GB2576202A - Method and apparatus for random access in an integrated access and backhaul communication system - Google Patents

Abstract

An integrated access and backhaul (IAB), wireless communication system comprises a first base station 222, a second base station 255, and a plurality of remote wireless communication units (206, 216, 226), wherein the second base station provides access to a core network, and the first base station requires access to the core network via the second base station. The second base station includes a transceiver and a processor operably coupled to the transceiver. The processor is arranged to configure a first random access channel (RACH), resource for use by the first base station; and configure a second RACH resource for use by the plurality of remote wireless communication units to access the second base station, wherein the configured second RACH is different to the configured first RACH. The invention seeks to alleviate problems with inter relay channel monitoring when a communication backhaul blockage occurs.

Description

METHOD AND APPARATUS FOR RANDOM ACCESS IN AN INTEGRATED ACCESS

AND BACKHAUL COMMUNICAHON SYSTEM

Technical Field [0001] The field of this invention relates generally to implementing random access in an integrated access and backhaul communication system.

Background [0002] In recent years, third generation (3G) wireless communications have evolved to the long term evolution (LTE) cellular communication standard, sometimes referred to as 4^th generation (4G) wireless communications. Both 3G and 4G technologies are compliant with third generation partnership project (3GPP™) standards. 4G networks and phones were designed to support mobile internet and higher speeds for activities, such as video streaming and gaming. The 3GPP™ standards are now developing a fifth generation (5G) of mobile wireless communications, which is set to initiate a step change in the delivery of better communications, for example powering businesses, improving communications within homes and spearheading advances such as driverless cars.

[0003] One of the potential technologies targeted to enable future cellular network deployment scenarios and applications is the support for wireless backhaul and relay links enabling flexible and very dense deployment of 5G-new radio (NR) cells without a need for densifying the transport network proportionately. Due to the expected larger bandwidth available for NR compared to long term evolved (LTE™) (e.g. mmWave spectrum) along with the native deployment of massive multiple-in/multiple-out (ΜΙΜΟ) or multi-beam systems in NR creates an opportunity to develop and deploy integrated access and backhaul (IAB) links. It is envisaged that this may allow easier deployment of a dense network of self-backhauled NR cells in a more integrated manner, by building upon many of the control and data channels/procedures defined for providing access to UEs. An example illustration of a network with such IAB links is shown in Figure 1, where IAB nodes (or relay nodes (rTRPs) or relay IAB nodes, as these terms are

- 1 used interchangeably herein) are configured to multiplex access and backhaul links in time, frequency, or space (e.g. beam-based operation).

[0004] Referring to FIG. 1, a known simplified 5G architecture diagram 100 illustrates how an Integrated Access and Backhaul (IAB) network is deployed. Here, a first 5G base station 102 supporting communications within a coverage area 104, including communication support for a wireless communication unit, sometimes referred to as a terminal device, such as a user equipment UE 106. In 5G, the UE 106 is able to support traditional Human Type Communications (HTC) or the new emerging Machine Type Communications (MTC). The known simplified architecture diagram 100 includes a second 5G base station 112 supporting communications within a coverage area 114, including communication support for a UE 116 and a third 5G base station 122 supporting communications within a coverage area 124, including communication support for a UE 126. A wireless backhaul connection 132, 133, generally an Xn (based on X2) interface connects the third 5G base station 122 with the first 5G base station 102 and second 5G base station 112. The third 5G base station 122 is also connected to the core network via a more traditional wired connection, such as fibre 134.

[0005] In this regard, in an IAB scenario, node A (i.e. third 5G base station 122) is considered a donor IAB node and node B (i.e. first 5G base station 102) and node C (i.e. second 5G base station 112) are identified as relay IAB nodes.

[0006] One of the main objectives of IAB is to provide radio access network (RAN)-based mechanisms to support dynamic route selection to accommodate short-term blocking and transmission of latency-sensitive traffic across backhaul links. This objective is also relevant to resource allocation (RA) between access and backhaul links under half-duplexing constraints. In the NR standard, there are three RA modes defined, namely time division multiplex (TDM), frequency division multiplex (FDM) and space division multiplex SDM (e.g. beam-based operation). No matter which RA scheme is applied, the inventors have identified that there always exists a problem for inter-relay channel monitoring for topology management when a communication (backhaul) blockage occurs.

[0007] When nodes B and C conduct random access, they can follow the same procedure as the UEs within the coverage of node A, e.g. UE 126. However, if the backhaul link 132 between

-2node B and node A is blocked, node B might need to be connected to node C to form a multi-hop relay network. In such a case, the distance between node B and node C could be much larger than the distance between the node C UE 116 and node C (i.e. second 5G base station 112). Since the random access preamble format is decided by the cell radius, the preamble used for node C UE 116 might not be suitable for another IAB node, e.g., node B (i.e. first 5G base station 102).

Summary of the Invention [0008] In a first aspect of the invention, an integrated access and backhaul, IAB, wireless communication system is described that includes a first base station, a second base station, and a plurality of remote wireless communication units, wherein the second base station provides access to a core network, and the first base station requires access to the core network via the second base station. The second base station includes: a transceiver; and a processor, operably coupled to the transceiver and arranged to: configure a first random access channel, RACH, resource for use by the first base station; and configure a second random access channel, RACH, resource for use by the plurality of remote wireless communication units to access the second base station, wherein the configured second RACH is different to the configured first RACH}.

[0009] In this manner, by configuring separate and distinct RACH operations for both the wireless remote communication units, e.g. UEs, and an IAB node to use a backhaul link, for example in a multi-hop relay arrangement, a more efficient use of the backhaul link can be achieved, particularly when a backhaul link is blocked.

[0010] In some optional examples, for example in a 5G system, the configured first RACH resource may include a different preamble format of the RACH compared to the configured second RACH. In some optional examples, the configured first RACH resource may include a different time configuration of the RACH compared to the configured second RACH. In some optional examples, the configured first RACH resource comprises a different frequency configuration of the RACH compared to the configured second RACH. In some optional examples, the configured first RACH resource may include a different random access periodicity

-3of the RACH compared to the configured second RACH. In some optional examples, the first RACK resource may be allocated with a lower periodicity than the second RACH resource. In some optional examples, the second RACH resource may be allocated for use before the first RACH resource. Moreover, there is no need to keep the same random access periodicity for UEs and IAB nodes since the connection between IAB nodes needs to be maintained after the first random access, and thus requires much less frequent random access when compared with the UE random access.

[0011] In some optional examples, the configured different RACH resources may include at least one from a group of: symbol, slot, subframe and system frame number, SFN. In some optional examples, a same initial RACH access may be enabled for access by both the first base station and the plurality of remote wireless communication units, prior to the processor being arranged to configure a subsequent first RACH resource for use by the first base station that differentiates the first RACH resource from the second access link RACH resource used by plurality of remote wireless communication units. In some optional examples, the configured first RACH resource may be configured for use by the first base station for both random access and backhaul link communications. In some optional examples, the configured first RACH resource may include a different orthogonal multiplexing configuration of the RACH compared to the configured second RACH. In some optional examples, the orthogonal multiplexing configuration of the RACH comprises at least one from a group of: frequency multiplexing of access link random access resources and backhaul link random access resources, time multiplexing of access link random access resources and backhaul link random access resources. In some optional examples, orthogonal time multiplexing configuration of the RACH may include at least one from a group of: time multiplexing of access link random access resources and backhaul link random access resources within a single time slot, time multiplexing of access link random access resources and backhaul link random access resources that are allocated different time slots, time multiplexing of access link random access resources and backhaul link random access resources that are allocated different bandwidth parts, BWP, of a carrier frequency.

[0012] In some optional examples, the first base station may be configured to perform a RACH with the second base station to support a wireless backhaul link via a relay node to form a

-4multi-hop relay backhaul link. In some optional examples, the first base station may be configured to perform a RACH with the second base station in response to a backhaul link being blocked.

[0013] In some optional examples, at least one RACH information element, IE, parameter in radio resource control, RRC, state, from a group of multiple sets of RACH parameters may be configured, where the at least one RACH IE parameter comprises expansion of at least one from a group of: RACH-ConfigCommon, RACH-ConfigGeneric, RACH-ConfigDedicated. In some optional examples, the expansion of the at least one RACH IE parameter may include at least one from a group of: definition of a new RRC IEs; adding of a new parameter to configure different RACH settings; expansion of a value range of current parameters, to differentiate between RACH configurations.

[0014] In a second aspect of the invention, second base station for an integrated access and backhaul, TAB, wireless communication system according to the first aspect is described.

[0015] In a third aspect of the invention, remote wireless communication unit, such as a UE, for an integrated access and backhaul, IAB, wireless communication system according to the first aspect is described.

[0016] In a fourth aspect of the invention, a method for random access in an integrated access and backhaul, IAB, wireless communication system performed by the second base station according to the second aspect is described.

[0017] In a fifth aspect of the invention, a method for random access in an integrated access and backhaul, IAB, wireless communication system performed by the remote wireless communication unit, such as a UE, according to the third aspect is described.

Brief Description of the Drawings [0018] Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, similar reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

-5[0019] FIG. 1 illustrates a known simplified 5G architecture configured to support IAB.

[0020] FIG. 2 illustrates a simplified 5G architecture configured to support IAB, according to examples of the invention.

[0021] FIG. 3 illustrates a block diagram of an UE, adapted in accordance with some example embodiments of the invention.

[0022] FIG. 4 illustrates a block diagram of an IAB base station (or node), adapted in accordance with some example embodiments of the invention.

[0023] FIG. 5 illustrates a representation of a random access resource allocation for access link, according to examples of the invention.

[0024] FIG. 6 illustrates a representation of a Random access resource allocation for backhaul link, according to examples of the invention.

[0025] FIG. 7 illustrates a representation of an IAB link that utilises TDM or SDM, according to examples of the invention [0026] FIG. 8 illustrates a representation of a Frequency multiplexing of access link and backhaul link random access resources, according to examples of the invention.

[0027] FIG. 9 illustrates a representation of a Time multiplexing of access link and backhaul link random access resources, according to examples of the invention.

[0028] FIG. 10 illustrates a representation of a Time multiplexing of access link and backhaul link random access resources, according to examples of the invention.

[0029] FIG. 11 illustrates a representation of a Time multiplexing of access link and backhaul link random access resources with respect to the carrier bandwidth part (BWP), according to examples of the invention.

[0030] FIG. 12 illustrates a simplified flowchart of a UE procedure, in accordance with some example embodiments of the invention.

[0031] FIG. 13 illustrates a simplified flowchart of a first method for a IAB node procedure, in accordance with some example embodiments of the invention.

-6[0032] FIG. 14 illustrates a simplified flowchart of a second method for a IAB node procedure, in accordance with some example embodiments of the invention.

[0033] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.

Detailed Description [0034] Examples of the invention describe a wireless communication system that includes a mechanism for improved efficiency of random access for IAB nodes in an IAB architecture. In particular, examples of the invention propose to use different random access configurations for IAB nodes and UEs. Within this concept, a number of approaches are described to differentiate the random access of IAB nodes and UEs, such as respective use of different preamble formats, respective use of different time/frequency configurations.

[0035] Although example embodiments of the invention are described with reference to different random access configurations for IAB nodes and UEs in a 5G architecture, it is envisaged that some aspects of the invention are not so constrained/limited. For example, it is envisaged that the different random access configurations may be enacted for a long Term

-7 Evolved (LTE™) system, or other such communication systems that utilise random access techniques.

[0036] Example embodiments are described with respect to FR2, since the main focus of IAB is on above FR2, i.e., 24.25 GHz - 52.6 GHz. However, it is envisaged that the examples described herein apply equally to FR1, i.e. 450 MHz - 6 GHz.

[0037] Example embodiments are described with reference to radio access networks, which term encompasses and is considered to be equivalent to and interchangeable with communication cells, namely the facilitation of communications within a cell that may access other parts of the communication system as a whole.

[0038] Referring now to FIG. 2, part of a wireless communication system 200 is shown in outline, in accordance with one example embodiment of the invention. The wireless communication system 200 illustrates how an Integrated Access and Backhaul (IAB) network may be deployed in accordance with one example embodiment of the invention, where separate RACK is provided for use by an IAB node, e.g. a relay IAB node requiring a backhaul link or RACK access, and UEs requiring RACH access. Here, a donor IAB node A (sometimes referred to as a parent IAB node) 222 is configured to receive first access control RACH requests 250 from wireless communication units, sometimes referred to as a terminal device, such as a user equipment UE 226. In the context of the present invention, a relay IAB node B (e.g. a 5G base station) 202 uses a separate second RACH to access the donor IAB node to form a backhaul link ‘AB’ 232. Such a backhaul link may also carry communications to/from a second UE B 206, which has used a RACH access 255 to connect to the relay IAB node B 202.

[0039] Similarly, a further relay IAB node C (e.g. a 5G base station) 212 uses a separate RACH to access the relay IAB node B 202 to form a backhaul link ‘BC’ 235, and thereafter the donor IAB node by joining the backhaul link ‘AB’ 232. Such a backhaul link may also carry communications to/from a third UE C 216, which has used a RACH access 260 to connect to the further relay IAB node C 212. In particular, examples of the invention propose to use different random access configurations for IAB nodes 202 and UEs such as UE 226. Within this concept, a number of approaches are described to differentiate the random access of IAB nodes and UEs,

-8such as respective use of different preamble formats, respective use of different time/frequency configurations [0040] In accordance with one example of the invention, the IAB nodes 202, 212 and UEs such as UE 226 are allocated different preamble formats within RACH, to identify to the recipient (donor) IAB node 222 whether the RACH emanated from another IAB node 202, for example due to a backhaul blockage, or whether the RACH emanated from a UE 226. In accordance with another example of the invention, the IAB nodes 202, 212 and UEs, such as UE 226, are allocated different time and/or frequency configurations within RACH, to identify to the recipient (donor) IAB node 222 whether the RACH emanated from another IAB node 202, for example due to a backhaul blockage, or whether the RACH emanated from a UE 226.

[0041] In the context of the present invention, the selection of preamble formats to be divided between IAB use and UE use can be made from the known preamble formats. The preamble formats for FR2 are defined in the below table 1 from the 3GPP standard at 6.3.3.1-2:

Table 1: Preamble formats for A.·, = 139 and Δ/^ΚΑ = 15-2-° kHz where μ e {0,1,2,3}

Format		Δ/Α	U	/VRA JVCP	Support for restricted sets
Al	139	15-2A kHz	2-2048v2A	288/C-2'	-
A2	139	15-2A kHz	4-2048v2A	5Ί6κ·Τμ	-
A3	139	15-2A kHz	6-2048v2A		-
Bl	139	15-2A kHz	2-2048v2A	1\6κ·Τμ	-
B2	139	15-2A kHz	4-2048v2A	Α&κ·Τμ	-
B3	139	15-2A kHz	6-2048v2A	5Μκ·Τμ	-
B4	139	15-2A kHz	12-2048v2A	936κ·2~μ	-
CO	139	15-2A kHz	2048Λ-2	1240α-2	-
C2	139	15-2A kHz	4-2048v2A	2048Λ-2

[0042] Access link and backhaul link have different requirements on random access link budget and preamble cyclic prefix (CP) length. For example, the random access link budget is

-9relevant to a repetition level of the random access signature, i.e., N_u. CP length, i.e., /ρ determines the cell size, and these parameters are defined in 3GPP TS38.213.

[0043] Furthermore, the access link, such as access link AA 250 requires a much higher random access link budget than the backhaul link AB 232 with IAB node 202 because of the much lower transmission power. However, it also requires a shorter CP length, since the distance between the UE 226 and its associated IAB node 222 is less than that between two IAB nodes 222, 202. In this regard, examples of the invention propose to use, say, the preamble C2 format for IAB RACH access to another IAB, as C2 contains the longest CP that is configured to both access link and backhaul link. Thus, the C2 preamble format is able to support 9.3 km as the maximum distance between two IAB nodes. However, since the random access signature is only repeated 4 times, the link budget might not be enough for access link. On the contrary, if a preamble B4 format with 12 repetitions is configured, the access link budget can be improved by 4.7 dB but the maximum distance supported is almost halved and thus IAB node B in FIG. 2 might not be able to establish connection with IAB node C. Thus, examples of the invention propose to adopt different preamble formats, dependent upon the specific prevailing conditions, which in most instances can be selected in the IAB node implementation.

[0044] FIG. 3 illustrates a high level block diagram of a wireless communication unit such as a user equipment (UE) 300 contains an antenna 302, for receiving transmissions, coupled to an antenna switch or duplexer 304 that provides isolation between receive and transmit chains within the UE 300. One or more receiver chains, as known in the art, include receiver front-end circuitry 306 (effectively providing reception, filtering and intermediate or base-band frequency conversion). The receiver front-end circuitry 306 is coupled to a signal processing module 308 (generally realized by a digital signal processor (DSP)). A skilled artisan will appreciate that the level of integration of receiver circuits or components may be, in some instances, implementation-dependent.

[0045] The controller 314 maintains overall operational control of the wireless communication unit 300. The controller 314 is also coupled to the receiver front-end circuitry 306 and the signal processing module 308. In some examples, the controller 314 is also coupled

-10to a frequency generation circuit 317 and a memory device 316 that selectively stores operating regimes, such as decoding/encoding functions, synchronization patterns, code sequences, and the like. A timer 318 is operably coupled to the controller 314 to control the timing of operations (e.g. transmission or reception of time-dependent signals) within the UE 300.

[0046] As regards the transmit chain, this essentially includes an input module 320, coupled in series through transmitter/modulation circuitry 322 and a power amplifier 324 to the antenna 302, antenna array, or plurality of antennas. The transmitter/ modulation circuitry 322 and the power amplifier 324 are operationally responsive to the controller 314.

[0047] The signal processor module 308 in the transmit chain may be implemented as distinct from the signal processor in the receive chain. Alternatively, a single processor may be used to implement a processing of both transmit and receive signals, as shown in FIG. 3. Clearly, the various components within the wireless communication unit 325 can be realized in discrete or integrated component form, with an ultimate structure therefore being an application-specific or design selection.

[0048] In accordance with examples of the invention, the processor 308 and transceiver (e.g. transmitter/modulation circuitry 322) of the IAB node are configured to communicate with another IAB node (e.g. 5G gNB) in an IAB architecture by using a RACH that is configured with a UE-specific preamble format, in order to distinguish the UE RACH from another RACH received at the recipient IAB node from another IAB node. The processor 308 and receiver frontend circuitry 306 are also configured to receive an acknowledgement of a successful RACH attempt in response to the UE-specific preamble format.

[0049] In accordance with examples of the invention, the processor 308 and transceiver (e.g. transmitter/modulation circuitry 322) of the UE are additionally or alternatively configured to communicate with an IAB node in an IAB architecture by using a RACH that is configured with UE-specific time and/or frequency configurations, in order to distinguish the UE RACH from another IAB node RACH. In this example, the processor 308 and receiver front-end circuitry 306 are configured to receive an acknowledgement of a successful RACH attempt in response to the UE-specific time and/or frequency configurations.

-11 [0050] Referring now to FIG. 4, high level block diagram of an IAB node (e.g. a 5G wireless base station) 400 is illustrated, where the IAB node 400 has been adapted in accordance with some example embodiments of the invention. The IAB node 400 contains an antenna 402, for receiving transmissions, coupled to an antenna switch or duplexer 404 that provides isolation between receive and transmit chains within the IAB node 400. One or more receiver chains, as known in the art, include receiver front-end circuitry 406 (effectively providing reception, filtering and intermediate or base-band frequency conversion). The receiver front-end circuitry 406 is coupled to a signal processing module 408 (generally realized by a digital signal processor (DSP)). A skilled artisan will appreciate that the level of integration of receiver circuits or components may be, in some instances, implementation-dependent.

[0051] The controller 414 maintains overall operational control of the IAB node 400. The controller 414 is also coupled to the receiver front-end circuitry 406 and the signal processing module 408. In some examples, the controller 414 is also coupled to a frequency generation circuit 417 and a memory device 416 that selectively stores operating regimes, such as decoding/encoding functions, synchronization patterns, code sequences, and the like. A timer 418 is operably coupled to the controller 414 to control the timing of operations (e.g. transmission or reception of time-dependent signals) within the IAB node 400.

[0052] As regards the transmit chain, this essentially includes an input module 420, coupled in series through transmitter/modulation circuitry 422 and a power amplifier 424 to the antenna 402, antenna array, or plurality of antennas. The transmitter/ modulation circuitry 422 and the power amplifier 424 are operationally responsive to the controller 414. The signal processor module 408 in the transmit chain may be implemented as distinct from the signal processor in the receive chain. Alternatively, a single processor may be used to implement a processing of both transmit and receive signals, as shown in FIG. 4. Clearly, the various components within the IAB node 400 can be realized in discrete or integrated component form, with an ultimate structure therefore being an application-specific or design selection.

[0053] In accordance with examples of the invention, the processor 408 and transceiver (e.g. transmitter/modulation circuitry 422) of the IAB are configured to communicate with another IAB node in an IAB architecture by using a RACH that is configured with an IAB node-specific preamble format, in order to distinguish the IAB node RACH from another RACH received at

-12the recipient IAB node from a UE. The processor 408 and receiver front-end circuitry 406 are also configured to receive an acknowledgement of a successful RACH attempt in response to the IAB node-specific preamble format.

[0054] In accordance with examples of the invention, the processor 408 and transceiver (e.g. transmitter/modulation circuitry 422) of the IAB node are additionally or alternatively configured to communicate with an IAB node in an IAB architecture by using a RACH that is configured with IAB node-specific time and/or frequency configurations, in order to distinguish the IAB node RACH from a UE RACH. In this example, the processor 408 and receiver frontend circuitry 406 are configured to receive an acknowledgement of a successful RACH attempt in response to the IAB node-specific time and/or frequency configurations.

Different time/frequency RACH configurations to differentiate access requests between lABs and UEs:

[0055] The number of UEs associated with one IAB node, e.g., IAB node C in FIG. 2, could be much larger than the number of IAB nodes connected to IAB node C. In fact, in practice, there might be only a very limited number of IAB nodes expected to be connected to a parent IAB node (i.e. an IAB node that serves relay IAB nodes). In NR, some resources in terms of symbol, slot, subframe and system frame number (SFN) are allocated for physical random access channels (PRACH) as shown in FIG. 5 and the periodicity of such resources are short so that UEs are able to transmit their random access preambles as soon as possible without causing too many collisions. Thus, referring now to FIG. 5, a representation 500 of a random access resource allocation for access link using different timeslots is illustrated, according to examples of the invention. For example, FIG. 5 illustrates a 5G subframe, with slot i 510 and slot i+2 514 allocated for PRACH 520. As the number of UEs associated with one (parent) IAB node, e.g., is likely to be much larger than the number of IAB nodes, examples of the invention propose that the UE is allocated more of the PRACH opportunities in more frequent timeslots, as compared to RACH allocations for IAB nodes.

-13 [0056] Thus, for IAB node random access, the collision probability is much lower due to a limited number of IAB nodes. Hence, the periodicity of such resources, between successively used RACH slots, can be configured larger as shown in FIG. 6. Referring now to FIG. 6, a representation 600 of a random access resource allocation for backhaul link for IAB nodes is illustrated, according to examples of the invention. Here, a 5G subframe, with slot i 610 and slot i+4 618 are allocated for PRACH 620 for use by IAB nodes.

[0057] In some examples of the invention, it is envisaged that an IAB node RACH may be distinguished from a UE RACH once the initial RACH access is completed. In this first case, it is envisaged that an IAB node initially performs a random access (RA) procedure as if the IAB node is a UE. Thus, in this example, the IAB node may use a same RACH preamble format as well as time-frequency resources as would be expected for use by a UE. However, if an IAB node is configured by its parent IAB node via, say, low layer signalling (e.g., DCI) or upper layer signalling (e.g., MAC CE or RRC), so that it is aware of radio resources allocated to backhaul links, and once the initial access is complete, the parent IAB node may allocate RACH resources for backhaul. In this example, these subsequently allocated backhaul resources are differentiated from access link RACH resources, and thus may be used by the IAB node for a backhaul.

[0058] Thus, in this example, two stages are performed: a first initial random access stage; and a second random access stage after the initial random access. In first initial random access stage, IAB nodes cannot differentiate access link random access resources/preamble formats from backhaul link random access resources/preamble formats. Thus, such information is broadcasted by the parent node. In the second random access stage, IAB nodes identify the backhaul link resources.

[0059] FIG. 7 illustrates a representation of an IAB link that utilises TDM 700 or SDM 750, according to the aforementioned example of the invention. In a first TDM 700 example, a first access channel (AC1) 720 includes downlink slots 710 and uplink slots 712. Once the initial access is complete, the parent IAB node may allocate first RACH resources for backhaul use (e.g. allocate first backhaul link resource (BH1) 730 and allocate second RACH resources for

-14access use (e.g. allocate second access link resource (AC2) 740, thereby distinguishing between

735 the UE RACH and IAB RACH.

[0060] In a second SDM 750 example, a first access channel (AC1) 770 again includes downlink slots 760 and uplink slots 762. Once the initial access is complete, the parent IAB node may allocate first RACH resources for backhaul use (e.g. allocate first backhaul link resource (BH1) 780 with a structure that enables backhaul link resources to use odd slot numbers for downlink and even number slot numbers for uplink). In contrast, the parent IAB node may allocate second RACH resources for access use that are distinguished from the backhaul link resources (e.g. allocate second access link resource (AC2) 790 with a structure that enables access link resources to use odd slot numbers for uplink and even number slot numbers for downlink.

[0061] It can be seen that for TDM access line AC1 and BH link BH1 still use the same time-frequency resources in slot i (DL) and slot i+1 (UL). For SDM, in slot i+1 the same timefrequency resources are actually used by access link AC1 (UL), backhaul link BHl(UL) and access link AC 2(DL). For both schemes, AC1 and BH1 use the same time-frequency resources in slot i+1 for UL, where the RACH resources should be allocated. In such a case, the backhaul resources and access resources are expected to be overlapping and thus cannot be differentiated. Therefore, orthogonal multiplexing should be applied if different preamble formats/periodicity configurations are needed for access link and backhaul link random access, to resolve such potential resource conflict problems.

[0062] In some examples of the invention, for orthogonal multiplexing may be employed to distinguish between IAB node usage of a RACH and a UE usage of a RACH. In some examples, it is envisaged that different preamble formats needed by access and backhaul links, respectively, may also configure orthogonal resources for access link and backhaul link random access in terms of time and/or frequency. In some examples, such orthogonal multiplexing may be employed from the beginning of RACH procedure.

-15 [0063] In a first orthogonal multiplexing example of the invention, orthogonal multiplexing is performed in a frequency domain, as illustrated in FIG. 8. FIG. 8 illustrates one example of a representation 800 of a frequency multiplexing of access link random access resources 830 and backhaul link random access resources 820, according to examples of the invention. In this example, both access link PRACH and backhaul link PRACH may utilise the same (or indeed different) time locations, e.g., symbol. However, the access link random access resources 830 and backhaul link random access resources 820, will always be separated and differentiated by use on the two different frequencies 832, 822, as shown in FIG. 8. In NR, it is already possible to configure multiple PRACH resources up to N. Thus, in some examples, it is envisaged that a bit map may be used to indicate the PRACH resources used for IAB or alternatively, ceiling(log2(N)) bits can be used to indicate one PRACH resource to be used for IAB.

[0064] One benefit of this first orthogonal multiplexing example of the invention is that it may provide maximum flexibility in the sense that the backhaul link random access can be completely separated from access link random access. However, this first orthogonal multiplexing example requires more resources allocated to PRACH.

[0065] In a second orthogonal multiplexing example of the invention, orthogonal multiplexing is performed in a time domain, as illustrated in FIG. 9, where some of the time resources for access PRACH are used for backhaul PRACH. FIG. 9 illustrates one example of a representation 900 of a time multiplexing of access link and backhaul link random access resources, according to examples of the invention. In this example, the same frequency is used for both backhaul PRACH 920 by the IAB node and access PRACH 930, for example by the IAB node or UE node. As illustrated, in this example, the ‘sharing’ between access link random access resources 930 and backhaul link random access resources 920 may be limited to sharing occasional time slots, such as slot i 910 and slot i+4 912, as shown, due to the less frequent need to support backhaul PRACH.

[0066] One benefit of this second orthogonal multiplexing example is that no additional resources are needed for backhaul PRACH. However, in some instances, it is envisaged that some disruption to access PRACH may be created.

-16[0067] FIG. 10 illustrates a third orthogonal multiplexing example representation 1000, according to examples of the invention. The third orthogonal multiplexing example representation 1000 also employs time multiplexing of access link and backhaul link random access resources. In this example, the same frequency is again used for both backhaul PRACH 1020 by the IAB node and access PRACH 1030, for example by the IAB node or UE node. As illustrated, in this example, the ‘sharing’ between access link random access resources 1030 and backhaul link random access resources 1020 may be limited to allocation of individual time slots for a particular use, such as slot i 1010 and slot i+2 1014 and slot i+4 1018 being allocated for access link random access resources 1030. In contrast, slot i+1 1012 and slot i+5 1019 are allocated for backhaul link random access resources 1020, as shown. Again, fewer backhaul link random access resources 1020 are allocated due to the less frequent need to support backhaul PRACH. However, as will be appreciated in the approach of FIG. 10, time domain multiplexing can be achieved with no disruption to access PRACH. However, additional resources are needed [0068] In some examples, it is envisaged that a combination of the first orthogonal multiplexing example approach and the second or third orthogonal multiplexing example approach may be employed, in order to achieve some balance between flexibility and resource efficiency.

[0069] Referring now to FIG. 11, a yet further representation 1100 is illustrated for orthogonal time multiplexing of access link and backhaul link random access resources with respect to the carrier bandwidth part (BWP), according to some examples of the invention. In this example, the separation of the PRACH is performed on a BWP basis. For example, this orthogonal time multiplexing of access link and backhaul link random access resources is particularly useful if the UE is only able to activate one BWP at a particular time, for example due to power consumption or complexity constraints. However, for IAB nodes these constraints can be removed. Hence, the IAB nodes can be allocated backhaul PRACH resources 1140 with fewer/no constraints. In this example, there is no need to activate the entire BWP, but the

-17respective PRACH allocations for the IAB nodes can be configured in a first BWP 1140 compared to a second, different BWP 1150 from the UE active BWP PRACH allocations for access link random access resources 1130 as shown in FIG. 11.

[0070] In this example, the slots used for respective orthogonal time multiplexing of access link and backhaul link random access resources remain separate and distinguishable.

[0071] In some examples, it is envisaged that multiple RACH parameter sets may be allocated for orthogonal time and/or frequency multiplexing of access link and backhaul link random access resources time if access link and backhaul link PRACH are configured in the same BWP. However, since RACH parameters are configured per BWP, there is no need to have multiple RACH parameter sets with in the same BWP and therefore no need to expand system information in RRC since the network is able to configure one RACH parameter set for each BWP.

[0072] Referring now to FIG. 12, a simplified flowchart 1200 of a UE procedure is illustrated, in accordance with some example embodiments of the invention. The flowchart 1200 starts at 1202 with the UE reading broadcast system information blocks (SIBs). At 1204, the UE determines whether the SIB indicates multiple RACH configurations. If, at 1204, the UE determines that the SIB does not indicate multiple RACH configurations, a default RACH configuration is used at 1210 and the flowchart then jumps to 1208. If, at 1204, the UE determines that the SIB does indicate multiple RACH configurations, then the UE uses the first or default RACH configuration at 1206. Thereafter, at 1208, the UE performs a RACH operation using the first or default RACH configuration as and when needed.

[0073] Referring now to FIG. 13 a simplified flowchart 1300 of a first method for an IAB node (e.g. a 5G base station (gNB)) procedure is illustrated, in accordance with some example embodiments of the invention. The flowchart 1300 starts at 1302 with the IAB node reading broadcast system information blocks (SIBs). At 1304, the IAB node uses a default RACH configuration. At 1306, the IAB node determines whether multiple RACH configurations are used. If, at 1306, the IAB node determines that multiple RACH configurations are used, then it

-18uses the RACH configuration for its IAB nodes. Thereafter, at 1308, the IAB node performs a RACK operation using the RACH configurations as and when needed. If, however, at 1306 the IAB node determines that multiple RACH configurations are not used, the flowchart jumps to 1308.

[0074] Referring now to FIG. 14, a simplified flowchart 1400 of a second method for an IAB node procedure is illustrated, in accordance with some example embodiments of the invention. The flowchart 1400 starts at 1402 with the IAB node reading broadcast system information blocks (SIBs). At 1404, the IAB node determines whether the SIB indicates multiple RACH configurations. If, at 1404, the IAB node determines that the SIB does not indicate multiple RACH configurations, a default RACH configuration is used at 1406 and the flowchart jumps to 1410. If, at 1404, the IAB node determines that the SIB does indicate multiple RACH configurations, then it uses the RACH configuration for its IAB nodes. Thereafter, at 1410, the IAB node performs a RACH operation using the RACH configurations as and when needed.

[0075] In particular, it is envisaged that the aforementioned inventive concept can be applied by a semiconductor manufacturer to any integrated circuit comprising a signal processor configured to perform any of the aforementioned operations. Furthermore, the inventive concept can be applied to any circuit that is able to configure, process, encode and/or decode signals for wireless distribution. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a digital signal processor, or application-specific integrated circuit (ASIC) and/or any other sub-system element.

[0076] It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units or processors, for example with respect to the signal processor may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controller. Hence, references to specific functional units are only to be seen as references to suitable means for

-19providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

[0077] Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

[0078] Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. Tn the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

[0079] Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

[0080] Thus, communication units such as gNBs functioning as IAB nodes and terminal devices such as UEs, a communication system and methods relating to RACH use for access and backhaul have been described, wherein the aforementioned disadvantages with prior art arrangements have been substantially alleviated.

[0081] In some examples, the aforementioned concepts may be implemented within the system information blocks (SIBs) on 3GPP™ standards. For example, after an initial cell

-20synchronization process is completed, a UE will read the master information block. Then the UE can read SIB1 and SIB2 in order to obtain useful information related to cell access, SIB scheduling and radio resource configuration. SIB2 carries radio resource configuration information including Random Access CHannel (RACH) related parameters that are common for all UEs. In this regards, it is not possible that the IAB node is able to configure two different sets of RACH parameters to both the UE and one or more other IAB nodes, respectively, at the same time.

[0082] In order to be able to configure multiple sets of RACH parameters, the RACH configuration information elemenets (IEs) in RRC, such as RACH-ConfigCommon, RACHConfigGeneric, RACH-ConfigDedicated may be expanded in order to cover multiple parameter sets. A flag, e.g., RACH-IAB should be added to indicate that additional information elements (IEs) or parameters are defined for IAB RACH. In some examples of the invention, three ways are proposed in order to achieve this:

(i) define new RRC IEs;

(ii) add new parameters to configure different RACH settings; and (iii) expand the value range of the current parameters, taking different RACH configurations into account.

[0083] If the UE finds that the same resources are allocated to both access and backhaul, it can assume that access PRACH is punctured by backhaul PRACH. One example of this UE determination is illustrated below, where the new parameters are highlighted in italicised bold.

RACH-ConfigCommon information element

- ASN1 START

- TAG-RACH-CONFIG-COMMON-START

RACH-ConfigCommon :: = SEQUENCE { rach-ConfigGeneric RACH-ConfigGeneric, rach-ConfigGenericIAB RACH-ConfigGeneric,

-21 totalNumberOfRA-Preambles

INTEGER (1..63)

OPTIONAL, -NeedS ssb-perRACH-OccasionAndCB-PreamblesPerSSB CHOICE { oneEighth ENUMERATED {n4,n8,nl2,nl6,n20,n24,n28,n32,n36,n40,n44,n48,n52,n56,n60,n64}, oneFourth ENUMERATED {n4,n8,nl2,nl6,n20,n24,n28,n32,n36,n40,n44,n48,n52,n56,n60,n64}, oneHalf ENUMERATED {n4,n8,nl2,nl6,n20,n24,n28,n32,n36,n40,n44,n48,n52,n56,n60,n64}, one ENUMERATED {n4,n8,n!2,nl6,n20,n24,n28,n32,n36,n40,n44,n48,n52,n56,n60,n64}, two {n4,n8,nl 2,nl 6,n20,n24,n28,n32}, four eight sixteen

ENUMERATED

INTEGER (1.. 16),

INTEGER (1..8),

INTEGER (1..4)

OPTIONAL, -NeedM groupBconfigured SEQUENCE { ra-Msg3SizeGroupA ENUMERATED { b56, bl44, b208, b256, b282, b480, b640, b800, bl000, spare?, spare6, spare5, spare4, spare3, spare2, sparel}, messagePowerOffsetGroupB ENUMERATED { minusinfinity, dBO, dB5, dB8, dB10, dB12, dB15, dB18}, numberOfRA-PreamblesGroupA INTEGER (1.. 64)

OPTIONAL, — NeedR

-22ra-ContentionResolutionTimer

ENUMERATED { sf8, sfl6, sf24, sf32, sf40, sf48, sf56, sf64}, rsrp-ThresholdS SB

RSRP-Range

OPTIONAL, -NeedR rsrp-ThresholdSSB-SUL

RSRP-Range

OPTIONAL, -CondSUL prach-RootS equencelndex 1839

1139

CHOICE {

INTEGER (0..837),

INTEGER (0..137) prach-RootS equencelndexl AB

1839

1139

CHOICE {

INTEGER (0..837),

INTEGER (0..137) msgl -SubcarrierSpacing msgl-SubcarrierSpacinglAB

OPTIONAL, -NeedS restrictedSetConfig {unrestrictedSet, restrictedSetTypeA, restrictedSetTypeB}, msg3 -transformPrecoding

SubcarrierSpacing

SubcarrierSpacing

ENUMERATED

ENUMERATED {enabled}

OPTIONAL, -NeedR restrictedSetConfig 1 restrictedSetTypeA, restrictedSetTypeB}, msg3 -transformPrecodingl AB

ENUMERATED {unrestrictedSet,

ENUMERATED {enabled}

OPTIONAL, -NeedR

- TAG-RACH-CONFIG-COMMON-STOP

- ASN1STOP

RACH-ConfigDedicated information element

- ASN1 START

- TAG-RACH-CONFIG-DEDICATED-START — FFS Standlone: resources for msgl-based on-demand SI request

RACH-ConfigDedicated :: = SEQUENCE {

cfra

CFRA

OPTIONAL, -NeedN

ra-Prioritization

RA-Prioritization

OPTIONAL, -NeedN

CFRA ::=	SEQUENCE{
occasions	SEQUENCE {
rach-ConfigGeneric	RACH-ConfigGeneric,
rach-ConfigGenericIAB	RACH-ConfigGeneric,
ssb-perRACH-Occasion	ENUMERATED {oneEighth, oneFourth,
oneHalf, one, two, four, eight, sixteen} ssb-perRACH-OccasionlAB	OPHONAL - Cond SSB-CFRA ENUMERATED {oneEighth, oneFourth,
oneHalf, one, two, four, eight, sixteen}	OPHONAL - Cond SSB-CFRA

OPHONAL, -NeedS

resources	CHOICE {
ssb	SEQUENCE{
ssb-ResourceList	SEQUENCE (SIZE(l ..maxRA-SSB-

Resources)) OF CFRA-SSB-Resource,

-24ra-ssb-OccasionMasklndex ra-ssb-OccasionMasklndexIAB csirs csirs-ResourceList

Resources)) OF CFRA-CSIRS-Resource, rsrp-ThresholdCSI-RS

CFRA-SSB-Resource ::= ssb ra-Preamblelndex ra-PreamblelndexIAB

INTEGER (0..15)

INTEGER (0..15)

SEQUENCE{

SEQUENCE (SIZE(l ..maxRA-CSIRS

RSRP-Range

SEQUENCE{

SSB-Index,

INTEGER (0..63),

INTEGER (0..63),

CFRA-CSIRS-Resource ::=

SEQUENCE { csi-RS CSI-RS-Index, ra-OccasionList SEQUENCE (SIZE(l ..maxRA·

OccasionsPerCSIRS)) OF INTEGER (0..maxRA-Occasions-1), ra-OccasionListl SEQUENCE (SIZE(l ..maxRAOccasionsPerCSIRS)) OF INTEGER (0..maxRA-Occasions-1), ra-Preamblelndex INTEGER (0..63), ra-PreamblelndexIAB INTEGER (0. .63),

- TAG-RACH-CONFIG-DEDICATED-STOP

- ASN1STOP

-25 [0084] In the above example, two RACH-ConfigGeneric IEs are configured. Alternatively, it is envisaged that only one RACH-ConfigGeneric IE may be configured as below. In some examples, the parameters related to power ramping may also be expanded, if needed, since IAB nodes can support higher transmission power (new range based on pl and p2 can be defined), and thus larger ramping steps. In some examples, the second set of parameters are optional and can be configured in certain scenarios, e.g.., IAB node random access is needed. In some examples, the RA response window can also be expanded to include larger values for IAB nodes and the emphasised (in bold and italicised) part is only an example:

RACH-ConfigGeneric information element

- ASN1 START

- TAG-RACH-CONFIG-GENERIC-START

RACH-ConfigGeneric ::= prach-Configurationlndex prach-ConfigurationlndexIAB msgl-FDM four, eight}, msgl-FDMLAB {one, two, four, eight} OPTIONAL, msg 1 -Frequency Start (0.. maxNrofPhy sicalResourceBlocks-1), msgl -FrequencyStartl (0. .maxNrofPhysicalResourceBlocks-1) OPTIONAL, zeroCorrelationZoneConfig zeroCorrelationZoneConfiglAB preambleReceivedTargetPower preambleReceivedTargetPowerlAB preambleTransMax n8, nlO, n20, n50, nlOO, n200, n400, n800, n!600},

SEQUENCE {

INTEGER (0..255),

INTEGER (0..255),

ENUMERATED {one, two,

ENUMERATED

INTEGER

INTEGER

INTEGER(0..15),

INTEGER(0..15) OPTIONAL, INTEGER (-202..-60),

INTEGER (-p 1. .-p2) OPTIONAL,

ENUMERATED {n3, n4, n5, n6, n7,

-26powerRampingStep dB6, dB8, dB10}, ra-ResponseWindow sllO, sl20, sl40, sl80, s360, s720, sl440},

- TAG-RACH-CONFIG-GENERIC-STOP

- ASN1STOP

ENUMERATED {dBO, dB2, dB4,

ENUMERATED {sll, sl2, sl4, sl8,

Claims (21)

1. An integrated access and backhaul, IAB, wireless communication system comprises a first base station, a second base station, and a plurality of remote wireless communication units, wherein the second base station provides access to a core network, and the first base station requires access to the core network via the second base station, wherein the second base station comprises:

a transceiver; and a processor, operably coupled to the transceiver and arranged to:

configure a first random access channel, RACH, resource for use by the first base station; and configure a second random access channel, RACH, resource for use by the plurality of remote wireless communication units to access the second base station, wherein the configured second RACH is different to the configured first RACH.

2. The IAB wireless communication system of Claim 1, wherein the configured first RACH resource comprises a different preamble format of the RACH compared to the configured second RACH.

3. The wireless communication system of Claim 1 or Claim 2, wherein the configured first RACH resource comprises a different time configuration of the RACH compared to the configured second RACH.

4. The wireless communication system of Claim 1 or Claim 2, wherein the configured first RACH resource comprises a different frequency configuration of the RACH compared to the configured second RACH.

5. The wireless communication system of any preceding Claim, wherein the configured first RACH resource comprises a different random access periodicity of the RACH compared to the configured second RACH.

6. The wireless communication system of Claim 5, wherein the first RACH resource is allocated with a lower periodicity than the second RACH resource.

7. The wireless communication system of any preceding Claim, wherein the second RACH resource is allocated for use before the first RACH resource.

8. The wireless communication system of any preceding Claim, wherein the configured different RACH resources comprise at least one from a group of: symbol, slot, subframe and system frame number, SFN.

9. The wireless communication system of any preceding Claim, wherein a same initial RACH access is enabled for access by both the first base station and the plurality of remote wireless communication units, prior to the processor being arranged to configure a subsequent first RACH resource for use by the first base station that differentiates the first RACH resource from the second access link RACH resource used by plurality of remote wireless communication units.

10. The wireless communication system of any preceding Claim, wherein the configured first RACH resource is configured for use by the first base station for both random access and backhaul link communications.

11. The wireless communication system of any preceding Claim, wherein the configured first RACH resource comprises a different orthogonal multiplexing configuration of the RACH compared to the configured second RACH.

12. The wireless communication system of Claim 11, wherein the orthogonal multiplexing configuration of the RACH comprises at least one from a group of: frequency multiplexing of access link random access resources and backhaul link random access resources, time multiplexing of access link random access resources and backhaul link random access resources.

13. The wireless communication system of Claim 12, wherein orthogonal time multiplexing configuration of the RACH comprises at least one from a group of: time multiplexing of access link random access resources and backhaul link random access resources within a single time slot, time multiplexing of access link random access resources and backhaul link random access resources that are allocated different time slots, time multiplexing of access link random access resources and backhaul link random access resources that are allocated different bandwidth parts, BWP, of a carrier frequency.

14. The wireless communication system of any preceding Claim wherein the first base station is configured to perform a RACH with the second base station to support a wireless backhaul link via a relay node to form a multi-hop relay backhaul link.

15. The wireless communication system of any preceding Claim wherein the first base station is configured to perform a RACH with the second base station in response to a backhaul link being blocked.

16. The wireless communication system of any preceding Claim wherein a flag indicating IAB RACH is activated and is added to radio resource control, RRC parameters, and at least one RACH information element, IE, parameter in radio resource control, RRC, state, from a group of multiple sets of RACH parameters are configured, where the at least one RACH IE parameter comprises expansion of at least one from a group of: RACH-ConfigCommon, RACHConfigGeneric, RACH-ConfigDedicated.

17. The wireless communication system of Claim 16 wherein the expansion of the at least one RACH IE parameter comprises at least one from a group of: definition of a new RRC IEs; adding of a new parameter to configure different RACH settings; expansion of a value range of current parameters, to differentiate between RACH configurations.

18. A second base station for an integrated access and backhaul, IAB, wireless communication system that communicates with a plurality of remote wireless communication

-30units, wherein the second base station comprises a processor, operably coupled to a transceiver and arranged to:

configure a first random access channel, RACH, resource for use by a first base station; and configure a second random access channel, RACH, resource for use by the plurality of remote wireless communication units to access the second base station, wherein the configured second RACH is different to the configured first RACH.

19. A remote wireless communication unit in an integrated access and backhaul, IAB, wireless communication system, wherein the remote wireless communication unit comprises:

a transceiver; and a processor, operably coupled to the transceiver and arranged to:

initiate a random access to a second base station on a second random access channel, RACH, resource, wherein the configured second RACH is different to a configured first RACH allocated for use by a first base station for random access and backhaul link communications.

20. A method for random access in an integrated access and backhaul, IAB, wireless communication system that comprises a first base station, a second base station and a plurality of remote wireless communication units, wherein the method comprises at the second base station:

configuring a first random access channel, RACH, resource for use by a first base station; and configuring a second random access channel, RACH, resource for use by the plurality of remote wireless communication units to access the second base station, wherein the configured second RACH is different to the configured first RACH.

21. A method for random access in an integrated access and backhaul, IAB, wireless communication system that comprises a first base station, a second base station and a plurality of remote wireless communication units, wherein the method comprises at a remote wireless communication unit:

-31 initiating a random access to a second base station on a second random access channel, RACH, resource, wherein the configured second RACH is different to a configured first RACH allocated for use by a first base station for random access and backhaul link communications.