System level performance of UMTS-FDD with covariance transformation based DL beamforming

This paper presents a comparison of two different uplink to downlink covariance matrix transformation methods that can be used in downlink beamforming for frequency selective FDD channels. The performance improvement obtained from the transformation methods is compared with that from the method, which directly uses the uplink covariance matrix for downlink beamforming. For this purpose, a dynamic system level simulator developed for investigating the capacity improvement of a UMTS-FDD system employing smart antennas at the base stations is used. Downlink capacity is used as a measure of the performance of the system by finding the number of users for which a certain quality of service (QoS) requirement is fulfilled. System level simulations are carried out for antenna arrays with 2, 4 and 8 elements. Simulation results show that the downlink capacity can be improved significantly with higher number of antenna elements only if a transformation method is used in order to overcome the effect of different uplink and downlink carrier frequencies.