Base station apparatus, wireless terminal apparatus, and wireless communication method

1. A base station apparatus that performs a wireless communication with a plurality of wireless terminal apparatuses according to Institute of Electrical and Electronics Engineers (IEEE) 802.11, comprising:

frame generation circuitry that generates one or more first Contention Free-End (CF-END) frames, each first CF-END frame including end information indicating that a Transmission OPportunity (TXOP) period assigned for communication with one of the plurality of wireless terminal apparatuses has expired and a Beacon element including identifier information associated with the base station apparatus, each of the one or more first CF-END frames being for use by another one of the plurality of wireless terminal apparatuses to start scan procedure, and

transmission circuitry that transmits the generated one or more first CF-END frames to the plurality of wireless terminal apparatuses by using a plurality of different transmission beams.

2. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates a second frame by synthesizing the end information indicating the expiration of the TXOP period and the Beacon element; and

the transmission circuitry transmits the second frame at an end of the TXOP period.

3. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates a CF-END frame of the one or more first CF-END frames from the end information indicating that the TXOP period has expired and generates a first Beacon element frame from the Beacon element, and

the transmission circuitry transmits the first CF-END frame and subsequently transmits the first Beacon element frame at an end of the TXOP period.

4. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates a plurality of third frames, each being generated by synthesizing the Beacon element and end information indicating that the TXOP period corresponding to one of a plurality of transmission beams has expired; and

the transmission circuitry sequentially transmits the plurality of synthesized third frames at an end of the TXOP period.

5. The base station apparatus according to claim 1 , wherein:

the frame generation circuitry

generates a first CF-END frame of the one or more first CF-END frames from the end information indicating that the TXOP period has expired, and

generates, from the Beacon element, a plurality of second Beacon element frames corresponding to a plurality of transmission beam directions, and

the transmission circuitry transmits, after the first CF-END frame is transmitted, the plurality of second Beacon element frames at an end of the TXOP period.

6. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates a first CF-END frame of the one or more first CF-END frames from the end information indicating that the TXOP period has expired and generates a first Beacon element frame from the Beacon element, and

the transmission circuitry transmits the first CF-END frame at an end of the TXOP period and transmits the first Beacon element frame after the TXOP period expires.

7. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates, from the Beacon element, a first Beacon element frame, and

the transmission circuitry transmits, after the expiration of the TXOP period, the first Beacon element frame.

8. The base station apparatus according to claim 1 , wherein

the frame generation circuitry

generates a first CF-END frame of the one or more first CF-END frames from the end information indicating that the TXOP period has expired, and

generates, from the Beacon element, a plurality of second Beacon element frames corresponding to a plurality of transmission beam directions, and

the transmission circuitry

transmits the first CF-END frame at an end of the TXOP period, and

transmits, after the expiration of the TXOP period, the plurality of second Beacon element frames in sequence.

9. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates, from the Beacon element, a plurality of second Beacon element frame corresponding to a plurality of transmission beam directions, and

the transmission circuitry transmits, after the expiration of the TXOP period, the plurality of second Beacon element frames in sequence.

10. The base station apparatus according to claim 1 , wherein the frame generation circuitry

generates a fourth frame by synthesizing information indicating that the TXOP period has expired, the Beacon element, and a plurality of fields used in beamforming training for the plurality of wireless terminal apparatuses, and

transmits the synthesized fourth frame at an end of the TXOP period.

11. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates a first CF-END frame of the one or more first CF-END frames from the end information indicating that the TXOP period has expired and generates a fifth frame by synthesizing the Beacon element and a plurality of fields used in beamforming training for the plurality of wireless terminal apparatuses, and

the transmission circuitry transmits, after the first CF-END frame is transmitted, the fifth frame at an end of the TXOP period.

12. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates a first CF-END frame of the one or more first CF-END frames from the end information indicating that the TXOP period has expired and generates a fifth frame by synthesizing the Beacon element and a plurality of fields used in beamforming training for the plurality of wireless terminal apparatuses, and

the transmission circuitry transmits the first CF-END frame at an end of the TXOP period and transmits the fifth frame after the TXOP period expires.

13. The base station apparatus according to claim 1 , wherein

the frame generation circuitry generates a fifth frame by synthesizing the Beacon element and a plurality of fields used in beamforming training for the plurality of wireless terminal apparatuses, and

the transmission circuitry transmits the fifth frame after the TXOP period expires.

14. The base station apparatus according to claim 1 , comprising a receiver that receives a third Contention Free-End (CF-END) frame which is information indicating expiration of the TXOP period from one of the plurality of wireless terminal apparatuses that acquired TXOP,

wherein after the third CF-END frame is received, the transmission circuitry transmits one or more generated first frames to the plurality of wireless terminal apparatuses.

15. A wireless terminal apparatus that performs wireless communication according to Institute of Electrical and Electronics Engineers (IEEE) 802.11 with a base station apparatus, comprising:

a judgement circuitry that judges whether a medium is clear;

a frame generation circuitry that generates a Probe Request frame to be transmitted to the base station apparatus;

a transmission circuitry that transmits the Probe Request frame in a case where the judgment indicates that the medium is clear; and

a first timer circuitry that counts a first predetermined time since the transmission of the Probe Request frame,

wherein the transmission circuitry, in a case where a response to the Probe Request frame is not received from the base station apparatus by a time when the first timer finishes the counting of the first predetermined time, waits without transmitting a next frame until one or more first Contention Free-End (CF-END) frames are transmitted at an end of a Transmission OPportunity (TXOP) period assigned to the base station apparatus, each first CF-END frame including a Beacon element including identifier information associated with the base station apparatus and end information indicating that the TXOP period has expired, each first CF-END frame being for use by another one of a plurality of wireless terminal apparatuses to start scan procedure, the one or more first CF-END frames being transmitted to the plurality of wireless terminal apparatuses by using a plurality of different transmission beams.

16. The wireless terminal apparatus according to claim 15 , comprising a second timer that counts a second predetermined time in a case where a response to the Probe Request frame is not received from the base station apparatus by a time when the first timer expires,

wherein the transmission circuitry retransmits the Probe Request frame, in a case where the one or more first CF-END frames are not received from the base station apparatus by a time when the second timer finishes the counting of the second predetermined time.

17. The wireless terminal apparatus according to claim 15 , wherein the transmission circuitry changes a transmission frequency and retransmits the Probe Request frame to the base station apparatus, in a case where the transmission circuitry hast not received a response to the Probe Request frame from the base station apparatus by a time when the first timer expires.

18. A wireless communication method in a wireless communication system including a plurality of wireless communication apparatuses and a base station apparatus that performs a wireless communication with the plurality of wireless terminal apparatuses according to Institute of Electrical and Electronics Engineers (IEEE802.11), the wireless communication method comprising performing processes performed by the base station apparatus, the processes comprising:

generating one or more first Contention Free-End (CF-END) frames, each first CF-END frame including end information indicating that a Transmission OPportunity (TXOP) period assigned for communication with one of the plurality of wireless terminal apparatuses has expired and including a Beacon element including identifier information associated with the base station apparatus, each of the one or more first CF-END frames being for use by another one of the plurality of wireless terminal apparatuses to start scan procedure; and

transmitting the generated one or more first CF-END frames to the plurality of wireless terminal apparatuses by using a plurality of different transmission beams.

19. The wireless communication method according to claim 18 , comprising performing processes performed by at least one of the plurality of wireless terminal apparatuses, the processes comprising:

judging whether a medium is clear;

in a case where the judgment indicates that the medium is clear, transmitting a Probe Request frame to the base station apparatus;

starting a first timer to count a first predetermined time since the transmission of the Probe Request frame; and

in a case where a response to the Probe Request frame is not received from the base station apparatus by a time when the first timer finishes the counting of the first predetermined time, waiting without transmitting a next frame until the one or more first CF-END frames is transmitted.