Beamforming loss due to tracking error in downlink SDMA

Beamforming and adaptive array processing are now being considered for 3/sup rd/ generation cellular communication systems. On the downlink, beamforming techniques and spatial division multiple access (SDMA) can reduce the adverse effects high data rate mobiles have upon the system capacity in a code division multiple access (CDMA) communications system. For 3/sup rd/ Generation systems, one approach is to assign SDMA channels to low mobility/high data rate mobile stations and provide a low data rate service via a sectorized antenna. The use of SDMA for high rate mobiles requires the base station to accurately estimate the direction of multipaths between the base station and SDMA mobile stations. This paper presents a simple, but intuitive model for analyzing the beamforming loss due to inaccuracies in estimating the direction of arrival of multipaths from SDMA mobiles and the loss due to periodic update of beam patterns to SDMA mobiles.