Radio communication apparatus and radio communication method

1. A radio communication system for receiving a transmission reservation request and transmitting a reservation acknowledgment that indicates a reserved transmission timing, the radio communication system comprising:

a control unit that controls transmission of a plurality of reservation acknowledgments in response to one transmission reservation request, wherein in response to the one transmission reservation request, a reservation acknowledgment to be transmitted after a previously transmitted reservation acknowledgment indicates a reserved transmission timing different from the reserved transmission timing acknowledged by the previously transmitted reservation acknowledgment.

2. The radio communication system according to claim 1 , wherein the control unit controls a radio transmitting unit to transmit any one reservation acknowledgment after a previously transmitted reservation acknowledgement among the plurality of reservation acknowledgments to be within a period of the transmission timing acknowledged in the previously transmitted reservation acknowledgment.

3. The radio communication system according to claim 1 , wherein a change in the reserved transmission timing is implemented in accordance with the transmitting conditions of another radio communication system.

4. The radio communication system according to claim 3 , wherein, referring to the reservation acknowledgment to be transmitted after a previously transmitted reservation acknowledgment, which indicates a reserved transmission timing different from the reserved transmission timing acknowledged by the previously transmitted reservation acknowledgment,

when a transmission rate of the other radio communication system becomes higher in accordance with a radio communication environment of the other radio communication system and thereby transmission of the other radio communication system is completed quicker than a transmission schedule, the change in the reserved transmission timing indicates an advancement of the reserved transmission timing from the reserved transmission timing acknowledged in the previously transmitted reservation acknowledgment; and

when the transmission of the other radio communication system is completed later than a transmission schedule, the change in the reserved transmission timing indicates a later reserved transmission timing from the reserved transmission timing acknowledged in the previously transmitted reservation acknowledgment.

5. The radio communication system according to claim 3 , wherein, the control unit controls a radio transmitting unit to transmit to the other radio communication system a transmission rate changing instruction in accordance with the radio communication environment of the other radio communication system and the control unit controls to change the transmission timing acknowledged with a first reservation acknowledgment with a second or subsequent reservation acknowledgement among the plurality of reservation acknowledgments when data transmission in regard to the other radio communication system will be completed earlier or later than the schedule of the transmission reservation on the basis of the contents of the transmission rate changing instruction and the amount of transmission data acquired or remaining to be transmitted from the other radio communication system.

6. The radio communication system according to claim 1 , wherein a period between a first transmission for reservation acknowledgment among the plurality of reservation acknowledgments and any one transmission for reservation acknowledgment after the first transmissions for reservation acknowledgment is set greater than or equal to a predetermined time period.

7. The radio communication system according to claim 1 , wherein the radio communication is for mobile communication and said radio communication system is a base station and said transmission reservation request is transmitted from a mobile station.

8. The radio communication system according to claim 1 , wherein the plurality of reservation acknowledgments have same contents but indicate different timing respectively.

9. The radio communication system according to claim 1 , wherein a first transmitting reservation acknowledgment includes identification information indicating whether further transmitting reservation acknowledgment will be transmitted.

10. A radio communication system for transmitting a transmission reservation request and receiving a reservation acknowledgment that indicates a reserved transmission timing, the communication system comprising:

a control unit that controls reception of a plurality of reservation acknowledgments received in response to one transmission reservation request and controls transmission of data in accordance with at least one reservation acknowledgment among the plurality of reservation acknowledgments, wherein in response to the one transmission reservation request, a reservation acknowledgment received after a previously received reservation acknowledgment indicates a reserved transmission timing different from the reserved transmission timing acknowledged by the previously received reservation acknowledgment.

11. A radio communication apparatus comprising:

a radio transmitting/receiving unit for transmitting a transmission reservation request and for receiving a transmission acknowledgment indicating a period including a plurality of transmission timings as a response to the transmission reservation request; and

a control unit for starting transmission, in accordance with the transmission acknowledgment, by a modulation method that is changed based on a radio communication environment, and for restricting a changing of the modulation method to keep the modulation method during the period indicated in the transmission acknowledgment even if the radio communication environment changes.

12. A radio communication method comprising:

reserving transmission by transmitting a transmission reservation request from a transmitting station and transmitting a transmission acknowledgment to the transmitting station in accordance with the transmission reservation request that indicates a reserved transmission timing; and

transmitting, to the transmitting station, a plurality of reservation acknowledgments with different timing in response to one transmission reservation request, wherein in response to the one transmission reservation request, a reservation acknowledgment transmitted after a previously transmitted reservation acknowledgment indicates a reserved transmission timing different from the reserved transmission timing acknowledged by the previously received reservation acknowledgment.

13. The radio communication system according to claim 1 , wherein the reserved transmission timing by the reservation acknowledgment to be transmitted after the previously transmitted reservation acknowledgment is used for an initial transmission of a data packet for which the reserved transmission timing has been acknowledged by the previously transmitted reservation acknowledgment.