Trunking efficiency in multi-carrier CDMA systems

As CDMA systems reach capacity, infrastructure providers expand them by offering multi-carrier capability. The capacity of an n-carrier system is at least n times the capacity of a single-carrier system. Using both mathematical modeling and simulation, we investigate the extent to which this capacity can be extended by judicious mobile-to-carrier assignment algorithms. The mathematical modeling considers a multi-carrier system as a number of parallel blocking systems with load balancing. We rely on a heavy-traffic approximation to estimate the blocking probability and capacity improvements. The simulation is a Monte Carlo model of a multi-cell, n-carrier, IS-95, CDMA cellular system. Each replication converges power control for a random set of mobiles and accumulates RF outage statistics. The capacity of the system is represented as the mean number of mobiles that may be served with an a priori RF outage probability. We compare this capacity against that of a similar simulation of a system with a single carrier of n-times the bandwidth. The latter capacity constitutes an upper bound for the capacity of an n-carrier system with any carrier assignment discipline. In contrast to common sense about trunking systems, the additional capacity ("trunking efficiency") due to carrier assignment disciplines is small.