Base station, communication device and method

Abstract

To provide a method and a device with good transmission inefficiency, such as session disruption (inter-beam handover), less signaling overhead, and / or increased retransmission requirements, for UE served via a directional beam.SOLUTION: In a cellular communication system, user equipment, which is a mobile phone and / or another mobile device, includes means for receiving a signal containing at least one beam from a base station during a user equipment initial access procedure, and means for determining which beam to use from the at least one beam based on an identifier for identifying the beam and a cell identifier for identifying a cell.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to communication systems. The present invention particularly, but not exclusively, relates to wireless communication systems and apparatus therefor operating in accordance with the 3rd Generation Partnership Project (3GPP®) standards or equivalents or derivatives thereof. The present invention particularly, but not exclusively, relates to mobility in so-called "next generation" systems using beamforming. [Background technology]

[0002] The latest developments in 3GPP standards are called Long Term Evolution (LTE) of the Evolved Packet Core (EPC) network and the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), also commonly referred to as "4G". Furthermore, the terms "5G" and "new radio" (NR) refer to evolving communications technologies that are expected to support a variety of applications and services. Various details of 5G networks are described, for example, in the "NGMN 5G White Paper" V1.0 by the Next Generation Mobile Networks (NGMN) Alliance, which is available at https: / / www.ngmn.org / 5G-white-paper.html. 3GPP intends to support 5G via the so-called 3GPP Next Generation (NextGen) Radio Access Network (RAN) and 3GPP NextGen Core Network.

[0003] Under 3GPP standards, a Node B (or eNB in ​​LTE, gNB in ​​5G) is a base station through which communication devices (user equipment or "UE") connect to a core network and communicate with other communication devices or remote servers. For simplicity, this application uses the term base station to refer to such base stations and the term mobile equipment or UE to refer to such communication devices. The core network (i.e., EPC in the case of LTE) hosts functions for (among other things) subscriber management, mobility management, charging, security, and call / session management, and provides connectivity of communication devices to external networks such as the Internet.

[0004] The communication device may be, for example, a mobile communication device such as a mobile phone, a smartphone, a user device, a personal digital assistant, a laptop / tablet computer, a web browser, an e-reader, etc. Such mobile (or generally stationary) devices are also typically operated by a user, although so-called "Internet of Things" (IoT) devices and similar machine-type communication (MTC) devices may also be connected to the network. For simplicity, the present application refers to mobile devices (or UEs) in the description, but it will be understood that the described techniques may be implemented on any communication device (mobile and / or generally stationary / data receiving) that can connect to a communication network for transmission.

[0005] 3GPP Technical Report (TR) 23.799 V0.7.0 describes possible architectures and general procedures for NextGen (5G) systems planned for Release 14 of the 3GPP standards. 3GPP is also studying the potential use of frequency bands up to 100 GHz for new (5G) radio access networks. To overcome the severe channel attenuation characteristics associated with certain high frequency bands (e.g., mmWave bands), directional beamforming and large-scale antenna techniques may also be used. The term "large-scale antenna" refers to an antenna having a large number (e.g., 100 or more) of antenna elements arranged in an array. Effectively, such a large-scale antenna can be used to communicate with multiple users simultaneously, thus facilitating multi-user MIMO (multiple-input and multiple-output) transmission. A base station (also called a transmit / receive point (TRP) in this case) may be configured to form respective beams for communicating with multiple UEs substantially simultaneously and to use associated directional beams.

[0006] 3GPP has agreed on some of the mobility-related requirements within 5G. Specifically, 3GPP intends to provide one or more TRPs per new radio (NR) base station (i.e., 5G base station, or gNB). As a baseline, each NR is expected to support a state with network-controlled mobility processing and a state with UE-controlled mobility. Measurement configurations related to typical inter-gNB network-controlled mobility are kept to a minimum. Thus, each UE is required to perform fewer (and possibly less detailed) measurements for mobility purposes (e.g., avoiding the need to provide detailed "cell" level information). However, more detailed information may be required in some cases. 3GPP also intends to minimize context transfer (between base stations) as a result of UE-based mobility.

[0007] Network controlled mobility may be RRC-driven at the cell level (i.e., controlling UE mobility using appropriate Radio Resource Control (RRC) signaling between the gNB and the UE) or may be provided with zero / minimal RRC involvement (e.g., at the MAC / PHY layer). Summary of the Invention [Problem to be solved by the invention]

[0008] However, especially in the higher frequency bands, obstructions (e.g., by obstacles) of the direct line-of-sight (LOS) path between the transmitter and receiver and / or the mobility of the UE may result in degradation of the quality of the radio link for that UE. Furthermore, some studies suggest that the radio channel may change very rapidly at mmWave frequencies, which may also result in transmission errors and / or an increased number of handovers for a particular UE. Thus, UEs served via directional beams are prone to losing connection with their base station and data loss. Furthermore, existing (e.g., LTE) mobility techniques are not applicable to 5G RAN due to technological differences and the bandwidth used.

[0009] It is expected that the relative unreliability of high frequency and directional beams may result in frequent changes in the beams used by active UEs and 5G base stations / TRPs, which may result, for example, in session interruptions (inter-beam handovers), increased signaling overhead, and / or transmission inefficiencies (e.g., increased need for retransmissions).

[0010] Accordingly, preferred exemplary embodiments of the present invention aim to provide a method and apparatus that addresses, or at least partially addresses, the above problems.

[0011] For ease of understanding for those skilled in the art, the present invention will be described in detail in the context of a 3GPP system (5G network), but the principles of the present invention can be applied to other systems. [Means for solving the problem]

[0012] In one aspect, the present invention provides a base station for a communication system, the base station comprising a controller and a communication unit, the controller configured to control communications within a communication area served by the base station, the communication area being formed by a plurality of directional beams, each of which covers a respective portion of the communication area served by the base station and each of which has a different beam identifier, and the communication unit configured to communicate control information relating to at least one communication device using at least one directional beam associated with the at least one communication device.

[0013] In another aspect, the present invention provides a communications device for a communications system comprising a base station providing a communications area formed by a plurality of directional beams covering respective portions of the communications area, each beam having a different beam identifier, the device comprising a controller and a communications unit configured to receive control information from the base station using at least one directional beam associated with the communications device.

[0014] Aspects of the invention also extend to corresponding systems, methods, and computer program products, such as computer readable storage media having stored thereon executable instructions for programming a programmable processor to perform the methods described in the aspects and possibilities described above or in the claims, and / or to provide an apparatus as described in any claim.

[0015] Each feature disclosed in this specification (which term includes the claims) and / or shown in the drawings may be incorporated in the present invention independently (or in combination) with other disclosed and / or shown features. In particular, but not by way of limitation, any feature of a claim depending from a particular independent claim may be introduced into that independent claim in any combination or individually.

[0016] Exemplary embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Effect of the Invention

[0017] [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 illustrates generally a cellular communication system in which exemplary embodiments of the present invention may be applied. [Diagram 2] FIG. 2 is a block diagram of a mobile device forming part of the system shown in FIG. [Diagram 3] FIG. 3 is a block diagram of a base station forming part of the system shown in FIG. [Figure 4] FIG. 4 illustrates generally a series of subframes that can be used for (control and user) data communication in the system of FIG. [Diagram 5] FIG. 5 is a schematic diagram of an example embodiment in which directional beams may be used. [Figure 6] FIG. 6 is a schematic diagram of another exemplary embodiment in which directional beams may be used. [Figure 7] FIG. 7 illustrates, in schematic form, yet another exemplary embodiment in which directional beams may be used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] overview FIG. 1 illustrates diagrammatically a communication network 1 in which user equipment 3 (cell phones and / or other mobile devices) can communicate with each other via base stations 5 (denoted as "gNB") using an appropriate radio access technology (RAT). It should be understood that in a 5G system, base stations are also referred to as transmit receive points (TRPs). In FIG. 1, five mobile devices 3 and one base station 5 are shown for illustrative purposes, as will be understood by those skilled in the art, but when implemented, the system will typically include other base stations and mobile devices.

[0020] Each base station 5 operates one or more associated cells via a TRP located at the base station (and / or one or more TRPs located remotely). In this example, for simplicity, the base station 5 operates a single cell. The base stations 5 are connected to a core network 7 (e.g. via appropriate gateways and / or user plane / control functions) and neighbouring base stations are also connected to each other (directly or via appropriate base station gateways). The core network 7 may include, among other things, a control plane manager entity and a user plane manager entity, one or more gateways (GWs) for providing connectivity between the base stations 5 and other networks (such as the Internet) and / or servers hosted outside the core network.

[0021] A mobile device 3 connects to an appropriate cell (depending on its location and possibly other factors, e.g. signal conditions, subscription data, capabilities, etc.) by establishing a Radio Resource Control (RRC) connection with the base station 5 serving that cell. The mobile device 3 and base station 5 (and other transmission points in the network) communicate over an appropriate radio interface that depends on the RAT used. The mobile device 3 communicates with the core network nodes using so-called Non-Access Stratum (NAS) signaling, which is relayed between the mobile device 3 and the appropriate core network node by the base station 5 / TRP serving the mobile device 3.

[0022] In this example, the base station 5 operates an associated antenna array (e.g., a large antenna) to provide multiple directional beams for communicating with various mobile devices 3 within the cell of the base station 5. Each beam is positioned to spread (transmit) in a different direction (three dimensions including elevation). Each beam has an associated identifier (e.g., an assigned "beam ID") that is unique (at least within the cell).

[0023] The beam configuration used by a cell identifies the number of beams and their associated beam pattern. In this example, the total number of beams is "N", i.e., beams #1 to #N, currently configured for base station 5's cell (where "N" is a positive integer, at least "1").

[0024] The base station 5 is advantageously configured to transmit within its cell (or within each cell if the base station operates multiple cells) a set of beam-specific reference signals (BRS). The mobile device 3 may be configured to use the associated BRS to perform signal strength and channel estimation measurements for each beam. Such beam-specific measurements are used (by the base station and / or the mobile device 3) to configure an appropriate set of beam(s) for the mobile device 3, which is referred to as the operational beam set (OBS) of the mobile device 3.

[0025] The OBS may be dynamically updated depending on, for example, signal conditions, loading in the cell, throughput and / or quality of service (QoS) required by the mobile device 3. Beneficially, when the OBS includes multiple beams, the likelihood of the mobile device 3 suffering a radio link failure (RLF), i.e., loss of connection with the base station 5, is significantly reduced, since in most cases there will be at least one directional beam that the mobile device 3 can use and / or new beams that are added (at least temporarily) to the OBS as needed.

[0026] Furthermore, the OBS may be advantageously used to support intra-cell mobility of the mobile device 3. In particular, as the mobile device 3 changes its location within the coverage area (cell) of the base station 5, new beams may be added to the OBS as needed (and beams that are no longer needed may be removed).

[0027] The mobile device 3 may be configured to perform and report more frequent signal measurements (e.g., detailed channel state information (CSI) measurements) for those beams included in the OBS of the mobile device 3 than for other beams. Thus, if an obstacle (e.g., temporary) exists between the mobile device 3 and the base station 5 (blocking the line of sight to a particular directional beam), such a change in signal conditions (and affected beam identification) can be detected relatively quickly. The base station 5 can also perform necessary adjustments in transmissions to the mobile device 3 to avoid disruptions and / or radio link failures due to the obstacle. However, beneficially, the mobile device 3 can most likely continue to communicate with the base station 5 using other suitable (unaffected) beams in its OBS. If a problem affecting a particular beam in the OBS persists, the base station 5 removes that beam from the OBS (e.g., after expiration of a predefined timer and / or after receiving a predefined number of reports indicating a problem with that beam).

[0028] Similarly, base station 5 may be configured to remove a beam from the OBS of mobile device 3 (and replace it with a different beam) due to the mobility of mobile device 3.

[0029] Thus, providing an OBS (and / or associated beam-specific reference signals) provides flexibility in providing service to mobile devices via a base station's cell, improved tolerance to signal propagation issues (e.g., obstructions) affecting high frequency radio beams, reduced risk of signal loss (e.g., while moving within a cell or between different cells), and faster and more efficient cell / beam acquisition by mobile devices resulting in reduced risk of radio link failure.

[0030] Mobile Devices FIG. 2 is a block diagram illustrating the main components of a mobile device 3 (e.g., a mobile phone or other user device) shown in FIG. 1. As shown in the figure, the mobile device 3 has a communication circuit 31 operable to transmit and receive signals to a base station 5 via one or more antennas 33. The mobile device 3 has a controller 37 that controls the operation of the mobile device 3. The controller 37 is associated with a memory 39 and is connected to the communication circuit 31. Although not necessary for its operation, the mobile device 3 may of course have all the usual functions of a conventional mobile phone 3 (such as a user interface 35), and this may be suitably provided by any one or any combination of hardware, software and firmware. The software may be pre-installed in the memory 39 and / or may be downloaded, for example, over a telecommunications network or from a removable data storage device (RMD).

[0031] The controller 37, in this example, is configured to control the overall operation of the mobile device 3 by means of program or software instructions stored in memory 39. As shown in the figure, these software instructions include, among other things, an operating system 41, a communication control module 43, a beam setting module 44, a mobility module 45, and a signal measurement module 46.

[0032] The communications control module 43 is operable to control communications between the mobile device 3 and its serving base station 5 (and other communications equipment connected to the base station 5, such as further mobile devices and / or core network nodes).

[0033] The beam configuration module 44 is responsible for managing the OBS (or each OBS) for the mobile device 3 used in the current serving cell (or cells), including, for example, adding and removing cells (e.g., based on information provided by the base station 5 and / or the signal measurement module 46).

[0034] The mobility module 45 is responsible for maintaining network attachment via an appropriate cell (of the base station 5) while the mobile device 3 is moving within the area covered by the telecommunications network 1. The mobility module 45 maintains the network connection by performing cell / beam reselection and / or handover procedures depending on signal conditions, etc. It will be appreciated that the mobility module 45 may perform cell / beam reselection and / or handover procedures even when the mobile device 3 is stationary, e.g., due to changing signal conditions, network load in the current cell, etc. The mobility module 45 also takes into account the OBS and / or current beam configuration (e.g., provided by the beam setting module 44) of the mobile device 3 for the current cell and / or potential handover candidate cells.

[0035] The signal measurement module 46 is responsible for obtaining signal quality measurements for cells / beams in the vicinity of the mobile device 3 and generating and transmitting associated signal measurement reports to the serving base station 5. The signal quality measurements are performed via beam-specific reference signals transmitted by the base station 5 based on an appropriate measurement configuration provided by the serving base station 5. The signal quality measurements may include, for example, (detailed) Channel State Information (CSI) measurements, Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Received Signal-to-Noise Ratio (SNR), and / or Signal-to-Interference-and-Noise Ratio (SINR) measurements and associated reports.

[0036] base station FIG. 3 is a block diagram illustrating the main components of the base station 5 shown in FIG. 1. As shown in the figure, the base station 5 includes a communication circuit 51 for transmitting and receiving signals to and from a communication device (such as a mobile device 3) via one or more antennas 53 (e.g., an antenna array / giant antenna), and a network interface 55 for transmitting and receiving signals to a network node (e.g., other base stations and / or nodes in the core network 7). The base station 5 has a controller 57 for controlling the operation of the base station 5. The controller 57 connects to a memory 59. Software may be pre-installed in the memory 59 and / or may be downloaded, for example, from a removable data storage device (RMD) via the telecommunications network 1. The controller 57 is configured to control the overall operation of the base station 5 by program instructions or software instructions stored in the memory 59, in this example. As shown in the figure, these software instructions include, among others, an operating system 61, a communication control module 63, a beam control module 64, and a measurement configuration module 66.

[0037] The communication control module 63 is operable to control communication between the base station 5, the mobile devices 3 (user equipment) and other network entities connected to the base station 5. The communication control module 63 also controls separate flows of downlink user traffic (via associated data radio bearers) and control data to be transmitted to communication devices associated to this base station 5, e.g. control data for core network services and / or mobility of the mobile devices 3 (including also general (non-UE specific) system information and reference signals).

[0038] The beam control module 64 is responsible for operating the OBS associated with each mobile device 3 within a cell (or multiple cells) of the base station 5, including, for example, adding and removing cells (e.g., based on signal measurements provided by the mobile device 3, the mobility of the mobile device 3, and / or other information associated with the cell, such as load information, etc.).

[0039] The measurement configuration module 66 is responsible for configuring the mobile device 3 to perform and report signal quality measurements for cells and / or beams in the vicinity of the mobile device 3 (e.g., cells / beams operated by this base station 5 and / or neighboring base stations). The measurement configuration module 66 obtains signal quality measurements by generating and sending appropriate measurement configurations to a particular mobile device 3 and receiving associated measurement reports. The measurement reports may be used, for example, when performing mobility and / or beam configuration procedures involving the mobile device 3 that provided the report.

[0040] In the above description, the mobile device 3 and base station 5 are described for ease of understanding as having several separate modules (such as a communications control module and a beam configuration / control module). While these modules may be provided in this manner in certain applications, e.g., in other applications where an existing system is modified to implement the invention, in systems designed from the outset with the features of the invention in mind, these modules may not be recognizable as separate entities, as they may be built into the overall operating system or code. These modules may be implemented in software, hardware, firmware, or a combination of these.

[0041] A more detailed explanation (with reference to Figures 4 to 7) is provided below regarding some of the ways in which directional beams / OBS can be used for communication between user equipment and TRPs (base stations) in a network.

[0042] operation The base station 5 is advantageously configured to transmit a set of beam-specific reference signals (BRS) in its cell (or in each cell if the base station operates multiple cells). For example, the base station 5 may transmit one BRS per beam ID. The mobile device 3 may use the associated BRS to perform signal strength and channel estimation measurements for each beam. The BRS is transmitted (e.g. periodically) using a beam pattern of the corresponding beam and using predefined time / frequency resources. It will be understood that different BRSs may be transmitted on the same time / frequency resources or different time / frequency resources (e.g. when "beam scanning" is employed). Preferably, various BRSs in the same cell are orthogonal to each other (over the set of time / frequency resources they are transmitted), while BRSs in different cells have low cross-correlation with each other. The BRS corresponding to a given beam ID is determined (by the mobile device 3) based on the beam ID and cell ID. In other words, the mobile device 3 may be able to construct a BRS for a particular beam (including the set of time / frequency resources on which the BRS is transmitted) based on the associated beam ID and cell ID.

[0043] Idle Mode and Initial Cell Selection When the mobile device 3 is in idle mode, it may perform an initial cell search using appropriate synchronization signals transmitted by the base station (via each of multiple beams configured within the base station's cell / coverage area).

[0044] 4 illustrates, in a schematic manner, an exemplary sequence of subframes (downlink subframes in this example) transmitted by a base station in each beam. As can be seen, the subframes include several (downlink) data subframes 80 in the base station 5, capable of transmitting data to the mobile devices 3 in its cell (and served via this particular beam). It should be understood that (although not shown in FIG. 4 for simplicity) each data subframe 80 may also carry control signals (e.g., scheduling information) and / or reference signals (for signal measurements).

[0045] Beneficially, the base station is configured to transmit (periodically) a properly formatted synchronization signal in a particular subframe (herein referred to as synchronization subframe 81). For example, such synchronization subframe 81 may be transmitted in a subframe prior to the subframe in which the system information (SI) broadcast is transmitted (denoted as SI information subframe 82 in FIG. 4). Thus, using the synchronization signal, the mobile device 3 can adapt its communication part to use the correct time / frequency resources in that particular beam before proceeding to receive the system information broadcast. This advantageously enables the mobile device 3 to find and connect to the base station 5 via that beam in a fast and efficient manner.

[0046] Specifically, to facilitate the mobile device 3 to perform a beam search for initial access (by performing a random access procedure), the following options may be used: a) Beamforming Downlink (DL) Synchronization Signal The mobile device may be configured to detect a cell ID from the synchronization signal and possibly an associated beam ID from a beam reference signal (BRS) transmitted on a particular beam. b) Beamforming DL System Information The mobile device 3 may be configured to obtain the necessary system information from the cells and possibly some beam-specific system information for communication via a particular beam. c) Beamformed UL Physical Random Access Channel (PRACH) Transmission (msg1) The PRACH resources may be configured using system information that the mobile device obtains in advance (i.e., before initiating the random access procedure by transmitting a so-called "msg1" transmission via a particular beam); and d) Beamformed DL random access message (msg2 / 4) The PRACH resources for transmitting msg2 / 4 (via a particular beam) may be configured using system information.

[0047] <Connected mode intra-cell mobility> It will be appreciated that while in connected mode (e.g., after performing appropriate beam search and random access procedures), a mobile device 3 can connect to its serving cell using one or more beams, referred to as an Operational Beam Set (OBS) for that mobile device 3. Such an OBS may include a (typically small) subset of beams in the cell of the base station 5 that are selected for communication with that mobile device 3 while in that base station's cell.

[0048] However, to take into account the mobility of mobile device 3 within the cell (and / or changing signal conditions within the cell), base station 5 may modify the OBS for mobile device 3 by adding or removing beams, for example, based on at least one of the following: Beam measurements (performed and reported by the mobile device 3 and / or derived by the base station 5 from UL transmissions by that mobile device 3). Beam load (traffic congestion) and Beam priority (this may be set by higher layers, e.g., for inter-cell interference coordination, etc.).

[0049] <OBS measurement of intra-cell mobility> To account for the mobility of the mobile device 3 within the cell, the base station 5 may also use beam measurements (performed and reported by the mobile device 3 and / or derived by the base station 5 from UL transmissions by that mobile device 3).

[0050] In this case, the beam measurements reported by mobile device 3 may include, for example, a reference signal received power (RSRP) and / or a signal-to-interference-plus-noise ratio (SINR) associated with each beam (measured using a respective BRS on each beam).

[0051] The mobile device 3 may be configured (by the serving base station 5 via appropriate measurement configuration signaling) to report measurements periodically and / or in an event-triggered manner. For example, a report may be triggered when the RSRP of a beam rises above or below a predefined threshold (absolute or relative to other beams) for a certain period of time. This is similar to handover measurements in LTE.

[0052] Optionally, the mobile device 3 may be configured to sort the beams in order of priority based on the measurements and report measurements only for the best beams (e.g., a predetermined number of beams), or report beam IDs associated with the best beams for that mobile device 3 (e.g., as a list).

[0053] However, it will be appreciated that mobile device 3 may request (without reporting actual measurements) that a particular beam or beams be added or removed from its OBS, thereby reducing the amount of signaling required between mobile device 3 and base station 5. Base station 5 may optionally specify a subset of beams to be measured and reported by mobile device 3 (e.g., before adding or removing them from the OBS).

[0054] In the case of time-division multiplexing (TDD) communication, the base station 5 may also be configured to utilize channel reciprocity to select the most appropriate beam for the OBS of the mobile device 3 based on the channel measurement values derived from the UL transmission from the mobile device 3.

[0055] Whenever the network (base station 5) modifies the OBS, it notifies the mobile device 3 using a properly formatted control signal (e.g., RRC signal).

[0056] <UE-specific data and control> Advantageously, the OBS may be used for i) UE-specific DL data transmission (similar to how the physical downlink shared channel or "PDSCH" is transmitted in an LTE cell) and ii) UE-specific DL control transmission (similar to the enhanced physical downlink control channel or "E-PDCCH" in LTE).

[0057] The OBS may be useful for at least reducing the amount of CSI signals and facilitating open-loop transmission diversity for a specific mobile device 3.

[0058] Specifically, the reduction in the amount of CSI signals may be achieved as follows. Typically, DL beamforming for the transmission of UE-specific channels is based on CSI reports from the UE (mobile device 3). However, when using the OBS, CSI measurements and signal overhead can be reduced by configuring the mobile device to transmit detailed CSI reports only for the beams within the OBS (using the associated BRSs on those beams for CSI measurement).

[0059] In particularly beneficial cases, the base station 5 may apply appropriate precoding (amplitude and phase weighting) for DL ​​transmissions across beams in the OBS based on CSI reports from the mobile device 3. In this case, a UE-specific DM-RS may be included in the transmission so that the mobile device 3 does not need to know the precoding weights used by the network.

[0060] The base station 5 may be configured to apply transmit diversity over beams in the OBS. In this case, the mobile device 3 may extract the transmitted signal from each beam using the BRS on each beam and then combine the transmitted signals before decoding. This scheme has the advantage that no detailed CSI is required from the mobile device 3.

[0061] <Common control signals> The mobile device 3 may need to receive certain control information from the network that is not specific to that UE and / or does not need to be broadcast throughout the cell of the base station 5. Such control information may include, but is not limited to, for example, random access response (RAR) messages 2 and 4, power control signals, and paging.

[0062] Base station 5 may transmit such common control information on all beams in the OBS (e.g., using open loop transmit diversity as described above), in which case mobile device 3 may use the BRS on each beam to demodulate the transmission on that beam and then combine the received data to improve communication reliability.

[0063] <Intra-cell mobility> 5(a) shows a schematic representation of a base station 5 operating multiple directional beams, with beams #3 and #4 currently assigned to the OBS of a mobile device 3. The OBS is shown using solid lines, while beams not included in the OBS are shown with dotted lines.

[0064] The diversity created by using multiple beams between the base station 5 and the mobile device 3 can significantly reduce the likelihood that the mobile device 3 will lose connection with the base station 5 due to failure and / or mobility (while in the cell of the base station 5), even when the base station 5 is operating a higher frequency band in its cell. That is, even if it loses one (or more) beams, the mobile device 3 is likely still connected to at least one beam (or beams) of the base station 5, and therefore must be able to tolerate a loss in received SNR (combined from multiple beams).

[0065] More specifically, FIG. 5(a) illustrates a schematic scenario in which a mobile device 3 is currently communicating with a base station 5 using an OBS comprising beams #3 and #4. Because these are included in the OBS, mobile device 3 is configured to send (relatively frequent) detailed CSI reports for beams #3 and #4, while mobile device 3 only sends periodic (infrequent) RSRP measurements for other beams (and / or RSRP measurements for beams #3 and #4).

[0066] As generally shown in FIG. 5(b), an obstacle (e.g., a vehicle) between the mobile device 3 and the base station 5 may cause a degradation in the RSRP of a beam (beam #4 in this example) in the OBS. However, such a change in signal conditions is beneficially tracked by CSI measurements of that beam, and the mobile device 3 can still receive DL transmissions via beam #3 (which currently does not suffer from signal quality degradation due to the obstruction). Thus, using the CSI measurements for the affected beam (#4), the base station 5 can (at least temporarily) make the necessary adjustments in its transmissions for the mobile device 3 (e.g., prioritize beam #3 over beam #4). If the CSI measurements for the affected beam still indicate poor signal conditions (e.g., over a period of time and / or number of CSI reports), the base station 5 may be configured to remove the affected beam from the OBS of the mobile device 3.

[0067] Similarly, the base station 5 may be configured to remove beams from the OBS of the mobile device 3 due to the mobility of the mobile device 3. Such a movement scenario is illustrated in FIG. 5(c). Specifically, in this example, as the mobile device 3 moves within the cell of the base station 5, the network (and / or the mobile device 3) monitors the signal conditions of the beams included in the OBS (e.g., using beam RSRP measurements and / or CSI) and decides to update the OBS by removing beam #4 and adding beam #2 when the mobile device 3 is no longer within the coverage area of ​​beam #4.

[0068] <Connected mode inter-cell mobility> The network (base station 5) may configure the mobile device 3 to perform measurements that take into account the beamforming gain available from beams used in neighboring cells in order to determine when to initiate a handover to the neighboring cell of the mobile device 3. Beneficially, therefore, when selecting a handover target cell for the mobile device 3, the serving base station 5 can select the most appropriate beam of the handover target cell such that the mobile device 3 can continue communicating via the new cell without experiencing significant data loss and / or delays.

[0069] To facilitate inter-cell mobility, the mobile device 3 may be configured to measure the signal strength of each beam in one or more neighboring cells (at least the cells / beams for which the current base station requests measurements). For example, the mobile device 3 may be configured to scan each beam ID (unique BRS) transmitted in the neighboring cells and report the ID of the strongest beam for each measured neighboring cell to the serving base station 5. If the serving base station 5 determines that a handover is required for the mobile device 3, the serving base station 5 may provide information identifying the most suitable beam for that mobile station 3 to the target cell during the handover procedure. If available to the mobile device 3, the serving base station 5 may also provide detailed measurements on such beams.

[0070] FIG. 6 illustrates generally a scenario in which a mobile device 3 performs a handover between a cell served by its current serving base station 5A ("Cell 1") and a neighbouring cell served by base station 5B ("Cell 2").

[0071] As can be seen, both base stations 5A and 5B operate multiple directional beams. First, the mobile device 3 communicates with the serving base station 5A using an OBS including beams #5 and #6 of cell 1. The mobile device 3 performs appropriate handover measurements to one or more neighboring cells (including cell 2) by measuring RSRP for all beams in its cell. In this example, the mobile device 3 reports strong RSRP for beams #2 and #3 in cell 2. Thus, when selecting cell 2 as the handover target cell, the current serving base station 5A can advantageously control the handover of the mobile device 3 to beams 2# and #3 of cell 2 as the optimal beams in that cell.

[0072] Therefore, when the mobile device 3 performs a handover to cell 2, it is potentially possible to connect via the most appropriate beam within that cell (assuming those beams are available to the mobile device 3). Even if not all beams with a good signal state within cell 2 are available to the mobile device 3 (e.g., due to the load within cell 2, etc.), the new base station 5B can still start providing service to the mobile device 3 via at least some of the appropriate candidate beams (and potentially add other beams to the OBS as the mobile device 3 moves around within the area covered by cell 2).

[0073] <In-cell OBS of CoMP> Figure 7 schematically shows a scenario in which the mobile device 3 communicates simultaneously via cell 1 operated by the base station 5A and cell 2 operated by the base station 5B. This scenario is in fact a variation of the Coordinated Multipoint (CoMP; coordinated transmission and reception between cells) transmission and reception scenario defined for LTE. However, in this case, the base station 5 is configured to allocate specific beams to the mobile device 3 rather than the entire component carrier. Such simultaneous transmission / reception can be performed, for example, when the mobile device 3 is located in a cell edge area and / or when the cells of adjacent base stations overlap. Therefore, in such a situation, the mobile device 3 can receive signals from multiple cells (and transmit signals via multiple cells), thereby significantly improving the downlink (or uplink) performance. Simultaneous transmission / reception (CoMP) may be used for two main purposes. i) To improve signal quality. (By transmitting / receiving the same signal via two or more cells) ii) To improve throughput (by achieving a higher overall data rate than possible by using only a single cell by transmitting different data via different cells).

[0074] In the scenario shown in Figure 7, mobile device 3 has a respective OBS for each cell in its CoMP measurement set (Cell1 and Cell2 in this example) and is configured to measure and report per-beam CSI for each beam of each OBS. Specifically, in this example, the OBS for mobile device 3 in cell 1 includes beams #5 and #6 of this cell, and the OBS for the same mobile device 3 in cell 2 includes beams #2 and #3 of cell 2. Thus, mobile device 3 is configured to perform per-beam CSI measurement and reporting for beams #5 and #6 of cell 1 and beams #2 and #3 of cell 2.

[0075] The CSI measurements for each beam may be reported to the same (e.g., master) base station 5 regardless of which base station operates that beam, and / or the CSI measurements may be reported to that particular base station. Regardless of which base station 5 the mobile device 3 reports to, the base stations 5 may be configured to exchange CoMP-related signals with each other via an inter-base station interface provided between them. The CoMP-related signals may include, for example, the CSI for each beam and similar information related to the OBS of the mobile device 3 (e.g., the beam ID included in the OBS).

[0076] Furthermore, when simultaneous transmission / reception is used, the decision to add / remove cells to / from the mobile device's 3CoMP measurement set may be based on the associated per-beam RSRP measurements (which may be obtained as described above). Thus, beneficially, with appropriate coordination between serving base stations, the signal conditions for the mobile device may be improved (while using narrow, high frequency directional beams) and / or throughput may be improved (by communicating through multiple cells) using beam-specific reference signals and respective OBS configurations within each cell.

[0077] Variations and substitutions Detailed exemplary embodiments and alternatives have been described above. As will be appreciated by those skilled in the art, many modifications and alternatives can be made to the above exemplary embodiments while still benefiting from the invention embodied therein. For purposes of illustration, only some of these alternatives and modifications are described.

[0078] It will be appreciated that the beam configuration may vary from cell to cell depending on the coverage / throughput requirements for a particular cell. For example, a large number of very narrow beams may be used for large cell radii, or a smaller number of relatively wide beams may be used to facilitate cell acquisition and reduce overhead for transmitting beam-specific reference signals. In some cases, the beam configuration may be configured for a single cell and define coverage for the entire cell (similar to conventional cells).

[0079] It will also be appreciated that the beam configuration of a given cell may be changed semi-statically for purposes such as self-organising network (SON) adaptation, e.g. Capacity and Coverage Optimisation (CCOpt). In this case, reconfiguration of a particular beam configuration may include changing the beamwidth of one or more beams and / or changing the number of beams (e.g. switching beams on or off).

[0080] When preparing for a handover between cells, if such information is available, the serving base station may inform the mobile device of the number of beams currently operating in the neighboring cell, so that the mobile device knows the range of beam IDs it needs to scan / measure. However, if such information is not available or transmitted to the mobile device, the mobile device may be configured to perform beam measurements assuming that the neighboring cell has the maximum number of beams possible. In any case, with information identifying the most suitable beam of the target cell, the mobile device does not need to perform extensive beam measurements when entering the target cell, since it already has a set of potential beams that may be considered for that OBS in the target cell.

[0081] In the above exemplary embodiment, the base station is described as transmitting multiple directional beams. It will be appreciated that data may be transmitted substantially simultaneously via multiple beams. However, in some cases, for example when hybrid (part analog and part digital) beamforming is used, it may not be possible to transmit all beams at once. It will be appreciated that in this case, a technique called "beam sweeping" (i.e., transmitting one beam at a time) can be used.

[0082] Instead of the network (base station) determining the OBS based on measurements from the mobile device, the mobile device may be configured to select a beam for its own OBS and (unless configured differently) report channel status information (CSI) only for the beam selected for its OBS by the mobile device 3. In this case, advantageously, the network can determine the OBS implicitly from the beam (beam ID) included in the CSI report. Since CSI reporting of beams in the OBS may be required anyway, this method has the advantage that no additional signaling is required when the mobile device is updating its OBS.

[0083] In the above example embodiment, the base station communicates with the mobile device using 3GPP wireless communication (radio access) technology. However, other wireless communication technologies (i.e., WLAN, Wi-Fi, WiMAX, Bluetooth, etc.) can be used between the base station and the mobile device in accordance with the above embodiment. The above example embodiment is also applicable to "non-mobile" or generally stationary user devices.

[0084] In the above description, the mobile device and base station have been described for ease of understanding as having several separate functional components or modules. These modules may be provided in this manner for a particular application, such as where an existing system is being modified to implement the present invention, such as in a system designed from the beginning with the features of the present invention in mind, but in a system designed from the beginning with the features of the present invention in mind, these modules may not be recognizable as separate entities, as they may be built into the overall operating system or code.

[0085] In the above exemplary embodiment, several software modules have been described. As will be appreciated by those skilled in the art, the software modules may be provided in compiled or uncompiled form, or may be provided to the base station, the mobility management entity, or the mobile device as a signal over a computer network or a recording medium. Furthermore, the functions performed by some or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of the base station or the mobile device to update their functions.

[0086] Each controller may include any suitable form of processing circuitry, including (but not limited to) the following: a microprocessor central processing unit (CPU), an arithmetic logic unit (ALU), input / output (IO) circuitry, internal memory / cache (program and / or data), processing register communication buses (e.g., control, data and / or address buses), direct memory access (DMA) functionality, counters, pointers and / or timers implemented in hardware or software, and / or the like.

[0087] The base station controller may be operable to control, for each communication device, a respective operational beam set (OBS) including at least one directional beam associated with that communication device.

[0088] The communication unit of the base station may be operable to receive from at least one communication device measurement results performed on respective reference signals transmitted via each beam, and the controller may be operable to determine each beam in the OBS based on the results of the measurements performed on the reference signals.

[0089] The communication unit of the base station may be operable to receive OBS-specific measurement results (e.g., channel state indicators, CSI, measurements) from the at least one communication device for beams included in the OBS for the at least one communication device.

[0090] The controller of the base station may be operable to control a handover for a particular communication device based on at least one of an OBS and a beam-specific reference signal associated with the communication device.

[0091] The base station controller may be operable to control coordinated multipoint (CoMP) for a particular communication device based on at least one of an OBS and a beam-specific reference signal associated with the communication device.

[0092] The communication unit of the base station may be operable to transmit respective control information including a reference signal via each beam. In this case, the respective reference signal transmitted via each beam may be a beam-specific reference signal. The communication unit of the base station may be configured to periodically transmit the respective reference signal in each beam using a predefined resource (e.g., time / frequency resource). The predefined resource may be specific to a particular beam. Alternatively, the predefined resource may be common to multiple (e.g., a subset or all) beams.

[0093] Each reference signal transmitted via each beam may depend on a corresponding beam identifier and a cell identifier associated with the communication area, and the resources used to transmit each reference signal via each beam may depend on the corresponding beam identifier and a cell identifier associated with the communication area.

[0094] The controller of the base station may be operable to control a beam configuration associated with a communication area of ​​the base station, and the communication unit of the base station may be operable to transmit (e.g., broadcast) within the communication area the beam configuration associated with the communication area. The beam configuration may define at least one of the number of beams within the communication area, the beam pattern within the communication area, the respective width associated with each beam, whether a particular beam is on or off, resources used for reference signal (or set of reference signals) transmission within a particular beam, and resources allocated for random access procedures per beam.

[0095] The base station communication unit may be operable to communicate each beam-specific system information using each directional beam. The base station communication unit may be operable to communicate, via each beam, information identifying resources for random access procedure signals via that beam. The base station communication unit may be operable to receive random access procedure signals from at least one communication device via the at least one beam using the identified resources.

[0096] The communication unit of the base station may be operable to apply transmit diversity to the at least one communication device using a plurality of directional beams associated with the at least one communication device, where the processor of the communication device may be operable to combine respective data received using each of the plurality of directional beams before decoding the data.

[0097] The communication section of the base station may be operable to transmit signals that are not specific to the at least one communication device (e.g., RAR messages 2 and 4, power control and / or paging) using multiple directional beams associated with the at least one communication device.

[0098] The base station may be equipped with a large antenna for forming multiple directional beams. The base station may be a base station of a next generation (NextGen or 5G) radio access network.

[0099] The controller of the communication device may be operable to perform measurements on respective reference signals transmitted via each beam, and the communication unit of the communication device may be operable to transmit the measurement results to the base station. The controller of the communication device may be operable to perform measurements (e.g., channel state indicator, CSI, measurements) on beams included in the OBS of the communication device, and the communication unit of the communication device may be operable to transmit the communication device results to the base station.

[0100] The controller of the communication device may be operable to control coordinated multi-cell transmission and reception (CoMP) via the base station based on at least one of an OBS and a beam-specific reference signal associated with the communication device within a communication area.

[0101] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0102] This application claims priority to UK Patent Application No. 1613902.4, filed August 12, 2016, the disclosure of which is incorporated herein in its entirety.

Claims

1. A base station, means for serving a communication area via a plurality of directional beams; means for transmitting, for a communication device, system information, control signals, and one or more reference signals using the directional beam based on a beam identifier of the directional beam corresponding to the communication device and a cell identifier corresponding to the communication area; Equipped with when the communication device detects that a signal quality of each of the at least one directional beam has deteriorated, a wireless link is maintained using at least one directional beam other than the at least one directional beam. Base station.

2. A communication device, comprising: means for receiving, from a base station serving a communication area via a plurality of directional beams, system information, control signals, and one or more reference signals based on a beam identifier of a directional beam corresponding to the communication device and a cell identifier corresponding to the communication area, using the directional beams; means for monitoring a signal quality of a corresponding plurality of said directional beams; means for detecting degradation of signal quality of each of at least one of said directional beams; means for maintaining a wireless link using at least one directional beam other than said at least one directional beam; A communication device comprising:

3. 1. A method in a base station, comprising: Serving a communication area via a plurality of directional beams; Transmitting system information, control signals, and one or more reference signals for a communication device using the directional beam based on a beam identifier of the directional beam corresponding to the communication device and a cell identifier corresponding to the communication region; Including, when the communication device detects that a signal quality of each of the at least one directional beam has deteriorated, a wireless link is maintained using at least one directional beam other than the at least one directional beam. method.

4. 1. A method in a communication device, comprising: receiving, from a base station serving a communication area via a plurality of directional beams, system information, control signals, and one or more reference signals based on a beam identifier of a directional beam corresponding to the communication device and a cell identifier corresponding to the communication area, using the directional beams; monitoring a signal quality of a corresponding plurality of said directional beams; detecting a degradation in signal quality of each of at least one of the directional beams; maintaining a wireless link using at least one directional beam other than the at least one directional beam; A method comprising:

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