Patent Application
20080220731
The present disclosure is generally related to communications and, more particularly, is related to systems and methods for frequency modulated communications.
Conventional analog reverse path optical links used in hybrid fiber/coax (HFC) networks often suffer from limited range capabilities. The transmitter optical output power and receiver optical input power is typically limited such that links are limited to distances within the range corresponding to transmitter optical output power and receiver optical input power.
Lasers used for reverse path signaling in the conventional approach to HFC network design are intensity modulated by the radio frequency electrical signals that contain information for transmission in the reverse path. Ideally the light intensity from these lasers is proportional to these electrical signals. The light is launched down a reverse path optical fiber and is attenuated by an amount that is a function of the length of that fiber. Radio frequency (RF) output power levels from conventional optical receivers are a function of the received optical input power. Variations in the length of optical fibers throughout the HFC network result in variations in the received optical power at the input of each optical receiver. Consequently, RF output power is manually adjusted at each optical receiver to compensate for variations in optical loss from link to link. Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and/or inadequacies.
Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
STS 100 can be configured to provide programming signals as digitally formatted signals in addition to delivering analog programming signals. Further, STS 100 can be configured to support one way broadcast services as well as both one-way data services and two-way media and data services. The two way operation of STS 100 can allow for user interactivity with services, such as Pay-Per-View programming, Near Video-On-Demand (NVOD) programming according to any of several known NVOD implementation methods, View-on-Demand (VOD) programming (according to any of several known VOD implementation methods), and interactive applications, such as Internet connections and interactive media guide (IMG) applications.
STS 100 may also be configured to provide interfaces, network control, transport control, session control, and servers to access content and services, and to distribute content and services to STT users. As shown in
Additionally, the network can be configured to transmit media content to a headend for further transmission to users downstream in the network. Data provided by one or more content providers (such as via satellite 104a, Internet 104b, Public Switched Telephone Network (PSTN) 104c, etc.) can be communicated by the content provider to headend 110. From headend 110, the received data may then be communicated over transmission medium 102 to one or more hubs 120a-120e. The hubs 120 can be coupled to one or more nodes 140, each of which may serve a local geographical area. Node 140 is coupled to feeders 170a and 170b, which are coupled to network STTs 160. As one of ordinary skill in the art should understand, STS 100 shown in
One can appreciate that, although a single headend 110 is illustrated in
Included in headend 110 are receivers 202a and 202b, which are coupled to satellite 104a and antenna 104d, respectively. As discussed above, programming data can be received from any of a plurality of different sources including (but not limited to) those illustrated in
These signals are sent to and received from the STTs, cable modems, voice interfaces, and other devices throughout the HFC network. Modems 216 can be configured to be responsible for transporting out-of-band Internet Protocol (IP) data traffic between distribution headend 110 and at least one STT 160, which can send data to at least one display device 150. Data from modem 216 can be routed by headend 110. Headend 110 can also be responsible for delivering upstream traffic (e.g., application data traffic) to the various server applications associated with headend 110. Although reference is made to STTs 160 in exemplary embodiments, the systems and methods enclosed herein also apply to cable modems that are connected to computers, voice interfaces for telephony, and telemetry electronics for monitoring network performance, as well as other devices that utilize two-way communication over an HFC network.
Additionally, headend 110 may include modulators 210a, 210b, and 210c, which are coupled to receiver 202a, receiver 202b, and multiplexor 208, respectively (as well as control system 220). Modulators 210a-210c are coupled to combiner 212. Combiner 212, as well as modem array 216 are coupled to transmission medium 102.
While not included in the nonlimiting example of
Additionally included in the nonlimiting example of hub 120 from
Although frequency modulation (FM) has been widely used for transmission of audio signals, FM may be used for many other functions, including modulation functions in headend 110 and node 140. Hub 110 or headend 160 may arrange a group of signals, which are signal sources for downstream signals, for preparation for downstream transmission to a subscriber's home or business, or other intended receiver of the downstream signal. This group of signals may be combined together into one or more composite signals using RF sub-carrier multiplexing. For example, each TV channel has its own RF sub-carrier on an individual frequency. There are sub-carriers that carry digital information such as non-limiting examples of digital television, high-speed data, etc.
For example, modulator 530 may convert an RF signal to an optical signal, and then, at node 555, the optical signal is converted back to an RF or electrical signal. Two-way communications utilize both downstream communications from headend/hub 510 to STT 560 and upstream communication from STT 560 back to headend/hub 510 or to cable modem termination system (CMTS) 590.
Whereas the downstream signals are sent, in one implementation, in the 50 MHz to 1000 MHz band, the upstream signals are typically sent in the 5 MHz to 40 MHz band (e.g., international systems may use other frequency bands).
On the upstream side, a second modulator 580 in node 555 modulates the RF electrical signal for propagation along transmission medium 545. The signal is received by receiver 585, where it may be converted back to an electrical signal for CMTS 590.
One or more problems may occur with this approach. One problem is the reach or range of the transmission medium. There may be a limited amount of fiber distance. With intensity modulation, for example, as the signal propagates down the fiber, the signal is attenuated and the receiver (e.g., node 555) has a limit at which it can no longer receive a meaningful signal due to reduced signal to noise ratio. A repeater may be used. However, a repeater may not be practical because a surface (e.g., a street) may have to be disturbed, electronic components may need to be remotely added to the system, and/or power may need to be provided to the electronic components, among other reasons. Another problem is that the output signal level varies in amplitude with the transmission distance.
To overcome these and/or other potential problems, instead of directly modulating the optical signal with the upstream RF signal, the RF upstream signal is first modulated by a wide-band FM modulator.
For example, modulator 730 may convert an RF signal to an optical signal, and then, at node 755, the optical signal is converted back to an RF or electrical signal. Two-way communications utilize both downstream communications from headend/hub 710 to STT 760 and upstream communication from STT 760 back to headend and/or hub 710 or to cable modem termination system (CMTS) 790. CMTS 790 may be included as a part of headend and/or hub 710 in some embodiments.
In one implementation, whereas the downstream signals are sent in the 50 MHz to 1000 MHz band, the upstream signals are sent in the 5 MHz to 40 MHz band. Referring to
In one exemplary embodiment, the carrier frequency (Fc) is between 1 GHz and 1.5 GHz. A wide-band FM modulated signal may be intensity modulated with a laser to produce an optical signal for transmission across transmission medium 745. In one non-limiting example, the FM carrier may be transmitted over optical fiber. The signal may be received by receiver 785 and then FM demodulator 795, which is communicatively coupled to CMTS 790. With an FM signal, the signal amplitude can drop much lower and still maintain data integrity at CMTS 790 with acceptable signal-to-noise ratio.
Embodiments of the present disclosure can be implemented in hardware, software, firmware, or a combination thereof. In at least one exemplary embodiment, the frequency modulation may be implemented in software or firmware that is stored in a memory (e.g., in a digital signal processor (DSP)) and that is executed by a suitable instruction execution system. If implemented in hardware, as in an alternative embodiment, the frequency modulation may be implemented with any or a combination of the following technologies, which are all well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc.
Any process descriptions or blocks in flow charts should be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process, and alternate implementations are included within the scope of the preferred embodiment of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present disclosure.
Embodiments of a frequency modulation program, which comprises an ordered listing of executable instructions for implementing logical functions, may be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer-readable medium” can be any mechanism that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a nonexhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM) (electronic), a read-only memory (ROM) (electronic), an erasable programmable read-only memory (EPROM or Flash memory) (electronic), an optical fiber (optical), and a portable compact disc read-only memory (CDROM) (optical). Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory. In addition, the scope of the present disclosure includes embodying the functionality of the preferred embodiments of the present disclosure in logic embodied in hardware or software-configured mediums. It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present disclosure and protected by the following claims.
