Radio base station apparatus, mobile terminal apparatus, radio communication system and radio communication method

A radio communication method comprising the steps of:

• generating a first downlink control signal to be transmitted to a mobile terminal apparatus by a physical downlink control channel and a second downlink control signal to be transmitted to the mobile terminal apparatus by an enhanced physical downlink control channel;
• multiplexing the first downlink control signal on a radio resource of first n symbols (n=1, 2 or 3) allocated to the physical downlink control channel in a subframe and frequency-division-multiplexing the second downlink control signal on a radio resource which is allocated to the enhanced physical downlink control channel and has predetermined symbols in a time domain following the symbols where the first downlink control signal is multiplexed in the subframe;
• and
• transmitting the first downlink control signal by the physical downlink control channel and the second downlink control signal by the enhanced physical downlink control channel,
• wherein, when CIF (Carrier Indicator Field) is configured, the second downlink control signal is multiplexed on a search space that is a resource of enhanced physical downlink control channel candidates determined based on a CIF value.