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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 case there are several communication path 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'.

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.

 

 

MAC E List in 38.321 v15.1

 

 

 

MAC E List in 38.321 v15.3

 

 

 

 

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

 

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