WO2015042818A1

WO2015042818A1 - Clustering method and apparatus for cross-subframe interference elimination and traffic adaptation and communications mechanism between baseband units

Info

Publication number: WO2015042818A1
Application number: PCT/CN2013/084288
Authority: WO
Inventors: Dalin Zhu; Zhennian SUN; Jianfei CAO; Ming Lei
Original assignee: Nec (China) Co., Ltd.
Priority date: 2013-09-26
Filing date: 2013-09-26
Publication date: 2015-04-02

Abstract

Embodiments of the disclosure provide a method and apparatus for cross-subframe interference elimination in a dynamic TDD system. The method comprises: dividing a plurality of cells in the TDD system into a plurality of disjoint primary cell clusters based on an interference indication and a first threshold for the interference indication; performing, in each of the plurality of primary cell clusters, a time-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference within each of the plurality of primary cell clusters; dividing cells in the plurality of primary cell clusters into a plurality of secondary cell clusters based on the interference indication and a second threshold therefor; and performing, in each of the plurality of secondary cell clusters, a frequency-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters.

Description

CLUSTERING METHOD AND APPARATUS FOR CROSS-SUBFRAME INTERFERENCE ELIMINATION AND TRAFFIC ADAPTATION AND COMMUNICATIONS MECHANISM BETWEEN

BASEBAND UNITS

FIELD OF THE INVENTION

[0001] Embodiments of the present invention generally relate to communication techniques. More particularly, embodiments of the present invention relate to methods and apparatuses for cross-subframe interference elimination.

BACKGROUND OF THE INVENTION

[0002] Generally, two different duplex modes are employed for separating the transmission directions from the user to the base station and back: Frequency Division Duplex (FDD) and Time Division Duplex (TDD). In the TDD mode, a single bandwidth is shared between uplink (UL) and downlink (DL), with the sharing being performed by allocating different periods of time to uplink and downlink.

[0003] Taking a Long Term Evolution (LTE) or LTE-Advanced (LTE-A) TDD system for example, there are seven different patterns of uplink/downlink switching, termed uplink-downlink configurations 0 through 6, which are schematically illustrated in Fig. 1.

[0004] As illustrated in Fig. 1 , a TDD radio frame consists of ten subframes 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, which are denoted as "D", subframes 2 to 4 and subframes 7 to 9 are used for the UL transmission, which are denoted as "U", and subframes 1 and 6 are used as special subframes, which are denoted as "S" and each of which comprises guard period (GP), Uplink Pilot Time Slot (UpPTS), Downlink Pilot Time Slot (DwPTS), etc.

[0005] The LTE TDD system allows for asymmetric UL-DL allocations by the seven different uplink-downlink configurations. Generally, the LTE TDD system statically or semi-statically allocates the UL-DL configuration among cells. Conventionally, all neighboring cells have the same uplink-downlink configuration, e.g., configuration 0, after configurations of the cells are deployed by the LTE TDD system. The configuration allocation is not changed during operation (static allocation) or is changed after years of operation (semi-static allocation).

[0006] In some scenarios, the static or semi-static allocation may not match the burst traffic conditions, e.g., the FTP (File Transfer Protocol) traffic. Accordingly, dynamic configuration allocation is proposed for matching the traffic conditions better. As such, the neighboring cells may have different uplink-downlink configurations from each other. By dynamically allocating UL-DL configurations to different cells, asymmetric DL and UL traffic demands may be well handled.

[0007] However, freely adjusting each cell's UL-DL configuration may result in significant cross-subframe interference, e.g., Cross-subframe Co-channel Interference (CCI), including both BS-BS CCI and UE-UE CCI, which would significantly degrade the system performance. This CCI is brought by the opposite-direction transmissions in neighboring cells when dynamic UL-DL configuration/reconfiguration is enabled.

[0008] Since the BSs usually have higher transmission power and more transmit antennas than the UEs, the BS-BS interference is more severe than the UE-UE interference. Therefore, there is a need to find interference avoidance/mitigation schemes for eliminating the negative impact on the system performance arising from the BS-BS CCI.

SUMMARY OF THE INVENTION

[0009] Embodiments of the present invention propose a solution to eliminate cross-subframe interference, especially the BS-BS interference. Specifically, Embodiments of the present invention provide a method and apparatus for cross-subframe interference elimination in a dynamic TDD system, such that the throughput in the system is effectively improved.

[0010] According to a first aspect of embodiments of the present invention, there is provided a method for cross-subframe interference elimination in a dynamic TDD system. The method may comprise: dividing a plurality of cells in the TDD system into a plurality of disjoint primary cell clusters based on an interference indication and a first threshold for the interference indication; performing, in each of the plurality of primary cell clusters, a time-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference within each of the plurality of primary cell clusters; dividing cells in the plurality of primary cell clusters into a plurality of secondary cell clusters based on the interference indication and a second threshold therefor; and performing, in each of the plurality of secondary cell clusters, a frequency-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters.

[0011] According to a second aspect of embodiments of the present invention, there is provided an apparatus for cross-subframe interference elimination in a dynamic TDD system. The apparatus may comprise: a primary cell clustering unit configured to divide a plurality of cells in the TDD system into a plurality of disjoint primary cell clusters based on an interference indication and a first threshold for the interference indication; a first resource allocation unit configured to perform, in each of the plurality of primary cell clusters, a time-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference within each of the plurality of primary cell clusters; a secondary cell clustering unit configured to divide cells in the plurality of primary cell clusters into a plurality of secondary cell clusters based on the interference indication and a second threshold therefor; and a second resource allocation unit configured to perform, in each of the plurality of secondary cell clusters, a frequency-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters.

[0012] By employing the proposed multi-tier cell clustering based coordinated resource allocation scheme, the system would benefit from improved cell-average, cell-edge performances and enhanced capability in adapting to the asymmetric traffic variations.

[0013] Other features and advantages of the embodiments of the present invention will also be apparent from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS [0014] Embodiments of the invention are presented in the sense of examples and their advantages are explained in greater detail below, with reference to the accompanying drawings, wherein:

[0015] Fig. 1 illustrates a diagram of DL/UL configurations in LTE TDD system as specified by 3GPP;

[0016] Fig. 2 illustrates an exemplary centralized random access network (RAN) which is applicable to implement the embodiments of the present invention;

[0017] Fig. 3 illustrates a schematic diagram of a dynamic TDD system comprising cross-subframe interference according to embodiments of the invention;

[0018] Fig. 4 illustrates a flow chart of a method for cross-subframe interference elimination in a dynamic TDD system according to embodiments of the invention;

[0019] Fig. 5 schematically illustrates a diagram of primary cell clustering and time-domain resource allocation within the primary cell clusters according to an embodiment of the present invention;

[0020] Fig. 6 schematically illustrates a diagram of primary cell clustering and secondary cell clustering in response to satisfying the first time-scale and to the second time-scale, respectively;

[0021] Fig. 7 illustrates a flow chart of a process for secondary cell clustering according to an embodiment of the present invention;

[0022] Fig. 8 illustrates a flow chart of a process for secondary cell clustering according to an embodiment of the present invention;

[0023] Figs. 9A and 9B illustrate specific implementations of the process 800 in Fig. 8;

[0024] Fig. 10 illustrates a table that stores the connections between RRUs/cells via edges according to an exemplary embodiment of the present invention;

[0025] Fig. 11 illustrates the updating of the table as illustrated in Fig. 10;

[0026] Fig. 12 illustrates the updating of the table as illustrated in Fig. 11;

[0027] Figs. 13A and 13B illustrate an alternative of the implementation as shown in Figs. 9A and 9B;

[0028] Fig. 14 schematically illustrates information exchange between BBUs in a dynamic TDD system according to an embodiment of the present invention; [0029] Fig. 15 schematically illustrates identified coordinated cells between two primary cell clusters according to an embodiment of the present invention;

[0030] Fig. 16 illustrates a block diagram of apparatus for cross-sub frame interference elimination in a dynamic TDD system according to embodiments of the present invention; and

[0031] Figs. 17 to 25 illustrate simulation results according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032] Embodiments of the invention will be described thoroughly hereinafter with reference to the accompanying drawings. It will be apparent to those skilled in the art that the invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments and specific details set forth herein. Like numbers refer to like elements throughout the specification.

[0033] The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, the usage of the phrases "certain embodiments," "some embodiments," or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. Thus, appearances of the phrases "in certain embodiments," "in some embodiments," "in other embodiments," or other similar language, throughout this specification do not necessarily all refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0034] Embodiments of the present invention may be applied in various dynamic TDD systems, including but not limited to a LTE or a LTE-A system. Given the rapid development in communications, there will of course also be future type wireless communication technologies and systems with which the present invention may be embodied. It should not be seen as limiting the scope of the invention to only the aforementioned system.

[0035] 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), a 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.

[0036] Furthermore, in a context of the present disclosure, a base station (BS) may represent, e.g., a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, a low power node such as a femto, a pico, and so on.

[0037] First, reference is made to Fig. 2, which illustrates an exemplary centralized random access network (RAN) which is applicable to implement the embodiments of the present invention. As shown in Fig 2, a centralized RAN comprises one or more BBU pools and a plurality of Remote Radio Units (RRUs). The plurality of RRUs are connected with a switch via an optical transport network. Each of the plurality of RRUs is comparable to a cell and installed at its respective local site with only radio frequency (RF) front-end functionalities. The plurality of RRUs may manage multiple cells and transmit, receive and/or measure signals in respective cells. The BBU pool may control, manage and/or coordinate operations of the plurality of RRUs.

[0038] Next, reference is made to Fig. 3, which illustrates a schematic diagram of a dynamic TDD system 300 having cross-sub frame interference according to embodiments of the invention. The system 300 is exemplarily illustrated as a LTE system. For a LTE TDD system, there are seven different patterns of uplink/downlink switching, termed uplink-downlink configurations 0 through 6, as illustrated in Fig. 1. The LTE TDD system allows for asymmetric UL-DL allocations by the seven different uplink-downlink configurations.

[0039] As shown in Fig 3, the system 300 comprises a first base station (BS) 301 and a second base station (BS) 302. The BS 301 manages a cell and a use equipment (UE) 311 is located in the cell and serveed by BS 301, wherein the cell is dynamically allocated with configuration 5 (D, S, U, D, D, D, D, D, D, D). At the same time, the BS 302 manages a cell and a use equipment (UE) 312 is located in the cell and serveed by BS 302, wherein the cell is dynamically allocated with configuration 6 (D, S, U, U, U, D, S, U, U, D). It can be seen that that the fifth sub frame (shown in shadow) of configuration 5 is different from that of configuration 6. Specifically, the fifth subframe of configuration 5 is "D", while the fifth subframe of configuration 6 is "U". In other words, BS 301 performs downlink transmission with UE 311 in the fifth subframe, and BS 302 performs uplink transmission with UE 312 in the fifth subframe. As such, in the fifth subframe, the downlink transmission from BS 301 to UE 311 may interfere with the uplink transmission from UE 312 to BS 302. Accordingly, a cross-sub frame interference occurs.

[0040] To alleviate the cross-subframe interference, the following embodiments of the present invention provide methods and apparatuses for cross-subframe interference elimination.

[0041] Reference is now made to Fig. 4, which illustrates a method 400 for cross-subframe interference elimination in a dynamic TDD system according to embodiments of the invention. In accordance with embodiments of the present invention, the method 400 may be carried out by, for example, a BS, a Baseband Unit (BBU) pool, a central unit, a controller, a server or any other suitable device in the TDD system.

[0042] In step S401, a plurality of cells in the TDD system is divided into a plurality of disjoint primary cell clusters based on an interference indication and a first threshold for the interference indication. Hereinafter, the step S401 is also referred to as the step of primary cell clustering for ease of illustration.

[0043] The interference indication (also referred to as interference metric) indicates an interference level among base stations for the plurality of cells. The interference indication may comprise, but not limited to inter-cell distance, path loss among cells, coupling loss among cells, mutual coupling loss (MCL) among cells, averaged MCL among cells; and geometry signal to interference and noise ratio (SINR). The first threshold for the interference indication can be predetermined. As can be appreciated by those skilled in the art, the predetermined first threshold is not limited to be a fixed value, instead, it is configurable. Those skilled in the art may predefine or preset the first threshold according to his/her experience, system conditions, historical values and/or other factors. For example, in the context of the MCL, the predetermined first threshold for the MCL may be -70dB.

[0044] In an embodiment, the step of primary cell clustering (step S401) may be dynamically performed every a predetermined time interval. In other words, in response to satisfying a first time-scale, the plurality of cells in the TDD system are divided into the plurality of disjoint primary cell clusters. The first time-scale can be monitored by a timer in a network controller, and can be in the order of millisecond, second, etc.

[0045] In the following, there is presented pseudo-codes of an exemplary algorithm for primary cell clustering based on the MCL.

c osen so ar

5: Initialize: $ξ

i while RRUy 6 Γ and y ψ- x do

7: if M CLftm/x-RfiVy < r_p then

: S% RRUy

9: en if

10: end while

12: end while

[0046] In the algorithm as presented above, τ_ρ represents the predetermined MCL threshold (i.e., the first threshold for MCL), NRRU represents the total number of RRUs, Γ represents the set that contains all RRUs, Δ _p represents the set of all primary cell clusters, and S represents the primary cell cluster that is anchored at RRUi. The algorithm is started by randomly selecting one RRU as the anchor point (also referred to as reference RRU). Other RRUs that have smaller MCLs than the predetermined MCL threshold to the reference RRU would be grouped into the same primary cell cluster.

Additionally, the maximum number of RRUs in each of the primary cell clusters is preset as three and the MCL threshold is set to be -70dB, which is the minimum coupling loss defined in related 3GPP specifications.

[0047] This process for primary cell clustering may continue for the rest of RRUs until all cells of interest are divided into disjoint primary cell clusters. As mentioned hereinabove, the primary cell clustering may be dynamically conducted every a predetermined time interval, e.g., 1000ms.

[0048] It is to be noted that, the step of primary cell clustering according to embodiments of the present invention may be implemented in other suitable ways. The above pseudo-codes are illustrated in the present disclosure for the purpose of example, rather than limitation.

[0049] With continued reference to Fig. 4, in step S402, in each of the plurality of primary cell clusters, a time-domain resource allocation is performed based on traffic conditions therein, such that cross-subframe interference within each of the plurality of primary cell clusters can be eliminated. Hereinafter, the step S402 is also referred to as the step of cluster-specific resource configuration/reconfiguration.

[0050] According to embodiments of the present invention, in order to eliminate the cross-subframe interference within each of the primary cell clusters, transmission directions are aligned between cells within the same primary cell cluster. That is, all cells within the same primary cell cluster will be assigned the same DL/UL configuration. On the other hand, the DL/UL configuration allocations are allowed to be different between different primary cell clusters, which will to some extent, ensure the asymmetric traffic adaptation between different primary cell clusters.

[0051] According to embodiments of the present invention, with respect to each of the primary cell clusters, the UL-DL configuration may be dynamically allocated based on DL to UL subframe ratios of available configurations (for example, as shown in Fig. 1) and an accumulated DL to UL data ratio of all cells in the specific primary cell cluster. For example, with respect to one primary cell cluster, in response to that time-scale for reconfiguration (i.e., the first time-scale) in the primary cell cluster is satisfied, an accumulated DL to UL data ratio for all cells in the primary cell cluster may be calculated based on data volume in a DL buffer and a UL buffer for all cells in the primary cell cluster; next, DL to UL subframe ratios of available configurations may be obtained; and a configuration whose DL to UL subframe ratio is closest to the accumulated DL to UL data ratio for all cells in the primary cell cluster may be selected from the available configurations as the UL-DL configuration to be allocated to the primary cell cluster. Alternatively, a configuration whose DL to UL subframe ratio is closest to the DL to UL data ratio for a dominant cell in the primary cell cluster may be selected from the available configurations as the UL-DL configuration to be allocated to the primary cell cluster.

[0052] Fig. 5 schematically illustrates a diagram of primary cell clustering and time-domain resource allocation within the primary cell clusters according to an embodiment of the present invention. As shown in Fig. 5, the plurality of cells in the TDD system are divided into, for example, four disjoint primary cell clusters, PCC 501, PCC 502, PCC 503 and PCC 504. The cells within the PCC 501 are dynamically allocated with the same configuration 5 (D, S, U, D, D, D, D, D, D, D), the cells within the PCC 502 are dynamically allocated with configuration 6 (D, S, U, U, U, D, S, U, U, D), the cells within the PCC 503 are dynamically allocated with configuration 2 (D, S, U, D, D, D, S, U, D, D), and the cell within the PCC 504 is dynamically allocated with the same configuration 5 (D, S, U, D, D, D, D, D, D, D).

[0053] It is to be noted that for cluster-specific resource configuration/reconfiguration (step S402), the information about traffic buffer status, preferred DL/UL configurations, selected DL/UL configurations and etc., should be conveyed between all relevant cells in the same primary cell cluster over the backhaul, and this information can also be distributed from the BBU pool to all relevant RRUs.

[0054] Referring back to Fig. 4, in step S403, cells in the plurality of primary cell clusters are divided into a plurality of secondary cell clusters based on the interference indication and a second threshold for the interference indication. Hereinafter, for ease of illustration, the step S403 is also referred to as the step of secondary cell clustering, as will be described later with reference to Figs. 5 to 13.

[0055] In step S404, there is performed, in each of the plurality of secondary cell clusters, a frequency-domain resource allocation based on traffic conditions therein, such that cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters can be eliminated.

[0056] In some embodiments of the present invention, in order to eliminate the cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters, there is employed the cross-subframe coordinated scheduling/beamforming (CCS/CCB) scheme to coordinate the scheduling decisions and the derivations of DL beamforming weights with respect to the secondary cell cluster of interest during crossed subframes.

[0057] As for the crossed subframes, more attentions are paid to reduce the

RPvU-RPvU CCI, and thus to enhance the UL throughput performance. Hence, the basic principles of the CCS/CCB scheme are (1) minimizing the power leakage from DL to UL, and (2) scheduling the UL UEs on the physical resource blocks (PRBs) that are least interfered by the co-scheduled DL UEs.

[0058] In some embodiments of the present invention, in order to eliminate the cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters, the following frequency-domain resource allocation scheme is employed. In particular, downlink and uplink transmissions in neighbor cells are allocated with different frequency RBs so that the interference between them can be avoided. More specifically, in this case, the allocations of DL and UL resources between neighbor cells during flexible subframes are orthogonal to each other.

[0059] It is to be noted that for cluster-based resource allocation (step S404) such as CCS/CCB as described above, the scheduling decisions, channel state information for both "fixed" and "flexible" subframes and etc., should be exchanged between all relevant cells within the same secondary cell cluster via X2 interface. This information can also be distributed from the BBU pool to all relevant RRUs.

[0060] Hereinafter, reference will be made to Figs. 5 to 13 to describe in detail the process for secondary cell clustering (step S403 in Fig. 4).

[0061] In an embodiment, the step of secondary cell clustering may be dynamically performed every a predetermined time interval. In other words, in response to satisfying a second time-scale, cells in the plurality of primary cell clusters are divided into the plurality of secondary cell clusters. The second time-scale can be monitored by a timer in a network controller, and can be in the order of millisecond, second, etc. A ratio of the first time-scale for primary cell clustering to the second time-scale for secondary cell clustering is equal to a positive integer that is greater than or equal to 1. For example, the first time-scale for primary cell clustering may be 1000ms, and the second time-scale for secondary cell clustering may be 200ms. The determination of the time scales for primary cell clustering and secondary cell clustering depends on practical implementation/requirements of the network. That is, the network controller will determine appropriate time scales for primary cell clustering and secondary cell clustering such that the associated performance metrics can be satisfied.

[0062] Fig. 6 schematically illustrates a diagram of primary cell clustering and secondary cell clustering in response to satisfying the first time-scale and to the second time-scale, respectively. As shown in Fig. 6, a ratio of the time-scale for primary cell clustering (i.e., the first time-scale) to the time-scale for secondary cell clustering (i.e., the second time-scale) is equal to 2. For example, the time-scale for primary cell clustering may be 400ms, and the time-scale for secondary cell clustering may be 200ms. At 601 and 602, in response to satisfying the time-scale for primary cell clustering, the process for primary cell clustering is conducted. At 611, 612 and 613, in response to satisfying the time-scale for secondary cell clustering, the process for secondary cell clustering is conducted.

[0063] With the time-domain resource allocation scheme as illustrated in Fig. 5, the cross-subframe interference within each of the plurality of primary cell clusters can be eliminated. However, in the case of Heterogeneous Network (HetNet) in which there are deployed, for example, a Marcocell, a RRH and s small-type base station node operating at a low power, such as picocell, femtocell, if the picocells/RRUs are densely deployed, the cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters may still have significant negative impact on the system performance.

[0064] In view of the above, embodiments of the present invention propose a multi-tier cell clustering scheme (e.g., as shown in Fig. 6) and coordinated resource allocation scheme based on the multi-tier cell clustering. In the multi-tier cell clustering, the primary cell clustering (step S401) may be considered as the first tier cell clustering, and the secondary cell clustering (step S403) may be considered as the second, third, fourth,..., nth tier cell clustering in response to satisfying the respective time-scale for secondary cell clustering, respectively. By performing a coordinated frequency-domain resource allocation in the secondary cell clusters, the cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters can be eliminated.

[0065] Fig. 7 illustrates a flow chart of a process 700 for secondary cell clustering according to an embodiment of the present invention. The process 700 may be considered as an embodiment of step S403 of method 400 described above with reference to Fig. 4. However, it is noted that this is only for the purpose of illustrating the principles of the present invention, rather than limiting the scope thereof.

[0066] In step S701, a base station is selected from the base stations for the cells in the plurality of primary cell clusters as a reference base station. In the specific implementation, a RRU is randomly selected from RRUs for the cells in the plurality of primary cell clusters as an anchor point (hereinafter, referred to as "reference RRU").

[0067] In step S702, values of the interference indication between the reference base station and the other base stations in the TDD system are determined.

[0068] As described above, the interference indication may comprise, but not limited to inter-cell distance, path loss among cells, coupling loss among cells, mutual coupling loss (MCL) among cells, averaged MCL among cells; and geometry signal to interference and noise ratio (SINR). In the specific implementation, the MCL is selected as the interference indication despite the fact that many other interference indications as mentioned hereinabove may be used.

[0069] According to embodiments of the present invention, there may be several ways to determine the MCL. For example, assuming that a RRUO perform downlink transmission with its UE and interferes with RRUl which is receiving uplink transmission from its UE, the MCL between RRUO and RRUl may be calculated as follows:

M ( ^' !..■; ^:;> , ,... /:/.Y j = 1 AGjijffjQ + l-l. \< > ,;^,;! j - P L _RR(j 0-RRiJi (Equation 1) where TAG_RRU0 denotes a transmit antenna gain of RRUO, RAG_RRM denotes a receive antenna gains of RRUl , and PL_RRU0__RRUL is the propagation loss between RRUO and RRUl .

[0070] Based on the MCL between RRUO and RRUl , the interference between

RRUO and RRUl may be determined, e.g., as follows:

I RRi?⁽)->RRUiL — PR.RU o +

4- RAGRRUX — P Lf_{m;()_ _RRi; i (Equation 2) where Ρ_χχυο represents the transmitted signal power from RRUO.

[0071] Based on Equation 1 , the MCLs between the reference RRU and the other RRUs in the TDD system may be determined.

[0072] From Equations 1 and 2, it can be seen that the MCL indicates the interference level between the two BSs. In other words, the MCL between RRUs/cells implies the potential RRU-RRU CCI level. In practice, MCLRRUO-RRUI is a negative value, which means that the larger the MCL is, the more attenuations the transmitted signals would suffer from. In addition, the MCL can be easily measured by each individual RRU as well. Hence, the MCL between RRUs may be employed as the interference metric in performing the primary/secondary cell clustering. All RRUs may report their MCL measurements to their respective BBUs, which enable the primary/secondary cell clustering in a centralized manner.

[0073] In step S703, the values of the interference indication are compared with the second threshold for the interference indication.

[0074] The second threshold can be predetermined. As can be appreciated by those skilled in the art, the predetermined second threshold is not limited to be a fixed value, instead, it is configurable. Those skilled in the art may predetermine or preset the second threshold according to his/her experience, system conditions, historical values and/or other factors. In general, the second threshold for the interference indication is determined such that the second threshold indicates a higher interference level among base stations for the plurality of cells than that indicated by the first threshold. In the specific implementation, the MCLs between the reference U and the other RRUs in the TDD system are compared with the second threshold for the MCL. For example, the predetermined second threshold for the MCL may be -90dB.

[0075] In step S704, the cells managed by the base stations are divided into the plurality of secondary cell clusters based on the comparing.

[0076] In the specific implementation, the cells managed by the RRUs that have smaller MCLs than the first threshold to the reference RRU would be grouped into the same primary cell cluster. For example, it is assumed that there are six RRUs (RRU 0, RRU 1, RRU 2, RRU 3, RRU 4, RRU 5) in a dynamic TDD system and the RRU 0 is randomly selected as the reference RRU. With the Equation 1, it is determined that the MCL1 between RRU 0 and RRU 1 is -95 dB, the MCL2 between RRU 0 and RRU 2 is -lOOdB, the MCL3 between RRU 0 and RRU 3 is -85 dB, the MCL4 between RRU 0 and RRU 4 is -80 dB, and the MCL5 between RRU 0 and RRU 5 is -75 dB. Since the MCL1 (-95 dB) between RRU 0 and RRU 1 is smaller than the second threshold -90dB, and the MCL2 (-100dB) between RRU 0 and RRU 2 is also smaller than the second threshold -90dB, the cells managed by RRU 0, RRU 1 and RRU 2 are grouped into the same secondary cell cluster.

[0077] This process for secondary cell clustering may continue for the rest of

RRUs until all cells of interest are divided into secondary cell clusters. For example, a new reference RRU (e.g. RRU 3) may be randomly re-selected from RRU 3, RRU 4 and RRU 5. With the Equation 1 , the MCL4' between RRU 3 and RRU 4, and the MCL5 ' between RRU 3 and RRU 5 can be determined. Based on the comparisons of MCL4' and MCL5 ' with the second threshold of -90dB, the cells managed by RRU 3, RRU 4 and RRU 5 can be grouped into one or more secondary cell clusters.

[0078] Additionally, the number of cells in each of the secondary cell clusters may also be limited to a predetermined value. The number of cells in each of the secondary cell clusters may be related to the signaling overhead, design degrees of freedom (DoFs), the computation complexity, and so on. Therefore, it will be preferable to limit the number of cells in each of the secondary cell clusters to a reasonable value, which may be determined by considering the above-mentioned factors, i.e., the signaling overhead, DoFs, the computation complexity, and etc. For example, the predetermined value may be set as 3 in advance, that is to say, at most three cells can be comprised in each of the secondary cell clusters.

[0079] As described above with reference to Fig. 6, the process for secondary cell clustering is dynamically performed every a predetermined time interval. In the specific implementation, since the reference RRU is selected randomly, the result of secondary cell clustering may vary from one reference RRU to another.

[0080] In the following, there is presented pseudo-codes of an exemplary algorithm for secondary cell clustering based on the MCL.

1 : input;

A≠ j, RRUi, RRUj€ Γ}; MCL threshold r,

2: output: Secondary cell cluster set (A_;¾:)

3; while All secondary ceil clusters are formed do

4: start: randomly select one RRU (e.g., IlHUx€ Γ) that has not been chosen so far

5: Initialize: ¾

6: while RRUy€ V and y≠ x do

7: if M CLuj ix- RRUy 5ί τ* then

8· <¾ «- nHUy

9: end if

}'■): en while

II: Δ* *™ <¾

2: end while

[0081] In the algorithm as presented above, x_s represents the predetermined MCL threshold (i.e., the second threshold for MCL), N_RRU represents the total number of RRUs, Γ represents the set that contains all RRUs, Δ _s represents the set of all secondary cell clusters, and r^eP^resent^{s me} secondary cell cluster that is anchored at RRUi.

[0082] It is to be noted that, the step of secondary cell clustering according to embodiments of the present invention may be implemented in other suitable ways. The above pseudo-codes are illustrated in the present disclosure for the purpose of example, rather than limitation.

[0083] Fig. 8 illustrates a flow chart of a process 800 for secondary cell clustering according to an embodiment of the present invention. The process 800 may be considered as another embodiment of step S403 of method 400 described above with reference to Fig. 4. However, it is noted that this is only for the purpose of illustrating the principles of the present invention, rather than limiting the scope thereof.

[0084] In step S801, neighboring cells from different primary cell clusters of the plurality of primary cell clusters are identified. In step S802, values of the interference indication between base stations for the neighboring cells are determined. In step S803, the values of the interference indication are compared with the second threshold. In step S804, the neighboring cells are grouped into the secondary cell clusters based on the comparing. With the process 800 for secondary cell clustering, highly interfered cells/RRUs with different DL/UL configurations or from different primary cell clusters are grouped into same secondary cell clusters.

[0085] Fig. 9A and 9B illustrates specific implementations of the process 800 in Fig. 8.

[0086] Reference is first made to Fig. 9A, which shows a graph illustrating an exemplary result of primary cell clustering according to an embodiment of the present invention. Each of the primary cell clusters is denoted as a polygon. RRU0, RRUI,..., RRU10 as shown in Fig. 9A may be considered as the neighboring RRUs from different primary cell clusters, for example, as identified in step S801 of Fig. 8.

[0087] In the specific implementation as shown in Fig. 9A, the MCL is selected as the interference indication among the RRUs. With Equation 1 as described above, the MCL among the RRU0, RRUI,..., RRU10 can be determined. Then, the MCLs among the RRU0, RRUI,..., RRU10 are compared with the second threshold for the MCL. For example, the second threshold for the MCL may be predetermined as -90dB. [0088] Next, all the identified RRUs/cells can be considered as vertices on the graph as shown in Fig. 9A. The following constraints, for example, may be set: (1) whether the MCL between two RRUs of RRUO, RRU1,..., RRU10 is smaller than the predetermined second threshold for the MCL; and (2) whether asymmetric traffics exist between two RRUs of RRUO, RRU1,..., RRU10.

[0089] In response to satisfying the above-mentioned constraints, the two RRUs can be connected by an edge. For example, the RRU4 is connected with RRUO, and the RRUO is in turn connected with the RRU5 and RRU3.

[0090] Thus, in the BBU pool as illustrated in Fig. 2, there may be built a table that stores the connections between RRUs/cells via edges, which is illustrated in Table 1 of Fig. 10 as an exemplary embodiment of the present invention. It is to be noted that cell 0, cell 1,..., cell 10 in Table 1 correspond to RRUO, RRU1,..., RRU10 in Fig. 9A. Thus, the connections between cell 0, cell 1,..., cell 10 via edges as illustrated in Table 1 indicates the connections between RRUO, RRU1,..., RRU10 via edges.

[0091] In Table 1, "a" represents cells which have same DL/UL configuration/within the same primary cell cluster, and thus "0 (a)" represents that there is no edge between the respective cells. For example, "0 (a)" in line 3, column 2, represents that the cell 0 and cell 1 are within the same primary cell cluster and thus there is no edge between the cellO and celll . "b" represents cells which have larger MCL than the second threshold for the MCL and thus "0 (b)" represents that there is no edge between the respective cells. "1" represents that there is one edge between the respective cells. For example, "1" in line 5, column 2, represents that there is one edge between the cell 4 and cell 0.

[0092] Then, Table 1 can be updated by weighting the edges of each pair of connected RRUs/cells with the determined respective MCL values, which is illustrated in Table 2 of Fig. 11.

[0093] In Table 2, "a" represents cells which have same DL/UL configuration/within the same primary cell cluster, and thus "0 (a)" represents that there is no edge between the respective cells. For example, "0 (a)" in line 3, column 2, represents that the cellO and celll are within the same primary cell cluster and thus there is no edge between the cellO and celll . "b" represents cells which have larger MCL than the second threshold for the MCL and thus "0 (b)" represents that there is no edge between the respective cells. "MCLi_j" represents that the MCL value between the connected cell i and cell j. For example, "MCL_3;0" in line 5, column 2, represents that the MCL value between the connected cell 3 and cell 0.

[0094] Next, Table 2 may be traversed so as to find a pair of connected RRUs/cells which have the smallest MCL therebeween. In this case, the cell 0 and cell 3 are founded. Accordingly, the RRU0 and RRU3 are founded.

[0095] Then, the pair of connected RRUs/cells can be grouped into a tentative secondary cell cluster. Thereafter, there may be selected one RRU from the RRUs connected to each of the pair of RRUs in the tentative secondary cell cluster that has the smallest MCL with respect to the pair of RRUs. Then, the one or more RRUs can be grouped into the tentative secondary cell cluster. In this case, the cell 4 is selected, and thus the RRU4 is selected. Thereby, a secondary cell cluster comprises cell 0, cell 3 and cell 4 as illustrated in Fig. 9B (in a dashed ellipse).

[0096] The process as described above continues until all necessary RRUs have been considered and/or the maximum number of a given secondary cell cluster is satisfied. As described above, the maximum number of cells in each of the secondary cell clusters can be predetermined by considering such factors as signaling overhead, DoFs, computation complexity, and etc. For example, the maximum number of cells in each of the secondary cell clusters may be set as 3 in advance, that is to say, at most three cells can be comprised in each of the secondary cell clusters.

[0097] Thereafter, by excluding those cells/RRUs that have already been grouped into the secondary cell clusters from consideration, the graph as shown in Fig. 9A can be updated to Fig. 9B. Accordingly, Table 2 can be updated to Table 3 as shown in Fig. 12. In Table 3, "0 (c)" represents cells that have been grouped into the tentative secondary cell cluster, and "0 (d)" represents cells that are connected with one or more cells in the tentative secondary cell cluster and have been grouped into the secondary cell clusters. Taking Fig. 9A for example, "0 (c)" represents cell 0 (RRU0) and cell 3 (RRU3) that have been grouped into the tentative secondary cell cluster, and "0 (d)" represents cell 4 (RRU4) that is connected with cell 0 (RRU0) and has been grouped into the secondary cell cluster.

[0098] The above described process may continue until all secondary cell clusters have been formed. [0099] In the following, there is presented pseudo-codes of an exemplary algorithm for calculating the connectivity on the graph Γ .

2: output: Set of edges (er)

3: while All RRUs in F are considered do

4: if RRUi€ όξ, RRU]€ δξ, x≠ y then

5: if MClRjwi- RKU_j≥ r_s then

6: '^·<'/¾. ,; ···· 1

7: e_r ~ edg_i

8: end if

9-, end i

SO: end while

[00100] It is to be noted that, the process for calculating the connectivity on the graph Γ may be implemented in other suitable ways. The above pseudo-codes are illustrated in the present disclosure for the purpose of example, rather than limitation.

[00101] It can be seen from Fig. 9A that the MCL between the RRU4 and RRUO is the smallest due to the smallest distance therebetween, and thus the RRU4 and RRUO are highly coupled with each other. However, the RRU4 and RRU3 are not connected with each other, and thus the RRU4 and RRU3 may not be highly coupled with each other. Thus, the graph as shown in Fig. 9B is considered to be a weakly connected graph (WCG).

[00102] As an alternative of the implementation as shown in Fig. 9A and 9B, after a pair of connected RRUs/cells (RRUO and RRU3) are grouped into a tentative secondary cell cluster, one or more RRUs which are highly coupled both with RRUO and RRU3 can be selected. In this case, the RRU5, instead of RRU4, is selected and grouped into the tentative secondary cell cluster, as shown in Figs. 13A and 13B.

[00103] It is to be also noted that in order to support dynamic primary/secondary cell clustering, necessary signaling mechanisms should be defined. Here, it is proposed to apply the RRC signaling to support the dynamic primary/secondary cell clustering. This method requires one clustering message per RRC connected user, unless a broadcast or a multicast approach is specified.

[00104] As described above, in some embodiments of the present invention, during the processes of primary cell clustering and secondary cell clustering, one RRU is randomly selected as the reference RRU, and other RRUs that have lower MCLs than the predetermined MCL threshold to the reference RRU would be grouped into the same primary/secondary cell cluster. Thus, frequent information exchange between relevant BBUs managing the RRUs may be required in order to support frequency-domain resource allocation within the secondary cell clusters.

[00105] Fig. 14 schematically illustrates information exchange between BBUs in a dynamic TDD system according to an embodiment of the present invention. In the dynamic TDD system as shown in Fig. 14, a BBU 1410 manages RRU 1412 and a BBU 1420 manages RRU 1422. The BBU 1410 and BBU 1420 belong to different BBU pool, and thus they communicate with each other via X2+ interface. The RRU 1412 and RRU 1422 coming from different primary cell clusters are within the same secondary cell cluster 1430 as denoted by a dashed ellipse. According to embodiments of the present invention, the RRUs 1412 and 1422 will report their interference measurements such as MCL measurements to their respective BBUs 1410 and 1420, and then the BBUs 1410 and 1420 will communicate with each other via X2+ interface so as to enable frequency-domain resource allocation within the same secondary cell cluster 1430. Thus, it is desired to propose a scheme for optimizing the mapping between BBUs and RRUs such that the frequency of information exchange between relevant BBUs can be reduced.

[00106] In the proposed scheme for optimizing the mapping between BBUs and RRUs, there are first identified coordinated cells among the plurality of primary cell clusters, induced by dividing the cells in the plurality of primary cell clusters into the plurality of secondary cell clusters.

[00107] Fig. 15 schematically illustrates identified coordinated cells between two primary cell clusters according to an embodiment of the present invention. In Fig. 15, cell 0, cell 1 and cell 2 are within one primary cell cluster as denoted by three solid ellipses, and cell 3 and cell 4 are within the other primary cell cluster as denoted by another two solid ellipses. As a result of performing secondary cell clustering, the cell 2 and cell 3 are divided into a secondary cell cluster 1501 denoted by a dashed ellipse. Thus, the cell 2 and cell 3 can be considered as coordinated cells between the two primary cell clusters, induced by dividing the cells in the two primary cell clusters into a secondary cell clusters. By performing the step of identifying coordinated cells among the plurality of primary cell clusters as described above, all the coordinated cells among the plurality of primary cell clusters can be found.

[00108] Then, there is calculated the total number of coordinated cells between two primary cell clusters induced by the secondary cell clustering. There may be built in the cloud a look-up table that stores the total number of coordinated cells between two primary cell clusters, as illustrated in Table 4.

Table 4

[00109] In Table 4, numbers without being followed by parentheses represent total numbers of coordinated cells between two primary cell clusters (PCCs). For example, "5" in line 5, column 4 represents a total number of coordinated cells between PCC3 and PCC2. Numbers followed by parentheses represent total numbers of cells in a primary cell cluster. For example, "0 (5)" in line 5, column 5 represents a total number of cells in PCC3.

[00110] In addition, at the initial phase, it is assumed that each primary cell cluster is managed by one BBU. For example, there exists the following mapping between BBU and PCC managed by the BBU.

[00111] BBU0={PPC0}

[00112] BBU1={PPC1 }

[00113] BBU2={PPC2}

[00114] BBU3={PPC3}

[00115] Next, there is sorted the number of the coordinated cells between two primary cell clusters of the plurality of primary cell clusters. Then, the primary cell clusters that have a largest number of coordinated cells therebetween is grouping into a group of primary cell clusters.

[00116] Taking Table 4 for example, PCC2 and PCC3 have a largest number of coordinated cells (i.e., "5"), and thus PCC2 and PCC3 can be grouped into a group of primary cell clusters. Accordingly, Table 4 can be updated to Table 5, as illustrated below.

Table 5

[00117] In Table 5, "0 (11)" in line 4, column 4 represents a total number of cells in the group of primary cell clusters comprising PCC2 and PCC3.

[00118] Accordingly, the mapping between BBU and PCC described above may be updated as below.

[00119] BBU0={PPC0}

[00120] BBU1={PPC1 }

[00121] BBU2={PPC2, PCC3}

[00122] Accordingly, the mapping table between BBUs and RRUs stored in the switch (as shown in Fig. 2, for example) should be updated such that the group of primary cell clusters comprising PCC2 and PCC3 is managed by a single BBU (for example, BBU2).

[00123] It is to be noted that the number limit of cells/RRUs that a single BBU or a single BBU pool can manage can be predetermined by considering such factors as processing capacity of a single BBU. For example, in the example as described with reference to Table 4 and Table 5, the number limit of cells is predetermined as 11. In this case, grouping the primary cell clusters that have a largest number of coordinated cells therebetween into a group of primary cell clusters may comprise comparing a total number of cells in the primary cell clusters that have the largest number of coordinated cells therebetween with the number limit of cells that the single baseband unit can manage; and in response to the total number of cells failing to exceed the number limit of cells, grouping the primary cell clusters that have the largest number of coordinated cells therebetween into a group of primary cell clusters.

[00124] In addition, in response to the total number of cells achieving the number limit of cells that the single BBU can manage, the Table 5 can be updated by removing the item associated with the single BBU, as illustrated in Table 6.

Table 6 [00125] The process as described above continues until all RRUs have been considered. In the example as described with reference to Table 4, Table 5 and Table 6, the resulting mapping between BBU and PCC is illustrated as below.

[00126] BBU0= {PPC0, PCC 1 }

[00127] BBU2={PPC2, PCC3}

[00128] The process of forming groups of primary cell clusters as described above may be dynamically conducted every tens/hundreds of milliseconds. For example, the time scale for forming groups of primary cell clusters may be the same as that for primary cell clustering.

[00129] With the proposed BBU-RRU mapping scheme as described above, the frequency/required bandwidth of information exchange between relevant BBUs in the cloud can be reduced.

[00130] Reference is now made to Fig. 16, which illustrates a block diagram of apparatus 1600 for cross-subframe interference elimination in a dynamic TDD system according to embodiments of the present invention. As shown in Fig. 16, the apparatus 1600 comprises: a primary cell clustering unit 1601 configured to divide a plurality of cells in the TDD system into a plurality of disjoint primary cell clusters based on an interference indication and a first threshold for the interference indication; a first resource allocation unit 1602 configured to perform, in each of the plurality of primary cell clusters, a time-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference within each of the plurality of primary cell clusters; a secondary cell clustering unit 1603 configured to divide cells in the plurality of primary cell clusters into a plurality of secondary cell clusters based on the interference indication and a second threshold therefor; and a second resource allocation unit 1604 configured to perform, in each of the plurality of secondary cell clusters, a frequency-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters.

[00131] In accordance with embodiments of the present invention, the apparatus 1600 may be implemented in a BS, a baseband unit (BBU) pool, a central unit, a controller, a server or any other suitable device.

[00132] In an exemplary embodiment, the second threshold for the interference indication indicates a higher interference level among base stations for the plurality of cells than that indicated by the first threshold.

[00133] In an exemplary embodiment, the primary cell clustering unit 1601 is further configured to divide the plurality of cells in the TDD system into the plurality of disjoint primary cell clusters in response to satisfying a first time-scale.

[00134] In an exemplary embodiment, the secondary cell clustering unit 1603 is further configured to divide cells in the plurality of primary cell clusters into the plurality of secondary cell clusters in response to satisfying a second time-scale, wherein a ratio of the first time-scale to the second time-scale is equal to a positive integer greater than 1.

[00135] In an exemplary embodiment, the secondary cell clustering unit 1603 comprises: a selecting unit configured to select a base station from the base stations for the cells in the plurality of primary cell clusters as a reference base station; a first determining unit configured to determine values of the interference indication between the reference base station and the other base stations; a first comparing unit configured to compare the values of the interference indication with the second threshold; and a dividing unit configured to divide the cells managed by the base stations into the plurality of secondary cell clusters based on the comparing.

[00136] In an exemplary embodiment, the secondary cell clustering unit 1603 comprises: a first identifying unit configured to identify neighboring cells from different primary cell clusters of the plurality of primary cell clusters; and a first grouping unit configured to group the neighboring cells into the secondary cell clusters.

[00137] In an exemplary embodiment, the first grouping unit comprises: a second determining unit configured to determine values of the interference indication between base stations for the neighboring cells; a second comparing unit configured to compare the values of the interference indication with the second threshold; and a second grouping unit configured to group the neighboring cells into the secondary cell clusters based on the comparing.

[00138] In an exemplary embodiment, the apparatus 1600 further comprising: a second identifying unit configured to identify coordinated cells among the plurality of primary cell clusters, induced by dividing the cells in the plurality of primary cell clusters into the plurality of secondary cell clusters; a sorting unit configured to sort a number of the coordinated cells between two primary cell clusters of the plurality of primary cell clusters; a third grouping unit configured to group the primary cell clusters that have a largest number of coordinated cells therebetween into a group of primary cell clusters; and a managing unit configured to manage the group of primary cell clusters by a single baseband unit.

[00139] In an exemplary embodiment, the third grouping unit comprises: a third comparing unit configured to compare a total number of cells in the primary cell clusters that have the largest number of coordinated cells therebetween with a number limit of cells that the single baseband unit can manage; and a fourth grouping unit configured to group the primary cell clusters that have the largest number of coordinated cells therebetween into a group of primary cell clusters, in response to the total number of cells failing to exceed the number limit of cells.

[00140] In embodiments of the present invention, the interference indication comprises one of the following: inter-cell distance; path loss among cells; coupling loss among cells; mutual coupling loss among cells; averaged mutual coupling loss among cells; and geometry signal to interference and noise ratio.

[00141] It is noted that the apparatus 1600 may be configured to implement functionalities as described with reference to Figs. 4-25. It is further noted that the components of the apparatus 1600 may be embodied in hardware, software, firmware, and/or any combination thereof. For example, the components of the apparatus 1600 may be respectively implemented by a circuit, a processor or any other appropriate selection device. Those skilled in the art will appreciate that the aforesaid examples are only for illustration not limitation.

[00142] In some embodiment of the present invention, the apparatus 1600 comprises at least one processor. The at least one processor suitable for use with embodiments of the present disclosure may include, by way of example, both general and special purpose processors already known or developed in the future. The apparatus 1600 further comprises at least one memory. The at least one memory may include, for example, semiconductor memory devices, e.g., RAM, ROM, EPROM, EEPROM, and flash memory devices. The at least one memory may be used to store program of computer executable instructions. The program can be written in any high-level and/or low-level compilable or interpretable programming languages. In accordance with embodiments, the computer executable instructions may be configured, with the at least one processor, to cause the apparatus 1600 to at least perform according to any of methods 400, 700 and 800 as discussed above.

[00143] In addition, Figs. 17 to 25 illustrate simulation results according to an embodiment of the present invention. Parameters used in the simulations are listed in

Table 7.

Parameters Assumptions used for simulation

System bandwidth 10MHz

Carrier frequency 2GHz

Macro deployment N/A

Outdoor Pico deployment PPP with density = 8^3 /500²

Outdoor Pico antenna pattern 2D, Omni-directional

Outdoor Pico antenna gain 5dBi

UE antenna gain OdBi

Outdoor Pico noise figure 13dB

UE noise figure 9dB

Outdoor Pico max transmission

24dBm

power

UE power class 23dBm (200mW)

UEs distribution PPP with density λ₂ = 0λ_ί

Shadowing standard deviation

6dB

between outdoor Pico cells

Shadowing correlation between

0

UEs

Shadowing correlation between

0.5

outdoor Picos

Shadowing standard deviation

3dB for LoS and 4dB for NLoS

between outdoor Pico and UE

HARQ retransmission scheme N/A

Small scaling fading channel ITU UMi

Else, PLLOS(R)=101.9+401oglO(Pv)

PL of outdoor Pico to outdoor For 2GHz, R in km

Pico NLOS:

Case 1 : PLNLOS(R)=169.36+401oglO(R), R in km. Prob(R)=0.5-min(0.5,5exp(-0.156/R))+min(0.5, 5exp(-R/0.03))

PLLOS( )=103.8+20.91oglO( )

PLNLOS(R)=145.4+37.51ogl0(Pv)

For 2GHz, R in km

PL of outdoor Pico to UE

Case 1 :

Prob(R)=0.5-min(0.5,5exp(-0.156/R))+min(0.5, 5exp(-R/0.03))

If R<=50m, PL(R)=98.45+201oglO(R), R in km

PL of UE to UE

Else, PL(R)=55.78+401oglO(R) For 2GHz, R in m

Single-user: FIFO

Scheduler

multi-user: PF in both time and frequency

Pico antenna configuration 2Tx, lRx

UE antenna configuration lTx, 2Rx

Receiver type MMSE

Time-scale for reconfiguration 10ms

Time-scale for primary cell

1000ms

clustering

Time-scale for secondary cell

200ms

clustering

MCL threshold for PCC 90dB

MCL threshold for SCC 60dB

Max. number of cells within the

3

same SCC for SCG and WCG

Max. number of cells managed

40

by a single BBU

Packet file size 2M

Table 7

[00144] It is to be noted that "Case 1" in Table 7 indicates the embodiment of the present invention described above with reference to Fig. 7.

[00145] In the simulations, the DL and UL metrics are collected separately. Moreover, packet throughput is defined as the packet size over the packet transmission time, including the packet waiting time in the buffer. Further, cell-average packet throughput (PT) is defined as the average packet throughput of all cells, and cell-edge PT is 5%-ile value from the cumulative density function (CDF) of average packet throughput from all UEs.

[00146] Figs. 17 and 18 illustrate empirical CDF of MCL and average cell cluster size, respectively. Figs. 19 and 20 illustrate empirical CDF of DL geometry SIN s and empirical CDF of UL geometry SINRs.

[00147] In Figs. 21 and 22, simulation results are provided in terms of the cell-average DL PT and UL PT performances in the following five cases.

• Case I : all cells employ the same DL/UL configuration without dynamic adjustment, denoted as "Ref. configuration #1". Additionally, "Ref. configuration #1" is employed by all cells of interest in the network. This scheme serves as a baseline scenario for comparison.

• Case II : only PCC with cluster-specific dynamic DL/UL configuration is performed, denoted as "COM".

• Case III: the embodiment of the present invention described above with reference to Fig. 13, denoted as "SCG".

• Case IV: the embodiment of the present invention described above with reference to Figs. 9A and 9B, denoted as "WCG".

• Case V : the embodiment of the present invention described above with reference to Fig. 7, denoted as "Random".

[00148] In Figs. 23 and 24, simulation results are provided in terms of the cell-edge DL PT and UL PT performances in the five cases as described above.

[00149] Figs. 25A and 25B illustrate the performance of BBU-RRU mapping according to embodiments as described above with reference to Fig. 15 and Tables 4-6.

[00150] 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.

[00151] The various blocks shown in FIGS. 2-5 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.

[00152] 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.

[00153] 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.

[00154] 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.

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.

Claims

WHAT IS CLAIMED IS:

1. A method for cross-subframe interference elimination in a dynamic Time Division Duplex (TDD) system, comprising:

dividing a plurality of cells in the TDD system into a plurality of disjoint primary cell clusters based on an interference indication and a first threshold for the interference indication;

performing, in each of the plurality of primary cell clusters, a time-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference within each of the plurality of primary cell clusters;

dividing cells in the plurality of primary cell clusters into a plurality of secondary cell clusters based on the interference indication and a second threshold therefor; and performing, in each of the plurality of secondary cell clusters, a frequency-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters.

2. The method according to Claim 1, wherein the second threshold for the interference indication indicates a higher interference level among base stations for the plurality of cells than that indicated by the first threshold.

3. The method according to Claim 2, wherein dividing a plurality of cells in the TDD system into a plurality of disjoint primary cell clusters based on an interference indication and a first threshold for the interference indication comprises:

in response to satisfying a first time-scale, dividing the plurality of cells in the

TDD system into the plurality of disjoint primary cell clusters.

4. The method according to Claim 3, wherein dividing cells in the plurality of primary cell clusters into a plurality of secondary cell clusters based on the interference indication and a second threshold therefor comprises:

in response to satisfying a second time-scale, dividing cells in the plurality of primary cell clusters into the plurality of secondary cell clusters, wherein a ratio of the first time-scale to the second time-scale is equal to a positive integer greater than 1.

5. The method according to Claim 4, wherein in response to satisfying a second time-scale, dividing cells in the plurality of primary cell clusters into the plurality of secondary cell clusters comprises:

selecting a base station from the base stations for the cells in the plurality of primary cell clusters as a reference base station;

determining values of the interference indication between the reference base station and the other base stations;

comparing the values of the interference indication with the second threshold; and dividing the cells managed by the base stations into the plurality of secondary cell clusters based on the comparing.

6. The method according to Claim 3, wherein dividing cells in the plurality of primary cell clusters into a plurality of secondary cell clusters based on the interference indication and a second threshold therefor comprises:

identifying neighboring cells from different primary cell clusters of the plurality of primary cell clusters; and

grouping the neighboring cells into the secondary cell clusters.

7. The method according to Claim 6, wherein grouping the neighboring cells into the secondary cell clusters comprises:

determining values of the interference indication between base stations for the neighboring cells;

comparing the values of the interference indication with the second threshold; and grouping the neighboring cells into the secondary cell clusters based on the comparing.

8. The method according to any one of Claims 1 to 7, further comprising:

identifying coordinated cells among the plurality of primary cell clusters, induced by dividing the cells in the plurality of primary cell clusters into the plurality of secondary cell clusters; sorting a number of the coordinated cells between two primary cell clusters of the plurality of primary cell clusters;

grouping the primary cell clusters that have a largest number of coordinated cells therebetween into a group of primary cell clusters; and

managing the group of primary cell clusters by a single baseband unit.

9. The method according to Claim 8, wherein grouping the primary cell clusters that have a largest number of coordinated cells therebetween into a group of primary cell clusters comprises:

comparing a total number of cells in the primary cell clusters that have the largest number of coordinated cells therebetween with a number limit of cells that the single baseband unit can manage; and

in response to the total number of cells failing to exceed the number limit of cells, grouping the primary cell clusters that have the largest number of coordinated cells therebetween into a group of primary cell clusters.

10. The method according to any one of Claims 1 to 9, wherein the interference indication comprises one of the following:

inter-cell distance;

path loss among cells;

coupling loss among cells;

mutual coupling loss among cells;

averaged mutual coupling loss among cells; and

geometry signal to interference and noise ratio.

11. An apparatus for cross-subframe interference elimination in a dynamic Time Division Duplex (TDD) system, comprising:

a primary cell clustering unit configured to divide a plurality of cells in the TDD system into a plurality of disjoint primary cell clusters based on an interference indication and a first threshold for the interference indication;

a first resource allocation unit configured to perform, in each of the plurality of primary cell clusters, a time-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference within each of the plurality of primary cell clusters;

a secondary cell clustering unit configured to divide cells in the plurality of primary cell clusters into a plurality of secondary cell clusters based on the interference indication and a second threshold therefor; and

a second resource allocation unit configured to perform, in each of the plurality of secondary cell clusters, a frequency-domain resource allocation based on traffic conditions therein, so as to eliminate cross-subframe interference between different primary cell clusters in the plurality of primary cell clusters.

12. The apparatus according to Claim 11, wherein the second threshold for the interference indication indicates a higher interference level among base stations for the plurality of cells than that indicated by the first threshold.

13. The apparatus according to Claim 12, wherein the primary cell clustering unit is further configured to divide the plurality of cells in the TDD system into the plurality of disjoint primary cell clusters in response to satisfying a first time-scale.

14. The apparatus according to Claim 13, wherein the secondary cell clustering unit is further configured to divide cells in the plurality of primary cell clusters into the plurality of secondary cell clusters in response to satisfying a second time-scale, wherein a ratio of the first time-scale to the second time-scale is equal to a positive integer greater than 1.

15. The apparatus according to Claim 14, wherein the secondary cell clustering unit comprises:

a selecting unit configured to select a base station from the base stations for the cells in the plurality of primary cell clusters as a reference base station;

a first determining unit configured to determine values of the interference indication between the reference base station and the other base stations;

a first comparing unit configured to compare the values of the interference indication with the second threshold; and a dividing unit configured to divide the cells managed by the base stations into the plurality of secondary cell clusters based on the comparing.

16. The apparatus according to Claim 13, wherein the secondary cell clustering unit comprises:

a first identifying unit configured to identify neighboring cells from different primary cell clusters of the plurality of primary cell clusters; and

a first grouping unit configured to group the neighboring cells into the secondary cell clusters.

17. The apparatus according to Claim 16, wherein the first grouping unit comprises:

a second determining unit configured to determine values of the interference indication between base stations for the neighboring cells;

a second comparing unit configured to compare the values of the interference indication with the second threshold; and

a second grouping unit configured to group the neighboring cells into the secondary cell clusters based on the comparing.

18. The apparatus according to any one of Claims 11 to 17, further comprising: a second identifying unit configured to identify coordinated cells among the plurality of primary cell clusters, induced by dividing the cells in the plurality of primary cell clusters into the plurality of secondary cell clusters;

a sorting unit configured to sort a number of the coordinated cells between two primary cell clusters of the plurality of primary cell clusters;

a third grouping unit configured to group the primary cell clusters that have a largest number of coordinated cells therebetween into a group of primary cell clusters; and

a managing unit configured to manage the group of primary cell clusters by a single baseband unit.

19. The apparatus according to Claim 18, wherein the third grouping unit comprises:

a third comparing unit configured to compare a total number of cells in the primary cell clusters that have the largest number of coordinated cells therebetween with a number limit of cells that the single baseband unit can manage; and

a fourth grouping unit configured to group the primary cell clusters that have the largest number of coordinated cells therebetween into a group of primary cell clusters, in response to the total number of cells failing to exceed the number limit of cells.