The implicit PUCCH resource determination for HARQ-ACK signal transmission in accordance to the second approach avoids a potential PUCCH resource collision but it also introduces some scheduling restrictions. For example, as the UE with EPDCCH transmission using DMRS port 1 uses PUCCH resource n_PUCCH=n_LCCE+1+N_PUCCH^L, the scheduler should ensure this PUCCH resource is not used for another HARQ-ACK signal transmission. This implies that if the respective EPDCCH transmissions consist of one LCCE, the next LCCE is not used for another EPDCCH transmission scheduling a PDSCH. Therefore, the functionality of the second approach requires that either transmissions of a number of spatially multiplexed EPDCCHs consist of at least a same or larger number of LCCEs or, in case they consist of a single LCCE, that the next LCCE is either not used for EPDCCH transmission or it is used for the transmission of EPDCCHs scheduling PUSCH transmissions.

In a third approach, PUCCH resource collision for HARQ-ACK signal transmissions when respective, spatially multiplexed, EPDCCH transmissions use a same first LCCE, is avoided by assigning a separate PUCCH offset for each DMRS port. Although the previous restrictions associated with the second approach are not significant, they can be avoided by the third approach at the expense of some additional PUCCH overhead. Then, a PUCCH resource for HARQ-ACK signal transmission associated with antenna port N_DMRS can be obtained as set forth in Equation (5).
n_PUCCH=n_L-CCE+N_PUCCH^L,NDMRS??(5)
where N_PUCCH^L,NDMRS is a PUCCH resource offset assigned to DMRS port N_DMRS.