A method of joining a cell by using a proxy coordinator. The method of joining a cell by using a proxy coordinator includes requesting a second device to operate as a proxy coordinator from a first device positioned out of a beacon frame reachable area of the cell, transmitting a time period to operate as the proxy coordinator allocated by a coordinator of the cell, informing the first device that the second device can operate as the proxy coordinator, transmitting a cell join request to the proxy coordinator from the first device through the second device, and transmitting a beacon frame including time allocation information from the coordinator to the first device through the second device.