An apparatus and method to perform communication in a wireless power transmission system are provided. A source device of the wireless power transmission system, includes a communication unit configured to transmit an access standard instruction on a communication channel having a frequency that is not used for wireless power transmission. The source device further includes a controller configured to assign, to a target device, a control identifier (ID) if a response signal responding to the access standard instruction is received from the target device. The controller is further configured to determine an initial wireless power to be transmitted to the target device based on a change in a temperature of the source device, or a battery state of the target device, or a change in an amount of a power received by the target device, or a change in a temperature of the target device, or any combination thereof.