Abstract:
An EPON for providing a subscriber with a high speed/high capacity data service and a real time digital broadcasting/image service includes an OLT for switching digital broadcasting/image data according to broadcasting/image selection information from each ONT, modulating the switched data into frequencies assigned to each ONT, coupling a broadcasting/image signal with a communication signal, and transmitting the coupled signal. The digital broadcasting/image data is transmitted from an outside broadcaster, the broadcasting/image signal is a combination of the modulated signals, and the communication signal is obtained by optically modulating communication data from an IP network. Further included in the EPON are multiple ONTs, and a divider for dividing the signal from the OLT for routing to each of the multiple ONTs, combining signals from the multiple ONTs, and transmitting the combined signal to the OLT.

Description:
CLAIM OF PRIORITY 
     This application claims priority to an application entitled “Ethernet passive optical network for convergence of broadcasting and communication,” filed in the Korean Intellectual Property Office on Jun. 30, 2003 and assigned Serial No. 2003-43846, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for serving a CAS broadcasting encrypted in various ways in a convergence system of broadcasting and communication. 
     2. Description of the Related Art 
     In order to effectively provide subscribers with a high speed/high capacity data service and a real time digital broadcasting/image service, data must be transmitted at a speed of more than 100 Mbps. However, such a high speed/high capacity data service and a real time digital broadcasting/image service cannot be provided by means of digital subscriber line (DSL) or a cable modem, which have attain at maximum a data transmission rate of merely 50 Mbps. In the spotlight at present, and as an outgrowth of research into types of high speed/high capacity data service, a passive optical network (hereinafter, referred to as PON) has been proposed as an economical solution. 
     PONs come in a number of varieties. There are, for example, ATM-PONs (Asynchronous Transfer Mode PONS), WDM-PONs (wavelength division multiplexing PONs) and Ethernet-PONs (hereinafter, referred to as EPON) which are based ATM-, WDM- and Ethernet-based, respectively. Moreover, for a high speed optical transmission to an ordinary home, a fiber to the home (FTTH) structure in the EPON has been proposed and is now being developed. 
     In general, the EPON has been basically developed to include communication data. In the EPON, for data transmission, an optical line terminal (hereinafter, referred to as OLT) transmits gigabit Ethernet signals at a speed of 1.25 Gbps to optical network terminals (hereinafter, referred to as ONTs) by means of a wavelength of 1550 nm. The ONTs likewise transmit gigabit Ethernet signals at a speed of 1.25 Gbps to the OLT, but by means of a wavelength of 1310 nm. 
     A growing need for broadcasting has required that the EPON employ broadcasting signals, and, for this, in an overlay broadcasting including method shown in  FIG. 1 , broadcasting signals are transmitted to the ONTs by means of wavelengths for broadcasting signals. These wavelengths differ from those utilized as communication data wavelengths. 
       FIG. 1  is a block diagram of a conventional EPON for convergence of broadcasting and communication. 
     As shown in  FIG. 1 , the conventional EPON for convergence of broadcasting and communication includes an OLT  100 , multiple ONTs  200 - 1  to  200 -N, a passive optical splitter  118 , and an optical cable. The OLT  100  is a sub-system located between a user and a service node, receives a broadcasting signal and a communication signal from a broadcaster and a communication service provider, converts the signals into an optical signal containing bundled components corresponding to the electrical signals, and then transmits one tied optical signal. The multiple ONTs  200 - 1  to  200 -N are user-side apparatuses and send information transmitted from the OLT  100  to a user. The optical cable connects the OLT  100  to the multiple ONTs  200 - 1  to  200 -N. 
     Specifically, the OLT  100  performs a light conversion for a broadcasting signal transmitted through a broadcasting network through elements  115 ,  116 , performs an optical amplification through element  117  for the converted signal, and then transmits the amplified signal. Further, the OLT  100  receives communication data from an internet protocol (hereinafter, referred to as IP) network through an IP router  111 , converts the communication data into an optical signal through element  112 , and then transmits the optical signal through element  113 . The OLT  100  receives data from the ONTs  200 - 1  to  200 -N and transmits the data to the IP network through the IP router  111 . 
     Each of the ONTs  200 - 1  to  200 -N receives a broadcasting signal through respective broadcasting receivers  119 - 1  to  119 -N, and transmits the broadcasting signal to a user through respective broadcasting set-top boxes (STBs)  122 - 1  to  122 -N. The ONTs  200 - 1  to  200 -N also receive communication data through receivers  120 - 1  to  120 -N, and transmit the communication data to a user through EPON ONT function processing units  123 - 1  to  123 -N. Furthermore, the ONTs  200 - 1  to  200 -N receive communication data transmitted from a user through the EPON ONT function processing units  123 - 1  to  123 -N, and transmit the communication data to the OLT  100  through burst mode transmitters  121 - 1  to  121 -N. 
     The above-described EPON for conventional broadcasting requires an erbium doped fiber amplifier (EDFA)  117 , which is an expensive optical amplifier for amplifying a broadcasting signal, in order to enable an OLT  100  to transmit an analog broadcasting signal to the ONTs  200 - 1  to  200 -N. On the other hand, if digital rather than analog broadcasting is involved, the expensive EDFA  117  is needed when the number of digital broadcasting channels increases. 
     Since all broadcasting channels are respectively transmitted to the ONTs  200 - 1  to  200 -N, the ONTs  200 - 1  to  200 -N need expensive optical receivers having specifications of high quality, such as high reception sensitivity and superior noise characteristic, in order to receive the transmitted broadcasting signals. 
     It is expected, moreover, that users will require in the future, in addition to digital broadcasting, real time digital image service of high quality. Unfortunately, however, the conventional EPON cannot deliver a real time digital image of high quality. 
     Furthermore, since the conventional EPON has no scheme (strategy; means; device) by which to enable the ONTs  200 - 1  to  200 -N to transmit information regarding broadcasting to the OLT  100 , it cannot realize an interactive broadcasting function which will eventually be required. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide an Ethernet passive optical network for convergence of broadcasting and communication, which can provide a user with high capacity and high speed communication data in addition to real time digital broadcasting/image signals of high quality. 
     It is another object of the present invention to provide an Ethernet passive optical network, in which an OLT selects broadcasting channels required by subscribers and transmits the selected channels to an ONT. Advantageously, the Ethernet passive optical network therefore need not employ an EDFA for multiple broadcastings or incur the concomitant expense. As a further consequence and benefit, the ONT can employ a low-price optical receiver meeting relatively low-quality specifications. 
     It is a further object of the present invention to provide an Ethernet passive optical network, in which a quality of service (QoS) can be secured in transmitting not only digital broadcasting but also a digital image of high quality which will be required by subscribers in the future. 
     It is still another object of the present invention to provide an Ethernet passive optical network, in which interactive broadcasting functions can be performed by transmitting broadcasting information through a communication data line in an EPON. In order to accomplish the aforementioned objects, according to an embodiment of the present, there is provided an EPON that includes an optical line terminal (OLT) for switching digital broadcasting and/or digital image data according to broadcasting and/or image selection information from each of multiple optical network terminals (ONTs). The OLT modulates the switched data into frequencies assigned to each ONT, couples with a communication signal a signal formed from combining the modulated data, and transmits the coupled signal. The digital broadcasting and/or digital image data is transmitted from an outside broadcaster. The communication signal is obtained by optically modulating communication data from an IP network. The EPON further includes the multiple ONTs, which are configured for receiving an optical signal from the OLT, dividing the optical signal into the combined signal and the communication signal, converting the divided signals into electrical signals, demodulating the converted combined signal into assigned frequencies, outputting the demodulated information and the converted communication signal to a user, receiving from the user communication data and the broadcasting and/or image selection information, and outputting the communication data and broadcasting and/or image selection information to the OLT. The EPON also has a divider for dividing the signal from the OLT among the multiple ONTs, joining signals from the multiple ONTs, and transmitting the joined signal to the OLT. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a conventional EPON for convergence of broadcasting and communication; 
         FIG. 2  is a block diagram of an EPON for convergence of broadcasting and communication according to an embodiment of the present invention; 
         FIG. 3  is an exemplary view showing a frequency domain, which is assigned according to a user, according to the present invention; and 
         FIG. 4  is a block diagram of a complex EPON for convergence of broadcasting and communication including multiple EPONs according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, a preferred embodiment according to the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, details of known functions and configuration incorporated herein will be omitted for clarity of presentation. 
       FIG. 2  shows, by way of illustrative and non-limitative example, a block diagram of an Ethernet passive optical network (hereinafter, referred to as EPON) for convergence of broadcasting and communication according to an embodiment of the present invention. 
     The EPON according to the present invention includes one OLT  300 , an optical divider  215  and 16 ONTs  400 - 1  to  400 - 16 . Each of ONTs  400 - 1  to  400 - 16  is assigned to a respective user. The OLT  300  includes a broadcasting/image channel selecting switch  21 , a broadcasting/image channel selection control unit  26 , quadrature amplitude modulation (hereinafter, referred to as QAM) modulators  22 - 1  to  22 - 32 , a combiner  24 , an optical transmitter  25 , an internet protocol (hereinafter, referred to as IP) router  27 , an EPON OLT function processing unit  28 , an optical transmitter  29 , an optical receiver  210 , and a wavelength division multiplexing (hereinafter, referred to as WDM) coupler  211 . 
     The broadcasting/image channel selecting switch  21  switches motion picture experts group (MPEG) broadcasting and image data. The broadcasting/image channel selection control unit  26  receives selection channel information from the ONTs  400 - 1  to  400 - 16  and transmits a control signal for selecting each broadcasting/image channel to the broadcasting/image channel selecting switch  21 . The QAM modulators  22 - 1  to  22 - 32  are connected to the broadcasting/image channel selecting switch  21  and digitally modulate the selected broadcasting/image channel. The combiner  24  is connected to the QAM modulators  22 - 1  to  22 - 32  and combines the modulated broadcasting/image signal. The optical transmitter  25  optically modulates the combined broadcasting/image signal, and the IP router  27  routes communication data to either an upper IP network or the EPON OLT function processing unit  28  for processing OLT functions of the EPON. The optical transmitter  29  optically modulates communication data and transmits the modulated communication data to the ONTs  400 - 1  to  400 - 16 . The optical receiver  210  receives an optical signal from the ONTs  400 - 1  to  400 - 16  and converts the received optical signal into electrical signals. The WDM coupler  211  couples the optical-modulated communication signal λ DOWN  with the optical-modulated broadcasting/image signal λ B . 
     Each ONT of the ONT  400 - 1  to ONT  400 - 16  includes a WDM coupler  216 , an optical receiver  217 , an optical transmitter  218 , an EPON ONT function processing unit  220 , an optical receiver  219 , a divider  221 , and QAM demodulators  222 ,  223 . The WDM coupler  216  divides the communication signal λ DOWN  and the broadcasting/image signal λ B  which are transmitted as an optical signal. The optical receiver  217  receives the divided communication signal λ DOWN  from the WDM coupler  216  and converts the communication signal λ DOWN  into an electrical signal. The optical transmitter  218  converts a communication signal from a user into an optical signal λ up  and transmits the converted optical signal λ UP  to the OLT  300 . The EPON ONT function processing unit  220  processes functions of the particular ONT. The optical receiver  219  receives the broadcasting/image signal λ B  and converts it into an electrical signal. The divider  221  divides this electrical signal into signals according to each image source. Each of the QAM demodulators  222 ,  223  detects a signal having a frequency component, which is assigned to each of ONTs  400 - 1  to  400 - 16 , and restores broadcasting/image data. 
     In upstream communication (from the ONT to the OLT), each user selects a broadcasting/image channel which the user wants to watch by means of a remote control, etc., and the selected signal, which is broadcasting/image channel selection data  225 , is transmitted from the ONTs to the broadcasting/image channel selection control unit  26  via the EPON. Digital broadcasting data and digital image data are inputted to the broadcasting/image channel selecting switch  21 . The broadcasting/image channel selecting switch  21  switches and outputs broadcasting/image channels, which each user wants to watch, by control signals of a broadcasting/image channel selection control unit  26 . 
     As a first step in the downstream communication (from the OLT to the ONU), the broadcasting/image channel selection control unit  26  controls the broadcasting/image channel selecting switch  21  to switch broadcasting/image channels  212 - 1  to  212 - 16  according to what each user wants to watch. For simplicity of demonstration,  FIG. 2  shows that each user or ONU is limited to a maximum of two from among broadcasting/image channels  212 - 1  to  212 - 16 , although the intended scope the present invention is not limited to a choice between merely two channels. For example, the user on ONU  400 - 16  is shown to have a choice between a channel on frequency f 16.1  or f 16.2 , either one of which may carry any one of the digital broadcasting or digital image channels inputted to the selection switch  21 . As described above, since the OLT  300  controls and transmits the broadcasting/image channels, there is no necessity of outputting multiple broadcasting/image channels. That is, there is no need for employing an EDFA used for including all broadcasting/image channels in the conventional PON structure. 
     As mentioned, two particular frequencies are assigned to each of ONTs  400 - 1  to  400 - 16 . Such an example of frequency assignment is shown in  FIG. 3 . As shown in  FIG. 3 , two frequencies f 1,1    31  and f 1,2    32  are assigned to the ONT  400 - 1  and two frequencies f 16,1    33  and f 16,2    34  are assigned to the ONT  400 - 16 . That is, two frequencies f i,1  and f i,2  are assigned to i-th ONT  400 -i. As described above, since different frequencies are assigned to each ONT, and broadcasting/image signals are transmitted from the OLT to the ONTs by means of different frequencies, collision between broadcasting/image signals for each ONT is prevented. 
     Broadcasting/image signals, which are selected by the ONT  400 - 1 , from among broadcasting/image data outputted from the broadcasting/image channel selecting switch  21  by means of such frequency assignment, are digitally modulated by the QAM modulators  22 - 1  to  22 - 32  each pair of which use the two frequencies f i,1  and f i,2  as carriers. 
     Next, the digitally modulated broadcasting/image signals are combined into one signal by the combiner  24 , and then the combined signal is optically modulated into an optical signal having a wavelength of λ B . The modulated optical signal is coupled with the optically modulated communication signal λ DOWN  by the WDM coupler  211 , and the coupled signal is transmitted to the ONTs  400 - 1  to  400 - 16 . 
     Preferably in parallel with the formation of the optically converted broadcasting/image signal λ B , communication data transmitted from an upper IP network is processed by the EPON OLT function processing unit  28 , which processes EPON functions, after passing through the IP router  27 . The processed signal is optically modulated into an optical signal having a wavelength of λ DOWN  by the optical transmitter  29 . Then, the modulated optical signal is coupled with the optically converted broadcasting/image signal λ B  by the WDM coupler  211 , and the coupled signal is transmitted to the ONTs  400 - 1  to  400 - 16 . 
     The wavelength λ DOWN  of the communication signal and the wavelength λ B  of the broadcasting/image signal are coupled by the WDM coupler  211 , and the coupled signal is sent to each of ONTs  400 - 1  to  400 - 16  via the optical divider  215 . 
     Next, the WDM coupler  216  in an input portion in the ONTs  400 - 1  to  400 - 16  re-divides the coupled signal into the communication signal λ DOWN  and the broadcasting/image signal λ B . The divided communication signal λ DOWN  is converted into an electrical signal by the optical receiver  217 , and the converted electrical signal is outputted as communication data (downstream)  224 - 1 , which are transmitted to terminal devices, such as a computer, via the EPON ONT function processing unit  220 . 
     The divided broadcasting/image signal λ B  is converted into an electrical signal by the optical receiver  219 , and the converted electrical signal is divided into two broadcasting/image signals f i,1 , f i,2  by the divider  221 . Only frequency components assigned to the respective ONT in the two divided signals are detected, and the detected frequency components are restored to digital broadcasting/image data  226 - 1 ,  226 - 2  by the QAM demodulators  222 ,  223 . These data  226 - 1 ,  226 - 2  are then transmitted to terminal devices such as a TV set. 
     Each ONT generates upstream data which include IP communication data  224 - 2  generated in a computer, etc., and broadcasting/image channel selection data  225  for watching digital broadcasting/image channel. Then, the EPON ONT function processing unit  220  solves such problems as data collision which may happen in the upstream data. Thereafter, the upstream data are optical-modulated into an optical signal having a wavelength of λ UP  by the optical transmitter  218 , and the modulated optical signal is transmitted to the OLT  300  via the WDM coupler  216  and the optical divider  215 . Herein, control operation of the OLT  300  is performed through broadcasting/image channel selection data  225  generated by the ONT. That data  225  may include an upstream signal in an interactive broadcasting which is processed in a similar manner. 
     The upstream signal transmitted to the OLT  300  is received by the optical receiver  210  through the WDM coupler  211  in the OLT  300 , and the received signal is converted into an electrical signal. 
     The converted upstream signal is transmitted to the EPON OLT function processing unit  28 . In the EPON OLT function processing unit  28 , the broadcasting/image channel selection data  225  in the upstream signal is transmitted to the broadcasting/image channel selection control unit  26 , and IP communication data in the upstream signal is transmitted to an upper IP network through the IP router  27 . 
       FIG. 4  is a block diagram depicting, in accordance with an embodiment of the present invention, an example of a complex EPON configured for convergence of broadcasting and communication and including multiple EPONs. The complex EPON shown in  FIG. 4  has a structure employing L number of OLTs and L x n number of ONTs. Digital broadcasting signals transmitted from either a service operator (SO) or a digital media center (DMC)  41  are divided into N number of MPEG digital broadcasting channels by a digital broadcasting channel-based divider  43 . Each of the divided MPEG digital broadcasting channels is divided into L number of channels by each of dividers  47 - 1  to  47 -N, and then each of the divided channels is transmitted to each of L number of EPON OLTs  49 - 1  to  49 -L. In addition, digital image data transmitted from a digital image source  42  are divided into M number of MPEG digital image channels by a digital image channel-based divider  44 . Each of the divided MPEG digital image channels is divided into L number of channels by each of dividers  48 - 1  to  48 -N, and then the divided channels are transmitted to L number of EPON OLTs  49 - 1  to  49 -L. Communication data transmitted from an IP network  45  are routed by an IP router  46 , and the routed data are transmitted to L number of EPON OLTs  49 - 1  to  49 -L. 
     As demonstrated above with regard to the present invention, an OLT selects broadcasting channels required by subscribers and transmits the selected channels to an ONT, so that the EPON need not employ an EDFA for including multiple broadcastings and the ONT can employ an optical receiver for receiving broadcastings with a low price and specifications of low quality. 
     Further, in the present invention, a quality of service (QoS) can be secured in transmitting not only a digital broadcasting but also a digital image of high quality which will be required by subscribers in the future. 
     Additionally with regard to the present invention, since broadcasting information is transmitted through a communication data line in an EPON, interactive broadcasting functions can be performed. 
     While the invention has been shown and described with reference to certain preferred embodiments 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.