Investigation on best combining scheme for diversity branches in joint MLD for PUCCH in LTE uplink

In Release 8 Long-Term Evolution (LTE) by the 3^rd Generation Partnership Project (3GPP), the uplink control channel called the physical uplink control channel (PUCCH) is specified. The PUCCH carries channel-quality indicator (CQI) and acknowledgement (ACK)/negative-acknowledgement (NACK) signals. This paper investigates the best scheme to combine diversity branches for joint maximum likelihood detection (MLD) for the PUCCH in the LTE uplink. Coherent combining of the correlation signals for two frequency-hopped slots and two receiver antennas reduces the noise components effectively; however, it incurs channel estimation error. Hence, we present decision-feedback channel estimation (DFCE) associated with the joint MLD. The correlation signals when combined in squared form do not require channel estimation. Based on link-level simulations, we clarify that the squared combining of the correlation signals for frequency-hopping diversity and antenna diversity branches is the most appropriate scheme based on the trade-off relationship between the effective suppression of noise components and the elimination of channel estimation error for the PUCCH using joint MLD in the LTE uplink.