JP2012511861A - Femto base station power saving method through sleep cycle synchronization - Google Patents

Abstract

The present invention relates to a wireless connection system, and more particularly, to a method for saving power in a femto base station. According to an embodiment of the present invention, a process of acquiring reference synchronization information used in a predetermined region so that the first femto base station can perform a sleep mode operation, and a terminal exists in the first femto base station If not, including a process of transitioning to a sleep mode and a process of synchronizing the first femto base station and at least one second femto base station belonging to the predetermined region using the reference synchronization information A power saving method is provided in which each femto base station included in the predetermined region synchronizes sleep mode operation using the reference synchronization information. Therefore, power consumption of the femto base station and interference with the macro cell can be minimized in a wireless connection system that supports the femto cell, and terminals in the femto cell can perform reliable communication.
[Selection] Figure 6

Description

  The present invention relates to a wireless connection system, and more particularly, to a method for saving power in a femto base station.

  Hereinafter, a femto cell will be briefly described.

  Femto refers to a very small unit of 10-15. In this sense, the femtocell means an ultra-small / low power home / office indoor base station. The femtocell is used in the same meaning as the picocell, but is used in the meaning having a more advanced function. The femtocell is a small cellular base station that is connected to a broadband router, and the voice and data of the 3G system as well as the existing 2G system can be connected to the backbone network of the mobile communication company through a DSL link or the like.

  Hereinafter, advantages of such a femtocell will be described.

  Recently, a research report that femtocell can be a detonator to promote 3G penetration and expand indoor coverage has received attention. By 2011, the number of femtocell terminal users worldwide is expected to increase to 102 million, and the installation of AP (Access Point) as a base station is expected to reach 32 million. "In technical terms, the enhancement of indoor coverage of technologies such as W-CDMA, HSDPA, and EVDO plays a very important role in service provision," said SBI Stuart Callow, chief analyst at ABI Research. Stuart Callow said, “Femtocell routes traffic through the IP network, which greatly enhances network quality and capacity, and at the same time, each mobile carrier invests in a backhaul leased line. Also has a significant benefit from a strategic and economic point of view. "

  Femtocells can enhance cell coverage and improve voice service quality. Also, each mobile carrier expects to be able to fully adapt its subscribers to 3G by providing data services through femtocells. The femtocell is called a femto base station (FBS) or a femto BTS (Base Transceiver Station).

  In summary, femtocells have the following advantages.

1. Increase cell coverage Reduction of infrastructure construction costs 2. Provision of new services Acceleration of FMC (Fixed Mobile Convergence)

  One or more femtocells may be grouped by specific service or region to form a femtocell group. For example, a femto cell group that is permitted to connect only to a specific terminal can be referred to as a closed subscriber group (CSG: Closed Subscriber Group, hereinafter referred to as “CSG”). The femto base station (FBS) can confirm the CSG identifier (CSG ID) of the terminal and allow only the terminal that has joined the CSG.

  FIG. 1 is a diagram illustrating an example of a network structure including a femto base station (FBS).

  A femto base station is an individual newly added to an existing network. Thus, there are additions or changes to the overall network structure by using femto base stations. The femto base station is directly connected to the Internet and can function as a base station. Therefore, the femto base station can perform almost all functions of a general macro base station. The femto base station can also receive data from a general macro base station and relay it to a terminal.

  FIG. 1 illustrates a form in which a femto network gateway (FNG) is added to an existing network structure. The FNG can communicate with an access service network (ASN) gateway and a connected service network (CSN). The FNG can use the Rx interface for communication with the ASN and the Ry interface for communication with the CSN.

  The femto base station is directly connected to the TCP / IP Internet network and can receive services from the CSN through the FNG. A terminal connected to the femto base station can receive services of functions such as authentication and IMS (IP Multimedia Subsystem) from the FNG or the CSN.

  The femto base station is connected to the base station via the R1 interface. This indicates that the femto base station can receive the downlink (DL: Down Link) channel of the macro base station. Further, the femto base station can transmit a control signal to the macro base station.

  In a generally used broadband wireless access system, power consumption of a macro base station (Macro BS) is not considered. However, in an environment that supports femtocells, the number of terminals that one femtocell supports services is limited (approximately 5 to 6 terminals). In some cases, the femtocell may not have a terminal that maintains a connection for a specific time.

  When such a situation is repeated, even when the femtocell does not need to provide a service to a specific terminal, there is a possibility that power consumption may occur by providing the service continuously. Further, when neighboring femto base stations use the same frequency band in the femto system, interference may occur between neighboring femto base stations.

  Therefore, there is a need for a method that can overcome this situation.

  The present invention has been made to solve the above-mentioned general technical problems, and an object of the present invention is to provide a method for minimizing the power consumption of a femto cell in a wireless connection system that supports the femto cell. It is to provide.

  Another object of the present invention is to reduce the power consumption of the femto cell and the interference with the macro cell when there is no terminal connected to the femto cell or when all the terminals connected to the femto cell transition to the idle mode. It is to provide a way to minimize.

  It is still another object of the present invention to enable a terminal to perform reliable communication when a femtocell is in a power saving mode.

  It is still another object of the present invention to provide a method for facilitating femto base station scanning of a terminal by matching operation periods for power saving of all femtocells of the same type or those of the same type. It is to provide.

  The technical problem to be achieved by the present invention is not limited to the technical problem mentioned above, and other technical problems that are not mentioned are normal in the technical field to which the present invention belongs from the following description. It will be clearly understood by those who have knowledge.

  To solve the above technical problem, the present invention discloses various methods for minimizing the power consumption of a femto base station.

  According to one aspect of the present invention, a method for conserving power at a femto base station includes obtaining reference synchronization information used in a predetermined region so that the first femto base station can perform sleep mode operation; When there is no terminal in one femto base station, the step of transitioning to a sleep mode, and using the reference synchronization information, the first femto base station and at least one second femto base station belonging to the predetermined region The femto base stations included in the predetermined region synchronize sleep mode operations using the reference synchronization information.

  Preferably, the reference synchronization information includes a sleep cycle, a listening interval, and an absolute or relative start frame, and the transition to the sleep mode in synchronization with the reference synchronization information includes the sleep cycle, the listening interval, and Transition to sleep mode to satisfy an absolute or relative start frame.

  Preferably, the reference synchronization information is set so as to have a predetermined listening interval and sleep cycle with reference to an already set start time.

  Preferably, the reference synchronization information is based on a listening interval and a sleep cycle set in the first femto base station and the at least one second femto base station, which are the femto base stations that have transitioned to the sleep mode first. It is what follows.

  Preferably, the sleep cycle is divided into a possible interval and an impossible interval.

  Preferably, in the sleep cycle, one of the possible section and the impossible section is started first.

  Preferably, the synchronization may be performed by starting from a frame in which a new sleep cycle of the reference synchronization information that starts first from when there is no terminal in the first femto base station.

  Preferably, the first femto base station broadcasts at least one of a synchronization channel and a super frame header (SFH) only in the possible section in sleep mode, and does not transmit or receive any data wirelessly in the impossible section. It is.

  Preferably, the synchronization channel is synchronized with the first femto base station and the at least one second femto base station.

  Preferably, the method further includes transmitting sleep mode information to the terminal, wherein the sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval based on the reference synchronization information.

  Preferably, the sleep mode information includes super frame header (SFH), additional system information, ranging response (RNG-RSP) message, neighbor advertisement (NBR-ADV) message, and femtocell base station low load mode indication (FCB- LDM-IND) message is transmitted to the terminal through at least one of them.

  Here, the neighbor advertisement message and the femtocell base station low load mode indication (FCB-LDM-IND) message are unicast or broadcast to the terminal.

  The predetermined area is a macro cell area.

  In addition, there are two or more reference synchronization information depending on the type of femtocell subscriber group located in the predetermined area.

  As another aspect of the present invention, a method for conserving power of a femto base station at a terminal is performed by superimposing a first femto base station entering a sleep mode in synchronization with reference synchronization information used in a predetermined area. Receiving a frame header (SFH) and a synchronization channel; and decoding at least one of the super frame header (SFH) and the synchronization channel to detect a cell identifier and a CSG identifier of the first femto base station. And, when the first femto base station is a femto base station to which the terminal has joined, connecting to the first femto base station, each femto base station included in the predetermined area Is to synchronize sleep mode operation using the reference synchronization information.

  Preferably, the reference synchronization information may include a sleep cycle, a listening interval, and an absolute or relative start frame.

  Preferably, the step of connecting to the first femto base station includes receiving sleep mode information from the first femto base station or macro base station, and using the received sleep mode information. Determining a sleep mode operation time of one femto base station and transmitting a predetermined code or message to the first femto base station.

  Preferably, the sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval based on the reference synchronization information, and the predetermined code or message is already set in a possible interval in the sleep cycle. And transmitted to the first femto base station through the uplink resources.

  Preferably, when connecting to any one second femto base station among the respective femto base stations included in the predetermined area, the first femto base grasped using the received sleep mode information. The station sleep mode operation time is used.

  According to another aspect of the present invention, a method for conserving power in a femto base station includes obtaining paging information of at least one terminal that transitions to an idle mode in the femto base station, and in the femto base station When all the at least one terminal enters the idle mode, the method may include a transition to the sleep mode in consideration of the acquired paging information of the at least one terminal.

  Preferably, the paging information includes at least one of a paging cycle, a paging offset, and paging listening interval information, and the paging cycle includes a paging listening interval and a non-listening interval, and the transition to the sleep mode includes: This is performed when all of the at least one terminal in the femto base station further satisfies the condition that it is a paging-incapable section.

  Preferably, the method may further include a step of transitioning to a normal mode when any one of the at least one terminal in the femto base station is not in the impossible period.

  Preferably, the femto base station shares reference synchronization information with one or more other femto base stations located in a predetermined region to which the femto base station belongs, and transits to the sleep mode. This is performed in synchronization with the shared reference synchronization information.

  A mobile terminal according to still another aspect of the present invention includes a processor and a radio communication (RF) module for transmitting and receiving a radio signal to and from the outside under the control of the processor. The wireless communication module is controlled to receive a super frame header (SFH) and a synchronization channel from a first femto base station that has entered sleep mode by synchronizing with reference synchronization information used in a predetermined region, and A cell identifier and a CSG identifier of the first femto base station are detected by decoding at least one of a frame header (SFH) and a synchronization channel, and the mobile terminal joins the first femto base station. If the base station is a femto base station, the wireless communication module is connected to the first femto base station. It is possible to control the Yuru.

  Here, it is desirable that each femto base station included in the predetermined region synchronizes sleep mode operation using the reference synchronization information.

  At this time, the reference synchronization information may include a sleep cycle, a listening interval, and an absolute or relative start frame.

  The processor controls the wireless communication module to receive sleep mode information from the first femto base station or macro base station, and uses the received sleep mode information to transmit the first femto base station. Controlling the wireless communication module to connect to the first femto base station so that a predetermined code or message is transmitted to the first femto base station. Can do.

  The sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval based on the reference synchronization information, and the predetermined code or message is already set as a possible interval in the sleep cycle. Preferably, it is transmitted to the first femto base station through uplink resources.

  In addition, when the processor connects to any one second femto base station among the femto base stations included in the predetermined area, the processor grasps the received first sleep mode information using the received sleep mode information. The sleep mode operation time point of one femto base station can be used.

  Each embodiment of the present invention has the following effects.

  First, by using each embodiment of the present invention, it is possible to minimize power consumption of a femto base station and interference with a macro cell in a wireless connection system that supports femto cells.

  Second, by using each embodiment of the present invention, even if the femto base station operates in the power saving mode, the terminals in the femto cell can perform reliable communication.

  Third, by using each embodiment of the present invention, the terminal can more efficiently scan the entire femto base station or the same type of femto base station existing in the predetermined area.

  The effects obtained by the present invention are not limited to the effects mentioned above, and other effects not mentioned are clearly apparent to those having ordinary knowledge in the technical field to which the present invention belongs from the following description. Will be understood.

It is a figure which shows an example of the network structure containing a femto base station (FBS). It is a state diagram which shows the change of the power mode of the femto base station by the 1st Example of this invention. It is a figure which shows the sleep cycle of the femto base station which the femto base station proposed by the 1st Example of this invention operates periodically in order to reduce power consumption and to reduce radio interference. It is a figure which shows an example of operation | movement of the femto base station which synchronizes with the reference | standard synchronization information by 1st Example of this invention, and changes to sleep mode. It is a figure which shows another example of operation | movement of the femto base station which synchronizes with the reference | standard synchronization information by 1st Example of this invention, and changes to sleep mode. It is a figure which shows an example of operation | movement of the terminal and femto base station relevant to 1st Example of this invention. FIG. 6 is a diagram illustrating an example of a method in which a femto base station associated with an embodiment of the present invention notifies sleep mode information to a terminal; It is a figure which shows another example of operation | movement of the terminal and femto base station relevant to the 1st Example of this invention. FIG. 7 is a diagram illustrating a power saving method in which different paging cycles of a plurality of terminals are considered in a femto base station related to the second embodiment of the present invention. FIG. 6 is a diagram illustrating a power saving method in which reference synchronization information is further considered in a femto base station associated with the second embodiment of the present invention. It is a block diagram which shows an example of a transmission end and receiving end structure as further another Example of this invention.

  The present invention relates to a wireless connection system. Hereinafter, embodiments of the present invention disclose various methods that can minimize power consumption of a femto base station.

  The following embodiments are obtained by combining the constituent elements and features of the present invention in a predetermined form. Each component or feature can be considered optional unless explicitly stated otherwise. Each component or feature can be implemented in a form that is not combined with other components or features. Also, some embodiments and / or features may be combined to form embodiments of the present invention. The order of each operation described in each embodiment of the present invention can be changed. Some configurations or features of one embodiment may be included in other embodiments or replaced with corresponding configurations or features of other embodiments.

  The description with reference to the drawings does not describe procedures or steps that may obscure the gist of the present invention, and does not describe procedures or steps that can be understood by those skilled in the art.

  In the present specification, each embodiment of the present invention has been described focusing on the data transmission / reception relationship between the base station and the terminal. Here, the base station is meaningful as a terminal node of a network that directly communicates with a terminal. The specific operations described as being performed by the base station in this document can also be performed by an upper node of the base station in some cases.

  That is, various operations performed for communication with a terminal in a network including a large number of network nodes including a base station can be performed by the base station or another network node other than the base station. At this time, the “base station” can be replaced with terms such as a fixed station, Node B, eNode B (eNB), and access point. In addition, “mobile station (MS)” can be replaced with terms such as UE (User Equipment), SS (Subscriber Station), MSS (Mobile Subscriber Station), or a terminal.

  The transmitting end means a node that transmits data or voice service, and the receiving end means a node that receives data or voice service. Therefore, in the uplink, a terminal can be a transmitting end and a base station can be a receiving end. Similarly, in the downlink, a terminal can be a receiving end and a base station can be a transmitting end.

  On the other hand, as the mobile terminal of the present invention, a PDA (Personal Digital Assistant), a cellular phone, a PCS (Personal Communication Service) phone, a GSM (Global System for Mobile phone), a WCDMA (Wideband MBS phone), a WCDMA (Wideband MBS phone). A phone or the like can be used.

  Each embodiment of the present invention can be implemented through various means. For example, each embodiment of the present invention can be implemented by hardware, firmware, software, or a combination thereof.

  In the case of implementation by hardware, the method according to each embodiment of the present invention includes one or more ASICs (application specific integrated circuits), DSPs (digital signal processing), DSPSs (digital signal coding). logic devices), FPGAs (field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

  In the case of implementation by firmware or software, the method according to each embodiment of the present invention can be implemented in the form of a module, procedure, function, or the like that performs the functions or operations described above. The software code is stored in the memory unit and driven by the processor. The memory unit is located inside or outside the processor, and can exchange data with the processor by various known means.

  Each embodiment of the present invention can be supported by a standard document disclosed in at least one of the IEEE 802 system, the 3GPP system, the 3GPP LTE system, and the 3GPP2 system which are wireless connection systems. That is, steps or portions of the embodiments of the present invention that are not described in order to clearly show the technical idea of the present invention can be supported by the respective documents. Also, all terms disclosed in this document can be explained by the standard document. In particular, each embodiment of the present invention can be supported by one or more of P802.16-2004, P802.16e-2005, and P802.16 Rev2 documents that are standard documents of the IEEE 802.16 system.

  The specific terms used in the following description are provided for facilitating the understanding of the present invention, and the use of such specific terms may take other forms without departing from the technical idea of the present invention. Can be changed.

(First embodiment)
The first embodiment of the present invention provides a method for conserving power by entering a sleep mode in synchronism with other femto base stations in a predetermined area at a femto base station.

  In this embodiment, it is assumed that the synchronization channel transmitted by the femto base station is synchronized with one or more other femto base stations located within a predetermined area to which the femto base station belongs. At this time, the predetermined area to which the femto base station belongs is an area corresponding to the entire network, a coverage area of at least one macro base station (MBS), a macro cell, or at least one paging group. Further, it is assumed that all femto base stations appearing in the present embodiment exist in the predetermined area.

  First, the femto base station can determine whether or not the sleep mode transition condition is satisfied in order to transition to the sleep mode. This will be described below with reference to FIG.

  FIG. 2 is a state diagram illustrating changes in the power mode of the femto base station according to the first embodiment of the present invention.

  Referring to FIG. 2, a femto base station can have two states. One is to operate in the normal mode, and the other is to operate in the sleep mode. In the sleep mode, the femto base station broadcasts at least one of synchronization information (eg, P-SCH, S-SCH) and super frame header (SFH) only during a predetermined period in the femto cell region, It means reducing power consumption by monitoring link availability. Here, the sleep mode can be referred to as a low load mode.

  The state of the femto base station transitions from one state to another state when a specific condition is satisfied. For example, the femto base station can operate a predetermined count, but the predetermined count can be determined by the number of terminals that have joined the CSG of the femto base station. That is, when the number of terminals that have joined the CSG is n, a count value of “n” indicates that all terminals that have joined the CSG are in the cell area of the femto base station. Also, the counter value is “0” when all the terminals that have joined the CSG of the femto base station have deviated from the cell area of the femto base station, or when all terminals have entered the idle mode or sleep mode. Indicates.

  That is, when the count value is “0” or “n” in FIG. 2, the femto base station can transition from the normal mode to the power saving mode (sleep mode or low duty mode). Therefore, the femto base station broadcasts only the minimum signal to be transmitted to each terminal in the power saving mode and stops the remaining operation, thereby minimizing the power consumption in the femto base station.

  However, in this embodiment, since the paging cycle of the terminal that has transitioned to the idle mode is not taken into consideration, it is desirable that the specific condition for the femto base station to transition to the sleep mode is that no terminal exists in the femto base station.

  Next, a sleep mode (Low Duty Mode) in which the femto base station can transition when the sleep mode transition condition described above is satisfied will be described with reference to FIG.

  FIG. 3 shows a sleep cycle of a femto base station in which the femto base station proposed in the first embodiment of the present invention operates periodically in order to reduce power consumption and reduce radio interference.

  Referring to FIG. 3, the sleep cycle of the femto base station can be composed of possible sections and impossible sections, and the role played by the femto base station in each section is as follows.

  First, the feasible section will be described. The femto base station can transmit a synchronization channel and / or a super frame header (SFH) to each terminal on the downlink during the possible section. In addition, the femto base station can monitor the presence / absence of a ranging code transmission, for example, a connection attempt transmitted by a terminal during an already established uplink period.

  Next, the impossible section will be described. The femto base station may block the uplink and the downlink during the impossible section, and may not transmit or receive any information on the radio. Through this, the femto base station can reduce interference with a neighboring femto base station or macro base station using the same frequency band, and at the same time reduce power consumption.

  The femto base station can start the possible section first or can start the impossible section first in a sleep cycle composed of such a possible section and an impossible section.

  However, in order for the femto base station to enter the sleep mode in synchronization with another femto base station, a reference for synchronizing is required. Here, entering the sleep mode in synchronization means that all the femto base stations that have transitioned to the sleep mode within a predetermined region simultaneously repeat the sleep cycle of the same length at the same time. That is, when any femto base station that operates in the sleep mode exists in the possible section, all other femto base stations that operate in the sleep mode also exist in the possible section, and vice versa. Are the same.

  Therefore, we propose a criterion that includes sleep cycle, listening interval and absolute or relative start frame for all femto base stations to operate in sleep mode in sync. This is referred to herein as “reference synchronization information” or “Low Duty Pattern”.

  In the reference synchronization, a sleep cycle having a possible interval and an impossible interval that are already set based on a predetermined time point is continuously repeated regardless of whether or not all femto base stations can sleep. This can be determined by at least one of a macro base station, a paging controller, and a femto base station in charge of a predetermined area.

  Further, the reference synchronization information may be a sleep cycle including a feasible interval and an impossible interval set in the femto base station that has first transited to the sleep mode among the femto base stations. In this case, the sleep cycle set by the femto base station that first transited to the sleep mode can be continuously maintained as reference synchronization information, and if there is no femto base station that operates in the sleep mode, initialization is performed. As a result, the sleep cycle of any femto base station that has transitioned to the sleep mode next can be determined as new reference synchronization information.

  The reference synchronization information determined by the above-described method can be maintained by at least one of a macro base station, at least one femto base station, and a paging controller in charge of a predetermined area, via a backbone network, or a macro. It is shared with other femto base stations through a predetermined message broadcasted by the base station wirelessly.

  First, a case where the femto base station transitions to the sleep mode in accordance with the reference sleep time set regardless of whether or not the sleep mode transition of other femto base stations is possible will be described with reference to FIG. FIG. 4 shows an example of the operation of the femto base station that shifts to the sleep mode in synchronization with the reference synchronization information according to the first embodiment of the present invention.

  Referring to FIG. 4, it can be seen that the reference synchronization information that repeats in a predetermined sleep cycle is set regardless of whether the sleep mode transition of other femto base stations is possible. The femto base station (Femto BS # 1) can acquire such reference synchronization information from at least one of the macro base station, another femto base station, and the paging controller (S401).

  Thereafter, when the terminal no longer exists in the femto base station, the femto base station can satisfy the condition for entering the sleep mode related to the present invention (S402).

  When the terminal no longer exists, the femto base station can immediately transition to the sleep mode according to the reference synchronization information, and the new sleep cycle of the reference synchronization information that comes first when there is no terminal in the femto base station It is also possible to transition to the sleep mode in synchronization with the start of (S403).

  The femto base station that has entered the sleep mode through the above-described process may perform the sleep mode by repeating the possible interval and the impossible interval according to the reference synchronization information until the terminal enters the coverage area and attempts to connect. it can.

  Next, the case where the sleep cycle set by the femto base station that has first transited to the sleep mode is set as the reference synchronization information will be described with reference to FIG. FIG. 5 shows another example of the operation of the femto base station that shifts to the sleep mode in synchronization with the reference synchronization information according to the first embodiment of the present invention.

  Referring to FIG. 5, assuming that no femto base station has transitioned to the sleep mode and there is no reference synchronization information that is already set, one femto base station (Femto BS # 2) Can enter the sleep mode (S501).

  At this time, the sleep cycle set by the femto base station (Femto BS # 2) that first transited to the sleep mode can be continuously set as the reference synchronization information, and the other femto base station (Femto BS # 1) Can acquire information on the reference synchronization information (S502).

  Thereafter, when the terminal no longer exists in the coverage area of the femto base station (Femto BS # 1), the femto base station (Femto BS # 1) can enter the sleep mode (S503).

  At this time, the femto base station (Femto BS # 1) can immediately transition to the sleep mode according to the reference synchronization information, and the reference synchronization information that comes first from when there is no terminal in its coverage area It is also possible to transition to the sleep mode in synchronization with the start of a new sleep cycle (S504).

  A process in which the terminal attempts to connect to the femto base station that has transitioned to the sleep mode by the above-described method will be described with reference to FIG. FIG. 6 shows an example of operations of the terminal and the femto base station related to the first embodiment of the present invention. In FIG. 6, it is assumed that the reference synchronization information is set in advance and shared by all femto base stations in a predetermined area, and is continuously maintained.

  Referring to FIG. 6, when the terminal enters the network of the femto base station, sleep mode information can be acquired from the femto base station (S601). Here, the sleep mode information refers to information transmitted to the terminal so that the femto base station can know in which form of sleep mode it operates. The sleep mode information can also be referred to as “low duty pattern information”.

  The sleep mode information includes the following information.

  1) Start frame: A frame number at which the femto base station transitions to the sleep mode. In the present invention, it is a frame number at the time when a new sleep cycle of the basic sleep period is started.

  2) Sleep cycle: A section in which the femto base station operates in the sleep mode, and is set in units of superframes.

  3) Listening section: Indicates a possible section among the sections in which the femto base station operates in the sleep mode. That is, during this interval, the femto base station transmits synchronization channel information and a super frame header (SFH) to the terminal, and monitors whether there is a ranging attempt transmitted by the terminal during the already configured uplink interval. be able to.

  When the sleep mode information is compared with the reference synchronization information, the sleep cycle and the listening interval of the sleep mode information are the same as the sleep cycle and the listening interval of the reference synchronization information. However, the start frame of the sleep mode information may differ from the start frame of the reference synchronization information depending on when the base station informs the terminal of the sleep mode information at the femto base station.

  Such sleep mode information can be transmitted to the terminal through various methods. For example, when a terminal attempts initial entry or location update to a femto base station or a macro base station, sleep mode information is included in a ranging response (RNG-RSP) message and transmitted to the terminal. For this reason, the ranging response message includes the contents shown in Table 1 below.

他の例として、マクロ基地局又は睡眠モードで動作中のフェムト基地局から放送されるスーパーフレームヘッダー（ＳＦＨ）に睡眠モード情報が含まれ、これが端末に伝送される。

As another example, sleep mode information is included in a super frame header (SFH) broadcast from a macro base station or a femto base station operating in the sleep mode, and this is transmitted to the terminal.

  As yet another example, a method of transmitting sleep mode information to a terminal using additional system information will be described with reference to FIG.

  FIG. 7 illustrates an example of a method by which a femto base station associated with an embodiment of the present invention informs a terminal of sleep mode information.

  Referring to FIG. 7, a superframe header (SFH) includes a subframe number indicating a position of additional system information including sleep mode information in a corresponding superframe. The terminal can know the subframe number in which the sleep mode information is transmitted by decoding the super frame header (SFH), and can acquire the sleep mode information by confirming the corresponding subframe. At this time, the additional system information is DCD (Downlink Channel Descriptor).

  As yet another example, sleep mode information may be included in a neighbor advertisement (MOB_NBR-ADV) message transmitted from a macro base station or a femto base station and transmitted to a terminal. Such a neighbor advertisement message may be broadcast by a macro base station or a femto base station, and may be unicast to a terminal through a unicast neighbor advertisement (unicast MOB_NBR-ADV) message.

  In addition, the sleep mode information is included in a dedicated message, for example, a femtocell base station low load mode indication (FCB-LDM-IND: FemtoCellBS-Low_Duty_Mode-Indication) message, which may be transmitted to the terminal. The FCB-LDM-IND message is unicast (unicast FCB-LDM-IND) or broadcast from the macro base station or the femto base station to the terminal.

  Referring to FIG. 6 again, when there is no terminal in the coverage area, the femto base station can enter the sleep mode in accordance with the start frame included in the sleep mode information (S602). Here, the time point indicated by the start frame is the time point when a new sleep cycle of the reference synchronization information is started. The femto base station that has entered the sleep mode can perform the sleep mode by alternately repeating the possible section and the impossible section in synchronization with the reference synchronization information.

  Thereafter, the terminal can acquire information on the femto base station by decoding a synchronization channel (eg, P-SCH or S-SCH) transmitted by the femto base station. For example, the terminal can decode the P-SCH and synchronize with the base station in time synchronization. The terminal can acquire cell identifier (Cell ID) information by decoding S-SCH after time synchronization. Also, the terminal can decode the superframe header (SFH) after decoding the P-SCH and S-SCH. Each control information used in the base station is included in the super frame header.

  However, in the embodiment of the present invention, the P-SCH includes an identifier of a femto base station or a macro base station, or type information indicating whether the corresponding cell region is a femto cell region or a macro cell region. In this case, the UE can acquire control information by decoding the superframe header after decoding the P-SCH.

  When it is determined that the terminal that has acquired the base station information and the synchronization information through the above-described method can connect to the femto base station, the femto base station in the power saving mode can be awakened by performing an initial connection to the femto base station. (S603). For this reason, the UE can transmit an initial ranging code or a ranging request (RNG-REQ) message to the femto base station using an uplink resource already set in a feasible interval in the femto base station sleep cycle.

  When there is an initial connection request from the terminal, the femto base station can wake up from the sleep mode and perform a normal mode operation (S604).

  Thereafter, when the terminal no longer exists in the network, the femto base station can transition to the sleep mode in synchronization with the reference synchronization information (S605).

  Next, with reference to FIG. 8, the case where an impossible section is started first in the sleep section of a basic sleep period is demonstrated.

  FIG. 8 shows another example of the operation of the terminal and the femto base station related to the first embodiment of the present invention.

  Referring to FIG. 8, the process of operating the femto base station in the sleep mode is basically the same as that in FIG. 6, but the impossible interval is started first in the sleep interval of the basic sleep period, and the possible interval comes next. You can see that it was set as follows. For simplification of the specification, description of overlapping parts is omitted. When it is determined that there is a high probability that another terminal will not enter immediately after the terminal no longer exists in the coverage area of the femto base station when the impossible section is started first in the sleep section in this way Useful to apply.

  On the other hand, as described above, all the femto base stations in the predetermined area perform the sleep mode operation in synchronization with the reference synchronization information. Therefore, when the terminal acquires sleep mode information once and grasps the sleep mode operation time of the femto base station, when the terminal tries to connect to another femto base station operating in the sleep mode, the sleep mode already acquired It is efficient because information can be reused without having to be updated. Further, when the entire wireless communication network operates at the same frequency, there is an effect of reducing interference by matching the reference synchronization information of each femto base station.

  In the present embodiment, the case where one reference synchronization information exists in a predetermined area has been described. However, two or more reference synchronization information may exist.

  For example, each femto base station that operates at the frequency of f1 can operate in the sleep mode in synchronization with reference synchronization information that is different from that of each femto base station that operates at the frequency of f2.

  As another example, different types of reference synchronization information can be provided depending on the type of femto base station located in a predetermined area. That is, each femto base station to which the closed subscriber group (CSG) is applied operates in the sleep mode according to the first reference synchronization information, and each femto base station to which the open intervention group (OSG) is applied is the second The sleep mode can be operated according to the reference synchronization information. Also, among the femto base stations to which CSG is applied, each CSG-Closed type femto base station that does not provide any service to terminals that are not subscribed to CSG is already set in terminals that are not subscribed to CSG. In addition, the CSG-Open type femto base station that provides the minimum service can operate in the sleep mode with reference synchronization information different from each other. At this time, the size of the predetermined area is an area corresponding to a macro cell.

  In this way, the same type of femto base stations can reduce interference between femto base stations by operating in the sleep mode with the same reference synchronization information. Furthermore, once the terminal acquires sleep mode information based on the reference synchronization information, the terminal can more easily scan the same type of femtocell.

(Second embodiment)
As another embodiment of the present invention, when each terminal existing in the cell area of the femto base station is in an idle mode, the femto base station adjusts to the paging cycle, paging offset, and paging listening interval of each terminal Can work in sleep mode.

  For example, the femto base station performs normal operation (normal operation; 16 m superframe transmission) in a paging listening period of the terminal, that is, a possible period, and in a non-listening period of the terminal, that is, an unusable period (for example, a paging cycle). Transition to sleep mode. Here, the sleep mode performed by the femto base station can be divided into a possible section and an impossible section, and the operations performed in each section are as described in the first embodiment, and thus redundant description is omitted. To do.

  However, in order for the femto base station to operate in the power saving mode in accordance with the paging cycle of each terminal, the paging cycle, paging listening period, paging disabled period, paging offset, etc. of all terminals in the femto cell region are the same. If there is, the femto base station simply repeats the sleep mode and the normal mode accordingly. However, if any one of the terminals within the coverage area of the femto base station has another paging cycle, a power saving method for the femto base station is required. This will be described with reference to FIG.

  FIG. 9 illustrates a power saving method in which different paging periods of a plurality of terminals are considered in the femto base station related to the second embodiment of the present invention.

  Referring to FIG. 9, there are three terminals (MS A, MS B, and MS C) in the coverage area of the femto base station, and each transitions to an idle mode with different paging periods and paging offsets. I understand that.

  The femto base station can exchange a deregistration request (DREG-REQ) message and a deregistration command (DREG-CMD) message with each terminal when each terminal transitions to the idle mode. Information on the paging cycle, paging offset and paging listening interval can be obtained. Since all terminals in the area have entered the idle mode, the terminal can transit to the sleep mode to save power.

  At this time, when the femto base station receives a paging notification that there is a call or packet transmitted from the paging controller to at least one of the three terminals, the femto base station transmits the paging notification through the paging message in the paging listening interval of the corresponding terminal. You must inform the corresponding terminal. Therefore, it is desirable that the femto base station operates in the normal mode when any one of the terminals existing in its coverage area exists in the paging listening section. On the other hand, the femto base station can operate in the sleep mode when all three terminals are present in the non-paging section.

  As a result, as shown in FIG. 9, the femto base station can repeat the sleep mode and the normal mode until one of the three terminals transitions to the normal mode.

  Also in the present embodiment, as in the first embodiment, all femto base stations in the predetermined area can repeat the possible section and the impossible section in the sleep mode in synchronization with the reference synchronization information. This will be described with reference to FIG.

  FIG. 10 illustrates a power saving method in which reference synchronization information is further considered in the femto base station associated with the second embodiment of the present invention.

  Referring to FIG. 10, as shown in FIG. 9, it can be seen that three terminals (MS A, MS B, and MS C) have transitioned to the idle mode with different paging periods and paging offsets in the network. . At this time, it is assumed that the reference sleep time that has already been set is shared by all the femto base stations in the predetermined area.

  The femto base station can repeat the sleep mode and the normal mode by the method described with reference to FIG. Here, since the femto base station knows the reference synchronization information that has already been set, when repeating the possible section and the impossible section in the sleep mode, the sleep mode is synchronized with the reference synchronization information to save power. be able to.

  In addition, when the terminal obtains one sleep mode information and grasps the sleep mode operation time of the femto base station, the terminal tries to connect to another femto base station that exists in a predetermined area and operates in the sleep mode. In this case, since it is not necessary to update the acquired sleep mode information and it can be reused, it is efficient.

  As still another embodiment of the present invention, a terminal and a base station (FBS, MBS) that can carry out the above-described embodiments of the present invention will be described.

  A terminal may operate as a transmitter on the uplink and as a receiver on the downlink. Also, the base station can operate as a receiver on the uplink and as a transmitter on the downlink. That is, the terminal and the base station can include a transmitter and a receiver for transmitting information or data.

  The transmitter and receiver can include processors, modules, portions, and / or means for performing embodiments of the invention. In particular, the transmitter and the receiver may include a module (means) for encrypting the message, a module for interpreting the encrypted message, an antenna for transmitting and receiving the message, and the like. An example of such a transmitting end and a receiving end will be described with reference to FIG.

  FIG. 11 is a block diagram showing an example of a transmitting end and receiving end structure as still another embodiment of the present invention.

  Referring to FIG. 11, the left side shows the structure of the transmitting end, and the right side shows the structure of the receiving end. The transmitting end and the receiving end may include antennas 5 and 10, processors 20 and 30, transmission modules (Tx module) 40 and 50, reception modules (Rx module) 60 and 70, and memories 80 and 90, respectively. Each component can perform a function corresponding to each other. Hereinafter, each component will be described in more detail.

  The antennas 5 and 10 perform a function of transmitting signals generated by the transmission modules 40 and 50 to the outside and receiving radio signals from the outside and transmitting them to the reception modules 60 and 70. If multiple antenna (MIMO) function is supported, more than two can be provided.

  Together, the antenna, the transmission module, and the reception module may constitute a radio communication (RF) module.

  Usually, the processors 20 and 30 control the overall operation of the transmitting end or the receiving end. For example, it is possible to perform a controller function, a service characteristic and a MAC (Medium Access Control) frame variable control function based on a radio wave environment, a handover function, an authentication and an encryption function, etc. for implementing the above-described embodiments of the present invention.

  In particular, a processor of a mobile terminal receives a superframe header and a synchronization channel from a femto base station that has entered sleep mode in synchronization with reference synchronization information, and attempts to connect to the femto base station. The operation can be controlled.

  For example, the processor receives a super frame header (SFH) and a synchronization channel from a first femto base station that has entered sleep mode in synchronization with the reference synchronization information, and at least one of the super frame header (SFH) and the synchronization channel When the cell identifier and the CSG identifier of the femto base station are detected by decoding one, and the femto base station is a femto base station to which the mobile terminal has joined, the wireless communication is performed so as to connect to the corresponding femto base station. The communication module can be controlled.

  As another example, the processor receives the sleep mode information from the femto base station or the macro base station by controlling the wireless communication module, and uses this to grasp the sleep mode operation time of the femto base station, and the predetermined code or The wireless communication module can be controlled to connect to the femto base station so that the message is transmitted to the femto base station.

  Also, the base station processor interprets the MAC message or data transmitted from the terminal, allocates necessary uplink resources to the terminal, generates an uplink grant to inform the terminal of the allocation details, and transmits this Can be scheduled.

  The transmission modules 40 and 50 can perform predetermined encoding and modulation on data that is scheduled from the processors 20 and 30 and transmitted to the outside, and then transmit the data to the antenna 10.

  The receiving modules 60 and 70 can decode and demodulate radio signals received from the outside via the antennas 5 and 10, restore them to the form of original data, and transmit them to the processors 20 and 30.

  The memories 80 and 90 can also store programs for processing and control of the processors 20 and 30, and perform functions for temporary storage of input / output data (such as sleep mode information based on reference synchronization information). You can also. The memories 80 and 90 are a flash memory type, a hard disk type, a multimedia card micro type, a card type memory (for example, SD or XD memory), a RAM (Random Access Memory), an SRAM (Static Random Access Memory), A ROM (Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), a PROM (Programmable Read-Only Memory), a magnetic memory, a magnetic disk, and an optical disk can be stored.

  On the other hand, the base station performs the controller function, orthogonal frequency division multiple access (OFDMA) packet scheduling, and time division duplex (TDD) packet scheduling for performing the above-described embodiments of the present invention. And channel multiplexing function, MAC frame variable control function according to service characteristics and radio wave environment, high-speed traffic real-time control function, handover function, authentication and encryption function, packet modulation / demodulation function for data transmission, high-speed packet channel coding function and A real-time modem control function is performed through at least one of the modules described above, or a separate function for performing such a function. Stage, such as modules or portions may further include a.

  The present invention may be embodied in other specific forms without departing from the spirit and essential characteristics of the invention. Accordingly, the above detailed description should not be construed as limiting in all aspects, but should be considered as exemplary. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the invention are included in the scope of the invention. In addition, it is possible to combine the claims which are not explicitly cited in the claims to constitute an embodiment, or to include new claims by amendment after application.

  Each embodiment of the present invention can be applied to various wireless connection systems. As an example of various wireless connection systems, 3GPP (3rd Generation Partnership Project), 3GPP2 and / or IEEE 802. xx (Institut of Electric and Electronic Engineers 802) system. Each embodiment of the present invention can be applied not only to the various wireless connection systems but also to all technical fields to which the various wireless connection systems are applied.

In addition, when the processor connects to any one second femto base station among the femto base stations included in the predetermined area, the processor grasps the received first sleep mode information using the received sleep mode information. The sleep mode operation time point of one femto base station can be used.
(Item 1)
A way to save power,
Obtaining reference synchronization information used in a predetermined region so that the first femto base station can perform sleep mode operation;
Transition to sleep mode if no terminal is present in the first femto base station;
Using the reference synchronization information to synchronize the first femto base station with at least one second femto base station belonging to the predetermined region,
Each femto base station included in the predetermined region synchronizes sleep mode operation using the reference synchronization information.
(Item 2)
The reference synchronization information includes a sleep cycle, a listening interval, and an absolute or relative start frame;
The step of transitioning to the sleep mode in synchronization with the reference synchronization information transitions to the sleep mode so as to satisfy the sleep cycle, the listening interval, and the absolute or relative start frame. Power saving method as described in.
(Item 3)
3. The power saving method according to item 2, wherein the reference synchronization information is set so as to have a predetermined listening interval and sleep cycle with reference to an already set start time.
(Item 4)
The reference synchronization information is based on a listening interval and a sleep cycle set in a femto base station that has transitioned to sleep mode first among the first femto base station and the at least one second femto base station. The power saving method according to Item 2.
(Item 5)
5. The power saving method according to item 3 or 4, wherein the sleep cycle is divided into a possible section and an impossible section.
(Item 6)
The femto base station broadcasts at least one of a synchronization channel and a super frame header (SFH) only in the possible section in sleep mode, and does not transmit or receive any data wirelessly in the impossible section. 5. The power saving method according to 5.
(Item 7)
The femto base station broadcasts at least one of a synchronization channel and a super frame header (SFH) only in the possible section in sleep mode, and does not transmit or receive any data wirelessly in the impossible section.
The power saving method according to item 5, wherein the synchronization channel is synchronized with the first femto base station and the at least one second femto base station.
(Item 8)
Further comprising transmitting sleep mode information to the terminal;
The method of claim 5, wherein the sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval according to the reference synchronization information.
(Item 9)
The sleep mode information is transmitted to the terminal through at least one of a super frame header (SFH), additional system information, a ranging response (RNG-RSP) message, and a neighbor advertisement (NBR-ADV) message. The power saving method according to item 8, wherein
(Item 10)
A method of conserving femto base station power at a terminal,
Receiving a super frame header (SFH) and a synchronization channel from a first femto base station entering a sleep mode in synchronization with reference synchronization information used in a predetermined area;
Decoding at least one of the super frame header (SFH) and a synchronization channel to detect a cell identifier and a CSG identifier of the first femto base station;
Connecting the first femto base station to the first femto base station when the first femto base station is a femto base station to which the terminal has joined,
Each femto base station included in the predetermined region synchronizes sleep mode operation using the reference synchronization information.
(Item 11)
The method of claim 10, wherein the reference synchronization information includes a sleep cycle, a listening interval, and an absolute or relative start frame.
(Item 12)
Connecting to the first femto base station comprises:
Receiving sleep mode information from the first femto base station or macro base station;
Using the received sleep mode information to determine a sleep mode operation point of the first femto base station and transmitting a predetermined code or message to the first femto base station. Power saving method as described in.
(Item 13)
The sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval according to the reference synchronization information,
[13] The method of claim 12, wherein the predetermined code or message is transmitted to the first femto base station through uplink resources already set in a possible interval in the sleep cycle.
(Item 14)
When the terminal connects to any one of the second femto base stations among the femto base stations included in the predetermined area, the first femto grasped by using the received sleep mode information. Item 14. The power saving method according to Item 13, wherein the sleep mode operation time point of the base station is used.
(Item 15)
A mobile terminal,
A processor;
A radio communication (RF) module for transmitting and receiving radio signals to and from the outside under the control of the processor,
The processor controls the wireless communication module to receive a super frame header (SFH) and a synchronization channel from a first femto base station that has entered sleep mode in synchronization with reference synchronization information used in a predetermined area. Then, at least one of the super frame header (SFH) and the synchronization channel is decoded to detect a cell identifier and a CSG identifier of the first femto base station, and the first femto base station detects the mobile terminal. If the machine is a subscribed femto base station, control the wireless communication module to connect to the first femto base station;
Each femto base station included in the predetermined area is a mobile terminal that synchronizes sleep mode operation using the reference synchronization information.
(Item 16)
The mobile terminal of claim 15, wherein the reference synchronization information includes a sleep cycle, a listening interval, and an absolute or relative start frame.
(Item 17)
The processor controls the wireless communication module to receive sleep mode information from the first femto base station or macro base station, and uses the received sleep mode information to sleep the first femto base station. Item 16. The item 16, wherein the mode operation time point is grasped, and the wireless communication module is controlled to connect to the first femto base station so that a predetermined code or message is transmitted to the first femto base station. Mobile terminal.
(Item 18)
The sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval according to the reference synchronization information,
The mobile terminal of claim 17, wherein the predetermined code or message is transmitted to the first femto base station through uplink resources already set in a possible section in the sleep cycle.
(Item 19)
When the processor connects to any one second femto base station among the femto base stations included in the predetermined area, the processor grasps the first femto using the received sleep mode information. Item 19. The mobile terminal according to Item 18, wherein the base station sleep mode operation point is used.

Claims (19)

A way to save power,
Obtaining reference synchronization information used in a predetermined region so that the first femto base station can perform sleep mode operation;
Transition to sleep mode if no terminal is present in the first femto base station;
Using the reference synchronization information to synchronize the first femto base station with at least one second femto base station belonging to the predetermined region,
Each femto base station included in the predetermined region synchronizes sleep mode operation using the reference synchronization information. The reference synchronization information includes a sleep cycle, a listening interval, and an absolute or relative start frame;
The step of transitioning to sleep mode in synchronization with the reference synchronization information transitions to sleep mode so as to satisfy the sleep cycle, listening interval, and absolute or relative start frame. The power saving method according to 1.   The power saving method according to claim 2, wherein the reference synchronization information is set to have a predetermined listening interval and a sleep cycle with reference to an already set start time.   The reference synchronization information is based on a listening interval and a sleep cycle set in the first femto base station and the femto base station that has transitioned to the sleep mode first among the at least one second femto base station. The power saving method according to claim 2.   The power saving method according to claim 3 or 4, wherein the sleep cycle is divided into a possible interval and an impossible interval.   The femto base station broadcasts at least one of a synchronization channel and a super frame header (SFH) only in the possible section in sleep mode, and does not transmit or receive any data wirelessly in the impossible section. Item 6. The power saving method according to Item 5. The femto base station broadcasts at least one of a synchronization channel and a super frame header (SFH) only in the possible section in sleep mode, and does not transmit or receive any data wirelessly in the impossible section.
The method of claim 5, wherein the synchronization channel is synchronized with the first femto base station and the at least one second femto base station. Further comprising transmitting sleep mode information to the terminal;
The power saving method according to claim 5, wherein the sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval according to the reference synchronization information.   The sleep mode information is transmitted to the terminal through at least one of a super frame header (SFH), additional system information, a ranging response (RNG-RSP) message, and a neighbor advertisement (NBR-ADV) message. The power saving method according to claim 8. A method of conserving femto base station power at a terminal,
Receiving a super frame header (SFH) and a synchronization channel from a first femto base station entering a sleep mode in synchronization with reference synchronization information used in a predetermined area;
Decoding at least one of the super frame header (SFH) and a synchronization channel to detect a cell identifier and a CSG identifier of the first femto base station;
Connecting the first femto base station to the first femto base station when the first femto base station is a femto base station to which the terminal has joined,
Each femto base station included in the predetermined region synchronizes sleep mode operation using the reference synchronization information.   The power saving method of claim 10, wherein the reference synchronization information includes a sleep cycle, a listening interval, and an absolute or relative start frame. Connecting to the first femto base station comprises:
Receiving sleep mode information from the first femto base station or macro base station;
Using the received sleep mode information to determine a sleep mode operation time point of the first femto base station and transmitting a predetermined code or message to the first femto base station. 11. The power saving method according to 11. The sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval according to the reference synchronization information,
The power saving method of claim 12, wherein the predetermined code or message is transmitted to the first femto base station through uplink resources already set in a possible interval in the sleep cycle.   When the terminal connects to any one of the second femto base stations among the femto base stations included in the predetermined area, the first femto grasped by using the received sleep mode information. The power saving method according to claim 13, wherein the sleep mode operation time of the base station is used. A mobile terminal,
A processor;
A radio communication (RF) module for transmitting and receiving radio signals to and from the outside under the control of the processor,
The processor controls the wireless communication module to receive a super frame header (SFH) and a synchronization channel from a first femto base station that has entered sleep mode in synchronization with reference synchronization information used in a predetermined area. Then, at least one of the super frame header (SFH) and the synchronization channel is decoded to detect a cell identifier and a CSG identifier of the first femto base station, and the first femto base station detects the mobile terminal. If the machine is a subscribed femto base station, control the wireless communication module to connect to the first femto base station;
Each femto base station included in the predetermined area is a mobile terminal that synchronizes sleep mode operation using the reference synchronization information.   The mobile terminal according to claim 15, wherein the reference synchronization information includes a sleep cycle, a listening interval, and an absolute or relative start frame.   The processor controls the wireless communication module to receive sleep mode information from the first femto base station or macro base station, and uses the received sleep mode information to sleep the first femto base station. The connection to the first femto base station is performed by controlling the wireless communication module so as to grasp a mode operation time point and transmit a predetermined code or message to the first femto base station. The mobile terminal described. The sleep mode information includes at least one of a sleep mode start frame, a sleep cycle, and a listening interval according to the reference synchronization information,
The mobile terminal according to claim 17, wherein the predetermined code or message is transmitted to the first femto base station through uplink resources already set in a possible section in the sleep cycle.   When the processor connects to any one second femto base station among the femto base stations included in the predetermined area, the processor grasps the first femto using the received sleep mode information. The mobile terminal according to claim 18, wherein the sleep mode operation time of the base station is used.

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