U.S. patent application number 14/753699 was filed with the patent office on 2015-11-19 for method for ue pattern indication and measurement for interference coordination.
The applicant listed for this patent is MEDIATEK INC.. Invention is credited to Yih-Shen Chen, Per Johan Mikael Johansson.
Application Number | 20150334731 14/753699 |
Document ID | / |
Family ID | 46020076 |
Filed Date | 2015-11-19 |
United States Patent
Application |
20150334731 |
Kind Code |
A1 |
Chen; Yih-Shen ; et
al. |
November 19, 2015 |
Method for UE Pattern Indication and Measurement for Interference
Coordination
Abstract
A method of inter-cell interference coordination is provided for
UE measurements and network access procedure. In a first
embodiment, a UE in idle mode performs measurements on received
radio signals applying a simplified radio resource restriction for
interference coordination. The UE determines the restricted radio
resource without receiving explicit measurement configuration. In a
second embodiment, during various phases of a network access
procedure, the UE indicates its interference status and/or
additional interference information to its serving base station to
enhance interference coordination. In a third embodiment, the UE in
connected mode performs measurements on both interference-protected
transmission resources and non-interference-protected transmission
resources. The UE measurement results are used for scheduling,
radio link monitoring, and/or mobility management to increase radio
spectrum efficiency and to improve user experience.
Inventors: |
Chen; Yih-Shen; (Hsinchu
City, TW) ; Johansson; Per Johan Mikael; (Kungsangen,
SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MEDIATEK INC. |
Hsinchu |
|
TW |
|
|
Family ID: |
46020076 |
Appl. No.: |
14/753699 |
Filed: |
June 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13373218 |
Nov 7, 2011 |
9072110 |
|
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14753699 |
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61411052 |
Nov 8, 2010 |
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61411539 |
Nov 9, 2010 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 72/082 20130101;
H04W 76/10 20180201; H04W 72/085 20130101; H04W 72/1231 20130101;
H04W 24/08 20130101; H04W 36/0094 20130101; H04W 48/02 20130101;
H04W 74/0833 20130101; H04W 74/0866 20130101; H04W 72/0406
20130101; H04W 36/0088 20130101; H04W 76/28 20180201; H04W 84/045
20130101; H04B 7/0626 20130101 |
International
Class: |
H04W 72/12 20060101
H04W072/12; H04W 76/02 20060101 H04W076/02; H04W 72/04 20060101
H04W072/04; H04W 72/08 20060101 H04W072/08; H04W 24/08 20060101
H04W024/08 |
Claims
1. A method, comprising: detecting a strong interfering cell by a
user equipment (UE) in a wireless communication system, wherein the
interfering cell is non-accessible to the UE; performing a network
access procedure with a base station; and indicating interference
coordination information to the base station during the network
access procedure.
2. The method of claim 1, wherein the network access procedure
comprises: transmitting a RACH preamble over a RACH resource,
wherein the RACH preamble belongs to a RACH preamble group
dedicated for strongly interfered UEs.
3. The method of claim 1, wherein the network access procedure
comprises: transmitting a RACH preamble over a RACH resource,
wherein the RACH resource belongs to a RACH resource group
dedicated for strongly interfered UEs.
4. The method of claim 1, wherein the network access procedure
comprises: transmitting a connection request message to the base
station after receiving an uplink grant, wherein the connection
request message contains an indicator indicating that the UE is
strongly interfered.
5. The method of claim 1, wherein the network access procedure
comprises: transmitting a connection request message to the base
station after receiving an uplink grant, wherein the connection
request message contains interference-protected resource pattern of
the interfering cell.
6. The method of claim 1, wherein the network access procedure
comprises: transmitting a connection setup complete message to the
base station after receiving a connection setup message, wherein
the connection setup complete message contains
interference-protected resource pattern of the interfering
cell.
7. The method of claim 1, further comprising: performing
measurement on configured measurement object after establishing a
connection with the base station; and transmitting a measurement
report to the base station, wherein the measurement report
comprises the interference coordination information.
8. The method of claim 7, wherein the UE decodes a broadcast
channel of the interfering cell, and wherein the interference
coordination information comprises a cell ID and/or an
interference-protected resource pattern of the interfering
cell.
9. A User Equipment (UE), comprising: a processor that enables the
UE to detect a strong interfering cell in a wireless communication
system, wherein the interfering cell is non-accessible to the UE,
and wherein the UE also performs a network access procedure with a
base station; and memory that stores interference coordination
information to be indicated to the base station during the network
access procedure.
10. The UE of claim 9, further comprising: a transmitter that
transmits a RACH preamble over a RACH resource, wherein the RACH
preamble belongs to a RACH preamble group dedicated for strongly
interfered UEs.
11. The UE of claim 9, further comprising: a transmitter that
transmits a RACH preamble over a RACH resource, wherein the RACH
resource belongs to a RACH resource group dedicated for strongly
interfered UEs.
12. The UE of claim 9, further comprising: a transmitter that
transmits a connection request message to the base station after
receiving an uplink grant, wherein the connection request message
contains an indicator indicating that the UE is strongly
interfered.
13. The UE of claim 9, further comprising: a transmitter that
transmits a connection request message to the base station after
receiving an uplink grant, wherein the connection request message
contains interference-protected resource pattern of the interfering
cell.
14. The UE of claim 9, further comprising: a transmitter that
transmits a connection setup complete message to the base station
after receiving a connection setup message, wherein the connection
setup complete message contains interference-protected resource
pattern of the interfering cell.
15. The UE of claim 9, further comprising: a measurement module
that performs measurement on configured measurement object after
establishing a connection with the base station; and a transmitter
that transmits a measurement report to the base station, wherein
the measurement report comprises the interference coordination
information.
16. The UE of claim 15, wherein the UE decodes a broadcast channel
of the interfering cell, and wherein the interference coordination
information comprises a cell ID and/or an interference-protected
resource pattern of the interfering cell.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation, and claims priority
under 35 U.S.C. .sctn.120 from nonprovisional U.S. patent
application Ser. No. 13/373,218, entitled "Method of UE Pattern
Indication and Measurement for Interference Coordination," filed on
Nov. 7, 2011, the subject matter of which is incorporated herein by
reference. Application Ser. No. 13/373,218, in turn, claims
priority under 35 U.S.C. .sctn.119 from U.S. Provisional
Application No. 61/411,052, entitled "Method of UE pattern
indication in Heterogeneous Network," filed on Nov. 8, 2010; U.S.
Provisional Application No. 61/411,539, entitled "Method for Static
interference Coordination," filed on Nov. 9, 2010, the subject
matter of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The disclosed embodiments relate generally to wireless
network communications, and, more particularly, to UE pattern
indication and measurement for inter-cell interface
coordination.
BACKGROUND
[0003] Inter-cell interference coordination (ICIC) was introduced
in Release-8/9 of the 3GPP LTE standards. The basic idea of ICIC is
keeping the inter-cell interferences under control by radio
resource management (RRM) methods. ICIC is inherently a multi-cell
RRM function that needs to take into account information (e.g. the
resource usage status and traffic load situation) from multiple
cells. Broadly speaking, the main target of any ICIC strategy is to
determine the resources (bandwidth and power) at each cell at any
time. Then (and typically), a scheduler assigns those resources to
users. Static ICIC schemes are attractive for operators since the
complexity of their deployment is very low and there is no need for
new extra signaling out of the standard. Static ICIC mostly relies
on the fractional frequency reuse concept, where the total system
bandwidth is divided into sub-bands and used by the scheduler
accordingly.
[0004] LTE Release-8/9 ICIC techniques, however, are not fully
effective in mitigating control channel interference. For example,
dominant interference condition has been shown when non-CSG (close
subscriber group) macrocell users are in close proximity of CSG
femtocells. Therefore, enhanced ICIC (eICIC) has been investigated
from Release-10 onwards to provide enhanced interference
management. In LTE/LTE-A Release-10, two main inter-cell
interference scenarios for eICIC were being discussed: Macro-Pico
scenario and Macro-Femto scenario. In general, almost-blank
subframe (ABS) or silenced subframe concept is introduced to reduce
inter-cell interference. When ABS is applied, the aggressor cell
suspends the scheduling or transmits with smaller power so that the
victim cell can conduct data transmission in the protected
subframes.
[0005] In Macro-Pico scenario, a macrocell is the aggressor and may
introduce strong interferences to picocells, which are called
victim cells. In this scenario, macrocell UEs operate typically in
connected mode. ABS is applied in the macrocell so that UEs can try
to search for picocells in the protected subframes. Several radio
resource management (RRM) technologies are available in LTE/LTE-A
systems to mitigate inter-cell interference. In one RRM scheme, a
UE may declare radio link failure (RLF) based on radio link
monitoring (RLM) measurements. Another possible RRM scheme is that
the UE may report measurement results to its serving base station
(eNB) for better scheduling and mobility management. Since only
some subframes are protected in picocell, such measurements should
be modified accordingly. Otherwise, the measurement results would
be largely affected by the interfering macrocell.
[0006] In Macro-Femto scenario, a non-accessible CSG femtocell is
the interferer and macrocell is the victim cell, and macrocell UEs
may be in connected mode or in idle mode. ABS is applied in the
femtocell. The current LTE RRM design has not investigated eICIC
for idle mode. However, for the case of Macro-Femto inter-cell
interference, UEs in idle mode also need interference coordination
to prevent from any cell selection and go out-of-service (OOS) in
cases when no alternative carrier is available. For example, when a
UE connected to a macrocell moves into the vicinity of a
non-accessible CSG femtocell, the UE can stay connected to the
macrocell thanks to inter-cell interference coordination. When the
UE goes to idle mode later on, UE measurements will indicate that
the macrocell is no longer suitable and the UE goes to out of
service. Without interference coordination, the UE in idle mode
cannot return to connected mode, unless the UE moves out of the
interfering of the femtocell. Therefore, UE measurements adapted to
interference coordination is desirable for UEs in idle mode.
[0007] In the presence of strong inter-cell interference, it is
also desirable that enhanced network access procedure such as
random access channel (RACH) procedure can be applied to improve
interference coordination. In addition, for UEs in connected mode,
UE measurement enhancements are also needed to increase radio
spectrum efficiency and to improve user experiences.
SUMMARY
[0008] A method of enhanced inter-cell interference coordination
(eICIC) is provided. To improve interference coordination, UE
measurements in both RCC_IDLE state and RCC_CONNECTED state are
enhanced, as well as network access procedure.
[0009] In a first embodiment, a UE in idle mode performs
measurements on received radio signals applying a simplified radio
resource restriction for interference coordination. The UE
determines the restricted radio resources without receiving
explicit measurement configuration. In one example, the restricted
radio resources correspond to subframes used for system broadcast
channels, paging channels and downlink common control channels.
[0010] In a second embodiment, during various phases of a network
access procedure, the UE indicates its interference status and/or
additional interference information to its serving base station to
enhance interference coordination. In one example, the network
access procedure is a random access channel (RACH) procedure. The
interference information may include CSG identification (CSG ID) or
silencing pattern of a non-accessible neighbor CSG femto base
station.
[0011] In a third embodiment, the UE in connected mode performs
measurements on both interference-protected transmission resources
and non-interference-protected transmission resources. The UE
measurement results are used for scheduling, RLM, and/or mobility
management to increase radio spectrum efficiency and to improve
user experience.
[0012] Other embodiments and advantages are described in the
detailed description below. This summary does not purport to define
the invention. The invention is defined by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The accompanying drawings, where like numerals indicate like
components, illustrate embodiments of the invention.
[0014] FIG. 1 illustrates an overall interference coordination
scheme in a wireless network in accordance with one novel
aspect.
[0015] FIG. 2 illustrates one embodiment of a method of UE
measurement for inter-cell interference coordination in RCC_IDLE
mode.
[0016] FIG. 3 illustrates one embodiment of interference
coordination enhancement during a RACH procedure.
[0017] FIG. 4 illustrates one embodiment of a method of UE
measurement for inter-cell interference coordination in RCC_IDLE
mode.
[0018] FIG. 5 is a flow chart of a method of UE measurements and
network access procedure for interference coordination in
accordance with one novel aspect.
DETAILED DESCRIPTION
[0019] Reference will now be made in detail to some embodiments of
the invention, examples of which are illustrated in the
accompanying drawings.
[0020] In LTE systems, two radio resource control (RRC) states
namely RRC_IDLE and RRC_CONNECTED are defined. In the RRC_IDLE
state, a UE can receive broadcast or multicast data, monitors a
paging channel to detect incoming calls, performs neighbor cell
measurements for cell selection/reselection, and acquires system
information broadcasting (MIB/SIB). Mobility function is totally
controlled by the UE in the RRC_IDLE state. In the RRC_CONNECTED
state, the transfer of unicast data to/from UE, and the transfer of
broadcast/multicast data to UE can take place. The UE monitors
control channels associated with the shared data channel to
determine scheduled data, provides channel quality feedback
information, performs neighbor cell measurements and measurement
reporting, and acquires MIB/SIB updating. Unlike the RRC_IDLE
state, mobility and handover fucntions in the RRC_CONNECTED state
are controlled by network and the UE provides assistance
information such as measurement reports.
[0021] A UE transits from RRC_IDLE state to RRC_CONNECTED state
when an RRC connection is successfully established. The RRC
connection is typically established via a network access procedure
such as a random access channel (RACH) procedure. In LTE
Release-10, enhanced inter-cell interference coordination (eICIC)
has been investigated. To improve interference coordination, UE
measurements in both RCC_IDLE state and RCC_CONNECTED state are
enhanced, as well as the RACH procedure.
[0022] FIG. 1 illustrates an overall inter-cell interference
coordination scheme in a wireless network 100 in accordance with
one novel aspect. Wireless network 100 comprises a user equipment
UE 101, a neighbor base station eNB 102, and a Macro base station
MeNB 103. UE101 is located within the coverage of a macrocell
provided by MeNB 103. Neighbor eNB102 represents a neighbor base
station of MeNB103. In a typical example, eNB102 is a Femto base
station or a Pico base station that provides smaller cell coverage
inside the macrocell of overlaying MeNB103. Such network deployment
creates Macro-Femto or Macro-Pico inter-cell interference
scenario.
[0023] In step 111, UE101 is in RRC_IDLE mode, and UE101 has not
established any RRC connection. In step 112, UE101 receives radio
signals in the macrocell from MeNB103, together with strong
interfering signals from eNB102 (e.g., eNB 102 is a non-accessible
CSG femto base station). In step 113, UE101 performs measurements
on the received radio signals, applying a simplified radio resource
restriction for interference coordination. In one embodiment, the
restricted radio resource is determined by UE101 without any
explicit configuration. In one example, the restricted radio
resources correspond to subframes used for system broadcast
channels, paging channels and downlink common control channel. In
step 114, UE101 performs a network access procedure with MeNB103.
In one embodiment, an enhanced RACH procedure is performed, during
which UE101 is able to indicate its interference status and/or
additional interference information to MeNB103 to improve
interference coordination. In step 115, UE101 enters RRC_CONNECTED
mode by establishing a RRC connection with its serving base station
MeNB103 after the RACH procedure. In step 116, UE101 decodes a
broadcast channel (BCH) of neighbor base station eNB102 and obtains
any interference-protected resource pattern (e.g., almost-blank
subframes (ABS) or silenced subframes) applied by eNB102. In
another embodiment, UE101 obtains the interference-protected
resource pattern information of eNB102 from the signaling message
of MeNB103. UE101 also receives measurement configuration from its
serving base station MeNB103 and obtains any interference-protected
or non-interference-protected radio resource pattern applied by
MeNB103. In step 117, UE101 performs measurements on
interference-protected radio resource. In step 118, UE101 performs
measurements on non-interference-protected radio resource. In step
119, UE101 sends measurements result to its serving MeNB103.
[0024] FIG. 2 illustrates one embodiment of a method of UE
measurement for interference coordination in RCC_IDLE mode in a
wireless network 200. Wireless network 200 comprises a macro base
station MeNB 201, a CSG femto base station FeNB202, and a UE 203.
In the example of FIG. 2, femtocell 212 controlled by FeNB202 is a
smaller cell located inside a larger overlaying macrocell 211
controlled by MeNB201. While UE203 is within the cell coverage of
macrocell 211, it is also located within the cell coverage of
femtocell 212. UE203 is initially in RCC_IDLE mode and performs
measurements for cell selection. For example, UE203 receives radio
signal 204 from MeNB201 and receives radio signal 205 from FeNB202.
From the received radio signals, UE203 finds that femtocell 212 is
the strongest cell. Unfortunately, femtocell 212 is not in UE203's
whitelist because FeNB202 is a non-accessible CSG femto base
station. Femtocell 212 thus becomes an interfering cell. UE203
needs to find a way to search for accessible cell (i.e., macrocell
211) and then inform MeNB201 the existence of FeNB202.
[0025] In one novel aspect, UE203 performs measurement with
simplified radio resource restriction for interference
coordination. The objective of the method is to minimize the need
for reconfigurations to control UE measurements, in the context of
interference coordination. One objective is to avoid UE measurement
reconfigurations, even if the radio resource restriction that
applies to transmission of data is changed. Another objective is to
avoid UE measurement reconfigurations, even if the UE moves across
cells that apply different radio resource restriction for
transmission of data. In a preferred embodiment, the need for
reconfigurations is zero, i.e., the UE applies a static radio
resource restriction for measurements. The benefits of the method
are most pronounced for UEs in idle mode. As low complexity and low
battery consumption is essential in idle mode, such method provides
the most simple approach with minimum need for reconfigurations. It
is noted, however, that such method is generally applicable for
measurements in connected mode.
[0026] FIG. 2 also illustrates a simplified block diagram of UE203
having various functional modules to carry out embodiments of the
present invention. UE203 comprises memory 221, a processor 222, a
measurement module 223, a radio frequency (RF) module 224 coupled
to an antenna 225. Antenna 225 transmits and receives RF signals.
RF module 224 receives EF signals from antenna 225, converts them
to baseband signals, and sends them to processor 222. RF module 224
also converts the received baseband signals from processor 222,
converts them to RF signals, and sends out to antenna 225.
Processor 222 processes baseband signals and invokes different
function modules to perform functionalities supported by UE203.
Memory 221 stores program instructions and data to control the
operation of UE203. In one novel aspect, measurement module 223
performs UE measurements with simplified radio resource restriction
for interference coordination. The measurement results are reported
to a serving base station for radio resource management (RRM)
purposes.
[0027] In general, for interference coordination, almost-blank
subframes (ABS) or silenced subframes are applied by devices that
cause interference (e.g., the aggressors) to protect devices that
are subjected to interference (e.g., the victims). ABS or silenced
subframes are also referred to as a type of protected radio
resource, or interference-protected radio resource.
Interference-protected resource is defined as a resource that is
not used, not fully used, or partially used by a cell (e.g., used
with power restriction, or only reference symbols are transmitted),
in order to create a better interference situation for UEs
connected to or camping on neighbor cells.
[0028] In the example of FIG. 2, femtocell 211 is the aggressor and
applies certain ABS or silenced subframes to reduce interference to
UE203. Ideally, UE203 should always perform measurements in the
silenced subframes to obtain the most accurate measurement results.
UE203, however, may not know about the silencing pattern of FeNB202
(e.g., a UE does not read the BCCH of non-accessible CSG in idle
mode). In addition, for LTE eICIC, the silencing pattern could
change due to changes in load condition, etc.; especially such
silencing pattern could be different for different cells for
optimal performance.
[0029] In one embodiment in accordance with a novel aspect, the
restricted radio resource selected for UE measurements is a subset
of radio resources that could be used for transmission/reception
for the UE if/when the UE is using the cell as its serving cell.
Typically, for UEs in high interference situations, where
interference coordination is needed, the resources that would be
selected to be available for transmission in one cell would be the
same resources that are subject to silencing in interferer cell. In
addition, the subset is a simpler and more static radio resource.
Therefore, there is no need to configure specifically for each cell
that the UE measures. Instead, it could be assumed that all cells
in a certain area could share the same subset of resources.
[0030] In one specific embodiment, the subset of radio resources is
selected to correspond to certain transmissions that are pre-known
to use certain radio resources. As illustrated in FIG. 2, macro
base station MeNB201 and UEs communicate with each other by sending
and receiving data carried in a series of superframes, each
contains four frames Frame #1-#4. Each frame in turn contains a
plurality of subframes. For LTE, the primary broadcast channel
(BCH), the primary and secondary synchronization symbols (PSS/SSS),
the transmission of System Information Block (SIB) type 1, and the
transmission of physical downlink control channel (PDCCH) and
paging control channel (PCH), are all performed in fixed
locations/subframes. For example, BCH appears in subframe #0 (SF0),
SIB1 in subframe #5 (SF5), and PCH in subframe #9 (SF9) for FDD.
Such essential channels would anyway always need to be protected
and the neighbor cells should try to refrain from scheduling in
those subframes; therefore, it could be assumed that such subframes
would be suitable for measurements. A benefit of such approach is
that the resource restriction for measurement can be completely
static and hard-coded, with minimum complexity, and with no
explicit signaling needed.
[0031] The novel UE measurements method may be applied by a UE for
cell selection/reselection in idle mode. By applying the restricted
resource for UE measurements, the UE is able to check the
suitability of a potential serving cell, and out of service (OOS)
events or any cell selection can be avoided, which leads to better
user experience. After the UE finds a suitable cell, the UE
performs a network access procedure with a serving base station to
establish RRC connection. In the presence of strong interference,
the UE applies enhanced network access procedure to improve
interference coordination.
[0032] FIG. 3 illustrates one embodiment of interference
coordination enhancement during a network access (e.g., RACH)
procedure in a wireless network 300. Wireless network 300 comprises
a UE 301 and a base station eNB 302. In general, without any
information from UE301, eNB302 tries to schedule "carefully". For
example, eNB302 schedules downlink RRC signaling at the same
subframes where PCH/BCH transmits, and hope that there is high
likelihood that such subframes are silenced by a neighbor
non-accessible CSG femtocell. On the other hand, if UE301 can
provide more information, then eNB302 can try to schedule
"intelligently" to improve resource usage and interference
management. In one novel aspect, UE301 provides additional
information to eNB302 via different steps of the enhanced RACH
procedure.
[0033] In step 311, UE301 transmits a RACH preamble to eNB302. The
RACH preamble is transmitted over a RACH opportunity (e.g., a RACH
resource block (RB)). If UE301 experiences strong interference from
neighbor cells (e.g., UE's strongest cell is a non-accessible CSG),
then UE301 indicates such status to eNB302. In a first option, a
dedicated preamble group is defined for all UEs whose strongest
cell is non-accessible CSG. If UE301 chooses a RACH preamble
belongs to the dedicated preamble group, then eNB302 can deduce
such status from the received RACH preamble. In a second option, a
dedicated RACH resource is defined for all UEs whose strongest cell
is non-accessible CSG. If UE301 transmits the RACH preamble over a
RACH RB belongs to the dedicated RACH resource, then eNB302 can
also deduce such status from the RACH RB. In step 312, eNB302
transmits a random access response (RAR) message via an uplink
PDCCH grant to UE301.
[0034] In step 313, UE301 sends a RRC connection request (RRC CR)
message (e.g., message 3) to eNB302 via an uplink common control
channel (CCCH). It is assumed that all messages on the CCCH are
size constrained. In a first option, UE301 uses a reserved bit in
the RRC CR message to indicate that the strongest cell for the UE
is a non-accessible CSG. In a second option, if eNB302 already
figures out the problematic scenario in the RACH preamble phase,
then eNB302 can allocate larger RB for UE301. UE301 is then able to
indicate CSG information as an additional IE in the RRC CR message.
The CSG information could be the CSG ID or the ABS pattern of the
CSG femto, which brings more scheduling flexibility for eNB302. In
step 314, eNB302 sends a contention resolution message to UE301,
followed by sending a RRC connection setup (RRC CS) message to
UE301 via the CCCH in step 315.
[0035] In step 316, UE301 sends a RRC connection setup complete
(RRC CS CMPL) message to eNB302 via a downlink control channel
(DCCH). The RRC connection setup complete message on the DCCH is
not size constrained. In one embodiment, UE301 sends the CSG
information as part of the RRC CS CMPL message. The CSG information
could be the CSG ID or the ABS pattern of the CSG femto, which
brings more scheduling flexibility for eNB302. Note that, if eNB302
detects that the UE is strongly interfered by the method in step
311, then eNB302 can intelligently schedule the messages of step
312 to step 316 onto protected subframes so that they can be
decoded correctly.
[0036] After completing the above-illustrated steps in the RACH
procedure, UE301 has camped on eNB302, established RRC connection
and moved to RRC_CONNECTED state in step 320. In step 321, UE301
receives a RRC reconfiguration (RECONFIG) message from eNB302 for
UE measurement configuration or reconfiguration. In step 322, UE301
responses with a RRC reconfiguration complete (RECONFIG CMPL)
message back to eNB302. UE301 starts to perform measurements in
step 330. In one novel aspect, when UE301 detects the existence of
non-accessible CSG femto, UE301 tries to decode the broadcast
control channel (BCCH) of the CSG femto and check if ABS is
enabled. If ABS is enabled, then UE301 tries to measure the CSG
femto in non-ABS subframes. Additionally, UE301 could also
separately measure the serving cell of eNB302 by all subframes and
ABS-only subframes. In step 331, UE301 sends measurement report to
eNB302. The measurement report is a natural place to report the ABS
pattern of the CSG femto to eNB302. Based on the measurement
report, eNB302 can make appropriate scheduling or handover
decisions accordingly. More details of UE measurements in connected
mode are now illustrated below in FIG. 4.
[0037] FIG. 4 illustrates one embodiment of a method of UE
measurement for inter-cell interference coordination in
RCC_CONNECTED mode in a wireless network 400. Wireless network 400
comprises a macro base station MeNB 401, a Pico base station PeNB
402, a Femto base station FeNB 403, and a plurality of UEs 404-406.
MeNB401 provides coverage for macrocell 411, PeNB402 provides
coverage for picocell 412 and a cell region extension (CRE) 413 of
the picocell, and FeNB403 provides coverage for femtocell 414. In
the example of FIG. 4, picocell 412 and PICO CRE 413 are located
inside overlaying macrocell 411, creating a Macro-Pico inter-cell
interference scenario. Similarly, femtocell 212 is located inside
overlaying macrocell 411, creating a Macro-Femto inter-cell
interference scenario. For interference coordination, MeNB401
applies certain ABS or silencing pattern (e.g., subframe p+1) to
protect Pico UEs, and FeNB403 applies certain ABS or silencing
pattern (e.g., subframe p+3) to protect Macro UEs located inside or
near the femtocell.
[0038] In current LTE Release 8/9, there is no measurement
restriction for the measuring of common reference signals (CRS). UE
measurement details are up to UE implementation. However, for
inter-cell interference situations, it is beneficial for UEs to
take into account measurement results for both
interference-protected transmission resources, and
non-interference-protected transmission resources. One example of
interference-protected resources is the ABS or silenced subframes
applied in macrocells for Macro-Pico scenario or applied in
femtocells for Macro-Femto scenario. There are two ways for UEs to
make measurements in accordance with this novel aspect. In a first
option, the UEs make specific measurements for
interference-protected resources, as well as specific measurements
for non-interference-protected resources. In a second option, the
UEs make specific measurements for interference-protected
resources, and unrestricted measurements that are assumed to apply
for both interference-protected and non-interference-protected
resources. The benefit for the second option is that in very
complex network environment, UEs may not know to what extent other
neighbor cells employ inter-cell interference coordination. In
RRC_CNNECTED state, accurate UE measurements are important so that
various RRM schemes can be applied to mitigate inter-cell
interference.
[0039] In a first embodiment, the novel UE measurements can be used
in CSI/CQI measurement for eNB scheduling. Take the Macro-Pico
scenario in FIG. 4 as an example. MeNB401 applies ABS in subframe
P+1, which becomes the interference-protected subframe for picocell
412 and PICO CRE 413. Other subframes p, p+2, and p+3 are
non-interference protected subframes. UE404 measures the CSI/CQI
over different resources. In one example, if the
serving-cell-non-interference-protected resources (i.e., subframes
p and p+2) have sufficient quality (i.e., seems to not be highly
used), then they could be used, resulting in increased resource
usage. In another example, if neighbor cells do not seem to make
use of the serving-cell-interference-protected resources (i.e.,
subframe p+1), as indicated by radio measurements for these
resources, then such protected resources could be used. In this
example, those protected resources are used in a secondary priority
fashion; that is, macrocell stops scheduling for UE404 in those
protected resources whenever neighbor cell activity is detected. In
yet another example of Macro-Femto scenario, if the difference
between measurement results for
neighbor-cell-interference-protected resources and
neighbor-cell-non-interference-protected resources start to become
very big, then this is an indication that it is beneficial to stop
using neighbor-non-interference-protected resources for UE404.
[0040] In a second embodiment, the novel UE measurements can be
used in RLM measurements for RLF procedure. In one RRM scheme, when
radio link failure (RLF) is declared, a UE may reselect to a cell
in another frequency band. If the measured radio signal strength or
quality of the serving cell becomes too low, then UE cannot
maintain connection with the serving cell. In RCC_CONNECTED mode,
radio link monitoring (RLM) measurements are done for this
particular purpose. In the example of FIG. 4, UE405 may receive
poor signal quality from MeNB402 because of the strong interference
from nearby FeNB402. In one novel aspect, UE405 performs RLM
measurements only on interference-protected radio resources (e.g.,
silenced subframe p+3 by FeNB403). It is assumed that UE405 can
always measure such resources, thus UE405 should not apply RLF
recovery procedure until the channel quality of the protected
resources are deteriorated below than a threshold. Benefit of such
approach is to reduce the number of RLFs that would be
unnecessarily triggered.
[0041] In a third embodiment, the novel UE measurements can be used
for RSRP/RSRQ measurements for mobility management. A possible
corresponding RRM scheme is that the UE may report measurement
results (e.g., poor reference signal received power or reference
signal received quality (RSRP/RSRQ) of a serving cell) to its
serving base station (eNB). In the example of FIG. 4, UE406 is
located at the edge of its serving cell 411. In one novel aspect,
serving cell RSRP/RSRQ measurement to be done for resources that
are protected or usable at the cell edge for UEs in the serving
cell, and neighbor cell RSRP/RSRQ measurement to be done for
resources that are protected or usable at the cell edge for UEs in
the neighbor cell. In one example, UE406 measures the RSRP/RSRQ of
serving cell 411 on all subframes (Measurement X1), and on ABS-only
subframes (Measurement X2) and report both measurements to MeNB401.
Based on Measurements X1 and X2, MeNB401 decides to initiate
handover or scheduling UE406 onto the ABS slots. For example, if X2
is much larger than X1, MeNB401 only schedules UE406 onto ABS slot.
On the other hand, if X2 is also bad, then MeNB401 handover UE406
to another frequency band. Benefit of such approach is that
handover decisions could become better, improving the RRM
efficiency and user experience. Mobility measurements could be
fairly compared to reflect the true situation that a UE would
experience in its scheduling at the cell edge, e.g., before and
after a potential handover.
[0042] FIG. 5 is a flow chart of a method of UE measurements and
network access procedure for interference coordination in
accordance with one novel aspect. A UE is initially in idle mode.
In step 501, the UE receives radio signals of a cell under
measurement. In step 502, the UE receives interfering radio signals
from a non-accessible neighbor cell. The UE determines interfered
radio resources. In step 503, the UE determines restricted radio
resources by excluding the interfered radio resources. In step 504,
the UE performs measurement of the cell on the restricted radio
resources. In one embodiment, the restricted radio resources
correspond to subframes used for system broadcast channels, paging
channels and downlink common control channel.
[0043] During a network access procedure, in step 511, the UE
detects a non-accessible strong interfering cell. In step 512, the
UE performs a RACH procedure with a base station. In step 513, the
UE indicates interference coordination information to the base
station during various phases of the RACH procedure. During the
RACH preamble transmission phase, the UE indicates that its
strongest cell is a non-accessible CSG via the selected dedicated
RACH preamble or dedicated RACH resource. During the RRC connection
request phase, the UE indicates that its strongest cell is a
non-accessible CSG via a reserved bit in the RRC CR message. The UE
may also indicate the CSG information via an additional IE in the
RRC CR message if larger RB is allocated. The CSG information could
be the CSG ID or the ABS pattern of the CSG femto. During the RRC
connection complete phase, the UE sends the CSG information as part
of the RRC CS CMPL message.
[0044] After the UE has established RRC connection with its serving
base station, the UE moves to connected mode in step 521. In step
522, the UE performs measurements on interference-protected radio
resources. In step 523, the UE performs measurements on
non-interference-protected radio resources. In one embodiment, UE
CSI/CQI measurements are applied for scheduling purpose. In another
example, UE RLM measurements are applied for RLF procedure. In yet
another example, UE RSRP/RSRQ measurements are applied for mobility
management. The benefits as compared to serving eNB always
"blindly" participate in interference coordination are increased
radio spectrum efficiency and improved user experience.
[0045] Although the present invention has been described in
connection with certain specific embodiments for instructional
purposes, the present invention is not limited thereto.
Accordingly, various modifications, adaptations, and combinations
of various features of the described embodiments can be practiced
without departing from the scope of the invention as set forth in
the claims.
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