CN102035601A - Method for improving transmission capacity of multimode fiber communication system - Google Patents

Abstract

The invention discloses a method for improving transmission capacity of a multimode fiber communication system, belongs to the field of optical communication transmission layers, and particularly relates to frequency multiplexing of multi-path signals of a transmitting end in the multimode fiber communication system. The multimode fiber communication system introduces sinusoidal carrier modulation at the transmitting end to modulate a path of newly increased orthogonal frequency division multiplexing (OFDM) signals to be the same frequency as cosine carrier modulation, and two paths of signals complex the same frequency range, so the frequency spectrum utilization rate is increased, and the transmission capacity of the multimode fiber communication system is greatly improved.

Description

A kind of method that improves the multimode optical fiber communication system transmission capacity

Technical field

The present invention's design belongs to optical communication transport layer field, is applied to the channeling of transmission signals in the multimode optical fiber communication system.

Background technology

Constantly improving and the continuous lifting of transmittability of fiber backbone network transmission technology, and the user makes that for the continuous growth of various broadband services demands the fiberize of short haul connection net is imperative.Multimode fiber is thick because of its core diameter, numerical aperture is big, needn't accurately aim at during connection, and is easy to operate simple; Be easy at building and house wiring; And with the preferred medium of advantage becomes short haul connection net such as its supporting component is cheap.Corning Incorporated calculates the cost that uses monomode fiber and multimode fiber and compares, and the network cost that uses monomode fiber is 4 times of multimode fiber.Multiple industry standard is as AT ﹠amp; The house service standard of T, the local area network standard of EIA, the 100Mbit/s Token Ring standard of American National Standards Institute, the computer data communication standards of IBM etc. all use multimode fiber as local transmission medium or interior distribution.The particularly commercialization of the vertical cavity surface emitting laser of novel cheapness (VCSEL), light beam end face that it is circular and high modulation rate have compensated the deficiency of LED, make the application of multimode fiber in network have more life.

But the serious modal dispersion of multimode fiber has restricted its bandwidth-distance product, and then has limited its transmittability.The transmittability that promotes multimode fiber becomes the research focus of our times.

In order to improve the transmittability of multimode fiber, people have proposed new technologies and methods, and as signal of telecommunication treatment technology, eccentric incident technology and multilevel coding technology etc., but these methods have all only been utilized the 3dB baseband portion of multimode fiber.The frequency response curve that studies show that multimode fiber is in low frequency region dull decline along with the increase of frequency; At but relatively flat of its frequency response curve of high-frequency region, form by the logical zone of a series of band, have abundant bandwidth resources.If this zone is rationally utilized, can fully expand the bandwidth resources of multimode fiber, be implemented in and carry out big capacity information communication in the multimode fiber.

In recent years, both at home and abroad brainstrust has carried out many research aspect the high-frequency region of multimode fiber utilizing, and has obtained gratifying achievement.The multicarrier multiplex technique is applied to multimode fiber communication, can utilizes the high-frequency region of multimode fiber to carry out big capacity information communication, the transmittability of expansion multimode fiber.Particularly the high-speed data-flow that will transmit exactly is divided into the relatively low parallel data stream of some speed and transmits simultaneously.Utilize the carrier modulation technology, the high-frequency band pass zone that these data flow that walk abreast are modulated to multimode fiber is respectively transmitted.This is equivalent to high-frequency region with multimode fiber and is divided into many subchannels and carries out transfer of data.Leaving enough protections at interval between each subchannel, is to carry out effective message transmission.This method can promote the transmittability of multimode fiber to a certain extent.

Summary of the invention

The present invention's design is based on sinusoidal carrier, is applied to a kind of novel frequency transmission signal multiplex mode of multimode optical fiber communication system.Compare with existing transmission signals multiplex mode, this mode is by introducing identical with former cosine carrier frequency at transmitting terminal, the sinusoidal carrier that the phase phasic difference is 90 °, with one tunnel newly-increased ofdm signal be modulated to the same radio frequency of cosine carrier on, the multiplexing same frequency domain of two paths of signals, the availability of frequency spectrum is increased, reach the purpose that improves the multimode optical fiber communication system transmission capacity with this.Fig. 1 represents the transmitting terminal that common multicarrier is multiplexing, and Fig. 2 represents to add the multiplexing transmitting terminal of sinusoidal carrier.

Suppose that the two independent ofdm signal is respectively m (t) and n (t), through the transmitting terminal signal of telecommunication after the carrier modulation be so

h(t)＝m(t)sin?wt+n(t)cos?wt (1)

F wherein _cIt is radio frequency.

Because receiving terminal adopts the PD pipe directly to detect reception, so through behind the intensity modulated laser, add the light carrier component, the modulated light signal of transmitting terminal is

E＝[h(t)+A]cos?w _ot (2)

F wherein _oBe optical frequency, A is a constant, Acos w _oT is the light carrier component.

Receiving terminal directly detects the current strength that obtains

$i=R{\left[(h+A)\cos w_{0}t\right]}^2$

$=R{(h+A)}^2{\left(\cos w_{0}t\right)}^2$

$=R(h^2+2\mathrm{hA}+A^2)\frac{1+\cos 2w_{0}t}{2}$

$=R[\frac{1}{2}(h^2+2\mathrm{hA}+A^2)+\frac{\cos 2w_{0}t}{2}(h^2+2\mathrm{hA}+A^2)]---\left(3\right)$

Wherein R is the constant factor that the PD pipe detects.

Because of 2w _oBe 2 times of optical frequencies, so in the bracket second

Can ignore.In first

Be DC component, can elimination.Because the existence of optical carrier ratio, so A is very big, h is very little,

Can ignore.So

i＝ARh (4)

Be that the receiving terminal detection obtains the signal of telecommunication h that transmitting terminal sends.

Receiving terminal signal of telecommunication i is carried out demodulation with cosine and sinusoidal carrier respectively, and the signal of telecommunication after modulating by cosine carrier is

$p=i\cos \mathrm{wt}$

$=\mathrm{ARh}\cos \mathrm{wt}$

$=\mathrm{AR}(m\sin \mathrm{wt}+n\cos \mathrm{wt})\cos \mathrm{wt}$

$=\frac{1}{2}\mathrm{AR}(m\sin 2\mathrm{wt}+n+n\cos 2\mathrm{wt})---\left(5\right)$

The signal of telecommunication after modulating by sinusoidal carrier is

$q=i\sin \mathrm{wt}$

$=\mathrm{ARh}\sin \mathrm{wt}$

$=\mathrm{AR}(m\sin \mathrm{wt}+n\cos \mathrm{wt})\sin \mathrm{wt}$

$=\frac{1}{2}\mathrm{AR}(m-m\cos 2\mathrm{wt}+n\sin 2\mathrm{wt})---\left(6\right)$

Because after above-mentioned two signals of telecommunication carry out filtering by low pass filter, 2 frequencys multiplication partly can be by elimination, obtains baseband signal respectively and is

$p=\frac{1}{2}\mathrm{ARn}---\left(7\right)$

With

$q=\frac{1}{2}\mathrm{ARm}---\left(8\right)$

So can obtain two independent ofdm signal m (t) and the n (t) that transmitting terminal sends respectively.

Description of drawings

In order to be illustrated more clearly in technology proposed by the invention, to do to introduce simply to the accompanying drawing of required use in the embodiment of the invention below, obviously, accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain other accompanying drawing according to these accompanying drawings.

Fig. 1 is the multiplexing transmitting terminal schematic diagram of common multicarrier;

Fig. 2 is for adding the multiplexing transmitting terminal schematic diagram of sinusoidal carrier;

Fig. 3 is for adding the multiplexing transmission system schematic diagram of sinusoidal carrier.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the invention, the technical scheme in the embodiment of the invention is carried out clear, complete description, obviously, described embodiment also only is a part of embodiment of the present invention, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills belong to the scope of protection of the invention not making the every other embodiment that is obtained under the creative work prerequisite.

Be the complete diagram of multimode optical fiber communication system as shown in Figure 3, this system has been divided into three parts, is respectively: transmitting terminal 315, optical transmission part 316 and receiving terminal 317.In transmitting terminal 315,301,302 and 303 represent the three paths of independent baseband OFDM signal of telecommunication respectively, and 304 expression frequencies are f _cThe cosine carrier modulator, 305 the expression frequencies be f _c, the sinusoidal carrier modulator that the phase phasic difference is 90 °, the electric territory of 306 expressions coupler, 307 expression intensity modulated lasers.301 nonpassage of signal are crossed any modulator and are modulated, 302 signals are through 304 cosine carrier modulators modulate, 303 signals are through 305 sinusoidal carrier modulators modulate, and 306 electric territory couplers are coupled above-mentioned three tunnel signals through ovennodulation, form total transmission signal of telecommunication.Send the signal of telecommunication and be modulated onto the light territory through 307 intensity modulated lasers.

At optical transmission part 316,308 expression multimode fibers.Transmitting terminal 315 output light signals transmit in 308 multimode fibers.

At receiving terminal 317,309 expression PD diodes, 312,313 and 314 all represent low pass filter, and 310 expression frequencies are f _cThe cosine carrier demodulator, 311 the expression frequencies be f _c, the sinusoidal carrier demodulator that the phase phasic difference is 90 °.Light signal forms and receives the signal of telecommunication through the direct detection of PD diode 309.Receive the signal of telecommunication and be divided into three the tunnel, the first via is reduced into former first via ofdm signal through low pass filter 312.The second the tunnel through after 310 demodulation of cosine carrier demodulator, is reduced into former the second road ofdm signal through low pass filter 313 again.After 311 demodulation of Third Road process sinusoidal carrier demodulator, be reduced into former Third Road ofdm signal through low pass filter 314 again.

By formula (1) to the derivation of formula (8) as can be seen, under the situation of newly-increased one road sinusoidal carrier modulation, receiving terminal still can correctly restore the original sender signal.This has proved the feasibility of the method, promptly by introducing identical with former cosine carrier frequency at transmitting terminal, the sinusoidal carrier that the phase phasic difference is 90 °, with one road ofdm signal be tuned to the same radio frequency of cosine carrier on, the multiplexing same frequency domain of two paths of signals, the availability of frequency spectrum is increased, thereby improved the multimode optical fiber communication system transmission capacity.This multimode optical fiber communication system to the short haul connection net has unusual meaning.

More than be to adopt a kind of special case of the present invention, i.e. the detailed introduction of newly-increased one road sinusoidal carrier modulation in a high-frequency band pass scope, the explanation of this enforcement just are used for helping to understand method of the present invention and core concept thereof; Simultaneously, for one of ordinary skill in the art, according to thought of the present invention, the part that all can change in specific embodiments and applications, in sum, this description should not be construed as limitation of the present invention.The various conspicuous change of under the situation of spirit that does not deviate from the method for the invention and claim scope it being carried out is all within protection scope of the present invention.

Claims (8)

1. one kind is applied to the scheme that multimode optical fiber communication system is improved its transmission capacity, it is characterized in that, described method may further comprise the steps:

(1) at the communication system transmitting terminal, the two independent ofdm signal is modulated to same frequency range by the cosine carrier and the sinusoidal carrier of same frequency respectively;

(2) at receiving terminal of communication system, the signal of telecommunication that is directly detected by PD pipe is respectively by the cosine carrier and the sinusoidal carrier demodulation of same frequency.

2. ofdm signal according to claim 1 is characterized in that this ofdm signal is a real number signal, in system initialisation phase, by allowing the mutual conjugation of subcarrier of FFT conversion, makes that the signal of output is a real number.

3. modulation frequency range according to claim 1 is characterized in that, this modulation frequency range is to have utilized the logical zone of band of multimode fiber frequency response HFS.

4. modulating frequency according to claim 1 is characterized in that, this modulating frequency must be determined by the transfer function frequency spectrum of concrete a certain communication system.

5. step according to claim 1 (1) is modulated to same frequency range by the cosine carrier and the sinusoidal carrier of same frequency respectively, it is characterized in that cosine carrier and sinusoidal carrier are same frequencys, realizes the frequency overlap of two-way ofdm signal with this.

6. step according to claim 1 (1) two independent ofdm signal, it is characterized in that, the purpose that 2 tunnel independence ofdm signals are modulated to same frequency respectively is in order to make frequency overlap, thereby reaches the transmission capacity of raising system, so and do not require the bandwidth unanimity of 2 road ofdm signals.

7. the signal of telecommunication that step according to claim 1 (2) is directly detected by PD pipe is respectively by the cosine carrier and the sinusoidal carrier demodulation of same frequency, it is characterized in that the cosine carrier of receiving terminal and sinusoidal carrier must be consistent with the carrier frequency of transmitting terminal.

8. PD pipe according to claim 1, it is characterized in that, what this communication system adopted is intensity modulated-direct detection mode, shows as: use the M-Z laser modulator to carry out intensity modulated at transmitting terminal, use the PD pipe that light signal is directly detected at receiving terminal.

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