Downlink Capacity Enhancement of UMTS

The UMTS FDD-mode specifications include several advanced features to improve the capacity including fast Power Control (PC), Transmit Diversity (TD), support for Adaptive Antennas (AA) and Soft Hand Over (SHO). The potential of these features has been analysed individually and in a combination by means of dynamic network simulations. Significant effort was put into generation of mapping tables to include the link performance from chip-level simulations. It was found that SHO could offer up to 50 % capacity improvement compared to hard hand over. This improvement, however, strongly depends on frequency and antenna diversity plus the mobile speed. Transmit diversity also shows a very high potential for capacity improvement - as high as 200% under certain conditions. Both open loop space-time and feedback mode maximal ratio transmission was investigated. The feed back mode type showed the best performance up to a medium mobile speed. The potential gain from transmit diversity is reduced in a combination with SHO due to the inherit macro-scopic diversity for mobiles in the SHO region. A 3-sectored AA base station configuration with 4 or 8 elements per sector was analysed. A switched beam approach was considered. The study included aspects of azimuth dispersion. The capacity gain is in the order of 130-180 % for the 4-element configuration. The project furthermore touches upon the combination of beamforming and transmit diversity. The work has been supported by Nokia Networks and STVF (Danish Technical Research Council). (Thomas Klingenbrunn, Preben Mogensen)