Optimizing downlink split-bearer operation in o-ran networks

Abstract

A method to optimize downlink split-bearer operation in an Open Radio Access Network where User Equipment that supports split bearer operation is analyzed the search space is divided into multiple regions to avoid reordering Transport Control Protocol packets, where the regions can include transmit on 4G LTE only, transmit on 5G NR only, transmit on 5G NR first, transmit on 4G LTE first, and proportionately dividing data transmission from the UE between 4G LTE and 5G NR based on the divided search space.

Description

Optimizing Downlink Split-Bearer Operation in O-RAN NetworksBACKGROUND1. Field of the Disclosure

[0001] The present disclosure is related to Open Radio Access Network (O-RAN) wireless networks. More particularly, the present disclosure is related to optimization of downlink split bearer operation in O-RAN networks.2. Description of Related Art

[0002] An overview of Next Generation Radio Access Network (NG-RAN) and 5G New Radio (NR) stacks are provided. 5G NR user and control plane functions with monolithic gNodeB (gNB) are shown in FIGS, la, lb and 2. For the user plane (shown in FIG. la, which is in accordance with 3GPP TS 38.300), physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP) and Service Data Adaptation Protocol (SDAP) sublayers originate in the UE 101 and are terminated in the gNB 102 on the network side.

[0003] As shown in FIG. lb, which is a block diagram illustrating the user plane protocols stacks for a Protocol Data Unit (PDU) session, in accordance with 3GPP TS 23.501, PDU layer 9010 corresponds to the PDU carried between the UE 101 and the Data Network (DN) 9011 over the PDU session. As shown in FDN, UE 101 is connected to the 5G Access Network (AN) 902, which AN 902 is in turn connected via an N3 interface to the Intermediate User Plane Function (I-UPF) 903a portion of the UPF 903, which I-UPF 903a is in turn connected via an N9 interface to the PDU session anchor 903b portion of the UPF 903, and which PDU session anchor 903b isconnected to the DN 9011. Centralized Unit User Plane (CU-UP) of AN 902 is connected to UPF 903b via a Backhaul (BH) path. The PDU session can correspond to IPv4, IPv6, or both types of IP packets, when the PDU session is of type IPv4, IPv6 or IPv4v6, respectively. General Packet Radio Service (GPRS) Tunneling Protocol - User Plane (GTP-U) shown in FIG. lb supports tunnelling user plane data over N3 and N9 interfaces and provides encapsulation of end user PDUs for N3 and N9 interfaces.

[0004] For the control plane, shown in FIG. 2, which is in accordance with 3GPP TS 38.300, Radio Resource Control (RRC), PDCP, RLC, MAC and PHY sublayers originate in the UE 101 and are terminated in the gNB 102 on the network side, and Non-Access Stratum (NAS) originate in the UE 101 and is terminated in the Access Mobility Function (AMF) 103 on the network side.

[0005] NG-RAN architecture from 3GPP TS 38.401 is shown in FIGS. 3-4. As shown in FIG. 3, the NG-RAN 301 comprises a set of gNBs 302 connected to the 5GC 303 through the NG interface. Each gNB comprises gNB-CU 304 and one or more gNB-DU 305 (see FIG. 3). As shown in FIG. 4 (which illustrates separation of CU-Control Plane (CU-CP) and CU-UP), El is the interface between gNB-CU-CP 304a and gNB-CU-UP 304b, Fl-C is the interface between gNB-CU-CP 304a and gNB-DU 305, and Fl-U is the interface between gNB-CU-UP 304b and gNB-DU 305. As shown in FIG. 4, gNB 302 can consist of a gNB-CU-CP 304a, multiple gNB- CU-UPs (or gNB-CU-UP instances) 304b and multiple gNB-DUs (or gNB-DU instances) 305. One gNB-DU 305 is connected to one gNB-CU-CP 304a, and gNB-CU-UP 304b is connected to one gNB-CU-CP 304a.

[0006] In this section, an overview of Layer 2 (L2) of 5GNR is disclosed in connection withFIGS. 5-7. L2 of 5G NR is split into the following sublayers (in accordance with 3GPP TS 38.300).

[0007] 1) Medium Access Control (MAC) 501 in FIGS. 5-7. Logical Channels (LCs) are Service Access Points (SAPs) between the MAC and RLC layers. This layer runs a MAC scheduler to schedule radio resources across different LCs (and their associated radio bearers). For the downlink direction, the MAC layer processes and sends RLC PDUs received on LCs to the PHY layer as Transport Blocks (TBs). For the uplink direction, it receives TBs from the PHY layer, processes these and sends them to the RLC layer using the LCs.

[0008] 2) RLC 502 in FIGS. 5-7. The RLC sublayer presents RLC channels to the PDCP sublayer. The RLC sublayer supports three transmission modes: RLC-Transparent Mode (RLC- TM), RLC-Unacknowledged Mode (RLC-UM) and RLC-Acknowledgement Mode (RLC-AM). RLC configuration is per logical channel. It hosts Automatic Repeat Request (ARQ) protocol for RLC-AM mode.

[0009] 3) PDCP 503 in FIGS. 5-7. The PDCP sublayer presents Radio Bearers (RBs) to the SDAP sublayer. There are two types of Radio Bearers: Data Radio Bearers (DRBs) for data and Signaling Radio Bearers (SRBs) for control planes.

[0010] 4) SDAP 504 in FIGS. 5-7. The SDAP maps QoS flows within a PDU session to a specific DRB.

[0011] FIG. 5 is a block diagram illustrating DL L2 structure, in accordance with 3GPP TS 38.300.

[0012] Open Radio Access Network (0-RAN) is based on disaggregated components which areconnected through open and standardized interfaces based on 3GPP NG-RAN. An overview of O-RAN with disaggregated RAN CU, DU (Distributed Unit), and RU (Radio Unit), near-realtime Radio Intelligent Controller (RIC) and non-real-time RIC is illustrated in FIG. 6.

[0013] As shown in FIG. 6, the CU (shown split as O-CU-CP 801a and O-CU-UP 801b) and the DU (shown as O-DU 802) are connected using the Fl interface (with Fl-C for control plane and Fl-U for user plane traffic) over a mid-haul (MH) path. One DU can host multiple cells (e.g., one DU could host 24 cells) and each cell can support many users. For example, one cell can support 800 Radio Resource Control (RRC)-connected users and out of these 800, there may be 250 Active users (i.e., users that have data to send at a given point of time).

[0014] A cell site can comprise multiple sectors, and each sector can support multiple cells. For example, one site could comprise three sectors and each sector could support eight cells (with each cell being on a different frequency band in each sector). One CU-CP could support multiple DUs and thus multiple cells. For example, a CU-CP could support 500 cells and around 100,000 User Equipment (UE). Each UE could support multiple DRBs and there could be multiple instances of CU-UP to serve these DRBs. For example, each UE could support 4 DRBs, and 400,000 DRBs (corresponding to 100,000 UEs) can be served by five CU-UP instances (and one CU-CP instance).

[0015] The DU can be in a private data center, or it could be located on a cell-site. The CU could also be in a private data center or even hosted on a public cloud system. The DU and CU, which are typically located at different physical locations, could be tens of kilometers apart. The CU communicates with a 5G core system, which could also be hosted in the same public cloud system (or could be hosted by a different cloud provider). A RU (shown as 0-RU 803 in FIG. 6)is located at a cell site and communicates with the DU via a Fronthaul (FH) interface.

[0016] The E2 nodes (CU and DU) are connected to the near-real-time RIC 132 using the E2 interface. The E2 interface is used to send data (e.g., user and / or cell KPMs) from the RAN and deploy control actions and policies to the RAN at near-real-time RIC 132. The applications or services at the near-real-time RIC 132 that deploys the control actions and policies to the RAN are called xApps. During the E2 setup procedures, the E2 node advertises the metrics it can expose, and an xApp in the near-RT RIC can send a subscription message specifying key performance metrics which are of interest. The near-real-time RIC 132 is connected to the non- real-time RIC 133 (which is shown as part of Service Management and Orchestration (SMO) Framework 805 in FIG. 6) using the Al interface. The applications that are hosted at non-RT- RIC are called rApps. Also shown in FIG. 6 are O-eNB 806 (which is shown as being connected to the near-real-time RIC 132 and the SMO Framework 805) and O-Cloud 804 (which is shown as being connected to the SMO Framework 805).

[0017] In this section, PDU sessions, DRBs, and Quality of Service (QoS) flows are discussed. In 5G networks, PDU connectivity service is a service that provides exchange of PDUs between a UE and a DN identified by a Data Network Name (DNN). The PDU Connectivity service is supported via PDU sessions that are established upon request from the UE. The DNN defines the interface to a specific external data network. One or more QoS flows can be supported in a PDU session. All the packets belonging to a specific QoS flow have the same 5G QoS Identifier (5QI). A PDU session consists of the following: DRBs which are between UE and CU in RAN; and an NG-U GTP tunnel which is between CU and UPF in the core network. FIG. 7 illustrates an example PDU session (in accordance with 3GPP TS 23.501) comprising multiple DRBs, where each DRB can comprise multiple QoS flows. In FIG. 7, three components are shown for thePDU session 901 : UE 101, AN 902; and UPF 903, which includes Packet Detection Rules (PDRs) 9031.

[0018] The following should be noted for 3GPP 5G network architecture, which is illustrated in FIG. 8 (in the context of multiple PDU sessions involving multiple DRBs and QoS Flow Identifiers (QFIs), which PDU sessions are implemented involving UE 101, gNodeB 102, UPF 903, and DNNs 9011a and 9011b) and FIG. 9 (in the context of Radio Resource Management (RRM) for connecting UE 101 to the network via RU 306 with a MAC Scheduler 1001).

[0019] 1) The transport connection between the base station (i.e., CU-UP 304b of FIG. 9) and the UPF 903 uses a single GTP-U tunnel per PDU session, as shown in FIGS. 8 and 9. The PDU session is identified using GTP-U TEID (Tunnel Endpoint Identifier).

[0020] 2) The transport connection between the DU 305 and the CU-UP 304b of FIG. 9 uses a single GTP-U tunnel per DRB (see also FIG. 8 and FIG. 9). The DU is provided with an UL GTP-U TEID and the CU is provided with the corresponding DL GTP-U TEID to allow for data communication for that DRB between DU and CU-UP.

[0021] 3) SDAP: a) The SDAP 504 Layer receives downlink data from the UPF 903 across the NG- U interface (see FIG. 9). b) The SDAP 504 maps one or more QoS Flow(s) onto a specific DRB. c) The SDAP header is present between the UE 101 and the CU (when reflective QoS is enabled), and includes a field to identify the QoS flow within a specific PDU session.

[0022] 4] GTP-U protocol includes a field to identify the QoS flow and is present between CU and UPF 903 (in the core network).

[0023] 5) One (logical) DU (or RLC) queue exists per DRB (or per logical channel) for RLC PDUs that are to be transmitted for the first time, as shown in FIG. 9. Separate logical queues may exist in DU for packets that are to be retransmitted to UE.

[0024] In this section, standardized 5QI to QoS characteristics mapping will be discussed. As per 3GPP TS 23.501, the one-to-one mapping of standardized 5QI values to 5G QoS characteristics is specified in Table 1 shown below.

[0025] The first column represents the 5QI value. The second column lists the different resource types, i.e., as one of non-Guaranteed Bit Rate (Non-GBR), GBR, Delay-critical GBR. The third column (“Default Priority Level”) represents the priority level Priority5QI, for which lower thevalue the higher the priority of the corresponding QoS flow. The fourth column represents the Packet Delay Budget (PDB), which defines an upper bound for the time that a packet may be delayed between the UE and the N6 termination point at the UPF. The fifth column represents the Packet Error Rate (PER). The sixth column represents the maximum data burst volume for del ay -critical GBR types. The seventh column represents an averaging window for GBR, delay critical GBR types.

[0026] Only a subset of 5QI values defined in 3GPP TS 23.501 are shown in Table 1. For example, 5QI value 1 is of resource type GBR with the default priority value of 20, PDB of 100ms, PER of 0.01, and averaging window of 2000 mS. Conversational voice falls under this category. Similarly, as shown in Table 1, 5QI value 7 is of resource type Non-GBR with the default priority value of 70, PDB of 100ms and PER of 0.001. Voice, video (live streaming), and interactive gaming fall under this category.

[0027] A block diagram, for an example RRM with a MAC Scheduler is shown in FIG. 9. L2 methods (such as MAC scheduler) play a critical role in allocating radio resources to different UEs in a cellular network.

[0028] FIG. 10 shows CU-UP sending DL User Data (DUD) to DU. FIG. 11 shows flow control feedback from CU-UP to DU. This is indicated as DL Data Delivery Status (DDDS) in FIG. 11.

[0029] DU can send Assistance Information Data (AID) to CU-UP as shown in FIG. 12 and this provides radio information to CU-UP over the Fl-U interface.

[0030] UE-Aggregate Maximum Bit Rate (AMBR). It limits the aggregate bit rate that can be expected to be provided across all non-GBR QoS flows for a UE. Uplink and downlink UE-AMBR are specified separately for each UE. A UE could be a 5G NR Standalone UE, a 4G LTE Standalone UE, a Non-Standalone (NSA) UE or a UE supporting Multiple Radio Access Technologies (Multi-RAT) or some other cellular technology. UE-AMBR is applicable to each such UE, and it is defined separately for uplink and downlink direction. For uplink traffic for a UE, AMBR is denoted as UL UE-AMBR and for downlink traffic for that UE, it is denoted as DL UE-AMBR.

[0031] For 5G Standalone (5G SA) networks, Session Management Function (SMF) in the 5GC (i.e., 5G Core) retrieves DL and UL UE-AMBR from the Unified Data Management (UDM) and provides this to Access and Mobility Management Function (AMF) in 5GC. As shown in FIG. 13, the AMF communicates this UE-AMBR to CU-CP of gNB using Next Generation Application Protocol (NGAP) via N2 interface.

[0032] For 5G NR base station (i.e., for gNB), gNB CU-CP communicates DL UE-AMBR to CU-UP using the E1AP protocol as specified in 3GPP TS 37.483 (and as shown in FIG. 13). The Information Element to communicate DL UE-AMBR from CU-CP to CU-UP is denoted as id-UEDLAggregateMaximumBitRate in 3GPP TS 37.483.

[0033] For 5G NR base station (i.e., for gNB), gNB CU-CP communicates UL UL-AMBR to DU using the F1AP protocol as specified in 3GPP TS 38.473 (and as shown in FIG. 13). The Information Element to communicate UL UE-AMBR from CU-CP to DU is denoted as id-GNB- DU-UE-AMBR-UL in 3 GPP TS 38.473.

[0034] Similarly, for 4G Standalone networks, Mobility Management Entity (MME) from the 4G EPC communicates DL UE-AMBR and UL UE-AMBR to the 4G base station, i.e., evolved NodeB (eNodeB) across Sl-C interface. eNodeB CU-CP communicates DL UE-AMBR to CU-UP, and CU-CP communicates UL UE-AMBR to DU across the VI -C interface as shown in FIG. 14.

[0035] Session-AMBR is described in this section. For 5G NR network, Session-AMBR limits the aggregate bit rate that can be expected to be provided across all non-GBR QoS flows for a specific PDU session. It can be defined separately for uplink and downlink direction. For uplink (UL) traffic for a session, it is denoted as UL Session-AMBR and for downlink (DL) traffic for that session, it is denoted as DL Session-AMBR. UL Session-AMBR is enforced by the UE and the UPF for uplink traffic while downlink session AMBR is enforced by the UPF for downlink traffic. Session AMBR is signaled to the UPF, to the UE and to the base station (i.e., 5G gNB). UE is provided with UL Session-AMBR from the 5GC (specifically by AMF from the 5G Core Network).

[0036] Session-AMBR and UE-AMBR are not applicable for GBR QoS flows.

[0037] Evolved Universal Terrestrial Radio Access-New Radio Dual Connectivity (EN-DC) architecture is shown in FIG. 15 and FIG. 16. In this architecture, the UE has a single RRC state, based on Master Node (MN) RRC and a single CP connection towards the MME of 4G Evolved Packet Core (EPC) as shown in FIG. 15. LTE eNB is the MN (denoted as Master eNB or MeNB) and 5G gNodeB is the Secondary Node (SN), denoted as SgNB (or Secondary gNB), in this EN- DC architecture. NR RRC messages can be routed from SgNB to MeNB via the X2-C interface and to the UE via the LTE-Uu air-interface.

[0038] FIG. 16 shows the data (user) plane for this EN-DC architecture. MeNB is connected to Serving Gateway (S-GW) of 4G EPC via the Sl-U interface. Similarly, the SgNB is connected to the S-GW via the Sl-U interface. For SN terminated split bearer, 4G EPC communicates datawith SgNB via the Sl-U interface and for MN terminated split bearer, 4G EPC communicates data with MeNB via the Sl-U interface. X2-U is used for user plane traffic between MeNB and SgNB.

[0039] FIG. 17 shows Master Cell Group (MCG), Secondary Cell Group (SCG) and split bearers from a UE perspective (as in 3GPP TS 37.340). In the EN-DC architecture, MCG has a group of 4G LTE cells and SCG includes a group of 5G NR cells. As in FIG. 17, NR-PDCP is used for higher layers, and LTE Evolved Universal Terrestrial Radio Access (E-UTRA) RLC / MAC / PHY and NR RLC / MAC / PHY are used at lower layers for split bearer.

[0040] FIG. 18 (as in 3GPP TS 37.340) shows MCG, SCG and split bearers from base station perspective. For SN terminated split bearer, NR-PDCP is used for at higher layers, and LTE (E- UTRA) RLC / MAC / PHY and NR RLC / MAC / PHY are used at lower layers for split bearer.

[0041] As shown in FIG. 19, for EN-DC (or other dual connectivity) architecture, UE-AMBR is split into MeNB UE-AMBR and SgNB UE-AMBR that are enforced by MeNB and SgNB respectively.

[0042] As in FIG. 20, MME communicates DL UE-AMBR and UL UE-AMBR to MeNB. CU- CP across the Sl-C interface. The MeNB splits this into DL MeNB UE-AMBR, UL MeNB UE- AMBR, DL SgNB UE-AMBR and UL SgNB UE-AMBR.

[0043] Next, the MeNB.CU-CP communicates DL MeNB UE-AMBR to MeNB.CU-UP and UL MeNB UE-AMBR to MeNB. DU. Also, MeNB.CU-CP communicates DL SgNB UE-AMBR and UL SgNB UE-AMBR to SgNB.CU-CP across the X2-C interface. Next, the SgNB.CU-CP communicates DL SgNB UE-AMBR to SgNB CU-UP across the El interface and UL SgNBUE-AMBR to SgNB.DU across the Fl-C interface as shown in FIG. 20.

[0044] EN-DC architecture with DL split bearer operation is described in FIG. 21. In FIG. 21, DL data (i.e. IP packets or NR PDCP SDUs) is communicated from 4G EPC to SgNB-CU-UP across the Sl-U interface and the DL traffic splitting operation for split bearer is carried out at the SgNB-CU-UP after doing NR PDCP processing at the SgNB-CU-UP. Note that incoming downlink NR PDCP SDUs (or IP packets) at the SgNB-CU-UP are transformed to NR PDCP PDUs after NR PDCP processing at the SgNB-CU-UP.

[0045] In FIG. 21, VI is the interface between MeNB.DU and MeNB-CU. Sl-Control plane (Sl -C) interface exists between MeNB-CU and 4G EPC for SN terminated split bearers.

[0046] DDDS and AID messages are sent from SgNB.DU to SgNB-CU-UP across the Fl-U interface as shown in FIG. 21. Also, DDDS and AID messages are sent from MeNB.DU to SgNB-CU-UP via the X2-U interface.

[0047] Note that UE can start with a MCG bearer (i.e., along the UE - MeNB - 4G EPC) path and MeNB can decide to switch this bearer to SN terminated split bearer. Alternatively, MeNB can directly decide to establish a SN terminated split bearer for a UE.

[0048] As part of DL traffic splitting operation at the SgNB-CU-UP, some of these NR PDCP PDUs are communicated from SgNB-CU-UP to SgNB.DU (across the Fl-U interface as in FIG. 21) and eventually to the UE via the 5GNR-Uu air-interface. These also get processed via NR RLC and NR MAC at SN (i.e. at SgNB.DU) as shown in FIG. 18.

[0049] Some other NRPDCP PDUs are communicated from SgNB-CU-UP to MeNB.DU (across the X2-U interface as in FIG. 21) and eventually to the UE via the 4G LTE-Uu air-interface. Note that these NR PDCP PDUs are also processed via E-UTRA RLC and E-UTRA MAC at MN (i.e. at MeNB.DU) as shown in FIG. 18 for split bearers.

[0050] Some of the steps for secondary node (i.e., SgNB in the EN-DC architecture) addition and downlink traffic splitting procedure based on 3GPP TS 37.340 are shown in FIG. 22 and FIG. 23. As shown in FIG. 22, MCG bearer is already established for this UE and MeNB decides to convert this to SgNB terminated split bearer.

[0051] As part of step 1) in FIG. 22, MeNB, specifically MeNB.CU-CP of MeNB, sends ‘SgNB Addition Request’ to SgNB.CU-CP. It contains information about the bearer for which SN (i.e., SgNB) split bearer needs to be established. It also informs DL SgNB UE-AMBR and UL SgNB UE-AMBR to SgNB.CU-CP. In step 2), SgNB.CU-CP sends ‘Bearer Context Setup Request’ message to SgNB.CU-UP using the E1AP protocol. As part of step 3), SgNB.CU-UP sends ‘Bearer Context Setup Response’ message to SgNB.CU-CP. Along with other parameters, QoS information about bearer is shared with SgNB.CU-UP as part of steps 2) and 3).

[0052] In step 4), UE Context Setup Request message is sent from SgNB.CU-CP to SgNB. DU across the Fl-C interface using the F1AP protocol. In step 5), SgNB. DU responds with UE Context Setup Response message to SgNB.CU-CP. Along with other parameters, QoS information about the bearer is shared with SgNB. DU as part of steps 5) and 6) in FIG. 22.

[0053] In step 6), Bearer Context Setup Request is sent from SgNB.CU-CP to SgNB.CU-UP and in step 7), Bearer Context Setup Response message is sent from SgNB.CU-UP to SgNB.CU-CP as in FIG. 22. In step 8), SgNB.CU-CP sends SgNB Addition Request Acknowledge message to MeNB (and specifically to MeNB.CU-CP of MeNB).

[0054] GTP-U tunnel to carry traffic between SgNB.CU-UP and SgNB.DU for 5G leg of SgNB terminated split bearer is also established as part of the steps shown in FIG. 22.

[0055] FIG. 23 shows some additional steps with which GTP-U tunnel to carry traffic on 4G leg is completely established between SgNB.CU-UP and MeNB (or specifically between SgNB.CU- UP and MeNB. DU for disaggregated base station architecture). It also shows where UE carries out random access procedure with SgNB to directly start getting data via SgNB (for the 5G leg).

[0056] In step 9) of FIG. 23, MeNB, specifically MeNB.CU-CP of MeNB, sends RRC Connection Reconfiguration to EN-DC UE and in step 10), this UE responds with RRC Reconfiguration Complete message. In step 1 1), MeNB, specifically MeNB.CU-CP of MeNB, sends SgNB Reconfiguration Complete to SgNB.CU-CP. As part of step 12), UE carries out random access procedures with SgNB. In step 13), MeNB, specifically MeNB.CU-CP of MeNB, sends ‘SN Status Transfer’ to SgNB-CU-CP’ (if bearer is using RLC AM).

[0057] Data forwarding from MeNB (specifically from MeNB.CU-UP of MeNB) to SgNB.CU- UP happens as part of steps 14) and 15) in FIG. 23. Next, SgNB.CU-UP also starts splitting traffic across 5G and 4G legs of the network. DL data towards 4G leg is sent as part of steps 16) and 17). DL data towards 5G leg is sent as part of steps 18) and 19). As part of step 20), MeNB interacts with 4G EPC to carry out path switch to make it SN terminated split bearer. 4G EPC starts sending DL data towards SgNB.CU-UP as part of step 21) after the path switch operation. SgNB.CU-UP continues to split traffic across 4G and 5G legs of the network.

[0058] The Inter-DU interface can be used for DU-to-DU communication. The protocol used for inter-DU communication is called D2-AP (D2-Application Layer). This is used for control plane information exchange between MeNB.DU and SgNB.DU in the EN-DC architecture.

[0059] A challenge occurs, however, when for DL Split bearer in Non-Standalone (NSA) architecture across 4G and 5G legs of the network, TCP packets must be reordered. For example, for each leg and each region of each leg, not knowing how to utilize each region most effectively limits achievable data rates.

[0060] Likewise, for Carrier Aggregation (CA) with LTE and / or CA with 5GNR, it is problematic if achievable data rates are not known.

[0061] Still further, it is problematic when frequency band-specific information is not communicated between CU-CP and CU-UP to facilitate operation within the different regions.

[0062] Accordingly, there is a need for method that overcomes, alleviates, and / or mitigates one or more of the aforementioned and other deleterious effects of prior art to optimize DL Split bearer operation.SUMMARY

[0063] What is provided is a method to optimize DL split-bearer operation in an 0-RAN where operating regions are divided into multiple regions to avoid reordering of TCP packets and improve throughput.

[0064] Also provided is a method to optimize DL split-bearer operation in an O-RAN where for CA (Carrier Aggregation) with LTE and / or CA with 5G NR, achievable data rates for each UE supporting split bearer are computed.

[0065] Further provided is a method to optimize DL split-bearer operation in an O-RAN where for the case when Dynamic Spectrum Sharing (DSS) is used on one or more component carriers.

[0066] Still further provided is a method to optimize DL split-bearer operation in an O-RAN where data transmissions between CU-CP and CU-UP are enhanced to communicate frequency band specific information to facilitate the use of the different regions effectively.

[0067] In one configuration, for DL Split bearer in NSA architecture, a solution is proposed where operating regions are divided into multiple regions, such as, transmit on LTE only, transmit on 5GNR only, transmit on 5G NR first, transmit on LTE first, proportionately divided between LTE and NR, and so on. This will help in being able to avoid reordering TCP packets and improve system throughput.

[0068] Additionally, for CA with LTE and / or CA with 5G NR, it is contemplated that achievable data rates for each UE supporting split bearer are computed. This is mapped to the RQI field in AID, which is communicated from the 4G DU to the common CU-UP, and from the 5G DU to the common CU-UP. The AID message given in 3GPP TS 38.425 is enhanced for this purpose.

[0069] Further, the above-described method can be enhanced when Dynamic Spectrum Sharing (DSS) is used on one or more component carriers.

[0070] Furthermore, the E1AP running between CU-CP and CU-UP is enhanced to communicate frequency band specific information, which functions to facilitate this method with different regions as described above.

[0071] For this application the following terms and definitions shall apply:

[0072] The term “data” as used herein means any indicia, signals, marks, symbols, domains, symbol sets, representations, and any other physical form or forms representing information, whether permanent or temporary, whether visible, audible, acoustic, electric, magnetic,electromagnetic or otherwise manifested. The term “data” as used to represent predetermined information in one physical form shall be deemed to encompass any and all representations of the same predetermined information in a different physical form or forms.

[0073] The term “network” as used herein includes both networks and internetworks of all kinds, including the Internet, and is not limited to any particular type of network or inter-network.

[0074] The terms “first” and “second” are used to distinguish one element, set, data, object or thing from another, and are not used to designate relative position or arrangement in time.

[0075] The terms “coupled”, “coupled to”, “coupled with”, “connected”, “connected to”, and “connected with” as used herein each mean a relationship between or among two or more devices, apparatus, files, programs, applications, media, components, networks, systems, subsystems, and / or means, constituting any one or more of (a) a connection, whether direct or through one or more other devices, apparatus, files, programs, applications, media, components, networks, systems, subsystems, or means, (b) a communications relationship, whether direct or through one or more other devices, apparatus, files, programs, applications, media, components, networks, systems, subsystems, or means, and / or (c) a functional relationship in which the operation of any one or more devices, apparatus, files, programs, applications, media, components, networks, systems, subsystems, or means depends, in whole or in part, on the operation of any one or more others thereof.

[0076] As used herein, the phrases "at least one", "one or more", "or" and "and / or" are open- ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions "at least one of A, B and C" ,"at least one of A, B, or C", "one or more of A, B, and C", "one or more of A, B, or C", "A, B, and / or C" and "A, B, or C" means A alone, B alone,C alone, A and B together, A and C together, B and C together, or A, B and C together.

[0077] Reference is made to Third Generation Partnership Project (3GPP), 0-RAN Alliance and the Internet Engineering Task Force (IETF) and related standards bodies in accordance with embodiments of the present disclosure. The present disclosure employs abbreviations, terms and technology defined in accord with Third Generation Partnership Project (3GPP), 0-RAN Alliance and / or Internet Engineering Task Force (IETF) technology standards and papers, including the following standards and definitions. 3GPP, 0-RAN and IETF technical specifications (TS), standards (including proposed standards), technical reports (TR), RFCs and other papers are incorporated by reference in their entirety hereby, define the related terms and architecture reference models that follow.

[0078] In one configuration, a method to optimize downlink (DL) split-bearer operation using 4G Long Term Evolution (4G LTE) and 5G New Radio (5G NR) for a User Equipment (UE) in an Open Radio Access Network (0-RAN) is provided comprising the steps of providing a Centralized Unit (CU) having a CU-Control Plane (CP) and CU-User Plane (UP), providing a 4G Distributed Unit (4G DU) coupled to the CU-UP, and providing a 5G Distributed Unit (5G DU) coupled to the CU-UP. The method is provided so that the UE supports split bearer operation coupled to both the 4G DU and the 5G DU. The method further comprises the step of dividing operating regions into multiple regions such that reordering Transport Control Protocol (TCP) packets is avoided, the multiple regions selected from the group consisting of transmit on 4G LTE only, transmit on 5G NR only, transmit on 5G NR first, transmit on 4G LTE first, and combinations thereof. Finally, the method comprises the step of dividing DL data transmission to the UE between 4G LTE and 5G NR according to the divided multiple regions.

[0079] The above-described and other features and advantages of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.DESCRIPTION OF THE DRAWINGS

[0080] FIG. la is a block diagram illustrating 5G NR User and Control plane functions with monolithic gNB according to the prior art.

[0081] FIG. lb is a block diagram illustrating the user plane protocols stacks for a PDU session according to FIG. la.

[0082] FIG. 2 is a block diagram illustrating the control plane according to FIG. la.

[0083] FIG. 3 is a block diagram illustrating a set of gNBs connected to the 5GC through the NG interface according to the prior art.

[0084] FIG. 4 is a block diagram illustrating the gNB according to FIG. 3.

[0085] FIG. 5 is a functional block diagram illustrating DL Layer 2 structure of 5G NR according to the prior art.

[0086] FIG. 6 is a block diagram of 0-RAN with disaggregated components according to the prior art.

[0087] FIG. 7 is a functional block diagram illustrating an example PDU session comprising multiple DRBs, where each DRB comprises multiple QoS flows according to the prior art.

[0088] FIG. 8 is a flow diagram illustrating 3GPP 5G network architecture according to FIG. 7according to the prior art.

[0089] FIG. 9 is a flow diagram illustrating Radio Resource Management for connecting UE to the network via RU with a MAC Scheduler according to FIGS. 2, 3, 5 and 7.

[0090] FIG. 10 is a functional block diagram illustrating sending DL User Data to the DU according to FIG. 6.

[0091] FIG. 11 is a functional block diagram illustrating flow control feedback from the CU-UP to the DU according to FIG. 6.

[0092] FIG. 12 is a functional block diagram illustrating sending Assistance Information Data from the DU to the CU-UP according to FIG. 6.

[0093] FIG. 13 is a functional block diagram illustrating DL and UL UE-AMBR retrieval provided to the 5GC according to FIG. 6.

[0094] FIG. 14 is a functional block diagram illustrating a Mobility Management Entity providing DL UE-AMBR and UL UE-AMBR to a 4G base station according to FIG. 6.

[0095] FIG. 15 is a functional block diagram illustrating the UE having a single RRC state, based on Master Node RRC and a single Control plane connection towards the Mobility Management Entity of 4G according to FIG. 14.

[0096] FIG. 16 is a functional block diagram illustrating the data user plane where the Master Node and the Secondary Node are connected to the Serving Gateway of 4G according to FIG. 14.

[0097] FIG. 17 is a functional block diagram illustrating the dual connectivity architecture fromthe UE perspective according to FIGS. 13 and 14.

[0098] FIG. 18 is a functional block diagram illustrating dual connectivity architecture from the base station perspective according to FIGS. 13 and 14.

[0099] FIG. 19 is a functional block diagram illustrating dual connectivity architecture where MeNB and SgNB UE-AMBR are enforced by MeNB and SgNB, respectively, according to FIG.18.

[0100] FIG. 20 is a functional block diagram illustrating the splitting of MeNB and SgNB UE-AMBR into DL and UL and the respective transmissions of the data according to FIG.19.

[0101] FIG. 21 is a functional block diagram illustrating Dual Connectivity architecture with downlink split bearer operation according to FIG. 19.

[0102] FIGS. 22 and 23 are flow diagrams illustrating steps for secondary node addition and DL traffic splitting according to FIG. 19.

[0103] FIG. 24 is a diagram illustrating Downlink Data Delivery Status Protocol Data Unit format (DDDS PDU) parameters at the data radio bearer level of a UE according to FIG.21.

[0104] FIG. 25 is a diagram illustrating Assistance Information Data Protocol Data Unit format (AID PDU) parameters at the data radio bearer level of a UE according to FIG. 21.

[0105] FIG. 26 is a diagram illustrating a data distribution policy selection process based on CQImin, offset and (rank, CQI) multiplication factor on LTE and NR leg according to oneconfiguration of the invention.

[0106] FIG. 27 shows subfields of the AID PDU in FIG. 25 illustrating information used to determine a DL rate the UE supports over the LTE and NR legs according to FIG. 26.

[0107] FIG. 28 illustrates how to encode the Radio Quality Index in two consecutive octets to reduce overhead according to FIG. 26.

[0108] FIG. 29 is a table illustrating a NR lookup table according to FIG. 26.

[0109] FIG. 30 is a table illustrating an LTE lookup table according to FIG. 26.

[0110] FIG. 31 shows subfields of the AID PDU in FIG. 25 illustrating carrier aggregation on LTE and NR legs sending two types of Assistance Information from the master and secondary node DUs to the secondary CU-UP according to FIG. 26.

[0111] FIG. 32 shows subfields of the AID PDU in FIG. 25 illustrating overhead on encoding CQI, and RQI in multiple octets according to FIG. 26.

[0112] FIG. 33 shows subfields of the AID PDU in FIG. 25 illustrating overhead on encoding RQI only according to FIG. 26.

[0113] FIG. 34 shows subfields of the AID PDU in FIG. 25 illustrating no extra overhead on either CQI or RQI for the 2nd octet according to FIG. 26 compared to FIGS. 33 and 34.DETAILED DESCRIPTION

[0114] Method I: Data Distribution Policy at SgNB.CU-UP to decide the data split across NR and LTE legs. As an example, for a given UE there are ‘n’ component carriersconfigured with channel bandwidths Bl, B2, Bnon SgNB.CU and ‘m’ component carriers configured with channel bandwidths Cl, C2, .. ., Cmon eNB.CU. Suppose n’<=n of the CCs is active with CBWs subset of {Bl, B2, .. ., Bn} at SgNB.DU, and m’<=m of the CCs is active with CBWs subset of {Cl, C2, ..., Cm} at MeNB.DU.

[0115] The achievable rate at MeNB.DU for each component carrier can be calculated using number of downlink subframes in a second for the component carrier, and an average Transport Block (TB) size, which can be computed as a function of Channel quality index (CQI) reported by UE which is mapped to a Modulation Coding Scheme (MCS), Rank, average number of physical resource blocks (PRBs) (which is the ratio of number of PRBs in each BW to the number of active UEs) and number of REs (after excluding control information) in the PRB, and. Then it is added across the active CCs to obtain the overall achievable rate at MeNB.DU for the UE.

[0116] Similarly, the achievable rate at SgNB.DU for each component carrier can be calculated using number of downlink subframes in a second for the component carrier, and an average Transport Block(TB) size, which can be computed as a function of CQI, which is mapped to a Modulation Coding Scheme (MCS), Rank, average number of physical resource blocks (PRBs) (which is the ratio of number of PRBs in each BW to the number of active UEs) and number of REs (after excluding control information) in the PRB, and. Then, it is added across the active CCs to obtain the overall achievable rate at SgNB.DU for the UE.

[0117] Both SgNB.DU and MeNB.DU send CQI, Rank and a CQI multiplication factor to SgNB.DU in the Assistance Information Data Protocol Data Unit format (AID PDU). CQI, Rank and CQI multiplication factor are encoded to ‘Average CQI’ field of AID PDU, which is ofsize one octet. In this octet first 4 bits are used to encode the CQI range from 0 to 15. Rank is encoded to next 3 bits. For example, rank=8 is supported on LTE and NR then it will be encoded using 3 bits and remaining one bit will be set used by CQI multiplication factor. At the SgNB DU, CQI Rank, CQI multiplication factor for each DU is decoded from the received AID PDUs from the respective DUs. It is to be noted multiplying CQI with Rank on LTE and NR leg hereafter referred to as avgCqiLTE and avgCqiNR respectively, the range of values it takes is from 0 to 120. At SgNB. DU, data distribution policy is selected based on CQImin, offset and CQI of NR and LTE leg, Rank of LTE leg on LTE and NR legs as shown in FIG. 26. Note avgCqiLTE for LTE leg and avgCqiNR for NR leg is shown in FIG. 26 as CQI*Rank.

[0118] In this case, we assume a single radio bearer configured for a UE but it will be applicable even if multiple radio bearers are configured for a UE. For downlink split bearer in NSA architecture, as shown in FIG. 21, DL user data will be split across NR and LTE legs. A Data Distribution Policy is defined at SgNB.CU-UP. The Data Distribution Policy refers to how a given amount of data should be distributed between the two legs. The pair (avgCqiLTE, avgCqiNR) determines the policy, and the policies considered here are proportional, IteOnly, nrOnly, IteFirst, nrFirst as shown in FIG. 26. Here, avgCqiLTE is the average CQI over the LTE leg and avgCqiNR is the average CQI over the NR leg for the UE being considered.

[0119] Data Distribution Policy maps the pair (avgCqiLTE, avgCqiNR) and the configuration parameter pair (cqimin, cqiOffset) to one of the policies in the set {proportional, IteOnly, nrOnly, IteFirst, nrFirst} as shown in FIG. 26. UE level CQI and rank on LTE and NR legs are used to compute the range of values on each axis as shown in FIG. 26. Along with it, (cqimin, cqiOffset) parameters on each axis are used to decide one of the data distribution policies among the set of policies proportional, IteOnly, nrOnly, IteFirst, nrFirst. DataDistribution Policy remains fixed until the next trigger for change of policy is available. The Triggers to execute Data Distribution functionality is based on at least one of the following PDUs received: Reception of DDDS PDU over the X2-U interface, Reception of DDDS PDU over the Fl-U interface, Reception of AID PDU over the Fl -U interface, Reception of AID PDU over the X2-U interface. Note that MeNB.DU need not send DDDS and AID PDUs together in a single GTP-U PDU. Same is applicable for SgNB.DU too.

[0120] The data distribution policy picks IteOnly if the average CQI on LTE leg is more than the minimum CQI, CQImm, and the average CQI on NR leg is less than or equal to the minimum CQI (CQImm), i.e., (avgCqiLTE> CQImm) AND (avgCqixR<= CQImm). Here, CQImiOs a configured parameter.

[0121] The data distribution policy picks nrOnly if the average CQI on LTE leg is less than or equal to the CQImm and the average CQI on NR leg is more than the CQImm, i.e., (avgCqiLTE<= CQImm) AND (avgCqiNR> CQImm).

[0122] The data distribution policy picks IteFirst if the average CQI on LTE leg is more than the sum of average CQI on NR leg and a CQI offset denoted as cqiOffset, and if the average CQI on NR leg is more than CQImm, i.e., (avgCqiiTE> avgCqixR + cqiOffset) AND (avgCqiNR > CQImm).

[0123] The data distribution policy picks nrFirst if the average CQI on LTE leg is more than CQImin and the average CQI on NR leg more than the sum of average CQI on LTE leg and CQI offset (cqiOffset), i.e., (avgCqiLTE ' CQImm) AND (avgCqi :R avgCqiLTE + cqiOffset).

[0124] The data distribution policy picks proportional policy in the remaining regions.The pseudo method is given as follows:If(avgCqiLTE<= CQImin) AND (avgCqiNR<= CQImin) { Policy <— proportional;Else If (avgCqiLTE<= CQImin) AND (avgCqiNR> CQImin) { Policy «— nrOnly;Else If(avgCqiLTE> CQImin) AND (avgCqiNR<= CQImin) { Policy «— IteOnly;}Else If(avgCqiLTE> avgCqiNR + cqiOffset && avgCqiNR > CQImn) { Policy <— IteFirst;Else If(avgCqiNR> avgCqiLTs+ cqiOffset && avgCqiuTE > CQImin) { Policy <— nrFirst;

[0125] In another embodiment, different parameters at UE level (for example CQI, rank, Latency, etc.) and Cell level (for example Cell load, and the like) can be used to define a set of policies and to decide one policy from the set of policies.

[0126] DDDS PDU format is added in FIG. 24 and AID PDU format is added in FIG. 25.

[0127] As shown in FIG. 21, SgNB.DU sends the UE radio bearer level parameters and cell level parameters encapsulated in one of Downlink Data Delivery Status (DDDS) PDU, and Assistance Information Data (AID) PDU and it is sent over Fl-U, interface to SgNB.CU-UP. Fl- U, interface is enhanced for this purpose. Similarly, MeNB.DU sends the UE radio bearer level parameters and cell level parameters encapsulated in DDDS and AID PDUs to SgNB.CU-UP. X2-U interface is enhanced for this purpose.

[0128] From MeNB.DU, Desired buffer size in bytes and Desired data rate as part of DDDS PDU, DL Radio Quality Index and Average CQI as part of AID PDU are sent to SgNB.CU-UP over X2-U interface. From SgNB.DU, Desired buffer size in bytes and Desired data rate as part of DDDS PDU, DL Radio Quality Index and Average CQI as part of AID PDU sent to SgNB.CU-UP over the Fl-U interface.

[0129] For a given radio bearer of a UE, once the data distribution policy is selected, the data is scheduled according to the policy based on desired buffer size, achievable rate and the number of PDCP SDU packets. For a given Data Distribution Policy (one from the above policies: proportional, IteOnly, nrOnly, IteFirst, nrFirst), Data Scheduling at SgNB.CU-UP refers to determination of the pair (XLTE, XNR), where % / . / / ; and XNR are the number of bytes to be scheduled for transmission on the LTE and NR transmission legs respectively. The policy will continue till a new DDDS PDU or / and AID PDU is received on NR or LTE leg for that bearer of that UE.

[0130] Solution: Method II: Encoding and decoding of achievable rate using only DL Radio Quality Index field (RQI) in AID PDU. Once the overall achievable rate for a given UE is calculated at MeNB.DU. MeNB.DU encodes the UE achievable rate on ‘DL Radio Quality Index field’ in the Assistance Information Data (AID) PDU defined in 3GPP 38.425 and sends over X2-U interface. X2-U interface is enhanced for this purpose. Based on the range of achievable rates possible for a given UE, multiple octets can be used in ‘DL Radio Quality Index’ PDU field. SgNB.CU-UP decodes this to know the rate the UE supports over the LTE leg.

[0131] Similarly, SgNB.DU encodes the UE achievable rate on ‘DL Radio Quality Indexfield’ in the Assistance Information Data (AID) PDU defined in 3GPP 38.425 and sends over Fl - U interface. Fl-U interface enhanced for this purpose. Based on the range of achievable data rates possible for a given UE, multiple Assistance Information Fields with Assistance Information Type equals to "DL Radio Quality Index” can be used in the AID PDU. SgNB.CU- UP decodes this to know the rate the UE supports over the NR leg.

[0132] For example, in FIG. 27 two Assistance Information Fields, with Assistance Information Type equals to "DL Radio Quality Index”, Number of octets for DL Radio Index- 1 are repeated for both the octets, which introduces an additional overhead. The RQI value ranges from 0 to 65535 using two octets. If it is used for rate maximum possible rate is 64Kbps.

[0133] In another way of encoding as shown in FIG. 28, encode the RQI in two consecutive octets to reduce the overhead. Here the number of octets for Radio Quality Index is two to represent two consecutive octets are used to encode the RQI. The RQI value ranges from 0 to 65535 using two octets. If it is used for rate, maximum possible rate will be 64Kbps.

[0134] Once the UE supported rates across the LTE and NR legs are known to the SgNB.CU-UP, based on the DL data (DL PDCP PDUs) for the radio bearer of the UE the data is scheduled using the data distribution policy shown in FIG. 26.

[0135] Solution: Method III Encoding and decoding of rate using RQI and CQI fields in AID PDU (Lookup table-based method); Method IIIA: No Carrier Aggregation on LTE and NR. In this method, we consider one component carrier (CC) on LTE and one CC on NR side, i.e., no carrier aggregation on LTE and NR leg. AID PDU will be sent from MeNB.DU to SgNB.CU-UP over X2-U interface and SgNB.DU to SgNB.CU-UP over Fl-U interface. In the AID PDU one octet is used to encode ‘DL Radio Quality Index (RQI)’ at MeNB.DU andSgNB.DU. It will take a value in 0 to 255. In the AID PDU one octet is used to encode ‘Average CQI (CQI)’ at MeNB.DU and SgNB.DU. In this octet, the first 4 bits are used to encode the CQI range from 0 to 15, based on the rank supported on LTE and NR. The remaining bits can be used to encode the rank. For suppose both supports up to rank 8 then the next 3 bits are used to encode the rank from 1 to 8. The remaining bit is set to 0 always. The AID PDU contains Number of Assistance Information Fields as two, with two Assistance Information types as CQI and RQI each with one octet as shown in FIG. 28.

[0136] This NR and LTE data rate tables are computed in the following manner and NR table is maintained at SgNB.DU and SgNB.CU-UP. LTE table is maintained at MeNB.DU and SgNB.CU-UP.

[0137] NR lookup Table shown in Fig. 29 is computed as a function of CQI and RQI. Refer to row with RQI = 255 in the table given in Fig. 29. Each entry in this row corresponds to the CQIrate (where CQIrate is the maximum data rate achievable for that CQI) for RQI = 255 and the corresponding CQI (which can be seen from the corresponding column in the table in Fig. 29). For example, CQIrate is 2230.1 Mbps for RQI=255 and CQI=14. Here, CQIrate for a given channel bandwidth (CBW) and subcarrier spacing (SCS) is computed using the maximum TB (transport block) size for that CQI (and its corresponding MCS). For example, for CBW = 100 MHz, 30 KHz SCS, DL FDD with maximum number of PRBs equal to 273, Rank 4, CQI=15 translates to CQIrate of 2359.7 Mbps (with RQI=255) in Fig. 29. Values in other rows of the table given in Fig. 29 (i.e. for RQI 0 to 254) are computed as CQIrate * - . Here,RQImaxRQlmax= 255 and overheads assumed are: PDCCH 1 symbol and DMRS 12 REs The NR lookup table is calculated in similar manner for any given deployment. The same NR look uptable is maintained at SgNB.DU and SgNB.CU-UP.

[0138] The achievable data rate ‘X’ at SgNB.DU for a given UE is calculated using average TB size and number of DL subframes (or slots) in a second. Here average TB size can be computed as a function of CQI and corresponding MCS, Rank, average number of PRBs and number of REs (after excluding control information). Achievable data rate X is conveyed to CU- UP using a CQI value and an RQI value. Given that the CQI value is already known, DU findsthe closest value of RQI from the lookup table (given in Fig. 29) such that \ CQ Irate * — — -V RQImax) ROI is a minimum non negative value. We define, X' = CQIrate * - . RQI value isRQ^max encoded into DL Radio Quality Index (RQI) field of AID PDU (one octet) and this information is sent (along with CQI value in another octet ‘Average CQI (CQI)’) from SgNB.DU to SgNB.CU-UP by enhancing the Fl-U interface. At SgNB.CU-UP, the received information (i.e. the CQI and RQI octets) is decoded and then the same NR lookup table is used to obtain the data rate, X’.

[0139] Similarly, LTE lookup Table shown in Fig. 30 is computed as function of CQIrate and RQI. Refer to row with RQI = 255 in the table given in Fig. 29. Each entry in this row corresponds to the CQIrate (where CQIrate is the maximum data rate achievable for that CQI) for RQI = 255 and the corresponding CQI (which can be seen from the corresponding column in the table in Fig. 30). For example, CQIrate is 252.0 Mbps for RQI=255 and CQI=10. Here, CQIrate for a given channel bandwidth (CBW), is computed using the maximum TB (transport block) size for that CQI (and its corresponding MCS). For example, CBW-20MHz, FDD-DL with max number of PRBs =100, Rank 4, CQI 15 and corresponding MCS 27 translates to CQIrate of 413 Mbps with RQI=255. Values in other rows of the table given in Fig. 30 (i.e. forRQI 0 to 254) are computed as Here, and overheadsassumed are: PDCCH 1 symbol and DMRS 12 REs. The LTE lookup table is calculated in similar manner for any given deployment. The same LTE look up table is maintained at MeNB.DU and SgNB.CU-UP.

[0140] The achievable data rate ‘Y’ at MeNB.DU for a given UE is calculated using average TB size and number of DL subframes in a second. Here average TB size can be computed as a function of CQI and corresponding MCS, Rank, average number of PRBs and number of REs (after excluding control information). Achievable data rate Y is conveyed to CU- UP using a CQI value and an RQI value. Given that CQI is already computed as mentioned earlier, DU finds the closest value of RQI from the lookup table (given in Fig. 30) such that is a minimum non — negative value. We define, Y' = CQIrate *RQI. RQI value is encoded into DL Radio Quality Index (RQI) field of AID PDU (one octet) RQImax and this information is sent (along with CQI value in another octet ‘Average CQI (CQI)’) from MeNB.DU to SgNB.CU-UP by enhancing the X2-U interface. At SgNB.CU-UP, the received information (i.e. the CQI and RQI octets) is decoded and then the same LTE lookup table is used to obtain the data rate, Y’ .

[0141] Once the UE supported achievable data rates across the LTE and NR legs are known to the SgNB.CU-UP, the data is proportionally divided across the NR and LTE legs based on the DL data (DL PDCP PDUs) of the radio bearer of the UE.

[0142] Method III B: Carrier Aggregation (CA) on LTE and NR. Consider carrier aggregation on LTE and NR leg. AID PDU will be sent from MeNB.DU to SgNB.CU-UP overX2-U interface and SgNB.DU to SgNB.CU-UP over Fl -U interface. In the AID PDU, one octet is used to encode ‘DL Radio Quality Index (RQI)’ at MeNB.DU and SgNB.DU. It will take a value in the range 0 to 255. In the AID PDU, based on number of active CCs (component carriers), one octet is used to encode ‘Average CQI (CQI)’ at MeNB.DU. Similarly, one octet is used to encode Average CQI at the SgNB.DU. In this octet, the first 4 bits are used to encode the CQI range from 0 to 15. The remaining bits can be used to encode rank. Both supports up to rank 8 then the next 3 bits are used to encode the rank from 1 to 8. The remaining bit is set to 0 always. Here we are sending two types of Assistance Information from MeNB.DU (and SgNB.DU) to SgNB.CU-UP as shown in FIG. 31.

[0143] In one embodiment, MeNB.DU and SgNB.DU each have multiple component carriers (CCs) connected to it. MeNB.DU and SgNB.DU maintain separate lookup tables for each CC. SgNB.CU-UP also maintains look up tables for CCs belonging to both DUs. AID PDUs are sent separately for each of the CCs to CU-UP. Suppose there are 2 active CCs at MeNB.DU and 4 active CCs at SgNB.DU, then maintain two separate lookup tables, one for each CC at MeNB.DU and SgNB.CU-UP (like FIG. 30). Similarly, 4 lookup tables, one for each CC at SgNB.DU and SgNB.CU-UP (like FIG. 29). For each UE connected to 6 CCs, 2 AID PDUs are sent by MeNB.DU and 4 AID PDUs are sent by SgNB.DU to the SgNB.CU-UP.Note that there will be total 6 lookup tables that will be present at SgNB.CU-UP, 2 corresponding to LTE CCs and 4 corresponding to NR CCs. The lookup table calculation procedure, encoding at MeNB.DU / SgNB.DU and decoding at SgNB.CU-UP stays the same as Method IIA. SgNB.CU-UP compute the aggregate achievable data rate for MeNB.DU, SgNB.DU by summing up achievable data rate for their respective CCs.

[0144] In another embodiment, for LTE and NR overall achievable data rates arecomputed by summing across all the active CCs of MeNB.DU and SgNB.DU respectively. At MeNB.DU (and at SgNB.DU), the CQI is averaged across CCs and encoded using the first four bits of Average CQI field in the AID PDU, then the next 3 bits are used to encode the rank, the last bit is used for the multiplication factor. The last bit is set as ‘0’ if the number of active CCs are 1 indicating the multiplication factor=l (It is similar to non-CA case). Here also, the AID PDU contains Number of Assistance Information Fields as two, with two Assistance Information types as CQI and RQI each with one octet as shown in FIG. 31.

[0145] The last bit (the multiplication factor) is set as ‘ 1 ’ in the corresponding Average CQI field if the number of active CCs are more than one at MeNB.DU / SgNB.DU. The lookup tables used at MeNB.DU / SgNB.DU and SgNB.CU-UP are the same as the 1 CC lookup table if the last bit is set to ‘O’. If the last bit is set as ‘ 1 ’ then each entry in the lookup table is multiplied with the corresponding configured multiplication factor for LTE and NR. The encoding and decoding of fields in DDDS and AID PDUs are same as Method II A (one CC case).

[0146] SOLUTION: METHOD IV. In this method, when multiple CCs are activated at MeNB.DU then the overall achievable data rate is computed and converted into binary. Then, it is sent using multiple octets over DL Radio Quality Index field in the AID PDU. X2-U interface is enhanced for this purpose. For each active CC at MeNB.DU, one octet is used to encode the Average CQI field in the AID PDU and send it to SgnB.CU-UP. X2-U interface is enhanced for this purpose. For the active CCs, the Average CQI octets are arranged in decreasing order of CBWs (channel bandwidths). In the octet, the first 4 bits are used to encode the CQI range from 0 to 15, the next 3 bits are used to encode the rank from 1 to 8. The remaining bit is set to 0.

[0147] For example, the achievable rate is sent using two RQI octet fields where twoactive CCs are provided, one CQI for each CC, then we suggest multiple ways to encode in AID PDU. In each case, the Number of Assistance Information Fields stays the same (i.e., it is four, two for RQI and two for CQI), but the over heads will be different. In FIG. 32, there is an overhead on encoding CQI, RQI in multiple octets, since repeated the Assistance Information Type, number of octets for Radio Quality information fields for the 2ndoctet as well. In FIG. 33, there is an overhead on encoding RQI only, since repeated the Assistance Information Type, number of octets for Radio Quality information fields for the 2ndoctet only for RQI (similarly can do for CQI). In FIG. 34, there is no extra overhead on either CQI or RQI for the 2ndoctet compared to FIG. 32, FIG. 33.

[0148] Similarly, when multiple CCs are activated at SgNB.DU then the overall achievable data rate is computed and converted into binary. Then, it is sent using multiple octets over DL Radio Quality Index field in the AID PDU. Fl-U interface is enhanced for this purpose. For each active CC at SgNB.DU, one octet is used to encode the Average CQI field in the AID PDU and send it to SgNB.CU-UP. Fl-U interface is enhanced for this purpose. For the active CCs, the Average CQI octets are arranged in decreasing order of CBWs. In the octet, the first 4 bits are used to encode the CQI range from 0 to 15, the next 3 bits are used to encode the rank from 1 to 8. The remaining bit is set to 0.

[0149] At any given time, for a UE assume there are N active CCs at MeNB.DU (and at SgNB.DU). SgNB.CU-UP shall computeWj * CQI j * rankj, where N is the number of octets of the protocol field with Assistance Information Type = Average CQI, where the weights Wj, j=l,2, .. ,,N are obtained as a function of CBW and sum over weights should be equal to one. In one embodiment, consider equal weights for all the CCs then Wj = -, for all j. Note that inthis case, CU-UP does not need to know about the CBWs across the CCs.

[0150] In another embodiment, highest weightage is given to the highest CBW among the active CCs and the second highest weightage to the second highest and so on. For example, one way to obtain this weight for CC j Wj as the ratio of CBWj to the sum of CBWj’s across all CBWs. For this to happen, SgNB CU-UP should be aware of CBWs across all CCs.

[0151] CU-CP can send CBWs over El interface to the CU-UP, assign the CBWs in descending order and send it to CU-UP, El interface is enhanced for this purpose. The weights can be assigned based on the CBW, for example high weight given to high CBW.

[0152] In another embodiment, applying the weights to the CQIs based on the bandwidth the overall CQI computations can be done at MeNB.DU and SgNB .DU. In this case, the Average CQI can be encoded using one octet and sent to SgNB. CU-UP. At SgNB. CU-UP, decode the Average CQI and the UE supported rates across the LTE and NR legs. At SgNB. CU- UP, based on the DL data (DL PDCP PDUs) for the UE the data is scheduled using the data distribution policy shown in FIG. 26.

[0153] SOLUTION: METHOD IV (DSS). LTE-NR spectrum sharing is a technology that allows service providers to deploy LTE and NR in the same CCs and bands, i.e., spectrum sharing enables both LTE and NR to be simultaneously deployed and share resources in the CC. In dynamic spectrum sharing (DSS), the time-frequency resources in the CC are dynamically assigned to either LTE or NR according to their respective traffic demands.

[0154] In case of CC with DSS, while calculating the achievable data rate for a UE at MeNB.DU (or SgNB. DU), consider only the average PRB resources that are allocated to the UE at MeNB.DU (or SgNB.DU). The resources allocated will change with time based on the trafficdemands on LTE and NR leg. Also, the overheads for PDCCH and DMRS and the like are increased due to DSS operation and thus the number of REs available for data transmission reduces. This reduces the average TB size and results in lower achievable rate for LTE (or NR). The achievable rate for LTE (or NR) may change more frequently. To account for the dynamic nature of achievable rate in DSS in the existing methods, the respective DU, on a significant change in the number of resources allocated, computes the achievable rates over LTE (or NR) leg. Then this achievable rate is encoded and sent over AID PDU by respective DU (MeNB.DU and SgNB.DU) and then sent to SgNB.CU-UP over. X2-U and Fl-U interfaces enhanced for this purpose. In this case, it may happen to send AID, DDDS PDUs more often relative to other methods. While this work is described for EN-DC, is also applicable for MR-DC in general.

[0155] While the present disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated, but that the disclosure will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method to optimize downlink (DL) split-bearer operation using 4G Long Term Evolution (4G LTE) and 5G New Radio (5G NR) for a User Equipment (UE) in an Open Radio Access Network (O-RAN) comprising the steps of: providing a Centralized Unit (CU) having a CU-Control Plane (CP) and CU-User Plane (UP); providing a 4G Distributed Unit (4G DU) coupled to the CU-UP; providing a 5G Distributed Unit (5G DU) coupled to the CU-UP; wherein the UE supports split bearer operation coupled to both the 4G DU and the 5G DU; dividing operating regions into multiple regions so that reordering Transport Control Protocol (TCP) packets is avoided, the multiple regions selected from the group consisting of: transmit on 4G LTE only, transmit on 5G NR only, transmit on 5G NR first, transmit on 4G LTE first, and combinations thereof; and dividing DL data transmission to the UE between 4G LTE and 5G NR according to the divided multiple regions.

2. The method according to claim 1, wherein each of the CU-CP and CU-UP are connected to a near real time Radio Intelligent Controller (NR RIC).

3. The method according to claim 1, further comprising the steps of: determining an achievable data rate for each User Equipment (UE) connected to the O- RAN and supporting split bearer operation at the 4G DU and the 5GDU; mapping the achievable data rates for each UE to a Channel Quality Index (CQI), Radio Quality Indication (RQI) field in Assistance Information Data (AID); transmitting the AID from the 4G DU to the CU-UP; and transmitting the AID from the 5G DU to the CU-UP.

4. The method of claim 3, wherein the 4G DU comprises a Master LTE eNodeB (MeNB.DU), the 5G DU comprises a Secondary gNodeB (SgNB.DU), and the CU-UP comprises a SgNB. CU-UP, the step of determining an achievable data rate includes the steps of: providing a first component carrier (CC) on LTE leg and a second CC on NR leg with no carrier aggregation (CA) on LTE or NR legs; sending Assistance Information Data Protocol Data Unit format (AID PDU) from the MeNB.DU to the SgNB.CU-UP over X2-U interface, and from the SgNB.DU to the SgNB.CU- UP over Fl -U interface; wherein one octet in the AID PDU is used to encode DL Radio Quality Index (RQI) at the MeNB.DU and the SgNB.DU, which takes a value in a range from 0 to 255; wherein one octet in the AID PDU is used to encode Average CQI field of the AID PDU at MeNB.DU and SgNB.DU, where a first four bits are used to encode the CQI in a range from 0 to 15 based on a rank supported on LTE and NR wherein remaining bits are used to encode a rank.

5. The method of claim 4, further comprising the steps of: generating a NR lookup table including achievable data rates that is computed as a function of CQI and RQI; wherein the NR lookup table is maintained at the SgNB.DU and the SgNB CU-UP; generating a LTE lookup table including achievable data rates that is computed as a function of CQIrate and RQI, where CQIrate is the maximum data rate achievable for a CQI; wherein the LTE lookup table is maintained at the MeNB.DU and the SgNB.CU-UP.

6. The method of claim 5, further comprising the steps of calculating an achievable data rate at the SgNB.DU for a given UE using average TB size and number of DL subframes in a second, where an average TB size is computed as a function of CQI and corresponding MCS, Rank, average number of PRBs and number of REs including: transmitting the achievable data rate to the CU-UP using a CQI value and an RQI value where the SgNB.DU finds the closest value of RQI from the NR lookup table; encoding the RQI value into DL RQI field of AID PDU, which is sent along with a CQI value from the SgNB.DU to the SgNB.CU-UP via the Fl-U interface; and decoding the RQI value and the CQI value at the SgNB.CU-UP.

7. The method of claim 6, further comprising the steps of calculating an achievable data rate at the MeNB.DU for a given UE is calculated using average TB size and number of DL subframes in a second, where an average TB size is computed as a function of CQI and corresponding MCS, Rank, average number of PRBs and number of REs including: transmitting the achievable data rate to the CU-UP using a CQI value and an RQI valuewhere the MeNB.DU finds the closest value of RQI from the LTE lookup table; encoding the RQI value into DL RQI field of AID PDU, which is sent along with a CQI value from the MeNB.DU to the SgNB.CU-UP via the X2-U interface; and decoding the RQI value and the CQI value at the SgNB.CU-UP.

8. The method of claim 1, wherein Dynamic Spectrum Sharing (DSS) is used on one or more component carriers (CC) enabling both LTE and NR to be simultaneously deployed and share resources in the CC, and wherein time-frequency resources in the CC are dynamically assigned to either LTE or NR according to their respective traffic demands.

9. The method of claim 1, further comprising the steps of: calculating an achievable data rate for a UE at the MeNB.DU or the SgNB.DU by considering only the average PRB resources that are allocated to the UE at the MeNB.DU or the SgNB.DU respectively, where the allocated resources will change with time based on traffic demands on the LTE leg and the NR leg; wherein when the change in allocated resources reaches or exceeds a threshold, the MeNB.DU or the SgNB.DU respectively computes achievable rates over the LTE leg or NR leg respectively, where the computed achievable rate is encoded and transmitted via AID PDU by the MeNB.DU or the SgNB.DU respectively to the SgNB.CU-UP.

10. The method of claim 1, wherein data transmissions between the CU-CP and the CU-UP are modified to communicate frequency band specific information to facilitate the use of the multiple regions.

11. The method of claim 1, wherein the CU comprises a master node CU (MeNB.CU) including a MeNB.CU User Plane (MeNB.CU-UP) and a MeNB.CU Control Plane (MeNB.CU- CP), and the 4G DU comprises a master node DU (MeNB.DU) and the 5G DU comprises a secondary node DU (SgNB.DU), and the UE comprises Evolved Universal Terrestrial Radio Access-New Radio Dual Connectivity (EN-DC) UE, the method further comprising the steps of: providing a secondary node CU (SgNB.CU) including a SgNB.CU Control Plane (SgNB.CU-CP) and a SgNB.CU User Plane (SgNB.CU-UP) and connecting the SgNB.DU to the SgNB.CU-CP and the SgNB.CU-UP; wherein the EN-DC UE is coupled to the MeNB.DU and the SgNB.DU.

12. The method of claim 11, wherein the step of dividing DL data transmission to the UE between 4G LTE and 5G NR according to the divided search space is performed at the SgNB.CU-UP.

13. The method of claim 12, wherein the DL data Packet Data Convergence Protocol Packet Data Units (DL PDCP PDUs) are proportionately divided across the 4G LTE and 5GNR.

14. The method of claim 13, wherein the 4G LTE comprises 4G Evolved Packet Core (EPC), the method further comprising the steps of: transmitting NR PDCP Service Data Units (NR PDCP SDUs) from the from the 4G EPC to the SgNB-CU-UP across an Sl-U interface; converting NR PDCP SDUs at the SgNB-CU-UP to NR PDCP PDUs, wherein thedividing of DL data transmission occurs after NR PDCP SDU to NR PDCP PDU conversion; communicating at least some of the NR PDCP PDUs from SgNB-CU-UP to SgNB.DU as part of the dividing of DL data transmission; transmitting the at least some of the NR PDCP PDUs to the UE via a 5G NR-Uu airinterface; and processing the at least some of the NR PDCP PDUs by a NR Radio Link Controller (NR RLC) and a NR Medium Access Control (NR MAC) at the SgNB.CU.

15. The method of claim 12, wherein as part of the dividing of DL data transmission at least some of the NR PDCP PDUs are communicated from SgNB-CU-UP to MeNB.DU.

16. The method of claim 15, wherein the at least some of the NR PDCP PDUs are transmitted to the UE via a 4G LTE-Uu air-interface and are processed by an Evolved Universal Terrestrial Radio Access Radio Link Controller (E-UTRA RLC) an E-UTRA Medium Access Control (E-UTRA MAC) at the MeNB.DU including carrier aggregation on the LTE leg and the NR leg.

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