| Summary: | In this thesis, we investigate the frequency division duplex (FDD) mode of the downlink of UMTS terrestrial radio access (UTRA) focusing on the signal to interference ratio (SIR) estimation for the closed loop power control (CLPC), diversity exploitation in both spatial and temporal domains and the suppression of multi-access interference that is encountered in handover regions, with the aid of a calibrated link-level simulator. Firstly, SIR estimation methods are studied for single and two-antenna transmissions and it is shown that when the common pilot channel (CPICH) is available, SIR could be estimated on that and related to the SIR for the dedicated physical channel (DPCH) through a simple relation. This way, a reduction in the overhead of the slot formats specified by the 3GPP, could be obtained. Secondly, factors influencing the handover performance such as the multipath fading correlation between radio channels of the two links, limited number of Rake fingers in a UE and imperfect channel estimation that cannot be modeled adequately at the system-level are investigated via link-level simulations. It is shown that the geometry factor has an influence on the handover performance and exhibits a threshold value (which depends on the correlation of the two links) above which the capacity starts degrading. The variation of the handover gain with the CLPC step-size, space-time transmit diversity (STTD) and receive antenna diversity is also quantified. Thirdly, blind interference suppression techniques are studied for the rejection of multi-access interference in handover regions. It is shown that the CLPC acts as an effective solution to the mismatch problem associated with the minimum output energy (MOE) detector. Furthermore, two methods are proposed for increasing the convergence speed of the MOE detector. Finally, chip-interleaved induced time diversity is investigated for multimedia broadcast / multicast services (MBMS) in UMTS, as a method of enhancing the downlink capacity. It is shown that the chip block interleaving with a block length of half the spreading factor provides similar diversity gain (by using only one transmit antenna) as that provided by STTD, but at the cost of an additional delay that is equal to the interleaving depth. Simulation results are presented for both the terrestrial and satellite modes of MBMS delivery for a range of mobile velocities.
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