Abstract: A method of interrogating a set of tags with an interrogator is provided. The method includes defining a duration of a wake-up superframe that matches that of a wake-up cycle of the tags; defining an integer number of time periods within the duration of the wake-up superframe such that each time that one of the set of tags wakes is within one of the time periods of the wake-up superframe, the tags waking within a particular time period defining a group of tags; providing a first wake-up signal in a first time period to wake a first group of the tags; and providing a second wake-up signal in a second time period wake a second group of the tags.