WO2001095525A2

WO2001095525A2 - Optical modules for redundancy in a broadband communication system

Info

Publication number: WO2001095525A2
Application number: PCT/US2001/017572
Authority: WO
Inventors: Forrest M. Farhan
Original assignee: Scientific-Atlanta, Inc
Priority date: 2000-06-02
Filing date: 2001-05-31
Publication date: 2001-12-13
Also published as: WO2001095525A3

Abstract

A broadband communication system (400) includes transmission equipment (405) and reception equipment (440) coupled by redundant optical paths (425, 430). The transmission equipment (405) includes electronic circuitry (410) for receiving an input signal and converting it to a standard communication protocol, such as PECL, to generate a standard format signal. Within the transmission equipment (405), redundant plug-in electrical-to-optical modules (415, 420) receive the standard format signal and generate redundant optical signals for transmission over the optical paths (425, 430). Each electrical-to-optical module (415, 420) includes electrical-to-optical conversion and transmission circuitry that is likely to fail, and each module (415, 420) is easily removable and replaceable. The reception equipment (440) includes redundant plug-in optical-to-electrical modules (445, 450) for receiving the redundant optical signals and generating therefrom redundant electrical signals that are formatted in accordance with the standard communication protocol. Electronic circuitry (455) receives the redundant electrical signals, selects one for processing, and generates an electrical output signal. Preferably, each optical-to-electrical module (445, 450) includes optical-to-electrical conversion circuitry that is likely to fail, and each module (445, 450) is easily removable and replaceable.

Description

OPTICAL MODULES FOR REDUNDANCY IN A BROADBAND COMMUNICATION

SYSTEM

INVENTORS: Forrest M. Farhan

RELATED APPLICATIONS

This patent application is related to U.S. patent application serial no. 09/263,451 (attorney's docket No. A-5498), entitled "Cable Television System With Delay Compensation In Reverse Path" by Forrest M. Farhan, filed on March 5, 1999 and assigned to the assignee hereof.

FIELD OF THE INVENTION

This invention relates generally to broadband communications, and more specifically to optical transmission and receiving equipment for use in such communication systems.

BACKGROUND OF THE INVENTION

Broadband communication systems, such as cable television systems, typically include a headend section for receiving satellite signals and demodulating the signals to an intermediate frequency (IF) or baseband. The down converted signals are then modulated with radio frequency (RF) carriers and converted to an optical signal for transmission from the headend section over fiber optic cable. Optical transmitters are distributed throughout the broadband communication system, such as at headends, for splitting and transmitting optical signals, and optical receivers are provided in remote locations within the distribution system for receiving the optical signals and converting them to radio frequency (RF) signals that are further transmitted along branches of the system over coaxial cable rather than fiber optic cable. Taps are situated along the coaxial cable to tap off downstream (also referred to as "outbound" or "forward") cable signals to subscribers of the system. Conventional cable television systems can also include a reverse path in which upstream (or

"reverse" or "inbound") signals are transmitted from subscriber equipment to the headend equipment. Reverse signals are processed by the taps, the optical nodes and/or hubs, and are finally delivered to the headend equipment, and the reverse signals may be optical or electrical, depending upon the communication media available for upstream transmission. Information transmitted by the subscriber equipment may, in some systems, be important enough to justify the use of redundant reverse paths. However, to date, no system has effectively solved the problems, such as time delays, expense, and difficulty of equipment replacement, presented by such redundancies. BRD--F DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional broadband communication system. FIGs. 2 and 3 are electrical block diagrams of conventional broadband communication systems in which redundant paths and equipment are utilized.

FIGs. 4 and 5 are electrical block diagrams of broadband communication systems including redundant equipment modules in accordance with the present invention.

FIGs. 6 and 7 are electrical block diagrams of modules configured for use in transmission and reception equipment, respectively, in accordance with a preferred embodiment of the present invention.

DETAD ED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows a broadband communications system, such as a cable television system 100 having both forward and reverse paths, i.e., having the ability to communicate downstream in the forward direction and upstream in the reverse direction. The communication system 100 includes a headend 105 for receiving satellite signals that are demodulated to baseband or an intermediate frequency (IF). The baseband signal is then converted to radio frequency (RF) signals, such as cable television signals, that are routed throughout the system 100 to subscriber equipment 130, such as set top decoders, televisions, or computers, located in the residences or offices of system subscribers. The headend 105 can, for instance, convert the IF/baseband signal to an optical signal that is transmitted over fiber optic cable 110, in which case a remotely located optical node 115 converts the optical signal to an electrical radio frequency (RF) signal for further transmission through the system 100 over coaxial cable 120. Taps 125 located along the cable 120 at various points in the distribution system split off portions of the RF signal for routing to subscriber equipment 130 coupled to subscriber drops provided at the taps 125.

The system 100, as mentioned, also has reverse transmission capability so that signals, such as data, video, or voice signals, generated by the subscriber equipment 130 can be provided back to the headend 105 for processing. The reverse signals travel through the taps 125 and any nodes 115 and other cable television equipment, e.g., reverse amplifiers, to the headend 105. In the configuration shown in FIG. 1, RF signals generated by the subscriber equipment 130 travel to the node 115, which converts the RF signals to optical signals for transmission over the fiber optic cable 110 to the headend 105.

The forward signals of cable television systems are typically separated from the reverse signals by frequency division multiplexing. In North America, forward signals are carried in the 50-750 MHz band, and reverse signals are carried in the 5-40 MHz band. Referring to FIGs. 2 and 3, block diagrams depict the use of equipment and path redundancy in conventional communication systems 200 and 300, respectively. In FIG. 2, an RF signal is received by a splitter 205, which splits the signal into two signal paths, each of which is coupled to a conventional optical transmitter 210, 215. Each optical transmitter 210, 215 includes typical amplification, filtering, conversion, and modulation circuitry for processing the RF signal, converting it to an optical signal, and transmitting the optical signal. Each optical transmitter 210, 215 is also coupled to a separate optical communication channel 220, 225. The optical communication channels 220, 225 are respectively coupled to optical receivers 230, 235, each of which includes conventional devices and circuitry for processing optical signals to yield corresponding RF signals, which are routed to a coupler 240.

The conventional system 200 includes two separate signal paths, i.e., Path A and Path B. During operation of the system 200, the outgoing RF signal from only a single path is used. For example, the Path A signal may be used under usual circumstances and, when a failure in equipment or communication channel is detected, the system 200 may be switched to use Path B instead. The detecting and switching process may be manual or automatic, and known processes may be used to accomplish the detecting and switching functions.

The transmitting equipment 205, 210, 215 can, for instance, be included in an optical node 115, hub, or headend equipment 105. The receiving equipment 230, 235, 240 can likewise be included in another node, hub, or headend equipment 105. Additionally, the redundancies may be included in the downstream distribution network of the system 200, the upstream distribution network, or both.

Because Paths A and B are redundant and, typically, diversely routed, failure of one path, such as could occur when a fiber optic cable is inadvertently cut, does not prevent reverse information from being transmitted upstream. As a result, the redundant Paths A and B provide a degree of reliability that is not present in systems without redundancy. This increased reliability, however, comes only through substantial increases in cost, since two transmitters, two receivers, and two communication channels must be purchased, installed, and monitored, resulting in manpower and equipment costs that do not affect systems that do not include such redundancy. FIG. 3 depicts a conventional system 300 in which upfront equipment costs are minimized by use of a single optical transmitter 305 in conjunction with an optical splitter 310. The optical splitter 310 splits the optical communication signal for transmission over two separate communication channels 315, 320, each of which is coupled to an optical receiver 325, 330. As in FIG. 2, the outputs of the optical receivers 325, 330 are provided to a coupler 335. Referring next to FIGs. 4 and 5, broadband communication systems 400 and 500, respectively, include redundant equipment manufactured in accordance with the present invention. In FIG. 4, system 400 includes transmission equipment 405 for receiving a single input signal, which may be an RF signal or digital signal, for example, and transmitting two corresponding optical output signals over separate optical channels 425, 430. The transmission equipment 405 of the present invention includes transmission electronics 410 for performing functions such as filtering, digitizing, shaping, and/or amplifying the input signal and converting the input signal to an appropriately formatted output signal, such as an intermediate frequency or baseband signal. The equipment 405 further includes electrical-to-optical (E- O) conversion circuitry and optical transmission devices, such as lasers, within redundant modules 415, 420. Preferably, each E->O module 415, 420 includes components that are more likely to have reliability problems. The transmission equipment 405 provides, at its output, a digital communication signal, such as a digital optical signal.

On the receiving end, the system 400 includes reception equipment 440 that includes two separate modules 445, 450, each of which comprises optical-to-electrical (O->E) conversion circuitry for receiving a digital signal, preferably optical in nature, and outputting an electrical signal. Electrical signals from the O->E modules 445, 450 are provided to reception electronics 455 comprising conventional circuitry for processing and further transmitting the resulting electrical signal. According to the present invention, redundancy can be limited to high-failure-rate components, i.e., the E-i O circuitry and the O- E circuitry of the modules 415, 420, 445, 450. As a result, the expense to the system operator is minimized, since duplication of more reliable components, i.e.., the electronics 410, 455, is not required.

Furthermore, service upgrades to the transmission and reception equipment 405, 440 are more efficient and less costly because only the updated section has to be replaced. Other components of the transmission equipment 405 and the reception equipment 440 can be retained for continued use. Technological evolutions in the electronics sections 410, 455 may therefore follow a different upgrade path than that of the optical topologies, which are represented by modules 415, 420, 445, 450. According to the present invention, each E->O module 415, 420 is configured to be easily removable from the transmission equipment 405 and also easily separated from the transmission electronics 410. By way of example, each module 415, 420 may be separately housed and coupled to a housing enclosing the electronics 410 by coaxial cable or another communication medium. Alternatively, the modules 415, 420 and the electronics 410 could be included within a single device housing, but each module 415, 420 could be mounted on a separate substrate or printed circuit board that is easily removed from the housing and easily replaced with another such module or perhaps mounted in a separate component, such as a plug-in component. The O- E modules 445, 450 should be similarly configured with respect to the reception electronics 455.

The transmission electronics 410 and the reception electronics 455 could likewise be configured for easy removal and replacement separately from the modules 415, 420, 445, 450. Like the modules 415, 420, 445, 450, the electronics 410, 455 could be housed separately or manufactured as removable plug-in components, modules, or separate substrates on which the electronic components are mounted.

FIG. 5 depicts a communication system 500 including redundancy at decreased cost. The transmission equipment 505 of FIG. 5 includes transmission electronics 510, a single E->O module 515, and an optical splitter 520 for providing two optical outputs, which are received by redundant O->E modules 530, 535 of reception equipment 525. Reception electronics 540 included in the reception equipment 525 further processes the incoming electrical signals to generate an RF output signal. In this embodiment, additional cost is saved by including only one E- O module 515.

According to the present invention, if a network operator requires, for instance, 3 dB more power out of the system transmission equipment 405, the operator can easily solve this problem by upgrading only the E- O modules 415, 420. The replaced modules 415, 420 can then be reused in other equipment that has the same optical specifications, regardless of the electrical specifications that are required. In conventional systems, on the other hand, the entire transmitter 210, 215, including both electronics and optics, would have to be scrapped or reused in an application with both matching electrical specifications and matching optical specifications. Additionally, in the prior art system, the new part(s) for the upgrade would be more expensive, and the replacement would be more labor intensive.

The transmission equipment 405, 505 of the present invention can be included within headend equipment, a node, or a hub, as can the reception equipment 440, 525. Within the transmission equipment 405, 505 and within the reception equipment 440, 525, communication between the separate modules and other electronics portions preferably takes place using a standard interface. For example, the transmission electronics module 410 could communicate with each of the E-i>O modules 415, 420 using a positive emitter coupled logic (PECL) interface. Referring next to FIG. 6, an electrical block diagram depicts modules configured for use in transmission equipment in accordance with a preferred embodiment of the present invention. As shown, the transmission electronics module 410 includes signal processing circuitry 605 and a serializer 610 for providing digital outputs 615 using a standard communication protocol, such as PECL. When redundant E- O modules 415, 420 are included within the transmission equipment, the serializer 610 further provided redundant outputs. The E-_»O module 415 preferably includes a laser driver 620 coupled to the standard interface 615. The laser driver 620 drives a laser 630, which is matched to the driver 620 by an impedance matching network 625.

In FIG. 7, reception equipment includes an O-- E module 445 and a reception electronics module 455 configured in accordance to the preferred embodiment of the present invention. The O- E module 445 includes a photodetector and transimpedance amplifiers 705 and a limiting amplifier 710, which provides outputs 715 formatted in accordance with a standard communication protocol, such as PECL. The reception electronics 455 includes a selector 720 that is coupled to outputs of all O-->E modules 445, 450 for selecting between them. A deserializer 725 then deserializes the selected signals to provide clock and data signals to signal processing circuitry 730.

Although it is preferable that the components of FIGs. 6 and 7 are included in the transmission electronics module 410, the E- O module 415, the O->E module 445, and the reception electronics module 455, one of ordinary skill in the art will appreciate that other components or additional components could be included in the modules. What is important is that the high failure rate components be included in separate modules that can be redundantly duplicated within a communication system and that these redundant modules be easily separated from, and be able to easily communicate with, other system equipment.

In summary, the broadband communication system described above includes redundant equipment and communication channels configured in a more efficient and less expensive manner than in prior art systems. More specifically, transmission equipment includes transmission electronics that are separated from optical circuitry such that the optical circuitry and/or the electronics may be easily disconnected from the other and removed from the transmission equipment for replacement. Similarly, the reception equipment within the system includes optical modules that are easily removed from the equipment and separated from the electronic portion. Therefore, only the less reliable optical portions need be replaced upon failure.

What is claimed is:

Claims

1. Transmission equipment for use in a broadband communication system, the transmission equipment comprising: . electronic circuitry for processing an input signal to generate an electrical signal; a first optical module for receiving the electrical signal and generating therefrom a first optical signal corresponding to the electrical signal; and a second optical module for receiving the electrical signal and generating therefrom a second optical signal corresponding to the electrical signal, wherein the first and second optical modules are redundant modules that separately process the electrical signal to generate redundant optical signals, and wherein the redundant modules are separately removable from the transmission equipment and from the electronic circuitry.

2. The transmission equipment of claim 1, wherein the first and second optical modules are each configured as a plug-in module that is removably inserted into and detached from the transmission equipment without necessitating removal of the electronic circuitry from the transmission equipment.

3. The transmission equipment of claim 1, wherein the first and second optical modules are each formed on a discrete substrate that is removably inserted into and detached from the transmission equipment without necessitating removal of the electronic circuitry from the transmission equipment.

4. The transmission equipment of claim 1, wherein the transmission equipment comprises an optical node.

5. The transmission equipment of claim 1, wherein the transmission equipment is located in the reverse path of the broadband communication system.

6. The transmission equipment of claim 1, wherein the first and second optical modules each include electrical-to-optical conversion circuitry.

7. The transmission equipment of claim 1, wherein the electronic circuitry comprises signal processing circuitry and a serializer for processing the input signal to generate the electrical signal, wherein the electrical signal is formatted in accordance with a standard communication protocol.

8. The transmission equipment of claim 1, wherein the first optical module includes a laser for transmitting the first optical signal and a laser driver for receiving the electrical signal and driving the laser.

9. Reception equipment for use in a broadband communication system, the reception equipment comprising: a first optical module for receiving a first optical signal and generating therefrom a first electrical signal corresponding to the first optical signal; a second optical module for receiving a second optical signal and generating therefrom a second electrical signal corresponding to the second optical signal; and electronic circuitry for processing the first and second electrical signals to generate an output signal corresponding to either of the first and second optical signals, wherein the first and second optical modules are redundant modules that separately process received optical signals to generate redundant electrical signals, and wherein the redundant modules are separately removable from the reception equipment and from the electronic circuitry.

10. The reception equipment of claim 9, wherein the first and second optical modules are each configured as a plug-in module that is removably inserted into and detached from the reception equipment without necessitating removal of the electronic circuitry from the reception equipment.

11. The reception equipment of claim 9, wherein the first and second optical modules are each formed on a discrete substrate that is removably inserted into and detached from the reception equipment without necessitating removal of the electronic circuitry from the reception equipment.

12. The reception equipment of claim 9, wherein the reception equipment comprises an optical node.

13. The reception equipment of claim 9, wherein the reception equipment is located in the reverse path of the broadband communication system.

14. The reception equipment of claim 9, wherein the first and second optical modules each include optical-to-electrical conversion circuitry.

15. The reception equipment of claim 9, wherein the first optical module includes a photodetector for receiving the first optical signal and generating therefrom the first electrical signal.

16. The reception equipment of claim 9, wherein the electronic circuitry comprises a selector for forwarding one of the first and second electrical signals, a deserializer for deserializing the selected one of the first and second electrical signals, and signal processing circuitry for generating the output signal.

17. A broadband communication system, comprising: a communication channel; transmission equipment for receiving an input signal and generating at least one optical signal for transmission over the communication channel, the at least one optical signal corresponding to the input signal, and the transmission equipment comprising: transmission electronic circuitry for converting the input signal to a digital electrical signal formatted in accordance with a first standard communication protocol; and at least one plug-in transmission module for processing the digital electrical signal to generate the at least one optical signal, wherein the at least one plug-in transmission module is detachably coupled to the transmission electronic circuitry and removable from the transmission equipment; and reception equipment for receiving the at least one optical signal over the communication channel and for generating therefrom an output signal corresponding to the input signal received by the transmission equipment, the reception equipment comprising: at least one plug-in reception module for processing the at least one optical signal to generate at least one electrical signal formatted in accordance with a second standard communication protocol; and reception electronic circuitry for receiving the at least one electrical signal, selecting therefrom a single electrical signal, and generating the output signal from the single electrical signal, wherein the at least one plug-in reception module is detachably coupled to the reception electronic circuitry and removable from the reception equipment.

18. The broadband communication system of claim 17, wherein the at least one plug- in transmission module comprises two redundant modules.

19. The broadband communication system of claim 17, wherein the at least one plug- in transmission module comprises: a laser driver for receiving the digital electrical signal; and a laser for generating the at least one optical signal in response to activation by the laser driver.

20. The broadband communication system of claim 17, wherein the at least one plug- in reception module comprises: a photodetector for converting the at least one optical module to the at least one electrical signal.