A comparison on the performance of the FDD and TDD modes of B-CDMA communications

Abstract

The performance of two modes of transmission power control of the broadband code division multiple access (B-CDMA) signals, the time division duplex (TDD) and frequency division duplex (FDD), on a modified Rayleigh modeled channel; and their respective effectivity of diversity reception are compared in order to find the most efficient method to be adopted for the future personal land mobile telecommunications systems (FPLMTS) standards. Computer simulation results indicate that the user capacity of the TDD mode is slightly better for a single path (no diversity) B-CDMA system. The capacity is significantly increased for multipath selection diversity combining systems for both modes, where the user capacity of the TDD reverse link is again slightly better. In the forward link, however, the capacity is only similar if the FDD mobile receivers have a diversity reception capability. Otherwise, the TDD system has a higher user capacity of about 4 dB, because a pre-selection diversity combining technique allows the realisation of diversity reception at TDD mobile units without increasing their complexity. The effect of variable transmission power, resulting from the power control function is investigated. The average transmitted power is measured to find the level of interference on neighboring cells and the resulting change in user capacity.