Capacity analysis of TDD cell sharing underutilized FDD uplink

This paper considers a two-layer hierarchical cell structure with the microcell employing the TDD system and the macrocell employing the FDD system. We determine the downlink and uplink capacities on the TDD system sharing the underutilized FDD uplink under the condition that the FDD and TDD systems share the same frequency band. Our analysis shows that in the course of planning the hierarchical cell structure, the optimum user distribution in the TDD cell can be found by utilizing the link balance and asymmetry between uplink and downlink in the TDD in order to improve the overall capacity.