Abstract:
A converter includes an optical fiber input port; an optical detector configured to receive an optical signal over the optical fiber input port and generate a first electrical signal carrying information; and a mixer in electrical communication with the optical detector configured to mix the first electrical signal with a radio frequency carrier wave producing a second electrical signal for transmission by an antenna. The second electrical signal carries the same information as the first electrical signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/477,860 filed Jun. 12, 2003, incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to communications systems.  
       BACKGROUND OF THE INVENTION  
       [0003]     Incumbent Local Exchange Carriers (ILECs), Competitive Local Exchange Carriers (CLECs) and Service Providers strive to deploy the most cost effective networks possible that provide broadband service links. Cost effectiveness is a relative term often measured by comparing the cost of equipment and material (also known as Capital Expenses CAPEX), the cost of service maintenance and operations (also known as Operational Expenses OPEX) and the cost of missed revenue generating opportunity due to deployment delays of alternative and competing network solutions. These cost comparisons are typically complex and difficult to obtain due to the nature of the broadband service links between a network&#39;s core and a building or a premise. One problem for providers of broadband service links stems from requirements to connect different types of communication equipment using multiple protocol conversions and communication link conversions. Typically, conversions are a large source of expense for ILECs, CLECs and Service Providers.  
         [0004]     For example, a broadband service link between a network&#39;s core and a building or premise may consist of three communication segments (fiber-wireless-fiber) each with multiple protocol and communication link conversions. At the network core, a SONET/SDH fiber may be connected to ATM communication equipment that performs add-drop-mux (ADM) functions in accordance with a SONET/SDH protocol. Line cards within the ATM communication equipment aggregate, switch and convert traffic to other protocols such as Ethernet, which are used across fiber distribution links such as Gigabit Ethernet (GbE). The fiber distribution links are connected to other communication equipment that perform wireless base-station functions that may include yet another protocol conversion to support the broadband wireless access (BWA) protocol in-use. The broadband service link propagates over the air. A wireless terminal terminates the BWA protocol in-use and converts back to an Ethernet or SONET/SDH protocol. The wireless terminal distributes broadband services across fiber links to a network terminal equipment residing at a building or premise. In this example, the broadband service link undergoes multiple protocol conversions and communication link conversions between the network&#39;s core and a premise.  
       SUMMARY OF THE INVENTION  
       [0005]     In general, in one aspect, the invention includes a converter including an optical fiber input port; an optical detector configured to receive an optical signal over the optical fiber input port and generate a first electrical signal carrying information; and a mixer in electrical communication with the optical detector configured to mix the first electrical signal with a radio frequency carrier wave producing a second electrical signal for transmission by an antenna. The second electrical signal carries the same information as the first electrical signal.  
         [0006]     Aspects of the invention may include one or more of the following features. The converter further includes a linear filter for filtering the first electrical signal. The converter further includes a linear filter for filtering the second electrical signal. The optical fiber input port is in optical communication with a first node in a passive optical network and the antenna is in electromagnetic communication with a second node in a passive optical network. The information includes overhead data according to a PON protocol. The information includes payload data coded to be transmitted in an optical system. The second electrical signal carries a same sequence of modulation symbols as the first electrical signal.  
         [0007]     In general, in another aspect, the invention includes a method for converting signals including receiving an optical signal over an optical fiber input port and generating a first electrical signal carrying information; and mixing the first electrical signal with a radio frequency carrier wave producing a second electrical signal for transmission by an antenna. The second electrical signal carries the same information as the first electrical signal.  
         [0008]     In general, in another aspect, the invention includes a converter including an antenna configured to receive a radio frequency signal; a mixer configured to down-convert a received radio frequency signal to a baseband electrical signal carrying information; and a laser driver in electrical communication with the mixer configured to modulate an optical signal with the baseband electrical signal producing a modulated optical signal for transmission over an optical fiber link. The modulated optical signal carries the same information as the baseband electrical signal.  
         [0009]     Aspects of the invention may include one or more of the following features. The converter includes a linear filter for filtering the radio frequency signal. The converter includes a linear filter for filtering the baseband electrical signal. The optical fiber input port is in optical communication with a first node in a passive optical network and the antenna is in electromagnetic communication with a second node in a passive optical network. The information includes overhead data according to a PON protocol. The information includes payload data coded to be transmitted in an optical system. The modulated optical signal carries a same sequence of modulation symbols as the baseband electrical signal.  
         [0010]     In general, in another aspect, the invention includes a method for converting signals including receiving a radio frequency signal; down-converting the received radio frequency signal to a baseband electrical signal carrying information; and modulating an optical signal with the baseband electrical signal producing a modulated optical signal for transmission over an optical fiber link. The modulated optical signal carries the same information as the baseband electrical signal.  
         [0011]     In general, in another aspect, the invention includes a converter including an optical fiber input port; an optical detector configured to receive an optical signal over the optical fiber input port and generate a first electrical signal carrying information; a first mixer in electrical communication with the optical detector configured to mix the first electrical signal with a radio frequency carrier wave producing a second electrical signal for transmission by an antenna; an antenna configured to receive a radio frequency signal; a second mixer configured to down-convert a received radio frequency signal to a baseband electrical signal carrying information; and a laser driver in electrical communication with the second mixer configured to modulate an optical signal with the baseband electrical signal producing a modulated optical signal for transmission over an optical fiber link. The modulated optical signal carries the same information as the baseband electrical signal. The second electrical signal carries the same information as the first electrical signal.  
         [0012]     Aspects of the invention may include one or more of the following features. The optical fiber input port is in optical communication with a first node in a passive optical network and the antenna is in electromagnetic communication with a second node in a passive optical network. The information in the first electrical signal and the information in the baseband electrical signal include overhead data according to a PON protocol. The information in the first electrical signal and the information in the baseband electrical signal include payload data coded to be transmitted in an optical system. The modulated optical signal carries a same sequence of modulation symbols as the baseband electrical signal and the second electrical signal carries a same sequence of modulation symbols as the first electrical signal.  
         [0013]     In general, in another aspect, the invention includes a method for converting signals including receiving an optical signal over an optical fiber input port and generating a first electrical signal carrying information; mixing the first electrical signal with a radio frequency carrier wave producing a second electrical signal for transmission by an antenna; receiving a radio frequency signal; down-converting the received radio frequency signal to a baseband electrical signal carrying information; and modulating an optical signal with the baseband electrical signal producing a modulated optical signal for transmission over an optical fiber link. The modulated optical signal carries the same information as the baseband electrical signal. The second electrical signal carries the same information as the first electrical signal.  
         [0014]     In general, in another aspect, the invention includes a link in a passive optical network, including a first converter configured to convert an input optical signal carrying information into a radio frequency signal for transmission by a first antenna; and a second converter configured to receive a radio signal transmitted from the first converter and convert the received radio signal into an output optical signal carrying the same information as the input optical signal.  
         [0015]     Aspects of the invention may include one or more of the following features. The information includes overhead data according to a PON protocol. The information includes payload data coded to be transmitted in an optical system. The output optical signal carries a same sequence of modulation symbols as the input optical signal. The second converter is further configured to convert a second input optical signal carrying information into a second radio frequency signal for transmission by a second antenna. The first converter is further configured to receive the second radio frequency signal transmitted from the second converter and convert the received radio frequency signal into a second output optical signal carrying the same information as the second input optical signal.  
         [0016]     In general, in another aspect, the invention includes a method including converting an input optical signal carrying information into a radio frequency signal for transmission by a first antenna; and receiving a radio signal transmitted from the first converter and convert the received radio signal into an output optical signal carrying the same information as the input optical signal.  
         [0017]     In general, in another aspect, the invention includes a passive optical network, including a first node in the network; a passive optical splitter in communication with the first node over a first optical fiber link; a second node in communication with the passive optical splitter over a second optical fiber link; and a third node in communication with the passive optical splitter over a link that includes a radio frequency link.  
         [0018]     Aspects of the invention may include one or more of the following features. The first node comprises an optical line terminator. The second node comprises an optical networking device. The third node comprises an optical networking device. The radio frequency link uses a same communication protocol as the first and second optical fiber links.  
         [0019]     In general, in another aspect, the invention includes a method for transmitting data over an optical network, the method including formatting a data stream according to an optical communication protocol; transmitting the formatted data stream as an optical signal from a first node in the optical network; receiving the transmitted optical signal at a second node in the optical network; converting the received optical signal to a radio frequency signal without changing the formatting of formatted data stream; transmitting the radio frequency signal from the second node to a third node in the optical network; receiving the radio frequency signal at the third node; converting the received radio frequency signal to an optical signal; and transmitting the converted optical signal over an optical link.  
         [0020]     Aspects of the invention may include one or more of the following features. The data stream includes coding the data stream. Formatting the data stream includes representing information in the data stream as a sequence of symbols.  
         [0021]     In general, in another aspect, the invention includes a method for distributing a signal in a passive optical network, including transmitting an optical signal for distribution in the passive optical network; splitting the optical signal for distribution to two or more nodes in the passive optical network; coupling the optical signal to a first node over an optical fiber link; and coupling the optical signal to a second node over a radio frequency link.  
         [0022]     Aspects of the invention may include formatting a data stream for transmission in the optical signal.  
         [0023]     Implementations of the invention may include one or more of the following advantages.  
         [0024]     PONs conventionally have a limit to the number of clients and a limit to the maximum distance (or reach) from an Optical Line Terminator (OLT) and a client Optical Network Unit (ONU) or Optical Network Terminal (ONT). This limit is primarily a function of optical power loss. An increase in the number of clients may lead to an increase in the number of splits in the fiber network and a decrease in the received optical power for the receivers of both OLT and client ONU/ONTs. Likewise, an increase in the maximum distance between an OLT and an ONU/ONT client may lead to a decrease in received optical power for the receivers of both OLT and ONU/ONT clients, the reduced optical power substantially reducing the number of clients the network is capable of supporting with a given optical power loss budget. Typically, a design trade off exists between number of clients and maximum reach. Augmenting an Optical Distribution Network (ODN) of a PON with wireless links may influence this design tradeoff.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a block diagram of a passive optical network (PON).  
         [0026]      FIG. 2  is a block diagram of an optical receiver and radio frequency transmitter converter.  
         [0027]      FIG. 3  is a block diagram of a radio frequency receiver and an optical transmitter converter.  
         [0028]      FIG. 4  is a block diagram of a bi-directional radio optical transceiver converter.  
         [0029]      FIG. 5  is a block diagram of a point-to-multipoint passive optical network system. 
     
    
     DETAILED DESCRIPTION  
       [0030]     Passive Optical Network (PON) links can be augmented to use radio frequency communications. A PON can be configured in a point-to-multipoint fiber optic network in a tree-branch network architecture.  FIG. 1  shows an example of a PON, where an Optical Line Terminator (OLT)  100  provides broadband communication to a plurality of client optical networking devices, including Optical Network Units (ONUs)  101  and Optical Network Terminals (ONTs)  102 , at nodes in an Optical Distribution Network (ODN)  50 . ODN  50  includes optical fibers  103 , splitters  104 , splices (not shown) and connectors (not shown) between an OLT  100  node and ONU  101  and ONT  102  nodes. Any of a variety of PON implementations may be used including implementations according to the ITU G.983, G.984 and IEEE 802.3ah specifications, which are hereby incorporated by reference, or a derivative thereof.  
         [0031]     In general, the role of an OLT  100  is to control information traffic between the OLT  100  and client ONUs  101  and ONTs  102  while interfacing with network service entities (not shown) to provide broadband service links across a PON. Each ONU  101  responds to the OLT&#39;s  100  control while passing information between the OLT  100  and network service interfaces (not shown) thereby allowing other broadband service links to be connected to a respective ONU  101 . ONTs  102  respond to an OLT&#39;s  100  control while terminating broadband service links between the OLT  100  and a user network interface (not shown), which is connected to the ONT  102 .  
         [0032]     PON links can be augmented to include a converter  150  at an intermediate node to receive optical fiber signals that are then transmitted as radio frequency signals and/or to receive radio frequency signals that are then transmitted as optical fiber signals. Converter  150  uses an optical communication protocol (e.g., a PON communication protocol), and no conversion of the received signals (other than optical to electrical and electrical to optical) is required. Accordingly, PON  50  is able to use an optical communication protocol for both optical links and links that include radio frequency links. PON  50  can use an RF link to extend an ODN without necessarily requiring the expense or complexity of stages to perform such functions as frame synchronization, decoding or re-coding of signals in accordance with an RF protocol. Instead, electrical signals associated with a received or transmitted optical signal and electrical signals associated with received or transmitted radio frequency signals can carry the same information. For example, payload data can remain coded according to a coding technique that is optimized for optical links. Overhead data associated with an optical communication protocol (e.g., data link layer framing overhead) can remain the same.  
         [0033]     The electrical signals and the associated radio frequency and/or optical signals can also represent a same “baseband signal” with a same sequence of modulation symbols without requiring reformatting. Formatting, as used herein, refers to a process of preparing a baseband signal from an input data stream for transmission over the PON. Formatting includes coding, framing, filtering, etc. Various overhead bits (overhead data) may be added to the input data stream (payload data) in accordance with the formatting process. Formatting also includes preparation of a sequence of modulation symbols yielding a baseband signal to represent the information in the signal.  
         [0034]     Modulation, as used herein, refers to the process of mixing a formatted baseband signal with a carrier, either optical or radio frequency. In some implementations, a baseband and/or modulated signal and its modulation symbols may be amplified, reshaped, retimed, regenerated, and/or filtered.  
         [0035]      FIG. 2  shows one implementation of a converter  150 A that converts optical fiber signals to radio frequency signals. Input optical fiber signals are received over an optical fiber  200 . An optical receiver  210  includes a photo detector (PD)  201  that converts the light transmitted over the fiber  200  into an electrical current. A transimpedance amplifier (TIA)  202  converts changes in input current to changes in output voltage. The TIA  202  takes the current input from the PD  201  and converts the current to a voltage. The voltage is input into a linear amplifier (LA)  203 . The LA  203  provides voltage gain on, what is typically, the relatively weak signal generated by the PD  201  and TIA  202 . The voltage is then input into a Mixer  204  that takes as input a Local Oscillator (LO) signal  205  and a Reference signal  211 . The mixer  204  modulates the reference  211  input with the LO signal  205  and generates an output signal whose frequency is the sum of the frequencies of the two input signals. The LO frequency  205  is a carrier signal meant to raise the center frequency of the reference signal  211  to a frequency suitable for radio transmission. The effect is that the reference signal  211  is up-shifted about the frequency of the LO signal  205  input. The output of the mixer  204  can then be input to an amplifier (Amp)  206 . Amp  206  provides sufficient power for radio frequency transmission with the Antenna  207 . Filters  208  and  209  may optionally be included to improve performance of the mixer  204 . The mixer  204  may optionally include intermediate frequency stages. Alternatively, the optical receiver  210  can include other types of receivers that generate an electrical signal from an optical signal.  
         [0036]      FIG. 3  shows an alternative implementation of a converter  150 B that converts received radio frequency signals to optical fiber signals. Input radio frequency signals are received by antenna  300 . A low noise amplifier (LNA)  301  provides amplification to the signal produced by the antenna  300  without adding significant noise. A mixer  302  mixes a local oscillator LO signal  303  and reference signal  310  and generates an output signal whose frequency is the difference of the frequencies of the two input signals. The mixer  302  down-converts the input from the LNA  301  producing a representation of the received radio frequency signal without the carrier. The output of the mixer  302  is provided as an input to a laser driver (Driver)  304  of an optical transmitter  309 . The laser driver  304  provides modulated current based on its input to a laser diode (LD)  305 . The LD  305  creates light transmission based on input from the laser driver  304 . For burst mode optical transmissions, the driver  304  may or may not provide current to the LD  305  when no radio transmissions are received. The light transmission is then provided to a fiber  306  that facilitates transmission of the communication received from the antenna  300 . Filters  307  and  308  may optionally be included to improve performance of the mixer  302 . The mixer  302  may optionally include intermediate frequency stages. Alternatively, the optical transmitter  309  can include other types of transmitters that generate an optical signal from an electrical signal.  
         [0037]     Both conversion processes of the converter  150 A and of the converter  150 B can be combined to enable bi-directional communications. An exemplary bi-directional converter  150 C is shown in  FIG. 4 . The mixers  204 , 302  have local oscillators LO 1    205  and L 0   2    303  that may or may not have the same frequency. When appropriate different frequencies are used, bidirectional communication can be made without other considerations. If a same frequency is used in each LO  205 ,  303 , then other techniques include different polarizations for transmitted rf fields or time division multiplexing may be used. The fiber link  400  may include a bi-directional fiber and/or multiple unidirectional fibers. The rf transceiver  401  may include one or more antennas. The optical transceiver  402  can use any of a variety of optical/electrical conversion techniques.  
         [0038]      FIG. 5  is a block diagram of a point-to-multipoint passive optical network system with augmented radio frequency links. The PON system includes an OLT  500  with ONUs  501  and ONTs  502  connected across fibers  503  and wireless links  504  provided by bi-directional converters  505   a ,  505   b . The bi-directional converters  505   a ,  505   b  may use different frequencies to transmit data between the OLT  500 , ONU  501  and ONT  502  in which case the LO input of the corresponding mixers will be different to match the corresponding transmit and receive frequencies. The ONUs  501  and ONTs  502  may be connected to the OLT  500  by a fiber link  503 . The ONUs  501  and ONTs  502  may be connected to the OLT  500  by a combination of fiber and a wireless link  504  using bi-directional converters  505   a ,  505   b . Multiple ONUs  501  and ONTs  502  may be connected to an OLT  500  by individual point-to-point wireless links (e.g., links  504 ) or by point-to-multipoint wireless links (e.g., link  506  where a bi-directional converter  505   a  supports a plurality of bi-directional converters  505   b ). Additionally, the ONUs  501  and ONTs  502  may be connected to the OLT  500  by multiple wireless links  504 . For example, in such a connection, a bi-directional converter  505   b  is connected to another bi-directional converter  505   a  by fiber link  503  as shown for module  507 . Alternative point-to-multipoint fiber optic network configurations with augmented wireless links may be used.  
         [0039]     As previously mentioned, a derivative specification may be used to implement the PON  50 . Derivative specifications may take into account increased communication delays because of the wireless links  504  as well as an increase in the number of ONU/ONT clients supported by the PON  50  as compared to conventional PON network specifications.  
         [0040]     Although the invention has been described in terms of particular implementations, one of ordinary skill in the art, in light of this teaching, can generate additional implementations and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.