Abstract:
A transmission apparatus includes: an amplifier configured to amplify a transmission signal; a calculation unit configured to calculate a standing-wave ratio based on the transmission signal and a signal from an antenna to the amplifier; and a controller configured to switch a state of the amplifier based on the state of the amplifier and the standing-wave ratio.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2012-228433 filed on Oct. 15, 2012, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiment discussed herein is related to a transmission apparatus and an output control method. 
       BACKGROUND 
       [0003]    In wireless communication system base stations, transmitters transmit wireless signals. A transmitter includes a high-frequency amplifier and an antenna coupled to an output terminal of the high-frequency amplifier through a transmission line. In a state in which impedance matching is not achieved among the high-frequency amplifier, the transmission line, and the antenna, when a wireless signal is transmitted with a large amount of power, a reflected wave obtained by reflecting, at the antenna, the wireless signal which is output from the high-frequency amplifier is input to the high-frequency amplifier. When the transmission power of a wireless signal is increased, the power of the reflected wave is also increased, resulting in damage to the high-frequency amplifier due to the reflected wave. 
         [0004]    Related art is disclosed in Japanese Laid-open Patent Publication No. 5-284047 or Japanese Laid-open Patent Publication No. 5-172879. 
       SUMMARY 
       [0005]    According to one aspect of the embodiments, a transmission apparatus includes: an amplifier configured to amplify a transmission signal; a calculation unit configured to calculate a standing-wave ratio based on the transmission signal and a signal from an antenna to the amplifier; and a controller configured to switch a state of the amplifier based on the state of the amplifier and the standing-wave ratio. 
         [0006]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0007]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  illustrates an example of a transmission apparatus; 
           [0009]      FIG. 2  illustrates an example of a process in a transmission apparatus; and 
           [0010]      FIG. 3  illustrates an example of a hardware configuration of a transmission apparatus. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0011]    To avoid damage to a high-frequency amplifier due to a reflected wave, for example, a transmitter measures the power of the reflected wave. When the measured power is larger than a certain level, it is determined that impedance matching is not achieved, and the output of the high-frequency amplifier is stopped. 
         [0012]    When the transmission power is decreased, the power of the reflected wave to be measured is also decreased. Therefore, when the transmission power is small, no impedance mismatching may be detected. Consequently, instead of the power of a reflected wave, a voltage standing wave ratio (VSWR) may be measured as an indicator of the impedance mismatching. A voltage standing wave ratio is a ratio of the power of a reflected wave to the output power of a high-frequency amplifier. A voltage standing wave ratio is used as an indicator of the impedance mismatching, whereby impedance mismatching may be detected even in a state in which the transmission power is small. 
         [0013]    However, an interfering wave from another system which is received at an antenna is not distinguishable from the reflected wave. Therefore, a high voltage standing wave ratio may be detected. Consequently, even when impedance matching is achieved, the output may be stopped, and no communication stability may be ensured. 
         [0014]    Components having the same function may be designated with an identical reference numeral, and the description may be omitted or reduced. 
         [0015]      FIG. 1  illustrates an example of a transmission apparatus. In  FIG. 1 , a transmission apparatus  10  includes a digital to analog (DA) converter  11 , an amplifier  12 , a circulator  13 , an antenna  14 , an analog to digital (AD) converter  15 , a calculation unit  16 , and an output controller  17 . The transmission apparatus  10  may be, for example, a transmission apparatus in a base station. 
         [0016]    The DA converter  11  converts a transmission signal received from an upstream apparatus, from a digital signal to an analog signal, and outputs the transmission signal which is an analog signal obtained through the conversion, to the amplifier  12 . 
         [0017]    The amplifier  12  amplifies the received transmission signal. The amplifier  12  is switched to an output state in which an amplified transmission signal is output, or a halt state in which output of an amplified transmission signal is stopped, based on a control signal from the output controller  17 . 
         [0018]    The circulator  13  is coupled to each of the amplifier  12 , the antenna  14 , and the AD converter  15 . The circulator  13  outputs a signal from a terminal corresponding to another terminal through which the signal is input. For example, the circulator  13  controls distribution of a signal. For example, a signal which is output from the amplifier  12  is output to the antenna  14 . A signal which is input from the side of the antenna  14  to the amplifier  12  is output to the AD converter  15 . 
         [0019]    The AD converter  15  converts a signal which is output from the circulator  13 , from an analog signal to a digital signal, and outputs the digital signal obtained through the conversion, to the calculation unit  16 . 
         [0020]    The calculation unit  16  calculates a standing-wave ratio based on the transmission signal and the signal which is output from the circulator  13 , for example, a signal transmitted from the antenna  14  to the amplifier  12 . For example, the calculation unit  16  calculates a voltage standing wave ratio (VSWR) based on the amplitude of the transmission signal and the amplitude of the signal which is output from the circulator  13 . A voltage standing wave ratio is a ratio of the amplitude of a signal which is output from the circulator  13  to the amplitude of a transmission signal. 
         [0021]    The output controller  17  switches the state of the amplifier  12  to an output state or the halt state, based on a first standing-wave ratio calculated in the output state of the amplifier  12 , and a second standing-wave ratio calculated in the suspend state. 
         [0022]    For example, the output controller  17  compares the first standing-wave ratio calculated in the output state of the amplifier  12  with a certain threshold. When the first standing-wave ratio is equal to or more than the certain threshold, the output controller  17  switches the state of the amplifier  12  from the output state to the suspend state. 
         [0023]    The output controller  17  compares the second standing-wave ratio calculated in the suspend state with the certain threshold. When the second standing-wave ratio is less than the certain threshold, the output controller  17  restarts the output of the amplifier  12 . When the second standing-wave ratio is equal to or more than the certain threshold, the output controller  17  continues stopping the output of the amplifier  12 . 
         [0024]    For example, the output controller  17  may include a determination unit  21  and a switching unit  22 . The comparison between a standing-wave ratio and the certain threshold is performed by the determination unit  21 , and the switching of the state of the amplifier  12  is performed based on a control signal which is output from the switching unit  22  to the amplifier  12 . 
         [0025]      FIG. 2  illustrates an example of a process in a transmission apparatus. The transmission apparatus  10  illustrated in  FIG. 1  may perform the process illustrated in  FIG. 2 . 
         [0026]    The output state of the amplifier  12  may be the normal state. In the normal state of the amplifier  12 , the calculation unit  16  calculates a standing-wave ratio based on the amplitude of a transmission signal and the amplitude of a signal which is output from the circulator  13  (in operation S 101 ). 
         [0027]    The output controller  17  determines whether or not the first standing-wave ratio calculated in the normal state of the amplifier  12  is equal to or more than the certain threshold (in operation S 102 ). 
         [0028]    If the first standing-wave ratio is equal to or more than the certain threshold (YES in operation S 102 ), the output controller  17  stops the output of the amplifier  12  (in operation S 103 ). Accordingly, the state of the amplifier  12  is switched to the suspend state. When the first standing-wave ratio is equal to or more than the certain threshold, an anomaly, for example, impedance mismatching, may occur in the transmission apparatus  10 . In this case, the output controller  17  switches the state of the amplifier  12  to the suspend state. 
         [0029]    In the suspend state of the amplifier  12 , the calculation unit  16  calculates a standing-wave ratio based on the amplitude of the transmission signal and the amplitude of the signal which is output from the circulator  13  (in operation S 104 ). 
         [0030]    The output controller  17  determines whether or not the second standing-wave ratio calculated in the suspend state of the amplifier  12  is equal to or more than the certain threshold (in operation S 105 ). 
         [0031]    If the second standing-wave ratio is less than the certain threshold (NO in operation S 105 ), the output controller  17  continues stopping the output of the amplifier  12  (in operation S 106 ). For example, in the case where a standing-wave ratio is equal to or more than the certain threshold in the output state, if switching of the amplifier  12  to the halt state causes the standing-wave ratio to be decreased, the output signal of the amplifier  12  may cause the rise in the standing-wave ratio in the normal state of the amplifier  12 . For example, in the case where a first standing-wave ratio is equal to or more than the certain threshold in the normal state of the amplifier  12 , after the amplifier  12  is switched from the normal state to the suspend state, when a second standing-wave ratio is less than the certain threshold in the suspend state, it may be determined that an anomaly exists in the transmission apparatus  10 . 
         [0032]    If the second standing-wave ratio is equal to or more than the certain threshold (YES in operation S 105 ), the output controller  17  restarts the output of the amplifier  12  (in operation S 107 ). For example, in the case where a standing-wave ratio is equal to or more than the certain threshold in the normal state and where the standing-wave ratio is still equal to or more than the certain threshold even after the amplifier  12  is switched to the halt state, the output signals of the amplifier  12  may cause the rise in the standing-wave ratio in the normal state. The rise in the standing-wave ratio in the normal state may be caused by, for example, an interfering wave from another system. In the case where a first standing-wave ratio is equal to or more than the certain threshold in the normal state, after the amplifier  12  is switched from the normal state to the suspend state, when a second standing-wave ratio is equal to or more than the certain threshold in the suspend state, it may be determined that no anomaly exists in the transmission apparatus  10 . 
         [0033]    In the transmission apparatus  10 , the calculation unit  16  calculates a standing-wave ratio based on a transmission signal and a signal transmitted from the antenna  14  to the amplifier  12 . When the first standing-wave ratio calculated in the normal state of the amplifier  12  is equal to or more than the certain threshold, the output controller  17  switches the state of the amplifier  12  from the output state to the suspend state. When the second standing-wave ratio calculated in the temporary stopped state is equal to or more than the certain threshold, the output controller  17  restarts the output of the amplifier  12 . When the second standing-wave ratio is less than the certain threshold, the output controller  17  continues stopping the output of the amplifier  12 . 
         [0034]    The output controller  17  determines whether an anomaly, for example, impedance mismatching, is present or absent in the transmission apparatus  10 , based on the first standing-wave ratio calculated in the output state and the second standing-wave ratio calculated in the suspend state. Accordingly, accuracy of the determination as to whether impedance mismatching is present or absent may be improved. When it is determined that an anomaly is present, the output controller  17  continues stopping the output of the amplifier  12 , whereby the amplifier  12  may be protected. When it is determined that an anomaly is absent, the output controller  17  restarts the output of the amplifier  12 . Even in the case where a standing-wave ratio rises, when it is recognized that the rise is caused by, for example, an interfering wave from another system and that no anomaly exists in the transmission apparatus  10 , the output of the amplifier  12  is not stopped, whereby the communication stability may be improved. 
         [0035]    The transmission apparatus  10  illustrated in  FIG. 1  may have a hardware configuration. 
         [0036]      FIG. 3  illustrates an example of a hardware configuration of a transmission apparatus. In  FIG. 3 , a transmission apparatus  100  and a transmission control apparatus  200  are illustrated. As illustrated in  FIG. 3 , the transmission apparatus  100  includes a connector  101 , a field programmable gate array (FPGA)  102 , a central processing unit (CPU)  103 , a digital to analog converter (DAC)  104 , an up converter  105 , a power amplifier (PA)  106 , a circulator  107 , a down converter  108 , and an analog to digital converter (ADC)  109 . The calculation unit  16  and the output controller  17  may correspond to integrated circuits, such as the FPGA  102  and the CPU  103 . 
         [0037]    For example, the process illustrated in  FIG. 2  may be performed by executing programs prepared in advance by a computer. For example, programs corresponding to the processes performed by the calculation unit  16  and the output controller  17  may be stored in a memory, and the CPU  103  may read out each of the programs so as to execute it as a process. 
         [0038]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.