The present disclosure provides a base station transmitter, a user equipment receiver and methods of operating a base station transmitter and a user equipment receiver. A second switching control circuit controls the on-time of a second switching element so that the time ratio of the on-time of the second switching element to the on-time of the first switching element becomes almost constant with respect to a change in a load current. The system divides a number space into n bins, wherein each bin is associated with m unique bits of the number space, and the number space contains the identification codes of the tags.