Abstract:
The present invention relates to an apparatus and method for reducing the interference caused by a femtocell in a wireless communication system. The method comprises the steps of: measuring the intensity of a signal received from a terminal when the transmission mode is deactivated; and controlling the transmission mode to be activated according to the signal intensity, and thus has the advantage of decreasing the influence effects caused by the femtocell and reducing the power consumption in a femto base station.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a wireless communication system providing a femtocell. More particularly, the present invention relates to an apparatus and method for reducing the interference caused by the femtocell in the wireless communication system. 
     In a cellular wireless communication system, a phenomenon in which communication between a terminal and a base station is not smoothly performed occurs, because a channel state is deteriorated due to a geographical requirement within a cell, a distance between the terminal and the base station, or the movement of the terminal. For example, even within a service area of the base station, a propagation shadow area can be formed by a sealed building such as an office or a house. If the terminal is located in the propagation shadow area, the base station fails to perform smooth communication because the channel state with the terminal is deteriorated. 
     Accordingly, the wireless communication system provides a femtocell service for solving a service problem of the propagation shadow area while providing a high speed data service. Here, the femtocell means a small cell area formed by a femto base station accessing a mobile communication core network through a broadband network installed in doors such as an office, a house, etc. 
     As described above, the wireless communication system can install a femto base station in the propagation shadow area and increase a capacity of the whole macro cell. However, a terminal accessing a macro base station and performing communication suffers a problem that communication quality is degraded by interference from a femtocell. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, one aspect of the present invention is to provide an apparatus and method for reducing the interference caused by a femtocell in a wireless communication system. 
     Another aspect of the present invention is to provide an apparatus and method for, when an accessing terminal no longer exists, deactivating a transmission mode in a femto base station of a wireless communication system. 
     A further aspect of the present invention is to provide an apparatus and method for controlling a transmission mode of a femto base station to be activated according to an uplink signal intensity of a terminal in a wireless communication system. 
     The above aspects are achieved by providing an anti-interference apparatus and method in a wireless communication system. 
     According to one aspect of the present invention, a method for controlling a transmit mode in a femto base station of a wireless communication system is provided. The method includes the steps of: measuring the intensity of a signal received from a terminal when the transmission mode is deactivated, and controlling the transmission mode to be activated considering the signal intensity. 
     According to another aspect of the present invention, an apparatus for controlling a transmission mode in a femto base station of a wireless communication system is provided. The apparatus includes a receiving unit for receiving a signal, a signal intensity measurement unit for measuring the intensity of a signal received through the receiving unit, and a transmission mode controller for, when the transmission mode is deactivated, controlling the transmission mode to be activated considering the signal intensity measured in the signal intensity measurement unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a diagram illustrating a construction of a wireless communication system including a femtocell according to an exemplary embodiment of the present invention; 
         FIG. 2  is a diagram illustrating a received signal intensity that a terminal experiences in a wireless communication system according to an exemplary embodiment of the present invention; 
         FIG. 3  is a diagram illustrating a procedure for controlling a transmission mode to be deactivated in a femto base station of a wireless communication system according to an exemplary embodiment of the present invention; 
         FIG. 4  is a diagram illustrating a procedure for controlling a transmission mode to be deactivated in a femto base station of a wireless communication system according to another exemplary embodiment of the present invention; 
         FIG. 5  is a diagram illustrating a construction of a wireless communication system including a femtocell according to another exemplary embodiment of the present invention; 
         FIG. 6  is a diagram illustrating a received signal intensity in a wireless communication system according to another exemplary embodiment of the present invention; 
         FIG. 7  is a diagram illustrating a procedure for controlling a transmission mode to be activated in a femto base station of a wireless communication system according to an exemplary embodiment of the present invention; 
         FIG. 8  is a diagram illustrating a procedure for controlling a transmission mode to be activated in a femto base station of a wireless communication system according to another exemplary embodiment of the present invention; and 
         FIG. 9  is a block diagram illustrating a construction of a femto base station in a wireless communication system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
     The following description is made for a technology for reducing the interference caused by a femtocell in a wireless communication system. 
     The wireless communication system providing a femto service is constructed as illustrated in  FIG. 1  below. 
       FIG. 1  illustrates a construction of a wireless communication system including a femtocell according to an exemplary embodiment of the present invention. 
     As illustrated in  FIG. 1 , a macro base station  100  manages one macro cell, and a femtocell managed by a femto base station  110  is located within the macro cell. 
     In case that a terminal is located within the femtocell at a P 1  time point  120 , the terminal accesses the femto base station  110  and performs communication. 
     If the terminal moves outside the femtocell at a P 2  time point  130 , the terminal accesses the macro base station  100  through handover and performs communication. 
     At this time, when the terminal hands over to the macro base station and thus a terminal accessing the femto base station  110  no longer exists, the femto base station  110  controls a transmission mode to be deactivated so as to reduce the interference effects exerted on the macro cell. For example, the femto base station  110  converts a transmit power into an OFF state. For another example, the femto base station  110  controls to minimize the transmit power. In the following description, it is assumed that, when the transmission mode of the femto base station is deactivated, the femto base station converts a transmit power into an OFF state. 
     As described above, a femto base station deactivates a transmit mode when a terminal accessing itself no longer exists. In this case, the transmit power of the femto base station is changed as illustrated in  FIG. 2  below. 
       FIG. 2  illustrates a received signal intensity that a terminal experiences in a wireless communication system according to an exemplary embodiment of the present invention. 
     As illustrated in  FIG. 2 , in case that a terminal is located within a femtocell at a P 1  time point  220 , the terminal detects a signal intensity  200  of a femto base station greater than a signal intensity  210  of a macro base station. Thus, the terminal accesses the femto base station at the P 1  time point  220  and performs communication. 
     If the terminal moves outside the femtocell, the signal intensity  210  of the macro base station detected by the terminal gradually increases more than the P 1  time point  220 . Contrary to this, the signal intensity  200  of the femto base station detected by the terminal gradually decreases less than the P 1  time point  220 . 
     Accordingly, if the terminal moves outside the femtocell at a P 2  time point  230 , the terminal detects the signal intensity  210  of the macro base station greater than the signal intensity  200  of the femto base station. Thus, the terminal performs handover to the macro base station. 
     If the femto base station is provided with a handover procedure completion signal from the terminal or macro base station at a P 3  time point  240  in a process of performing a handover procedure of the terminal, the femto base station converts a transmit power into an OFF state. Here, the femto base station converts the transmit power into the OFF state only when a terminal providing a service no longer exists besides the terminal having handed over to the macro base station at the P 3  time point  240 . 
     As described above, a femto base station controls a transmit power as illustrated in  FIG. 3  below depending on the existence or non-existence of a terminal accessing itself. 
       FIG. 3  illustrates a procedure for controlling a transmission mode to be deactivated in a femto base station of a wireless communication system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , first, in step  301 , the femto base station performs communication with at least one terminal accessing itself. 
     After that, the femto base station proceeds to step  303  and identifies if a handover request signal is received from a terminal accessing itself. That is, the femto base station identifies if a signal requesting that the terminal accessing itself hands over to a macro base station or adjacent different femto base station is received. 
     If the handover request signal is received, the femto base station proceeds to step  305  and performs a handover procedure for the terminal such that the terminal transmitting the handover request signal accesses the macro base station or adjacent different femto base station. 
     After that, the femto base station proceeds to step  307  and identifies if a handover completion signal for the terminal is received. For example, the femto base station identifies if the handover completion signal is received from the terminal. For another example, the femto base station can identify if the handover completion signal is received from the macro base station to which the terminal hands over. For further example, the femto base station can identify if the handover completion signal is received from the adjacent different femto base station to which the terminal hands over. 
     If the handover completion signal is received, the femto base station proceeds to step  309  and identifies if a terminal providing a service exists. That is, the femto base station identifies if a terminal accessing itself exists. 
     If a terminal providing a service exists, the femto base station returns to step  301  and performs communication with at least one terminal accessing itself. 
     On the other hand, if a terminal providing a service no longer exists, the femto base station proceeds to step  311  and deactivates a transmission mode. That is, the femto base station converts a transmit power into an OFF state. At this time, the femto base station converts into the OFF state by lowering a level of the transmit power step by step. 
     After that, the femto base station terminates the algorithm of the present invention. 
     In the aforementioned exemplary embodiment, a femto base station converts a transmit power into an OFF state, when a terminal hands over to a macro base station or a different femto base station and thus a terminal accessing itself no longer exists. Here, that the terminal accessing the femto base station no longer exists means that a terminal performing voice call and data communication through the femto base station no longer exists. That is, although a plurality of terminals being in an idle mode exist within a cell of the femto base station, the femto base station judges that an accessing terminal no longer exists, and deactivates the transmission mode. Here, the terminal being in the idle mode means a terminal not performing voice call and data communication. 
     In another exemplary embodiment, when a terminal having provided a service drops a call and thus an accessing terminal no longer exists, a femto base station deactivates a transmission mode. For example, in case that a terminal is located within a femtocell at a P 1  time point  120  as illustrated in  FIG. 1  above, the femto base station  110  maintains the transmission mode in an activation state and provides a service to the terminal. If the terminal drops a call and thus a terminal accessing the femto base station  110  no longer exists, the femto base station  110  deactivates the transmission mode as illustrated in  FIG. 4  below. 
       FIG. 4  illustrates a procedure for controlling a transmission mode of a femto base station to be deactivated in a wireless communication system according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , first, in step  401 , the femto base station performs communication with at least one terminal accessing itself. 
     After that, the femto base station proceeds to step  403  and identifies if a call connection with the terminal having provided a service is released. For example, the femto base station measures an uplink signal intensity of the terminal having provided the service and identifies if the call connection with the terminal is released. For another example, the femto base station identifies if a call connection release signal is received from the terminal providing the service. 
     If the call connection with the terminal having provided the service is released, the femto base station proceeds to step  405  and identifies if a terminal providing a service exists. That is, the femto base station identifies if a terminal accessing itself exists. 
     If a terminal providing a service exists, the femto base station returns to step  401  and performs communication with at least one terminal accessing itself. 
     On the other hand, if a terminal providing a service no longer exists, the femto base station proceeds to step  407  and deactivates a transmission mode. That is, the femto base station converts a transmit power into an OFF state. At this time, the femto base station converts into the OFF state by lowering a level of the transmit power step by step. 
     After that, the femto base station terminates the algorithm of the present invention. 
     As described above, a femto base station deactivates a transmission mode to reduce the interference effects exerted on an adjacent different femtocell or a macro cell, when a terminal accessing itself no longer exists. 
     In this case, the femto base station of the deactivated transmission mode can activate the transmission mode considering the intensity of an uplink signal of a terminal. For example, when a terminal hands over to a deactivated femto base station as illustrated in  FIG. 5  below, the femto base station activates the transmission mode to provide a service to the terminal. That is, the femto base station converts a transmit power into an ON state. 
       FIG. 5  illustrates a construction of a wireless communication system including a femtocell according to another exemplary embodiment of the present invention. 
     As illustrated in  FIG. 5 , a macro base station  500  manages one macro cell, and a femtocell managed by a femto base station  510  is located within the macro cell. 
     In case that a terminal is located outside the femtocell at a T 1  time point  520 , the terminal accesses the macro base station  500  and performs communication. 
     If the terminal moves inside the femtocell at a T 2  time point  520 , the terminal hands over to the femto base station  510  and performs communication. 
     At this time, when a transmission mode of the femto base station  510  is in a deactivation state, the femto base station  510  activates the transmission mode according to a signal intensity of the terminal. For example, in case that the signal intensity of the terminal increases more than a reference value, the femto base station  510  converts a transmit power for providing a service to the terminal, into an ON state. 
     As described above, a femto base station of a deactivated transmission mode converts a transmit power into an ON state when a terminal accessing itself exists, so as to provide a service to the terminal. In this case, the transmit power of the femto base station changes as illustrated in  FIG. 6  below. 
       FIG. 6  illustrates a received signal intensity in a wireless communication system according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 6 ,  FIG. 6A  shows the intensity  600  of an uplink signal of a terminal detected in a femto base station, and  FIG. 6B  shows a signal intensity  630  of the femto base station and a signal intensity  620  of the macro base station that are detected in the terminal. 
     As illustrated in  FIG. 6A , in case that the terminal is located outside a femtocell at a T 1  time point  640 , the intensity  600  of the uplink signal of the terminal detected by the femto base station is weak. Here, it is assumed that the femto base station is in a deactivation state at the T 1  time point. 
     If the terminal moves inside the femtocell at a T 2  time point  650 , the signal intensity  600  of the terminal detected by the femto base station increases more than at the T 1  time point  640 . 
     Also, when the signal intensity  600  of the terminal detected by the femto base station increases more than a reference value as at a T 3  time point  660 , the femto base station activates a transmission mode in order to provide a service to the terminal. That is, the femto base station converts a transmit power into an ON state. 
     As illustrated in  FIG. 6B , in case that the terminal is located outside the femtocell at the T 1  time point  640 , the terminal detects a signal intensity  620  of the macro base station greater than a signal intensity  630  of the femto base station. Thus, during the T 1  time point  640 , the terminal accesses the macro base station and performs communication. 
     In case that the terminal moves inside the femtocell, at the T 3  time point  660 , the femto base station converts the transmit power into the ON state as illustrated in  FIG. 6A  above. Thus, the signal intensity  630  of the femto base station detected by the terminal increases gradually. 
     If the signal intensity  630  of the femto base station greater than the signal intensity  620  of the macro base station detected the terminal as at a T 4  time point  670 , the terminal performs handover to the femto base station. 
     In case a terminal hands over from a macro base station to a femto base station as above, the femto base station controls a transmit power as illustrated in  FIG. 7  below. 
       FIG. 7  illustrates a procedure for controlling a transmission mode of a femto base station to be activated in a wireless communication system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , first, in step  701 , the femto base station deactivates a transmission mode to reduce the interference effects exerted on a macro base station or an adjacent different femto base station, when a terminal accessing itself no longer exists. 
     When the transmission mode is in a deactivation state, the femto base station proceeds to step  703  and identifies if a signal is received from the terminal. At this time, when the transmission mode is in the deactivation state, a reception mode maintains an activation state and thus, the femto base station can receive the signal from the terminal. 
     If the signal is received from the terminal, the femto base station proceeds to step  705  and measures the intensity of the signal received from the terminal. Here, the signal received from the terminal includes a ranging signal transmitted by the terminal, a signal periodically transmitted, or a signal separately defined for transmission mode control of the femto base station. 
     After measuring the intensity of the signal, the femto base station proceeds to step  707  and compares the intensity of the signal with a reference value. 
     If the intensity of the signal is less than or is equal to the reference value, the femto base station proceeds to step  710  and maintains the deactivation state of the transmission mode. 
     On the other hand, in case that the intensity of the signal is greater than the reference value, the femto base station proceeds to step  709  and activates the transmission mode. That is, the femto base station converts a transmit power into an ON state. At this time, the femto base station converts into the ON state by increasing a level of the transmit power step by step. 
     When the transmission mode is activated, the femto base station proceeds to step  711  and performs a handover procedure for the terminal whose received signal intensity is greater than the reference value. 
     After that, the femto base station terminates the algorithm of the present invention. 
     In the aforementioned exemplary embodiment, in case that a terminal accessing a macro base station moves within a femtocell, a femto base station of a deactivated transmission mode activates the transmission mode according to a signal intensity of the terminal. 
     In another exemplary embodiment, when a terminal having been in a deactivation state or idle state within a femtocell is activated, a femto base station of a deactivated transmission mode may activate the transmission mode according to a signal intensity of the terminal as illustrated in  FIG. 8  below. That is, when a terminal to perform communication through itself exists, the femto base station of the deactivated transmission mode converts a transmit power into an ON state according to a received signal intensity of the terminal. 
       FIG. 8  illustrates a procedure for controlling a transmission mode of a femto base station to be activated in a wireless communication system according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 8 , first, in step  801 , the femto base station deactivates a transmission mode to reduce the interference effects exerted on a macro base station or an adjacent different femto base station, when a terminal accessing itself no longer exists. 
     When the transmission mode is in a deactivation state, the femto base station proceeds to step  803  and identifies if a signal is received from the terminal. At this time, when the transmission mode is in the deactivation state, a reception mode maintains an activation state and thus, the femto base station can receive the signal from the terminal. 
     If the signal is received from the terminal, the femto base station proceeds to step  805  and measures the intensity of the signal received from the terminal. Here, the signal received from the terminal includes a ranging signal transmitted by the terminal, a signal periodically transmitted by the terminal, or a signal separately defined for transmission mode control of the femto base station. 
     After measuring the intensity of the signal, the femto base station proceeds to step  807  and compares the measured intensity of the signal with a reference value. 
     If the measured intensity of the signal is less than or is equal to the reference value, the femto base station proceeds to step  801  and maintains the deactivation state of the transmission mode. 
     On the other hand, in case that the measured intensity of the signal is greater than the reference value, the femto base station proceeds to step  809  and activates the transmission mode. That is, the femto base station converts a transmit power into an ON state. At this time, the femto base station converts into the ON state by increasing a level of the transmit power step by step. 
     When the transmission mode is activated, the femto base station proceeds to step  811  and performs communication with the terminal whose received signal intensity is greater than the reference value. 
     After that, the femto base station terminates the algorithm of the present invention. 
     The following description is made for a construction of a femto base station for controlling a transmission mode according to the intensity of a signal received from a terminal. 
       FIG. 9  illustrates a construction of a femto base station in a wireless communication system according to the present invention. 
     As illustrated in  FIG. 9 , a terminal includes a duplexer  900 , a receiving unit  910 , a transmitting unit  920 , a controller  930 , a signal intensity measurement unit  940 , and a transmission mode controller  950 . 
     According to a duplexing scheme, the duplexer  900  transmits a transmit signal provided from the transmitting unit  920  through an antenna, and provides a receive signal from the antenna to the receiving unit  910 . 
     The receiving unit  910  restores data from a signal provided from the duplxer  900 , and forwards to the controller  930 . For example, the receiving unit  910  includes an RF reception block, a demodulation block, a channel decoding block, etc. The RF reception block is composed of a filter, an RF preprocessor, etc. In case that using an orthogonal frequency division multiplexing scheme, the demodulation block is composed of an FFT operator for extracting data loaded in each subcarrier, etc. The channel decoding block is composed of a demodulator, a deinterleaver, a channel decoder, etc. 
     The controller  930  controls the general transmission/reception operation of the femto base station. Also, the controller  930  controls a transmit mode according to the control of the transmission mode controller  950  so as to reduce the interference effects exerted on a macro cell or an adjacent different femtocell. That is, the controller  930  turns ON/OFF a transmit power according to the control of the transmission mode controller  950 . For example, when the transmit power is in an OFF state, the controller  930  converts into an ON state by increasing the transmit power step by step according to the control of the transmission mode controller  950 . On the other hand, when the transmit power is in the ON state, the controller  930  converts into the OFF state by decreasing the transmit power step by step according to the control of the transmission mode controller  950 . 
     The signal intensity measurement unit  940  measures the intensity of an uplink signal of a terminal provided through the controller  930  and provides to the transmission mode controller  950 . At this time, the signal intensity measurement unit  940  measures the signal intensity of the terminal using a ranging signal transmitted by the terminal, a signal periodically transmitted by the terminal, or a signal separately defined for transmission mode control of the femto base station and transmitted by the terminal. 
     When a transmission mode is in an activation state, the transmission mode controller  950  controls the controller  930  to deactivate the transmission mode when a terminal accessing the femto base station no longer exists. For example, when the terminal accessing the femto base station no longer exists through handover or call connection release with the terminal, the transmission mode controller  950  controls the controller  930  to deactivate the transmission mode. At this time, the transmission mode controller  950  can identify the call connection release of the terminal according to a call release signal received from the terminal or a signal intensity received from the terminal in the signal intensity measurement unit  940 . 
     When the transmission mode is in a deactivation state, the transmission mode controller  950  controls the controller  930  to activate the transmission mode according to the intensity of a signal provided from a terminal provided from the signal intensity measurement unit  940 . For example, the transmission mode controller  950  controls the controller  930  to activate the transmission mode when a signal intensity provided from the signal intensity measurement unit  940  is greater than a reference value. 
     The transmitting unit  920  converts a transmit signal into a form for transmission through wireless resources according to the control of the controller  930  and provides to the duplexer  900 . For example, the transmitting unit  920  includes a channel encoding block, a modulation block, an RF transmission block, and the like. The channel encoding block is composed of a modulator, an interleaver, a channel encoder, and the like. In case that using an orthogonal frequency division multiplexing scheme, the modulation block is composed of an IFFT operator for mapping data to each subcarrier, and the like. The RF transmission block is composed of a filter, an RF preprocessor, and the like. 
     In the aforementioned construction, the controller  930  is a protocol controller, and controls the signal intensity measurement unit  940  and the transmission mode controller  950 . That is, the controller  930  can perform functions of the signal intensity measurement unit  940  and the transmission mode controller  950 . These are separately constructed and shown in order to distinguish and describe respective functions in the present invention. Thus, in an actual realization, construction can be such that all of them are processed in the controller  930 , or construction can be such that only part of them is processed in the controller  930 . 
     As described above, there is an advantage that a femto base station controls a transmit mode according to an uplink signal intensity of a terminal, thereby being capable of decreasing the interference effects caused by a femtocell and reducing the power consumption of the femto base station in a wireless communication system. 
     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.