LTE: CQI and Transport Block Size

Questions / Problems description:

1- Concerning the CQIs sent by the user equipment each TTI, is there any correlation between the CQIs in the same TTI in different PRBs?
2- The second question is about Transport Block Sizes as they are introduced in the 3GPP specifications: how are these values calculated? Is it logical that the Transport Block Size isn’t a increasing function of the transport block index?
Thank you very much.

Answers:

  1. There’s no correlation between CQIs in the same TTI in different PRBs. The UE may transmit single CQI (called wideband) that tells the eNB how on average the UE see the whole channel (without pointing to any specific PRB). Alternatively the UE may transmit the so called subband CQI, where it points to specific subbands (typically they correspond to multiple consecutive PRBs) where UE reports on how it sees the channel in frequency selective manner (but in this case also UE points to specific spectrum part separately).
  2. The Transport Block Sizes are calculated based on: the MCS (modulation and coding scheme), the number of allocated PRBs and the number of available REs depending on how many e.g. are there REs taken for PDCCH, RS etc. So the transport block size does not increase linearly with the increase of the index itself, e.g. we might have e.g. the same number of allocated PRBs but the number of available REs will be smaller because of e.g. 3OFDMA symbols carying PDCCH or the same number of REs in a PRB but different MCS for the allocation.
  • Share this post:

One thought on “LTE: CQI and Transport Block Size

You have to be 4G University Member to post your comment.
Login or Become a member of 4G University (it's quick and free)