Used for ACK/NAK of UL-SCH transmissions
Transmitted in
โข Time
โ Normal duration: 1st OFDM symbol
โ Extended duration: Over 2 or 3 OFDM symbols
โข Frequency
โ Spanning all system bandwidth
โ Mapping depending on Cell ID
FDM multiplexed with other DL control channels
Support of CDM multiplexing of multiple PHICHs
โข PHICHs mapped to same resources constitute a PHICH group.
โข Coding: ACK bit repeated 3 times before โspreadingโ
โข Spreading of coded bits using Hadamard codes
โ SF = 4 for normal CP (results in 12 RE)
โ SF = 2 for extended CP (results in 6 RE)
