U.S. patent number RE45,505 [Application Number 13/974,255] was granted by the patent office on 2015-05-05 for localization of a mobile device in distributed antenna communications system.
This patent grant is currently assigned to ADC Telecommunications, Inc.. The grantee listed for this patent is ADC Telecommunications, Inc.. Invention is credited to Stefan Scheinert, Peter Walther.
United States Patent |
RE45,505 |
Scheinert , et al. |
May 5, 2015 |
Localization of a mobile device in distributed antenna
communications system
Abstract
The present invention provides a method and apparatus for
localization of a mobile device in a distributed antenna
communications system. In accordance with an embodiment of the
invention, a distributed antenna system includes a plurality of
distributed antennas that are communicatively coupled to a hub. A
mobile communications device to be located is communicatively
coupled to the hub via one or more of the antennas. The method for
locating the mobile device comprises: receiving a message at the
hub that identifies the mobile device to be located; discriminating
among communications signals received from each of the distributed
antennas using a channel and a spreading code to identify a signal
from the mobile device; identifying messages from the mobile device
to be located; and determining which of the antennas is closest to
the mobile device to be located by monitoring received signal
strength of the identified signal.
Inventors: |
Scheinert; Stefan (San Jose,
CA), Walther; Peter (Milpitas, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
ADC Telecommunications, Inc. |
Shakopee |
MN |
US |
|
|
Assignee: |
ADC Telecommunications, Inc.
(Berwyn, PA)
|
Family
ID: |
39774605 |
Appl.
No.: |
13/974,255 |
Filed: |
August 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
11728123 |
Mar 23, 2007 |
8005050 |
Aug 23, 2011 |
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Current U.S.
Class: |
370/335; 455/101;
370/328; 455/562.1; 370/320; 455/456.2 |
Current CPC
Class: |
H04W
64/003 (20130101); H04W 64/00 (20130101); G01S
5/02 (20130101) |
Current International
Class: |
H04B
7/216 (20060101) |
Field of
Search: |
;455/13.3,33.3,19,83,562.1,575.7 ;370/335,339,320,101,328 |
References Cited
[Referenced By]
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Apr 2004 |
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WO |
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|
Primary Examiner: Shaheed; Khalid
Attorney, Agent or Firm: Fogg & Powers LLC
Claims
What is claimed is:
1. A method for locating a mobile communications device in a
distributed antenna system in which plural distributed antennas are
communicatively coupled to a hub and in which the mobile device is
communicatively coupled to the hub via one or more of the antennas,
the method comprising: receiving at the hub communication signals
from the plural distributed antennas; combining the received
communication signals to produce a combined signal; forwarding the
combined signal to a base station, wherein the mobile device is
communicatively coupled to the base station via the hub; receiving
a message at the hub that identifies the mobile device to be
located; discriminating, at the hub, among communications signals
received from each of the distributed antennas using a channel and
a spreading code to identify a signal from the mobile device; and
determining which of the antennas is closest to the mobile device
to be located by monitoring received signal strength of the
identified signal.
2. The method according to claim 1, wherein the mobile device
communicates using a CDMA protocol for cellular communications.
3. The method according to claim 1, wherein the message identifies
the mobile device according to its channel and the spreading
code.
4. The method according to claim 1, further comprising sending a
notification of the location of the antenna determined to be
closest to the mobile device for facilitating locating the mobile
device.
5. The method according to claim 1, wherein a notification is sent
from an emitter associated with the antenna determined to be
closest via a wireless personal area network.
6. The method according to claim 1, wherein a notification is sent
from an emitter associated with the antenna determined to be
closest in the form of a human perceptible signal.
7. The method according to claim 1, wherein the notification is
sent via a wide area network.
8. The method according to claim 1, wherein the monitoring of
received signal strength of the identified signal is performed at
the hub.
9. The method according to claim 1, wherein the monitoring of
received signal strength of the identified signal is performed at
the antennas.
10. The method according to claim 1, wherein a plurality of base
stations are coupled to the hub and further comprising queuing the
message at the hub until a prior request to locate a mobile device
has been processed.
11. A distributed antenna system comprising: a base station
configured for communication with a telecommunications network; a
multi-port hub connected to the base station that receives
communication signals on a plurality of ports of the multi-port hub
from a plurality of distributed antennas and combines the received
communication signals for forwarding a combined signal to the base
station, .Iadd.wherein the multi-port hub is configured to receive
a message at the multi-port hub that identifies the mobile device
to be located, and .Iaddend.wherein the multi-port hub comprises: a
de-spreader that uses a spreading code to identify a signal from a
mobile communications device to be located; and a controller that
determines which of the antennas is closest to the mobile device to
be located by monitoring received signal strength of the identified
signal.
12. A method for locating a mobile device in a distributed antenna
system in which plural distributed antennas are communicatively
coupled to a hub and in which the mobile device is communicatively
coupled to the hub via one or more of the antennas, the method
comprising: receiving at the hub communication signals from the
plural distributed antennas; combining at the hub the received
communication signals to produce a combined signal; forwarding the
combined signal from the hub to a base station, wherein the mobile
device is communicatively coupled to the base station via the hub;
.[.receiving an indication at the hub that notifies the hub of
commencement of locating the mobile device;.]. .[.instructing.].
.Iadd.in connection with .Iaddend.the mobile device .[.to
modulate.]. .Iadd.modulating .Iaddend.its output power.[.;.].
.Iadd.for locating the mobile device:.Iaddend. identifying, at the
hub, a received signal from the mobile device having modulated
output power; and identifying a particular antenna unit among the
plurality having a highest received power level for the received
signal from the mobile device having modulated output power.
13. The method according to claim 12, wherein the mobile device
communicates using a CDMA protocol for cellular communications.
14. The method according to claim .[.12.]. .Iadd.36.Iaddend.,
wherein the indication is a message that identifies the mobile
device according to its frequency channel or according to its
frequency channel and timeslot.
15. The method according to claim 12, wherein the mobile device
communicates using a TDMA protocol for cellular communications.
16. The method according to claim 12, further comprising sending a
notification of the location of the antenna determined to be
closest to the mobile device for facilitating locating the mobile
device.
17. The method according to claim 12, wherein a notification is
sent from an emitter associated with the antenna determined to be
closest via a wireless personal area network.
18. The method according to claim 12, wherein a notification is
sent from an emitter associated with the antenna determined to be
closest in the form of a human perceptible signal.
19. The method according to claim .[.12.]. .Iadd.18.Iaddend.,
wherein the notification is sent via a wide area network.
20. The method according to claim 12, wherein the identifying the
received signal from the mobile device having modulated output
power is performed at the hub.
21. The method according to claim 12, wherein the identifying the
received signal from the mobile device having modulated output
power is performed at the antennas.
22. The method according to claim .[.12.]. .Iadd.36.Iaddend.,
wherein a plurality of base stations are coupled to the hub and
wherein the indication is set in a register until a prior request
to locate a mobile device has been processed.
23. A distributed antenna system comprising: a base station
configured for communication with a telecommunications network; and
a multi-port hub connected to the base station that receives
communication signals on a plurality of ports of the multi-port hub
from a plurality of distributed antennas and combines the received
communication signals for forwarding a combined signal to the base
station, wherein the multi-port hub determines which of the
antennas is closest to a mobile device to be located .[.by the base
station by instructing.]. .Iadd.in connection with .Iaddend.the
mobile device .[.to modulate.]. .Iadd.modulating .Iaddend.its
output power.[.,.]. .Iadd.by .Iaddend.the hub identifying a
received signal from the mobile device by its modulated output
power.[.,.]. and identifying a particular antenna unit among the
plurality having a highest received power level for received signal
from the mobile device by its modulated output power.
24. A method for locating a mobile communications device in a
distributed antenna system in which plural distributed antennas are
communicatively coupled to a hub and in which the mobile device is
communicatively coupled to the hub via one or more of the antennas,
the method comprising: receiving at the hub communication signals
from the plural distributed antennas; combining at the hub the
received communication signals to produce a combined signal;
forwarding the combined signal from the hub to a base station,
wherein the mobile device is communicatively coupled to the base
station via the hub; receiving a message at the hub that identifies
the mobile device to be located; identifying, at the hub, a
received signal from the mobile device in a frequency channel and
timeslot of the mobile device; and determining which of the
antennas is closest to the mobile device to be located by
monitoring received signal strength of the identified signal.
25. The method according to claim 24, wherein the mobile device
communicates using a TDMA protocol for cellular communications.
26. The method according to claim 24, wherein the message
identifies the mobile device according to its frequency channel and
timeslot.
27. The method according to claim 24, further comprising sending a
notification of the location of the antenna determined to be
closest to the mobile device for facilitating locating the mobile
device.
28. The method according to claim 24, wherein a notification is
sent from an emitter associated with the antenna determined to be
closest via a wireless personal area network.
29. The method according to claim 24, wherein a notification is
sent from an emitter associated with the antenna determined to be
closest in the form of a human perceptible signal.
30. The method according to claim .[.24.]. .Iadd.29.Iaddend.,
wherein the notification is sent via a wide area network.
31. The method according to claim 24, wherein the monitoring of
received signal strength of the identified signal is performed at
the hub.
32. The method according to claim 24, wherein the monitoring of
received signal strength of the identified signal is performed at
the antennas.
33. The method according to claim 24, wherein a plurality of base
stations are coupled to the hub and further comprising queuing the
message at the hub until a prior request to locate a mobile device
has been processed.
34. A distributed antenna system comprising: a base station
configured for communication with a telecommunications network; and
a multi-port hub connected to the base station that receives
communication signals on a plurality of ports of the multi-port hub
from a plurality of distributed antennas and combines the received
communication signals for forwarding a combined signal to the base
station, wherein the multi-port hub determines which of the
antennas is closest to a mobile device to be located by identifying
a received signal from the mobile device by its frequency channel
and timeslot, and identifying a particular antenna unit among the
plurality having a highest received power level for the received
signal from the mobile device.
.Iadd.35. The method of claim 1, further comprising: receiving a
message at the hub that identifies the mobile device to be
located..Iaddend.
.Iadd.36. The method of claim 12, further comprising: receiving an
indication at the hub that notifies the hub of commencement of
locating the mobile device; and instructing the mobile device
to-modulate its output power..Iaddend.
.Iadd.37. The method of claim 24, further comprising: receiving a
message at the hub that identifies the mobile device to be
located..Iaddend.
Description
.Iadd.This application is a reissue of application Ser. No.
11/728,123, filed Mar. 23, 2007, which issued as U.S. Pat. No.
8,005,050..Iaddend.
FIELD OF THE INVENTION
The present invention relates to the field of wireless
communications and, more particularly, to localization of mobile
devices in a distributed antenna communications system.
BACKGROUND OF THE INVENTION
A conventional distributed antenna system (DAS) provides indoor or
outdoor coverage for wireless communications. Transmitted power is
divided among several antennas in distributed locations so as to
provide a large coverage area using less transmitted power than
would be required by a single antenna system. The antennas of a
typical DAS are connected to a cellular base station and are used
for cellular mobile communications.
It can be desired to locate a mobile device within a DAS, for
example, for emergency purposes (e.g., 911 calls). However, because
the received signals from the distributed antennas are typically
combined in the uplink to the base station receiver, the base
station has no ability to determine which of the distributed
antennas is closest to the transmitting mobile device.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for
localization of a mobile device in a distributed antenna
communications system. In accordance with an embodiment of the
invention, a distributed antenna system includes a plurality of
distributed antennas that are communicatively coupled to a hub. A
mobile communications device to be located is communicatively
coupled to the hub via one or more of the antennas. The method for
locating the mobile device comprises: receiving a message at the
hub that identifies the mobile device to be located; discriminating
among communications signals received from each of the distributed
antennas using a channel and a spreading code to identify a signal
from the mobile device; and determining which of the antennas is
closest to the mobile device to be located by monitoring received
signal strength of the identified signal.
In accordance with an alternative embodiment of the method, the
method comprises: receiving an indication at the hub that notifies
the hub of commencement of locating the mobile device; instructing
the mobile device to modulate its output power; identifying a
received signal from the mobile device having modulated output
power; and identifying a particular antenna unit among the
plurality having a highest received power level from the mobile
device.
In accordance with an another alternative embodiment of the method,
the method comprises: receiving a message at the hub that
identifies the mobile device to be located; identifying a received
signal from the mobile device in a frequency channel and timeslot
of the mobile device; and determining which of the antennas is
closest to the mobile device to be located by monitoring received
signal strength of the identified signal
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is described with respect to particular
exemplary embodiments thereof and reference is accordingly made to
the drawings in which:
FIG. 1 illustrates a distributed antenna communications system in
accordance with an embodiment of the present invention;
FIG. 2 illustrates a method of locating a mobile device in a
distributed antenna communications system in accordance with an
embodiment of the present invention;
FIG. 3 illustrates a timing diagram showing modulated output power
of a mobile device being located in accordance with an embodiment
of the present invention;
FIG. 4 illustrates a distributed antenna communications system in
accordance with an alternative embodiment of the present
invention;
FIG. 5 illustrates an alternative method of locating a mobile
device in a distributed antenna communications system in accordance
with an embodiment of the present invention;
FIG. 6 illustrates distributed antenna units having location
transmitters in accordance with an embodiment of the present
invention;
FIG. 7 illustrates distributed antenna units having signal strength
measurement capability in accordance with an embodiment of the
present invention;
FIG. 8 illustrates a distributed antenna communications system
having multiple base stations in accordance with an embodiment of
the present invention;
FIG. 9 illustrates a timing diagram for responding to multiple
requests to locate mobile devices in accordance with an embodiment
of the present invention; and
FIG. 10 illustrates a distributed antenna communications system
having multiple base stations in accordance with an alternative
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a distributed antenna communications system 100
in accordance with an embodiment of the present invention. The
system 100 includes a communications hub 102, a base station 104, a
plurality of distributed antennas 106a-n coupled to ports of the
hub 102 and one or more mobile communications devices 108a-n that
are communicatively coupled to the hub 102 via the antennas 106a-n.
The base station 104 may be located at the site of a cellular
service provider and may be coupled to a telephone network via a
backhaul 110. The hub 102 may be located at the premises of a
telecommunications subscriber with the antennas 106a-n being
distributed throughout the premises. For example, the hub 102 may
be located within a building (e.g., in a utility room) with the
antennas distributed throughout the building so as to provide
indoor coverage areas for mobile devices 108a-n. The mobile devices
108a-n may be, for example, cell phones. While three mobile devices
108a-n and three antennas 106a-n are illustrated, it will be
apparent that more or fewer of either may be present. In an
embodiment, up to eight antennas 106a-n may be coupled to a single
hub 102. Additionally, one or more of the antennas 106a-n may be
located outdoors.
The system 100 preferably provides for two-way communications. For
the downlink, telecommunications signals are received by the base
station 104 from the telephone network and distributed to the
antennas 106a-n. To accomplish this, a transceiver 112 may receive
the downlink signal from the base station 104. The transceiver 112
then amplifies the downlink signal to an appropriate level for
forwarding to a distribution node 114. The distribution node 114
then repeats and distributes the signal to a plurality of
transceivers 116a-n such that each of the transceivers 116a-n
receives a copy of the downlink signal. The transceivers 116a-n
each transmits the signal received from the distribution node 114
via a corresponding one of the antennas 106a-n. The mobile devices
108a-n each pick up the downlink signal from one or more of the
antennas 106a-n.
For the uplink, signals from the mobile devices 108a-n are received
by the transceivers 116a-n via the antennas 106a-n. The signals are
then forwarded to the distribution node 114 which combines the
signals (e.g., by simple summation) into a combined signal. The
combined signal is transmitted to the base station 104 by the
transceiver 112. The base station 104 then forwards the combined
signal to the telephone network.
In an embodiment, the downlink signal from the base station 104 is
RF (Radio Frequency). For example, this signal is communicated via
a cable or via a wireless link between the transceiver 112 and the
base station 104. In this case, the transceiver 112 may
down-convert the downlink signal from RF to IF. This signal is then
distributed to the transceivers 116a-n in IF. The transceivers
116a-n up-convert the IF signal to RF (Radio Frequency) before
transmitting the signal to the mobile devices 108a-n. For the
uplink, the transceivers 116a-n down-convert RF signals received
from the mobile devices 108a-n to IF. These IF signals are then
processed and combined for delivery to the transceiver 112 in IF.
The transceiver 112 then up-converts the IF signal to RF for
delivery the base station 104
So that multiple mobile devices 108a-n may communicate via the
system 100 simultaneously, each communicates in a different
channel. For example, CDMA (Code-Division, Multiple Access)
protocols for cellular communication, such as UMTS (Universal
Mobile Telecommunications System), or TDMA (Time-Division,
Multiple-Access) protocols for cellular communication, such as GSM
(Global System for Mobile Communications) may be employed by the
system 100. Thus, for the downlink, the same signal including the
various channels is transmitted via each of the antennas 106a-n so
that it may be received by any of the mobile devices 108a-n without
regard to which of the antennas 106a-n is closest to a particular
one of the mobile devices. For the up-link, the signal from a
particular mobile device may be picked up by one or more antennas
106a-n. As shown in FIG. 1, the signal from device 108a is picked
up by antennas 106a and 106b, though the signal may be stronger at
one of the antennas than the other. As is also shown in FIG. 1, the
signal from device 108b is picked up only by antenna 106n. The
signal from device 108n is also picked up only by the antenna 106n.
All of the signals picked up by any of the antennas 106-n are
combined at node 114 and included in the combined signal received
at the base station 104.
Because the signals from the mobile devices 108a-n are combined,
the base station 104 is not able to determine which of the antennas
106a-n is picking up the signal from a particular mobile device
and, thus, the base station 104 cannot determine the location of
that mobile device. It may be desired, however, to locate a
particular mobile device within the system 100, for example, for
emergency purposes (e.g., 911 calls).
FIG. 2 illustrates a method 200 of locating a mobile device in a
distributed antenna communications system in accordance with an
embodiment of the present invention. The method 200 may be employed
within the system 100 of FIG. 1. In a step 202, localization is
initiated. For example, the base station 104 may receive an
emergency 911 call from one of the mobile units 108a or 108b. The
base station 104 may then initiate localization of the calling
mobile unit so as to assist emergency personnel to locate the
caller. This may be accomplished by the base station 104 sending a
message to the hub 102 which instructs elements of the hub 102 that
localization is being initiated. The message sent to the hub 102
may also identify the mobile device to be localized, though this is
not always necessary. If the mobile device is identified by the
message, the message may identify the mobile device by the
frequency channel (e.g. for UMTS) it is operating in or by its
frequency channel and timeslot (e.g. for GSM). As shown in FIG. 1,
a hub controller 118 may receive this message from the base station
104.
In addition, in step 202, the mobile device being localized is
instructed to modulate its output power so that its output power
changes over time. For example, the base station 104 may send a
message to the particular device instructing it to adjust its
output power to first level (e.g., 10 mW). Then, the base station
104 may send another message instructing the device to adjust its
output power to a second level (e.g., 50 mW). The base station 104
may send a series of such messages to the particular mobile device
being localized so that the level of its output power follows an
identifiable pattern.
FIG. 3 illustrates a timing diagram showing modulated output power
of a mobile device being located in accordance with an embodiment
of the present invention. As shown in FIG. 3, the mobile device
adjusts its output power to a first level L.sub.1 at a time t.sub.0
in response to a received instruction. Then, the mobile device
adjusts its output power to a second level L.sub.2 at a time
t.sub.1 in response to another received instruction. Later, the
mobile device adjusts it output power to the first level L.sub.1 at
time t.sub.2 in response to yet another received instruction. In
this manner, the output power level of the mobile device follows an
identifiable pattern. While FIG. 3 shows the level oscillating
between two levels at uniform time intervals, this is not
necessary. All that is needed for the output power to follow a
pattern which is distinct from that of any other mobile device
communicating within the system 100.
Returning to FIG. 2, in a step 204, one or more of the antennas
106a-n that receives the modulated signal are identified. This may
be accomplished by the hub 102 measuring the strength of the
different signals received from each of the distributed antennas
106a-n. As shown in FIG. 1, a signal strength meter 120 is coupled
to lines 122a-n from each of the transceivers 116a-n. The signal
strength meter may simultaneously monitor all of the lines 122a-n
or it may cycle through the lines 122a-n, measuring signal strength
on the lines one-at-a-time. Further, the signal strength meter 120
may be tuned to the appropriate channel identified by the base
station 104 for the mobile device to be located. In addition, for
TDMS protocols, measurement intervals may optionally be timed to
coincide with the timeslot being used by the mobile device. To
accomplish this, the base station 104 may provide framing reference
information to the controller 118. Alternatively, the signal
strength meter can measure the combined strength of a frequency
range that includes several channels without regard to
timeslot.
In response to the initiation message sent in step 202, the
controller 118 may then monitor the strength of the signals
measured by the meter 120 and identify which signal or signals
received from the distributed antennas 106a-n contains the distinct
power modulation pattern. If only one of the signals contains the
pattern, this indicates that the mobile device sending the pattern
is located in the vicinity of the one of the antennas 106a-n that
received that particular signal. Because the location of each of
the antennas 106a-n is known, the location of the mobile device is
determined from this information.
If more than one of the signals received from the distributed
antennas 106a-n contain the distinct power modulation pattern, the
controller 118 may further determine which of the distributed
antennas 106a-n receives the highest level of the distinct
modulation pattern in step 206. This indicates that the mobile
device sending the pattern is located closest to the one of the
antennas that received the strongest level of the particular
signal. Because the location of each of the antennas 106a-n is
known, the location of the mobile device is determined from this
information. Step 206 need not be performed if only one antenna
receives a signal from the mobile device whose location is to be
determined.
The method described above can be used to determine the location of
a mobile device using CDMA or TDMA protocols and does not require
the hub 102 to have knowledge of the particular frequency channel
or timeslot of the mobile device. In an alternative embodiment
applicable to TDMA protocols, such as GSM, the mobile device need
not modulate its output power to be localized. Rather, the
frequency channel and timeslot being used by the mobile device can
be used to uniquely identify the signal from the mobile device.
This is because it can be expected that no other device will be
operating in the same channel and timeslot at the same time. To
determine which of the antennas 106a-n is closest to the mobile
device, the signal strength from each of the antennas 106a-n is
measured at the frequency and the timeslot of the mobile device and
compared to determine which is strongest and, therefore, closest to
the mobile device. More particularly, in a first step, localization
is initiated by the base station 104 sending a message to the hub
102 which identifies the mobile device to be localized. The message
may identify the mobile device by its frequency channel and
timeslot. In a second step, the strength of the signal received
from each of the distributed antennas 106a-n is measured for the
frequency channel and timeslot of the mobile device being located.
This may be accomplished by tuning the signal strength meter 120 to
the frequency channel being used by the mobile device and by the
controller 118 timing measurement intervals so that they coincide
with the timeslot being used by that mobile device (using framing
reference information received from the base station 104). As
before, the signal strength meter 120 may simultaneously monitor
all of the lines 122a-n or it may cycle through the lines 122a-n,
measuring signal strength on the lines one-at-a-time. If a signal
is detected in the frequency channel and timeslot from only one of
the antennas 106a-n, this indicates that the mobile device is
located in the vicinity of that one of the antennas. Because the
location of each of the antennas 106a-n is known, the location of
the mobile device is determined from this information. If more than
one of the distributed antennas 106a-n picks up the signal in the
frequency channel and timeslot of the mobile device being located,
the controller 118 may further determine which of the distributed
antennas 106a-n receives the highest level in that frequency
channel and timeslot. This indicates that the mobile device is
located closest to the one of the antennas that received the
strongest level in the frequency channel and timeslot.
FIG. 4 illustrates a distributed antenna communications system 100'
in accordance with an alternative embodiment of the present
invention. This embodiment is applicable to CDMA protocols, such as
UMTS that use spread spectrum channel modulation schemes. The
system 100' of FIG. 4 may be identical to the system 100 of FIG. 1
with differences described below. Accordingly, like reference
numerals are used for corresponding elements of FIGS. 1 and 4. The
system 100' differs from the system 100 of FIG. 1 in that a
de-spreader 124 is provided. The de-spreader 124 uses spreading
codes to discriminate among channels included in the signals
received from the mobile devices 108a-n on lines 122a-n (via the
antennas 106a-n and transceivers 116a-n). This may be accomplished
by the de-spreader converting the IF signals to baseband and by
applying a spreading code. Thus, by using the spreading code of the
mobile device to be located, the de-spreader removes components of
the received signal that are contributed by other mobile devices
operating within the system 100'. The meter 120 and controller 118
monitor the levels corresponding to the identified channel and
compares those levels for each of the antennas 106a-n to determine
which of the antennas 106a-n is closest to the mobile device being
located.
FIG. 5 illustrates a method 500 of locating a mobile device in a
distributed antenna communications system in accordance with an
embodiment of the present invention. The method 500 may be employed
within the system 100' of FIG. 4. In a step 502, localization is
initiated. For example, the base station 104 may receive an
emergency 911 call from one of the mobile units 108a or 108b. The
base station 104 may then initiate localization of the calling
mobile unit so as to assist emergency personnel to locate the
caller. This may be accomplished by the base station 104 sending a
message to the hub 102 which identifies the mobile device to be
localized. The message may, for example, identify the mobile device
by its frequency channel and unique transmission spreading code.
The hub controller 118 may receive this message from the base
station 104.
In a step 504, one or more signals received by the hub 102 from the
mobile devices 108a-n are identified as originating from the mobile
device whose location is to be determined. This may be accomplished
by the de-spreader 124 using the spreading code to discriminate the
signal from the mobile device being located from the other signals
received from the transceivers 116a-n of the hub 102. The signal
strength meter 120 measures the level of the discriminated signal
from each of the antennas 106a-n. If the discriminated signal is
picked up by only one of the antennas, this indicates that the
mobile device is located in the vicinity of the one of the antennas
106a-n that picked up the signal. Because the location of each of
the antennas 106a-n is known, the location of the mobile device is
determined from this information.
If more than one of the distributed antennas 106a-n picked up the
discriminated signal from the mobile device, the controller 118 may
further determine which of the distributed antennas 106a-n receives
the highest level of the signal in step 506. To accomplish this,
the signal strength meter 120 and controller 118 may monitor and
compare the signal levels received from the antennas that are
picking up the signal to determine which has the highest level.
Because the location of each of the antennas 106a-n is known, the
location of the mobile device is determined from this information.
Step 506 need not be performed if only one antenna receives a
signal from the mobile device whose location is to be
determined.
Once the particular mobile device is located using any of the
localization methods described herein, additional steps may be
taken to send a notification of the location to personnel for
facilitating locating the mobile device and, thus, the caller. For
example, an e-mail may be automatically generated by the controller
118 and sent to an emergency call processing center via the base
station 104 and a wide area computer network (e.g. the Internet) so
that emergency personnel can be informed of the caller's location.
As another example, a message or signal may be sent by the
controller 118 to circuitry associated with the nearest antenna
which then activates an optical and/or acoustical signal which can
be perceived by emergency personnel or which sends a message which
can be perceived by equipment carried by emergency personnel.
FIG. 6 illustrates an embodiment in which each distributed antenna
106a-n is associated with an antenna unit 126a-n having a location
emitter 128a-n. Once the antenna closest to the mobile device being
located is identified by the controller 118 (FIGS. 1 and 4), the
controller 118 may send a signal to the antenna unit 126a-n
associated with that particular antenna 106a-n, instructing
activation of its location emitter 128a-n. The activation signal
may be sent via a wired connection (e.g. via the antenna unit's
connection to the hub) or via a wireless connection (e.g. sent
directly to the antenna unit).
The particular location emitter 128a-n which is determined to be
closest to the mobile device being located may then emit a human
perceptible signal, such as an optical signal (e.g. a flashing
light), or an audible signal (e.g. a beeping sound). This emitted
signal may then be used to facilitate personnel in locating that
particular antenna unit and, thus, the particular mobile device and
caller. Alternatively, the particular location emitter 128a-n may
send short range wireless message to equipment carried by personnel
attempting to locate the caller. For example, the location emitters
128a-n may operate in accordance with a wireless personal area
network (PAN) protocol such as Bluetooth or ZigBee. This message
may include location information which facilitates personnel in
locating the particular antenna unit and, thus, the particular
mobile device and caller. For example, the location information may
be in the form of a text message, such as "Go up the stairs to the
second floor and proceed down the hallway to the right" or "The
caller is located in the southeastern wing of the building."
In the embodiments described above, signal strength information is
obtained by measuring the signals at the hub 102. In an alternative
embodiment, the signal strength measurements may be performed at
the antennas. FIG. 7 illustrates distributed antenna units having
signal strength measurement capability in accordance with an
embodiment of the present invention. As shown in FIG. 7, each
antenna unit 126a-n is equipped with a corresponding signal
measurement device 130a-n. Each measurement device 130a-n may
include a controller, a signal strength meter, and, optionally, a
de-spreader which operate similarly to the hub controller 118,
meter 120 and de-spreader 124 described above in reference to FIGS.
1 and 4. More particularly, messages received by the hub controller
118 from the base station 104 may be forwarded to the controllers
of the measurement devices 130a-n. These messages notify the
measurement devices 130a-n of initiation of localization of a
mobile device and may also identify the mobile device to be
located. In response, each measurement device 130a-n takes signal
strength measurements (as described herein with respect to the
meter 120 of FIGS. 1 and 4) and reports the results to the hub
controller 118. In an embodiment, these signal strength
measurements may be performed in an identified channel and timeslot
using framing information or using a spreading code received from
the hub controller 118.
The hub controller 118 then uses the received results to determine
whether any of the antennas 106a-n are picking up the signal from
the mobile device to be located. If only one antenna 106a-n is
picking up the signal, this indicates that the mobile device is
located in the vicinity of the one of the antennas 106a-n that
picked up the signal. If more than one of the distributed antennas
106a-n picked up the signal from the mobile device, the controller
118 may further determine which of the distributed antennas 106a-n
receives the highest level of the signal by comparing the signal
levels reported by the corresponding antenna units 126a-n.
In the embodiments described above, a single base station 104 is
coupled to the hub 102. In other embodiments, two or more base
stations may be coupled to the hub 102. FIG. 8 illustrates a
distributed antenna communications system having multiple base
stations 104a-n in accordance with an embodiment of the present
invention. As shown in FIG. 8, each of the base stations 104a-n is
coupled to the transceiver 112 for uplink and downlink
communications with the mobile units 108a-n (FIGS. 1 and 4). In
addition, each of the base stations 104a-n is coupled to the
controller 118 via a corresponding one of communication links
132a-n and via a register 134. Each of the links 132a-n carries
bidirectional serial communications. Thus, each of the links 132a-n
may include a first signal line for communication from the
corresponding base unit 104a-n to the controller 118 and a second
signal line for communication from the controller 118 to the
corresponding base station 104a-n.
When any of the base stations 104a-n determines that a mobile
device is to be located (e.g. in response to receiving a 911 call),
that base station 104a-n raises its signal line to the controller
118. This sets a corresponding indicator bit in the register 134.
The set indicator bit indicates to the controller 118 that the
corresponding base station is ready to initiate localization of a
mobile device. If the controller 118 is not already responding to a
set indicator bit from another base station, the controller 118
responds to the base station by raising the corresponding signal
line to the base station. Upon receiving this response, the base
station instructs the mobile unit being located to modulate its
output power. The controller 118 then determines the location of
the mobile unit as described herein with reference to FIGS. 1 and
3. Once the mobile device has been located, the controller 118 may
clear (i.e. reset) the indicator bit in the register 134. The
controller 118 may then respond to any other set indicator bits in
the register 134. In this manner, the controller 118 may process
multiple requests to locate mobile devices in the order in which
they are received.
FIG. 9 illustrates a timing diagram for responding to multiple
requests to locate mobile devices in accordance with an embodiment
of the present invention. As shown in FIG. 9, after a first request
(Request.sub.1) is received by the controller 118 and no other
request is currently pending, the first request is processed by
localizing the mobile device corresponding to the first request.
Then, while the first request is still being processed, a second
request (Request.sub.2) is received. Localizing of the mobile
device corresponding to the second request is commenced after the
localizing of the mobile device corresponding to the first request
is completed.
FIG. 10 illustrates a distributed antenna communications system
having multiple base stations in accordance with an alternative
embodiment of the present invention. As shown in FIG. 10, each of
the plurality of base stations 104a-n is coupled to the transceiver
112 for uplink and downlink communications with the mobile units
108a-n (FIGS. 1 and 4). In addition, each of the base stations
104a-n is coupled to the controller 118 via a shared communication
bus 136. Thus, each of the base stations 104a-n may communicate
with the controller 118 via the bus 136.
When any of the base stations 104a-n determines that a mobile
device is to be located (e.g. in response to receiving a 911 call),
that base station 104a-n sends a message to the controller 118. The
message identifies the originating base station and notifies the
controller 118 that the base station is ready to commence
localization of a mobile device. The message may also identify the
mobile device to be located such as by its frequency channel and
timeslot or spreading code. If the controller 118 is not already
responding to such a request message from another base station (or
to a prior request from the same base station), the controller 118
responds to the base station with a response message which notifies
the base station that its request is ready to be processed. Upon
receiving this response, the base station may instruct the mobile
unit being located to modulate its output power (as described above
with reference to FIGS. 1 and 3). Alternatively, the controller 118
may localize the mobile device by performing signal strength
measurements for the identified frequency channel, frequency
channel and timeslot or by using an appropriate spreading code (as
described herein).
Once the mobile device has been located, the controller 118 may
then respond to any other request messages. In this manner, the
controller 118 may process multiple requests to locate mobile
devices in the order in which they are received. While the
embodiments of FIGS. 8 and 10 show three base stations 104a-n, it
will be apparent that the system may be implemented with one, two
or more than three base stations.
The foregoing detailed description of the present invention is
provided for the purposes of illustration and is not intended to be
exhaustive or to limit the invention to the embodiments disclosed.
Accordingly, the scope of the present invention is defined by the
appended claims.
* * * * *
References