U.S. patent application number 14/562933 was filed with the patent office on 2015-05-21 for method and arrangement for dl-otdoa (downlink observed time difference of arrival) positioning in a lte (long term evolution) wireless communications system.
The applicant listed for this patent is Telefonaktiebolaget LM Ericsson (publ). Invention is credited to Dirk Gerstenberger, Daniel Larsson.
Application Number | 20150139061 14/562933 |
Document ID | / |
Family ID | 41323610 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150139061 |
Kind Code |
A1 |
Gerstenberger; Dirk ; et
al. |
May 21, 2015 |
Method and Arrangement for DL-OTDOA (Downlink Observed Time
Difference of Arrival) Positioning in a LTE (Long Term Evolution)
Wireless Communications System
Abstract
The present invention relates generally to methods and
arrangements for positioning in a wireless communications system.
In particular, the present invention relates to improving
positioning accuracy. The invention provides methods and
arrangements for scheduling positioning subframes for allowing
aligning of positioning subframes across a number of cells in order
to reduce the interference from data symbols of cells in the
neighborhood of a cell serving the UE that is performing
positioning measurements. A time instance during which transmission
of the positioning subframes is to occur in a wireless
communications network is selected. The base stations in the
wireless communications network are informed about the selected
time instance, whereupon the base stations schedule and transmit
the positioning subframes based on the selected time instance,
whereby the positioning subframes are aligned throughout the
network.
Inventors: |
Gerstenberger; Dirk;
(Vallentuna, SE) ; Larsson; Daniel; (Vallentuna,
SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Telefonaktiebolaget LM Ericsson (publ) |
Stockholm |
|
SE |
|
|
Family ID: |
41323610 |
Appl. No.: |
14/562933 |
Filed: |
December 8, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13255445 |
Sep 8, 2011 |
8908586 |
|
|
PCT/SE2009/050773 |
Jun 18, 2009 |
|
|
|
14562933 |
|
|
|
|
61158876 |
Mar 10, 2009 |
|
|
|
Current U.S.
Class: |
370/312 ;
370/336 |
Current CPC
Class: |
H04W 36/385 20130101;
H04W 72/0446 20130101; H04W 64/003 20130101; H04W 72/005 20130101;
H04L 5/0033 20130101 |
Class at
Publication: |
370/312 ;
370/336 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04L 5/00 20060101 H04L005/00; H04W 72/00 20060101
H04W072/00 |
Claims
1. A method in a network node for scheduling the transmission of
positioning subframes from different base stations in a wireless
communications network, the method comprising: selecting a time
period during which transmission of positioning subframes is to
occur from one or more of the different base stations; and
informing one or more of the base stations that positioning
subframes are to be transmitted during the selected time period to
thereby align the positioning subframes across the different base
stations.
2. The method according to claim 1, wherein normal subframes in the
wireless communication network each include a region in which data
is scheduled, and wherein no data is scheduled in at least a
portion of a corresponding region of positioning subframes in the
wireless communication network.
3. The method according to claim 1, wherein the positioning
subframes are Multicast Broadcast Multimedia Single Frequency
Network subframes.
4. The method according to claim 1, wherein the selected time
period is associated with a system frame number.
5. The method according to claim 1, further comprising: retrieving
system time information obtained from a global system clock or a
Global Positioning System receiver; and informing the one or more
base stations of the system time information.
6. The method according to claim 1, wherein the network node is a
positioning node.
7. The method according to claim 1, wherein the network node is an
evolved Serving Mobile Location Center.
8. The method according to claim 1, wherein the network node is one
of the different base stations.
9. The method according to claim 8, further comprising: scheduling
the transmission of a positioning subframe from the network node
based on at least the selected time period; and transmitting the
scheduled positioning subframe.
10. The method according to claim 9, wherein said scheduling
comprises scheduling the transmission of a positioning subframe to
occur during a time period which deviates from the selected time
period by less than half the length of a subframe.
11. The method according to claim 9, further comprising scheduling
transmission of the positioning subframe from the network node also
based on system time information.
12. The method according to claim 8, further comprising: receiving
information from another one of the base stations indicating that
transmission of a positioning subframe from that base station is
scheduled to occur during a time period that is different from the
selected time period; and adjusting the selected time period
according to the time period indicated by the received
information.
13. The method according to claim 12, further comprising informing
one or more of the different base stations that transmission of
positioning subframes is to occur during the time period indicated
by the received information.
14. The method according to claim 12, wherein said receiving
comprises receiving the information over an X2 interface.
15. A method in a base station of a wireless communications network
for scheduling the transmission of a positioning subframe from that
base station, the method comprising: receiving from a network node
information indicating a time period during which the transmission
of positioning subframes is to occur from one or more different
base stations in the network; scheduling the transmission of a
positioning subframe from said base station based on the time
period indicated by the received information to thereby align the
positioning subframes across the different base stations; and
transmitting the scheduled positioning subframe.
16. The method according to claim 15, wherein normal subframes in
the wireless communication network each include a region in which
data is scheduled, and wherein no data is scheduled in at least a
portion of a corresponding region of positioning subframes in the
wireless communication network.
17. The method according to claim 15, wherein the positioning
subframes are Multicast Broadcast Multimedia Single Frequency
Network subframes.
18. The method according to claim 15, wherein the time period
indicated by the received information is associated with a system
frame number.
19. The method according to claim 15, wherein said scheduling
comprises scheduling the transmission of a positioning subframe to
occur during a time period which deviates from the selected time
period by less than half the length of a subframe.
20. The method according to claim 15, further comprising: receiving
system time information obtained from a global system clock or a
Global Positioning System receiver; and scheduling the transmission
of the positioning subframe from said base station also based on
said system time information.
21. The method according to claim 15, wherein said network node is
a positioning node.
22. The method according to claim 15, wherein said network node is
an evolved Serving Mobile Location Center.
23. The method according to claim 15, further comprising informing
one or more of the different base stations that transmission of
positioning subframes is to occur during the time period indicated
by the received information.
24. The method according to claim 23, wherein the network node is a
base station and said informing is performed over an X2
interface.
25. The method according to claim 24, wherein the network node is a
base station.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 13/255,445, which was filed on Sep. 8, 2011,
which is a national stage application of PCT/SE2009/050773, filed
Jun. 18, 2009, and claims benefit of U.S. Provisional Application
61/158,876, filed Mar. 10, 2009, the disclosures of each of which
are incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates generally to methods and
arrangements for positioning in a wireless communications system.
In particular, the present invention relates to improving
positioning accuracy by allowing for aligning of positioning
subframes.
BACKGROUND
[0003] UTRAN (Universal Terrestrial Radio Access Network) is a term
that identifies the radio access network of a UMTS (Universal
Mobile Telecommunications System), wherein the UTRAN consists of
Radio Network Controllers (RNCs) and NodeBs i.e. radio base
stations. The NodeBs communicate wirelessly with mobile user
equipments and the RNCs control the NodeBs. The RNCs are further
connected to the Core Network (CN). Evolved UTRAN (E-UTRAN) is an
evolution of the UTRAN towards a high-data rate, low-latency and
packet-optimised radio access network. Further the E-UTRAN consists
of NodeBs, and the NodeBs are interconnected and further connected
to the Evolved Packet Core network (EPC). E-UTRAN is also being
referred to as Long Term Evolution (LTE) and is standardized within
the 3rd Generation Partnership Project (3GPP).
[0004] The third generation cellular systems such as WCDMA
(Wideband Code Division Multiple Access) may be equipped with a
number of different positioning methods, thereby enabling location
services to the cellular subscribers. These methods are generally
applicable also in wireless communications systems using other
radio access technologies, such as the LTE. The methods that are
available include [0005] Cell identity (Cell-ID) positioning.
[0006] Enhanced cell identity (Ecell-ID) positioning [0007]
Assisted GPS (A-GPS) positioning [0008] Downlink time difference of
arrival--with idle periods in the downlink (OTDOA-IPDL) positioning
[0009] Uplink time difference of arrival (UTDOA) positioning
[0010] Cell-ID positioning determines the cell to which the user
equipment (UE) is connected. The position of the user is hence
determined with cell granularity. Typically the radio network
controller of the radio network (RAN) determines a 315 corner
polygon that determines the geographical extension of the cell. The
corners of this polygon are given as latitude, longitude pairs in
the WGS84 geographical reference system. The cell-ID method is the
backbone of all cellular positioning system since it is always
available when the UE can be connected to the system.
[0011] Ecell-ID positioning augments the Cell-ID positioning with
auxiliary information that narrows down the area that is determined
by the cell polygon. A useful method in the WCDMA system is the
round trip time (RTT) measurement. This measurement determines the
travel time back and forth from the radio base station (RBS) to the
UE and back. Using the speed of light, the distance from the known
position of the RBS to the UE can be calculated, which determines a
circular strip around the RBS where the UE is located. The
thickness of the strip is determined by the measurement
uncertainty. The Ecell-ID method is obtained by noticing that the
UE is located both in the cell and in the circular strip. Hence,
the UE is located in the intersection of these two geographical
regions.
[0012] A-GPS positioning is an enhancement of the US military
global positioning system (GPS). GPS reference receivers attached
to e.g. a cellular communication system, collect assistance data
that, when transmitted to GPS receivers in terminals connected to
the cellular communication system, enhances the performance of the
GPS terminal receivers. Typically, A-GPS accuracy can become as
good as 10 meters also without differential operation. The accuracy
becomes worse in dense urban areas and indoors, where the
sensitivity is often not high enough for detection of the very weak
signals from the GPS satellites. Advantages of A-GPS includes a
high accuracy, the method easily meets the North-American emergency
positioning E-911 requirements of 50 meters for 67% of all
positionings and 150 meters for 95% of all positionings. A drawback
is the limited indoor coverage, which is a result of the low
ranging signal strengths that are obtained at ground level.
[0013] OTDOA-IPDL positioning is similar to A-GPS in that it relies
on time difference of arrival measurements. However, the OTDOA-IPDL
method uses UE measurements of Pilot radio (CPICH in WCDMA) signals
transmitted from several RBSs. The measurement results are
signalled to the RNC, where a hyperbolic trilateration method is
used for calculation of the position of the UE. In order to enhance
the hearability of the RBSs in the UE, there is a possibility to
use idle periods in the downlink (IPDL), to attenuate the
transmissions from the RBS to which the UE is connected. This
reduces the interference and hence enhances the hearability of
other RBSs. A tentative advantage with OTDOA-IPDL is that it
theoretically provides a better indoor coverage than does
A-GPS.
[0014] UTDOA positioning is another positioning method. It is
similar to A-GPS in that it relies on time difference of arrival
measurements. However, the UTDOA method uses RBS (or separate
location measurement unit (LMU)) measurements of signals
transmitted from the positioned UE. The transmitted signal is
detected in a number of RBSs or LMUs, after which the measured
results are signalled to a positioning node where the position of
the UE is determined by a trilateration method. In order to be able
to detect the time of arrival from measurements of opportunity from
the UE, a reference signal first needs to be created in a
master-LMU or master RBS. This is done by decoding of the signal,
followed by reconstruction of the chip stream that then forms the
reference signal. An advantage of UTDOA positioning is that it
provides a better indoor coverage than does A-GPS. Outdoor accuracy
is normally inferior to A-GPS though.
[0015] An issue with terrestrial time difference of arrival
methods, i.e. OTDOA-IPDL and UTDOA, is the receiver sensitivity
when positioning is considered. Theoretically, the methods can
provide a 3-D position from 4 times of arrival measurements
(equivalent to three time difference of arrival
(pseudo)measurements). However, radio propagation conditions are
far less beneficial than for A-GPS, since OTDOA-IPDL and UTDOA
ranging signals propagate along the surface of the earth, whereas
A-GPS signals propagate from above. The terrestrial positioning
methods therefore suffer more from non-line-of-sight (LOS)
propagation and multipath propagation. This results in outlier
measurements, whose suppression requires the availability of excess
detections i.e. detections from significantly more than the minimum
number of RBSs. In practice, to achieve a useful positioning
accuracy, at least 6-8 RBSs need to be detected in the UE in case
OTDOA-IPDL positioning is used. For UTDOA positioning at least 6-8
RBSs need to detect the UE transmissions in order to obtain useful
position estimates in practical environments.
[0016] The consequence of the above is that more remote RBSs need
to be detected (OTDOA-IPDL) or detect (UTDOA). This means that
lower signal strengths need to be detected with high probability.
Calculations typically show that signals need to be detected down
to about -40 dB C/I. Further, the pre-detection step needs to
enhance the signal to about 11-13 dB C/I in order to achieve a
sufficiently low false alarm rate. In essence, the processing gain
for positioning purposes in any CDMA system needs to be 50-55 dB
for terrestrial positioning to be useful. This is significantly
more than what is needed for other services, which means that
positioning sensitivity requirements need to be assessed at the
definition phase of the air-interface.
[0017] For LTE, a possible positioning technique is Downlink OTDOA,
using UE measurements on measurement signals, e.g. reference
signals and/or synchronization signals, on multiple cells during
designated low interference subframes, an example being MBSFN
(Multicast Broadcast Multimedia Single Frequency Network)
subframes.
[0018] However, the main problem of the third generation cellular
systems positioning methods remains and can be summarized as
follows: [0019] A-GPS positioning is a high precision technology
with one main drawback--indoor positioning availability. [0020]
OTDOA-IPDL and UTDOA positioning have the technical potential to
provide better indoor coverage than A-GPS and to deliver good
precision. However, the presently available detection sensitivities
are not sufficient to provide a good enough accuracy. Rather,
accuracy figures in between A-GPS and Cell-ID can be expected.
[0021] Thus, a problem in current positioning solutions for
wireless communications systems such as LTE is that it is difficult
to achieve sufficient positioning accuracy with reasonable receiver
detection sensitivities.
SUMMARY
[0022] It is therefore an object of the present invention to
provide a mechanism for improving positioning accuracy in a
wireless communications system.
[0023] The present invention focuses on techniques that can relax
the very hard detection sensitivity requirements. The object is
achieved according to the present invention by selecting a time
instance during which transmission of positioning subframes is to
occur; and by informing the base stations comprised in the wireless
communications network about the first time instance for allowing
aligning of positioning subframes. The base stations schedule the
positioning subframes based on the time instance and transmit the
positioning subframes accordingly.
[0024] In accordance with a first aspect of the present invention a
method in a network node for scheduling positioning subframes is
provided. The network node is comprised in a wireless
communications network and connected to at least a first base
station. The first base station is capable of transmitting
positioning subframes. The method comprises a step of selecting a
first time instance during which transmission of the positioning
subframes is to occur. For allowing aligning of positioning
subframe the first base station is informed about the first time
instance.
[0025] In accordance with a second aspect of the present invention
a method in a base station for scheduling positioning subframes is
provided. The base station is comprised in a wireless
communications network and connected to at least one network node.
The method comprises a step of receiving information about a first
time instance during which transmission of positioning subframes is
to occur from the at least one network node. For allowing aligning
of positioning subframe scheduling of positioning subframes is
based on at least the time instance. In further step the method
transmits the scheduled positioning subframes.
[0026] In accordance with a third aspect of the present invention a
first arrangement for scheduling positioning subframes is provided.
The arrangement is adapted to be comprised in a network node, which
is comprised in a wireless communications network and connected to
at least a first base station. The at least first base station is
capable of transmitting positioning subframes. Furthermore, the
arrangement comprises a selection unit arranged to select a first
time instance during which transmission of the positioning
subframes is to occur. Additionally, the arrangement comprises an
informing unit arranged to inform the at least first base station
about the first time instance for allowing aligning of positioning
subframes.
[0027] In accordance with a fourth aspect of the present invention
a second arrangement for scheduling positioning subframes is
provided. The arrangement is adapted to be comprised in a base
station, which is comprised in a wireless communications network
and connected to at least one network node. The arrangement
comprises a receiving unit arranged to receive information about a
first time instance during which transmission of positioning
subframes is to occur from the at least one network node.
Furthermore, the arrangement comprises a scheduling unit arranged
to schedule the positioning subframes based on at least the first
time instance for allowing aligning of positioning subframes.
Additionally, the arrangement comprises a transmitting unit
arranged to transmit the scheduled positioning subframes.
[0028] An advantage of the present invention is that when a number
of base stations all transmit their positioning subframes at
roughly the same time instance, the positioning subframes will
become aligned across a number of cells. Thereby, the interference
from data symbols of cells in the neighborhood of the cell serving
a user equipment performing positioning measurements such as DL
OTDOA measurements is reduced. Hence, the hearability in the
wireless communications system is improved, which has the effect of
improving the positioning accuracy without increasing the detection
sensitivity in the receiver.
[0029] Other objects, advantages and novel features of the
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] For a better understanding, reference is made to the
following drawings and preferred embodiments of the invention.
[0031] FIG. 1 illustrates a part of a cellular wireless
communications system wherein the present invention may be
implemented.
[0032] FIG. 2 is a schematic diagram illustrating an arrangement of
subframes according to the prior art.
[0033] FIG. 3 is a schematic diagram illustrating an arrangement of
positioning subframes in an unsynchronized network, resulting in
coarse alignment.
[0034] FIG. 4 illustrates a flowchart for scheduling positioning
subframes wherein a positioning node selects the time instance for
scheduling the positioning subframes and informs the neighboring
eNodeBs about the time instance.
[0035] FIG. 5 illustrates a flowchart for scheduling positioning
subframes wherein a positioning node selects the time instance for
scheduling the positioning subframes and informs one or several
eNodeBs about the time instance, whereupon the one or several
eNodeBs informs the neighboring eNodeBs.
[0036] FIG. 6 illustrates a flowchart for scheduling positioning
subframes wherein an eNodeB selects the time instance for
scheduling the positioning subframes and informs the neighboring
eNodeBs about the time instance.
[0037] FIG. 7 illustrates a flowchart for scheduling positioning
subframes wherein each eNodeB selects the time instance for
scheduling the positioning subframes and informs the neighboring
eNodeBs about the time instance, whereupon each eNodeB adjust the
scheduling of the positioning subframes if needed.
[0038] FIG. 8 is a schematic block diagram illustrating an
arrangement in a network node such as a positioning node or base
station.
[0039] FIG. 9 is a schematic block diagram illustrating an
arrangement in a base station.
DETAILED DESCRIPTION
[0040] In the following description, for purposes of explanation
and not limitation, specific details are set forth, such as
particular sequences of steps, signaling protocols and device
configurations in order to provide a thorough understanding of the
present invention. It will be apparent to one skilled in the art
that the present invention may be practiced in other embodiments
that depart from these specific details.
[0041] Moreover, those skilled in the art will appreciate that the
means and functions explained herein below may be implemented using
software functioning in conjunction with a programmed
microprocessor or general purpose computer, and/or using an
application specific integrated circuit (ASIC). It will also be
appreciated that while the current invention is primarily described
in the form of methods and devices, the invention may also be
embodied in a computer program product as well as a system
comprising a computer processor and a memory coupled to the
processor, wherein the memory is encoded with one or more programs
that may perform the functions disclosed herein.
[0042] As previously mentioned, a possible positioning method for
use in a cellular wireless communications system such as the LTE is
the downlink time difference of arrival (DL OTDOA), using UE
measurements on measurement signals, e.g. reference signals and/or
synchronization signals, on multiple cells during designated low
interference subframes.
[0043] FIG. 1 illustrates a part of a cellular wireless
communications system such as the LTE, wherein a cell is denoted
11, a base station covering the cell 11 is denoted 13 in the
figure. The positioning method used in the LTE could be the DL
OTDOA, using UE measurements on measurement signals, e.g. reference
signals and synchronization signals, on multiple cells 11 b-11e
during designated low interference subframes. The UE 12 in the
serving cell 1 Ia tries to measure on the measurement signals of
cells 11 b-1 Ie in the neighborhood of the serving cell 1 Ia during
designated low interference subframes transmitted from a base
station 13a, i.e. an eNodeB, in the cell 1 Ia serving the UE 12. It
should however be noted that the cells 1 Ib-1 Ie are not
necessarily strictly adjacent cells. The positioning method DL
OTDOA is performed by a positioning node 10 in the cellular
wireless communications system.
[0044] In an unsynchronized network, the timing of designated low
interference subframes is in general not aligned. Thus the data
symbols transmitted in the subframes from the eNodeBs 13b-13e in
the neighborhood cells 11 b-1 Ie are overlapping with the
measurement symbols of the cells 11 b-1 Ie the UE 12 is trying to
measure on. This means that, although the designated low
interference subframe in the serving cell is removing the strongest
interferer (i.e. the own data symbols), hearability is still a
challenging task. A schematic diagram illustrating an arrangement
of subframes according to the described prior art is illustrated in
FIG. 2. The control region of the subframe is indicated in black,
the data symbols by hatching and the measurement symbols shown as
small white squares. The large overlaid rectangle indicates the
measurement part during which the data symbols are potentially
interfering with the measurement symbols.
[0045] The present invention provides methods and arrangement for
scheduling positioning subframes for allowing aligning of
positioning subframes across a number of cells 11 a-11 e in order
to reduce the interference from data symbols of cells 11b-11e in
the neighborhood of the cell IIa serving the UE 12 that is
performing DL OTDOA measurements. A schematic diagram illustrating
an arrangement of positioning subframes in an unsynchronized
network implementing the present invention, resulting in coarse
alignment, is illustrated in FIG. 3.
[0046] The invention provides methods and arrangement for
scheduling positioning subframes, wherein a time instance during
which transmission of the positioning subframes is to occur in a
wireless communications network. The base stations in the wireless
communications network are informed about the selected time
instance, whereupon the base stations schedule and transmit the
positioning subframes based on the selected time instance, whereby
the positioning subframes are aligned throughout the part of the
wireless communications network in which the base stations are
comprised.
[0047] For the purpose of this disclosure, the term "positioning
subframe" is to be interpreted as a subframe which causes no
interference, or a limited amount of interference, with other
subframes transmitted by another eNodeB on the same frequency
resource. In practice, a positioning subframe could for example be
a subframe which has no data scheduled in it, which has no data
scheduled in a part or parts of it, or which has less than the
maximum possible amount of data scheduled in it, or in a part or
parts of it. A positioning subframe may also be interpreted as a
subframe comprising at least one reference symbol (sometimes
denoted reference signal, pilot symbol, or pilot signal) which is
designed to enable measurements to be performed, e.g. by a UE. The
measurements may, for instance, be utilized for positioning
purposes. A positioning subframe may also be an MBSFN subframe. A
MBSFN subframe is a subframe with only two OFDM (Orthogonal
Frequency Division Multiplexing) symbols for PDCCH (Physical
Downlink Control Channel). Other than that, it may be empty or
contain some other form of reference symbol pattern or data.
[0048] It should be pointed out that in some embodiments of the
present invention different types of positioning subframes are used
in the participating eNodeBs, i.e. it is possible to use e.g. MBSFN
subframes in some eNodeBs and other types of subframes without data
in other eNodeBs.
[0049] We now turn to FIGS. 4-9 which show flowcharts of the
methods and schematically block diagrams of the arrangements
according to embodiments of the present invention.
[0050] FIG. 4 illustrates a flowchart of a method in a network node
and a base station according to one embodiment of the present
invention. In a first step, the network node selects 40 a time
instance during which transmission of the positioning subframes is
to occur in the wireless communications network. In the next step,
the network node informs 41 one or several eNodeBs 13 about the
selected time instance. The one or several eNodeBs 13 receives 42
the time instance from the network node and schedules 43 the
positioning subframes based on the received time instance. The
positioning subframes are then transmitted 44 by the one or several
eNodeBs 13 in accordance with the scheduling performed in the
preceding step, whereby the positioning subframes are aligned.
[0051] In some embodiments of the present invention the positioning
subframes are scheduled with a starting time which deviates less
than or equal to half a subframe length from the selected time
instance, resulting in coarse alignment, as illustrated in FIG.
3.
[0052] A wireless communication system utilizes global system frame
numbers (SFNs) to base identification of frames of information
transmitted by the communication system. The time instance during
which the transmission of the positioning subframes is to occur is
in one embodiment associated with a specific system frame
number.
[0053] The network node could be a positioning node in the LTE,
which could be a separate network node or integrated in an eNodeB
or any other network node. In one embodiment the network node is an
eSMLC (evolved Serving Mobile Location Center), which is either a
separate network element or integrated functionality in the BSC
that contains the functionality required to support location
services.
[0054] Another embodiment of the present invention is shown in FIG.
5, illustrating a flowchart of a method in a network node and base
stations. In a first step, the network node selects 50 a time
instance during which transmission of the positioning subframes is
to occur in the wireless communications network. In the next step,
the network node informs 51 one or several eNodeBs 13a about the
selected time instance. The one or several eNodeBs 13a receives 52
the time instance from the network node and schedules 53 the
positioning subframes based on the received time instance. The
positioning subframes are then transmitted 54 by the one or several
eNodeBs 13a in accordance with the scheduling performed in the
preceding step. The one or several eNodeBs 13a then informs 55
other neighboring eNodeBs 13b-13e about the selected time instance
in a further step of the method. The one or several neighboring
eNodeBs 13b-13e receives 56 the time instance and schedules 57 the
positioning subframes based on the received time instance. Further,
the one or several neighboring eNodeBs 13b-13e transmits 58 the
positioning subframes in accordance with the scheduling performed
in the preceding step, whereby the positioning subframes are
aligned throughout the part of the network comprising the
participating eNodeBs 13a-13e. In one embodiment of the present
invention the positioning subframes are aligned throughout the
whole wireless communications network. In one embodiment the
informing step 55 and the receiving step 56 are performed by
sending a message from eNodeB 13a to the neighboring eNodeBs
13b-13e over an X2 interface.
[0055] Yet another embodiment of the present invention is shown in
FIG. 6, illustrating a flowchart of a method in at least two base
stations. In a first step, the eNodeB 13a selects 60 a time
instance during which transmission of the positioning subframes is
to occur in the wireless communications network. In the next step,
the eNodeB 13a informs 61 one or several eNodeBs 13b-13e about the
selected time instance. The eNodeB 13a schedules 62 the positioning
subframes based on the received time instance. Further, the eNodeB
13a transmits 63 the positioning subframes in accordance with the
scheduling performed in the preceding step. The one or several
eNodeBs 13b-13e receives 64 information about the selected time
instance and schedules 65 the positioning subframes based on the
received time instance. Finally, the one or several eNodeBs 13b-13e
transmits 66 the positioning subframes in accordance with the
scheduling in the preceding step, whereby the positioning subframes
are aligned throughout the part of the network comprising the
participating eNodeBs 13a-13e. In one embodiment the informing step
61 and the receiving step 64 are performed by sending a message
from the eNodeB 13a to the participating eNodeBs 13b-13e over the
X2 interface.
[0056] Yet another embodiment of the present invention is shown in
FIG. 7, illustrating a flowchart of a method in a base station. In
a first step, the eNodeB 13a selects 70 a time instance during
which transmission of the positioning subframes is to occur in the
wireless communications network. In the next step, the eNodeB 13a
receives 71 information from at least one neighboring eNodeB 13b
comprised in the wireless communications network about a selected
time instance selected by the neighboring eNodeB 13b. In one
embodiment the receiving step 71 is performed by receiving a
message from the neighboring eNodeB 13b over the X2 interface. In
one embodiment the message also comprises information about the
number of eNodeBs in the wireless communications network that
schedule the positioning subframes at the received time instance.
The eNodeB 13a then adjusts 72 the selected time instance according
to the received time instance in the preceding step. In the next
step, the eNodeB informs 73 the neighboring eNodeBs 13b about the
adjusted time instance. In one embodiment the informing step 73 is
performed by sending a message to the neighboring eNodeB 13b over
the X2 interface. In one embodiment the message also comprises
information about the number of eNodeBs in the wireless
communications network that schedule the positioning subframes at
the adjusted time instance. The eNodeB 13a schedules 74 the
positioning subframes based on the adjusted time instance. Further,
the eNodeB 13a transmits 75 the positioning subframes in accordance
with the scheduling performed in the preceding step, whereby the
positioning subframes are aligned throughout the part of the
network comprising the participating eNodeBs 13a-13b. In a further
embodiment the eNodeB 13a informs 76 a further eNodeB 13c about the
adjusted time instance. Obviously, the method could be implemented
in the whole wireless communications network, whereby the
positioning subframes are aligned throughout the whole network.
[0057] One example of how the embodiment of the present invention
illustrated in FIG. 7 could be implemented is outlined in the
following. Other ways to implement the present invention could
however also be possible.
[0058] If the number of eNodeBs following the timing, i.e. the time
instance, for scheduling positioning subframes reported on X2
between the eNodeBs, is larger or equal to the number of eNodeBs
following the timing of the eNodeB, i.e. the time instance selected
by the eNodeB, receiving the message on X2, the receiving eNodeB
adjusts its own timing according to the information received on X2.
The receiving eNodeB also updates its own timing for scheduling
positioning subframes if it has previously not received any timing
report on X2. After adjusting its own timing the eNodeB should
report its new timing to all its neighboring eNodeBs on X2.
Moreover, another list of eNodeBs than the neighboring eNodeBs may
also be applicable.
[0059] However, if the number of eNodeBs following the timing for
scheduling positioning subframes reported on X2 is less than the
number of eNodeBs following the timing of the eNodeB receiving the
timing report on X2, the receiving eNodeB sends a timing report
over X2 to all the eNodeBs that have different timing for
scheduling positioning subframes. In the case wherein the eNodeB
receives a timing report on X2 which corresponds to the same timing
as currently used in the receiving eNodeB for scheduling
positioning subframes, the receiving eNodeB updates its own list of
eNodeBs following the timing according to the received message. The
receiving eNodeB also sends it own list to the source eNodeB if the
receiving eNodeB has knowledge about other eNodeBs that have the
same timing but were not included in the report received on X2.
[0060] In some embodiments previously mentioned a system time
instance is retrieved to which the selected and/or adjusted time
instance is related. The system time instance is obtained from a
GPS receiver or from a global system clock. The network node
informs the one or several eNodeBs 13 about the system time
information in some embodiments. In the embodiments wherein the
system time information is available the selected and/or the
adjusted time instance is related to the system time information
i.e. the scheduling of the positioning subframes is based on both
first time instance and the system time information.
[0061] To perform the method steps for scheduling positioning
subframes, a network node may comprise an arrangement 800 depicted
in FIG. 8. The arrangement 800 comprises a processor 810 and a time
instance selection unit 820 arranged to select the time instance
during which transmission of the positioning subframes is to occur.
The arrangement further comprises an informing unit 830 arranged to
inform the one or several eNodeBs 13a-13e about the time
instance.
[0062] In some embodiment the network node comprising the
arrangement is a positioning node 10, a SMLC or an eNodeB 13a.
[0063] In some embodiment, the network node is a base station i.e.
an eNodeB 13a, wherein a scheduling unit 840 arranged to schedule
the positioning subframes based on the time instance is comprised
in the arrangement 800. The arrangement further comprises a
transmitting unit 850 arranged to transmit the scheduled
positioning subframes. In one embodiment, the arrangement comprises
a receiving unit 860 arranged to receive information from another
eNodeB 13b about a time instance used by that eNodeB 13b for
scheduling positioning subframes. An adjusting unit 870 arranged to
adjust the time instance according to the received time instance is
comprised in the arrangement 800. In some embodiments the informing
unit 830 is arranged to inform yet a further eNodeB 13c about the
adjusted first time instance and/or the received time instance from
the eNodeB 13b.
[0064] Additionally, the arrangement 800 comprises a retrieving
unit 880 arranged to retrieve system time information obtained from
a global clock or a GPS receiver in some embodiments of the present
invention. In these embodiments the informing unit 830 is arranged
to inform the eNodeB about the system time information.
[0065] To perform the method steps for scheduling positioning
subframes, a base station, i.e. an eNodeB 13a, may comprise an
arrangement 900 depicted in FIG. 9. The arrangement 900 comprises a
processor 910 and a time instance receiving unit 920 arranged to
receive the time instance during which transmission of the
positioning subframes is to occur. The arrangement 900 further
comprises a scheduling unit 930 arranged to schedule the
positioning subframes based on the time instance. Moreover, the
arrangement comprises a transmitting unit 940 arranged to transmit
the scheduled positioning subframes. In some embodiments, the
arrangement further comprises an informing unit 950 arranged to
inform the one or several eNodeBs 13b-13e about the time
instance.
[0066] Additionally, the arrangement 900 comprises a receiving unit
960 arranged to receive system time information, obtained from a
global clock or a GPS receiver, from a network node in some
embodiments of the present invention. In these embodiments the
scheduling unit 930 is arranged to schedule the positioning
subframes based on the time instance and the system time
information.
[0067] It should be mentioned that the arrangement 900 comprises an
X2 interface and in the embodiments wherein the network node is a
base station the arrangement 800 also comprises an X2
interface.
[0068] It should be noted that the present invention is applicable
in both Frequency Division Duplex (FDD) and Time Division Duplex
(TDD) mode of the LTE.
[0069] Additionally, it should be noted that although terminology
from 3GPP LTE has been used in this disclosure to exemplify the
invention, this should not be seen as limiting the scope of the
invention to only the aforementioned system. Other wireless
systems, in particular OFDM-based systems such as WiMax, may also
benefit from exploiting the ideas covered within this
disclosure.
[0070] When using the word "comprise" or "comprising" it shall be
interpreted as non-limiting, i.e. meaning "consist at least
of".
[0071] Modifications and other embodiments of the disclosed
invention will come to mind to one skilled in the art having the
benefit of the teachings presented in the foregoing descriptions
and the associated drawings. Therefore, it is to be understood that
the invention is not to be limited to the specific embodiments
disclosed and that modifications and other embodiments are intended
to be included within the scope of this disclosure. Although
specific terms may be employed herein, they are used in a generic
and descriptive sense only and not for purposes of limitation.
* * * * *