Closed loop transmit diversity in WCDMA HS-DSCH

The paper summarizes the system performance of the high speed downlink shared channel (HS-DSCH) in WCDMA using closed loop mode 1 transmit diversity. The results show that, scheduling one user at a time in the Pedestrian A channel model, transmit diversity yields similar capacity gains as the sector antenna. On the other hand, in highly dispersive channels, a loss in the system throughput relative to the sector antenna, is observed. This loss is mainly due to random spatial interference patterns (the so called flashlight effect), that are present in the HS-DSCH setting when a single user is scheduled with the maximum available resources (power/codes) at each time instant. In order to mitigate the flashlight effect, a simple scheme is proposed in which multiple users are simultaneously scheduled using different scrambling codes. Scheduling multiple users makes the interference almost spatially white, resulting in a system throughput gain.