CENTRAL CONTROLLER FIELD OF THE INVENTION

[0001] Embodiments of the present disclosure generally relate to wireless communication techniques and more particularly relate to a method and apparatus for cross-subframe co-channel interference (CCI) mitigation in a Time Division Duplex (TDD) system, a method and apparatus for channel state condition measuring and reporting and a network central controller.

BACKGROUND OF THE INVENTION

[0002] With the fast development of the wireless communication data service, requirements on data rate and the coverage quality are constantly increasing. As the next generation cellular communication standard, a Long Term Evolution (LTE) or

LTE- Advance system can operate in both Frequency Division Duplex (FDD) mode and

Time Division Duplex (TDD) mode.

[0003] In the Time Division LTE (TD-LTE) system, there has been advantageously proposed an asymmetrical downlink/uplink (UL/DL) resource configuration scheme as so to adapt to the asymmetrical UL/DL data traffic. In the scheme, there are provided seven different semi-statically UL/DL configurations, which are schematically illustrated in Fig. 1.

[0004] As illustrated in Fig. 1, a TDD radio frame consists of ten sub frames labeled with 0 to 9. Each of the subframes may be used for DL transmission or UL transmission, or used as a special subframe between the DL period and the UL period.

Taking configuration 0 as an example, subframes 0 and 5 are used for the DL transmission, subframes 2 to 4 and subframes 7 to 9 are used for the UL transmission and subframes 1 and 6 are used as special subframes, which are labeled as "D", "U" and

"S" respectively.

[0005] The asymmetrical UL/DL resource configuration scheme provides seven UL/DL configurations, from which the base station can select a suitable configuration based on the UL data size and the DL data size. Therefore, this semi-static resource allocation could improve the resource utilization rate. However, since traffic requirements may be fluctuating significantly, in some cases, the semi-static resource allocation may not match instantaneous traffic condition. Hence, a dynamic UL/DL resource configuration has been proposed, wherein a time-scale for reconfiguration is suggested to be tens/hundreds of milliseconds so as to be more adaptive to the traffic requirements.

[0006] By dynamically reconfiguring the UL/DL allocation, the network may benefit from traffic adaptation in both DL and UL directions. However, in such a dynamical configuration scheme, it might further result in the CCI due to the mismatched transmission directions in neighboring cells. Moreover, in dense deployment of RRUs/sites, the CCI problems become serious.

[0007] A scenario of two cells (Cell 0 and Cell 1) illustrated in Fig. 2A will be taken as an example, wherein Cell 0 uses configuration 5 and Cell 1 uses configuration 6. As illustrated in Fig. 2B, at subframes 3, 4, 7 and 8 which are designated for DL transmission for Cell 0 and for UL transmission for Cell 1 respectively, the DL transmission from RRUO to user equipment UE 0 will be interfered greatly by the UL transmission Cell 1, i.e., there will be a UE-UE CCI as illustrated in Fig. 2A; similarly, the reception quality of remote radio unit RRU 1 in Cell 1 would also be degraded due to the power leakage from RRUO in Cell 0 during its downlink transmission, i.e., RRU-RRU CCI as illustrated in Fig. 2B. Hence, the benefits obtained by adaptive UL/DL allocation would be dramatically undermined due to these CCIs.

[0008] Centralized Radio Access Network (C-RAN) is a newly proposed architecture for Radio Access Network (RAN), which is considered as the next generation RAN architecture with reduced total cost of ownership (TCO) and enhanced system quality of signal (QoS). In the C-RAN, all processing capabilities (including those for baseband) are pooled at the so-called Baseband Unit (BBU) hotel with a plurality of distributed remote radio units (RRUs). By leveraging the centralized RAN infrastructure, it may well support various advanced interference coordination schemes such as Coordinated Multiple Points (CoMP), Enhanced Inter-cell Interference Coordination(elCIC), and etc.

[0009] Usually, the CCI problem may be tackled by means of cluster-specific cooperative reconfiguration and/or coordinated interference management in the C-RAN. In technical document Rl-131879 (CATT, 3 GPP RAN1#73, Fukuoka, Japan, May 20th-24th, 2013), there is disclosed a mutual coupling loss (MCL)-based cell clustering, in which a fixed MCL threshold is employed and the cluster-specific dynamic UL/DL reconfiguration is employed so that transmission direction are aligned within the same cluster and are different between different clusters. In technical document Rl- 132486, (Qualcomm, 3 GPP RAN1#73, Fukuoka, Japan, May 20th-24th, 2013), potential cell clustering schemes in dynamic TDD systems are discussed, and especially, de-clustering and dual threshold clustering schemes are presented. In 3GPP TR 36.828 VI 1.0.0 (2012-06), four potential interference mitigation (IM) schemes are provided, i.e., cell clustering IM, scheduling dependent IM, (3) IM based on elCIC/FelCIC schemes, and (4) interference suppressing IM. Besides, in PCT patent application publication PCT/CN2012/073146, entitled "Adaptive CQI Feedback based Interference Measurement and Management in LTE/TDD Downlink Assuming Mismatched TDD DL-UL Configurations," there is further disclosed an adaptive CQI feedback based region division UE-UE CCIC approach. This approach can be easily implemented and can capture interference experienced by the UE(s) during the CCI subframe(s) and in the approach, a threshold for region division is adaptively adjusted according to the received long-term CQIs in flexible subframes.

[0010] However, the performance of those cluster based interference coordination schemes highly relies on results of cell clustering. Sometimes, it can not achieve expected interference mitigation effects. Therefore, there is a need for a new interference mitigation scheme in the art.

SUMMARY OF THE INVENTION

[0011] In view of the foregoing, the present disclosure provides a new solution for CCI mitigation in TDD system, so as to solve or at least partially mitigate at least a part of problems in the prior art.

[0012] According to a first aspect of the present disclosure, there is provided a method for CCI mitigation in a TDD system. The method may comprise identifying a cluster-edge user equipment from user equipments in a cluster comprising at least one cell, based on information about large-scale fading for channels allocated to the user equipments; and allocating resource to the cluster-edge user equipment so that at least one of flexible subframes in uplink/downlink configuration is disabled, so as to mitigate the CCI.

[0013] In an embodiment of the present disclosure, the method may further comprise performing an adaptive cell clustering based on mutual coupling loss (MCL) with a dynamically adjusted MCL threshold so as to form the cluster comprising at least one cell.

[0014] In an embodiment of the present disclosure, the performing the adaptive cell clustering may further comprise: obtaining current system performance metrics and system statistics information indicating historical system performance metrics;; determining the MCL threshold based on the current system performance metrics and the system statistics information; and performing a cell clustering based on the determined MCL threshold.

[0015] According to a second aspect of the present disclosure, there is provided a method for channel state condition measurement and reporting in a TDD system. The method may comprise: receiving a measurement indication, which indicate a user equipment to measure channel state condition only on the subframes that are not disabled; measuring the channel state condition on subframes that are not disabled; and reporting the measured channel state condition to a serving node.

[0016] According to a third aspect of the present disclosure, there is provided an apparatus for CCI mitigation in a TDD system. The apparatus may comprise: an user equipment identification unit, configured to identify a cluster-edge user equipment from user equipments in a cluster comprising at least one cell, based on information about large-scale fading for channels allocated to the user equipments; and a resource allocation unit, configured to allocate resource to the cluster-edge user equipment so that at least one of flexible subframes in uplink/downlink configuration is disabled, so as to mitigate the CCI

[0017] According to a fourth aspect of the present disclosure, there is provided an apparatus for channel state condition measurement and reporting in a TDD system. The apparatus may comprise: measurement indication receiving unit, configured to receive a measurement indication, which indicates a user equipment to measure channel state condition only on the subframes that are not disabled; state condition measuring unit, configured to measure the channel state condition on subframes that are not disabled; and state condition reporting unit, configured to report the measured channel state condition to a serving node.

[0018] According to a fifth aspect of the present disclosure, there is further provided a network central controller, comprising: an adaptive cell clustering controller, configured to perform an adaptive cell clustering based on mutual coupling loss (MCL) with a dynamically adjusted MCL threshold to form at least one cluster; an uplink/downlink(UL/DL) reconfiguration controller configured to perform UL/DL reconfiguration operations for the at least one cluster to determine an UL/DL configuration for each of the at least one cluster; a time-domain resource partition controller configured to perform a time-domain resource partition on the UL/DL configuration for each of the at least one cluster for cluster-edge user equipments so that at least one of flexible subframes in UL/DL configuration is disabled, so as to mitigate the CCI.

[0019] According to a sixth aspect of the present disclosure, there is further provided, a computer-readable storage media with computer program code embodied thereon, the computer program code configured to, when executed, cause an apparatus to perform actions in the method according to any one of embodiments of the first aspect.

[0020] According to a seventh aspect of the present disclosure, there is further provided, a computer-readable storage media with computer program code embodied thereon, the computer program code configured to, when executed, cause an apparatus to perform actions in the method according to any one of embodiments of the second aspect.

[0021] According to an eighth aspect of the present disclosure, there is provided a computer program product comprising a computer-readable storage media according to the sixth aspect.

[0022] According to an ninth aspect of the present disclosure, there is provided a computer program product comprising a computer-readable storage media according to the seventh aspect.

[0023] With the embodiments of the present disclosure, the ICC may be mitigated substantially, and it may benefit from improved cell-average cell-edge performances and enhanced capability in adapting to the asymmetric traffic variations. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other features of the present disclosure will become more apparent through detailed explanation on the embodiments as illustrated in the embodiments with reference to the accompanying drawings throughout which like reference numbers represent same or similar components and wherein:

[0025] Figs. 1 schematically illustrates a diagram of UL/DL configurations in LTE TDD system as specified by 3 GPP;

[0026] Fig. 2A schematically illustrates an example of CCIs in a two-cell scenario;

[0027] Fig. 2B schematically illustrates subframes at which CCI may be caused in the scenario of Fig. 2A ;

[0028] Fig. 3 schematically illustrates a network in which embodiments of the present disclosure may be implemented;

[0029] Fig. 4 schematically illustrates a flow chart of a method for time-domain resource partition according to an embodiment of the present disclosure;

[0030] Fig. 5 schematically illustrates a diagram of cluster-edge and cluster-center UEs according to an embodiment of the present disclosure;

[0031] Fig. 6 schematically illustrates diagrams of fixed subframes and flexible subframes in UL/DL configurations;

[0032] Fig. 7 schematically illustrates a diagram showing time-domain resource partition according to an embodiment of the present disclosure;

[0033] Fig. 8 schematically illustrates a flow chart of an adaptive cell clustering according to an embodiment of the present disclosure;

[0034] Figs. 9 A to 9G schematically illustrates impact of the MCL thresholds on system performance;

[0035] Fig. 10 schematically illustrates a flow chart of a method a CCI mitigation in TDD according to an embodiment of the present disclosure;

[0036] Fig. 11 schematically illustrates the cumulative density (CDF) of UL geometry SINRs of various MCL thresholds according to an embodiment of the present disclosure;

[0037] Fig. 12 schematically illustrates an exemplary signaling flow diagram for performing time-domain resource allocation according to an embodiment of the present disclosure;

[0038] Fig. 13 schematically illustrates a diagram of channel state condition measuring and reporting according to an embodiment of the present disclosure;

[0039] Fig. 14 schematically illustrates a flow chart of channel state condition measuring an reporting according to an embodiment of the present disclosure;

[0040] Fig. 15 schematically illustrates a network central controller according to an embodiment of the present disclosure;

[0041] Fig. 16 schematically illustrates a block diagram of an apparatus for CCI mitigation in a TDD system according to an embodiment of the present disclosure;

[0042] Fig. 17 schematically illustrates a block diagram of an adaptive clustering cell according to an embodiment of the present disclosure; and

[0043] Fig. 18 schematically illustrates block diagram of an apparatus for channel state condition measuring and reporting according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0044] Hereinafter, the present disclosure will be described in details through embodiments with reference to the accompanying drawings. It should be appreciated that these embodiments are presented only to enable those skilled in the art to better understand and implement the present disclosure, not intended to limit the scope of the present disclosure in any manner.

[0045] In the accompanying drawings, various embodiments of the present disclosure are illustrated in block diagrams, flow charts and other diagrams. Each block in the flowcharts or block may represent a module, a program, or a part of code, which contains one or more executable instructions for performing specified logic functions. Besides, although these blocks are illustrated in particular sequences for performing the steps of the methods, as a matter of fact, they may not necessarily be performed strictly according to the illustrated sequence. For example, they might be performed in reverse sequence or simultaneously, which is dependent on natures of respective operations. It should also be noted that block diagrams and/or each block in the flowcharts and a combination of thereof may be implemented by a dedicated hardware-based system for performing specified functions/operations or by a combination of dedicated hardware and computer instructions.

[0046] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the/said [element, device, component, means, step, etc]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, unit, step, etc., without excluding a plurality of such devices, components, means, units, steps, etc., unless explicitly stated otherwise. Besides, the indefinite article "a/an" as used herein does not exclude a plurality of such steps, units, modules, devices, and objects, and etc.

[0047] Additionally, in a context of the present disclosure, a user equipment (UE) may refer to a terminal, a Mobile Terminal (MT), a Subscriber Station (SS), a Portable Subscriber Station (PSS), Mobile Station (MS), or an Access Terminal (AT), and some or all of the functions of the UE, the terminal, the MT, the SS, the PSS, the MS, or the AT may be included. Furthermore, in the context of the present disclosure, the term "BS" may represent, e.g., a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a radio header (RH), a remote radio head (RRH), a relay, or a low power node such as a femto, a pico, and so on.

[0048] For a better understanding of the present disclosure, the following description will be made to embodiments of the present disclosure by taking a cloud based TDD heterogeneous networks as an example. However, as can be appreciated by those skilled in the art, the present invention can be applicable to any other suitable communication system.

[0049] First, reference will made to Fig. 3 to describe a cloud based TDD heterogeneous networks in which embodiments of the present disclosure may be implemented. As illustrated, in the centralized RAN (Radio Access Network) network, there are densely deployed a plurality of remote radio units (RRUs), a RRU is comparable to a cell and installed at each local site with only radio frequency (RF) front-end functionalities. All RRUs are connected with a central control unit (CCU) through an optical fiber network. All the processing units/capabilities (including a base-band) are pooled in BBU pools at the CCUs. Due to such a centralized RAN architecture, it provides a possibility to formulate the UL/DL reconfiguration as the corporative control and implemented efficiently in the present disclosure.

[0050] Hereinafter, the method for CCI mitigation in a TTD system as provided in the present disclosure will be described at length with reference to Figs. 4 to 14. First, a time-domain resource partition (TRP) as proposed in the present invention will be described first.

Time-domain Resource Partition (TRP)

[0051] Reference is first made to Fig. 4, which schematically illustrates a flow chart of a method for time-domain resource partition according to an embodiment of the present disclosure. As illustrated in Fig. 4, fist at S401, a cluster-edge user equipment is identified from user equipments in a cluster comprising at least one cell, based on information about large-scale fading for channels allocated to the user equipments.

[0052] In embodiments of the present disclosure, UEs in a cluster may be categorized into "cluster-central UEs" and "cluster-edge UEs." The cluster-central UEs means UEs that are severed in a good channel quality and suffer from little interference in a sense of long term, and the cluster-edge UEs means UEs that suffer a lot from interference and are severed in a bad channel quality in a long term.

[0053] Thus, the cluster-edge UEs may be identified based on information that may reflect a long term channel quality. In the present disclosure, information about large-scale fading for channels allocated to the user equipments is used. The identifying may be performed by comparing the information about large-scale fading for channels allocated to the user equipments and a channel fading threshold. The appropriate information about large-scale fading for channels may comprise geometry signal to interference-plus-noise ratio (SINR), coupling loss, and so on. Hereinafter geometry SINR will be taken as an example, but the present disclosure is not limited thereto. The geometry SINR of UE i in cell j in a cluster may be calculated as

Equation (1) wherein P _j denotes the transmit power of the transmitter of UE I;, Ij denotes the set of all active UEs of cell j; denotes the path gain from UE i to its serving RRU j; which is linear and in terms of power; M denotes the set of all formed cell clusters; M' denotes the cell cluster that cell j is involved in, wherein M' <≡ M; g(p,q ₎ denotes the transmission direction between UE p and RRU q.

[0054] The g(p,q) may be expressed as follows q DL transmission from RRU q to UE p

g(P,<l)

p UL transmission from UE p to RRU q

Equation (2)

[0055] In an embodiment of the present disclosure, it employs 5%-percentile SINR observed from a CDF of the UL geometry SINRs of all UES as a target SINR threshold, which may denoted as & . Hence, it may obtain the following function

1 SINR", ≥&

uQ)

0 SINR?, < «9

Equation (3) wherein u j)=0 denotes that UE j is labeled as a cluster-center UE; u(j)=l denotes that UE j is labeled as a cluster-edge UE. In such a way, a cluster-edge UE may be identified. However, it should be noted that 5%-percentile SINR threshold is only an example and other percentile SINR threshold may also be feasible, which depends on practical implementation of the network. Actually, the percentile SINR threshold can be determined by some measured values such as High Interference Indicator (HII), Overload Indicator (OI), Relative Narrowband Transmit Power (RNTP) and etc.

[0056] Then, at step S402, resource allocation is performed to allocate resource for the cluster-edge user equipment so that at least one of flexible subframes in uplink/downlink configuration is disabled, so as to mitigate the CCI.

[0057] In the present disclosure, subframes may be divided into flexible subframes and fixed subframes. A flexible subframe means a subframe that may be used to transmit both UL signals and DL signals and the fixed subframe denotes a subframe that is fixed to transmit one of UL signals or DL signals. Hereinafter, the flexible subframes and the fixed subframes will be described with reference to Fig. 6.

[0058] As illustrated in Fig. 6, in the seven different configurations 0 to 6, subframes 0 and 5 are used to transmit DL signals, subframe 1 is a special subframe which may be also considered to transmit DL signals, and subframe 6 is used to transmit DL signals or is designed as a special subframe and thus it may be consider to transmit DL signals. However, subframes 3 to 4 and 7 to 9 may transmit both UL signals and DL signals. Thus, subframe 0 to 2 and 5 to 6 are called as fixed subframes, while subframes 3 to 4 and 7 to 9 may be called as flexible subframes.

[0059] It may be appreciated that if a UE is scheduled in the fixed subframes, they will not suffer from CCI while if UE is scheduled in flexible subframes, they will possibly suffer from severe CCI if UL/DL configurations are allowed to be different between clusters.

[0060] Therefore, in the present disclosure, there is proposed a restricted time-domain resource allocation scheme (i.e., time-domain resource partition "TRP") such that the cluster-center UEs are allowed to be scheduled in both "fixed" and "flexible" subframes, while the cluster-edge UEs are allowed to be scheduled only in "fixed" subframes, so as to avoid strong inter-cluster CCI.

[0061] An example about how to schedule different types of UEs in different types of subframes will be described with reference to Fig. 7. As illustrated in Fig. 7, in this example, there are four cell clusters, i.e., cell cluster-I, cell cluster-II, cell cluster- Ill, and cell cluster-IV. For a purpose of illustration, cell cluster-IV comprising only cell is taken as an example. However, it should be noted that similar procedure can be easily extended to the case that a cluster contains a plurality of cells. In Fig. 7, in cell cluster-IV, UE 0 is identified as a cluster-edge UE, and both UE 1 and UE 2 are determined as cluster-center UEs. Therefore, regarding the three UEs, they may all be scheduled in fixed subframes while only the cluster-center UEs, i.e., UE 1 and UE 2, can be scheduled in the flexible subframes. That is to say, for the cluster-edge UE, flexible subframes are disabled.

[0062] It may be appreciated that cluster-center UEs usually have a good channel quality and thus CCI will not bring about a significant affect. However, for cluster-edge UEs which have a bad channel quality, they may suffer from the CCI a lot. Thus, by means of disabling flexible subframes for cluster-edge UEs, it may achieve a substantially improved channel quality at a cost of limited throughput decrease. It should be noted that there may be provided a time-domain resource partition option, the TRP method may be performed only if the time-domain resource partition is set as enabled.

Adaptive Cell Clustering

[0063] Besides, as described in background, the performance of those cluster based interference coordination schemes highly relies on results of cell clustering. Therefore, to improve the performance of those cluster based interference coordination schemes, in the present disclosure, there is further proposed an adaptive cell clustering (ACC) algorithm that dynamically adjusts the cell cluster size according to the collected system statistics information (SSI) indicating historical system performance metrics and system performance metrics.

[0064] Next, reference will be made to Fig. 8 to describe the adaptive cell clustering according to an embodiment of the present disclosure. As illustrated in Fig. 8, first as step S801 , it may obtain current system performance metrics and system statistics information indicating historical system performance metrics.

[0065] In an embodiment of the present disclosure, three performance metrics indicators are used, i.e., (a) UL cell-edge packet throughput; (b) sum cell-average packet throughput of DL transmission and UL transmission; and (c) an indicator representing suitability of the cell clustering.

[0066] The UL cell-edge packet throughput may be denoted as Ri and it may be defined as the UL cell-edge packet throughput observed after z ^' -th cell clustering. The sum cell-average packet throughput of DL transmission and UL transmission may also be denoted as Q and defined as the sum cell-average packet throughput after z ^' -th cell clustering. More specifically, the sum cell-average packet throughput of DL transmission and UL transmission Q may be represented by

Equation (4) wherein Cf denotes the cell-average packet throughput of DL transmission; and ^u denotes the cell-average packet throughput of UL transmission.

[0067] The indicator representing suitability of the cell clustering may be represented, for example, by the difference between the real traffic demands and the actually transmitted packets in both DL and UL directions. If Bf _k and B" _k respectively denotes the total number of packets arrived in cell /Vs DL and UL buffers before (z ^' +i)-th clustering process, and P _t ^D _k and P" _k respectively denotes the total number of packets that have been processed in cell /Vs DL and UL transmissions before (z+i)-th clustering process, then the indicator representing suitability of the cell clustering may be represented for exam le by

Equation (5)

[0068] Then at step S802, it may determine the MCL threshold based on the system statistics information and the current performance metrics. In the present disclosure, there is proposed to use a set of potential MCL thresholds rather than one single MCL threshold.

[0069] In order to learn effect of the MCL threshold, the inventors have made some simulations to study the effect of the MCL thresholds on the cluster size and the system performance. Simulations results are illustrated in Figs. 9A to 9G. From these simulation results, it may be seen that the mean size of cell clusters is mainly determined by the MCL threshold based on which the cell clustering is performed. Moreover, with the increasing MCL threshold, the cell-average sum DL and UL throughput, the cell-average DL throughput, the cell-edge DL throughput will decrease the cell-edge UL throughput will increase, and the cell-average UL throughput will increase first and then decrease while the squared error of DL.DL ration will increase gradually.

[0070] Based on these simulation results, a set of potential MCL thresholds may be constructed as follows:

n _MC L = {40, 50, 60,70, 140}dB

Equation (6)

[0071] During each cell clustering, one of the predetermined MCL thresholds will be selected by the central controller of the network based on system statistics information and current system performance metric.

[0072] In the present disclosure, there is proposed an indicator φ (x,y,z), which may be represented as follows: 0 Remain the MCL threshold

φ(χ,γ,ζ) 1 Increase the MCL threshold

- 1 Decrease the MCL threshold

Equation (7) wherein parameters x, y and z denotes the above mentioned system performance metrics Ri, Ci and Q _t respectively.

[0073] In an embodiment of the present disclosure, the value of indicator φ (x,y,z) may be determined based on decision rules or triggering events.

■ if C _t ≥(l + a)C _i _ ₁ and Q _i <(l + a)Q _i _ ₁ , φ( R^C^Q, )=Q;

■ if C,. Kfl + aJC^ and Q _t >(l + a)Q _l _ _l , MR _i ,C _i ,Q _i ) = A;

■ if R. ≥(l + a)R _i _ _l ,C _i ≥(l + a)C _i _ _l and Q _t >(l + a)Q _i _ ₁ , tfR.,C _i ,Q _i ) = 0;

■ if R. <(l + a)R _i _ _x , C _t ≥(l + aJC^ and Q _t > (1 + a)Q _i _ ₁ , R. ,C _i ,Q _i )=\;

■ if R _t >(\ + a)R _i _ _l , C,. Kfl + aJC^ and Q _i <(l + a)Q _i _ ₁ , φ( R _i ,C _i ,Q _i )=0;

■ if R _t <(\ + a)R _i _ _i , C _i <(l + a)C _i _ _l and Q, ≤(l + a)Q _i _ ₁ , φ( R^C^Q, )=l wherein a is a scaling factor that ensures the decision rules would be triggered only when the performance is better/worse enough in contrast to the collected historical performance statistics. By selecting an appropriate a (e.g. a=0.1), unnecessary adaptation which may have negative impact on the system performance will be avoided.

[0074] In the decision rules and trigger events, the system capability in adapting to the asymmetric traffic demands has a higher priority than the cell-edge performance; if the decision as to how to adjust the MCL threshold can not be made by simply comparing the traffic adaptation capability, the cell-edge performance will play a role in determining the appropriate MCL threshold. On the other hand, if the performance indicators of interest are better than previously measured performance statistics, conservative method is applied which remains the MCL threshold and keep it as it is.

[0075] For example, it may assume that the MCL threshold at z ^' -th cell clustering is 90dB, if it has the flowing relationship

R _t <(l + a )R^ , C,. ≥(l + a )C _{ _ _X and Q _t >(l + a )C _X i 1

then it may determine that the value ΐφ( R _i ,C _i ,Q _i ) equals to 1. Thus, the MCL threshold at (z ^' +7)-th cell clustering would be increased by one index, i.e., the value should be lOOdB.

[0076] Next, at step S803, it may perform the cell clustering based on the determined MCL threshold. The cell clustering can be conducted either in a dynamic manner or a semi-static manner. The time-scale or time period for cell clustering can be in the order of millisecond, second, minute, hour and etc. It should be noted that the selection of appropriate time-scale for adaptive cell clustering plays an important role. If the time-scale is too small, the accuracy of the collected system statistics information may not be guaranteed; on the other hand, if the time-scale is too large, the system capability in adapting to the performance variations may be compromised. Moreover, the selection of appropriate time-scale should avoid disruptive performance jumps due to the adaptation.

[0077] In an embodiment of the present disclosure, the cell clustering may be performed in a dynamic manner, wherein the time-scale is in the order of millisecond, or more specifically, in the order of 200ms or even more such as 400ms, 600ms, 800ms or even 1000ms. The cell cluster may start by randomly selecting RRUs as anchor points. Other RRUs that have smaller MCL than the predetermined MCL threshold to the anchor RRUs would be categorized into the same clusters associated with the anchor RRUs. In embodiments of the present disclosure, the clusters are not overlapped with each other (i. e., disjoint). For a purpose of illustration, an exemplary pseudo-code of the MCL-based cell clustering algorithm is presented as follows:

Algorithm 1 MCL-based cell clustering algorithm

1 : input: {MCLRRW-RRUJ, i≠j,RRUi,RR Uj Γο) ; MCL threshold τ

2: output: Cell cluster set (Ac)

3: while all cell cluster are formed do

4: start: randomly select one RRU (e.g., RRUx £7 ^~ c) that has not been

chosen so far

5: initialize: δχ

6: while RRU _y £ ^~ c and x≠y do

7 : if MCL _{RR UX} . _RR u _y T then

8: dx ^RRU end if

end while end while

[0078] In the above algorithm, τ denotes the MCL threshold; i ^~ c denotes the set contains all RRUs of interest; N _c represents the total number of Us contained in the set i ^~ c; Ac denotes the set of all cell clusters; N _TC denotes the number of cell clusters; Si ^Ac _, represents the cell cluster that is anchored at RRU;.

[0079] After the cell clustering, it may perform a cluster-specific reconfiguration, which means that the UL/DL configurations are no longer determined with respect to an individual cell, but are chosen on the basis of cell clusters. In embodiments of the present disclosure, the cluster-specific reconfiguration refers to the scheme that the same UL/DL configuration is determined for a cell cluster for a purpose of intra-cluster CCI elimination; on the other hand, the UL/DL configurations employed by different clusters could be different in a subframe for asymmetric traffic adaptation. More specifically, the ratio of the accumulated buffered DL and UL data volumes regarding a cell cluster is first calculated; then, the UL/DL configuration that has the closest UL/DL ratio to the calculated ratio would be selected as reconfiguration for the cell cluster. Straightforwardly, the performance of the cluster-specific reconfiguration highly relies on the cell clustering outcomes. In fact, in the present disclosure, the cell-specific reconfiguration may be considered as one special case of the cluster-specific reconfiguration when the cluster contains only one cell.

[0080] After the cluster-specific reconfiguration, whether to perform the proposed TRP or not is also an implementation problem depending on practical requirements. For example, it may assume that the TRP is always performed. Or alternatively, the TPR are performed only when the TRP is set as enabled.

[0081] Fig. 10 schematically illustrates a method of CCI mitigation with a combined ACC and TRP according to an embodiment of the present disclosure. As illustrated in Fig. 10, first at step SI 001, it determines whether the time-scale for cell clustering is satisfied. If no, the procedure goes back to "start"; otherwise, the procedure proceeds into step SI 002 at which it is determined whether the ACC is enabled. If the ACC is not enabled, the procedure enters step SI 004 and the MCL-based cell clustering is performed for example with a predetermined MCL threshold, instead of a dynamically adjusted MCL threshold. If the ACC is enabled, the procedure enters step SI 003, wherein the MCL threshold is adjusted dynamically based on the method as described wither reference to Fig. 8 and then at step SI 004, the MCL-based cell clustering is performed based on the adjusted MCL threshold. After that, at step SI 005, a cluster-specific dynamic UL/DL reconfiguration is performed on the cell clusters so as to determine the UL/DL configuration for each of the cell clusters. Next, at step SI 006, it determines whether TRP is enabled. If not, the procedure ends; if the TRP is enabled, then the procedure goes into step SI 007 at which the TRP is performed on the determined UL/DL configuration for at least one of the cell clusters.

[0082] It should be noted that the target SINR threshold for identifying the cell-center UEs and the cell-edge UEs will vary with the adjusted MCL threshold when, for example, a percentile geometry SINR is set as the target SINR threshold. This means for different MCL thresholds, it may obtain different cell clusters and the target SINR threshold corresponding to the percentile geometry SINR will also change. Fig. 11 schematically illustrates a CDF of UL geometry SINRs of various MCL thresholds. From the figure, it is clear that the target SINR threshold varies with respect to the MCL thresholds. In other word, the target SINR threshold will vary during the process of ACC.

[0083] Next, reference is made to Fig. 12, which schematically illustrates an exemplary signaling flow diagram for performing time-domain resource allocation according to an embodiment of the present disclosure. As illustrated, first at step SI 201, a cell clustering adaption decision will be sent from the BBU pool to the RRU to inform the RRU its cell clustering adaption decision. Then, it will further send a UL/DL configuration adaption decision to the RRU at step S1202, so as to notify the RRUs of the UL/DL configuration for the cell cluster. Furthermore, a time-domain resource partition decision will also be transmitted to the RRU at step SI 203 so that the RRU can learn whether the TRP is enabled. After that, the RRU may update its configuration at step S1204, and more specifically, it may perform the synchronization, change RF and other necessary operations in accordance with the BBU pool's decisions. Then, the RRU may transmit with updated configuration at step SI 205. Besides, updated configurations will be also be transmitted to the UE from the BBU pool at S1206. After receiving the updated configurations, the UE may respond at step S1207 so as to change RF, detect primary synchronization sequence/ secondary synchronization sequence (PSS/SSS), perform RRM measurements and etc. Afterwards, at step S1208, a random access channel (RACH) procedure may be performed between the UE and the RRU to complete the initialization procedure. Subsequently, the RRU will use, for example, RRC signaling or a broadcast or a multicast approach to notify the UE of the adaptive cell clustering results. The UE will measure channel state conditions such as RRM/CSI and so on, and then transmit the measurement report to the RRU at step S1210. Next, at step S1211, the communication may be performed between the UE and the RRU with updated configurations.

[0084] Besides, in the present disclosure, if the TRP is performed, then flexible subfames will be disabled for cluster-edge UEs while for the cluster-center UEs, both flexible subframes and fixed subframes are enabled. Accordingly, the channel state condition measuring and reporting should be modified to adapt the solution as proposed in the present disclosure. Fig. 13 schematically illustrates a diagram of channel state condition measuring and reporting according to an embodiment of the present disclosure. As illustrated, for cluster-center UEs for which both fixed subframes and flexible subframes are enabled, the channel state condition measuring and reporting may be performed as usual, i.e. channel state condition (such as CSI, CQI and SRS)for both fixed subframes and flexible subframes are measured and reported for using by a serving node. That is to say, both channel state condition CSIo, CQIo and SRSo and CSIi, CQIi and SRSi for fixed subframes and flexible subframes will be used. However, for the cluster-edge UEs for which only fixed subframes are enabled, only the channel state condition for fixed subframes are measured and reported, and only channel state condition CSIo, CQIo and SRSo for fixed subframes will be used.

[0085] Fig. 14 schematically illustrates a flow chart of channel state condition measurement according to an embodiment of the present disclosure. As illustrated in Fig. 14, first as step S1401, a channel state condition measurement indication is received. The indication indicates a UE to measure channel state condition only on the subframes that are not disabled. Then at step S1402, the UE measures the channel state condition on subframes that are not disabled. The subframes that are disabled comprise at least one of flexible subframes in uplink/downlink configuration and preferably, all of flexible subframes in uplink/downlink configuration are disabled. In an embodiment of the present disclosure, the flexible subframes in UL/DL configuration comprise subframe 3, 4, 7, 8 and 9. The channel state condition may comprise for example channel station indicator, channel quality indicator, and sounding reference signal. Then at step SI 403, the UE may report the measured channel state condition to the RRU.

[0086] Additionally, Fig. 15 schematically illustrates a network central controller according to an embodiment of the present disclosure. As illustrated in Fig. 15, the network central controller 1500 may comprise ACC controller 1510, a UL/DL reconfiguration controller 1520, a T P controller 1530 and a storage device 1540. The ACC controller 1510 may be configured to perform an adaptive cell clustering based on mutual coupling loss (MCL) with a dynamically adjusted MCL threshold to form at least one cluster. The UL/DL reconfiguration controller 1520 is configured to perform of UL/DL reconfiguration operations for the at least one cluster to determine an UL/DL configuration for each of the at least one cluster. The TRP controller 1530 may be configured to control perform a time-domain resource partition on the UL/DL configuration for each of the at least one cluster for cluster-edge user equipments so that at least one of flexible subframes in UL/DL configuration is disabled, so as to mitigate the CCI.

[0087] Specifically, the ACC controller 1510 may further comprise: an adaptation timer 1511, an ACC performance metrics computation module 1512, a triggering module 1513, and a clustering performing module 1514. The adaptation timer 1511 is a timer configured to control time period of an adaptive cell clustering operation. The adaptation time 1511 will monitor whether the time-scale for the ACC is satisfied or not. If the time-scale for UL/DL reconfiguration is satisfied, it will trigger the ACC process. The ACC performance metrics computation module 1512, configured to compute current system performance metrics based on measurements stored in a statistics information and measurements storage 1540. The triggering module 1513 configured to determine the MCL threshold based on the system statistics information stored in the statistics information and measurements storage 1540 and the current system performance metrics. In other word, the triggering module 1513 will make the adaption decision by selecting an appropriate MCL threshold. Then a clustering performing module 1514 may be configured to perform a cell clustering based on the determined MCL threshold. The cell clustering results will be notified to both the UL/DL reconfiguration controller 1520 and the T P controller 1530.

[0088] The UL/DL reconfiguration controller 1520 further comprises a reconfiguration timer 1521, a reconfiguration performance metric computation module 1522, and a UL/DL configuration performing module 1524. The reconfiguration timer

1521 may be configured to control time period of an UL/DL reconfiguration operation. Specifically, the reconfiguration time 1521 monitors whether the time-scale for UL/DL reconfiguration is satisfied or not. If the time-scale for reconfiguration is satisfied, it will trigger the reconfiguration process. The performance metrics computation module

1522 may be configured to compute current system performance metrics for UL/DL reconfiguration from the measurement stored in the SSI and measurement storage devicel540. The UL/DL reconfiguration performing module 1524 may be configured to perform the UL/DL reconfiguration operation based on the current system performance metrics to determine the UL/DL configuration for each of the at least one cluster.

[0089] The TRP controller 1530 may further comprise a TRP performance metrics computation module 1532 and a scheduling decision module 1534. The performance metrics computation module 1532 may be configured to obtain information about large-scale fading for channels allocated to the user equipments so as to identify cluster-edge user equipments in each of the at least one cluster, from the performance information stored in the SSI and measurements storage device 1540. The scheduling decision module 1534 may be configured to allocate resource to the cluster-edge user equipment so that at least one of flexible subframes in uplink/downlink configuration is disabled, so as to mitigate the CCI.

[0090] Besides, in the present disclosure, there are further provided apparatus for CCI mitigation in a TTD system. Reference is made to Fig. 16, which schematically illustrates a block diagram of an apparatus for CCI mitigation in a TDD system according to an embodiment of the present disclosure. As illustrated in Fig. 16, the apparatus may comprise a user equipment identification unit 1610 and a resource allocation unit 1620. The user equipment identification unit 1610 may be configured to identify a cluster-edge user equipment from user equipments in a cluster comprising at least one cell, based on information about large-scale fading for channels allocated to the user equipments. The resource allocation unit 1620 may be configured to allocate resource to the cluster-edge user equipment so that at least one of flexible subframes in uplink/downlink configuration is disabled, so as to mitigate the CCI.

[0091] In an embodiment of the present disclosure, the user equipment identification unit 1610 may be further configured to identify a cluster-edge user equipment by comparing the information about large-scale fading for channels allocated to the user equipments and a channel fading threshold.

[0092] In another embodiment of the present disclosure, the information about large-scale fading may comprise one or more of: coupling loss; geometry signal to interference-plus-noise ratio; and geographical locations of the user equipments.

[0093] In a further embodiment of the present disclosure, the flexible subframes in uplink/downlink configuration may comprise subframe 3, 4, 7, 8 and 9.

[0094] In a yet further embodiment of the present disclosure, the user equipment identification unit 1610 and the resource allocation unit 1620 may function when time-domain resource partition is set as enabled.

[0095] In a still further embodiment of the present disclosure, the apparatus 1600 may further comprise an adaptive cell clustering unit 1630, configured to perform an adaptive cell clustering based on mutual coupling loss (MCL) with a dynamically adjusted MCL threshold, so as to form the cluster comprising at least one cell.

[0096] As illustrated in Fig. 17 which schematically illustrates an apparatus for adaptive cell clustering according to an embodiment of the represent disclosure, the adaptive cell clustering unit 1630 may further comprise: an information obtaining unit 1631, configured to obtain current system performance metrics and system statistics information indicating historical system performance metrics; a threshold determination unit 1632, configured to determine the MCL threshold based on the current system performance metrics and the system statistics information; and a clustering performing unit 1633, configured to perform cell clustering based on the determined MCL threshold.

[0097] In another embodiment of the present disclosure, the threshold determination unit 1632 may be further configured to determine whether to increase, maintain or decrease an old MCL threshold based on the current system performance metrics and the system statistics information; and select, from a set of MCL thresholds containing a plurality of potential MCL thresholds, a new MCL threshold as the determined MCL threshold based on the determining and the old MCL threshold.

[0098] In a further embodiment of the present disclosure, the system performance metrics comprises: UL cell-edge packet throughput; sum cell-average packet throughput of DL transmission and UL transmission; an indicator representing suitability of the cell clustering.

[0099] In a still further embodiment of the present disclosure, the adaptive cell clustering unit 1630 may function when the adaptive cell clustering is set as enabled.

[00100] In a still further embodiment of the present disclosure, the channel fading threshold may vary with the dynamically adjusted MCL threshold.

[00101] In a still yet further embodiment of the present disclosure, the apparatus

1600may further comprising, a measurement indication sending unit 1640, configured to send a measurement indication to the cluster-edge user equipment to indicate the cluster-edge user equipment to measure channel state condition only on the subframes that are not disabled.

[00102] In a yet still further embodiment of the present disclosure, all of flexible subframes in UL/DL configuration are disabled for the cluster-edge user equipment.

[00103] Next, reference will be made to Fig. 18, to describe an apparatus for channel state condition measuring and reporting in a TDD system. The apparatus 1800 may comprise a measurement indication receiving unit 1810, a state condition measuring unit 1820, and a state condition reporting unit 1830. The measurement indication receiving unit 1810 may be configured to receive a measurement indication, which indicates a user equipment to measure channel state condition only on the subframes that are not disabled. The state condition measuring unit 1820 may be configured to measure the channel state condition on subframes that are not disabled. The state condition reporting unit 1830 may be configured to report the measured channel state condition to a serving node.

[00104] In an embodiment of the present disclosure, the subframes that are disabled may comprise at least one of flexible sub frames in uplink/downlink configuration. The flexible sub frames in uplink/downlink configuration comprise subframe 3, 4, 7, 8 and 9. Preferably, all of flexible subframes in uplink/downlink configuration may be disabled. Besides, the channel state condition comprises one or more of channel station indicator, channel quality indicator, and sounding reference signal.

[00105] With the embodiments of the present disclosure, the CCI may be mitigated substantially, and it may benefit from improved cell-average cell-edge performances and enhanced capability in adapting to the asymmetric traffic variations.

[00106] In the present disclosure, an exemplary set of potential MCL thresholds are used to describe the embodiments of the present disclosure. However, it may be appreciated that the present disclosure is not limited thereto, the number of MCL thresholds and their step size may vary dependent on practical deployment.

[00107] Besides, in embodiments of the present disclosure, three performance indicators R _t , Q and C, and associated SSI are used. However, it may be noted that different performance indicators and their SSI (such as resource usage status) may also be collected and used to conduct the adaptive cell clustering as long as the desired performance metrics may be optimized.

[00108] Moreover, in the embodiments of the present disclosure, specific MCL threshold decision rules/triggering events are used to adjust the cell cluster size; however, it should be appreciated that different decision rules/triggering events may also be adopted.

[00109] In embodiments of the present disclosure, the proposed cell clustering procedure is performed in a centralized manner. However, it may also be performed in a distributed way and in such a case, necessary performance metrics and SSI may be exchanged between relevant base stations so that a joint decision may be made.

[00110] Additionally, in the embodiments of the present disclosure, the proposed cell clustering is evaluated and incorporated into the cluster-specific reconfiguration; however, it should be noted that the proposed cell clustering may also be transparent to the radio access technologies that are employed as long as necessary SSI and/or measurements can be obtained.

[00111] In addition, the UL geometry SIN s are used to categorize UEs into cluster-center UEs and cluster-edge UEs. Nevertheless, the skilled in the art should appreciate that any other suitable interference indicators such as sub-band CQIs, pure interference levels may also be used. Moreover, although, the target SIN threshold is set as 5%-percentile geometry SINRs of all active UEs, the skilled in the art will note that different methods of determining the target SINR threshold may be employed as well such as those method used in FFR.

[00112] Furthermore, in the present disclosure, the proposed TRP is used to mitigate cluster boundary effect. However, it should be noted that the proposed TRP may also be performed by incorporating into other CCIS methods.

[00113] In the above description, the TDD-LTE system is taken as an example, however, it is also possible to apply the solution as proposed to any other appropriate TDD system. Beside, hereinabove, embodiments in which all flexible subframe are disabled for cluster-edge UEs are described in details, however, the skilled in the art may understand that it may also benefit if at least part of the flexible subframes are disabled for cluster -edge UEs. Besides, the present invention has been described with specific algorithm, but the present disclosure is not limited thereto, any other suitable algorithm may also be employed.

[00114] Additionally, based on the above description, the skilled in the art would appreciate that the present disclosure may be embodied in an apparatus, a method, or a computer program product. In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the exemplary embodiments of this disclosure may be illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[00115] The various blocks shown in the companying drawings may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s). At least some aspects of the exemplary embodiments of the disclosures may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this disclosure may be realized in an apparatus that is embodied as an integrated circuit, FPGA or ASIC that is configurable to operate in accordance with the exemplary embodiments of the present disclosure.

[00116] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any disclosure or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular disclosures. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[00117] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[00118] Various modifications, adaptations to the foregoing exemplary embodiments of this disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. Any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this disclosure. Furthermore, other embodiments of the disclosures set forth herein will come to mind to one skilled in the art to which these embodiments of the disclosure pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.

[00119] Therefore, it is to be understood that the embodiments of the disclosure are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are used herein, they are used in a generic and descriptive sense only and not for purposes of limitation.