Uplink weight signaling for HSUPA closed loop transmit diversity

摘要

3GPP is investigating uplink transmit diversity alternatives for High Speed Uplink Packet Access. This paper studies closed loop beamforming transmit diversity where NodeB determines transmit antenna weight vectors and additional feedback is used for signaling the optimal weights to the user equipment. The used transmit antenna weights are signaled back to the NodeB in order to ensure correct decoding. This approach is benchmarked against the results where the used weights are not signaled back to the NodeB. Performance is analyzed in various conditions on system level against the performance without uplink weight signaling. The results show that signaling the used weights increases the performance over the case without uplink signaling especially with higher bit error rates. However, uplink weight signaling requires additional signaling bits which may not be justified if weight feedback bit error rates are expected to be low. Additionally when uplink weight signaling is used, even if the weight signaled in downlink were correctly received, signaling errors can happen in uplink which also will result in incorrect decoding at the NodeB.