Radio resource sharing and capacity of some multiple access methods in hierarchical cell structures

To decrease total system cost and improve efficiency, in future mobile communication systems, we can implement a structure of multiple cells covering an area. This is often referred to as a hierarchical cell structure, HCS. We compare five methods of sharing the scarce radio resources in a two-layer HCS: (i) DS-CDMA in macrocells and TDMA in microcells; (ii) TDMA in macrocells and DS-CDMA in microcells; (iii) DS-CDMA in both macrocells and microcells on the same frequency band; (iv) TDMA in both layers with frequency splitting; and (v) TDMA in both layers with reuse of macro frequencies in microcells. Through simulation we study the system capacities, i.e., the number of users supported per cell. Highest capacities are achieved by method (iv) and (v). Method (v) could also be used in a CDMA type of system if it is possible to have more than one carrier.