In this paper, we present a power adjustment scheme to dynamically enlarge\nand shrink power coverage to speed up tag identification in a RFID system.\nBy dividing a TDMA frame into time slots, the proposed power adjustment\nscheme can adaptively increase or decrease the transmission power of a reader.\nSpecifically, due to the contention for a TDMA slot from numerous tags,\nthree states of a slot could exist; they are respectively referred to as successful,\ncollided, and idle states. An adjustment factor based on the three states is designed\nto dynamically adjust the transmission power of a reader. The design\nof the adjustment factor considers two different aspects. When the number of\nidle state far exceeds the number of collided state, the first aspect will enlarge\nthe power such that more tags within the coverage can be concurrently identified.\nOn the other hand, when the number of idle state is much smaller than\nthe number of collided state, the second aspect will shrink the power such\nthat the number of tags within the coverage is significantly reduced. The\nproposed power adjustment scheme is simulated using NS-3. In the simulation,\nwe design three different topologies which place tags in three distributions,\nuniform, random, and hotspot. From the simulation results, we demonstrate\nthat the proposed power adjustment scheme can speed up the tag\nidentification and save energy consumption, particularly when a large number\nof tags are placed in hotspot distribution.
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