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