Content for  TS 38.321  Word version:  18.3.0

The Guard Symbols MAC CEs (i.e. Provided Guard Symbols MAC CE and Desired Guard Symbols MAC CE) for Case-6 and Case-7 timing modes are identified by the MAC subheader with eLCIDs as specified in Table 6.2.1-1b for DL-SCH and in Table 6.2.1-2b for UL-SCH. The MAC CEs have fixed size and consist of three octets each, defined as follows (Figure 6.1.3.37-1 and Figure 6.1.3.37-2):

• R: Reserved bit, set to 0;
• Serving Cell ID: This field indicates the identity of the Serving Cell for which the MAC CE applies. The length of the field is 5 bits;
• Sub-carrier spacing (SCS): This field indicates the subcarrier spacing used as reference for the guard spacing. The length of this field is 2bits. The values for the SCS field are shown in Table 6.1.3.22-2;
• Number of Guard Symbols (NmbGS_i): This field indicates the number of guard symbols for the switching scenarios shown in Table 5.18.19-2.

The Case-7 Timing advance offset MAC CE is identified by MAC subheader with eLCID as specified in Table 6.2.1-1b. The Case-7 Timing advance offset MAC CE is related to the Case-7 timing mode, has a fixed size and consists of two octets defined as follows (Figure 6.1.3.21-1):

• R: Reserved bit, set to 0;
• T_offset,2: This field indicates the value (-3072, -3071, …, 1023) used to control the amount of timing adjustment that MAC entity indicates (as specified in TS 38.213). The length of the field is 12 bits.

The Case-6 Timing Request MAC CE is identified by MAC subheader with eLCID as specified in Table 6.2.1-2b. This MAC CE is used by the IAB-MT node to inform its parent node whether Case-6 timing is required for simultaneous operation. It has a fixed size of zero bits.

The Positioning Measurement Gap Activation/deactivation request MAC CE is identified by MAC subheader with eLCID as specified in Table 6.2.1-2b. It has a fixed 8-bit size defined as follows (Figure 6.1.3.40-1):

• Positioning MG ID: This field indicates the identifier for the pre-configured positioning measurement gap. The length of the field is 4 bits;
• A/D: This field indicates the activation or deactivation of the Positioning Measurement Gap. The field is set to 1 to indicate activation, otherwise it indicates deactivation. The length of the field is 1 bit;
• R: Reserved bit, set to 0.

The Positioning Measurement Gap Activation/Deactivation Command MAC CE is identified by MAC subheader with eLCID as specified in Table 6.2.1-1b. It has a fixed 8-bit size defined as follows (Figure 6.1.3.41-1):

• Positioning MG ID: This field indicates the identifier for the preconfigured positioning measurement gap. The length of the field is 4 bits;
• A/D: This field indicates the activation or deactivation of the Positioning Measurement Gap. The field is set to 1 to indicate activation, otherwise it indicates deactivation. The length of the field is 1 bit;
• R: Reserved bit, set to 0.