Patent Description:
The present application is directed to mechanisms for synchronous signal and physical broadcast channel (SSB) transmission in new radio unlicensed (NR-U).

In NR, the SSB carries the essential signal and information such as the primary synchronization signal (PSS), secondary synchronization signal (SSS) and Physical Broadcast Channel (PBCH). These are used by a UE to get synchronization and Master Information Block (MIB) in both the initial cell search and connected state. If a UE cannot detect the SSB, the UE will have critical issues and will not be able to function in the NR system.

In NR-U, the gNB may not be able to transmit the SSB burst set on the pre-defined/configured location. This may be due to the LBT failure (channel is not available). This causes issues for UEs to detect SSB.

What is desired in the art are mechanisms to improve the reliability of SSB transmission in NR-U. Cited references include <NPL>, and <NPL>.

In order to facilitate a more robust understanding of the application, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed to limit the application and are intended only to be illustrative.

A detailed description of the illustrative embodiments will be discussed in reference to various figures, embodiments and aspects herein. Although this description provides detailed examples of possible implementations, it should be understood that the details are intended to be examples and thus do not limit the scope of the application.

Reference in this specification to "one embodiment," "an embodiment," "one or more embodiments," "an aspect" or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Moreover, the term "embodiment" in various places in the specification is not necessarily referring to the same embodiment. That is, various features are described which may be exhibited by some embodiments and not by the other.

According to one aspect of the application, mechanisms and procedures for a gNB to transmit the SSB in NR-U are envisaged. In another aspect of the application, mechanisms and procedures for a UE to detect the SSB in NR-U are envisaged. In an embodiment, several SSB transmissions may be bundled together. If the bundle cannot be transmitted at the configured location due to LBT failure, it may be shifted within a configured transmission window.

In another embodiment, beam-based LBT may be performed for each SSB. The SSBs with a successful LBT will be transmitted. For the failed LBTs, the gNB may perform another round(s) of LBT to determine whether the associated SSBs can be transmitted.

In yet another embodiment, SSB transmission may be performed in succession, i.e., one by one. A window is applied for each SSB's transmission to improve reliability.

In yet even another embodiment, the index order carried by SSB may be flexible. The SSB may be transmitted at any SSB location with successful beam base LBT within the SSB burst transmission.

It is further envisaged in this application the offset by which the SSB has shifted can be indicated by the gNB to a UE with one of the following exemplary schemes:.

Provided below are definitions for terms and phrases commonly used in this application in Table <NUM>.

The 3rd Generation Partnership Project (3GPP) develops technical standards for cellular telecommunications network technologies, including radio access, the core transport network, and service capabilities - including work on codecs, security, and quality of service. Recent radio access technology (RAT) standards include WCDMA (commonly referred as <NUM>), LTE (commonly referred as <NUM>), and LTE-Advanced standards. 3GPP has begun working on the standardization of next generation cellular technology, called NR, which is also referred to as "<NUM>". 3GPP NR standards development is expected to include the definition of next generation radio access technology (new RAT), which is expected to include the provision of new flexible radio access below <NUM>, and the provision of new ultra-mobile broadband radio access above <NUM>. The flexible radio access is expected to consist of a new, non-backwards compatible radio access in new spectrum below <NUM>, and it is expected to include different operating modes that can be multiplexed together in the same spectrum to address a broad set of 3GPP NR use cases with diverging requirements. The ultra-mobile broadband is expected to include cmWave and mmWave spectrum that will provide the opportunity for ultra-mobile broadband access for, e.g., indoor applications and hotspots. In particular, the ultra-mobile broadband is expected to share a common design framework with the flexible radio access below <NUM>, with cmWave and mmWave specific design optimizations.

3GPP has identified a variety of use cases that NR is expected to support, resulting in a wide variety of user experience requirements for data rate, latency, and mobility. The use cases include the following general categories: enhanced mobile broadband (e.g., broadband access in dense areas, indoor ultra-high broadband access, broadband access in a crowd, <NUM>+ Mbps everywhere, ultra-low cost broadband access, mobile broadband in vehicles), critical communications, massive machine type communications, network operation (e.g., network slicing, routing, migration and interworking, energy savings), and enhanced vehicle-to-everything (eV2X) communications. Specific service and applications in these categories include, e.g., monitoring and sensor networks, device remote controlling, bi-directional remote controlling, personal cloud computing, video streaming, wireless cloud-based office, first responder connectivity, automotive ecall, disaster alerts, real-time gaming, multi-person video calls, autonomous driving, augmented reality, tactile internet, and virtual reality to name a few. All of these use cases and others are contemplated herein.

<FIG> illustrates one embodiment of an example communications system <NUM> in which the methods and apparatuses described and claimed herein may be embodied. As shown, the example communications system <NUM> may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, and/or 102d (which generally or collectively may be referred to as WTRU <NUM>), a radio access network (RAN) <NUM>/<NUM>/<NUM>/103b/104b/105b, a core network <NUM>/<NUM>/<NUM>, a public switched telephone network (PSTN) <NUM>, the Internet <NUM>, and other networks <NUM>, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102a, 102b, 102c, 102d, 102e may be any type of apparatus or device configured to operate and/or communicate in a wireless environment. Although each WTRU 102a, 102b, 102c, 102d, 102e is depicted in <FIG> as a hand-held wireless communications apparatus, it is understood that with the wide variety of use cases contemplated for <NUM> wireless communications, each WTRU may comprise or be embodied in any type of apparatus or device configured to transmit and/or receive wireless signals, including, by way of example only, user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a tablet, a netbook, a notebook computer, a personal computer, a wireless sensor, consumer electronics, a wearable device such as a smart watch or smart clothing, a medical or eHealth device, a robot, industrial equipment, a drone, a vehicle such as a car, truck, train, or airplane, and the like.

The communications system <NUM> may also include a base station 114a and a base station 114b. Base stations 114a may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c to facilitate access to one or more communication networks, such as the core network <NUM>/<NUM>/<NUM>, the Internet <NUM>, and/or the other networks <NUM>. Base stations 114b may be any type of device configured to wiredly and/or wirelessly interface with at least one of the RRHs (Remote Radio Heads) 118a, 118b and/or TRPs (Transmission and Reception Points) 119a, 119b to facilitate access to one or more communication networks, such as the core network <NUM>/<NUM>/<NUM>, the Internet <NUM>, and/or the other networks <NUM>. RRHs 118a, 118b may be any type of device configured to wirelessly interface with at least one of the WTRU 102c, to facilitate access to one or more communication networks, such as the core network <NUM>/<NUM>/<NUM>, the Internet <NUM>, and/or the other networks <NUM>. TRPs 119a, 119b may be any type of device configured to wirelessly interface with at least one of the WTRU 102d, to facilitate access to one or more communication networks, such as the core network <NUM>/<NUM>/<NUM>, the Internet <NUM>, and/or the other networks <NUM>. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like.

The base station 114a may be part of the RAN <NUM>/<NUM>/<NUM>, which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114b may be part of the RAN 103b/104b/105b, which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The base station 114b may be configured to transmit and/or receive wired and/or wireless signals within a particular geographic region, which may be referred to as a cell (not shown). Thus, in an embodiment, the base station 114a may include three transceivers, e.g., one for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell.

The base stations 114a may communicate with one or more of the WTRUs 102a, 102b, 102c over an air interface <NUM>/<NUM>/<NUM>, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, cmWave, mmWave, etc.). The air interface <NUM>/<NUM>/<NUM> may be established using any suitable radio access technology (RAT).

The base stations 114b may communicate with one or more of the RRHs 118a, 118b and/or TRPs 119a, 119b over a wired or air interface 115b/116b/117b, which may be any suitable wired (e.g., cable, optical fiber, etc.) or wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, cmWave, mmWave, etc.). The air interface 115b/116b/117b may be established using any suitable radio access technology (RAT).

The RRHs 118a, 118b and/or TRPs 119a, 119b may communicate with one or more of the WTRUs 102c, 102d over an air interface 115c/116c/117c, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, cmWave, mmWave, etc.). The air interface 115c/116c/117c may be established using any suitable radio access technology (RAT).

For example, the base station 114a in the RAN <NUM>/<NUM>/<NUM> and the WTRUs 102a, 102b, 102c, or RRHs 118a, 118b and TRPs 119a, 119b in the RAN 103b/104b/105b and the WTRUs 102c, 102d, may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface <NUM>/<NUM>/<NUM> or 115c/116c/117c respectively using wideband CDMA (WCDMA).

In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c, or RRHs 118a, 118b and TRPs 119a, 119b in the RAN 103b/104b/105b and the WTRUs 102c, 102d, may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface <NUM>/<NUM>/<NUM> or 115c/116c/117c respectively using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A). In the future, the air interface <NUM>/<NUM>/<NUM> may implement 3GPP NR technology.

In an embodiment, the base station 114a in the RAN <NUM>/<NUM>/<NUM> and the WTRUs 102a, 102b, 102c, or RRHs 118a, 118b and TRPs 119a, 119b in the RAN 103b/104b/105b and the WTRUs 102c, 102d, may implement radio technologies such as IEEE <NUM> (e.g., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard <NUM> (IS-<NUM>), Interim Standard <NUM> (IS-<NUM>), Interim Standard <NUM> (IS-<NUM>), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

The base station 114c in <FIG> may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In an embodiment, the base station 114c and the WTRUs 102e, may implement a radio technology such as IEEE <NUM> to establish a wireless local area network (WLAN). In an embodiment, the base station 114c and the WTRUs 102d, may implement a radio technology such as IEEE <NUM> to establish a wireless personal area network (WPAN). In yet an embodiment, the base station 114c and the WTRUs 102e, may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. Thus, the base station 114c may not be required to access the Internet <NUM> via the core network <NUM>/<NUM>/<NUM>.

The RAN <NUM>/<NUM>/<NUM> and/or RAN 103b/104b/105b may be in communication with the core network <NUM>/<NUM>/<NUM>, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network <NUM>/<NUM>/<NUM> may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication.

Although not shown in <FIG>, it will be appreciated that the RAN <NUM>/<NUM>/<NUM> and/or RAN 103b/104b/105b and/or the core network <NUM>/<NUM>/<NUM> may be in direct or indirect communication with other RANs that employ the same RAT as the RAN <NUM>/<NUM>/<NUM> and/or RAN 103b/104b/105b or a different RAT. For example, in addition to being connected to the RAN <NUM>/<NUM>/<NUM> and/or RAN 103b/104b/105b, which may be utilizing an E-UTRA radio technology, the core network <NUM>/<NUM>/<NUM> may also be in communication with another RAN (not shown) employing a GSM radio technology.

The core network <NUM>/<NUM>/<NUM> may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d, 102e to access the PSTN <NUM>, the Internet <NUM>, and/or other networks <NUM>. For example, the networks <NUM> may include another core network connected to one or more RANs, which may employ the same RAT as the RAN <NUM>/<NUM>/<NUM> and/or RAN 103b/104b/105b or a different RAT.

Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system <NUM> may include multi-mode capabilities, e.g., the WTRUs 102a, 102b, 102c, 102d, and 102e may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102e shown in <FIG> may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114c, which may employ an IEEE <NUM> radio technology.

<FIG> is a block diagram of an example apparatus or device configured for wireless communications in accordance with the embodiments illustrated herein, such as for example, a WTRU <NUM>. As shown in <FIG>, the example WTRU <NUM> may include a processor <NUM>, a transceiver <NUM>, a transmit/receive element <NUM>, a speaker/microphone <NUM>, a keypad <NUM>, a display/touchpad/indicators <NUM>, non-removable memory <NUM>, removable memory <NUM>, a power source <NUM>, a global positioning system (GPS) chipset <NUM>, and other peripherals <NUM>. Also, embodiments contemplate that the base stations 114a and 114b, and/or the nodes that base stations 114a and 114b may represent, such as but not limited to transceiver station (BTS), a Node-B, a site controller, an access point (AP), a home node-B, an evolved home node-B (eNodeB), a home evolved node-B (HeNB), a home evolved node-B gateway, and proxy nodes, among others, may include some or all of the elements depicted in <FIG> and described herein.

The transmit/receive element <NUM> may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface <NUM>/<NUM>/<NUM>. For example, in an embodiment, the transmit/receive element <NUM> may be an antenna configured to transmit and/or receive RF signals. In an embodiment, the transmit/receive Although not shown in <FIG>, it will be appreciated that the RAN <NUM>/<NUM>/<NUM> and/or the core network <NUM>/<NUM>/<NUM> may be in direct or indirect communication with other RANs that employ the same RAT as the RAN <NUM>/<NUM>/<NUM> or a different RAT. For example, in addition to being connected to the RAN <NUM>/<NUM>/<NUM>, which may be utilizing an E-UTRA radio technology, the core network <NUM>/<NUM>/<NUM> may also be in communication with another RAN (not shown) employing a GSM radio technology.

The core network <NUM>/<NUM>/<NUM> may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN <NUM>, the Internet <NUM>, and/or other networks <NUM>. For example, the networks <NUM> may include another core network connected to one or more RANs, which may employ the same RAT as the RAN <NUM>/<NUM>/<NUM> or a different RAT.

Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system <NUM> may include multi-mode capabilities, e.g., the WTRUs 102a, 102b, 102c, and 102d may include multiple transceivers for communicating with different wireless networks over different wireless links.

The transmit/receive element <NUM> may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface <NUM>/<NUM>/<NUM>. For example, in an embodiment, the transmit/receive element <NUM> may be an antenna configured to transmit and/or receive RF signals. In yet an embodiment, the transmit/receive element <NUM> may be configured to transmit and receive both RF and light signals.

Thus, in an embodiment, the WTRU <NUM> may include two or more transmit/receive elements <NUM> (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface <NUM>/<NUM>/<NUM>.

The processor <NUM> of the WTRU <NUM> may be coupled to, and may receive user input data from, the speaker/microphone <NUM>, the keypad <NUM>, and/or the display/touchpad/indicators <NUM> (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor <NUM> may also output user data to the speaker/microphone <NUM>, the keypad <NUM>, and/or the display/touchpad/indicators <NUM>. In an embodiment, the processor <NUM> may access information from, and store data in, memory that is not physically located on the WTRU <NUM>, such as on a server or a home computer (not shown).

For example, the power source <NUM> may include one or more dry cell batteries, solar cells, fuel cells, and the like.

For example, the peripherals <NUM> may include various sensors such as an accelerometer, biometrics (e.g., finger print) sensors, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port or other interconnect interfaces, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like.

The WTRU <NUM> may be embodied in other apparatuses or devices, such as a sensor, consumer electronics, a wearable device such as a smart watch or smart clothing, a medical or eHealth device, a robot, industrial equipment, a drone, a vehicle such as a car, truck, train, or airplane. The WTRU <NUM> may connect to other components, modules, or systems of such apparatuses or devices via one or more interconnect interfaces, such as an interconnect interface that may comprise one of the peripherals <NUM>.

As noted above, the RAN <NUM> may employ a UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface <NUM>. As shown in <FIG>, the RAN <NUM> may include Node-Bs 140a, 140b, 140c, which may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface <NUM>. The Node-Bs 140a, 140b, 140c may each be associated with a particular cell (not shown) within the RAN <NUM>. The RAN <NUM> may also include RNCs 142a, 142b. It will be appreciated that the RAN <NUM> may include any number of Node-Bs and RNCs while remaining consistent with an embodiment.

As shown in <FIG>, the Node-Bs 140a, 140b may be in communication with the RNC 142a. Additionally, the Node-B 140c may be in communication with the RNC 142b. The Node-Bs 140a, 140b, 140c may communicate with the respective RNCs 142a, 142b via an Iub interface. The RNCs 142a, 142b may be in communication with one another via an Iur interface. Each of the RNCs 142a, 142b may be configured to control the respective Node-Bs 140a, 140b, 140c to which it is connected. In addition, each of the RNCs 142a, 142b may be configured to carry out or support other functionality, such as outer loop power control, load control, admission control, packet scheduling, handover control, macro-diversity, security functions, data encryption, and the like.

As noted above, the RAN <NUM> may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface <NUM>.

In an embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the eNode-B 160a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

Each of the eNode-Bs 160a, 160b, and 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like.

The MME <NUM> may be connected to each of the eNode-Bs 160a, 160b, and 160c in the RAN <NUM> via an S1 interface and may serve as a control node. The MME <NUM> may also provide a control plane function for switching between the RAN <NUM> and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

The serving gateway <NUM> may be connected to each of the eNode-Bs 160a, 160b, and 160c in the RAN <NUM> via the S1 interface. The serving gateway <NUM> may generally route and forward user data packets to/from the WTRUs 102a, 102b, 102c. The serving gateway <NUM> may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

The RAN <NUM> may be an access service network (ASN) that employs IEEE <NUM> radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface <NUM>. As will be further discussed below, the communication links between the different functional entities of the WTRUs 102a, 102b, 102c, the RAN <NUM>, and the core network <NUM> may be defined as reference points.

As shown in <FIG>, the RAN <NUM> may include base stations 180a, 180b, 180c, and an ASN gateway <NUM>, though it will be appreciated that the RAN <NUM> may include any number of base stations and ASN gateways while remaining consistent with an embodiment. The base stations 180a, 180b, 180c may each be associated with a particular cell in the RAN <NUM> and may include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface <NUM>. In an embodiment, the base stations 180a, 180b, 180c may implement MIMO technology. Thus, the base station 180a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a. The base stations 180a, 180b, 180c may also provide mobility management functions, such as handoff triggering, tunnel establishment, radio resource management, traffic classification, quality of service (QoS) policy enforcement, and the like. The ASN gateway <NUM> may serve as a traffic aggregation point and may be responsible for paging, caching of subscriber profiles, routing to the core network <NUM>, and the like.

The air interface <NUM> between the WTRUs 102a, 102b, 102c and the RAN <NUM> may be defined as an R1 reference point that implements the IEEE <NUM> specification. In addition, each of the WTRUs 102a, 102b, and 102c may establish a logical interface (not shown) with the core network <NUM>. The logical interface between the WTRUs 102a, 102b, 102c and the core network <NUM> may be defined as an R2 reference point, which may be used for authentication, authorization, IP host configuration management, and/or mobility management.

The communication link between each of the base stations 180a, 180b, and 180c may be defined as an R8 reference point that includes protocols for facilitating WTRU handovers and the transfer of data between base stations. The communication link between the base stations 180a, 180b, 180c and the ASN gateway <NUM> may be defined as an R6 reference point. The R6 reference point may include protocols for facilitating mobility management based on mobility events associated with each of the WTRUs 102a, 102b, 102c.

The MIP-HA may be responsible for IP address management, and may enable the WTRUs 102a, 102b, and 102c to roam between different ASNs and/or different core networks. The MIP-HA <NUM> may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet <NUM>, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The AAA server <NUM> may be responsible for user authentication and for supporting user services. The gateway <NUM> may facilitate interworking with other networks. For example, the gateway <NUM> may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN <NUM>, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. In addition, the gateway <NUM> may provide the WTRUs 102a, 102b, 102c with access to the networks <NUM>, which may include other wired or wireless networks that are owned and/or operated by other service providers.

The core network entities described herein and illustrated in <FIG>, <FIG>, <FIG>, and <FIG> are identified by the names given to those entities in certain existing 3GPP specifications, but it is understood that in the future those entities and functionalities may be identified by other names and certain entities or functions may be combined in future specifications published by 3GPP, including future 3GPP NR specifications. Thus, the particular network entities and functionalities described and illustrated in <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> are provided by way of example only, and it is understood that the subject matter disclosed and claimed herein may be embodied or implemented in any similar communication system, whether presently defined or defined in the future.

<FIG> is a block diagram of an exemplary computing system <NUM> in which one or more apparatuses of the communications networks illustrated in <FIG>, <FIG>, <FIG> and <FIG> may be embodied, such as certain nodes or functional entities in the RAN <NUM>/<NUM>/<NUM>, Core Network <NUM>/<NUM>/<NUM>, PSTN <NUM>, Internet <NUM>, or Other Networks <NUM>. Computing system <NUM> may comprise a computer or server and may be controlled primarily by computer readable instructions, which may be in the form of software, wherever, or by whatever means such software is stored or accessed. Such computer readable instructions may be executed within a processor <NUM>, to cause computing system <NUM> to do work. The processor <NUM> may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the computing system <NUM> to operate in a communications network. Coprocessor <NUM> is an optional processor, distinct from main processor <NUM>, that may perform additional functions or assist processor <NUM>. Processor <NUM> and/or coprocessor <NUM> may receive, generate, and process data related to the methods and apparatuses disclosed herein.

In operation, processor <NUM> fetches, decodes, and executes instructions, and transfers information to and from other resources via the computing system's main data-transfer path, system bus <NUM>. Such a system bus connects the components in computing system <NUM> and defines the medium for data exchange. System bus <NUM> typically includes data lines for sending data, address lines for sending addresses, and control lines for sending interrupts and for operating the system bus. An example of such a system bus <NUM> is the PCI (Peripheral Component Interconnect) bus.

Memories coupled to system bus <NUM> include random access memory (RAM) <NUM> and read only memory (ROM) <NUM>. Such memories include circuitry that allows information to be stored and retrieved. ROMs <NUM> generally contain stored data that cannot easily be modified. Data stored in RAM <NUM> can be read or changed by processor <NUM> or other hardware devices. Access to RAM <NUM> and/or ROM <NUM> may be controlled by memory controller <NUM>. Memory controller <NUM> may provide an address translation function that translates virtual addresses into physical addresses as instructions are executed. Memory controller <NUM> may also provide a memory protection function that isolates processes within the system and isolates system processes from user processes. Thus, a program running in a first mode can access only memory mapped by its own process virtual address space; it cannot access memory within another process's virtual address space unless memory sharing between the processes has been set up.

In addition, computing system <NUM> may contain peripherals controller <NUM> responsible for communicating instructions from processor <NUM> to peripherals, such as printer <NUM>, keyboard <NUM>, mouse <NUM>, and disk drive <NUM>.

Display <NUM>, which is controlled by display controller <NUM>, is used to display visual output generated by computing system <NUM>. Such visual output may include text, graphics, animated graphics, and video. The visual output may be provided in the form of a graphical user interface (GUI). One example of the GUI is shown in FIG. Display <NUM> may be implemented with a CRT-based video display, an LCD-based flat-panel display, gas plasma-based flat-panel display, or a touch-panel. Display controller <NUM> includes electronic components required to generate a video signal that is sent to display <NUM>.

Still further, computing system <NUM> may contain communication circuitry, such as for example a network adapter <NUM>, that may be used to connect computing system <NUM> to an external communications network, such as the RAN <NUM>/<NUM>/<NUM>, Core Network <NUM>/<NUM>/<NUM>, PSTN <NUM>, Internet <NUM>, or Other Networks <NUM> of <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, to enable the computing system <NUM> to communicate with other nodes or functional entities of those networks. The communication circuitry, alone or in combination with the processor <NUM>, may be used to perform the transmitting and receiving steps of certain apparatuses, nodes, or functional entities described herein.

It is understood that any or all of the apparatuses, systems, methods and processes described herein may be embodied in the form of computer executable instructions (e.g., program code) stored on a computer-readable storage medium which instructions, when executed by a processor, such as processors <NUM> or <NUM>, cause the processor to perform and/or implement the systems, methods and processes described herein. Specifically, any of the steps, operations or functions described herein may be implemented in the form of such computer executable instructions, executing on the processor of an apparatus or computing system configured for wireless and/or wired network communications. Computer readable storage media include volatile and nonvolatile, removable and non-removable media implemented in any non-transitory (e.g., tangible or physical) method or technology for storage of information, but such computer readable storage media do not includes signals. Computer readable storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible or physical medium which can be used to store the desired information and which can be accessed by a computing system.

As specified in 3GPP TS <NUM>, Physical Layer Procedures, for Release13 and Release <NUM>, Licensed-assisted access (LAA) targets the carrier aggregation (CA) operation in which one or more low power secondary cells (SCells) operate in unlicensed spectrum in sub <NUM>. LAA deployment scenarios encompass scenarios with and without macro coverage, both outdoor and indoor small cell deployments, and both co-location and non-co-location (with ideal backhaul) between licensed and unlicensed carriers, as shown in <FIG>.

Scenario <NUM> of <FIG> depicts carrier aggregation between licensed macro cell (F1) and unlicensed small cell (F3). Meanwhile, scenario <NUM> of <FIG> depicts carrier aggregation between licensed small cell (F2) and unlicensed small cell (F3) without macro cell coverage. Subsequently, scenario <NUM> of <FIG> depicts a licensed macro cell and small cell (F1), with carrier aggregation between licensed small cell (F1) and unlicensed small cell (F3).

Further, scenario <NUM> <FIG> depicts a licensed macro cell (F1), licensed small cell (F2), and unlicensed small cell (F3). Scenario <NUM> includes carrier aggregation between licensed small cell (F2) and unlicensed small cell (F3). If there is ideal backhaul between macro cell and small cell, there can be carrier aggregation between macro cell (F1), licensed small cell (F2) and unlicensed small cell (F3). If dual connectivity is enabled, there can be dual connectivity between macro cell and small cell.

Since the unlicensed band can be utilized by different deployments specified by different standards, several regulatory requirements are imposed to insure fair coexistence between all incumbent users. For example, these regulatory requirements include constraints on transmit power mask, transmit bandwidth, interference with weather radars, etc..

In addition, another main requirement is a channel access procedure. For example, the LBT procedure is defined as a mechanism by which an equipment applies a clear channel assessment (CCA) check before using the channel. The CCA utilizes energy detection to determine the presence or absence of other signals on a channel. In turn, this determines whether a channel is occupied or clear, respectively. European and Japanese regulations mandate the usage of LBT in the unlicensed bands. Apart from regulatory requirements, carrier sensing via LBT is one way for fair sharing of the unlicensed spectrum. Hence, it is considered important for fair and friendly operation in the unlicensed spectrum in a single global solution framework.

In Release <NUM>, several channel access procedures are introduced to be performed by eNB and UE for both downlink (DL) and UL transmissions, respectively. The main channel access procedure is described in Section <NUM> of TS <NUM> Release <NUM>.

In mmWave, there is a wide range of unlicensed spectrum that can be further utilized to attain higher data rates than attained by operating in sub <NUM> frequency band. Consequently, RAN#<NUM> introduced a new SI for NR based access to unlicensed spectrum. The main goals of the current SI include studying the different physical channels and procedures in NR-U, and how they have to be modified. The goals also include introducing new physical channels or procedures to cope with NR-U challenges. This accounts for operating in mmWave deploying narrow beams for transmission and reception above <NUM> up to <NUM> or even above <NUM> bands. Procedures to enhance the co-existence between NR-U and other technologies operating in the unlicensed, e.g., Wi-Fi devices, LTE-based LAA devices, other NR-U devices, etc., and meet the regulatory requirements are currently under study.

According to an aspect of the application in NR, SSB allows the UE to obtain pertinent information of synchronization, frame boundary etc. In NR-U, UEs in different services (e.g., NR, WIFI) share the same unlicensed spectrum. Accordingly, the UE and gNB perform LBT to make sure the channel is not occupied before transmission. This feature introduces uncertainty to the periodic or semi-persistent scheduled transmissions such as SSB transmission. Considering the essentials of SSB in cell search, synchronization etc., it is envisaged that the SSB transmission may be categorized with high priority in channel access priority class with no backoff time or have a smallest backoff time among all the channel accessing backoff times.

In an embodiment, the SSB will have a higher possibility to be transmitted with the tradeoff that having a smaller maximum channel occupation time (MCOT) Tmcot, e.g., Tmcoc = <NUM> for channel access priority class <NUM> in LAA. In NR, the SSBs are transmitted in the SSB burst set which may last up to <NUM>. The whole SSB burst set transmission may not be able to fit into the Tmcot with priority class <NUM>, e.g., subcarrier spacing case A and case D. Therefore, it is envisaged in NR-U that the SSB burst set may be divided and transmitted in several subsets to fulfill the Tmcot requirement. An example is shown in <FIG> using subcarrier spacing case A in NR. The subcarrier spacing is <NUM> and carrier frequency <NUM> ≤ f ≤ <NUM>. In this case, the whole SSB burst set contains <NUM> SSBs which can't fill into the Tmcot. The gNB may divide the SSB burst set into two SSB burst subsets and each SSB burst subset's duration is less than <NUM>. The gNB performs LBT and transmits a first subset and repeats the procedure for the second subset.

Alternatively, the gNB may divide the SSB burst set into finer granularity such as <NUM> subsets where each subset contains <NUM> SSBs. It is envisaged that each subset may contain one or multiple SSB bursts. The periodicity of the SSB burst subset may be the same as the periodicity of the SSB burst set. Once the SSB burst subsets are determined, it may be transmitted in one of the following exemplary ways:.

In a first way, a UE may be configured by the gNB to receive multiple SSB burst subsets in one radio frame. An example of this way is exemplarily shown in <FIG>. In this case, a UE may be configured with one occasion to monitor all the SSB burst subsets.

In a second way, a UE may be configured by the gNB to receive the SSB burst subsets in different radio frames. An example of this way is exemplarily shown in <FIG>. In this case, a UE may be configured with different occasions to monitor different the SSB burst subsets.

For the case where the whole SSB burst set can be filled into the Tmcot such as the subcarrier spacing case B, C and E, the SSB burst set may also be divided into multiple SSB burst subsets and transmitted, e.g., the gNB may transmit the SSB burst subset after the LBT with a channel occupation duration shorter than the Tmcot.

According to yet another embodiment, to further enhance reliability of the SSB transmission, it is envisaged the SSB burst set/subset may be transmitted in the STTC (SSB Transmission Timing Configuration). An example depiction is provided in <FIG>. The time duration of the STTC may be pre-configured or specified. Alternatively, it may be configured/signaled by the gNB through RRC signaling, and/or MAC CE. For example, a UE may be configured with RRC message SSB_Tansmission_Timing_duration to indicate the duration of the STTC which may be <NUM>, <NUM> or etc. Within one STTC, multiple LBTs may be performed. The SSB burst set/subset may be transmitted after successful LBT and one or more SSB burst set/subset may be transmitted within one STTC. In an alternative embodiment, instead of only monitoring the SSB in one fixed location in time, a UE may monitor the SSB multiple times within the configured STTC to detect the transmitted SSB.

According to even another aspect of the application in NR, multiple SSBs are bundled in the SS burst set. The SS burst set is transmitted at the pre-defined/configured location. In NR-U, the gNB performs LBT before the SSB Burst transmission. The SSB transmission may still be bundled together. An example of success LBT for bundled SSB transmission at the pre-defined/configured location is shown in <FIG>.

According to this example in <FIG>, omni-direction LBT or beam-based directional LBT may be performed before the configured SSB transmission. With the successful LBT on the omni-direction or all the directional beams, the SSB can be transmitted on the pre-defined/configured location as an SSB burst set. No additional LBT is need during this SSB burst set transmission if the gNB is able to occupy the channel in this duration. It is envisaged that bundled SSB transmissions may be shifted in the STTC. In this case, the SSB index order is not changed within the bundled SSB transmission (e.g., SSB #<NUM>, SSB #<NUM>, SSB #<NUM>, SSB #<NUM>), but SSB #<NUM> location can be changed within the radio frame. Multiple LBT may be performed by the gNB within the STTC. The LBT may be performed by one of the following exemplary options:.

Option <NUM>: The gNB may perform LBT right before the possible SSB transmission location with one attempt. The possible SSB transmission location may be determined based on the resolution of the offset. This may be pre-defined in the spec or may be configured in the STTC. The possible location for SSBi = SSBi location specified + j*slot, where j is the iterations of LBT process after the initial LBT failure for SSBi. This assumes the SSB <NUM> is configured to be transmitted at symbol <NUM> of slot <NUM>. If the offset is a number of slots, the first possible SSB transmission location for SSB <NUM> is at symbol <NUM> of slot <NUM>, and the second possible SSB transmission location for SSB <NUM> is at symbol <NUM> of slot <NUM> etc. If the LBT succeeds, the gNB will transmit the shifted SSB. If the LBT fails, the gNB may perform LBT before the next possible SSB transmission location. This option is exemplarily depicted in <FIG>. The gNB may perform <NUM>µs LBT with no backoff time at symbol <NUM> in slot <NUM>. The LBT can be either omni-direction LBT or beam-based directional LBT. If it fails, the gNB may perform <NUM>µs LBT with no backoff time at symbol <NUM> in slot <NUM>. If the LBT succeeds in slot <NUM>, the bundled SSB may be transmitted starting from the symbol <NUM> of slot <NUM> to the symbol <NUM> of slot <NUM>.

Option <NUM>: The gNB may perform LBT before the possible SSB transmission location with multiple attempts. The possible SSB transmission location may be determined based on the resolution of the offset which may be pre-defined in the spec or may be configured in the STTC. The possible location for SSBi = SSBi location specified + j *slot, where j is the iterations of LBT process after the initial LBT failure for SSBi. If the LBT succeeds earlier than the possible SSB transmission location, reservation signal will be transmitted to occupy the channel and SSB will be transmitted on the possible SSB transmission location. An exemplary illustration is shown in <FIG>. The gNB may perform <NUM>µs LBT with no backoff time at symbol <NUM> in slot <NUM>. The LBT can be either omni-direction LBT or beam-based directional LBT. If it fails, the gNB may continue to perform LBT. If the LBT succeeds at symbol <NUM> in slot <NUM>, reservation signal may be transmitted to hold the channel which may last a few number of symbols. Note the reservation signal cannot be arbitrarily long due to the limitation of the MCOT. Ultimately, the bundled SSB may be transmitted starting from the symbol <NUM> of slot <NUM> to the symbol <NUM> of slot <NUM>.

In an embodiment, the bundled SSB transmission is shifted in the STTC. In this scenario, a fixed offset Δ is introduced to all the SSBs from the radio frame boundary. For example, the offset may be in number of slots as shown in <FIG> and <FIG>. In this case, Δ= k slot(s) where k = <NUM>, <NUM>, <NUM>,. , K - <NUM>.

In an alternative embodiment, the offset may be in number of SSB locations. The possible SSB transmission location may be determined based on the resolution of the offset and may be predefined in the spec or may be configured in the STTC. This assumes SSB <NUM> is configured to be transmitted at symbol <NUM> of slot <NUM>. If the offset is the number of SSB locations, the first possible SSB transmission location determined by the offset resolution and iterations of LBT process after the initial LBT failure for SSB <NUM> is at symbol <NUM> of slot <NUM>. The second possible SSB transmission location for SSB <NUM> is at symbol <NUM> of slot <NUM>, etc. An exemplary embodiment is shown in <FIG>. The LBT may fail at symbol <NUM> in slot <NUM> but succeed at symbol <NUM> in slot <NUM>. In this scenario, the bundled SSB may be shifted by one SSB location and transmitted. In other words, the SSB <NUM> is transmitted on the location supposed to transmit for SSB <NUM>, the SSB <NUM> is transmitted on the location supposed to transmit SSB <NUM>, etc. The offset will be the SSB index difference between the schedule SSB index and the actual transmitted SSB index.

In the example shown in <FIG>, the offset is equal to <NUM>. The offset is a logic value, a UE need to map the logic value to physical location based on a specific SSB configuration. In this example, LBT is performed right before the possible SSB transmission location determined by the offset resolution and iterations of LBT process after the initial LBT failure and no reservation signal is used. In an alternative embodiment, a reservation signal may be employed for this solution.

In another case, the SSB index order may be changed within the bundled SSB transmission when the SSB bundle is shifted. For example, the SSB index order may be cyclically shifted, e.g., the cyclically shifted SSB index order may be SSB #<NUM>, SSB #<NUM>, SSB #<NUM>, SSB #<NUM>.

According to an embodiment, to determine the frame boundary, a UE needs to be aware of the information of both the SSB block index and offset Δ. An example of offset Δ is shown in <FIG>. To achieve the information of the offset, a UE may indicate the value of offset Δ using one of the following options:.

Option <NUM>: The value of offset Δ may be indicated by the payload of PBCH. For example, PBCH of all beams may carry same payload and indicate the offset from the frame boundary (<NUM> bits for <NUM> locations). For example, if there are <NUM> or <NUM> SSBs within the SSB burst set transmission, the reserved PBCH payload bits aA+<NUM>,aA+<NUM> may be used to indicate the offset Δ. A UE may determine the frame boundary with the information of SSB block index and offset Δ. Alternatively, some additional field may be added to the PBCH to convey the value of offset Δ.

Option 1a: The offset Δ may be indicated by applying a mask to the CRC bits of the PBCH payload. The UE decodes the PBCH and applies different masks to the CRC. The mask that makes the CRC checksum successful is used to indicate the offset Δ.

Option <NUM>: The value of offset Δ may be indicated through PBCH DMRS. The PBCH DMRS may be initialized by the offset Δ. An example is provided below as follows: <MAT>.

When a UE detects the PBCH DMRS by blindly cross-correlation, it determines the offset value based on the PBCH DMRS sequence.

Option <NUM>: The value of offset Δ may be jointly indicated through PBCH DMRS and payload of PBCH, e.g., assume <NUM> bits are needed to indicate the offset Δ, the two MSB may be indicated in the payload of the PBCH. The one LSB may be indicated by the PBCH DMRS by using different sequences initialized by LSB of the offset.

Option <NUM>: This is based upon the requirement of channel occupation in the frequency of the unlicensed band. In NR-U, the SSB may be repeated in the frequency domain and transmitted on the same beam to achieve the requirement. An exemplary embodiment is depicted in <FIG>.

In NR, the PBCH DMRS is used to blindly detect up to <NUM> LSB bits of the SSB index. If the offset Δ also must be indicated, the number of blind decoding increases and the PBCH DMRS may not be sufficiently robust. It is envisaged that the SSB repetition may advantageously be employed to indicate the offset Δ.

If the SSB is repeated, spreading codes may be applied to the PBCH DMRS. Different spreading code may be used for different SSBs, e.g., the PBCH DMRS of SSB <NUM> may be spread with [<NUM><NUM><NUM><NUM>], the PBCH DMRS of SSB <NUM> may be spread with [<NUM><NUM> -<NUM> -<NUM>], the PBCH DMRS of SSB <NUM> may be spread with [<NUM> -<NUM><NUM> -<NUM>] etc. The value of offset Δ may be implicitly indicated by the spreading code. For example, when Δ= <NUM>, the PBCH DMRS of SSB is spread with [<NUM><NUM><NUM><NUM>], when Δ= <NUM>, the PBCH DMRS of SSB is spread with [<NUM><NUM> -<NUM> -<NUM>], etc..

Option <NUM>: The value of offset Δ may be indicated by the RMSI PDCCH or RMSI PDSCH. In NR-U, the RMSI CORESET and/or RMSI PDSCH may be transmitted in the same slot associated with the transmitted SSB. For example, the RMSI CORESET and SSB may be FDM-ed in the same slot as shown in <FIG>. A new field may be added to the RMSI PDCCH to carry the SSB offset value Δ. When a UE detects the SSB, it may decode the RMSI PDCCH that transmitted in the same slot to determine the offset that the SSB may be shifted. Therefore, the UE can determine out the frame boundary. A UE may determine the location of the RMSI PDCCH by some rules pre-defined in the spec or by the RMSI-PDCCH-Config message configured in MIB. The UE may determine PDCCH monitoring occasions from the k least significant bits of RMSI-PDCCH-Config. If both M and O provided by the k least significant bits of RMSI-PDCCH-Config are equal to <NUM>, the RMSI CORESET may be FDM-ed with SSB in the same slot.

In an alternative embodiment, the RSMI CORESET may be TDM-ed with the SSB in the same slot as shown in <FIG>. For example, the SSB <NUM> is transmitted from symbol <NUM> to symbol <NUM>. The corresponding RMSI CORESET and/or PDSCH may be transmitted from symbol <NUM> to symbol <NUM>. In the frequency domain, The RBs used to transmit the RMSI CORESET/PDSCH and the SSB may be different as shown in the figure; TDM-ed and FDM-ed. In an alternative embodiment, the same RBs may be used to transmit the RMSI CORESET/PDSCH and the SSB.

In yet another embodiment, gNB may perform LBT one beam a time. For example, starting from SSB <NUM>, gNB first performs LBT for SSB <NUM>. If SSB <NUM> is transmitted, gNB transmits SSB <NUM> and performs LBT for next SSB, e.g., SSB <NUM>. If SSB <NUM> cannot be transmitted, the remaining SSB burst (SSB <NUM>, SSB <NUM>, SSB <NUM>, SSB <NUM>) is shifted and gNB performs LBT for SSB <NUM> in next time occasion. If SSB <NUM> is transmitted in time occasion k but SSB <NUM> cannot be transmitted in time occasion k+<NUM>. The remaining SSB burst (SSB <NUM>, SSB <NUM>, SSB <NUM>) is shifted and gNB performs LBT for SSB <NUM> in the next time occasion (time occasion k+<NUM>). This procedure is repeated until all the SSBs in the burst are transmitted or until the STTC window is expired.

For initial cell selection for a UE in idle state or inactive state, it is envisaged to assume some fixed STTC, e.g., the UE may assume the duration of the STTC is <NUM>, as pre-defined in the spec. The UE may determine the frame boundary based on the pre-defined STTC, detected SSB transmission offset Δ, etc..

For a UE in connected state, the UE may be configured with the STTC by one or more of the RRC signaling, MAC CE. The UE may determine the frame boundary based on the SSB index, detected SSB transmission offset Δ etc. An example of the procedure for monitoring and receiving the bundled SSB transmission is shown in <FIG>.

According to another aspect of the application in NR-U, it is envisaged that SSB transmission may not be bundled, e.g., the gNB may perform beam-based directional LBT for all the beams before the schedule SSB transmission. For the beams with successful LBT, the corresponding SSBs will be transmitted. For the beams with LBT failure, the gNB may skip the transmission of corresponding SSBs. This is exemplarily shown in <FIG>. The gNB performs beam-based directional LBT. It may perform LBT for all <NUM> beams before slot <NUM> of subframe <NUM>. Alternatively, it may perform LBT for beam <NUM> and beam <NUM> before slot <NUM> of subframe <NUM>. It may perform LBT for beam <NUM> and beam <NUM> before slot <NUM> of subframe <NUM>. Only LBT for beam <NUM> and beam <NUM> are succeeded. Therefore, only SSB #<NUM> and SSB #<NUM> are transmitted at the scheduled location. Meanwhile, SSB #<NUM> and SSB #<NUM> are dropped.

Dropping SSB transmission may be critical given its essentiality in NR systems. To improve reliability of SSB transmission, in addition to scheduled SSB transmission, a UE may be configured with opportunistic SSB transmission to monitor the dropped SSB transmission due to LBT failure, e.g., SSB #<NUM> and SSB #<NUM> are dropped due to beam-based LBT failure in the scheduled SSB transmission. Then, the gNB may perform beam-based directional LBT for the dropped SSBs before configured opportunistic SSB transmission. The corresponding SSBs will be transmitted during the configured opportunistic SSB transmission if the beam-based LBT is succeeded. The LBT can either be LBT with no backoff time, or LBT with a contention window such as channel access priority class <NUM>. The resources may not be used for other transmissions regardless of the SSB being transmitted in opportunistic SSB transmission. In so doing, the opportunistic resource may be empty if the SSB is not sent. A UE may always assume data is rate matched around the opportunistic resource. Within one opportunistic SSB transmission, multiple SSBs may be transmitted after corresponding LBT successes. Alternatively, opportunistic SSB transmission may be beam specific, e.g., each SSB is configured with dedicated opportunistic SSB transmission configuration. The opportunistic SSB transmission may be configured with one of the following options:.

Option <NUM>: A UE may be configured to monitor the opportunistic SSB transmission within the STTC after the scheduled SSB transmission. An example embodiment is shown in <FIG>. In this example, opportunistic SSB transmission is beam specific and SSB <NUM> and SSB <NUM> both fail in scheduled transmission. Successful LBT for SSB <NUM> is performed at symbol <NUM> in slot <NUM>. SSB1 is transmitted from symbol <NUM> to symbol <NUM> in configured slot <NUM>. A successful LBT for SSB <NUM> is performed at symbol <NUM> in slot <NUM>. Then the SSB1 is transmitted from symbol <NUM> to symbol <NUM> in slot <NUM>.

In this case, SSB specific offset ΔSSB,i may be introduced to each SSB from the frame boundary. A UE may determine the frame boundary by the information of both SSB specific offset ΔSSB,i indicated and the SSB index.

Option <NUM>: A UE may be not configured with STTC. A UE may be configured to monitor opportunistic SSB transmission occasions between two scheduled SSB transmissions. An exemplary embodiment is shown in <FIG>. SSB <NUM> and SSB <NUM> both fail in the scheduled transmission. A LBT for SSB <NUM> and SSB <NUM> is performed at symbol <NUM> in slot k. Within opportunistic SSB transmission occasion, one shot LBT and a transmission attempt may be performed. Alternatively, STTC may be configured where multiple LBT and transmission attempts may be performed. If STTC is configured, the SSB offset ΔSSB,i or Δ may be employed by the UE to determine the frame boundary.

Option <NUM>: A UE may be configured with STTC. The UE may be also configured with opportunistic SSB transmission occasions both two STTCs. An exemplary embodiment is shown in <FIG>. Within the STTC, if any SSB is not transmitted at the schedule location due to LBT failure, it may be shifted (e.g., transmit in opportunistic transmission or opportunistic transmission b etc.). Between two STTCs, a UE may be configured with SSB transmission occasions, i.e., transmit in opportunistic transmission occasion <NUM>, opportunistic transmission occasion <NUM>, etc. The gNB may perform cat <NUM> or cat <NUM> LBT before each opportunistic transmission occasion. If the channel is clear, the gNB will transmit the SSB within the opportunistic transmission occasion. If the channel is not clear, the gNB will skip the opportunistic transmission occasion. For each opportunistic transmission occasion, the same SSB may be transmitted, e.g., gNB may do LBT and try to transmit all the <NUM> SSBs (SSB0, SSB <NUM>, SSB <NUM>, SSB3) in both opportunistic transmission occasion <NUM> and opportunistic transmission occasion <NUM>. In an alternative embodiment, different SSBs may be transmitted in different opportunistic transmission occasions, e.g., gNB may do LBT and try to transmit SSB <NUM> and SSB <NUM> in opportunistic transmission occasion <NUM>. The gNB may do LBT and attempt transmission of SSB <NUM> and SSB <NUM> in opportunistic transmission occasion <NUM>.

According to another embodiment, for initial cell selection, a UE in idle state or inactive state may assume some fixed STTC, e.g., duration, as pre-defined in the spec. The UE may determine the frame boundary based on the pre-defined STTC, detected SSB transmission offset Δ or ΔSSB,i etc..

For a UE in connected state, the UE may be configured with the STTC by one or more of the RRC signaling and MAC CE. The UE may determine the frame boundary based on the pre-defined/configured STTC, detected SSB transmission offset Δ or ΔSSB,i etc. An example of the procedure for monitoring and receiving the SSB transmission with opportunistic transmission is shown in <FIG>.

According to yet another aspect of the application, it is envisaged that a UE may be configured to monitor dedicated STTC for each SSB or each two SSBs. An example is shown in <FIG>.

Within one SSB burst set transmission period (e.g., <NUM>), the STTC may be configured for each two SSBs transmitted in one slot (instead of the whole burst or half burst). Assume <NUM> numerology and <NUM>, SSB <NUM> and SSB <NUM> may be transmitted in any slot of the <NUM> slots. Then SSB <NUM> and SSB <NUM> may slide across the <NUM> slots within its STTC. The STTCs may be contiguous, e.g., staring from <NUM>, <NUM>, <NUM> etc. Alternatively, the STTCs may be non-contiguous, e.g., staring from <NUM>, <NUM>, <NUM> etc. Within each STTC, the offset Δ of the SSB transmission need to be indicated to the UE for determining the frame boundary.

For initial cell selection, a UE in idle state or inactive state, it may assume some fixed STTC, e.g., duration and time location, as pre-defined in the spec. The UE may determine the frame boundary based on the pre-defined STTC, SSB transmission offset Δ etc..

For a UE in a connected state, the UE may be configured with the STTC by one or more of the RRC signaling and MAC CE. The UE may determine the frame boundary based on the configured STTC, SSB transmission offset Δ etc..

An exemplary procedure for monitoring and receiving the dedicated SSB transmission with STTC is provided in <FIG>. The UE may repeat the procedure for different SSBs in different configured STTC.

In yet a further aspect of the application, in NR, the SSB is transmitted on the fixed SSB location, e.g., the SSB #<NUM> is transmitted on SSB location <NUM>, SSB #<NUM> is transmitted on SSB location <NUM>. Therefore, within the SSB transmission, the order of the SSB index is fixed, e.g., SSB #<NUM>, SSB #<NUM>, SSB #<NUM>, SSB #<NUM>.

In NR-U, it is envisaged that a UE may be configured to monitor the SSB transmission with flexible order index. , SSB index order can be different within the burst. The same SSB may be transmitted on different SSB locations within the SSB burst set/subset transmission. An exemplary embodiment is shown in <FIG>.

The gNB may perform beam-based directional LBT for all the beams before slot <NUM> of subframe <NUM>. If the channel for the scheduled SSB is available, the gNB may transmit the scheduled SSB on the scheduled location, e.g., the channel is available for SSB1, then the SSB <NUM> is transmitted on the SSB location <NUM>. If the channel for the scheduled SSB is not available while the channel for the other SSB is available, the gNB may transmit the available SSB on the that location, e.g., the channel for SSB <NUM> is not available while the channel for SSB2 is available, then the SSB <NUM> may be transmitted on the SSB location <NUM>. For the SSBs that have already been transmitted, the gNB will not perform beam-based LBT for that beam in the rest LBT occasion within one SSB burst set/subset transmission. When multiple un-transmitted SSB channels are available for one SSB location, the SSB that has missed its schedule SSB location may have higher transmission priority. For example, SSB <NUM> cannot be transmitted on SSB location <NUM> due to LBT failure. While the channels for SSB <NUM> and SSB <NUM> are available. SSB <NUM> may be transmitted on SSB location <NUM>. If some of the SSBs are not able to be transmitted within the MCOT, gNB may drop those beams. Alternatively, STTC may be configured and opportunistic transmission may be performed for the failed SSBs.

To determine where the SSB is actually transmitted, a UE may provide with the offset value ΔSSS,i for each SSB. The offset value may be negative. If so, one more bit may be needed to represent whether the value is positive or negative.

In an alternative embodiment, the SSB location index information may be carried by the PBCH DMRS and PBCH payload. For example, if there are <NUM> SSBs within the SSB burst set transmission, the PBCH payload bits aA+<NUM>,aA+<NUM>,aA+<NUM> may be the 6th, 5th, and 4th bits of SSB location index. The PBCH DMRS may be initialized by the SSB location index with <MAT><MAT>
where,.

In this case, the PBCH payload maybe different for the same SSB index in different SSB transmissions. A UE may use the SSB block location index to determine the frame boundary. Furthermore, if STTC is used to enhance the SSB transmission, for initial cell selection, a UE in idle state or inactive state may assume some fixed STTC, e.g., duration, as pre-defined in the spec. The UE may determine the frame boundary based on the pre-defined STTC, detected SSB transmission offset Δ, SSB block location index etc. For a UE in connected state, the UE may be configured with the STTC by one or more of the RRC signaling and MAC CE. The UE may determine the frame boundary based on the pre-defined/configured STTC, detected SSB transmission offset Δ, SSB location index etc. An exemplary embodiment of the procedure for monitoring and receiving the SSB transmission with flexible index order is illustrated in <FIG>.

The solutions proposed for indicating the offset Δ may also be applied here to indicate the SSB block location index.

According to yet even another aspect of the application, when a STTC is used for SSB transmission, the SSB transmission may be shifted in the timing window. If the SSB transmission is shifted, it may overlap with other configurations or scheduling such as semi-persistent scheduling or PRACH resources. In this scenario, the following options are envisaged:.

Option <NUM>: When a UE detects the SSB transmission is shifted, the UE may assume the other configuration and/or scheduling are not shifted. An example of the impact of the SSB shifting on the PRACH resource is exemplary shown in <FIG>. These illustrations show scenarios where the SSB <NUM> is transmitted on the schedule location. The timing difference between the SSB <NUM> transmission and the corresponding PRACH resource is denoted as offset k. <FIG> shows the scenario where the SSB <NUM> transmission is shifted by Δ due to the LBT failure at the scheduled location. The PRACH resource is not shifted. As a result, the timing difference between the SSB transmission and corresponding PRACH resource becomes k - Δ.

If k - Δ is smaller than the time a UE needs to switch from Dl to UL, the UE may drop the PRACH. A UE may first determine the frame boundary using the achieved SSB index and SSB transmission offset Δ. Then, the UE may perform PRACH procedure at the configured RACH resource (same location) regardless of whether the SSB transmission shifts. If a UE missed the first PRACH resource due to the SSB shifting, it may perform the RACH procedure at the next available PRACH resource. The same rationale may also apply to the paging indication (PI), semi persistent resources, etc. If the SSB overlaps with other transmissions, such as other reference signals or data due to the shifting, the other transmission may be dropped, punctured by the SSB, or rate matched around the SSB.

Option <NUM>: When a UE detects the SSB transmission has shifted, the UE may assume the other configuration and/or scheduling has shifted, respectively. An exemplary embodiment depicting the impact of SSB shifting on the PRACH resource is shown in <FIG>. When the SSB <NUM> transmission is shifted by Δ due to LBT failure at the scheduled location, the PRACH resource may be also shifted. For example, the PRACH resource is also shifted by Δ. In so doing, the timing difference between the reception of the SSB <NUM> and PRACH resource is not changed, e.g., still is offset k.

When the PRACH is shifted, it may follow one of the following alternatives:.

The same idea may also apply to the paging indication (PI), semi persistent resources, etc. If the SSB is overlapped with other transmissions such as other reference signals or data due to shifting, the other transmission may be dropped, punctured by the SSB, or rate matched around the SSB.

This solution may work well for the configuration that is FDM-ed with the SSB. An example is shown in <FIG>. If the RMSI is FDM-ed transmitted with the SSB, it will respectively shift if the SSB shifts.

According to the present disclosure, it is understood that any or all of the systems, methods and processes described herein may be embodied in the form of computer executable instructions, e.g., program code, stored on a computer-readable storage medium which instructions, when executed by a machine, such as a computer, server, M2M terminal device, M2M gateway device, transit device or the like, perform and/or implement the systems, methods and processes described herein. Specifically, any of the steps, operations or functions described above may be implemented in the form of such computer executable instructions. Computer readable storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, but such computer readable storage media do not includes signals. Computer readable storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other physical medium which can be used to store the desired information and which can be accessed by a computer.

Claim 1:
A wireless transit / receive unit (<NUM>), WTRU, comprising:
a non-transitory memory (<NUM>) including instructions stored thereon for monitoring synchronous signals and physical broadcast channels, SSBs, from a network node; and
a processor (<NUM>), operably coupled to the non-transitory memory, configured to execute the instructions of:
receiving, from a network node, an SSB Transmission Timing Configuration, STTC, where the STTC is a time interval with plural locations accommodating transmission of the SSBs for shifting of a scheduled SSB transmission following Listen Before Talk, LBT, failure, wherein a time duration of the STTC is configured via RRC signaling;
monitoring the STTC for the SSBs; and
determining a first one of the SSBs in a first slot of a subframe in a scheduled SSB transmission in the STTC has been transmitted at a first scheduled location, where the scheduled SSB transmission of the first one of the SSBs is based upon confirmation of a successful LBT available channel prior to the scheduled SSB transmission in the STTC.