GB2623740A

GB2623740A - Random access to network

Info

Publication number: GB2623740A
Application number: GB2214813.4A
Authority: GB
Inventors: Sedin Jonas; Tesanovic Milos
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2022-10-07
Filing date: 2022-10-07
Publication date: 2024-05-01
Also published as: WO2024076183A1; GB202214813D0

Abstract

A method, for a User Equipment (UE), for performing random access in a network is disclosed. The method comprises: selecting a Synchronisation Signal Block (SSB); and performing random access to a network entity based on the selected SSB, wherein the SSB is selected based on an SSB group to which the SSB belongs. The first SSB group may be associated with a first network entity (e.g. gNB) and one or more second SSB groups may be associated with one or more second entities (e.g. NCR, Network-Controlled Repeater). In this way the UE may choose e.g. through dynamic thresholds adapted to the event causing the random access procedure, whether to attach to a gNB or NCR SSB or the SSB selection scheme may be adapted to the type of event that triggered the random access. Reference Signal Received Power, RSRP, thresholds of the SSBs may be used as conditions for selecting the SSB.

Description

Random Access to Network BACKGROUND

Field

Certain examples of the present disclosure provide a technique for performing random access to a network. For example, certain examples of the present disclosure provide a technique for performing random access to a 31d Generation Partnership Project (3GPP) 5th Generation (5G) New Radio (NR) network including a Network Control Repeater (NCR).

Description of the Related Art

Random access is a procedure that allows a User Equipment (UE) to make an unscheduled connection to a network. Random access may be triggered by a number of situations, for example initial UE access to the network, handover, reconnection following connection failure, etc. Figure la illustrates a typical random access procedure in which a UE connects to a base station (e.g. eNB or gNB). For example, the procedure in Figure la is used in Long Term Evolution (LTE). In a first step 101, the UE selects resources (e.g. time and frequency resources) for performing random access. Then, the UE and eNB exchange a sequence of four messages. The first message (Msgl: preamble/PRACH) transmitted from UE to eNB includes a preamble selected from a set of (e.g. 64) orthogonal preambles. The second message (Msg2: Random Access Response (RAR)) transmitted from eNB to UE is a response to Msgl and includes timing advance information to correct the timing of the UE, and an uplink grant for the third message. The third message (Msg3) transmitted from UE to eNB over Physical Uplink Shared CHannel (PUSCH) includes a (scheduled) first Radio Resource Control (RRC) message (e.g. R RCSetupRequest, RRCResumeRequest, RRCReestablishmentRequest, RRCReconfigurationComplete, etc. depending on the situation) and may also contain user plane data. The fourth message (Msg4) transmitted from eNB to UE over Physical Downlink Shared CHannel (PDSCH) includes a second RRC message in response to the first RRC message (e.g. RRCSetup, RRCResume, etc.) and includes a contention resolution Medium Access Control (MAC) Control Element (CE). The fourth message is sent in the case of Contention-Based Random Access (CBRA) but not in the case of Contention-Free Random Access (CFRA).

Figure lb illustrates an alternative random access procedure adopted in 3GPP Release 16 in which the four-step procedure of Figure la is reduced to two steps by combining messages. In a first step, the UE selects resources for performing random access. Then, the UE and gNB 1.

exchange a sequence of two messages. The first message (MsgA) transmitted from UE to gNB corresponds to a combination of Msgl and Msg3 of Figure la and includes a preamble, and a first RRC message or user plane data. The second message (MsgB) transmitted from gNB to UE corresponds to a combination of Msg2 and Msg4 of Figure la and includes timing advance information and contention resolution information.

As noted above, in Figures la and lb, before the messages are sent, the UE needs to select the correct random access resources, comprising PRACH (Physical Random Access CHannel) resources in time and frequency as well as a specific preamble. These selections may be made according to a variety of techniques, including the following.

* Supplementary UpLink (SUL) vs Normal UpLink (NUL), which may include comparing a Reference Signal Received Power (RSRP) with the cell with a threshold, rsrpThresholdSSB-SUL.

* Bandwidth Part (BWP) selection.

* 2-step vs 4-step, which may be preamble divided or entirely separate PRACH resources.

* Msg3 repetitions, in which the UE selects a specific preamble to signal that it is capable of performing Msg3 repetitions and that it may be needed for coverage purposes.

* CBRA vs CFRA, wherein if the UE is configured with CFRA but the RSRP is low, the UE may instead select the configured CBRA resources.

* Synchronization Signal Block (SSB) selection * Random access group A/B, in which if the UE has good coverage and a large Msg3 payload, it can signal through preambles that it needs a larger Msg3 payload.

The random access procedure may be triggered by a number of events, for example as described in 3GPP 38.300, V17.2.0, Clause 9.2.6: Initial access from RRC IDLE; - RRC Connection Re-establishment procedure; - DL or LT data arrival, during RRC COATATECTED or during RRC INACTIVE while SDT procedure (see clause 18.0) is ongoing when UL synchronisation status is "non-synchronised"; - UL data arrival, during RRC COAAECTED or during RRC LNACTIVE while SDT procedure is ongoing, when there are no PUCCH resources for SR available: - SR failure; - Request by RRC upon synchronous reconfiguration (e.g. handover); - RRC Connection Resume procedure from RRC - To establish time alignment fi,r a secondary TAG; -Request for Other SI (see clause 7.3); - Beam failure recovery; - Consistent UT, I.RT failure on Sped!: - SDT R.Re 1VACI11,1± (see clause 189 - Positioning purpose during 1e1fC7 CONNECIED requiring n lont access procedure, e.g., when liming dvance is needed for CIE positioning.

In order to provide enhanced network coverage, a variety of different types of network nodes have been developed. For example, a Radio Frequency (RF) repeater may be deployed to amplify and forward any signal that it receives to supplement coverage provided by a regular cell. An enhanced type of repeater node, called a Network-Controlled Repeater (NCR), is currently under development and is a Release 18 Study Item/Work Item (3GPP RP-213700).

Figure 2 illustrates the network architecture of NCR communication. As shown, the NCR receives and forwards signals from gNB to UE via an NCR-Fwd link. The NCR also receives control signals from gNB via a NCR-Mobile Termination (MT) link, which are used to configure the NCR. Once configured, the NCR provides an amplify-and-forward function that is transparent to the UE. Accordingly, gNB may communicate with UE directly or through an NCR.

A 5G NR base station provides multi-beam operation in which the base station may transmit a signal through a relatively narrow beam (in the spatial domain) steered in a particular direction (directional transmission). The base station may transmit a signal through two or more such beams steered in respective different directions (see Figure 3). Each beam may be identified by a beam index (e.g. SSB index). It is intended that an NCR deployed in a 5G NR network is also capable of directional transmission via beamforming.

A UE may detect signals transmitted through the different beams. Due to factors including the relative locations of the UE and base station, and the different steering directions of the beams, the UE typically detects the signals with different signal strengths/power, with beams steered towards the UE typically being received with the highest signal strength/power.

The beam-based concept for 5G NR may be used in the random access procedure. A UE may measure different SSBs of a cell, and during the random access procedure the UE will select one SSB and a preamble that is associated with that specific SSB. When the network receives a preamble, the network will thus be aware of which SSB that the UE is attempting to connect through.

When an NCR is deployed, to make the NCR transparent to the UE for the random access procedure, the gNB may allocate a set of SSB indices to the NCR when the NCR registers to the network, for example as described in 3GPP R1-2203741, Section 5. This procedure is illustrated in Figure 3, in which SSB indices 9 and 10 are allocated to the NCR while other SSB indices 1-8 remain with gNB. The UE may then perform the random access procedure via SSBs transmitted via SSB indices allocated to the NCR as though the random access procedure was performed via the gNB. As illustrated in Figure 3, the UE may measure and perform random access to a beam originating from a different location compared to the gNB.

The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.

SUMMARY

It is an aim of certain examples of the present disclosure to address, solve and/or mitigate, at least partly, at least one of the problems and/or disadvantages associated with the related art, for example at least one of the problems and/or disadvantages described herein. It is an aim of certain examples of the present disclosure to provide at least one advantage over the related art, for example at least one of the advantages described herein.

The present invention is defined in the independent claims. Advantageous features are defined in the dependent claims.

Embodiments or examples disclosed in the description and/or figures falling outside the scope of the claims are to be understood as examples useful for understanding the present invention.

Other aspects, advantages and salient features of the invention will become apparent to those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figures la and lb illustrate examples of a random access procedure; Figure 2 illustrates the network architecture of NCR communication; Figure 3 illustrates a technique in which gNB allocate a set of SSB indices to an NCR for a random access procedure; Figure 4 illustrates an example of a UE selecting an NCR-associated SSB during a random access event; Figure 5 is a flow diagram of a method for performing a random access procedure; Figures 6a-d and 7 are flow diagrams of various methods for selecting an SSB; and Figure 8 is a block diagram of an exemplary network entity that may be used in certain examples of the present disclosure.

DETAILED DESCRIPTION

The following description of examples of the present disclosure, with reference to the accompanying drawings, is provided to assist in a comprehensive understanding of the present invention, as defined by the claims. The description includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the examples described herein can be made without departing from the scope of the invention.

The same or similar components may be designated by the same or similar reference numerals, although they may be illustrated in different drawings.

Detailed descriptions of techniques, structures, constructions, functions or processes known in the art may be omitted for clarity and conciseness, and to avoid obscuring the subject matter of the present invention.

The terms and words used herein are not limited to the bibliographical or standard meanings, but, are merely used to enable a clear and consistent understanding of the invention.

Throughout the description and claims of this specification, the words "comprise", "include" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other features, elements, components, integers, steps, processes, operations, functions, characteristics, properties and/or groups thereof.

Throughout the description and claims of this specification, the singular form, for example "a", "an" and "the", encompasses the plural unless the context otherwise requires. For example, reference to "an object" includes reference to one or more of such objects. Throughout the description and claims of this specification, language in the general form of "X for Y" (where Y is some action, process, operation, function, activity or step and X is some means for carrying out that action, process, operation, function, activity or step) encompasses means X adapted, configured or arranged specifically, but not necessarily exclusively, to do Y. Features, elements, components, integers, steps, processes, operations, functions, characteristics, properties and/or groups thereof described or disclosed in conjunction with a particular aspect, embodiment, example or claim are to be understood to be applicable to any other aspect, embodiment, example or claim described herein unless incompatible therewith.

The skilled person will appreciate that the techniques described herein may be used in any suitable combination.

Certain examples of the present disclosure provide methods, apparatus and systems for performing random access to a network. For example, certain examples of the present disclosure provide methods, apparatus and systems for performing random access to a 3GPP 5G NR network including an NCR. However, the skilled person will appreciate that the present invention is not limited to these examples, and may be applied in any suitable system or standard, for example one or more existing and/or future generation wireless communication systems or standards, including any existing or future releases of the same standards specification, for example 3GPP 5G.

The following examples are applicable to, and use terminology associated with, 3GPP 5G. However, the skilled person will appreciate that the techniques disclosed herein are not limited to 3GPP 5G. For example, the functionality of the various network entities and other features disclosed herein may be applied to corresponding or equivalent entities or features in other communication systems or standards. Corresponding or equivalent entities or features may be regarded as entities or features that perform the same or similar role, function or purpose within the network.

A particular network entity may be implemented as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, and/or as a virtualised function instantiated on an appropriate platform, e.g. on a cloud infrastructure.

Certain examples of the present disclosure may be provided in the form of an apparatus/device/network entity configured to perform one or more defined network functions and/or a method therefor. Certain examples of the present disclosure may be provided in the form of a system (e.g. network or wireless communication system) comprising one or more such apparatuses/devices/network entities, and/or a method therefor.

At least the following problem exist in view of the related art: While an NCR can be deployed without expected impact to a UE through appropriate SSB-layouts, some problem may arise. For example, one problem is that a control link is needed between the NCR and the gNB in order to control the NCR transmissions. Therefore, when a UE connects to an NCR rather than a gNB, the NCR-MT and NCR-Fwd components may need to be activated.

In a random access procedure, the selection of an SSB can be rather dynamic. For example, the following is described in 3GPP TS 38.321, Clause 5.1.2, in relation to how an SSB is selected (emphasis added): I= else (i.e. for the contention-based Random Access preamble selection): 2> if at least one of the SSBs with SS-RSRP above rsrp-lhresholciSSE is available: 3> select an SSB with SS-RSRP above rsrp-lhreshold.SSB.

2> else: 3> select an' SSB.

Thus, how a UE selects a specific SSB is not always specified if there are multiple SSBs that are above the rsrp-ThresholdSSB. For example, this may cause problems if selecting an SSB actually results in selecting a different access point (e.g. NCR vs gNB) very dynamically.

As noted above, random access is performed in many different cases For example, some cases involve radio-related failures and some involve synchronization issues. During a failure when communicating with a gNB, the UE might select an SSB associated with an NCR.

However, due inactivity of the NCR, the NCR might not be activated rapidly and therefore a quick response might not be possible. This problem may be especially acute in the case of non-initial random access, such as for Beam Failure Recovery (BFR) and similar. One example of this problem is illustrated in Figure 4.

Accordingly, what is required is one or more techniques for selecting an SSB when performing random access that avoid certain problems associated with the related art, for example the problems discussed above. Certain examples of the present disclosure provide one or more techniques for selecting an SSB that aims to restrict a UE from dynamically switching between gNB and NCR.

Herein, NCR and gNB may be referred to as different network elements, entities and/or nodes.

The skilled person will appreciate that the techniques described herein may be applied to network elements, entities and/or nodes other than NCR and gNB.

Certain examples of the present disclosure provide a method, for a User Equipment (UE), for performing random access in a network, the method comprising: selecting a Synchronisation Signal Block (SSB); and performing random access to a network entity based on the selected 30 SSB, wherein the SSB is selected based on an SSB group to which the SSB belongs.

In certain examples, a plurality of SSB groups may be configured including a first SSB group and one or more second SSB groups.

In certain examples, the first SSB group may be associated with a first network entity (e.g. gNB), and the one or more second SSB groups may be associated with one or more second network entities (e.g. NCR).

In certain examples, the method may further comprise determining a network entity to which the UE is, or was, connected, wherein the first SSB group may be associated with the determined network entity.

In certain examples, the method may further comprise receiving, by the UE from the network, when the UE is in connected mode, information (e.g. a flag, system information, dedicated signalling and/or broadcast signal) indicating to which network entity, or through which SSB group, the UE is connected.

In certain examples, the SSB may be selected from the first SSB group.

In certain examples, the method may further comprise selecting, by the UE. one of the first SSB group and the second SSB group.

In certain examples, if the first SSB group is selected, the SSB may be selected from the first SSB group, and if the second SSB group is selected, the SSB may be selected from the second SSB group.

In certain examples, the SSB may be selected based on a first condition and/or a second condition, wherein the first condition may comprise: the first SSB group includes an SSB for which the Reference Signal Received Power (RSRP) for the SSB exceeds a first threshold, and wherein the second condition may comprise: the second SSB group includes an SSB for which the RSRP for the SSB exceeds a second threshold.

In certain examples, the first threshold and/or the second threshold may be dynamically configurable.

In certain examples, the SSB may be selected based on one or more of: if the first condition is satisfied, the SSB may be selected from the first SSB group; if the first condition is not satisfied and the second condition is satisfied, the SSB may be selected from the second SSB group; if the first condition is not satisfied and the second condition is not satisfied, the SSB may be selected from the first SSB group and/or the second SSB group; and if both the first condition and the second condition are satisfied, the SSB may be selected from the SSB group through which the UE is currently connected or was previously connected.

In certain examples, the SSB may be selected based on one or more of: when the first condition is satisfied and the SSB is selected from the first SSB group, the SSB may be selected from among SSBs of the first SSB group for which the first threshold is exceeded; when the second condition is satisfied and the SSB is selected from the second SSB group, the SSB may be selected from among SSBs of the second SSB group for which the second threshold is exceeded; when the first condition is not satisfied and the SSB is selected from the first SSB group, the SSB may be selected from among any SSBs of the first SSB group; when the second condition is not satisfied and the SSB is selected from the second SSB group, the SSB may be selected from among any SSBs of the second SSB group; and when both the first condition and the second condition are satisfied, the SSB through which the UE is currently connected or was previously connected may be selected as the SSB.

In certain examples, the method may further comprise receiving signalling for determining which SSBs belong to the first and second SSB groups.

In certain examples, performing random access based on the selected SSB may comprise: attempting random access a first time based on the selected SSB; and attempting random access a second time based on the same selected SSB.

In certain examples, performing random access based on the selected SSB may comprise: attempting random access a first time based on the selected SSB; and attempting random access a second time based on an SSB belonging to the same SSB group as the selected In certain examples, the method may further comprise: triggering the random access based on occurrence of an event, and selecting a scheme for selecting the SSB based on the type of event that triggers the random access.

In certain examples, the type of event may include one or more of initial access from RRC_IDLE; RRC Connection Re-establishment procedure; DL and/or UL data arrival; SR failure; request by RRC upon synchronous reconfiguration; RRC Connection Resume procedure from RRC_INACTIVE; establishment of time alignment for a secondary TAG; request for Other SI; beam failure recovery; consistent UL LBT failure on SpCell; SDT in RRC INACTIVE; and positioning purpose during RRC CONNECTED.

In certain examples, performing random access based on the selected SSB may comprise: selecting a preamble based on the selected SSB; and performing random access using the selected preamble.

Certain examples of the present disclosure provide an apparatus (e.g. a UE) for performing random access in a network, the apparatus being configured to perform a method according to any aspect, example, claim or embodiment disclosed herein.

Certain examples of the present disclosure provide a network (or wireless communication system) comprising an apparatus according to any aspect, example, claim or embodiment disclosed herein Certain examples of the present disclosure provide a computer program comprising instructions which, when the program is executed by a computer or processor, cause the computer or processor to carry out a method according to any aspect, example, claim or embodiment disclosed herein.

Certain examples of the present disclosure provide a computer or processor-readable data carrier having stored thereon a computer program according to any aspect, example, claim or embodiment disclosed herein.

Figure 5 is a flowchart of a method for performing a random access procedure. For example, the method of Figure 5 may be applied in a network configurations illustrated in any of Figures 1-4. In a first step 501, the UE triggers random access. Any suitable trigger may be used in various examples of the present disclosure. Various non-limiting examples are described above. In a next step 503, the UE selects an SSB. For example, the UE may select an SSB from among a first set of SSBs (e.g. gNB SSBs) and a second set of SSBs (e.g. NCR SSBs). Various non-limiting examples of rules for selecting the SSB are described further below. Although not shown in Figure 5, the UE may perform a step of selecting a preamble from a preamble group associated with the selected SSB. In a next step 505, the UE performs random access based on the selected SSB (e.g. using the selected preamble).

In certain examples, the particular rule(s) used to select the SSB (e.g. select between gNB SSBs and NCR SSBs) in step 503 may depend on the type of event that triggered the random access.

For example, for initial access or random access triggered by beam failure, one or more rules may be applied to select an SSB with no or relatively few restrictions, for example to allow the UE to perform random access to an NCR node from RRC_IDLE, rather than being restricted from accessing the NCR in favour of the gNB.

For example, for random access triggered by SR failure or random access used for positioning purposes, one or more rules, for example one or more rules disclosed herein, may be applied to select an SSB with more restrictions. For SR failure, this may be important to prevent the UE from suddenly "disappearing" from a gNB to an NCR or the other way around, where, for example, the failure might be due to congestion in the network rather than related to failures of the Scheduling Request.

For example, for random access triggered by one or more other types of events, one or more other rules may be applied, for example one or more rules disclosed herein with one or more modifications. Such modification may include changes to the SSB selection thresholds, for example so that another NCR beam is only selected following NCR beam failure if the quality is higher than nominally expected.

The following disclose various exemplary rules for selecting an SSB. The skilled person will appreciate that these rules, as well as any other techniques disclosed herein, may be used in any suitable combinations.

In certain examples, the UE may determine a network entity (e.g. NCR or gNB) and may select an SSB in consideration of the determined network entity. In certain examples, the determination may be made based on which network entity the UE is, or has been, connected to. In other examples, the determination may be made based on a selection by the UE.

In certain examples, the UE may determine whether it is connected to an NCR or gNB. For example, this determination may be made in advance of a random access procedure. The UE may select an SSB based on a result of the determination. For example, the UE may select an SSB such that the UE does not switch connection from a current network node to a different network node (e.g. from an NCR to a gNB, or the other way around). The relevant information for allowing the UE to make the determination could be indicated by the network to the UE, for example through system information, or any dedicated signaling. In certain examples, the information may be indicated only when a UE is connected to an NCR node. In certain examples, the information may be implicit. For example, the information may be deduced based on information obtained by the UE indicating which SSB the UE is connected to. For example, the UE may save the SSB-index used by the UE to perform initial access and/or subsequent access.

In certain examples, one or more of the following rules may be applied in order to restrict or improve the dynamic movement between a gNB and an NCR SSB. In the following examples, different levels of restrictions may be applied. For example, one or more rules imposing a "hard" restriction" may be applied. Alternatively, one or more rules may be applied imposing a "soft" restriction.

According to an exemplary "hard" restriction, a UE should remain on an SSB that is associated with either the gNB or the NCR and not switch between if random access is triggered. In this case, the network may signal and configure certain SSBs that are associated with the gNB and certain SSBs that are associated with the NCR. For example, this may be possible for UEs in connected mode or inactive mode (RRC_INACTIVE) that are aware of whether they are connected to a gNB or an NCR.

The following is an example of a procedure applying a hard restriction.

1. UE is configured with information regarding a first set of SSBs associated with NCR and a second set of SSBs associated with gNB, so that the UE knows which SSBs are associated with NCR and which SSBs are associated with gNB 2. UE triggers random access 3. UE selects from SSBs associated with NCR (first set) and SSBs associated with gNB (second set) according to the following rules: a. If UE is connected to gNB -> select gNB SSB b. If UE is connected to NCR -> select NCR SSB 4. UE performs random access to gNB or NCR according to the selection According to an exemplary "soft" restriction, a UE should preferably remain on an SSB that is associated with either the gNB or the NCR and not switch between if random access is triggered, but some switching may be allowed in certain situations. For example, if a UE is connected to a certain network entity, SSBs associated with that network entity may be prioritised over SSBs associated with other network entities in the SSB selection process.

In certain examples, one or more thresholds may be configured, and switching may be permitted based on the thresholds. For example, UE may be configured with one or more thresholds associated with NCR and gNB SSBs and the one or more thresholds may be used to select between NCR SSB and gNB SSB. In some examples, a single threshold rsrpThresholdSSB may apply to both NCR and gNB, while in other examples independent thresholds rsrp-ThresholdSSB-NCR and rsrp-ThresholdSSB-gNB may apply to NCR and gNB, respectively. In certain examples the thresholds may be configurable (e.g. dynamically configurable).

Various examples will now be described in which a UE is configured with two thresholds. According to an exemplary rule, if the RSRP to NCR SSB is larger than rsrp-ThresholdSSBNCR then UE may select an NCR SSB. According to another exemplary rule, if RSRP to gNB SSB is larger than rsrp-ThresholdSSB-gNB then UE may select a gNB SSB. According to another exemplary rule, if both NCR and gNB SSBs are above the respective threshold then UE may select any SSB. According to another exemplary rule, if both NCR and gNB SSBs are above the respective threshold then UE may select the same SSB (group) as previously used/associated with. According to another exemplary rule, if none of NCR and gNB SSBs are above the respective threshold then UE may select any SSB. In certain examples, when permitted, UE may select an SSB that UE was associated with before triggering the random access procedure.

The above rules may be applied in any suitable combination and may be applied in combination with any other suitable alternative and/or additional rules. Figures 6a-d are flow diagrams of various exemplary methods for selecting an SSB according to the application of certain rules.

According to the above rules, switching between gNB and NCR is not fully restricted, but rather switching is permitted, for example if the RSRP is much higher to a specific gNB or NCR. For example, in Figure 6a, UE is connected to NCR and the UE selects any NCR or gNB SSB at the last step. In Figure 6b, the UE only selects gNB SSB. In Figure 6c, the UE is connected to gNB and selects any NCR or gNB SSB at the last step. In Figure 6d, the UE only selects NCR SSB.

In certain example, the selection of SSBs may be performed based on rsrp-Threshold offsets instead of configuring full threshold(s) for the NCR or gNB SSBs. In particular, the two thresholds rsrp-ThresholdSSB-NCR and rsrp-ThresholdSSB-gNB may be defined based on a single threshold rsrp-ThresholdSSB and respective offset values rsrp-OffsetSSB-NCR and rsrp-OffsetSSB-gNB. For example, this may be an offset with a value range of {AO, -8.....0, 2" 10}, or any other suitable values, that is configured each of NCR and gNB. For example, the threshold rsrp-ThresholdSSB may be pre-configured, or may be signaled separately or together with the offset values.

In certain examples, the selection of an SSB may be based on UE selection of a network entity. For example, the selection of the NCR or gNB may be done before SSB selection.

Figure 7 is a flow diagram of an exemplary method for selecting an SSB based on a selection. In this example, the UE first selects whether to perform random access to NCR or to gNB and then uses the appropriate rsrp threshold. In certain examples, this may be done through the Random Access Indication and Partitioning framework (also referred to as common RACH framework). In certain examples, this may be done by the UE comparing the RSRP to a threshold to an SSB that is associated with NCR or gNB and then determining based upon this that NCR or gNB should be selected.

Herein, various examples are described in which an SSB is selected from among a first set (or group) of SSBs associated with a first network entity (e.g. NCR) and a second set (or group) of SSBs associated with a second network entity (e.g. gNB). The skilled person will appreciate that the present disclosure is not limited to these examples. For example, more generally, an SSB may be selected from among a first set (or group) of SSBs (SSB set/group) and a second set (or group) of SSBs (SSB set/group), where the first and second sets of SSBs are not necessarily associated with particular network entities. The skilled person will appreciate that various techniques disclosed herein may be applied with this more general definition.

In certain examples, the UE is not allowed to switch SSBs in between Msg1 (preamble) attempts. Thus, when the UE performs random access, it selects one SSB and continues to use the same SSB and selects preamble from that preamble group. According to this technique, the UE does not switch between NCR and gNB once one SSB has been selected. This may be important, for example when performing idle mode random access.

Any suitable technique may be applied to signal to, or inform, the UE which SSBs belong to NCR and gNB. Suitable exemplary techniques include one or more of the following, which may be used individually or in any suitable combination.

* A list of preambles for each of gNB and NCR may be explicitly signalled.

* Only a list of preambles for NCR may be signalled. In this case, the UE may deduce the gNB preambles, for example based on the number of SSBs, which the UE may be aware of.

* The first NCR preamble only may be signalled. In this case, the set of SSBs {1,... ,X1} may be gNB SSBs, while the set of preambles {X,...,Y} may be NCR SSBS, where X is the first NCR preamble and Y is the total number of preambles.

* Differential signalling may be used. In this case, only indices in a previously shared list for those SSBs (preambles) whose allocation has changed may be signalled.

* New system information or other dedicated signaling indicating a pre-configured split of preambles (SSBs) may be used.

Figure 8 is a block diagram of an exemplary network entity that may be used in examples of the present disclosure. The skilled person will appreciate that a network entity may be implemented, for example, as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, and/or as a virtualised function instantiated on an appropriate platform, e.g. on a cloud infrastructure.

The entity 800 comprises a processor (or controller) 801, a transmitter 803 and a receiver 805. The receiver 805 is configured for receiving one or more messages from one or more other network entities, for example as described above. The transmitter 803 is configured for transmitting one or more messages to one or more other network entities, for example as described above. The processor 801 is configured for performing one or more operations, for example according to the operations as described above.

The techniques described herein may be implemented using any suitably configured apparatus and/or system. Such an apparatus and/or system may be configured to perform a method according to any aspect, embodiment, example or claim disclosed herein. Such an apparatus may comprise one or more elements, for example one or more of receivers, transmitters, transceivers, processors, controllers, modules, units, and the like, each element configured to perform one or more corresponding processes, operations and/or method steps for implementing the techniques described herein. For example, an operation/function of X may be performed by a module configured to perform X (or an X-module). The one or more elements may be implemented in the form of hardware, software, or any combination of hardware and software.

It will be appreciated that examples of the present disclosure may be implemented in the form of hardware, software or any combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage, for example a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape or the like.

It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement certain examples of the present disclosure.

Accordingly, certain examples provide a program comprising code for implementing a method, apparatus or system according to any example, embodiment, aspect and/or claim disclosed herein, and/or a machine-readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium, for example a communication signal carried over a wired or wireless connection.

While the invention has been shown and described with reference to certain examples, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention, as defined by the appended claims.

Abbreviations/Definitions In the present disclosure, the following acronyms/definitions are used.

3GPP 3" Generation Partnership Project 5G 5th Generation BFR Beam Failure Recovery BWP Bandwidth Part CBRA Contention-Based Random Access CE Control Element CFRA Contention-Free Random Access DL Down Link eNB Base Station Fwd Forward gNB 5G NR Base Station LBT Listen Before Talk LTE Long Term Evolution MAC Medium Access Control Msg Message MT Mobile Termination NCR Network-Controlled Repeater NR New Radio NUL Normal UpLink PDSCH Physical Downlink Shared CHannel PRACH Physical Random Access CHannel PUSCH Physical Uplink Shared CHannel RACH Random Access CHannel RAR Random Access Response RF Radio Frequency RRC Radio Resource Control RSRP Reference Signal Received Power SDT Small Data Transmission SI System Information SR Scheduling Request SS Synchronization Signal SSB Synchronization Signal Block SUL Supplementary UpLink TAG Timing Advance Group

TS Technical Specification

UE User Equipment UL Up Link

Claims

Claims 1. A method, for a User Equipment (UE), for performing random access in a network, the method comprising: selecting a Synchronisation Signal Block (SSB); and performing random access to a network entity based on the selected SSB, wherein the SSB is selected based on an SSB group to which the SSB belongs.
2. A method according to claim 1, wherein a plurality of SSB groups are configured including a first SSB group and one or more second SSB groups.
3. A method according to claim 2, wherein the first SSB group is associated with a first network entity (e.g. gNB), and the one or more second SSB groups are associated with one or more second network entities (e.g. NCR).
4. A method according to claim 3, further comprising determining a network entity to which the UE is, or was, connected, wherein the first SSB group is associated with the determined network entity.
5. A method according to any preceding claim, further comprising receiving, by the UE from the network, when the UE is in connected mode, information (e.g. a flag, system information, dedicated signalling and/or broadcast signal) indicating to which network entity, or through which SSB group, the UE is connected.
6. A method according to claim 4 or 5, wherein the SSB is selected from the first SSB group.
7. A method according to any of claims 2 to 6, further comprising selecting, by the UE, one of the first SSB group and the second SSB group.
8. A method according to claim 7, wherein if the first SSB group is selected, the SSB is selected from the first SSB group, and if the second SSB group is selected, the SSB is selected from the second SSB group.
9. A method according to any of claims 2 to 8, wherein the SSB is selected based on a first condition and/or a second condition, wherein the first condition comprises: the first SSB group includes an SSB for which the Reference Signal Received Power (RSRP) for the SSB exceeds a first threshold, and wherein the second condition comprises: the second SSB group includes an SSB for which the RSRP for the SSB exceeds a second threshold.
10. A method according to claim 9, wherein the first threshold and/or the second threshold are dynamically configurable.
11. A method according to claim 9 or 10, wherein the SSB is selected based on one or more of: if the first condition is satisfied, the SSB is selected from the first SSB group; if the first condition is not satisfied and the second condition is satisfied, the SSB is selected from the second SSB group; if the first condition is not satisfied and the second condition is not satisfied, the SSB is selected from the first SSB group and/or the second SSB group; and if both the first condition and the second condition are satisfied, the SSB is selected from the SSB group through which the UE is currently connected or was previously connected.
12. A method according to any of claims 8 to 11, wherein the SSB is selected based on one or more of: when the first condition is satisfied and the SSB is selected from the first SSB group, the SSB is selected from among SSBs of the first SSB group for which the first threshold is exceeded; when the second condition is satisfied and the SSB is selected from the second SSB group, the SSB is selected from among SSBs of the second SSB group for which the second threshold is exceeded; when the first condition is not satisfied and the SSB is selected from the first SSB group, the SSB is selected from among any SSBs of the first SSB group; when the second condition is not satisfied and the SSB is selected from the second 30 SSB group, the SSB is selected from among any SSBs of the second SSB group; and when both the first condition and the second condition are satisfied, the SSB through which the UE is currently connected or was previously connected is selected as the SSB.
13. A method according to any of claims 2 to 12, further comprising receiving signalling for determining which SSBs belong to the first and second SSB groups.
14. A method according to any preceding claim, wherein performing random access based on the selected SSB comprises: attempting random access a first time based on the selected SSB; and attempting random access a second time based on the same selected SSB.
15. A method according to any preceding claim, wherein performing random access based on the selected SSB comprises: attempting random access a first time based on the selected SSB; and attempting random access a second time based on an SSB belonging to the same 10 SSB group as the selected SSB.
16. A method according to any preceding claim, further comprising: triggering the random access based on occurrence of an event; and selecting a scheme for selecting the SSB based on the type of event that triggers the random access.
17. A method according to claim 16, wherein the type of event includes one or more of: initial access from RRC_IDLE; RRC Connection Re-establishment procedure; DL and/or UL data arrival; SR failure; request by RRC upon synchronous reconfiguration; RRC Connection Resume procedure from RRC_INACTIVE; establishment of time alignment for a secondary TAG; request for Other SI; beam failure recovery; consistent UL LBT failure on SpCell; SDT in RRC_INACTIVE; and positioning purpose during RRC_CONNECTED.
18. A method according to any preceding claim, wherein performing random access based on the selected SSB comprises: selecting a preamble based on the selected SSB; and performing random access using the selected preamble.
19. An apparatus (e.g. a UE) for performing random access in a network, the apparatus being configured to perform the method of any of claims 1 to 18.
20. A network (or wireless communication system) comprising an apparatus according to claim 19.
21. A computer program comprising instructions which, when the program is executed by a computer or processor, cause the computer or processor to carry out a method according to any of claims 1 to 18.
22. A computer or processor-readable data carrier having stored thereon a computer program according to claim 21.