Method and apparatus for cell reselection

Various embodiments of the present invention provide a method for cell reselection, comprising: receiving, at a user equipment, system information from a network node that is shared by two or more operator networks, wherein the system information comprises first information associated with at least one operator network related to one or more neighboring cells for the user equipment; determining whether there is an operator network accessible to the user equipment in the at least one operator network, based at least in part on the first information; and performing a cell reselection procedure only when one or more accessible operator networks are determined.

RELATED APPLICATION

This application was originally filed as PCT Application No. PCT/CN2013/070938 filed Jan. 24, 2013.

FIELD OF THE INVENTION

Example and non-limiting embodiments of this invention relate generally to communications networks, and more particularly to cell reselection in a communication system with the sharing of a radio access network (RAN) among multiple public land mobile networks (PLMNs).

BACKGROUND OF THE INVENTION

In the future, it is foreseen that there will be a huge increase in the wireless data transmission using wireless networks and wireless connections. In order to handle this big increase in wireless data, the discussion is going towards a need for smaller cell sizes and more efficient network offloading opportunities by use of e.g. hotspots. Work is ongoing internally in some companies and also in open forums like 3rd Generation Partnership Project (3GPP) on how to enable efficient sharing of a RAN in order to allow different operators to share the RAN.

RAN sharing is not new, but in the future it is likely to even further share a RAN in order to keep operators cost low while still ensuring offloading by small cells (and still have a reasonable number of eNBs deployed in the environment). When a small cell RAN is shared (e.g. on 3.5 GHz carrier), it does not necessarily mean that a macro RAN (e.g. large area coverage) is shared among the operators that share the small cell RAN (hotspot RAN).

One problem arises in such configuration when idle mode (or similar) mobility is supported. Assuming that the idle mode mobility will be similar as in legacy, the mobility related information for idle mode mobility is based on broadcast information—i.e. information received by all user equipments (UEs). In such scenario, it is not possible to distinguish UEs e.g. based on their release version or their Home Public Land Mobile Network (HPLMN). Therefore, all UEs will receive all the broadcast information including also mobility related information.

As illustrated inFIG. 1, the problem arises when there are two UEs: UE1with subscription to PLMN1and UE2with subscription to PLMN2. An access point (AP) is shared between the two PLMNs but the macro network is only accessible to UEs with correct subscription. That is, UE1cannot access eNB2deployed in PLMN2and UE2cannot access eNB1deployed in PLMN1.

On the other hand, the mobility information broadcast by the AP has to include carrier information for both carriers of eNB1and eNB2(different carriers) as it has to be the information enabling mobility for both UE1and UE2. The UEs cannot distinguish the mobility information and as a result, UE1will search, detect and measure cells from PLMN2(on carrier2) in mobility evaluation although access is not allowed, and similarly UE2will search, detect and measure cells from PLMN1(on carrier1) in mobility evaluation. This scenario leads to a number of unnecessary reselections and possibly also unnecessary signaling.

3GPP TS 36.304 describes the idle mode mobility of a UE, and 3GPP TS 36.331 defines the system information required for supporting idle mode reselection procedures. However, the 3GPP TS 36.331 assumes that an access network is connected to one PLMN that is under control of a single network operator. Therefore, the system information stated therein is not involving any information associated with PLMNs sharing a same RAN.

SUMMARY OF THE INVENTION

Example embodiments of the present invention propose a method to enable a UE at an early stage to distinguish accessible carriers from non-accessible carriers. A UE could be able to distinguish whether an intra-freq/inter-freq measurement to a neighboring cell should be initiated or not, which could save unnecessary measurements and possibly signaling in the Uu interface for the UE. Via such knowledge, a UE could avoid measuring the carrier/cell which is not suitable for itself, during the cell reselection. This will improve the measurement efficiency for idle mode UEs, and reduce power consumption of the UEs.

An aspect of the invention relates to a method for cell reselection. The method comprises: receiving, at a user equipment, system information from a network node that is shared by two or more operator networks, wherein the system information comprises first information associated with at least one operator network related to one or more neighboring cells for the user equipment; determining whether there is an operator network accessible to the user equipment in the at least one operator network, based at least in part on the first information; and performing a cell reselection procedure only when one or more accessible operator networks are determined.

A second aspect of the invention relates to another method. The method comprises: obtaining, at a network node shared by two or more operator networks, first information associated with at least one operator network related to one or more neighboring cells of a user equipment communicatively connected to the network node; and broadcasting the first information in system information to the user equipment.

A third aspect of the invention relates to an apparatus for wireless communications. The apparatus comprises: a transmitter; a receiver; a processor; and at least one memory including program code that, when executed by the processor, cause the apparatus to: receive system information from a network node that is shared by two or more operator networks, wherein the system information comprises first information associated with at least one operator network related to one or more neighboring cells of the apparatus; determine whether there is an operator network accessible to the apparatus in the at least one operator network, based at least in part on the first information; and perform a cell reselection procedure only when one or more accessible operator networks are determined.

A fourth aspect of the invention relates to an apparatus for sharing by two or more operator networks. The apparatus comprises: a transmitter; a receiver; a processor; and at least one memory including program code that, when executed by the processor, cause the apparatus to: obtain first information associated with at least one operator network related to one or more neighboring cells of a user equipment communicatively connected to the apparatus; and broadcast the first information in system information to the user equipment.

DETAILED DESCRIPTION OF EMBODIMENTS

It is to be noted that the following exemplary description mainly refers to specifications being used as non-limiting examples for certain exemplary network configurations and deployments. In particular, Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and Long Term Evolution Hotspot indoor (LET-Hi) are used as non-limiting examples for the applicability of thus described exemplary aspects and embodiments. As such, the description of exemplary aspects and embodiments given herein specifically refers to terminology which is directly related thereto. Such terminology is only used in the context of the presented non-limiting examples, and does naturally not limit the invention in any way. Rather, any other communication systems, bands, network configurations or system deployments, etc. may also be utilized as long as compliant with the features described herein.

Hereinafter, various embodiments and implementations of the present invention and its aspects or embodiments are described using several alternatives. It is generally noted that, according to certain needs and constraints, all of the described alternatives may be provided alone or in any conceivable combination (also including combinations of individual features of the various alternatives).

In an E-UTRAN mobile network, a UE in idle mode needs to camp on a cell so as to receive system information from a PLMN, receive paging messages and cell broadcast messages etc. The UE in idle mode already camped on a cell regularly looks to see if there is a better cell. If there is a better one, or if there is a downlink signaling failure etc., a cell reselection occurs. The mobility of a UE in idle mode comprises intra-frequency (intra-freq) mobility and inter-frequency (inter-freq) mobility as well as inter-RAT (Radio Access Technology) mobility. The intra-freq mobility occurs when the current serving cell and the target cell to move to operate on a same carrier frequency. On the other hand, the inter-freq mobility occurs when the target cell to move to operates on a different carrier frequency as compared to the current serving cell. It is similar for the inter-RAT mobility except that the new target cell will be operating in another RAT. During the cell reselection procedure, the network controls a UE to perform measurements for intra/inter-frequency mobility by using broadcast information or dedicated control. The measurements for neighboring cells performed by the UE comprise intra-freq measurements and may also comprise inter-freq measurements and inter-RAT measurements.

FIG. 1is an exemplary diagram illustrating a communication system100according to embodiments of the present invention. The communication system100typically comprises a common radio access network110shared by two or more operator networks, such as PLMNs. The common radio access network110comprises a network node, such as an access point (AP)101communicably coupled to two base stations, e.g. eNBs in E-UTRAN, within two PLMNs operated by respective operators. The communication system100also comprises multiple UEs, for example UE1and UE2as shown inFIG. 1. UE1and UE2have subscribed to PLMN1and PLMN2respectively. The UEs typically maintain a list of all accessible PLMNs in their Subscriber Identity Module (SIM)/Universal Subscriber Identity Module (USIM) or memory. However, it shall be understood that the number of PLMNs, eNBs and UEs as illustrated inFIG. 1is only for illustration and shall not be construed as limiting. In one embodiment, the network node may be, but not limited to, LTE-Hi AP or LTE-ELA AP.

FIG. 2is an exemplary flowchart of a method200for cell reselection employed at the UE in the communication system as shown inFIG. 1, according to embodiments of the present invention. As shown in the figure, in block210, the UE receives system information from AP101. The system information comprises PLMN information associated with the PLMN(s) related to neighboring cells of the serving cell for the UE. In one embodiment, the PLMN information comprises a list of PLMNs to which an intra-freq carrier of the neighboring cells belongs. In another embodiment, the PLMN information comprises, for each of inter-freq or inter-RAT carriers, a list of PLMNs to which a corresponding one of the inter-freq/RAT carriers belongs. In yet another embodiment, the PLMN information further comprises information indicating an association between each of the neighboring cells on each of the intra-freq/inter-freq/RAT carriers and the PLMN(s). In this embodiment, if the UE already determines there are accessible PLMNs associated with a given carrier (e.g. an intra-freq or inter-freq/RAT carrier), and if some of the PLMNs associated with that given carrier are accessible while others are not, the UE will further determine which neighboring cells on that given carrier belong to the accessible PLMNs and then perform measurements related to these neighboring cells. In yet another embodiment, the PLMN information comprises a list of PLMNs to which one or more neighboring cells on a single carrier belong. In the following description, illustrative but non limiting examples of the PLMN information will be given with reference toFIGS. 4-8.

Next in block212, the UE determines whether there is any PLMN accessible to the user equipment in the PLMN(s) involved in the PLMN information. Then in block214, only when one or more PLMNs are determined to be accessible, may a cell reselection procedure be performed by the UE through for example, performing intra-freq or inter-freq/RAT cell detection and measurements. Otherwise, no cell reselection procedure will be performed.

FIG. 3is an exemplary flowchart of a method300for cell reselection employed at the network node, such as access point in the communication system100as shown inFIG. 1, according to embodiments of the present invention. As shown in the figure, in block310, the network node obtains PLMN information associated with the PLMN(s) for each carrier of the neighboring cells or for each of the neighboring cells when setting up interfaces between the network node and neighboring base stations (eNBs). Next in block312, the network node broadcast the PLMN information in system information to all UEs, for example, via Broadcast Control Channels (BCCHs) or system information blocks (SIBs).

In the following description, illustrative examples of the PLMN information as included in the system information will be exemplarily described with reference toFIGS. 4-8. Examples of the system information are chosen by referring to the 3GPP TS 36.331 in which thirteen types of System Information Blocks have been defined for conveying system information. In that specification, a SystemInformationBlockType4 information element (IE) is defined to contain neighboring cell related information relevant only for intra-frequency cell reselection and the IE includes cells with specific reselection parameters as well as blacklisted cells; a SystemInformationBlockType5 IE is defined to contain information relevant only for inter-frequency cell reselection i.e. information about other E-UTRA frequencies and the IE may include cell reselection parameters common for a frequency as well as cell specific reselection parameters; a SystemInformationBlockType6 IE is defined to contain information relevant only for inter-RAT cell re-selection, i.e. information about UTRA (Universal Terrestrial RAN) frequencies and UTRA neighbouring cells relevant for cell re-selection; a SystemInformationBlockType7 IE is defined to contain information relevant only for inter-RAT cell re-selection, i.e. information about GERAN (GSM (Global System for Mobile Communications)/EDGE (Enhanced Data rates for GSM Evolution) RAN) frequencies relevant for cell re-selection; a SystemInformationBlockType8 IE is defined to contain information relevant only for inter-RAT cell re-selection, i.e. information about CDMA2000 (Code Division Multiple Access 2000) frequencies and CDMA2000 neighbouring cells relevant forcell re-selection. Hereinafter, SystemInformationBlockType4 IE, SystemInformationBlockType5 IE and SystemInformationBlockType6 IE with the PLMN information configured therein will be exemplarily described in ASN.1 as examples of the system information according to the embodiments of the present invention.

FIGS. 4-8respectively illustrate the PLMN information for intra-frequency mobility per carrier level, inter-frequency mobility per carrier level, inter-RAT mobility per carrier level, intra-frequency mobility per cell level and inter-frequency mobility per cell level.

FIG. 4is an exemplary description illustrating system information including SystemInformationBlockType4 IE400for intra-freq mobility per carrier level according to one embodiment of the present invention. Since an intra-freq carrier may belong to different PLMNs, additional-plmn-IdentityList information is comprised in the IE400as shown inFIG. 4to indicate the association between the intra-freq carrier and the PLMN(s). This information may include, but not limited to, a list of identities of the PLMNs to which the intra-freq carrier belongs. Upon receipt of the IE400, the UE will check whether an associated PLMN is an allowable PLMN for itself or not, for example, by checking whether the identity of the associated PLMN is included in a list of allowed PLMNs maintained in the UE. If the identity of the associated PLMN is found in the list, it can be determined that the associated PLMN is allowed and thus accessible to the UE. If no accessible PLMN is found, no cell reselection to cells on the intra-freq carrier will be triggered and thus no intra-frequency measurement will be performed.

FIG. 5is an exemplary description illustrating system information including SystemInformationBlockType5 IE500for inter-freq mobility per carrier level according to one embodiment of the present invention. In this embodiment, the IE500comprises a list of inter-freq carrier frequencies. For each single inter-freq carrier frequency, additional-plmn-Identitylist information is provided, which includes the PLMN information of that single inter-freq carrier frequency. Such PLMN information indicates the association between that single inter-freq carrier and the PLMN(s), for example, it may comprise a list of identities of the PLMNs to which the single inter-freq carrier belongs. Upon receipt of the IE500, the UE will check whether an associated PLMN of a given inter-freq carrier is an allowable PLMN, for example, by checking whether the identity of the associated PLMN is included in the list of allowed PLMNs maintained in the UE. If the identity of the associated PLMN is found in the list, it can be determined that the associated PLMN is allowed and thus that given inter-freq carrier is accessible to the UE. If no accessible PLMN is found, the carrier is not accessible by the UE and no cell reselection to that inter-freq carrier should be triggered and thus no inter-freq measurement related to the neighboring cells on that inter-freq carrier would need to be performed. For example, in the scenario as illustrated inFIG. 1, UE1with subscription to PLMN1(cells on carrier1) will, while being camped on the AP, be able to know based on the PLMN information received from the AP that the carrier2, on which eNB2operates, belongs to PLMN2which is not among the allowed PLMNs. Based on this, the UE can determine that cells on carrier frequency2are not suitable for camping hence the UE does not have to perform cell detection and measurements on this carrier, leading to that no cell reselection will be triggered to cells on the carrier frequency2.

FIG. 6is an exemplary description illustrating system information including SystemInformationBlockType6 IE600for inter-RAT mobility per carrier level according to one embodiment of the present invention. As illustrated, the IE600comprises a list of inter-RAT carrier frequencies, and the RAT used in this embodiment refers to UTRAN. For GERAN cases, SystemInformationBlockType7 may be employed and for CDMA2000 cases, SystemInformationBlockType7 may be employed. In the current example as shown inFIG. 6, for each single inter-RAT carrier frequency, additional-plmn-Identitylist information is provided, which includes the PLMN information of that single inter-RAT carrier frequency. Such PLMN information indicates the association between that single inter-RAT carrier and the PLMN(s), for example, it may comprise a list of identities of the PLMNs to which the single inter-RAT carrier belongs. Upon receipt of the IE600, the UE will check whether an associated PLMN of a given inter-RAT carrier is an allowable PLMN, for example, by checking whether the identity of the associated PLMN is included in the list of allowed PLMNs maintained in the UE. If the identity of the associated PLMN is found in the list, it can be determined that the associated PLMN is allowed and thus that given inter-RAT carrier is accessible to the UE. If no accessible PLMN is found, that given inter-RAT carrier is not accessible by the UE and no cell reselection to that carrier should be triggered and thus no inter-RAT measurement related to the neighboring cells on that carrier would need to be performed.

The PLMN information for each of inter-freq/RAT carriers or intra-freq carrier could be obtained by the AP, e.g. LTE-Hi AP, when setting up interfaces between the AP and neighboring eNBs (e.g. eNB1and eNB2). Some backhaul procedures known in the art could be utilized to implement such information exchanging, and thus will not be detailed herein.

Alternatively, the PLMN information may be provided per cell level.

FIG. 7is an exemplary description illustrating system information including SystemInformationBlockType4 IE700for intra-freq mobility per cell level according to one embodiment of the present invention. In this embodiment, the IE700may comprise a list of intra-freq neighboring cells with specific cell reselection parameters. The intra-freq neighboring cells used herein refer to neighboring cells on the same carrier frequency as the current serving cell of the UE. Taking network sharing in consideration, a single neighboring cell may belong to different PLMNs. Therefore, for each single intra-freq neighboring cell, additional-plmn-Identitylist information is provided to indicate the association between that intra-freq neighboring cell and the PLMNs. Similar to the IE400as described with reference toFIG. 4, such information may comprise a list of identities of the PLMNs to which the single intra-freq neighboring cell belongs. From UE's point of view, the UE will base on this information to tell to which PLMN a given intra-freq neighboring cell belongs and thereby determine whether the potential target PLMN is an allowable one or not. If no accessible PLMN is found, then no reselection to that intra-freq neighboring cell will happen. However, the indication of the association between a neighboring cell and the PLMNs is not limited to listing the PLMN information for each cell in a list. Alternatively, it can be implemented by either making a list of cells operated by the PLMNs in the list or making for each PLMN in the list a list of cells operated by that PLMN. But more changes to the ASN.1 would be required.

FIG. 8is an exemplary diagram illustrating system information including SystemInformationBlockType5 IE800for inter-freq mobility per cell level according to one embodiment of the present invention. In this embodiment, the IE800comprises a list of inter-freq carrier frequencies. For each single carrier frequency, a list of inter-freq neighboring cells is provided, and further, for each single inter-freq neighboring cell, additional-plmn-Identitylist information is provided to indicate the association between the inter-freq neighboring cell on that single inter-freq carrier and the PLMNs. From UE's point of view, the UE will base on this information to tell which PLMN a given inter-freq neighboring cell on a given inter-freq carrier belongs to and thereby determine whether the potential target PLMN is an allowable one or not. If no accessible PLMN is found, then no reselection to that given inter-freq neighboring cell on that given inter-freq carrier will happen and no inter-freq measurement related to that inter-freq neighboring will be performed.

As for the inter-RAT mobility per cell level, a SystemInformationBlockType6, 7 or 8 IE may also be used in the similar way as illustrated inFIG. 8such that the PLMN information indicating the association between inter-RAT neighboring cells and the PLMNs is comprised in the IE, which will not be detailed herein for the sake of conciseness.

In the foregoing, the system information comprises the PLMN information either per carrier level or per cell level. However, the system information can comprise the PLMN information per both carrier and cell levels. For example, the PLMN information may combine the additional-plmn-Identitylist information as included in the IE400and the additional-plmn-Identitylist information as included in the IE700or combine the additional-plmn-Identitylist information as included in the IE500and the additional-plmn-Identitylist information as included in the IE800. In this example, upon receipt of the PLMN information, the UE first determines whether there is an accessible PLMN associated with a given carrier (intra-freq or inter-freq carrier). If no accessible PLMN is found, then no cell reselection to that given carrier will be triggered and thus no measurement related to the neighboring cells on that given carrier will be performed. If some of the PLMNs associated with that given carrier are accessible and others are not, then the UE will further determine which neighboring cells on that given carrier belong to the accessible PLMNs and then perform measurements related to these neighboring cells. The above additional-plmn-Identitylist information for each of intra-freq neighboring cells or inter-freq or inter-RAT neighboring cells is broadcast in the system information of the AP, e.g. LTE-Hi AP, which could be obtained by the AP during an interface (S1′/X3) setup procedure between the AP and an associated eNB.

FIG. 9illustrates a simplified block diagram of an AP901and a UE902that are suitable for use in practicing the exemplary embodiments of the present invention. The UE902includes a data processor (DP)903, a memory (MEM)904coupled to the DP903, and a suitable RF transmitter TX and receiver RX905(which need not to be implemented in a same component) coupled to the DP903. The MEM904stores a program (PROG)906. The TX/RX905is for bidirectional wireless communications with the AP901. Note that the TX/RX905has at least one antenna to facilitate communication; multiple antennas may be employed for multiple-input multiple-output MIMO communications in which case the UE902may have multiple TXs and/or RXs.

The AP901includes a data processor (DP)907, a memory (MEM)908coupled to the DP907, and a suitable RF transmitter TX and receiver RX909coupled to the DP907. The MEM908stores a program (PROG)910. The TX/RX909is for bidirectional wireless communications with the UE902. Note that the TX/RX909has at least one antenna to facilitate communication. The AP901may be coupled via a data path to one or more external networks or systems, such as the internet, for example.

At least one of the PROGs906and910is assumed to include program instructions that, when executed by the associated DPs903and907, enable the UE902and AP901to operate in accordance with the exemplary embodiments of this invention, as discussed herein with the methods200or300.

The embodiments of the present invention may be implemented by computer software executable by one or more of the DPs903,907of the UE902and the AP901, or by hardware, or by a combination of software and hardware.

The MEMs904and908may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one MEM is shown in the AP901or UE902, there may be several physically distinct memory units in the AP901or UE902. The DPs903and907may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non limiting examples. Either or both of the UE902and the AP901may have multiple processors, such as for example an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

Although the above description is based on E-UTRAN, LTE-Hi, and AP, it should not be construed as limiting the spirit and scope of the present invention. The idea and concept can be generalized to also cover normal E-UTRAN macro layout, HetNet deployments and other deployments in which RAN sharing is used. In addition, the examples of ASN.1 are merely examples for illustrating how to implement the idea in E-UTRAN and should not be construed as limiting.

The foregoing computer program instructions can be, for example, sub-routines and/or functions. A computer program product in one embodiment of the invention comprises at least one computer readable storage medium, on which the foregoing computer program instructions are stored. The computer readable storage medium can be, for example, an optical compact disk or an electronic memory apparatus like a RAM (random access memory) or a ROM (read only memory).

LIST OF ABBREVIATIONS

3GPP 3rd generation partnership project

AP access point

ASN.1 abstract syntax notation one

BCCH broadcast control channel

BS base station

CDMA code division multiple access

DP data processor

DSP digital signal processor

E-UTRAN evolved UMTS terrestrial radio access network

EDGE enhanced data rates for GSM evolution

GERAN GSM/EDGE radio access network

GSM global system for mobile communications

HPLMN home public land mobile network

IE information element

LTE long term evolution

PDA personal digital assistant

PLMN public land mobile network

RAN radio access network

RAT radio access technology

UE user equipment

USIM universal subscriber identity module

UTRAN universal terrestrial radio access network

RAM random access memory

ROM read only memory

SIM subscriber identity module

HetNet heterogeneous network