U.S. patent application number 12/858809 was filed with the patent office on 2011-09-22 for method and apparatus for muting signaling in a wireless communication network.
Invention is credited to Muhammad Ali Kazmi, Iana Siomina.
Application Number | 20110230144 12/858809 |
Document ID | / |
Family ID | 44647613 |
Filed Date | 2011-09-22 |
United States Patent
Application |
20110230144 |
Kind Code |
A1 |
Siomina; Iana ; et
al. |
September 22, 2011 |
Method and Apparatus for Muting Signaling in a Wireless
Communication Network
Abstract
In one aspect, the present invention provides a simple method of
signaling reference signal muting information to receiving radio
equipment, such as items of user equipment (UEs). The reference
signals may be positioning reference signals and/or cell-specific
reference signals, for example. In one or more embodiments, the
present invention proposes a general solution whereby the receiving
radio equipment is informed not only on whether muting is used in
general in a cell, but also the particular timing and formatting of
such muting. Further, the contemplated method provides for the use
of dynamic muting patterns, and thus avoids the need for statically
defined muting patterns, and provides for coordinated muting
control, across two or more network cells. In at least one
embodiment, static or less dynamic aspects of the muting
configuration is signaled via higher-layer signaling, while
lower-layer signaling is used to signal more dynamic aspects of the
muting configuration.
Inventors: |
Siomina; Iana; (Solna,
SE) ; Kazmi; Muhammad Ali; (Bromma, SE) |
Family ID: |
44647613 |
Appl. No.: |
12/858809 |
Filed: |
August 18, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61314724 |
Mar 17, 2010 |
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Current U.S.
Class: |
455/68 |
Current CPC
Class: |
H04L 5/0044 20130101;
H04W 74/002 20130101; G01S 1/042 20130101; G01S 1/20 20130101; H04W
64/00 20130101; H04L 5/0048 20130101 |
Class at
Publication: |
455/68 |
International
Class: |
H04B 7/00 20060101
H04B007/00 |
Claims
1. A method of controlling the transmission of reference signals in
a wireless communication network, said method comprising:
transmitting reference signals at recurring occasions, for use in
making reference signal measurements at receiving radio equipment;
muting the reference signals in certain ones of the occasions,
according to a muting configuration; and transmitting muting
configuration information indicating said muting configuration, to
inform said receiving radio equipment of said muting configuration;
said muting configuration information including one or more of: a
bandwidth parameter identifying the portion of reference signal
bandwidth to which muting applies; a subframes parameter indicating
the number of consecutive subframes within an occasion to which
muting applies; and a muting occasion parameter indicating
occasions to which muting applies.
2. The method of claim 1, wherein the reference signals are
positioning reference signals transmitted at defined positioning
occasions by at least one base station in the wireless
communications network, and wherein said positioning reference
signals are used by the receiving radio equipment in making
positioning-related measurements.
3. The method of claim 1, wherein the receiving radio equipment
comprises at least one of: one or more user equipments (UEs)
associated with users of the wireless communication network; and
one or more fixed nodes within the wireless communication
network.
4. The method of claim 1, wherein said transmitting reference
signals comprises transmitting reference signals from one or more
base stations in the wireless communication network, each said base
station associated with a respective cell.
5. The method of claim 4, further comprising determining the muting
configuration on a per-cell basis.
6. The method of claim 4, wherein the one or more base stations
comprise a plurality of base stations associated with respective
ones in a plurality of associated cells, and further comprising
determining the muting configuration cooperatively across the
plurality of associated cells.
7. The method of claim 4, further comprising determining, at each
base station, the muting configuration to be used by the base
station based at least in part on control signaling received at the
base station from a higher-layer node in the wireless communication
network.
8. The method of claim 7, wherein the wireless communication
network comprises a Long Term Evolution (LTE) network, or an
LTE-Advanced network, and the base station comprises an eNodeB, and
further comprising exchanging control signaling between the eNodeB
and an E-SMLC that controls one or more aspects of the muting
configuration of the base station.
9. The method of claim 4, further comprising determining, at each
base station, the muting configuration to be used by the base
station, based at least in part on exchanging muting configuration
information or muting control signaling with one or more
neighboring base stations.
10. The method of claim 1, wherein said transmitting muting
configuration information comprises transmitting, via lower layer
signaling, the muting occasion indicator as a flag or other
indicator indicating whether muting will be used in an indicated or
known occasion, and transmitting, via higher layer signaling, one
or both of the bandwidth and subframes parameters, to complement
the lower layer signaling of the muting occasion parameter, such
that the receiving radio equipment is apprised of whether muting
applies to a given occasion via the muting occasion parameter, and
apprised of one or both the reference signal bandwidth and the
number of consecutive subframes to which such muting applies, for
that given occasion.
11. The method of claim 10, wherein said lower layer signaling
comprises physical layer or Medium Access Control (MAC) layer
protocol signaling.
12. The method of claim 10, wherein said higher layer signaling
comprises Radio Resource Control (RRC) or LTE Positioning Protocol
(LPP) signaling.
13. The method of claim 1, wherein said transmitting muting
configuration information comprises transmitting the muting
configuration information from a base station, via lower layer
signaling.
14. A base station for use in a wireless communication network that
transmits reference signals, said base station comprising: a
transmitter configured to transmit reference signals at recurring
occasions, for use in making reference signal measurements at
receiving radio equipment; a processing circuit operatively
associated with the transmitter and configured to mute the
reference signals in certain ones of the occasions, in accordance
with a muting configuration; and wherein said processing circuit is
configured to transmit, via said transmitter, muting configuration
information indicating said muting configuration, to inform said
receiving radio equipment of said muting, and wherein the muting
configuration information includes one or more of: a bandwidth
parameter identifying the portion of reference signal bandwidth to
which muting applies; a subframes parameter indicating the number
of consecutive subframes within an occasion to which muting
applies; and a muting occasion parameter indicating occasions to
which muting applies.
15. The base station of claim 14, wherein the base station includes
a core network communication interface for receiving muting control
signaling via higher-layer signaling from another node in the
wireless communication network, and wherein the processing circuit
is configured to determine or otherwise set the muting
configuration of the base station, based at least in part on said
muting control signaling.
16. The base station of claim 15, wherein the wireless
communication network comprises a Long Term Evolution (LTE)
network, or an LTE-Advanced network, and the base station comprises
an eNodeB, and wherein said muting control signaling received at
the base station comprises signaling from an E-SMLC that controls
one or more aspects of the muting configuration of the base
station.
17. The base station of claim 14, wherein the base station is
configured to transmit, via lower-layer signaling, the muting
occasion indicator as a flag or other indicator indicating whether
muting will be used in an indicated or known occasion, and to
transmit, via higher-layer signaling, one or both of the bandwidth
and subframes parameters, to complement the lower-layer signaling
of the muting occasion parameter, such that the receiving radio
equipment is apprised of whether muting applies to a given occasion
via the muting occasion parameter, and apprised of one or both the
reference signal bandwidth and the number of consecutive subframes
to which such muting applies, for that given occasion.
18. The base station of claim 14, wherein the base station
comprises an eNodeB, a home eNodeB, a pico base station, or a relay
node.
19. The base station of claim 14, wherein the base station includes
an inter-base-station communication interface and is configured to
determine one or more aspects of the muting configuration
cooperatively, with one or more neighboring base stations, based on
exchanging inter-base-station signaling via the inter-base-station
communication interface.
20. The base station of claim 14, wherein the base station includes
a core network communication interface configured for communicating
directly or indirectly with one or more core network nodes,
including a positioning node, and wherein the base station is
configured to receive signaling from the positioning node that sets
or otherwise controls one or more aspects of the muting
configuration of the base station.
21. The base station of claim 14, wherein the processing circuit is
configured to autonomously determine the muting configuration to be
used by the base station.
22. The base station of claim 14, wherein the reference signals are
positioning reference signals transmitted at recurring positioning
occasions.
23. A positioning node for use with a wireless communication
network, said positioning node comprising: one or more processing
circuits configured to determine a muting configuration used by one
or more base stations for controlling muting of positioning
reference signals transmitted at recurring positioning occasions by
the one or more base stations; and a communication interface
operatively associated with the one or more processing circuits and
configured to perform at least one of: receive signaling from the
one or more base stations, from which the one or more processing
circuits determine the muting configuration of the one or more base
stations, and send corresponding muting configuration information
as higher-layer signaling for receipt by radio equipment receiving
the positioning reference signals; and send muting control
signaling to the one or more base stations, to control reference
signal muting by said one or more base stations, in accordance with
the muting configuration.
24. The positioning node of claim 23, wherein the positioning node
is configured to generate the muting configuration information to
indicate when or how muting will be applied by the one or more base
stations, for indicated or known positioning occasions, and to send
at least a portion of the muting configuration information as
higher-layer signaling, for transmission by the one or more base
stations to the radio equipment receiving the positioning reference
signals.
25. The positioning node of claim 23, wherein the one or more
processing circuits are configured to control muting of the
positioning reference signals in coordinated fashion across two or
more cells of the radio access network, said two or more cells
associated with said one or more base stations, and wherein the
muting control signaling sent by the positioning node is configured
to effect coordinated muting control across the two or more
cells.
26. The positioning node of claim 25, wherein the one or more
processing circuits are configured to coordinate, as across the two
or more cells, at least one of the following: the timing or
selection of which positioning occasions have muting applied to
them; the positioning reference signal bandwidth to which muting is
applied in one or more positioning occasions; and the number of
consecutive subframes to which muting is applied within a given
positioning occasion.
27. A method at a positioning node, for use within a wireless
communication network, said method comprising: determining a muting
configuration used by one or more base stations for controlling
muting of positioning reference signals transmitted at recurring
positioning occasions from the one or more base; and further
comprising at least one of: receiving signaling from the one or
more base stations, and determining the muting configuration of the
one or more base stations from said received signaling, and sending
corresponding muting configuration information as higher-layer
signaling for receipt by radio equipment receiving the positioning
reference signals; and sending muting control signaling to the one
or more base stations, to control reference signal muting by said
one or more base stations, in accordance with the muting
configuration.
28. The method of claim 27, further comprising generating the
muting configuration information such that it indicates when or how
muting will be applied by the one or more base stations, for
indicated or known positioning occasions, and sending at least a
portion of the muting configuration information as higher-layer
signaling, for transmission by the one or more base stations to
radio equipment receiving the positioning reference signals.
29. The method of claim 27, wherein said muting control signaling
coordinates muting of the positioning reference signals across two
or more cells of the wireless communication network, wherein the
two or more cells are associated with the one or more base
stations,
30. The positioning node of claim 27, wherein the muting control
signaling is generated to coordinate at least one of the following
across the two or more cells: the timing or selection of which
positioning occasions have muting applied to them; the positioning
reference signal bandwidth to which muting is applied in one or
more positioning occasions; and the number of consecutive subframes
to which muting is applied within a given positioning occasion.
31. A method in a radio apparatus of controlling measurement of
reference signals that are transmitted by a wireless communication
network at recurring occasions, said method comprising: receiving
signaling from the wireless communication network that conveys one
or more of the following muting parameters: a bandwidth parameter
identifying the portion of reference signal bandwidth to which
muting applies; a subframes parameter indicating the number of
consecutive subframes within an occasion to which muting applies;
and a muting occasion parameter indicating occasions to which
muting applies; and controlling reference signal measurement by the
radio apparatus, in accordance with the received muting
parameters.
32. A radio apparatus comprising: a receiver configured to receive
reference signals transmitted from a wireless communication network
at recurring occasions, and to receive signaling from the wireless
communication network that conveys one or more of the following
muting parameters that define a muting configuration used by the
wireless communication network for muting the reference signals in
one or more cells of the wireless communication network, said one
or more muting parameters including at least one of: a bandwidth
parameter identifying the portion of reference signal bandwidth to
which muting applies; a subframes parameter indicating the number
of consecutive subframes within an occasion to which muting
applies; and a muting occasion parameter indicating occasions to
which muting applies; and one or more processing circuits that are
operatively associated with the receiver and are configured to
control reference signal measurement by the radio apparatus, in
accordance with the received muting parameters.
33. The method of claim 6, wherein determining the muting
configuration cooperatively across the plurality of associated
cells comprises determining one or more muting patterns to be used
across the plurality of associated cells.
34. The method of claim 33, further comprising transmitting muting
occasion indicators from each base station in the plurality of base
stations, in accordance with the one or more muting patterns.
Description
RELATED APPLICATIONS
[0001] This application claims priority from the U.S. provisional
patent application filed on 17 Mar. 2010 and identified by
Application No. 61/314,724.
FIELD OF THE INVENTION
[0002] The present invention generally relates to interference
management in wireless communications networks, and particularly
relates to controlling the muting of reference signals transmitted
by one or more base stations in the network and signaling related
muting configuration information.
BACKGROUND
[0003] Wireless communication networks use reference signal
transmissions to support a variety of key functions. In this
regard, a "reference" signal provides receiving radio equipment
with some type of reference information--timing, frequency, phase,
etc.--that enables certain measurements by the receiving equipment.
For example, cell-specific reference signals, also referred to as
common reference signals or CRSs provide receiving radio equipment
with a basis for estimating propagation channel conditions. Other
physical-layer reference signals include so called positioning
reference signals or PRSs, which are particularly contemplated for
newer, more capable networks, such as those based on the 3GPP Long
Term Evolution (LTE) standards.
[0004] Release 9 of LTE, for example, contemplates the use of PRSs
to enable and improve the burgeoning host of positioning-dependent
services that are or will be offered in such networks. That is,
beyond the law enforcement and safety requirements associated with
positioning mobile stations and other user equipment, there is an
increasing range of positioning-dependent applications and
services, all relying on the ability of these newer wireless
communication networks to efficiently and accurately support
positioning services.
[0005] Indeed, the possibility of identifying user geographical
location in the network has enabled a large variety of commercial
and non-commercial services, e.g., navigation assistance, social
networking, location-aware advertising, emergency calls, etc.
Different services may have different positioning accuracy
requirements imposed by the application. In addition, some
regulatory requirements on the positioning accuracy for basic
emergency services exist in some countries, i.e. FCC E911 in the
U.S.
[0006] In many environments, the position can be accurately
estimated by using positioning methods based on GPS (Global
Positioning System). However, contemporary networks also often have
the possibility to assist UEs in order to improve the terminal
receiver sensitivity and GPS startup performance (Assisted-GPS
positioning, or A-GPS). GPS or A-GPS receivers, however, may not
necessarily be available in all wireless terminals. Furthermore,
GPS is known to have a high failure incidence in indoor
environments and urban canyons. A complementary terrestrial
positioning method, called Observed Time Difference of Arrival
(OTDOA), has therefore been standardized by 3GPP. Correspondingly,
PRSs play a key role in OTDOA measurements.
[0007] With OTDOA, the receiving radio equipment measures the
timing differences for reference signals received from multiple
distinct locations. For each (measured) neighbor cell, the
equipment measures Reference Signal Time Difference (RSTD), which
is the relative timing difference between a neighbor cell and the
reference cell. The position estimate for the receiving equipment
is then found as the intersection of hyperbolas corresponding to
the measured RSTDs. At least three measurements from geographically
dispersed base stations with a good geometry are needed to solve
for two coordinates of the receiving equipment and the receiving
equipment clock bias.
[0008] More particularly, to solve for position, precise knowledge
of the transmitter locations and transmit timing offset is needed.
Position calculation can be conducted, for example, by a
positioning server (eSMLC in LTE) or by the receiving equipment,
which often is an item of user equipment (UE), such as a mobile
terminal or other type of portable communication device. The former
approach is referred to as a UE-assisted positioning mode, while
the latter is a UE-based positioning mode. As noted, LTE has
introduced the use of new physical signals dedicated for
positioning (PRSs), as defined in 3GPP TS 36.211, "Evolved
Universal Terrestrial Radio Access (E-UTRA); Physical Channels and
Modulation Positioning Reference Signals."
[0009] PRSs generally are transmitted from one antenna port from a
given base station for a corresponding cell according to a
pre-defined pattern. A frequency shift, which is a function of the
physical cell identity or PCI, can be applied to the specified PRS
patterns, to generate orthogonal patterns and modeling an effective
frequency reuse of six. Doing so makes it possible to significantly
reduce neighbor cell interference as measured on the PRS for a
given cell. Interference reduction on the PRS measurements
correspondingly leads to improved positioning measurements.
[0010] Even though PRSs have been specifically designed for
positioning measurements and in general are characterized by better
signal quality than other reference signals, the current LTE
standard does not mandate using PRSs. Other reference signals, the
earlier mentioned CRSs can, in principle, be used for positioning
measurements.
[0011] If PRSs are used, they are transmitted in pre-defined
positioning subframes grouped by several consecutive subframes,
with N.sub.PRS subframes in each positioning occasion. The
positioning occasions are recurring, e.g., repeated according to a
defined periodic interval having a certain periodicity of N
subframes. According to 3GPP TS 36.211, the standardized periods
for N are 160, 320, 640, and 1280 ms, and the number of consecutive
subframes N.sub.PRS that define each positioning occasion are 1, 2,
4, and 6.
[0012] Because OTDOA-based positioning requires that PRSs be
measured from multiple distinct locations, a receiving radio
apparatus (user equipment or other radio node in the network) may
have to work with a wide range of received signal strengths, e.g.,
the PRSs received from neighboring cells may be significantly
weaker than the PRSs received from a serving cell. Furthermore,
without at least approximate knowledge of when particular ones of
the PRSs are expected to arrive in time and what PRS patterns are
being used (e.g., arrangements within the time-frequency grid of
OFDM signal subframes), the receiving radio apparatus is obligated
to perform PRS searching within potentially large time-frequency
windows. That, of course, increases the processing resources and
the time needed for making PRS measurements, and tends to lower the
accuracy of the results.
[0013] To facilitate such measurements, it is known for the network
to transmit assistance data, which includes, among other things,
reference cell information, neighbor cell lists containing PCIs of
neighbor cells, the number of consecutive downlink subframes that
constitute a positioning occasion, and the overall transmission
bandwidth used for PRS transmission, frequency, etc.
[0014] Further, it is known to mute PRSs, where "muting" means
transmitting with zero power (or low power) at certain positioning
occasions. Such muting applies to all PRS resource elements--i.e.,
defined OFDM subcarriers at defined symbol times--within the same
subframe and over the entire PRS transmission bandwidth. However,
to date, the 3GPP standards do not specify how muting is to be
implemented, nor do they specify signaling for communicating muting
information to UEs or other receiving equipment that might be
making use of the PRSs being transmitted by a given cell or a given
cluster of neighboring cells.
[0015] Certain muting arrangements, however, have been
contemplated. One contemplated approach is to use random muting by
cells. Here, each eNodeB decides whether or not to mute its PRS
transmissions for a given positioning occasion (or occasions)
according to some probability. In the most basic contemplation of
this approach, each eNodeB (cell) in the network independently
makes muting decisions (according to some defined probability),
without any coordination between the cells. The probability used to
make the muting decision is statically configured per eNodeB or per
cell.
[0016] While this approach offers certain advantages in terms of
simplicity on the network side, it leaves receiving radio equipment
with the same burdensome processing tasks, as said equipment has no
knowledge of the random muting operations. A further issue is the
inability to know the optimal probabilities to use for making the
muting decision, and the fact that such probabilities likely change
in dependence on complex interrelationships between cells (varying
geometry, etc.), and may even change depending upon times of day,
etc.
[0017] Another approach relies on a limited set of muting patterns,
and maps these patterns according to PCIs. This approach allows a
UE or other radio receiver to determine when PRSs are transmitted
(or muted) in any given cell of interest, based on receiving
information regarding the association between muting patterns and
PCIs--e.g., a table. However, this approach requires signaling the
actual patterns or hard-coding them into the receiving equipment.
That latter approach may not be practical for some types of
equipment. Besides, the static nature of such mapping has its own
disadvantages.
[0018] Another approach proposes sending UEs an indication of
whether or not autonomous muting is activated. A Boolean indicator
is transmitted for the reference cell and also all neighbor cells
as a part of the assistance data. When the indicator is FALSE, the
UE can avoid blind detection of PRS muting, optimize detection
thresholds and thus improve the positioning performance. However,
with the indicator set to TRUE, the UE still does not receive
information indicating when and for which resource blocks (RBs)
muting occurs, meaning that the UE still needs to blindly detect
when PRS muting is used in each cell.
SUMMARY
[0019] In one aspect, the present invention provides a simple
method of signaling reference signal muting information to
receiving radio equipment, such as UEs. (The reference signals may
be, e.g., PRSs and/or CRSs.) In one or more embodiments, the
present invention proposes a general solution whereby the receiving
radio equipment is informed not only on whether muting is used in
general in a cell, but also the particular timing and formatting of
such muting. Further, the contemplated method provides for the use
of dynamic muting patterns, and thus avoids the need for statically
defined muting patterns, and provides for coordinated muting
control, across two or more network cells.
[0020] Accordingly, in one embodiment, the present invention
comprises a method of controlling the transmission of reference
signals in a wireless communication network. The method includes
transmitting reference signals at recurring occasions, for use in
making reference signal measurements at receiving radio equipment.
The method further includes muting the reference signals in certain
ones of the occasions, in accordance with a muting configuration,
and transmitting muting configuration information indicating said
muting configuration, to inform the receiving radio equipment
regarding one or more aspects of said muting.
[0021] In particular, the muting configuration information includes
one or more of: a bandwidth parameter identifying the portion of
reference signal bandwidth to which muting applies; a subframes
parameter indicating the number of consecutive subframes within an
occasion to which muting applies; and a muting occasion parameter
indicating occasions to which muting applies. (In at least one
embodiment, in cases where no muting bandwidth parameter is
signaled, the receiving radio equipment is configured to assume
that muting is applied over the entire reference signal
transmission bandwidth.) Such information allows the receiving
radio equipment--network node, UE, or other radio apparatus--to
know exactly when and how reference signals are muted. In turn,
that knowledge provides for improved accuracy in acquiring and
measuring reference signals, and for reduced processing complexity
through, for example, the elimination or reduction in blind
searching.
[0022] In another embodiment, the present invention comprises a
base station for use in a wireless communication network that
transmits reference signals in a wireless communication network.
The base station includes a transmitter configured to transmit
reference signals at recurring occasions, for use in making
reference signal measurements at receiving radio equipment, and a
processing circuit that is operatively associated with the
transmitter and configured to mute the reference signals in certain
ones of the occasions, in accordance with a muting configuration.
In particular, the processing circuit is configured to transmit,
via said transmitter, muting configuration information indicating
the muting configuration, to inform the receiving radio equipment
regarding one or more aspects of the muting.
[0023] In yet another embodiment, the present invention comprises a
method and apparatus in a positioning node that is configured for
use with a wireless communication network. The positioning node
includes one or more processing circuits configured to determine a
muting configuration used to control muting of positioning
reference signals transmitted at recurring positioning occasions
from one or more base stations in the wireless communication
network. In one embodiment, the positioning node determines the
muting configuration based on signaling received from the base
station(s), i.e., the base stations inform the positioning node as
to their muting configuration(s). In at least one such embodiment,
the positioning node generates muting configuration information
based on the signaling received from the base station(s), and it
sends this muting configuration information as higher-layer
signaling, to assist radio equipment with measuring the positioning
reference signals transmitted from the base stations, in accordance
with the muting configurations of those base stations.
[0024] In another embodiment, the one or more processing circuits
are configured to decide the muting configuration(s) to be
used--here, "determining" the muting configurations of the one or
more base station(s) means generating the muting configuration
information at the positioning node. In at least one such
embodiment, the positioning node is configured to send muting
control signaling to the base station(s), to effect muting control
in accordance with the determined muting configurations.
[0025] In either case, the positioning node further includes a
communication interface operatively associated with the one or more
processing circuits. This communication interface, which may
incorporate more than one physical interface and/or signaling
protocols, is configured for sending the muting configuration
information and/or sending the muting control signaling, and, in
applicable embodiments, receiving signaling from the base stations
indicating their muting configuration(s). It should be understood
that such signaling between the positioning node and the base
stations may be direct or indirect.
[0026] In at least one embodiment, the one or more processing
circuits are configured to generate muting configuration
information that indicates when or how muting will be applied by
the one or more base stations, for indicated or known positioning
occasions. The positioning node sends corresponding muting
configuration information as higher-layer signaling, for
transmission by the one or more base stations to radio equipment
receiving the positioning reference signals.
[0027] In another embodiment, a base station is configured to
generate the muting configuration and send it to a positioning
node. In turn, the positioning node sends this information as
assistance data--e.g., the positioning node sends positioning
reference signal measurement assistance data to an item of user
equipment. The BS then applies the generated muting configuration,
i.e., it transmits or does not transmit reference signals
accordingly. In this same embodiment and/or others, the base
station is equipped with an interface over which the muting
configuration is exchanged with other base stations, to provide for
distributed coordination of muting configurations.
[0028] In another embodiment, the present invention provides a
method and apparatus, for controlling measurement of reference
signals at a receiving radio apparatus. The reference signals are
transmitted by a wireless communication network at recurring
occasions, and the receiving radio apparatus is, for example, a UE
or another node in the network.
[0029] In any case, the contemplated method includes receiving
signaling from the wireless communication network that conveys one
or more of the following muting parameters: a bandwidth parameter
identifying the portion of reference signal bandwidth to which
muting applies; a subframes parameter indicating the number of
consecutive subframes within an occasion to which muting applies;
and a muting occasion parameter indicating occasions to which
muting applies. Correspondingly, the method includes controlling
reference signal measurement by the radio apparatus, in accordance
with the received muting parameters.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a block diagram of one embodiment of a wireless
communication network.
[0031] FIG. 2 is a logic flow diagram of one embodiment of a method
of muting reference signals in accordance with a muting
configuration, and transmitting corresponding muting configuration
information.
[0032] FIG. 3 is a block diagram of one embodiment of a base
station, e.g., an eNodeB in an LTE network.
[0033] FIG. 4 is a block diagram of one embodiment of a muting
control node, that provides muting control for one or more cells in
a wireless communication network.
[0034] FIGS. 5A-C are logic flow diagrams of various embodiments of
a method of determining muting configurations and corresponding
muting control, and sending corresponding muting control
information.
[0035] FIG. 6 is a logic flow diagram of one embodiment of a method
of receiving muting configuration information (muting parameters)
at user equipment or other radio equipment making reference signal
measurements, and controlling such measurements according to the
received muting parameters.
[0036] FIG. 7 is a block diagram of one embodiment of a radio
apparatus (e.g., UE or other radio equipment) that is configured to
receive muting configuration information and to control its
measurements of reference signals according to that
information.
[0037] FIGS. 8 and 9 are diagrams illustrating different
embodiments for applying muting to a subset of subframes within a
given reference signal transmission occasion in which the reference
signals span a number of subframes.
[0038] FIG. 10 is an example table of muting configuration
parameter values, which can be used for configuring the muting of
positioning reference signals.
DETAILED DESCRIPTION
[0039] As a non-limiting example, FIG. 1 illustrates one embodiment
of a wireless communication network 10, which includes a Radio
Access Network (RAN) 12 and an associated Core Network (CN) 14. The
RAN 12 includes a number of base stations 16, e.g., BS 16-1, 16-2,
and so on. Unless needed for clarity, the reference number 16 is
used to refer to BSs 16 in both singular and plural senses. Each BS
16 provides one or more "cells" 18, e.g., cell 18-1 corresponding
to BS 16-1, cell 18-2 corresponding to BS 16-2, and so on. The
cells 18 represent the radio service coverage provided by each BS
16, for supporting communications with user equipment 20, e.g., UE
20-1, UE 20-2, and so on.
[0040] Correspondingly, the CN 14 communicatively links the UEs 20
to each other and/or to communications equipment in other networks,
such as the Internet, the PSTN, etc. To that end, the CN 14
includes a number of nodes or other functional entities. By way of
simplified example, the illustrated CN 14 is depicted as including
a Serving Gateway (SGW) 22, a Mobility Management Entity (MME) 24,
and a Positioning Node 26. In one or more embodiments where the
network 10 comprises an LTE network, or an LTE advanced network,
the positioning node 26 comprises an E-SMLC or SLP, or another type
of network-based positioning node.
[0041] To support positioning operations, e.g., OTDOA measurements,
the network 10 in one or more embodiments transmits PRSs at
recurring positioning occasions, e.g., at periodic frame/subframe
intervals. In the same or other embodiments, the network 10
transmits CRSs at recurring occasions. Correspondingly, in at least
one embodiment the present invention provides a method of
controlling the transmission of reference signals (RSs) within the
network 10 (e.g., within all or a portion of the network).
[0042] As shown in FIG. 2, the method 200 includes transmitting RSs
at recurring occasions, for use in making reference signal
measurements at receiving radio equipment (Block 202); muting the
reference signals in certain ones of the occasions, in accordance
with a muting configuration (Block 204); and transmitting muting
configuration information indicating said muting configuration, to
inform said receiving radio equipment regarding one or more aspects
of said muting (Block 206). In at least one such embodiment, the
muting configuration information includes one or more of: a
bandwidth parameter identifying the portion of reference signal
bandwidth to which muting applies; a subframes parameter indicating
the number of consecutive subframes within an occasion to which
muting applies; and a muting occasion parameter indicating
occasions to which muting applies.
[0043] FIG. 3 illustrates an example embodiment of a base station
16, which is configured to implement method 200, or variations of
it. In particular, the base station 16 is configured for use in a
wireless communication network that transmits reference signals,
and it comprises: a transmitter configured to transmit reference
signals at recurring occasions, for use in making reference signal
measurements at receiving radio equipment. Here, the transmitter is
included in the transceiver circuits 30, which may comprise OFDM
(with or without MIMO) radio transmission and reception
circuits.
[0044] The base station 16 further includes a number of
communication and control circuits 32, including a processing
circuit operatively associated with the transmitter and configured
to mute the reference signals in certain ones of the occasions, in
accordance with a muting configuration. Here, the processing
circuit comprises, e.g., one or more reference signal (RS) muting
control circuits 34, which may be one or more microprocessor based
circuits, or other digital signal processing circuits.
[0045] In particular, the processing circuit is configured to
transmit, via said transmitter, muting configuration information
indicating said muting configuration, to inform said receiving
radio equipment regarding one or more aspects of said muting, and
wherein the muting configuration information includes one or more
of: a bandwidth parameter identifying the portion of reference
signal bandwidth to which muting applies; a subframes parameter
indicating the number of consecutive subframes within an occasion
to which muting applies; and a muting occasion parameter indicating
occasions to which muting applies.
[0046] The base station 16 further includes a core network
communication interface 36 for receiving muting control signaling
from a higher-layer node in the wireless communication network 10,
e.g., from the positioning node 26. Further, the processing circuit
is configured to determine or otherwise set the muting
configuration of the base station 16, based at least in part on
said muting control signaling received from the higher-layer node.
In one embodiment, the core network communication interface 36
provides for communicating directly or indirectly with one or more
core network nodes, including a positioning node 26, and the base
station 16 is configured to receive signaling from the positioning
node 26 that sets or otherwise controls one or more aspects of the
muting configuration of the base station 16.
[0047] As an example, the illustrated base station 16 comprises an
eNodeB, where the network 10 comprises an LTE network, or LTE
Advanced network. Here, as an example, the muting control signaling
received at the base station 16 comprises signaling from an E-SMLC
(as the positioning node 26) which controls one or more aspects of
the muting configuration of the base station 16.
[0048] Further, in at least one embodiment, the base station 16 is
configured to transmit, via lower-layer signaling, the previously
noted muting occasion indicator as a flag or other indicator
indicating whether muting will be used in an indicated or known
occasion, and to transmit, via higher-layer signaling, one or both
of the bandwidth and subframes parameters, to complement the
lower-layer signaling of the muting occasion parameter. This
arrangement is advantageous, for example, because it allows
lower-overhead signaling of the muting occasion indicator, which
may be more dynamic than the bandwidth/subframe details of muting.
In any case, such signaling allows for the receiving radio
equipment to be apprised of whether muting applies to a given
occasion via the muting occasion parameter (via lower-layer
signaling), and apprised of the reference signal bandwidth and the
number of consecutive subframes (via higher-layer signaling), to
which such muting applies for that given occasion.
[0049] In other contemplated embodiments, the base station 16
comprises a home eNodeB (e.g., for residential use), a pico base
station (e.g., for providing small-cell coverage), or a relay node
(e.g., for extending base station coverage). Regardless, in at
least one embodiment, the base station includes an
inter-base-station communication interface 38 and is configured to
determine one or more aspects of the muting configuration
cooperatively, with one or more neighboring base stations 16, based
on exchanging inter-base-station signaling via the
inter-base-station communication interface 38. Of course, as noted,
in at least one embodiment, the processing circuit (e.g., RS muting
control circuit(s) 34) is configured to determine the muting
configuration to be used by the base station 16, and that
determination is made autonomously in at least one embodiment.
[0050] Returning to the method 200 introduced in FIG. 2, in one or
more embodiments, the reference signals (RSs) are positioning
reference signals (PRSs) transmitted at defined positioning
occasions by at least one base station 16 in the network 10, where
the PRSs are used by the receiving radio equipment in making
positioning-related measurements.
[0051] Further, in at least one embodiment, "muting" the reference
signals in any given occasion comprises transmitting the reference
signals at zero or reduced power. Here, "reduced" power is a
transmit power below that which would be used in the absence of
muting, and preferably significantly below the "normal" levels of
transmit power used for transmitting references signals when they
are not muted.
[0052] Still further, in at least one embodiment, the method
relates to a plurality of base stations 16 associated with
respective ones in a plurality of associated cells 18, and further
comprises determining the muting configuration cooperatively across
the plurality of associated cells 18. In at least one such
embodiment, determining the muting configuration cooperatively
across the plurality of associated cells 18 comprises determining
one or more muting patterns to be used across the plurality of
associated cells 18. Further, in at least one such embodiment, each
base station 16 in the plurality of base stations 16 transmits
muting occasion indicators, in accordance with the one or more
muting patterns. That is, the muting occasion indicators as
transmitted are dynamically updated to reflect the muting
pattern(s).
[0053] Broadly, the method 200 may be carried out, for example, at
one or more of the base stations 16 illustrated in FIG. 1, or in an
even larger plurality. In at least one embodiment, each base
station 16 autonomously determines its muting configuration, and
correspondingly transmits muting configuration information. Also,
in at least one embodiment, a base station 16 is configured to
determine its muting configuration and send signaling to another
node that is configured to send signaling that indicates the base
station's muting configuration. As one example, the base station 16
determines its muting configuration and sends signaling to a
positioning node 26. In turn, the positioning node 26 sends
signaling to one or more UEs 20 that indicates the base station's
muting configuration. e.g., the positioning node 26 includes muting
configuration information in the positioning reference signal
assistance data that it sends to the UEs 20 by way of higher-layer
signaling that is carried through one or more base stations 16.
[0054] In such an embodiment, or in yet another embodiment, two or
more base stations 16 exchange muting configuration
information--e.g., LTE eNodeBs communicating through their X2
interfaces. In at least one such embodiment, the two or more base
stations 16 cooperatively determine the muting configurations to be
used by each one of them, or at least share their respective muting
configurations with each other. In yet another embodiment, another
node (or nodes) in the network, other than the base stations 16,
determines at least part of the muting configuration, and the base
stations 16 implement that configuration accordingly.
[0055] For example, FIG. 4 illustrates a muting control node 40,
which may be, for example, the positioning control node 26 shown in
FIG. 1. The muting control node 40 is configured to provide
per-cell or cooperatively determined muting control (i.e., muting
control that is coordinated across two or more cells). In the
illustration, the muting control node 40 provides muting control
for three example cells, 18-1, 18-2, and 18-3. Notably, the muting
control node 40 is, in one or more embodiments, configured to
control the muting of one or more types of reference signals that
are transmitted in the cells 18, and configured to send (e.g.,
transparently through the associated base stations 16) muting
control information, so that receiving radio equipment is informed
of the muting configuration.
[0056] The illustrated embodiment of the node 40 comprises one or
more processing circuits 42 that are configured to generate muting
control signaling for controlling muting of reference signals
transmitted at recurring positioning occasions from one or more
base stations 16 in the RAN 12 of the network 10. Further, a
communication interface 44 is operatively associated with the one
or more processing circuits 42 and the processing circuits 42 use
the communication interface 44 to send the muting control signaling
to the one or more base stations 16.
[0057] In at least one embodiment, of the node 40, the one or more
processing circuits 42 are further configured to generate muting
configuration information that indicates when or how muting will be
applied by the one or more base stations 16, for indicated or known
occasions, and to send the muting configuration information as
higher-layer signaling, for transmission by the one or more base
stations 16 to radio equipment receiving the reference signals
(e.g., UEs 20 and/or other nodes in the network 10).
[0058] Further, as noted, in at least one embodiment, the one or
more processing circuits 42 are configured to control muting of the
reference signals in coordinated fashion across two or more cells
18 of the radio access network, said two or more cells 18
associated with said one or more base stations 16. In at least one
such embodiment, the one or more processing circuits 42 are
configured to coordinate, as across the two or more cells 18, at
least one of the following: the timing or selection of which
reference signal occasions have muting applied to them; the
reference signal bandwidth to which muting is applied in one or
more (reference signal transmission) occasions; and the number of
consecutive subframes to which muting is applied within a given
occasion.
[0059] FIG. 5A illustrates a method 500A implemented, for example,
at the node 40, corresponding to the above-described structural
configuration of the node 40. The method 500A includes controlling
muting of RSs in one or more cells 18 of the network 10 (Block
502)--e.g., a method where a node acts in some centralized sense as
a muting configuration controller for the RSs being transmitted in
two or more cells 18 in the network 10. The illustrated method 500A
further includes sending higher-layer signaling, conveying (at
least some of) the muting configuration information, corresponding
to the muting control, for transmission to receiving radio
equipment (Block 504), e.g., to the UEs 20 operating in the one or
more cells 18.
[0060] As an example, the higher layer signaling comprises Radio
Resource Control (RRC) or LPP signaling. In a particular example,
certain aspects of the muting configuration are configured using
higher-layer signaling. Example aspects include muting bandwidth
information. In at least one such embodiment, other aspects of the
muting configuration are signaled using lower-layer signaling, such
as physical layer signaling and/or MAC layer signaling. Lower-layer
signaling is advantageous, for example, when signaling frequently
changing aspects of the muting configuration, such as the muting
occasion indicators.
[0061] FIGS. 5B and 5C show variations of the method 500A, which
may be advantageously carried out at a positioning node 26, such as
an E-SMLC in an LTE network. For example, in the method 500B, one
sees a positioning node 26 that is configured to determine the
muting configuration of one or more base stations 16, based on
receiving signaling (directly or indirectly) from the base stations
16, where that signaling indicates the muting configuration(s) of
the base stations 16 (Block 506). Correspondingly, the positioning
node 26 sends higher-layer signaling conveying muting configuration
information (Block 508), e.g., indicating the muting configuration
in use at the base station(s) 16. That higher-layer signaling
targets radio equipment, e.g., UEs 20, to assist them in making
positioning reference signal measurements with respect to the base
station(s) 16, in accordance with the muting configuration(s) of
the base station(s) 16.
[0062] Thus, the method 500B can be understood as an embodiment
where one or more base station(s) 16 individually or cooperatively
determine their muting configurations while communicating e.g. over
the X2 interface, and one or more of them send signaling to the
positioning node 26, to inform the positioning node 26 of the
muting configurations. Because certain aspects of the muting
configuration are advantageously signaled via higher-layer
signaling, receiving such signaling from the base stations 16
allows the positioning node 26 to generate corresponding muting
configuration information that it then sends to targeted UEs 20 or
other radio equipment, to inform those recipients of the muting
configuration(s) in use at the base stations 16.
[0063] FIG. 5C illustrates an alternative method 500C, where the
positioning node 26 determines the muting configuration(s) not
based on the base station(s) 16 informing it of the decided
configurations, but rather on the positioning node itself deciding
the muting configuration(s) to be used by the base station(s) 16
(Block 510). As a non-limiting example, this embodiment is
advantageous in implementations where coordination of muting
configurations across two or more cells 18 of the network 10 is
desired--e.g., a positioning node 26 can provide centralized
control and coordination of the muting configurations used by any
one or more groups of base stations 16, based on being provisioned
with base-station/cell neighbor information, etc.
[0064] In any case, the method 500C further includes the
positioning node 26 generating/sending muting control signaling to
the base station(s), to effect muting control in accordance with
the muting configuration(s) decided by the positioning node 26
(Block 512). Note, too, that in one such embodiment, the base
stations 16 send all muting configuration information as
lower-layer signaling, to assist radio equipment with measuring
their reference signals in accordance with the muting
configurations. That is, although the positioning node 26
determines all or at least some aspects of the muting
configuration(s) used by the base station(s) 16, the base stations
themselves generate and send the lower-layer signaling used to
convey the corresponding muting configuration to the receiving
radio equipment.
[0065] However, in another embodiment, the positioning node 26
again decides all or some aspects of the muting configuration(s) to
be used by the base station(s) 16. However, the positioning node
26, in addition to sending control signaling to the base station(s)
16 to implement the muting configuration(s) at those base stations
16, also sends higher-layer signaling to one or more UEs 20 or
other receiving equipment. As before, that higher-layer signaling
indicates some or all aspects of the muting configuration(s) used
by the base station(s) 16.
[0066] As for the receiving radio equipment--i.e., equipment that
receives the reference signals and acts on the muting configuration
information FIG. 6 illustrates an example processing method 600.
The illustrated method 600 includes receiving signaling conveying
one or more muting parameters (Block 602). (As previously
described, these muting parameters indicate one or more aspects of
the muting configuration--i.e., they inform the receiving radio
equipment of the muting configuration used to control reference
signal muting.) The receiving radio equipment includes processing
circuitry that is configured to interpret the received muting
control information, and to correspondingly control its reference
signal measurements, according to the received muting parameters
(Block 604).
[0067] Correspondingly, FIG. 7 illustrates an example embodiment of
receiving radio equipment 50, which may be configured to implement
the method 600 of FIG. 6, or variations of that method. The
equipment 50 includes transceiver circuits 52, e.g., a wireless
communication transceiver comprising MIMO/OFDM transmitter and
receiver circuitry for LTE communications. The equipment 50 further
comprises communication and control circuits 54, which comprise,
for example, fixed and/or programmable circuitry, such as one or
more microprocessor-based circuits.
[0068] The circuits 54 include reference signal (RS) acquisition
and processing control circuitry 56, including received RS muting
information detection and processing circuitry 58. With this
configuration, the equipment 50 configures one or more aspects of
its reference signal measurement operations according to muting
control information received from the network 10, via its
transceiver circuits 52. For example, it may forego reference
signal measurements for certain cells on certain time/frequency
resources, based on its knowledge that muting is applied at those
times and/or frequencies. Further, it may make more accurate
measurements of the received reference signals, based on knowing
which time/frequency resources within particular subframes to which
muting is applied, and/or based on knowing which cell reference
signals are muted, how they are muted, and when they are muted.
Note that in one or more embodiments, "muting" a reference signal
comprises the transmitting node reducing the transmit power
allocated to that signal, where such reduction is potentially
significant (e.g., in terms of dBs, as compared to non-muted
transmission power). The power offset value or indicator used for
such reduction can be signaled.
[0069] In at least one embodiment, one or more of the UEs 20 are
configured according to the example of FIG. 7. However, it should
be understood that other nodes in the network 10 also may be
configured to receive muting configuration information, and to
control their own acquisition and processing of reference signals
according to that received muting configuration information.
[0070] For example, the equipment 50 receives signaling from the
network 10 that conveys one or more of the following muting
parameters: a bandwidth parameter identifying the portion of
reference signal bandwidth to which muting applies; a subframes
parameter indicating the number of consecutive subframes within an
occasion to which muting applies; and a muting occasion parameter
indicating occasions to which muting applies. (Note that FIG. 8
illustrates muting the middle portion of a given reference signal
bandwidth, and FIG. 9 illustrates muting the outer portions of a
given reference signal bandwidth.) Correspondingly, the equipment
50 controls its reference signal measurements, in accordance with
the received muting parameters.
[0071] In detailing the possibilities for providing receiving radio
equipment with those muting parameters in the context of PRSs, it
is contemplated herein to provide UEs 20, and other radio
apparatuses that receive and make measurements on the reference
signals, with knowledge about the positioning reference
configuration in a cell 18 (reference signals to be measured, their
transmission bandwidth, subframes for positioning measurements and
their periodicity, etc.). This assumption is relevant for the
serving cell 18, but also neighbor cells 18 that the UE may have
detected blindly (even for reasons other than mobility, i.e., not
necessarily for positioning purposes).
[0072] As noted, the muting configuration information can be
provided using lower-layer signaling, higher-layer signaling, or
some combination of lower-layer and higher-layer signaling. As an
LTE-based example of lower-layer signaling, prior to every
positioning occasion, each eNodeB sends a command or an indicator
(e.g. one bit) to the UEs 20 via lower-layer signaling such as in a
Medium Access Control (MAC) Protocol Data Unit (PDU), or as a part
of the scheduling information, which maps to the Physical Downlink
Control Channel (PDCCH). Thus, lower-layer signaling in this
example can be understood as some form of control channel
signaling, carrying information related to the physical layer (L1)
or Layer 2, such as MAC.
[0073] In LTE, L1/L2 control information is sent via PDCCH, and UEs
20 are required to decode the PDCCH, which is sent in every
subframe, so that the UEs 20 acquire scheduling information etc. In
one embodiment herein, it is proposed to send a 1-bit command in
each cell 18, via lower-layer signaling, indicating whether muting
will or will not be used in the cell 18 during the next positioning
occasion. In general, muting configuration signaling may refer by
default to an "indicated" positioning occasion, which may be
signaled to the UEs 20, or known to the UEs 20, such as based on
the UEs being configured to use a default assumption that the
signaled muting configuration information pertains to the next
positioning occasion.
[0074] In an example command configuration, "0" or other such
indication means muting is NOT used in the cell 18, in the next
occasion and "1" therefore means that muting is used in the next
positioning occasion. The opposite logical meanings obviously can
be used, or another approach to indicating the used/not-used status
of muting for each muting occasion.
[0075] However, in one embodiment, each base station 16 is
configured to send the command only if the base station's
corresponding cell 18 will be muted in the next occasion.
Otherwise, i.e., in the absence of the command, the UEs 20 (or
other receiving radio equipment) assume that muting will not be
used in the cell 18 during the next positioning occasion. Further,
the UEs 20 or other receiving equipment may be configured to
maintain the assumption that muting is not used, until the
reception of the next command indicating that muting will be
used.
[0076] Advantageously, the UEs 20 or other receiving radio
equipment do not have to perform blind detection when muting is
used--that is, the knowledge that muting is applied to reference
signals during a given reference signal transmission occasion
allows the receiving radio equipment to forego blind searching.
Eliminating blind detection significantly reduces UE complexity,
lowers UE power consumption and decreases UE processing
requirements.
[0077] In another embodiment, the subframes during which PRSs can
be muted within a positioning occasion are known a priori to the
UEs 20 and the network 10. For example, if muting is indicated for
a given positioning occasion, then the UEs can assume that this
applies to all subframes with the indicated positioning occasion.
Alternatively, muting may apply only to specific subframes of the
indicated occasion. For example, only the first or second half of a
given positioning occasion will be muted. Whether the first or
second half is muted may be known or otherwise set according to
cell IDs, for example.
[0078] The above described muting indicator may be a 1-bit command,
and serve as a type of ON/OFF signaling. Under low signal quality
(e.g. low SNR, high BER, low received power, etc.) the receiving
radio equipment may not be able to reliably detect the muting
indicator command. This issue may lead a UE 20 or other receiving
radio equipment to make a false deciision--i.e., an erroneous
conclusion about whether muting will or will not be used for a
given occasion.
[0079] As an advantageous mitigation technique, however, it is
proposed herein to configure UEs 20 or other receiving radio
equipment to adopt a defined default behavior. For example, under
unreliable conditions, e.g., as determined by the UE 20 based on
unreliable reception of the muting indicator, or based on other
reception quality measurements or indicators, the UE 20 may be
configured to assume that muting is not used for the occasion for
which the decision is being taken (i.e., the next occasion, or a
known future occasion). This configuration has the advantage of
detecting and measuring reference signals for the occasion at
issue, but also may result in the UE 20 searching for reference
signals that are, in fact, muted for the occasion at issue. Thus,
an alternate mitigation technique is based on configuring the UEs
20 to assume that muting is used. That is, in cases where a given
UE 20 determines that the muting indicator is unreliably received,
that UE 20 makes the default determination that muting will be used
for the positioning occasion at issue (i.e., the next occasion, or
some other known future occasion).
[0080] Additionally, the UE 20 is, in one or more embodiments
contemplated herein, configured to collect statistics on the
unreliably detected muting indication commands over a certain time
and report the results to the network 10. In turn, the network 10
is configured to use such information as the basis for determining
that the transmit power of the muting indication commands should be
increased or decreased. Increasing the power improves reception and
thus that decision is taken when the reliability statistics
indicate an unacceptably high unreliability. Conversely, decreasing
the power reduces inter-cell and intra-cell (if present)
interference and that decision thus is taken when the reliability
statistics indicate reliability that is better than needed, e.g. by
comparing the number or the ratio of erroneous muting commands to a
threshold.
[0081] Such power control is, in at least one embodiment,
implemented at the individual base station 16, where processing
circuitry (e.g., the RS muting control circuits 34, shown in FIG.
3) at the base station 16 is configured to evaluate the reliability
statistics for muting indicator reception from at least one UE 20,
and preferably multiple UEs 20, and to control transmit power
increases and decreases based on that evaluation. Note, here, that
the transmit power control increases and decreases may comprise
increasing or decreasing a variable transmit power ratio. That is,
there may be a baseline power control scheme that expresses the
transmit power of the muting indicator commands relative to a
reference signal (pilot, control, etc.), which is directly power
controlled based on reception quality feedback from the UEs 20. In
such cases, the base station 16 increases or decreases the transmit
power ratio used for setting the power of the muting indicator
transmissions, based on the reliability statistics.
[0082] As for producing those statistics, at least some of the UEs
20 are configured in one or more embodiments to report the
reception reliability results on an event basis, e.g., to send a
report if the total number of unreliable commands exceeds a
threshold. The threshold may be configured by the network, may be a
pre-defined value or may be implementation specifically at the UE
20. Each base station 16 also may be configured to autonomously
increase the power of the muting indicator commands, if the
reported measurements exhibit large error. Note that an LTE eNodeB,
as such a base station 16, could be configured to perform such
control in consideration on, e.g., the PDCCH Interference Impact
parameter, which is signaled over the X2 interface between
eNodeBs.
[0083] In one embodiment, when the lower-layer signaling can be
decoded by a UE 20 only in the serving cell 18, the network 10
ensures that no other cell 18 included in the assistance data sent
by the network 10 mutes during a given positioning occasion for the
UE 20. This configuration provides advantages for scenarios when a
UE 20 can read low-layer signaling (e.g. control channels) only for
its serving cell. In such cases, the muting command only tells the
UE that its serving cell (or alternatively, the reference cell) is
muted or not. However, at least in some networks, even such
limiting muting indications may be enough, because it at least
allows the UE 20 to receive muting indications for the presumably
strongest interferers--i.e., the reference signals transmitted in
the serving or reference cell--and that can be sufficient to
improve its measurements of reference signals from other cells. As
for the other cells, the UE 20 may be configured to assume (if it
has to assume anything) that they are not muted at the times its
reference or serving cell is muted and it is left to the network
implementation how to ensure that this UE assumption is correct,
which is possible by ensuring the separation in time/space of the
reference signal muting in neighbor cells. So, in an example
implementation, a UE whose reference or serving cell is muted is
informed before the muting occurs and it can use that information
to make strategic determinations as to when to make measurements
for its neighboring cells.
[0084] As such assistance data to the UE 20 is typically provided
by positioning node 26, e.g. an E-SMLC in the LTE control plane,
the positioning node 26 is, in one or more embodiments, configured
to coordinate muting control across a set or subset of cells, to
accomplish the above-described control. Also, in such cases, the
muting indicator informs the UE 20 about muting in the reference
cell 18. Note that the reference cell 18 is not necessarily the
UE's serving cell 18, but the UE 20 is aware of which cell 18 is
considered to be the positioning reference cell 18, based on the
positioning assistance information received from the network
10.
[0085] Of course, in other embodiments described herein, the UEs 20
receive the muting configuration information based on a combination
of lower-layer and higher-layer signaling. Such embodiments allow
for (logically) combining the lower layer muting indicator commands
with the higher layer signaling, which may be, e.g., radio resource
control (RRC), signaling, LTE positioning protocol (LPP) signaling,
etc. Such combining enables any given UE 20 to acquire more
comprehensive information about the muting applied in any given
occasion in any given cell 18. As an example, the lower-layer
signaling provides the UE 20 with muting indicator commands,
indicating whether or not muting will be applied, while the higher
layer signaling indicates the structure or arrangement, or other
details, regarding the particular manner in which such muting will
be applied. For example, as noted, the higher-layer signaling can
be used to indicate which subframes are muted and/or to indicate
the particular time and/or frequency resources to which muting is
applied. In a specific example, the higher layer signaling conveys
information about the muting bandwidth, which is the part of the
configured RS transmission bandwidth over which the RS is
temporarily not transmitted.
[0086] The configuration via higher layer signaling can be done in
a semi-static manner, e.g. at a call setup or occasionally during
the call. Furthermore the higher layer configuration can be done by
the base stations 16 (e.g., by eNodeBs in LTE) or by the
positioning node 26 (e.g., an E-SMLC in LTE), or by any other
appropriately configured radio node in the network 10.
[0087] This arrangement allows the use of higher-layer signaling
protocols to be used to carry static or semi-static information
about the particular manner in which muting will be applied, while
the more dynamic signaling of the muting indicators is done via
lower-layer signaling, where those indicators indicate the
selective application of muting to given reference signal
transmission occasions. In other words, higher-layer signaling can
be used to indicate how muting is applied--this can be understood
as configuring the reference signal operations of the UEs 20 or
other receiving radio equipment, to accommodate the particular
structure of reference signal muting that will be used--and
lower-layer signaling is then used to indicate when muting is
applied.
[0088] A specific example comprises using higher-layer signaling to
indicate that muting is applied only to the first half of subframes
within any given reference signal occasion, or that muting is
applied only to the first two subframes within any given occasion,
etc. Further, as a refinement of this method, it is contemplated
herein that a number of predefined muting configurations can be
identified, with each such identity identifying a specific subframe
muting arrangement, muting bandwidth configuration, etc.
[0089] With this approach, the signaling overhead is reduced by
signaling the muting configuration ID or IDs, which are known to
the UEs 20 or other receiving radio equipment. That is, rather than
signaling the actual configuration information, the network 10
signals the muting configuration ID, and the UEs 20 or other
receiving radio equipment use that signaled ID to look up the
particulars of the muting configuration, such as held in a
memory-retained data structure (e.g., look-up table), which stores
muting configuration details indexed by muting configuration
ID.
[0090] Regardless of the particular implementation details for such
combined signaling, one advantage using a combination of
higher-layer and lower-layer signaling is the flexibility thereby
obtained; namely, UEs 20 are informed both about the reference
signal occasions to which muting is applied, and further informed
about the particular manner in which such muting is implemented,
e.g., the subframes and the muting bandwidth that are muted in the
involved occasion. Notably, such information can be provided on a
per-cell basis, via signaling originating from or otherwise flowing
through the base stations 16 that serve the involved cells 18.
[0091] Further, using higher-layer signaling, detailed muting
configuration information can be sent, e.g., in conjunction with
other, related information. For example, in the case where PRSs and
positioning occasions are at issue, higher-layer signaling can be
used to send positioning assistance information, and to send muting
configuration information in conjunction with or as part of that
positioning assistance information. As noted, such signaling may
occur over logical links between a UE 20 and a positioning node 26,
where a logical link may comprise more than one physical link and
can be represented, for example, by the LTE Positioning Protocol
(LPP). When signaled over LPP, the muting configuration information
could be included, for example, as a part of the following
information elements: OTDOA-ReferenceCellInfo and
OTDOA-NeighborCellInfo, which comprise the OTDOA assistance
information for the reference cell and a neighbor cell,
respectively.
[0092] In addition to communicating muting configuration
information to the UEs 20, at least some aspects of the muting
configuration are agreed upon between the base station 16 and the
positioning node 26. (In an LTE example, such signaling can be done
between an eNodeB and an E-SMLC using the standardized LPP Annex
(LPPa) protocol.) Depending on where the muting configuration is
decided in the network 10 (e.g., at the E-SMLC, or at the eNodeB),
the muting information is transmitted either from the base station
16 to the positioning node 26, or in the opposite direction.
Further, if the muting configuration is decided in some other part
of the network 10, the positioning node 26 and/or the base station
16 are configured to receive that information directly or
indirectly from that other node.
[0093] Further, the proposed signaling may be implemented in the
control plane or in the user plane, and, as noted, the
determination of the muting configuration can be determined for or
at each cell 18 independent (per cell basis), or determined
cooperatively across a number of cells 18, e.g., across given
neighboring cells 18. Regardless, each cell 18 transmits the muting
configuration information applicable to it. For resource
efficiency, however, one or more embodiments contemplate not
signaling muting configuration information when muting is, in
general, not used within the cell 18. (This is different than the
case where muting is in general use within the cell 18, but is
selectively applied or not applied to given reference signal
occasions.) Correspondingly, UEs 20 that are configured to
otherwise receive and process muting configuration information can
be programmed or otherwise configured to interpret the absence of
muting configuration information from a given cell 18 as meaning
that muting is not in use for that cell 18.
[0094] Broadly, the present invention proposes one or more methods
and apparatuses which avoid the necessity of using a long-term
pre-determined, and/or statically fixed muting pattern, and avoids
locking the network 10 into sub-optimal pattern variations (such as
are imposed by cell-specific randomization of muting). Instead,
with the present invention and its ability to efficiently
determine, control, coordinate, and signal muting configuration
details, the network 10 is free to decide what particular muting
configuration is best, at any given time, or for any given area or
areas of the network 10. Furthermore, the UE is also informed about
the muted PRS and thus has a possibility to optimize the
measurement process and achieve better measurement accuracy, at a
complexity lower than it would be required without muting
signaling.
[0095] As contemplated in one or more embodiments, the muting
configuration is characterized by at least one of the following
parameters or any combination of them: muting bandwidth; the number
of consecutive subframes to which muting is applied, and a muting
occasion index. In at least one embodiment, the muting bandwidth is
the part of the configured RS transmission bandwidth over which the
RS is temporarily not transmitted.
[0096] In LTE, for example, PRS transmission bandwidth is typically
configured with respect to the system bandwidth center, so one
embodiment herein applies the same rule for muting bandwidth
configuration, i.e. the muting bandwidth parameter indicates a
given number X of muted resource blocks (RBs), which are assumed to
be located at the center of the PRS bandwidth, and are assumed to
be blanked in a given positioning occasion or for a given period.
(Refer again to FIG. 8.) If the muting bandwidth is not signaled,
the UE may assume that muting is applied over the entire PRS
transmission bandwidth.
[0097] In principle, there is no limitation on the muted PRS
bandwidth, except that it cannot exceed the PRS transmission
bandwidth. However, to avoid the centering problem, it makes sense
to require that the difference between the system bandwidth and the
muting bandwidth is an even number or zero (the same actually
applies for the difference between the system bandwidth and the PRS
transmission bandwidth).
[0098] In one embodiment, it is also possible to mute PRS over the
X/2 edge RBs, as taken from each end of the configured PRS
transmission bandwidth. This may be achieved, for example, by
signaling X with a minus sign. (Refer again to FIG. 9, to see an
example of edgewise muting. Note that muting edges of the PRS
transmission bandwidth in a short-term may look similar to reducing
PRS transmission bandwidth. However, changing the actual PRS
transmission bandwidth would require re-transmission of positioning
assistance data with the adjusted bandwidth. (Changing back to the
original bandwidth would require yet more signaling.) Thus, the
muting bandwidth control via the muting parameter is a more
efficient approach.
[0099] As for the muting parameter indicating the number of
consecutive subframes to which muting applies, according to the
current LTE standards for PRS, the maximum defined number of
consecutive subframes to be used for PRS transmission in one
positioning occasion is six. When all these subframes are
configured for positioning, it may or may not be necessary to apply
muting over the entire positioning occasion. The present invention
advantageously allows for the efficient signaling of which
particular subframes are muted and/or where muting is applied
within a given positioning occasion.
[0100] As a default for one or more embodiment, when the number of
consecutive muted subframes is not signaled, the UEs 20 are
configured to assume that PRSs are muted in the corresponding cell
over the entire positioning occasion indicated for muting (no
matter how many positioning subframes it spans over). Otherwise,
the signaled number shall apply. In any case, in one or more
embodiments, one bit is used for this parameter. For example, "0"
means that the first N.sub.PRS/2 set of positioning subframes are
muted during the positioning occasion indicated for muting, e.g.
the first 3 subframes out of 6 subframes during a positioning
occasion having 6 subframes in total. Conversely, a "1" means that
second N.sub.PRS/2 set of positioning subframes are muted during
the positioning occasion indicated for muting, e.g. the last 3
subframes out of the 6 subframes. In such embodiments, the PRS
muting subframe offset with respect to the first subframe of the
positioning occasion is either zero or N.sub.PRS/2.
[0101] As for the muting occasion index, it has been shown in 3GPP
RAN4 studies that four positioning occasions are sufficient in most
cases for detecting a single cell, even under a pessimistic network
configuration (asynchronous network, smallest bandwidth). Thus, as
one non-limiting example, the muting configuration can be set so
that positioning occasions are muted according to a periodicity of
four.
[0102] More generally, it is assumed that one out of a larger
number of occasions is muted, and that such an arrangement applies
to recurring occasions so that the muting periodicity is known. For
example, assuming that the muting periodicity spans four occasions,
two bits can be used for signaling the muting occasion index,
wherein: 00 means muting in the first positioning occasion, 01
means muting in the second positioning occasion, 10 means muting in
the third positioning occasion, and 11 means muting in the fourth
positioning occasion.
[0103] If one represents the muting periodicity as T.sub.MPRS, then
one may view the muting occasion index as representing an occasion
offset relative to the start of each new muting period. That is,
representing the muting occasion index as .DELTA..sub.MPRS, one
sees that .DELTA..sub.MPRS.epsilon.{0, 1, . . . , T.sub.MPRS-1}.
With respect to 3GPP TS 36.211, Evolved Universal Terrestrial Radio
Access (E-UTRA); Physical channels and modulation, T.sub.MPRS is
defined as the reference signal periodicity in subframes, and
.DELTA..sub.MPRS indicates the reference signal subframe
offset.
[0104] Thus, in one embodiment, the muting configuration
information signaled from a given cell 18 includes a value for
T.sub.MPRS, which indicates the periodicity of muting--e.g., muting
applied every X reference signal occasions--and a value for
.DELTA..sub.MPRS, which indicates the particular occasion within
the set of occasions spanned by that period to which muting is
applied.
[0105] Further, while the present invention provides the network 10
with the ability to dynamically adopt or revise muting
configurations in individual cells 18, and across groups of cells
18, it still may be desirable to define a limited set of muting
configurations and specify them as muting patterns which could be
standardized.
[0106] Further, it is proposed for one or more embodiments herein
to define the RS muting configuration index as various combinations
of .DELTA..sub.MPRS and T.sub.MPRS which satisfy the following
equation:
(10.times.n.sub.f+.left brkt-bot.n.sub.s/2.right
brkt-bot.-.DELTA.-T.sub.PRS.DELTA..sub.MPRS)mod(T.sub.PRST.sub.MPRS)=0
where .DELTA. is set to a desired offset value, and n.sub.f and
n.sub.s are the system frame number and the slot number within a
radio frame, respectively. FIG. 10 depicts a table 1 illustrating
examples of tabulated RS muting configuration indexes I.sub.MPRS,
derived under the assumption that muting applies to either the
first or the second half of the positioning occasion indicated for
muting (i.e. .DELTA. takes values .DELTA..sub.1 and
.DELTA..sub.2).
[0107] With the above in mind, the present invention in its various
embodiments offers a number of advantages. Non-limiting example
advantages include: flexible muting configuration with simple
signaling; no need for pre-defined PRS muting patterns; reduced UE
complexity, processing, power consumption, simultaneous with
improved reference signal measurement performance. In part, the
reduced UE complexity stems from the need for blind detection at
the UE (since the present invention provides the UE with knowledge
of when/where muting is used).
[0108] Further, as noted, the present invention can be implemented
using control-plane based operations, or based on user plane and/or
UE operations, or combinations of these approaches. Furthermore,
while certain aspects of the present invention have been
highlighted in the specific context of PRSs, the present invention
is directly applicable to other types of reference signals, which
may or may not be used for positioning measurements.
[0109] Finally, modifications and other embodiments of the
disclosed invention(s) 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(s) is/are 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.
* * * * *