Institute for Systems Research
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Item Handover and Channel Allocation Mechanisms in Mobile Satellite Networks(1999) Koutsopoulos, Iordanis; Tassiulas, Leandros; ISR; CSHCNIn this work we study first handover prediction in non-geostationary mobile satellite networks. The ultimate choice of the transition path depends on UT position and signal strength. We investigate the procedure of beam monitoring and propose UT maximum residence as the criterion for path selection.The UT must operate both in full- and half-duplex mode, the latter being desirable when power limitations are imposed. We propose a scheme that achieves this goal and guarantees efficient diversity provision. Constant delay contours on the earth's surface are defined. The problem of reliable time delay acquisition is addressed, in case synchronization is lost. The SBS solves that either by using the known estimate of UT position or by requesting a measurement report by the UT.
The problem of channel allocation appears in cellular networks of every kind. Calls arising in the cell overlap area have access to channels of more than one base station and may choose which base station they will use to establish connection. In that case the problems of base station and channel assignment arise jointly.
We address the problem in a linear cellular network and aim at the minimumnumber of utilized channels. We present two algorithms: The first one expands Load Balancing in clique populations and is Sequential Clique Load Balancing (SCLB). The second one is named Clique Load Balancing with Inverse Water-Filling (CLB-IWF). In a dynamic environment, we unify SCLB and CLB-IWF into CLB-DA, which comprises Dynamic Allocation. CLB-DA is compared with Least Loaded Routing (LLR) policy and with Random Routing policy. We finally deduce that at light loads CLB-DA outperforms LLR, attaining smaller blocking probability, whereas at heavier loads all three policies converge.
Item Optimization of Connection-Oriented, Mobile, Hybrid Network Systems(1998) ElBatt, Tamer A.; Ephremides, Anthony; ISR; CSHCNIn 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.