Patent ID: 7911325

Claim:
An endpoint device for responding to an interrogator after receiving an interrogating signal containing a main carrier by transmitting a reflected signal generated by modulating the main carrier with appropriate information, the endpoint device comprising: an individual-frequency-utilization-ratio setting portion operable to set a distribution of an individual frequency utilization ratio which is a ratio of time period during which each frequency channel is used as a hopping frequency of a subcarrier signal in which a frequency hopping is implemented and which is used to modulate the main carrier, over a predetermined range of frequency of the subcarrier signal that consists of a plurality of mutually adjacent frequency channels; a frequency determining portion operable on the basis of the distribution of the individual frequency utilization ratio set by the individual-frequency-utilization-ratio setting portion to determine a frequency of the subcarrier signal by random selection within the predetermined range of frequency; a battery cell; and a power-source-information detecting portion operable to detect at least two discrete operating states of the battery cell, the at least two discrete operating states of the battery cell being at least able to power the endpoint device; wherein in response to a supply voltage of the battery cell being lower than a predetermined threshold value, the individual-frequency-utilization-ratio setting portion is configured to shift a statistical center frequency of the distribution of the individual frequency utilization ratio to a lower frequency by selecting a first individual-frequency-utilization-ratio distribution pattern from a plurality of individual-frequency-utilization-ratio distribution patterns that includes at least the first individual-frequency-utilization-ratio distribution pattern and a second individual-frequency-utilization ratio-distribution pattern, wherein the first individual-frequency-utilization-ratio distribution pattern is relatively high in the relatively low frequency channels and the second individual-frequency-utilization-ratio distribution pattern is relatively high in the relatively high frequency channels.