A New Dynamic Channel Management Scheme to Increase the Performance Index of for Cellular Networks

This letter presents a Dynamic Channel Management Scheme (DCMS), using both an One-Layer Cellular Architecture (OLCA) and a Two-Layer Cellular Architecture (TLCA), for use in areas with random offered traffic load. The philosophy of DCMS is that is based either on OLCA or TLCA proposed to the optimization of the handoff blocking probability performance of High-Speed Moving Terminals (HSMT) and the call blocking probability of the rest calls in a congested urban area, with random offered traffic load. Also the number of channels assigned to microcells and umbrella cell, is regulated dynamically in order to have the above results. INTRODUCTION: The rapid increase in demand for mobile communications has led the industries into research and development efforts towards a new generation of wireless cellular systems. One of the major challenges in such networks is the utilization of limited resources, effectively, in order to provide high availability of service. The performance index used for measuring the efficiency of a channel assignment scheme is the call blocking probability and especially the handoff blocking probability. A great effort has been spent in order to study the channel assignment and the handoff process and to minimize the involved handoff blocking probability [1],[2],[3]. The handoff blocking probability is considered to be more important than the blocking probability of new calls, because the calls are already in active mode and the corresponding QoS is more sensitive for the handoff calls. An examined model adopts a traffic analysis for cellular mobile networks with prioritized handoff procedure, where all calls are serviced by the microcells (Typical Cellular System One Layer Cellular Architecture– OLCA)[1],[2]. Also, is shown a model where handoff calls of HSMT are serviced by the umbrella layer and both the new calls of HSMT and Low Speed Moving Terminals (LSMT) and the handoff calls of LSMT by the microcellular layer. The number of channels that assigned to microcells and umbrella cell is fixed for long time periods and is selected in order to contribute to the decrement of the mean call blocking probability, during this long period. [3]. The following assumptions, without affecting the results, are considered: a) the terminals are characterized as LSMT or HSMT according to the speed they move. b) Random offered traffic load in every microcell and c) same mean channel holding time Th and μH (μH =1/TH) are considered for HSMT and LSMT both in microcells and umbrella cell. New and handoff calls of LSMT are generated in the area of microcell (i) according to a Poisson point process, with mean 3 rates of ( ) i R Λ , ( ) i Rh Λ respectively, while new calls and handoff calls of HSMT are generated with mean rates of ( ) i R Λ , ( ) i Rh Λ per cell. The relative mobilities for microcell i are defined as: ( ) ( ) ( ) ( ) ( ) i i i i a R Rh Rh L Λ + Λ Λ = for LSMT (1), ( ) ( ) ( ) ( ) ( ) i i i i a R Rh Rh H Λ + Λ Λ = for HSMT (2). The total relative mobility for both HSMT and LSMT, for microcell (i), is given by: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) i i i i i i i a R Rh R Rh Rh Rh HL Λ + Λ + Λ + Λ Λ + Λ = (3). The offered load for microcell i is: ( ) ( ) ( ) ( ) ( ) ( ) H R Rh R Rh i i i i i Toff μ Λ + Λ + Λ + Λ = (4) THE PROPOSED DYNAMIC CHANNEL MANAGEMENT SCHEME BASED BOTH ON A ONE-LAYER CELLULAR ARCHITECTURE AND ON A TWO-LAYER CELLULAR ARCHITECTURE: The DCMS is based both on a One-Layer Cellular Architecture as described in [1],[2] and on a Two-Layer Architecture, as TLCA described in [3]. The number of layers (one or two) that is used depends on which architecture gives better optimization to the cellular system proposed to the offered traffic load. Let n be the number of microcells that consist the microcellular layer. The total offered load in the system is: ( ) ∑ = = n i off tot off i T T 1 (5). Let CS is the total number of channels in the system. In the microcellular layer, priority is given to handoff attempts by assigning guard channels Ch(i) exclusively for handoff calls of LSMT among the C(i) channels in microcell i. The remaining (C(i)-Ch(i)) channels are shared by both new calls of HSMT and LSMT and handoff calls of LSMT [3]. Let Cu be the channels assigned to umbrella cell to serve only handoff calls of HSMT. Hence: ( ) u n i S C i C C + = ∑ (6). The mean rate of generation of handoff calls of HSMT is ) (i Rh Λ for cell i, so the mean rate generated in the umbrella is ( ) ∑Λ n