EP3857943A1

EP3857943A1 - Network entity and base stations for network access management

Info

Publication number: EP3857943A1
Application number: EP18786264.4A
Authority: EP
Inventors: Alexandros KALOXYLOS; Chan Zhou; Panagiotis SPAPIS
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2018-10-09
Filing date: 2018-10-09
Publication date: 2021-08-04
Also published as: CN112889306A; CN112889306B; WO2020074066A1

Abstract

The invention relates to a network management entity (101) for managing access of a user equipment (107) to a wireless communication network (100) having a plurality of base stations, wherein the network management entity (101) is configured to select for a first base station (103), which is configured to serve the user equipment (107), a second base station (105) from the plurality of base stations as a backup base station for the user equipment (107).

Description

NETWORK ENTITY AND BASE STATIONS FOR NETWORK ACCESS MANAGEMENT

TECHNICAL FIELD

In general, the present invention relates to communication networks. More specifically, the present invention relates to a network management entity for managing access of a user equipment to a wireless communication network, a base station and a user equipment of the wireless communication network.

BACKGROUND

Vehicular communication use cases (often referred to as V2V and or V2X) require high reliability and availability. The reliability is defined as the proper reception of a message in a certain time period and availability is the amount of time when the system is able to operate reliably (see EU FP7 INFSO-ICT-317669 METIS, D1.1 Scenarios, requirements and KPIs for 5G mobile and wireless system, Popovski et. al., 2013). In general, both terms can be captured by the term reliability in a broad sense. However, due to hardware and software failures some parts of a V2X network do not manage to perform as planned so the forecasted service cannot be delivered in a reliable way.

If a user equipment (UE) is unexpectedly out of coverage, i.e., a situation called“cell outage”, due to, for example, a failure of an access network element (e.g., a base station, eNB or gNB), the UE has to be re-connected with a new access network element and resumes its operations. For simplicity, all the access network elements in the following will be called a base station (BS) and this term will include all types of access network elements such as a base station, eNB, gNB, etc.

Conventionally, the cell outage can be handled by self-healing: neighboring base stations (BSs) usually detect a cell outage and use algorithms to increase or modify their own coverage to fill in the spectrum hole by increasing their transmission power. Algorithms have been proposed to even predict such outages based on data analytics schemes (see M. Zeeshan et. al., Towards Proactive Context-Aware Self-Healing for 5G networks, Computer Networks, Elsevier, 2017). However, these actions are related to a network re-configuration of base stations. The UE needs still to perform cell selection and then re-connect as soon as possible to the new BS resulting in further delays. The cell outage can also be handled by a forward handover: the UE has to re-connect very rapidly to a new base station (BS). Currently this process may require a delay up to 50-60 milliseconds for a backward handover (see K. Alexandris et. al. , Analyzing X2 Handover in LTE/LTE-A, IEEE WiOpt 2016). This has to be minimized for delay-critical services that require delays of 3 to 50 milliseconds.

Moreover, cell re-selection has to be improved: in particular, when the UE detects radio link problems, it starts the Radio Link Failure (RLF) Timer (e.g., 50 milliseconds), and then the UE searches for a suitable new base station (BS) and attempts to re-establish its connection to this target BS. If the target BS does not have the context for the UE, it fetches the context of the UE from the source BS. In case of a BS failure, this would add delays since the new BS does not know from where to retrieve the UE context and has to obtain it from a mobility server (e.g., Mobility Management Entity in LTE systems).

As discussed above, it is obvious that the current approaches of the state of the art do not manage to perform fast reconnection (i.e. , fast forward handover) to the network, since the UE has to identify the base station to attach to and the base station selected by the UE may not have the UE context available and, thus, has to retrieve it from the core network, thus adding delays.

Apart from the standards, some studies have tried to deal with the cell outage problem. For instance, US20090046573 identifies a mechanism for forward handover not due to a BS failure but due to a link failure. However, the described mechanism is not suitable for low latency services such as vehicular communications, since it cannot solve the problem of context transfer in case of failures and requires the whole cell selection and reselection procedure to be performed.

Furthermore, CN101800982 provides a mechanism aiming to reduce the authentication time in case of a failure. However, the problem of the context transfer and a new serving BS is still not solved.

In light of the above, there is a need for improved devices and methods for managing access of a user equipment to a wireless communication network.

SUMMARY It is an object of the invention to provide improved devices and methods for managing access of a user equipment to a wireless communication network.

The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

Generally, embodiments of the invention relate to a network management entity for managing access of a user equipment to a wireless communication network efficiently with reduced delay time, a base station as well as a user equipment for such a wireless communication network.

Embodiments of the invention facilitate the network to deliver a service even when a failure of a serving access network element happens by using backup access network elements (e.g., base stations, access points, etc.). The backup access network elements are fully prepared to accommodate a user equipment (UE) in case the serving access network element fails. Additionally, the UE can also be informed which is the backup access network element for facilitating the fast connection to it.

More specifically, according to a first aspect, the invention relates to a network management entity for managing access of a user equipment to a wireless communication network having a plurality of base stations, wherein the network management entity is configured to select for a first base station, which is configured to serve the user equipment, at least one second base station from the plurality of base stations, which is configured to server the user equipment as a backup base station.

The network management entity could be a network management system and/or a mobility management server/function.

Thus, an improved network management entity is provided for managing access of a user equipment to a wireless communication network with reduced delays.

In a further possible implementation form of the first aspect, the network management entity is configured to select the second base station from the plurality of base stations on the basis of information about the first base station. In a further possible implementation form of the first aspect, the user equipment is a mobile user equipment and the network management entity is configured to select the second base station from the plurality of base stations on the basis of information about a location and/or a motion state, i.e. direction and/or velocity, of the user equipment.

In a further possible implementation form of the first aspect, the network management entity is configured to obtain context information about the user equipment and to provide the context information to the selected second base station, wherein the context information allows the selected second base station to establish a connection with the user equipment.

The context information can be an identifier of the UE.

In a further possible implementation form of the first aspect, the network management entity is configured to provide the context information about the user equipment to the selected second base station, when providing the context information to the first base station, in response to the user equipment attaching, in particular an attachment request to the first base station, wherein the context information allows the selected second base station to establish a connection with the user equipment.

In a further possible implementation form of the first aspect, the network management entity is configured to provide information, in particular an address and/or an identifier, about the selected second base station to the first base station and to trigger the first base station to provide context information about the user equipment to the selected second base station, wherein the context information allows the selected second base station to establish a connection with the user equipment.

In a further possible implementation form of the first aspect, the network management entity is configured to provide information, in particular an address and/or an identifier, about the selected second base station and/or a timer for a failure identification to the user equipment and/or a mobility management server.

In a further possible implementation form of the first aspect, the network management entity is configured to trigger the user equipment to disconnect from the first base station and to attach to the selected second base station.

In a further possible implementation form of the first aspect, the network management entity is configured, in case the user equipment performs a handover to a third base station for serving the user equipment, to select a fourth base station as a new backup base station for the user equipment.

The fourth base station can be the first base station, the second base station or a different one.

According to a second aspect, the invention relates to a first base station for providing a user equipment access to a wireless communication network having a plurality of base stations, wherein the first base station is configured to: select from the plurality of base stations a second base station as a backup base station for the user equipment; and/or receive information, in particular an address and/or an identifier, about the second base station selected as a backup base station for the user equipment.

Thus, an improved serving base station is provided, allowing a user equipment access to a wireless, in particular 5G, communication network having a plurality of base stations efficiently with reduced time delays.

In a further possible implementation form of the second aspect, the first base station is configured to obtain context information about the user equipment and to provide the context information to the second base station, wherein the context information allows the second base station to establish a connection with the user equipment.

In a further possible implementation form of the second aspect, the first base station is configured to select the second base station from the plurality of base stations on the basis of radio measurements provided by the user equipment.

The above radio measurements could be received signal strength (RSS), received signal strength indicator (RSSI), reference signal received power (RSRP), reference signal received quality (RSRQ) or any other type of radio measurement.

In a further possible implementation form of the second aspect, the first base station is configured to provide information, in particular an address and/or an identifier, about the second base station selected as a backup base station to the user equipment.

In a further possible implementation form of the second aspect, the first base station is configured to trigger the user equipment to disconnect from the first base station and to attach to the second base station. According to a third aspect the invention relates to a second base station for serving as a backup base station for a user equipment in a wireless communication network having a plurality of base stations, wherein the second base station is configured to: receive context information about the user equipment, wherein the user equipment is currently being served or going to be served by a first base station; and reserve (i.e. pre-allocate) on the basis of the context information one or more PRACH preambles for the user equipment for accessing the second base station.

Thus, an improved backup base station is provided, allowing a user equipment access to a wireless, in particular 5G, communication network having a plurality of base stations efficiently with reduced time delays.

In a further possible implementation form of the third aspect, the second base station is configured to provide the one or more PRACH preambles to the user equipment via the first base station.

According to a fourth aspect the invention relates to a third base station for providing a user equipment access to a wireless communication network having a plurality of base stations, wherein the third base station is configured to: in response to a handover of the user equipment from a first serving base station to the third base station, select from the plurality of base stations a fourth base station as a backup base station for the user equipment; and/or receive information, in particular an address and/or an identifier, about a fourth base station selected as a backup base station for the user equipment.

Thus, an improved base station being a handover target base station is provided, allowing a user equipment access to a wireless, in particular 5G, communication network having a plurality of base stations efficiently with reduced time delays.

According to a fifth aspect the invention relates to a user equipment for accessing a wireless communication network having a plurality of base stations, wherein the user equipment is configured to: receive from a first base station information, in particular an address and/or an identifier, about a second base station selected as a backup base station for the user equipment; and disconnect from the first base station and attach to the second base station on the basis of the information about the second base station. Thus, an improved user equipment is provided, allowing the user equipment access to a wireless, in particular 5G, communication network having a plurality of base stations efficiently with reduced time delay.

In a further possible implementation form of the fifth aspect, the user equipment is configured to receive from the first base station one or more PRACH preambles and to attach to the second base station using the one or more PRACH preambles.

In a further possible implementation form of the fifth aspect, the user equipment is configured to trigger the handover to the second base station, for instance, due to the expiration of a timer. The timer can be provided by the first base station. Alternatively, the timer can be preconfigured or statically configured.

According to a sixth aspect the invention relates to a wireless communication network comprising a network management entity according to the first aspect, a plurality of base stations according to any one of the second to fourth aspect and/or a user equipment according to the fifth aspect.

Thus, an improved wireless communication network is provided, allowing a user equipment access to the wireless communication network efficiently with reduced time delays.

According to a seventh aspect the invention relates to a method for managing access of a user equipment to a wireless communication network having a plurality of base stations.

The method comprises the steps of selecting for a first base station, which is configured to serve the user equipment, a second base station from the plurality of base stations as a backup base station for the user equipment.

Thus, an improved method is provided, allowing a user equipment access to a wireless, in particular 5G, communication network efficiently with reduced time delays.

The invention can be implemented in hardware and/or software.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect to the following figures, wherein: Figure 1 shows a schematic diagram of a wireless communication network according to an embodiment;

Figure 2 shows a schematic diagram illustrating a configuration procedure according to an embodiment;

Figure 3 shows a schematic diagram illustrating an attachment procedure according to an embodiment;

Figure 4 shows a schematic diagram illustrating a forward handover procedure according to an embodiment;

Figure 5 shows a schematic diagram illustrating a forward handover procedure according to an embodiment;

Figure 6 shows a schematic diagram illustrating a procedure for identifying a backup base station according to an embodiment;

Figure 7 shows a schematic diagram illustrating a procedure for context transfer upon handover according to an embodiment; and

Figure 8 shows a schematic diagram illustrating a method for managing access of a user equipment to a wireless communication network according to an embodiment.

In the various figures, identical reference signs will be used for identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the present invention may be placed. It will be appreciated that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the present invention is defined by the appended claims. For instance, it will be appreciated that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures.

Moreover, in the following detailed description as well as in the claims embodiments with different functional blocks or processing units are described, which are connected with each other or exchange signals. It will be appreciated that the present invention covers embodiments as well, which include additional functional blocks or processing units that are arranged between the functional blocks or processing units of the embodiments described below.

Finally, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.

As will be described in more detail in the following, embodiments of the invention can reduce the time required for a user equipment (UE) to handover to a new base station (BS), in case of a failure from the serving base station, by defining backup base stations which will serve the UE. According to the embodiments of the invention, a backup base station can be identified and signaled to the UE, and the context of a UE can be transferred to the backup base station when it is being transferred to the serving base station for being used in case the serving base station fails. Furthermore, the UE can be informed about its backup base station so as to be able to perform fast connection to the pre-identified/predefined base station. Further optimizations such as Physical Random Access Channel Preamble (PRACH preamble) pre-allocation to the UEs may take place.

Figure 1 shows a schematic diagram of an exemplary wireless communication network 100 according to an embodiment, wherein the wireless communication network 100 comprises a network management entity 101 , a user equipment (UE) 107 as well as a plurality of base stations including a first base station 103 and a second base station 105. In this embodiment, the network management entity 101 is a mobility server, the first base station 103 is currently serving or going to serve the user equipment 107 and the second base station 105 is a backup base station. In further embodiments described below, the network management entity 101 can be a Network Management, NM, system or server or implemented as both a mobility server and a NM server. Once the UE 107 connects to the first base station 103, the UE context, in particular an identifier of the EU 107, can be transferred to both the serving base station 103 and the backup base station 105, which is signaled to the UE 107. If the first base station 103 fails, then the UE 107 can identify the failure and can directly connect to the second base station 105 without having to perform cell selection and without having to perform the connection establishment procedure with the UE context transfer from the mobility server 101 to the backup base station 105.

In other words, the network management entity 101 is configured to select for the first base station 103, which is currently serving or going to serve the user equipment 107, the second base station 105 from the plurality of base stations as a backup base station for the user equipment 107 on the basis of information about the first base station 103 or/and information about a location and/or a motion state of the user equipment 107.

Furthermore, the network management entity 101 can be configured to obtain context information about the user equipment 107 and to provide the context information to the second base station 105, when providing the context information to the first base station 103, in response to the user equipment attaching, in particular an attachment request to the first base station 103. The context information allows the second base station 105 to establish a connection with the user equipment 107.

Furthermore, the network management entity 101 can be configured to provide information, in particular an address and/or an identifier, about the second base station 105 to the first base station 103 and to trigger the first base station 103 to provide context information about the user equipment 107 to the second base station 105. Also, the network management entity 101 can provide information about the second base station 105 to the user equipment 107 and/or a mobility management server.

Alternatively, the first base station 103 can be configured to select from the plurality of base stations a second base station 105 as a backup base station for the user equipment 107 and/or receive information about a second base station 105 selected as a backup base station for the user equipment 107. The first base station 103 can obtain context information about the user equipment 107 and to provide the context information to the second base station 105, wherein the context information allows the second base station 105 to establish a connection with the user equipment 107. In an embodiment, the first base station 103 can be configured to select the second base station 105 from the plurality of base stations on the basis of radio measurements provided by the user equipment 107, wherein the radio measurements could be received signal strength (RSS), received signal strength indicator (RSSI), reference signal received power (RSRP), reference signal received quality (RSRQ) or any other radio measurement.

In an embodiment, the first base station 103 can be configured to provide information about the second base station 105 selected as a backup base station to the user equipment 107. The user equipment 107 can be configured to receive from the first base station 103 information about the second base station 105 selected as a backup base station for the user equipment 107 and disconnect from the first base station 103 and attach to the second base station 105 on the basis of the information about the second base station 105.

The second base station 105 for serving as a backup base station for the user equipment 107 can be configured to receive context information about the user equipment 107 and reserve on the basis of the context information one or more PRACH preambles for the user equipment 107.

In an embodiment, the network management entity, in particular mobility server 101 can be configured to trigger the user equipment 107 to disconnect from the first base station 103 and to attach to the second base station 105. Or the first base station 103 can also trigger the user equipment 107 to disconnect from the first base station 103 and to attach to the second base station 105. Then, the user equipment 107 can be configured to disconnect from the first base station 103 and attach to the second base station 105 on the basis of the information about the second base station 105.

In an embodiment, the second base station 105 is configured to provide one or more PRACH preambles to the user equipment 107 via the first base station 103, and the user equipment 107 is configured to receive from the first base station 103 one or more PRACH preambles and to attach to the second base station 105 using the one or more PRACH preambles.

In a further embodiment, the network management entity 101 is configured to select a fourth base station as a new backup base station for the user equipment 107, in case the user equipment 107 performs a handover to a third base station for serving the user equipment 107. Alternatively, the third base station can select from the plurality of base stations a fourth base station as a backup base station for the user equipment 107, in response to a handover of the user equipment 107 from the first base station 103 to the third base station. Moreover, the third base station can receive information about a fourth base station selected as a backup base station for the user equipment 107.

Thus, embodiments of the invention enable the identification of backup base stations to serve the UE 107 in case the serving base station fails. Moreover, the backup base station can be p re-configured in terms of context transferring and preparation to serve a UE that comes from a failed base station. As already described above, embodiments of the invention can include additional aspects, such as the RACH (Random Access Channel Preamble) preamble provision in advance for reducing the reconnection time, or the network operation in handovers.

Embodiments of the invention may be split into three procedures: first of all, a configuration procedure when a backup base station is being identified; secondly, an attachment procedure when the UE 107 attaches to the network 100 and is being informed or configured about to perform forward handover in case of a failure; thirdly, a forward handover procedure when the UE 107 is being handed over to a new base station because of a failure. These procedures will be further elaborated in the following under reference to figures 2 to 5.

Figure 2 shows a schematic diagram illustrating a configuration procedure 200 when the backup base station 105 according to an embodiment is being identified.

During the configuration procedure, a Network Management (NM) system 101 b identifies at least one backup base station (bBS) 105 for every base station in case it fails. This information is being provided to the Mobility Management (MM) server 101 a (step 201 in figure 2). Thus, in the embodiment shown in figure 2 the network management entity, i.e. mobility server 101 of figure 1 is implemented in a distributed fashion as the NM system 101 b and the MM server 101 a, as already described above. Alternative implementations could integrate the presence of this information to one or more centrally located servers with similar functionality. For instance, in an embodiment the MM server 101 a could also provide the functionality of the NM system 101 b and, therefore, implement the network management entity 101 according to embodiments of the invention.

Figure 3 shows a schematic diagram illustrating an attachment procedure 300 according to an embodiment when the UE 107 attaches to the network 100 and is being informed or configured to perform forward handover in case of a failure. The procedure 300 shown in figure 3 comprises the following steps:

Step 301 : the UE 107 sends an attachment request to the serving base station 103.

Step 303: the serving base station 103 forwards the attachment request to the mobility management (MM) server 101 a.

Step 305: the mobility management (MM) server 101 a transmits an initial context setup response with the typical parameters and information about a backup base station, in particular an identifier, to the serving base station 103. Additionally, it may provide timer information to be used by the UE 107 for the identification of a BS failure. This can be a RFL timer known from LTE.

Step 307: the serving base station 103 performs RRC connection reconfiguration to the UE 107 (as will be appreciated embodiments of the invention can make use of radio control protocols other than LTE RRC). In this message it provides the typical RRC parameters together with information about a backup base station, in particular an identifier, to the serving base station 103. Additionally, it may provide the timer information to be used by the UE 107 for the identification of a BS failure.

Step 309: the UE 107 sends a message indicating“RRC connection complete” to the serving base station 103.

Step 31 1 : the base station 103 sends a response to the initial context setup request to the mobility management (MM) server 101 a.

Step 313: the mobility management (MM) server 101 a transmits a context setup request to a backup base station 105, wherein the mobility management (MM) server 101 a provides the UE context to the backup base station 105 together with an indication that it will act as a backup base station 105.

Upon the configuration, the mobility management (MM) server 101 a is aware of a suitable backup base station (bBS) 105 for every base station in the area under its control. Thus, after the UE 107 attaches to the network, the UE context is being transferred to the serving base station 103. The attachment procedure here refers to an initial connection of a UE to the network 100, which is similar to the attachment process of a UE in the LTE network systems.

Once the attachment procedure is finalized, the serving base station 103 responds accordingly to the mobility management (MM) server 101 a and the later provides the UE context to the backup base station (bBS) 105, together with an indication that the base station will act as a backup base station (bBS) 105 for the respective UE. The backup base station (bBS) 105 does not reserve resources for the UE operation but maintains the UE context. This is captured by the inactive state in LTE systems (also known as Connected Inactive, Idle Connected, etc).

In a further embodiment, the backup base station (bBS) 105 may reserve a RACH preamble for the UE 107 in case of a failure so as to minimize the time required for the fast UE connection to the backup base station (bBS) 105. The backup base station (bBS) 105 will inform the serving base station 103 about this reservation and the latter will provide this information to the UE 107 respectively.

In a further embodiment, the UE context can be transferred to the backup base station (bBS) 105 directly from the base station 103.

According to an embodiment, fast forward handover may happen for two reasons: the UE 107 identifies the failure or/and the serving base station 103 identifies a failure and indicates to the UE 107 that it should handover. The specific implementations for these two cases can be implemented using different signaling, which is described in more detail below under reference to figures 4 and 5.

Figure 4 shows a schematic diagram illustrating a forward handover procedure according to an embodiment, wherein the UE 107 is being handed over to a new base station because the UE 107 identifies a failure.

The UE 107 is provided with a timer which indicates a radio link failure or a base station failure. This may be the radio link failure (RLF) timer existing in LTE systems for indicating the need for a forward handover due to a link failure or a new timer for the identification of a base station failure. In Figure 3, an exemplary implementation is shown on how this timer can be provided to the UE 107 in the RRC connection reconfiguration, during the initial attach. In other implementations the timer may be preconfigured to the UE 107. Once this timer expires, the UE 107 performs a Radio Resource Control (like the RRC in LTE systems, for simplicity hereafter referred to as RRC) connection request to the backup base station (bBS) 105 already known to the UE 107. If a RACH preamble is available, then the UE 107 will use it for performing fast connection re-establishment. The backup base station (bBS) 105, since it has the UE context already available, may proceed to connection re establishment without having to communicate with the mobility management (MM) server 101 a or any other core network entity in advance. Then, once the RRC connection is re established the backup base station (bBS) 105 can inform the mobility management (MM) server 101 a accordingly and ask for data path switching and new bearer setup. An exemplary procedure for a forward handover is schematically captured in figure 4. The procedure 400 shown in figure 4 comprises the following steps:

Step 401 : the UE 107 sends a request for RRC connection re-establishment to the backup base station (bBS) 105.

Step 403: the backup base station (bBS) 105 responds to the UE 107.

Step 405: the UE 107 informs the backup base station (bBS) 105 about RRC connection reestablishment complete.

Step 407: the backup base station (bBS) 105 sends a path switch request to the mobility management (MM) server 101 a.

Step 409: the mobility management (MM) server 101 a sends an acknowledgement message for path switch request to the backup base station 105.

Figure 5 shows a schematic diagram illustrating a forward handover procedure according to an embodiment, wherein the UE 107 is being handed over to a new base station because the serving base station 103 identifies a failure.

If the base station 103 identifies that it may not offer the service any more due to a partial failure, it may signal this to the UE 107 and the latter may proceed to a forward handover without waiting for the timer to expire. Upon the notification from the base station 103, the UE 107 performs an RRC connection request to the backup base station (bBS) 105 already known to the UE 107. If a RACH preamble is available, then the UE 107 can use it for performing fast connection re-establishment. The backup base station (bBS) 105, since it has the UE 107 context already available, may proceed to connection re-establishment without having to communicate with the mobility management (MM) server 101 a or any other core network entity in advance. Then, once the RRC connection is re-established the backup base station (bBS) 105 will inform the mobility management (MM) server 101 a accordingly and ask for data path switching and new bearer setup. An exemplary procedure for a forward handover is schematically captured in figure 5. The procedure 500 shown in figure 5 comprises the following steps:

Step 501 : the base station 103 signals to the UE 107 that it may not offer the service any more due to a partial failure.

Step 503: the UE 107 sends a request for RRC connection re-establishment to the backup base station (bBS) 105.

Step 505: the backup base station (bBS) 105 responds to the UE 107. Step 507: the UE 107 informs the backup base station (bBS) 105 about RRC connection reestablishment complete.

Step 509: the backup base station (bBS) 105 sends a path switch request to the mobility management (MM) server 101 a.

Step 51 1 : the mobility management (MM) server 101 a sends an acknowledgement message for path switch request to the backup base station 105.

According to an embodiment, the backup base station 105 can be selected from a plurality of base stations on the basis of radio measurements provided by the user equipment 107, wherein the radio measurements could be a received signal strength (RSS), a received signal strength indicator (RSSI), a reference signal received power (RSRP), a reference signal received quality (RSRQ) or any other type of radio measurement.

Figure 6 shows a schematic diagram illustrating a procedure for identifying a backup base station 105 according to an embodiment, wherein the backup base station 105 is identified via the radio measurements by the UE 107. The procedure 600 shown in figure 6 comprises the following steps:

Step 601 : the UE 107 sends an attachment request to the serving base station 103.

Step 603: the serving base station 103 forwards the attachment request to the mobility management (MM) server 101 a.

Step 605: the mobility management (MM) server 101 a transmits an initial context setup request for typical parameters to the serving base station 103.

Step 607: the serving base station 103 performs RRC connection reconfiguration to the UE 107.

Step 609: the UE 107 sends a message indicating“RRC connection complete” to the serving base station 103.

Step 61 1 : the UE 107 provides its handover measurements to the serving base station 103. Step 613: the serving base station 103 informs the selected base station 105 that it is selected as a backup base station 105 and provides the UE context to the selected backup base station 105.

As shown in figure 6, the backup base station 105 is identified by the serving base station 103 based on the handover measurements of the UE 107. In particular, upon the UE attachment to the network 100, the UE context is being transferred to the serving base station 103. The attachment procedure here refers to the initial connection of the UE 107 to the network 100, which can be similar to the attachment process of a UE in the LTE network systems.

The UE 107 provides its handover measurements to the serving base station 103. Thus, the serving base station 103 identifies the most suitable base station from its neighboring base stations to act as the backup base station 105 in case of a failure. The serving base station 103 can further inform the selected base station 105 and meanwhile may directly provide the UE context for the selected backup base station 105. The serving base station 103 may also provide the UE context for the selected backup base station 105 in a later phase, or alternatively the mobility management (MM) server 101 a may provide the UE context to the selected backup base station 105.

In a further embodiment, a new backup base station has to be identified and its context has to be transferred accordingly when the UE 107 performs a handover. This may be done either directly from the serving base station 103 or from the mobility management (MM) server 101 a. The backup base station may be identified based on the lists of the mobility management (MM) server 101 a provided by the network management system 101 b or from the UE measurements (once the handover is finalized).

Figure 7 shows a schematic diagram illustrating a procedure for context transfer upon handover according to an embodiment. The procedure 700 shown in figure 7 comprises the following steps:

Step 701 : the UE 107 sends measurement reports to the serving (source) base station 103. Step 703: The serving (source) base station 103 identifies a target base station 731 based on the measurements sent from the UE 107.

Step 705: the handover is executed.

Step 707: the target base station 731 performs RRC connection reconfiguration to the UE 107.

Step 709: the UE 107 sends a message indicating“RRC connection complete” to the target base station 731.

Step 71 1 : the target base station 731 sends a path switch request to the mobility management (MM) server 101 a.

Step 713: the mobility management (MM) server 101 a sends a response to the path switch request to the target base station 731. Step 715: the mobility management (MM) server 101 a transmits a context setup request for typical parameters of initial context setup, request, or indication to act as a backup base station to the backup base station 105.

As shown in figure 7, the backup base station 105 is identified based on the lists of the mobility management (MM) server 101 a. The source (serving) base station 103 identifies the target base station based on the UE measurements (standard procedure) and then the handover is executed. Upon the execution of the handover, the target (now serving) base station informs the UE 107 for the backup base station along with typical parameters such as the timer for the failure. The mobility management (MM) server 101 a is informed about path switching because of the handover and then automatically provides the context of the UE 107 to the backup base station 105 accordingly.

Figure 8 shows a schematic diagram illustrating a method 800 for managing access of the user equipment 107 to the wireless communication network 100 having a plurality of base stations according to an embodiment. The method comprises the step 801 of selecting for the first base station 103, which is configured to serve, i.e. currently serving or going to serve the user equipment 107, a second base station 105 from the plurality of base stations as a backup base station for the user equipment 107.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms“coupled” and“connected”, along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein.

Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A network management entity (101 ) for managing access of a user equipment (107) to a wireless communication network (100) having a plurality of base stations, wherein the network management entity (101 ) is configured to select for a first base station (103), which is configured to serve the user equipment (107), a second base station (105) from the plurality of base stations, which is configured to serve the user equipment (107) as a backup base station.

2. The network management entity (101 ) of claim 1 , wherein the network management entity (101 ) is configured to select the second base station (105) from the plurality of base stations on the basis of information about the first base station (103).

3. The network management entity (101 ) of claim 1 or 2, wherein the user equipment (107) is a mobile user equipment and wherein the network management entity (101 ) is configured to select the second base station (105) from the plurality of base stations on the basis of information about a location and/or a motion state of the user equipment (107).

4. The network management entity (101 ) of any one of the preceding claims, wherein the network management entity (101 ) is configured to obtain context information about the user equipment (107) and to provide the context information to the second base station (105), wherein the context information allows the second base station (105) to establish a connection with the user equipment (107).

5. The network management entity (101 ) of claim 4, wherein the network management entity (101 ) is configured to provide the context information about the user equipment (107) to the second base station (105), when providing the context information to the first base station (103), in response to the user equipment attaching, in particular an attachment request to the first base station (103), wherein the context information allows the second base station (105) to establish a connection with the user equipment (107).

6. The network management entity (101 ) of any one of the preceding claims, wherein the network management entity (101 ) is configured to provide information about the second base station (105) to the first base station (103) and to trigger the first base station (103) to provide context information about the user equipment (107) to the second base station (105), wherein the context information allows the second base station (105) to establish a connection with the user equipment (107).

7. The network management entity (101 ) of any one of the preceding claims, wherein the network management entity (101 ) is configured to provide information about the second base station (105) and/or a timer for a failure identification to the user equipment (107) and/or a mobility management server.

8. The network management entity (101 ) of any one of the preceding claims, wherein the network management entity (101 ) is configured to trigger the user equipment (107) to disconnect from the first base station (103) and to attach to the second base station (105).

9. The network management entity (101 ) of any one of the preceding claims, wherein the network management entity (101 ) is configured, in case the user equipment (107) performs a handover to a third base station for serving the user equipment (107), to select a fourth base station as a new backup base station for the user equipment (107).

10. A first base station (103) for providing a user equipment (107) access to a wireless communication network (100) having a plurality of base stations, wherein the first base station (103) is configured to: select from the plurality of base stations a second base station (105) as a backup base station for the user equipment (107); and/or receive information about a second base station (105) selected as a backup base station for the user equipment (107).

1 1. The first base station (103) of claim 10, wherein the first base station (103) is configured to obtain context information about the user equipment (107) and to provide the context information to the second base station (105), wherein the context information allows the second base station (105) to establish a connection with the user equipment (107).

12. The first base station (103) of claim 10 or 1 1 , wherein the first base station (103) is configured to select the second base station (105) from the plurality of base stations on the basis of radio measurements provided by the user equipment (107).

13. The first base station (103) of any one of claims 10 to 12, wherein the first base station (103) is configured to provide information about the second base station (105) selected as a backup base station to the user equipment (107).

14. The first base station (103) of any one of claims 10 to 13, wherein the first base station (103) is configured to trigger the user equipment (107) to disconnect from the first base station (103) and to attach to the second base station (105).

15. A second base station (105) for serving as a backup base station for a user equipment (107) in a wireless communication network (100) having a plurality of base stations, wherein the second base station (105) is configured to: receive context information about the user equipment (107), wherein the user equipment (107) is currently being served or going to be served by a first base station (103); and reserve on the basis of the context information one or more PRACH preambles for the user equipment (107).

16. The second base station (105) of claim 15, wherein the second base station (105) is configured to provide the one or more PRACH preambles to the user equipment (107) via the first base station (103).

17. A third base station for providing a user equipment (107) access to a wireless communication network (100) having a plurality of base stations, wherein the third base station is configured to: in response to a handover of the user equipment (107) from a first base station (103) to the third base station, select from the plurality of base stations a fourth base station as a backup base station for the user equipment (107); and/or receive information about a fourth base station selected as a backup base station for the user equipment (107).

18. A user equipment (107) for accessing a wireless communication network (100) having a plurality of base stations, wherein the user equipment (107) is configured to: receive from a first base station (103) information about a second base station (105) selected as a backup base station for the user equipment (107); and disconnect from the first base station (103) and attach to the second base station (105) on the basis of the information about the second base station (105).

19. The user equipment (107) of claim 18, wherein the user equipment (107) is configured to receive from the first base station (103) one or more PRACH preambles and to attach to the second base station (105) using the one or more PRACH preambles.

20. The user equipment (107) of claim 18 or 19, wherein the user equipment (107) is configured to trigger the handover to the second base station (105), in particular in response to an expiration of a timer.

21. A wireless communication network (100) comprising a network management entity (101 ) according to any one of claims 1 to 9, a plurality of base stations according to any one of claims 10 to 15 and/or a user equipment (107) according to claims 18, 19 or 20.

22. A method (800) for managing access of a user equipment (107) to a wireless communication network (100) having a plurality of base stations, wherein the method (800) comprises the step 801 of selecting for a first base station (103), which is configured to serve the user equipment (107), a second base station (105) from the plurality of base stations as a backup base station for the user equipment (107).