WO2011002262A2

WO2011002262A2 - Operating method of femto base station in mobile wireless access system

Info

Publication number: WO2011002262A2
Application number: PCT/KR2010/004336
Authority: WO
Inventors: 김은경; 차재선; 정수정; 김주희; 임광재; 이현; 김원익; 장성철; 윤철식; 김남기
Original assignee: 한국전자통신연구원
Priority date: 2009-07-02
Filing date: 2010-07-02
Publication date: 2011-01-06
Also published as: WO2011002262A3

Abstract

Disclosed is an operating method of a femto base station. The method comprises the steps of: transmitting information related to a first Low Duty Operation (LDO) pattern including length information of Available Interval (AI) as an active state of the femto base station and length information of Unavailable Interval (UAI) as an inactive state of the femto base station, to a terminal; and operating on the basis of the first LDO pattern formed by repeating a first LDO cycle that is a sequence of the AI and the UAI, wherein the information related to the first LDO pattern further includes a super frame offset that is information inducing a starting point of the first LDO cycle.

Description

Operation Method of Femto Base Station in Mobile Radio Access System

The present invention relates to wireless communications, and more particularly, to a method of operating a femto base station.

The IEEE 802.16 Task Group, which defines the next generation air interface standard, and the WiMAX Forum, a non-profit organization that provides services and network specifications for IEEE 802.16-based broadband wireless access systems, increases system efficiency and indoors. In order to improve the quality of service (QoS) in the environment, standards standardization for a wireless access system supporting femtocell is underway. The WiMAX Forum defines femto base stations as low-power, low-cost base stations that connect to IP networks through fixed wireless links or local broadband wired links.

1 is a diagram illustrating a structure of a network including a femtocell system. The femto base station is connected to an IP network spread in homes and offices, and provides a mobile communication service by accessing a core network of a mobile communication system through an IP network. That is, the femto base station may be connected to the core network of the mobile communication system through a digital subscriber line (DSL). The user of the mobile communication system may be provided with a service through an existing macro-cell outdoors, and may be provided with a femtocell indoors. Femtocell improves indoor coverage of mobile communication system by supplementing the deterioration of existing macrocell service in the building, and can provide service to specific users only. Can provide services. In addition, femtocells can provide new services that are not provided in macrocells, and the spread of femtocells can accelerate fixed-mobile convergence (FMC) and reduce industrial infrastructure costs.

In a mobile radio access system supporting a femtocell, a femto base station is divided into a power off state, an initialization state, and an operational state. The power off state is a state in which a femto base station is turned off before powering on, or in an initialization state or an operating state. That is, the terminal is no longer in service. The initialization state is entered when the femto base station starts to receive power. It sets air interface parameters such as initial system parameter acquisition, physical / MAC (PHY / MAC) layer parameter determination, and topology acquisition. It performs time and frequency synchronization via GPS, Global Positioning System (GPS), wired interface, and IEEE 1588.

When the femto base station successfully connects to the network, the femto base station enters an operational state. When at least one terminal accesses the coverage of the femto base station and receives a service, the femto base station enters a normal operation mode and performs a role of a base station. Femto base stations also support Low Duty Operation (LDO) mode to reduce the amount of interference with neighboring cells. The femto base station entering the LDO mode repeats an interval between an availability interval (hereinafter referred to as AI) and an unavailability interval (hereinafter referred to as an UAI). The femto base station entering the AI operates in an active mode. On the other hand, the femto base station entering the UAI does not exchange any information with the terminal on an air interface (air interface) in order to minimize the amount of interference.

The femto base station in the normal operation mode may enter the LDO mode if all of the terminals belonging to the sleep (idle) mode, the idle mode (idle) or none of the terminals belong to it. In femto base stations entering the LDO mode, AI and UAI may be formed differently according to the situation of each base station. That is, the AI and UAI patterns of femto base stations in the LDO mode may be different for each base station.

The above-described prior art relates to the entry conditions of the normal operation mode and the LDO mode and the operating method of the LDO mode in the operation mode state of the femto base station. However, since the conventional technology is only a reference to a general technology, detailed descriptions of switching conditions of an operating state to be considered in an actual femto base station and a method of determining an LDO cycle, which is the basis of the operation of the LDO mode, are described. I need more.

The present invention provides a femto base station for setting an LDO cycle that is the basis of a low duty operation (LDO) mode in a mobile radio access system supporting a femtocell and variably setting an LDO cycle according to a communication performance environment. In providing a method of operation.

In one aspect of the present invention, a method of operating a femto base station is provided. The method includes length information of an Available Interval (AI) in which the femto base station is activated and length information of an Unavailable Interval (UAI) in which the femto base station is inactive. Transmitting the first low duty operation (LDO) pattern related information to the terminal and the first LDO pattern formed by repeating a first LDO cycle which is a sequence of the AI and the UAI. and operating based on a pattern, wherein the first LDO pattern related information further includes a superframe offset which is information about a start point of the first LDO cycle.

The first LDO pattern related information may be transmitted in a subscription response message corresponding to the network subscription request message of the terminal.

The length of the AI and the length of the UAI may be at least one superframe.

The starting point of the first LDO cycle can be derived by a next modulo operation, where the operation is N mod (a + b) = SFO, where N is the starting point of the first LDO cycle. Is a superframe number indicating a, a is the length of the AI, b is the length of the UAI, and SFO is the superframe offset.

The method may further include receiving a signal including the information of the terminal from the terminal, and variably performing a second LDO cycle in which the first LDO cycle is changed based on at least one of the information of the terminal and system information of the femto base station. And setting and transmitting information regarding the second LDO pattern including the second LDO cycle to the terminal, wherein the femto base station may operate based on the second LDO pattern.

The method further includes switching to the normal operation mode of the femto base station in the LDO mode when receiving a request signal from a macro base station, a core network, or the terminal. It may include.

The request signal may include the femto base station access request signal signal of a terminal not connected to the femto base station.

The request signal may include a handover (HO) request signal of one or more terminals connected to an adjacent femto base station.

The request signal may include the exit of idle mode signal of the one or more terminals in an idle mode state.

The request signal may include a termination of sleep mode signal of the one or more terminals in a sleep mode state.

The request signal may include a signal for changing a carrier frequency of the femto base station.

According to an embodiment of the present invention, a femto base station can be more efficiently and accurately managed in a mobile radio access system supporting a femtocell. In particular, by varying the LDO cycle in the low-mission operation mode, it is possible to operate the mobile radio access system efficiently while reflecting the situation of the femtocell system simply and flexibly.

1 is a diagram illustrating a structure of a network including a femtocell system.

2 is a block diagram illustrating an operation state and a state transition of a femto base station.

3 illustrates an operation of an LDO mode femto base station according to an embodiment of the present invention.

It is a flow chart.

4 is a diagram illustrating a structure of an LDO cycle determined based on a paging cycle according to an embodiment of the present invention.

5 is a diagram illustrating a structure of an LDO cycle determined based on a listening window according to an embodiment of the present invention.

6 is a view showing that the variable operation based on the LDO cycle according to an embodiment of the present invention.

7 is a diagram illustrating a structure of an LDO cycle that is variably set in consideration of an LDO cycle of a neighboring base station according to an embodiment of the present invention.

8 is a flowchart illustrating operation mode switching of a femto base station according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

FIG. 2 is a diagram illustrating an operation state and a state transition of a femto base station (BS).

Referring to FIG. 2, a femto base station operates in three main states: a power off state, an initialization state, and an operational state. When the femto base station in the operating state loses synchronization with the femto base station of the macro base station (macro BS) or another femtocell connected to the macro base station, the femto base station is switched to the initialization state and performs synchronization. In addition, when the connection with the backhaul is lost, the operation of transmitting and receiving data to and from the wireless terminal is stopped, and handover (HO) to a neighboring macro-cell or femtocell to the terminal receiving the service before the interruption. You can ask to be done. The femto base station disconnected from the backhaul attempts to reconnect and, when reconnected, synchronizes again and enters operational mode. In this case, if there is no terminal that is serviced within the coverage of the femto base station, all the terminals are in the idle mode or the sleep mode, or if necessary, low duty operation (LDO) mode immediately You can enter In case of unexpected or scheduled power off in the operating state, the femto base station informs the terminal of out of service information and performs power down.In this case, as described above, the femto base station can perform the HO as a macro cell or a femtocell. You can ask to be done. In this case, the service departure information notified to the terminal includes an out of service reason and an estimated time. This is also intended to prevent the terminal from joining or resubscribing to a femto base station that cuts off power.

If one or more terminals are receiving service within the coverage of the femto base station, the femto base station maintains a normal operation mode. The femto base station in the normal operation mode periodically synchronizes with the overlay macro base station through GPS, wired interface, IEEE 1588, and the like, and the system status such as the frequency assignment of the femtocell under the control of the femto base station is controlled. system status) information is displayed.

If the terminal does not exist in the coverage of the femto base station, or even if the terminal exists in both the idle (idle) mode or sleep (sleep) mode, the switch to the LDO mode. The femto base station in the LDO mode is an invalid mode operating in an active mode and an inactive mode operating in an inactive mode in which no information is transmitted and received over the air to minimize interference. Repeat the interval (Unavailability Interval (UAI)). Such a sequence of AI and UAI is called an LDO cycle, and the femto base station is operated by an LDO pattern in which the LDO cycle is formed repeatedly. During the AI, the femto base station is activated on the air interface for operations such as synchronization, paging, system information transmission, ranging, or data traffic transmission. Also, during the UAI, the femto base station performs no transmission over the air and performs synchronization with the overlay macro base station or measurement of interference with neighbor cells.

3 is a flowchart illustrating the operation of an LDO mode femto base station according to an embodiment of the present invention.

The first terminal 310 and the second terminal 320 transmit a subscription request message (AAI_REG-REQ) to the femto base station 330, respectively (S311 and S312). The femto base station transmits a subscription response message (AAI_REG-RSP) to the first terminal 310 and the second terminal 320 in response to the received subscription request message (S321 and S322). The subscription response message transmitted by the femto base station 330 includes information on the LDO pattern that is the basis of the LDO operation of the femto base station 330. In this figure, although the information on the LDO pattern is shown to be transmitted in a message, it may be stored in advance in the terminal.

The information about the LDO pattern may include a Start of LDO, an AI length, and a UAI length indicating a start time of the LDO mode. In this case, the Start of LDO may be a superframe offset. In this case, each of the AI length and the UAI length may be in a superframe unit. The start of one LDO cycle forming the LDO pattern is the Nth superframe that satisfies 'N modulo (AI + UAI) = super frame offset'. One LDO cycle is arranged with AI and UAI based on a specific Nth superframe satisfying the above equation, and the length of the LDO cycle has the sum of the AI length and the UAI length. At least one N th superframe, which is a start point of an LDO cycle that satisfies the above-described modular operation, may be at least one. Thus, at least one LDO cycle is formed continuously and repeatedly, which in turn forms an LDO pattern.

Thereafter, when both of the terminals 310 and 320 subscribed to the femto base station 330 operate in the idle mode or the sleep mode, the femto base station enters the LDO mode. At this time, the LDO pattern is activated and the femto base station 330 operates according to the LDO pattern. However, when the terminals 310 and 320 are connected to the femto base station 330, the existing LDO pattern needs to be modified. That is, the LDO cycle, which is a sequence of AIs and UAIs, is variably set by reflecting information of a UE or femtocell system information connected to the LDO pattern that is the LDO mode operation base of the femto base station 330. It is necessary to decide.

The femto base station 330 receives information of the terminal 310 entering the idle mode (S331) and receives information of the terminal 320 entering the sleep mode (S332) and the femtocell system information that the base station itself has. A change LDO cycle is determined based on the information of the terminal obtained through the reception process (S340). The femto base station 330 that determines the change LDO cycle transmits the LDO related information including the determined change LDO cycle to the terminals 310 and 320, respectively (S351 and S352), and operates in the changed LDO mode based on the change LDO pattern (S360). )do.

The LDO related information S351 and S352 transmitted by the femto base station 330 includes an LDO indication parameter indicating an operation state of the base station, and an LDO start indicating a time point when the femto base station 330 operates in the LDO mode. It may include an action time for LDO initiation parameter, a frequency assignment of a femto base station (FA), or information on a changed LDO pattern. The LDO related information may be system information broadcast by the femto base station 330. In addition, the changed LDO-related information may be included in a subscription response message (AAI_REG-RSP) transmitted by the femto base station 330 to the terminal in response to the subscription request message transmitted by the terminal.

The LDO indication parameter informs whether the femto base station is in the normal operation mode or the LDO mode in the operating state. It is periodically located between a femto base station and a terminal in a predetermined location defined by the system. The terminal in the coverage can be known through the SFH (Super Frame Header), the terminal in the neighbor cell (neighbor cell) is informed by the neighbor cell base station through the neighbor BS list, or handed from the neighbor cell to the current femto cell It can be informed through a handover signaling message (HO signaling message) when over.

The LDO Start Action Time parameter indicates when the femto base station operates in LDO mode. In this case, the neighbor base station may inform the state and time of the changed mode of the femto base station in the neighbor cell list. It can also tell you when to start if the LDO cycle pattern changes. That is, after the action time ends, the new LDO pattern is applied. At this time, the neighbor cell is notified of the change time, so that the neighbor cell can know when to apply the changed LDO pattern of the femtocell. The HO start time can be determined according to the AI according to the newly started LDO or the changed LDO. The UE in femtocell coverage according to the newly changed LDO pattern, the idle mode terminal performs paging according to the AI, and the sleep mode terminal can perform the uplink operation that can be performed in the listening window according to the AI and change the sleep mode parameter to the action time. The application time can be determined according to the terminal. When the UE stores several LDO patterns and stores them, the UE can refer to the LDO cycle for the pattern number when the femtocell base station notifies the UE of only the pattern number assigned to each LDO pattern. have. This may also apply to other neighbor cells. The time of application of the pattern is informed via action time.

The femtocell FA notifies the terminal to join or re-entry (HO) to the current femto base station, so that the terminal subscribes by performing frequency synchronization.

The information about the change LDO pattern may include information about a Start of LDO indicating the start time of the new LDO mode, the length of the change LDO cycle, or the length of the AI, and optionally further include information about the UAI length. . The lengths of the AI and UAI can vary, so they may differ from those in traditional LDO cycles. The length of the LDO cycle may be reported in units of a super frame in a period of AI + UAI, and at this time, the sleep mode terminal may inform a power of 2 to effectively apply when a change of the sleep window is applied. . The AI length may also be indicated in units of superframes, and the sleep mode terminal may inform the power of 2 to effectively apply when the change of the sleep window is applied. If the length of the UAI is not set initially, the start point of the UAI and the length of the UAI can be known in two ways: Start of UAI = Start of LDO + AI Length, and UAI Length = LDO Cycle Length-Length. If the modified LDO pattern has a sequence similar to that of the existing LDO pattern, the changed LDO pattern may be transmitted in the same manner as the information related to the existing LDO pattern.

4 to 7 are views for explaining the modified LDO cycle in detail. Hereinafter, the modified LDO cycle and the modified LDO pattern in the embodiment of FIG. 3 will be referred to as an LDO cycle and an LDO pattern.

Referring to FIG. 4, an LDO cycle according to an embodiment of the present invention may be set based on a paging cycle of a terminal operating in an idle mode connected to a femto base station operating in an LDO mode. In other words, the AI may be determined according to a paging interval of a paging cycle. The uppermost LDO cycle 1 of FIG. 4 shows the LDO cycle structure when one paging offset is included in one paging group. LDO cycles 2 and 3 show the LDO cycle structure when having multiple paging offsets in one or more paging groups. As such, when the LDO cycle is determined based on the paging cycle, the AI is determined by considering all paging intervals.

Referring to FIG. 5, it can be seen that the listening window of the terminal operating in the sleep mode is overlapped with the AI of the LDO cycle. The terminal operating in the sleep mode receives an uplink transmission opportunity from the base station during the listening window period. When the base station operates in the LDO mode, the terminal cannot perform the uplink transmission even if the listening window period is in the UAI period. Therefore, when determining the LDO cycle, the listening window of the terminal and the AI should be set to overlap.

If the listening window does not overlap the AI, the LDO cycle must be determined anew, or the base station operating in LDO mode must be switched to normal operation mode. Accordingly, in order for the base station to switch to the normal operation mode, the terminal may send a signal such as a CDMA ranging code to the base station. To support this, the base station may monitor and open a minimum uplink control channel to receive a signal of the terminal even in the UAI.

If both an idle mode terminal and a sleep mode terminal exist in the femto base station, the LDO cycle should be determined in consideration of both the paging cycle and the listening window. In this case, the paging cycle

Referring to FIG. 6, when an uplink operation is possible, the UE may perform an uplink operation according to AI. However, when the uplink operation is not possible, that is, when the UE performs the uplink operation of the UAI as shown in FIG. 6, a series of processes are required to enable the uplink operation. Case 1 represents an operation for delaying uplink operation. When the terminal wants to make a request in the UAI period (t ₁ ), the base station may delay uplink operation until the next AI (t ₂ ) and perform the delay. Case 2 shows the resetting of the LDO cycle to temporarily switch the UAI interval to AI. The UE may send a signal such as a CDMA ranging code to the base station to temporarily convert the UAI to AI. Accordingly, the base station can monitor and open a minimum uplink control channel for receiving a signal from the MS in the UAI. Case 3 shows that the AI is temporarily extended when the uplink operation is impossible during the listening window and the listening window needs to be extended. The terminal performs an uplink operation in a listening window but further performs an uplink operation

To extend this, so the LDO cycle also supports UAI to AI

As long as you can temporarily switch the AI can be extended.

Referring to FIG. 7, when the neighbor femto base station operates in the LDO mode, the current LDO cycle may be determined based on the LDO cycle of the neighbor femto base station. When the neighbor femto base station B operates as an LDO, if the current LDO cycle is changed based on the neighbor LDO cycle, continuous service is provided to the UE handing over from the neighbor femto base station B to the original femto base station A. In FIG. 7, the LDO cycle may be determined by using the AI including both the AI of the LDO cycle of the femto base station B and the AI of the LDO cycle of the femto base station A as a new AI, but the LDO cycle may be determined by using only the overlapping AI sections as the new AI. have. In addition, only the LDO cycle of the original femto base station may be newly determined, and the LDO cycle of the original femto base station and the LDO cycle of the neighboring femto base station may be converted into a new LDO cycle.

Referring to FIG. 8, when a femto base station 810 receives a request signal from a macro base station (macro BS) 820, a core network 830, and a terminal 840 while operating in an LDO mode (S810). (S820) The operation mode is switched to enter the normal operation mode (S830). Since the request signal transmitted from the terminal 840 to the femto base station 810 corresponds to an uplink signal, the femto base station 810 transmits an uplink signal while operating in the uplink LDO mode as in the normal operation mode. It can be monitored continuously. The request signal includes a message for the terminal 840 within the femto base station 810 coverage to join the network, a message for handover, an exit of sleep mode message of the sleep mode terminal, and an idle mode. The idle mode termination message of the terminal and the LDO mode termination request through a signal such as a CDMA ranging code when the terminal 840 in the femtocell needs to terminate the LDO mode for various reasons may be used. There may be. In addition to the request signal, when the femto base station 810 is changing the carrier frequency (carrier frequency), when the terminal that is not uplink operation wants the uplink operation in the sleep period (in the case of the terminal capable of uplink operation LDO mode) Uplink operation can be performed while maintaining the < RTI ID = 0.0 >) < / RTI > and a section in which a listening window overlaps for a plurality of terminals in the sleep mode state or a section in which a paging segment for a plurality of terminals in the idle mode does not exist. If the femtocell system needs to exit the LDO mode, for example, if the LDO cycle cannot be determined, it is possible to switch to the normal operation mode.

As mentioned above, preferred embodiments of the present invention have been described in detail, but those skilled in the art to which the present invention pertains should understand the present invention without departing from the spirit and scope of the present invention as defined in the appended claims. It will be appreciated that various modifications or changes can be made. The above embodiments are only to be understood as technical idea, and should not be construed as being limited thereto. Accordingly, the scope of the present invention is not limited by the specific embodiments, but is determined by the claims, and changes in the future embodiments of the present invention will not depart from the technology of the present invention.

Claims

A method of operating a femto base station, the length information of an available interval (AI) in which the femto base station is activated and an unavailable interval (UAI) in which the femto base station is inactivated Transmitting information related to a first low duty operation (LDO) pattern including length information to a terminal; And operating based on the first LDO pattern formed by repetition of a first LDO cycle, which is a sequence of the AI and the UAI, wherein the information about the first LDO pattern may include: And a superframe offset which is information for deriving the start of the first LDO cycle.
The method of claim 1, wherein the first LDO pattern related information is transmitted in a subscription response message corresponding to the network subscription request message of the terminal.
The method of claim 1, wherein the length of the AI and the length of the UAI are at least one superframe.
The method of claim 3, wherein the start of the first LDO cycle is derived by a next modulo operation. N mod (a + b) = SFO, where N is the first LDO. Is a superframe number indicating the start of a cycle, a is the length of the AI, b is the length of the UAI, and SFO is the superframe offset.
The method of claim 1, wherein the method receives a signal including information of the terminal from the terminal, and wherein the first LDO cycle is changed based on at least one of the information of the terminal and system information of the femto base station. And variably setting two LDO cycles, and transmitting information about a second LDO pattern including the second LDO cycle to the terminal, wherein the femto base station operates based on the second LDO pattern. Characterized in that the method.
The femto base station according to claim 1, wherein the femto base station in the LDO mode switches to a normal operation mode when a request signal is received from a macro base station, a core network, or the terminal. Further comprising.
The method of claim 6, wherein the request signal comprises the femto base station access request signal signal of a terminal that is not connected to the femto base station.
The method of claim 6, wherein the request signal comprises a handover (HO) request signal of one or more terminals connected to an adjacent femto base station.
The method of claim 6, wherein the request signal comprises an exit of idle mode signal of the one or more terminals in an idle mode.
The method of claim 6, wherein the request signal comprises a termination of sleep mode signal of the one or more terminals in a sleep mode state.
The method of claim 6, wherein the request signal comprises a signal for changing a carrier frequency of the femto base station.