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PHICH duration has two options: normal and extended, the difference is that normal duration used only 1 OFDM symbol, while extended duration will use 2 or 3 OFDM symbols. Extended duration is useful for smaller channel bandwidth, such as 1.4MHz, in which case there is only 6 PRBs in total, frequency diversity is lower than that of larger bandwidth such as 20M, so time diversity can be explored to improve the PHICH performance.

PHICH resource have several options: 1/6, 1/2, 1, 2, this parameter together with channel bandwidth determines the maximum number of PHICH groups. Since PHICH is used for HARQ feedback of UL transmission, so the PHICH resources needed depends on the number of UEs which have active UL services (or simply the number of active UEs). PHICH resource also limits the available number of PDCCH CCEs, so actual setting of this parameters is a balancing consideration.