Maximum likelihood localization in the presence of channel uncertainties
Some embodiments include a wireless sensor network system. Other embodiments of related systems and methods are also disclosed.
1. A method of localizing a sensor node device in communication with a plurality of anchor sensors each having a known location, the communication occurring over a wireless fading communication channel, the method comprising:
transmitting a first signal from each anchor sensor of the plurality of anchor sensors to the sensor node device over the wireless fading communication channel;
receiving the first signal at the sensor node device;
transmitting a second signal from the sensor node device to each anchor sensor of the plurality of anchor sensors, wherein the transmitting occurs over the wireless fading communication channel after receipt of the first signal;
receiving the second signal at each anchor sensor of the plurality of anchor sensors during a first time period after such anchor sensor transmitted the first signal;
determining for each anchor sensor of the plurality of anchor sensors a time-of-arrival measurement based at least in part upon the first time period;
determining a maximum likelihood estimation for the sensor node device communicating over the wireless fading communication channel, the maximum likelihood estimation comprising a fading parameter for the wireless fading communication channel; and
displaying at a computer video display a location estimation of the sensor node device based at least in part on the maximum likelihood estimation,
wherein:
determining the maximum likelihood estimation for the sensor node device communicating over the wireless fading communication channel comprises computing a maximum likelihood estimator {circumflex over (z)} as follows:
z
^
=
arg
min
z
∑
i
=
1
M
log
[
1
2
σ
T
2
(
τ
^
i
-
d
i
c
)
2
+
m
]
,
where a true distance d i between an i th anchor sensor of the plurality of anchor sensors and the sensor node device is denoted as d i =∥p i −z∥ 2 , p i represents cartesian coordinates of the i th anchor sensor of the plurality of anchor sensors, M represents a quantity of the plurality of anchor sensors, z represents cartesian coordinates of the sensor node device, {circumflex over (τ)} i represents the time-of-arrival measurement for the i th anchor sensor of the plurality of anchor sensors, c is a speed of propagation, σ T 2 is a variance of the time-of-arrival measurements, and m is the fading parameter for the wireless fading communication channel.
2. The method of claim 1 further comprising:
determining a Cramer-Rao lower bound benchmark for a one-dimensional network involving communication over the wireless fading communication channel.
3. The method of claim 1 further comprising:
determining a Cramer-Rao lower bound benchmark for a two-dimensional network involving communication over the wireless fading communication channel.
4. The method of claim 1 further comprising:
determining a modified Cramer-Rao lower bound benchmark for a one-dimensional network involving communication over the wireless fading communication channel.
5. The method of claim 1 further comprising:
determining a modified Cramer-Rao lower bound benchmark for a two-dimensional network involving communication over the wireless fading communication channel.
6. The method of claim 1 , wherein:
the wireless fading communication channel comprises a small-scale fading environment, such that a fading of at least one of the first signal or the second signal changes by moving the sensor node device a distance of approximately 5 cm to approximately 10 cm.
7. The method of claim 1 , wherein:
at least one of the plurality of anchor sensors comprises a base station in a cellular or wireless data telecommunications network; and
the sensor node device comprises a mobile phone.
8. A wireless sensor network system comprising:
a sensor node device;
a plurality of anchor sensors each having a known location and in communication with the sensor node device over a wireless fading communication channel; and
a computer system comprising one or more processing modules and one or more non-transitory memory storage modules storing computer instructions configured to run on the one or more processing modules and perform the acts of:
receiving from each anchor sensor of the plurality of anchor sensors a time-of-arrival measurement; and
determining a maximum likelihood estimation for the sensor node device communicating over the wireless fading communication channel, the maximum likelihood estimation comprising a fading parameter for the wireless fading communication channel,
wherein the computer instructions are further configured such that:
determining the maximum likelihood estimation for the sensor node device communicating over the wireless fading communication channel comprises computing a maximum likelihood estimator {circumflex over (z)} as follows:
z
^
=
arg
min
z
∑
i
=
1
M
log
[
1
2
σ
T
2
(
τ
^
i
-
d
i
c
)
2
+
m
]
,
where a true distance d i between an i th anchor sensor of the plurality of anchor sensors and the sensor node device is denoted as d i =∥p i −z∥ 2 , p i represents cartesian coordinates of the i th anchor sensor of the plurality of anchor sensors, M represents a quantity of the plurality of anchor sensors, z represents cartesian coordinates of the sensor node device, {circumflex over (τ)} i represents the time-of-arrival measurement for the i th anchor sensor of the plurality of anchor sensors, c is a speed of propagation, σ T 2 is a variance of the time-of-arrival measurements, and m is the fading parameter for the wireless fading communication channel.
9. The wireless sensor network system of claim 8 , wherein:
the computer system further comprises a computer video display; and
the computer instructions are further configured to cause the computer system to display the maximum likelihood estimation at the computer video display.
10. The wireless sensor network system of claim 8 , wherein the computer instructions are further configured to perform the act of:
determining a Cramer-Rao lower bound benchmark for a one-dimensional network involving communication over the wireless fading communication channel.
11. The wireless sensor network system of claim 8 , wherein the computer instructions are further configured to perform the act of:
determining a Cramer-Rao lower bound benchmark for a two-dimensional network involving communication over the wireless fading communication channel.
12. The wireless sensor network system of claim 8 , wherein the computer instructions are further configured to perform the act of:
determining a modified Cramer-Rao lower bound benchmark for a one-dimensional network involving communication over the wireless fading communication channel.
13. The wireless sensor network system of claim 8 , wherein the computer instructions are further configured to perform the act of:
determining a modified Cramer-Rao lower bound benchmark for a two-dimensional network involving communication over the wireless fading communication channel.
14. The wireless sensor network system of claim 8 , wherein:
the wireless fading communication channel comprises a small-scale fading environment, such that a fading of at least one of a first signal or a second signal changes by moving the sensor node device a distance of approximately 5 cm to approximately 10 cm.
15. The wireless sensor network system of claim 8 , wherein:
at least one of the plurality of anchor sensors comprises a base station in a cellular or wireless data telecommunications network; and
the sensor node device comprises a mobile phone.
16. A method of providing a wireless sensor network system comprising:
providing a sensor node device;
providing a plurality of anchor sensors each having a known location and in communication with the sensor node device over a wireless fading communication channel; and
providing a computer system comprising a computer video display, the computer system having non-transitory memory storing instructions that cause the computer system to:
receive from each anchor sensor a time-of-arrival measurement;
determine a maximum likelihood estimation for the sensor node device communicating over the wireless fading communication channel by computing a maximum likelihood estimator {circumflex over (z)} as follows:
z
^
=
arg
min
z
∑
i
=
1
M
log
[
1
2
σ
T
2
(
τ
^
i
-
d
i
c
)
2
+
m
]
,
where a true distance d i between an i th anchor sensor of the plurality of anchor sensors and the sensor node device is denoted as d i =∥p i −z∥ 2 , p i represents cartesian coordinates of the i th anchor sensor of the plurality of anchor sensors, M represents a quantity of the plurality of anchor sensors, z represents cartesian coordinates of the sensor node device, {circumflex over (τ)} i represents the time-of-arrival measurement for the i th anchor sensor of the plurality of anchor sensors, c is a speed of propagation, σ T 2 is a variance of the time-of-arrival measurements, and m is a fading parameter for the wireless fading communication channel; and
display at the computer video display a location estimation of the sensor node device based at least in part on the maximum likelihood estimation, the maximum likelihood estimation comprising the fading parameter for the wireless fading communication channel.
17. The method of claim 16 , wherein the instructions further cause the computer system to:
determine a modified Cramer-Rao lower bound benchmark for a one-dimensional network involving communication over the wireless fading communication channel.
18. The method of claim 16 , wherein the instructions further cause the computer system to:
determine a modified Cramer-Rao lower bound benchmark for a two-dimensional network involving communication over the wireless fading communication channel.
19. The method of claim 16 , wherein the instructions further cause the computer system to:
determine a Cramer-Rao lower bound benchmark for a one-dimensional network involving communication over the wireless fading communication channel.
20. The method of claim 16 , wherein the instructions further cause the computer system to:
determine a Cramer-Rao lower bound benchmark for a two-dimensional network involving communication over the wireless fading communication channel.