DCI (Downlink Control Information) is message that carries resource assignments for a UE or group of UE’s. EnodeB can transmit many DCI’s or PDCCH’s in a subframe. eNodeB need to send a lot of parameters to the UE for its operation but there may be the cases that some information is not required for a particular UE. This is the reason why we need different formats for sending the information, which are called DCI formats.
DCI format 0 is used for uplink allocation, all other formats are used for allocating the resources in downlink.
- Format 0 for transmission of resources to UE for sending their uplink data
- Format 1for downlink allocation of resources for Single Input Multiple Output (SIMO)case
- Format 1Afor downlink allocation of resources for SIMO operation or allocating a dedicated preample signature to a UE for random access
- Format 1Bfor transmission control information of Multiple Input Multiple Output (MIMO) rank 1 based compact resource assignment
- Format 1Cfor very compact transmission of PDSCH assignment
- Format 1Dsame as format1B with additional information of power offset
- Format 2and Format2A for transmission of DL-SCH allocation for closed and open loop MIMO operation, respectively
- Format 3and format3A for transmission of TPC command for an uplink channel
We will explain the structure of each format later with their sizes and thorough explanation of their specific use.
Allocation of resources happens in terms of CCE ( Control Channel Elements ).