HSPA Uplink Speeds from 1 to 11.5 MBit/s

A couple of days ago I had a post on the currently defined downlink speeds of HSPA from 1 to 80 MBit/s. As the uplink is just as important as the downlink for many application, 3GPP has also kept improving data rates in this direction. The following table shows the speeds defined up to Release 8 of 25.306.

  • Category 1 , 10ms:  0.7 MBit/s
  • Category 2,    2ms:  1.4 MBit/s
  • Category 3, same as 2 but only 10ms TTI
  • Category 4,    2ms:  2.8 MBit/s
  • Category 5,  10ms:  2.0 MBit/s (no, not a mistake, it's slower)
  • Category 6,    2ms:  5.7 MBit/s
  • Category 7,    2ms: 11.5 MBit/s

For the nitty gritty details see table 5.1g. To get to the raw speeds quoted above, divide the maximum number of bits per transport block by the transport block length (the tranmit time interval). Example: Category 2 mobiles can send up to 14484 bits in 10ms (TTI). That's 14484 bit / 0.001s = 1.448 MBit/s. Note that there are 2 TTI lengths, 10ms and 2ms. For higher speeds, shorter TTIs are needed and the 2ms block has to be used for maximum speed.

The speed increases are achieved by lowering the Spreading Factor from 4 to 2 (i.e. how many bits (or chips to be exact) are required to encode one user data bit on the air interface) and by increasing the number of simultaneous code streams (from one in category 1 to four in category 7).

A strong word of caution: Like for the downlink, these values are top speeds. The higher the maximum speed the less likely it is a user will experience them in a live newtork as the signal conditions under which they are achievable are only available in an ever shrinking part of a cell. Most users will not see such high speeds, especially when they are indoors and have no line of sight to the base station antennas.