User terminal, radio base station, downlink control channel receiving method and mobile communication system

A radio base station that transmits an enhanced downlink control channel frequency-division-multiplexed with a downlink shared channel, the radio base station comprising:

• a transmission section that transmits a first or a second value of a Physical Hybrid-ARQ Indicator Channel (PHICH) duration, the first value indicating that an extended PHICH is not applied and the second value indicating that the extended PHICH is applied;
• and
• a mapping section that maps the enhanced downlink control channel to an orthogonal frequency division multiplexing (OFDM) symbol that starts with a starting position based on the PHICH duration, wherein
• the transmission section transmits the second value by higher layer signaling for a control format indicator (CFI) value that is equal to a number of OFDM symbols to which the PHICH is multiplexed, and
• wherein when the first value is received, the PHICH is allocated and multiplexed to only a single OFDM symbol;
• wherein when the second value is received, the PHICH is allocated and multiplexed to a plurality of OFDM symbols.

A method of receiving a downlink control channel for a user terminal to receive an enhanced downlink control channel frequency-division-multiplexed with a downlink shared channel from a radio base station, the method comprising:

• in the radio base station, transmitting a first or a second value of a Physical Hybrid-ARQ Indicator Channel (PHICH) duration;
• and
• in the user terminal, detecting a starting position of an orthogonal frequency division multiplexing (OFDM) symbol for the enhanced downlink control channel in a subframe based on the PHICH duration, wherein
• when the second value is signaled by higher layer signaling, the user terminal detects that a control format indicator (CFI) value is equal to a number of OFDM symbols to which the PHICH is multiplexed, and
• wherein when the first value is received, the PHICH is allocated and multiplexed to only a single OFDM symbol;
• wherein when the second value is received, the PHICH is allocated and multiplexed to a plurality of OFDM symbols.

A mobile communication system for a user terminal to receive an enhanced downlink control channel frequency-division-multiplexed with a downlink shared channel from a radio base station, the mobile communication system comprising:

• the radio base station transmitting a first or a second value of a Physical Hybrid-ARQ Indicator Channel (PHICH) duration;
• and
• the user terminal detecting a starting position of an orthogonal frequency division multiplexing (OFDM) symbol for the enhanced downlink control channel in a subframe based on the PHICH duration, wherein
• when the second value is signaled by higher layer signaling, the user terminal detects that a control format indicator (CFI) value is equal to a number of OFDM symbols to which the PHICH is multiplexed, and
• wherein when the first value is received, the PHICH is allocated and multiplexed to only a single OFDM symbol;
• wherein when the second value is received, the PHICH is allocated and multiplexed to a plurality of OFDM symbols.