U.S. patent application number 13/031397 was filed with the patent office on 2012-08-23 for signal measurement on component carriers in wireless communication systems.
This patent application is currently assigned to MOTOROLA MOBILITY, INC.. Invention is credited to Sandeep H. Krishnamurthy, Ravi Kuchibhotla, Murali Narasimha.
Application Number | 20120214540 13/031397 |
Document ID | / |
Family ID | 45768307 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120214540 |
Kind Code |
A1 |
Narasimha; Murali ; et
al. |
August 23, 2012 |
Signal Measurement on Component Carriers in Wireless Communication
Systems
Abstract
A method in a wireless communication device includes performing
measurements of a first serving cell on a first carrier frequency
at a first rate, determining whether a signal level of a second
serving cell on a second carrier frequency exceeds a threshold, and
performing measurements of the first serving cell at a second rate
if the signal level of the second serving cell is below the
threshold, wherein the second rate is higher than the first
rate.
Inventors: |
Narasimha; Murali; (Lake
Zurich, IL) ; Krishnamurthy; Sandeep H.; (Arlington
Heights, IL) ; Kuchibhotla; Ravi; (Gurnee,
IL) |
Assignee: |
MOTOROLA MOBILITY, INC.
Libertyville
IL
|
Family ID: |
45768307 |
Appl. No.: |
13/031397 |
Filed: |
February 21, 2011 |
Current U.S.
Class: |
455/525 ;
455/507 |
Current CPC
Class: |
H04L 5/0007 20130101;
H04W 36/30 20130101; H04W 24/10 20130101 |
Class at
Publication: |
455/525 ;
455/507 |
International
Class: |
H04B 7/26 20060101
H04B007/26; H04B 7/24 20060101 H04B007/24 |
Claims
1. A method in a wireless communication device, the method
comprising: performing measurements of a first serving cell on a
first carrier frequency at a first rate; determining whether a
signal level of a second serving cell on a second carrier frequency
is below a threshold; and performing measurements of the first
serving cell at a second rate if the signal level of the second
serving cell is below the threshold, the second rate higher than
the first rate.
2. The method of claim 1 further comprising reporting information
based on at least some of the measurements to a first base
station.
3. The method of claim 2, wherein reporting information includes
reporting information based on at least the measurements performed
on the first serving cell at the second rate.
4. The method of claim 1 further comprising receiving a handover
command from the first base station in response to sending the
measurement report.
5. The method of claim 4 further comprising handing over to a
second base station in a location different than the first base
station in response to receiving the handover command.
6. The method of claim 4, wherein the first serving cell on the
first carrier frequency is a deactivated serving cell, the method
further comprising configuring the first serving cell as a primary
serving cell in response to receiving the handover command.
7. The method of claim 1, wherein the wireless communication
terminal is configured for carrier aggregation, and wherein the
first carrier frequency is a deactivated carrier and wherein the
second carrier frequency is a primary carrier frequency.
8. The method of claim 1 further comprising filtering the
measurements performed on the first serving cell, wherein reporting
at least some of the measurements to the first base station
includes reporting the filtered measurements.
9. A method in a wireless communication base station, the method
comprising: configuring a wireless communication terminal for
carrier aggregation on a primary serving cell on a first carrier
frequency and on a secondary serving cell on a second carrier
frequency; determining a secondary serving cell measurement
threshold for measurements of the secondary serving cell when the
secondary serving cell is deactivated; signaling the secondary
serving cell measurement threshold to the wireless communication
terminal; receiving a measurement report from the wireless
communication terminal, the measurement report based on
measurements of the secondary serving cell on the second carrier
frequency at a rate dependent on whether a signal measured on the
primary serving cell is below the secondary serving cell
measurement threshold; signaling a handover command to the wireless
communication terminal based on the measurement report.
10. The method of claim 9, wherein the handover command signals the
wireless communication terminal to hand over to a second base
station in a location different than a location of the wireless
communication base station.
12. The method of claim 9, wherein the rate of measurements of the
secondary serving cell on the second carrier frequency increase
when the signal measured on the primary serving cell is below the
secondary serving cell measurement threshold.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates generally to wireless
communications and, more particularly, to measurement of component
carriers in wireless communication systems.
BACKGROUND
[0002] Carrier aggregation (CA) will be used in future 3GPP LTE
wireless communication networks to provide improved data rates to
users. Carrier aggregation includes transmitting data to or
receiving data from user equipment (UE) on multiple carrier
frequencies (component carriers). The wider bandwidth enables
higher data rates.
[0003] A UE can generally be configured with a set of component
carriers (CCs). Specifically, the UE is configured with a cell on
each component carrier. Some of these cells may be activated. The
activated cells can be used to send and receive data (i.e., the
activated cells can be used for scheduling). The UE has up-to-date
system information for all configured cells. Therefore, after a
cell has been configured, it can be quickly activated. Thus, when
there is a need for aggregating multiple CCs (e.g., upon the
occurrence of a large burst of data), the network can activate
configured cells on one or more of the CCs. Generally, there is a
designated primary cell (Pcell) on a CC that is referred to as the
primary CC, which is always activated. The other configured cells
are referred to as Scells (and the corresponding CCs are referred
to as secondary CCs).
[0004] The maintenance of a configured CC set in addition to an
activated CC set enables battery conservation in the UE while
providing CCs that can be activated when necessary, for example,
when there is a substantial amount of data to be transmitted.
[0005] It is expected that multiple carriers will be activated only
when there is a substantial amount of data to be transmitted. This
implies that CCs will remain in the configured but deactivated
state for extended time periods. It is essential to perform RRM
measurements of cells on the deactivated CCs so that the
appropriate CCs (and cells) can be activated. Performing
measurements of multiple CCs requires the UE to operate its RF
frontend at a higher bandwidth (in the case of intra-band
aggregation), or to use an alternate transceiver for measurements.
Both of these options cause significant power consumption in the
UE. Performing frequent measurements of CCs with activated cells
does not result in substantial additional power consumption since
the UE is required to be able to receive control channels and data
channels from the activated cells anyway (and therefore the RF
front end needs to be able to receive the activated CCs). A UE is
generally not expected to receive control and data channels on
deactivated secondary cells. UEs are configured with secondary
cells in the deactivated state for extended time periods.
Cumulatively, measurements of cells on secondary CCs can consume
large amounts of power. Thus it is generally considered beneficial
to control the rate at which measurements of cells on secondary CCs
are performed to minimize power consumption. That is, it is
beneficial to perform measurements of cells on deactivated
secondary CCs less frequently than measurements of cells on the
primary CC and cells on activated secondary CCs.
[0006] The various aspects, features and advantages of the
invention will become more fully apparent to those having ordinary
skill in the art upon careful consideration of the following
Detailed Description thereof with the accompanying drawings
described below. The drawings may have been simplified for clarity
and are not necessarily drawn to scale.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 illustrates an exemplary wireless communication
system employing carrier aggregation.
[0008] FIG. 2 illustrates the actual conditions experienced by the
UE in FIG. 1.
[0009] FIG. 3 illustrates apparent radio conditions experienced by
a UE in FIG. 1 making measurements on CC2 at a lower measurement
rate than the primary cell CC1.
[0010] FIG. 4 illustrates a process flow diagram.
[0011] FIG. 5 illustrates more accurate radio conditions
experienced by the UE in FIG. 1 making measurements on CC2 at a
measurement rate higher than the lower measurement rate of FIG.
3.
[0012] FIG. 6 illustrates another process flow diagram.
[0013] FIG. 7 illustrates averaging Layer 1 measurements and
generating Layer 3 filtered measurements based on the Layer 1
measurements.
DETAILED DESCRIPTION
[0014] In FIG. 1, a wireless communication system 100 comprises one
or more fixed base infrastructure units 101, 102 forming a network
distributed over a geographical region for serving remote units in
the time and/or frequency and/or spatial domain. A base unit may
also be referred to as an access point, access terminal, base, base
station, NodeB, enhanced NodeB (eNodeB), Home NodeB (HNB), Home
eNodeB (HeNB), Macro eNodeB (MeNB), Donor eNodeB (DeNB), relay node
(RN), femtocell, femto-node, network node or by other terminology
used in the art. The one or more base units each comprise one or
more transmitters for downlink transmissions and one or more
receivers for uplink transmissions. The base units are generally
part of a radio access network that includes one or more
controllers communicably coupled to one or more corresponding base
units. The access network is generally communicably coupled to one
or more core networks, which may be coupled to other networks like
the Internet and public switched telephone networks among others.
These and other elements of access and core networks are not
illustrated but are known generally by those having ordinary skill
in the art.
[0015] In FIG. 1, the one or more base units serve a number of
remote units, for example, remote unit 103, within a corresponding
serving area, for example, a cell or a cell sector, via a wireless
communication link. The remote units may be fixed or mobile. The
remote units may also be referred to as subscriber units, mobiles,
mobile stations, mobile units, users, terminals, subscriber
stations, user equipment (UE), user terminals, wireless
communication devices, relay node, or by other terminology used in
the art. The remote units also comprise one or more transmitters
and one or more receivers. In FIG. 1, the base units and remote
unit communicates in the time and/or frequency and/or spatial
domain. Sometimes the base unit is referred to as a serving or
connected or anchor cell for the remote unit. The remote units may
also communicate with the base unit via a relay node.
[0016] In one implementation, the wireless communication system is
compliant with the 3GPP Universal Mobile Telecommunications System
(UMTS) LTE protocol, also referred to as EUTRA or 3GPP LTE or some
later generation thereof, wherein the base unit transmits using an
orthogonal frequency division multiplexing (OFDM) modulation scheme
on the downlink and the user terminals transmit on the uplink using
a single carrier frequency division multiple access (SC-FDMA)
scheme. The instant disclosure is particularly relevant to 3GPP LTE
Release 8 (Rel-8), 3GPP LTE Release 9 (Rel-9) and LTE Release 10
(Rel-10) and possibly later evolutions, but may also be applicable
to other wireless communication systems. More generally the
wireless communication system may implement some other open or
proprietary communication protocol, for example, IEEE 802.16(d)
(WiMAX), IEEE 802.16(e) (mobile WiMAX), among other existing and
future protocols. The disclosure is not intended to be implemented
in any particular wireless communication system architecture or
protocol. The architecture may also include the use of spreading
techniques such as multi-carrier CDMA (MC-CDMA), multi-carrier
direct sequence CDMA (MC-DS-CDMA), Orthogonal Frequency and Code
Division Multiplexing (OFCDM) with one or two dimensional
spreading. The architecture in which the features of the instant
disclosure are implemented may also be based on simpler time and/or
frequency division multiplexing/multiple access techniques, or a
combination of these various techniques. In alternate embodiments,
the wireless communication system may utilize other communication
system protocols including, but not limited to, TDMA or direct
sequence CDMA. The communication system may be a Time Division
Duplex (TDD) or Frequency Division Duplex (FDD) system.
[0017] In aggregated carrier (AC) systems, a User Equipment (UE)
can receive and transmit control and data signaling on multiple
component carriers (CCs). In FIG. 1, for example, the UE 103 is
configured for carrier aggregation and receives from base station
101 a first component carrier (CC1) and a second component carrier
(CC2) wherein CC1 is a primary cell (Pcell) and CC2 is a secondary
cell (Scell). Initially, the UE may communicate with the network by
receiving only a single CC (Primary or Anchor CC). In some
implementations, the network sends a configuration message (SI
configuration message) to the UE on the primary CC with system
information (SI) corresponding to other CCs on which the network
may schedule the UE. The SI typically includes CC specific
information that the UE is required to store in order to
communicate with the network on other CCs. The SI can include CC
specific information such as CC carrier frequency, downlink (DL)
bandwidth, number of antennas, downlink reference signal power,
uplink (UL) power control parameters and other information that
does not change frequently. In some aggregated carrier systems,
base station sends the SI configuration message to the UE using
Radio Resource Configuration (RRC) signaling, since the SI does not
change frequently and the payload associated with the SI
configuration is relatively large. Upon receipt of the SI
configuration, the UE stores the SI for other CCs but continues to
communicate with the network by only receiving the primary CC. The
other CCs for which the UE has received SI and the primary CC
constitute the UE's "configured CC set".
[0018] Performing measurements of cells on deactivated secondary
CCs less frequently than measurements of cells on primary CC can
reduce power consumption. However, having different measurement
periods can lead to incorrect mobility decisions at the network. In
FIG. 1 for example, the UE 103 is connected to eNB1 and is
configured with CC1 as a primary cell (PCell) and CC2 as a
secondary cell (Scell). The UE is moving towards eNB2. If the Scell
is deactivated (CC2 deactivated), the measurement rate on CC2 is
less than the rate on CC1. For example, the measurement period for
the primary cell may be 200 ms and the measurement period for the
secondary cell may be 1600 ms. In FIG. 1, an inter-eNB handover
should be triggered when CC1 from eNB2 102 is better than the
primary cell on eNB1 101 (based on an A3 event measurement report).
FIG. 2 illustrates the actual radio conditions experienced by the
UE in FIG. 1. However, the different measurement periods for the
primary cell and secondary cell on eNB 101 lead to a different view
of the radio conditions at the UE as illustrated in FIG. 2. FIG. 3
illustrates Layer 3 (L3) filtered measurements at the UE. Since the
measurements of the secondary cell are occurring less frequently,
the secondary cell measurements as observed by the UE lag the
actual radio conditions experienced by the UE. Since the UE
includes in measurement reports to the base station L3 filtered
measurements of the secondary cell, the UE will report that the
secondary cell is better than the primary cell as shown in FIG. 3.
This result may cause the eNB1 101 to attempt a primary cell change
instead of an inter-eNB handover. An Inter-eNB handover is more
appropriate since signal levels of CC1 and CC2 on eNB1 are actually
less than CC1 on eNB2. Furthermore, a primary cell change on eNB1
could fail since the CC2 signal is lower than the reported
measurement and another handover or primary cell change would be
required. Similarly, the different measurement periods can also
cause unnecessary inter-eNB handovers when a primary cell change is
needed. In the carrier aggregation context, the problem occurs only
with deactivated secondary cells. If the secondary cell is
activated, the measurements occur at the same rate as the primary
cell. However, since the eNB does not know exactly when a handover
will be required, it is not practical to pre-activate the secondary
cell. Besides, such an approach would defeat the purpose of
activation and deactivation.
[0019] Although the problem is described above in the context of
carrier aggregation, similar or related issues can occur in other
scenarios. For example, coexistence of multiple radios in the UE
(in-device coexistence) can in some cases lead to similar
measurement related problems. Consider the case where the UE has an
LTE transceiver and a WiFi transceiver wherein WiFi transmissions
by the UE can impact the LTE reception at the UE and LTE
transmission by the UE can impact the WiFi reception at the UE.
Specifically, when WiFi transmission activity is started, the
measurements on the LTE side see a sudden and significant
impact.
[0020] According to a first aspect of the disclosure illustrated in
the process flow diagram 400 of FIG. 4, a wireless communication
device performs measurements of a first serving cell on a first
carrier frequency at a first rate at 410. At 420, the UE determines
whether a signal level of a second serving cell on a second carrier
frequency is below a threshold. In one embodiment, the threshold is
a secondary serving cell measurement threshold signaled to the UE
by the base station. In other embodiments, the threshold is stored
locally or is obtained from some other source. At 430, the UE
performs measurements of the first serving cell at a second rate if
the signal level of the second serving cell is below the threshold.
In one instantiation, the rate of measurements of the secondary
serving cell on the second carrier frequency (and, if necessary,
other cells on the second carrier frequency) increase when the
signal measured on the primary serving cell is below the threshold.
In some embodiments, the measurements performed on the carrier
frequencies are filtered, for example, by a layer 3 (L3) filtering
process implemented using an infinite impulse response filter or
other suitable filter.
[0021] The UE generally comprises a controller coupled to a
wireless transceiver wherein the controller is configured to
perform measurements on the carrier frequencies as described above.
The measurement functionality performed by the controller may be
implemented by a digital processor that executes software or
firmware stored on a memory device. Similarly, the controller may
perform the filtering functionality and other functions described
herein by executing software or firmware. Alternatively the
functionality of the UE may be performed by equivalent hardware or
by a combination of hardware and software.
[0022] In one implementation, the UE is configured for carrier
aggregation and the first carrier frequency is a deactivated
carrier and the second carrier frequency is a primary carrier
frequency. According to this implementation, the UE increases the
rate at which measurements are made on the deactivated carrier when
the signal on the primary carrier falls below the threshold to more
accurately assess radio conditions to which the UE is subject. In
some implementations, the eNB configures the UE for carrier
aggregation on a primary serving cell on a first carrier frequency
and on a secondary serving cell on a second carrier frequency. As
suggested above, the eNB may also determine a secondary serving
cell measurement threshold to the wireless communication terminal.
The eNB may signal the secondary serving cell measurement threshold
to the wireless communication terminal. Thus the UE is provided a
primary cell signal threshold below which measurements of cells on
deactivated secondary CCs is performed more frequently. For
example, referring to the above scenario, if the UE observes that
the primary cell signal is above the threshold, the UE performs
measurements of deactivated secondary cell with a relatively long
measurement period of 1600 ms to reduce power consumption. When the
UE observes that the primary cell signal drops below the threshold,
the UE performs measurements of the deactivated secondary cell with
a measurement period of 480 ms. Alternatively, other measurement
periods may also be used.
[0023] In another implementation, the UE increases the rate at
which measurements are made on the deactivated carrier when the
difference between the signal on the primary carrier and a signal
on another carrier rises above a threshold. In some
implementations, the eNB configures the UE for carrier aggregation
on a primary serving cell on a first carrier frequency and on a
secondary serving cell on a second carrier frequency. The eNB may
also configure a measurement reporting offset, so that the wireless
communication terminal reports measurements if the difference
between the signal level of a cell other than the primary serving
cell and the signal level of the primary cell is higher than the
measurement reporting offset. For example, the UE is configured
with an A3 measurement event, the event set to trigger when a
neighbor cell signal is higher than the primary serving cell signal
by more than the measurement reporting offset. The UE reports
measurements when the A3 measurement event is triggered. In
addition to reporting measurements, the UE performs measurements of
cells on deactivated secondary CCs more frequently. For example,
referring to the above scenario, if the UE observes that the
neighbor cell signal is not higher than the signal of the primary
cell by the measurement reporting offset, the UE performs
measurements of deactivated secondary cell with a relatively long
measurement period, for example, 1600 ms, to reduce power
consumption. When the UE observes that the neighbor cell signal is
higher than the signal of the primary cell by at least the
measurement reporting offset, the UE performs measurements of the
deactivated secondary cell with a measurement period, for example
480 ms. Alternatively, other measurement periods may also be
used.
[0024] FIG. 5 illustrates the effect of applying the second
measurement rate to the first serving cell, which corresponds to
the deactivated carrier in the aggregated carrier implementation.
The more accurate radio conditions (illustrated in FIG. 5) produced
using the second measurement rate indicate that the UE should
perform an inter-base station handover from eNB1 to eNB2, rather
than an intra-base station handover suggested by the radio
conditions measured at the lower rate (as illustrated in FIG. 3).
In some implementations, the eNB commands the UE to perform the
handover as described further below, but more generally the
handover decision may be made autonomously by the UE.
[0025] In other implementations, the UE could be a multimode
device, for example, a WiFi enabled LTE device. In this
implementation, the UE can perform measurements of one or more of
the serving cells more frequently based on WiFi activity being
initiated or based on some other criteria.
[0026] The base station also comprises a controller coupled to a
wireless transceiver wherein the controller is configured to
perform the various functions described herein including
configuring the UE for aggregated carrier operation and
transmission of the threshold to the UE in embodiments for
implementations that require it, receipt and processing of
measurement reports from the UE, handover analyses and command
transmission, among other functions performed by the base station.
Alternatively the functionality of the eNB may be performed by
equivalent hardware or by a combination of hardware and
software.
[0027] In FIG. 4, at 440, in some embodiments the UE reports
information based on at least some of the measurements to a first
base station. In the aggregated carrier implementation above, for
example, the information is based on at least the measurements
performed on the first serving cell at the second rate, since these
measurements more accurately depict the radio conditions
experienced by the UE. In some embodiments, the measurements
performed on the first serving cell are filtered as described above
and the UE reports the filtered measurements to the eNB or base
station. In other implementations however, the UE may choose to
selectively not report some measurements, filtered or otherwise, a
base station. Such embodiments include those where the UE makes
handover decisions autonomously or where the UE provides handover
assistance information to the base station based on the
measurements.
[0028] In response to sending a measurement report to the eNB, the
UE may receive a handover command from eNB. Generally, the handover
command may be for an intra-base-station handover or for an
inter-base-station handover. An inter-base-station handover is a
handover from a first base station to a second base station serving
a different coverage area than that of the first base station, for
example, from eNB1 to eNB2 in FIG. 1. In one embodiment, an
intra-base-station handover is a change in primary serving cell. In
FIG. 1, for example, the deactivated secondary cell CC2 could be
made the primary serving cell in an intra-base-station handover in
response to receiving the handover command. Further, an
intra-base-station handover can include a change of primary cell
from a first cell of the base station on a first frequency to a
second cell of the same base station on a second frequency, wherein
the second cell is served by a remote antenna or a remote radio
head that is communicably coupled to the base station. Remote
antennas and remote radio heads are different from base stations in
that they transmit and receive RF signals, but do not have most or
all of the higher layer functionality associated with a base
station such as scheduling, medium access control, connectivity to
neighboring base stations etc. For such functionality, the remote
antennas and remote radio heads may rely on the associated base
station.
[0029] According to another aspect of the disclosure, the UE
provides the network information indicating that certain secondary
cell measurements are not reliable. For example, the UE can mark
some of the reported measurements as "not reliable". Alternatively,
the UE can omit measurements that are not reliable. The UE can
determine the reliability of the secondary cell measurements in
various ways, some examples of which are described below. In one
embodiment, the UE can consider the L3 filtered measurements to be
unreliable if the variance of L1 measurements (on which the L3
filtering measurements are based) in a measurement period is higher
than a specified threshold. For example, if the difference between
the highest L1 measurement and the lowest L1 measurement sample
exceeds a threshold. In another embodiment, the measurements to be
reported to the eNB may be considered unreliable if either the L3
filter measurements or the L1 measurements on which the L3 filter
measurements are based are older than a specified duration. This
solution can also be applied to resolve measurements related issues
in a multi-mode UE having multiple radio transceivers. For example,
if the UE is equipped with a WiFi transceiver, the UE can
experience a much lower measurements when WiFi transmission is
occurring. In such a situation, the UE can mark measurements as
unreliable or omit them if WiFi activity is ongoing when the
measurements are performed.
[0030] According to another aspect of the disclosure illustrated in
the process diagram of FIG. 6, a wireless communication terminal
generates a first averaged signal measurement on a first carrier
frequency, wherein the first averaged signal measurement is based
on a first averaging period at 620. At 620, the UE produces a first
filter output based on the first averaged signal measurement
weighted by a first weight. At 630, the UE generates a second
averaged signal measurement on the first carrier frequency, wherein
the second averaged signal measurement is based on a second
averaging period. At 640, the UE produces a second filter output
based on the first filter output and based on the second averaged
signal measurement weighted by a second weight, wherein the first
weight is less than the second weight if the second averaging
period is greater than a threshold.
[0031] Generally, the UE produces a third filter output subsequent
to producing the second filter output wherein the third filter
output is based on the first weight or at least a weight different
than the second weight. Thus the second weight is used only for one
or more filter cycles with the effect of diminishing the impact of
older filter outputs on the most recent filter output to provide
the eNB with a more accurate indication of the radio conditions
experienced by the UE.
[0032] In some implementations, the UE receives a message from an
eNB ordering the UE to perform the signal measurements on the first
carrier frequency using the second averaging period, as described
further below. According to this implementation, the wireless
communication infrastructure entity, or eNB, transmits a signal
measurement averaging period for a first carrier frequency, wherein
the signal measurement averaging period is transmitted to a
wireless communication terminal configured for aggregated carrier
operation. As suggested above, the eNB receives a filter output
from the UE, wherein the filter output is generated based on a
weighted signal measurement on the first carrier frequency, the
signal measurement is averaged over the signal measurement
averaging period, and the weight is dependent on the signal
measurement averaging period. After making a handover decision
based on the filter output received, the eNB may transmit a
handover command to the UE as discussed further below.
[0033] In a more particular implementation, the UE produces the
first filter output using a first filter coefficient and the UE
produces the second filter output using a second filter coefficient
if the second averaging period is greater than the threshold,
wherein the second filter coefficient is different than the first
filter coefficient. In one embodiment, the first filter output and
second filter output are produced using an infinite impulse
response filter, although other suitable filters may be used in
other embodiments. In one embodiment, the first averaged signal
measurement and the second averaged signal measurement are averaged
layer 1 signal measurements, and the first and second filter
outputs are layer 3 filtered measurements.
[0034] In one application, the second filter coefficient has a
value that negates the first filter output component of the second
filter output. More generally however the first filter output need
not be negated entirely. Generally, the UE adjusts L3 filter
coefficient to ensure that more recent measurements are weighted
more heavily. One example of L3 filtering is based on the following
IIR filter:
F.sub.n=(1-a)F.sub.n-1+aM.sub.n,
[0035] Where F.sub.n is the new filtered measurement, F.sub.n-1 is
the previous filtered measurement and M.sub.n is the new L3
measurement, and a=1/(2.sup.(k/4)), where k is the filter
coefficient. Thus the UE can use the following techniques to ensure
more recent measurements are weighted more heavily than less recent
measurements. For example, when the UE is configured with a
secondary cell measurement period that is larger than the primary
measurement period, the UE can select a larger value of `a` (i.e.,
choose a smaller value of k) for filtering of secondary cell
measurements than that used for primary cell measurement filtering.
When the UE notices that the latest (or latest n) secondary cell
(Scell) measurement is much higher than the previous measurements,
the UE uses an `a` value of 1 to remove the effects of previous
measurements from the filter for one or more L3 filter iterations.
This effectively amounts to resetting the filter. Subsequently the
UE can resume using a default or other optimized normal value of
`a`.
[0036] In some situations, it may be beneficial to use an `a` value
of greater than 1 to apply a higher weight to the most recent
measurements. This can serve as a faster trigger for certain
actions in the UE. For example, using an `a` greater than 1 can
cause the L3 filtered measurement to meet some measurement
reporting criteria and hence cause the UE to transmit a measurement
report to the base station sooner than it would with `a=1`.
[0037] FIG. 7 illustrates Layer 1 (L1) signal measurements
(M.sub.n-1) averaged over a first measurement averaging period on a
carrier frequency and the corresponding generation of a Layer 3
filter output (F.sub.n-1) based on the averaged L1 signal
measurement (M.sub.n-1) and based on a prior filtered output
(F.sub.n-2) wherein a weighting factor is applied to the filter
output (F.sub.n-1) and the averaged signal measurements
(M.sub.n-1). Also illustrated are L1 signal measurements (Mn)
averaged over a second measurement average period and the
corresponding generation of a Layer 3 filter output (F.sub.n) based
on the averaged L1 signal measurement (M.sub.n) and based on the
prior filtered output (F.sub.n-1) wherein a different weighting
factor is applied to the prior filter output (F.sub.n-1) and the
averaged signal measurement (M.sub.n) such that the prior filter
output is negated or weighted less than the averaged signal
measurement (M.sub.n). After at least one iteration using the
second measurement averaging period and the different weighting
factor, L1 measurements revert to using the first measurement
averaging period and a weighting factor that weights prior L3
filter outputs more heavily than does the second weighting
factor.
[0038] In some embodiments, the UE reports the second filter output
to a serving base station, which may use the report to make a
handover decision. Thus in some instances, the UE receives a
handover command from the serving base station in response to the
report. The handover may be an intra-base-station handover or an
inter-base-station handover. If the handover command is for an
inter-base-station handover, the UE hands over to a second base
station in a location different than the serving base station in
response to receiving the command. In embodiments where the
wireless communication terminal is configured for carrier
aggregation and wherein the first carrier frequency is a
deactivated carrier, the first serving cell may be configured as
the primary serving cell in response to receiving the handover
command.
[0039] As suggested above, this embodiment can be applied to
resolve measurements related issues in a multi-mode UE having
multiple radio transceivers, each of the transceivers supporting
different radio technologies or similar radio technologies in
different bands of the wireless spectrum. For example, if the UE is
equipped with a WiFi transceiver, when the UE transmits WiFi
signals, the UE can experience a sudden decrease in measurements.
In such a situation, the UE can use a higher value of "a" (weight
the more recent measurements more heavily) when WiFi activity is
ongoing. The UE can also reset the filter by setting a=1 when WiFi
activity is initiated. This can provide a more accurate view of the
radio conditions when transmission of WiFi signals is started.
After the WiFi activity ends, the UE can revert to using a lower
value of `a`.
[0040] According to another aspect of the disclosure, a wireless
communication base station, or eNB, configures a wireless
communication terminal to operate on a first serving cell on a
first carrier frequency and on a second serving cell on a second
carrier frequency. Such a configuration may be for carrier
aggregation. The base station also configures the wireless
communication terminal to use a first measurement period for the
first serving cell and a second measurement period for the second
serving cell. For example, the eNB in FIG. 1 configures a
measurement period on the deactivated secondary cell CC2 that is
considerably longer than the measurement period on the primary cell
CC1. When the base station determines that a signal level at the
wireless communication terminal of the first serving cell is below
a threshold, the base station configures the wireless communication
terminal to use a third measurement period for the second serving
cell.
[0041] Such a determination may be made by the base station based
on one or more measurement reports sent from the UE to the eNB. For
example, the UE may be configured with periodical radio resource
measurement (RRM) reporting. If a measurement report indicates that
the primary cell drops below a threshold, the eNB can consider the
primary cell signal to be deteriorating and reconfigures the
measurement period for the deactivated cell as indicated above. The
UE may be configured with event based RRM measurement reporting
(e.g., A3 event) for the primary cell, such that the reporting
occurs well before a handover is necessary. For this embodiment, a
very conservative A3 offset is used. If a measurement report is
triggered based on this event, the eNB can use the report as an
indication that the primary cell signal is deteriorating and
reconfigure the measurement period of the secondary as indicated
above. The eNB may also observe a channel quality indication (CQI)
of the primary cell dropping below a threshold and based on this
assume that the primary cell signal is deteriorating. It can then
reconfigure the measurement period as indicated above.
[0042] As mentioned above, the solutions above can be applied to
resolve measurements related issues in a multi-mode UE having
multiple radio transceivers, each of the transceivers supporting
different radio technologies or similar radio technologies in
different bands of the wireless spectrum. For example, the network
can configure more frequent measurements in response to an
indication from the UE that WiFi activity has been/will be
initiated.
[0043] In other embodiments, the base station can select values of
a filter coefficient to signal to the terminal. The base station
can select values of the filter coefficient based on interference
reported by the UE. For example, the UE reports measurements to the
base station, the measurements indicating interference. If the
interference is higher than a threshold, the base station can
select a filter coefficient that results in a higher weight for the
more recent measurements. Alternatively, the base station can
select values of the filter coefficient based on another RAT. For
example, the base station can receive an indication from the UE
that a transceiver for another RAT is active at the UE. The base
station can then select a filter coefficient suited to perform more
accurate measurements taking one or more of the following criteria
into account: activity on the other RAT, transmission frequency of
the other RAT and characteristics of the other RAT.
[0044] Although the solutions are described in terms of radio
resource management (RRM) measurements, the same principles can be
applied to channel state information (CSI) measurements. This can
be especially useful in obtaining reliable measurements in
multi-mode UEs having multiple radio transceivers. For example, the
UE can perform more frequent measurements and reporting of channel
quality indication (CQI) when WiFi activity is initiated. The UE
can also mark some CQI measurements as unreliable or omit them if
WiFi activity is ongoing. Furthermore, the UE can use different
filtering/averaging of CQI measurements when WiFi activity is
initiated.
[0045] While the present disclosure and the best modes thereof have
been described in a manner establishing possession and enabling
those of ordinary skill to make and use the same, it will be
understood and appreciated that there are equivalents to the
exemplary embodiments disclosed herein and that modifications and
variations may be made thereto without departing from the scope and
spirit of the inventions, which are to be limited not by the
exemplary embodiments but by the appended claims.
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