Random access procedure

Abstract

In accordance with an example embodiment of the present disclosure, there is provided an apparatus comprising means for obtaining one or more cell-specific indicators, where the cell-specific indicators comprise a configuration for an aspect of a random access procedure, the random access procedure comprising a transmission of a first message with repetition, wherein the cell specific indicator comprises a repetition configuration for determining one or more candidate random access channel (RACH) occasion (RO) sequences for transmission of the first message with repetition; using a repetition configuration to determine and select an RO sequence among RO candidate sequences for transmission of the first message having repetition; and using the selected RO sequence for transmission of the first message with repetition.

Description

Technical Field

[0001] Various example embodiments relate to a random access procedure for a mobile network. Background Art

[0002] This section provides useful background information, but does not constitute an admission that any of the techniques described herein represent prior art.

[0003] The random access procedure is used to initiate data transmission in mobile networks.

[0004] The present disclosure relates to the development of random access procedures, and more particularly to random access messages with repetitions. Summary of the invention

[0005] The scope of protection sought by various embodiments of the present disclosure is set out by the independent claims. Embodiments and features described in this specification that do not fall under the scope of the independent claims, if any, should be interpreted as examples that aid in understanding the various exemplary embodiments.

[0006] According to a first exemplary aspect of the present disclosure, there is provided an apparatus comprising means for performing the following operations:

[0007] obtaining one or more cell-specific indicators, wherein the cell-specific indicators include a configuration for aspects of a random access procedure including transmission of a first message with repetitions, wherein the cell-specific indicators include a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions;

[0008] using the repetition configuration to determine and select an RO sequence among RO candidate sequences for transmission of a first message having repetitions; and

[0009] The selected RO sequence is used for transmission of the first message with repetitions.

[0010] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, determining and selecting an RO sequence is performed by: using a repetition configuration to determine an RO candidate sequence for transmission of a first message with repetition; and selecting one of the determined RO candidate sequences.

[0011] In some example embodiments, either alone or in combination with other embodiments of different aspects of the present disclosure, determining and selecting an RO sequence is performed by: using a repetitive configuration to determine one or more candidates for a first RO in a sequence and selecting one of the candidates as the first RO in the sequence; and iteratively determining one or more subsequent candidates for a subsequent RO in the sequence based on a previously selected RO in the sequence and selecting one of the subsequent candidates as a subsequent RO in the sequence until a desired number of ROs have been selected.

[0012] In some example embodiments, either alone or in combination with other embodiments of different aspects of the present disclosure, the selection is performed in a round-robin manner when there are more than one RO or RO sequence to choose from.

[0013] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, selecting the RO sequence is performed entirely before the first transmission of the first message with repetitions.

[0014] In some example embodiments, either alone or in combination with other embodiments of different aspects of the present disclosure, selection of an RO sequence is performed concurrently with transmission of a first message having a repetition, wherein the repetition of the first message is sent after selecting the RO on which to send the repetition and before selecting the RO for transmission of the subsequent repetition of the first message if there is an RO for transmission of the subsequent repetition of the first message.

[0015] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the ROs in the selected RO sequence occupy different time resources.

[0016] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, one or more cell-specific indicators are received from a network.

[0017] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the apparatus of the first aspect is a user equipment or is included in a user equipment.

[0018] According to a second exemplary aspect of the present disclosure, there is provided an apparatus comprising means for performing the following operations:

[0019] defining one or more cell-specific indicators, wherein the cell-specific indicator comprises a configuration for aspects of a random access procedure comprising transmission of a first message with repetitions, wherein the cell-specific indicator comprises a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions; and

[0020] The defined one or more cell-specific indicators are provided to a user equipment UE so that the UE determines and selects an RO sequence among RO candidate sequences for transmission of the first message with repetition.

[0021] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the apparatus of the second aspect is a network element or is included in a network element. The network element may be, for example, a gNB. The network element may be a physical device or a virtualized network function, including, for example, one or more virtual machines (VMs) operating on a virtualization platform including one or more virtualization servers.

[0022] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the repetition configuration groups multiple ROs in different frequency / time instances together to form one or more RO candidate sequences.

[0023] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the repetition configuration includes a density parameter for generating one or more random sparse matrices for determining connections from one RO to a subsequent RO of the RO candidate sequence.

[0024] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the repetition configuration includes one or more sparse matrices providing information on whether a RO is part of a RO candidate sequence.

[0025] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the repetition configuration includes one or more combination indicators providing a ranking of one or more RO combinations among all possible RO combinations, wherein one combination indicates an RO candidate sequence.

[0026] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the repetition configuration includes a first binary sequence indicating a first RO in the RO candidate sequence and a second binary sequence indicating a group of ROs to which the remaining ROs in the RO candidate sequence belong.

[0027] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the repetition configuration comprises N*M bits for each configured RO candidate sequence, where N is the number of ROs in the RO candidate sequence, and each M-bit group indicates one RO in each group of consecutive ROs.

[0028] In some example embodiments, either alone or in combination with other embodiments of different aspects of the present disclosure, the RO candidate sequences have in common at least one of: the first RO or the last RO, and the repetition configuration includes one or more single indications of one or more common ROs in the RO candidate sequences and sequence-specific indications of other ROs.

[0029] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, one or more cell-specific indicators include a preamble configuration for more than one preamble for transmission of the first message with repetition, so that the UE selects the preamble for transmission of the first message with repetition.

[0030] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the one or more cell-specific indicators include a maximum time configuration for the UE to determine a maximum duration of transmission of the first message with repetitions.

[0031] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, the random access procedure is contention-based random access (CBRA).

[0032] In some example embodiments, alone or in combination with other embodiments of different aspects of the present disclosure, components of the apparatus of the first aspect and / or the second aspect include: at least one processor; and at least one memory including executable instructions that, when executed by the at least one processor, cause execution of the apparatus.

[0033] According to a third exemplary aspect of the present disclosure, there is provided a method comprising:

[0034] obtaining one or more cell-specific indicators, wherein the cell-specific indicators include a configuration for aspects of a random access procedure including transmission of a first message with repetitions, wherein the cell-specific indicators include a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions;

[0035] using the repetition configuration to determine and select an RO sequence among RO candidate sequences for transmission of a first message having repetitions; and

[0036] The selected RO sequence is used for transmission of the first message with repetitions.

[0037] According to a fourth exemplary aspect of the present disclosure, there is provided a method comprising:

[0038] defining one or more cell-specific indicators, wherein the cell-specific indicator comprises a configuration for aspects of a random access procedure comprising transmission of a first message with repetitions, wherein the cell-specific indicator comprises a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions; and

[0039] The defined one or more cell-specific indicators are provided to a user equipment UE so that the UE determines and selects an RO sequence among RO candidate sequences for transmission of the first message with repetition.

[0040] According to a fifth exemplary aspect of the present disclosure, there is provided a computer executable program instruction configured to cause at least the following operations to be performed:

[0041] obtaining one or more cell-specific indicators, wherein the cell-specific indicators include a configuration for aspects of a random access procedure including transmission of a first message with repetitions, wherein the cell-specific indicators include a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions;

[0042] using the repetition configuration to determine and select an RO sequence among RO candidate sequences for transmission of a first message having repetitions; and

[0043] The selected RO sequence is used for transmission of the first message with repetitions.

[0044] According to a sixth exemplary aspect of the present disclosure, there is provided a computer executable program instruction configured to cause at least the following operations to be performed:

[0045] defining one or more cell-specific indicators, wherein the cell-specific indicator comprises a configuration for aspects of a random access procedure comprising transmission of a first message with repetitions, wherein the cell-specific indicator comprises a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions; and

[0046] The defined one or more cell-specific indicators are provided to a user equipment UE so that the UE determines and selects an RO sequence among RO candidate sequences for transmission of the first message with repetition.

[0047] The computer program of the fifth example aspect and / or the sixth example aspect may be stored in a non-transitory computer-readable storage medium.

[0048] Any of the foregoing storage media may include digital data storage devices such as data disks or floppy disks, optical storage devices, magnetic storage devices, holographic storage devices, magneto-optical storage devices, phase change memory, resistive random access memory, magnetic random access memory, solid electrolyte memory, ferroelectric random access memory, organic memory, or polymer memory. The storage medium may be formed as a device having no other substantial functions besides storing memory, or may be formed as part of a device having other functions, including but not limited to the memory of a computer, a chipset, and a subcomponent of an electronic device.

[0049] According to a seventh exemplary aspect of the present invention, there is provided an apparatus comprising at least one processor and at least one memory storing instructions which, when executed by the processor, cause the apparatus to perform:

[0050] obtaining one or more cell-specific indicators, wherein the cell-specific indicators include a configuration for aspects of a random access procedure including transmission of a first message with repetitions, wherein the cell-specific indicators include a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions;

[0051] using the repetition configuration to determine and select an RO sequence among RO candidate sequences for transmission of a first message having repetitions; and

[0052] The selected RO sequence is used for transmission of the first message with repetitions.

[0053] According to an eighth exemplary aspect of the present disclosure, there is provided an apparatus comprising at least one processor and at least one memory, the at least one memory storing instructions which, when executed by the processor, cause the apparatus to perform:

[0054] defining one or more cell-specific indicators, wherein the cell-specific indicator comprises a configuration for aspects of a random access procedure comprising transmission of a first message with repetitions, wherein the cell-specific indicator comprises a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions; and

[0055] The defined one or more cell-specific indicators are provided to a user equipment UE so that the UE determines and selects an RO sequence among RO candidate sequences for transmission of the first message with repetition.

[0056] In the foregoing, various non-binding example aspects and embodiments of the present invention have been described. The embodiments in the foregoing are only used to explain selected aspects or steps that can be utilized in the implementation of the embodiments of the present disclosure. Some embodiments may be presented with reference to only certain example aspects. It should be appreciated that the corresponding embodiments may also be applied to other example aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] For a more complete understanding of example embodiments of the present invention, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0058] Figure 1 A signaling diagram showing the 4-step RACH procedure for 5G NR;

[0059] Figure 2 An example of time domain resource determination for RACH opportunities is shown;

[0060] Figure 3 An example of SSB to RO mapping is shown;

[0061] Figures 4 to 6 Flowcharts illustrating the processes of some example embodiments;

[0062] Figure 7 Some implementation alternatives of the example embodiments are listed;

[0063] Figure 8 is a graphical representation of some examples of RO sequences;

[0064] Fig. 9 A random sparse matrix of an example embodiment is shown;

[0065] FIG. 10A to FIG. 10B Details of some example embodiments are shown; and

[0066] Fig.11 A block diagram of an apparatus of an example embodiment is shown. DETAILED DESCRIPTION

[0067] Example embodiments of the present disclosure and their potential advantages are described with reference to the accompanying drawings. Figures 1 to 11 In this document, the same reference numerals represent the same parts or steps.

[0068] In the following, various exemplary embodiments of the present disclosure will be discussed in detail in the context of 5G NR technology. However, it should be noted that in addition to 5G NR, various exemplary embodiments of the present disclosure may also be equally applicable to other mobile networks and radio communication technologies (e.g., future technologies such as 6G technology or any subsequently developed technology).

[0069] In 5G NR, two contention-based random access (CBRA) procedures are supported, namely 4-step random access channel (RACH) (Rel-15) and 2-step RACH (Rel-16). For illustration purposes and simplicity, the present disclosure focuses on 4-step RACH, but various example embodiments of the present disclosure are equally applicable to 2-step RACH.

[0070] Figure 1 A signaling diagram showing the 4-step RACH procedure for 5G NR. Figure 1 A user equipment (UE) 101 and an NR Node B (gNB) 102 are shown. Figure 1 The 4-step RACH process shown in the messages can be summarized as follows:

[0071] -First message Msg1 (also called PRACH): UE 101 sends a specific preamble to gNB 102 via the Physical Random Access Channel (PRACH) using a specific resource called RACH Opportunity (RO).

[0072] -Second message Msg2 (also called RAR): gNB 102 replies with a random access response (RAR) message, which includes the detected preamble ID, timing advance command, temporary cell RNTI, radio network temporary identifier (TC-RNTI) and UL grant for transmitting the third message Msg3 on the physical uplink shared channel (PUSCH).

[0073] - Third message Msg3 (also called RRC request): UE 101 responds to Msg2 using an ID for contention resolution through a predetermined PUSCH.

[0074] -Fourth message Msg4 (also called RRC setup): gNB 102 sends a contention resolution message with a contention resolution ID.

[0075] After receiving Msg4, if Msg4 carries its contention resolution ID, UE 101 sends an ACK on the PUCCH. This completes the 4-step RACH. It is worth noting that before Msg1, there is also a preliminary step of sending and receiving synchronization signal blocks (SSBs), namely DL beam scanning, which is not a formal part of the RACH process. As a result of this preliminary step, UE 101 selects the index of the preferred SSB beam and decodes the relevant physical broadcast channel (PBCH) to obtain the master information block (MIB), system information block (SIB), etc. The UE also uses this index to identify the appropriate RO for the preamble transmission (i.e., Msg1) based on the SSB to RO mapping implicitly conveyed by SIB1.

[0076] 2-step RACH with Figure 1The 4-step RACH shown in FIG. 1 is similar to the 4-step RACH shown in FIG. 1 , except that Msg1 and Msg3 are combined into MsgA and sent out without waiting for the intermediate feedback from the network (i.e. Figure 1 Similarly, gNB combines Msg2 and Msg4 into MsgB. Various embodiments of the present disclosure may also be applied to Figure 1 The preamble / Msg1 part of MsgA or 2-step RACH.

[0077] Hereinafter, configuration of RACH occasion (RO) will be discussed in order to better understand various embodiments of the present disclosure.

[0078] The time domain resources of the RACH occasions are configured via higher layer signaling through prach-ConfigurationIndex (in rach-ConfigGeneric), which acts as an indicator of a row of a table specified in 3GPP specification TS38.211 V17.3.0 (clause 6.3.3.2). Using the parameters indicated by prach-ConfigurationIndex, the UE determines the preamble format of the PRACH to find the RO on the time domain as specified in the 3GPP specification.

[0079] Figure 2 An example of time domain resource determination for a RACH opportunity is shown. In the example shown, the prach-ConfigurationIndex is 251. Using this index, the UE determines the following:

[0080] - Preamble format C2 should be used.

[0081] -RO is allocated to satisfy n SFN mod 1=0 (i.e. all SFN numbers are valid) SFN ) place.

[0082] - Within each of the determined SFNs, ROs are allocated at subframe numbers 2 and 7.

[0083] - Within each of the determined subframes, the remaining parameters in the considered row indicate that the RO will start at symbol number 0, 6, 14, 20. The symbol numbers are counted consecutively regardless of the number of slots within the subframe, which depends on the subcarrier spacing configured for the PRACH.

[0084] - The RO duration is 6 symbols (although the actual duration of the preamble format may be less than this).

[0085] Finally, the validity of the determined RO must be checked. The RO is determined to be valid if it is within a UL symbol, or if it has a sufficient gap after the last SSB / DL symbol in the case where the RO is within a flexible symbol.

[0086] Regarding the frequency domain, the parameters msg1-FrequencyStart and msg1-FDM configured in RACH-ConfigGeneric indicate the offset of the lowest RO in the frequency domain and the number of ROs multiplexed in the frequency domain for a group of back-to-back OFDM symbols, respectively. The number of resource blocks (RBs) occupied by each RO (expressed in the number of RBs for PUSCH) is specified in the 3GPP specification, which depends on the configured preamble length and the subcarrier spacing of PRACH and PUSCH.

[0087] Mapping the SSB index to the determined RO is necessary so that the UE knows which RO is associated with the SSB index selected during the preliminary steps before the RACH procedure starts. Different SSB indices are beamformed in different directions in a cell, so selecting the wrong SSB index may cause the RACH procedure to fail.

[0088] For this purpose, the parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB is configured in RACH-ConfigCommon. This parameter indicates: (i) the number of SSB indices per RO, and (ii) the number of contention-based preambles per SSB index. Once this information is available to the UE, the UE maps the SSB index to the time-frequency grid of the RO (determined as described above) in increasing order of frequency resource index, time resource index of the RO within the PRACH slot, and PRACH slot.

[0089] Figure 3 An example of SSB to RO mapping is shown. Figure 3 Explains how Figure 2 An example of determining a valid RO in one frame as described in . Assume the following additional configuration: DDSUU slot structure, Msg1-FDM=two, and ssb-perRACH-OccasionAndCB-PreamblesPerSSB is half. Based on this configuration, two ROs are multiplexed in the frequency domain (Msg1-FDM=two), and any two FDM ROs are mapped to the same SSB index (ssb-perRACH-OccasionAndCB-PreamblesPerSSB=1 / 2).

[0090] The 4G LTE specification includes a Msg1 repetition feature to ensure Msg1 transmission for better coverage. The inventors of the present disclosure have observed that the Msg1 repetition feature of 4G LTE is not directly applicable to 5G NR because there are differences between LTE and NR systems in terms of the radio air interface. 5G NR is based on a beam-based architecture that heavily relies on analog and / or digital beamforming. This is not the case in LTE, where beam management is more fundamental.

[0091] In the context of 5G NR, there are some challenges associated with the Msg1 repetition feature. Consider a 5G NR scenario where the gNB serves UEs with a certain number of analog / digital beams and where different UEs can repeat Msg1 a certain number of times without a specific limit on Msg1 repetition, so Msg1 collisions are likely to occur. In such a scenario, in the case of repetitions, the CE UE consumes a lot of time and energy to send multiple (e.g. 4 or 8) Msg1 repetitions compared to a single Msg1 transmission, which may span a long time interval until it is finally discovered that a collision has occurred at the gNB side and the Msg1 needs to be resent. This timeline becomes even longer when considering that the UL slots may not always be consecutive (e.g. in TDD systems) and multiple SSB indices (up to 64 in FR2) may be in use at the network. Therefore, collisions in Msg1 repetitions may cause huge delays in initial access and should be avoided, especially in the case of low SNR CE UEs at the cell edge performing Msg1 repetitions. Furthermore, it is not always feasible to assign completely independent resources (ie, preamble and RO) to multiple UEs performing Msg1 repetition.

[0092] Furthermore, it should be noted that a UE whose Msg1 transmission has been detected is assigned a temporary identity only after the Msg1 itself has been received. Therefore, even if dedicated resources are configured for Msg1 repetition, the gNB has no constructive means to distinguish between two UEs repeating Msg1, as these resources can only be cell-specific. This may hinder the achievability of coherent combining of multiple Msg1s at the gNB when multiple UEs attempt to exploit the repetition for access. This may degrade the performance of Msg1 transmissions and reduce the practical usability of Msg1 repetition.

[0093] Various embodiments of the present disclosure are discussed in detail below, which provide Msg1 repetition features suitable for 5G NR. The technical solution is to define one or more RO candidate sequences for transmission of Msg1 with repetition in the network. Then allow the UE to select the RO sequence among the candidate sequences.

[0094] To simplify the detailed disclosure of some example embodiments, a group of back-to-back OFDM symbols is defined as a time instance, ie, the duration of one RO in a slot.

[0095] Figure 4 A flow chart showing a process of an example embodiment is shown. The process may be performed, for example, in a UE (such as Figure 1 UE 101) or Fig.11 The process includes the following steps:

[0096] Step 401: Obtain one or more cell-specific indicators. The cell-specific indicator includes a configuration for aspects of a RACH process including transmission of a first message with repetitions. In addition, the cell-specific indicator includes a repetition configuration for determining one or more RO candidate sequences for transmission of a first message (Msg1) with repetitions. That is, the repetition configuration defines one or more RO candidate sequences for selection by a UE of the corresponding cell.

[0097] Typically, the repetitive configuration groups multiple ROs in different frequency / time instances together to form one or more RO candidate sequences. The grouping may be provided as a relationship between ROs configured via higher layer parameters prach-ConfigurationIndex and ssb-perRACH-OccasionAndCB-PreamblesPerSSB.

[0098] According to an example embodiment, the RO candidate sequence has the following properties:

[0099] - ROs sharing the same time resource may not be part of the same sequence.

[0100] - The ROs in the sequence are ordered according to their indexes (as per the specification), for example, first in increasing order of frequency resource index, second in increasing order of time resource index, and third in increasing order of PRACH slot index.

[0101] -Sequences may overlap, i.e. the same RO may be part of more than one sequence. A RO that is part of more than one candidate sequence corresponds to a node in the graph where there are multiple incoming and / or outgoing edges. This feature provides a low probability of collision with a minimum number of resources.

[0102] In an example embodiment, the one or more cell-specific indicators may also include a preamble configuration for more than one preamble for transmission of the first message with repetitions. The preamble configuration may be used in the UE to select a preamble for transmission of the first message with repetitions. In an example embodiment, the preambles used for transmission of the first message with repetitions may be part of a reserved set, i.e., they may not be selected by a UE that does not perform transmission of the first message with repetitions.

[0103] In an example embodiment, the one or more cell-specific indicators may also include a maximum time configuration. The maximum time configuration may be used in the UE to determine a maximum duration for transmission of the first message with repetitions. Details of implementation examples of the maximum time configuration will be discussed later in this disclosure.

[0104] The cell-specific indicator may be provided to the UE from the network (e.g., gNB), for example, by broadcasting or signaling the information in the corresponding cell. Such broadcasting or signaling may be done before the formal RACH procedure, for example, in a preliminary step of sending and receiving synchronization signal blocks (SSBs), etc. The UE may use the repetitive configuration in conjunction with the higher layer parameters prach-ConfigurationIndex and ssb-perRACH-OccasionAndCB-PreamblesPerSSB defined for the RACH procedure.

[0105] Step 402: The repetition configuration is used to determine and select an RO sequence for transmission of a first message with repetitions.

[0106] Step 402 can be implemented by first determining all RO candidate sequences according to the repetition configuration and then selecting one of the determined candidate sequences. Alternatively, an iterative process can be implemented without completely determining all possible candidate sequences. In this iterative process, one or more candidates for the first RO of the sequence are determined according to the repetition configuration and one of these candidates is selected. Then, subsequent ROs are iteratively determined and selected until the required number of ROs have been selected, so that one or more subsequent candidates for the subsequent RO of the sequence are determined based on the previously selected RO and one of the determined subsequent candidates is selected. In this way, the selected RO sequence is completely determined, while other candidate sequences are not necessarily determined because they are not necessarily needed at all. Whenever there is more than one RO or RO sequence to choose from, the selection can be performed in a cyclic manner.

[0107] Step 402 may include using repeated configuration in conjunction with parameters prach-ConfigurationIndex and ssb-perRACH-OccasionAndCB-PreamblesPerSSB.

[0108] According to an example embodiment, the ROs in the selected RO sequence occupy different time resources.

[0109] Step 403: The selected RO sequence is then used for transmission of the first message with repetitions in the RACH process.

[0110] It should be noted that the selection of the RO sequence can be performed completely before the transmission of the first Msg1 repetition, i.e., the UE determines and selects the entire RO sequence to be used for sending N Msg1 repetitions before starting the transmission of Msg1 with repetitions. Alternatively, the selection of the RO sequence can be performed concurrently with the transmission of N Msg1 repetitions, i.e., the first Msg1 repetition can be sent immediately after the first RO in the sequence has been selected (and if there are more repetitions to be sent, before selecting the RO of the next Msg1 repetition, or at least before selecting the entire RO sequence).

[0111] Figure 5 A flow chart showing a process of an example embodiment is shown. The process may be performed, for example, in a process such as Figure 1 gNB network element or Fig.11 The process includes the following steps:

[0112] Step 501: define one or more cell-specific indicators. The cell-specific indicator includes a configuration for aspects of a RACH process, the RACH process including transmission of a first message with repetition. In addition, the cell-specific indicator includes a repetition configuration for determining one or more RO candidate sequences for transmission of the first message with repetition. That is, defining one or more cell-specific indicators includes defining one or more RO candidate sequences for selection by a UE of the corresponding cell.

[0113] In an example embodiment, the one or more cell-specific indicators may also include preamble configurations of more than one preamble for transmission of the first message with repetitions, so that the UE selects a preamble for transmission of the first message with repetitions.

[0114] In an example embodiment, the one or more cell-specific indicators may also include a maximum time configuration in order for the UE to determine a maximum duration of transmission of the first message with repetitions.

[0115] The maximum time configuration may be expressed as a function of the number of subframes, a function of the number of system radio frames, a function of the number of ROs, a function of the number of OFDM symbols and / or a function of a PRACH configuration or association period.

[0116] In an example embodiment, the repetition configuration is defined in conjunction with the parameters prach-ConfigurationIndex and ssb-perRACH-OccasionAndCB-PreamblesPerSSB defined for the RACH procedure.

[0117] There may be multiple repetition configurations in a cell. This may be useful, for example, when more than one Msg1 repetition number is supported in a cell (e.g. N=2 and N=4 repetitions), or to provide additional diversity when only one N value is supported in the cell. The choice will depend on the network, where one or several cell-specific parameters may be defined to cover all possible supported repetition numbers or to provide higher diversity for RO selection at the UE.

[0118] Step 502: Provide the defined one or more cell-specific indicators for use in the UE. This can be done by broadcasting one or more cell-specific indicators in the cell. The UE in the cell can then determine and select the RO sequence for the first message of the transmission of the RACH process repetition.

[0119] Figure 6 A flow chart showing a process of an example embodiment is shown. The process may be performed, for example, in a UE (such as Figure 1 UE 101) or Fig.11 The process includes the following steps:

[0120] Step 601: Obtain one or more cell-specific indicators. The cell-specific indicator includes a configuration of aspects of a RACH process, the RACH process including the transmission of a first message with repetitions. In addition, the cell-specific indicator includes a repetition configuration for determining one or more RO candidate sequences for the transmission of the first message with repetitions. The cell-specific (multiple) indicators may also include a preamble configuration and a maximum time configuration, such as in combination with Figure 4 Step 401 and Figure 5 as discussed in step 501.

[0121] Step 602: One or more cell-specific indicators are used to configure RACH resources for transmission of the first message Msg1 with repetitions, and determine the following:

[0122] - RO candidate sequences for transmission of Msg1 with N repetitions within the configured maximum duration, and

[0123] - Preamble for transmission of Msg1 with N repetitions.

[0124] Step 603: Check whether there are one or more determined candidate sequences.

[0125] Step 604: If it is concluded that there is one determined candidate sequence, the determined candidate sequence is selected, and transmission of Msg1 with N repetitions is performed using N ROs of the selected sequence.

[0126] Step 605: If it is concluded that there is more than one determined candidate sequence, then check whether all determined candidate sequences share the same first (or last) RO.

[0127] Step 606: If it is concluded that all determined candidate sequences share the same first RO, then the first RO common to all determined sequences is selected.

[0128] Step 607: If it is concluded that all determined candidate sequences do not share the same first RO, one of the ROs determined to be the first RO in the sequence is selected. The selection may be performed in a round-robin manner. The selection mechanism may be defined in a cell-specific indicator or hard-coded in the specification. When the first RO is not selected in a round-robin manner, different UEs may be separated at the network, for example, by a transmitted preamble.

[0129] Step 608: Select one of the possible next ROs after the selected first RO. The selection may be performed in a round-robin manner. The selection mechanism may be defined in a cell specific indicator or hard coded in the specification.

[0130] Step 609: Check whether N ROs have been selected. If it is concluded that N ROs have not been selected, the process returns to step 608 to select the next RO.

[0131] Step 610: If it is concluded that N ROs have been selected, transmission of Msg1 with N repetitions is performed using a sequence of the N selected ROs.

[0132] Figure 7 is a graph representation of some examples of RO candidate sequences. Each RO sequence is represented by a set of nodes connected by directed edges. The nodes are arranged in a matrix, where nodes in the same row share the same frequency resource, and nodes in the same column share the same time resource. The index of the frequency resource occupied by the node increases from bottom to top, and the index of the time resource increases from left to right.

[0133] exist Figure 7 Three RO candidate sequences are shown in:

[0134] 1.[RO#1RO#6RO#11RO#13]

[0135] 2.[RO#1RO#6RO#8RO#13]

[0136] 3.[RO#1RO#4RO#8RO#13]

[0137] In a first practical example, the UE receives a signal including Figure 7 Based on the repetition configuration, the UE completely determines three candidate sequences of RO1-3, and then selects one of the determined sequences, for example, 1. [RO#1RO#6RO#11RO#13].

[0138] In a second practical example, the UE receives a signal including Figure 7 Now, instead of fully determining three sequences, the UE determines at least one complete sequence, which is the sequence that will eventually be selected, as follows:

[0139] -UE determines and selects RO#1

[0140] -UE determines RO#4 and RO#6 and selects RO#6

[0141] -UE determines RO#8 and RO#11 and selects RO#11

[0142] -UE determines and selects RO#13, thus sequence 1 has been selected. [RO#1RO#6RO#11RO#13]

[0143] Figure 8 Implementation alternatives of some example embodiments are listed. Different alternatives that can be used to communicate the repetition configuration to the UE are listed. Some of the listed alternatives can be combined or used in parallel.

[0144] Alternative 801: The repetition configuration includes a density parameter for generating one or more random sparse matrices for determining connections from one RO to a subsequent RO of a sequence of RO candidates.

[0145] In this embodiment, the UE generates one or more random sparse matrices or vectors based on the density parameter that provide connectivity from one RO to subsequently configured ROs associated with the same SSB index and within a configured maximum duration of transmission of a first message with repetition.

[0146] A sparse matrix / vector is a matrix / vector of ones and zeros where the density of ones (the number of ones out of the total number of entries) is equal to the density of the configuration. To randomize each RO in the sequence ( Figure 7 The number of next ROs (e.g., Figure 7The sparse matrix / vector should be randomly generated with a seed that depends at least on the time and frequency resources occupied by the considered (multiple) ROs. In addition, the seed may depend on the SSB index associated with the RO. The network may also configure a set of one or more cell-specific seeds to give the network greater control over which ROs are part of which sequence.

[0147] Fig. 9 A random sparse matrix of an example embodiment is shown. The size of the matrix shown is 16×16, where the density of configurations is equal to 6% (14 ones on 16×16 entries), associated with 16 configured ROs (which may or may not be as follows Figure 7 ), these ROs may be part of a RO sequence, such as Figure 7 as shown (where the connected nodes are part of the same sequence).

[0148] exist Fig. 9 In the example of , the bit corresponding to row 6 and column 11 is set to 1, indicating that there is a connection between RO#11 and RO#6. The same principle applies to other ROs. Symmetrically, the bit corresponding to row 11 and column 6 is also set to 1. Therefore, determining the RO in each sequence does not require an indication of the entire matrix, but only an indication of the portion below or above its main diagonal 910.

[0149] As an alternative, instead of a sparse matrix, several sparse vectors may be generated, one for each RO in each sequence, to represent the next RO(s) in the sequence or sequences including the RO under consideration at the next time instance. Specifically, for each RO under consideration in the sequence, the number of next ROs in the next time instance is equal to the minimum number of sequences including the RO under consideration. Figure 7 In the example of , for each RO in a given time instance, there are four (4) possible candidates for the next RO in the sequence, and therefore a random sparse vector of length 4 with a configured density needs to be created for each RO in the RO sequence. Figure 7 In the example, the density of RO#1 is configured to be 0.5 (there are 2 next ROs in the next time instance, i.e., RO#1 is included in at least 2 sequences), while the density of RO#4 is configured to be 0.25 (there is 1 next RO in the next time instance, i.e., RO#4 is included in at least one sequence).

[0150] In the example implementation, only one density value is configured to generate a sparse matrix or vector. Depending on the total number of sequences that the network wishes to configure and the number of overlaps between them (i.e., the same RO belongs to two or more sequences), the density value will be different, and fewer or more bits will be required for lower and larger maximum numbers of sequences including the RO under consideration. For example, considering the case of a sparse matrix and quantizing the matrix density with a step size of 10% (e.g. [10%, 20%, ... 100%]), 10 states need to be represented by the density value, which will require a total of 4 bits for configuring it.

[0151] Alternative 802: The repetition configuration includes one or more sparse matrices that provide information on whether a RO is part of a RO candidate sequence.

[0152] In this embodiment, the repetition configuration is provided in the form of a sparse matrix or vector that provides information about whether a RO is part of a sequence. If applicable, the information is provided for each configured RO associated with the same SSB index and within the configured maximum duration of the transmission of the first message with repetition, regardless of whether the RO is actually part of the sequence. The interpretation of the configuration is the same as in alternative 801.

[0153] Considering that only half of the matrix is ​​necessary to indicate all configured sequences, a total of 128 bits (16*16 / 2) are needed for 16 configured ROs associated with the same SSB index and within the configured maximum duration of transmission with repeated first messages.

[0154] Although this approach requires more bits than alternative 801, it has the advantage of giving the possibility to fully control the connections between ROs through repeated configuration.

[0155] Alternative 803: The repetition configuration includes one or more combination indicators for providing a ranking of one or more RO combinations among all possible RO combinations of RO candidate sequences, wherein one RO combination indicates one RO candidate sequence.

[0156] In this embodiment, the sequence of each of the N ROs (for transmission of the first message with N repetitions) in the K consecutive ROs associated with the same SSB beam is ordered according to its index (determined according to the specification). The combination indicator provides a ranking of one of all possible N RO combinations among the K ROs for transmitting the first message with N repetitions. A combination indicator is used The bit indicates a sequence of N ROs out of K consecutive ROs. If L>1 sequences are configured by the network, each sequence is independently indicated using the ranking of the corresponding combination, and the total bit width of the combined indicator for all sequences is Bit.

[0157] exist Figure 7 In the example of , three (3) sequences of 4 out of 16 nodes / ROs are represented (and thus configured to the UE). This only requires 33 bits.

[0158] Alternative 804: The repetition configuration includes a first binary sequence indicating a first RO in the RO candidate sequence and a second binary sequence indicating a group of ROs to which the remaining ROs in the RO candidate sequence belong.

[0159] In this embodiment, K consecutive ROs associated with the same SSB beam are sorted according to their indices (determined according to the specification) and grouped into groups of at most F consecutive ROs. In this context, F can be the number of ROs in the same time instance, or it can be a parameter signaled by the network using an additional indicator. Each RO in a group of F consecutive ROs is represented by The network indicates at least one RO in the first group of F consecutive ROs by using a first binary sequence of at least M bits. The UE can then determine the valid RO sequence by determining the remaining ROs in each RO sequence in the remaining groups of F consecutive ROs. The remaining groups of F consecutive ROs can be back-to-back and after the first group of F consecutive ROs, or the network can additionally indicate a second binary sequence of T≥N bits to indicate the remaining groups of F consecutive ROs in which the remaining ROs are located. The latter may require the network to indicate the value of T unless it is hard-coded in the specification. In an example embodiment, for each considered RO in the sequence, the next (multiple) ROs in the sequence (located in any subsequent (multiple) groups of F consecutive ROs) are associated with (multiple) binary sequences that differ from the binary sequence associated with the current RO by only α bits, i.e., Hamming distance = α.

[0160] FIG. 10A to FIG. 10B Details of some example embodiments of alternative 804 are shown.

[0161] Fig. 10A Example: The number of ROs in a set of consecutive ROs is 4 (i.e., F = 4), that is, bits to represent each RO in each group of F=4 consecutive ROs (in this example, assume that F is equal to the number of ROs in a time instance). Assume that the initial RO indicated by the network in the first group of F consecutive ROs is associated with the first binary sequence 10, and assume that α=1 (i.e., the minimum Hamming distance). Furthermore, in this example, assume that the remaining groups of F consecutive ROs are back-to-back and follow the first group of F consecutive ROs. Then, the second group of F consecutive ROs (according to Fig. 10AThe next valid RO in the second column of the example in (the second column of the example in) is the RO associated with the binary sequence 00 and 11 (which differs from 10 by only 1 bit). Similarly, starting with the valid RO associated with the sequence 00, the next valid RO in the third group (third column) of F consecutive ROs is the RO associated with the binary sequence 01 and 10. The same method is applied to each valid RO until the maximum number of ROs per sequence (N) is reached. A total bit width of 2 bits is required in this example.

[0162] Fig. 10B Example: The number of ROs in a set of consecutive ROs is 4 (i.e., F = 4), that is, bits to indicate each RO in each group of F=4 consecutive ROs (in this example, it is assumed that F is equal to the number of ROs in the time instance). Assume that the initial RO indicated by the gNB in ​​the first group of F consecutive ROs is associated with a first binary sequence 10, and α=1 (i.e., the minimum Hamming distance). In addition, assume that the network also indicates a second binary sequence of T=6 bits for indicating the group of F consecutive ROs in which the remaining ROs are located. Each bit in the second binary sequence indicates whether the corresponding group of the subsequent F consecutive ROs includes one of the remaining ROs. For example, if such a binary sequence is as Fig. 10B As shown in [0 1 1 0 0 1], the group of F consecutive ROs including the remaining ROs of the sequence is the third, fourth and seventh groups of F consecutive ROs (or according to Fig. 10B The example in is the 3rd, 4th and 7th columns). The method then proceeds as follows. The next valid RO in the 3rd group (3rd column) of F consecutive ROs is the RO associated with the binary sequence 00 and 11 (which differs from 10 by only 1 bit). Similarly, starting with the valid RO associated with the binary sequence 00, the next valid RO in the 4th group (4th column) of F consecutive ROs is the RO associated with the binary sequence 01 and 10. The same method is applied to each valid RO until the number of ROs for each sequence (N) is reached. This example requires 2+6=8 bits to indicate the first binary sequence and the second binary sequence, and additionally requires bits for indicating the value of T, for example, it may require bits are used to indicate T (if T is not hardcoded in the specification). Therefore, the total bit width required in this example is Bit.

[0163] Alternative 805: The repeating configuration includes N*M bits for each configured RO candidate sequence, where N is the number of ROs in the RO candidate sequence, and each group of M bits indicates one RO in each group of consecutive ROs.

[0164] In this embodiment, the network indicates each sequence of N ROs using N*M bits, where each group The bit indicates one RO in each group of F consecutive ROs (which may correspond to, for example, Figure 7 nodes in the columns in , assuming in this example that F is equal to the number of ROs in the time instance).

[0165] An example of alternative 805 is discussed below: Figure 7 In the scenario, N = 4 and therefore, Figure 7 Each RO sequence in is indicated by 4*2=8 bits, where each group of 2 bits indicates one RO in the RO sequence. For example, the highest, middle and lowest paths / sequences of ROs can be represented by [10 01 00 10], [10 01 11 10] and [10 11 1110], respectively, which requires a bit width of 3*8=24 bits to be signaled. In addition, if the parameter F needs to be configured and sent by the network, it will be required Bit.

[0166] Alternative 805 may be particularly convenient when the number of ROs in the same time instance is greater than one.

[0167] Alternative 806: The RO candidate sequences have a common first RO and / or last RO, and the repetition configuration includes one or more single indications of one or more common ROs in the RO candidate sequences and sequence-specific indications of other ROs.

[0168] In this embodiment, all sequences of N ROs share the same first RO and / or last RO. Such ROs are indicated only once, and ROs other than such common ROs are indicated only via an indicator for each sequence.

[0169] An example of alternative 805 is discussed below: Figure 7 In , all RO sequences share the same first RO and last RO, both of which are associated with the binary sequence 10. Then, the network needs 4 bits to indicate the two common ROs, and 4 bits to indicate the remaining ROs for each RO sequence. Therefore, the network only needs to indicate the following sequences (the order can be different)

[10] ,

[10] ,

[0100] , [01 11], and [11 11] to indicate the two common ROs, and all the remaining ROs in all sequences, resulting in a total of 16 bits.

[0170] Another example of alternative 805 is discussed below: Fig. 10AIn the example, all RO sequences share the same first RO, which is associated with the binary sequence 10. The network then needs 2 bits to indicate the common RO, and 6 bits to indicate the remaining ROs in each RO sequence. Therefore, the network only needs to indicate the following sequence (the order can be different)

[10] , [00 0100], [00 1000], [00 01 11], [00 10 11], [11 01 00], [11 01 11], [1110 00] [11 10 11], to indicate the first common RO, and all the remaining ROs of all sequences, resulting in a total of 50 bits.

[0171] Fig.11 1 shows a block diagram of an apparatus 1100 according to an example embodiment. The apparatus 1100 may be used as a network element (such as Figure 1 gNB 102) or as a UE (such as Figure 1 The apparatus 1100 typically includes a memory 1140 including a computer program code 1150. The apparatus 1100 also includes a processor 1120 for controlling the operation of the apparatus 1100 using the computer program code 1150, and a communication unit 1110 for communicating with other nodes. In addition, the apparatus 1100 may include a user interface unit 1130.

[0172] The communication unit 1110 includes, for example, one or more of the following: a local area network (LAN) port; a wireless local area network (WLAN) unit; a Bluetooth unit; a cellular data communication unit; or a satellite data communication unit. The communication interface 1110 may support one or more different communication technologies. The communication interface 1110 may support Ethernet communication and / or IP-based communication. The device 1100 may also or alternatively include more than one communication interface 1110. The processor 1120 includes, for example, any one or more of the following: a main control unit (MCU); a microprocessor; a digital signal processor (DSP); an application-specific integrated circuit (ASIC); a field programmable gate array; and a microcontroller. The user interface unit 1130 may include circuits for receiving input from a user of the device 1100, for example, via a keyboard; a graphical user interface of a display; a voice recognition circuit; or an accessory device; such as a headset; and circuits for providing output to the user via, for example, a graphical user interface or a speaker. Each part may be implemented using more than one corresponding or different element, for example, the memory and storage device may be multiplied for capacity and / or redundancy purposes. Similarly, processing and / or communications may be accomplished using multiple parallel or elements for capacity and / or redundancy purposes.

[0173] The computer program code 1150 may control the apparatus 1100 to implement one or more exemplary embodiments of the present disclosure, such as Figures 4 to 6process and combination Figures 7 to 9 and FIG. 10A to FIG. 10B Further details are discussed.

[0174] As used in this application, the term "circuitry" may refer to one, more, or all of the following:

[0175] (a) hardware circuit implementation only (such as implementation in analog and / or digital circuits only) and;

[0176] (b) a combination of hardware circuitry and software such as (where applicable):

[0177] (i) a combination of analog and / or digital hardware circuits and software / firmware; and

[0178] (ii) any portion of hardware processor(s) with software (including digital signal processor(s), software and memory(s) that work together to enable a device (such as a mobile phone or server) to perform various functions); and

[0179] (c) Hardware circuits and or processor(s), such as microprocessor(s) or portions of microprocessor(s), that require software (e.g., firmware) for operation, but where the software is not required for operation, the software may not be present.

[0180] This definition of circuitry applies to all uses of the term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of only a hardware circuit or processor (or multiple processors) or portions of a hardware circuit or processor and their accompanying software and / or firmware. For example, and if applicable to a particular claim element, the term circuitry also covers a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in a server, cellular network device, or other computing or network device.

[0181] Without limiting in any way the scope, interpretation, or application of the claims appearing below, the technical effect of one or more of the example embodiments disclosed herein is an improved random access procedure. Another technical effect of one or more of the example embodiments disclosed herein is providing details of a random access procedure suitable for 5G NR. More specifically, various embodiments provide for configuration and determination of RACH resources for Msg1 repetition in a manner suitable for 5G NR.

[0182] Another technical effect of one or more of the example embodiments disclosed herein is that it can reduce the probability of collision between UEs with insufficient coverage that perform Msg1 repetition. Another technical effect of one or more of the example embodiments disclosed herein is that the detection complexity at the receiver (to distinguish UEs) can be reduced, for example compared to a system in which the UE can randomly select a RO without a structured method of RO determination and selection. Various example embodiments provide that the number of blind decoding instances may be lower than in some other methods. Another technical effect of one or more of the example embodiments disclosed herein is that the actual availability of the Msg1 repetition feature can be increased. Another technical effect of one or more of the example embodiments disclosed herein is that the amount of resources required for Msg1 repetition will not increase excessively.

[0183] Embodiments of the present disclosure may be implemented in software, hardware, application logic, or a combination of software, hardware, and application logic. The software, application logic, and / or hardware may reside, for example, on the gNB 102 or on the UE 101. In an example embodiment, the application logic, software, or instruction set is maintained on any of a variety of conventional computer-readable media. In the context of this document, a "computer-readable medium" may be any non-transitory medium or component that can contain, store, communicate, propagate, or transport instructions for use by or in conjunction with an instruction execution system, apparatus, or device (such as a computer), an example of which is Fig.11 Computers described and depicted in the . Computer-readable media may include computer-readable storage media, which may be any medium or component that can contain or store instructions for use by or in connection with an instruction execution system, apparatus, or device (such as a computer).

[0184] If desired, the different functions discussed herein may be performed in a different order and / or concurrently with each other. In addition, if desired, one or more functions described above may be optional or may be combined.

[0185] Although various aspects of the disclosure are set out in independent claims, further aspects may comprise other combinations of features from the described embodiments and / or dependent claims with features of the independent claims than just the combinations explicitly set out in the claims.

[0186] It is also noted herein that while the foregoing describes example embodiments, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present disclosure as defined in the appended claims.

[0187] List of abbreviations

[0188] UE: User Equipment

[0189] gNB: NR Node B

[0190] Msg1: Message 1

[0191] PRACH: Physical Random Access Channel

[0192] RACH: Random Access Channel

[0193] RO: RACH timing

[0194] FDM: Frequency Domain Multiplexing

[0195] SS / PBCH: Synchronization Signal / Physical Broadcast Channel

[0196] SSB: Synchronization Signal Block

[0197] FR1: Frequency Range 1

[0198] FR2: Frequency Range 2

[0199] SIB1: System Information Block 1

[0200] TDD: Time Division Duplex

[0201] FDD: Frequency Division Duplex

[0202] OFDM: Orthogonal Frequency Division Multiplexing

[0203] CE: Coverage Enhancement

Claims

1. An apparatus comprising components for performing the following operations: obtaining one or more cell-specific indicators, wherein the cell-specific indicators include a configuration for aspects of a random access procedure, the random access procedure including transmission of a first message with repetitions, wherein the cell-specific indicators include a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions; using the repetition configuration to determine and select an RO sequence among the RO candidate sequences for transmission of the first message with repetition; as well as The selected RO sequence is used for transmission of the first message with repetitions.

2. The apparatus according to claim 1, wherein determining and selecting the RO sequence is performed by: using the repetition configuration to determine the RO candidate sequence for transmission of the first message with repetitions; and One of the determined RO candidate sequences is selected.

3. The apparatus according to claim 1, wherein determining and selecting the RO sequence is performed by: using the repetition configuration to determine one or more candidates for a first RO in the sequence and selecting one of the candidates as the first RO in the sequence; and Based on the previously selected ROs in the sequence, one or more subsequent candidates for a subsequent RO in the sequence are iteratively determined and one of the subsequent candidates is selected as the subsequent RO in the sequence until a desired number of ROs have been selected.

4. An apparatus according to any preceding claim, wherein when there is more than one RO or RO sequence to select from, the selection is performed in a round-robin manner.

5. The apparatus of any preceding claim, wherein selecting the RO sequence is performed entirely prior to a first transmission of the first message with repetition.

6. The apparatus of any one of claims 1 to 4, wherein selecting the RO sequence is performed concurrently with transmission of the first message with repetitions, wherein the repetition of the first message is sent after selecting the RO on which to send the repetition and before selecting the RO for transmission of the subsequent repetition of the first message if there is an RO for transmission of the subsequent repetition of the first message.

7. The apparatus according to any preceding claim, wherein the selected ROs in the RO sequence occupy different time resources.

8. An apparatus according to any preceding claim, wherein the one or more cell-specific indicators are received from a network.

9. An apparatus according to any preceding claim, wherein the apparatus is or is comprised in user equipment.

10. An apparatus comprising means for performing the following operations: defining one or more cell-specific indicators, wherein the cell-specific indicators include configurations for aspects of a random access procedure, the random access procedure including transmission of a first message with repetitions, wherein the cell-specific indicators include repetition configurations for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions; and The defined one or more cell-specific indicators are provided to a user equipment (UE) so that the UE determines and selects a RO sequence among the RO candidate sequences for transmission of the first message with repetition. The apparatus according to claim 10 , wherein the apparatus is a network element or is comprised in a network element.

12. The apparatus of any preceding claim, wherein the repetition configuration groups together multiple ROs in different frequency / time instances to form the one or more RO candidate sequences.

13. The apparatus according to any one of claims 1 to 12, wherein the repetition configuration comprises a density parameter for generating one or more random sparse matrices, the one or more random sparse matrices being used to determine the connection of the RO candidate sequence from one RO to a subsequent RO.

14. The apparatus according to any one of claims 1 to 12, wherein the repetition configuration comprises one or more sparse matrices providing information on whether a RO is part of a RO candidate sequence.

15. The apparatus according to any one of claims 1 to 12, wherein the repetition configuration comprises one or more combination indicators providing a ranking of one or more RO combinations among all possible RO combinations, wherein one combination indicates one RO candidate sequence. 16 . The apparatus according to claim 1 , wherein the repetition configuration comprises a first binary sequence indicating a first RO in the RO candidate sequence and a second binary sequence indicating a group of ROs to which the remaining ROs in the RO candidate sequence belong.

17. The apparatus according to any one of claims 1 to 12, wherein the repetition configuration comprises N*M bits for each configured RO candidate sequence, wherein N is the number of ROs in the RO candidate sequence, and each group of M bits indicates one RO in each group of consecutive ROs.

18. The apparatus according to any one of claims 1 to 12, wherein the RO candidate sequences have at least one of the following in common: a first RO or a last RO, and the repetitive configuration includes one or more single indications of one or more of the common ROs in the RO candidate sequences and sequence-specific indications of other ROs.

19. The apparatus of any preceding claim, wherein the one or more cell-specific indicators include preamble configurations for more than one preamble for transmission of the first message with repetition, so that a UE selects a preamble for transmission of the first message with repetition.

20. An apparatus according to any preceding claim, wherein the one or more cell-specific indicators comprise a maximum time configuration for a UE to determine a maximum duration for transmission of the first message with repetitions.

21. The apparatus according to any preceding claim, wherein the random access procedure is contention-based random access (CBRA).

22. An apparatus according to any preceding claim, wherein the component comprises: at least one processor; and at least one memory including executable instructions that, when executed by the at least one processor, cause the execution of the apparatus.

23. A method comprising: obtaining one or more cell-specific indicators, wherein the cell-specific indicators include a configuration for aspects of a random access procedure, the random access procedure including transmission of a first message with repetitions, wherein the cell-specific indicators include a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions; using the repetition configuration to determine and select an RO sequence among the RO candidate sequences for transmission of the first message with repetition; as well as The selected RO sequence is used for transmission of the first message with repetitions.

24. A computer program comprising instructions stored thereon for performing at least the following operations: obtaining one or more cell-specific indicators, wherein the cell-specific indicators include a configuration for aspects of a random access procedure, the random access procedure including transmission of a first message with repetitions, wherein the cell-specific indicators include a repetition configuration for determining one or more candidate random access channel (RACH) opportunities (RO) sequences for transmission of the first message with repetitions; using the repetition configuration to determine and select an RO sequence among the RO candidate sequences for transmission of the first message with repetition; as well as The selected RO sequence is used for transmission of the first message with repetitions.

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