Performance modeling and analysis of Hierarchical Cellular Structures

Hierarchical Cellular Structures (HCS) have become a major requirement in 3G mobile systems. In this paper, a new general bidirectional call-overflow scheme for a two-tier HCS, which allows calls to overflow between the macrocells and microcells and cell selection in hierarchical architecture based on the velocity of the mobile making the calls, is considered. In order to evaluate the performance of such hierarchical systems, we develop an more accurate microcell (macrocell) model which was obtained by extending a Markov Modulated Poisson Process (MMPP) analytical framework based on IPP overflowed traffic from the other layer by a M/M/C/C queueing system which model the microcell (macrocell) overflowing traffic to the other layer. Theoretical analysis and numerical evaluation show that our analytical model is more reliable. In addition, new call blocking and hand off dropping is insensitive to the velocity threshold which is used to assign calls to different layers and may be adjusted according to traffic load in our scheme.