Exemplary embodiments are directed to wireless power transfer. A transmitter generates an electromagnetic field at a resonant frequency with a transmit antenna to create a coupling-mode region within a near field of the transmit antenna. The transmitter defines a beginning of a recurring period by on-off keying the electromagnetic field during a synchronization portion of the recurring period. During a power transmission portion of the recurring period, the transmitter couples portions of the electromagnetic field to different receive antennas of various receiver devices within the coupling-mode region. The transmitter also determines a power allocation within the recurring period for the various receiver devices disposed within the coupling-mode region and adjusts a power level of the near field radiation responsive to power requirements received from the receiver devices.