Patent Publication Number: US-2021194745-A1

Title: Efficient utilization of ssbs in new radio systems

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/608,186, filed Oct. 25, 2019, which is based on PCT filing PCT/US2018/030204, filed Apr. 30, 2018, which claims the benefit of U.S. provisional application Nos. 62/500,901, filed May 3, 2017; 62/519,532, filed Jun. 14, 2017; and Ser. No. 62/543,119, filed Aug. 9, 2017, the contents of each are hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     General requirements set out by ITU-R, NGMN and 3GPP, broadly classify the use cases for emerging 5G systems include Enhanced Mobile Broadband (eMBB), Massive Machine Type Communications (mMTC) and Ultra Reliable and Low latency Communications (URLLC). Different use cases may focus on different requirements such as higher data rate, higher spectrum efficiency, low power and higher energy efficiency, lower latency and higher reliability. A wide range of spectrum bands ranging from 700 MHz to 80 GHz may be considered for a variety of deployment scenarios. 
     As carrier frequency increases, severe path loss can be experienced and may limit coverage. Transmission in millimeter wave systems may also suffer from non-line-of-sight losses such as diffraction loss, penetration loss, oxygen absorption loss, foliage loss or the like. During initial access, a base station and wireless transmit/receive units (WTRUs) may need to overcome these high path losses and discover each other. 
     SUMMARY 
     Methods and an apparatus for performing synchronization in New Radio (NR) systems are disclosed. According to the disclosed subject matter, an operational frequency band may be determined. The frequency band may correspond to a WTRU. On a condition that the operational frequency band is a lower frequency, a synchronization signal block (SSB) index may be implicitly. On a condition that the operational frequency band is a higher frequency, an SSB index may be determined based on a hybrid method which includes determining the SSB index using both an implicit and an explicit method. A configuration of actually transmitted SSBs may be determined using a multi-level two stage compressed indication where SSB groups are determined based on a coarse indicator and actually transmitted SSBs with the SSB groups are determined based on a fine indicator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, wherein like reference numerals in the figures indicate like elements, and wherein: 
         FIG. 1A  is a system diagram illustrating an example communications system in which one or more disclosed embodiments may be implemented; 
         FIG. 1B  is a system diagram illustrating an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in  FIG. 1A  according to an embodiment; 
         FIG. 1C  is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communications system illustrated in  FIG. 1A  according to an embodiment; 
         FIG. 1D  is a system diagram illustrating a further example RAN and a further example CN that may be used within the communications system illustrated in  FIG. 1A  according to an embodiment; 
         FIG. 2  shows an example of synchronization signal (SS) burst with x ms cycle and multiple SSBs in a SS burst; 
         FIG. 3A  shows a diagram for determining SS Block (SSB) presence, index, and half radio frame timing; 
         FIG. 3B  shows an example diagram for determining a SSB timing index indicator and half radio frame indicator; 
         FIG. 4  shows an example SSB index time indication employing hybrid CRC masking and control field; 
         FIG. 5  shows an SSB index time indication employing hybrid scrambling code and control field; 
         FIG. 6  shows an SSB transmission method; 
         FIG. 7  shows an SSB timing information indication method; 
         FIG. 8  shows SSB indication employing starting point and its associated segment-wise bitmap; and 
         FIG. 9  shows SSB indication employing SSB grouping and reduced bitmap. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a diagram illustrating an example communications system  100  in which one or more disclosed embodiments may be implemented. The communications system  100  may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system  100  may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems  100  may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique-word DFT-Spread OFDM (ZT UW DTS-s OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like. 
     As shown in  FIG. 1A , the communications system  100  may include wireless transmit/receive units (WTRUs)  102   a,    102   b,    102   c,    102   d,  a RAN  104 / 113 , a CN  106 / 115 , a public switched telephone network (PSTN)  108 , the Internet  110 , and other networks  112 , 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  102   a,    102   b,    102   c,    102   d  may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs  102   a,    102   b,    102   c,    102   d,  any of which may be referred to as a “station” and/or a “STA”, may be configured to transmit and/or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. Any of the WTRUs  102   a,    102   b,    102   c  and  102   d  may be interchangeably referred to as a UE. 
     The communications systems  100  may also include a base station  114   a  and/or a base station  114   b.  Each of the base stations  114   a,    114   b  may be any type of device configured to wirelessly interface with at least one of the WTRUs  102   a,    102   b,    102   c,    102   d  to facilitate access to one or more communication networks, such as the CN  106 / 115 , the Internet  110 , and/or the other networks  112 . By way of example, the base stations  114   a,   114   b  may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a gNB, a NR NodeB, a site controller, an access point (AP), a wireless router, and the like. While the base stations  114   a,    114   b  are each depicted as a single element, it will be appreciated that the base stations  114   a,    114   b  may include any number of interconnected base stations and/or network elements. 
     The base station  114   a  may be part of the RAN  104 / 113 , 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  114   a  and/or the base station  114   b  may be configured to transmit and/or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for a wireless service to a specific geographical area that may be relatively fixed or that may change over time. The cell may further be divided into cell sectors. For example, the cell associated with the base station  114   a  may be divided into three sectors. Thus, in one embodiment, the base station  114   a  may include three transceivers, i.e., one for each sector of the cell. In an embodiment, the base station  114   a  may employ multiple-input multiple output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming may be used to transmit and/or receive signals in desired spatial directions. 
     The base stations  114   a,    114   b  may communicate with one or more of the WTRUs  102   a,    102   b,    102   c,    102   d  over an air interface  116 , which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface  116  may be established using any suitable radio access technology (RAT). 
     More specifically, as noted above, the communications system  100  may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station  114   a  in the RAN  104 / 113  and the WTRUs  102   a,    102   b,    102   c  may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface  115 / 116 / 117  using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink (DL) Packet Access (HSDPA) and/or High-Speed UL Packet Access (HSUPA). 
     In an embodiment, the base station  114   a  and the WTRUs  102   a,    102   b,    102   c  may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface  116  using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A) and/or LTE-Advanced Pro (LTE-A Pro). 
     In an embodiment, the base station  114   a  and the WTRUs  102   a,    102   b,    102   c  may implement a radio technology such as NR Radio Access, which may establish the air interface  116  using New Radio (NR). 
     In an embodiment, the base station  114   a  and the WTRUs  102   a,    102   b,    102   c  may implement multiple radio access technologies. For example, the base station  114   a  and the WTRUs  102   a,    102   b,    102   c  may implement LTE radio access and NR radio access together, for instance using dual connectivity (DC) principles. Thus, the air interface utilized by WTRUs  102   a,    102   b,    102   c  may be characterized by multiple types of radio access technologies and/or transmissions sent to/from multiple types of base stations (e.g., a eNB and a gNB). 
     In other embodiments, the base station  114   a  and the WTRUs  102   a,    102   b,    102   c  may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like. 
     The base station  114   b  in  FIG. 1A  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, an industrial facility, an air corridor (e.g., for use by drones), a roadway, and the like. In one embodiment, the base station  114   b  and the WTRUs  102   c,    102   d  may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In an embodiment, the base station  114   b  and the WTRUs  102   c,    102   d  may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station  114   b  and the WTRUs  102   c,    102   d  may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR etc.) to establish a picocell or femtocell. As shown in  FIG. 1A , the base station  114   b  may have a direct connection to the Internet  110 . Thus, the base station  114   b  may not be required to access the Internet  110  via the CN  106 / 115 . 
     The RAN  104 / 113  may be in communication with the CN  106 / 115 , 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  102   a,    102   b,    102   c,    102   d.  The data may have varying quality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN  106 / 115  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. 1A , it will be appreciated that the RAN  104 / 113  and/or the CN  106 / 115  may be in direct or indirect communication with other RANs that employ the same RAT as the RAN  104 / 113  or a different RAT. For example, in addition to being connected to the RAN  104 / 113 , which may be utilizing a NR radio technology, the CN  106 / 115  may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology. 
     The CN  106 / 115  may also serve as a gateway for the WTRUs  102   a,    102   b,    102   c,    102   d  to access the PSTN  108 , the Internet  110 , and/or the other networks  112 . The PSTN  108  may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet  110  may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and/or the internet protocol (IP) in the TCP/IP internet protocol suite. The networks  112  may include wired and/or wireless communications networks owned and/or operated by other service providers. For example, the networks  112  may include another CN connected to one or more RANs, which may employ the same RAT as the RAN  104 / 113  or a different RAT. 
     Some or all of the WTRUs  102   a,    102   b,    102   c,    102   d  in the communications system  100  may include multi-mode capabilities (e.g., the WTRUs  102   a,    102   b,    102   c,    102   d  may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU  102   c  shown in  FIG. 1A  may be configured to communicate with the base station  114   a,  which may employ a cellular-based radio technology, and with the base station  114   b,  which may employ an IEEE 802 radio technology. 
       FIG. 1B  is a system diagram illustrating an example WTRU  102 . As shown in  FIG. 1B , the WTRU  102  may include a processor  118 , a transceiver  120 , a transmit/receive element  122 , a speaker/microphone  124 , a keypad  126 , a display/touchpad  128 , non-removable memory  130 , removable memory  132 , a power source  134 , a global positioning system (GPS) chipset  136 , and/or other peripherals  138 , among others. It will be appreciated that the WTRU  102  may include any sub-combination of the foregoing elements while remaining consistent with an embodiment. 
     The processor  118  may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor  118  may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU  102  to operate in a wireless environment. The processor  118  may be coupled to the transceiver  120 , which may be coupled to the transmit/receive element  122 . While  FIG. 1B  depicts the processor  118  and the transceiver  120  as separate components, it will be appreciated that the processor  118  and the transceiver  120  may be integrated together in an electronic package or chip. 
     The transmit/receive element  122  may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station  114   a ) over the air interface  116 . For example, in one embodiment, the transmit/receive element  122  may be an antenna configured to transmit and/or receive RF signals. In an embodiment, the transmit/receive element  122  may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element  122  may be configured to transmit and/or receive both RF and light signals. It will be appreciated that the transmit/receive element  122  may be configured to transmit and/or receive any combination of wireless signals. 
     Although the transmit/receive element  122  is depicted in  FIG. 1B  as a single element, the WTRU  102  may include any number of transmit/receive elements  122 . More specifically, the WTRU  102  may employ MIMO technology. Thus, in one embodiment, the WTRU  102  may include two or more transmit/receive elements  122  (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface  116 . 
     The transceiver  120  may be configured to modulate the signals that are to be transmitted by the transmit/receive element  122  and to demodulate the signals that are received by the transmit/receive element  122 . As noted above, the WTRU  102  may have multi-mode capabilities. Thus, the transceiver  120  may include multiple transceivers for enabling the WTRU  102  to communicate via multiple RATs, such as NR and IEEE 802.11, for example. 
     The processor  118  of the WTRU  102  may be coupled to, and may receive user input data from, the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128  (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor  118  may also output user data to the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128 . In addition, the processor  118  may access information from, and store data in, any type of suitable memory, such as the non-removable memory  130  and/or the removable memory  132 . The non-removable memory  130  may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory  132  may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor  118  may access information from, and store data in, memory that is not physically located on the WTRU  102 , such as on a server or a home computer (not shown). 
     The processor  118  may receive power from the power source  134 , and may be configured to distribute and/or control the power to the other components in the WTRU  102 . The power source  134  may be any suitable device for powering the WTRU  102 . For example, the power source  134  may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like. 
     The processor  118  may also be coupled to the GPS chipset  136 , which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU  102 . In addition to, or in lieu of, the information from the GPS chipset  136 , the WTRU  102  may receive location information over the air interface  116  from a base station (e.g., base stations  114   a,    114   b ) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU  102  may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment. 
     The processor  118  may further be coupled to other peripherals  138 , which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals  138  may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs and/or video), a universal serial bus (USB) port, 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, a Virtual Reality and/or Augmented Reality (VR/AR) device, an activity tracker, and the like. The peripherals  138  may include one or more sensors, the sensors may be one or more of a gyroscope, an accelerometer, a hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor; an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and/or a humidity sensor. 
     The WTRU  102  may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the UL (e.g., for transmission) and downlink (e.g., for reception) may be concurrent and/or simultaneous. The full duplex radio may include an interference management unit  139  to reduce and or substantially eliminate self-interference via either hardware (e.g., a choke) or signal processing via a processor (e.g., a separate processor (not shown) or via processor  118 ). In an embodiment, the WTRU  102  may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the UL (e.g., for transmission) or the downlink (e.g., for reception)). 
       FIG. 1C  is a system diagram illustrating the RAN  104  and the CN  106  according to an embodiment. As noted above, the RAN  104  may employ an E-UTRA radio technology to communicate with the WTRUs  102   a,    102   b,    102   c  over the air interface  116 . The RAN  104  may also be in communication with the CN  106 . 
     The RAN  104  may include eNode-Bs  160   a,    160   b,    160   c,  though it will be appreciated that the RAN  104  may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs  160   a,    160   b,    160   c  may each include one or more transceivers for communicating with the WTRUs  102   a,    102   b,    102   c  over the air interface  116 . In one embodiment, the eNode-Bs  160   a,    160   b,    160   c  may implement MIMO technology. Thus, the eNode-B  160   a,  for example, may use multiple antennas to transmit wireless signals to, and/or receive wireless signals from, the WTRU  102   a.    
     Each of the eNode-Bs  160   a,    160   b,    160   c  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 UL and/or DL, and the like. As shown in  FIG. 1C , the eNode-Bs  160   a,    160   b,    160   c  may communicate with one another over an X2 interface. 
     The CN  106  shown in  FIG. 1C  may include a mobility management entity (MME)  162 , a serving gateway (SGW)  164 , and a packet data network (PDN) gateway (or PGW)  166 . While each of the foregoing elements are depicted as part of the CN  106 , it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator. 
     The MME  162  may be connected to each of the eNode-Bs  162   a,    162   b,    162   c  in the RAN  104  via an S1 interface and may serve as a control node. For example, the MME  162  may be responsible for authenticating users of the WTRUs  102   a,    102   b,    102   c,  bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs  102   a,    102   b,    102   c,  and the like. The MME  162  may provide a control plane function for switching between the RAN  104  and other RANs (not shown) that employ other radio technologies, such as GSM and/or WCDMA. 
     The SGW  164  may be connected to each of the eNode Bs  160   a,    160   b,    160   c  in the RAN  104  via the S1 interface. The SGW  164  may generally route and forward user data packets to/from the WTRUs  102   a,    102   b,    102   c.  The SGW  164  may perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when DL data is available for the WTRUs  102   a,    102   b,    102   c,  managing and storing contexts of the WTRUs  102   a,    102   b,    102   c,  and the like. 
     The SGW  164  may be connected to the PGW  166 , which may provide the WTRUs  102   a,    102   b,    102   c  with access to packet-switched networks, such as the Internet  110 , to facilitate communications between the WTRUs  102   a,    102   b,    102   c  and IP-enabled devices. 
     The CN  106  may facilitate communications with other networks. For example, the CN  106  may provide the WTRUs  102   a,    102   b,    102   c  with access to circuit-switched networks, such as the PSTN  108 , to facilitate communications between the WTRUs  102   a,    102   b,    102   c  and traditional land-line communications devices. For example, the CN  106  may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN  106  and the PSTN  108 . In addition, the CN  106  may provide the WTRUs  102   a,    102   b,    102   c  with access to the other networks  112 , which may include other wired and/or wireless networks that are owned and/or operated by other service providers. 
     Although the WTRU is described in  FIGS. 1A-1D  as a wireless terminal, it is contemplated that in certain representative embodiments that such a terminal may use (e.g., temporarily or permanently) wired communication interfaces with the communication network. 
     In representative embodiments, the other network  112  may be a WLAN. 
     A WLAN in Infrastructure Basic Service Set (BSS) mode may have an Access Point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have an access or an interface to a Distribution System (DS) or another type of wired/wireless network that carries traffic in to and/or out of the BSS. Traffic to STAs that originates from outside the BSS may arrive through the AP and may be delivered to the STAs. Traffic originating from STAs to destinations outside the BSS may be sent to the AP to be delivered to respective destinations. Traffic between STAs within the BSS may be sent through the AP, for example, where the source STA may send traffic to the AP and the AP may deliver the traffic to the destination STA. The traffic between STAs within a BSS may be considered and/or referred to as peer-to-peer traffic. The peer-to-peer traffic may be sent between (e.g., directly between) the source and destination STAs with a direct link setup (DLS). In certain representative embodiments, the DLS may use an 802.11e DLS or an 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and the STAs (e.g., all of the STAs) within or using the IBSS may communicate directly with each other. The IBSS mode of communication may sometimes be referred to herein as an “ad-hoc” mode of communication. 
     When using the 802.11ac infrastructure mode of operation or a similar mode of operations, the AP may transmit a beacon on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20 MHz wide bandwidth) or a dynamically set width via signaling. The primary channel may be the operating channel of the BSS and may be used by the STAs to establish a connection with the AP. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) may be implemented, for example in in 802.11 systems. For CSMA/CA, the STAs (e.g., every STA), including the AP, may sense the primary channel. If the primary channel is sensed/detected and/or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS. 
     High Throughput (HT) STAs may use a 40 MHz wide channel for communication, for example, via a combination of the primary 20 MHz channel with an adjacent or nonadjacent 20 MHz channel to form a 40 MHz wide channel. 
     Very High Throughput (VHT) STAs may support 20MHz, 40 MHz, 80 MHz, and/or 160 MHz wide channels. The 40 MHz, and/or 80 MHz, channels may be formed by combining contiguous 20 MHz channels. A 160 MHz channel may be formed by combining 8 contiguous 20 MHz channels, or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80 configuration, the data, after channel encoding, may be passed through a segment parser that may divide the data into two streams. Inverse Fast Fourier Transform (IFFT) processing, and time domain processing, may be done on each stream separately. The streams may be mapped on to the two 80 MHz channels, and the data may be transmitted by a transmitting STA. At the receiver of the receiving STA, the above described operation for the 80+80 configuration may be reversed, and the combined data may be sent to the Medium Access Control (MAC). 
     Sub 1 GHz modes of operation are supported by 802.11af and 802.11ah. The channel operating bandwidths, and carriers, are reduced in 802.11af and 802.11ah relative to those used in 802.11n, and 802.11ac. 802.11af supports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah may support Meter Type Control/Machine-Type Communications, such as MTC devices in a macro coverage area. MTC devices may have certain capabilities, for example, limited capabilities including support for (e.g., only support for) certain and/or limited bandwidths. The MTC devices may include a battery with a battery life above a threshold (e.g., to maintain a very long battery life). 
     WLAN systems, which may support multiple channels, and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include a channel which may be designated as the primary channel. The primary channel may have a bandwidth equal to the largest common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and/or limited by a STA, from among all STAs in operating in a BSS, which supports the smallest bandwidth operating mode. In the example of 802.11ah, the primary channel may be 1 MHz wide for STAs (e.g., MTC type devices) that support (e.g., only support) a 1 MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and/or other channel bandwidth operating modes. Carrier sensing and/or Network Allocation Vector (NAV) settings may depend on the status of the primary channel. If the primary channel is busy, for example, due to a STA (which supports only a 1 MHz operating mode), transmitting to the AP, the entire available frequency bands may be considered busy even though a majority of the frequency bands remains idle and may be available. 
     In the United States, the available frequency bands, which may be used by 802.11ah, are from 902 MHz to 928 MHz. In Korea, the available frequency bands are from 917.5 MHz to 923.5 MHz. In Japan, the available frequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidth available for 802.11ah is 6 MHz to 26 MHz depending on the country code. 
       FIG. 1D  is a system diagram illustrating the RAN  113  and the CN  115  according to an embodiment. As noted above, the RAN  113  may employ an NR radio technology to communicate with the WTRUs  102   a,    102   b,    102   c  over the air interface  116 . The RAN  113  may also be in communication with the CN  115 . 
     The RAN  113  may include gNBs  180   a,    180   b,    180   c,  though it will be appreciated that the RAN  113  may include any number of gNBs while remaining consistent with an embodiment. The gNBs  180   a,    180   b,    180   c  may each include one or more transceivers for communicating with the WTRUs  102   a,    102   b,    102   c  over the air interface  116 . In one embodiment, the gNBs  180   a,    180   b,    180   c  may implement MIMO technology. For example, gNBs  180   a,    108   b  may utilize beamforming to transmit signals to and/or receive signals from the gNBs  180   a,    180   b,    180   c.  Thus, the gNB  180   a,  for example, may use multiple antennas to transmit wireless signals to, and/or receive wireless signals from, the WTRU  102   a.  In an embodiment, the gNBs  180   a,    180   b,    180   c  may implement carrier aggregation technology. For example, the gNB  180   a  may transmit multiple component carriers to the WTRU  102   a  (not shown). A subset of these component carriers may be on unlicensed spectrum while the remaining component carriers may be on licensed spectrum. In an embodiment, the gNBs  180   a,    180   b,    180   c  may implement Coordinated Multi-Point (CoMP) technology. For example, WTRU  102   a  may receive coordinated transmissions from gNB  180   a  and gNB  180   b  (and/or gNB  180   c ). 
     The WTRUs  102   a,    102   b,    102   c  may communicate with gNBs  180   a,    180   b,    180   c  using transmissions associated with a scalable numerology. For example, the OFDM symbol spacing and/or OFDM subcarrier spacing may vary for different transmissions, different cells, and/or different portions of the wireless transmission spectrum. The WTRUs  102   a,    102   b,    102   c  may communicate with gNBs  180   a,    180   b,    180   c  using subframe or transmission time intervals (TTIs) of various or scalable lengths (e.g., containing varying number of OFDM symbols and/or lasting varying lengths of absolute time). 
     The gNBs  180   a,    180   b,    180   c  may be configured to communicate with the WTRUs  102   a,    102   b,    102   c  in a standalone configuration and/or a non-standalone configuration. In the standalone configuration, WTRUs  102   a,    102   b,    102   c  may communicate with gNBs  180   a,    180   b,    180   c  without also accessing other RANs (e.g., such as eNode-Bs  160   a,    160   b,    160   c ). In the standalone configuration, WTRUs  102   a,    102   b,    102   c  may utilize one or more of gNBs  180   a,    180   b,    180   c  as a mobility anchor point. In the standalone configuration, WTRUs  102   a,    102   b,    102   c  may communicate with gNBs  180   a,    180   b,    180   c  using signals in an unlicensed band. In a non-standalone configuration WTRUs  102   a,    102   b,    102   c  may communicate with/connect to gNBs  180   a,    180   b,    180   c  while also communicating with/connecting to another RAN such as eNode-Bs  160   a,    160   b,    160   c.  For example, WTRUs  102   a,    102   b,    102   c  may implement DC principles to communicate with one or more gNBs  180   a,    180   b,    180   c  and one or more eNode-Bs  160   a,    160   b,    160   c  substantially simultaneously. In the non-standalone configuration, eNode-Bs  160   a,    160   b,    160   c  may serve as a mobility anchor for WTRUs  102   a,    102   b,    102   c  and gNBs  180   a,    180   b,    180   c  may provide additional coverage and/or throughput for servicing WTRUs  102   a,    102   b,    102   c.    
     Each of the gNBs  180   a,    180   b,    180   c  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 UL and/or DL, support of network slicing, dual connectivity, interworking between NR and E-UTRA, routing of user plane data towards User Plane Function (UPF)  184   a,    184   b,  routing of control plane information towards Access and Mobility Management Function (AMF)  182   a,    182   b  and the like. As shown in  FIG. 1D , the gNBs  180   a,    180   b,    180   c  may communicate with one another over an Xn interface. 
     The CN  115  shown in  FIG. 1D  may include at least one AMF  182   a,    182   b,  at least one UPF  184   a,    184   b,  at least one Session Management Function (SMF)  183   a,    183   b,  and possibly a Data Network (DN)  185   a,    185   b.  While each of the foregoing elements are depicted as part of the CN  115 , it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator. 
     The AMF  182   a,    182   b  may be connected to one or more of the gNBs  180   a,    180   b,    180   c  in the RAN  113  via an N2 interface and may serve as a control node. For example, the AMF  182   a,    182   b  may be responsible for authenticating users of the WTRUs  102   a,    102   b,    102   c,  support for network slicing (e.g., handling of different PDU sessions with different requirements), selecting a particular SMF  183   a,    183   b,  management of the registration area, termination of NAS signaling, mobility management, and the like. Network slicing may be used by the AMF  182   a,    182   b  in order to customize CN support for WTRUs  102   a,    102   b,    102   c  based on the types of services being utilized WTRUs  102   a,    102   b,    102   c.  For example, different network slices may be established for different use cases such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for machine type communication (MTC) access, and/or the like. The AMF  162  may provide a control plane function for switching between the RAN  113  and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and/or non-3GPP access technologies such as WiFi. 
     The SMF  183   a,    183   b  may be connected to an AMF  182   a,    182   b  in the CN  115  via an N11 interface. The SMF  183   a,    183   b  may also be connected to a UPF  184   a,    184   b  in the CN  115  via an N4 interface. The SMF  183   a,    183   b  may select and control the UPF  184   a,    184   b  and configure the routing of traffic through the UPF  184   a,    184   b.  The SMF  183   a,    183   b  may perform other functions, such as managing and allocating UE IP address, managing PDU sessions, controlling policy enforcement and QoS, providing downlink data notifications, and the like. A PDU session type may be IP-based, non-IP based, Ethernet-based, and the like. 
     The UPF  184   a,    184   b  may be connected to one or more of the gNBs  180   a,    180   b,    180   c  in the RAN  113  via an N3 interface, which may provide the WTRUs  102   a,    102   b,    102   c  with access to packet-switched networks, such as the Internet  110 , to facilitate communications between the WTRUs  102   a,    102   b,    102   c  and IP-enabled devices. The UPF  184 ,  184   b  may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering downlink packets, providing mobility anchoring, and the like. 
     The CN  115  may facilitate communications with other networks. For example, the CN  115  may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN  115  and the PSTN  108 . In addition, the CN  115  may provide the WTRUs  102   a,    102   b,    102   c  with access to the other networks  112 , which may include other wired and/or wireless networks that are owned and/or operated by other service providers. In one embodiment, the WTRUs  102   a,    102   b,    102   c  may be connected to a local Data Network (DN)  185   a,    185   b  through the UPF  184   a,    184   b  via the N3 interface to the UPF  184   a,    184   b  and an N6 interface between the UPF  184   a,    184   b  and the DN  185   a,    185   b.    
     In view of  FIGS. 1A-1D , and the corresponding description of  FIGS. 1A-1D , one or more, or all, of the functions described herein with regard to one or more of: WTRU  102   a - d,  Base Station  114   a - b,  eNode-B  160   a - c,  MME  162 , SGW  164 , PGW  166 , gNB  180   a - c,  AMF  182   a - ab,  UPF  184   a - b,  SMF  183   a - b,  DN  185   a - b,  and/or any other device(s) described herein, may be performed by one or more emulation devices (not shown). The emulation devices may be one or more devices configured to emulate one or more, or all, of the functions described herein. For example, the emulation devices may be used to test other devices and/or to simulate network and/or WTRU functions. 
     The emulation devices may be designed to implement one or more tests of other devices in a lab environment and/or in an operator network environment. For example, the one or more emulation devices may perform the one or more, or all, functions while being fully or partially implemented and/or deployed as part of a wired and/or wireless communication network in order to test other devices within the communication network. The one or more emulation devices may perform the one or more, or all, functions while being temporarily implemented/deployed as part of a wired and/or wireless communication network. The emulation device may be directly coupled to another device for purposes of testing and/or may performing testing using over-the-air wireless communications. 
     The one or more emulation devices may perform the one or more, including all, functions while not being implemented/deployed as part of a wired and/or wireless communication network. For example, the emulation devices may be utilized in a testing scenario in a testing laboratory and/or a non-deployed (e.g., testing) wired and/or wireless communication network in order to implement testing of one or more components. The one or more emulation devices may be test equipment. Direct RF coupling and/or wireless communications via RF circuitry (e.g., which may include one or more antennas) may be used by the emulation devices to transmit and/or receive data. 
     LTE initial synchronization utilizes a cell search procedure where a WTRU acquires time and frequency synchronization with a cell and detects the Cell ID of that cell. The LTE synchronization signals are transmitted in the 0 th  and 5 th  subframes of every radio frame and are used for time and frequency synchronization during initialization. A WTRU may synchronize sequentially to the OFDM symbol, slot, subframe, half-frame, and radio frame based on the synchronization signals. The two synchronization signals are the Primary Synchronization Signal (PSS) and the Secondary Synchronization Signal (SSS). The PSS may be used to obtain slot, subframe and half-frame boundary. It may also provide physical layer cell identity (PCI) within the cell identity group. The SSS may be used to obtain the radio frame boundary. It also enables the UE to determine the cell identity group, which may range from 0 to 167. Following a successful synchronization and PCI acquisition, the WTRU may decode the Physical Broadcast Channel (PBCH) with the help of cell specific reference signals (CRS) and acquire the master information block (MIB) information regarding system bandwidth, System Frame Number (SFN) and PHICH configuration. LTE synchronization signals and PBCH may be transmitted continuously according to a standardized periodicity. 
     In an LTE system, a single beam is used for initial access. In a New Radio (NR) system, a synchronization signal burst (SS burst) may be used when multiple beams are used for initial access and where the SS burst may be transmitted periodically such as, for example, approximately every 20 ms, and each SS burst may include one or more SSB. One or more SSBs in a SS burst may be associated with one or more beams and the number of SSBs in a SS burst may be determined by a gNB based on the number of beams used at the gNB. As an example, if N beams are used at a gNB, N SSBs may be used or transmitted in a SS burst. Each SSB may include a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a PBCH (physical broadcasting channel).  FIG. 2  shows an example of synchronization signal (SS) burst with x ms cycle and multiple SSBs in SS bursts  200 . As shown in  FIG. 2 , each SS burst  200  may include SSBs  201  labeled 1 through N which may be cycled every x ms and may each comprise a PSS  202 , a SS  203 , and a PCBH  204  component. As shown, the X axis indicates time and the Y axis indicated frequency. 
     In NR systems, synchronization signals (SS) may be used to achieve time synchronization between a gNB and a wireless transmit/receive unit (WTRU). More particularly, a WTRU may need to know the SSB information including a block index time indication to be used to decode such block information and for time synchronization. Further, some SSBs may be used to transmit synchronization signals while other SSBs may not be used to transmit synchronization signals. This may be partly due to antenna and beam configurations at gNB or Tx/RX points (TRP). Accordingly, techniques to obtain SSB index time indication and to reuse or use the unused SSBs are needed. Additionally, used SSBs may serve as reference points for a WTRU to perform more precise measurement. Access to unused SSB information may allow a WTRU to obtain or determine used SSB information. Accordingly, a WTRU may use the known reference timing points for measurement purposes. 
     In accordance with the subject matter disclosed herein, a WTRU may know SSB information including time indication to acquire time synchronization between gNB/TRP and the WTRU. Further, SSBs may carry an index, which may be used for time indication for a WTRU to acquire time synchronization. The index may be indicated to the WTRU to support more precise measurement as well as to increase system efficiency and throughput. In accordance with the subject matter disclosed herein, the proposed solutions may also be used for acquiring time synchronization or SSB information between devices such as, for example, gNBs, between TRPs and between gNB and TRP. 
     Efficient techniques for determining SSB presence, SSB index, and half radio frame (HRF) timing are shown in  FIG. 3A . These techniques may be employed by any applicable component such as, for example, a processor internal or external to a WTRU. At  310 , a WTRU configuration may be detected and, at  320 , a determination may be made regarding whether the frequency band associated with the WTRU configuration detected at  310  is equal to, greater than or less than a threshold frequency band. As a non-limiting example, the threshold frequency band may be 6 GHz and a determination regarding whether the frequency band for a detected SSB is greater than (or equal to) or less than 6 GHz may be made at  320 . 
     If the frequency band for an SSB is determined to be below the threshold frequency band, as shown at  330 , an SSB index may be determined implicitly from a PBCH demodulation reference signal (DMRS) sequence. Alternatively, if the frequency band for an SSB is determined to be above or equal to a threshold frequency band, as shown at  335 , a portion of an SSB index may be determined implicitly from a PBCH DMRS sequence and the rest of the SSB index may be determined explicitly from a PBCH payload. An SSB index determined implicitly may be determined based on the energy levels or correlation levels of a signal such that bits in the SSB index may correspond to energy levels or correlation levels of a signal exceeding an energy or correlation threshold. A correlator may be employed to determine the energy level or correlation level. It will be understood that other techniques or thresholds may be used to detect the bits in an SSB index. 
     As shown at  340 , HRF timing may be determined based on either the implicit SSB index determination of  330  or the partial implicit and partial explicit determination of the SSB index of  335 . 
     At  350 , a configuration of transmitted SSBs may be received via any applicable manner such as via a multi-level two stage compressed indication. In a multi-level two stage compressed indication, as shown at  352 , the configuration may include a first indicator which may contain information to enable a determination of which SSB groups are transmitted. The first indicator at  352  may be a coarse indicator that provides a Group-Bitmap to enable determination of which SSB groups are transmitted. As shown at  354 , the configuration may include a second indicator that may contain information to enable a determination of SS/PBCH blocks are transmitted within an SS group. The second indicator at  354  may be a fine indicator that provides a Bitmap in Group to enable determination of which SS/PBCH blocks are transmitted within an SSB group, e.g., within a transmitted SSB group. 
     At  360 , one or more actually transmitted SSBs may be monitored. The one or more actually transmitted SSBs may correspond to the SSBs for which the configuration is received at  350 . 
       FIG. 3B  shows an example diagram for determining SSB presence, index, and HRF for a SSB with a frequency band that is greater than or equal to a threshold frequency band, as disclosed herein. As noted in  FIG. 3A , a portion of the SSB block may be determined implicitly and a portion may be determined explicitly for SSBs with a frequency band greater than a threshold frequency band. As shown in  FIG. 3B , a signal with a PBCH may be received at  365  and a determination may be made that a characteristic of the signal, such as a frequency band, is greater than or equal to a threshold, such as a frequency threshold. Based on the determination, a hybrid technique for SSB index indication may be applied such that, at  370  an implicit determination is made and at  380  an explicit determination is made. At  370 , a portion  371  of the SSB index may be indicated based on PBCH DMRS detection. Additionally, a half radio frame indicator  372  may also be indicated based on PBCH DMRS detection. At  380 , a portion  381  of the SSB index may be indicated based on PBCH payload decoding. Additionally, a half radio frame indicator  382  may also be indicated based on PBCH payload decoding. 
     At  385 , the half radio frame indicator  382  indicated via the explicit PBCH decoding at  380  may be compared to the half radio frame indicator  372  indicated via the implicit PBCH DMRS detection at  370 . A match of the two half radio frame indicators  372  and  382  may result in the determination and/or confirmation of the half radio frame indicator h0  387 . 
     The portion  371  of the SSB index indicated via the explicit PBCH decoding at  380  may be combined with the portion  381  of the SSB index indicated via the implicit PBCH DMRS detection at  370  at  390 . The combining may provide the SSB timing index indicator  395  that includes, for example, bits indicated via the PBCH decoding  38  and the PBCH DMRS detection  370 . Additionally, the PBCH channel and payload may be decoded to obtain other timing information  383  such as a system frame numbers. 
     As disclosed herein, SSB index time indications may be based on frequency bands. A value L may vary based on frequency bands and may denote a maximum number of SSBs in a SS burst set. Higher frequency bands may employ larger number of beams while lower frequency bands may employ smaller number of beams. Accordingly, as an example, a larger L may correspond to a higher frequency band and a smaller L may correspond to a lower frequency band. Further, SSB index time indications, SSB index frequency indications, or combination of SSB index time and frequency indications may be based on frequency bands. It will be understood that the solutions disclosed herein for SSB index indication may be applied to SSB index time and/or frequency indication. As a non-limiting example, an SSB index time and/or frequency indication may be received via a multi-level two stage compressed indication. 
     According to an embodiment, an SSB index time indication technique may be determined based on a threshold value such that an SSB with a characteristic lower than the threshold value may result in indicating a SSB index using an first method and a characteristic higher than the threshold value may result in indicating n SSB index using a second different method. The threshold value may be a threshold L value and may be an integer value such as, for example, 16. For a given SSB if L&lt;threshold L value, such as L=2, 4 or 8, an SSB index may be indicated using a first method. The first method may include implicit methods which may employ, for example, CRC masking, sequence-based indications, indication using DMRS, scrambling, or the like. According to such implicit methods, L CRC masks or L sequences, L hypotheses, L hypotheses using DMRS, scrambling, etc. may be used. If L&gt;threshold L value, such as L=64, SSB index may be indicated using another method. For example, an SSB index may be carried in NR-PBCH using explicit methods, implicit methods or combination of explicit and implicit methods such as a hybrid method. It will be understood that an L value may be determined based on the configuration of a WTRU such that, for a given configuration such as a frequency band associated with the WTRU, a corresponding L value may be determined. 
     SSB index indication may be based on L in a hybrid method such that an implicit SSB index indication is used if L&lt;T where T=16, L=4 and 8 and an explicit SSB index indication is used if L&gt;=T where T=16 and L=64. SSB index indications may be based on L in another hybrid method such that an implicit SSB index indication is used if L&lt;T where, for example, T=16, L=4 and 8, and a combination of implicit and explicit SSB index indication is used if L&gt;=T where, for example, T=16 and L=64 
     According to another hybrid method, LSBs for SSB index may be indicated using CRC masking or sequence-based indication, indication using DMRS, scrambling, etc., whereas MSBs for SSB index may be indicated in a payload or signal. For example, K1 bits for LSB may be indicated using PBCH CRC masking or sequence-based indication, indication using DMRS, scrambling, etc., and K2 bits for MSB may be indicated in a PBCH payload or PBCH signal. 
     A unified hybrid method across different frequency bands for SSB index may be implemented such that a WTRU or any applicable device may perform any one or a combination of receiving a PBCH signal and decoding a PBCH channel, performing CRC demasking or sequence-based detection, detection using DMRS, descrambling, etc., obtaining K1 bits from CRC demasking or sequence-based detection, detection using DMRS, descrambling, etc., and mapping, and/or outputting K1 bits as an SSB index time indication. For higher frequency bands, a WTRU or other applicable device may continue to perform any one or a combination of obtaining K2 bits from control field of the decoded PBCH channel and outputting both K1 and K2 bits as SSB index time indication bits. Here, K1 may be the LSBs for SSB index time indication and K2 may be the MSBs for SSB index time indication. 
       FIG. 4  shows an example SSB index time indication employing hybrid CRC masking and control field. As shown, at  410 , a PBCH signal is received. At  420 , a PBCH channel is decoded and a CRC is demasked at  430 . As a result of the CRC demasking at  430 , K1 bits may be obtained from the CRC masking mapping at  440 . At  450 , a determination whether the frequency meets a frequency band threshold is made. The determination may be made based on whether the frequency is greater than, equal to, or less than a threshold frequency. If the frequency is below the threshold frequency, K1 bits are output as a SSB index time indication at  454 . If the frequency is above the threshold frequency, K2 bits are obtained from a control filed in the PBCH channel at  456  and K1+K2 bits are output as a SSB index time indication at  460 . 
     Table 1 shows an example CRC masking table for an SSB index time indication where of L=4. As shown, the CRC masking #0 may correspond to SSB index time indication bits  00  and CRC masking #3 may correspond to SSB index time indication bits  11 . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 CRC masking 
               
            
           
           
               
               
               
            
               
                   
                   
                 SSB index time indication bits 
               
               
                   
                 CRC masking 
                 (L = 4) 
               
               
                   
                   
               
               
                   
                 CRC # 0 
                 00 
               
               
                   
                 CRC # 1 
                 01 
               
               
                   
                 CRC # 2 
                 10 
               
               
                   
                 CRC # 3 
                 11 
               
               
                   
                   
               
            
           
         
       
     
     According to another hybrid method, scrambling processing may be used for to indicate SSB indexes and LSBs for SSB index and MSBs for SSB indexes may be indicated in payloads or signals. For example, K1 bits for LSBs of an SSB index may be indicated using PBCH scrambling and K2 bits for MSBs of SSB index may be indicated in PBCH payload or PBCH signal. 
     For lower frequency bands, a WTRU or other applicable device may perform one or more of receiving a PBCH signal and descrambling a PBCH channel, decoding a PBCH channel, performing CRC verification, obtaining K1 bits from scrambling mapping and CRC verification, and outputting K1 bits as SSB index time indication. For higher frequency bands, a WTRU or other applicable device may additionally perform one or more of obtaining K2 bits from control field of decoded a PBCH channel, and outputting both K1 and K2 bits as SSB index time indication bits. K1 may be the LSBs for SSB index time indication and K2 may be the MSBs for SSB index time indication. 
       FIG. 5  shows an example SSB index time indication employing a hybrid scrambling code and control field. As shown, at  510 , a PBCH signal is received. At  520 , a PBCH signal is descrambled a PBCH channel is decoded at  530 . At  540  a CRC check is conducted and K1 bits are obtained from applicable scramble code or scramble code mapping at  550 . For example, scramble code or scramble code mapping may be performed for a PBCH, such as PBCH DMRS and/or PBCH payload. At  560 , a determination whether the frequency meets a frequency band threshold is made. The determination may be made based on whether the frequency is greater than, equal to, or less than a threshold frequency. If the frequency is below the threshold frequency, K1 bits are output as a SSB index time indication at  564 . If the frequency is above the threshold frequency, K2 bits are obtained from a control filed in the PBCH channel at  566  and K1+K2 bits are output as a SSB index time indication at  570 . 
     According to another hybrid method, SSB index indication may be based on partitioning. Here, SSB index indication may be implicit for least significant bits (LSBs) such as, for example, K1 bits, and explicit for most significant bits (MSBs) such as, for example, K2 bits. The L threshold value used in such a solution may be, for example, 16 or 64. Alternatively or in addition, the SSB index may be partitioned into two parts including SSB index within an SS burst (SSB group) and SS burst index (SSB group index) within a SS burst set. An SS burst may be a SSB group or the like. An SS burst index may be SSB group index or the like. The SSB index indication may be implicit for SSB index within an SS burst, for example, for K1 bits, and explicit for SS burst index within an SS burst set, for example, for K2 bits. The L threshold value used in such a solution may be, for example, 16 or 64. Alternatively or in addition, the SSB index bits may be partitioned into two parts based on K1 bits and K2 bits. The SSB indication may be explicit for SSB index, such as, for example, for K1 bits if only K1 bits are present and may be implicit for SSB index based on K2 if total bits exceed K1 bits. 
     SSB index indication for one partition may be explicit such that part of an SSB index may correspond to part of a payload on NR-PBCH. For example, K2 bits may be carried in a PBCH payload. The K2 bits may be coded, rate-matched and interleaved along with other bits of a NR-PBCH and transmitted on data resource elements (RE). An explicit transmission may suffer from delay in decoding such that, for example, an SSB index may not be determined until decoding of the NR-PBCH at a receiver. Accordingly, for coherently detecting the NR-PBCH, a self-contained DMRS may be added. Although the DMRS may comprise one or more sequences known to a receiver, different sequences and shifts may be applied to implicitly indicate a part of an SSB index such as the part that is not explicitly indicated. As an example, K1 bits may be indicated implicitly using a DMRS and a receiver may detect which hypothesis of a DMRS variation is mostly likely transmitted to implicitly decode the SSB index. Accordingly, the receiver may not wait for an entire PBCH to be decoded to determine the SSB index. 
     A DMRS may comprise a gold sequence such that two M sequences may be generated and two different cyclic shifts m0 and m1 for the two M sequences may undergo an XOR operation with each other. The resulting sequence may be binary phase shift keying (BPSK) modulated and then may be repeated or truncated to fill the DMRS. A WTRU or other applicable device may use a combination function of m0 and m1 to indicate SSB index. Table 2 shows an example number of bits and number of m combinations (m0, m1) that correspond to L, a number of SSBs. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 L (# of SSBs) 
                 # of bits 
                 # of m combinations (m0, m1) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 2 
                 4 
               
               
                 8 
                 3 
                 8 
               
               
                 6 
                 6 
                 64 
               
               
                   
               
            
           
         
       
     
     As an example, for L=4, the m0 and m1 combinations of Table 3 may be applied. As shown, a 0 SSB index may correspond to a (m0 m1) combination of (0 1). 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 SSB index 
                 (m0 m1) combination 
               
               
                   
                   
               
             
            
               
                   
                 0 
                 (0 1) 
               
               
                   
                 1 
                 (0 2) 
               
               
                   
                 2 
                 (1 2) 
               
               
                   
                 3 
                 (1 3) 
               
               
                   
                   
               
            
           
         
       
     
     A DMRS may comprise one M sequence where m0 may be used to indicate SSB index. Table 4 shows an example number of bits and number of m0 values that correspond to L, a number of SSBs. As shown, as an example, 4 SSBs may correspond to 2 bits and 4 m0 m sequences. 
     
       
         
           
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 L (# of SSBs) 
                 # of bits 
                 # of m0 (m sequence) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 2 
                 4 
               
               
                 8 
                 3 
                 8 
               
               
                 64 
                 6 
                 64 
               
               
                   
               
            
           
         
       
     
     As an example, for L=4, the m0 values of Table 5 may be applicable. As shown, a 0 SSB index may correspond to a 0 m0 value. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 SSB index 
                 m0 
               
               
                   
                   
               
             
            
               
                   
                 0 
                 0 
               
               
                   
                 1 
                 1 
               
               
                   
                 2 
                 2 
               
               
                   
                 3 
                 3 
               
               
                   
                   
               
            
           
         
       
     
     A DMRS may comprise multiple M sequences where sequence IDs and shift m0 may be used to indicate SSB index. 
     A DMRS may comprise a Zadoff-Chu (ZC) sequence. ZC sequences may be used to indicate an SSB index such that CS may be used to indicate the SSB index, a root index of ZC may be used to indicate the SSB index, or a combination of CS and root index may be used to indicate SSB index. Table 6 shows an example number of bits and number of CS values that correspond to L, a number of SSBs. 
     
       
         
           
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 L (# of SSBs) 
                 # of bits 
                 # of CS (ZC) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 2 
                 4 
               
               
                 8 
                 3 
                 8 
               
               
                 64 
                 6 
                 64 
               
               
                   
               
            
           
         
       
     
     As an example, for L=4, the CS ZC values of Table 7 may be applicable. As shown, a 0 SSB index may correspond to a 0 CS value and a 3 SSB index may correspond to a 36 CS value. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 SSB index 
                 CS (ZC) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 0 
               
               
                   
                 1 
                 12 
               
               
                   
                 2 
                 24 
               
               
                   
                 3 
                 36 
               
               
                   
                   
               
            
           
         
       
     
     A DMRS may comprise a ZC sequence with a cover code and the cover code may be another sequence such as an m sequence. The ZC and the cover code may be multiplied or XORed with each other and m0 may be used to indicate SSB indexes. Table 8 shows an example number of bits and number of m0 values that are ZC multiplied or XORed with a cover code and that correspond to L, a number of SSBs. 
     
       
         
           
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                   
                   
                 # of m0 
               
               
                 L (# of SSBs) 
                 # of bits 
                 (ZC with m sequence) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 2 
                 4 
               
               
                 8 
                 3 
                 8 
               
               
                 64 
                 6 
                 64 
               
               
                   
               
            
           
         
       
     
     Alternatively, a combination of CS (ZC) and m0 (M) may be used to indicate SSB indexes where a DMRS comprises a ZC sequence with a cover code and the cover code is another sequence such as an m sequence. The ZC and the cover code may be multiplied or XORed with each other. Table 9 shows an example number of bits and number of CS (ZC) and m0 (M sequence) combination values that correspond to L, a number of SSBs. 
     
       
         
           
               
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                   
                   
                 # of CS (ZC) and m0 
               
               
                 L (# of SSBs) 
                 # of bits 
                 (M sequence) combinations 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 2 
                 4 
               
               
                 8 
                 3 
                 8 
               
               
                 64 
                 6 
                 64 
               
               
                   
               
            
           
         
       
     
     As an example, for L=4, the CS (ZC) and m0 (M sequence) combinations (CS, m0) shown in Table 10 may be applicable. As shown, a 0 SSB index may correspond to a (0,0) CS (ZC) and m0 (M sequence) combination (CS, m0) and a 3 SSB index may correspond to a (12, 1) CS (ZC) and m0 (M sequence) combination (CS, m0). 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                   
                 CS (ZC) and m0 (M sequence) combinations 
               
               
                   
                 SSB index 
                 (CS, m0) 
               
               
                   
                   
               
             
            
               
                   
                 0 
                  (0, 0) 
               
               
                   
                 1 
                  (0, 1) 
               
               
                   
                 2 
                 (12, 0) 
               
               
                   
                 3 
                 (12, 1) 
               
               
                   
                   
               
            
           
         
       
     
     According to a method, DMRS positions or locations may be used to indicate SSB indexes. Table 11 shows an example number of bits and number of DMRS positions that correspond to L, a number of SSBs. 
     
       
         
           
               
               
               
             
               
                 TABLE 11 
               
               
                   
               
               
                 L (# of SSBs) 
                 # of bits 
                 # of DMRS positions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 2 
                 4 
               
               
                 8 
                 3 
                 8 
               
               
                 64 
                 6 
                 64 
               
               
                   
               
            
           
         
       
     
     As an example, for L=4, the DMRS positions shown in Table 12 may be applicable. As shown, a 0 SSB index may correspond to a position X and a 3 SSB index may correspond to a position W. 
     
       
         
           
               
               
             
               
                 TABLE 12 
               
               
                   
               
               
                 SSB index 
                 DMRS positions 
               
               
                   
               
             
            
               
                 0 
                 Position x 
               
               
                 1 
                 Position y 
               
               
                 2 
                 Position z 
               
               
                 3 
                 Position w 
               
               
                   
               
            
           
         
       
     
     According to a method, a combination of DMRS positions/locations and sequences may be used to indicate SSB indexes. A subset of bits, or example, one or two bits, may be indicated via the DMRS location. Bits not indicated by the DMRS location may be indicated via one or more sequences. A combination of CS and/or m0/m1 and/or positions may be used to indicate SSB indexes. Table 13 shows an example number of bits and number of CS (ZC), m0 (m sequence) and position combination that correspond to L, a number of SSBs. 
     
       
         
           
               
               
               
             
               
                 TABLE 13 
               
               
                   
               
               
                   
                   
                 # of CS (ZC), m0 
               
               
                   
                   
                 (m sequence) and positions 
               
               
                 L (# of SSBs) 
                 # of bits 
                 combinations 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 2 
                 4 
               
               
                 8 
                 3 
                 8 
               
               
                 64 
                 6 
                 64 
               
               
                   
               
            
           
         
       
     
     According to a method, DMRS phase rotation of OFDM symbols may be used to indicate SSB indexes. A subset of bits may be indicated via phase rotations and another subset or the rest of the bits may be indicated via sequences. For example, for multiple OFDM symbols, phase rotation may be applied on the second or remaining N−1 PBCH OFDM symbols with respect to the first PBCH OFDM symbol for total N PBCH OFDM symbols. Alternatively, some bits may be indicated via the phase rotations for some resource blocks (RBs) while other bits may be indicated via the phase rotations for other RBs. 
     According to a method, different scrambling codes may be used for PBCH OFDM symbols to indicate SSB indexes. Table 14 shows an example number of bits and number of scrambling code combinations that correspond to L, a number of SSBs. 
     
       
         
           
               
               
               
             
               
                 TABLE 14 
               
               
                   
               
               
                   
                   
                 # of scrambling code 
               
               
                 • L (# of SSBs) 
                 # of bits 
                 combinations of two symbols 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 4 
                 2 
                 4 
               
               
                 8 
                 3 
                 8 
               
               
                 64 
                 6 
                 64 
               
               
                   
               
            
           
         
       
     
     Gold sequences or m sequences may be generated using polynomials. For example, if the length of the M sequences is 31, which may be repeated, a combination of the following polynomials may be used: 
         g ( x )= x 5 +x 2+1 
         g ( x )= x 5 +x 4 +x 3 +x 2+1 
         g ( x )= x 5 +x 4 +x 2 +x+ 1 
     As another example, if the length of M Sequences is 63, such as for higher density DMRS, a combination of the following polynomials may be used: 
         g ( x )= x   6   +x+ 1 
         g ( x )= x   6   +x   5   +x   2   +x+ 1 
         g ( x )= x   6   +x   5   +x   3   +x   2 +1. 
     It will be understood that other polynomials such as irreducible primitive polynomials may also be used. Further, Cyclic Shifts in two sequences may be defined using following the equations: 
         s   1   (m0) ( n )= (( n+m 0)mod  L ) 
         s   2   (m1) ( n )= (( n+m 1)mod  L ) 
     where the s1, s2 correspond to two m sequences of length L. Additionally, m0 and m1 may correspond to two cyclic shifts, and the value of n may range from 0 to L−1. 
     It will be understood that any one or a combination of the methods described herein may be used for SSB index indication. 
     It will also be understood that in addition or as an alternative to DMRS indication, implicit solutions for hybrid indication may also use scrambling, CRC, and/or Redundancy Version (RV). 
     A 1-bit for Repetition Indication may also be used. Such 1-bit for Repetition Indication may use DMRS, scrambling, CRC, and/or RV for SSB index indication. Such 1-bit for Repetition Indication may also be carried in a PBCH payload. Additionally, an additional 1-bit for half radio frame indication may also be used. Such 1-bit for half radio frame indication may utilize DMRS, scrambling, CRC, RV for indication. Such 1-bit for half radio frame indication may also be carried in PBCH payload. For example, such 1-bit for half radio frame indication may be indicated or carried in scrambling and PBCH payload. 
     Methods for performing SSB transmission such as with timing information indication are described herein. 
     According to an implementation, an implicit indication method for SSB transmission is used if a characteristic, such as a frequency, is lower than a threshold. For example, an implicit indication technique for SSB transmission is used if the frequency is lower than a threshold frequency of 6 GHz. As a specific example of an implicit indication technique, a sequence based indication method may be used. A number of bits, such as X bits, may be encoded implicitly using a sequence such as a reference sequence. The SSB index may be encoded in a scrambling sequence such as, for example, a PN code. A DMRS may be used to encode the SSB index indication such that, for example, a scrambling sequence or PN code may be used for a DMRS to indicate SSB index. Alternatively, an SSB index may be encoded in CRC, scrambling for payload or using other implicit methods. Scrambling may be a function of SSB index. Scrambling, whethersame or different, may be used for DMRS and/or payload in PBCH. 
     A hybrid indication method for SSB transmission may be used of a characteristic, such as a frequency, is higher than a threshold. For example, if the frequency is equal to or higher than 6 GHz, then a hybrid indication method may be used. A hybrid indication method may employ both implicit and explicit indication techniques such as, for example, a combination of DMRS and PBCH payload may be used. A number of bits, such as X bits, of an SSB index may be encoded in PBCH DMRS sequences and another number or the remaining bits, such as Y bits, of an SSB index may be encoded in PBCH payload. To facilitate A PBCH payload may reserve X+Y bits for the SSB index to facilitate the encoding. Additionally, if the frequency is lower than the threshold, such as lower than 6 GHz in this example, then Y bits may be reserved or Y bits or a subset of Y bits may be reused for other purposes such as assisting the indication of the location of cell-defining SSB or for supporting additional system operations such as assisting the indication of presence/absence of cell-defining SSB. 
       FIG. 6  shows an illustrative example of a SSB transmission method. At  610 , an SSB is transmitted via a downlink. An SSB transmission may be carrier frequency dependent or frequency band dependent. For example, at  620  a determination may be made whether a carrier frequency fc is high such that it is higher than or equal to a certain predefined carrier frequency fc1 where fc&gt;=fc1. If fc is determined to be greater than or equal to fc1, then the SSB index bits may be partitioned into two parts at  650 . A first part of the SSB index may be assigned X bits and a second part SSB index may be assigned Y bits at  660  where the total SSB index bits are Nt bits which is equal to X+Y bits. The first part of the SSB index, such as the assigned X bits may be encoded via a DMRS at  645 . The second part of the SSB index, such as the assigned Y bits, may be encoded in PBCH payload such as the data channel and may be encoded in the PBCH data channel using encoding operation of Polar codes. 
     As shown at  630 , a determination that carrier frequency fc is high but not higher than a certain predefined carrier frequency fc1 such that fc&lt;fc1, but higher than another predefined carrier frequency fc2 such that fc&gt;fc2, and fc2&lt;fc1 may be made. If, fc&gt;fc2, and fc2&lt;fc1 then the SSB index may be partitioned into two parts at  650 . It will be understood that the determinations  620  and  630  may occur at the same time or simultaneously and may be made inherently based on the frequency fc and without a determination being made. If partitioned, at  660 , a first part of the SSB index may be assigned X bits and a second part of the SSB index may be assigned Y bits. Alternatively, if partitioned, a second part of the SSB index may not be assigned any bit. If partitioned and if the second part SSB index is assigned Y bits, the total SSB index bits may be Nt, which equals X+Y bits. If the second part SSB index is not assigned any bit, the total SSB index bits may be Nt=X bits. At  645 , the first part SSB index may be encoded in DMRS such that X bits for the first part of the SSB index may be encoded using a DMRS sequence. If the second part SSB index is assigned bits, then, at  665 , Y bits for the second part SSB index may be encoded in the PBCH data channel using, for example, an encoding operation of Polar codes. Alternatively, Y bits for the second part SSB index may be ignored or discarded. Alternatively, Y bits for the second part SSB index may be reused for other system information or control information purposes. 
     As shown at  630 , a determination that carrier frequency fc is high but not higher than a certain predefined carrier frequency fc1 such that fc&lt;fc1, but higher than another predefined carrier frequency fc2 such that fc&gt;fc2, and fc2&lt;fc1 may be made. If fc&gt;fc2, and fc2&lt;fc1 then the SSB index may not be partitioned into parts at  640 . It will be understood that the determinations  620  and  630  may occur at the same time or simultaneously and may be made inherently based on the frequency fc and without a determination being made. At  640 , the entire SSB index may be assigned X bits. The total SSB index bits may be designated by Nt which equals X bits. At  645 , the SSB index may be encoded in DMRS such that X bits for the SSB index may be encoded using the DMRS sequence. 
     As shown at  631 , a determination carrier frequency fc is low and lower than a predefined carrier frequency fc2 such that fc&lt;fc2 may be made. If fc&lt;fc2 then the SSB index may not be partitioned into parts. It will be understood that the determinations  620 ,  630 , and  631  may occur at the same time or simultaneously and may be made inherently based on the frequency fc and without a determination being made. The SSB index may be assigned Z bits. The total SSB index bits are Nt=Z bits. The SSB index may be encoded in DMRS. Z bits for the SSB index may be encoded using DMRS sequence. 
     A PBCH data channel and reference signal, such as a DMRS, may be received. It will be understood that the PBCH data channel and reference signal may be received separately or may be received together. A portion of SSB time index bits may be obtained by detecting the PBCH reference signal. Additionally, the PBCH data channel may be descrambled and decoded using a channel-coding scheme such as via Polar codes. Another portion of the SSB time index bits may be obtained by decoding the PBCH channel and payload. A complete set of bits for the SSB time index bits may be obtained by combining the portion of the SSB time index obtained via the PBCH reference signal, such as the DMRS, and the portion of the SSB time index obtained via the decoded PBCH data channel. Additionally, the PBCH channel and payload may be decoded to obtain other timing information such as a system frame number and/or half radio frame number. 
       FIG. 7  shows an example SSB timing information indication method. At  710 , a WTRU may receive a PBCH reference signal and data channel. At  720 , the WTRU may detect a DMRS via the reference signal and may obtain a part of the SSB time index bits by detecting the DMRS reference signal. As shown at  725 , bits b 2 , b 1 , and b 0  for part of a SSB time index may be received. At  730 , the WTRU may receive the PBCH data channel and may descramble and decode the PBCH channel using a channel coding scheme such as via Polar codes. The WTRU may obtain another part of the SSB time index by descrambling and/or decoding the PBCH channel such as bits b 5 , b 5 , and b 3  as shown at  735 . A complete set of bits b 0 , b 1 , b 2 , b 3 , b 4 , and b 5  for the SSB time index bits may be obtained at  740  by combining the portion of the SSB time index obtained via the PBCH reference signal, such as the DMRS, at  725  and the portion of the SSB time index obtained via the decoded PBCH data channel at  735 . Additionally, the PBCH channel and payload may be decoded to obtain other timing information such as a system frame number indicator  750  and/or half radio frame number  760 . 
     Methods for performing sequence based SSB transmissions are disclosed herein. According to a first method, an SSB index may be encoded in a sequence such as DMRS for SSB transmission. According to a method, multiple sequences may be generated where a Sequence A, or sequence type A, may be a function of a cell ID and a Sequence B, or sequence type B, may be a function of cell ID and an SSB index. Sequences, such as sequence A and B, may be generated using initialization, cyclic shifts, frequency shifts, etc. The initialization of sequence A may be a function of cell ID and the initialization of sequence B may be a function of cell ID and SSB index. Cyclic shifts and/or frequency shifts of sequence A may be a function of cell ID and cyclic shifts and/or frequency shifts of sequence B may be a function of cell ID and SSB index. Sequences may be multiplied with phase rotations based on the SSB index and may have the same or different lengths. 
     A DMRS sequence may be mapped to DMRS REs. A DMRS sequence A may be mapped to DMRS REs within a first set of PBCH OFDM symbols. A DMRS sequence B may be mapped to DMRS REs within a second set of PBCH OFDM symbols. A set of PBCH OFDM symbols may contain one or more OFDM symbols. For each PBCH OFDM symbol, DMRS sequences to DMRS REs may be mapped for lower frequency index, subcarrier index or RE index and higher frequency index, subcarrier index or RE index separately and/or at different times. The lower frequency index, subcarrier index, or RE index may be mapped before the higher frequency index, subcarrier index or RE index. 
     According to another method, multiple sequences where a sequence A, or sequence type A, is a function of cell ID and a sequence B, or sequence type B, is a function of cell ID and a SSB index. Sequences such as sequences A and B may be generated using initialization, cyclic shifts, frequency shifts, etc. Sequences may be multiplied with phase rotations based on a SSB index and may have the same or different lengths. DMRS sequence length may be a function of an RE mapping method such that if a DMRS is mapped to the REs overlapping with SSS bandwidth, then the DMRS may have a length L 1 . If a DMRS is mapped to the REs not overlapping with SSS bandwidth, then the DMRS may have length L 2 . Length L 1  may not equal length L 2  such that, for example, length L 1  may be equal or less than length L 2 . 
     A DMRS sequence may be mapped to DMRS REs using any one or a combination of methods. 
     According to a DMRS sequence mapping method, a DMRS sequence A of length L 1  may be mapped to DMRS REs within a first set of PBCH OFDM symbols and a DMRS sequence B, of length L 2 , may be mapped to DMRS REs within a second set of PBCH OFDM symbols. Length L 1  may be equal to length L 2 . When mapping a DMRS sequence to DMRS REs, REs may be mapped in frequency first separately from being mapped in time. The Res may be mapped in frequency first and then may be mapped in time. For example, mapping DMRS sequence to DMRS REs may start with a lower frequency index, subcarrier index or RE index and then a higher frequency index, subcarrier index or RE index later. The mapping may then continue for a subsequent time such as, for a OFDM symbol index, slot index, non-slot index or mini-slot index. 
     According to another DMRS sequence mapping method, a DMRS sequence A of length L 1  may be mapped to DMRS REs in DMRS REs overlapping with SSS bandwidth within a first set of PBCH OFDM symbols. A DMRS sequence B of length L 2  may be mapped to DMRS REs in DMRS REs overlapping with SSS bandwidth within a first set of PBCH OFDM symbols and all DMRS REs within a second set of PBCH OFDM symbols. Length L 1  may be different from length L 2 . For example, length L 2  may be equal or greater than length L 1 . When mapping a DMRS sequence to DMRS REs, the REs may be mapped in frequency separately than in time such as being mapped in frequency first then being mapped in time. For example, mapping a DMRS sequence to DMRS REs may start with a lower frequency index, subcarrier index or RE index than a higher frequency index, subcarrier index or RE index later. The mapping may continue for a subsequent time such as, for example OFDM symbol index, slot index, non-slot index or mini-slot index. 
     According to another DMRS sequence mapping method, DMRS sequence A of length L 1  may be mapped to DMRS REs in DMRS REs overlapping with SSS bandwidth within a first and second set of PBCH OFDM symbols. A DMRS sequence B of length L 2  may be mapped to DMRS REs in DMRS REs overlapping with SSS bandwidth within the first and second set of PBCH OFDM symbols. Length L 1  may be different from length L 2 . For example, length L 2  may be equal or greater than length L 1 . When mapping a DMRS sequence to DMRS REs, the REs may be mapped in frequency separately than in time such as being mapped in frequency first then being mapped in time. For example, mapping a DMRS sequence to DMRS REs may start with a lower OFDM symbol index, slot index or mini-slot index than a higher lower OFDM symbol index, slot index or mini-slot index later. The mapping may continue for a subsequent time such as, for example OFDM symbol index, slot index, non-slot index or mini-slot index. 
     DMRS RE positions may be fixed or may be a function of cell ID. A DMRS RE position may be a function of a shift, which may be a function of cell ID. A DMRS RE position offset may be a function of a shift, which may be a function of cell ID. A DMRS RE position and/or offset may be fixed or employ a fixed offset. 
     Indications of used or unused SS blocks may be provided based on techniques disclosed herein. Reusing unused SSBs for transmission may allow system resources to be more efficiently utilized and system throughput to be enhanced. Unused SSB may be indicated by one or more methods including, but not limited to, simple bitmap, star point with duration and/or number of used SSBs, hybrid starting point with segment-wise bitmap, or the like. 
     In accordance with a simple bitmap method, an L-bit indicator may be used to indicate unused SSBs. The L-bit indicator may employ a simple bitmap such as, for example, for N unused  SSBs, L bits with N unused  bit locations, being marked as unused, may be used. A value, such as “0”, may be used to mark unused SSBs and a different value, such as “1” may be used to mark used SSBs. For L=64 SSBs, 64 bits signaling overhead may be required. 
     In accordance with a start point with duration and/or number of used SSBs method, two indicators may be used such that one indicator may indicate the starting point of used or unused SSBs, and the other indicator may be used to indicate the number of used or unused SSBs. As an example, a N start  starting points indicator may be used such that log 2  (N start ) bits may be needed. In addition, log 2  (N unused ) bits may be needed to indicate unused SSBs. Accordingly, a total of log 2  (N start )+log 2  (N unused ) bits may be needed. As an example, for N start =64 and N unused =16, a maximum of 10 overhead bits may be required. Using this method may result in a significant reduction in signaling overhead, compared to using the simple bitmap method. 
     In accordance with a hybrid method such as a hybrid starting point with segment-wise bitmap, two indicators may be used such that one indicator may indicate the starting point and the other indicator may indicate the used or unused SSBs associated with the indicated starting point. As an example, for N start =4 and N SS_block,i =16, where i=1, 2, 3, 4, maximum 2+16 bits overhead may be required. This may indicate a starting point and N SS_block,i  associated with the i-th starting point. If extended to indicate two starting points, then 2×(2+16)=36 bits signaling overhead may be required. 
       FIG. 8  shows an example diagram for an SSB indication employing a hybrid starting point with segment-wise bitmap method. As shown, SSB groups starting points are indicated by  810  and contain N SSBs  820  in each group. A bit  830  may correspond to each SSB  820  within a SSB group. As shown, the total number of SSBs is represented by L. 
     According to another method, SSB groupings may be used to indicate used and unused SSBs. SSBs may be grouped such that each group may have N SS_grp,i  SSBs for a group i. The grouping may include equal size or unequal size grouping. After the grouping, the resulting number of SS groups may be denoted as L SS_group  where L SS_group ≤L. A group-bitmap may be used to indicate the L SS_group  SSB group and L SS_group  bits may be used for the group-bitmap. For equal sized grouping, the number of SS groups may be determined by 
     
       
         
           
             
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     As an example, for L=64 and N SS_grp,i =4 for all i, L SS_group =16. Therefore, a total of 16 bits for signaling overhead may be required. SSB grouping may employ localized groupings or distributed groupings. 
       FIG. 9  shows SSB indications via SSB grouping and reduced bitmap where the groupings are equal sized. SS bulk groups are indicated by  910  and contain N SSBs  920  in each group. A total of K SS bulk groups  910  are provided. As shown, the total number of SSBs is represented by L. Each of the bits  930  correspond to a group such that the first group  910  is represented by b 0  and the last group  910  is represented by b(K−1). 
     According to another method, multi-level indexing may be used to indicate used and unused SSBs. An SS burst index and SSB index may be used. Two bitmap indicators may be used such that a first bitmap indicator (Group-Bitmap) may correspond to an SS burst index (e.g., an SSB group index) and a second bitmap indicator (Bitmap-in-Group) may correspond to an SSB index. The first bitmap indicator may be used to indicate the used SS bursts and the second bitmap indicator may be used to indicate the used or unused SSBs in the SS bursts that are indicated as used. An SS burst may be a SSB group, or the like. The first bitmap indicator may be used as coarse indicator and the second bitmap indicator may be used as fine indicator, as disclosed herein. 
     According to another method, an OFDM symbol index may be used to indicate the inactive OFDM symbols within an SSB. The OFDM symbol index may be used to indicate inactive OFDM symbols across all SSBs. The used or unused OFDM symbols may be the same for every SSB. Alternatively, the OFDM symbol index may be used to indicate inactive OFDM symbols for a part of the used SSBs. The number of OFDM symbols per slot or subframe may be different depending on, for example, frequency bands and/or subcarrier spacing (SCS). For example, for a SCS of 15 KHz, 14 OFDM symbols per 2-slot (or 7 OFDM symbols per slot) may be present. For a SCS of 30 KHz, 28 OFDM symbols per 2-slot (or 14 OFDM symbols per slot) may be present. For a SCS of 120 KHz: 112 OFDM symbols per 2-slot (or 56 OFDM symbols per slot) may be present. For a SCS of 240 KHz, 224 OFDM symbols per 2-slot (or 112 OFDM symbols per slot) may be present. 
     An indication of SSB measurement time window and duration may be provided such that used SSBs may be utilized for measurement purpose. A time location of a used SSB may be provided and may facilitate the measurement for serving cells as well as neighbor cells. For example, a WTRU may receive the time location of used SSBs and may facilitate the measurement for serving cell and neighbor cells. Additionally, unused SSB may also be utilized for measurement purpose. For example, a WTRU may be receive the time location of unused SSBs and may use the time location of the unused SSBs to facilitate measurements such as, for example, interference measurements or signal strengths from neighbor cells. 
     A WTRU or other applicable device may receive a set of parameters for used and/or unused SSBs. The parameters may include, but are not limited to one or more measurement windows, timing parameters, duration parameters, offset and/or periodicity. The parameters may be provided via one or more indicators. 
     In an idle mode, a set of parameters for used and/or unused SSBs may be received or provided via NR-PBCH, via remaining minimum system information, and/or via other system information. 
     In a radio resource control (RRC) connected mode, a set of parameters for used and/or unused SSBs may be signaled via RRC signaling, MAC or MAC CE, and/or physical layer signaling such as NR-PDCCH or NR-ePDCCH. 
     According to methods disclosed herein, SSBs may be reused. As disclosed herein, SSBs can be used for transmitting synchronization signals and channels. To more efficiently utilize SSBs, other signals or channels may reuse a subset of SSBs to improve system throughput, reduce overhead and enhance spectrum efficiency. SSBs may be reused for other signals or channel transmissions such as, for example, for control and/or data transmission and reception, for CSI-RS transmission such as that performed using TDM, FDM, or hybrid methods, and/or for paging downlink control information (DCI). 
     Additionally, SSBs may be reused for control channel transmissions. For example, SSBs may be reused for control signaling to enable URLLC transmission, NR-PDCCH, NR-ePDCCH, paging signal or paging DCI, control channel for URLLC, NR-PUCCH, and/or scheduling requests (SR). 
     Additionally, SSBs may be reused for data channel transmission. For example, SSBs may be reused for URLLC transmission or mini-slot transmission such as for paging channels, paging PDSCH, and/or URLLC data channel. 
     Additionally, SSBs may be reused for reference signal transmission. For example, SSBs may be reused for CSI-RS transmission such as for channel state information reference signals (CSI-RS), and/or sound reference signals (SRS). 
     Unused SSBs may allow for the resources reserved for SSBs to be reused for other signal or channel transmissions, as described herein. Additionally or alternatively, a set or subset of SSBs may be transmitted but may not be used for initial access or synchronization purposes. Such set or subset of SSBs may be transmitted to support other procedures such as, for example, beam management. For DL beam management SSBs may be used to enable P−1, P−2 and P−3 procedures. 
     Further, in idle mode, used and/or unused SSBs may be signaled. The SSBs may be signaled via, for example, NR-PBCH where bits representing unused SSBs may be carried in a NR-PBCH payload. Alternatively or in addition, the SSBs may be signaled via remaining minimum system information where bits representing unused SSBs may be carried in remaining minimum system information that can be scheduled by NR-PBCH. Alternatively or in addition, SSBs may be signaled via other system information where bits representing unused SSBs may be carried in other system information that can be scheduled by the remaining minimum system information. 
     In RRC connected mode, used and/or unused SSBs may be signaled via, for example, RRC signaling, MAC or MAC CE, and/or physical layer signaling such as NR-PDCCH or NR-ePDCCH. 
     Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.