Determining inoperativity of a remote antenna tilt mechanism

Abstract

Example embodiments may relate to detection of overshooting cells in a radio network. A computer-implemented method may comprise: requesting a remote antenna tilt mechanism to adjust an antenna of a cell to a first tilt angle for a first time period; determining a first set of users served by the cell during the first time period; requesting the remote antenna tilt mechanism to adjust the antenna of the cell to a second tilt angle for a second time period; determining a second set of users served by the cell during the second time period; and determining the remote antenna tilt mechanism to be inoperative based on similarity of the first set of users and the second set of users.

Description

communications. Some example embodiments relate to testing operativity of remote antenna tilt mechanisms 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 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 determine inoperativity of remote antenna tilt (RET) mechanism(s) in a cellular communication network. This enables to improve performance of the network, for example by replacement of any inoperable RET mechanisms or by considering the inoperativity of the RET mechanism(s) when optimizing antenna tilt configurations in the network. 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: requesting a remote antenna tilt mechanism to adjust an antenna of a cell to a first tilt angle for a first time period; determining a first set of users served by the cell during the first time period; requesting the remote antenna tilt mechanism to adjust the antenna of the cell to a second tilt angle for a second time period; determining a second set of users served by the cell during the second time period; and determining the remote antenna tilt mechanism to be inoperative based on similarity of the first set of users and the second set of users.

[0006] According to an example embodiment of the first aspect, the method may comprise: in response to determining the remote antenna tilt mechanism to be inoperative: outputting an indication of the remote antenna tilt mechanism to be inoperative, or refraining from requesting the remote antenna tilt mechanism to adjust the antenna tilt of the cell.

[0007] According to an example embodiment of the first aspect, the indication of the remote antenna tilt mechanism to be inoperative comprises an automated service ticket.

[0008] According to an example embodiment of the first aspect, the method may comprise: determining the similarity of the first set of users and the second set of users based on one or more of the following: user identities of the first set of users and the second set of users, timing advance distributions of the first set of users and the second set of users, maximum timing advance values of the first set of users and the second set of users, distance distributions of the first set of users and the second set of users, maximum distance of the first set of users and the second set of users, or received signal strength distributions of the first set of users and the second set of users.

[0009] According to an example embodiment of the first aspect, the method may comprise: determining a first set of static users of the cell during the first time period; determining a second set of static users of the cell during the second time period; determining the first set of users to include the first set of static users; and determining the second set of users to include the second set of static users.

[0010] According to an example embodiment of the first aspect, the method may comprise: determining not to include non-static users of the cell to the first set of users or the second set of users.

[0011] According to an example embodiment of the first aspect, a difference between the first tilt angle and the second tilt angle is at least 75 percent of a tilt range of the antenna.

[0012] According to an example embodiment of the first aspect, the first tilt angle comprises a maximum tilt angle of the antenna, or wherein the second tilt angle comprises a minimum tilt angle of the antenna.

[0013] According to an example embodiment of the first aspect, the method may comprise: initiating determination of the inoperability of the remote antenna mechanism, in response to receiving an indication of installation of the antenna.

[0014] According to an example embodiment of the first aspect, the cell is served by a transmission site at a first frequency range.

[0015] According to an example embodiment of the first aspect, the transmission site is further configured to serve a second cell at second frequency range, and wherein the first frequency range is higher than the second frequency range.

[0016] According to an example embodiment of the first aspect, the method may comprise: requesting a plurality of remote antenna tilt mechanisms of the transmission site to adjust antennas of a plurality of cells to respective first tilt angles for the first time period and respective second tilt angles for the second time period; determining, for the plurality of cells, respective first sets of users and respective second sets of users; and determining at least one of the plurality of remote antenna tilt mechanisms to be inoperative based on similarity of the respective first sets of users and the respective second sets of users.

[0017] According to an example embodiment of the first aspect, the plurality of cells belong to different sectors of the transmission site.

[0018] According to an example embodiment of the first aspect, the method may comprise: determining the plurality of cells based on distances between transmission sites of the plurality of cells exceeding a threshold, and / or determining the plurality of cells based on sectors of the plurality of cells not pointing towards each other.

[0019] According to a second aspect, an apparatus may comprise means for performing any example embodiment of the method of the first aspect.

[0020] 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.

[0021] 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: : request a remote antenna tilt mechanism to adjust an antenna of a cell to a first tilt angle for a first time period; determine a first set of users served by the cell during the first time period; request the remote antenna tilt mechanism to adjust the antenna of the cell to a second tilt angle for a second time period; determine a second set of users served by the cell during the second time period; and determine the remote antenna tilt mechanism to be inoperative based on similarity of the first set of users and the second set of users. 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.

[0022] 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

[0023] 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:

[0024] FIG. 1 illustrates an example of a cellular communication network;

[0025] FIG. 2 illustrates an example of an apparatus configured to practise one or more example embodiments;

[0026] FIG. 3 illustrates an example of a flow chart for determining inoperativity of remote antenna tilt mechanism(s);

[0027] FIG. 4 illustrates an example of a coverage area of a cell with a minimum tilt angle;

[0028] FIG. 5 illustrates an example of a coverage area of a cell with a maximum tilt angle;

[0029] FIG. 6 illustrates an example of a vertical power radiation pattern of a tilted antenna;

[0030] FIG. 7 illustrates examples of distance distributions of users for different antenna tilts of a cell;

[0031] FIG. 8 illustrates an example of a table indicative of a number of users of a cell at different distance ranges during different time periods; and

[0032] FIG. 9 illustrates examples of a method for determining a remote antenna tilt mechanism to be inoperative.

[0033] Like references are used to designate like parts in the accompanying drawings.DETAILED DESCRIPTION

[0034] 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.

[0035] FIG. 1 illustrates an example of a cellular communication network. Communication network 100 may comprise one or more devices, which may be also 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. Communication network100 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 3 GPP 5G NR (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.

[0036] 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 maybe configured to serve cells 132-1, 132-2, and 132-3, for example at respective sectors of the transmission site at which access node 122 is deployed. 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 132-1, 132-2, 132-3, 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 cells 134-1, 134-2, 134-3, and optionally one or more other cells. RAN 120 may comprise further access nodes, e.g., access node 126, with respective cell(s).

[0037] 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 maybe 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 optimize antenna tilts of cells, such as cell 132-1, within RAN 120.

[0038] 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.

[0039] 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. Timing advance 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.

[0040] 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. Even though some overlapping may be useful for handover purposes, it may be generally desired to minimize the signal level outside the dominance area.Overshooting is one example of a phenomenon that may occur due to wrong antenna tilting. Another example is the emergence of coverage holes between cells.

[0041] 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.

[0042] 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. Also, network controller 140 may be configured to detect undershooting cells, e.g., cells, where the power radiation pattern of the antenna is directed unnecessarily steep towards the ground. Network controller 140 may be configured to detect overshooting and undershooting cells and to perform corresponding counteraction(s), e.g., antenna downtilting or uptilting, by RET, or otherwise adjust the antenna tilts to optimize operation of RAN 120. Uptilting / downtilting a cell may comprise uptilting / downtilting the vertical power radiation pattern of an antenna of the cell. Tilting an antenna may comprise electrically adjusting the direction of the power radiation pattern, for example by applying differently delayed and / or weighted versions of transmitted / received signals.

[0043] RET mechanisms may be however prone to malfunction and therefore a request to adjust the antenna tilt may not be always effective. This may adversely affect network optimization because network controller 140 may not be aware of the actual antenna tilts in RAN 120. Any RET mechanism being inoperative, e.g., not being able to adjust the antenna tilt at all or not being able to adjust the antenna tilt as requested, may cause degradation of network performance. An inoperative RET mechanism may be for example malfunctional, unresponsive, or ineffective. It may therefore be desired to identify and either replace or disable inoperative RET mechanisms in the network.

[0044] Example embodiments of the present disclosure provide methods for testing operativity of RET mechanisms. This enables to improve optimization of network performance by identifying and either replacing or disabling inoperative RET mechanisms. For example, new RET mechanisms may be configured to be tested right after installation, which enables to get them instantly replaced. Already installed RET mechanisms may be configured to be tested according to a configurable schedule, for example once or twice a year.

[0045] 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.

[0046] 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. Forexample, 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.).

[0047] 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.

[0048] 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.

[0049] 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 a processor 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 GateArrays (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).

[0050] 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.

[0051] 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.

[0052] FIG. 3 illustrates an example of a flow chart for determining inoperativity of RET mechanism(s). Even though operations of the flow chart 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 methods for determining RET mechanism(s) to be inoperative may be construed from the operations of the flow chart. For example, some of the operations may not be performed in all example embodiments.

[0053] Network controller 140 may be configured to initiate the determination of the inoperativity of the RET mechanism(s), for example in response to receiving an indication of installation of respective antenna(s). Network controller 140 may be for example configured to receive site configuration information from RAN 120 indicative of a change of antenna configuration of particular transmission site(s). Detecting in operative RET mechanisms provides the benefit of enabling to avoid trying to control antenna tilts with inoperative RET mechanisms.

[0054] At operation 301, network controller 140 may determine (e.g., select) one or more cells for RET testing. Network controller 140 may be configured to select cell(s) associated with recently (e.g., within a predetermined time period) installedantennas. If network controller 140 determined multiple cells, network controller 140 may be configured to perform RET testing for the determined cells as a group, for example simultaneously, e.g., within one iteration of the outermost loop of the flow chart of FIG. 3. Simultaneous performance of RET testing may comprise adjusting antenna tilts of the cells for substantially same time periods, as will be further described with reference to operations 302 and 304.

[0055] Network controller 140 may be configured to determine the cells to be tested as a group based on distances between transmission sites of the cells, e.g., the distance of the transmission sites exceeding a threshold, for example 20 km, 30 km, 40 km, or the like. Network controller 140 may for example determine to select cells of access nodes 122 and 126 to be tested as a group, if the distance between respective transmission sites is above the threshold. This provides the benefit of enabling simultaneous RET testing for multiple cells without the testing of one cell affecting the other cells to be tested. This enables to perform RET testing over entire RAN 120 faster. If the distance is above the threshold, network controller 140 may be configured not to consider directions of the sectors of the cells, because the distance alone may be sufficient for guaranteeing independent RET testing for the selected cells.

[0056] Alternatively, or additionally, network controller 140 may be configured to determine the cells to be tested based on directions of sectors of the cells, for example such that the sectors of the selected cells do not point towards each other. Network controller 140 may determine a sector to point to another sector, if the sectors, as extending away from respective transmission sites, intersect at a point that is within a threshold distance from both of the transmission sites. A sector may be determined not to point to another sector, if the sectors do not intersect at a point that is within the threshold distance from both of the transmission sites. For example, network controller 140 might select cells 132-1, 132-2, 132-3, 134-3, 136-1, 136-2, 136-3 to be tested as a group, but not to select cells 134-1 and 134-2 to be tested with this group, because sectors of cells 134-1, 134-2 may be considered to point at the sector of cell 132-1.

[0057] Alternatively, or additionally, network controller 140 may determine the cells to be tested based on the cells belonging to different sectors of a transmissionsite. This provides the benefit of avoiding RET testing of one of the cells to significantly affect RET testing of other cells of the same transmission site. For example, network controller 140 might determine cells 132-1, 132-2, 132-3 of access node 122 to be tested as a group, because in the example of FIG. 1 they belong to different sectors of the respective transmission site.

[0058] Alternatively, or additionally, network controller 140 may be configured to determine the cell(s) to be tested based on the frequency range of the cell(s) served by the transmission site(s), for example the cell(s) belonging to a particular frequency range. This preferred frequency range may be also referred to as a first frequency range and it may comprise, for example, the LTE2100 frequency band (e.g., 1920 to 2170 MHzj or the LTE 1800 band (e.g., 1710 to 1880 MHz). The first frequency range may comprise a capacity layer of RAN 120. The capacity layer may be configured to provide sufficient transmission capacity at areas with a high number of users.

[0059] The transmission site may be further configured to serve cells also at a second frequency range, which may be lower than the first frequency range. The second frequency range may for example comprise the LTE800 frequency band (e.g., 791 to 962 MHz). The second frequency range may comprise a coverage layer of the network. The coverage layer may be configured to provide sufficient geographical coverage in RAN 120. Selecting cell(s) of the higher frequency range for RET testing provides the benefit of increasing the likelihood of causing observable changes associated with users of the cell(s), e.g., in their user identities, timing advance values (TA), distances, received signal strengths, or other parameters. This benefit is provided for example because signals with higher frequency attenuate faster than signals with lower frequency. Furthermore, the higher frequency band generally has more transmission capacity and therefore the number of users of the cell(s) may be higher in the capacity layer.

[0060] At operation 302, network controller 140 may request RET mechanism(s) of the determined cell(s) to adjust antenna(s) of the determined cell(s) to a first tilt angle for a first time period. Examples of different tilt angles are provided in FIG. 4 and FIG. 5. The tilt angle may comprise the angle between the direction of the vertical radiation pattern of the antenna, e.g., the direction of themain lobe of the vertical radiation pattern of the antenna and a horizontal line, as illustrated in FIG. 6.

[0061] In FIG. 6, the vertical radiation pattern 601 is illustrated with the solid curve and the horizontal line is illustrated by a dotted line. The vertical direction of departure from the antenna is mostly defined by the main lobe the vertical radiation pattern and parts surrounding the main lobe, as illustrated by region 602. 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.

[0062] When the tilt angle is at its maximum (ctmax) the coverage area of the respective cell is generally minimized. When the tilt angle is at its minimumthe coverage area of the respective cell is 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. For the purposes of explaining example embodiments of the present disclosure, the tilt angle is defined as the angle between the direction of the vertical radiation pattern and a horizontal line.

[0063] The first tilt angle may be different for different cell(s). For example, network controller 140 may be configured to request the RET mechanism(s) of the cell(s) to be adjusted to the maximum tilt angle, which may or may not be different for different cells. The first tilt angle may be higher than a currently configured tilt angle of a cell. Network controller 140 may be for example configured to request the RET mechanism(s) to increase the tilt angle, for example by a certain margin (e.g., 1 to 4 degrees), to increase the tilt angle to particular value (e.g., 10 degrees) or to adjust the tilt angle to the maximum tilt angle of the cell (e.g., 12 degrees). Requesting the RET mechanism to adjust the antenna to the first tilt angle may therefore comprise a request to increase the antenna tilt, not necessarily defining the resulting tilt angle in the request. It is however possible that the requestcomprises an indication of a particular tilt angle, e.g., 10 degrees, or a particular increment of the tilt angle.

[0064] At operation 303, network controller 140 may determine users served by the cell(s) during the first time period. A set of users of a cell during the first time period may be referred to as a first set of users. If more than one cell was determined at operation 301, separate first sets of users may be determined for different cells. For example, network controller 140 may be configured to collect information regarding the user identities of the users served by the cell(s) during the first time period. This information may be received from the access node(s) of the cell(s), the NMS, the OSS, or another network device configured to maintain information about users of cells. . Note that during the first time period the antenna(s) of the cell(s) are supposed to be at the first tilt angle(s), but the actual tilt angle(s) may depend on whether the respective RET mechanism(s) are operative or not.

[0065] An example of the first set of users is illustrated in FIG. 4 with the white circles. These users are served by cell 132-1, which has been adjusted to its maximum tilt angle (amax). The coverage are of cell 132-1 is therefore relatively small and only five users are served by cell 132-1. Users served by cell 134-1 are illustrated with the dotted circles.

[0066] Network controller 140 may be configured to determine at least one parameter for the first set of users, for example one or more of the following: timing advance values of the users, a maximum timing advance value of the users, distances of the users from access node 122, a maximum distance (dm„r) from access node 122, received signal strength values of the users (e.g., reference signal received power, RSRP). The maximum timing advance value of the users may comprise the maximum timing advance value among the timing advance values of the first set of users. The maximum distance may comprise the maximum distance among the distances of the first set of users, e.g., as measured from the access node of the cell, the antenna of the cell, or the transmission site of the cell. For example, users of cell 132-1 may be configured to transmit their location information to access node 122, which may be configured to calculate the distances between the location of access node 122 and the users.

[0067] The first set of users may comprise static and / or non-static users of the cell during the first time period. A static user may be a user that is substantially stationary. A static user may move to some extent (e.g., within a room), but such that movement of the static user does not cause a handover to be considered by the network. Network controller 140 may determine a user to be static for example based on number of and / or identities of cells accessed by the user, for example during a time period. For example, if the number of accessed cells (e.g., as identified by cell identifiers) meets a condition, for example is below a threshold, network controller 140 may determine the user to be static. Examples of the time period include a day, a certain number of days, a week, etc. The period used for determining whether a user is static may fully or partially precede the first time period. The period used for determining whether a user is static may be longer than the first time period, or the second time period of operation 304. This provides the benefit of improving reliability of determining the static users. A non-static user may comprise a user that is not static, e.g., a mobile user for which a handover is performed frequently, for example at least once during the time period for determining whether the user is static.

[0068] Alternatively, or additionally, network controller 140 may be configured to use stability of timing advance value(s) of a user as a basis for determining whether the user is a static user. Timing advance may reflect the distance of the user from an access node of the associated cell. For example, if variance of the timing advance (e.g., at the same cell) value is within a predetermined range, for example during the first and second time periods, network controller 140 may determine that the user is static. It is however also possible to exploit timing advance values of the same user at other cells as well. Using multiple timing advance values may be beneficial, since one timing advance value may indicate only a distance from one access node and not any direction. Using timing advance values from different cells enables determining distances from different access nodes with different angles to the user, thereby enabling more accurate localization of the user. If more than one timing advance value (e.g., associated with different transmission sites) is stable, it is possible to more reliably determine that the user is static. Network controller 140 may be therefore configured to determine that a user is static based on stability oftiming advance values of the user at a plurality of cells (e.g., the cell subject to RET testing and one or more neighbouring cells of that cell).

[0069] The two parameters, i.e., number of accessed cells and timing advance value(s), may be also used together, for example such that network controller 140 is configured to determine the user to be static, in response to determining that both conditions are met. Data of a static user may include for example location of the user. Location of the user may be signalled by the user to network controller 140, or network controller 140 may determine user’s location by other means, for example triangularization based on signals transmitted by UE 110 to different access nodes.

[0070] Network controller 140 may collect subscriber data of users (e.g., not only static users), for example in order to determine whether a particular user is static. One example of such subscriber data is the address of the subscriber. For example, if the location of the user matches to an address included in the subscriber data (e.g., home address), network controller 140 may determine that the user is static. In one example, users may be mapped to building identifiers (ID) of map data based on their current location. In this case, network controller 140 may determine that the user is static, if a building ID associated with the current location of the user corresponds to the address included in the subscriber data. The address may be used as an alternative to, or in combination with, the above conditions on the number of accessed cells and / or the stability of the timing advance value(s).

[0071] Network controller 140 may determine to include both static and nonstatic users of the cell in the first set of users. The first set of users may therefore include users that are either static or non-static. This provides the benefit of reducing complexity, because network controller 140 does not need to make a distinction between static and non-static users.

[0072] Alternatively, network controller 140 may be configured to determine a first set of static users of the cell during the first time period. Network controller 140 may determine to include the first set of static users in the first set of users. Network controller 140 may determine not to include non-static users of the cell (e.g., users not determined to be static users) to the first set of users. This provides the benefit of improving reliability of determining operativity of the RETmechanism(s), because of enabling to disregard changes associated with mobile users. Furthermore, the complexity is reduced since a subset of the users of the cell may be considered.

[0073] At operation 304, network controller 140 may request RET mechanism(s) of the determined cell(s) to adjust antenna(s) of the determined cell(s) to a second tilt angle for a second time period. The second time period may be subsequent to the first time period. The second tilt angle may be different for different cell(s), for example for similar reasons as described for the first tilt angle with reference to operation 302. For example, network controller 140 may be configured to request the RET mechanism(s) of the cell(s) to be adjusted to the minimum tilt angle, which may or may not be different for different cells. The second tilt angle may be lower than the tilt angle of the cell configured before the adjustment of operation 302, which may be also referred to as the original tilt angle. Network controller 140 may be for example configured to request the RET mechanism(s) to decrease the tilt angle, for example by a certain margin (e.g., 1 to 4 degrees) below the original tilt angle, to adjust the tilt angle to a particular value (e.g., 2 degrees), or to adjust the tilt angle to the minimum tilt angle of the cell (e.g., 0 degrees). Requesting the RET mechanism to adjust the antenna to the second tilt angle may therefore comprise a request to decrease the antenna tilt, but not necessarily defining the resulting tilt angle in the request.

[0074] The first tilt angle and second tilt angle may be configured such that their difference is expected to cause a change in user identities of the users served by the cell and / or parameter(s) of the users. As noted above, the first and second tilt angles may be the maximum and minimum tilt angles of the antenna. This provides the benefit of maximising the expected change in the user identities of the users served by the cell during the first and second time periods or parameter(s) of the users. It is however possible to apply tilt angle(s) different from the maximum or minimum tilt angles, if the tilt angles during the first and second time periods are different enough to cause an observable change in the user identities or parameter(s). For example, the difference between the first and second tilt angles may be at least 75 %, at least 85 %, or at least 90 % of the tilt range of the antenna. Tilt range ofthe antenna may comprise the range between the maximum and minimum tilt angles of the antenna.

[0075] At operation 305, network controller 140 may determine users served by the cell(s) during the second time period. A set of users of a cell during the second time period may be referred to as a second set of users. If more than one cell was determined at operation 301, separate second sets of users may be determined for different cells. Network controller 140 may be configured to collect information regarding the user identities of the users served by the cell(s) during the second time period and / or parameters of the users, as already described with reference to operation 303 for the first time period. During the second time period the antenna(s) of the cell(s) are supposed to be at the second tilt angle(s), depending on whether the respective RET mechanism(s) are operative or not.

[0076] An example of the second set of users is illustrated in FIG. 5 with the white circles, which again represent the users served by cell 132-1. In this example, the tilt angle of cell 132-1 has been adjusted to its minimumresulting in larger coverage area of cell 132-1, when compared to FIG.4. In this example, ten users are served by cell 132-1. Users served by cell 134-1 are again illustrated with the dotted circles. Note that values of the parameters described with reference to operation 303, e.g., the timing advance values or distances (e.g., their maximum value) may be now different, because the set of users may be at least partially different. Also, users belonging to the first set may have moved within cell 132-1, thereby affecting the parameter(s). Operativity of the RET mechanisms may be determined based on similarity of the first and second set of users, e.g., based on their identities and / or parameters, because generally the adjustment of the antenna tilt should cause a change in the identities and / or parameters of the users served by the cell.

[0077] Similar to operation 303, the second set of users may comprise static and / or non-static users of the cell during the second time period. Network controller 140 may be configured to determine to include both static and non-static users of the cell in the second set of users. Alternatively, network controller 140 may be configured to include the second set of static users in the second set of users.Network controller 140 may be configured to determine not to include non-static users of the cell to the second set of users.

[0078] At operation 306, network controller 140 may determine similarity of the users served by a cell during the first and second time periods, for example similarity between the first set of users and the second set of users as determined at operations 303 and 305. If the first and second sets of users include static users and not non-static users, network controller 140 may determine the similarity between static users of the cell during the first and second time periods. Network controller 140 may be configured to determine the similarity of the users based on user identities of the users and / or the parameters associated with the users, as will be further described below.

[0079] Network controller 140 may be configured to determine similarity of the sets of users based on user identities. For example, network controller 140 may determine a number of users that appear in either the first or the second sets of users, but not in both of them. Network controller 140 may for example determine the similarity of the sets of users as the percentage of users appearing in both the first and second sets of users relative to the total number of different user identities in the first and second sets of users. Smaller difference in the users identities between the sets of users may indicate higher similarity between the sets of users.

[0080] Alternatively, or additionally, network controller 140 may be configured to determine the similarity of the sets of users based on timing advance distributions of the first and second sets of users. Network controller 140 may use the timing advance values of users at to the cell that is subject to RET testing. For example, network controller 140 may be configured to determine the similarity of the sets of users as, or based on, a difference in at least one statistical quantity of the timing advance values of the first and second sets of users, for example as the difference between average, median, or a particular percentile of the timing advance values of the first and second sets of users. Smaller difference in the timing advance distributions of the sets of users may indicate higher similarity between the sets of users.

[0081] Alternatively, or additionally, network controller 140 may be configured to determine the similarity of the sets of users based on distance distributions of thefirst and second sets of users. Network controller 140 may be configured to determine the similarity of the sets of users based on a difference in at least one statistical quantity of the distance distribution. For example, network controller 140 may be configured to determine the similarity of the sets of users as, or based on, the difference between average, median, or a particular percentile of distances of the first and second sets of users, e.g., from the access node of the cell, the antenna, or the transmission site. Smaller difference in the distance distributions of the sets of users may indicate higher similarity between the sets of users.

[0082] Alternatively, or additionally, network controller 140 may be configured to determine the similarity of the sets of users based on received signal strength distributions of the first and second sets of users. Network controller 140 may be configured to determine the similarity of the sets of users based on a difference in at least one statistical quantity of the received signal strength distribution. For example, network controller 140 may be configured to determine the similarity of the sets of users as, or based on, the difference between average, median, or a particular percentile of received signal strength values of the first and second sets of users. Smaller difference in the received signal strength distributions of the sets of users may indicate higher similarity between the sets of users.

[0083] Using a parameter distribution such as the timing advance distribution, the distance distribution, or the received signal strength distribution provides the benefit of improving reliability of determining similarity of the sets of users, because the similarity is determined based on a potentially large number of users. Furthermore, using a high percentile (e.g., A-th percentile, where N > 50, N > 75, or N > 90, but N < 100) of the timing advance, distance distribution, or received signal strength values provides the benefit of emphasizing edge users of the cell, which are most likely to be affected by antenna tilting, while still enabling to consider a sufficient number of users.

[0084] Alternatively, or additionally, network controller 140 may be configured to determine the similarity of the sets of users based on maximum timing advance values of the first and second sets of users. For example, network controller 140 may be configured to determine the similarity of the sets of users as, or based on, the difference between the maximum timing advance values of the first and secondsets of users. Smaller difference in the maximum timing advance values of the sets of users may indicate higher similarity between the sets of users.

[0085] Alternatively, or additionally, network controller 140 may be configured to determine the similarity of the sets of users based on the maximum distance values (i / max) of the first and second sets of users. For example, network controller 140 may be configured to determine the similarity of the sets of users as, or based on, the difference between the maximum distance values of the first and second sets of users. Smaller difference in the maximum distance values of the sets of users may indicate higher similarity between the sets of users.

[0086] Using the maximum timing advance values or the maximum distance values provides the benefit of reducing complexity of determining similarity of the sets of users, while directing the evaluation to edge users of the cell, which are most likely to be affected by the adjustment of the tilt angle.

[0087] At operation 307, network controller 140 may determine whether at least one similarity criterion for the first and second sets of users is met. The similarity criterion may include one or more of the following: the amount (e.g., number or percentage) of users appearing in one of the two sets of users but not appearing in both of them being below threshold, the difference between timing advance distributions (e.g., average, median, or particular percentile) of the two sets of users being below a threshold; the proportion of users appearing in both of the two sets of users with respect to the total number of different users in the two sets of users being above a threshold; the difference between timing advance distributions (e.g., average, median, or particular percentile) of the two sets of users being below a threshold; the difference between the maximum timing advance values of the two sets of users being below a threshold; the difference between distance distributions (e.g., a statistical quantity such as average, median, or particular percentile) of the two sets of users being below a threshold; the difference between the maximum distance values of the two sets of users being below a threshold; or the difference between received signal strength distributions (e.g., a statistical quantity such as average, median, or particular percentile) of the two sets of users being below a threshold. Note that network controller 140 may be configured to consider one or more similarity criteria, when evaluating similarity of the two sets of users. Thesimilarity criterion of operation 307 may therefore be a combination of different similarity criteria. If the similarity criterion is not met, network controller 140 may proceed to operation 308. If the similarity criterion is met, network controller 140 may proceed to operation 309.

[0088] At operation 308, network controller 140 may determine, based on dissimilarity of the first and second sets of users, that the RET mechanism of the cell is operative. Network controller 140 may be configured to determine that the RET mechanism is operative, for example in response to determining that the similarity criterion, similarity criteria, or at least one of the similarity criteria of operation 307 is not met. Network controller 140 may determine that the RET mechanism is operative, in response to determining that the first and second sets of users are sufficiently dissimilar, e.g., if the request to adjust the antenna tilt causes an expected change in the user identities of the users served by the cell, or parameter(s) of the users. Network controller 140 may be configured to determine that the first and second sets of users are sufficiently dissimilar, in response to determining that the similarity criterion is not met. Network controller 140 may be configured to determine that the RET mechanism of the cell is operative, if the first and second sets of users are sufficiently dissimilar.

[0089] Network controller 140 may be configured to move back to operation 306 to process another cell, in order to determine similarity of respective first and second sets of users for that cell. If there are no further cells to be processed, network controller 140 may end the procedure or move back to execution of operation 301 to determine further cell(s) for RET testing.

[0090] At operation 309, network controller 140 may determine that the RET mechanism of the cell is inoperative. Network controller 140 may be configured to determine that the RET mechanism of the cell is inoperative based on similarity of the first and second sets of users. For example, network controller 140 may determine that the RET mechanism of the cell is inoperative, in response to determining that the similarity criterion of operation 307 is met. In other words, network controller 140 may determine that the RET mechanism is operative, if the request to adjust the antenna tilt does not cause an expected change in the user identities of the users served by the cell, or parameter(s) of the users.

[0091] At operation 310, network controller 140 may disable RET for the cell for which the RET mechanism was determined to be inoperative. For example, network controller 140 may be configured to refrain from requesting the RET mechanism to adjust the antenna tilt, in response to determining that the RET mechanism is inoperative. This provides the benefit of avoiding unnecessary requests for adjusting antenna tilt of the cell. This also enables network controller 140 to more accurately maintain information about current antenna tilts of different cells in RAN 120. This improves coverage optimization, because network controller 140 may take into account the information about inoperative RET mechanisms and refrain from trying to optimize antenna tilts of respective cells. Network controller 140 may also take into account the information about inoperative RET mechanisms when determining how to adjust antenna tilts of neighbouring cells.

[0092] At operation 311, network controller 140 may output an indication of the RET mechanism of the cell being inoperative. Network controller 140 may be configured to output the indication via a user interface, for example user interface 210. The indication may comprise a visual or textual indication. Alternatively, or additionally, network controller 140 may be configured to output the indication by transmitting it to another device, for example via communication interface 208. The indication may comprise an automated service ticket. An automated service ticket may comprise information configured to be recorded on a database for enabling a human user to handle service requests. Outputting the indication provides the benefit of enabling replacement of inoperative RET mechanisms in RAN 120. By efficient detection of inoperative RET mechanisms and enablement of corrective actions, either automatically or manually by a service man, overall network performance may be improved.

[0093] Note that network controller 140 may be configured to perform either operation 310 or 311, or both of them. Subsequently, network controller 140 may be configured to move back to operation 306 to process another cell, if multiple cells were determined at operation 301. It is however possible that network controller 140 is configured to simultaneously (e.g., in parallel) perform operations 306 to 311 , or a subset of them, for multiple cells. If there are no further cells to beprocessed after operation 310 or 311, network controller 140 may be configured to end the procedure or move back to execution of operation 301 to determine further cell(s) for RET testing.

[0094] In general, different variations of the procedure of FIG. 3 may be implemented. For example, network controller 140 may be configured to apply a smaller tilt angle at operation 302 and a higher tilt angle at operation 304. Furthermore, at operations 302 and 304, network controller 140 may be configured to request a plurality of RET mechanisms (e.g., RET mechanisms of same transmission site) to adjust antennas of multiple cells to respective first tilt angles for the first time period and to respective second tilt angles for the second time period. At operations 303 and 305, network controller 140 may be configured to determine respective first and second sets of users for the different cells. Network controller 140 may be configured to determine operativity of the RET mechanisms of the different cells, for example by iterating operations 306 to 311, or a subset thereof, for the different cells and respective first and second sets of users. Network controller 140 may be configured to determine at least one of the RET mechanisms to be inoperative based on similarity of the respective first sets of users and the respective second sets of users. For example, network controller 140 may be configured to determine the RET mechanism to be inoperative for cells for which the similarity criterion is met at operation 307. This provides the benefit of enabling simultaneous adjustment of the tilt angles for a group of cells subject to RET testing, which reduces the overall time consumed for RET testing in RAN 120. As noted above, the group of cells may be determined at operation 301 such that testing of the cells does not affect the other cells of the group. Network controller 140 may be configured to test different groups of cells, for example by iterating the outer loop of FIG. 3.

[0095] FIG. 7 illustrates examples of distance distributions of users for different antenna tilts of a cell. Network controller 140 may be configured to determine the distance of a user from the access node, antenna, or transmission site of the cell based on location information of the users and / or their timing advance values. The different curves indicates the distribution of users at different distances (km) for different tilt angles. The distribution of users is plotted as the share (%) of the totalnumber of users of the cell at a certain distance range (e.g., 0-1 km, 1-2 km, 2-3 km, etc.). The solid curve (without any dots) indicates the share of users with a normal tilt angle. The curves with white and black dots indicate the share of users with maximum and minimum tilt angles, respectively. The curve with the white dots may therefore represent the first set of users of the cell during the first time period. The curve with the black dots may represent the second set of users of the cell during the second time period. It is observed that the share of users at short distances decreases when adjusting the tilt angle form the maximum tilt angle to the minimum tilt angle. And the share of users at long distances (e.g., 28-30 km) increases when adjusting the tilt angle form the maximum tilt angle to the minimum tilt angle. A change in the distance distribution of the users is therefore observed and network controller 140 may determine that the RET mechanism of the cell is operative, because the distance distributions are sufficiently dissimilar.

[0096] FIG. 8 illustrates an example of a table indicative of a number of users of a cell at different distance ranges during different time periods. The table covers hours 13 to 22 for two cells associated with different frequency ranges LTE2100 and LTE1800 for one day. Between 13 and 16 the antenna tilts of respective cells have been requested to be normal, between 17 and 18 the antenna tilts have been requested to be at their maximum value(s), between 18 and 19 the antenna tilts have been requested to be adjusted from their maximum value(s) to their minimum value(s), between 19 and 20 the antenna tilts have been requested to be at their minimum value(s), between 20 and 21 the antenna tilts have been requested to be adjusted from their minimum value(s) back to their normal value(s), which have bee requested to be kept until 22 o’clock. The number of users at distance ranges 0 to 4 km and 26 to 29 km for respective time periods are provided in the remaining columns.

[0097] Considering the LTE2100 cell, it is observed that there are lots of long distance samples at 26 to 29 km, even though the tilt angle is supposed to be at its maximum. On the other hand, there is a low number of long distance samples when the tilt angle is supposed to be at its minimum. Accordingly, network controller 140 may determine that the RET mechanism of the LTE2100 cell is inoperative. Considering the LTE1800 cell, it is observed that there is no substantial change inthe number of long distance users even though the tilt angle is adjusted from its maximum to its minimum. Accordingly, network controller 140 may determine that the RET mechanism of the LTE1800 cell is inoperative.

[0098] The first and second time periods may comprise first and second reporting periods of the cell, respectively. A reporting period of a cell may comprise a period for recording the user identities or parameter(s) of the users served by the cell. For example, network controller 140 may be configured to receive periodical (e.g., hourly) reports indicative of the user identities or parameter(s) of the users served by the cell during the reporting period.

[0099] The first and second time periods for adjusting the antenna tilt of the cell to respective values may be selected such that the antenna tilt is requested to be at a desired value (e.g., maximum or minimum) for the entire duration of the reporting period. This provides the benefit of ensuring that the antenna is supposed to be at the requested tilt angle during the time for collecting the information on the users, e.g., their user identities or parameters. For example, in case an hourly reporting period is configured, network controller 140 may request the RET mechanism of the LTE2100 cell to adjust the antenna of the LTE2100 cell to its maximum for the full hour between 17:00 and 18:00.

[0100] FIG. 9 illustrates an example of a method for determining a remote antenna tilt mechanism to be inoperative. 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.

[0101] At 901, the method may comprise requesting a remote antenna tilt mechanism to adjust an antenna of a cell to a first tilt angle for a first time period.

[0102] At 902, the method may comprise determining a first set of users served by the cell during the first time period.

[0103] At 903, the method may comprise requesting the remote antenna tilt mechanism to adjust the antenna of the cell to a second tilt angle for a second time period.

[0104] At 904, the method may comprise determining a second set of users served by the cell during the second time period.

[0105] At 905, the method may comprise determining the remote antenna tilt mechanism to be inoperative based on similarity of the first set of users and the second set of users.

[0106] 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.

[0107] 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).

[0108] 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.

[0109] 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 10] 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 1 1 ] 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 1 2] 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 1 3] 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 14] 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: requesting a remote antenna tilt mechanism to adjust an antenna of a cell to a first tilt angle for a first time period; determining a first set of users served by the cell during the first time period; requesting the remote antenna tilt mechanism to adjust the antenna of the cell to a second tilt angle for a second time period; determining a second set of users served by the cell during the second time period; and determining the remote antenna tilt mechanism to be inoperative based on similarity of the first set of users and the second set of users.

2. The method according to claim 1, further comprising: in response to determining the remote antenna tilt mechanism to be inoperative: outputting an indication of the remote antenna tilt mechanism to be inoperative, or refraining from requesting the remote antenna tilt mechanism to adjust the antenna tilt of the cell.

3. The method according to claim 2, wherein the indication of the remote antenna tilt mechanism to be inoperative comprises an automated service ticket.

4. The method according to any of claims 1 to 3, further comprising: determining the similarity of the first set of users and the second set of users based on one or more of the following: user identities of the first set of users and the second set of users; timing advance distributions of the first set of users and the second set of users, maximum timing advance values of the first set of users and the second set of users,distance distributions of the first set of users and the second set of users, maximum distance of the first set of users and the second set of users, or received signal strength distributions of the first set of users and the second set of users.

5. The method according to any of claims 1 to 4, further comprising: determining a first set of static users of the cell during the first time period; determining a second set of static users of the cell during the second time period; determining the first set of users to include the first set of static users; and determining the second set of users to include the second set of static users.

6. The method according to claim 5, further comprising: determining not to include non-static users of the cell to the first set of users or the second set of users.

7. The method according to any of claims 1 to 6, wherein a difference between the first tilt angle and the second tilt angle is at least 75 percent of a tilt range of the antenna.

8. The method according to any of claims 1 to 7, wherein the first tilt angle comprises a maximum tilt angle of the antenna, or wherein the second tilt angle comprises a minimum tilt angle of the antenna.

9. The method according to any of claims 1 to 8, further comprising: initiating determination of the inoperability of the remote antenna mechanism, in response to receiving an indication of installation of the antenna.

10. The method according to any of claims 1 to 9, wherein the cell is served by a transmission site at a first frequency range.

11. The method according to claim 10, wherein the transmission site is further configured to serve a second cell at second frequency range, and wherein the first frequency range is higher than the second frequency range.

12. The method according to claim 10 or 11, further comprising: requesting a plurality of remote antenna tilt mechanisms of the transmission site to adjust antennas of a plurality of cells to respective first tilt angles for the first time period and respective second tilt angles for the second time period; determining, for the plurality of cells, respective first sets of users and respective second sets of users; and determining at least one of the plurality of remote antenna tilt mechanisms to be inoperative based on similarity of the respective first sets of users and the respective second sets of users.

13. The method according to claim 12, wherein the plurality of cells belong to different sectors of the transmission site.

14. The method according to claim 12, further comprising: determining the plurality of cells based on distances between transmission sites of the plurality of cells exceeding a threshold, and / or determining the plurality of cells based on sectors of the plurality of cells not pointing towards each other.

15. An apparatus comprising means for performing the method according to any of claims 1 to 14.

16. The apparatus according to claim 15, wherein the means comprises: at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

17. 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 14.

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