4.3 Transport format detection

25.2123GPPMultiplexing and channel coding (FDD)Release 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

If the transport format set of a TrCH i contains more than one transport format, the transport format can be detected according to one of the following methods:

– TFCI based detection: This method is applicable when the transport format combination is signalled using the TFCI field;

– explicit blind detection: This method typically consists of detecting the TF of TrCH i by use of channel decoding and CRC check;

– guided detection: This method is applicable when there is at least one other TrCH i’, hereafter called guiding TrCH, such that:

– the guiding TrCH has the same TTI duration as the TrCH under consideration, i.e. F_i’ = F_i;

– different TFs of the TrCH under consideration correspond to different TFs of the guiding TrCH;

– explicit blind detection is used on the guiding TrCH.

If the transport format set for a TrCH i does not contain more than one transport format with more than zero transport blocks, no explicit blind transport format detection needs to be performed for this TrCH. The UE can use guided detection for this TrCH or single transport format detection, where the UE always assumes the transport format corresponding to more than zero transport blocks for decoding.

For uplink, blind transport format detection is a network controlled option. For downlink, the UE shall be capable of performing blind transport format detection, if certain restrictions on the configured transport channels are fulfilled.

4.3.1 Blind transport format detection

When no TFCI is available then explicit blind detection or guided detection shall be performed on all TrCHs within the CCTrCH that have more than one transport format and that do not use single transport format detection. The UE shall only be required to support blind transport format detection if all of the following restrictions are fulfilled:

1. either only one CCTrCH is received, or one CCTrCH of dedicated type and one CCTrCH of common type for HS-DSCH are received by the UE;

If only one CCTrCH is received by the UE, the following conditions apply to that CCTrCH and those TrCHs that are multiplexed on the CCTrCH. If one CCTrCH of dedicated type and one CCTrCH of common type for HS-DSCH are received by the UE, the following conditions apply to the dedicated type CCTrCH and the TrCHs that are multiplexed on the dedicated type CCTrCH.

2. the number of CCTrCH bits received per radio frame is 600 or less;

3. the number of transport format combinations of the CCTrCH is 64 or less;

4. fixed positions of the transport channels is used on the CCTrCH to be detectable;

5. convolutional coding is used on all explicitly detectable TrCHs;

6. CRC with non-zero length is appended to all transport blocks on all explicitly detectable TrCHs;

7. at least one transport block shall be transmitted per TTI on each explicitly detectable TrCH;

8. the number of explicitly detectable TrCHs is 3 or less;

9. for all explicitly detectable TrCHs i, the number of code blocks in one TTI (C_i) shall not exceed 1;

10. the sum of the transport format set sizes of all explicitly detectable TrCHs, is 16 or less. The transport format set size is defined as the number of transport formats within the transport format set;

11. there is at least one TrCH that can be used as the guiding transport channel for all transport channels using guided detection.

Examples of blind transport format detection methods are given in annex A.

4.3.1A Single transport format detection

When no TFCI is available, then single transport format detection shall be applied on all TrCHs within the CCTrCH that have a transport format set not containing more than one transport format with more than zero transport blocks and that do not use guided detection. The UE shall only be required to support single transport format detection if the following restrictions are fulfilled:

1. For each transport channel that is single transport format detected, CRC with non-zero length is appended to all transport blocks within the non-zero transport block transport format;

2. fixed positions of the transport channels is used on the CCTrCH to be detectable.

4.3.2 Transport format detection based on TFCI

If a TFCI is available, then TFCI based detection shall be applicable to all TrCHs within the CCTrCH. The TFCI informs the receiver about the transport format combination of the CCTrCHs. As soon as the TFCI is detected, the transport format combination, and hence the transport formats of the individual transport channels are known.

If higher layers indicate that S-CCPCHs can be soft combined during a period of consecutive TTIs, then the same TFC is used on those S-CCPCHs for each combinable TTI. The UE may therefore detect TFCI on one S-CCPCH to determine the TFC on all S-CCPCHs that can be soft combined. (S-CCPCH soft combining is further specified in [4]).

4.3.3 Coding of Transport-Format-Combination Indicator (TFCI)

The TFCI is encoded using a (32, 10) sub-code of the second order Reed-Muller code. The coding procedure is as shown in figure 9.

Figure 9: Channel coding of TFCI information bits

If the TFCI consist of less than 10 bits, it is padded with zeros to 10 bits, by setting the most significant bits to zero. The length of the TFCI code word is 32 bits.

The code words of the (32,10) sub-code of second order Reed-Muller code are linear combination of 10 basis sequences. The basis sequences are as in the following table 8.

Table 8: Basis sequences for (32,10) TFCI code

i	M_i,0	M_i,1	M_i,2	M_i,3	M_i,4	M_i,5	M_i,6	M_i,7	M_i,8	M_i,9
0	1	0	0	0	0	1	0	0	0	0
1	0	1	0	0	0	1	1	0	0	0
2	1	1	0	0	0	1	0	0	0	1
3	0	0	1	0	0	1	1	0	1	1
4	1	0	1	0	0	1	0	0	0	1
5	0	1	1	0	0	1	0	0	1	0
6	1	1	1	0	0	1	0	1	0	0
7	0	0	0	1	0	1	0	1	1	0
8	1	0	0	1	0	1	1	1	1	0
9	0	1	0	1	0	1	1	0	1	1
10	1	1	0	1	0	1	0	0	1	1
11	0	0	1	1	0	1	0	1	1	0
12	1	0	1	1	0	1	0	1	0	1
13	0	1	1	1	0	1	1	0	0	1
14	1	1	1	1	0	1	1	1	1	1
15	1	0	0	0	1	1	1	1	0	0
16	0	1	0	0	1	1	1	1	0	1
17	1	1	0	0	1	1	1	0	1	0
18	0	0	1	0	1	1	0	1	1	1
19	1	0	1	0	1	1	0	1	0	1
20	0	1	1	0	1	1	0	0	1	1
21	1	1	1	0	1	1	0	1	1	1
22	0	0	0	1	1	1	0	1	0	0
23	1	0	0	1	1	1	1	1	0	1
24	0	1	0	1	1	1	1	0	1	0
25	1	1	0	1	1	1	1	0	0	1
26	0	0	1	1	1	1	0	0	1	0
27	1	0	1	1	1	1	1	1	0	0
28	0	1	1	1	1	1	1	1	1	0
29	1	1	1	1	1	1	1	1	1	1
30	0	0	0	0	0	1	0	0	0	0
31	0	0	0	0	1	1	1	0	0	0

When UL_DPCH_10ms_Mode is not configured by higher layers, the TFCI information bits a₀, a₁, a₂, a₃, a₄, a₅, a₆, a₇, a₈, a₉(where a₀ is LSB and a₉ is MSB) shall correspond to the TFC index (expressed in unsigned binary form) defined by the RRC layer to reference the TFC of the CCTrCH in the associated DPCH radio frame.

When UL_DPCH_10ms_Mode is configured by higher layers, the TFCI information bits a₀, a₁, a₂, a₃, a₄, a₅, a₆, a₇, a₈, a₉(where a₀ is LSB and a₉ is MSB) shall correspond to unsigned binary expression of the sum of the TFC index and the size of TFCS.

The output code word bits b_i are given by:

where i = 0, …, 31.

The output bits are denoted by b_k, k = 0, 1, 2, …, 31.

In downlink, when the SF < 128 the encoded TFCI code words are repeated yielding 8 encoded TFCI bits per slot in normal mode and 16 encoded TFCI bits per slot in compressed mode. Mapping of repeated bits to slots is explained in subclause 4.3.5.

4.3.4 Void

4.3.5 Mapping of TFCI words

4.3.5.1 Mapping of TFCI word in normal mode in downlink, and in uplink when uplink DPCCH slot format is not 5

The bits of the code word are directly mapped to the slots of the radio frame. Within a slot the bit with lower index is transmitted before the bit with higher index. The coded bits b_k, are mapped to the transmitted TFCI bits d_k, according to the following formula:

d_k = b_k_{mod 32}

For uplink physical channels regardless of the SF and downlink physical channels, if SF128, k = 0, 1, 2, …, 29. Note that this means that bits b₃₀ and b₃₁ are not transmitted.

For downlink physical channels whose SF < 128, k = 0, 1, 2, …, 119. Note that this means that bits b₀ to b₂₃ are transmitted four times and bits b₂₄ to b₃₁ are transmitted three times.

4.3.5.1A Mapping of TFCI word in normal mode in uplink when uplink DPCCH slot format is 5

In each 20ms CI, the first 10 slots of uplink DPCCH contain TFCI bits. The bits of the codeword are directly mapped to the slots of the radio frame. Within a slot, the bit with lower index is transmitted before the bit with higher index. The coded bits b_k, are mapped to the transmitted TFCI bits d_k, according to the following formula:

d_k = b_k, , for k = 0,…, 19.

4.3.5.1.1 Mapping of TFCI bits for Secondary CCPCH with 16QAM

For MBSFN transmissions with 16QAM, the coded bits b_k, are mapped to the transmitted TFCI bits according to the following formulas:

d_4k = b_{2k mod 32} ,

d_4k+₁ = b_2k_{+1 mod 32} ,

d_4k+₂ = ( d_4k + d_4k+₁) mod 2,

d_4k+₃ = ( 1 + d_4k + d_4k+₁) mod 2,

where k = 0, 1, 2,…, 59 for SF < 128 and k = 0, 1, 2,…, 14 for SF128.

4.3.5.2 Mapping of TFCI word in compressed mode

The mapping of the TFCI bits in compressed mode is different for uplink, downlink with SF  128 and downlink with SF < 128.

4.3.5.2.1 Uplink compressed mode

4.3.5.2.1.1 Uplink DPCCH slot formats other than 5

For uplink compressed mode, the slot format is changed so that no TFCI coded bits are lost. The different slot formats in compressed mode do not match the exact number of TFCI coded bits for all possible TGLs. Repetition of the TFCI bits is therefore used.

Denote the number of bits available in the TFCI fields of one compressed radio frame by D and the number of bits in the TFCI field in a slot by N_TFCI. The parameter E is used to determine the number of the first TFCI bit to be repeated.

E= N_firstN_TFCI, if the start of the transmission gap is allocated to the current frame.

E = 0, if the start of the transmission gap is allocated to the previous frame and the end of the transmission gap is allocated to the current frame.

The TFCI coded bits b_k are mapped to the bits in the TFCI fields d_k. The following relations define the mapping for each compressed frame.

d_k = b_k

where k = 0, 1, 2, …, min (31, D-1).

If D > 32, the remaining positions are filled by repetition (in reversed order):

d_D-k_-1 = b₍_E+k_{) mod 32}

where k = 0, …, D-33.

4.3.5.2.1.2 Uplink DPCCH slot format 5

In each 20ms CI, the first 10 UL DPCCH slots that are not in a compressed mode transmission gap contain TFCI information. The bits of the codeword are directly mapped to these slots. Within a slot, the bit with lower index is transmitted before the bit with higher index. The coded bits b_k, are mapped to the transmitted TFCI bits d_k, according to the following formula:

d_k = b_k, , for k = 0,…, 19.

4.3.5.2.2 Downlink compressed mode

For downlink compressed mode, the slot format is changed so that no TFCI coded bits are lost. The different slot formats in compressed mode do not match the exact number of TFCI bits for all possible TGLs. DTX is therefore used if the number of bits available in the TFCI fields in one compressed frame exceeds the number of TFCI bits given from the slot format. The block of bits in the TFCI fields where DTX is used starts on the first TFCI field after the transmission gap. If there are more bits available in the TFCI fields before the transmission gap than TFCI bits, DTX is also used on the bits in the last TFCI fields before the transmission gap.

E = N_firstN_TFCI, if the start of the transmission gap is allocated to the current frame.

E = 0, if the start of the transmission gap is allocated to the previous frame and the end of the transmission gap is allocated to the current frame.

Denote the total number of TFCI bits to be transmitted by F. F = 32 for slot formats nA or nB, where n = 0, 1, …, 11 (see table 11 in [2]). Otherwise, F = 128. The TFCI coded bits b_k are mapped to the bits in the TFCI fields d_k. The following relations define the mapping for each compressed frame.

If E > 0,

d_k = b_k_{mod 32}

where k = 0, 1, 2, …, min (E, F)-1.

If E < F,

d_k+D-F = b_k_{mod 32}

where k = E, …, F -1.

DTX is used on d_k where k = min (E, F), …, min (E, F) +D – F -1.