The physical downlink shared channel (PDSCH) may carry user data and higher-layer signaling to the UE 105. The physical downlink control channel (PDCCH) may carry information about the transport format and resource allocations related to the PDSCH channel, among other things. It may also inform the UE 105 about the transport format, resource allocation, and hybrid automatic repeat request (HARD) information related to the uplink shared channel. Typically, downlink scheduling (assigning control and shared channel resource blocks to the UE 105 within a cell) may be performed at the AN 110 based on channel quality information fed back from any of the UE 105. The downlink resource assignment information may be sent on the PDCCH used for (for example, assigned to) the UE 105.
The PDCCH may use control channel elements (CCEs) to convey the control information. Before being mapped to resource elements, the PDCCH complex-valued symbols may first be organized into quadruplets, which may then be permuted using a sub-block interleaver for rate matching. Each PDCCH may be transmitted using one or more of these CCEs, where each CCE may correspond to nine sets of four physical resource elements known as resource element groups (REGs). Four Quadrature Phase Shift Keying (QPSK) symbols may be mapped to each REG. The PDCCH can be transmitted using one or more CCEs, depending on the size of the downlink control information (DCI) and the channel condition.