In cellular systems, the available spectrum is partitioned among the BSs, and a given frequency is reused at the closest possible distance that the radio link will allow. Smaller cells have a shorter distance between reused frequencies, and this results in increased spectral efficiency and traffic carrying capacity.
Dramatic improvement in spectral efficiency is the main reason for the interest in microcells. However, the microcellular propagation environment is highly erratic. Distributed resource allocation algorithms must be used to maintain high link quality.
The available spectrum is limited. The design process of selecting and allocating channel groups for all cellular base stations within a system is called frequency reuse or frequency planning.
The cell sizes, the ability of radio links to withstand interference, and the ability of the cellular system to react to variations in traffic are the main factors that determine the spectral efficiency of a cellular system.