via a simple feedback from the clients. Simulation results that reveal significant performance improvement over fixed-bit-rate broadcasting in environments characterized by locality of client demands are presented