Wireless power transfer method, apparatus and system

A wireless power receiver for receiving power in a wireless manner, the wireless power receiver comprising:

• a power receiving unit configured to receive power in a wireless manner from a wireless power transmitter;
• and
• a power reception control unit configured to:
• generate information of the wireless power receiver based on a load modulation within a slot being allocated to the wireless power receiver while the wireless power is received from a wireless power transmitter;
• generate first information of the wireless power receiver based on the load modulation within a first unallocated slot among the plurality of slots, wherein the first information is in collision with second information generated by another wireless power receiver;
• demodulate a collision related signal of the wireless power transmitter based on a frequency shift keying (FSK);
• and
• execute a collision resolution mechanism.