Backscatter devices and systems having digital architectures for OFDM backscatter
Examples of digital architectures for OFDM backscatter communication are described herein that use RF switches and discrete loads to implement digitally controlled single-sideband OFDM backscatter devices. One or more transforms may be implemented, including one or more IFFTs, LUTs, and/or numerically-controlled oscillators using one or more sine LUTs.
1. A backscatter device comprising:
a modulator configured to receive data and provide modulated data comprising one or more symbols;
a transform configured to convert the modulated data to a sequence of digital values wherein the transform comprises two or more numerically controlled oscillators configured to produce, at least in part, desired frequency components of an orthogonal frequency division multiplexed (OFDM) signal to be transmitted; and
at least one switch configured to couple selected impedances to an antenna in accordance with the sequence of digital values to backscatter an incident signal and transmit the data.
2. The backscatter device of claim 1 , wherein the at least one switch comprises one digitally-controlled radio frequency (RF) switch.
3. The backscatter device of claim 1 , wherein the modulated data comprise multi-tone symbol sequences.
4. The backscatter device of claim 1 , wherein the modulated data comprise OFDM signals.
5. The backscatter device of claim 1 , wherein the transform comprises an inverse Fourier transform.
6. The backscatter device of claim 5 , wherein the transform comprises a pruned or sparse transform.
7. The backscatter device of claim 1 , wherein the incident signal comprises a continuous wave signal.
8. The backscatter device of claim 1 , wherein the incident signal comprises a modulated signal.
9. The backscatter device of claim 1 , wherein the data is formatted in accordance with a Wi-Fi packet format or a Bluetooth packet format.
10. A backscatter device of claim 1 , comprising:
a modulator configured to receive data and provide modulated data comprising one or more symbols;
a transform configured to convert the modulated data to a sequence of digital values, wherein the transform comprises one or more look-up tables; and
at least one switch configured to couple selected impedances to an antenna in accordance with the sequence of digital values to backscatter an incident signal and transmit the data.
11. The backscatter device of claim 10 , wherein the one or more look-up tables comprise pre-computed time domain sequences indexed by groups of symbols.
12. The backscatter device of claim 11 , wherein the one or more look-up tables comprise a sparse group of the pre-computed time domain sequences indexed by the groups of symbols, and wherein a count of the time domain sequences is less than a count of possible groups of symbols.
13. A backscatter device comprising:
a modulator configured to receive data and provide modulated data comprising one or more symbols;
a transform configured to convert the modulated data to a sequence of digital values;
at least one switch configured to couple selected impedances to an antenna in accordance with the sequence of digital values to backscatter an incident signal and transmit the data; and
wherein the sequence of digital values is conveyed to the at least one switch via a delta-sigma modulator, a sigma-delta modulator, or another pulse-density modulator.
14. The backscatter device of claim 13 , wherein an output signal of the delta-sigma modulator, the sigma-delta modulator, or the pulse-density modulator is filtered by an analog filter.
15. The backscatter device of claim 14 , wherein the analog filter comprises a low-pass filter.
16. The backscatter device of claim 13 , wherein an output spectrum of the pulse-density modulator comprises frequency components that comprise, at least in part, desired frequency components of an orthogonal frequency division multiplexed (OFDM) signal to be transmitted.
17. A method comprising:
modulate input data to provide modulated data;
transform the modulated data to a sequence of digital values, wherein said transform comprises using one or more look-up tables; and
couple selected impedances to an antenna using a switch controlled by the sequence of digital values to backscatter an incident signal and transmit the data.
18. The method of claim 17 , wherein the modulated data comprise orthogonal frequency division multiplexed (OFDM) signals.
19. The method of claim 17 , wherein said transform comprises using an inverse Fourier transform.
20. The method of claim 17 , wherein said controlling of the switch by the sequence of digital values comprises using a delta-sigma modulator, a sigma-delta modulator, or another pulse-density modulator.