Secure Channel Estimation Architecture
Wireless communication between two electronic devices may be used to determine a distance between the two devices, even in the presence of an otherwise-disruptive attacker. A wireless receiver system of one device may receive a true wireless ranging signal from a first transmitting device and a false wireless ranging signal from an attacker. The wireless receiver system may correlate the wireless signals with a known preamble sequence and perform channel estimation using the result, obtaining a channel impulse response for the wireless signals. The wireless receiver system may filter the channel impulse response for the plurality of wireless signals by removing at least part of the channel impulse response due to the false wireless ranging signal while not removing at least part of the channel impulse response due to the true wireless ranging signal. The receiver system may perform a wireless ranging operation using the filtered channel impulse response.
1 . An electronic device, comprising:
an antenna configured to receive a first wireless signal from a first transmitting device, the first wireless signal having a first preamble and a cryptographically secure value, the cryptographically secure value being shared by the first transmitting device and the electronic device, and a second wireless signal from a second transmitting device, the second wireless signal having a second preamble that imitates at least part of the first preamble; and
a receiver system coupled to the antenna and configured to
filter at least part of the second wireless signal from the first wireless signal based at least in part on the cryptographically secure value of the first wireless signal,
determine a time-of-flight of the first wireless signal after filtering at least part of the second wireless signal, and
determine a first path correction using a channel estimation for the first wireless signal based on the time-of-flight.
2 . The electronic device of claim 1 , comprising an analog-to-digital converter configured to convert the first wireless signal and the second wireless signal to a digitized form, wherein the receiver system is configured to receive the digitized form of the first wireless signal and the second wireless signal from the analog-to-digital converter.
3 . The electronic device of claim 1 , wherein the antenna is configured to receive the second wireless signal via an indirect path between the electronic device and the first transmitting device, the indirect path traversing a greater distance than a free-space path between the electronic device and the first transmitting device, and the second wireless signal representing a delayed version of the first wireless signal.
4 . The electronic device of claim 1 , wherein the receiver system is configured to identify that the first wireless signal and not the second wireless signal was received via a free-space path between the electronic device and the first transmitting device when the second wireless signal has a higher signal strength than the first wireless signal.
5 . The electronic device of claim 1 , wherein the receiver system is configured to identify that the first wireless signal and not the second wireless signal was received via a free-space path between the electronic device and the first transmitting device based at least in part on an earlier detection of a component of the first preamble of the first wireless signal.
6 . The electronic device of claim 1 , wherein the receiver system is configured to correlate a local copy of the cryptographically secure value with the first wireless signal and with the second wireless signal to filter the first wireless signal from the second wireless signal.
7 . The electronic device of claim 1 , wherein the receiver system is configured to correlate a digital sample of the first wireless signal with a known preamble sequence to determine a preamble correlation signal, the preamble correlation signal indicative of a wireless signal communicated through a free-space channel or a reflected channel.
8 . The electronic device of claim 1 , wherein the receiver system is configured to perform the channel estimation for the first wireless signal using the first preamble of the first wireless signal.
9 . A method comprising:
receiving, via a receiver system, a first wireless signal from a first electronic device and a second wireless signal from a second electronic device, wherein the first wireless signal comprises a first preamble and a cryptographically secure value and the second wireless signal comprises a second preamble;
filtering, via the receiver system, the second wireless signal from the first wireless signal; and
estimating, via processing circuitry, a wireless channel of a shortest free-space path based at least in part on filtering the second wireless signal from the first wireless signal.
10 . The method of claim 9 , wherein filtering the second wireless signal is based on a local copy of the cryptographically secure value, the cryptographically secure value indicative of wireless signals being transmitted from trusted or known devices.
11 . The method of claim 9 , wherein the first preamble and the second preamble are public known values.
12 . The method of claim 9 , wherein the first preamble and the second preamble are plaintext.
13 . The method of claim 9 , wherein filtering utilizes the cryptographically secure value and estimating the wireless channel of the shortest free-space path utilizes the first preamble and the second preamble.
14 . The method of claim 9 , comprising determining, via the processing circuitry, a physical distance from the first electronic device based on a time-of-flight of the first wireless signal and a physical parameter of speed of electromagnetic radiation.
15 . The method of claim 9 , comprising
receiving, via the receiver system, a third wireless signal comprising a third preamble and a false cryptographically secure value; and
filtering, via the receiver system, the third wireless signal from the first wireless signal based at least in part on a first correlation of the false cryptographically secure value with a locally stored copy of the cryptographically secure value being less correlated than a second correlation of the cryptographically secure value of the first wireless signal with the locally stored copy of the cryptographically secure value.
16 . The method of claim 9 , comprising
receiving, via the receiver system, a third wireless signal comprising a third preamble and a false cryptographically secure value;
determining, via the processing circuitry, a first correlation between the cryptographically secure value of the first wireless signal and a locally stored copy of the cryptographically secure value;
determining, via the processing circuitry, a second correlation between the false cryptographically secure value of the third wireless signal and the locally stored copy of the cryptographically secure value, the second correlation comprising a noise pattern caused by correlating the false cryptographically secure value and the cryptographically secure value; and
filtering, via receiver system, the third wireless signal from the first wireless signal based at least in part on the noise pattern.
17 . The method of claim 16 , comprising
determining, via the processing circuitry, a time-of-flight of the first wireless signal; and
estimating, via the processing circuitry, the wireless channel of the shortest free-space path based at least in part on the time-of-flight of the first wireless signal without determining the time-of-flight of the second wireless signal, the third wireless signal, or both.
18 . One or more tangible, non-transitory, machine-readable media comprising instructions that, when executed by one or more processors of the machine, cause the machine to:
receive a plurality of wireless signals, each of the plurality of wireless signals comprising a preamble and a secure value;
compare the preamble of each of the plurality of wireless signals with a stored secure value;
filter one or more wireless signals of the plurality of wireless signals from the plurality of wireless signals based on one or more mismatches between the secure value of each of the one or more wireless signals and the stored secure value; and
determine an earliest channel using the preamble of remaining one or more wireless signals of the plurality of wireless signals.
19 . The one or more tangible, non-transitory, machine-readable media of claim 18 , wherein the secure value comprises a cryptographically secure pseudorandom number.
20 . The one or more tangible, non-transitory, machine-readable media of claim 18 , wherein the earliest channel corresponds to a shortest direct path.