WO2015147707A1

WO2015147707A1 - Method and network node for providing overlap information in a cellular network

Info

Publication number: WO2015147707A1
Application number: PCT/SE2014/050353
Authority: WO
Inventors: Fredric Kronestedt; Stefan STRÖM
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-03-24
Filing date: 2014-03-24
Publication date: 2015-10-01

Abstract

A method and network node for providing knowledge of overlapping radio coverage of a first base station (400) as input for operating a cellular network. The network node collects measurements (4:1) made by wireless devices (402) served by the first base station on downlink radio signals transmitted from at least one neighboring base station (404). The network node further determines (4:2) information about whether the at least one neighboring base station provides a radio coverage which overlaps the radio coverage of the first base station based on whether the collected measurements satisfy a predefined overlap condition and provides (4:3) the determined information as input for operating (4:4) the cellular network. For example, the first base station may be temporarily deactivated if the information indicates sufficient overlap by the at least one neighboring base station. The network node may be the first base station (400) itself or some other node that is used for controlling the network.

Description

METHOD AND NETWORK NODE FOR PROVIDING OVERLAP INFORMATION

IN A CELLULAR NETWORK

Technical field

The present disclosure relates generally to a method and a network node of a cellular network for wireless communication, for providing information about overlapping radio coverage as input for operating the cellular network.

Background

In recent years, different types of cellular networks for wireless communication have been developed to provide radio access for various wireless terminals in different areas. The cellular networks, sometimes also called radio networks, are constantly improved to provide better coverage and capacity to meet the demands from subscribers using services and increasingly advanced terminals, e.g.

smartphones and tablets, which may require considerable amounts of bandwidth and resources for transport of data and signaling in the networks. As a result, it is common to configure a network with cells of varying types and sizes, e.g. in an overlapping fashion, to provide needed capacity and flexibility depending on expected traffic intensity in different areas, the cells forming a so-called

heterogeneous cellular network.

A heterogeneous cellular network may comprise hierarchically arranged nodes, including macro nodes transmitting with relatively high power and covering relatively large areas typically of a size in the order of kilometers, and so-called low power nodes transmitting with relatively low power and covering areas typically of a size in the order of a few meters, e.g. micro, pico, femto and relay nodes, to mention some customary examples. The low power nodes may be employed together with the macro nodes in an overlapping fashion to locally provide added capacity in so-called "hot spot" areas such that multiple small areas served by such micro/pico/femto/relay nodes may be located within the area served by a macro node. It is also possible to employ a low power node to provide coverage in an area that has poor coverage by the macro node due to inadequate signal propagation. Fig. 1 illustrates a hierarchical cell configuration where a large cell C1 is covered by a macro base station 100 and a plurality of smaller cells C2 are covered by low power nodes 102. In this case, all smaller cells C2 are overlapped by the larger cell C1 . Overlap may also occur between cells of similar size. In the field of cellular radio technology, the term "wireless device" is commonly used and will be used in this disclosure to represent any wireless communication entity capable of radio communication with a radio node of a cellular network including receiving and sending radio signals. Another common term in this field is "User Equipment, UE" which is often used for various wireless devices such as e.g. mobile telephones, tablets, laptop computers, machine-to-machine type of devices such as sensors, counters or measuring entities.

Further, the term "base station" will be used here to represent any node of a cellular network that is arranged to communicate radio signals with wireless devices sometimes also referred to as a network node, radio node, e-NodeB, eNB, NB, base transceiver station, access point, etc. Throughout this disclosure, the terms "radio node" and "User Equipment, UE" can further be used instead of base station and wireless device, respectively.

The flexibility in a cellular network of today means that the base stations therein can be operated in different ways depending on the needs for communication services in the area. There are thus great possibilities to save costs and improve capacity depending on the current traffic situation, e.g. by saving power, reducing interference, efficient operation of radio equipment, efficient management of radio resources, efficient configuration of hardware, and so forth. For example, a base station may be turned off during certain periods of time to save power when it is possible to serve any wireless devices from another base station. However, it may be difficult to know whether a coverage area of a certain base station is also covered by one or more other base stations. It is thus a problem to decide whether a base station can be replaced by another base station or not in order to serve wireless devices in a certain area. Such knowledge could be utilized for supporting and optimizing operation of the cellular network. Summary

It is an object of embodiments described herein to address at least some of the problems and issues outlined above. It is possible to achieve this object and others by using a method and a network node as defined in the attached

independent claims.

According to one aspect, a method is performed by a network node in a cellular network for wireless communication, for providing knowledge of overlapping radio coverage of a first base station as input for operating the cellular network. In this method, the network node collects measurements, made by wireless devices served by the first base station, on downlink radio signals transmitted from at least one neighboring base station. The network node then determines information about whether the at least one neighboring base station provides a radio coverage which overlaps the radio coverage of the first base station based on whether the collected measurements satisfy a predefined overlap condition. The network node further provides the determined information as input for operating the cellular network.

According to another aspect, a network node is provided in a cellular network for wireless communication. The network node is arranged to provide knowledge of overlapping radio coverage of a first base station as input for operating the cellular network. The network node comprises means configured to collect measurements, made by wireless devices served by the first base station, on downlink radio signals transmitted from at least one neighboring base station. This may be achieved by means of a collecting module in the network node.

The network node further comprises means configured to determine information about whether the at least one neighboring base station provides a radio coverage which overlaps the radio coverage of the first base station based on whether the collected measurements satisfy a predefined overlap condition, and to provide the determined information as input for operating the cellular network. This may be achieved by means of a determining module and a providing module in the network node. Some advantages that may be achieved by using the above method and network node include that knowledge of whether a cell of the first base station is

overlapped or not by one or more other cells, as implied by the above overlap information, can be utilized for improving performance and capacity in the cellular network in several possible ways. For example, a base station may be deactivated at least temporarily to save power and reduce interference if its coverage area is found to be overlapped by another base station. A base station may also be configured, managed and/or tuned efficiently depending on the overlap information. Another advantage is that the wireless devices typically perform and report such measurements frequently to their serving base station anyway, e.g. to support handover operations or evaluation of neighboring cells, and the

measurements are thus easily available.

The above solution may be implemented in a computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to perform the method according to any of the embodiments described herein.

The solution may also be implemented in a carrier containing the above computer program, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium. The above method and network node may be configured and implemented according to different optional embodiments to accomplish further features and benefits, to be described below.

Brief description of drawings

The solution will now be described in more detail by means of exemplary embodiments and with reference to the accompanying drawings, in which:

Fig. 1 is a schematic overview illustrating a hierarchical cell configuration in a cellular network, according to the prior art. Fig. 2 is a schematic overview illustrating an example of overlapping radio coverage in a cellular network, where at least some of the embodiments described herein could be used.

Fig. 3 is a flow chart illustrating a procedure in a network node, according to some possible embodiments.

Fig. 4 is a schematic overview illustrating an example of a network arrangement where the solution is implemented, according to further possible embodiments.

Fig. 5 is a schematic overview illustrating another example of a network

arrangement where the solution is implemented, according to further possible embodiments.

Fig. 6 is a flow chart illustrating an example of how a network node may operate to implement the solution, according to further possible embodiments.

Fig. 7 is another flow chart illustrating an alternative example of how a network node may operate to implement the solution, according to further possible embodiments.

Fig. 8 is a block diagram illustrating a network node in more detail, according to further possible embodiments.

Detailed description

Briefly described, a solution is devised that potentially enables enhanced operation of a cellular network basically by determining information about whether radio coverage of a first base station is overlapped by radio coverage of one or more other base stations which will be referred to as "neighboring" base stations hereafter for simplicity. This overlap information may thus be useful for operating the cellular network, e.g., a cell may be temporarily inactivated to save power and reduce interference, among other things, if the cell area is deemed to be covered by other base stations to serve any wireless terminals present in that area. More detailed examples of how the overlap information might be utilized to generally improve performance and/or save costs in the cellular network, will be outlined later below.

In this solution it is recognized that such overlap of a first base station's radio coverage may actually be suggested in measurements made by various wireless devices on radio signals transmitted from one or more neighboring base stations while the wireless terminals are being served by the first base station. Wireless devices are typically required to perform and report such measurements anyway to support management of their connection with the network, and this can be utilized in this solution as well without requiring the wireless devices to perform any extra measurements. By collecting such measurements on signals from neighboring base stations and by evaluating the measurements in comparison with a predefined overlap condition, useful information about overlapping radio coverage can be obtained per cell, which will now be described in more detail with reference to some illustrative but non-limiting examples and embodiments. The number of measurements that indicate overlap according to the predefined overlap condition is counted in relation to the total number of collected

measurements, to determine a "percentage" of overlap which can also be seen as an overlap probability. For example, the predefined overlap condition may dictate that the first base station is considered to be overlapped if the percentage of measurements indicating overlap is above a certain limit. A measurement may be counted as indicating overlap if it is above or below a certain threshold, depending on what metric has been measured. If the measured metric is signal strength, the measurement should be above a certain signal strength threshold to be counted as a measurement indicating overlap. On the other hand, if the measured metric is path loss, the measurement should be below a certain path loss threshold to be counted as a measurement indicating overlap.

Fig. 2 illustrates an example of how different cells in a cellular network for wireless communication may overlap with one another in terms of radio coverage. For simplicity, the radio coverage areas of the cells in this figure are shown as regular circles while in reality the geometrical form of a cell's coverage area is typically much more irregular and complex. In this context, radio coverage means basically that when a wireless device is present within the coverage area of a base station, the device is able to communicate radio signals successfully with the base station.

It was mentioned above that hierarchical cell structures are becoming more and more desirable to employ in cellular networks mainly to meet the growing demands for increased capacity and improved performance. In this example, a relatively large cell area C1 is covered by a base station 200, which may be a macro node, while two smaller cell areas C2 and C3 are covered by other base stations 202 and 204, respectively, which may be micro/pico/femto/relay nodes in a hierarchical fashion. The cell areas C2 and C3 are illustrative in that cell area C2 is completely overlapped by the larger cell area C1 while cell area C3 is only partly overlapped by the larger cell area C1 . It should be noted however that the embodiments described herein are not limited to hierarchical cell structures but can be applied in any cell structures with cells of any size and form.

In Fig. 2, two wireless devices D1 and D2 are present in cell area C2 and being served by the base station 202, while two other wireless devices D3 and D4 are present in cell area C3 and being served by the base station 204. As mentioned above, this solution utilizes measurements made by wireless devices on signals transmitted from one or more neighboring base stations to determine overlap information. It is customary that wireless devices are required to perform such measurements and to report them to their respective serving base station on a regular basis in support of their ongoing connection, e.g. to enable efficient management of radio resources and evaluation of candidate target cells for handover or the like, which is well-known in the art.

It can thus be expected that such measurements on signals from neighboring base stations are available anyway according to regular procedures which is possible to utilize for this solution as well. However, the solution does not exclude the possibility to instruct the wireless devices to perform and report "dedicated" measurements to be used specifically for determining overlap information in the manner described herein. Fig. 2 further illustrates schematically a central "network manager" 206 in which the solution may be implemented, which may be an Operation and Maintenance, O&M, node or some equivalent node depending on network configuration and terminology used. The network manager 206 may collect reported measurements from any of the base stations 200, 202, 204, as indicated by dashed arrows, in order to evaluate any overlapping radio coverage. Alternatively, the functionality and embodiments described herein may be implemented in one or more of the base stations or in a Radio Network Controller, RNC, controlling the base stations, which will also be discussed later below. Each of the base stations 202 and 204 is configured to evaluate coverage overlap from their neighboring base station 200 as follows. Only one neighboring base station is considered in this example but it should be noted that the described procedure can be applied for more than one neighboring base station. In the example of Fig. 2, the base station 202 receives measurement reports from the served devices D1 and D2 with measurements made on radio signals transmitted from the base station 200 which may be specific Reference Signals, RS, which are commonly and frequently transmitted by base stations for the purpose of enabling wireless devices to measure reception of the signals RS, e.g. in terms of signal strength and/or signal quality according to regular procedures. In this example, the signal measurements reported from both devices D1 and D2 to base station 202 all satisfy a certain threshold condition, e.g. by being above or below a certain threshold depending on what metric has been measured, and it can therefore be deduced from these measurements that the neighboring base station 200 provides a radio coverage which overlaps the radio coverage of the base station 202. Hence, 100% of the collected measurements indicate

overlapping radio coverage by base station 200. This information can then be provided as useful input for operating the cellular network. In this case it may be possible to deactivate the base station 202, e.g. for a certain period of time to save costs such as when the traffic load is low and resources are available, since it has been determined that 100% radio coverage is provided by the base station 200 in the cell area C2, which is thus capable of serving any wireless devices in that area C2.

The base station 204 likewise receives measurement reports from the served devices D3 and D4 on the radio signals RS from the base station 200. In this case, the base station 204 determines that the signal measurements reported from device D3 satisfy the threshold condition and thus indicate coverage overlap, and device D3 is shown to be located within the cell C1 . On the other hand, the base station 204 determines that the signal measurements reported from device D4 do not satisfy the threshold condition, and device D4 is accordingly shown to be located outside the cell C1 . Hence, only 50% of the collected measurements indicate overlapping radio coverage by base station 200 since the measurements made by device D3 indicate overlap while the measurements made by device D4 do not indicate overlap. It may therefore be deduced that the neighboring base station 200 does not provide a satisfactory radio coverage which overlaps the radio coverage of the base station 202, e.g. at least not sufficient for deactivating the cell C3.

This overlap information can then be provided as useful input for operating the cellular network. For example, the predefined overlap condition may dictate that if the percentage of measurements which indicate overlap is above a certain limit, e.g. 90%, the cell may be marked as being reliably overlapped, otherwise not, which may be provided as an overlap indication for the evaluated first base station in the aforementioned information as input for operating the network. The determined percentage as such may also be provided as a more detailed overlap indication, being effectively an overlap probability, in the information as input for operating the network.

It should be noted that the above example is greatly simplified for illustrative purposes showing only two measuring wireless devices in each cell C2, C3, while in reality a large number of measurements from numerous wireless devices should preferably be collected, e.g. over an extended period of time, to obtain a

reasonably reliable basis and statistics for the evaluation of overlapping radio coverage. An example of how this solution may be carried out will now be described with reference to the flow chart in Fig. 3 which illustrates actions performed by a network node in a cellular network for wireless communication. The network node is arranged to provide knowledge of overlapping radio coverage of a first base station as input for operating the cellular network. As indicated above, the network node in this procedure may be implemented in the first base station itself or in a radio network controlling node such as any of the above-mentioned well-known nodes O&M and RNC, depending on how the network is configured, although the solution is not limited to these examples. A first action 300 illustrates that the network node collects measurements on downlink radio signals transmitted from at least one neighboring base station, which measurements have been made by wireless devices when being served by the first base station. In this context the measurements may refer to signal strength and/or signal quality depending on the implementation. The measured downlink radio signals may be specific reference signals or any other measurable signals from the neighbor(s) that can be used for this solution. In some possible embodiments, the collected measurements may, without limitation, comprise handover measurements reported by the wireless devices for evaluation of target cells. The wireless devices are typically instructed by the first base station to report such measurements according to a so-called neighbor list identifying a number of base stations which are neighbors to the first base station. The collected

measurements may also comprise periodic measurements reported by the wireless devices according to a reporting scheme, that is regardless of whether a handover is forthcoming or not. This action may be performed over an extended period of time by collecting measurements made by a considerable number of wireless devices, e.g. during several days, in order to attain a useful and sufficient statistic basis for determining how well the neighboring base station's downlink radio signals can be received within the coverage area of the first base station. If the network node is

implemented in a node other than the first base station, any measurements by wireless devices are actually obtained from the first base station currently serving the wireless devices since they are required to report such measurements to their serving base station.

In a further action 302, the network node basically evaluates a predefined overlap condition for each neighboring base station based on the collected measurements, e.g. to determine whether the coverage area of the first base station is overlapped by the neighboring base station, and possibly in what degree it is overlapped. For example in a possible embodiment, the predefined overlap condition may dictate that a percentage of the collected measurements indicating a downlink signal strength above a certain signal strength threshold should be above a first preset limit. In another possible embodiment, the predefined overlap condition may dictate a percentage of the collected measurements indicating a pathloss below a certain pathloss threshold should be above a second preset limit. It is also possible to have requirements for both signal strength and pathloss in the predefined overlap condition and the solution is not limited in this respect. In the simplified example shown in Fig. 2, the percentage of collected measurements on signals from base station 100 indicating a downlink signal strength above the signal strength threshold is 100% in cell C2 of base station 202, which should be above the first preset limit, but only 50% in cell C3 of base station 204 which may be below the second preset limit. Thus, another action 304 illustrates that the network node determines information about whether the at least one neighboring base station provides a radio coverage which overlaps the radio coverage of the first base station based on whether the obtained measurements satisfy the predefined overlap condition. As mentioned above, this information may comprise a simple indication of whether the first base station's coverage area is overlapped or not, and may also comprise a more detailed percentage or probability of overlap. In a possible embodiment, the network node may determine the above information further based on

measurements made by the at least one neighboring base station on uplink signals by wireless devices served by the first base station. Such measurements on uplink signals may thus also be indicative of whether the first base station's coverage area is overlapped by the neighboring base station. In a final action 306, the network node provides the determined information as input for operating the cellular network. For example, this overlap information may be sent to a suitable node that is used for managing and controlling the network, such as an O&M node or the like. Some examples of how this information might be used in the network to generally improve capacity, performance and efficiency and/or reduce costs, are presented below. In further possible embodiments, the network node may thus provide the determined information as input for at least one of the following:

A) De-activation of the first base station during periods of low traffic load, which may be done in order to save costs by reducing power consumption and other operational activities. As mentioned above, a base station that is found to be overlapped by another base station may be turned off or be put into some low-power operation mode such as "standby" or the like, e.g. during certain periods when low traffic load is expected, since any devices present in the area can be served by the other base station.

B) Determination of power backup for the first base station. If the first base station is found to be overlapped by another base station, at least to some degree as indicated by the above-described percentage or overlap probability, it may be possible to save considerable costs by reducing or even omitting equipment for power backup at the first base station.

C) Management of radio resources. If the first base station is found to be overlapped by another base station, it may be possible to distribute the use of radio resources among the first and neighboring base stations which may provide an efficient use of the radio resources, e.g. defined by time intervals, carrier frequencies and/or codes.

D) Distribution of traffic load between the first base station and the at least one neighboring base station. If the first base station is found to be overlapped by another base station, it may be possible to let one or more wireless devices make a handover from the overlapping base station to the first base station or vice versa, e.g. in order to offload a heavily loaded cell. E) Determination of repair of malfunction in the first base station. If the first base station is found to be overlapped by another base station, it may not be necessary to repair the first base station immediately since any devices present in the area can be served by the other base station before the repair is completed. In that case, such repair work can be made more efficiently at a selected time that is practically suitable e.g. in terms of coordination with other maintenance work.

F) Tuning the first base station and/or the at least one neighboring base station to avoid or reduce interference. If the first base station is found to be overlapped by another base station, it may be possible to, at least temporarily, tune the first base station to only partly cover its nominal cell since the parts that will not be covered by the first base station are likely covered by the other base station. To mention some non-limiting examples, this may be done by adjusting the first base station's antenna configuration and/or reducing its output power.

In the above examples, the determined information is used as input at least for operating the first base station in some way. However, the term "operating the cellular network" should be understood broadly in this description and it may also imply that the determined information is used, alternatively or additionally, as input for operating the at least one neighboring base station, e.g. according to any of the above examples, particularly if it can be assumed that the at least one neighboring base station is overlapped by the first base station. Such overlap of coverage between base stations may e.g. indicate that there is a risk for interference between communications in the respective cells. In this case, "operating the cellular network" may also include various actions and mechanisms for reducing or avoiding inter-cell interference between the coverage area of the first base station and the coverage area of the at least one neighboring base station. For example, the known mechanisms of Inter-Cell Interference Coordination, ICIC, may be employed if the determined information implies a high degree of coverage overlap. In another possible embodiment, the at least one neighboring base station may include at least two neighboring base stations which jointly provide a radio coverage that overlaps the radio coverage of the first base station. In this case, any wireless device present within the overlapped coverage area may be served by two base stations jointly and simultaneously and will thus be able to receive and transmit radio signals from/to both base stations. For example, two or more base stations may jointly serve a so-called combined cell covered by multiple base stations, or they may serve a primary cell and one or more secondary cells, respectively, using technique which is known as such in the art.

In another example, some of the collected measurements may indicate that a first base station BS1 is overlapped by two neighboring base stations BS2 and BS3. If 100 measurements have been collected in total and 80 of them fulfil the threshold condition, it can be deduced that the cell has an overlap percentage of 80% by either BS2 or BS3 or both. In other words, 80 measurements indicate overlap by BS2 and/or BS3. If the overlap condition requires that 80% is enough for overlap, it may be decided that the base station BS1 can be deactivated if the other base stations BS2 and BS3 have resources available to serve any wireless devices in the area.

Fig. 4 illustrates an example of how the above-described procedure and network node may be implemented in practice. In this example, a first base station 400 serves various wireless devices 402 and the above-described network node resides in the first base station 400 itself. A first action 4:1 illustrates that the first base station 400 collects measurements made by the wireless devices 402 on downlink radio signals transmitted from at least one neighboring base station 404, by receiving measurement reports from the wireless devices 402, basically as described for action 300 above. The first base station 400 then determines overlap information based on the collected measurements, in a next action 4:2, basically as described for actions 302 and 304 above. The first base station 400 further provides the overlap information as input for operating the cellular network by sending the information to an O&M node 406 in a further action 4:3, basically as described for action 306 above. Another action 4:4 illustrates finally that the O&M node 406 is able to operate the network using the overlap information, examples of which have been given above.

Fig. 5 illustrates another example of how the above-described procedure and network node may be implemented in practice. In this example, a first base station 500 serves various wireless devices 502 which are configured to perform measurements on downlink radio signals transmitted from at least one neighboring base station 504. In contrast to the example of Fig. 4, the above-described network node resides in an O&M node 506 instead of in the base station 500. A first action 5:1 illustrates that the first base station 500 collects measurements by receiving measurement reports from the wireless devices 502, as similar to action 4:1 in the previous example.

After having collected a sufficient amount of measurements, the first base station 500 forwards measurement results to the O&M node 506, in a further action 5:2. Optionally, the base station may compile or arrange the measurements in a suitable manner before sending them to the O&M node 506, e.g. by specifying how many measurements that are above or below some threshold, or by determining certain statistic parameters such as average, maximum or minimum values of the measured metric, e.g. depending on the time of day, and so forth. Then, the O&M node 506 determines overlap information based on the collected measurements, in a next action 5:3, basically as described for actions 302 and

304 above. The O&M node 506 further provides and uses the overlap information as input for operating the cellular network in a final shown action 5:4, basically as described for action 306 above.

Two illustrative examples of how this solution may be implemented in practice will now be described with reference to the flow charts in Figs 6 and 7 which illustrate actions performed by a network node in a cellular network, for providing

knowledge of overlapping radio coverage of a first base station. These examples illustrate specifically how actions 304 and 306 above may be carried out and they are applicable regardless of whether the network node is implemented in the first base station, an O&M node or an RNC. The example in Fig. 6 assumes that the above-described predefined overlap condition dictates that a percentage of the collected measurements indicating a downlink signal strength above a certain signal strength threshold should be above a first preset limit denoted "Z1 ".

In a first action 600, the network node collects measurements of signal strength of downlink radio signals transmitted from a neighboring base station, which measurements have been made by wireless devices when being served by the first base station. This action corresponds to action 300 above. A next action 602 illustrates that the network node determines a percentage of the collected signal strength measurements that are above a certain signal strength threshold, implying that the respective measurement indicates coverage overlap. The network node determines in another action 604 whether the determined percentage is above the first limit Z1 , i.e. whether the predefined overlap condition is satisfied or not. If so, the neighboring base station is indicated as overlapping relative the first base station, in an action 606, or expressed differently, the coverage area of the first base station is considered to be overlapped by the neighboring base station. On the other hand if the determined percentage is not above the first limit Z1 , the neighboring base station is indicated as non- overlapping, in an action 608. It should be noted that actions 602-608 correspond to actions 302 and 304 above.

In contrast to Fig. 6, the example of Fig. 7 assumes that the above-described predefined overlap condition dictates that a percentage of the collected

measurements indicating a pathloss below a certain pathloss threshold should be above a second preset limit denoted "Z2". In a first action 700, the network node collects measurements on downlink radio signals transmitted from a neighboring base station, which measurements have been made by wireless devices when being served by the first base station. This action likewise corresponds to action 300 above. A next action 702 illustrates that the network node determines a percentage of the collected measurements that indicate a pathloss below a certain pathloss threshold, implying that the respective measurement indicates coverage overlap. The network node determines in another action 704 whether the determined percentage is above the second limit Z2, i.e. whether the predefined overlap condition is satisfied or not. If so, the neighboring base station is indicated as overlapping relative the first base station, in an action 706, or expressed differently, the coverage area of the first base station is considered to be overlapped by the neighboring base station. On the other hand if the determined percentage is not above the second limit Z2, the neighboring base station is indicated as non-overlapping, in an action 708. It should be noted that actions 702-708 also correspond to actions 302 and 304 above. A detailed but non-limiting example of how a network node in a cellular network for wireless communication may be structured with some possible functional entities such as modules, circuits or units, to bring about the above-described functionality of the network node, is illustrated by the block diagram in Fig. 8. In this figure, the network node 800 is arranged to provide knowledge of overlapping radio coverage of a first base station "BS1 " as input for operating the cellular network. The network node 800 may be configured to operate according to any of the examples and embodiments of employing the solution as described above and as follows. In particular, the network node 800 may comprise means arranged or configured to perform at least the actions of the flow chart in Fig. 3 and possibly also to operate according to any of Figs 2 and 4-7 in the manner described above. In order to put any of this into practice, the network node 800 may be implemented with a communication circuit C, a memory M and an operable processor P comprising various functional modules as described below.

More specifically, the network node 800 comprises means configured to collect measurements, made by wireless devices 802 served by the first base station BS1 , on downlink radio signals transmitted from at least one neighboring base station 804. This collecting operation may be performed by a collecting module 800a, e.g. in the manner described for action 300 above. The network node 800 also comprises means configured to determine information about whether the at least one neighboring base station 804 provides a radio coverage which overlaps the radio coverage of the first base station BS1 based on whether the collected measurements satisfy a predefined overlap condition. This determining operation may be performed by a determining module 800b, e.g. in the manner described for actions 302 and 304 above.

The network node 800 also comprises means configured to provide the

determined information as input for operating the cellular network, e.g. to an O&M node or the like. This providing operation may be performed by an providing module 800c, e.g. in the manner described for action 306 above.

It should be noted that Fig. 8 illustrates some possible functional modules in the network node 800 and the skilled person is able to implement these functional modules in practice using suitable software and hardware. Thus, the solution is generally not limited to the shown structures of the network node 800, and the functional modules 800a-c may be configured to operate according to any of the features described in this disclosure, where appropriate.

The embodiments and features described herein may be implemented in a computer program comprising computer readable code which, when run on a network node, causes the network node to perform the above actions e.g. as described for Fig. 3. Further, the above-described embodiments may be implemented in a computer program product comprising a computer readable medium on which the above computer program is stored. The computer program product may be a compact disc or other carrier suitable for holding the computer program. Some examples of how the computer program and computer program product can be realized in practice are outlined below.

The functional modules 800a-c described above for Fig 8 may be implemented in the network node 800 by means of program modules of a respective computer program comprising code means which, when run by the processor "P" causes the network node 800 to perform the above-described actions and procedures. The processor P may comprise a single Central Processing Unit (CPU), or could comprise two or more processing units. For example, the processor P may include a general purpose microprocessor, an instruction set processor and/or related chips sets and/or a special purpose microprocessor such as an Application Specific Integrated Circuit (ASIC). The processor P may also comprise a storage for caching purposes.

Each computer program may be carried by a computer program product in the network node 800 in the form of the shown memory M having a computer readable medium and being connected to the processor P. The computer program product or memory M thus comprises a computer readable medium on which the computer program is stored e.g. in the form of computer program modules. For example, the memory M may be a flash memory, a Random-Access Memory (RAM), a Readonly Memory (ROM) or an Electrically Erasable Programmable ROM (EEPROM), and the program modules m could in alternative embodiments be distributed on different computer program products in the form of memories within the network node 800.

Advantages that may be accomplished by using the described solution include that a network operator is able to save costs, increase capacity and/or to improve performance in the cellular network by utilizing knowledge about which cells in the network have overlapped coverage and which cells have not. The cells may also be ranked or rated with respect to the degree of overlap, i.e. the above-described percentage or probability of overlap, which information may further be used for certain operational decisions in the network such as deciding when to make repair or maintenance work, deactivate cells, management of radio resources, omitting power backup equipment, and so forth. Some detailed examples of how the overlap information might be used in a cellular network have been presented above.

While the solution has been described with reference to specific exemplifying embodiments, the description is generally only intended to illustrate the inventive concept and should not be taken as limiting the scope of the solution. For example, the terms "base station", "wireless device", "network node" and "overlap condition" have been used throughout this disclosure, although any other corresponding entities, functions, and/or parameters could also be used having the features and characteristics described here. The solution is defined by the appended claims.

Claims

1 . A method performed by a network node (400, 506, 800) in a cellular network for wireless communication, for providing knowledge of overlapping radio coverage of a first base station (400, 500) as input for operating the cellular network, the method comprising:

- collecting (300) measurements, made by wireless devices (402, 502, 802) served by the first base station, on downlink radio signals transmitted from at least one neighboring base station (404, 504, 804),

- determining (304) information about whether the at least one neighboring base station provides a radio coverage which overlaps the radio coverage of the first base station based on whether the collected measurements satisfy a predefined overlap condition, and

- providing (306) the determined information as input for operating the cellular network.

2. A method according to claim 1 , wherein the predefined overlap condition dictates that a percentage of the collected measurements indicating a downlink signal strength above a certain signal strength threshold is above a first limit (Z1 ).

3. A method according to claim 1 or 2, wherein the predefined overlap condition dictates that a percentage of the collected measurements indicating a pathloss below a certain pathloss threshold is above a second limit (Z2).

4. A method according to any of claims 1 -3, wherein the collected measurements comprise at least one of: handover measurements reported by the wireless devices for evaluation of target cells, and periodic measurements reported by the wireless devices according to a reporting scheme.

5. A method according to any of claims 1 -4, wherein the information is determined further based on measurements made by the at least one neighboring base station on uplink signals by wireless devices served by the first base station.

6. A method according to any of claims 1 -5, wherein the network node is any of: the first base station, a Radio Network Controller RNC, and an Operation and Maintenance, O&M, node.

7. A method according to any of claims 1 -6, wherein the at least one neighboring base station includes at least two neighboring base stations which jointly provide a radio coverage which overlaps the radio coverage of the first base station.

8. A method according to any of claims 1 -7, wherein the determined information is provided as input for at least one of: - de-activation of the first base station during periods of low traffic load,

- determination of power backup for the first base station,

- management of radio resources,

- distribution of traffic load between the first base station and the at least one neighboring base station, - determination of repair of malfunction in the first base station, and

- tuning the first base station and/or the at least one neighboring base station to avoid or reduce interference.

9. A network node (400, 506, 800) in a cellular network for wireless communication, the network node being arranged to provide knowledge of overlapping radio coverage of a first base station (400, 500) as input for operating the cellular network, the network node comprising means configured to:

- collect measurements, made by wireless devices (402, 502, 802) served by the first base station, on downlink radio signals transmitted from at least one neighboring base station (404, 504, 804), - determine information about whether the at least one neighboring base station provides a radio coverage which overlaps the radio coverage of the first base station based on whether the collected measurements satisfy a predefined overlap condition, and

- provide the determined information as input for operating the cellular network.

10. A network node (400, 506, 800) according to claim 9, wherein the predefined overlap condition dictates that a percentage of the collected

measurements indicating a downlink signal strength above a certain signal strength threshold is above a first limit (Z1 ).

1 1 . A network node (400, 506, 800) according to claim 9 or 10, wherein the predefined overlap condition dictates that a percentage of the collected

measurements indicating a pathloss below a certain pathloss threshold is above a second limit (Z2).

12. A network node (400, 506, 800) according to any of claims 9-1 1 , wherein the collected measurements comprise at least one of: handover measurements reported by the wireless devices for evaluation of target cells, and periodic measurements reported by the wireless devices according to a reporting scheme.

13. A network node (400, 506, 800) according to any of claims 9-12, wherein the network node is configured to determine the information further based on measurements made by the at least one neighboring base station on uplink signals by wireless devices served by the first base station.

14. A network node (400, 506, 800) according to any of claims 9-13, wherein the network node is any of: the first base station, a Radio Network Controller RNC, and an Operation and Maintenance, O&M, node.

15. A network node (400, 506, 800) according to any of claims 9-14, wherein the at least one neighboring base station includes at least two neighboring base stations which jointly provide a radio coverage which overlaps the radio coverage of the first base station.

16. A network node (400, 506, 800) according to any of claims 9-15, wherein the network node is configured to provide the determined information as input for at least one of:

- de-activation of the first base station during periods of low traffic load, - determination of power backup for the first base station,

- management of radio resources,

- distribution of traffic load between the first base station and the at least one neighboring base station,

- determination of repair of malfunction in the first base station, and - tuning the first base station and/or the at least one neighboring base station to avoid or reduce interference.

17. A computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to perform the method according to any of claims 1 -8.

18. A carrier containing the computer program of claim 17, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.