Adaptive channel reservation scheme for soft handoff in DS-CDMA cellular systems

Soft handoff techniques in direct-sequence code division multiple-access (D S-CDMA) systems provide mobile calls with seamless connections between adja cent cells. Channel reservation schemes are used to give high priority to m ore important soft handoff attempts over new call attempts. However, since the number of soft handoff attempts varies according to environmental condi tions, fixed reservation schemes for handoff attempts can be inefficient, A n adaptive channel reservation scheme is herein proposed to control the siz e of reservation capacity according to varying the number of soft handoff a ttempts. The proposed scheme also includes a balancing procedure between so ft handoff failure and new call blocking to maximize the system capacity. T o evaluate the performance of the proposed scheme, a Markovian model is dev eloped that considers the interference-limited capacity effect of DS-CDMA s ystems. Analytical result shows that the proposed scheme yields a considera ble enhancement in terms of new call blocking and soft handoff failure prob abilities when compared with the conventional fixed channel reservation sch eme.