Abstract:
A method of gain control in a fiberoptic repeating system is disclosed. By the present invention, the signal levels of an optical cable can be frequently monitored without affecting the control operations of the base station. Thus, damped signal levels can effectively be compensated.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fiberoptic repeating system, and more particularly to a method for a gain control in a fiberoptic repeating system in a communication system. 
     BACKGROUND OF THE INVENTION 
     Generally, areas such as mountains, valleys and underground receive a weak transmission or are isolated completely from any radio waves due to the geographical situation. Thus, many base stations must be constructed to provide communication services in these shaded areas, requiring costly equipments and management. As the demand for communication services rises, the cost also increases, thereby creating a problem. 
     As one solution to this problems, a fiberoptic repeating system has been proposed and is currently being used commercially. However, a considerable amount of signal damping results in the optical cables of such a fiberoptic repeating system. Therefore, to compensate the signal damping, a gain control unit has also been proposed for the fiberoptic repeating system. 
     A fiberoptic repeating system in the related art generally includes a base station  1 , a master repeater  2 , and one of a plurality of a slave repeaters  3 , as shown in  FIG. 1 . The slave repeater  3  receives and/or transmits RF signals within a remote region, and the master repeater  2  relays data between the base station  2  and the slave repeater  3 . 
     More specifically, the master repeater  2  includes a driver amplifier  20  which amplifies an RF signal transmitted from the base station  1 ; an optic/RF converter  23  which converts from an amplified RF signal received through the driver amplifier  20  into an optic signal for transmission through an optical cable  4  or from an optic signal transmitted through the optical cable  4  into an RF signal; a master repeater controller  21  which monitors an operational state of the elements of the master repeater  2 , controls the operation of the master repeater  2  or the slave repeater  3  according to a control signal of the base station  1 , detects a level of RF signal amplified through the driver amplifier  20  and outputs the detected level as a digital reference value; and a MODEM  22  which modulates the output of the master repeater controller  21  and transmits the output to the slave repeater  3  side through the optic/RF converter  23 . 
     The slave repeater  3  includes an optic/RF converter  31  which converts an optic signal transmitted through the optical cable  4  into an RF signal or converts an RF signal received through a receiving antenna into an optic signal for transmission through the optical cable  4 ; a driver amplifier  30  and a high-power amplifier  34  which amplifies an output of the optic/RF converter  31 ; a low noise amplifier  35  which amplifies the RF signal received through the receiving antenna and transmits the amplified RF signal to the optic/RF converter  31 ; a MODEM  32  which demodulates the digital reference signal received through the optic/RF converter  31 ; and a slave repeater controller  33  which detects a level of the RF signal received through the optic/RF converter  31 , compares the detected level with a digital reference value transmitted through the MODEM  32 , and adjusts a gain level of the driver amplifier  30  to compensate the difference. 
     The signal transmission and reception operations in the fiberoptic system of  FIG. 1  is as follows. 
     An RF signal is received through a receiving antenna of the slave repeater  3  and is amplified by a constant level through the low noise amplifier  35 . The amplified RF signal is then transmitted to the base station  1  via the optic/RF converters  31  and  23 . Thereafter, the base station  1  transmits a corresponding RF signal to an appropriate terminal of a receiving party via the master repeater  2  and the slave repeater  3 . 
     Particularly, the RF signal transmitted by the base station  1  is amplified by a constant level through the driver amplifier  20 , and is converted into an optic signal through the optic/RF converter  23 . Also, the master repeater controller  21  periodically detects a level of the RF signal output from the driver amplifier  20 , converts the detected level into a digital MODEM RF signal level, modulates the digital MODEM RF signal level through the MODEM  22 , and transmits the modulated digital MODEM RF signal level through the optic/RF converter  23 . 
     The optic signal transmitted by the optic/RF converter  23  is demodulated into a digital MODEM RF signal through the optic/RF converter  31  and the MODEM  32  of the slave repeater  3 , and is input to the slave repeater controller  33 . The slave repeater controller  33  stores the level of the digital MODEM RF signal as a reference level. Also, the optic signal transmitted by the optic/RF converter  23  is converted into a RF signal through the optic/RF converter  31  and input to the driver amplifier  30 . Thus, the slave repeater controller  33  converts the RF signal input to the driver amplifier  30  into a digital signal, compares the level of the digital signal with the reference level, and controls a gain level of the driver amplifier  30  to compensate a damping of the RF signal level by the differential value. Accordingly, the RF signal with a compensated signal level is amplified into a radio-transmittable level by the high power amplifier  34 , and is transmitted to a corresponding terminal through the transmission antenna. 
     Furthermore, the master repeater controller  21  of the master repeater  2  and the slave repeater controller  33  of the slave repeater  3  respectively monitor the operational states of elements  20 ˜ 23  and  31 ˜ 35 . Accordingly, when a specific control signal, e.g. a gain control signal of the slave repeater  3 , is transmitted from the base station  1  to the master repeater  2 , the master repeater controller  21  modulates the corresponding gain control signal through the MODEM  22  and transmits the modulated gain control signal to the slave repeater  3 . The slave repeater controller  33  demodulates the gain control signal through the MODEM  32 , reads the content of the gain control signal and controls a gain of the driver amplifier  30 . 
     In the fiberoptic repeating system as described above, the RF signal levels are periodically detected and become reference signals for calculation of the damping rates of the RF signal levels to compensate the gain damping. Thus, the intervals for the periodic detection of the reference levels must be short in order to deal with the frequent change of the RF signal levels. As a result, the control operations of a base station cannot always be executed for each determination of the reference level within the given interval. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art. 
     A primary object of the present invention is to provide a method for a gain control of a fiberoptic repeating system capable of frequently monitoring the signal levels of an optical cable, without influencing the control operation of a base station, to thereby compensating a damping the signal levels. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
     To achieve the objects and in accordance with the purposes of the invention, as embodied and broadly described herein, a method for gain control in a fiberoptic repeating system composed of a base station, a master repeater and a slave repeater comprises: detecting MODEM modulation signal levels of the master repeater transmitted via an optical cable from a controller of the slave repeater; comparing the MODEM modulation signal levels with a reference level and calculating the differential values; and controlling a gain of the amplifier for an RF signal amplification so as to correspond to the calculated differential value, and compensating the damping of RF signals transmitted from the master repeater to the slave repeater. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
         FIG. 1  is a block diagram of a fiberoptic repeating system in the related art; 
         FIG. 2  is a block diagram of a fiberoptic repeating system in accordance with the present invention; and 
         FIGS. 3 and 4  are drawings illustrating a method according to preferred embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 2  is a block diagram showing the construction of the fiberoptic repeating system according to the present invention. Referring to  FIG. 2 , the present fiberoptic repeating system includes a master repeater  2  and a slave repeater  3  with respectively the same elements  20 ˜ 23  and  30 ˜ 35  as the master repeater  2  and the slave repeater  3  of the fiberoptic repeating system of  FIG. 1 . In the present fiberoptic repeating system, however, the amplified level of RF signal within the master repeater  2  is not detected. Also, the level of RF signal input to the driver amplifier  30  is not detected from the RF signal reception line. In the present invention, the modulated MODEM signal output by the optical/RF converter  31  is detected. 
     The remaining functions of elements  20 ˜ 23  and  30 ˜ 35  of the present fiberoptic repeating system in  FIG. 2  operates in the same manner as the corresponding elements of the fiberoptic repeating system as described with reference to  FIG. 1 . The transmission and reception operations of signals in the fiberoptic repeating system according to the present invention is as follows. 
     An RF signal is received through a receiving antenna of the slave repeater  3  and is amplified by a constant level through the low noise amplifier  35 . The amplified RF signal is then transmitted to the base station  1  via the optic/RF converters  31  and  23 . Thereafter, the base station  1  transmits a corresponding RF signal to an appropriate terminal of a receiving party via the master repeater  2  and the slave repeater  3 . 
     The RF signal transmitted by the base station  1  is amplified by a constant level through the driver amplifier  20 , and is converted into an optic signal through the optic/RF converter  23 . Also, a modulated MODEM signal of a constant level is output from the MODEM  22  unless the master repeater controller  21  transmits a control signal of the base station  1 . Thus, the modulated MODEM signal of a predetermined level is mixed with the RF signal from the driver amplifier  20  and converted into an optic signal through the optic/RF converter  23 . 
     The optic signal converted by the optic/RF converter  23  is damped by a constant level during the transmission through the optical cable  4 . The damped optical signal is converted into an electric signal, and is separated into an RF signal and a modulation MODEM signal through the optic/RF converter  31 . Subsequently, the RF signal is transmitted to a driver amplifier  30  through an interior transmission line, and the modulated MODEM signal is transmitted to the slave repeater controller  33  through the MODEM  32 . 
     In the preferred embodiment, the output level of the MODEM  22  is a predetermined value, which is known by the slave repeater controller  33 , unless the master repeater controller  21  transmits a control signal of the base station  1 . Thus, after detecting a level of the modulated MODEM signal damped through the optical cable  4 , a difference between the modulated MODEM signal level and the output level of the MODEM  22  can be obtained. 
     Because the signals are transmitted through the same optical cable  4 , the modulated MODEM signal and the RF signal are affected by a same damping rate. Accordingly, the slave repeater controller  33  controls an amplification gain of the driver amplifier  30  using the obtained difference between the modulated MODEM signal level and the output level of the MODEM  22 . Namely, the slave repeater controller  33  controls the amplification gain to increase the RF signal level by the obtained difference, thereby compensating the damped signal level. 
     Therefore, RF signal transmitted to the driver amplifier  30  is amplified by the amplification gain controlled by the slave repeater controller  33 , and is also amplified in a radio-transmissible signal level through a high power amplifier  34 . The amplified RF signal is then transmitted to a corresponding terminal through a transmission antenna. 
     The master repeater controller  21  of the master repeater  2  and the slave repeater controller  33  of the slave repeater  3  respectively monitor the operational state of elements  20 ˜ 23  and  33 ˜ 35 . Moreover, when a specific control signal, e.g. a gain control signal of the slave repeater  3 , is transmitted from the base station  1  to the master repeater  2 , the master repeater controller  21  of the master repeater  2  modulates the corresponding gain control signal through the MODEM  22  and transmits it to the slave repeater  3 . Thereafter, the slave repeater  3  demodulates it through the MODEM  32 , reads the content of the control and controls a gain of a corresponding driver amplifier  30 . 
     In sum, in the method for gain control in the fiberoptic repeating system of present invention, consequently, a MODEM modulated signal of a constant level is always detected regardless of a signal transmission from the base station. This allows a knowledge of a damping rate, and according to that, an amplification gain is controlled. Therefore, a fast gain compensation can be executed to increase the efficiency in a signal transmission. 
     The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.