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Orthogonal Frequency Coding for SAW Device Applications

Orthogonal Frequency Coding for SAW Device Applications. D.C. Malocha 1 , D. Puccio, and D. Gallagher, Electrical & Computer Engineering Department, University of Central Florida, Orlando, FL, 32816-2450 dcm@ece.engr.ucf.edu 1. Orthogonal Frequency Coding (OFC) Introduction.

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Orthogonal Frequency Coding for SAW Device Applications

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  1. Orthogonal Frequency Coding for SAW Device Applications D.C. Malocha1, D. Puccio, and D. Gallagher, Electrical & Computer Engineering Department, University of Central Florida, Orlando, FL, 32816-2450 dcm@ece.engr.ucf.edu 1

  2. Orthogonal Frequency Coding (OFC) Introduction • Fixed time length for a chip, , and fixed chip carrier frequency, fC. • Fixed relationship between time length and center frequency or where N = # of carrier cycles per chip. • Relationship between chip time and chip nullbandwidth, NBW: fc/NBWc=2N or Fc/NBWc=2N+1. • There will be multiple chips in a bit.

  3. Orthogonal Frequency Coding (OFC) Six Element Basis Set • Chip length sets the bandwidth; NBW=2/Tc • fc*Tc=N • Null frequencies @ fc1 occur at peak of fc2

  4. Linear Stepped ChirpFrequency Response - 7 Chips/Bit

  5. Schematic of OFC SAW ID Tag Linear Stepped Chirp Time Response with 7 Chips Defining an OFC Bit

  6. 1 Chip Conventional PN CodingSingle Carrier Frequency BPSK 7 Chip Barker Code

  7. Auto CorrelationPN Coding Single Carrier BPSK 7 Chip Barker Code • Single Carrier Frequency • Processing gain is proportional to chips/bit • Sidelobes dependent on code

  8. 1 Chip OFC Time/ Frequency Response7 Chip

  9. PN-OFC vs. Single Carrier BPSK PN-OFC vs. Single Carrier PN OFC 7-Chip vs. Single Carrier BPSK Frequency Response For PN, PG=7 For OFC, PG=49 OFC 7-Chip vs. Single Carrier PN Code Frequency Response

  10. Time Autocorrelation Comparison OFC 7-Chip vs. BPSK Single CarrierTime Autocorrelation OFC vs. Single Carrier PN with 7 Chips Time Autocorrelation For PN, compressed pulse width is 2 chips For OFC, compressed pulse width is 0.29 chips

  11. 2 Differing OFC CodesTime Domain Code Diversity

  12. 2 Differing OFC CodesFrequency Domain Code Diversity

  13. Autocorrelation of OFC7 Chip Barker CodeNo-PN Code and With PN-Code

  14. OFC 1 Bit Long, 7 Chips/BitWith No PN Coding

  15. OFC 1 Bit Long, 7 Chips/BitWith PN Coding

  16. OFC 3 Bit Long, 7 Chips/BitNo PN Coding

  17. OFC 3 Bit Long, 7 Chips/BitWith PN Coding

  18. OFC System Schematic

  19. OFC Tag SchematicReflector Structure

  20. Plots of 3 Bit, 7 Chips/Bit OFC System Simulation Ideal OFC TAG OFC with Chirp Tag Return Signal is 28 Bits long OFC with |Chirp|2

  21. 3 Bit, 7 Chips/Bit SimulationIdeal vs. System Autocorrelation

  22. OFC Auto and Cross Correlation 3 Bits, 7 Chips/Bit

  23. Conclusions and Discussion • OFC SAW Technique • a viable way of tagging multi-sensors • inherent processing gain • reduces pulse ambiguity for sensor • inherent security – OFC and PN coding • Implementable in transducers or reflectors • Modeling shows expected results • First SAW sensor embodiment is successful (Puccio, et.al. this symposium)

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