Control Regionĭownlink control signaling is located at the start of each downlink subframe (up to the first three OFDM symbols). If no CRC error is detected the UE determines that PDCCH carries its own control information. The RNTI is used to demask a PDCCH candidate's CRC. The UE uses its Radio Network Temporary Identifier (RNTI) to try and decode candidates. The UE finds the PDCCH specific to it by monitoring a set of PDCCH candidates (a set of consecutive CCEs on which a PDCCH could be mapped) in every subframe. Multiple PDCCHs can be transmitted in a single subframe which may and may not be all relevant to a particular UE.
Finally, the modulated symbols are interleaved and mapped to physical Resource Elements (REs).Īfter performing deinterleaving, deprecoding, symbol combining, symbol demodulation and descrambling at the receiver, the UE is required to perform blind decoding of the PDCCH payload as it is not aware of the detailed control channel structure, including the number of control channels and the number of CCEs to which each control channel is mapped. These coded bits are then converted to complex modulated symbols after performing operations including scrambling, QPSK modulation, layer mapping and precoding. PDCCH payload, are then mapped to Control Channel Elements (CCEs) according to the PDCCH format. To form the PDCCH payload the DCI undergoes channel coding: addition of a CRC attachment followed by convolutional coding and rate matching according to PDCCH format capacity.
The Downlink Control Information (DCI) is transmitted through the Physical Downlink Control Channel (PDCCH) and includes information about the DL-SCH resource allocation (the set of resource blocks containing the DL-SCH), transport format and information related to the DL-SCH Hybrid Automatic Repeat reQuest (ARQ). This control signaling enables a UE to successfully receive, demodulate, and decode the DL-SCH. To support the transmission of downlink and uplink transport channels Downlink Shared Channel(DL-SCH) and Uplink Shared Channel (UL-SCH) control signaling is required.
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