WO2011131221A1

WO2011131221A1 - Method and device for data processing in a wireless network

Info

Publication number: WO2011131221A1
Application number: PCT/EP2010/055106
Authority: WO
Inventors: Richard Waldhauser; Bernhard Wegmann; Ingo Viering; Dirk Rose; Cinzia Gesuina Elena Sartori
Original assignee: Nokia Siemens Networks Oy
Priority date: 2010-04-19
Filing date: 2010-04-19
Publication date: 2011-10-27

Abstract

A method and a device for data processing in a wireless network are provided, wherein pursuant to a radio link failure of a mobile terminal, a message is conveyed from a node of a first radio access technology to a node of a second radio access technology. Furthermore, a communication system is suggested comprising said device.

Description

Method and device for data processing in a wireless network

The invention relates to a method and to a device for data processing in a wireless network. Also, a communication system comprising at least one such device is suggested.

With two or more radio access networks (RANs) simultaneously being driven by a single operator, an increasing need for an efficient traffic management between these RANs emerges comprising inter-RAT (radio access technology) mobility

(e.g., cell change or handover) . However, dimensioning and configuring mobility parameters is already challenging even for the intra-RAT case and becomes even more complex with regard to the inter-RAT scenario.

Radio link failures (RLFs) in an inter-RAT mobility context may have different root causes. In order to trigger a suitable countermeasure, e.g., in terms of configuration parameter update, the root cause has to be determined.

However, in case an RLF occurs when there is an inter-RAT handover problem, the source base station and the target base station may have different information with regard to the RLF. Furthermore, performance monitoring is merely counting the number of RLFs that are reported by a base station.

2G and 3G networks provide the following means for root cause analysis :

a) Drive testing: If performance monitoring counters

accumulate RLFs or even call drops in a particular service area, operators launch drive tests for a

detailed analysis.

b) History of dropped call: Also, a message flow of a

dropped call can be traced or stored. Hence, an analysis of such dropped call can be conducted (off-line) at a later time.

c) Analyzing traces on interfaces, IMSI/IMEI.

d) Key Performance Indicator and Performance Monitoring

counter analysis. In case of intra-LTE, a handover is prepared by passing all necessary information to the target base station (eNodeB) (e.g., E-RAB attributes and RRC context) . The mobile terminal (also referred to as user equipment, UE) keeps the

identification of a source eNodeB together with some context information to enable a call re-establishment in case a handover problem (e.g., RLF after handover) occurs. 3GPP Rel.9 establishes additional messages between the eNodeBs via an X2 interface, which are directed to root cause analysis triggered by an RRC re-establishment request message. This message is sent by the UE and contains information about the physical cell identity (PCI) and the UE identity that was assigned to the UE by the last eNodeB that was serving this UE before the radio link failure occurred. If the eNodeB receives the RRC reestablishment request message with a PCI that belongs to a neighbor eNodeB, an "RLF Indication"- message will be sent to the neighbor eNodeB. If the root cause analysis results in a "handover too early" or a

"handover to wrong cell" root cause, the eNodeB that

conducted a wrong decision is informed by a "handover

report "-message about this result. Both "handover indication" and "handover report" messages are sent via the X2 interface between eNodeBs .

Disadvantageously, there is no such mechanism for the inter- RAT case between LTE and legacy (e.g., 2G and/or 3G)

technologies. The LTE approach cannot be used, because there is no X2 interface and no RRC re-establishment request message.

The problem to be solved is to overcome the disadvantages set forth above and in particular to provide an efficient

approach for inter-RAT root cause analysis.

This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims. In order to overcome this problem, a method for data

processing in a wireless network is suggested,

- wherein pursuant to a radio link failure of a mobile terminal, a message is conveyed from a node of a first radio access technology to a node of a second radio access technology.

It is noted that radio access technologies could be: 2G, 3G, LTE access technologies or any access technology as defined in an existing or upcoming mobile communication standard.

It is also noted that the first radio access technology and the second radio access technology are different.

It is further noted that the message can be conveyed between different radio access technologies via a core network.

Hence, a root cause analysis can be conducted in a

distributed manner by exchanging information between the nodes of the different radio access technologies. This approach therefore provides an efficient solution for a root cause analysis for an inter-RAT scenario. It is noted that the inter-RAT operation may be based on coverage driven, service driven or load balancing driven handover between overlaying radio access networks. The approach provided in particular enables self optimizing networks (SONs) and/or mobility robustness optimization (MRO) for inter-RAT mobility.

One aspect of MRO comprises optimizing network configuration parameters (e.g., handover trigger parameters, handover thresholds or timers) in a way that radio link failures

(RLFs) and even call drops due to handover are reduced. In order to make the right decision in terms of parameter optimization, the approach suggested further provides a more detailed root cause information. In an embodiment, after the radio link failure the mobile terminal is connected to the node of the first radio access technology .

It is noted that the mobile terminal may have been connected to the node of the second radio access technology prior to said radio link failure. In another embodiment, one of the first or second radio access technology is an LTE access technology and the other is in particular a legacy radio access technology.

The legacy radio access technology may be a 2G or a 3G access technology.

In a further embodiment, a root cause analysis of the radio link failure is conducted by the node of the first radio access technology based on information provided by the mobile terminal.

The root cause analysis or a portion of a root cause analysis can be conducted by a processing algorithm implemented at the node of the first radio access technology.

The root cause analysis referred to herein may be a part of a root cause analysis conducted in a distributed way on

different entities. In a next embodiment, the information provided by the mobile terminal comprises at least one of the following:

- an address information of the node of the second

radio access technology to which it was connected prior to the radio link failure;

- a context information of the mobile terminal that can be used to identify a context of this mobile terminal at the node of the second access technology;

- additional information. It is also an embodiment that the message conveyed from the node of the first radio access technology to the node of the second radio access technology comprises at least one of the following:

- an address information of the node of the first radio access technology;

- additional information.

The additional information may comprise a result of a pre^¬ analysis of the root cause conducted by the node of the first radio access technology in particular based on information locally available at this node and/or information provided by the mobile terminal (e.g., measurement results).

Pursuant to another embodiment, a root cause analysis is conducted by the node of the second radio access technology based on the message provided.

Hence, information between different radio access

technologies can be used for evaluating the root cause for inter-RAT mobility problems.

According to an embodiment, based on the root cause analysis, at least one of the following steps is conducted:

- a first message is sent to the node of the first

radio access technology indicating that a handover of the mobile terminal occurred too early;

- a second message is sent to the node of the first

radio access technology or to a node of a third radio access technology indicating that a handover of the mobile terminal occurred to the wrong radio access technology;

- no message is sent indicating that the handover of the mobile terminal occurred too late. It is noted that at least two of the three radio access technologies may be different. The root cause analysis can be reported to a management system in order to provide

appropriate countermeasures, e.g., to avoid or reduce future radio link failures.

According to another embodiment, the root cause analysis is conducted by the node of the second radio access technology based on the message provided and based on information locally available.

Hence, the node of the first radio access technology

receiving the message from the mobile terminal may use information conveyed by the message and information that is locally available at the node of the first radio access technology, e.g., statistics based on the information of previous radio link failures, in order to decide whether or not the node where the radio link failure occurred (e.g., the node of the second radio access technology) needs to be involved in the root cause analysis.

In yet another embodiment, the node of the first radio access technology or the node of the second radio access technology informs at least one other node that served the mobile terminal about a result of the root cause analysis.

For example, the node of the first radio access technology may send a message to the node of the second radio access technology (where the radio link failure occurred) if the root cause analysis cannot be conducted merely with

information locally available at this node of the first radio access technology. The node of the second radio access technology may send a message to another node (e.g., the node of the first access technology or a separate node (which may of the first, the second or a third access technology) if the root cause analysis concluded that the handover was either too late or directed to the wrong radio access technology. If the node of the second radio access technology concludes that the

handover has been conducted too late, no message may be conveyed to a node of the first, second or third radio access technology .

Hence, counter measures could be initiated or triggered by any of the nodes and/or a central node or any centralized component, e.g., a management system.

Hence, a serving radio node can be made aware that there exists a problem that needs to be corrected, but also the information of the cause of the problem can be conveyed to other radio nodes in adjacent radio access technologies RATs within the communication system.

Also, extensions could be added to existing messages

exchanged between the different entities, e.g., with regard to the interface between the mobile terminal and the node of the respective radio access technology and/or with regard to the interface between the node of the radio access technology and the node that served the mobile terminal prior to radio link failure. Hence, an appropriate information can be conveyed between the devices and recognized by the different entities .

According to a next embodiment, mobility parameters of the wireless network are set or changed based on the root cause analysis provided.

A processing algorithm can be provided with the node of the respective radio access technology and such processing algorithm may, e.g., update counters for a management plane's monitoring function or issue a notification to a centralized OAM node via interfaces of the management plane. The problem stated above is also solved by a device for data processing in a wireless network comprising a processing unit that is arranged

- for conveying a message from a node of a first radio access technology to a node of a second radio access technology pursuant to a radio link failure of a mobile terminal.

According to an embodiment, said device is a device of the wireless network, in particular a network node, a base station or a base station controller.

It is further noted that said processing unit can comprise at least one, in particular several, means that are arranged to execute the steps of the method described herein. The means may be logically or physically separated; in particular several logically separate means could be combined in at least one physical unit. Said processing unit may comprise at least one of the

following: a processor, a microcontroller, a hard-wired circuit, an ASIC, an FPGA, a logic device.

The solution provided herein further comprises a computer program product directly loadable into a memory of a digital computer, comprising software code portions for performing the steps of the method as described herein.

In addition, the problem stated above is solved by a

computer-readable medium, e.g., storage of any kind, having computer-executable instructions adapted to cause a computer system to perform the method as described herein.

Furthermore, the problem stated above is solved by a

communication system comprising at least one device as described herein. In the drawings, like reference characters may refer to the same parts. The drawings illustrate principles of the

invention. In the following, embodiments of the invention are described in reference to the following drawings, in which:

Fig.l shows a schematic diagram visualizing a root cause analysis conducted between different RATs based on a radio link failure (RLF) ; Fig.2 shows a schematic diagram visualizing a next step of the root cause analysis depicted in Fig.l.

The approach provided herein in particular comprises a root cause analysis for failures occurring in an inter-RAT scenario or operation regarding, e.g., inter-RAT mobility. The root cause analysis can be conducted in a distributed manner by exchanging information between the nodes of the different RATs. Exchanging and combining available information distributed among the nodes involved helps identifying the root cause of a failure and thus initiating a suitable countermeasure .

Fig.l shows a schematic diagram visualizing a root cause analysis conducted between different RATs based on a radio link failure (RLF) .

A UE 101 has an active connection with a RAN node 102. Based on measurement reports from the UE 101 or because of other mobility triggers, the RAN node 102 may decide to initiate a handover procedure for this UE 101 from the RAN node 102 towards a RAN node 103. The reason for such handover may be the UE 101 moving away from the RAN node 102 and approaching the RAN node 103.

The UE 10 lexperiences an RLF on the connection with the RAN node 102. The RLF may be caused by any problem during an inter-RAT mobility procedure, e.g., a wrong configuration of inter-RAT handover parameters. Due to the RLF, the active connection between the UE 101 and the RAN node 102 drops. The UE 101 recognizes a strong signal received from the RAN node 103 and selects the RAN node 103 to establish the connection, which has been interrupted by the RLF at the RAN node 102.

The UE 101 may then transfer information referred to as

INF_ADDR_RAT_RLF to an RAN node 103 that has been selected by the UE 101 for reconnection purposes. The RAN node 102 is a network element of an RAT 104 and the RAN node 103 is a network element of an RAT 105, wherein both RATs 104, 105 are different .

The RAN node 103 then conveys a message 107 via a core network 106 to the RAN node 102.

The UE 101 further conveys information, referred to as

INF_CONTEXT_ACCESS, that can be used to identify "UE specific context", referred to as INF_UE_CONTEXT" at the RAN node 102. Such UE specific context could have been stored at the RAN node 102, wherein the RAN node 102 can be identified by an information (or address) referred to as INF_ADDR_RAT_RLF, which is also conveyed from the UE 101 to the RAN node 103. In order to identify the right context INF_UE_CONTEXT at the RAN node 102, the information INF_CONTEXT_ACCESS may comprise a cell identity and the identity of the UE 101 that has been assigned to this UE 101 when it was served by that cell. For example, in E-UTRAN the information INF_CONTEXT_ACCESS may comprise a physical cell identity (PCI) or an evolved cell global identity (ECGI) and a cell radio network

temporary identifier (C-RNTI) that was assigned for that UE by the eNodeB (RAN node) when serving this UE in that cell. It is possible to use either PCI or ECGI or both. Using the ECGI bears the advantage of being globally unique in a PLMN; however, using the PCI may also suffice, because the PCI could be unique at least within an extended neighborhood of cells .

The UE 101 may also provide further information, referred to as INF_ADDITIONAL, to the RAN node 103. Such further

information INF_ADDITIONAL could be used for analyzing the root cause of the RLF.

The information INF_ADDR_RAT_RLF, INF_CONTEXT_ACCESS and INF_ADDITIONAL (which can be optional) may be added to an already existing message of a connection establishment or a connection re-establishment procedure or to another (e.g., newly defined) procedure. The information transfer between the UE 101 and RAN node 103 may be conducted by different, in particular separate, messages and/or procedures.

The root cause analysis may (at least partially) be conducted by a processing algorithm 108 located at the RAN node 103 based on the information INF_ADDR_RAT_RLF, INF_CONTEXT_ACCESS and (optionally) INF_ADDITIONAL transferred by the UE 101 and information that may be locally available at the RAN node 103, e.g., statistical data from previous root cause analysis in particular related to other UEs. Hence, the processing algorithm 108 can conduct a (partial) root cause analysis without the need of further processing algorithms located in other RAT nodes being involved. The processing algorithm may thus, e.g., update counters for a management plane's monitoring function or issue a

notification to a centralized OAM node via the interfaces of the management plane. However, the processing algorithm 103 may - based on the available information - reach to the conclusion that a processing algorithm 109 located at another RAT's controlling radio node (here: the RAN node 102) is required to perform an efficient root cause analysis with regard to the particular RLF. This RAN node 102 can be identified and thus addressed by the information

INF_ADDR_RAT_RLF supplied by the UE 101 as indicated above. The information that has to be transferred from the RAN node 103 (i.e. the controlling radio node of the RAT to which the UE 101 established a connection) to the RAN node 102 (i.e. the controlling radio node to which the UE 101 was connected before the RLF occurred) may comprise at least the address information of the sender INF_ADDR_RAT_EST and the

information INF_CONTEXT_ACCESS . The processing algorithm 108 of the RAN node 103 (being the source of the information transfer) may also add further information INF_ADDITIONAL_0THER_RAT to such message 107 conveyed to the RAN node 102. Said further information

INF_ADDITIONAL_0THER_RAT may help analyzing the root cause of the RLF. For example, the information INF_ADDITIONAL conveyed by the UE 101 to the RAN node 103 could be a part of this information INF_ADDITIONAL_0THER_RAT .

The processing algorithm 109 in the RAN node 102 (the

"analyzing node") may thus access the UE ' s context

information INF_UE_CONTEXT by utilizing the information

INF_CONTEXT_ACCESS conveyed by the message 107.

The context information INF_UE_CONTEXT may comprise a set of information, which was needed when the UE 101 was being served by the RAN node 102. The context information

INF_UE_CONTEXT was stored at the RAN node 102 when the UE 101 entered (was connected to) the RAN node 102 based on a connected mode mobility activity. As this context information INF_UE_CONTEXT is stored for some time at the RAN node 102 before being deleted, it may still be available when the message 107 arrives from the RAN node 103. The processing algorithm 109 may thus use this context information

INF_UE_CONTEXT for the root cause analysis.

Fig.2 shows a schematic diagram visualizing a next step of the root cause analysis depicted in Fig.l. Depending on the result of the root cause analysis, it may be necessary

- to inform the RAN node 103 (identified by the

information INF_ADDR_RAT_EST ) by a message 204 sent from the RAN node 102 to the RAN node 103; or

- to inform an additional RAN node 201 of another RAT 205 by sending a message 203 from the RAN node 102 to this RAN node 201. It is noted that the RAT 205 can be the same radio access technology as either the RAT 104 or the RAT 105. Also, the RAT 205 can be different from both RATs 104, 105.

The address information INF_ADDRESS_RAT of this RAN node 201 can be retrieved from the UE context INF_UE_CONTEXT .

For example, the RAN node 103 identified by

INF_ADDRES_RAT_EST can be informed by the RAN node 102 in case the root cause analysis (conducted by the processing algorithm 109) detects that the handover has been conducted too early. The RAN node 201 identified by the address information INF_ADDRESS_RAT can be informed in case the root cause analysis (conducted by the processing algorithm 109) detects that the handover has been conducted to the wrong RAT. In addition, the processing algorithm 109 may decide not to convey any message to another node in case the root cause analysis indicates that the handover has been conducted too late . As stated above, the processing algorithm 108 at the RAN node 103 may provide a pre-analysis of the root cause of the RLF. Based on this pre-analysis, the processing algorithm 108 may conclude that a local root cause analysis is feasible. In this case, no message 107 needs to be sent.

Otherwise, the RAN node 103 conveys the message 107 to the RAN node 102. After having received this message 107, the processing algorithm 109 of the RAN node 102 performs the root cause analysis using the information conveyed by the message 107 and the (locally available) context information INF_UE_CONTEXT associated with the UE 101. As a result of the root cause analysis conducted by the processing algorithm 109, the RAN node, which served the UE 101 before the RAN node 102 via a different RAT (compared to the RAT of the RAN node 102), may have to be informed about the result of the root cause analysis (see Fig.2) . Pursuant to such information, countermeasures , e.g., to avoid future RLFs, can be initiated.

There are various alternatives for conveying information between the RAN nodes of different RATs involved. The messages 107, 203 and 204 shown in Fig.l and Fig.2 are conveyed via the core network 106.

The approach suggested herein can be implemented, e.g., by providing or defining the following procedures:

- Add information elements (IEs) to existing

procedures ;

- Add IEs to existing containers that are transferred transparently across the core network;

- Use an RAN Information Management (RIM) framework.

It is noted that a procedure may comprise one or more messages that can be conveyed between network nodes of the wireless network. It is further noted that the blocks shown in Fig.l and Fig.2 could be implemented by a person skilled in the art as various physical units, wherein the mobile terminal 101 or the RAN nodes 102, 103, 201 could be realized each as at least one logical entity that may be deployed as hardware, program code, e.g., software and/or firmware, running on a processing unit, e.g., a computer, microcontroller, ASIC, FPGA and/or any other logic device. The functionality described herein may be based on an

existing component of a (wireless) network, which is extended by means of software and/or hardware. The RAN node mentioned herein could also be referred to as any base station, base transceiver station or base station controller pursuant to any communication standard.

The RAN node shown may comprise at least one logical or physical processing unit that is arranged for conveying a message to a node of another radio access technology; this message may be provided pursuant to a radio link failure of a mobile terminal.

List of Abbreviations :

3GPP 3rd Generation Partnership Project

C-RNTI Cell Radio Network Temporary Identifier

ECGI Evolved Cell Global Identity

eNodeB evolved NodeB (base station)

E-RAB E-UTRAN Radio Access Bearer

E-UTRAN Evolved UTRAN

IE Information Element

MRO Mobility Robustness Optimization

OAM Operation Administration and Maintenance

LTE Long-Term Evolution

PCI Physical Cell Identity

PLMN Public Land Mobile Network

PM Performance Monitoring

RAN Radio Access Network

RAT Radio Access Technology

RIM RAN Information Management

RLF Radio Link Failure

RRC Radio Resource Control

UE User Equipment (mobile terminal)

UMTS Universal Mobile Telecommunications System

UTRAN UMTS Terrestrial Radio Access Network

Claims

A method for data processing in a wireless network,

The method according to claim 1, wherein after the radio link failure the mobile terminal is connected to the node of the first radio access technology.

The method according to any of the preceding claims, wherein one of the first or second radio access

technology is an LTE access technology and the other is in particular a legacy radio access technology.

The method according to any of the preceding claims, wherein a root cause analysis of the radio link failure is conducted by the node of the first radio access technology based on information provided by the mobile terminal .

The method according to claim 4, wherein the information provided by the mobile terminal comprises at least one of the following:

- an address information of the node of the second

- additional information.

The method according to any of the preceding claims, wherein the message conveyed from the node of the first radio access technology to the node of the second radio access technology comprises at least one of the

following : - an address information of the node of the first radio access technology;

- additional information.

The method according to any of the preceding claims, wherein a root cause analysis is conducted by the node of the second radio access technology based on the message provided.

The method according to claim 7, wherein based on the root cause analysis, at least one of the following steps is conducted:

- a first message is sent to the node of the first

- a second message is sent to the node of the first

- no message is sent indicating that the handover of the mobile terminal occurred too late.

The method according to any of claims 7 or 8, wherein the root cause analysis is conducted by the node of the second radio access technology based on the message provided and based on information locally available.

The method according to any of claims 4 to 9, wherein the node of the first radio access technology or the node of the second radio access technology informs at least one other node that served the mobile terminal about a result of the root cause analysis.

11. The method according to any of claims 4 to 10, wherein mobility parameters of the wireless network are set or changed based on the root cause analysis provided.

12. A device for data processing in a wireless network

comprising a processing unit that is arranged

13. The device according to claim 12, wherein said device is a device of the wireless network, in particular a network node, a base station or a base station

controller .

14. A communication system comprising at least one device according to any of claims 12 or 13.