WO2014175794A1

WO2014175794A1 - Methods and apparatus for determining a neighbor cell from ue measurements

Info

Publication number: WO2014175794A1
Application number: PCT/SE2013/050455
Authority: WO
Inventors: Johan Magnusson; Peter Lundh; Thomas ÖSTMAN
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2013-04-25
Filing date: 2013-04-25
Publication date: 2014-10-30

Abstract

A Radio Network Controller (RNC) receives one or more UE measurement reports. A report includes for each of multiple measured cells a cell identifier of the measured cell and a UE timing offset between the measured cell's SFN count and a connection frame number (CFN) count or the like in the serving cell. The RNC determines a corresponding RBS phase difference for each of the multiple measured cells based on a difference between the RFN count and a BFN count corresponding to each of the measured cells. Measured cells having the same cell identifier are identified, and the RNC determines, for each of the identified measured cells, a determined difference based on its RBS phase difference to a RBS phase difference of the serving cell, its cell timing difference to a cell timing difference of the serving cell, and a connection frame number difference between the UE timing offset, and the identified measured cell's connection frame number. The RNC selects one or more of the identified measured cells based on the determined difference for each of the identified measured cells.

Description

METHODS AND APPARATUS FOR DETERMINING A NEIGHBOR CELL

FROM UE MEASUREMENTS

TECHNICAL FIELD

[0001] The technology relates to cellular radio communications, and in particular, to determining a neighbor cell from UE measurement reports.

BACKGROUND

[0002] The technology in this application is described in an example context of a

Universal Terrestrial Radio Access Network (UTRAN) / Wideband Code Division Multiple Access (WCDMA) system. In a UTRAN type of system, the air interface, referred to as the Uu interface, is between User Equipments (UEs) (sometimes referred to as mobile stations or other terms) and radio base stations (RBSs or BSs) called NodeBs. Each NodeB serves one or more cell coverage areas. The Iub interface is between NodeBs and a Radio Network

Controller (RNC). The Iur interface is between RNCs. An RNC also communicates with one or more core network nodes which are connected to one or more other networks, e.g. the Internet, public and private telephone networks, etc.

[0003] WCDMA-based UTRAN is standardized by a standards body referred to as

3 GPP, (see 3 GPP technical specifications (TS) 25.133, 25.331, and 25.402 for example), and uses macro-diversity where the UEs may be connected to multiple cells when the cells have similar characteristics. Macro-diversity is useful in CDMA systems because cells need to receive signals transmitted from UEs with about the same power level. This means that the cells that require the lowest transmit power from the UE "win" in the sense they are selected to serve the UE communication. It also means that macro-diversity combining is needed in the Node B or/and RNC nodes that are involved in the UE communication.

[0004] Each time a UE performs a handover, i.e., adding, removing or changing cells in an Active Set (AS), an Active Set Update message is sent to UE and involved RBSs/cells in the network. The UE is instructed to measure on all cells in the AS and a Monitored Set (MS) in real time. When UE detects a good neighbor cell, it sends a measurement report with a certain event, e.g. Event la. All other cells than listed in AS and MS are called Detected Set (DS) cells. [0005] Soft handover (SHO) is used for dedicated channels, e.g., CELL DCH channels in UTRAN. A Measurement Report (MR) from the UE containing an SHO "event" contains a Scrambling Code (SC) of the target cell(s) for SHO. Unfortunately, a scrambling code by itself is not enough information for the RNC to determine to which specific cell the UE's measurement report corresponds. This is because a unique one-to-one relationship does not exist between a cell's scrambling code and the cell's Cell Global Identity (CGI), e.g., Public Land Mobile radio Network (PLMN) identifier (ID), RNC ID, and Cell ID (within the RNC). As a result, radio network operators try to deploy cells in a way in which cells with the same scrambling codes are separated in order to avoid scrambling code collisions. In this way, a UE measurement report with a cell measurement event that includes a cell scrambling code can be compared with the cells in a UE's defined Neighbor Cell Relations (NCR) list corresponding to the measured set. If there is no scrambling code overlap in cells in the NCR list/measured set, then there is no problem with determining which cell corresponds to the UE's measurement report based purely on this scrambling code information. When the UE's measurement report contains a scrambling code that matches a Neighbor Relation in the measured set, the SRNC performs a HandOver (HO) of the UE connection to that matched neighbor cell, sometimes called a target cell, and assumes that this target cell is the correct one corresponding to the UE's measurement report.

[0006] When the UE sends a measurement report for a cell in the detected set, the cell's scrambling code may or may not be part of the known Neighbor Cell Relations list in the SRNC for this UE and its Active Set, called Neighbor Set (NS). If the scrambling code is defined in any of the SRNC's Neighbor Cell Lists of the cells in the Active Set (the NS), it is a Valid Cell, and the RNC initiates handover to the corresponding cell. But if the scrambling code is not defined in SRNC's Neighbor Cell Lists, the RNC discards the UE's measurement report. These undefined scrambling code cells are referred to as Invalid Cells.

[0007] But as mentioned above, the problem is the absence of a unique one-to-one relation between a scrambling code and each cell. The primary scrambling code is the Physical Cell Identity (PCI) in WCDMA, and there are only 512 of them. Some are used for inter- operation between network operators using the same frequency. Moreover, the scrambling codes used in the network are not always populated perfectly, and as a result, the effective number of scrambling codes may be even further reduced. A PLMN operator may deploy or have the ability to deploy a large number of cells in a radio network, e.g., on the order of 10,000-50,000 cells or more. The trend is for smaller cells, especially when macro-cells are deployed with the maximum number of frequencies and maximum power for good coverage and capacity. Ultimately, the number of available scrambling codes is limited and less than the number of cells. A desirable goal is to enable the RNC to identify one or a subset of cells that likely correspond to the actually measured cell in a UE's measurement report from a set of multiple cells that have the same cell identifier such as the same cell scrambling code.

SUMMARY

[0008] A Radio Network Controller (RNC) is described for a cellular communications system. The RNC communicates with base stations, and each base station is associated with one or more cells including a first one of the base stations serving a user equipment (UE) connected via a serving cell to the cellular communications system. The RNC maintains an RNC frame number (RFN) count or the like, and each of the base stations maintains a base station frame number (BFN) count or the like. Each cell has a corresponding cell timing difference, resulting in a difference between a system frame number (SFN) count in the cell and the BFN count.

[0009] The RNC receives one or more UE measurement reports. A report includes for each of multiple measured cells a cell identifier of the measured cell and a UE timing offset between the measured cell's SFN count and a connection frame number (CFN) count or the like in the serving cell established for the UE's connection with the cellular communications system. The RNC determines a corresponding RBS phase difference for each of the multiple measured cells based on a difference between the RFN count and a BFN count corresponding to each of the measured cells. Measured cells having a same cell identifier are identified, and the RNC determines, for each of the identified measured cells, a determined difference based on its RBS phase difference to a RBS phase difference of the serving cell, its cell timing difference to a cell timing difference of the serving cell, and a connection frame number difference between the UE timing offset, and the identified measured cell's connection frame number. The RNC selects one or more of the identified measured cells based on the determined difference for each of the identified measured cells.

[0010] In example embodiments, the RNC selects a subset of one or more identified measured cells for handover of the UE connection from the identified measured cells. In other example embodiments, the RNC selects a subset of one or more identified measured cells for automatic neighbor cell relations for the UE. [0011] One example selection approach is for the RNC to select the identified measured cell having a smallest determined difference within a predetermined margin. In another example approach, the RNC selects the identified measured cell having a determined difference less than or equal to a predetermined threshold or margin.

[0012] In example embodiments, the RNC stores in memory each of the measured cells information including a corresponding cell phase difference, a corresponding cell timing difference, and a corresponding cell identifier. The cell identifier may be used as an index or address to access the stored information.

[0013] In other example embodiments, the RNC receives measured cell information from another RNC and generates, for each of the measured cells from the other RNC, a software link or relationship to a corresponding cell phase difference, a corresponding cell timing difference, a corresponding cell identifier, and a connection frame number.

[0014] In an example application, the cellular communications system employs wideband code division multiplex (WCDMA), the RNC is a serving RNC (SRNC), and the cell identifier is a scrambling code. The RNC may then discriminate between measured cells having the same scrambling code, i.e., the measured cell identifier includes a scrambling code. Moreover, in the WCDMA example system, the cell timing difference may be a tCell time, the connection timing offset includes a CFN offset, and the UE timing difference includes an SFN- CFN offset.

BRIEF DESCRIPTION OF THE FIGURES

[0015] Figure 1 shows an example cellular communications system with an example

RNC, two RBSs each serving multiple cells, and a UE.

[0016] Figure 2 shows an example timing diagram that illustrates various timing relationships and offsets.

[0017] Figure 3 is a flowchart illustrating example, non-limiting procedures performed by a RNC.

[0018] Figure 4 is an example, non-limiting function block diagram of an RNC for performing the functions in Figure 3 and other functions.

[0019] Figure 5 shows an example offset table with cell scrambling code as an index.

[0020] Figure 6 illustrates in tree form example elements for an offset table.

[0021] Figure 7 illustrates an example cell selection methodology. DESCRIPTION OF NON-LIMITING EXAMPLE EMBODIMENTS

[0022] The following sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. But it will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. In some instances, detailed descriptions of well known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

[0023] Individual function and flowchart blocks are shown in the figures. Those skilled in the art will appreciate that the functions of those blocks may be implemented using individual hardware circuits, using software programs and data in conjunction with a suitably programmed microprocessor or general purpose computer, using applications specific integrated circuitry (ASIC), using one or more digital signal processors (DSPs), and using field programmable gate array(s) (FPGAs).

[0024] The software program instructions and data may be stored on computer- readable storage medium and when the instructions are executed by a computer or other suitable processor control, the computer or processor performs the functions, and (where appropriate) state machines capable of performing such functions.

[0025] Although process steps, algorithms or the like may be described or claimed in a particular sequential order, such processes may be configured to work in different orders. In other words, any sequence or order of steps that may be explicitly described or claimed does not necessarily indicate a requirement that the steps be performed in that order. The steps of processes described herein may be performed in any order possible. Further, some steps may be performed simultaneously despite being described or implied as occurring non- simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modifications thereto, does not imply that the illustrated process or any of its steps are necessary to the invention(s), and does not imply that the illustrated process is preferred. A description of a process may be a description of an apparatus for performing the process. The apparatus that performs the process can include, e.g., a processor and those input devices and output devices that are appropriate to perform the process.

[0026] In terms of computer implementation, a computer is generally understood to comprise one or more processors or one or more controllers, and the terms computer, processor, and controller may be employed interchangeably. When provided by a computer, processor, or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, the term "processor" or "controller" also refers to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above.

[0027] Although the description is given for user equipment (UE), it should be understood by the skilled in the art that "UE" is a non-limiting term comprising any wireless device or node equipped with a radio interface allowing for at least one of: transmitting signals in UL and receiving and/or measuring signals in DL. Some examples of a UE in its general sense include a mobile station, mobile phone, smart phone, PDA, laptop, sensor, fixed relay, mobile relay, a radio network node (e.g., an LMU or a femto base station or a small base station using the terminal technology). A UE performs measurements in one or more frequencies, carrier frequencies, component carriers or frequency bands and can operate in a single-radio access technology (RAT) or multi-RAT or multi- standard mode.

[0028] One or more cells are associated with a radio base station, and a base station comprises in a general sense any node transmitting radio signals in the downlink (DL) and/or receiving radio signals in the uplink (UL). Some example base stations are eNodeB, e B, Node B, macro/micro/pico radio base station, home eNodeB, relay, repeater, sensor, transmitting-only radio nodes or receiving-only radio nodes. A base station may operate or at least perform measurements in one or more frequencies, carrier frequencies, or frequency bands. It may also be a single-radio access technology (RAT), multi-RAT, or multi- standard node, e.g., using the same or different base band modules for different RATs. [0029] The signaling between nodes may be either via direct links or logical links (e.g. via higher layer protocols and/or via one or more network nodes). For example, signaling from a coordinating node may pass another network node, e.g., a radio node.

[0030] The example embodiments are described in the non-limiting example context of a UTRAN type system. However, the technology is not limited to UTRAN, but may apply to any other suitable Radio Access Network (RAN).

[0031] Figure 1 shows an example cellular communications system with an example

RNC, RBS1 and RBS2 each serving multiple cells, and a UE. RBS1 serves multiple cells including Cells la and lb, and RBS2 serves multiple cells including Cell 2a. Currently, Cell lb is serving the UE, and Cell la and Cell 2a are neighbor cells that are measured by the UE. Note also that both neighbor Cells la and 2a have the same primary scrambling code pSC=A so that they cannot be distinguished by their primary scrambling code in a UE measurement report for a neighbor cell that includes information associated with pSC=A.

[0032] The technology in this application enables a control node, in the example below the RNC, to identify and select one or a subset of cells that likely correspond to the actually measured cell in a UE's measurement report from a large set of cells that have the same cell scrambling codes or other cell identifiers. The inventors realized that various existing timing information for cells could be used to distinguish between cells with the same cell identifiers.

[0033] But first a bit of foundation is helpful. A UTRAN system like that in Figure 1 is an asynchronous system and there the various nodes must synchronize with each other in order to effectively communicate. UTRAN sends information in frames, and each frame is numbered. There is a system frame number (SFN), an RNC frame number (RFN), a base station frame number (BFN), and a connection frame number (CFN). Reference is made to Figure 2 which shows an example timing diagram that illustrates various timing relationships and offsets in UTRAN.

[0034] The RNC maintains a CFN count for the timing relation between a UE connection and the UTRAN, and a SFN count for the timing relation between the UTRAN and each cell. The SFN in Cell la differs from the SFN in Cell 2a: Cell la has SFN count la and Cell 2a has SFN count 2a. The SFN count in the UTRAN example has a range from 0 to 4095, and the CFN count has an example range from 0 to 255, i.e., 16 cycles of CFN is equal to 1 cycle of SFN so modulo 256 arithmetic is applied to derive the CFN from SFN. The SFN differs from the CFN by a frame offset and a chip offset. [0035] Each base station has a BFN count so that RBS1 has a BFN1 count, and RBS2 has a different BFN2 count. The difference between a cell's SFN count and BFN count is a cell timing difference referred to as tCell. So Cell la has a tCell la, and Cell 2a has a tCell 2a. There is also a timing relation between the RNC's RFN and each base station's BFN referred to as a RBS phase difference φ. Therefore, the RBS phase difference φΐ for the RNC and RBS1 is RFN-BFN1, and the RBS phase difference φ2 for the RNC and RBS2 is RFN-BFN2. The connection timing offset at each of cells Celll and Cell2 is labeled CFN offset and is the timing offset of the connection's CFN from the cell's SFN. The UE measures or detects the timing difference between the CFN and the neighbor cell's broadcasted timing. This UE measured timing offset is referred to as SFN-CFN Offset.

[0036] The inventors recognized that these timing offset values are typically already available in UTRAN type systems. For example, the RNC typically includes a node synchronization ("node sync") table that includes RBS phase difference φ and cell timing difference tCell information for various cells and base stations under its control. The UE measured timing offset SFN-CFN Offset for measured cells is typically provided in UE measurement reports for macro-diversity handover purposes. For example, the SFN-CFN Offset is provided as information in UE SHO Measurement Reports, e.g., for Events la, lc or Id, with the known CFN and various downlink HO Offset (DHO) values in a Serving Radio Network Controller (SRNC). The inventors discovered that using this information allows selection between cells that have a same cell identifier (e.g., a same primary scrambling code) in a UE's measurement reports.

[0037] These various timing offset values make it possible to reduce the number of unknown neighbor cells with the same scrambling code from multiple possible cells to one or a few, e.g., from 10 to 1 in an example case, due to the randomness between RNC and RBS phase counters. This includes neighbor cells served by the SRNC as well as neighbor cells served by other neighboring RNCs. One example below uses timing offset values between the SRNC and its RBS nodes. Another example described includes Inter-RNC timing offset values which are shared between Neighbor RNCs. In both examples, the number of cell candidates is reduced when populating Automatic Neighbor Relation (ANR) Candidate Relation Statistics (CRS) and when evaluating the number of candidate cells for handover based on UE measurement reports that include multiple neighbor cells having a same cell identifier.

[0038] Figure 3 is a flowchart illustrating example, non-limiting procedures performed by a RNC. The RNC receives UE measurement reports including, for each of multiple measured cells, a cell identifier of the measured cell and a UE timing offset between a measured cell's SFN count and a CFN count established for the UE's connection with the cellular communications system (step SI). A corresponding RBS phase difference is determined for each of the multiple measured cells based on a difference between the RFN count and a BFN count corresponding to each of the measured cells (step S2). The RNC identifies measured cells having a same cell identifier (step S3), and for each of the identified measured cells, the RNC determines a difference based on its RBS phase difference to a RBS phase difference of the serving cell, its cell timing difference to a cell timing difference of the serving cell, and a connection frame number difference between the UE timing offset, and the identified measured cell's connection frame number (step S4). One or more of the identified measured cells is selected based on the determined difference for each of the identified measured cells, e.g., for UE handover, UE automatic neighbor cell relations, etc. (step S5).

[0039] Figure 4 is an example, non-limiting function block diagram of an RNC for performing the functions in Figure 3 and other functions related to the technology described in this application. The functional units may be implemented or realized by machine which may take any of several forms, such as (for example) electronic circuitry in the form of a computer implementation platform or a hardware circuit platform. A computer implementation of the machine may be realized by or implemented as one or more computer processors or controllers as those terms are herein expansively defined, and which may execute instructions stored on non-transitory computer-readable storage media. In such a computer implementation, the machine platform may comprise, in addition to a processor(s), memory including comprise random access memory, read only memory, an application memory including coded non instructions which can be executed by the processor to perform acts describe, other memory such as cache memory, for example. Another example of the machine uses hardware circuitry, e.g., an application specific integrated circuit (ASIC), a digital signal processor (DSP), a programmable gate array (PGA), etc., where circuit elements are structured and operated to perform the various acts described.

[0040] The RNC 10 includes one or more data processors 12, a Frame Number (FN) counter along with multiple CFN counts (defined as offsets to the RFN) 13, one or more memories 14 storing data 16 and one or more computer programs 18 executable by the one or more data processors 12, and one or more databases 26. The database(s) or other memory 26 store tables 28 with offset information, automatic neighbor cell relation tables 30, and UE measurement information 32 used for handover. The RNC has multiple interfaces for communicating with other nodes including interfaces 20 with base stations it controls, interfaces 22 with other RNCs, and other network communication interfaces 24 such core network node interfaces.

[0041] The RNC database 26 may store a table of synchronization data for all base stations controlled by the RNC 10. The synchronization table includes a phase difference φ between the RNC's RFN count value and each RBS's BFN frame number count value. The synchronization table also may include the tCell value associated with each of the base station cells, which as described above is a different between a cell's SFN count value and its base station's BFN count value. This table is referred to as an SFN Cell Offset table since it stores information that relates the RNC s RFN to the SFN of each cell. The SFN Cell Offset table also may include a corresponding scrambling code for each cell. The scrambling code may be used as a key index to the SFN Cell Offset table and to sort the list of cells periodically or otherwise, e.g., as a background activity every hour. The RNC also checks for newly- configured cells and/or cells removed. The table may be amended and sorted, for example, when a new cell is configured, when a cell is deleted, or when a scrambling code is changed for a cell.

[0042] Figure 5 shows an example SFN Cell Offset table with cell primary scrambling code (pSC in this example) as an index for sorting the table. Note that the sorted table reveals that two cells share the same scrambling code 18, and three other cells share the same primary scrambling code 19. Consider the following examples. In example 1, assume that a handover is desired to a target cell associated with a UE measurement report including pSC19. Even though two cells have pSC19 in the table, only cell-ID Sth3 Offset values (Boffl9+tCell) matches the UE reported HO Offset values included in the UE measurement report. Because the SRNC can determine the correct cell ID is Sth3 based on its offset values, the SRNC selects this cell for handover. In example 2, assume again that a handover is desired to a target cell with a UE measurement report including pSC19. But now the Offset values for both cell IDs Sth4 and Sth5 match the UE measurement report HO Offset. Even though the SRNC cannot select just one cell, it does reduce the number of cells with matching scrambling code 19 from three to two. The SRNC may initiate a radio link uplink measurements setup procedure where for example cell Sth4 can hear the UE, while cell Sth5 can not, or the SRNC may simply select one of the two, e.g., Sth4, and then select Sth5 if Sth4 fails, etc. [0043] Figure 6 illustrates in tree form example elements for an SFN Cell Offset table.

The tree illustrates that for each RBS there is one RFN-BFN phase difference. Each RBS controls one or more cells each with one tCell.

[0044] Information from an SFN Cell Offset table may be used to reduce the number of possible Intra-RNC target cell candidates. In current UTRAN, there are only 512 different primary scrambling codes. For an RNC that controls 1000 cells, the number of candidate cells using the same scrambling code may be relatively, e.g., 2 or 3. But if the RNC must manage 20,000 cells, the number of candidate cells having the same scrambling code may be relatively high, e.g., 50 assuming a noisy scrambling code spectrum. In either situation, information from an SFN Cell Offset table may be used to reduce number of candidate cells from many to one or a smaller number by comparing SFN-CFN-Offset information provided in a UE

Measurement Report (MR) with data in the SFN Cell Offset table. For example, the RNC extracts φ and tCell information for all cells having a same scrambling code from a SFN Cell Offset table. The RNC compares offsets provided in the UE measurement reports with cell offsets from the SFN Cell Offset table. In some example embodiments, the comparison process uses a qualifying uncertainty parameter. The RNC may output all candidate cell which match (e.g., zero, one or many), and when no candidate cell matches, the RNC may conclude that the target cell may probably be controlled by in a neighbor RNC.

[0045] Figure 7 illustrates an example cell selection methodology using SFN Cell

Offset information φ and tCell, SC cell identifier, UE measurement report information containing an associated scrambling code, SFN-CFN offset, and CFN Offset, and if desired, a comparison margin parameter. As a background activity, the RNC measures the phase difference cp=BFN-RFN for each RBS controlled by the RNC. The RNC stores this phase difference information together with the tCell of the cells in an SFN Cell Offset table. The RNC receives a measurement report from the UE including the scrambling code and CFN-SFN offset of a neighbor cell. Multiple cells may have the reported scrambling code. To determine what physical cell the measurement report actually relates to, the RNC uses the received CFN- SFN offset and the CFN offset of the connection along with the information stored in the SFN Cell Offset table. The CFN offset is a value that the RNC selects when the first radio link to the UE is established. In a 3 GPP example, the CFN offset value can be in the range 0-80 ms and is conveyed to the RNS in NBAP signaling and the UE in RRC signaling. Neighbor cells are identified that match the UE reported scrambling code and include within a configurable margin an SFN-CFN offset that corresponds to the reported SFN-CFN Offset. [0046] A non-limiting example comparison is now described referring to Figure 1. The

UE is served by Cell lb and sends a measurement report for a cell with a scrambling code SC=A. For a neighboring cells la and 2a, SFNla and SFN2a are determined:

SFN la = tCellla + φΐ + RFN

SFN lb = tCelllb + φΐ + RFN

SFN2a = tCell2a + φ2 + RFN.

In the UE measurement report, a primary scrambling code pSC and SFN-CFN offset are included. The RNC does not know if the measured cell is Cell la or Cell 2a because both have pSC=A. The RNC calculates an X value for both Cell la or Cell 2a using the measurement report information and the cell information in the SFN Offset chart for those same cells.

For Cell la:

X_la=( (pi - q>2) + (tCellla-tCelllb) + (CFN_offset-[SFN-CFN offset]) For Cell2a:

X_2a=( q>l - q>2) + (tCellla-tCell2a) + (CFN_offset-[SFN-CFN offset])

The X value that is equal to zero or within a predetermined margin amount is the likely correct cell is selected. For example, if the UE reports Event la with values: pSC=20 and SFN-CFN Offset = 50, X_la = 0.4 and X_2a = 122.5. Accordingly, Cell la is selected.

[0047] Non-limiting example embodiments may also employ Inter-RNC SFN Cell

Offset information φ and tCell with SC cell identifier for neighboring RNC cells, associated with different RNCs, plus Inter-RNC phase information, for each of the neighbor RNCs. The Inter-RNC phase information is measured, and SFN Cell Offset information φ and tCell with SC cell identifier are exchanged between RNCs for neighboring RBS nodes and cells.

[0048] The technology described includes many advantages and has multiple applications. It may be used to identify which neighboring cell from among multiple neighboring cells having the same cell identifier, e.g., a same scrambling code, most likely corresponds to the cell identified in a UE measurement report. Even if a single neighbor cell cannot be decided, e.g., multiple cells are within the margin, the technology significantly reduces the number of neighboring cells identified to a much more manageable number.

Example applications include evaluating target cells for handover, populating statistics in an ANR algorithm, performing other ANR operations, and/or identifying new cells, e.g., other cells than those in a current neighbor set in an SRNC. The technology is also useful in assigning/reusing cell identifiers to particular cells in a network such as heterogeneous network with a large number of cells.

[0049] Although the description above contains many specifics, they should not be construed as limiting but as merely providing illustrations of some presently preferred embodiments. Embodiments described herein may be considered as independent embodiments or may be considered in any combination with each other to describe non-limiting examples. Indeed, the technology fully encompasses other embodiments which may become apparent to those skilled in the art. 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 a device or method to address each and every problem sought to be solved by the described technology for it to be encompassed hereby.

Claims

Claims:

1. A method for a Radio Network Controller, RNC, (10) in a cellular

communications system, the RNC communicating with base stations each associated with one or more cells including a first one of the base stations serving a user equipment, UE, connected via a serving cell to the cellular communications system, where the RNC maintains a RNC frame number, RFN, count and each of the base stations maintains a base station frame number, BFN, count, and where each cell has a corresponding cell timing difference resulting in a difference between a system frame number, SFN, count in the cell and the BFN count corresponding to the cell, the method in the RNC comprising:

receiving one or more UE measurement reports including for each of multiple measured cells a cell identifier of the measured cell and a UE timing offset between the measured cell's SFN count and a connection frame number, CFN, count in the serving cell established for the UE's connection with the cellular communications system (SI);

determining a corresponding RBS phase difference for each of the multiple measured cells based on a difference between the RFN count and a BFN count corresponding to each of the measured cells (S2);

identifying measured cells having a same cell identifier (S3);

determining, for each of the identified measured cells, a determined difference based on its RBS phase difference to a RBS phase difference of the serving cell, its cell timing difference to a cell timing difference of the serving cell, and a connection frame number difference between the UE timing offset, and the identified measured cell's connection frame number (S4); and

selecting one or more of the identified measured cells based on the determined difference for each of the identified measured cells (S5).

2. The method in claim 1, wherein the selecting step includes selecting a subset of one or more identified measured cells for handover of the UE connection from the identified measured cells.

3. The method in claim 1, wherein the selecting step includes selecting a subset of one or more identified measured cells for automatic neighbor cell relations for the UE.

4. The method in any of claims 1-3, wherein the selecting step includes selecting the identified measured cell having a smallest determined difference within a predetermined margin.

5. The method in any of claims claim 1-3, wherein the selecting step includes selecting the identified measured cell having a determined difference less than or equal to a predetermined threshold or margin.

6. The method of any of the preceding claims, further comprising storing for each cell information including a corresponding cell phase difference, a corresponding cell timing difference, and a corresponding cell identifier.

7. The method in claim 6, further comprising using the cell identifier as an index or address to access the stored information.

8. The method of any of the preceding claims, further comprising:

receiving measured cell information from another RNC, and

generating, for each of the measured cells from the other RNC, a software link or relationship to a corresponding cell phase difference, a corresponding cell timing difference, a corresponding cell identifier, and a connection frame number.

9. The method of any of the preceding claims, wherein the cellular

communications system employs wideband code division multiplex, WCDMA, the RNC is a serving RNC, SRNC, and the cell identifier is a primary scrambling code.

10. The method in claim 9, wherein the selecting step discriminates between measured cells having the same scrambling code.

11. The method in claim 9, wherein the measured cell identifier includes a scrambling code, the cell timing difference is a tCell time, the connection timing offset includes a CFN offset, and the UE timing difference includes an SFN-CFN offset.

12. A radio network controller, RNC, node (10) for a cellular communications system having a system frame number, SFN, count, the RNC configured to communicate with base stations each associated with one or more cells including a first one of the base stations serving a user equipment, UE, connected via a serving cell to the cellular communications system, where each of the base stations maintains a base station frame number, BFN, count, the RNC comprising:

an RNC frame number, RFN, counter (13), where each cell has a corresponding cell timing difference based on difference between the SFN count and the BFN count corresponding to the base station serving that cell configured to communicate with the UE via a radio base station over a radio interface;

an interface (20) configured to receive one or more UE measurement reports including for each of multiple measured cells a cell identifier of the measured cell and a UE timing offset between the measured cell's SFN count and a connection frame number, CFN, count in the serving cell established for the UE's connection with the cellular communications system;

one or more processors (12), connected for communication with the RFN counter and the interface, configured to:

determine a corresponding RBS phase difference for each of the multiple measured cells based on a difference between the RFN count and a BFN count corresponding to each of the measured cells;

identify measured cells having a same cell identifier;

determine, for each of the identified measured cells, a determined difference based on its RBS phase difference to a RBS phase difference of the serving cell, its cell timing difference to a cell timing difference of the serving cell, and a connection frame number difference between the UE timing offset, and the identified measured cell's connection frame number; and

select one or more of the identified measured cells based on the determined difference for each of the identified measured cells.

13. The RNC node in claim 12, wherein the one or more processors is configured to select a subset of one or more identified measured cells for handover of the UE connection from the identified target cells.

14. The RNC node in claim 12, wherein the one or more processors is configured to select a subset of one or more identified measured cells for automatic neighbor cell relations for the UE.

15. The RNC node in any of claims 12-14, wherein the one or more processors is configured to select the identified measured cell having a smallest determined difference within a predetermined margin.

16. The RNC node in any of claims 12-14, wherein the one or more processors is configured to select the identified measured cell having a determined difference less than or equal to a predetermined threshold or margin.

17. The RNC node in any of claims 12-16, further comprising a memory configured to store, for each cell, information including a corresponding cell phase difference, a corresponding cell timing difference, a corresponding cell identifier, and a connection frame number.

18. The RNC node in claim 17, wherein the one or more processors is configured to use the cell identifier as an index or address to access the stored information.

19. The RNC node in any of claims claim 12-18, wherein the receiver is configured to receive measured cell information from another RNC, and

wherein the one or more processors is configured to generate, for each of the measured cells from the other RNC, a software link or relationship to a corresponding cell phase difference, a corresponding cell timing difference, a corresponding cell identifier, and a connection frame number.

20. The RNC node in any of claims 12-19, wherein the cellular communications system employs wideband code division multiplex (WCDMA), the RNC is a serving RNC, SRNC, and the cell identifier is a primary scrambling code.

21. The RNC node in claim 20, wherein the one or more processors is configured to discriminate between measured cells having the same scrambling code based on the determined difference for each of the identified measured cells.

22. The RNC node in claim 20, wherein the measured cell identifier includes a scrambling code, the cell timing difference is a tCell time, the connection timing offset includes a CFN offset, and the UE timing difference includes an SFN-CFN offset.