Abstract:
Provided is a compact base station apparatus (HeNB) whereby frame timing can precisely be synchronized between HeNB and MeNB, thereby suppressing the interference in an upstream channel. In HeNB ( 100 ), which forms a cell smaller than a cell formed by MeNB, frame timing detecting unit ( 111 ) detects, based on a sync signal received from MeNB, the frame timing of MeNB; a control unit ( 116 ) uses the frame timing of MeNB to set the frame timing of a downstream channel in HeNB ( 100 ); a transmission RF unit ( 118 ) transmits, in accordance with the frame timing of the downstream channel in HeNB ( 100 ), a preamble to MeNB; and a TA command extracting unit ( 114 ) acquires, from a response signal responsive to the preamble, information indicating a difference in frame timing between MeNB and HeNB ( 100 ).

Description:
TECHNICAL FIELD 
     The present invention relates to a micro base station apparatus and a frame timing difference information acquiring method. 
     BACKGROUND ART 
     Recently, a micro base station apparatus referred to as a femto cell (home base station: Home eNB, hereinafter, referred to as HeNB), which forms a small cell having a smaller communication area than that of a conventional cell has been developed for compensation of a dead zone in mobile phone networks. 
     Conventional large base station apparatuses to form cells having a large communication area (Macro base station: Macro eNB, hereinafter, referred to as an MeNB) determine the frame timing based on highly accurate time information acquired by, for example, GPS (Global Positioning System). Thus, highly accurate frame timing synchronization can be established between MeNBs. In contrast to this, considering costs and that HeNBs are mainly placed in buildings, it is difficult to provide HeNBs with GPS etc., and therefore the frame timings between an HeNB and MeNBs located around the HeNB are not synchronized with accuracy. 
     In view of the amount of calculations, it is desirable that the frame timings between an HeNB and an MeNB be synchronized with high accuracy so that the HeNB suppresses (cancels) interference from the MeNB. However, as described above, a large amount of calculations are required for suppressing interference from an MeNB when an HeNB cannot synchronize frame timing between the HeNB and an MeNB, and therefore apparatus costs rise, sharply. 
     Meanwhile, as a conventional technique for synchronizing the frame timings between the HeNB and the MeNB, the following technique is cited as an example. Specifically, Non-Patent Literature 1 proposes a technique in which an HeNB searches for a PBCH (Physical Broadcast Channel) and a SCH (Synchronization Channel) from an MeNB and thereby determines the frame timing of the HeNB. In the above conventional technique, the HeNB synchronizes the frame timing between the HeNB and the MeNB by searching for a PBCH and a SCH from the MeNB and determining the frame timing of the HeNB. 
     CITATION LIST 
     Non-Patent Literature 
     NPL 1 
     
         
         R4-093091, “Reducing HeNB interference to Macro eNB control channels” (Motorola) 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the above conventional technique does not take into account a propagation delay caused by the distance between an HeNB and an MeNB, so that the frame timings may not be synchronized accurately between an HeNB and MeNB. 
     If frame timing synchronization between the HeNB and the MeNB is not established, synchronization cannot be established between the MeNB and a communication terminal apparatus connected with the HeNB (hereinafter, referred to as an HUE). Accordingly, signals from the HUE may interfere with the MeNB over a plurality of subframes in uplink. Furthermore, synchronization is not established between the HeNB and a communication terminal apparatus which is from among communication terminal apparatuses connected with the MeNB (hereinafter, each referred to as an MUE) and is located in the vicinity of the HeNB (that is to say, an MUE having a small propagation delay between the HeNB). Therefore, the HeNB cannot suppress interference due to signals from the MUE located in the vicinity of the HeNB. That is to say, the HeNB may receive interference due to signals from the MUE over a plurality of subframes in uplink. 
     In view of the above, if the frame timings are not accurately synchronized between an HeNB and an MeNB, there arises a problem that interference occurs in uplink. 
     It is an object of the present invention to provide a micro base station apparatus and a method for acquiring frame timing difference information that can accurately synchronize frame timing between an HeNB and an MeNB, and suppress interference in uplink. 
     Solution to Problem 
     A micro base station apparatus according to a first aspect of the present invention is a micro base station apparatus and employs a configuration including a detection section that detects a frame timing of the macro base station apparatus using a synchronization signal transmitted from the macro base station apparatus; a control section that sets a downlink frame timing in the micro base station apparatus based on the frame timing of the macro base station apparatus; a transmission section that transmits an initial connection request signal to the macro base station apparatus in accordance with the downlink frame timing; and an acquiring section that acquires information showing a frame timing difference between the macro base station apparatus and the micro base station apparatus from a response signal to the initial connection request signal. 
     A method for acquiring frame timing difference according to the second aspect of the present invention is a method for acquiring frame timing difference information in a micro base station apparatus forming a smaller cell than a cell formed by a macro base station apparatus and employs a configuration to include the steps of detecting a frame timing of the macro base station apparatus using a synchronization signal transmitted from the macro base station apparatus; setting a downlink frame timing in the micro base station apparatus based on the frame timing of the macro base station apparatus; transmitting an initial connection request signal to the macro base station apparatus in accordance with the downlink frame timing; and acquiring information showing a frame timing difference between the macro base station apparatus and the micro base station apparatus from a response signal to the initial connection request signal. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to accurately synchronize frame timing between an HeNB and an MeNB and suppress interference in uplink. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of an HeNB according to Embodiment 1 of the present invention; 
         FIG. 2  is a sequence diagram of a surrounding search mode according to Embodiment 1 of the present invention; 
         FIG. 3  illustrates a process for setting frame timing according to Embodiment 1 of the present invention; 
         FIG. 4  is a block diagram showing a configuration of an HeNB according to Embodiment 2 of the present invention; 
         FIG. 5  is a sequence diagram of a surrounding search mode according to Embodiment 2 of the present invention; and 
         FIG. 6  is a drawing showing a process for setting frame timing according to Embodiment 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments according to the present invention will be described below in detail with reference to the drawings. In the following explanation, an LTE (Long Term Evolution) which is one of the next-generation communication schemes will be described as an example. In the following explanation, an operation mode in an HeNB includes a surrounding search mode for searching for an MeNB located in a surrounding region and a main mode for transmitting uplink signals and downlink signals. 
     (Embodiment 1) 
       FIG. 1  is a block diagram showing a configuration of an HeNB according to the present embodiment. In HeNB  100  shown in  FIG. 1 , RF reception section  103  receives signals from an MeNB or UEs (HUEs and MUEs) through antenna  101  and duplexer  102 . 
     Reception switching section  104  switches the reception mode to outputting received signals (downlink signals from MeNB) to symbol timing detecting section  107  and FFT section  108  in a surrounding search mode, and to outputting uplink received signals from HUEs to FFT section  105  in a main mode, 
     FFT section  105  performs a discrete Fourier transformation on the received signals. 
     Channel demultiplexing section  106  demultiplexes signals after the discrete Fourier transformation per channel. 
     Symbol timing detecting section  107  detects symbol timing through CP (Cyclic Prefix) correlation calculation in downlink of an MeNB using signals input from reception switching section  104 . 
     FFT (Fast Fourier Transform) section  108  performs a discrete Fourier transformation on received signals input from reception switching section  104 , in accordance with the symbol timing detected in symbol timing detecting section  107 . 
     Channel demultiplexing section  109  demultiplexes signals subjected to a discrete Fourier transformation per channel. For example, channel demultiplexing section  109  demultiplexes signals subjected to a discrete Fourier transformation per channel, and acquires, for example, P-SCH (Primary Synchronization Channel), S-SCH (Secondary Synchronization Channel), PBCH (Physical Broadcast Channel), PDSCH (Physical Downlink Shared Channel), and reference signals (Reference Signal: RS). Channel demultiplexing section  109  outputs the demultiplexed signals to subframe timing detecting section  110 , frame timing detecting section  111 , MIB extracting section  112 , SIB extracting section  113 , TA command extracting section  114 , and RSRP measurement section  115 . 
     Subframe timing detecting section  110  detects a subframe timing through a P-SCH correlation calculation and S-SCH correlation calculation when symbol timing detection succeeds in symbol timing detecting section  107 . Also, subframe timing detecting section  110  detects a cell ID of an MeNB from an S-SCH cell ID group number and P-SCH ID number. 
     Frame timing detecting section  111  detects frame timing by PBCH detection when subframe timing detection succeeds in subframe timing detecting section  110 . Symbol timing detecting section  107 , subframe timing detecting section  110 , and frame timing detecting section  111  detect the frame timing of an MeNB using downlink signals from the MeNB (for example, P-SCH, S-SCH, and PBCH). 
     MIB (Master Information Block) extracting section  112  extracts an MIB from PBCH based on various timing information acquired by processes in symbol timing detecting section  107 , subframe timing detecting section  110  and frame timing detecting section  111 , and the cell ID acquired by a process in subframe timing detecting section  110 . The MIB is superimposed on PBCH and arranged in the first slot of the top subframe of each frame. 
     SIB (System Information Block) extracting section  113  extracts a SIB from PDSCH. The SIB is transmitted thorough PDSCH and transmission timing of the SIB is designated by an MIB. By this means, HeNB  100  collects base station information of an MeNB contained in an SIB. The base station information of the MeNB contains, for example, a channel bandwidth, a PRACH-config and a CP length. 
     TA command (Timing Advanced command) extracting section  114  extracts a TA command from a RAR (Random Access Response) superimposed on PDSCH. An RAR is a response signal to a Random Access Preamble (an initial connection request signal, hereinafter referred to as a preamble) to be described later. A TA command also contains information showing a frame timing difference between the MeNB and HeNB  100 . That is to say, TA command extracting section  114  acquires information indicating the frame timing difference between the MeNB and HeNB  100  from a response signal to a preamble. 
     RSRP (Reference Signal Received Power) measurement section  115  generates a replica (RS replica) of downlink reference signals (RS) of MeNB based on base station information from the MeNB and measures RSRP from the RS replica and actually received reference signals (reception RS) input from channel demultiplexing section  109 . 
     Control section  116  detects the presence of an interfering MeNB when symbol timing detecting section  107 , subframe timing detecting section  110 , and frame timing detecting section  111  succeed in all processes (when the frame timing of the MeNB is detected) in a surrounding search mode. Control section  116  then acquires the cell ID acquired in subframe timing detecting section  110  as a cell ID of the interfering MeNB. Control section  116  sets the frame timing detected in frame timing detecting section  111  as a downlink frame timing in HeNB  100 . 
     Control section  116  also controls preamble transmission in accordance with base station information of an MeNB contained in the SIB acquired in SIB extracting section  113  (for example, a channel bandwidth, a PRACH-config, and a CP length) and the set frame timing. By this means, transmission RF section  118  transmits a preamble to an MeNB in accordance with the downlink frame timing set in control section  116 . After transmission of the preamble, the control section  116  acquires a TA command contained in a RAR which is a response signal to the preamble, from TA command extracting section  114 . 
     Control section  116  sets an uplink frame timing using a downlink frame timing, and a frame timing difference between an MeNB and HeNB  100  shown in a TA command. Specifically, control section  116  sets a frame timing acquired by shifting a downlink frame timing by the frame timing difference between the MeNB and HeNB  100  as an uplink frame timing in HeNB  100 . Control section  116  then controls signal transmission and reception in accordance with the set downlink frame timing and an adjusted uplink frame timing in a main mode. 
     Control section  116  recognizes that HeNB  100  forms an isolated cell when any of the processes in symbol timing detecting section  107 , subframe timing detecting section  110 , and frame timing detecting section  111  fails (a case where frame timing of an MeNB is not detected) in a surrounding search mode. In this case, control section  116  sets a frame timing in uplink and downlink of HeNB  100  independently of an MeNB. Control section  116  controls transmission of uplink signals and downlink signals in accordance with the set frame timing in a main mode. 
     IFFT (Inverse Fast Fourier Transform) section  117  performs a discrete inverse Fourier transformation on signals input from control section  116  (uplink signals, downlink signals or a preamble) and transmission RF section  118  transmits the signals through duplexer  102  and antenna  101 . 
     Next, a surrounding search mode in HeNB  100  ( FIG. 1 ) according to the present embodiment will be described using  FIG. 2  and  FIG. 3 . 
     HeNB  100  shown in  FIG. 1  searches for P-SCH, S-SCH, and PBCH of an MeNB, performs an initial frame synchronization, and acquires a cell ID of the MeNB (step  101  (hereinafter, referred to as ST) shown in  FIG. 2 ). Specifically, HeNB  100  enters the surrounding search mode and synchronizes with downlink of an MeNB located at a surrounding region immediately after power-on. To put it more specifically, HeNB  100  establishes synchronization through following three step (a) to (c). 
     (a) Symbol timing detecting section  107  detects symbol timing through CP correlation calculation in downlink of an MeNB using signals input from reception switching section  104 . 
     (b) Subframe timing detecting section  110  detects a subframe timing through a P-SCH correlation calculation and S-SCH correlation calculation when the symbol timing detection succeeds. 
     (c) Frame timing detecting section  111  detects frame timing through PBCH detection when subframe timing detection succeeds. 
     Here, when all the processes in the above (a) to (c) succeed, that is to say, when P-SCH, S-SCH, and PBCH are detected, a success of the detection is notified to control section  116 . Control section  116  receives the notification, determines a successful initial frame synchronization and sets frame the timing of the MeNB detected through the initial frame synchronization as a downlink frame timing (hereinafter, referred to as a DL frame timing) in HeNB  100  (ST 102 ). Control section  116  also sets the DL frame timing in HeNB  100  to PRACH timing which is preamble transmission timing. 
     Here, as shown in  FIG. 2 , a distance between an MeNB and HeNB  100  is assumed to be D[m]. In this case, there is propagation delay time Δt(=D/c)[sec] (c is velocity of light (3×10 8 [m/s])) in between an MeNB frame timing and an HeNB  100  frame timing after initial frame synchronization as shown in  FIG. 3A . An MeNB determines the frame timing using, for example, GPS as described above. 
     Control section  116  also detects the presence of interfering MeNB and acquires a cell ID of the interfering MeNB from subframe timing detecting section  110 . Then, MIB extracting section  112  extracts an MIB from PBCH based on the various timing information and the cell ID detected in the process (a) to (c). 
     SIB extracting section  113  also extracts a SIB from PDSCH based on transmission timing designated by an MIB (ST 103 ). In view of the above, HeNB  100  acquires base station information of MeNB contained in the SIB (ST 104 ). 
     Next, RSRP measurement section  115  generates a replica (RS replica) of downlink reference signals (DL RS) of an MeNB based on base station information of the MeNB acquired in ST 104  and measures an RSRP from the RS replica and actually received reference signals (ST 105 ), The RSRP is notified to control section  116 , Control section  116  receives the notification and acquires a pathloss (a DL pathloss) between an MeNB and HeNB  100  (ST 106 ). 
     Next, control section  116  controls preamble transmission using the PRACH timing set in ST 102  (that is to say, the DL frame timing in HeNB  100 ) (ST 107 ). By this means, HeNB  100  transmits a preamble to the MeNB in subframe  0  which is PRACH timing, shown in  FIG. 3B , for example. 
     At this time, An MeNB receives a preamble from HeNB  100  Δt[sec] after HeNB  100  transmits the preamble as shown in  FIG. 3B . That is to say, there is a 2Δt frame timing difference between the MeNB and HeNB  100  upon reception of a preamble at the MeNB (frame timing of HeNB  100  is delayed for 2Δt) as shown in  FIG. 3B . Then, the MeNB transmits an RAR containing a TA command to instruct correction of the frame timing difference (2Δt) between the MeNB and HeNB  100 , to the HeNB  100  in, for example, subframe  3  shown in  FIG. 3B  (ST 108 ). TA command extracting section  114  of HeNB  100  acquires the TA command from the RAR received in ST 108  (a frame timing difference (2Δt) between the MeNB and HeNB  100 ) (ST 109 ). 
     Control section  116  of HeNB  100  then sets an UL frame timing in subframe  4  so that the UL frame timing can start earlier by the frame timing difference (2Δt) between the MeNB and HeNB  100 , using the TA command acquired in subframe  3  shown in  FIG. 3B  (ST 110 ). At this time, no DL frame timing is changed, Accordingly, for example, the UL frame timing of HeNB  100  is set to start earlier than the frame timing of the MeNB by Δt[sec] as shown in  FIG. 3B . When HeNB  100  transmits signals in subframe  4  shown in  FIG. 3B , the MeNB receives the signals after Δt[sec], that is to say, in subframe  4  in the MeNB. Accordingly, the frame timing of the MeNB matches (synchronizes with) the frame timing of HeNB  100 . Then, control section  116  keeps the set frame timing information of uplink and downlink, and ends the surrounding search mode. 
     HeNB  100  sets a DL frame timing with reference to DL frame timing of an MeNB in this way (ST 102 ). On the other hand, HeNB  100  sets an UL frame timing through the same process as a process upon start of a UE (an MUE or an HUE) (an RACH process) as shown in  FIG. 2  (ST 110 ). That is to say, HeNB  100  establishes synchronization of the UL frame timing between an MeNB and HeNB  100  by acting as if HeNB  100  is an MUE for the MeNB in a surrounding search mode. 
     In view of the above, UL frame timing synchronization between an MeNB and HeNB  100  enables synchronization between HUEs and the MeNB, thereby making it possible to suppress interference with the MeNB due to signals from the HUEs in the uplink. Furthermore, since synchronization can be established between MUEs located in the vicinity of an HeNB and the HeNB, HeNB  100  can suppress interference due to signals from MUEs in the uplink by means of, for example, an interference removing (interference canceller) process (not shown). 
     On the other hand, HeNB  100  recognizes that HeNB  100  forms an isolated cell and sets a DL frame timing and an UL frame timing independently of an MeNB (that is to say, autonomously) upon a failure in any of the above processes (a) to (c) (in a case where frame timing of MeNB is not detected). In this case, although frame timing synchronization is not established between an MeNB and HeNB  100 , HeNB  100  is an isolated cell, and therefore can communicate with the MeNB with no interference. 
     According to the present embodiment, it is possible to accurately synchronize frame timing between an HeNB and an MeNB and suppress interference in uplink. 
     (Embodiment 2) 
       FIG. 4  is a block diagram showing a configuration of an HeNB according to the present embodiment. Here, in  FIG. 4 , the same components as in  FIG. 1  will be assigned the same reference numerals, and overlapping descriptions will be omitted. 
     In HeNB  200  shown in  FIG. 4 , control section  201  detects the presence of an interfering MeNB when all processes succeed in symbol timing detecting section  107 , subframe timing detecting section  110 , and frame timing detecting section  111  (a case where frame timing of an MeNB is detected) in a surrounding search mode as with control section  116  ( FIG. 1 ) in the present Embodiment 1. Control section  201  then acquires a cell ID acquired in subframe timing detecting section  110  as a cell ID of the interfering MeNB. Control section  201  sets the frame timing detected in frame timing detecting section  111  as uplink frame timing and downlink frame timing in HeNB  100 . 
     Control section  201  also controls preamble transmission in accordance with base station information of the MeNB contained in a SIB acquired in SIB extracting section  113  and the set frame timing. After transmission of a preamble, control section  201  acquires a TA command contained in an RAR which is a response signal to the preamble, from TA command extracting section  114 . At this time, control section  201  stores a frame timing difference between an MeNB and HeNB  200  shown in TA command as propagation delay time information showing propagation delay time between the MeNB and the HeNB. Then, control section  201  outputs the propagation delay time information to interference removal section  202 . 
     Control section  201  recognizes that HeNB  200  forms an isolated cell, when any of the processes of symbol timing detecting section  107 , subframe timing detecting section  110 , and frame timing detecting section  111  fails (a case where frame timing of MeNB is not detected) in a surrounding search mode, similarly to the control section  116  ( FIG. 1 ) according to Embodiment 1. Control section  201  then sets the frame timings in uplink and downlink of HeNB  200  independently of MeNB. Control section  201  controls transmission of uplink signals and downlink signals in accordance with the set frame timing in a main mode. 
     Interference removal section  202  suppresses interference signals from received signals input from channel demultiplexing section  106  and acquires a desired signal. An Interference removal scheme includes, for example, a JMAP (Joint Maximum A Posterior) scheme. At this time, interference removal section  202  removes interference components from received signals using propagation delay time information input from control section  201  (that is to say, a frame timing difference between an MeNB and HeNB  200 . Interference removal section  202  outputs received signals in which interference components are removed to control section  201 . 
     Next, a surrounding search mode in HeNB  200  ( FIG. 1 ) according to the present embodiment will be described using  FIG. 5  and  FIG. 6 . Here, in  FIG. 5 , the same process as in Embodiment 1 ( FIG. 2 ) will be assigned the same reference numerals, and overlapping descriptions will be omitted. 
     That is to say, control section  201  of HeNB  200  shown in  FIG. 1  sets the frame timing of an MeNB detected through initial frame synchronization as with ST 101  of Embodiment 1 to a DL frame timing and an UL frame timing in HeNB  200  as shown in  FIG. 5  and  FIG. 6  (ST 201 ) immediately after power-on. 
     Control section  201  of HeNB  200  acquires a frame timing difference between an MeNB and HeNB  200  contained in a TA command acquired in ST 109  as propagation delay time information showing propagation delay time between the MeNB and HeNB  200  (2Δt in  FIG. 6B ) (ST 202 ), and ends a surrounding search mode. 
     Then, interference removal section  202  of HeNB  200  removes interference from received signals (performs an interference canceller process) in a main mode. At this time, interference removal section  202  suppresses interference components from received signals using the propagation delay time information acquired in control section  201  in ST 202  shown in  FIG. 5  and acquires desired signals. 
     Here, a case will be described where HeNB  200  receives signals from MUEs located in the vicinity of HeNB  200  (UEs which may interfere with HeNB  200 ). Focusing on subframe  2  shown in  FIG. 6B , since an UL frame timing of an MUE located in the vicinity of HeNB  200  synchronizes with a connection-destination MeNB, the UL frame timing of the MUE is set to start earlier than frame timing of the MeNB by Δt in consideration of propagation delay (Δt) between the MeNB and the MUE. By contrast with this, the DL/UL frame timings set in a surrounding search mode in HeNB  200  are set to start later than the frame timing of the MeNB by propagation delay time Δt between the MeNB and HeNB  200  as shown in  FIG. 6A . Also, a propagation delay between HeNB  200  and an MUE located in the vicinity of HeNB  200  is small in comparison with the propagation delay between an MeNB and HeNB  200  (MUE) and can be ignored. Accordingly, there is a frame timing difference of propagation delay time (2Δt) between HeNB  200  and MeNB, between HeNB  200  and an MUE as shown in  FIG. 6B . 
     Interference removal section  202  of HeNB  200  makes adjustment to delay frame timing of received signals containing signals from an MUE located in the vicinity of HeNB  200  (interference signals to HeNB  200 ), by propagation delay time (2Δt) and removes interference from the received signals after the frame timing adjustment to suppress interference. That is to say, interference removal section  202  adjusts frame timing of interference signals from an MUE and synchronizes the adjusted frame timing of the interference signals with frame timing of HeNB  200  in an interference removal process. 
     That is to say, although the frame timing of an MUE located in the vicinity of an HeNB and the frame timing of HeNB  200  are different each other actually, synchronization can be established between the MUE located in the vicinity of HeNB  200  (that is to say, an MeNB) and HeNB  200  through an interference removal process. HeNB  200  therefore can suppress interference due to signals from an MUE located in the vicinity of HeNB  200  in uplink. 
     HeNB  200  recognizes that HeNB  200  forms an isolated cell and sets a DL frame timing and an UL frame timing independently of an MeNB (that is to say, autonomously) when frame timing of MeNB is not detected in a surrounding search mode as with Embodiment 1. In this case, although frame timing synchronization is not established between an MeNB and HeNB  200 , HeNB  200  is an isolated cell, so that it is possible to perform communication with no interference for the MeNB as with Embodiment 1. 
     As described above, according to the present embodiment, it is possible to suppress interference in uplink by taking account of frame timing difference between an HeNB and an MeNB during interference removal process as in Embodiment 1. 
     Furthermore, according to the present embodiment, an HeNB sets both uplink frame timing and downlink frame timing based on a result of initial frame synchronization with an MeNB upon a surrounding search. Thus, an HeNB can readily manage frame timing as compared to Embodiment 1 (that is to say, a case where an UL frame timing is adjusted based on a TA command). 
     Embodiments of the present invention have been described above. 
     The embodiments have been described by employing an LTE case as example, but the present invention is not limited to this, and can also be applied to all radio communication schemes which allow a mixture of an MeNB and an HeNB. 
     The disclosure of Japanese Patent Application No.2010-046634, filed on Mar. 3, 2010, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The present invention is suitable for a mobile communication system including an MeNB, an MUE, an HeNB, and an HUE. 
     REFERENCE SIGNS LIST 
     
         
           100 ,  200  HeNB 
           101  Antenna 
           102  Duplexer 
           103  RF reception section 
           104  Reception switching section 
           105 ,  108  FFT section 
           106 ,  109  Channel demultiplexing section 
           107  Symbol timing detecting section 
           110  Subframe timing detecting section 
           111  Frame timing detecting section 
           112  MIB extracting section 
           113  SIB extracting section 
           114  TA command extracting section 
           115  RSRP measurement section 
           116 ,  201  control section 
           117  IFFT section 
           118  RF transmission section 
           202  Interference removal section