A two-level physical structure is defined for better diversity for both distributed and localized transmission in enhanced physical downlink control channel (ePDCCH). First level is a physical unit of enhanced resource element groups (eREGs), where the group of REs is predefined for each eREG. Second level is a logical unit of enhanced control channel elements (eCCEs), where the group of eREGs is predefined or configurable by higher layer for each eCCE. For distributed transmission of ePDCCH, eCCE consists of several eREGs that are distributed in multiple non-contiguous PRBs spreading over the whole channel frequency. Downlink control information (DCI) is transmitted on a number of aggregated eCCEs according to the modulation and coding level required. The utilization reference signals of antenna ports for ePDCCH demodulation is based on the logical order of eCCEs and the aggregation level for DCI transmission.