U.S. patent application number 09/185765 was filed with the patent office on 2001-12-13 for method and arrangement for locating a mobile station.
Invention is credited to RANTALAINEN, TIMO, RUUTU, VILLE.
Application Number | 20010051526 09/185765 |
Document ID | / |
Family ID | 8549882 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051526 |
Kind Code |
A1 |
RUUTU, VILLE ; et
al. |
December 13, 2001 |
METHOD AND ARRANGEMENT FOR LOCATING A MOBILE STATION
Abstract
The invention relates to a method for locating a mobile station
(5) my means of radio signals between the mobile station (5) and
the mobile station network (1a, 2a, 3a, 4a) by forming separate
location channels in addition to the communication channels. The
location channels are, among others, the location access channel
and the location receipt channel. The access channel is used to
send a burst, which includes the identification of the mobile
station (5), such as the International Mobile Subscriber
Identification (IMSI). The location channels can be used in the
locating methods based on the angle of arrival, time difference and
transition time of the radio transmission, for example.
Inventors: |
RUUTU, VILLE; (HELSINKI,
FI) ; RANTALAINEN, TIMO; (HELSINKI, FI) |
Correspondence
Address: |
CLARENCE A GREEN
PERMAN & GREEN
425 POST ROAD
FAIRFIELD
CT
06430
|
Family ID: |
8549882 |
Appl. No.: |
09/185765 |
Filed: |
November 4, 1998 |
Current U.S.
Class: |
455/456.6 ;
455/450 |
Current CPC
Class: |
H04W 64/00 20130101 |
Class at
Publication: |
455/456 ;
455/435; 455/450 |
International
Class: |
H04Q 007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 1997 |
FI |
974153 |
Claims
1. A method for locating a mobile station by means of radio signals
between the mobile station and a mobile station network,
characterized in that at least one separate location channel is
formed between the mobile station and the mobile station network in
addition to other channels, to which location channel radio
communications related to location determination of the mobile
station is concentrated.
2. A method according to claim 1, characterized in that two
location channels are formed, the first of which is used for radio
communications from the mobile station to the network and the
second for radio communications from the network to the mobile
station.
3. A method according to claim 1 or 2, characterized in that a
burst is sent (6a, 6b) in the first or second location channel, and
properties, such as time of arrival and/or angle of arrival of the
burst are measured (7a, 7b) for the location determination (9a, 9b)
when the burst is received.
4. A method according to claim 3, characterized in that a
measurement (7a, 7b) of differences in the times of arrival of the
bursts is performed from an impulse response.
5. A method according to claim 3 or 4, characterized in that the
burst contains a mobile station identification (14).
6. A method according to claim 5, characterized in that the
identification (14) is an International Mobile Subscriber
Identification (IMSI).
7. A method according to any one of the preceding claims 1 to 6,
characterized in that the location channels are used in a locating
method based on an angle of arrival of a radio transmission.
8. A method according to any one of the preceding claims 1 to 6,
characterized in that the location channels are used in a locating
method based on differences in times of arrival of a radio
transmission.
9. A method according to any one of the preceding claims 1 to 6,
characterized in that the location channels are used in a locating
method based on a transition time of a radio transmission.
10. A mobile station, which comprises a locating device for
locating the mobile station by means of radio signals between the
mobile station (5) and a mobile station network, characterized in
that the locating device comprises a processor (21) for performing
locating routines, a memory (22) for saving the locating routines
and measurement results, and a transmitter (25) for transmitting a
first burst.
11. A mobile station according to claim 10, characterized in that
the locating device also comprises a receiver for receiving an
acknowledgement signal.
12. A mobile station according to claim 11, characterized in that a
receiver is used to receive a second burst, and that the locating
device also comprises a clock (23) for determining time of arrival
of the second burst, and that the locating routines include at
least determining a time difference between the bursts.
13. A base station for locating a mobile station (5) by means of
radio signals between the mobile station (5) and a mobile station
network, characterized in that it comprises a processor (27) for
performing locating routines, a memory (28) for saving the locating
routines and measurement results, a clock (29) for determining time
of arrival of a first burst, an antenna (30) for transforming the
first burst into an electric signal, and a receiver (31) for
receiving the first burst from the antenna.
14. A base station according to claim 13, characterized in that it
also comprises a transmitter (32) and an antenna (33) for
transmitting a second burst and that the locating routines include
at least determining a time of arrival of a burst.
15. A base station according to claim 13, characterized in that the
antenna (30) is a direction finding antenna for determining a
direction of arrival of the first burst, and that the locating
routines include at least determining the direction of the first
burst.
16. An arrangement for locating a mobile station (5) by means of
radio signals between a mobile station (5) and the mobile station
network, characterized in that it consists of the mobile station
(5), which comprises a processor (21) for performing locating
routines, a memory (22) for saving the locating routines and
measurement results, a transmitter (25) for transmitting a first
burst; and of at least two or three base stations depending on the
locating method, which comprise a processor (27) for performing
locating routines, a memory (28) for saving the locating routines
and measurement results, a clock (29) for determining time of
arrival of the first burst, an antenna (30) for transforming the
first burst into an electric signal, and a receiver (31) for
receiving the first burst from the antenna.
17. An arrangement according to claim 16, characterized in that the
mobile station also comprises a receiver (24) for receiving an
acknowledgement signal.
18. An arrangement according to claim 17, characterized in that the
receiver (24) of the mobile station is used to receive a second
burst, and that the mobile station also comprises a clock (23) for
determining a time of arrival of the second burst, and that the
locating routines include at least determining a time difference
between the bursts and that the base station also comprises a
transmitter (32) and an antenna (33) for transmitting the second
burst.
19. A location service centre for locating a mobile station (5) by
means of radio signals between the mobile station (5) and a mobile
station network, characterized in that it comprises a processor
(35) for performing locating routines, which include at least
determining location of the mobile station by means of burst
measurement results received from base stations, a memory (36) for
saving the locating routines and measurement results, a receiver
(37) for receiving the measurement results from the base stations
in a signalling channel, and a transmitter (38) for sending
commands to the base stations in the signalling channel.
Description
[0001] The invention relates to the method defined in the preamble
of claim 1 for locating a mobile station. The invention also
relates to a mobile station defined in the preamble of claim 10 for
locating a mobile station. In addition, the invention relates to a
base station defined in the preamble of claim 13 for locating a
mobile station. Furthermore, the invention relates to the
arrangement defined in the preamble of claim 16 for locating a
mobile station. In addition to that, the invention relates to the
location service centre defined in the preamble of claim 19 for
locating a mobile station.
[0002] Methods for determining the position of a mobile station are
known previously, which methods are based on transferring radio
signals between a mobile station and a mobile station network, and
the measurement and signal processing thereof. Usually the mobile
station network has a central controlling device, which controls
the location process and the receivers participating in it. In
these methods, location is usually based on two basic
arrangements:
[0003] 1. The mobile station operates as a receiver, and there are
several transmitters in the mobile station network. The smallest
number of transmitters depends on the location method. This
arrangement is known as the mobile station based setting.
[0004] 2. The mobile station operates as a transmitter, and there
are several receivers in the mobile station network. The smallest
number of receivers depends on the location method. This
arrangement is known as the network based setting.
[0005] One such location method is a method based on the
measurement of the angle of arrival (AOA) of the radio
transmission, which uses direction finding (DF), in which method
the mobile station transmits a radio signal to at least two base
stations, which examine the angle of arrival of the signal and
transmit the measurement results to the location service centre.
Because of the inaccuracy of the AOA measurement, instead of
defining an accurate angle, a sector from which the signal comes
from is defined in this method. The mobile station is situated at
the intersection of the arrival sectors. Two sectors are sufficient
for the determination, but if there are more, the measurement
becomes more accurate. The locations of the base stations are used
as the basis of comparison for locating the mobile station. Another
such location method is a method based on the transition time of a
radio transmission. In this method, at least three base stations
send a radio signal to a mobile station on the basis of the
network, and the mobile station examines the observed time
difference (OTD) of arrival of the signals, and, based on the
mobile station, the mobile station transmits a radio signal to at
least three base transceiver stations (BTS), which examine the
observed time difference of arrival (TDOA) of the signals. In the
location service centre (LSC), the arrival times are used to form
at least two hyperbolas, at the intersection of which the mobile
station is located. Because of the inaccuracy of the arrival times,
the hyperbolas are expanded as wide bands, the intersection of
which limits an area and not a certain point. The location of the
hyperbolas is determined in relation to the location of the base
stations.
[0006] A third such locating method is based on the radio
transmission delay, which method uses the transition time between
the mobile station and the base station. In this method, the mobile
station and the base station exchange radio signals, the times of
arrival (TOA) of which are examined. The transition time must be
determined between the mobile station and at least three base
stations. In mobile station systems based on Time Division Multiple
Access (TDMA), it is necessary to know the transition time of the
radio transmission between the mobile station and the base station
in order to avoid the overlapping of the time intervals. On the
basis of the transition time, the distance of the mobile station
from the base station is determined as a location circle in which
the radius corresponds to distance and in which the central point
is at the base station. There must be at least three of the
location circles. The intersection of these circles is the location
of the mobile station. One such TOA location method is the Timing
Advance (TA) method, which is planned to be used in the GSM system.
In the GSM system, as is known, the to-and-from transmission time
between the mobile station and the base station is measured. From
this it is possible to calculate the distance between the mobile
station and the base station.
[0007] There is also a system known as Timing Advance, in which the
mobile station is forced to carry out consecutive connection
switchings to the neighbouring base stations for determining its
location.
[0008] Other such location methods are the Satellite-based Global
Positioning System (GPS), using the identity of the serving cell
and measuring the intensity of the signal received.
[0009] The known network-based methods have the drawback that heavy
signalling is needed between the base stations and the service
centre that carries out the location determination. In this method,
the mobile station operates as a transmitter, and the network
provides the receivers.
[0010] A further problem in the known network-based methods is the
required coordination in the network. For example, the location
service centre indicates to the receiving base stations which
channels they should listen to according to the mobile station to
be located, or in accordance with the basic settings of the base
station, certain predetermined channels are listened to. The
channels are indicated by means of time and frequency information,
for example. In addition, the measurement results are transferred
in the network, which adds to the load on the network.
[0011] Furthermore, some known methods based on transition time,
such as TA, have the problem that a two-way connection must be
established from the mobile station to many base stations before
the location can be determined.
[0012] In addition, the known system has the drawback that the
location process is slow.
[0013] The purpose of the invention is to provide a new method for
locating a mobile station and to eliminate the above mentioned
drawbacks.
[0014] The method according to the invention is characterized in
what is set forth in claim 1. The mobile station according to the
invention is characterized in what is set forth in claim 10. The
base station according to the invention is characterized in what is
set forth in claim 13. The arrangement according to the invention
is characterized in what is set forth in claim 16. The location
service centre according to the invention is characterized in what
is set forth in claim 19. Preferred embodiments of the invention
are presented in the dependent claims.
[0015] The invention relates to a method for determining the
location of a mobile station by means of radio signals between the
mobile station and the mobile station network. In the manner
according to the invention, at least one separate location channel
is formed between the mobile station and the network in addition to
other channels, to which location channel the radio communications
related to the measurement of the location of the mobile station is
concentrated. All other radio communication related to the location
of the mobile station is also preferably concentrated to this
channel. Other channels here mean all the known channels used
between the mobile station network and the mobile station, such as
the channels for ordinary communications and signalling.
[0016] In one application of the method, two location channels are
formed, of which the first location channel is used for radio
communications from the mobile station to the network and the
second for radio communications from the network to the mobile
station. These are called the Location Access CHannel (LACH) and
the Location Receipt CHannel (LRCH). The location access channel
resembles the Random Access CHannel (RACH) in the uplink direction
of the GSM system, and the location receipt channel resembles the
Access Grant CHannel (AGCH) in the downlink direction. Uplink means
communications from the mobile station to the network and downlink
means communications from the network to the mobile station. In the
location access channel, it is possible to send a location signal
from the mobile station to the mobile station network at any time
without coordination, because the mobile station knows the
frequency and interval used in the location access channel, e.g. in
the GSM system, and the base stations constantly monitor the
channel for location signals. For example, in the Broadcast Control
CHannel (BCCH) of the GSM system, a cell can inform the mobile
stations of the location access channel by sending information of
the frequency and time interval.
[0017] In one embodiment of the method, the measurement of the
differences between the times of arrival is carried out from the
impulse response.
[0018] In one application of the method, the first signal burst
contains the identification information of the mobile station.
[0019] In another application of the method, the identification
information is the International Mobile Subscriber Identification
(IMSI).
[0020] The invention also relates to a mobile station, which
comprises a locating device for determining the location by means
of radio signals between the mobile station and the mobile station
network. According to the invention, the locating device
comprises
[0021] a processor for carrying out the locating routines,
[0022] memory for saving the locating routines and the measurement
results, and
[0023] a transmitter for transmitting the first signal burst.
[0024] In one embodiment of the mobile station, the locating device
also comprises a receiver for receiving the acknowledgement
signal.
[0025] In one embodiment of the mobile station, the receiver is
used for receiving the second signal burst, and the locating device
also comprises a clock for determining the time of arrival of the
burst, and the locating routines include at least determining the
time difference between the bursts. Here signal bursts mean bursts
received from different base stations.
[0026] The invention also relates to a base station for locating
the mobile station by radio signals between the mobile station and
the mobile station network. According to the invention, it
comprises
[0027] a processor for carrying out the locating routines,
[0028] a memory for saving the locating routines and the
measurement results,
[0029] a clock for determining the time of arrival of the first
burst,
[0030] an antenna for transforming the first burst into an electric
signal, and
[0031] a receiver for receiving the first burst from the
antenna.
[0032] In one embodiment of the base station, it also includes a
transmitter and an antenna for transmitting a second burst, and the
locating routines include at least the determination of the time of
arrival of the burst.
[0033] In another embodiment of the base station, the antenna is a
direction finding antenna for determining the direction of arrival
of the first signal burst, and the locating routines include at
least the direction finding of the signal bursts.
[0034] The invention also relates to an arrangement for locating a
mobile station by means of radio signals between the mobile station
and the mobile station network. According to the invention, the
arrangement consists of a mobile station, which comprises
[0035] a processor for carrying out the locating routines,
[0036] a memory for saving the locating routines and measurement
results, and
[0037] a transmitter for transmitting the first signal burst;
[0038] and of at least two or three base stations depending on the
locating method, which comprise
[0039] a processor for carrying out the locating routines,
[0040] a memory for saving the locating routines and measurement
results,
[0041] a clock for determining the time of arrival of the first
signal burst,
[0042] an antenna for transforming the first signal burst into an
electric signal,
[0043] a receiver for receiving the first signal burst from the
antenna.
[0044] In one application of the arrangement, the mobile station
also comprises a receiver for receiving the acknowledgement
signal.
[0045] In another application of the arrangement, the receiver of
the mobile station is used for receiving a second signal burst, and
the mobile station also comprises a clock for determining the time
of arrival of the second signal burst, and the locating routines of
the processor of the mobile station include at least the
determination of the time difference between the bursts, and the
base stations also comprise a transmitter and an antenna for
transmitting a second signal burst.
[0046] The invention also relates to a location service centre for
locating the mobile station by means of radio signals between the
mobile station and the mobile station network. In practice, the
Location Service Center (LSC) is only a computer which performs the
calculation routines, maintains data bases, such as base station
coordinates, starts the location determination and gives location
information to the applications. According to the invention it
comprises
[0047] a processor for carrying out the locating routines, which
include at least determining the location of the mobile station on
the basis of burst measurement results received from the base
stations,
[0048] a memory for saving the locating routines and measurement
results,
[0049] a receiver for receiving measurement results in the
signalling channel from base stations, and
[0050] a transmitter for transmitting commands in the signalling
channel to the base stations.
[0051] The invention has the advantage that by means of a separate
location channel, the need for signalling in the network between
the location service centre and the base stations is reduced. The
first signal burst of the location access channel sent by the
mobile station is a kind of command, to which the receivers of the
base stations of the mobile station network can react for measuring
the necessary location information, for transmitting the
measurement results to the location service centre and for sending
a possible acknowledgement to the mobile station.
[0052] Two location channels provide the advantage of
bi-directional interaction during the location process. With only
one location channel available, it is only possible to transmit the
first signal burst from the mobile station to the network with
predetermined repetition for locating the mobile station.
[0053] A further advantage of the invention is the fact that with a
separate location channel, it is possible to transmit long signal
bursts, which contain the mobile station identification.
[0054] In addition, the invention has the advantage that when an
emergency call begins, locating can be carried out quickly and
automatically.
[0055] In the following, the invention will be described in more
detail with reference to the accompanying drawing, in which
[0056] FIG. 1 shows the components of an arrangement according to
the invention,
[0057] FIG. 2 shows the essential steps of the mobile station
locating method in a flow chart,
[0058] FIG. 3 shows the alternative contents of the first signal
burst of a location access channel,
[0059] FIG. 4 shows the contents of the second signal burst of a
location receipt channel,
[0060] FIG. 5 shows an impulse response in coordinates,
[0061] FIG. 6 shows the components of a mobile station according to
the invention in a block diagram,
[0062] FIG. 7 shows the components of a base station according to
the invention in a block diagram, and
[0063] FIG. 8 shows the components of a location service centre
according to the invention in a block diagram.
[0064] FIG. 1a shows some components of the arrangement according
to the invention that are essential for the invention in the
locating method based on the angle of arrival of the radio
transmission. The mobile station 5 is situated in the service area
of the base stations 1a, 2a, 3a. The base stations 1a, 2a, 3a have
been switched in the mobile station network to the location service
centre 4a. The mobile station 5 and the base stations 1a, 2a, 3a
preferably exchange signal bursts for locating the mobile station.
The base stations 1a, 2a, 3a include direction finding antennas, by
which the first signal bursts sent by the mobile station 5 are
determined as coming from the directions 1aa, 2aa, 3aa. Due to the
inaccuracy of the determination, the directions 1aa, 2aa, 3aa are
narrow sectors at the intersection of which the mobile station 5 is
situated. The location service centre 4a has the suitable
calculation routines for this locating method and information of
the locations of the base stations 1a, 2a, 3a.
[0065] FIG. 1b shows components of the arrangement according to the
invention which are essential for the invention in the locating
method based on the time difference of arrival of the radio
transmission. The mobile station 5 is situated in the service area
of the base stations 1b, 2b, 3b. The base stations 1b, 2b, 3b are
connected to the location determination service centre 4b in the
mobile station network. The mobile station 5 and the base stations
1b, 2b, 3b preferably exchange signal bursts for the location. The
base stations 1b, 2b, 3b comprise normal reception antennas by
which the first signal bursts sent by the mobile station 5 are
received. From the observed time differences between the first
signal bursts received by the base stations 1b, 3b from the mobile
station 5, a hyperbola 1-3bb is defined, which hyperbola passes
through the mobile station 5 and between the base stations 1b, 3b.
From the observed time differences between the first signal bursts
received by the base stations 2b, 3b from the mobile station 5, a
hyperbola 2-3bb is defined, which hyperbola passes through the
mobile station 5 and between the base stations 2b, 3b. Due to the
inaccuracy of the determination, the hyperbolas 1-3bb, 2-3bb are
strip-like curves at the intersection of which the mobile station 5
is situated. The location service centre 4b has the suitable
calculation routines for this locating method and information of
the locations of the base stations 1b, 2b, 3b.
[0066] FIG. 1c shows components of the arrangement according to the
invention which are essential for the invention in the locating
method based on the times of arrival of the radio transmission. The
mobile station 5 is situated in the service area of the base
stations 1c, 2c, 3c. The base stations 1c, 2c, 3c have been
connected to the location service centre 4c in the mobile station
network. The mobile station 5 and the base stations 1c, 2c, 3c
preferably exchange signal bursts for the location. The base
stations 1c, 2c, 3c include normal reception antennas by which the
first signal bursts sent by the mobile station 5 are received. From
the observed times of arrival of the first signal bursts received
by the base stations 1c, 2c, 3c from the mobile station 5, the
radii of the circles 1cc, 2cc, 3cc are defined. The mobile station
5 is situated at the intersection of these circles 1cc, 2cc, 3cc.
Due to the inaccuracy of the determination of the times of arrival,
the circles 1cc, 2cc, 3cc are widened at their circumferences. The
mobile station 5 is situated at the intersection of these circles.
The location service centre 4c has the suitable calculation
routines for this locating method and information of the location
of the base stations 1c, 2c, 3c.
[0067] In the GSM system, e.g., the locating based on the times of
arrival of the radio transmission as described above can be
performed by using the Timing Advance measurement. In this
measurement, the mobile station times its transmission separately
to correspond to the timing of each neighbouring base station. Thus
the mobile station listens to the bursts of the base station in
question and adjusts the timing of the transmission accordingly.
The first bursts sent by the mobile station are received at the
base station in question, and their timing is late twice as much as
the propagation delay. The distance between the mobile station and
the base station can be defined from this. The mobile station
examines different neighbouring base stations in turn, or at least
the serving base station and two neighbouring base stations.
[0068] FIG. 2a shows the essential steps of operation of the mobile
station locating method according to the invention as a flow chart.
At first, the first signal burst 6a is sent from the mobile station
in the location access channel to the receiver of the base station
of the mobile station network. The next step, 7a, is to measure at
the base station from the first signal burst the information needed
in the locating method in use and to receive the identification of
the mobile station. According to different locating methods (cf.
FIGS. 1a, 1b, 1c), either the angle of arrival or time of arrival
of the first signal burst is measured. In the next step 8a, this
information is transferred to the location service centre, in which
the mobile station is located, 9a, using that information. If the
locating 9a did not succeed, 10a, the process returns to the
beginning to wait for the next first signal burst 6a from the
mobile station. When the location 9a has succeeded, 10a, the next
step 11a is to send from the base station to the mobile station a
second acknowledgement burst in the location receipt channel and to
end the process.
[0069] FIG. 2b shows the essential steps of operation of an
alternative mobile station locating method in a flow chart. In the
first step 6b, a first signal burst is sent from the mobile station
in the location access channel to the receiver of the base station
of the mobile station network. In the next step 7b, information
according to the locating method in use is measured from the first
signal burst in the base station and the mobile station
identification is received. According to different locating methods
(cf. FIGS. 1a, 1b, 1c), either the angle of arrival or the time of
arrival of the first signal burst is measured. If the measurement
of the signal burst at step 7b did not succeed, 10b, the process
returns to the beginning to wait for the next first signal burst 6b
from the mobile station. When the measurement of the signal burst
7b has succeeded, 10b, the measurement results are transferred at
step 8b to the location service centre, and a second
acknowledgement burst is sent at step 11b from the base station to
the mobile station in the location receipt channel, and the mobile
station is located, 9b.
[0070] FIG. 3 shows the alternative contents of the first signal
burst of a location access channel. The first signal burst of the
location access channel is sent from the mobile station to the
mobile station network. The first signal burst starts at 12 and
ends at 15 with tail bits (TB). After the first tail bits 12, there
follows a training sequence 13, followed by an information part 14.
As is known, the training sequence 13 contains a series of bits,
which can be identified in the reception as the training sequence.
The information part 14 contains alternatively one of the following
identifications:
[0071] a unique mobile station identification 14a, such as the
International Mobile Subscriber Identification (IMSI) or a
Temporary Mobile Subscriber Identification (TMSI),
[0072] a unique mobile station identification and the target base
station identification, such as the Cell Identity (CI) or the
channel number and the Base Station Identity Code (BSIC) 14b,
[0073] a temporary mobile station identification 14c,
[0074] a temporary mobile station identification and the target
base station identification 14d,
[0075] a unique mobile station identification and the cause and/or
priority 14e of the location request,
[0076] a unique mobile station identification and the target base
station identification and the cause and/or priority 14f of the
location determination request,
[0077] a temporary mobile station identification and the cause
and/or priority 14g of the location determination request, and
[0078] a temporary mobile station identification and the target
base station identification and the cause and/or priority 14h of
the location determination request.
[0079] FIG. 4 shows the contents of the second signal burst of a
location determination receipt channel. The second signal burst of
the receipt channel is sent from the mobile station network to the
mobile station. The second signal burst starts 16 and ends 19 with
Tail Bits (TB). The first tail bits 16 are followed by a Training
sequence 17, followed by an information sequence 18. The
information sequence 18 contains the identification of the
transmitting base station and the identification of the target
mobile station 18a. The base station identification consists, e.g.,
of the cell identification or channel number and the base station
identification code. The identification of the target mobile
station is determined by how the mobile station has been identified
in the access channel.
[0080] FIG. 5 shows an impulse response of the signal burst in
coordinates. The impulse response is determined either by the
mobile station or the base station. The time difference between the
signal burst to be transferred in the location channel and the
reference, such as the training sequence of the signal burst, is
determined from the impulse response. These training sequences are
identical. When the time difference has been estimated correctly,
the training sequences correlate well in the impulse response. The
horizontal axis of the figure represents time and the vertical axis
represents the normalized correlation, which receives values from
0.0 to 1.0. The response columns 1-9 and 22-33 show ignorably
little correlation to the training sequence, from which it is
concluded that the time difference is not in an area that
corresponds to these columns. The response columns 10-21 show an
observable correlation to the training sequence, from which it is
concluded that the time difference is in an area that corresponds
to these columns. The response columns 15-17 show a full or nearly
full correlation. Thus the time difference is about 15-17 time
units, such as samples or bits. A dashed line in the coordinates
represents the Th1 threshold level, which the highest response
column must preferably exceed to be acceptable. A dashed line is
also drawn in the coordinates to represent the Th2 threshold level,
below which the surrounding response columns must preferably be so
that the highest response column would be acceptable.
[0081] FIG. 6 shows components of a mobile station according to the
invention which are essential for the invention in a block diagram.
The mobile station comprises a processor 21 for performing the
locating routines. The locating routines include at least the
reception of second signal bursts sent from the base station to the
mobile station and a possible registration or determination of
timing advance on the basis of the correlation of the training
sequences. The mobile station also comprises a memory 22 for saving
the locating routines, such as the calculation formulas of the
impulse response and the measurement results, such as the values of
the impulse responses. In order to find out the exact timing of
second signal bursts, the mobile station also comprises a clock 23
and a receiver 24 for receiving the second signal bursts.
[0082] In addition, a transmitter 25 is used for sending the first
signal bursts from the mobile station to the base station. The
different units of the mobile station are connected through the
connection bus 26.
[0083] FIG. 7 shows components of a base station according to the
invention that are essential for the invention as a block diagram.
The base station comprises a processor 27 for performing the
locating routines, such as the calculation formulas of the impulse
response, a memory 28 for saving the locating routines and
measurement results, such as the values of the impulse responses, a
clock 29 for determining the time of arrival of the first signal
bursts to be sent from the mobile station to the base station, an
ordinary antenna and/or a direction finding antenna 30 for
transforming the first signal bursts into electric form and
alternatively also for determining the direction of arrival, a
receiver 31 for receiving the first signal bursts from the
direction finding antenna and a transmitter 32 and an antenna 33
for transmitting second signal bursts from the base station to the
mobile station. When the locating method based on time of arrival
is used, only an ordinary receiving antenna 30 is needed. When the
locating method based on direction finding is used, a direction
finding antenna 30 is needed for determining the direction of the
received transmission. When the methods are combined, both antennas
30 are possibly needed. The different units of the base station are
connected via the connection bus 34. For the sake of clarity,
devices that are used for connecting to the signalling channels of
the location service centre and that connect the base station
preferably by wire to the service centre, have been omitted from
the figure.
[0084] FIG. 8 shows components of a location service centre (LSC)
according to the invention as a block diagram. In practice, the
location service centre is a computer, which at least performs the
calculation routines, maintains data bases, such as the coordinates
of base stations, starts the locating process and gives location
information to applications. The service centre comprises a
processor 35 for locating the mobile station by means of the
information received from the base stations, a memory 36 for saving
the location determination routines, such as calculation formulas,
and the measurement results, such as the calculated time
differences of the signal bursts, a receiver 37 for receiving
measurement data from the base stations, and a transmitter 38 for
requesting measurement data from the base stations. The receiver 37
and the transmitter 38 are in this case preferably devices used for
switching the signalling channels, which devices connect the
service centre preferably by wire to the base stations and possibly
also to the mobile stations. The different units of the service
centre are switched to one another via a connection bus 39.
[0085] Locating in a manner according to the invention is examined
by way of example. The location process is started on the
initiative of the mobile station user or the mobile station
network. The user selects an operation that starts the location
from the menu of the mobile station, or a request to start the
location is sent from the mobile station network. On the basis of
an emergency call, e.g., the location is started automatically.
When the location is started, the mobile station receives as
normally the timing of the neighbouring base stations in
synchronization bursts, and normal neighbouring cell measurements
are performed by the mobile station.
[0086] In the location access channel, the first signal burst is
sent 6 from the mobile station to one or more base stations. The
mobile station and the base stations do not need to be synchronized
to one another. However, when required, the transmission from the
mobile station is performed in a manner required by the frame
structure of the receiving base station, which is important
particularly in a locating method based on transition time. The
first signal burst contains the mobile station identification 14,
such as the international mobile subscriber identification, which
connects the signal logically with a certain mobile station. One
prior art random access burst has eight bits, three of which are
allocated to the access cause and five to the random separator
which identifies different mobile stations. The identification
according to the invention is preferably also eight bits long. Many
base stations share the first signal burst of the same channel or
different channels are used for different base stations. If
different channels are used, the first signal burst is sent
separately to each base station participating in the location
process. Different locating signals can be sent if many different
location access channels are used.
[0087] When needed, the local channel configuration is notified to
the mobile station from the serving cell. The base stations send 8
the identification code contained by the signal burst, their own
identification code and the measurement results related to the
location to the location service centre. In the service centre, the
information received from various base stations are combined 9 and
the location of the mobile station is calculated.
[0088] According to the invention, particularly when based on the
angle of arrival of the radio transmission, there must be at least
two of the base stations that receive the radio transmission. These
base stations 1a, 2a, 3a have direction finding antennas, by which
the identification 14 of the mobile station is received and the
direction of arrival 1aa, 2aa, 3aa is determined 7. This
information is sent 8 to the location service centre 4a, in which,
by processing the information received and the location coordinates
of the base stations 1a, 2a, 3a, the location of the mobile station
5 is calculated in a manner known per se. The mobile station 5 is
situated at the intersection of the directions 1aa, 2aa, 3aa
measured by antennas. The location is found with two directions
1aa, 2aa, and more directions make it more accurate.
[0089] According to the invention, particularly when based on the
time difference of arrival observed in the reception of the radio
transmission, all the base stations 1b, 2b, 3b participating in the
location process can share the same signal burst of the same
location access channel. In this case, using the Code Division
Multiple Access (CDMA) provides an advantage, because by it the
collisions of the first signal bursts sent 6 by different mobile
stations 5 are reduced. The identification 14 of the mobile station
5 is received at the base stations 1b, 2b, 3b, like in the case of
location determination based on the angle of arrival as described
above, and the exact time of arrival 7 of the first signal burst.
This information is sent 8 to the location service centre 4b, where
the data are processed and the location of the mobile station 5 is
calculated 9 in a manner known per se. Processing the observed time
differences provides the hyperbolas 1-3bb, 2-3bb, passing between
the base stations 1b, 2b, 3b, at the intersection of which the
mobile station 5 is located. After this, the base station 1b, 2b,
3b sends the mobile station 5 acknowledgement of the location
determination as above.
[0090] According to the invention, particularly when based on the
transition time of the radio transmission, the time of arrival of
the first signal burst sent from the mobile station 5 is measured 7
at the base station 1c, 2c, 3c, the identification 14 of the mobile
station 5 is read and this information is sent 8 to the location
service centre 4c for calculating 9 the location. The arrival times
are used to determine the location circles 1cc, 2cc, 3cc around the
base stations 1c, 2c, 3c. The mobile station 5 is situated at the
intersection of these circles 1cc, 2cc, 3cc or some other point
which is an optimum location estimate. For example, it can happen
that the circles do not intersect at the same point, whereby one
possibility is to select as the location estimate of the mobile
station the point from which the sum of the distances to different
circles is the smallest.
[0091] When the location determination is started, the first
location signal bursts are sent 6 from the mobile station. When
required, the first bursts can also be sent 6 according to a
certain predetermined sequencing or randomly. In the mobile station
it is not necessary to wait for the possible acknowledgements 11 of
the first bursts before sending the next first burst. For example,
the first burst is sent 6 from the mobile station to many different
base stations and acknowledgements are waited for between
transmissions.
[0092] In common for all the methods presented above, after the
location determination, the base station sends 11 to the mobile
station in the location receipt channel the second acknowledgement
burst, if this has been implemented. By this it is ensured that all
the first bursts have been received and that the location has been
determined 9 and no more transmissions are needed. The
acknowledgement 11 can also be sent by each base station, based on
the reception 7 of the first burst at the base station.
[0093] By combining the methods based on the angle of arrival and
the time difference of the radio transmission, it is possible to
make the locating more accurate. Then both the angle of arrival and
the timing advance are determined from the same signal
simultaneously.
[0094] Due to capacity, mobile stations generally share the
location access channels between themselves. One access channel is
preferably dedicated for one base station so that many mobile
stations transmit to the uplink direction in the same channel, or
the same access channel is divided between many base stations, e.g.
for reasons of capacity, whereby the first signal burst must
include the identification of the receiving base station. The
transmissions of different mobile stations can collide, which
causes loss of transmission, whereby all the base stations do not
receive a location signal. When Code Division Multiple Access
(CDMA) is used, there is not a significant amount of collisions or
no collisions at all, whereby many mobile stations can transmit the
first signal burst in the same channel.
[0095] The location receipt channel is used for sending
notification from the base station to the mobile station of a
successful receipt of the first burst. Preferably, many base
stations notify of the receipt at different times so that the
transmissions do not collide temporally in the same channel. In the
mobile station, it is concluded from the receipts whether a
sufficient number of base stations has successfully received the
first burst. From the receipts it is also concluded whether a
collision has taken place and a decision of a retransmission of the
first burst is taken. In cases of collision, the methods that have
to be used are random access methods, such as the Aloha method,
whereby there is a random waiting time in the mobile station before
retransmission, in order to reduce the likelihood of a new
collision in the same channel with the same transmitter. The Code
Division Multiple Access (CDMA) can also be used in this channel.
It is possible to send acknowledgement to the mobile station to
indicate that the total procedure of location determination has
succeeded.
[0096] The locating method according to the invention is
particularly useful in connection with emergency calls, because the
method makes it considerably faster and easier to locate the caller
who needs help than the present methods. With the prior art
methods, the mobile station is used to make a call to the mobile
station network, where the emergency call is detected, the
information is sent to the location service centre, which further
sends commands to the base stations. When the method according to
the invention is used most preferably, the first bursts are
immediately sent from the mobile station to the mobile station
network, where these signals are received and transferred to the
location service centre, where the location is determined
immediately. Possible collisions in the location channels naturally
slow down the location determination a little, but this can be
solved by dedicating one location access channel entirely for
emergency calls.
[0097] In the present GSM network, the random access bursts have
reserve values by which the new type of burst is determined. In the
case of the emergency call, for example, the mobile station sends
the first bursts formed like this to the neighbouring base
stations, in which these new bursts are received. The bursts
contain the random temporary identification created by the mobile
station for its recognition. Later the mobile station must report
its real identity, such as TMSI or IMSI, and the temporary
identification used by it to the location service centre, so that
the correlation between them is obtzined. The base stations measure
the first bursts, such as random access bursts, but do not start to
establish a connection to the mobile station but only report the
measurement results to the location service centre. Each
measurement result is followed by the temporary identification
created by the base station, so that the mobile station can be
located in the location service centre. Because the number of
alternatives for a temporary identification of random access bursts
is small, this implementation can only be used in rare cases, such
as emergency calls.
[0098] The invention can be implemented in the present GSM network
or in the future systems, such as the Universal Mobile
Telecommunication System (UMTS) in the following manner, for
example. A location channel is determined, which channel allows
using longer first bursts than the present random access channel.
The first burst to be transferred in this location channel
preferably contains the mobile station identification, such as the
International Mobile Subscriber Identification (IMSI) or the
Temporary Mobile Subscriber Identification (TMSI). In the location
channel it is also possible to transfer the first bursts more
often. The problem of overlapping bursts can partly be solved by
using the Code Division Multiple Access (CDMA) with random code.
These codes can be selected from a predefined series. Due to this,
when several mobile stations send bursts immediately, the base
station can decode all of them.
[0099] The invention is not limited to the above embodiments only,
but many modifications are possible without departing from the
scope defined by the attached claims.
* * * * *