A method of updating channel information by a mobile station (MS) that is in power saving mode is disclosed. More specifically, the method includes the MS which receives status information of a first channel descriptor and transmission frame information which includes when the first channel descriptor is to be transmitted. Furthermore, the MS compares status information of the first channel descriptor with status information of a second channel descriptor. Here, the second channel descriptor is stored in the MS. Lastly, if the compared status information are different, the MS receives the first channel descriptor according to the transmission frame information.