Abstract:
A first conversion unit ( 201 ) converts a signal from a time domain to a frequency domain. A signal extraction unit ( 202 ) extracts common channel information included in the signal which has been converted by the first conversion unit ( 201 ). A signal substitution unit ( 207 ) restores the common channel information which has been extracted by the signal extraction unit ( 202 ). An addition unit ( 208 ) substitutes the common channel information which has been restored by the signal substitution unit ( 207 ) for the common channel information included in the signal which has been converted by the first conversion unit ( 201 ). A second conversion unit ( 209 ) converts the signal including the common channel information substituted, which has been converted by the first conversion unit ( 201 ), from the frequency domain to the time domain.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to relay apparatuses and relay methods, and relates, for example, to a relay apparatus and a relay method that relay signals transmitted and received between a base station and a communication terminal apparatus. 
       BACKGROUND ART 
       [0002]    In recent years, there has been a demand for mobile communication systems to support high-capacity and a high transmission rate. Meanwhile, the frequency resources become tighter due to the development of wider-band systems or the presence of a plurality of systems. For this reason, use of high-frequency radio bands has been under study in recent years. Generally, attenuation due to a transmission distance is larger with a high-frequency radio band than with a low-frequency radio band. As a result, high-quality communication can be expected in an area near a base station, while a large distance from the base station degrades the communication quality. Here, the communication quality may be degraded even in the area near the base station by effects due to shielding by an exterior wall of a building, and the like. 
         [0003]    The communication quality can be improved by reducing a communication range for each base station and increasing the number of base stations to be installed. However, the installation of a large number of base stations requires reasonable costs. Hence, there is a need for a system that can realize high-quality communication while suppressing an increase in the number of base stations to be installed. 
         [0004]    As a technique that can meet this need, relay apparatuses have been studied. The relay apparatus means an apparatus that performs both or any one of relaying a signal transmitted from the base station, to a communication terminal apparatus, and relaying a signal transmitted from the communication terminal apparatus, to the base station. 
         [0005]    For example, Non-Patent Literature 1 describes two types of systems: a regenerative relay system configured to regenerate a transmission signal once in the relay apparatus; and a non-regenerative relay system configured not to regenerate the transmission signal in the relay station apparatus. In the following explanation, the regenerative relay system is referred to as a “relay,” and the non-regenerative relay system is referred to as a “repeater.” 
         [0006]    The repeater receives a signal from a base station, then only amplifies the signal, and retransmits the signal. The basic function of the repeater is only amplification. The repeater can be thus formed by providing an amplifier between a reception antenna and a transmission antenna, resulting in a relatively simple apparatus configuration. Moreover, the repeater is also advantageous in terms of a delay time in the relay process. 
         [0007]    In contrast, the relay receives a signal from a base station, then demodulates and decodes the received signal, then encodes and modulates the signal again, and transmits the signal. Specifically, the relay applies down-conversion and analog/digital conversion in a radio receiving unit to the signal received by an antenna. Moreover, the relay performs demodulation in a digital signal processing unit. The relay also performs an error-correction process for the demodulated signal in a decoding unit to obtain a bit sequence consisting of “1” and “0” transmitted from the base station. The relay then performs error-correction coding and modulation processing in an encoding unit and a modulation unit, performs digital/analog conversion and up-conversion, and then transmits the processed signal from an antenna. The use of relay in building a system makes it possible to improve the error rate characteristic of the entire system because of the above described processing. 
         [0008]    The use of either repeater or relay thus can be expected to bring about advantageous effects on measures against dead zones and on increase in coverage of the base station. 
       CITATION LIST 
     Non-Patent Literature 
       [0000]    
       
         NPL 1 Tsuyoshi Miyano, Hidekazu Murata, Kiyomichi Araki, “Cooperative Relaying Technique with Space Time Block Code for Multihop Communications among Single Antenna Terminals,” Technical Report of IEICE, A-P2003-342, RCS2003-365, pp. 71-76, March 2004. 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    However, when a repeater is used in building a system in the conventional apparatus, there arises a problem that the error rate characteristic of the entire system is deteriorated even though the amount of delay in the entire system is reduced. Meanwhile, when a relay is used in building a system in the conventional apparatus, there arises a problem that the amount of delay in the entire system is increased even though the error rate characteristic of the entire system is improved. 
         [0011]    An object of the present invention is thus to provide a relay apparatus and a relay method that can both improve the error rate characteristic and reduce the amount of delay. 
       Solution to Problem 
       [0012]    A relay apparatus reflecting one aspect of the present invention is a relay apparatus that relays a signal, the apparatus including a receiving unit that receives a signal; an extracting unit that extracts particular information included in the received signal; a replacement unit that restores the particular information extracted by the extracting unit, and replaces the particular information included in the received signal with the restored particular information; and a transmitting unit that transmits a signal including the particular information left after the replacement by the replacement unit. 
         [0013]    A relay method reflecting one aspect of the present invention is a relay method in a relay apparatus that relays a signal, the method including the steps of receiving a signal; extracting particular information included in the received signal; restoring the extracted particular information, and replacing the particular information included in the received signal with the restored particular information; and transmitting a signal including the particular information left after the replacement. 
       Advantageous Effects of Invention 
       [0014]    The present invention can both improve the error rate characteristic and reduce the amount of delay. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a block diagram illustrating a configuration of a relay apparatus according to Embodiment 1 of the present invention; 
           [0016]      FIG. 2  is a block diagram illustrating a configuration of a digital signal processing unit according to Embodiment 1 of the present invention; 
           [0017]      FIG. 3  is a diagram illustrating a signal frame in LTE according to Embodiment 1 of the present invention; 
           [0018]      FIG. 4  is a block diagram illustrating a configuration of the digital signal processing unit according to Embodiment 2 of the present invention; 
           [0019]      FIG. 5  is a block diagram illustrating a configuration of the digital signal processing unit according to Embodiment 3 of the present invention; 
           [0020]      FIG. 6  is a block diagram illustrating a configuration of the digital signal processing unit according to Embodiment 4 of the present invention; and 
           [0021]      FIG. 7  is a block diagram illustrating a configuration of the digital signal processing unit according to Embodiment 5 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]    Embodiments of the present invention will be described below in detail with reference to the drawings. It should be noted that, in each of the following embodiments, a relay apparatus that relays Down Link communication of LTE (Long Term Evolution), which is one of the next-generation radio communication systems, that is, communication from a base station to a communication terminal apparatus will be described as an example. 
       Embodiment 1 
       [0023]      FIG. 1  is a block diagram illustrating a configuration of relay apparatus  100  according to Embodiment 1 of the present invention. 
         [0024]    Relay apparatus  100  is mainly formed of antenna  101 , radio receiving unit  102 , digital signal processing unit  103 , radio transmitting unit  104 , and antenna  105 . Each configuration will be described below in detail. 
         [0025]    Antenna  101  receives a signal from the base station (not illustrated) and outputs the signal to radio receiving unit  102 . 
         [0026]    Radio receiving unit  102  converts the frequency of the signal input from antenna  101 , from a radio frequency into a baseband frequency, and outputs the signal to digital signal processing unit  103 . 
         [0027]    Digital signal processing unit  103  performs digital signal processing for the signal input from radio receiving unit  102 , and outputs the signal to radio transmitting unit  104 . The configuration of and the processing in digital signal processing unit  103  will be described later in detail. 
         [0028]    Radio transmitting unit  104  converts the frequency of the signal input from digital signal processing unit  103 , from the baseband frequency into the radio frequency, and outputs the signal to antenna  105 . 
         [0029]    Antenna  105  transmits the signal input from radio transmitting unit  104 , to a communication terminal apparatus (not illustrated). 
         [0030]    Hereinabove, the explanation of the configuration of relay apparatus  100  is completed. 
         [0031]    Next, the configuration of digital signal processing unit  103  will be described using  FIG. 2 .  FIG. 2  is a block diagram illustrating the configuration of digital signal processing unit  103 . 
         [0032]    Digital signal processing unit  103  is mainly formed of first transform unit  201 , signal extracting unit  202 , common information demodulation unit  203 , common information decoding unit  204 , common information re-encoding unit  205 , common information re-modulation unit  206 , signal replacement unit  207 , addition unit  208 , and second transform unit  209 . Each configuration will be described below in detail. 
         [0033]    First transform unit  201  applies Fast Fourier Transform (FFT) to the signal input from radio receiving unit  102 , to transform the signal from a time domain into a frequency domain. Then, first transform unit  201  outputs the signal transformed into the frequency domain to signal extracting unit  202 . 
         [0034]    Signal extracting unit  202  extracts common channel information from the signal input from first transform unit  201 , and outputs the extracted common channel information to common information demodulation unit  203 . Moreover, signal extracting unit  202  outputs the signal input from first transform unit  201  to addition unit  208 . It should be noted that the common channel information will be described later. 
         [0035]    Common information demodulation unit  203  demodulates the common channel information input from signal extracting unit  202 , and outputs the common channel information to common information decoding unit  204 . 
         [0036]    Common information decoding unit  204  decodes the common channel information input from common information demodulation unit  203 , and outputs the common channel information to common information re-encoding unit  205 . 
         [0037]    Common information re-encoding unit  205  encodes (re-encodes) the common channel information input from common information decoding unit  204 , again, and outputs the common channel information to common information re-modulation unit  206 . 
         [0038]    Common information re-modulation unit  206  modulates (re-modulates) the common channel information input from common information re-encoding unit  205 , again, and outputs the common channel information to signal replacement unit  207 . 
         [0039]    Signal replacement unit  207  outputs the common channel information input from common information re-modulation unit  206 , to addition unit  208 , at a timing of replacing the common channel information included in the signal received by relay apparatus  100 , with the common channel information input from common information re-modulation unit  206 . 
         [0040]    Addition unit  208  replaces the common channel information included in the signal input from signal extracting unit  202 , with the common channel information input from signal replacement unit  207 . On this occasion, addition unit  208  replaces only the common channel information, and does not replace information other than the common channel information. Then, addition unit  208  outputs the signal in which the common channel information has been replaced, to second transform unit  209 . 
         [0041]    Second transform unit  209  applies Inverse Fast Fourier Transform (IFFT) to the signal input from addition unit  208 , to transform the signal from the frequency domain into the time domain. Moreover, second transform unit  209  adds a CP (Cyclic Prefix) to the signal transformed into the time domain, and outputs the signal to radio transmitting unit  104 . 
         [0042]    Hereinabove, the description of the configuration of digital signal processing unit  103  is completed. 
         [0043]    Next, a method of replacing the common channel information will be described using  FIG. 3 .  FIG. 3  is a diagram illustrating a signal frame in the down link communication in LIE.  FIGS. 3  ( a ) and ( b ) illustrate the signal frame in slots contiguous to each other. 
         [0044]    As illustrated in  FIG. 3 , the signal frame of LIE includes PDCCH (Physical Downlink Control Channel) signal # 301 , Reference Signal # 302 , Secondary Synchronization Signal (SSS) # 303 , Primary Synchronization Signal (PSS) # 304 , PBCH (Physical Broadcast Channel) signal # 305 , and PDSCH (Physical Downlink Shared Channel) signal # 306 . In  FIG. 3 , portions indicated with white color correspond to PDSCH signal # 306 . 
         [0045]    Here, PDCCH signal # 301  is used to communicate mapping information on PDSCH signal # 306  to the communication terminal apparatus. Moreover, Reference Signal # 302  is used to perform various measurements of channel estimation and the like by the communication terminal apparatus. Moreover, Secondary Synchronization Signal # 303  reports the beginning of a frame and a Cell ID group number of the signal transmitted from the base station, and is used to establish synchronization with a radio frame and identify a Cell ID. Moreover, Primary Synchronization Signal # 304  is transmitted in order that the communication terminal apparatus can synchronize with the signal transmitted from the base station. Moreover, PBCH signal # 305  is used to report an SFN (System Frame Number) indicating a frame number, the number of transmission antennas of the base station, and a mapping position of a Control Channel, which is information required for decoding the Control Channel. Moreover, PDSCH signal # 306  transmits common information (for example, SIB; System Information Block) and dedicated information to the communication terminal apparatus. Moreover, the common information is various kinds of information related to the base station, and is information required for the communication terminal apparatus to communicate with the base station. Moreover, the dedicated information is information unique to the communication terminal apparatus (user). 
         [0046]    For example, in LTE and LTE Advanced, which are currently in the process of standardization in standards body, 3GPP, physical channels can be classified into two types: a common channel and a dedicated channel. In the present embodiment, the common information transmitted via PBCH signal # 305 , PDCCH signal # 301  and PDSCH signal # 306  is regarded as the common channel information, and the dedicated information transmitted via PDSCH signal # 306  is regarded as dedicated channel information. 
         [0047]    Moreover, in order to receive the dedicated channel information, it is necessary to correctly receive the common channel information first. In other words, if the common channel information can be correctly received, it becomes possible to receive the dedicated channel information. Accordingly, it becomes possible to improve the characteristic by compensating only the common channel information. 
         [0048]    A turbo code used to encode the dedicated channel involves a large amount of processing in a decoding process in the communication terminal apparatus and is one of main causes for delay in the relay. In contrast, a code that can be decoded by a relatively simple process is used to encode the common channel. 
         [0049]    As described above, in the present embodiment, relay apparatus  100  extracts the common channel information included in the received signal, restores the extracted common channel information, and performs the replacement. Incidentally, the replacement process is preferably performed for each channel. Moreover, in the present embodiment, the common channel information to be replaced can be any one piece or any multiple pieces of the common information transmitted via PBCH signal # 305 , PDCCH signal # 301  and PDSCH signal # 306 . 
         [0050]    In this way, according to the present embodiment, it is possible to both improve the error rate characteristic and reduce the amount of delay. In other words, according to the present embodiment, it is possible to improve the error rate characteristic as compared with the conventional repeater, and reduce the processing delay as compared with the conventional relay. 
       Embodiment 2 
       [0051]      FIG. 4  is a block diagram illustrating a configuration of digital signal processing unit  400  according to Embodiment 2 of the present invention. In the present embodiment, the configuration of the relay apparatus is identical to that shown in  FIG. 1  except that digital signal processing unit  400  is provided instead of digital signal processing unit  103  in  FIG. 1 . Thus, the explanation of the configuration will be omitted. Moreover, in a description of the present embodiment, reference numerals of  FIG. 1  are used to denote the configuration of the relay apparatus except digital signal processing unit  400 . 
         [0052]    Digital signal processing unit  400  is mainly formed of P-SS detection unit  401 , P-SS generation unit  402 , signal replacement unit  403 , first transform unit  404 , signal extracting unit  405 , addition unit  406 , and second transform unit  407 . Each component will be described below in detail. 
         [0053]    P-SS detection unit  401  detects the Primary Synchronization Signal from the signal input from radio receiving unit  102 . Moreover, P-SS detection unit  401  extracts a P-SS number included in the detected Primary Synchronization Signal, and outputs the extracted P-SS number to P-SS generation unit  402 . Moreover, P-SS detection unit  401  controls a timing of demodulation in first transform unit  404 , based on the detected Primary Synchronization Signal. 
         [0054]    P-SS generation unit  402  previously stores a replica of the Primary Synchronization Signal in association with the P-SS number. Moreover, P-SS generation unit  402  selects the replica of the Primary Synchronization Signal corresponding to the P-SS number input from P-SS detection unit  401 , and outputs the Primary Synchronization Signal of the selected replica, to signal replacement unit  403 . 
         [0055]    Signal replacement unit  403  outputs the Primary Synchronization Signal input from P-SS generation unit  402 , to addition unit  406 , at a timing of replacing the Primary Synchronization Signal included in the signal received by relay apparatus  100 , with the Primary Synchronization Signal input from P-SS generation unit  402 . On this occasion, signal replacement unit  403  replaces only the Primary Synchronization Signal, and does not replace the signals other than the Primary Synchronization Signal. 
         [0056]    First transform unit  404  applies the Fast Fourier Transform to the signal input from radio receiving unit  102 , to transform the signal in the time domain into the signal in the frequency domain, at the timing controlled by P-SS detection unit  401 . Then, first transform unit  404  outputs the signal transformed into the frequency domain, to signal extracting unit  405 . 
         [0057]    Signal extracting unit  405  deletes the Primary Synchronization Signal from the signal input from first transform unit  404 , and output the signal to addition unit  406 . 
         [0058]    Addition unit  406  inserts the Primary Synchronization Signal input from signal replacement unit  403 , at a location where the Primary Synchronization Signal has been arranged in the signal input from signal extracting unit  405 , to replace the Primary Synchronization Signal. Then, addition unit  406  outputs the signal in which the Primary Synchronization Signal has been replaced, to second transform unit  407 . 
         [0059]    Second transform unit  407  applies the Inverse Fast Fourier Transform to the signal input from addition unit  406 , to transform the signal in the frequency domain into the signal in the time domain. Moreover, second transform unit  407  adds a CP to the signal transformed into the time domain, and outputs the signal to radio transmitting unit  104 . 
         [0060]    In the present embodiment, relay apparatus  100  replaces Primary Synchronization Signal # 304  of  FIG. 3 . 
         [0061]    Moreover, in order to receive the common channel information and the dedicated channel information, it is necessary to correctly receive the Primary Synchronization Signal first. In other words, if the Primary Synchronization Signal can be correctly received, it becomes possible to receive the common channel information and the dedicated channel information. Accordingly, it becomes possible to improve the characteristic by compensating the Primary Synchronization Signal. It should be noted that the reason why it is easier to decode the Primary Synchronization Signal than the dedicated channel is the same as that in Embodiment 1 as described above. 
         [0062]    Moreover, in the present embodiment, the detection of the Primary Synchronization Signal in P-SS detection unit  401 , and the selection of the replica of the Primary Synchronization Signal in P-SS generation unit  402  may be performed once unless the P-SS number changes. In this case, each time a signal is input to digital signal processing unit  400 , signal replacement unit  403  repeatedly performs only a process of replacing the Primary Synchronization Signal included in the input signal, with the selected replica. 
         [0063]    In this way, according to the present embodiment, it is possible to both improve the error rate characteristic and reduce the amount of delay. In other words, according to the present embodiment, it is possible to improve the error rate characteristic as compared with the conventional repeater, and is also possible to reduce the processing delay as compared with the conventional relay. Moreover, according to the present embodiment, propagation distortions or noises can be eliminated by replacing the Primary Synchronization Signal. Thus, the accuracy of detecting the Primary Synchronization Signal in the communication terminal apparatus can be improved. 
       Embodiment 3 
       [0064]      FIG. 5  is a block diagram illustrating a configuration of digital signal processing unit  500  according to Embodiment 3 of the present invention. It should be noted that, in the present embodiment, the configuration of the relay apparatus is identical to that shown in  FIG. 1  except that digital signal processing unit  500  is provided instead of digital signal processing unit  103  in  FIG. 1 . Thus, the explanation of the configuration will be omitted. Moreover, in the explanation of the present embodiment, reference numerals of  FIG. 1  are used to denote the configuration of the relay apparatus except digital signal processing unit  500 . 
         [0065]    Digital signal processing unit  500  is mainly formed of first transform unit  501 , signal extracting unit  502 , S-SS detection unit  503 , S-SS generation unit  504 , signal replacement unit  505 , addition unit  506 , and second transform unit  507 . Each component will be described below in detail. 
         [0066]    First transform unit  501  applies the Fast Fourier Transform to the signal input from radio receiving unit  102 , to transform the signal from the time domain into the frequency domain. Then, first transform unit  501  outputs the signal transformed into the frequency domain, to signal extracting unit  502 . 
         [0067]    Signal extracting unit  502  extracts the Secondary Synchronization Signal from the signal input from first transform unit  501 , and outputs the extracted Secondary Synchronization Signal to S-SS detection unit  503 . Moreover, signal extracting unit  502  outputs the signal input from first transform unit  501 , to addition unit  506 . 
         [0068]    S-SS detection unit  503  detects the Cell ID group number from the Secondary Synchronization Signal input from signal extracting unit  502 , and outputs the detected Cell ID group number to S-SS generation unit  504 . Here, the Cell ID group number is a number identifying each of grouped base stations. 
         [0069]    S-SS generation unit  504  previously stores a replica of the Secondary Synchronization Signal in association with the Cell ID group number. Moreover, S-SS generation unit  504  selects the replica of the Secondary Synchronization Signal corresponding to the Cell ID group number input from S-SS detection unit  503 , and outputs the Secondary Synchronization Signal of the selected replica, to signal replacement unit  505 . 
         [0070]    Signal replacement unit  505  outputs the Secondary Synchronization Signal input from S-SS generation unit  504 , to addition unit  506 , at a timing of replacing the Secondary Synchronization Signal included in the signal received by relay apparatus  100 , with the Secondary Synchronization Signal input from S-SS generation unit  504 . On this occasion, signal replacement unit  505  replaces only the Secondary Synchronization Signal, and does not replace the signals other than the Secondary Synchronization Signal. 
         [0071]    Addition unit  506  replaces the Secondary Synchronization Signal included in the signal input from signal extracting unit  502 , with the Secondary Synchronization Signal input from signal replacement unit  505 . Then, addition unit  506  outputs the signal in which the Secondary Synchronization Signal has been replaced, to second transform unit  507 . 
         [0072]    Second transform unit  507  applies the Inverse Fast Fourier Transform to the signal input from addition unit  506 , to transform the signal from the frequency domain into the time domain. Moreover, second transform unit  507  adds a CP to the signal transformed into the time domain, and outputs the signal to radio transmitting unit  104 . 
         [0073]    In the present embodiment, relay apparatus  100  replaces Secondary Synchronization Signal # 303  of  FIG. 3 . 
         [0074]    Moreover, in order to receive the common channel information and the dedicated channel information, it is necessary to correctly receive the Secondary Synchronization Signal first. In other words, if the Secondary Synchronization Signal can be correctly received, it becomes possible to receive the common channel information and the dedicated channel information. Accordingly, it becomes possible to improve the characteristic by compensating the Secondary Synchronization Signal. It should be noted that the reason why it is easier to decode the Secondary Synchronization Signal than the dedicated channel is similar to Embodiment 1 as described above. 
         [0075]    Moreover, in the present embodiment, the detection of the Secondary Synchronization Signal in S-SS detection unit  503 , and the selection of the replica of the Secondary Synchronization Signal in S-SS generation unit  504  may be performed only once unless the Cell ID group number changes. In this case, each time a signal is input to digital signal processing unit  500 , signal replacement unit  505  repeatedly performs only the process of replacing the Secondary Synchronization Signal included in the input signal, with the selected replica. 
         [0076]    Moreover, normally, the detection of the Secondary Synchronization Signal is performed after the detection of the Primary Synchronization Signal. Accordingly, the present embodiment is preferably combined with Embodiment 2 as described above. Moreover, decoding of the PBCH signal is performed after the detection of the Primary Synchronization Signal and the Secondary Synchronization Signal. Moreover, decoding of the PDCCH signal is performed after the detection of the Primary Synchronization Signal and the Secondary Synchronization Signal, and after the decoding of the PBCH signal. Moreover, decoding of the PDSCH signal is performed after the detection of the Primary Synchronization Signal and the Secondary Synchronization Signal, and after the decoding of the PBCH signal and the PDCCH signal. Accordingly, the present embodiment is preferably combined with Embodiment 1 and Embodiment 2 as described above. 
         [0077]    In this way, according to the present embodiment, it is possible to both improve the error rate characteristic and reduce the amount of delay. In other words, according to the present embodiment, it is possible to improve the error rate characteristic as compared with the conventional repeater, and reduce the processing delay as compared with the conventional relay. Moreover, according to the present embodiment, the propagation distortions or noises can be eliminated by replacing the Secondary Synchronization Signal. Thus, the accuracy of detecting the Secondary Synchronization Signal in the communication terminal apparatus can be improved. 
       Embodiment 4 
       [0078]      FIG. 6  is a block diagram illustrating a configuration of digital signal processing unit  600  according to Embodiment 4 of the present invention. 
         [0079]    Digital signal processing unit  600  illustrated in  FIG. 6  has S-SS generation unit  601  instead of S-SS generation unit  504 , in contrast to digital signal processing unit  500  according to Embodiment 3 illustrated in  FIG. 5 . It should be noted that, in  FIG. 6 , portions identical to the configuration shown in  FIG. 5  are assigned the same reference numerals, and the explanations of the identical portions will be omitted. 
         [0080]    Digital signal processing unit  600  is mainly formed of first transform unit  501 , signal extracting unit  502 , S-SS detection unit  503 , signal replacement unit  505 , addition unit  506 , second transform unit  507 , and S-SS generation unit  601 . The portions of the configuration different from Embodiment 3 will be described below. 
         [0081]    S-SS detection unit  503  detects the Cell ID group number from the Secondary Synchronization Signal input from signal extracting unit  502 , and outputs the detected Cell ID group number to S-SS generation unit  601 . 
         [0082]    S-SS generation unit  601  previously stores the replica of the Secondary Synchronization Signal in association with the Cell ID group number. Moreover, S-SS generation unit  601  selects the replica of the Secondary Synchronization Signal corresponding to the Cell ID group number input from S-SS detection unit  503 . Moreover, S-SS generation unit  601  adds relay apparatus specific information specific to relay apparatus  100 , to the Secondary Synchronization Signal of the selected replica. On this occasion, S-SS generation unit  601  may delete identification information on the base station and add the relay apparatus specific information, or may add the relay apparatus specific information without deleting the identification information on the base station. Then, S-SS generation unit  601  outputs the Secondary Synchronization Signal to which the relay apparatus specific information has been added, to signal replacement unit  505 . 
         [0083]    Signal replacement unit  505  outputs the Secondary Synchronization Signal input from S-SS generation unit  601 , to addition unit  506 , at a timing of replacing the Secondary Synchronization Signal included in the signal received by relay apparatus  100 , with the Secondary Synchronization Signal input from S-SS generation unit  601 . On this occasion, signal replacement unit  505  replaces only the Secondary Synchronization Signal, and does not replace the signals other than the Secondary Synchronization Signal. 
         [0084]    In the present embodiment, relay apparatus  100  replaces Secondary Synchronization Signal # 303  of  FIG. 3 . 
         [0085]    In this way, according to the present embodiment, in addition to the above described effect of Embodiment 3, the communication terminal apparatus, which has received the signal transmitted from the relay apparatus, is enabled to recognize that the direct transmission source of the signal is not the base station but the relay apparatus. As a result, the communication terminal apparatus can avoid confusing the signal transmitted from the base station with the signal transmitted from the relay station and performing the wrong processing. 
       Embodiment 5 
       [0086]      FIG. 7  is a block diagram illustrating a configuration of digital signal processing unit  700  according to Embodiment 5 of the present invention. 
         [0087]    Digital signal processing unit  700  illustrated in  FIG. 7  has common information re-encoding unit  701  instead of common information re-encoding unit  205 , in contrast to digital signal processing unit  103  according to Embodiment 1 illustrated in  FIG. 2 . It should be noted that, in  FIG. 7 , the portions of the configuration identical to the configuration shown in  FIG. 2  are assigned the same reference numerals, and the explanations of the identical portions will be omitted. Moreover, in the explanation of the present embodiment, reference numerals of  FIG. 1  are used to denote the configuration of the relay apparatus except digital signal processing unit  700 . 
         [0088]    Common information decoding unit  204  decodes the common channel information input from common information demodulation unit  203 , and outputs the common channel information to common information re-encoding unit  701 . 
         [0089]    Common information re-encoding unit  701  adds a relay apparatus identifier unique to relay apparatus  100 , to the common channel information input from common information decoding unit  204 . On this occasion, common information re-encoding unit  701  may delete the identification information on the base station and add the relay apparatus identifier, or may add the relay apparatus identifier without deleting the identification information on the base station. Moreover, common information re-encoding unit  701  encodes (re-encodes) the common channel information to which the relay apparatus identifier has been added, again, and outputs the common channel information to common information re-modulation unit  206 . 
         [0090]    Common information re-modulation unit  206  modulates (re-modulates) the common channel information input from common information re-encoding unit  701 , again, and outputs the common channel information to signal replacement unit  207 . 
         [0091]    In the present embodiment, relay apparatus  100  replaces, for example, PDSCH signal # 306  of  FIG. 3 . It should be noted that while the PDSCH signal is replaced in the above embodiment, the present embodiment is not limited to this case, and one or two or more pieces of the common channel information, other than the PDSCH signal, may be replaced, or the entire common channel information including the PDSCH signal may be replaced. On this occasion, the relay apparatus identifier is added to the common channel information with which the replacement is performed. 
         [0092]    In this way, according to the present embodiment, in addition to the above described effect of Embodiment 1, the communication terminal apparatus, which has received the signal transmitted from the relay apparatus, is enabled to recognize that the direct transmission source of the signal is not the base station but the relay apparatus. As a result, it is possible to avoid confusing the signal transmitted from the base station with the signal transmitted from the relay station and performing the wrong processing. 
         [0093]    The signals of the frame in LIE are replaced in Embodiment 1 to Embodiment 5 as described above. The present invention is not limited to this case, however, and can replace signals of a frame in an optional communication system other than LTE. Moreover, the relay apparatus that relays the signal transmitted from the base station to the communication terminal apparatus is described as an example in Embodiment 1 to Embodiment 5 above. The present invention is not limited to this case, however, and can be also applied to a relay apparatus that relays a signal transmitted from the communication terminal apparatus to the base station. 
         [0094]    Moreover, the configuration using the first transform unit and the second transform unit is employed in Embodiment 1 to Embodiment 5 as described above, but the present invention is not limited to this case. For example, if the present invention is applied to a communication system not requiring the Fast Fourier Transform to perform the processing of transform from the time domain into the frequency domain, the first transform unit and the second transform unit can be omitted. 
         [0095]    The content of the disclosure of the specification, the drawings and the abstract included in Japanese Patent Application No. 2010-6924 filed on Jan. 15, 2010 is incorporated in the present application by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0096]    The relay apparatus and the relay method according to the present invention are suitable, for example, for relaying the signals transmitted and received between a base station and a communication terminal apparatus. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           103  digital signal processing unit 
           201  first transform unit 
           202  signal extracting unit 
           203  common information demodulation unit 
           204  common information decoding unit 
           205  common information re-encoding unit 
           206  common information re-modulation unit 
           207  signal replacement unit 
           208  addition unit 
           209  second transform unit