Introducing Dual Pilot Closed Loop Transmit Diversity for High Speed Uplink Packet Access

The alternatives for HSUPA uplink transmit diversity are being currently investigated in 3GPP. This paper addresses the uplink transmit diversity from the perspective of closed loop beamforming where NodeB determines transmit antenna weights, and additional feedback is used for signaling the optimal weights to the user equipment. More precisely, this paper introduces a novel transmit diversity technique which involves transmitting two non-beamformed DPCCH (pilot) signals from two antennas whereas the actual data part of the signal is beamformed. Additionally, the dual pilot transmit diversity technique is benchmarked on system level in various conditions against the baseline system performance without transmit diversity. The studies show cell level throughput gains up to 53 % in Pedestrian A channel and up to 26 % in Vehicular A channel comparing to the baseline system. The highest relative gains are achieved in highly loaded cells with long inter-site distances.