Uplink MIMO for HSPA

Multiple-input multiple-output (MIMO) techniques were recently proposed for HSUPA in 3GPP. In this paper, we show that compared to the baseline non-MIMO transmission, the beam-forming closed loop transmission diversity (CLTD) can provide clear UE Tx power saving but sometimes only little throughput gain. Spatial multiplexing can provide substantial throughput gain while the cost in increased UE Tx power can be limited by e.g. adopting rank two transmission only under favorable channel condition. With proper rank adaptation a MIMO transmission supporting spatial multiplexing can provide 15% to 30% throughput gain compared to the baseline nonMIMO transmission for 2 Rx antennas while 20% to 60% throughput gain for 4 Rx antennas. With pure beam-forming CLTD the throughput gain is less than 13.5% for 2 Rx antennas while just 1.5% or less for 4 Rx antennas.