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LTE-BL/CE (LTE-M1) - MCS/TBS Determination

 

Downlink TBS Determination

 

TBS (Transport Block Size) for BL/CE UE is determined by 36.213 Table 7.1.7.2.1-1: Transport block size table as in legacy LTE. The difference between M1 and legacy LTE lies in mapping between I_MCS and I_TBS and the possible range of I_MCS.

 

36.213-7.1.7 Modulation order and transport block size determination states as follows :

  • When PDSCH is scheduled by DCI format 6-1A
    • the number of MCS field is 4, it means the maximum MCS is 15
  • When PDSCH is scheduled by DCI format 6-2
    • the number of MCS field is 3, it means the maximum MCS is 7
  • When PDSCH is scheduled by DCI format 6-1B
    • the number of MCS field is 4 and I_MCS = I_TBS
  • When PDSCH is to carry SystemInformationBlockType1-BR

 

 

Uplink TBS Determination

 

36.213-8.6.1 Modulation order and redundancy version determination  and 8.6.2 Transport block size determination states as follows :

  • The modulation order is determined according to following table  CEModeB UE is not expected to receive a DCI format 6-0B indicating I_MCS >= 10.
  • For CEModeA, TBS of a user data PUSCH (except PUSCH scheduled by Random Access Response) is determined by following table.

< 36.213-Table 8.6.1-2: Modulation and TBS index table for PUSCH >

 

 

Reference

 

[1] 3GPP TS 36.331 V13.2.0 (2016-06)

[2]3GPP TS 36.213 V13.2.0 (2016-06) Physical layer procedures