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LTE-BL/CE (LTE-M1) - MPDCCH/DCI

 

MPDCCH stands for MTC physical downlink control channel. It is a special type of PDCCH designed for bandwidth-reduced operation. According to 36.300 - 5.1.3, MPDCCH has following characteristics  :

  • MPDCCH is very similar to EPDCCH (You may think of MPDCCH as LTE-M1 version of EPDCCH)
  • MPDCCH carries common and UE-specific signalling.
  • MPDCCH can be transmitted single time or transmitted with the repetition (the number of repetition is configured by higher layer signaling message)
  • Several different IEs in RRC message configures the number of MPDCCH repetition depending on the application of the MPDCCH as listed below.
    • mpdcch-NumRepetition
    • mpdcch-NumRepetition-RA
    • mpdcch-NumRepetition-Paging
  • Multiple MPDCCHs are supported and a UE monitors a set of MPDCCHs.
  • MPDCCHs are formed by aggregation of enhanced control channel elements(eCCE), each eCCE consisting of a set of resource elements.
  • Different code rates for MPDCCHs are realized by aggregating different numbers of eCCE.
  • An MPDCCH can use either localized or distributed transmission
  • MPDCCH supports RA-RNTI, SI-RNTI, P-RNTI, C-RNTI, Temporary C-RNTI and SPS C-RNTI.

 

Followings are the list of topics that help you understand

 

 

ECCEs for MPDCCH

 

As a group of CCE is used to carry a PDCCH and a group of ECCE is used to carry EPDCCH, a group of ECCE is used to carry MPDCCH as well. (Refer to eREG to RE Mapping for ECCE structure). Number of ECCEs required to carry a MPDCCH varies depending on cases as follows :

 

Case 1 : FDD or TDD CE ModeA with No Repetition (Same as in EPDCCH)

 

< 36.211 Table 6.8A.1-1: Number of EREGs per ECCE >

 

Case 2 : TDD CE ModeA with Repetition

 

< 36.211 Table 6.8B.1-1: Number of EREGs per ECCE for frame structure type 2 >

 

 

MPDCCH Format

 

As there are multiple different PDCCH format in legacy LTE, there are several different EPDCCH/MPDCCH formats for LTE-M1. Depending on a couple of factors, one of two different sets of EPDCCH/MPDCCH formats are used. Number of ECCEs for each EPDCCH/MPDCCH are slightly different between the two sets.

 

Case 1 : MPDCCH associated with 2 or 4 PRBs, No Repetition.

 

< 36.211 Table 6.8A.1-2: Supported EPDCCH formats >

 

Case 2 : MPDCCH associated with 2 or 4 PRBs, Repetition

 

< 36.211 Table 6.8B.1-2: Supported MPDCCH formats >

 

 

DCI format for BL Operation

 

We use special DCI formats for BL Operations. At high level operation, the function of these new DCIs are similar to DCIs for legacy LTE. There is slight differences in terms of details.

 

 

Format 6-0A

 

This is to schedule PUSCH (i.e, UL Grant). It has the same role as DCI Format 0 in legacy LTE.

 

Followings are the summary of the DCI contents based on 36.212 V13.2.0 (2016-06) - 5.3.3.1.10

 

< Format 6-0A for FDD >

Field

# of Bits

Description

Flag for format 6-0A/format 6-1A differentiation

1

0 - 6-0A, 1 - 6-1A

Frequency Hopping flag

1

 

Resource Block assignment

5+ (Variable)

- (Variable) is defined in Uplink RB Assignment bits

- 5 Bits indicate RIV in RA Type 2

Modulation Coding Scheme

4

 

Repetition Number

2

See PUSCH Subframe Assignment

HARQ Process Number

3

 

New Data Indicator

1

 

Redundancy Version

2

 

TPC Command for scheduled PUSCH

2

 

CSI Request

1

 
SRS Request

1

 
DCI subframe repetition number

2

 

 

 

< Format 6-0A for TDD >

Field

# of Bits

Description

Flag for format 6-0A/format 6-1A differentiation

1

0 - 6-0A, 1 - 6-1A

Frequency Hopping flag

1

 

Resource Block assignment

5+ (Variable)

- (Variable) is defined in Uplink RB Assignment bits

- 5 Bits indicate RIV in RA Type 2

Modulation Coding Scheme

4

 

Repetition Number

2

See PUSCH Subframe Assignment

HARQ Process Number

3

 

New Data Indicator

1

 

Redundancy Version

2

 

TPC Command for scheduled PUSCH

2

 

UL Index

2

 
Downlink Assignment Index

2

 
CSI Request

1

 
SRS Request

1

 
DCI subframe repetition number

2

 

 

 

 

Format 6-0B

 

This is to schedule PUSCH (i.e, UL Grant). It has the same role as DCI Format 0 in legacy LTE.

 

Followings are the summary of the DCI contents based on 36.212 V13.2.0 (2016-06) - 5.3.3.1.11

 

Field

# of Bits

Description

Flag for format 6-0B/format 6-1B differentiation

1

0 - 6-0B, 1 - 6-1B

Resource Block assignment

3+ (Variable)

Uplink RB Assignment bits

Modulation Coding Scheme

4

 

Repetition Number

3

See PUSCH Subframe Assignment

HARQ Process Number

1

 

New Data Indicator

1

 
DCI subframe repetition number

2

 

 

 

Format 6-1A

 

This is used for following purpose :

  • to schedule PDSCH.
  • to schedule Random Access Procedure initiated by a PDCCH Order

Followings are the summary of the DCI contents based on 36.212 V13.2.0 (2016-06) - 5.3.3.1.12

 

< For User Data - FDD, CRC scrambled by C-RNTI >

Field

# of Bits

Description

Flag for format 6-0A/format 6-1A differentiation

1

0 - 6-0A, 1 - 6-1A

Frequency Hopping flag

1

 

Resource Block assignment

5+ (Variable)

- (Variable) is defined in Downlink RB Assignment bits

- 5 Bits indicate RIV in RA Type 2

Modulation Coding Scheme

4

MCS/TBS Determination

Repetition Number

2

See PDSCH Subframe Assignment

HARQ Process Number

3

 

New Data Indicator

1

 

Redundancy Version

2

 

TPC Command for scheduled PUCCH

2

 

Downlink Assignment Index

4 or 2 or 0

See 36.212-Table 5.3.3.1.2-2

Antenna Port(s) and Scrambling Identity

2

 
TMPI information for precoding

2 or 4

See 36.212-Table 5.3.3.1.3A-1

PMI configuration for precoding

1

 
HARQ-ACK resource offset

2

 
DCI subframe repetition number

2

 

 

 

< For User Data - TDD, CRC scrambled by C-RNTI >

Field

# of Bits

Description

Flag for format 6-0A/format 6-1A differentiation

1

0 - 6-0A, 1 - 6-1A

Frequency Hopping flag

1

 

Resource Block assignment

5+ (Variable)

- (Variable) is defined in Downlink RB Assignment bits

- 5 Bits indicate RIV in RA Type 2

Modulation Coding Scheme

4

MCS/TBS Determination

Repetition Number

2

See PDSCH Subframe Assignment

HARQ Process Number

4

 

New Data Indicator

1

 

Redundancy Version

2

 

TPC Command for scheduled PUCCH

2

 

Downlink Assignment Index

4 or 2 or 0

See 36.212-Table 5.3.3.1.2-2

Antenna Port(s) and Scrambling Identity

2

 
TMPI information for precoding

2 or 4

See 36.212-Table 5.3.3.1.3A-1

PMI configuration for precoding

1

 
HARQ-ACK resource offset

2

 
DCI subframe repetition number

2

 

 

 

< For Scheduling Random Access Procedure, CRC scrambled by C-RNTI >

Field

# of Bits

Description

Flag for format 6-0A/format 6-1A differentiation

1

0 - 6-0A, 1 - 6-1A

Frequency Hopping flag

1

 

Resource Block assignment

5+ (Variable)

- (Variable) is defined in Downlink RB Assignment bits

- 5 Bits indicate RIV in RA Type 2

Preamble Index

6

 

PRACH Mask Index

4

 

Starting CE Level

2

See CE Level

All Remaining Bits

 

Set to be 0

 

 

< For User Data - FDD, CRC scrambled by RA-RNTI >

Field

# of Bits

Description

Flag for format 6-0A/format 6-1A differentiation

1

0 - 6-0A, 1 - 6-1A

Frequency Hopping flag

1

 

Resource Block assignment

5+ (Variable)

- (Variable) is defined in Downlink RB Assignment bits

- 5 Bits indicate RIV in RA Type 2

Modulation Coding Scheme

4

MCS/TBS Determination

Repetition Number

2

See PDSCH Subframe Assignment

HARQ Process Number

3

Reserved

New Data Indicator

1

Reserved

Redundancy Version

2

 

TPC Command for scheduled PUCCH

2

 

Downlink Assignment Index

4 or 2 or 0

Reserved

Antenna Port(s) and Scrambling Identity

2

 
TMPI information for precoding

2 or 4

See 36.212-Table 5.3.3.1.3A-1

PMI configuration for precoding

1

 
HARQ-ACK resource offset

2

Reserved

DCI subframe repetition number

2

 

 

 

< For User Data - TDD, CRC scrambled by C-RNTI >

Field

# of Bits

Description

Flag for format 6-0A/format 6-1A differentiation

1

0 - 6-0A, 1 - 6-1A

Frequency Hopping flag

1

 

Resource Block assignment

5+ (Variable)

- (Variable) is defined in Downlink RB Assignment bits

- 5 Bits indicate RIV in RA Type 2

Modulation Coding Scheme

4

MCS/TBS Determination

Repetition Number

2

See PDSCH Subframe Assignment

HARQ Process Number

4

Reserved

New Data Indicator

1

Reserved

Redundancy Version

2

 

TPC Command for scheduled PUCCH

2

 

Downlink Assignment Index

4 or 2 or 0

Reserved

Antenna Port(s) and Scrambling Identity

2

 
TMPI information for precoding

2 or 4

See 36.212-Table 5.3.3.1.3A-1

PMI configuration for precoding

1

 
HARQ-ACK resource offset

2

Reserved

DCI subframe repetition number

2

 

 

 

Format 6-1B

 

This is used to schedule PDSCH

 

Followings are the summary of the DCI contents based on 36.212 V13.2.0 (2016-06) - 5.3.3.1.13

 

< For User Data - CRC scrambled by C-RNTI >

Field

# of Bits

Description

Flag for format 6-0B/format 6-1B differentiation

1

0 - 6-0B, 1 - 6-1B

Modulation Coding Scheme

4

MCS/TBS Determination

Resource Block assignment

1+ (Variable)

- (Variable) is defined in Downlink RB Assignment bits

- 1 bit

     0 : Assign PRB 0,1,2,3

     1 : Assign full 6 RB

Repetition Number

3

See PDSCH Subframe Assignment

HARQ Process Number

1

 

New Data Indicator

1

 

HARQ-ACK resource offset

2

 
DCI subframe repetition number

2

 

 

 

< For Scheduling Random Access Procedure, CRC scrambled by C-RNTI >

Field

# of Bits

Description

Flag for format 6-0B/format 6-1B differentiation

1

0 - 6-0B, 1 - 6-1B

Reserved bits

2+ (Variable)

Downlink RB Assignment bits

Preamble Index

6

 

PRACH Mask Index

4

 

Starting CE Level

2

See CE Level

All Remaining Bits

 

Set to be 0

 

 

< For User Data, CRC scrambled by RA-RNTI >

Field

# of Bits

Description

Flag for format 6-0B/format 6-1B differentiation

1

0 - 6-0B, 1 - 6-1B

Modulation Coding Scheme

4

MCS/TBS Determination

Resource Block assignment

1+ (Variable)

- (Variable) is defined in Downlink RB Assignment bits

- 1 bit

     0 : Assign PRB 0,1,2,3

     1 : Assign full 6 RB

Repetition Number

3

 

HARQ Process Number

1

Reserved

New Data Indicator

1

Reserved

HARQ-ACK resource offset

2

Reserved

DCI subframe repetition number

2

 

 

 

Format 6-2

 

This is used to schedule Paging and Direct Indication

 

Followings are the summary of the DCI contents based on 36.212 V13.2.0 (2016-06) - 5.3.3.1.14

 

< When Flag = 0 , Direct Indication>

Field

# of Bits

Description

Flag for paging/direct indication differentiation

1

0 - direct indication, 1 - paging

Direct Indication Information

8

 

Reserved for all remaining bits

 

 

 

< When Flag = 1 , Paging>

Field

# of Bits

Description

Flag for paging/direct indication differentiation

1

0 - direct indication, 1 - paging

Resource Block assignment

(Variable)

Downlink RB Assignment bits

Modulation and Coding Scheme

3

MCS/TBS Determination

Repetition Number

3

 
DCI subframe repetition number

2

 

 

 

 

Tables and Figures for Parameter Details

 

 

< Uplink Resource Block Assignment bits >

 

The number of bits for MSB part of Uplink Resource Block assignment is determined by following table. As shown here, the bit length varies depending on system bandwidth. Actually this bit length is the one that is required to represents all the narrowband index for each system bandwidth.

 

 

 

< Downlink Resource Block Assignment bits>

 

The number of bits for MSB part of Downlink Resource Block assignment is determined by following table. As shown here, the bit length varies depending on system bandwidth. Actually this bit length is the one that is required to represents all the narrowband index for each system bandwidth.

 

 

 

< 36.212-Table 5.3.3.1.2-2: Number of bits for Downlink Assignment Index. >

 

 

< 36.212-Table 5.3.3.1.3A-1: Number of bits for TPMI information. >

 

 

 

 

 

 

Reference

 

 

[1] 3GPP TS 36.211 V13.2.0 (2016-06)

[2]