WO2023282806A1

WO2023282806A1 - Methods and network entities for handling allocation of physical cell identities in a wireless communication network

Info

Publication number: WO2023282806A1
Application number: PCT/SE2021/050702
Authority: WO
Inventors: Tobias AHLSTRÖM; Daniel Henriksson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2021-07-08
Filing date: 2021-07-08
Publication date: 2023-01-12

Abstract

Disclosed is a method for handling allocation of Physical Cell Identities, PCI, in a wireless communication network (100). The method comprises obtaining information on two or more cells (50, 52) that are neighbors or a neighbor´s neighbors, the two or more cells having the same PCI, and information on their current PCI, and obtaining, for each of the two or more cells (50, 52), information on PCIs that the cell can choose from. The method further comprises obtaining information on PCI of cells (56, 58) that are neighbors to any of the two or more cells (50, 52), and obtaining information on a number of cell changes for UEs (140), performed to and/or from each of the two or more cells (50, 52) and a number of cell changes for UEs performed to and/or from each of the cells (56, 58) that are neighbors to any of the two or more cells, over a defined time period. The method further comprises determining which of the two or more cells (50, 52) that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, based on the information on the current PCI for the two or more cells (50, 52) and the PCIs of the cells (56, 58) that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells (50, 52) and on the information on the number of cell changes performed for UEs to and/or from each of the cells (56, 58) that are neighbors to any of the two or more cells; and changing PCI for the determined cell to the determined PCI, when it is determined to change PCI.

Description

METHODS AND NETWORK ENTITIES FOR HANDLING ALLOCATION OF PHYSICAL CELL IDENTITIES IN A WIRELESS COMMUNICATION NETWORK

Technical Field

[0001] The present disclosure relates generally to methods and network entities for handling allocation of Physical Cell Identities, PCIs, in a wireless communication network. The present disclosure further relates to computer programs and carriers corresponding to the above methods and entities.

Background

[0002] The main task of a wireless communication network is to provide good radio connections for wireless communication devices, aka wireless devices aka User Equipments (UEs) to carry communication services the users of the UEs want to utilize. In this process it its central to find the most suitable cells or antenna beams (in the following only referred to as cells) for every UE as it moves around. This is today performed by requesting the UE to measure strength and quality of radio signals sent from radio access network (RAN) nodes handling the cells, both of serving cells and of neighbor cells. The serving cell is the cell in which the UE resides/is connected to. The neighbor cells are cells that are neighbors to the serving cell and which the UE may transit into as it moves around. The results of the measurements of strength and quality of serving cells and neighbor cells are reported by the UE to the RAN, which makes a decision what cell(s) shall serve the mobile in the following. These measurements of strength and quality that are reported to the RAN are normally accompanied with the physical cell identity (PCI) of the cell in order for the RAN to know which measurement belongs to which cell.

[0003] In order to limit the amount of communication resources needed for sending the ID of the cell together with the measurements, the PCI has a limited number of bits, compared to a global cell identity (CGI) which is very long and therefore a unique ID for each cell. As the PCI is such a limited resource it needs to be reused throughout the network. This means that a PCI conflict situation may occur. A PCI conflict occurs when the PCIs are reused too tightly in the network so that two cells that are neighbors or neighbors’ neighbors use the same PCI. The PCI conflict situation can be divided into two different situations, PCI confusion and PCI collision. A PCI confusion occurs when a first cell has two neighbor cells where both those neighbor cells have the same PCI and frequency. Then it will be confusing for the first cell, which of the two cells that the different measurements sent from the UE refers to. A PCI collision occurs when the first cell has a neighbor that has the same PCI as the first cell has. When there is a PCI collision, it is not possible for the UE to detect that it gets out of coverage of the first cell and into the second cell with the same PCI as the first cell. The result will most probably be a lost call.

[0004] A good PCI allocation without PCI conflicts is important since it will provide the following benefits: Better mobility features performance, Increased throughput in the network, improved New Radio (NR) utilization in Non-Stand Alone (NSA) systems, Better carrier aggregation performance, Increased retainability, and Reduced interference, among others. NSA systems are systems where a first network node of a first radio access technology has a direct signaling connection with a core network, but a second network node of a second radio access technology only has signaling connection with the core network node via the first network node. Here the term signaling connection is equivalent to control plane connection

[0005] In a PCI conflict scenario, it might not be obvious which cell that should change PCI to resolve the PCI conflict. This might be especially challenging in a distributed system. Existing methods for resolving PCI conflicts suggest that one of the cells involved in the PCI conflict changes PCI. This might end up in a situation where the PCI conflict is not resolved, or a new PCI conflict is created. This might happen when the cell that is about to change PCI cannot find a suitable vacant PCI since all PCIs it can choose from are used by its neighbor cells or its neighbors’ neighboring cells. Also, it may happen that some PCIs are reserved for reasons such as other the PCI is used by types of cells, such as home base stations, which limits the number of PCIs that the cell can choose from, or when two operators use the same frequency and not want PCI collisions, which may happen e.g. at a country border. Consequently, there is a need of an improved method for handling PCI conflicts.

Summary

[0006] It is an object of the invention to address at least some of the problems and issues outlined above. It is possible to achieve these objects and others by using methods and network entities as defined in the attached independent claims.

[0007] According to one aspect, a method is provided for handling allocation of PCIs in a wireless communication network. The method comprises obtaining information on two or more cells that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI, and obtaining, for each of the two or more cells, information on PCIs that the cell can choose from. The method further comprises obtaining information on PCI of cells that are neighbors to any of the two or more cells and obtaining information on a number of cell changes for UEs, performed to and/or from each of the two or more cells and a number of cell changes for UEs performed to and/or from each of the cells that are neighbors to any of the two or more cells, over a defined time period. The method further comprises determining which of the two or more cells that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, based on the information on the current PCI for the two or more cells and the PCIs of the cells that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells and on the information on the number of cell changes performed for UEs to and/or from each of the cells that are neighbors to any of the two or more cells. The method further comprises changing PCI for the determined cell to the determined PCI, when it is determined to change PCI.

[0008] According to another aspect, one or more network entities is provided, the one or more network entities being configured for handling allocation of PCIs in a wireless communication network and configured to operate in a wireless communication network. The one or more network entities comprises processing circuitry and a memory. The memory contains instructions executable by said processing circuitry, whereby the one or more network entities is operative for obtaining information on two or more cells that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI, and obtaining, for each of the two or more cells, information on PCIs that the cell can choose from. The one or more network entities is further operative for obtaining information on PCI of cells that are neighbors to any of the two or more cells, and obtaining information on a number of cell changes for UEs performed to and/or from each of the two or more cells, and a number of cell changes for UEs performed to and/or from each of the cells that are neighbors to any of the two or more cells, over a defined time period. The one or more network entities is further operative for determining which of the two or more cells that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, based on the information on the current PCI for the two or more cells and the PCIs of the cells that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells and on the information on the number of cell changes performed for UEs to and/or from each of the cells that are neighbors to any of the two or more cells, and changing PCI for the determined cell to the determined PCI, when it is determined to change PCI.

[0009] According to other aspects, computer programs and carriers are also provided, the details of which will be described in the claims and the detailed description.

[00010] Further possible features and benefits of this solution will become apparent from the detailed description below.

Brief Description of Drawings

[00011 ] The solution will now be described in more detail by means of exemplary embodiments and with reference to the accompanying drawings, in which: [00012] Fig. 1 is a schematic diagram of an example of a wireless communication network in which the present invention may be used.

[00013] Fig 2 is a schematic diagram of another example of a wireless communication network in which the present invention may be used.

[00014] Fig. 3 is a flow chart illustrating a method for handling PCIs, according to possible embodiments.

[00015] Fig. 4 is a diagram with ovals and arrows illustrating an example of usage of the present invention.

[00016] Fig. 5 is a diagram with ovals and arrows illustrating another example of usage of the present invention.

[00017] Fig. 6 is a schematic diagram of cells and RAN nodes illustrating another example of usage of the present invention.

[00018] Fig. 7 is a signaling diagram according to embodiments.

[00019] Fig. 8 is another signaling diagram according to other embodiments.

[00020] Fig. 9 is a schematic block diagram of a distributed implementation of embodiments of the invention.

[00021] Fig. 10 is a schematic block diagram of an O-RAN network for implementing embodiments of the invention.

[00022] Fig. 11 is a schematic block diagram illustrating one or more network entities in more detail, according to further possible embodiments.

Detailed Description

[00023] Briefly described, a solution is provided for improving handling of PCI conflicts occurring in a wireless communication network. The solution is based on the observance that the severity of a PCI conflict may be different, depending on the amount of traffic a cell relation pair carries, i.e. impacting more or less UEs in for example a mobility use case. Therefore, in case of a detected PCI conflict, it is determined which of the cells that have the same PCI that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed. This determination is performed based on the number of cell changes performed for UEs to and/or from each of the cells that have the same PCI and on information on number of cell changes performed for UEs to and/or from each of the cells that are neighbors to any of the cells that have the same PCI. Thereafter, PCI is changed for the determined cell to the determined PCI, when it is determined to change PCI. Hereby, PCI conflicts can be solved neatly, negatively affecting as few UEs as possible.

[00024] Figures 1 and 2 describe wireless communication networks 100 in which the present invention may be used. The wireless communication networks each comprises RAN nodes aka base stations 130, 132, 134 (fig. 1) and 136, 138 (fig. 2). Each of the RAN nodes 130, 132, 134, 136, 138 is in, or is adapted for, wireless communication with wireless communication devices aka UEs 140 (fig. 1) and 142 (fig. 2). Each RAN node 130, 132, 134, 136, 138 provides radio access in one or more cells 50, 51 , 52, 53, 54, 55, 56, 57, 58 (fig. 1 ) and 60, 61 , 62, 63, 64, 65 (fig. 2). A cell is a logical set of parameters and resources for supporting wireless communication in an area. A RAN node is the hardware that provides the coverage in the cell.

[00025] The wireless communication network 100 may be any kind of wireless communication network that can provide radio access to wireless communication devices. Example of such wireless communication networks are networks based on Global System for Mobile communication (GSM), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Code Division Multiple Access 2000 (CDMA 2000), Long Term Evolution (LTE), LTE Advanced, Wireless Local Area Networks (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), WiMAX Advanced, as well as fifth generation (5G) wireless communication networks based on technology such as New Radio (NR), and any possible future sixth generation (6G) wireless communication network. [00026] The RAN nodes 130, 132, 134, 136, 138 may be any kind of network node that can provide wireless access to a UE 140, 142 alone or in combination with another RAN node. Examples of RAN nodes are a base station (BS), a radio BS, a base transceiver station, a BS controller, a network controller, a Node B (NB), an evolved Node B (eNB), a gNodeB (gNB), a Multi-cell/multicast Coordination Entity, a relay node, an access point (AP), a radio AP, a remote radio unit (RRU), a remote radio head (RRH) and a multi-standard BS (MSR BS).

[00027] The wireless communication device 140, 142, may be any type of device capable of wirelessly communicating with a RAN node 130, 132, 134, 136, 138 using radio signals. For example, the wireless communication device 140, 142 may be a User Equipment (UE), a machine type UE or a UE capable of machine to machine (M2M) communication, a sensor, a tablet, a mobile terminal, a smart phone, a laptop embedded equipped (LEE), a laptop mounted equipment (LME), a USB dongle, a Customer Premises Equipment (CPE) etc.

[00028] In the examples shown in figs. 1 and 2, each RAN node 130, 132, 134, 136, 138 serves three cells each. However, any of the RAN nodes may be of other types that serves less than or more than three cells. In fig. 1 , RAN node 130 serves cells 54, 55 and 57, RAN node 132 serves cells 52, 53 and 56, and RAN node 134 serves cells 50, 51 and 58. In fig. 2, RAN node 136 serves cells 62, 64 and 65 and RAN node 138 serves cells 60, 61 and 63.

[00029] Fig. 1 illustrates a scenario where cell 52 and cell 50 has the same PCI, here called A. RAN node 130 that serves cell 54, which is a neighbor to both cell 50 and cell 52 then experiences PCI confusion due to its neighboring cells 50 and 52 having the same PCI. For example, when the RAN node 130 receives measurements sent from UE 140 camping in cell 54, measurements that the UE 140 has taken on signals originating from the RAN node 134 handling cell 50 and the RAN node 132 handling cell 52 will have the same PCI A and therefore the RAN node 130 will not know whether those measurements are related to cell 50 or cell 52. [00030] Fig. 2 illustrates a scenario where neighboring cells 60 and 62 have the same PCI A, which means that there is a PCI collision here. A UE 142 residing in cell 62 handled by RAN node 136 and travelling towards cell 60 handled by RAN node 138 will then not know from which RAN node which signals are received, as the signals are accompanied with the same PCI.

[00031] Fig. 3, in conjunction with fig. 1 and/or 2, presents a method for handling such PCI conflicts. Thus, fig. 3 shows a method for handling allocation of PCIs in a wireless communication network 100. The method may be performed by a single network node or by two or more network nodes in communication with each other. The method comprises obtaining 202 information on two or more cells 50, 52; 60, 62 that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI, and obtaining 204, for each of the two or more cells 50, 52; 60, 62, information on PCIs that the cell can choose from. The method further comprises obtaining 206 information on PCI of cells 56, 58; 66, 68 that are neighbors to any of the two or more cells 50, 52; 60,

62, and obtaining 208 information on a number of cell changes for User Equipments, UEs 140; 142, performed to and/or from each of the two or more cells 50, 52; 60, 62 and a number of cell changes for UEs performed to and/or from each of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells, over a defined time period. The method further comprises determining 210 which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, based on the information on the current PCI for the two or more cells 50, 52; 60,

62 and the PCIs of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells 50, 52; 60, 62 and on the information on the number of cell changes performed for UEs to and/or from each of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells; and changing 212 PCI for the determined cell to the determined PCI, when it is determined to change PCI. [00032] Two cells being neighbors means that they are overlapping or adjacent to each other. A UE can travel directly between the two neighboring cells without needing to pass through another cell. Two cells being neighbor^'s neighbors means that there is one cell and possibly not more than one cell in between the two cells. In other words, a UE passing from one of the two cells to the other of the two cells needs to pass through one cell reach the other cell. The PCIs that a cell can choose from may be defined based on restrictions enforced on the network for different reasons, such as operator configurations/restrictions, for example if certain PCIs are used by other operators over country borders or reserved for other cells that need special handling. A “cell change" in e.g. “obtaining information on number of cell changes” signifies that a UE leaves or enters the cell in question. The cell change could be the result of a handover or of a cell re-selection process, for example. The defined time period for which the information on a number of cell changes is obtained may be a time period over which a statistically reliable information of UE cell changes can be achieved, for example 1 day. The determination of which of the two or more cells that should change PCI and to which PCI it should change is determined in order to achieve a lowest possible negative effect on UEs of the wireless communication network. For example, if a cell can change to a PCI that is not used by any of its neighbors or neighbor’s neighbors, the change will not add any negative effect to any of the UEs of the network. According to another example, if the original PCI conflict affects 500 UEs in the two or more cells and a change to another PCI would affect 300 UEs of another cell, the change of PCI is still more advantageous to the network than keeping the PCIs as they are.

[00033] According to an embodiment, the determination 210 of which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, is performed in order to minimize a negative effect of UEs connected to cells 56, 58; 66, 68 in the wireless communication network that are neighbors or neighbors^' neighbors and that will have the same PCI after the change. In other words, based on the number of UE cell changes for cells that have the same PCI before a cell chanae and different alternatives for PCI changes and the number of UE cell changes for cells that have the same PCI after such possible alternative cell changes, it is selected to change PCI for the cell of the at least two cells that have the same PCI and to the alternative of the PCI changes that has the lowest negative effect on UEs connected to cells of the network.

[00034] According to an embodiment, the determination 210 of which of the two or more cells 50, 52; 60, 62 that should change PCI is performed so that the one of the two or more cells 50, 52; 60, 62 that has the least number of cell changes according to the obtained 208 information on number of cell changes over the defined time period changes PCI. This is an implementation which would require little computation and therefore produces a quick result needing low computational power.

[00035] According to another embodiment, the method further comprises obtaining 207 information on PCI of cells 57 that are a neighbor^'s neighbor to any of the two or more cells 50, 52; 60, 62. Further, the obtaining 208 of information on number of cell changes also comprises obtaining information on number of cell changes to and/or from each of the cells 57 that are a neighbor^'s neighbor to any of the two or more cells. Further, the determining 210 of which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change is further based on the PCIs of the cells 57 that are a neighbor^'s neighbor to any of the two or more cells 50, 5260, 62 and the information on the number of cell changes to and/or from each of the cells 57 that are a neighbor^'s neighbor to any of the two or more cells. By also taking into account number of cell changes to and/or from cells that are neighbor^'s neighbors to any of the two or more cells when determining which of the two or more cells that should change PCI and to which PCI the determined cell should change, can result in an even better cell planning, and minimizing the negative impact on UEs in the network.

[00036] According to another embodiment, the determination 210 of which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change or whether no PCI change is to be performed comprises associating a cost for each of the PCIs that each of the two or more cells 50, 52; 60, 62 can choose from, based on the information on the current PCI for the two or more cells and the PCIs of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells 50, 52;

60, 62 and on the information on the number of cell changes performed for UEs to and/or from each of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells, the cost for a PCI of each of the associated PCIs being higher the more UEs that are affected negatively by choosing the PCI, and selecting the PCI that has the lowest cost and its corresponding cell of the two or more cells 50, 52; 60, 62.

[00037] According to yet another embodiment, the determination 210 of which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change or whether no PCI change is to be performed comprises: Associating a cost for each of the two or more cells 50, 52; 60, 62 using the same PCI based on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells 50, 52; 60, 62. The determination 210 further comprises associating a cost for individual of the PCIs that each of the two or more cells 50, 52; 60, 62 can choose from based on the number of cell changes for UEs performed to and/or from each of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells. This involves the cost where any of the two or more cells 50, 52; 60, 62 would select the same PCI as any of the cells 56, 58; 66, 68 that are neighbors or neighbor’s neighbors to the one or more cells. The method then proceeds by selecting the PCI that has the lowest cost and its corresponding cell of the two or more cells 50, 52; 60, 62 to use hereinafter.

[00038] In other words, a cost is associated with each possible PCI in terms of which neighboring cell that will use the same PCI as any of the two or more cells, where the cost is determined based on number of cell changes to and/or from each of the cells that will have the same PCI, and the PCI with the lowest cost for the network is selected. This also involves associating a cost with the current PCI association. If the current PCI association already has the lowest cost, the PCI association may be kept as it is, that is, the same PCI association as is already in use may be selected.

[00039] According to an alternative of the above embodiment, a PCI of the PCIs that any of the two or more cells 50, 52; 60, 62 can choose from that is not used by any of the neighbors or neighbors’ neighbor to that cell is associated a lowest possible cost. In other words, when there is a PCI that is vacant to one of the at least two cells, that means this PCI is not used by any of the neighbors or neighbors’ neighbor of that cell, this PCI will get the lowest possible cost, possibly zero, and therefore this PCI will be selected.

[00040] According to another embodiment, in the associating of a cost for each of the PCIs that each of the two or more cells 50, 52; 60, 62 can choose from, same PCI for two neighboring cells has a higher cost than same PCI for two cells that are neighbors^' neighbors, the cost preferably being 3 times higher. This means that a cell change for a UE to/from a cell that would trigger PCI collision (i.e. neighboring cells having same PCI) has a higher cost than a cell change for a UE to/from a cell that would trigger PCI confusion (i.e. neighbor^'s neighbor having same PCI). For example, a cell change in a cell triggering PCI collision has value 3 and a cell change in a cell triggering PCI confusion has value 1.

[00041] According to an embodiment, the obtaining 202 of information on two or more cells 50, 52; 60, 62 that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI, also comprises obtaining information on two or more cells that are neighbors and that have the same PCI modulo 6 or modulo 30, and information on their current PCI. Hereby we also take account for PCI collisions based on the same PCI modulo 6 and the same PCI modulo 30.

[00042] According to another embodiment, the network entity or entities that is responsible for determining which RAN node that needs to change PCI on one or more of its cells should gather data, including information on available PCIs to choose from per cell, from all RAN nodes that have cells that are involved in the PCI conflict. This is done to make the best decision on what node that needs to change PCI of one or more of its managed cells.

[00043] Normally a cell can choose a PCI. The cell may be able to choose PCI from an entire PCI space. In this case, the information on available PCIs for this cell would be the entire PCI space. However, the information on available PCIs can also be restricted by operator configuration or country border agreements. In the PCI information, PCIs of the PCI space that are not possible to assign since they in their turn would create a new conflict or violate for example PCI mod 6 can be marked as available but not fully free.

[00044] Note also that the severity of selecting a PCI that is used or partly used, (i.e. same PCI modulo 6 or modulo 30) by a neighbor cell may be different, since a cell relation pair might carry less or more traffic, i.e. impacting more or less UEs in for example a mobility use case. Also, different types of PCI confusions have different severity. For example, the severity of a PCI collision is high as a PCI collision always results in a dropped UE connection for UEs crossing over from one cell to another when the two cells have the same PCI. Further, the total network impact may vary as the number of UEs crossing a cell border vary between cell borders. Further, an impact of a drop causes not only a dropped call but also a cost for setting up a new UE connection or restoring connections on or from the other side, generating load in the network as well as reduced end user experience. A PCI confusion on the other hand can most of the time be mitigated to reduce the risk of a UE drop with more or less impact on throughput for the end user, but is most likely not visible at all from the UE. It will also slightly increase the load on the network to mitigate. In total, a lot less load and additional signaling compared to a drop. Here this impact may also be more or less depending on how many UEs crossing the border between the two cells. As a third example, PCI Modulo 6 values or modulo 30 values create Channel State Information Reference Signal (CSI-RS) collision avoidance functionality working as expected it also impacts functionality based on Tracking Reference Symbol (TRS). To make the feature Physical Uplink Control Channel (PUCCH) Group Hopping working as expected, PCI Modulo 30 values should be set differently in adjacent cells. To use the same PCI modulo 6 or modulo30 in adjacent cells does not cause drops but may impact the throughput on UEs close to the cell border between those adjacent cells.

[00045] In one embodiment, every PCI in the available PCI list is associated with a cost for selection of that PCI. This cost considers the impact on the traffic according to the impact on UE as well as the load impact on the network based on the information above. This can be used for selecting a PCI in the situation the PCI conflict cannot be resolved completely, or even when the PCI conflict can be resolved such a cost can be used as it implies a very low cost of changing to a PCI that has no PCI conflict.

[00046] In yet another embodiment, when involved in a PCI confusion the node that initiate the PCI change is normally not one of the nodes that needs to change PCI of one of its cells. It is more probably either the node that suffers from the PCI confusion, or a centralized node. The node that initiates the change compares the list of PCIs given by the other nodes and decides what node should change PCI.

[00047] According to an embodiment, the method of handling PCI conflicts comprises the following: Collection of available PCIs from RAN nodes which cells are involved in the PCI conflict; associating available PCIs with a cost and comparing the PCI that is currently used from other possible PCIs in terms of cost for the network and the UEs. In this way different possible PCI alternatives can be compared to each other and the PCI with least impact on the actual network performance, that is the PCI with the lowest cost, can be chosen as the PCI to which one of the cells experiencing a PCI conflict should change. In a distributed system, the collection of available PCIs and the cost/weight are sent between two nodes using signals on a standardized interface, like F1, X2, Xn etc. This may be a two-step approach. In the first step, the at least two nodes that could change PCI for its respective cell to resolve the conflict can look at its respective free PCI space and also the cost of assigning any of the free PCIs to its respective cell. In the second step, the list of PCIs and their respective costs are compared between the at least two nodes to determine which node’s cell should change PCI.

[00048] According to one embodiment, every PCI in a list of available PCIs is associated with a cost aka weight for selection of that PCI. This can be used for selecting a PCI in the situation the PCI conflict cannot be solved completely. For example, if no conflict free PCI can be selected without violating any considerations it could still be better to select such a PCI to resolve a more severe conflict. It can also be used to compare one conflict against another one. The cost for selection of a PCI is based on the amount of cell changes that has been performed by UEs over a certain time period to/from cells that have the same PCI when the certain PCI in the list of available PCI will be selected as new PCI for one of the cells that experience a PCI conflict. A PCI conflict has a negative effect on UEs in cells experiencing such a conflict, especially for UEs changing cells from/to a cell that experiences a PCI conflict. The higher number of UEs that changes cells from/to a cell experiencing a PCI conflict the higher the negative effect on the network, and therefore the higher cost for having that cell involved in a PCI conflict, As an example, there is a much lower cost in terms of negative network effect with a PCI conflict for a cell relation that carries 1 handover (HO) every day compared to one that carries 100 or 1000 or even 10000 HOs every day. Hence, a PCI will carry more cost the more HOs it might impact in terms of that a cell uses the same PCI as one of its neighbors having X number of HO on that relation, then the cost depends on X. Note also that the cost for having the same PCI can be combined from several cells. So, the cost of all neighbors or possibly even neighbor’s neighbors needs to be considered.

[00049] This embodiment is illustrated by an example of different costs, with reference to fig. 4. In the exemplary wireless communication network of fig. 4, there are 7 cells, called X1-X7. Cell X3 has the same PCI C as its neighbor cells X2, X4 and X6. Consequently, cell X3, which is neighboring to all those cells and therefore contributes to a severe PCI conflict, needs to change PCI. In total there are three PCIs to choose from, PCI A, B and C. PCI A is used by cell X7, which is a neighbor to cell X6 and a neighbor’s neighbor to cell X3 via cell X6. PCI A is also used by cell X5, which is a neighbor to cell X4 and a neighbor’s neighbor to cell X3 via cell X4. PCI B is used by cell X1 , which is a neighbor to cell X2 and a neighbor’s neighbor to cell X3 via cell X2. The arrows between the cells and the numbers between the arrows symbolizes number of cell changes such as HOs per day from one cell to the other in the direction of the arrows. So, if cell X3 would change to PCI A it would mean that cell X3 and its neighbor’s neighbors X5 and X7 would get the same PCI and cells X4 and X6 would experience a PCI confusion. Such a PCI confusion would have a negative effect on UEs changing from cell X6 to cell X7 and cell X3, and from cell X4 to cell X3 and cell X5. With the example numbers of fig. 4, there will be 700 + 700 + 700 + 700 + = 2800 UEs negatively affected by a PCI confusion per day, statistically. In comparison, if cell X3 would change to PCI B, cell X3 will have the same PCI as cell X1 only. This will negatively affect UEs changing from cell X2 to cells X1 and X3, which are 500 + 1000 = 1500 UEs negatively affected by a PCI confusion per day. As a result, the method will determine that cell X3 should change to PCI B in order to get the lowest negative effect on UEs in the network. As a comparison, if PCI C would be kept it would severely impact all UEs changing between cell X3 and cells X6, X2 orX4, that is 4* 700 + 2*500 = 3800 UEs. Further, a PCI collision is more severe to the network than a PCI confusion.

[00050] Another example is illustrated in fig. 5. In addition to the scenario of fig. 4, here there is also another neighbor cell to cell X3 called cell X8, having PCI B. Then cell X3 will change to PCI A as this will be the lowest cost alternative this time: Cell X3 changing to PCI A impacts 4x700 UEs per day, as cells X4 and X6 will experience a PCI confusion. Cell X3 changing to PCI B would impact 1000+500 +2x100 UEs, where 2x100 will be dropped calls and not HO-issues and dropped calls are more costly. In other words, Cell X2 will experience a PCI confusion due to cell X1 and X3 having the same PCI, and there will be a PCI collision between X3 and X8, due to the neighboring cells having the same PCI. Further, keeping PCI C for cell X3 impacts 4*700 + 2*500 = 3800 UEs as a PCI collision between X2, X3, X4 and X6, i.e. resulting in UE drops of those UEs traveling between those cells. Consequently, cell X3 will change to PCI A as this is the lowest cost alternative. [00051] Yet another example, not shown, is where selecting PCI A for one cell is associated to PCI modulo 6 considerations with a neighbor cell on the same antenna tower where the cell border is quite large. But selecting PCI B might cause PCI confusions with various cost and/or PCI collisions. Here PCI A might still be less costly compared to PCI B.

[00052] Yet another example is shown in fig. 6. Here there are three RAN nodes A, B and C each providing radio coverage to three separate sector cells, wherein cell a has PCI 7 and belongs Node A, cell b has PCI 7 and belongs to Node B and cell c has PCI 9 and belongs to Node C. Consequently, cell c experiences a PCI confusion as cell a and cell b has the same PCI. In one example, node A might have a possible PCI X for cell a to choose from, which results in no PCI collision but a PCI confusion impacting say 5 UEs per day (relating to the smallest cost from node A) while Node B might have a possible PCI for cell b to choose from, which causes a PCI modulo consequence impacting all UEs in the area. In this case the conflict of impacting 5 UEs could come with a smaller cost and be mitigated via other procedures compared to a comparatively smaller modulo consequence per UE but a totally rather large throughput degradation for the network.

[00053] Further, a PCI confusion can be handled by performing Cell Global Identity (CGI) measurements on any UE (delaying any action) that suffer from poor HO statistics /re-establishment. However, performing CGI measurements takes time and therefore comes with a delay of the service. In addition. CGI measurements may not be possible to perform with some types of services or some types of UEs. The usage of a cell involved in a conflict comes with a cost both on the UE itself in terms of throughput degradation, drop calls etc. but also on the system. How often a certain relation is used is therefore an important aspect as it is better to solve a PCI conflict impacting thousands of UEs every day than a PCI conflict impacting only a few UEs. one that have significantly less impact. [00054] Going back to fig. 6, it can be seen that both Node A and Node B need to become aware of that they are involved in a PCI confusion, as they both have a Neighbor c that in terms have another Neighbor with the same PCI as themselves. Node A and Node B can be informed of the PCI confusion via communication over the Xn interface in NR and the X2 interface in LTE as already defined in 3GPP. Xn and X2 interfaces are interfaces between RAN nodes. If one of Node A or Node B change PCI for its cell a or b, respectively, to resolve the PCI conflict, the change of PCI is communicated over e.g. the same interface and other nodes, including C, gets information that the PCI of one of the cells has changed and can conclude that there no longer exists a PCI confusion. Here each of their cells needs to find out available PCIs to choose from and select one. In another embodiment, each RAN node collects its available PCIs in a list and the cost of changing those and passes that information to a central network node or any of the nodes A, B and C that can compare the lists and determine what cell that needs to change PCI.

[00055] But note that given the improvement and possibilities provided by for example different Machine learning techniques based on data in node C, it might be so that node C does not really suffer from the confusion and can instead by using side information determine if a UE is in coverage area of a cell managed by node B or node A with none or only a small effort, hence the PCI confusion might not be needed to be resolved from node C perspective. This information is in Node C, but can also be passed along to the central node that initiate the change, to take such information into consideration when determining the cost for different PCIs.

[00056] According to an embodiment, in order to make a better selection of PCIs that the RAN nodes can select from, the PCIs used by each Neighbors Neighbor per Neighbor is also communicated between RAN nodes as an addition on existing X2 and XN messages. Together with the PCIs used, the cost of each PCI may also be communicated. Such information may be sent for example in NR whenever NR Neighbor Information Information Element (IE) is sent as an optional information element. The NR Neighbor Information IA may be included in e.g. Xn Setup Request, Xn Setup Response or Next Generation (NG) RAN Node Configuration update messages sent between the involved RAN nodes.

[00057] The IE Neighbor Information NR is mentioned in 3GPP TS 38.423 v16, chapter 9.2.2.13 for Xn Setup Request as well as for Xn Setup Response and for NG RAN Node Configuration update messages. All those messages contain Neighbor cell information NR where the new IE can be added. The new IE may be called “Relation Importance” and may contain an indication of importance and cost related to the problem for the source cell if another neighbor cell would assign the same PCI as the corresponding neighbor. The “Relation Importance” may be expressed for example as an integer between 0 and MAX value, where 0 means no PCI conflict and MAX means maximum PCI conflict.

[00058] In a centralized network, this information, i.e. importance and cost, can be sent to a centralized node, for example an Operation and Maintenance (O&M) system, as illustrated in fig. 7, where it is exemplified for an NR network. In such an embodiment, each RAN node (gNB in NR) 302, 304 determine 1.1 each neighbor importance, such as cost. The determined neighbor importance is sent 1.2 to the O&M system 306 that distributes 1.3 the neighbor importance out to the respective gNB 302, 304 that use 1.4 the received neighbor importance information when selecting PCI. Alternatively, the neighbor importance for the nodes is determined at the centralized node. A Non-Real-time Radio Access Network Intelligent Controller (RIC) is a possible part of an O&M implementation.

[00059] Another embodiment is shown in fig. 8. This embodiment is shown for an NR network but can applicable to other types of networks. A first RAN node gNB C, which may for example be a RAN node that experiences PCI confusion from its two neighbors gNB A and gNB B, that is, gNB A and gNB B have cells that have the same PCI, sends 2.1 a request for available PCIs to gNB A and gNB B (Available PCIReq). In response, gNB A and gNB B each collects 2.2 data of its neighbors and its neighbor’s neighbors, the data comprising information of PCI that each neighbor and neighbor’s neighbor uses and the cost for changing to any of the available PCIs. This obtained data is sent 2.3 back (Available PCIResp) to the gNB C, by gNB A and gNB B. Based on the received data, i.e. available PCIs and costs for each PCI, gNB C selects 2.4 which of the cells of gNB A and gNB B that should change PCI and to which PCI the selected cell should change. The selection is sent 2.5 (PCIChange Required) at least to the RAN node, which cell is to change PCI, here gNB B, the selection comprising the PCI that the cell of gNB B should change to.

[00060] Here as mentioned earlier, the available PCIs may be all allowed PCIs each cell can choose from and is created and defined by the operator considering country borders etc., but it may also be the entire PCI space.

n another embodiment every PCI in the available PCI list is marked, see “PCI availability” in the table below. This information could be used by a receiving node when selecting which PCI to select when changing, since they in turn does not create a new conflict or violate for example PCI mod 6.

In yet another embodiment the information is expanded by adding a weight/cost for every entry in the PCI in the available PCI list. This could for example be done like in the following table, see the posts “PCI Available” and “PCI cost”.

[00061] According to one embodiment, the present invention may be realized as a centralized solution. In other words, one or more network entities configured for handling allocation of PCIs according to above and below embodiments may be situated in a centralized network environment. The centralized environment may according to an embodiment of an NG-RAN shown in fig. 9 comprise a number of radio control function (RCF) 402, 404, which may be situated in a centralized part of a gNB or an ng-eNB, i.e. an eNB connected to 5th generation core network. The RCF may be located physically in a distributed entity close to the radio nodes (RN) 406, 408 or in a data center in a central location or on suitable hardware somewhere in between. The RCF is also known as a Central Unit Control Plane function (CU-CP) and the RN is also known as Distributed Unit (DU).

[00062] According to another embodiment shown in fig. 10, the present invention may be implemented in an Open Radio Access Network (O-RAN) architecture. The described functions such as the functions for determining, obtaining, transmitting and using cell properties and PCIs can partly or completely be located in a Non-real time Radio Access Network Intelligent Controller (Non-RT RIC) 502 of the O-RAN, in a Near-real time Radio Access Network Intelligent Controller (Near RT RIC) 504, in an Open Central Unit (0- CU) 506 or in an Open Distributed Unit (O-DU) 508. If the Xn or X2 interfaces are used for communication with other nodes and part of the function is not implemented in the O-CU, the interfaces in between the mentioned parts have to be used to convey information. The O-RAN architecture further comprises an Open Radio Unit (O-RU) 510. The Non-RT Ric may be situated in a Service Management and Orchestration (SMO) 512.

[00063] Fig. 10, in conjunction with fig. 1 or 2, shows one or more network entities 600 configured for handling allocation of PCIs in a wireless communication network 100, the one or more network entities 600 being configured to operate in a wireless communication network 100. The one or more network entities 600 comprises processing circuitry 603 and a memory 604. The memory 604 contains instructions executable by said processing circuitry, whereby the one or more network entities 600 is operative for obtaining information on two or more cells 50, 52; 60, 62 that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI, and obtaining, for each of the two or more cells 50, 52; 60, 62, information on PCIs that the cell can choose from. The one or more network entities is further operative for obtaining information on PCI of cells 56, 58; 66, 68 that are neighbors to any of the two or more cells 50, 52; 60, 62, and obtaining information on a number of cell changes for UEs 140, 142 performed to and/or from each of the two or more cells 50, 52;

60, 62, and a number of cell changes for UEs performed to and/or from each of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells, over a defined time period. The one or more network entities is further operative for determining which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, based on the information on the current PCI for the two or more cells 50, 52; 60, 62 and the PCIs of the cells 56, 58; 66, 68 that are neighbors to anv of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells 50, 52;

60, 62, and on the information on the number of cell changes performed for UEs to and/or from each of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells, and changing PCI for the determined cell to the determined PCI, when it is determined to change PCI.

[00064] The one or more network entities 600 may be realized at or in one of the RAN nodes that handles one of the involved cells. Alternatively, the one or more network entities 600 may be arranged at or in any other network node of the wireless communication network 100. Alternatively, the one or more network entities 600 may be realized as a group of network nodes, wherein functionality of the one or more network entities 600 is spread out over the group of network nodes. The group of network nodes may be different physical, or virtual, nodes of the network. This alternative realization may be called a cloud-solution.

[00065] According to an embodiment, the one or more network entities 600 is operative for performing the determination of which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, in order to minimize a negative effect of UEs connected to cells 56, 58; 66, 68 in the wireless communication network that are neighbors or neighbors^' neighbors and that will have the same PCI after the change.

[00066] According to another embodiment, the one or more network entities 600 is operative for performing the determination of which of the two or more cells 50, 52; 60, 62 that should change PCI so that the one of the two or more cells 50, 52; 60, 62 that has the least number of cell changes according to the obtained information on number of cell changes over the defined time period changes PCI.

[00067] According to another embodiment, the one or more network entities 600 is further operative for obtaining information on PCI of cells 57 that are a neighbor^'s neighbor to any of the two or more cells 50, 52; 60, 62. Further, the one or more entities 600 is operative for the obtaining of information on number of cell changes by further obtaining information on number of cell changes to and/or from each of the cells 57 that are a neighbor^'s neighbor to any of the two or more cells. Also, the one or more entities 600 is operative for the determining of which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change further based on the PCIs of the cells 57 that are a neighbor^'s neighbor to any of the two or more cells and the information on the number of cell changes to and/or from each of the cells 57 that are a neighbor^'s neighbor to any of the two or more cells.

[00068] According to another embodiment, the one or more network entities 600 is operative for determining which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change or whether no PCI change is to be performed by associating a cost for each of the PCIs that each of the two or more cells 50, 52; 60, 62 can choose from. The cost is associated based on the information on the current PCI for the two or more cells and the PCIs of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells 50, 52; 60, 62 and on the information on the number of cell changes performed for UEs to and/or from each of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells. Also, the cost for a PCI of each of the associated PCIs is higher the more UEs that are affected negatively by choosing the PCI. The one or more network entities is further operative for selecting the PCI that has the lowest cost and its corresponding cell of the two or more cells 50, 52; 60, 62.

[00069] According to yet another embodiment, the one or more network entities 600 is operative for the determination of which of the two or more cells 50, 52; 60, 62 that should change PCI and to which PCI the determined cell should change or whether no PCI change is to be performed by the following: Associating a cost for each of the two or more cells 50, 52; 60, 62 using the same PCI based on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells 50, 52; 60, 62; Associating a cost for individual of the PCIs that each of the two or more cells 50, 52; 60, 62 can choose from based on the number of cell changes for UEs performed to and/or from each of the cells 56, 58; 66, 68 that are neighbors to any of the two or more cells where any of the two or more cells 50, 52; 60, 62 would select the same PCI as any of the cells 56, 58; 66, 68 that are neighbors or neighbor’s neighbors to the one or more cells; and selecting the PCI that has the lowest cost and its corresponding cell of the two or more cells 50, 52; 60, 62 to use hereinafter.

[00070] According to yet another embodiment, a PCI of the PCIs that any of the two or more cells 50, 52; 60, 62 can choose from that is not used by any of the neighbors or neighbors’ neighbor to that cell is associated a lowest possible cost.

[00071] According to still another embodiment, the one or more network entities 600 is operative for, in the associating of a cost for each of the PCIs that each of the two or more cells 50, 52; 60, 62 can choose from, giving same PCI for two neighboring cells a higher cost than same PCI for two cells that are neighbors^' neighbors, the cost preferably being 3 times higher.

[00072] According to still another embodiment, the one or more network entities 600 is operative for the obtaining of information on two or more cells 50, 52; 60, 62 that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI, also by obtaining information on two or more cells that are neighbors and that have the same PCI modulo 6 or modulo 30, and information on their current PCI.

[00073] According to other embodiments, the one or more network entities 600 may further comprise a communication unit 602, which may be considered to comprise conventional means for wireless communication with the wireless device 140, such as a transceiver for wireless transmission and reception of signals in the communication network, in case the one or more network 600 entities is realized in or at a RAN node. The communication unit 602 may also comprise conventional means for communication with other network nodes of the wireless communication network 100. The instructions executable by said processing circuitry 603 may be arranged as a computer program 605 stored e.g. in said memory 604. The processing circuitry 603 and the memory 604 may be arranged in a sub arrangement 601. The sub-arrangement 601 may be a micro-processor and adequate software and storage therefore, a Programmable Logic Device, PLD, or other electronic component(s)/processing circuit(s) configured to perform the methods mentioned above. The processing circuitry 603 may comprise one or more programmable processor, application-specific integrated circuits, field programmable gate arrays or combinations of these adapted to execute instructions.

[00074] The computer program 605 may be arranged such that when its instructions are run in the processing circuitry, they cause the one or more network entities 600 to perform the steps described in any of the described embodiments of the one or more network entities 600 and its method. The computer program 605 may be carried by a computer program product connectable to the processing circuitry 603. The computer program product may be the memory 604, or at least arranged in the memory. The memory 604 may be realized as for example a RAM (Random-access memory), ROM (Read-Only Memory) or an EEPROM (Electrical Erasable Programmable ROM). In some embodiments, a carrier may contain the computer program 605. The carrier may be one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or computer readable storage medium. The computer- readable storage medium may be e.g. a CD, DVD or flash memory, from which the program could be downloaded into the memory 604. Alternatively, the computer program may be stored on a server or any other entity to which the one or more network entities 600 has access via the communication unit 602. The computer program 605 may then be downloaded from the server into the memory 604.

[00075] Although the description above contains a plurality of specificities, these should not be construed as limiting the scope of the concept described herein but as merely providing illustrations of some exemplifying embodiments of the described concept. It will be appreciated that the scope of the presently described concept fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the presently described concept is accordingly not to be limited. Reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more." All structural and functional equivalents to the elements of the above- described embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed hereby. Moreover, it is not necessary for an apparatus or method to address each and every problem sought to be solved by the presently described concept, for it to be encompassed hereby. In the exemplary figures, a broken line generally signifies that the feature within the broken line is optional.

Claims

1. A method for handling allocation of Physical Cell Identities, PCI, in a wireless communication network (100), the method comprising: obtaining (202) information on two or more cells (50, 52; 60, 62) that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI; obtaining (204), for each of the two or more cells (50, 52; 60, 62), information on PCIs that the cell can choose from; obtaining (206) information on PCI of cells (56, 58; 66, 68) that are neighbors to any of the two or more cells (50, 52; 60, 62); obtaining (208) information on a number of cell changes for User Equipments, UEs (140, 142), performed to and/or from each of the two or more cells (50, 52; 60, 62) and a number of cell changes for UEs performed to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells, over a defined time period; determining (210) which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, based on the information on the current PCI for the two or more cells (50, 52; 60, 62) and the PCIs of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells (50, 52; 60, 62) and on the information on the number of cell changes performed for UEs to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells; and changing (212) PCI for the determined cell to the determined PCI, when it is determined to change PCI.

2. Method according to claim 1 , wherein the determination (210) of which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, is performed in order to minimize a negative effect of UEs connected to cells (56, 58; 66, 68) in the wireless communication network that are neighbors or neighbors^' neighbors and that will have the same PCI after the change.

3. Method according to claim 1 or 2, wherein the determination (210) of which of the two or more cells (50, 52; 60, 62) that should change PCI is performed so that the one of the two or more cells (50, 52; 60, 62) that has the least number of cell changes according to the obtained (208) information on number of cell changes over the defined time period changes PCI.

4. Method according to any of the preceding claims, further comprising: obtaining (207) information on PCI of cells (57) that are a neighbor^'s neighbor to any of the two or more cells (50, 52; 60, 62), and wherein the obtaining (208) of information on number of cell changes further comprises obtaining information on number of cell changes to and/or from each of the cells (57) that are a neighbor^'s neighbor to any of the two or more cells, and wherein the determining (210) of which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change is further based on the PCIs of the cells (57) that are a neighbor^'s neighbor to any of the two or more cells and the information on the number of cell changes to and/or from each of the cells (57) that are a neighbor^'s neighbor to any of the two or more cells.

5. Method according to any of the preceding claims, wherein the determination (210) of which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change or whether no PCI change is to be performed comprises: associating a cost for each of the PCIs that each of the two or more cells (50, 52; 60, 62) can choose from, based on the information on the current PCI for the two or more cells and the PCIs of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells (50, 52; 60, 62) and on the information on the number of cell changes performed for UEs to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells, the cost for a PCI of each of the associated PCIs being higher the more UEs that are affected negatively by choosing the PCI, and selecting the PCI that has the lowest cost and its corresponding cell of the two or more cells (50, 52; 60, 62).

6. Method according to any of the preceding claims, wherein the determination (210) of which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change or whether no PCI change is to be performed comprises: associating a cost for each of the two or more cells (50, 52; 60, 62) using the same PCI based on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells (50, 52; 60, 62), and associating a cost for individual of the PCIs that each of the two or more cells (50, 52; 60, 62) can choose from based on the number of cell changes for UEs performed to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells where any of the two or more cells (50, 52; 60, 62) would select the same PCI as any of the cells (56, 58; 66, 68) that are neighbors or neighbor’s neighbors to the one or more cells, and selecting the PCI that has the lowest cost and its corresponding cell of the two or more cells (50, 52; 60, 62) to use hereinafter.

7. Method according to claim 6, wherein a PCI of the PCIs that any of the two or more cells (50, 52; 60, 62) can choose from that is not used by any of the neighbors or neighbors’ neighbor to that cell is associated a lowest possible cost.

8. Method according to any of claims 5-7, wherein in the associating of a cost for each of the PCIs that each of the two or more cells (50, 52; 60, 62) can choose from, same PCI for two neighboring cells has a higher cost than same PCI for two cells that are neighbors^' neighbors, the cost preferably being 3 times higher.

9. Method according to any of the preceding claims, wherein the obtaining (202) of information on two or more cells (50, 52; 60, 62) that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI, also comprises obtaining information on two or more cells that are neighbors and that have the same PCI modulo 6 or modulo 30, and information on their current PCI.

10. One or more network entities (600) configured for handling allocation of Physical Cell Identities, PCI, in a wireless communication network (100), the one or more network entities (600) being configured to operate in a wireless communication network (100), the one or more network entities (600) comprising processing circuitry (603) and a memory (604), said memory containing instructions executable by said processing circuitry, whereby the one or more network entities (600) is operative for: obtaining information on two or more cells (50, 52; 60, 62) that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI; obtaining, for each of the two or more cells (50, 52; 60, 62), information on PCIs that the cell can choose from; obtaining information on PCI of cells (56, 58; 66, 68) that are neighbors to any of the two or more cells (50, 52; 60, 62); obtaining information on a number of cell changes for UEs (140; 142), performed to and/or from each of the two or more cells (50, 52; 60, 62) and a number of cell changes for UEs performed to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells, over a defined time period; determining which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, based on the information on the current PCI for the two or more cells (50, 52; 60, 62) and the PCIs of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells (50, 52; 60, 62) and on the information on the number of cell changes performed for UEs to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells; and changing PCI for the determined cell to the determined PCI, when it is determined to change PCI.

11. One or more entities (600) according to claim 10, operative for performing the determination of which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, in order to minimize a negative effect of UEs connected to cells (56, 58; 66, 68) in the wireless communication network that are neighbors or neighbors^' neighbors and that will have the same PCI after the change.

12. One or more entities (600) according to claim 10 or 11 , operative for performing the determination of which of the two or more cells (50, 52; 60, 62) that should change PCI so that the one of the two or more cells (50, 52; 60, 62) that has the least number of cell changes according to the obtained information on number of cell changes over the defined time period changes PCI.

13. One or more entities (600) according to any of claims 10-12, further being operative for: obtaining information on PCI of cells (57) that are a neighbor^'s neighbor to any of the two or more cells (50, 52; 60, 62), and wherein the one or more entities (600) is operative for the obtaining of information on number of cell changes by further obtaining information on number of cell changes to and/or from each of the cells (57) that are a neighbor^'s neighbor to any of the two or more cells, and wherein the one or more entities (600) is operative for the determining of which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change further based on the PCIs of the cells (57) that are a neighbor^'s neighbor to any of the two or more cells and the information on the number of cell changes to and/or from each of the cells (57) that are a neighbor^'s neighbor to any of the two or more cells.

14. One or more entities (600) according to any of claims 10-13, operative for the determination of which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change or whether no PCI change is to be performed by: associating a cost for each of the PCIs that each of the two or more cells (50, 52; 60, 62) can choose from, based on the information on the current PCI for the two or more cells and the PCIs of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells (50, 52; 60, 62) and on the information on the number of cell changes performed for UEs to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells, the cost for a PCI of each of the associated PCIs being higher the more UEs that are affected negatively by choosing the PCI, and selecting the PCI that has the lowest cost and its corresponding cell of the two or more cells (50, 52; 60, 62).

15. One or more entities (600) according to any of claims 10-14, operative for the determination of which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change or whether no PCI change is to be performed by: associating a cost for each of the two or more cells (50, 52; 60, 62) using the same PCI based on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells (50, 52; 60, 62), and associating a cost for individual of the PCIs that each of the two or more cells (50, 52; 60, 62) can choose from based on the number of cell changes for UEs performed to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells where any of the two or more cells (50, 52; 60, 62) would select the same PCI as any of the cells (56, 58; 66, 68) that are neighbors or neighbor’s neighbors to the one or more cells, and selecting the PCI that has the lowest cost and its corresponding cell of the two or more cells (50, 52; 60, 62) to use hereinafter.

16. One or more entities (600) according to claim 15, wherein a PCI of the PCIs that any of the two or more cells (50, 52; 60, 62) can choose from that is not used by any of the neighbors or neighbors’ neighbor to that cell is associated a lowest possible cost.

17. One or more entities (600) according to any of claims 14-16, wherein in the associating of a cost for each of the PCIs that each of the two or more cells (50, 52; 60, 62) can choose from, same PCI for two neighboring cells has a higher cost than same PCI for two cells that are neighbors^' neighbors, the cost preferably being 3 times higher.

18. One or more entities (600) according to any of claims 10-17, operative for the obtaining of information on two or more cells (50, 52; 60, 62) that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI, also by obtaining information on two or more cells that are neighbors and that have the same PCI modulo 6 or modulo 30, and information on their current PCI.

19. A computer program (605) comprising instructions, which, when executed by at least one processing circuitry of one or more network entities (600) of a wireless communication network, configured for handling allocation of Physical Cell Identities, PCI, causes the one or more network entities (600) to perform the following steps: obtaining information on two or more cells (50, 52; 60, 62) that are neighbors or a neighbor^'s neighbors, the two or more cells having the same PCI, and information on their current PCI; obtaining, for each of the two or more cells (50, 52; 60, 62), information on PCIs that the cell can choose from; obtaining information on PCI of cells (56, 58; 66, 68) that are neighbors to any of the two or more cells (50, 52; 60, 62); obtaining information on a number of cell changes for UEs (140; 142), performed to and/or from each of the two or more cells (50, 52; 60, 62) and a number of cell changes for UEs performed to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells, over a defined time period; determining which of the two or more cells (50, 52; 60, 62) that should change PCI and to which PCI the determined cell should change, or whether no PCI change is to be performed, based on the information on the current PCI for the two or more cells (50, 52; 60, 62) and the PCIs of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells as well as on the information on the number of cell changes performed for UEs to and/or from each of the two or more cells (50, 52; 60, 62) and on the information on the number of cell changes performed for UEs to and/or from each of the cells (56, 58; 66, 68) that are neighbors to any of the two or more cells; and changing PCI for the determined cell to the determined PCI, when it is determined to change PCI.

20. A carrier containing the computer program (605) according to claim 19, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, an electric signal or a computer readable storage medium.