Abstract:
Millimeter-wave (mmWave) band communication is a very promising technology for 5G small cells. In practice, such a new system will coexist with legacy or evolved microwave band systems, such as E-UTRAN LTE macro-cell cellular systems, for a long time to come. Considering the typical scenarios where a macro cell offers umbrella coverage for clusters of small cells, several control plane (C-plane) architectural choices of macro-assisted 5G mmWave systems from both UE and network&#39;s perspectives are evaluated. Termed macro-assisted mmWave, an effective end-to-end integration of the futuristic mmWave small cells and microwave macro cells shall promise the benefits of both yet avoid individual limitations. The proposed On-demand Reconfiguration C-Place Architecture (ORCA) for Macro-assisted Millimeter Wave (mmWave) small cells is designed to meet 5G expectations of dense deployment of small cells and UEs and beamformed intermittent Gbps links.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is filed under 35 U.S.C. §111(a) and is based on and hereby claims priority under 35 U.S.C. §120 and §365(c) from International Application No. PCT/CN2015/077425, with an international filing date of Apr. 24, 2015. This application is a continuation of International Application No. PCT/CN2015/077425, which is pending as of the filing date of this application, and the United States is a designated state in International Application No. PCT/CN2015/077425. The disclosure of each of the foregoing documents is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosed embodiments relate generally to wireless communication, and, more particularly, to control plane architecture integrating Millimeter Wave smallcell and microwave macrocell. 
       BACKGROUND 
       [0003]    The upcoming next generation “5G” Millimeter Wave (mmWave) small cell is expected to coexist with microwave (E-UTRAN) macro cells for a long time. The macro-assisted mmWave cellular systems exploit the fact that mmWave small cells and microwave macro cells may compensate each other very well in coverage area, link capacity, spectrum availability, and service robustness. 
         [0004]    The mmWave bands above 10 GHz offer abundant spectrum, possibly at license free or at least efficiently shared, where bands may span contiguously for hundreds of megahertz or even gigahertz. Comparatively, microwave bands below 6 GHz are known for suffering from shortage, known as “bandwidth crunch”, and are fragmented bands of tens of megahertz with expensive licensing. 
         [0005]    Due to the high carrier frequency, an mmWave system enjoys the natural compactness of RF system design of potentially tens or hundreds of antennas in a very small area, but it also has the physical barriers of poor penetration, small channel coherence time, big propagation loss due to atmosphere gaseous losses and precipitation attenuation. That is why mmWave systems usually need highly directional beamforming techniques to meet the tight link budget even for a small cell coverage. Comparatively, microwave systems have much smaller propagation path loss, and hence wider coverage, but greater multipath dissipation and scattering that may translate to severe inter-cell interference. 
         [0006]    Given different channel characteristics, at the radio access system level, mmWave systems may promise gigabit-rate links within limited (small cell) coverage that are yet coupled with challenging beam-tracking and intermittent links in low-to-medium mobility in particular. On the other hand, the legacy microwave systems offer proven record of robust wide-area coverage, e.g., macrocell services even for high mobility users at a service rate of up to hundreds of megabits. 
         [0007]    From both network and radio access&#39;s perspectives, mmWave is currently considered a very promising choice for in-door or out-of-door “5G” cellular small cells, which may compensate microwave macro-cell in shortage of spectrum or in need for economical high-speed data services. In particular, the small cells offer downlink (DL) throughput boosting or coverage extension for an umbrella macro-cell at its edge. On the other hand, macro-cell coverage makes up mmWave&#39;s directional coverage limitation and bursty link disruption by offering reliable omni-directional overlay services for time-critical or mission-critical control signaling, or offering more robust and seamless services for low-rate high-mobility voice users. Together they constitute a layered communication infrastructure that promise reliability, wide coverage, economical yet diversified mobile QoS services. 
         [0008]    The gradual deployment of mmWave small cell systems, just as many other previous wireless systems, may initially be standalone Greenfield or macro-assisted hotspots, then clusters of contiguous small cells overlaid on top of existing macro cells, and eventually large scales of dense deployment of mmWave small cells to host many stationary or mobile users, e.g., in stadiums or urban areas under a central controller. 
         [0009]    Overall, macro-assisted mmWave small cells demand a scalable multi-RAT integration architecture that affect both UE and networks. Control and data plane shall be separated because they may not always go through the same radio access. Design of control and user plane architecture shall be scalable and consider 5G mmWave deployment scenarios. Clustered or Dense deployment of mmWave small cells under the coverage of a macrocell with the following characteristics shall be focused on: UEs are of dual active RFs in mmWave band and microwave bands; no ideal backhaul link between small cell BS (SBS) and macrocell BS (MBS); dense mmWave small cells and UEs under an umbrella microwave macrocell; mmWave smallcell is similar to LTE at upper layers but like a new RAT otherwise at lower layers; and Gbps rate of mmWave links but with intermittent connectivity. 
         [0010]    The existing LTE DuCo architecture is not fine-tuned for mmWave small cells that has new radio characteristics and faces new 5G requirements as well. The LTE DuCo architecture is designed only for some less dense deployed, relatively low-rate microwave smallcell scenarios, and not fine-tuned for stationary or dense scenarios with Gbps mmWave small cells. A control plane architecture to integrate mmWave small cells and microwave macrocell effectively is sought. 
       SUMMARY 
       [0011]    A control plane architecture to integrate Millimeter Wave (mmWave) small cells and microwave macro-cells effectively is proposed. The architecture keeps the same underlying hardware (HW) architecture intact, but overlay on top of it multiple logical C-plane architecture setups by on-demand software (SW) configuration. The proposed On-demand Reconfiguration C-Place Architecture (ORCA) for Macro-assisted mmWave small cells is designed to meet 5G expectations of dense deployment of small cells and UEs and beamformed intermittent Gbps links. Although mmWave small cells may work independently, macro-assisted mmWave systems offer the following potential advantages: more robust mobility support, resilience to mmWave link outage, small-area throughput boosting and wide-area signaling coverage. In light of the 5G expectation and macro-assistance, the deployment scenarios are classified based on density and UE&#39;s mobility level. Such criteria helps to evaluate any specific system architecture with respect to each specific scenario or all scenarios. 
         [0012]    In one embodiment, a first C-plane setup is applied for dense stationary UEs where control signaling is offloaded from macro base station (MBS) to mmWave smallcell base stations (SBSs). A second C-plane setup is applied for high-mobility UEs where robust control signaling is provided by MBS. A third C-plane setup is applied for dual-RF low-mobility UEs capable of refined RRM split where dual connection signaling paths are provided by both MBS and mmWave SBSs. 
         [0013]    Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
           [0015]      FIG. 1  illustrates a heterogeneous network (HetNet) with On-demand Reconfiguration C-Place Architecture (ORCA) for Macro-assisted Millimeter Wave (mmWave) small cells in accordance with one novel aspect. 
           [0016]      FIG. 2A  is a simplified block diagram of a user equipment (UE) that carry certain embodiments of the present invention. 
           [0017]      FIG. 2B  illustrates mmWave smallcell deployment scenarios with ORCA. 
           [0018]      FIG. 3  illustrates a first C-Plane setup under a first network deployment scenario. 
           [0019]      FIG. 4  illustrates a second C-Plane setup under a second network deployment scenario. 
           [0020]      FIG. 5  illustrates a third C-Plane setup under a third network deployment scenario. 
           [0021]      FIG. 6  illustrates an example of a UE having different C-Plane setups with different small cell base stations. 
           [0022]      FIGS. 7A and 7B  illustrate an example of a UE changing C-Plane setups. 
           [0023]      FIG. 8  illustrates UE-side configuration for C-Plane setup transition. 
           [0024]      FIG. 9  illustrates network-side configuration and macrocell operation for C-Plane setup transition. 
           [0025]      FIG. 10  illustrates network-side configuration and smallcell operation for C-Plane setup transition. 
           [0026]      FIG. 11  is a flow chart of a method of ORCA for Macro-assisted Millimeter Wave (mmWave) small cells from UE perspective in accordance with one novel aspect. 
           [0027]      FIG. 12  is a flow chart of a method of ORCA for Macro-assisted Millimeter Wave (mmWave) small cells from network perspective in accordance with one novel aspect. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0029]      FIG. 1  illustrates a heterogeneous network (HetNet)  100  with On-demand Reconfiguration C-Place Architecture (ORCA) for Macro-assisted Millimeter Wave (mmWave) small cells in accordance with one novel aspect. HetNet  100  comprises a macro base station (MeNB or MBS) serving a macrocell  110  and a plurality of mmWave smallcell base stations (Secondary eNB (SeNB) or SBS) including SBS1 and SBS2 serving small cells. The mmWave small cells are deployed under the coverage of the macrocell  110 . User equipment UE1 is initially located within smallcell  120  served by SBS1 while UE2 is initially located within smallcell  130  served by SBS2. In a typical Clustered or Dense deployment of mmWave smallcell scenario, a cluster of or dense mmWave small cells and UEs are under the umbrella microwave macrocell  110 . 
         [0030]    The existing LTE 3GPP HetNet dual connectivity (DuCo) architecture is designed only for less dense deployed, relatively low-rate microwave smallcell scenarios that is not fine-tuned for stationary or dense scenarios with Gbps mmWave small cells. The 3GPP HetNet DuCo defines control-plane and user-plane split with single radio resource control (RRC) for HetNet mobility, and flow/bearer data split. In control plane, control signaling with RRC/S1-MME anchor is at the macrocell only. The single RRC anchor provides simple and robust handover (HO) but no diversity, single failure point at the macro base station with X2 latency. The control plane is not designed to handle very dense deployment of small cells, UEs, and many intermittent links with signaling errors. In the example of  FIG. 1 , according to LTE DuCo control plane architecture, the MeNB provides the single RRC anchor for all UEs in mmWave small cells. Given intermittent dense mmWave links, the MeNB may see signaling storms or potential control latency for UEs. The single RRC anchor provides no C-plane diversity for UEs in reaction to different levels of mobility, beamforming, power, and load. 
         [0031]    In accordance with one novel aspect, a control plane architecture to integrate mmWave small cells and microwave macro cells effectively is proposed. The On-demand Reconfiguration C-Place Architecture (ORCA) for Macro-assisted Millimeter Wave (mmWave) small cells is designed to meet 5G expectations of dense deployment of small cells and UEs and beamformed intermittent Gbps links. ORCA is also designed to meet the E-UTRAN constraints of limited and costly microwave spectrum, limited macrocell processing power, backhaul link and CN capacity. Further, ORCA is designed to consider the deployment scenarios following classification criteria of connection/UE/cell density, UE mobility level, backhaul quality, and integration with macrocell-macro-assisted mmWave small cells. For example, given the limited processing resources and link capacity with existing E-UTRAN MeNB/MBS, anchoring data path and control functionalities at the MBS, as in existing HetNet DuCo or PDCP-level LTE-WiFi Aggregation, may not scale up gracefully with the 5G expectation of dense connections and small RAN latency, e.g., up to 100 connections/km 2  and end-to-end RAN latency as small as 1-5 ms, respectively. 
         [0032]    The proposed ORCA revises the LTE DuCo C-plane architecture with scenario-specific and on-demand configurability. ORCA utilizes the X2-C interference but reduces inter-BS sync-up. The master BS overwrites slave or secondary BSs on configuration and UE capability negotiation, and peer-to-peer BSs have detailed functional split. ORCA redefines C-plane and RRM functional split between macrocell and smallcell for localized and fast radio control. ORCA also provides flexible (context/load) scenario based end-to-end configuration. ORCA provides UE on-demand C-plane diversity for robustness, saves the (RACH, signaling) resources at MBS, and reduces the latency between UE and SBSs. 
         [0033]      FIG. 2A  is a simplified block diagram of a user equipment UE  201  that carry certain embodiments of the present invention. UE  201  has an antenna (or antenna array)  214 , which transmits and receives radio signals. A RF transceiver module (or dual RF modules)  213 , coupled with the antenna, receives RF signals from antenna  214 , converts them to baseband signals and sends them to processor  212  via baseband module (or dual BB modules)  215 . RF transceiver  213  also converts received baseband signals from processor  212  via baseband module  215 , converts them to RF signals, and sends out to antenna  214 . Processor  212  processes the received baseband signals and invokes different functional modules to perform features in UE  201 . Memory  211  stores program instructions and data to control the operations of UE  201 . 
         [0034]    UE  201  also includes a 3GPP protocol stack module  226  supporting various protocol layers including NAS  225 , AS/RRC  224 , PDCP/RLC  223 , MAC  222  and PHY  221 , a TCP/IP protocol stack module  227 , an application module APP  228 , and a management module  230  including a configuration module  231 , a mobility module  232 , and a control module  233 . The different circuits and modules are function circuits and modules that can be configured and implemented by software, firmware, hardware, or any combination thereof. For example, each circuit or module may comprise processor  212  plus corresponding software codes. The function circuits and modules, when executed by processor  212  (via program instructions and data contained in memory  211 ), interwork with each other to allow UE  201  to perform certain embodiments of the present invention accordingly. Configuration module  231  obtains C-plane setup preference information, mobility module  232  determines UE mobility based on UE speed, movement, and cell count, control module  233  determines and applies a preferred C-plane setup for the UE dynamically. 
         [0035]      FIG. 2B  illustrates mmWave smallcell deployment scenarios with ORCA. Under the proposed ORCA, the general assumption is that E-UTRAN and 5G may coexist for a long time. The macro-assisted mmWave concept is to exploit the fact that mmWave and microwave wireless coverage may compensate each other well. Examples of 5G requirements are: Ultra Dense Network with high-density of smallcells, users per cell, and connections per area, e.g., up to 100 connections/km 2 , with traffic density up to 10 Tbps/km 2 ; Reduced latency with end-to-end RAN delay as small as 1-5 ms; Gbps rate user experienced throughput; Rich applications with context-aware diverse QoSs and different mobility levels; and Multi-RAT support with backward compatibility and forward scalability, and multi-mode RFs at UE and BS. Generally, 5G is expected to offer 50× times more spectrum, 20× times of more density, and 10× times of higher efficiency. So far only mmWave bands can meet the first expectation. 
         [0036]    Although mmWave small cells may work independently, macro-assisted mmWave systems offer the following potential advantages: more robust mobility support, resilience to mmWave link outage, small-area throughput boosting and wide-area signaling coverage. As a result, a new flexible, end-to-end architecture to integrate E-UTRAN and mmWave small cells is needed. Different deployment scenarios demand for different and sometimes conflicting architecture setups. Operators cannot afford a static yet inefficient architecture, nor an ever-changing architecture particularly with ever-changing hardware (UE, RAN, and EPC equipment) requirements. Operators want to have one set of HW that supports all scenarios and even futuristic scenarios at affordable cost (CAPEX/OPEX), yet offering customized services for individual users. The examples may include SDN, NFV, Centralized RAN (C-RAN) etc. Although C-plane and U-plane separation offers flexibility, but different mmWave deployment scenarios still demand for different C-plane architectures. 
         [0037]    In light of the above, the proposed ORCA keeps the same underlying HW architecture intact, but overlay on top of it multiple logical C-plane architecture setups by on-demand software configuration. For each C-plane setup scenario, either the UE or the network operator may trigger SW (re)configuration of the architecture setup based on real-time needs, context/load situations, and UE capability. The same UE may see multiple different logical architecture setups active at different moments that corresponds to different scenarios. The same UE may see different logical architecture setups with different SBSs. Different UEs that have different (mobility, load, or context) scenarios may be configured with different logical architecture setups even if they are served by the same physical entities (MBS, SBS, MME/EPC, etc.) For each architecture setup, there could be further refined C-Plane RRM functional split between the underlying network entities. For the future mmWave deployment scenarios or evolving macrocell E-UTRAN HW, the proposed on-demand architecture may also evolve accordingly without incurring extra CAPEX/OPEX. For example, ORCA may evolve into C-RAN type of architecture easily, as C-RAN type of configuration becomes one of the embodiments of the C-plane architecture setup under ORCA. 
         [0038]      FIG. 3  illustrates a first C-Plane setup under a first network deployment scenario in HetNet  300 . HetNet  300  comprises a mobility management entity MME  301 , a macro base station MBS  302 , an mmWave smallcell base station SBS  303 , and a user equipment UE  304 . UE  304  is under the coverage of both macrocell and smallcell and maintains dual connectivity with both MBS  302  and SBS  303 . In this embodiment, UE  304  is a stationary UE and settles down within the SBS  303  smallcell coverage. In addition, there may be a lot of other stationary UEs and mmWave small cells densely deployed under microwave macrocell served by MBS  302 . Under this deployment scenario, a first C-plane setup is applied for UE  304 . In control plane, the anchor control signaling for the UE is provided by SBS  303  (e.g., via Uu (RRC) interface) and by MME  301  (e.g., via S1-MME interface). This way, control signaling for dense stationary UEs are localized in small cells, e.g., the MBS offloads the control signaling to each corresponding SBS for dense stationary UEs. 
         [0039]      FIG. 4  illustrates a second C-Plane setup under a second network deployment scenario in HetNet  400 . HetNet  400  comprises a mobility management entity MME  401 , a macro base station MBS  402 , an mmWave smallcell base station SBS  403 , and a user equipment UE  404 . UE  404  is under the coverage of both macrocell and smallcell and maintains dual connectivity with both MBS  402  and SBS  403 . In this embodiment, UE  404  is a high-mobility UE and may frequently move in-and-out of the coverage of any particular mmWave smallcell. Under this deployment scenario, a second C-plane setup is applied for UE  404 . In control plane, the anchor control signaling for the UE is provided by MBS  402  (e.g., via Uu (RRC) interface) and by MME  401  (e.g., via S1-MME interface). This way, robust control signaling for high-mobility UEs are provided. 
         [0040]      FIG. 5  illustrates a third C-Plane setup under a third network deployment scenario in HetNet  500 . HetNet  500  comprises a mobility management entity MME  501 , a macro base station MBS  502 , an mmWave smallcell base station SBS  503 , and a user equipment UE  504 . UE  504  is under the coverage of both macrocell and smallcell and maintains dual connectivity with both MBS  502  and SBS  503 . In this embodiment, UE  504  is a dual-RF low-mobility UE capable of supporting dual-connection signaling paths and refined RRM function split. Under this deployment scenario, a third C-plane setup is applied for UE  504 . In control plane, a first anchor control signaling path for the UE is provided by MBS  502  (e.g., via Uu interface and anchor RRC) and by MME  501  (e.g., via S1-MME interface), a second assisting or peering control signaling path for the UE is provided by SBS  503  (e.g., via Uu interface and assist RRC) and by MME  501  (e.g., via assisting or peering Si-MME interface). This C-plane setup is suitable for 1) stationary UEs that start moving or when an original mmWave link degrades, or for 2) high-mobility UEs that slow down and an active mmWave link becomes operational. 
         [0041]      FIG. 6  illustrates an example of a UE having different C-Plane setups with different small cell base stations in a HetNet  600 . HetNet  600  comprises a mobility management entity MME, a macrocell base station MBS serving microwave macrocell, a first smallcell base station SBS1 serving a first mmWave smallcell, a second smallcell base station SBS2 serving a second mmWave smallcell, and a user equipment UE1. Under ORCA, the same UE may see different logical (SW configured) architecture setups with different SBSs. In the example of  FIG. 6 , UE1 is in the coverage of the macrocell and both two small cells. UE1 applies the third C-plane setup with MBS and SBS1. For example, the MBS provides anchor RRC signaling to UE1 and SBS1 provides assisting RRC signaling to UE1. At the same time, UE1 applies the first C-plane setup with MBS and SBS2. For example, SBS2 provides anchor RRC signaling to UE1 and MBS offloads control signaling to SBS2. 
         [0042]      FIGS. 7A and 7B  illustrate an example of a UE changing C-Plane setups in a HetNet  700 . HetNet  700  comprises a mobility management entity MME, a macrocell base station MBS, a first smallcell base station SBS1, a second smallcell base station SBS2, and a user equipment UE1. Under ORCA, the same UE may see multiple different logical (SW configured) architecture setups active at different moments that corresponds to different scenarios. As depicted in  FIG. 7A  (SCENARIO #A), UE1 is a stationary UE located inside SBS1&#39;s coverage. UE1 applies the first C-plane setup with SBS1, i.e., SBS1 provides the anchor RRC signaling to UE1. Later, UE1 moves under SBS1&#39;s coverage, slowly across the boundary of the neighboring small cell served by SBS2 under the umbrella of the same MBS. When UE1 just starts moving and is still under SBS1&#39;s coverage (SCENARIO #B), UE1 applies the third C-plane setup with the MBS and SBS1, i.e., both MBS and SBS1 provide control signaling to UE1. When UE1 keeps moving and enters SBS2&#39;s coverage (SCENARIO #C), UE1 then applies the third C-plane setup with the MBS SBS2, i.e., both MBS and SBS2 provide control signaling to UE1. As depicted in  FIG. 7B  (SCENARIO #D), UE1 settles down with SBS2&#39;s coverage and becomes a stationary UE. UE1 then applies the first C-plane setup with SBS2, i.e., SBS2 provides the anchor RRC signaling to UE1. Alternatively, as depicted in  FIG. 7B  (SCENARIO #E), UE1 moves out of the small cells with high speed, i.e., becomes a high-mobility UE. As a result, UE1 applies the second C-plane setup with the MBS, i.e., MBS provides the anchor RRC signaling to UE1. Note that the S1-MME interface between the MME and SBS1/SBS2 can be used to speed up the mobility messaging, while the S1-MME interface between the MME and the MBS is for high-mobility UEs out of smallcell coverage. It is a network-side behavior on how to configure the S1-MME or how to sync-up among the base stations. 
         [0043]      FIG. 8  illustrates UE-side configuration for C-Plane setup transition. Under ORCA, a UE-specific end-to-end C-plane setup can be transitioned based on UE-trigger, Network (NW)-trigger, or UE-NW jointly configuration. The initial C-plane setup can be selected by the UE based on macrocell load (e.g., RACH contention) and mmW smallcell load/beam patterns that are known to the umbrella MBS and broadcasted to the UE. On-demand C-plane setup transitions may be triggered by UE-mobility scenario changes, excessive signaling latency, timer expiry, or NW/UE real-time demand. In step  801 , a dual-band UE powers up and scans microwave macrocell first. In step  802 , the UE checks whether the radio signal quality in macrocell is above a threshold. If the answer is yes, then in step  803 , the UE performs cell selection and system information decoding. Based on received system information, in step  804 , the UE checks whether there is assistance information for small cells. If the answer is No, then in step  807 , the UE performs RACH and RRC setup procedure with the macrocell and applies C-plane setup 2 in step  812 . The MBS provides control signaling to the UE. 
         [0044]    If the answer to step  802  is No, then in step  806 , the UE performs scanning, RACH, RRC setup procedure with the selected small cells. In step  811 , the UE applies C-plane setup 1 and receiving control signaling from the selected SBS. If the answer to step  804  is yes, then in step  805 , the UE checks whether the macrocell has high load and whether the UE has low-mobility. If the answer is yes, then the UE also goes to step  806 . If the answer is No, then the UE goes to step  808  and checks whether the UE has high-mobility. If the answer is yes, then the UE goes to step  807 . If the answer is No, then the goes to step  809  and performs scanning, RACH, RRC setup procedure with multiple cells (macrocell by MBS and smallcell by SBS). In step  813 , the UE applies C-plane setup 3 and receives anchor control signaling from MBS and assisted control signaling from SBS. 
         [0045]    When UE is in C-plane setup 2 (step  812 ), if the UE slows down and an active mmWave link becomes operational, then the UE can trigger C-plane setup transition and change to setup 3 (step  813 ). If the UE then settles down in an mmWave smallcell, then the UE can trigger another C-plane setup transition and change to setup 1 (step  811 ). If the UE starts moving or if the existing mmWave link degrades, then the UE again triggers C-plane setup transition and changes back to setup 3 (step  813 ). Finally, if the UE speeds up or if the existing mmWave link degrades, then the UE triggers another C-plane setup transition and change to setup 2 (step  812 ). 
         [0046]      FIG. 9  illustrates network-side configuration and macrocell operation for C-Plane setup transition. Under ORCA, a UE-specific end-to-end C-plane setup can be suggested by the network-side serving BS in macrocell or small cells. Any conflict can be resolved by macro and small cell sync-up across C2 or MME, and eventually depends on UE&#39;s final decision (in one embodiment). From NW-side macrocell operation perspective, in step  901 , the MBS monitors small cell addition, removal, or modification, signaling load, RACH resources, and C-plane setup transition request from the UE, etc. In step  902 , the MBS checks whether the assistance system information for mmWave small cells has changed. If the answer is yes, then in step  904 , the MBS broadcasts updated new system information to the UEs and goes to step  906 . In step  906 , the MBS checks whether a UE has triggered transition request between C-plane setup 2 and setup 3. If the answer is yes, then in step  908 , the MBS performs X2 sync-up with its peer or slave SBS on the UE and then updates MME and macrocell RRC state and record in step  910 . The MBS then goes back to step  901  repeating the operation. 
         [0047]    If the answer to step  902  is No, then in step  903 , the MBS checks whether there is too many low-mobility UEs in C-plane setup 2 and setup 3. If the answer is No, then the MBS goes to step  906  directly. If the answer is yes, then the MBS goes to step  905  and suggests the UE to transition to C-plane setup 1 or setup 3 and then goes back to step  901 . 
         [0048]    If the answer to step  906  is No, then in step  907 , the MBS checks whether a UE has triggered transition request between C-plane setup 1 and setup 3. If the answer is no, then the MBS goes back to step  901 . If the answer is yes, then the MBS goes to step  909  and performs X2 sync-up with the target SBS about anchor RRC switching for the UE. In step  911 , the MBS performs RRC connection update. Finally, the MBS updates MME and macrocell RRC state and record in step  910 . The MBS then goes back to step  901  repeating the operation. 
         [0049]      FIG. 10  illustrates network-side configuration and smallcell operation for C-Plane setup transition. Under ORCA, a UE-specific end-to-end C-plane setup can be suggested by the network-side serving BS in macrocell or small cells. Any conflict can be resolved by macro and small cell sync-up across C2 or MME, and eventually depends on UE&#39;s final decision (in one embodiment). From NW-side smallcell operation perspective, in step  1001 , an SBS monitors UE mobility, mmWave link quality, macrocell sync-up message, UE C-plane setup transition requests etc. In step  1002 , the SBS checks whether a UE in setup 1 starts moving or the mmWave link degrades. If the answer is no, then the SBS checks whether a UE in setup 3 but its mobility level changes. If the answer is no. then the SBS further checks whether a UE has triggered C-plane transition request to get out of setup 2. If the answer is yes, then the SBS performs X2 sync-up with its peer or master MBS on the UE and then updates MME and smallcell RRC state and record in step  1010 . The SBS then goes back to step  1001  repeating the operation. 
         [0050]    If the answer to step  1002  is yes, then in step  1003 , the SBS suggests the UE to transition to C-plane setup 3 and then goes back to step  1001 . If the answer to step  1004  is also yes, then in step  1005 , the SBS suggests the UE to transition to C-plane setup 1 or setup 2 and then goes back to step  1001 . 
         [0051]    If the answer to step  1006  is no, then in step  1007 , the SBS checks whether a UE has triggered C-plane transition request to get out of setup 3. If the answer is no, then the SBS goes back to step  1001 . If the answer is yes, then the MBS goes to step  1009  and performs X2 sync-up with the MBS about anchor RRC switching or macro fallback for the UE. In step  1011 , the SBS performs RRC connection update. Finally, the SBS updates MME and smallcell RRC state and record in step  1010 . The SBS then goes back to step  1001  repeating the operation. 
         [0052]      FIG. 11  is a flow chart of a method of ORCA for Macro-assisted Millimeter Wave (mmWave) small cells from network perspective in accordance with one novel aspect. In step  1101 , a base station obtains C-plane setup preference information in a HetNet having a macrocell and overlaying mmWave small cells. In step  1102 , the base station determines an updated C-plane setup based on the C-plane setup preference information for a UE having dual connectivity with a macro base station and a smallcell base station. In step  1103 , the base station performs C-plane setup update according to the updated C-plane setup of the UE. In one embodiment, the C-plane setup preference information comprises at least one of a smallcell addition and removal and modification, a signaling load, a network density, available radio access resources, link quality of the macrocell and small cells, a UE mobility, and a C-plane setup transition request from the UE. A specific C-plane setup comprises one or more base stations that perform radio resource control (RRC) and radio resource management (RRM) functionalities for the UE. The C-plane setup update involves performing X2 sync and RRC connection update between the MBS and the SBS. The updated C-plane setup is dynamically applied via software configuration based on the same set of hardware in the network. 
         [0053]      FIG. 12  is a flow chart of a method of ORCA for Macro-assisted Millimeter Wave (mmWave) small cells from UE perspective in accordance with one novel aspect. In step  1201 , a UE obtains C-plane setup preference information in a HetNet having a macrocell and overlaying mmWave small cells. In step  1202 , the UE determines an updated C-plane setup based on the C-plane setup preference information. The UE maintains dual connectivity with a macro base station and a smallcell base station. In step  1203 , the UE performs C-plane setup update according to the updated C-plane setup pf the UE. The C-plane setup preference information comprises a UE mobility and assistance information from the network. A specific C-plane setup comprises one or more base stations that perform radio resource control (RRC) and radio resource management (RRM) functionalities for the UE. In one embodiment, the updated C-plane setup is different from a previously applied C-plane setup for the same UE. In another embodiment, the updated C-plane setup associated with the SBS is different from a second C-plane setup associated with a second SBS for the same UE at the same time. 
         [0054]    Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.