This article is dedicated to DCI formats that are used in LTE downlink. DCI stands for downlink control information and there are various DCI formats used in LTE in PDCCH. The DCI format is nothing but a predefined format in which the downlink control information is packed/formed and transmitted in PDCCH. Below are moe details on DCI formats,
Why are these DCI formats required? Simple, it tells the UE how to get its data which is transmitted on PDSCH in the same subframe. So DCI format transmitted in PDCCH, is like a map for a UE to find and decode PDSCH from the resource grid. The DCI format gives the UE, details such as number of resource blocks, resource allocation type, modulation scheme, transport block, redundancy version, coding rate etc. Each DCI format, when encoding is attached with a CRC that is scrambled with the a UE-RNTI to which the PDSCH is intended to. So only that UE can decode the DCI format and hence the corresponding PDSCH. The packed DCI information is the payload to the PDCCH encoding chain.
The DCI formats are further classified into downlink DCI formats and uplink DCI formats. The different DCI formats are as below,
- Downlink DCI Formats
- Format 1 – Used for scheduling a PDSCH codeword. Only a single transport block can be scheduled here using resource allocation type2 (localized or distribtued)
- Format 1A – Used for scheduling a PDSCH codeword. Only a single transport block can be scheduled here using resource allocation type-0/type-1
- Format 1B – Used for scheduling a PDSCH codeword with Rank-1 assignment
- Format 1C – Very compact scheduling of a PDSCH codeword. A single transport block can be scheduled using resource allocation type2 distributed always
- Format 1D – Used for scheduling Multi-user MIMO cases
- Format 2 – Used for scheduling of PDSCH in closed loop spatial multiplexing
- Format 2A – Used for scheduling of PDSCH in open loop spatial multiplexing
- Uplink DCI Formats
- Format 0 – Used for scheduling of PUSCH (uplink grant)
- Format 3 – Uplink transmit power control with 2 bit power adjustment
- Format 3A – Uplink transmit power control with 1 bit power adjustment
The DCI formats are coupled with different transmission modes and resource allocation types in downlink.