U.S. patent number 9,271,205 [Application Number 14/445,222] was granted by the patent office on 2016-02-23 for measurement management in small-cell systems.
This patent grant is currently assigned to Google Technology Holdings LLC. The grantee listed for this patent is MOTOROLA MOBILITY LLC. Invention is credited to Sandeep Krishnamurthy, Vijay Nangia, Murali Narasimha, Ajit Nimbalker, Ravikiran Nory.
United States Patent |
9,271,205 |
Nory , et al. |
February 23, 2016 |
Measurement management in small-cell systems
Abstract
A system and method for neighbor-cell measurement reporting in a
cellular environment supporting multistate cells limits measurement
reporting by requiring that state-specific trigger conditions are
met. Thus for example, a dormant cell may need to meet more
stringent measurement conditions before a report is generated by
the user device, since a current primary cell may prefer to hand
off to an active cell. In particular, state-specific thresholds,
offsets, and hysteresis values may be used to enforce a preference
for active cells, for example.
Inventors: |
Nory; Ravikiran (Buffalo Grove,
IL), Krishnamurthy; Sandeep (Mountain View, CA), Nangia;
Vijay (Algonquin, IL), Narasimha; Murali (Vernon Hills,
IL), Nimbalker; Ajit (Buffalo Grove, IL) |
Applicant: |
Name |
City |
State |
Country |
Type |
MOTOROLA MOBILITY LLC |
Chicago |
IL |
US |
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Assignee: |
Google Technology Holdings LLC
(Mountain View, CA)
|
Family
ID: |
52995957 |
Appl.
No.: |
14/445,222 |
Filed: |
July 29, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150118968 A1 |
Apr 30, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61898049 |
Oct 31, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
36/00837 (20180801); H04W 36/0085 (20180801); H04W
36/00835 (20180801) |
Current International
Class: |
H04W
36/00 (20090101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2012118414 |
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Sep 2012 |
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WO |
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2014024001 |
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Feb 2014 |
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WO |
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Other References
Huawei, Hisilicon: "Measurement and procedure enhancements for
transition time reduction of small cell on/off", 3GPP TSG RAN WG1
Meeting #74bis, R1-134065, Guangzhon, China, Oct. 7-11, 2013, all
pages. cited by applicant .
NTT DOCOMO: "Views on efficient intra-frequency small cell
discovery", 3GPP TSG RAN WG1 Meeting #74bis, R1-134498, Guangzhou,
China, Oct. 7-11, 2013, all pages. cited by applicant .
NTT DOCOMO: "Vies on efficient inter-frequency small cell
discovery", 3GPP TSG RAN WG1 Meeting #74bis, R1-134497, Guangzhou,
China, Oct. 7-11, 2013, all pages. cited by applicant .
International Search Report and Written Opinion for Application No.
PCT?US2014/062851 dated Feb. 27, 2015. cited by applicant .
Mediatek Inc., "Methods for Efficient Discovery of Small Cells",
R1- 130225, 3GPP TSG-RAN WG1 #72, St Julian's, Malta, Jan. 28,
2013-Feb. 1, 2013. cited by applicant.
|
Primary Examiner: Sharma; Sujatha
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims priority to U.S. Provisional Patent
Application 61/898,049, filed on Oct. 31, 2013, which is
incorporated herein by reference in its entirety.
Claims
We claim:
1. A method for measurement reporting in a cellular user device
connected to a primary cell and being within receiving range of a
second cell, the method comprising: measuring a signal from the
second cell; determining a measurement quantity based on the
measurement; determining a cell state associated with the second
cell; evaluating a trigger condition using both the measurement
quantity and the cell state; and transmitting a measurement report
if the trigger condition is satisfied.
2. The method of claim 1 wherein determining a cell state
associated with the second cell comprises determining whether the
second cell is in an active state or in a dormant state.
3. The method of claim 2 wherein the active state is a state
wherein the second cell transmits reference signals with a
periodicity that is equal to or shorter than 5 ms and the dormant
state is a state wherein the second cell transmits reference
signals with a periodicity greater than 5 ms.
4. The method of claim 1 wherein measuring a signal from the second
cell comprises measuring one of the following signals corresponding
to the second cell: a common reference signal, a primary
synchronization signal, a secondary synchronization signal, a
small-cell discovery signal, a positioning reference signal, and a
channel-state information reference signal.
5. The method of claim 1 wherein determining a measurement quantity
comprises determining one of the following measurement quantities:
a reference signal received power and a reference signal received
quality.
6. The method of claim 2 wherein evaluating a trigger condition
using both the measurement quantity and the cell state further
comprises evaluating the trigger condition using a first
cell-specific offset value if the second cell is in active state
and evaluating the trigger condition using a second cell-specific
offset value if the second cell is in dormant state.
7. The method of claim 2 wherein evaluating a trigger condition
using both the measurement quantity and the cell state further
comprises evaluating the trigger condition using a first hysteresis
parameter value if the second cell is in active state and
evaluating the trigger condition using a second hysteresis
parameter value if the second cell is in dormant state.
8. The method of claim 2 wherein evaluating a trigger condition
using both the measurement quantity and the cell state further
comprises evaluating the trigger condition by comparing the
measurement quantity to a first threshold value if the second cell
is in active state and evaluating the trigger condition by
comparing the measurement quantity to a second threshold value if
the second cell is in dormant state.
9. The method of claim 8 wherein the second threshold value is
greater than the first threshold value.
10. The method of claim 2 further comprising: measuring a second
signal from a third cell; determining a second measurement quantity
based on the measured second signal; determining if the second
measurement quantity is smaller than a third threshold value; and
transmitting a measurement report including the second measurement
quantity to the primary cell if the second measurement quantity is
smaller than the third threshold and the trigger condition is
satisfied.
11. A method for configuring a cellular user device for measurement
reporting, the cellular user device being connected to a primary
cell and being within receiving range of a neighboring cell, the
method comprising transmitting a configuration from the primary
cell to the cellular user device, the configuration including
information for determining a trigger condition for reporting a
measurement of a characteristic of the neighboring cell, the
trigger condition being based upon both the measurement and a state
of the neighbor cell.
12. The method of claim 11 wherein the state of the neighbor cell
is one of an active state and a dormant state, wherein in the
active state, the neighbor cell transmits reference signals with a
periodicity equal to or shorter than 5 ms, and in the dormant state
the neighbor cell transmits reference signals with a periodicity
greater than 5 ms.
13. The method of claim 11 wherein the measured characteristic is
measured relative to a common reference signal, a primary
synchronization signal, a secondary synchronization signal, a
small-cell discovery signal, a positioning reference signal, and a
channel-state information reference signal.
14. The method of claim 11 wherein the measured characteristic is
one of a reference signal received power and a reference signal
received quality.
15. The method of claim 12 wherein the information used for
determining the trigger condition includes a first cell-specific
offset value for use if the neighbor cell is in the active state
and a second cell-specific offset value for use if the neighbor
cell is in the dormant state.
16. The method of claim 12 wherein the information used for
determining the trigger condition includes a first hysteresis
parameter value for use if the neighbor cell is in the active state
and a second hysteresis parameter value for use if the neighbor
cell is in the dormant state.
17. The method of claim 12 wherein the information used for
determining the trigger condition includes a first threshold value
for comparison to the measured characteristic of the neighboring
cell for use if the second cell is in active state and a second
threshold value for comparison to the measured characteristic of
the neighboring cell for use if the second cell is in dormant
state.
18. The method of claim 17 wherein the second threshold value is
greater than the first threshold value.
19. A cellular user device comprising: a processor; and a
measurement module run by the processor, the measurement module
being configured to measure a characteristic of a neighbor cell
while the cellular user device is connected to a primary cell and
to determine whether to transmit a measurement report to the
primary cell by applying a trigger condition, wherein the trigger
condition depends upon both the measured characteristic and a state
of the neighbor cell.
20. The cellular user device in accordance with claim 19, wherein
the state of the neighbor cell is one of an active state, wherein
the neighbor cell transmits reference signals with a periodicity
equal to or shorter than 5 ms, and a dormant state, wherein the
neighbor cell transmits reference signals with a periodicity
greater than 5 ms.
Description
TECHNICAL FIELD
The present disclosure is related generally to mobile-device
network utilization and, more particularly, to a system and method
for enhancing user-device measurement of cell attributes.
BACKGROUND
Mobile communications devices such as cellphones are now smaller
than anyone could have imagined just ten years ago. Some of the
credit for this diminutive sizing and convenience belongs to the
advances that have taken place in battery technology. However,
regardless of battery capacity and power density, efficient usage
of what battery power exists is also important in allowing device
providers to utilize smaller batteries onboard.
One important consumer of power in any wireless communication
device is the radio-frequency transmitter. Naturally, the further
away the potential recipient of the transmitted signals is, the
more powerful the transmitted signal must be. In this regard,
devices that utilize a cellular communications network need only
communicate with the nearest suitable cell, and as the device
moves, and other cells come into range and become more suitable,
the device may be "handed over" to another cell to continue
communications.
This process generally requires that the device monitor nearby
cells in addition to the cell with which the device is currently in
communication. This current cell, sometimes referred to as the
primary cell, may configure the device to monitor the other cells,
sometimes called neighboring or secondary cells, in a certain
manner. Currently, such configurations entail supplying a list of
trigger conditions and instructing the device to measure the signal
characteristics of the other cells and, when triggered to do so,
report those measurements back to the primary cell.
The present disclosure is directed to a system that may enhance
cell measurement and report triggering. However, it should be
appreciated that any such benefits are not a limitation on the
scope of the disclosed principles or of the attached claims, except
to the extent expressly noted in the claims. Additionally, the
discussion of technology in this Background section is merely
reflective of inventor observations or considerations and is not
intended to be admitted or assumed prior art as to the discussed
details. Moreover, the identification of the desirability of a
certain course of action is the inventors' observation, not an
art-recognized desirability.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
While the appended claims set forth the features of the present
techniques with particularity, these techniques, together with
their objects and advantages, may be best understood from the
following detailed description taken in conjunction with the
accompanying drawings of which:
FIG. 1 is a generalized schematic of an example device with respect
to which the presently disclosed innovations may be
implemented;
FIG. 2 is a network schematic showing an environment within which
embodiments of the disclosed principles may be implemented;
FIG. 3 is a frame and slot diagram showing the timing of
discovery-signal transmission;
FIG. 4 is a network schematic showing a cellular environment
supporting multistate cells within which embodiments of the
disclosed principles may be implemented; and
FIG. 5 is a flowchart showing a process of measurement-report
triggering in accordance with various embodiments of the disclosed
principles.
DETAILED DESCRIPTION
Turning now to a more detailed discussion in conjunction with the
attached figures, techniques of the present disclosure are
illustrated as being implemented in a suitable environment. The
following description is based on embodiments of the disclosed
principles and should not be taken as limiting the claims with
regard to alternative embodiments that are not explicitly described
herein. Thus, for example, while FIG. 1 illustrates an example
mobile device with respect to which embodiments of the disclosed
principles may be implemented, it will be appreciated that many
other devices such as, but not limited to, laptop computers, tablet
computers, personal computers, embedded automobile computing
systems, and so on, may also be used.
The schematic diagram of FIG. 1 shows an exemplary device 110
forming part of an environment within which aspects of the present
disclosure may be implemented. In particular, the schematic diagram
illustrates a user device 110 including several exemplary
components. A user device used in an example of the disclosed
principles, e.g., user device 110, may sometimes be referred to as
user equipment ("UE"). It will be appreciated that additional or
alternative components may be used in a given implementation
depending upon user preference, cost, and other considerations.
In the illustrated embodiment, the components of the user device
110 include a display screen 120, a measurement module 130, a
processor 140, a memory 150, one or more input components 160, and
one or more output components 170. The input components 160 may
include speech- and text-input facilities, for example, while the
output components 170 may include visual- and audible-output
facilities, e.g., one or more displays and audio outputs.
The processor 140 may be any of a microprocessor, microcomputer,
application-specific integrated circuit, or the like. For example,
the processor 140 can be implemented by one or more microprocessors
or controllers from any desired family or manufacturer. Similarly,
the memory 150 may reside on the same integrated circuit as the
processor 140. Additionally or alternatively, the memory 150 may be
accessed via a network, e.g., via cloud-based storage. The memory
150 may include a random-access memory and a read-only memory, such
as a hard drive or flash memory.
The information that is stored by the memory 150 can include
program code associated with one or more operating systems or
applications as well as informational data, e.g., program
parameters, process data, etc. The operating system and
applications are typically implemented via executable instructions
stored in a non-transitory computer-readable medium (e.g., memory
150) to control basic functions of the electronic device 110. Such
functions may include, for example, interaction among various
internal components and storage and retrieval of applications and
data to and from the memory 150.
By way of example, the measurement module 130 may comprise an
instance of code executed by the processor 140 wherein the code has
been retrieved from read-only memory in the memory 150. While
running, the code may be stored in random-access memory of the
memory 150, and the processor may also use the random-access memory
to temporarily hold process parameters and data.
The illustrated device 110 also includes a network interface module
180 to provide wireless communications to and from the device 110.
The network interface module 180 may include multiple
communications interfaces, e.g., for cellular, WiFi, broadband and
other communications. A power supply 190, such as a battery, is
included for providing power to the device 110 and its components.
In an embodiment, all or some of the internal components
communicate with one another by way of one or more shared or
dedicated internal communication links 195, such as an internal
bus.
Further with respect to the applications, these typically utilize
the operating system to provide more specific functionality, such
as file-system service and handling of protected and unprotected
data stored in the memory 150. Although many applications may
govern standard or required functionality of the user device 110,
in many cases applications govern optional or specialized
functionality, which can be provided, in some cases, by third-party
vendors unrelated to the device manufacturer.
Finally, with respect to informational data, e.g., program
parameters and process data, this non-executable information can be
referenced, manipulated, or written by the operating system or an
application. Such informational data can include, for example, data
that are preprogrammed into the device during manufacture, data
that are created by the device, or any of a variety of types of
information that are uploaded to, downloaded from, or otherwise
accessed at servers or other devices with which the device 110 is
in communication during its ongoing operation.
In an embodiment, the device 110 is programmed such that the
processor 140 and memory 150 interact with the other components of
the device 110 to perform a variety of functions. The processor 140
may include or implement various modules and execute programs for
initiating different activities such as launching an application,
transferring data, and toggling through various graphical user
interface objects (e.g., toggling through various icons that are
linked to executable applications). As noted above, one such module
or program is the measurement module 130, which will be explained
in greater detailed below.
Turning to FIG. 2, a simplified network schematic is illustrated,
showing a mobile user device 200 and a cellular environment 201
within which the device 200 operates. The illustrated environment
201 includes a primary cell 202 as well as a first secondary or
neighbor cell 203 and a second secondary cell 204. The primary cell
202 is designated as such because the user device 200 is currently
in communication with the cell 202.
Each cell 202, 203, 204 is generated by a respective cell node 205,
206, 207 comprising the hardware and software needed to send and
receive wireless communications to and from a cellular user device
and to communicate in turn with a communication network over which
the device user's messages are sent and received.
With respect to the secondary cells 203, 204, the user device 200
may periodically evaluate the signal strength of these cells as
seen at the user device 200 and report the measured values to the
node 205 of the primary cell 202. Generally, the node 205 will
configure the device 200 as to the conditions under which to make
such measurements by supplying signal strength-based trigger
conditions. By comparing the signal strength that the user device
200 experiences from the primary cell 202 with the signal strength
that the user device 200 experiences from the secondary cells 203,
204, the node 205 of the primary cell 202 is able to manage the
timing and target of any hand-off operation as the mobile user
device 200 moves into another cell.
Within certain protocols, e.g., the Long Term Evolution ("LTE")
Rel12 protocol for cellular systems and communications, cells may
exist in one of multiple states including an active state and a
dormant state. A discovery channel and signal may be used to convey
the cell mode when a cell can operate in multiple states. In
general, in the dormant state, the periodicity of periodic non-UE
specific transmissions (e.g., synchronization signals,
transmissions related to system information) from the cell can be
longer (e.g., 1 ms every 100 ms or 5 ms every 1 s) as compared to
the periodicity of such transmissions when the cell is in the
active state (e.g., 1 ms every 5 ms or multiple symbols in every 1
ms subframe).
Enabling a cell to occasionally operate in a dormant state not only
reduces overall energy consumption of the cell but also reduces
overall network interference. The dormant and active states may be
implemented in a number ways. For example, when operating in
dormant state, a cell may periodically transmit a synchronization
signal. The cell may also transmit, at a longer periodicity, a
physical broadcast channel (usually referred to as a discovery
channel) that is associated with the discovery signal. When the
cell is in the active state, it can transmit additional
synchronization signals and broadcast channels with a shorter
periodicity when compared to the dormant state.
FIG. 3 provides a timing diagram illustrating this approach. The
figure shows multiple radio frames 300, 301, 302, some transmitted
when the cell is in an active state (300, 302), and others
transmitted when the cell is in a dormant state (301). In LTE, each
radio frame has 10 ms duration and consists of 20 slots 303
numbered from 0 to 19. In the illustrated example, each slot is 0.5
ms. Consecutive slots can be referred to as subframes (e.g. slot 0,
1 is one subframe, slots 2, 3 another subframe, and so on). The
radio frames may be indexed with a System Frame Number ("SFN").
In this example, when the cell is in the dormant state, it
transmits a discovery channel 304 in every 15.sup.th radio frame
(that is, in radio frames satisfying SFN mod 15=0). The discovery
signal 305 may be present in all slots or only a subset of slots
within that radio frame (e.g., slots 0, 1, 9, 10). The
discovery-signal transmissions may be the only periodic non-UE
specific transmissions made by the cell in dormant state.
When the cell is in the active state, it transmits all the
synchronization signals and broadcast channels required to support
UEs and any required legacy UEs. Therefore, in the active state, at
least the following periodic non-UE specific transmissions are made
by the cell: Primary Synchronization Signal ("PSS") in slot 0 and
10 of every radio frame; Secondary Synchronization Signal ("SSS")
in slot 0 and 10 of every radio frame; Physical Broadcast Channel
carrying MasterInformationBlock in slot 1 of every radio frame in
active state; Physical Downlink Shared CHannel ("PDSCH") carrying
SystemInformationBlock1 information in every alternate radio frame
(i.e., radio frames satisfying SFN mod 2=0) and associated Physical
Downlink Control CHannel ("PDCCH") to indicate the PDSCH resource
blocks ("RBs"); PDSCH carrying other system information blocks in a
plurality of radio frames conformant with the system information
scheduling mechanisms in LTE Rel8/9/10/11 and associated PDCCH to
indicate the PDSCH RBs; and Common Reference Signals ("CRS") in
every slot of every radio frame except for the second slot in a
Multi-Broadcast Single-Frequency Network ("MBSFN") subframe. (MBSFN
subframe information is typically signaled in SIB2.)
Given the above list, a cell in the active state 302 has at least
one transmission in every subframe, i.e., a periodicity of at least
once every 1 ms. As indicated above, CRS may not be transmitted in
the second slot of some subframes (MBSFN subframes). In addition to
the transmissions in the above list, the cell can also transmit the
discovery signal when in the active state. If the discovery signal
has a structure that is detectible in fewer slots than the slots
required for detecting PSS/SSS, then the transmission of the
discovery signal in the active state will help in reducing the
measurement burden of UEs making inter-frequency measurements on
the cell transmitting the discovery signal.
For example, the first secondary cell 203 can transmit a discovery
signal on a carrier with center frequency f.sub.1 and with a
periodicity of once every 150 ms. The user device 200 connected to
the primary cell 202 operating on a carrier with center frequency
f.sub.2 can attempt to detect the first secondary cell 203 by
either attempting to detect PSS or SSS on the first secondary cell
203 or the discovery signal on the first secondary cell 203.
In another example implementation, the active-state transmissions
made by a cell may be similar to the active-state transmissions
described above, except that in the dormant state 301, the cell
transmits other reference signals and channels in addition to the
discovery signal. For example, the dormant state transmissions by
the cell may include: Reduced-CRS transmissions (i.e., transmission
of a pilot sequence in 5th subframe of every radio frame on
resource elements corresponding to a CRS antenna port; New
broadcast channel transmissions that are associated with
Demodulation reference signals instead of CRS; and New control
channel transmissions such as a common search space for Enhanced
PDCCH.
Such transmissions can be used by advanced UEs (e.g., UEs
supporting LTE Rel12) for connecting to and communicating with the
cell even when it is in the dormant state. The energy spent by the
cell in the dormant state of this implementation is higher than the
energy spent in the dormant state of the previously described
example. However, when compared to the energy spent in the active
state of either, the energy spent is still lower.
It is possible to use a combination of the foregoing
implementations. For example, a cell may be configured to support
three states including: an active state (similar to the active
state of the first example implementation); a semi-dormant state
(similar to the dormant state of the second example
implementation); and a dormant state (similar to the dormant state
of the first example implementation).
In addition to the periodic non-UE specific transmissions discussed
so far, a cell supports event-triggered transmissions such as
Paging indications (when a paging message is received from a Public
Land Mobile Network associated with the cell) and Random-Access
Procedure ("RACH") response transmissions (when a RACH is received
from a UE camped or connected to the cell). In some implementations
(e.g., the second example above) such transmissions can be
supported by the cell in both of the dormant and active states.
In other implementations, the cell may switch from the dormant
state to the active state in response to such events and make the
related transmissions in the active state. In some other
implementations, the cell may remain in the dormant state for some
events and switch to the active state for other events. For
example, a cell may transmit a paging indication while in the
dormant state, and then wait for a RACH transmission in response to
the paging indication before switching to the active state to
transmit a RACH response.
As noted above, a user device may be configured by its primary cell
node to measure neighboring cells on a triggered basis to
facilitate a later hand off. This is particularly true with respect
to legacy LTE systems. However, in systems such as LTE Rel12
compliant systems, wherein cells support two states (e.g., dormant
and active), the continuation by the UE of measurement via legacy
procedures will cause unnecessary measurement reports. This is
detrimental both to device performance and to network
efficiency.
In an embodiment of the disclosed principles, the measurement
triggers for measuring characteristics of non-primary cells are
adapted based on cell state in systems supporting multistate cells.
In particular, the disclosed examples discuss illustrative
mechanisms to optimize the UE measurement reporting procedure for
systems that include multi-state cells.
The simplified network diagram of FIG. 4 shows a cellular network
environment 400 wherein a mobile user device 401 is in proximity to
a number of cells 402, 403, 404, 405, 406 (associated with nodes
eNB1, eNB2, eNB3, eNB4, eNB5). The shorthand "eNB" refers to
"evolved Node B," meaning an LTE-compliant node B.
In the illustrated state, the mobile user device 401 is connected
to cell 402 (eNB1) and has as its neighboring cells each of cells
eNB2, eNB3, eNB4, and eNB5. Because the user device 401 is mobile,
it may at some point be more suitable to connect to a neighboring
node rather than to the current primary node. Thus, the user device
401 is configured by the primary node eNB1 (402) to measure one or
more characteristics of the neighboring nodes according to certain
rules.
In particular, in an embodiment, when the device 401 performs
measurements with respect to neighboring cells (e.g., Radio
Resource Management measurements in connected mode or cell
selection or reselection measurements in idle mode), measurement
triggers are adapted based on whether measured multistate cells are
in the dormant state (or "off" state) or the active state (or "on"
state).
When the device 401 is in the connected mode as shown, the
measurement trigger will generally determine whether the device 401
sends a measurement report corresponding to a neighbor cell to the
primary cell. The device 401 employs different trigger conditions
depending on whether the neighbor cell is in the active state or
the dormant state.
For example, the user device 401 is configured in an embodiment
such that when a neighbor cell of interest is in the active state,
a measurement report is triggered when a measurement quantity
associated with the neighbor cell exceeds a first threshold value
(e.g., Reference Signal Received Power ("RSRP") measured from CRS,
RSRP measured from small-cell discovery signal ("SCDS"), etc.).
However, when the neighbor cell is in the dormant state, the user
device 401 triggers a measurement report only when the measurement
quantity associated with the neighbor cell exceeds a second
threshold value that may be more stringent than the first threshold
value. In this way, measurements may be triggered less frequently
when the neighbor cell of interest is in the dormant state.
In this example, setting the second threshold higher (more
difficult to meet) than the first threshold allows the network to
enforce a preference to handover the user device 401 to an active
cell rather than to a dormant cell. The second threshold may be an
absolute threshold or an offset related to the first threshold. The
offset or delta between the first threshold and the second
threshold may be predetermined or signaled to the user device 401.
Moreover, the offset may be configured on a per-cell basis or may
be common for all or a subset of the cells (e.g., for a certain
frequency layer of cells).
When the user device 401 is in the idle mode, the measurement
trigger determines whether the user device 401 reselects from the
current camped cell (associated with eNB1) to another cell. The
reselection criteria, like the measurement criteria, may be
different based on whether the other cell is in active or dormant
state.
It will be appreciated, as alluded to above, that different cells
may operate on different frequencies. For the sake of example
assume that eNB 1 operates on a carrier frequency f.sub.1, eNB2 and
eNB3 operate cells on the same carrier frequency, and eNB4 and eNB5
operate cells on a different carrier frequency f.sub.2.
In legacy LTE systems, the user device 401 is configured by its
primary cell 402 to measure some or all of its neighbor cells and
report the measurements, e.g., according to predefined events such
as when cell offsets change, signal magnitudes change, relative
measurements of these values change, and so on (depending upon how
the primary cell actually configures the device 401). The
interested reader may review LTE specification 3GPP TS 36.331 to
learn more about these events, but in general they relate to signal
strength and offset, compared to threshold values and compared to
other cells.
Considering the system of FIG. 4, assume that cells 402, 404, and
406 are in the active state, while cells 403 and 405 are in the
dormant state. For such a system, applying the same measurement
triggering and reporting procedure for both dormant and active
cells may not be efficient. For example, considering that cell 402
is the primary cell of the user device 401, if the user device 401
measures cells 404 and 405, and if both cells are 3 dB better than
cell 402, then the user device 401 would include both cells in its
measurement report using legacy procedures because the
signal-characteristic thresholds for reporting are met.
However, in a system wherein multistate cells exist, the primary
cell may prefer to hand over the user device to an active cell
rather than to a dormant cell. If the primary cell is aware of the
state of the cells included in the device's measurement report, it
can enforce this preference to reduce unnecessary signaling
overhead and also to improve device- and network-energy efficiency.
The primary cell may determine the state of other cells either via
inter-eNB signaling or via additional bits included in the device's
measurement report.
For example, if the user device determines that a cell is in the
dormant state and also determines that the cell satisfies a
particular measurement event, it may include an additional dormant
state indicator (for example, via an extra bit in the measurement
report) to inform the primary cell that the report corresponds to a
dormant cell. Allowing the user device to indicate cell state
reduces the need for frequent signaling among cells to exchange
their states.
Consider an event that entails comparison of the signal magnitude
of the neighbor, frequency-specific offset of the neighbor and
cell-specific offset of the neighbor less a hysteresis value to
prevent oscillation, with the signal magnitude of the primary,
frequency-specific offset of the primary and cell-specific offset
of the primary plus an offset. In legacy systems, the user device
401 sends a measurement report if at least the following condition
is satisfied: Mn+Ofn+Ocn-Hys>Mp+Ofp+Ocp+Off Where Mn is the
measurement result of the neighboring cell (no offsets), Ofn is the
frequency-specific offset of the frequency of the neighbor cell,
Ocn is the cell-specific offset of the neighbor cell (set to zero
if not configured for the neighbor cell), Mp is the measurement
result of the primary cell (no offsets), Ofp is the
frequency-specific offset of the primary frequency, Ocp is the
cell-specific offset of the Primary cell (set to zero if not
configured for the Primary cell), Hys is the hysteresis parameter
for this event, and Off is the offset parameter for this event. The
values Mn and Mp are expressed in dBm in case of RSRP or in dB in
case of Reference Signal Received Quality ("RSRQ"). The values of
Ofn, Ocn, Ofp, Ocp, Hys and Off are expressed in dB.
In an embodiment applicable within a multistate cell environment
such as that shown in FIG. 4, reporting is more efficiently
triggered by applying a different triggering approach as summarized
by the following expression for the same example event:
Mn+Ofn+Ocn-Hys>Mp+Ofp+Ocp+Off+dormant_delta where dormant_delta
is set to 0 if the measured cell is in the active state and is set
to a network configured value (e.g., 2 dB) if the cell is in the
dormant state. Another option is to have a larger hysteresis values
for dormant cells as shown in the inequality below:
Mn+Ofn+Ocn-(Hys+Hys_delta)>Mp+Ofp+Ocp+Off where Hys_delta is set
to 0 if the measured cell is in the active state and is set to a
network configured value (e.g., 2 dB) if the cell is in the dormant
state.
In an alternative approach, the network can configure the UE with
two different cell-specific offset Oc values, one for the dormant
state and another for the active state. For example, for the
neighbor cell "cell n," the user device 401 can be configured with
two cell-specific offset values, Ocn1 (corresponding to the dormant
state) and Ocn2 (corresponding to the active state).
Optionally, the primary cell can be configured with Ocp1
(corresponding to the dormant state) and Ocp2 (corresponding to the
active state). The user device 401 determines whether the cell is
in the active or dormant state and uses the appropriate offset
value while evaluating a measurement trigger condition involving
that cell.
For example, in keeping with the foregoing, if the primary cell is
in the active state and the neighbor cell n is in the dormant
state, then the user device 401 can apply the following expression
as a trigger condition for sending a measurement report:
Mn+Ofn+Ocn1-Hys>Mp+Ofp+Ocp2+Off If the primary cell is in the
active state and neighbor cell n is also in the active state, then
the user device 401 instead applies the following expression as a
trigger condition for sending a measurement report:
Mn+Ofn+Ocn2-Hys>Mp+Ofp+Ocp2+Off
In some cases, the user device 401 needs to compare a measurement
quantity to a threshold value rather than perform a cross-cell
comparison. For such trigger conditions, the user device 401 may be
configured with a first threshold value corresponding to a
dormant-state measurement and a second threshold value
corresponding to an active-state measurement.
For example, one event of interest is when the primary cell becomes
worse than a threshold1 and a neighbor cell becomes better than a
threshold2. In keeping with the disclosed principles, this event is
detected by configuring the user device 401 with two different
thresholds `threshold 1a` and `threshold1d` that apply to Primary
cell measurements and two different thresholds `threshold 2a` and
`threshold2d` that apply to neighbor-cell measurements. The user
device 401 determines if the measurement trigger condition is
satisfied using the following conditions: If both the primary cell
and the neighbor cell are in the dormant state, then the trigger
condition is satisfied when the primary cell signal strength
becomes worse than threshold1d and the neighbor cell signal
strength becomes better than threshold2d; If both primary cell and
the neighbor cell are in the active state, then the trigger
condition is satisfied when the primary cell signal strength
becomes worse than threshold1a and the neighbor cell signal
strength becomes better than threshold2a; If the primary cell is in
the active state and the neighbor cell is in the dormant state,
then the trigger condition is satisfied when the primary cell
signal strength becomes worse than threshold1a and the neighbor
cell signal strength becomes better than threshold2d; and If the
primary cell is in dormant state and the neighbor cell is in the
active state, then the trigger condition is satisfied when the
primary cell signal strength becomes worse than threshold1d and the
neighbor cell signal strength becomes better than threshold2a.
Although these principles may be applied in a number of different
ways, an illustrative mode of application is shown in the flowchart
500 of FIG. 5. The disclosed process begins at stage 501, wherein a
user device such as device 401 is operating in a cellular
environment supporting multistate cells and having one or more
dormant cells and one or more active cells. The user device is
connected to one of the active cells (the primary cell).
At stage 502 of the process 500, the primary cell configures the
user device for efficient neighbor-cell measurement reporting by
providing a trigger condition linking the cell state to a
cell-measurement quantity, e.g., signal strength or frequency
offset. As noted, examples of signals that may be measured include
a CRS, PSS, SSS, SCDS, positioning reference signal, and
channel-state information reference signal. The user device
measures a signal with respect to a cell other than the primary
cell at stage 503 and determines a state of the measured cell at
stage 504. It will be appreciated that stages 503 and 504 may occur
in any order or may occur in parallel. At stage 505, the user
device determines the measurement quantity based on the
measurement.
The user device then evaluates the trigger condition using both the
measurement quantity and the cell state at stage 506. If the
trigger condition is satisfied, then the user device transmits a
measurement report to the primary cell node at stage 507.
Otherwise, the user device does not send a measurement report, and
the process 500 returns to stage 503. This process will continue
until the primary cell reconfigures the user device or the device
leaves the primary cell or is powered down.
In legacy systems, after measuring a particular RSRP or RSRQ value,
the user device applies a filtering function (layer-3 filtering)
such as shown below: F.sub.n=(1-a)F.sub.n-1+aM.sub.n. Here,
a=1/2.sup.(k/4), and the parameter k (a value between 0 and 19) is
configured by the network separately for RSRP and RSRQ
measurements. For intra-frequency RSRP measurements, the filter
coefficient is set by the network assuming a sample rate of 200
ms.
In systems where dormant and active cells are present, the network
can configure a different filter coefficient for filtering
measurements of dormant and active cells. For example the network
may configure the UE to choose k=4 for measurements on active cells
and k=0 for measurements on dormant cells given the longer
periodicity of samples measured on dormant cells.
In an alternative approach, the UE may adapt the layer-3 filter
such that the time characteristics of the filter are preserved at
different input rates corresponding to the dormant and active state
of the cell.
New triggering criterion may be employed with systems with active
and dormant cells. For example, in an embodiment, when a dormant
cell becomes better by an offset than any active cell, the user
device sends a measurement report corresponding to the dormant
neighbor cell. In particular, if a dormant cell is 3 dB better than
any of the active cells, then it may be beneficial from a network
efficiency perspective to wake up the dormant cell (either via
inter-eNB signaling or via UE-based triggering) and have the user
device trigger a measurement report in this case.
In view of the many possible embodiments to which the principles of
the present disclosure may be applied, it should be recognized that
the embodiments described herein with respect to the drawing
figures are meant to be illustrative only and should not be taken
as limiting the scope of the claims. Therefore, the techniques as
described herein contemplate all such embodiments as may come
within the scope of the following claims and equivalents
thereof.
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