一個在無線行動通訊下的二階段適性式通話允入控制機制

Abstract

In general, an abrupt termination of an on-going conversation will definitely upset the caller more than a rejection of the call in the first place. Call admission control is one of the essential elements for ensuring the QoS of forced call terminations due to handoff call dropping. In the thesis, we present a two-phase adaptive call admission control scheme based on the guard channel scheme to guarantee handoff call dropping probability and keep new call blocking probability as low as possible. The phase one is to allocate guard channels based on a non-linear programming model subject to minimize the absolute difference between theoretical handoff call dropping probability and QoS threshold of it, then to operate in coordination with a channel adjustment mechanism in phase two for guaranteeing the QoS agreement of handoff call dropping probability. The features of the proposed mechanism are 1) perform a simple measurement on call arrivals and dropping rate in response to traffic fluctuation; 2) periodical channel allocation by an adequate number of guard channels to lower the blocking probability of new calls; 3) automatic adjust guard channel space by estimated dropping rate to guarantee the handoff dropping probability. Extensive simulation results show that our scheme outperforms other adaptive schemes by steadily satisfying the hard constraint on handoff call dropping probability while maintaining new call blocking probability lower than it.

In general, an abrupt termination of an on-going conversation will definitely upset the caller more than a rejection of the call in the first place. Call admission control is one of the essential elements for ensuring the QoS of forced call terminations due to handoff call dropping. In the thesis, we present a two-phase adaptive call admission control scheme based on the guard channel scheme to guarantee handoff call dropping probability and keep new call blocking probability as low as possible. The phase one is to allocate guard channels based on a non-linear programming model subject to minimize the absolute difference between theoretical handoff call dropping probability and QoS threshold of it, then to operate in coordination with a channel adjustment mechanism in phase two for guaranteeing the QoS agreement of handoff call dropping probability. The features of the proposed mechanism are 1) perform a simple measurement on call arrivals and dropping rate in response to traffic fluctuation; 2) periodical channel allocation by an adequate number of guard channels to lower the blocking probability of new calls; 3) automatic adjust guard channel space by estimated dropping rate to guarantee the handoff dropping probability. Extensive simulation results show that our scheme outperforms other adaptive schemes by steadily satisfying the hard constraint on handoff call dropping probability while maintaining new call blocking probability lower than it.