Physical channel segmentation divides the bits among the different physical channels when more than one HS-PDSCH is used.
The second rate-matching stage matches the resulting number of bits to the number of physical channel bits available in the HS-PDSCH set during the TTI.
Of the three slots within a 2-ms subframe, the first slot carries critical information for HS-PDSCH reception, such as the channelization code set and the modulation scheme.
The number of HS-PDSCHs and the modulation format define the number of physical channel bits after RV selection (960 bits for QPSK modulation x 5 = 4,800 bits).
The number of HS-PDSCHs or code channels that map onto a single HS-DSCH can vary dynamically between 1 and 15.