Following is from 25.321 Table 9.2.3.3.x. The HS-SCCH does not send the transport block size in bits. It sends a 6-bit index k, and the UE looks up the size in a table of 25.321. The table depends on the HS-DSCH category of the UE, and on whether the bit aligned or the octet aligned table applies. Let's see first how the table is chosen, and then go through all thirteen 1.28 Mcps TDD tables.

• Which Table Applies
• Bit Aligned Tables
• Octet Aligned Tables
• Reference

Which Table Applies

Two questions pick the table. The first is the HS-DSCH physical layer category of the UE. The categories come in groups of three, and the three categories of a group share one table. The second is which MAC entity is in use, because it decides between bit aligned and octet aligned sizes.

25.321 v19.0.0 clause 9.2.3.3 gives the rule. When MAC-hs is used and neither HS-DSCH SPS nor E-DCH SPS operation is enabled, the bit aligned table applies. When MAC-ehs is used, or MAC-hs with HS-DSCH SPS or E-DCH SPS operation, the octet aligned table applies. In CELL_FACH, CELL_PCH or URA_PCH state with HS-DSCH reception, the UE uses the octet aligned table of category 9.

Inside a group of three, the categories differ only in the total number of soft channel bits. The maximum number of HS-DSCH timeslots per TTI and the largest transport block are the same, as 25.306 Table 5.1c shows. That is why one table serves the whole group. The table below maps each group to its tables, with the numbering this page uses.

Index k = 0 means NULL, and the Node B never uses it to signal a size. Indexes 1 to 63 grow by a nearly constant ratio. Take the bit aligned table of categories 1 to 3 as an example. There, k = 1 is 240 bits and k = 63 is 2788 bits, so each step adds about 4 percent.

• One table serves three categories : the categories of a group differ only in soft channel bits.
• The MAC entity picks bit aligned or octet aligned : MAC-hs without SPS uses bit aligned sizes, and MAC-ehs uses octet aligned sizes.
• Common state reception uses one fixed table : in CELL_FACH, CELL_PCH and URA_PCH the octet aligned table of category 9 applies.

Bit Aligned Tables

The five tables below are the bit aligned tables, for categories 1 to 15 with MAC-hs. A size in these tables can be any number of bits, for example 249 or 1037 bits in the table for categories 1 to 3. Each table ends at k = 63 with the largest transport block of its group. That value equals the maximum number of HS-DSCH transport channel bits per TTI in 25.306.

Table 9.2.3.3.1: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [1, 3], bit aligned

Table 9.2.3.3.2: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [4, 6], bit aligned

Table 9.2.3.3.3: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [7, 9], bit aligned

Table 9.2.3.3.4: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [10, 12], bit aligned

Table 9.2.3.3.5: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [13,15], bit aligned

• The bit aligned tables cover categories 1 to 15 only : categories 16 and above always use the octet aligned tables.
• k = 63 gives the largest block of the group : 2788, 5600, 8416, 11226 and 14043 bits.
• The smallest block is 240 bits in every table : the tables differ in how fast the size grows with k.

Octet Aligned Tables

The eight tables below are the octet aligned tables. Every size in them is a multiple of 8 bits. They apply with MAC-ehs, with MAC-hs when SPS is enabled, and in the common states with the category 9 table.

Keep one change of numbering in mind when you open 25.321 v19.0.0. The tables there are numbered Table 9.2.3.3-1 to Table 9.2.3.3-13, and the titles of the last six tables name the MIMO categories as well. Tables 9.2.3.3-8 to 9.2.3.3-10 also serve categories 25 to 27 when MIMO is enabled. Tables 9.2.3.3-11 to 9.2.3.3-13 serve categories 25 to 27 when MIMO is not enabled, and categories 28 to 30. The sizes themselves are the same as in the tables below.

Table 9.2.3.3.6: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [1, 3], octet aligned

Table 9.2.3.3.7: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [4, 6], octet aligned

Table 9.2.3.3.8: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [7, 9], octet aligned

Table 9.2.3.3.9: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [10, 12], octet aligned

Table 9.2.3.3.10 : HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [13,15], octet aligned

Table 9.2.3.3.11: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [16,18], octet aligned

Table 9.2.3.3.12: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [19,21], octet aligned

Table 9.2.3.3.13: HSDPA Transport Block Sizes for 1.28 Mcps TDD, for HS-DSCH physical layer category [22,24], octet aligned

• Every octet aligned size is a multiple of 8 bits : the largest block for categories 1 to 3 is 2784 bits here and 2788 bits in the bit aligned table.
• Categories 16 to 24 have only octet aligned tables : these are the categories that support 64QAM.
• HS-DSCH reception in the common states uses the category 9 table : that is Table 9.2.3.3.8 on this page.

Reference

• 3GPP TS 25.321 v19.0.0 : clause 9.2.3.3, transport block size for 1.28 Mcps TDD
• 3GPP TS 25.306 v19.0.0 : Table 5.1c, 1.28 Mcps TDD HS-DSCH physical layer categories