On channel management in CDMA cellular systems

Abstract

CDMA scheme has become a most promising technology for the future cellular systems due to its various advantages. As for all other systems, it is essential for the CDMA cellular system operator to provide services with the smallest number of failures, good quality and the widest availability. These needs motivate us to develop new call control strategies and to analyze the load offered to a cell in the CDMA cellular system. One of the most important merits of the CDMA cellular system is its soft handoff capability provided by path diversity. Once in the soft handoff region, a mobile is usually linked via multiple, typically two, signal paths to neighboring base stations, guaranteeing a smooth switchover to a target base station. Additional improvement in the grade of service may also be achieved when multiple signals thus received of distinguishable quality. This capability, however, incurs extra load on the system due to the increase in the number of channels occupied and reserved for path diversity. The larger the soft handoff region is, the more the traffic load is offered to the CDMA system. In this thesis, therefore, the functional relationship between the size of the region and the amount of offered load due to the path diversity is analyzed for the efficient operation of the CDMA system. To expedite the load analysis, two kinds of loads, attributable respectively to new and handoff calls, are differentiated with additional objective of accommodating advance features like giving handoff calls priority. Further dividing handoff calls into two kinds, we derive a load balance equation for the CDMA system, which consists of an infinite number of identical cells. From this equation, three different loads at a cell are all exactly obtained in association with the size of the soft handoff region. Comparative analysis with the case of hard handoff shows how many extra channels to reserve for the path diversity in a given soft handoff region. A novel handoff cal...