WO2012092785A1

WO2012092785A1 - System and method for optical fibre communication with adaptive modulation

Info

Publication number: WO2012092785A1
Application number: PCT/CN2011/080234
Authority: WO
Inventors: 高健
Original assignee: 中兴通讯股份有限公司
Priority date: 2011-01-06
Filing date: 2011-09-27
Publication date: 2012-07-12
Also published as: CN102098105A

Abstract

Disclosed are a system and a method for optical fibre communication with adaptive modulation, and the system includes a plurality of communication terminals. Each communication terminal includes: a receiving module, used for receiving an optical signal transmitted via an optical fibre from an opposite communication terminal and converting the same into a communication signal; a processing module for the received signal, used for receiving the communication signal and demodulating the same to obtain a demodulated signal; an adaptive judging module, used for assessing the demodulated signal to obtain an assessed value of the transmission quality, comparing the assessed value of the transmission quality with a preset threshold value, and then selecting and determining a corresponding modulation mode according to the result of the comparison; a generating module for the modulated signal, used for generating a modulated digital signal according to the selected modulation mode; and a transmitting module, used for converting the modulated digital signal into a modulated analogue signal which is transmitted via an optical fibre to the opposite communication terminal after electro-optical conversion. The present invention better solves the problem that it is difficult for the communication terminal to change its modulation mode and the problem of low re-utilization rate.

Description

Method and system for optical fiber communication with adaptive modulation

The present invention relates to optical fiber communication technology, and more particularly to an optical fiber communication technology for adaptively adjusting a modulation mode of a transmission signal based on feedback information. Background technique

At present, optical networks are rapidly developing toward high-speed and large-capacity, and the modulation methods in optical fiber communication systems are becoming increasingly complex, including from Non Return Zero (NRZ) and Return Zero (RZ). On-Off Keying (OOK), gradually developed into Differential Phase-Shift Keying (DPS:), Differential Quadrature Phase-Shift Keying (DQPSK), among which The modulation method of DQPSK has been commercialized in 40G systems. However, as the rate is further increased, the existing techniques cannot solve the effects of dispersion and polarization mode dispersion (PMD) caused by high rate. Quaternary Phase Shift Keying (QPS:), Quadrature Amplitude Modulation (QAM), and Orthogonal Frequency Division Multiplexing (OFDM) technology have become research hotspots. . These technologies have been introduced into the field of optical communications. On the one hand, due to the increasing rate of bearer networks, digital signal processing techniques are needed to solve the problem of inter-symbol interference (ISI) caused by dispersion and PMD. It is the rapid development of digital signal processing devices, which makes it possible to process tens of Gbit-level data streams in real time by Field-Programmable Gate Array (FPGA).

In the existing optical fiber communication system, no matter which of the above modulation formats is adopted, since the signal transmitting end device constituted by the analog device is different depending on the modulation method, the modulation method of each system is selected in the design unless Replace the device, otherwise you can no longer switch to other modulation Format. The operating costs of replacing equipment are very high. Therefore, it is very meaningful to propose an optical fiber communication technology with adaptive modulation. Summary of the invention

It is an object of the present invention to provide a method and system for adaptively modulated optical fiber communication, which can better solve the problem that the communication terminal switching modulation mode is relatively difficult.

According to an aspect of the present invention, an adaptive modulation optical fiber communication system is provided, comprising a plurality of communication terminals, each communication terminal comprising: a receiving module, a receiving signal processing module, an adaptive decision module, a modulation signal generating module, and transmitting Module; among them,

a receiving module, configured to receive an optical signal transmitted by the communication terminal of the other party via the optical fiber and convert the electrical signal into an electrical communication signal;

a receiving signal processing module, configured to receive a communication signal and demodulate the same to obtain a demodulated signal; an adaptive decision module, configured to evaluate the demodulated signal to obtain a transmission quality evaluation value and to transmit a transmission quality evaluation value and a preset threshold The values are compared, and then the corresponding modulation mode is selected and determined according to the comparison result;

a modulation signal generating module, configured to generate a digital modulated signal according to the selected modulation mode; and a transmitting module, configured to convert the digital modulated signal into an analog modulated signal, and transmit the optical modulated light to the other communication terminal via the optical fiber.

Preferably, the modulation method comprises: a non-return-to-zero code (NRZ), a return-to-zero code (RZ), a differential phase shift keying (DPS:), a quadrature phase shift keying (QPS:), and a quadrature amplitude modulation ( QAM), Orthogonal Frequency Division Multiplexing (OFDM).

Preferably, the transmission quality evaluation value is an optical signal-to-noise ratio (OSNR) tolerance of the communication signal. Pre-preferred, the transmitting module comprises: a digital-to-analog converter (DAC), a tunable laser, and a polarization beam splitter of the transmitting module ( PBS), modulator, polarization combiner (PBC) and combiner (OMU); a DAC for receiving a digital modulated signal and converting it into an analog modulated signal;

a tunable laser for outputting a PBS of a tunable optical signal transmitting module whose wavelength can be continuously changed within a certain range, for receiving a tunable optical signal and dividing it into two polarization states to obtain a polarization state optical signal;

a modulator for receiving an analog modulated signal output by the digital-to-analog converter and a polarized light signal output by the PBS and converting the analog modulated signal into an optical signal;

PBC, configured to receive and combine the optical signals output by the modulator;

The OMU is configured to receive an optical signal output by the PBC, perform frequency division multiplexing on the optical signal, and obtain a frequency division multiplexed optical signal, and send the optical signal to the communication terminal via the optical fiber.

Preferably, the receiving module comprises: a splitter (ODU), a PBS of the receiving module, a local oscillator laser, a mixer, a balanced receiver, and an analog-to-digital converter (ADC);

The ODU is configured to receive an optical signal sent by the communication terminal of the other party via the optical fiber, and perform frequency division and multiplexing to obtain a frequency division and division multiplexing signal;

a PBS of the receiving module, configured to receive the frequency division multiplexed signal and divide it into two orthogonal polarization states to obtain an orthogonal polarization state optical signal;

a local oscillator laser for generating a local oscillator signal;

a mixer, configured to receive the orthogonal polarization state optical signal and the local oscillator optical signal and perform mixing to obtain a mixed frequency signal;

a balanced receiver for receiving a mixed signal and converting it into an analog electrical signal;

An ADC that receives an analog signal and converts it into a digital communication signal.

According to another aspect of the present invention, a method of adaptively modulated fiber optic communication is provided, the method comprising:

A. when the communication terminal performs optical fiber communication, receiving an optical signal transmitted by the communication terminal of the other party via the optical fiber and converting it into a communication signal; B. Demodulating the communication signal to obtain a demodulated signal;

C. The demodulated signal is evaluated to obtain a transmission quality evaluation value, and the transmission quality evaluation value is compared with a preset threshold value, and then the corresponding modulation mode is selected and determined according to the comparison result;

D. generating a digital modulated signal according to the selected modulation mode;

E. Convert the digital modulated signal into an analog modulated signal, and then transmit it to the other communication terminal via the optical fiber after being converted by electro-optical.

Preferably, the modulation method includes: NRZ, RZ, DPS:, QPS:, QAM, OFDM. Preferably, the preset threshold value is set according to the principle of minimizing the bit error rate or maximizing the communication amount.

Preferably, the transmission quality evaluation value is an OSNR tolerance of the communication signal, and the preset threshold value is a threshold value of a preset OSNR tolerance.

Preferably, step C is:

The optical signal-to-noise ratio OSNR tolerance of the communication signal and the threshold of the preset OSNR tolerance are selected. The channel capacity is selected next to the modulation mode of the current channel capacity, otherwise the modulation mode is not changed.

Compared with the prior art, the present invention has the following advantages: The present invention can change the modulation mode according to the application scenario, can ensure the reliability of the transmission system, and fully utilize the spectrum resources. In addition, the present invention utilizes a digital device to generate and demodulate signals. The adaptive adjustment of the modulation mode greatly improves the reuse rate of the system compared with the conventional system, and has a very obvious cost advantage. DRAWINGS

1 is a schematic structural diagram of a communication terminal of an adaptive modulation optical fiber communication system according to an embodiment of the present invention;

1 is a flowchart of an adaptive modulation optical fiber communication method according to an embodiment of the present invention; and FIG. 3 is a flowchart of an adaptive selection modulation mode control algorithm according to an embodiment of the present invention. detailed description

The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

The present invention relates to the following modulation schemes: RZ, NRZ, DPS:, QPS:, QAM, OFDM. These modulation schemes are intrinsically linked, laying the foundation for hardware multiplexing for the adaptive modulation of the present invention.

Quadrature Amplitude Modulation (QAM) is the use of two independent baseband digital signals to suppress the two-band modulation of two mutually orthogonal co-frequency carriers, using the nature of the spectrally orthogonality of the modulated signal in the same bandwidth. Realize two parallel signals transmission. The signal expression of QAM is:

S _MQAM (t) = [∑ X _n g(t -nT _s )] cos 0) _c t - Y _n g(t -nT ] sin 0) _c t

- (1)

Further expressed as:

QPSK is a special form of QAM. When A and ^{y are} taken as ±1, QAM is QPSK, when " ¹ " is ¹ ^ ³ is 16QAM, and ¹ ^ ³ ^ ⁵ ^ ⁷ is 64QAM.

The OFDM symbol is the sum of a plurality of modulated orthogonal subcarrier signals, wherein the modulation mode of each subcarrier may select phase shift keying PSK or quadrature amplitude modulation QAM. If N is used to indicate the number of subchannels, T is the width of the OFDM symbol, and (i = 0, 1, ..., Ν - 1) is the data symbol assigned to each subchannel, which is the carrier frequency. An OFDM symbol starting from ⁼ ^ can be represented by equation (3):

^{≤t≤ +T} (3) The following equivalent baseband signals are often used to describe the output signal of OFDM:

X d

≤t≤t +T (4) The cross component, the OFDM symbol can be further expressed as:

s(t) = Real(d _i+N/2 )cosO)J + Imag(d _i+N/2 )sinO) _c t ( 5 ) can be expressed as:

S(t) = A(t) cos co _c t - B(t) sin _c t

The first binary-on-off keying (OOK) modulation method used in optical fiber communication systems, such as RZ, NRZ, and c. s^ ₌₁ , B(t) sin ω _ε ί ₌₀ .

The same can be expressed as:

S(t) = A(t) cos 0) _c t - B(t) sin coj ( 6 ) From the above analysis, it can be seen that RZ, NRZ, DPSK, QPSK, QAM, and OFDM can be expressed by the following equation.

S(t) = A(t) cos 0) _c t - B(t) sin _c t ( 7 ) where 0, o is a function of the sequence to be transmitted, which can be generated by the modulation signal generation module, when different modulation methods are used The modulation signal generation module can generate different 0, ^Β ^.

^), multiplied by eos^, sin^, respectively, is modulated by a Mach-Zehnder modulator or an impulse noise protection (InP) modulator. It is then converted to an analog signal by a digital to analog conversion device. This lays the hardware foundation for the implementation of adaptive modulation. Digital signal processing equipment, digital-to-analog converters, electric/optical conversion equipment, optical transmission, receiving equipment, optical/electrical conversion equipment, and analog-to-digital conversion equipment can all be implemented by the same hardware device, and thus can be multiplexed by hardware. Based on the above analysis, the present invention proposes an adaptive modulation method and system for optical fiber communication, as follows:

An adaptive modulation optical fiber communication system is composed of a plurality of communication terminals. 1 is a schematic structural diagram of a communication terminal of an adaptive modulation optical fiber communication system according to an embodiment of the present invention. As shown in FIG. 1, the communication terminal includes a receiving module 1, a receiving signal processing module 2, an adaptive decision module 3, and modulation. The signal generating module 4 and the transmitting module 5; wherein, the specific structure of each module is: The receiving module 1 includes: a splitter 0DU11, a polarization concentrating beam splitter (PBS) 12 of the receiving module, a local oscillator laser 13, and a first a mixer 141, a second mixer 142, First balanced receiver (O/E) 151, second 0/E 152, third 0/E 153, fourth 0/E 154, first analog to digital converter (ADC) 161, second ADC 162, third ADC 163, Four ADC164.

The transmitting module 5 includes: a first digital-to-analog converter (DAC) 561, a second DAC 562, a third DAC 563, a fourth DAC 564, a tunable laser 55, a PBS 54 of a transmitting module, and a first Mach-Zehnder modulation. 531, second Mach-Zehnder modulator 532, third Mach-Zehnder modulator 533, fourth Mach-Zehnder modulator 534, polarization combiner (PBC, Polarization Beam Combiner) 52, combiner OMU51 The first driver 571, the second driver 572, the third driver 573, and the fourth driver 574. Among them, the Mach-Zehnder modulator can be replaced by the InP modulator.

Receive signal processing module 2, adaptive decision module 3, modulation signal generation module 4 can be

The FPGA or DSP chipset is constructed.

The receiving module 1 is configured to receive an optical signal transmitted by the communication terminal of the other party via the optical fiber and convert it into a communication signal, and input the signal to the received signal processing module 2;

Specifically, after receiving the optical signal sent by the communication terminal of the other party via the optical fiber, the receiving module 1 uses the coherent light detection method to separate the received optical carrier by the demultiplexer ODU11 and input it to the PBS 12, and the optical signal separated by the ODU 11 The PBS 12 is further divided into two orthogonal polarization state optical signals and input to the first mixer 141, and input to the second mixer 142. The local oscillation laser 13 having a frequency close to the signal light and having a line width of 100 kHz generates a local oscillation light signal and inputs it to the first mixer 141 and the second mixer 142. The orthogonal polarization optical signal output from the PBS 12 and the local oscillation optical signal output from the local oscillator laser 13 are mixed in a 90-degree mixer 141 and a mixer 142, and each polarization state has two orthogonal signals (1, Q). Road). The two orthogonal signals output by the mixer 141 are input to the balanced receiver 151 and the balanced receiver 152, respectively, and the two orthogonal signals output by the mixer 142 are input to the balanced receiver 153 and the balanced receiver 154, respectively. Perform photoelectric conversion to convert an optical signal into an electrical signal. The output four electrical signals pass through four analog-to-digital converters ADC161, ADC162, and ADC 163 with sufficient bandwidth and sampling rate. The ADC 164 converts the analog signal into a digital signal. The original four-way digital communication signal recovered through the above processing is input to the received signal processing module 2.

The receiving signal processing module 2 is configured to receive the communication signal input by the receiving module 1, demodulate the demodulated signal, and input the signal to the adaptive decision module 3;

Specifically, this embodiment takes the signals of the OFDM and OAM modulation modes as an example.

If the input signal is OFDM, the received signal processing module 1 first synchronizes, adjusts the frequency offset of the OFDM subcarrier, overcomes the phase noise of the local oscillator laser 13, and then removes the cyclic prefix, performs serial fast conversion, and performs fast Fourier transform ( The Fast Fourier Transform (FFT) operation demodulates the orthogonal subcarriers of the OFDM, performs constellation inverse mapping, recovers the binary code stream, obtains a demodulated signal, and inputs the signal to the adaptive decision module 3.

If the input signal is QAM, the received signal processing module 2 first performs digital clock recovery, and then demultiplexes by equalization and polarization. Among them, equalization is to eliminate signal crosstalk caused by linear factors of the channel. Then, frequency offset estimation and phase offset estimation are performed, and finally, decoding and data recovery are performed to obtain a demodulated signal, and the signal is input to the adaptive decision module 3.

The adaptive decision module 3 is configured to evaluate the demodulated signal to obtain a transmission quality evaluation value, compare the transmission quality evaluation value with a preset threshold value, and then select and determine a corresponding modulation method according to the comparison result. ;

Specifically, the adaptive decision module 3 determines the demodulated signal output by the received received signal processing module 2, selects a corresponding modulation mode, and notifies the modulated signal generating module 4, specifically: the adaptive decision module 3 receives the received signal. The demodulated signal is evaluated to obtain a transmission quality evaluation value, the transmission quality evaluation value and a preset threshold value are compared, and then the corresponding modulation method is selected and determined according to the comparison result. Among them, the optional modulation methods include RZ, NRZ, DPSK, QPSK, QAM, OFDM. The six modulation methods described above have advantages and disadvantages in terms of transmission quality and system capacity. OOK can achieve the best optical signal noise ratio (OSNR) performance, but the bandwidth utilization is the lowest. OFDM can achieve maximum spectrum utilization, but OSNR performance and non-line Poor performance.

The predetermined threshold value may be set according to the principle of maximizing the communication capacity or minimizing the bit error rate. This embodiment adopts the principle of minimizing the bit error rate. For example, the modulation mode in the current system is OFDM, and the set OSNR tolerance is 14 dB, and the adaptive decision module 3 monitors the current signal with an OSNR tolerance of 15 dB, which exceeds a preset threshold of 14 dB. Switch the modulation mode. The adaptive decision module 3 first switches the modulation mode OFDM to a modulation mode that is second only to the OFDM system, and is set to DQPS:. After the handover is completed, the adaptive decision module 3 continues to monitor the operation index. If the OSNR tolerance of the DQPSK can meet the preset 14 dB requirement, the adaptive decision module 3 determines that the modulation mode is DQPSK. If the modulation mode still fails to meet the requirements, the adaptive decision module 3 continues to switch in a direction with smaller capacity and better OSNR performance.

The modulation signal generating module 4 is configured to generate a digital modulation signal according to a modulation mode selected by the adaptive decision module 3 and input the signal to the transmitting module 5;

For example, assuming that the adaptive decision module 3 selects the OFDM modulation mode, the modulated signal generation module 4 generates an OFDM signal. The signal generation process is as follows: After the binary code stream is serial-to-parallel transformed, constellation mapping is performed to obtain a complex signal, and for the communication terminal to perform synchronization and other signal processing, a pilot and a training sequence are inserted in the communication terminal. Then, through the Inverse Fast Fourier Transform (IFFT) operation, the signal is modulated onto N orthogonal subcarriers, and finally the cyclic prefix is inserted to obtain a digital modulated signal and input to the transmitting module 5.

For example, assuming that the adaptive decision module 3 selects the QAM modulation mode, the modulated signal generation module 4 generates a QAM signal. The signal generation process is as follows: After the binary code stream is serially converted and converted, the level conversion of 2 to L is performed according to the number of constellations, and a digital modulated signal is obtained and input to the transmission module 5.

The transmitting module 5 is configured to convert the signal into an analog modulated signal after being received by the electronically modulated signal, and then transmit the optical signal to the other communication terminal via the optical fiber. Specifically, the digital modulated signals input to the transmitting module 5 are respectively input to the DAC561, the DAC562, the DAC563, and the DAC564, and converted into analog signals, and the conversion of the transmitting end electric domain is completed.

In the optical domain, the tunable laser 55 outputs a tunable optical signal whose wavelength can be continuously changed within a certain range, and the polarization beam splitter PBS54 divides the optical signal output from the tunable laser 55 into two polarization states to obtain two polarization states. Signals, one of which is input to the first Mach-Zehnder modulator 531 and the second Mach-Zehnder modulator 532, and the other input to the third Mach-Zehnder modulator 533 and the fourth Mach-Zehnder modulator 534 in. The analog signal outputted by the DAC 561 is amplified by the first driver 571 and input to the Mach-Zehnder modulator 531 and converted into the first I optical signal. The analog signal output from the DAC 562 is amplified by the first driver 572 and input to the Mach-Zehnder modulation. The 532 is converted into a first Q optical signal, and the analog signal output by the DAC 563 is amplified by the first driver 573 and input to the Mach-Zehnder modulator 533 and converted into a second I optical signal. The analog signal output by the DAC 564 is A driver 574 is amplified and input to the Mach-Zehnder modulator 534 and converted into a second Q optical signal. The first I optical signal and the first Q optical signal form a polarization optical signal and are input to the PBC 52. The second I optical signal and the second Q optical signal form a polarization optical signal and are input to the PBC 52. The PBC 52 couples the input two polarization states into a beam of light and inputs it into the combiner OMU51. The combiner OMU51 frequency-multiplexes the optical signals processed by the different wavelengths of the PBC52 and transmits them to the other party via the optical fiber. terminal. The Mach-Zehnder modulator is used to convert the change of the electrical signal into a change of the optical signal to realize the modulation of the light intensity. At the same time, the Mach-Zehnder modulator achieves the modulation of different sidebands by controlling the bias voltage. Among them, the Mach-Zehnder modulator can be replaced by the InP modulator.

1 is a flow chart of an adaptive modulation optical fiber communication method provided by the present invention. As shown in FIG. 1, the method includes the following steps:

Step S201, when the communication terminal performs optical fiber communication, receiving an optical signal transmitted by the communication terminal of the other party via the optical fiber and converting it into a communication signal; Specifically, the communication terminal adopts a coherent light detection method, and the received optical signal sent by the counterpart communication terminal via the optical fiber is divided into two orthogonal polarization states by the PBS, and is mixed with the local oscillator laser in the 90-degree mixer. Four signals are output, each of which has two orthogonal signals (1, Q), and after photoelectric conversion and analog-to-digital conversion, the original four-way communication signal is recovered by digital signal processing.

Step S202, demodulating the communication signal to obtain a demodulated signal;

Specifically, the communication signal is demodulated, and the obtained binary in the demodulation process is sampled to obtain a demodulated signal.

Assuming that the received signal is OFDM, the synchronization is first performed, the frequency offset of the OFDM subcarrier is adjusted, the phase noise of the local oscillator laser is overcome, the cyclic prefix is removed, the FFT operation is performed after the serial-to-parallel transform, and the orthogonal subcarriers of the OFDM are demodulated. Then, the constellation inverse mapping is performed, and the binary code stream is restored to obtain a demodulated signal.

Assuming that the received signal is QAM, digital clock recovery is first performed, followed by equalization and polarization demultiplexing, where the effect of equalization is to eliminate signal crosstalk due to linear factors of the channel. Then, frequency offset estimation and phase offset estimation are performed, and finally decoding and data recovery are performed to obtain a demodulated signal.

Step S203, the demodulated signal is evaluated to obtain a transmission quality evaluation value, and the transmission quality evaluation value is compared with a preset threshold value, and then the corresponding modulation mode is selected and determined according to the comparison result;

Specifically, the demodulated signal is evaluated to obtain a transmission quality evaluation value, the transmission quality evaluation value and a preset threshold value are compared, and the corresponding modulation method is selected and determined according to the comparison result. Among them, the preset threshold value can be set according to the principle of maximizing the communication capacity or minimizing the bit error rate, and the optional modulation modes include RZ, NRZ, DPSK, QPSK, QAM, OFDM. RZ, NRZ, DPSK, QPSK are widely used in optical transmission systems. QAM, OFDM is the modulation method in the next generation optical transmission system in the experimental stage.

The process of minimizing the bit error rate principle is as follows: For example, modulation in the current system The mode is OFDM, the OSNR tolerance is set to 14dB, and the OSNR tolerance of the current signal is monitored to be 15 dB, which exceeds the preset threshold of 14 dB. In this case, the modulation mode switching is required. First, the modulation mode OFDM is switched to the modulation mode whose capacity is second only to the OFDM system, and is set to DQPS:. After the completion of the handover, the operation indicator is continuously monitored. If the OSNR tolerance of the DQPSK can meet the set 14 dB requirement, the modulation mode is determined to be DQPSK. If the modulation mode still fails to meet the requirements, the switching to the direction of smaller capacity and better OSNR performance continues.

Step S204, generating a digital modulated signal according to the selected modulation mode;

Specifically, for example, if the adaptive decision module 3 selects the OFDM modulation mode, the modulation signal generation module 4 generates an OFDM signal. The signal generation process is as follows: After the binary code stream is serially and transformed, the constellation mapping is performed to obtain a complex signal, and the pilot and the training sequence are inserted at the transmitting end for the purpose of synchronizing signal processing such as the communication terminal. Then, through the IFFT operation, the signal is modulated onto N orthogonal subcarriers, and finally the cyclic prefix is inserted to obtain two signals of I and Q.

For example, assuming that the adaptive decision module 3 selects the QAM modulation mode, the modulated signal generation module 4 generates a QAM signal. The signal generation process is as follows: After the binary code stream is serially converted and converted, the level conversion of 2 to L is performed according to the number of constellations, and two signals of I and Q are obtained.

Step S205, converting the digital modulated signal into an analog modulated signal, and transmitting the optical modulated signal to the other communication terminal via the optical fiber.

Specifically, the digital modulated signal is converted into an analog signal by the DAC, and the transformation of the transmitting side electric domain is completed.

In the optical domain, the polarization beam splitter PBS splits the light of the tunable laser into two polarization states, each of which outputs light to a modulator, the modulator comprising: a Mach-Zehnder modulator, or InP Modulator. The analog signal outputted by the DAC is amplified by the driver and converted into optical signals of two polarization states modulated by light by a modulator. The polarization synthesizer PBC couples the optical signals of the two polarization states into one optical signal. Finally, the combiner OMU frequency division multiplexing optical signals processed by PBC And sent to the other party's communication terminal via optical fiber.

FIG. 3 is a flowchart of an adaptive selection modulation mode control algorithm according to an embodiment of the present invention. As shown in FIG. 3, the process includes the following steps:

Step S301, evaluating a current device transmission quality;

Specifically, the current signal is evaluated to obtain a transmission quality evaluation value of the signal, that is, a capacity of the optical signal-to-noise ratio OSNR of the modulation signal.

Step S302, comparing with a preset threshold value;

Specifically, the preset threshold value can be set according to the principle of maximizing the communication capacity or minimizing the error rate.

The processing procedure using the principle of minimizing the bit error rate is as follows: For example, the modulation mode in the current system is OFDM, and the optical signal noise ratio (OSNR, Optical Noise Ratio) is set to 14 dB, and the OSNR capacity of the current signal is monitored. The limit is 15 dB, which exceeds the preset threshold of 14 dB. In this case, the modulation mode switching is required.

Step S303, selecting a modulation mode according to the comparison result;

Specifically, the modulation mode OFDM is first switched to the modulation mode whose capacity is second only to the OFDM system, and is set to DQPS:. After the completion of the handover, the operation indicators are continuously monitored. If the OSNR tolerance of the DQPSK can meet the set 14 dB requirement, the modulation mode is determined to be DQPSK. If the modulation method still fails to meet the requirements, the switching to the smaller capacity and better OSNR performance is continued.

Step S304, feeding back the modulation mode to the current device.

In summary, the present invention can ensure the reliability of the transmission system and make full use of the spectrum resources by adaptively selecting the modulation mode of the transmission signal according to the preset threshold value. In addition, the present invention utilizes a digital device to generate a solution. The signal is modulated to digitize the implementation of signal processing. Compared with the traditional system, the multiplexing rate is increased, the flexibility is increased, the cost is reduced, and the reliability of signal transmission, system throughput and other performance indicators are very Obvious cost advantage.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. All modifications, equivalent substitutions and improvements made within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims

Claim

An optical fiber communication system with adaptive modulation, comprising a plurality of communication terminals, wherein each of the communication terminals comprises: a receiving module, a receiving signal processing module, an adaptive decision module, a modulation signal generating module, and a transmitting module. ; among them,

a receiving module, configured to receive an optical signal transmitted by the communication terminal of the other party via the optical fiber and convert the signal into a communication signal;

a receiving signal processing module, configured to receive the communication signal and demodulate the signal to obtain a demodulated signal;

An adaptive decision module, configured to evaluate the demodulated signal to obtain a transmission quality evaluation value, compare the transmission quality evaluation value with a preset threshold value, and then select and determine a corresponding modulation mode according to the comparison result;

And a modulation signal generating module, configured to generate a digital modulation signal according to the selected modulation mode; and a transmitting module, configured to convert the digital modulation signal into an analog modulation signal, and after being converted by electro-optical conversion, sent to the communication terminal of the other party via the optical fiber.

2. The system according to claim 1, wherein the modulation method comprises: a non-return to zero code (NRZ), a return-to-zero code (RZ), a differential phase shift keying (DPSK), and a four-phase phase shift. Keying

(QPSK), Quadrature Amplitude Modulation (QAM), Orthogonal Frequency Division Multiplexing (OFDM).

3. The system according to claim 1, wherein the transmission quality evaluation value is an optical signal to noise ratio (OSNR) tolerance of the communication signal, and the preset threshold value is preset. The threshold of the OSNR tolerance.

The system according to any one of claims 1 to 3, wherein the transmitting module comprises: a digital-to-analog converter (DAC), a tunable laser, a polarization splitter (PBS) of the transmitting module, and modulation , a polarization combiner (PBC) and a combiner (OMU);

a DAC, configured to receive the digital modulated signal and convert it into an analog modulated signal; a tunable laser for outputting a tunable optical signal whose wavelength can be continuously varied within a certain range a PBS of the transmitting module, configured to receive the tunable optical signal and divide it into two polarization states to obtain a polarization optical signal;

a modulator, configured to receive the analog modulated signal and the polarized light signal and convert the analog modulated signal into an optical signal;

a PBC, configured to receive and combine the optical signals output by the modulator;

The OMU is configured to receive the optical signal output by the PBC, perform frequency division multiplexing on the frequency division to obtain a frequency division multiplexed optical signal, and send the optical signal to the communication terminal via the optical fiber.

The system according to any one of claims 1 to 3, wherein the receiving module comprises: a splitter (ODU), a receiving module PBS, a local oscillator laser, a mixer, a balanced receiver, and An analog to digital converter (ADC);

a PBS of the receiving module, configured to receive the demultiplexed frequency division multiplexed signal and divide it into two orthogonal polarization states to obtain an orthogonal polarization state optical signal;

a local oscillator laser for generating a local oscillator signal;

a mixer, configured to receive the orthogonal polarization state optical signal and the local oscillator optical signal and perform mixing to obtain a mixed signal;

a balanced receiver for receiving the converted signal and converting it into an analog electrical signal; an ADC for receiving the analog electrical signal and converting it into a digital communication signal.

6. A method of adaptively modulated optical fiber communication, the method comprising:

A. when the communication terminal performs optical fiber communication, receiving an optical signal transmitted by the communication terminal of the other party via the optical fiber and converting it into a communication signal;

B. Demodulating the communication signal to obtain a demodulated signal;

C. evaluating the demodulated signal to obtain a transmission quality evaluation value and evaluating the transmission quality The evaluation is compared with a preset threshold value, and then the corresponding modulation method is selected and determined according to the comparison result;

E. Converting the digital modulated signal into an analog modulated signal, and transmitting the optical modulated signal to the other communication terminal via the optical fiber.

The method according to claim 6, wherein the modulation method comprises: NRZ, RZ, DPS:, QPSK, QAM, OFDM.

8. Method according to claim 6 or 7, characterized in that the predetermined threshold value is set according to the principle of minimizing the bit error rate or maximizing the traffic.

The method according to claim 6 or 7, wherein the transmission quality evaluation value is an OSNR tolerance of the communication signal, and the preset threshold value is a preset OSNR tolerance. Threshold.

The method according to claim 9, wherein the step C is: comparing an optical signal-to-noise ratio OSNR tolerance of the communication signal with a preset threshold value of an OSNR tolerance, if The OSNR tolerance of the communication signal exceeds a preset threshold of OSNR tolerance, and the channel capacity is selected to be next to the modulation mode of the current channel capacity, otherwise the modulation mode is not changed.