U.S. patent application number 14/719518 was filed with the patent office on 2015-09-10 for measurement handling with carrier aggregation.
The applicant listed for this patent is Optis Cellular Technology, LLC. Invention is credited to Walter Muller, Mats Sagfors.
Application Number | 20150257025 14/719518 |
Document ID | / |
Family ID | 43531211 |
Filed Date | 2015-09-10 |
United States Patent
Application |
20150257025 |
Kind Code |
A1 |
Sagfors; Mats ; et
al. |
September 10, 2015 |
MEASUREMENT HANDLING WITH CARRIER AGGREGATION
Abstract
Measurement handling is of interest in a user equipment (UE) in
connected mode, with the UE being configured with multiple downlink
component carriers (CCs). The UE evaluates the signal quality of a
specific CC of the configured CCs against a configurable threshold
to determine the need for neighbor cell measurements. The UE
performs neighbor cell measurements if the signal quality of the
specific CC is below the configurable threshold. In this way,
robust and efficient measurement handling is provided, even though
the UE is configured with multiple component carriers.
Inventors: |
Sagfors; Mats; (Kyrkslatt,
FI) ; Muller; Walter; (Upplands Vasby, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Optis Cellular Technology, LLC |
Plano |
TX |
US |
|
|
Family ID: |
43531211 |
Appl. No.: |
14/719518 |
Filed: |
May 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12972460 |
Dec 18, 2010 |
9042835 |
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14719518 |
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PCT/EP2010/069619 |
Dec 14, 2010 |
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12972460 |
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61293875 |
Jan 11, 2010 |
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Current U.S.
Class: |
455/67.11 |
Current CPC
Class: |
H04W 24/08 20130101;
H04W 36/00835 20180801; H04W 36/0085 20180801; H04W 72/042
20130101; H04W 36/0083 20130101 |
International
Class: |
H04W 24/08 20060101
H04W024/08; H04W 36/00 20060101 H04W036/00 |
Claims
1. A method of measurement handling in a user equipment (UE) in
connected mode, the UE being configured with multiple downlink
component carriers (CCs), the method comprising: evaluating a
signal quality of a specific CC of the configured CCs against a
configurable threshold to determine a need for neighbor cell
measurements; and performing neighbor cell measurements if the
signal quality of the specific CC is below the configurable
threshold.
Description
BACKGROUND
[0001] Carrier Aggregation
[0002] The Third Generation Partnership Project (3GPP) Long Term
Evolution (LTE) Release 8 (Rel-8) standard for wireless
communication systems has recently been finalized, supporting
bandwidths up to 20 megahertz (MHz). LTE and High-Speed Packet
Access (HSPA) are sometimes called "third generation" (3G)
communication systems and are currently being standardized by the
3GPP. The LTE specifications can be seen as an evolution of the
current wideband code division multiple access (WCDMA)
specifications.
[0003] An LTE system uses orthogonal frequency division multiplex
(OFDM) as a multiple access technique (called OFDMA) in the
downlink (DL) from system nodes to user equipments (UEs). An LTE
system has channel bandwidths ranging from about 1.4 MHz to 20 MHz,
and supports throughputs of more than 100 megabits per second
(Mb/s) on the largest-bandwidth channels. One type of physical
channel defined for the LTE downlink is the physical downlink
shared channel (PDSCH), which conveys information from higher
layers in the LTE protocol stack and to which one or more specific
transport channels are mapped. Control information is conveyed by a
physical uplink control channel (PUCCH) and by a physical downlink
control channel (PDCCH). LTE channels are described in 3GPP
Technical Specification (TS) 36.211 V8.4.0, Physical Channels and
Modulation (Release 8) (September 2008), among other
specifications.
[0004] An IMT-Advanced communication system uses an internet
protocol (IP) multimedia subsystem (IMS) of an LTE, HSPA, or other
communication system for IMS multimedia telephony (IMT). In the IMT
advanced system (which may be called a "fourth generation" (4G)
mobile communication system), bandwidths of 100 MHz and larger are
being considered. The 3GPP promulgates the LTE, HSPA, WCDMA, and
IMT specifications, and specifications that standardize other kinds
of cellular wireless communication systems.
[0005] In order to meet the upcoming IMT-Advanced requirements,
3GPP has initiated work on LTE-Advanced. One of the parts of
LTE-Advanced is to support bandwidths larger than 20 MHz. This will
be achieved using a concept called "Carrier Aggregation", where
multiple carrier components, each of which may be up to 20 MHz
wide, are aggregated together. Carrier aggregation is planned for
Release 10 (Rel-10) of the 3GPP LTE specifications.
[0006] Carrier aggregation implies that an LTE Rel-10 terminal can
receive multiple component carriers, where the component carriers
have, or at least the possibility to have, the same structure as a
Rel-8 carrier. Carrier aggregation is illustrated in FIG. 1, in
which 5 bands of 20 MHz each are aggregated together.
[0007] Carriers can be aggregated contiguously, like in FIG. 1, or
they may be aggregated from discontinuous portions in the frequency
domain, such that, e.g., parts of the aggregated carriers may be
contiguous, and other aggregated carriers appear somewhere else in
the spectrum, as schematically illustrated in FIG. 2.
[0008] The artisan will understand that the blocks shown in FIGS. 1
and 2 are compliant with the LTE specifications. With the carrier
aggregation concept, it may be possible to support, among other
things: [0009] higher bit-rates; [0010] farming of non-contiguous
spectrum--e.g., provide high bit-rates and better capacity also in
cases when an operator lacks contiguous spectrum; [0011] fast and
efficient load balancing between carriers.
[0012] It should be noted that carrier aggregation is a
user-equipment-centric concept, in that one user equipment (UE) can
be configured to use, e.g., the two left-most carriers in FIG. 2,
another UE can be configured to use only a single carrier, and a
third UE can be configured to use all of the carriers depicted in
FIG. 2.
[0013] Thus, an eNodeB (eNB) (i.e., an LTE radio base station) may
be in control of all four carriers depicted in FIG. 2, but Rel-10
UEs may have different Configured Component Carriers (Configured
CCs) that each Rel-10 UE is configured to use. The aggregated
carriers may also be available for Rel-8 UEs, meaning that each of
the carriers may be independently available for single-cell
operation.
[0014] A particular and relevant example of a plausible carrier
aggregation scenario includes the case when two or more Rel-8
compatible downlink carriers are aggregated for a UE. It should be
noted that carrier aggregation is typically and mainly relevant for
a Connected UE, which is a UE that is actively involved in
transmission to and from an eNB (which can generally be a E-UTRAN
base station), and thus has a connection with the eNB controlling
the aggregated carriers.
[0015] Mobility and Measurements
[0016] In Connected mode, mobility (i.e., handovers between cells)
is controlled by the network based on, among other things,
measurements provided to the network by the UE. Based on
measurement reports received from the UE, the eNB may deduce if a
handover is needed. If so, the eNB may then issue a handover to
another cell, possibly so that the other cell is controlled by
another eNB.
[0017] Measurement configurations are controlled by the eNB, i.e.,
the eNB tells the UE, e.g., when to perform measurements, what to
measure, and how to report. Such controlling information sent from
the eNB to the UE includes, e.g., information of how measurements
should be filtered, different thresholds for the triggers that
trigger report, what to measure, how to report, and what to include
in the report.
[0018] The Rel-8 LTE specifications support a versatile measurement
model where different events with thresholds can be configured,
such that the UE sends measurement reports to the network when,
e.g., the relative signal strength between the current "Serving
Cell" and a "Neighbor Cell" is changing, such that a handover may
be necessary. This can occur, e.g., when the UE moves from one cell
to another, as depicted in FIG. 3, which is a plot of received
signal level vs. time or distance.
[0019] In Rel-8, the "Serving Cell" denotes the cell that the UE is
connected to, while the "Neighbor Cell" may be another cell in
close proximity on the same frequency (intra-frequency
measurements), or on a different frequency (inter-frequency
measurements). The neighbor may also use a different Radio Access
Technology (inter-RAT measurements).
[0020] Rel-8 includes different event-triggers for issuing reports
from the UE to the eNB, when certain conditions are fulfilled. For
example, Rel-8 includes the trigger Event A3 defined as follows:
[0021] Event A3: Neighbor cell becomes amount of offset better than
serving cell.
[0022] Additional triggers and definitions can be found in the LTE
specification, 3GPP Technical Specification (TS) 36.331 V8.8.0,
Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Resource
Control (RRC), Protocol Specification (Release 8) (December
2009).
[0023] In 3GPP TS 25.331 V9.0.0, Radio Resource Control (Release 9)
(September 2009), UTRAN trigger events are defined.
[0024] For clarity, we here list some of the definitions used in
Clause 5.5 of 3GPP TS 36.331:
[0025] 1. Measurement objects: The objects on which the UE shall
perform the measurements.
[0026] 2. Reporting configurations: A list of reporting
configurations including e.g. the aforementioned trigger
configurations.
[0027] 3. Measurement identities: A list of measurement identities
where each measurement identity links one measurement object with
one reporting configuration.
[0028] Additional definitions can be found in Clause 5.5 of 3GPP TS
36.331, for example.
[0029] Considering Event A3, it is thus possible to configure an
A3-event on a measurement object, such that if any Neighbor on that
object grows stronger than the Serving cell (plus some configurable
thresholds), then the UE shall send a measurement report that
includes information about the measured radio environment of the
UE. The report is constructed with relevant information, such that
the eNB can decide if a handover is required or at least
beneficial.
[0030] The Rel-8 measurement object may be the carrier "defined" by
the Serving Cell, in which case the Neighbor and Serving are on the
same frequency. The term "intra-frequency" is often used.
Alternatively, the object may be a different, "inter-frequency"
object, as illustrated by FIG. 4.
[0031] The same, or different, reporting configurations for A3 (or
other) events could be configured for the two objects in the
figure.
[0032] A characteristic of this Rel-8 model of relevance for the
present invention is the fact that the UE has a single Serving
Cell.
[0033] The s-Measure Parameter
[0034] The procedures for measuring on neighbor cells consume UE
power. In Rel-8, there has therefore been defined a parameter
called s-Measure, by which the measurement activities of a UE can
be reduced at times when there is no need to perform neighbor cell
search and measurements.
[0035] From Clause 6.3.5 of 3GPP TS 36.331:
[0036] s-Measure
[0037] Serving cell quality threshold controlling whether or not
the UE is required to perform measurements of intra-frequency,
inter-frequency and inter-RAT neighbouring cells. Value "0"
indicates to disable s-Measure.
[0038] Thus, a UE needs to perform neighbor-cell measurements only
if the quality of the serving cell is below a certain threshold. In
Rel-8, the quality is evaluated in terms of the received RSRP
(Reference Signal Received Power). If the received signal power
from the serving cell is high, then the UE does not need to perform
any neighbor cell measurements, as the current serving cell is
assumed to be strong enough in absolute terms. FIG. 5 illustrates
the use of s-Measure, where the curve is a schematic illustration
of received signal level as a function of time or distance.
[0039] In IDLE mode, the mobility is UE-controlled, such that the
UE selects the best cell to camp upon based on specified criteria
and related parameters, where the parameters are typically
broadcast in the cell. For LTE, this is described in, for example,
Clause 5.2 of 3GPP TS 36.304 V8.8.0, User Equipment (UE) Procedures
in Idle Mode (Release 8) (December 2009). This cell selection,
where the UE selects one unique cell to camp on, is based on cell
search and measurements. Also here, the network may broadcast
parameters S-intrasearch and S-nonintrasearch, such that a UE may
omit any cell search and measurements for cell selection on intra-
and inter-frequency carriers, respectively, if the received quality
of the present serving cell is greater than the aforementioned
threshold parameters.
[0040] A problem with the measurement configuration and event
triggers arises when Carrier Aggregation is introduced. Now, a UE
may be "served" on multiple frequencies, and there arises an
ambiguity of what the "Serving Cell" in FIG. 4 actually is.
Specifically, the 3GPP RAN2 working group has recently agreed that
each component carrier is a separate measurement object, as
illustrated in FIG. 6.
[0041] Further reference can be made to 3GPP R2-100826: Report of
3GPP TSG RAN WG2 meeting #68 held Nov. 9-13, 2009.
[0042] In terms of the Rel-8 model, the UE now has three serving
cells in the illustrated example.
[0043] Assume now that a UE is configured with three Component
Carriers (CCs). With Rel-8 nomenclature, the UE in FIG. 6 would now
have three "Serving Cells". The term "Component Carrier", or CC,
may for example be defined as a downlink (DL) frequency that a UE
is currently configured with, such that the UE is prepared to
receive that DL carrier. In the following the terms "Component
Carrier" and "serving cell" will be used more or less
interchangeably.
[0044] FIG. 7 is a schematic diagram illustrating of an example of
a situation when a UE is served by multiple serving cells or
carrier components. FIG. 7 shows a first base station 1 and a
second base station 2. The first base station 1 is currently a
serving base station serving a user equipment, UE, 3 and the second
base station 2 is a neighbor base station. As mentioned above, the
UE 3 may be configured with multiple serving cells, or so-called
component carriers, CCs, which relate to carriers on different
frequencies (f).
[0045] A particular problem is that it is unclear how the s-Measure
evaluation and similar evaluation of the need for neighbor cell
measurements for a UE with multiple, aggregated Component Carriers
should be performed.
SUMMARY
[0046] It is an object to provide improved measurement handling in
user equipment configured with multiple downlink component
carriers.
[0047] This object is met by embodiments as defined by the
accompanying patent claims.
[0048] In a first aspect, there is provided a method of measurement
handling in a user equipment, UE, in connected mode, with the UE
being configured with multiple downlink component carriers, CCs. A
basic idea is to evaluate the signal quality of a specific CC of
the configured CCs against a configurable threshold to determine
the need for neighbor cell measurements, and perform neighbor cell
measurements if the signal quality of the specific CC is below the
configurable threshold.
[0049] In this way, robust and efficient measurement handling is
provided, even though the UE is configured with multiple component
carriers.
[0050] In a second aspect, there is provided a control unit for
measurement handling in a user equipment, UE, in connected mode,
with the UE being configured with multiple downlink component
carriers, CCs. The control unit comprises at least one processing
circuit configured to evaluate the signal quality of a specific CC
of the configured CCs against a configurable threshold to determine
the need for neighbor cell measurements, and request neighbor cell
measurements if the signal quality of the specific CC is below the
configurable threshold.
[0051] In a third aspect, there is provided a user equipment, UE,
configured for measurement handling in connected mode. The UE is
configured with multiple downlink component carriers, CCs. The UE
comprises at least one processing circuit configured to evaluate
the signal quality of a specific CC of the configured CCs against a
configurable threshold to determine the need for neighbor cell
measurements, and request neighbor cell measurements to be
performed if the signal quality of the specific CC is below the
configurable threshold. The UE also comprises at least one
measurement circuit configured to perform, if requested, the
neighbor cell measurements.
[0052] In a fourth aspect, there is provided a non-transitory
computer-readable medium having stored therein a set of
instructions for performing, when executed by a computer-based
system, measurement handling in a user equipment, UE, in connected
mode, with the UE being configured with multiple downlink component
carriers, CCs. In the measurement handling, the signal quality of a
specific CC of the configured CCs is evaluated against a
configurable threshold to determine the need for neighbor cell
measurements, and neighbor cell measurements are requested to be
performed if the signal quality of the specific CC is below the
configurable threshold.
[0053] In yet another aspect, there is provided a method of
measurement handling in a user equipment, UE, in connected mode,
with the UE being configured with multiple downlink component
carriers, CCs. The UE is configured with multiple thresholds, where
each of the thresholds relate to at least one measurement object,
and the threshold is used for evaluating, for the CC on the object,
whether there is a need to perform neighbor cell measurements on
this particular object.
[0054] Other advantages offered by the invention will be
appreciated when reading the below description of embodiments of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] The invention, together with further objects and advantages
thereof, may best be understood by making reference to this
description taken together with the accompanying drawings, in
which:
[0056] FIG. 1 is a schematic diagram illustrating the concept of
carrier aggregation.
[0057] FIG. 2 is a schematic diagram illustrating contiguous and
non-contiguous carriers with different bandwidths.
[0058] FIG. 3 is a schematic diagram illustrating an example of a
handover measurement model.
[0059] FIG. 4 is a schematic diagram illustrating an example of A3
events applied both to an intra-frequency and inter-frequency
object.
[0060] FIG. 5 is a schematic diagram illustrating an example of the
use of s-Measure in the form of a plot of received signal level vs.
time or distance.
[0061] FIG. 6 is a schematic diagram illustrating an example of a
situation when a UE is configured with three DL component
carriers.
[0062] FIG. 7 is a schematic diagram illustrating of an example of
a situation when a UE is served by multiple serving cells or
carrier components.
[0063] FIG. 8 is a schematic flow diagram illustrating an example
of a method for measurement handling according to an
embodiment.
[0064] FIG. 9 is a schematic flow diagram illustrating an example
of a method for measurement handling according to another
embodiment.
[0065] FIGS. 10A-B are schematic diagrams illustrating an example
of aggregation of carriers in different-size cells.
[0066] FIG. 11 is a schematic diagram illustrating an example of a
possible solution for event evaluation on a carrier that includes a
CC.
[0067] FIG. 12 is a schematic diagram illustrating an example of
the problem related to inter-frequency event evaluation.
[0068] FIG. 13 is a schematic diagram illustrating an example of
received signal level vs. time or distance plot for a UE configured
with multiple CCs.
[0069] FIGS. 14A-B are schematic diagrams illustrating a situation
with CCs on different carrier frequencies.
[0070] FIG. 15 is a schematic diagram illustrating an example of a
situation with multiple CCs and different thresholds.
[0071] FIG. 16 is a schematic flow diagram illustrating an example
of a method for measurement handling according to a particular
embodiment.
[0072] FIG. 17 is a schematic flow diagram illustrating an example
of a method for measurement handling according to another
particular embodiment
[0073] FIG. 18 is a schematic diagram illustrating an example of a
control unit for measurement handling according to an embodiment of
the invention.
[0074] FIG. 19 is a schematic diagram illustrating an example of a
user equipment configured for measurement handling according to an
embodiment of the invention.
[0075] FIG. 20 is a schematic diagram illustrating an example of a
typical cellular radio communication system.
[0076] FIG. 21 is a schematic block diagram illustrating an example
of a portion of a user equipment according to an embodiment.
[0077] FIG. 22 is a schematic diagram illustrating an example of a
computer-implemented control unit for measurement handling, as well
as a computer-readable medium according to an embodiment.
[0078] FIG. 23 is a schematic flow diagram of an example of a
method for measurement handling in a UE, where the UE is configured
with multiple thresholds, according to an embodiment.
DETAILED DESCRIPTION
[0079] FIG. 8 is a schematic flow diagram illustrating an example
of a method for measurement handling in a user equipment, UE, in
connected mode, with the UE being configured with multiple downlink
component carriers, CCs, also referred to as serving cells,
according to an embodiment.
[0080] Step S1 involves evaluating the signal quality of a specific
CC of the configured CCs against a configurable threshold to
determine the need for neighbor cell measurements. Step S2 involves
performing neighbor cell measurements if the signal quality of the
specific CC is below the configurable threshold.
[0081] In this way, robust and efficient measurement handling is
provided, even though the UE is configured with multiple component
carriers.
[0082] Normally, as a complementary optional action, the UE is
allowed to omit neighbor cell measurements if the signal quality of
the specific CC exceeds the configurable threshold, as indicated by
the optional step S3 in the flow diagram of FIG. 8.
[0083] For example, the UE can receive information representative
of the specific CC, with the specific CC being configured using the
Radio Resource Control, RRC, protocol. In a particular example, the
UE receives information representative of the specific CC, with the
specific CC being semi-statically configured in the UE by signaling
according to the applicable RRC protocol, such that the UE
evaluates the signal quality of this CC against the configurable
threshold. The UE can then maintain information about the specific
CC as the CC to be evaluated against the threshold.
[0084] By way of example, the specific CC to be used for evaluating
the need for neighbour cell measurements can be the so-called
PCell, or Primary Cell. In particular, the PCell can be used as
reference for s-Measure evaluation.
[0085] For example, with PCell as the specific CC to be used for
evaluating the need for neighbour cell measurements, the following
definitions for measurement handling can be used: [0086] s-Measure
is the PCell quality threshold controlling whether or not the UE is
required to perform measurements of intra-frequency,
inter-frequency and/or inter-RAT (Radio Access Technology)
neighboring cells. [0087] If s-Measure is configured and the PCell
quality (such as received power), after suitable filtering, is
lower than this value, then perform measurements of neighboring
cell(s) on the frequency/frequencies and/or RAT(s) of the concerned
measurement object(s).
[0088] The PCell can be changed by a handover command from the base
station. Thus, the specific CC to be used as reference CC in this
particular context can be selected and controlled with higher-layer
signaling. For example, the reference CC can be signaled using the
Radio Resource Control, RRC, protocol.
[0089] The network can thus perform a change of PCell by RRC
signaling. For example, in E-UTRAN, the eNB can perform a PCell
change by means of the handover procedure, i.e. using an
RRCConnectionReconfiguration message including
mobilityControlInfo.
[0090] In the 3GPP document R2-097514: Report of 3GPP TSG RAN WG2
meeting #67bis held Oct. 12-16, 2009, a special cell that provides
security input and NAS mobility information was introduced.
[0091] In an example embodiment, the UE evaluates the need for
measurements on neighbor cells residing on carriers on which the UE
has no CC, also referred to as inter-frequency or inter-RAT (Radio
Access Technology) measurements by comparing the signal quality of
the specific CC to the configurable threshold. The UE can also be
required to perform neighbor cell measurements on at least one
other carrier on which the UE has a CC, also referred to as
intra-frequency measurements.
[0092] The need for neighbour cell measurements is normally
evaluated with respect to physical layer measurements related to
the specific reference CC.
[0093] FIG. 9 is a schematic flow diagram illustrating an example
of a method for measurement handling in a user equipment according
to another embodiment. In optional step S11, information
representative of a specific CC is received; the specific CC being
configured using RRC. In optional step S12, the UE maintains
information about the specific CC as the CC to be evaluated against
a threshold. In optional step S13, the quality of the specific CC
is determined. The quality can be determined based on measurements
or based on estimation. The UE can determine the quality, or
alternatively the UE can receive this information as input to be
used in the measurement handling procedure. In step S14, the UE
evaluates the signal quality of the specific CC of the configured
CCs against a configurable threshold to determine the need for
neighbor cell measurements. In step S15, the UE performs neighbor
cell measurements if the signal quality of the specific CC is below
the threshold. The complementary action of allowing the UE to omit
neighbour cell measurements if the signal quality exceeds the
threshold is not illustrated in the flow diagram of FIG. 9. In
optional step S16, the UE evaluates, based on the neighbour cell
measurements and measurements of the specific CC, an event-trigger
for issuing a measurement report from the UE to support
network-controlled mobility.
[0094] According to an aspect of the present invention, there is
thus provided a method of measurement handling in a UE configured
with multiple downlink component carriers, where the UE is allowed
to omit any measurements on neighboring cells or downlink carriers
if the quality of at least one of the Configured Component Carriers
exceeds a configurable threshold.
[0095] In a particular example, the at least one CC is the best CC
of the configured CC. In another example, the at least one CC is
semi-statically configured in the UE by signaling according to the
applicable RRC protocol, such that the UE evaluates the quality of
this CC against the configurable threshold. In another example, the
at least one CC can be the CC with the best coverage, the largest
bandwidth, the highest bit-rate, or the least required UL power on
the corresponding UL carrier.
[0096] As previously mentioned, yet another alternative is to use
the so-called PCell, or Primary Cell, as a specific reference CC
for evaluating the need for neighbor cell measurements.
[0097] Furthermore, the measurement omission criteria and
thresholds relate to the UE in Connected mode, and the measurements
are typically intended for measurement reporting to support
network-controlled mobility.
[0098] For a better understanding of the invention, it can be
useful to review and analyze some of the problems encountered when
a UE is served by multiple CCs.
[0099] As previously mentioned, a particular problem is that it is
unclear how the s-Measure evaluation and similar evaluation of the
need for neighbor cell measurements for a UE with multiple,
aggregated Component Carriers should be performed.
[0100] In Rel-8, the UE is "served" by one downlink carrier against
which the s-Measure criterion is evaluated. In Rel-10, the UE may
be "served" by multiple downlink CCs, and it is unclear how, or
against which of the CCs that the s-Measure criterion or criteria
should be evaluated.
[0101] It should be noted that carriers having quite diverse
propagation conditions can also be aggregated. Thus, the received
signal power or quality in the UE of the different component
carriers can be quite different. The antennas of the different
component carriers can also be oriented differently, meaning that
the received power of the component carriers can vary depending on
the position of the UE. Thus, it is not evident how the s-Measure
criterion should be evaluated when the UE is configured with
multiple carriers.
[0102] This is particularly true for example in deployments where
macro-cells and smaller (micro-) cells (or CCs) are aggregated
together, as schematically illustrated in FIGS. 10A-B.
[0103] It is schematically illustrated how the measured RSRP
(Reference Signal Received Power), RSRQ (Reference Signal Received
Quality) or similar physical layer measurements of three CCs vary
over time (FIG. 10A) as a UE moves along the dotted-line trajectory
(FIG. 10B). The CCs are assumed to all be transmitted from antennas
in the center of the circles. The circles on the right-hand-side
conceptually illustrate the coverage border of the DL carriers that
define the three configured CCs.
[0104] It can happen as indicated in FIG. 10A that the UE's
received signal strength of a first CC (e.g. CC1) is strongest in
one position, while another CC (e.g. CC3) is strongest in another.
Here, a particular example is shown where the cell (CC3) with the
smallest coverage is best in very close proximity to the antennas,
which could be the case, e.g., if different down-tilting is
used.
[0105] Thus, it is unclear what criterion should be evaluated to
deduce if the UE is required to perform measurements on neighbor
cells.
[0106] Another issue concerns the reference carrier for measurement
triggering. It is possible that some events will be compared
towards an intra-frequency carrier only, as illustrated in FIG.
11.
[0107] Such event evaluations can be particularly useful for
detecting the interference level on specific carriers on which the
UE has a CC. However, all measurement objects do not carry any
configured CC. This is true, for example, for inter-frequency and
inter-RAT objects. Then, it is possible that, for such
measurements, a reference among the configured CCs will be used as
illustrated by FIG. 12.
[0108] Such inter-frequency or inter-RAT measurement triggers that
are evaluated against a Serving Cell in Rel-8 can now be evaluated
against one specific CC among the configured CCs. For example, the
CC illustrated as the CC on Object 2 in FIG. 12 could be selected
based on various different criteria, e.g. such that Object 2 is the
best of the CCs, e.g. in terms of RSRP or RSRQ.
[0109] With the different reference CCs for intra- and
inter-frequency measurements above, it remains unclear if the UE is
allowed to stop measurements on all neighbors, if some or all, or
some specific CC is above or below some threshold. Clearly, in FIG.
11, the neighbor on Object 1 is compared with the CC on Object 1,
while the neighbor on Object 4 in FIG. 12 is compared with the CC
on Object 2. It is not clear whether the s-Measure criterion should
be evaluated separately for each Object.
[0110] It should be noted that the example above is developed using
Event A3, but the problems are equally applicable to all other
events involving a neighbor on an object.
[0111] The "goodness" (i.e., good, better, best, as used here) is
determined by evaluating some physical layer measurements, where a
stronger physical layer measurement typically, and in current art,
indicates that a cell or CC is "better" or "stronger" than the
other. The quality is thus normally the signal quality such as
received signal power or similar measure of signal strength. In
LTE, such measurements include RSRP (Reference Signal Received
Power) and RSRQ (Reference Signal Received Quality). However, the
present invention is equally applicable to any measurement related
to the measured object.
[0112] In many cases, the term "cell" can be interchanged with DL
carrier, provided the carrier is configured with objects that can
be used as CCs for a UE.
[0113] As explained, a basic idea is to evaluate the signal quality
of a specific CC of the configured CCs against a configurable
threshold to determine the need for neighbor cell measurements, and
perform neighbor cell measurements only if the signal quality of
the specific CC is below the threshold
[0114] The present invention is now described in detail using
specific examples:
[0115] In a first aspect of the present invention, there is now a
UE that has been configured with multiple CCs. In the example
illustrated in FIG. 13, the UE is configured with three CCs.
[0116] In this particular example, there is provided a method of
omitting neighbor cell measurements if, e.g., the RSRP power or
similar representation of the quality of at least one component
carrier exceeds a configurable threshold, as illustrated in FIG.
13. Once the received power of at least one CC (FIG. 13 shows all
CCs) drops below the threshold, then the UE is required to perform
neighbor cell measurements. Here, it is illustrated that one of the
carriers is strongest in absolute terms.
[0117] It should be understood that respective, different
thresholds related to each of the three carriers can be configured,
such that the relative received power or quality of the CCs can be
compared. Alternatively, a CC to be evaluated against a threshold
can be implicitly or explicitly configurable, e.g., using the RRC
protocol. As an example, the so-called PCell, or Primary Cell, can
be used as a specific reference CC for evaluating the need for
neighbor cell measurements. In yet another alternative, the CC to
be used in the evaluation can be based on different criteria
related to the CC with the best coverage, the largest bandwidth,
the highest bit-rate, or least the required uplink (UL) power on
the corresponding UL carrier.
[0118] If the power of all, or at least one specific, CC goes below
the aforementioned threshold, then the UE is required to perform
neighbor cell measurements, e.g., such that configured events like
A3, A4, A5, B1, or B2 can be evaluated for neighbor cells. Such an
evaluation is illustrated by the example in the previously
described FIG. 3 for Event A3.
[0119] FIG. 3 illustrates a situation where a reference cell (here
denoted "serving cell", but that can also be the CC that is used in
the event evaluation) becomes weaker. It is here assumed that the
UE is connected to this ("serving") CC, and a neighbor cell is
compared to the aforementioned CC. Now, and as described
previously, a UE can be connected to multiple CCs. Thus, in
different event evaluations, the reference (denoted "Serving" in
the FIG. 3) can be different for various event evaluations.
[0120] Different references can be needed, e.g., in a network
deployment, where a first eNB(1) is controlling two carriers, and a
second eNB(2) is controlling one carrier. For illustrative
purposes, assume that the first eNB(1) is controlling carriers on
700 MHz and 1900 MHz, and the second eNB(2) is controlling one
carrier one 1900 MHz DL carrier only, as illustrated in FIGS.
14A-B. As is generally known in the industry, a 700 MHz carrier has
much better coverage compared to a 1900 MHz carrier, which is
schematically illustrated in FIG. 14B.
[0121] In a manner similar to FIG. 10B, FIG. 14B show an example
where a UE is assumed to move from close proximity to eNB(1) toward
eNB(2), as illustrated by the dashed line. In this example, the UE
is configured with two CCs, one on 700 MHz and another on 1900 MHz,
as illustrated in FIG. 14A. As can be seen from FIG. 14B, the 700
MHz CC has much better coverage (i.e., a greater area), partly also
covering the 1900 MHz cell controlled by eNB(2). Now, with a single
threshold "s-Measure" related to Object 1 (700 MHz), it could
happen that the 1900 MHz CC controlled by eNB(2) remains
undetected, because the threshold comparison to Object 1 will
result in an evaluation concluding that no neighbor cell
measurements are required. Thus, a UE can therefore still be
scheduled from eNB(1) on the 1900 MHz carrier resulting in severe
interference on the neighboring 1900 MHz cell controlled by eNB(2).
In addition, it can be impossible for eNB(1) to decide upon any
possible handover to eNB(2), to the 1900 MHz carrier, since no such
reports identifying this cell has been provided.
[0122] Thus, according to a further aspect of the present
invention, there can be provided in addition to the first described
threshold (denoted s-Measure, as before), another threshold related
to Object 2, as illustrated by FIG. 15. This other threshold
(denoted s-Intra-Meas in FIG. 15), can be specifically related to
Object 2, or it can be related to all objects that have a CC
configured.
[0123] As illustrated by FIG. 15, according to the present
invention, there is now a condition where a UE is required to
measure on Object 2, if the power or quality of the CC on object 2
falls below the configurable threshold s-Intra-Meas.
[0124] Still, the UE can in a particular example embodiment omit
any neighbor cell measurements on other objects, provided no
conditions related to those other objects require neighbor cell
measurements. In the example in FIG. 15, the UE can thus omit any
measurements on Object 1 until the s-Measure criterion requires
measurements, unless the UE has a configured threshold
(s-intra-Meas) specifically associated with Object 1 as well.
[0125] As a further example, the UE can omit inter-frequency or
inter-RAT measurements, even if neighbor cell measurements on
Object 2 are required according to the present invention.
[0126] The need for inter-frequency or inter-RAT measurements can
be evaluated against the first threshold "s-Measure", where the
evaluation is performed for one specific CC of the configured
CCs.
[0127] FIG. 16 is a schematic flow diagram illustrating an example
of a method for measurement handling according to a particular
embodiment. In step S21, the UE is allowed to omit measurements on
neighbor cells residing on carriers on which the UE has no CC, also
referred to as inter-frequency or inter-RAT, Radio Access
Technology, measurements, if the quality of the specific CC exceeds
a configurable first threshold. In step S22, the UE is required to
continue measurements on a neighbor cell residing on at least one
other carrier on which the UE has a CC, also referred to as
intra-frequency measurements, if the quality of the CC on that
other carrier is below a second configurable threshold.
[0128] According to an aspect of the present invention, there is
thus provided a method of measurement handling in a UE configured
with multiple downlink component carriers, [0129] where the UE is
allowed to omit measurements on neighbor cells or objects on which
the UE has no CC (inter-frequency or inter-RAT measurements), if
the quality of at least one CC exceeds a configurable first
threshold (the complementary action being to perform the
measurements when below the first threshold); and [0130] the UE is
required to continue measurements on a neighbor cell on at least
one other object on which the UE has a CC (intra-frequency
measurements), if the quality of the CC on that other object is
below a second configurable threshold.
[0131] In a particular example, the at least one CC is the best CC
of the configured CC. In a second example, the at least one CC is
semi-statically configured in the UE by RRC-protocol signaling,
such that the UE evaluates the quality of this CC against the
configurable threshold. In yet another example, separate
configurable thresholds are configured for evaluating the need to
perform intra-frequency measurements on an object with a CC.
[0132] FIG. 17 is a schematic flow diagram illustrating an example
of a method for measurement handling according to another
particular embodiment. In step S31, a first threshold is configured
to control inter-frequency or inter-RAT, Radio Access Technology,
measurements. In step S32, at least one other threshold is
configured to control intra-frequency measurements. In step S33,
the UE is allowed to omit inter-frequency or inter-RAT measurements
if a measured parameter related to the specific CC exceeds the
first threshold. In step S34, the UE is allowed to omit
intra-frequency measurements on at least one intra-frequency
carrier, if a measured parameter on the at least one
intra-frequency carrier exceeds one of the at least one other
configurable threshold.
[0133] According to an aspect of the present invention, there is
thus provided a method of configuring multiple thresholds
determining the necessity for a UE to perform neighbor cell
measurements, where [0134] a first threshold is configured to
control inter-frequency or inter-RAT measurements, [0135] at least
one other threshold is configured to control intra-frequency
measurements, [0136] the UE is allowed to omit inter-frequency or
inter-RAT measurements if a measured parameter related to one CC
exceeds the first threshold (the complementary action being to
perform the measurements when below the first threshold), and
[0137] the UE is allowed to omit intra-frequency measurements on at
least one intra-frequency object, if a measured parameter on the at
least one intra-frequency object exceeds one of the at least one
other configurable thresholds (the complementary action being to
perform the measurements when below one or more of the at least one
other configurable thresholds).
[0138] In a particular example, separate intra-frequency thresholds
for each intra-frequency object are configured such that the
evaluation of the necessity to perform intra-frequency measurements
is performed separately for each object. In another particular
example, the UE is allowed to omit measurements on an
intra-frequency object, if no threshold is configured for
specifically to that object, and the measured parameter related to
one CC exceeds the first threshold.
[0139] Thus, and as already partly described, according to the
present invention it shall be possible to configure a UE with
multiple thresholds, as illustrated in the schematic flow diagram
of FIG. 23. The UE is configured with multiple thresholds (step
S41). Each of the thresholds relate to at least one measurement
object, and the threshold is used for evaluating whether there is a
need to perform neighbor cell measurements on this particular
object (step S42). In this evaluation, the CC on that object is
used for the evaluation.
[0140] According to further aspects of the present invention,
apparatus in user equipments and computer-readable media for
measurement handling are provided.
[0141] FIG. 18 is a schematic diagram illustrating an example of a
control unit for measurement handling according to an embodiment of
the invention. The control unit 208 is configured for measurement
handling in a user equipment, UE, in connected mode. The UE is
configured with multiple downlink component carriers, CCs, also
referred to as serving cells. The control unit 208 comprises one or
more processing circuits 218 configured to evaluate the signal
quality of a specific CC of the configured CCs against a
configurable threshold to determine the need for neighbor cell
measurements, and request neighbor cell measurements if the signal
quality of the specific CC is below the configurable threshold.
[0142] The processing circuit(s) 218 is/are typically also
configured to allow the UE to omit neighbor cell measurements if
the quality of the specific CC exceeds the configurable
threshold.
[0143] The control unit 208 can be configured to receive
information about the specific CC, with the specific CC being
configured using for example the Radio Resource Control, RRC,
protocol.
[0144] For example, the control unit 208 is configured to receive
information about the specific CC, with the specific CC being
semi-statically configured in the UE by signaling according to the
applicable RRC protocol, such that the quality of this CC is
evaluated against the configurable threshold.
[0145] Alternatively, the control unit 208 decides which one of the
configured CCs to use as the specific CC. Anyway, the control unit,
or alternatively the UE in which the control unit is arranged, will
normally be configured to maintain information about the specific
CC as the CC to be evaluated against the threshold. The control
unit 208, or the UE, can receive information about the quality of
the specific CC, or request measurements of the quality of the
specific CC. Once the quality of the specific CC is received, the
processing circuit(s) 218 can evaluate the need for neighbor cell
measurements. Normally, the control unit 218 is configured to
perform the evaluation with respect to physical layer measurements
related to the specific CC, or at least an estimate of the received
signal quality of the specific CC.
[0146] In an example embodiment, the processing circuit(s) 218
is/are configured to evaluate the need for measurements on neighbor
cells residing on carriers on which the UE has no CC, also referred
to as inter-frequency or inter-RAT, Radio Access Technology,
measurements. For example, the processing circuit(s) 218 can be
configured to perform s-Measure evaluation for the specific CC, and
configured to evaluate the need for inter-frequency or inter-RAT,
Radio Access Technology, measurements against an s-Measure
threshold for the specific CC.
[0147] In the control unit 208, the processing circuit(s) 218 can
include one or more programmed processors configured to perform the
measurement handling, as will be explained in more detail later
on.
[0148] FIG. 19 is a schematic diagram illustrating an example of a
user equipment configured for measurement handling in connected
mode according to an embodiment of the invention. The UE is
configured with multiple downlink component carriers, CCs, also
referred to as serving cells. The UE 200 comprises one or more
measurement circuits 205, and a control unit 208, which in turn
comprises one or more processing circuits 218 for measurement
handling. The processing circuit(s) 218 is/are configured to
evaluate the signal quality of a specific CC of the configured CCs
against a configurable threshold to determine the need for neighbor
cell measurements, and request (REQUEST) neighbor cell measurements
to be performed if the signal quality of the specific CC is below a
configurable threshold. The measurement circuit(s) 205 is/are
configured to perform, if requested, the neighbor cell
measurements.
[0149] The processing circuit(s) 218 is/are typically also
configured to allow the UE to omit neighbor cell measurements if
the quality of the specific CC exceeds the configurable threshold.
In practice, this normally means that suitable control information
is generated by the processing circuit(s) 218 so that the UE knows
that it is not required to perform neighbor cell measurements.
[0150] The UE 200 can be configured to receive information about
the specific CC, with the specific CC being configured using for
example the Radio Resource Control, RRC, protocol, as previously
explained.
[0151] For example, the UE is configured to receive information
about the specific CC, with the specific CC being semi-statically
configured in the UE by signaling according to the applicable RRC
protocol, such that the quality of this CC is evaluated against the
configurable threshold.
[0152] The UE 200 is preferably configured to maintain information
about the specific CC as the CC to be evaluated against the
threshold. This information can for example be maintained in memory
228, which is typically located within the control unit 208 or
located externally to the control unit 208 but still within the UE
200.
[0153] In an example embodiment, the processing circuit(s) 218
is/are configured to evaluate the need for measurements on neighbor
cells residing on carriers on which the UE has no CC, also referred
to as inter-frequency or inter-RAT, Radio Access Technology,
measurements.
[0154] The UE 200 can also include one or more circuit(s) 207
configured to determine the signal quality of the specific CC,
normally determined as received signal strength. The circuit(s) 207
can be integrated in the measurement circuit (s) 208, if desired.
The quality information can then be transferred, for example on
request, to the control unit 208, and the processing circuit (s)
218 in particular.
[0155] Further, the processing circuit(s) 218 can optionally be
configured to evaluate, based on the neighbor cell measurements and
measurements of the specific CC, an event-trigger for issuing a
measurement report from the UE to support network-controlled
mobility.
[0156] By way of example, the processing circuit(s) 218 includes
one or more programmed processors configured to perform the
measurement handling. Other implementations will be discussed later
on.
[0157] The control unit 208 can be configured to perform any of the
above-described methods for measurement handling.
[0158] FIG. 20 depicts a typical cellular radio communication
system 10. Radio network controllers (RNCs) 12, 14 control various
radio network functions, including for example radio access bearer
setup, diversity handover, etc. In general, each RNC directs calls
to and from a UE, such as a mobile station (MS), mobile phone, or
other remote terminal, via appropriate base station(s) (BSs), which
communicate with each other through DL (or forward) and UL (or
reverse) channels. In the example illustrated in FIG. 20, RNC 12 is
shown coupled to BSs 16, 18, 20, and RNC 14 is shown coupled to BSs
22, 24, 26. The use of WCDMA nomenclature is merely for
facilitating for persons with WCDMA knowledge to understand LTE
node functionality.
[0159] Each BS, or eNodeB in LTE vocabulary, serves a geographical
area that is divided into one or more cell(s). In the example
illustrated in FIG. 20, BS 26 is shown as having five antenna
sectors S1-S5, which can be said to make up the cell of the BS 26,
although a sector or other area served by signals from a BS can
also be called a cell. In addition, a BS can use more than one
antenna to transmit signals to a UE. The BSs are typically coupled
to their corresponding RNCs by dedicated telephone lines, optical
fiber links, microwave links, etc. The RNCs 12, 14 are connected
with external networks such as the public switched telephone
network (PSTN), the internet, etc. through one or more core network
nodes, such as a mobile switching center (not shown) and/or a
packet radio service node (not shown).
[0160] It should be understood that the arrangement of
functionalities depicted in FIG. 20 can be modified in LTE and
other communication systems. For example, the functionality of the
RNCs 12, 14 can be moved to the eNodeBs 22, 24, 26, and other
functionalities can be moved to other nodes in the network. It will
also be understood that a base station can use multiple transmit
antennas to transmit information into a cell/sector/area, and those
different transmit antennas can send respective, different pilot
signals.
[0161] FIG. 21 is a block diagram of an example of a portion of a
UE 200 that is suitable for implementing the methods described
above. For simplicity, only some parts of the UE 200 are shown in
the figure. It will also be understood that the UE can be
implemented by other arrangements and/or combinations of the
functional blocks shown in FIG. 21.
[0162] Signals from eNBs are received through an antenna 202 and
down-converted to base-band signals by a front-end receiver (Fe RX)
204. On a regular basis for all detected cells, the received signal
code power (RSCP) is estimated and the received signal strength
indication (RSSI) is computed by an RSSI scanner 206 that operates
under the control of a control unit 208. An RSCP can be estimated
by, for example, de-spreading the base-band signal from a detected
cell with the scrambling code (and common pilot channel (CPICH)
channelization code) corresponding to the cell. In LTE,
cell-specific or UE-specific reference symbols can be used. Methods
of computing RSSIs are well known in the art. In suitable
communication systems, for example, the RSSI can be estimated by
computing the variance of the received signal over a given time
period.
[0163] The control unit 208 uses the RSSI scan information in
identifying radio carriers and analyzing the UE's radio environment
according to the methods described above. The control unit 208
stores information determined in the analysis in a suitable memory
210, and retrieves stored information as needed. Based on the
results of such searches and other information, the control unit
208 controls the operation of the Fe RX 204 and scanner 206 to
carry out cell searches and other procedures specified for the
wireless communication system as described above. Thus, the Fe RX
204, scanner 206, and control unit 208 form an analyzer configured
to analyze received radio signals transmitted by at least one cell
in the wireless communication system and to determine information
about a radio environment of the receiver by analyzing the received
radio signals. It will be appreciated that the UE 200 also
typically includes a modulator 212 and a front-end transmitter (Fe
TX) 214 and other devices for sending information to the network
and using received information.
[0164] The control unit 208 and other blocks of the UE 200 can be
implemented by one or more suitably programmed electronic
processors, collections of logic gates, etc. that processes
information stored in one or more memories 210. The stored
information can include program instructions and data that enable
the control unit to implement the methods described above. It will
be appreciated that the control unit typically includes timers,
etc. that facilitate its operations.
[0165] It will be appreciated that the methods and devices
described above can be combined and re-arranged in a variety of
equivalent ways, and that the methods can be performed by one or
more suitably programmed or configured digital signal processors
and other known electronic circuits (e.g., discrete logic gates
interconnected to perform a specialized function, or
application-specific integrated circuits). Many aspects of this
invention are described in terms of sequences of actions that can
be performed by, for example, elements of a programmable computer
system. UEs embodying this invention include, for example, mobile
telephones, pagers, headsets, laptop computers and other mobile
terminals, and the like. Moreover, this invention can additionally
be considered to be embodied entirely within any form of
computer-readable storage medium having stored therein an
appropriate set of instructions for use by or in connection with an
instruction-execution system, apparatus, or device, such as a
computer-based system, processor-containing system, or other system
that can fetch instructions from a medium and execute the
instructions.
[0166] In general, the steps, functions, procedures and/or circuits
described above can be implemented in hardware using any
conventional technology, such as discrete circuit or integrated
circuit technology, including both general-purpose electronic
circuitry and application-specific circuitry.
[0167] Alternatively, at least some of the steps, functions,
procedures and/or blocks described above can be implemented in
software for execution by a suitable computer or processing circuit
such as a microprocessor, Digital Signal Processor (DSP) and/or any
suitable programmable logic device such as a Field Programmable
Gate Array (FPGA) device and a Programmable Logic Controller (PLC)
device.
[0168] It should also be understood that it can be possible to
re-use the general processing capabilities of any conventional
unit. It can also be possible to re-use existing software, e.g. by
reprogramming of the existing software or by adding new software
components.
[0169] The software can be realized as a computer program product,
which is normally carried on a computer-readable medium, for
example a CD, DVD, USB memory, hard drive or any other conventional
memory device. The software can thus be loaded into the operating
memory of a computer for execution by the processor of the
computer. The computer/processor does not have to be dedicated to
only execute the above-described steps, functions, procedure and/or
blocks, but can also execute other software tasks. In the
following, an example of a computer implementation of a control
unit will be described with reference to FIG. 22.
[0170] FIG. 22 is a schematic diagram illustrating an example of a
computer-implemented control unit for measurement event evaluation,
as well as a computer-readable medium according to an embodiment.
The computer-implemented control unit 208 illustrated in the
example of FIG. 19 comprises a processor 310, a memory system 320,
an input/output (I/O) controller 330, a driver 340 for a
computer-readable medium 400, and a system bus 350.
[0171] In this example, the relevant steps, functions and/or
procedures for measurement handling are implemented in software 318
to enable evaluation of the need to perform neighbor cell
measurements and carried on the computer-readable medium 400.
[0172] More particularly, the software includes instructions for
performing, when executed by a computer-based system, measurement
handling in a UE in connected mode. In the measurement handling to
be executed the signal quality of a specific CC of the configured
CCs is evaluated against a configurable threshold to determine the
need for neighbor cell measurements, and neighbor cell measurements
are requested to be performed if the signal quality of the specific
CC is below the configurable threshold.
[0173] The computer-readable medium 400 is inserted into the driver
340, and the software 318 for measurement handling is loaded into
the memory system 320 via the system bus 350. The processor 310 and
the memory system 320 are also interconnected via the system bus
350 to enable normal software execution.
[0174] The I/O controller 330 is interconnected to the processor
and/or the memory system via the system bus 350 or a dedicated I/O
bus (not shown) to enable input and/or output of relevant data such
as input parameter(s) and/or resulting output parameter(s). More
particularly, the I/O controller 330 can receive information about
the specific CC as input, for possible storage of this information
in a suitable memory location 328 in the memory system 320. The I/O
controller 330 can also receive information about the quality of
the specific CC as input, and provide a request to perform neighbor
cell measurements or complementary information allowing the UE to
omit such measurements as output.
[0175] The embodiments described above are to be understood as a
few illustrative examples of the present invention. It will be
understood by those skilled in the art that various modifications,
combinations and changes can be made to the embodiments without
departing from the scope of the present invention. In particular,
different part solutions in the different embodiments can be
combined in other configurations, where technically possible. The
scope of the present invention is, however, defined by the appended
claims.
* * * * *