U.S. patent application number 15/482940 was filed with the patent office on 2017-08-10 for failure event report extension for inter-rat radio link failure.
The applicant listed for this patent is MEDIATEK INC.. Invention is credited to Yih-Shen Chen, Per Johan Mikael Johansson, Shiang-Jiun Lin, William Plumb.
Application Number | 20170230878 15/482940 |
Document ID | / |
Family ID | 49235682 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170230878 |
Kind Code |
A1 |
Johansson; Per Johan Mikael ;
et al. |
August 10, 2017 |
Failure Event Report Extension for Inter-RAT Radio Link Failure
Abstract
A method of inter-RAT failure event report is proposed. A UE
detects a failure event in a first cell served by a first base
station, and the first cell belongs to a first RAT. The failure
event may include a radio link failure or a handover failure. The
UE then performs an RRC establishment procedure with a second cell
served by a second base station, and the second cell belongs to a
second RAT. After the RRC establishment, the UE transmits a failure
event report to the wireless network. The failure event can be a
radio link failure, or be associated with a mobility command such
as a handover command. By providing more reliable information in
the failure event report than a network solution could provide,
inter-RAT mobility performance can be improved.
Inventors: |
Johansson; Per Johan Mikael;
(Kungsangen, SE) ; Lin; Shiang-Jiun; (Hsinchu
City, TW) ; Chen; Yih-Shen; (Hsinchu City, TW)
; Plumb; William; (Charlestown, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MEDIATEK INC. |
Hsinchu |
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TW |
|
|
Family ID: |
49235682 |
Appl. No.: |
15/482940 |
Filed: |
April 10, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13688124 |
Nov 28, 2012 |
9661510 |
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15482940 |
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13435234 |
Mar 30, 2012 |
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13688124 |
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61470042 |
Mar 31, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 41/0686 20130101;
H04W 76/19 20180201; H04W 36/00 20130101; H04W 36/14 20130101; H04W
36/36 20130101; H04W 24/02 20130101; H04L 41/0631 20130101; H04W
24/04 20130101 |
International
Class: |
H04W 36/14 20060101
H04W036/14; H04W 36/36 20060101 H04W036/36 |
Claims
1. A method, comprising: detecting a failure event by a user
equipment (UE) in a first cell served by a first base station in a
wireless communication network, wherein the first cell belongs to a
first radio access technology (RAT); performing a radio resource
control (RRC) establishment procedure with a selected second cell
served by a second base station, wherein the second cell belongs to
a second RAT as attempting to connect to the second RAT; recording
information related to attempting to the second RAT if the
attempting to connect to the second RAT is unsuccessful; and
transmitting a failure event report to the first cell belongs to
the first RAT, wherein the failure event report is related to the
recorded information related to the unsuccessful attempting to
connect to the second RAT, wherein the failure event report
comprises an identity and a carrier frequency of the second RAT,
and wherein the first RAT and second RAT belong to different radio
access technologies.
2. The method of claim 1, further comprising: receiving a mobility
command by the UE to move a radio connection from the first RAT to
the second RAT, wherein the mobility command is a handover
command.
3. A user equipment (UE), comprising: a failure event management
circuit that detects a failure event in a first cell served by a
first base station, wherein the first cell belongs to a first radio
access technology (RAT); a connection management circuit that
performs a radio resource control (RRC) establishment procedure
with a second cell served by a second base station, wherein the
second cell belongs to a second RAT as attempting to connect to the
second RAT, wherein the failure event management circuit records
information related to attempting to the second RAT when the
attempting to connect to the second RAT is unsuccessful; and a
transmitter that transmits a failure event report to the first cell
belongs to the first RAT, wherein the failure event report
comprises the recorded information related to the unsuccessful
attempting to connect to the second RAT, wherein the failure event
report comprises an identity and a carrier frequency of the second
RAT, and wherein the first RAT and second RAT belong to different
radio access technologies.
4. The UE of claim 3, further comprising: a receiver that receives
a mobility command to move a radio connection from the first RAT to
the second RAT, wherein the mobility command is a handover command.
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. 13/688,124, entitled "Failure Event Report
Extension for Inter-RAT Radio Link Failure," filed on Nov. 28,
2012, the subject matter of which is incorporated herein by
reference. Application Ser. No. 13/688,124, in turn, is a
continuation-in-part of, and claims priority under 35 U.S.C.
.sctn.120 from nonprovisional U.S. patent application Ser. No.
13/435,234, entitled "Failure Event Report Correlation for
Distributed RAN Self-Organization," filed on Mar. 30, 2012, the
subject matter of which is incorporated herein by reference.
Application Ser. No. 13/435,234, in turn, claims priority under 35
U.S.C. .sctn.119 from U.S. Provisional Application No. 61/470,042,
entitled "Failure Event Report Correlation for Distributed RAN
Self-Organization," filed on Mar. 31, 2011, the subject matter of
which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The disclosed embodiments relate generally to failure event
reporting, and, more particularly, to failure event report
extensions for inter-RAT radio link failure.
BACKGROUND
[0003] Self-organization is the process where a structure or
pattern appears in a system without a central authority or external
element imposing it through planning. The vision of
self-organization networks (SON), which is in line with the views
of 3GPP (3.sup.rd Generation Partnership Project), is that future
radio access network needs to be easier to plan, configure, manage,
optimize, and heal compared to how it used to be. SON has been
codified by the 3GPP Release 8 specifications in a series of
standards. Newly added base stations should be self-configured in
line with a `plug-and-play` paradigm, while all operational base
stations will regularly self-optimize parameters and algorithms
behavior in response to observed network performance and radio
conditions. Furthermore, self-healing mechanism can be triggered to
temporarily compensate for a detected equipment outage, while
awaiting a more permanent solution.
[0004] In 3GPP networks, Mobility Optimization including MRO
(Mobility Robustness Optimization) is a reactive self-optimization
function executing in eNodeB that is assumed to optimize handover
(HO) parameters. For example, eNodeB needs to optimize UE
measurement configuration and HO algorithm behavior to find
acceptable or as low as possible HO problem rate, as well as to
find a balanced ping-pong rate or HO rate. In a too late HO
problem, a connection failure occurs in the source cell before the
handover was initiated or during a handover. The UE attempts to
re-establish the radio link connection in the target cell (if
handover was initiated) or in a cell that is not the source cell
(if handover was not initiated). In a too early HO problem, a
connection failure occurs shortly after a successful handover from
a source cell to a target cell or during a handover. The UE
attempts to re-establish the radio link connection in the source
cell. In a wrong cell HO problem, a connection failure occurs
shortly after a successful handover from a source cell to a target
cell or during a handover. The UE attempts to re-establish the
radio link connection in a cell other than the source cell and the
target cell.
[0005] After a failure, e.g., a radio link failure (RLF) or
handover failure (HOF), if UE can find another suitable cell of the
same RAT, then UE will attempt radio resource control (RRC)
re-establishment. According to existing Rel-9 procedures, after a
successful re-establishment attempt, the network can use X2 RLF
indication procedure to notify the eNB of the previous UE serving
cell, and this eNB may do accounting based on this indication for
mobility optimization. In Rel-10, the UE may do RLF report also
after RRC establishment, e.g., after RRC re-establishment fails,
possibly due to non-preparation, and when the subsequent NAS
recovery succeeds.
[0006] However, there is no way for the network to correlate the
subsequent RLF report with the UE context in the previous serving
cell. Thus, if 3GPP goes ahead as proposed, then undoubtedly there
will be double bookkeeping. First, statistics will be updated based
on RRC re-establishment attempts (where RRC re-establishment
fails), and statistics will again be updated based on UE RLF
report. The Rel-9 and the suggested Rel-10 methods are not fully
compatible with each other. Such double bookkeeping will make
failure statistics unreliable, and may cause incorrect MRO
actions.
[0007] Together with the contents in the RLF report, the network
known information about the UE at the time of failure is essential
in determining what should be the corrective actions for certain
failures. For some failures, the most suitable corrective actions
may be non-MRO actions, such as reconfiguration of interference
coordination scheme or changes to power control etc. Because the UE
context in the previous serving cell (e.g., its Cell Radio Network
Temporary ID (C-RNTI)) is already known to the network, a solution
is sought to always be able to correlate the network-known
information with the RLF report to avoid double bookkeeping and to
improve MRO decision for SON.
[0008] Another potential problem is that RLF reports may be
delivered to a base-station very late, e.g. a day after the failure
happened. Normally a base-station will not keep the UE context and
keep the CRNTI of a UE non-reserved for a very long time, and
normally a base-station has limited memory for such storage.
SUMMARY
[0009] A method of failure event report correlation is proposed.
The method supports correlation of network known information and a
failure event report in cases when UE establishes a fresh RRC
connection, e.g. after Idle mode or after being connected in
another Radio Access Technology, and also takes into account that
base stations have limited storage for old UE contexts.
[0010] A UE detects a failure event in a first cell served by a
first base station, and the UE is assigned with a previous C-RNTI.
The failure event may include a radio link failure, a handover
failure, or a RACH failure. If the UE goes to Idle, e.g. due to a
failed RRC re-establishment or the UE goes to another RAT and comes
back, the UE then performs an RRC establishment procedure with a
second base station, and the UE is assigned with a new C-RNTI. In
some cases, the second and the first base stations could be the
same. After the RRC establishment, the UE transmits a failure event
report along with the correlation information to the second base
station. The second base station then forwards the failure event
report and the previous C-RNTI or other correlation information to
the first base station. The first base station can correlate the
failure event report with the previous failure event indication and
with UE information stored in the base-station based on the
previous C-RNTI or other correlation information to avoid double
bookkeeping and improve MRO decision for SON.
[0011] In a first embodiment, the UE receives the correlation
information from the second base station during an RRC
re-establishment procedure, where the UE provides its previous
C-RNTI. The correlation information can uniquely identify the UE.
For example, the correlation information is contained in a new
information element (IE) provided by the second base station in an
RRC re-establishment reject message. The UE just echoes the
correlation information back to the second base station later on,
along with the failure event report. This is a very low overhead
and simple method.
[0012] In a second embodiment, which is one specific example of the
first embodiment, the UE receives and deduces the correlation
information from a random access channel (RACH) procedure with the
second base station during the RRC re-establishment procedure. The
correlation information is based on the RACH resource used for the
RRC re-establishment procedure. For example, the correlation
information may include the RACH preamble and timing information
such as the system frame number (SFN) used for the RACH
transmission that was successful.
[0013] In another specific example, the UE receives the correlation
information from the first base station during the ongoing RRC
connection. The correlation information can uniquely identify the
UE or identify a class of UEs. The class of UEs would typically be
a group of UEs with similar handover and handover measurement
parameter settings or parameters that affect how Handover signaling
messages are transmitted. For example, the correlation information
is contained in a new information element (IE) provided by the
first base station in an RRC message. The UE just echoes the
correlation information back to the second base station later on,
along with the failure event report. This is a very low overhead
and simple method.
[0014] In a third embodiment, the UE does not receive the
correlation information from the base station during the RRC
re-establishment procedure. When the UE transmits the failure event
report, the UE also transmits an indication of the existence of the
previous RRC re-establishment attempt to the second base station.
For example, the indication may be a Boolean variable of {RRC REEST
ATTEMPT=TRUE}. When the first base station receives such indication
forwarded by the second base station, it may still be able to
correlate the failure event report with the previous failure
event.
[0015] In a fourth embodiment, the UE only provides the correlation
information if it is fresh. In one example, the UE determines the
freshness of the correlation information based on a timer, i.e.,
the time elapsed from the failure event to the failure event
reporting should not exceed a certain threshold. In another
example, the UE determines the freshness of the correlation
information based on the knowledge that the UE has not dwelled on
another RAT. If the correlation information is not fresh and no
longer useful, then it is discarded by the UE. Instead, the UE may
indicate the earlier RRC re-establishment attempt via a Boolean
variable along with the failure event report.
[0016] A method of inter-RAT failure event report is also proposed.
A UE detects a failure event in a first cell served by a first base
station, and the first cell belongs to a first RAT. The failure
event may include a radio link failure or a handover failure. The
UE then performs an RRC establishment procedure with a second cell
served by a second base station, and the second cell belongs to a
second RAT. After the RRC establishment, the UE transmits a failure
event report to the wireless network. In one embodiment, the
failure event report comprises an identity, a carrier frequency and
a radio access technology of the cell where RRC establishment is
performed, and the information is reported to the first RAT. In
another embodiment, the failure event report comprises an identity,
a carrier frequency and a radio access technology of the cell
wherein the failure event was triggered, and the information is
reported to the second RAT.
[0017] The failure event can be associated with a mobility command
including a handover command, a redirection, an NACC, a CSFB, and
enhanced CSFB, or an SRVCC, for the UE to move to a target cell of
another RAT. In one embodiment, the mobility command is a handover
command, and the recorded information comprises whether the
handover command is blind. In another embodiment, the recorded
information comprises a type of failure to be one of the target
cell not found, the target not suitable/not allowed, or access
failed in the target cell.
[0018] 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
[0019] FIG. 1 illustrates a wireless communication network with
failure event report correlation in accordance with one novel
aspect.
[0020] FIG. 2 is a simplified block diagram of a user equipment in
accordance with one novel aspect.
[0021] FIG. 3 illustrates a first embodiment of reporting failure
event with correlation information.
[0022] FIG. 4 illustrates a second embodiment of reporting failure
event with correlation information.
[0023] FIG. 5 illustrates a third embodiment of reporting failure
event with correlation information.
[0024] FIG. 6 illustrates a fourth embodiment of reporting failure
event with correlation information.
[0025] FIG. 7 is a flow chart of a method of detecting and
reporting failure event by a user equipment in accordance with one
novel aspect.
[0026] FIG. 8 is a flow chart of a method of handling failure event
with correlation information by a base station in accordance with
one novel aspect.
[0027] FIG. 9 illustrates one embodiment of reporting inter-RAT HOF
due to too early handover command in a wireless communication
network.
[0028] FIG. 10 illustrates one embodiment of reporting inter-RAT
HOF due to too late handover command in a wireless communication
network.
[0029] FIG. 11 illustrates one embodiment of reporting inter-RAT
RLF to a source network in a wireless communication network.
[0030] FIG. 12 illustrates one embodiment of reporting inter-RAT
RLF to a target network in a wireless communication network.
[0031] FIG. 13 illustrates one embodiment of reporting inter-RAT
HOF/RLF to the network where the failure event is triggered in a
wireless communication network.
[0032] FIG. 14 is a flow chart of sending IRAT RLF in a wireless
communication network in accordance with one novel aspect.
[0033] FIG. 15 is a flow chart of sending IRAT HOF in a wireless
communication network in accordance with one novel aspect.
DETAILED DESCRIPTION
[0034] Reference will now be made in detail to some embodiments of
the invention, examples of which are illustrated in the
accompanying drawings.
[0035] FIG. 1 illustrates a wireless communication network 100 with
failure event report and correlation in accordance with one novel
aspect. Wireless communication network 100 comprises a plurality of
base stations (eNB 101, eNB 102, and eNB 103) and a user equipment
UE 104. UE 104 is originally served by eNB 101 in cell 111 and is
in RRC_CONNECTED state. Later, UE 104 detects a radio link failure
(RLF), and records radio signal measurement information before the
RLF for later reporting (step 121). After detecting the failure
event, UE 104 stays in RCC_CONNECTED mode and performs cell
selection. Once a suitable cell is found, UE 104 attempts RRC
re-establishment. For example, UE 104 selects cell 112 and performs
RRC re-establishment with eNB 102 (step 122). The RRC
re-establishment procedure is a quick and mostly-RAN-local
procedure, and may work only if cell 112 is prepared, e.g., only if
eNB 102 already has the UE context information. For example, the
RRC re-establishment procedure will succeed if UE 104 tries to
re-setup the connection to the same eNB 101 where UE 104 was
earlier connected, or if eNB 102 has been previously prepared by
eNB 101 where UE 104 was previously connected (e.g., at handover or
re-establishment preparation). In many other cases, however, there
is little chance that the target cell has the UE context
information. The RRC re-establishment message from the UE includes
UE identification information such as the Cell Radio Network
Temporary ID (C-RNTI) of the UE and the cell ID of the cell where
the UE was previously connected.
[0036] During the RRC re-establishment, eNB 102 forwards an RLF
indication along with UE identification information to the previous
serving eNB 101 via X2 interface. If the RRC re-establishment
fails, then UE 104 changes its state from RRC_CONNECTED to RRC_IDLE
and may perform cell selection procedure. Once a suitable cell is
found, UE 104 attempts RRC establishment. Usually, the same cell is
selected as the one where the UE attempted RRC re-establishment. In
one embodiment, eNB 102 sends certain correlation information {X}
to UE 104 if the RRC re-establishment fails. The correlation
information {X} is any information that can identify the UE as the
UE that failed the RRC re-establishment.
[0037] In one embodiment of FIG. 1, UE 104 selects cell 112 and
performs RRC establishment with eNB 102 (step 123). As compared to
the RRC re-establishment procedure, the RRC establishment procedure
involves the core network to greater extent, takes slightly longer
time, but assumes no prior knowledge of the UE in the RAN. RAN does
not know whether the UE was previously connected because no such
information is provided to the RAN. In fact, RAN has no ability to
identify the UE and the UE is given a new C-RNTI. This also applies
to the case when the RRC re-establishment has just failed and
NAS-recovery triggers the RRC connection setup.
[0038] During the RRC establishment procedure, UE 104 indicates to
eNB 102 that there is an RLF report available. Upon receiving an
information request from eNB 102, UE 104 sends the RLF report along
with the correlation information {X} to eNB 102. In one embodiment,
based on the correlation information {X}, eNB 102 is able to
determine the previous UE identity. In step 124, eNB 102 forwards
the received RLF report, together with the previous UE identity, to
the previous serving eNB 101 via X2 interface. This information
enables eNB 101 to identify the UE in connection with the earlier
RLF failure event, which was already indicated by eNB 102 to eNB
101 during the RRC re-establishment via X2 interface. Based on the
provided information, eNB 101 can correlate the X2 RLF report with
the earlier X2 RLF indication, and with previous UE context
information that eNB 101 has stored.
[0039] In another embodiment of FIG. 1, UE 104 goes to another
radio access technology (RAT) (step 125). UE 104 may stay there for
significant amount of time before attempting RRC establishment with
eNB 103 (step 126). While UE 104 keeps the RLF information for
later reporting, it discards any correlation information {X}
because such information is no longer fresh and useful, because it
is assumed that eNB 101 has discarded the stored UE context at this
time. As a result, in step 127, eNB 103 simply forwards the RLF
report to eNB 101 without UE identity information. Instead, UE 104
may indicate to eNB 103 that a previous RCC re-establishment
procedure has failed, and eNB 103 forwards such indication to eNB
101 along with the RLF report. Based on such indication, eNB 101
may still be able to correlate the X2 RLF report with the earlier
X2 RLF indication, or at least avoid double bookkeeping for the
failure event.
[0040] RRC re-establishment is an optimized procedure built on the
assumption that UE identifies itself in such a way that the UE
context of the UE can be identified. On the other hand, RRC
establishment, e.g., mobility with redirection, RAN does not know
if/where UE was previously connected. Therefore, the strong benefit
in providing a solution based on correlation is that: a) it is both
backwards compatible with other solutions based on X2 RLF
indication message and it is future proof; and b) it enables the
combination of network knowledge and information reported by the UE
in the failure event report, to make good quality conclusions, and
to reduce requirement of the contents of the UE failure event
report because information already known in the network does not
need to be reported by the UE. The failure event is either radio
link failure, handover failure, or RACH failure. Scenario would
apply to all the cases because they may all be caused by mobility
problems, and they may generate first a RRC re-establishment, then
if failed a following RRC establishment triggered by NAS.
[0041] FIG. 2 is a simplified block diagram of a user equipment UE
201 in accordance with one novel aspect. UE 201 comprises memory
211, a processor 212, a transceiver 213 coupled to an antenna 214.
UE 201 also comprise various modules including a measurement module
215 that performs radio signal measurements, a failure event
management module 216 that detects failure events and manages
failure event reporting, and an RRC connection management module
217 that performs cell (re)selection and RRC (re)establishment
procedures. The different modules are function modules that can be
implemented by software, firmware, hardware, or any combination
thereof. The function modules, when executed by the processor 212
(e.g., via executing program code 218), allow UE 201 to perform
various functions accordingly. A base station may comprise similar
structure including various function modules to support related
functionalities.
[0042] FIG. 3 illustrates a first embodiment of reporting failure
event with correlation information in a wireless communication
network 300. Wireless communication network 300 comprises a first
eNB 301, a second eNB 302, and a UE 303. Initially, UE 303 is in
RRC_CONNECTED mode, and communicates with its serving eNB 301 in a
serving cell over an established RRC connection (step 311). With
the RRC connection, eNB 301 stores UE context information, which is
associated with the identity of UE 303 with respect to the RRC
connection. For example, the UE identity information may include
the C-RNTI, the cell ID, and the message authentication code
(MAC-I) for the RRC connection. Later, UE 303 detects a failure
event such as an RLF in step 321. UE 303 records radio signal
measurement information related to the RLF failure event for future
reporting. The RLF report may include radio signal measurements
(e.g., RSRP/RSRQ measurements) before the time of the RLF. UE 303
stays in RRC_CONNECTED mode and performs cell selection.
[0043] In step 331, UE 303 starts to perform RRC re-establishment
with eNB 302 and sends an RRC re-establishment request to eNB 302.
The RRC re-establishment request contains the UE identity
information with respect to the earlier RRC connection, such as the
previous C-RNTI, the previous cell ID, and the previous MAC-I. Upon
receiving the RRC re-establishment request, eNB 302 forwards an RLF
indication to eNB 301 via X2 interface. The RLF indication contains
the earlier UE identity so that eNB 301 can identify the
corresponding UE. The RLF indication, however, does not contain the
actual RLF report because no secure RRC connection has been
established between UE 303 and eNB 302.
[0044] In the example of FIG. 3, the RRC re-establishment procedure
fails because eNB 302 has not been prepared before the
re-establishment attempt. In step 333, eNB 302 sends an RRC
re-establishment reject message to UE 303. In one novel aspect, the
RRC re-establishment reject message also contains correlation
information {X}, which may be contained in a new information
element (IE). The correlation information {X} is any information
that can be used by eNB 302 later to identify UE 303. Upon
receiving the RRC re-establishment reject message, UE 303 goes to
RRC_IDLE mode in step 341. NAS triggers RRC connection
establishment immediately thereafter. Typically, if UE 303 does not
quickly go away, then eNB 302 is still the target base station for
UE 303.
[0045] In step 351, UE 303 performs RRC establishment procedure
with eNB 302. The RRC establishment procedure is a heavy-weight
procedure, during which the UE and the eNB performs various levels
of downlink (DL) and uplink (DL) synchronization, negotiation and
configuration, and finally establish a new RRC connection. RAN/eNB
302 does not know whether UE 303 was previously connected and
failed because no such information is provided to the RAN/eNB 302.
UE 303 is also assigned with a new C-RNTI. Upon the completion of
the connection setup, in step 361, UE 303 sends an RRC connection
setup complete message to eNB 302. This message also indicates to
eNB 302 that UE 303 has an RLF report available. In step 362, eNB
302 sends a UE information request message to UE 303. The request
message requests UE 303 to send the available RLF report. In step
363, UE 303 sends an information response message back to eNB 302.
The response message contains the RLF report, along with the
correlation information {X}.
[0046] Once eNB 302 received the RLF report and the correlation
information {X}, eNB 302 can identify UE 303 based on the
correlation information. More specifically, eNB 302 sends the
correlation information {X} to UE 303 in the RRC re-establishment
reject message (step 333), and now UE 303 simply echoes back the
same correlation information {X} (step 363). The correlation
information {X} is uniquely associated with the previous UE
identity information, which is received in the RRC re-establishment
request message in step 331. As a result, eNB 302 can identify UE
303 and obtain the previous UE identity information. In step 364,
eNB 302 forwards the received RLF report to the previous serving
eNB 301. In addition, eNB 302 also sends the previous UE identity
information (e.g., previous C-RNTI, previous cell ID, and MAC-I) of
UE 303 to eNB 301 via X2 interface.
[0047] Based on the UE identity, eNB 301 is able to correlate the
received RLF report with the earlier RLF indication received in
step 332 for the same UE 303, and with previous UE context stored
in eNB 301, to avoid double bookkeeping. In addition, eNB 301 is
able to make better MRO decision based on measurements contained in
the RLF report. By using correlation, UE 303 is not burdened to
keep track of and log the identity information or to add the UE
identity information into the RLF report, because such information
is already known in the network. Normally it is desirable to keep
the UEs as simple as possible, and put as much complexity as
possible in the network. The correlation information {X} is any
information that can be used to identify a UE, or can be part of
the UE identity information itself.
[0048] FIG. 4 illustrates a second embodiment of reporting failure
event with correlation information in a wireless communication
network 400. Wireless communication network 400 comprises a first
eNB 401, a second eNB 402, and a UE 403. FIG. 4 is similar to FIG.
3, where UE 403 was initially connected to eNB 401 (step 411), but
is later connected to eNB 402 after detecting a failure event (step
421). In the example of FIG. 4, however, a specific example of
correlation information is illustrated. In step 431, UE 403
performs a random access channel (RACH) procedure with eNB 402 over
certain RACH resource such as a certain RACH preamble code over a
RACH opportunity with a certain system frame number (SFN) for RACH
transmission. After successful RACH attempt, UE 403 sends a RRC
re-establishment request to eNB 402 in step 432. The RRC
re-establishment request includes the UE identity of UE 403 with
respect to its previous connection with eNB 401. In step 433, eNB
402 forwards an RLF indication to eNB 401 via X2 interface. The RLF
indication also contains the UE identity information so that eNB
401 can identify the corresponding UE.
[0049] Because eNB 402 has not been prepared, the RRC
re-establishment procedure fails. In step 434, eNB 402 sends an RRC
re-establishment reject message to UE 403. Step 441 through step
462 of FIG. 4 is again similar to step 341 through step 362 of FIG.
3. In step 463, UE 403 sends an information response message back
to eNB 402. The response message contains the RLF report, along
with the correlation information {RACH resource} of the successful
RACH attempt. Because the RACH resource is typically uniquely
associated with UE 403, eNB 402 will be able to identify UE 403
with such correlation information. Once eNB 402 received the RLF
report and the correlation information {RACH resource}, it can
identify the previous UE identity of UE 403 based on the
correlation information. In step 464, eNB 401 receives the RLF
report, as well as the previous UE identity of UE 403 (e.g.,
previous C-RNTI, previous cell ID, and MAC-I). Based on the UE
identity, eNB 401 is able to determine that the received RLF report
is related to the earlier RLF indication received in step 432 for
the same UE 403 to avoid double bookkeeping. In addition, eNB 401
is able to make better MRO decision based on the detailed
measurements contained in the RLF report.
[0050] In one specific example, UE 403 receives correlation
information from the first base station eNB 401 during the ongoing
RRC connection. The correlation information can uniquely identify
the UE or identify a class of UEs that uses the same or similar
parameters. For example, UE 403 receives the correlation
information that is contained in a new information element (IE)
provided by eNB 401 in an RRC message. UE 403 sends the correlation
information to eNB 402 later on together with the failure event
report, which is forwarded to eNB 401 along with the failure event
report.
[0051] In another specific example, the second base station and the
first base station could be the same. For example, the UE is first
connected to a first cell served by the first base station, and
then performs RRC connection setup with a second cell or event the
same cell served by the same base station.
[0052] FIG. 5 illustrates a third embodiment of reporting failure
event with correlation information in a wireless communication
network 500. Wireless communication network 500 comprises a first
eNB 501, a second eNB 502, and a UE 503. FIG. 5 is similar to FIG.
3, where UE 503 was initially connected to eNB 501 (step 511), but
is later connected to eNB 502 after detecting a failure event (step
521). In the example of FIG. 5, however, eNB 502 does not provide
any correlation information to UE 503 when RRC re-establishment
fails (step 533). The other difference is in step 563. In step 563,
UE 503 sends an information response message back to eNB 502. The
response message contains the RLF report. The response message,
however, does not any UE identity information. Instead, the
response message includes an indication of the existence of the
previous RRC re-establishment attempt. For example, the response
message may contain a Boolean variable of {RRC REEST ATTEMPT=TRUE}.
In step 564, eNB 501 receives the RLF report as well as the Boolean
variable forwarded by eNB 502. Although eNB 501 does not know the
exact UE identity associated with the RLF report, based on the
Boolean variable, eNB 501 is still likely to be able to "guess"
that the RLF report is related to a previous failure event
indicated in step 532.
[0053] This is a simple way for UE to indicate that there may be
case of double bookkeeping. The UE simply remembers and indicates
that it performed a RRC re-establishment attempt following upon the
failure event for which there is failure event information to
report. Furthermore, UE only makes such indication if there was
assurance that the RRC re-establishment request message was
received by the RAN (e.g., step 531). The assurance can be an RLC
acknowledgement (ACK), a MAC/HARQ ACK, or an RRC response message
received such as an RRC re-establishment reject message (e.g., step
532). This is because the RRC re-establishment may fail for other
reasons such as a bad radio connection, and the request message
never has been properly delivered to the RAN. In such cases, no X2
RLF indication message is generated, and there is no risk that an
RLF report delivered later would cause double bookkeeping. Thus by
taking into account transmission failures, failure event statistics
is more precise to reduce the number of bad MRO decisions.
[0054] FIG. 6 illustrates a fourth embodiment of reporting failure
event with correlation information in a wireless communication
network 600. Wireless communication network 500 comprises a first
eNB 601, a second eNB 602, a third eNB 603, and a UE 604. FIG. 6 is
similar to FIG. 3, where UE 604 was initially connected to eNB 601
(step 611), but later detects a failure event (step 621) and
attempts an RRC re-establishment procedure with eNB 602 (step 631).
UE 604 also receives correlation information {X} when RRC
re-establishment fails (step 633). In the example of FIG. 6,
however, UE 604 does not attempt RRC establishment with eNB 602
immediately. Instead, UE 604 goes to RRC_IDLE mode, and then stays
there for a while or goes to another RAT. While the RLF report may
be kept by the UE for a long time (e.g., for up to 48 hours), the
correlation information for the purpose of identifying UE and
determining UE context is only useful if it is fresh, e.g., based
on a timer or based on the knowledge that UE has not dwelled on
another RAT.
[0055] In the example of FIG. 6, UE 604 goes to another RAT.
Therefore, UE 604 discards correlation information {X} because it
is no longer fresh. Step 651 through step 662 of FIG. 6 is again
similar to step 351 through step 362 of FIG. 3, with the only
difference that UE 604 performs RRC establishment with a different
eNB 603 in another RAT. In step 663, UE 604 sends an information
response message back to eNB 603. The response message contains the
RLF report, but no longer contains the already discarded
correlation information {X}. Instead, similar to the third
embodiment illustrated in FIG. 5, the response message contains an
indication of the existence of the previous RRC re-establishment
attempt. For example, the response message may contain a Boolean
variable of {RRC REEST ATTEMPT=TRUE}. In step 664, eNB 601 receives
the RLF report as well as the Boolean variable forwarded by eNB
603. Although eNB 601 does not know the exact UE identity
associated with the RLF report, based on the Boolean variable, eNB
601 is likely to be able to "guess" that the RLF report is related
to a previous failure event indicated in step 632.
[0056] The benefit of providing correlation information only if
fresh is two-fold. First, overhead can be reduced because the UE
avoid providing the correlation information when not needed, i.e.,
when RAN has lost the UE context and correlation is no longer
useful. Second, possible miss-correlation can be avoided, e.g., a
new UE could have been allocated the C-RNTI used by another UE
previously, and its context should not be correlated with a certain
failure event report. Alternatively, the correlation information is
provided only in the RRC connection immediately following a failed
RRC re-establishment, i.e., the RRC connection that is result of
NAS-recovery triggered RRC establishment. Such principle is
extremely simple to implement, e.g., no timer is needed, and UE
does not need to remember anything about another RAT.
[0057] FIG. 7 is a flow chart of a method of detecting and
reporting failure event by a user equipment in accordance with one
novel aspect. In step 701, the UE detects a failure event in a
first cell served by a first base station. The failure event may
include a radio link failure, a handover failure, or a RACH
failure. In step 702, the UE performs an RRC establishment
procedure in a second cell, which may be served by a second base
station. In step 703, the UE transmits a failure event report to
the second base station after RRC establishment. The UE also
transmits correlation information of the failure event along with
the failure event report, and the correlation information enables
the base station to identify the UE with regard to the failure
event.
[0058] FIG. 8 is a flow chart of a method of handling failure event
with correlation information by a base station in accordance with
one novel aspect. In step 801, the base station receives an RRC
re-establishment request from a UE. The request indicates a failure
event of the UE having a first C-RNTI served by an original base
station. In step 802, the base station transmits an RRC
re-establishment response to the UE. In step 803, the base station
performs RRC establishment procedure with the UE and assigns the UE
a second C-RNTI. In step 804, the base station receives a failure
event report as well as the correlation information from the UE.
The correlation information refers to an earlier RRC
re-establishment attempt associated with the failure event.
[0059] As illustrated above, correlation information for RLF report
is provided by UE to the network only if it is fresh. For inter-RAT
(IRAT) cases, it may not make sense at all to try to correlate UE
context and RLF report. Inter-vendor signaling needs to be tested
and it is likely that network will not support all cases of
inter-RAT interaction. Thus for inter-RAT cases and possibly for
inter-frequency cases, where there may also be a multi-vendor RAN
situation, a more general approach may be to introduce all
information that is needed for non-ambiguous conclusions into the
RLF report itself than relying on network correlation. Therefore,
the concept of providing correlation information can be easily
extended and applied in inter-RAT or inter-frequency cases--That
is, instead of providing correlation information, the UE provides
full information about the relevant RNTI and the cell
identification information together with the RLF report to the
network. Additional details of such inter-RAT RLF report are now
described below.
[0060] RLF report is used to optimize handover parameters and to
detect coverage problems. In general, RLF report is used in LTE
allowing UE to report information to the network about a connection
failure event, such as a radio link failure or a handover failure.
The reported information includes available geographical location
information and available mobility measurement results. However,
the current LTE RLF report only applies for intra-RAT cases. In
many networks of today, inter-RAT mobility performance is very poor
and is not easily detected because of limited OAM interaction
between systems of different radio access technologies.
[0061] It is an object of the current invention to address the
shortcomings of prior art by adding sufficient information to the
RLF report to make it applicable and usable for inter-RAT cases.
Based on RLF report, corrective actions and adjustments can be
adopted by the network to mitigate the failures. By providing more
reliable information in the RLF report than a network solution
could provide, inter-RAT mobility performance can be improved.
[0062] In one embodiment, information configured in the UE
regulating and limiting measurement opportunities for IRAT is
included in the RLF report. The UE configuration information being
in effect when the failure event occurs. This way it would be
possible to deduce the expected UE mobility performance and thus
know how to classify the failure event, in order to determine the
severity of the problems. More specifically, it is proposed that
information about measurement gap configuration, indication of
which RATs or number of RATs the UE measures on, and indication of
which carrier frequencies or number of carrier frequencies the UE
measures on, is included in the RLF report.
[0063] One important scenario of inter-RAT mobility failure is when
UE is commanded by the network to change RAT and the UE fails to
connect to the target RAT. This is referred to as inter-RAT or IRAT
handover failure (HOF), although the intention is that also other
kinds of network ordered mobility would be included, e.g.,
redirection, cell change, with or without network assistance (where
the network may add information that helps the UE to connect
quicker to the target cell). Due to system interoperability
complexity, IRAT mobility is often supported using only simple
mechanisms. For example, the current LTE RLF report does not
support reporting information related to IRAT handover failure.
[0064] In one novel aspect, UE that is connected to a radio access
node (e.g., a serving base station) being configured by the network
to move its connection from one radio access technology to another
radio access technology, or to an access using another Duplexing
mode than the serving cell, and the move of connection fails, the
UE stores logged information that is related to the failure, and
the logged information can later be retrieved by the network. Here,
it is assumed that a common trigger for detection of such failure
is a timer timeout, and the timer is started when the UE receives
the network command to move the connection from one RAT to another
RAT. It is also assumed that the UE may need to do network checking
towards multiple PLMN IDs in order to determine if it is allowed to
report the recorded failure event.
[0065] FIG. 9 illustrates one embodiment of reporting inter-RAT HOF
to the network due to too early handover command in a wireless
communication network 900. Wireless communication network 900
comprises a UE 901, a first RAT1 902 (e.g., the source network),
and a second RAT2 903 (e.g., the target network). In step 911, UE
901 is connected to the source network RAT1. In step 912, UE 901
records and reports mobility measurement results to RAT1. In step
913, UE 901 receives a handover command from the source network
RAT1 to connect to the target network RAT2. However, this HO
command is sent too early. In step 914, UE 901 attempts to connect
to the target network RAT2. However, the handover attempt fails due
to too early HO command. UE 901 then records information related to
the failure. In step 915, UE 901 connects back to the source
network RAT1. UE 901 then reports the recorded IRAT HOF information
to the source network RAT1.
[0066] As illustrated in FIG. 9, when a UE cannot connect to a
target cell or a target RAT, the expected behavior is that the UE
will try to go back to the source cell where the UE receives the
handover command (e.g., UE 901 connects back to the source network
RAT1). It is assumed that corrective action to improve IRAT
mobility performance is most likely to be taken in the source cell,
considering that configuration parameters for determining when to
or if to perform IRAT handover would reside there. Furthermore, it
is assumed that networks of different RATs have different OAM
systems that may not be well connected. It seems a good idea to
allow Radio access networks and Core networks of different RATs to
have as little interaction as possible to reduce interoperability
problems. Therefore, the IRAT HOF information is reported to the
source network, the source RAT, or the source cell.
[0067] For IRAT mobility, the mobility measurements in step 912
have a particular meaning in detecting "blind" handovers (i.e.,
mobility that is commanded by the network without UE providing a
measurement report with measurement results of the target cell as a
trigger for the handover). The corrective action for failed blind
handovers could be that UEs will be configured to do measurements
before handover. The usage of blind handovers is particularly
widespread in IRAT scenarios where handover decision is based on
service requirements. However, sometimes UE would be configured to
do measurements, e.g., event-based measurements to trigger
handover, but the UE would still be handover to other RAT blindly
based on service trigger for handover. In such cases, while the
handover is still regarded as blind, it may not be possible to
deduce the blind handover by looking at the measurements report in
the RLF report. Thus, it is proposed that the UE shall be able to
report whether a handover is blind, i.e., if there was a
measurement report for the target cell reported to the network
before the mobility command. In one example, the recorded IRAF HOF
information comprises explicit indication of whether a handover is
blind.
[0068] FIG. 10 illustrates one embodiment of reporting inter-RAT
HOF to the network due to too late handover command in a wireless
communication network 1000. Wireless communication network 1000
comprises a UE 1001, a first RAT1 1002 (e.g., the source network),
and a second RAT2 1003 (e.g., the target network). In step 1011, UE
1001 is connected to the source network RAT1. In step 1012, UE 1001
records and reports mobility measurement results to RAT1. In step
1013, UE 1001 receives a handover command from the source network
RAT1 to connect to the target network RAT2. However, this HO
command is sent too late. Before receiving the HO command, UE 1001
encounters a radio link failure in RAT1. UE 1001 then records
information related to the failure. In step 1014, UE 1001 attempts
to connect to the target network RAT2 and is successfully connected
to RAT2. In step 1015, UE 1001 connects back to the source network
RAT1 and reports IRAT HOF information to the source network
RAT1.
[0069] IRAT mobility is often done for service reasons and some
types of mobility may be more likely to fail than other types,
e.g., due to latency to connect to the target cell. Thus, the
corrective action to fix problems may be to determine a better
performing type of mobility. Thus, it is proposed that the IRAT HOF
information to be recorded and reported in step 1015 includes the
type of and reason for the purpose of mobility: handover,
redirection, NACC (Network Assisted Cell Change), CSFB
(Circuit-switched Fallback), Enhanced CSFB, and SRVCC (Single Radio
Voice Call Continuity), etc.
[0070] Furthermore, the corrective action may sometimes be done by
the target cell. In order to know if corrective action by the
target cell may be possible (e.g., provide more RACH resource to
address high access load blocking), more information about the
failure reason needs to be known. It is proposed that the IRAT HOF
information to be recorded and reported in step 1015 includes the
type of failure: target cell not found, target cell not suitable or
not allowed, and access attempted by the UE but failed in the
target cell.
[0071] In addition to IRAT handover failure, a very likely
connection failure scenario is UE encounters a connection failure
when the UE connects to one cell (e.g., radio link failure), and
the UE then connects to another RAT after the failure. This is
referred to as inter-RAT RLF or IRAT RLF. For such failure, the
current LTE RLF report may sometimes provide information, for
example, the UE includes available mobility measurement results. If
available mobility measurement results at RLF indicates that there
is no intra-frequency neighbor but an IRAT neighbor is suitable,
then it could be assumed that handover to the IRAT neighbor may
have prevented the failure.
[0072] However, a problem is that UE may not report in the RLF
report measurements for an IRAT neighbor. One reason could be that
the UE does not have a configuration for IRAT mobility measurements
(not provided, e.g., for battery saving reasons). Another reason
could be that the Stop-measure threshold in the serving cell is set
too aggressively, allowing the UE to not do IRAT measurements in
the source cell. In one novel aspect, for UE being connected to a
radio access node (e.g., a serving base station) detects a radio
link failure, UE subsequently doing a connection establishment to
another radio access technology or to an access using another
Duplexing mode than the previous serving cell, the UE stores logged
information that is related to the RLF and the another RAT or the
access. The logged information can later be retrieved by the
network.
[0073] FIG. 11 illustrates one embodiment of reporting inter-RAT
RLF to the source network in a wireless communication network 1100.
Wireless communication network 1100 comprises a UE 1101, a first
RAT1 1102 (e.g., the source network), and a second RAT2 1103 (e.g.,
the target network). In step 1111, UE 1101 is connected to the
source network RAT1. In step 1112, UE 1101 detects that the radio
link to the source network fails. UE 1101 thus records information
relevant to this failure. In step 1113, UE selects a target cell
and connects to the target network RAT2 by performing an RRC
establishment procedure. UE 1101 records information related to
RAT2 and the selected target cell where the UE connects. For
example, the recorded information includes the selected target cell
ID that comprises the PCI (PSC+frequency) of RAT2. In step 1114, UE
1101 leaves RAT2, e.g., due to radio coverage or due to service no
longer needed. In step 1115, UE 1101 returns to RAT1 and goes to
connected mode, e.g., due to radio coverage or due to service
needed. In step 1116, UE 1101 reports IRAT RLF to the source
network RAT1. The IRAT RLF report includes the recorded information
about the radio link failure event, and about the UE 1101
connecting to the target RAT2 and/or the selected target cell after
the failure. This information is needed to identify a potential
neighboring cell of a different RAT that may be unknown to the
original serving eNB.
[0074] As illustrated in FIG. 11, to support that networks of
different RATs are not well connected, in OAM domain and in PLMN,
and to support that corrective actions are taken in the cell where
the failure occurred, UE 1101 is able to report the recorded IRAT
RLF information to the source network/RAT/cell, i.e., where the
failure happened. More specifically, UE 1101 records the identity,
the carrier frequency, and the RAT of the selected cell where UE
1101 does the connection establishment, alternatively a global cell
identity from which the carrier frequency and RAT could be deduced.
Knowing the RAT, the carrier frequency, and the identity of the
target cell, the network could ensure that there is an inter-RAT
measurement configuration to enable IRAT mobility. Knowing the
identity of the (re)connection cell would make it possible for the
network to address RLF by triggering handover to the identified
cell earlier.
[0075] It is also assumed that the UE could record the time from
the radio link failure trigger until connection attempt for which
the connection setup is successful (e.g., when UE has selected the
target cell to connect). In cases when UE cannot do measurements
before the failure happens (e.g., when UE has not IRAT measurement
configuration), then it could be assumed that the (re)connection
cell is a good handover candidate if the time from failure to
connection is short.
[0076] FIG. 12 illustrates one embodiment of reporting inter-RAT
RLF to the target network in a wireless communication network 1200.
Wireless communication network 1200 comprises a UE 1201, a first
RAT1 1202 (e.g., the source network), and a second RAT2 1203 (e.g.,
the target network). In step 1211, UE 1201 is connected to the
source network RAT1. In step 1212, UE 1201 detects that the radio
link to the source network fails. UE 1201 thus records information
relevant to this failure. In step 1213, UE 1201 selects a target
cell and connects to the target network RAT2 by performing an RRC
establishment procedure. In step 1214, UE 1201 reports IRAT RLF to
the target network RAT2. The IRAT RLF report includes recorded
information about the radio link failure event. To support a more
sophisticated networks of different RATs that are well connected,
which may be likely in the future, UE 1201 reports the recorded
information to the target network/RAT/cell, i.e., where the UE
connects after a failure has happened.
[0077] Regardless of where the UE makes the IRAT RLF report to the
source RAT or to the target RAT, it is assumed that the cell where
the failure happened need to be the primary place for corrective
actions. It is proposed that the UE records the identity, the
carrier frequency and the RAT of the cell where the radio link
failure was triggered, or a global identity from which the RAT and
frequency could be deduced. The recorded information is included in
the RLF report and then transmitted to the source/target RAT. Such
information would make it much easier to identify the cell where
corrective action may be done.
[0078] Regardless of where the UE makes report to the source RAT or
to the target RAT, in order to support correlation of failure with
the exact UE configuration used in the source cell where the
failure happened, to support more sophisticated corrective actions,
it is proposed that UE also records the following information: RNTI
value that was used for the UE in the source cell (e.g., was unique
at least in the source cell or in the source RAN), and time
information that makes it possible to deduce when the provided RNTI
value was used by the UE (e.g., the elapsed time from the
occurrence of the failure to the reporting of the failure).
[0079] In the example of FIG. 11 and FIG. 12, the radio link
failure occurs in the source network and is likely to be caused by
too late handover. Likewise, radio link failure can occur in the
target network and is likely to be cause by too early handover.
[0080] FIG. 13 illustrates one embodiment of reporting inter-RAT
HOF/RLF to the network where the failure event is triggered in a
wireless communication network 1300. Wireless communication network
1300 comprises a UE 1301, a first RAT1 1302 (e.g., the source
network), and a second RAT2 1303 (e.g., the target network). In
step 1311, UE 1301 is connected to a source cell in the source
network RAT1. In step 1312, UE 1301 receives a handover command
from the source network RAT1 to connect to the target network RAT2.
However, this HO command is sent too early. In step 1313, UE 1301
attempts to connect to the target network RAT2. However, the
handover attempt fails due to too early HO command. Alternatively,
UE 1301 may successfully connect to RAT2 initially, but shortly
after, it encounters radio link failure. UE 1301 then records
information related to the HOF/RLF. In step 1314, UE 1301 selects a
target cell in RAT1 and connects to RAT1. Because HOF is triggered
in RAT1, UE 1301 may report the IRAT HOF to RAT1.
[0081] In the example of FIG. 13, in step 1315, when UE 1301 is
connected back to RAT2 where the RLF is triggered, UE 1301 reports
IRAT RLF to RAT2. The IRAT RLF report may include both the selected
cell ID and the previous cell ID. The selected ID includes the PCI
of the target cell in RAT1 where UE 1301 attempts to connect after
the RLF in RAT2 (e.g., in step 1314). This is needed in order to
distinguish this scenario from the scenario where UE 1301 connects
to another cell after the failure. The previous cell ID includes
the PCI of the source cell in RAT1 where UE 1301 was previously
served before the handover (e.g., in step 1311). This is needed to
enable sending a notification from RAT2 to RAT1.
[0082] FIG. 14 is a flow chart of sending IRAT RLF in a wireless
communication network in accordance with one novel aspect. In step
1401, a UE detects a failure event in a first cell served by a
first base station, and the first cell belongs to a first RAT. In
step 1402, the UE performs an RRC establishment procedure with a
selected second cell served by a second base station, and the
second cell belongs to a second RAT. In step 1403, the UE transmits
a failure event report to the wireless communication network. The
failure event report comprises logged information related to the
failure event. In one embodiment, the failure event report
comprises an identity, a carrier frequency and a radio access
technology of the cell where RRC establishment is performed, and
the information is reported to the first RAT. In another
embodiment, the failure event report comprises an identity, a
carrier frequency and a radio access technology of the cell wherein
the failure event was triggered, and the information is reported to
the second RAT.
[0083] FIG. 15 is a flow chart of sending IRAT HOF in a wireless
communication network in accordance with one novel aspect. In step
1501, a UE establishes a radio connection in a first cell belonging
to a first RAT. In step 1502, the UE receives a mobility command to
move the radio connection from the first RAT to a target cell
belonging to a second RAT. The mobility command is one of a
handover command, a redirection, an NACC, a CSFB, and enhanced
CSFB, or an SRVCC. In step 1503, the UE detects a failure event
associated with the mobility command and records information
related to the failure event. In step 1504, the UE reports the
recorded inter-RAT failure event information to the network (e.g.,
where the failure event occurred or triggered). In one embodiment,
the mobility command is a handover command, and the recorded
information comprises whether the handover command is blind. In
another embodiment, the recorded information comprises a type of
failure to be one of the target cell not found, the target not
suitable/not allowed, or access failed in the target cell.
[0084] 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.
* * * * *