Channel recovery using group delay information
In one embodiment, a method includes: determining, for each of a plurality of first channels of a wireless link between an initiator device and a reflector device, a channel response metric; providing, for each of a plurality of second channels comprising advertisement channels, a predetermined value for a channel response metric; calculating a group delay for each of the plurality of first channels and each of the plurality of second channels based on the channel response metric for the corresponding channel and the channel response metric for a neighboring channel; determining a group delay metric based on the group delay for the plurality of first channels and the plurality of second channels; and calculating, for each of the plurality of second channels, a channel response metric based on the channel response metric for the neighboring channel and the group delay metric.
1 . A method comprising:
determining, for each of a plurality of first channels of a wireless link between an initiator device and a reflector device, a channel response metric;
providing, for each of a plurality of second channels comprising advertisement channels, a predetermined value for a channel response metric;
calculating a group delay for each of the plurality of first channels and each of the plurality of second channels based on the channel response metric for the corresponding channel and the channel response metric for a neighboring channel;
determining a group delay metric based on the group delay for the plurality of first channels and the plurality of second channels;
calculating, for each of the plurality of second channels, a channel response metric based on the channel response metric for the neighboring channel and the group delay metric;
determining a distance between the initiator device and the reflector device based, at least in part, on the channel response metric for each of the plurality of first channels and the calculated channel response metric for each of the plurality of second channels;
and
enabling access to a protected location based, at least in part, on the distance between the initiator device and the reflector device.
2 . The method of claim 1 , further comprising:
identifying, based at least in part on the distance, that the reflector device is within a threshold distance of the initiator device; and
enabling the access to the protected location based on identifying that the reflector device is within the threshold distance of the initiator device.
3 . The method of claim 1 , further comprising:
storing, for each of the plurality of first channels, the channel response metric in an entry of a channel sounding array; and
storing, for each of the plurality of second channels, the predetermined value for the channel response metric in an entry of the channel sounding array.
4 . The method of claim 3 , further comprising, for each of the plurality of second channels, updating the stored predetermined value for the channel response metric to the calculated channel response metric.
5 . The method of claim 1 , wherein providing, for each of the plurality of second channels, the predetermined value comprises providing a zero value for each of the plurality of second channels.
6 . The method of claim 1 , wherein providing, for each of the plurality of second channels, the predetermined value comprises providing a linear regression of the channel response metric for at least one neighboring channel for each of the plurality of second channels.
7 . The method of claim 1 , further comprising determining a plurality of channel response metrics for each of the first plurality of channels, each of the plurality of channel response metrics associated with an antenna of a plurality of antennas.
8 . The method of claim 1 , wherein determining, for each of the plurality of first channels, the channel response metric comprising determining a square (H 2 ) of a channel response (H) for the corresponding channel of the plurality of first channels.
9 . The method of claim 8 , further comprising calculating the group delay according to: G(f)=−diff(unwrap(angle(H 2 (f)), where H 2 (f) is the channel response metric for the corresponding channel, unwrap is a function to unwrap a phase of the angle to a linear phase, and diff is a difference function between the phase of the channel response metric of two consecutive channels of the wireless link.
10 . The method of claim 9 , further comprising calculating, for each of the plurality of second channels, the channel response metric according to: T=S*exp(rot_count*i+G_mean), where T is the channel response metric for the corresponding channel of the plurality of second channels, S is the channel response metric for a neighboring channel of the plurality of first channels, rot_count is a distance between the corresponding channel of the plurality of second channels and the neighboring channel, and G_mean comprises the group delay metric.
11 . An apparatus comprising:
at least one antenna;
a transceiver coupled to the at least one antenna, the transceiver to transmit and receive radio frequency (RF) signals, the transceiver comprising:
a RF circuit to transmit and receive the RF signals; and
at least one digital circuit coupled to the RF circuit to process digital signals, the at least one digital circuit to initiate a channel sounding process with a device to couple to the apparatus via a wireless link to:
determine, for each of a plurality of first channels of the wireless link, a channel response metric, and store the channel response metric in a channel sounding array; and
provide, for each of a plurality of second channels of the wireless link comprising advertisement channels, a predetermined value for a channel response metric, and store the predetermined value in the channel sounding array; and
a processor coupled to the transceiver, the processor to:
access the channel sounding array and calculate a group delay for each of the plurality of first channels and each of the plurality of second channels based on the channel response metric for the corresponding channel and the channel response metric for a neighboring channel;
determine a group delay metric based on the group delay for the plurality of first channels and the plurality of second channels;
calculate, for each of the plurality of second channels, a channel response metric based on the channel response metric for the neighboring channel and the group delay metric;
determine a distance between the apparatus and the device based at least in part on the channel response metric for each of the plurality of first channels and the calculated channel response metric for each of the plurality of second channels; and
control access to a protected location based at least in part on the distance.
12 . The apparatus of claim 11 , further comprising a non-volatile memory coupled to the at least one processor, wherein the non-volatile memory is to store a protocol stack, the protocol stack comprising instructions to perform the channel sounding process.
13 . The apparatus of claim 12 , wherein the protocol stack further comprises instructions to calculate the group delay for each of the plurality of first channels and each of the plurality of second channels.
14 . The apparatus of claim 11 , wherein the at least one digital circuit is to determine, for each of the plurality of first channels, the channel response metric comprising determining a square (H 2 ) of a channel response (H) for the corresponding channel of the plurality of first channels.
15 . The apparatus of claim 14 , wherein the processor is to calculate the group delay according to: G(f)=−diff(unwrap(angle(H 2 (f)), where H 2 (f) is the channel response metric for a corresponding channel, unwrap is a function to unwrap a phase of the angle to a linear phase, and diff is a difference function between the phase of the channel response metric of two consecutive channels of the wireless link.
16 . The apparatus of claim 11 , wherein the apparatus comprises a vehicle computing system of a vehicle, and in response to a determination that the device comprising a key fob is within a threshold distance of the vehicle computing system, is to cause the vehicle to be unlocked.
17 . At least one non-transitory storage medium comprising instructions that when executed by at least one processor cause the at least one processor to perform a method comprising:
determining, for each of a plurality of first channels of a wireless link between an initiator device and a reflector device, a channel response metric;
providing, for each of a plurality of second channels of the wireless link, the plurality of second channels comprising advertisement channels, a predetermined value for a channel response metric;
calculating a group delay for each of the plurality of first channels and each of the plurality of second channels based on the channel response metric for the corresponding channel and the channel response metric for a neighboring channel;
determining a group delay metric based on the group delay for the plurality of first channels and the plurality of second channels;
calculating, for each of the plurality of second channels, a channel response metric based on the channel response metric for the neighboring channel and the group delay metric;
determining a distance between the initiator device and the reflector device based, at least in part, on the channel response metric for each of the plurality of first channels and the calculated channel response metric for each of the plurality of second channels; and
enabling access to a protected location based, at least in part, on the distance between the initiator device and the reflector device.
18 . The at least one non-transitory storage medium of claim 17 , wherein the method further comprises:
identifying, based at least in part on the distance, that the reflector device is within a threshold distance of the initiator device; and
enabling access to the protected location based on identifying that the reflector device is within the threshold distance of the initiator device.
19 . The at least one non-transitory storage medium of claim 17 , wherein the method further comprises:
determining, for each of the plurality of first channels, the channel response metric comprising a square (H 2 ) of a channel response (H) for the corresponding channel of the plurality of first channels;
calculating the group delay according to: G(f)=−diff(unwrap(angle(H 2 (f)), where unwrap is a function to unwrap a phase of the angle to a linear phase, and diff is a difference function between the phase of the channel response metric of two consecutive channels of the wireless link; and
calculating, for each of the plurality of second channels, the channel response metric according to: T=S*exp(rot_count*i+G_mean), where T is the channel response metric for the corresponding channel of the plurality of second channels, S is the channel response metric for a neighboring channel of the plurality of first channels, rot_count is a distance between the corresponding channel of the plurality of second channels and the neighboring channel, and G_mean comprises the group delay metric.