5G PDCCH and 5G PDSCH
5G PDCCH is used
to carry Downlink Control Information (DCI), and following types of DCI are
supported in NR.
* PDSCH assignments to convey TB(s) to a certain
UE, including time/frequency-domain resource information
* PUSCH grants for a certain UE to transmit a
TB, including time/frequency-domain resource information
* Slot format indication, where how each of
symbols within a slot is indicated
* Pre-emption indication, which is used to
inform UEs that there is no DL transmission on the informed
time/frequency-domain resources
* UL transmit power control (TPC)
* Each device monitors a number of PDCCHs, typically once
per slot although it is possible to configure more frequent monitoring to
support traffic requiring very low latency. Upon detection of a valid PDCCH,
the device follows downlink control information contained in the PDCCH, e.g.,
the scheduling decision so that the device receives PDSCH (or transmits PUSCH)
accordingly.
* The PDCCHs are
transmitted in one or more control resource sets (CORESETs). A CORESET spans overdone,
two or three OFDM symbol(s) in time domain and over a configurable bandwidth in
the frequency domain. This is needed in order to handle devices with different
bandwidth capabilities and also beneficial from a forward-compatibility
perspective. One control channel element (CCE) is defined as 6 resource element
groups (REGs), where 1 REG is composed of 12 resource elements (REs). In a
CORESET, a PDCCH with DM-RS can be mapped on one or more CCEs as shown in
Figure. Different number of CCEs (aggregation level) provides different coding
rate for the control channels.
There are
different formats for DCI transmitted on a PDCCH as shown in DCI Table. A UE
monitors one or more PDCCH candidates for DCI with CRC scrambled by a certain
RNTI in PDCCH common search space (CSS) set and/or UE-specific search space
(USS) set. DCI format is distinguished by the PDCCH payload size and the RNTI
scrambling the CRC.
NR DCI formats
DCI format
|
RNTI
|
Notes
|
DCI format 0_0
|
RA-RNTI, TC-RNTI, C-RNTI, CS-RNTI
|
Monitored on CSS or USS
Scheduling PUSCH
|
DCI format 0_1
|
C-RNTI, CS-RNTI
|
Monitored in USS
Scheduling PUSCH
|
DCI format 1_0
|
SI-RNTI, RA-RNTI,
P-RNTI, C-RNTI, CS-RNTI
|
Monitored in CSS or USS
Scheduling PDSCH
|
DCI format 1_1
|
C-RNTI, CS-RNTI
|
Monitored in USS
Scheduling PDSCH
|
DCI format 2_0
|
SFI-RNTI
|
Monitored in CSS
Indicating slot format for slot(s)
|
DCI format 2_1
|
INT-RNTI
|
Monitored in CSS
Indicating pre-emption of DL resource
|
DCI format 2_2
|
TPC-PUSCH-RNTI, TPC-PUCCH-RNTI
|
Monitored in CSS
Group-TPC command for PUSCH/PUCCH
|
DCI format 2_3
|
TPC-SRS-RNTI
|
Monitored in CSS
Group-command for SRS
|
PDSCH is used to
transmit one or two transport blocks (TBs). A DCI in a PDCCH can assign a PDSCH
transmission with DM-RS (and other RS if any). The PDSCH is decoded based on
the information in the PDCCH, for example, time/frequency-domain resource, modulation,
and layer. PDSCH transmissions are processed with durations from 2 to 14
symbols. The number of layers for PDSCH transmissions is 8. HARQ feedback/retransmission
is supported for PDSCH transmissions as mentioned in HARQ Post.
