WO2015167546A1

WO2015167546A1 - Transmission control for bearer split under dual connectivity

Info

Publication number: WO2015167546A1
Application number: PCT/US2014/036207
Authority: WO
Inventors: Amitav Mukherjee; Salam Akoum; Joydeep Acharya
Original assignee: Hitachi, Ltd.
Priority date: 2014-04-30
Filing date: 2014-04-30
Publication date: 2015-11-05

Abstract

Dual connectivity (DC) is a paradigm where a UE is equipped with multiple transmit/receive modules and consumes radio resources from one or more Master eNBs (MeNBs) and Secondary eNBs (SeNBs) simultaneously. In the downlink split bearer DC architecture, the MeNB splits an EPS bearer at the radio level and forwards a portion of the bearer contents to the SeNB which serves it to the UE. Example implementations described herein are directed to how the MeNB performs transmission control and buffer management of the split bearer with minimal coordination from the SeNBs.

Description

TRANSMISSION CONTROL FOR BEARER SPLIT UNDER DUAL

CONNECTIVITY

Field

[001] The present disclosure is generally related to wireless systems, and more specifically, to transmission control for base stations.

Related Art

[002] Dual connectivity (DC) is a paradigm where user equipment (UE) is equipped with multiple transmit/receive modules and consumes radio resources from one or more Master enhanced node Bs (MeNBs) and Secondary eNBs (SeNBs) simultaneously. In the downlink split bearer DC architecture, the MeNB splits an Evolved Packet System (EPS) bearer at the radio level and forwards a portion of the bearer contents to the SeNB which serves it to the UE.

[003] In the related art, the general network deployment of dual connectivity in Release 12 Long Term Evolution (Rel-12 LTE) with split bearers is shown in FIG. 1. The split bearer scenario is also known as architecture 3C in 3rd Generation Partnership Project (3GPP) terminology. The UE is assumed to be equipped with multiple transmitter and receiver modules. The MeNB and SeNB may operate on the same or different frequency bands. Within the MeNB there may be multiple component carriers that constitute a Master Cell Group. Similarly, the SeNB may control multiple component carriers that are the Secondary Cell group.

[004] FIG. 1 illustrates an example dual connectivity operation to a UE with a non-ideal backhaul between the MeNB and the SeNB.

[005] In FIG. 1, the Sl-U interface terminates in MeNB 100 and there is no direct link from the serving gateway (S-GW) to the SeNB 110. The MeNB 100 forwards split bearer traffic to the SeNB 110 via a non-ideal backhaul link. For the bearer split case, there is a separate and independent Radio Link Control (RLC) bearer, also at the UE 120 side, per eNB configured to deliver Packet Data Convergence Protocol (PDCP) Protocol Data Units

(PDUs) of the PDCP bearer, which terminates at the MeNB 100. Each PDCP entity has its own PDCP buffers implemented on a per radio bearer basis. This aspect is depicted in more detail in FIG. 2, where it is seen that the PDCP layer resides at the MeNB 200. In Long Term Evolution (LTE), the PDCP status report message is transmitted from the receiver PDCP entity to the transmitter PDCP entity to inform the transmitter PDCP about the PDCP PDUs that were received or not received by the receiver PDCP. Thus, non- received PDCP SDUs can be retransmitted and received PDCP SDUs need not be retransmitted. Related art buffer management methods for non-bearer split cases mostly use PDCP discard timers or random early detection (RED). Further description of the system in FIG. 2 is provided below.

Summary

[006] Example implementations described herein are directed to how the MeNB performs transmission control and buffer management of the split bearer with minimal coordination from the SeNBs.

[007] Aspects of the present disclosure may include a first base station configured to manage one or more second base stations. The first base station may include a memory configured to store information indicative of a quality of a radio link between a user equipment (UE) and the one or more second base stations; the UE being served by the first base station and the one or more second base stations; and a processor, configured to calculate a packet data convergence protocol (PDCP) data allocation ratio between the first base station and the one or more second base stations based on the information; transmit first data to the UE based on the PDCP data allocation ratio; and transmit second data to the one or more second base stations through a backhaul for transmission to the UE, based on the PDCP data allocation ratio.

[008] Aspects of the present disclosure may include a method involving managing at a first base station, information indicative of a quality of a radio link between a user equipment (UE) and one or more second base stations; the UE being served by the first base station and the one or more second base stations; calculating a packet data convergence protocol (PDCP) data allocation ratio between the first base station and the one or more second base stations based on the information; transmitting first data to the UE based on the PDCP data allocation ratio; and transmitting second data to the one or more second base stations through a backhaul for transmission to the UE, based on the PDCP data allocation ratio. [009] Aspects of the present disclosure may include a computer program containing instructions for executing a process, the instructions involving managing at a first base station, information indicative of a quality of a radio link between a user equipment (UE) and one or more second base stations; the UE being served by the first base station and the one or more second base stations; calculating a packet data convergence protocol (PDCP) data allocation ratio between the first base station and the one or more second base stations based on the information; transmitting first data to the UE based on the PDCP data allocation ratio; and transmitting second data to the one or more second base stations through a backhaul for transmission to the UE, based on the PDCP data allocation ratio. The computer program may be stored in a non-transitory computer readable medium.

Brief Description of the Drawings

[010] FIG. 1 illustrates an example dual connectivity operation to a UE with a non-ideal backhaul between the MeNB and the SeNB.

[011] FIG. 2 illustrates an example of logical entities within MeNB, SeNB and UE protocol stack for regular and split bearers.

[012] FIG. 3 illustrates an example MeNB and SeNB hardware configuration, in accordance with an example implementation.

[013] FIG. 4 illustrates an example flow diagram for the split bearer management module of an MeNB and communication with an SeNB, in accordance with an example implementation.

[014] FIG. 5 illustrates a flow diagram overview of PDCP buffer management by the MeNB under DC bearer split, in accordance with an example implementation.

Detailed description

[015] The following detailed description provides further details of the figures and example implementations of the present application. Reference numerals and descriptions of redundant elements between figures are omitted for clarity. Terms used throughout the description are provided as examples and are not intended to be limiting. For example, the use of the term "automatic" may involve fully automatic or semi-automatic implementations involving user or administrator control over certain aspects of the implementation, depending on the desired implementation of one of ordinary skill in the art practicing implementations of the present application. The terms enhanced node B (eNodeB), small cell (SC), base station (BS) and pico cell may be utilized interchangeably throughout the example implementations. The terms traffic and data may also be utilized interchangeably throughout the example implementations. The implementations described herein are also not intended to be limiting, and can be implemented in various ways, depending on the desired implementation.

[016] Possible difficulties in DC include the MeNB and SeNB schedulers operating independently, wherein a non-ideal backhaul link is assumed to exist between them. Thus, Transmission Time Interval (TTI) level coordination and Coordinated Multipoint Transaction (CoMP) or Coordinated Scheduling-Coordinated Beam forming (CS-CB) techniques may not be available for DC scenarios. In the split bearer DC architecture, the MeNB splits an EPS bearer at the radio level, and controls how much of the bearer contents are forwarded to the SeNB(s) and how much is transmitted by itself to the UE. Example implementations described herein include methods for MeNB transmission control and buffer management in the downlink split bearer case while taking into account backhaul latency.

[017] Example implementations may address various scenarios. For example, for cases where the MeNB has only statistical information regarding SeNB buffer levels and quality of SeNB-to-UE radio links, methods associated with the example implementations may be applied. Further, example implementations may be applied for when the MeNB has partial information regarding SeNB buffer levels and quality of SeNB-to-UEs radio links based on feedback reports from the SeNB(s) and/or UE.

[018] In example implementations, there is a method for PDCP buffer management and flow control by the MeNB in bearer split scenarios. In example implementations, a message sent by the MeNB to trigger PDCP status reporting from the UE may be utilized.

[019] FIG. 2 illustrates an example of logical entities within the MeNB, SeNB and UE protocol stack for regular and split bearers.

[020] To illustrate the problem solved by example implementations in the present disclosure, consider the case where a MeNB 200 configures bearer split with a single SeNB 201. However, it should be noted that the foregoing problem need not be solved to effectuate the example implementations, and that other problems or no problems may be solved without departing from the inventive concept.

[021] The logical entities at the MeNB 200, SeNB 201, and UE 202 are shown in FIG. 2. Here, the protocol stack including PDCP 210, RLC 215, and Medium Access Control (MAC) 225 entities at the MeNB 200 and PDCP 270, RLC 265, MAC 260 entities at the UE 202, respectively, correspond to a regular, non-split bearer that is transmitted via the MeNB 200. The split bearer involves MeNB 200 entities 230, 240, and 245, SeNB 201 entities 250 and 255, and UE 202 entities 275, 280, 285. Since no PDCP entity exists at the SeNB for the split bearer, the MeNB PDCP entity 230 must perform PDCP buffer management and flow control for the split bearer traffic. A general approach for MeNB buffer management is described below for various scenarios.

[022] FIG. 3 illustrates an example MeNB and SeNB hardware configuration, in accordance with an example implementation. The MeNB 300 and the SeNB 301 may interact with each other through an X2 or Xn interface 350, which is used to exchange traffic and communications for a bearer split operation between the MeNB 300 and the SeNB 301 via a backhaul. Data forwarding to the SeNB 301 for split bearers occurs via the X2 or Xn interface 350. In the example, only one SeNB is illustrated, however, the MeNB 300 may interact with multiple SeNBs depending on the desired implementation.

[023] MeNB 300 may include a processor 310, a main memory 315, and an I/O interface 335 that are communicatively coupled together by a communication bus 305. The processor 310 is configured to conduct aspects of split bearer management module 311 configured to perform buffer management and transmission control of the split bearer data as described in this disclosure with respect to FIG. 4. The main memory 315 is configured to store information indicative of a quality of a radio link between a user equipment (UE) and the SeNB; as well as modules for execution by the processor 310. Memory 315 may take the form of a computer readable storage medium (e.g., non-transitory) or can be replaced with a computer readable signal medium (e.g., non-transitory) as described in the disclosure. I/O interface 335 may be utilized to facilitate communications for an administrator of the MeNB 300.

[024] SeNB 301 is similarly configured to MeNB 300 and may include a processor 320, a main memory 325, and an I/O interface 345 that are communicatively coupled together by a communication bus 306. The processor 320 is configured to conduct operations for the SeNB 301. The main memory 325 is configured to store information for the SeNB 301 to perform operations and may be used as a buffer for sending traffic to associated UEs. Memory 325 may take the form of a computer readable storage medium (e.g., non- transitory) or can be replaced with a computer readable signal medium (e.g., non- transitory) as described in the disclosure. I/O interface 345 may be utilized to facilitate communications for an administrator of the SeNB 301.

[025] FIG. 4 illustrates an example flow diagram for the split bearer management module of an MeNB and communication with an SeNB, in accordance with an example implementation.

[026] At 400, the split bearer management module 311 configures the split bearer operation with the SeNB 301. The split bearer operation configuration is sent by the X2 interface if the MeNB 311 is a macro base station, or an Xn interface if the MeNB 311 is a small cell.

[027] At 401, the SeNB 301 receives and accepts the split bearer configuration from the split bearer management module 311 through the interface. If the SeNB 301 is configured to handle split bearer operations, then buffer levels and/or radio channel state information (CSI) is reported to the MeNB 311. Further detail for this flow is provided with respect to FIG. 5.

[028] At 402 the split bearer management module 311 receives the report from the SeNB and computes PDCP data routing for the SeNB. The computation for the PDCP data routing may be optimized over different parameters. Further detail for this flow is provided in the description below.

[029] At 403, the split bearer management module 311 initiates data forwarding to the SeNB 301. At 404, the SeNB 301 receives the data from the MeNB and forwards the PDCP data received from the MeNB to the associated UE.

[030] MeNB transmission control

[031] One difference between DC and Rel-11 CoMP transmission is that in CoMP, eNBs within the coordination set share CSI and optionally UE data, and can serve a UE on the same resource block (RB) if so desired. Furthermore, in coordinated scheduling (CS), eNBs within the CoMP coordination set logically have a single scheduler. In contrast, under DC, MeNB and SeNB can be configured with independent schedulers and operate with minimal coordination at the physical (PHY) layer.

[032] For MeNB buffer management with split bearers, the following situations may occur. Consider the case of DC split bearer operation involving 1 MeNB and N SeNBs, i.e., the MeNB can choose to forward a portion of the split bearer traffic to one or more SeNBs and serve the remaining bearer contents to the UE by itself. Let dt be the backhaul delay to the i^th SeNB, i = Ι, . , . ,Ν. The MeNB is denoted with index i = 0 and has backhaul delay d₀ = 0 .

[033] Let A (t) represent the total incoming traffic from higher (IP) layer at time t to the

MeNB PDCP entity (entity 230 in FIG. 2) for an EPS bearer that is split at radio level by the MeNB. A(t) can be a stationary stochastic process which is not controlled by the MeNB, wherein the statistics are assumed to be known to the MeNB via observation.

[034] Two deployment scenarios can be considered. In a first scenario the MeNB has error-free, reliable backhaul links to all the SeNBs, (e.g. via fiber). In a second scenario the MeNB has unreliable backhaul links to all the SeNBs, (e.g. via wireless links). The PDCP data allocation ratio can then be calculated based on these scenarios as described below.

[035] For the first scenario involving a reliable backhaul, the RLC buffer level or data queue at an arbitrary eNB evolves over discrete time steps as follows:

Q, [' + 1] = [■[_*] + A [t - d, ] - (1 - F_t [t ]) S, [t ] , i = 0, 1, ... , TV

(1)

Where [a]⁺ = max{a, 0}.

[036] Here, A_i [t] is the amount of PDCP traffic routed or forwarded over i^th SeNB by the MeNB at time t, such that ∑"₀A [^r] = ^[^r] _· ^O] i^{s a} Bernoulli random variable which represents the radio or PHY layer probability of link failure from eNB i to the UE. Each F_t [t] has the following distribution: Pr{ ₍ [/] = l} = p,

Pr{F_i [t] = = l- p_i

[037] 5, [t] is the amount of data served by the PHY layer at time t. s_t [t] is also a random variable since it is a function of the random eNB-to-UE wireless channels. The impact of backhaul delay is reflected in (1) where it is seen that data forwarded by the MeNB at time t arrives at the i^th SeNB after a delay of d{.

[038] For a second scenario with an unreliable backhaul, the RLC buffer level or data queue at an arbitrary eNB evolves as follows:

Qi [* + !] = [S ['] + A [t - d, ] (l - G, [t]) - (l - F_t [/]) S_t [t] , i = 0, 1, ... , TV

(2)

[039] Here, in addition to the parameters defined for (1), due to the unreliable backhaul an additional Bernoulli random variable G, [t] indicating MeNB-to-SeNB backhaul failure is introduced. Each G. [t] has the following distribution:

Pr{G, [/] = l} = ¾

Pr{G, [r] = 0} = l- ¾.

For the MeNB, Pr{G₀ [t] = 1} = 0 Vr.

[040] Example implementations address how the MeNB can optimize the data routing parameter vector [^, [?],..., [*]]^" · The traffic management policy adopted by the MeNB depends on the amount of information available to it regarding SeNB buffer levels, backhaul link quality, and radio link quality to the UEs. As described above, the following cases can arise. In a first case, the MeNB has only statistical information regarding SeNB buffer levels and quality of backhaul (if applicable) and SeNB-to-UE radio links. In a second case, the MeNB has partial information regarding SeNB buffer levels and quality of backhaul (if applicable) and SeNB-to-UEs radio links based on feedback reports from the SeNB(s) and/or UE.

[041] For either information case, a non-limiting example of an optimization criterion is to minimize the average difference between the PDCP data routed to a SeNB and the data it can actually serve over the radio link to the UE. This example implementation will mitigate the chance of buffer overflow at the SeNBs on average. For the first scenario with a reliable backhaul, the criterion is of the form

s.t.∑^N^ A, [t] = A [t], ft

(3)

[042] where £{■} denotes statistical expectation. For the second scenario with an unreliable backhaul, the criterion is of the form

(4)

[043] An alternative criterion may be to optimize _ [t] ,... , A_N [r]]^™ ₀ so as to keep the probability of any SeNB queue exceeding a certain size X below some pre-specified threshold, i.e., PT{Q_i . [t] > x}≤ ε for i = 0,1,... , 7V.

[044] For either scenario, the MeNB solves the optimization problem to obtain an initial PDCP traffic splitting allocation ratio, where the inputs to the optimization are based on statistical or partial CSI. The outcome of solving these optimization criteria is the optimal PDCP buffer management policy adopted by the MeNB for the split bearer. In an example implementation, the PDCP data allocation ratio can be calculated with the parameters as described above to minimize an average difference between PDCP data allocated to SeNBs associated with the MeNB and the buffer availability of the SeNBs. How the MeNB can acquire information regarding SeNB buffer levels and CSI parameters is described below.

[045] MeNB information acquisition

[046] The amount of coordination between MeNB and SeNB can be implemented in systems such as Rel-12 LTE. As a worst-case scenario, there may be no feedback from SeNBs regarding buffer levels or radio link CSI. In such a case, the MeNB may configure the UE to report Reference Signal Received Power (RSRP) or Reference Signal Received Quality (RSRQ) of the SeNB-to-UE link.

[047] Example implementations can provide functionality in Rel-12 LTE for having the UE report SeNB CSI or SeNB out-of-sync indications to MeNB. Example implementations provide functionality in Rel-12 LTE so that the SeNB may be allowed to send UE Radio Received Measurement (RRM) measurements to the MeNB. Thus, a variety of mechanisms can be used to acquire radio link CSI and acquire at least the statistics of random variables F_t [t] and s_t [t] . Further, in the second scenario, the MeNB can autonomously learn the statistics of the backhaul link failure parameter

by observing backhaul traffic. After learning these distributions, the MeNB can solve the optimization problems described previously in (3) and (4).

[048] Although the MeNB can optimize average performance metrics based on (3) or (4), example implementations may also facilitate avoidance of SeNB buffer overflows in real time. For example, in LTE, the PDCP status report is an existing message that can be utilized for buffer management. The status report is a PDCP control message carrying an actual reception indication of service messages and is applied to a PDCP reestablishment process. A series of messages starting from the first lost message during reestablishment correspond to the sequences in a one to one manner. In the status report, each PDCP PDU has a corresponding bit, with 1 meaning received and 0 meaning lost. However, related art implementations send the report to the transmitter side PDCP entity only during PDCP reestablishment. Furthermore, related art implementations do not support continuous PDCP status reporting from UE to MeNB.

[049] In example implementations, a message is sent from the MeNB to the UE to trigger aperiodic PDCP status reporting outside of the PDCP reestablishment process. The instances when this status request message is sent are autonomously decided by the MeNB according to the desired implementation. The contents of the reply from the UE can be similar to the existing PDCP status report depending on the desired implementation. The

MeNB periodically obtains some form of CSI of the SeNB-to-UE links via different methods as described above, and based on this information can request the status report from the UE to check if the MeNB is routing too much traffic at a particular time instance to some SeNB. For example, if the optimization solution says that at time t forward 80% of the bearer contents to SeNB k, but the SeNB-to-UE RSRP at around time t is poor, then the MeNB can send this request as a check and modify the pre-computed traffic split if needed.

[050] From the example implementations, the MeNB can therefore maintain a normal or regular bearer configuration and a split bearer configuration together. Data processed by the normal bearer configuration can be transmitted to the associated UEs, and data processed by the split bearer configuration is transmitted based on the calculated PDCP data allocation ratio as described above. As the PDCP data allocation ratio is updated in real time from the PDCP status reports, the MeNB can be configured to send more or less traffic through the SeNB, while transmitting more or less traffic through the MeNB. In example implementations, UEs can receive PDCP traffic through the normal bearer configuration from the MeNB depending on the desired implementation of the operator of the MeNB. For example, UEs indicated to receive higher priority (e.g., through a micropayment system) can be configured to only receive traffic from the normal bearer of the MeNB.

[051] The overall PDCP buffer management procedure at the MeNB in dual connectivity with split bearer is depicted in FIG. 5. FIG. 5 illustrates a flow diagram overview of PDCP buffer management by the MeNB under DC bearer split, in accordance with an example implementation.

[052] At 505, the MeNB configures the associated one or more SeNBs with a split bearer configuration.

[053] At 510, the SeNBs associated with the MeNB accept the split bearer operation and allocate radio resources.

[054] At 515, the MeNB infers SeNB buffer levels and radio CSI. This can be conducted indirectly through calculations from the statistical information that is indicative of the buffer levels and/or the quality of the radio link between the UE and the one or more SeNBs as disclosed above, or can be explicitly given to the MeNB from the SeNB or UE feedback, depending on the desired implementation. The information can be stored into the memory of the MeNB. [055] At 520, the MeNB computes PDCP data routing parameters and forwards the data to the SeNBs according to a calculated PDCP data allocation ratio. The calculations for the PDCP data allocation ratio are described above with relation to the backhaul quality and are based on the information received in the flow from 515. The MeNB can transmit some of the PDCP data to the UE based on the calculated allocation ratio and forward or transmit the remaining PDCP data to the one or more SeNBs for transmission to the UE according to the PDCP data allocation ratio. The PDCP data allocation ratio can be calculated for each split bearer managed by the MeNB as described above.

[056] At 525, the MeNB updates PDCP data routing parameters in real time, based on the acquired CSI to mitigate the probability of SeNB congestion. The MeNB can facilitate the flow by sending a request for a PDCP status report from the UE, and update the information based on a receipt of the PDCP status report. The PDCP status report can be in the form of the new message as described above. Based on the received PDCP status report, the MeNB can adjust the PDCP allocation ratio based on desired performance metrics. For example, one metric can involve minimizing an average difference between PDCP data allocated to the SeNBs and buffer availability of the SeNBs.

[057] The example implementations can be applicable for dual connectivity operation where a MeNB performs buffer management for split bearers that are routed to one or more SeNBs over non-ideal backhaul links. The algorithms proposed in the example implementations can apply to Rel-12 LTE systems and beyond.

[058] Finally, some portions of the detailed description are presented in terms of algorithms and symbolic representations of operations within a computer. These algorithmic descriptions and symbolic representations are the means used by those skilled in the data processing arts to convey the essence of their innovations to others skilled in the art. An algorithm is a series of defined steps leading to a desired end state or result. In example implementations, the steps carried out require physical manipulations of tangible quantities for achieving a tangible result.

[059] Unless specifically stated otherwise, as apparent from the discussion, it is appreciated that throughout the description, discussions utilizing terms such as "processing," "computing," "calculating," "determining," "displaying," or the like, can include the actions and processes of a computer system or other information processing device that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system's memories or registers or other information storage, transmission or display devices.

[060] Example implementations may also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may include one or more general-purpose computers selectively activated or reconfigured by one or more computer programs. Such computer programs may be stored in a computer readable medium, such as a computer-readable storage medium or a computer-readable signal medium. A computer-readable storage medium may involve tangible mediums such as, but not limited to optical disks, magnetic disks, read-only memories, random access memories, solid state devices and drives, or any other types of tangible or non-transitory media suitable for storing electronic information. A computer readable signal medium may include mediums such as carrier waves. The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Computer programs can involve pure software implementations that involve instructions that perform the operations of the desired implementation.

[061] Various general-purpose systems may be used with programs and modules in accordance with the examples herein, or it may prove convenient to construct a more specialized apparatus to perform desired method steps. In addition, the example implementations are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the example implementations as described herein. The instructions of the programming language(s) may be executed by one or more processing devices, e.g., central processing units (CPUs), processors, or controllers.

[062] As is known in the art, the operations described above can be performed by hardware, software, or some combination of software and hardware. Various aspects of the example implementations may be implemented using circuits and logic devices

(hardware), while other aspects may be implemented using instructions stored on a machine-readable medium (software), which if executed by a processor, would cause the processor to perform a method to carry out implementations of the present application.

Further, some example implementations of the present application may be performed solely in hardware, whereas other example implementations may be performed solely in software. Moreover, the various functions described can be performed in a single unit, or can be spread across a number of components in any number of ways. When performed by software, the methods may be executed by a processor, such as a general purpose computer, based on instructions stored on a computer-readable medium. If desired, the instructions can be stored on the medium in a compressed and/or encrypted format.

[063] Moreover, other implementations of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the teachings of the present application. Various aspects and/or components of the described example implementations may be used singly or in any combination. It is intended that the specification and example implementations be considered as examples only, with the true scope and spirit of the present application being indicated by the following claims.

Claims

CLAIMS What is claimed is:

1. A first base station configured to manage one or more second base stations, the first base station comprising: a memory configured to store information indicative of a quality of a radio link between a user equipment (UE) and the one or more second base stations; the UE being served by the first base station and the one or more second base stations; a processor, configured to: calculate a packet data convergence protocol (PDCP) data allocation ratio between the first base station and the one or more second base stations based on the information; transmit first data to the UE based on the PDCP data allocation ratio; and transmit second data to the one or more second base stations through a backhaul for transmission to the UE, based on the PDCP data allocation ratio.

2. The base station of claim 1, wherein the processor is configured to calculate the PDCP data allocation ratio for each split bearer managed by the first base station.

3. The base station of claim 1, wherein the information comprises statistical information indicative of an estimation of buffer levels of the one or more second base stations, and wherein the processor is configured to calculate the PDCP data allocation ratio based on the statistical information.

4. The base station of claim 1 , wherein the processor is further configured to send a request for a PDCP status report from the UE, and update the information based on a receipt of the PDCP status report.

5. The base station of claim 1, wherein the processor is configured to manage a normal bearer configuration and a split bearer configuration, wherein data processed by the normal bearer configuration is transmitted to the UE, and wherein data processed by the split bearer configuration is transmitted based on the PDCP data allocation ratio.

6. The base station of claim 1, wherein the processor is configured to calculate the PDCP data allocation ratio to minimize an average difference between PDCP data allocated to the one or more second base stations, and buffer availability of the one or more second base stations.

7. The base station of claim 1, wherein the processor is configured to calculate the PDCP data allocation ratio based on backhaul quality of the backhaul.

8. A method comprising: managing at a first base station, information indicative of a quality of a radio link between a user equipment (UE) and one or more second base stations; the UE being served by the first base station and the one or more second base stations; calculating a packet data convergence protocol (PDCP) data allocation ratio between the first base station and the one or more second base stations based on the information; transmitting first data to the UE based on the PDCP data allocation ratio; and transmitting second data to the one or more second base stations through a backhaul for transmission to the UE, based on the PDCP data allocation ratio.

9. The method of claim 8, wherein the calculating the PDCP data allocation ratio is conducted for each split bearer managed by the first base station.

10. The method of claim 8, wherein the information comprises statistical information indicative of an estimation of buffer levels of the one or more second base stations, and wherein the calculating the PDCP data allocation ratio is based on the statistical information.

11. The method of claim 8, further comprising sending a request for a PDCP status report from the UE, and updating the information based on a receipt of the PDCP status report.

12. The method of claim 8, further comprising managing a normal bearer configuration and a split bearer configuration at a first base station, wherein data processed by the normal bearer configuration is transmitted to the UE, and wherein data processed by the split bearer configuration is transmitted based on the PDCP data allocation ratio.

13. The method of claim 8, wherein the calculating the PDCP data allocation ratio is conducted to minimize an average difference between PDCP data allocated to the one or more second base stations, and buffer availability of the one or more second base stations.

14. The method of claim 8, wherein the calculating the PDCP data allocation ratio is based on backhaul quality of the backhaul.

15. A computer program containing instructions for executing a process, the instructions comprising: managing at a first base station, information indicative of a quality of a radio link between a user equipment (UE) and one or more second base stations; the UE being served by the first base station and the one or more second base stations; calculating a packet data convergence protocol (PDCP) data allocation ratio between the first base station and the one or more second base stations based on the information; transmitting first data to the UE based on the PDCP data allocation ratio; and transmitting second data to the one or more second base stations through a backhaul for transmission to the UE, based on the PDCP data allocation ratio.