Abstract:
An optical network is provided. The optical network includes a station to convert a downstream radio frequency (RF) signal to a downstream optical signal and convert an upstream optical signal to an upstream RF signal; and a remote access unit (RAU) to convert the downstream optical signal to a downstream RF signal and to convert the upstream RF signal to the upstream optical signal, wherein the RAU determines a non-transmission band portion on which data is not carried from the downstream RF signal and inputs upstream data in the non-transmission band.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. § 119 to an application entitled “Optical Network for Bi-Directional Wireless Communication,” filed in the Korean Intellectual Property Office on Jan. 26, 2006 and assigned Serial No. 2006-8306, the contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to bi-directional wireless communication and in particular, to a bi-directional wireless communication network in which optical fiber and wireless communication are coupled. 
         [0004]    2. Description of the Related Art 
         [0005]    When using various wireless communication media, such as 2G, 3G, wireless local area network (WLAN), wireless Internet communication, and portable broadcasting, a large area/space is needed to construct base stations and/or relay stations. To optimize the area for a base station or a relay station, it is necessary to accommodate the various wireless communication media in an in-building type solution. Such a solution is commonly used for base stations and/or relay stations an existing optical communication networks. In an optical network for a radio over fiber (ROF) scheme wherein optical communication uses an optical fiber in a certain section and a wireless communication method in another section are combined have been suggested. The optical network of the ROF scheme can use heterogeneous data transmission methods, such as time division multiplexing (TDM) and sub-carrier multiplexing. Such heterogeneous data transmission methods are applied to various communication media and improve communication capacity and rate. 
         [0006]      FIG. 1  is a schematic diagram of a conventional optical network  100  for wireless communication. Referring to  FIG. 1 , the conventional optical network  100  includes a central station (CS)  110 , and a remote access unit (RAU)  120  linked to the CS  110  through an optical fiber. 
         [0007]    The CS  110  includes an electro-optic converter  111  and an opto-electric converter  112 . The electro-optic converter  111  converts a downstream radio frequency (RF) signal to a downstream optical signal. The opto-electric converter  112  converts an upstream optical signal input from the RAU  120  to an upstream RF signal. Each of the downstream and upstream optical signals is composed of a timeslot, a sub-carrier, and a broadcasting channel. 
         [0008]    The RAU  120  includes an opto-electric converter  121  to convert the downstream optical signal to the downstream RF signal, a first amplifier  123  to amplify the downstream RF signal, a second amplifier  124  to amplify the upstream RF signal, an electro-optic converter  122  convert the amplified upstream RF signal to the upstream optical signal and output the converted upstream optical signal to the CS  110 , an antenna  126  to receive the upstream RF signal and transmit the downstream RF signal, and a circulator  125  to output the downstream RF signal to the antenna  126  and output the upstream RF signal to the second amplifier  124 . 
         [0009]      FIG. 2  is a schematic diagram of another conventional optical network  200 . Referring to  FIG. 2 , the conventional optical network  200  includes a CS  210  and an RAU  220 , which are linked to each other through an optical fiber. 
         [0010]    The CS  210  includes an electro-optic converter  211  to convert a downstream RF signal to a downstream optical signal and an opto-electric converter  212  to detect data by converting an upstream optical signal to an upstream RF signal. The downstream optical signal is composed of TDM timeslots, sub-carrier channels, a broadcasting channel, and a control signal. The upstream optical signal is composed of upstream timeslots and sub-carrier channels. 
         [0011]    The RAU  220  includes an opto-electric converter  221  to convert the downstream optical signal to the downstream RF signal, an antenna  232  to transmit the downstream RF signal and receive the upstream RF signal, an electro-optic converter  222  to convert the upstream RF signal to the upstream optical signal, first and second amplifiers  225  and  231 , a demultiplexer  223 , a controller  224 , first to third couplers  226 ,  228 , and  227 , and a switch  229 . 
         [0012]    The demultiplexer  223  extracts only a control signal from the downstream RF signal and outputs the extracted control signal to the controller  224 . The controller  224  controls the switch  229  to alternatively input and output upstream and downstream timeslots. The first coupler  226  separates the downstream RF signal into a broadcasting channel, a sub-carrier channel, and a timeslot and outputs the separated timeslot to the switch  229 . The separated sub-carrier channel is input to the second coupler  228  through the third coupler  227 . The separated broadcasting channel is directly input to the second coupler  228 . 
         [0013]    The second coupler  228  couples the downstream timeslot, sub-carrier channel, and broadcasting channel into the downstream RF signal and outputs the downstream RF signal to the antenna  232 . In addition, the second coupler  228  separates the upstream RF signal input from the antenna  232  into upstream sub-carrier channel and timeslot. The upstream timeslot separated by the second coupler  228  is input to the second amplifier  231  through the switch  229 . The upstream sub-carrier channel is directly input to the second amplifier  231 . 
         [0014]    The controller  224  controls the switch  229  using a control signal. The switch  229  inputs/outputs the upstream and downstream timeslot(s), which are not overlapped. 
         [0015]    However, when the timeslot and sub-carrier channel are used without being separated, there may be a problem of degradation due to mutual interference. In addition, when the timeslot and sub-carrier channel are separated and used, a separate control signal must be provided not to overlap the upstream and downstream timeslots. 
       SUMMARY OF THE INVENTION 
       [0016]    An object of the present invention is to substantially reduce or solve at least the above problems and/or disadvantages in the art. Accordingly, an object of the present invention is to provide a bi-directional wireless communication optical network for preventing degradation without a control signal. 
         [0017]    According to the principles of the present invention, an optical network is provided includes a station to convert a downstream radio frequency (RF) signal to a downstream optical signal and convert an upstream optical signal to an upstream RF signal; and a remote access unit (RAU) to convert the downstream optical signal to a downstream RF signal and to convert the upstream RF signal to the upstream optical signal, wherein the RAU determines a non-transmission band portion on which data is not carried from the downstream RF signal and inputs upstream data in the non-transmission band. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawing in which: 
           [0019]      FIG. 1  is a schematic diagram of a conventional optical network for wireless communication: 
           [0020]      FIG. 2  is a schematic diagram of another conventional optical network; 
           [0021]      FIG. 3  is a schematic diagram of an optical network for bi-directional wireless communication according to a preferred embodiment of the present invention; 
           [0022]      FIG. 4  is a block diagram of a controller of  FIG. 3 ; and 
           [0023]      FIG. 5  is a diagram showing a downstream timeslot input to the controller of  FIG. 3  and a downstream timeslot output from a signal extractor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. For the purposes of clarity and simplicity, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
         [0025]      FIG. 3  is a schematic diagram of an optical network  300  for bi-directional wireless communication according to a preferred embodiment of the present invention. Referring to  FIG. 3 , the optical network  300  includes a station  310 , hereinafter central station (CS)  310 , to convert a downstream RF signal (composed of downstream channel and timeslot) to a downstream optical signal and convert an upstream optical signal to an upstream RF signal (composed of upstream channel and timeslot) and an RAU  320  to convert the downstream optical signal input from the CS  310  to a downstream RF signal and transmit the downstream RF signal and to convert the upstream RF signal received in a wireless manner to the upstream optical signal and transmit the upstream optical signal to the CS  310 . 
         [0026]    The CS  310  includes a downstream electro-optic converter  311  to convert the downstream RF signal to the downstream optical signal and an upstream converter  312  to convert the upstream optical signal to the upstream RF signal. The CS  310  can be linked to the RAU  320  through a wired line such as an optical fiber. 
         [0027]    The RAU  320  includes a downstream opto-electric converter  321 , an upstream electro-optic converter  322 , first to third couplers  325 ,  328 , and  327 , first and second amplifiers  323  and  324 , an antenna  329  for transmit the downstream RF signal and receive the upstream RF signal, a splitter  326 , a switch  340 , and a controller  330 . 
         [0028]    The downstream opto-electric converter  321  is linked to the downstream electro-optic converter  311  of the CS  310 . The downstream converter  321  converts the downstream optical signal input from the CS  310  to the downstream RF signal, and outputs the downstream RF signal to the first coupler  325 . 
         [0029]    The first coupler  325  separates the downstream RF signal input from the downstream opto-electric converter  321  into a downstream timeslot, a downstream broadcasting channel, and a downstream sub-carrier channel. The downstream timeslot separated by the first coupler  325  is input to the splitter  326 . The downstream broadcasting channel is input to the second coupler  328 . The downstream sub-carrier channel is input to the second coupler  328  through the third coupler  327 . 
         [0030]    The upstream electro-optic converter  322  is linked to the upstream opto-electric converter  312  of the CS  310 . The upstream electro-optic converter  322  converts the upstream RF signal to the upstream optical signal, and outputs the upstream optical signal to the CS  310 . 
         [0031]    The second coupler  328  separates the upstream RF signal input from the antenna  329  into an upstream timeslot, an upstream broadcasting channel, and an upstream sub-carrier channel. The second coupler  328  outputs the separated upstream timeslot to the switch  340 , and directly outputs the separated upstream sub-carrier channel to the second amplifier  324 . The second coupler  328  also couples the downstream broadcasting channel input from the first coupler  325 , the downstream sub-carrier channel input from the third coupler  327 , and the downstream timeslot input from the switch  340  into the downstream RF signal and outputs the downstream RF signal to the antenna  239 . 
         [0032]    The splitter  326  is located between the first coupler  325  and the switch  340 . The splitter  326  splits a portion of the downstream timeslot separated by the first coupler  325 . The splitter  326  outputs the split portion of the downstream timeslot to the controller  330  and the remaining portion of the downstream timeslot to the switch  340 . 
         [0033]    The controller  330  controls the switch  340  so that not to overlap the upstream and downstream timeslots input to the switch  340 . The controller  330  determines a non-transmission band on which data is not carried from the downstream timeslot split by the splitter  326 . The splitter  330  then controls the switch  340  to alternatively input and output the upstream and downstream timeslots by connecting a contact point to the splitter  326  or the second coupler  328 . 
         [0034]      FIG. 4  is a block diagram of the controller  330  of  FIG. 3 .  FIG. 5  is a diagram showing the downstream timeslot input to the controller  330  of  FIG. 3  and a downstream timeslot output from a signal extractor (pulse detector). Referring to  FIGS. 4 and 5 , the controller  330  includes a pulse detector  331 , a low pass filter (LPF)  332 , a limiting amplifier  333 , a comparator  334 , a delay adjuster  335 , and a reference voltage generator  336 . 
         [0035]    The pulse detector  331  detects an envelope pattern waveform as illustrated in  FIG. 5A  from the downstream timeslot input from the splitter  326 .  FIG. 5A  shows the downstream timeslot, which is composed of a transmission band (Downlink) on which data is carried and a non-transmission band (TTG, Uplink, and RTG) on which data is not carried, input to the controller  330 . 
         [0036]    The TTG illustrated in  FIG. 5A  indicates an area to determine a trailing edge of the transmission band The RTG indicates an area to determine a leading edge of a subsequent timeslot. The Uplink commonly indicates an idle band for an upstream timeslot. In addition, the Δt illustrated in  FIG. 5B  indicates the time varying before and after data transmission of a timeslot. 
         [0037]    The LPF  332  cancels noise, such as a ripple, from the timeslot waveform detected by the pulse detector  331 . The limiting amplifier  333  limits the level of the timeslot input from the LPF  332 . 
         [0038]    The comparator  334  determines the non-transmission band by comparing a pre-set level of a reference voltage input from the reference voltage generator  336  to the level of the timeslot input from the limiting amplifier  333 . The delay adjuster  335  controls the switch  340  so that the upstream timeslot can pass the switch  340  in the non-transmission band determined by the comparator  334 . 
         [0039]    Referring back to  FIG. 3 , the controller  330  controls the switch  340  to connect a first port ( 1 ) to the splitter  326  and a second port ( 2 ) to the second coupler  328  during the transmission band of the downstream timeslot. The controller  330  also controls the switch  340  to connect the second port ( 2 ) to the second coupler  328  and a third port ( 3 ) to the second amplifier  324  during the non-transmission band of the downstream timeslot. 
         [0040]    The first amplifier  323  is located between the downstream opto-electric converter  321  and the first coupler  325 . The first amplifier  323  amplifies the downstream RF signal and outputs the amplified downstream RF signal to the first coupler  325 . The second amplifier  324  amplifies the upstream RF signal and outputs the amplified upstream RF signal to the upstream electro-optic converter  322 . 
         [0041]    The third coupler  327  outputs the downstream sub-carrier channel input from the first coupler  325  to the second coupler  328 . In addition the third coupler  327  outputs the upstream sub-carrier channel input from the second coupler  328  to the second amplifier  324 . 
         [0042]    As described above, according to the principles of the present invention, by determining transmission and non-transmission bands from a downstream timeslot and controlling the downstream timeslot and an upstream timeslot, which are not overlapped, a CS does not have to input a separate control signal. Moreover, a separate control signal does not have to be input to an electro-optic converter. Thus, the modulation index of channels and timeslot can be increased. 
         [0043]    While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.