WO2013156051A1

WO2013156051A1 - Controlling cell reselection

Info

Publication number: WO2013156051A1
Application number: PCT/EP2012/056918
Authority: WO
Inventors: Daniela Laselva; Benny Vejlgaard; Klaus Ingemann Pedersen
Original assignee: Nokia Siemens Networks Oy
Priority date: 2012-04-16
Filing date: 2012-04-16
Publication date: 2013-10-24

Abstract

It is described a method for controlling a reselection of a cell by a user equipment (101) within a cellular network system (100). The cellular network system (100) comprises a plurality of cells (102-106), wherein the user equipment is served by a source cell and reselects a target cell based on a predefined reselection scheme. The predefined reselection scheme is based on priorities being assigned to each cell of the plurality of cells. The method comprises determining, by the user equipment (101), a mobility state of the user equipment, wherein the mobility state of the user equipment (101) is indicative for a velocity of the user equipment (101) relatively to the plurality of cells (102-107), adapting the predefined reselection scheme by adapting the priorities being assigned to each cell of the plurality of cells based on a cell type characteristic of each cell and the determined mobility state, and controlling the reselection of the target cell based on the adapted reselection scheme.

Description

DESCRIPTION Title

Controlling cell reselection

Field of invention

The present invention relates to the field of cellular networks and in particular to heterogeneous networks, in which user equipments perform cell reselection.

Art Background

Cellular network systems may be arranged in multi-layer cellular systems - also referred to as heterogeneous networks (HetNet). In this context, multi-layer refers to cases with a mixture of macro base stations and small power base stations (for instance pico and mi- cro). Macro-layer and pico/micro layer may also be implemented in different radio access technologies (RAT), for example GSM macro layer and LTE micro layer.

User equipments (UEs) moving through a heterogeneous network may need to be handed over between different cells when being in a connected mode or may need to perform cell reselection when being in an idle mode. This may be the case for instance in LTE (e.g.,

Advanced) or WCDMA systems. In particular for UEs in a high or medium mobility state may need to perform handovers or cell reselections. Idle mode refers to a UE in RRCJdle state according to the LTE terminology or in idle, CELL_PCH and CELL_FACH states according to the WCDMA terminology.

The cell selection and reselection processes are run autonomously by the UE in idle mode according to standardized reselection procedures and related network configured parameters. For instance, E-UTRAN and UTRAN (Rel-8 and onward) supports a priority based cell reselection procedure for inter-frequency and inter-RAT reselections (3GPP TS 36.304 / 35.304) referred to as the Absolute Priority method. A camping UE, i.e. , a UE in idle mode being served by one cell, may also need to detect autonomously its mobility state (TS 36.304 / 25.304), and if in high- or medium-mobility state, the UE may apply speed dependent scaling rules to the reselection parameters if configured by the network.

In common systems, the network can configure the "Speed dependent ScalingFactor for Treselection" from the following set of values {0.25, 0.50, 0.75, 1 .00} (TS 32.592). This means that the scaled timer Treselection for UEs in medium and high mobility states can only be shortened favouring faster cell reselections. The latter is likely the desired behav- iour if the target cell is a macro cell or in case of an outbound reselection from a low power node or small cell (e.g. micro, pico cell), for example in order to minimize mobility problems due to a sharp drop in signal strength and quality in the camping cell.

However, such scaling may also cause undesired effects such as UEs entering a small cell faster, i.e. faster inbound cell reselections towards a small target cell. This may result in frequent reselections and especially in the situation that a U E - moving to connected mode - may be then served by the low power node which may lead to frequent handovers, ping pongs, radio link failures, and performance degradation. On the other hand, allowing fast moving UEs to camp on and being served by low power nodes can be a valid target in case of e.g. coverage holes at the macro overlay.

It should be noted that similar speed dependent scaling may also be applied to UEs in connected mode, so the considerations above on cell reselections can be applied to handovers as well.

There may be a need for an improved system and method for controlling cell reselection by a user equipment avoiding or at least reducing the above mentioned problems.

Summary of the Invention

This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the present invention are described by the dependent claims. According to a first aspect of the invention there is provided a method for controlling a reselection of a cell by a user equipment (U E) within a cellular network system. The cellular network system comprises a plurality of cells, wherein the user equipment is served by a source cell and reselects a target cell based on a predefined reselection scheme. The predefined reselection scheme is based on (e.g., absolute) priorities being assigned to each cell of the plurality of cells. The method comprises determining, by the user equipment, a mobility state of the user equipment, wherein the mobility state of the user equip- ment is indicative for a velocity of the user equipment relatively to the plurality of cells, adapting the predefined reselection scheme by adapting the (absolute) priorities being assigned to each cell of the plurality of cells based on a cell type characteristic of each cell and the determined mobility state, and controlling the reselection of the target cell based on the adapted reselection scheme.

The method can be implemented at the UE which can modify the predefined reselection priorities, for instance being configured by the network, for example via a central control unit, based on the knowledge of the cell type characteristic. That is, a UE in a specific mobility state overrides with adapted reselection priority value(s) the absolute predefined pri- orities of specific cells, which have been received via the network.

The described method relates in particular to LTE Advanced or WCDMA systems and in particular to HetNet measurements, but is not limited to these environments. The herein described method refers to handling cell reselection by a UE being based on priorities, for instance like the Absolute Priority reselection scheme.

The idea of the herein described method is to provide an improved handling of cell reselection by adapting priorities being assigned to cells. This adaptation is based on a mobility state of the UE as well as on a cell type characteristic. Thus, a determination and adap- tation may be performed so that appropriate cells may be preferred during reselection, instead of only considering the mobility state and providing a faster cell reselection.

The term "mobility state" in this context may refer to a velocity of a user equipment. It may refer in particular to a velocity relatively to the plurality of cells. In case, the user equip- ment is moving and is connected to a network which is also moving (for instance in a train or airplane), the velocity of the user equipment in relation to the cells will be low or zero.

The term "user equipment" in this context may be any type of communication end device, which is capable of performing the described adaptations and method. The UE may be in particular a cellular mobile phone, a Personal Digital Assistant (PDA), a notebook computer, a printer and/or any other movable communication device. The "plurality of cells" may be any kind of cell as being used in cellular network systems, in particular in heterogeneous networks. Each cell may be assigned to a base station. The term "base station" in this context may denote any kind of physical entity being able to hold one or more cells. A base station in this context may be any kind of network device providing the functionality for serving one or more cells; it may also be a transceiver node in communication with a centralized entity. The base station may be for example an eNodeB or eNB.

The "predefined reselection scheme" may be provide instructions for a UE how to reselect cells. The scheme may be based on (absolute) priorities being associated with cells, or with frequencies being assigned to cells. During reselection procedure, the UE may prefer to reselect a cell having a higher associated priority. Based on the herein described method, specific cells may be higher prioritized than other cells, and may thus be preferred by the UE during reselection.

The priorities may be defined by priority values being associated with each cell. Identical priority values may be associated with more than one cell, in particular with cells of the same cell type characteristic. According to an embodiment of the invention, the user equipment is in idle mode.

Idle mode may refer to a state of the UE, wherein the UE does not perform data transmissions but only exchanges information with base stations for keeping the connection. However, also when being in idle mode, the UE might need to be "handed over" between dif- ferent cells, which is called "cell reselection".

According to a further embodiment of the invention, the idle mode is an idle state of radio resource control. For a radio resource control (RRC) connection, the UE may be in an idle state, i.e., not

RRC connected, during times where no data transmission is required.

According to a further embodiment of the invention, the mobility state of the user equipment is determined as high, medium, or normal. In LTE, the mobility state is defined or determined based on the number of mobility events (cell reselections when I DLE, or handovers when CONNECTED) which took place within a time window, as specified by TCRmax. For instance, as defined in TR 36.304, chapter 5.2.4.3, besides normal-mobility state, a high-mobility and a medium-mobility state are applicable if the parameters (TCRmax, NCR_H, NCR_M and TCRmaxHyst) are sent in the system information broadcast of the serving cell. Medium-mobility state criteria are detected if the number of cell reselections during the time period TCRmax exceeds NCR_M and not exceeds NCR_H. High-mobility state criteria are detected if the number of cell reselections during the time period

TCRmax exceeds NCR_H. The UE shall not count consecutive reselections between same two cells into mobility state detection criteria if the same cell is reselected just after one other reselection. It is further defined that the U E shall, if the criteria for high-mobility state are detected, enter high-mobility state; else if the criteria for medium-mobility state are detected, enter medium-mobility state; else if criteria for either medium- or high- mobility state are not detected during time period TCRmaxHyst, enter normal-mobility state. If the UE is in high- or medium-mobility state, the UE shall apply the speed dependent scaling rules as defined in subclause 5.2.4.3.1. In TS 36.331 , chapter 5.5.6.2, it is described that the above described procedure is adapted for CONNECTED mode by counting handovers instead of reselections.

The determination of the mobility state may either be carried out by a base station or directly by the UE.

According to a further embodiment of the invention, adapting the predefined reselection scheme is carried out in case the mobility state is determined as high or medium.

The adaptation of the priorities may be necessary during high or medium mobility state, in which states the UE is moving with a higher velocity or at least traverses more cells than in normal mobility state. In particular in high or medium mobility state, it may be desired to adapt the priorities in order to avoid that the UE reselects specific cells.

According to a further embodiment of the invention, the plurality of cells are of different cell type characteristics, the cell type characteristics comprising at least one of cell type, cell coverage, cell capacity, and cell size. This may refer in particular to the case of heterogeneous networks, comprising different cells. The term "cell type characteristics" may refer to cell characteristics or properties.

The cell type may be defined for instance by macro, micro, pico, femto. The cell coverage may define for instance a region (vertical or horizontal), in which a connection via the cell may be provided for a UE. The cell capacity may define the amount of communications (e.g., for multiple UEs, per UE) which may be supported. Cell capacity and cell coverage may also be combined under the term cell deployment. The cell size may define the size of a cell for instance via an enumerated value (e.g., large, medium, small, very small) or via a numerical absolute value (for instance diameter or perimeter, which may be specified in meter or centimeter).

In addition, the cells may have an assigned cell priority referring to a priority cell status. This may denote that a cell with a higher priority may be preferred or prioritized over other cells. The priority may be independent of the size or other properties of the cells. According to the herein described method, the priorities may be adapted based on the size or other properties of the cells and the determined mobility state of the UE.

According to a further embodiment of the invention, the method further comprises deter- mining the cell type characteristic of each cell of the plurality of cells.

This determination may be carried out by a central control unit or may be performed by the UE, for instance based on broadcast information being provided to the UE. According to a further embodiment of the invention, determining the cell type characteristic comprises associating physical cell identities of cells with a cell type.

The UE may then determine the cell type characteristic of neighboring cells by determining the physical cell identities of these cells. Based on this, the UE may be able to adapt the reselection scheme.

According to a further embodiment, adapting the (absolute) priorities comprises lowering the (absolute) priorities of cells having a cell type characteristic being indicative for a specific cell, in particular a small cell.

A "small cell" in this context may refer to a cell having a small coverage or representing a low power mode. By lowering the priorities of specific cells, it may be achieved that the UE only reselects desired cells having a higher priority. The adaptation of the priorities may correspond to exchanging or overriding the predefined (absolute) priorities. For instance, a UE in medi- urn or high mobility state may override with the lowest reselection priority value(s) the priorities of small cells / low power cells received by the network.

According to a further embodiment, the (absolute) priorities are lowered for a defined time period.

This may correspond to a temporarily adaptation or lowering of the priorities. The time period may be measured by using a timer, for instance. This may provide the advantage that the UE may use the predefined reselection scheme after the defined time period without performing additional steps.

According to a second aspect of the invention, there is provided a user equipment for controlling a reselection of a cell by the user equipment within a cellular network system. The cellular network system comprises a plurality of cells. The user equipment is served by a source cell and is adapted to reselect a target cell based on a predefined reselection scheme. The predefined reselection scheme is based on (absolute) priorities being assigned to each cell of the plurality of cells. The user equipment comprises a determination unit being adapted to determine a mobility state of the user equipment, wherein the mobility state of the user equipment is indicative for a velocity of the user equipment relatively to the plurality of cells. The user equipment further comprises an adaptation unit being adapted to adapt the predefined reselection scheme by adapting the (absolute) priorities being assigned to each cell of the plurality of cells based on a cell type characteristic of each cell and the determined mobility state. In addition, the user equipment comprises a control unit being adapted to control the reselection of the target cell based on the adapted reselection scheme.

The user equipment (UE) may be any type of communication end device, which is capable of providing the described functionalities. The UE may be in particular a cellular mobile phone, a Personal Digital Assistant (PDA), a notebook computer, a printer and/or any other movable communication device.

The user equipment may comprise a receiving unit or receiver which is adapted for receiving signals from base stations serving the plurality of cells. The user equipment may com- prise a transmitting unit for transmitting signals. The transmitting unit may be a transmitter as known by a skilled person. The receiver and the transmitting unit may be implemented as one single unit, for example as a transceiver. The transceiver or the receiver and the transmitting unit may be adapted to communicate with base stations of the plurality of cells via an antenna.

The user equipment may comprise a determination unit, an adaptation unit and a control unit as described above. The determination unit, the adaptation unit and the control unit of the user equipment may be implemented for example as part of a common control unit, like a CPU or a microcontroller. The determination unit and the transceiver may be coupled or may be implemented as one single unit. The determination unit may be adapted to receive signals being indicative for the mobility state via the transceiver.

According to a third aspect of the invention, there is provided a base station being adapted to communicate with the user equipment having the above mentioned features.

The base station may be any type of access point or point of attachment, which is capable of providing a wireless access to a cellular network system. Thereby, the wireless access may be provided for a user equipment or for any other network element, which is capable of communicating in a wireless manner. The base station may be an eNodeB, eNB, home NodeB or HNB, or any other kind of access point. Each cell of the plurality of cells may be assigned to one base station, wherein one base station may also serve more than one cell. The base station may comprise a receiving unit, for example a receiver as known by a skilled person. The base station may also comprise a transmitting or sending unit, for example a transmitter. The receiver and the transmitter may be implemented as one single unit, for example as a transceiver. The transceiver or the receiving unit and the sending unit may be adapted to communicate with the user equipment via an antenna.

The base station may also comprise a control unit for instance for controlling the reselec- tion scheme. The control unit may be implemented as a single unit or may be implemented for example as part of a standard control unit, like a CPU or a microcontroller. According to a fourth aspect of the invention, there is provided a cellular network system. The cellular network system comprises a user equipment as described above. Generally herein, the method and embodiments of the method according to the first aspect may include performing one or more functions described with regard to the second, third or fourth aspect or an embodiment thereof. Vice versa, the user equipment, the base station or the cellular network system and embodiments thereof according to the second, third and fourth aspect may include units or devices for performing one or more functions described with regard to the first aspect or an embodiment thereof.

According to a fifth aspect of the herein disclosed subject-matter, a computer program for controlling a reselection of a cell by a user equipment is provided, the computer program being adapted for, when executed by a data processor assembly, controlling the method as set forth in the first aspect or an embodiment thereof.

As used herein, reference to a computer program is intended to be equivalent to a reference to a program element and/or a computer readable medium containing instructions for controlling a computer system to coordinate the performance of the above described method.

The computer program may be implemented as computer readable instruction code by use of any suitable programming language, such as, for example, JAVA, C++, and may be stored on a computer-readable medium (removable disk, volatile or non-volatile memory, embedded memory/processor, etc.). The instruction code is operable to program a computer or any other programmable device to carry out the intended functions. The computer program may be available from a network, such as the World Wide Web, from which it may be downloaded.

The herein disclosed subject matter may be realized by means of a computer program respectively software. However, the herein disclosed subject matter may also be realized by means of one or more specific electronic circuits respectively hardware. Furthermore, the herein disclosed subject matter may also be realized in a hybrid form, i.e. in a combi- nation of software modules and hardware modules.

In the above there have been described and in the following there will be described exemplary embodiments of the subject matter disclosed herein with reference to a cellular network system, a base station, a user equipment and a method of controlling a reselection of a cell by a user equipment. It has to be pointed out that of course any combination of features relating to different aspects of the herein disclosed subject matter is also possible. In particular, some embodiments have been described with reference to apparatus type embodiments whereas other embodiments have been described with reference to method type embodiments. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one aspect also any combination between features relating to different aspects or embodiments, for example even between features of the apparatus type embodiments and features of the method type embodiments is considered to be disclosed with this application.

The aspects and embodiments defined above and further aspects and embodiments of the present invention are apparent from the examples to be described hereinafter and are explained with reference to the drawings, but to which the invention is not limited.

Brief Description of the Drawing

Figure 1 shows a cellular network system according to an exemplary embodiment of the present invention.

Figure 2 shows a user equipment and a base station within a cellular network system ac- cording to an exemplary embodiment of the invention.

It is noted that in different figures, similar or identical elements are provided with the same reference signs.

Detailed Description

In the following, embodiments of the herein disclosed subject matter are illustrated with reference to the drawings and reference to aspects of current standards, such as LTE. However, such reference to current standards is only exemplary and should not be considered as limiting the scope of the claims.

Figure 1 shows a cellular network system 100. The cellular network system 100 comprises a plurality of cells 102-106. A user equipment 101 , which moves through the network, may perform and control a cell reselection as described below. During movement of the UE 101 within the network, cell reselections or handovers may be carried out. This may be based on a predefined cell reselection scheme. The predefined cell reselection scheme associates a priority value with each cell 102-106, for instance identical priority values for cells having identical cell type characteristics.

To improve existing cell reselection methods, the UE 101 may adapt the priorities being associated with the cells according to the predefined reselection scheme. As shown in Figure 1 , cells 102, 104 and 105 represent macro cells and cell 103 represents a smaller cell or lower power node, for instance a micro or pico cell.

When the UE is moving fast through the network, it may be desirable to avoid reselections to small cells, as this may lead inter alia to a high amount of reselections due to the low coverage of the small cells. The UE 101 may determine its mobility and may adapt the predefined reselection scheme by adapting the priorities being assigned to each cell of the plurality of cells 102-106 based on a cell type characteristic of each cell and the determined mobility state. For instance, the UE 101 may adapt the priority of the small cell 103 by lowering the priority when being in a high or medium mobility state. Thus, the UE may prefer the greater cells 102, 104 and 105 for future cell reselection. In another case, the UE 101 might not change the priorities of the cells 102-106 when being in a normal mobility case. In this case, the UE may choose each cell for reselection equilibrated.

The cell selection and reselection processes may run autonomously by the UE in idle mode according to standardized reselection procedures and related network configured parameters. Network topologies may support a priority based cell reselection procedure for inter-frequency and inter-RAT reselections referred to as the Absolute Priority method.

A camping UE may also detect autonomously its mobility state, and if in high- or medium- mobility state, the UE may apply speed dependent scaling rules to the reselection parameters if configured by the network. The network may define speed dependent scaling for Treselection and Qhyst parameters. For instance, TS 36.304, Sect. 5.2.4.3.1 , states that:

If High-mobility state is detected:

Add the sf-High of "Speed dependent ScalingFactor for Q_hyst" to Q_hyst if sent on system information For E-UTRAN cells multiply Treselection_EUTRA by the sf-High of "Speed dependent ScalingFactor for Treselection_EUTRA" if sent on system information

In common network systems, the network can configure the "Speed dependent

ScalingFactor for Treselection" from the following set of values {0.25, 0.50, 0.75, 1 .00} (TS 32.592). This means that the scaled Treselection for UEs in medium and high mobility states can only be shortened favouring faster cell reselections. The latter is likely the desired behaviour if the target cell is a macro cell or in case of an outbound reselection from a low power node / small cell (e.g. micro, pico cell) in order to e.g. minimize mobility prob- lems due to a sharp drop in signal strength and quality in the camping cell. However, such scaling may also cause undesired effects such as UEs entering a small cell faster, i.e. faster inbound cell reselections towards a small target cell. This may result in frequent reselections and especially in the situation that a UE - moving to connected mode - may be then served by the low power node which may lead to frequent handovers, ping pongs, radio link failures, and performance degradation. On the other hand, allowing fast moving UEs to camp on and being served by low power nodes can be a valid target in case of e.g. coverage holes at the macro overlay. Similar speed dependent scaling is also applied to UEs in connected mode, so the considerations above on cell reselections can be applied to handovers as well.

Based on the current specifications, black listing small cells for fast moving UEs could be used. However, this is a hard control which can cause link failures in case of coverage holes of the macro overlay. Additionally, it is not straightforward to differentiate the monitored cells for low and high mobility UEs.

3GPP specifies for UTRAN an optional cell reselection procedure referred to as Hierarchical Cell Structure, HCS, (TS 25.304) which includes selection rules differentiated based on the UE high mobility state which may remove the issues:

UEs in non High Mobility State prefer to reselect to a cell with higher HCS priority · UEs in High Mobility State prefer to reselect to a cell with equal or lower HCS priority

However, HCS is optional, applies only to UTRAN and the Absolute Priorities method would override HCS rules for inter-frequency and inter-RAT reselections if used as well for instance because of coexistence of UTRAN and E-UTRAN (i.e. Absolute Priorities are mandatory for E-UTRAN). However, the common network systems do not provide an improved handling of fast moving UEs when in idle mode.

According to the herein described method and system, a soft avoidance of reselecting low power nodes for medium and high mobility UEs may be added to the Absolute Priority reselection scheme. The mechanism can be implemented at the UE which may modify the network configured reselection priorities based on the knowledge of the cell type. That is, a UE in medium and high mobility may override with the lowest reselection priority val- ue(s) the priorities of small cells / low power cells received by the network.

The knowledge of the cell type at the UE side may be provided for instance by associating neighbour physical cell identities (PhyCell IDs) with the cell types.

Such avoidance may guarantee that a fast moving UE could camp on the safer overlay cell - whenever possible - such that the UE will not need to make a handover immediately before data connection starts. An additional benefit may consist in the soft avoidance mechanism which may guarantee that fast moving UEs may avoid reselecting to small cells as long as there is macro overlay coverage. Instead, in case of e.g. a macro coverage hole, reselections can happen also to small cells.

Priorities may be assigned to different frequencies or inter-RAT frequencies and provided to the UEs in the system information (broadcasted), in the RRCConnectionRelease message (UE dedicated), or by inheriting from another RAT at inter-RAT cell reselection. A possible implementation of the method is for the UE to override the acquired priorities for those cells which are associated to small cell types if in medium or high mobility state.

With the eventually overridden absolute priorities in place, the reselection decision may undergo regular absolute priority criteria as follows:

- A UE reselects to a higher priority frequency or RAT if the targeted cell fulfils the condition Squal > Thresh_Xihig_hQ/p

- A UE will reselect to a lower or equal priority cell

o if the serving cell fulfils Squal < Thresh_serVing,iowQ/p and

o if Squal > Thresh_Xi|_0WQ/p is met for the targeted cell during the time interval

Treselection where the quality or signal strength thresholds Thresh_X hignQ / p, Thresh_serVj_ng |_0WQ / p, and Thresh_XiiowQ / p are broadcasted in the system information (3GPP TS 36.331 / 25.331). Figure 2 shows a cellular network system 200 according to a further exemplary embodiment of the invention. The cellular network system comprises a base station 201 and a user equipment 101. The base station 201 may serve one or more cells of the cellular network system 200.

The user equipment 101 comprises a determination unit 203, an adaptation unit 204, and a control unit 205. The determination unit 203 is adapted to determine a mobility state of the user equipment 101. The mobility state of the user equipment is indicative for a veloci- ty of the user equipment relatively to the plurality of cells.

The adaptation unit is adapted to adapt the predefined reselection scheme by adapting the priorities being assigned to each cell of the plurality of cells based on a cell type characteristic of each cell and the determined mobility state. The control unit is adapted to con- trol the reselection of the target cell based on the adapted reselection scheme.

The user equipment (UE) may be any type of communication end device, which is capable of providing the described functionalities. The UE may be in particular a cellular mobile phone, a Personal Digital Assistant (PDA), a notebook computer, a printer and/or any oth- er movable communication device.

The user equipment may comprise a receiving unit or receiver which is adapted for receiving signals from base stations serving the plurality of cells. The user equipment may comprise a transmitting unit for transmitting signals. The transmitting unit may be a transmitter as known by a skilled person. The receiver and the transmitting unit may be implemented as one single unit, for example as a transceiver 202. The transceiver or the receiver and the transmitting unit may be adapted to communicate with base stations of the plurality of cells via an antenna, for instance with the base station 201 as shown in Figure 2. The determination unit 203, the adaptation unit 204 and the control unit 205 of the user equipment may be implemented for example as part of a control unit, like a CPU or a microcontroller. The determination unit and the transceiver may be coupled or may be implemented as one single unit. The determination unit 203 may be adapted to receive signals being indicative for the mobility state via the transceiver 202, for instance from the base station 201. The base station may be any type of access point or point of attachment, which is capable of providing a wireless access to a cellular network system. Thereby, the wireless access may be provided for a user equipment or for any other network element, which is capable of communicating in a wireless manner. The base station may be an eNodeB, eNB, home NodeB or HNB, or any other kind of access point. Each cell of the plurality of cells may be assigned to one base station, wherein one base station may also serve more than one cell.

The base station may comprise a receiving unit, for example a receiver as known by a skilled person. The base station may also comprise a transmitting or sending unit, for example a transmitter. The receiver and the transmitter may be implemented as one single unit, for example as a transceiver 206. The transceiver or the receiving unit and the sending unit may be adapted to communicate with the user equipment via an antenna. The base station may also comprise a control unit 207 for instance for controlling the rese- lection scheme. The control unit may be implemented as a single unit or may be implemented for example as part of a standard control unit, like a CPU or a microcontroller.

Having regard to the subject matter disclosed herein, it should be mentioned that, al- though some embodiments refer to a "base station", "eNB", etc., it should be understood that each of these references is considered to implicitly disclose a respective reference to the general term "network component" or, in still other embodiments, to the term "network access node". Also other terms which relate to specific standards or specific communication techniques are considered to implicitly disclose the respective general term with the desired functionality.

It should further be noted that a user equipment or base station as disclosed herein is not limited to dedicated entities as described in some embodiments. Rather, the herein disclosed subject matter may be implemented in various ways in various locations in the communication network while still providing the desired functionality.

According to embodiments of the invention, any suitable entity (e.g. components, units and devices) disclosed herein, e.g. the determination unit, are at least in part provided in the form of respective computer programs which enable a processor device to provide the functionality of the respective entities as disclosed herein. According to other embodiments, any suitable entity disclosed herein may be provided in hardware. According to other - hybrid - embodiments, some entities may be provided in software while other entities are provided in hardware.

It should be noted that any entity disclosed herein (e.g. components, units and devices) are not limited to a dedicated entity as described in some embodiments. Rather, the herein disclosed subject matter may be implemented in various ways and with various granularities on device level while still providing the desired functionality. Further, it should be noted that according to embodiments a separate entity (e.g. a software module, a hardware module or a hybrid module) may be provided for each of the functions disclosed herein. According to other embodiments, an entity (e.g. a software module, a hardware module or a hybrid module (combined software/hardware module)) is configured for providing two or more functions as disclosed herein.

It should be noted that the term "comprising" does not exclude other elements or steps. It may also be possible in further refinements of the invention to combine features from different embodiments described herein above. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

List of reference signs:

100 Cellular network system

101 User equipment

102 Cell

103 Cell

104 Cell

105 Cell

106 Cell

200 Cellular network system

201 Base station

202 Transceiver of user equipment

203 Determination unit of user equipment

204 Adaptation unit of user equipment

205 Control unit of user equipment

206 Transceiver of base station

207 Control unit of base station

Claims

CLAIMS:

1. A method for controlling a reselection of a cell by a user equipment (101) within a cellular network system (100), the cellular network system (100) comprising a plurality of cells (102-106), wherein the user equipment is served by a source cell and reselects a target cell based on a predefined reselection scheme, the predefined reselection scheme being based on priorities being assigned to each cell of the plurality of cells (102-106), the method comprising

determining, by the user equipment (101 ), a mobility state of the user equipment, wherein the mobility state of the user equipment (101) is indicative for a velocity of the user equipment (101) relatively to the plurality of cells (102-106),

adapting the predefined reselection scheme by adapting the priorities being assigned to each cell of the plurality of cells (102-106) based on a cell type characteristic of each cell and the determined mobility state, and

controlling the reselection of the target cell based on the adapted reselection scheme.

2. The method as set forth in claim 1 , wherein the user equipment (101 ) is in idle mode.

3. The method as set forth in claim 2, wherein the idle mode is an idle state of radio resource control.

4. The method as set forth in any one of the preceding claims, wherein the mobility state of the user equipment (101 ) is determined as high, medium, or normal.

5. The method as set forth in claim 4, wherein adapting the predefined reselection scheme is carried out in case the mobility state is determined as high or medium.

6. The method as set forth in any one of the preceding claims, wherein the plurality of cells (102-106) are of different cell type characteristics, the cell type characteristics comprising at least one of cell type, cell coverage, cell capacity, and cell size.

7. The method as set forth in any one of the preceding claims, further comprising determining the cell type characteristic of each cell of the plurality of cells (102-106).

8. The method as set forth in claim 7, wherein determining the cell type characteristic comprises associating physical cell identities of cells with a cell type.

9. The method as set forth in any one of the preceding claims, wherein adapting the priorities comprises lowering the priorities of cells having a cell type characteristic being indicative for a specific cell.

10. The method as set forth in claim 9, wherein the priorities are lowered for a defined time period.

11. A user equipment (101) for controlling a reselection of a cell by the user equipment (101) within a cellular network system (100), the cellular network system (100) comprising a plurality of cells (102-106), wherein the user equipment (101) is served by a source cell and is adapted to reselect a target cell based on a predefined reselection scheme, the predefined reselection scheme being based on priorities being assigned to each cell of the plurality of cells (102-106), the user equipment (101) comprising

a determination unit (203) being adapted to determine a mobility state of the user equipment (101), wherein the mobility state of the user equipment (101) is indicative for a velocity of the user equipment (101) relatively to the plurality of cells (102-106),

an adaptation unit (204) being adapted to adapt the predefined reselection scheme by adapting the priorities being assigned to each cell of the plurality of cells (102-106) based on a cell type characteristic of each cell and the determined mobility state, and a control unit (205) being adapted to control the reselection of the target cell based on the adapted reselection scheme.

12. A base station (201) being adapted to communicate with the user equipment (101) as set forth in claim 1 1.

13. A cellular network system (100), the cellular network system comprising a user equipment (101) as set forth in claim 11.