Section: 6.8.2 PDCCH multiplexing and scrambling
Content: The block of bits on each of the control channels to be transmitted in a subframe, where is the number of bits in one subframe to be transmitted on physical downlink control channel number , shall be multiplexed, resulting in a block of bits , where is the number of PDCCHs transmitted in the subframe. The block of bits shall be scrambled with a cell-specific sequence prior to modulation, resulting in a block of scrambled bits according to where the scrambling sequence is given by clause 7.2. The scrambling sequence generator shall be initialised with at the start of each subframe. CCE number corresponds to bits . If necessary, <NIL> elements shall be inserted in the block of bits prior to scrambling to ensure that the PDCCHs starts at the CCE positions as described in TS 36.213[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures ]  [4] and to ensure that the length of the scrambled block of bits matches the amount of resource-element groups not assigned to PCFICH or PHICH.