Tilting of neighbouring cells to compensate cell outage

Abstract

Example embodiments may relate to adjusting antenna tilt to compensate the loss of coverage due to outage of a more cell in a cellular communication network. A computer- implemented method may comprise: detecting an outage of a cell of a cellular communication network; determining, based on a timing advance value distribution of the cell, a reference point located at a coverage area of the cell; determining a plurality of candidate cells based on radiation patterns of the plurality of candidate cells being directed towards the reference point; selecting, from the plurality of candidate cells, at least one candidate cell for antenna tilting, wherein the selection of the at least one candidate cell is based on received signal strength values associated with the reference point or timing advance values of the at least one candidate cell relative to the reference point; and causing tilting of an antenna of the at least one candidate cell.

Description

TILTING OF NEIGHBOURING CELLS TO COMPENSATE CELLOUTAGETECHNICAL FIELD

[0001] Various example embodiments generally relate to the field of wireless communications. Some example embodiments relate to adjusting antenna tilt to compensate the loss of coverage due to outage of a more cell in a cellular communication network.BACKGROUND

[0002] Wireless communication may be implemented with a cellular radio network comprising transmission sites that offer communication services via multiple cells. A cell may correspond to certain geographical coverage area and be operated on a particular frequency. Antenna tilt may refer to an angle at which a radiation pattern of an antenna is vertically inclined. Antenna tilt may be used in cellular communication systems to optimize signal coverage and interference and thereby to improve performance of the network.SUMMARY

[0003] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0004] Example embodiments of the present disclosure enable to. . . This benefit may be achieved by the features of the independent claims. Further example embodiments are provided in the dependent claims, the description, and the drawings.

[0005] According to a first aspect, a computer-implemented method is disclosed. The method may comprise: detecting an outage of a cell of a cellular communication network; determining, based on a timing advance value distributionof the cell, a reference point located at a coverage area of the cell; determining a plurality of candidate cells based on radiation patterns of the plurality of candidate cells being directed towards the reference point; selecting, from the plurality of candidate cells, at least one candidate cell for antenna tilting, wherein the selection of the at least one candidate cell is based on received signal strength values associated with the reference point or timing advance values of the at least one candidate cell relative to the reference point; and causing tilting of an antenna of the at least one candidate cell.

[0006] According to an example embodiment of the first aspect, the reference point comprises an estimated geographical concentration point of users served by the cell.

[0007] According to an example embodiment of the first aspect, the method may comprise: selecting the reference point from a geographical region associated with an / / -th percentile of timing advance values of the cell.

[0008] According to an example embodiment of the first aspect, n is in the range of 50 to 70.

[0009] According to an example embodiment of the first aspect, the method may comprise: selecting the reference point from a geographical region associated with a timing advance value bin having a highest number of users among timing advance value bins of the cell.

[0010] According to an example embodiment of the first aspect, the method may comprise: selecting the reference point from a geographical region associated with a beam configured to serve a highest number of users among beams of the cell.

[0011] According to an example embodiment of the first aspect, the method may comprise: receiving the received signal strength values of the plurality of candidate cells as measured by a subset of the users served by the first cell, wherein the subset of the users is associated with the reference point; and selecting the at least one candidate cell based on a distribution of the received signal strength values of the at least one candidate cell satisfying at least one first condition.

[0012] According to an example embodiment of the first aspect, the method may comprise: selecting the subset of users based on determining the subset of users to belong to at least one timing advance value bin associated with the reference point.

[0013] According to an example embodiment of the first aspect, the method may comprise: selecting the subset of users based on determining the subset of users to belong to the timing advance value bin associated with the highest number of users among the timing advance value bins of the cell.

[0014] According to an example embodiment of the first aspect, the at least one first condition comprises: an average value of the distribution of the received signal strength values of the at least one candidate cell exceeding a signal strength threshold, an average value of the distribution of the received signal strength values of the at least one candidate cell, incremented with a standard deviation of the distribution of the received signal strength values of the at least one candidate cell, exceeding the signal strength threshold, or an m-th percentile value of the distribution of the received signal strength values of the at least one candidate cell exceeding the signal strength threshold.

[0015] According to an example embodiment of the first aspect, the at least one first condition further comprises a number of the received signal strength values of the at least one candidate cell exceeding a sample count threshold.

[0016] According to an example embodiment of the first aspect, the method may comprise: receiving timing advance values of the plurality of candidate cells; selecting the at least one candidate cell based on a distribution of the timing advance values of the at least one candidate cell satisfying at least one second condition.

[0017] According to an example embodiment of the first aspect, the at least one second condition is relative to the reference point.

[0018] According to an example embodiment of the first aspect, the at least one second condition comprises at least one of: a &-th percentile of the timing advance values of the at least one candidate cell corresponding to a distance between a transmission site of the at least one candidate cell and the reference point, or a timing advance value bin having a highest number of users among timing advance value bins of the at least one candidate cell corresponding to a distance that isshorter than the distance between a transmission site of the at least one candidate cell and the reference point.

[0019] According to an example embodiment of the first aspect, the k is in the range of 90 to 95.

[0020] According to an example embodiment of the first aspect, the method may comprise: determining that the radiation patterns of the plurality of candidate cells are directed towards the reference point based on determining, for each of the plurality of candidate cells, that a predetermined portion of a horizontal radiation pattern of a respective candidate cell points towards the reference point.

[0021] According to an example embodiment of the first aspect, the predetermined portion comprises: a sector between half-power points of the horizontal radiation pattern, or a sector between half-power points of the horizontal radiation pattern expanded with a predetermined margin.

[0022] According to an example embodiment of the first aspect, the tilting of the antenna of the at least one candidate cell comprises adjusting a maximum gain region of a vertical radiation pattern of the antenna of the at least one candidate cell to be directed towards the reference point.

[0023] According to a second aspect, an apparatus may comprise means for performing any example embodiment of the method of the first aspect.

[0024] According to an example embodiment of the second aspect, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform the method according to any example embodiment of the method of the first aspect.

[0025] According to a third aspect, computer program or a computer program product may comprise program code configured to, when executed by a processor, cause an apparatus at least to perform any example embodiment of the method of the first aspect.

[0026] According to a fourth aspect, an apparatus may comprise at least one processor; and at least one memory including computer program code; the at least one memory and the computer code configured to, with the at least one processor, cause the apparatus at least to: detect an outage of a cell of a cellular communicationnetwork; determine, based on a timing advance value distribution of the cell, a reference point located at a coverage area of the cell; determine a plurality of candidate cells based on radiation patterns of the plurality of candidate cells being directed towards the reference point; select, from the plurality of candidate cells, at least one candidate cell for antenna tilting, wherein the selection of the at least one candidate cell is based on received signal strength values associated with the reference point or timing advance values of the at least one candidate cell relative to the reference point; and cause tilting of an antenna of the at least one candidate cell. The computer program may be configured to, with the at least one processor, cause the apparatus to perform any example embodiment of the method of the first aspect.

[0027] Any example embodiment may be combined with one or more other example embodiments. Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings.DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which are included to provide a further understanding of the example embodiments and constitute a part of this specification, illustrate example embodiments and together with the description help to understand the example embodiments. In the drawings:

[0029] FIG. 1 illustrates an example of a cellular communication network;

[0030] FIG. 2 illustrates an example of an apparatus configured to practise one or more example embodiments;

[0031] FIG. 3 illustrates an example of a flow chart for compensating outage of a cell by tilting other cell(s);

[0032] FIG. 4 illustrates an example of a flow chart for determining cell(s) to be tilted based on received signal strength values;

[0033] FIG. 5 illustrates an example of candidate cell selection based on received signal strength values of candidate cells;

[0034] FIG. 6 illustrates an example of received signal strength data and timing advance data of different cells;

[0035] FIG. 7 illustrates an example of a received signal strength data of a serving cell and a candidate cell associated with different timing advance ranges of the serving cell;

[0036] FIG. 8 illustrates an example of received signal strength distribution at a timing advance range associated with a reference point;

[0037] FIG. 9 illustrates an example of uptilting a vertical antenna radiation pattern;

[0038] FIG. 10 illustrates an example of a flow chart for determining cell(s) to be tilted based on timing advance values;

[0039] FIG. 11 illustrates an example of candidate site selection based on timing advance values of the candidate cells;

[0040] FIG. 12 illustrates an example of selecting a reference point in case of beamforming;

[0041] FIG. 13 illustrates examples of a method for compensating outage of a cell.

[0042] Like references are used to designate like parts in the accompanying drawings.DETAILED DESCRIPTION

[0043] Reference will now be made in detail to example embodiments, examples of which are illustrated in the accompanying drawings. The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

[0044] FIG. 1 illustrates an example of a cellular communication network. Communication network 100 may comprise one or more devices, which may bealso referred to as client nodes, user nodes, user equipment (UE), terminal devices, or simply users. An example of such a device is UE 110, which may communicate with one or more access nodes of radio access network (RAN) 120. An access node may be also referred to as an access point or a base station.

[0045] Communication network 100 may be configured for example in accordance with the 4thor 5thgeneration (4G, 5G) digital cellular communication networks, as defined by the 3rdGeneration Partnership Project (3 GPP). In one example, communication network 100 may operate according to 3 GPP (4G) LTE (Long-Term Evolution) or 3GPP 5GNR (New Radio) standards. Access nodes 122, 124, 126 of RAN 120 may for example comprise 5thgeneration access nodes (gNB) or 4thgeneration access nodes (eNodeB). It is however appreciated that example embodiments presented herein are not limited to these example networks and may be applied in any present or future wireless communication networks, or combinations thereof, for example other type of cellular networks, short-range wireless networks, multicast networks, broadcast networks, or the like.

[0046] An access node may provide communication services within one or more cells, illustrated in FIG. 1 with dotted circles, which may correspond to geographical area(s) covered by signals transmitted by the access node. Communication network 100 may therefore comprise a cellular radio network. For example, access node 122 may be configured to serve cells 122-1, 122-2, and 122- 3, for example at respective sectors of the transmission site at which access node 122 is deployed.

[0047] A transmission site may comprise a geographical location comprising equipment for serving cell(s), for example access node circuitry and antenna(s) configured to enable communication with users. A sector may comprise a range of angles at the horizontal direction from an access node. A sector may comprise one or more cells on one or more frequencies. For example, access node 122, or in general the respective transmission site, might be configured with three 120-degree sectors comprising respective cells 122-1, 122-2, 122-3, and optionally one or more other cells. Similarly, access node 124, or in general the respective transmission site, might be configured with three 120-degree sectors comprising respective cells124-1, 124-2, 124-3, and optionally one or more other cells. RAN 120 may comprise further access nodes, e.g., access node 126, with respective cell(s) 126-1, 126-2, 126-3.

[0048] Communication network 100 may comprise a core network 130, which may comprise various network functions (NF) for establishing, configuring, and controlling data communication sessions of users, for example UE 110. Communication network 100 may comprise a network controller 140, which may be responsible of configuring various operations of RAN 120 and / or core network 130. Even though illustrated as a separate entity, network controller 140 may be alternatively embodied as part of core network 130. Even though some operations have been described as being performed by network controller 140, it is understood that similar functions may be performed alternatively by other network device(s) or network function(s) of communication network 100. One task of network controller 140 may be to monitor performance of the cells, detect cell outages, and optimize antenna tilts of the cells accordingly.

[0049] Even though not illustrated in FIG. 1, communication network 100 may comprise a network management system (NMS), or another entity, which may be configured to process and store performance management data of communication network 100. The performance management data may comprise various types of information collected from different network elements, for example access nodes 122, 124, 126 of RAN 120. The NMS may be configured to operate as a centralized data management system (e.g., a server), which processes the collected data and provides it for network management functions, for example for antenna tilting applications. Alternatively, similar functionality may be provided at an operations support system (OSS) of communication network 100, or another network device.

[0050] Examples of the performance data include timing advance (TA) values and received signal strength data (e.g., reference signal received power, RSRP) of different users at different cells. Timing advance may be used in communication network 100 to synchronize transmission and reception between an individual user and the serving access node such that the propagation time of the signal over a particular distance between the user and the access node is compensated. Timingadvance values may therefore correlate with distances of users from the access node and the same applies also to received signal strength due to the propagation loss. Each user may be assigned, e.g., by the serving cell, a timing advance value. The timing advance value may however change depending on the location of the user within the cell. A serving cell of a user may be the cell that is currently providing service to UE 110. For example, the serving cell may be responsible for maintaining the connection between UE 110 and the network or handling tasks such as establishment of voice calls or data transmission.

[0051] A dominance area of a cell may comprise a geographical area in which the cell has the strongest signal level. Handover between cells may be performed when UE 110 is at or near the border of the dominance area. Coverage areas cells may overlap to some extent, for example to facilitate smooth handover for mobile users. The serving cell of a user may be changed when another cell has the strongest signal level. Hysteresis may be however applied to prevent unnecessary switching of the serving cell when a user is at the borderline of cells. Term ‘coverage’ may refer to the ability of UE 110 to communicate with the network at a particular location. Cell overlap may refer to a situation where more than one base station and its cells provide coverage in the same geographical area. It may be however generally desired to reduce the overlap by downtilting antennas, while still enabling sufficient coverage and mobility in the network. For example, too extensive overlap may reduce the SINK and thereby also the capacity of the network, which is one reason for using downtilting in mobile networks. Downtilting may refer to tilting the antenna, or its radiation pattern, towards the earth. Tilting of a cell may comprise tilting at least one antenna of the cell, e.g., an antenna configured to receive and / or transmit signals for serving users of the cell.

[0052] Interference between cells may occur due to non-optimal antenna tilting. For example, insufficient antenna downtilt may be observed in communication network 100 as overshooting, e.g., directing the power radiation pattern of the antenna unnecessarily high, thereby extending the coverage area of the associated cell. Uptilting / downtilting a cell may comprise uptilting / downtilting the vertical power radiation pattern of an antenna of the cell. Tilting an antenna may compriseelectrically adjusting the direction of the power radiation pattern, for example by applying differently delayed and / or weighted versions of transmitted / received signals.

[0053] Dominance and coverage areas of cells may be adjusted by a remote antenna tilt (RET) mechanism, which may be configured to adjust antenna tilt of a cell, for example upon a request received from network controller 140, or another control entity of communication network 100. In general, a RET mechanism may comprise any solution for remotely adjusting antenna tilt of a cell, for example in contrast to manually redirecting the antenna at the transmission site. For example, the RET mechanism may comprise a motor coupled to a phase shifter and be configured to adjust the phase shift generated by the phase shifter, in order to cause the vertical power radiation pattern of the antenna to change. Adjusting the power radiation pattern by such a mechanism may be called electrical tilting (E-tilting). Mechanical antenna tilting may refer to mechanically adjusting the antenna tilt by rotating the antenna itself. RET may be used to optimize network performance by improving coverage of the network or by reducing interference between cells. Antenna tilt of a cell may be adjusted in order to affect the received signal strength at different locations, for example to improve coverage or to reduce interference between cells. Any type of antenna tilting may be used to implement example embodiments of the present disclosure.

[0054] Cell outages, which may comprise time periods when one or more cells or sites in cellular communication network 100 become non-operational, may lead to significant service disruptions for mobile users. The causes of cell outages may range from power supply interruptions, which may be temporarily mitigated by battery backups, to planned maintenance breaks or even hostile activities. Maintenance breaks may be needed for example when adding new technology on a transmission site, such as 5G New Radio (NR) on top of existing 4G Long-term Evolution (LTE) site, or when adding new frequency layers on transmission sites, such as NR 700 MHz layer on existing NR 3500 MHz site. In this case, the transmission site may need to be locked due to radiation safety margins such that radiation limit(s) are not exceeded for the construction workers.

[0055] Although the mobile network infrastructure may incorporate overlapping cells to ensure redundancy, it may be generally desired to minimize the overlaps by downtilting antennas. This provides the benefit of enabling to avoid unnecessary interference and degradation of signal quality, for example the signal-to- interference-plus-noise ratio (SINK). This improves capacity and performance of the network. However, this optimization presents a challenge when a base station goes offline, as downtilted antennas may not be able to compensate for the loss of coverage effectively. As a result, the network may suffer from increased coverage holes and reduced service continuity during cell outages.

[0056] Example embodiments of the present disclosure address the problem of compensating for coverage loss caused by a cell outage by introducing methods for tilting the antenna(s) of at least some surrounding access node(s). Adjusting the antenna tilt enables neighbouring cells to extend their coverage, thereby filling the coverage hole left by the offline cell. For example, suitable candidate cells for antenna tilting may be identified by leveraging mobile measurement reports (MMRs) and analysing timing advance data and / or received signal strength (RSRP) data of surrounding cells. The methods described herein provide a dynamic, data- driven approach to maintaining sufficient coverage in the network, and improve reliability and performance of the network during cell outages. The disclosed example embodiments not only enable to maintain service continuity but also to minimize the impact of coverage loss by effectively redistributing the network load.

[0057] FIG. 2 illustrates an example embodiment of an apparatus 200 configured to perform one or more example embodiments. Apparatus 200 may be for example used to implement network controller 140. Apparatus 200 may comprise at least one processor 202. The at least one processor 202 may comprise, for example, one or more of various processing devices or processor circuitry, such as for example a co-processor, a microprocessor, a controller, a digital signal processor (DSP), a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC), a field programmable gate array(FPGA), a microcontroller unit (MCU), a hardware accelerator, a special-purpose computer chip, or the like.

[0058] Apparatus 200 may further comprise at least one memory 204. The at least one memory 204 may be configured to store, for example, computer program code or the like, for example operating system software and application software. The at least one memory 204 may comprise one or more volatile memory devices, one or more non-volatile memory devices, and / or a combination thereof. For example, the at least one memory 204 may be embodied as magnetic storage devices (such as hard disk drives, floppy disks, magnetic tapes, etc.), optical magnetic storage devices, or semiconductor memories (such as mask ROM, PROM (programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random access memory), etc.).

[0059] Apparatus 200 may further comprise a communication interface 208 configured to enable apparatus 200 to transmit and / or receive information to / from other devices, functions, or entities. In one example, apparatus 200 may use communication interface 208 to output indication(s) of inoperative RET mechanisms to an automated service ticket system. Apparatus 200 may further comprise a user interface 210, for example for configuring apparatus 200 or for providing user output by the apparatus, such as for example visual and / or audible signal(s), for example by speaker(s), display(s), light(s), or the like. User interface 210 may be for example configured to output indication(s) of inoperative RET mechanisms to a human user.

[0060] When apparatus 200 is configured to implement some functionality, some component and / or components of apparatus 200, such as for example the at least one processor 202 and / or the at least one memory 204, may be configured to implement this functionality. Furthermore, when the at least one processor 202 is configured to implement some functionality, this functionality may be implemented using program code 206 comprised, for example, in the at least one memory 204.

[0061] The functionality described herein may be performed, at least in part, by one or more computer program product components such as for example software components. According to an embodiment, the apparatus comprises aprocessor or processor circuitry, such as for example a microcontroller, configured by the program code when executed to execute the embodiments of the operations and functionality described. A computer program or a computer program product may therefore comprise instructions for causing, when executed, apparatus 200 to perform the method(s) described herein. Alternatively, or in addition, the functionality described herein can be performed, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs), application-specific Integrated Circuits (ASICs), applicationspecific Standard Products (ASSPs), System-on-a-chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), Graphics Processing Units (GPUs).

[0062] Apparatus 200 comprises means for performing at least one method described herein. In one example, the means comprises the at least one processor 202, the at least one memory 204 including program code 206 configured to, when executed by the at least one processor, cause the apparatus 200 to perform the method.

[0063] Apparatus 200 may comprise a computing device such as for example an access point, a base station, a server, a network device, a network function device, or the like. Although apparatus 200 is illustrated as a single device it is appreciated that, wherever applicable, functions of apparatus 200 may be distributed to a plurality of devices, for example to implement example embodiments as a cloud computing service.

[0064] FIG. 3 illustrates an example of a flow chart for compensating outage of a cell by tilting other cell(s). Even though operations of the flow charts of the present disclosure, for example flow chart 300, have been described using network controller 140 as an example, it is understood that operations of the flow chart may be alternatively implemented by any other suitable network device, or a combination of network devices. Different example embodiments may be construed from the operations of the flow chart. For example, some of the operations may not be performed in all example embodiments or they may be replaced by alternative implementations falling within the scope of the claims.

[0065] At operation 301, network controller 140 may detect an outage of cell, in this example outage of cell 122-1. Network controller 140 may be configured to detect the outage for example based on key performance indicator(s) (KPI) such as a decrease in load level of the cell, termination of data traffic via the cell, detecting communication equipment of the cell or respective transmission site to become non- responsive, or by an indication of a planned cell outage, e.g., via a user interface or communication interface of network controller 140. In general, various KPIs may be used for detecting the outage, including cell availability or cell traffic. For example, network controller 140 may be configured to determine cell 122-1, or Site A, to be in outage, if cell 122-1 is not available or if the amount of traffic via cell 122-1 goes to zero. In general, finer resolution of KPIs may be desired, but for example one-minute resolution may be used, meaning that information on the data traffic of the cell and availability of the cell may be configured to be obtained once a minute. Network controller 140 may be however configured to apply a filtering window or an integration window. For example, network controller 140 may be configured to detect an outage, in response to detecting the cell or transmission site to be down (e.g., based on the cell not being responsive / available or based on decreased load level) for certain period of time, such as 30-60 minutes.

[0066] At operation 302, network controller 140 may determine cell(s) to be tilted in order to compensate for the outage of cell 122-1. Examples of how to determine the cell(s) to be tilted will be described with reference to FIG. 4 and FIG. 10.

[0067] At operation 303, network controller 140 may cause antenna(s) of the determined cell(s) to be tilted. Tilting may comprise uptilting, for example in order to extend coverage of another cell, e.g., cell 124-1, to the geographical region covered by cell 122-1 before the outage. However, in some example embodiments tilting may comprise downtilting, for example in order to direct vertical radiation pattern of a cell closer to respective transmission site to compensate for outage of another cell that previously served that region. Network controller 140 may be configured to cause tilting of the antenna(s) of the determined cells for example by transmitting a command to a remote antenna tilt (RET) mechanism of the cell, orby outputting a service ticket for instructing a serviceman to manually perform the tilting. Tilting the antenna provides the benefit that the change in coverage of the tilted cell(s) compensates for the outage of cell 122-1. Performance degradation, e.g., loss in overall data transmission capacity, caused by the outage may be therefore avoided or mitigated.

[0068] At operation 304, network controller 140 may detect cell 122-1 to recover from the outage, for example based on identifying cell 122-1, or the transmission site configured to serve cell 122-1, to come back on air. Network controller 140 may be configured to detect cell 122-1 to have recovered from the outage for example based on KPI(s) such as an increase of the load level of cell 122-1, detecting communication equipment of cell 122-1, or the respective transmission site, to become responsive again, or by an indication of the planned cell outage having been ended, for example via the user interface or the communication interface of network controller 140.

[0069] At operation 305, network controller 140 may revert to original antenna tilt(s), e.g., to antenna tilts used before the adjustment of operation 303. In other words, network controller 140 may cause roll-back of the antenna(s) tilted in connection with operation 303. Network controller 140 may be configured to cause reverting of the antennas of the tilted cell(s) to the original tilt angle(s) by transmitting a command to the RET mechanism(s) of the tilted cell(s), or by outputting another service ticket for instructing the serviceman to manually perform the tilting.

[0070] FIG. 4 illustrates an example of a flow chart for determining cell(s) to be tilted based on received signal strength values. Flow chart 302-1 is provided as an example for implementing operation 302 of FIG. 3. Flow chart 302-lprovides example(s) of mobile measurement report (MMR) based antenna tilting. Referring now to FIG. 5 and FIG. 6, it is assumed in this example that Cell A (e.g., cell 122- 1) of Site A experiences an outage. Considering the sector pointing almost upwards north in FIG. 5 (Cell A), the TA bins are presented as arcs towards the sector direction. The density of shading depends on the number of users within the TA bin. The denser the shading the higher the number of users in that TA bin.

[0071] Raw data with received signal strength levels (RSRP) of Cell A at different TA values (in metres) presented in the table of FIG. 6. The table further comprises RSRP levels of different candidate cells (cell IDs 92, 330, 2, 25, 21) as measured by users of Cell A. The measurements may comprise handover measurements and therefore Cell A may be also referred to as a source cell of a handover and the candidate cells may be referred to as target cells of a handover. The cell ID may comprise a physical cell ID (PCI). The PCI might not be unique within cellular communication network 100 and therefore the same PCI might be used by different cells. Network controller 140 may be configured to disambiguate the PCI by map the PCI to the closet cell from “Cell A” having the PCI in question.

[0072] The rightmost column indicates the measured power level of a signal from a particular candidate cell. This power level may be used as basis for determining which candidate cells to select for antenna tilting, because, e.g., when combined with Cell A and its TA, it tells the potential of the candidate cell to provide coverage at the distance given by the TA value. For example, on the first row, PCI = 92 is reported at the distance of 349 meters from the transmission site of Cell A at RSRP level of -96 dBm. This indicates that at 349 meters the candidate cell with PCI = 92 is a good candidate for providing coverage in case Cell A (e.g., along with whole Site A) goes to outage. As mentioned, PCIs may be mapped to unambiguous cell IDs of the candidate cell, for example PCI = 92 might be mapped to Site B.

[0073] In the example of FIG. 5, cellular communication network 100 comprises Site A, Site B, Site C, Site D and Site E. The question is which of those sites, or their cells, provide effective coverage compensation in case Site A goes to outage. To clarify this question, FIG. 7 illustrates an example of RSRP values of a serving cell, and a candidate cell associated with different timing advance ranges of the serving cell. The x-axis represents the distance in meters corresponding to TA values of users, the primary y-axis represents sample count per distance, and the secondary y-axis represents the RSRP values (dBm). The RSRP of the cell going to outage (Cell A, cell 122-1) is marked with the black line with white dots and the average RSRP of the candidate cells that could compensate the coverage loss ismarked with the black line without dots. For example, at distance range of 351— 428 m the cell going to outage is reported on average at -103 dBm RSRP level, whereas the candidate cells are reported at around -106 dBm. This demonstrates that there is overlapping coverage in the area. Therefore, it is possible to compensate the loss of coverage from Site A by uptilting the candidate cells. It may be however desired to identify candidate cell(s) that have the most potential for compensating the coverage loss. An example of determining and tilting suitable candidate cells will be now described with reference to operations 401 to 406.

[0074] At operation 401, network controller 140 may determine a reference point. The reference point may be located at the coverage area, e.g., dominance area of cell 122-1, which is provided again as an example of the cell detected to be in outage. Determining the reference point may comprise determining a location of the reference point, for example as geographical coordinates. Cell 122-1 may be also referred to as a first cell. Network controller 140 may be configured to determine the reference point based on timing advance (TA) value distribution of cell 122-1. The TA value distribution of cell may comprise information on the number of users assigned with particular TA values or TA values belonging to particular ranges of TA values, e.g., TA bins. Network controller 140 may be configured to select a reference point that corresponds to an estimated geographical concentration point of users served by cell 122-1. The timing advance value distribution reflects the geographical concentration point of the users.

[0075] However, any suitable method for estimating the geographical concentration point of users may be used. One example of determining the reference point is illustrated in FIG. 5, where the differently shaded regions correspond to particular TA ranges. As noted above, the different TA bins correspond to different distance ranges from the transmission site (Site A) of cell 122-1.

[0076] As illustrated in FIG. 5, network controller 140 may be configured to select reference point 502 from the geographical region associated with the TA value bin having the highest number of users among the TA value bins of cell 122- 1. Reference point 502 may be therefore within the region defined by this TA bin. This provides the benefit of selecting reference point 502 to be located at a position,where most of the users are estimated be located. In other words, reference point 502 may comprise an estimated geographical concentration point of users served by cell 122-1. Network controller 140 may be configured to determine the reference point to be substantially in the middle of the sector of cell 122-1 and / or in the middle of the distance range of the selected TA bin. Other locations within the region defined by the TA bin may be however used instead. For example, using information about the number of users being served by different beams of cell 122- 1 may result in selecting reference point 502 not to be located in the middle of the sector, as will be further described with reference to FIG. 12.

[0077] Alternatively, controller 140 may be configured to select reference point 502 from a geographical region associated with a particular percentile of the TA value distribution, for example an / / -th percentile, where n may be for example within the range of 50 to 70. This is another way for selecting reference point 502 to be at a location, where most of the users are estimated be located, i.e., at the estimated geographical concentration point of users served by cell 122-1.

[0078] Reference point 502 may be subsequently used for estimating how tilting of other cells, e.g., cell 124-1, would affect coverage at reference point 502. Selecting reference point 502 to be located at the estimated geographical concentration point of users provides the benefit of enabling to estimate the effect of tilting the other cell(s) at a point where it affects most users of cell 122-1. Compensation of the outage of cell 122-1 may be therefore performed considering the distribution of users at cell 122-1, which enables to optimize compensation of the coverage loss, for example in terms of the number and identity of the tilted cells and the amount of adjustment of the antenna tilt.

[0079] As another example, network controller 140 may be configured to calculate, from the TA value distribution of cell 122-1, a sample cumulative distribution function (CDF). A suitable percentile might be then selected, examples of practical values ranging from the 50th(=median) to the 70thpercentile. Alternatively, network controller 140 might use the TA bin with the most samples (e.g., users).

[0080] At operation 402, network controller 140 may determine candidate cells for antenna tilting. Network controller 140 may be configured to determine the candidate cells based on radiation patterns of the candidate cells, for example such that network controller 140 determines to include in the set of candidate cells the cells whose (horizontal) radiation pattern is directed to reference point 502. Network controller 140 may be configured to determine the radiation pattern of a cell (e.g., the antenna of the cell) to be directed towards reference point 502, if reference point 502 is within the half-power (-3 dB) beam width of the radiation pattern, as illustrated in FIG. 5 for Site B. In general, network controller 140 may be configured to determine that the radiation patterns of the candidate cells are directed towards reference point 502 based on determining, e.g., for each of the candidate cells, that a predetermined portion of the horizontal radiation pattern of the respective cell points towards reference point 502. The predetermined portion may be for example the sector between half-power points of the horizontal radiation pattern, e.g., the main lobe thereof, optionally extended with a margin, such as an angular margin. Network controller 140 may therefore use reference point 502 for assessing whether other cells have potential for providing more coverage at the coverage area of cell 122-1 by tilting their antennas.

[0081] Network controller 140 may be therefore configured to use reference point 502 for assessing potential cells that could provide more coverage by antenna tilting. In some example embodiments, network controller 140 might be configured to apply the margin (e.g., a certain offset angle such as 5°) beyond the half-power beamwidth. This provides the benefit of considering more cells as candidate cells for antenna tilting when trying to compensate for the outage. Coverage compensation in case of cell outage may be therefore further improved. In this case, also Site D might qualify for antenna tilting.

[0082] In general, considering the direction of the radiation pattern provides the benefit of enabling to ensure that tilting antenna(s) of the candidate cells really has potential to affect the coverage at reference point 502. For example, considering Site D, a user located at reference point 502 might receive a signal from Site D via a horizontal sidelobe of the radiation pattern of the respective antenna (cf., thedashed arrow). However, tilting of the antenna might not significantly affect the coverage at reference point 502, because reference point 502 is not located in the direction of the main lobe of the horizontal radiation pattern of Site D. Using the half-power criterion, it is clear that also Site C would qualify for tilting but Site E would not.

[0083] At operation 403, network controller 140 may receive received signal strength values (e.g., RSRP values) of the candidate cell(s). The received signal strength values may comprise values measured by a subset of the users served by cell 122-1. The received signal strength values may comprise received signal strength values of signal(s) of the candidate cell(s), e.g., signal(s) transmitted by access node(s) configured to serve the candidate cell(s).

[0084] Network controller 140 may be configured to select the subset of users, for example based on determining that the subset of users belongs to TA bin(s) associated with reference point 502, for example the TA bin corresponding to reference point 502 and optionally one or more neighbouring TA bins of that TA bin. This provides the benefit of optimising selection of the candidate cell(s) for tilting based on the geographical concentration of users at the cell going to outage. Network controller 140 may be for example configured to select the subset of users based on determining that the subset of users belongs to the TA value bin associated with the highest number of users among the TA value bins of the cell in outage.

[0085] The subset of users may be therefore associated with reference point 502, for example by being located in proximity of reference point (e.g., within a threshold distance from it) or by being located at the geographical region associated with the TA bin of reference point 502. The received signal strength values may be therefore associated with reference point 502, e.g., by being measured by the subset of users associated with reference point 502.

[0086] At operation 404, network controller 140 may select, from the candidate cell(s) determined at operation 402, at least one of the candidate cells for tilting. The selection of the at least one candidate cell may be based on the received signal strength values associated with the reference point, as described with reference to operation 403. This provides the benefit of enabling tilting of cells for which thereceived signal strength at the geographical concentration point is such that it indicates potential for compensating the coverage loss caused by the cell outage.

[0087] Network controller 140 may be configured to select the candidate cell(s) for tilting based on determining that the distribution of the received signal strength values of candidate cell(s) satisfy certain condition(s), also referred to as first condition(s).

[0088] The first condition(s) may include an average value of the distribution of the received signal strength values of the candidate cell(s) exceeding a signal strength threshold. For example, controller 140 may be configured to select a candidate cell for tilting, in response to determining that received signal strength values of the candidate cell(s), as measured by users of cell 122-1, are higher than he signal strength threshold. This provides the benefit of enabling to ensure that signal strength of the candidate cell(s) selected for tilting is sufficient such that the tilting is expected to have meaningful contribution for compensating for the coverage loss.

[0089] As another example, the first condition may comprise an average value of the distribution of the received signal strength values of the candidate cell(s), optionally incremented with a standard deviation of the distribution of the received signal strength values of the candidate cell(s), exceeding the signal strength threshold. For example, controller 140 may be configured to select a candidate cell for tilting, in response to determining that the average value of the received signal strength values of the candidate cell(s), when incremented by their standard deviation, are higher than he signal strength threshold. The signal strength threshold may be therefore effectively lowered by the standard deviation of the received signal strength values. This provides the benefit of also enabling selection candidate cells, for which the average signal strength would not meet the condition, but which still include users with sufficiently high received signal strength. Compensation of the coverage loss may be therefore improved by tilting more cells.

[0090] As another example, the first condition may comprise an m -th percentile value of the distribution of the received signal strength values of the candidate cell(s) exceeding the signal strength threshold. For example, controller 140 may beconfigured to select a candidate cell for tilting, in response to determining that the / 77-th percentile value of the received signal strength values of the candidate cell(s) is higher than he signal strength threshold. Parameter m may take any suitable value, for example between 5 and 10. This provides the benefit of enabling tuning of the threshold such that it better captures the potential of the selected candidate cell(s) to compensate for the coverage loss. Using a relatively low value such as in the range of 5 to 10 provides the benefit of including more cells in the set of candidate cells selected for tilting, which may improve compensation of the coverage loss.

[0091] As another example, the first condition may comprise a number of the received signal strength values of the candidate cell(s) exceeding a sample count threshold. The sample count threshold may be for example in the range of 100 to 1000 samples. This condition may be applied as a pre-condition for the other examples of the first condition, for example such that network controller 140 first evaluates the sample count and determines not to select cell(s) for which the sample count threshold is not fulfilled. Determining not to select cell(s) for tilting may be therefore without considering whether the cell(s) fulfil the other first condition(s). This provides the benefit of improving reliability of compensating the coverage loss, because it enables to ensure that the candidate cells are selected based on statistically meaningful information about the potential of the cell(s) to contribute in compensation of the coverage loss.

[0092] Network controller 140 may therefore first determine the candidate cells located within the transmission sector (e.g., the half-power beamwidth) and then calculate the received signal strength (e.g., RSRP) values or distribution, which the candidate cells provide at reference point 502. As noted above, the received signal strength values may include average values, median values, certain percentile values, or average values incremented with the standard deviation, for example. Network controller 140 may be configured to determine that the candidate cells fulfilling received signal strength requirement(s) are eligible for tilting. Practical example values of the signal strength threshold could be for example in the range of-115 dBm to -120 dBm. In addition, network controller 140 might be configured to take into account the sample counts of the cells. For example, network controller240 might be configured to select candidate cell(s) for tilting only if the number of received signal strength samples exceeds a minimum threshold. On the other hand, network controller 140 might be configured not to cause tilting of cells if the sample count is below the minimum threshold (e.g., by not selecting such cells for tilting).

[0093] At operation 405, network controller 140 may determine new tilt angles for the candidate cell(s) selected at operation 404 for tilting. An example of determining the new tilt angle is illustrated in FIG. 9. A vertical radiation pattern of an antenna of a cell is illustrated by the antenna gain (dB) curve 902 in different directions of a vertical plane. The vertical direction of departure from the antenna may be mostly defined by the main lobe the vertical radiation pattern and parts surrounding the main lobe, as illustrated by the maximum gain region. The main lobe may be responsible for providing the gain of the antenna. Parts of the vertical radiation pattern near the main lobe may define how much the antenna is able to reduce the radiated power towards the horizon or the sky. In general, it may be desired to direct the main lobe towards areas where the users (e.g., subscribers) are located. Adjusting the tilt angle may comprise effectively rotating the vertical radiation pattern, or in general, adjusting the vertical radiation pattern such that the direction of the main lobe of the vertical radiation patters is changed.

[0094] The tilt angle of an antenna may be for example defined as the angle between the direction of the vertical radiation pattern (e.g., its maximum gain direction) and a horizontal line. Hence, when the tilt angle is at its maximum, the coverage area of the respective cell may be generally minimized. When the tilt angle is at its minimum, the coverage area of the respective cell may be generally maximized. It is however also possible to define the tilt angle such that it is the angle between the direction of the vertical radiation pattern and a vertical line.

[0095] As illustrated in FIG. 9, the maximum gain region of the vertical radiation pattern may comprise a region in proximity of the highest gain of the antenna. For example, the maximum gain region may comprise an angular range around the direction of the highest gain of the antenna, or a region where the antenna gain is above a threshold, which may be for example in the range of -1 to -3 dB. Network controller 140 may be configured to determine the new tilt angle such thatthe maximum gain region is directed towards reference point 502. Hence, tilting the antenna(s) of the candidate cell(s) may comprise adjusting the maximum gain region of the vertical radiation pattern of the antenna(s) to be directed towards reference point 502. Therefore, network controller 140 may use the vertical antenna radiation pattern to determine a new tilt angle, which increases the received signal strength of the candidate cell at reference point 502.

[0096] Network controller 140 may be configured to determine the new tilt angle based on geometry information such as height of the antenna from ground level and the distance of reference point 502 from the transmission site of the cell in question. For example, in case of FIG. 5, network controller 140 may use the geometry and determine to adjust the tilt angle of Site B, more precisely the cell / sector pointing towards reference point 502 such that the maximum gain of the antenna is directed to reference point 502.

[0097] At operation 406, network controller 140 may estimate the achievable coverage gain. The achievable coverage gain may be estimated based on the antenna gain between points of the vertical radiation pattern pointing towards reference point 502 before and after the tilting. In FIG. 9 the radiation pattern is depicted before uptilting and it is observed that uptilting the antenna to the new tilt angle significantly increases the antenna gain in the direction of reference point 502. The difference in the gain can be read from the polar coordinates, where each step corresponds to 20 dB difference in gain. It can be seen that easily an order of 10 to 15 dB increase can be achieved in received signal strength by applying the new tilt angle.

[0098] Network controller 140 may be configured not to cause the antenna tilting (cf. operation 303), if the estimated coverage gain is not high enough. For example, network controller 140 may be configured to cause tilting of the antenna of a candidate cell (e.g., by moving from operation 406 to operation 303), in response to determining that the estimated coverage gain exceeds a threshold (e.g., a coverage gain threshold such as 1-2 dB). On the other hand, network controller 140 may be configured to determine not to cause tilting of the antenna of a candidate cell, in response to determining that the estimated coverage gain is below thethreshold. This provides the benefit of avoiding unnecessary tilting of antennas for which the contribution to the compensation of the coverage loss would be low.

[0099] Example embodiments of FIG. 4 therefore improve coverage loss compensation based on using received signal strength levels of other cells at the estimated geographical concentration point of the cell in outage. Even though particular operations and their orders have been illustrated in FIG. 4, it is understood that various modifications may be made to implement different example embodiments. For example, in some example embodiments operation 406 might not be present or a default value of antenna uptilt might be applied in operation 405.

[0100] FIG. 10 illustrates an example of a flow chart for determining cell(s) to be tilted based on timing advance values. Flow chart 302-2 is provided as an example for implementing operation 302 of FIG. 3 and, with reference to FIG. 11, it provides example(s) of TA value based antenna tilting to compensate outage of the upwards pointing cell of Site A, for example when received signal strength data is not available. TA bins of cells of Sites A and B are again presented as arcs, with denser shading being again indicative of higher density of users within the corresponding TA bin.

[0101] A difference between the mobile measurement report (MMR) based antenna tilting of FIG. 4 and the TA value-based antenna tilting is that the TA value based antenna tilting may be performed without availability of received signal strength values per TA bin. Instead of using received signal strength, network controller 140 may be configured to select the candidate cells for tilting by using TA values of the candidate cells to estimate their overlap with the cell in outage and their potential for coverage enhancement at refence point 502.

[0102] At operations 401 and 402, network controller 140 may determine reference point 502 and candidate cells for tilting, as described with reference to FIG. 4.

[0103] At operation 1003, network controller 140 may receive timing advance values of the candidate cells. The timing advance values of the candidate cells may comprise timing advance values assigned to users for communicating via the candidate cells. For example, a user located near reference point 502 might have afirst timing advance value falling to the fifth TA bin for the cell of Site A (cf. , TA value of the cell in outage) and a second timing advance value falling within the eighth TA bin for the cell of Site B (cf. , TA value of a candidate cell).

[0104] At operation 1004, network controller 140 may select, based on the TA values of the candidate cells, at least one of the candidate cells for tilting. Network controller 140 may be configured to determine, e.g., for each candidate cell, a TA value distribution. The TA value distribution may comprise indications of the number of TA values falling within different TA bins.

[0105] Network controller 140 may be configured to select the candidate cell(s) for tilting based on determining that the TA distribution(s) of the candidate cell(s) satisfy certain condition(s), also referred to as second condition(s). The second condition(s) may be relative to reference point 502. For example, the second condition(s) may comprise at least one threshold or criterion for at least one quantity that is dependent on geographical location of reference point 502. This provides the benefit of enabling to take into account the TA distribution of the candidate cell with respect to reference point 502, which may represent the estimated concentration point of users, when determining whether to select the candidate cell for antenna tilting. The potential of being able to compensate for the coverage loss may be therefore effectively estimated, which improves selection of the candidate cells for antenna tilting.

[0106] For example, network controller 140 may be configured to select a &-th percentile of the TA values of a candidate cell. Network controller 140 may be configured to compare the distance between the transmission site of the candidate cell and the distance associated with the &-th percentile of the TA values of the candidate cell. Network controller 140 may be configured to select the candidate cell for tilting, if the two distances correspond to each other. In other words, network controller 140 may be configured to select a candidate cell for tilting, based on determining that the distribution of the TA values of the candidate cell satisfies the condition of the &-th percentile of the TA values of the candidate cell corresponding to the distance between the transmission site of the candidate cell and reference point 502. In case of uptilting, parameter k may be for example in therange of 90 to 97, for example 95. Selecting k = 95 enables to ensure that 5% of the traffic in Site B traffic is still coming from at least the distance of reference point 502. This provides the benefit of enabling to ensure that uptilting of the candidate cell has potential for compensating for the coverage loss of the cell in outage. It is however noted that in case of downtilting the value of parameter k may be different, for example in the range of 10 to 20. This provides the benefit of enabling to ensure that downtilting of the candidate cell has potential for compensating for the coverage loss.

[0107] An example of selecting a candidate site for antenna tilting based on TA values of the candidate cell is illustrated in FIG. 11. If network controller 140 is configured with k= 95 and 95 % of the users of the cell 124-1 are located within TA bins 1 - 8 of cell 124-1, network controller 140 may determine that distance d between Site B and reference point 502 corresponds to the 95thpercentile of TA values or the respective distance, e.g., based on determining that the difference between the distances is below a threshold. Consequently, network controller 140 may select cell 124-1 for uptilting to compensate for outage of cell 122-1.

[0108] As another example, network controller 140 may be configured to use the distance of the TA bin having the highest number of users in the candidate cell. In the example of FIG. 5 this is the fifth TA bin of cell 124-1. Network controller 140 may be for example configured to select a candidate cell for (up)tilting, based on determining that the distribution of the TA values of the candidate cell satisfies the condition of the TA value bin having the highest number of users among TA bins of the candidate cell corresponding to a distance that is shorter than the distance between the transmission site of the candidate cell and reference point 502. For example, network controller 140 may select cell 124-1 for (up)tilting, in response to determining that the distance of the 5thTA bin of cell 124-1 is shorter that the distance between Site B and reference point 502. Again, this provides the benefit of enabling to ensure that uptilting of the candidate cell has potential for compensating for the coverage loss of the cell in outage. In case of downtilting, network controller 140 may be configured to select a candidate cell for downtilting, based on determining that the distribution of the TA values of the candidate cell satisfies thecondition of the TA value bin having the highest number of users among TA bins of the candidate cell corresponding to a distance that is longer than the distance between the transmission site of the candidate cell and reference point 502

[0109] Operations 1003 and 1004 therefore provide an alternative implementation for selecting certain candidate cell(s) for tilting. Flow chart 302-2 may thereafter continue by execution of operations 405 and / or 406, as already described with reference to FIG. 4. As noted above, operations of FIG. 10 may be used for example when compensating the coverage loss due to cell outage and when received signal strength data is not available.[001 10] FIG. 12 illustrates an example of selecting a reference point in case of beamforming. In beamforming, phased array antennas may be used to control direction of transmission and reception of signals, for example by adjusting the phase and amplitude of the signal when provided to different antenna elements to create a focused beam. In the example of FIG. 12, users of cell 122-1 are served by four beams. The density of the shading indicates again the number of users of a particular beam. Therefore, the leftmost beam has the highest number of users among the four beams of cell 122-1. As illustrated in FIG. 12, network controller 140 may be configured to select reference point 502 from the geographical region associated with the beam configured to serve the highest number of users among beams of the cell. This provides the benefit of enabling the geographical concentration of the users to be estimated more accurately.[001 1 1 ] Network controller 140 may be configured to determine reference point 502 based on both the TA value distribution of the cell in outage and the distribution of users among the beams of that cell. For example, network controller 140 may be configured to determine the direction of reference point 502 from the transmission site of the cell based on the beam utilization information, for example select the direction to be within (e.g., in the middle of) the beam configured to serve the highest number of users among beams of the cell. Additionally, network controller 140 may be configured to determine the distance of reference point 502 from the transmission site of the cell based on the TA value distribution, for example as described with reference to FIG. 3. In some example embodiment, networkcontroller 140 may be configured to determine the TA value distribution based on users served by the beam configured to serve the highest number of users, e.g., not including users served by other beams. Using the beam utilization improves compensation of the coverage loss, because reference point 502 more accurately represents the geographical concentration of the users of the cell in outage. Example embodiments generally improve compensation of cell outages in a cellular communication network.[001 12] FIG. 13 illustrates an example of a method for compensating coverage loss due to cell outage. The method may be computer-implemented, for example by network controller 140, or a control apparatus configured to control the functioning thereof, when installed therein.[001 1 3] At 1301, the method may comprise detecting an outage of a cell of a cellular communication network.[001 14] At 1302, the method may comprise determining, based on a timing advance value distribution of the cell, a reference point located at a coverage area of the cell.[001 1 5] At 1303, the method may comprise determining a plurality of candidate cells based on radiation patterns of the plurality of candidate cells being directed towards the reference point.[001 16] At 1304, the method may comprise selecting, from the plurality of candidate cells, at least one candidate cell for antenna tilting, wherein the selection of the at least one candidate cell is based on received signal strength values associated with the reference point or timing advance values of the at least one candidate cell relative to the reference point.[001 1 7] At 1305, the method may comprise causing tilting of an antenna of the at least one candidate cell.[001 18] Further features of the method directly result for example from the functionalities of network controller 140, or in general apparatus 200, as described throughout the specification and in the appended claims and are therefore not repeated here. Different variations of the method may be also applied, as described in connection with the various example embodiments.[001 1 9] An apparatus, such as for example a network device configured to implement one or more network functions or entities, may be configured to perform or cause performance of any aspect of the method(s) described herein. Further, a computer program or a computer program product may comprise instructions for causing, when executed, an apparatus to perform any aspect of the method(s) described herein. Further, an apparatus may comprise means for performing any aspect of the method(s) described herein. According to an example embodiment, the means comprises at least one processor, and memory including program code, the at least one processor, and program code configured to, when executed by the at least one processor, cause performance of any aspect of the method(s).[001 20] Any range or device value given herein may be extended or altered without losing the effect sought. Also, any embodiment may be combined with another embodiment unless explicitly disallowed.[001 21 ] Although the subject matter has been described in language specific to structural features and / or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.[001 22] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item may refer to one or more of those items.[001 23] The steps or operations of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the scope of the subject matter described herein. Aspects of any of the example embodiments described above may be combined with aspects of any of the other example embodiments described to form further example embodiments without losing the effect sought.[001 24] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements. Term “or” may be understood to also cover a case where both of the items separated by “or” are included. Hence, “or” may be understood as an inclusive “or” rather than an exclusive “or”. As used herein “at least one” or “one or more” may be understood as “any one of the at least one” or “any one of the one or more”.[001 25] The term 'comprising' is used herein to mean including the method, blocks, or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements. [001 26] Although subjects may be referred to as ‘first’ or ‘second’ subjects, this does not necessarily indicate any order or importance of the subjects. Instead, such attributes may be used solely for the purpose of making a difference between subjects.[001 27] It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from scope of this specification.

Claims

CLAIMS1. A computer-implemented method, comprising: detecting an outage of a cell of a cellular communication network; determining, based on a timing advance value distribution of the cell, a reference point located at a coverage area of the cell; determining a plurality of candidate cells based on radiation patterns of the plurality of candidate cells being directed towards the reference point; selecting, from the plurality of candidate cells, at least one candidate cell for antenna tilting, wherein the selection of the at least one candidate cell is based on received signal strength values associated with the reference point or timing advance values of the at least one candidate cell relative to the reference point; and causing tilting of an antenna of the at least one candidate cell.

2. The method according to claim 1, wherein the reference point comprises an estimated geographical concentration point of users served by the cell.

3. The method according to claim 1 or 2, further comprising: selecting the reference point from a geographical region associated with an / / -th percentile of timing advance values of the cell.

4. The method according to claim 3, wherein n is in the range of 50 to 70.

5. The method according to any of claims 1 to 3, further comprising: selecting the reference point from a geographical region associated with a timing advance value bin having a highest number of users among timing advance value bins of the cell.

6. The method according to any of claims 1 to 5, further comprising: selecting the reference point from a geographical region associated with a beam configured to serve a highest number of users among beams of the cell.

7. The method according to any of claims 1 to 6, further comprising: receiving the received signal strength values of the plurality of candidate cells as measured by a subset of the users served by the first cell, wherein the subset of the users is associated with the reference point; and selecting the at least one candidate cell based on a distribution of the received signal strength values of the at least one candidate cell satisfying at least one first condition.

8. The method according to claim 7, further comprising: selecting the subset of users based on determining the subset of users to belong to at least one timing advance value bin associated with the reference point.

9. The method according to claims 5 and 7, further comprising: selecting the subset of users based on determining the subset of users to belong to the timing advance value bin associated with the highest number of users among the timing advance value bins of the cell.

10. The method according to any of claims 7 to 9, wherein the at least one first condition comprises: an average value of the distribution of the received signal strength values of the at least one candidate cell exceeding a signal strength threshold, an average value of the distribution of the received signal strength values of the at least one candidate cell, incremented with a standard deviation of the distribution of the received signal strength values of the at least one candidate cell, exceeding the signal strength threshold, or an / 77-th percentile value of the distribution of the received signal strength values of the at least one candidate cell exceeding the signal strength threshold.

11. The method according to claim 10, wherein the at least one first condition further comprises a number of the received signal strength values of the at least one candidate cell exceeding a sample count threshold.

12. The method according to any of claims 1 to 11, further comprising: receiving timing advance values of the plurality of candidate cells; selecting the at least one candidate cell based on a distribution of the timing advance values of the at least one candidate cell satisfying at least one second condition.

13. The method according to claim 12, wherein the at least one second condition is relative to the reference point.

14. The method according to claim 12 or 13, wherein the at least one second condition comprises at least one of a &-th percentile of the timing advance values of the at least one candidate cell corresponding to a distance between a transmission site of the at least one candidate cell and the reference point, or a timing advance value bin having a highest number of users among timing advance value bins of the at least one candidate cell corresponding to a distance that is shorter than the distance between a transmission site of the at least one candidate cell and the reference point.

15. The method according to claim 14, wherein is in the range of 90 to 95.

16. The method according to any of claims 1 to 15, further comprising: determining that the radiation patterns of the plurality of candidate cells are directed towards the reference point based on determining, for each of the plurality of candidate cells, that a predetermined portion of a horizontal radiation pattern of a respective candidate cell points towards the reference point.

17. The method according to claim 16, wherein the predetermined portion comprises: a sector between half-power points of the horizontal radiation pattern, or a sector between half-power points of the horizontal radiation pattern expanded with a predetermined margin.

18. The method according to any of claims 1 to 17, wherein the tilting of the antenna of the at least one candidate cell comprises adjusting a maximum gain region of a vertical radiation pattern of the antenna of the at least one candidate cell to be directed towards the reference point.

19. An apparatus comprising means for performing the method according to any of claims 1 to 18.

20. The apparatus according to claim 19, wherein the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform the method according to any of claims 1 to 18.

21. A computer program comprising program code configured to, when executed by a processor, cause an apparatus at least to perform the method according to any of claims 1 to 18.

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