WO2019208994A1

WO2019208994A1 - Method and apparatus for supporting integrated backhaul and access link in wireless communication system

Info

Publication number: WO2019208994A1
Application number: PCT/KR2019/004851
Authority: WO
Inventors: Yunjung Yi; Hyangsun YOU; Youngtae Kim
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2018-04-23
Filing date: 2019-04-23
Publication date: 2019-10-31
Anticipated expiration: 2020-10-23

Abstract

A method and apparatus for supporting an integrated backhaul and access (IAB) link in a new radio access technology (RAT) system is provided. An IAB node transmits a first discovery signal for a link between the first node and a second node, and transmits a second discovery signal for a link between the first node and a UE. A synchronization raster of the first discovery signal is different from a synchronization raster of the second discovery signal.

Description

METHOD AND APPARATUS FOR SUPPORTING INTEGRATED BACKHAUL AND ACCESS LINK IN WIRELESS COMMUNICATION SYSTEM

The present invention relates to wireless communications, and more particularly, to a method and apparatus for supporting an integrated backhaul and access (IAB) link in a new radio access technology (RAT) system.

3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

Work has started in international telecommunication union (ITU) and 3GPP to develop requirements and specifications for new radio (NR) systems. 3GPP has to identify and develop the technology components needed for successfully standardizing the new RAT timely satisfying both the urgent market needs, and the more long-term requirements set forth by the ITU radio communication sector (ITU-R) international mobile telecommunications (IMT)-2020 process. Further, the NR should be able to use any spectrum band ranging at least up to 100 GHz that may be made available for wireless communications even in a more distant future.

The NR targets a single technical framework addressing all usage scenarios, requirements and deployment scenarios including enhanced mobile broadband (eMBB), massive machine-type-communications (mMTC), ultra-reliable and low latency communications (URLLC), etc. The NR shall be inherently forward compatible.

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 NR cells without the need for densifying the transport network proportionately.

Due to the expected larger bandwidth available for NR compared to LTE (e.g. mmWave spectrum) along with the native deployment of massive multiple-input multiple-output (MIMO) or multi-beam systems in NR creates an opportunity to develop and deploy integrated access and backhaul (IAB) links. 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. Due to deployment of IAB links, relay nodes can multiplex access and backhaul links in time, frequency, or space (e.g. beam-based operation).

The present invention discusses mechanisms to efficiently support integrated backhaul and access (IAB) links.

In an aspect, a method performed by a first node in a wireless communication system is provided. The method includes transmitting a first discovery signal for a link between the first node and a second node, and transmitting a second discovery signal for a link between the first node and a UE. A synchronization raster of the first discovery signal is different from a synchronization raster of the second discovery signal.

In another aspect, a first node in a wireless communication system is provided. The first node includes a memory, a transceiver, and a processor, operably coupled to the memory and the transceiver, and configured to control the transceiver to transmit a first discovery signal for a link between the first node and a second node, and control the transceiver to transmit a second discovery signal for a link between the first node and a UE. A synchronization raster of the first discovery signal is different from a synchronization raster of the second discovery signal.

IAB links can be supported efficiently.

FIG. 1 shows an example of a wireless communication system to which technical features of the present invention can be applied.

FIG. 2 shows another example of a wireless communication system to which technical features of the present invention can be applied.

FIG. 3 shows an example of a frame structure to which technical features of the present invention can be applied.

FIG. 4 shows another example of a frame structure to which technical features of the present invention can be applied.

FIG. 5 shows an example of a subframe structure used to minimize latency of data transmission when TDD is used in NR.

FIG. 6 shows an example of a resource grid to which technical features of the present invention can be applied.

FIG. 7 shows an example of a synchronization channel to which technical features of the present invention can be applied.

FIG. 8 shows an example of a frequency allocation scheme to which technical features of the present invention can be applied.

FIG. 9 shows an example of multiple BWPs to which technical features of the present invention can be applied.

FIG. 10 shows an example of IAB links to which technical features of the present invention can be applied.

FIG. 11 shows an example of IAB links to which technical features of the present invention can be applied.

FIG. 12 shows an example of a method for transmitting discovery signals according to an embodiment of the present invention.

FIG. 13 shows an example of topology between IAB nodes to which technical features of the present invention can be applied.

FIG. 14 shows an example of topology between IAB nodes to which technical features of the present invention can be applied.

FIG. 15 shows an example of slot boundary alignment between different nodes according to the topology shown in FIG. 14.

FIG. 16 shows option 1 for scenario of different timing cases according to an embodiment of the present invention.

FIG. 17 shows option 2 for scenario of different timing cases according to an embodiment of the present invention.

FIG. 18 shows an IAB node to implement an embodiment of the present invention.

FIG. 19 shows more detailed IAB node to implement an embodiment of the present invention.

FIG. 20 shows other IAB node or donor node to implement an embodiment of the present invention.

The technical features described below may be used by a communication standard by the 3rd generation partnership project (3GPP) standardization organization, a communication standard by the institute of electrical and electronics engineers (IEEE), etc. For example, the communication standards by the 3GPP standardization organization include long-term evolution (LTE) and/or evolution of LTE systems. The evolution of LTE systems includes LTE-advanced (LTE-A), LTE-A Pro, and/or 5G new radio (NR). The communication standard by the IEEE standardization organization includes a wireless local area network (WLAN) system such as IEEE 802.11a/b/g/n/ac/ax. The above system uses various multiple access technologies such as orthogonal frequency division multiple access (OFDMA) and/or single carrier frequency division multiple access (SC-FDMA) for downlink (DL) and/or uplink (DL). For example, only OFDMA may be used for DL and only SC-FDMA may be used for UL. Alternatively, OFDMA and SC-FDMA may be used for DL and/or UL.

In this document, the term "/" and "," should be interpreted to indicate "and/or." For instance, the expression "A/B" may mean "A and/or B." Further, "A, B" may mean "A and/or B." Further, "A/B/C" may mean "at least one of A, B, and/or C." Also, "A, B, C" may mean "at least one of A, B, and/or C."

Further, in the document, the term "or" should be interpreted to indicate "and/or." For instance, the expression "A or B" may comprise 1) only A, 2) only B, and/or 3) both A and B. In other words, the term "or" in this document should be interpreted to indicate "additionally or alternatively."

FIG. 1 shows an example of a wireless communication system to which technical features of the present invention can be applied. Specifically, FIG. 1 shows a system architecture based on an evolved-UMTS terrestrial radio access network (E-UTRAN). The aforementioned LTE is a part of an evolved-UTMS (e-UMTS) using the E-UTRAN.

Referring to FIG. 1, the wireless communication system includes one or more user equipment (UE; 10), an E-UTRAN and an evolved packet core (EPC). The UE 10 refers to a communication equipment carried by a user. The UE 10 may be fixed or mobile. The UE 10 may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN consists of one or more base station (BS) 20. The BS 20 provides the E-UTRA user plane and control plane protocol terminations towards the UE 10. The BS 20 is generally a fixed station that communicates with the UE 10. The BS 20 hosts the functions, such as inter-cell radio resource management (RRM), radio bearer (RB) control, connection mobility control, radio admission control, measurement configuration/provision, dynamic resource allocation (scheduler), etc. The BS may be referred to as another terminology, such as an evolved NodeB (eNB), a base transceiver system (BTS), an access point (AP), etc.

A downlink (DL) denotes communication from the BS 20 to the UE 10. An uplink (UL) denotes communication from the UE 10 to the BS 20. A sidelink (SL) denotes communication between the UEs 10. In the DL, a transmitter may be a part of the BS 20, and a receiver may be a part of the UE 10. In the UL, the transmitter may be a part of the UE 10, and the receiver may be a part of the BS 20. In the SL, the transmitter and receiver may be a part of the UE 10.

The EPC includes a mobility management entity (MME), a serving gateway (S-GW) and a packet data network (PDN) gateway (P-GW). The MME hosts the functions, such as non-access stratum (NAS) security, idle state mobility handling, evolved packet system (EPS) bearer control, etc. The S-GW hosts the functions, such as mobility anchoring, etc. The S-GW is a gateway having an E-UTRAN as an endpoint. For convenience, MME/S-GW 30 will be referred to herein simply as a "gateway," but it is understood that this entity includes both the MME and S-GW. The P-GW hosts the functions, such as UE Internet protocol (IP) address allocation, packet filtering, etc. The P-GW is a gateway having a PDN as an endpoint. The P-GW is connected to an external network.

The UE 10 is connected to the BS 20 by means of the Uu interface. The UEs 10 are interconnected with each other by means of the PC5 interface. The BSs 20 are interconnected with each other by means of the X2 interface. The BSs 20 are also connected by means of the S1 interface to the EPC, more specifically to the MME by means of the S1-MME interface and to the S-GW by means of the S1-U interface. The S1 interface supports a many-to-many relation between MMEs/S-GWs and BSs.

FIG. 2 shows another example of a wireless communication system to which technical features of the present invention can be applied. Specifically, FIG. 2 shows a system architecture based on a 5G new radio access technology (NR) system. The entity used in the 5G NR system (hereinafter, simply referred to as "NR") may absorb some or all of the functions of the entities introduced in FIG. 1 (e.g. eNB, MME, S-GW). The entity used in the NR system may be identified by the name "NG" for distinction from the LTE.

In the following description, for NR, 3GPP TS 38 series (3GPP TS 38.211, 38.212, 38.213, 38.214, 38.331, etc.) can be referred to in order to facilitate understanding of the following description.

Referring to FIG. 2, the wireless communication system includes one or more UE 11, a next-generation RAN (NG-RAN) and a 5th generation core network (5GC). The NG-RAN consists of at least one NG-RAN node. The NG-RAN node is an entity corresponding to the BS 20 shown in FIG. 1. The NG-RAN node consists of at least one gNB 21 and/or at least one ng-eNB 22. The gNB 21 provides NR user plane and control plane protocol terminations towards the UE 11. The ng-eNB 22 provides E-UTRA user plane and control plane protocol terminations towards the UE 11.

The 5GC includes an access and mobility management function (AMF), a user plane function (UPF) and a session management function (SMF). The AMF hosts the functions, such as NAS security, idle state mobility handling, etc. The AMF is an entity including the functions of the conventional MME. The UPF hosts the functions, such as mobility anchoring, protocol data unit (PDU) handling. The UPF an entity including the functions of the conventional S-GW. The SMF hosts the functions, such as UE IP address allocation, PDU session control.

The gNBs and ng-eNBs are interconnected with each other by means of the Xn interface. The gNBs and ng-eNBs are also connected by means of the NG interfaces to the 5GC, more specifically to the AMF by means of the NG-C interface and to the UPF by means of the NG-U interface.

Hereinafter, frame structure/physical resources in NR is described.

In LTE/LTE-A, one radio frame consists of 10 subframes, and one subframe consists of 2 slots. A length of one subframe may be 1ms, and a length of one slot may be 0.5ms. Time for transmitting one transport block by higher layer to physical layer (generally over one subframe) is defined as a transmission time interval (TTI). A TTI may be the minimum unit of scheduling.

In NR, DL and UL transmissions are performed over a radio frame with a duration of 10ms. Each radio frame includes 10 subframes. Thus, one subframe corresponds to 1ms. Each radio frame is divided into two half-frames.

Unlike LTE/LTE-A, NR supports various numerologies, and accordingly, the structure of the radio frame may be varied. NR supports multiple subcarrier spacings in frequency domain. Table 1 shows multiple numerologies supported in NR. Each numerology may be identified by index μ.

μ	Subcarrier spacing (kHz)	Cyclic prefix	Supported for data	Supported for synchronization
0	15	Normal	Yes	Yes
1	30	Normal	Yes	Yes
2	60	Normal, Extended	Yes	No
3	120	Normal	Yes	Yes
4	240	Normal	No	Yes

Referring to Table 1, a subcarrier spacing may be set to any one of 15, 30, 60, 120, and 240 kHz, which is identified by index μ. However, subcarrier spacings shown in Table 1 are merely exemplary, and specific subcarrier spacings may be changed. Therefore, each subcarrier spacing (e.g. μ=0,1...4) may be represented as a first subcarrier spacing, a second subcarrier spacing...Nth subcarrier spacing.

Referring to Table 1, transmission of user data (e.g. physical uplink shared channel (PUSCH), physical downlink shared channel (PDSCH)) may not be supported depending on the subcarrier spacing. That is, transmission of user data may not be supported only in at least one specific subcarrier spacing (e.g. 240 kHz).

In addition, referring to Table 1, a synchronization channel (e.g. a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a physical broadcast channel (PBCH)) may not be supported depending on the subcarrier spacing. That is, the synchronization channel may not be supported only in at least one specific subcarrier spacing (e.g. 60 kHz).

One subframe includes N_symb ^subframe,μ = N_symb ^slot * N_slot ^subframe,μ consecutive OFDM symbols. In NR, a number of slots and a number of symbols included in one radio frame/subframe may be different according to various numerologies, i.e. various subcarrier spacings.

Table 2 shows an example of a number of OFDM symbols per slot (N_symb ^slot), a number of slots per radio frame (N_symb ^frame,μ), and a number of slots per subframe (N_symb ^subframe,μ) for each numerology in normal cyclic prefix (CP).

μ	Number of OFDM symbols per slot(N_symb ^slot)	Number of slots per radio frame (N_symb ^frame,μ)	Number of slots per subframe(N_symb ^subframe,μ)
0	14	10	1
1	14	20	2
2	14	40	4
3	14	80	8
4	14	160	16

Referring to Table 2, when a first numerology corresponding to μ=0 is applied, one radio frame includes 10 subframes, one subframe includes to one slot, and one slot consists of 14 symbols.

Table 3 shows an example of a number of OFDM symbols per slot (N_symb ^slot), a number of slots per radio frame (N_symb ^frame,μ), and a number of slots per subframe (N_symb ^subframe,μ) for each numerology in extended CP.

μ	Number of OFDM symbols per slot(N_symb ^slot)	Number of slots per radio frame (N_symb ^frame,μ)	Number of slots per subframe(N_symb ^subframe,μ)
2	12	40	4

Referring to Table 3, μ=2 is only supported in extended CP. One radio frame includes 10 subframes, one subframe includes to 4 slots, and one slot consists of 12 symbols.

In the present specification, a symbol refers to a signal transmitted during a specific time interval. For example, a symbol may refer to a signal generated by OFDM processing. That is, a symbol in the present specification may refer to an OFDM/OFDMA symbol, or SC-FDMA symbol, etc. A CP may be located between each symbol.

FIG. 3 shows an example of a frame structure to which technical features of the present invention can be applied. In FIG. 3, a subcarrier spacing is 15 kHz, which corresponds to μ=0.

FIG. 4 shows another example of a frame structure to which technical features of the present invention can be applied. In FIG. 4, a subcarrier spacing is 30 kHz, which corresponds to μ=1.

Meanwhile, a frequency division duplex (FDD) and/or a time division duplex (TDD) may be applied to a wireless communication system to which an embodiment of the present invention is applied. When TDD is applied, in LTE/LTE-A, UL subframes and DL subframes are allocated in units of subframes.

In NR, symbols in a slot may be classified as a DL symbol (denoted by D), a flexible symbol (denoted by X), and a UL symbol (denoted by U). In a slot in a DL frame, the UE shall assume that DL transmissions only occur in DL symbols or flexible symbols. In a slot in an UL frame, the UE shall only transmit in UL symbols or flexible symbols. The flexible symbol may be referred to as another terminology, such as reserved symbol, other symbol, unknown symbol, etc.

Table 4 shows an example of a slot format which is identified by a corresponding format index. The contents of the Table 4 may be commonly applied to a specific cell, or may be commonly applied to adjacent cells, or may be applied individually or differently to each UE.

Format

Symbol number in a slot

0

1

2

3

4

5

6

7

8

9

10

11

12

13

0

D

1

U

2

X

3

D

X

...

For convenience of explanation, Table 4 shows only a part of the slot format actually defined in NR. The specific allocation scheme may be changed or added.

The UE may receive a slot format configuration via a higher layer signaling (i.e. radio resource control (RRC) signaling). Or, the UE may receive a slot format configuration via downlink control information (DCI) which is received on PDCCH. Or, the UE may receive a slot format configuration via combination of higher layer signaling and DCI.

FIG. 5 shows an example of a subframe structure used to minimize latency of data transmission when TDD is used in NR. The subframe structure shown in FIG. 5 may be called a self-contained subframe structure.

Referring to FIG. 5, the subframe includes DL control channel in the first symbol, and UL control channel in the last symbol. The remaining symbols may be used for DL data transmission and/or for UL data transmission. According to this subframe structure, DL transmission and UL transmission may sequentially proceed in one subframe. Accordingly, the UE may both receive DL data and transmit UL acknowledgement/non-acknowledgement (ACK/NACK) in the subframe. As a result, it may take less time to retransmit data when a data transmission error occurs, thereby minimizing the latency of final data transmission.

In the self-contained subframe structure, a time gap may be required for the transition process from the transmission mode to the reception mode or from the reception mode to the transmission mode. For this purpose, some symbols at the time of switching from DL to UL in the subframe structure may be set to the guard period (GP).

FIG. 6 shows an example of a resource grid to which technical features of the present invention can be applied. An example shown in FIG. 6 is a time-frequency resource grid used in NR. An example shown in FIG. 6 may be applied to UL and/or DL.

Referring to FIG. 6, multiple slots are included within one subframe on the time domain. Specifically, when expressed according to the value of "μ", "14·2μ" symbols may be expressed in the resource grid. Also, one resource block (RB) may occupy 12 consecutive subcarriers. One RB may be referred to as a physical resource block (PRB), and 12 resource elements (REs) may be included in each PRB. The number of allocatable RBs may be determined based on a minimum value and a maximum value. The number of allocatable RBs may be configured individually according to the numerology ("μ"). The number of allocatable RBs may be configured to the same value for UL and DL, or may be configured to different values for UL and DL.

Hereinafter, a cell search in NR is described.

The UE may perform cell search in order to acquire time and/or frequency synchronization with a cell and to acquire a cell identifier (ID). Synchronization channels such as PSS, SSS, and PBCH may be used for cell search.

FIG. 7 shows an example of a synchronization channel to which technical features of the present invention can be applied. Referring to FIG. 7, the PSS and SSS may include one symbol and 127 subcarriers. The PBCH may include 3 symbols and 240 subcarriers.

The PSS is used for synchronization signal (SS)/PBCH block symbol timing acquisition. The PSS indicates 3 hypotheses for cell ID identification. The SSS is used for cell ID identification. The SSS indicates 336 hypotheses. Consequently, 1008 physical layer cell IDs may be configured by the PSS and the SSS.

The SS/PBCH block may be repeatedly transmitted according to a predetermined pattern within the 5ms window. For example, when L SS/PBCH blocks are transmitted, all of SS/PBCH block #1 through SS/PBCH block #L may contain the same information, but may be transmitted through beams in different directions. That is, quasi co-located (QCL) relationship may not be applied to the SS/PBCH blocks within the 5ms window. The beams used to receive the SS/PBCH block may be used in subsequent operations between the UE and the network (e.g. random access operations). The SS/PBCH block may be repeated by a specific period. The repetition period may be configured individually according to the numerology.

Referring to FIG. 7, the PBCH has a bandwidth of 20 RBs for the 2nd/4th symbols and 8 RBs for the 3rd symbol. The PBCH includes a demodulation reference signal (DM-RS) for decoding the PBCH. The frequency domain for the DM-RS is determined according to the cell ID. Unlike LTE/LTE-A, since a cell-specific reference signal (CRS) is not defined in NR, a special DM-RS is defined for decoding the PBCH (i.e. PBCH-DMRS). The PBCH-DMRS may contain information indicating an SS/PBCH block index.

The PBCH performs various functions. For example, the PBCH may perform a function of broadcasting a master information block (MIB). System information (SI) is divided into a minimum SI and other SI. The minimum SI may be divided into MIB and system information block type-1 (SIB1). The minimum SI excluding the MIB may be referred to as a remaining minimum SI (RMSI). That is, the RMSI may refer to the SIB1.

The MIB includes information necessary for decoding SIB1. For example, the MIB may include information on a subcarrier spacing applied to SIB1 (and MSG 2/4 used in the random access procedure, other SI), information on a frequency offset between the SS/PBCH block and the subsequently transmitted RB, information on a bandwidth of the PDCCH/SIB, and information for decoding the PDCCH (e.g. information on search-space/control resource set (CORESET)/DM-RS, etc., which will be described later). The MIB may be periodically transmitted, and the same information may be repeatedly transmitted during 80ms time interval. The SIB1 may be repeatedly transmitted through the PDSCH. The SIB1 includes control information for initial access of the UE and information for decoding another SIB.

Hereinafter, DL control channel in NR is described.

The search space for the PDCCH corresponds to aggregation of control channel candidates on which the UE performs blind decoding. In LTE/LTE-A, the search space for the PDCCH is divided into a common search space (CSS) and a UE-specific search space (USS). The size of each search space and/or the size of a control channel element (CCE) included in the PDCCH are determined according to the PDCCH format.

In NR, a resource-element group (REG) and a CCE for the PDCCH are defined. In NR, the concept of CORESET is defined. Specifically, one REG corresponds to 12 REs, i.e. one RB transmitted through one OFDM symbol. Each REG includes a DM-RS. One CCE includes a plurality of REGs (e.g. 6 REGs). The PDCCH may be transmitted through a resource consisting of 1, 2, 4, 8, or 16 CCEs. The number of CCEs may be determined according to the aggregation level. That is, one CCE when the aggregation level is 1, 2 CCEs when the aggregation level is 2, 4 CCEs when the aggregation level is 4, 8 CCEs when the aggregation level is 8, 16 CCEs when the aggregation level is 16, may be included in the PDCCH for a specific UE.

The CORESET is a set of resources for control signal transmission. The CORESET may be defined on 1/2/3 OFDM symbols and multiple RBs. In LTE/LTE-A, the number of symbols used for the PDCCH is defined by a physical control format indicator channel (PCFICH). However, the PCFICH is not used in NR. Instead, the number of symbols used for the CORESET may be defined by the RRC message (and/or PBCH/SIB1). Also, in LTE/LTE-A, since the frequency bandwidth of the PDCCH is the same as the entire system bandwidth, so there is no signaling regarding the frequency bandwidth of the PDCCH. In NR, the frequency domain of the CORESET may be defined by the RRC message (and/or PBCH/SIB1) in a unit of RB.

The base station may transmit information on the CORESET to the UE. For example, information on the CORESET configuration may be transmitted for each CORESET. Via the information on the CORESET configuration, at least one of a time duration of the corresponding CORESET (e.g. 1/2/3 symbol), frequency domain resources (e.g. RB set), REG-to-CCE mapping type (e.g. whether interleaving is applied or not), precoding granularity, a REG bundling size (when the REG-to-CCE mapping type is interleaving), an interleaver size (when the REG-to-CCE mapping type is interleaving) and a DMRS configuration (e.g. scrambling ID) may be transmitted. When interleaving to distribute the CCE to 1-symbol CORESET is applied, bundling of two or six REGs may be performed. Bundling of two or six REGs may be performed on the two symbols CORESET, and time first mapping may be applied. Bundling of three or six REGs may be performed on the three symbols CORESET, and a time first mapping may be applied. When REG bundling is performed, the UE may assume the same precoding for the corresponding bundling unit.

In NR, the search space for the PDCCH is divided into CSS and USS. The search space may be configured in CORESET. As an example, one search space may be defined in one CORESET. In this case, CORESET for CSS and CORESET for USS may be configured, respectively. As another example, a plurality of search spaces may be defined in one CORESET. That is, CSS and USS may be configured in the same CORESET. In the following example, CSS means CORESET in which CSS is configured, and USS means CORESET in which USS is configured. Since the USS may be indicated by the RRC message, an RRC connection may be required for the UE to decode the USS. The USS may include control information for PDSCH decoding assigned to the UE.

Since the PDCCH needs to be decoded even when the RRC configuration is not completed, CSS should also be defined. For example, CSS may be defined when a PDCCH for decoding a PDSCH that conveys SIB1 is configured or when a PDCCH for receiving MSG 2/4 is configured in a random access procedure. Like LTE/LTE-A, in NR, the PDCCH may be scrambled by a radio network temporary identifier (RNTI) for a specific purpose.

A resource allocation in NR is described.

In NR, a specific number (e.g. up to 4) of bandwidth parts (BWPs) may be defined. A BWP (or carrier BWP) is a set of consecutive PRBs, and may be represented by a consecutive subsets of common RBs (CRBs). Each RB in the CRB may be represented by CRB1, CRB2, etc., beginning with CRB0.

FIG. 8 shows an example of a frequency allocation scheme to which technical features of the present invention can be applied. Referring to FIG. 8, multiple BWPs may be defined in the CRB grid. A reference point of the CRB grid (which may be referred to as a common reference point, a starting point, etc.) is referred to as so-called "point A" in NR. The point A is indicated by the RMSI (i.e. SIB1). Specifically, the frequency offset between the frequency band in which the SS/PBCH block is transmitted and the point A may be indicated through the RMSI. The point A corresponds to the center frequency of the CRB0. Further, the point A may be a point at which the variable "k" indicating the frequency band of the RE is set to zero in NR. The multiple BWPs shown in FIG. 8 is configured to one cell (e.g. primary cell (PCell)). A plurality of BWPs may be configured for each cell individually or commonly.

Referring to FIG. 8, each BWP may be defined by a size and starting point from CRB0. For example, the first BWP, i.e. BWP #0, may be defined by a starting point through an offset from CRB0, and a size of the BWP #0 may be determined through the size for BWP #0.

A specific number (e.g. up to four) of BWPs may be configured for the UE. Even if a plurality of BWPs are configured, only a specific number (e.g. one) of BWPs may be activated per cell for a given time period. However, when the UE is configured with a supplementary uplink (SUL) carrier, maximum of four BWPs may be additionally configured on the SUL carrier and one BWP may be activated for a given time. The number of configurable BWPs and/or the number of activated BWPs may be configured commonly or individually for UL and DL. Also, the numerology and/or CP for the DL BWP and/or the numerology and/or CP for the UL BWP may be configured to the UE via DL signaling. The UE can receive PDSCH, PDCCH, channel state information (CSI) RS and/or tracking RS (TRS) only on the active DL BWP. Also, the UE can transmit PUSCH and/or physical uplink control channel (PUCCH) only on the active UL BWP.

FIG. 9 shows an example of multiple BWPs to which technical features of the present invention can be applied. Referring to FIG. 9, 3 BWPs may be configured. The first BWP may span 40 MHz band, and a subcarrier spacing of 15 kHz may be applied. The second BWP may span 10 MHz band, and a subcarrier spacing of 15 kHz may be applied. The third BWP may span 20 MHz band and a subcarrier spacing of 60 kHz may be applied. The UE may configure at least one BWP among the 3 BWPs as an active BWP, and may perform UL and/or DL data communication via the active BWP.

A time resource may be indicated in a manner that indicates a time difference/offset based on a transmission time point of a PDCCH allocating DL or UL resources. For example, the start point of the PDSCH/PUSCH corresponding to the PDCCH and the number of symbols occupied by the PDSCH / PUSCH may be indicated.

Carrier aggregation (CA) is described. Like LTE/LTE-A, CA can be supported in NR. That is, it is possible to aggregate continuous or discontinuous component carriers (CCs) to increase the bandwidth and consequently increase the bit rate. Each CC may correspond to a (serving) cell, and each CC/cell may be divided into a primary serving cell (PSC)/primary CC (PCC) or a secondary serving cell (SSC)/secondary CC (SCC).

Integrated backhaul and access (IAB) is described.

Referring to FIG. 10, multiple nodes (i.e. node A/B/C) may multiplex access and backhaul links in time, frequency, or space (e.g. beam-based operation). Each node may provide access link to UE. Each node may provide backhaul to other node. Each node may referred to as relay transmission and reception point (rTRP).

The operation of the different links may be on the same or different frequencies (also termed 'in-band' and 'out-band' relays). While efficient support of out-band relays is important for some NR deployment scenarios, it is critically important to understand the requirements of in-band operation which imply tighter interworking with the access links operating on the same frequency to accommodate duplex constraints and avoid/mitigate interference.

In addition, operating NR systems in mmWave spectrum presents some unique challenges including experiencing severe short-term blocking that may not be readily mitigated by present RRC-based handover mechanisms due to the larger time-scales required for completion of the procedures compared to short-term blocking. Overcoming short-term blocking in mmWave systems may require fast RAN-based mechanisms for switching between nodes, which do not necessarily require involvement of the core network. The above described need to mitigate short-term blocking for NR operation in mmWave spectrum along with the desire for easier deployment of self-backhauled NR cells creates a need for the development of an integrated framework that allows fast switching of access and backhaul links. Over-the-air (OTA) coordination between nodes can also be considered to mitigate interference and support end-to-end route selection and optimization.

The following requirements and aspects should be addressed by the IAB for NR:

- Efficient and flexible operation for both in-band and out-band relaying in indoor and outdoor scenarios

- Multi-hop and redundant connectivity

- End-to-end route selection and optimization

- Support of backhaul links with high spectral efficiency

- Support of legacy NR UEs

In the present invention, a method for scheduling and/or coordinating transmission/reception directions and transmission/reception timing between links in an IAB environment is proposed. For the convenience, the present invention will be described on the assumption of an in-band environment, but the present invention can also be applied in an out-band environment. Also, the present invention will be described in consideration of an environment in which a donor gNB (DgNB), a relay node (RN), and a UE operate in a half-duplex manner, but the present invention can also be applied in environments where DgNB, RN, and UE operate in a full-duplex manner.

In the present invention, when there are two nodes (DgNB, RN) and each node is node A and node B, and when node A schedules node B (i.e. node B is associated with node A), the backhaul link connecting the two nodes is referred to as nodeA-nodeB backhaul link. Similarly, when node A schedules UE 1 (i.e. UE 1 is associated with node A), the access link connecting node A and UE 1 is referred to as nodeA-UE1 access link.

In the present invention, for convenience of description, backhaul links with IAB nodes scheduled by a specific IAB node are referred to as backhaul links of the corresponding IAB node, and an access link with a UE scheduled by a specific IAB node is referred to as an access link of the corresponding IAB node. For example, RN1-RN2 backhaul link and RN1-RN3 backhaul link become backhaul links of RN1, and RN1-UE2 access link and RN1-UE4 access link become access links of RN1.

In the present invention, for convenience of description, when there are RNs receiving and transmitting data from a specific DgNB to transmit/receive data to/from the UE, the backhaul links between the DgNB and the RNs are referred to as a backhaul link under the DgNB. Also, the access links between RNs connected by backhaul links under a particular DgNB and UEs are referred to as an access link under the DgNB.

Referring to FIG. 11, DgNB and UE1 is connected by access link, i.e. DgNB-UE1 access link. DgNB and RN1 is connected by backhaul link, i.e. DgNB-RN1 backhaul link. RN1 and UE2 is connected by access link, i.e. RN1-UE2 access link. RN1 and RN2 is connected by backhaul link, i.e. RN1-RN2 backhaul link. RN2 and UE3 is connected by access link, i.e. RN2-UE3 access link. Furthermore, the DgNB-RN1 backhaul link and the RN1-RN2 backhaul link become backhaul links under the DgNB. The DgNB-UE1 access link, the RN1-UE2 access link and the RN2-UE2 access link become access links under the DgNB.

In the present invention, the IAB node refers to a node, except the donor node, performing relaying operation between other IAB nodes and/or donor node. That is, the IAB node is connected by backhaul links with other IAB nodes and/or donor node, and connected by access link with UEs.

Hereinafter, various aspects of the present invention to support efficient IAB operation are described according to embodiments of the present invention.

1. Discovery mechanism among devices for backhaul links

In a multi-hop relay scenario, it is necessary to discover other IAB nodes and donor nodes, and build connections dynamically. At least, semi-static mechanisms to update connectivity or topology among IAB/donor nodes seem necessary.

In designing a mechanism for inter-IAB node discovery, two approaches can be generally considered. One approach is to design separate discovery signals (e.g. separate SS/PBCH blocks) between backhaul link and access link. The other approach is to use the common SS/PBCH block between backhaul link and access link. Depending on the general approach, the required operation and/or specification impacts can be different.

(1) Separate discovery signals between backhaul link and access link

If separate discovery signals are used for backhaul link compared to access link, the design of discovery signal needs to consider the impact on UEs connected by access link. It is not desirable that discovery signals for backhaul link are discovered by UEs. If UEs discover discovery signals for backhaul link which are targeted mainly for backhaul communication, the UE may select non-best cell which can lead performance degradation on access link. For example, if an IAB node knows that there is another donor node or other IAB nodes towards specific beam directions, it may broadcast only subset of beams instead of transmitting all possible beams. The subset of beams nay be different from set of beams mainly used for access link. If UE is associated with an IAB node for that beam used for backhaul link but not used for access link, the UE will suffer from performance degradation due to different beam setup. As the main benefits of separating discovery signals between backhaul link and access link is to provide discovery signals with low overhead optimized for backhaul signalling, it is not desirable that the discovery signal for backhaul link is also discovered by UEs.

In this sense, the present invention proposes that discovery signals are transmitted in non-sync-raster such that legacy UEs cannot discover discovery signals for backhaul link. To place discovery signals in non-sync-raster so as that IAB nodes should be able to discover each other, a fixed offset may be added in each synchronization raster. For example, a fixed offset of 200 kHz or 180 kHz or 12 times of subcarrier spacing used for synchronization for backhaul link may be added in each synchronization raster. For this, a set of fixed frequency locations may be configured per frequency band/range. Or, different approaches (e.g. different mapping sequence in SS/PBCH block, different positions of PSS/SSS, different relative frequency positions between PSS/SSS and PBCH, etc.) may also be considered. In actual discovery signal design, SS/PBCH block and/or CSI-RS based beam management signals may be reused.

When separate SS/PBCH blocks is considered for discovery signals for backhaul link, the following optimization may be considered.

- RMSI CORESET configuration: It may not be necessary to broadcast all RMSI to IAB nodes. In this case, RMSI CORESET configuration framework may be reused, and the RMSI CORESET configuration may indicates time/frequency resource where backhaul DL can be expected. In the configured time/frequency resources, any backhaul DL transmission can be considered including necessary forwarding of system information.

- Random access channel (RACH) configuration: Different from UEs, IAB nodes are rather limited in terms of the number. Thus, it may not be necessary to perform any contention-based RACH procedure. Instead, a RACH preamble may be pre-assigned to each IAB node. The RACH preamble may be selected based on a rule depending on cell ID or IAB node ID. The RACH preamble may be transmitted in the configured RACH resources if the IAB node wants to make a connection with the donor node. In general, RACH configuration may provide a minimum set of backhaul UL resources used for backhaul link such that IAB nodes can initiate connection procedure or transmit backhaul signals back to the donor node.

- PBCH configuration may include minimum set of backhaul DL and UL resources for that IAB node. For an example as a rule to determine minimum set of backhaul DL and UL resources, slot X or symbols where SS/PBCH block is transmitted for discovery signals may be assumed to be backhaul DL resources, and the next slot or successive symbols may be assumed to be backhaul UL resources. Alternatively, in slot X where SS/PBCH block is transmitted, the first 1-7 symbols may be assumed as backhaul DL resources while the following 8-14 symbols may be assumed to be backhaul UL resources. DL-UL switching and timing advance (TA) may be absorbed in backhaul UL resources rather than backhaul DL resources. In other words, effective number of symbols for backhaul UL resources may be smaller than 7 symbols.

- If extended CP is used, numerology used in backhaul link may be broadcasted via PBCH.

- When different discovery signals are used between backhaul link and access link, different beams may be used. Wider beam may be used for discovery signals for backhaul link assuming some information about potential locations of IAB nodes. To minimize additional discovery signals, different beams may be used for discovery signals for backhaul link. In that case, additional offset may be indicated to each IAB node. Each IAB node may add the indicated additional offset to reference signal received power (RSRP) based on wider beam measurement. In other words, the potential gain between narrow beam and wider beam may be indicated to each IAB node such that each IAB node can consider additional narrow beam gain for data/control transmission.

More generally, if separate discovery signals are used between backhaul link and access link, the following approaches may be considered.

1) Transmit SS/PBCH block separately for backhaul links with shared SIBs: As information in SIBs are necessary for backhaul links, particularly for RACH configuration, even with separate SS/PBCH block, SIBs can be shared between backhaul link and access link. For this, the following options may be considered.

- Option 1: SS/PBCH block for backhaul link may contain PBCH which contains information about SIBs (e.g. RMSI CORESET configuration). In this case, offset between SS/PBCH block for backhaul link and SS/PBCH block access link and/or time/frequency information of RMSI CORESET (relative offset to determine time/frequency location of RMSI CORESET/search space #0 monitoring occasion) may be informed such that a UE can locate access link's SIBs via reading PBCH of access link.

That is, PBCH included in SS/PBCH block for backhaul link may indicate time/frequency location and/or time/frequency offset between SS/PBCH block for backhaul link and SS/PBCH block for access link such that an IAB node reads SS/PBCH block for access link to determine RMSI search space. The reason of additional SS/PBCH block for backhaul link is to address half-duplex constraints of IAB nodes. To differentiate between SS/PBCH block for backhaul link and SS/PBCH block for access link, different synchronization raster or different scrambling in PBCH or different mapping of PSS/SSS (or PSS/SSS/PBCH) may be used. PSS/SSS in SS/PBCH block for backhaul link and PSS/SSS in SS/PBCH block for access link may be the same in this case. The offset value may be smaller than the periodicity of RMSI transmission (e.g. 20ms). If the periodicity of SS/PBCH block for backhaul link is multiple of periodicity of RMSI transmission, the same value may transmitted in each SS/PBCH block for backhaul link. Otherwise, the value may also be changed.

In this case, by indicating time/frequency offset between SS/PBCH block for backhaul link and SS/PBCH block for access link, SS/PBCH block offset may not be needed. In addition, system frame number (SFN) value may not be needed as SS/PBCH block for backhaul link is used only for discovery purpose. To be able to access the cell, it is required to monitor SS/PBCH block for access link (at least PBCH) for this approach. SFN field can be used for indicating offset or periodicity of SS/PBCH block for backhaul link.

- Option 2: PBCH of SS/PBCH block for backhaul link may indicate RMSI search space. RMSI-Config may be indicated, and additional offset in terms of number of slots and the number of subcarriers to apply in the indicated RMSI-Config may be configured. In other words, additional time/frequency offset may be used to determine actual time/frequency of RMSI search space (i.e. time/frequency information of RMSI search space by RMSI-Config + configured additional offset defines actual RMSI search space). For this, one of SCSCommon (by assuming fixed numerology for RMSI), DM-RS location (by assuming fixed position), cellbared (assuming no baring) and intrafrequencyReselection (by assuming always disabled or enabled) fields in PBCH (and possibly spare bit) may be used for indicating the additional time/frequency offset.

In this case, SS/PBCH block offset may be used to indicate the offset between SS/PBCH block for backhaul link and RMSI PRB grid. The value may be different from SS/PBCH block for access link. In addition, SFN may be needed, and SFN bits may not be sufficient if the periodicity of SS/PBCH block for backhaul link is larger than SS/PBCH block for access link.

In general, option 1 makes more sense where SS/PBCH block for backhaul link is transmitted for discovery purpose with rather infrequent periodicity compared to SS/PBCH block for access link. When an IAB node wants to access the network (e.g. cell access procedure), the IAB node may obtain necessary information by reading SS/PBCH blocks for access link and SIBs.

2) Transmit SS/PBCH block separately for backhaul links with dedicated SIBs for backhaul links: this approach may require similar mechanism used in SS/PBCH block for access link and RMSI transmission including possible periodicity.

3) Share SS/PBCH block between backhaul link and access link with dedicated SIBs for backhaul links: Additional resource for SIBs for backhaul link needs to be implicitly determined (e.g. by assuming fixed offset in time and/or frequency resources for SIBs for access link).

FIG. 12 shows an example of a method for transmitting discovery signals according to an embodiment of the present invention. The present invention described above under "(1) Separate discovery signals between backhaul link and access link" may be applied to this embodiment. In this embodiment, a first node may be a first IAB node, and a second node may be a second IAB node. A link between the first node and the second node may be a backhaul link, and a link between the first node and a UE may be an access link.

In step S1200, the first node transmits a first discovery signal for a link between the first node and a second node. In step S1210, the first node transmits a second discovery signal for a link between the first node and a UE. A synchronization raster of the first discovery signal is different from a synchronization raster of the second discovery signal.

A first offset may be applied to the synchronization raster of the first discovery signal, a second offset may be applied to the synchronization raster of the second discovery signal, and the first offset and the second offset is different from each other. The first discovery signal and the second discovery signal may use different mapping sequences. A frequency position of a synchronization signal in the first discovery signal and a frequency position of a synchronization signal in the second discovery signal may be different from each other. A relative frequency position of a synchronization signal and a PBCH in the first discovery signal and a relative frequency position of a synchronization signal and a PBCH in the second discovery signal may be different from each other.

The first node may transmit information on a time and/or frequency resource for the link between the first node and the second node. Accordingly, DL transmission may be performed to the second node via the link between the first node and the second node based on the time and/or frequency resource.

The first node may transmit, to the second node, information on a minimum set of resources for DL transmission via the link between the first node and the second node and information on a minimum set of resources for UL transmission via the link between the first node and the second node.

The first node may transmit information on an offset to the second node. The offset may be applied to RSRP measurement of the second node.

A SIB may be shared among the link between the first node and the second node and the link between the first node and the UE. In this case, the first discovery signal may include information on the SIB. The first discovery signal may include information on a time/frequency location of the second discovery signal and/or information on a time/frequency offset between the first discovery signal and the second discovery signal. A synchronization signal in the first discovery signal and a synchronization signal in the second discovery signal may be same. The first discovery signal may include information on a search space of RMSI.

Or, a SIB may be dedicated for the link between the first node and the second node.

According to embodiment of the present invention shown in FIG. 12, the discovery signal for backhaul link and the discovery signal for access link can be transmitted separately. Therefore, it can be avoided for the UE to discover the discovery signal for backhaul link, which is mainly targeted to IAB nodes.

(2) Common discovery signals between backhaul link and access link

Common channels between backhaul link and access link may be used. The main benefits of this approach is low overhead, as discovery signals are shared between backhaul link and access link. Otherwise, each IAB node/donor node needs to transmit discovery signal for backhaul link separate from synchronization signals/SIB transmission for access link. To utilize the common/shared discovery signals, it is necessary that the IAB nodes do not transmit discovery signals while obtaining discovery signals from other potential donor nodes. This may be done by configuring different discovery signal transmission periodicity among donor node and IAB nodes. Or, the IAB node may obtain synchronization at system booting via SS/PBCH block and then maintain synchronization via tracking RS (which is also configured by a donor node for each or for IAB nodes) and/or channel state information RS (CSI-RS). Necessary configuration for tracking RS and/or CSI- configuration may be exchanged via backhaul signalling. The transmission of tracking RS for backhaul link may be sparser that that for access link. In that sense, larger periodicity on tracking RS for backhaul link may be used. When discovery signals for access links are shared between backhaul link and access link, as all beams are not needed for backhaul measurement, information on subset of beams for further measurements may be indicated. In other words, once an IAN node discovers the best beam towards donor node, donor node may indicate candidate beams based on the detected best beam which will be used for further measurement/beam failure/recovery procedure. Continuous measurement may be necessary for load balancing or learning new topology.

More generally, different approaches for discovery signals may be considered as follows.

(1) IAB node may always use dedicated discovery signals for backhaul link for cell search. After cell search, connection procedure may follow access link. To support this, information on access link's SIB as mentioned above needs to be indicated by discovery signals for backhaul link.

(2) IAB node may use discovery signals for access link for cell search before connection. After connection, the IAB node may use discovery signals to detect new IAB nodes. In this case, discovery signals can be triggered aperiodically by the donor node or a new IAB node. Measurements on discovered IAB nodes may be done based on SS/PBCH blocks for access link or CSI-RS or any other reference signals which can be possibly shared with access link.

(3) IAB node may always use discovery signals for access link. A new IAB node may be associated with a donor node. The donor node may configure measurement resources for the newly joined IABs such that route reselection can be achieved for existing IAB nodes. To utilize this approach, tight synchronizations among IAB nodes may be assumed. If synchronization to a new IAB node is needed, additional discovery signals may be considered as mentioned in (2) above. Depending on the synchronization scenario, either (2) or (3) can be used. Which option is used can be configured by a donor node or requested by an IAB node.

Discovery signal design for backhaul link is described. It is expected that the discovery signal for backhaul link is transmitted rather sporadically that the discovery signal for access link. In that sense, it's generally desirable to repeat signals to improve detection and measurement performance. Accordingly, the followings may be considered.

- The number of repetition may be configured per each discovery signal occasion. To address half-duplex, an IAB node may have multiple discovery signal occasions, and each discovery signal occasion may contain repeated discovery signal transmission.

For repetition, only PSS/SSS in the discovery signal may be repeated instead of repeating PBCH as well. To support this, K-1 PSS and K-1 SSS may be added before one SS/PBCH block such that there is K PSS and K SSS and 1 PBCH in one discovery signal occasion.

For CSI-RS, repetition may occur in frequency and/or time domain. Instead of repetition, the number of used REs for CSI-RS or different CSI-RS pattern may also be considered.

- The number of repetitions may be determined implicitly based on discovery signal periodicity. For example, for larger discovery signal periodicity, the more repetition in one discovery signal occasion may be considered. This is to balance the overall detection time of discovery signal.

Aperiodic trigger of the discovery signal for backhaul link is described. To address half-duplex of IAB node, it is essential that IAB nodes which need to discover each other may not transmit simultaneously. When aperiodic discovery signal for backhaul link is triggered, a set of discovery signal occasions may also be specified in the trigger request. An IAB node may select one discovery signal occasion from the set of discovery signal occasions. The followings may be considered for the selection.

- Each IAB node may be assigned with an ID which can be used to select the discovery signal occasion for its turn to transmit.

- The requester may also indicate {IAB node identifier, time/frequency occasion} where each IAB node transmits discovery signals at the given time/frequency resource.

- Each IAB node may select one discovery signal occasion randomly. To minimize the impact where some IAB nodes may not hear due to collision, each IAB node may transmit discovery signals multiple times. The number of repetition may be configured by a donor node. Or, the number of repetitions may be fixed per frequency range. While multiple transmissions are enabled, each IAB node may select multiple resources randomly or with a pattern. The pattern may be determined based on the previously selected discovery signal occasion and Node-ID%N1. Here, N1, N2, N3…Nk may be a fixed value which can have different value per each repetition. This is to avoid constant collision among a set of IAB nodes.

2. Measurement configuration in consideration of half-duplex

In designing of discovery signal configuration/transmission timing, half-duplex constraints should be considered. IAB nodes should be able to discover each other in different time. There may be a few approaches considered to make it sure that each IAB node would have at least one opportunity to identify/hear its neighbour IAB node(s). In other words, discovery signal reception and transmission timing among IAB nodes may be managed such that there is at least one opportunity that one IAB node hears another IAB node.

IAB measurement timing configuration (IMTC), like discovery measurement timing configuration (DMTC) and/or SS/PBCH block measurement timing configuration (SMTC), may be configured. The IAB measurement timing configuration may include periodicity of discovery signal transmission, offset of discovery signal transmission and duration of discovery signal transmission. As each IAB node needs to transmit discovery signals with measurements, it should be further clarified how each IAB node transmits discovery signals and perform measurements. The followings may be considered.

(1) Individual transmission opportunity: For example, discovery signal occasions may be defined within each IAB measurement timing configuration. The discovery signal occasion may defined as follows exemplarily.

- Within a duration, N slots may be counted. Semi-statically configured DL slot or flexible slot may be counted as K slots, where K is the number of potential discovery signal occasions within a slot based on numerology used in discovery signal. Semi-statically configured UL slot may be counted as zero. Mixed DL and UL slot may be counted as K1 slot, where K1 is the number of potential discovery signal occasions within a slot based on slot format assuming discovery signal can be transmitted on DL or flexible resource. Instead of counting both flexible and DL resource as potential discovery signal occasions, only DL resources may be counted as potential discovery signal occasion. Furthermore, if backhaul link and access link use different slot formation indication configuration, only backhaul DL (or backhaul DL/flexible) resources configured dynamically and/or semi-statically may be counted as potential discovery signal occasion.

- N slots per each periodicity may be same across IMTC interval.

- Each IAB may select its discovery signal occasion as IAB_ID % N. That is, Each IAB node may select its discovery signal occasion based on its ID. The drawback of this approach is that IAB nodes with IDs with same remainder cannot hear each other. To overcome this, duration may be guaranteed to allow at least M discovery signal transmission opportunity. M is the number of IAB nodes in the system (or connected to the same donor node or a predefined number). This is to allow that only one IAB node transmits at a given time to allow other IAB nodes to hear. To support this, each donor node may indicate which transmission occasion (or transmission opportunity index) can be used for each IAB node.

(2) Grouping mechanism

To scale with the number of IAB nodes, if there is P discovery signal occasions with M IAB nodes, it is generally true that an IAB node cannot discover/hear ceil {(M/P)-1} IAB nodes. To minimize the impact on system performance, it is necessary to group M/P nodes such that each IAB node may not need to discover each other within the same group. Thus, it is generally considered as grouping mechanism of M IAB nods to P groups.

Assuming each IMTC with P transmission opportunities, the following grouping mechanisms may be considered. Each IAB node may select K groups out of P groups. In selected group's opportunity, each IAB nod may transmit its discovery signal. In other groups' opportunity, each IAB nodes may listen other nodes' possible transmission. The number of selected groups may be determined based on IAB node's hop count. If an IAB node has multiple paths such that it has multiple hop counts, the IAB node may use the largest hop count to determine the number of groups or transmission. The number of groups per each hop may be determined/configured by a donor node as well.

FIG. 13 shows an example of topology between IAB nodes to which technical features of the present invention can be applied. The grouping mechanisms described here may be explained by the topology between IAB nodes shown in FIG. 13.

Referring to FIG. 13, node 1 is a donor node.

IAB nodes

2, 3, 4, 5, 8 are connected to node 1. Each of

IAB nodes

2, 3, 4, 5, 8 has a hop count of 1. IAB node 6 is connected to IAB node 3. IAB node 6 has a hop count of 2. IAB node 7 is connected to IAB node 4. IAB node 7 has a hop count of 2. IAB node 8 is connected to IAB node 5. IAB node 8 has a hop count of 1 towards node 1, and a hop count of 2 towards IAB node 5. IAB node 9 is connected to

IAB node

3, 7. IAB node 9 has a hop count of 2 towards IAB node 3, and a hop count of 3 towards IAB node 7. IAB node 10 is connected to IAB node 7. IAB node 10 has a hop count of 3.

K groups out of P groups may be selected as follows.

- K groups may be selected randomly among P groups by each IAB node.

- P groups may be sub-grouped per each hop count. For each sub-group, each IAB node belonging to the same hop count may select K groups randomly.

- 1st group may include IAB nodes with even hop. 2nd group may include IAB nodes with odd hop. 3rd group may include IAB nodes with even hop, without child(s) with even hop, or IAB nodes with even hop, without parent(s) with even hop. 4th group may include IAB nodes with odd hop, without child(s) with odd hop, or IAB nodes with odd hop, without parent(s) with odd hop. After 4 times, all IAB nodes can hear from each other at least between parent and child.

To discover IAB nodes within the same hop count, for each hop count, each IAB may be assigned with index. All IAB nodes with the same index in each hop count may transmit simultaneously. In other words, in additional T transmission opportunities (T is the maximum number of IAB nodes in a hop count), IAB node with different index may transmit discovery signal. If there is less opportunity than T+4 in an IMTC, further grouping may be considered among IAB nodes with the same hop count.

Table 5 shows an example of transmission opportunity of discovery signals for each IAB node following the above grouping mechanism.

1st transmission opportunity	IAB nodes				1, 6, 7, 8
2nd transmission opportunity	IAB nodes						2, 3, 4, 5, 9, 10
3rd transmission opportunity	IAB nodes			1, 6, 7
4th transmission opportunity	IAB nodes					2, 3, 4, 5, 10
5th transmission opportunity	IAB nodes				1, 2, 6, 9
6th transmission opportunity	IAB nodes			3, 7, 10
7th transmission opportunity	IAB nodes		4, 8
8th transmission opportunity	IAB node	5

- As there is high possibility that there can be potential parents/children with two hop away, instead of grouping IAB nodes with even/odd hop, IAB nodes may be grouped into 3 groups, i.e. hop count%3 = 0, hop count%3 =1, and hop count%3 = 2. By this way, even though more time units are needed for communication, it possibility of discovery may be increased. Even with this approach, it may be further considerable to allow discovery signal transmission to discover IAB nodes with potentially more than 2 hop difference between the current path and a new path with a new intermediate IAB node. Given the low probability of such case, whether to skip discovery signal transmission of IAB nodes with child(s) or parent(s) with hop count difference more than 2 may be configured. After three group's transmission, round-robin or random transmission among IAB nodes belonging to the same group may be considered. When determining hop count, each IAB node may select primary path, and each IAB node may indicate which parent is in the primary path such that all IAB nodes can know its primary path children.

Table 6 shows an example of transmission opportunity of discovery signals for each IAB node following the above grouping mechanism.

1st transmission opportunity	IAB nodes		1, 9, 10
2nd transmission opportunity	IAB nodes			2, 3, 4, 5
3rd transmission opportunity	IAB nodes		6, 7, 8
4th transmission opportunity	IAB nodes		1, 2, 6
5th transmission opportunity	IAB nodes		9, 3, 7
6th transmission opportunity	IAB nodes		10, 4, 8
7th transmission opportunity	IAB node	5

3. DL/UL via different frequency including supplemental UL (SUL)/FDD spectrum

Relay operations may occur in different frequencies between DL and UL. The examples may include FDD spectrum for DL and TDD spectrum in SUL band for UL. If such frequency spectrum is used, for back link and access link, the following options may be considered.

(1) Access DL and backhaul DL (from donor to IAB node) may occur in DL resource/spectrum. This implies that IAB node needs to receive and transmit in DL spectrum. Unless in-band full duplex capability is supported, this requires time division multiplexing (TDM) between transmission and reception in DL spectrum in the IAB node.

For relay operation, the following two approaches may be considered.

- The IAB nodes may operate half-duplex operation in DL and UL spectrum respectively. Half-duplex TDM may be determined independently (or jointly);

- The IAB nodes may operate FDD in DL and UL uplink spectrum respectively. DL frequency may change between two (i.e. DL spectrum for access link and UL spectrum for backhaul UL transmission) and UL frequency may change between two (i.e. DL spectrum for backhaul DL reception and UL spectrum for access link)

(2) Access DL and gNB DL may occur in DL resource/spectrum, while backhaul DL (except for gNB) may occur in UL resource/spectrum.

(3) The IAB nodes may operate transmission on DL spectrum only for access link, whereas backhaul link uses UL spectrum for both transmission/reception.

Depending on which hardware option is used for backhaul link operation and also for timing option, different operation for slot formation indication may be considered as follows. For example, IAB node may be synchronized with donor node based on radio interface. In this case, slot boundary alignment between the IAB node and donor node may have propagation delay gap from the absolute timing perspective. Or, the IAB node and donor doe may have exact slot boundary alignment. Or, the IAB node and donor doe may align slot boundary which allows same timing at the associated UE by donor node and IAB nodes. If an IAB node behaves half-duplex between reception and transmission in a DL spectrum, DL-UL switching latency may be needed. If an IAB node connects to different IAB nodes for DL and UL, TA handling may be necessary.

Referring to FIG. 14, the donor node is connected to UE1 via access link P4. The donor node is connected to RN1 via backhaul link P1. The RN1 is connected to UE2 via access link P5. The RN1 is connected to the RN2 via backhaul link P2. The RN2 is connected to UE3 via access link P3.

Referring to FIG. 15, the following cases may be considered.

(1) Case 1: From IAB node perspective, access DL transmission and backhaul DL transmission occur at DL spectrum. This implies that the IAB node needs to perform reception and transmission at DL spectrum. In this case, IAB node needs UL-DL switching and timing adjustment, if necessary. It is not generally desirable to complicate SFI of access links. In this sense, necessary gap may be used before DL slots of access link. It is desirable to absorb the gap in DL slot of back link. As the donor node does not need DL-UL switching or timing adjustment, the gap may not be needed for the donor node and may be used for access link.

In that sense, slot format XXX…XD..D may be used for access link if backhaul link and access link are multiplexed by TDM. The number of D symbols may be 1 or a few symbols depending on the necessary switching time and adjustment gap. Or, DL may be shared between backhaul link and access link in this case. The similar issue occur between IAB nodes when multi-hop is used. Furthermore, if DL timing for the access link of the IAB node is aligned with DL timing for the access link of the donor node, additional gap may also be needed to align slot boundary between IAB node and donor node. To accommodate the DL-UL switching gap and TA (to align slot boundary), guard period may be used between backhaul DL and access DL for IAB node. The gap may be created by puncturing a few symbols of backhaul DL to minimize the impact on UEs. The gap may be created by explicit SFI configuration/indication or implicitly by scheduling.

(2) Case 2: Assuming relay UL operation occurs at UL spectrum sharing between backhaul link and access link, opposite issue of case 1 may occur in UL due to DL-UL switching and timing advance. As mentioned above, similar issue may occur in DL spectrum if slot boundary of access links are aligned among IAB nodes and donor node(s).

In terms of UL timing, the following two approaches may be considered.

- Option 1: UL slot boundary of access link of IAB node may be aligned with its DL slot boundary. Referring to FIG. 15, if this approach is used, additional TA for backhaul UL of IAB node should be absorbed as an additional gap, which results in resource waste in backhaul UL.

- Option 2: UL slot boundary of access link of IAB node may be aligned with DL slot boundary of a donor node. In other words, UL slot boundary of IAB node may also be shifted by timing advance (or similar value to TA depending on the scheme). To transmit data to the donor node, timing advance may be expected to align UL at donor node. In general, the donor node may not change its protocol/behaviour considerably. Also, it is not desirable to change network protocols in access links for legacy UEs. Considering these, it is more natural to assume that timing advance is also used in IAB node nodes for UL transmission in backhaul link.

Thus, case 2 needs to include timing advance for IAB node and switching gap. The access network needs to be aligned with DL slot boundary at IAB node/donor node. More specifically, to handle cross-link interference effectively, it is generally desirable to align UL slot boundary of each UEs (regardless of with which IAB node the UE has associated) to the DL slot boundary of donor node. In other words, within coverage of the donor node, IAB nodes may perform synchronization based on air interface such that the UL slot boundary of a UE associated with that IAB node can reflect propagation delay from IAB node appropriately.

Accordingly, the slot boundary of UL access link may need to be aligned with slot boundary of IAB node, which can eliminate the gap between backhaul link and access uplink. The present invention proposes that the DL slot boundary of IAB node is aligned with DL slot boundary of the donor node + propagation delay, while the UL slot boundary of IAB node is aligned with DL/UL slot boundary of the donor node in consideration of propagation delay. In other words, UL slot boundary of IAB node may be shifted by timing advance compared to DL slot boundary of the IAB node. This may be applied at least in paired spectrum or different frequency used between DL and UL or SUL case.

Referring to FIG. 15, if this approach is used, UL slot boundary of IAB node may not be aligned with its DL slot boundary. If this approach is used in unpaired spectrum, it can lead higher gap between any DL and UL. However, it is proposed that the same approach may be used at least when unpaired spectrum is used along with SUL, where SUL spectrum is used for backhaul link and access links. Moreover, it is also proposed to configure slot boundary used in DL and/or UL. For DL, whether to adjust DL slot timing based on propagation delay between donor node (or parent IAB node) and itself may be configured/determined by the donor node (or parent IAB node). For UL timing, similar configuration may also be possible, and actual value may be configured by timing advance value. Timing advance value may be negative depending on conditions even for absolute TA adjustments.

The indicated timing advance value (if this mechanism is used) may not represent twice of propagation delay between donor node (or parent IAB node) to an IAB node. Thus, when network synchronization based timing advance is used, some considerations may be necessary. First solution is to inform propagation delay measured at donor node (or parent IAB node) to a child IAB node. Second approach is to transmit synchronization signals by adjusting timing gap between DL slot boundary and UL slot boundary such that propagation delay can be computed by reception timing of synchronization signals and timing advance values. As this may not be easily feasible, additional offset to shift UL and/or DL slot boundary compared to nominal DL/UL slot boundary may be indicated. The nominal slot boundary means that DL slot boundary is same as slot boundary of the donor node, and UL slot boundary at an IAB node is determined by DL slot boundary. In other words, the same DL/UL slot boundary may be used.

More generally, timing relationship among different IAB nodes may be considered as follows. For each option described below, there are case(s) that each option works the best. The present invention proposes that each AIB node determine timing scenario for backhaul link and access link depending on scenario and broadcast its timing information and/or scenario to neighbouring IAB nodes/donor nodes such that appropriate gap/SFI can be generated. The timing scenario may be determined based on various factors. For example, relay node scenario (e.g. coverage scenario or throughput enhancement scenario), whether coordinated multi-point (CoMP) transmission is used or not between IAB nodes (e.g. whether joint reception or dynamic point selection (DPS) at UE is supported), multiplexing scheme between backhaul link and access link (e.g. TDM may allow different timing between backhaul link and access link, while frequency division multiplexing (FDM)/spatial multiplexing (SDM) may need tighter/aligned timing between backhaul link and access link), etc., may be used for determining the timing scenario. In terms of detailed signalling, information on the gap between DL slot boundary and UL slot boundary and information on timing advance value of each IAB node may be included. As each IAB node may need to align its timing option, instead of selecting timing option at each IAB node, a donor node may select timing option used within IAB nodes connected to the same donor node. If an IAB node is connected to more than one donor node, this may lead multiple timing options that the IAB node may need to follow.

A few scenarios of different timing cases may be considered as follows. For the convenience, unpaired spectrum is assumed, but the present invention can also be applied to paired spectrum.

(1) Donor node's backhaul link and access links are aligned

- Option 1: Backhaul link of the IAB node may be aligned as if a UE against its donor node and IAB node's backhaul link and access link may be aligned. FIG. 16 shows option 1 for scenario of different timing cases according to an embodiment of the present invention. This allows efficient multiplexing between backhaul link between donor node and IAB node and access link between IAB node and UE. However, this may increase the necessary gap between DL and UL per each hop. Furthermore, this makes UE's DL slot boundary dependent on the serving cell, and thus, collaboration between IAB nodes for the same UE may not be easily possible.

- Option 2: Backhaul link of the IAB node may be aligned as if a UE against its donor node and access link timing may be aligned from a UE perspective. FIG. 17 shows option 2 for scenario of different timing cases according to an embodiment of the present invention.

(2) Donor node's backhaul link and access links may not be aligned.

4. Backhaul link resource allocation in consideration of half-duplex and multi-beam

Depending on resource sharing between access link and backhaul link, possible resource allocation mechanism among IAB nodes/donor nodes may be different. Particularly, if an IAB node has more than one parent IAB node/donor node, how to align TX-RX beams between multiple links may need to be considered.

In terms of resource allocation between a parent IAB node to a child IAB node (or vice versa), the following approaches may be considered.

(1) Fully distributed: Each donor/IAB node may allocate CORESET(s), and each child IAB node of itself may monitor allocated CORESET. In CORESET configuration, transmission configuration indicator (TCI) state may also be indicated such that RX beam of a child IAB node can be determined at the child IAB node. Similarly, UL resources may be semi-statically or dynamically configured with UL TX beam information. PDSCH from a parent IAB node may occur within a time duration after a DCI (e.g. within a few symbols, within a slot, within a few slots). By receiving CORESET configuration with this restriction, each IAB node may determine whether there is any conflict resources in which different parent IAB nodes use different RX beams for potential communication.

To determine CORESET configuration of a child IAB node, each child IAB node may inform the following information.

- An intended DL/UL configuration/resources for access links: If access link and backhaul link are shared, in addition to DL/UL information, intended beams (RX/TX beams) in each resource also needs to be indicated such that a parent IAB node can determine which resources can be shared among backhaul link between parent/child IAB nodes and access link of the child IAB node.

- CORESET configurations from another parent IAB node if a child IAB node has multiple parent IAB nodes: All information from other parent IAB nodes (if more than two parent IAB nodes) may be forwarded to one parent IAB node. In other words, each parent IAB node may know configurations of other parent IAB nodes to the child IAB node.

Based on the above information, colliding resources may be used by parent IAB node with higher priority. The parent IAB node with higher priority may be determined based on at least one of the followings:

- IAB node ID (or donor node may have the highest priority)

- Hop count to the child IAB node via the parent IAB node

- Each path may have different priority.

- By selection of the child IAB node: The child IAB node may select which CORESET to monitor for colliding resources.

The main drawback of this approach is that cross-link interference may occur as there is no coordination. Furthermore, if a child IAB node has multiple parent IAB nodes, collision from multiple parent IAB nodes may be increased.

(2) Centralized TDM + distributed CORESET configuration: IAB nodes may be multiplexed by TDM based on hop count to mitigate cross-link interference and half-duplex constraint by a donor node or by a rule, and distributed mechanism within each allocated resource may be applied. For example, resources for backhaul link may be divided into two units. The first unit may be used for IAB nodes with even hop and the second unit may be used for IAB nodes with odd hop. For the case of multi-path, resources for backhaul link and/or IAB nodes may be further divided for different cases. For each IAB node, based on TDM, a set of resources may be determined where each IAB node can transmit. Within that resource, each IAB node may configure CORESET configuration to each child IAB node similar to (1). Similar handling for multi-path handling may be considered as well. To support this approach, each child IAB node may inform the following information.

- Multi-paths (parent IAB nodes) and hop count of each path to its parent IAB node(s)

- Primary path (if any) or bearer split information (from donor node to each parent IAB node)

(3) Fully centralized: Based on RX-TX beam between a child IAB node and a parent IAB node, the donor node may determine resource allocations among multiple links to minimize cross-link interference and maximize resource efficiency.

Instead of CORESET configuration, each IAB node/donor node may indicate intended TX beam resources, and each child IAB node may determine which resource to monitor based on measurement results for the best beam or configured TCI state.

5. Resource configuration mechanism

When multi-hop and multi-path IAB nodes are in the system, the overall connection procedure may be as follows.

(1) An IAB node searches neighbor IAB nodes/donor nodes based on SS/PBCH blocks for access link.

(2) For an identified IAB nodes/donor nodes, the IAB node attempts to make RRC connection via access link procedure. For indicating the IAB node, separate RACH resource or indication in Msg3 or via RRC connection or via UE capability reporting may be considered.

(3) The IAB node may make multiple RRC connections if supported. In setting up multiple RRC connections, it is necessary to differentiate primary path and secondary paths. Further, the IAB node may also indicate whether it is desired to receive packet data convergence protocol (PDCP) duplication. In other words, when multiple RRC connections is used, either dual connectivity architecture with or without PDCP duplication may be considered depending on the scenario. Other than primary path, the IAB node may make RRC_INACTIVE connection instead of RRC_CONNECTED connection. It may be requested via selection of RACH resource (separate RACH resource between RRC_CONNECTED and RRC_INACTIVE) or via Msg3 or via RRC connection.

(4) Once the IAB node makes at least one RRC connection, the IAB node performs gNB function of the IAB node. To behave as a gNB, the IAB node may determine frame boundary, slot index, SS/PBCH block transmission occasion, etc., compared to the parent IAB node/donor node. In determining such information, different approaches depending on resource partitioning/coordination mechanism among IAB nodes may be considered as follows.

- Frame boundary and SS/PBCH block transmission occasions may be aligned with parent IAB node(s). This implies that SS/PBCH block transmission among IAB nodes are coincided such that they may not discover or read other IAB nodes' SS/PBCH block after RRC connection. This will also complicate the reading of SIB1 (i.e. RMSI) and other potential SIB information via access link. This may require IAB-dedicated indication of SS/PBCH block transmission between parent IAB nodes and child IAB nodes. Furthermore, transmission of tracking RS may be additionally necessary via backhaul link. Alternatively, when a child IAB node needs to read an IAB parent node, the child IAB node may create temporary measurement gap. Or, after connection, based on TRS/CSI-RS, all the tracking and measurements may be assumed along with dedicated SIB updates.

- Frame boundary and SS/PBCH block transmission occasions may be determined based on parent IAB node(s). This is to avoid collision between SS/PBCH block transmission from parent IAB node(s) and from the child IAB node. For example, grouping may be done based on hop count, and each IAB node may determine its group among {(even, even), (even, odd), (odd, even), (odd, odd)}. Here, (even, even) means that the IAB node will use 1st and 3rd transmission occasion, (even, odd) means that the IAB node will use 1st and 4th transmission occasion, and (odd, odd) means that that the IAB node will use 2nd and 4th transmission occasion. In non-transmission occasion, each IAB node can listen on it's parent IAB node(s). To minimize collision between parent IAB node(s) and child IAB node(s), opposite grouping may be selected (e.g. parent IAB node may use (even, even), and a child IAB node may use (odd, odd)).

The frame boundary may be shifted by 5ms for IAB nodes with odd hop in the selected group. Or, frame boundary may be maintained as same, and SS/PBCH block transmission occasions may be shifted. Among 20ms, SS/PBCH block transmission of each group may occur as two chunks with 5ms window, and 5ms window may be selected based on the group. For example, (odd, odd) group may select 2nd and 4th chunk of 5ms window among 20ms window. Instead of 20ms, different periodicity may also be used. By this way, a child IAB node may be able to monitor SIB(s)/SS/PBCH block on a parent IAB node as long as the grouping is maintained and the connection is maintained. However, this will may increase the overall SS/PBCH block transmission time in the system.

(5) For a CORESET configuration of a parent IAB node to a child IAB node, CORESET configuration may be multiplexed by TDM among IAB nodes based on slot.

- If SS/PBCH block transmissions multiplexed by TDM among IAB nodes with different hop count, CORESET configuration may also follow SS/PBCH block transmission occasion, and a parent IAB node may configure a CORESET to a child IAB node on the time duration selected for SS/PBCH block transmission occasion. This implies that CORESET configuration may have long periodicity (e.g. 10ms or 15ms depending on the group), and thus may lead unnecessarily overhead.

- If SS/PBCH block transmissions are aligned, CORESET configuration to a child IAB node may not utilize the same symbols/slot to SS/PBCH block transmission occasion. This is to avoid request on a child IAB node to monitor CORESET in the same time where the child IAB node needs to transmit. The slots or symbols of potential SS/PBCH block transmission occasions may be reserved for access link which will be used to schedule control/data to UEs. By excluding SS/PBCH block transmission occasions (and also potentially reserved resources for UEs), other resources may be grouped to 4 time durations as mentioned above, and each IAB node may select different groups for potential transmission. The resource may be divided in M slots or 1 slot or K symbols. For example, if SS/PBCH block transmissions are reserved for 5ms in every 20ms, 5ms in every 20ms may be reserved for access links, and 15ms in every 20ms may be divided into four groups in slot level. For example, with 120 kHz subcarrier spacing, subframe #6 may contain 1^st, 5^th slot for first group, 2^nd, 6^th slot for second group, 3^rd, 7^th slot for third group, and 4^th, 8^th slot for fourth group. These group may be repeated in every subframe for 15ms.

- When there is unused resources on potential SS/PBCH block transmission occasions, such resources may also be used for TDM partitioning.

(5) CSI-RS/tracking RS configuration for beam measurement, radio link monitoring (RLM), radio resource management (RRM), etc.

- The same resource where CORESET can be configured may also be used for configuring other RS.

- To minimize the latency, instead of slot level TDM for CORESET configuration, half-slot TDM may also be considered.

When distributed approach is used, each IAB node may determine CORESET, RS transmission configuration, and/or intended DL/UL configurations and/or intended SFI information for backhaul link and access link. When an IAB node receives the information from its parent IAB node(s), the IAB node may also forward the received information to its child IAB node(s) such that the child IAB node(s) can make its decision in consideration of resource allocation information of both its parent IAB node(s) and its grand-parent IAB node(s). For example, the same CORESET/RS transmission configuration of its grand-parent IAB node(s) may be utilized such that parent IAB node(s) nodes and the child IAB node can have opposite resource planning/allocation.

FIG. 18 shows an IAB node to implement an embodiment of the present invention. The present invention described above for IAB node may be applied to this embodiment.

An IAB node 1800 includes a processor 1810, a memory 1820 and a transceiver 1830. The processor 1810 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 1310.

Specifically, the processor 1810 is configured to control the transceiver 1830 to transmit a first discovery signal for a link between the first node and a second node. The processor 1810 is configured to control the transceiver 1830 to transmit a second discovery signal for a link between the first node and a UE. A synchronization raster of the first discovery signal is different from a synchronization raster of the second discovery signal.

The processor 1810 may be configured to control the transceiver 1830 to transmit information on a time and/or frequency resource for the link between the first node and the second node. Accordingly, DL transmission may be performed to the second node via the link between the first node and the second node based on the time and/or frequency resource.

The processor 1810 may be configured to control the transceiver 1830 to transmit, to the second node, information on a minimum set of resources for DL transmission via the link between the first node and the second node and information on a minimum set of resources for UL transmission via the link between the first node and the second node.

The processor 1810 may be configured to control the transceiver 1830 to transmit information on an offset to the second node. The offset may be applied to RSRP measurement of the second node.

The memory 1820 is operatively coupled with the processor 1810 and stores a variety of information to operate the processor 1810. The transceiver 1830 is operatively coupled with the processor 1810, and transmits and/or receives a radio signal.

The processor 1810 may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The memory 1820 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. The transceiver 1830 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in the memory 1820 and executed by the processor 1810. The memory 1820 can be implemented within the processor 1810 or external to the processor 1810 in which case those can be communicatively coupled to the processor 1810 via various means as is known in the art.

According to embodiment of the present invention shown in FIG. 18, the discovery signal for backhaul link and the discovery signal for access link can be transmitted separately. Therefore, it can be avoided for the UE to discover the discovery signal for backhaul link, which is mainly targeted to IAB nodes.

FIG. 19 shows more detailed IAB node to implement an embodiment of the present invention. The present invention described above for IAB node may be applied to this embodiment.

An IAB node includes a processor 1910, a power management module 1911, a battery 1912, a display 1913, a keypad 1914, a subscriber identification module (SIM) card 1915, a memory 1920, a transceiver 1930, one or more antennas 1931, a speaker 1940, and a microphone 1941.

The processor 1910 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 1910. The processor 1910 may include ASIC, other chipset, logic circuit and/or data processing device. The processor 1910 may be an application processor (AP). The processor 1910 may include at least one of a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), a modem (modulator and demodulator). An example of the processor 1910 may be found in SNAPDRAGON^TM series of processors made by Qualcomm^®, EXYNOS^TM series of processors made by Samsung^®, A series of processors made by Apple^®, HELIO^TM series of processors made by MediaTek^®, ATOM^TM series of processors made by Intel^® or a corresponding next generation processor.

The processor 1910 is configured to control the IAB node to transmit a first discovery signal for a link between the first node and a second node. The processor 1910 is configured to control the IAB node to transmit a second discovery signal for a link between the first node and a UE. A synchronization raster of the first discovery signal is different from a synchronization raster of the second discovery signal.

The processor 1910 may be configured to control the IAB node to transmit information on a time and/or frequency resource for the link between the first node and the second node. Accordingly, DL transmission may be performed to the second node via the link between the first node and the second node based on the time and/or frequency resource.

The processor 1910 may be configured to control the IAB node to transmit, to the second node, information on a minimum set of resources for DL transmission via the link between the first node and the second node and information on a minimum set of resources for UL transmission via the link between the first node and the second node.

The processor 1910 may be configured to control the IAB node to transmit information on an offset to the second node. The offset may be applied to RSRP measurement of the second node.

The power management module 1911 manages power for the processor 1910 and/or the transceiver 1930. The battery 1912 supplies power to the power management module 1911. The display 1913 outputs results processed by the processor 1910. The keypad 1914 receives inputs to be used by the processor 1910. The keypad 1914 may be shown on the display 1913. The SIM card 1915 is an　integrated circuit　that is intended to　securely store the　international mobile subscriber identity　(IMSI) number and its related　key, which are used to identify and authenticate subscribers on　mobile telephony　devices (such as　mobile phones　and　computers). It is also possible to store contact information on many SIM cards.

The memory 1920 is operatively coupled with the processor 1910 and stores a variety of information to operate the processor 1910. The memory 1920 may include ROM, RAM, flash memory, memory card, storage medium and/or other storage device. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in the memory 1920 and executed by the processor 1910. The memory 1920 can be implemented within the processor 1910 or external to the processor 1910 in which case those can be communicatively coupled to the processor 1910 via various means as is known in the art.

The transceiver 1930 is operatively coupled with the processor 1910, and transmits and/or receives a radio signal. The transceiver 1930 includes a transmitter and a receiver. The transceiver 1930 may include baseband circuitry to process radio frequency signals. The transceiver 1930 controls the one or more antennas 1931 to transmit and/or receive a radio signal.

The speaker 1940 outputs sound-related results processed by the processor 1910. The microphone 1941 receives sound-related inputs to be used by the processor 1910.

According to embodiment of the present invention shown in FIG. 19, the discovery signal for backhaul link and the discovery signal for access link can be transmitted separately. Therefore, it can be avoided for the UE to discover the discovery signal for backhaul link, which is mainly targeted to IAB nodes.

Other IAB node or donor node 2000 includes a processor 2010, a memory 2020 and a transceiver 2030. The processor 2010 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 2010. The memory 2020 is operatively coupled with the processor 2010 and stores a variety of information to operate the processor 2010. The transceiver 2030 is operatively coupled with the processor 2010, and transmits and/or receives a radio signal.

The processor 2010 may include ASIC, other chipset, logic circuit and/or data processing device. The memory 2020 may include ROM, RAM, flash memory, memory card, storage medium and/or other storage device. The transceiver 2030 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in the memory 2020 and executed by the processor 2010. The memory 2020 can be implemented within the processor 2010 or external to the processor 2010 in which case those can be communicatively coupled to the processor 2010 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While for purposed of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from what is depicted and described herein. Moreover, one skilled in the art would understand that the steps illustrated in the flow diagram are not exclusive and other steps may be included or one or more of the steps in the example flow diagram may be deleted without affecting the scope of the present disclosure.

Claims

A method performed by a first node in a wireless communication system, the method comprising:

transmitting a first discovery signal for a link between the first node and a second node; and

transmitting a second discovery signal for a link between the first node and a UE,

wherein a synchronization raster of the first discovery signal is different from a synchronization raster of the second discovery signal.
The method of claim 1, wherein a first offset is applied to the synchronization raster of the first discovery signal,

wherein a second offset is applied to the synchronization raster of the second discovery signal, and

wherein the first offset and the second offset is different from each other.
The method of claim 1, wherein the first discovery signal and the second discovery signal use different mapping sequences.
The method of claim 1, wherein a frequency position of a synchronization signal in the first discovery signal and a frequency position of a synchronization signal in the second discovery signal is different from each other.
The method of claim 1, wherein a relative frequency position of a synchronization signal and a physical broadcast channel (PBCH) in the first discovery signal and a relative frequency position of a synchronization signal and a PBCH in the second discovery signal is different from each other.
The method of claim 1, further comprising:

transmitting information on a time and/or frequency resource for the link between the first node and the second node; and

performing downlink (DL) transmission to the second node via the link between the first node and the second node based on the time and/or frequency resource.
The method of claim 1, further comprising transmitting, to the second node, information on a minimum set of resources for DL transmission via the link between the first node and the second node and information on a minimum set of resources for uplink (UL) transmission via the link between the first node and the second node.
The method of clam 1, further comprising transmitting information on an offset to the second node, and

wherein the offset is applied to a reference signal received power (RSRP) measurement of the second node.
The method of claim 1, wherein a system information block (SIB) is shared among the link between the first node and the second node and the link between the first node and the UE.
The method of claim 9, wherein the first discovery signal includes information on the SIB.
The method of claim 9, wherein the first discovery signal includes information on a time/frequency location of the second discovery signal and/or information on a time/frequency offset between the first discovery signal and the second discovery signal.
The method of claim 11, wherein a synchronization signal in the first discovery signal and a synchronization signal in the second discovery signal are same.
The method of claim 9, wherein the first discovery signal includes information on a search space of a remaining minimum system information (RMSI).
The method of claim 1, wherein a SIB is dedicated for the link between the first node and the second node.
A first node in a wireless communication system, the first node comprising:

a memory;

a transceiver; and

a processor, operably coupled to the memory and the transceiver, and configured to:

control the transceiver to transmit a first discovery signal for a link between the first node and a second node, and

control the transceiver to transmit a second discovery signal for a link between the first node and a UE,

wherein a synchronization raster of the first discovery signal is different from a synchronization raster of the second discovery signal.