Institute for Systems Research

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Author: search.filters.author.ElBatt, Tamer A.

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    Cell Size in Hybrid Wireless Systems
    (1999) ElBatt, Tamer A.; Ephremides, Anthony; Ephremides, Anthony; ISR; CSHCN
    In this paper we study, analytically and via simulation, the impact ofreducing the cell size of a wireless system on the system capacity andhand-off failure rate. First, we focus on a pure cellular system. Wedevelop exact and approximate models for cellular systems in order toemphasize the blocking probability/forced termination probabilitytrade-off. This trade-off motivates the problem of optimizing the systemperformance with respect to the cell size. For hybrid systems, weinvestigate how jointly optimizing the number of cells per spot-beam, andthe bandwidth partitioning could improve the QoS parameters of interest.For both systems, the numerical solution is only feasible for smallnumber of cells. For large systems, a simulation study is presented.

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    Frequency Reuse Impact on the Optimum Channel Allocation for a Hybrid Mobile System
    (1999) ElBatt, Tamer A.; Ephremides, Anthony; Ephremides, Anthony; ISR; CSHCN
    In this paper we study the effect of the frequency reuse constraints inboth layers on the optimum channel allocation for a multi-cell/multi-spot-beam hybrid system. We adopt a specific multi-faceted cost function thatincorporates call-dropping due to unsuccessful hand-off attempts, andblocking of new calls. The minimization of the cost function is attemptedby choosing the optimal split of the total number of channels betweenthe cellular and the satellite layers. This complex optimization problemis solved by means of standard clock simulation techniques along with theadaptive partitioned random search global optimization technique and theordinal optimization approach.
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    Optimization of Connection-Oriented, Mobile, Hybrid Network Systems
    (1998) ElBatt, Tamer A.; Ephremides, Anthony; ISR; CSHCN
    In this paper 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 hand-offs. We incorporate the possibility of call-dropping due to unsuccessful hand-off attempts, in addition to satellite propagation delays along with the probability of new call blocking and formulate a specific cost function that must be ultimately minimized. The minimization is to be carried out by choosing (1) the optimal split of the total number of channels between the cellular and the satellite systems, and (2) 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 (hand- off-based) process that results from the mobility model. This complex optimization problem is solved by means of both numerical and standard clock simulation techniques along with the ordinal optimization approach. This paper was presented at the "17th AIAA International Communications Satellite Systems Conference and Exhibit", February 24-26, 1998, Yokohama, Japan.