An HSUPA UE reports one E-DCH physical layer category, and that single number tells the network how fast the UE can send. The category fixes the number of E-DPDCH codes, the smallest spreading factor, the TTI lengths and the largest transport block. This page shows the category table of 25.306 and then explains how the peak rate in the last column follows from it.

• E-DCH Physical Layer Categories
• Where the Peak Rates Come From
• Reference

E-DCH Physical Layer Categories

Which uplink data rates can a given HSUPA UE reach? The table below answers that for each category. Categories 1 to 6 are the original HSUPA categories, and categories 7 to 12 were added later for 16QAM, dual cell E-DCH, 64QAM and uplink MIMO.

The bit columns follow 25.306 v19.0.0 Table 5.1g, where they are the maximum number of bits of one E-DCH transport block. Earlier versions of this page listed 7296, 14592, 2919, 5837 and 11520 bits, with peak rates of 0.73, 1.46, 2.92 and 5.76 Mbps. Those older values still appear in many documents, but they are not the values of the current table.

The notes under Table 5.1g add the details that the columns cannot show. They matter as much as the numbers, because two categories with the same row values can still differ in modulation or in the number of carriers.

• Four codes : means two codes at SF2 and two codes at SF4 in parallel. So the minimum spreading factor of SF2 applies to only half of the codes.
• Categories 1 to 6 : support QPSK only.
• Category 7 : supports QPSK with both TTIs and adds 16QAM with the 2 ms TTI.
• Categories 8 and 9 : support dual cell E-DCH, with QPSK only in category 8 and with QPSK and 16QAM in category 9.
• Category 10 : supports QPSK, 16QAM and 64QAM on one carrier.
• Categories 11 and 12 : support uplink MIMO, with QPSK and 16QAM in category 11 and with 64QAM added in category 12.
• Categories 8 to 12 : support MAC-i/is, the improved layer 2 for the uplink.

• The category is a set of limits : codes, spreading factor, TTI and transport block size are all fixed by one number.
• Newer categories are 2 ms only : categories 8 to 12 drop the 10 ms TTI.
• Check the notes, not only the columns : the modulation, the dual cell support and the uplink MIMO support are in the notes under the table.

Where the Peak Rates Come From

How is the Maximum Bit rate column calculated, since 25.306 does not list it? It is the largest transport block divided by the TTI length. For categories that send two transport blocks in one TTI, the rate is doubled.

Let's take Category 6 as an example. Its largest 2 ms transport block is 11484 bits, and 11484 bits every 2 ms is 5.74 Mbps. With the 10 ms TTI, the same category sends at most 20000 bits every 10 ms, which is only 2.00 Mbps. So the 2 ms TTI is what gives categories 2, 4 and 6 their higher peak rate.

The physical channel explains why 11484 bits is close to the limit. 25.211 Table 5B gives 1920 bits per 2 ms subframe for one SF4 code and 3840 bits for one SF2 code. Two SF2 codes and two SF4 codes therefore carry 2 x 3840 + 2 x 1920 = 11520 channel bits in one subframe. A transport block of 11484 bits in 11520 channel bits leaves almost no room for channel coding, so this peak rate needs very good radio conditions.

The newer categories reach higher rates in two ways. Category 7 and category 10 use higher order modulation on one carrier, so one transport block grows to 22996 or 34507 bits. Categories 8 and 9 send one transport block on each of two carriers, and categories 11 and 12 send two transport blocks with uplink MIMO. For these four categories the rate in the table is two transport blocks every 2 ms.

• Peak rate = largest transport block / TTI : for example 11484 bits / 2 ms = 5.74 Mbps for Category 6.
• Two blocks per TTI double the rate : dual cell E-DCH in categories 8 and 9, and uplink MIMO in categories 11 and 12.
• The Category 6 peak is almost uncoded : 11484 bits of data sit in 11520 channel bits.

Reference

[1] 3GPP TS 25.306 v19.0.0 - Table 5.1g, FDD E-DCH physical layer categories, and the notes under it

[2] 3GPP TS 25.211 v19.0.0 - Table 5B, E-DPDCH slot formats