The effects of inter-system interference in UMTS at 1920 MHz

The Universal Mobile Telecommunications System (UMTS) is composed of an FDD and TDD mode. Both modes have an adjacent carrier at 1920 MHz. The implications thereof for system capacity are analysed. In this context, the FDD mode is assumed to account for full spatial coverage and the TDD mode is employed to cover areas with increased traffic 'hot spots'. The separation distance of the TDD and FDD base station (BS) and the load in each system are varied. It is shown that the capacity in the FDD system is reduced by less than 5% for a BS separation distance greater than 300 m. Contrary to this, the capacity reduction in the TDD system is only below 5% for a BS separation of less than 1000 m. This clearly yields a trade-off which limits the degree of freedom in planning the network in this particular case.