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WO2001056197A2 - Systeme de communication numerique aller - Google Patents

Systeme de communication numerique aller Download PDF

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Publication number
WO2001056197A2
WO2001056197A2 PCT/US2001/002503 US0102503W WO0156197A2 WO 2001056197 A2 WO2001056197 A2 WO 2001056197A2 US 0102503 W US0102503 W US 0102503W WO 0156197 A2 WO0156197 A2 WO 0156197A2
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WO
WIPO (PCT)
Prior art keywords
analog
digital
signal
electrical signal
optical
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2001/002503
Other languages
English (en)
Other versions
WO2001056197A3 (fr
Inventor
Forrest M. Farhan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Scientific Atlanta LLC
Original Assignee
Scientific Atlanta LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scientific Atlanta LLC filed Critical Scientific Atlanta LLC
Publication of WO2001056197A2 publication Critical patent/WO2001056197A2/fr
Publication of WO2001056197A3 publication Critical patent/WO2001056197A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/22—Adaptations for optical transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/504—Laser transmitters using direct modulation

Definitions

  • This invention relates generally to broadband communications systems, and more specifically to systems for the distribution of video, digital, and other information signals from a transmitting station to number of receiving stations via optical fibers.
  • Cable television (CATV) systems typically include a headend section for receiving high frequency signals and demodulating them to baseband.
  • signal sources may include satellites for digital and analog television programming, public telephony networks for voice telephony, and digital networks, such as the Internet, for the transfer of computer generated data.
  • the headend transforms these signals to a composite broadband frequency division multiplexed analog signal that is transmitted via fiber optic cable to nodal stations, i.e., nodes, in the cable distribution plant.
  • the optical signal is received and converted to a radio frequency (RF) electrical signal that is carried to individual subscribers by a "tree" network of coaxial conductors and amplifiers.
  • RF radio frequency
  • FIG. 1 is a block diagram of a bidirectional hybrid fiber/coax broadband distribution system in accordance with the present invention.
  • FIG. 2 is a block diagram showing the input and output ports of an analog-to-digital converter in accordance with the present invention.
  • FIG. 3 is a graph showing the input and output spectra of an undersampled analog to digital conversion process in accordance with the present invention.
  • FIG. 4 is a block diagram of an optical transmission system in accordance with the present invention.
  • FIG. 5 is a block diagram of an alternative optical transmitter employed in a broadband communication system in accordance with the present invention.
  • FIG. 1 shows the optical portion of a hybrid fiber/coax (HFC) broadband distribution system, such as a cable television system, that is bidirectional and in which the majority of the available bandwidth is devoted to the distribution of analog and television signals from a headend station 1 10 to individual subscribers 155.
  • HFC hybrid fiber/coax
  • Forward, or downstream, distribution occurs in the frequency range of about 50 MHz to 750 MHz or higher.
  • satellite transmissions of analog and digital television signals are received by the headend station 110 and converted to an intermediate radio frequency by one or more receivers 112.
  • a digital transceiver 1 14 and/or telephony transceiver 1 16 may provide bidirectional links between the headend station 110 and external systems that are usually land-based.
  • the digital transceiver 1 14 can be connected to the Internet, and the telephony unit 1 16 communicates with a public telephone network.
  • these units 1 14, 116 transform electronic signals at an intermediate frequency, or other acceptable format, to modulator/demodulator 120 via RF cables 118.
  • the modulator/demodulator 120 processes and combines the forward- travelling RF signals in a manner suitable for transmission by the laser transmitter included within the transceiver 126.
  • Optical information signals are carried from the headend 1 10 by optical fibers 130 to one or more fiber optic nodes 142 that convert the optical signals to RF electronic signals. These RF signals are distributed to subscriber equipment 155 by RF branches that may include one or more coaxial transmission lines 144, distribution amplifiers 146, line extenders 148, taps 150, and coaxial service lines 152 that connect the individual subscribers 155 to the system.
  • subscriber generated information that may include special programming requests, Internet communications, and voice telephony are transmitted in the reverse or upstream direction through the coaxial portion of the HFC plant to the fiber optic node 142 via a separate frequency than that of the forward band.
  • this information is converted to a form suitable for optical transmission and sent, via laser transmitter, to the optical transceiver 126 at the headend station 1 10.
  • the optical receiver 126 within the headend 110 converts the received upstream optical signal to an electronic form that can be processed by the modulator/demodulator 120.
  • This unit 120 identifies, splits, and reformats appropriate portions of the return signal in a manner that is compatible with cable program selectors, the Internet, and the public telephone network, as necessary.
  • optical transceivers that are located throughout the optical portion of an HFC plant transmit information using an analog modulation format, such as intensity or amplitude modulation. While capable of transmitting high-bandwidth information signals, this modulation technique has a number of drawbacks. Specifically, nonlinearities in the fiber optic cable produce a degradation in the signal quality with distance. Furthermore, analog modulation schemes are highly sensitive to variations in the input signal level and the electro-optical properties of the transmitting laser. For example, nonlinearities in the optical signal may be caused or worsened by temperature fluctuations and/or changes of the electrical characteristics of the laser diode junction with environment and time.
  • the reverse path of the optical plant of the present invention transmits signals in an on/off keyed digital format to avoid problems presented by return path analog transmissions. More specifically, the reverse-directed RF signals received by the nodes 142 are digitized using conventional analog-to-digital converters and transmitted as a serial bit stream to the headend station 1 10. Because the optical information signal consists of a series of l's and 0's, reductions in the signal-to-noise ratio due to nonlinearities in the fiber and laser transmitter are minimized.
  • the comparatively narrow bandwidth and low frequency of the return band (5 MHz - 40 MHz according to most standards) permit on/off keying to be realized in a straightforward and economical fashion.
  • Key to this ease of deployment is the availability of component-level analog-to-digital converters with sampling rates exceeding 80 MHz. Operated at their maximum clock speed, these components can digitize any return signal without violating the Nyquist criterion.
  • This well-known principle states that significant distortion will be present in the digitized signal in cases where the highest frequency in the input spectrum exceeds the sampling rate of the analog-to-digital converter (ADC).
  • ADC analog-to-digital converter
  • the forward-directed information is generally transmitted at RF frequencies between 50 MHZ and 750 MHz.
  • ADCs operate at clock speeds of about 100 MHz, digitization of the forward-directed RF signal violates the Nyquist criterion. Therefore, direct application of the Farhan reverse digital invention to the forward direction would be likely to lead to an decrease in the signal-to- noise ratio far in excess of any improvement afforded by on/off keyed transmission, at least in cases in which conventional ADCs are used.
  • the ADC 200 includes an RF signal input 210 and a clock input 213.
  • the RF input signal is sampled at a rate determined by the clock. For example, an ADC 200 with a sampling rate of 100 MHz would determine the amplitude of the RF input signal at 10 nsec intervals. These amplitudes are expressed as binary numbers that are output on the parallel bus 218 at the sampling rate.
  • FIG. 3 shows graphs of the spectra of an idealized input signal 310 and the ADC output 315 under conditions where the sampling frequency 320 exceeds the bandwidth 325 of the input signal but is significantly smaller than the lowest input frequency 330.
  • f represents the value of the minimum input frequency 330
  • f h represents the value of the maximum input frequency 335.
  • the lowest frequency image 345 is a baseband representation of the input signal 310 starting at 0 MHz.
  • the properties of this distortion may be advantageously used to establish one or more forward-directed, on/off keyed channels in the optical portion of the broadband distribution system of FIG. 1. If a frequency band in the input spectrum with a width ⁇ that is less than half the ADC sampling frequency is selected using a conventional bandpass filter, the distorted output of the ADC will contain a baseband image of the input signal. This image may be isolated using a digital low pass filter and subsequently transmitted using known technology. Bandpass filters having different center frequencies may be used to establish additional channels up to the limiting case in which the entire desired input spectrum is covered.
  • FIG. 4 is a block diagram of an optical communications system 400 that utilizes the method described with reference to FIG. 3 to digitize RF analog signals for subsequent transmission in the frequency band between about 700 MHz and 750 MHz.
  • an analog input signal with a frequency spectrum covering the band from 50 MHz to 750 MHz is applied to the input 405 of the optical transmitter 410, which can, for example, be located in a headend section of a broadband communication system.
  • An analog bandpass filter 408 selects the desired frequency band to be transmitted via on/off keying.
  • the desired band is 50 MHz wide, with a minimum frequency, f ⁇ , equal to 700 MHz and a maximum frequency, f h , of 750 MHz.
  • An RF transmission line 412 carries signals lying within the selected frequency band to the input of the ADC 415.
  • the sampling frequency of the ADC 415 is fixed by the clock input 418 at 100 MHz, a value equal to or greater than twice the bandwidth of the analog input signal.
  • the ADC 415 undersamples the input, thereby generating a distorted series of digital output values on the parallel output bus 420.
  • the frequency spectrum of the ADC output contains images of the input spectrum that are shifted to lower values by integral multiples of the sampling frequency.
  • the fourteenth image has a minimum frequency of zero and and maximum frequency of 50 MHz. This can be verified by subtracting fourteen times the sampling frequency (50 MHz) from the minimum frequency of the analog input (700 MHz).
  • a photodiode detector 455 converts the optical signal to a serial electronic bitstream 458.
  • a deserializer 460 converts the photodiode output to a parallel format that is sent to a digital-to-analog converter (DAC) 465 on the parallel bus 462.
  • the deserializer 460 extracts transmitted clock frequency information to generate a local clock signal 464 for the digital to analog conversion process.
  • the analog signal generated by the DAC 465 is filtered by a low pass filter 467 to remove components lying outside the 0 - 50 MHz band.
  • the local clock signal 464 is also used to synchronize a phase-locked loop 469 that generates a frequency equal to the shift between the transmitter input spectrum and that spectrum actually transmitted.
  • the frequency shift is equal to 700 MHz.
  • the output 470 of the phase-locked loop 469 is mixed with the filtered DAC output 472 using a conventional RF mixer 475.
  • the output of the mixer 475 includes an image of the baseband analog signal that is shifted by 700 MHz. Frequency components lying outside the 700 MHz - 750 MHz band are removed from the mixer output by a conventional analog bandpass filter 478.
  • the receiver output 480 will be an image of bandpass-filter-selected transmitter input signal.
  • the teachings herein can be applied to any ADC process in which the input data is undersampled and the bandwidth of the input signal is less than the sampling rate.
  • the development of ADC components with faster sampling rates may, at some point, make it desirable to use the teachings herein to transmit the entire 700 MHz-wide forward broadband signal, or larger sub-bands thereof, using on/off keyed digital modulation.
  • ADCs were available with sampling rates of greater than 200 MHz, such as 300 MHz, the forward broadband signal spectrum could be divided into five segments for transmission along a single fiber using wavelength or time division multiplexing.
  • parallel processing branches within an optical transmitter 500 can be employed to divide the incoming analog signal spectrum into equal 50 MHz sub-bands. This can be done, for example, by providing the analog input 505 to multiple bandpass filters 510, each of which pass a separate 50 MHz segment of the signal. When bandpass filters 510 are used to pass 50 MHz segments and the incoming signal has a frequency range of 50 MHz to 750 MHz, fourteen bandpass filters would receive the analog signal. The first would pass signals at 50-100 MHz, the second would pass 100-150 MHz, the third would pass 150- 200 MHz, and so on. It will be appreciated that this parallel processing scheme can be used to pass an analog signal having a frequency spectrum that is different from, greater, or smaller than that set forth in this example.
  • each bandpass filter 510 The outputs of each bandpass filter 510 are then provided to an ADC 515, which digitizes the signal as explained with reference to FIGs. 3 and 4.
  • the resulting digital signals are filtered by digital lowpass filters 520 and passed to an interleaver 525, which uses time division multiplexing to generate interleaved outputs.
  • the interleaved outputs are serialized and framed by device 530, subsequent to which the resulting serial bit stream is transmitted as a digital optical signal by the laser transmitter 535. In this manner, the entire forward band, or larger parts thereof, can be digitally transmitted throughout the broadband communication system.
  • the digital transmission system described above provides for the optical transmission of one or more bands of a broadband analog signal via optical fiber while preventing many of the problems inherent in prior art analog systems. As a result, information can be sent from the headend station to the subscriber in a more reliable and less expensive manner.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Multimedia (AREA)
  • Optics & Photonics (AREA)
  • Electromagnetism (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Optical Communication System (AREA)

Abstract

L'invention concerne un système de communication à large bande comprenant un émetteur optique (410) permettant de recevoir un signal électrique analogique et d'émettre un signal optique numérique. L'émetteur (410) comprend un filtre analogique (415) possédant une bande passante destinée à filtrer le signal électrique analogique afin de générer un signal analogique à bande passante limitée possédant une fréquence inférieure et une fréquence supérieure. Le signal analogique à bande passante limitée est échantillonné au moyen d'un convertisseur analogique-numérique (CAN) (415) à une fréquence d'échantillonnage supérieure ou égale à la bande passante du filtre analogique (408), générant ainsi un signal électrique numérique décalé en fréquence par rapport au signal électrique analogique. La fréquence inférieure du signal analogique à bande passante limitée est supérieure à la fréquence d'échantillonnage utilisée par le convertisseur (415). Un filtre numérique (422) traite ensuite la sortie du convertisseur analogique-numérique (415) afin de passer le signal électrique numérique décalé en fréquence, puis un émetteur laser (435) transmet ledit signal.
PCT/US2001/002503 2000-01-28 2001-01-25 Systeme de communication numerique aller Ceased WO2001056197A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US49409700A 2000-01-28 2000-01-28
US09/494,097 2000-01-28

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WO2001056197A2 true WO2001056197A2 (fr) 2001-08-02
WO2001056197A3 WO2001056197A3 (fr) 2002-01-17

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9820171B2 (en) 2010-09-14 2017-11-14 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US9867052B2 (en) 2000-03-27 2018-01-09 Commscope Technologies Llc Multiprotocol antenna system for multiple service providers
US10080178B2 (en) 2006-12-26 2018-09-18 Dali Wireless, Inc. Distributed antenna system
US10498434B2 (en) 2000-07-19 2019-12-03 CommScope Technolgies LLC Point-to-multipoint digital radio frequency transport
US10499269B2 (en) 2015-11-12 2019-12-03 Commscope Technologies Llc Systems and methods for assigning controlled nodes to channel interfaces of a controller
US11159129B2 (en) 2002-05-01 2021-10-26 Dali Wireless, Inc. Power amplifier time-delay invariant predistortion methods and apparatus
US11297603B2 (en) 2010-08-17 2022-04-05 Dali Wireless, Inc. Neutral host architecture for a distributed antenna system
US11418155B2 (en) 2002-05-01 2022-08-16 Dali Wireless, Inc. Digital hybrid mode power amplifier system
CN115276805A (zh) * 2022-06-27 2022-11-01 深圳麦科信科技有限公司 激光传输电路、激光传输组件和电子测量仪器
USRE50112E1 (en) 2002-12-03 2024-09-03 Outdoor Wireless Networks LLC Distributed digital antenna system

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5032908A (en) * 1989-10-23 1991-07-16 Westinghouse Electric Corp. High definition television acoustic charge transport filter bank
US5627879A (en) * 1992-09-17 1997-05-06 Adc Telecommunications, Inc. Cellular communications system with centralized base stations and distributed antenna units

Cited By (24)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9867052B2 (en) 2000-03-27 2018-01-09 Commscope Technologies Llc Multiprotocol antenna system for multiple service providers
US10321328B2 (en) 2000-03-27 2019-06-11 Commscope Technologies Llc Multiprotocol antenna system for multiple service providers
US10498434B2 (en) 2000-07-19 2019-12-03 CommScope Technolgies LLC Point-to-multipoint digital radio frequency transport
US10505635B2 (en) 2000-07-19 2019-12-10 Commscope Technologies Llc Point-to-multipoint digital radio frequency transport
US11159129B2 (en) 2002-05-01 2021-10-26 Dali Wireless, Inc. Power amplifier time-delay invariant predistortion methods and apparatus
US11418155B2 (en) 2002-05-01 2022-08-16 Dali Wireless, Inc. Digital hybrid mode power amplifier system
USRE50112E1 (en) 2002-12-03 2024-09-03 Outdoor Wireless Networks LLC Distributed digital antenna system
US10080178B2 (en) 2006-12-26 2018-09-18 Dali Wireless, Inc. Distributed antenna system
US10334499B2 (en) 2006-12-26 2019-06-25 Dali Wireless, Inc. Distributed antenna system
US11818642B2 (en) 2006-12-26 2023-11-14 Dali Wireless, Inc. Distributed antenna system
US11006343B2 (en) 2006-12-26 2021-05-11 Dali Wireless, Inc. Distributed antenna system
US11297603B2 (en) 2010-08-17 2022-04-05 Dali Wireless, Inc. Neutral host architecture for a distributed antenna system
US11013005B2 (en) 2010-09-14 2021-05-18 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US9820171B2 (en) 2010-09-14 2017-11-14 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US10743317B1 (en) 2010-09-14 2020-08-11 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US11368957B2 (en) 2010-09-14 2022-06-21 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US10701695B2 (en) 2010-09-14 2020-06-30 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US20220295487A1 (en) 2010-09-14 2022-09-15 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US11805504B2 (en) 2010-09-14 2023-10-31 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US10159074B2 (en) 2010-09-14 2018-12-18 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US12382444B2 (en) 2010-09-14 2025-08-05 Dali Wireless, Inc. Remotely reconfigurable distributed antenna system and methods
US10499269B2 (en) 2015-11-12 2019-12-03 Commscope Technologies Llc Systems and methods for assigning controlled nodes to channel interfaces of a controller
CN115276805A (zh) * 2022-06-27 2022-11-01 深圳麦科信科技有限公司 激光传输电路、激光传输组件和电子测量仪器
CN115276805B (zh) * 2022-06-27 2023-08-29 深圳麦科信科技有限公司 激光传输电路、激光传输组件和电子测量仪器

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