WO2017126945A1

WO2017126945A1 - Network architecture and protocols for a unified wireless backhaul and access network

Info

Publication number: WO2017126945A1
Application number: PCT/KR2017/000755
Authority: WO
Inventors: Boon Loong Ng; Jayshree Bharatia
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2016-01-22
Filing date: 2017-01-23
Publication date: 2017-07-27

Abstract

The present disclosure relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution (LTE). A method by a first master base station associated with a secondary base station in a wireless communication system supporting a dual connectivity, the method comprising: transmitting, to a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, establishing a second IP tunnel between the first master base station and the second master base station if a second message is received and transmitting, to the secondary base station, a third message to release a third IP tunnel between the first master base station and the secondary base station.

Description

NETWORK ARCHITECTURE AND PROTOCOLS FOR A UNIFIED WIRELESS BACKHAUL AND ACCESS NETWORK

The present application relates generally backhaul and access network in wireless communication systems. More specifically, this disclosure relates to network architecture and protocols for a unified wireless backhaul and access network.

To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.

The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.

In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.

In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier(FBMC), non-orthogonal multiple access(NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

5th generation (5G) mobile communications, initial commercialization of which is expected around 2020, is recently gathering increased momentum with all the worldwide technical activities on the various candidate technologies from industry and academia. The candidate enablers for the 5G mobile communications include massive antenna technologies, from legacy cellular frequency bands up to high frequencies, to provide beamforming gain and support increased capacity, new waveform (e.g., a new radio access technology (RAT)) to flexibly accommodate various services/applications with different requirements, new multiple access schemes to support massive connections, and so on.

The International Telecommunication Union (ITU) has categorized the usage scenarios for international mobile telecommunications (IMT) for 2020 and beyond into 3 main groups such as enhanced mobile broadband, massive machine type communications (MTC), and ultra-reliable and low latency communications. In addition, the ITC has specified target requirements such as peak data rates of 20 gigabit per second (Gb/s), user experienced data rates of 100 megabit per second (Mb/s), a spectrum efficiency improvement of 3X, support for up to 500 kilometer per hour (km/h) mobility, 1 millisecond (ms) latency, a connection density of 106 devices/km2, a network energy efficiency improvement of 100X and an area traffic capacity of 10 Mb/s/m2. While all the requirements need not be met simultaneously, the design of 5G networks should provide flexibility to support various applications meeting part of the above requirements on a use case basis.

In one embodiment, a method by a first master base station associated with a secondary base station in a wireless communication system supporting a dual connectivity, the method comprising: transmitting, to a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, establishing a second IP tunnel between the first master base station and the second master base station if a second message is received and transmitting, to the secondary base station, a third message to release a third IP tunnel between the first master base station and the secondary base station.

Preferably, wherein user data is transferred from the first master base station to the secondary base station via the second master base station based on the first IP tunnel and the second IP tunnel, and wherein the user data is transmitted from the secondary base station to a terminal which is connected to the secondary base station.

Preferably, further comprising: transmitting, to the second master base station, a fourth to release the first IP tunnel and the second IP tunnel if a session for the user data is terminated.

Preferably, wherein the first message includes a create connection request message, wherein the second message includes a create connection response message, wherein the third message includes a secondary base station release required message, and wherein the fourth message includes a terminate connection request message.

In another embodiment, a method by a second master base station in a wireless communication system supporting a dual connectivity, the method comprising: receiving, from a first master base station associated with a secondary base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, allocating a resource to the first IP tunnel for establishing the first IP tunnel and transmitting, to the first master base station, a second message to establish a second IP tunnel between the first master base station and the second master base station.

Preferably, further comprising: releasing resources for the first IP tunnel and the second IP tunnel if a third message to release the first IP tunnel and the second IP tunnel is received from the first master base station.

Preferably, wherein the first message includes a create connection request message, wherein the second message includes a create connection response message, wherein the third message includes a terminate connection request message.

In another embodiment, A method by a secondary base station associated with a first master base station in a wireless communication system supporting a dual connectivity, the method comprising: receiving, from a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, allocating a resource to the first IP tunnel for establishing the first IP tunnel and after a second IP tunnel between the first master base station and the second master base station is established, receiving, from the first master base station, a second message to release a third IP tunnel between the first master base station and the secondary base station.

In another embodiment, A first master base station associated with a secondary base station in a wireless communication system supporting a dual connectivity, the first master base station comprising: a transceiver configured to transmit and receive a signal and a controller configured to transmit, to a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, to establish a second IP tunnel between the first master base station and the second master base station if a second message is received, and to transmit, to the secondary base station, a third message to release a third IP tunnel between the first master base station and the secondary base station.

Preferably, wherein the controller is further configured to transmit, to the second master base station, a fourth to release the first IP tunnel and the second IP tunnel if a session for the user data is terminated.

In another embodiment, a second master base station in a wireless communication system supporting a dual connectivity, the second master base station comprising: a transceiver configured to transmit and receive a signal and a controller configured to receive, from a first master base station associated with a secondary base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, to allocate a resource to the first IP tunnel for establishing the first IP tunnel, and to transmit, to the first master base station, a second message to establish a second IP tunnel between the first master base station and the second master base station.

Preferably, wherein the controller is further configured to release resources for the first IP tunnel and the second IP tunnel if a third message to release the first IP tunnel and the second IP tunnel is received from the first master base station.

In another embodiment, a secondary base station associated with a first master base station in a wireless communication system supporting a dual connectivity, the secondary base station comprising: a transceiver configured to transmit and receive a signal and a controller configured to receive, from a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, to allocate a resource to the first IP tunnel for establishing the first IP tunnel, and after a second IP tunnel between the first master base station and the second master base station is established, to receive, from the first master base station, a second message to release a third IP tunnel between the first master base station and the secondary base station.

The present disclosure relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates beyond 4th-Generation (4G) communication system such as long term evolution (LTE). Embodiments of the present disclosure provide an enabling flexible numerology in multi-user MIMO systems.

For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:

FIGURE 1 illustrates an example of wireless communication network according to embodiments of the present disclosure;

FIGURE 2 illustrates an example unified wireless backhaul and access system according to embodiments of the present disclosure;

FIGURE 3 illustrates an example unified wireless backhaul and access system with different anchor BS association by the relay BS and the UE according to embodiments of the present disclosure;

FIGURE 4 illustrates an example of dual connectivity;

FIGURE 5 illustrates an example Use of same CPF/UPF for supporting SeNB according to embodiments of the present disclosure;

FIGURE 6A and FIGURE 6B illustrate an example Call flow for same CPF/UPF supporting SeNB according to embodiments of the present disclosure;

FIGURE 7 illustrates an example Call flow for same CPF/UPF supporting multiple connectivity with SeNB according to embodiments of the present disclosure;

FIGURE 8A and FIGURE 8B illustrate an example Call flow showing preservation of SeNB Context according to embodiments of the present disclosure;

FIGURE 9 illustrates an example Use of different CPF/UPF for supporting SeNB according to embodiments of the present disclosure;

FIGURE 10 illustrates an example Call flow for different CPF/UPF supporting SeNB according to embodiments of the present disclosure;

FIGURE 11A and FIGURE 11B illustrate an example Call flow for same CPF/UPF supporting SeNB (HO) according to embodiments of the present disclosure;

FIGURE 12A and FIGURE 12B illustrate an example Call flow showing preservation of SeNB Context (HO) according to embodiments of the present disclosure; and

FIGURE 13 illustrates an example Call flow for different CPF/UPF supporting SeNB (HO) according to embodiments of the present disclosure.

FIGURE 14 illustrates a block diagram illustrating a structure of a MeNB 1 according to an embodiment of the present disclosure.

FIGURE 15 illustrates a block diagram illustrating a structure of a MeNB 2 according to an embodiment of the present disclosure.

FIGURE 16 illustrates a block diagram illustrating a structure of a SeNB according to an embodiment of the present disclosure.

Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms “transmit,” “receive,” and “communicate,” as well as derivatives thereof, encompass both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, means to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The term “controller” means any device, system or part thereof that controls at least one operation. Such a controller may be implemented in hardware or a combination of hardware and software and/or firmware. The functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.

Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device.

Definitions for other certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases.

FIGURES 1 through FIGURE 13, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

The following document is hereby incorporated by reference into the present disclosure as if fully set forth herein: 3GPP TS 36.300 v13.0.0, “E-UTRA and E-UTRAN, Overall description, Stage 2.”

The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission coverage, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques and the like are discussed in 5G communication systems.

In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul communication, moving network, cooperative communication, coordinated multi-points (CoMP) transmission and reception, interference mitigation and cancellation and the like.

In the 5G system, hybrid frequency shift keying and quadrature amplitude modulation (FQAM) and sliding window superposition coding (SWSC) as an adaptive modulation and coding (AMC) technique, and filter bank multi carrier (FBMC), non-orthogonal multiple access(NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

Depending on the network type, the term “base station” or “BS” can refer to any component (or collection of components) configured to provide wireless access to a network, such as transmit point (TP), transmit-receive point (TRP), an enhanced base station (eNodeB or eNB), a 5G base station (gNB), a macrocell, a femtocell, a WiFi access point (AP), or other wirelessly enabled devices. Base stations may provide wireless access in accordance with one or more wireless communication protocols, e.g., 5G 3GPP new radio interface/access (NR), long term evolution (LTE) , LTE advanced (LTE-A) , high speed packet access (HSPA), Wi-Fi 802.11a/b/g/n/ac, etc. For the sake of convenience, the terms “BS” and “TRP” are used interchangeably in this patent document to refer to network infrastructure components that provide wireless access to remote terminals. Also, depending on the network type, the term “user equipment” or “UE” can refer to any component such as “mobile station,” “subscriber station,” “remote terminal,” “wireless terminal,” “receive point,” or “user device.” For the sake of convenience, the terms “user equipment” and “UE” are used in this patent document to refer to remote wireless equipment that wirelessly accesses a BS, whether the UE is a mobile device (such as a mobile telephone or smartphone) or is normally considered a stationary device (such as a desktop computer or vending machine).

In wireless communication systems, several parameters are adapted on a UE-specific basis such as the modulation, the coding scheme or the rank of transmissions. However, in current cellular systems such as a long-term evolution (LTE), most numerology parameters such as the sub-carrier spacing or the length of the cyclic prefix (CP) for the users is cell-specific and common to the UEs. An LTE, for example, has a sub-carrier spacing of 15 kHz for transmissions (except for broadcast services using multicast- broadcast single-frequency network (MBSFN), which is fixed at 7.5 kHz sub-carrier spacing). For 5G communications, new requirements discussed would benefit from adaptation of the sub-carrier spacing and/or CP length on a per user basis.

In particular, varying the sub-carrier spacing depending on the UE can provide the some advantages. One advantage is low latency transmissions. In such example, wider sub-carrier spacing can lead to shorter symbol duration, which reduces the transmission latency. The FFT/IFFT size also reduces, which can reduce the power consumption requirements. Another advantage is improved channel estimation for high speed users. At higher speeds, there is lower correlation between channel measurements. Hence, channel estimation should be done more frequently, which can be enabled with shorter symbol duration or wider subcarrier spacing. This can be beneficial for vehicular communication systems. Yet another advantage is low peak-to average power ratio (PAPR), as smaller sub-carrier spacing can lower PAPR. Yet another advantage is to be able to better support large bandwidth systems. Using 15 KHz sub-carrier spacings for large bandwidth systems would require large FFT sizes, which may lead to implementation constraints. For example, a 120 MHz system would require a FFT of size 8192 or larger. If wider subcarrier spacing is utilized, the FFT size can be reduced. Yet another advantage is for better supporting mmWave systems. At mmWave frequencies, a larger sub-carrier spacing may be required to compensate for increased phase noise in the RF.

In particular, varying the CP length depending on the UE can provide advantages, including improved efficiency; since the CP is an overhead for the transmission, reducing the CP can lead to improved efficiency in transmission.

It has been shown that with under TDD channel reciprocity assumption, 64-Tx-antenna full-dimensional; multi-input multi-output (FD-MIMO) allowing high-order multi-user-MIMO (MU-MIMO) with signal-to-leakage-ratio (SLNR) precoding achieves up to ~6x cell-average and cell-edge throughput gain, as against 8-Tx-antenna baseline with maximum-ratio-transmission (MRT) transmissions.

When all-user-full-bandwidth (AUFB) scheduling method is used, a serving cell schedules the users served by the serving cell in the full BW with applying MU-MIMO precoding. The AUFB achieves almost 1.5x superior performance to PF-4. In addition to the performance benefits, AUFB scheduling has complexity benefits - the complexity is very small as compared to other methods. One of the challenges to use AUFB in practice is that eNB needs to have accurate channel state information (CSI) to realize this performance. In frequency division duplexing (FDD) systems in which CSI is obtained from UE feedback, the level of CSI accuracy may not be sufficient for AUFB/SLNR to achieve the performance, mainly owing to the quantization errors. However, in TDD systems, the CSI is obtained from channel sounding and channel reciprocity (with Tx/Rx calibration), which seem to be a more promising candidate for obtaining the performance of the AUFB/SLNR.

For FD-MIMO considered in 3GPP specification, it is assumed that the antennas equipped at the eNB are placed in a rectangular fashion. The FDD CSI feedback design is made according to this assumption, and the CSI feedback may not be able to be used for other antenna configurations, e.g., spherical or cylindrical antenna configurations. However, in TDD systems, channel sounding and channel reciprocity can be exploited to generate accurate CSI for any antenna configurations. Hence, it can be said that channel sounding based MIMO systems are more versatile to be used for various antenna configurations than CSI feedback based schemes.

The present disclosure relates generally to wireless communication systems. A communication system includes a DownLink (DL) that conveys signals from transmission points such as Base Stations (BSs) or eNodeBs to User Equipments (UEs) and an UpLink (UL) that conveys signals from UEs to reception points such as eNodeBs. A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a cellular phone, a personal computer device, etc. An eNodeB, which is generally a fixed station, may also be referred to as an access point or other equivalent terminology.

FIGURE 1 illustrates an example embodiment of a wireless communication network 100 according to this disclosure. As shown in FIGURE 5, the wireless network 100 includes an eNodeB (eNB) 101, an eNB 102, and an eNB 103. The eNB 101 communicates with the eNB 102 and the eNB 103. The eNB 101 also communicates with an Internet Protocol (IP) network 130, such as the Internet, a proprietary IP network, or other data network. The eNB 102 and the eNB 103 are able to access the network 130 via the eNB 101 in this example.

The eNB 102 provides wireless broadband access to the network 130 (via the eNB 101) to user equipment (UE) within a coverage area 120 of the eNB 102. The UEs here include UE 111, which may be located in a small business (SB); UE 112, which may be located in an enterprise (E); UE 113, which may be located in a WiFi hotspot (HS); UE 114, which may be located in a first residence (R); UE 115, which may be located in a second residence (R); and UE 116, which may be a mobile device (M) (such as a cell phone, wireless laptop computer, or wireless personal digital assistant). Each of the UEs 111-116 may represent a mobile device or a stationary device. The eNB 103 provides wireless broadband access to the network 130 (via the eNB 101) to UEs within a coverage area 125 of the eNB 103. The UEs here include the UE 115 and the UE 116. In some embodiments, one or more of the eNBs 101-103 may communicate with each other and with the UEs 111-116 using LTE or LTE-A techniques. Additionally, one or more of the eNBs 101-103 can communicate using inter-eNB coordination methods as described herein.

Dotted lines show the approximate extents of the

coverage areas

120 and 125, which are shown as approximately circular for illustration and explanation only. The

coverage areas

120 and 125 may have other shapes, including irregular shapes, depending upon factors like the configurations of the eNBs and variations in radio environments associated with natural and man-made obstructions.

Depending on the network type, other well-known terms may be used instead of “eNodeB” or “eNB” for each of the components 101-103, such as “base station” or “access point.” For the sake of convenience, the terms “eNodeB” and “eNB” are used here to refer to each of the network infrastructure components that provides wireless access to remote wireless equipment. Also, depending on the network type, other well-known terms may be used instead of “user equipment” or “UE” for each of the components 111-116, such as “mobile station” (MS), “subscriber station” (SS), “remote terminal” (RT), “wireless terminal” (WT), and “user device.” For the sake of convenience, the terms “user equipment” and “UE” are used here to refer to remote wireless equipment that wirelessly accesses an eNB, whether the UE is a mobile device (such as a cell phone) or is normally considered a stationary device (such as a desktop computer or vending machine).

In some embodiments, the eNBs 101-103 may communicate with each other and with the UEs 111-116 using Orthogonal Frequency-Division Multiplexing (OFDM) or Orthogonal Frequency-Division Multiple Access (OFDMA) techniques. Also, each eNB 101-103 can have a globally unique identifier, such as a unique base station identifier (BSID). A BSID is often a media access control (MAC) identifier. Each eNB 101-103 can have multiple cells (such as when one sector represents one cell), and each cell can have a physical cell identifier or a preamble sequence, which is often carried in a synchronization channel.

Although FIGURE 1 illustrates one example of a wireless network 100, various changes may be made to FIGURE 1. For example, the network 100 could include any number of eNBs and any number of UEs in any suitable arrangement. Also, the eNB 101 could communicate directly with any number of UEs and provide those UEs with wireless broadband access to the network 130. Further, the eNB 101 could provide access to other or additional external networks, such as an external telephone network. In addition, the makeup and arrangement of the wireless network 100 is for illustration only.

According to [1], E-UTRAN supports Dual Connectivity (DC) operation whereby a multiple Rx/Tx UE in RRC_CONNECTED is configured to utilize radio resources provided by two distinct schedulers, located in two eNBs connected via a non-ideal backhaul over the X2 interface. eNBs involved in DC for a certain UE may assume two different roles: an eNB may either act as an MeNB or as an SeNB. In DC a UE is connected to one MeNB and one SeNB. The configured set of serving cells for a UE includes of two subsets: the Master Cell Group (MCG) containing one or more serving cells of the MeNB, and the Secondary Cell Group (SCG) containing one or more serving cells of the SeNB.

A base station (BS) can provide wireless access services to one or more UEs on one or more frequency bands. In addition, the BS can also provide wireless backhaul services to one or more relay BSs on all or a subset of the frequency bands used for the BS’s wireless access services, without minimum or no performance impact to its serving UEs. Such BS is referred to as an anchor BS. A relay BS can also have wired backhaul connection to the anchor BS. The relay BS provides wireless access services to multiple UEs on one or more frequency bands used as backhaul between the anchor BS and the relay BS. In other words, the time-frequency resources of a frequency band are shared among the wireless access of the anchor BS, the wireless access of the relay BS and the wireless backhaul of the relay BS. The relay BS supports eNB functionality. From a UE’s perspective, the relay BS is seen as an eNB. The present disclosure can enable a new relay BS to be deployed and attached to an anchor BS, or an idle relay BS to be activated, without the need to install wired backhaul connection between the anchor BS and the relay BS, and with minimum or no negative performance impact to the other relay BSs that are either wirelessly attached or wired to the same anchor BS, and the UEs served by the anchor BS and the other relay BSs. Such wireless system is called a unified wireless backhaul and access network.

FIGURE 2 illustrates an example unified wireless backhaul and access system according to embodiments of the present disclosure. Referring to FIGURE 2, an anchor BS (210) is configured with two frequency bands (f1 and f2) where f1 has a larger coverage area (250) than that of f2 (260), because f1 is of lower frequency (e.g. 600MHz - 2GHz) than that of f2 (e.g. 3GHz - 300GHz). A relay BS (230) is configured with one frequency band (f2) with coverage area 270. A UE 220 which is within the coverage at f1 of the anchor BS but is out of coverage of the anchor BS or relay BS at f2 is served by the anchor BS via the access link 221. A UE 240 which is within the coverage of the relay BS 230 at f2 can be associated with the relay BS 230 at f2 with access link 242. When the UE is also within the coverage of the anchor BS at f1, the UE can also be associated with the anchor BS at f1 with access link 241 simultaneously using a dual connectivity or a carrier aggregation configuration. In this case, the control plane signaling (RRC and mobility handling) and/or high QoS data can be delivered to the UE via f1, and best effort traffic can be delivered to the UE via f2. In case of dual connectivity, from the UE’s perspective the anchor BS is the MeNB and the relay BS is the SeNB. In one alternative, both DL and UL are supported for relay BS-UE communications. In another alternative, only DL may be supported for relay BS-UE communications and the UL is supported via UE-to-anchor BS communications.

It is noted that a standalone system based on frequency f2 is also possible. In this case, frequency f1 in Figure 2 as well as the corresponding connection 221 between UEs to the anchor BS on f1 are not present.

In certain deployment scenarios, a UE can be associated with a first anchor BS at f1 and a relay BS at f2, but the anchor BS that the relay BS is associated with, or is attached to, is a second anchor BS (i.e. not the same as the first anchor BS). This configuration is beneficial when the relay BS is actually not within the coverage of the first anchor BS at f2 or if the backhaul link to the first anchor BS is not suitable due to poor SINR condition (such as a result of blockage).

FIGURE 3 illustrates an example unified wireless backhaul and access system with different anchor BS association by the relay BS and the UE according to embodiments of the present disclosure. Referring to FIGURE 3, the relay BS (330) is associated with, or is attached to, anchor BS 380 (with backhaul link 332), whereas its served UE 240 is associated with the anchor BS 210 at f1. When the UE is configured with dual connectivity, the anchor BS 210 is the MeNB and the relay BS 330 is the SeNB.

In the above example, it may be necessary that SeNB has an ability to connect to a different Master eNB (MeNB) than the one providing coverage layer for UE when the UE is in Dual Connectivity (DC) mode. In this scenario, the UE will communicate to Secondary eNB (SeNB) of MeNB2 and MeNB1 simultaneously. Existing 3GPP specification allows single CPF to control traffic for MeNB and SeNB. In this scenario, having a single CPF may not always be possible. The present disclosure provides a solution so that same CPF will able to manage resources from MeNB and SeNB resided under different MeNB.

As defined in 3GPP TS 36.300 v13.0.0, there is one AN-CPF connection for the UE between the MeNB (Master eNB) and the CPF when it is in DC mode. AN-CPF connection represents connectivity between the Access Network (AN) and the Control Plane Function (CPF) resided in the network. CPF is the controlling entity in the network which is responsible for managing resources for mobility and session/connection management. In EPC, it will be Mobile Management Entity (MME) while in 5G next generation architecture, it is Session Management Function (SM). The AN-CPF function is equivalent to S1-MME interface in 4G while it could be the interface between the AN and SM (potentially via Mobility Management function) in 5G next generation architecture. Similarly, AN-UPF connection represents bearer connection between the AN and the User Plane Function (UPF) in the network. The UPF is the user plane/bearer entity in the network which is responsible for transmitting user data. In the EPC it is the user plane function of the Serving Gateway (SGW) and also PDN Gateway (PGW). In this document, UPF represents entity similar to SGW in the EPC. In 5G next generation, UPF is referred as User Plane or User Plane Function.

FIGURE 4 illustrates an example of dual connectivity.

If the UE is connected to a SeNB in a different area which is not covered by MeNB1 but is covered by another MeNB (MeNB2), it is not always possible to just have single control interface since the CPF for MeNB1 (CPF1) and MeNB2 might be different (CPF2). Since the CPF selects corresponding UPF for user data transmission, the UPF may also be different in those cases. This brings up the following two options for supporting the SeNB in a different area which is not covered by MeNB1: continue to use existing CPF1 and UPF1 for MeNB1 and SeNB; and/or continue to use existing CPF1 and UPF1 for MeNB1 and establish new connectivity for SeNB with CPF2 and UPF2.

There is a need to support a procedure to set up a SeNB that is covered by (or attached to) a different MeNB (MeNB 2) than that serving the UE (MeNB1). In addition, due to UE mobility, there is also a need to support a procedure to perform SCG handover from a SeNB covered by (or attached to) the MeNB serving the UE (MeNB1) to another SeNB covered by (or attached to) another MeNB (MeNB2). For both procedures, MeNB1 determines that SeNB is now in the area supported under new MeNB (MeNB2). Such determination can be based on physical layer RRM measurement results reported by the UE. Receipt of this request at the MeNB2 over X2-C for SCG configuration or SCG handover is considered a trigger for supporting either option 1 or option 2 detailed as a part of this disclosure.

This disclosure is applicable for supporting above two options for the following scenarios where SeNB may be stationary or mobile: the coverage of the SeNB with existing MeNB may fades away due to signal blockage and hence there is a need of having multiple backhaul (connectivity between SeNB and multiple MeNB); and when UE roams to a new location of different SeNB attached to different MeNB.

FIGURE 5 illustrates an example Use of same CPF/UPF for supporting SeNB according to embodiments of the present disclosure.

Description in this disclosure refers having an IP tunnel for X2-U interface. There are no technical reasons for limiting this as just IP tunnel. It could also be non-IP tunnel.

Option 1a: Use of same CPF/UPF for supporting Target SeNB (signal blockage). This is the solution in which CPF1 can still be able to manage resources of MeNB1 as well as SeNB. To do so, it may be necessary that control and user data is sent between SeNB and MeNB1 via MeNB2. This can be achieved by supporting X2-C and X2-U interfaces between MeNB1 and MeNB2. In this case, SeNB supports split model where user data is transmitted through MeNB2. X2-U is transmitted over dedicated IP tunnel which may or may not be specific to 3GPP. For 4G, this IP tunnel could be IP tunnel.

FIGURE 6A and FIGURE 6B illustrate an example Call flow for same CPF/UPF supporting SeNB according to embodiments of the present disclosure.

As shown in FIGURE 6A, Step 1: The MeNB1 determines that signal strength with the SeNB has been weakened. It sends a SeNB Create Connection Request message over an X2-C interface to the MeNB2 which is a master eNB under which SeNB is resided. This request includes the Secondary Cell Group (SCG) configuration of the SeNB, bearers for which dual connectivity is configured, type of bearer connectivity and resources such as ports, tunnel identifiers etc. to be used for establishing IP tunnel (X2-U) between two MeNBs.

Step 2: The MeNB2 allocates resources for establishing IP tunnel with the targeted SeNB. It then sends an Establish Tunnel Request message to the SeNB along with the tunnel identifiers. Upon receipt of this message, the SeNB allocates IP tunnel resources and sends its tunnel identifiers to the MeNB2 in the Establish Tunnel Response message. If there are no enough resources available at the MeNB2 or SeNB, a failure message is returned to the MeNB1. Otherwise the MeNB2 initiates IP tunnel establishment with the MeNB1 after allocating resources. This information is sent to the MeNB1 in the Create Connection Response message.

Step 3: The MeNB1 instructs SeNB to release IP tunnel connection which was established between the MeNB1 and SeNB. The user data is transferred through the IP tunnel between two MeNB2 and the also between the SeNB and MeNB2.

Step 4: After some time, the session terminates. At that time, the MeNB1 sends a Terminate Connection Request to the current MeNB serving the SeNB which may have been requested to establish IP tunnel for this session earlier. The above figure shows this message sent to the MeNB2.

Step 5: Once this connection termination is received from the MeNB1, the MeNB2 instructs SeNB to release IP tunnel connection which was established between the MeNB2 and SeNB. It also releases resources for the tunnel established with the MeNB1. The MeNB2 sends a Terminate Connection Response message to the MeNB1 indicating successful deallocation of the resources. Procedures that may be necessary for connection reconfiguration between the UE and MeNBs and/or between the new MeNB and SeNB are not described in lengthy detail herein in the interests of brevity. Refer to 3GPP TS 36.300 v13.0.0 for further details and references

Option 1b: Multiple Connectivity Support (signal blockage). In the above discussion, the connectivity between the MeNB1 and SeNB is released once the connectivity between the new MeNB (MeNB2) and SeNB is established and confirmed. In the situation where the connection between the SeNB and MeNB1 fades away due to temporary blockage or similar situations, it is possible that the signal between SeNB and MeNB1 becomes stronger again due to clearing of the earlier blockage after attaching to the MeNB2. If the connectivity between MeNB1 and SeNB was released as a result of weaker signal strength (blockage), it may be necessary to re-establish the connectivity between them for normal operation.

One of the option is to preserve the previously established connectivity between MeNB1 and SeNB. The MeNB1 will make use of total number of connection contexts allowed and total number of current connections and decide whether to save context of the previous connectivity. For that it may be necessary to have a system-wide provisioning parameter determining how many connection context can be saved for a given UE. Information/count on the total number of current connections is managed at the MeNB. Note that at a given time, there is one connection context active between MeNB1 and SeNB. If the total number of current connection contexts exceeds the total number of connection contexts allowed, the MeNB1 may use local policy to manage existing connection contexts. It may make intelligent use of existing radio strength to determine which connection contexts are out of reach (and hence released) based on current coverage.

FIGURE 7 illustrates an example Call flow for same CPF/UPF supporting multiple connectivity with SeNB according to embodiments of the present disclosure.

The following example scenario shows the impact on the roaming when the UE roams back to the location of MeNB1 from the area of MeNB2.

FIGURE 8A and FIGURE 8B illustrate an example Call flow showing preservation of SeNB Context according to embodiments of the present disclosure.

First two steps shown in top shaded part of the above figure is similar to figure 6A and figure 6B. The additional steps are discussed as below:

Step 3: Instead of instructing SeNB to release resources for X2-U connection between the MeNB1 and SeNB, MeNB1 instructs SeNB to stop transmitting data for this UE. As a result of this step, the connection (tunnel) established between MeNB1 and SeNB still remains intact but the status of the connectivity context becomes Inactive. The MeNB1 sends an Active Transfer Request to the SeNB along with the MeNB2 address to make it aware that data transmission will be using new X2-U interface between MeNBs and MeNB2 and SeNB. It is recommended to monitor the duration of this inactive status of each inactive IP tunnel by using timer or similar mechanism. This will prevent holding tunnel resources too long and avoid any potential system specific issues.

Step 4: At the later time, the UE moves back to the location area of MeNB1. At that time, MeNB1 informs MeNB2 to stop data transmission toward SeNB by sending Data Transfer Stop Request message

Step 5: The MeNB2 instructs the SeNB to deactivate X2-U tunnel status by sending Deactivate Transfer Request message. After getting successful response from the SeNB, the MeNB2 responds MeNB1 with the Data Transfer Stop Response message.

Step 6: Upon receipt of the response from MeNB2, the MeNB1 informs SeNB to resume data transmission with it by sending Active Transfer Request with its address. This resumes data transfer using X2-U tunnel between the SeNB and MeNB1.

Step 7: After some time, the session terminates. At that time, the MeNB1 sends a Terminate Connection Request to the MeNBs which may have been requested to establish IP tunnel for this session earlier. The figure 8B shows this message sent to the MeNB2.

Step 8: Once this connection termination is received from the MeNB1, the MeNB2 instructs SeNB to release IP tunnel which was established between the MeNB2 and SeNB. It also releases resources for the tunnel established with the MeNB1. The MeNB2 sends a Terminate Connection Response message to the MeNB1 indicating successful deallocation of the resources.

Step 9: the MeNB1 also instructs SeNB to release IP tunnel which was established between the MeNB1 and SeNB. This completes the release of the resources associated with supporting multiple backhauls.

As indicated in the above call flow steps, management of the connectivity context is done by MeNB1. Once the data session of this UE is released, MeNB1 will communicate with the relevant MeNBs having active or inactive connectivity status and request them to release the resources used for that UE session by explicitly sending Terminate Connection Request message to them. Note that one user plane connection (X2-U) remains active at a time between the SeNB and MeNB. Procedures that may be necessary for connection reconfiguration between the UE and MeNBs and/or between the new MeNB and SeNB are not described in lengthy detail herein in the interests of brevity. Refer to 3GPP TS 36.300 v13.0.0 for further details and references.

FIGURE 9 illustrates an example Use of different CPF/UPF for supporting SeNB according to embodiments of the present disclosure.

Option 2: Use of different CPF/UPF for supporting Target SeNB (signal blockage). As defined in 3GPP TS 36.300 v13.0.0, there is one AN-CPF connection for the UE between the MeNB (Master eNB) and the CPF when it is in DC mode. This option relaxes this limitation and allows having control and user place connectivity with the CPF and UPF respectively in the area served by another master eNB (referred as MeNB2) in this document. This is illustrated in FIGURE 9.

FIGURE 10 illustrates an example Call flow for different CPF/UPF supporting SeNB according to embodiments of the present disclosure.

Step 1: The MeNB1 determines that the signal strength with SeNB has weakened. It sends a SeNB Create Connection Request message over an X2-C interface to the MeNB2 which is a master eNB under which SeNB is resided. This request includes the SCG configuration of the SeNB, type of bearer connectivity and bearers for which dual connectivity is configured.

Step 2: Upon receipt of the Create Connection Request, the MeNB2 initiates establishment of AN-UPF tunnel by sending Establish Connection Request to the SeNB. The SeNB then establishes AN-UPF connection as defined by 3GPP specification 3GPP 29.060. Upon successful establishment of this AN-UPF tunnel between SeNB and UPF2, the MeNB2 is notified which then responds with Establish Connection Response to the MeNB1.

Step 3: The MeNB1 instructs SeNB to release AN-UPF connection with the UPF1. At this stage, the user data is transferred over AN-UPF interface between the SeNB and UPF2 while the signaling/control for that is supported by the CPF2.

Step 4: After some time, the session terminates. At that time, the MeNB2 deallocates/releases the resources for AN-UPF. Procedures that may be necessary for connection reconfiguration between the UE and MeNBs and/or between the new MeNB and SeNB and new establishment of AN-UPF requiring potential update of the user plane path towards the UPF2 are not described in lengthy detail herein in the interests of brevity. Refer to 3GPP TS 36.300 v13.0.0 for further details and references.

FIGURE 11A and FIGURE 11B illustrate an example Call flow for same CPF/UPF supporting SeNB (HO) according to embodiments of the present disclosure.

Option 3a: Use of same CPF/UPF for supporting Target SeNB (handover to new SeNB due to mobility). This is the inter MeNB handover where the UE roams from the serving SeNB area to target SeNB are under a new MeNB (MeNB2). In this solution CPF1 can still be able to manage bearer resources of MeNB. To do so, it may be necessary that control and user data is sent between target SeNB and MeNB1 via MeNB2. This can be achieved by supporting X2-C and X2-U interfaces between MeNB1 and MeNB2. In this case, SeNB supports split model where user data is transmitted through MeNB2. X2-U is also referred as IP tunnel in this document since it is using IP tunnel to exchange user data. The following figure illustrates an example call flow which provides brief details on steps involved for this scenario.

Step 1: The MeNB1 determines that SeNB is no longer having a strong signal and hence there is a need of handing over the session to the new SeNB. Since the target SeNB is in the area covered by another MeNB (MeNB2), the MeNB sends a SeNB a Create Connection Request message over an X2-C interface. This request includes the SCG configuration of the SeNB, the type of bearer used, bearers for which dual connectivity is configured, handover indication and tunnel identifiers to be used for establishing IP tunnel (X2-U) between two MeNBs.

Step 2: The MeNB2 allocates resources for establishing IP tunnel with the targeted SeNB. It then sends an Establish Tunnel Request message to the SeNB along with the tunnel identifiers. Upon receipt of this message, the SeNB allocates IP tunnel resources and sends its tunnel identifiers to the MeNB2 in the Establish Tunnel Response message. If there are no enough resources available at the MeNB2 or target SeNB, a failure message is returned to the MeNB1. Otherwise the MeNB2 initiate IP tunnel establishment with the MeNB1. This response is sent to the MeNB1 in the Create Connection Response message.

Step 3: The MeNB1 instructs source SeNB to release IP tunnel connection which was established between the MeNB1 and that SeNB. The user data is now transferred through the IP tunnel between two MeNB2 and the also between the target SeNB and MeNB2.

Step 5: Once this connection termination is received from the MeNB1, the MeNB2 instructs target SeNB to release IP tunnel which was established between the MeNB2 and target SeNB. It also releases resources for the tunnel established with the MeNB1. The MeNB2 sends a Terminate Connection Response message to the MeNB1 indicating successful deallocation of the resources. Procedures that may be necessary for connection reconfiguration between the UE and MeNBs and/or between the new MeNB and target SeNB are not described in lengthy detail herein in the interests of brevity. Refer to 3GPP TS 36.300 v13.0.0 for further details and references.

Option 3b: Multiple Connectivity Support (handover to new SeNB due to mobility). In option 3a, the connectivity between the MeNB1 and Serving SeNB is released once the connectivity between MeNB1 and SeNB is established and confirmed. In the situation where the UE roams in the boundary locations of MeNB1 and MeNB2, it is possible that UE roams back to MeNB1 area (due to Ping-Pong effect) from MeNB2 area. If the connectivity between MeNB1 and SeNB was released as a result of weaker signal strength, it may be necessary to re-establish the connectivity between them so that the UE can get coverage in that area.

One of the options is to preserve the previously established connectivity between MeNB1 and SeNB. The MeNB1 will make use of total number of connection contexts allowed and total number of current connections and decide whether to save context of the previous connectivity. For that it may be necessary to have a system-wide provisioning parameter determining how many connection context can be saved for a given UE. Information/count on the total number of current connections is managed at the MeNB. Note that at a given time, there is one connection context active between MeNB1 and SeNB. If the total number of current connection contexts exceeds the total number of connection contexts allowed, the MeNB1 may use local policy to manage existing connection contexts. It may make intelligent use of existing radio strength to determine which connection contexts are out of reach (and hence released) based on current coverage.

FIGURE 12A and FIGURE 12B illustrate an example Call flow showing preservation of SeNB Context (HO) according to embodiments of the present disclosure. FIGURE 12A and FIGURE 12B show an example scenario shows the impact on the roaming when the UE roams back to the location of MeNB1 from the area of MeNB2. First two steps shown in top shaded part of the above figure 12A is similar to FIGURE 6A. The additional steps are discussed as below:

Step 3: Instead of instructing source SeNB to release resources for X2-U connection between the MeNB1 and SeNB, MeNB1 instructs source SeNB to stop transmitting data for this UE. As a result of this step, the connection (tunnel) established between MeNB1 and serving SeNB still remains intact but the status of the connectivity context becomes Inactive. The MeNB1 sends an Active Transfer Request to the serving SeNB along with the MeNB2 address to make it aware that data transmission will be using new X2-U interface between MeNBs and MeNB2 and SeNB. It is recommended to monitor the duration of this inactive status of each inactive IP tunnel by using timer or similar mechanism. This will prevent holding tunnel resources too long and avoid any potential system specific issues.

Step 4: At the later time, the UE moves back to the location area of MeNB1. At that time, MeNB1 informs MeNB2 to stop data transmission toward target SeNB by sending Data Transfer Stop Request message.

Step 5: The MeNB2 instructs the target SeNB to deactivate X2-U tunnel status by sending Deactivate Transfer Request message. After getting successful response from the target SeNB, the MeNB2 responds MeNB1 with the Data Transfer Stop Response message.

Step 6: Upon receipt of the response from MeNB2, the MeNB1 informs SeNB to resume data transmission with it by sending Active Transfer Request with its address. This resumes data transfer using X2-U tunnel between the serving SeNB and MeNB1.

Step 7: After some time, the session terminates. At that time, the MeNB1 sends a Terminate Connection Request to the MeNBs which may have been requested to establish IP tunnel for this session earlier. The above figure shows this message sent to the MeNB2.

Step 8: Once this connection termination is received from the MeNB1, the MeNB2 instructs target SeNB to release IP tunnel which was established between the MeNB2 and SeNB. It also releases resources for the tunnel established with the MeNB1. The MeNB2 sends a Terminate Connection Response message to the MeNB1 indicating successful deallocation of the resources.

Step 9: the MeNB1 also instructs serving SeNB to release IP tunnel which was established between the MeNB1 and serving SeNB. This completes the release of the resources associated with supporting multiple backhauls.

As indicated in the above call flow steps, management of the connectivity context is done by MeNB1. Once the data session of this UE is released, MeNB1 will communicate with the relevant MeNBs having active or inactive connectivity status and request them to release the resources used for that UE session by explicitly sending Terminate Connection Request message to them. Note that one user plane connection (X2-U) remains active at a time between the SeNB and MeNB. Procedures that may be necessary for connection reconfiguration between the UE and MeNBs and/or between the new MeNB and SeNB are not described here for simplicity. Refer to 3GPP TS 36.300 v13.0.0 for further details and references.

Option 4: Use of different CPF/UPF for supporting Target SeNB (handover to new SeNB due to mobility). As defined in 3GPP TS 36.300 v13.0.0, there is one AN-CPF connection for the UE between the MeNB (Master eNB) and the CPF when it is in DC mode. This option relaxes this limitation and allows having control and user place connectivity with the CPF and UPF respectively in the area served by another master eNB (referred as MeNB2) in this document. This is illustrated in FIGURE 9. FIGURE 13 illustrates an example call flow which provides brief details on steps involved for this scenario.

Step 1: The MeNB1 determines that SeNB is no longer having a strong signal and hence there is a need of handing over the session to the new SeNB. Since the target SeNB is in the area covered by another MeNB (MeNB2), the MeNB sends a SeNB a Create Connection Request message over an X2-C interface. This request includes the SCG configuration of the SeNB, type of bearer used (relay vs AN-UPF), handover indication, bearers for which dual connectivity is configured and tunnel identifiers to be used for establishing IP tunnel (X2-U) between two MeNBs.

Step 2: Upon receipt of the Create Connection Request, the MeNB2 initiates establishment of AN-UPF tunnel by sending Establish Connection Request to the target SeNB. The target SeNB then establishes AN-UPF connection as defined by 3GPP specification 3GPP 29.060. Upon successful establishment of this AN-UPF tunnel between target SeNB and UPF2, the MeNB2 is notified which then responds with Establish Connection Response to the MeNB1.

Step 3: The MeNB1 instructs serving SeNB to release AN-UPF connection with the UPF1. At this stage, the user data is transferred over AN-UPF interface between the target SeNB and UPF2 while the signaling/control for that is supported by the CPF2.

Step 4: After some time, the session terminates. At that time, the MeNB2 deallocates/releases the resources for AN-UPF.

Procedures that may be necessary for connection reconfiguration between the UE and MeNBs and/or between the new MeNB and SeNB and new establishment of AN-UPF requiring potential update of the user plane path towards the UPF2 are not described in lengthy detail herein in the interests of brevity. Refer to 3GPP TS 36.300 v13.0.0 for further details and references.

FIGURE 14 is a block diagram illustrating a structure of a MeNB1 according to an embodiment of the present disclosure.

In reference to FIG. 14, the MeNB1 1400 may include a transceiver 1410 for transmitting and receiving a signal and a controller 1430 for controlling overall operations of the MeNB1 1400.

The controller 1430 may transmit, to a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, establish a second IP tunnel between the first master base station and the second master base station if a second message is received, and transmit, to the secondary base station, a third message to release a third IP tunnel between the first master base station and the secondary base station.

The operations of the MeNB1 1400 and the controller 1430 are not limited to the above description made with FIG. 14, and they may include all MeNB1 operations described with reference to from FIG. 1 to FIG. 13.

FIGURE 15 is a block diagram illustrating a structure of a MeNB2 according to an embodiment of the present disclosure.

In reference to FIG. 15, the MeNB2 1500 may include a transceiver 1510 for transmitting and receiving a signal and a controller 1530 for controlling overall operations of the MeNB2 1500.

The controller 1530 may receive , from a first master base station associated with a secondary base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, allocate a resource to the first IP tunnel for establishing the first IP tunnel, and transmit, to the first master base station, a second message to establish a second IP tunnel between the first master base station and the second master base station.

The operations of the MeNB2 1500 and the controller 1530 are not limited to the above description made with FIG. 15, and they may include all MeNB2 operations described with reference to from FIG. 1 to FIG. 13.

FIGURE 16 is a block diagram illustrating a structure of a SeNB 1 according to an embodiment of the present disclosure.

In reference to FIG. 16, the SeNB 1600 may include a transceiver 1610 for transmitting and receiving a signal and a controller 1630 for controlling overall operations of the SeNB1 1600.

The controller 1630 may receive, from a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, allocate a resource to the first IP tunnel for establishing the first IP tunnel, and after a second IP tunnel between the first master base station and the second master base station is established, receive, from the first master base station, a second message to release a third IP tunnel between the first master base station and the secondary base station.

The operations of the SeNB 1600 and the controller 1630 are not limited to the above description made with FIG. 16, and they may include all SeNB operations described with reference to from FIG. 1 to FIG. 13.

Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.

None of the description in this application should be read as implying that any particular element, step, or function is an essential element that must be included in the claims scope. The scope of patented subject matter is defined only by the claims. Moreover, none of the claims are intended to invoke 35 U.S.C. § 112(f) unless the exact words “means for” are followed by a participle.

Claims

A method by a first master base station associated with a secondary base station in a wireless communication system supporting a dual connectivity, the method comprising:

transmitting, to a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station;

establishing a second IP tunnel between the first master base station and the second master base station if a second message is received; and

transmitting, to the secondary base station, a third message to release a third IP tunnel between the first master base station and the secondary base station.
The method of claim 1, wherein user data is transferred from the first master base station to the secondary base station via the second master base station based on the first IP tunnel and the second IP tunnel, and

wherein the user data is transmitted from the secondary base station to a terminal which is connected to the secondary base station.
The method of claim 2, further comprising:

transmitting, to the second master base station, a fourth to release the first IP tunnel and the second IP tunnel if a session for the user data is terminated,

wherein the first message includes a create connection request message,

wherein the second message includes a create connection response message, wherein the third message includes a secondary base station release required message, and

wherein the fourth message includes a terminate connection request message.
A method by a second master base station in a wireless communication system supporting a dual connectivity, the method comprising:

receiving, from a first master base station associated with a secondary base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station;

allocating a resource to the first IP tunnel for establishing the first IP tunnel; and

transmitting, to the first master base station, a second message to establish a second IP tunnel between the first master base station and the second master base station.
The method of claim 4, wherein user data is transferred from the first master base station to the secondary base station via the second master base station based on the first IP tunnel and the second IP tunnel, and

wherein the user data is transmitted from the secondary base station to a terminal which is connected to the secondary base station.
The method of claim 5, further comprising:

releasing resources for the first IP tunnel and the second IP tunnel if a third message to release the first IP tunnel and the second IP tunnel is received from the first master base station,

wherein the first message includes a create connection request message,

wherein the second message includes a create connection response message, and

wherein the third message includes a terminate connection request message.
A method by a secondary base station associated with a first master base station in a wireless communication system supporting a dual connectivity, the method comprising:

receiving, from a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station;

allocating a resource to the first IP tunnel for establishing the first IP tunnel; and

after a second IP tunnel between the first master base station and the second master base station is established, receiving, from the first master base station, a second message to release a third IP tunnel between the first master base station and the secondary base station.
The method of claim 7, wherein user data is transferred from the first master base station to the secondary base station via the second master base station based on the first IP tunnel and the second IP tunnel, and

wherein the user data is transmitted from the secondary base station to a terminal which is connected to the secondary base station.
A first master base station associated with a secondary base station in a wireless communication system supporting a dual connectivity, the first master base station comprising:

a transceiver configured to transmit and receive a signal; and

a controller configured to transmit, to a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, to establish a second IP tunnel between the first master base station and the second master base station if a second message is received, and to transmit, to the secondary base station, a third message to release a third IP tunnel between the first master base station and the secondary base station.
The first master base station of claim 9, wherein user data is transferred from the first master base station to the secondary base station via the second master base station based on the first IP tunnel and the second IP tunnel, and

wherein the user data is transmitted from the secondary base station to a terminal which is connected to the secondary base station.
The first master base station of claim 10,

wherein the controller is further configured to transmit, to the second master base station, a fourth to release the first IP tunnel and the second IP tunnel if a session for the user data is terminated,

wherein the first message includes a create connection request message,

wherein the second message includes a create connection response message, wherein the third message includes a secondary base station release required message, and

wherein the fourth message includes a terminate connection request message.
A second master base station in a wireless communication system supporting a dual connectivity, the second master base station comprising:

a transceiver configured to transmit and receive a signal; and

a controller configured to receive, from a first master base station associated with a secondary base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, to allocate a resource to the first IP tunnel for establishing the first IP tunnel, and to transmit, to the first master base station, a second message to establish a second IP tunnel between the first master base station and the second master base station.
The second master base station of claim 12, wherein user data is transferred from the first master base station to the secondary base station via the second master base station based on the first IP tunnel and the second IP tunnel, and

wherein the user data is transmitted from the secondary base station to a terminal which is connected to the secondary base station.
The second master base station of claim 13, wherein the controller is further configured to release resources for the first IP tunnel and the second IP tunnel if a third message to release the first IP tunnel and the second IP tunnel is received from the first master base station,

wherein the first message includes a create connection request message,

wherein the second message includes a create connection response message, and

wherein the third message includes a terminate connection request message.
A secondary base station associated with a first master base station in a wireless communication system supporting a dual connectivity, the secondary base station comprising:

a transceiver configured to transmit and receive a signal; and

a controller configured to receive, from a second master base station, a first message to establish a first internet protocol (IP) tunnel between the second master base station and the secondary base station, to allocate a resource to the first IP tunnel for establishing the first IP tunnel, and after a second IP tunnel between the first master base station and the second master base station is established, to receive, from the first master base station, a second message to release a third IP tunnel between the first master base station and the secondary base station,

wherein user data is transferred from the first master base station to the secondary base station via the second master base station based on the first IP tunnel and the second IP tunnel, and

wherein the user data is transmitted from the secondary base station to a terminal which is connected to the secondary base station.