Backscatter systems, devices, and techniques utilizing CSS modulation and/or higher order harmonic cancellation
Examples of backscatter systems, device, and techniques are described herein. Example backscatter devices may utilize CSS modulation to provide backscatter signals including CSS signals (e.g., LoRa packets). Utilizing CSS modulation may advantageously allow for backscatter communication over wide areas. Examples of backscatter devices described herein may toggle the impedance of the backscatter device between multiple (e.g., eight) impedances to reduce and/or eliminate higher order harmonic components in the backscatter signal (e.g., third and fifth harmonic components).
1. A backscatter device comprising:
an antenna configured to backscatter a carrier signal having a first frequency;
baseband circuitry configured to provide a frequency plan for chirp spread spectrum symbols for transmission;
a frequency synthesizer coupled to the baseband circuitry and configured to provide an output signal in accordance with the frequency plan; and
a switch coupled to the antenna, the switch configured to control an impedance of the backscatter device to backscatter the carrier signal in accordance with the output signal such that the first frequency is mixed with the output signal to transmit a chirp spread spectrum signal comprising the chirp spread spectrum symbols.
2. The backscatter device of claim 1 , wherein the output signal comprises a square wave having a frequency changing over me in accordance with the frequency plan.
3. The backscatter device of claim 1 , wherein the frequency synthesizer comprises a variable oscillator.
4. The backscatter device of claim 3 , wherein the variable oscillator comprises a voltage controlled oscillator.
5. The backscatter device of claim 4 , further comprising a digital to analog converter coupled to the baseband circuitry and the voltage controlled oscillator, the digital to analog converter configured to translate the frequency plan to analog voltages and provide the analog voltages to the voltage controlled oscillator.
6. The backscatter device of claim 5 , wherein the digital to analog converter comprises a bit resolution corresponding to a spreading factor used by the backscatter device.
7. The backscatter device of claim 1 , wherein the frequency synthesizer comprises a direct digital synthesizer.
8. The backscatter device of claim 1 , wherein the switch is configured to switch between eight impedance values of the backscatter device.
9. The backscatter device of claim 8 , wherein the switch is configured to backscatter the carrier signal such that a third harmonic of the chirp spread spectrum signal is suppressed.
10. The backscatter device of claim 1 , wherein the chirp spread spectrum signal is arranged in accordance with a LoRa protocol.
11. The backscatter device of claim 1 , wherein one of the chirp spread spectrum symbols comprises a signal having a linearly increasing frequency, and wherein another of the chirp spread spectrum symbols comprises a shifted version of the signal.
12. The backscatter device of claim 1 , wherein the carrier signal comprises a spread spectrum signal, a frequency hopping signal, a single tone signal, or combinations thereof.
13. A backscatter device comprising:
an antenna configured to backscatter a carrier signal having a first frequency;
baseband circuitry configured to provide data for transmission;
a modulator coupled to the baseband circuitry and configured to provide an output signal in accordance with the data; and
a switch coupled to the antenna, the switch configured to control an impedance of the backscatter device to backscatter the carrier signal in accordance with the output signal such that the first frequency is mixed with the output signal to transmit a backscattered signal, wherein the backscattered signal has suppressed third and fifth harmonic components.
14. The backscatter device of claim 13 , wherein the switch is configured to switch between eight impedance values of the backscatter device.
15. The backscatter device of claim 13 , wherein the modulator is configured to perform amplitude modulation, phase modulation, frequency modulation, or combinations thereof.
16. The backscatter device of claim 13 , wherein the data for transmission comprises chirp spread spectrum symbols and wherein the backscattered signal comprises a chirp spread spectrum signal.
17. A system comprising:
a carrier signal generator configured to provide a carrier signal having a first frequency;
a backscatter device positioned to backscatter the carrier signal to provide a backscattered signal comprising a chirp spread spectrum signal, wherein the backscatter device comprises a switch coupled to an antenna, the switch configured to control an impedance of the backscatter device to backscatter the carrier signal in accordance with an output signal from a frequency synthesizer, such that the first frequency is mixed with the output signal to provide the chirp spread spectrum signal; and
a receiver configured to receive the chirp spread spectrum signal.
18. The system of claim 17 , wherein the backscatter device and the receiver are separated by greater than 100 meters.
19. The system of claim 17 , wherein the backscatter device comprises a dermal patch or a contact lens.
20. The system of claim 17 , wherein the carrier signal generator and the receiver are integrated into a same hybrid device.
21. The system of claim 20 , wherein the same hybrid device is configured to implement full duplex communication.
22. The system of claim 17 , further comprising a plurality of backscatter devices, wherein each of the plurality of backscatter devices is configured to backscatter the carrier signal into a respective different channel.