The DL control region in FIG. 1 uses a maximum of M_symb^DL=3 OFDM symbols and transmits a control signal substantially over a total DL BW. This configuration limits PDCCH capacity and cannot achieve interference coordination in the frequency domain among PDCCH transmissions from different NodeBs. There are several cases where expanded PDCCH capacity or PDCCH interference coordination in the frequency domain is needed for transmission of control signals. One such case is use of spatial multiplexing for PDSCH transmissions where multiple PDCCHs schedule same PDSCH resources to multiple UEs and expanded PDCCH capacity is needed. Another case is for heterogeneous networks where DL transmissions in a first cell experience strong interference from DL transmissions in a second cell, and interference coordination in the frequency domain between the two cells is needed.

A direct extension of the maximum DL control region size to more than M_symb^DL=3 OFDM symbols is not possible at least due to the requirement to support legacy UEs, which cannot be aware of such an extension. An alternative is to support DL control signaling in the conventional PDSCH region by using individual PRBs. A PDCCH transmitted in PRBs of the conventional PDSCH region are referred to as Enhanced PDCCH (EPDCCH).

FIG. 6 is a diagram illustrating EPDCCH transmissions in a DL subframe.