Multi-Input Multi-Output Wireless Optical Communication Simulation System Against Atmospheric Turbulence

Abstract

The multi-input multi-output wireless optical communication simulation system capable of counteracting atmospheric turbulence belongs to the field of optical communication technology, and includes a controllable atmospheric turbulence cell, a signal generator, a first microwave amplifier, a first Mach-Zehnder modulator, a first erbium-doped fiber amplifier, a transmission lens group, a modulator drive circuit, a first laser, a first polarization controller, a second microwave amplifier, a second Mach-Zehnder modulator, a second erbium-doped fiber amplifier, a modulator drive circuit II, a second laser, a second polarization controller, a detector, and an eye diagram monitor. The present invention adopts a multi-input multi-output wireless optical communication transmission system, uses a controllable atmospheric turbulence cell to simulate turbulence, counteracts channel attenuation through the mutually independent channel attenuation methods suffered by different transmission links, can effectively reduce the impact of atmospheric turbulence on the communication link, further explore the channel transmission characteristics, greatly reduce the experimental cost, and improve the stability of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication, and particularly relates to a multi-input multi-output wireless optical communication simulation system capable of counteracting atmospheric turbulence. Background Art

[0002] Free Space Optics (FSO) technology has the same advantages as optical fiber communication, such as larger capacity, better confidentiality, and smaller size than radio frequency (RF) radio communication. In addition, it has the characteristics of no need for special cable erection and good flexibility in RF communication, which can complement the application scope not suitable for optical fiber communication, and has advantages in areas where it is not easy or inconvenient to erect cables, and is simpler for the expansion of network links. Therefore, FSO has become one of the most promising next-generation wireless information transmission technologies.

[0003] Currently, Multiple-Input Multiple-Output (MIMO) technology can effectively reduce the interference of atmospheric turbulence on wireless optical communication and improve the quality of received optical signals. MIMO wireless transmission technology uses multiple antennas at both ends of the wireless link to transmit and receive simultaneously, which can fully exploit spatial resources. It can double the communication capacity of the existing system without increasing spectrum resources and transmission power, and at the same time has stronger anti-interference and anti-fading capabilities in the spatial link, which is an important transmission technology. MIMO technology has unique advantages compared with other techniques for suppressing scintillation. The atmospheric coherence length is on the order of centimeters, so the distance between the transmitter and the receiver does not need to be too large to achieve good diversity performance, while microwave communication antennas require a certain interval to make the correlation of each path signal very small. Therefore, MIMO technology can promote the miniaturization of FSO system equipment. In addition, using multiple transmitting apertures for the antenna can increase the total transmission power and greatly reduce the probability of the communication link being interrupted due to the laser being blocked by obstacles.

[0004] However, since the laser has a shorter wavelength than microwave, wireless optical communication mainly using the atmosphere as the transmission medium is more strongly interfered by turbulence and has higher requirements for directivity and alignment. In addition, the drastic changes in the atmosphere, such as atmospheric turbulence of different scales commonly existing in the atmosphere, have obvious interference on wireless optical communication, especially the optical communication of the atmospheric link between points. Atmospheric turbulence refers to the irregular rise and fall of the air molecule density, and the turbulence effect is the direct impact of atmospheric turbulence on the beam propagation. The atmospheric turbulence effect causes the received optical signal to have light intensity scintillation and spot drift, generating a large amount of random noise and reducing the transmission effect of the communication system. Atmospheric turbulence will also cause random fading of the atmospheric channel, resulting in performance degradation phenomena such as an increase in the bit error rate and signal delay of the wireless optical communication system. At present, most of the research on the channel transmission characteristics in atmospheric turbulence adopts the single-channel communication mode, and there is no relevant report on the simulation device using MIMO wireless transmission technology to explore the channel transmission characteristics in atmospheric turbulence. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a multiple-input multiple-output wireless optical communication simulation system capable of counteracting atmospheric turbulence, which is used to solve the technical problem that there is no relevant report on the simulation device for exploring the channel transmission characteristics in atmospheric turbulence by using MIMO wireless transmission technology in the prior art.

[0006] A multiple-input multiple-output wireless optical communication simulation system capable of counteracting atmospheric turbulence includes a controllable atmospheric turbulence cell, a signal generator, a first microwave amplifier, a first Mach-Zehnder modulator, a first erbium-doped fiber amplifier, a transmission lens group, a modulator driving circuit, a first laser, a first polarization controller, a second microwave amplifier, a second Mach-Zehnder modulator, a second erbium-doped fiber amplifier, a modulator driving circuit II, a second laser, a second polarization controller, a detector, and an eye diagram monitor. Among them, the signal generator, the first microwave amplifier, the first Mach-Zehnder modulator, the first erbium-doped fiber amplifier, the modulator driving circuit, the first laser, and the first polarization controller constitute the first transmission link of the communication system; the signal generator, the second microwave amplifier, the second Mach-Zehnder modulator, the second erbium-doped fiber amplifier, the modulator driving circuit II, the second laser, and the second polarization controller constitute the second transmission link of the communication system;

[0007] The specific connection relationship of the first transmission link of the communication system is as follows: the signal generator is connected to the input end of the first microwave amplifier; the first Mach-Zehnder modulator is respectively connected to the output end of the first microwave amplifier and the modulator driving circuit, the first Mach-Zehnder modulator is connected to the first laser through the first polarization controller, and the output end of the first Mach-Zehnder modulator is connected to the input end of the first erbium-doped fiber amplifier; the output end of the first erbium-doped fiber amplifier is connected to the input end of the transmission lens group;

[0008] The specific connection relationship of the second transmission link of the communication system is as follows: the signal generator is connected to the input end of the second microwave amplifier; the second Mach-Zehnder modulator is respectively connected to the output end of the second microwave amplifier and the modulator driving circuit II, the second Mach-Zehnder modulator is connected to the second laser through the second polarization controller, and the output end of the second Mach-Zehnder modulator is connected to the input end of the second erbium-doped fiber amplifier; the output end of the second erbium-doped fiber amplifier is connected to the input end of the transmission lens group;

[0009] The controllable atmospheric turbulence cell simulates atmospheric turbulence; the output end of the transmission lens group is connected to the detector, and the transmission lens group uses the atmospheric turbulence simulated by the controllable atmospheric turbulence cell as the optical path transmission channel; the detector is connected to the eye diagram monitor.

[0010] The transmission lens group includes a first optical path transmitting mirror, a first optical path receiving mirror, a second optical path receiving mirror, and a second optical path transmitting mirror; the first optical path transmitting mirror is optically connected to the first optical path receiving mirror and the second optical path receiving mirror respectively after passing through the atmospheric turbulence simulated by the controllable atmospheric turbulence cell as the optical path transmission channel, and the optical path transmission channel is the controllable atmospheric turbulence cell; the second optical path transmitting mirror is optically connected to the first optical path receiving mirror and the second optical path receiving mirror respectively after passing through the atmospheric turbulence simulated by the controllable atmospheric turbulence cell as the optical path transmission channel; the first optical path receiving mirror and the second optical path receiving mirror are both connected to the detector.

[0011] The signal generator is a semiconductor laser, with an output wavelength of 1530 nm to 1570 nm and an emission power of more than 7 dbm.

[0012] The transmission rate of the detector is above 4 Gbit / s.

[0013] Through the above design, the present invention can bring the following beneficial effects:

[0014] The present invention adopts a multi-input multi-output wireless optical communication transmission system, uses a controllable atmospheric turbulence cell to simulate turbulence, and counteracts channel attenuation through the mutually independent channel attenuation methods received by different transmission links, which can effectively reduce the impact of atmospheric turbulence on the communication link, and then explore the channel transmission characteristics, greatly reduce the experimental cost, and improve the stability of the system.

[0015] The present invention is used to study the anti-turbulence ability of wireless optical communication systems, has a simple structure, is easy to build, is easy to understand, has strong anti-electromagnetic interference ability, does not occupy additional spectrum resources, is small in size and light in weight, can work continuously, is suitable for mass production, can be widely applied, and is especially suitable for the field of optical communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The following further describes the present invention in conjunction with the drawings and specific embodiments:

[0017] Figure 1 It is a schematic structural diagram of a multi-input multi-output wireless optical communication simulation system of the present invention that can counteract atmospheric turbulence.

[0018] Figure 2 It is a schematic structural diagram of the transmission lens group in a multi-input multi-output wireless optical communication simulation system of the present invention that can counteract atmospheric turbulence.

[0019] Figure 3 It is a schematic structural diagram of the controllable atmospheric turbulence cell in a multi-input multi-output wireless optical communication simulation system of the present invention that can counteract atmospheric turbulence.

[0020] Figure 4This is a comparison diagram of the transmission eye diagram of the multi-input multi-output wireless optical communication simulation system that can combat atmospheric turbulence according to the present invention.

[0021] Figure 5 This is the transmission error code curve diagram of the multi-input multi-output wireless optical communication simulation system that can combat atmospheric turbulence according to the present invention.

[0022] In the figure, 1 - signal generator, 2 - first microwave amplifier, 3 - first Mach-Zehnder modulator, 4 - first erbium-doped fiber amplifier, 5 - transmission lens group, 6 - modulator drive circuit, 7 - first laser, 8 - first polarization controller, 9 - second microwave amplifier, 10 - second Mach-Zehnder modulator, 11 - second erbium-doped fiber amplifier, 12 - modulator drive circuit II, 13 - second laser, 14 - second polarization controller, 15 - detector, 16 - eye diagram instrument, 17 - controllable atmospheric turbulence cell, 501 - first optical path transmitting mirror, 502 - first optical path receiving mirror, 503 - second optical path receiving mirror, 504 - second optical path transmitting mirror, 1701 - heating plate, 1702 - cover plate, 1703 - asbestos board, 1704 - optical transmission window. Detailed implementation mode

[0023] As shown in the figure, the multi-input multi-output wireless optical communication simulation system that can combat atmospheric turbulence includes a controllable atmospheric turbulence cell 17, a signal generator 1, a first microwave amplifier 2, a first Mach-Zehnder modulator 3, a first erbium-doped fiber amplifier 4, a transmission lens group 5, a modulator drive circuit 6, a first laser 7, a first polarization controller 8, a second microwave amplifier 9, a second Mach-Zehnder modulator 10, a second erbium-doped fiber amplifier 11, a modulator drive circuit II 12, a second laser 13, a second polarization controller 14, a detector 15, and an eye diagram instrument 16. Among them, the signal generator 1, the first microwave amplifier 2, the first Mach-Zehnder modulator 3, the first erbium-doped fiber amplifier 4, the modulator drive circuit 6, the first laser 7, and the first polarization controller 8 constitute the first transmission link of the communication system, and the signal generator 1, the second microwave amplifier 9, the second Mach-Zehnder modulator 10, the second erbium-doped fiber amplifier 11, the modulator drive circuit II 12, the second laser 13, and the second polarization controller 14 constitute the second transmission link of the communication system;

[0024] The specific connection relationship of the first transmission link of the communication system is as follows: The signal generator 1 is connected to the input end of the first microwave amplifier 2; The first Mach-Zehnder modulator 3 is respectively connected to the output end of the first microwave amplifier 2 and the modulator drive circuit 6. The first Mach-Zehnder modulator 3 is connected to the first laser 7 through the first polarization controller 8. The output end of the first Mach-Zehnder modulator 3 is connected to the input end of the first erbium-doped fiber amplifier 4; The output end of the first erbium-doped fiber amplifier 4 is connected to the input end of the transmission lens group 5;

[0025] The specific connection relationship of the second transmission link of the communication system is as follows: The signal generator 1 is connected to the input end of the second microwave amplifier 9; The second Mach-Zehnder modulator 10 is respectively connected to the output end of the second microwave amplifier 9 and the modulator drive circuit II 12. The second Mach-Zehnder modulator 10 is connected to the second laser 13 through the second polarization controller 14. The output end of the second Mach-Zehnder modulator 10 is connected to the input end of the second erbium-doped fiber amplifier 11; The output end of the second erbium-doped fiber amplifier 11 is connected to the input end of the transmission lens group 5;

[0026] The controllable atmospheric turbulence cell 17 simulates atmospheric turbulence; The output end of the transmission lens group 5 is connected to the detector 15. The transmission lens group 5 uses the atmospheric turbulence simulated by the controllable atmospheric turbulence cell 17 as the optical path transmission channel; The detector 15 is connected to the eye diagram analyzer 16.

[0027] The transmission rate of the detector 15 is above 4 Gbit / s.

[0028] The signal generator 1 is a semiconductor laser, with an output wavelength of 1530 nm to 1570 nm and an emission power above 7 dbm. The signal generator 1 uses an arbitrary waveform generator to generate non-return-to-zero pulse NRZ signals, which are amplified by a microwave amplifier, then signal-modulated by a Mach-Zehnder modulator to convert the electrical signal into an optical signal, and then transmitted through the transmitting antenna through the controllable atmospheric turbulence cell 17 for free-space signal transmission. After being received by the receiving antenna, the signal is detected by the detector 15, and finally the transmission quality is checked by the eye diagram analyzer 16.

[0029] Among them, the wavelength of the laser is 1550 nm, and the maximum output power is 7 dbm. The erbium-doped fiber selects a single-mode erbium-doped fiber with a high doping concentration as the gain fiber, with an output band of 1550 nm and a length of 15 cm.

[0030] Figure 2FIG. 5 is a schematic structural diagram of a transmission lens group, and the lens band is required to be at 1550 nm. The transmission lens group 5 includes a first optical path transmitting mirror 501, a first optical path receiving mirror 502, a second optical path receiving mirror 503, and a second optical path transmitting mirror 504; the first optical path transmitting mirror 501 passes through the atmospheric turbulence simulated by the controllable atmospheric turbulence cell 17 as an optical path transmission channel and is respectively optically connected to the first optical path receiving mirror 502 and the second optical path receiving mirror 503. The optical path transmission channel is the controllable atmospheric turbulence cell 17; the second optical path transmitting mirror 504 passes through the atmospheric turbulence simulated by the controllable atmospheric turbulence cell 17 as an optical path transmission channel and is respectively optically connected to the first optical path receiving mirror 502 and the second optical path receiving mirror 503; the first optical path receiving mirror 502 and the second optical path receiving mirror 503 are simultaneously connected to the detector 15.

[0031] As Figure 3 shown, the controllable atmospheric turbulence cell 17 consists of a box simulating the atmosphere and an automatic controller. A heating plate 1701 is laid at the bottom of the box, and a circulating cooling pipe is also laid on the cover plate 1702 on the box. An asbestos board 1703 for heat preservation is laid on the side wall of the box. An optical transmission window 1704 is provided on the side wall of the box. A high-temperature detector is installed inside the box. The box is filled with circulating water, and the circulating water circulates through an external circulating pump. When the temperature difference between the heated surface and the water-cooled surface of the circulating water remains constant, turbulence will be formed. The turbulence simulation box is equipped with a high-temperature detector to measure the high temperature of each part of the box in real time, and the working temperature of the heating plate 1701 in the box is accurately adjusted through the automatic controller. Compared with the atmospheric turbulence simulated by using a spatial light modulator and a rotating phase plate, the hot air or convective atmospheric turbulence is closer to the real atmospheric turbulence in physical properties and has the advantages of simple structure and easy control.

[0032] Figure 4 FIGS. a, b, and c are eye diagrams of a pulsed communication signal modulated by a signal with a transmission rate of 4 Gbps passing through different transmission environments. The transmission system is in a no-turbulence state in FIG. a, a weak-turbulence state in FIG. b, and a medium-strong-turbulence state in FIG. c. The eye diagram is measured by an Agilent 86100C optical eye diagram meter. It can be seen that the eye opening is obvious, indicating that the modulation system is stable. By comparing the shapes of the eye diagrams, the negative impact of atmospheric turbulence motion on transmission can be found. The distortion of the signal waveform is specifically manifested as the closing of the eyelids of the eye diagram caused by atmospheric turbulence motion and the gradual deterioration of the eye diagram. The comparative analysis of the eye diagrams also proves the effectiveness of the atmospheric turbulence simulation channel. The eye diagrams at the receiving end of a wireless optical communication MIMO system are measured in the cases of no turbulence, weak turbulence, and medium-strong turbulence channels.

[0033] Figure 5It is the system transmission error code curve. The bit error rate refers to the ratio of the total number of error code elements in the digital code elements to the total number of all digital code elements within the measured time limit. Affected by various conditions such as natural light, communication equipment, and link loss, there is a large difference between the bit sequence received by the detector and the input bit sequence. Within a given time range, the larger the bit error rate, the worse the data transmission quality. Therefore, the bit error rate can be used to measure the performance of the communication system and evaluate the quality of the transmitted signal. Assuming that only atmospheric turbulence affects the transmission quality of the communication system, the signal-to-noise ratio expression is:

[0034]

[0035] In the formula, I0 is the signal intensity, <I n > is the average noise, is the amplitude of the light wave without considering turbulence, is the noise amplitude.

[0036] For weak turbulence,

[0037] k is the wave number, k = 2π / λ, where λ represents the wavelength of the light wave; L is the transmission distance of the laser, C n 2 is the atmospheric refractive index structure constant.

[0038] For the wireless optical communication system, the bit error rate at the receiving end is expressed as follows: erfc(x) represents the complementary error function, and the Q parameter is defined as:

[0039] Among them, I1 is the signal intensity value when the bit received by the receiver is "1", σ1 is the noise intensity value when the bit received by the receiver is "1"; I0 is the signal intensity value when the bit received by the receiver is "0", and σ0 is the noise intensity value when the bit received by the receiver is "0".

[0040] The received power and the signal-to-noise ratio have a one-to-one correspondence. Therefore, in the experiment, by measuring the relationship curve between the received bit error rate and the received signal power of the wireless optical communication MIMO system after transmission through the variable atmospheric turbulence intensity simulation channel, it can be found that as the turbulence intensity increases, the BER gradually increases. When the signal is transmitted without turbulence and the bit error rate is 3.8×10 -3 it is the forward error correction (FEC) limit, and the MIMO communication system can still perform information transmission.

[0041] MIMO technology uses multiple input and multiple output antennas simultaneously. Among all the improvement technologies, it is the most effective and practical technology for compensating the atmospheric channel. By using MIMO technology, it is possible to multiply the channel capacity of the communication system without additional occupation of spectrum resources and without additional increase in the antenna transmission power.

[0042] A multiple-input multiple-output wireless optical communication system for controllable atmospheric turbulence. During use, an arbitrary waveform generator needs to be turned on to send NRZ data at a specified rate, and at the same time, the laser emission power is controlled to achieve the simultaneous output of two signals. The signals are transmitted through an atmospheric turbulence simulation pool, and the two signals are received at the receiving end. The eye diagram status and the error code curve show that in the transmission environment of the controllable atmospheric turbulence simulation pool, when simulating a transmission distance of 1 kilometer, the received signal can be demodulated and received, and the error code is within the allowable range. Therefore, the present invention can improve the reliability of the transmission system, while enhancing the transmission efficiency of the wireless optical communication system, and promoting the application of multiple-input multiple-output systems in more cutting-edge fields.

Claims

1. A multi-input multi-output wireless optical communication simulation system capable of counteracting atmospheric turbulence, characterized in that: It includes a controllable atmospheric turbulence cell (17), a signal generator (1), a first microwave amplifier (2), a first Mach-Zehnder modulator (3), a first erbium-doped fiber amplifier (4), a transmission lens group (5), a modulator drive circuit (6), a first laser (7), a first polarization controller (8), a second microwave amplifier (9), a second Mach-Zehnder modulator (10), a second erbium-doped fiber amplifier (11), a modulator drive circuit II (12), a second laser (13), a second polarization controller (14), a detector (15) and an eye diagram monitor (16). Among them, the signal generator (1), the first microwave amplifier (2), the first Mach-Zehnder modulator (3), the first erbium-doped fiber amplifier (4), the modulator drive circuit (6), the first laser (7) and the first polarization controller (8) constitute the first transmission link of the communication system. The signal generator (1), the second microwave amplifier (9), the second Mach-Zehnder modulator (10), the second erbium-doped fiber amplifier (11), the modulator drive circuit II (12), the second laser (13) and the second polarization controller (14) constitute the second transmission link of the communication system; The specific connection relationship of the first transmission link of the communication system is as follows: The signal generator (1) is connected to the input end of the first microwave amplifier (2); The first Mach-Zehnder modulator (3) is respectively connected to the output end of the first microwave amplifier (2) and the modulator drive circuit (6). The first Mach-Zehnder modulator (3) is connected to the first laser (7) through the first polarization controller (8). The output end of the first Mach-Zehnder modulator (3) is connected to the input end of the first erbium-doped fiber amplifier (4); The output end of the first erbium-doped fiber amplifier (4) is connected to the input end of the transmission lens group (5); The specific connection relationship of the second transmission link of the communication system is as follows: The signal generator (1) is connected to the input end of the second microwave amplifier (9); The second Mach-Zehnder modulator (10) is respectively connected to the output end of the second microwave amplifier (9) and the modulator drive circuit II (12). The second Mach-Zehnder modulator (10) is connected to the second laser (13) through the second polarization controller (14). The output end of the second Mach-Zehnder modulator (10) is connected to the input end of the second erbium-doped fiber amplifier (11); The output end of the second erbium-doped fiber amplifier (11) is connected to the input end of the transmission lens group (5); The controllable atmospheric turbulence cell (17) simulates atmospheric turbulence; The output end of the transmission lens group (5) is connected to the detector (15). The transmission lens group (5) uses the atmospheric turbulence simulated by the controllable atmospheric turbulence cell (17) as the optical path transmission channel; The detector (15) is connected to the eye diagram monitor (16).

2. The multi-input multi-output wireless optical communication simulation system capable of counteracting atmospheric turbulence according to claim 1, characterized in that: The transmission lens group (5) includes a first optical path transmitting mirror (501), a first optical path receiving mirror (502), a second optical path receiving mirror (503), and a second optical path transmitting mirror (504); the first optical path transmitting mirror (501) is optically connected to the first optical path receiving mirror (502) and the second optical path receiving mirror (503) respectively after passing through the atmospheric turbulence simulated by the controllable atmospheric turbulence cell (17) as the optical path transmission channel, and the optical path transmission channel is the controllable atmospheric turbulence cell (17); the second optical path transmitting mirror (504) is optically connected to the first optical path receiving mirror (502) and the second optical path receiving mirror (503) respectively after passing through the atmospheric turbulence simulated by the controllable atmospheric turbulence cell (17) as the optical path transmission channel; the first optical path receiving mirror (502) and the second optical path receiving mirror (503) are simultaneously connected to the detector (15).

3. The multi-input multi-output wireless optical communication simulation system capable of counteracting atmospheric turbulence according to claim 1, wherein: The signal generator (1) is a semiconductor laser, with an output wavelength of 1530 nm to 1570 nm and a transmission power of more than 7 dbm.

4. The multi-input multi-output wireless optical communication simulation system capable of counteracting atmospheric turbulence according to claim 1, characterized in that: The transmission rate of the detector (15) is above 4 Gbit / s.

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