Disclosure herein, a communication device in a wireless communication network, a communication system, control method, and communication program. Background technique [0002]Base station and the communication between terminals is carried out in radio frame units. For example, Non-Patent Document 1, in LTE (Long Term Evolution) system, communication between the base station and the terminal is defined to be performed in the subframe (subframe) units. [0003]Base station and terminal has a receiver therein. Receiver error t data transmission timing tx_err and multipath propagation delay t prop due to the effects of, receiving data at a plurality of reception timings. [0004]A and 23B are conceptual diagrams receiver receives the data in the plurality of reception timings. For example, in Figure 23A, the receiver timing t 0 and the timing t 1 receives the subframe # 0 in. Here, the timing T 1 , the timing T 0 T than det is a timing delayed by. T Det A, error T Tx_err and multi-path propagation delay T Prop is the sum of the. Similarly, the receiver timing t 2 and time t 3 receives the subframe # 1 at. Here, the timing t 3 , the timing t 2 t than det a timing delayed by. [0005] 　The receiver receives the timing t 0 or t 2 , or t 1 or t 3 and to the top by extracting data of one subframe, performs reception processing. [0006] 　Here, in the situation shown in FIG. 23A, the following problem occurs. For example, the receiver receives the timing t 1 to initiate the extraction of data of subframe # 0 in the first. Further the receiver, the reception timing t 3 to start the extraction of data in subframe # 1 by the first. In this case, the receiver receives the timing t 1 to the end of the data subframe # 0 received by the reception timing t 2 in the form of the top part of the subframe # 1 of the data received in a mix, it extracts data and will. Therefore, the reception timing t 1 and the data of the subframe # 0 received by the reception timing t 2 subframe # 1 of the data the data received at will overlap. As a result, interference occurs between the sub-frame due to the overlap, a problem that communication quality deteriorates. [0007] 　For this problem, for example, there is a technique of adding a CP to the head of the symbols in a subframe (Cyclic Prefix) (cyclic prefix). In Figure 23B, it shows a conceptual diagram of the case of adding the CP to the head of the symbol within the subframe. Here, CP length, the error t transmission timing det assume greater than. For example, the receiver receives the timing t 1 to initiate the extraction of data of subframe # 0 in which CP has been added to the first. Further the receiver, the reception timing t 3 to start the extraction of data in subframe # 1 of CP is added to the top. In the situation shown in Figure 23B, since the CP is added to each subframe, the reception timing t 1 and the data of the subframe # 0 received by the reception timing t 2 subframe # 1 of the data received by overlap that there is no. [0008] 　However, if the error of transmission timing between the base stations is more than the CP length, interference between sub-frame described above occurs. Therefore, it is necessary to synchronize the transmission timing between base stations. [0009] 　Generally, as a typical method of achieving synchronization between base stations, GPS (Global Positioning System), IEEE 1558 v2, and a method of using a reference signal and the like. [0010] 　Hereinafter, described with respect to shortcomings or advantages of the above method. [0011] 　First, the case of using the GPS to the inter-base station synchronization, it is necessary to attach the GPS device to the base station. However, by attaching the GPS device, a high price of the base station is concerned. Further, in an environment where radio wave of the GPS satellite indoor can not receive, has a problem that it is impossible to achieve synchronization between base stations by GPS. [0012] 　Next, the case of using the IEEE 1558 v2 between the base station synchronization, reduce the inter-base station synchronization via a wired backhaul. Therefore, if there is a delay in the backhaul, it has problems such as synchronization error increases. [0013] 　On the other hand, when using the reference signal to the inter-base station synchronization, the base station may achieve inter base station synchronization using a reference signal transmitted from other base stations. Since additional devices for achieving inter-base station synchronization is not required, cost of the base station is expected. Furthermore, failure does not exist between the base station synchronization in the room. [0014] 　One method of using a reference signal between the base station synchronization, for example, Non-Patent Document 2, Network Listening (NL) (hereinafter, the network listening) method called is defined. [0015] 　Hereinafter, described with respect to inter-base station synchronization method using a conventional network listening. [0016] 　24 shows a typical network configuration in the network listening. source BS1 synchronization source base station, the target BS2 shows the synchronization target base station. source BS1 has a freestanding synchronization means such as GPS, it is possible to achieve synchronization with high accuracy. Further, source BS1 transmits a reference signal used in order to inter-base station synchronization for target BS2. On the other hand, target BS2 has no autonomous synchronization means such as GPS. target BS2 by using a reference signal transmitted from the source BS1, it is synchronized with the source BS1. CITATION Non-patent literature [0017] Non-patent Document 1: 3GPP TS36.211 Non-patent Document 2: 3GPP TR36.872 Summary of the Invention Problems that the Invention is to Solve [0018] 　However, for example, as in the technique disclosed in Non-Patent Document 2, in using a reference signal promote inter-base station synchronization techniques, if a bad channel state between the base stations, or, if the noise is strong, one of the base stations, when it is intended to synchronize using only the reference signal to be transmitted from the other base stations, may deteriorate the synchronization accuracy between the base stations. [0019] 　Therefore, one of the objective to be achieved is the embodiment disclosed herein, when a bad channel state between the base stations, or, even if the noise is strong, the synchronization between the base station base station capable of improving the accuracy is to provide a method and a program. Means for Solving the Problems [0020] 　The base station of this embodiment, the first reference signal and the communication unit from the first base station receives the second reference signal transmitted from a different communication device to be transmitted from the first base station When, the first reference signal and the based on the second reference signal, having an execution unit for synchronizing with the first base station. [0021] 　Communication system of the present embodiment, the first base station, a different communication apparatus from said first base station in a communication system comprising a base station, the first base station, first to the base station transmits a reference signal, the communication device transmits the second reference signal to the communication device, the base station, the first reference signal and a communication unit for receiving said second reference signal When, the first reference signal and the based on the second reference signal, having an execution unit for synchronizing with the first base station. [0022] 　The method for a base station of this embodiment, a first reference signal transmitted from the first base station, and a second reference signal transmitted from a different communication apparatus from said first base station a step of receiving, the first reference signal and the based on the second reference signal, and a step of synchronizing said first base station. [0023] 　Program of the present embodiment, the steps of receiving a first reference signal transmitted from the first base station, and a second reference signal transmitted from a different communication apparatus from said first base station, based on said first reference signal and the second reference signal, and a step of synchronizing said first base station. Effect of the Invention [0024] 　According to the above-described embodiment, when a bad channel state between the base stations, or, even if the noise is strong, it is possible to improve the accuracy of synchronization between the base stations. BRIEF DESCRIPTION OF THE DRAWINGS [0025] FIG. 1 is a block diagram of a communication system according to the first embodiment. FIG. 2 is a block diagram of a base station according to the first embodiment. 3 is a flowchart of the operation of the base station according to the first embodiment. 4 is a block diagram of a base station according to the second embodiment. It is an example of FIG. 5 the power delay profile signal. 6 is a flowchart of the operation of the base station according to the second embodiment. 7 is a block diagram of a base station according to a modification of the second embodiment. 8 is a flowchart of the operation of the base station according to a modification of the second embodiment. 9 is a block diagram of a base station according to a modification of the second embodiment. FIG. 10 is a flowchart of the operation of the base station according to a modification of the second embodiment. 11 is a block diagram of a base station according to the third embodiment. 12 is a flowchart of the operation of the base station according to the third embodiment. 13 is a block diagram of a base station according to the fourth embodiment. 14 is a flowchart of the operation of the base station according to the fourth embodiment. 15 is a block diagram of a base station according to the fifth embodiment. 16 is a flowchart of the operation of the base station according to the fifth embodiment. 17 is a block diagram of a communication system according to the sixth embodiment. 18 is a block diagram of a base station according to a sixth embodiment. 19 is a flowchart of the operation of the base station according to the sixth embodiment. FIG. 20 is a flowchart of the operation of the base station according to the sixth embodiment. 21 is a flowchart of the operation of the base station according to the sixth embodiment. FIG. 22 is an exemplary block diagram of a communication system according to the first to sixth embodiments. [Figure 23A] receiver is a conceptual diagram for receiving data at a plurality of reception timings. [Figure 23B] receiver is a conceptual diagram for receiving data at a plurality of reception timings. A common network configuration in FIG. 24 network listening. DESCRIPTION OF THE INVENTION [0026] 　Hereinafter, specific embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same reference numerals, for clarity of description, repeated explanation is omitted as appropriate. [0027] 　A plurality of embodiments described below can can either be carried out independently, also be implemented in appropriate combination. These several embodiments have different novel features together. Accordingly, the plurality of embodiments, contribute to solving the different purpose or task to each other, which contributes to achieve different effects from each other. [0028] 　 　FIG 1 shows a configuration example of a communication system according to this embodiment. The communication system communication service, providing both for example, voice communication or packet data communication, or these. Referring to FIG. 1, the communication system includes a base station 100, the first base station 101 and the communication device 102. The base station 100 communicate with each other and the first base station 101 and the communication device 102. [0029] 　The communication device 102 where shows like a base station intended to be synchronized with the first base station 101. [0030] 　Figure 2 shows an example of the configuration of a base station 100 in the first embodiment. [0031] 　The base station 100 includes a communication unit 10 and execution unit 20 at least. [0032] 　The communication unit 10 is connected with an external device by wire or wirelessly, with an external device, transmits or receives various information. In the present embodiment, the communication unit 10 receives the first reference signal transmitted from the first base station 101 and a second reference signal transmitted from the communication device 102. [0033] 　Execution unit 20, based on the first reference signal by the communication unit 10 has received and the second reference signal to synchronize with the first base station 101. [0034] 　Next, operation of the base station 100 of this embodiment will be described with reference to FIG. [0035] 　At step S100, the communication unit 10 receives the first reference signal transmitted from the first base station 101 and a second reference signal transmitted from the communication device 102. [0036] 　In step S101, execution unit 20, based on a first reference signal and a second reference signal by the communication unit 10 is received in S100, synchronization with the first base station 101. [0037] 　As described above, the base station 100 in the present embodiment, the first reference signal transmitted from the first base station 101, based on the second reference signal transmitted from the communication device 102, the synchronized with one base station 101. Therefore, a poor channel state between the base station and the first base station 101, or, even if the noise is strong, it is possible to improve the synchronization accuracy between the first base station 101. [0038] 　 　In the present embodiment, a description will be given of a first embodiment of the construction and operation more concrete embodiment mentioned above. [0039] 　Figure 4 shows an example of a configuration of a base station 200 in the second embodiment. [0040] 　The base station 200 includes a communication unit 10, the execution unit 21 at least. The communication unit 10 is the same as the first embodiment. [0041] 　Execution unit 21 includes a first reception timing detecting unit 210, a second reception timing detecting unit 211, the reception timing combining unit 212, a synchronization error detection unit 213 and the synchronization error correcting unit 214 at least. [0042] 　First reception timing detecting unit 210, based on the first reference signal by the communication unit 10 has received from the first base station 101, the first reception timing t Rx_1st detected. Specifically, the first reception timing detecting unit 210 uses the first reference signal by the communication unit 10 has received, and information about the reference signal of the first base station 101, generates a power delay profile signal to. [0043] 　Figure 5 is an example of a power delay profile signal first reception timing detecting unit 210 generates. In the graph shown in FIG. 5, the vertical axis represents the signal intensity (Power Delay Profile), the abscissa represents the time (Time), respectively. Power delay profile signal, causes the peak at a timing corresponding to the leading portion of the reference signal. First reception timing detecting unit 210, a timing a peak occurs in the power delay profile signal, a first reception timing t Rx_1st detected as. [0044] 　Second reception timing detecting unit 211, based on the second reference signal by the communication unit 10 has received from the communication device 102, a second reception timing t Rx_2nd detected. Second reception timing t Rx_2nd detection method is similar to the first reception timing detecting unit 210. [0045] 　Reception timing combining unit 212, the first reception timing t of the first reception timing detecting unit 210 detects rx_1st and, second receive timing t second reception timing detecting unit 211 detects rx_2nd based on the reception timing T Rx is calculated. [0046] 　Synchronization error detecting unit 213, the reception timing t is the reception timing synthesis unit 212 computed rx and past reception timing t stored in the synchronization error detection unit 213 Rx_pre based on the synchronization timing error t using Equation 1 err to calculate. (Equation 1) [0047] 　Here, the past reception timing t Rx_pre The reception timing combining unit 212 receives the timing t rx from operation of calculating, N times (N is a natural number) refers to reception timing calculated before. Past reception timing t Rx_pre If is not stored in the synchronization error detecting unit 213, past reception timing t Rx_pre a = 0. [0048] 　Synchronization error correcting unit 214, the synchronization timing error t the synchronization error detecting unit 213 to calculate err is used to adjust the reception timing of its own station (the base station 200). Specifically, synchronization timing error t err if is positive, the synchronization error correcting unit 214 controls the own station so as to delay the transmission timing. Conversely, the synchronization timing error t err when is a negative value, the synchronization error correcting unit 214 controls the own station to advance the transmission timing. [0049] 　Next, the operation of the base station 200 of this embodiment will be described with reference to FIG. [0050] 　Step S200 is similar to step S100 of the first embodiment. [0051] 　In step S201, the first reception timing detecting unit 210, based on the first reference signal by the communication unit 10 has received from the first base station 101, the first reception timing t Rx_1st detected. [0052] 　In step S202, the second reception timing detecting unit 211, based on the second reference signal by the communication unit 10 has received from the communication device 102, a second reception timing t Rx_2nd detected. [0053] 　In step S203, the reception timing combining unit 212, the first reception timing t of the first reception timing detecting unit 210 detects rx_1st and, second receive timing t second reception timing detecting unit 211 detects rx_2nd and based on the reception timing t rx is calculated. [0054] 　In step S204, the synchronization error detecting unit 213, the reception timing t is the reception timing synthesis unit 212 computed rx and past reception timing t stored in the synchronization error detection unit 213 Rx_pre based on the synchronization using Equation 1 timing error T Err is calculated. [0055] 　In step S205, the synchronization error correcting unit 214, the synchronization timing error t the synchronization error detecting unit 213 to calculate err is used to adjust the reception timing of its own station (the base station 200). [0056] 　As described above, the base station 200 in the present embodiment, the first reception timing detected based on the first reference signal transmitted from the first base station 101, the second to be transmitted from the communication device 102 based on the second reception timing detected based on the reference signal to synchronize with the first base station 101. Therefore, a poor channel state between the base station and the first base station 101, or, even if the noise is strong, it is possible to improve the synchronization accuracy between the first base station 101. [0057] 　In a modification of this embodiment, the following embodiments are also contemplated. [0058] 　Figure 7 shows an example of the configuration of a base station 240 according to a modification of this embodiment. [0059] 　The base station 240 includes a communication unit 10, the execution unit 22 at least. The communication unit 10 performs the same operation as described in the first embodiment. [0060] 　Execution unit 22 includes the first reception timing detecting unit 210, a second reception timing detecting unit 211, the reception timing storage unit 220, the reception timing combining unit 221, a synchronization error detection unit 223 and the synchronization error correcting unit 214 at least. First reception timing detecting unit 210, a second reception timing detecting unit 211 and the synchronization error correcting unit 214 performs the same operation as described in the second embodiment. [0061] 　Reception timing storage unit 220, the first reception timing t of the first reception timing detecting unit 210 detects rx_1st and, second second receive timing t reception timing detection unit 211 detects the rx_2nd to and a period of time to over save. In other words, reception timing memory unit 220 the latest first reception timing t Rx_1st (N) and the latest of the second receive timing t Rx_2nd and (N), past the first reception timing t Rx_1st (i) (provided that , i is 0 ≦ i 　In the present embodiment, a description will be given of variations of the first or second embodiment described above. [0090] 　Figure 11 shows an example of the configuration of a base station 300 in the third embodiment. [0091] 　The base station 300 includes a communication unit 10, the execution unit 27 and the first determination section 30 at least. The communication unit 10 performs the same operation as the first embodiment. [0092] 　The first determination unit 30, based on a first reference signal by the communication unit 10 has received from the first base station 101, a second reference signal by the communication unit 10 has received from the communication device 102 and a first determining whether taken as the base station 101 synchronization. [0093] 　Execution unit 27, based on the determination result of the first determination unit 30, synchronizing with the first base station 101. Execution unit 27 have a function corresponding to the execution unit 22 or execution unit 23 in the modified example of the first embodiment may also perform part 20 in the form or the second embodiment definitive execution unit 21 and the second embodiment, it may have. [0094] 　Next, operation of the base station 300 of this embodiment will be described with reference to FIG. 12. [0095] 　Step S300 is similar to step S100 of the first embodiment. [0096] 　In step S301, the first determination unit 30, based on the communication unit 10 and the first reference signal received from the first base station 101, a second reference signal by the communication unit 10 has received from the communication device 102 and , it is determined whether synchronization with the first base station 101. Determination result of step S301 is, indicating that "not synchronized with the first base station 101" (step S301: NO), the operation ends. [0097] 　On the other hand, the determination result of step S301 is, indicating that "the first base station 301 synchronize" (step S301: YES), the process proceeds to a step S302. [0098] 　In step S302, execution unit 27, based on the determination result of the first determination unit 30 in step S301, synchronizing with the first base station 101. [0099] 　As described above, the base station 300 in the present embodiment, the first reference signal transmitted from the first base station 101, based on the second reference signal transmitted from the communication device 102, the determining whether to synchronize with the first base station 101, based on the determination result, synchronized with the first base station 101. Therefore, according to the base station 300 in the present embodiment, the determination of whether synchronization with the first base station 101, can be performed more accurately. [0100] 　 　In the present embodiment, a description will be given of a third embodiment in which the construction and operation more concrete embodiment mentioned above. [0101] 　Figure 13 shows an example of the configuration of a base station 400 according to the fourth embodiment. [0102] 　The base station 400 includes a communication unit 10, execution unit 28, the first determination unit 31, the reception level synthesis unit 40, a noise level synthesizing unit 50 and the calculating section 60 at least. The communication unit 10 performs the same operation as the first embodiment. [0103] 　Reception level synthesis unit 40 includes a first reference signal by the communication unit 10 has received from the first base station 101, based on a second reference signal by the communication unit 10 receives from the communication apparatus 102, the reception level P calculate. [0104] 　Noise level synthesis unit 50, based on the communication unit 10 and the first reference signal received from the first base station 101, a second reference signal by the communication unit 10 receives from the communication apparatus 102 and the noise level sigma 2 It is calculated. Noise level sigma 2 is, for example, a value indicating the intensity of the noise. [0105] 　Calculating unit 60, the noise level σ noise level synthesis unit 50 has calculated 2 based on the first threshold value thr using Equation 3 det is calculated. (Equation 3) [0106] 　Here, thr Det_rel is a relative detection threshold to be set as a parameter. [0107] 　The first determination unit 31, the reception level P calculated by the reception level synthesis unit 40, a first threshold value thr calculated by calculation unit 60 det based on greater or not than a first base determining station 101 and whether to synchronize. [0108] 　Execution unit 28, based on the determination result of the first determination unit 31, synchronizing with the first base station 101. [0109] 　Next, operation of the base station 400 of this embodiment will be described with reference to FIG. 14. [0110] 　Step S400 is similar to step S100 of the first embodiment. [0111] 　In step S401, the reception level synthesis unit 40, based on the communication unit 10 and the first reference signal received from the first base station 101, a second reference signal by the communication unit 10 receives from the communication apparatus 102 and, It calculates a reception level P. [0112] 　In step S402, the noise level synthesis unit 50, based on the communication unit 10 and the first reference signal received from the first base station 101, a second reference signal by the communication unit 10 receives from the communication apparatus 102 and, noise level sigma 2 is calculated. [0113] 　In step S403, calculation unit 60, noise level σ calculated by the noise level synthesis unit 50 2 on the basis of a first threshold value thr using Equation 3 det is calculated. [0114] 　In step S404, the first determination unit 31, the reception level P calculated by the reception level synthesis unit 40, a first threshold value thr calculated by calculation unit 60 det based on greater or not than, determining whether to synchronize with the first base station 101. [0115] 　Determination in step S404 is "reception level P is the first threshold value thr det smaller than" it, that is "reception level P 　In the present embodiment, a description will be given of modifications of the first to fourth embodiments described above. [0120] 　Figure 15 shows an example of a configuration of a base station 500 in the fifth embodiment. [0121] 　The base station 500 includes a communication unit 10, execution unit 29, the first determination unit 31, the reception level synthesis unit 40, the noise level synthesis unit 50, calculation unit 60, a measuring unit 70 and the second determination portion 80 at least. Calculator 10, the first determination unit 31, the reception level synthesis unit 40, the noise level synthesizing unit 50 and the calculating unit 60 performs the same operation as the fourth embodiment. [0122] 　Measuring unit 70 measures the period of non-synchronized with the first base station 101. Measurement unit 70, a period that is not synchronized with the first base station 101, may be measured by the timer, it may be measured by counting the number of times that were not synchronized. [0123] 　The second determination unit 80, the measurement result of the measuring unit 70 determines whether exceeds a second threshold. [0124] 　Next, operation of the base station 500 of this embodiment will be described with reference to FIG. 16. [0125] 　Each step S500 ~ step S503 and step S505 is the same as the operation of steps S400 ~ step S403 and step S405 of the fourth embodiment. [0126] 　In step S504, the first determination unit 31, the reception level P calculated by the reception level synthesis unit 40, a first threshold value thr calculated by calculation unit 60 det based on greater or not than, determining whether to synchronize with the first base station 101. [0127] 　Determination in step S504 is "reception level P is the first threshold value thr det smaller than" it, that is "reception level P 　In the present embodiment, a description will be given of modifications of the first to fifth embodiments described above. [0134] 　Figure 17 shows a configuration example of a communication system according to a sixth embodiment. Referring to FIG. 17, the communication system includes a Source BS (Source Base Station) 3, Target BS (Target Base Station) 4 and the base station 600 (own station). The base station 600 communicates with each other and Source BS3 and Target BS4. [0135] 　Here Source BS3 is synchronized source base station, Target BS4 is the synchronization target base station, respectively. [0136] 　Source BS3 corresponds to the first base station 101 in the first to fifth embodiments. Source BS3 has an autonomous synchronization means such as GPS, it is possible to achieve synchronization with high accuracy. Further, Source BS3, relative to Target BS4 and the base station 600 transmits a first reference signal. [0137] 　Target BS4 corresponds to the communication device 102 in the first to fifth embodiments. Target BS4 has no autonomous synchronization means such as GPS, be synchronized with the Source BS3 the Source BS3 as the synchronization source. Furthermore, Target BS4 generates a second reference signal to the base station 600 transmits the second reference signal to the base station 600. [0138] 　Figure 18 shows an example of the configuration of a base station 600 in the sixth embodiment. [0139] 　The base station 600 includes a communication unit 601, A / D conversion unit 602, Source BS reception level measuring unit 603, Target BS reception level measuring unit 604, the reception level storing unit 605, the reception level synthesis unit 606, Source BS noise level measuring unit 607, Traget BS noise level measurement unit 608, the noise level synthesis unit 609, the synchronization determination unit 610, Source BS reception timing detecting section 611, Target BS reception timing detecting unit 612, the reception timing storage unit 613, the reception timing combining unit 614, having at least a synchronization error detection unit 615 and the synchronization error correcting unit 616. [0140] 　The communication unit 601 performs the same operation as the communication unit 10 of the first to fifth embodiments. [0141] 　A / D conversion unit 602, a first reference signal communication section 601 has received and the second reference signal to A / D-conversion, respectively, generating a first digital received reference signal and the second digital received reference signal to. Here, the first reference signal and the second reference signal may be input to the A / D converter as a reception reference signal subjected to various effects such as channel and noise. [0142] 　A / D conversion unit 602, the first digital received reference signal, and outputs the Source BS reception level measuring unit 603, Source BS noise level measuring unit 607 and the Source BS reception timing detecting section 611. A / D conversion unit 602, the second digital received reference signal, and outputs the Target BS reception level measuring unit 604, Traget BS noise level measuring unit 608 and the Target BS reception timing detecting section 612. [0143] 　Source BS reception level measuring unit 603 corresponds to the first reception level measuring unit 24 according to a modification of the second embodiment. Source BS reception level measuring unit 603, a first digital received reference signal, using information on the reference signal Source BS3 notified in advance via the backhaul, the first received for the first digital received reference signal level P Source the measure. Source BS reception level measuring unit 603, the first reception level P measured source outputs to the reception level storing unit 605. [0144] 　Target BS reception level measuring unit 604 corresponds to the second reception level measuring unit 25 according to a modification of the second embodiment. Target BS reception level measuring unit 604, a second digital received reference signal, using information on the reference signal Target BS4 in advance notified via backhaul, the second reception for the second digital received reference signal level P Target the measure. Target BS reception level measuring unit 604, a second reception level P was measured target output to the reception level storing unit 605. [0145] 　Reception level storing unit 605 corresponds to the reception level storing unit 26 according to a modification of the second embodiment. Reception level storing unit 605, the first reception level P source and a second reception level P target is kept around and a period of time. Therefore, the reception level storing unit 605, the latest first reception level P source (N) and the latest second reception level P target and (N), past the first reception level P source (i) and historical second reception level P target stores a (i). [0146] 　Reception level storing unit 605, saved latest first reception level P source (N) and the latest second reception level P target and (N), and outputs the reception level synthesis section 606. The reception level storing unit 605, saved latest first reception level P source (N), past the first reception level P source (i), the latest second reception level P target (N) and past second reception level P target outputs the (i) the reception timing combining section 614. [0147] 　Reception level synthesis unit 606, the latest first reception level P source (N) and the latest second reception level P target based on the (N), the program calculates the reception level P using Equation 4. (Equation 4) [0148] Here,　w P_source , w P_target respectively the first reception level P source and a second reception level P target is the weighting coefficient for a settable as parameters. Reception level synthesis unit 606 outputs the received level P calculated in the synchronization determination unit 610. [0149] 　Source BS noise level measuring unit 607, a first digital received reference signal, using information on the reference signal Source BS3 notified in advance via the backhaul, the first noise level sigma 2 source to measure. Source BS noise level measuring unit 607, a first noise level σ was measured 2 source outputs a noise-level synthesis section 609. [0150] 　Traget BS noise level measurement unit 608, a second digital received reference signal, using information on the reference signal Target BS4 in advance notified via backhaul, second noise level sigma 2 target is measured. Target BS noise level measurement unit 608, the second noise level σ was measured 2 target and outputs a noise-level synthesis section 609. [0151] 　Noise level synthesis unit 609, a first noise level sigma 2 source and a second noise level sigma 2 target using a noise level sigma 2 calculated. Noise level synthesis unit 609, the noise level σ was calculated 2 and outputs to the synchronization processing determination unit 610. [0152] 　Synchronization determination unit 610 corresponds to the first determination unit 31 and the calculating unit 60 in the fourth embodiment. Synchronization processing determination unit 610, the noise level σ noise level synthesis unit 609 has calculated 2 based on the first threshold value thr using Equation 3 det is calculated. [0153] 　Furthermore, the synchronization determination unit 610, the reception level P reception level synthesizer 605 is calculated, the first threshold value thr det based on whether greater than, it is determined whether synchronization with Source BS3. [0154] 　Also, the synchronization determination unit 610 also corresponds to the fourth measurement section 70 and the second determination portion 80 in the embodiment. Synchronization processing determination unit 610, if it is determined that the "Source BS3 not synchronized", the synchronization incomplete counter c Non_sync (n) (where n is the synchronization determination unit 610 does not synchronized with the "Source BS3 to update the representative of) the number of times it is determined that ". Specifically, the synchronization processing determination unit 610, the synchronization incomplete counter c Non_sync the value of (n) c Non_sync (n) = c Non_sync updates as (n-1) +1. [0155] 　Furthermore, the synchronization determination unit 610, the synchronization incomplete counter c Non_sync maximum synchronous update period T a (n) Max_sync compare. Maximum synchronous update period T Max_sync and, the second corresponds to the threshold in the fifth embodiment, showing the upper limit of the number of determined not synchronized with the Source BS3. Synchronization processing determination unit 610, the comparison result is "c Non_sync (n) ≧ T Max_sync case", it determines to perform inter-base station synchronization. On the other hand, the synchronization determination unit 610, the comparison result is "c Non_sync (n)