PDCCH (Physical Downlink Control Channel)


As in LTE, NR PDCCH is the physical channel that carries DCI and this would be one of the most important channel which is supposed to be very robust and easily decoded even in harsh radio condition.


Overall channel coding and physical layer process is also similar to LTE PDCCH as listed below with a few differences like channel coding.




PDCCH Transport Process






(1) Information Element Multiplexing


This is a process of generating a bit string of DCI carrying various control and scheduling information. Refer to DCI page to see the details of the contents.


If the size of DCI is less than 12 bit, it will be zero padded until it become 12 bits (Ref [1]).  



(2) CRC Attachment


< CRC Attach >


As you see here, 24 bits CRC is appeded to DCI data.




< Masking with RNTI >


After CRC Attach, the last 16 bit is masked with a specific RNTI. Using this RNTI, UE figures out which UE the DCI is for and what is the usage of the DCI.




< Interleaving >


After RNTI masking, the data is interleaved so that CRC bits are distributed among information bits. This interleaver supports a max input size of 164 bits meaning that DCI without CRC can be max 140 bits.(Ref [1])



(3) Channel Coding





(4) Rate Matching





(5) Scrambling





(6) Modulation





(7) Resource Element Mapping




RRC Parameters






PDCCH-Config ::=                        SEQUENCE {

    controlResourceSetToAddModList          SEQUENCE(SIZE (1..3))

                                                OF ControlResourceSet         OPTIONAL,

    controlResourceSetToReleaseList         SEQUENCE(SIZE (1..3))

                                                OF ControlResourceSetId       OPTIONAL,

    searchSpacesToAddModList                SEQUENCE(SIZE (1..10))

                                                OF SearchSpace                OPTIONAL,

    searchSpacesToReleaseList               SEQUENCE(SIZE (1..10))

                                                OF SearchSpaceId              OPTIONAL,

    downlinkPreemption                      SetupRelease { DownlinkPreemption }  OPTIONAL, 

    slotFormatIndicator                     SetupRelease { SlotFormatIndicator } OPTIONAL,  

    tpc-PUSCH                               SetupRelease { PUSCH-TPC-CommandConfig }  OPTIONAL,

    tpc-PUCCH                               SetupRelease { PUCCH-TPC-CommandConfig }  OPTIONAL,







[1] Understanding the Heart of the 5G Air Interface: An Overview of Physical Downlink Control Channel for 5G New Radio (NR)  

  - by Kazuki Takeda‡, Huilin Xu‡, Taehyoung Kim§, Karol Schober∧, and Xingqin Lin#

        ‡Qualcomm Inc., §Samsung Electronics,∧Nokia, #Ericsson Inc.