As the cells shrink and mobility increases in personal communication services (PCS), an increased number of handoff occurs overloading the signaling network. One major motivation to employ microcell/macrocell overlays is to increase the capacity without increasing the handoff rates. A cellular system consisting of two tiers with microcell in the lower-tier and multiple levels of (macro)cells in the upper-tier, is considered to separately serve mobiles with different speeds. The dimension of the upper-tier cell is approximately derived based on the mean velocity of mobiles the cell intends to serve. Finally, the effect of misusing the upper-tier resources is analyzed in terms of each tier call blocking rate.
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