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Fig 1.6.7
In Type 2, allocation is done for continguously allocated resource blocks. So the starting RB (RBSTART) and number of resource blocks (LCRBs) are indicated to UE with the help of resource indication value (RIV) as per formula below:
IF (LCRBs - 1) ≤ int( NDLRB/2 )
THEN
RIV = NDLRB . (LCRBs - 1) + RBSTART
ELSE
RIV = NDLRB . (NDLRB - LCRBs + 1) + (NDLRB - 1 - RBSTART)
It is of course possible to indicate allocation with (RBSTART, LCRBs) rather than RIV, but with RIV, we can save one bit. I wrote a Perl script that if given RIV (for particular for NDLRB) will print out RBSTART and LCRBs, based on above formula. Drop me a mail samir.s.amberkar@gmail.com if you would like to try it.
As we have seen all three allocation types, it is interesting to compare three with in terms of number of bits required. Below graph shows the bits needed to specify allocation for various RBs. For exact values, refer Annex A.3. Calculation and plotting is done with spreadsheet.
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