Information delivery through broadcasting in satellite communication networks

Satellite broadcast is an important candidate for large-scale multimedia in formation distribution due to the inherent wide-range multicasting capabili ty of satellites and the asymmetry of satellite communications (high bandwi dth downlink, limited bandwidth uplink) that matches nicely the information flow asymmetry in multimedia applications, We consider a data broadcasting model that is encountered in most asymmetric satellite communication envir onments. The problem of scheduling the data broadcast such that average res ponse time experienced by the users is low is considered. In a push-based s ystem, where the users cannot place requests directly to the server and the broadcast schedule should be determined based solely on the access probabi lities, we formulate a deterministic dynamic optimization problem, the solu tion of which provides the optimal broadcast schedule, properties of the op timal solution are obtained and then we propose a suboptimal dynamic policy which achieves average response time close to the lower bound. In a pull-b ased system where the users may place requests about information items dire ctly to the server, the scheduling can be based on the number of pending re quests for each item. Suboptimal policies with good performance are obtaine d in this case as well. If a user has local memory, it can alleviate its ac cess latency by selectively prefetching the items from the broadcast and st oring them in the memory. A good memory management strategy can substantial ly reduce the user's access latency. An optimal memory management policy is identified, that minimizes the expected aggregate latency. Memory update s trategies with limited look-ahead are presented as implementable approximat ions of the optimal policy as well. We also consider the problem of joint b roadcast scheduling and user's cache management and propos a joint optimiza tion scheme which can achieve the performance up to 40% better than the exi sting non-joint approach. (C) 1999 Elsevier Science Ltd. All rights reserve d.