Abstract:
A software definable transceiver capable of digitally synthesizing, transmitting and receiving a modulated, composite cable television signal is provided. This embodiment of the present invention provides a software definable cable television signal synthesizer capable of digitally synthesizing cable television signals for both analog and digital modulations. The software definable system is also capable of simultaneously synthesizing a plurality of input channels of cable content, and appropriately modulating the input channels into a plurality of output cable television channels. This Abstract is provided for the sole purpose of complying with the Abstract requirement rules that allow a reader to quickly ascertain the subject matter of the disclosure contained herein. This Abstract is submitted with the explicit understanding that it will not be used to interpret or to limit the scope or the meaning of the claims.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to communications. More particularly, the invention concerns a software-definable cable television network head-end.  
       BACKGROUND OF THE INVENTION  
       [0002]     The Information Age is upon us. Access to vast quantities of information through a variety of different communication systems are changing the way people work, entertain themselves, and communicate with each other. For example, as a result of increased telecommunications competition mapped out by Congress in the 1996 Telecommunications Reform Act, traditional cable television program providers have evolved into full-service providers of advanced video, voice and data services for homes and businesses. A number of competing cable companies now offer cable systems that deliver all of the just-described services via a single broadband network.  
         [0003]     Bandwidth, a measure of the capacity of a communications medium to transmit and receive data, has become increasingly important with the continuing growth in data transmission demands. Applications such as in-home movies-on-demand, video teleconferencing, and interactive video in homes and offices require high data transmission rates.  
         [0004]     Broadband communication systems such as cable television networks, and “fiber to the premises” (FTTP) networks, and multiple service operators (MSOs), generally employ a combination of band limited coaxial cables coupled to optical fiber systems to transmit and receive data. Conventional approaches for transmitting communication signals through a medium such as a band-limited cable and the remaining supporting infrastructure entails modulating the communication signal using parameters such as frequency and amplitude that lie within the normal conductive range of the medium. Many costly and complicated schemes have been developed to increase the bandwidth in conventional broadband systems. Some of these schemes use sophisticated switching or signal time-sharing arrangements. However, each of these methods is costly and complex.  
         [0005]     For example, current broadband cable television “head-end” architectures require a significant amount of infrastructure hardware. Efficiency may be compromised because of the relatively rigid, and limited, nature of the system hardware elements in use, particularly at the head-end of the cable television system, which generally comprises multiple racks of components such as dedicated modulators, signal combiners, multiplexers and amplifiers. However, enhancements, upgrades and maintenance to these components, and others located in the field, are costly because such actions often involve physical removal and replacement of these hardware components with more expensive units, requiring an investment in hardware as well as labor. In addition, maintenance and upgrades require undesirable periods of system, or channel unavailability to the consumer. Moreover, these hardware components require relatively substantial amounts of power and physical space.  
         [0006]     Another deficiency in current broadband systems lies in the limited ability of the broadband provider to timely locate and replace failed, or failing, components or monitor and verify system functionality at remote locations “downstream” from the head-end. Such components include, for example, fiber optic transceivers and field amplifiers for boosting the signal strength at various points in the broadband network. Current procedures call for a technician to perform periodic preventive maintenance that optimizes system performance and mitigates the likelihood of component failure, requiring the technician to travel to the site of each component to physically inspect, test, and replace it as necessary. Though costly and time-consuming, scheduled component inspections and replacements are still more desirable than recovering from system outages.  
         [0007]     Therefore, there remains a need to overcome one or more of the limitations in the above-described, existing art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Various embodiments of the present invention taught herein are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which:  
         [0009]      FIG. 1  is an illustration of a conventional cable, or hybrid fiber-coax communication system topology including a head-end;  
         [0010]      FIG. 2  is an illustration of signal processing generally performed at the head-end of a conventional cable, or hybrid fiber-coax communication system as shown in  FIG. 1 ;  
         [0011]      FIG. 3  is an illustration of one embodiment of the present invention comprising high-speed analog-to-digital (ADC) and digital-to-analog (DAC) components;  
         [0012]      FIG. 4  is an illustration of one embodiment of the present invention comprising a main processing module utilizing one or more processing units for digital signal synthesis;  
         [0013]      FIG. 5  is an illustration of one embodiment of a processing unit for digital signal synthesis based on digital signal processing components;  
         [0014]      FIG. 6  is an illustration of one embodiment of a digital signal synthesis processing unit employing a buffered waveform look-up table;  
         [0015]      FIG. 7  is an illustration of another embodiment of a digital signal synthesis processing unit employing multiple buffered waveform look-up tables;  
         [0016]      FIG. 8  is an illustration of different communication methods;  
         [0017]      FIG. 9  is an illustration of two ultra-wideband pulses;  
         [0018]      FIG. 10  is an illustration of one embodiment of the present invention wherein ultra-wideband (UWB) communication signals are injected into a cable, or hybrid fiber-coax TV channel spectrum;  
         [0019]      FIG. 11  is an illustration of a status request and response message protocol process flow;  
         [0020]      FIG. 12  is an illustration of an autonomous status response message protocol process flow;  
         [0021]      FIG. 13  is an illustration of one embodiment of the present invention in which in-device sensors provide system performance measurement information to the cable, or hybrid fiber-coax head-end;  
         [0022]      FIG. 14  is an illustration of optimal partitioning of power levels between conventional cable channel content and UWB content;  
         [0023]      FIG. 15  is an illustration of general functions of UWB system components in one embodiment of the present invention; and  
         [0024]      FIG. 16  is an illustration of current Federal Communication Commission mandated emission limits for UWB devices in the United States. 
     
    
       [0025]     It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. The Figures are provided for the purpose of illustrating one or more embodiments of the invention with the explicit understanding that they will not be used to limit the scope or the meaning of the claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     In the following paragraphs, the present invention will be described in detail by way of example with reference to the attached drawings. While this invention is capable of embodiment in many different forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. That is, throughout this description, the embodiments and examples shown should be considered as exemplars, rather than as limitations on the present invention. Descriptions of well known components, methods and/or processing techniques are omitted so as to not unnecessarily obscure the invention. As used herein, the “present invention” refers to any one of the embodiments of the invention described herein, and any equivalents. Furthermore, reference to various feature(s) of the “present invention” throughout this document does not mean that all claimed embodiments or methods must include the referenced feature(s).  
         [0027]     The present invention provides an interactive, software definable transceiver capable of digitally synthesizing, transmitting and receiving a modulated, composite cable television signal system at the cable head-end.  
         [0028]     One embodiment of the invention provides a software definable digital signal synthesizer including a high-speed processor and a high-speed digital-to-analog converter (DAC). One feature of the present invention is that the high-speed processor and high-speed DAC operate at speeds capable of synthesizing communication signals in any portion of cable television channel spectrum. Another feature of the present invention is that the high-speed processor is capable of running software that supports synthesis of cable television signals according to multiple different data formats, modulation methods, and channel allocations. The present invention may be reprogrammed to additionally support future video standards, modulation methods and data format standards.  
         [0029]     This embodiment of the present invention provides a software definable cable television signal synthesizer capable of digitally synthesizing cable television signals for both analog and digital modulations, containing multiple television channels. The software definable system is also capable of simultaneously synthesizing a plurality of input channels of radio frequency cable content, and appropriately modulating the input channels to a plurality of output cable television channels.  
         [0030]     In another embodiment, the cable head-end transmitter and remote cable television system components are capable of transmitting ultra-wideband (UWB) signals that may occupy some or all of the radio frequencies used to transmit the TV signals, independent of, or simultaneously with, transmission of the TV signals.  
         [0031]     Generally, a traditional cable television provider, a community antenna television provider, a community access television provider, a cable television provider, a hybrid fiber-coax television provider, an Internet service provider, an IPTV provider or any other provider of television, audio, voice and/or Internet data generally receives broadcast signals at a central station, either from terrestrial cables, over-the-air broadcast, and/or from one or more antennas that receive signals from communications satellite(s). The broadcast signals are processed, combined, and then distributed, usually by coaxial and/or fiber-optic cable, from the central station to nodes located in business or residential areas.  
         [0032]     As can be inferred from the above list, cable television networks are currently deployed using several different topologies and configurations. The most common configurations found today include coaxial cable and Hybrid Fiber-Coax Systems (HFCS) that employ both fiber optic and coaxial cables. These systems may employ both analog and digital signals. Systems that employ only analog signals are further characterized by their use of established NTSC/PAL (National Television Standards Committee/Phase Alternation Line) modulation, with requires use of frequency carriers at 6 or 8 MHz intervals.  
         [0033]     With reference to  FIG. 1 , a conventional hybrid fiber-coax system (HFCS), or network, is illustrated. It will be appreciated that the HFCS network may be part of a multiple service operator system, and that specific architecture components may vary, from network to network. The HFCS employs a combination analog-digital topology, as both coaxial 45 (analog), and fiber optic 55 (digital) media are used. According to the frequency allocations specified by the ANSI/EIA-542-1997 standard that usually arranges the analog channels from 2 to 78, each modulated in 6 MHz allocations, using frequencies from 55 to 547 MHz. When using HFCS, digital channels typically start at channel 79 and go to 136 and occupy a frequency range from 553 to 865 MHz. In some extended HFCS systems, channel assignments can go as high as channel 158 or 997 MHz. 1 gigahertz is currently the upper frequency limit, as network components, such as amplifiers and TV tuners are incapable of operation above that frequency. The current ANSI/EIA-542-1997 standard only defines and assigns channels to 997 MHz. However, the actual wire or cable media is generally capable of carrying frequencies up to 3 GHz and beyond.  
         [0034]     In both analog cable and HFCS systems, a satellite downlink containing video, audio, Internet, and/or other data is received at antenna  10 , and enters the cable company&#39;s “head-end”  25  at the router  20 , shown in  FIG. 1 . Additional video and/or other data streams  15  (non-satellite received), including data received by fiber optic cable  12  may feed data to the router  20 . Individual video and other data streams (either NTSC, MPEG, or any other employed protocol) are extracted from the satellite downlink stream or other data streams  15  and routed to channel modulators  30 A-N, each specific to an individual television channel. Alternatively, the radio frequency (RF) content received from the satellite antenna  10  and other data streams  15  are presented substantially directly to the channel modulators  30 . In both cases, an initial task performed by each channel modulator  30  is to reject frequency content from the input broadband RF signal that is extraneous to the particular output cable channel assigned to the specific channel modulator  30 . After input channel filtering, the received channel content is converted from the input channel carrier frequency to the carrier frequency of the output cable channel. The outputs from each channel modulator  30  are then sent to combiner  40  and combined into one broadband RF signal. From this point the composite, broadband RF signal containing the combined channels is amplified and sent, either by coaxial cable  45  or fiber optic  55  cable, to cable television customers. The broadband RF signal may be amplified by field amplifiers  70 , and ultimately received by the customers, or other end-users equipment  80 , such as a set-top box, or other device.  
         [0035]     Referring now to  FIG. 2 , some components of the cable head-end  25 , as shown in  FIG. 1 , are illustrated. Generally, the head-end  25  includes one or more routers  20 , channel modulators  30 , and combiners  40 , and in HFCS, a fiber optic modulator  50 . It will be appreciated that the cable head-end  25  may include other components as well. The router  20  forwards the data stream, that may comprise both, or one of, the satellite downlink stream or the other data streams  15  to a band-pass filter (BPF)  105 . BPF  105  is structured to reject frequency content not pertaining to the output cable channel assigned to the specific channel modulator  30 . The specific channel signal is then mixed with a carrier, which is generated by a local oscillator (LO)  115 , which mixes the specific channel signal to an intermediate frequency (IF) by mixer  110 . This mixing step converts the channel signal to a signal at the IF frequency. This step is commonly performed in television signal processing to allow a single circuit design to accommodate many different input and output channel frequencies. By converting a channel signal at an arbitrary input channel frequency to a standard IF, subsequent processing may be performed with circuitry designed to operate at IF instead of at a multiplicity of possible channel frequencies.  
         [0036]     Referring again to  FIG. 2 , the channel signal, once converted to IF, is then passed through a secondary BPF  120  to remove extraneous signal energy outside of the IF band. For North American (i.e., NTSC) implementations, the IF is typically between 41 and 47 MHz. In this example, the picture, or video and sound, or audio carriers are then separated. The picture signal occupies the spectrum from about 41.75 to 46.5 MHz, and the audio rides on a 41.25 MHz carrier. Accordingly, the signal is supplied a video BPF  130 , and an audio BPF  135 . The video BPF  130  filters the picture signal of audio content and the audio BPF  135  filters the audio signal of picture content. The two filtered signal streams are then recombined at combiner  140  into a single signal, centered at IF. A secondary local oscillator (LO)  150  generates a carrier signal and secondary mixer  145  multiplies the combined signal by the carrier signal. Secondary mixer  145  places the signal content at the desired frequency for transmission. The output of channel modulator  30  is then combined with similar outputs from other channel modulators by combiner  40  to produce the composite signal  525 .  
         [0037]     The routers  20 , channel modulators  30 , and combiners  40  used in a cable television head-end  25  are typically discrete hardware components employing mostly analog circuitry. It will be appreciated that in some instances, analog components may have higher power requirements than their digital counterparts. Further, each channel modulator  30  modulates a single channel and, therefore, literally hundreds of channel modulators  30  are required in every cable head-end  25  to accommodate the hundreds of channels available on most cable television networks. Moreover, a considerable amount of physical space is required to house rows upon rows of racks containing the channel modulators and associated components. The cable head-end  25  represents a substantial investment for cable operators.  
         [0038]     Referring now to  FIG. 3 , which illustrates a software-definable head-end (SDHE)  75 , constructed according to one embodiment of the present invention. One application of the SDHE  75  allows for the replacement of the multiple channel modulators  30 A-N and combiner  40 . One feature of the SDHE  75  is that it performs direct digital synthesis of a signal that is equivalent to the composite signal  525  present at the output of the RF combiner  40 . That is, the SDHE  75  provides direct digital synthesis of the composite, broadband output cable television signal. As shown in  FIG. 3 , in one embodiment, a high-speed analog-to-digital converter (ADC)  180  receives analog content from satellite antennas  10  and/or other data streams  15 . The content from the satellite antennas  10  may be pre-processed prior to employing the present invention. Additional content may be provided from any number of other sources. One feature of present invention is that the ADC  180  will have the capacity to adequately “over sample” the analog input signals. This is because Nyquist sampling theory holds that the minimum sampling frequency at which a signal may be accurately resolved is twice the highest frequency content of the signal. In alternative embodiments, to provide more robust frequency resolution, “4-times over sampling” may be employed.  
         [0039]     The digital data, either from digital sources or following conversion by analog to digital converter  180 , the resulting digital data stream  190  comprising sampled content is passed to a programmable digital processing module  200 . The digital processing module  200  may perform tasks such as channel separation, filtering, input-to-output channel conversion, and channel recombination. The output of digital processing module  200  comprises a sampled version of the combined broadband signal containing the input cable channels now reassigned to cable television channels. Moreover, the digital data stream generated by the processing module  200  represents a digitized equivalent of the composite signal  525  produced by the combiner  40  shown in  FIG. 1 . As shown in  FIG. 3 , the sampled composite signal is passed to a high-speed DAC  210  for conversion, resulting in the composite signal  525 . The composite signal is passed from the DAC  210  to a coax cable  45  and/or a fiber optic modulator  50  before distribution over a fiber optic cable  55 .  
         [0040]     As shown in  FIG. 4 , one embodiment of the digital processing module  200  is illustrated. The incoming digital data stream  190  to passed to one or more processing units  202 A-D. It will be appreciated that though  FIG. 4  depicts this embodiment of the invention as employing four processing units  202 A-D, the invention is not limited to this number of processing units  202 . The output of each processing unit  202  may comprise one or more input signals received over the digital data stream  190 , each modulated to an output cable channel carrier according to the input-to-output channel mapping employed by a specific cable service provider. The output  203 A-D of each processing unit  202 A-D is passed to a digital combiner  205  that sums the outputs in a similar manner to the combiner  40 , shown in  FIG. 1 . The output of digital combiner  205  is a sampled composite broadband cable signal that is passed to the high-speed DAC  210 . The DAC  210  converts the sampled broadband signal into its analog equivalent, representing a digitally synthesized equivalent of the broadband signal that is generated at the output of an analog combiner  40 , shown in  FIG. 1 . One feature of the SDHE  75  is that the cost, complexity and power consumption of the head-end  25  is reduced by replacing functionality formerly carried out by numerous analog components with a single re-programmable digital apparatus. This greatly reduces the cost of a head-end  25 .  
         [0041]     One feature of the present invention is that the software, or logic installed on digital processing units  202  may be modified, or replaced after initial installation. Substantial functional flexibility is thereby provided since any new computational requirements demanded of the processing units  202  can be implemented without costly modification or replacement of hardware. Thus, capabilities to manage new and different video, audio, and data formats, including high definition television (HDTV), and to redefine channel assignments and carrier frequencies are easily implemented. As video compression and decompression methods continually improve and evolve, these new methods can be implemented at the cable head-end  25  by simply reprogramming the appropriate processing units  202 . It is further contemplated that re-programming of the processing units  202  may occur at any time, including during the installation process, “on-the-fly” (while the system is in operation), when required to handle transient or periodic processing tasks, and when the head-end  25  may be shut down for maintenance. In one embodiment of the invention, the processing units  202  may further act as real-time control mechanisms to maintain various signal transmission parameters within desired tolerances. Cable television channel signal transmission power may be controlled, for example, to maintain frequency assignment, carrier to noise ratios, and other parameters at optimal levels according to feedback information from intermediate cable network devices such as amplifiers, splitters, and fiber optic receivers, and end-user devices such as set-top-boxes, and wireless devices that may be fed from the set-top-boxes.  
         [0042]     It is anticipated that these wireless devices may include Wireless Personal Area Network (WPAN) devices, such as BLUETOOTH devices or WPAN ultra-wideband devices, Wireless Local Area Devices (WLAN), such as WI-FI devices or WLAN ultra-wideband devices, and Wireless Metropolitan Area Network (WMAN) devices such as WI-MAX devices. (BLUETOOTH is a registered trademark of Bluetooth SIG, Inc. of Delaware)  
         [0043]     Another embodiment of the invention contemplates that each of the processing units  202 , shown in  FIG. 4 , may comprise a specialized microprocessor dedicated to digital signal processing, known as a “digital signal processor” (DSP). The DSP may be reprogrammable through a variety of methods after installation and during operation. For this embodiment of the invention, the tasks for the DSP may include modulating the input digital waveforms to one or more specific channel frequencies. Other tasks may include decompressing certain data prior to processing, such as video that may have been compressed using MPEG-2, MPEG-4, JPEG 2000, or other compression methods, or converting data from one storage or transmission format to another. Real-time control of various channel signal transmission parameters can be realized, for example, by structuring the DSP to read parametric values from memory. Signal power, amplitude, and filtering characteristics can thus be updated as needed by providing a separate control process to copy new parameters to appropriate memory locations where they are read and subsequently implemented by the DSP. As shown in  FIG. 4 , the digitized streams from the processing units  202  employing a DSP are routed to combiner  205 , and the resulting composite signal is passed to the high-speed DAC  210 .  
         [0044]     In another embodiment of the invention, each processing unit  202  may comprise one or more field programmable gate arrays (FPGA). A FPGA is a logic device that is generally reprogrammable after manufacture. There are many varieties of FPGA, several of which possess the capability to be reprogrammed while in-system (i.e., installed with new/modified software). These include, for example, those based on static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), and flash-erase EPROM (FLASH) technology. In another embodiment of the present invention, each processing unit  202  comprises one or more dedicated state machines. Functional re-programmability is enabled for both FPGAs and dedicated state machines by writing new processing parameters to accessible memory.  
         [0045]     Referring again to  FIG. 4 , one method of employing this aspect of the present invention is as follows. In this embodiment, the input signal  190  comprises a frequency-division-multiplexed signal. It will be appreciated that other types of signals may comprise the input signal  190 . The bandwidth of a the digitized, frequency-division-multiplexed input signal  190  is distributed among a plurality of processing units  202  (four shown) comprising the programmable digital processing module  200 . By way of example and not limitation, input signal  190  may have a bandwidth of approximately 1 GHz, partitioned among four processing units  202  as follows: 0-240 MHz to a first unit  202 A, 240-480 MHz to a second unit  202 B, 480-720 MHz to a third unit  202 C, and 720-960 MHz to a fourth unit  202 D. It is anticipated that partitioning may include the calculation of a Fast Fourier Transform output. For the purposes of this example the 1 GHz input signal was over-sampled at 4 GHz. It will be appreciated that other sampling methods, requiring less over-sampling, may be employed.  
         [0046]     One embodiment of a processing unit  202  is illustrated in  FIG. 5 . This embodiment comprises an input stage  215 , a DSP  270 , and an output stage  275 . It will be appreciated that the arrangement of these components may vary from the illustration, for example, the output stage  275  may be located on a different component than the processing unit  202 . The input signal  190  is passed through a digital BPF  220  in the input stage  215 . The digital BPF  220  is structured to reject frequencies outside of the assigned partition of the input bandwidth.  
         [0047]     For example, in the frequency-partitioning arrangement described above, the second processing unit  202 B rejects frequencies outside of the range from 240-480 MHz. The filtered signal is next received by digital mixer  230  that “down-converts” the signal to a base-band frequency range of 0-240 MHz. The digital mixer  230  accomplishes this down conversion by multiplying the filtered digital output sequence from the digital BPF  220  by a stored digital carrier sequence 235 at 240 MHz, creating copies of the signal at 0 Hz and at 480 MHz. The resulting signal is then passed through a low pass filter (LPF)  250  to reject frequency content above 240 MHz, leaving only the low frequency copy at base-band. The down-converted signal may now be decimated or “down-sampled” because it retains the 4 GHz sampling rate applied to the original 1 GHz signal. However, the 4 GHz sampling rate is no longer necessary to accurately resolve the frequency content of the filtered, 240-480 MHz partition, now down-converted to the 0-240 MHz range. Accordingly, the signal may then be down-sampled by decimator  260 . The resulting digital signal is then passed from the input stage  215  to the DSP  270 , thus completing input stage processing. It will be appreciated that one advantage gained by down-sampling lies in commensurately reducing the workload imposed on DSP  270 , requiring it to process data at one-fourth of the rate from which the original signal arrived at the input stage  215  from ADC  180 .  
         [0048]     Shown in  FIG. 5 , the DSP  270  may be structured to perform many tasks with the digital data down-sampled, and received from, the input stage  215 . These tasks may include, but are not limited to, separate picture and audio signal filtering, signal power adjustment, and data reformatting. Task flexibility may be effected, for instance, by storing digital filter tap weights in memory  320  to which a separate controller  330  may write updated weight values for access by the DSP  270 . Real-time power adjustments can be made by structuring the separate controller  330  to write periodically updated signal power parameters to memory, which the DSP  270  can read and use.  
         [0049]     In one embodiment, DSP  270  contains a bank of band-pass filters  274 A-N, each of the bank of BPFs  274 A-N is structured to reject frequency content outside the range of some single input channel frequency. In the present example, there would be forty  6  MHz channels residing in the 0-240 MHz base band signal passed to DSP  270 . This would result in forty band-pass filters  274  each structured to pass one channel each. It will be appreciated that a BPF may be implemented digitally by a finite impulse response (FIR) filter, and that a FIR filter is defined essentially by the number filter taps it employs and filter weights assigned to the taps. One feature of the present invention is that the filter weights can be software-defined allowing for reconfiguration. This redefinition may be accomplished by controller  330  modifying sets of filter tap weights in a memory  320  accessed by any one of the bank of BPFs  274 A-N. When directed, the controller  330  may copy new or updated filter tap weights to specific locations in memory  320  and may therefore effect configuration changes to any of the bank of BPFs  274 A-N.  
         [0050]     The output stage  275  of the processing unit  202  generates a combined signal  203  containing one or more channels. In the current example, there are forty input channels, received from a bank of forty processing blocks  276 A-N. Each processing block  276 A-N may perform one or more functions, such as signal filtering, signal amplitude adjustment, signal power adjustment, and data reformatting, among others. The output of each processing block  276 A-N comprises a digital stream with a 6 MHz bandwidth representing the processed content of a single input cable channel.  
         [0051]     One of the primary tasks performed at the cable head-end  25  is to convert content on each input cable channel to some output cable channel according to the input-to-output channel mapping employed by the cable service provider. The output stage  275  accomplishes this by first providing that each per-channel digital stream generated by the bank of processing blocks  276 A-N is interpolated onto the frequency of the carrier by interpolators  280 A-N. Each processed stream is then multiplied by discrete samples of the appropriate carrier by carrier mixers  290 A-N. These discrete samples can be stored as digital carrier sequences  300 A-N. Each discrete carrier sequence, which may be any one of carrier sequences  300 A-N, may be accessed from memory  320  instead of being hard-coded or created by analog circuitry. At any time, the controller  330  may copy a digital carrier sequence representing a different channel up-conversion to the memory location in common memory  320  accessed by, for example, carrier mixer  290 B. One feature of this embodiment is that the input-to-output channel mapping may be modified in real time, providing operational flexibility not made available by current analog systems.  
         [0052]     Each processed stream is then multiplied by discrete samples of the appropriate carrier by carrier mixers  290 A-N. Following up-conversion to the appropriate frequency band, a plurality of like-processed signals are combined by processing combiner  310 . The overall result is an output  203  representing a frequency division multiplex of the output channel content provided by each of the processor units  202 A-D. As shown in  FIG. 4 , the output  203  from all the processing units  202 A-D are combined in digital combiner  205  and the resulting composite signal is passed to the high-speed DAC  210 .  
         [0053]     In another embodiment of the present invention, the processing units  202 A-D may comprise one or more devices utilizing a list, or look-up-table (LUT) of buffered waveforms as an alternative to manipulating digital data received over the digital stream  190  from the ADC  180 . One feature of this embodiment is that it reduces the computational complexity from calculating a waveform to matching and copying an output waveform from a storage location in memory. The LUT methods used in this embodiment of the invention are designed to allow DSP functions to keep up with very high speed ADC and DAC components.  
         [0054]     Referring to  FIG. 6 , an alternative embodiment output stage  275  is illustrated. Output from processors  276 A-N is passed to buffered output stage  315 . In one embodiment, one buffered output stage  315  may receive all the output from each processor  276 A-N, or alternatively, one or more buffered output stages  315  may receive output from corresponding processors  276 A-N. As illustrated in  FIG. 6 , output from the processors  276 A-N may be routed to partitioner  340  to be divided into discrete blocks of data such as “words” or “symbols.” Generally, a symbol is something that represents something else. For example, a certain voltage level may be used to represent a “1” or a “0,” or an absence of a voltage may be used to represent a “1” or a “0.” It will be appreciated that any number of binary digits (0 or 1) may be represented by a symbol, and that the symbol itself may be a positive or a negative voltage, an absence of a voltage, or some other type of representation.  
         [0055]     For example, a symbol output from partitioner  340  is written to a symbol register  350 . Association logic  360  can then perform a matching association between the input symbol and a “dictionary” of data symbols  370 A-N stored in a memory buffer. Waveform buffer  380  contains a collection of digitized waveforms  380 A-N, where each waveform  380 A-N is associated with a buffered data symbol  370 A-N. Associating a buffered waveform to a buffered data symbol replaces the computation of a DSP-generated output waveform, as discussed above, in connection with  FIG. 5 . One feature of this aspect of the invention is the increased speed realized by obtaining a waveform from memory, rather than computing a waveform. Once a match between the input symbol and a buffered data symbol  370 A-N is successfully accomplished, the stored digital waveform  380 A-N corresponding to the buffered data symbol  370 A-N is accessed and passed to output  203 .  
         [0056]     Alternatively, the data symbols may be partitioned in data partitioner  340  and then associated with one or more corresponding buffered waveforms obtained from the waveform buffer  380 . In this embodiment, the symbol register  350  and association logic  360  are eliminated, or merged into the data partitioner  340 .  
         [0057]     The buffered digital waveforms are equivalent to sampled versions of analog waveforms modulated to contain the information provided by the input symbol. When transmitted onto a cable television network, or other type of network, this waveform conveys the information contained by the input symbol to end-user equipment  80 , as seen in  FIG. 1 . Digital copies of modulated waveforms reside in waveform buffers  380 A-N and are addressed, or “looked up,” in waveform buffers  380 A-N according to the input symbol. Each digital copy of the modulated waveforms comprise a group of digital values. The digital values are copied from waveform buffers  380 A-N and passed to output  203 . As each new input symbol is presented to buffered output stage  315 , an appropriate digitized waveform is matched and passed to output  203 . The resulting output  203 , which comprises content of one or more cable channels, is then passed to the digital combiner  205 , where it is combined with the rest of the cable television channel content generated by the processing units  202 A-D, as shown in  FIG. 4 . The combined signal is then passed to the high-speed DAC  210  which generates the RF cable television signal.  
         [0058]     In one embodiment of the present invention, the buffered waveforms  380 A-N may include waveforms from a number of different communication methods. For example, the buffered waveforms  380 A-N may comprise discrete samples of an Orthogonal Frequency Division Multiplexed (OFDM) signals at different transmission frequencies. Alternatively, the buffered waveforms  380 A-N may include discrete samples of a QAM modulated waveform at different transmission frequencies. It is anticipated that virtually any communications waveform may be generated by storing, and using the appropriate buffered waveforms  380 A-N.  
         [0059]     Another embodiment of the present invention is illustrated in  FIG. 7 , which illustrates a multiple-buffered output stage  375 . This embodiment comprises multiple buffered waveform tables  382 A-D. It will be appreciated that more than four buffered waveform tables may be employed, with only four tables illustrated for clarity. One feature of this embodiment is that it allows each of the buffered waveform tables  382 A-D to contain different sets of digital waveforms. For example, table  382 A may contain output waveforms modulated to an arbitrary cable channel X, table  382 B may contain waveforms for an arbitrary cable channel Y, and table  382 C may contain waveforms for an arbitrary cable channel Z.  
         [0060]     Controller  330  instructs a logical switch  384  to access the desired waveform, from one of the multiple buffered waveform tables  382 A-D. For example, if output for cable channel Y is desired, the logical switch  384  is instructed to associate buffered data symbols stored in the “dictionary” of data symbols  370 A-N with the appropriate waveform stored in one of the buffered waveform tables  382 A-D.  
         [0061]     Similar to the buffered output stage  315  illustrated in  FIG. 6 , the multiple-buffered output stage  375  receives digital data from one or more of the processors  276 A-N. The data is received by the data partitioner  340  which partitions the data into blocks of data comprising input symbols. The resulting input symbol is written to a symbol register  350  where it is accessed by association logic  360  which matches the input symbol to a data symbol buffered in the data symbol “dictionary,” or table  370 A-N. Once a match is made between the input symbol and a data symbol buffered in the data symbol table  370 A-N, the appropriate buffered waveform table  382 A-D, selected by the logical switch  384 , is accessed and the stored digital waveform corresponding to the matched data symbol in data symbol table  370 A-N is retrieved. The retrieved digital waveform is then passed to the output  203 .  
         [0062]     The digital waveforms stored in the both the buffered waveform tables  380 A-N and the multiple buffered waveform tables  382 A-D are equivalent to sampled versions of analog waveforms modulated to contain information provided by the input symbol. Using the look-up-table method employing buffered waveforms provided in this embodiment of the invention, the output  203  can comprise virtually any type of communication waveform.  
         [0063]     In addition to providing digital synthesis of cable channel signals at the cable head-end, other aspects of the present invention provide communication capabilities employing ultra-wideband (UWB) technology for the cable head-end and for remote devices populating the cable television infrastructure.  
         [0064]     Referring now to  FIGS. 1 and 10 , in a hybrid fiber-coax system (HFCS), the combined broadband signal leaves the head-end  25  through fiber optic modulator  50  which transmits optical signals through fiber optic cable  55  for distribution into the field, such as residential neighborhoods, or business districts. Access nodes  85 , which are located downstream of the head-end  25 , receive the optical signal from the fiber, convert it to an RF signal and retransmit the RF signal on coax cable  45 . Components that may be found in an access node  85  include fiber demodulators  60 , filters (not shown), field amplifiers  70 , as well as RF transmitters (not shown). The coax cable  45  distributes the signal to customers&#39; end user equipment  80 , such as TV&#39;s, set-top-boxes, cable modems, and other devices, such as wireless personal area network devices, wireless local area network devices, and wireless metropolitan area network devices. At the access node  85  the broadband signal is extracted from the fiber optic cable  55  and transferred to a coaxial cable  45  that connects to individual homes, apartments, businesses, universities, and other customers. In a HFCS, support of multiple customers is typically accomplished by the use of multiple access nodes  85 , that may be located on telephone poles, underground, or at ground level. However, as the signal is continuously split at the access nodes  85 , the quality of the signal is diminished, thereby diminishing the video, audio, and other data quality.  
         [0065]     The digital channels that typically reside on cable television channels  79  and higher are fundamentally different than the analog channels that generally reside on channels  2  through  78 . The analog channels comprise analog modulated carriers. The digital channels are digitally modulated using Quadrature Amplitude Modulation (QAM). QAM  16  transmits 4 bits per signal, QAM  32 ,  64 , and  256  each transmit 5, 6 and 8 bits per symbol, respectively. HFCS networks usually employ QAM levels up to QAM  256  to enable up to multiple independent, substantially simultaneous MPEG video streams to be transmitted in a single 6 MHz channel allocation.  
         [0066]     At the customer&#39;s location, the coaxial cable is connected to end-user equipment  80  typically comprising a device connected to a television, telephone, or computer. The end-user equipment  80  receives and de-modulates the RF signal conveying the video, audio, voice, Internet or other data. Although a television can directly receive the analog signal, a set-top box is generally required to receive the digitally encoded channels.  
         [0067]     Communication systems employing coaxial cable  45  suffer from performance limitations caused by distance-related signal loss, signal interference, ambient noise, and spurious noise. These limitations affect the available system bandwidth, distance, and data carrying capacity of the system because the thermal noise floor and signal interference in the conductor (i.e., fiber optic and co-axial cables) overcome the transmitted signal. Moreover, noise within the network significantly limits the available bandwidth of the network. The conventional wisdom for overcoming this limitation is to boost the power (i.e., increase the voltage of the signal) at the transmitter to boost the voltage level of the signal relative to the noise at the receiver. Boosting the power at the transmitter helps enable the receiver to separate the noise from the desired signal. However, signal transmission power is typically limited to specified maximum levels, leaving the overall performance of coaxial cable systems still significantly limited by noise inherent in the system.  
         [0068]     Maximizing the available bandwidth of an established cable network, while co-existing with the conventional data signals transmitted through the network, represents an opportunity to leverage the existing cable network infrastructure to enable delivery of greater functionality and additional services. Several methods and techniques have been proposed, but they generally require replacement of existing network components and are hence costly. However, exceptional increases in bandwidth, and thus HFCS, and other networks, functionality and capability may be realized through the use of ultra-wideband (UWB) communication methods.  
         [0069]     The embodiments of the present invention discussed below employ ultra-wideband communication technology. Referring to  FIGS. 8 and 9 , impulse-type ultra-wideband (UWB) communication employs discrete pulses of electromagnetic energy that are emitted at, for example, nanosecond or picosecond intervals (generally tens of picoseconds to a few nanoseconds in duration). For this reason, this type of ultra-wideband is often called “impulse radio.” That is, the UWB pulses may be transmitted without modulation onto a sine wave, or a sinusoidal carrier, in contrast with conventional carrier wave communication technology. This type of UWB generally requires neither an assigned frequency nor a power amplifier.  
         [0070]     An example of a conventional carrier wave communication technology is illustrated in  FIG. 8 . IEEE 802.11a is a wireless local area network (LAN) protocol, which transmits a sinusoidal radio frequency signal at a 5 GHz center frequency, with a radio frequency spread of about 5 MHz. As defined herein, a carrier wave is an electromagnetic wave of a specified frequency and amplitude that is emitted by a radio transmitter in order to carry information. The 802.11 protocol is an example of a carrier wave communication technology. The carrier wave comprises a substantially continuous sinusoidal waveform having a specific narrow radio frequency (5 MHz) that has a duration that may range from seconds to minutes.  
         [0071]     In contrast, an ultra-wideband (UWB) pulse may have a 2.0 GHz center frequency, with a frequency spread of approximately 4 GHz, as shown in  FIG. 9 , which illustrates two typical UWB pulses.  FIG. 9  illustrates that the shorter the UWB pulse in time, the broader the spread of its frequency spectrum. This is because bandwidth is inversely proportional to the time duration of the pulse. A 600-picosecond UWB pulse can have about a 1.8 GHz center frequency, with a frequency spread of approximately 1.6 GHz and a 300-picosecond UWB pulse can have about a 3 GHz center frequency, with a frequency spread of approximately 3.3 GHz. Thus, UWB pulses generally do not operate at a specific frequency, but rather over a extensive range of frequencies, as shown in  FIG. 8 . Either of the pulses shown in  FIG. 9  may be frequency shifted, for example, by using heterodyning, to have essentially the same bandwidth but centered at any desired frequency. And because UWB pulses are spread across an extremely wide frequency range, UWB communication systems allow communications at very high data rates, such as 100&#39;s of megabits per second, 1 gigabit per second, or greater.  
         [0072]     Several different methods of ultra-wideband (UWB) communications have been proposed. For wireless UWB communications in the United States, all of these methods must meet the constraints recently established by the Federal Communications Commission (FCC) in their Report and Order issued Apr. 22, 2002 (ET Docket 98-153). Currently, the FCC is allowing limited UWB communications, but as UWB systems are deployed, and additional experience with this new technology is gained, the FCC may revise its current limits and allow for expanded use of UWB communication technology.  
         [0073]     The FCC April 22 Report and Order requires that UWB pulses, or signals occupy greater than 20% fractional bandwidth or 500 megahertz, whichever is smaller. Fractional bandwidth is defined as 2 times the difference between the high and low 10 dB cutoff frequencies divided by the sum of the high and low 10 dB cutoff frequencies. Specifically, the fractional bandwidth equation is:  
         Fractional   ⁢           ⁢   Bandwidth     =     2   ⁢         f   h     -     f   l           f   h     +     f   l               
 
         [0074]     where f h  is the high 10 dB cutoff frequency, and f l  is the low 10 dB cutoff frequency.  
         [0075]     Stated differently, fractional bandwidth is the percentage of a signal&#39;s center frequency that the signal occupies. For example, a signal having a center frequency of 10 MHz, and a bandwidth of 2 MHz (i.e., from 9 to 11 MHz), has a 20% fractional bandwidth. That is, center frequency, f c =(f h +f l )/2  
         [0076]      FIG. 16  illustrates the ultra-wideband emission limits for indoor systems mandated by the April 22 Report and Order. The Report and Order constrains UWB communications to the frequency spectrum between 3.1 GHz and 10.6 GHz, with intentional emissions to not exceed −41.3 dBm/MHz. The report and order also established emission limits for hand-held UWB systems, vehicular radar systems, medical imaging systems, surveillance systems, through-wall imaging systems, ground penetrating radar and other UWB systems. It will be appreciated that the invention described herein may be employed indoors, and/or outdoors, and may be fixed, and/or mobile, and may employ either a wireless or wire media for a communication channel.  
         [0077]     Generally, in the case of wireless communications, a multiplicity of UWB pulses may be transmitted at relatively low power density (milliwatts per megahertz). However, an alternative UWB communication system, located outside the United States, may transmit at a higher power density. For example, UWB pulses may be transmitted between 30 dBm to −50 dBm.  
         [0078]     Generally, UWB pulses, however, transmitted through many wire media will not interfere with wireless radio frequency transmissions. Therefore, the power (sampled at a single frequency) of UWB pulses transmitted though wire media may range from about +30 dBm to about −140 dBm. The FCC&#39;s April 22 Report and Order does not apply to communications through wire media.  
         [0079]     Communication standards committees associated with the International Institute of Electrical and Electronics Engineers (IEEE) are considering a number of ultra-wideband (UWB) wireless communication methods that meet the constraints established by the FCC. One UWB communication method may transmit UWB pulses that occupy 500 MHz bands within the 7.5 GHz FCC allocation (from 3.1 GHz to 10.6 GHz). In one embodiment of this communication method, UWB pulses have about a 2-nanosecond duration, which corresponds to about a 500 MHz bandwidth. The center frequency of the UWB pulses can be varied to place them wherever desired within the 7.5 GHz allocation. In another embodiment of this communication method, an Inverse Fast Fourier Transform (IFFT) is performed on parallel data to produce  122  carriers, each approximately 4.125 MHz wide. In this embodiment, also known as Orthogonal Frequency Division Multiplexing (OFDM), the resultant UWB pulse, or signal is approximately 506 MHz wide, and has approximately 242-nanosecond duration. It meets the FCC rules for UWB communications because it is an aggregation of many relatively narrow band carriers rather than because of the duration of each pulse.  
         [0080]     Another UWB communication method being evaluated by the IEEE standards committees comprises transmitting discrete UWB pulses that occupy greater than 500 MHz of frequency spectrum. For example, in one embodiment of this communication method, UWB pulse durations may vary from 2 nanoseconds, which occupies about 500 MHz, to about 133 picoseconds, which occupies about 7.5 GHz of bandwidth. That is, a single UWB pulse may occupy substantially all of the entire allocation for communications (from 3.1 GHz to 10.6 GHz).  
         [0081]     Yet another UWB communication method being evaluated by the IEEE standards committees comprises transmitting a sequence of pulses that may be approximately 0.7 nanoseconds or less in duration, and at a chipping rate of approximately 1.4 giga pulses per second. The pulses are modulated using a Direct-Sequence modulation technique, and is called DS-UWB. Operation in two bands is contemplated, with one band is centered near 4 GHz with a 1.4 GHz wide signal, while the second band is centered near 8 GHz, with a 2.8 GHz wide UWB signal. Operation may occur at either or both of the UWB bands. Data rates between about 28 Megabits/second to as much as 1,320 Megabits/second are contemplated.  
         [0082]     Another method of UWB communications comprises transmitting a modulated continuous carrier wave where the frequency occupied by the transmitted signal occupies more than the required 20 percent fractional bandwidth. In this method the continuous carrier wave may be modulated in a time period that creates the frequency band occupancy. For example, if a 4 GHz carrier is modulated using binary phase shift keying (BPSK) with data time periods of 750 picoseconds, the resultant signal may occupy 1.3 GHz of bandwidth around a center frequency of 4 GHz. In this example, the fractional bandwidth is approximately 32.5%. This signal would be considered UWB under the FCC regulation discussed above.  
         [0083]     Thus, described above are four different methods of ultra-wideband (UWB) communication. It will be appreciated that the present invention may be employed by any of the above-described UWB methods, or others yet to be developed.  
         [0084]     One feature of UWB is that it may transmit a signal with a power spectral density that is generally evenly spread over the entire bandwidth occupied by the signal. As discussed above, HFCS cable channels typically use AM or QAM modulation, although other modulation methods may be employed. Due to the very spread power spectral density of UWB, at the HFCS cable channel frequencies, the UWB signal&#39;s power is well below the minimum power detected by the HFCS system. Thus, UWB signals do not interfere with the demodulation and recovery of the original AM or QAM data signals. UWB technology thus makes use of the dynamic range of the channel to transmit data, without interfering with the carrier signals. Moreover, given the high data rates possible with UWB technology, injecting UWB signals into the outgoing RF stream at the head-end  25  of a cable television network adds substantially greater information bandwidth to the system without interfering with existing, conventional cable channel content.  
         [0085]     In addition to providing digital synthesis of cable channel signals at the cable head-end  25 , as discussed above, other embodiments of the present invention provide communication capabilities employing ultra-wideband (UWB) technology for the cable head-end  25  and for remote devices populating the cable television infrastructure. This aspect of the present invention provides methods enabling communications between the cable head-end  25  and remote cable television system components such as fiber-optic modulators  50  or de-modulators  60 , field amplifiers  70 , access nodes  85  and end-user equipment  80 .  
         [0086]     Referring now to  FIG. 10 , further embodiments of the present invention provide for a full duplex communication scheme including an “upstream” channel employing UWB technology, and conventional communication methods. One feature of this upstream channel is that it enables communication from cable television infrastructure components (such as fiber-optic modulators  50 , end-user equipment  80 , and access nodes  85  containing de-modulators  60 , field amplifiers  70 , and splitters (not shown)) to the cable head-end  25 . Corresponding “downstream” communications from the cable head-end  25  and cable television infrastructure components may be similarly accomplished using UWB or conventional methods over the downstream channels.  
         [0087]     As shown in  FIG. 10 , end user equipment  80  and access node devices  85 , which may include filters, RF transmitters (not shown), fiber optic modulators  50 , de-modulators  60 , and field amplifiers  70 , may perform several functions, such as: responding to status queries from the cable head-end  25 ; providing autonomous status reports at various times; and providing autonomous status reports when some exception, error, out-of-tolerance condition, or failure has occurred. Additionally, the head-end  25  may set an alert condition when an out-of-tolerance message is received from the access node devices  85 . As shown in  FIG. 10 , the access node devices  85  may include some, all, or additional devices not illustrated. For example, a fiber optic modulator  50  is required in or near the head end  25 , to receive and modulate the channel signals onto the fiber optic cable that is used to distribute the channel signals. At an access node, a fiber optic demodulator  60  demodulates the channel signals, and transfers them to a co-axial cable. However, “upstream” signals may need to be sent to the head end  25 . Thus, the access node may also include a fiber optic modulator  50 , which modulates the “upstream” signal and sends it up the fiber optic cable to the head end  25 .  
         [0088]     Many cable television access node devices  85  require periodic maintenance checks which are usually accomplished by a technician traveling to the site of the component to monitor, test and perform a physical inspection. Moreover, many functioning access node devices  85  are replaced as a matter of procedure to mitigate the likelihood of failure and consequent network unavailability. Aspects of the present invention that communicate status information between the cable head-end  25  and access node devices  85  enable more efficient and cost-effective maintenance procedures. For example, an access node device  85  may be replaced when reports from the access node device  85  indicates an error or a failure mode, instead of requiring prophylactic replacement according to a fixed maintenance schedule. One feature of this aspect of the invention is that each access device  85  may include an individual, or specific address, or identifier, that allows each access device  85  to be individually identified and/or controlled.  
         [0089]     One feature of the present invention includes optimization of network parameters in real-time. For example, status reports from access node devices  85  and/or end user equipment  80  may contain environmental and network performance measurements, including, for example, per-channel signal strengths. In that instance, the cable head-end  25  may adjust the signal transmission power of a channel in order to maximize its Carrier-to-Noise Ratio (CNR) according to specified upper and lower limits, while possibly also simultaneously optimizing the dynamic range of the region lying below the range of the channel content and extending still lower to the thermal noise level of the cable television conductors. The upper and lower dynamic ranges may therefore be adjusted and optimized in real-time according to signal power measurements fed back from the access node devices  85  and/or end user equipment  80 . This capability maintains optimal conditions for signal transmission in the network, improving network performance. In one embodiment, these, and other network parameters may be optimized for UWB communications. In addition, status information relating to one, or more of the access node devices  85  may be transmitted to the head-end  25 . For example, status information may include an access node device  85  temperature, power consumption, saturation condition, frequency response, and other information of interest.  
         [0090]     As shown in  FIG. 10 , a communication channel  90  is provided that enables “upstream” communications from access node devices  85  to the cable head-end  25 , and “downstream” from the cable head-end  25  to the access node devices  85  and/or end-user equipment  80 . In one embodiment of the invention, illustrated in  FIG. 11 , the processing module  200  of the cable head-end  25  dispatches a status request message in step  400  downstream over the communications channel  90  to an access node device  85  and/or to end-user equipment  80 . The access node device  85  and/or the end-user equipment  80  then formulates a status response message and dispatches the response message upstream over the communications channel  90  to the processing unit  200  at the head-end  25 . The processing module  200  tests to determine if a response has been received in step  405 . If a response has been received, the network status information is processed in step  410  and a determination made, in step  415 , as to whether a responsive action is required. If an action is not required, processing returns to the first step  400  to dispatch a new status request message. If an action is required, however, the action is performed in step  420  at the head-end  25  before returning to the first step to dispatch a new status request  400 . Actions performed in step  420  may include logging maintenance or component health information, notifying maintenance personnel of the health, or lack thereof, of any access node devices  85  and/or any end-user equipment  80 , dispatching information downstream to any access node devices  85  and/or to any end-user equipment  80 , and effecting a control response according to information included in the status report. It will be appreciated that the step of dispatching status request messages  400  may be accomplished on a one-by-one basis to individual access node devices  85  and/or to individual end-user equipment  80  or “broadcast” to more than one device on the network.  
         [0091]     In one method of the present invention, access node devices  85  and/or end-user equipment  80  autonomously dispatch status messages to the processing module  200  at the cable head-end  25 , eliminating the need for the processing module  200  to dispatch status requests. As shown in  FIG. 12 , in step  440 , the processing module  200  receives status reports from all, or some of, the access node devices  85  and/or end-user equipment  80  on the network. In step  445 , a check is performed to determine whether any status messages from devices of interest have actually been received. If no status reports are determined as missing, the received status reports are evaluated in step  450 . If status reports are determined as missing, the identities or addresses of the access node devices  85  and/or end-user equipment  80  that did not report may be logged in step  446 . A test is performed in step  447  to determine if an action at the head-end  25  by the processing module  200  is required. If so, the action is performed in step  448 . The actions that may be performed in step  448  include but are not limited to: logging maintenance of access node devices  85  and/or end-user equipment  80  health information; notifying maintenance personnel of access node devices  85  and/or end-user equipment  80  health indications; dispatching information downstream to the access node devices  85  and/or end-user equipment  80 ; and effecting a control response according to information included in the status report from the access node devices  85  and/or end-user equipment  80 . If no action is required, then the status reports received from are evaluated in step  450 . A test is performed in step  455  to determine whether any actions at the head-end by the processing module  200  are required in response to the status report evaluations of step  450 . If no actions are required, then the process returns to the initial step  440  of receiving status reports. If one or more actions are required, those actions are performed in step  456  before the process returns to the initial step  440  of receiving status reports. The actions performed may include: logging maintenance of access node devices  85  and/or end-user equipment  80  health information; notifying maintenance personnel of access node devices  85  and/or end-user equipment  80  health indications; dispatching information downstream to the access node devices  85  and/or end-user equipment  80 ; effecting a control response according to information included in the status report from the access node devices  85  and/or end-user equipment  80 ; and setting an alert condition at head-end  25 .  
         [0092]     One embodiment of the present invention provides a method for controlling cable system, or network performance parameters from the cable head-end  25  according to information communicated by access node devices  85  and/or end-user equipment  80 . Referring to  FIG. 13 , cable television system access node devices  85 , such as fiber optic modulators  50 , and de-modulators  60 , field amplifiers  70 , and end-user equipment  80  may include a sensor  460 , or the functional equivalent of a sensor  460 , capable of measuring one or more environmental or cable system performance parameters. Information obtained form the sensors  460  may be communicated to the head-end  25 . For example, the sensor  460  on field amplifier  70  may measure the high and/or low cable signal power levels on the various channels. Communicating measurements of these power levels over the communication channel  90  to the cable head-end  25  may thus enable corrective adjustments at the head-end  25  to tailor the signal so that the signal transmission power levels lie within desired tolerances as measured at the field amplifier  70 .  
         [0093]     One feature of the present invention is that it allows for management of bandwidth and signal power conditions in a cable television architecture. As shown in  FIG. 14 , transmission power requirements for conventional, relatively narrow-band communications are typically constrained to lie within an upper range  485  defined by specified maximum  470  and minimum  480  signal power levels. A lower range  495  is defined as that below the upper range  485  and above the thermal noise power level  490 . The lower range  495  is typically not used for conventional channel communications, but is useful for UWB communications signals. Real-time feedback from access node devices  85  and/or end-user equipment  80  would enable control mechanisms at the head-end  25  to maintain signal power levels in the optimal ranges for specific frequencies.  
         [0094]     Another embodiment of the present invention enables ultra-wideband (UWB) communication signals to be transmitted through the cable network. Shown in  FIG. 15 , the cable head-end  25  generates a conventional radio frequency (RF) signal that is transmitted through the cable network. Though a cable network typically comprises a plurality of access node devices  85  and end-user equipment  80  components, a single representative device  87  is shown in  FIG. 15 . For example, the single representative device  87  may comprise fiber optic modulators  50 , and de-modulators  60 , field amplifiers  70 , and end-user equipment  80 .  
         [0095]     As discussed above, the RF signal is typically passed to the cable head-end  25  from satellite antennas  10  and local sources  15 . According to one embodiment of the present invention, the RF signal is then passed to the ADC  180 , which produces a digitized equivalent signal. The digitized signal is conveyed to the processing module  200  for general processing, usually comprising signal conditioning steps and conversion to appropriate output cable channels, as discussed above. From the processing module  200 , the digital composite cable signal is passed to a DAC  210  for conversion into an RF signal.  
         [0096]     According to an embodiment of the invention, tasks performed by the processing module  200  also include formulating messages containing information for one or more devices  87  on the cable network. The messages are encoded by the processing module  200  and routed to an UWB modulator  500 , which converts the encoded message into an UWB signal. The UWB signal is combined with the signal generated by DAC  210  in a way as to not interfere with the reception of the conventional signals, by UWB summer  212 . Alternatively, the UWB data may be combined with the conventionally modulated data prior to conversion to an analog signal by DAC  210 . The UWB waveforms may then be transmitted through the cable network. At the remote device  87 , the cable signal is received and passed to an UWB demodulator  510 . The UWB demodulator  510  demodulates the UWB signals to recover the encoded message conveyed by the UWB signals. The encoded message is next passed to a UWB processing module  530  that decodes the message and processes the information. The UWB processing module  530  may then formulate a response to the received message. The UWB processing module  530  may also receive environmental and network parameter measurements from a local sensor device  460  in addition to the encoded message from the demodulator  510 . For example, according to one embodiment of the invention, the sensor device  460  measures received channel signal power levels. Response information and sensor measurements, if any, are encoded by the UWB processing module  530  into a response message and passed to an UWB modulator  500 . The modulated UWB waveforms are then combined with other upstream signals, if present, by a UWB combiner  212 . At the head-end  25  the signal routed to an UWB demodulator  510 . The demodulator  510  demodulates the signals to recover the encoded message from the device  87 . The encoded message is next passed to the head-end  25  processing module  200  to decode the message and processes the information.  
         [0097]     Under this communications scheme, UWB messages are “broadcast” onto the cable network, thus creating a potential problem. That is, without corrective action, any device on the network could potentially receive and process messages not destined for it, including those messages the device itself has sent to one or more other devices. In one embodiment of the invention, this problem is addressed by encoding into each transmitted message a unique device identification (ID) or address specifying “to” which device the message is destined and another ID indicating “from” which device the message originated. Each device may then reject any messages not containing its ID as a destination address. Referring to  FIG. 15 , the head-end  25  processing module  200  and UWB processing module  530  are therefore precluded from responding to their own transmitted UWB messages, or to messages not destined to them.  
         [0098]     Referring again to  FIG. 15 , which illustrates another method of the present invention. The cable head-end  25  may query access node devices  85  and/or end-user equipment  80  on the cable network for various types of status information. In this method, a status request is encoded by the processing module  200  at the cable head-end  25 , the encoded message is then sent to UWB modulator  500 , and sent to combiner  212  where it is combined with the cable channel stream and transmitted onto the cable network. A cable network device  87  then receives the RF cable channel stream. The UWB signals are demodulated by UWB demodulator  510  and the encoded message is passed to the UWB processing module  530  for decoding. The UWB processing module  530  processes the information contained in the request, and formulates a status response as needed. Information received from a sensor  460  may also be incorporated into the response. In one embodiment of the invention, the sensor information may comprise channel power level measurements. The status response is then encoded by UWB processing module  530 . The status response is next sent to UWB modulator  500 , and combined with other upstream signals, if any, in combiner  212  for upstream transmission.  
         [0099]     At the head-end  25 , a copy of the signal is routed to an UWB demodulator  510 . The encoded status response recovered by UWB demodulator  510  is passed to the processing module  200 . The processing module  200  performs tasks to determine the status of the cable network device  87  and, in one embodiment of the invention, analyzes the channel power level measurements included in the status response. The power level measurements for one or more channels may therefore be used to determine whether actual channel power levels are within specified tolerances. Referring to  FIG. 14 , maximum  470  and minimum  480  power levels define an optimal operating range, or upper range  485  for conventional channel content. This simultaneously ensures that the lower power range  495  is available for UWB communications.  
         [0100]     In one embodiment of the invention, the signal energy of the UWB data stream is spread across a bandwidth that may range from about 50 MHz to approximately  870  MHz, 1 GHz, or higher. Referring to  FIG. 14 , this ensures that the signal energy present at any frequency is significantly below the upper power range  485  of existing, conventional RF cable carrier signals and above the thermal noise floor  490  of the cable conductor.  
         [0101]     For example, if the power levels on a particular channel do not exceed the lower bound  480 , the processing module may responsively adjust the power levels to optimal levels during the digital synthesis of the signal, as described above. Alternatively the head-end  25  may set an alert notifying cable plant personnel of an out-of-tolerance condition. Thus, real-time analysis of communication channel power levels may provided by the methods disclosed by this embodiment of the invention.  
         [0102]     It will be appreciated that the UWB modulator  500  and UWB demodulator  510 , illustrated in  FIG. 15 , may include some or all of several components, including a controller, a digital signal processor, an analog coder/decoder, one or more devices for data access management, and associated cabling and electronics. The controller may include error control and data compression functions. The analog coder/decoder may include an analog to digital conversion function and vice versa. The data access management device or devices may include various interface functions for interfacing to wired media such as phone lines and coaxial cables. Additionally, these devices may employ communications technologies other than UWB for communicating status and other types of information. Accordingly, the invention is not limited with respect which type of RF communications transport messages to and from head-end  25  to cable network devices  87 .  
         [0103]     Thus, it is seen that apparatus&#39; and methods for digitally synthesizing cable television channel data, transmitting and receiving status reports from remote network devices, and transmitting and receiving UWB signals through a cable television network are provided. One skilled in the art will appreciate that the present invention can be practiced by other than the above-described embodiments, which are presented in this description for purposes of illustration and not of limitation. The specification and drawings are not intended to limit the exclusionary scope of this patent document. It is noted that various equivalents for the particular embodiments discussed in this description may practice the invention as well. That is, while the present invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims. The fact that a product, process or method exhibits differences from one or more of the above-described exemplary embodiments does not mean that the product or process is outside the scope (literal scope and/or other legally-recognized scope) of the following claims.