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Method and apparatus for cell reselection for a wireless communication device

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20140050129 patent thumbnailZoom

Method and apparatus for cell reselection for a wireless communication device


A method and apparatus for cell reselection for a wireless communication device are disclosed.
Related Terms: Wireless Communication Device Wireless Cell Reselection Reselection

Browse recent Blackberry Limited patents - Waterloo, CA
USPTO Applicaton #: #20140050129 - Class: 370280 (USPTO) -
Multiplex Communications > Duplex >Communication Over Free Space >Time Division



Inventors: Raghavendra Magadi Rangaiah, Andrew John Farnsworth, Takashi Suzuki

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The Patent Description & Claims data below is from USPTO Patent Application 20140050129, Method and apparatus for cell reselection for a wireless communication device.

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RELATED APPLICATIONS

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

1. Technical Field

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.

2. Description of the Related Art

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.

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.

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).

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.

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

Embodiments will now be described, by way of example only, with reference to the attached drawings, in which:

FIG. 1 is a diagram capturing the current 3GPP standardised UE behaviour as described therein;

FIG. 2 is a flow diagram capturing the current 3GPP standardised UE behaviour as described therein;

FIG. 3 is a diagram capturing the current 3GPP standardised UE behaviour as described therein;

FIG. 4 is a diagram capturing the current 3GPP standardised UE behaviour as described therein;

FIG. 5 is a flow diagram illustrating steps performed according to a first aspect of the approach described herein;

FIG. 6 is a flow diagram illustrating steps performed according to an alternative related to the first aspect of the approach described herein;

FIG. 7 is a flow diagram illustrating steps performed according to an alternative related to the first aspect of the approach described herein;

FIG. 8 is a flow diagram illustrating steps performed according to an alternative related to the first aspect of the approach described herein;

FIG. 9 is a flow diagram illustrating steps performed according to a second aspect of the approach described herein;

FIG. 10 is a flow diagram illustrating steps performed according to a third aspect of the approach described herein;

FIG. 11 shows an overview of a network and a UE device;

FIG. 12 is a block diagram illustrating an embodiment of a protocol stack provided in a UE device; and

FIG. 13 is a block diagram illustrating a UE device.

The same reference numerals are used in different figures to denote similar elements.

DETAILED DESCRIPTION

OF THE DRAWINGS

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.

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

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.

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.

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.

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.

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.

SIB 11, 11bis and 12 contain information related to cell reselection. More specifically their content typically includes:

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.

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.

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.

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.

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.

The Standard 3GPP TS 25.331v10.4.0 “Radio Resource Control (RRC); Protocol specification (Release 10), 2011-06, specifies the following:

8.1.1.6.11a System Information Block type 11bis

The UE should store all relevant IEs included in this system information block. The UE shall: 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;

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.

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.

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.

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.

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:

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.

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.

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.

T4 UE successfully reselects to Cell 2.

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.

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.

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:

T1 UE is in CELL_DCH state.

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.

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.

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.

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.

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.

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

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:

The UE should store all relevant IEs included in this system information block. The UE shall: 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;

According to example 1:

The UE should store all relevant IEs included in this system information block. The UE shall: 2> if the UE has not received SIB 11, the UE shall start measurements and cell reselection evaluation of cells listed in SIB 11bis;

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stats Patent Info
Application #
US 20140050129 A1
Publish Date
02/20/2014
Document #
14064947
File Date
10/28/2013
USPTO Class
370280
Other USPTO Classes
455437
International Class
04W36/00
Drawings
9


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