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openairinterface5g/doc/rach_processing_in_gNB.md
Robert Schmidt 8107939f08 Change OAI license to CSSL v1.0 (and others)
- all RAN code, CI code, configuration files, dockerfiles, in CSSL v1.0
- all deployment code (openshift, charts, ancillary files like shell
  scripts), in MIT
- documentation in CC-BY-4.0
- exceptions might apply and are listed in NOTICE
- there is a new LICENSES folder with all licenses
- CONTRIBUTIONS.md has been updated accordingly

For automated changes based on OAI PL v1.1:

    perl -i~ -0pe 's/\/\*.*Licensed to the OpenAirInterface.*openairinterface.org\n#?/\/*\n * SPDX-License-Identifier: LicenseRef-CSSL-1.0\n/s' **/*.{c,h,cpp}
    perl -i~ -0pe 's/\/\*.*Licensed to the OpenAirInterface.*openairinterface.org\n#?/\/*\n * SPDX-License-Identifier: LicenseRef-CSSL-1.0\n/s' **/*.ts
    perl -i~ -0pe 's/<!--.*Licensed to the OpenAirInterface.*openairinterface.org\n.*-->/<!-- SPDX-License-Identifier: LicenseRef-CSSL-1.0 -->/s' **/*.xml

The rest (cmake, files with missing license, cmake) manually.
2026-03-27 16:36:37 +01:00

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<!-- SPDX-License-Identifier: CC-BY-4.0 -->
# The gNB RACH Processing
## 1. Collect I/Q Samples
The gNB/ru main loop, in `ru_thread()`
If there is rach occasions in this slot
this main loop calls `rx_nr_prach_ru()` that stores the I/Q samples in the `prach_item_t` context.
## 2. Process the Samples
`L1_rx_thread()` has received slot indication by msg on queue `resp_L1`, it calls `rx_func() => L1_nr_prach_procedures()`
`L1_nr_prach_procedures()` fills `nfapi_nr_rach_indication_t` structure from result of `rx_nr_prach()` that process the content of `rxsigF[prachOccasion][aa]`
`rx_func()` sends the decoded rach to upper processing by call to `NR_UL_indication()` that calls `handle_nr_rach() => nr_initiate_ra_proc()`.
`nr_initiate_ra_proc()` creates a UE context if it needs, then sets `UE.ra.ra_state` to what it should do.
## 3. Send the RACH DL
`tx_func()` that is launched by `L1_tx_thread()` as it gets `L1_tx_out` msg (from main loop in [1.](#1-collect-iq-samples))
`tx_func()=>run_scheduler_monolithic()=>gNB_dlsch_ulsch_scheduler()=>nr_scheduler_RA()`
`nr_scheduler_RA()` process all existing UE contexts, to see it it has to schedule a RACH DL.
## 4. Global Synchronisation
`resp_L1` msg for ([2.](#2-process-the-samples)) is created in `tx_func()` that is launched by `L1_tx_thread()` (see [3.](#3-send-the-rach-dl)) when it receives slot indication as it gets `L1_tx_out` msg
this msg is sent by the main loop (see [1.](#1-collect-iq-samples))
`tx_func()=>run_scheduler_monolithic()=>nr_schedule_response ()=>nr_schedule_ul_tti_req ()=> nr_schedule_rx_prach()`
writes in the triggering structure to ([1.](#1-collect-iq-samples)) that it will have to run `rx_nr_prach_ru()` in a given future slot.