KR20100048834A - Method for power saving of femto base station - Google Patents

Abstract

PURPOSE: A method for power saving of a femto base station is provided to minimize the power consumption of a femto base station in a wireless access system that supports a femto cell. CONSTITUTION: A terminal subscribed in a femto base station and the connection between the terminal and the femto base station are set up and released(S301). If the connection with the terminal is set up, a count is increased. If the connection with the terminal is released, the count is decreased(S302). If the count corresponds to a threshold value, the femto base station is transited into a power saving mode. The threshold value indicates that all terminals are connected to the femto base station or the connection is released.

Description

Method for Power Saving of Femto Base Station}

The present invention relates to a wireless access system. The present invention also relates to a method for minimizing power consumption of 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, a femtocell means an indoor base station for a small / low power home / office. Pamptocells are used in a similar sense to picocells, but have a more advanced function. A femtocell is a small cellular base station that connects to a broadband router that can connect voice and data from existing 2G systems as well as 3G systems to the carrier's backbone network via DSL links.

The merits of such a femtocell are described as follows.

Recently, a research report was announced that femtocell could be a catalyst for promoting 3G distribution and widening indoor coverage. By 2011, the number of femtocell terminal users will increase to 120 million, and 32 million AP (Access Point) base stations are expected to be installed. Stuart Carlow, senior analyst at ABI Research, said, "In terms of technology, strengthening indoor coverage of technologies like W-CDMA, HSDPA, and EVDO plays an important role in providing services." In addition, Stuart Carlow said, “Pamtocells can greatly improve network quality and capacity by routing traffic through IP networks, while also reducing OPEX investments in backhaul leased lines by mobile operators. Said.

Femtocells can enhance cell coverage and improve the quality of voice services. Mobile carriers also anticipate that subscribers will be fully adaptable to 3G by providing data services via femtocells. The femtocell may be referred to as a femto base station (FBS) or a femto base transceiver station (BTS).

In summary, femtocells have the following advantages:

1. Cell Coverage Improvement

2. Infrastructure cost decrease

3. New service Offering

4.FMC (Fixed Mobile Convergence) Acceleration

One or more femtocells may be grouped by specific service or region to form a femtocell group. For example, a femtocell group allowed to access only a specific terminal may be referred to as a closed subscriber group (CSG). The femto base station (FBS) may check the CSG ID (CSG ID) of the terminal and allow access only to the terminal subscribed to the CSG.

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

The femto base station is a newly added entity to the existing network. Therefore, as the femto base station is used, there are things to be added or changed in the overall network structure. The femto base station can directly access the Internet and perform a function as a base station. Therefore, the femto base station can perform almost all the functions of the general macro base station. In addition, the femto base station may receive data from a general macro base station and relay the data to the terminal.

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

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

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

In commonly used broadband wireless access systems, the power consumption of the macro base station (Macro BS) has not been taken into account. However, in an environment that supports a femtocell, the number of terminals supporting a service by one femtocell is limited (about 5 to 6 terminals). In some cases, the femtocell may not have a terminal for maintaining a connection for a specific time.

If such a situation is repeated, power consumption may occur as the femtocell continuously provides a service even when it is not necessary to provide a service to a specific terminal. In addition, when nearby 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 way to overcome this situation.

The present invention has been made to solve the problems of the general technique as described above, an object of the present invention is to provide a method for minimizing the power consumption of the femtocell in a wireless access system supporting the femtocell.

Another object of the present invention is to provide a method for minimizing the power consumption of a femtocell when a terminal that is connected to a femtocell does not exist or all the terminals that are establishing a connection transition to the idle mode.

Still another object of the present invention is to provide a method for a specific terminal to communicate with a femtocell in a power saving mode when the femtocell is in a power saving mode.

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

According to an aspect of the present invention, a method for saving power in a femto base station includes: establishing or terminating a connection with a terminal subscribed to the femto base station and setting a connection with the terminal, increasing a count, and establishing a connection with the terminal. The termination may include reducing the count and, if the count corresponds to a predetermined threshold, the femto base station transitions to a power saving mode.

In one aspect of the present invention, the predetermined threshold may indicate a case where all terminals subscribed to the femto base station are disconnected from the femto base station or the connection is established with the femto base station.

In an aspect of the present invention, the femto base station may broadcast only a synchronization channel in a power saving mode and may not transmit any data in the remaining sections. In this case, the synchronization channel may include a main synchronization channel (P-SCH) and a floating channel (S-SCH). In addition, the floating channel may include cell identifier information and closed subscriber group (CSG) identifier information.

In one aspect of the present invention, the main synchronization channel may include at least one of a femto base station identifier and type information indicating whether the current cell is a femtocell or a macro cell.

In an aspect of the present invention, the femto base station may broadcast only a synchronization channel and a broadcast channel in a power saving mode and may not transmit any data in the remaining sections.

According to an aspect of the present invention, the femto base station may further include receiving a predetermined code requesting to switch from the terminal to the normal mode in the power saving mode. In this case, the predetermined code may be a general code or an initial ranging code. In addition, the femto base station may decode one of the uplink subframes to receive a predetermined code in a power saving mode. In this case, the uplink subframe is preferably the first uplink subframe of the frame in which the femto base station broadcasts a synchronization channel.

In another aspect of the present invention, there is provided a method for saving power in a femto base station, the method comprising: receiving a broadcast channel from a femto base station in a power saving mode, decoding the broadcast channel, detecting a cell identifier and a CSG identifier of the femto base station, and a femto base station. If the terminal is a subscribed femto base station may include performing a connection to the femto base station.

Another aspect of the present invention may further include receiving a general code for performing the access from a macro base station. In addition, another aspect of the present invention may further include receiving a broadcast channel including a general code for performing a connection from the femto base station.

In another aspect of the present invention, the broadcast channel may include a main broadcast channel and a sub broadcast channel, and the sub broadcast channel may include a cell identifier and a CSG identifier.

In another aspect of the present invention, the broadcast channel may include a main broadcast channel and a sub broadcast channel, and the main broadcast channel may include an identifier of a femto base station and a type field indicating whether a current cell is a femtocell or a macrocell.

In another aspect of the present invention, the performing of the access may be performed by the terminal transmitting a general code to the femto base station in a predetermined subframe among the uplink subframes included in the frame in which the broadcast channel is transmitted. In this case, the predetermined subframe may be the first uplink subframe.

According to the embodiments of the present invention, the following effects are obtained.

First, by using the embodiments of the present invention, it is possible to minimize the power consumption of the femto base station in the radio access system supporting the femtocell.

Second, by using the embodiments of the present invention, even after the femtocell enters the power saving mode, the terminal can communicate with the femtocell.

The present invention relates to a wireless access system. Hereinafter, embodiments of the present invention disclose various methods capable of minimizing power consumption of a femto base station.

The following embodiments are a combination of elements and features of the present invention in a predetermined form. Each component or feature may be considered to be optional unless otherwise stated. Each component or feature may be implemented in a form that is not combined with other components or features. In addition, some of the elements and / or features may be combined to form an embodiment of the present invention. The order of the operations described in the embodiments of the present invention may be changed. Some configurations or features of certain embodiments may be included in other embodiments, or may be replaced with corresponding configurations or features of other embodiments.

In the description of the drawings, procedures or steps which may obscure the gist of the present invention are not described, and procedures or steps that can be understood by those skilled in the art are not described.

In the present specification, embodiments of the present invention have been described based on data transmission / reception relations between a base station and a terminal. Here, the base station has a meaning as a terminal node of a network that directly communicates with the terminal. The specific operation described as performed by the base station in this document may 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 consisting of a plurality of network nodes including a base station may be performed by the base station or other network nodes other than the base station. In this case, the 'base station' may be replaced by terms such as a fixed station, a Node B, an eNode B (eNB), and an access point. In addition, the term “mobile station (MS)” may be replaced with terms such as a user equipment (UE), a subscriber station (SS), a mobile subscriber station (MSS), or a mobile terminal.

In addition, the transmitting end refers to a node transmitting data or voice service, and the receiving end refers to a node receiving data or voice service. Therefore, in uplink, a terminal may be a transmitting end and a base station may be a receiving end. Similarly, in downlink, a terminal may be a receiving end and a base station may be a transmitting end.

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

Embodiments of the invention may be implemented through various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof.

In the case of a hardware implementation, the method according to embodiments of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs). Field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and the like.

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

Embodiments of the present invention may be supported by standard documents disclosed in at least one of the wireless access systems IEEE 802 system, 3GPP system, 3GPP LTE system and 3GPP2 system. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all terms disclosed in the present document can be described by the above standard document. In particular, embodiments of the present invention may be supported by one or more of the standard documents P802.16-2004, P802.16e-2005, and P802.16Rev2 documents of the IEEE 802.16 system.

Specific terms used in the following description are provided to help the understanding of the present invention, and the use of the specific terms may be modified in other forms without departing from the technical spirit of the present invention.

2 is a state diagram illustrating a change in a power mode of a femto base station as an embodiment of the present invention.

Referring to FIG. 2, the femto base station may have two states. One is to operate in normal mode and the other is to operate in power saving mode. The power saving mode means that the femto base station broadcasts only synchronization information (eg, main synchronization channel, floating channel) in the femtocell area, thereby reducing power consumption. In this case, the femto base station may further transmit a broadcast channel (BCH) as well as synchronization information in a power saving mode according to a channel environment or a user's requirement.

The state of the femto base station transitions from one state to another if certain conditions are satisfied. For example, the femto base station may operate a predetermined count, which may be determined by the number of terminals subscribed to the CSG of the femto base station. That is, when the number of terminals subscribed to the CSG is n, the count value 'n' indicates that all the terminals subscribed to the CSG have entered the cell area of the femto base station. In addition, when the counter value is '0', all of the terminals subscribed to the CSG of the femto base station are out of the cell area of the femto base station, or all of the terminals enter the idle mode.

That is, when the count value is '0' or 'n' in FIG. 2, the femto base station transitions from the normal mode to the power saving mode. Accordingly, the femto base station broadcasts only the minimum control signals transmitted to the terminals in the power saving mode and stops the remaining operations, thereby minimizing the power consumed by the femto base station.

In addition, when the value of the count is greater than 0 and less than n, it indicates that one or more terminals of the active mode are included in the cell area of the femto base station. In this case, the femto base station transitions from the power saving mode to the normal mode to operate in the normal mode.

3 is a diagram illustrating an operation of a femto base station as an embodiment of the present invention.

A femto base station (FBS) may provide a service to one or more terminals while operating a femto cell. In this case, it is assumed that the terminal is subscribed to the closed subscriber group (CSG) providing a specific service. In addition, the femto base station may provide the services of the CSG to the terminals.

In this process, the femto base station (FBS) and the terminal (MS) establishes a connection with each other, performing procedures such as location update, network entry or re-entry, and idle mode entry. Can be terminated (S301).

The femto base station may manage the number of terminals connected in the femtocell area through a count (S302).

If the connection is established between the femto base station and the terminal in step S301, the count increases by '1', and when the connection between the femto base station and the terminal is terminated, the count decreases by '1'. For example, if the terminal performs a location update or network reentry procedure while moving to the femtocell region, the count is increased by one, and when the terminal receiving the service in the femtocell region enters the idle mode, the count is decreased by one.

When the count value managed by the femto base station in step S302 is '0' or 'n', the femto base station may enter a power saving mode and perform a power saving mode operation. In this case, the femto base station may transmit only a Primary Synchronization Channel (P-SCH) and a Secondary Synchronization Channel (S-SCH) to the terminal (S303 and S304).

If the count value managed by the femto base station in step S302 is greater than 0 and less than n, the femto base station continues to operate in the normal mode. The count value is greater than 0 and less than n because it indicates that a terminal to provide a service exists in the cell area of the femto base station.

In embodiments of the present invention, the terminal may obtain base station information by decoding a synchronization channel (eg, P-SCH or S-SCH) transmitted by a femto base station or a macro base station.

For example, the UE may synchronize time with the base station by decoding the P-SCH. After the UE synchronizes time synchronization, the UE may obtain cell identifier (Cell ID) information by decoding the S-SCH. In addition, the terminal may decode the BCH after decoding the P-SCH, S-SCH. The BCH may include control information used in the base station.

However, in the embodiment of the present invention, if the P-SCH includes an identifier of a femto base station or a macro base station or type information indicating whether a corresponding cell area is a femtocell area or a macrocell area, the terminal decodes the P-SCH. Control information may be obtained by decoding the BCH.

4 illustrates a frame structure used in a femto base station in a power saving mode according to an embodiment of the present invention.

Referring to FIG. 4, one superframe has a time period of 20 ms and may include four frames. One frame may include one or more subframes, but one frame preferably includes eight subframes.

The eight subframes may be composed of five DL subframes and three UL subframes. Of course, the configuration ratio of the downlink and uplink subframe in a particular frame may be variously changed, such as 4: 4 or 6: 2.

In FIG. 4, the femto base station is in a power saving mode. That is, when (1) no terminal is established in the femto base station (count = 0) or all terminals with all connections established are in idle mode (see FIG. 3), or (2) all terminals permitting CSG to the femto base station When this connection is established, the femto base station can enter a power saving mode.

(One) Femto  UE is established in the cell area of the base station ( Connected MS )

Referring to FIG. 4, the femto base station may broadcast a main synchronization channel to the terminals in the first downlink subframe of the first frame included in the superframe. In addition, the femto base station may encode a floating channel in the first downlink subframe of the second, third and fourth frames to broadcast to the terminals.

In this case, since the femto base station is in a power saving mode, no information may be transmitted in the remaining frame period after broadcasting the main synchronization channel or the floating channel.

That is, when there is no terminal connected to its cell coverage, the femto base station can broadcast only sync channels (P-SCH, S-SCH) except for other information in its cell area. Through this, the femto base station can significantly reduce interference with nearby femto base stations using the same frequency band. In addition, the femto base station may enter a sleep state (for example, a state not transmitting data) in a frame period in which a sync channel is not transmitted, thereby minimizing power consumption.

According to another embodiment of the present invention, when all of the terminals existing in the cell area of the femto base station are in the idle mode, the femto base station may be configured with a paging cycle, a paging offset, and a paging listening interval of the terminals. It can operate in Power Saving Mode according to Listening Interval.

For example, the femto base station performs a normal operation (16m superframe transmission) in the paging listening interval of the terminal and the synchronization channel (P-SCH, S) in the non-listening period (eg, paging period) of the terminal. Only SCH) can be transmitted. In this case, the femto base station may additionally transmit a broadcast channel (BCH) in addition to the synchronization channel.

However, in order for the femto base station to operate in a power saving mode according to the paging period of the terminals, it is preferable that the paging period, paging listening interval, paging unavailable period, and paging offset of all terminals in the femtocell region are the same. In general, since the number of terminals subscribed to each femto base station is small, such an embodiment can be performed by setting the idle mode operation of the terminal subscribed to each femto base station to the same.

(2) Femto  All terminals subscribed to the base station Femto  When a connection is established with a base station

When all terminals subscribed to the Closed Subscribe Group (CSG) of the femto base station are connected within the cell area of the femto base station, the femto base station does not need to transmit information necessary for access to the terminals. For example, when a UE having a CSG value other than the CSG value allowed by the femto base station enters a cell area, the femto base station may detect only a cell ID or CSG ID level information. Only sync channels (P-SCH, S-SCH) can be transmitted.

That is, the femto base station encodes only a synchronization channel excluding unnecessary information (for example, BCH, DL broadcast message, etc.) in the terminal and broadcasts the terminal to minimize the power consumption and transmit a small amount of information to thereby use the adjacent frequency. Interference between femto base stations can be minimized.

If a femto base station does not exist in its cell area, the femto base station may operate in a sleep mode and broadcast only a synchronization channel to the terminal. In addition, the femto base station may further transmit a broadcast channel according to a user's request or channel environment.

FIG. 5 is a diagram illustrating one of a method for performing a normal mode operation with a femto base station in a power saving mode according to another embodiment of the present invention.

When the terminal enters the femtocell area and decodes the P-SCH and the S-SCH, the terminal may detect a cell ID and a CSG ID of the femtocell. The terminal may determine whether it can access the femto base station (FBS) through the cell identifier and the CSG ID.

If it is determined that the terminal can connect to the femtocell, it is necessary to wake up the femto base station (FBS) of the power saving mode in order to receive information required for the connection from the femto base station (FBS).

Referring to FIG. 5, the femto base station FBS is currently in a power saving mode (S501).

Accordingly, the femto base station (FBS) can broadcast the P-SCH and the S-SCH to the femtocell area (S502, S503).

One or more terminals in the femtocell region may detect the cell identifier and the CSG ID by decoding the information collected by the P-SCH and the S-SCH broadcast by the femto base station (S504).

In this case, when it is determined in step S504 that the specific terminal can access the femto base station, the specific terminal may wake up the femto base station in the power saving mode by performing initial access (Initial Access) to the femto base station (S505).

In step S505 the terminal may transmit an initial ranging code (Initial Raging Code) to the femto base station to perform the initial access.

The femto base station may be in a power saving mode and may operate in a normal mode when there is an initial access request from a specific terminal (S506).

6 is a diagram illustrating a method for performing initial access to a femto base station in a power saving mode according to another embodiment of the present invention.

In step S504 of FIG. 5, the UE decodes a primary sync channel (P-SCH) and a secondary sync channel (S-SCH) broadcasted by the femto base station, and recognizes that the terminal can access the corresponding femto base station. In this case, the terminal needs to change the femto base station in the power saving mode to the normal mode in order to access the femto base station.

The UE may perform initial access to the femto base station in an uplink subframe (UL-Subframe) after the S-SCH is broadcast. The femto base station may broadcast the S-SCH to the terminal three times in total. In this case, the terminal may perform an initial access in one frame among the frames on which three S-SCHs are broadcast. For example, the UE may perform initial access to the femto base station in the first uplink subframe of the frame on which the S-SCH is broadcast.

FIG. 6 illustrates that the UE performs initial access in the first uplink subframe of the fourth frame of the super frame when the UE detects the cell identifier and the CSG identifier after decoding the P-SCH and the three S-SCHs from the femto base station. The case is shown.

If the UE decodes both the P-SCH and the three S-SCHs, but fails to detect the cell identifier and the CSG identifier of the femto base station (FBS), the P-SCH and S-SCH of the next super frame are decoded. After detecting the cell identifier CSG ID, initial access may be performed in the first UL subframe.

In FIG. 6, the femto base station broadcasts only the P-SCH and B-SCH and may operate in a power saving mode in the remaining sections. However, the femto base station may decode the first subframe of each frame to receive the uplink code that the terminal can transmit.

FIG. 7 is a diagram illustrating one of methods for performing a normal mode operation with a femto base station in a power saving mode according to another embodiment of the present invention.

One or more femto base stations (FBS) may be included in a macro base station (MBS). That is, a plurality of femto base stations may be included in the cell area of one macro base station. The macro base station may manage the femto base station. In addition, the femto base station may provide a service directly to the terminal by accessing the Internet network, or relay the data and the like from the macro base station to transmit to the terminal.

The macro base station may transmit a common code to the terminal. The general code refers to a code transmitted from the terminal to the femto base station in order to change the femto base station in the power saving mode to the normal mode (S701).

Table 1 below shows an example of a general code format used in step S701.

Type Length Value Scope Common Code: Awakening code for all femto Cell (common code sent to Femto BS to wake up Sleep mode Femto BS) BCH, Additional system information

The common code represents a code for waking up the femto base station in power saving mode. Referring to Table 1, a general code may be transmitted to a terminal through a control channel, a broadcast channel, or additional system information.

The femto base station is currently in a power saving mode. Therefore, the femto base station may transmit only the P-SCH and the S-SCH to one or more terminals in the femtocell (S703).

However, in FIG. 7, it is assumed that even if the UE decodes only the P-SCH, whether the corresponding cell is a femtocell or a macrocell can be detected. For example, it is assumed that a P-SCH includes a femto base station identifier (FBS ID) or a type field indicating a type of a corresponding cell.

When the UE decodes the P-SCH and the corresponding cell is a femtocell and recognizes that the femto base station is a femto base station subscribed thereto through the FBS ID, the terminal may access the femto base station. Therefore, the terminal may wake up the femto base station in the power saving mode by transmitting the general code received from the macro base station in step S701 to the femto base station in the power saving mode (S705).

FIG. 8 is a diagram illustrating another method of performing a normal mode operation with a femto base station in a power saving mode according to another embodiment of the present invention.

In FIG. 8, it is assumed that the femto base station is currently in a power saving mode.

The femto base station may broadcast a sync channel (SCH) to one or more terminals in a power saving mode (S801).

In addition, the femto base station may transmit a broadcast channel (BCH) including predetermined information required for connection in addition to the synchronization channel to the terminal (S803).

In this case, the broadcast channel (BCH) may include general code information for waking up the femto base station in the power saving mode. That is, the femto base station may directly include the general codes of Table 1 in the BCH and transmit them to the terminal, or may include information about the general codes in the BCH and transmit them to the terminal. Therefore, the terminal may decode the general code information included in the BCH to be used later when accessing the femto base station.

When the terminal decodes the sync channel broadcast from the femto base station and recognizes that the femto base station is a subscribed femto base station, the terminal may access the corresponding femto base station. Therefore, the terminal may transmit a general code to the femto base station (S805).

The femto base station receiving the general code may wake up from the power saving mode and operate in the normal mode. Through this, the femto base station may provide a service to the terminal.

9 is a diagram illustrating a method of transmitting a general code to a femto base station in a power saving mode according to another embodiment of the present invention.

Even if the UE decodes only the P-SCH broadcast by the femto base station, it is assumed that the corresponding cell is a femtocell and that the femtocell can recognize that the femtocell is subscribed to the UE. Of course, the terminal may perform access to the femto base station after decoding both the P-SCH and the S-SCH.

The terminal may wake up the femto base station in power saving mode by transmitting an initial ranging code from the first uplink subframe of the first frame in the superframe to the femto base station in order to wake the femto base station in power saving mode. . In this case, the terminal may use the general code of Table 1 as the initial ranging code.

The femto base station in the power saving mode may recognize that the terminal has transmitted the general code to wake itself by decoding the general code transmitted by the terminal. Therefore, the femto base station can wake up from the power saving mode and operate in the normal mode.

Accordingly, the femto base station in the power saving mode broadcasts only P-SCH and S-SCH information in every super frame, and operates in a normal mode only in an uplink ranging period (eg, the first UL frame of every frame). The remaining sections can operate in a power saving mode.

In embodiments of the present invention, it is assumed that the femto base station decodes the first uplink subframe of each frame included in the superframe. However, according to a user's requirement or channel environment, the femto base station may decode one of the second or third uplink subframes to receive the initial ranging code or the general code.

Referring to FIG. 9, a super frame header (SFH) transmitted in a first frame included in a super frame may include a sync channel (SCH) and a broadcast channel (BCH). In this case, the synchronization channel may include a main synchronization channel (P-SCH) and a floating channel (S-SCH). In this case, since only the floating channel is transmitted in the second to fourth frames of the remaining super frames, the main synchronization channel may be transmitted once and the floating channel may be transmitted four times in total.

In this case, when the UE includes information required for access to the femto base station in the main synchronization channel, the UE may perform access to the femto base station in the first uplink subframe of the first frame. In addition, when the terminal can detect information necessary for access by decoding up to the floating channel, the terminal may access the femto base station in the first uplink subframe of a specific frame.

FIG. 10 is a diagram illustrating a method for confirming whether a femto base station is in a power saving mode by another embodiment of the present invention.

FIG. 10 illustrates a method in which a femto base station transmits a P-SCH in a first frame during a power saving mode period, and then transmits an S-SCH only in a specific frame period without transmitting an S-SCH every three remaining frame periods. Indicates to operate in economy mode.

When the mobile terminal decodes only the synchronization channel broadcast by the femto base station, it is difficult to determine whether the current femto base station is in a power saving mode or a normal mode. In general, the femto base station operating in the normal mode and the femto base station operating in the power saving mode transmit the synchronization channel in all frames within the super frame.

In this case, the femto base station preferably transmits an explicit message to the terminal to inform the terminal whether it is operating in a power saving mode. However, another embodiment of the present invention discloses a method in which a terminal can determine an operating state of a femto base station without transmitting a message regarding whether the femto base station is operating in a power saving mode.

Referring to FIG. 10, the femto base station broadcasts a P-SCH to terminals in a femtocell in the first frame of every superframe. However, the femto base station may transmit the S-SCH only in a predetermined frame without transmitting all of the S-SCH in a specific superframe.

For example, the femto base station broadcasts the S-SCH in the next frame after transmitting the P-SCH in superframes A and C, and then does not broadcast the S-SCH in the third and fourth frames. In addition, the femto base station may broadcast the P-SCH in the superframes B and D and then broadcast the S-SCH to the UE in every frame.

That is, the femto base station may broadcast the synchronization channel only in a predetermined frame without transmitting the synchronization channel to the terminal in every frame in a specific superframe. Accordingly, the terminal may recognize that the femto base station operates in a power saving mode (eg, sleep mode) when the synchronization channel cannot be decoded at the time when the synchronization channel is expected to be broadcast.

In another variation of another embodiment of the present invention, the femto base station in power saving mode may broadcast the S-SCH only in a specific frame after broadcasting the P-SCH in all superframes. For example, the femto base station may broadcast the S-SCH only in one frame of the second to fourth frames and may not broadcast the S-SCH in another frame. In this case, the UE may previously obtain information on a specific frame on which the S-SCH is broadcast from the femto base station or the macro base station. Accordingly, the UE may recognize that the femto base station operates in a power saving mode by decoding the S-SCH only in a specific frame.

In the above-described embodiments of the present invention, information on the power saving mode state (for example, a sleep cycle, a sleep offset, a sleep interval, and a sleep interval of a femto base station) and timing information (E.g., a superframe number in which the femto base station operates in the sleep mode) indicates that the femto base station or macro base station broadcasts (BCH), additional system information, MOB-RNG-RSP message and / or MOB_NBR. It can be transmitted to the terminal through the -ADV message.

The invention can be embodied in other specific forms without departing from the spirit and essential features of the invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention. In addition, the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship or may be incorporated as new claims by post-application correction.

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

2 is a state diagram illustrating a change in a power mode of a femto base station as an embodiment of the present invention.

3 is a diagram illustrating an operation of a femto base station as an embodiment of the present invention.

4 illustrates a frame structure used in a femto base station in a power saving mode according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating one of a method for performing a normal mode operation with a femto base station in a power saving mode according to another embodiment of the present invention.

6 is a diagram illustrating a method for performing initial access to a femto base station in a power saving mode according to another embodiment of the present invention.

FIG. 7 is a diagram illustrating one of methods for performing a normal mode operation with a femto base station in a power saving mode according to another embodiment of the present invention.

FIG. 8 is a diagram illustrating another method of performing a normal mode operation with a femto base station in a power saving mode according to another embodiment of the present invention.

9 is a diagram illustrating a method of transmitting a general code to a femto base station in a power saving mode according to another embodiment of the present invention.

FIG. 10 is a diagram illustrating a method for confirming whether a femto base station is in a power saving mode by another embodiment of the present invention.

Claims (18)

In a method for saving power in a femto base station, Establishing or terminating a connection with a terminal subscribed to the femto base station; Increasing the count when establishing a connection with the terminal and decreasing the count when disconnecting with the terminal; And And when the count corresponds to a predetermined threshold value, the femto base station transitions to a power saving mode. The method of claim 1, The predetermined threshold value is And a case in which all terminals subscribed to the femto base station are disconnected from the femto base station or the connection is established with the femto base station. The method of claim 1, The femto base station broadcasts only a synchronization channel in a power saving mode, and does not transmit any data in the remaining sections. The method of claim 3, wherein The sync channel includes a main synchronous channel (P-SCH) and a floating channel (S-SCH). The method of claim 4, wherein And said floating channel comprises cell identifier information and closed subscriber group (CSG) identifier information. The method of claim 4, wherein The main synchronization channel comprises at least one of the femto base station identifier and the type information indicating whether the current cell is a femtocell or a macrocell. The method of claim 1, The femto base station broadcasts only a synchronization channel and a broadcast channel in a power saving mode, and does not transmit any data in the remaining sections. The method according to claim 3 or 7, The femto base station further comprises the step of receiving a predetermined code requesting to switch to the normal mode from the terminal in the power saving mode, power saving method. The method of claim 8, The predetermined code is a power saving method, characterized in that the general code or the initial ranging code. The method of claim 8, And the femto base station decodes one of uplink subframes in order to receive the predetermined code in a power saving mode. The method of claim 8, The uplink subframe, And a first uplink subframe of the frame on which the synchronization channel is broadcast. In a method for saving power in a femto base station, Receiving a broadcast channel from the femto base station in a power saving mode; Decoding the broadcast channel to detect a cell identifier and a CSG identifier of the femto base station; And And if the femto base station is a femto base station subscribed to a terminal, performing a connection to the femto base station. The method of claim 12, And receiving a general code for performing the access from a macro base station. The method of claim 12, And receiving a broadcast channel including a general code for performing the access from the femto base station. The method of claim 12, The broadcast channel includes a main broadcast channel and a sub broadcast channel, The sub-broadcast channel includes the cell identifier and the CSG identifier. The method of claim 12, The broadcast channel includes a main broadcast channel and a sub broadcast channel, The main broadcast channel is a power saving method comprising an identifier of the femto base station and a type field indicating whether the current cell is a femtocell or a macrocell. The method according to claim 13 or 14, Performing the connection, And transmitting the general code to the femto base station in a predetermined subframe among uplink subframes included in the frame in which the broadcasting channel is transmitted. The method of claim 17, The predetermined subframe is a power saving method, characterized in that the first uplink subframe.

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