5G/NR - MCS/TBS/Code Rate                                            Home : www.sharetechnote.com

 

 

 

 

 

MCS / TBS / Code Rate

 

The concept of MCS (Modulation Coding Scheme), Code Rate, TB (Transport Block) and TBS (Transport Block Size) are same as LTE MCS, Code Rate, TBS.

 

 

 

PDSCH Transport Block Size Determination

 

NR MCS and Code Rate are determined by a predefined table as in 38.214 - Table 5.1.3.1-1 and 38.214 - Table 5.1.3.1-2, which is pretty straight forward. However, determining TBS (Transport block size) in NR is more complicated than the one in LTE. In case of LTE, all the possibility of RBS are precalculated and listed as a big table. However, in NR the TBS determination process is described as a sequence of algorithm as summarized below (I think it will take a while to get familiar with this process). This is an illustration based on 38.214 - 5.1.3.2 Transport block size determination.

 

 

 

As you see in the process illustrated above, the initial input for this algorithm is Ninfo. However, to figure out this Ninfo also requires long calculation process as below.

 

 

 

< 38.214 - Table 5.1.3.2-1: Quantized number of REs allocated for PDSCH within a PRB >

 

 

< 38.214  - Table 5.1.3.1-1: MCS index table 1 for PDSCH >

MCS Index

IMCS

Modulation Order

Qm

Target code Rate x [1024]

R

Spectral

efficiency

0

2

120

  0.2344

1

2

157

  0.3066

2

2

193

  0.3770

3

2

251

  0.4902

4

2

308

  0.6016

5

2

379

  0.7402

6

2

449

  0.8770

7

2

526

  1.0273

8

2

602

  1.1758

9

2

679

  1.3262

10

4

340

  1.3281

11

4

378

  1.4766

12

4

434

  1.6953

13

4

490

  1.9141

14

4

553

  2.1602

15

4

616

  2.4063

16

4

658

  2.5703

17

6

438

  2.5664

18

6

466

  2.7305

19

6

517

  3.0293

20

6

567

  3.3223

21

6

616

  3.6094

22

6

666

  3.9023

23

6

719

  4.2129

24

6

772

  4.5234

25

6

822

  4.8164

26

6

873

  5.1152

27

6

910

  5.3320

28

6

948

  5.5547

29

2

reserved

30

4

reserved

31

6

reserved

 

 

< 38.214 - Table 5.1.3.1-2: MCS index table 2 for PDSCH >

MCS Index

IMCS 

Modulation Order

Qm

Target code Rate x

[1024]

R

Spectral

efficiency

0

2

120

0.2344

1

2

193

0.377

2

2

308

0.6016

3

2

449

0.877

4

2

602

1.1758

5

4

378

1.4766

6

4

434

1.6953

7

4

490

1.9141

8

4

553

2.1602

9

4

616

2.4063

10

4

658

2.5703

11

6

466

2.7305

12

6

517

3.0293

13

6

567

3.3223

14

6

616

3.6094

15

6

666

3.9023

16

6

719

4.2129

17

6

772

4.5234

18

6

822

4.8164

19

6

873

5.1152

20

8

682.5

5.332

21

8

711

5.5547

22

8

754

5.8906

23

8

797

6.2266

24

8

841

6.5703

25

8

885

6.9141

26

8

916.5

7.1602

27

8

948

7.4063

28

2

reserved

29

4

reserved

30

6

reserved

31

8

reserved

 

 

< 38.214 - Table 5.1.3.1-3: MCS index table 3 for PDSCH >

MCS Index

IMCS 

Modulation Order

Qm

Target code Rate x

[1024]

R

Spectral

efficiency

0

2

30

0.0586

1

2

40

0.0781

2

2

50

0.0977

3

2

64

0.1250

4

2

78

0.1523

5

2

99

0.1934

6

2

120

0.2344

7

2

157

0.3066

8

2

193

0.3770

9

2

251

0.4902

10

2

308

0.6016

11

2

379

0.7402

12

2

449

0.8770

13

2

526

1.0273

14

2

602

1.1758

15

4

340

1.3281

16

4

378

1.4766

17

4

434

1.6953

18

4

490

1.9141

19

4

553

2.1602

20

4

616

2.4063

21

6

438

2.5664

22

6

466

2.7305

23

6

517

3.0293

24

6

567

3.3223

25

6

616

3.6094

26

6

666

3.9023

27

6

719

4.2129

28

6

772

4.5234

29

2

reserved

30

4

reserved

31

6

reserved

 

 

< 38.214  - Table 5.1.3.2-2: TBS for N_info <= 3824  >

Index

TBS

Index

TBS

Index

TBS

Index

TBS

1

24

31

336

61

1288

91

3624

2

32

32

352

62

1320

92

3752

3

40

33

368

63

1352

93

3824

4

48

34

384

64

1416

 

 

5

56

35

408

65

1480

 

 

6

64

36

432

66

1544

 

 

7

72

37

456

67

1608

 

 

8

80

38

480

68

1672

 

 

9

88

39

504

69

1736

 

 

10

96

40

528

70

1800

 

 

11

104

41

552

71

1864

 

 

12

112

42

576

72

1928

 

 

13

120

43

608

73

2024

 

 

14

128

44

640

74

2088

 

 

15

136

45

672

75

2152

 

 

16

144

46

704

76

2216

 

 

17

152

47

736

77

2280

 

 

18

160

48

768

78

2408

 

 

19

168

49

808

79

2472

 

 

20

176

50

848

80

2536

 

 

21

184

51

888

81

2600

 

 

22

192

52

928

82

2664

 

 

23

208

53

984

83

2728

 

 

24

224

54

1032

84

2792

 

 

25

240

55

1064

85

2856

 

 

26

256

56

1128

86

2976

 

 

27

272

57

1160

87

3104

 

 

28

288

58

1192

88

3240

 

 

29

304

59

1224

89

3368

 

 

30

320

60

1256

90

3496

 

 

 

 

 

PUSCH Transport Block Size Determination

 

PUSCH Transport block size is influenced by RRC Parameters at the stage of determining Modulation Order and Code Rate and this makes it so difficult and complicated to understand the whole process of TBS(Transport Size) Determination. The RRC parameters involved in this process is highlighted in red as shown below.

 

 

38.331 15.3 (2018-10)

 

PUSCH-Config ::= SEQUENCE {

    dataScramblingIdentityPUSCH                 INTEGER (0..1023) OPTIONAL,

    txConfig                                    ENUMERATED {codebook, nonCodebook}

    dmrs-UplinkForPUSCH-MappingTypeA            SetupRelease { DMRS-UplinkConfig }

    dmrs-UplinkForPUSCH-MappingTypeB            SetupRelease { DMRS-UplinkConfig }

    pusch-PowerControl                          PUSCH-PowerControl

    frequencyHopping                            ENUMERATED {intraSlot, interSlot}

    frequencyHoppingOffsetLists                 SEQUENCE (SIZE (1..4)) OF

                                                     INTEGER (1.. maxNrofPhysicalResourceBlocks-1)

    resourceAllocation                          ENUMERATED { resourceAllocationType0,

                                                             resourceAllocationType1,

                                                             dynamicSwitch},

    pusch-TimeDomainAllocationList              SetupRelease {

                                                         PUSCH-TimeDomainResourceAllocationList

                                                }

    pusch-AggregationFactor                     ENUMERATED { n2, n4, n8 }

    mcs-Table                                   ENUMERATED {qam256, qam64LowSE}

    mcs-TableTransformPrecoder                  ENUMERATED {qam256, qam64LowSE}

    transformPrecoder                           ENUMERATED {enabled, disabled}

    codebookSubset                              ENUMERATED {fullyAndPartialAndNonCoherent,

                                                            partialAndNonCoherent,

                                                            nonCoherent}

    maxRank                                     INTEGER (1..4)

    rbg-Size                                    ENUMERATED { config2}

    uci-OnPUSCH                                 SetupRelease { UCI-OnPUSCH }

    tp-pi2BPSK                                  ENUMERATED {enabled}

    ...

}

 

 

ConfiguredGrantConfig ::= SEQUENCE {

   frequencyHopping ENUMERATED                 {intraSlot, interSlot} ,

    cg-DMRS-Configuration                       DMRS-UplinkConfig,

    mcs-Table                                   ENUMERATED {qam256, qam64LowSE}

    mcs-TableTransformPrecoder                  ENUMERATED {qam256, qam64LowSE}

    uci-OnPUSCH SetupRelease                    { CG-UCI-OnPUSCH } OPTIONAL,

    resourceAllocation                          ENUMERATED { resourceAllocationType0,

                                                             resourceAllocationType1,

                                                             dynamicSwitch },

    rbg-Size                                    ENUMERATED {config2},

    powerControlLoopToUse                       ENUMERATED {n0, n1},

    p0-PUSCH-Alpha                              P0-PUSCH-AlphaSetId,

    transformPrecoder                           ENUMERATED {enabled, disabled},

    nrofHARQ-Processes                          INTEGER(1..16),

    repK                                        ENUMERATED {n1, n2, n4, n8},

    repK-RV                                     ENUMERATED {s1-0231, s2-0303, s3-0000},

    periodicity                                 ENUMERATED {

                                                    sym2, sym7, sym1x14, sym2x14, sym4x14,

                                                    sym5x14, sym8x14, sym10x14, sym16x14,

                                                    sym20x14,sym32x14, sym40x14, sym64x14,

                                                    sym80x14, sym128x14, sym160x14, sym256x14,

                                                    sym320x14, sym512x14,sym640x14, sym1024x14,

                                                    sym1280x14, sym2560x14, sym5120x14,sym6,

                                                    sym1x12, sym2x12, sym4x12, sym5x12,

                                                    sym8x12, sym10x12, sym16x12, sym20x12,

                                                    sym32x12,sym40x12, sym64x12, sym80x12,

                                                    sym128x12, sym160x12, sym256x12, sym320x12,

                                                    sym512x12, sym640x12,sym1280x12, sym2560x12

                                                },

    configuredGrantTimer                        INTEGER (1..64) OPTIONAL, -- Need R

    rrc-ConfiguredUplinkGrant                   SEQUENCE {

                                                   timeDomainOffset          INTEGER (0..5119),

                                                   timeDomainAllocation      INTEGER (0..15),

                                                   frequencyDomainAllocation BIT STRING (SIZE(18)),

                                                   antennaPort               INTEGER (0..31),

                                                   dmrs-SeqInitialization    INTEGER (0..1),

                                                   precodingAndNumberOfLayers  INTEGER (0..63),

                                                   srs-ResourceIndicator       INTEGER (0..15),

                                                   mcsAndTBS                   INTEGER (0..31),

                                                   frequencyHoppingOffset      

                                                                INTEGER (1.. maxNrofPhysicalResourceBlocks-1)

                                                   pathlossReferenceIndex        

                                                                INTEGER (0..maxNrofPUSCH-PathlossReferenceRSs-1)

                                                    ...

                                               } OPTIONAL, -- Need R

    ...

}

 

 

 

< Modulation order and target code rate determination >

 

I created following table based on the descriptions in 28.214-6.1.4.1(v15.3 - Oct 2018).

Transform

Precoding

mcs-Table

mcs-Table

TransformPrecoder

RNTI

DCI

MCS Index

Table

PUSCH-Config

Configured

GrantConfig

PUSCH-Config

Configured

GrantConfig

diabled

qam256

N/A

N/A

C-RNTI

SP-CSI-RNTI

0_1

5.1.3.1-2

diabled

qam64LowSE

N/A

N/A

NOT MCS-C-RNTI

C-RNTI

SP-CSI-RNTI

 

5.1.3.1-3

diabled

N/A

qam256

N/A

MCS-C-RNT

 

5.1.3.1-3

diabled

N/A

qam64LowSE

N/A

CS-RNTI

 

5.1.3.1-3

diabled

none of the above

5.1.3.1-1

enabled

qam256

 

 

C-RNTI

SP-CSI-RNTI

0_1

5.1.3.1-2

enabled

qam64LowSE

 

 

NOT MCS-C-RNTI

C-RNTI

SP-CSI-RNTI

 

6.1.4.1-2

enabled

 

 

 

MCS-C-RNT

 

6.1.4.1-2

enabled

 

qam256

 

CS-RNTI

 

5.1.3.1-2

enabled

 

qam64LowSE

 

CS-RNTI

 

6.1.4.1-2

enabled

none of the above

6.1.4.1-1

 

 

 

< Transport block size determination >

 

I created following summary based on the descriptions in 28.214-6.1.4.2 (v15.3 - Oct 2018).

 

 

Case 1 : I_MCS is not in 'reserved' range.

 

NOTE : The condition for this case is described in 28.214-6.1.4.2 (v15.3 - Oct 2018) as follows. At first, it looks very confusing. It looked like three different 'if statement' with conflicting condition. But looking more closely, I realized all of these three lines makes up a single 'if statement'. You see all of these three lines are combined by 'or'.

 

- 0 <= I_MCS <≤ 27 and transform precoding is disabled and Table 5.1.3.1-2 is used, or

- 0 <≤ I_MCS <≤ 28 and transform precoding is disabled and a table other than Table 5.1.3.1-2 is used, or

- 0 <≤ I_MCS <≤ 27 and transform precoding is enabled

 

 

Case 2 : I_MCS is in 'reserved' range.

 

 

 

 

Reference

 

[1]