|
MAC CE (MAC Control Element)
The purpose and function of NR MAC CE is almost same as LTE MAC CE.
When we say 'communication between UE and Network', we normally think about only signaling message (RRC or NAS message). When I say 'communication' in this case, it means 'control command exchange' between UE and network, not the data traffic.
In UMTS case, it is true that only RRC and NAS message functions as communication between UE and Network, but in LTE and NR a special type of communication is introduced working at MAC Layer. It implies that there are special MAC structure that carries special control information. These special MAC structure carrying the control information is called 'MAC CE', which means 'MAC Control Element'. Motivation for this kind of communication would be obvious. It would be much faster comparing
to RRC layer or NAS layer communication.
This special MAC structure is implemented as a special bit string in LCID field of MAC Header (Refer to LTE MAC page for the details of MAC header).
There are
several MAC CE in downlink MAC and also several MAC CE in uplink MAC. Following table from 38.213 shows the LCID types of MAC header. The parts marked in red rectangle is LCID representing various MAC CE. These are relatively small set of MAC CE defined in 38.321 Rel 15 - 6.2.1. You may see this gets longer as new release comes out as you have seen in LTE.
As in LTE, the structure and functionality of MAC CE would be an area that is evolving continuously as new 3GPP release comes out. In this section, I will consollidates MAC CE LCID structure from different releases so that we can keep track of the structure and functional evolution of MAC CE.
NOTE : The definition of LCID and eLCID is stated as follows in 38.321-6.2.1.
LCID: The Logical Channel ID field identifies the logical channel instance of the corresponding MAC SDU or the type of the corresponding MAC CE or padding as described in 38.321-Tables 6.2.1-1, 6.2.1-1c and 6.2.1-2 for the DL-SCH and UL-SCH respectively. There is one LCID field per MAC subheader. The size of the LCID field is 6 bits. If the LCID field is set to 34, one additional octet is present in the MAC subheader containing the eLCID field and follow the octet containing LCID field. If
the LCID field is set to 33, two additional octets are present in the MAC subheader containing the eLCID field and these two additional octets follow the octet containing LCID field.
eLCID: The extended Logical Channel ID field identifies the logical channel instance of the corresponding MAC SDU or the type of the corresponding MAC CE as described in 38.321-tables 6.2.1-1a, 6.2.1-1b, 6.2.1-2a and 6.2.1-2b for the DL-SCH and UL-SCH respectively. The size of the eLCID field is either 8 bits or 16 bits.
< 38.321 - Table 6.2.1-1: Values of LCID for DL-SCH >
|
Codepoint/Index
|
LCID values
|
|
0
|
CCCH
|
|
1–32
|
Identity of the logical channel of DCCH, DTCH and multicast MTCH
|
|
33
|
Extended logical channel ID field (two-octet eLCID field)
|
|
34
|
Extended logical channel ID field (one-octet eLCID field)
|
|
35–46
|
Reserved
|
|
47
|
Recommended bit rate
|
|
48
|
SP ZP CSI-RS Resource Set Activation/Deactivation
|
|
49
|
PUCCH spatial relation Activation/Deactivation
|
|
50
|
SP SRS Activation/Deactivation
|
|
51
|
SP CSI reporting on PUCCH Activation/Deactivation
|
|
52
|
TCI State Indication for UE-specific PDCCH
|
|
53
|
TCI States Activation/Deactivation for UE-specific PDSCH
|
|
54
|
Aperiodic CSI Trigger State Subselection
|
|
55
|
SP CSI-RS/CSI-IM Resource Set Activation/Deactivation
|
|
56
|
Duplication Activation/Deactivation
|
|
57
|
SCell Activation/Deactivation (four octets)
|
|
58
|
SCell Activation/Deactivation (one octet)
|
|
59
|
Long DRX Command
|
|
60
|
DRX Command
|
|
61
|
Timing Advance Command
|
|
62
|
UE Contention Resolution Identity
|
|
63
|
Padding
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< 38.321 - Table 6.2.1-1a: Values of two-octet eLCID for DL-SCH >
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Codepoint
|
Index
|
LCID values
|
|
0 to (216 − 1)
|
320 to (216 + 319)
|
Identity of the logical channel
|
< 38.321 - Table 6.2.1-1b: Values of one-octet eLCID for DL-SCH >
|
Codepoint
|
Index
|
LCID values
|
|
0 to 207
|
64 to 271
|
Reserved
|
|
208
|
272
|
On-demand SSB Activation/Deactivation (one octet eL field)
|
|
209
|
273
|
On-demand SSB Activation/Deactivation (four octet eL field)
|
|
210
|
274
|
SP CSI-RS/CSI-IM Resource Set Activation/Deactivation
|
|
211
|
275
|
UL Rate Control
|
|
212
|
276
|
Pathloss Offset Update
|
|
213
|
277
|
SP CSI-RS/CSI-IM Resource Set Activation/Deactivation for Candidate Cell
|
|
214
|
278
|
Enhanced LTM Cell Switch Command
|
|
215
|
279
|
Aggregated SP Positioning SRS Activation/Deactivation
|
|
216
|
280
|
Enhanced SP CSI reporting on PUCCH Activation/Deactivation
|
|
217
|
281
|
Cross-RRH TCI State Indication for UE-specific PDCCH
|
|
218
|
282
|
LTM Cell Switch Command
|
|
219
|
283
|
Candidate Cell TCI States Activation/Deactivation
|
|
220
|
284
|
SP SSB Based Beam Indication
|
|
221
|
285
|
Activation/Deactivation for Joint TCI States
|
|
222
|
286
|
Enhanced Unified TCI states Activation/Deactivation MAC CE for Joint TCI States
|
|
223
|
287
|
Enhanced Unified TCI states Activation/Deactivation MAC CE for Separate TCI States
|
|
224
|
288
|
NCR Access Link Beam Indication
|
|
225
|
289
|
NCR Downlink Backhaul Link Beam Indication
|
|
226
|
290
|
NCR Uplink Backhaul Link Beam Indication
|
|
227
|
291
|
Serving Cell Set based SRS TCI State Indication
|
|
228
|
292
|
SP/IAP SRS TCI State Indication
|
|
229
|
293
|
BFD-RS Indication
|
|
230
|
294
|
Differential Koffset
|
|
231
|
295
|
Enhanced SCell Activation/Deactivation (one octet eL field)
|
|
232
|
296
|
Enhanced SCell Activation/Deactivation (four octet eL field)
|
|
233
|
297
|
Unified TCI States Activation/Deactivation
|
|
234
|
298
|
PUCCH Power Control Set Update for multiple PUCCH repetition
|
|
235
|
299
|
PUCCH spatial relation Activation/Deactivation for multiple TRP PUCCH repetition
|
|
236
|
300
|
Enhanced TCI States Indication for UE-specific PDCCH
|
|
237
|
301
|
Positioning Measurement Gap Activation/Deactivation Command
|
|
238
|
302
|
PPW Activation/Deactivation Command
|
|
239
|
303
|
DL Tx Power Adjustment
|
|
240
|
304
|
Timing Case Indication
|
|
241
|
305
|
Child DL-BU Resetting Beam Indication
|
|
242
|
306
|
Case-7 Timing advance offset
|
|
243
|
307
|
Provided Guard Symbols for Case-6 timing
|
|
244
|
308
|
Provided Guard Symbols for Case-7 timing
|
|
245
|
309
|
Serving Cell Set based SRS Spatial Relation Indication
|
|
246
|
310
|
PUCCH Pathloss Reference RS Update
|
|
247
|
311
|
Pathloss Reference RS Update
|
|
248
|
312
|
Enhanced SP/IAP SRS Spatial Relation Indication
|
|
249
|
313
|
Enhanced PUCCH Spatial Relation Activation/Deactivation
|
|
250
|
314
|
Enhanced TCI States Activation/Deactivation for UE-specific PDSCH
|
|
251
|
315
|
Duplication RLC Activation/Deactivation
|
|
252
|
316
|
Absolute Timing Advance Command
|
|
253
|
317
|
SP Positioning SRS Activation/Deactivation
|
|
254
|
318
|
Provided Guard Symbols
|
|
255
|
319
|
Timing Delta
|
< 38.321 - Table 6.2.1-1c: Values of LCID for MBS multicast MCCH and MBS broadcast on DL-SCH >
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Codepoint/Index
|
LCID values
|
|
0
|
Broadcast MCCH or multicast MCCH
|
|
1–32
|
Identity of the logical channel of broadcast MTCH
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|
33–63
|
Reserved
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< 38.321 - Table 6.2.1-2: Values of LCID for UL-SCH when the LX field is not present or is set to 0 >
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Codepoint/Index
|
LCID values
|
|
0
|
CCCH of size 64 bits, except for an (e)RedCap UE
|
|
1–32
|
Identity of the logical channel of DCCH and DTCH
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|
33
|
Extended logical channel ID field (two-octet eLCID field)
|
|
34
|
Extended logical channel ID field (one-octet eLCID field)
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|
35
|
CCCH of size 48 bits for a RedCap UE
|
|
36
|
CCCH of size 64 bits for a RedCap UE
|
|
37–42
|
Reserved
|
|
43
|
Truncated Enhanced BFR (one octet C)
|
|
44
|
Timing Advance Report
|
|
45
|
Truncated Sidelink BSR
|
|
46
|
Sidelink BSR
|
|
47
|
Reserved
|
|
48
|
LBT failure (four octets)
|
|
49
|
LBT failure (one octet)
|
|
50
|
BFR (one octet C)
|
|
51
|
Truncated BFR (one octet C)
|
|
52
|
CCCH of size 48 bits, except for an (e)RedCap UE
|
|
53
|
Recommended bit rate query
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|
54
|
Multiple Entry PHR (four octets C)
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|
55
|
Configured Grant Confirmation
|
|
56
|
Multiple Entry PHR (one octet C)
|
|
57
|
Single Entry PHR
|
|
58
|
C-RNTI
|
|
59
|
Short Truncated BSR
|
|
60
|
Long Truncated BSR
|
|
61
|
Short BSR
|
|
62
|
Long BSR
|
|
63
|
Padding
|
|
NOTE: CCCH of size 48 bits and CCCH of size 64 bits are referred to as CCCH and CCCHH, respectively, in TS 38.331.
|
< 38.321 - Table 6.2.1-2a: Values of two-octet eLCID for UL-SCH >
| Codepoint |
Index |
LCID values
|
|
0 to (215 − 1)
|
320 to (215 + 319)
|
Identity of the logical channel
|
< 38.321 - Table 6.2.1-2b: Values of one-octet eLCID for UL-SCH >
|
Codepoint
|
Index
|
LCID values
|
|
0 to 214
|
64 to 278
|
Reserved
|
|
215
|
279
|
Multiple Entry Delay Status Report
|
|
216
|
280
|
UL Rate Control
|
|
217
|
281
|
Event Triggered L1 Measurement Report
|
|
218
|
282
|
Truncated Event Triggered L1 Measurement Report
|
|
219
|
283
|
Enhanced Multiple Entry PHR for multiple TRP ST×2P (four octets C)
|
|
220
|
284
|
Enhanced Multiple Entry PHR for multiple TRP ST×2P (one octets C)
|
|
221
|
285
|
Enhanced Single Entry PHR for multiple TRP ST×2P
|
|
222
|
286
|
SL LBT Failure
|
|
223
|
287
|
Enhanced Multiple Entry PHR with assumed PUSCH (four octets C)
|
|
224
|
288
|
Enhanced Multiple Entry PHR with assumed PUSCH (one octets C)
|
|
225
|
289
|
Single Entry PHR with assumed PUSCH
|
|
226
|
290
|
SL-PRS Resource Request
|
|
227
|
291
|
Refined Long BSR
|
|
228
|
292
|
Multiple Entry Delay Status Report
|
|
229
|
293
|
Enhanced Multiple Entry PHR for multiple TRP (four octets C)
|
|
230
|
294
|
Enhanced Multiple Entry PHR for multiple TRP (one octets C)
|
|
231
|
295
|
Enhanced Single Entry PHR for multiple TRP
|
|
232
|
296
|
Enhanced Multiple Entry PHR (four octets C)
|
|
233
|
297
|
Enhanced Multiple Entry PHR (one octets C)
|
|
234
|
298
|
Enhanced Single Entry PHR
|
|
235
|
299
|
Enhanced BFR (one octet C)
|
|
236
|
300
|
Truncated Enhanced BFR (one octet C)
|
|
237
|
301
|
Positioning Measurement Gap Activation/Deactivation Request
|
|
238
|
302
|
IAB-MT Recommended Beam Indication
|
|
239
|
303
|
Desired IAB-MT PSD range
|
|
240
|
304
|
Desired DL Tx Power Adjustment
|
|
241
|
305
|
Case-6 Timing Request
|
|
242
|
306
|
Desired Guard Symbols for Case 6 timing
|
|
243
|
307
|
Desired Guard Symbols for Case 7 timing
|
|
244
|
308
|
Extended Short Truncated BSR
|
|
245
|
309
|
Extended Long Truncated BSR
|
|
246
|
310
|
Extended Short BSR
|
|
247
|
311
|
Extended Long BSR
|
|
248
|
312
|
Extended Pre-emptive BSR
|
|
249
|
313
|
BFR (four octets C)
|
|
250
|
314
|
Truncated BFR (four octets C)
|
|
251
|
315
|
Multiple Entry Configured Grant Confirmation
|
|
252
|
316
|
Single Entry Configured Grant Confirmation
|
|
253
|
317
|
Desired Guard Symbols
|
|
254
|
318
|
BFR (octets C)
|
|
255
|
319
|
Pre-emptive BSR
|
< 38.321 - Table 6.2.1-2c: Values of LCID for UL-SCH when the LX field is set to 1 >
|
Codepoint
|
Index
|
LCID values
|
|
0
|
(215 + 320)
|
CCCH of size 48 bits for an/eRedCap UE
|
|
1
|
(215 + 321)
|
CCCH of size 64 bits for an/eRedCap UE
|
|
2
|
(215 + 322)
|
CCCH of size 48 bits for PUCCH repetition of Msg4 HARQ-ACK, except for an (e)RedCap UE
|
|
3
|
(215 + 323)
|
CCCH of size 64 bits for PUCCH repetition of Msg4 HARQ-ACK, except for an (e)RedCap UE
|
|
4
|
(215 + 324)
|
CCCH of size 48 bits for PUCCH repetition of Msg4 HARQ-ACK of a RedCap UE
|
|
5
|
(215 + 325)
|
CCCH of size 64 bits for PUCCH repetition of Msg4 HARQ-ACK of a RedCap UE
|
|
6
|
(215 + 326)
|
CCCH of size 48 bits for PUCCH repetition of Msg4 HARQ-ACK of an eRedCap UE
|
|
7
|
(215 + 327)
|
CCCH of size 64 bits for PUCCH repetition of Msg4 HARQ-ACK of an eRedCap UE
|
|
8
|
(215 + 328)
|
CCCH of size 48 bits for PDSCH repetition of Msg4, except for an (e)RedCap UE
|
|
9
|
(215 + 329)
|
CCCH of size 64 bits for PDSCH repetition of Msg4, except for an (e)RedCap UE
|
|
10
|
(215 + 330)
|
CCCH of size 48 bits for PDSCH repetition of Msg4 of a RedCap UE
|
|
11
|
(215 + 331)
|
CCCH of size 64 bits for PDSCH repetition of Msg4 of a RedCap UE
|
|
12
|
(215 + 332)
|
CCCH of size 48 bits for PDSCH repetition of Msg4 of an eRedCap UE
|
|
13
|
(215 + 333)
|
CCCH of size 64 bits for PDSCH repetition of Msg4 of an eRedCap UE
|
|
14
|
(215 + 334)
|
CCCH of size 48 bits for PUCCH repetition of Msg4 HARQ-ACK and PDSCH repetition of Msg4, except for an (e)RedCap UE
|
|
15
|
(215 + 335)
|
CCCH of size 64 bits for PUCCH repetition of Msg4 HARQ-ACK and PDSCH repetition of Msg4, except for an (e)RedCap UE
|
|
16
|
(215 + 336)
|
CCCH of size 48 bits for PUCCH repetition of Msg4 HARQ-ACK and PDSCH repetition of Msg4 of a RedCap UE
|
|
17
|
(215 + 337)
|
CCCH of size 64 bits for PUCCH repetition of Msg4 HARQ-ACK and PDSCH repetition of Msg4 of a RedCap UE
|
|
18
|
(215 + 338)
|
CCCH of size 48 bits for PUCCH repetition of Msg4 HARQ-ACK and PDSCH repetition of Msg4 of an eRedCap UE
|
|
19
|
(215 + 339)
|
CCCH of size 64 bits for PUCCH repetition of Msg4 HARQ-ACK and PDSCH repetition of Msg4 of an eRedCap UE
|
|
20 to 63
|
(215 + 340) to (215 + 383)
|
Reserved
|
|
NOTE 1: The MAC entity may use the code point corresponding to a given feature or feature combination only if network indicates support for the corresponding feature or feature combination.
NOTE 2: CCCH of size 48 bits and CCCH of size 64 bits are referred to as CCCH and CCCH1, respectively, in TS 38.331.
NOTE 3: For UE capable of PUCCH repetition of Msg4 HARQ-ACK, the MAC entity uses the code points corresponding to PUCCH repetition of Msg4 HARQ-ACK if numberOfMsg4HARQ-ACK-Repetitions is configured and rsrp-ThresholdMsg4HARQ-ACK is not set, or rsrp-ThresholdMsg4HARQ-ACK is configured and the RSRP of the downlink pathloss reference is less than rsrp-ThresholdMsg4HARQ-ACK.
|
Followings are the list of the MAC CEs specified in 38.321 as of now. Since each of these items is a pretty big top, I will create a separate page for each of these items.
|
MAC CE
|
Reference
|
|
Buffer Status Report
|
38.321 - 6.1.3.1
|
|
C-RNTI
|
38.321 - 6.1.3.2
|
|
UE Contention Resolution Identity
|
38.321 - 6.1.3.3
|
|
Timing Advance Command
|
38.321 - 6.1.3.4
|
|
DRX Command
|
38.321 - 6.1.3.5
|
|
Long DRX Command
|
38.321 - 6.1.3.6
|
|
Configured Grant Confirmation
|
38.321 - 6.1.3.7
|
|
Single Entry PHR
|
38.321 - 6.1.3.8
|
|
Multiple Entry PHR
|
38.321 - 6.1.3.9
|
|
SCell Activation/Deactivation
|
38.321 - 6.1.3.10
|
|
Duplication Activation/Deactivation
|
38.321 - 6.1.3.11
|
|
SP CSI-RS / CSI-IM Resource Set Activation/Deactivation MAC CE
|
38.321 - 6.1.3.12
|
|
Aperiodic CSI Trigger State Subselection MAC CE
|
38.321 - 6.1.3.13
|
|
TCI States Activation/Deactivation for UE-specific PDSCH MAC CE
|
38.321 - 6.1.3.14
|
|
TCI State Indication for UE-specific PDCCH MAC CE
|
38.321 - 6.1.3.15
|
|
SP CSI reporting on PUCCH Activation/Deactivation MAC CE
|
38.321 - 6.1.3.16
|
|
SP SRS Activation/Deactivation MAC CE
|
38.321 - 6.1.3.17
|
|
PUCCH spatial relation Activation/Deactivation MAC CE
|
38.321 - 6.1.3.18
|
|
SP ZP CSI-RS Resource Set Activation/Deactivation MAC CE
|
38.321 - 6.1.3.19
|
|
Recommended bit rate MAC CE
|
38.321 - 6.1.3.20
|
Reference
[1]
|