PCFICH will indicate PDCCH symbols.
How long UE will decode PCFICH, every TTI or subframe, or frame or something else?
PCFICH is carried in every subframe and the mapping to resource grid is a function of physical cell id and system bandwidth. Without decoding PCFICH, UE cant know how many symbols PDCCH spanned across. So, UE attempts to decode it every subframe.
@pradeep PHICH also present in every sub frame i think we need to read that aswell to decode PDCCH. So do we need to read PHICH also in every subframe.
True. To decode the actual PDCCH REs, UE will first decode the CFI and gets to know teh number of symbols for PDCCH (control region). UE gets PHICH RE info from MIB. PDCCH = Control region - PCFICH - PHICH. But the actual question was on PCFICH. So, I answered only that part.