Patent ID: 8135445

Claim:
A method of performing a ranging process between a base station and a mobile station in a wireless access system, comprising: transmitting a sleep request message to a base station to request transition to a sleep mode; receiving a sleep response message in response to the sleep request message from the base station, wherein the sleep response message comprises a periodic ranging time; entering the sleep mode; transmitting a ranging request through uplink resources allocated by the base station when the periodic ranging time is reached; receiving a ranging response message from the base station in response to the ranging request message, wherein the ranging response message comprises a next periodic ranging time; if a value of the next periodic ranging time in the ranging response message is set to zero to indicate an existence of downlink data, terminating the sleep mode; and if a value of the next periodic ranging time is not zero, transmitting another ranging request message through the resources allocated by the base station when the next periodic ranging time has been reached.