In addition to the LCCE aggregation level in case of localized EPDCCH, the DMRS antenna port may also be considered in the adaptive use of transmitter antenna diversity (when configured) for HARQ-ACK signal transmission. If the DMRS antenna port is not the first one, it may be associated with the use of spatial EPDCCH multiplexing. To avoid an increased probability of PUCCH resource collision in this case, since use of spatial EPDCCH multiplexing is assumed to be transparent to UEs, transmitter antenna diversity for HARQ-ACK signaling may not apply if the DMRS antenna port for a respective EPDCCH is not the first one.

Furthermore, a dynamic determination by a UE as to whether it shall apply transmitter antenna diversity (when configured) for HARQ-ACK signaling can be based on the modulation scheme used for the transmissions of the respective EPDCCH. If QAM16 is used, a UE can be assumed to have good link quality and small path-loss to a NodeB and may not apply transmitter antenna diversity for a respective HARQ-ACK signal. The reverse applies when QPSK is used to transmit a respective EPDCCH.

Dynamic indication of whether a UE should apply transmitter antenna diversity (when configured) for HARQ-ACK signaling can be supported through an inclusion of a respective 1-bit field (with, for example, 0 indicating transmitter antenna diversity and 1 indicating single transmitter antenna) in a DCI format conveyed by each EPDCCH associated with a PDSCH.

The fourth embodiment of the present invention considers methods and apparatus for a UE to determine a PUCCH resource for a HARQ-ACK signal transmission in response to an EPDCCH detection, when possible ECCE aggregation levels for an EPDCCH type (distributed or localized) vary per subframe and, in particular, when an existence of an aggregation level of 1 ECCE varies per subframe.