Transmission Mode

For the basic understanding on Transmission Mode, please refer to my previous post on Transmission Mode (for Release 8). I would highlight the new TM introduced in Release 10. The two tables reproduced below were captured at Release 10, so the downlink one ends at Mode 9 and the uplink one at Mode 2. The last section on this page says what 36.213 v19.4.0 carries instead.

Downlink Transmission Mode

You would see new TMs every time you get additional antenna ports being used and they bring some new idea of using those antenna ports. But as far as I see from the several carrier network configuration as of now (Aug 2013), I only see TM3 being used in the field. (Please let me know if you see other TMs being used in the field).

The table below is the one that ties a transmission mode to the DCI format that schedules it. Each mode has two rows: a fallback row on DCI format 1A, and a row for the format the mode actually uses. The brackets down the right hand side are the author's, and they mark which modes each release added.

< 36.213 Table 7.1-5 : PDCCH and PDSCH configured by C-RNTI >

36.213 Table 7.1-5, PDCCH and PDSCH configured by C-RNTI, transmission modes 1 to 9

Every mode keeps a fallback on DCI format 1A : the 1A row of each mode is reachable from the common search space as well as the UE specific one. The network can therefore schedule a UE whatever mode it is in.

The fallback is not the same scheme in every mode : Mode 1 falls back to single-antenna port, port 0, while Modes 2 to 6 fall back to transmit diversity. Modes 7, 8 and 9 make it conditional on the number of PBCH antenna ports.

Mode 8 is the Release 9 entry : DCI format 2B gives dual layer transmission on ports 7 and 8, or a single antenna port, port 7 or 8.

Mode 9 is the Release 10 entry : DCI format 2C reaches up to 8 layer transmission on ports 7 to 14. Its 1A row splits by subframe type, and an MBSFN subframe uses single-antenna port, port 7.

You can find good introductions on TM9 in the following link :

Transmission Mode and Reference Signal

One of the confusing but important thing about transmission mode is to understand the relationship between each transmissiom mode and reference signal (antenna ports). For this, refer to Reference Signal (Antenna Port Number) vs Transmission Mode in Reference Signal (Downlink) page.

Uplink Transmission Mode

The uplink side of the same idea is far smaller. Only two uplink transmission modes were ever defined, because the uplink gained spatial multiplexing once and the specification never added a third mode. The table below is the uplink counterpart of the downlink one above.

The columns are the same four as the downlink table, and the last one names the PUSCH transmission scheme rather than the PDSCH one.

< 36.213 Table 8-3 : PDCCH and PUSCH configured by C-RNTI >

36.213 Table 8-3, PDCCH and PUSCH configured by C-RNTI, uplink transmission modes 1 and 2

Mode 1 has one row and one scheme : DCI format 0 from either search space, and single-antenna port, port 10.

Mode 2 keeps that row and adds one : DCI format 0 still gives single-antenna port, port 10, and DCI format 4 gives closed-loop spatial multiplexing.

The fallback pattern matches the downlink : the format reachable from the common search space is the single layer one, and the multi-layer format is UE specific only.

The mode is a semi-static choice : 36.213 says the UE is configured by higher layer signalling into one of the two modes, so a scheduler cannot move a UE between them from one subframe to the next.

Table 8-3 is one of a family of four : 36.213 v19.4.0 carries Table 8-3A for EPDCCH, Table 8-3B for MPDCCH and Table 8-3C for SPDCCH beside it, and Table 8-5 covers the SPS C-RNTI case.

A LAA SCell configures the two paths separately : 36.213 sets the uplink transmission mode for autonomous transmissions independently of the one for grant based transmissions. It does not expect mode 2 for the first with mode 1 for the second on the same SCell.

Transmission Mode 9

For Beam Forming aspect of TM9, refer to Beam Forming in LTE section. What follows is the DCI format that carries TM9 scheduling. The first two tables give the field list of format 2C, once for a normal subframe and once with the carrier indicator present, and the two after them work a real hex string through that field list.

The field list below is DCI format 2C as it is sent to a UE configured with C-RNTI or SPS C-RNTI. Read the length column first, because several of the fields are sized by the bandwidth and by the mode rather than fixed.

Format 2C (Release 10) - C-RNTI, SPS C-RNTI - Normal
Field Name	Length (Bits)	Comment
Resource allocation header	1	RA Type 0 or RA Type 1
Resource block assignment for RA Type 0	6 (1.4 Mhz) 8 (3 Mhz) 13 (5 Mhz) 17 (10 Mhz) 19 (15 Mhz) 25 (20 Mhz)	Applicable only when Resource allocation header = 0 (RA Type 0) Refer to RA Type page
Subset	N/A (1.4 Mhz) 1 (3 Mhz) 1 (5 Mhz) 2 (10 Mhz) 2 (15 Mhz) 2 (20 Mhz)	Applicable only when Resource allocation header = 1 (RA Type 1) Refer to RA Type page
Shift	N/A (1.4 Mhz) 1 (3 Mhz) 1 (5 Mhz) 1 (10 Mhz) 1 (15 Mhz) 1 (20 Mhz)	Applicable only when Resource allocation header = 1 (RA Type 1) Refer to RA Type page
Resource block assignment for RA Type 1	N/A (1.4 Mhz) 6 (3 Mhz) 13 (5 Mhz) 14 (10 Mhz) 16 (15 Mhz) 22 (20 Mhz)	Applicable only when Resource allocation header = 1 (RA Type 1) Refer to RA Type page
TPC for PUCCH	2	See Power Control section
Downlink Assignment Index	2	Only Applicable to TDD uplink –downlink configuration 1-6.
HARQ Process	3 (FDD) 4 (TDD)
Ports-SCID-Number of Layers	3 (FDD)
MCS for Transport Block 1	5
NDI for Transport Block 1	1
RV for Transport Block 1	2
MCS for Transport Block 2	5
NDI for Transport Block 2	1
RV for Transport Block 2	2

The list below is the same format with the carrier indicator field present. Cross carrier scheduling adds those three bits at the front, and nothing else in the format moves.

Format 2C (Release 10) - C-RNTI, SPS C-RNTI - CFI
Field Name	Length (Bits)	Comment
Carrier Indicator	3
Resource allocation header	1	RA Type 0 or RA Type 1
Resource block assignment for RA Type 0	6 (1.4 Mhz) 8 (3 Mhz) 13 (5 Mhz) 17 (10 Mhz) 19 (15 Mhz) 25 (20 Mhz)	Applicable only when Resource allocation header = 0 (RA Type 0) Refer to RA Type page
Subset	N/A (1.4 Mhz) 1 (3 Mhz) 1 (5 Mhz) 2 (10 Mhz) 2 (15 Mhz) 2 (20 Mhz)	Applicable only when Resource allocation header = 1 (RA Type 1) Refer to RA Type page
Shift	N/A (1.4 Mhz) 1 (3 Mhz) 1 (5 Mhz) 1 (10 Mhz) 1 (15 Mhz) 1 (20 Mhz)	Applicable only when Resource allocation header = 1 (RA Type 1) Refer to RA Type page
Resource block assignment for RA Type 1	N/A (1.4 Mhz) 6 (3 Mhz) 13 (5 Mhz) 14 (10 Mhz) 16 (15 Mhz) 22 (20 Mhz)	Applicable only when Resource allocation header = 1 (RA Type 1) Refer to RA Type page
TPC for PUCCH	2	See Power Control section
Downlink Assignment Index	2	Only Applicable to TDD uplink –downlink configuration 1-6.
HARQ Process	3 (FDD) 4 (TDD)
Ports-SCID-Number of Layers	3 (FDD)	See 36.212 Table 5.3.3.1.5C-1
MCS for Transport Block 1	5
NDI for Transport Block 1	1
RV for Transport Block 1	2
MCS for Transport Block 2	5
NDI for Transport Block 2	1
RV for Transport Block 2	2

One field in that list needs a table of its own. The antenna port, scrambling identity and layer count travel as a single three bit index, and the picture below is what the index means at each of its eight values.

< 36.212 Table 5.3.3.1.5C-1: Antenna port(s), scrambling identity and number of layers indication >

36.212 Table 5.3.3.1.5C-1, antenna ports, scrambling identity and number of layers indication for one and two codewords

The left half is the single codeword case : values 0 to 3 give one layer on port 7 or port 8 with nSCID at 0 or 1. Values 4 to 6 give 2, 3 and 4 layers, and value 7 is Reserved.

The right half is the two codeword case : values 0 and 1 give 2 layers on ports 7-8 with nSCID at 0 or 1. Values 2 to 7 run from 3 layers on ports 7-9 up to 8 layers on ports 7-14.

Only the single codeword half carries nSCID : the two codeword half spends its two spare values on a scrambling identity for the 2 layer case alone. That is why it reaches 8 layers in eight values while the other half stops at 4.

The table below takes one real format 2C payload field by field. The hex string in its header row is the whole DCI, and each row shows the bits that field took and what those bits meant.

Example 1 : FDD - Format 2C (Release 10) - C-RNTI, SPS C-RNTI - Normal = 7E0000102F2F00
Field Name	Value (Binary)	Meaning
Resource allocation header	0	RA Type 0
Resource block assignment for RA Type 0	1111110000000000000000000	24 RBs
TPC for PUCCH	01
HARQ Process	000
Ports-SCID-Number of Layers	000
MCS for Transport Block 1	10111(23 Dec)
NDI for Transport Block 1	1
RV for Transport Block 1	00
MCS for Transport Block 2	10111(23 Dec)
NDI for Transport Block 2	1
RV for Transport Block 2	00

The second worked example uses the same field list and a different payload. Comparing the two row by row shows which fields a scheduler moves from one subframe to the next.

Example 2 : FDD - Format 2C (Release 10) - C-RNTI, SPS C-RNTI - Normal = 7E0000102F0140
Field Name	Value (Binary)	Meaning
Resource allocation header	0	RA Type 0
Resource block assignment for RA Type 0	1111110000000000000000000	24 RBs
TPC for PUCCH	01
HARQ Process	000
Ports-SCID-Number of Layers	000
MCS for Transport Block 1	10111(23 Dec)
NDI for Transport Block 1	1
RV for Transport Block 1	00
MCS for Transport Block 2	00000(0 Dec)
NDI for Transport Block 2	1
RV for Transport Block 2	01

What the current release adds to these tables

Both pictures above are screenshots, and both are behind the specification they came from. 36.213 has reached v19.4.0 and it now carries a mode the downlink table does not show, a family of DCI formats neither table shows, and three sibling tables for the control channels that were added after PDCCH.

The downlink table runs to Mode 10 : 36.213 v19.4.0 adds Mode 10 with DCI format 2D, which is the CoMP mode. Its 1A row reads exactly as Mode 9's does, and its 2D row reads as Mode 9's 2C row does.

Every mode gained a short TTI format : Modes 1 and 2 list DCI format 7-1A beside format 1, Mode 3 lists 7-1B beside 2A, and Mode 4 lists 7-1C beside 2. Mode 6 lists 7-1D, Mode 8 lists 7-1E beside 2B, Mode 9 lists 7-1F beside 2C, and Mode 10 lists 7-1G beside 2D.

Mode 9 does more than the picture says : its 2C row now also covers transmit diversity on ports 7-8, dual layer transmission on ports 7-8 when semiOpenLoop is configured, and single-antenna port 7, 8, 11 or 13 when dmrs-tableAlt is configured.

Three sibling tables were added beside it : Table 7.1-5A covers EPDCCH, Table 7.1-5B covers MPDCCH and Table 7.1-5C covers SPDCCH. The picture above is the PDCCH table alone.

The uplink still stops at Mode 2 : Table 8-3 has gained no third mode. It has gained formats, though. Mode 1 now also takes DCI format 0A, 0B, 0C or 7-0A, and Mode 2 also takes 0A, 0B, 0C and 4A, 4B or 7-0B beside the format 4 the picture shows.

The antenna port table is still exact : 36.212 v19.3.0 Table 5.3.3.1.5C-1 reads value for value as the picture above shows it, including the Reserved entry at value 7.

A four bit version now sits beside it : when dmrs-tableAlt is configured the field is four bits and Table 5.3.3.1.5C-2 applies instead. That one carries ports 11 and 13 and an OCC of 4, neither of which appears in the three bit table.

Reference

Two specifications carry the tables on this page. Both were resolved at their latest published version at the time of writing.

3GPP TS 36.213 v19.4.0, E-UTRA Physical layer procedures. Table 7.1-5 for the downlink transmission modes and Table 8-3 for the uplink ones.
3GPP TS 36.212 v19.3.0, E-UTRA Multiplexing and channel coding. Clause 5.3.3.1.5C for DCI format 2C and Table 5.3.3.1.5C-1 for the antenna port indication.