WO2017089898A1

WO2017089898A1 - Methods and apparatuses for communicating with virtual cell and associated communication system

Info

Publication number: WO2017089898A1
Application number: PCT/IB2016/001855
Authority: WO
Inventors: Feng She; Haiyou Guo
Original assignee: Alcatel Lucent
Priority date: 2015-11-24
Filing date: 2016-11-18
Publication date: 2017-06-01
Also published as: CN106788646A; CN106788646B

Abstract

Embodiments of the present disclosure provide methods and apparatuses for communication and a corresponding communication System. In a communication method implemented at a macro base station, configuration information related to an UL reference signal to be transmitted by UE is transmitted to candidate small cells among a plurality of small cells. The configuration information is used by the candidate small cells to receive the UL reference signal to determine channel state information, and the channel state information indicates channel quality of a channel between the UE and the respective candidate small cell. The method further comprises receiving, from at least one of the candidate small cells, channel state information that satisfies a predetermined condition and determining, based on the received channel state information, a virtual cell for data communication of the UE. The virtual cell is formed with one or more of the at least one candidate small cell.

Description

METHODS AND APPARATUSES FOR

COMMUNICATING WITH VIRTUAL CELL AND ASSOCIATED COMMUNICATION SYSTEM

TECHNOLOGY

[0001] Embodiments of the present disclosure generally relate to the field of wireless communications and more specifically, to methods and apparatuses for communicating with a virtual cell and a communication system.

BACKGROUND

[0002] In recent years, traffic demands in mobile networks are growing continuously both in terms of total capacities of the networks and bit rates required by individual users. To meet the demands, one possible solution is to deploy a very dense network which is so called as ultra-dense network (UDN). For example, dozens or hundreds of micro base stations or wireless access nodes may be deployed within a coverage area (for example, a macro cell) of a macro base station such as macro eNB (MeNB). These micro base stations may include for example small base stations, pico base stations, femto base stations, and the like. Their coverage areas are correspondingly called as small cells, pico cell, femto cells and the like. Hereinafter, the base stations deployed in a macro cell are collectively referred to as "micro base stations" and the cells within the macro cell are collectively referred to as "small cells".

[0003] In UDN, small cells may assist in diverting traffic for the macro cell to meet the demands on the total capacity of the network and bit rates required by individual users. However, there may be some problems in such dense network. One of the problems is that user equipment (UE) may have to deal with strong interference. Another problem is that there may be more frequent handovers among the small cells due to the mobility of UE. To address the above problems, a mechanism of virtual cell has been proposed recently. A virtual cell is consisted of a plurality of small cells or wireless access nodes. During the communication, one of the wireless access nodes in the virtual cell acts as a master access node to take charge of scheduling all the small cells in that virtual cell.

[0004] Small cell discovery in UDN is critical to guarantee effective traffic diversion from the macro base station to the small cells. In the mechanism of virtual cell, small cell discovery and virtual cell forming are fundamental to facilitate virtual cell-based data communication. If latency of the small cell discovery and virtual cell forming is large, system performance may be dramatically degraded.

[0005] In current small cell discovery solution, a small cell is discovered based on downlink (DL, from the base station to UE) signals. The base station or wireless access node of the small cell periodically broadcasts a discovery signal and the UE discovers a potential small cell by probing the discovery signal. However, the system performance can hardly be improved if the small cells are discovered by a traditional discovery solution to form a virtual cell for communication. The main problem is that latency of the small cell discovery based on the DL signal is quite large due to the periodicity of the discovery signal and its measurement and report. The latency is generally ranged from several hundred milliseconds to several seconds. Therefore, the large latency of the small cell discovery results in latency of the virtual cell forming, thereby significantly degrading the overall system performance.

[0006] Hence, it is desired to provide a solution to improve the small cell discovery and virtual cell forming so as to facilitate data communication of user equipment in the virtual cell.

SUMMARY

[0007] An objective of embodiments of the present disclosure is to provide a scheme for communicating with a virtual cell.

[0008] According to a first aspect of the present disclosure, there is provided a method implemented at a macro base station. The method includes transmitting, to candidate small cells among a plurality of small cells, configuration information related to an uplink (UL) reference signal to be transmitted by user equipment (UE). The configuration information is used by the candidate small cells to receive the UL reference signal to determine channel state information, and the channel state information indicates channel quality of a channel between the UE and the respective candidate small cell. The method further includes receiving, from at least one of the candidate small cells, channel state information that satisfies a predetermined condition and determining, based on the received channel state information, a virtual cell for data communication of UE. The virtual cell is formed with one or more of at least one candidate small cell.

[0009] According to a second aspect of the present disclosure, there is provided a method implemented at a micro base station of a small cell. The method includes receiving, from a macro base station, configuration information related to an UL reference signal to be transmitted by UE. The method also includes receiving, based on the configuration information, the UL reference signal from the UE to determine channel state information, the channel state information indicating channel quality of a channel between the UE and the small cells. The method further includes in response to the channel state information satisfying a predetermined condition, transmitting the channel state information to the macro base station for determining a virtual cell for data communication of the UE. The virtual cell is formed with at least the small cell.

[0010] According to a third aspect of the present disclosure, there is provided a communication method implemented at UE. The method includes transmitting an UL reference signal to a candidate small cell, such that the candidate small cell receives, based on configuration information related to the UL reference signal that is received from the macro base station, the UL reference signal for determining channel state information and transmits to the macro base station in response to the channel state information satisfying a predetermined condition. The channel state information indicates state information of a channel between the UE and the candidate small cell.

[0011] According to a fourth aspect of the present disclosure, there is provided a communication apparatus in a macro base station. The apparatus includes a configuration information transmitting unit configured to transmit, to candidate small cells among a plurality of small cells, configuration information related to an UL reference signal to be transmitted by UE. The configuration information is used by the candidate small cells to receive the UL reference signal to determine channel state information, the channel state information indicating channel quality of a channel between the UE and the respective candidate small cell. The apparatus further includes a state information receiving unit configured to receive, from at least one of the candidate small cells, channel state information that satisfies a predetermined condition and a virtual cell determining unit configured to determine a virtual cell for data communication of the UE based on the received channel state information. The virtual cell is formed with one or more of the at least one candidate cell.

[0012] According to a fifth aspect of the present disclosure, there is provided a communication apparatus in a micro base station of a small cell. The apparatus includes a configuration information receiving unit configured to receive, from a macro base station, configuration information related to an UL reference signal to be transmitted by UE. The apparatus also includes a state information determining unit configured to receive, based on the configuration information, the UL reference signal from the UE to determine the channel state information, the channel state information indicating channel quality of a channel between the UE and the small cell. The apparatus further includes a state information transmitting unit configured to transmit, in response to the channel state information satisfying a predetermined condition, the channel state information to the macro base station for determining a virtual cell for data communication of the UE. The virtual cell is at least formed with at least the small cell.

[0013] According to a sixth aspect of the present disclosure, there is provided a communication apparatus in UE. The apparatus includes an UL reference signal transmitting unit configured to transmit an UL reference signal to a candidate small cell, such that the candidate small cell receives, based on configuration information related to the UL reference signal received from the macro base station, the UL reference signal for determining channel state information and transmits the channel state information to the macro base station in response to the channel state information satisfying a predetermined condition. The channel state information indicates state information of a channel between the UE and the candidate small cell.

[0014] According to a seventh aspect of the present disclosure, there is provided a communication system. The system includes a macro base station including the apparatus discussed in the above fourth aspect. The system also includes at least one micro base station of at least one small cell including the apparatus discussed in the above fifth aspect. The system further includes UE including the apparatus discussed in the above sixth aspect.

[0015] Through the following description, it would be appreciated that according to example embodiments of the present disclosure, a virtual cell is determined based on an UL reference signal transmitted by UE on uplink. Whenever UE is in need, for example, when the UE moves to a new location or has data to be transmitted, it may autonomously transmit the UL reference signal so as to discover available small cells and discover or form a virtual cell for data communication. The macro base station can provide configuration information related to the UL reference signal for candidate small cells to facilitate detecting the UL reference signal. In such manner, the latency of the small cell discovery is significantly reduced compared with the traditional small cell discovery based on the downlink discovery signal transmitted periodically, which may therefore enhance the overall performance of the system. Other advantages of the example embodiments of the present disclosure will be apparent through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objectives, features, and advantages of example embodiments of the present disclosure will become apparent through the following detailed description with reference to the accompanying drawings. Some example embodiments of the present disclosure are illustrated by way of example but not limitation in the drawings in which:

[0017] Fig. 1 is a diagram illustrating an example environment in which a system and/or method described herein may be implemented;

[0018] Fig. 2 illustrates a block diagram of an example computer system/server suitable for implementing embodiments of the present disclosure;

[0019] Fig. 3 illustrates a flowchart of a communication method implemented at a macro base station according to an embodiment of the present disclosure;

[0020] Fig. 4 illustrates a schematic diagram of a communication process between a macro base station, a micro base station, and user equipment according to an embodiment of the present disclosure;

[0021] Fig. 5 illustrates a schematic diagram of a communication process between a macro base station, a micro base station, and user equipment according to another embodiment of the present disclosure;

[0022] Fig. 6 illustrates a schematic diagram of a communication process between a macro base station, a micro base station, and user equipment according to a further embodiment of the present disclosure;

[0023] Fig. 7 illustrates a block diagram of a communication apparatus in a macro base station according to one embodiment of the present disclosure;

[0024] Fig. 8 illustrates a block diagram of a communication apparatus in a micro base station of a small cell according to one embodiment of the present disclosure; and

[0025] Fig. 9 shows a block diagram of a communication apparatus in UE according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

[0026] Principles of example embodiments disclosed herein will now be described with reference to various example embodiments illustrated in the drawings. It would be appreciated that description of those embodiments is merely to enable those skilled in the art to better understand and thus implement example embodiments of the present disclosure and is not intended for limiting the scope disclosed herein in any manner.

[0027] As used herein, the term "includes" and its variants are to be read as open-ended terms that mean "includes, but is not limited to." The term "or" is to be read as "and/or" unless the context clearly indicates otherwise. The term "based on" is to be read as "based at least in part on." The term "one example embodiment" and "an example embodiment" are to be read as "at least one example embodiment."

[0028] In description of embodiments of the present disclosure, 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 functions of the UE, terminal, MT, SS, PSS, MS or AT may be included therein. The UE may be any type of mobile terminal, fixed terminal or portable terminal, such as mobile telephone, station, unit, device, multimedia computer, multimedia tablet, Internet node, communicator, desk-top compute, laptop computer, notable computer, netbook computer, tablet computer, personal communication system (PCS) device, personal navigation device, personal digital assistant (PDA), audio/video player, digital camera/video camera, positioning device, television receiver, radio broadcast receiver, E-book device, gaming device, or any combinations thereof, including accessories and peripherals of these devices or any combination thereof. It is appreciated that it can support any type of interface for a user (such as a "wearable" circuit).

[0029] In description of embodiments of the present disclosure, the term "base station (BS)" is sometimes called "BS/node," "wireless access node" or "transport node" to be consistent with 3GPP terms. It should be noted that the term "BS/node," "node," "transport node," and "BS" have the same meaning in the present disclosure, and each of them may indicate a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a radio header (RH), a remote radio head (RRH), a relay, a low power node such as a femto station and a pico station, and the like. Coverage of a base station or a geographic area where service of the base station is provided is referred to as a cell.

[0030] In the description of embodiments of the present disclosure, the term "macro base station" refers to a base station with a wider coverage area, which is sometimes also called as MeNB (Macro eNB) and the coverage area of the macro base station is known as a macro cell. The term "micro base station" refers to a base station with a narrower coverage area and also includes a pico station, femto station, or the like. The coverage area of the micro base station is known as a small cell, which also correspondingly includes a pico cell, femto cell, or the like. The macro cell of the macro base station includes a plurality of small cells.

[0031] Fig. 1 is a diagram illustrating an example environment 100 in which a system and/or method described in the present disclosure may be implemented. The example environment 100 shows an example part of an ultra-dense network (UDN). As shown, a geographical area 150 of a macro base station 110 (that is, a macro cell 150) includes user equipment served. A plurality of small cells 160 are deployed within the macro cell 150 and are served by corresponding micro base stations 121-127 and 131-38. The coverage areas of the plurality of small cells may overlap. The small cells 160 can offload data communication of the macro base station 110 so as to improve the total throughput of the system and the data transmission bit rate of a single user.

[0032] In UDN, a virtual cell is introduced to reduce excessive interference between small cells and avoid frequent handovers of UE among small cells. A virtual cell is consisted of a plurality of small cells and act as a single cell to communicate with the user equipment. In the example of Fig. 1, the small cells served by the micro base stations 121-127 form a virtual cell, which acts as a single cell to communicate with UE 140. Each virtual cell may also include a master small cell that takes charge of data transmission scheduling, resource scheduling and the like in the entire virtual cell and transmits scheduling information to other small cells in the virtual cell to implement cooperative transmission. In the example of Fig. 1, the small cell served by the micro base station 124 is a master small cell of the virtual cell.

[0033] In embodiments of the present disclosure, the UE 140 can be connected to both a macro base station 110 and a micro base station of small cells such as the micro base station 124. That is to say, the UE 140 supports dual connectivity. The small cells that form the virtual cell are generally in an active state so as to serve UE within the coverage of the virtual cell. One or more small cells in the coverage of the macro cell 150 may stay in a sleep state, for example, the small cells served by the micro base stations 131-138 are in a sleep state in the example of Fig. 1.

[0034] Although Fig. 1 shows that a plurality of small cells are included in the macro cell 150 and there are activated small cells and dormant small cells therein, in some other embodiments, the macro cell 150 includes more or less small cells, more or less activated small cells, and/or more or less dormant small cells. In addition, although Fig. 1 illustrates that one virtual cell is formed within the macro cell 150, two or more virtual small cells may exist in some other embodiments. In addition, though only the UE 140 is shown, there may be more UEs that are served by the illustrated virtual cell or other virtual cells or are directly served by some small cells or the macro cell 150 in other embodiments.

[0035] Fig. 2 illustrates a block diagram of an example computer system/server suitable for implementing embodiments of the present disclosure. In some embodiments, the macro base station 110, micro base stations 121-127 and 131-138 and UE 140 may include one or more computer systems/servers 12 and/or one or more components in the computer system/server 12. The computer system/server 12 shown in Fig. 2 is only an example and shall not limit the functionality and application of embodiments of the present application in any regards.

[0036] As shown in Fig. 2, the computer system/server 12 can be implemented in the form of a general-purpose computing device. The components of the computer system/server 12 may include, but are not limited to, one or more processors or processing units 16, a system memory 28, and a bus 18 connecting various system components (including the system memory 28 and the processing units 16).

[0037] The bus 18 represents one or more of bus architectures, including a memory bus or a memory controller, a peripheral bus, an accelerated graphics port, and a processor or a local bus utilizing any of various bus architecture. By way of example but not limiting, such architectures include an Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus.

[0038] The computer system/server 12 typically includes various computer system readable media. The media can be any available media accessible by the computer system/server 12, including volatile and non-volatile media, removable and non-removable media.

[0039] The system memory 28 may include a computer system readable media in the form of volatile memory, such as a memory 30 and/or a buffer 32. The computer system/server 12 may further include other removable or non-removable and volatile or non-volatile computer system memory media. Although not shown in Fig. 2, a disc drive is provided for reading from and writing to a removable and non-volatile disc (for example, floppy disc) and an optical drive is provided for reading from and writing to a removable non- volatile optical disc (for example, CD-ROM, DVD-ROM or other optical media). In such case, each drive is connected to the bus 18 via one or more data media interfaces. The memory 28 includes at least one program product having a group of (for example, at least one) program modules configured to implement functions of embodiments of the present application.

[0040] A program/utility tool 40 having a set of (or at least one) program module(s) 42 may be stored in the memory 28 for instance. Such program module 42 include, but is not limited to, an operation system, one or more applications, other program modules, and program data; each or a certain any combination of these examples may include an implementation of the network environment. The program module 42 generally performs the functions and/or methods described in the embodiments of the present disclosure.

[0041] As required, the computer system/server 12 may also communicate with one or more external devices (for example, a display device 24, a memory device 14 or the like.), or may also communicate with one or more devices enabling the user to interact with the computer system/server 12, and/or communicate with any devices (for example, a network card, a modem and the like.) that enable the computer system/server 12 to communicate with one or more other computing devices. The communication is performed through an input/output (I/O) interface 22. Moreover, the computer system/server 12 may also communicate with one or more networks (for example, a local area network (LAN), a wide area network (WAN) and/or a public network such as Internet) through a network adapter 20. The network adapter 20 communicates with other modules of the computer system/server 12 through the bus 18 as shown. It should be understood that although not being illustrated, other hardware and/or software modules may be utilized in combination with the computer system/server 12, which include, but are not limited to, a microcode, a device driver, a redundancy processing unit, an external disc drive array, a RAID system, a disc drive, a data back-up storage system and the like.

[0042] Embodiments of the present disclosure will be described in details below. The embodiments of the present disclosure provide a scheme for communicating with a virtual cell. The scheme discovers small cells based on an uplink (UL) reference link transmitted by a UE and determines a virtual cell for data communication of the UE. The virtual cell may be formed based on the discovered small cells. The scheme involves operations performed by a macro base station of a macro cell where UE is located, micro base stations of potential small cells that are used for forming a virtual cell and UE.

[0043] Reference is first made to Fig. 3, which shows a flowchart for a communication method 300 of the present disclosure from the perspective of a macro base station. Although some example blocks of the method 300 are shown in Fig. 3, the method 300 may include additional blocks, less blocks, different blocks, or blocks arranged in a different manner from those depicted in Fig. 3 in some embodiments. Alternatively, or in addition, two or more blocks of the method 300 may be performed in parallel. In some embodiments, the method 300 may be implemented by the macro base station 110 in Fig. 1. The coverage area of the macro base station 110 includes a plurality of small cells (or wireless access nodes of the small cells).

[0044] As shown in Fig. 3, the method 300 includes transmitting, by the macro base station at step 310, configuration information related to an UL reference signal to be transmitted by UE to candidate small cells among a plurality of small cells. In some embodiments, the configuration information is transmitted to wireless access nodes of the candidate small cells. In some embodiments, the UE is located within coverage of the macro cell of the macro base station and has established a connection with the macro base station.

[0045] According to embodiments of the present disclosure, when UE moves to a new area and/or has data traffic to be transmitted, it may broadcast an UL reference signal and expect to acquire a cell for data communication. In some embodiments, the UL reference signal may include a sounding reference signal. In other embodiments, the UE may also transmit other reference signals. In a virtual cell mechanism-based network, the macro base station coordinates with a plurality of small cells within its coverage area so as to determine a virtual cell for data communication of the UE.

[0046] In order to determine whether a given small cell is suitable to be used for forming a virtual cell to serve a UE, one of the important factors is channel quality of a channel between the small cell and the UE (for example, the UL channel). The small cell may receive the UL reference signal from the UE and measure channel state information (CSI) indicating channel quality therebetween based on the UL reference signal. To enable the small cell to receive UL reference signal from the UE, the macro base station may transmit configuration information related to the UL reference signal to the small cell. The small cell may thus receive the UL reference signal based on that configuration information. In some embodiments, the configuration information related to the UL reference signal may include, but is not limited to, a transmission cycle of the UL reference signal, a time-frequency position of transmission, information related to decoding of the UL reference signal and the like. In some embodiments, since the UE has established a connection with the macro base station, the macro base station may obtain the configuration information in advance.

[0047] In embodiments of the present disclosure, the macro base station, prior to transmitting configuration information related to the UL reference signal, may determine some potential candidate small cells that are capable of serving the UE from the plurality of small cells within the coverage of the macro cell, and transmit the configuration information of the UL reference signal to the determined candidate small cells only Therefore, a candidate small cell refers to one of the plurality small cells that is covered by the macro cell and has the potential to form a virtual cell for data communication of UE. In some embodiments, the candidate small cells may include a small cell(s) in a sleep state, for example, the small cells that are not used to form a virtual cell. In these embodiments, the macro base station may obtain the location of the UE and determine the dormant small cell(s) with a short distance to the UE (for example, a distance within a predetermined threshold) as the candidate small cell(s). Alternatively, or in addition, the candidate small cells may include a small cell(s) in a virtual cell that is already formed. In such case, the macro base station may determine, based on the location of UE, that the UE is located within the coverage area of the formed virtual cell and thus may select a small cell(s) forming the virtual cell as a candidate small cell(s). In some other embodiments, the macro base station may determine all the small cells within the coverage of the macro cell as the candidate small cells. The scope of the present disclosure is not limited in this regard.

[0048] Based on the location of the UE and the situation of the small cells within the coverage of the macro cell, there may be three different scenarios. A first possible scenario is that the UE moves to an area where no virtual cell exists. In other words, in this area, the small cells are all in a sleep state. A second possible scenario is that the UE moves to an area where a virtual cell has been formed. A third possible scenario is that the UE is located in an area where both the formed virtual cell and one or more dormant small cells exist. These three possible scenarios will be discussed in details below.

[0049] The method 300 proceeds to step 320 where the macro base station receives, from at least one of the candidate small cells, channel state information (CSI) that satisfies a predetermined condition.

[0050] As mentioned above, after receiving the configuration information related to the UL reference signal, each candidate small cell can receive the UL reference signal broadcasted by the UE based on the configuration information and then estimate channel quality (that is, the channel state information) of a channel between the candidate small cell and the UE. In some embodiments, CSI may include strength of the UL reference signal received by the candidate small cells. For example, the CSI may be represented by one or more of a received signal reference power (RSRP), received signal reference quality (RSRQ), or a channel quality indicator (CQI). Since the distance or link condition between each candidate cell and the UE varies, the CSI measured by each candidate small cell may differ. In some embodiments, if the CSI determined by one candidate small cell satisfies the predetermined condition, for example, if the RSRP or RSRQ is greater than the predetermined threshold, the candidate small cell may feed the determined CSI back to the macro base station.

[0051] After receiving CSI feedback by one or more candidate small cells, the macro base station determines, at step 330 of the method 300, a virtual cell for data communication of UE based on the received CSI. In some embodiments, the macro base station makes a decision related to the virtual cell based on some predetermined strategies. In some embodiments, the macro base station may also transmit the information related to the virtual cell to the UE and the small cells within the virtual cell to facilitate data communication between the UE and the virtual cell. According to embodiments of the present disclosure, the virtual cell determined by the macro base station may be formed with one or more of the candidate small cells from which the CSI is received. The virtual cell determined by the macro base station may differ dependent on the aforementioned various scenarios.

[0052] Based on the previous description, it can be seen that the virtual cell is determined based on the UL reference signal transmitted by the UE on the uplink. Whenever UE is in need, for example, when UE moves to a new location or has data to be transmitted, it may autonomously transmit the uplink reference signal so as to discover available small cells and to discover or form a virtual cell for data communication with the available small cells. The macro base station may provide the configuration information related to the UL reference signal the candidate small cells for detecting the UL reference signal. In such manner, the latency of the small cell discovery is significantly reduced compared with the traditional small cell discovery based on the downlink discovery signal transmitted periodically, which may therefore enhance the overall performance of the system.

[0053] Fig. 4 shows a schematic diagram of a communication process 400 in the scenario where the UE is located within an area where no virtual cell exists. This process involves the UE under concern, a macro base station of a macro cell where the UE is located, and micro base stations of dormant small cells around the UE. [0054] At step SI, the macro base station transmits to each of the dormant micro base stations configuration information related to an UL reference signal to be transmitted by UE. In some embodiments, the dormant micro base stations under concern include base stations of small cells that are within the coverage of the macro cell and are determined by the macro base station as candidate small cells. For example, the dormant micro base stations include a micro base station in a sleep state and having a distance to the UE within a predetermined threshold. In some embodiments, the configuration information related to the UL reference signal includes, but not is limited to, a transmission cycle of the UL reference signal, a time-frequency position of transmission, information related to decoding of the UL reference signal and the like. In some embodiments, since the UE has established a connection with the macro base station, the macro base station may obtain the configuration information related to the UL reference signal of the UE.

[0055] At step S2, each micro base station that receives the configuration information may receive, bases on the configuration information, the UL reference signal from the UE and measure the channel quality information (CSI) of channels between the micro base station and the UE. In some embodiments, the micro base station can estimate RSRP or RSRQ of the UL reference signal. In other embodiments, the micro base station can also use other parameters to indicate the channel quality between the micro base station and UE. The scope of the present disclosure is not restricted in this regard. In some other embodiments, the micro base station can further decode the UL reference signal based on the received configuration information, for example, decoding information in the configuration information, and use the decoding as the basis for pre-coding of the following data communication with UE.

[0056] At step S3, the micro base station determines whether the measured CSI satisfies the predetermined condition, and transmits the measured CSI to the macro base station if the predetermined condition is satisfied, for example, if the RSRP or RSRQ is greater than the predetermined threshold.

[0057] At step S4, the macro base station determines how to form a new virtual cell based on the CSI received from one or more micro base stations. In some embodiments, the macro base station may select one or more small cells from the small cells corresponding to the micro base stations that transmit the CSI to form a new virtual cell. For example, the macro base station may select a plurality of small cells having high CSI to form a new virtual cell. Alternatively, or in addition, the macro base station may select, based on the locations of the small cells that transmit the CSI, several adjacent small cells to form a virtual cell. The macro base station may also determine how to form a new virtual cell depend on other strategies. For example, the macro base station may combine small cells corresponding to all the micro base stations that transmit the CSI into a new virtual cell, or randomly select some of the small cells to form a virtual cell.

[0058] In some embodiments, after determining to form a new virtual cell, the macro base station may also configure information related to the virtual cell. In one embodiment, the macro base station selects one small cell from the small cells forming a new virtual cell as a master small cell. The master small cell is responsible for scheduling in the virtual cell. For example, the master small cell may take charge of resource scheduling for all the small cells within the virtual cell. In some embodiments, the master small cell may transmit scheduling information to other small cells in the virtual cell to implement cooperative transmission. For example, the master small cell is in charge of transmitting control channels to the UE. The master small cell may also take charge of scheduling data communication of the UE served by the virtual cell, for example, coordinating one or more of the small cells in the virtual cell to transmit data to the UE or receive data from the UE. The micro base station serving the master small cell may also be called as a master transport point MTP, a master wireless access node, or a master micro base station.

[0059] In another embodiment, the macro base station may configure a virtual cell identifier (ID) for the new virtual cell. Alternatively, or in addition, the macro base station may also configure a channel transmission mode for the new virtual cell, and/or configuration of a downlink (DL) reference signal (for example, a cycle, a time-frequency position, an encoding and decoding manners, and the like) and configuration of a synchronous signal (for example, a cycle, a time-frequency position, an encoding and decoding manners, and the like) for each small cell in the virtual cell. The DL reference signal may include a CSTRS (Channel State Information-Reference Signal) in one example.

[0060] At step S5, the macro base station transmits an activation message and information related to the virtual cell to the micro base station corresponding to each small cell forming the virtual cell. In some embodiments, the micro base station is switched to an active state in response to the received activation message so as to communicate data with the UE. In some embodiments, the information related to the virtual cell includes a virtual cell ID and a physical cell ID of each small cell forming the virtual cell. The virtual cell ID may be used to address the whole virtual cell. In such manner, each small cell forming the virtual cell knows that it has been used to form a virtual cell and is aware of the virtual cell ID and physical cell IDs of other member small cells.

[0061] Alternatively, or in addition, the information related to the virtual cell may include configuration information related to the master small cell that is in charge of scheduling in the virtual cell, for example, the physical cell ID or other configuration information of the master small cell. In some other embodiments, the information related to the virtual cell may also include configuration information related to the DL reference signal and/or related to a synchronous signal of each small cell forming the virtual cell, for example, a cycle, a time-frequency position and information related to decoding of the DL reference signal and/or synchronous signal. Accordingly, the small cell is aware of how to transmit the DL reference signal and/or synchronous signal in the active state. In some other embodiments, information related to configuration of the DL reference signal and/or synchronous signal of the small cell may be combined into the activation message and then transmitted to the micro base station.

[0062] At step S6, the macro base station transmits information related to the virtual cell. The information transmitted in this step may be identical or similar to the information related to the virtual cell and transmitted to the micro base station at step S5. In some embodiments, the virtual cell may be assigned with a plurality of virtual cell IDs for identifying this virtual cell. For example, each UE served by the virtual cell is assigned with a corresponding virtual cell ID. In this case, the macro base station may only transmit the UE its corresponding virtual cell ID. The macro base station may also transmit the virtual cell IDs of the virtual cell to each small cell therein at step S5. In other cases such as in the multiple user-multiple input multiple output (MU-MIMO) case, a common virtual cell ID may be assigned to a plurality of users.

[0063] At step S7, the UE may also feed the CSI back to the master small cell of the virtual cell. In some embodiments, each micro base station of the virtual cell may broadcast the DL reference signal based on its configuration information. After receiving from the macro base station the configuration information related to the DL reference signal of each small cell in the virtual cell at step S6, the UE may receive the DL reference signal based on the configuration information and measure channel quality of a channel from each micro base station to the UE to obtain a CSI. The UE reports the CSI to the master micro base station of the virtual cell. Obtaining the CSI here may help the subsequent data transmission between the micro base station and UE. For example, the micro base station may decode the CSI and use the decoding as the basis for pre-coding during the subsequent data transmission process. It should be understood that step S7 is optional.

[0064] At step S8, a data communication process between the UE and the virtual cell (that is, the respective small cells forming the virtual cell) is performed. During this process, the master small cell of the virtual cell may take charge of scheduling.

[0065] Fig. 5 illustrates a schematic diagram of a communication process 500 in the above second scenario where the UE is located within an area with a formed virtual cell. The process involves a UE under concern, a macro base station of a macro cell where UE is located and micro base stations corresponding to small cells in the formed virtual cell. It should note that these small cells or micro base stations are all in an active state.

[0066] In the process 500, steps SI to S3 are similar to steps SI to S3 of the process 400. The difference lies in that, the macro base station transmits to the micro base stations of the small cells in the formed virtual cell the configuration information related to the UL reference signal to be transmitted by the UE. All the micro base stations receive the UL reference signal and measure the CSI based on the configuration information. Those micro base stations in which the CSI is measured as satisfying the predetermined condition may transmit reports of the measured CSI to the macro base station.

[0067] In some embodiments, step S3 in the process 500 further includes transmitting to the macro base station channel state information between each small cell in the virtual cell and user equipment currently served by the virtual cell. For example, since the micro base station of the master small cell in the virtual cell may obtain a CSI between each small cell and its corresponding user equipment in the virtual cell, the master micro base station may report the CSI to the macro base station. In some embodiments, only the CSI between one or more of the small cells in the virtual cell and one or more of the UEs currently served are reported. The scope of the present disclosure is not limited in this regard.

[0068] Based on the CSI received from the small cells of the virtual cell, including the CSI associated with the UEs currently served by the virtual cell, the macro base station determines at step S4 whether the virtual cell can serve the UE. The macro base station may make the decision based on certain strategies such as certain optimization strategies. In some embodiments, the macro base station determines, based on the received CSI, to use the formed virtual cell for data communication of the UE. That is, the macro base station schedules the UE to the formed virtual cell. In other embodiments, the macro base station determines, based on the received CSI, to divide the formed virtual cell into two or more new virtual cells and use one of the new virtual cells for data communication of the UE under concern. The newly divided virtual cells may include one or more small cells of the original virtual cell. In these embodiments, the macro base station may correspondingly schedule a UE served by the original virtual cell into a newly divided virtual cell.

[0069] No matter whether the original virtual cell is maintained to serve this new entering UE or is divided to serve it, certain modifications may be made to the virtual cell that is determined for serving the UE (even for the case that the original virtual cell is maintained to serve the UE because a new UE is added in this virtual cell, which means a modification to this cell). Therefore, the macro base station reconfigures information related to the virtual cell serving for the UE, which information may include one or more of the items as discussed above with reference to Fig. 4. For example, the macro base station may employ a new virtual cell ID. Alternatively, or in addition, the macro base station may also configure a channel transmission mode for the virtual cell, and/or configuration of a downlink (UL) reference signal and a synchronous signal for each small cell in the virtual cell. In the case where the original virtual cell is maintained, the macro base station may decide to allow the master small cell in the virtual cell to carry on taking charge of the scheduling task, or may choose another small cell to act as the master small cell. In the case where the original virtual cell is divided, the macro base station may determine a master small cell for each divided virtual cell.

[0070] At step S5, the macro base station transmits to each small cell in the virtual cell serving the UE information related to that virtual cell, which information includes, but is not limited to, a virtual cell ID, a physical cell ID of each small cell forming the virtual cell, configuration information related to the master small cell in charge of scheduling in the virtual cell, and configuration information related to a downlink reference signal for each small cell forming the virtual cell.

[0071] At step S6, the macro base station transmits information related to the virtual cell to the UE. Step S6 in the process 500 is similar to the step S6 in process 400.

[0072] At step S7, UE feeds a CSI back to the master small cell of the virtual cell and a data communication process between the UE and the virtual cell (that is, the small cells forming the virtual cell) is performed at step S8. Steps S7 and S8 in the process 500 are similar to steps S7 and S8 in the process 400. [0073] Fig. 6 illustrates a schematic diagram of a communication process 600 according to the above third scenario where the UE is located in an area where both a formed virtual cell and one or more dormant small cells exist. This process involves the UE under concern, a macro base station of a macro cell where the UE is located, dormant micro base station(s) the around UE and the micro base stations corresponding to the small cells in the formed virtual cell.

[0074] In process 600, steps SI to S2 in the process 400 are similar to steps SI to S2 in the process 500. The difference lies in that the macro base station transmits configuration information related to the UL reference signal to be transmitted by UE to the micro base stations of the small cells in the formed virtual cell and the dormant micro base station(s) around the UE. Those micro base stations receive the UL reference signal and measure CSI based on the configuration information.

[0075] At step S3, a dormant micro base station(s) in which the CSI is measured as satisfying the predetermined condition reports the measured CSI to the macro base station. The step is similar to step S3 in the process 400.

[0076] At step S4, a micro base station(s) of the small cells in the virtual cell in which the CSI is measured as satisfying the predetermined condition reports the measured CSI to the macro base station. Similar to step S3 of the process 500, the micro base stations of small cells in the formed virtual cell, for example, the master micro base station of the virtual cell, may transmit to the macro base station channel state information between each small cell in its virtual cell and user equipment current served by the virtual cell.

[0077] At step S5, the macro base station determines, based on the CSI received from the micro base stations of the small cells, whether the dormant small cells are combined into the formed virtual cell or whether the UE is served by the formed virtual cell. The macro base station may make the decision based on certain strategies such as certain optimization strategies. In some embodiments, the macro base station may select one or more small cells from among the dormant small cells receiving the CSI and combine the selected small cells into the formed virtual cell. In some embodiments, the macro base station may determine not to serve the UE by the formed virtual cell but to form a new virtual cell with the selected small cells. In some embodiments, the macro base station may determine to serve the UE with the formed virtual cell, where the virtual cell requires no modification. Alternatively, in some other embodiments, the virtual cell may be divided into a plurality of virtual cells and the data transmission of UE is performed with one of the divided virtual cells.

[0078] Regardless of the decision made by the macro base station at step S5, certain modifications may be made to the virtual cell that is determined for serving the UE (even for the case that the original virtual cell is directly used to serve the UE because a new UE is added in the virtual cell, which means a modification to this cell). Therefore, the base station reconfigures information related to the virtual cell serving for the UE, which information may include one or more of the items as discussed above with reference to Fig. 4. For example, the macro base station may employ a new virtual cell ID. Alternatively, or in addition, the macro base station may also configure a channel transmission mode for the virtual cell, and/or configuration of a UL reference signal and a synchronous signal for each small cell in the virtual cell. In the case where the original virtual cell is directly used, the macro base station may decide to allow the master small cell in the virtual cell to carry on taking charge of the scheduling task, or may choose another small cell to act as the master small cell. In other cases, the macro base station may determine a master small cell for the newly formed virtual cell.

[0079] At step S6, the macro base station transmits to each small cell in the virtual cell serving the UE information related to the virtual cell, which information includes, but is not limited to, a virtual cell ID, a physical cell ID of each small cell forming the virtual cell, configuration information related to the master small cell in charge of scheduling in the virtual cell, and configuration information related to a downlink reference signal for each small cell forming the virtual cell. If the virtual cell serving the UE further includes a dormant small cell(s), the macro station may also transmit an activation message to the base stations of these small cells at step S6 so as to switch the small cells from the sleep state to the active state.

[0080] At step S7, the macro base station transmits information related to the virtual cell to the UE. Step S7 in the process 600 is similar to the step S6 in the process 400 or 500.

[0081] At step S8, UE feeds a CSI back to the master small cell of the virtual cell and a data communication process between the UE and the virtual cell (that is, the small cells forming the virtual cell) is performed at step S9. Steps S8 and S9 in the process 600 are similar to steps S7 and S8 in the process 400 or 500.

[0082] Although Figs. 4-6 illustrate one UE, a similar process may also be implemented for other UEs in the macro cell for communication with a virtual cell. Although Figs. 4-6 illustrate example steps of the processes 400-600, in some embodiments, the processes 400, 500 or 600 may include additional steps, lesser steps, different steps, or steps arranged differently from those depicted in Figs. 4-6. For example, step S7 in the processes 400 and 500 and step S8 in the process 600 may be omitted. Alternatively, or in addition, two or more steps of the process 400, 500 or 600 may be performed in parallel. For example, steps S5 and S6 in the process 400 and 500 or steps S6 and S7 in process 600 may be performed in parallel.

[0083] Fig. 7 illustrates a block diagram of an apparatus 700 for communicating with a virtual cell in a macro base station according to an embodiment of the present disclosure. The coverage area of the macro base station includes a plurality of small cells. The apparatus 700 may be the macro base station 110 shown in Fig. 1 in an example or may be included therein.

[0084] As shown in Fig. 7, the apparatus 700 includes a configuration information transmitting unit 710 configured to transmit, to candidate small cells of a plurality of small cells, configuration information related to an UL reference signal to be transmitted by UE. The configuration information is used by the candidate small cells to receive the UL reference signal to determine channel state information, and the channel state information indicates channel quality of a channel between the UE and the respective candidate small cell. The apparatus 700 further includes a state information receiving unit 720 configured to receive, from at least one of the candidate small cells, channel state information that satisfies a predetermined condition and a virtual cell determining unit 730 configured to determine a virtual cell for data communication of the UE based on the received channel state information, the virtual cell being formed with one or more of the at least one candidate cell.

[0085] According to some embodiments, the apparatus 700 may further include a candidate small cell determining unit configured to determine a small cell in a sleep state and having distances to the UE within a predetermined threshold as one of the candidate small cells.

[0086] According to some embodiments, the virtual cell determining unit 730 may further include a small cell selecting unit configured to select, based on the channel state information, one or more small cells from at least one candidate small cell. The virtual cell determining unit 730 may also include a first determining unit configured to determine, if the UE is located within coverage of a formed virtual cell, to combine the selected small cells into the formed virtual cell or to form a new virtual cell; and a second determining unit configured to determine, if the UE is located outside the coverage of the formed virtual cell, to form a new virtual cell with the selected small cells.

[0087] According to some embodiments, the apparatus 700 may further include a master small cell selecting unit to select, in response to determining to form a new virtual cell with the selected small cells, a small cell from the small cells forming the new virtual cell as a master small cell, the master small cell being in charge of scheduling in the virtual cell.

[0088] According to some embodiments, the apparatus 700 may further include a small cell activating unit configured to transmit an activation message to the small cells forming the virtual cell to activate at least one of the small cells in the sleep state.

[0089] According to some embodiments, the UE may be located within coverage of the formed virtual cell and the apparatus 700 may further include a candidate small cell determining unit configured to determine a small cell in the formed virtual cell as one of the candidate small cells.

[0090] According to some embodiments, the virtual cell determining unit 730 may include any of the following: a first determining unit configured to determine, based on the channel state information, to utilize the formed virtual cell for data communication of the UE; or a second determining unit configured to determine, based on the channel state information, to form a new virtual cell with at least one small cell in the formed virtual cell to facilitate data communication of the UE.

[0091] According to some embodiments, the above channel state information is first channel state information and the state information receiving unit 720 may be further configured to receive second channel state information from a master small cell of an formed virtual cell, wherein the second channel state information indicates channel quality of channels between small cells in the formed virtual cell and UE currently served by the formed virtual cell. In these embodiments, the virtual cell determining unit is configured to determine, based on the first and second channel state information, the virtual cell for data communication of the UE.

[0092] According to some embodiments, the apparatus 700 may further include a virtual cell information transmitting unit configured to transmit, to the UE and each small cell forming the virtual cell, information related to the virtual cell, the information related to the virtual cell including at least one of: a virtual cell identifier (ID) of the virtual cell, a physical cell ID of each small cell forming the virtual cell, configuration information related to the master small cell in charge of scheduling in the virtual cell, and configuration information related to a downlink reference signal of each small cell forming the virtual cell.

[0093] Fig. 8 illustrates a block diagram of an apparatus 800 of communicating with a virtual cell in a micro base station of a small cell according to an embodiment of the present disclosure. The apparatus 800 may be a micro base station 121-127 or 131-138 shown in Fig. 1 in an example or be included therein.

[0094] As shown in Fig. 8, the apparatus 800 includes a configuration information transmitting unit 810 configured to receive, from a macro base station, configuration information related to an UL reference signal to be transmitted by UE. The small cell is within the coverage area of the macro base station. The apparatus 800 further includes a state information determining unit 820 configured to receive, based on the configuration information, the UL reference signal from the UE to determine channel state information, the channel state information indicating channel quality of a channel between the UE and the small cell. The apparatus 800 further includes a state information transmitting unit 830 configured to transmit, in response to the channel state information satisfying a predetermined condition, the channel state information to the macro base station for determining a virtual cell for data communication of the UE, the virtual cell being formed with at least the small cell.

[0095] According to some embodiments, the small cells may be in a sleep state and has a distance to the UE within a predetermined threshold and the macro base station determines to combine the small cell into a formed virtual cell or to form a new virtual cell with the small cell.

[0096] According to some embodiments, the apparatus 800 may further include an activation message receiving unit configured to receive an activation message from the macro base station; and an active state switching unit configured to, in response to the activation message, switch to an active state.

[0097] According to some embodiments, the small cell may be included in a formed virtual cell and the macro base station determines, based on the channel state information, to use the formed virtual cell for data communication of the UE or to form a new virtual cell at least with the small cell to facilitate data communication of the UE.

[0098] According to some embodiments, the small cell may be a master small cell that is in charge of scheduling in the formed virtual cell. If the channel state information is first channel state information, the state information transmitting unit 830 may be further configured to transmit second channel state information to the macro base station, the second channel state information indicating channel quality of a channel between a small cell in the formed virtual cell and UE currently served by the formed virtual cell.

[0099] According to some embodiments, the apparatus 800 further includes a virtual cell information receiving unit configured to receive information related to the virtual cell from the macro base station, the information related to the virtual cell including at least one of: a virtual cell identifier (ID) of the virtual cell, a physical cell ID of each small cell forming the virtual cell, configuration information related to the master small cell in charge of scheduling in the virtual cell, and configuration information related to a downlink reference signal of each small cell forming the virtual cell.

[00100] According to some embodiments, the small cell may be determined by the macro base station as a master small cell in a virtual cell for data communication of the UE. In some embodiments, the apparatus 800 may further include a downlink reference signal transmitting unit configured to transmit a downlink reference signal to the UE; and a UE state information receiving unit configured to receive from the UE third channel state information for data communication of the UE, the third channel state information indicating channel quality of a channel between the UE and each small cell forming the virtual cell.

[00101] Fig. 9 shows a block diagram of an apparatus 900 of communicating with a virtual cell in UE according to an embodiment of the present disclosure. The apparatus 900 may be UE 140 shown in Fig. 1 in an example, or be included therein.

[00102] As shown in Fig. 9, the apparatus 900 includes an UL reference signal transmitting unit 910 configured to transmit an UL reference signal to a candidate small cell, such that the candidate cell receive, based on configuration information related to the UL reference signal received from a macro base station, the UL reference signal for determining channel state information and transmits the channel state information to the macro base station in response to the channel state information satisfying a predetermined condition. The channel state information indicates state information of a channel between the UE and the candidate small cell

[00103] According to some embodiments, the candidate small cell may include at least one of: a small cell in a sleep state and having a distance to the UE within a predetermined threshold; or a small cell within a formed virtual cell, the UE being located within coverage of the formed virtual cell . [00104] According to some embodiments, the apparatus 900 may further include a virtual cell information receiving unit configured to receive from the macro base station information related to the virtual cell, the information related to the virtual cell including at least one of: a virtual cell identifier (ID) of the virtual cell, a physical cell ID of each small cell forming the virtual cell, configuration information related to the master small cell in charge of scheduling in the virtual cell, and configuration information related to a downlink reference signal of each small cell forming the virtual cell.

[00105] According to some embodiments, the aforementioned channel state information is first channel state information. The apparatus 900 further includes a downlink reference signal receiving unit configured to receive a downlink reference signal from each small cell forming the virtual cell. The apparatus 900 may also include a UE state information determining unit configured to determine, based on the received downlink reference signal, second channel state information for the data communication of the UE, the second state information indicating channel quality of a channel between the UE and the small cell forming the virtual cell. The apparatus 900 may further include a UE state information transmitting unit configured to transmit the second channel state information to a master small cell in charge of scheduling in the virtual cell.

[00106] It is seen that the apparatus 700 of Fig. 7 may implement operations of the macro base station as described in the processes shown in any of Figs.3 to 6. The apparatus 800 of Fig. 8 may implement operations of a micro base station of a small cell as described in these processes and the apparatus 900 of Fig. 9 may implement operations of the UE as described in the processes. Although not shown, the apparatus 700, 800, or 900 may include more functional units to implement various embodiments described in combination with Figs. 3 to 6.

[00107] Embodiments of the present disclosure further provide a communication system, comprising a macro base station including the apparatus 700 as described in Fig. 7. The communication system further includes at least one micro base station of at least one small cell in the coverage area of the macro base station, and each micro base station includes the apparatus 800 as described in Fig. 8. The communication system further includes UE including the apparatus 900 as described in Fig. 9.

[00108] It would be noted that the embodiments of the present disclosure can be implemented in software, hardware, or a combination thereof. The hardware part can be implemented by a special logic; the software part can be stored in a memory and executed by a suitable instruction execution system such as a microprocessor or special purpose hardware. Ordinary skilled in the art may understand that the above method and system may be implemented with computer executable instructions and/or in processor-controlled code, for example, such code is provided on a carrier medium such as a magnetic disk, CD, or DVD-ROM, or a programmable memory such as a read-only memory (firmware), or a data bearer such as an optical or electronic signal bearer. The apparatuses and their units in the present disclosure may be implemented by hardware circuitry of a programmable hardware device such as a hyper-scale integrated circuit or gate array, a semiconductor such as a logical chip or transistor, or hardware circuitry of a programmable hardware device such as a field-programmable gate array or a programmable logical device, or implemented by software executed by various processors, or implemented by any combination of the above hardware circuitry and software.

[00109] It would be noted that although various units or sub-units of the apparatus have been mentioned in the above detailed description, such partitioning is not for limitation. In practice, according to the embodiments of the present invention, the features and functions of two or more units described above may be embodied in one unit. In turn, the features and functions of one unit described above may be further embodied in more units.

[00110] Further, although operations of the present methods are described in a particular order in the drawings, it does not require or imply that these operations are necessarily performed according to this particular sequence, or a desired outcome can only be achieved by performing all shown operations. On the contrary, the execution order for the steps as depicted in the flowcharts may be varied. Alternatively, or in addition, some steps may be omitted, a plurality of steps may be merged into one step, or a step may be divided into a plurality of steps for execution.

[00111] Although the present disclosure has been described with reference to various embodiments, it should be understood that the present disclosure is not limited to the disclosed embodiments. The present disclosure is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the appended claims. The scope of the appended claims meets the broadest explanations and covers all such modifications and equivalent structures and functions.

Claims

I/We Claim:

1. A method implemented at a macro base station, comprising:

transmitting, to candidate small cells among a plurality of small cells, configuration information related to an uplink reference signal to be transmitted by user equipment, the configuration information being used by the candidate small cells to receive the uplink reference signal to determine channel state information, and the channel state information indicating channel quality of a channel between the user equipment and the respective candidate small cell;

receiving, from at least one of the candidate small cells, channel state information that satisfies a predetermined condition; and

determining, based on the received channel state information, a virtual cell for data communication of the user equipment, the virtual cell being formed with one or more of the at least one candidate small cell.

2. The method of claim 1, further comprising:

determining a small cell in a sleep state and having distances to the user equipment within a predetermined threshold as one of the candidate small cells.

3. The method of claim 2, wherein determining, based on the channel state information, a virtual cell for data communication of the user equipment comprises:

selecting, based on the channel state information, one or more small cells from the at least one candidate small cell;

if the user equipment is located within coverage of a formed virtual cell, combining the selected small cells into the formed virtual cell or forming a new virtual cell; and

if the user equipment is located outside the coverage of the formed virtual cell, determining to form a new virtual cell with the selected small cells.

4. The method of claim 3, further comprising:

in response to determining to form a new virtual cell with the selected small cells, selecting a small cell from the small cells forming the new virtual cell as a master small cell, the master small cell being in charge of scheduling in the virtual cell and transmitting scheduling information to other small cells in the new virtual cell to implement cooperative transmission.

5. The method of claim 2, further comprising:

transmitting an activation message to the small cells forming the virtual cell to activate at least one of the small cells in the sleep state.

6. The method of claim 1, wherein if the user equipment is located within the coverage of the formed virtual cell, the method further comprises:

determining a small cell within the formed virtual cell as one of the candidate small cells.

7. The method of claim 6, wherein determining, based on the channel state information, a virtual cell for data communication of the user equipment comprises one of the following:

determining, based on the channel state information, to utilize the formed virtual cell for data communication of the user equipment; or

determining, based on the channel state information, to form a new virtual cell with at least one small cell in the formed virtual cell to facilitate data communication of the user equipment.

8. The method of claim 6, wherein the channel state information is first channel state information, the method further comprising:

receiving second channel state information from the master small cell of the formed virtual cell, the second channel state information indicating channel quality of a channel between a small cell in the formed virtual cell and user equipment currently served by the formed virtual cell, and

wherein determining, based on the channel state information, a virtual cell for data communication of the user equipment comprises:

determining the virtual cell for data communication of the user equipment based on the first and second channel state information.

9. The method of any of claims 1 to 8, further comprising:

transmitting information related to the virtual cell to the user equipment and each small cell forming the virtual cell, the information related to the virtual cell including at least one of: a virtual cell identifier (ID) of the virtual cell,

a physical cell ID of each small cell forming the virtual cell,

configuration information related to the master small cell in charge of scheduling in the virtual cell, and

configuration information related to a downlink reference signal of each small cell forming the virtual cell.

10. A communication method implemented at a micro base station of a small cell, comprising:

receiving, from a macro base station, configuration information related to an uplink reference signal to be transmitted by user equipment;

receiving, based on the configuration information, the uplink reference signal from the user equipment to determine channel state information, the channel state information indicating channel quality of a channel between the user equipment and the small cell;

in response to the channel state information satisfying a predetermined condition, transmitting the channel state information to the macro base station for determining a virtual cell for data communication of the user equipment, the virtual cell being formed with at least the small cell.

11. The method of claim 10, wherein the small cell is a small cell that is in a sleep state and has a distance to the user equipment within a predetermined threshold, and the macro base station determines to combine the small cell into a formed virtual cell or to form a new virtual cell with the small cell.

12. The method of claim 11, further comprising:

receiving an activation message from the macro base station; and

in response to the activation message, switching to an active state.

13. The method of claim 10, wherein the small cell is included in a formed virtual cell and the macro base station determines, based on the channel state information, to use the formed virtual cell for data communication of the user equipment or to form a new virtual cell with at least the small cell to facilitate data communication of the user equipment.

14. The method of claim 13, wherein the small cell is a master cell that is in charge of scheduling in the formed virtual cell, and the channel state information is first channel state information, the method further comprising:

transmitting second channel state information to the macro base station, the second channel state information indicating channel quality of a channel between a small cell in the formed virtual cell and user equipment currently served by the formed virtual cell.

15. The method of claim 10, further comprising:

receiving information related to the virtual cell from the macro base station, the information related to the virtual cell including at least one of:

a virtual cell identifier (ID) of the virtual cell,

a physical cell ID of each small cell forming the virtual cell,

16. The method of any of claims 10 to 15, wherein the small cell is determined by the macro base station as a master small cell in a virtual cell for data communication of the user equipment, the method further comprising:

transmitting a downlink reference signal to the user equipment; and

receiving from the user equipment third channel state information for data communication of the user equipment, the third channel state information indicating channel quality of a channel between the user equipment and each small cell forming the virtual cell.

17. A communication method implemented at user equipment, comprising:

transmitting an uplink reference signal to a candidate small cell, such that the candidate cell receives, based on configuration information related to the uplink reference signal that is received from a macro base station, the uplink reference signal for determining channel state information and transmits the channel state information to the macro base station in response to the channel state information satisfying a predetermined condition, the channel state information indicating state information of a channel between the user equipment and the candidate small cell.

The method of claim 17, wherein the candidate small cell includes at least one of:

a small cell in a sleep state and having a distance to the user equipment within a predetermined threshold; or

a small cell within a formed virtual cell, the user equipment being located within coverage of the formed virtual cell.

19. The method of claim 17, further comprising:

receiving from the macro base station information related to the virtual cell, the information related to the virtual cell including at least one of:

a virtual cell identifier (ID) of the virtual cell,

a physical cell ID of each small cell forming the virtual cell,

20. The method of any of claims 17 to 19, wherein the channel state information is first channel state information, the method further comprising:

receiving a downlink reference signal from a small cell forming the virtual cell; and determining, based on the received downlink reference signal, second channel state information for the data communication of the user equipment, the second state information indicating channel quality of a channel between the user equipment and the small cell forming the virtual cell; and

transmitting the second channel state information to a master small cell in charge of scheduling in the virtual cell.

21. A communication apparatus in a macro base station, comprising:

a configuration information transmitting unit configured to transmit, to candidate small cells among a plurality of small cells, configuration information related to an uplink reference signal to be transmitted by user equipment, the configuration information being used by the candidate small cells to receive the uplink reference signal to determine channel state information, and the channel state information indicating channel quality of a channel between the user equipment and the respective candidate small cell;

a state information receiving unit configured to receive, from at least one of the candidate small cells, channel state information that satisfies a predetermined condition; and a virtual cell determining unit configured to determine a virtual cell for data communication of the user equipment based on the received channel state information, the virtual cell being formed with one or more of the at least one candidate cell.

22. The apparatus of claim 21, further comprising:

a candidate small cell determining unit configured to determine a small cell in a sleep state and having distances to the user equipment within a predetermined threshold as one of the candidate small cells.

23. The apparatus of claim 22, wherein the virtual cell determining unit comprises: a small cell selecting unit configured to select, based on the channel state information, one or more small cells from the at least one candidate small cell;

a first determining unit configured to determine, if the user equipment is located within coverage of a formed virtual cell, to combine the selected small cells into the formed virtual cell or to form a new virtual cell; and

a second determining unit configured to determine, if the user equipment is located outside the coverage of the formed virtual cell, to form a new virtual cell with the selected small cells.

24. The apparatus of claim 23, further comprising:

a master small cell selecting unit to select, in response to determining to form a new virtual cell with the selected small cells, a small cell from the small cells forming the new virtual cell as a master small cell, the master small cell being in charge of scheduling in the virtual cell and transmitting scheduling information to other small cells in the new virtual cell to implement cooperative transmission.

25. The apparatus of claim 22, further comprising:

a small cell activating unit configured to transmit an activation message to the small cells forming the virtual cell to activate at least one of the small cells in the sleep state.

26. The apparatus of claim 21, wherein the user equipment is located within coverage of the formed virtual cell and the apparatus further comprises:

a candidate small cell determining unit configured to determine a small cell in the formed virtual cell as one of the candidate small cells.

27. The apparatus of claim 26, wherein the virtual cell determining unit comprises any of the following:

a first determining unit configured to determine, based on the channel state information, to utilize the formed virtual cell for data communication of the user equipment; or

a second determining unit configured to determine, based on the channel state information, to form a new virtual cell with at least one small cell in the formed virtual cell to facilitate data communication of the user equipment.

28. The apparatus of claim 26, wherein the channel state information is first channel state information and the state information receiving unit is further configured to receive second channel state information from a master small cell of an formed virtual cell, wherein the second channel state information indicates channel quality of a channel between a small cell in the formed virtual cell and user equipment currently served by the formed virtual cell, and

wherein the virtual cell determining unit is configured to determine, based on the first and second channel state information, the virtual cell for data communication of the user equipment.

29. The apparatus of any of claims 21 to 28, further comprising:

a virtual cell information transmitting unit configured to transmit, to the user equipment and each small cell forming the virtual cell, information related to the virtual cell, the information related to the virtual cell including at least one of:

a virtual cell identifier (ID) of the virtual cell,

a physical cell ID of each small cell forming the virtual cell,

30. A communication apparatus in a micro base station of a small cell, comprising: a configuration information receiving unit configured to receive, from a macro base station, configuration information related to an uplink reference signal to be transmitted by user equipment;

a state information determining unit configured to receive, based on the configuration information, the uplink reference signal from the user equipment to determine channel state information, the channel state information indicating channel quality of a channel between the user equipment and the small cell; and

a state information transmitting unit configured to transmit, in response to the channel state information satisfying a predetermined condition, the channel state information to the macro base station for determining a virtual cell for data communication of the user equipment, the virtual cell being formed with at least the small cell.

31. The apparatus of claim 30, wherein the small cell is in a sleep state and has a distance to the user equipment within a predetermined threshold, and the macro base station determines to combine the small cell into a formed virtual cell or to form a new virtual cell with the small cell.

32. The apparatus of claim 31, further comprising:

an activation message receiving unit configured to receive an activation message from the macro base station; and

an active state switching unit configured to, in response to the activation message, switch to an active state.

33. The apparatus of claim 30, wherein the small cell is included in a formed virtual cell and the macro base station determines, based on the channel state information, to use the formed virtual cell for data communication of the user equipment or to form a new virtual cell at least with the small cell to facilitate data communication of the user equipment.

34. The apparatus of claim 33, wherein the small cell is a master small cell that is in charge of scheduling in the formed virtual cell, and the channel state information is first channel state information, and

wherein the state information transmitting unit is further configured to transmit second channel state information to the macro base station, the second channel state information indicating channel quality of a channel between a small cell in the formed virtual cell and user equipment currently served by the formed virtual cell.

35. The apparatus of claim 30, further comprising:

a virtual cell information receiving unit configured to receive information related to the virtual cell from the macro base station, the information related to the virtual cell including at least one of:

a virtual cell identifier (ID) of the virtual cell,

a physical cell ID of each small cell forming the virtual cell,

36. The apparatus of any of claims 30 to 35, wherein the small cell is determined by the macro base station as a master small cell in a virtual cell for data communication of the user equipment, the apparatus further comprising:

a downlink reference signal transmitting unit configured to transmit a downlink reference signal to the user equipment; and

a user equipment state information receiving unit configured to receive from the user equipment third channel state information for data communication of the user equipment, the third channel state information indicating channel quality of a channel between the user equipment and each small cell forming the virtual cell.

37. A communication apparatus in user equipment, comprising:

an uplink reference signal transmitting unit configured to transmit an uplink reference signal to a candidate small cell, such that the candidate cell receive, based on configuration information related to the uplink reference signal received from a macro base station, the uplink reference signal for determining channel state information and transmits the channel state information to the macro base station in response to the channel state information satisfying a predetermined condition, the channel state information indicating state information of a channel between the user equipment and the candidate small cell.

38. The apparatus of claim 37, wherein the candidate small cell includes at least one of:

39. The apparatus of claim 37, further comprising:

a virtual cell information receiving unit configured to receive from the macro base station information related to the virtual cell, the information related to the virtual cell including at least one of:

a virtual cell identifier (ID) of the virtual cell,

a physical cell ID of each small cell forming the virtual cell,

40. The apparatus of any of claims 37 to 39, wherein the channel state information is first channel state information, the apparatus further comprising:

a downlink reference signal receiving unit configured to receive a downlink reference signal from each small cell forming the virtual cell;

a user equipment state information determining unit configured to determine, based on the received downlink reference signal, second channel state information for the data communication of the user equipment, the second state information indicating channel quality of a channel between the user equipment and the small cell forming the virtual cell; and

a user equipment state information transmitting unit configured to transmit the second channel state information to a master small cell in charge of scheduling in the virtual cell.

41. A communication system, comprising:

a macro base station, including an apparatus according to any of claims 21 to 29;

at least one micro base station of at least one small cell including an apparatus according to any of claims 30 to 36; and

user equipment including an apparatus according to any of claims 37 to 40.