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Frequency hopping spread spectrum passive acoustic wave identification device
| Details |
Inventors: Nysen, Paul A.;
Assignee: X-Cyte, Inc. (San Jose, CA)
Primary Examiner: Horabik; Michael
Assistant Examiner: Bangachon; William
Attorney, Agent or Firm: Thelen Reid & Priest LLP
A system and method for interrogating a passive acoustic transponder, producing a transponder signal having characteristic set of signal perturbations in response to an interrogation signal, comprising a signal generator, producing an interrogation signal having a plurality of differing frequencies; a receiver, for receiving the transponder signal; a mixer, for mixing the transponder signal with a signal corresponding to the interrogation signal, to produce a mixed output; an integrator, integrating the mixed output to define an integrated phase-amplitude response of the received transponder signal; and an analyzer, receiving a plurality of integrated phase-amplitude responses corresponding to the plurality of differing frequencies, for determining the characteristic set of signal perturbations of the passive acoustic transponder. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will now be described with reference to the drawings.
Identical elements in the various figures are designated with the same reference numerals.
An interrogation system according to the present invention is provided which employs a frequency hopping spread spectrum signal having a pseudorandom sequence which excites a set of frequencies.
Typically, the interrogation sequence is repeated continuously.
The interrogation signal occupies, for example, a band of approximately 20 MHz centered at 915 MHz.
The band is divided into 128 discrete frequencies, each of occupies a period of about 15 μS.
For example, with a frequency hopping period of 15 μS, the system generates an interrogation pulse at a selected frequency for 7.
5 μS, is silent and insensitive for 300 nS to eliminate near-field echos, and then listens for 4 μS for the return signal.
The system is then silent and insensitive for the remaining portion of the cycle, about 3.
5 μS.
The interrogation signal is generated by a digitally controlled oscillator, including a phase locked loop with voltage controlled amplifier.
The sequence is generated by a sequence generator which sets the digital controls of the digitally controlled oscillator to a desired state and with a desired sequence.
One possible scheme is to evenly spread energy through the band, without concentrating the wave energy in a narrow range for an extended period, with a repeated pseudorandom sequence of 128 different frequencies.
The sequence generator may include a lookup table or algorithmic pseudorandom sequence generator.
A typical passive transponder device for use with the system has 16 degrees of freedom in its code space, generated by four bidirectional transducers, each wave having two sets of delay pad elements.
Thus, the interrogator system analyzer must resolve the 16 degrees of freedom in order to identify the encoding of the transponder
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