WO2015084334A1

WO2015084334A1 - Method and apparatus for small cell activation

Info

Publication number: WO2015084334A1
Application number: PCT/US2013/072882
Authority: WO
Inventors: Long GAO; Sudhanshu Gaur; Joydeep Acharya
Original assignee: Hitachi, Ltd.
Priority date: 2013-12-03
Filing date: 2013-12-03
Publication date: 2015-06-11

Abstract

Example implementations are directed to small cell activation systems and methods in a LTE-Advanced network. Each small cell in a cluster turns itself on following a given period and time offset. For a particular small cell, the activation procedure is divided into two stages. In the first stage, the small cell sends a reference signal and broadcasts system information. It collects the traffic information of its associated UEs and sends the information to its neighboring cells via backhaul. The small cell does not serve any UE in this stage. Any UE that is associated to it will be handed over to one of its neighboring active cells when packets arrive. In the second stage, the small cell decides whether to turn itself on based on the collected information and feedbacks from its neighboring cells, and will serve its associated UEs if it decides to turn itself on.

Description

METHOD AND APPARATUS FOR SMALL CELL ACTIVATION BACKGROUND

Field [0001] Example implementations of the present application are related to wireless systems, and more specifically, towards small cell activation in heterogeneous networks. Related Art [0002] In related art Long Term Evolution (LTE) Advanced Heterogeneous Networks, a large number of small cells are deployed in the coverage area of a macro cell. The small cells can enhance the system throughput by providing cell-splitting gain. However, they may cause significant extra interference in the network especially for dense deployment. In an example configuration shown in FIG. 1 serving two UEs UE1 and UE2, the four small cells SC1, SC2, SC3 and SC4 may cause considerable interference to the UEs (e.g. UE1) that are associated to the macro cell. If the inter cell interference is not well managed, the deployment of small cell may degrade the system throughput. [0003] In the related art, pico cell range expansion may be utilized to mitigate the interference. The basic idea is to transfer the macro UEs that suffer strong interference from the pico cells to one of the pico cells with a handover bias. Meanwhile, the macro cell mutes some subframes to reduce the interference to the pico cells within its coverage area. SUMMARY

[0004] Aspects of the present disclosure may include a computer configured to manage a cluster involving a plurality of base stations. The computer may involve a memory configured to store an activation schedule for the cluster, the activation schedule involving period information for the cluster and offset information for each of the plurality of base stations in the cluster; and a processor configured to transmit the period information and corresponding ones of the offset information to each of the plurality of base stations in the cluster. The offset information can be different for each of the plurality of base stations in the cluster. [0005] Aspects of the present disclosure may further include a computer program for managing a cluster involving a plurality of base stations. The computer program may involve code for storing an activation schedule for the cluster, the activation schedule including period information for the cluster and offset information for each of the plurality of base stations in the cluster; and code for transmitting the period information and corresponding ones of the offset information to each of the plurality of base stations in the cluster. The offset information may be different for each of the plurality of base stations in the cluster. The computer program may be stored on a computer readable storage medium or a computer readable signal medium which can be executed by a hardware system such as a computer or a processor. [0006] Aspects of the present disclosure may further include a first base station, coupled to one or more second base stations by a backhaul and configured to manage a cluster formed from the one or more second base stations. The first base station may involve a memory configured to store an activation schedule for the cluster, the activation schedule comprising period information for the cluster and offset information for each of the one or more second base stations in the cluster; and a processor configured to transmit the period information and corresponding ones of the offset information to each of the one or more second base stations in the cluster. The offset information may be different for each of the one or more second base stations in the cluster.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 illustrates an example of dense small cell deployment. [0008] FIG. 2 is an illustration of small cell on/off in dense deployment scenario, in accordance with an example implementation. [0009] FIG. 3 illustrates a block diagram of an eNodeB in accordance with an example implementation. [0010] FIG. 4 illustrates an example activation timeline for the small cells in a cluster in accordance with an example implementation. [0011] FIG. 5 illustrates an example network architecture of the OAM server in accordance with an example implementation. [0012] FIG. 6 illustrates a block diagram of an OAM server, in accordance with an example implementation. [0013] FIG. 7 illustrates an example of how the OAM server configures the activation parameters of a small cell, in accordance with an example implementation. [0014] FIG. 8 illustrates an example procedure of deactivating a small cell permanently, in accordance with an example implementation. [0015] FIG. 9 illustrates an example two-stage procedure for small cell activation, in accordance with an example implementation. [0016] FIG. 10 illustrates an activation mechanism for a small cell in two-cell scenarios, in accordance with an example implementation. [0017] FIG. 11 illustrates a scenario with two small cells, in accordance with an example implementation. [0018] FIG. 12 is a scenario with a macro cell and a small cell, in accordance with an example implementation. [0019] FIG. 13 illustrates an activation mechanism for a small cell for a multiple macro small cell scenario, in accordance with an example implementation. [0020] FIG. 14 illustrates small cell control by the macro eNodeB in accordance with an example implementation. DETAILED DESCRIPTION OF THE DRAWINGS

[0021] The following detailed description provides further details of the figures and example implementations of the present application. Reference numerals and descriptions of redundant elements between figures are omitted for clarity. Terms used throughout the description are provided as examples and are not intended to be limiting. For example, the use of the term “automatic” may involve fully automatic or semi-automatic implementations involving user or administrator control over certain aspects of the implementation, depending on the desired implementation of one of ordinary skill in the art practicing implementations of the present application. The terms enhanced node B (eNodeB), small cell (SC), base station (BS) and pico cell may be utilized interchangeably throughout the example implementations. The implementations described herein are also not intended to be limiting, and can be implemented in various ways, depending on the desired implementation. [0022] In a LTE-Advanced network, a large number of small cells can be deployed in a macro coverage area for throughput enhancement. Since keeping all small cells always active is not energy efficient and may cause considerable interference in the network, a small cell can turn itself ON/OFF based on the traffic demand and interference environment. Example implementations described herein focus on the mechanism of small cell activation (i.e. switching from the status“OFF” to“ON”) in the dense small cell deployment scenario. [0023] Consider the dense small cell deployment scenario, where a large number of small cells are deployed within the coverage area of a macro cell. In this scenario, a small cell may dynamically turn itself ON/OFF for energy saving and interference reduction. [0024] FIG. 2 is an illustration of small cell on/off in dense deployment scenario, in accordance with an example implementation. In this example, a small cell with a solid circle indicates that the small cell is in ON status. A small cell with a dotted circle means that it is in OFF status. A small cell can dynamically switch between ON and OFF based on the traffic demand and interference environment. While a small cell can decide when to switch off based on one or more parameters (e.g. the number of its associated UEs is small or below a threshold), the mechanism for a small cell to switch on should be designed to avoid a sudden“jump” of the interference level in its neighboring cells. In the example as shown in FIG. 2, if Small Cells SC2 and/or SC3 in OFF status switch ON, the interference level experienced by UE 1 will suddenly increase by a significant amount. If the macro cannot capture this interference jump and use the same Modulation and Coding Scheme (MCS), the data transmission to UE 1 may fail. [0025] In a LTE-Advanced network, a large number of small cells can be deployed in a macro coverage area for throughput enhancement. Since keeping all small cells always active is not energy efficient and may cause considerable interference in the network, it is desirable that a small cell can turn itself ON/OFF based on the traffic demand and interference environment. Example implementations described herein focus on the mechanism of small cell activation (e.g. switching from the status“OFF” to“ON”) in the dense small cell deployment scenario. [0026] In example implementations, a mechanism for small cell activation is utilized in a LTE-Advanced network. In the example implementations, each small cell in a cluster turns itself on following a given period and time offset. For a particular small cell, the activation procedure is divided into two stages. [0027] In the first stage, the small cell sends a reference signal and broadcasts its system information. The small cell collects the traffic information of its associated UEs and sends the information to its neighboring cells via the backhaul. The small cell does not serve any UE in this stage. Any UE that is associated to the small cell will be handed over to one of its neighboring active cells when packets arrive. [0028] In the second stage, the small cell decides whether turn itself on or not based on the collected information and feedbacks from its neighboring cells. The small cell will start serving its associated UEs if it decides to turn itself on. [0029] FIG. 3 illustrates a block diagram of an eNodeB in accordance with an example implementation. The block diagram of an eNodeB 300 in the example implementations is shown in FIG. 3, which could be a macro eNodeB or small cell eNodeB. The eNodeB 300 may include the following modules: the Central Processing Unit (CPU) 301, the baseband processor 302, the UE scheduler 303, the Xn interface 304, the Operation Administration Maintenance (OAM) interface 305, and the memory 306. The CPU 301 collects the traffic information of the associated UEs and performs a handover procedure in the preparation stage of the cell activation. The baseband processor 302 generates baseband signaling including the reference signal and the system information. The UE scheduler 303 assigns radio resources to UEs when the small cell is in ON status. The Xn interface 304 is used to exchange traffic and interference information between two eNodeBs in order to coordinate small cell activation. The OAM interface 305 is used to configure the activation period and offset for the eNodeB. The memory 306 stores the expected activation time and interference level of its neighboring cells. Memory 306 may take the form of a computer readable storage medium or can be replaced with a computer readable signal medium as described below. The detailed functions of each module are explained below. [0030] FIG. 4 illustrates an example activation timeline for the small cells in a cluster in accordance with an example implementation. The small cells may be deployed in clusters. For example, SC1-SC4 are deployed as a cluster of small cells as illustrated in FIG. 2. Each small cell in a cluster is allowed to activate only at certain time instances. FIG. 4 illustrates an example of the activation timeline for the four small cells in FIG. 2. Each small cell can switch on following a common period T but at a different time offset to ensure that they will not turn on at the same time. In the example of FIG. 4, the time offset for SC 1 is zero. [0031] For the example of FIG. 4, if a small cell is in ON status at the time instant where it is allowed to be turned on, it will continue be in ON status. For example, SC2 is already ON at time instant (2T+offset for SC2), it will remain in ON status until the condition of turning off is satisfied. Further, a small cell may decide not turn itself on in the time instant where it is allowed to be turned on. For example, SC1 may decide not switch on at time instant 2T as shown in FIG. 4. [0032] FIG. 5 illustrates an example network architecture of the OAM server in accordance with an example implementation. The activation period and offset for each cell within a cluster is configured by the OAM server at the time the small cell is deployed. The OAM server can also reconfigure those values and inform the small cell via the OAM interface at any time after the small cell is deployed. In addition, the OAM server can also deactivate a small cell permanently. An OAM server can manage one or more small cell clusters as illustrated in FIG. 5. All small cells under its management are connected to the OAM server via the OAM interface. The OAM server also does not have to be a separate server entity. In example implementations, the macro eNodeB or one of the small cell eNodeBs can also host or perform the functions of the OAM server. [0033] FIG. 6 illustrates a block diagram of an OAM server, in accordance with an example implementation. The OAM server 600 may include the following modules. The CPU module 601 is configured to assign/release a cell ID with activation period and offset to/from a small cell. The OAM interface 602 is configured to configure activation/deactivation parameters for each small cell. The memory 603 is configured to store a table indicating the availability of each cell ID that the OAM server manages. An example of such a table is shown in Table I below. The operations of the OAM server are further described with respect to FIG. 7 and FIG. 8. Table I: An OAM table containing activation period and offset

[0034] FIG. 7 illustrates an example of how the OAM server configures the activation parameters of a small cell, in accordance with an example implementation. The CPU of the OAM server selects one available cell ID (whose occupancy status shows“available”) at 700 and sends the selected cell ID with the corresponding activation period and offset to the small cell via the OAM interface. The small cell sends the activation confirmation after it receives the activation configuration from the OAM server via the OAM interface and performs the cell activation accordingly as shown at 701. After receiving the activation confirmation from the small cell, the CPU of the OAM server updates the cell ID management table in the memory by marking the corresponding cell ID as“occupied” in the occupancy status field as shown at 702. [0035] FIG. 8 illustrates an example procedure of deactivating a small cell, in accordance with an example implementation. The CPU of the OAM server sends a deactivation command to a small cell via the OAM interface. After receiving the deactivation command, the small cell sends a confirmation back to the OAM server and deactivates itself as shown at 800. After receiving the deactivation command from the small cell, the CPU of the OAM server updates the cell ID management table in the memory by marking the cell ID of the deactivated cell as“available” in the occupancy status field as shown at 801. [0036] FIG. 9 illustrates an example two-stage procedure for small cell activation, in accordance with an example implementation. At the time instant where a small cell is allowed to be turned on, the small cell performs a two-stage procedure as illustrates in FIG. 9. In the first preparation stage, the small cell sends a reference signal and broadcasts its system information to allow UEs to attach to the small cell. However, the small cell does not serve any UE, but rather collects the traffic information of its associated UEs in this stage. If any of the associated UEs need transmit/receive packets, the small cell will handover the UE to one of its neighboring active cells. If the small cell decides to switch on in the end of the first stage, the small cell servers its associated UEs in the second stage. Note that the small cell may decide not to switch on in the end of first stage. In this case, the second stage will not occur. In an example implementation, all small cells can have the same duration for the preparation stage, which is a predefined system parameter and known to all small cells. After the initial preparation stage, the small cell may begin to serve UEs in the second serving stage if the small cell is configured to turn on and server UEs during the preparation stage. The preparation stage can be based on the period and offset information as illustrated in Table I above. For example, a base station hosting the OAM server or a separate OAM server can instruct the other base stations in the cluster to being the activation procedure, thereby entering the preparation stage. Based on the time reserved to stay active, each of the base stations in the cluster can determine an appropriate time length for the preparation stage and the serving stage. [0037] FIG. 10 illustrates an activation mechanism for a small cell in two-cell scenarios, in accordance with an example implementation. In this example, a two-cell scenario is considered for illustration purposes, however, the example implementations described herein are not limited to a two-cell scenario and can be extended to a multiple cell scenario according to the desired implementation as illustrated, for example, in FIG. 13. Cell 1 is a small cell which is in OFF status. Cell 2 could be either a small cell (as illustrated in FIG. 11) or a macro cell (as illustrated in FIG. 12), which is in ON status. At the time instant where cell 1 is allowed to activate, the following flow can occur. [0038] At 1001, the CPU of Cell 1 instructs the baseband processor to generate a reference signal and system information, which is utilized by UEs to perform cell acquisition. Cell 1 sends the reference signal and broadcasts its system information for UEs to attach to Cell 1. At 1002, the CPU of Cell 1 collects the traffic information of its associated UEs and estimates the traffic load (e.g., in terms of the number of resource blocks to carry the traffic). The traffic information could include the number of associated UEs, the expected packet arrival rate, and other traffic related parameters, depending on the desired implementation. At 1003, Cell 1 sends the traffic load and/or interference information to Cell 2 via the Xn interface. Existing X2 signaling indicating the traffic load and interference level (to the neighboring cell) can be reused. For example, the Release 8 Relative Narrowband Transmit Power (RNTP) can be used to indicate the interference level. The traffic load information could be the number of resource blocks that are expected to use. Enhanced backhaul signaling for traffic load and interference indication over Xn interface can also be used. [0039] At 1004, the CPU of Cell 2 estimates the expected interference from Cell 1 based on the received traffic load and/or interference information. The CPU of Cell 2 updates the table stored in the memory, which indicates the interference level and activation time of its neighboring cells. An example of this table is illustrated in Table II below. At 1005, the CPU of cell 2 estimates the expected activation time of Cell 1. Cell 2 updates the table stored in the memory, which indicates the interference level and activation time of its neighboring cells. At 1006, Cell 2 sends activation/deactivation suggestions to Cell 1. If Cell 1 has no response or responds with activation, Cell 2 will adjust its transmission parameters such as Modulation and Coding Scheme (MCS) based on the estimated interference level from Cell 1 and its expected activation time. If Cell 1 responds with keeping the current OFF status, Cell 2 may decide to ignore the interference from Cell 1 when considering interference. Note that if Cell 2 is a small cell, Cell 1 may not follow its activation/deactivation suggestion. However, if Cell 2 is a macro cell, it is possible to configure Cell 1 such that it always follows the activation/deactivation suggestions from the macro cell, depending on the desired implementation. Table II: Expected interference level and activation time for each neighboring cell

[0040] Further, variations of the flow of FIG. 10 can be implemented depending on the desired implementation. For example, the flow at 1006 may be omitted and the flow can proceed without the sending of suggestions. [0041] FIG. 11 illustrates a scenario with two small cells, in accordance with an example implementation. Specifically, FIG. 11 illustrates an example implementation of the scenario of FIG. 10 when both Cell 1 and Cell 2 are small cells. In the example of FIG. 11, Cell 1 is in the OFF status and Cell 2 is another small cell that is active. [0042] FIG. 12 is a scenario with a macro cell and a small cell, in accordance with an example implementation. Specifically, FIG. 11 illustrates an example implementation of the scenario of FIG. 10 when both Cell 1 and Cell 2 are small cells. In the example of FIG. 11, Cell 1 is in the OFF status and Cell 2 is another small cell that is active. [0043] FIG. 13 illustrates an activation mechanism for a small cell for a general scenario, in accordance with an example implementation. In FIG. 13, the flowchart of the small cell activation mechanism in a multiple macro/small cell scenario is illustrated. Assume that Cell 1 and Cell 2 are two small cells which are in OFF status. At the time instant where Cell 1 is allowed to be activated, the following flow can occur. The flow is similar to the flow of FIG. 10, only extended to illustrate a scenario involving more than two cells. [0044] At 1301, the CPU of Cell 1 instructs the baseband processor to generate a reference signal and system information, which is utilized by the UEs to perform cell acquisition. Cell 1 sends the reference signal and broadcasts its system information for UEs to attach to Cell 1. At 1302, the CPU of Cell 1 collects the traffic information of its associated UEs and estimates the traffic load (e.g. in terms of the number of resource blocks to carry the traffic). The traffic information can include the number of associated UEs, the expected packet arrival rate, and other traffic related parameters, depending on the desired implementation. At 1303, Cell 1 sends the traffic load and/or interference information to its neighboring active cells (e.g. Cell 3, Cell 4… Cell n) via the Xn interface. [0045] At 1304, the neighboring cells of Cell 1 estimates the expected interference from Cell 1 based on the received traffic load and/or interference information. At 1305, the neighboring cells of Cell 1 estimate the expected activation time of Cell 1. At 1306, the neighboring cells of Cell 1 send activation/deactivation suggestions to Cell 1, respectively. If Cell 1 has no response or responds with activation, the neighboring cells will adjust its transmission parameters such as MCS based on the estimated interference level from Cell 1 and its expected activation time. If Cell 1 responds with keeping the current OFF status, its neighboring cell may decide to ignore the interference from Cell 1 when considering interference. [0046] At the time instant where Cell 2 is allowed to be activated, the following flow can occur when Cell 1 is already activated. At 1307, the CPU of Cell 2 instructs the baseband processor to generate reference signal and system information, which is utilized by the UEs to perform cell acquisition. Cell 2 sends the reference signal and broadcasts its system information for UEs to attach to Cell 2. At 1308, the CPU of Cell 2 collects the traffic information of its associated UEs and estimates the traffic load (e.g. in terms of the number of resource blocks to carry the traffic). The traffic information can include the number of associated UEs, the expected packet arrival rate, and other traffic related parameters, depending on the desired implementation. At 1309, Cell 2 sends the traffic load and/or interference information to its neighboring active cells (Cell 1, Cell 3… Cell n) via the Xn interface. [0047] At 1310, the neighboring cells of Cell 2 estimates the expected interference from Cell 2 based on the received traffic load and/or interference information. At 1311 the neighboring cells of Cell 2 estimates the expected activation time of Cell 2. At 1312, the neighboring cells of Cell 2 send activation/deactivation suggestions to Cell 2, respectively. If Cell 2 has no response or responds with activation, its neighboring cells will adjust its transmission parameters such as MCS based on the estimated interference level from Cell 2 and its expected activation time. If Cell 2 responds with keeping the current OFF status, its neighboring cell may decide to ignore the interference from Cell 2 when considering interference. [0048] Further, variations of the flow of FIG. 13 can be implemented depending on the desired implementation. For example, the flow at 1306 and 1312 may be omitted and the flow can proceed without the sending of suggestions. [0049] FIG. 14 illustrates small cell control by the macro eNodeB in accordance with an example implementation. The activation of small cells can also be controlled by the macro eNodeB as illustrated in FIG. 14. In this example, assume that small cells 1-n are in “OFF” status. Each of the small cells sends its traffic load and/or interference level to the macro eNodeB sequentially. After collecting all the information from its neighboring small cells, the macro eNodeB makes a joint decision for all small cells and informs the small cells of the decision via the Xn interface. The process is similar to FIG. 13, only that the macro cell controls all of the operations and dictates which of the small cells can activate or deactivate. [0050] Finally, some portions of the detailed description are presented in terms of algorithms and symbolic representations of operations within a computer. These algorithmic descriptions and symbolic representations are the means used by those skilled in the data processing arts to most effectively convey the essence of their innovations to others skilled in the art. An algorithm is a series of defined steps leading to a desired end state or result. In example implementations, the steps carried out require physical manipulations of tangible quantities for achieving a tangible result. [0051] Unless specifically stated otherwise, as apparent from the discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing,”“computing,”“calculating,”“determining,”“displaying,” or the like, can include the actions and processes of a computer system or other information processing device that manipulates and transforms data represented as physical (electronic) quantities within the computer system’s registers and memories into other data similarly represented as physical quantities within the computer system’s memories or registers or other information storage, transmission or display devices. [0052] Example implementations may also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may include one or more general-purpose computers selectively activated or reconfigured by one or more computer programs. Such computer programs may be stored in a computer readable medium, such as a computer-readable storage medium or a computer-readable signal medium. A computer-readable storage medium may involve tangible mediums such as, but not limited to optical disks, magnetic disks, read-only memories, random access memories, solid state devices and drives, or any other types of tangible or non-transitory media suitable for storing electronic information. A computer readable signal medium may include mediums such as carrier waves. The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Computer programs can involve pure software implementations that involve instructions that perform the operations of the desired implementation. [0053] Various general-purpose systems may be used with programs and modules in accordance with the examples herein, or it may prove convenient to construct a more specialized apparatus to perform desired method steps. In addition, the example implementations are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the example implementations as described herein. The instructions of the programming language(s) may be executed by one or more processing devices, e.g., central processing units (CPUs), processors, or controllers. [0054] As is known in the art, the operations described above can be performed by hardware, software, or some combination of software and hardware. Various aspects of the example implementations may be implemented using circuits and logic devices (hardware), while other aspects may be implemented using instructions stored on a machine-readable medium (software), which if executed by a processor, would cause the processor to perform a method to carry out implementations of the present application. Further, some example implementations of the present application may be performed solely in hardware, whereas other example implementations may be performed solely in software. Moreover, the various functions described can be performed in a single unit, or can be spread across a number of components in any number of ways. When performed by software, the methods may be executed by a processor, such as a general purpose computer, based on instructions stored on a computer-readable medium. If desired, the instructions can be stored on the medium in a compressed and/or encrypted format. [0055] Moreover, other implementations of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the teachings of the present application. Various aspects and/or components of the described example implementations may be used singly or in any combination. It is intended that the specification and example implementations be considered as examples only, with the true scope and spirit of the present application being indicated by the following claims.

Claims

What is claimed is: 1. A computer configured to manage a cluster comprising a plurality of base stations, the computer comprising: a memory configured to store an activation schedule for the cluster, the activation schedule comprising period information for the cluster and offset information for each of the plurality of base stations in the cluster; a processor configured to transmit the period information and corresponding ones of the offset information to each of the plurality of base stations in the cluster, wherein the offset information is different for each of the plurality of base stations in the cluster. 2. The computer of claim 1, wherein the processor is configured to select ones of the plurality of base stations in the cluster that is available for activation based on the period information and to transmit activation parameters to the selected ones of the plurality of base stations. 3. The computer of claim 1, wherein the offset information for the each of the plurality of base stations in the cluster is indicative of an offset of time from a period indicated in the period information for which the each of the plurality of base stations in the cluster can activate. 4. The computer of claim 3, wherein the processor is further configured to estimate preparation time based on the offset information for each of the plurality of base stations in the cluster. 5. The computer of claim 1, wherein the memory is configured to store traffic load information for each of the plurality of base stations in the cluster, and wherein the processor is further configured to estimate interference for the plurality of base stations in the cluster based on traffic load information. 6. A computer program for managing a cluster comprising a plurality of base stations, the computer program comprising: code for storing an activation schedule for the cluster, the activation schedule comprising period information for the cluster and offset information for each of the plurality of base stations in the cluster; code for transmitting the period information and corresponding ones of the offset information to each of the plurality of base stations in the cluster, wherein the offset information is different for each of the plurality of base stations in the cluster. 7. The computer program of claim 6, wherein the processor is configured to select ones of the plurality of base stations in the cluster that is available for activation based on the period information and to transmit activation parameters to the selected ones of the plurality of base stations. 8. The computer program of claim 6, wherein the offset information for the each of the plurality of base stations in the cluster is indicative of an offset of time from a period indicated in the period information for which the each of the plurality of base stations in the cluster can activate. 9. The computer program of claim 8, further comprising code for estimating preparation time based on the offset information for each of the plurality of base stations in the cluster. 10. The computer program of claim 6, further comprising code for storing traffic load information for each of the plurality of base stations in the cluster, and code for estimating interference for the plurality of base stations in the cluster based on traffic load information. 11. A first base station, coupled to one or more second base stations by a backhaul and configured to manage a cluster formed from the one or more second base stations, comprising: a memory configured to store an activation schedule for the cluster, the activation schedule comprising period information for the cluster and offset information for each of the one or more second base stations in the cluster; a processor configured to transmit the period information and corresponding ones of the offset information to each of the one or more second base stations in the cluster, wherein the offset information is different for each of the one or more second base stations in the cluster. 12. The first base station of claim 11, wherein the processor is configured to select ones of the one or more second base stations in the cluster that is available for activation based on the period information and to transmit activation parameters to the selected ones of the one or more second base stations. 13. The first base station of claim 11, wherein the offset information for the each of the one or more second base stations in the cluster is indicative of an offset of time from a period indicated in the period information for which the each of the one or more second base stations in the cluster can activate. 14. The first base station of claim 13, wherein each of the one or more second base stations in the cluster enters into a preparation stage based on the offset information for each of the one or more second base stations in the cluster and determines whether to activate or not based on the preparation stage. 15. The first base station of claim 11, wherein the memory is configured to store traffic load information for each of the one or more second base stations in the cluster, and wherein the processor is further configured to estimate interference for the one or more second base stations in the cluster based on traffic load information.