Abstract:
Disclosed are an apparatus for controlling a wide-band signal transmission gain, which differently applies a transmission gain by the unit of an intermediate frequency (IF) at a transmitting side of a wide-band multi-IF wireless communication system which can convert multiple baseband digital signals into IF signals and thereafter, multiplex and simultaneously transmit the converted IF signals and a signal processing method of the same.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2015-0022363 filed in the Korean Intellectual Property Office on Feb. 13, 2015, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an apparatus for controlling a wide-band signal transmission gain in wireless communication systems and a signal processing method of the same, and more particularly, to an apparatus for controlling a wide-band signal transmission gain, which differently applies a transmission gain by the unit of an intermediate frequency (IF) at a transmitting side of a wide-band multi-IF wireless communication system which can convert multiple baseband digital signals into IF signals and thereafter, multiplex and simultaneously transmit the converted IF signals and a signal processing method of the same. 
     BACKGROUND ART 
     In general, at a transmitting side of a wireless communication system, a digital to analog converter (DAC) apparatus is provided, and as a result, a function to convert a digital signal into an analog signal is performed. As such, when the digital signal is converted into the analog signal, since the DAC does not perform sampling with an ideal impulse signal but performs sampling in a sample and hold scheme, an amplitude of a frequency response is not flat and drops like a sync waveform as illustrated in  FIG. 1 . 
     In this case, like {circle around (1)} and {circle around (2)} of  FIG. 1 , in the case of a narrow-band signal having a relatively small bandwidth, attenuation does not frequently occur in a whole frequency band interval, but like {circle around (3)}, attenuation of several dB occurs in a wide-band signal having a large bandwidth. 
     As a result, a system in which a wide-band multi-IF signal is transmitted has a frequency response characteristic, in which when respective IF signals are sampled through the DAC, as the frequency becomes high, the amplitude of the signal is further attenuated. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a method and an apparatus which prevent frequency response characteristics of intermediate frequency signals from being attenuated even after a multi-intermediate frequency signal passes through a DAC. 
     An exemplary embodiment of the present invention provides an apparatus for controlling a wide-band signal transmission gain, including: a baseband processor generating a plurality of baseband digital signals and outputting the generated baseband digital signals by controlling gains of the generated baseband digital signals; a multi-IF converter converting the plurality of baseband digital signals output from the baseband processor into digital IF signals and multiplexing the converted digital IF signals and outputting the multiplexed digital IF signals; and a digital-to-analog converter converting the multiplexed digital IF signals output from the multi-IF converter into analog IF signals. 
     Another exemplary embodiment of the present invention provides a signal processing method of an apparatus for controlling a wide-band signal transmission gain, including: generating a plurality of baseband digital signals; controlling gains of the plurality of generated baseband digital signals; converting the baseband digital signals having the controlled gains into digital IF signals; multiplexing the converted digital IF signals; and converting the multiplexed digital IF signals into analog IF signals. 
     According to exemplary embodiments of the present invention, even after a multiple intermediate frequency signal passes through a DAC, frequency response characteristics of intermediate frequency signals are prevented from being attenuated. 
     The exemplary embodiments of the present invention are illustrative only, and various modifications, changes, substitutions, and additions may be made without departing from the technical spirit and scope of the appended claims by those skilled in the art, and it will be appreciated that the modifications and changes are included in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a frequency response characteristic depending on DAC sampling in the related art. 
         FIG. 2  is a configuration diagram illustrating a configuration of an apparatus for controlling a transmission gain according to an exemplary embodiment of the present invention. 
         FIG. 3  is a configuration diagram illustrating, in more detail, a configuration of a baseband processor in  FIG. 2 . 
         FIG. 4  is a flowchart for describing a method for controlling a transmission gain according to an exemplary embodiment of the present invention. 
         FIG. 5  is a diagram illustrating a frequency response characteristic depending on DAC sampling after controlling a transmission gain according to the present invention. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION 
     Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be interpreted as being limited to typical or dictionary meanings, but should be interpreted as having meanings and concepts which comply with the technical spirit of the present invention, based on the principle that an inventor can appropriately define the concept of the term to describe his/her own invention in the best manner Therefore, configurations illustrated in the embodiments and drawings disclosed in the present specification are only the most preferred embodiment of the present invention and do not represent all of the technical spirit of the present invention, and thus it is to be understood that various equivalents and modified examples, which may replace the configurations, are possible when filing the present application. 
       FIG. 2  is a configuration diagram illustrating a configuration of an apparatus for controlling a transmission gain according to an exemplary embodiment of the present invention, which may be applied to a mobile front hole base station system configuring an intermediate frequency over fiber (IFoF) link for transmitting a multiple intermediate frequency (IF) signal. 
     The apparatus for controlling the transmission gain of  FIG. 2  includes a baseband processor  100 , a multiple intermediate frequency converter  200 , and a digital to analog converter (DAC)  300 . 
     The baseband processor  100  individually generates a plurality of digital signals which are baseband-processed and individually controls transmission gains for the plurality of baseband digital signals according to an amplitude characteristic of a frequency response depending on a sampling scheme of the digital-to-analog converter  300  and outputs the controlled transmission gains to the multiple intermediate frequency converter  200 . That is, the amplitude characteristic of the frequency response depending on the sampling scheme of the digital-to-analog converter  300 , that is, information on attenuation amounts for respective intermediate frequencies generated while the multiple intermediate frequency signal passes through the digital-to-analog converter  300  is configured in the baseband processor  100  and the baseband processor  100  individually preamplifies the respective baseband digital signals to correspond to an attenuation amount for each predetermined intermediate frequency and outputs the amplified digital signals to the multiple intermediate frequency converter  200 . 
     The multi-IF converter  200  allocates different intermediate frequencies to the plurality of respective baseband digital signals output from the baseband processor  100  and converts the baseband digital signals into digital IF signals and multiplexes the converted digital IF signals and outputs the multiplexed digital IF signals to the digital-to-analog converter  300 . That is, the multi-IF converter  200  generates a multiplexed IF wide-band signal to be output to the digital-to-analog converter  300 . 
     The digital-to-analog converter (DAC)  300  converts the multiplexed digital IF signal (multi-IF signal) into an analog IF signal. 
       FIG. 3  is a configuration diagram illustrating, in more detail, a configuration of a baseband processor  100  in  FIG. 2 . 
     The baseband processor  100  includes a plurality of modems  112 ,  114 , . . . ,  116 , a plurality of amplifiers  122 ,  124 , . . . ,  126 , and a transmission gain controller  130 . 
     The plurality of modems  112 ,  114 , . . . ,  116  converts communication signals (subscriber signals) applied from subscribers into baseband digital signals, respectively and outputs the baseband digital signals. 
     The plurality of amplifiers  122 ,  124 , . . . ,  126  is provided to correspond to the plurality of modems  112 ,  114 , . . . ,  116  one to one and each of the amplifiers  122 ,  124 , . . . ,  126  amplifies the baseband digital signal output from each of the modems  112 ,  114 , . . . ,  116  corresponding thereto according to a gain control signal from the transmission gain controller  130  and outputs the amplified baseband digital signal to the multi-IF converter  20 . That is, the amplifiers  122 ,  124 , . . . ,  126  digitally increase gains of the baseband digital signals corresponding thereto, respectively. 
     The transmission gain controller  130  generates gain control signals for individually controlling magnitudes of the baseband digital signals corresponding to the respective IFs according to an attenuation amount for each predetermined IF and outputs the generated gain control signals to the amplifiers  122 ,  124 , . . . ,  126 . That is, the transmission gain controller  130  generates a gain control signal for previously increasing the magnitude of each baseband digital signal by an attenuation amount to correspond to the amount attenuated while the signal of each IF of the multiplexed digital IF signal output from the multi-IF converter  200  passes through the digital-to-analog converter  300  and outputs the generated gain control signal to the amplifiers  122 ,  124 , . . . ,  126 . In this case, the attenuation amount for each IF as an amount attenuated while the digital IF signals pass through the DAC  300  due to an amplitude characteristic of a frequency response depending on a sampling scheme of the DAC is determined by a unique characteristic value of the DAC  300 . Therefore, the attenuation amount for each IF may depend on the DAC  300  used in the wireless communication systems and is previously calculated and set at the time of designing the system. 
       FIG. 4  is a flowchart for describing a method for controlling a transmission gain according to an exemplary embodiment of the present invention. 
     When the DAC  300  to be used in the apparatus for controlling the transmission gain of  FIG. 3  is selected, the amplitude characteristic of the frequency response depending on the sampling scheme of the DAC  300  is calculated (step  410 ). 
     An attenuation amount of the magnitude (amplitude) of the digital IF signal is verified by the DAC  300  for each IF of the multi-IF converter  200  by using the amplitude characteristic of the frequency response calculated in step  410  to store and set information on the attenuation amount in a memory (not illustrated) (step  420 ). 
     For example, in the case of the frequency response illustrated in  FIG. 1 , representative values of frequency responses to IFs IF 1 , IF 2 , . . . , IFn are −0.2 dB, −0.8 dB, . . . , −2.5 dB, respectively. That is, it can be seen that digital IF signals having the IFs IF 1 , IF 2 , . . . , IFn are attenuated by 0.2 dB, 0.8 dB, . . . , 2.5 dB, respectively while passing through the DAC  300 . 
     The attenuation amount for each IF by the DAC  300  is calculated and stored in advance. 
     When the wireless communication systems operate, the transmission gain controller  300  generates gain control signals for controlling magnitudes of baseband digital signals corresponding to the respective IFs IF 1 , IF 2 , . . . , IFn by using the information on the attenuation amount for each predetermined IF in step  420  and thereafter, outputs the generated gain control signals to amplifiers  122 ,  124 , . . . ,  126  corresponding thereto (step  430 ). 
     That is, gain control signals instructing the magnitudes of the baseband digital signals corresponding to the respective IFs IF 1 , IF 2 , . . . , IFn to be amplified by the corresponding attenuation amount according to the attenuation amounts of the respective IFs IF 1 , IF 2 , . . . , IFn attenuated by the DAC  300  are applied to the respective amplifiers  122 ,  124 , . . . ,  126 . 
     The amplifiers  122 ,  124 , . . . ,  126  that receive the gain control signals from the transmission gain controller  130  amplify the input baseband digital signals according to the gain control signals to increase gains and thereafter, outputs the baseband digital signals having the increased gains to the multi-IF converter  200  (step  440 ). 
     For example, when the DAC  300  has the frequency response as illustrated in  FIG. 1 , the baseband digital signal corresponding to the IF IF 1  is amplified by 0.2 dB, the baseband digital signal corresponding to the IF IF 2  is amplified by 0.8 dB, and the baseband digital signal corresponding to the IF IFn is amplified by 2.5 dB. 
       FIG. 5  is a diagram illustrating a frequency response characteristic depending on sampling of a DAC  300  after controlling a transmission gain according to the present invention. 
     The magnitudes of the baseband digital signals corresponding to the respective intermediate frequencies IFs IF 1 , IF 2 , . . . , IFn are, in advance, amplified by the amounts to be attenuated by the DAC  300 , and as a result, a previously amplified amount and the amount attenuated by the DAC  300  are offset. Therefore, the amplitudes of the frequency responses of the signals output from the DAC  300  are flattened as illustrated in  FIG. 5 . 
     The exemplary embodiments of the present invention are illustrative only, and various modifications, changes, substitutions, and additions may be made without departing from the technical spirit and scope of the appended claims by those skilled in the art, and it will be appreciated that the modifications and changes are included in the appended claims.