To identify an RFID tag in a field of RFID tags, an interrogator sends a series of commands to implement an arbitration scheme. The commands include differentiation, selection, and modulation information. The tag uses the differentiation information to differentiate commands sent by the interrogator from commands sent by other interrogators that may be within communication range of the tag. The selection information is used by the tag to determine if the tag is a member of a group selected by the interrogator for response to the interrogator. If the tag is a member of the selected group, the tag may send a reply that is modulated using a modulation type selected by the modulation information. In accordance with one of the modulation types, one of three different pulse waveforms is selected by the interrogator via the modulation information to multiply with the baseband waveform of the reply from the tag.