U.S. patent application number 14/998552 was filed with the patent office on 2017-07-20 for method for location determination using radio signals.
The applicant listed for this patent is CIHOLAS, INC. Invention is credited to Justin Emrys Bennett, Mike E. Ciholas, Daniel Lawrence Morris.
Application Number | 20170205493 14/998552 |
Document ID | / |
Family ID | 59296261 |
Filed Date | 2017-07-20 |
United States Patent
Application |
20170205493 |
Kind Code |
A1 |
Ciholas; Mike E. ; et
al. |
July 20, 2017 |
Method for location determination using radio signals
Abstract
A system and method for location of objects in 2-dimensional and
3-dimensional space using a minimum number of timed RF
transmissions. System consists of a mobile device and a plurality
of surveyed anchors. Two-Way Ranging (TWR) is done between the tag
and any single anchor and the distance between the tag and
remaining anchors is determined through listening to, or snooping,
the TWR packet transmissions.
Inventors: |
Ciholas; Mike E.;
(Evansville, IN) ; Bennett; Justin Emrys;
(Newburgh, IN) ; Morris; Daniel Lawrence; (Elyria,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CIHOLAS, INC |
NEWBURGH |
IN |
US |
|
|
Family ID: |
59296261 |
Appl. No.: |
14/998552 |
Filed: |
January 20, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S 5/30 20130101; H04W
4/023 20130101; G01S 5/14 20130101; G01S 5/0221 20130101; G01S
13/765 20130101 |
International
Class: |
G01S 5/02 20060101
G01S005/02; H04W 4/02 20060101 H04W004/02 |
Claims
1-12. (canceled)
13. A method for determining the location of a tag object in an
unknown location using radio signals comprising the steps of:
transmitting a first RF data packet from said tag object (T) and
recording the time (t1) at which the first RF data packet was
transmitted; receiving said first RF data packet at a primary
stationary anchor (Am) at a first known location (Xm, Ym, Zm) and
recording the time (m1) at which the first RF data packet was
received at the primary stationary anchor (Am); receiving said
first RF data packet at a secondary stationary anchor (As) at a
second known location (Xs, Ys, Zs), a first known distance (dms)
between said first known location and said second known location
being known, and recording the time (s1) at which the first RF data
packet was received at the secondary stationary anchor (As);
transmitting a second RF data packet from said primary stationary
anchor (Am) and recording the time (m2) at which the second RF data
packet was transmitted; receiving said second RF data packet at
said tag object (T) and recording the time (t2) at which the second
RF data packet was received at the tag object (T); receiving said
second RF data packet at said secondary stationary anchor (As) and
recording the time (s2) at which the second RF data packet was
received at the secondary stationary anchor(As); transmitting a
third RF data packet from said tag object (T) and recording the
time (t3) at which the third RF data packet was transmitted;
receiving said third RF data packet at said primary stationary
anchor (Am) and recording the time (m3) at which the third RF data
packet was received at the primary stationary anchor(Am); receiving
said third RF data packet at said secondary stationary anchor (As)
and recording the time (s3) at which the third RF data packet was
received at the secondary stationary anchor (As); communicating the
collected timing data between the primary stationary anchor (Am)
and the secondary stationary anchor (As); computing a first unknown
distance (dmt) between the tag object (T) and the primary
stationary anchor (Am) based on the collected timing data;
computing a second unknown distance (dst) between the tag object
(T) and the secondary stationary anchor (As) based on the timing
data, the first known distance (dms) and the first unknown distance
(dmt); and computing the location (xt, yt) of the tag object (T)
based on the first known distance (dms), first unknown distance
(dmt) and second unknown distance (dst).
14. The method for determining the location of a tag object (T)
according to claim 13 wherein the step of computing the first
unknown distance (dmt) is performed using the equation d mt = C ( t
2 - t 1 ) - ( m 2 - m 1 ) + ( m 3 - m 2 ) - ( t 3 - t 2 ) 4 .
##EQU00006##
15. The method for determining the location of a tag object (T)
according to claim 14 wherein the step of computing the second
unknown distance (dst) is performed using the equation d st = d ms
- C ( ( s 3 - s 1 ) ( t 3 - t 1 ) ( s 2 - s 1 ) + t 1 ) + C ( ( m 3
- m 1 ) ( t 3 - t 1 ) ( m 2 - m 1 ) + t 1 ) + d mt ##EQU00007##
16. The method for determining the location of a tag object (T)
according to claim 15 wherein the step of computing the location
(xt, yt) of the tag object (T) is performed using trigonometric
relationships.
17. The method for determining the location of a tag object
according to claim 13 wherein a plurality of secondary stationary
anchors are provided, each one of said plurality of secondary
stationary anchors being associated with a different known location
and the distance between each secondary stationary anchor and the
primary anchor is known; said steps of receiving said first, second
and third RF data packets at the secondary stationary anchor and
recording the times are performed at each of the plurality of
secondary stationary anchors; said step of computing the distance
between the tag object and the secondary stationary anchor is
performed for each of the plurality of secondary stationary
anchors; and said step of computing the location of the tag object
provides the location of the tag object in three dimensions (xt,
yt, zt).
18. The method for determining the location of a tag object
according to claim 13 wherein first and second secondary stationary
anchors are provided, said first secondary stationary anchor (As)
associated with said second known location (Xs, Ys, Zs) and said
second secondary stationary anchor (An) being associated with a
third known location (Xn, Yn, Zn) and the distance between each of
the first and second secondary stationary anchors and the primary
anchor is known; said steps of receiving said first, second and
third RF data packets at the secondary stationary anchor and
recording the times are performed at each of the first and second
secondary stationary anchors, wherein the first known distance
(dms) is the distance between the primary stationary anchor (Am)
and the first secondary stationary anchor (As) and a second known
distance (dmn) is the distance between the primary stationary
anchor (Am) and the second secondary anchor (An); said method
comprising the further steps of: computing a third unknown distance
(dnt) between the tag object (T) and the second secondary
stationary anchor (An) based on the collected timing data, the
second known distance (dmn) and the calculated first unknown
distance (dmt); and computing the location (xt, yt, zt) of the tag
object (T) based on the computed unknown first distance (dmt),
second unknown distance (dst) and third unknown distance (dnt).
19. The method for determining the location of a tag object (T)
according to claim 18 wherein the step of computing the third
unknown distance (dnt) is performed using the equation d nt = d mn
- C ( ( n 3 - n 1 ) ( t 3 - t 1 ) ( n 2 - n 1 ) + t 1 ) ) / ( + C (
( m 3 - m 1 ) ( t 3 - t 1 ) ( m 2 - m 1 ) + t 1 ) + d mt
##EQU00008##
20. The method for determining the location of a tag object (T)
according to claim 19 wherein the step of computing the location
(Xt, Yt, Zt) of the tag object (T) is performed using trigonometric
relationships.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to location of objects using
radio frequency (RF) transmissions.
BACKGROUND OF THE INVENTION
[0002] Existing systems that use RF transmissions to determine
distance between devices use a method described as Two Way Ranging
(TWR). In TWR the distance between RF devices is determined using a
series of at least three transmissions. Determining relative
position of multiple devices in 2D and 3D space using TWR requires
3.sup.N-1 (where N is the number of devices) transmissions. The
total number of transmissions for determining location with TWR
becomes cumbersome for electronic devices by consuming RF air time
and battery power.
[0003] To reduce time spent sending and receiving RF transmissions,
as well as reduce battery usage, a method is needed to determine
the distances between multiple devices using a single set of three
transmissions. Such a system provides a huge advantage over
traditional TWR systems that require 3.sup.N-1 transmissions.
SUMMARY OF THE INVENTION
[0004] A system of RF devices capable of sending and receiving
signals and accurately measuring transmit and receive times. Given
sufficient granularity of measured time the distances between
objects are determined mathematically.
[0005] In one embodiment of the invention the distances between
objects are used to determine the location of a mobile device with
respect to surveyed devices in a 2-dimensional (2D) space, using
only three RF transmissions between the devices.
[0006] In another embodiment of the invention the distances between
objects are used to determine the location of a mobile device with
respect to surveyed devices in 3-dimensional (3D) space, using only
three RF transmissions between the devices.
[0007] The invention accordingly comprises several steps, the
relation of one or more of those steps, the embodiment of the
construction of the apparatus' features, and the combinations of
the elements and arrangement of parts adapted to affect such steps.
All is exemplified in the following detailed disclosure, and the
scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a more complete understanding of the invention,
reference is made to the following description and accompanying
drawings, in which:
[0009] FIG. 1 is an example arrangement of RF capable nodes;
[0010] FIG. 2 is an example of a 2D capable RF node
arrangement;
[0011] FIG. 3 is a notional time delay representation of three RF
packets exchanged between two devices; and
[0012] FIG. 4 is a 3D pyramid depicting the distances associated
with a system used to obtain 3D position for a mobile node.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] In accordance with the first aspect of the invention, a
system for tracking a mobile object in 2D space includes an RF tag
object and system of anchor objects shown in FIG. 1. The tag object
[1] is mobile in the environment and is capable of transmitting and
receiving RF transmissions. The tag object [1] is also capable of
precise timing of RF reception and transmission. The system of
anchors consists of a first anchor object [2], capable of timing
transmission and reception of RF transmissions, and a plurality of
anchor objects [3] capable of timing reception of RF transmissions.
The first anchor object [2], and the plurality of anchor objects
[3] are located in known, or surveyed, positions in the
environment.
[0014] The arrangement in FIG. 2 shows an exemplary arrangement of
a preferred embodiment. In FIG. 2, one sees a tag object T [4] as
well as two anchor objects Am [5] and As [6]. In this arrangement a
series of three packets are exchanged between the tag T [4] and
anchor Am [5]. FIG. 3 shows a notional representation of the three
packet transmissions and timing. In FIG. 3, time t.sub.1 [7] is the
transmit time for the first packet transmitted by tag T [4] as
measured in that tags T [4] time base. Time m.sub.1 [8] is the
reception time for the first packet at the anchor Am [5] as
measured in the anchors Am [5] time base. The following two packets
have similar times m.sub.2 [9], t.sub.2 [10], t.sub.3 [11], and
m.sub.3 [12] associated with them and measured in the respective
devices time base. To produce a distance between the tag T [4] and
anchor Am [5] the packet timings are combined in equation (1),
where C is the speed of light and d.sub.mt is the output distance
between the tag T [4] and the anchor Am [5]:
d mt = C ( t 2 - t 1 ) - ( m 2 - m 1 ) + ( m 3 - m 2 ) - ( t 3 - t
2 ) 4 ( 1 ) ##EQU00001##
[0015] In the above equation the distance d.sub.mt is obtained
between the two devices. Since the anchors are in surveyed
locations the distance d.sub.ms between anchor Am [5] and As [6] is
also known. The three packets shown in FIG. 3 are also received at
anchor As [6] as measured in anchor As [6] time base. By listening,
or snooping, these transmissions it is possible to generate another
set of time stamps for the system reception of packet one at As [6]
(s.sub.1), packet two at As [6] (s.sub.2), and packet three at As
[6] (s.sub.3). These new timestamps are combined with d.sub.mt and
d.sub.ms in equation order to generate a distance between the
anchor As [6] and the tag T [4] (d.sub.st)
d st = d ms - C ( ( s 3 - s 1 ) ( t 3 - t 1 ) ( s 2 - s 1 ) + t 1 )
+ C ( ( m 3 - m 1 ) ( t 3 - t 1 ) ( m 2 - m 1 ) + t 1 ) + d mt ( 2
) ##EQU00002##
[0016] Given the three distances d.sub.mt, d.sub.ms, and d.sub.st
the location of the T [4] can be computed using standard
trignometric constructs as follows in equation (3):
.DELTA. x t = d mt cos ( .+-. .theta. ) .DELTA. y t = d mt sin (
.+-. .theta. ) .gamma. = arctan ( y s - y m x s - x m ) [ x t y t ]
= [ cos .gamma. - sin .gamma. sin .gamma. cos .gamma. ] [ .DELTA. x
t .DELTA. y t ] + [ x m y m ] ( 3 ) ##EQU00003##
[0017] Yet another implementation includes the addition of one or
more surveyed anchors in order to achieve a 3D position of the tag
with respect to the anchors. The arrangement in FIG. 4 shows an
exemplary arrangement of a plurality of anchors allowing for 3D
position determination of tag T [13]. In the arrangement shown in
FIG. 4 there is a mobile tag T [13] at an unknown location and
multiple anchors Am [14], As [15], and Ns [16] at known, or
surveyed, locations. Once again, the distances d.sub.mt and
d.sub.st can be determined using equations (1) and (2)
respectively. In order to locate the tag in 3D space it is also
necessary to determine the distance d.sub.nt between the anchor Ns
[16] and the tag T [13]. This can be done using the TWR Plus Snoop
equation (2) substituting values associated with anchor Ns [16].
The distance d.sub.mn between anchor Am [14] and Ns [16] is
substituted for d.sub.ms. As with the above system it is possible
to generate a set of time stamps (n.sub.1, n.sub.2, and n.sub.3)
for the reception of the three packets at Ns [16]. These values are
substituted for (s.sub.1, s.sub.2, and s.sub.3) respectively. The
resultant equation (4) is used to determine the distance
d.sub.nt.
d nt = d mn - C ( ( n 3 - n 1 ) ( t 3 - t 1 ) ( n 2 - n 1 ) + t 1 )
+ C ( ( m 3 - m 1 ) ( t 3 - t 1 ) ( m 2 - m 1 ) + t 1 ) + d mt ( 4
) ##EQU00004##
[0018] Given the distances between the anchors and the tag T [13]
d.sub.mt, d.sub.nt and d.sub.st, along with the known locations and
distances between the anchors it becomes possible to compute the
location of T [13] using standard trigonometric constructs as
follows in equation
.alpha. = arctan ( z n - z m y n - y m ) ##EQU00005## .beta. =
arctan ( z s - z m x s - x m ) ##EQU00005.2## .gamma. = arctan ( y
s - y m x s - x m ) [ x t y t z t ] = [ 1 0 0 0 cos .alpha. - sin
.alpha. 0 sin .alpha. cos .alpha. ] [ cos .beta. 0 sin .beta. 0 1 0
- sin .beta. 0 cos .beta. ] [ cos .gamma. - sin .gamma. 0 sin
.gamma. cos .gamma. 0 0 0 1 ] [ .DELTA. x t .DELTA. y t .DELTA. z t
] + [ x m y m z m ] ##EQU00005.3##
[0019] The substitutions made above in equation (4) can be made for
any number of anchors in the system allowing for position of the
tag T [13] to be determined with greater accuracy.
[0020] It will thus be seen that the objects set forth above, among
those made apparent from the preceding description, are efficiently
attained and, because certain changes may be made in carrying out
the above method and in the construction(s) set forth without
departing from the spirit and scope of the invention, it is
intended that all matter contained in the above description and
shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
[0021] It is also to be understood that the following claims are
intended to cover all of the generic and specific features of the
invention herein described and all statements of the scope of the
invention which, as a matter of language, might be said to fall
therebetween.
* * * * *