Macro/microcellular systems have recently been proposed to accommodate both fast and slow moving users. If macrocells and microcells reuse the same frequency band in a macro/microcellular system, the interference between both types of cells can become a critical problem and degrade system capacity, particularly in CDMA systems. In this paper, Frequency Division CDMA (FD-CDMA) is applied to CDMA macro/spot-microcellular systems and uplink capacity is evaluated. The CDMA frequency band is divided into several subbands and both macrocells and microcells reuse the same subbands simultaneously. Interference signals from both types of cells are dispersed by dividing the frequency band, and performance degradation resulting from interference is reduced at both the macrocell and microcell. By reusing the same frequency band for macrocells and microcells, the system capacities become more flexible and can be changed according to variations in traffic. This paper describes the detail of the FD-CDMA system. Uplink capacities are calculated for some cell conditions such as microcell size or location through simulation evaluations. A comparison with a non-reuse subband system as well as results of adaptive control of subbands are described.
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