The search space for the second control channel group can be expressed as Equation (4):
L·{(Y_k+m)mod └N_CCE,k/L┘}+i, m=0, . . . , M^(L)?1, i=0, . . . , L?1 for UE specific control channel with antenna port set #2 and Y_k=(A·Y_k-1)mod D??(3)
where Y_k starts with the dedicated UE identifier (ID); and A and D are 39827 and 65537, respectively.

According to Equations (3) and (4), the search spaces are determined with different values of Y_k. The first group is determined with the UE group identifier, and the second group is determined with a unique UE identifier. That is, the control channel region for multiple UEs configured at the same location but varies continuously at every subframe. The UE-specific control channels for the respective UEs are transmitted at random positions. In this way, it is possible to avoid repeated collisions.

FIG. 5 is a diagram illustrating a mechanism of control channel detection according to a second exemplary embodiment of the present invention. Referring to FIG. 5, the eNB according to the second exemplary embodiment of the present invention configures different control channel transmission resources and maps the logical control channel resources thereto respectively using the same search space. The eNB transmits the control channels mapped to the resources using different reference signals or different reference signal ports. The terminal receives the control channels mapped to the different control channel regions in the same search space using the different reference signals or different reference signal ports.