Wireless communications system, communications apparatus, and processing method

1. A wireless communications system comprising:

a second communications apparatus; and

a first communications apparatus configured to use a predetermined band shared with a second wireless communications system and receive a wireless signal from the second communications apparatus, wherein

the first communications apparatus is further configured to assign to the second communications apparatus, a first candidate and a second candidate for a utilization resource in the predetermined band by transmitting information about the first candidate and the second candidate using a physical downlink control channel (PDCCH),

the second communications apparatus configured to perform radio resource idle state detection based on a result of assignment of the first candidate and the second candidate by the first communications apparatus, the second communications apparatus further configured to use the first candidate and transmit the wireless signal to the first communications apparatus when the first candidate is idle, and to use the second candidate and transmit the wireless signal to the first communications apparatus, when the first candidate is not idle and the second candidate is idle, and

the assignment of the first candidate and the second candidate by the first communication apparatus is performed by allocating a plurality of subframes.

2. The wireless communications system according to claim 1 , wherein

the first communications apparatus receives the wireless signal from the second communications apparatus by performing a reception process based on the first candidate and the second candidate assigned to the second communications apparatus.

3. The wireless communications system according to claim 1 , wherein

the first communications apparatus receives the wireless signal from the second communications apparatus by performing a reception process for the first candidate and by performing the reception process for the second candidate when the wireless signal from the second communications apparatus is not received by the reception process for the first candidate.

4. The wireless communications system according to claim 1 , comprising

a plurality of the second communications apparatuses, wherein

the first communications apparatus assigns the first candidate and the second candidate for a utilization resource in the predetermined band to respective second communications apparatuses among the plurality of the second communications apparatuses, the first communications apparatus assigning the first candidate and the second candidate so as to enable overlap among the plurality of the second communications apparatuses.

5. The wireless communications system according to claim 4 , wherein

the first communications apparatus assigns a same second candidate to the respective second communications apparatuses among the plurality of the second communications apparatuses, as the second candidate, and

the respective second communications apparatuses perform idle state detection for the second candidate by mutually differing backoff durations.

6. The wireless communications system according to claim 4 , wherein

the respective second communications apparatuses among the plurality of the second communications apparatuses detect an idle state of the first candidate by a first backoff duration and detect an idle state of the second candidate by a second backoff duration that is longer than the first backoff duration, and

among the plurality of the second communications apparatuses, second communications apparatuses assigned a same utilization resource have mutually differing backoff durations.

7. The wireless communications system according to claim 4 , wherein

the plurality of the second communications apparatuses includes a first second-communications-apparatus and a second second-communications-apparatus,

the first communications apparatus assigns to the first second-communications-apparatus, the first candidate, which overlaps the second candidate assigned to the second second-communications-apparatus, and the second candidate, which overlaps the first candidate assigned to the second second-communications-apparatus, and

the first second-communications-apparatus and the second second-communications-apparatus each detects an idle state of the assigned second candidate at a timing later than that for detecting an idle state of the assigned first candidate.

8. The wireless communications system according to claim 1 , wherein

the first communications apparatus performs the radio resource idle state detection in the predetermined band and assigns to the second communications apparatus, the first candidate and the second candidate included in a radio resource detected to be idle.

9. A communications apparatus comprising:

a memory; and

a processor coupled to the memory, the processor configured to:

use a predetermined band shared with a second wireless communications system and receive a wireless signal from a second communications apparatus,

assign to the second communications apparatus, a first candidate and a second candidate for a utilization resource in the predetermined band by transmitting information about the first candidate and the second candidate using a physical downlink control channel (PDCCH); and

receive the wireless signal transmitted by the second communications apparatus, the wireless signal being received by performing a reception process based on the first candidate and the second candidate assigned to the second communications apparatus,

wherein assignment of the first candidate and the second candidate to the second communications apparatus is performed by allocating a plurality of subframes.

10. A communications apparatus comprising:

a memory; and

a processor coupled to the memory, the processor configured to:

use a predetermined band shared with another wireless communications system and transmit a wireless signal to a second communications apparatus,

perform radio resource idle state detection based on a result of assignment of a first candidate and a second candidate to the communications apparatus, the assignment being based on information received about the first candidate and the second candidate using a physical downlink control channel (PDCCH), the first candidate and the second candidate being for a utilization resource in the predetermined band; and

transmit the wireless signal to the second communications apparatus, based on a result of the detection, the wireless signal being transmitted using the first candidate when the first candidate is idle, and the wireless signal being transmitted using the second candidate when the first candidate is not idle and the second candidate is idle,

wherein the assignment of the first candidate and the second candidate to the communications apparatus by the second communications apparatus is performed by allocating a plurality of subframes.

11. The wireless communications system according to claim 1 , wherein the first communications apparatus assigns the first candidate and the second candidate to the second communications apparatus for each data transmission from the second communications apparatus to the first communications apparatus.