Passive entry/passive start systems implementing music algorithm based angle of arrival determinations for signals received via circular polarized antennas

1. An access system for a vehicle, the access system comprising:

a plurality of antennas configured to each receive a signal transmitted from a portable access device to the vehicle, wherein the plurality of antennas respectively comprise

a circular polarized antenna comprising a conductive ring-shaped body having an inner hole,

a circular isolator connected to the conductive ring-shaped body, and

a linear polarized antenna connected to the circular polarized antenna and the circular isolator and extending outward from the circular isolator, wherein the linear polarized antenna comprises

a sleeve, and

a conductive element extending through the sleeve, and

wherein the linear polarized antenna extends orthogonal to a radius of the circular polarized antenna; and

an access module configured to

downconvert the received signal to generate an in-phase signal and a quadrature phase signal,

execute a music algorithm to determine angles of arrival of the received signal as received at the plurality of antennas,

determine a distance between the portable access device and the vehicle based on the angles of arrival, and

permit access to the vehicle based on the distance.

2. The access system of claim 1 , wherein the access module is configured to, while executing the music algorithm:

collect analytic signal samples of the signal received at each of the plurality of antennas to generate a received data matrix;

estimate a data covariance matrix based on the received data matrix;

use an eigenvalue decomposition process to determine a M×M matrix based on the data covariance matrix, where M is an integer greater than or equal to 2;

determine a number of impinging signals;

separate the M×M matrix into a plurality of matrices;

compute a music spectrum based on one of the plurality of matrices; and

perform a peak search on the music spectrum to determine the angles of arrival.

3. The access system of claim 2 , wherein the access module is configured to:

perform a covariance smoothing method to generate a modified covariance matrix; and

use the eigenvalue decomposition process to determine the M×M matrix based on the modified covariance matrix.

4. The access system of claim 2 , wherein the access module is configured to, while generating the received data matrix:

based on the phase angle vector, generate a recreated in-phase and quadrature phase sample vector for each of the plurality of antennas; and

generate the received data matrix based on the recreated in-phase and quadrature phase sample vector for each of the plurality of antennas.

5. The access system of claim 4 , wherein the access module is configured to:

create a time vector corresponding to the in-phase and quadrature phase sample vector;

discard some analytic signal samples taken near antenna switching times;

unwrap each repetition portion of remaining samples with a step size of π, wherein the remaining samples refer to the analytic signal samples remaining after discarding the some analytic signal samples;

average frequency of sinusoids of the remaining samples;

find average slope of the remaining samples;

measure a standard deviation of the average slope;

determine which of the plurality of antennas is misaligned based on measured standard deviation; and

for each of the plurality of antennas, interpolate a straight line of points on the time vector to generate a reconstructed phase angle vector.

6. The access system of claim 5 , wherein the access module is configured to:

if the standard deviation is greater than a predetermined threshold, check which one of the plurality of antennas has an inaccurate alignment; and

for the one of the plurality of antennas, remeasure the standard deviation of the average slope.

7. The access system of claim 1 , wherein the access module is configured to perform a clean method comprising:

performing an iterative process comprising

identifying source signals of the received signal using the music algorithm,

removing the source signals, one at a time, from the received signal using a calibrated array manifold comprising the plurality of antennas, and

forcing a position of a source signal to an offset location and calculating angle of arrival direction of a remaining signal; and

while performing the iterative process, converging to a new set of impinging angles of arrival.

8. A vehicle comprising:

the access system of claim 1 ;

a body; and

a roof, a center console, a floor or an at least partially enclosed metal structure,

wherein the plurality of antennas are implemented in at least one of the roof, the center console, the floor, or the at least partially enclosed metal structure.

9. The vehicle of claim 8 , wherein the plurality of antennas comprise a multi-axis polarized RF antenna assembly, wherein the multi-axis polarized RF antenna assembly comprises the circular polarized antenna and is oriented in the roof.

10. A method of operating an access system of a vehicle, the method comprising:

receiving a signal transmitted from a portable access device to the vehicle at each of a plurality of antennas, wherein one of the plurality of antennas is a circular polarized antenna;

downconverting the received signal to generate an in-phase signal and a quadrature phase signal;

executing a music algorithm to determine angles of arrival of the received signal as received at the plurality of antennas;

while executing the music algorithm, collecting analytic signal samples of the signal received at each of the plurality of antennas to generate a received data matrix, wherein while generating the received data matrix

converting an in-phase and quadrature phase sample vector to a phase angle vector,

creating a time vector corresponding to the in-phase and quadrature phase sample vector,

discarding some of the analytic signal samples taken near antenna switching times,

unwrapping each repetition portion of remaining samples with a step size of π, wherein the remaining samples refer to the analytic signal samples remaining after discarding the some analytic signal samples,

averaging frequency of sinusoids of the remaining samples,

determining average slope of the remaining samples,

measuring standard deviation of the average slope,

determining which of the plurality of antennas is misaligned based on measured standard deviation, and

for each of the plurality of antennas, interpolating a straight line of points on the time vector to generate a reconstructed phase angle vector,

determining a distance between the portable access device and the vehicle based on the angles of arrival; and

permitting access to the vehicle based on the distance.

11. The method of claim 10 , wherein executing the music algorithm comprises:

estimating a data covariance matrix based on the received data matrix;

using an eigenvalue decomposition process to determine a M×M matrix based on the data covariance matrix, where M is an integer greater than or equal to 2;

determining a number of impinging signals;

separating the M×M matrix into a plurality of matrices;

computing a music spectrum based on one of the plurality of matrices; and

performing a peak search on the music spectrum to determine the angles of arrival.

12. The method of claim 11 , further comprising:

performing a covariance smoothing method to generate a modified covariance matrix; and

using the eigenvalue decomposition process to determine the M×M matrix based on the modified covariance matrix.

13. The method of claim 11 , further comprising, while generating the received data matrix:

based on the phase angle vector, generating a recreated in-phase and quadrature phase sample vector for each of the plurality of antennas; and

generating the received data matrix based on the recreated in-phase and quadrature phase sample vector for each of the plurality of antennas.

14. The method of claim 10 , further comprising:

if the standard deviation is greater than a predetermined threshold, checking which one of the plurality of antennas has an inaccurate alignment; and

for the one of the plurality of antennas, remeasuring the standard deviation of the average slope.

15. The method of claim 10 , wherein:

the vehicle comprises (i) a body and (ii) a roof, a center console, a floor or an at least partially enclosed metal structure; and

the plurality of antennas are implemented in at least one of the roof, the center console, the floor, or the at least partially enclosed metal structure.

16. The method of claim 15 , wherein:

the plurality of antennas comprise a multi-axis polarized RF antenna assembly; and

the multi-axis polarized RF antenna assembly comprises the circular polarized antenna and is oriented in the roof.

17. A method of operating an access system of a vehicle, the method comprising:

receiving a signal transmitted from a portable access device to the vehicle at each of a plurality of antennas, wherein one of the plurality of antennas is a circular polarized antenna;

downconverting the received signal to generate an in-phase signal and a quadrature phase signal;

executing a music algorithm to determine angles of arrival of the received signal as received at the plurality of antennas; performing a clean method comprising:

identifying source signals of the received signal using the music algorithm;

performing an iterative process comprising

removing the source signals, one at a time, from the received signal using a calibrated array manifold comprising the plurality of antennas, and

forcing a position of a source signal to an offset location and recalculating angle of arrival direction of a remaining signal; and

while performing the iterative process, converging to a new set of impinging angles of arrival;

determining a distance between the portable access device and the vehicle based on the new set of impinging angles of arrival; and

permitting access to the vehicle based on the distance.

18. An access system for a vehicle, the access system comprising:

a plurality of antennas configured to each receive a signal transmitted from a portable access device to the vehicle, wherein the plurality of antennas as a system comprise

a first circular polarized antenna comprising a conductive ring-shaped body having an inner hole,

a first circular isolator connected to the conductive ring-shaped body, and

a first linear polarized antenna connected to the first circular polarized antenna and the first circular isolator and extending outward from the first circular isolator, wherein the first linear polarized antenna comprises

a sleeve, and

a conductive element extending through the sleeve, and

wherein the first linear polarized antenna extends orthogonal to a radius of the first circular polarized antenna; and

an access module configured to

downconvert the received signal to generate an in-phase signal and a quadrature phase signal,

execute a music algorithm to determine angles of arrival of the received signal as received at the plurality of antennas,

determine a distance between the portable access device and the vehicle based on the angles of arrival, and

permit access to the vehicle based on the distance.

19. The access system of claim 18 , wherein:

the plurality of antennas respectively comprise

a plurality of circular polarized antennas including the first linear polarized antenna,

a plurality of circular isolators including the first circular isolator, and

a plurality of linear polarized antennas include the first linear polarized antenna; and

each of the plurality of antennas comprises

a respective one of the plurality of circular polarized antennas,

a respective one of the plurality of circular isolators, and

a respective one of the plurality of linear polarized antennas.