WIRELESS POWER TRANSFER

A power receiver (105) communicates to a power transmitter (101) using load modulation data symbols modulated by a chip sequence with a chip sequence being divided into load time intervals with different modulation loads. The power transmitter (101) comprises a receiver (207) which includes a load measurer (209) determining measured load values of the power transfer signal for load time intervals. A chip determiner circuit (211) determines a received chip sequence from the measured load values where the received chip sequence comprises a sequence of chip values. Each chip value is determined in response to a difference between measured load values for at least two modulation load time intervals of the chip. A store (215) stores a set of chip sequences with each chip sequence linked to a data symbol. A detector (213) detects a received data symbol value in response to a correlation between the received chip sequence and chip sequences of the set of chip sequences.