WO2016096001A1 - Cell shaping in wireless communications networks - Google Patents

Abstract

There is provided a method for shaping cells in a wireless communications network. The method is performed by a network node. The method comprises acquiring previously stored spatial channel characteristics for wireless devices (WDs), the WDs being associated with a set of radio access network nodes (RANNs), the spatial channel characteristics for at least one WD of the WDs being measured between the at least one WD and at least two RANNs in the set of RANNs. The method comprises determining beam forming parameters for shaping cells for at least one RANN in the set of RANNs based on the acquired spatial channel characteristics and on a change in operation state for at least another RANN in the set of RANNs. The method comprises notifying at least one of the RANNs in the set of RANNs of the determined beam forming parameters. There is also provided a corresponding network node and computer program.

Description

CELL SHAPING IN WIRELESS COMMUNICATIONS NETWORKS

TECHNICAL FIELD

Embodiments presented herein relate to cell shaping in wireless

communications networks, and particularly to methods, a network node, a computer program, and a computer program product for shaping cells in a wireless communications network.

BACKGROUND

In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its

parameters and the physical environment in which the communications network is deployed.

For example, one parameter in providing good performance and capacity for a given communications protocol in a communications network is the antenna systems used by the radio access network (RAN) nodes in the communications network and/or the wireless devices (WDs) with which the RANNs communicate so as to provide network coverage for the WDs.

Advanced antenna systems may be used to significantly enhance performance of wireless communication systems in both uplink (UL, i.e., from WD to RANN) and downlink (DL, i.e., from RANN to WD). In the downlink, there are three basic approaches for utilizing the antenna: diversity, multiplexing and beam forming.

With beam forming, the radiation pattern of the antenna may be controlled by transmitting a signal from a plurality of elements with an element specific gain and phase. In this way, radiation patterns with different pointing directions and transmission and/or reception beam widths in both elevation and azimuth directions may be created.

With so called WD specific beam forming, (narrower) beams may be formed to specific WDs in order to increase the receive signal power in these specific WDs while at the same time controlling interference generated to other WDs receiving data transmission.

WD specific beam forming is not the only form of beam forming. In mobile broadband systems based e.g., on High Speed Packet Access (HSPA) and Long Term Evolution (LTE), a common reference signal is transmitted (e.g., on a Common Pilot Channel (CPICH) or as cell specific reference signals (CRS)). Such signals may be used by WDs both for measurements to select a RANN to communicate with, as well as a demodulation reference signal for data to be received by both single and multiple WDs served by one RANN. Often, the area where a specific cell specific reference signal is received with highest power (as compared to cell specific reference signals transmitted from other RANNs) is referred to as a cell, and beam forming of the cell specific reference signal may therefore be referred to as "cell shaping".

In general, locations where no common reference signals may be received experience coverage loss. When deploying a communications network or during operation of an already deployed communications network, cell shaping may be performed to ensure that wireless devices have coverage from at least one RANN. One form of cell shaping used in existing cellular communications networks is electrical and mechanical down tilt, where coverage of the cell and interference between multiple cells can be adjusted by changing the elevation angle of the radiated beam (i.e., by changing the pointing direction of the antenna at the RANN). Commonly used sector antennas employ a form of cell specific beam forming. More specifically, an array of vertically stacked antenna element connected with a passive feeder network may be used, and the feeder network may hence implement the beam forming at radio frequencies. In such cases, individual antenna elements, or groups of antenna elements are not visible at base band.

However, in future advanced antenna systems, it is envisioned that elements or groups of elements will be controlled, and also observable, at baseband. As mentioned above, network planning is commonly done such that at least one RANN provides coverage in a given area, or cell. When a cell or a RANN is incapable of delivering its expected services by operating in a reduced mode by one out of several reasons, for example power shortage or other hardware failures, there will most likely be several locations in the

communications network that will experience loss of coverage. A RANN operating in such a reduced mode will be hereinafter referred to as a RANN in outage. Loss of coverage is an unwanted situation for operators. Thus, mitigation of this coverage loss until the lost cell is up and running would be valuable for network operators.

There exist a few automatic mechanisms that change the tilt setting based on some network measurements in order to adaptively change the antenna system to current network conditions. Existing mechanisms are designed for commonly used sector antennas of today where individual elements or groups of elements are not observable at baseband and do hence not exploit the full potential benefits of advanced antenna systems. In addition to tilt, which is the pointing direction in elevation, the elevation beam width can also be adjusted. It may for example be increased for a smaller cell in a dense high rise area where the positions of WDs in the cell are dispersed within a wide range of elevation angles. Similarly, the horizontal pointing direction and beam width in azimuth may be changed to better match the distribution of traffic.

An existing solution is to try different settings, observe the communications network performance and keep the setting that gives the best performance. However, since WDs cannot be served in coverage holes, the poor

performance for these WDs cannot be observed by the communications network. Current automatic tilt solutions try to mitigate this issue by changing the tilt in small steps, to avoid coverage holes. This however still does not a guarantee that coverage is maintained and it makes the adaptation slow.

Furthermore, there is also an inherent conflict when it comes to the period during which measurements are made. On one hand, it is desirable to measure for only short periods to enable decently rapid adaptation to perhaps even match fluctuations in the traffic, but on the other hand one would like to measure over somewhat longer time to capture performance that is relevant for all user position distributions. Hence, there is still a need for an improved cell shaping in wireless

communications networks.

SUMMARY

An object of embodiments herein is to provide efficient cell shaping in wireless communications networks. According to a first aspect there is presented a method for shaping cells in a wireless communications network. The method is performed by a network node. The method comprises acquiring previously stored spatial channel characteristics for wireless devices (WDs), the WDs being associated with a set of radio access network nodes (RANNs), the spatial channel

characteristics for at least one WD of the WDs being measured between the at least one WD and at least two RANNs in the set of RANNs. The method comprises determining beam forming parameters for shaping cells for at least one RANN in the set of RANNs based on the acquired spatial channel characteristics and on a change in operation state for at least another RANN in the set of RANNs. The method comprises notifying at least one of the RANNs in the set of RANNs of the determined beam forming parameters.

Advantageously this provides efficient cell shaping in wireless

communications networks.

Advantageously this provides an efficient mechanism to mitigate coverage problems when at least one RANN has a change in operation state.

Advantageously this provides an efficient mechanism to directly compensate loss when at least one RANN has a change in operation state. Advantageously, using previously stored spatial channel characteristics enables a rapid change to restore the original cell coverage setting once the at least one RANN has returned to an operational operation state.

According to a second aspect there is presented a network node for shaping cells in a wireless communications network. The network node comprises a processing unit. The processing unit is configured to acquire previously stored spatial channel characteristics for wireless devices (WDs), the WDs being associated with a set of radio access network nodes (RANNs), the spatial channel characteristics for at least one WD of the WDs being measured between the at least one WD and at least two RANNs in the set of RANNs. The processing unit is configured to determine beam forming parameters for shaping cells for at least one RANN in the set of RANNs based on the acquired spatial channel characteristics and on a change in operation state for at least another RANN in the set of RANNs. The processing unit is configured to notify at least one of the RANNs in the set of RANNs of the determined beam forming parameters.

According to a third aspect there is presented a computer program for shaping cells in a wireless communications network, the computer program comprising computer program code which, when run on a processing unit of a network node, causes the processing unit to perform a method according to the first aspect.

According to a fourth aspect there is presented a computer program product comprising a computer program according to the third aspect and a computer readable means on which the computer program is stored. It is to be noted that any feature of the first, second, third and fourth aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, and/or fourth aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

Figs, la and lb are schematic diagrams illustrating communications networks according to embodiments; Fig. 2a is a schematic diagram showing functional units of a network node according to an embodiment;

Fig. 2b is a schematic diagram showing functional modules of a network node according to an embodiment;

Fig. 3 shows one example of a computer program product comprising computer readable means according to an embodiment; and

Figs. 4, 5, 6, and 7 are flowcharts of methods according to embodiments.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

Fig. la is a schematic diagram illustrating a communications network 10a where embodiments presented herein can be applied. The communications network 10a comprises radio access network (RAN) nodes na, lib lie. The RANNs na, lib nc may be any combination of radio base stations such as base transceiver stations, node Bs, and/or evolved node Bs. The RANNs na, lib lie may further be any combination of macro RANNs, and micro, or pico, RANNs. Each RANN na, lib, lie provides network coverage in a respective coverage region (see, Fig. lb) by transmitting transmission beams Ri, R2, R3 in that coverage region. Each such coverage region forms a cell. Hence, the wireless communications network 10a, may regarded as a cellular wireless communications network. Each RANN 11a, lib 11c is assumed to be

operatively connected to a core network, as exemplified by one central network node 15. In some embodiments the central network node 15 is radio network controller (RNC). The core network may in turn be operatively connected to a service and data providing wide area network. The RANNs 11a, 11b 11c may further be operatively connected to a network node 12. The network node 12, which may be a centralized network node, will be further disclosed below.

Hence, a wireless device 13 served by one of the RANNs 11a, lib, lib may thereby access services and data as provided by the wide area network. The wireless devices 13 may be any combination of mobile stations, mobile phones, handsets, wireless local loop phones, user equipment (UE), smartphones, laptop computers, and/or tablet computers.

Fig. lb is another schematic diagram illustrating a communications network 10b where embodiments presented herein can be applied. The

communications network 10b of Fig. lb is similar to the communications network 10a of Fig. la but differs that the central network node 15 is not illustrated. Further, in the illustrative example of Fig. lb the coverage regions, or cells 14a, 14b, 14c of each RANN 11a, 11b, 11c have been schematically illustrated. Each cell 14a, 14b, 14c can be shaped by applying beam forming parameters at the RANNs 11a, 11b, 11c.

As noted above, by applying such beam forming, the radiation pattern of the antenna at a RANN 11a, lib, 11c may be controlled by transmitting a signal from a plurality of elements with an element specific gain and phase. In this way, radiation patterns with different pointing directions and transmission and/or reception beam widths in both elevation and azimuth directions may be created. As also noted above, there is still a need for an improved cell shaping in wireless communications networks 10a, 10b. There are several ways in which candidate cell shaping weights can be determined. One way is to try different beam forming weights, for example corresponding to an increase or decrease of the current tilt in one or several cells. Then, the network performance may be observed and settings that are good may be kept. The procedure may then be repeated for the kept settings. As mentioned above, one issue with this approach is that when the weights are changed, undesired coverage holes may be created, and the length of the measurement period to get reliable statistics is uncertain. However, such measurements results or evaluations may only provide the performance for the WDs 13 currently served in the communications network 10a, 10b. Therefore, WDs 13 that are not connected to the communications network 10a, 10b due to coverage loss form a cell outage will not contribute to the evaluations, and such an algorithm will thus not compensate for lack of coverage.

As will be further disclosed below, at least some of the herein disclosed embodiments are based on collecting and saving spatial channel

characteristics from WDs 13. Such previously stored spatial channel characteristics may then be used to assess coverage for different cell shapes before the performance of them is evaluated. The performance may be based not only for WDs 13 currently in the communications network 10a, 10b but also for WDs 13 that have previously been connected to the communications network 10a, 10b.

At least some of the herein disclosed embodiments are thus based on using previously collected spatial channel characteristics of multiple cells for WDs 13 that are or have been connected to the communications network 10a, 10b. The collected data is then used to find the best cell shapes (i.e. antennas settings) of one or several cells that, for example mitigate(s) coverage loss in case of cell outage or other changes in operation state for at least one of the RANNs 11a, 11b, 11c.

The embodiments disclosed herein particularly relate to cell shaping in wireless communications networks 10a, 10b. In order to obtain such cell shaping there is provided a network node, methods performed by the network node, a computer program comprising code, for example in the form of a computer program product, that when run on a processing unit of a network node, causes the processing unit to perform the method.

Fig. 2a schematically illustrates, in terms of a number of functional units, the components of a network node 11a, lib, 11c, 12 according to an embodiment. A processing unit 21 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc., capable of executing software instructions stored in a computer program product 31 (as in Fig. 3), e.g. in the form of a storage medium 23. Thus the processing unit 21 is thereby arranged to execute methods as herein disclosed. The storage medium 23 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The network node 11a, lib, 11c, 12 may further comprise a communications interface 22 for communications with any combination of at least one other network node 11a, lib, 11c, 12, at least one central network node 15, and at least one WD 13. As such the communications interface 22 may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of antennas for radio communications and ports for wired

communications. The processing unit 21 controls the general operation of the network node 11a, 11b, 11c, 12 e.g. by sending data and control signals to the communications interface 22 and the storage medium 23, by receiving data and reports from the communications interface 22, and by retrieving data and instructions from the storage medium 23. Other components, as well as the related functionality, of the network node 11a, lib, 11c, 12 are omitted in order not to obscure the concepts presented herein.

Fig. 2b schematically illustrates, in terms of a number of functional modules, the components of a network node 11a, 11b, 11c, 12 according to an

embodiment. The network node 11a, lib, 11c, 12 of Fig. 2b comprises a number of functional modules; an acquire module 21a configured to perform below disclosed steps S102, S104, S112, a determine module 21b configured to perform any of below disclosed step S108, Sio8a, Sio8b, S118, and a notify module 21c configured to perform below disclosed step S110. The network node 11a, 11b, 11c, 12 of Fig. 2b may further comprises a number of optional functional modules, such as any of a modify module 2id configured to perform below disclosed step S1114, a send and/or receive module 2ie configured to perform below disclosed step S1116, a generate module 2if configured to perform below disclosed step S106, and a compare module 2ig configured to perform below step Sio8c. The functionality of each functional module 2ia-g will be further disclosed below in the context of which the functional modules 2ia-g may be used. In general terms, each functional module 2ia-g may be implemented in hardware or in software. Preferably, one or more or all functional modules 2ia-g may be implemented by the processing unit 21, possibly in cooperation with functional units 22 and/or 23. The processing unit 21 may thus be arranged to from the storage medium 23 fetch instructions as provided by a functional module 2ia-g and to execute these instructions, thereby performing any steps as will be disclosed hereinafter. The network node na, lib, nc, 12 may be provided as a standalone device or as a part of a further device. For example, the network node 11a, 11b, 11c, 12 may be provided in a radio access network node or a central controller node. The network node 11a, 11b, 11c, 12 may be provided as an integral part of the radio access network node or a central controller node. That is, the

components of the network node 11a, lib, 11c, 12 may be integrated with other components of the radio access network node or a central controller node; some components of the radio access network node or a central controller node and the network node 11a, 11b, 11c, 12 may be shared. For example, if the radio access network node or a central controller node as such comprises a processing unit, this processing unit may be arranged to perform the actions of the processing unit 21 of with the network node 11a, lib, 11c, 12. Alternatively the network node 11a, 11b, 11c, 12 may be provided as a separate unit in the radio access network node or a central controller node. Fig- 3 shows one example of a computer program product 31 comprising computer readable means 33. On this computer readable means 33, a computer program 32 can be stored, which computer program 32 can cause the processing unit 21 and thereto operatively coupled entities and devices, such as the communications interface 22 and the storage medium 23, to execute methods according to embodiments described herein. The computer program 32 and/or computer program product 31 may thus provide means for performing any steps as herein disclosed.

In the example of Fig. 3, the computer program product 31 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 31 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 32 is here schematically shown as a track on the depicted optical disk, the computer program 32 can be stored in any way which is suitable for the computer program product 31.

Figs. 4, 5, 6, and 7 are flow charts illustrating embodiments of methods related to cell shaping in wireless communications networks 10a, 10b. The methods are performed by the network node 11a, 12. The methods are advantageously provided as computer programs 32.

Reference is now made to Fig. 4 illustrating a method for cell shaping in wireless communications networks 10a, 10b as performed by the network node 11a, 12 according to an embodiment. The network node 11a, 12 is configured to, in a step S102, acquire previously stored spatial channel characteristics for wireless devices (WDs) 13. The WDs 13 are associated with a set of radio access network (RAN) nodes 11a, 11b, 11c. The spatial channel characteristics for at least one WD 13 of the WDs have been measured between the WDs 13 and at least two RANNs in the set of RANNs 11a, 11b, 11c. The spatial channel characteristics for the remaining WDs of the WDs may have been measured between these remaining WDs and a respective at least one RANN (i.e., one RANN, or two RANNs, or three RANNs, etc.) in the set of RANNs 11a, lib, 11c. The spatial channel

characteristics may have been measured by the WD 13 or some other entity than the WD 13, e.g. by a RANN 11a, lib, 11c on the uplink. Further, it might be that some WDs 13 can only hear /be covered by a single RANN 11a, lib, 11c. Thus, the previously stored measurements are to be interpreted as "samples" or "measurements" that are collected by WDs 13 or RANNs 11a, 11b, 11c and each measurement may be associated with a set of RANNs 11a, 11b, 11c. For example, a single WD 13 may collect multiple measurements or samples, where each measurement may be associated with a different set of RANNs 11a, 11b, 11c. The WDs 13 are mobile and hence may be used to collect multiple measurements at different points in time, likely corresponding to different locations. The network node 11a, 12 is configured to, in a step S108, determine beam forming parameters for shaping cells 14a, 14b, 14c for at least one RANN in the set of RANNs 11a, 11b, 11c based on the acquired spatial channel characteristics and on a change in operation state for at least another RANN in the set of RANNs. Cell shaping may thereby be performed in one cell 14a, 14b, 14c at a time using the joint coverage provided by multiple RANNs 11a, 11b, 11c, but not necessarily that multiple RANNs 11a, 11b, 11c need to be beam formed. Though changing the beam forming in one cell 14a, 14b, 14c may change the cell shapes also in the neighbour cells 14a, 14b, 14c. In general terms, cell shapes are assumed to be realized by means of beam forming which means that each cell 14a, 14b, 14c has a set of beam forming weights. In some embodiments with an advanced antenna system, the beam forming weights are applied on the elements or groups of elements available at baseband and the channel characteristics refers to the channels of these available elements.

The network node 11a, 12 is configured to, in a step S110, notify at least one of the RANNs in the set of RANNs 11a, lib, 11c of the determined beam forming parameters.

Hence, spatial channel characteristics between WDs and several RANNs may be determined and stored in a centralized or distributed fashion. A database storing such spatial channel characteristics may thus comprise spatial channel characteristics not only for positions were WDs currently in the communications network are located but also for positions where WDs connected to the communications network have been located in the past. When a cell shape is to be changed in one or several cells, the network node 11a, 11b, 11c, 12 may evaluate the coverage probability using the database and the intended cell shape. In such a way coverage losses may be mitigated in locations where there has been coverage in the past, assuming the spatial channel characteristics have remained approximately the same since being measured. Each sample in the database may contain measurements to multiple RANNs. Given the information of what cell that is impacted by the change in operation state, a list of the locations that was served by this cell and that now might suffer from loss of coverage may be created. Information regarding which RANN(s) that are candidates (i.e., which RANN(s) that may be chosen as the so-called another RANN) for providing coverage may be deduced from the list. For the set of candidate RANN(s) the antenna settings, by means of beam forming parameters, may be determined such that sufficient coverage and performance is maintained for all locations. Embodiments relating to further details of cell shaping in wireless

communications networks 10a, 10b will now be disclosed.

In some embodiment, the spatial channel characteristics comprises channel correlation matrices determined from UL measurements scaled with path gain obtained from terminal reference signal received power (RSRP) measurements, and the cell shapes are represented by weight vectors comprising the amplitude and phase excitations of the common signal to be transmitted from the plurality of antenna elements. The network node 11a, 11b, 11c, 12 may then evaluate the received signal power for the cell shapes to confirm that further coverage is not lost. Particular details of such

embodiments as well as further embodiments will now be disclosed in detail.

In another embodiment, the spatial channel characteristics comprise measurements done by the WDs 13 on reference signals transmitted in the downlink from multiple RANNs 11a, lib, 11c. Each RANN 11a, lib, 11c may transmit multiple reference signals, such as so called CSI-RS in LTE, each reference signal being beam-formed with a candidate cell shaping weight.

Each one of the spatial channel characteristics may comprise a spatial relation between at least one of the WDs 13 and at least one of the RANNs 11a, 11b, 11c. The information given by the spatial relation can thus be used to describe from what position/location of (and/or direction to) the WD 13 (in relation to at least one of the RANNs 11a, 11b, 11c) the spatial channel characteristics were measured.

The beam forming parameters may be provided as beam forming weight vectors. There may be different ways to determine the beam forming parameters. The beam forming parameters may have previously been stored in a database. Determining the beam forming parameters as in step S108 may thus comprise retrieving the beam forming parameters from the database. Additionally or alternatively, the beam forming parameters may be determined using a reconfigurable antenna system - self-organizing network (RAS-SON) algorithm. The RAS-SON algorithm may be executed in a computer implemented simulation of the network using a model of the network. Different network models are a such known in the art and further description thereof is therefore omitted. The determined beam shaping parameters may be stored in a database. There may be different situations corresponding to a change in operation state of the so-called another RANN. For example, the change in operation state may correspond situations where the so-called another RANN has its transmission power changed, has a malfunction, or experiences a service failure. There may be different examples of previously stored spatial channel characteristics. For example, the previously stored spatial channel

characteristics may represent spatial channel characteristics having been measured at initial access of the WDs 13. For example, the previously stored spatial channel characteristics may represent spatial channel characteristics having been periodically measured.

Further, historical measurements may guarantee network coverage of historical WD locations. Hence, the spatial channel characteristics may be spatial channel characteristics of at least some WDs 13 no longer served by any of the RANNs 11a, lib, 11c when the spatial channel characteristics are acquired by the network node 11a, 12. However, the methods disclosed herein works with only current locations as well. Thus channel characteristics need not to be old/historical data.

Each RANN may be associated with a level of importance. The level of importance may be associated with a specific area. Hence, in this way, different areas may have different levels of importance. The beam forming parameters may then be determined based on the level of importance for the so-called another RANN. This enables the possibility of defining areas of high importance that never are allowed to have coverage loss.

There may be different ways of providing the notifying in step S110. For example, the notifying may be based on X2 interface signalling. The X2 interface (and thus how it as such may be used for signalling) is as such known in the art.

There may be different ways of how the RANNs in the set of RANNs are related. For example, the set of RANNs 11a, 11b, 11c may corresponds to all RANNs of one central network node 15, such as one radio network controller, RNC.

Reference is now made to Fig. 5 illustrating methods for cell shaping in wireless communications networks 10a, 10b as performed by the network node 11a, 12 according to further embodiments. In some embodiments, the database may be used to determine candidate cell shapes to be evaluated at the different cells. Being able to estimate the performance for all samples, the network node 11a, 12 may evaluate what systems settings that would improve performance for example for the cell edge users. It may further be possible to estimate the network performance given some system model.

There may be different ways for the network node 11a, 12 may to determine when to determine the beam forming parameters. For example, there may be a reporting mechanism that triggers the determination in step S108. The network node 11a, 12 may thus be configured to in an optional step S104 acquire an indication of the change in operation state. The indication may either be associated with a RANN going from a state of normal operation to a state of not normal operation, or vice versa. The state of not normal operation may be a state of malfunction, outage, congestion, etc. The network node 11a, 12 may then be configured to in an optional step Sio8a determine the beam forming parameters in response to having acquired the indication.

The change in operation state may be an actual change in operation state in the communication network 10a, 10b. The beam forming parameters may then be determined at the instant of the change in operation state. That is, in one embodiment, the network node 11a, 12 calculates, at the instant of the change in operation state, the beam forming parameters that should be used by nearby cells to restore as much of the lost coverage as possible.

The change in operation state may represent a simulated change in operation state in the communication network 10a, 10b. The beam forming parameters may then be determined so as to quickly cover an emulated change in operation state of a RANN when the actual change in operation state occurs. Coverage contribution from the RANN(s) experiencing the emulated change in operation state is neglected during simulation. That is, in one

embodiment, the network node 11a, 12 pre-calculates a set of beam forming parameters that may be used in the case at least one of the RANNs

experiences a change in operation state.

The change in operation state may pertain to an outage of the at least one RANN. Alternatively, the change in operation state may pertain to a restored operation after outage of the at least another RANN in the set of RANNs. Given the database, it is possible to emulate the coverage holes that will appear in case of cell outage. This is done by neglecting any contribution from the emulated outage cell (i.e., from the RANNs experiencing a change in operation state pertaining to outage) when evaluating the coverage. The pre- calculated (precaution) beam forming parameters may then be applied more rapidly in case of an actual outage. l8

There are more examples of change in operation state than outage. For example, the change in operation state may pertain to a change in

transmission power, a change in traffic handling capacity, a malfunction, or a service failure of the so-called at least another RANN. Hence, the indication as acquired in step S104 may be an indication of (changed) transmission power, an indication of change in traffic handling capacity, an indication of malfunction, or an indication of service failure of the so-called at least another RANN.

In general terms, according to at least some of the herein disclosed embodiments, before the cell shapes are adjusted in the actual wireless communications network 10a, 10b, a database comprising previously stored spatial channel characteristics for WDs 13 may thus be used to evaluate the coverage for the new proposed set of cell shaping weights, as defined by the determined beam forming parameters. More specifically, such a database may comprise a large number of samples, and each sample may comprise spatial channel characteristics to a set of RANNs 11a, 11b, 11c (or at least one RANN 11a, 11b, 11c). Hence, the beam forming parameters may be

determined without affecting the real network.

A list of locations of cells may be created to deduce information in order to facilitate determination of the beam forming parameters. Particularly, the network node 11a, 12 may be configured to in an optional step S106 generate a list comprising location information of each RANN associated with the change in operation state. The network node 11a, 12 may then be configured to in an optional step Sio8b determine the beam forming parameters based on the location information.

With knowledge of the spatial channel characteristic and the cell shapes currently applied in the RANNs 11a, 11b, 11c, an estimate of the received signal power to the RANNs 11a, lib, 11c associated with this measurement point can be formed. By comparing the highest received power with a minimum requirement of received signal power, it may be established whether or not the sample point has sufficient coverage. By using all (or a subset of) the measured points in the database, an estimate of the coverage, or the coverage probability can be obtained. An estimate of a signal to interference (and noise) ratio may be formed to further assess the network coverage. Hence, the network node 11a, 12 may be configured to, in an optional step Sio8c, determine the coverage by comparing a network performance measure, such as quality of service (QoS), for example based on received power, estimated signal to noise ratio, estimated signal to

interference and noise ratio, and/or estimated bit rate to appropriate threshold values. Further, the beam forming parameters may be determined based on network coverage probabilities. If the coverage is deemed to be sufficient, e.g. 95% or 99% percent of evaluated points have sufficient network coverage, the set of weights can be applied so as to change the cell shape. If network coverage is determined not to be sufficient, the network node 11a, 12 may choose not to apply the candidate cell shapes and thereby avoid creating a (new) coverage hole. Alternatively, after having evaluated several settings of beam forming parameters, the RANNs 11a, 11b, 11c may choose to apply the settings that gives the highest fraction of evaluated points with sufficient coverage.

There may be different ways of measuring the network coverage. For example, the network coverage may relate to coverage of a specific service channel and/or a specific control channel for a WD 13. Hence, if a WD 13 is able to receive a specific service channel and/or a specific control channel it may be defined as being within coverage.

There may be different examples of spatial channel characteristics and different ways to collect the spatial channel characteristics. In general terms, the term spatial channel characteristic may denote a measurement or estimate of how the signal strength and phase of a link varies as a function of element (or group of elements) position within an antenna array. Some examples will now be disclosed. The spatial channel characteristics may be based on reference signals such as demodulation reference signals (DMRSs), sounding reference signals (SRS), CSI reference signals (CSI-RS), or uplink random-access channel (UL RACH) signals. The spatial channel

characteristics may represent direct channel estimates corresponding to the radio channel between each element or groups of elements and the WD, represented by a vector h. The spatial channel characteristics may be provided by means of a correlation/covariance matrix, R = E {h^H * h] estimated with an appropriately formed sample covariance matrix from several direct channel estimates. The spatial channel characteristics may represent direction of arrival/departure estimates, typically estimated from h or R using various model-based or sub-space-based methods as known in the literature. The spatial channel characteristics may represent signal strength estimates for a set of different excitations vectors w_1} ... , w_N, e.g. the estimate Sj = wj * h or the magnitude/power of this estimate P = w_jRwj¹. Hence, in summary, the spatial channel characteristics may relate to at least one of a pointing direction for radio waves transmitted or received by the RANNs, channel correlation or covariance matrices determined from uplink measurements, and signal strength estimates over multiple antenna elements or beam forms. Further, the spatial channel characteristics may represent measurements of sounding reference signals (SRS), and/or channel state information reference signals (CSI-RS), or be provided as RSRP reports (see, below). The spatial channel characteristics can hence be used to estimate the received signal quality for multiple different candidate cell shapes.

In the uplink of LTE, a WD 13 may be configured to send a known signal for channel sounding purposes, a so called sounding reference signal (SRS). A RANN 11a, 11b, 11c that is aware of an SRS transmission may be enabled to use the known signal to perform a spatial channel estimate.

In some embodiments, the serving RANN 11a for a specific WD 13 exchanges the SRS allocations of one or more of its served WDs 13 with its neighbor RANN(s) 12b, 12c, enabling all such RANN(s) lib, 11c to individually form spatial channel estimates of their links towards each such WD 13. In such particular embodiments, each RANN 11a, lib, 11c may form a covariance matrix estimate. However embodiments where other measures are used can also be considered within the scope of the herein disclosed embodiments. Further, the covariance matrix estimates may be transformed from the uplink frequency to the downlink frequency such that they better represent the spatial channel characteristics for the frequency on which beam forming will be applied.

A spatial characteristics report may be generated for each such spatial channel characteristics. Further, the spatial channel characteristics may be provided in reports from each WD 13. The report may includes not only the spatial channel characteristics itself but also the identity of the measuring cell, and/or an identifier of the WD 13 for which the measurement was performed. Each report may thus further comprise a cell identity, a WD identity, and/or an indication of beam forming parameters for the spatial channel characteristics in the report. Each report may further comprise traffic prioritization information (disclosing e.g., if the corresponding data traffic is from an emergency call, or from users associated with public safety). Each report may further comprise a timestamp indicating a point in time when the report was generated.

Such reports may be sent for inclusion in the centralized or distributed database. These reports may first be aggregated on a per- WD basis, e.g. at the serving RANN 11a. All this information may thus be considered when determining beam forming parameters for shaping cells 14a, 14b, 14c as in step S108 above.

As noted above, RSRP measurements may additionally and/or alternatively be used, not only to determine the serving RANN 11a in general, but also to determine which are the neighbor RANN(s) lib, 11c mentioned above. The RSRP measurements may be performed on cell specific reference signals and the measurements may therefore depend on the cell shaping weights used at the time of measurements. To be able to predict the received signal power for a different set of cell shaping weights, the measurements may need to be associated with the cell shaping weights used during the measurements. In some embodiment, the WD 13 performs the measurements for several different cell shaping candidate weights, referred to as excitation weights above. In an LTE setting, feedback from the WD 13 may be used for coordinated multipoint (CoMP) using CSI-RS of several cells. In such settings, the WD 13 may report RSRP measurements for one or several candidate beam shapes of multiple cells directly to the serving RANN 11a.

A coverage prediction for a specific existing or historical RANN-to-WD link when considering a hypothetical candidate cell shape can be formed by considering the combined effect of the spatial channel characteristics and the hypothetical radiation pattern. The signal strength of a particular link in terms of the RSRP that the WD 13 will experience may be estimated as: _ RSRPWD * Wcandidate * R * ^wcandidate

wmeas * R * meas

Here, the term RSRP thus is the estimated signal strength in terms of RSRP. Further, RSRP_WD is the measured RSRP value, w_candidate is the considered weight vector over the elements in the antenna array (thereby forming the radiation pattern/cell shape), R is the spatial correlation matrix, and w_meas is the weight vector for which the RSRP value was measured.

Other embodiments consider the angles of arrival/departure (θ, φ) in relation to a hypothetical radiation pattern G(0, φ) and involves deriving an estimate of the antenna gain that the WD 13 will experience. The network node 11a, 12 may be configured to in an optional step S112 acquire further spatial channel characteristics from at least one of the WDs 13. The further spatial channel characteristics may be representative of the determined beam forming parameters being used by the at least one RANN. Hence, the network node 11a, 12 may thereby received feedback regarding how deployment of the determined beam forming parameters have affected coverage in the communication network 10a, 10b. A flag may thereby be set regarding if the determined beam forming parameters improved coverage (or not). The stored spatial channel characteristics may be modified based on recent occurrences in the communication network 10a, 10b. For example, the network node 11a, 12 may be configured to in an optional step S114 modify the previously stored spatial channel characteristics based on the acquired further spatial channel characteristics.

The beam forming parameters may, upon restoration of the change in operation state, be reset to the ones used before the change in operation state. Particularly, the network node 11a, 12 may be configured to in an optional step S116 receive an indication of a further change in operation state, and in response thereto, in an optional step S118, determine updated beam forming parameters for shaping the cells based on the acquired spatial channel characteristics. For example, in order to determine the updated beam forming parameters the currently used beam forming parameters, i.e., the beam forming parameters used before performing step S108, may be stored in the database so as to provide a backup.

The spatial channel characteristics may be stored in either a centralized or distributed database.

In a centralized implementation each RANN 11a, lib, 11c may select a candidate cell shape to be evaluated and reports this to other entities, such as other RANNs 11a, lib, 11c, in the communications network 10a, 10b. A centralized network node 12 may then determine a set of RANNs 11a, lib, 11c (one or several) that may try their proposed solution, in such way that the coverage for the whole communications network 10a, 10b is maintained. In other embodiments the centralized network node 12 uses the full database to evaluate a set of cell shaping settings that should be tested in the RANNs 11a, 11b, 11c (for one or multiple simultaneous RANNs 11a, lib, 11c), and reports this to each RANN 11a, lib, 11c under consideration.

In a distributed implementation, each RANN 11a, lib, 11c may keep a list of measurement samples of spatial channel characteristics. Each sample may comprise measurements between one WD 13 and at least one RANN 11a, 11b, lie. From the list it can be deduced which RANN(s) 11a, lib, 11c that can provide network coverage for the samples. For the case of simultaneous changes of antenna settings on several RANNs 11a, lib, 11c, one RANN 11a may query the other RANNs lib, 11c which weights they intend to use and then check that enough network coverage is provided. For changes that only consider the one RANN 11a the querying becomes obsolete. A token describing which RANN 11a, 11b, 11c is allowed to change the cell shape may be circulated among the RANNs 11a, 11b, 11c.

Combinations of distributed and centralized schemes may be possible, where each RANN 11a, 11b, 11c has partial information of the database in order to determine the antenna settings by means of beam forming parameters for shaping cells, whereas the centralized network node 12 may ensure network coverage for the whole communications network 10a, 10b. For example, the circulating token may further comprise an indication of what cell shapes are to be used by a particular RANN 11a, lib, 11c. The other RANNs receiving the token may thus use this information when determining their own cell shapes, For example, if a particular RANN indicates that a narrow beam is to be used, other RANNs may have to use wide beams in order to avoid areas of outage in the cell. Fig. 6 is a flowchart of a method for handling spatial channel characteristics according to an embodiment.

Step S202: For WDs 13 that have a connection with the communications network 10a, 10b, one or several measurements of the spatial channel characteristics to one or several RANNs 11a, lib 11c is/are performed. This can be performed in conjunction with initial access to the communications network 10a, 10b, periodically, or aperiodically during the connection with the communications network 10a, 10b.

Step S204: The measured characteristics are then stored in a database. The database is thus updated. Each WD 13 has a serving RANN 11a, and the database may be implemented either in a distributed or centralized fashion (see, above). If it is implemented in a distributed fashion, measurements may be stored in the database in the serving RANN 11a where for the case with a centralized database, the measurements may be sent to, and stored in, a central database.

Fig. 7 is a flowchart of a method for cell shaping in wireless communications networks 10a, 10b according to a particular embodiment.

S302: A change in operation state for at least another RANN in the set of RANNs is detected. The change in operation state may be actual or simulated. One way to implement step S302 is to perform step S104.

S304: If beam forming parameters exist, step S314 is entered; if not, step S306 is entered.

S306: Coverage is determined for a set of beam forming parameters for at least one RANN (i.e., for the so-called another RANN) in the communication network 10a, 10b having the change in operation state. One way to

implement step S306 is to perform steps S102, S106, S108, Sio8a, Sio8b.

S308: Usage of the determined beam forming parameters in the

communication network 10a, 10b is evaluated based on some network performance measure, such as quality of service (QoS). One way to

implement step S308 is to perform step Sio8c.

S310: If the determined beam forming parameters provide sufficient coverage and/or network performance step S310 is entered; if not, step S306 is entered.

S312: If the change in operation state is an actual change in operation state, step S314 is entered, and if not (i.e., if the change in operation state is simulated), step S318 is entered. S314: The determined beam shaping parameters are deployed in the communication network 10a, 10b. One way to implement step S314 is to perform step S110.

S316: The currently used beam shaping parameters are stored so as to provide a backup.

S318: The determined beam shaping parameters are stored in a database.

As noted above, the spatial channel characteristics may be stored in a database. As further noted above, each sample in the database may contain measurements to multiple RANNs. As further noted above, also the determined beam shaping parameters may be stored in a database. The spatial channel characteristics and the determined beam shaping parameters may be stored in the same database. Further aspects of such a database and how spatial channel characteristics and beam shaping parameters may be stored in such a database will now be disclosed. Using such a database may thus account for locations where WDs have been in the past, and not only WDs currently being in active or idle state in the wireless communications network 10a, 10b. As noted above, the

consideration of past locations of the WDs reduces the risk of creating coverage holes in the network when performing cell shaping. Such databases can thus be utilized during static beamforming, such as cell specific beamforming and cell shaping.

It is foreseen that automatic cell shaping within networks, as well as storage of data that may be used for such functionality, will become more common in future networks, especially as networks become denser and offline network planning in complex environments becomes even more difficult.

Some issues that may arise in the above mentioned uses of the database will be summarized next. Different aspect of how these issues may be mitigated will then be disclosed. Storage size aspect: WDs continuously report their channel status (such that spatial channel characteristics may be stored). If all information is logged and stored, the size of the database will continuously increase. This will become an issue both from the available storage perspective (in terms of size) as well as in terms of how all data will be processed. In general terms, the more data that is taken into account by e.g. a cell specific beam forming algorithm, the more computationally demanding the beam forming optimization will be.

Timeliness of data aspect: The spatial channel characteristics describe how the signal power of the RANNs should be spread in space in order to reach the receivers of the WDs. Thus, the signal power will depend on the environments surrounding the RANNs. Even if the environmental properties of the wireless channel as such do not change during a short time period, construction of new buildings and growth of vegetation etc. will affect the spatial properties. Thus, there will be a need to update the entries in the database to keep accuracy and timeliness. Other examples include, but are not limited to, considerations of the capabilities of the WDs in the network. Over time the initial WDs in the network will be replaced by newer WDs that may be equipped with more advanced functionality that may affect the potential for the RANNs in the network to utilize beam forming. Such a functionality could be a consequence of an increased number of antennas in the WD and/or support for newer standard releases of signalling in the network that allow for more advanced measurements and beam forming.

Significance aspect: One way to use a database with a fixed database storage size is to use a first in first out (FIFO) principle. However, in a database as described above, different samples will have different significance. There might be locations that are of more importance than others (for emergency call purposes etc.), or when several samples represent the same location. How to prioritize the significance of data generally depends on what the database is intended for, and a FIFO principle may not be the best way to optimize the content of a database with purposes of storing spatial channel characteristics. Database distribution aspect: Wireless networks may span a large

geographical area containing a large number of RANN sites. Collecting and storing data in a single database may not be preferred for all networks, and thus storing data in a distributed database may be considered. When distributing a database with purposes of storing spatial channel

characteristics, there will most likely be an overlap between the samples within the separate storage locations. Maintaining and optimizing a distributed database based on criterions for a centralized database may create unexpected issues in systems when performing beamforming based on the database entries.

The herein disclosed database enables provisioning of efficient methods for collecting and storing spatial channel characteristics from WDs to be used for assessing coverage for different cell shapes before the performance of the WDs are evaluated, based not only for WDs currently in the network (i.e., in either active state or idle state) but also for WDs that have previously been operatively connected to the network. The maintenance of (entries in) the database comprising stored spatial channel characteristics is based on what database is intended to be used for.

Advantageously, the herein disclosed database enables timeliness of data within a report to be maintained, which increases stability and performance of mechanisms for shaping cells in a wireless communications network relying on the database entries.

Advantageously, the herein disclosed database has a reasonable data size and number of inputs to ensure efficient usage of the database to be maintained, which may increase the feasibility of mechanisms for, for example, obtaining accuracy of data and estimates based on the data, and making a distributed database implementations feasible without undue degradation of network performance and gains from cell shaping.

An example of a database as herein disclosed may be based on a first set of arrays (such as rows in a table structure) representing the RANNs and a second set of arrays (such as columns in the table structure) representing the spatial channel characteristics measurements. Some measurements may span multiple RANNs while others concern only a single RANN. Each new measurement may end up as a new column in such a table structure. One aspect of the proposed database is to keep the database practical in size, timely, accurate, and suitable for the beamforming purpose for which it is intended to be used. This purpose, as disclosed above, is to provide information enabling improved network coverage and/or performance. The performance will be a result of the beam forms applied in multiple cells in the network, and will also be a function of what measurements the beamforming is based on and hence on the content of the database and which of the items stored in the database that are used by the beamforming mechanism.

Database maintenance is applied on stored spatial channel characteristics which may be obtained from one or several measurements phases in one or several cells (i.e., from one or more RANN 11a, lib, 11c). The embodiments presented herein concerns mechanisms enabling efficient (better than FIFO or similar approaches) maintenance of the database entries (distributed and centralized) depending on the intended purpose of the database is supposed to be used. In general terms, new entries are inserted into the database, or old entries are removed, if a certain selection criterion is met. The selection criterion is determined in a way to ensure that the database is of a feasible size, and contains accurate and timely entries that are suitable for the purpose for which the database is used, thereby enhancing the effectiveness of the used beamforming/cell shaping mechanisms and hence providing improved network performance. Additionally, the criterion may be determined to allow an efficient distributed implementation. Entries may be combined instead of inserted or removed separately.

For ease of explanation one of the aspects (storage size, timeliness of data, significance, and database distribution) will now be addressed one at the time. However, as the skilled person understands, the below presented mechanisms may be combined.

Storage size aspect: Quantization of entries is an efficient mechanism for maintaining the overall size of the database. The quantization may depend on what the database is intended for, but also on aspects such as fundamental limitations on the beam patterns (beam shapes) that each active (array) antenna may realize.

For example, the granularity of the quantized spatial channel data, aimed to be used with the realizable beam patterns (typically determined by some codebook constraint) does not need to be finer than what in the end may be measured at a WD. This may provide limits on the resolution of the entries (e.g., in terms of absolute numbers in terms of decimal precision) in the spatial channel characteristics data, or the spatial dimensions the data represents (e.g., main directions in angular domain, etc.). Moreover, another type of quantization is to only store unique entries of the spatial channel characteristics data. Several WDs 13 (possibly at separate locations) may have similar spatial channel characteristics. In such cases one entry that may represent multiple WD measurements may be stored, possibly complemented by a counter indicating the number of measurements sharing this similarity. According to another example it may be more efficient to only store data for locations where coverage may be difficult to obtain. Some measurements may correspond to WD locations that will always be in coverage no matter what antenna settings are used in the network, hence these measurements are obsolete for the intended purpose of the database and may be discarded. Another example is to group measurements that represent positions which are always in coverage into a single combined entry as described above.

Timeliness of data aspect: Entries in the database may become outdated for different reasons, such as changes in the environment, in the network, or in the WD. By tagging each measurement with e.g. a time stamp, a WD ID, and/or a WD capability identifier, it may be possible to introduce a so-called cleaning function that removes entries based on these tags. A number of examples are given next.

Timestamp; Time when first measured: Such a timestamp may be used as an indicator on when the data was collected, and a sorting of the database in a FIFO manner may utilize this input.

Timestamp; Time when last measured: Such a timestamp may, in combined with the above indicator, implement a clever version of the FIFO in that only old unused samples are removed from the database.

WD ID: Measurements from a WD belonging to a user that is no longer a subscriber may be discarded in favor of measurements from WDs of still- active subscribers.

Terminal capabilities: Measurements from legacy WDs may become obsolete, e.g. if the network is upgraded to a new standard release or if the population of such WDs in the network falls below a certain threshold (such that the operator no longer needs to consider them in the network operation).

Significance aspect: Different samples/entries in the database may be of different importance. As noted above, examples of this may be that certain areas are in extra importance of coverage due to the need for emergency calls etc. Other aspects that affect the significance are when compression and/or quantization of the data occurs. In a case of a single stationary WD 13 constantly reporting the same spatial channel characteristics information compared to a scenario where several WDs report spatial channel

characteristics information that are quantized to the same value/entry, the importance of separate samples/entries may be quantified with different counters that represent different aspects that may be of importance. A number of examples are given next.

General Significance: This kind of indicator may give the possibility to classify data/location as extra important that may not be discarded due to manual consideration. For example, even if data is not used for a long time, coverage at certain locations may be needed in order to guarantee emergency calls, etc.

Traffic: A measure on the traffic served (based on a certain spatial

characteristic) may indicate a hotspot or other areas of importance. Bad performance indicators: Logging/stamping data based on poor performance may be valuable. For example, a metric may indicate which WDs and/or locations to prioritize, even if other database entries represent locations with more data or higher WD count. Another indicator could be a handover failure; such failures may be reduced if those locations are well represented in the database.

Measurement quality: The measurement quality may be provided by a quality indicator, such as an error estimate, of the measurement report. This may give indications on what samples to remove first from the database when a prioritization of which entries to keep in the database is needed. Database distribution aspect: In a distributed database implementation, not all entries in the database are available at the same location or node. Each entry (or all entries in a row, see above) may be available in one of a set of distributed databases. One of the databases in the set could correspond to a single RANN or group of co-located RANNs or RANNs in the same geographical area. Either each measurement is available in only one database in the set, or it is copied/share among several sets. Typically an entry could be copied in all sets that include RANNs that are part of the measurements.

In any case, the maintenance of these databases could need some form of synchronization in order to serve the purpose of supporting beamforming in the network. Some examples, in the context of a database used to ensure coverage when performing cell shaping, are given next.

A database that discards an entry in the database due to any of the reasons outlined above may need to inform other databases where the same measurement is stored in order for these other databases to also discard the measurement. This may be achieved by the database discarding the entry passing a message containing a unique identifier of the entry to be discarded to the other databases.

An entry could be moved from one database to another. As an illustrative example, assume that the coverage of a certain WD location is considered when performing cell shaping of a certain group of RANNs or cells. However, in the report from this location also other RANNs outside this group are identified. If the database considered in the cell shaping of the first group of RANNs becomes full, then the entry could be moved to a different database used for cell shaping (some of) the other cells included in the report. A message containing the entry, and also notification of which RANNs can no longer be relied on to provide coverage, may therefore be passed. Associated hand-shaking between the RANNs may also be needed to ensure that the new group of RANNs has the ability and accepts to assume the responsibility for this location.

Operation of the herein disclosed database may be summarized as follows. The database is configured for inserting and removing entries in the database, where the entries represent spatial channel characteristics measurements between WDs and RANNs, where at least one measurement is associated with at least two RANNs. The database is configured to evaluate an entry based on a selection criterion. The database is configured to selectively insert, remove, or combine the entry with other entries in the database if the selection criterion is triggered. Examples of the selection criterion have been provided above. The database may have a central or distributed implementation. In a distributed implementation the database at a first location may be configured to perform hand-shaking with a database at a second location when an entry in the database at the first location is removed, or moved to the database at the second location.

The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims. For example, although only one WD 13 is illustrated in Figs la and lb it is readily understood that the communications network 10a, 10b may comprise a plurality of WDs 13. Further, although only three RANNs 11a, 11b, 11c are illustrated in Figs la and lb it is readily understood that the communications network 10a, 10b may comprise a plurality of RANNs 11a, 11b, 11c. The herein disclosed embodiments are not limited to a specific number of WDs or a specific number of RANNs.

Claims

1. A method for shaping cells (14a, 14b, 14c) in a wireless communications network (10a, 10b), the method being performed by a network node (11a, 12), the method comprising:

acquiring (S102) previously stored spatial channel characteristics for wireless devices (13), WDs, the WDs being associated with a set of radio access network nodes (11a, lib, 11c), RANNs, the spatial channel

characteristics for at least one WD of the WDs being measured between the at least one WD and at least two RANNs in the set of RANNs;

determining (S108) beam forming parameters for shaping cells (14a,

14b, 14c) for at least one RANN in the set of RANNs based on the acquired spatial channel characteristics and on a change in operation state for at least another RANN in the set of RANNs; and

notifying (S110) at least one of the RANNs in the set of RANNs of the determined beam forming parameters.

2. The method according to claim 1, further comprising:

acquiring (S112) further spatial channel characteristics from at least one of the WDs, said further spatial channel characteristics being representative of said determined beam forming parameters being used by said at least one RANN.

3. The method according to claim 2, further comprising:

modifying (S114) said previously stored spatial channel characteristics based on said acquired further spatial channel characteristics.

4. The method according to any of the preceding claims, further

comprising:

acquiring (S104) an indication of said change in operation state for said at least another RANN; and

determining (Sio8a) said beam forming parameters in response to having acquired said indication.

5. The method according to claim 4, wherein said indication represents an actual change in operation state in said wireless communications network.

6. The method according to claim 4, wherein said indication represents a simulated change in operation state in said wireless communications network.

7. The method according to claim 4, wherein said indication outage corresponds to said another RANN having its transmission power changed, having a malfunction, or experiencing a service failure.

8. The method according to any of the preceding claims, wherein said change in operation pertains to an outage of said at least another RANN in the set of RANNs.

9. The method according to claim 1, wherein said change in operation state pertains to a restored operation after outage of said at least another RANN in the set of RANNs.

10. The method according to claim 1, wherein said change in operation state pertains to a change in transmission power, a change in traffic handling capacity, a malfunction, or a service failure.

11. The method according to any of the preceding claims, wherein said beam forming parameters previously have been stored in a database, and wherein determining said beam forming parameters comprises retrieving said beam forming parameters from said database.

12. The method according to any of the preceding claims, wherein said previously stored spatial channel characteristics represents spatial channel characteristics having been measured at initial access of the WDs,

periodically, or aperiodically.

13. The method according to any of the preceding claims, wherein said beam forming parameters are determined using a reconfigurable antenna system - self-organizing network, RAS-SON, algorithm.

14. The method according to any of the preceding claims, wherein the spatial channel characteristics are based on demodulation reference signals, DMRSs, or uplink random-access channel, UL RACH, signals.

15. The method according to any of the preceding claims, further comprising:

receiving (S116) an indication of a further change in operation state , and in response thereto:

determining (S118) updated beam forming parameters for shaping said cells based on the acquired spatial channel characteristics.

16. The method according to any of the preceding claims, wherein each RANN is associated with a level of importance, and wherein said beam forming parameters are determined based on said level of importance for said another RANN.

17. The method according to any of the preceding claims, further comprising:

generating (S106) a list comprising location information of each RANN associated with said change in operation state; and

determining (Sio8b) said beam forming parameters based on said location information.

18. The method according to any of the preceding claims, wherein each one of the spatial channel characteristics comprises a spatial relation between at least one of the WDs and at least one of the RANNs.

19. The method according to any of the preceding claims, wherein the spatial channel characteristics are spatial channel characteristics of at least some WDs no longer served by any of the RANNs when said spatial channel characteristics are acquired by said network node.

20. The method according to any of the preceding claims, wherein the spatial channel characteristics relate to at least one of a pointing direction for radio waves transmitted or received by the RANNs, channel correlation or covariance matrices determined from uplink measurements, and signal strength estimates over multiple antenna elements or beam forms.

21. The method according to any of the preceding claims, wherein the beam forming parameters are provided as beam forming weight vectors.

22. The method according to any of the preceding claims, wherein determining said change in operation state comprises:

comparing (Sio8c) at least one of received power, estimated signal to noise ratio, estimated signal to interference and noise ratio, and estimated bit rate, to respective threshold values.

23. The method according to any of the preceding claims, wherein said change in operation state corresponds to no network coverage, said network coverage relating to coverage of at least one of a specific service channel and a specific control channel.

24. The method according to any of the preceding claims, wherein said notifying is based on X2 interface signalling.

25. A network node (11a, 12) for shaping cells (14a, 14b, 14c) in a wireless communications network (10a, 10b), the network node comprising a processing unit (21), the processing unit being configured to:

acquire previously stored spatial channel characteristics for wireless devices (13), WDs, the WDs being associated with a set of radio access network nodes (11a, lib, 11c), RANNs, the spatial channel characteristics for at least one WD of the WDs being measured between the at least one WD and at least two RANNs in the set of RANNs;

determine beam forming parameters for shaping cells (14a, 14b, 14c) for at least one RANN in the set of RANNs based on the acquired spatial channel characteristics and on a change in operation state for at least another RANN in the set of RANNs; and

notify at least one of the RANNs in the set of RANNs of the determined beam forming parameters.

26. A computer program (32) for shaping cells (14a, 14b, 14c) in a wireless communications network (10a, 10b), the computer program comprising computer program code which, when run on a processing unit (21) of a network node (11a, 12) causes the processing unit to:

acquire (S102) previously stored spatial channel characteristics for wireless devices (13), WDs, the WDs being associated with a set of radio access network nodes (11a, 11b, 11c), RANNs, the spatial channel

characteristics for at least one WD of the WDs being measured between the at least one WD and at least two RANNs in the set of RANNs;

determine (S108) beam forming parameters for shaping cells (14a, 14b, 14c) for at least one RANN in the set of RANNs based on the acquired spatial channel characteristics and on a change in operation state for at least another RANN in the set of RANNs; and

notify (S110) at least one of the RANNs in the set of RANNs of the determined beam forming parameters.

27. A computer program product (31) comprising a computer program (32) according claim 26, and a computer readable means (33) on which the computer program is stored.