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Decentralized radio frequency identification system

  • US 8,143,996 B2
  • Filed: 01/08/2008
  • Issued: 03/27/2012
  • Est. Priority Date: 01/08/2007
  • Status: Expired due to Fees
First Claim
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1. A decentralized RFID system comprising:

  • a first reader for transmitting a first carrier signal;

    a second reader for transmitting a second carrier signal;

    a tag for receiving the first and second carrier signals, wherein the tag is responsive to the first carrier signal to transmit a first backscatter signal, and wherein the tag is responsive to the second carrier signal to transmit a second backscatter signal; and

    wherein the first and second readers further include a first processor and a second processors, respectively, and wherein the first processor measures a degree of interference from the second carrier signal, and wherein the second processor measures a degree of interference from the first carrier signal, the first and second processor each executing instructions to;

    adjust a respective transmission power level of the first and second carrier signals being transmitted from the first and second readers, respectively, as a function of the measured degree of interference;

    calculate a new transmission power level of the corresponding first and second readers based on the degree of interference measured at the first and second readers and an estimated channel behavior at a next time step, wherein the new transmission power level is controlled such that an expected signal-to-noise ratio reaches a signal-to-noise ratio required for a desired reading range for the first and second readers,wherein a selective back-off scheme is employed by each of the first and second readers to ensure that both the first and second readers achieve a respective desired read range, the selective back-off scheme;

    determining on a percentage of time the first and second readers achieve a respective desired read range based on time a respective first or second reader has attained the required signal-to-noise ratio;

    executing an algorithm that uses a logarithm function of the percentage of time to determine an amount of time for each of the first and second readers to wait before return to the respective transmission power levels, the algorithm comprising;


    τ

    w=10·

    [log10

    +0.01)+2]wherein ρ

    is the percentage of time a respective first and second reader has attained the required signal-to-noise ratio and τ

    W is the amount of time a respective first and second readers to wait before return to the respective transmission power levels.

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