On the capacity of a GSM frequency hopping network with intelligent underlay-overlay

This paper describes a method to increase the capacity of a digital cellular network, like GSM, without having to increase the number of available frequencies or base stations. The idea is to split the frequency spectrum into two bands. One consisting of frequencies that can only be used when a high C/I ratio is ensured, the super frequencies, and the other consisting of frequencies that can be used throughout the whole cell, the regular frequencies. The minimum frequency reuse distance of the super frequencies can therefore be smaller than the reuse distance of the regular layer frequencies. By combining this reuse partitioning with frequency hopping, an increase in the network capacity in terms of carried traffic per cell is achieved. Simulations have indicated that for slow moving mobiles a gain of approximately 35% is achieved by this new feature when compared with a frequency hopping network. For faster moving mobiles the simulated gain is lower, approximately 26%. Modifications are proposed to optimise the simulated algorithms, to improve the capacity in terms of carried traffic per cell even further.