Wireless communication system and method, and wireless communication apparatus

1. A wireless communication system comprising:

a first apparatus and a second apparatus that perform wireless communication with each other,

wherein the first apparatus sends a first reference signal, and starts signal transmission to the second apparatus with a first period from a time point at which a first offset time passes from sending the first reference signal,

the second apparatus starts signal transmission to the first apparatus with the first period from a time point at which a second offset time, which is different from the first offset time, passes from sending the first reference signal, and

the first apparatus transmits a signal indicating a time obtained by adding the first offset time and a fixed time, which is shorter than one period of the first period, as the second offset time to the second apparatus before starting the signal transmission.

2. The wireless communication system according to claim 1 , wherein the first apparatus sends the first reference signal with a second period, which is longer than the first period.

3. The wireless communication system according to claim 2 , wherein the first apparatus transmits a signal indicating a time obtained by adding the first offset time and a fixed time, which is shorter than one period of the first period, as the second offset time to the second apparatus before starting the signal transmission.

4. The wireless communication system according to claim 3 , wherein said wireless communication system uses a carrier sense multiple access/collision avoidance (CSMA/CA) method in accordance with IEEE 802.11 standard.

5. The wireless communication system according to claim 4 , wherein the first offset time is greater than a value that is obtained by adding a doubled value of Distributed Inter Frame Space (DIFS), a maximum value of a contention window, and an occupancy time associated with the signal transmission.

6. The wireless communication system according to claim 4 , wherein the first offset time is greater than a value that is obtained by adding a doubled value of Distributed Inter Frame Space (DIFS), a maximum value of a contention window, an occupancy time associated with the transmission of the first signal, a Short Inter Frame Space (SIFS), and an occupancy time associated with an ACK frame.

7. The wireless communication system according to claim 2 , wherein said wireless communication system uses a carrier sense multiple access/collision avoidance (CSMA/CA) in accordance with IEEE 802.11 standard.

8. The wireless communication system according to claim 7 , wherein the first offset time is greater than a value that is obtained by adding a doubled value of Distributed Inter Frame Space (DIFS), a maximum value of a contention window, and an occupancy time associated with the signal transmission.

9. The wireless communication system according to claim 7 , wherein the first offset time is greater than a value that is obtained by adding a doubled value of Distributed Inter Frame Space (DIFS), a maximum value of a contention window, an occupancy time associated with the transmission of the first signal, a Short Inter Frame Space (SIFS), and an occupancy time associated with an ACK frame.

10. The wireless communication system according to claim 1 , wherein said wireless communication system uses a carrier sense multiple access/collision avoidance (CSMA/CA) method in accordance with IEEE 802.11 standard.

11. The wireless communication system according to claim 10 , wherein the first offset time is greater than a value that is obtained by adding a doubled value of Distributed Inter Frame Space (DIFS), a maximum value of a contention window, and an occupancy time associated with the signal transmission.

12. The wireless communication system according to claim 10 , wherein the first offset time is greater than a value that is obtained by adding a doubled value of Distributed Inter Frame Space (DIFS), a maximum value of a contention window, an occupancy time associated with the transmission of the first signal, a Short Inter Frame Space (SIFS), and an occupancy time associated with an ACK frame.

13. The wireless communication system according to claim 1 , wherein the first apparatus transmits a signal indicating a third offset time, to another wireless communication system, which is different from said wireless communication system, so that a second reference signal associated with the another wireless communication system is sent at a time point at which only for the third offset time passes from sending the first reference signal.

14. An apparatus, which is one of two apparatuses in a wireless communication system, said apparatus comprising:

a communicating device configured to perform signal transmission to other apparatus out of the two apparatuses with a first period;

a beacon configured to send a reference signal; and

a Central Processing Unit (CPU) configured to determine offset times respectively associated with the two apparatuses,

wherein the communicating device transmits a signal indicating an offset time of the other apparatus, and starts the signal transmission to the other apparatus with the first period from a time point at which an offset time of said apparatus passes from sending the reference signal, and

the communicating device transmits a signal indicating a time obtained by adding the offset time of the apparatus and a fixed time, which is shorter than one period of the first period, as the offset time of the other apparatus to the other apparatus before starting the signal transmission.