Clock selection in fronthaul networks

Abstract

Generally, the present subject matter relates to clock selection in a fronthaul network. In some implementations, clock selection in a fronthaul network can include selecting one DU from among multiple DUs communicatively coupled to a plurality of distributed units (DUs), radio units (RUs), and a service management and orchestration (SMO) to serve as a master clock for a communication system including the DUs, the RUs, and transmitting a request to the RU, triggering the RU to select one of the DUs to be the master clock. The SMO can be communicatively coupled to the RUs and the plurality of DUs.

Description

[Technical Field]

[0001] In some implementations, the present subject matter relates to communication systems, and in particular to clock selection in fronthaul networks. [Background technology]

[0002] In today's world, cellular networks provide on-demand communication capabilities to individuals and business entities. Typically, cellular networks are wireless networks that can be distributed over a terrestrial area called a cell. Each such cell is served by at least one fixed-location transceiver, referred to as a cell site or base station. Each cell can use a different set of frequencies from its neighboring cells to avoid interference and provide improved service within each cell. Together, the cells provide wireless coverage over a wide geographic area, allowing numerous mobile phones and / or other wireless devices or portable transceivers to communicate with each other and with fixed transceivers and phones anywhere in the network. Such communication is performed through base stations, even when a communicating mobile transceiver passes through more than one cell. Major wireless communication providers deploy such cell sites worldwide, allowing communicating mobile phones and mobile computing devices to connect to public switched telephone networks and the public Internet.

[0003] A mobile phone is a portable telephone that can receive and / or make telephone and / or data calls through a cell site or communication tower by using radio waves to transmit signals to and from the mobile phone. From the perspective of a large number of mobile phone users, current mobile phone networks offer limited and shared resources. In this regard, cell sites and handsets can change frequencies and use low-power transmitters to allow simultaneous use of the network by many callers with less interference. Coverage by a cell site can depend on the particular geographic location and / or the number of users that can potentially use the network. For example, in a city, a cell site may have a range of up to about 1 / 2 mile. In suburban areas, the range may be as long as 5 miles. In some areas, users can receive signals from cell sites as far away as 25 miles.

[0004] The following are some examples of digital cellular technologies used by communications providers: Global System for Mobile Communications ("GSM"), General Packet Radio Service ("GPRS"), cdmaOne, CDMA2000, Evolution-Data Optimized ("EV-DO"), Enhanced Data Rates for GSM Evolution ("EDGE"), Universal Mobile Telecommunications System ("UMTS"), Digital Enhanced Cordless Telecommunications ("DECT"), Digital AMPS ("IS-136 / TDMA"), and Integrated Digital Enhanced Network ("iDEN"). Long Term Evolution, or 4G LTE, developed by the Third Generation Partnership Project ("3GPP") standards organization, is a standard for high-speed data wireless communications for mobile phones and data terminals. 5G standards are currently being developed and deployed. 3GPP cellular technologies such as LTE and 5G NR are evolutions of previous generations of 3GPP technologies such as GSM / EDGE and UMTS / HSPA digital cellular technologies, and allow for increased capacity and speeds by using different air interfaces along with core network improvements.

[0005] A cellular network may be divided into a radio access network and a core network. The radio access network (RAN) may include network functions capable of handling radio layer communication processing. The core network may include network functions capable of handling higher layer communication (e.g., Internet Protocol (IP), transport layer, and application layer). In some cases, the RAN function may be divided into a baseband unit function and a radio unit function. Here, the radio unit connected to the baseband unit via a fronthaul network may be responsible for lower layer processing, for example, of the radio physical layer, and the baseband unit may be responsible for higher layer radio protocols (e.g., MAC, RLC, etc.). Summary of the Invention [Problem to be solved by the invention]

[0006] In an Open Radio Access Network (O-RAN), communications over a fronthaul network may be synchronized in time and frequency by synchronized clocks of devices communicating over the fronthaul network. Synchronization may allow messages communicated over the fronthaul network to be transmitted and received properly. Synchronization may be achieved using a timing grandmaster to which clocks are synchronized. However, if the timing grandmaster fails, synchronization also fails, jeopardizing proper communication over the fronthaul network. [Means for solving the problem]

[0007] In some implementations, the present subject matter relates to a computer-implemented method that may include selecting one DU from among a plurality of DUs communicatively coupled to a service management and orchestration unit (SMO) to serve as a master clock for a communication system including a plurality of DUs, a radio unit (RU), and a service management and orchestration unit (SMO), the DUs being communicatively coupled to the RUs, and transmitting a request to the RUs to trigger the RUs to select one of the DUs to be the master clock. The SMO may be communicatively coupled to the RUs and the plurality of DUs.

[0008] In some implementations, the current subject may include one or more of the following optional features: In some implementations, the SMO may trigger the selection. Additionally, the SMO may send a request to the RU.

[0009] In some implementations, the SMO may trigger a selection through one of the DUs to instruct the RU to perform the selection. Further, one of the DUs may send a request to the RU.

[0010] In some implementations, the method may further include receiving a signal from each of the DUs that can function as a master clock among the plurality of DUs. The selection may be directed to only the plurality of DUs that can function as a master clock.

[0011] In some implementations, one of the DUs may function as a master clock at or just before the selection is performed. The method may further include excluding one of the DUs from being selected. Further, the exclusion may exclude one of the DUs from the selection and future selections, and / or a failure of one of the DUs may trigger the selection.

[0012] In some implementations, the request may be a remote procedure call (RPC) request.

[0013] In some implementations, the communication system may include an open radio access network (O-RAN) architecture.

[0014] Non-transitory computer program products (i.e., physically embodied computer program products) storing instructions that, when executed by one or more data processors of one or more computing systems, cause at least one data processor to perform the operations described herein are also described. Similarly, computer systems are described that may include one or more data processors and memory coupled to the one or more data processors. The memory may store, on a temporary or permanent basis, instructions that cause at least one processor to perform one or more of the operations described herein. In addition, methods may be implemented by one or more data processors within a single computing system or distributed across two or more computing systems. Such computing systems may be connected to exchange data and / or commands or other instructions, etc., over one or more connections (including, but not limited to, connections over a network (e.g., the Internet, a wireless wide area network, a local area network, a wide area network, a wired network, etc.)), such as via a direct connection between one or more of the multiple computing systems.

[0015] Details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims. [Brief explanation of the drawings]

[0016] The following accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate certain aspects of the presently disclosed subject matter and, together with the description, serve to explain some of the principles associated with the disclosed implementations.

[0017] FIG. 1a illustrates an exemplary conventional "long term evolution" ("LTE") communications system.

[0018] FIG. 1b shows further details of the exemplary LTE system shown in FIG. 1a.

[0019] FIG. 1c shows additional details of the "evolved packet core" of the exemplary LTE system shown in FIG. 1a.

[0020] FIG. 1d illustrates an exemplary "evolved Node B" for the exemplary LTE system shown in FIG. 1a.

[0021] FIG. 2 illustrates further details of the "evolved Node B" shown in FIGS. 1a-d.

[0022] FIG. 3 illustrates an exemplary virtual radio access network according to some implementations of the current subject matter.

[0023] FIG. 4 shows an exemplary 3GPP split architecture for providing its users with use of higher frequency bands.

[0024] FIG. 5a illustrates an exemplary 5G wireless communication system.

[0025] FIG. 5b shows an example layer architecture for a split gNB and / or a split ng-eNB (e.g., a “next generation eNB” that may be connected to 5GC).

[0026] Figure 5c shows an exemplary functional split in the gNB architecture shown in Figures 5a-b.

[0027] FIG. 6 illustrates an exemplary system that may be used in clock selection in a fronthaul network, according to some implementations of the current subject matter.

[0028] FIG. 7 illustrates an exemplary implementation of the system of FIG. 6 according to some implementations of the current subject matter.

[0029] FIG. 8 illustrates another exemplary implementation of the system of FIG. 6, according to some implementations of the current subject matter.

[0030] FIG. 9 illustrates an exemplary method for clock selection in a fronthaul network according to some implementations of the current subject matter.

[0031] FIG. 10 illustrates an example implementation of a system in which the method of FIG. 9 may be implemented, according to some implementations of the current subject matter.

[0032] FIG. 11 illustrates an exemplary system according to some implementations of the current subject matter.

[0033] FIG. 12 illustrates an exemplary method according to some implementations of the current subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present subject matter can provide systems and methods that can be implemented in wireless communication systems. Such systems can include various wireless communication systems, including 5G New Radio communication systems, "long term evolution" communication systems, and the like.

[0035] Generally, the present subject matter relates to clock selection in fronthaul networks.

[0036] In some implementations of the present subject matter, a distributed unit (DU) can function as a timing grandmaster in the O-RAN architecture to synchronize timing and frequency over the architecture's fronthaul network. The O-RAN architecture may include multiple DUs, with at least two of the DUs capable of functioning as timing grandmasters for multiple radio units (RUs). Only one DU may function as timing grandmaster at a time. If a problem occurs with the DU currently functioning as timing grandmaster, communication over the fronthaul connection may not function properly or at all. Selecting a new timing grandmaster from among the DUs capable of functioning as timing grandmasters (other than the one currently functioning as timing grandmaster) relieves the problematic DU currently functioning as timing grandmaster from its timing grandmaster duties, and synchronization may be properly achieved using the new timing grandmaster. However, if the timing stack in the DU currently functioning as timing grandmaster is working properly but there are problems with the rest of the DU applications, switching to a different timing grandmaster DU is not currently supported by O-RAN. In some implementations of the present subject matter, one DU out of multiple DUs capable of functioning as timing grandmasters in the O-RAN architecture may be selected to function as the timing grandmaster.

[0037] One or more aspects of the present subject matter may be integrated into transmitter and / or receiver components of a base station (e.g., gNodeB, eNodeB, etc.) in such communication systems. The following is a general discussion of long-term evolution communication systems and 5G New Radio communication systems. I. "Long-term evolution" communication systems

[0038] 1a-c and 2 illustrate an exemplary conventional long-term evolution ("LTE") communication system 100 along with its various components. The LTE system, or 4G LTE, as it is commercially known, conforms to a standard for high-speed data wireless communication for mobile phones and data terminals. The standard incorporates GSM / EDGE ("Global System for Mobile Communications" / "Enhanced Data rates for GSM Evolution") and UMTS / HSPA ("Universal Mobile Telecommunications System" / "High Speed ​​Packet Access") network technologies. The standard was developed by 3GPP ("3rd Generation Partnership Project").

[0039] As shown in FIG. 1a, system 100 may include an “evolved universal terrestrial radio access network” (“EUTRAN”) 102, an “evolved packet core” (“EPC”) 108, and a “packet data network” (“PDN”) 101 through which EUTRAN 102 and EPC 108 provide communication between user equipment 104 and PDN 101. EUTRAN 102 may include multiple “evolved Node Bs” (“eNodeBs” or “ENODEBs” or “enodeb” or “eNBs”) or base stations 106(a, b, c) (as shown in FIG. 1b) that provide communication capabilities to multiple user equipment 104(a, b, c). User equipment 104 may be a mobile phone, a smartphone, a tablet, a personal computer, a personal digital assistant (“PDA”), a server, a data terminal, and / or any other type of user equipment, and / or any combination thereof. User equipment 104 can connect to the EPC 108 and therefore the PDN 101 via any eNodeB 106. Typically, user equipment 104 can connect to the eNodeB 106 that is closest in distance. In the LTE system 100, the EUTRAN 102 and the EPC 108 cooperate to provide connectivity, mobility, and services to user equipment 104.

[0040] Figure 1b illustrates further details of the network 100 shown in Figure 1a. As previously mentioned, the EUTRAN 102 includes multiple eNodeBs 106, also known as cell sites. The eNodeBs 106 provide radio functionality and perform key control functions, including scheduling of air link resources or radio resource management, active mode mobility or handover, and admission control for services. The eNodeBs 106 are responsible for selecting which mobility management entity (MME, as shown in Figure 1c) serves the user equipment 104 and for protocol features such as header compression and encryption. The eNodeBs 106 that make up the EUTRAN 102 cooperate with each other for radio resource management and handover.

[0041] Communication between the user equipment 104 and the eNodeB 106 occurs over an air interface 122 (also known as the "LTE-Uu" interface). As shown in FIG. 1b, the air interface 122 provides communication between the user equipment 104b and the eNodeB 106a. The air interface 122 uses Orthogonal Frequency Division Multiple Access ("OFDMA") and Single-Carrier Frequency Division Multiple Access ("SC-FDMA"), an OFDMA variant, on the downlink and uplink, respectively. OFDMA enables the use of multiple known antenna technologies, such as "Multiple Input Multiple Output" ("MIMO").

[0042] The air interface 122 uses various protocols, including radio resource control ("RRC") for signaling between the user equipment 104 and the eNodeB 106 and non-access stratum ("NAS") for signaling between the user equipment 104 and the MME (as shown in FIG. 1c). In addition to signaling, user traffic is transferred between the user equipment 104 and the eNodeB 106. Both signaling and traffic in the system 100 are carried by physical layer ("PHY") channels.

[0043] Multiple eNodeBs 106 may be interconnected with each other using X2 interfaces 130(a, b, c). As shown in FIG. 1b, X2 interface 130a provides interconnection between eNodeB 106a and eNodeB 106b, X2 interface 130b provides interconnection between eNodeB 106a and eNodeB 106c, and X2 interface 130c provides interconnection between eNodeB 106b and eNodeB 106c. The X2 interfaces may be established between two eNodeBs to provide for the exchange of signals that may include load- or interference-related information and handover-related information. The eNodeBs 106 communicate with the “evolved packet core” 108 via S1 interfaces 124(a, b, c). The S1 interface 124 may be divided into two interfaces: One is the control plane (shown in FIG. 1c as control plane interface (S1-MME interface) 128) and the other is the user plane (shown in FIG. 1c as user plane interface (S1-U interface) 125).

[0044] The EPC 108 establishes and enables "Quality of Service" ("QoS") for user services and allows the user equipment 104 to maintain a consistent Internet Protocol ("IP") address while moving, where each node in the network 100 has its own IP address. The EPC 108 is designed to work with legacy wireless networks. The EPC 108 is also designed to separate the control plane (i.e., signaling) and user plane (i.e., traffic) in the core network architecture, allowing for greater flexibility in implementation and independent scalability of control and user data functions.

[0045] The architecture of the EPC 108, which is for packet data, is shown in more detail in Figure 1c. The EPC 108 includes a Serving Gateway (S-GW) 110, a PDN Gateway (P-GW) 112, a Mobility Management Entity ("MME") 114, a Home Subscriber Server ("HSS") 116 (the subscriber database for the EPC 108), and a Policy Control and Charging Rules Function ("PCRF") 118. Some of these (such as the S-GW, P-GW, MME, and HSS) are often combined into a node according to the manufacturer's implementation.

[0046] The S-GW 110 functions as an IP packet data router and is the user equipment's bearer path anchor in the EPC 108. Thus, as the user equipment moves from one eNodeB 106 to another during mobility operation, the S-GW 110 remains the same, and the bearer path towards the EUTRAN 102 is switched to talk to the new eNodeB 106 serving the user equipment 104. If the user equipment 104 moves to the domain of another S-GW 110, the MME 114 forwards all of the user equipment's bearer paths to the new S-GW. The S-GW 110 establishes bearer paths for the user equipment to one or more P-GWs 112. When downstream data is received for an idle user equipment, the S-GW 110 buffers the downstream packets and requests the MME 114 to identify and re-establish the bearer path to and through the EUTRAN 102.

[0047] The P-GW 112 is the gateway between the EPC 108 (and thus the user equipment 104 and EUTRAN 102) and the PDN 101 (shown in FIG. 1a). The P-GW 112 acts as a router for user traffic and performs functions on behalf of the user equipment. These include IP address allocation for the user equipment, packet filtering of downstream user traffic to ensure it is placed on the appropriate bearer path, and enabling downstream QoS, including data rate. Depending on the services a subscriber is using, there may be multiple user data bearer paths between the user equipment 104 and the P-GW 112. A subscriber can use services on PDNs served by different P-GWs. In this case, the user equipment has at least one bearer path established to each P-GW 112. During handover of a user equipment from one eNodeB to another, if the S-GW 110 also changes, the bearer path from the P-GW 112 is switched to the new S-GW.

[0048] The MME 114 manages the user equipment 104 in the EPC 108 (including managing subscriber authentication, maintaining context for authenticated user equipment 104, establishing a data bearer path in the network for user traffic, and keeping track of the location of idle mobiles that have not detached from the network). For idle user equipment 104 that needs to reconnect to the access network to receive downstream data, the MME 114 initiates paging to identify the user equipment and reestablish a bearer path to and through the EUTRAN 102. The MME 114 for a particular user equipment 104 is selected by the eNodeB 106 from which the user equipment 104 initiates system access. The MME is typically part of a collection of MMEs in the EPC 108 for load sharing and redundancy purposes. In establishing a user's data bearer path, the MME 114 is responsible for selecting the P-GW 112 and S-GW 110 that constitute the ends of the data path through the EPC 108.

[0049] The PCRF 118 is responsible for policy control decision making and controlling the flow-based charging functionality in the Policy Control Activation Function ("PCEF") residing in the P-GW 110. The PCRF 118 provides QoS authorization (QoS Class Identifier ("QCI") and bitrate) that determines how a particular data flow is treated in the PCEF and ensures that this is in line with the user's subscription profile.

[0050] As previously mentioned, IP services 119 are provided by PDN 101 (shown in FIG. 1a).

[0051] 1d shows an example configuration of an eNodeB 106. The eNodeB 106 may include at least one "remote radio head" ("RRH") 132 (typically, there may be three RRHs 132) and a baseband unit ("BBU") 134. The RRHs 132 may be connected to an antenna 136. The RRHs 132 and BBU 134 may be connected using an optical interface compliant with the "common public radio interface" ("CPRI") / "enhanced CPRI" ("eCPRI") 142 specification, using an RRH-specific custom control and user plane framing method or an O-RAN Alliance-compliant control and user plane framing method. The operation of the eNodeB 106 may be characterized using the following standard parameters (and specifications): radio frequency band (Band 4, Band 9, Band 17, etc.), bandwidth (5, 10, 15, 20 MHz), access scheme (downlink: OFDMA; uplink: SC-OFDMA), antenna technology (single-user and multi-user MIMO; uplink: single-user and multi-user MIMO), number of sectors (up to 6), maximum transmission rate (downlink: 150 Mb / s; uplink: 50 Mb / s), S1 / X2 interface (1000base-SX, 1000base-T), and mobile environment (up to 350 km / h). The BBU 134 may be responsible for digital baseband signal processing, S1 line termination, X2 line termination, call processing, and monitoring control processing. IP packets received from the EPC 108 (not shown in FIG. 1d) may be modulated into digital baseband signals and transmitted to the RRH 132. Conversely, digital baseband signals received from the RRH 132 may be demodulated into IP packets for transmission to the EPC 108.

[0052] The RRH 132 can transmit and receive wireless signals using an antenna 136. The RRH 132 can convert digital baseband signals from the BBU 134 to radio frequency ("RF") signals (using a converter ("CONV") 140) and can power amplify (using an amplifier ("AMP") 138) for transmission to the user equipment 104 (not shown in FIG. 1d). Conversely, RF signals received from the user equipment 104 are amplified (using AMP 138) and converted (using CONV 140) to digital baseband signals for transmission to the BBU 134.

[0053] Figure 2 shows additional details of an exemplary eNodeB 106. The eNodeB 106 includes multiple layers: "LTE Layer 1" 202, "LTE Layer 2" 204, and "LTE Layer 3" 206. LTE Layer 1 includes the physical layer ("PHY"). LTE Layer 2 includes media access control ("MAC"), radio link control ("RLC"), and packet data convergence protocol ("PDCP"). LTE Layer 3 includes various functions and protocols, including radio resource control ("RRC"), dynamic resource allocation, eNodeB measurement configuration and provisioning, radio admission control, connection mobility control, and radio resource management ("RRM"). The RLC protocol is an "automatic repeat request" ("ARQ") fragmentation protocol used over the cellular air interface. The RRC protocol handles LTE Layer 3 control plane signaling between user equipment and the EUTRAN. The RRC includes functions for connection establishment and release, system information broadcast, radio bearer establishment / reconfiguration and release, RRC connection mobility procedures, paging notification and release, and outer loop power control. The PDCP performs IP header compression and decompression, user data transfer, and sequence number maintenance for radio bearers. The BBU 134 shown in FIG. 1d may include LTE layers L1-L3.

[0054] One of the primary functions of the eNodeB 106 is radio resource management, including scheduling of both uplink and downlink air interface resources for the user equipment 104, control of bearer resources, and admission control. As an agent for the EPC 108, the eNodeB 106 is responsible for forwarding paging messages used to identify idle mobiles. The eNodeB 106 also communicates over-the-air common control channel information, header compression, encryption and decryption of over-the-air user data, and establishes handover reporting and trigger criteria. As previously mentioned, the eNodeB 106 can cooperate with other eNodeBs 106 over the X2 interface for handover and interference management purposes. The eNodeB 106 communicates with the MME of the EPC via the S1-MME interface and with the S-GW over the S1-U interface. Furthermore, the eNodeB 106 exchanges user data with the S-GW over the S1-U interface. The eNodeBs 106 and the EPC 108 have a many-to-many relationship to support load sharing and redundancy among the MMEs and S-GWs. The eNodeB 106 selects an MME from a group of MMEs so that the load can be shared by multiple MMEs to avoid congestion. II. 5G NR Wireless Communication Network

[0055] In some implementations, the current subject matter relates to 5G new radio ("NR") communication systems. 5G NR is the next communication standard after the 4G / IMT-Advanced standard. 5G networks offer higher capacity than current 4G, allowing more mobile broadband users per unit area and enabling consumption of higher and / or unlimited data volumes in gigabytes per month and per user. This may enable users to stream high-resolution media using their mobile devices much of each day (even when it is not possible to do the same with Wi-Fi networks). 5G networks have improved support for device-to-device communication, lower cost, lower latency than 4G equipment, and lower battery consumption. Such networks have data rates of tens of megabits per second for many users, data rates of 100 Mb / s for metropolitan areas, simultaneous 1 Gb / s for users in a restricted area (e.g., an office floor), many simultaneous connections for wireless sensor networks, improved spectral efficiency, improved coverage, improved signaling efficiency, and 1-10 ms latency, a reduced latency compared to existing systems.

[0056] 3 illustrates an exemplary virtual radio access network 300. The network 300 can provide communication between various components, including a base station (e.g., eNodeB, gNodeB) 301, radio equipment 307, aggregation units 302, digital units 304, and wireless devices 306. The components in the system 300 can be communicatively coupled to the core using backhaul links 305. The aggregation units (“CUs”) 302 can be communicatively coupled to the distributed units (“DUs”) 304 using midhaul connections 308. The radio frequency (“RUs”) components 306 can be communicatively coupled to the DUs 304 using fronthaul connections 310.

[0057] In some implementations, the CU 302 can provide intelligent communication capabilities to one or more DU units 304. The units 302, 304 can include one or more base stations, macro base stations, micro base stations, "remote radio heads," etc., and / or any combination thereof.

[0058] In a lower layer split ("LLS") architecture environment, the CPRI bandwidth requirements for NR can be several hundred Gb / s. CPRI compression can be implemented in the DU and RU (shown in Figure 3). In 5G communication systems, compressed CPRI over Ethernet frames is denoted as eCPRI and is the recommended fronthaul network. The architecture can enable standardization of fronthaul / midhaul, which can include fronthaul with higher layer split (e.g., "Option 2" or "Option 3-1" (higher / lower RLC split architecture)) and L1 split architecture ("Option 7").

[0059] In some implementations, a lower layer split architecture (e.g., "Option 7") may include a receiver in the uplink, joint processing across multiple transmission points (TPs) for both DL / UL, and transport bandwidth and latency requirements for ease of deployment. Additionally, the subject lower layer split architecture may include a split between cell-level and user-level processing, which may include cell-level processing in a remote unit ("RU") and user-level processing in a DU. Additionally, using the subject lower layer split architecture, frequency-domain samples may be transported over the Ethernet fronthaul, which may be compressed to reduce fronthaul bandwidth.

[0060] 4 illustrates an example communication system 400 that can implement 5G technology and provide users with access to higher frequency bands (e.g., above 10 GHz). The system 400 can include a macrocell 402 and small cells 404, 406.

[0061] The mobile device 408 may be configured to communicate with one or more of the small cells 404, 406. The system 400 may enable separation of the control plane (C-plane) and user plane (U-plane) between the macrocell 402 and the small cells 404, 406 using different frequency bands. In particular, the small cells 404, 406 may be configured to utilize higher frequency bands when communicating with the mobile device 408. The macrocell 402 may utilize existing cellular bands for C-plane communications. The mobile device 408 may be communicatively coupled via the U-plane 412, where the small cell (e.g., the small cell 406) may provide higher data rates and more flexible, cost-effective, and energy-efficient operation. The macrocell 402 may maintain good connectivity and mobility via the C-plane 410. Furthermore, in some cases, LTE and NR may be transmitted on the same frequency.

[0062] FIG. 5a illustrates an exemplary 5G wireless communication system 500 according to some implementations of the present subject matter. The system 500 may be configured to have a lower layer split architecture in accordance with "Option 7-2." The system 500 may include a core network 502 (e.g., 5G Core) and one or more gNodeBs (or gNBs), which may have an aggregation unit (gNB-CU). The gNB-CU may be logically separated into a control plane portion (gNB-CU-CP) 504 and one or more user plane portions (gNB-CU-UP) 506. The control plane portion 504 and the user plane portion 506 may be configured to be communicatively coupled using an E1 communication interface 514 (defined in the 3GPP standard). The control plane portion 504 may be configured to be responsible for executing the RRC and PDCP protocols of the radio stack.

[0063] The control plane and user plane portions 504, 506 of the aggregation unit of the gNB may be configured to be communicatively coupled to one or more distributed units (DUs) 508, 510 according to a higher layer split architecture. The distributed units 508, 510 may be configured to execute the upper RLC, MAC, and PHY layer protocols of the radio stack. The control plane portion 504 may be configured to be communicatively coupled to the distributed units 508, 510 using an F1-C communication interface 516, and the user plane portion 506 may be configured to be communicatively coupled to the distributed units 508, 510 using an F1-U communication interface 518. The distributed units 508, 510 may be coupled to one or more remote radio units (RUs) 512 via a fronthaul network 520 (which may include one of a switch, a link, etc.) and may communicate with one or more user equipment (not shown in FIG. 5a). The remote radio unit 512 may be configured to execute the lower portions of the PHY layer protocol and provide antenna capabilities to the remote unit for communication with user equipment (similar to the discussion above with respect to FIGS. 1a-2).

[0064] Figure 5b shows an example layer architecture 530 for a split gNB. The architecture 530, which may be configured as a virtualized and disaggregated radio access network (RAN) architecture (layers L1, L2, L3 and radio processing may be virtualized and disaggregated in the aggregation unit, distributed unit, and radio unit), may be implemented in the communication system 500 shown in Figure 5a. As shown in Figure 5b, the gNB-DU 508 may be communicatively coupled to the gNB-CU-CP control plane portion 504 (also shown in Figure 5a) and the gNB-CU-UP user plane portion 506. Each of the components 504, 506, 508 may be configured to include one or more layers.

[0065] The gNB-DU 508 may include RLC, MAC, and PHY layers, as well as various communication sublayers. These may include an F1-Application Protocol (F1-AP) sublayer, a GPRS Tunneling Protocol (GTPU) sublayer, a Stream Control Transmission Protocol (SCTP) sublayer, a User Datagram Protocol (UDP) sublayer, and an Internet Protocol (IP) sublayer. As previously described, the distribution unit 508 may be communicatively coupled to the control plane portion 504 of the aggregation unit, which may include the F1-AP, SCTP, and IP sublayers, and the Radio Resource Control and PDCP Control (PDCP-C) sublayers. Furthermore, the distribution unit 508 may be communicatively coupled to the user plane portion 506 of the aggregation unit of the gNB. The user plane portion 506 may include the Service Data Adaptation Protocol (SDAP), PDCP User (PDCP-U), GTPU, UDP, and IP sublayers.

[0066] Figure 5c shows an example functional split in the gNB architecture shown in Figures 5a-b. As shown in Figure 5c, the gNB-DU 508 may be communicatively coupled to the gNB-CU-CP 504 and the GNB-CU-UP 506 using an F1-C communication interface. The gNB-CU-CP 504 and the GNB-CU-UP 506 may be communicatively coupled using an E1 communication interface. A higher portion of the PHY layer (or Layer 1) may be performed by the gNB-DU 508, and a lower portion of the PHY layer may be performed by the RU (not shown in Figure 5c). As shown in Figure 5c, the RRC and PDCP-C portions may be performed by the control plane portion 504, and the SDAP and PDCP-U portions may be performed by the user plane portion 506.

[0067] Some of the functions of the PHY layer in a 5G communication network may include error detection on transport channels and suggestion to higher layers, FEC encoding / decoding of transport channels, hybrid ARQ soft combining, rate matching of coded transport channels to physical channels, mapping of coded transport channels onto physical channels, power weighting of physical channels, modulation and demodulation of physical channels, frequency and time synchronization, radio characteristic measurements and suggestion to higher layers, MIMO antenna processing, digital and analog beamforming, RF processing, and other functions.

[0068] The MAC sublayer of Layer 2 may perform beam management, random access procedures, mapping between logical channels and transport channels, concatenation of multiple MAC service data units (SDUs) belonging to one logical channel into transport blocks (TBs), multiplexing / demultiplexing of SDUs belonging to logical channels to / from TBs delivered on transport channels to / from the physical layer, scheduling of reporting information, error correction via HARQ, priority handling between logical channels for one UE, priority handling between UEs via dynamic scheduling, transport format selection, and other functions. The RLC sublayer's functions may include forwarding upper layer packet data units (PDUs), error correction via ARQ, reordering of data PDUs, duplication and protocol error detection, reestablishment, etc. The PDCP sublayer may be responsible for forwarding user data, various functions during reestablishment procedures, retransmission of SDUs, discarding SDUs in the uplink, forwarding of control plane data, and others.

[0069] The RRC sublayer of Layer 3 may perform functions such as broadcasting system information to the NAS and AS, establishing, maintaining and releasing RRC connections, security, establishing, configuring, maintaining and releasing point-to-point radio bearers, mobility functions, reporting, and other functions. III. Clock Selection in Fronthaul Networks

[0070] In some implementations of the present subject matter, a distributed unit (DU) can function as a timing grandmaster (also referred to as a "grandmaster" or "master clock") in an O-RAN architecture to synchronize timing and frequency across the architecture's fronthaul network. The fronthaul network is highly sensitive to latency and jitter. RUs typically listen for C-plane and U-plane messages within a specific time window per slot. The arrival times of the first and last messages for a specific slot and / or symbol at the RU and DU depend, among other things, on the parameters / design of their respective receive windows. Latency and / or jitter in the fronthaul connection, which can contribute to timing errors, can adversely affect the functionality of the RU and / or DU because timing errors lead to clock drift for the receive / transmit window duration, making slot and symbol boundaries undetectable. Synchronization can reduce, if not eliminate, the effects of latency and jitter, so the RU and DU operate properly.

[0071] The grandmaster can send synchronization information to clocks on its segment of the network. All clocks that receive synchronization information from the grandmaster can synchronize directly to it. The "precision time protocol" (PTP) (originally defined in the IEEE 1588-2002 standard) can be used to synchronize the clocks. PTP can be used to achieve clock accuracy in the sub-microsecond range. Both the DU and RU can be configured to use the PTP protocol for clock synchronization purposes.

[0072] An O-RAN architecture may include multiple DUs, with at least two of the DUs capable of functioning as grandmasters for multiple RUs. Only one DU may be selected to function as grandmaster at a time. If the DU currently functioning as grandmaster goes offline or experiences an error, communication over the fronthaul connection may be improper or impossible. Examples of such errors include the DU being in locked state or holdover, or the DU having internal errors and jitter that may result in delays in C-plane and U-plane packet transmission over the fronthaul connection. When a DU is in holdover, the DU in holdover signals deteriorated clock quality so that the RU can automatically select a new grandmaster, for example, by using the BMCA mechanism as discussed herein. Selecting a new grandmaster from among the DUs capable of functioning as grandmasters (other than the one currently functioning as grandmaster) relieves the problematic DU currently functioning as grandmaster from its duties, and synchronization using the new grandmaster may be properly achieved. However, if the timing stack in the DU currently acting as timing grandmaster is working properly but there are issues with the rest of the DU application, then switching to such a different grandmaster DU is not currently supported by O-RAN.

[0073] In some implementations of the present subject matter, one DU among multiple DUs capable of functioning as grandmasters in an O-RAN architecture can be selected to function as the grandmaster. In some implementations of the present subject matter, a service management and orchestration (SMO) to which multiple DUs are communicatively coupled can trigger the selection of a new grandmaster by an RU. Such an implementation may be interpreted as a hybrid model because the SMO and DU can each provide control over one or more RUs. The SMO can trigger one or more RUs to switch to another DU as grandmaster, and the new grandmaster DU, in its role as grandmaster, can provide synchronized control over one or more RUs. The hybrid model may also enable grandmaster switching if a failure occurs in the DU currently functioning as grandmaster that prevents it from triggering a switch to a new grandmaster. In other implementations of the present subject matter, the SMO can trigger the selection of a new grandmaster by an RU through a DU. Such an implementation may be interpreted as a hierarchical model because multiple DUs provide control over one or more RUs. A DU currently acting as grandmaster can trigger one or more RUs to switch to another DU as grandmaster, and the new grandmaster DU, in its role as grandmaster, can provide synchronization control for one or more RUs. Because the communication for grandmaster switching occurs over the fronthaul connection (fronthaul communication link) between the DU and RU, the hierarchical model may allow the SMO to use its processing resources for other tasks and / or reduce bandwidth usage across the network.

[0074] The NETCONF / YANG protocol (or application layer mode of communication) may be used for the operation and / or management of network functions. NETCONF / YANG is a network management protocol developed and standardized by the Internet Engineering Task Force (IETF) under the RFC 4741 and RFC 6241 standards. The NETCONF / YANG protocol provides mechanisms for installing, manipulating, and deleting the configuration of network devices.

[0075] In some implementations of the present subject matter, to trigger a grandmaster switch from one DU to another, a request received by the RU from the SMO (hybrid model) or DU (hierarchical model) can be sent as a remote procedure call (RPC) request in "o-ran-sync.yang" according to the NETCONF / YANG protocol. In this way, clock selection may utilize existing network functions.

[0076] Table 1 shows the types of messages, along with the direction of transmission, that may be transmitted over a fronthaul communication link between a DU and an RU (e.g., the fronthaul connection 310 between the DU 304 and the RU 306 in FIG. 3, the fronthaul connection over the fronthaul network 520 between the DU 508 and one of the RUs 512 in FIG. 5a, the fronthaul connection over the fronthaul network 520 between the DU 510 and one of the RUs 512 in FIG. 5a, the fronthaul connection between the RU 604 and one of the DUs 602a, 602b, ..., 602n in FIG. 6, the fronthaul connection between one of the RUs 704a, 704b, 704c and one of the DUs 702a, 702b, 702c in FIG. 7, the fronthaul connection between one of the RUs 804a, 804b, 804c and one of the DUs 802a, 802b, 802c in FIG. 8, etc.). Messages may be transmitted in the control plane (C-plane), user plane (U-plane), synchronization plane (S-plane), and management plane (M-plane). The C-plane may include uplink and downlink messages (DU to RU and RU to DU). The U-plane may also include uplink (RU to DU) and downlink (DU to RU) messages, in which IQ samples may be transmitted to / from user equipment. The uplink / downlink direction is not applicable to the transmission of messages in the synchronization and management planes. The S-plane includes messages carrying timing information related to the timing grandmaster. The M-plane carries messages related to configuration (DU to RU) and notification / measurements (RU to DU). [Table 1]

[0077] As mentioned above, the LLS architecture (lower layer split architecture) may include a split between cell-level and user-level processing, which may include cell-level processing in the RU and user-level processing in the DU. In the O-RAN architecture, an LLS control plane (LLS-C) logical interface between the RU and DU may be used for C-plane communication between the RU and DU. Time synchronization (clocks (e.g., in the RU and DU) are synchronized to a common time) and frequency synchronization (clocks (e.g., in the RU and DU) are synchronized in frequency) may facilitate effective C-plane communication.

[0078] The "Control, User and Synchronization Plane Specification" of the O-RAN Working Group 4 (Open Fronthaul Interfaces WG) defines the C-plane, U-plane, and S-plane protocols for the DU (O-DU) and RU (O-RU) used on the fronthaul connection with the lower layer split (LLS) architecture. In each of the LLS-C1 and LLS-C2 architectures, the DU can function as a timing grandmaster (e.g., the G.8275.2 precision time protocol (PTP) master on the fronthaul connection for the RU). In the LLS-C1 architecture, the RU synchronizes directly with the DU. In the LLS-C2 architecture, the RU does not synchronize directly with the DU because one or more switches are placed between the RU and the DU.

[0079] 6 illustrates an implementation of a system 600 that may be used in clock selection in a fronthaul network in accordance with some implementations of the current subject matter. System 600 may be a radio access network operating in a wireless communication environment (e.g., 4G, LTE, 5G, etc.). System 600, as shown in FIG. 6, is an O-RAN architecture and may include components as described above and other components contemplated by one of ordinary skill in the art.

[0080] The system 600 may include one or more distributed units DU 602a, DU 602b, ..., DU 602n, a service management and orchestration (SMO) component 604, and a radio unit (RU) 606. In FIG. 6, the suffix "n" represents any integer greater than or equal to 3 to indicate that any number of DUs may be included in the system 600. Also, in FIG. 6, the DUs 602a, DU 602b, ..., DU 602n are denoted as "O-DUs" to indicate that the DUs in this illustrated implementation are O-RAN distributed units (e.g., the DUs are components in an O-RAN architecture), and the RU 606 is denoted as "O-RU" to indicate that the RUs in this illustrated implementation are O-RAN radio units (e.g., the RUs are components in an O-RAN architecture).

[0081] The DUs 602a, 602b, 602n may be configured to be communicatively coupled to an SMO component 604. The SMO component 604 may be configured to be communicatively coupled to the RU 606. Two or more DUs 602a, 602b, 602n may also be configured to be communicatively coupled to each other, where one of the DUs 602a, 602b, ..., 602n (e.g., the first DU 602a) may be implemented and / or function as a host and / or primary distributed unit, and one or more other DUs 602a, 602b, 602n (e.g., the second through n-th DUs 602b, 602n) may be implemented and / or function as tenant and / or secondary and / or shared resource operator distributed units.

[0082] In some implementations, the DUs 602a, 602b, ..., 602n may be from the same mobile network operator (MNO). In other implementations, one or more of the DUs 602a, 602b, 602n may be from a different MNO than one or more of the other DUs 602a, 602b, 602n.

[0083] 7 illustrates a system 700 that is an implementation of the system 600 in the LLS-C1 architecture. The system 700 may include one or more DUs 702a, 702b, and 702c, each of which may be communicatively coupled to one or more RUs 704, 704b, and 704c. While the system 700 is shown with three DUs 702a, 702b, and 702c, other numbers of DUs are possible. Also, while the system 700 is shown with three RUs 704, 704b, and 704c, other numbers of RUs are possible. The system 700 also includes an SMO (e.g., SMO 604) that may be communicatively coupled to the DUs 702a, 702b, and 702c.

[0084] Two of the DUs 702a, 702b in this illustrated implementation include grandmasters 706a, 706b. Although the grandmasters 706a, 706b are shown in FIG. 7 as being integrated with the respective DUs 702a, 702b, one or more of the grandmasters 706a, 706b may be external and communicatively coupled to the respective DUs 702a, 702b so as to be uniquely associated therewith. The third DU 702c in this illustrated implementation is not configured to function as a grandmaster. Thus, one of the two DUs 702a, 702b can function as a grandmaster for one or more RUs 704a, 704b, 704c at a time. In other words, all DUs in the LLS-C1 architecture except for one of the DUs are configured to function as grandmasters. Other implementations of the LLS-C1 architecture may have other combinations of one or more DUs configured to function as grandmasters and zero or more DUs that are not configured to function as grandmasters (e.g., all DUs in the LLS-C1 architecture are configured to function as grandmasters, all but two of the DUs in the LLS-C1 architecture are configured to function as grandmasters, all but three of the DUs in the LLS-C1 architecture are configured to function as grandmasters, etc.).

[0085] 8 illustrates a system 800 that is an implementation of the system 600 in the LLS-C2 architecture. The system 800 may include one or more DUs 802a, 802b, and 802c, each of which may be communicatively coupled to one or more RUs 804a, 804b, and 804c via a switch 808. While the system 800 is shown with three DUs 802a, 802b, and 802c, other numbers of DUs are possible. Also, while the system 800 is shown with three RUs 804, 804b, and 804c, other numbers of RUs are possible. The system 800 also includes an SMO (e.g., SMO 604) that may be communicatively coupled to the DUs 802a, 802b, and 802c.

[0086] Two of the DUs 802a, 802b in this illustrated implementation include grandmasters 806a, 806b, which may include, for example, time synchronization cards. While the grandmasters 806a, 806b are shown in FIG. 8 as being integrated with the respective DUs 802a, 802b, one or more of the grandmasters 806a, 806b may be external and communicatively coupled to the respective DUs 802a, 802b so as to be uniquely associated with them. The third DU 802c in this illustrated implementation is not configured to function as a grandmaster. Thus, one of the two DUs 802a, 802b can function as a grandmaster for one or more RUs 804, 804b, 804c at a time. In other words, all DUs in the LLS-C2 architecture except for one of the DUs are configured to function as grandmasters. Other implementations of the LLS-C2 architecture may have other combinations of one or more DUs configured to function as grandmasters and zero or more DUs that are not configured to function as grandmasters (e.g., all DUs in the LLS-C2 architecture are configured to function as grandmasters, all but two of the DUs in the LLS-C2 architecture are configured to function as grandmasters, all but three of the DUs in the LLS-C2 architecture are configured to function as grandmasters, etc.).

[0087] 9 illustrates one implementation of a method 900 for performing clock selection in a fronthaul network in accordance with some implementations of the current subject matter. For ease of explanation, the method 900 is described with respect to an implementation of the system 1000 shown in FIG. 10, but may also be implemented with respect to other systems (e.g., the system 600 of FIG. 6 (e.g., the system 700 of FIG. 7, the system 800 of FIG. 8, etc.)).

[0088] The system 1000 of Figure 10 may be configured and used generally similarly to that described above with respect to the system 600 of Figure 6. The system 1000 may include first, second, and third DUs 1002a, 1002b, and 1002c. The RU 1004 is communicatively coupled to the DUs 1002a, 1002b, and 1002c (e.g., in an LLS-C1 architecture as in Figure 7 or in an LLS-C2 architecture as in Figure 8), and the SMO 1006 is communicatively coupled to the DUs 1002a, 1002b, and 1002c. As described above, different numbers of DUs and different numbers of RUs are possible.

[0089] The first DU 1002a (labeled "host DU" in FIG. 10) is the current grandmaster. As shown in FIG. 10, the clock of the RU 1004 is synchronized to the clock of the host DU 1002a, for example, by a timing grandmaster. The second and third DUs 1002b and 1002c are shown in FIG. 10 as tenant DUs.

[0090] The method 900 may include each of the DUs 1002a, 1002b, and 1002c broadcasting (e.g., advertising) 902 whether or not it can function as a timing grandmaster. For purposes of discussing the method 900 of FIG. 9, it is assumed that all of the DUs 1002a, 1002b, and 1002c can function as grandmasters. However, as previously described, one or more DUs in a system may not be capable of functioning as grandmasters, where two or more other DUs in the system are capable of functioning as grandmasters. Thus, in this illustrated implementation, each of the DUs 1002a, 1002b, and 1002c broadcasts 902 that it can function as a timing grandmaster.

[0091] The broadcasting 902 may include each of the DUs 1002a, 1002b, and 1002c broadcasting 902 its grandmaster capability to the RU 1004. This helps the RU 1004 select a new master clock in the hybrid model 1008 or the hierarchical model 1010. The broadcasting 902 may be triggered upon connection of the DU to the fronthaul network. In other words, connection of the DU to the fronthaul network can trigger broadcasting 902 of whether the DU can function as a grandmaster. In this way, a newly connected DU becomes available to function as a grandmaster very quickly.

[0092] When a new master clock is needed (904), a new master clock may be selected. A new master clock may be needed (904) under a variety of different circumstances. For example, as described above, an error may occur in the current master clock that impairs or may impair its ability to function as grandmaster, creating a situation in which a new master clock should be selected. In this manner, a new master clock may be dynamically selected based on the failure status of the master clock, which is indicated to the RU 1004 by a request sent to and received by the RU 1004 (906).

[0093] The master clock is aware of its own status, e.g., aware of the occurrence of an error that is configured to automatically trigger a change in grandmaster. In response to detecting such an error, in each of the hybrid model 1008 and the hierarchical model 1010, the current master clock, e.g., the host DU 1002a, may be configured to send a notification to the SMO 1006 that a new grandmaster is needed. The notification may or may not include information indicating why a new grandmaster is needed, e.g., it may or may not identify the error that occurred. The first DU 1002a, which identifies that an error has occurred through its typical functionality, may be configured to trigger the sending of the notification to the SMO 1006. Receipt of the notification at the SMO 1006 may be configured to cause the SMO 1006 to exclude the host DU 1002a from possible future selection as grandmaster, because the notification informs the SMO 1006 that the host DU 1002a is unsuitable to function as grandmaster. The resolution of the error in the host DU 1002a may be configured to trigger the host DU 1002a to rebroadcast that it can function as a timing grandmaster, allowing it to be considered again to function as a grandmaster.

[0094] In another example, in the hybrid model 1008 or the hierarchical model 1010, the host DU 1002a may go offline and become unable to communicate over the fronthaul network. The SMO 1006 is aware of the offline status of the host DU 1002a through typical functions of the SMO 1006.

[0095] In yet another example, in the hybrid model 1008 or the hierarchical model 1010, the SMO 1006 may determine that a predetermined amount of time has passed since the host DU 1002a was selected as the grandmaster. The passage of the predetermined amount of time may be configured to automatically trigger a change in grandmaster. Using time as a trigger for changing the grandmaster may be useful in providing efficient load balancing by helping to prevent one DU from taking on a higher processing load than other DUs because DUs can take turns acting as grandmaster. The predetermined amount of time may be stored in the memory of the SMO 1006, and a counter or timer in the SMO 1006 may be used to know when the predetermined amount of time has passed. The predetermined amount of time may be, for example, 10 minutes, although other amounts of time are possible.

[0096] Whether the system is configured as a hybrid model 1008 or a hierarchical model 1010, the SMO 1006 triggers the RU 1004 to select a new master clock. In some implementations of the present subject matter, only a hierarchical model may be provided for the fronthaul network. In some implementations of the present subject matter, only a hybrid model may be provided for the fronthaul network. In some implementations of the present subject matter, a hierarchical model and a hybrid model may each be provided for the fronthaul network, and only one of the hierarchical and hybrid models may be active at a time, e.g., controlled by the SMO 1006.

[0097] In some implementations of the current subject matter, the selection of a new master clock 906 may be performed by the RU 1004 by executing a "Best Master Clock Algorithm" (BMCA) to select a new master clock from among tenant DUs 1002b, 1002c with known capabilities to act as grandmasters (e.g., DUs not currently acting as master clocks). The previously performed broadcasting 902 (and rebroadcasting, if performed by any of the DUs 1002a, 1002b, 1002c) has provided such knowledge to the RU 1004. Using the BMCA to select a new master clock leverages existing functionality. Since clock selection is performed by the RU 1004 by default using the PTP BMCA, the selection of a new master clock by the RU 1004 may be achieved beyond the "PTP1588 BMCA" mechanism.

[0098] In some implementations of the current subject matter, instead of performing BMCA, a grandmaster may be selected 906 based on a predetermined selection order of the DUs 1002a, 1002b, 1002c. The predetermined selection order may be based on the order in which the DUs 1002a, 1002b, 1002c connect to the fronthaul network, which may allow the predetermined selection order to be dynamically adjusted to reflect, for example, that new DUs connect to the fronthaul network and broadcast their grandmaster capabilities. Basing the grandmaster selection 906 on a predetermined selection order may facilitate load balancing because each DU 1002a, 1002b, 1002c is selected 906 to serve as grandmaster at times as far apart as possible.

[0099] 10 , in the hybrid model 1008, in response to learning that the current grandmaster DU, for example, the first DU 1002a, is experiencing an error, the SMO 1006 can send a request 1004 to the RU 1004 (1012) to inform the RU 1004 to select a new master clock (908). The request may be an RPC request in “o-ran-sync.yang.” Receipt of the RPC request 904 at the RU 1004 can trigger the RU 1004 to select a new master clock (e.g., execute a BMCA) to switch (1016) from the host DU 1002a as the grandmaster to the DU 1002b or 1002c as the newly selected grandmaster. The switching 1016 may include the RU 1004 synchronizing its clock with the new master clock (e.g., the second DU 1002b or the third DU 1002c). Receipt 904 of the RPC request at the RU 1004 may also trigger the RU 1004 to send 1014 a reply to the SMO 1006 acknowledging 906 receipt of the RPC request. The sent 1014 reply may also indicate that the RU 1004 successfully performed the switch 1016. In some implementations, the switching 1016 occurs after the reply is sent 1014; in this case, the reply does not include such an indication.

[0100] In some implementations of the hybrid model, in response to learning that the current grandmaster DU has experienced an error, the SMO 1006 can send a confirmation message to the host DU 1002a. In this manner, the host DU 1002a may be informed that it does not need to perform further operations related to functioning as a grandmaster if such execution has not yet terminated due to the occurrence of one or more errors.

[0101] As shown in FIG. 10 , in the hierarchical model 1010, in response to learning that the current grandmaster DU, for example, the first DU 1002a, has an error, the SMO 1006 can send a message to the host DU 1002a requesting the host DU 1002a to send a request 1004 to the RU informing the RU 1004 to select a new master clock (1022). The request is an RPC request in “o-ran-sync.yang.” Receipt 906 of the RPC request at the RU 1004 can trigger the RU 1004 to select a new master clock from one of the other DUs 1002b or 1002c (e.g., perform BMCA). Switching 1026 may include the RU 1004 synchronizing its clock with the new master clock (e.g., the second DU 1002b or the third DU 1002c). Receipt 906 of the RPC request at the RU 1004 may also trigger the RU 1004 to send (1024) a reply to the first DU 1002a that sent (1022) the RPC request to the DU 1004, acknowledging receipt of the RPC request (906). The sent (1024) reply may also indicate that the RU 1004 successfully performed the switch 1026. In some implementations, the switching 1026 occurs after the reply is sent (1024). In this case, the reply does not include such an indication.

[0102] The method 900 then continues iteratively, with another selection 906 of a grandmaster being made if the need 904 arises again.

[0103] Although only one RU 1004 is shown in the implementation of FIG. 10, there may be multiple RUs with the host DU 1002a acting as grandmaster, with each RU receiving an RPC request as described above to trigger switching and similarly switching to a new grandmaster.

[0104] In some implementations, the present subject matter may be configured to be implemented in a system 1100 as shown in FIG. 11 . The system 1100 may include one or more of a processor 1110, a memory 1120, a storage device 1130, and an input / output device 1140. Each of the components 1110, 1120, 1130, and 1140 may be interconnected using a system bus 1150. The processor 1110 may be configured to process instructions for execution within the system 1100. In some implementations, the processor 1110 may be a single-threaded processor. In alternative implementations, the processor 1110 may be a multi-threaded processor. The processor 1110 may be further configured to process instructions stored in the memory 1120 or the storage device 1130, including receiving or transmitting information through the input / output device 1140. The memory 1120 may store information within the system 1100. In some implementations, the memory 1120 may be a computer-readable medium. In alternative implementations, memory 1120 may be a volatile memory unit. Furthermore, in some implementations, memory 1120 may be a non-volatile memory unit. Storage device 1130 may provide mass storage for system 1100. In some implementations, storage device 1130 may be a computer-readable medium. In alternative implementations, storage device 1130 may be a floppy disk device, a hard disk device, an optical disk device, a tape device, a non-volatile solid-state memory, or any other type of storage device. Input / output device 1140 may be configured to provide input / output operations for system 1100. In some implementations, input / output device 1140 may include a keyboard and / or a pointing device. In alternative implementations, input / output device 1140 may include a display unit for displaying a graphical user interface.

[0105] 12 illustrates an exemplary method 1200 for clock selection in a fronthaul network in accordance with some implementations of the present subject matter. Method 1200 may be performed, for example, using the implementations shown and described with respect to FIGS.

[0106] The method 1200 is directed to a radio unit (e.g., RU 306 in FIG. 3 , RU 512 in FIG. 5 a , RU 606 in FIG. 6 , RUs 704 a, 704 b, and 704 c in FIG. 7 , RUs 804 a, 804 b, and 804 c in FIG. 8 ) configured to function as a master clock for a communication system including a plurality of DUs, RUs, and service management and orchestration units (e.g., SMO 604 in FIG. 6 , SMO 1006 in FIG. 10 , etc.). 3, DUs 508 and 510 in FIGS. 5a-5c, DUs 602a, 602b, and 602n in FIG. 6, DUs 702a, 702b, and 702c in FIG. 7, DUs 802a, 802b, and 802c in FIG. 8, and DUs 1002a, 1002b, and 1002c in FIG. 10, etc.) communicatively coupled to the RU. Method 1200 also includes transmitting a request to the RU, triggering the RU to select one of the DUs to be the master clock. The SMO is communicatively coupled to the RU and the multiple DUs.

[0107] In some implementations, the current subject may include one or more of the following optional features:

[0108] In some implementations, the SMO may trigger the selection and may also send a request to the RU.

[0109] In some implementations, the SMO may trigger a selection through one of the DUs to instruct the RU to perform the selection. Furthermore, one of the selected DUs may send a request to one or more RUs using the previous DU as the master clock.

[0110] In some implementations, the method may further include receiving a signal from each of the DUs that can function as a master clock among the plurality of DUs. The selection may be directed to only the plurality of DUs that can function as a master clock.

[0111] In some implementations, one of the DUs may function as a master clock at or just before the selection is performed. The method may further include excluding one of the DUs from being selected. Further, the exclusion may exclude one of the DUs from the selection and future selections, and / or a failure of one of the DUs may trigger the selection.

[0112] In some implementations, the request may be a remote procedure call (RPC) request.

[0113] In some implementations, the communication system may include an open radio access network (O-RAN) architecture.

[0114] The systems and methods disclosed herein may be embodied in various forms, including, for example, a data processor such as a computer including a database, digital electronic circuitry, firmware, software, or any combination thereof. Furthermore, the above-described features and other aspects and principles of the disclosed implementations may be implemented in various environments. Such environments and associated applications may be specially configured to perform the various processes and operations of the disclosed implementations, or they may include general-purpose computers or computing platforms selectively activated or reconfigured by code to provide the required functionality. The processes disclosed herein are not inherently related to any particular computer, network, architecture, environment, or other apparatus, but may be implemented by any suitable combination of hardware, software, and / or firmware. For example, various general-purpose devices may be used with programs written in accordance with the teachings of the disclosed implementations, or it may be more convenient to configure specialized devices or systems to perform the required methods and techniques.

[0115] The systems and methods disclosed herein may be implemented as a computer program product (i.e., a computer program tangibly embodied in an information carrier (e.g., a machine-readable storage device or a propagated signal) for execution by or to control the operation of a data processing apparatus (e.g., a programmable processor, computer, or multi-computer)). The computer program may be written in any form of programming language, including compiled or interpreted languages, and may be deployed in any form, including a stand-alone program or a module, component, subroutine, or other unit suitable for use in a computing environment. The computer program may be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communications network.

[0116] As used herein, the term "user" may refer to any entity, including a person or a computer.

[0117] Although ordinal numbers such as first, second, etc. may refer to an order in some circumstances, ordinal numbers used in this document do not necessarily imply an order. For example, ordinal numbers may be used simply to distinguish one item from another. For example, distinguishing a first event from a second event does not necessarily imply a chronological order or a fixed reference system (just as the first event in one paragraph of a description may be different from the first event in another paragraph of the description).

[0118] The above description is intended to be illustrative, but not limiting, of the scope of the invention, which is defined by the appended claims. Other implementations are within the scope of the following claims.

[0119] These computer programs, software, software applications, applications, components, or codes, which may also be referred to as programs, include machine instructions for a programmable processor and may be implemented in a high-level procedural and / or object-oriented programming language and / or assembly / machine language. As used herein, the term "machine-readable medium" refers to any computer program product, apparatus, and / or device (e.g., magnetic disks, optical disks, memory, and programmable logic devices (PLDs)) used to provide machine instructions and / or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal used to provide machine instructions and / or data to a programmable processor. A machine-readable medium may non-transitory store such machine instructions (e.g., non-transitory solid-state memory or a magnetic hard drive or any equivalent storage medium). Alternatively or additionally, a machine-readable medium may store such machine instructions in a transitory manner (e.g., processor cache or other random access memory associated with one or more physical processor cores).

[0120] To provide for user interaction, the subject matter described herein may be implemented on a computer having a display device, such as a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user, and a keyboard and pointing device, such as a mouse or trackball, through which the user can provide input to the computer. Other types of devices may also be used to provide for user interaction. For example, feedback provided to the user may be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback. Input from the user may be received in any form, including, but not limited to, acoustic, speech, or tactile input.

[0121] The subject matter described herein may be implemented in a computing system that includes back-end components such as one or more data servers, or middleware components such as one or more application servers, or front-end components such as one or more client computers having a graphical user interface or web browser through which a user can interact with an implementation of the subject matter described herein, or any combination of such back-end, middleware, or front-end components. The components of the system may be interconnected by any form or medium of digital data communication, such as a communications network. Examples of communications networks include, but are not limited to, a local area network ("LAN"), a wide area network ("WAN"), and the Internet.

[0122] A computing system may include clients and servers. Clients and servers are generally, but not limited to, remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

[0123] The implementations presented in the foregoing description do not represent all implementations consistent with the subject matter described herein. Rather, they are merely some examples consistent with aspects related to the described subject matter. While a few variations have been described in detail above, other modifications or additions are possible. In particular, additional features and / or variations may be provided in addition to those presented herein. For example, the implementations described above may be directed to various combinations and subcombinations of the disclosed features and / or combinations and subcombinations of some additional features disclosed above. In addition, the logic flow depicted in the accompanying figures and / or described herein does not necessarily require the particular order depicted or sequential order to achieve desirable results. Other implementations may also be within the scope of the following claims.

Claims

1. selecting one DU from among a plurality of distributed units (DUs), a radio unit (RU), and a service management and orchestration (SMO) to function as a master clock for a communication system including the DUs, the RUs, and the DUs being communicatively coupled to the RUs; Sending a request to the RU, triggering the RU to select one of the DUs to be the master clock; Equipped with The SMO is communicatively coupled to the RU and the plurality of DUs. A computer-implemented method.

2. The method of claim 1 , wherein the SMO triggers the selecting.

3. The method of claim 2 , wherein the SMO transmits the request to the RU.

4. The method of claim 1 , wherein the SMO triggers the selection through one of the DUs to instruct the RU to perform the selection.

5. The method of claim 4 , wherein one of the DUs sends the request to the RU.

6. Further comprising receiving a signal from each of the DUs that can function as a master clock among the plurality of DUs; The selecting is performed only on the plurality of DUs that can function as a master clock.

6. The method according to any one of claims 1 to 5.

7. One of the DUs functions as the master clock at or just before the selecting is performed; The method further comprises removing one of the DUs from being selected.

6. The method according to any one of claims 1 to 5.

8. The method of claim 7 , wherein the exclusion excludes one of the DUs from the selection and future selections.

9. The method of claim 7 , wherein a failure of one of the DUs triggers the selecting.

10. The method of claim 1 , wherein the request is a remote procedure call (RPC) request.

11. The method of claim 1 , wherein the communication system comprises an Open Radio Access Network (O-RAN) architecture.

12. selecting one DU from among a plurality of distributed units (DUs), a radio unit (RU), and a service management and orchestration (SMO) to function as a master clock for a communication system including the DUs, the RUs, and the DUs being communicatively coupled to the RUs; Sending a request to the RU, triggering the RU to select one of the DUs to be the master clock; performing an operation comprising: The SMO is communicatively coupled to the RU and the plurality of DUs. Device.

13. The apparatus of claim 12 , wherein the SMO triggers the selecting.

14. The apparatus of claim 13 , wherein the SMO transmits the request to the RU.

15. The apparatus of claim 12 , wherein the SMO triggers the selecting through one of the DUs to perform the transmitting.

16. The apparatus of claim 15 , wherein one of the DUs transmits the request to the RU.

17. The operation further comprises receiving a signal from each of the DUs that can function as a master clock among the plurality of DUs; The selecting is performed only on the plurality of DUs that can function as a master clock.

17. Apparatus according to any one of claims 12 to 16.

18. One of the DUs functions as the master clock at or just before the selecting is performed; The method further comprises removing one of the DUs from being selected.

17. Apparatus according to any one of claims 12 to 16.

19. The apparatus of claim 18 , wherein the exclusion excludes one of the DUs from the selection and future selections.

20. When executed, selecting one DU from among a plurality of distributed units (DUs), a radio unit (RU), and a service management and orchestration (SMO) to function as a master clock for a communication system including the DUs, the RUs, and the DUs being communicatively coupled to the RUs; Sending a request to the RU, triggering the RU to select one of the DUs to be the master clock; causing a computer to perform operations comprising: The SMO is communicatively coupled to the RU and the plurality of DUs. program.

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