CA1183218A - Optical data transmission system - Google Patents
Optical data transmission systemInfo
- Publication number
- CA1183218A CA1183218A CA000363751A CA363751A CA1183218A CA 1183218 A CA1183218 A CA 1183218A CA 000363751 A CA000363751 A CA 000363751A CA 363751 A CA363751 A CA 363751A CA 1183218 A CA1183218 A CA 1183218A
- Authority
- CA
- Canada
- Prior art keywords
- data
- optical
- transmitter
- receiver
- signals
- 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.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
-
- 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
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2589—Bidirectional transmission
- H04B10/25891—Transmission components
Landscapes
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optical Communication System (AREA)
- Dc Digital Transmission (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An optical transmission system for data employing an optical transmitter modulated by the data and at least one light-conductive fiber connecting the transmitter with an optical receiver, which is connected in series with a data sink. At the transmitting end, the data are additionally spectrally spread, by means of a coder connected ahead of the transmitter, for transmission over the light-conductive fiber and at the receiving end the spectral spread of the data is reversed by a decoder connected behind the receiver.
An optical transmission system for data employing an optical transmitter modulated by the data and at least one light-conductive fiber connecting the transmitter with an optical receiver, which is connected in series with a data sink. At the transmitting end, the data are additionally spectrally spread, by means of a coder connected ahead of the transmitter, for transmission over the light-conductive fiber and at the receiving end the spectral spread of the data is reversed by a decoder connected behind the receiver.
Description
:~8~
BACKGROUND OF THE INVENl'ION
The present invention relates to a data transmission system for data including an optical data transmitter which is modulated by the data, and at least one light-conductive fiber connecting the transmitter to an optical receiver which is followed by a data sink.
Optical transmission systems are known which comprise relatively short transmission sections, each equipped with at least one light-conductive fiber as the optical transmission medium, and amplifiers or repeaters connected between the sections. U.S. Patent No. 3,845,293 issued October 29th, 1974 to M. Borner discloses such a system which is sui-table for the transmission of PCM (pulse code modulated) data. The arnplifying distance, i.e. the maximum distance between an optical transmitter and the next optical receiver, is here ~etermined essentially by the maximum possible gain Vmax of the optical receiver and by the attenuation ~x per kilometer o~ the liyht-conductive fiber which is employed as the optical -transmis.sion medium. Thus, a large number of intermediate amplifiers or repeaters are required to cover large distances~
which increases the cost for such a transmission system.
SUMM~RY OF THE INVENTION
It is the object of the present invention to provide an improved -transmission system of -the type men-tioned above in which the ampliEying distance is increased, and hence the -332~ ~3 number of amplifiers or repeaters required for a given distance is clecreased, The above object is generally achieved according to thc present invention in that, based on the above-mentioned transmission system, at the transmitting end the data present in analog or digital form is additionally spectrally spread, by means of a coder inserted ahead of the transmitter, for transmission through the light-conductive fiber and, this spread is reversed at the receiving end by means of a decoder connected behind the receiver, i.e., between the receiver and the data sink.
According to another broad aspect of the invention there is pro-vided an optical data transmission system comprising an encoder for spect-rally spreading optical data signals, an optical transmitter for transmitting the spectrally spread signals, at least one fibre-optical conductor for conducting the transmitted signals, an optical receiver for receiving the conducted signals, a plurality of relay stations which are arranged between the transmitter and the receiver to amplify the conducted signals and which are spaced apart from each other and from the transmitter and the receiver in each case by a distance which is determined by the attenuation of the conductor and increased by an amount dependent on the degree of spectral spread:ing of the signals, a decoder for cancelling the spectral spreading oE the signals received by the receiver, and data receiving means for receiv ing a data input from the decoder.
BRIEF DESCRIPTION OF THE DRAWINGS
The Figure is a schematic circuit diagram of an optical data transmission system according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Spreading code methods are known for data -transmission, for example Erom the paper entitled "Spe]ctrale Spreizung als Multiplex-Verfahren" (Spec-tral Spreading as a Mu]tiplex Method) by Aldinger, Herold and Krick, pub-lished in the periodical "NTZ" Vol. 28 ~1975), No. 3, pages 79-88, wherein the data is modulated onto an analog or digital carrier.
.~ . .
The base band signal, which is narrowbanded compared to the channel bandwidth, is spectrally spread to the channe~ band-width by means Gf the spreading code method. At the receiving end, this spread is reversed again by multiplication with the synchronized code word. This compression at the receiving end lifts the desired signal out of -the received signal level. In this way, it is possible to receive signals which lie considerably below the noise level.
In light-conductive fibers, the available bandwidth of the fiber itself - see, for example, the attenuation curve shown in the paper hy Takahashi, entitled "Preparation of Low Loss Multi-Component Glass Fibers" published in the periodical REVIEW OF THE ELECTRICAL COMMUNICATION LABORATORIES, Volume 27, No. 1-2, January February 1979, page 26, or in ELECTRONICS
LETTERS, September 29th, 1977, Volume 13, No. 20, page 609 -is substantially greater than the bandwidth that can be utilized by the available transmitting elements, see "Design Process for Fibreoptic Systems Follows Familiar Rules" in F,I,F.CTRONICS, September 16th, 1976, page 113. With the presently ~0 preferred multimode fibers and with light emitting diodes (LED), it is possible to obtain a product relationship of the amplify-ing distance and the bandwidth of about 500 MHz x km. Any comrnercially available diode of suitable frequency can be used as the transmitting element LED.
In single mode fibers, the transmission bandwidth is given practically only the dispersion of fiber materia] and by the emission bandwidth of the transmitter. Using a single wal~e laser as the transmitter, amplifying distance - bandwidth products of about 50~000 ~z x km can be expected.
According to the present invention the previously a~Jailable amplifying distance is now increased in that the data are additionally spectrally spread during transmission. This is done by utilizing the fact that light-conductive fibers - in contrast to cable lines - have a substanti-ally frequency independent attentuation over a very broad frequency band (see "Fibre-Optical Communication Systems", THE RADIO AND ELECT~ONIC ENCI-NEER, Volume 43,No. 11, page 670). Thus, the transmission rate can be varied over a very broad range without any adverse effect on the attentuation per kilometer. In principle, the spreading can be effected with analog as well as digital types of modulation. However, the present invention is most advantageous with a digital data flow.
The drawing figure is a schematic representation of a trans-mission system constructed according to the present invention. The data emanating from the data source 1 are spectrally spread by the coder 2 before they are fed to an optical transmitter 3 to modulate the carrier of same.
The output of the transmitter 3 is connected with an associated optical receiver 5 by means of at least one light-conductive .,,'.~'', .
fiber 4. Any commercially available low attentuation fiber can be used as the light-conductive fiber 4. The output of the receiver 5 is connec~ed in series with a decoder 6 ~Jhich reverses the spectral spreading produced by the coder 2 and feeds the resultant signal to the data sink 7.
A multimode fiber can be used as the light-conductive fiber 4. However, the present invention can he used to par-ticular advantage when using single mode fibers for the light-conductive fibers 4. Multimode and single mode fibers are disclosed, for example, in "Optical Fibre Transmission -Single Mode vs. Multimode" by Maslowski in CONF. PROC.
WORLD TELECO~MUNICATION FORUM, Geneva, October 6-th-8th, 1975.
Essentially limited by the required signal to noise ratio with respect to the thermal noise of the optical receiver, the digital da-ta can be spread over a very large range by adding in fill bits to every useful bit. The bit rate on the transmission path, i.e., in -the light-conductive fiber 4, is then increased with respect to the useful bit rate by the factor (n~l). At the receiving end, this permits the accep-tance by the optical receiver 5 of smaller input signals,thereby permitting a greater maximum gain Vmax. However, this means an increase in the required amplifying field length _, i.e. the length of the section of optical trans-mission line 4. For extreme cases, it is further possible to spread the data to be transmitted over the bandwidth of ~everal light-conductive fibers in order to realize the greates-t possible amplifying distance _.
The increase G in the signal to noise ratio depends on the degree of spreading, i.e. on the number of fill bits, and is approximately G = lOlog n. A spread n = 100 bits thus brings about an improvement in the signal to noise ratio of 20 dB. If, for example, Vma = 52 dB, with an attenuation = 4 dB/km, a distance of 13 km can be bridged by a section f light-conductive fiber 4 without intermediate amplification.
Increasing the spread by n = 100 bits, increases Vmax to 72 dB
and the required amplifying field length _ to 18 km.
It is to be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.
BACKGROUND OF THE INVENl'ION
The present invention relates to a data transmission system for data including an optical data transmitter which is modulated by the data, and at least one light-conductive fiber connecting the transmitter to an optical receiver which is followed by a data sink.
Optical transmission systems are known which comprise relatively short transmission sections, each equipped with at least one light-conductive fiber as the optical transmission medium, and amplifiers or repeaters connected between the sections. U.S. Patent No. 3,845,293 issued October 29th, 1974 to M. Borner discloses such a system which is sui-table for the transmission of PCM (pulse code modulated) data. The arnplifying distance, i.e. the maximum distance between an optical transmitter and the next optical receiver, is here ~etermined essentially by the maximum possible gain Vmax of the optical receiver and by the attenuation ~x per kilometer o~ the liyht-conductive fiber which is employed as the optical -transmis.sion medium. Thus, a large number of intermediate amplifiers or repeaters are required to cover large distances~
which increases the cost for such a transmission system.
SUMM~RY OF THE INVENTION
It is the object of the present invention to provide an improved -transmission system of -the type men-tioned above in which the ampliEying distance is increased, and hence the -332~ ~3 number of amplifiers or repeaters required for a given distance is clecreased, The above object is generally achieved according to thc present invention in that, based on the above-mentioned transmission system, at the transmitting end the data present in analog or digital form is additionally spectrally spread, by means of a coder inserted ahead of the transmitter, for transmission through the light-conductive fiber and, this spread is reversed at the receiving end by means of a decoder connected behind the receiver, i.e., between the receiver and the data sink.
According to another broad aspect of the invention there is pro-vided an optical data transmission system comprising an encoder for spect-rally spreading optical data signals, an optical transmitter for transmitting the spectrally spread signals, at least one fibre-optical conductor for conducting the transmitted signals, an optical receiver for receiving the conducted signals, a plurality of relay stations which are arranged between the transmitter and the receiver to amplify the conducted signals and which are spaced apart from each other and from the transmitter and the receiver in each case by a distance which is determined by the attenuation of the conductor and increased by an amount dependent on the degree of spectral spread:ing of the signals, a decoder for cancelling the spectral spreading oE the signals received by the receiver, and data receiving means for receiv ing a data input from the decoder.
BRIEF DESCRIPTION OF THE DRAWINGS
The Figure is a schematic circuit diagram of an optical data transmission system according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Spreading code methods are known for data -transmission, for example Erom the paper entitled "Spe]ctrale Spreizung als Multiplex-Verfahren" (Spec-tral Spreading as a Mu]tiplex Method) by Aldinger, Herold and Krick, pub-lished in the periodical "NTZ" Vol. 28 ~1975), No. 3, pages 79-88, wherein the data is modulated onto an analog or digital carrier.
.~ . .
The base band signal, which is narrowbanded compared to the channel bandwidth, is spectrally spread to the channe~ band-width by means Gf the spreading code method. At the receiving end, this spread is reversed again by multiplication with the synchronized code word. This compression at the receiving end lifts the desired signal out of -the received signal level. In this way, it is possible to receive signals which lie considerably below the noise level.
In light-conductive fibers, the available bandwidth of the fiber itself - see, for example, the attenuation curve shown in the paper hy Takahashi, entitled "Preparation of Low Loss Multi-Component Glass Fibers" published in the periodical REVIEW OF THE ELECTRICAL COMMUNICATION LABORATORIES, Volume 27, No. 1-2, January February 1979, page 26, or in ELECTRONICS
LETTERS, September 29th, 1977, Volume 13, No. 20, page 609 -is substantially greater than the bandwidth that can be utilized by the available transmitting elements, see "Design Process for Fibreoptic Systems Follows Familiar Rules" in F,I,F.CTRONICS, September 16th, 1976, page 113. With the presently ~0 preferred multimode fibers and with light emitting diodes (LED), it is possible to obtain a product relationship of the amplify-ing distance and the bandwidth of about 500 MHz x km. Any comrnercially available diode of suitable frequency can be used as the transmitting element LED.
In single mode fibers, the transmission bandwidth is given practically only the dispersion of fiber materia] and by the emission bandwidth of the transmitter. Using a single wal~e laser as the transmitter, amplifying distance - bandwidth products of about 50~000 ~z x km can be expected.
According to the present invention the previously a~Jailable amplifying distance is now increased in that the data are additionally spectrally spread during transmission. This is done by utilizing the fact that light-conductive fibers - in contrast to cable lines - have a substanti-ally frequency independent attentuation over a very broad frequency band (see "Fibre-Optical Communication Systems", THE RADIO AND ELECT~ONIC ENCI-NEER, Volume 43,No. 11, page 670). Thus, the transmission rate can be varied over a very broad range without any adverse effect on the attentuation per kilometer. In principle, the spreading can be effected with analog as well as digital types of modulation. However, the present invention is most advantageous with a digital data flow.
The drawing figure is a schematic representation of a trans-mission system constructed according to the present invention. The data emanating from the data source 1 are spectrally spread by the coder 2 before they are fed to an optical transmitter 3 to modulate the carrier of same.
The output of the transmitter 3 is connected with an associated optical receiver 5 by means of at least one light-conductive .,,'.~'', .
fiber 4. Any commercially available low attentuation fiber can be used as the light-conductive fiber 4. The output of the receiver 5 is connec~ed in series with a decoder 6 ~Jhich reverses the spectral spreading produced by the coder 2 and feeds the resultant signal to the data sink 7.
A multimode fiber can be used as the light-conductive fiber 4. However, the present invention can he used to par-ticular advantage when using single mode fibers for the light-conductive fibers 4. Multimode and single mode fibers are disclosed, for example, in "Optical Fibre Transmission -Single Mode vs. Multimode" by Maslowski in CONF. PROC.
WORLD TELECO~MUNICATION FORUM, Geneva, October 6-th-8th, 1975.
Essentially limited by the required signal to noise ratio with respect to the thermal noise of the optical receiver, the digital da-ta can be spread over a very large range by adding in fill bits to every useful bit. The bit rate on the transmission path, i.e., in -the light-conductive fiber 4, is then increased with respect to the useful bit rate by the factor (n~l). At the receiving end, this permits the accep-tance by the optical receiver 5 of smaller input signals,thereby permitting a greater maximum gain Vmax. However, this means an increase in the required amplifying field length _, i.e. the length of the section of optical trans-mission line 4. For extreme cases, it is further possible to spread the data to be transmitted over the bandwidth of ~everal light-conductive fibers in order to realize the greates-t possible amplifying distance _.
The increase G in the signal to noise ratio depends on the degree of spreading, i.e. on the number of fill bits, and is approximately G = lOlog n. A spread n = 100 bits thus brings about an improvement in the signal to noise ratio of 20 dB. If, for example, Vma = 52 dB, with an attenuation = 4 dB/km, a distance of 13 km can be bridged by a section f light-conductive fiber 4 without intermediate amplification.
Increasing the spread by n = 100 bits, increases Vmax to 72 dB
and the required amplifying field length _ to 18 km.
It is to be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a transmission system for data including a source of data, an optical transmitter for transmitting a carrier signal modulated by the data from said source, an optical receiver where output is connected in series with a data sink, and at least one light-conductive fiber connecting said transmitter with said optical receiver, the improvement comprising a coder means, connected ahead of said transmitter at the transmitting end, for spectrally spreading the data for transmission over said light-conductive fiber, and decoder means, connected behind said receiver, for reversing the spectral spread produced by said coder means.
2. Transmission system as defined in claim 1 wherein said at least one light-conductive fiber is a single mode light-conductive fiber.
3. An optical data transmission system comprising an encoder for spectrally spreading optical data signals, an optical transmitter for trans-mitting the spectrally spread signals, at least one fibre-optical conductor for conducting the transmitted signals, an optical receiver for receiving the conducted signals, a plurality of relay stations which are arranged between the transmitter and the receiver to amplify the conducted signals and which are spaced apart from each other and from the transmitter and the receiver in each case by a distance which is determined by the attenuation of the conductor and increased by an amount dependent on the degree of spectral spreading of the signals, a decoder for cancelling the spectral spreading of the signals received by the receiver, and data receiving means for receiving a data input from the decoder.
4. A system as claimed in claim 3, comprising a plurality of such conductors.
5. A system as claimed in claim 3, wherein the conductor is a mono-mode fibre.
6. A system as claimed in claim 4, wherein each conductor is a mono-mode fibre.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2944501.0 | 1979-11-03 | ||
| DE19792944501 DE2944501A1 (en) | 1979-11-03 | 1979-11-03 | DATA TRANSFER SYSTEM |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1183218A true CA1183218A (en) | 1985-02-26 |
Family
ID=6085118
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000363751A Expired CA1183218A (en) | 1979-11-03 | 1980-10-31 | Optical data transmission system |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5698046A (en) |
| CA (1) | CA1183218A (en) |
| DE (1) | DE2944501A1 (en) |
| FR (1) | FR2469056B1 (en) |
| GB (1) | GB2063467B (en) |
| SE (1) | SE456295B (en) |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1806251A1 (en) * | 1968-10-09 | 1970-07-02 | Telefunken Patent | Method for the transmission of separate information |
| DE2248211C3 (en) * | 1972-10-02 | 1980-01-03 | Allgemeine Elektricitaets-Gesellschaft Aeg-Telefunken, 1000 Berlin Und 6000 Frankfurt | Fiber line communication system |
| FR2467512A1 (en) * | 1979-10-15 | 1981-04-17 | Crouzet Sa | INTEGRAL SIMULTANEOUS MULTI-ACCESS TRANSMISSION SYSTEM ON OPTICAL FIBER TRANSMISSION LINES |
-
1979
- 1979-11-03 DE DE19792944501 patent/DE2944501A1/en active Granted
-
1980
- 1980-10-30 GB GB8034923A patent/GB2063467B/en not_active Expired
- 1980-10-31 JP JP15241980A patent/JPS5698046A/en active Pending
- 1980-10-31 CA CA000363751A patent/CA1183218A/en not_active Expired
- 1980-10-31 FR FR8023372A patent/FR2469056B1/en not_active Expired
- 1980-11-03 SE SE8007702A patent/SE456295B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5698046A (en) | 1981-08-07 |
| FR2469056A1 (en) | 1981-05-08 |
| GB2063467A (en) | 1981-06-03 |
| DE2944501A1 (en) | 1981-05-07 |
| DE2944501C2 (en) | 1989-03-09 |
| SE8007702L (en) | 1981-05-04 |
| SE456295B (en) | 1988-09-19 |
| FR2469056B1 (en) | 1986-05-23 |
| GB2063467B (en) | 1983-10-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry | ||
| MKEX | Expiry |
Effective date: 20020226 |