UE, RAN node, and methods performed by them

Abstract

To provide a method and a device that efficiently and effectively support or improve one or more uplink carriers of such a plurality of carriers that can be used by UE.SOLUTION: In a cellular communication system in which user equipment (UE) initiates a random access channel (RACH) procedure by sending one or more messages including a random access preamble to a 5G base station, the base station selects an uplink carrier for initial access by the UE and notifies the UE of an UL (Uplink) carrier selected by the base station as part of the RACH procedure.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to communication systems, and in particular, but not exclusively, to wireless communication systems and devices thereof operating in accordance with 3GPP (3rd Generation Partnership Project) standards or equivalents or derivatives thereof. The present invention is particularly relevant to uplink (UL) sharing between so-called New Radio (NR) / Next Generation (NG) / 5G type communication devices with Long Term Evolution (LTE) type communication devices, but relates to efficient selection of supplementary uplink (SUL) carrier frequencies, in particular UL carriers. [Background technology]

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

[0003] In 3GPP standards, a NodeB (or "eNB" in LTE, "gNB" in 5G) is a base station through which communication devices (user equipment or "UE") connect to the core network and communicate with other communication devices or remote servers. Communication devices are mobile communication devices, such as mobile phones, smartphones, user equipment, personal digital assistants, laptop / tablet computers, web browsers, and e-book readers. Such mobile (or generally stationary) devices are typically operated by users. (So-called "Internet of Things" devices and similar machine-type communication devices can also be connected to the network.) For simplicity, this application uses the term base station to refer to such base stations and the term mobile device or UE to refer to such communication devices. The core network (e.g., EPC for LTE, NGC for NR / 5G) hosts functions for subscriber management, mobility management, charging, security, and call / session management (among others), and provides communication devices' connectivity to external networks, such as the Internet.

[0004] It is proposed that a UE be configured with multiple uplink (UL) carriers on different frequencies, with at least one LTE carrier on a first frequency and at least one NR carrier on a second, different carrier frequency. In one supported example, the UE is restricted to operating on only a single UL carrier of a given pair of carriers, including an LTE carrier and an NR carrier. However, simultaneous operation of the UE on two (or more) UL carriers is also supported.

[0005] Furthermore, from an NR perspective, it is proposed that a Supplementary Uplink (SUL) frequency should be provided to support the case where only uplink resources of a carrier are present. The SUL frequency can be used to support a complementary access link (including from a random access perspective) to another NR dedicated uplink frequency (for Time Division Duplex (TDD) and / or Frequency Division Duplex (FDD)) where the UE can select Physical Random Access Channel (PRACH) resources on either the NR TDD / FDD uplink frequency or the SUL frequency.

[0006] The SUL frequencies can be frequencies shared with LTE UL (at least if the NR spectrum is below 6 GHz). Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention seeks to provide a method and associated apparatus that supports or improves upon one or more of the above proposals / agreements in an efficient and effective manner.

[0008] In considering the above proposals / agreements, the inventors recognized that the possibility of using multiple different UL carriers (e.g., SUL carriers and NR dedicated carriers) presents many issues, particularly regarding UL carrier selection for initial access, which have not yet been resolved in an efficient manner. Specifically, the inventors identified the need to balance the sometimes conflicting risks of increased power consumption overhead, interference on PRACH resources, undesirable access times associated with, for example, repeated failed access attempts, and / or suboptimal UL carrier selection resulting from the use of measurements that may not accurately reflect the relative UL carrier quality.

[0009] For example, the SUL carrier operates in a scenario where there are only UL resources for the carrier from an NR perspective. This presents a challenge for efficient and effective UL carrier selection (especially when the SUL operates in an LTE-compatible range) because while the UE can estimate the UL path loss based on the DL signal and path loss offset, there may be a very large frequency offset between the UL and DL, which can lead to inaccurate path loss estimation (e.g., differences in UL-DL path loss due to subcarrier spacing and antenna dimensions). Therefore, the UE may not be able to support accurate time / frequency tracking or path loss estimation of the SUL carrier based on the paired DL (or same-frequency) carrier corresponding to the SUL carrier. Therefore, relying on estimates based on DL measurements to inform UL carrier selection can result in a high incidence of suboptimal carrier selection. Furthermore, if the UE can only estimate coverage levels based on DL measurements, insufficient resources on the selected UL carrier may result in increased PRACH blocking rates and associated reduced user data rates. This may require the gNB to reconfigure its initial carrier frequency selection and potentially retune the UE's radio frequency. [Means for solving the problem]

[0010] In one aspect of the present invention, there is provided a method performed by User Equipment (UE) of a cellular communication system, the method comprising: initiating a Random Access Channel (RACH) procedure by transmitting at least one message including a random access preamble to a Radio Access Network (RAN) device, the at least one message being transmitted using at least one Uplink (UL) carrier of a plurality of UL carriers available to the UE; receiving, from the apparatus of the RAN, an indication of a UL carrier selected by the apparatus of the RAN from the plurality of UL carriers usable by the UE as part of the RACH procedure; Equipped with.

[0011] According to one aspect of the present invention, there is provided a method performed by an apparatus of a Radio Access Network (RAN) in a cellular communication system, the method comprising: receiving at least one message from a User Equipment (UE) including a random access preamble for initiating a Random Access Channel (RACH) procedure; the at least one message is received using at least one uplink (UL) carrier of multiple UL carriers available to the UE; selecting a UL carrier for subsequent use by the UE from the plurality of UL carriers available for use by the UE; transmitting to the UE as part of the RACH procedure an indication of the UL carrier selected by the device of the RAN from the plurality of UL carriers available for use by the UE; Equipped with.

[0012] According to one aspect of the present invention, there is provided a User Equipment (UE) for a cellular communication system, the UE comprising: a transceiver and a controller, The controller Initiating a Random Access Channel (RACH) procedure by transmitting at least one message including a random access preamble to a Radio Access Network (RAN) device; the at least one message is transmitted using at least one uplink (UL) carrier of a plurality of UL carriers available to the UE; receiving, from the apparatus of the RAN, an indication of a UL carrier selected by the apparatus of the RAN from the plurality of UL carriers available for use by the UE as part of the RACH procedure; and controlling the transceiver so that User equipment.

[0013] According to one aspect of the present invention, there is provided an apparatus for a Radio Access Network (RAN) of a cellular communication system, the apparatus comprising: a transceiver and a controller, The controller receiving at least one message from a user equipment (UE) including a random access preamble for initiating a random access channel (RACH) procedure; the at least one message is received using at least one uplink (UL) carrier of multiple UL carriers available to the UE; selecting a UL carrier for subsequent use by the UE from the plurality of UL carriers available to the UE; transmitting to the UE as part of the RACH procedure an indication of the UL carrier selected by the device of the RAN from the plurality of UL carriers available for use by the UE; and controlling the transceiver so that RAN equipment.

[0014] According to one aspect of the present invention, there is provided a User Equipment (UE) for a cellular communication system, the UE comprising: means for initiating a Random Access Channel (RACH) procedure by transmitting at least one message including a random access preamble to a device of a Radio Access Network (RAN); the at least one message is transmitted using at least one uplink (UL) carrier of a plurality of UL carriers available to the UE; means for receiving, from the apparatus of the RAN, an indication of a UL carrier selected by the apparatus of the RAN from the plurality of UL carriers usable by the UE as part of the RACH procedure; A user equipment comprising:

[0015] According to one aspect of the present invention, there is provided an apparatus for a Radio Access Network (RAN) of a cellular communication system, the apparatus comprising: means for receiving from a User Equipment (UE) at least one message including a random access preamble for initiating a Random Access Channel (RACH) procedure; the at least one message is received using at least one uplink (UL) carrier of multiple UL carriers available to the UE; means for selecting a UL carrier for subsequent use by the UE from the plurality of UL carriers available to the UE; means for transmitting to the UE, as part of the RACH procedure, an indication of the UL carrier selected by the device of the RAN from the plurality of UL carriers available to the UE; RAN apparatus comprising:

[0016] Aspects of the present invention extend to computer program products such as computer readable storage media storing instructions operable to program a programmable processor to perform the methods described above or recited in the claims and / or aspects and possibilities for programming a computer suitably adapted to provide an apparatus as described in any of the claims.

[0017] Each feature disclosed in this specification and / or shown in the drawings (this term includes claims) may be incorporated into the present invention independently (or in combination) with other disclosed and / or shown features. In particular, but not limited to, any feature of a claim dependent on a particular independent claim may be introduced into that independent claim in any combination or individually.

[0018] Exemplary embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 shows a schematic diagram of a cellular communication system. [Figure 2] FIG. 2 is a block diagram of user equipment that may form part of the system shown in FIG. [Figure 3] FIG. 3 is a block diagram of a radio access network device forming part of the system shown in FIG. [Figure 4] FIG. 4 is a simplified message sequence diagram illustrating an exemplary manner in which an initial access procedure may be performed in the system of FIG. [Figure 5] FIG. 5 is a simplified message sequence diagram illustrating another exemplary manner in which an initial access procedure may be performed in the system of FIG. [Figure 6] FIG. 6 includes simplified message sequence diagrams (a) and (b) illustrating another exemplary manner in which an initial access procedure may be performed in the system of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] overview FIG. 1 schematically illustrates a communications network 1 in which user equipment (UE) 3 (mobile phones and / or other communications devices) can communicate with each other via radio access network (RAN) equipment 5 using appropriate radio access technologies (RATs), and in the illustrated example comprising an LTE base station or “eNB” 5-1 and an NR / 5G base station or “gNB” 5-2. In this example, UE 3 can communicate as an LTE UE 3-1 supporting at least LTE radio access technology via the eNB 5-1 portion of the RAN 5. UE 3 can also communicate as an NR / 5G UE 3-2 supporting one or more 5G radio access technologies via the gNB 5-2 portion of the RAN equipment 5. However, it will be understood that UE 3 need not have LTE capabilities and may support only 5G capabilities.

[0021] As one skilled in the art will appreciate, although one mobile device 3 (with three possible UE configurations) and one base station 5 are shown in FIG. 1 for illustrative purposes, when implemented, the system will typically include other base stations and mobile devices.

[0022] In this example, the RAN devices eNB 5-1 and gNB 5-2 are co-located with respective base stations operating one or more associated cells, and the UE 3 connects to the appropriate cell (depending on their location and possibly other factors, such as signal conditions, subscription data, capabilities, etc.) by establishing a Radio Resource Control (RRC) connection with the base stations 5-1, 5-2 operating the cells.

[0023] The RAN device 5 is connected to a core network 7 via an appropriate interface. The core network 7 comprises NR / 5G functions necessary to support communication of the UE 3 via the gNB 5-2. The core network 7 includes functions providing, for example, control plane management, user plane management, mobility management, etc. The core network 7 also comprises partial or complete EPC functions to support communication of the UE 3 via the eNB 5-1.

[0024] The UE 3 and the RAN equipment 5 are configured to use multiple carriers (or "component carriers") for uplink (UL) communications from the UE 3 to the RAN equipment 5 and downlink (DL) communications from the RAN equipment 5 to the UE 3. These UL and DL carriers operate on many different carrier frequencies. In this example, the UL carrier includes a supplementary uplink (SUL) carrier on an SUL frequency (F1 in the illustrated example) and at least one separate NR dedicated UL carrier on a corresponding UL frequency (F2) that is different from that of the SUL carrier. In this example, the SUL carrier is on a frequency within the range used by LTE and therefore can be shared between LTE and NR (i.e., the LTE UL and NR UL share UL subframes of the LTE frequency). However, it is understood that the SUL carrier is a separate NR UL carrier and may operate on a frequency range not normally used for LTE. The UL carrier may also include other UL carriers (e.g., an LTE dedicated UL carrier on a different frequency). In this example, the DL carriers include at least one carrier for NR DL transmission on a frequency (F3) different from the uplink (UL) frequency and at least one carrier for LTE DL transmission on a frequency (Fn) different from the NR DL frequency.

[0025] Beneficially, gNB5-2 is configured to be able to select the UL carrier used by UE3 for initial UL access (e.g., to be either supplemental UL frequency F1 or NR dedicated UL frequency F2). Thus, by having gNB5-2 configure the NR UE's initial UL carrier selection, gNB5-2 can advantageously schedule data and control channels that take into account coverage levels and resource availability (which gNB5-2 can estimate more accurately than UE3).

[0026] To support gNB5-2 in configuring initial UE UL carrier selection, UE3 and gNB5-2 are advantageously configured to use a modified UL initial access procedure that has the potential to reduce delays by avoiding unnecessary procedures (e.g., RRC connection reconfiguration procedures).

[0027] Specifically, gNB5-2 is advantageously configured to provide an indication of the UL carrier selected for initial access before completion of the setup of the connection (e.g., RRC connection) between UE3 and gNB5-2 during the initial access procedure (e.g., before an RRC connection complete message is sent from UE3 to gNB5-2). In the example described below, the indication is advantageously provided in Msg4 of the random access channel procedure (e.g., Connection Resolution / RRC Connection Setup message), although it will be understood that the indication may be provided in any suitable message from gNB5-2 to UE3.

[0028] Many variations of modified UL initial access procedures that can be used to provide an indication of the UL carrier selected for initial access are described in more detail below. While all of the disclosed procedures have different advantages and tradeoffs compared to one another, they each represent an efficient and effective way of performing UL carrier selection by the gNB 5-2 to the UE 3 to be used for initial access and to indicate the results of such selection.

[0029] User Equipment FIG. 2 is a block diagram illustrating the major components of the UE 3 (e.g., a mobile phone or other user equipment) shown in FIG. 1. As shown, the UE 3 has transceiver circuitry 31 operable to transmit signals to and receive signals from the base stations 5-1, 5-2 functions of the RAN equipment 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 coupled to the transceiver circuitry 31. Although not necessary for its operation, the mobile device 3 of course has all the usual functionality of a conventional mobile phone 3 (e.g., a user interface 35), which may be provided by one or any combination of hardware, software, and firmware, as appropriate. Software may be pre-installed in the memory 39 and / or downloaded, for example, over a communications network or from, for example, a removable data storage device (RMD).

[0030] Controller 37, in this example, is configured to control the overall operation of UE 3 by means of program or software instructions stored in memory 39. As shown, these software instructions comprise, among other things, an operating system 41, a communications control module 43 including several radio access technology modules (such as an LTE module 44 and an NR / 5G module 45) for accessing compatible radio access networks, an initial access module 46, and a UL carrier management module 47.

[0031] The communication control module 43 is operable to control communications between the UE 3 and the base stations 5-1, 5-2 (and other communication devices connected to the base stations 5-1, 5-2, such as further mobile devices / or network nodes). The LTE module 44 is responsible for operating the UE as an LTE UE 3-1 and, in particular, managing communications with an eNB 5-1 operating in accordance with current LTE standards (e.g., 3G / 4G base stations) and other nodes / devices connecting to such base stations. The NR / 5G module 45 is responsible for operating the UE as an NR / 5G UE 3-2 and, in particular, managing communications with a gNB 5-2 operating in accordance with NextGen (5G) standards and other nodes / devices connecting to such NextGen base stations.

[0032] The initial access module 46 is operable to control the UE 3 during an initial access procedure with the eNB 5-1 and / or the gNB 5-2, including generating, transmitting, and receiving messages during a Physical Random Access Channel (PRACH) procedure. The initial access module 46 manages, for example, the generation and transmission of Msg1, which carries an appropriate random access preamble and temporary identifier (e.g., a Random Access Radio Network Temporary Identifier, RA-RNTI), and Msg3 (e.g., a connection request), as well as the reception and processing of Msg0, which assigns a preamble (e.g., if required for contention-free access), Msg2, which carries a Random Access Response (RAR) message, and any Msg4 (e.g., a contention resolution / connection setup request). The initial access module 46 is also operable to identify the uplink carrier to be used in the PRACH procedure (e.g., for Msg1 transmission). As will be described in more detail below, UE3 may identify the uplink carrier to use for the PRACH procedure by selecting the uplink carrier itself, and / or may identify the uplink carrier to use for the PRACH procedure based on a selection made by gNB5-2.

[0033] The UL carrier management module 47 manages the handling of UL carrier communications, including, for example, configuring UL communications for initial access on the uplink carrier selected by the gNB 5-2 and indicated to the UE 3 in the initial access procedure (e.g., Msg4).

[0034] RAN equipment Figure 3 is a block diagram illustrating the main components of the RAN equipment 5 shown in Figure 1. As shown, the RAN equipment 5 includes transceiver circuitry 51 for transmitting signals to and receiving signals from communication devices (such as UE 3) via one or more antennas 53, and at least one core network interface 55 for transmitting signals to and receiving signals from the core network 7.

[0035] The RAN equipment 5 includes a controller 57 that controls the operation of the RAN equipment 5. The controller 57 is associated with a memory 59. Although not necessarily shown in FIG. 3 , the RAN equipment 5 includes all of the typical functionality of a cellular telephone network base station, which may be provided by one or any combination of hardware, software, and firmware. The software may be pre-installed in the memory 59 and / or downloaded, for example, via the communications network 1 or from a removable data storage device (RMD). The controller 57, in this example, is configured to control the overall operation of the RAN equipment 5 by program or software instructions stored in the memory 59. As shown, these software instructions include, among other things, an operating system 61, a communications control module 63 that includes multiple base station modules (such as an eNB module 65 and a gNB module 67) for providing the functionality of a corresponding base station, an initial access management module 68, and a UL carrier management module 69.

[0036] The communication control module 63 is operable to control communications between the RAN apparatus 5 and the UE 3 (and other network elements connected to the RAN apparatus 5). The eNB module 65 is responsible for managing communications with the UE 3 when the RAN apparatus 5 operates as an eNB 5-1, in particular when operating in accordance with current LTE standards (and / or one or more LTE dedicated UEs). The gNB module 67 is responsible for managing communications with the UE 3 when the RAN apparatus 5 operates as a gNB 5-2, in particular when operating as an NR UE in accordance with NextGen (5G) standards (and / or one or more NR dedicated UEs).

[0037] The initial access management module 68 is operable to control the RAN device 5 during an initial access procedure, including the generation, transmission, and reception of messages during a Physical Random Access Channel (PRACH) procedure with the UE 3. The initial access management module 68 manages, for example, the reception and processing of Msg1, which carries an appropriate random access preamble and temporary identifier (e.g., a Random Access Radio Network Temporary Identifier, RA-RNTI), and Msg3 (e.g., a connection request), Msg0, which assigns a preamble (e.g., if required for contention-free access), Msg2, which carries a Random Access Response (RAR) message, and any Msg4 (e.g., a resolution / connection setup request). In particular, the initial access management module 68 is operable to manage the initial access procedure when acting as the gNB 5-2, particularly with regard to identifying the uplink carrier used in the PRACH procedure (e.g., for Msg1 transmission). As will be explained in more detail below, gNB5-2 selects the uplink carrier to use for the PRACH procedure and signals this to UE3 using appropriate signaling (e.g., using synchronization signals, system information (e.g., via the Master Information Block (MIB)), via other signals broadcast on the Physical Broadcast Channel (PBCH), and / or using appropriately configured RRC signaling).

[0038] The UL carrier management module 69 manages the handling of UL carrier communications, including, for example, configuring UL communications for initial access on an uplink carrier selected by gNB5-2 and indicated to UE3 in the initial access procedure (e.g., in Msg4).

[0039] Method 1 - Uplink carrier of PRACH preamble indicated by gNB FIG. 4 is a simplified message sequence diagram illustrating an exemplary method of an initial access procedure implemented within the system of FIG. 1 to provide UE 3 with efficient and effective indication of the selected UL carrier from gNB 5-2 (or the gNB portion of RAN equipment 5).

[0040] As seen in S400, in this example, the NR gNB5-2 indicates to UE3 on the NR DL the carrier to be used for the PRACH procedure using appropriate signaling (e.g., using synchronization signals, system information (e.g., via the Master Information Block (MIB) and / or other signals broadcast on the Physical Broadcast Channel (PBCH) and / or using appropriately configured RRC signaling).

[0041] Next, at S402, UE3 transmits a first message of the PRACH procedure (known in the art as "Msg1") to gNB5-2 to initiate the random access procedure. PRACH Msg1 typically includes a PRACH preamble sequence with a corresponding Radio Access Radio Network Temporary Identifier (RA-RNTI) and a selected preamble index. At this point, although not shown, UE3 begins monitoring the Physical Downlink Control Channel (PDCCH) associated with the RA-RNTI. If there is no response, this monitoring typically continues for the number of subframes specified by a predefined random access response window size.

[0042] At S403, gNB5-2 sends to UE3 a Random Access Response (RAR) message (commonly known in the art as "Msg2") carrying an uplink grant for the next message from UE3, along with a Temporary Cell Radio Network Temporary Identifier ("Temporary C-RNTI" or "T_CRNTI") and possibly a backoff indicator and / or timing advance command. UE3 detects the PDCCH associated with the RA-RNTI and identifies the Downlink Control Indicator / Information (DCI) carried by the PDCCH and required for decoding the Physical Downlink Shared Channel (PDSCH). UE3 uses the DCI to decode the PDSCH and thus extract the information carried by the RAR message.

[0043] At this stage, the UE3 typically checks whether the RAR message contains a Backoff Indicator (BI). If a BI is found, the UE3 typically sets the corresponding backoff parameters specified by the BI. If a BI is not found, the UE3 typically sets the backoff parameters to zero (0). The UE3 also checks whether the RAR message contains a random access preamble identifier that matches the one the UE3 used in Msg1. If there is a match, the UE3 considers that the correct RAR message has been received and processes the associated timing advance command in the RAR message and the received UL grant value.

[0044] At S404, UE3 transmits a third message of the PRACH procedure (commonly known in the art as "Msg3") to gNB5-2. UE3 transmits this message using a Physical Uplink Shared Channel (PUSCH) using the radio resources allocated by the UL Grant specified in the RAR message. The exact timing of the PUSCH transmission may be adjusted by a timing advance value included in the RAR message.

[0045] At S406, gNB5-2 selects an uplink carrier to be used for initial access. While this step is shown as occurring after reception of Msg3, it is understood that it may occur at any suitable time, including before Msg3 (or in parallel with other parts of the PRACH procedure). In this example, because gNB5-2 only receives the PRACH request (Msg1) on a single uplink carrier, gNB5-2 does not have uplink measurements on both uplink carriers. Therefore, the selection may take into account information received from UE3 (e.g., DL Reference Signal Received Power (RSRP), power headroom reports, etc.), even though this information may not accurately reflect the path loss conditions experienced on the uplink. It is understood that the selection may also take into account uplink measurements of the uplink carrier on which the PRACH is received.

[0046] At S408, gNB5-2 notifies UE3 of the selected UL carrier by including an indication of the UL carrier selection in a Contention Resolution Message (commonly known in the art as "Msg4"), in this example, along with a Contention Resolution ID (CRID).

[0047] If necessary, gNB5-2 may request further information (e.g., RSRP measurements, transmit power, power headroom reports, etc.) from UE3, as shown in S410. Upon receiving the requested information, gNB5-2 may make its uplink carrier selection (or a decision to request the UE to re-initiate the PRACH procedure for another carrier) based on such further information (results of DL measurements) received from UE3, as shown in S412.

[0048] Although not shown, gNB 5-2 may request UE 3 to initiate a PRACH procedure using another carrier and notify PRACH resources accordingly, which may typically occur, for example, after a further information request / response and before the transmission of Msg4.

[0049] Method 2 - UE Selected Uplink Carrier for PRACH Preamble FIG. 5 is a simplified message sequence diagram illustrating another exemplary method of an initial access procedure implemented in the system of FIG. 1 that provides efficient and effective indication of a selected UL carrier from gNB 5-2 (or the gNB portion of RAN equipment 5) to UE 3.

[0050] Because the procedure is similar to that of Figure 4, the description of the corresponding steps in Figure 4 applies to the procedure of Figure 5 (even if not repeated for brevity). However, unlike the procedure of Figure 4, in this example, as seen at S500, UE3 (and not NR gNB5-2) selects the carrier to use for the PRACH procedure (e.g., based on an estimate of path loss and / or carrier priorities assigned to each carrier to prioritize which carrier is selected first).

[0051] Next, at S502, UE3 sends a first message of the PRACH procedure to gNB5-2 to initiate a random access procedure including a PRACH preamble sequence together with the corresponding RA-RNTI and the selected preamble index, as described with reference to FIG. 4.

[0052] As described with reference to FIG. 4, at S503, gNB5-2 sends to UE3 an RAR message (Msg2) carrying an uplink grant for Msg3 from UE3 together with a temporary C-RNTI and possibly a backoff indicator and / or a timing advance command.

[0053] As described with reference to Figure 4, at S504, UE3 transmits Msg3 to gNB5-2 on a Physical Uplink Shared Channel (PUSCH) using the radio resources allocated by the UL grant specified in the RAR message. The exact timing of the PUSCH transmission may be adjusted by a timing advance value included in the RAR message.

[0054] At S506, gNB5-2 selects an uplink carrier to be used for initial access. As described with reference to FIG. 4, this step is shown as occurring after reception of Msg3, but may occur at any suitable juncture, including before Msg3 (or in parallel with other parts of the PRACH procedure). In this example, because gNB5-2 only receives the PRACH request (Msg1) on a single uplink carrier, gNB5-2 does not have uplink measurements on both uplink carriers. Therefore, the selection may take into account information received from UE3 (e.g., DL Reference Signal Received Power (RSRP), power headroom reports, etc.), even though this information may not accurately reflect the path loss conditions experienced on the uplink. It will be understood that the selection may also take into account uplink measurements on the uplink carrier on which the PRACH is received.

[0055] At S508, as described with reference to FIG. 4, gNB 5-2 notifies UE 3 of the selected UL carrier by including an instruction for UL carrier selection in a Contention Resolution Message (Msg4), in this example, together with a Contention Resolution ID (CRID).

[0056] Although not shown, gNB5-2 may also request UE3 to initiate a PRACH procedure using another carrier and notify PRACH resources accordingly.

[0057] If necessary, gNB5-2 may request further information (e.g., RSRP measurements, power headroom reports, etc.) from UE3, as shown in S510. Upon receiving the requested information, as shown in S512, gNB5-2 may base its uplink carrier selection on such further information received from UE3 (or a decision to request the UE to re-initiate the PRACH procedure towards another carrier).

[0058] Analysis of Methods 1 and 2 It can be seen that methods 1 and 2 offer potential advantages in terms of UE power consumption, as only a selected number of UEs need to transmit PRACH preambles on both uplink frequencies. This also means that the number of UEs using each UL carrier of the PRACH is minimized, thereby minimizing the risk of interference to PRACH resources.

[0059] Thus, although PRACH blocking on a given UE's selected UL carrier may result in repeated attempts to obtain initial access, the UE can still obtain UL initial access using the optimized carrier with reduced latency, even though the gNB5-2's determination of the need to transmit PRACH towards another carrier is based on the UE's RSRP measurement (which may be inaccurate).

[0060] Method 3 - Multiple uplink carriers used for PRACH preamble 6(a) and (b) are simplified message sequence diagrams illustrating another exemplary way in which the initial access procedure can be implemented in the system of FIG. 1 to provide efficient and effective indication of the selected UL carrier from gNB 5-2 (or the gNB portion of RAN equipment 5) to UE 3.

[0061] The procedure is similar to that in Figures 4 and 5, so the descriptions of the corresponding steps in Figures 4 and 5 apply to the procedure in Figure 6 (even if they are not repeated for the sake of brevity).

[0062] Unlike the procedures of Figures 4 and 5, in this example there is no pre-selection of an UL carrier for PRACH preamble transmission. Instead, UE 3 transmits the PRACH preamble on both UL carriers. Specifically, as seen in S600-1 to S600-2, UE 3 sequentially transmits multiple Msg1 type messages on each respective carrier (each Msg1 is described with reference to Figures 4 and 5). However, transmission of Msg1 for a particular carrier may be conditional on the estimated path loss for that carrier being below a predetermined threshold, based on DL measurements.

[0063] Figure 6(a) shows the procedure when gNB5-2 receives preambles on both carriers from the same UE 3. Figure 6(b) shows the procedure when gNB5-2 receives preambles on only a single carrier from UE 3.

[0064] At S603, gNB5-2 sends to UE3 a Random Access Response (RAR) message ("Msg2") carrying an uplink grant for the next message from UE3, along with a temporary cell radio network temporary identifier ("Temporary C-RNTI" or "T_CRNTI"), and possibly a backoff indicator and / or timing advance command (as described with reference to Figures 4 and 5).

[0065] At S604, UE3 transmits Msg3 to gNB5-2 on the Physical Uplink Shared Channel (PUSCH) using the radio resources allocated by the UL grant specified by the RAR message (as broadly described with reference to Figures 4 and 5).

[0066] If gNB5-2 receives preambles on both carriers from the same UE3 (as shown in Figure 6(a)), gNB5-2 makes a UL carrier selection based on UL measurements of the received uplink signal at S606.

[0067] As shown in Figure 6(b), if gNB 5-2 detects a preamble only on a subset of carriers (e.g., a single carrier), it may request more information from UE 3 (e.g., RSRP measurements, power headroom reports, etc.), as shown at S610. Upon receiving the requested information, as shown at S612, gNB 5-2 may make its uplink carrier selection based on such further information (DL measurements) received from UE 3.

[0068] As described with reference to Figures 4 and 5, at S608, gNB5-2 notifies UE3 of the selected UL carrier by including an instruction for UL carrier selection in a contention resolution message (Msg4) together with a contention resolution ID (CRID), in this example.

[0069] Upon receiving notification of the gNB UL carrier selection, UE3 stops attempting to transmit Msg1.

[0070] Analysis of Method 3 It can be seen that with Method 3, UE3 can obtain UL initial access on the optimal carrier in a relatively short (and therefore advantageous) timescale. Furthermore, gNB5-2 can select the UL carrier based on accurate UL measurements (if it receives preambles on both carriers).

[0071] Thus, although there may be a small overhead associated with transmitting the PRACH preamble on both uplink carriers (in terms of UE power consumption), Method 3 may cause more interference to PRACH resources compared to Methods 1 and 2 (although mitigated by the relatively short PRACH transmission time), but the UE may nevertheless use the optimal carrier to obtain UL initial access with reduced delay.

[0072] Therefore, switching the PRACH preamble sequence transmission of Method 3 on available UL carriers (F1 and F2) during initial access attempts (Msg1) is a particularly effective option, either alone or after several failures on at least one selected carrier. NR can support multiple consecutive Msg1 transmissions on different UL carriers at the start of the monitoring RAR window, or consecutive Msg1 transmissions on different UL carriers within contention-free random access after the end of the monitoring RAR window, in both contention-free and contention-based random access. NR supports the timing of Msg2 and Msg3 transmissions in slots or "minislots" (the smallest scheduling unit possible in the current time domain, i.e., smaller than a slot).

[0073] The above mechanism may therefore improve user data rates and reduce the total number of attempts by the UE to gain access, especially compared to scenarios where there is a high PRACH blocking rate due to limited resources on a particular carrier.

[0074] Modifications and substitutions Detailed exemplary embodiments have been described above. As those skilled in the art will appreciate, many modifications and alternatives can be made to the above embodiments and still benefit from the invention embodied therein. By way of example, only some of these alternatives and modifications will be described.

[0075] For example, while the exemplary system describes RAN equipment in which the eNB and gNB are co-located and share some hardware and software modules, it will be understood that the eNB and gNB may be separate with their own individual hardware and software. The RAN equipment may, in accordance with known 5G developments, divide functionality into at least one distributed (or "remote") unit (DU) that communicates with the UE and a central unit (CU) between the DU and the core network. For example, higher layer functionality is provided by the CU and lower layer functionality is provided by the DU.

[0076] The term "component carrier" or "carrier" as used in the description, with reference to refer to an UL carrier and a DL carrier, represents a distinct communication (or "transmission") bandwidth within a discrete time / frequency resource (e.g., a physical resource block (PRB)) that can be scheduled. The term "carrier" in this context should not be confused with the term "subcarrier." A "subcarrier" represents the smallest unit of frequency used in a cellular communication system as described and is typically allocated in groups (commonly referred to as PRBs) within a given communication time interval (e.g., a transmission time interval (TTI), minislot, slot, subframe, etc.). Thus, a component carrier represents a transmission (UL, DL, or both) bandwidth that includes multiple (typically tens) PRBs, with each PRB including multiple (typically many, e.g., 12) subcarriers. In other words, the transmission bandwidth associated with each carrier typically includes hundreds of subcarriers.

[0077] It is understood that the request to restart the RACH procedure using a different UL carrier may implicitly or explicitly provide an indication of the UL carrier selected by the gNB.

[0078] It will be appreciated that a suitably adapted Msg2 may be used for a request for further information by the gNB and a suitably adapted Msg2 may be used for a response from the UE. The messages may be adapted, for example, by adding additional fields to the request / response information elements.

[0079] A request to initiate a PRACH procedure using another carrier (and / or a request for additional information) is triggered when the estimated path loss of a carrier based on DL measurements falls below some threshold. A request to initiate a PRACH procedure using another carrier may be considered a "request for further measurements" because it is used to perform UL measurements on the new carrier as well as the original carrier on which the PRACH was transmitted. The gNB may make such a request, for example, by transmitting a preamble for the new carrier. Alternatively or additionally, the gNB may request UL transmissions on some configured UL reference signal subcarriers (as part of the request to initiate a PRACH procedure using another carrier or as a separate request) to enable uplink measurements (e.g., to provide a basis for more accurate path loss estimation of the corresponding uplink carrier). UE3 may transmit such UL reference signals using gaps in the time domain (or frequency domain) for the transmission of Msg1. It will be appreciated that in such a request, it may be advantageous to transmit a UE identifier (UE-ID) along with the PRACH preamble to identify the correct UE as the target of the request.

[0080] It will be appreciated that a RACH procedure similar to that shown and described with reference to Figures 4 to 6 may be used to support the gNB and update the UE UL carrier selection during the RACH procedure. Specifically, for example, if the UE is informed of the UL carrier selected by the gNB for initial access, the gNB may update the later selected UL carrier during a further RACH procedure and inform the UE accordingly (e.g., as described with reference to Figures 4 to 6).

[0081] 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 and may be supplied to the subject device (UE, RAN, NB, gNB, etc.) as a signal over a computer network or on a recording medium. Furthermore, the functionality performed by some or all of this software may be performed using one or more discrete hardware circuits. However, the use of software is recommended to facilitate updating the base station or mobile device to update functionality.

[0082] Each controller forming part of the apparatus described herein may comprise any suitable form of processing circuitry including, for example, but not limited to, one or more hardware implemented computer processors, microprocessors, central processing units (CPUs), arithmetic logic units (ALUs), input / output (IO) circuitry, internal memory / cache (program and / or data), processing registers, communication buses (e.g., control, data, and / or address buses), direct memory access (DMA) facilities, hardware or software implemented counters, pointers, and / or timers, and / or the like.

[0083] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0084] The above-described exemplary embodiments are described in whole or in part in the following appendices, but are not limited thereto.

[0085] (Appendix 1) 1. A method performed by User Equipment (UE) of a cellular communication system, comprising: initiating a Random Access Channel (RACH) procedure by transmitting at least one message including a random access preamble to a Radio Access Network (RAN) device, the at least one message being transmitted using at least one Uplink (UL) carrier of a plurality of UL carriers available to the UE; receiving, from the apparatus of the RAN, an indication of a UL carrier selected by the apparatus of the RAN from the plurality of UL carriers usable by the UE as part of the RACH procedure; A method for providing the above.

[0086] (Appendix 2) the at least one UL carrier used to transmit the message including a random access preamble includes a UL carrier previously indicated by the device of the RAN; The method described in Appendix 1.

[0087] (Appendix 3) the at least one UL carrier used to transmit the message including a random access preamble includes a UL carrier selected by the UE; The method described in Appendix 1.

[0088] (Appendix 4) receiving a request to restart the RACH procedure using a different carrier from the plurality of UL carriers. 4. The method of any one of appendices 1 to 3.

[0089] (Appendix 5) the request to restart the RACH procedure using a different carrier of the plurality of UL carriers includes at least one of a PRACH preamble of the different carrier of the plurality of UL carriers and an identifier of the UE. The method described in Appendix 4.

[0090] (Appendix 6) the request to restart the RACH procedure using a different UL carrier provides an indication of a UL carrier selected by the device of the RAN from the plurality of UL carriers available to the UE. 6. The method according to claim 4 or 5.

[0091] (Appendix 7) and receiving a request for further information (e.g., at least one of a Reference Signal Received Power (RSRP) measurement and a power headroom report) to inform the selection of an UL carrier by the device of the RAN. 7. The method of any one of appendixes 1 to 6.

[0092] (Appendix 8) providing the requested additional information. The method described in Appendix 7.

[0093] (Appendix 9) receiving a request for an UL transmission on an UL reference signal subcarrier; transmitting a reference signal on the UL reference signal subcarrier; 8. The method of any one of claims 1 to 7, further comprising:

[0094] (Appendix 10) the selection of the UL carrier by the device of the RAN is based on at least one uplink (UL) measurement of the at least one UL carrier of the plurality of UL carriers over which the at least one message including a random access preamble is transmitted. 10. The method of any one of appendices 1 to 9.

[0095] (Appendix 11) the initiating includes transmitting a plurality of messages to a device in a Radio Access Network (RAN), each message including a random access preamble; each of the plurality of messages being transmitted using a different one of the plurality of UL carriers available to the UE; The method described in Appendix 1.

[0096] (Appendix 12) and wherein the selection of an UL carrier by the device of the RAN is based on UL measurements, where the device of the RAN receives a respective preamble on each of the plurality of carriers. The method described in Appendix 11.

[0097] (Appendix 13) If the device of the RAN does not receive a respective preamble on all of the plurality of carriers, the device of the RAN sends a request for further information (e.g., at least one of a Reference Signal Received Power (RSRP) measurement and a power headroom report) to inform the device of the RAN's selection of an UL carrier; The method further includes receiving the request for further information. 13. The method of claim 11 or 12.

[0098] (Appendix 14) providing the requested additional information. The method described in Appendix 13.

[0099] (Appendix 15) At least one carrier of the plurality of UL carriers is a New Radio (NR) or 5G dedicated UL carrier (e.g., having associated communication bandwidth that is not shared with LTE); 15. The method of any one of appendixes 1 to 14.

[0100] (Appendix 16) At least one carrier among the plurality of UL carriers is a Supplementary Uplink (SUL) carrier. 16. The method of any one of appendixes 1 to 15.

[0101] (Appendix 17) the SUL carrier is a UL carrier shared between a New Radio (NR) or 5G type communication system and a Long Term Evolution (LTE) type communication system (e.g., used by both systems and having an associated communication bandwidth); The method described in Appendix 16.

[0102] (Appendix 18) the indication of the UL carrier selected by the device of the RAN is received before the connection to the device of the RAN is completed (e.g., before a connection complete message is sent by the UE); 18. The method of any one of appendices 1 to 17.

[0103] (Appendix 19) the indication of the UL carrier selected by the device of the RAN is received in message 4 (Msg4 - e.g., a Contention Resolution Message) of the RACH procedure; 19. The method of any one of appendixes 1 to 18.

[0104] (Appendix 20) The devices of the RAN include New Radio (NR) or 5G base stations (gNB), 20. The method of any one of appendixes 1 to 19.

[0105] (Appendix 21) the devices of the RAN include a Long Term Evolution (LTE) base station (eNB); 21. The method of any one of appendixes 1 to 20.

[0106] (Appendix 22) and further including a further indication of a UL carrier selected by the device of the RAN from the plurality of UL carriers available for use by the UE to update the UL carrier used by the UE during a subsequent RACH procedure. 22. The method of any one of appendices 1 to 21.

[0107] (Appendix 23) 1. A method performed by a device of a Radio Access Network (RAN) in a cellular communication system, comprising: receiving at least one message from a User Equipment (UE) including a random access preamble for initiating a Random Access Channel (RACH) procedure; the at least one message is received using at least one uplink (UL) carrier of multiple UL carriers available to the UE; selecting a UL carrier for subsequent use by the UE from the plurality of UL carriers available for use by the UE; transmitting to the UE as part of the RACH procedure an indication of the UL carrier selected by the device of the RAN from the plurality of UL carriers available for use by the UE; A method for providing the above.

[0108] (Appendix 24) A user equipment (UE) of a cellular communication system, a transceiver and a controller, The controller Initiating a Random Access Channel (RACH) procedure by transmitting at least one message including a random access preamble to a Radio Access Network (RAN) device; the at least one message is transmitted using at least one uplink (UL) carrier of a plurality of UL carriers available to the UE; receiving, from the apparatus of the RAN, an indication of a UL carrier selected by the apparatus of the RAN from the plurality of UL carriers available for use by the UE as part of the RACH procedure; and controlling the transceiver so that User equipment.

[0109] (Appendix 25) 1. A device in a Radio Access Network (RAN) of a cellular communication system, comprising: a transceiver and a controller, The controller receiving at least one message from a user equipment (UE) including a random access preamble for initiating a random access channel (RACH) procedure; the at least one message is received using at least one uplink (UL) carrier of multiple UL carriers available to the UE; selecting a UL carrier for subsequent use by the UE from the plurality of UL carriers available to the UE; transmitting to the UE as part of the RACH procedure an indication of the UL carrier selected by the device of the RAN from the plurality of UL carriers available for use by the UE; and controlling the transceiver so that RAN equipment.

[0110] (Appendix 26) A cellular communication system comprising at least one device according to claim 25 and at least one user equipment according to claim 24.

[0111] (Appendix 27) 26. A computer-implementable instruction product comprising computer-implementable instructions for configuring a programmable device as the apparatus of Clause 25 or as the user equipment of Clause 24.

[0112] This application is based on and claims the benefit of priority from UK patent application No. 1709678.5 filed on 16 June 2017.

Claims

1. means for receiving an indicator from a Radio Access Network (RAN) node indicating an uplink carrier, whether the uplink carrier is a non-Supplementary Uplink (non-SUL) carrier or a Supplementary Uplink (SUL) carrier; means for transmitting a first message (Msg1) to the RAN node on a Random Access Channel (RACH) using the one of the uplink carriers indicated by the indicator; Equipped with the first message includes a Radio Network Temporary Identifier (RNTI) corresponding to an uplink carrier used to transmit the first message; the non-auxiliary uplink carrier is included in an operating frequency band of a first radio access technology; the auxiliary uplink carrier is included in an operating frequency band of the first radio access technology and an operating frequency band of a second radio access technology; User Equipment (UE).

2. means for transmitting an indicator to a User Equipment (UE) indicating whether the uplink carrier is a non-Supplementary Uplink (non-SUL) carrier or a Supplementary Uplink (SUL) carrier; means for receiving a first message (Msg1) on a Random Access Channel (RACH) using the one of the uplink carriers indicated by the indicator; Equipped with the first message includes a Radio Network Temporary Identifier (RNTI) corresponding to an uplink carrier used to transmit the first message; the non-auxiliary uplink carrier is included in an operating frequency band of a first radio access technology; the auxiliary uplink carrier is included in an operating frequency band of the first radio access technology and an operating frequency band of a second radio access technology; Radio Access Network (RAN) nodes.

3. receiving an indicator from a Radio Access Network (RAN) node indicating an uplink carrier, either a non-Supplementary Uplink (non-SUL) carrier or a Supplementary Uplink (SUL) carrier; transmitting a first message (Msg1) on a Random Access Channel (RACH) using the one of the uplink carriers indicated by the indicator; Including, the first message includes a Radio Network Temporary Identifier (RNTI) corresponding to an uplink carrier used to transmit the first message; the non-auxiliary uplink carrier is included in an operating frequency band of a first radio access technology; the auxiliary uplink carrier is included in an operating frequency band of the first radio access technology and an operating frequency band of a second radio access technology; A method in a User Equipment (UE).

4. transmitting an indicator to a User Equipment (UE) indicating an uplink carrier, whether the uplink carrier is a non-Supplementary Uplink (non-SUL) carrier or a Supplementary Uplink (SUL) carrier; receiving a first message (Msg1) on a Random Access Channel (RACH) using the one of the uplink carriers indicated by the indicator; and Including, the first message includes a Radio Network Temporary Identifier (RNTI) corresponding to an uplink carrier used to transmit the first message; the non-auxiliary uplink carrier is included in an operating frequency band of a first radio access technology; the auxiliary uplink carrier is included in an operating frequency band of the first radio access technology and an operating frequency band of a second radio access technology; A method in a Radio Access Network (RAN) node.

Images