WO2012154096A1 - Methods and arrangements for handling neighbor cell relations in a cellular network - Google Patents

Abstract

A method in a first base station (105) for handling neighbor cell relations in a cellular network (100) is provided. The first base station (105) receives a system information broadcasted from a second base station (115) serving a cell (120) comprised in the cellular network (100), The system information is received in a receiver comprised in the first base station (105). The receiver is of a user equipment type and configured to receive broadcasted information from neighbor base stations including the second base station (115), The first base station (105) extracts a cell information related to the cell (120) from the system information. The first base station further establishes a neighbor cell relation with the cell (120) based on the extracted cell information.

Description

METHODS AND ARRANGEMENTS FOR HANDLING NEIGHBOR CELL RELATIONS IN

A CELLULAR NETWORK

TECHNICAL FIELD

Embodiments herein relate to a base station and a method in a base station, Sn particular, embodiments herein relate to handling neighbor cell relations in a cellular network.

BACKGROU D

Sn a typical cellular network, also referred to as a wireless communication system, User Equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks (CNs).

A user equipment is a mobile terminal by which a subscriber can access services offered by an operator's core network and services outside operator's network to which the operator's RAN and CN provide access. The user equipments may be for example communication devices such as mobile telephones, cellular telephones, or laptops with wireless capability. The user equipments may be portable, pocket-storabSe, hand-held, computer-comprised, or vehicle-mounted mobiie devices, enabled to communicate voice and/or ό ΐ&, via the radio access network, with another entity, such as another mobile station or a server.

User equipments are enabled to communicate wireiessiy in the celiular network. The communication may be performed e.g. between two user equipments, between a user equipment and a reguiar telephone and/or between the user equipment and a server via the radio access network and possibly one or more core networks, comprised within the cellular network.

The cellular network covers a geographicai area which is divided into cell areas. Each eel! area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. ^*eN8", "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 e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also on cell size.

In the context of this disclosure, any kind of base station as described above will be referred to as a "base station" or a Radio Base Station (RBS). However, in parts of this disclosure, a distinction will be made between macro base stations and low power base stations. The low power base station consumes less power than the macro base station, for example due to the lower transmission power used, Examples of low power base stations are pico base stations, relays and home base stations, which may be for example femto cei!s operating either in a cluster of femto cells or as single femto cell deployments.

A user equipment as described above, will in this disclosure be referred to as a user equipment or a UE,

In some radio access networks, several base stations may be connected, e.g. by landiines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or io each other.

The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GS is an abbreviation for Global System for Mobile Communications

(originally: Groupe Special Mobile).

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to one or more core networks. The eNBs are also directly connected to each other through a so called X2 Interface.

UMTS is a third generation, 3G, mobile communication system, which evolved from the second generation, 2G, mobile communication system GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (VVCD A) access tech ofogy, UMTS Terrestrial Radio Access Network (UTRAN) ;s essentially a radio access network using wideband code division multiple access for user equipments. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies,

A ceil is the geographicai area where radio coverage is provided by the base station at a base station site. One base station, situated at the base station site, ma 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 user equipments within range of the base stations. The ceil from within which the communication between a user equipment and a base station is communicated, is referred to as the serving cell for that user equipment.

To support mobility of user equipments between ceils in a cellular network, so called handovers must be performed. Handovers are necessary for example when a user equipment leaves one cell and moves into another cell. Otherwise, for example an ongoing caiS would be dropped, due to loss of radio coverage,

A handover may be a change of serving ceil, so that a user equipment being served by one cell, becomes served by another cell instead.

To enable handovers, the different cells in the cellular network must be

identifiable. Therefore, each cell in the radio access network broadcasts a well-defined signature sequence that reveals its identity.

Some of the broadcast celi identities are reused in the radio access network, and are therefore not globally unique. In UTRAN, the reused cell identity is the downlink scrambling code, and in LTE, it Is the Physical Cell Identity (PCI). These reused cell identities are used for exampl for measurement reporting performed by the user equipments about neighboring ceils.

In addition to the reused ceil identities, uniqu celi identifiers, so called Cell Global Identifiers (CGis), may also be broadcast from within each cell. The E-UTRAN CGI (E- CGI) is an example of a unique cei! identifier. The unique cell identifiers may identify the cell uniquely within all different mobile networks. The unique cell identifier may be used for example for handover routing i.e. for the handover sourc node to communicate with the handover target node.

Another identity broadcasted as part of the system Information is for example the Public fv obi!e Network Identity (PLMN ID) that uniquely identifies the mobile network, and the system information may include one or more PIMU IDs in each cell. Still another identity broadcasted may be the Closed Subscriber Group ID (CSG-SD) that may be used to define which user equipments are allowed to access a specific cell. Even still another identity broadcasted is the Tracking Area Code (TAG) that may be used for example for Mobility Management procedures by the user equipments,

To facilitate the handling of handovers, neighbor ceil relations (NCR) have been introduced in many radio access networks, in a neighbo cell relation there is sufficient information about the cells in question to provide for a possible handover of a user equipment between the cells experiencing the neighbor ceil relation. Such requested information may comprise for example the above mentioned cell information regarding ceil identity, as well as information regarding which radio neiwork node that is controlling the base station, serving the cell In question. For the purpose of radio network node identification, each radio network node may be associated with a unique radio network node identifier.

An example of a neighbor ce!i relation is the mapping between the reused cell S identity and the unique cell identifier and the TAG. When a user equipment reports the reused cell identity, the neighbor ceil relation may be used to find out the unique ceil identifier and the TAG for handover purposes.

The information needed to establish the neighbor cell relations may for example be compiled through drive tests or planning tool computations,

0 A problem is that drive tests are time and cost consuming, and that planning tools may not be fully accurate.

The information needed to provide the neighbor ceil relations may also be provided by user equipment assisted measurements. An example of this is the Automatic Neighbor Relation (AMR) function in 3GPP LTE, where the user equipment reports some5 of, or all, the above mentioned ceil identifiers, for example both the non-unique eel! identifier as well as the globally unique cell identifier, upon request from the serving cell.

In an E-UTRAN radio access network neighbor cell relations to neighbor base stations are to a large extent automated by the AMR feature. ANR is a feature aiming to relieve the operator from needing to manually configure the neighbor cell lists and0 associations, i.e. Neighbor Relation Lists. It is currently only standardized in LTE/SAE eNodeBs and user equipments, but may be used to retrieve information about LTE/SAE, WCD!ViA and GSM neighbor cells.

The ANR function is described in the following;

Assume that an eNB serving cell A has an ANR function. As part of the normal5 procedures, the eNS instructs a user equipment it is serving to perform measurements on neighbor cells. The user equipment then sends a measurement report regarding a cell B. This report may contain Cell B's PCS, but not its E-CGi. If the cell B is on the same frequency, or carrier, as the current serving cell, cell A, the user equipment may detect ceil 8 without any interruption in the communication towards Ceil A, However, if cell B is0 on another carrier, then th user equipment may need measurement gaps in the form of idie periods to be able to detect the Ceil 8 and its PCI. The eNB then instructs the user equipment, using the newiy discovered PCI as parameter, to read the E-CGI, the TAG, and all available PLMN !D(s) of th cell B. To do so, the eNB may need to schedule appropriate idle periods to allow the user equipment to read the E-CGi from the broadcast5 channel of the detected neighbor cell, Cell B, The required measurement gaps, or idle periods, may be even longer for the case when the Cell B is on another frequency, or carrier, than the Cei! A. When the user equipment has found out the Cell 8:s E-CGI, the user equipment reports the detected E-CGI to the eNB. In addition, the user equipment reports the Tracking Area Code (TAC) and a!l PLMN IDs that it has detected. If the detected cell 8 is a CSG or hybrid ceil, the user equipment also reports the CSG ID to the eNB. The eNB may then decide to add this neighbor relation, i.e. establish a neighbor ceii relation with cell B, and may use the acquired parameters to update the Neighbor Relation List, if needed, it may for example setup a new X2 interface towards the eNB serving the Cell B,

To summarize, the user equipment based ANR may be used to retrieve

information about the following identities, e.g. in addition to the measurement results: PCI, E-CGI, TAC, aii broadcasted PLMN-lDs, and in the case of so called closed or Hybrid CSG cells, CSG ID. A problem is however, thai the ANR is defined as an optional feature for the user equipments, which means that only a limited set of user equipments are available for the cellular network to exercise ANR. Further, the ANR feature consumes additional user equipment battery and may incur interruptions in user data.

The above mentioned problems may be relevant in cellular networks covering areas with high traffic, i.e. high concentration of users, In those areas if may be desirable to deploy additional capacity to keep the user satisfaction. The added capacity may then be in the form of additional macro base stations or in the form of low power base stations, with Iower output power, that cover smaller ceils in order to concentrate the capacity boost on a smaller area. There may also be areas with bad coverage where there is a need for coverage extension. Here too, a low powe base station may be depioyed to concentrate the coverage boost in a small area.

One argument for choosing low power base stations in the above cases is that the impact on the macro network may be minimized, e.g. a smaller area where the macro network may experience interference.

Currently there is a strong drive in the industry in the direction towards the use of iow power base stations. The different terms used for this type of cellular network deployments are Heterogeneous networks, multilayer networks, or shortly HetNets.

The HetNets however, require additional neighbor ceii relations to be established. Hence, the above mentioned problems may be highly relevant for such eeiluiar networks. SUMMARY

In view of the discussion above, it is an object for embodiments herein to provide an improved way of handling neighbor eel! relations in a cellular network.

According to a first aspect, the object is achieved by a method in a first base station for handling neighbor cell relations in a cellular network. The first base station is comprised in the ceiiuiar network. The first base station receives a system information broadcasted from a second base station serving a ce!! comprised in the ceiiuiar network. The system information is received in a receiver comprised in the first base station. The receiver is of a user equipment type and configured to receive broadcasted information from neighbor base stations including the second base station.

The first base station extracts a ce!i information related to the cei! from the system information. The first base station further establishes a neighbor cell relation with the ce!! based on the extracted cei information,

According to a second aspect, the object is achieved by a first base station for handling neighbor cell relations in a ceiiuiar network. The first base station is comprised in the ceiiuiar network. The first base station comprises a receiver. The receiver is of a user equipment type and configured to receive broadcasted information from neighbor bas stations including a second base station serving a cell comprised in the cellula network. The receiver is further configured to receive a system information broadcasted from the second base station. The first base station further comprises an extraction unit. The extraction unit is configured for extracting a cell information related to the cell from the system information. The first base station further comprises an establishing unit Th establishing unit is configured to establish a neighbor cell relation with the cell based on the extracted cell information.

Since the first base station uses a receiver of user equipment type to receive information that is broadcasted in neighbouring cells, the base station can derive cell information necessary for setting up a neighbour cell relation with a neighbouring cell without relying on user equipment measurements and/or drive tests or planning tools, which results in an improved way of handling neighbour cell relations in the cellular network. An advantage of embodiments herein is that they a!iow the cellular network to be configured without any user equipment intervention or even user equipment existence in the cellular network.

A further advantage is that this also enables the first base station to become configured as part of the cellular network with regards to a neighbor ceil relation without having to wait for a user equipment to detect and report it to the cellular network to trigger an existing user equipment based-based ANR feature. This is important because it better supports ad hoc cell deployment for example of low power base stations in between macro base stations in the cellular network with minimal cell planning, while maintaining a required performance in the ceiiular network.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic block diagram illustrating an embodiment of a cellular network. Figure 2 is a combined signalling scheme and flowchart illustrating embodiments in a cellular network.

Figure 3 is a flowchart depicting embodiments of a method in a first base station.

Figure 4 is a schematic block diagram illustrating embodiments of a first base station.

DETAILED DESCRIPTION

Embodiments herein may be exemplified in the following non-!imiting description of embodiments.

Figure 1 depicts a ceiiular network 100 in which embodiments herein may be implemented. The cellular network 100 may in some embodiments apply to one or more of the previously mentioned radio access technologies, and hence to one, or a

combination, of for example LTE, WCD^'MA, GSM, or any other any 3GPP radio access technology, and to cases where multiple radio access networks are deployed in the same geographical area.

in this example, the ceiiular network 100 is, by way of example, a heterogeneous network, HetNet, of LTE type, which is referred to as E-UTRAN. This may also be referred to as a System Architecture Evolution (SAE) network. The other name for the LTE/SAE network is the Evolved Packet System (EPS), which comprises both the Evolved UTRAN {E-UTRAN} radio access network and the Evolved Packet Core (EPC) core network. The cellular network 100 may in some embodiments apply to one or more of the previously mentioned radio access technologies, and hence to one, or a combination, of for example LTE, WCDMA, GSM, or any other any 3GPP radio access technology.

The cellular network 100 comprises a first base station 10S. The first base station 105 may be e,g, a radio base station, such as an eNB, NodeB^", ' B node', or BTS, depending on the technology and terminology used. The first base station 105 may be of different classes, for example a macro base station, such as for example a eNodeB, or a iow power base station, such as for example a home eNodeB, pico base station, or fernto base station, based on transmission power and thereby also on cell size. Sn this example, the first base station is a iow power base station i the form of a pico base station, covering a rather small ceH 110. In some embodiments, the first base station 105 may serve more than one cell, which may be of another size. An example of a power output of a iow power base station may be about 2 watts or less. For a macro base station, an output power may be for example tens of watts.

The cellular network 100 further comprises a second tease station 116, serving ee ! 20 and a third base station 125, serving a cell 130.

The second base station 115 and the third base station 125 may also be of any of the above mentioned types. Sn this example, however, the second base station 115 and the third base 125 station are both macro base stations in the form of eNBs. In other embodiments, the second and third base stations, 1 15, 25, are not of the same type.

The celiuiar network 100 further comprises a cluster of femto cells 13§, served for example by separate iow power base stations. Sn some embodiments, single femto eel! deployments may also exist in the celiuiar network 100.

To facilitate the handling of handovers in the ceiiular network 100, neighbor ceii relations may be established. Sn a neighbor eel! relation there is sufficient information about the cells in question to provide for a possible handover of a user equipment between the ceils experiencing the neighbor ceii relation. Such requested information may comprise for example the previously mentioned ceii information regarding cell identity, as well as information regarding which radio network node that is controlling the base station, serving the ceii in question. This cell-specific information is broadcasted from within the various ceils.

According to embodiments herein, the first base station 105 comprises a user equipment type receiver. This is to allow detection of the celiuiar network coverage, for example system information such as a cell identity broadcasted in the cells 120, 130 and 135. The receiver, being of a user equipment type, is configured to receive broadcasted information from neighbor bass stations including the second base station 115. Figure 2 illustrates how a method for handling neighbor cell relations in the cellular network 100 according to some embodiments herein may be implemented. The

5 action comprises the foilowing actions, which actions may be taken in any suitable order.

In action 201 , which is optional, the first base station 05 allocates time resources for listening to, i.e. receiving, broadcasted system information from

neighbouring cells, such as for example the eel! 120 served by the second base station 10 115, and the ceil 130 served by the third base station 125. By allocating specific time resources for this purpose, the first base station 105 may perform the receiving during a time period of reduced interference from other transmissions in the cellular network 100. This wiSS be further elaborated later in relation to figure 3.

15 In action 292, the second base station 115 broadcasts system information such as Master Information Block (Mi B) and different System Information Block (SIB) messages for example comprising eeSi information about the cell 120 served by the second base station 115 such as for example the unique cell identifier, the TAC, the PLMN \D, etc of the cell 120. The second base station may aiso broadcast information on

20 lower layers that are not normally part of the system information. The reused ceil identity is an example of such information.

In action 203, the first base station 105 receives, through its receiver of user equipment type, the broadcasted system information from the cell 120. In this example, 25 the first base station 105 also receives (not shown) broadcasted information from the third base station 125 and the cluster of femto ceils 135.

In action 204, the first base statio 105 extracts eel! information which is necessary to establish a neighbor cell relation with the cell 120, from the received 30 broadcasted information, in some embodiments, the extracted ceil information may

comprise for example at least one of PCI, EGGS, E-UTRAN Absolute Radio Frequency Channel Number (EARFC ), TAC, some or all broadcasted PL N- Ds and CSG ID.

In some embodiments, the cell information may comprise some of, or the same, information as is retrieved, or measured, by a user equipment in the cellular network 100 35 for the purpose of AMR. In action 205, the first base station 105 establishes a neighbor cell relation with the ceii 115 based on the extracted ceil information. This may comprise for example the following. The first base station 105 may create a local neighbor cell relation for the ceii 5 120 by associating a detected reused eel! identity with the extracted cell information. The first base station 105 may also contact the second base station 115, for example using the X2 -interface, to provide information to the second base station 1 15 so that it may add a local neighbor cell relation in the second base station 115 for the cell 110.

10 In action 208, the first base station 105 transmits, or forwards, the extracted cell information to the third base station 125, to assist the third base station 125 in

establishing a neighbor ce!i relation with the ceil 120. The base station 105 may also transmit the received information related to the cell 130 and the femto cells 135 to the second base station 115 for the same purpose.

15

Sn action 207, the third base station 125 establishes a neighbor cell relation with the cell 120 based on the cell information.

Hence, according to embodiments herein, a neighbor cell relation is established 20 between the first base station 105 and the second base station 115 without relying o user equipments, planning tools, or drive tests. Thanks to embodiments herein, wherein the first base station 105 receives broadcasted system information directly from the second base station 1 5, and extracts the necessary cell information for establishment of a neighbor cell relation with the cell 120, the first bas station 105 may configure itself 25 with regards to a neighbor cell relation in the cellular network 100.

Moreover, according to some embodiments herein, the first base station 105 further assists the third base station 125 in establishing a neighbor cell relation with the cell 120, by forwarding the extracted cell information related to the cell 120 to the third base station 125, possibly over a X2 interface.

30

Embodiments herein, relating to a method in the first base station 105 for handling neighbor ceil relations in the cellular network 100 will now be described and furthe elaborated with reference to the flowchart depicted in figure 3. As previously mentioned, the first base station 105 Is comprised in the cellular network 100. The first base station 35 105 may be of any of the above in relation to figure 1 described types. The method comprises the following actions, which actions may be taken in any suitable order:

Action 391

This is an optional action according to which the first base station 105 allocates a time resource for the receiving of a broadcasted information which wiil be described below in relation to action 302, and wherein the receiving is performed in the allocated time resource.

in some embodiments, the first base station 0S is further configured to schedule transmissions to and/or from a user equipment comprised in the celSular network 100. The allocation may then comprise scheduling the transmissions to provide the time resource.

In some embodiments, the transmissions are scheduled to create idle gaps between transmissions, which gaps, or part of which gaps, may be allocated for the receiving of broadcasted information,

According to some embodiments, the allocated time resource is associated to a time of deployment of the first base station 105 or a time of power up of the first base station 105. This may be practical since the allocation may be easier because less, if any, ordinary data transmissions may be performed at this time.

in some embodiments, the allocated time resource corresponds to a time when transmission gaps occur due to spontaneous reduction in transmission activity. For example, small cells may have few users and may be more likely empty at night time.

In some embodiments, the allocated time resource corresponds to so called almost blank subframes, i.e. subframes, or time intervals, when no, or little, data is to be scheduled,

I some embodiments, the subframe timing may be offset between th first base station 105 and one or more of the other base stations, such as the base stations 1 15 and 125, to reduce the interference of the allocated time resource.

In some embodiments, a subframe timing may be offset between one or more macro and pico celis, so that a System Information Block type 1 (SSB1 ) of a macro cell, which may contain cell information necessar for the establishment of neighbor celi relation with the cell, does not collide with a SiBI of the pico cell.

For example, a subframe broadcasted in the ceil 120 which comprises celi information in the form of one or more of E-CGI, TAC and CSG ID, may be offset to avoid that this subframe collides with the SIB1 transmitted by the first base station 105 in the celi 110. Allocating time resources according to any of the above described ways is useful since the user equipment receiver, which as previously described is located in the first base station 105, may be limited by interference generated by a transmitter, such as a transmitter located in the first base station 105 itself,

A base station, serving ma y user equipments, such as for example the second base station 115 and the third base station 12S being macro eNbs in the previous example, may have a high duty cycle, it may thus be unlikely that the user equipment receiver located in the first base station 110 succeeds in decoding information from surrounding cells, including strong macro cells such as the ceils 120 and 130 in the same example, while a transmitter in the first base station 110 is active.

The self-interference problem may be more severe in Frequency Division Duplex Universal Terrestrial Radio Access Network (FDD UTRAN), because base stations forming part of FDD UTRAN are basically transmitting some information, e.g. Common Pilot Channel (CP(G.H), all the time. Hence, some embodiments of this optional action 301 , for example embodiments wherein the allocated time resource is associated to a time of deployment of the first base station 105 or a time of power up of the first base station 10S, may be useful for a cellular network 100 of FDD UTRAN type. Action 302

in this action the first base station 105 receives a system information broadcasted from the second base station 1 15 serving the cell 120 comprised in the cellular network 100. The system information is received in a receiver comprised in the first base station 105. The receiver is of a user equipment type and configured to receive broadcasted information from neighbor base stations including the second base station 115.

According to some embodiments, the first base station 105 is a Sow power base station and/or the second base station 1 15 is a macro base station, such as for example in the previously described exam pie.

The third base station 125 may in some embodiments be of any of the above in relation to figure 1 described types.

The user equipment type receiver in the first base station 105 may in some embodiments further be used for receiving information about the mobile network coverage. This ma in some embodiments include any types of detected cells, such as system information broadcasted in any of the ceils 120, 130, which may be for example different macro ceils, and/or the cells 135, which may be a cluster of femto cei!s, as previously described in relation to figure 1.

Action 303

In this action the first base station 105 extracts a cell information related to the cell

120 from the system information.

The extracted cell information may be necessary for estabiishing a neighbor ceii relation with the cell 120,

In some embodiments, the extracted cell information may comprise for example at ieast one of the previously mentioned PCI, ECGl, EARCFN, TAG, PLMN-IDs and CSG ID, for the celi 120.

Action 304

in this action the first base station 105 establishes a neighbor cell relation with the ceil 120 based on the extracted cell information. This may comprise establishing a X2- interface to the second base station 1 15, which may in some embodiments be a macro base station.

In some embodiments, the first base station 105 further informs the second base station 115 about other neighbor cells it has detected, such as for example the ceii 130 served by the third base station 125 or the cluster of femto cells 135,

In som embodiments, such ceii information may comprise for example at Ieast one of the previousl mentioned PCI, E-CGi, EARCFN, TAC, PLMN-IDs and CSG ID for that respective ceil.

In some embodiments, the information may be included in any one of a X2 setup request, a X2 setup response, a eNB configuration update or a eNB configuration update acknowledge message.

In some embodiments, this action comprises transmitting ceii information about the own cell 1 0 to the second base station 115, Action 305

This is also an optional action, according to which the first base station 105 transmits the extracted ceii information to the third base station 125 comprised in the cellular network 100. Thereby the first base station 105 assists the third base station 125 in establishing a neighbor ceil relation with the ceil 120, The third base station 125 may be of any of the above in relation to figure 1 described types. This action may comprise establishing a X2-interface, or a iur interface, to the third base station 135,

To perform the actions above for handling neighbor cell relations in the cellular 5 network 100, the first base station 105 comprises an arrangement schematicatiy depicted in figure 4. As mentioned above, the first base station 105 is comprised in the cellular network 100,

The term "configured to" used herein may also be referred to as "arranged to".

10 The first base station 05 comprises a receive 400. The receiver 400 is of a user equipment type and configured to receive broadcasted information from neighbor base stations including the second base station 115 serving the cell 120 comprised in the cellular network 100. The receiver 400 is further configured to receive a system information broadcasted from the second base station 115. According to some

15 embodiments, the first base station 105 is a low power base station, and/or ^'the second base station 115 is a macro base station.

The first base station 105 further comprises an extraction u it 410. The extraction unit 410 is configured for extracting a cell information related to the cell 120 20 from the system information.

The first base station 105 further comprises an establishing unit 420. The establishing unit 420 is configured to establish a neighbor cell relation with the cell 120 based on the extracted cell Information.

25

According to some embodiments, the first base station 105 further comprises a transmitter 430. The transmitter 430 is configured to transmit the extracted cell information to the third base station 125 comprised in the cellular network 100, thereby assisting the third base station 125 in establishing a neighbor cell relation with the cell 30 120. This may comprise establishing a X2-tnterface, or a lur interface, to the third base station 135.

According to some embodiments, the first base station 105 further comprises art allocation unit 440. The allocation unit 440 may be configured to allocate a time resource for the receiving of the broadcasted system information. The receiver 400 may then further be configured to perform the receiving in the allocated time resource.

According to some embodiments, the allocation unit 440 is further configured to S schedule transmissions to and/or from a user equipment comprised in the cellular network 100. The allocation unit 440 may then further be configured to schedule the transmissions to provide the time resource.

According to some embodiments the allocated time resource may be associated to a time of deployment of the first base station 05, or a time of power up of the first base0 station 105.

The embodiments of the first base station 105 for handling neighbor cell relations in a ceiiular network 100 may be implemented through one o more processors, such as a processor 450 in the first base station 105 depicted in figure 4, together with computer5 program code for performing the actions of 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 base station 105.

One such carrier may be in the form of a CD ROM disc, ft is however feasible with0 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 base station 105 e.g. remotely.

The first base station 105 may further comprise a memory 460 comprising one or more memory units. The memory 460 may be arranged to be used to store data such as5 for example information related to the allocated time resources, th broadcasted system information, the extracted cell information and/or information related to one or more neighbour cell relations. It may further be arranged to store applications to perform the actions of the embodiments herein when being executed in the first base station 105. 0 According to embodiments herein, as previously mentioned, neighbor ceil relations may be estabilshed without relying on user equipment measurements and reporting. This may be advantageous since it may reduce the need for user equipment based AMR functionality. As also previously mentioned, user equipment based AN may be problematic for several reasons: AMR is defined as an optional feature for the user equipments, which means thai a limited set of user equipments may be available for the cellular network 100 to exercise ANR.

The ANR feature consumes additional user equipment battery. This may be due to 5 the user equipment having to be active in what should have been a silence period, or due to that a release of connection is deferred in order to acquire ANR information. Also, for inter frequency measurements the user equipment may need to switch to other bands.

The user equipment based ANR feature may further incur interruptions in user data for user equipments performing the ANR, depending on how weli the cellular network 10 100 is able to select inactive user equipments.

Thanks to some embodiments herein, it becomes possible for the first base station 105, for example in the form of a low power base station such as a pico base station, to ensure that it instantly gets configured as part of the ceiiuiar network 100 once it is installed, without the need to wait for a user equipment to detect and report it to trigger a 15 user equipment based ANR feature.

This may be important to better support ad hoc low power ceil deployment in macro cellular networks, with minimal ceil planning, while keeping good network performance.

According to some embodiments herein, the cellular network 100 is of LTE-type.

20 The first base station 105 may then establish an X2~interface to macro base stations, such as the second base station 115 in the previously in relation to figure 2 described example, serving a selected subset of the detected ceils. The X2 -signalling may then be extended to allow the exchange of at least the same information as over LTE-Uu interface, I.e. the air interface between a user equipment and an eNB in the LTE case,

25 used as part of user equipment based ANR.

According to some embodiments, the first base station 105 informs a neighboring macro base station about the detected neighbors, for example at X2 -establishment or at X2-update.

Embodiments herein may be relevant for HetNet-scenarios which have not yet 30 been considered in the 3GPP standardization. In HetNets, for example, all neighbor cells to a pico cell may be neighbors to the macro cell covering the pico cell as we!!. This doesn't at aii apply to the original Macro cell-Macro Cell relation i.e. the neighbors of one macro cell are by no means necessarily neighbors to another macro ceil.

The embodiments are not limited to the above-described embodiments. Various 35 alternatives, modifications and equivalents may be used. When using the word "comprise" or "comprising" it shall be interpreted as non- limiting, i.e. meaning "consist at least of.

The embodimenis herein are not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments shouid not be taken as iimiiing the scope of the invention, which is defined by the appending claims.

Claims

1. A method in a first base station (105) for handling neighbor ceil relations in a cellular network (100), which first base station (105) is comprised in the cellular network (100), the method comprising:

- receiving (203, 302}, a system information broadcasted from a second base station (1 5) serving a celi (120) comprised in the cellular network (100), which system information is received in a receiver comprised in the first base station (105), which receiver is of a user equipment type and configured to receive broadcasted information from neighbor base stations including the second base station (1 15),

- extracting (204, 303), from the system information, a cell information related to the cell (120), and

- establishing (205, 304) a neighbor cell relation with the cell (120) based on the extracted cell information.

2. The method according to claim 1 , further comprising transmitting (206, 305) the extracted cell information to a third base station (125) comprised in the cellular network (100), thereby assisting the third base station (125) in establishing a neighbor cell relation with the cell (120).

3. The method according to claim 1 or 2, further comprising allocating (201, 301} a time resource for the receiving (203, 302), and wherein the receiving (203, 302) is performed in the allocated time resource. 4. The method according to claim 3, wherein the first base station (105) is further configured to schedule transmissions to and/or from a user equipment comprised in the cellular network (100), and wherein the allocation (201 , 301) comprises scheduling the transmissions to provide the time resource, 5. The method according to claim 3, wherein the allocated time resource is associated to a time of deployment of the first base station (105) or a time of power up of the first base station (105). 8. The method according to any one of the preceding claims, wherein the first base station (105) is a Sow power base station, and/or wherein the second base station (115) is a macro base station. 7, A first bas station (105) for handling neighbor cell relations in a cellular network

(100), which first base station (105) is comprised in the cellular network (100), the first base station (105) comprising:

- a receiver (400), which receiver (400) is of a user equipment type and configured to receive broadcasted information from neighbor base stations including a second base station (1 5) serving a ce!i (120) comprised in the cellular network (100), and which receiver (400) is further configured to receive a system information broadcasted from the second base station (115)

- an extraction unit (410), configured for extracting a cell information related to the cell (120) from the system information, and

- an establishing unit (420), configured to establish a neighbor cell relation with the cell (120) based on the extracted cell information,

8. The first base station (105) according to claim 7, further comprising a transmitter (430), configured to transmit the extracted cell information to a third base station (125) comprised in the cellular network (100), thereby assisting the third base station (125) in establishing a neighbor cell relation with the cell (120).

9. The first base station (105) according to claim 7 or 8, further comprising an allocation unit (440) configured to allocate a time resource for the receiving of the broadcasted system information, and wherein the receiver (400) is further configured to perform the receiving tn the allocated time resource,

10. The first base station (105) according to claim 9, wherein the allocation unit (440) is further configured to schedule transmissions to and/or from a user equipment comprised in the cellular network (100), and wherein the allocation unit (440) is further configured to schedule the transmissions to provide the time resource.

1 1. The first base station (105) according to claim 9, wherein the allocated time resource is associated to a time of deployment of the first base station (105), or a time of power up of the first base station ( 105). 12. The first base station (105) according to any one of the preceding ciaims, wherein the first base station (105) is a low power base station, and/or wherein the second base station (115) is a macro base station.