CN1133289C - Code overlapped fast hopping optical CDMA access system - Google Patents
Code overlapped fast hopping optical CDMA access system Download PDFInfo
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- CN1133289C CN1133289C CN01132218A CN01132218A CN1133289C CN 1133289 C CN1133289 C CN 1133289C CN 01132218 A CN01132218 A CN 01132218A CN 01132218 A CN01132218 A CN 01132218A CN 1133289 C CN1133289 C CN 1133289C
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Abstract
The present invention provides a code overlapped fast hopping optical CDMA access system. The light source is directly modulated by the data bit of the user terminal in an optical encoder, and the generated broadband optical pulses enter an optical fibre raster and the line array of an optical fibre delay line through an optical circulator; the center reflecting wavelength position of the optical fibre raster of an optical decoder is opposite to the corresponding optical encoder; the data extraction circuit in a conventional IM/DD digital optical transmission system is used to extract the data bits; the length of the optical fibre delay line of the optical encoder and the optical decoder is c T/ 2n <eff>. The present invention omits the electric pulse compression and the stretching process of the encoding and decoding process, and simplifies the system structure; the advantages of free addressing, good security, little light power loss, etc., of the traditional fast hopping optical CDMA system are reserved and the information bit rate and the system throughput of users are enhanced; the communication cost is reduced and the system economical efficiency is greatly improved. The present invention can be used for region networks of the full optical region, optical access networks, optical fibre local area networks and other optical fiber bus systems, and thus, has good application prospect.
Description
Technical field:
The present invention relates to a kind of fast hopping optical CDMA access system, relate in particular to a kind of novel code overlapped fast hopping optical CDMA connecting system that is easy to realize, can realize that information bit directly modulates wideband light source, the code overlapped transmission of spread spectrum, decoding output directly detects, and then judgement output.Can be used for systems such as metropolitan area network, Access Network, local area network (LAN), belong to technical field of optical fiber communication.
Background technology:
Along with developing rapidly of Fibre Optical Communication Technology, backbone network has been realized fiberize basically, the transmission capacity of system increases greatly, but the development with new data service of increasing rapidly along with traffic carrying capacity, metropolitan area network and Access Network can't satisfy the requirement of development communication technologies, become the bottleneck of network, optical fiber is introduced metropolitan area network and Access Network just becomes the preferred plan that addresses this problem.At present, the solution of optical fiber metropolitan area network mainly is all optical network that adopts based on wave division multiplexing WDM and optical cross-connect OXC.The solution of Access Network mainly contains active optical access network AON based on SDH, based on passive optical access network PON, the HFC etc. of ATM.Which type of topological structure no matter these modes adopt, the multiple access access control problem that all exists a plurality of ONU to share the optical fiber medium and carry out up direction communication, great majority adopt the TDMA mode at present, exist bandwidth availability ratio low (because expense is bigger), access control complexity (needing synchronization timing), insert problems such as having time-delay, network management complexity.Optical code division multiple access OCDMA access technology is introduced fiber optic communication field with code division multiple access CDMA access way, and utilize the high-speed light information processing technology to carry out encoding and decoding, can realize not having the asynchronous access of delay, and network control is simple, service transparency is good, is one of preferred plan of following broadband access and high-speed lan.
In present existing OCDMA system schema, fast hopping optical CDMA FFH-OCDMA access scheme has lot of advantages, as completely without source structure, can free addressing, be easy to integrated, power system capacity is big, and the error rate is relatively low, is very promising a kind of scheme, being subjected to extensive concern, is the research focus of present OCDMA technical field.
At traditional (H.Fathallah of FFH-OCDMA system, and L.A.Rusch, " Passive opticalfast frequency-hop CDMA communications system; " J.Lightwave Technol, 17 (3), pp397-405,1999.) in, frequency hopping OCDMA system is divided into some (q 's) frequency crack (Frequency Slot, i.e. wavelength) with the available bandwidth of optical fiber, by a plurality of users are shared.Each user has oneself a address code (frequency hopping pattern), according to this address code, each data bit (bit period is T) is become N time slot (Qie Pu) by spread spectrum, the wavelength of each Qie Punei light pulse has nothing in common with each other, the light pulse of each Qie Punei saltus step between different wavelength like this forms the fast frequency hopping spread-spectrum signal.At receiving terminal, the light decoder adopts the matched filtering principle that data are extracted from the signal that receives.
The optical encoder of frequency hopping OCDMA system adopts the structure of optical fiber Bragg raster (FBG) and fibre delay line cascade.The foveal reflex wavelength difference of each fiber grating, and with length be cT
c/ 2n
EffFibre delay line series connection, T
cFor cutting general width, T
c=T/N, T are data bit period.Here c is the light velocity in the vacuum, n
EffBe the effective refractive index in the optical fiber.In this coding, data bit is through OOK modulation ultrashort pulse wideband light source, and the generation width is T
cLight pulse.This short pulse enters encoder through optical circulator, and each fiber grating is passed through in light pulse successively, and it is λ that grating makes centre wavelength
iSpectral component reflection laggardly go into the optical circulator output port because each grating foveal reflex wavelength difference, and the delayed difference of pulse of different wave length, so just form frequency hopping and encode.The structure and the optical encoder of light decoder are basic identical, also adopt " fibre delay line+fiber grating " cascade to constitute, but the position of fiber grating are opposite with encoder.Fiber grating in this optical encoder can be realized the change of foveal reflex wavelength by temperature control or Stress Control (as adopt piezoelectric device on each FBG), so can realize free addressing easily.
In this traditional F FH-OCDMA system, to comprise N duration be T because data bit is encoded into one
cCut general frequency expansion sequence, the duration of this sequence is a bit period T, and the frequency expansion sequence of adjacent bit is a but crossover not in succession.Require to have a circuit in transmitter, it is T that the data pulse of an electricity is compressed into width
cUltrashort pulse remove to modulate wideband light source; The width that requires to have a circuit to decode and to export after light-to-current inversion in receiver is T
cPulse stretching be information bit.These two processes all require certain timing accuracy, so the complexity of system on circuit rises.And for given light source, its user data rate is the 1/N of light source maximum modulation speed, so user data rate is lower, relative communications cost is higher.
Summary of the invention:
The objective of the invention is at the deficiencies in the prior art, a kind of novel code overlapped fast hopping optical CDMA connecting system that is easy to realize is proposed, make it to have simple in structure and the big characteristics of information throughput, can overcome high complexity, higher cost and the lower problems such as throughput of traditional F FH-OCDMA system.
In order to realize such purpose, the code overlapped fast hopping optical CDMA connecting system that the present invention proposes adopts stelliform connection topology configuration or adopts bus-type, tree topology, fiber optic network is made up of passive devices such as optical fiber, coupler, optical branching devices, links to each other with user terminal by optical encoder, light decoder.An optical encoder and a light decoder are arranged respectively in the transmitter of each user terminal and the receiver in the system, optical encoder spreads to coded sequence with the user profile bit and sends in the fiber optic network, light signal in the fiber optic network enters the light decoder that receives the user through splitter, finish signal decoding, give its user terminal the information bit data.
Each user's optical encoder is linked in sequence and is formed by wideband light source, optical circulator, N Prague (Bragg) fiber grating, fibre delay line, and wherein, N is an integer, is the time domain spread spectrum coefficient of the fast frequency hopping address code that adopts of system.In the codec of code overlapped FFH-OCDMA of the present invention system, fibre delay line length is cT/2n
EffRather than the cT of traditional F FH-OCDMA system
c/ 2n
EffThe data bit direct modulation light of user terminal is sent the broadband optimal pulse that width equals bit period, enters fiber grating and fibre delay line linear array through optical circulator.The light decoder that receives user side is made up of optical circulator, a fibre delay line and N fiber grating.The position of the foveal reflex wavelength of this N fiber grating is opposite with corresponding optical encoder, such coded sequence is behind the fibre delay line of varying number, N pulse coincides together again, form a pulse, the width of this pulse equals the cycle of data bit, just can directly extract data bit so finish after the light-to-current inversion passing threshold judgement by photo-detector.Because the data direct modulation light is so the frequency expansion sequence of adjacent bit is overlapped.
In the system of the present invention, data are to send and directly modulate wideband light source (not having the pulse compression process in the traditional F FH-OCDMA system) continuously, producing width is the broadband optimal pulse of T, light pulse enters the encoder that constitutes from optical circulator, Bragg fiber grating (FBG) and fibre delay line, and producing by N width is frequency expansion sequence T, that the mutually different light pulse of wavelength is formed.Like this, it is general that each user profile bit spread spectrum becomes N to cut, and the spread-spectrum signal of each bit takies the time of N bit, and the spread-spectrum signal of each bit all and the spread-spectrum signal of the bit adjacent with it overlapping (N-1 bit period is overlapping).Because the address code in the FFH-OCDMA system has a special attribute: the code word auto-correlation function does not have secondary lobe, that is to say, do not exist user's auto-correlation to disturb in the system, light decoder in the receiver user can coincide N light pulse of frequency expansion sequence again, forms a pulse output.So the signal of the adjacent bit that same user sends can not interfere with each other after decoding.Therefore, in the code overlapped FFH-OCDMA system that the present invention proposes, receiver user utilizes the light decoder directly signal to be reverted to data bit, omit the pulse stretching process in traditional FFH-OCDMA system, but utilized traditional intensity modulated/direct simple phase-locked loop circuit, photo-detector and decision device of adopting in (IM/DD) digital light transmission system of detecting just can finish the data bit extraction.Electric pulse compression and broadening process in the Code And Decode process have so just been saved, and these two processes realize that for the two-forty system difficulty is bigger, and be subjected to clock drift that factors such as variation of ambient temperature cause and electromagnetic interference effect easily and produce the inaccuracy and the error code of pulse duration, thereby simplified system configuration, reduce cost, improved performance.
In our code overlapped FFH-OCDMA system, address code adopts substance commonly used among the traditional F FH-OCDMA to close sequence (One-coincident Sequence), does not need to construct special code word, therefore also has the advantage of easy design.Our system adopts the fiber grating+fibre delay line structure completely without the source in addition, and structure is very simple, and the cost of codec is lower, and the error of fibre delay line is relatively easily controlled.
In system of the present invention, the accessible information bit rate of each user equals the modulation rate (in traditional F FH-OCDAM system, the user profile bit rate is the 1/N of modulation of source speed) of light source, so the user profile bit rate has improved N doubly.The information bit rate that has improved each user has also just reduced the communications cost of unit information, so system economy is greatly improved.This just makes it be well suited for present metropolitan area network and Access Network in the future.
In the system of the present invention, when system user number during less than (N+1), under the situation of not considering noise, the user can realize errorless code communication, and the errorless code communication number of users of legacy system is N/2, so the no error code number of users of native system has enlarged two times.If take the forward error correction measure, number of users can also improve.
In system of the present invention, the information throughput of system greatly improves.If the modulation rate of given light source is M, then each user's information bit rate is M just, and for N user, the total throughout of system is NM.And traditional FFH-OCDMA system, each user's information bit rate is M/N, system's maximum number of user is q (number of wavelengths that q takies for the address code collection), so its total throughout is qM/N, and in the known address code, all have q＜＜N
2Relation, so overall system throughput has improved N
2/ q doubly.If we adopt the address code of q=N+1, system so of the present invention can reach the throughput of present WDM (wavelength division multiplexing) system, so just have great advantage on systematic function, and aspects such as the realization difficulty of system, cost, ease for maintenance, confidentiality, webmaster complexity all are better than wdm system.
System of the present invention can also adopt document H.Fathallah, and L.A.Rusch, " Robust opticalFFH-CDMA communications:coding in place of frequency and temperaturecontrols; " IEEE Journal of Lightwave Technology, Vol.17, No.8, p1284-1293, Aug.1999. the address code that proposes in, just can effectively overcome the drift of the fiber grating foveal reflex wavelength that variation of ambient temperature causes, the robustness of raising system, this greatly reduces complexity and cost for the temperature control measure of the necessary costliness of wdm system.So system of the present invention can provide the economy than better access performance of WDM and Geng Jia.
System of the present invention has kept the advantage of traditional F FH-OCDMA system, as can free addressing, plurality of advantages such as good confidentiality, optical power loss be little.
The present invention can be used for full light metropolitan area network, optical access network and optical local area network and other optical fiber common bus systems (as the internal bus of naval vessel and aircraft) field, and also can be used for the backbone network field after adopting the dispersion compensation measure, have fabulous application prospect.
Description of drawings:
Fig. 1 is the theory diagram of system of the present invention.
Fig. 2 is the optical encoder and the light decoder structural representation of system of the present invention.
Fig. 2 (a) is an optical encoder, and Fig. 2 (b) is the light decoder.Wherein, 1 is that wideband light source, 2 is that optical circulator, 3 is that fibre delay line, 4 is that Bragg fiber grating, 6 is that optical fiber, 7 is that broadband optimal pulse, 8 is the narrow band light pulse.
Fig. 3 sends the code overlapped schematic diagram of signal for user in the system of the present invention.
Embodiment:
Fig. 1 is the theory diagram of system of the present invention.
System has as shown in Figure 1 adopted stelliform connection topology configuration.N user terminal arranged in the system, an optical encoder and a light decoder are arranged respectively in each user's transmitter and the receiver.Optical encoder spreads to coded sequence with the user profile bit and sends in the fiber optic network, and fiber optic network is made up of passive devices such as optical fiber, coupler, optical branching devices.Light signal in the fiber optic network enters the light decoder that receives the user through splitter, finishes signal decoding, gives its user terminal with the information bit data.
Fig. 2 is the optical encoder and the light decoder structural representation of system of the present invention.
Wherein, Fig. 2 (a) is an optical encoder of the present invention, and Fig. 2 (b) is a smooth decoder of the present invention.This is typical N=4, the optical encoder of the number of wavelengths q=5 that the address code collection takies and light decoder.
Shown in Fig. 2 (a), each user's optical encoder is linked in sequence by wideband light source (1), optical circulator (2), a N Bragg fiber grating (4), fibre delay line (3) and optical fiber (6) and forms.N is a code word size.Light source (1) can be LED, EDFA/ASE light source, or other wideband light sources.The data bit direct modulation light of user terminal is sent the broadband optimal pulse (7) that width equals bit period.Light pulse (7) enters fiber grating (4) and fibre delay line (3) linear array through the port of optical circulator (2).The foveal reflex wavelength of fiber grating has nothing in common with each other in an encoder, so different arrowband (relative) light pulse (8) of centre wavelength that width is T of each fiber grating reflection.
In the encoder of system of the present invention, fibre delay line length is cT/2n
EffRather than the cT of traditional F FH-OCDMA system
c/ 2n
Eff, T=NT in the formula
c, be data bit period.So light pulse sequence that just to have formed a duration be NT.This sequence enters fiber optic network through optical circulator (2), is broadcast to all users.
Shown in Fig. 2 (b), the present invention has similar structure at the light decoder that receives user side, is made up of optical circulator (2), fibre delay line (3) and N fiber grating (4).The position of the foveal reflex wavelength of this N fiber grating is opposite with corresponding optical encoder, such coded sequence is behind the fibre delay line of varying number, N pulse coincides together again, form a pulse, the width of this pulse equals the cycle of data bit, just can directly extract data bit so finish after the light-to-current inversion passing threshold judgement by photo-detector (5).Because the data direct modulation light is so the frequency expansion sequence of adjacent bit is overlapped.
Fig. 3 sends the code overlapped schematic diagram of signal for user in the system of the present invention.
Provided the waveform behind decoder decode among Fig. 3, data pattern is an example with " 1101 " among the figure, and wherein the 3rd bit is " 0 ", and its waveform is a dotted lines, and meaning does not have light signal.As can be seen from Figure 3, receiver can directly carry out threshold value judgement output after light-to-current inversion.
Claims (1)
1, a kind of code overlapped fast hopping optical CDMA connecting system, by optical fiber, coupler, the fiber optic network that passive devices such as optical branching device are formed passes through optical encoder, the light decoder links to each other with user terminal, user's optical encoder spreads to coded sequence with the user profile bit and sends in the fiber optic network, light signal in the fiber optic network enters the light decoder that receives the user through splitter, finish signal decoding, give its user terminal with the information bit data, the optical encoder that it is characterized in that each user is by wideband light source (1), optical circulator (2), N Prague (Bragg) fiber grating (4), length is cT/2n
EffFibre delay line (3) and optical fiber (6) composition that is linked in sequence, wherein, N is an integer, is the time domain spread spectrum coefficient of the fast frequency hopping address code that adopts of system, T is a data bit period, c is the light velocity in the vacuum, n
EffBe the optical fiber effective refractive index, the broadband optimal pulse (7) that the width that the data bit direct modulation light of user terminal is sent equals bit period enters fiber grating (4) and fibre delay line (3) linear array through optical circulator (2), different narrow band light pulse (8) of centre wavelength that width is T of each bragg grating (4) reflection, the light decoder that receives user side is cT/2n by optical circulator (2), length equally
EffFibre delay line (3) and N bragg grating (4) form, the position of the foveal reflex wavelength of fiber grating (4) is opposite with corresponding optical encoder, adopts traditional intensity modulated/direct phase-locked loop circuit, photo-detector and decision device that detects in (IM/DD) digital light transmission system to finish data bit and extract.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101788310A (en) * | 2010-02-11 | 2010-07-28 | 西南交通大学 | Fiber bragg grating track sensing system based on optical code division multiple access technique |
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| CN100454801C (en) * | 2005-01-13 | 2009-01-21 | 华中科技大学 | Optical coder and decoder with four phase modulation |
| JP4655845B2 (en) * | 2005-09-15 | 2011-03-23 | 沖電気工業株式会社 | Optical pulse time spreader |
| CN101030822B (en) * | 2006-02-27 | 2012-02-01 | 华为技术有限公司 | Optical network unit, optical line terminal, passive fiber-optic access network and its transmission |
| CN102055584B (en) * | 2009-10-28 | 2012-12-12 | 中国科学院半导体研究所 | Optical-fiber secret communication device and data encryption method thereof |
| CN102386977A (en) * | 2011-10-20 | 2012-03-21 | 航天科工深圳（集团）有限公司 | Data transmitting and receiving method, device and equipment for optical fiber transmission |
| CN102685614B (en) * | 2012-05-28 | 2014-09-03 | 哈尔滨工业大学 | Optical codec based on cascade tunable optical fiber delay lines and optical fiber Bragg grating structure |
| CN105119658B (en) * | 2015-09-08 | 2017-06-16 | 上海嘉强自动化技术有限公司 | The EtherCAT EPON stelliform connection topology configurations of ECATPON principal and subordinate's one |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101788310A (en) * | 2010-02-11 | 2010-07-28 | 西南交通大学 | Fiber bragg grating track sensing system based on optical code division multiple access technique |
| CN101788310B (en) * | 2010-02-11 | 2011-10-26 | 西南交通大学 | Fiber bragg grating track sensing system based on optical code division multiple access technique |
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