Abstract:
In a mobile communication service system, a repeater is installed to cover a shadow area. Provided is a radio frequency (RF) repeater that may select between an interference cancellation device and a software-defined radio (SDR) device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority from Korean Patent Application No. 10-2016-0026808, filed on Mar. 4, 2016, in the Korean Intellectual Property Office, the contents of which are incorporated herein by reference in their entirety. 
       BACKGROUND 
       [0002]    Field 
         [0003]    One or more example embodiments relate to a radio frequency (RF) repeater, and more particularly, to an RF repeater that may select between an interference cancellation device and a software-defined radio (SDR) device. 
         [0004]    Description of Related Art 
         [0005]    In a mobile communication system, repeaters are installed to cover shadow areas. Among the repeaters, there may be a repeater not having an interference cancellation function. In a case in which signals between input and output antennas of the repeater are not isolated, a signal output from the output antenna is fed back to the input antenna of the repeater, whereby oscillation is caused by the feedback signal. In this example, signals may not be serviced smoothly and products may be damaged. When a repeater is installed in an environment where oscillation occurs, the repeater decreases an output strength and outputs low-strength signals, which creates another shadow area. 
         [0006]    To solve such issues, an existing interference cancellation repeater has restricted resources for digital signal processing and limits of sampling, and thus may not be installed, operate, and perform an interference cancellation function properly in a frequency environment where various preferred frequency signals and non-preferred frequency signals coexist in a wide band. 
       SUMMARY 
       [0007]    Herein, an RF repeater is suggested to solve such issues. 
         [0008]    An aspect provides a repeater that may use an interference cancellation device to secure a service radius irrespective of an insufficient distance between antennas in a suburb or island area where a frequency environment is relatively less complex, and may select a software-defined radio (SDR) device suitable for an urban environment when complex frequency processing takes priority over interference cancellation in a service environment where a frequency environment is relatively complex, like an urban or a dense urban area. 
         [0009]    According to an aspect, there is provided a radio frequency (RF) repeater including an RF down-converter configured to receive an analog signal and perform frequency down-conversion, a digitizer configured to perform digital signal processing, and an RF up-converter configured to perform frequency up-conversion to generate a signal with a frequency equal to that of the received analog signal and transmit the generated signal. 
         [0010]    The digitizer may include an interference cancellation digitizer configured to perform interference cancellation, and an SDR digitizer configured to filter and process a complex frequency. 
         [0011]    The interference cancellation digitizer may include an analog-to-digital converter (ADC) configured to convert an analog signal into a digital signal, an interference cancellation digital processor configured to determine whether a feedback signal is present by analyzing a correlation between the digital signal and a temporary previously transmitted signal, and to cancel the feedback signal when the feedback signal is present, and a digital-to-analog converter (DAC) configured to convert a signal output from the interference cancellation digital processor into an analog signal to be transmitted. 
         [0012]    The SDR digitizer may include an ADC configured to convert an analog signal into a digital signal, an SDR digital processor configured to block a frequency signal component of an unnecessary channel in the digital signal and allow a frequency signal component of a necessary channel in the digital signal to pass through digital filtering, and to perform channel equalization through channel level control, and a DAC configured to convert a signal output from the SDR digital processor into an analog signal to be transmitted. 
         [0013]    The RF repeater may further include a controller configured to select a desired route between the interference cancellation digitizer and the SDR digitizer, perform setting with respect to frequency processing, select a route of the RF down-converter and a route of the RF up-converter, perform setting with respect to frequency processing, and a variety of controls, and a power supply configured to supply power to each part in a system. 
         [0014]    Additional aspects of example embodiments will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure. 
         [0015]    According to an example embodiment, by selecting a device suitable for a frequency environment of an installation site, a quality of communication service may be improved, irrespective of restrictions in the frequency environment. 
         [0016]    According to an example embodiment, there is provided technology that may secure a relatively wide service radius by selecting an SDR device suitable for channel setting in a complex frequency environment when a repeater is installed in an urban frequency environment where adjacent and non-adjacent signals coexist complicatedly in a band, and selecting an interference cancellation device when the repeater is installed in a suburb where a frequency environment is relatively simple. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    These and/or other aspects, features, and advantages of the disclosure will become apparent and more readily appreciated from the following description of example embodiments, taken in conjunction with the accompanying drawings of which: 
           [0018]      FIG. 1  is a diagram illustrating an interference cancellation repeater; 
           [0019]      FIG. 2  is a diagram illustrating a configuration of the interference cancellation repeater of  FIG. 1 ; 
           [0020]      FIG. 3  is a diagram illustrating an example of applying a general interference cancellation repeater to a complex frequency environment; 
           [0021]      FIG. 4  is a diagram illustrating a radio frequency (RF) repeater according to an example embodiment; 
           [0022]      FIG. 5  is a diagram illustrating an example of applying an RF repeater in a complex frequency environment according to an example embodiment; 
           [0023]      FIG. 6  is a diagram illustrating a configuration of an RF repeater according to an example embodiment; 
           [0024]      FIG. 7  is a diagram illustrating a software-defined radio (SDR) processor of an RF repeater according to an example embodiment; 
           [0025]      FIGS. 8A, 8B, and 8C  are diagrams illustrating configurations of RF down-converters according to example embodiments; and 
           [0026]      FIGS. 9A, 9B, and 9C  are diagrams illustrating configurations of RF up-converters according to example embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Hereinafter, example embodiments will be described in detail with reference to the accompanying drawings. Duplicated description and detailed description related to a known function or configuration which may make the purpose of the present disclosure unnecessarily ambiguous will be omitted here. The example embodiments are provided to more fully explain the present disclosure to those having ordinary knowledge in the art to which the present disclosure pertains. Accordingly, shapes and sizes of elements in the drawings may be exaggerated for the purpose of clarity. 
         [0028]    The example embodiments are provided to more fully describe the present disclosure to those having ordinary knowledge in the art to which the present disclosure pertains. The example embodiments may be modified in many different forms and the scope of the present disclosure should not be construed as limited to the example embodiments set forth herein; rather, these example embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. 
         [0029]    In describing the example embodiments, when it is determined detailed description related to a related known function or configuration may make the purpose of the present disclosure unnecessarily ambiguous, the detailed description will be omitted here. Moreover, it is also noted that, although reference numerals are used in the following description, they are used only to distinguish one element from another element. Further, it should be noted that if it is described in the specification that one element is “connected,” “coupled,” or “joined” to another element, the one element may be “directly connected,” “directly coupled,” or “directly joined” to the other element. However, unless otherwise specified, it should be understood that an intervening element may be present. 
         [0030]    The terminologies used herein are used to appropriately describe the example embodiments, and thus may be changed depending on a user, the intent of an operator, or a custom. 
         [0031]    Accordingly, the terminologies should be defined based on the following overall description of this specification. Like reference numerals refer to the like elements throughout the description of the figures. 
         [0032]      FIG. 1  is a diagram illustrating an existing general interference cancellation repeater  1   a . The interference cancellation repeater  1   a  is a repeater that cancels oscillation occurring through a repetitive cycle process in which a signal output by amplifying an input signal is fed back as an input such that the original input signal and the feedback signal are combined and amplified. In general, to prevent oscillation in a repeater, a gain of the repeater needs to be restricted to be at least 15 decibels (dB) lower than antenna isolation. The interference cancellation repeater  1   a  may set a higher gain by cancelling oscillation. 
         [0033]      FIG. 2  is a diagram illustrating a configuration of the general interference cancellation repeater  1   a . When a radio frequency (RF) signal is received through an antenna, an RF down-converter  10  generates an intermediate frequency (IF) signal by performing frequency down-conversion with respect to the received RF signal. The generated IF signal is input into an analog-to-digital converter (ADC)  21 , and converted into a digital signal by the ADC  21 . The digital signal is input into an interference canceller  22 , and a feedback signal is removed from the digital signal. The feedback-removed digital signal is input into a digital-to-analog converter (DAC)  23 , and converted into an analog signal by the DAC  23 . The analog signal is input into an RF up-converter  60 . The RF up-converter  60  performs frequency up-conversion and amplification with respect to the input analog signal. The amplified signal is output through another antenna. 
         [0034]      FIG. 3  is a diagram illustrating an example of applying a general interference cancellation repeater to a complex frequency environment. Referring to  FIG. 3 , a service signal  3   a  of a base transceiver system (BTS)  2   a  that services five service channels is an example of a source signal serviced in a complex radio wave and frequency environment, for example, a downtown area. The service signal  3   a  is altered into a signal  3   b  with a changed level for each service channel due to distortion caused by fading in a wireless section  4   a.    
         [0035]    The signal  3   b  is altered into a signal  6   a  mixed with interference by being synthesized  5   a  with a frequency interference signal  4   b  including signals serviced by another provider and various adjacent interference signals, and the signal  6   a  is input into the interference cancellation repeater  1   a . The interference cancellation repeater  1   a  amplifies the signal  6   a , and outputs an amplified mixed signal  7   a . The interference cancellation repeater  1   a  regards the mixed signal  6   a  as the original reference signal, and amplifies the mixed signal  7   a  from which oscillation is cancelled without removing components of the frequency interference signal  4   b . The amplified output signal includes the interference signals and the service signals together, and has a distortion of level for each channel of the service signals. Thus, the existing general interference cancellation repeater  1   a  may not improve a quality of service and secure a service radius. 
         [0036]      FIG. 4  is a diagram illustrating an RF repeater according to an example embodiment. 
         [0037]    An RF signal received from the BTS  2   a  undergoes frequency down-conversion through an RF down-converter  100 , and is transmitted to an interference cancellation digitizer  200  or an SDR digitizer  300  of a digitizer  900 . When a route to the interference cancellation digitizer  200  is selected by a controller  400 , an ADC  210  of the interference cancellation digitizer  200  converts the received signal into a digital signal, and a feedback cancellation processor  220  cancels feedback interference from the digital signal. A DAC  230  converts the interference-cancelled digital signal into an analog signal and transmits the analog signal to an RF up-converter  600 . When a route to the SDR digitizer  300  is selected by the controller  400 , the output signal of the RF down-converter  100  is transmitted to an ADC  310 . The ADC  310  converts the received signal into a digital signal. An SDR processor  320  performs channel filtering through a channel filter, and performs equalization by adjusting a level for each channel through an equalizer. The equalized signal is transmitted to a DAC  330 . The DAC  330  converts the received signal into an analog signal, and transmits the analog signal to the RF up-converter  600 . When one of the route to the interference cancellation digitizer  200  and the route to the SDR digitizer  300  is selected by the controller  400 , the RF up-converter  600  performs frequency up-conversion and level amplification with respect to the received signal, and outputs the amplified signal through an antenna. 
         [0038]    An operation of the channel filter may be set through a control program linked with the controller  400  to select a channel to be filtered, set a bandwidth, and select a roll-off value. 
         [0039]    An operation of the equalizer may be set through the control program linked with the controller  400  to determine whether levels are to be equalized based on a level of a lowest-level channel, a highest level, or a reference value desired for each channel. 
         [0040]      FIG. 5  is a diagram illustrating an example of applying an RF repeater in a complex frequency environment according to an example embodiment. 
         [0041]    The general interference cancellation repeater  1   a  regards the mixed signal  6   a  as the original reference signal, amplifies the mixed signal  6   a  from which oscillation is cancelled, and outputs the mixed signal  7   a . However, an improved RF repeater  1   b  of  FIG. 5  outputs a signal  7 - 1   a  with a uniform level for each channel by removing components of the frequency interference signal  4   b  and equalizing channels, thereby improving a quality of service. 
         [0042]      FIG. 6  is a diagram illustrating a configuration of an RF repeater according to an example embodiment. 
         [0043]    The RF repeater  1   b  includes an RF down-converter  1000  configured to perform frequency down-conversion and gain control with respect to an RF signal received from a BTS and transmit the signal to an interference cancellation digitizer  2000  or an SDR digitizer  3000  of a digitizer  9000 , the interference cancellation digitizer  2000 , the SDR digitizer  3000 , an RF up-converter  6000  configured to perform frequency up-conversion and gain control, a controller  4000 , and a power supply  5000 . 
         [0044]    The interference cancellation digitizer  2000  includes an ADC  2100 , a feedback cancellation processor  2200  configured to cancel feedback interference, a DAC  2300 , a feedback cancellation digital power supply  2500  configured to supply power to the interference cancellation digitizer  2000 , and an interference cancellation power switch  2600  configured to interrupt power of the interference cancellation digital power supply  2500 . 
         [0045]    The SDR digitizer  3000  includes an ADC  3100 , an SDR processor  3200  configured to perform channel filtering and equalization of a level for each channel based on user settings, a DAC  3300 , an SDR digital power supply  3500  configured to supply power to the SDR digitizer  3000 , and an SDR power switch  3600  configured to interrupt power of the SDR digital power supply  3500 . 
         [0046]    The interference cancellation power switch  2600  and the SDR power switch  3600  are switches to be controlled based on a control signal, and connected to the power supply  5000  for power supply. The interference cancellation power switch  2600  and the SDR power switch  3600  are interrupted based on user settings through the controller  4000  via control lines electrically connected to the controller  4000 . When a user selects the interference cancellation digitizer  2000 , the interference cancellation power switch  2600  is turned on. When the user selects the SDR digitizer  3000 , the SDR power switch  3600  is turned on. 
         [0047]    The interference cancellation digitizer  2000  and the SDR digitizer  3000  are electrically connected to the controller  4000 . Thus, set values thereof may be changed based on user settings, and power interruption may be controlled. Referring to the RF down-converter  1000  of  FIG. 8A , an RF gain controller  1001  performs low-noise amplification and gain control with respect to an RF signal received from the BTS  2   a , and transmits the RF signal to a mixer  1002 . The mixer  1002  outputs an IF signal corresponding to a local oscillation (LO) frequency based on the LO frequency output from a phase lock loop (PLL)  1003  through a control signal of the controller  400  by user settings. In this example, when a user sets the interference cancellation digitizer  2000  to operate through the controller  4000 , the PLL  1003  outputs an LO_ 1  frequency signal and the mixer  1002  outputs an IF_ 1  signal. When the user sets the SDR digitizer  2000  to operate, the PLL  1003  outputs an LO_ 2  frequency signal and the mixer  1002  outputs an IF_ 2  signal. 
         [0048]    When the interference cancellation digitizer  2000  is selected through the controller  4000  based on the user settings, switches  1004 ,  1007 , and  1009  each operates at a first contact point. When the SDR digitizer  3000  is selected, the switches  1004 ,  1007 , and  1009  each operates at a second contact point. 
         [0049]    A band-pass filter (BPF) performs filtering. When the interference cancellation digitizer  2000  is selected, the IF_ 1  signal output from the mixer  1002  is filtered through a BPF_ 1   1005 . When the SDR digitizer  3000  is selected, the IF_ 2  signal output from the mixer  1002  is filtered through a BPF_ 2   1006 . 
         [0050]    The IF signal passing through the BPF  1005  or  1006  undergoes gain amplification and control, and is output via a route selected using the switch  1009 . 
         [0051]    The BPF  1005  or  1006  may be omitted if unnecessary depending on an implementation situation. 
         [0052]    In other examples of RF down-converters of  FIGS. 8B and 8C , a direct conversion scheme in which an RF signal is input directly into the ADC  2100  or  3100  is used rather than an IF scheme, depending on an implementation situation of the digitizer  9000 . A route from an RF down-converter  1000 - 2  or  1000 - 3  to the ADC  2100  or  3100  using the direct conversion scheme does not include a mixer and a PLL. The route is set by selecting the route using a switch  1014  or  1024 . The RF up-converter  6000  performs frequency up-conversion and gain control with respect to the signal transmitted from the DAC  2300  of the interference cancellation digitizer  2000  or the DAC  3300  of the SDR digitizer  3000 , and outputs the corresponding signal through an antenna. 
         [0053]      FIG. 9A  illustrates an RF up-converter  6000 - 1 . In detail,  FIG. 9A  illustrates an example in which an input frequency of the ACD  2100  of the interference cancellation digitizer  2000  is equal to an output frequency of the DAC  2300 , and an input frequency of the ADC  3100  of the SDR digitizer  3000  is equal to an output frequency of the DAC  3300 . When a signal corresponding to a route selected by a user is input through the DAC  2300  or  3300 , a switch  6005  operates at a contact point of the corresponding route based on a control of the controller  4000 , and a mixer  6006  performs frequency up-conversion with respect to the input signal into an RF signal based on an LO frequency signal provided from a PLL_ 2   6009 , performs filtering, gain amplification, and level adjustment, and outputs the corresponding signal. 
         [0054]      FIG. 9B  illustrates an RF up-converter  6000 - 2 . In detail,  FIG. 9B  illustrates an example in which an output frequency of the DAC  2300  of the interference cancellation digitizer  2000  is an RF equal to an input frequency of the RF down-converter  1000  in a case in which a frequency direct conversion scheme is used, and an output frequency of the DAC  3300  of the SDR digitizer  3000  is an IF. The example of  FIG. 9B  also includes a case in which one of the output frequencies of the DAC  2300  and the DAC  3300  is an IF, and the other is an RF.  FIG 9C  illustrates an RF up-converter  6000 - 3 . In detail,  FIG. 9C  illustrates an example in which an output frequency of the DAC  2300  or  3300  is an RF equal to an input frequency of the RF down-converter  1000 . 
         [0055]    When a user selects an operation of the interference cancellation digitizer  2000  or the SDR digitizer  3000  through a control program, the controller  4000  controls the corresponding power switch  2600  or  3600 , controls a frequency and a route of the RF down-converter  1000 , and controls a frequency and a route of the RF up-converter  6000 ,  6000 - 1 ,  6000 - 2 , or  6000 - 3 . 
         [0056]    In other embodiments, the various features discussed with respect to each embodiment above can be combined in various different ways. In still other embodiments, other modifications may be made, while still implementing the concepts and features discussed above with respect to the various example embodiments. 
         [0057]    While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is instead intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.