39 lines
2.5 KiB
Markdown
39 lines
2.5 KiB
Markdown
# PHY and MAC Interface
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The PHY sends scheduling requests and data indication to MAC via `nr_ue_dl_indication` for DL path and `nr_ue_ul_indication()` for UL path and the MAC sends scheduling configuration to PHY via `nr_ue_scheduled_response()`. The following diagram shows the interaction for PDCCH and PDSCH reception.
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```mermaid
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sequenceDiagram
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PHY->>+MAC: Requests for PDCCH config (via nr_ue_dl_indication)
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MAC->>+PHY: Schedules PDCCH reception (via nr_ue_scheduled_response)
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PHY->>+MAC: Indicates decoded DCI(s) (via nr_ue_dl_indication)
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MAC->>+PHY: Schedules PDSCH reception (via nr_ue_scheduled_response)
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```
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# Multi-threading Design
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The `UE_thread` function in `nr-ue.c` is the main top level thread that interacts with the radio unit. Once the thread spawns, it starts the 'Initial Synchronization'. Once its complete, the regular processing of slots commences.
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The UE exits when at any point in operation it gets out of synchronization. When the command line option `--non-stop` is used, the UE goes to 'Initial Synchronization' mode when it loses synchronization with gNB. However, this feature is not fully implemented and it is a work in progress at the time of writing this documentation. This will be the default behavior (not a command line option) when the feature is fully implemented.
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UE uses actors which are threads dedicated to particular activity. Sync Actor handles initial sync. DL Actors handle DLSCH PHY procedures. UL procedures are are run on the UL Actor
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## Initial Synchronization Block
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```mermaid
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graph TD
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start(Start) -->|UE_thread| rxRu["RU read<br/>(Reads two frames)"]
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rxRu --> |Sync Actor| sync["SSB detection<br/>(PSS & SSS detection<br/>PBCH decoding<br/>SIB decoding)"]
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rxRu --> |UE_thread| rxRuDummy["RU read<br/>(Dummy read till sync detection to avoid buffer overflow at radio)"]
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sync --> |UE_thread| frameSync["Frame synchronization<br/>(Shift received samples to align with frame)"]
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rxRuDummy --> |UE_thread| frameSync
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```
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## Regular Slot Processing
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```mermaid
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graph TD
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sync["Frame synchronization<br/>(Shift received samples to align with frame)"] -->|UE_thread| hw_read["RU read (slot n)"]
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hw_read --> |UE_thread| rxPreProc["PBCH & PDCCH decoding (slot n)"]
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hw_read --> |UL Actor| txProc["Tx processing (slot n+3)<br/>PUSCH encode<br/>PUCCH encode (wait for DLSCH in slot n+3-k1 to finish)<br/>RU write"]
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rxPreProc --> |DL Actor| rxProc["PDSCH decoding (slot n)"]
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rxPreProc --> |UE_thread| join(Merge)
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join --> |Go to next slot<br/>UE_thread| hw_read
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```
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