Investigation of PUCCH structure with SRS transmission based on BS-CDMA for LTE-Advanced carrier aggregation

In LTE-Advanced, carrier aggregation (CA) employing multiple component carriers (CCs) is supported, and multiple acknowledgement (ACK)/ negative ACK (NACK) bits associated with multiple CCs are required. In order to convey multiple ACK/NACK bits for downlink CA, a physical uplink control channel (PUCCH) based on block spread code division multiple access (BS-CDMA) is used in the LTE-Advanced uplink. There are two PUCCH structures depending on the presence of a sounding reference signal (SRS), which is used to measure the uplink channel quality. In the subframe with SRS transmission, the last symbol in each PUCCH is removed to avoid simultaneous transmissions of the ACK/NACK and SRS so that the single-carrier property is sustained. In this paper, we investigate the optimum PUCCH structure with SRS transmission based on BS-CDMA in the uplink. We propose two schemes: one removes the ACK/NACK symbol and the other removes the demodulation RS symbol. The ACK/NACK performance for these two schemes is evaluated by computer simulation considering discontinuous transmission (DTX) detection at the base station receiver.