CN1894969A - System for improving digit telecommunication signal return route characteristic sampling radio frequency character connected to head-end modulator - Google Patents
System for improving digit telecommunication signal return route characteristic sampling radio frequency character connected to head-end modulator Download PDFInfo
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Abstract
An hfc return path system for digital communication signals using a sampled rf word interface to head-end demodulators, provides higher performance equipment at an equivalent or lower cost and more flexible and efficient interfacing and traffic multiplexing. The return path signal from the fiber optic node to the head end/hub is represented ones and zeroes, and the digital receiver at the head end/hub includes an optical receiver for receiving the serial stream of optical ones and zeroes and converting the optical digital signal to an electrical digital signal, a deserializer for deserializing the serial stream of digital words and synchronization information into parallel digital words, a digital filter for processing the deserialized digital words to interface digitally to an application receiver and a digital interface for interacting and forwarding the processed parallel digital words to the application receiver.
Description
The cross reference of related application
The present invention relates to the common transfer pending application of exercise question for " using the HFC return path system of digital translation and transmission ", submit to and transfer on April 21st, 2000, sequence number is 09/556,731, is incorporated herein by reference.The invention still further relates to the U.S. Provisional Application of submitting on June 2nd, 2,000 60/208,748, in this combination and as a reference whole.
FIELD OF THE INVENTION
The present invention relates generally to cable TV coaxial hybrid fiber (CATV HFC) return path system, particularly, use the system of the sampling RF word of the demodulator that is connected to head end with the return path performance of improvement digital communication signal.
Background of the present invention
The existing technology return path CATV head end of HFC system and hub (hub) equipment utilization the linear light detection, amplify before some specially designed receiver stops subsequently and handles, the special design of described receiver is specific at that specific cable machinery realization backhaul communication.In the multiple application that intersects, use the bandwidth that exists in the opposite direction, can there be multiple, synchronous, different return path signal of communication.For traditional HFC of North America, this bandwidth is the 5-40 megahertz.The conventional method that tackles the link signal by the return path Optical Fiber Transmission is, Analog signals is so that arrive behind node the waveform that replicating original as far as possible closely produces.Guarantee to obtain enough performances by standard laser, receiver and RF system, do not degenerate to outside essential a certain amount of of success communication to guarantee signal.But, there are a lot of designs and implementation issue, it makes this method difficult and uneconomical, they comprise the simulated laser standard, laser second-order response characteristic, optical link length constraint, the expensive test and the simulation headend of standard-reinforcement, the calibration of analog parameter and maintenance damage the quality of traffic carrying capacity apparatus sensitive and the additional signal of existing equipment.All of these factors taken together causes the whole high cost issues of the high performance analog machine of exploitation.
These problems were present in the work of architecture advances of the laser of continuous improvement simulated laser device and return path receiver performance, higher power and HFC in the past always.But each above-mentioned problem still exists.
Therefore, the present invention is directed to a kind of return path system that is used for digital communication signal of this problem exploitation, its use is connected to the RF word interface of the sampling of head end demodulator, to provide expense lower device design, identical or low-cost under can obtain the equipment of superior performance, have multiple effective interface and communication service multiplexed flexibly.
Summary of the invention
The present invention is connected to the sampling RF word interface of head end demodulator by use, to improve the return path performance of digital communication signal, promptly, the information content that contains in the sampling with the digital return path transmission is directly delivered to, prepare the application receiver of direct-connected suitable realization, thereby eliminated typical D/A switch process and eliminated the signal corruption that may cause thus.
According to one embodiment of present invention, in cable television system, the reduction perfect representation is that the method for 1 and 0 return path signal comprises the following steps: that (1) receives the serial flow of the digital word that has suitable synchronizing information, being identified in the border between the word, and the also timing of original position itself; (2) the unstring serial flow and the synchronizing information of digital word; (3) when the needs numeral is connected to the application receiver, handle the digital word of unstringing; (4) to using the Parallel Digital formula word that the receiver transmission is handled.
Another embodiment of the present invention provides the system of the return path signal that a kind of being used in the coaxial hybrid fiber cable television system of using the base band serial optical to transmit reduce digital word, and wherein the return path signal from the optics node of optical fiber to head end/hub is by being expressed as 1 and 0 with its whole coding.Described system comprises the application receiver of digital backhaul receiver and arbitrary number.The digital backhaul receiver of system comprises optical receiver, and it receives the serial flow of optics 1 and 0 from optical fiber, and converts optical digital signal to electric digital signal; Deserializer, it unstrings the serial flow of digital word and synchronizing information; Digital filter, it handles the digital word of unstringing, and is connected to the application receiver with numeral; And comprising interface, it connects the Parallel Digital formula word of handling and sends at least one that use in the receiver.
In each embodiment, digital filter or treatment step have been eliminated the front end dummy run phase of digital word, directly be provided to the digital word interface of data/address bus to the digital receiver part of the demodulator of using receiver, and replace the function of front end dummy run phase with the digital function that is equal to.
Can realize described system and/or method at CATV head end or hub.
In a preferred embodiment of the invention, if the data/address bus word length of digital receiver less than the length of parallel word, the least important position of digital filter or digital processing step intercepting then, with interface at least one application receiver.In addition, if the word length of digital receiver surpasses the length of transmission link, then parallel word zero padding.
At last, can use logical conversion (logical translation) equipment as the interface of using between receiver and the transmission link, or as a part of using receiver.A kind of field programmable gate array (Field Programmble Gate Array (FPGA)) can be used as this equipment and uses.
Brief description of drawings
The detailed description of doing below in conjunction with accompanying drawing will make that above-mentioned and other purposes of the present invention and feature and advantage are clearer.
Fig. 1 has a primary element figure that Direct Digital switches to the digital return path transfer system of head end receiver according to of the present invention.
Describe in detail
In the simplified block diagram of Fig. 1, provided and used the sampling RF word interface that is connected to the head end demodulator, be used to improve the system's primary element and the method for the return path performance of digital communication signal.
Basically, the reverse path of CATV head end or hub can continue from multiple, from the communication of a plurality of different transmission sources of user's family.The present invention at first relies on available senior return path equipment.Such system adopts fully and said method diverse ways transmission information from node.As the above-mentioned related application of quoting at cross reference disclosed respectively as described in advanced person's method be that user from the return path samples and arrives the analog waveform of node.Subsequently, with the sampled digital coding, so that from the transmitter to the head end/link of hub can be made of the digit optical transmitter and receiver.Therefore, the information that transmits in its system becomes bit string.
A plurality of advantages of digital backhaul methods have been summarized in explanation formerly open.This openly is the damage that the most important thing is at the actual erasure signal in node analog-digital conversion (A/D) back.Requiring optical system now only has been reliable binary effect, reproduces one of two analogues value.With regard to numeral, these values are " 0 " and " 1 ", and represent with two different optical power levels (level).This method is applied to the optical link of HFC, eliminates or has alleviated to a great extent.The relevant signal corruption problem that causes by relevant laser transmitter, nonlinear fiber, optical receiver and RF amplifier.
As described in the corresponding application, receive the serial flow of digital word at the node optical transmitter, and transmit this digital word to optical receiver.The realization of all bit streams on RF-light transfer point, import immediately in the desirable equation of standardized transmission, and simplified the network formation, quickened research, and be incorporated in the HFC infrastructure with its reliable technique through checking with gratifying level.In addition, since the advantage of distance, the trunking that makes it possible to use inactive component or move hub fully.
But the damage of erasure signal is not having under the signal corruption outside node, relies on the ability of the digital word of head end reduction transmission.Carry out this operated system and method below with reference to Fig. 1 explanation, that is, between HFC return path communication link and terminal equipment receiver, provide the interface of digital word.
Mention in front open in, several advantages have been described.But the processing that the digit optical system carries out under that situation is to use digital-analog convertor (D/A) to duplicate the broadband analog output signal for finishing.From the viewpoint of the legacy system of still implementing the analog receiver technology, this method is valuable.But for the return path transmission such as the advanced person of cable modem etc., preferably interface is to demodulated equipment.
The method that is connected with the head end terminal equipment that is proposed has been utilized, in the advantage of the various researchs of using specific integrated circuit (ASIC), very lagre scale integrated circuit (VLSIC) (VISI) and Digital Signal Processing.Modern modem technology combines receiver on digital received machine technology-chip-on single digital integrated circuit or in the chipset, realize multiple multiplexing (manycomplex synchronization) synchronously, balanced (equalization) and measuring ability.These functions can digitally be carried out because typical modern communications receiver will be tuned to interesting channel, with its filtering, the waveform of sampling filtering on the increment in cycle then.
Described as above-mentioned work activities with regard to node, the information of representing by sampling can convert the position that is used for digital processing subsequently in the remainder of receiver.This is to be undertaken by each simulated sampling with N position word of numeral.At this, N is the figure place (as 8,10,12) of the resolution (resolution) in A/D converter.At present, existing very big progress in the VLSI circuit that design of communications is used, and the receiver of high speed design is just utilizing these advantages.The HFC system also can utilize the advantage of these processing now, and consequently (by) eliminates the D/A switch process of the application demodulator with digital receiver.Remove this step, and direct interface is to the digital receiver with available digital word, a kind of mechanism that can erasure signal damages is provided, and the designs simplification at the analog machine of head end (or hub) can be become the bus and the prefabricated card-inserting device of digital network.
Referring to Fig. 1, it is clearly shown that a digital return path system completely.Though those skilled in the art should be understood that the technology of just Fig. 1 explanation and are arranged on " head end " part of figure,, according to the structure of the whole HFC in using, it also can be placed on hub location.The function of the D/A converter in digital back haul system is the broadband 5-40 megahertz input that reconstruct exists on node.Subsequently, when on traditional return path receiver (RPR) equipment, handling the return path signal, handle this RF signal.That is, before being connected to the application receiver of restore information, it is separated, amplification, decay etc.But, comprise that the simulation process of D/A itself causes signal degradation, the possible loss or the damage of the information of transmission, and complicated level is set problem.For the receiver of the advanced person such as cable modem, the RF signal is down converted to intermediate frequency or the base band frequency in receiver front end.Then, use sample this signal and convert the digital signal of information reverting again to of A/D converter in receiver.Because additional conversion of transmitting the centre of undesirable signal corruption to simulation, make this complete head end processing-D/A conversion, amplification, separation, tuning, A/D conversion-quilt is unnecessarily complicated.
But according to the recent progress that high-speed figure is handled, making no longer needs always to be connected to receiver with conventional return path RF input in the past.Therefore, the information content that contains in the sampling that the digital return path system transmits can directly be sent to the application receiver of the suitable configuration that is ready to digital interface.In Fig. 1, by digital backhaul receiver is enlarged the additional functional elements that is labeled as " digital processing ", this point shown in the square frame in Fig. 1 " head end ".Particularly, in Fig. 1, at the serial flow that receives the digital word that transmits on the optical link on the fibre optic receiver 10.Serial-to-parallel transducer (SERDES) or deserializer 20 convert the serial flow of digital word to Parallel Digital formula word, and described parallel word is sent to digital processing square frame 30." digital processing " in fact refers to, finish in the data word of expression simulated sampling and use must exist between the receiver, comprises actual filter function, the processing stage of required each of each function.This method requires described digital backhaul receiver:
Eliminate the front end dummy run phase;
The interface of digital word is provided to the digital receiver partial data bus (or buffer) of digital demodulator 100; With
When needed, the function that replaces the front end dummy run phase with the digital function that is equal to.
It should be noted that with reference to (3) big event of front-end functionality is to regulate analog signal level, with the A/D converter of correct driving receiver.Should be understood that this crucial function items no longer needs.In addition, digital receiver is realized the synchronous last fine tuning stage in numerical portion.Therefore, the last conversion of base band has been a digital function, and the technology of digital tuner has obtained good development.Therefore, the Core Feature of digital front-end is the expansion of digital filtering and synchronizing function.
Those skilled in the art should be understood that the important consideration that correctly realizes the numeral switching is between digital delivery mechanism and application receiver " interface definition ".This interface is made up of N parallel-by-bit word of expression effective information and the proper signal exchange that signal post needs between two subsystems (digital backhaul and digital receiver).In addition, it is synchronous that described interface is included in the clock signal of necessity of every side.Have, the digital delivery method of return path realizes from the node to the head end or the serial baseband transmission of hub again.Described serial flow is that position and word are synchronous, and occurs the parallel word of the primary sample that numeral gets at node on exporting.
Depend on the concrete enforcement of digital backhaul, the size of described parallel word can change.The data/address bus that transmits the digital receiver of the information of sampling for device generally is the fixed word length size.The size of possible this bus word length is less than the parallel word length that exists.At this moment, block least important position (LSB), and interface is to using receiver from transfer system.Have information dropout in this is handled, still, because it is the restriction that sets in described digital receiver IC, it is the information that all can lose in any situation.
In addition, if the word size of digital receiver itself surpasses transmission link, so by in additional position, using zero padding, to switch parallel word.In this topological structure, must assess the effect of low resolution.But this is a typical case, technically guarantees that normally transmission link surpasses the performance parameter of modulator-demodulator, damages transmission signals with minimum degree ground.
Another material particular of interface is to guarantee to communicate by letter successfully or effectively said " language " or agreement.Use receiver and usually have specific standard, particularly the numerical portion in the receiver design has analog-and digital-function.Such receiver can be connected by logical conversion (translation) equipment, and as using field programmable gate array (FPGA), its is handled from the data word of passing through it of transmission link, and with the feasible suitable receiver data/address bus of their formats.Can realize digital processing (those skilled in the art should be understood that FPGA can be the part of digital return path receiver, and are as described below, and independent FPGA also can be a part of using receiver, but in general is not like this) with FPGA.The receiver of some feature can not have addressable data/address bus, or is analog receiver fully, in this situation, is necessary the digital backhaul of reconstruct band D/A.But advanced receiver has the structure interface of more abundant definition, by common use prior art or by entrusting exploitation to realize, to guarantee standardization.At this moment, this realization comprises, when advanced person's receiver circuit exploitation, is designed into the access of receiver data/address bus, and is implemented in originally on one's body gate array or converting means of receiver, to transmit digital backhaul word sequence to receiver.
In the exploitation of the receiver in modern times, the direct digital interface definition can be applied to new design at once because prior art comprises, and transmit in the corresponding to high speed data receiver of interface type that needs between link and the receiver data/address bus and handle.In legacy system,, can require to develop the other interface equipment that allows the visit digital function to the constraint on the receiver function accessibility.Finally, some legacy systems and particularly all analog receivers as incomplete redesign, will not have above-mentioned advantage.In such a case, the D/A output intent can be best suited for.But in most of such situations, the design of such receiver will be operated on open-and-shut modulation function, and digitized enforcement develop and field fast.Such situation is also arranged, and these better simply receivers will run into the minimum benefit in performance that obtains from digital interface, because with regard to these typical modulation schemes, the additional simulation of reconstruct damages unimportant for link performance.
The present invention is tangible with the short-term benefit of the digital communication signal system and method for the sampling RF word interface that is connected to the head end demodulator: flexibility greatly in using the processing reinforcement; Can connect CATV head end terminal equipment etc. neatly.But, in the several years, can receive greatest benefit, because return path has been opened and processing to the conversion of all, transmit, multiplexed, the possibility of a lot of networkings relevant with terminal device interface.
Though specifically illustrate and described various embodiment, should be appreciated that by above-mentioned instruction, the present invention will comprise various modifications and variations, and in the scope of appended claim and can not depart from the spirit and scope of the present invention.
Claims (22)
- One kind in cable television system the reduction perfect representation be the method for one and zero return path signal, comprise the following steps:Reception has the serial flow of the digital word of suitable synchronizing information, is identified in the border between the word, and the also timing of original position itself;The serial flow of the digital word of unstringing and synchronizing information;The digital word that processing is unstringed arrives the application receiver with digital ground interface; WithTo using the Parallel Digital formula word that the receiver transmission is handled.
- 2. the treating step comprises the following step according to the process of claim 1 wherein:Eliminate the front end dummy run phase of digital word;The interface of digital word directly is provided to the digital receiver partial data bus of the demodulator of using receiver; WithThe function that replaces the front end dummy run phase with the digital function that is equal to.
- 3. according to the process of claim 1 wherein that described method realizes at the head end of CATV.
- 4. according to the process of claim 1 wherein that described method realizes at the hub of CATV.
- 5. according to the process of claim 1 wherein that using receiver comprises the digital demodulator that has digital receiver.
- 6. according to the method for claim 5, if wherein the data/address bus word length of digital receiver is less than parallel word length, then digital filter blocks least important position to be connected to the application receiver.
- 7. according to the method for claim 5,, then use the zero padding parallel word if wherein the size of the word of digital receiver surpasses the size of transmission link.
- 8. use between receiver and the transmission link according to the process of claim 1 wherein that logical conversion equipment is connected.
- 9. method according to Claim 8, wherein said logical conversion equipment are to use the part of receiver.
- 10. according to the method for claim 9, wherein said logical conversion equipment is field programmable gate array.
- 11. according to the method for claim 10, wherein after the step of unstringing is unstringed the serial flow and synchronizing information of digital word, described field programmable gate array deal with data word, and the described data of the data/address bus of receiver are used in format.
- 12. the system of a return path signal that reduces digital word, it uses in the coaxial hybrid fiber cable television system that the base band serial optical transmits, wherein the return path signal from the optics node of optical fiber to head end/hub is represented as one and zero by whole coding, described system comprises digital backhaul receiver and a plurality of application receiver, and the numeral of this system is returned receiver and comprised:Conversion/receiving system, it receives optics one and zero serial flow from optical fiber, and converts optical digital signal to electric digital signal;Separate string devices, it unstrings the serial flow of digital word and synchronizing information;Digital processing unit, it handles the digital word of unstringing, with the digital application receiver that joins to; WithInterface arrangement, it connects the Parallel Digital formula word of handling and send at least one of a plurality of application receivers.
- 13. according to the system of claim 12, wherein said digital processing unit comprises:Eliminate the device of the front end dummy run phase of digital word;The device of digital word interface directly is provided to the digital receiver partial data bus of the demodulator of using receiver;With being equal to the device that digital function replaces front end dummy run phase function.
- 14. according to the system of claim 12,, wherein said system realizes at the head end of CATV.
- 15. according to the system of claim 12, wherein said system realizes at the hub of CATV.
- 16. according to the method for claim 12, wherein at least one application receiver comprises the digital demodulator that has digital receiver.
- 17. according to the system of claim 16, if wherein the data/address bus word length of digital receiver is less than parallel word length, then digital filter blocks least important figure place, uses receiver to be connected at least one.
- 18. according to the system of claim 16, if wherein the size of the word of digital receiver is then used the zero padding parallel word above the size of transmission link.
- 19. according to the system of claim 12, wherein the logical conversion device is connected at least one application receiver and transmits between the link.
- 20. according to the system of claim 19, wherein said logical conversion device is a part of using receiver.
- 21. according to the system of claim 20, wherein said logical conversion device is a field programmable gate array.
- 22., wherein unstring behind the serial flow of digital word and synchronizing information separating string devices according to the system of claim 21, described field programmable gate array deal with data word, and the described data of the data/address bus of receiver are used in format.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/US2001/018006 WO2001095626A2 (en) | 2000-06-02 | 2001-06-01 | A system for improved return path performance for digital communication signals |
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| Publication Number | Publication Date |
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| CN1894969A true CN1894969A (en) | 2007-01-10 |
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| CNA018106064A Pending CN1894969A (en) | 2001-06-01 | 2001-06-01 | System for improving digit telecommunication signal return route characteristic sampling radio frequency character connected to head-end modulator |
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