Patent Publication Number: US-2020288324-A1

Title: Centralized coordination for shared spectrum systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY 
     This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/815,777 filed on Mar. 8, 2019. The above-identified provisional patent application is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to wireless communication systems, and more specifically, to centralized coordination for shared spectrum systems. 
     BACKGROUND 
     A communication system includes a downlink (DL) that conveys signals from transmission points, such as base stations (BSs), to reception points, such as user equipments (UEs). The communication system also includes an uplink (UL) that conveys signals from transmission points, such as UEs, to reception points, such as BSs. 
     Increasing the deployment density of BSs is a way to increase data throughput, via spatial reuse of frequencies. In fact, such spatial reuse has been one of the main contributors for increase in system throughput since the early days of cellular communication. While improving spatial reuse, a dense BS deployment may be inevitable at millimeter wave (mm-wave) and terahertz (THz) frequencies to improve coverage, by compensating for the pathloss and blockage. 
     Another way of increasing data throughput in the United States involves the opening of unlicensed or shared spectrums. For example, 3.55-3.7 GHz Citizens Broadband Radio Service (CBRS) band has a unique three-tiered, hierarchical access model, which includes incumbent (Federal user, Fixed Satellite Service), priority access licensees (PALs), and general authorized access (GAA) in descending order of priority. In another example, 5925-7125 MHz band and 5925-6425 MHz band are under consideration in United States and European Union, respectively, for unlicensed use. In yet another example, 37-38.6 GHz band is expected to be opened and shared between commercial systems and future federal systems. The sharing framework is expected to be distinguished from general unlicensed spectrum. 
     SUMMARY 
     Embodiments of the present disclosure include an electronic device and corresponding method for managing a shared spectrum, and a base station (BS) for operating in a shared spectrum. One embodiment is directed to an electronic device that includes a memory storing instructions for managing the shared spectrum, and a processor operably connected to the memory and configured to execute the instructions to cause the electronic device to obtain coexistence measurement reports (CMRs) from the plurality of BSs; identify interference relationships among the plurality of BSs based on the CMRs; assign a set of BSs to one or more basic allocation units (BAUs) in a plurality of BAUs based on the interference relationships; and transmit a spectrum access grant (SAG) to the set of BSs, wherein the SAG includes BAU assignments for the set of BSs. Each BAU in the plurality of BAUs is a time/frequency unit and the set of BSs includes a primary BS and a secondary BS. The secondary BS can transmit in the one or more BAUs when a transmission of the secondary BS does not interfere with a transmission of the primary BS. 
     Another embodiment is directed to a BS for operating in a shared spectrum. The BS includes a transceiver configured to transmit a coexistence measurement report (CMR) to a shared spectrum manager (SSM) and receive a spectrum access grant (SAG) originating from the SSM which includes a set of assignments for one or more basic allocation units (BAUs) for the BS. The CMR indicates interference relationships between the BS and neighboring BSs. Each of the one or more BAUs is a time/frequency unit, and the set of assignments indicates that the BS is a primary BS or a secondary BS that can transmit in the one or more BAUs when a transmission of the secondary BS does not interfere with a transmission of another primary BS assigned to the one or more BAUs. The BS also includes a processor operably connected to the transceiver, the processor configured to generate the CMR and identify transmission opportunities for the BS based on the set of assignments for the one or more BAUs. 
     Yet another embodiment is directed to a method for managing a shared spectrum. The method includes obtaining coexistence measurement reports (CMRs) from the plurality of BSs, identifying interference relationships among the plurality of BSs based on the CMRs, assigning a set of BSs to one or more (basic allocation units) BAUs in a plurality of BAUs based on the interference relationships, and transmitting a spectrum access grant (SAG) to the set of BSs which includes BAU assignments for the set of BSs. Each BAU in the plurality of BAUs is a time/frequency unit. In addition, the set of BSs includes a primary BS and a secondary BS that can transmit in the one or more BAUs when a transmission of the secondary BS does not interfere with a transmission of the primary BS. 
     Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether those elements are in physical contact with one another. The terms “transmit,” “receive,” and “communicate,” as well as derivatives thereof, encompass both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, means to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The term “controller” means any device, system or part thereof that controls at least one operation. Such a controller may be implemented in hardware or a combination of hardware and software and/or firmware. The functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. Likewise, the term “set” means one or more. Accordingly, a set of items can be a single item or a collection of two or more items. 
     Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device. 
     Definitions for other certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an exemplary networked computing system according to various embodiments of this disclosure; 
         FIG. 2  illustrates an exemplary base station (BS) in the networked computing system according to various embodiments of this disclosure; 
         FIG. 3  illustrates an exemplary electronic device for managing a shared spectrum in the networked computing system according to various embodiments of this disclosure; 
         FIG. 4  illustrates a network for spectrum sharing according to various embodiments of this disclosure; 
         FIG. 5  illustrates another network for spectrum sharing according to various embodiments of this disclosure; 
         FIG. 6  illustrates a data transmission frame structure for spectrum sharing according to various embodiments of this disclosure; 
         FIG. 7  illustrates assignment of base allocation units (BAUs) in a data transmission phase (DTP) for spectrum sharing according to various embodiments of this disclosure; 
         FIG. 8  illustrates a graph of a detection threshold function according to various embodiments of this disclosure; 
         FIG. 9  illustrates a flowchart for a general DTP access procedure according to various embodiments of this disclosure; 
         FIG. 10  illustrates another flowchart for a general DTP access procedure according to various embodiments of this disclosure; 
         FIG. 11  illustrates a flowchart for determining transmission opportunities in a DTP by a base station according to various embodiments of this disclosure; 
         FIG. 12  illustrates an opportunistic data transmission period (ODTP) access scheme by a base station according to various embodiments of this disclosure; 
         FIG. 13  illustrates a flowchart for signaling of coexistence measurement reports (CMRs) and spectrum access grants (SAGs) according to various embodiments of this disclosure; 
         FIG. 14  illustrates a flowchart for periodic and aperiodic signaling of CMRs and SAGs according to various embodiments of this disclosure; 
         FIG. 15  illustrates a signal flow diagram for periodic signaling of CMRs and SAGs according to various embodiments of this disclosure; 
         FIG. 16  illustrates a signal flow diagram for aperiodic signaling of CMRs and SAGs according to various embodiments of this disclosure; 
         FIG. 17  illustrates a flowchart for computing a network interference graph and connected components according to various embodiments of this disclosure; 
         FIG. 18  illustrates a flowchart for computing resource reservation ratios according to various embodiments of this disclosure; 
         FIGS. 19A-19C  illustrate steps for assigning BAUs from a network interference graph according to various embodiments of this disclosure; and 
         FIG. 20  illustrates a flowchart for managing a shared spectrum according to various embodiments of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The figures included herein, and the various embodiments used to describe the principles of the present disclosure are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Further, those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged wireless communication system. 
     Spectrum utilizations fluctuate temporally and geographically. Sharing the spectrum via multiplexing between different entities will enable more efficient utilization of the spectrum, whether it is unlicensed or shared spectrum. As used herein, the term “shared spectrum” is used in an inclusive manner without the distinction between the shared spectrum and unlicensed spectrum and it also includes not only the currently available spectrums but also spectrums that will be made available in the future. 
     In existing unlicensed spectrums, e.g., 2.4 GHz, 5 GHz, channel access is based on random access, i.e., carrier sense multiple access/collision avoidance (CSMA/CA). It is known that CSMA/CA with exponential backoff lowers the airtime utilization efficiency when the network densifies. Sharing is non-cooperative as it is based on regulations set by regulatory bodies and controlled by fixed rules. Fundamentally, there is no guarantee of spectrum access. Therefore, it may be disadvantageous for operators to use these unlicensed spectrums to deploy infrastructure systems for providing paid services to mobile subscribers, since the reliability and accessibility of the service cannot be guaranteed. 
     Novel aspects of this disclosure improve over this scheme by enabling multiplexing of users in the time dimension as well. Additionally, the medium access control scheme allows a secondary user to opportunistically access resources when the primary user is idle, or in the case that the primary user will not be impacted by interference from the secondary user&#39;s transmission. 
       FIG. 1  illustrates an exemplary networked computing system according to various embodiments of this disclosure. The embodiment of the wireless network  100  shown in  FIG. 1  is for illustration only. Other embodiments of the wireless network  100  could be used without departing from the scope of this disclosure. 
     As shown in  FIG. 1 , the wireless network  100  includes an gNodeB (gNB)  101 , an gNB  102 , and an gNB  103 . The gNB  101  communicates with the gNB  102  and the gNB  103 . The gNB  101  also communicates with at least one Internet Protocol (IP) network  130 , such as the Internet, a proprietary IP network, or other data network. 
     The gNB  102  provides wireless broadband access to the network  130  for a first plurality of user equipments (UEs) within a coverage area  120  of the gNB  102 . The first plurality of UEs includes a UE  111 , which may be located in a small business (SB); a UE  112 , which may be located in an enterprise (E); a UE  113 , which may be located in a WiFi hotspot (HS); a UE  114 , which may be located in a first residence (R); a UE  115 , which may be located in a second residence (R); and a UE  116 , which may be a mobile device (M) like a cell phone, a wireless laptop, a wireless PDA, or the like. The gNB  103  provides wireless broadband access to the network  130  for a second plurality of UEs within a coverage area  125  of the gNB  103 . The second plurality of UEs includes the UE  115  and the UE  116 . In some embodiments, one or more of the gNBs  101 - 103  may communicate with each other and with the UEs  111 - 116  using 5G, LTE, LTE-A, WiMAX, WiFi, or other wireless communication techniques. 
     Depending on the network type, other well-known terms may be used instead of “gNodeB” or “gNB,” such as “base station” or “access point.” For the sake of convenience, the terms “gNodeB” and “gNB” are used in this patent document to refer to network infrastructure components that provide wireless access to remote terminals. Also, depending on the network type, other well-known terms may be used instead of “user equipment” or “UE,” such as “mobile station,” “subscriber station,” “remote terminal,” “wireless terminal,” or “user device.” For the sake of convenience, the terms “user equipment” and “UE” are used in this patent document to refer to remote wireless equipment that wirelessly accesses an gNB, whether the UE is a mobile device (such as a mobile telephone or smartphone) or is normally considered a stationary device (such as a desktop computer or vending machine). 
     Dotted lines show the approximate extents of the coverage areas  120  and  125 , which are shown as approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the coverage areas associated with gNBs, such as the coverage areas  120  and  125 , may have other shapes, including irregular shapes, depending upon the configuration of the gNBs and variations in the radio environment associated with natural and man-made obstructions. 
     As described in more detail below, BSs in a networked computing system can be managed to allow spectrum sharing based on interference relationships between BSs. In some embodiments, a shared spectrum manager in the networked computing system can provide a centralized resource coordination and assignment scheme by transmitting spectrum access grants to the BSs based upon coexistence measurement reports received from the BSs. As discussed in more detail in the paragraphs that follow, the SSM enables priority-based and opportunistic channel access through assigning different offsets to MNO and/or each base station. 
     Although  FIG. 1  illustrates one example of a wireless network  100 , various changes may be made to  FIG. 1 . For example, the wireless network  100  could include any number of gNBs and any number of UEs in any suitable arrangement. Also, the gNB  101  could communicate directly with any number of UEs and provide those UEs with wireless broadband access to the network  130 . Similarly, each gNB  102 - 103  could communicate directly with the network  130  and provide UEs with direct wireless broadband access to the network  130 . Further, the gNB  101 ,  102 , and/or  103  could provide access to other or additional external networks, such as external telephone networks or other types of data networks. 
       FIG. 2  illustrates an exemplary base station (BS) according to various embodiments of this disclosure. The embodiment of the gNB  102  illustrated in  FIG. 2  is for illustration only, and the gNBs  101  and  103  of  FIG. 1  could have the same or similar configuration. However, gNBs come in a wide variety of configurations, and  FIG. 2  does not limit the scope of this disclosure to any particular implementation of an gNB. 
     As shown in  FIG. 2 , the gNB  102  includes multiple antennas  280   a - 280   n,  multiple RF transceivers  282   a - 282   n,  transmit (TX) processing circuitry  284 , and receive (RX) processing circuitry  286 . The gNB  102  also includes a controller/processor  288 , a memory  290 , and a backhaul or network interface  292 . 
     The RF transceivers  282   a - 282   n  receive, from the antennas  280   a - 280   n,  incoming RF signals, such as signals transmitted by UEs in the network  100 . The RF transceivers  282   a - 282   n  down-convert the incoming RF signals to generate IF or baseband signals. The IF or baseband signals are sent to the RX processing circuitry  286 , which generates processed baseband signals by filtering, decoding, and/or digitizing the baseband or IF signals. The RX processing circuitry  286  transmits the processed baseband signals to the controller/processor  288  for further processing. 
     The TX processing circuitry  284  receives analog or digital data (such as voice data, web data, e-mail, or interactive video game data) from the controller/processor  288 . The TX processing circuitry  284  encodes, multiplexes, and/or digitizes the outgoing baseband data to generate processed baseband or IF signals. The RF transceivers  282   a - 282   n  receive the outgoing processed baseband or IF signals from the TX processing circuitry  284  and up-converts the baseband or IF signals to RF signals that are transmitted via the antennas  280   a - 280   n.    
     The controller/processor  288  can include one or more processors or other processing devices that control the overall operation of the gNB  102 . For example, the controller/processor  288  could control the reception of forward channel signals and the transmission of reverse channel signals by the RF transceivers  282   a - 282   n,  the RX processing circuitry  286 , and the TX processing circuitry  284  in accordance with well-known principles. The controller/processor  288  could support additional functions as well, such as more advanced wireless communication functions. For instance, the controller/processor  288  could support beam forming or directional routing operations in which outgoing signals from multiple antennas  280   a - 280   n  are weighted differently to effectively steer the outgoing signals in a desired direction. Any of a wide variety of other functions could be supported in the gNB  102  by the controller/processor  288 . In some embodiments, the controller/processor  288  includes at least one microprocessor or microcontroller. 
     The controller/processor  288  is also capable of executing programs and other processes resident in the memory  290 , such as a basic OS. The controller/processor  288  can move data into or out of the memory  290  as required by an executing process. 
     The controller/processor  288  is also coupled to the backhaul or network interface  292 . The backhaul or network interface  292  allows the gNB  102  to communicate with other devices or systems over a backhaul connection or over a network. The interface  292  could support communications over any suitable wired or wireless connection(s). For example, when the gNB  102  is implemented as part of a cellular communication system (such as one supporting 5G, LTE, or LTE-A), the interface  292  could allow the gNB  102  to communicate with other gNBs over a wired or wireless backhaul connection. When the gNB  102  is implemented as an access point, the interface  292  could allow the gNB  102  to communicate over a wired or wireless local area network or over a wired or wireless connection to a larger network (such as the Internet). The interface  292  includes any suitable structure supporting communications over a wired or wireless connection, such as an Ethernet or RF transceiver. 
     The memory  290  is coupled to the controller/processor  288 . Part of the memory  290  could include a RAM, and another part of the memory  290  could include a Flash memory or other ROM. 
     As described in more detail below, base stations in a networked computing system can be assigned as primary, secondary, and/or tertiary users of shared spectrum resources (i.e., BAUs) based on interference relationships with other neighboring BSs. Primary base station stations can transmit on a channel without first sensing the channel. Secondary base stations can transmit on the channel after a sensing operation determines that its data transmissions would not interfere with data transmissions of primary base stations. Tertiary base stations can transmit data on a channel in an opportunistic data transmission period, if available. 
     Although  FIG. 2  illustrates one example of gNB  102 , various changes may be made to  FIG. 2 . For example, the gNB  102  could include any number of each component shown in  FIG. 2 . As a particular example, an access point could include a number of interfaces  292 , and the controller/processor  288  could support routing functions to route data between different network addresses. As another particular example, while shown as including a single instance of TX processing circuitry  284  and a single instance of RX processing circuitry  286 , the gNB  102  could include multiple instances of each (such as one per RF transceiver). Also, various components in  FIG. 2  could be combined, further subdivided, or omitted and additional components could be added according to particular needs. 
       FIG. 3  illustrates an exemplary electronic device for managing a shared spectrum in the networked computing system according to various embodiments of this disclosure. In one embodiment, the electronic device is a shared spectrum manager implemented as a server  300 , which can represent server  104  in  FIG. 1 . 
     As shown in  FIG. 3 , the server  300  includes a bus system  305 , which supports communication between at least one processing device  310 , at least one storage device  315 , at least one communications unit  320 , and at least one input/output (I/O) unit  325 . 
     The processing device  310  executes instructions that may be loaded into a memory  330 . The processing device  310  may include any suitable number(s) and type(s) of processors or other devices in any suitable arrangement. Example types of processing devices  310  include microprocessors, microcontrollers, digital signal processors, field programmable gate arrays, application specific integrated circuits, and discreet circuitry. 
     The memory  330  and a persistent storage  335  are examples of storage devices  315 , which represent any structure(s) capable of storing and facilitating retrieval of information (such as data, program code, and/or other suitable information on a temporary or permanent basis). The memory  330  may represent a random access memory or any other suitable volatile or non-volatile storage device(s). The persistent storage  335  may contain one or more components or devices supporting longer-term storage of data, such as a ready only memory, hard drive, Flash memory, or optical disc. 
     The communications unit  320  supports communications with other systems or devices. For example, the communications unit  320  could include a network interface card or a wireless transceiver facilitating communications over the network  130 . The communications unit  320  may support communications through any suitable physical or wireless communication link(s). 
     The I/O unit  325  allows for input and output of data. For example, the I/O unit  325  may provide a connection for user input through a keyboard, mouse, keypad, touchscreen, or other suitable input device. The I/O unit  325  may also send output to a display, printer, or other suitable output device. 
     As described in more detail below, the server  300  can serve as a shared spectrum manager in a networked computing system can coordinate resource assignment to enable priority-based and opportunistic channel access through use of offsets in base allocation units identifiable by time slots and frequency bands. 
     Although  FIG. 3  illustrates an example of an electronic device in a computing system for managing a shared spectrum among a plurality of base stations, such as base stations  101 ,  102 , and  103  in  FIG. 1 , various changes may be made to  FIG. 3 . For example, various components in  FIG. 3  can be combined, further subdivided, or omitted and additional components could be added according to particular needs. In addition, as with computing and communication networks, servers can come in a wide variety of configurations, and  FIG. 3  does not limit this disclosure to any particular server. 
       FIG. 4  illustrates a network for spectrum sharing according to various embodiments of this disclosure. Network  400  is a network computing system such as networked computing system  100  in  FIG. 1 . 
     The network  400  includes multiple BSs from different mobile network operators (MNOs), i.e., wireless service providers, coexisting in proximity with each other. As an example, BS  401  and BS  404  belong to the same MNO, e.g., “MNO B”, and BS  402  and BS  403  belong to another operator, e.g., “MNO A”. However, the particular depiction of the network in  FIG. 4  is exemplary and not limiting. Thus, in other embodiments, the number of mobile network operators can differ, each with different systems and technologies sharing the spectrum. 
     In  FIG. 4 , BSs that interfere with one another are connected by dashed lines  405 . For example, BS  401  and BS  404  interfere with each other and are connected by dashed line  405   a;  BS  401  and BS  402  interfere with each other and are connected by dashed line  405   e;  BS  402  and BS  404  interfere with each other and are connected by dashed line  405   d;  BS  403  and BS  404  interfere with each other and are connected by dashed line  405   b;  and BS  403  and BS  402  interfere with each other and are connected by dashed line  405   c.  BS  401  and BS  403  are separated by enough of a distance to prevent interference with one another. 
     Each of the BSs  401 ,  402 ,  403 , and  404  are connected by their respective backhaul links  407  to shared spectrum manager (SSM)  406 . SSM  406  is one or more electronic devices for managing the shared spectrum, such as electronic device  300  in  FIG. 3 . In a non-limiting embodiment, the SSM  406  is an entity in the core network of each MNO and configured to communicate with each other to manage the shared spectrum among BSs of all the MNOs. In another non-limiting embodiment, the SSM  406  is a third-party entity that does not belong to any of the MNOs but is configured to communicate with the different operators&#39; networks for managing the shared spectrum among BSs of the MNOs. 
       FIG. 5  illustrates another network for spectrum sharing according to various embodiments of this disclosure. Network  500  is a network computing system such as networked computing system  100  in  FIG. 1 . 
     The network  500  differs from the network  400  in that each BS communicates with an entity in its own MNO core network (CN) over backhaul links  507  rather than communicating directly to SSM  406 . In this embodiment in  FIG. 5 , BSs  402  and  403  communicate with CN entity  504   a  over backhaul links  507   a  and BSs  401  and  402  communicate with CN entity  504   b  over backhaul links  507   b.  The CN entities  504   a  and  504   b  communicate with SSM  406  over their respective communication links  510 . CN entities  504   a  and  504   b  can handle aggregation of data and/or transfer of messages, such as measurement reports, from the BSs to the SSM  406 . The CN entities may also handle reception of messages from the SSM  406  on behalf of the BSs along with handling configuration of the BSs based on the parameters in these messages. 
       FIG. 6  illustrates a data transmission frame structure for spectrum sharing according to various embodiments of this disclosure. The frame structure  600  defines the resources that are shared among BSs in a networked computing system, such as networked computing system  100  in  FIG. 1 , network  400  in  FIG. 4 , and network  500  in  FIG. 5 . 
     Frame structure  600  includes data transmission phase (DTP) cycles  602   a  through  602   n,  which are repeated sequences of time slots that can occupy a number of frequency spectrum bands (i.e., channels)  606 . In  FIG. 6 , frame structure  600  has M spectrum bands f 1  through f M . 
     A time slot over one frequency band is referred to as a Basic Allocation Unit (BAU). In the embodiment in  FIG. 6 , each DTP cycle  602  has K time slots  604   a  through  604   k  in the time dimension spanning M frequency bands. Thus, each DTP cycle can include a total of K×M BAUs. However, in other embodiments, the number of spectrum bands, time slots, bandwidth, center frequency, and duration of time slots can differ. 
       FIG. 7  illustrates assignment of base allocation units (BAUs) over one data transmission phage (DTP) cycle for spectrum sharing according to various embodiments of this disclosure. In this embodiment, DTP cycle  700  includes a set of BAUs  702  over a single frequency  706 . 
     BSs A 1 , A 2 , B 1 , and B 2  correspond to BSs  402 ,  403 ,  401 , and  404  in  FIG. 4 , respectively. Thus, BS B 1  and A 2  are geographically separated and not in an interfering relationship so that they can be assigned to the same BAUs  704   b  and  704   e  for transmission. In contrast, BSs  401 ,  402 , and  404  are in a mutually interfering relationship, as are BSs  402 ,  403 , and  404 . Thus, BSs  401 ,  402 , and  404  are assigned BAUs in an orthogonal manner. Likewise, BSs  402 ,  403 , and  404  are assigned BAUs in an orthogonal manner. For example, BS A 1  of MNO A can transmit in BAUs  704   a  and  704   d.  BS B 2  of MNO B can transmit in BAU  704   c,  which is orthogonal to BAUs  704   a  and  704   d.    
     BAUs  705  are Not Allocated (NA) to any MNO/BS and may be accessed according to the opportunistic access scheme described in  FIG. 12  that follows. 
     Overview of Sharing Framework 
     Each of the BAUs in the set of BAUs  702  can be shared between one or more primary base stations and one or more secondary base stations. BSs assigned to a BAU may also be referred to in the alternative as “a user” of the resource. Further, a primary base station may also be referred to as a “protected base station” or a “protected user”. 
     MNOs or a set of BSs assigned to a BAU can be granted protected access to one or more BAUs, which effectively prioritizes the availability of these resources for the protected users over other users. Protected access may be controlled by issuing Spectrum Access Grants (SAGs) to MNOs and/or BSs by an SSM, such as SSM  406  in  FIGS. 4 and 5 . The SSM  406  may serve as a database of SAGs which can be accessed by the protected user. SAGs may be transmitted as messages to users over the connections depicted in  FIGS. 4 and 5 . In one embodiment, SAGs include information elements indicating that BAUs are reserved for specific users. These are known as “protected BAUs”. Protected BAU assignments may be issued to MNOs by a central spectrum licensing authority, such as a government regulator. 
     In another example, MNOs or network entities belonging to each MNO may negotiate among themselves to establish protected BAU assignments. The assignment of protected BAUs may change over time and may be periodically updated. In a SAG, BAU assignments may be assigned to individual BSs, a set of multiple BSs or an entire MNO network. As an example, the assignments for the BAUs in slots  604  may indicate that the MNO A network may access resources (f 1 ,t 1 ) of the DTP cycle. How the resources are utilized by different BSs belonging to MNO A may then be decided independently by the MNO. 
     Each BAU may be divided into symbols  712 . The primary assignees, i.e., primary base stations, of the BAU may begin transmitting in a prioritized transmission period  716   a  without first performing spectrum sensing. In the BAU  704   e,  the prioritized transmission period  716   a  is found at the beginning of the BAU. In this example in  FIG. 7 , BSs A 2  and B 1  are the primary base stations assigned to BAU  704   e.  One or more BSs may also be assigned to one or more secondary transmission opportunity (TXOP) offsets  716   b  and  716   c.  These TXOP offsets may also be referred to herein as “offset periods”. BSs may be assigned to a secondary TXOP by the SSM, which provides additional opportunities for BSs to transmit within the BAU. TXOP offset assignments may also be provided in the SAG and can also apply to assigned BAUs  704   a,    704   b,    704   c,  and  704   d.  Multiple BSs may be assigned to the same TXOP offset and a given BS may have multiple TXOP offsets assigned. In this illustrative embodiment, BS A 1  and B 2  are secondary BSs transmitting in offset periods  716   b  and  716   c,  respectively. 
     Before transmitting at the secondary TXOP offsets, the corresponding BS may first sense the channel during the Clear Channel Assessment (CCA) periods  714 , as described below in flowchart  1100  in  FIG. 11 . If the channel is clear, the BS can begin transmitting at the following TXOP offset and may transmit for the remaining duration of the BAU, or for some Maximum Channel Occupancy Time (MCOT), if specified. The MCOT is the maximum time duration that a BS may transmit within the BAU before releasing the resource. Additionally, a BAU may be configured with an Opportunistic Data Transmission Period (ODTP)  718 , which also may involve the CCA procedure in flowchart  1100 . The location of the secondary TXOPs and ODTP within the BAU period may be indicated by the SSM in the SAG. Secondary TXOP and ODTP locations, along with the location and duration of the CCA periods, may be specified in terms of individual symbol, sample or time offsets. In another embodiment the TXOP and ODTP can be chosen by each BS or each MNO in a distributed fashion, either randomly or based on some metric. 
     DTP Resource Access with Protected Access Users 
     In one embodiment, assignment of resources via SAGs may restrict access to BAUs by only protected users specified in the SAGs, which prevents other MNOs and/or BSs from transmitting in these resources regardless of whether they could cause interference with the protected user or users. In another embodiment, a “soft licensing” scheme may be employed where the protected users are considered the primary assignee of the protected BAUs and may transmit in these resources without first needing to sense the channel for ongoing transmissions from other users. However, this embodiment, secondary users may opportunistically access the same BAU if the primary users are not actively utilizing the BAU or if the secondary user&#39;s transmission would not cause significant interference to the primary users. As an example, LBT may be employed by a secondary user to avoid collision with a primary user in the same BAU. By specifying TXOP offsets in a SAG, secondary users may be granted priority access to protected BAUs but with lower priority than the primary users. Each TXOP offset may apply to one or more secondary users. 
     As an alternative embodiment, any user may operate as a secondary user and transmit at specified TXOP offsets, regardless of whether they have been granted explicit access to the BAU in a SAG. In another embodiment, secondary offsets durations can be extended, and a group of BSs may be assigned to contend for access of the duration of the slot via LBT. Thus, the TXOP offset will function as a higher priority ODTP window. 
       FIG. 8  illustrates a graph of a detection threshold function according to various embodiments of this disclosure. The detection threshold function represented by graph  800  can be used by a BS to determine whether transmission in a secondary transmission opportunity is permissible, as described in more detail in  FIG. 11  that follows. 
       FIG. 9  illustrates a flowchart for a general DTP access procedure according to various embodiments of this disclosure. The operations depicted in flowchart  900  can be implemented in a BS, such as BS  200  in  FIG. 2 . 
     In operation  902 , a check is made for available assigned resources. A BS receiving assigned resources is a primary or protected BS for the assigned resource. In operation  904 , a check is made for available opportunistic resources. ABS receiving opportunistic resources is secondary BS for the assigned resource. In a non-limiting embodiment, the assigned resources and opportunistic resources are provided in a spectrum access grant (SAG). The SAG can be generated by a shared spectrum manager (SSM), such as SSM  406  in  FIGS. 4 and 5 . 
     Thereafter, in operation  906  transmission resources are identified based on the checks made in operation  902  and  904 . The identified resources can be an assigned resource and/or an opportunistic resource. In operation  908 , data is transmitted using the identified resources. 
       FIG. 10  illustrates another flowchart for a general DTP access procedure according to various embodiments of this disclosure. The operations depicted in flowchart  1000  can be implemented in a BS, such as BS  200  in  FIG. 2 . 
     In operation  1002 , a check is made for available assigned resources. In operation  1004 , if assigned resources are not available, a check is made for available opportunistic resources. Thereafter, in operation  906  transmission resources are identified based on the checks made in operation  1002  and  1004 . According to flowchart  1000 , if assigned resources are available to a BS in operation  1002 , then the BS will not perform a check for opportunistic resources in operation  1004 . In operation  908 , data is transmitted using the identified resources. 
       FIG. 11  illustrates a flowchart for determining transmission opportunities in a DTP by a base station according to various embodiments of this disclosure. The operations depicted in flowchart  1100  can be implemented in a BS, such as BS  200  in  FIG. 2 , to access DTP resources for a specific BAU. 
     Flowchart  1100  begins at operation  1102  with a determination as to whether the BS intends to transmit data, i.e., whether the BS has data to transmit. If the BS does not have data to transmit, then flowchart  1100  proceeds to operation  1104  where the BS remains in an idle state. However, at operation  1102 , if the determination is made that the BS has data to transmit, then a determination is made whether the BS is assigned to a protected BAU in operation  1106 . If the BS is assigned to a protected BAU, then flowchart  1100  proceeds to operation  1108  and the BS transmits its data on the protected BAU. In one embodiment, the BS can transmit its data at the start of its assigned BAU without first sensing the channel. 
     It may the case that the BAU is assigned to protected users, but the users are idle during the slot duration, possibly due to having an empty transmit data buffer or other reasons. Also, it is possible that secondary users (who are not allocated as primary users of the BAU), due to geographical separation and/or transmission power requirements, may be able to transmit in the protected BAU without causing high interference, which would affect the on-going transmission of the primary, protected users. It is also possible that the BAU is marked NA in the SAG and thus available to all users for opportunistic transmission. In the case of a NA BAU, the entire duration of the BAU may be treated as an ODTP and accessed in the manner described in more detail in  FIG. 12 . 
     Returning back to operation  1106 , if the determination is made that the BS is not assigned to a protected BAU, then flowchart  1100  proceeds to operation  1110  where a subsequent determination is made as to whether the BS is assigned to an alternate transmission opportunity, i.e., secondary transmission opportunity, in the BAU, such as secondary transmission opportunities  716   b  and  716   c  in  FIG. 7 . If the BS is assigned an alternate transmission opportunity as determined in operation  1110 , then flowchart  1100  proceeds to operation  1112  and the channel is sensed during the clear channel assessment (CCA) period prior to transmission. In a non-limiting embodiment, the sensing may be performed by detecting RF energy over one or more CCA periods of duration T CCA . The location and duration of the CCA periods may be specified in terms of the symbol index, sample indices, or time or sample offset. 
     In operation  1114 , the received power, P RX , is computed over the CCA period. In one embodiment, P RX  may be the total power from other transmitters. In another embodiment, the received power measurements are considered for each neighboring BS in the comparison operation. In this embodiment, the BS may detect a signal transmitted by neighboring BSs allowing the BS to identify these neighbors. 
     In operation  1116  the received power, P RX , is compared to a threshold. In one embodiment, the threshold may be a function of the intended TX power of the BS, TH(P TX ), as illustrated in  FIG. 8 . In some embodiments, the threshold function can incorporate a detection margin δ to control the spatial reuse. In one embodiment, δ can be set to zero. In another embodiment, δ can be set to a positive value to control the level of the spatial reuse by setting a larger δ value to further discourage opportunistic transmission. In one embodiment, the value δ can be fixed. In another embodiment, the value δ can be different between the BSs belonging to the same network and between the BSs belonging to different networks. That is, there could be δ inter-op  and δ intra-op . With this distinction, a spatial reuse can be allowed more readily and generously between the BSs in the same network. In another embodiment, TH(·) can take the value δ as an input and may return the output threshold value adjusted according to the value δ. 
     In one embodiment, the threshold or threshold function, along with the detection margin δ, may be fixed to a value or a specific function or selected among preconfigured values and functions. In another embodiment, it may be assigned dynamically by the SSM in the SAG or negotiated between MNOs with or without assistance from the SSM, or it may be determined by some other means. 
     Returning to operation  1116 , if P RX  is not greater than the threshold, then flowchart  1100  proceeds from operation  1116  to operation  1118  where the BS may begin transmitting at the assigned transmission opportunity offset following the CCA period and continue transmitting for the remaining duration of the BAU. In another embodiment, the transmission may continue for a specified maximum channel occupancy time, which is less than the remaining BAU duration. 
     If P RX  is greater than the threshold, then flowchart  1100  proceeds from operation  1116  to operation  1120  where a determination is made as to whether the transmission power, P TX , can be decreased. If the transmission power cannot be decreased, then flowchart  1100  proceeds from operation  1120  to operation  1104  to allow the BS to return to the idle state for the remainder of the BAU. If the transmission power can be decreased, then the transmission power is updated in operation  1122  and flowchart  1100  cycles through operations  1114 ,  1116 ,  1120 , and  1122  until the received power does not exceed the threshold in operation  11166  so that the BS can proceed to operation  1118  to being transmission. 
     Even if a BS is not assigned to the BAU as a primary BS in operation  1106  or a secondary base station in operation  1110 , the BS may still have the opportunity to transmit in the opportunistic data transmission period (ODTP) as a tertiary base station. Thus, if the determination is made that an alternate transmission opportunity has not been assigned in operation  1110 , then flowchart  1100  can proceed to operation  1124  where a determination is made as to whether an ODTP is available. If an ODTP is not available, then flowchart  1100  proceeds to operation  1104  and the BS remains idle for the remainder of the BAU. However, if an ODTP is available in operation  1124 , then flowchart  1100  proceeds to operation  1126  to sense the channel during the CCA period within the ODTP. In the case of transmission in the ODTP, the BS may have to defer transmission until after an additional backoff period, as illustrated by backoff period  1206  in  FIG. 12 . 
     From operation  1126 , flowchart proceeds to operation  1114  to evaluate the received power and provide the BS with an opportunity to reduce its transmit power, if possible. If the BS is not able to sufficiently reduce its power to avoid interference with an ongoing transmission of its neighbor in the ODTP, the BS will return to the idle state in operation  1104 . 
     Opportunistic DTP Access Coordination 
     As already mentioned, ODTPs can be accessed opportunistically by any BS, regardless of protected BAU or secondary TXOP assignments. The ODTP can be accessed in a similar fashion to an assigned TXOPs by first performing the CCA procedure (e.g., operations  1126 ,  1114 , and  1116  in  FIG. 11 ) and transmitting if the channel is clear within the CCA period. 
       FIG. 12  illustrates an opportunistic data transmission period (ODTP) access scheme by a base station according to various embodiments of this disclosure. The ODTP access scheme can be implemented in ODTP  1200 , which is similar to ODTP  718  in  FIG. 7 . In another embodiment, the ODTP access scheme can be implemented in a non-allocated BAU, i.e., a non-assigned BAU, such as NA BAUs  705  in  FIG. 7 . 
     Following the channel busy state  1202 , there may be a minimum defer duration  1204 , D min , left idle as the original user may resume its transmission. Thus, this minimum defer duration is a means of providing higher priority to the BS which reserved the resource. After D min  duration of inactivity, it may be assumed that the original owner has released the reserved resource. After the channel is sensed as idle for the defer duration, a BS will perform additional channel sensing with optional random backoff selected from backoff period  1208 . The backoff period  1208  is formed from a set of time units  1206 . In one embodiment, the number of random backoff time units  1206  is randomly determined. As an example, a random number can be uniformly drawn from [X, Y] value range, where X and Y are non-negative integers representing the minimum and maximum possible values, respectively, of the backoff period  1208 . In one embodiment, X can be 0. In one embodiment, Y, namely the contention window size (CWS), may be configured or informed to the BSs. In another embodiment, Y can be varying and negotiated between the operators. In one embodiment Y can be common. In another embodiment, Y can be cell specific. In yet another embodiment, Y can be operator specific. After successful channel sensing over the optional random backoff period, the BS may start data transmission in the data transmission state  1210  until the end  1212  of the ODTP. In another embodiment, there may be a specified MCOT after which the BS will cease transmitting and release the resource. 
     Coexistence Measurement Reports 
     To facilitate configuration of BSs by the SSM, each BS may be configured to send Coexistence Measurement Reports (CMRs) to the SSM. A CMR sent by a given BS may include but is not limited to the following list of information elements. The SSM may also specify which of the following information elements are requested, so that the BS may send a subset of the following to the SSM or any required entities. 
     Identifying information for the MNO and BS. This information element can include the Mobile Network Code (MNC), Mobile Country Code (MCC), the Extended Cell Global Identifier (ECGI), the Physical Cell Identifier (PCI), and/or other similar and related identifiers. 
     A list of neighboring BSs. This information element can also include associated power levels measured either at the BS or its mobile users, if available. The measurements may be specified on a per-BAU basis. 
     A list of neighboring BSs and their power levels. This information element can be reported by the current mobile users connected to the BS. These measurements may be specified whenever there are changes in the extended interference map between other BSs and the reporting BS&#39;s connected mobile users. The list may contain all other BSs detected by the BS or may be restricted to the set of BSs exceeding a threshold over the reporting period, along with an indication of the BAUs in which the other BSs were detected. Received power may be determined at the BS&#39;s receiver by receiving the synchronization signals, reference signals or other signals transmitted by neighboring BSs and reported as a value, e.g., in dBm, measured at the receiver, or some quantized representation of the value. The list may also indicate whether neighboring BSs may be allowed to be assigned to the same protected BAU, or the BS is explicitly requesting to be assigned to the same BAU as these other BSs. This may occur when the BS has multiple neighboring BSs belonging to the same MNO network, which are able to coordinate access among themselves. 
     A list of specific BSs that have been detected as causing detrimental interference to its users. This information element may also include the indices of protected BAUs in which this interference is occurring. The BS may thus explicitly request to be assigned orthogonal resources from these indicated BSs. 
     The intended TX power of the BS. This information element can include a single value applying to all BAUs or a list of values per BAU may be provided. 
     RSSI, RSRP and/or RSRQ measurements reported by the mobile users of the BS. This information element can include individual measurements compiled and reported as a list or aggregated in some fashion, such as by taking the average measurement or other statistics, or by computing a histogram of measurement values. Measurements may be reported as the original values measured at the mobile receivers or by some quantized values, which are encoded from the original values. Separate measurements or aggregated measurements may be provided for each BAU. 
     Load or demand information for the BS. This information element can include an indicator of whether there is buffered data at the BS, the amount of buffered data (either represented as the total quantity of bytes or as a quantized or encoded value representing a range of byte quantities), as well as an estimate of how many BAUs are requested by the BS for data transmission in the DTP. Load information reports may also be differentiated by priority level of different traffic. 
     Channel occupancy measurement(s). This information element can indicate the percentage of time that the channel is measured as busy over the entire DTP or for individual slots or BAUs. 
     Indicator(s) specifying protected DTP BAUs that are no longer used or requested by the original assignee BS. 
     Indicator(s) specifying DTP BAU indices in which strong interference is detected by the BAU. 
     A timestamp or time index indicating when the above measurements were performed. 
     In some embodiments, transmission of CMRs may be triggered periodically with some fixed period, such as every N cycles for some positive integer N, as shown in  FIG. 15 . In other embodiments, CMRs may also be triggered aperiodically based on a CMR Request sent from the SSM to the BS, as shown in  FIG. 16 . A CMR may also be triggered by each individual BS or network provider upon noticing, for example, a significant change in the interference levels or the list of neighbors. The scope for this CMR update can be local (BS specific), network provider specific or global. 
     Spectrum Access Grants 
     As previously described, SAG messages can be sent by an SSM to a BS, or a network entity controlling one or more BSs, in order to configure the BSs and assign resources in units of BAUs. SAGs may contain but are not limited to the following information elements. 
     Identifiers specifying the BSs or network entities for which the SAG is intended. 
     Overall frame structure. This information element can include the number of DTP cycles, DTP cycle size (i.e., the values of N and K from  FIG. 6 ) or, alternatively, the number of slots and slot length. 
     Detection threshold function parameters. This information element can specify the slope of function TH(P TX ) and TH max , TH min . 
     Maximum allowed transmission power. 
     Contention window size. This information element provides for opportunistic channel access. 
     Protection margin δ for opportunistic channel access. 
     Assignment of a synchronization source. This information element is used to derive the timing of DTP cycle transmissions. 
     The BAU allocation for each MNO or BS. This information element may include indicators specifying whether the BAU assignment is per-MNO or per-individual BS. In one embodiment, the protected BAU allocation may be specified by carrier frequency and bandwidth in the frequency dimension, slot indices in the time dimension (denoted by the pair {starting instance, duration} or {starting instance, end instance}), or any combination of these or equivalent encoded or representative parameters. In another embodiment, the BAU allocation may be specified by a bitmap where the allocation list is encoded into a binary number or vector, where each binary digit or place value being set to “1” or a pre-defined value can indicate the corresponding BAU index (or, equivalently, slot and/or frequency band index) is allocated to the recipient of the SAG. The location of the BAUs corresponding to binary digits in the bitmap may not be consecutive but may follow a pre-established pattern where BAUs are located non-consecutively in time and/or frequency. In yet another embodiment, the BAU allocation may follow some pre-established pattern, which is indicated by a parameter in the SAG. 
     The TXOP offset assignments for each MNO or BS. This information element specifies the location of assigned TXOPs and may follow the same formats as described above for the BAU assignments. 
     An indicator signaling the availability of the ODTP within a specified BAU. This information element may also specify the start and duration of the ODTP, if enabled. 
     The Maximum Channel Occupancy Time. This information element can specify the maximum duration of transmissions. 
     A timestamp or time index for indicating when the above parameters may be applied by the BS. 
     Signaling of CMRs and SAGs 
       FIG. 13  illustrates a flowchart for signaling of coexistence measurement reports (CMRs) and spectrum access grants (SAGs) according to various embodiments of this disclosure. The operations depicted in flowchart  1300  can be implemented in a BS, such as BS  200  in  FIG. 2 . Further, flowchart  1300  can be performed by a BS as a means to register itself with the SSM, such as SSM  406  in  FIG. 4 , for onboarding onto the network. 
     In operation  1302 , the BS joins the network. In operation  1304 , an initial CMR is sent to the SSM. The CMR can include some or all of the information elements described above and, optionally, a connection notification information element notifying the SSM that the cell is newly active. In one embodiment, the CMR may simply serve as a request for updating the resource allocation in the SAG and may not necessarily contain any additional information elements. In operation  1306 , a SAG message is received with initial configuration information, such as initial BAU or secondary transmission opportunity assignments along with any other configuration parameters. The SAG is received from the SSM, or a CN entity connected to the SSM, such as CN entity  504  in  FIG. 5 . 
       FIG. 14  illustrates a flowchart for periodic and aperiodic signaling of CMRs and SAGs according to various embodiments of this disclosure. The operations depicted in flowchart  1400  can be implemented in a BS, such as BS  200  in  FIG. 2 . In addition, the operations of flowchart  1400  can be performed after operations in flowchart  1300 , i.e., after a BS has already been onboarded onto the network. 
     In operation  1402 , a trigger is received to send a CMR. The trigger can be received periodically after some fixed duration, as described in  FIG. 15 , or received aperiodically, as described in  FIG. 16 . 
     In operation  1404 , a CMR is sent to the SSM. Thereafter, a SAG may be received from the SSM for updating BAU allocation in operation  1406  if changes are required. Thus, in some embodiments, a SAG received in operation  1406  may not the BS with protected BAUs. 
     In between receiving SAG list updates, each BS may query its local cache of SAG allocations to determine its assigned configuration parameters and current BAU allocation. In an alternative embodiment, a separate network entity, such as a core network node within the MNO network of the BS, e.g., CN entity  504  in  FIG. 5 , may contact the SSM, on behalf of the BS, and handle reception of CMRs or constituent data elements from the BS, SAG messages from the SSM and/or configuration of the BS based on the SAG parameters. In an alternative embodiment, a BS may send an updated CMR of its own volition to request new BAU allocation from the SSM. This can be done, for example, in instances where there are changes to the circumstances of the BS&#39;s connected mobile users, including connection status, location, or link performance. 
       FIG. 15  illustrates a signal flow diagram for periodic signaling of CMRs and SAGs according to various embodiments of this disclosure. The steps depicted in signal flow diagram  1500  can be implemented between a BS  1502  and an SSM  1504  in a communications network. As an example, the steps in signal flow diagram  1500  can represent signal transmission between BS  401  and SSM  406  in  FIG. 4 . 
     In signal flow diagram  1500 , a periodic coexistence measurement report timer is triggered in s 1506 . In response, the BS  1502  transmits a CMR to SSM  1504  in s 1508 . In s 1510  the SSM  1504  transmits a SAG to the BS  1502 . 
       FIG. 16  illustrates a signal flow diagram for aperiodic signaling of CMRs and SAGs according to various embodiments of this disclosure. The steps depicted in signal flow diagram  1600  can be implemented between a BS  1602  and an SSM  1604  in a communications network. As an example, the steps in signal flow diagram  1500  can represent signal transmission between BS  401  and SSM  406  in  FIG. 4 . 
     In s 1606 , the SSM  1604  transmits a CMR request to BS  1602 . In response, the BS  1602  transmits the requested CMR in s 1608 . Thereafter, the SSM  1604  transmits a SAG to the BS  1602  in s 1610 . 
     Interference Graph Computation 
       FIG. 17  illustrates a flowchart for computing a network interference graph and connected components according to various embodiments of this disclosure. Operations of flowchart  1700  can be implemented in an SSM, such as SSM  406  in  FIGS. 4 and 5 . 
     An SSM generates a network interference graph based on information provided in the CMRs. The network interference graph facilitates the allocation of BAUs to different users. The interference graph represents the interference relationships between BSs in the network. 
     In operation  1702 , an interference graph G I  is computed. The interference graph G I =(V I , E I ) is a function of V I  and E I , where V I  is the set of vertices v representing BSs in the network and E I  is the set of edges e representing interference relationships between BSs. An edge e=(v TX ,v RX ) is included in E I  if the received power at BS v RX  from BS v TX  (reported by the BSs to the SSM in CMR messages) exceeds a threshold. This threshold may be a function of the intended TX power of v RX , as in operation  1116  of  FIG. 11 , and determined by the SSM based on the intended TX power reported in a CMR. 
     In some embodiments, interference graph G I  is not a connected graph. A connected graph is defined as a graph where, for all pairs of vertices v 1 , v 2 ∈V, a path exists connecting v 1  and v 2 . Thus G I  may have one or more connected component subgraphs, where there is exists no path between the vertices of each component subgraph. In other words, G I  may be partitioned into one or more connected components G c  in the set S G ={G 1 ,G 2 , . . . ,G M }, where M is the number of connected components and there exists no edge between any pair of subgraphs in S G . 
     In operation  1704 , the interference graph G I  is partitioned into subgraphs S G . Connected components of G I  can be computed by applying one of the well-known algorithms used for this purpose. 
     In operation  1706 , the set S G  is returned and may be used by the SSM for assigning resources (i.e. BAUs) to BSs. The BAUs can be orthogonal or even non-orthogonal in cases to allow for higher resource efficiency. The SSM may be able to perform the resource assignment independently for each connected component G c  due to the constituent BSs of each component having no mutual interference relationship. 
     Spectrum Assignment Algorithm 
     An exemplary algorithm is provided in  FIG. 18  which may be used by an SSM or equivalent entity for assigning BSs to BAUs within a time/frequency/code slot or channel. The algorithm may be performed by the SSM in order to partition the network into a set of nodes that may be assigned to orthogonal resources, while the remaining set of nodes may share resources to improve spatial reuse. The SSM proceeds by evaluating each BS in order of the number of interference relationships. For each BS, a new graph is computed by taking the subgraph of the BS and its neighbors in the interference graph, along with any edges between these nodes, and then removing the BS and its adjacent edges from this subgraph. The resource reservation ratio, which determines the fraction of resources the BS may be assigned under equal sharing, can then be computed as a function of the number of nodes in each connected component (isolated subgraph) of the resulting graph. Formally, the SSM can perform the below operations on one of the connected components of the interference graph G, which for simplicity is denoted G=(V,E), where V is the set of vertices representing BSs and E is the set of edges representing interference relationships between BSs. 
       FIG. 18  illustrates a flowchart for computing resource reservation ratios according to various embodiments of this disclosure. The operations depicted in flowchart  1800  can be implemented in an SSM, such as SSM  406  in  FIGS. 4 and 5 . 
     Flowchart  1800  begins at operation  1802  by identifying the vertex i in V having the most edges in E, i.e., 
     
       
         
           
             
               i 
               = 
               
                 
                   
                     arg 
                      
                     max 
                   
                   
                     v 
                     ∈ 
                     V 
                   
                 
                  
                 
                    
                   
                     E 
                     v 
                   
                    
                 
               
             
             , 
           
         
       
     
     where E v  is the set of edges adjacent to vertex v, with ties broken arbitrarily. 
     In operation  1804 , the subgraph G i =(V i ,E i ) of G is computed, where V i  is the set containing vertex i and its adjacent vertices u∈V, s.t. ∃e∈E where e=(i, u), and E i  contains all edges in E shared by vertices in V i  (i.e., i and its neighbors u). 
     In operation  1806 , the graph G′ i =(V′ i ,E′ i ) is computed by removing vertex i and all of its edges E i  from G i . In operation  1008 , the graph G′ i  is partitioned into connected components G′ ik =(V′ ik ,E′ ik ), k∈{1, . . . , K}. The SSM initially considers the subgraph G′ ik=1  for further processing. 
     In operation  1810 , the maximum number of vertices N i  over all connected components G′ ik  is computed. In operation  1012 , the SSM computes the reservation ratio as 
     
       
         
           
             
               R 
               i 
             
             = 
             
               
                 α 
                 i 
               
               
                 
                   N 
                   i 
                 
                 + 
                 1 
               
             
           
         
       
     
     where α i  is a parameter that may be used to control the priority of different BSs or MNO users. The resource reservation ratio is the fraction of resources in each DTP cycle allocated to BS i. By setting α 1 =1, equal priority is offered to each user. However, by increasing α i &gt;1, BS i may be given a larger portion of the time-domain resources. 
     In operation  1814 , a determination is made as to whether all vertices for this connected component of G has been evaluated. If all vertices for the connected component of G has been evaluated, then flowchart  1800  proceeds to operation  1816  and returns the vector of resource reservation ratios R={R v } for all v∈V. However, if all vertices for the connected component of G has not been evaluated, then flowchart  1800  proceeds to operation  1818  and selects the vertex with the next most edges in E and sets i equal to the index of this vertex in operation  1820  and returns to operation  1804 . 
       FIGS. 19A-19C  illustrate steps for assigning BAUs from a network interference graph according to various embodiments of this disclosure. The steps depicted in flowchart  1900  can be implemented in an SSM, such as SSM  406  in  FIGS. 4 and 5 . 
     In a first step  1901  the interference graph G is computed. In one embodiment, the interference graph is computed in the manner described in operation  1702  in  FIG. 17  with each vertex representing a BS and each edge representing an interference relationship between nearby BSs. In this case, there is only one connected component, which is the entire graph G. 
     In a second step  1902 , vertex A is determined to have the most edges and the subgraph G A  is constructed. This step  1902  corresponds with operations  1802  and  1804  in  FIG. 18 . 
     In a third step  1903 , the graph G′ A  is computed by removing vertex A and its edges. Also, in the third step  1903 , G′ A  is partitioned into three connected components. Two of the connected components contain two vertices, so following operation  1810  in  FIG. 18 , N A =2 and, by operation  1812  in  FIG. 18 , R=⅓ (assuming α i =1). 
     In the fourth step  1904  and the fifth step  1905 , the operations  1804  through  1812  in  FIG. 18  are repeated for vertex B, which has the next most edges of all vertices in G. The procedure may be then repeated for vertices G, C, D, E, H, F, and I, in this order and by breaking ties between edge counts arbitrarily, until the reservation ratios {R i } have been computed for all vertices. Finally, the resource allocation shown in the final step  1906  of  FIG. 11  can be derived from the ratios {R i }. 
       FIG. 20  illustrates a flowchart for managing a shared spectrum according to various embodiments of this disclosure. The operations of flowchart  2000  can be implemented in an SSM, such as SSM  406  in  FIGS. 4 and 5 . 
     Flowchart  2000  begins at operation  2002  by obtaining coexistence measurement reports (CMRs) from the plurality of BSs. The CMRs may be obtained periodically or aperiodically. In some embodiments, the CMR may be obtained from the plurality of BSs after the SSM sends a CMR request. 
     In operation  2004 , interference relationships are identified among the plurality of BSs based on the CMRs. In one embodiment, interference between BSs is determined based on a threshold power level so that at least some interference between base stations can be tolerated. Interference can be determined as described in operation  1116  in  FIG. 11 . 
     In operation  2006 , a set of BSs is assigned to one or more basic allocation units (BAUs) in a plurality of BAUs based on the interference relationships. The set of BSs includes a primary BS and a secondary BS, and the secondary BS can transmit in the one or more BAUs when a transmission of the secondary BS does not interfere with a transmission of the primary BS. 
     In some embodiments, operation  2006  includes assigning the primary BS to a prioritized transmission period in the one or more BAUs, which allows the primary BS to transmit in the prioritized transmission period without performing channel sensing; and assigning the secondary BS to an offset period in the one or more BAUs, which allows the secondary BS to transmit in the offset period after performing channel sensing. 
     In some embodiments, operation  2006  includes assigning another primary BS to one or more other BAUs in the plurality of BAUs based on the interference relationships. When the other primary BS interferes with the primary BS, the one or more other BAUs is orthogonal to the one or more BAUs. 
     In some embodiments, operation  2006  also includes assigning a tertiary BS to the one or more BAUs for transmitting in an opportunistic data transmission period (ODTP) in the one or more BAUs. The tertiary BS can transmit in the ODTP after performing a listen-before-talk procedure. 
     In operation  2008 , a spectrum access grant (SAG) is transmitted to the set of BSs, the SAG including BAU assignments for the set of BSs. 
     Although this disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that this disclosure encompass such changes and modifications as fall within the scope of the appended claims.