Base station, user equipment and method

Abstract

To provide a radio base station, a reception method, and an integrated circuit for achieving an improved (cell) measurement procedure.SOLUTION: In a mobile communication system, a serving radio base station gNB1 comprises a transceiver for receiving a measurement report comprising a measurement result from a communication device UE, and a processing circuit for determining from the measurement report that a beamformed reference signal controlled by a neighboring radio base station gNB2 is not comprised in the measurement result, wherein in accordance with the reception of the measurement report, the serving radio base station sends a request message to the neighboring radio base station to provide a beamformed reference signal to the communication device, and wherein the transceiver sends a notification message comprising information on the beamformed reference signal to the communication device.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present disclosure is directed to methods, devices and articles relating to communication systems, such as 3GPP communication systems. [Background technology]

[0002] The 3rd Generation Partnership Project (3GPP) is currently working toward the release (Release 15) of technical specifications for next-generation cellular technology, also known as the fifth generation (5G). The 3GPP Technical Specification Group (TSG) Radio Access Network (RAN) Meeting No. 71 (Gutenberg, March 2016) approved the first 5G study item, "Study on New Radio Access Technology," which includes RAN1, RAN2, RAN3, and RAN4, and is expected to become the Release 15 work item that will define the first 5G standard. The aim of the study is to develop a "New Radio (NR)" access technology (RAT) that operates in the frequency range up to 100 GHz and supports the wide range of use cases defined during the RAN requirements study (see, for example, Non-Patent Document 1, available at www.3gpp.org and incorporated herein by reference in its entirety).

[0003] One objective is to provide a single technical framework that addresses all usage scenarios, requirements, and deployment scenarios defined in TR38.913, including at least enhanced mobile broadband (eMBB), ultra-reliable and low-latency communications (URLLC), and massive machine-based communications (mMTC). For example, eMBB deployment scenarios can include indoor hotspots, dense urban, rural, urban macro, and high-speed. URLLC deployment scenarios can include industrial control systems, mobile health management (remote monitoring, diagnosis, and treatment), real-time control of vehicles, wide-area surveillance, and smart grid control systems. mMTC can include scenarios using multiple devices for non-time-critical data transfer, such as smart wearables and sensor networks. A second objective is to achieve backward compatibility. Backward compatibility with Long Term Evolution (LTE, LTE-A) cellular systems is not required, which facilitates the introduction of entirely new system designs and / or novel features.

[0004] The basic physical layer signal waveform will be based on OFDM, with potential support for non-orthogonal waveforms and multiple access. For example, DFT-S-OFDM, and / or variants of DFT-S-OFDM, and / or additional features on top of OFDM, such as filtering / windowing, are further considered. In LTE, CP-based OFDM and DFT-S-OFDM are used as waveforms for downlink and uplink transmissions, respectively. One of the design goals of NR is to seek waveforms that are as common as possible for the downlink, uplink, and sidelink.

[0005] In addition to waveforms, some basic frame structures and channel coding schemes will be developed to achieve the above objectives. The study will also seek common knowledge on what will be needed in terms of radio protocol structures and architectures to achieve the above objectives. Furthermore, the technical capabilities needed to enable new RATs to address the above objectives will be considered, including efficient multiplexing of traffic for different services and use cases of the same contiguous block of spectrum.

[0006] Because 3GPP's NR standardization for the 5G system is just beginning, some issues remain unclear. For example, there are ongoing discussions on how to support downlink transmission of reference signals and respective synchronization signals for UEs. Such reference / synchronization signals can be used by UEs for various purposes, such as cell synchronization, measurements to determine channel quality, and / or measurements of UE mobility in relation to RRM (radio resource management) (e.g., for UEs in RRC IDLE and / or RRC CONNECTED modes). It is important to establish and define procedures that allow reference / synchronization signals to be fully utilized by gNBs and UEs to maximize their benefits. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] 3GPP TR38.913 “Study on Scenarios and Requirements for Next Generation Access Technologies”, current version 14.2.0 [Non-patent document 2] Technical Report TR38.804 v14.0.0 [Non-patent document 3] TS38.300 v.2.0, section 4

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[0008] In one non-limiting and exemplary embodiment, it is facilitated to realize an improved (cell) measurement procedure involving various entities (UE, gNB). [Means for solving the problem]

[0009] In one general aspect, the techniques disclosed herein feature a radio base station serving a user equipment in a first radio cell of a mobile communication system. The radio base station includes processing circuitry for determining that a neighbor radio base station is not providing a beamformed reference signal to the user equipment. The neighbor radio base station controls transmission of an omnidirectional reference signal and a beamformed reference signal in its neighbor radio cell. A transmitter of the radio base station transmits a reference signal request to the neighbor radio base station. The reference signal request requests the neighbor radio base station to provide a beamformed reference signal to the user equipment. A receiver of the radio base station receives a reference signal request response from the neighbor radio base station, the reference signal request response including information about transmission of the requested beamformed reference signal. The transmitter transmits a notification message to the user equipment, the notification message including information about the requested beamformed reference signal.

[0010] In one general aspect, the techniques disclosed herein feature a radio base station of a mobile communication system that controls transmission of an omnidirectional reference signal and a beamformed reference signal in a first radio cell of the radio base station. The radio base station includes a processing circuit that determines to transmit information about the beamformed reference signal to one or more neighboring radio base stations. A transmitter of the radio base station transmits a reference signal notification message to the one or more neighboring radio base stations, the reference signal notification message including scheduling information for the beamformed reference signal that enables identifying radio resources used by the radio base station to transmit the beamformed reference signal.

[0011] In one general aspect, the techniques disclosed herein feature a user equipment of a mobile communication system. The user equipment includes processing circuitry for determining that a neighboring radio base station is not providing a beamformed reference signal to the user equipment. The neighboring radio base station controls transmission of omnidirectional reference signals and beamformed reference signals in its neighboring radio cell. A transmitter of the user equipment transmits a reference signal request to a serving radio base station serving the user equipment. The reference signal request requests the serving radio base station to request the neighboring radio base station to provide a beamformed reference signal to the user equipment. A receiver of the user equipment receives a notification message from the serving radio base station, the notification message including information about the requested beamformed reference signal.

[0012] In one general aspect, the techniques disclosed herein feature a method of operating a radio base station serving user equipment in a first radio cell of a mobile communication system. The method includes the following steps performed by the radio base station: determining that a neighboring radio base station is not providing a beamformed reference signal to the user equipment; the neighboring radio base station controls transmission of an omnidirectional reference signal and a beamformed reference signal in the neighboring radio cell; transmitting a reference signal request to the neighboring radio base station, the reference signal request requesting the neighboring radio base station to provide a beamformed reference signal to the user equipment; receiving a reference signal request response from the neighboring radio base station, the reference signal request response including information about the transmission of the requested beamformed reference signal; and transmitting a notification message to the user equipment, the notification message including information about the requested beamformed reference signal.

[0013] In one general first aspect, the techniques disclosed herein feature a method of operating a user equipment in a mobile communication system, the method including the following steps performed by the user equipment: determining that a neighboring radio base station is not providing a beamformed reference signal to the user equipment; the neighboring radio base station controls transmission of an omnidirectional reference signal and a beamformed reference signal in its neighboring radio cell; transmitting a reference signal request to a serving radio base station serving the user equipment; the reference signal request requesting the serving radio base station to request the neighboring radio base station to provide a beamformed reference signal to the user equipment; and receiving a notification message from the serving radio base station including information about the requested beamformed reference signal.

[0014] It should be noted that the general or specific embodiments may be realized as a system, a method, an integrated circuit, a computer program, a storage medium, or any selective combination thereof.

[0015] Further benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. These benefits and / or advantages may be obtained individually by various embodiments and features of the specification and drawings, but not all of these embodiments and features are necessary to obtain one or more of such benefits and / or advantages.

[0016] In the following, exemplary embodiments will be described in more detail with reference to the accompanying figures and drawings. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 illustrates an example architecture of a 3GPP NR system. [Figure 2] FIG. 1 illustrates an exemplary user and control plane architecture for an LTE eNB, gNB, and UE. [Figure 3] FIG. 1 illustrates a 5G NR user plane protocol stack. [Figure 4] FIG. 1 illustrates the control plane protocol stack for 5G NR. [Figure 5] 1 is an exemplary signaling diagram of an X2 handover procedure in an LTE communication system. [Figure 6] 1A and 1B show an overview of mobility-related RRM operations for RRC IDLE and RRC CONNECTED, respectively. [Figure 7] 1A and 1B show an overview of mobility-related RRM operations for RRC IDLE and RRC CONNECTED, respectively. [Figure 8] FIG. 1 illustrates a scenario to illustrate a potential problem where a neighboring gNB is not transmitting any beamformed NR connection reference signals. [Figure 9] FIG. 1 illustrates a scenario to illustrate a potential problem where a neighboring gNB is transmitting a beamformed NR connection reference signal in a direction other than the direction in which the UE is located. [Figure 10]FIG. 1 illustrates a scenario to illustrate a potential problem where a UE does not have the necessary scheduling information for beamformed NR connection reference signals transmitted from a neighboring gNB. [Figure 11] FIG. 1 illustrates a scenario to illustrate a potential problem where a UE handover is adversely affected by a switched-off beam of an NR connection reference signal. [Figure 12] FIG. 1 illustrates an exemplary simplified configuration of a UE and an eNB. [Figure 13] A signaling diagram of an improved inter-gNB coordination procedure initiated by a serving gNB serving a UE. [Figure 14] A signaling diagram of an improved inter-gNB coordination procedure initiated by a UE. [Figure 15] FIG. 10 illustrates an example MAC control element that may be used in a UE-initiated reference signal request message. [Figure 16] A diagram showing an example PDCP control PDU that can be used in a UE-initiated reference signal request message. [Figure 17] A signaling diagram of an improved inter-gNB coordination procedure initiated by neighboring gNBs. DETAILED DESCRIPTION OF THE INVENTION

[0018] Basis of this Disclosure 5G NR System Architecture and Protocol Stack As presented in the Background section, 3GPP is working towards the next release of fifth-generation cellular technology, which involves the development of New Radio Access Technologies (NR), simply referred to as 5G, operating in the frequency range up to 100 GHz. 3GPP must identify and develop the technical building blocks necessary to successfully standardize an NR system to meet both immediate market needs and more long-term requirements in a timely manner. To achieve this, the evolution of the air interface and radio network architecture is being considered under the study item "New Radio Access Technologies." The results and consensus are summarized in Non-Patent Document 2, which is incorporated herein by reference in its entirety.

[0019] In particular, there was tentative agreement on the overall system architecture. The NG-RAN (Next Generation Radio Access Network) consists of gNBs, which provide the NG radio access user plane (SDAP / PDCP / RLC / MAC / PHY) and control plane (RRC) protocol termination for UEs. The gNBs are interconnected with each other by an Xn interface. The gNBs are also connected to the NGC (Next Generation Core) by a Next Generation (NG) interface, and more specifically to the AMF (Access and Mobility Management Function) by an N2 interface and to the UPF (User Plane Function) by an N3 interface. The NG-RAN architecture is shown in Figure 1, taken from Non-Patent Document 3, which is incorporated herein by reference in its entirety.

[0020] Various different supported deployment scenarios are currently being discussed, as reflected, for example, in 3GPP TS 38.301, which is incorporated herein by reference in its entirety. For example, a decentralized deployment scenario (3GPP TS 38.301, where a centralized deployment is illustrated in Section 5.4) is presented in which base stations supporting 5G NR can be deployed. Figure 2 illustrates an exemplary decentralized deployment scenario, based on Figure 5.2.-1 of TR 38.301, and further illustrates an LTE eNB and user equipment (UE) connected to both a gNB and an LTE eNB (which should be understood as an eNB according to the aforementioned 3GPP standard releases, such as LTE and LTE-A). As noted above, the NR 5G new eNB may be exemplarily referred to as a gNB.

[0021] For example, the eLTE eNB defined in TR38.801 is an evolution of the eNB that supports connectivity with EPC (Evolved Packet Core) and NGC (Next Generation Core).

[0022] The NR user plane protocol stack, as currently defined in Non-Patent Document 6, is shown in Figure 3. The PDCP, RLC, and MAC sublayers are terminated in the gNB on the network side. In addition, a new access stratum (AS) sublayer (SDAP, Service Data Adaptation Protocol) is introduced on top of PDCP as described in Non-Patent Document 7. The NR control plane protocol stack, as defined in Non-Patent Document 8, is shown in Figure 4. An overview of Layer 2 functions is given in Non-Patent Document 9. The functions of the PDCP, RLC, and MAC sublayers are listed in Non-Patent Document 10. The functions of the RRC layer are listed in Non-Patent Document 11. Each subclause of the above-mentioned Non-Patent Document 12 is incorporated herein by reference.

[0023] The new NR layer currently assumed for the 5G system may be based on the user plane layer configuration currently used in the LTE(-A) communication system. However, it should be noted that not all details of the NR layer have yet been finalized.

[0024] RRC State In LTE, the RRC state machine consists of only two states: an RRC idle state, which is primarily characterized by significant power savings, UE autonomous mobility, and no established UE connectivity to the core network, and an RRC connected state, which allows the UE to transmit user plane data while mobility is network controlled to support lossless service continuity.

[0025] RRC for NR 5G, as currently defined in 3GPP TS 36.1100, which is incorporated herein by reference, supports three states: RRC Idle, RRC Inactive, and RRC Connected, and enables the following state transitions as defined in 3GPP TS 36.1100, which is incorporated herein by reference:

[0026] As is evident, the new RRC state Inactivity is defined for 5G 3GPP new radio technologies to benefit when supporting a wider range of services such as eMBB (enhanced Mobile Broadband), mMTC (Massive Machine Based Communications) and URLLC (Ultra Reliable and Low Latency Communications), which have very different requirements in terms of signaling, power saving, latency etc. Therefore, the new RRC Inactivity state should be designed in a way that minimizes signaling, power consumption and resource costs in the radio access network and core network, while still allowing, for example, data transfer to be initiated with low latency.

[0027] LTE handover procedure Mobility is an important procedure in LTE communication systems. For a UE in active mode, there are two types of handover procedures in LTE: the S1 handover procedure and the X2 handover procedure. For intra-LTE mobility, handover via the X2 interface is typically used for inter-eNodeB mobility. Therefore, X2 handover is triggered by default unless there is an established X2 interface or the source eNodeB is configured to use another handover instead (e.g., S1 handover).

[0028] FIG. 5 shows a brief, exemplary, and simplified overview of an intra-X2LTE handover.

[0029] An X2 handover includes a preparation phase (steps 4 to 6), an execution phase (steps 7 to 9) and a completion phase (after step 9). An X2 intra-LTE handover is performed directly between two eNodeBs. Other entities in the core network (e.g., MME (Mobility Management Entity)) are only informed at the end of the handover procedure once the handover is successful in order to activate a path switch to the new eNB. Step 2, called Measurement Control, refers to the cell measurement and measurement reporting procedures performed between the UE and the serving eNodeB (herein "source LTE eNB"). As will become clear later, this application mainly presents an improved procedure regarding step 2 above.

[0030] In step 8, the state transition message indicates the sequence number and hyperframe number that the target eNodeB should assign to the first packet that has to be sent and that does not yet have a sequence number assigned.

[0031] Further information about mobility procedures in LTE can be found, for example, in Non-Patent Document 15, which is incorporated herein by reference, and Non-Patent Document 16, which is incorporated herein by reference.

[0032] LTE-(A) - Synchronization signals, reference signals and RRM measurements User equipment wishing to access an LTE cell must first undertake a cell search procedure to determine the time and frequency parameters required to demodulate the downlink and transmit uplink signals with the correct timing. The cell search procedure in LTE begins with a synchronization procedure that uses two specially designed physical signals broadcast in each cell: the primary synchronization signal (PSS) and the secondary synchronization signal (SSS). These two signals not only enable time and frequency synchronization, but also provide the UE with the cell's physical layer identity and cyclic prefix length, and inform the UE whether the cell uses frequency division duplexing (FDD) or time division multiplexing (TDD).

[0033] The PSS and SSS are transmitted periodically, twice per 10 ms radio frame. In an FDD cell, the PSS is always located in the last OFDM (orthogonal frequency division multiplexing) symbol of the first and eleventh slots of each radio frame, allowing the UE to acquire slot boundary timing regardless of the cyclic prefix length. The SSS is located in the symbol immediately preceding the PSS. In a TDD cell, the PSS is located in the third OFDM symbol of the third and thirteenth slots, and the SSS is located three symbols earlier. The PSS and SSS are transmitted in the center six resource blocks, allowing the frequency mapping of these synchronization signals to be invariant to the system bandwidth, thereby allowing the UE to synchronize with the network without any prior knowledge of the allocated bandwidth.

[0034] Further detailed information about LTE reference signals and LTE synchronization signals (e.g., PSS and SSS configurations) can be found, for example, in Non-Patent Document 17 and Non-Patent Document 18, both of which are incorporated herein by reference.

[0035] Once synchronization between the eNodeB and the UE is achieved, LTE becomes a coherent communication system that uses equalization and detection algorithms to exploit knowledge of the channel impulse response (CIR). Optimal reception through coherent detection typically requires an accurate estimation of the propagation channel. For this purpose, known reference signals are inserted into the transmitted signal structure. To estimate the channel as accurately as possible, all interrelationships between the channel coefficients over time, frequency, and space must be taken into account. Since reference signals are only sent by certain OFDM resource elements (i.e., by certain OFDM symbols on certain subcarriers), channel estimates for resource elements that do not carry a reference signal must be calculated by interpolation.

[0036] In the LTE downlink, at least five different types of reference signals are provided: Cell-specific reference signals (often called common reference signals), UE-specific reference signals (often called demodulation reference signals, DM-RS), MBSFN-specific reference signals, which are used only for multimedia broadcast single frequency network operation; Positioning reference signals, which, from Release 9 onwards, may be embedded in specific positioning subframes for the purpose of UE position measurement; Channel State Information (CSI) reference signals, which are introduced in Release 10 specifically for downlink channel state estimation, but not for data demodulation.

[0037] UE-specific reference signals can be transmitted in addition to cell-specific reference signals and are embedded only in reference blocks where PDSCH is mapped to these UEs. When UE-specific reference signals are transmitted, UEs are expected to use the UE-specific reference signals to obtain channel estimates for demodulating the data in the corresponding PDSCH resource blocks. A typical use of UE-specific reference signals is to enable beamforming of data transmissions to a specific UE. The eNodeB can use a correlated array of physical antenna elements to generate a narrow beam in the direction of a specific UE. This narrow beam is due to the different channel responses between the eNodeB and the UE, allowing the UE to coherently demodulate the beamformed data using the UE-specific reference signals. In Release 9, UE-specific reference signals are newly designed to extend support for dual-layer transmission, which can include transmission of two spatial layers to a single UE.

[0038] In LTE-based communication systems, radio resource management (RRM) encompasses a wide range of techniques and procedures, including power control, scheduling, cell search, cell reselection, handover, radio link or connection monitoring, and connection establishment and re-establishment. Cell search in E-UTRAN (LTE) is one of the most fundamental aspects of mobility, allowing a UE to obtain carrier frequency, timing, and physical cell identity (PCI).

[0039] Furthermore, the RRM related operations undertaken by the UE can be broadly categorized into those related to the RRC-IDLE state and those related to the RRC-CONNECTED state. An overview of mobility related RRM operations in RRC IDLE and RRC CONNECTED is shown in Figures 6 and 7.

[0040] Mobility for an RRC-IDLE UE may include measuring and evaluating the serving cell, measuring neighboring cells, evaluating neighboring cells for cell reselection, obtaining system information for the target cell, and cell reselection towards the target cell. Mobility for an RRC-CONNECTED UE distinguishes between the various scenarios shown in Figure 7.

[0041] Measurements of the serving cell and any neighboring cells are typically made periodically by the UE, and may also involve the transmission of measurement reports from the UE to its serving eNB.

[0042] The UE reports measurement information according to the measurement configuration provided by the E-UTRAN and applicable to the UE in RRC_Connected state. The measurement configuration can be provided to the UE by dedicated signaling, e.g. using the RRCConnectionReconfiguration or RRCConnectionResume messages. The UE can be configured to report measurement information to the eNB to support UE mobility management. The following measurement configuration elements can be signaled via the RRCConnectionReconfiguration message:

[0043] Measurement Object: The measurement object defines what the UE should measure, such as carrier frequency. The measurement object may include a list of cells to be considered, as well as related parameters (e.g., frequency or cell-specific offsets).

[0044] Reporting configuration: The reporting configuration consists of the criteria that causes the UE to send measurement reports (periodic or event-triggered), as well as details of what information the UE is expected to report (e.g., quantities such as Received Signal Code Power (TSCP) in UMTS or Reference Signal Received Power (RSRP) in LTE).

[0045] Measurement Identification Information: These identify the measurement and define the applicable measurement targets and reporting settings.

[0046] Quantity Settings: The quantity settings define the filtering that should be used for each measurement.

[0047] Measurement Gap: A measurement gap defines a period during which no uplink or downlink transmissions are scheduled so that the UE can make measurements.

[0048] In LTE, several events A1 to A5, B1, B2 are defined for event-triggered measurement reporting, such as when the serving cell becomes better than an absolute threshold (A1), or worse than an absolute threshold (A2), or when a neighboring cell becomes better than an offset to the serving cell (A3). Events B1 and B2 are provided for inter-RAT (Radio Access Technology) mobility, where event B1 is triggered when a neighboring cell becomes better than an absolute threshold, and event B2 is triggered when the serving cell becomes worse than an absolute threshold and the neighboring cell becomes better than another absolute threshold.

[0049] E-UTRAN can influence the entry conditions by setting the values ​​of some configurable parameters used in these conditions, such as one or more of the thresholds, offsets, etc.

[0050] In addition to event-triggered reporting, the UE can be configured to perform periodic measurement reporting, in which case some of the parameters can be configured similarly to event-triggered reporting, except that the UE starts reporting immediately rather than only after the event has occurred.

[0051] In the measurement report message, the UE includes only the measurement results for a single measurement. In other words, the measurements are not combined for reporting purposes. If multiple cells trigger a report, the UE includes these cells in descending order of the value of the reporting quantity. That is, the best cell is reported first.

[0052] More detailed information can be found in the technical specification "Electronics for the Electronics and Information Processing System," IEEE Transactions on Electronics, Information and Communications Technology Vol.

[0053] 5G NR - Synchronization Signals, Reference Signals and RRM Measurements 5G NR communication systems are also expected to require synchronization and reference signals, but these signals must be designed to enable UEs and gNBs to meet the diverse requirements imposed by the new 5G NR technology.

[0054] Because at least the data channel must be beamformed to achieve the high data rates required for new 5G wireless technology systems, NR beamforming is expected to be widely used at higher frequencies. Therefore, to enable a UE in an RRC CONNECTED state to detect a reference signal for RRM measurements while receiving a beamformed data channel, the reference signal can also be beamformed so that its signal strength and that of the data channel are within the dynamic range of the UE receiver. Furthermore, in high-frequency deployments relying on beamforming, the SINR (signal-to-interference-and-noise power ratio) can degrade significantly very quickly due to, for example, beam obstruction, shadowing, etc. Therefore, robust mobility procedures require synchronization and / or reference signals for measurements that should be available at least more frequently for UEs in RRC CONNECTED mode than for UEs in RRC IDLE mode.

[0055] So far, with respect to 5G NR communication systems, it has been discussed that for RRM measurements of (Layer 3) mobility, always-on reference signals that should also provide substantially omnidirectional coverage are used, at least for UEs in the RRC IDLE state. Omnidirectionality of reference signals can be achieved by using an omnidirectional transmission pattern that spreads simultaneously in all directions of the radio cell. Alternatively, omnidirectionality of reference signals can also be achieved by using a beam transmission pattern that substantially covers only a specific direction (area) of the radio cell, but in this case the beam is "swept" across the entire radio cell and omnidirectionality is achieved within a specific period of time required for this sweeping process to reach the initial direction.

[0056] Meanwhile, for UEs in the RRC CONNECTED state, the possibility of using one or more additional reference signals, possibly transmitted in a beam-like manner, is currently being discussed. The additional reference signals for 5G NR could be similar to the CSI reference signals already defined for LET (see the discussion above) and / or could include further reference signals designed separately from the CSI reference signals. The flexible use of additional and / or further reference signals in RRC CONNECTED UEs makes it possible to meet the above requirements while simultaneously controlling and limiting system overhead and delay. Specifically, performing RRM measurements based on additional reference signals has proven more accurate and can therefore reduce handover delays. One reason could be that the additional reference signals are emitted from the same beam as the data transmission and / or are transmitted over a wide spectrum.

[0057] The reference signals currently considered as RRC IDLE may be the same as or similar to the synchronization signals or cell-specific reference signals used in LTE, i.e., PSS and / or SSS, as briefly discussed above. For example, NR IDLE reference signals can be transmitted omnidirectionally, unlike any additional NR CONNECTED reference signals, which can be beamformed (like data channels). NR IDLE reference signals can be transmitted more sparsely compared to NR CONNECTED reference signals. Furthermore, NR CONNECTED reference signals can be turned on / off and / or be configurable.

[0058] In summary, in the following, it is exemplarily assumed that, for a 5G NR communication system, an omnidirectional reference signal (similar to LTE PSS and SSS, which may also be referred to as a synchronization signal in light of possible implementations) is used for RRM measurements by a UE in RRC IDLE state (hereinafter referred to as an NR IDLE reference signal for ease of reference). For further convenience, it is further exemplarily assumed in the following that at least one additional beamformed reference signal in NR (possibly similar to an LTE CSI-RS) is used for RRM measurements by a UE in RRC CONNECTED state (hereinafter referred to as an NR Connected reference signal for ease of reference).

[0059] Furthermore, adaptive resource allocation can be foreseen for additional reference signals to obtain maximum benefit and comply with design requirements for reference signals. For example, additional references can be switched off by the gNB, e.g., when there are no UEs in RRC_CONNECTED state being served within the served area of ​​the beam. In addition, the resources used to transmit additional reference signals do not need to be fixed but can change dynamically. This is different from, for example, synchronization signals (PSS, SSS) known from LTE, where the locations of PSS and SSS within the configured frequency carriers are known to the UE. The network may provide some configuration information (e.g., time and / or frequency indication) to the UE so that the UE knows where the additional NR reference signals will be transmitted.

[0060] It should be noted that 3GPP standardization of new 5G wireless technologies is ongoing, and the terminology of layers and entities assumed above may change during the standardization process without affecting the functionality of embodiments of the present invention.

[0061] As explained in the above sections, 5G cellular systems are currently discussing how to design reference signals within radio cells for UE mobility purposes in RRC connected and RRC idle states. At least two different reference signals, the NR idle reference signal and the NR connection reference signal, are to be used for RRM measurement purposes within radio cells. Unlike the NR idle reference signal, the NR connection reference signal is unlikely to be transmitted omnidirectionally and, furthermore, is not always on (e.g., it could be switched off to save energy or reduce interference). However, this can lead to the following problems:

[0062] The following scenario is assumed to illustrate this problem in conjunction with Figures 8-11: A UE is currently served by a gNB (serving gNB) and is located at the edge of the serving gNB's radio cell. The UE can receive reference signals transmitted from the serving gNB, such as an exemplary NR connection reference signal (illustrated as a beam) and an NR idle reference signal (not shown separately, covering the radio cell).

[0063] 8, the neighboring gNB is not transmitting an NR connection reference signal, e.g., has already been switched off to save power, considering that there are no RRC connected UEs served by the beam (or corresponding data beam) from the neighboring gNB. As a result, the UE cannot receive the NR connection reference signal and must perform neighbor cell measurements based only on the NR idle reference signal, which the neighboring gNB is assumed to always transmit.

[0064] Another problem may be that one or more NR connection reference signals are indeed transmitted by neighboring gNBs. Figure 9 exemplarily shows one beam representing one NR connection reference signal. However, none of the NR connection reference signal beams are directed toward the UE's position, so the UE still cannot receive additional reference signals to improve measurements made on neighboring cells.

[0065] In another problematic scenario, as shown in Figure 10, there is indeed an NR connection reference signal transmitted from a neighboring gNB that reaches the UE. However, the UE is still unable to receive the additional reference signal because it does not know the radio resource used by the neighboring gNB to transmit this additional reference signal beam. This scenario assumes that the time-frequency radio resource used for the transmitted NR connection reference signal is dynamically or semi-dynamically selected by the neighboring gNB.

[0066] In either case, as will be briefly explained in connection with FIG. 11, there may be many situations in which a UE is unable to receive additional reference signals of neighboring cells (NR connection reference cells) and therefore is unable to utilize the additional reference signals for its measurements made to neighboring cells, for example as part of a mobility (handover) procedure.

[0067] Specifically, FIG. 11 illustrates two radio cells of two gNBs (gNB1 and gNB2) with respective cell coverage of NR connection reference signals (shown as beams C1B1, ... C2B3) and NR idle reference signals (shown as omnidirectional and oval). Furthermore, it is assumed that beam C2B1 is switched off (dashed beam). A UE is located in the overlap region of the two radio cells at time t1 and therefore receives the NR idle reference signal C1 of gNB1, the NR idle reference signal C2 of gNB2, and the NR connection reference signal C1B3 of gNB1. Accordingly, the UE can perform cell measurements for both radio cells, but the measurements of the radio cell of gNB2 are based only on the NR idle reference signal C2 because the NR connection reference signal C2B1 is switched off.

[0068] Note that 3GPP considers mobility requirements such that the gNB (making the handover decision) should only compare measurements made based on the same type of reference signal, meaning that the serving gNB1 may not be allowed to compare measurements made on C2 with measurements made on C1B3. Given the low accuracy of measurements based only on NR idle reference signals, the gNB1 may not be able to make a proper handover decision.

[0069] For example, at t1, gNB1 may decide not to handover, assuming that the measurements performed by the UE for C1 and C2 are substantially the same and that the measurement performed for C1B3 is higher than the non-existent measurement (=0) for C2B1. Assuming that the UE moves further toward gNB2 and leaves the coverage area of ​​gNB1, at time t2, the measurement performed based on C2 becomes better (e.g., has better signal quality) than the measurement performed based on C1. Meanwhile, at t2, the measurement result for C1B3 is still higher than the measurement result for C2B1. Therefore, it is unclear how gNB1 makes a handover decision. gNB1 may decide to trigger a handover of the UE to gNB2's radio cell, in which case gNB2 will switch on C2B1 (because there is an RRC connected UE) and eventually serve the UE using the beam of C2B1 at a later time t3. Therefore, there will be a delay in the handover and the UE may also experience a degradation in QoS between t1 and t3. Conversely, if NB1 still decides not to handover, the signal strength from gNB1 will decrease so much that the UE will eventually have to declare a radio link failure.

[0070] Accordingly, the present disclosure provides a solution that tends to overcome one or more of the disadvantages and / or meets one or more of the above-mentioned requirements.

[0071] Detailed Description of the Disclosure The following describes UEs, base stations, and procedures for new radio access technologies considered in 5G mobile communication systems. Various embodiments and variations are also described. The following detailed disclosure will be facilitated by, and may be based at least in part on, the discussion and insights set forth in the "Basis of the Disclosure" section above.

[0072] However, it should be noted that, in general, very little is actually agreed upon regarding 5G cellular communication systems, and therefore, many assumptions must be made below to clearly explain the principles underlying the present disclosure. However, these assumptions should be understood as merely examples that should not limit the scope of the present disclosure. Those skilled in the art will recognize that the principles disclosed below and presented in the claims can be applied to various scenarios and in ways not explicitly stated herein.

[0073] Furthermore, although the specific terminology to be used in the context of the new radio access technology of the upcoming 3GPP 5G communication system has not yet been fully determined, the terminology used below is closely related to the terminology used in the LTE / LTE-A system or in the current considerations of 3GPP 5G. Therefore, those skilled in the art will appreciate that the scope of the present invention and its protection should not be limited to the specific terminology illustratively used herein due to the lack of newer or finally agreed-upon terminology, but should be more broadly understood in terms of the functions and concepts underlying the functions and principles of the present disclosure.

[0074] For example, a mobile station, or mobile node, or user terminal, or user equipment (UE) is a physical entity in a communication network. A node may have several functional entities. A functional entity refers to a software or hardware module that implements and / or provides a set of predetermined functions to other functional entities of the node or the network. A node may have one or more interfaces that connect the node to intervening communication facilities or media over which the node can communicate. Similarly, a network entity may have logical interfaces that connect a functional entity to intervening communication facilities or media over which it can communicate with other functional entities or correspondent nodes.

[0075] As used herein, the term "base station" or "radio base station" refers to a physical entity in a communication network. The physical entity performs several control tasks, including one or more scheduling and configuration tasks, for communication devices. It should be noted that base station functions and communication device functions can also be integrated into a single device. For example, a mobile terminal can also implement the functions of a base station for other terminals. The term used in LTE is eNB (or eNodeB), while the term currently used for 5G NR is gNB.

[0076] The term "omni-directional reference signal" refers to a reference signal that has practically omnidirectional coverage; this signal can also be obtained by using a "sweeping" beam, which covers different areas at different times but covers the entire area of ​​the radio cell after each full sweep. Omnidirectionality should thus be understood in contrast to "beamformed", in that the beam only covers a limited (possibly narrow), non-circular area of ​​the radio cell. Accordingly, the term "beamformed reference signal" refers to a reference signal that is transmitted (from a gNB) within a limited (possibly narrow), non-circular area of ​​the radio cell and therefore intentionally does not cover the complete radio cell coverage.

[0077] 12 shows a general, simplified, exemplary block diagram of a user equipment (also referred to as a communication device) and a scheduling device (here assumed to be located in a base station, e.g., an LTE eNB or a 5G NR gNB). The UE and the eNB / gNB communicate with each other via a (radio) physical channel using their respective transceivers.

[0078] A communication device may include a transceiver and a processing circuit. The transceiver may then include a receiver and a transmitter. The processing circuit may be one or more pieces of hardware, such as one or more processors or any LSI. Between the transceiver and the processing circuit, there is an input / output point (or node), through which the processing circuit can control the transceiver in operation, i.e., control the receiver and / or transmitter, and exchange receive / transmit data. The transceiver may include an RF (radio frequency) front, including one or more antennas, amplifiers, RF modulators / demodulators, etc. The processing circuit may perform control tasks, such as controlling the transceiver to transmit user data and control data provided by the processing circuit and / or to receive user data and control data that are further processed by the processing circuit. The processing circuit may also be responsible for performing processes, such as judging, determining, calculating, measuring, etc. The transmitter may be responsible for performing transmission processing. The receiver may be responsible for receiving processing.

[0079] A simple exemplary scenario is assumed below based on the previously discussed FIG. 11, in which a UE, here connected to its serving gNB1, is moving within the corresponding radio cell, eventually reaching the overlapping coverage area of ​​another neighboring radio cell (here gNB2). The UE is configured to perform several cell measurements, e.g., for the current gNB1 radio cell, but also for neighboring cells, such as neighboring radio cells of gNB2, if applicable. One exemplary option is to reuse the LTE procedures for configuring the cell measurements to be performed by the UE, as briefly described above. Accordingly, gNB1 can configure the UE using a measurement control message (e.g., as part of an RRCConnectionReconfiguration message) containing various elements, such as measurement object, reporting configuration, measurement identity, quantity configuration, measurement gap, etc.

[0080] For example, the UE can be configured to perform cell measurements on NR idle reference signals and, if available, on NR connection reference signals. In one exemplary implementation, separate measurements are performed for each reference signal, e.g., by configuring separate measurement objects.

[0081] According to one exemplary embodiment, to receive dynamically assigned NR connection reference signals transmitted from gNB1, the UE can be equipped with appropriate information about the NR connection reference signals so that the UE knows where the reference signals are transmitted and how they are received. There are various possible implementations of dynamically assigned NR connection reference signals. For example, NR connection reference signals can be dynamically transmitted over separate radio resources in the frequency and time domains. On the other hand, NR connection reference signals can be transmitted at fixed time instances or at specific frequencies known to the UE in advance. The periodicity and duration of NR connection reference signal transmissions can be variable or fixed.

[0082] The particular implementation selected for dynamically allocating NR connection reference signals determines how much information needs to be provided to the UE to enable it to receive NR connection reference signals transmitted from gNB1. Invariant parameters (e.g., time, frequency, periodicity, etc.) can be known to the UE when the UE connects to a cell, e.g., from initial configuration by gNB1, or from the UE's program code (e.g., fixed by 3GPP specifications), or other suitable mechanisms. Conversely, dynamically changing parameters need to be provided to the UE in a timely and appropriate manner.

[0083] As can be seen from the exemplary scenario in Figure 11, it is assumed that gNB1 transmits an NR idle reference signal (C1) omnidirectionally, thereby covering substantially the entire serving radio cell area. Furthermore, as shown in Figure 11, beamformed NR connection reference signals (C1B1, C1B2, C1B3) are transmitted from gNB1. Therefore, a UE located in the area of ​​beam C1B3 can make cell measurements for the serving radio cell based on the NR idle reference signal C1 as well as the NR connection reference signal C1B3.

[0084] Furthermore, gNB2 also transmits its own NR idle reference signal omnidirectionally (C2) and beamformed NR connection reference signals (C2B2, C2B3). The third NR connection reference signal (C2B1) is now switched off and therefore not transmitted from gNB2. Therefore, cell measurements made by the UE on neighboring radio cells of gNB2 use only the NR idle reference signal transmitted from gNB2, since the other beams C2B2, C2B3 are not available at the UE's location.

[0085] The UE is configured to prepare and send measurement reports to the serving gNB1. Measurement reports can be triggered, for example, periodically or based on specific preconfigured events. Some events that trigger measurements have already been presented in connection with the LTE measurement reporting procedure above. Some or all of these LTE events A1-A5, B1, and B2 can be reused for the 5G NR measurement reporting procedure. Alternatively, or in addition, other events may be defined to trigger measurement reports, for example, in connection with additional reference signals, such as NR connection reference signals. For example, separate events can be defined for NR connection reference signals and NR idle reference signals.

[0086] According to an embodiment of the improved measurement reporting procedure, the measurement report prepared and provided by the UE may also provide information on whether the accompanying measurement result was calculated based on NR idle reference signals and / or NR connection reference signals. For example, for each measurement result, apart from providing the actual metric value (e.g., RSRP value and / or RSRQ value), possibly the cell ID of the measurement cell (e.g., a neighbor cell, which may not include the cell ID of the serving cell), and possibly the corresponding measurement ID, the measurement report may present a flag to indicate the basis of the calculation, i.e., whether the result was calculated based on NR idle reference signals or NR connection reference signals. In one exemplary embodiment, a measurement flag MF=0 may mean that the accompanying measurement result was calculated based only on NR idle reference signals, whereas a measurement flag MF=1 conversely means that the accompanying measurement result was calculated based on NR connection reference signals.

[0087] Another improvement to the measurement reporting procedure eliminates the need to use a measurement flag, thus avoiding the overhead caused by said flag. Instead, the serving gNB configures the measurements to be performed by the UE so that measurements based on NR idle reference signals can be distinguished from measurements based on NR connection reference signals. For example, the serving gNB defines one measurement object with a specific measurement (object) ID for measuring neighboring cells based on NR idle reference signals, while defining another measurement object with a different measurement (object) ID for measuring neighboring cells based on NR connection reference signals. This can be achieved, for example, by using a corresponding flag to distinguish between the two measurement bases in a measurement control message for each (or several) measurement object sent to the UE. Thus, the UE performs cell measurements according to the indicated measurement configuration and then prepares a measurement report including the results of the measurements accordingly. The measurement report may also include a measurement result ID for each measurement result, so that when the serving gNB1 receives the measurement report, it can determine the association between the received measurement result ID and the configured measurement target ID and, from that association, deduce whether the measurement result was obtained based on an NR idle reference signal or an NR connection reference signal.

[0088] Another embodiment of the improved measurement reporting procedure is for the serving gNB to configure the reporting to be performed by the UE so that reports based on NR idle reference signals can be distinguished from reports based on NR connection reference signals. For example, the serving gNB defines one reporting configuration with a specific configuration ID for reporting measurements based on NR idle reference signals, while defining another reporting configuration with a different configuration ID for reporting neighbor cells based on NR connection reference signals. This can be achieved, for example, by using a corresponding flag to distinguish between the two measurement bases in the measurement control message for each (or several) reporting configuration sent to the UE. Thus, the UE performs measurement reporting according to the indicated reporting configuration and then prepares a measurement report including the results of the measurement accordingly. The measurement report can also include a measurement result ID for each measurement result, so that when the serving gNB receives a measurement report, it can identify the association between the received measurement result ID and the configured reporting configuration ID and deduce from the association whether the measurement result was obtained based on NR idle reference signals or NR connection reference signals.

[0089] Using this improved measurement reporting procedure, the serving gNB can distinguish the measurement basis of measurements made by the UE, i.e., whether the UE measured based on NR idle reference signals or NR connection reference signals. This information can be used by the gNB1, for example, to be able to compare reference signal measurements of the same type, since this comparison is important because making handover decisions based on comparisons of reference signals of the same type is more accurate and therefore more favorable to the user equipment.

[0090] In order to improve the cell measurement procedure, another advantageous embodiment of inter-gNB coordination (here exemplarily between serving gNB1 and gNB2) is described below, which makes it particularly easy to overcome the problems already identified. The following embodiment of inter-gNB coordination naturally provides the UE with the opportunity to receive NR connection reference signals of neighboring cells, provided that the neighboring cells indeed decide to support the transmission of NR connection reference signals to the UE.

[0091] In general, inter-gNB coordination can be initiated by the UE, the serving gNB, and / or the neighboring gNB, as presented separately below. First, we will discuss inter-gNB coordination initiated by the serving gNB and the UE, because this inter-gNB coordination occupies most of the processing compared to neighboring gNB-initiated inter-gNB coordination.

[0092] At some point, the serving gNB determines that the UE is not being provided with an NR connection reference signal that has left a neighboring cell, which can be detrimental to measurement accuracy and can lead to one or more of the problems already discussed above. Furthermore, the absence of an NR connection reference signal from a neighboring gNB in ​​the area in which the UE is located can also be an indication that the neighboring gNB is already heavily loaded (and therefore trying to save energy where possible) and is unwilling or unable to provide (data) coverage to another UE.

[0093] Now that the source of this potential problem is known, the serving gNB can decide to request a neighboring gNB to provide the missing NR connection reference signal to the UE. As a result, the serving gNB sends a reference signal request to the neighboring gNB, requesting that it provide an NR connection reference signal to the UE. This request message may include, for example, cell identities of neighboring cells of the neighboring gNB. In addition, this request message may also optionally include user equipment mobility information to enable the neighboring gNB to determine the UE's location. There are various implementations of what this mobility information (sometimes referred to as location information) includes. In one embodiment, the UE's location is represented by its GPS (Global Positioning System) coordinates, which can be obtained from the UE.

[0094] Another implementation of the UE location information uses the LTE Positioning Protocol (LPP), which allows the gNB1 to determine the location of the UE. In this way, the gNB1 can also use the LPP protocol to obtain GPS coordinates from, for example, an Evolved-Serving Mobile Location Center connected to the UE. A detailed definition of LPP can be found in Non-Patent Document 20, which is incorporated herein by reference, and Non-Patent Document 21, which is incorporated herein by reference.

[0095] Another implementation of the UE location information in the reference signal request message is based on measurements obtained by the UE. Specifically, the serving gNB can estimate from measurements where the UE is located. For example, this can be done by comparing measurements performed by the UE for several cells, thereby determining relevant RSRP information. While less accurate than GPS coordinates, such location information may be sufficient to allow neighboring UEs to determine whether to provide the UE with the requested NR connection reference signal.

[0096] In yet another implementation of the UE location information in the reference signal request message, the gNB can simply put the measurement report (part or all of it) into the reference signal request message, in which case neighboring gNBs may have to derive the UE location from the measurement results, if necessary or relevant, in the same or similar manner as detailed for gNB1 in the previous embodiment.

[0097] The following table shows an exemplary embodiment of a reference signal request message.

[0098] [Table 1]

[0099] The neighboring gNB can then decide whether to provide an NR connection reference signal to the UE after receiving a reference signal request message from the UE's serving gNB. This decision by the neighboring gNB can take into account various different considerations. For example, the neighboring gNB may already be serving too many UEs or may already have limited power output, so in either case the neighboring gNB may decide not to provide an NR connection reference signal to the UE (and would later have to reject a possible handover request from the serving gNB anyway). On the other hand, the neighboring gNB can also take into account the UE's location information when deciding whether to provide an NR connection reference signal to the UE. For example, it can be exemplarily assumed that an NR connection reference signal is already being transmitted from neighboring gNB2, but in a direction different from the direction in which the UE is located. In this case, instead of transmitting an additional beam for the NR connection reference signal, it may be sufficient to simply change the direction of an already available beam for the NR connection reference signal so that the NR connection reference signal can reach the UE's location. In this case, the neighboring gNB2 can decide to provide the UE with an NR connection reference signal, since it does not need to consume extra power and the change in beam direction can even be limited to a specific period of time.

[0100] According to another scenario, neighboring gNBs may also take into account the interference that may be caused within a radio cell by transmitting one or more beams of NR connection reference signals.

[0101] As just described, a neighboring gNB can decide whether to provide an NR connection reference signal to the UE. However, in either case, the neighboring gNB can respond to the received reference signal request from the serving gNB1 by providing appropriate information about the transmission of the requested NR connection reference signal. The content of this reference signal request response message depends on the result of the decision to provide or not provide an NR connection reference signal to the UE.

[0102] If the neighboring gNB2 decides not to provide the UE with NR connection reference signals, the response message may simply include an information element corresponding to the denial of the request. Optionally, the serving gNB may then inform the UE of this denial so that the UE can continue to perform measurements solely based on NR idle reference signals and thus avoid attempting to measure unavailable NR connection reference signals. Furthermore, in this case, the UE no longer initiates inter-gNB coordination, since inter-gNB coordination has already been rejected. Optionally, the UE may even stop measuring the NR connection reference signals of the serving cell, since meaningful measurement comparisons are not possible if no NR connection reference signals are transmitted to other neighboring cells.

[0103] The response message may include the cell ID of the neighboring cell so that the serving gNB can determine which radio cell (and which request) the response relates to.

[0104] On the other hand, if the neighboring gNB2 decides to provide the UE with an NR connection reference signal, the reference signal response message may include a confirmation of the request and, if necessary or advantageous, may also include other information related to the requested NR connection reference signal.

[0105] For example, the reference request response may include scheduling information for NR connection reference signals to be transferred to the UE, thereby enabling the UE to receive the NR connection reference signals. The scheduling information may indicate frequency and / or time domain radio resources used by the neighboring gNB2 to transmit the requested NR connection reference signals. However, all or part of the scheduling information may not necessarily be included in the reference request response message. For example, the frequency and / or time of the radio resources may be fixed in the 3GPP standard or may already be known to the UE or gNB1 from a previous information exchange, obviating the need for further exchange of scheduling information. In response to a previous reference signal request message for the same or another UE, the gNB2 may have already provided the gNB1 with scheduling information for the requested NR connection reference signals. Therefore, the presence of scheduling information in the reference signal response message is optional.

[0106] Furthermore, according to another exemplary embodiment, even if gNB2 decides to provide the UE with an NR connection reference signal as requested, it may separately decide to limit the duration for which the NR connection reference signal is provided to the UE. This limitation may be done to still save energy and / or reduce interference while simultaneously still providing the UE with an opportunity to make accurate measurements of neighboring cells. After the duration has elapsed, the neighboring gNB may switch off or revert the beamformed NR connection reference signal. In this case, gNB2 may or may not include corresponding duration information in the reference signal request response message, which then (after being forwarded to gNB1 and the UE) allows gNB1 and the UE to know during which period extended measurements may be made using the NR connection reference signal.

[0107] Additionally or alternatively, gNB2 can decide to transmit NR connection reference signals to the UE with a certain periodicity rather than always. Again, such transmission may be advantageous for gNB2, for example, to save energy and / or reduce interference. In such cases, gNB2 may or may not include corresponding periodicity information in the reference signal request response message, which then (after being forwarded to gNB1 and the UE) allows gNB1 and the UE to know with which periodicity NR connection reference signals are transmitted from gNB2.

[0108] The following table shows a specific exemplary implementation of this reference signal request response message:

[0109] [Table 2]

[0110] The TRPs mentioned above represent transmission / reception points and are used in the art to delimit beams (or beamformed transmissions). Therefore, the above exemplary response signal includes a list of beams transmitted from gNB2 (identified by the associated cell ID) in neighboring cells, each including a beam index number as a mandatory information element, and scheduling, duration, and periodicity information as optional information elements.

[0111] As described above, when gNB2 decides to provide an NR connection reference signal to the UE, it can decide whether to establish a new beam for transmitting the NR connection reference signal to the UE or to change the direction and / or transmission power of another beam used for an already transmitted NR connection reference signal so that it can reach the UE.

[0112] The serving gNB1 is notified accordingly using a reference signal request response message as discussed above. The serving gNB1 can then notify the UE by sending a notification message to the UE, including information about the requested NR connection reference signal. The content of this notification message may vary substantially based on the implementation and assumed scenario. Sending a notification message may even be unnecessary in scenarios where the UE can receive the requested NR connection reference signal without further information after the signal becomes available at a neighboring gNB (e.g., is switched on or the beam of an already available NR connection reference signal is re-directed to the UE).

[0113] On the other hand, the notification message may contain the necessary scheduling information (in the frequency and / or time domain), and / or duration information, and / or periodicity information, all of which may be necessary for the UE to be able to properly receive and process the requested NR connection reference signals.

[0114] One exemplary embodiment of this notification message sent from the serving gNB to the UE is an RRCConnectionReconfiguration message used by the serving base station to provide the UE with new measurement configurations, possibly including necessary information about requested NR connection reference signals. For example, new measurement objects can be defined for new NR connection reference signals, or previously defined measurement objects can be adapted accordingly. The new or adapted measurement objects can then indicate how to perform measurements involving NR connection reference signals.

[0115] Alternatively, the notification message can also be implemented in the form of a MAC Control element or a control signal at the PHY layer.

[0116] In either case, the UE should be able to receive the requested NR connection reference signals. In response, the UE performs cell measurements on neighboring cells using the NR connection reference signals, thereby improving the accuracy of the measurement results, which are then provided to the serving radio base station as measurement reports that can then be used by the gNB2, for example, to make a decision on whether or not to handover the UE to the neighboring cell. Thus, the problems during the handover procedure described above in connection with FIG. 11 are mitigated in view of the availability of improved measurements for the NR connection reference signals.

[0117] This improved inter-gNB coordination according to one of the various embodiments described above can mitigate the problems resulting from using NR connection reference signals. NR connection reference signals have unique characteristics, such as their limited coverage area (in the form of a beam), not always being on (because they can be switched off), and the ability to be dynamically or semi-dynamically scheduled (e.g., frequency and / or time radio resources may change). These unique characteristics of this additional reference signal for RRC-connected UEs provide various advantages described above, such as improved adaptability, potential energy savings, and potential interference mitigation. The use of improved inter-gNB coordination can maintain these advantages of using NR connection reference signals with such characteristics while allowing UEs to fully utilize NR connection reference signals to improve measurement accuracy.

[0118] It has been briefly described above that at some point the serving gNB determines that the user equipment is not provided with NR connection reference signals from a neighboring cell, which may be detrimental to measurement accuracy and may lead to one or more of the problems already discussed above. As described below, conceptually, there are at least two different solutions for how the serving gNB determines that the user equipment is not provided with NR connection reference signals. According to one solution, this determination is made by the gNB1 based on measurement reports received from the UE (serving gNB-initiated inter-gNB coordination). According to a second solution, the UE first determines that it is not receiving NR connection reference signals and therefore initiates inter-gNB coordination itself by triggering the gNB1, as described below.

[0119] For serving gNB-initiated inter-eNodeB coordination, the serving gNB receives a measurement report from the UE, e.g., using the improved measurement report format, as described above. The serving gNB then analyzes the content of the measurement report, particularly the results of measurements made by the UE on neighboring cells. As described above, the improved measurement report may include information (e.g., a flag or measurement ID) that allows the serving gNB to distinguish which measurements were made on NR idle reference signals and which measurements were made on NR connection reference signals. For example, if the serving gNB determines that the UE made measurements on neighboring cells based only on NR idle reference signals and not on NR connection reference signals, the serving gNB may decide to initiate inter-gNB coordination to request the neighboring cells to also provide NR connection reference signals to the UE.

[0120] In a more specific exemplary embodiment, one or more specific events are defined that may trigger the serving gNB to initiate the inter-gNB coordination described above. For example, one event may be that the UE has not reported measurements of NR connection reference signals of a particular neighboring cell for a long period of time. Another event may be that the UE has not reported measurements of NR connection reference signals of a particular neighboring cell and the link quality between the UE and the serving gNB has deteriorated below a certain threshold. Another exemplary event may be that the UE has not reported measurements of NR connection reference signals of a particular neighboring cell and the UE mobility (e.g., movement speed) exceeds a certain threshold.

[0121] With regard to UE-initiated inter-gNB coordination, the UE determines that it has not received an NR connection reference signal of a neighboring cell and therefore initiates inter-gNB coordination to request a neighboring gNB to provide an NR connection reference signal to the UE. For example, the UE receives an NR idle reference signal and therefore knows that it is within the coverage of a neighboring radio cell, but also notices that it has not received the corresponding NR connection reference signal of this neighboring radio cell. If the UE wants to improve measurement accuracy based on the NR connection reference signal, the UE can decide to send a corresponding UE-initiated reference signal request to its serving gNB, which may indicate one or more radio cells from which the UE also wants to receive NR connection reference signals. Then, upon receiving the request from the UE, the serving gNB can decide whether to further forward the request to the neighboring gNB for which the request is intended. For example, the serving gNB may already know that the neighboring gNB cannot serve another UE, or may know that the neighboring base station is actually an eNB and not a gNB. In both cases, the serving gNB may decide not to comply with the UE's request.

[0122] As described in detail above, it is exemplarily assumed that the serving gNB requests a neighboring gNB to provide an NR connection reference signal in response to a UE request, and therefore the serving gNB transmits a reference signal request to the neighboring cell.

[0123] To summarize the above, inter-gNB coordination can be initiated by the UE or the serving gNB. Corresponding exemplary simplified implementations of such a solution are shown in Figures 13 and 14, respectively, and are described in summary below.

[0124] FIG. 13, which illustrates message exchanges between the UE and gNB1 and gNB2, pertains to inter-gNB coordination initiated by the serving gNB (see box "Request NR Connection RS from gNB2"). As shown in FIG. 13, it is exemplarily assumed that the UE is initially configured to perform measurements (see arrow "Measurement Control"). Following the scenario assumed in FIG. 11, it is assumed that the serving gNB1 transmits NR idle reference signals as well as NR connection reference signals, both of which are received by the UE (see dashed arrows). Meanwhile, the neighboring gNB2 transmits NR idle reference signals (see dashed arrows) but not NR connection reference signals to the UE. Following the initially configured measurement configuration, the UE eventually provides a measurement report to the serving gNB1, from which the serving gNB1 can determine that the NR connection reference signals of the neighboring gNB2 are not received by the UE (see above for details). Thus, the serving gNB1 can decide to request the neighboring gNB2 to provide the UE with an NR connection reference signal by sending a corresponding request (see arrow "NR Connection RS Request"). The neighboring gNB2 can then decide whether to provide the UE with an NR connection reference signal. According to the decision made in gNB2, a corresponding response message is then sent back from gNB2 to gNB1. In FIG. 13, it is further assumed that the neighboring gNB2 does indeed accept to provide the UE with an NR connection reference signal and accordingly transmits an NR connection reference signal to the UE, as indicated by the dashed arrow. The serving gNB1 can inform the UE about the result of the request, for example, by sending another measurement control message (e.g., to provide scheduling information for the NR connection reference signal).

[0125] The UE then proceeds to perform cell measurements, also based on the newly provided NR connection reference signals, and can provide the measurement results as a measurement report to the serving gNB1. The measurement results can then be used by the serving gNB1 to decide whether to handover the UE to a neighboring cell, in which case a corresponding handover request can be sent to the neighboring gNB2 in an appropriate manner (e.g., known from LTE). Since the subsequent steps are not particularly relevant to the ideas and embodiments presented in this application, Figure 13 ends with the transmission of the handover request message. The procedure can continue, for example, according to a typical handover procedure in LTE described in connection with Figure 5.

[0126] On the other hand, Figure 14 largely corresponds to the embodiment discussed above in connection with Figure 13 with respect to UE-initiated inter-gNB coordination. As can be seen by comparing Figures 13 and 14, the main difference is that the UE (rather than the serving gNB1) decides at some point to request gNB2 to provide the UE with an NR connection reference signal (see box "Request NR Connection RS from gNB2") and therefore sends a UE-initiated NR connection reference signal request (see arrow "UE NR Connection RS Request") to the serving gNB1. Then, as exemplarily assumed in Figure 14, the serving gNB1 decides to comply with the UE's request and sends an NR connection reference signal request to the neighboring gNB2. The remaining steps in Figure 14 are the same or similar to those described above in connection with Figure 13.

[0127] 14 can be implemented in various ways, and a basic example solution could simply include the cell IDs of neighboring cells (e.g., obtained from NR idle reference signals) to identify the cells from which the UE wants to receive NR connection reference signals. Furthermore, the UE-initiated reference signal request could also include various cell IDs in case the UE wants to request NR connection reference signal transmissions from various neighboring cells.

[0128] In an exemplary solution, the UE may use a MAC Control element as a UE-initiated reference signal request message. A unique LCID value (e.g., a non-reserved LCID value, e.g., 01100) known to both the UE and the gNB1 identifies the MAC Control element as a UE-initiated reference signal request. As already mentioned with respect to the basic solution, the MAC Control element may contain information that allows the gNB1 to identify the cell or cells for which the reference signal request is indicated. One solution for cell identification could be to carry the cell ID directly in the MAC Control element, but this may significantly increase the size of the MAC Control element, especially if the reference signal request refers to several radio cells.

[0129] Another solution for cell identification can be to provide a cell bitmap, which, together with the measurement report, allows the gNB1 to identify the radio cell for which the request is indicated. Thus, the size of the MAC Control element can be significantly reduced. Specifically, a 7-bit bitmap, for example, is provided in the MAC Control element, with each bit associated with a specific measurement result in the measurement report. The measurement report then includes, for the measurement results of neighboring cells, the cell IDs of these neighboring cells as well, so that the bitmap identifies the measurement results (and thus the radio cells and their IDs) for which the UE requests the transmission of NR connection reference signals. The UE must ensure that the cell bitmap in the MAC Control element properly indicates the measurement results in the measurement report associated with the radio cell for which the UE requests the transmission of NR connection reference signals.

[0130] An exemplary MAC Control element is shown in Figure 15, which shows a 7-bit C1 to C7 cell bitmap in the second octet, which can be used to indicate to which of the neighboring cells whose measurement results are included in the measurement report a reference signal request should be sent (by setting the respective bit to, for example, 1).

[0131] In another exemplary solution, the UE can use a PDCP control PDU as a UE-initiated reference signal request message. A unique PDU type value (one of the non-reserved PDU type values, e.g., 100) known to both the UE and the gNB1 identifies the PDCP control PDU as a UE-initiated reference signal request message. As discussed in detail for the MAC Control element solution, the PDCP control PDU can contain information that enables the gNB1 to identify one or more cells for which a reference signal request is indicated. The two solutions discussed in detail above for cell identification in the MAC Control element can be applied to PDCP control PDUs as well.

[0132] An exemplary PDCP control PDU is shown in Figure 16. As already explained in connection with Figure 15, a 7-bit C1 to C7 cell bitmap is exemplarily assumed for the purpose of identifying radio cells for which the UE is requesting additional transmissions of NR connection reference signals.

[0133] Instead of being initiated by either the serving gNB or the UE as described above, inter-gNB coordination may also be initiated by a neighboring gNB (here, for example, gNB2). In this case, the neighboring gNB2 informs the serving gNB1 serving the UE (and possibly other neighboring gNBs) of the transmission of NR connection reference signals in gNB2's radio cell. This may include informing the other gNBs of scheduling information, e.g., frequency and time domain radio resources, used by gNB2 to transmit NR connection reference signals. This scheduling information may be necessary to enable the UE to receive NR connection reference signals from gNB2.

[0134] As already explained with respect to the previous embodiment, other information may also be necessary for the UE to properly receive and process the NR connection reference signals. For example, the transmission of the reference signals may be limited to a particular period of time or may occur with a particular periodicity. Accordingly, duration and / or periodicity information in addition to scheduling information may also be provided to neighboring gNBs.

[0135] Even after providing the scheduling information (and possibly other information) to other gNBs, gNB2 can still decide to maintain or not maintain one or more beams for transmitting NR connection reference signals. As already explained for the previous solution, gNB2 may decide to switch off some beams to save energy and / or reduce interference within its radio cell, especially when RRC connected UEs are not located within the coverage area of ​​said beams. Alternatively, gNB2 may also decide to change the direction and / or transmission power of some beams, for example, to (temporarily) provide NR connection reference signals in another coverage area. Conversely, gNB2 may also decide to switch on some deactivated beams for NR connection reference signals at some point.

[0136] In one exemplary implementation, gNB2 may decide to send another notification message to neighboring gNBs so that they are kept updated on the state (e.g., switched off, switched on, changed direction, etc.) of the beam for transmitting NR connection reference signals from gNB2. These subsequent notification messages may be similar to the first notification message described above. In another exemplary implementation, the subsequent notification messages may be simplified by simply identifying one or more beams whose state has changed (e.g., now switched off or on, or changed direction). For this purpose, the various beams for transmitting NR connection reference signals are each associated with a beam index to uniquely identify the beam transmitted from gNB2. The beam index may already be transmitted to other gNBs together with the scheduling information in the first notification message of the inter-gNB coordination. In that case, the subsequent notification may simply include the beam index of the beam whose activation state has been changed, allowing the receiving neighboring gNB to deduce which beam (according to the corresponding scheduling information) is no longer transmitted from gNB2 (or is unavailable again).

[0137] 17 illustrates an exemplary message exchange for inter-gNB coordination initiated by neighboring gNB2. As illustrated, it is assumed that gNB2 informs other neighboring gNBs of the transmission of NR connection reference signals. This may occur, for example, when starting the transmission of NR connection reference signals for the first time. In response, gNB2 transmits a reference signal notification message to one or more neighboring gNBs (here, illustratively to gNB1). The reference signal notification message corresponds to that described above and may therefore include a cell ID and, optionally, scheduling information for the NR connection reference signals.

[0138] When a neighboring gNB receives a notification message from gNB2, it may optionally acknowledge receipt of the notification message by returning a receipt acknowledgement message to gNB2, as exemplarily shown in FIG. 17.

[0139] 17 may then illustratively continue by transmitting a measurement control message to the UE, e.g., to provide the UE with information about the NR connection reference signals of gNB2. However, this measurement control message transmitted to the UE may not be necessary, e.g., if the UE is not in the vicinity of gNB2 or if the UE does not have the capability to measure the NR connection reference signals anyway.

[0140] 17 also illustrates a process for switching off an NR connection reference signal (or at least one beam thereof), which may trigger the transmission of another reference signal notification message to inform one or more neighboring gNBs of the switched-off reference signal. As explained above, in one exemplary implementation, this subsequent notification may only need to include a beam index identifying the beam being switched off. FIG. 17 illustratively assumes that the UE has not been informed of the switched-off beam, e.g., because it is not appropriate at that time.

[0141] The following table shows the content of an exemplary NR connection reference signal notification message sent from gNB2 to another neighboring gNB.

[0142] [Table 3]

[0143] As can be seen, the message contains the cell ID of the gNB2 as a mandatory element and is assumed to contain a list of beams, for each of which a beam index (TRP index number) is mandatory, and scheduling and periodicity information is provided as optional information elements.

[0144] As described in the previous solution, NR connection reference signals can be scheduled dynamically, i.e., according to changing radio resources. However, this is undesirable in the sense that the neighboring gNB-initiated inter-gNB coordination must be advantageously triggered every time the scheduling is dynamically adapted. Therefore, the neighboring gNB-initiated inter-gNB coordination described above can be advantageous especially when the scheduling information of the NR connection reference signals does not change frequently, so that the initially transmitted scheduling information remains valid for a long time.

[0145] Since the neighbor cells can be updated with valid scheduling information, the serving gNB1 knows that the NR connection reference signal beam is being transmitted from gNB2 and can therefore configure measurements to be made by the UE promptly in advance accordingly. In this regard, the serving gNB1 can send a measurement control message to the UE, for example, when the UE is close to gNB2 and / or at an earlier time, also taking into account whether the maximum number of measurement configurations for the UE has been reached.

[0146] As previously explained, the UE then performs cell measurements according to the measurement-controlled configuration and sends a measurement report to its serving gNB accordingly. The measurement report can then be used, for example, by the serving gNB to make a decision on whether to hand over the UE to a neighboring cell. As exemplarily shown in Figure 17, the serving gNB1 can initiate the handover by sending a handover request to the neighboring gNB2.

[0147] Several different solutions for improving inter-gNB coordination have been described above that differ conceptually, specifically with regard to which entity initiates inter-gNB coordination. It should be noted that although these different solutions have been described separately from each other, they can also be applied in parallel, i.e. in combination so as to obtain the maximum benefit of each solution.

[0148] For example, inter-gNB coordination initiated by a neighboring gNB can be applied to notify other gNBs in advance. Additionally, assuming, for example, that the UE does not receive gNB2's NR connection reference signal, UE-initiated inter-gNB coordination or serving-gNB-initiated inter-gNB coordination can be used to request transmission of an NR connection reference signal from gNB2. In response to the request, gNB2 can then switch on a beam to provide the NR connection reference signal to the UE or appropriately change the direction of another beam already providing the NR connection reference signal. Because the necessary scheduling information is already known to gNB1 due to the previous neighboring-gNB-initiated inter-gNB coordination, gNB2 does not need to provide such information again in response to the serving gNB. Furthermore, if the serving gNB has already provided the corresponding measurement configuration information during the neighboring-gNB-initiated inter-gNB coordination, it may no longer be necessary to appropriately configure the UE for measurements.

[0149] Similarly, inter-gNB coordination can be initiated in parallel by the UE or the serving gNB.

[0150] Another aspect According to a first aspect, there is provided a radio base station serving a user equipment in a first radio cell of a mobile communication system. The radio base station comprises a processing circuit for determining that a neighboring radio base station is not providing a beamformed reference signal to the user equipment. The neighboring radio base station controls transmission of an omnidirectional reference signal and a beamformed reference signal in its neighboring radio cell. A transmitter of the radio base station transmits a reference signal request to the neighboring radio base station. The reference signal request requests the neighboring radio base station to provide a beamformed reference signal to the user equipment. A receiver of the radio base station receives a reference signal request response from the neighboring radio base station, the reference signal request response including information about the transmission of the requested beamformed reference signal. The transmitter transmits a notification message to the user equipment, the notification message including information about the requested beamformed reference signal.

[0151] According to a second aspect provided in addition to the first aspect, the reference signal request response indicates that a neighboring radio base station will not provide the requested beamformed reference signal to the user equipment. In one optional embodiment, the notification message sent to the user equipment indicates that the requested beamformed reference signal will not be provided to the user equipment.

[0152] According to a third aspect provided in addition to the first or second aspect, the reference signal request response indicates that a neighboring radio base station provides the requested beamformed reference signal to the user equipment. In an optional embodiment, the reference signal request response further includes scheduling information for the requested beamformed reference signal. In an optional embodiment, the scheduling information identifies radio resources in the frequency domain and / or the time domain. In an optional embodiment, the notification message sent to the user equipment includes the scheduling information for the requested beamformed reference signal so that the user equipment can receive the requested beamformed reference signal.

[0153] According to a fourth aspect provided in addition to one of the first to third aspects, the reference signal request includes information for deriving a position of the user equipment. In an optional embodiment, the information for deriving the position includes global positioning system coordinates, or relative measurement results calculated from measurement reports received from the user equipment, or measurement reports received from the user equipment. In an optional embodiment, the reference signal request further includes identification information of neighboring radio cells.

[0154] According to a fifth aspect provided in addition to one of the first to fourth aspects, the reference signal request response includes a list of beams for transmitting the requested beamformed reference signal. In one optional embodiment, for each beam in the list, the reference signal request response includes: duration information about the period during which the requested beamforming reference signal is transmitted from a neighboring radio base station; and / or Contains periodicity information about the periodicity of the time at which the requested beamforming reference signals are transmitted from neighboring radio base stations.

[0155] According to a sixth aspect provided in addition to one of the first to fifth aspects, a receiver receives from a user equipment measurement results including one or more results of measurements made by the user equipment for at least neighboring radio cells. The processing circuit determines based on the received measurement report that the neighboring radio base station does not provide a beamformed reference signal to the user equipment, and decides to transmit a reference signal request to the neighboring radio base station if the one or more measurement results for the neighboring radio cell include results of measurements made by the user equipment based on an omnidirectional reference signal but do not include results of measurements made by the user equipment based on a requested beamformed reference signal. In an optional embodiment, the measurement result is associated with a flag in the measurement report indicating whether the associated measurement result was calculated based on an omnidirectional reference signal and / or a beamformed reference signal, and / or the measurement result is associated with a measurement identification information, and based on this identification information the processing circuit determines, during operation, whether the associated measurement result was calculated based on an omnidirectional reference signal and / or a beamformed reference signal.

[0156] According to a seventh aspect provided in addition to one of the first to sixth aspects, a receiver receives, from a user equipment, a user equipment-initiated reference signal request requesting a beamformed reference signal to be provided by a neighboring radio base station. A processing circuit determines, based on the received user equipment-initiated reference signal request, that the neighboring radio base station is not providing a beamformed reference signal to the user equipment. The processing circuit determines, based on the received user equipment-initiated reference signal request, to transmit the reference signal request to the neighboring radio base station.

[0157] According to an eighth aspect provided in addition to the seventh aspect, the user equipment initiated reference signal request includes information identifying neighboring radio cells, and optionally includes information identifying at least another radio cell for which a corresponding beamformed reference signal is requested. In an optional embodiment, the user equipment initiated reference signal request is a Medium Access Control (MAC) control element, the MAC control element including a pre-defined logical channel identifier identifying the user equipment initiated reference signal request. Alternatively, the user equipment initiated reference signal request is a Packet Data Convergence Protocol Control Packet Data Unit (PDCP control PDU), the PDCP control PDU including a pre-defined type identifier identifying the user equipment initiated reference signal request.

[0158] According to a ninth aspect, provided in addition to one of the first to eighth aspects, the omnidirectional reference signal is obtained by transmitting the reference signal in all directions substantially simultaneously and / or by transmitting the reference signal in the form of a beam whose direction is continuously varied in time so as to be transmitted in such an omnidirectional manner.

[0159] According to a tenth aspect provided in addition to one of the first to ninth aspects, a radio base station controls transmission of a second omnidirectional reference signal in a first radio cell and transmission of a second beamformed reference signal in the first radio cell. A receiver receives a second reference signal request from another radio base station requesting that the second beamformed reference signal be provided to another user equipment. A processing circuit determines whether to provide the second beamformed reference signal to the other user equipment. When providing the second beamformed reference signal to the other user equipment, the radio base station performs the following: switching on transmission of a second beamformed reference signal and / or changing the direction and / or transmit power of the second beamformed reference signal so that another user equipment can receive the second beamformed reference signal; transmitting scheduling information to another radio base station for the requested second beamformed reference signal, and optionally the scheduling information identifying frequency and / or time domain radio resources to be used by the radio base station for transmitting the requested second beamformed reference signal; Optionally, determining a time period during which a second beamformed reference signal should be provided to another user equipment; Do at least one of the following:

[0160] If the second beamformed reference signal is not to be provided to the other user equipment, the radio base station transmits a second reference signal request response to the other radio base station to inform the other user equipment that the radio base station will not provide the requested second beamformed reference signal to the other user equipment.

[0161] According to an eleventh aspect provided in addition to one of the first to tenth aspects, the processing circuit determines whether to hand over the user equipment to a neighboring radio base station based on a measurement report received from the user equipment, the measurement report including results of measurements made by the user equipment on neighboring radio cells, and if yes, the transmitter transmits a handover request to the neighboring radio base station.

[0162] According to a twelfth aspect, there is provided a radio base station of a mobile communication system, the radio base station controls transmission of an omnidirectional reference signal and a beamformed reference signal in a first radio cell of the radio base station, the radio base station comprises: a processing circuit for determining to transmit information about the beamformed reference signal to one or more neighboring radio base stations, and a transmitter of the radio base station transmits to the one or more neighboring radio base stations a reference signal notification message including scheduling information for the beamformed reference signal that enables identifying radio resources used by the radio base station to transmit the beamformed reference signal.

[0163] According to a thirteenth aspect provided in addition to the twelfth aspect, a transmitter transmits an omnidirectional reference signal and a beamformed reference signal in a first radio cell. In an optional implementation, the processing circuitry determines whether to switch off transmission of the beamformed reference signal or whether to change a direction of the beamformed reference signal.

[0164] According to a fourteenth aspect provided in addition to the twelfth or thirteenth aspect, the reference signal notification message includes an identity of the first radio cell and further includes a list of beams for transmitting the beamformed reference signal. In an optional embodiment, for each beam in the list, the reference signal notification message includes: Scheduling information, and duration information about the period during which the beamforming reference signal is transmitted from the radio base station; and / or Periodicity information about the time periodicity of the beamforming reference signals transmitted from the radio base station Includes.

[0165] According to a 15th aspect provided in addition to one of the 12th to 14th aspects, the reference signal notification message includes identification information of a beamformed reference signal, and the transmitter transmits another reference signal notification message including the identification information of the beamformed reference signal to one or more neighboring radio base stations to inform the one or more neighboring radio base stations that the identified beamformed reference signal is currently switched on or off.

[0166] According to a sixteenth aspect, there is provided a user equipment for a mobile communication system. The user equipment comprises a processing circuit for determining that a neighboring radio base station is not providing a beamformed reference signal to the user equipment. The neighboring radio base station controls transmission of an omnidirectional reference signal and a beamformed reference signal in its neighboring radio cell. A transmitter of the user equipment transmits a reference signal request to a serving radio base station serving the user equipment. The reference signal request requests the serving radio base station to request the neighboring radio base station to provide a beamformed reference signal to the user equipment. A receiver of the user equipment receives a notification message from the serving radio base station, the notification message including information about the requested beamformed reference signal.

[0167] According to a 17th aspect provided in addition to the 16th aspect, a receiver receives an omnidirectional reference signal and a beamformed reference signal. A processing circuit performs measurements on the omnidirectional reference signal and the beamformed reference signal. The processing circuit prepares a measurement report including results of the performed measurements. In an optional embodiment, the measurement result is associated with a flag in the measurement report indicating whether the associated measurement result was calculated based on the omnidirectional reference signal and / or the beamformed reference signal, and / or the measurement result is associated with a measurement identification based on which the serving radio base station determines whether the associated measurement result was calculated based on the omnidirectional reference signal and / or the beamformed reference signal.

[0168] According to an 18th aspect provided in addition to the 16th or 17th aspect, the reference signal request transmitted from the user equipment includes information identifying a neighboring radio cell of a neighboring radio base station, and optionally includes information identifying at least another radio cell for which a corresponding beamformed reference signal is requested. In an optional embodiment, the reference signal request is a Medium Access Control (MAC) control element, and the MAC control element includes a predetermined logical channel identifier that identifies the reference signal request. Alternatively, the reference signal request is a Packet Data Convergence Protocol Control Packet Data Unit (PDCP control PDU), and the PDCP control PDU includes a predetermined type identifier that identifies the reference signal request.

[0169] According to a 19th aspect provided in addition to the 18th aspect, the information for identifying a neighboring radio cell is a radio cell identity or a bitmap having two or more bits, each of the bits of the bitmap being associated with a result of a measurement in a measurement report prepared by the user equipment for the neighboring cell, each result being associated with a radio cell identity of the neighboring radio cell.

[0170] According to a twentieth aspect, there is provided a method for operating a radio base station serving a user equipment in a first radio cell of a mobile communication system, the method comprising the following steps performed by the radio base station: determining that a neighboring radio base station is not providing a beamformed reference signal to the user equipment; the neighboring radio base station controls transmission of an omnidirectional reference signal and a beamformed reference signal in the neighboring radio cell; sending a reference signal request to the neighboring radio base station, the reference signal request requesting the neighboring radio base station to provide a beamformed reference signal to the user equipment; receiving a reference signal request response from the neighboring radio base station, the reference signal request response including information about the transmission of the requested beamformed reference signal; and sending a notification message to the user equipment, the notification message including information about the requested beamformed reference signal.

[0171] According to a 21st aspect, there is provided a method of operating a user equipment in a mobile communication system, the method comprising the following steps, performed by the user equipment: determining that a neighboring radio base station is not providing a beamformed reference signal to the user equipment; the neighboring radio base station controls transmission of omnidirectional reference signals and beamformed reference signals in its neighboring radio cell; a reference signal request is sent to a serving radio base station serving the user equipment; the reference signal request requests the serving radio base station to request the neighboring radio base station to provide a beamformed reference signal to the user equipment; and receiving a notification message from the serving radio base station including information about the requested beamformed reference signal.

[0172] Hardware and Software Implementations of the Disclosure The present disclosure can be realized by software, hardware, or software in combination with hardware. Each functional block used in the description of each embodiment above can be partially or entirely realized by an LSI such as an integrated circuit, and each process described in each embodiment can be partially or entirely controlled by the same LSI or a combination of multiple LSIs. An LSI can be formed as an individual chip, or a single chip can be formed to include some or all of the functional blocks. An LSI can include a data input / output unit coupled thereto. In this specification, an LSI may be referred to as an IC (integrated circuit), a system LSI, a very large-scale integrated circuit, or an ultra-large-scale integrated circuit (ULSI) depending on the level of integration. However, the technique for implementing an integrated circuit is not limited to an LSI, and it may be realized using a dedicated circuit, a general-purpose processor, or a special-purpose processor. In addition, an FPGA (field-programmable gate array), which can be programmed after the LSI is manufactured, or a reconfigurable processor, which can reconfigure the connections and settings of circuit cells arranged within the LSI, can also be used. The present disclosure can be realized as digital processing or analog processing. If future integrated circuit technology replaces LSI as a result of advances in semiconductor technology or other derivative technologies, functional blocks can also be integrated using that future integrated circuit technology.

[0173] Furthermore, the various embodiments may also be implemented by software modules, which are executed by a processor or directly in hardware. Also, a combination of software modules and hardware implementations may be possible. The software modules may be stored on any kind of computer-readable storage medium, for example, RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. It should be further noted that individual features of the various embodiments may, individually or in any combination, be material for other embodiments.

[0174] Those skilled in the art will appreciate that many variations and / or modifications may be made to the present disclosure shown in the specific embodiments, which are therefore to be considered in all respects as illustrative and not restrictive.

Claims

1. A radio base station, a transceiver for receiving a measurement report from a communication device, the measurement report including the measurement results; a processing circuit for determining from the measurement report that a beamformed reference signal controlled by a neighboring radio base station is not included in the measurement result; Equipped with sending a request message to the neighboring radio base station to provide the beamformed reference signal to the communication device in response to receiving the measurement report; The transceiver transmits a notification message to the communication device, the notification message including information about the beamformed reference signal.

2. The radio base station according to claim 1 , wherein the radio base station receives a response message from the neighboring radio base station indicating that the neighboring radio base station does not provide the beamformed reference signal to the communication device.

3. The radio base station according to claim 1 , wherein the request message includes identification information of the neighboring radio base station.

4. The radio base station according to claim 1 , wherein the measurement result is associated with information that distinguishes between the measurement of the beamformed reference signal and the measurement of the omnidirectional reference signal.

5. The radio base station according to claim 1 , wherein the transceiver transmits the measurement results to the neighboring radio base stations.

6. 2. The radio base station according to claim 1, wherein when the radio base station receives a response message from the neighboring radio base station indicating that the radio base station will provide the beamformed reference signal to the communication device, the response message includes scheduling information for the beamformed reference signal, and the scheduling information identifies radio resources in the frequency domain or the time domain.

7. 2. The radio base station according to claim 1, wherein when the radio base station receives a response message from the neighboring radio base station indicating that the beamformed reference signal will be provided to the communication device, the response message includes a list of beams for transmitting the beamformed reference signal.

8. 2. The radio base station according to claim 1, wherein the measurement result is associated with a measurement identification, the measurement identification indicating at least one of that the associated measurement result is based on an omnidirectional reference signal or that the associated measurement result is based on the beamformed reference signal.

9. the processing circuit determines whether to hand over the communication device to the neighboring radio base station based on the measurement result; The radio base station according to claim 1 , wherein, when it is decided to perform a handover, the transceiver transmits a handover request to the neighboring radio base station.

10. 1. A communication device, comprising: a processing circuit that determines not to include beamformed reference signals controlled by neighboring radio base stations in the measurement results; a transceiver configured to transmit a measurement report including the measurement results to a serving radio base station; Equipped with a request message is transmitted by the serving radio base station in response to the transmission of the measurement report, so that the neighboring radio base station provides the beamformed reference signal to the communication device; A communications device, wherein the transceiver receives a notification message from the serving radio base station, the notification message including information regarding the beamformed reference signal.

11. The communications device of claim 10 , wherein the communications device prepares the measurement results in accordance with a measurement configuration configured by the serving radio base station.

12. The communications device of claim 10 , wherein the measurement results include a plurality of results of measurements made on a plurality of neighboring radio cells.

13. 11. The communications device of claim 10, wherein the measurement result is associated with a measurement identification, and based on the measurement identification, the serving radio base station indicates at least one of that the associated measurement result is based on an omnidirectional reference signal or that the beamformed reference signal is based on the measurement result.

14. receiving a measurement report from the communication device, the measurement report including the measurement results; determining from the measurement report that a beamformed reference signal controlled by a neighboring radio base station is not included in the measurement result; Including, sending a request message to the neighboring radio base station to provide the beamformed reference signal to the communication device in response to receiving the measurement report; A method of transmitting a notification message to the communication device, the notification message including information regarding the beamformed reference signal.

15. determining that beamformed reference signals controlled by neighboring radio base stations are not included in the measurement results; transmitting a measurement report including the measurement result to a serving radio base station; Including, a request message is transmitted by the serving radio base station in response to the transmission of the measurement report, so that the neighboring radio base station provides the beamformed reference signal to the communication device; receiving a notification message from the serving radio base station, the notification message including information regarding the beamformed reference signal;

16. An integrated circuit for controlling processing of a radio base station of a mobile communication system, the processing comprising: receiving a measurement report from the communication device, the measurement report including the measurement results; determining, from the measurement report, that the measurement result does not include a beamformed reference signal controlled by a neighboring radio base station; Including, sending a request message to the neighboring radio base station to provide the beamformed reference signal to the communication device in response to receiving the measurement report; An integrated circuit that transmits a notification message to the communication device that includes information regarding the beamformed reference signal.

17. 1. An integrated circuit for controlling processing of a communication device in a mobile communication system, the processing comprising: determining that beamformed reference signals controlled by neighboring radio base stations are not included in the measurement results; transmitting a measurement report including the measurement result to a serving radio base station; Including, a request message is transmitted by the serving radio base station in response to the transmission of the measurement report, so that the neighboring radio base station provides the beamformed reference signal to the communication device; an integrated circuit that receives a notification message from the serving radio base station, the notification message including information regarding the beamformed reference signal;

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