From LTE specification the PDCCH carries the Downlink Control Information (DCI). In addition to DCI there is a Control Format Indicator (CFI) wich indicates the size of PDCCH in OFDM symbols. The CFI information is carried by the PCFICH.
First of all the DCI information comes from the MAC interface trhough the following function:
| Function | Source | Callee |
|---|---|---|
| get_dci_sdu() | openair2/LAYER2/MAC/eNB_scheduler_primitives.c:98 | openair1/SCHED/phy_procedures_lte_eNb.c:1244 |
The DCI encoding and modulation have the following steps:
| # | Step | Executed at |
|---|---|---|
| 1 | CRC Attachment based on UE RNTI | ccodelte_encode() |
| 2 | Channel Coding | ccodelte_encode() |
| 3.1 | Rate Matching: Sub Block Interleaver | sub_block_interleaving_cc() |
| 3.2 | Rate Matching: Bit Collection/Selection | lte_rate_matching_cc() |
| 4 | Multiplexing and Scrambling | pdcch_scrambling() |
| 5 | QPSK Modulation | generate_dci_top():2301 |
| 6 | Layer Mapping | pdcch_interleaving() |
| 7 | Precoding | generate_dci_top():2301 |
| 8 | Resource Mapping | generate_dci_top():2361 |
These steps are executed inside the following function (or one of its child)
| Function | Source | Callee |
|---|---|---|
| generate_dci_top() | openair1/PHY/LTE_TRANSPORT/dci.c:2182 | /openair1/SCHED/phy_procedures_lte_eNb.c:1387 |
There is a tree view of the main procedures and functions executed by generate_dci_top
- generate_dci_top()
- get_num_pdcch_symbols() - Evaluate the number of necessary CCE's and find the number of symbols
- generate_pcfich() - Generate the PCFICH
- generate_dci0()
- dci_encoding()
- ccodelte_encode() - Execure Channel coding and CRC attachment
- sub_block_interleaving_cc() -
- lte_rate_matching_cc() -
- dci_encoding()
- pdcch_scrambling()
- Modulation (SISO or TX Diversity) - QPSK Modulation
- pdcch_interleaving()
- Resource Element Mapping
The PCFICH is encoded together with PDCCH at the function [generate_pcfich()](https://github.com/joary/openairinterface5g/tree/study/openair1/PHY/LTE_TRANSPORT/pcfich.c#L135)
The CFI encoding and modulation have the following steps:
| # | Step | Executed at |
|---|---|---|
| 1 | Channel Coding | pcfich_scrambling() |
| 2 | Scrambling | pcfich_scrambling() |
| 3 | QPSK Modulation | generate_pcfich():164 |
| 4 | Layer Mapping | |
| 5 | Precoding | generate_pcfich():164 |
| 6 | Resource Mapping | generate_pcfich():191 |
A tree view of the main procedures and functions executed at generate_pcfich is shown below:
- generate_pcfich() - Generate the PCFICH
- pcfich_scrabling() - Get CFI info, execute channel coding and Scramble data
- Modulate PCFICH (SISO or TX Diversity)
- Map into resource elements of each REG