Ambient RF backscatter communication for vehicle remote control and sensing

1. A communication system for a vehicle comprising:

an electrical system having a battery;

a wireless fob mounted to the vehicle without direct connection to the electrical system, wherein the wireless fob comprises an RF-harvesting power supply responsive to ambient RF signals and a switchable antenna generating a backscatter communication signal encoding commands or data from the wireless fob;

a receiver in the vehicle adapted to detect the backscatter communication signal from the wireless fob;

a harvesting emulator in the vehicle responsive to the ambient RF signals to duplicate a concurrent response present in the RF-harvesting power supply of the wireless fob; and

a vehicle-powered RF transmitter in the vehicle activated to broadcast energizing RF radiation around the vehicle when the duplicated response is below a threshold.

2. The communication system of claim 1 wherein the wireless fob is comprised of an entry keypad.

3. The communication system of claim 1 wherein the wireless fob is comprised of a tire pressure monitoring system (TPMS).

4. The communication system of claim 1 wherein the wireless fob is comprised of self-triggering wireless sensor.

5. The communication system of claim 1 wherein the receiver is comprised of a transceiver adapted to i) modulate the energizing RF radiation according to an identifying tag, and ii) detect ancillary tags broadcast by other vehicles within respective energizing RF radiation of the other vehicles;

wherein activation of the vehicle-powered RF transmitter further depends on ancillary tags being received.

6. The communication system of claim 5 wherein ancillary tags are adapted to identify a group of cooperating vehicles to which the vehicle belongs, and when a detected tag identifies the group then the vehicle-powered RF transmitter is not activated.

7. The communication system of claim 5 further comprising a moderator adapted to communicate with moderators in the other vehicles to cooperatively assign respective vehicle-powered RF transmitters for broadcasting the energizing RF radiation one at a time.

8. The communication system of claim 7 wherein an assigned transmitter is determined in response to a highest one of respective states of charge of respective storage batteries in the vehicles.

9. The communication system of claim 7 wherein an assigned transmitter is determined by cycling between respective vehicles for predetermined periods of time in order to share a power consumption among the respective vehicles.

10. The communication system of claim 1 wherein activation of the vehicle-powered RF transmitter is prevented when a state of charge of a storage battery in the vehicle is below a power-reserve threshold.

11. A vehicular communication method for a vehicle including an electrical system with a battery, comprising the steps of:

operating a backscatter fob to generate a backscatter communication signal using power harvested from a local RF environment including ambient RF signals, wherein the backscatter fob is mounted to the vehicle without direct connection to the electrical system, and wherein the backscatter fob comprises an RF-harvesting power supply responsive to ambient RF signals and a switchable antenna generating the backscatter communication signal to encode commands or data from the backscatter fob;

emulating the power harvesting of the backscatter fob in a vehicle mounted emulator receiving the ambient RF signals to provide a measured power; and

activating a vehicle-powered transmitter to boost the local RF environment when the measured power is below a threshold to increase the power harvested in the backscatter fob.

12. The method of claim 11 wherein the backscatter fob is comprised of an entry keypad, the method further comprising:

detecting backscatter by the entry keypad of an RF signal transmitted by the vehicle-powered transmitter to boost the local RF environment; and

demodulating the detected backscatter to recover authentication data and user commands manually selected at the entry keypad.

13. The method of claim 11 wherein the fob is comprised of an entry keypad, the method further comprising:

detecting backscatter by the entry keypad of an ambient RF signal from a remote broadcaster to the local RF environment; and

demodulating the detected backscatter to recover authentication data and user commands manually selected at the entry keypad.

14. The method of claim 11 wherein the backscatter fob is comprised of a tire pressure monitoring system (TPMS).

15. The method of claim 11 wherein the backscatter fob is comprised of self-triggering wireless sensor.