Patent Publication Number: US-11647472-B2

Title: Timing and frame structure in an integrated access backhaul (IAB) network

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. Non-Provisional patent application Ser. No. 16/154,585 filed Oct. 8, 2018, which claims priority to and the benefit of U.S. Provisional Patent Application No. 62/570,003, filed Oct. 9, 2017, each of which is hereby incorporated by reference in its entirety as if fully set forth below and for all applicable purposes. 
    
    
     TECHNICAL FIELD 
     This application generally relates to wireless communication systems, and more particularly to communicating access data and backhaul data over wireless links in an integrated access backhaul (IAB) network. Embodiments of the technology can enable and provide solutions and techniques for wireless communication devices (e.g., base stations and user equipment devices (UEs)) in an IAB network to maintain synchronization and determine transmission and/or reception timelines and frame structures for communications. 
     INTRODUCTION 
     Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems, (e.g., a Long Term Evolution (LTE) system). A wireless multiple-access communications system may include a number of base stations (BSs), each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE). 
     To meet the growing demands for expanded mobile broadband connectivity, wireless communication technologies are advancing from the LTE technology to a fifth generation (5G) new radio (NR) technology. 5G NR may provision for access traffic and backhaul traffic at gigabit-level throughput. Access traffic refers to traffic between an access node (e.g., a base station) and a UE. Backhaul traffic refers to traffic among access nodes and a core network. 
     BRIEF SUMMARY OF SOME EXAMPLES 
     The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later. 
     Embodiments of the present disclosure provide mechanisms for communicating in an integrated access backhaul (IAB) network employing a multi-hop topology (e.g., a spanning tree) to transport radio access traffic and backhaul traffic. For example, a BS or a UE may function as a relay node (e.g., a parent node or a child node) and at least one BS in direct communication with a core network may function as a root node. A relay node may exchange synchronization information with one or more other relay nodes, adjust an internal synchronization reference, and/or determine transmission and/or reception timelines and/or frame structures (e.g., gap periods and cyclic prefixes (CPs)) for communicating radio access traffic and/or backhaul traffic with the one or more other relay nodes. 
     For example, in an aspect of the disclosure, a method of wireless communication includes receiving, by a first wireless communication device from one or more wireless communication devices of a multi-hop wireless network, synchronization information associated with the one or more wireless communication devices. The method further includes determining, by the first wireless communication device, a transmission timing adjustment for a second wireless communication device of the one or more wireless communication devices based on at least some of the synchronization information. The method further includes transmitting, by the first wireless communication device, a message instructing the second wireless communication device to communicate with a third wireless communication device of the one or more wireless communication devices based on the transmission timing adjustment. 
     In an additional aspect of the disclosure, an apparatus includes a transceiver configured to receive, from one or more wireless communication devices of a multi-hop wireless network, synchronization information associated with the one or more wireless communication devices. The apparatus also includes a processor configured to determine a transmission timing adjustment for a first wireless communication device of the one or more wireless communication devices based on at least some of the synchronization information. The transceiver is further configured to transmit a message instructing the first wireless communication device to communicate with a second wireless communication device of the one or more wireless communication devices based on the transmission timing adjustment. 
     In an additional aspect of the disclosure, an apparatus includes means for receiving, from one or more wireless communication devices of a multi-hop wireless network, synchronization information associated with the one or more wireless communication devices. The apparatus further includes means for determining a transmission timing adjustment for a first wireless communication device of the one or more wireless communication devices based on at least some of the synchronization information. The apparatus further includes means for transmitting a message instructing the first wireless communication device to communicate with a second wireless communication device of the one or more wireless communication devices based on the transmission timing adjustment. 
     In an additional aspect of the disclosure, program code is recorded on a non-transitory computer-readable medium. The program code includes code for causing a first wireless communication device to receive, from one or more wireless communication devices of a multi-hop wireless network, synchronization information associated with the one or more wireless communication devices. The program code further includes code for causing the first wireless communication device to determine a transmission timing adjustment for a second wireless communication device of the one or more wireless communication devices based on at least some of the synchronization information. The program code further includes code for causing the first wireless communication device to transmit a message instructing the second wireless communication device to communicate with a third wireless communication device of the one or more wireless communication devices based on the transmission timing adjustment. 
     Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain embodiments and figures below, all embodiments of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a wireless communication network according to embodiments of the present disclosure. 
         FIG.  2    illustrates an integrated access backhaul (IAB) network according to embodiments of the present disclosure. 
         FIG.  3    illustrates an IAB network according to embodiments of the present disclosure. 
         FIG.  4    illustrates an IAB network topology according to embodiments of the present disclosure. 
         FIG.  5    illustrates an IAB network resource sharing method according to embodiments of the present disclosure. 
         FIG.  6    is a block diagram of an exemplary user equipment (UE) according to embodiments of the present disclosure. 
         FIG.  7    is a block diagram of an exemplary base station (BS) according to embodiments of the present disclosure. 
         FIG.  8    is a timing diagram illustrating a scheduling method for a wireless access network according to embodiments of the present disclosure. 
         FIG.  9    is a timing diagram illustrating a scheduling method for an IAB network according to embodiments of the present disclosure. 
         FIG.  10    is a timing diagram illustrating a scheduling method for an IAB network according to embodiments of the present disclosure. 
         FIG.  11    is a signaling diagramming illustrating an IAB communication method according to embodiments of the present disclosure. 
         FIG.  12    is a signaling diagramming illustrating an IAB communication method according to embodiments of the present disclosure. 
         FIG.  13    illustrates a distributed synchronization method according to embodiments of the present disclosure. 
         FIG.  14    illustrates a centralized synchronization method transmission method according to embodiments of the present disclosure. 
         FIG.  15    is a signaling diagramming illustrating a distributed synchronization method according to embodiments of the present disclosure. 
         FIG.  16    is a signaling diagramming illustrating a centralized synchronization method according to embodiments of the present disclosure. 
         FIG.  17    illustrates a wireless backhaul network according to embodiments of the present disclosure. 
         FIG.  18    illustrates a traffic routing overlay in a wireless backhaul network according to embodiments of the present disclosure. 
         FIG.  19    illustrates a synchronization overlay in a wireless backhaul network according to embodiments of the present disclosure. 
         FIG.  20    illustrates a synchronization overlay in a wireless backhaul network according to embodiments of the present disclosure. 
         FIG.  21    is a signaling diagram illustrating an IAB communication method according to embodiments of the present disclosure. 
         FIG.  22    is a flow diagram of a method for communicating in an IAB network according to embodiments of the present disclosure. 
         FIG.  23    is a flow diagram of a method for managing synchronization references in an IAB network according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form to avoid obscuring such concepts. 
     Techniques described herein may be used for various wireless communication networks. These networks can include code-division multiple access (CDMA), time-division multiple access (TDMA), frequency-division multiple access (FDMA), orthogonal frequency-division multiple access (OFDMA), single-carrier FDMA (SC-FDMA) and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). CDMA2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies, such as a next generation network including 5G NR. Some 5G NR networks (aka (e.g., 5th Generation) (5G) operating in mmWave bands) can operate in a variety of frequency bands (e.g., mmWave or sub-6 Ghz) that covers both licensed and unlicensed spectrum. 
     The present disclosure describes mechanisms and techniques for communicating in an IAB network. An IAB network may include a combination of wireless access links between BSs and UEs and wireless backhaul links between the BSs. The IAB network may employ a multi-hop topology (e.g., a spanning tree) for transporting access traffic and backhaul traffic. One of the BSs may be configured with an optical fiber connection in communication with a core network. In some scenarios a BS may function as an anchoring node (e.g., a root node) to transport backhaul traffic between a core network and the IAB network. In other scenarios one BS may serve the role of a central node in conjunction with connections to a core network. And in some arrangements, BSs and the UEs may be referred to as relay nodes in the network. 
     BSs can serve a variety of roles in a network in either a static or dynamic nature. For example, each BS may have one or more parent nodes. These parent nodes can include other BSs. BSs may have one or more child nodes, which may include other BSs and/or UEs. The UEs may function as child nodes. Parent nodes may function as access nodes to child nodes. Parent nodes may be referred to as access functionality (ACF)-nodes. Child nodes may function as UEs to parent nodes and may be referred to as UE functionality (UEF)-nodes. BSs may function as an ACF-node when communicating with a child node and may function as a UEF-node when communicating with a parent node. The disclosed embodiments generally provide signaling mechanisms for nodes in an IAB network to maintain synchronization and determine transmission and/or reception timelines and frame structures for communications. Given a variety of topological arrangements of IAB networks and constraints/demands placed on a network synchronization helps overall network functions and performance for positive user experiences. 
     In an embodiment, a relay node may maintain and track one or more synchronization references for communications in a network. A synchronization reference can be an internal reference at a node or an external reference such as a global positioning system (GPS) connected to the node. Relay nodes may exchange synchronization information, for example, via messages or reference signals. A central entity can collect synchronization reports from the relay nodes and configure the relay nodes with synchronization adjustments. Thus, a relay node may adjust an internal synchronization reference based on synchronization information received from other relay nodes, timing information received from a GPS, adjustments received from a central entity, and/or adjustments received from a particular relay node selected by the central entity. Accordingly, the present disclosure provides techniques for over-the-air (OTA) synchronization in a multi-hop IAB network. 
     In an embodiment, when a relay node functions as an ACF-node, the relay node may determine or utilize a number of parameters. These can include gap periods, transmit timing, receiving time, and/or cyclic prefix (CP) mode (e.g., a normal CP mode or an extended CP (ECP) mode) for communicating with corresponding UEF-nodes. In an embodiment, a central entity may determine adjustment information including gap periods, transmit timing adjustment, receiving time adjustment, and/or CP mode for the relay nodes to communicate with each other and may provide the adjustment information to the relay nodes. 
     Aspects of the technology discussed herein can provide several benefits. For example, the use of ACF-UEF relationships among the relay nodes can leverage at least some of the current LTE technologies, such as scheduling and timing advance mechanisms. The use of multiple synchronization references and exchange of synchronization information allows the nodes to synchronize with each other and synchronize to a reliable synchronization source (e.g., a GPS). The flexibility of selecting between an ECP mode, a gap period insertion, and/or a transmit and/or receive timing adjustment can avoid interference and increase resource utilization efficiency. These and other benefits are more fully recognized and discussed below. 
       FIG.  1    illustrates a wireless communication network  100  according to embodiments of the present disclosure. The network  100  includes a plurality of BSs  105 , a plurality of UEs  115 , and a core network  130 . The network  100  may be a LTE network, a LTE-A network, a millimeter wave (mmW) network, a new radio (NR) network, a 5G network, or any other successor network to LTE. 
     The BSs  105  may wirelessly communicate with the UEs  115  via one or more BS antennas. Each BS  105  may provide communication coverage for a respective geographic coverage area  110 . In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS and/or a BS subsystem serving the coverage area, depending on the context in which the term is used. In the example shown in  FIG.  1   , the BSs  105   a ,  105   b ,  105   c ,  105   d , and  105   e  are examples of macro BSs for the coverage areas  110   a ,  110   b ,  110   c ,  110   d , and  110   e , respectively. 
     Communication links  125  shown in the network  100  may include uplink (UL) transmissions from a UE  115  to a BS  105 , or downlink (DL) transmissions, from a BS  105  to a UE  115 . The communication links  125  are referred to as wireless access links. The UEs  115  may be dispersed throughout the network  100 , and each UE  115  may be stationary or mobile. A UE  115  may also be referred to as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. A UE  115  may also be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a personal electronic device, a handheld device, a personal computer, a wireless local loop (WLL) station, an Internet of things (IoT) device, an Internet of Everything (IoE) device, a machine type communication (MTC) device, an appliance, an automobile, or the like. 
     The BSs  105  may communicate with the core network  130  and with one another via optical fiber links  134 . The core network  130  may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs  105  (e.g., which may be an example of an evolved NodeB (eNB), a next generation NodeB (gNB), or an access node controller (ANC)) may interface with the core network  130  through the backhaul links  134  (e.g., S1, S2, etc.) and may perform radio configuration and scheduling for communication with the UEs  115 . In various examples, the BSs  105  may communicate, either directly or indirectly (e.g., through core network  130 ), with each other over the backhaul links  134  (e.g., X1, X2, etc.). 
     Each BS  105  may also communicate with a number of UEs  115  through a number of other BSs  105 , where the BS  105  may be an example of a smart radio head. In alternative configurations, various functions of each BS  105  may be distributed across various BSs  105  (e.g., radio heads and access network controllers) or consolidated into a single BS  105 . 
     In some implementations, the network  100  utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the UL. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. The system bandwidth may also be partitioned into subbands. 
     In an embodiment, the BSs  105  can assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks) for DL and UL transmissions in the network  100 . DL refers to the transmission direction from a BS  105  to a UE  115 , whereas UL refers to the transmission direction from a UE  115  to a BS  105 . The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes, for example, about 10. Each subframe can be divided into slots, for example, about 2. In a frequency-division duplexing (FDD) mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes a UL subframe in a UL frequency band and a DL subframe in a DL frequency band. In a time-division duplexing (TDD) mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (e.g., DL subframes) in a radio frame may be used for DL transmissions and another subset of the subframes (e.g., UL subframes) in the radio frame may be used for UL transmissions. 
     The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs  105  and the UEs  115 . For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational bandwidth or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS  105  may transmit cell-specific reference signals (CRSs) and/or channel state information-reference signals (CSI-RSs) to enable a UE  115  to estimate a DL channel. Similarly, a UE  115  may transmit sounding reference signals (SRSs) to enable a BS  105  to estimate a UL channel. Control information may include resource assignments and protocol controls. Data may include protocol data and/or operational data. In some embodiments, the BSs  105  and the UEs  115  may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication that UL communication. A UL-centric subframe may include a longer duration for UL communication that UL communication. 
     In an embodiment, a UE  115  attempting to access the network  100  may perform an initial cell search by detecting a primary synchronization signal (PSS) from a BS  105 . The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE  115  may then receive a secondary synchronization signal (SSS). The SSS may enable radio frame synchronization, and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The SSS may also enable detection of a duplexing mode and a cyclic prefix length. Some systems, such as TDD systems, may transmit an SSS but not a PSS. Both the PSS and the SSS may be located in a central portion of a carrier, respectively. After receiving the PSS and SSS, the UE  115  may receive a master information block (MIB), which may be transmitted in the physical broadcast channel (PBCH). The MIB may contain system bandwidth information, a system frame number (SFN), and a Physical Hybrid-ARQ Indicator Channel (PHICH) configuration. After decoding the MIB, the UE  115  may receive one or more system information blocks (SIBs). For example, SIB1 may contain cell access parameters and scheduling information for other SIBs. Decoding SIB1 may enable the UE  115  to receive SIB2. SIB2 may contain radio resource configuration (RRC) configuration information related to random access channel (RACH) procedures, paging, physical uplink control channel (PUCCH), physical uplink shared channel (PUSCH), power control, SRS, and cell barring. After obtaining the MIB and/or the SIBs, the UE  115  can perform random access procedures to establish a connection with the BS  105 . After establishing the connection, the UE  115  and the BS  105  can enter a normal operation stage, where operational data may be exchanged. 
       FIG.  2    illustrates an IAB network  200  according to embodiments of the present disclosure. The network  200  is substantially similar to the network  100 . For example, the BSs  105  communicates with the UEs  115  over the wireless access links  125 . However, in the network  200 , only one BS (e.g., the BS  105   c ) is connected to an optical fiber backhaul link  134 . The other BSs  105   a ,  105   b ,  105   d , and  105   e  wirelessly communicate with each other and with the BS  105   c  over wireless backhaul links  234 . The BS  105   c  connected to the optical fiber backhaul link  134  may function as an anchor for the other BSs  105   a ,  105   b ,  105   d , and  105   e  to communicate the core network  130 , as described in greater detail herein. The wireless access links  125  and the wireless backhaul links  234  may share resources for communications in the network  200 . The network  200  may also be referred to as a self-backhauling network. The network  200  can improve wireless link capacity, reduce latency, and reduce deployment cost. 
       FIG.  3    illustrates an IAB network  300  according to embodiments of the present disclosure. The network  300  is similar to the network  200  and illustrates the use of millimeter wave (mmWav) frequency band for communications. In the network  300 , a single BS (e.g., the BS  105   c ) is connected to an optical fiber backhaul link  134 . The other BSs  105   a ,  105   b ,  105   d , and  105   e  communicate with each other and with the BS  105   c  using directional beams  334 , for example, over the wireless links  234 . The BSs  105  may also communicate with the UEs  115  using narrow directional beams  325 , for example, over the wireless links  125 . The directional beams  334  may be substantially similar to the directional beams  325 . For example, the BSs  105  may use analog beamforming and/or digital beamforming to form the directional beams  334  and  325  for transmission and/or reception. Similarly, the UEs  115  may use analog beamforming and/or digital beamforming to form the directional beams  325  for transmission and/or reception. The use of mmmWav can increase network throughput and reduce latency. The use of narrow directional beams  334  and  325  can minimize inter-link interference. Thus, the network  300  can improve system performance. 
       FIG.  4    illustrates an IAB network topology  400  according to embodiments of the present disclosure. The topology  400  can be employed by the networks  200  and  300 . For example, the BSs  105  and the UEs  115  can be configured to form a logical spanning tree configuration as shown in the topology  400  for communicating access traffic and/or backhaul traffic. The topology  400  may include an anchor  410  coupled to an optical fiber link  134  for communication with a core network (e.g., the core network  130 ). The anchor  410  may correspond to the BS  105   c  in the networks  200  and  300 . 
     The topology  400  includes a plurality of logical levels  402 . In the example of  FIG.  4   , the topology  400  includes three levels  402 , shown as  402   a ,  402   b , and  402   c . In some other embodiments, the topology  400  can include any suitable number of levels  402  (e.g., two, three, four, five, or six). Each level  402  may include a combination of UEs  115  and BSs  105  interconnected by logical links  404 , shown as  404   a ,  404   b , and  404   c . For example, a logical link  404  between a BS  105  and a UE  115  may correspond to a wireless access link  125 , whereas a logical link  404  between two BSs  105  may correspond to a wireless backhaul link  234 . The BSs  105  and the UEs  115  may be referred to as relay nodes in the topology  400 . 
     The nodes (e.g., the BSs  105 ) in the level  402   a  can function as relays for the nodes in the level  402   b , for example, to relay backhaul traffic between the nodes and the anchor  410 . Similarly, the nodes (e.g., the BSs  105 ) in the level  402   b  can function as relays for the nodes in the level  402   c . For example, the nodes in the level  402   a  are parent nodes to the nodes in the level  402   b , and the nodes in the level  402   c  are child nodes to the nodes in level  402   b . The parent nodes may function as ACF-nodes and the child nodes may function as UEF-nodes. 
     For example, a BS  105  may implement both ACF and UEF and may function as an ACF-node and an UEF-node depending on which node the BS is communicating with. For example, a BS  105  (shown as pattern-filled) in the level  402   b  may function as an access node when communicating with a BS  105  or a UE  115  in the level  402   c . Alternatively, the BS  105  may function as a UE when communicating with a BS  105  in the level  402   a . When a communication is with a node in a higher level or with a less number of hops to the anchor  410 , the communication is referred to as a UL communication. When a communication is with a node in a lower level or with a greater number of hops to the anchor  410 , the communication is referred to as a DL communication. In some embodiments, the anchor  410  may allocate resources for the links  404 . Mechanisms for scheduling UL and DL transmissions and/or allocating resources based on the topology  400  are described in greater detail herein. 
       FIG.  5    illustrates an IAB network resource sharing method  500  according to embodiments of the present disclosure. The method  500  illustrates resource partitioning for use in the topology  400 . In  FIG.  5   , the x-axis represents time in some constant units. The method  500  time-partition resources in an IAB network (e.g., the networks  200  and  300 ) into resources  510  and  520 . The resources  510  and  520  can include time-frequency resources. For example, each resource  510  or  520  may include a number of symbols (e.g., OFDM symbols) in time and a number of subcarriers in frequency. In some embodiments, each resource  510  or  520  shown may correspond to a subframe, a slot, or a transmission time interval (TTI), which may carry one media access control (MAC) layer transport block. 
     As an example, the method  500  may assign the resources  510  to the links  404   a  and  404   c  in the topology  400  for communicating UL and/or DL traffic. The method  500  may assign the resources  520  to the links  404   b  in the topology  400  for communicating UL and/or DL traffic. The time-partitioning of the resources in the alternating manner shown in the method  500  can reduce interference between the different levels  402 , overcome the half-duplex constraint, and reduce transmit-receive gap periods. 
       FIG.  6    is a block diagram of an exemplary UE  600  according to embodiments of the present disclosure. The UE  600  may be a UE  115  as discussed above. As shown, the UE  600  may include a processor  602 , a memory  604 , an IAB communication module  608 , a transceiver  610  including a modem subsystem  612  and a radio frequency (RF) unit  614 , and one or more antennas  616 . These elements may be in direct or indirect communication with each other, for example via one or more buses. 
     The processor  602  may include a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor  602  may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The memory  604  may include a cache memory (e.g., a cache memory of the processor  602 ), random access memory (RAM), magnetoresistive RAM (MRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), flash memory, solid state memory device, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In an embodiment, the memory  604  includes a non-transitory computer-readable medium. The memory  604  may store instructions  606 . The instructions  606  may include instructions that, when executed by the processor  602 , cause the processor  602  to perform the operations described herein with reference to the UEs  115  in connection with embodiments of the present disclosure. Instructions  606  may also be referred to as code. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement(s). For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” may include a single computer-readable statement or many computer-readable statements. 
     The IAB communication module  608  may be implemented via hardware, software, or combinations thereof. For example, the IAB communication module  608  may be implemented as a processor, circuit, and/or instructions  606  stored in the memory  604  and executed by the processor  602 . The IAB communication module  608  may be used for various aspects of the present disclosure. For example, the IAB communication module  608  is configured to maintain multiple synchronization references, provide synchronization information (e.g., including timing and/or frequency) associated with the synchronization references to other nodes (e.g., the BSs  105 ), receive synchronization information from other nodes, receive synchronization adjustment commands, receive scheduling information (e.g., gap periods, transmission timing, and/or reception timing), adjust synchronization references based on the received synchronization information and/or the received commands, and/or communicate with other nodes based on received scheduling information, as described in greater detail herein. 
     As shown, the transceiver  610  may include the modem subsystem  612  and the RF unit  614 . The transceiver  610  can be configured to communicate bi-directionally with other devices, such as the BSs  105 . The modem subsystem  612  may be configured to modulate and/or encode the data from the memory  604  and/or the IAB communication module  608  according to a modulation and coding method (MCS), e.g., a low-density parity check (LDPC) coding method, a turbo coding method, a convolutional coding method, a digital beamforming method, etc. The RF unit  614  may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data from the modem subsystem  612  (on outbound transmissions) or of transmissions originating from another source such as a UE  115  or a BS  105 . The RF unit  614  may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver  610 , the modem subsystem  612  and the RF unit  614  may be separate devices that are coupled together at the UE  115  to enable the UE  115  to communicate with other devices. 
     The RF unit  614  may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas  616  for transmission to one or more other devices. This may include, for example, transmission of reservation signals, reservation response signals, and/or any communication signal according to embodiments of the present disclosure. The antennas  616  may further receive data messages transmitted from other devices. This may include, for example, reception of synchronization information, synchronization adjustment commands, and/or scheduling adjustment information according to embodiments of the present disclosure. The antennas  616  may provide the received data messages for processing and/or demodulation at the transceiver  610 . The antennas  616  may include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit  614  may configure the antennas  616 . 
       FIG.  7    is a block diagram of an exemplary BS  700  according to embodiments of the present disclosure. The BS  700  may be a BS  105  as discussed above. A shown, the BS  700  may include a processor  702 , a memory  704 , a IAB communication module  708 , a transceiver  710  including a modem subsystem  712  and a RF unit  714 , and one or more antennas  716 . These elements may be in direct or indirect communication with each other, for example via one or more buses. 
     The processor  702  may have various features as a specific-type processor. For example, these may include a CPU, a DSP, an ASIC, a controller, a FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor  702  may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The memory  704  may include a cache memory (e.g., a cache memory of the processor  702 ), RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, a solid state memory device, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some embodiments, the memory  704  may include a non-transitory computer-readable medium. The memory  704  may store instructions  706 . The instructions  706  may include instructions that, when executed by the processor  702 , cause the processor  702  to perform operations described herein. Instructions  706  may also be referred to as code, which may be interpreted broadly to include any type of computer-readable statement(s) as discussed above with respect to  FIG.  7   . 
     The IAB communication module  708  may be implemented via hardware, software, or combinations thereof. For example, the IAB communication module  708  may be implemented as a processor, circuit, and/or instructions  706  stored in the memory  604  and executed by the processor  702 . The IAB communication module  708  may be used for various aspects of the present disclosure. For example, the IAB communication module  708  is configured to maintain multiple synchronization references, provide synchronization information (e.g., including timing and/or frequency) associated with the synchronization references to other nodes (e.g., the BSs  105  and the UEs  115  and  600 ), receive synchronization information from other nodes, receive synchronization adjustment commands, adjust synchronization references based on the received synchronization information or the received commands, receive scheduling information (e.g., gap periods, transmission timing, and/or reception timing) for communication with nodes at a higher level (e.g., less hops away from an anchor  410  than the BS  700 ), determine scheduling information for communication with nodes at a lower level (e.g., more hops away from an anchor  410  than the BS  700 ), and/or communicate with nodes based on the received scheduling information and the determined scheduling information, as described in greater detail herein. 
     As shown, the transceiver  710  may include the modem subsystem  712  and the RF unit  714 . The transceiver  710  can be configured to communicate bi-directionally with other devices, such as the UEs  115  and/or another core network element. The modem subsystem  712  may be configured to modulate and/or encode data according to a MCS, e.g., a LDPC coding method, a turbo coding method, a convolutional coding method, a digital beamforming method, etc. The RF unit  714  may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data from the modem subsystem  712  (on outbound transmissions) or of transmissions originating from another source such as a UE  115 . The RF unit  714  may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver  710 , the modem subsystem  712  and the RF unit  714  may be separate devices that are coupled together at the BS  105  to enable the BS  105  to communicate with other devices. 
     The RF unit  714  may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas  716  for transmission to one or more other devices. This may include, for example, transmission of information to complete attachment to a network and communication with a camped UE  115  according to embodiments of the present disclosure. The antennas  716  may further receive data messages transmitted from other devices and provide the received data messages for processing and/or demodulation at the transceiver  710 . The antennas  716  may include multiple antennas of similar or different designs in order to sustain multiple transmission links. 
       FIGS.  8 - 10    illustrate various timelines for communicating over wireless access links (e.g., the wireless access links  125 ) and wireless backhaul links (e.g., the wireless backhaul links  234 ). In  FIGS.  8 - 10   , the x-axes represent time in some constant units. The illustrated timelines set forth how various method embodiments can be implemented and are described in detail below. 
       FIG.  8    is a timing diagram illustrating a scheduling method  800  for a wireless access network according to embodiments of the present disclosure. The method  800  may be employed by a BS (e.g., the BSs  105 ) to communicate with a UE (e.g., the UEs  115 ) over a wireless access link (e.g., the wireless access links  125 ). The method  800  is illustrated with one UE for simplicity of discussion, but may be scaled to include any suitable number of UEs (e.g., five, ten, twenty, or more than twenty). 
     The method  800  generally shows BS/UE communications via the vertical lines shown in the drawing. As shown, in the method  800 , the BS may transmit DL signals  810  to the UE, for example, based on a timing reference of the BS (e.g., as shown by the DL transmit (Tx) timeline  802 ). The UE may receive the DL signals  810  after a propagation delay  830  as shown by the DL receive (Rx) timeline  804 . The UE may transmit UL signals  820  to the BS, for example, based on a timing reference provided by the BS as shown by the UL Tx timeline  806 . 
     To determine a schedule for the UE, the BS may estimate a round trip time (RTT)  832  between the BS and the UE, for example, based on a random access procedure. The propagation delay  830  may correspond to half of the RTT  832 . The BS may transmit a timing advance (TA) command to the UE instructing the UE to transmit at an earlier time than an expected scheduled transmit time. The UE is expected to track the DL timing of the BS and adjust the UE&#39;s UL timing based the DL timing. For example, the BS may schedule the UE to transmit at a particular time according to the timeline  802 . The UE may transmit at an earlier time than the scheduled transmit time based on the TA command so that the transmission can reach the BS at an arrival time according to the BS&#39;s timeline  802 . 
     In addition, the BS may schedule the UE by providing a gap period for the UE to switch between transmit and receive. For example, the BS may schedule the UE to transmit a UL signal  820  sometime after a reception time of the DL signal  810  instead of immediately after a reception of the DL signal  810 . As shown, there is a gap period  834  between the reception of a DL signal  810  and the transmission of a UL signal  820 . While the method  800  is described in the context of a BS communicating with a UE over a wireless access link, the method  800  can be applied to a BS communicating with another BS over a wireless backhaul link, as described in greater detail herein. 
       FIG.  9    is a timing diagram illustrating a scheduling method  900  for an IAB network according to embodiments of the present disclosure.  FIG.  9    illustrates communications between multiple components as represented by the vertical lines. The method  900  may be employed by a BS (e.g., the BSs  105 ) to communicate with a UE (e.g., the UEs  115 ) over a wireless access link (e.g., the wireless access links  125 ) or another BS over a wireless backhaul link (e.g., the wireless backhaul links  234 ) in an IAB network (e.g., the networks  200  and  300 ). The method  900  illustrates three nodes R 1 , R 2 , and R 3  in three levels (e.g., the levels  402 ) for simplicity of discussion, but may be scaled to include any suitable number nodes (e.g., five, ten, twenty, or more than twenty) configured in any suitable number of levels (e.g., four, five, or more than five). 
     Nodes R 1 , R 2 , and R 3  may correspond to a portion of the topology  400 . For example, node R 1  may be at a hop h 1  (e.g., the levels  402 ) with respect to the anchor  410 , where h 1  is a positive integer. The method  900  may be used in conjunction with the method  500 . For example, node R 1  and the node R 2  may correspond to BSs  105 , and the node R 3  may correspond to a BS  105  or a UE  115 . The DL 1  Tx timeline  902 , the DL 1  Rx timeline  904 , and the UL 1  Tx timeline  906  between the node R 1  and the node R 2  are similar to the timeline  802 ,  804 , and  806 , respectively. In some scenarios, the node R 1  may function as a parent node or an ACF-node to the node R 2 . The node R 1  may transmit DL signals  910  according to a timing reference of the node RE The DL signals  910  may arrive at the node R 2  after a propagation delay. The node R 1  may transmit a TA command to the node R 2 . The node R 2  may track the DL timing of the node R 1 , receive the TA command, and transmit UL signals  920  based on the TA command. 
     In some scenarios, nodes of  FIG.  9    may communicate with each other based on scheduling (e.g., timing-based scheduling). For example, the node R 2  can communicate with the node R 3  (e.g., a child node or a UEF-node to the node R 2 ). The node R 2  can select a DL transmit timing reference (e.g., DL 2  Tx) for transmitting DL signals  930  to the node R 3 .  FIG.  9    illustrates three options  932 ,  934 , and  936  for the DL 2  Tx timeline  908 . 
     In the first option  932 , the node R 2  may use a single transmit timing reference by aligning the DL transmit timing of the node R 2  to the UL transmit timing of the node R 2 . 
     In the second option  934 , the node R 2  may use two transmit timing references, one for UL transmissions based on instructions from the node R 1  and another one for DL transmissions. The node R 2  may align the DL transmit timing of the node R 2  to a DL transmit timing of a parent node or an ACF-node (e.g., the node R 1 ) of the node R 2 . 
     In the third option  936 , the node R 2  may use two transmit timing references, one for UL transmissions based on instructions from the node R 1  and another one for DL transmissions. The node R 2  may align the DL transmit timing of the node R 2  to the DL receive timing (e.g., a reception time of the DL signals  910 ) of the node R 2 . 
     The node R 2  may select any one of the options  932 ,  934 , and  936 . However, the first option  932  and the third option  936  may lead to a large timing misalignment between nodes in the network depending on the number of hops (e.g., the levels  402 ) due to the accumulative effects of propagation delays (e.g., the delay  830 ) from one hop to the next. The second option  934  may provide the least amount timing misalignment since all DL transmit timing in the network may be aligned to the DL transmit timing of a top-level node (e.g., the anchor  410 ). 
     After selecting a timing reference for DL transmit, the node R 2  may schedule UL and/or DL communications with the node R 3 . The node R 2  may include a gap period in a schedule as required for the node R 3  to switch between receive and transmit. The node R 2  may further measure interference (e.g., cross-link interference) in the network, monitor transmissions (e.g., transmission error rates) in the network, and schedule the UL transmissions based on the measured interference (e.g., to minimize cross-link interference) and the monitored information (e.g., to minimize transmission error rates). 
       FIG.  10    is a timing diagram illustrating a scheduling method  1000  for an IAB network according to embodiments of the present disclosure.  FIG.  10    illustrates communications between multiple components as represented by the vertical lines. The method  1000  may be employed by BSs (e.g., the BSs  105 ) to communicate with each other over wireless backhaul links (e.g., the wireless backhaul links  234 ) in an IAB network (e.g., the networks  200  and  300 ). The method  1000  illustrates a node R 2  having two parent nodes R 1  and R 2  (e.g., in a mesh topology) for simplicity of discussion, but may be scaled to include any suitable number of parent nodes (e.g., three, four, five, or six). The nodes R 1 , R 2 , and R 3  may correspond to the BSs  105 . The nodes R 1 , R 2 , and R 3  may correspond to a portion of the topology  400 . For example, the node R 1  may be at a hop h 1  with respect to the anchor  410  and the node R 2  may be at a hop h 2  with respect to the anchor  410 , where h 1  and h 2  are positive integers. The method  1000  may be used in conjunction with the method  500 . 
     In the method  1000 , the node R 1  may transmit DL signals  1010  according to a timing reference of the node R 1  as shown by the DL 1  Tx timeline  1001 . The DL signals  1010  may arrive at the node R 3  after a propagation delay as shown by the DL 1  Rx timeline  1003 . The node R 2  may transmit DL signals  1020  according to a timing reference of the node R 2  as shown by the DL 2  Tx timeline  1002 . The DL signals  1020  may arrive at the node R 3  after a propagation delay as shown by the DL 2  Rx timeline  1005 . 
     The node R 3  may transmit UL signals  1030  based on a timing reference instructed by the node R 1  (e.g., via a TA command) as shown by the UL 1  Tx timeline  1004 . Similarly, the node R 3  may transmit UL signals  1040  based on a timing reference instructed by the node R 2  (e.g., via a TA command) as shown by the UL 2  Tx timeline  1006 . 
     When the node R 3  employs the second option  934  described in the method  900  with respect to  FIG.  9   , the node R 3  may align the DL transmit timing of the node R 3  to an average timing of the parent nodes R 1  and R 2 . When employing the second option  934 , the maximum gap period required may correspond to a maximum RTT in the network, for example, a maximum RTT  1050  from the parent nodes R 1  and R 2  to the node R 3  as shown. After aligning or selecting a timing reference, the node R 3  may determine gap periods for scheduling communications with child nodes or UEF-nodes of the node R 3  as a function of the timing reference, as described in greater detail herein. 
     As shown in the methods  800 ,  900 , and  1000 , the present disclosure provides techniques for timing alignment across multi-hop IAB networks. In an example, DL transmission timing is aligned across IAB nodes (e.g., the BSs  105  and the relay nodes  1310 ) and IAB donors (e.g., the anchor  410 , the BSs  105 , and the relay nodes  1310 )) as shown by the option  934 . In an example, DL and UL transmission timing is aligned within an IAB-node as shown by the option  932 . 
       FIG.  11    is a signaling diagramming illustrating an IAB communication method  1100  according to embodiments of the present disclosure. The method  1100  is implemented among relay nodes R 1 , R 2 , and R 3 . The node R 1  may correspond to a BS (e.g., the BSs  105  and  700  and the anchor  410 ) and may function as an ACF-node to the nodes R 2  and R 3 . The nodes R 2  and R 3  may correspond to BSs and/or UEs (e.g., the UEs  115  and  600 ) and may function as UEF-nodes to the node RE Steps of the method  1100  can be executed by computing devices (e.g., a processor, processing circuit, and/or other suitable component) of the relay nodes. As illustrated, the method  1100  includes a number of enumerated steps, but embodiments of the method  1100  may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order. Use of the label “step” is to describe an action or activity as opposed to setting a prescribed or required order of events. 
     At step  1110 , the node R 1  determines a first gap period (e.g., the period  834 ) for communicating with the node R 2 . For example, the node R 1  may receive a report from the node R 2 . The reports may include capability information, a transmit-receive switching requirement, a synchronization reference switching requirement, or scheduling information of the node R 2 . The capability information may include a UE-category or a power class of the node R 2  and/or frequency bands, radio access technologies (RATs), measurement and reporting supported by the node R 2 , and/or features supported by the node R 2 . The transmit-receive switching requirement refers to the amount of time required for the node R 2  to switch from a transmit mode to a receive mode or from a receive mode to a transmit mode. The synchronization reference switching requirement refers to the amount of time for the node R 2  to switching between two or more synchronization references. The node R 1  may determine the first gap period based on the report. 
     At step  1120 , the node R 1  determines a second gap period (e.g., the period  834 ) for communicating with the node R 3 , for example, based on a transmit-receive switching of the node R 3 . 
     At step  1130 , the node R 1  communicates with the node R 2  based on the first gap period. For example, the node R 1  may determine a DL transmission time for transmitting to the node R 2  and/or a UL transmission time for the node R 2  based on the first gap period. 
     At step  1140 , the node R 1  communicates with the node R 3  based on the second gap period. For example, the node R 1  may determine a DL transmission time for transmitting to the node R 3  and/or a UL transmission time for the node R 3  based on the second gap period. 
     In some embodiments, the first gap period and the second gap period can be indicated in downlink control information (DCI) along with scheduling information. For example, in the context of LTE or NR, the node R 1  may transmit a physical downlink control channel (PDCCH) signal indicating a schedule for communicating a signal with the node R 2 . The PDCCH signal may include a DCI indicating a gap period. Alternatively, gap periods can be indicated in other DCI, media access control (MAC) control element (CEs), MIBs, SIBs, and/or a RRC messages. 
     As can be seen, in the method  1100 , an ACF-node or a parent node (e.g., the node R 1 ) may determine a UEF-specific gap period for communicating with a UEF-node or a child node (e.g., the nodes R 2  and R 3 ). 
       FIG.  12    is a signaling diagramming illustrating an IAB communication method  1200  according to embodiments of the present disclosure. The method  1200  is implemented among relay nodes R 1 , R 2 , and R 3 . The node R 1  may correspond to a BS (e.g., the BSs  105  and  700  and the anchor  410 ) and may function as an ACF-node to the nodes R 2  and R 3 . The nodes R 2  and R 3  may correspond to BSs and/or UEs (e.g., the UEs  115  and  600 ) and may function as UEF-nodes to the node RE Steps of the method  1200  can be executed by computing devices (e.g., a processor, processing circuit, and/or other suitable component) of the relay nodes. As illustrated, the method  1200  includes a number of enumerated steps, but embodiments of the method  1200  may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order. 
     The method  1200  may improve resource utilization efficiency compared to the method  1100 . For example, gap periods can be wasteful in terms of resource utilization since gap periods are idle periods with no transmission. When a parent node (e.g., the node R 1 ) determines that all of its child nodes (e.g., the nodes R 2  and R 3 ) require a certain gap period, the parent node may adjust (e.g., advance or delay) a timing reference of the parent node. In other words, the parent node may adjust a frame boundary or a slot boundary for communicating with the child nodes. 
     Alternatively, when the parent node determines that multiple gap periods in a slot for communicating with the child nodes, the parent node may switch from a normal cyclic prefix (CP) mode to an extended CP (ECP) mode. CP refers to the prefixing of a symbol with a repetition of an end of the symbol. CP is used in OFDM symbols to mitigate inter-symbol interference (ISI). An ECP refers to a CP with an extended time duration compared to a normal CP. 
     At step  1210 , the node R 1  adjusts the node R 1 &#39;s timing reference. For example, the node R 1  may determine the adjustment such that the adjustment may not cause interference to other relay nodes in the network or create scheduling conflicts with other relay nodes. The adjustment may be a delaying of and advancing of the timing reference or an inclusion of an ECP. 
     At step  1220 , the node R 1  communicates with the node R 2  based on the adjusted timing reference. 
     At step  1230 , the node R 1  communicates with the node R 3  based on the adjusted timing reference. 
     Accordingly, the present disclosure provides techniques for alignments between IAB nodes and/or IAB donors or within an IAB node based on a slot-level-alignment or a symbol-level-alignment. 
       FIGS.  13 - 16    illustrate various mechanisms for maintaining and/or refining synchronization in an IAB network (e.g., the networks  200  and  300 ), for example, based on a timing reference of an anchor (e.g., the anchor  410 ), a relay node (e.g., the BSs  105  and the UEs  115 ) with a GPS connection, a selected relay node, and/or a central entity. 
       FIG.  13    illustrates a distributed synchronization method  1300  according to embodiments of the present disclosure. The method  1300  may be employed by BSs (e.g., the BSs  105 ) and UEs (e.g., the UEs  115 ) in an IAB network (e.g., the network  100 ). The method  1300  illustrates four relay nodes  1310  with one relay node including a GPS  1320  for simplicity of discussion, but may be scaled to include any suitable number of relay nodes (e.g., five, six, ten, or more than ten) and/or GPS connections (e.g., three, four, five, or six). 
     In the method  1300 , the node R 1   1310  may correspond to a BS and the nodes R 2 , R 3 , and R 4   1310  can be a BS or a UE. In an embodiment, the node R 1   1310  may be an anchor (e.g., the anchor  410 ) in the network. Each of the nodes  1310  may maintain one or more synchronization references and may communicate synchronization information (e.g., timing information and/or frequency information) with each other. Each node  1310  may adjust the node  1310 &#39;s synchronization references based on synchronization information received from other nodes. 
     The nodes  1310  may exchange synchronization information related to internal timing references with each other. In addition, the node R 2   1310  may transmit synchronization information based on a timing provided by the GPS  1320  to the node R 1   1310 . The nodes  1310  may receive synchronization information from one or more sources (e.g., other nodes  1310  and/or the GPS  1320 ) and may adjust an internal timing reference based on the received synchronization information. 
       FIG.  14    illustrates a centralized synchronization method  1400  according to embodiments of the present disclosure. The method  1400  may be employed by BSs (e.g., the BSs  105 ) and UEs (e.g., the UEs  115 ) in an IAB network (e.g., the network  100 ). The method  1400  is substantially similar to the method  1300 , but employs a central entity  1410  to determine adjustments for synchronization references of the nodes  1310 . The central entity  1410  may be a logical entity and may be physically mapped to any node in a network, for example, an anchoring node, a relay node  1310 , or a dedicated node. 
     In the method  1400 , the central entity  1410  may collect synchronization information from the nodes  1310 . The central entity  1410  may determine synchronization adjustments for the nodes  1310  based on the collected synchronization information. The central entity  1410  may transmit the determined synchronization adjustments to corresponding nodes  1310 . 
       FIG.  15    is a signaling diagramming illustrating a distributed synchronization method  1500  according to embodiments of the present disclosure. The method  1500  is implemented between a relay node R 1  (e.g. the BSs  105  and the UEs  115  and the nodes  1310 ) and other relay nodes (e.g. the BSs  105  and the UEs  115  and the nodes  1310 ) in an IAB network (e.g., the network  100 ). The node R 1  may be coupled to a GPS (e.g., the GPS  1320 ). The other relay nodes may include a combination of UEF-nodes of the node R 1  and ACF-nodes of the node R 1 . The method  1500  may employ similar mechanisms as described in the method  1300  with respect to  FIG.  13   . Steps of the method  1500  can be executed by computing devices (e.g., a processor, processing circuit, and/or other suitable component) of the relay nodes. As illustrated, the method  1500  includes a number of enumerated steps, but embodiments of the method  1500  may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order. 
     At step  1510 , the GPS transmits timing information to the node R 1 . 
     At step  1520 , one or more other relay nodes may transmit messages to the node R 1 . Each message may include synchronization information associated with a synchronization reference (e.g., a GPS  1320  or an internal synchronization reference) of a corresponding relay node. The synchronization information can include timing information or frequency information. The message may indicate an amount of timing adjustment and/or an amount of frequency adjustment for the node RE In some embodiments, the messages are LTE or NR MAC CEs. 
     At step  1530 , one or more other relay nodes may transmit synchronization reference signals, for example, based on synchronization references at corresponding relay nodes. The synchronization reference signals may be layer 1 (L1) (e.g., physical layer) signals including a predetermined signal sequence. In some embodiments, the synchronization reference signals may be carried in NR synchronization signal (SS) blocks. 
     In an embodiment, the synchronization reference signals and/or the messages may be transmitted based on a semi-static schedule. In an embodiment, the synchronization reference signals and/or the messages may be transmitted in response to a request from the node R 1 . 
     At step  1540 , the node R 1  may adjust synchronization references of the node R 1  based on the timing information received from the GPS, the synchronization information in the received messages, and/or measurements (e.g., timing and/or frequency measurements) of the received synchronization reference signals. 
     In an embodiment, the node R 1  may adjust the synchronization references of the node R 1  upon detecting a difference between the synchronization references of the node R 1  and the received synchronization reference signals exceeding a threshold. 
     In some embodiments, there can be a priority level associated with each source of the synchronization information. The information about the priority level may be included in each corresponding synchronization message indicating a source of the synchronization information, for example, whether the synchronization information is based on a GPS or an internal synchronization reference. Additionally or alternatively, the information about the priority level may be indicated through other messages, by other nodes in the system, or acquired from upper layer. In some embodiments, each message can include a priority level indicating a hop count or level (e.g., the level  402 ) at which a corresponding node is located. Thus, a node (e.g., the node R 1 ) receiving the synchronization information may adjust the node&#39;s internal synchronization reference as a function of the priority levels. For example, the node may adjust an internal synchronization reference based on an average determined from the highest priority synchronization information. 
       FIG.  16    is a signaling diagramming illustrating a centralized synchronization method  1600  according to embodiments of the present disclosure. The method  1600  is implemented between a central entity (e.g., the central entity  1410 ) and relay nodes (e.g. the BSs  105  and the UEs  115 ) in an IAB network (e.g., the network  100 ). The method  1600  may employ similar mechanisms as described in the method  1400  with respect to  FIG.  14   . Steps of the method  1600  can be executed by computing devices (e.g., a processor, processing circuit, and/or other suitable component) of the relay nodes. As illustrated, the method  1600  includes a number of enumerated steps, but embodiments of the method  1600  may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order. 
     At step  1610 , the relay nodes may transmit synchronization information to the central entity. The synchronization information may correspond to timing and/or frequency information of a synchronization reference (e.g., a GPS  1320  or an internal synchronization reference) of a corresponding relay node. 
     At step  1620 , the central entity may determine adjustments for synchronization references of the relay nodes based on the received synchronization information. 
     At step  1630 , the central entity may transmit the determined synchronization adjustments to corresponding relay nodes. For example, the central entity may instruct a first relay node to communicate with a second relay node using a particular adjustment. In some embodiments, the adjustments may include gap periods, transmit timing adjustments, receive timing adjustments, synchronization timing adjustments, and/or synchronization frequency adjustments. In some embodiments, the central entity may further receive reports from the relay nodes. The reports may include capability information, scheduling information, transmit-receive switching requirements, synchronization reference switching requirements associated with the relay nodes. The central entity may determine the gap periods and/or cyclic prefix configurations (e.g., normal CP or ECP) based on the reports. In some embodiments, the synchronization information and the adjustments may be carried in NR or LTE RRC messages. 
       FIG.  17    illustrates a wireless backhaul network  1700  according to embodiments of the present disclosure. The network  1700  may be similar to the networks  200  and  300 . The network  1700  includes a plurality of relay nodes  1310  shown as R 1  to R 11 . Some of the nodes  1310  (e.g., R 5  and R 8 ) may include connections to GPSs  1320 . The network  1700  may employ the topology  400  to establish multi-hop relay links  1702 . The node R 1   1310  may be an anchoring node (e.g., the anchor  410 ) in communication with a core network (e.g., the network  130 ) via an optical fiber link (e.g., the optical fiber link  134 ). The node R 1   1310  may function as an intermediary to relay backhaul traffic between the core network and the other nodes  1310 . 
       FIG.  18    illustrates a traffic routing overlay  1800  over the wireless backhaul network  1700  according to embodiments of the present disclosure. The traffic routing overlay  1800  includes traffic routes  1802  established among the nodes  1310  for routing traffic in the network  1700 . The traffic routes  1802  may or may not be overlaid on top of all the links  1702 . For example, while the node R 7   1310  and the node R 8   1310  can be connected by a link  1702 , the traffic routing overlay  1800  does not include a traffic route  1802  between the node R 7   1310  and the node R 8   1310 . The traffic routing overlay  1800  may partition and allocate resources for the traffic routes  1802  (e.g., overlaid over the links  1702 ) to transport traffic among the nodes  1310 , for example, using the method  500 . The traffic routing overlay  1800  can include various network control and/or management operations such as keep alive and link maintenance operations. 
       FIG.  19    illustrates a synchronization overlay  1900  over the wireless backhaul network  1700  according to embodiments of the present disclosure. The synchronization overlay  1900  is based on the traffic routing overlay  1800 . The synchronization overlay  1900  reuses the traffic routes  1802  established by the traffic routing overlay  1800  and resources allocated by the traffic routing overlay  1800  to transport synchronization information and/or adjustment instructions in the among the nodes  1310 . The synchronization overlay  1900  can support on-demand exchange of synchronization information and/or adjustments. The synchronization overlay  1900  can also leverage network controls (e.g., keep alive and link maintenance protocols) supported by the traffic routing overlay  1800 . 
       FIG.  20    illustrates a synchronization overlay  2000  over the wireless backhaul network  1700  according to embodiments of the present disclosure. Instead of reusing the traffic routing overlay  1800  as in the overlay  1900 , the overlay  2000  may establish routes  2002  over the links  1702 . The routes  2002  may be different from the traffic routes  1802 . For example, the overlay  2000  may establish the routes  2002  based on synchronization sources (e.g., the GPSs  1320 ) available in the network  1700 . Thus, the overlay  2000  may provide better utilization of synchronization sources, but may be required to allocate resources, determine schedules, and/or other network controls separate from the overlay  1800 . 
     When a network (e.g., the networks  200  and  300 ) employs the overlay  1900  (e.g., reusing the traffic overlay  1800 ), UEF-nodes in the network can provide synchronization feedbacks to corresponding ACF-nodes, for example, via MAC CEs. ACF-nodes in the network may receive the feedbacks from corresponding UEF-nodes and adjusts synchronization references based on the feedbacks. 
     When a network employs the overlays  1900  or  2000 , relay nodes in the network can send physical reference signals (e.g., in synchronization signal blocks (SSBs)). Other relay nodes in the network may receive the physical reference signals and may adjust corresponding synchronization references based on measurements of the received physical reference signals, for example, for frequency tracking. 
       FIG.  21    is a signaling diagramming illustrating a synchronization method  2100  according to embodiments of the present disclosure. The method  2100  is implemented between a relay node R 1  (e.g. the nodes  1310  and the BSs  105  and  700 ) and other relay nodes (e.g. the nodes  1310 , the BSs  105  and  700 , and the UEs  115  and  600 ) in an IAB network (e.g., the network  100 ). The other relay nodes may be UEF-nodes or child nodes of the node R 1 . The node R 1  and the other relay nodes may be part of the overlay  1900  or  2000 . Steps of the method  2100  can be executed by computing devices (e.g., a processor, processing circuit, and/or other suitable component) of the relay nodes. As illustrated, the method  2100  includes a number of enumerated steps, but embodiments of the method  2100  may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order. 
     At step  2110 , the node R 1  determines a first synchronization reference adjustment for one or more internal synchronization references of the node R 1 . The first adjustment may be relatively small, for example, a few samples or less than a symbol time period. The node R 1  may adjust the internal synchronization references and continue to communicate with the other relay nodes. 
     At step  2120 , the node R 1  communicates with the other relay nodes based on the adjusted synchronization references. 
     At step  2130 , the other relay nodes may track the adjustment based on the communications with the node R 1 . For example, a relay node may receive a communication or synchronization signal from the node R 1  and may detect the adjustment from the received communication signal. Thus, the relay node may adjust an internal synchronization reference of the node based on the detected adjustment. 
     At step  2140 , after a period of time, the node R 1  determines a second synchronization reference adjustment for the internal synchronization references. The second adjustment may be relatively large, for example, greater than a symbol time period. The node R 1  may determine that a resynchronization is required from the other relay nodes. 
     At step  2150 , the node R 1  transmits a resynchronization request to the other relay nodes. The node R 1  may transmit the resynchronization request in a broadcast mode. The node R 1  may additionally indicate resource and/or configuration information (e.g., a set of synchronization reference signals or synchronization pulses) that the other relay nodes may use for the resynchronization. In some embodiments, the node R 1  may further indicate a resynchronization configuration, for example, including an amount of the adjustment and/or when the adjustment becomes effective (e.g., an offset time period or a number of slots with respect to a transmission time of the request). 
     At step  2160 , upon receiving the resynchronization request, the other relay nodes may perform resynchronization based on the request. For example, a relay node may receive synchronization reference signals based on the resources and/or configuration indicated in the request and may adjust corresponding internal synchronization references at a start time corresponding to the offset time period or slot number indicated in the request. While the method  2100  is described in the context of time synchronization and adjustment, the method  2100  can be applied to perform frequency synchronization and adjustment. 
       FIG.  22    is a flow diagram of a method  2200  for communicating in an IAB network according to embodiments of the present disclosure. The network may be similar to the networks  200 ,  300 , and  1700  and may be configured with the topology  400  and/or the overlays  1800 ,  1900 , and  2000 . Steps of the method  2200  can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device, such as the BSs  105  and  700  and the UEs  115  and  600 . The method  2200  may employ similar mechanisms as in the methods  500 ,  800 ,  900 ,  1000 ,  1100 ,  1200 ,  1300 ,  1400 ,  1500 ,  1600 , and  2100  described with respect to  FIGS.  5 ,  8 ,  9 ,  10 ,  11 ,  12 ,  13 ,  14 ,  15 ,  16 , and  21   , respectively. As illustrated, the method  2200  includes a number of enumerated steps, but embodiments of the method  2200  may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order. 
     At step  2210 , the method  2200  includes receiving, by a first wireless communication device, synchronization information from one or more wireless relay devices. The first wireless communication device and the one or more wireless relay devices may correspond to the relay nodes  1310 . 
     At step  2220 , the method  2200  includes adjusting, by the first wireless communication device, one or more synchronization references based on at least some of the synchronization information. 
     At step  2230 , the method  2200  includes communicating, by the first wireless communication device with the one or more wireless relay devices, communication signals based on the one or more adjusted synchronization references. The communication signals can include a combination of backhaul traffic and access traffic. 
     In an embodiment, the first wireless communication device may be a BS and the one or more wireless relay devices can include parent nodes (e.g., ACF-nodes) and/or child nodes (e.g., UEF-nodes) of the first wireless communication devices. For example, the one or more wireless relay devices may include a combination of UEs (e.g., child nodes) and other BSs (e.g., child nodes and/or parent nodes). The UEs may be served by the BS over wireless access links (e.g., the wireless access links  125 ). The BS may relay backhaul traffic for other BSs over wireless backhaul links (e.g., the wireless backhaul links  234 ). 
     In an embodiment, the first wireless communication device may receive the synchronization information by receiving, from a first wireless relay device of the one or more wireless relay devices, a message including at least one of timing information associated with a synchronization reference of the first wireless relay device, frequency information associated with the synchronization reference of the first wireless relay device, capability information of the first wireless relay device, scheduling information of the first wireless relay device, a transmit-receive switching requirement of the first wireless relay device, or a synchronization reference switching requirement of the first wireless relay device. 
     In an embodiment, the first wireless communication device may receive the synchronization information by receiving, from a first wireless relay device of the one or more wireless relay devices, a synchronization reference signal that is based on a synchronization reference of the first wireless relay device. The first wireless communication device can determine frequency offset and/or timing offset based on measurements of the received synchronization reference signals. 
     In an embodiment, the synchronization information may include priority level information. The priority level information may include the source of the synchronization information, for example, whether the synchronization information is obtained from a GPS or an internal synchronization reference of a corresponding relay node. The priority level information may also include a hop count indicating the number of hops (e.g., the levels  402 ) with respect to original sources of corresponding synchronization references. Thus, the first wireless communication device can adjust the one or more synchronization references as a function of the priority levels. 
     In an embodiment, the first wireless communication device may receive the synchronization information from a central entity (e.g., the central entity  1410 ). In an embodiment, the first wireless communication device may further receive at least one of timing information or frequency information from an external synchronization source and may adjust the one or more synchronization references further based on the at least one of timing information or frequency information. The external synchronization source may be a GPS (e.g., the GPS  1320 ) or a synchronization source provided by another radio access technology (RAT). In some embodiments, the first wireless communication device may request for the synchronization information. In some other embodiments, the first wireless communication device may receive the synchronization information based on a semi-static schedule. In an embodiment, the first communication device may transmit synchronization information associated with the one or more synchronization references based on at least one of a schedule, a synchronization information request, a measurement of the one or more synchronization references, or the adjusting of the one or more synchronization references. 
     In an embodiment, the first wireless communication device may relay backhaul traffic of the one or more wireless relay devices to an anchoring wireless communication device (e.g., the anchor  410 ) in communication with a core network (e.g., the core network  130 ) via an optical fiber link (e.g., the optical fiber link  134 ). The first wireless communication device may communicate with the one or more wireless relay devices based on a DL transmit timing of the anchoring wireless communication device, for example, using the second option  934  shown in the method  900 . 
     In an embodiment, the first wireless communication device may communicate with the one or more wireless relay devices using UEF-specific gap period (e.g., the gap period  834 ) based on each wireless relay device&#39;s capability (e.g., transmit-receive switching time). For example, the first wireless communication device may determine a first gap period based on a capability parameter of a first wireless relay device of the one or more wireless relay devices. The first wireless communication device may determine a second gap period based on a capability parameter of a second wireless relay device of the one or more wireless relay devices, the second gap period different from the first gap period. The first wireless communication device may communicate with the first wireless relay device and the second wireless relay device based on the first gap period and the second gap period, respectively. 
     In an embodiment, the first wireless communication device can determine a gap period based on measurements and indication received from parent nodes (e.g., ACF-nodes) and/or child nodes (e.g., the UEF-nodes) of the first wireless communication device. In an embodiment, the first wireless communication device can determine a gap period based on schedules of the first wireless communication device or schedules of other relay nodes. In an embodiment, the first wireless communication device can determine a gap period based on commands received from a central entity. 
     In some embodiments, a gap period can be located at any position within a slot, for example, at the beginning of a slot, at the end of a slot, or in the middle of the slot. The gap period can be network-wide, cell-specific, and/or UEF-specific. In some embodiments, a gap period may change from slot to slot. In some embodiments, a gap period can be semi-statically configured with a semi-persistent pattern. 
     In an embodiment, the first wireless communication device may simultaneously communicate with a first wireless relay device and a second wireless relay device of the one or more wireless relay devices. The first wireless communication may communicate with the first wireless relay device using a first synchronization reference and may communicate with the second wireless relay device using a second synchronization reference that is different from the first synchronization reference. 
     In an embodiment, the first wireless communication device may switch from a normal CP to an ECP during the communication based on capability parameters of the one or more wireless relay devices. When the first wireless communication device multiplexes communication with multiple relay devices, there may be a need to extend the duration of a CP (e.g., to an ECP) to accommodate the different timings of the multiple relay devices in order to avoid ISI. 
     In an embodiment, the first wireless communication device may use different antenna sub-arrays and different digital chains when communicating simultaneously with multiple wireless relay devices. In such an embodiment, the first wireless communication device may not be required to switch to an ECP mode. In another embodiment, the first wireless communication device may use different antenna sub-arrays with a single digital chain or a single antenna sub-array with multi-finger beamforming. In such an embodiment, the first wireless communication device may be required to switch to an ECP mode and multiplex the communications, for example, using frequency-division multiplexing (FDM). 
     In an embodiment, the first wireless communication device may communicate with a first wireless relay device of the one or more wireless relay devices, a first communication signal of the communication signals during a first time period based on a first synchronization reference of the one or more synchronization references. The first wireless communication device may communicate with a second wireless relay device of the one or more wireless relay devices, a second communication signal of the communication signals during a second time period subsequent to the first time period based on a second synchronization reference of the one or more synchronization references that is different than the first synchronization reference. For example, the first wireless communication device may transmit and/or receive a reference signal (e.g., a CSI-RS), a control signal, and/or a data signal by sweeping transmit and/or receive beams towards different directions over consecutive time periods. In some embodiments, common resources may be allocated to multiple relay devices for transmitting synchronization signals or beam references signals. Since different relay devices can have different propagation delays, the use of ECP may be beneficial to accommodate the different delays. 
     While a schedule may accommodate timing misalignment among different nodes and/or avoid ISI by introducing gap periods or using an ECP mode, there is a tradeoff between the use of ECP and gap periods. The use of ECP increases overheads in all symbols within a slot. However, when a schedule requires multiple gap periods within a slot, the use of ECP may be suitable. Conversely, when a schedule does not require multiple switching between different synchronization references, the use of gap periods may be suitable. For example, a relay node may sweep multiple directions towards one node based on a first synchronization reference and then sweep multiple directions towards another node based on a second synchronization reference. In such a scenario, the relay node may require a single gap period between the two sweeps, which may be more efficient than using an ECP for all symbols. 
     In an embodiment, the first wireless communication device can determine whether to select a normal CP or an ECP based on measurements and indication received from parent nodes (e.g., ACF-nodes) and/or child nodes (e.g., the UEF-nodes) of the first wireless communication device, schedules of the first wireless communication device, schedules of other relay nodes, and/or commands received from a central entity. 
       FIG.  23    is a flow diagram of a method  2300  for managing synchronization references in an IAB network according to embodiments of the present disclosure. The network may be similar to the networks  200 ,  300 , and  1700  and may be configured with the topology  400  and/or the overlays  1800 ,  1900 , and  2000 . Steps of the method  2300  can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device, such as the BSs  105  and  700  and the central entity  1410 . The method  2300  may employ similar mechanisms as in the methods  500 ,  800 ,  900 ,  1000 ,  1100 ,  1200 ,  1300 ,  1400 ,  1500 ,  1600 , and  2100  described with respect to  FIGS.  5 ,  8 ,  9 ,  10 ,  11 ,  12 ,  13 ,  14 ,  15 ,  16 , and  21   , respectively. As illustrated, the method  2300  includes a number of enumerated steps, but embodiments of the method  2300  may include additional steps before, after, and in between the enumerated steps. In some embodiments, one or more of the enumerated steps may be omitted or performed in a different order. 
     At step  2310 , the method  2300  includes receiving, by a central entity from one or more wireless relay devices (e.g., the BSs  105  and  700 , the UEs  115  and  600 , and the relay nodes  1310 ), synchronization information associated with the one or more wireless relay devices. The synchronization information may include frequency information and/or timing information associated with synchronization references of the one or more wireless relay devices. 
     At step  2320 , the method  2300  includes determining, by the central entity, a synchronization reference adjustment based on at least some of the synchronization information. The adjustment may include a gap period, a cyclic prefix configuration, a timing synchronization adjustment, a frequency synchronization adjustment, a transmit timing adjustment, and/or a receive timing adjustment. 
     At step  2330 , the method  2300  includes transmitting, by the central entity, a message instructing a first wireless relay device of the one or more wireless relay devices to communicate with a second wireless relay device of the one or more wireless relay devices based on the synchronization reference adjustment. 
     In an embodiment, the central entity can collect reports from the one or more wireless relay devices. The reports can include at least one of capability information of the one or more wireless relay devices, scheduling information of the one or more wireless relay devices, transmit-receive switching requirements of the one or more wireless relay devices, synchronization reference switching requirements of the one or more wireless relay devices, or priority levels associated with synchronization reference sources of the one or more wireless relay devices. The central entity can determine at least one of the gap period or the cyclic prefix configuration for the first wireless relay device to communicate with the second wireless relay device based on the reports. 
     In an embodiment, the first wireless communication device and the second wireless communication devices may both be BSs, where the adjustment is for backhaul communication. For example, the first wireless communication device may be a parent node or an ACF-node of the second wireless communication device. Alternatively, the first wireless communication device may be a child node or a UEF-node of the second wireless communication device. 
     In an embodiment, the first wireless communication device may be a BS and the second wireless communication device may be a UE, where the adjustment is for access communication. 
     In another embodiment, the first wireless communication device may be a UE and the second wireless communication device may be a BS, where the adjustment is for access communication. 
     Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). 
     The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items (for example, a list of items prefaced by a phrase such as “at least one of” or “one or more of”) indicates an inclusive list such that, for example, a list of [at least one of A, B, or C] means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). 
     Embodiments of the present disclosure further include a computer-readable medium having program code recorded thereon, the program code comprising code for causing a first wireless communication device to receive synchronization information associated with one or more wireless relay devices; code for causing the first wireless communication device to adjust one or more synchronization references based on at least some of the synchronization information; and code for causing the first wireless communication device to communicate, with the one or more wireless relay devices, communication signals based on the one or more adjusted synchronization references, wherein at least one of the communication signals includes backhaul traffic. 
     The computer-readable medium further includes wherein the code for causing the first wireless communication device to receive the synchronization information is further configured to receive, from a first wireless relay device of the one or more wireless relay devices, a message including at least one of timing information associated with a synchronization reference of the first wireless relay device, frequency information associated with the synchronization reference of the first wireless relay device, capability information of the first wireless relay device, scheduling information of the first wireless relay device, a transmit-receive switching requirement of the first wireless relay device, or a synchronization reference switching requirement of the first wireless relay device. The computer-readable medium further includes wherein the code for causing the first wireless communication device to receive the synchronization information is further configured to receive, from a first wireless relay device of the one or more wireless relay devices, a synchronization reference signal that is based on a synchronization reference of the first wireless relay device. The computer-readable medium further includes wherein the code for causing the first wireless communication device to receive the synchronization information is further configured to receive priority levels associated with sources of the synchronization information, and wherein the adjusting includes adjusting the one or more synchronization references based on the priority levels. The computer-readable medium further includes wherein the code for causing the first wireless communication device to receive the synchronization information is further configured to receive priority levels associated with hop counts of the one or more wireless relay devices with respect to original sources of corresponding synchronization references, and wherein the adjusting includes adjusting the one or more synchronization references based on the priority levels. The computer-readable medium further includes wherein the code for causing the first wireless communication device to receive the synchronization information is further configured to receive, from a central entity, the synchronization information. The computer-readable medium further includes code for causing the first wireless communication device to receive, from an external synchronization source, at least one of timing information or frequency information; and code for causing the first wireless communication device to adjust the one or more synchronization references further based on the at least one of timing information or frequency information. The computer-readable medium further includes wherein the external synchronization source includes at least one of a global positioning system (GPS) or a synchronization source of another radio access technology (RAT). The computer-readable medium further includes code for causing the first wireless communication device to transmit a message requesting for the synchronization information. The computer-readable medium further includes code for causing the first wireless communication device to transmit synchronization information associated with the one or more synchronization references based on at least one of a schedule, a synchronization information request, a measurement of the one or more synchronization references, or the adjusting of the one or more synchronization references. The computer-readable medium further includes code for causing the first wireless communication device to relay, to an anchoring wireless communication device that is in communication with a core network via an optical fiber link, a first communication signal of the communication signals, wherein the code for causing the first wireless communication device to communicate the communication signals is further configured to transmit, to a first wireless relay device of the one or more wireless relay devices, a second communication signal based on a downlink transmit timing of the anchoring wireless communication device. The computer-readable medium further includes wherein the code for causing the first wireless communication device to communicating the communication signals is further configured to communicate, with a first wireless relay device of the one or more wireless relay devices, a second communication signal of the communication signals including access traffic. The computer-readable medium further includes code for causing the first wireless communication device to transmit a message requesting the one or more wireless relay devices to resynchronize to the one or more adjusted synchronization references. The computer-readable medium further includes code for causing the first wireless communication device to transmit a configuration for resynchronizing to the one or more adjusted synchronization references. The computer-readable medium further includes code for causing the first wireless communication device to determine a first gap period based on at least one of a capability parameter of a first wireless relay device of the one or more wireless relay devices, scheduling information of the first wireless relay device, a transmit-receive switching requirement of the first wireless relay device, or a synchronization reference switching requirement of the first wireless relay device; and code for causing the first wireless communication device to determine a second gap period based on at least one a capability parameter of a second wireless relay device of the one or more wireless relay devices, scheduling information of the second wireless relay device, a transmit-receive switching requirement of the second wireless relay device, or a synchronization reference switching requirement of the second wireless relay device, the second gap period different from the first gap period. The computer-readable medium further includes wherein the code for causing the first wireless communication device to communicate the communication signals is further configured to transmit, to the first wireless relay device, a message indicating the first gap period; transmit, to the second wireless relay device, a message indicating the second gap period; communicate with the first wireless relay device based on the first gap period; and communicate with the second wireless relay device based on the second gap period. The computer-readable medium further includes wherein the code for causing the first wireless communication device to communicate the communication signals by switching from a normal cyclic prefix to an extended cyclic prefix based on at least one of capability parameters of the one or more wireless relay devices, transmit-receive switching requirements of the one or more wireless relay devices, synchronization reference switching requirements of the one or more wireless relay devices, or synchronization references of the one or more wireless relay devices. The computer-readable medium further includes wherein the code for causing the first wireless communication device to communicate the communication signals is further configured to communicate, with a first wireless relay device of the one or more wireless relay devices, a first communication signal based on a first synchronization reference of the one or more synchronization references; and communicate, with a second wireless relay device of the one or more wireless relay devices, a second communication signal based on a second synchronization reference of the one or more synchronization references that is different than the first synchronization reference. The computer-readable medium further includes wherein the code for causing the first wireless communication device to communicate the communication signals is further configured to communicate the first communication signal in concurrent with the second communication signal. The computer-readable medium further includes wherein the code for causing the first wireless communication device to communicate the communication signals is further configured to communicate, with a first wireless relay device of the one or more wireless relay devices, a first communication signal of the communication signals during a first time period based on a first synchronization reference of the one or more synchronization references; and communicate, with a second wireless relay device of the one or more wireless relay devices, a second communication signal of the communication signals during a second time period subsequent to the first time period based on a second synchronization reference of the one or more synchronization references that is different than the first synchronization reference. 
     Embodiments of the present disclosure further include a computer-readable medium having program code recorded thereon, the program code comprising code for causing a central unit to receive, from one or more wireless relay devices, synchronization information associated with the one or more wireless relay devices; code for causing the central unit to determine a synchronization reference adjustment based on at least some of the synchronization information; and code for causing the central unit to transmit a message to instruct a first wireless relay device of the one or more wireless relay devices to communicate with a second wireless relay device of the one or more wireless relay devices based on the synchronization reference adjustment. 
     The computer-readable medium further includes wherein the code for causing the central unit to receive the synchronization information is further configured to receive at least one of frequency information associated with synchronization references of the one or more wireless relay devices or timing information associated with the synchronization references of the one or more wireless relay devices. The computer-readable medium further includes wherein the code for causing the central unit to transmit the message is further configured to transmit the synchronization reference adjustment including at least one of a gap period, a cyclic prefix configuration, a timing synchronization adjustment, a frequency synchronization adjustment, a transmit timing adjustment, or a receive timing adjustment. The computer-readable medium further includes code for causing the central unit to receive, from the one or more wireless relay devices, reports including at least one of capability information of the one or more wireless relay devices, scheduling information of the one or more wireless relay devices, transmit-receive switching requirements of the one or more wireless relay devices, synchronization reference switching requirements of the one or more wireless relay devices, or priority levels associated with synchronization reference sources of the one or more wireless relay devices; and code for causing the central unit to determine at least one of the gap period or the cyclic prefix configuration for the first wireless relay device to communicate with the second wireless relay device based on the reports. 
     Embodiments of the present disclosure further include an apparatus comprising means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for receiving synchronization information associated with one or more wireless relay devices; means (e.g., processors  602  and  702 ) for adjusting one or more synchronization references based on at least some of the synchronization information; and means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for communicating, with the one or more wireless relay devices, communication signals based on the one or more adjusted synchronization references, wherein at least one of the communication signals includes backhaul traffic. 
     The apparatus further includes wherein means for receiving the synchronization information is further configured to receive, from a first wireless relay device of the one or more wireless relay devices, a message including at least one of timing information associated with a synchronization reference of the first wireless relay device, frequency information associated with the synchronization reference of the first wireless relay device, capability information of the first wireless relay device, scheduling information of the first wireless relay device, a transmit-receive switching requirement of the first wireless relay device, or a synchronization reference switching requirement of the first wireless relay device. The apparatus further includes wherein the means for receiving the synchronization information is further configured to receive, from a first wireless relay device of the one or more wireless relay devices, a synchronization reference signal that is based on a synchronization reference of the first wireless relay device. The apparatus further includes wherein the means for receiving the synchronization information is further configured to receive priority levels associated with sources of the synchronization information, and wherein the adjusting includes adjusting the one or more synchronization references based on the priority levels. The apparatus further includes wherein the means for receiving the synchronization information is further configured to receive priority levels associated with hop counts of the one or more wireless relay devices with respect to original sources of corresponding synchronization references, and wherein the adjusting includes adjusting the one or more synchronization references based on the priority levels. The apparatus further includes wherein the means for receiving the synchronization information is further configured to receive, from a central entity, the synchronization information. The apparatus further includes means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for receiving from an external synchronization source, at least one of timing information or frequency information, and wherein the means for adjusting the one or more synchronization references to adjust the one or more synchronization references further based on the at least one of timing information or frequency information. The apparatus further includes wherein the external synchronization source includes at least one of a global positioning system (GPS) or a synchronization source of another radio access technology (RAT). The apparatus further includes means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for transmitting a message requesting for the synchronization information. The apparatus further includes means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for transmitting synchronization information associated with the one or more synchronization references based on at least one of a schedule, a synchronization information request, a measurement of the one or more synchronization references, or the adjusting of the one or more synchronization references. The apparatus further includes means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for relaying, to an anchoring wireless communication device that is in communication with a core network via an optical fiber link, a first communication signal of the communication signals, wherein the means for communicating the communication signals is further configured to transmit, to a first wireless relay device of the one or more wireless relay devices, a second communication signal based on a downlink transmit timing of the anchoring wireless communication device. The apparatus further includes wherein the means for communicating the communication signals is further configured to communicate, with a first wireless relay device of the one or more wireless relay devices, a second communication signal of the communication signals including access traffic. The apparatus further includes means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for transmitting a message requesting the one or more wireless relay devices to resynchronize to the one or more adjusted synchronization references. The apparatus further includes means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for transmitting a configuration for resynchronizing to the one or more adjusted synchronization references. The apparatus further includes means (e.g., processors  602  and  702 ) for determining a first gap period based on at least one of a capability parameter of a first wireless relay device of the one or more wireless relay devices, scheduling information of the first wireless relay device, a transmit-receive switching requirement of the first wireless relay device, or a synchronization reference switching requirement of the first wireless relay device; and means (e.g., processors  602  and  702 ) for determining a second gap period based on at least one of a capability parameter of a second wireless relay device of the one or more wireless relay devices, scheduling information of the second wireless relay device, a transmit-receive switching requirement of the second wireless relay device, or a synchronization reference switching requirement of the second wireless relay device, the second gap period different from the first gap period. The apparatus further includes wherein the means for communicating the communication signals is further configured to transmit, to the first wireless relay device, a message indicating the first gap period; transmit, to the second wireless relay device, a message indicating the second gap period; communicate with the first wireless relay device based on the first gap period; and communicate with the second wireless relay device based on the second gap period. The apparatus further includes wherein the means for communicating the communication signals is further configured to switch from a normal cyclic prefix to an extended cyclic prefix based on at least one of capability parameters of the one or more wireless relay devices, transmit-receive switching requirements of the one or more wireless relay devices, synchronization reference switching requirements of the one or more wireless relay devices, or synchronization references of the one or more wireless relay devices. The apparatus further includes wherein the means for communicating the communication signals is further configured to communicate, with a first wireless relay device of the one or more wireless relay devices, a first communication signal based on a first synchronization reference of the one or more synchronization references; and communicate, with a second wireless relay device of the one or more wireless relay devices, a second communication signal based on a second synchronization reference of the one or more synchronization references that is different than the first synchronization reference. The apparatus further includes wherein the means for communicating the communication signals is further configured to communicate the first communication signal in concurrent with the second communication signal. The apparatus further includes wherein the means for communicating the communication signals is further configured to communicate, with a first wireless relay device of the one or more wireless relay devices, a first communication signal of the communication signals during a first time period based on a first synchronization reference of the one or more synchronization references; and communicate, with a second wireless relay device of the one or more wireless relay devices, a second communication signal of the communication signals during a second time period subsequent to the first time period based on a second synchronization reference of the one or more synchronization references that is different than the first synchronization reference. 
     Embodiments of the present disclosure further include an apparatus comprising means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for receiving, from one or more wireless relay devices, synchronization information associated with one or more wireless relay devices; means (e.g., processors  602  and  702 ) for determining a synchronization reference adjustment based on at least some of the synchronization information; and means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for transmitting a message to instruct a first wireless relay device of the one or more wireless relay devices to communicate with a second wireless relay device of the one or more wireless relay devices based on the synchronization reference adjustment. 
     The apparatus further includes wherein the means for receiving the synchronization information is further configured to receive at least one of frequency information associated with synchronization references of the one or more wireless relay devices or timing information associated with the synchronization references of the one or more wireless relay devices. The apparatus further includes wherein the message includes the synchronization reference adjustment including at least one of a gap period, a cyclic prefix configuration, a timing synchronization adjustment, a frequency synchronization adjustment, a transmit timing adjustment, or a receive timing adjustment. The apparatus further includes means (e.g., the transceivers  610  and  710  and antennas  616  and  716 ) for receiving, from the one or more wireless relay devices, reports including at least one of capability information of the one or more wireless relay devices, scheduling information of the one or more wireless relay devices, transmit-receive switching requirements of the one or more wireless relay devices, synchronization reference switching requirements of the one or more wireless relay devices, or priority levels associated with synchronization reference sources of the one or more wireless relay devices; and means (e.g., processors  602  and  702 ) for determining at least one of the gap period or the cyclic prefix configuration for the first wireless relay device to communicate with the second wireless relay device based on the reports. 
     As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the spirit and scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.