Capacity-expandable access device, digital optical fiber distribution system employing capacity-expandable access device, and capacity expansion switching method

The invention discloses a capacity-expandable access device. The device is provided with a first working mode as a master monitoring station and a second working mode as a slave monitoring station, and comprises radio frequency (RF) transceiving modules, a digital processing module and a user interface, wherein the RF transceiving modules are connected with the digital processing module and used to achieve two-way data transmission between the digital processing module and a base station; the digital processing module is used to process received data and output processed data; and the user interface is connected with the digital processing module and used to receive and respond to a mode switching request, so that the working mode of the capacity-expandable access device can be switched between the first working mode and the second working mode. The capacity-expandable access device can be used as both a master access unit and a slave access unit; and a user only needs to send the switching request as needed