WO2016163937A1

WO2016163937A1 - Handover rejection of incompatible user equipment categories

Info

Publication number: WO2016163937A1
Application number: PCT/SE2016/050287
Authority: WO
Inventors: Kai-Erik Sunell; Henrik Enbuske
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2015-04-10
Filing date: 2016-04-06
Publication date: 2016-10-13

Abstract

A method in a first network node for handover preparation of a user equipment of an additional category in a wireless communications network, wherein the additional category is new relative to one or more legacy categories. The first network node sends (301) to a second network node a message comprising information indicating a request for preparation 5 of a handover of the user equipment, the message including an out-of-range value for one or more fields. The first network node receives (302) from the second network node a message indicating failure to prepare the handover. In some embodiments, the first network node interprets (303) the message indicating failure to prepare the handover as an indication that the second network node does not support any user equipment of the additional category.10

Description

HANDOVER REJECTION OF INCOMPATIBLE USER EQUIPMENT CATEGORIES

TECHNICAL FIELD

The present disclosure is generally related to wireless communication networks, and more particularly related to a method in a network node for handover preparation for user equipment, a method in a user equipment, and a user equipment.

BACKGROUND

Wireless communication devices, referred to herein as "terminals," are also known as, e.g., User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations.

Terminals are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network. Examples of wireless communication systems are Long Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS) and Global System for Mobile communications (GSM). Embodiments herein are illustrated with examples from the Evolved Universal Terrestrial Radio Access (EUTRA), also known as the LTE system.

Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer- comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.

A cellular communications network covers a geographical area that is divided into cell areas, with each cell area being served by an access node such as a base station, e.g. a Radio

Base Station (RBS), which sometimes may be referred to as e.g. "eNB", "eNodeB", "NodeB", "B node", or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes, such as macro eNodeB, home eNodeB, or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the term

"downlink" (DL) is used for the transmission path from the base station to the mobile station. The expression "uplink" (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.

In Long Term Evolution (LTE) networks, as specified by the 3rd Generation Partnership Project (3GPP), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to one or more core networks. The 3GPP LTE radio access standards have been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission in LTE is controlled by the radio base station.

One important function in 3GPP cellular radio technologies is the control of user mobility by using the Radio Resource Control (RRC) and X2AP protocols. The network controls the handover of UEs in RRC Connected mode from one cell to another, whereas a UE in idle mode performs cell selection and reselection itself.

When the UE is handed over from a source cell to a target cell, handover preparation is needed. Upon handover preparation, the target radio base station or eNB is provided the current UE RRC configuration comprised in the handover preparation information message (the HandoverPreparationlnformation message, for example as described in technical Specification TS36.331 , version 12.1.0). This message is used to transfer the E-UTRA RRC information used by the target eNB during handover preparation, and includes UE capability information. The target eNB decides upon an RRC configuration for the UE, to be used after the handover, and therefore a RRC configuration message is transparently sent to the UE via the source eNB as an octet string comprised in the handover command. Normally, a full configuration is required if the target eNB has a different Access Stratum (AS) version than the source eNB.

If the RRC configuration in the handover preparation message is incomplete or the source cell has configured the UE with a RRC protocol version that is not comprehended by the target eNB, the target eNB typically performs a full configuration, if possible. In other words, the target eNB performs a reconfiguration from scratch, in these situations. Otherwise the target eNB may modify or maintain the current RRC configuration.

3GPP has recently agreed, within the scope of a low-cost Machine Type Communication (MTC) work item, to introduce a new UE category termed as category 0, which is considered a "low complexity" category. The UE category defines a combined set of UE capabilities. A draft Change Request (CR) for the introduction of category 0 is available in R2-140964, as presented during RAN2#85 meeting in Prague, February 10-14, 2014, Prague, Czech Republic.

The UEs of this new category are less capable than UEs of legacy category 1 , which was previously the least capable legacy category. "Legacy category UEs" are UEs that implement an older version of the RRC protocol than the new category 0 UE does; these legacy category UEs are defined as categories 1-5, according to Release 8 of the 3GPP standards. Category 0 UEs are thus non-backward-compatible with earlier categories, in the sense that they are less capable than legacy categories, and a UE of such a category does not support any legacy categories as a fallback.

This lack of backwards compatibility can cause problems when a category 0 UE is handed over to a "legacy" target eNB, i.e., an eNB that implements an older version of the RRC protocol than the new category UE 0 UE does. Upon handover of a category 0 UE to a legacy target eNB, the handover preparation phase will be successful, but the subsequent handover will fail, because the legacy eNB and the new category UE, i.e., the category 0 UE, are only partly compatible when it comes to the RRC protocol. Following the handover failure, the category 0 UE will then experience a radio link failure. Subsequently, the category 0 UE will try to trigger RRC Connection Re-establishment which also will fail for the same reason of non-compatibility. Finally, the category 0 UE will transition to idle mode where it will search for suitable cells. The failed handover and the unsuccessful RRC

Connection Re-establishment will result in unnecessary signalling in the network and in shorter battery lifetime for the UE. Further, connection drops may also result.

To handle mobility for non-backward compatible categories, it has been agreed to rely on Operations and Management (OAM) functions, where the OAM functionality attempts to ensure that UEs with non-backward categories are not handed over to a target eNB that does not support non-backward compatible categories. However, OAM is not an automated function. Usually, cell and eNB compatibilities are added manually in databases, and updated after changes in network deployment or nodes. Updates of these databases are subject to potential errors and relatively long delays, e.g., whenever any of the network nodes (eNBs) are updated through software (and hardware) upgrade. Consequently, unnecessary signalling caused by failed handovers and unsuccessful RRC connection re- establishments may occur, which impairs network resource utilization and shortens the UE battery lifetime.

SUMMARY

It is therefore an object of embodiments herein to provide an improved way of handover preparation of user equipments (UEs). According to a first aspect of embodiments herein, the object is achieved by a method in a first network node for handover preparation of a UE of an additional category in a wireless communication network, where the additional category is new relative to one or more legacy categories. The handover preparation is performed between a first cell served by the first network node and a second cell served by a second network node. The first network node, the second network node, the first cell and the second cell are comprised in the wireless communications network.

The first network node sends to the second network node a message comprising information indicating a request for preparation of a handover of the UE, the message including an out- of-range value for one or more fields. The first network node receives from the second network node a message indicating failure to prepare the handover. In some embodiments, the first network node interprets the message indicating failure to prepare the handover as an indication that the second network node does not support any UE of the additional category. According to a second aspect of embodiments herein, the object is achieved by a first network node for handover preparation of a UE of an additional category in a wireless communication network), where the additional category is new relative to one or more legacy categories. The wireless communications network is configured to comprise the first network node configured to serve a first cell. The wireless communications network is further configured to comprise a second network node configured to serve a second cell. The handover preparation is to be performed between the first cell and the second cell.

The first network node is configured to send to the second network node a message comprising information indicating a request for preparation of a handover of the UE, the message including an out-of-range value for one or more fields. The first network node is further configured to receive from the second network node a message indicating failure to prepare the handover. In some embodiments, the first network node is further configured to interpret the message indicating failure to prepare the handover as an indication that the second network node does not support any UE of the additional category.

According to a third aspect of embodiments herein, the object is achieved by a method in a second network node for handover preparation of a UE of an additional category in a wireless communications network, where the additional category is new relative to one or more legacy categories. The handover preparation is performed between a first cell served by a first network node and a second cell served by the second network node. The first network node, the second network node, the first cell and the second cell are comprised in the wireless communications network. The second network node receives from the first network node a message comprising information indicating a request for preparation of a handover of the UE, the message including an out-of-range value for one or more fields. The second network node further sends to the first network node a message indicating failure to prepare the handover based on the received information indicating the request for preparation of the handover. The failure to prepare the handover indicates to the first network node that the second network node does not support any UE of the additional category.

According to a fourth aspect of embodiments herein, the object is achieved by a second network node for handover preparation of a UE of an additional category in a wireless communications network, where the additional category is new relative to one or more legacy categories. The wireless communications network comprises a first network node configured to serve a first cell and a second network node configured to serve the second cell. The handover preparation is to be performed between the first cell and the second cell. The second network node is configured to receive from the first network node a message comprising information indicating a request for preparation of a handover of the user equipment, the message including an out-of-range value for one or more fields. The second network node is further configured to send to the first network node a message indicating failure to prepare the handover based on the received information indicating the request for preparation of the handover. The failure to prepare the handover indicates to the first network node that the second network node does not support any UE of the additional category.

According to a fifth aspect of embodiments herein, a method is implemented in a UE of an additional category, where the additional category is new relative to one or more legacy categories. The method includes sending, to a first network node, a message comprising capability information, the message including an out-of-range value for one or more fields. In some embodiments, this message is sent in response to receiving a request for capability information from the first network node.

According to a corresponding sixth aspect, a UE of an additional category, where the additional category is new relative to one or more legacy categories, is configured to carry out the method summarized immediately above.

In several embodiments, then, the first network node sends to the second network node a request for preparation of the handover, the message including an out-of-range value for one or more fields, and receives a message indicating failure to prepare the handover, because the second network node is not configured to handle the out-of-range value. The out-of- range value may have been received by the first network node as part of capability information provided to the first network node by the user equipment.

Since the first network node interprets the message indicating failure to prepare the handover as an indication that the second network node does not support any UE of the additional category, the first network node avoids handover failure of UE of the additional category.

An advantage with embodiments herein is that embodiments herein enable unnecessary signalling, caused by failed handovers and unsuccessful RRC connection re-establishments, to be avoided. Consequently, network resources are used in a more efficient manner and UE battery lifetime is prolonged. A further advantage is that connection drops are avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments herein are described in more detail with reference to attached drawings in which:

Figure 1 is a schematic block diagram illustrating embodiments of a wireless communications network;

Figure 2 is a combined signalling diagram and flowchart illustrating embodiments of a method in a wireless communications network;

Figure 3 is a flowchart illustrating embodiments of a method in a first network node;

Figure 4 is a schematic block diagram illustrating embodiments of a first network node;

Figure 5 is a flowchart illustrating embodiments of a method in a second network node;

Figure 6 is a schematic block diagram illustrating embodiments of a second network node;

Figure 7 is a flowchart illustrating embodiments of a method in a user equipment; and

Figure 8 is a schematic block diagram illustrating embodiments of a user equipment. DETAILED DESCRIPTION

As part of developing embodiments herein, a problem will first be identified and discussed. When a UE is handed over from a source cell to a target cell, handover preparation is needed. Upon handover preparation, the target radio base station or eNB is provided a current UE RRC configuration, in a handover preparation information message. The target eNB decides an RRC configuration for the UE, to be used after the handover, and therefore an RRC configuration message is transparently sent to the UE via the source eNB as an octet string comprised in a handover command.

If the RRC configuration in the handover preparation message is incomplete, or if the source cell has configured the UE with an RRC protocol version that is not comprehended by the target eNB, the target eNB typically performs a full configuration, if possible, i.e., the target eNB performs a reconfiguration from scratch. Otherwise, the target eNB may modify or maintain the current UE RRC configuration.

Upon handover of a category 0 UE to a legacy target eNB the legacy target eNB may erroneously assume that the category 0 UE may be successfully configured as the least capable legacy category, such as category 1. Consequently, the handover fails and the category 0 UE experiences a radio link failure. Subsequently, the UE tries to trigger RRC Connection Re-establishment which also fails. Finally, the UE transitions to Idle mode where it searches for suitable cells. All of this has the disadvantage of causing unnecessary signalling, due to the failed handovers and the unsuccessful RRC connection re- establishment requests, which results in the inefficient use of bandwidth.

Embodiments herein address the issue of handover failure due to network nodes that do not support specific user equipment types or specific categories of user equipment. Specifically, embodiments herein prevent the handover of category 0 UEs to base stations that do not support MTC user equipment, such as category 0 UEs, by causing these handovers to be rejected by the target eNB before the user equipment is handed over.

More specifically, in the LTE context, if a UE is of non-backwards compatible category, it populates the legacy (Rel-8 fallback) category protocol field with a value that is outside of the currently specified range. This is possible because there are some unspecified bit combinations for the legacy category field that can be used without causing any decoding problems. If the UE does not indicate any specified value for the fallback category and the target eNB does not support (or comprehend) the UE's non-backwards compatible category, the target eNB rejects the handover request due to incomplete or missing UE category information. In that way, the source eNB can try to handover the UE to another eNB or to another frequency. Currently, the protocol field is specified in subclause 6.3.6 of the 3GPP specifications for the EUTRA RRC protocol, 3GPP TS 36.331 , v. 12.5.0 (March 2015), as an integer type with a value range from 1 to 5. Since the presence of the field is mandatory, according to Release 8 of the specifications for LTE systems, it should be populated with a value even if the UE does not support any legacy category. This is currently captured in the field description in the specifications by specifying a requirement that the UE shall populate the field with any value within the range from 1 to 5, as follows:

- UE DL category as defined in TS 36.306 [5]. ForASN. 1 compatibility, a UE indicating DL category 0 shall also indicate any of the categories (1..5) in ue- Category (without suffix), which is ignored by the eNB. The field ue-

CategoryDL-r12 is set to values 0, 13 and 14 in this version of the specification.

Since the value range from 1 to 5 requires 5 code points, the encoding of the field value requires 3 bits. However, a 3-bit sequence has 8 possible bit combinations, and therefore the field has 3 unused or unspecified values. This means that the field can be populated with a value that does not have any specified semantics but that does not create decoding problems at the receiver side, because the decoding itself does not fail so long as the encoded number of bits remains unchanged.

It can thus be argued that the current requirement is unnecessary or even

counterproductive, because it mandates that the UE populate the field with a legacy category value that is not actually supported by the UE. The field usage could be changed to a recommendation to populate the field with a value that is outside of the range but still possible to represent with 3 bits combinations. This is advantageous in the sense that the target eNB would always reject a handover preparation if the UE is of non-backwards compatible category which is not supported by the target eNB. Such a handover preparation to a target eNB that does not support non-backwards compatible categories could occur because of a failure in OAM procedures, for example, such as when an OAM database is not up-to-date.

In LTE systems, if an eNB does not have UE capability information for a given UE, it will send a UECapabilityEnquiry message to the UE. Upon receipt of the UECapabilityEnquiry message, the UE will respond by sending a UECapabilitylnformation message that includes the UE-EUTRA-Capability IE described above. Thus, in some embodiments of the presently disclosed techniques, apparatus, and systems, a UE of an additional category (e.g.., category 0), which is new with respect to an earlier version of the protocols governing handover-related messages (e.g., the LTE Release 8 specifications for RRC), populates a field in a capability message sent to the network with an out-of-range value, with respect to that earlier version. More specifically, in the LTE context, the UE may populate the "UE- category" field of the UE-EUTRA-Capability information element (IE) with an out-of-range value, e.g., a value outside of the 1-5 range specified in legacy versions of the LTE specification. Embodiments thus introduce a modification of the handover preparation information message in the RRC protocol. It will be appreciated, however, that the format of the handover preparation information message remains consistent with legacy versions of the protocol, and thus can be decoded by legacy nodes. This modified handover preparation information message is intended to be used for handover preparation of UEs of specific categories, such as category 0 UEs, which are not compatible with old categories when it comes to the RRC protocol. The handover preparation is rejected by legacy eNBs because one of the fields in the handover preparation information message is provided with an out-of- range value. More specifically for LTE, the modified handover preparation information message for a category 0 UE in some embodiments is provided with an out-of-range value for the "UE-category" field of the UE-EUTRA-Capability information element (IE). The target eNB will reject the Handover Request because of the out-of-range value, thus causing a failed handover preparation.

Upon failed handover preparation, the source eNB does not trigger any handover procedure. Instead the source eNB may, in some embodiments, interpret a handover failure as an indication that the target eNB does not support UEs of the specific category, such as category 0 UEs. Following the failure of handover preparations the source eNB may either try to handover the UE of the specific category, such as the category 0 UE, to another eNB or to another frequency, or releases the RRC connection.

Figure 1 depicts parts of an example wireless communications network 100 in which embodiments herein may be implemented. The one or more wireless communications networks 100 may for example be LTE, , GSM, any 3GPP wireless communications network, or any cellular wireless communications network or system capable of handling UEs of more than one category or of different capabilities. Embodiments herein are illustrated with examples from an Evolved Universal Terrestrial Radio Access (EUTRA) network also known as LTE network.

The wireless communications network 100 comprises a plurality of base stations and/or other network nodes. More specifically, the wireless communications network 100 comprises a first network node 1 11. The first network node 11 1 is also referred to herein as a source network node. The wireless communications network 100 further comprises a second network node 112. The second network node 112 is also referred to herein as a candidate or target network node.

The term "network node" may correspond to any type of radio network node or any network node, which communicates with at least a radio network node. For example, the first and second network nodes 1 11 , 1 12 may each be a base station, such as an eNB. The base station may also be referred to as a NodeB, an evolved Node B (eNB, eNode B), a base transceiver station (BTS), Access Point Base Station, base station router, or any other network unit capable of communicating with a user equipment within a cell served by the base station depending e.g. on the radio access technology and terminology used. In some embodiments, the first network node 11 1 and the second network node 1 12 belong to two different wireless communications networks. For example, the first network node 1 11 may belong to an UMTS network and the second network node 112 may belong to an LTE network. The first network node 1 11 may then be a Radio Network Controller (RNC) in the UMTS network, for example. The first network node 111 serves a first cell 121 , also referred to as a source cell, and the second network node 1 12 serves a second cell 122, also referred to as a candidate cell or target cell. A cell is a geographical area where radio coverage is provided by network node equipment such as Wi-Fi access point (AP) equipment or base station equipment at a base station site or at remote locations in Remote Radio Units (RRU). The first network node is an example of such network node equipment. The cell definition may also incorporate frequency bands and radio access technology used for transmissions, which means that two different cells may cover the same geographical area but using different frequency bands. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying cells uniquely in the whole of a wireless communication network is also broadcasted in the cells.

Network nodes, such as base stations and Wi-Fi APs, communicate over the air or radio interface operating on radio frequencies with the user equipments (UEs) within range of the network nodes. The UEs transmit data over the radio interface to network nodes, such base stations and Wi-Fi AP, in UL transmissions, and network nodes, such as Wi-Fi AP and base stations, transmit data over an air or radio interface to the UEs in DL transmissions.

The first network node 11 1 communicates with UEs in the first cell 121 , such as a user equipment 140, also referred to as a UE or a wireless device. The UE 140 is to be handed over to a cell different from the first cell 121. The handover may for example be due to mobility of the UE 140. The UE 140 in this example scenario is of an additional category, relative to one or more legacy categories. The additional category may be category 0. The UE 140 may be an MTC UE, in some embodiments. In the example scenario under discussion, the second network node 112 does not support this additional category.

The UE 140 may be a mobile terminal or a wireless terminal, a mobile phone, a computer with wireless capability, such as a laptop, a Personal Digital Assistants (PDAs) or a tablet computer, sometimes referred to as a surf plate, a device-to-device UE, an MTC UE or UE capable of machine-to-machine (M2M) communication, an iPad, smart phone, Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), USB dongles, etc., or any other radio network unit capable of communicating over a radio link in a wireless communications network. Note that the terms "user equipment" and "UE" as used in this document may refer to wireless devices such as Machine-to-machine (M2M) devices, even though these devices do not have any user present.

In this section, embodiments of the techniques and apparatus disclosed herein will be illustrated in more detail by a number of exemplary embodiments. It should be noted that these embodiments are not mutually exclusive. Components from one embodiment may be tacitly assumed to be present in another embodiment and it will be obvious to a person skilled in the art how those components may be used in the other exemplary embodiments.

Figure 2 is a combined signalling diagram and flow chart that describes actions that may take place to prepare handover of the user equipment 140 of the additional category, such as a UE of category 0, between the first cell 121 served by the first network node 11 1 and the second cell 122 served by the second network node 112 according to embodiments herein.

Action 201

In this action the first network node 1 11 chooses a candidate target cell for handover of the user equipment 140, where the user equipment is of an additional category (e.g., category 0), relative to one or more legacy categories (e.g., categories 1-5). The handover may, for example, be triggered by mobility.

Action 202

The first network node 11 1 sends a message to the second network node 1 12. The message comprises information on handover preparation for the user equipment 140. The information indicates a request for preparation of handover of the user equipment 140. More specifically, the information comprises at least one information field that includes an out-of- range value, with respect to legacy versions of the protocol that governs handover-related communications (i.e., the RRC protocol, in LTE networks). The second network node 112 is a legacy eNB that does not support communication with user equipment of the additional category, such as category 0 UEs. According to

embodiments herein, the second network node 112, e.g., target eNB, will not erroneously assume that the user equipment 140 of the additional category may be successfully configured as, e.g., the least capable legacy category, such as category 1 , since the message from the first network node 1 11 includes an out-of-range value for at least one field.

The message may, for example, comprise a Handover Preparation Information message. The Handover Preparation Information message may comprise information on the capability of the user equipment 140 of the additional category. The Handover Preparation Information message may be of the form specified by LTE Release-8, but with an out-of-range value for at least one field, with respect to the Release 8 standards. More particularly, the Handover Preparation Information message may include an out-of-range value, such as "0," for the UE-category" field of the UE-EUTRA-Capability information element (IE). The message comprising handover preparation information may be generally used to transfer RRC information to be used by the target eNB, which in this case is the second network node 1 12, during handover preparation, including UE capability information. The handover preparation will be rejected by legacy eNBs, such as the second network node 1 12, upon receipt of the message, because of the out-of-range value for the field.

Action 203

Only those target eNBs that are implementing the new version of the protocol governing handover-related messages are able to comprehend the message, because it includes the out-of-range value, e.g., for the UE-Capability field. Accordingly, the second network node 1 12, e.g. target eNB, will reject the handover preparation information message. In other words, when the second network node 1 12 has received the message comprising information on the handover preparation for the user equipment 140 of the additional category, the second network node 1 12 sends to the first network node 1 11 a message indicating failure to prepare the handover based on the received information indicating the request for preparation of the handover for user equipment of the additional category. Action 204

The first network node 1 11 receives the message indicating failure to prepare the handover, and takes alternative steps for the UE, such as selecting another target eNB or frequency, and attempting another handover preparation, and/or releasing the RRC connection. In some embodiments, the first network node 11 1 interprets the message indicating failure to prepare the handover as an indication that the second network node 1 12 does not support any user equipment of the additional category.

Action 205

Once the first network node 11 1 , i.e., the source eNB, has received the message indicating failure of handover preparation as a response to the request for preparation of the handover, it may infer that the second network node 112, the target eNB, does not support user equipment of the additional category, such as category 0 UEs. In some embodiments, then, the first network node 11 1 may subsequently disregard the second network node 1 12 as a potential candidate for handover of any user equipment of the additional category. Embodiments of a method in the first network node 11 1 for handover preparation of the user equipment 140 of the additional category in the wireless communications network 100 will now be described with reference to a flowchart depicted in Figure 3.

The handover preparation is performed between the first cell 121 , also referred to as the source cell, served by the first network node 11 1 , and the second cell 122, also referred to as the candidate cell or target cell, served by the second network node 1 12. As mentioned above, the user equipment 140 is of an additional category, with respect to one or more legacy categories, which additional category may indicate that the user equipment 140 has capability for MTC, for example. This additional category may be category 0, for instance. In some embodiments the user equipment 140 is of the MTC type. In some embodiments the additional category has limited capabilities compared to the least capable legacy category, such as category 1.

The method comprises the following actions, which actions may be taken in any suitable order.

Action 301

The first network node 1 11 sends a message to the second network node 112. The message comprises information on handover preparation for the user equipment 140. The information indicates a request for preparation of handover of the user equipment 140. More specifically, the information comprises at least one information field that includes an out-of- range value, with respect to legacy versions of the protocol that governs handover-related communications (i.e., the RRC protocol, in LTE networks).

The message may, for example, comprise a Handover Preparation Information message. The Handover Preparation Information message may comprise information on the capability of the user equipment 140 of the additional category. The Handover Preparation Information message may be of the form specified by LTE Release-8, but with an out-of-range value for at least one field, with respect to the Release 8 standards. More particularly, the Handover Preparation Information message may include an out-of-range value, such as "0," for the UE-category" field of the UE-EUTRA-Capability information element (IE).

A sending module 510 in the first network node 11 1 may be configured to perform action 301. In some embodiments, this sending module 510 is implemented using a processor executing suitable program instructions stored in a computer-readable medium, such as memory 590, where the processor is operably connected to a communications interface configured for communications with the second network node 1 12, such as via the X2 interface specified by the 3GPP standards. The combination of the processor with the memory comprising program instructions for execution by the processor is referred to hereinafter as a "processing circuit."

Action 302

The first network node 11 1 receives the message indicating failure to prepare the handover from the second network node 1 12. A receiving module 520 in the first network node 1 11 may be configured to perform action 302. Again, in some embodiments, this receiving module 520 is implemented using a processor executing suitable program instructions stored in a computer-readable medium, where the processor is operably connected to a communications interface configured for communications with the second network node 1 12, such as via the X2 interface specified by the 3GPP standards. This processor may be the same processor with which the sending module 510 is implemented.

Action 303

The first network node 11 1 then interprets the message indicating failure to prepare the handover as an indication that the second network node 1 12 does not support any user equipment of the additional category.

An interpreting module 530 in the first network node 1 11 may be configured to perform action 301. Once more, in some embodiments this interpreting module 530 is implemented using a processor executing suitable program instructions stored in a computer-readable medium; the processor may be the same processor used to implement the sending module 510 and/or receiving module 520.

Action 304

In some embodiments, the first network node 11 1 may disregard the second network node 1 12 as a potential candidate for handover of any user equipment of the additional category. In other words, the first network node 1 11 selects a potential candidate base station for handover of any user equipment of the additional category, and specifically for the user equipment 140 for which the handover preparation message was sent, based on the action of interpreting the received message indicating failure to prepare the handover.

A disregarding module 540 in the first network node 11 1 may be configured to perform action 301. This disregarding module may be implemented with a processor executing suitable program instructions stored in a computer-readable medium; the processor may be the same processor used to implement the sending module 510 and/or receiving module 520 and/or the interpreting module 530.

To perform the method actions for handover preparation of the user equipment 140 of the additional category in the wireless communications network 100 described above in relation to Figure 3, the first network node 11 1 may comprise the arrangement depicted in Figure 4. As mentioned above, the wireless communications network 100 is configured to comprise the first network node 1 11 configured to serve the first cell 121. The wireless

communications network 100 is further configured to comprise the second network node 112 configured to serve the second cell 122. The handover preparation is to be performed between the first cell 121 and the second cell 122.

The first network node 11 1 is configured to, e.g., by means of the sending module 510, send a message to the second network node 112. The message comprises information on handover preparation for the user equipment 140. The information indicates a request for preparation of handover of the user equipment 140. More specifically, the information comprises at least one information field that includes an out-of-range value, with respect to legacy versions of the protocol that governs handover-related communications (i.e., the RRC protocol, in LTE networks).

The sending module 510 may be implemented by a transmitter in the first network node 1 11. In some embodiments this transmitter is implemented with processor 580, utilizing program instructions in memory 590, in conjunction with a communication interface circuit in the first network node 11 1 , where the communication interface circuit is configured for communication with one or more other network nodes, including second network node 1 12.

The first network node 11 1 is further configured to, e.g. by means of the receiving module 520 configured to, receive the message indicating failure to prepare the handover. The receiving module 520 may be implemented by a receiver in the first network node 11 1. In some embodiments this receiver is implemented with processor 580, utilizing program instructions in memory 590, in conjunction with a communication interface circuit in the first network node 11 1 , where the communication interface circuit is configured for

communication with one or more other network nodes, including second network node 1 12.

The first network node 11 1 is further configured to, e.g., by means of the interpreting module 530, interpret the message indicating failure to prepare the handover as the indication that the second network node 1 12 does not support any user equipment of the additional category. The first network node 1 11 may further be configured to, e.g. by means of the disregarding module 540, disregard the second network node 112 as a potential candidate for handover of the user equipment 140 of the additional category. The interpreting module 530 and/or the disregarding module 540 may be implemented using processor 580 in the first network node 11 1.

The first network node 1 11 may further be configured to, e.g., by means of a memory 590, store indications, messages, categories of user equipment and capabilities of user equipment, information, data, configurations, schedulings, and applications etc. The memory 590 comprises one or more memory units. The memory 590 is further configured to store information, data, configurations, schedulings, configurations and applications, etc., to perform the methods herein when being executed in the first network node 11 1.

The embodiments herein to perform handover preparation of the user equipment 140 in the wireless communications network 100 may be implemented through one or more processors, such as the processor 580 in the first network node 1 11 depicted in Figure 4, together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the first network node 11 1. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the first network node 11 1. Thus, the methods according to the embodiments described herein for the first network node 1 11 may be implemented by means of a computer program product, comprising instructions, i.e., software code portions, which, when executed on at least one processor, cause the at least one processor to carry out the actions described herein, as performed by first network node 11 1. The computer program product may be stored on a computer-readable storage medium. The computer-readable storage medium, having stored there on the computer program, may comprise the instructions which, when executed on at least one processor, cause the at least one processor to carry out the actions described herein, as performed by first network node 1 11. In some embodiments, the computer-readable storage medium may be a non-transitory computer-readable storage medium.

Those skilled in the art will also appreciate that the sending module 510, the receiving module 520, the interpreting module 530 and the disregarding module 540 described above may refer to a combination of analogue and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in a memory, that when executed by the one or more processors such as the processor 580 perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a System-on-a-Chip (SoC). Embodiments of a method in the second network node 112 for handover preparation of the user equipment 140 of the additional category in the wireless communications network 100 will now be described with reference to a flowchart depicted in Figure 5. As mentioned above, the first network node 1 11 serves the first cell 121 , also referred to as the source cell, the second network node 112 serves the second cell 122, also referred to as the candidate cell or target cell.

The user equipment 140, which has an additional category relative to one or more legacy categories, is to be handed over to a cell different from the first cell 121. In some

embodiments the additional category has limited capabilities compared to the least capable legacy category, such as category 1. The additional category may comprise category 0. In some embodiments the user equipment 140 is of the MTC type.

The method comprises the following actions, which actions may be taken in any suitable order. Action 601

The second network node 1 12 receives from the first network node 11 1 a message comprising information on the handover preparation for the user equipment 140 of the additional category. The message comprises information on handover preparation for the user equipment 140. The information indicates a request for preparation of handover of the user equipment 140. More specifically, the information comprises at least one information field that includes an out-of-range value, with respect to legacy versions of the protocol that governs handover-related communications (i.e., the RRC protocol, in LTE networks).

Action 602

In response to receiving the message, the second network node 112 sends to the first network node 1 11 a message indicating failure to prepare the handover based on the received information indicating the request for preparation of the handover. The failure to prepare the handover indicates to the first network node 1 11 that the second network node 1 12 does not support any user equipment of the additional category.

To perform the method actions for handover preparation of the user equipment 140 of the additional category in the wireless communications network 100 described above in relation to Figure 5, the first network node 1 11 may be configured according to the description below. As mentioned above, the wireless communications network 100 is configured to comprise the first network node 1 11 configured to serve the first cell 121. The wireless

communications network 100 is further configured to comprise the second network node 1 12 configured to serve the second cell 122. The handover preparation is to be performed between the first cell 121 and the second cell 122. The second network node 112 is configured to, e.g., by means of a receiving module 710, receive from the first network node 11 1 a message comprising information indicating the request for preparation of the handover of the user equipment 140. The message comprises information on handover preparation for the user equipment 140. The information indicates a request for preparation of handover of the user equipment 140. More specifically, the information comprises at least one information field that includes an out-of-range value, with respect to legacy versions of the protocol that governs handover-related communications (i.e., the RRC protocol, in LTE networks).

The receiving module 710 may be implemented by a receiver in the second network node 112; this receiver may be implemented in a manner similar to that described above in connection with the first network node 1 11 , e.g., utilizing processor 780 and memory 790, in connection with a communications interface circuit. Again, the combination of a processor with a memory storing program instructions for execution by the processor may be referred to herein as a "processing circuit."

The second network node 1 12 is further configured to, e.g., by means of a sending module 720, send to the first network node 11 1 a message indicating failure to prepare the handover. The second network node 1 12 is configured to send the message based on the received information indicating the request for preparation of the handover. The failure to prepare the handover indicates to the first network node 1 11 that the second network node 1 12 does not support any user equipment of the additional category.

The sending module 720 may be implemented by a transmitter in the second network node 112; this transmitter may be implemented in a manner similar to that described above in connection with the first network node 1 11 , e.g., utilizing processor 780 and memory 790, in connection with a communications interface circuit.

Embodiments of a method in a UE 410 of the additional category in the wireless

communications network 100 will now be described with reference to a flowchart depicted in Figure 7. As mentioned above, a first network node 11 1 serves the first cell 121 , also referred to as the source cell, the second network node 1 12 serves the second cell 122, also referred to as the candidate cell or target cell.

The user equipment 140 has an additional category relative to one or more legacy categories. In some embodiments the additional category has limited capabilities compared to the least capable legacy category, such as category 1. The additional category may comprise category 0. In some embodiments the user equipment 140 is of the MTC type.

The method comprises the following actions, which actions may be taken in any suitable order. Action 710

In some embodiments, the UE 410 receives from the first network node 1 11 a request for capability information for the user equipment 140. In some embodiments, the request for capability information may comprise a UECapabilityEnquiry message. It will be appreciated that this request may not occur in every instance or implementation of the illustrated method; in some embodiments, the subsequent operations may be triggered by other events, such as an initial attachment to the first network node 11 1.

Action 720

Upon receipt of the request for capability information (or in response to some other trigger), the UE sends a message that includes capability information, the message including an out- of-range value for at least one field. In some embodiments, the message is a

UECapabilitylnformation message. More particularly, in some embodiments of the presently disclosed techniques, apparatus, and systems, a UE of an additional category (e.g.., category 0) with respect to an earlier version of the protocols governing handover-related messages (e.g., the LTE Release 8 specifications for RRC), populates a field in a capability message sent to the network with an out-of-range value, with respect to that earlier version. More specifically, in the LTE context, the UE may populate the "UE-category" field of the UE- EUTRA-Capability information element (IE) with an out-of-range value, e.g., a value outside of the 1-5 range specified in legacy versions of the LTE specification.

To perform the method actions described above in relation to Figure 7, the UE 410 may be configured according to the illustration in Figure 8 and the description below.

The UE 410 is configured to, e.g., by means of a receiving module 810, receive from the first network node 1 11 a request for capability information for the user equipment 140. In some embodiments, the request for capability information may comprise UECapabilityEnquiry message. The receiving module 810 may be implemented by a receiver in the UE 410; this receiver may be implemented utilizing a processor 880 executing program instructions stored in a memory 890, in connection with a radio transceiver circuit configured for communication with one or more radio access nodes, including network node 11 1. The UE 410 is further configured to, e.g., by means of a sending module 820, send to the first network node 1 11 a message that includes capability information, the message including an out-of-range value for at least one field. In some embodiments, the message is a UECapabilitylnformation message. More particularly, in some embodiments of the presently disclosed techniques, apparatus, and systems, a UE of an additional category (e.g.., category 0) with respect to an earlier version of the protocols governing handover- related messages (e.g., the LTE Release 8 specifications for RRC), populates a field in a capability message sent to the network with an out-of-range value, with respect to that earlier version. More specifically, in the LTE context, the UE may populate the "UE- category" field of the UE-EUTRA-Capability information element (IE) with an out-of-range value, e.g., a value outside of the 1-5 range specified in legacy versions of the LTE specification.

The sending module 820 may be implemented by a transmitter in the second network node 112; this transmitter may be implemented utilizing a processor 880 executing program instructions stored in a memory 890, in connection with a radio transceiver circuit configured for communication with one or more radio access nodes, including network node 11 1.

As used herein, the words "comprise" and "comprising" should be interpreted as non- limiting, i.e., meaning "consist at least of" or, more simply "include" and "including."

The embodiments herein are not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope, which is defined by the appending claims.

Note that although terminology from 3GPP LTE/SAE has been used in this disclosure to exemplify the embodiments herein, this should not be seen as limiting the scope of the embodiments herein to only the aforementioned system. Other wireless systems may also benefit from exploiting the ideas covered within this disclosure.

Claims

CLAIMS What is claimed is:

1. A method in a first network node (11 1) for handover preparation of a user equipment (140) of an additional category in a wireless communications network (100), wherein the additional category is new relative to one or more legacy categories, wherein the handover preparation is performed between a first cell (121) served by the first network node (11 1) and a second cell (122) served by a second network node (112), which first network node (1 11), second network node (1 12), first cell (1 11) and second cell (122) are comprised in the wireless communications network (100), the method comprising:

sending (202, 301) to the second network node (1 12) a message comprising

information indicating a request for preparation of a handover of the user equipment (140), the message including an out-of-range value for one or more fields; and

receiving (203, 302) from the second network node (1 12) a message indicating

failure to prepare the handover.

2. The method of claim 1 , further comprising interpreting (204, 303) the message indicating failure to prepare the handover as an indication that the second network node (1 12) does not support any user equipment of the additional category.

3. The method of claim 1 or 2, further comprising disregarding (205, 304) the second network node (1 12) as a potential candidate for handover of any user equipment of the additional category.

4. The method of any of claims 1-3, wherein the message comprises a Handover

Preparation Information message comprising information on the capability of the user equipment (140) of the additional category.

5. The method of any of claims 1-4, wherein the additional category is category 0.

6. The method of any of claims 1-5, wherein the user equipment (140) is of a Machine Type Communication, MTC, type.

7. The method of any of claims 1-6, wherein the message comprises an out-of-range value for a UE-capability field in a UE-EUTRA-Capability information element, IE.

8. A first network node (11 1) for handover preparation of a user equipment (140) of an additional category in a wireless communications network (100), wherein the additional category is new relative to one or more legacy categories, wherein the wireless

communications network (100) is configured to comprise the first network node (1 11) configured to serve a first cell (121), and wherein the wireless communications network (100) is further configured to comprise a second network node (112) configured to serve a second cell (122), and wherein the handover preparation is to be performed between the first cell (121) and the second cell (122), and wherein the first network node (11 1) is configured to:

send to the second network node (1 12) a message comprising information indicating a request for preparation of a handover of the user equipment (140), the message including an out-of-range value for one or more fields; and receive from the second network node (112) a message indicating failure to prepare the handover.

9. The first network node (11 1) of claim 8, wherein the first network node (1 11) is further configured to interpret the message indicating failure to prepare the handover as an indication that the second network node (112) does not support any user equipment of the additional category.

10. The first network node (1 11 ) of claim 8 or 9, wherein the first network node (1 11 ) is further configured to disregard the second network node (1 12) as a potential candidate for handover of any user equipment of the additional category.

1 1. The first network node (1 11) of any of claims 8-10, wherein the message comprises a Handover Preparation Information message comprising information on the capability of the user equipment (140) of the additional category.

12. The first network node (1 11) of any of claims 8-1 1 , wherein the additional category comprises category 0.

13. The first network node (1 11) of any of claims 8-12, wherein the user equipment (140) is of a Machine Type Communication, MTC, type.

14. The first network node (1 11) of any of claims 8-13, wherein the message comprises an out-of-range value for a UE-capability field in a UE-EUTRA-Capability information element, IE.

15. A method in a user equipment (140) of an additional category in a wireless communications network (100), wherein the additional category is new relative to one or more legacy categories, the method comprising:

sending (720) to a first network node (11 1) a message comprising capability

information, the message including an out-of-range value for one or more fields.

16. The method of claim 15, further comprising receiving (710) a request for capability information from the first network node (11 1), wherein said sending (720) is in response to the request for capability information.

17. The method of claim 15 or 16, wherein the additional category comprises category 0.

18. The method of any of claims 15-17, wherein the user equipment (140) is of a Machine Type Communication, MTC, type.

19. A user equipment (140) of an additional category in a wireless communications network (100), wherein the additional category is new relative to one or more legacy categories, wherein the user equipment (140) is configured to:

send to a first network node (11 1) a message comprising capability information, the message including an out-of-range value for one or more fields.

20. The user equipment (140) of claim 19, wherein the user equipment (140) is further configured to receive a request for capability information from the first network node (1 11), and to send the message in response to the request for capability information.

21. The method of claim 19 or 20, wherein the additional category comprises category 0.

22. The user equipment (140) of any of claims 19-21 , wherein the user equipment (140) is of a Machine Type Communication, MTC, type.