U.S. patent application number 14/064947 was filed with the patent office on 2014-02-20 for method and apparatus for cell reselection for a wireless communication device.
This patent application is currently assigned to BlackBerry Limited. The applicant listed for this patent is BlackBerry Limited. Invention is credited to Andrew John Farnsworth, Raghavendra Magadi Rangaiah, Takashi Suzuki.
Application Number | 20140050129 14/064947 |
Document ID | / |
Family ID | 48172924 |
Filed Date | 2014-02-20 |
United States Patent
Application |
20140050129 |
Kind Code |
A1 |
Magadi Rangaiah; Raghavendra ;
et al. |
February 20, 2014 |
Method and Apparatus for Cell Reselection for a Wireless
Communication Device
Abstract
A method and apparatus for cell reselection for a wireless
communication device are disclosed.
Inventors: |
Magadi Rangaiah; Raghavendra;
(West Bromwich, GB) ; Farnsworth; Andrew John;
(Bromsgrove, GB) ; Suzuki; Takashi; (Ichikawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BlackBerry Limited |
Waterloo |
|
CA |
|
|
Assignee: |
BlackBerry Limited
Waterloo
CA
|
Family ID: |
48172924 |
Appl. No.: |
14/064947 |
Filed: |
October 28, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13286723 |
Nov 1, 2011 |
8600388 |
|
|
14064947 |
|
|
|
|
Current U.S.
Class: |
370/280 ;
455/437 |
Current CPC
Class: |
H04W 48/12 20130101;
H04W 36/0061 20130101; H04W 48/20 20130101 |
Class at
Publication: |
370/280 ;
455/437 |
International
Class: |
H04W 36/00 20060101
H04W036/00 |
Claims
1. A method for cell reselection in a user equipment UE for use in
a mobile telecommunications system, in which the UE is arranged to
receive a plurality of system information blocks, SIBs, including a
primary SIB and a secondary SIB of the same type, and in which the
UE is camped on a first cell, and in which the cells listed
comprise a second cell for reselection; the method comprising:
conditional on receipt of the secondary SIB before receipt of the
primary SIB: starting measurements, and cell reselection
evaluation, of cells listed in the secondary SIB; reselecting to
the second cell conditional upon satisfying a predetermined
criteria; and in which the predetermined criteria relates to a
quality of the first cell, and in which the predetermined criteria
comprises at least one of: a received signal strength of the first
cell or a signal-to-interference ratio of the first cell is below a
threshold; the UE has attempted to receive the primary SIB for more
than a predetermined period of time; and for a communications
channel carrying the SIBs, an indication of errors on the channel
is above a threshold.
2. The method as claimed in claim 1, in which the predetermined
criteria relates to a quality of the first cell and the quality of
the second cell.
3. The method as claimed in claim 1, in which the predetermined
criteria comprises: Srxlev.sub.ServingCell<=S.sub.SIB11-threshP
or Squal.sub.ServingCell<=S.sub.SIB11-threshQ.
4. The method as claimed in claim 1, further comprising: initiating
a secondary SIB treselection timer for a cell listed in the
secondary SIB; and when the secondary SIB treselection timer
expires: reselecting to a cell listed in the primary SIB or the
secondary SIB dependent at least in part upon whether there is a
running primary SIB treselection timer for a cell listed in the
primary SIB.
5. The method as claimed in claim 1, further comprising: initiating
a secondary SIB treselection timer for a cell listed in the
secondary SIB; and when the secondary SIB treselection timer
expires: reselecting to a cell listed in the primary SIB or the
secondary SIB dependent at least in part upon whether there is a
running primary SIB treselection timer for a cell listed in the
primary SIB; and further comprising: conditional on there being no
primary SIB treselection timer running: reselecting to a cell
listed in the secondary SIB.
6. The method as claimed in claim 1, further comprising: initiating
a secondary SIB treselection timer for a cell listed in the
secondary SIB; and when the secondary SIB treselection timer
expires: reselecting to a cell listed in the primary SIB or the
secondary SIB dependent at least in part upon whether there is a
running primary SIB treselection timer for a cell listed in the
primary SIB; and conditional on there being a primary SIB
treselection timer running: reselecting to a cell listed in the
primary SIB if the primary SIB treselection timer expires and the
cell in the primary SIB satisfies a reselection criteria, and
assessing whether there is a further primary SIB treselection timer
running if the primary SIB treselection timer stops.
7. The method as claimed in claim 1, further comprising:
conditional on receiving no indication that a previously received
primary SIB is no longer valid: starting measurements, and cell
reselection evaluation, of cells listed in the previously received
primary SIB.
8. The method as claimed in claim 1, in which the UE is camped on a
primary cell prior to camping on the first cell, the method further
comprising: conditional on receiving no information that a
previously received primary SIB is no longer valid: starting
measurements, and cell reselection evaluation, of cells listed in
the previously received primary SIB; the previously received
primary SIB received when the UE is camped on the previous
cell.
9. The method as claimed in claim 1, in which the secondary SIB
comprises the information elements IEs "Intra-frequency cell info
list", "Inter-frequency cell info list" and "Inter-RAT cell info
list", one or more of the IEs comprising the listed cells.
10. The method as claimed in claim 1, in which the secondary SIB
comprises the information IE "Inter-RAT info list", in which the
Inter-RAT cell info list comprises cells associated with a radio
access technology (RAT) different to a RAT associated with the
first cell.
11. The method as claimed in claim 1, in which receipt of the
primary SIB comprises the UE successfully receiving system
information from the primary SIB.
12. The method as claimed in claim 1, in which the type of SIB is
type 11, the primary SIB comprises SIB 11, and the secondary SIB
comprises SIB11bis.
13. The method as claimed in claim 1, in which at least one or more
of the first cell, second cell and cells listed, is associated with
either frequency division duplex, FFD, or time division duplex,
TDD.
14. A user equipment device, UE, comprising: a processor; and a
memory; the UE adapted for cell reselection and arranged to receive
a plurality of system information blocks SIBs including a primary
SIB and a secondary SIB of the same type; the UE operable so that:
conditional on receipt of the secondary SIB before the primary SIB:
start measurements and call reselection evaluation, of cells listed
in the secondary SIB; reselect to the second cell conditional upon
satisfying a predetermined criteria; and in which predetermined
criteria relates to a quality of the first cell, and in which the
predetermined criteria comprises at least one of: a received signal
strength of the first cell or a signal-to-interference ratio of the
first cell is below a threshold; the UE has attempted to receive
the primary SIB for more than a predetermined period of time; and
for a communications channel carrying the SIBs, an indication of
errors on the channel is above a threshold.
15. The device as claimed in claim 14, further operable to:
reselect to the second cell conditional upon satisfying a
predetermined criteria; and in which the predetermined criteria
relates to a quality of the first cell and the quality of the
second cell.
16. The device as claimed in claim 14, further operable to:
reselect to the second cell conditional upon satisfying a
predetermined criteria; in which the predetermined criteria
comprises: Srxlev.sub.ServingCell<=S.sub.SIB11-threshP or
Squal.sub.ServingCell<=S.sub.SIB11-threshQ.
17. The device as claimed in claim 14, further operable to:
initiate a secondary SIB treselection timer for a cell listed in
the secondary SIB; and when the secondary SIB treselection timer
expires: reselect to a cell listed in the primary SIB or the
secondary SIB dependent at least in part upon whether there is a
running primary SIB treselection timer for a cell listed in the
primary SIB.
18. The device as claimed in claim 14, further operable to:
initiate a secondary SIB treselection timer for a cell listed in
the secondary SIB; and when the secondary SIB treselection timer
expires: reselect to a cell listed in the primary SIB or the
secondary SIB dependent at least in part upon whether there is a
running primary SIB treselection timer for a cell listed in the
primary SIB; and further conditional on there being no primary SIB
treselection timer running: reselect to a cell listed in the
secondary SIB.
19. The device as claimed in claim 14, further operable to:
initiate a secondary SIB treselection timer for a cell listed in
the secondary SIB; and when the secondary SIB treselection timer
expires: reselect to a cell listed in the primary SIB or the
secondary SIB dependent at least in part upon whether there is a
running primary SIB treselection timer for a cell listed in the
primary SIB; and conditional on there being a primary SIB
treselection timer running: reselect to a cell listed in the
primary SIB if the primary SIB treselection timer expires and the
cell in the primary SIB satisfies a reselection criteria, and
assess whether there is a further primary SIB treselection timer
running if the primary SIB treselection timer stops.
20. The device as claimed in claim 14, further operable to:
conditional on receiving no indication that a previously received
primary SIB is no longer valid: start measurements, and cell
reselection evaluation, of cells listed in the previously received
primary SIB.
21. The device as claimed in claim 14, in which the UE is camped on
a primary cell prior to camping on the first cell, the UE further
operable to: conditional on receiving no information that a
previously received primary SIB is no longer valid: start
measurements, and all reselection evaluation, of cells listed in
the previously received primary SIB; the previously received
primary SIB received when the UE is camped on the previous
cell.
22. The device as claimed in claim 14, in which the secondary SIB
comprises the information elements IEs "Intra-frequency cell info
list", "Inter-frequency cell info list" and "Inter-RAT cell info
list", one or more of the IEs comprising the listed cells.
23. The device as claimed in claim 14, in which receipt of the
primary SIB comprises the UE successfully receiving system
information from the primary SIB; or in which the type of SIB is
type 11, the primary SIB comprises SIB 11, and the secondary SIB
comprises SIB11bis.
24. A non-transitory computer readable medium having computer
executable instructions stored thereon, the computer executable
instructions arranged, in use, to cause a device, that comprises a
processor; and a memory; where the device is adapted for cell
reselection and arranged to receive a plurality of system
information blocks SIBs including a primary SIB and a secondary SIB
of the same type; to be operable to: conditional on receipt of the
secondary SIB before the primary SIB: start measurements and call
reselection evaluation, of cells listed in the secondary SIB;
reselect to the second cell conditional upon satisfying a
predetermined criteria; and in which predetermined criteria relates
to a quality of the first cell, and in which the predetermined
criteria comprises at least one of: a received signal strength of
the first cell or a signal-to-interference ratio of the first cell
is below a threshold; the UE has attempted to receive the primary
SIB for more than a predetermined period of time; and for a
communications channel carrying the SIBs, an indication of errors
on the channel is above a threshold.
25. A non-transitory computer program comprising computer
executable instructions arranged, in use in a device, that
comprises a processor; and a memory; where the device is adapted
for cell reselection and arranged to receive a plurality of system
information blocks SIBs including a primary SIB and a secondary SIB
of the same type; to cause the device to be operable to:
conditional on receipt of the secondary SIB before the primary SIB:
start measurements and call reselection evaluation, of cells listed
in the secondary SIB; reselect to the second cell conditional upon
satisfying a predetermined criteria; and in which predetermined
criteria relates to a quality of the first cell, and in which the
predetermined criteria comprises at least one of: a received signal
strength of the first cell or a signal-to-interference ratio of the
first cell is below a threshold; the UE has attempted to receive
the primary SIB for more than a predetermined period of time; and
for a communications channel carrying the SIBs, an indication of
errors on the channel is above a threshold.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 13/286,723, filed Nov. 1, 2011, the contents
of which are incorporated herein by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] This application relates to mobile telecommunications
systems in general, and in particular relates to a method and
apparatus for handling UE mobility information for a wireless
communication device. In particular, though not limited to, the
application relates to a method and apparatus for cell
reselection.
[0004] 2. Description of the Related Art
[0005] In a typical cellular radio system, mobile user equipment
(UE) communicates via a radio access network (RAN) to a core
network. User equipment (UE) comprises various types of equipment
such as mobile telephones (also known as cellular or cell phones),
lap tops with wireless communication capability, personal digital
assistants (PDAs) etc. These may be portable, hand held, pocket
sized, installed in a vehicle etc and communicate voice and/or data
signals with the radio access network.
[0006] A radio access network covers a geographical area typically
divided into a plurality of cell areas. Each cell area is served by
at least one base station, which in UMTS may be referred to as a
Node B. Each cell is typically identified by a unique identifier
which is broadcast in the cell. The base stations communicate at
radio frequencies over an air interface with the UEs within range
of the base station. Several base stations may be connected to a
radio network controller (RNC) which controls various activities of
the base Stations. The radio Network controllers are typically
connected to a core network.
[0007] UMTS is a third generation public land mobile
telecommunication system. Various standardization bodies are known
to publish and set standards for third generation public land
mobile telecommunication systems, each in their respective areas of
competence. For instance, the 3GPP (Third Generation Partnership
Project) in addition to publishing and setting standards for UMTS,
also publishes and sets standards GSM (Global System for Mobile
Communications) 3GPP2 (Third Generation Partnership Project 2)
publishes and sets standards for CDMA (Code Division Multiple
Access).
[0008] The 3GPP Technical Specification 25.331, release 10
addresses some aspects of UMTS RRC (Radio Resource Control)
protocol requirements between the UMTS Terrestrial Radio Access
Network (UTRAN) and the mobile user equipment (UE). 3GPP Technical
Specification 25.304, release 10, addresses some UE procedures in
Idle mode and procedures for cell reselection in connected mode.
3GPP Technical Specification 25.133, release 10, addresses some
requirements for support of radio resource management (FDD). The
specifications are referred to herein as the "Standard", and are
incorporated herein by reference.
[0009] More particularly clause 8.1.1.6.11a of the 25.331
specification relates to some aspects of handling information in
System Information Block (SIB) type 11 bis. Clause 5.2.6 of the
25.304 specification relates to some aspects of cell reselection
evaluation process. Clause 4.2.2.1 of the 25.133 specification
relates to some aspects of measurement and evaluation of cell
selection criteria of a serving cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Embodiments will now be described, by way of example only,
with reference to the attached drawings, in which:
[0011] FIG. 1 is a diagram capturing the current 3GPP standardised
UE behaviour as described therein;
[0012] FIG. 2 is a flow diagram capturing the current 3GPP
standardised UE behaviour as described therein;
[0013] FIG. 3 is a diagram capturing the current 3GPP standardised
UE behaviour as described therein;
[0014] FIG. 4 is a diagram capturing the current 3GPP standardised
UE behaviour as described therein;
[0015] FIG. 5 is a flow diagram illustrating steps performed
according to a first aspect of the approach described herein;
[0016] FIG. 6 is a flow diagram illustrating steps performed
according to an alternative related to the first aspect of the
approach described herein;
[0017] FIG. 7 is a flow diagram illustrating steps performed
according to an alternative related to the first aspect of the
approach described herein;
[0018] FIG. 8 is a flow diagram illustrating steps performed
according to an alternative related to the first aspect of the
approach described herein;
[0019] FIG. 9 is a flow diagram illustrating steps performed
according to a second aspect of the approach described herein;
[0020] FIG. 10 is a flow diagram illustrating steps performed
according to a third aspect of the approach described herein;
[0021] FIG. 11 shows an overview of a network and a UE device;
[0022] FIG. 12 is a block diagram illustrating an embodiment of a
protocol stack provided in a UE device; and
[0023] FIG. 13 is a block diagram illustrating a UE device.
[0024] The same reference numerals are used in different figures to
denote similar elements.
DETAILED DESCRIPTION OF THE DRAWINGS
[0025] A method and apparatus for cell reselection for a wireless
communication device is described herein. In the following
description, for the purposes of explanation, numerous specific
details are set forth in order to provide a thorough understanding
of the new, inventive, and non-obvious concepts disclosed herein
(hereinafter "concepts" or "concept"). It will be apparent,
however, to one skilled in the art that the technique may be
practised without these specific details. In other instances,
well-known structures and devices are shown in block diagram form
in order to avoid unnecessarily obscuring the concepts disclosed
herein.
[0026] The needs identified in the foregoing Background, and other
needs and objects that will become apparent from the following
description, are achieved by, in one aspect, a method and apparatus
for cell reselection for a wireless communication device. In other
aspects, the concept encompasses a wireless telecommunication
device and a computer-readable medium configured to carry out the
foregoing actions, as well as a data carrier carrying thereon or
therein data indicative of instructions executable by processing
means to cause those means to carry out the foregoing actions.
Examples are CD-ROMs, memory sticks, dongles, transmitted signals,
downloaded files etc. In particular, the method may be implemented
in a mobile telecommunications device, with or without voice
capabilities, or other electronic devices such as handheld or
portable devices.
Overview
[0027] An overview of is now given of existing problems and how
they are addressed according to the approaches described below. In
the Figures, like reference numerals denote like
components/messages and are not described unless repetition is
required.
[0028] User equipment (UE) mobility within a network, such as a
Universal Terrestrial Radio Access Network (UTRAN), may be either
UE controlled or network controlled. In the case of a UTRAN
network, UE controlled mobility is used in Idle mode and the states
CELL_PCH, URA_PCH, CELL_FACH of Radio Resource Control (RRC)
Connected mode and network controlled mobility is used in the
CELL_DCH state of RRC Connected mode.
[0029] In the case of UE controlled mobility, the UE chooses a
serving cell on which to `camp` by the processes of cell selection
and cell reselection. Cell selection is the process of choosing a
serving cell when the UE does not currently have a serving cell
(for example, when the UE has been first switched on, or when the
UE is returning from loss of network coverage). Cell reselection is
the process of changing from one serving cell to another serving
cell. Typically the cell reselection process involves first
performing measurements of the signal strength and/or signal
quality of the serving cell and a number of candidate neighbour
cells and then reselecting to one of the neighbour cells that is
determined to offer better signal strength and/or quality than the
current serving cell.
[0030] The network guides or assists the UE controlled cell
reselection by providing control information in broadcast system
information messages. The information may include neighbour cell
lists to identify the carrier frequency and identity of candidate
neighbour cells for cell reselection, and may also include various
offsets, thresholds and other parameters to allow the network to
control the UE's cell reselection behaviour. In a UTRAN cell, the
broadcast Master Information Block (MIB) and System Information
Block (SIB) Type 3, 4, 11, 11bis, 12, 18, and 19 messages may
contain information related to cell reselection.
[0031] UTRAN system information is structured into a number of SIBs
with each SIB carrying a set of related system information. The
SIBs are repeatedly transmitted on the Broadcast Control Channel
(BCCH) of every UTRAN cell. For transmission, large SIBs are
segmented into up to 16 segments of size 222 bits, giving a maximum
possible SIB size of 3552 bits.
[0032] SIB 11, 11bis and 12 contain information related to cell
reselection. More specifically their content typically
includes:
[0033] A list of up to 32 intra-frequency cells (i.e. cells on the
same UTRAN carrier frequency as the cell broadcasting the
information) that are identified by their primary scrambling code
(PSC). In addition for each listed cell, there may be additional
parameters (e.g. thresholds and offsets) that enable the network to
control the UE's cell reselection behaviour.
[0034] A list of up to 32 inter-frequency cells (i.e. cells on a
different UTRAN carrier frequency from the cell broadcasting the
information) that are identified by a UTRAN Absolute Radio
Frequency Channel Number (UARFCN) and PSC. Again, additional
parameters may be included for each cell.
[0035] A list of up to 32 inter-RAT cells (i.e. cells using a
different Radio Access Technology (RAT) such as GERAN). Again,
additional parameters may be included for each cell.
[0036] SIB11 and SIB11bis are used by UEs that are in Idle mode and
SIB12 is used, in addition to SIB11 and SIB11bis, by UEs that are
in RRC Connected mode. It has been suggested that the maximum SIB
size of 3552 bits could be the limiting factor in determining how
many cells could be included in the neighbour cell lists in SIB 11
(i.e. it may not be possible to fit 32 intra-frequency, 32
inter-frequency and 32 inter-RAT cells, together with associated
parameters, in SIB11 due to the 3552 bit limit). To address this
problem, SIB11bis provides extra capacity to send the neighbour
cell lists (although the maximum cells of each type that may be
included across SIB11 and SIB11bis may remain the same at 32).
SIB11bis is a "secondary" SIB to SIB11, the "primary" SIB11, in
that SIB11 is to be received (received successfully and processed)
first before there can be measurements and reselection evaluation
of cells listed within SIB11bis. There could be more than one such
secondary SIB to a primary SIB. Also, SIB11 would typically be
populated in preference to SIB11bis. SIB11 and 11bis are of the
same type, in that they can generally contain the same type of
information. Two SIBs are of the same type if a set of items is
constructed by taking items from both SIBs. The set of items can be
constructed as a list, a table, a queue etc. In one example, the
set of items can be a list of neighbour cells, presented in SIB11
and SIB11bis in two parts, for instance. The information is such
that, in one example, good systems information is ensured when
using information from only the primary SIB, or when information
from both SIBs when combined. SIB11bis can be thought of,
essentially, as an overflow to SIB11.
[0037] The neighbour cell lists contained in SIB11, SIB11bis and
SIB12 are used to build a UE internal variable CELL_INFO_LIST and
the order of the cells in this variable is derived from applying
SIB11, then SIB11bis, then SIB12. The cells in this variable are
used for measurements and measurement reporting if the UE later
moves into CELL_DCH, for example. A problem identified is that if
the UE were to place the cells in the variable in the wrong order
(for example, deriving the order from SIB11bis, then SIB11 and then
SIB12) and the UE moves into CELL_DCH state then subsequent updates
to the list (addition, removal, or updating of cell information
performed by reference to the cell's position in the list) as the
UE moves and also inter-RAT measurements reports (which report
cells by reference to their position in the list) would not be
interpreted correctly. The order of the cells in the variable may
not have any impact on cell reselection operation.
[0038] The Standard 3GPP TS 25.331v10.4.0 "Radio Resource Control
(RRC); Protocol specification (Release 10), 2011-06, specifies the
following:
[0039] 8.1.1.6.11a System Information Block type 11bis
[0040] The UE should store all relevant IEs included in this system
information block. The UE shall: [0041] 1> after reception of
SIB 11 act upon the received IEs "Intra-frequency cell info list",
"Inter-frequency cell info list" and "Inter-RAT cell info list" as
described in subclause 8.6.7.3;
[0042] From the above requirement, the UE is required to have
received (received and processed) SIB11 before it processes
SIB11bis. This means that if SIB11bis is received before SIB11 the
UE waits for SIB11 to be received and then it processes SIB11 and
then SIB11bis. This ensures that the CELL_INFO_LIST is constructed
in the correct order but has the consequence that measurements of
cells listed in SIB11bis are not started until SIB11 has been
received as well. Conversely, there is no such requirement for
SIB11bis to be received before SIB11 is processed. This means that
if SIB11 is received before SIB11bis the UE does not need to wait
for SIB11bis before it processes SIB11 and starts measurements of
the cells listed in SIB11.
[0043] A problem with delaying the measurement and reselection to
cells listed in SIB11bis until after SIB11 has been received, is
that the UE may lose coverage (or go out of service) of the serving
cell and have to start a cell selection procedure, when one of the
cells listed in SIB11bis may have been a suitable candidate for
cell reselection. Thus the UE will experience an unnecessary
interruption in service. During such a service interruption, the UE
can not receive paging for mobile terminated calls or data
activity, and can not initiate mobile originated calls or data
activity.
[0044] Typically, both SIB11 and SIB11bis may be scheduled with the
same repetition period. SIB11 is likely to be close to the maximum
SIB size and therefore segmented into 16 or nearly 16 segments, all
of which are transmitted within the repetition period. SIB11bis is
likely to be smaller and hence have fewer segments to be
transmitted within the same repetition period. If the coverage is
poor then it may take many seconds (even up to, for example, 20 s)
to receive SIB11. This is due to the large number of segments of
the SIB and the necessity for all of the segments to be received
correctly before the complete SIB can be reconstructed.
[0045] Consequently, in such conditions it is a quite common
occurrence in the field that the UE does lose coverage of the
serving cell before it has successfully received SIB11. Given that
SIB11bis is an overflow SIB used by operators when SIB11 size nears
the maximum possible SIB size, SIB11bis may be relatively small and
therefore have relatively few segments compared to SIB11. Therefore
it is quite likely that SIB11bis may be successfully received
before SIB11.
[0046] To illustrate the behaviour according to the Standard, FIG.
1 shows a scenario where SIB11 and SIB11bis are successfully
acquired from a Cell 1 and the UE successfully reselects to Cell 2.
The sequence of events is as follows:
[0047] T1 UE is in Idle mode (or CELL_PCH, URA_PCH or CELL_FACH)
and reselects into Cell 1 which is broadcasting both SIB11 and
SIB11bis. The UE starts the acquisition of both SIBs.
[0048] T2 UE successfully acquires SIB11bis that contains the
information on Cell 3 which may be on a different carrier frequency
from Cell 1 and Cell 2.
[0049] T3 UE successfully acquires SIB11 that contains the
information on Cell 2. The UE starts performing measurements and
cell reselection evaluation according to the combined list of cells
from SIB11 and SIB11bis.
[0050] T4 UE successfully reselects to Cell 2.
[0051] This standard behaviour is also illustrated in the flow
diagram of FIG. 2. In step 200, the UE is in one of Idle mode, or
one of the connected states URA_PCH, Cell_PCH, or Cell_FACH. The UE
selects or reselects a cell that is broadcasting SIB11 and SIB11bis
and in 210, the UE starts to acquire SIB11 and SIB11bis. In 220, it
is determined whether SIB11bis has been acquired before SIB11. If
so, then in 230 the UE waits for SIB11 to be received, with the
method returning to step 220.
[0052] If SIB11bis has not been acquired first, then in 240, when
SIB11 has been acquired, the UE starts measurements and reselection
evaluation towards, or "of", cells in SIB11, and also SIB11bis once
acquired.
[0053] However, FIG. 3 shows an example according to the behaviour
in line with the Standard where SIB11bis is acquired from a cell
but SIB11 is not successfully acquired. As a consequence the UE
goes out of service before it can perform a cell reselection. The
sequence of events is as follows:
[0054] T1 UE is in CELL_DCH state.
[0055] T2 UE is moved from CELL_DCH state, say, to Idle mode,
CELL_PCH, URA_PCH or CELL_FACH. At the release of CELL_DCH state
the UE selects Cell 1 which is broadcasting both SIB11 and
SIB11bis. The UE starts the acquisition of both SIBs.
[0056] T3 UE successfully acquires SIB11bis that contains the
information on Cell 3 which may be on a different carrier frequency
from Cell 1 and Cell 2.
[0057] T4 Before the UE successfully acquires SIB11, the signal
level of Cell 1 drops so that the cell no longer meets the cell
selection criteria (i.e. S<=0). When this condition occurs, the
Standard 3GPP TS 25.133v10.2.0 "Requirements for support of radio
resource management (FDD) (Release 10)", 2011 requires the UE to
continue searching for cells listed in system information for a
period of 12 s (if the UE is in Idle mode, CELL_PCH state or
URA_PCH state, or for a period of 4 s if the UE is in CELL_FACH
state). As the UE has not yet acquired SIB11, and has acquired but
not yet acted on the content of SIB11bis, the UE does have any cell
list to use during this, for example, 12 s or 4 s period. As a
consequence, no alternative cell can be found during this 12 s or 4
s period; the only way in which the UE could return to service
during this period is if the quality of the serving cell
improves.
[0058] T5 At the end of the 4 s or 12 s period, having not found
any cell to which to reselect, the UE goes Out of Service (OoS).
The UE starts a cell selection process.
[0059] T6 During the cell selection process the UE finds and
selects either cell 2 or cell 3. It is likely that the UE will find
and select cell 2 before cell 3 as the UE might typically search
for other cells on the current carrier frequency before expanding
the search to other carrier frequencies.
[0060] In the scenario in FIG. 1, the UE had sufficient time to
acquire SIB11 and SIB11bis before it became necessary to perform a
cell reselection from Cell 1 to Cell 2. In contrast, in the
scenario in FIG. 3 there was insufficient time to acquire SIB11 and
SIB11bis before cell reselection was necessary. In this particular
example there was insufficient time because the UE was moved from
DCH state to Idle (or PCH/FACH states) close to the edge of Cell 1
but there may be many other scenarios where there is little time to
acquire the SIBs before reselection is necessary.
EXAMPLE 1
[0061] As discussed above, the Standard 25.331v9.4.0: section
8.1.1.6.11a describes behaviour of the UE in relation to SIB
11bis:
[0062] The UE should store all relevant IEs included in this system
information block. The UE shall: [0063] 1> after reception of
SIB 11 act upon the received IEs "Intra-frequency cell info list",
"Inter-frequency cell info list" and "Inter-RAT cell info list" as
described in subclause 8.6.7.3;
[0064] According to example 1:
[0065] The UE should store all relevant IEs included in this system
information block. The UE shall: [0066] 2> if the UE has not
received SIB 11, the UE shall start measurements and cell
reselection evaluation of cells listed in SIB 11bis;
[0067] after reception of SIB 11 act upon the received IEs
"Intra-frequency cell info list", "Inter-frequency cell info list"
and "Inter-RAT cell info list" as described in subclause
8.6.7.3;
[0068] In this example, it is in receipt of SIB11 the UE starts
measurements and cell reselection evaluation of cells listed in
SIB11bis. In other words, this example applies to a UE that does
not have a SIB11 from the serving cell that is indicated as being
valid when it receives SIB11bis. By allowing measurements and cell
reselection evaluation of the cells listed in SIB11bis, instead of
waiting for the reception of SIB11, this example offers the
advantage of reducing unnecessary service interruptions.
[0069] FIG. 4 shows the same scenario as FIG. 1 or 3, but with the
UE implementing example 1. Steps T1 and T2 are identical to those
in FIG. 3. The sequence of events is as follows:
[0070] T1 UE is in CELL_DCH state.
[0071] T2 UE is moved from CELL_DCH state to Idle mode, CELL_PCH,
URA_PCH or CELL_FACH. At the release of CELL_DCH state the UE
selects Cell 1 which is broadcasting both SIB11 and SIB11bis. The
UE starts acquisition of both SIBs.
[0072] T3 UE successfully acquires SIB11bis that contains the
information on Cell 3 which may be on a different carrier frequency
from Cell 1 and Cell 2. The UE starts performing measurements and
cell reselection evaluation according to the list of cells from
SIB11bis.
[0073] T4 UE successfully reselects to Cell 3.
[0074] The UE may reselect to a cell that may not necessarily be
the most appropriate neighbour cell for reselection. For example,
if the UE was using the complete neighbour cell list compiled from
both SIB11 and SIB11bis then the UE might reselect to a cell A,
whereas if the UE received SIB11bis first then it may end up
reselecting a less optimal cell B from SIB11bis even before SIB11
is received. The cells listed in SIB11bis may be less appropriate
cells for reselection as one deployment approach would be for the
network operator to populate SIB11 with the most likely reselection
candidates. Although the UE may reselect to a less appropriate cell
for reselection, this is probably preferable to a service
interruption.
[0075] The flow diagram of FIG. 5 also illustrates example 1. In
step 500, the UE moves into one of Idle mode, or one of the
connected states URA_PCH, Cell_PCH, or Cell_FACH. The UE selects a
cell in 510 that is broadcasting SIB11 and SIB11bis and starts
(initiates) to acquire SIB11 and SIB11bis. In 520, it is determined
whether SIB11bis has been acquired before SIB11.
[0076] If this is the case, then in 530 the UE starts measurements
and reselection evaluation of (towards) cells listed in SIB11bis
without waiting for receipt of SIB11. That is, measurement and
reselection evaluation of SIB11bis information are begun
independent of receipt, or later receipt, of SIB11.
[0077] If SIB11bis has not been received first, then, according to
the Standard, in 540, when SIB11 has been received, the UE starts
measurements and reselection evaluation towards cells in SIB11, and
also cells in SIB11bis once it is acquired.
EXAMPLE 1a
[0078] Example 1a is an alternative that can be used in conjunction
with example 1. This alternative aims to improve the trade-off
between avoiding unnecessary service interruptions and the risk of
reselection to a less than optimal cell. Example la may in other
alternatives, be applied together with examples 1b and/or 1c
discussed below.
[0079] According to example 1a, when the UE has received SIB11bis
before it has received SIB11, the UE starts measurements on the
cells listed in SIB11bis but does not allow cell reselection to any
of those cells if the quality (Ec/No for example) of the current
serving cell is good. When SIB11 is received and the complete
neighbour cell list is available then the UE allows reselection to
any cell in the complete list compiled from SIB11 and SIB11bis.
However, if the quality of the current serving cell is poor, then
the UE does allow cell reselection to those cells in SIB11bis
before SIB11 has been received in order to minimise the unnecessary
service interruptions.
[0080] In the 25.331 standard, example wording to reflect this
change is as follows:
[0081] The UE should store all relevant IEs included in this system
information block. The UE shall: [0082] 1> before reception of
SIB11 the UE shall act according to the requirements in [25.304];
after reception of SIB 11 act upon the received IEs
"Intra-frequency cell info list", "Inter-frequency cell info list"
and "Inter-RAT cell info list" as described in subclause 8.6.7.3;
The 25.304 Standard could include the wording:
[0083] 5.2.6.1.2b Measurements for cell lists in System Information
Block type 11bis
[0084] If the UE has received SIB11bis but not received SIB 11, the
UE shall: [0085] perform measurements on all cells listed in
SIB11bis according to the measurement rules above; [0086] if
Srxlev.sub.ServingCell<=S.sub.SIB11-threshP or
Squal.sub.ServingCell<=S.sub.SIB11-threshQ; [0087] allow
reselection to any of the cells listed in SIB 11bis, in accordance
with the requirements elsewhere in this specification; [0088] else:
[0089] not allow reselection to any of the cells listed in SIB
11bis;
[0090] where S.sub.SIB11-threshP and S.sub.SIB11-threshQ are values
that could be fixed, or signalled by another SIB, for instance.
[0091] Example 1a is illustrated in FIG. 6. The method steps
preceding and including 530 shown in FIG. 6, can be, and are in
this illustration, the same as those including and preceding 530 in
FIG. 5.
[0092] After 530, according to this variant to example 1, in 650
there is an assessment of whether the quality of the cell the UE is
currently camped on satisfies predetermined criteria. If it does,
then in 660 the UE stays camped on the current cell.
[0093] If the quality of the cell the UE is currently camped on
does not satisfy predetermined criteria, then in 670, the UE
reselects to a cell listed in SIB11bis assuming SIB11bis is a
better cell.
[0094] There are several possible options for judging of the
serving cell quality is poor. These include, but are not limited
to, for example:
[0095] The serving cell received signal strength (also referred to
as the Received Signal Code Power or RSCP) is below a threshold, or
the serving cell signal to interference ratio (also referred to as
Ec/Io) is below a threshold. It would be possible to reuse an
existing threshold such as Qrxlevmin or Qqualmin which are used
today in criteria for a cell to be suitable, or it would be
possible to define new thresholds specifically for this purpose, or
it would be possible to define a margin or offset above or below an
existing threshold.
[0096] SIB11 is not successfully received after attempting to
receive it for a certain time. This could be a fixed predetermined
time such as 10 s, or could be a time derived from the repetition
period of SIB11 (e.g. 3.times. repetition period), or could be a
time signalled from the network to the UE in another SIB, for
example.
[0097] Absolute number of CRC errors, or the rate of CRC errors on
the PCCPCH (the physical channel that carries the system
information), exceeds a threshold.
[0098] In relation to the final option, in one example, to
determine the quality of Pccpch reception the reception of data on
Pccpch can be monitored. Every 20 ms zero or one transport blocks
are received in this example. When a transport block is received,
it will contain a CRC checksum. This enables the validity of the
transport block to be checked by performing a checksum verification
process. If the transmitted bits are correctly received, then the
checksum verification process will identify the transport block as
passing the CRC check. If some of the bits have been corrupted so
that the received bits are different from the transmitted bits,
then it is very likely that the transport block will fail the CRC
check. Passing and failing transport blocks can be referred to as
having good and bad CRCs respectively.
[0099] When decoding Pccpch, because scheduling information is
available, transport blocks may not be decoded every 20 ms. So
every 20 ms there are three possible states for a transport block
reception--no transport block (TB), TB with good CRC, or TB with
bad CRC.
[0100] One approach to implementing this example includes tracking
the CRC error rate (CRC errors/sec) every second. After setting up
Pccpch, the CRC Timer can be started when the first bad CRC on
Pccpch is received. For any CRC error rate, the approach then
decrements the CRC count every sec by MIN (a minimum threshold
value--a "good" CRC count). When CRC count eventually reaches a
maximum threshold number then the cell is barred.
[0101] The quality of Pccpch can be judged based on a combination
of the rate of TBs of good CRCs and the rate of TBs with bad
CRCs.
[0102] It is noted that in this example, 650 follows after 530.
That is, neighbour cell measurements are begun on receipt of
SIB11bis, even before a determination in relation to the
predetermined criteria in 650. This has advantages such as allowing
faster reselection because of the time between starting
measurements and getting the first measurement. However, in
alternatives, 650 and 530 may be reversed so that there is
effectively a different time for starting measurements. Similar
alternatives exist in relation to other examples in relation to
FIGS. 7-10, for instance.
[0103] The advantages of this approach include reducing the
unnecessary service interruptions by not requiring a UE to reselect
if current serving cell quality is acceptable. This also has the
advantage of saving resources.
EXAMPLE 1b
[0104] Example 1b is another alternative that can be used in
conjunction with example 1 to minimise the risk of reselection to a
less than optimal cell from SIB11bis when a cell listed in SIB11
(that is not yet successfully acquired) may be available. This
alternative 1b may be applied together with 1a and/or 1c.
[0105] According to the Standard 25.331v9.4.0, 8.1.1.6.11a
[0106] The UE should store all relevant IEs included in this system
information block. The UE shall: [0107] 1> after reception of
SIB 11 act upon the received IEs "Intra-frequency cell info list",
"Inter-frequency cell info list" and "Inter-RAT cell info list" as
described in subclause 8.6.7.3;
[0108] According to this example 1b, the UE is only permitted to
reselect to a cell from SIB11bis, prior to successful acquisition
of SIB11, if that cell meets an additional criteria for the quality
of the candidate neighbour cell from SIB11bis. That is, reselection
is conditional upon an extra condition related to the candidate
cell (in addition to the candidate cell satisfying usual cell
reselection criteria.)
[0109] Example 1b is illustrated in FIG. 7. The method steps
preceding and including 530 shown in FIG. 7, can be, and are in
this illustration, the same as those including and preceding 530 in
FIG. 5. After 530, according to this variant to example 1, in 750
there is an assessment of whether a candidate cell from SIB11bis
satisfies predetermined criteria. If it does not, then in 760 the
UE stays camped on the current cell.
[0110] If the quality of the candidate cell the does satisfy a
predetermined criteria, then in 770, the UE reselects to the
candidate cell listed in SIB11bis.
[0111] Examples of the additional criteria are:
[0112] The measured signal level of the neighbour cell from
SIB11bis must be greater than a threshold. This could be specified
as an RSCP or Ec/Io threshold or both.
[0113] An additional offset could be added into the cell
reselection criteria. For example the criteria could be:
QUAL(neighbour)>QUAL
(serving)+Offset(Cell)+Hysteresis+Offset(SIB11bis).
[0114] Another example of additional criteria relates to use of
Treselection. Treselection is a timer that is started when the
measured signal level (RSCP or Ec/Io) of a neighbour cell meets the
cell reselection criteria. Typically the cell reselection criteria
are that the signal level of the neighbour cell is better than that
of the serving cell plus an offset value and/or a hysteresis value.
Normally, if the cell reselection criteria are met for a period at
least as long as Treselection then the UE performs reselection to
the neighbour cell. The purpose of the Treselection timer is to
provide some hysteresis in the time domain. The cell reselection
criteria and the behaviour of Treselection is defined in 3GPP TS
25.304v10.4.0 "User Equipment (UE) procedures in Idle mode and
procedures for cell reselection in connected mode (Release 10)",
2011-06.
[0115] The further example criteria comprises
[0116] use of a longer Treselection value which means that the
neighbour cell would have to meet the cell reselection criteria for
longer before the reselection can be triggered. This longer value
could be signalled, or perhaps a specified algorithm could be used,
such as using 2*Treselection when reselecting to a SIB11bis
neighbour cell when SIB11 has not been read.
[0117] The additional parameters could be provided to the UE via
system information broadcast, for example, in SIB3.
[0118] The alternative 1b, whether considered alone with example 1,
or together with 1a and/or 1c, provides the advantages of reducing
unnecessary service interruption and the risk of reselection to a
less than optimal cell from SIB11bis.
EXAMPLE 1c
[0119] Example 1c is another alternative that can be used together
with example 1 to reduce the risk of reselection to a less than
optimal cell from SIB11bis when a cell listed in SIB11 (that is not
yet successfully acquired) may be available. Example 1c may be
applied together with 1a and/or 1b.
[0120] If, as described in example 1, the UE starts performing
measurements and cell reselection evaluation of cells listed in
SIB11bis before SIB11 has been successfully acquired then it is
possible that the UE could have Treselection running for a cell in
SIB11bis at the instant when the UE does successfully acquire
SIB11.
[0121] In this example, the UE can reselect to one of the cells
from SIB11 rather than reselect to the cell from SIB11bis
immediately that the Treselection timer expires.
[0122] To achieve this it is proposed that if Treselection was
started for a cell from SIB11bis before SIB11 was acquired, then
when Treselection for this cell expires the UE checks to see if
Treselection is running for any cell from SIB11. If Treselection is
running for a cell from SIB11 then the UE does not immediately
reselect to the cell from SIB11bis but waits for Treselection for
the SIB11 cell to expire or stop. If Treselection expires for the
SIB11 cell then the UE will reselect to the SIB11 cell if it is a
better cell. If Treselection is stopped for the SIB11 cell, because
this cell no longer meets the cell reselection criteria, then the
UE may reselect to the cell from SIB11bis. Alternatively, if
Treselection is stopped for the SIB11 cell, and a Treselection
timer is running for another cell from SIB11, then the UE may
continue to wait until for that that Treselection timer to stop
expire before further reselection. This is illustrated in more
detail in FIG. 8.
[0123] Example 1c is illustrated in FIG. 8. The method steps
preceding and including 530 shown in FIG. 8, can be, and are in
this illustration, the same as those including and preceding 530 in
FIG. 5. After 530, according to this variant to example 1, in 850,
a cell listed in SIB11bis is determined to meet the cell
reselection criteria and and thus a Treselection timer for the cell
listed in SIB11bis is begun. Moving on to 882, when this timer has
expired, there is an assessment of whether a Treselection timer is
running for a better cell listed in SIB11, which may happen if
SIB11 has been subsequently acquired and a better cell listed in
SIB11 has been measured and found to meet the cell reselection
criteria.
[0124] If there is no Treselection timer running for a cell listed
in SIB11, then in 892, the UE reselects to a candidate cell from
SIB11bis.
[0125] If in 884 there is a Treselection timer running for a better
cell listed in SIB11, then the UE waits for the Treselection timer
for the cell listed in SIB11 to expire or be stopped. In 886, the
SIB11 timer expires, and then in 890 if a subsequent measurement
confirms that the cell from SIB11 has satisfied a reselection
criteria for at least Treselection (not shown), the UE reselects to
the cell listed in SIB11.
[0126] Or, in 888, the Treselection timer for the SIB11 cell stops,
for example because the measurements of that cell indicate that the
cell no longer meets the cell reselection criteria. In this case,
the method reverts to checking to see in 882 if there is a
Treselection timer running for a(nother) better cell listed in
SIB11. If there are no other cells listed in SIB11 that have a
timer running, then the UE can reselect to the candidate cell
listed in SIB11bis. However, if there are other SIB11 better cells
with a running Treselection timer, then the UE may again wait to
see if their timers expire in the period between a Treselection
time for the SIB11bis candidate cell after receipt of SIB11 and
follow the procedure described above if they do.
[0127] If a time is reached at which the SIB11bis candidate cell
has satisfied a reselection criteria for Treselection since SIB11
has been received, then the UE will reselect to the SIB11bis cell
at this time regardless of whether there are any Treselection
timers running for cells from SIB11.
[0128] It is noted that in this example, reselection is on
Treselection expiry; and this can be applicable to variations of
the other examples described herein. However, there are variations
of the examples that are not limited to reselection exactly on
expiry of Treselection, in which reselection may occur at a
different time, for example after a further measurement after
Treselection expiry.
[0129] To illustrate (not shown) by way of further example,
Treselection is set at 3 s, and UE is camped on cell 1 in idle. At
t=0 SIB11bis is received, and Treselection is started for cell 2
which is better than cell 1. At t=1 s SIB11 is received and
Treselection started for cell 3 which is better than cell 2 (and
cell 1).
[0130] At t=3 s, Treselection expires for cell 2. In this example,
even though we started Treselection for cell 2 earlier, because
there is a better cell to which the UE would have reselected, the
UE would not optimally select cell 2 at t=3 s.
[0131] Effectively, there is deferring reselection to cell 2 until
a decision is made about cell 3. If Treselection expires for cell 3
(and a subsequent measurement confirms that cell 3 has satisfied
the reselection criteria for at least Treselection) then there is
reselection to cell 3. If Treselection is stopped for cell 3
because reselection criteria are no longer satisfied, then cell 3
is no longer a block to reselection to cell 2.
[0132] There may be other cells from SIB11 with Treselection
running however which would still block reselection to cell 2.
However, time t=4 s is reached, then cell 2 has satisfied the
reselection criteria for Treselection since SIB11 was received,
then the UE reselects to it at this time regardless of whether
Treselection is running for any cells in SIB11.
[0133] Even if Treselection is running for cell 4 from SIB11, but
cell 2 is better (ranked higher) than cell 4, then cell 4 won't
block reselection to cell 2.
[0134] The temporary blocking is intended to allow better cells to
"catch up" in running Treselection, to prevent the head-start given
to SIB11bis cells because SIB11 hadn't arrived yet causing
reselection to a cell that isn't the best neighbour cell.
[0135] The alternative 1c, whether considered alone with example 1,
or together with 1a and/or 1b, also provides the advantages of
reducing unnecessary service interruption, and also reducing the
risk of reselection to a less than optimal cell from SIB11bis.
EXAMPLE 2
[0136] Example 2 may be used in addition to solution 1/1a/1b/1c, or
as an alternative on its own.
[0137] This solution addresses the UE behaviour when the serving
cell no longer meets the cell selection criteria (i.e. S<=0).
This corresponds to the instant T4 in FIG. 3. According to this
example, during the 12 s/4 s period during which the UE is required
to search and perform measurements on cells provided in system
information, the UE uses neighbour cell information from any SIB
(SIB11, SIB11bis, and in another example, SIB12) that it has
acquired even if not all SIBs have been acquired. That is, UE uses
the neighbour cell information from SIB11bis, even if SIB11 has not
yet been acquired.
[0138] Example 2, when considered in addition to example 1 for
instance, is illustrated in FIG. 9. The method steps preceeding and
including 530 shown in FIG. 9, can be, and are in this
illustration, the same as those including and preceding 530 in FIG.
5. After 530, according to this example, in 990, there is an
assessment of whether the serving cell (the cell the UE is
currently camped on) meets the cell selection criteria.
[0139] If in 992, it is determined that the serving cell fails to
meet cell selection criteria, the UE performs measurements and
reselection evaluation on the serving cell and neighbouring cells
for 12 seconds in DRX and 4 seconds in FACH, according to the
Standard. After this time, in this example, the UE begins to make
measurements and cell reselection evaluation of cells listed in any
SIB that has already been acquired. This is independent of whether
there are some SIBs from a set of SIBs for measurement control
information--such as SIB11, SIB11bis and SIB12, that are yet to be
acquired. So in this example, measurements and cell reselection can
be begun towards cells listed in SIB11bis even before receipt of
SIB11, say.
[0140] If the serving cell does meet the cell selection criteria,
then in 994, the method proceeds according to the steps illustrated
in FIG. 5 at 530, optionally extending to steps 650, 750, 850 etc.,
for examples 1a, 1b, or 1c.
[0141] 4.2.2.1 of the 25.133v10.20 standard describes measurement
and evaluation of cell selection criteria S of a serving cell, with
changes consistent with this example indicated here.
[0142] The UE shall measure the CPICH Ec/Io and CPICH RSCP level of
the serving cell and evaluate the cell selection criterion S
defined in [1] for the serving cell at least every DRX cycle. The
UE shall filter the CPICH Ec/Io and CPICH RSCP measurements of the
serving cell using at least 2 measurements. Within the set of
measurements used for the filtering, at least two measurements
shall be spaced by, at least T.sub.measureFDD/2 (see table
4.1).
[0143] If the UE has evaluated in N.sub.serv consecutive DRX cycles
that the serving cell does not fulfil the cell selection criterion
S, the UE shall initiate the measurements of all applicable
neighbour cells indicated in the measurement control system
information, regardless of the measurement rules currently limiting
UE measurement activities. If the UE has not successfully acquired
a complete set of measurement control system information (System
Information Block 11, 11bis and 12) the UE shall initiate the
measurements of all applicable neighbour cells indicated in the
measurement control system information that has been acquired.
[0144] If the UE has not found any new suitable cell based on
searches and measurements of the neighbour cells indicated in the
measurement control system information for 12 s, the UE shall
initiate cell selection procedures for the selected PLMN as defined
in [1].
[0145] After this 12 s period a UE in Cell:PCH or URA_PCH is
considered to be "out of service area" and shall perform actions
according to 25.331.
[0146] On transition from CELL_DCH to CELL_PCH/URA_PCH, if a UE
cannot find a suitable UTRA cell, then it is considered to be "out
of service area" and shall perform actions according to [16].
[0147] If the S criterion of the serving cell is no longer
fulfilled, the UE may suspend MBMS reception if necessary to
improve the UE's ability to find a suitable cell.
[0148] If the S criterion of the serving cell is fulfilled, the
measurement requirements when a MBMS reception is active are
specified in sections 4.2.2.2 and 4.2.2.9.
EXAMPLE 3
[0149] Example 3 requires that SIB11bis must have been acquired,
but SIB11 from the current serving cell has not been successfully
acquired. The UE uses a SIB11 that may be otherwise available, such
as one acquired from a previous serving cell, one from a
neighbouring cell that is identified as a neighbouring cell from
the SIB11bis from the current serving cell; or a cached SIB11 from
the serving cell; for example. This example can be used on its own,
or in combination with example 1, 1a, 1b, 1c, and/or 2.
[0150] SIB11bis is typically used for a UE in urban city areas
where the radii of the cells are small and there are many neighbour
cells. Neighbour cells contained in the SIB11 would be not only
direct neighbours to the serving cell but also not direct
neighbours. In such deployments, neighbour cell lists broadcast in
the serving cell and the in the direct neighbour cells would
contain many common cells. Therefore, in the situation where cell
reselection is required urgently (the serving cell radio condition
is not good) and SIB11 is not yet available then according to this
example, the UE uses the SIB11 received in the previous cell. In
one preferable example, this is on condition or assumption that
SIB11 is not known to be invalid due to a changed value tag. The UE
is likely to have detected and have recent measurement data for
some of the common cells, and so advantageously cell selection or
reselection can be relatively quick.
[0151] The UE may determine that a SIB is invalid if, after
reception of the SIB, the UE received an indication that system
information has changed, and a value tag for the SIB that is
different from the value tag that was stored at reception of the
SIB. Determining that a SIB is invalid is a trigger for the UE to
start re-acquiring that that SIB. In the scenario the UE may have
acquired SIB11 from the previous cell, have received an indication
that system information has changed and a changed value tag for
SIB11, and hence determined that SIB11 is invalid.
[0152] The UE then reselects to another cell before it has been
able to re-acquire SIB11.
[0153] Example 3, when considered in addition to example 1 for
instance, is illustrated in FIG. 10. The method steps preceeding
and including 530 shown in FIG. 10, can be, and are in this
illustration, the same as those including and preceding 530 in FIG.
5. After 530, according to this example, in 1045, there is a
determination of whether there is a previous SIB11 available. If
there is not 1047; the method returns to continuing measurement and
reselection evaluation of cells listed in SIB11bis 530, to be
augmented by SIB11 measurements when SIB11 is received.
[0154] If there is a previous SIB11 available 1048, then in 1050,
there is an assessment of whether the previous SIB11 is still
valid. In the example illustrated, there is a determination
(optional in some variations) of whether there has been a
indication that the previous SIB11 is not valid; 1050. If not 1055,
then in 1060, the UE starts measurements and cell selection or
reselection towards cells listed in the previous SIB11.
[0155] If it is determined that there has been an indication that
the previous SIB11 is not valid 1070, then the method continues at
530 (optionally extending to steps 650, 750, 850, 990 etc., of
examples 1a, 1b, 1c, and/or 2.
[0156] An alternative, as mentioned above, to considering use of
SIB11 from a previous serving cell, is to determine whether there
is available a SIB11 that is identified as from a neighbouring cell
in the SIB11bis (or SIB11bis and SIB12 in connected mode) received
from the serving cell.
[0157] A further alternative is to consider use of a cached SIB11
from the serving cell, in the case where this SIB11 is indicated to
have changed since it was read.
[0158] SIB11bis can contain less favourable candidates e.g.
inter-frequency or inter RAT cells. Hence, using the valid SIB11
from the previous cell according to this example would more likely
result in an intra-frequency reselection, avoiding unnecessary
inter-frequency or inter-RAT reselections.
[0159] The cells lists in SIB11, SIB11bis and SIB12 can contain
offset values to bias the cell reselection criteria. These offset
values are specific to the specific serving cell/neighbour cell
pair. There may be risk associated in applying an offset value in
the current serving cell that had been acquired from the previous
serving cell. In areas where different offset values are used
frequently (e.g. urban canyons) the SIB11bis or another SIB
indicates, in an alternative to this example, the use of SIB11 from
the previous cell is not allowed. This has the advantage of
reducing the risk of the UE performing an incorrect reselection, or
not selecting when it should.
[0160] FIG. 11 shows an overview of a network and a UE device.
Clearly in practice there may be many UE devices operating with the
network but, for the sake of simplicity, FIG. 11 only shows a
single UE device 700. For the purposes of illustration, FIG. 11
also shows a network 719 having a few components. It will be clear
to a person skilled in the art that in practice a network will
include far more components than those shown.
[0161] FIG. 11 shows an overview of the radio access network 719
(UTRAN) used in a UMTS system. The network 1119 as shown in FIG. 11
comprises three Radio Network Subsystems (RNS) 2. Each RNS has a
Radio Network Controller (RNC) 4. Each RNS 2 has one or more Node B
6 which are similar in function to a Base Transmitter Station of a
GSM radio access network. User Equipment UE 1100 may be mobile
within the radio access network. Radio connections (indicated by
the straight dotted lines in FIG. 11) are established between the
UE and one or more of the Node Bs in the UTRAN.
[0162] The radio network controller controls the use and
reliability of the radio resources within the RNS 1102. Each RNC
may also connected to a 3G mobile switching centre 10 (3G MSC) and
a 3G serving GPRS support node 12 (3G SGSN).
[0163] An RNC 1104 controls one or more Node B's. An RNC plus its
Node B's together make up an RNS 1102. A Node B controls one or
more cells. Each cell is uniquely identified by a frequency and a
primary scrambling code (primary CPICH in FDD, primary CCPCH in
TDD).
[0164] Generally in UMTS a cell refers to a radio network object
that can be uniquely identified by a UE from a cell identifier that
is broadcast over geographical areas from a UTRAN access point. A
UTRAN access point is a conceptual point within the UTRAN
performing radio transmission and reception. A UTRAN access point
is associated with one specific cell i.e., there exists one UTRAN
access point for each cell. It is the UTRAN-side end point of a
radio link. A single physical Node B 1106 may operate as more than
one cell since it may operate at multiple frequencies and/or with
multiple scrambling codes.
[0165] FIG. 12 is a block diagram illustrating an embodiment of a
protocol stack provided in a UE. A Radio Resource Controller (RRC)
block 1232 is a sub layer of Layer 3 1230 of a UMTS protocol stack
1200. The RRC 1232 exists in the control plane only and provides an
information transfer service to the non-access stratum NAS 1234.
The RRC 1232 is responsible for controlling the configuration of
radio interface Layer 1 1210 and Layer 2 1220. When the UTRAN
wishes to change the UE configuration it will issue a message to
the UE containing a command to invoke a specific RRC procedure. The
RRC layer 1232 of the UE decodes this message and initiates the
appropriate RRC procedure. Generally when the procedure has been
completed (either successfully or not) then the RRC sends a
response message to the UTRAN (via the lower layers) informing the
UTRAN of the outcome. It should be noted that there are a few
scenarios where the RRC will not issue a response message to the
UTRAN and, in those cases the RRC need not and does not reply.
[0166] The strategies for a method and apparatus for cell
reselection for a wireless communication device as discussed above
with reference to the drawings may be implemented by the RRC block
1232.
[0167] Turning now to FIG. 13, FIG. 13 is a block diagram
illustrating a mobile device, which can act as a UE and co-operate
with the apparatus and methods of FIGS. 1 to 10, and which is an
exemplary wireless communication device. Mobile station 1300 is
preferably a two-way wireless communication device having at least
voice and data communication capabilities. Mobile station 1300
preferably has the capability to communicate with other computer
systems on the Internet. Depending on the exact functionality
provided, the wireless device may be referred to as a data
messaging device, a two-way pager, a wireless e-mail device, a
cellular telephone with data messaging capabilities, a wireless
Internet appliance, or a data communication device, as
examples.
[0168] Where mobile station 1300 is enabled for two-way
communication, it will incorporate a communication subsystem 1311,
including both a receiver 1312 and a transmitter 1314, as well as
associated components such as one or more, preferably embedded or
internal, antenna elements 1316 and 1318, local oscillators (LOs)
1313, and processing means such as a processing module such as a
digital signal processor (DSP) 1320. As will be apparent to those
skilled in the field of communications, the particular design of
the communication subsystem 1311 will be dependent upon the
communication network in which the device is intended to operate.
For example, mobile station 1300 may include a communication
subsystem 1311 designed to operate within the Mobitex.TM. mobile
communication system, the DataTAC.TM. mobile communication system,
GPRS network, UMTS network, EDGE network or LTE network.
[0169] Network access requirements will also vary depending upon
the type of network 1302. For example, in the Mobitex and DataTAC
networks, mobile station 1300 is registered on the network using a
unique identification number associated with each mobile station.
In LTE, UMTS and GPRS networks, however, network access is
associated with a subscriber or user of mobile station 1300. A GPRS
mobile station therefore requires a subscriber identity module
(SIM) card in order to operate on a GPRS network. Without a valid
SIM card, a GPRS mobile station will not be fully functional. Local
or non-network communication functions, as well as legally required
functions (if any) such as "911" emergency calling, may be
available, but mobile station 1300 will be unable to carry out any
other functions involving communications over the network 1302. The
SIM interface 1344 is normally similar to a card-slot into which a
SIM card can be inserted and ejected like a diskette or PCMCIA
card. The SIM card can have approximately 64K of memory and hold
many key configuration 1351, and other information 1353 such as
identification, and subscriber related information.
[0170] When required network registration or activation procedures
have been completed, mobile station 1300 may send and receive
communication signals over the network 1302. Signals received by
antenna 1316 through communication network 1302 are input to
receiver 912, which may perform such common receiver functions as
signal amplification, frequency down conversion, filtering, channel
selection and the like, and in the example system shown in FIG. 13,
analog to digital (A/D) conversion. A/D conversion of a received
signal allows more complex communication functions such as
demodulation and decoding to be performed in the DSP 1320. In a
similar manner, signals to be transmitted are processed, including
modulation and encoding for example, by DSP 1320 and input to
transmitter 1314 for digital to analog conversion, frequency up
conversion, filtering, amplification and transmission over the
communication network 1302 via antenna 1318. DSP 1320 not only
processes communication signals, but also provides for receiver and
transmitter control. For example, the gains applied to
communication signals in receiver 1312 and transmitter 1314 may be
adaptively controlled through automatic gain control algorithms
implemented in DSP 1320.
[0171] Mobile station 1300 preferably includes processing means
such as a microprocessor 1338 which controls the overall operation
of the device. Communication functions, including at least data and
voice communications, are performed through communication subsystem
1311. Microprocessor 1338 also interacts with further device
subsystems such as the display 1322, flash memory 1324, random
access memory (RAM) 1326, auxiliary input/output (I/O) subsystems
1328, serial port 1330, keyboard 1332, speaker 1334, microphone
1336, a short-range communications subsystem 1340 and any other
device subsystems generally designated as 1342.
[0172] Some of the subsystems shown in FIG. 13 perform
communication-related functions, whereas other subsystems may
provide "resident" or on-device functions. Notably, some
subsystems, such as keyboard 1332 and display 1322, for example,
may be used for both communication-related functions, such as
entering a text message for transmission over a communication
network, and device-resident functions such as a calculator or task
list.
[0173] Operating system software used by the microprocessor 1338 is
preferably stored in a persistent store such as flash memory 1324,
which may instead be a read-only memory (ROM) or similar storage
element (not shown). Those skilled in the art will appreciate that
the operating system, specific device applications, or parts
thereof, may be temporarily loaded into a volatile memory such as
RAM 1326. Received communication signals may also be stored in RAM
1326.
[0174] As shown, flash memory 1324 can be segregated into different
areas for both computer programs 1358 and program data storage
1350, 1352, 1354 and 1356. These different storage types indicate
that each program can allocate a portion of flash memory 1324 for
their own data storage requirements. Microprocessor 1338, in
addition to its operating system functions, preferably enables
execution of software applications on the mobile station. A
predetermined set of applications that control basic operations,
including at least data and voice communication applications for
example, will normally be installed on mobile station 1300 during
manufacturing. A preferred software application may be a personal
information manager (PIM) application having the ability to
organize and manage data items relating to the user of the mobile
station such as, but not limited to, e-mail, calendar events, voice
mails, appointments, and task items. Naturally, one or more memory
stores would be available on the mobile station to facilitate
storage of PIM data items. Such PIM application would preferably
have the ability to send and receive data items, via the wireless
network 1302. In a preferred embodiment, the PIM data items are
seamlessly integrated, synchronized and updated, via the wireless
network 1302, with the mobile station user's corresponding data
items stored or associated with a host computer system.
[0175] Further applications may also be loaded onto the mobile
station 1300 through the network 1302, an auxiliary I/O subsystem
1328, serial port 1330, short-range communications subsystem 1340
or any other suitable subsystem 1342, and installed by a user in
the RAM 1326 or preferably a non-volatile store (not shown) for
execution by the microprocessor 1338. Such flexibility in
application installation increases the functionality of the device
and may provide enhanced on-device functions, communication-related
functions, or both. For example, secure communication applications
may enable electronic commerce functions and other such financial
transactions to be performed using the mobile station 1300.
[0176] In a data communication mode, a received signal such as a
text message or web page download will be processed by the
communication subsystem 1311 and input to the microprocessor 1338,
which preferably further processes the received signal for output
to the display 1322, or alternatively to an auxiliary I/O device
1328. A user of mobile station 1300 may also compose data items
such as email messages for example, using the keyboard 1332, which
is preferably a complete alphanumeric keyboard or telephone-type
keypad, in conjunction with the display 1322 and possibly an
auxiliary I/O device 1328. Such composed items may then be
transmitted over a communication network through the communication
subsystem 1311.
[0177] For voice communications, overall operation of mobile
station 1300 is similar, except that received signals would
preferably be output to a speaker 1334 and signals for transmission
would be generated by a microphone 1336. Alternative voice or audio
I/O subsystems, such as a voice message recording subsystem, may
also be implemented on mobile station 1300. Although voice or audio
signal output is preferably accomplished primarily through the
speaker 1334, display 1322 may also be used to provide an
indication of the identity of a calling party, the duration of a
voice call, or other voice call related information for
example.
[0178] Serial port 1330 in FIG. 13, would normally be implemented
in a personal digital assistant (PDA)-type mobile station for which
synchronization with a user's desktop computer (not shown) may be
desirable, but is an optional device component. Such a port 1330
would enable a user to set preferences through an external device
or software application and would extend the capabilities of mobile
station 1300 by providing for information or software downloads to
mobile station 1300 other than through a wireless communication
network. The alternate download path may for example be used to
load an encryption key onto the device through a direct and thus
reliable and trusted connection to thereby enable secure device
communication.
[0179] Other communications subsystems 1340, such as a short-range
communications subsystem, is a further optional component which may
provide for communication between mobile station 1300 and different
systems or devices, which need not necessarily be similar devices.
For example, the subsystem 1340 may include an infrared device and
associated circuits and components or a Bluetooth.TM. communication
module to provide for communication with similarly enabled systems
and devices.
[0180] When mobile device 1300 is used as a UE, protocol stacks
1346 include a method and apparatus for cell reselection for a
wireless communication device.
Extensions and Alternatives
[0181] In the foregoing specification, concepts have been described
with reference to specific embodiments thereof. It will, however,
be evident that various modifications and changes may be made
thereto without departing from the scope of the technique. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than a restrictive sense.
[0182] It is to be noted that the methods as described have actions
being carried out in a particular order. However, it would be clear
to a person skilled in the art that the order of any actions
performed, where the context permits, can be varied and thus the
ordering as described herein is not intended to be limiting.
[0183] It is also to be noted that where a method has been
described it is also intended that protection is also sought for a
device arranged to carry out the method and where features have
been claimed independently of each other these may be used together
with other claimed features.
[0184] Furthermore it will be noted that the apparatus described
herein may comprise a single component such as a UE or UTRAN or
other user equipment or access network components, a combination of
multiple such components for example in communication with one
another or a sub-network or full network of such components.
[0185] In one example there is provided a method for cell selection
or reselection in a user equipment UE for use in a mobile
telecommunications system, in which the UE is arranged to receive a
plurality of system information blocks (SIBs) including a primary
SIB and a secondary SIB of the same type; the method comprising:
conditional on receipt of the secondary SIB before receipt of the
primary SIB; starting (initiating) measurements, and cell
reselection evaluation of cells listed in the secondary SIB.
[0186] Embodiments have been described herein in relation to 3GPP
specifications. However the method and apparatus described are not
intended to be limited to the specifications or the versions
thereof referred to herein but may be applicable to future versions
or other specifications.
[0187] A portion of the disclosure of this patent document contains
material which is subject to copyright protection. The copyright
owner has no objection to the facsimile reproduction by anyone of
the patent document or patent disclosure, as it appears in the
Patent and Trademark Office patent file or records, but otherwise
reserves all copyright rights whatsoever.
* * * * *