Optimization of connection-oriented, mobile, hybrid network systems

We consider the extension of a cellular system by means of satellite channels. Specifically, we consider an area covered by a number of cells, that is also covered by a number of spot beams. We consider connection-oriented service, and call durations are assumed to be exponentially distributed. Also, users are mobile and, as such, they may cross cell and/or spot-beam boundaries, thus necessitating handoffs. We incorporate the possibility of call dropping due to unsuccessful handoff attempts, in addition to satellite propagation delays along with the probability of new call blocking, and formulate a specific multifaceted cost function that must be ultimately minimized. The minimization is to be carried out by choosing: (1) the optimal partitioning of channels between the cellular and the satellite systems, and (ii) the call admission and assignment policy, subject to the constraints of a demand vector that consists of an exogenous (new-call) generation process and an internal (handoff-based) process that results from the mobility model. Two subproblems of this complex optimization problem are solved by means of numerical techniques and by means of so-called standard clock simulation techniques. In this solution method, we employ the ordinal optimization approach which focuses on preserving the performance rank, rather than the performance prediction of the different control policies. We find that the "double" coverage, through both cellular and satellite resources, results in substantial improvement over pure terrestrial or pure satellite systems for parameter values that correspond to practical environments.