Resource allocation to PDCCH

Explain Resource allocation to PDCCH? What is CCE ?

Elements allocated to the PDCCH are grouped into quadruplets (groups of 4 Resource Elements). The number of quadruplets(REG) available to the PDCCH is equal to the number of quadruplets within the set of OFDMA symbols signaled by the PCFICH, which have not already been allocated to the PCFICH.

Re source element quadruplets are grouped into Control Channel Elements (CCE). There are 9 quadruplets within a single CCE. i.e. 36 Resource Elements per CCE. The PDCCH uses QPSK modulation so a single CCE can transfer 72 bits.

1 CCE = 9 continuous REG’s ( Resource element Group )
1 REG = 4 RE ( Resource Element )