Bidirectional millimeter wave terahertz seamless optical fiber wireless integrated system

Abstract

The invention belongs to the technical field of optical fiber wireless converged communication, and particularly relates to a bidirectional millimeter wave terahertz seamless optical fiber wireless integrated system. The system comprises an electrical / optical conversion module in a central unit / distributed unit, a downlink millimeter wave / terahertz generation module in an active antenna unit, a downlink receiving and digital signal processing module in a user side, an uplink millimeter wave / terahertz generation module in the user side, and an uplink receiving and electrical / optical conversion module in the active antenna unit. And an optical / electric conversion and digital signal processing module in the central unit / distributed unit. The all-photon up-down conversion technology is adopted on the optical fiber network side of the system, direct conversion of millimeter wave / terahertz and optical signals at the optical fiber end is achieved, and seamless integration of the millimeter wave / terahertz and the optical fiber network is achieved; the system provided by the invention has efficient two-way transmission capability, supports simultaneous transmission of an uplink and a downlink, and remarkably improves the data transmission rate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical wireless communication, and particularly relates to a bidirectional millimeter wave terahertz seamless optical wireless integrated system. BACKGROUND

[0002] Under the background of rapid development of communication technology, the demand for wireless communication presents an exponential growth trend, which is pushing the communication technology to evolve to a higher level. With the global communication network moving towards a more advanced wireless communication system, the development and efficient use of high-frequency millimeter wave and terahertz spectrum resources have become one of the key technologies to support the future sixth-generation mobile communication (6G) system. As a leading technology system for future communication needs, 6G communication network is committed to realizing the deep integration and seamless integration of millimeter wave / terahertz and optical networks, thereby building a communication transmission system with ultra-high speed and ultra-large capacity, and ensuring stable and reliable communication connection services in complex electromagnetic environments.

[0003] Bidirectional optical pre-transmission is a key link to ensure the efficient operation of the communication system. It is responsible for high-speed and large-capacity data transmission between the core network and the base station, and it needs to ensure that the downlink data is stably transmitted from the core network to the base station, and the uplink data is reliably transmitted from the base station to the core network. However, to achieve efficient bidirectional optical pre-transmission, the problem of seamless integration of millimeter wave / terahertz and optical networks needs to be solved.

[0004] At present, existing research has made some progress in solving the problem of integration of millimeter wave / terahertz and optical networks. Some research uses all-optical up-conversion and down-conversion technology to establish an optical fiber-wireless-optical fiber bridge, which confirms the feasibility of seamless integration of millimeter wave and optical fiber, but this system cannot support simultaneous transmission of uplink and downlink. Some research has demonstrated a bidirectional optical fiber-millimeter wave system, but this system performs poorly in terms of data rate and operating frequency band of uplink and downlink, and is difficult to meet the growing demand for communication capacity in the future. Moreover, some systems use remote local oscillator transmission to generate a local oscillator signal for electronic down-conversion through optical heterodyne method, which reduces the dependence of active antenna unit (AAU) on electronic components, but does not effectively reduce the complexity of AAU.

[0005] Traditional electronic methods have obvious limitations in the generation and reception of millimeter waves / terahertz. In contrast, photonic-based millimeter wave / terahertz generation and reception technology utilizes the high-frequency characteristics of light and has the ability to implement ultra-wideband signal processing, and can generate signals with wider bandwidth and higher frequency. Moreover, optical signals are almost not affected by electromagnetic interference during transmission, and photonic-based systems have stronger stability and reliability in complex electromagnetic environments, making it possible to effectively connect optical and wireless communication systems. However, existing photonic-related technologies still face many challenges in practical applications and have not yet fully realized their potential to achieve efficient, stable and widely used fiber-wireless integrated communication. SUMMARY

[0006] The purpose of the present application is to provide a bidirectional millimeter wave / terahertz seamless fiber-wireless integrated system with low structural complexity, strong transmission capacity and high transmission efficiency.

[0007] The bidirectional millimeter wave / terahertz seamless fiber-wireless integrated system provided by the present application uses all-optical up-conversion and down-conversion technology on the fiber network side to achieve direct conversion of millimeter waves / terahertz and optical signals at the fiber end (including conversion of millimeter waves / terahertz to light and conversion of light to millimeter waves / terahertz), achieving seamless integration of millimeter waves / terahertz and fiber networks. It includes an electrical / optical conversion module in the central unit / distributed unit, a downlink millimeter wave / terahertz generation module in the active antenna unit, a downlink reception and digital signal processing module in the user terminal, an uplink millimeter wave / terahertz generation module in the user terminal, an uplink reception and electrical / optical conversion module in the active antenna unit, and an optical / electrical conversion and digital signal processing module in the central unit / distributed unit. Wherein: The electrical / optical conversion module in the central unit / distributed unit generates a communication signal for downlink transmission, modulates the downlink communication signal onto a laser to complete electrical / optical conversion, and sends it to the active antenna unit through the optical fiber; The downlink millimeter wave / terahertz generation module in the active antenna unit generates millimeter wave / terahertz signals from the optical signal modulated by the electrical / optical conversion module in the central unit / distributed unit and transmits the downlink millimeter wave / terahertz signal through the antenna; The downlink reception and digital signal processing module in the user terminal receives the millimeter wave / terahertz signal transmitted by the active antenna unit, performs digital signal processing of the downlink signal after down-conversion; The uplink millimeter wave / terahertz generation module in the user terminal generates a communication signal for uplink transmission, generates a millimeter wave / terahertz signal using electronic up-conversion of the communication signal, and transmits the uplink millimeter wave / terahertz signal through the antenna; The uplink receiving and electric / optical conversion module in the active antenna unit receives the uplink millimeter wave / terahertz signal, and sends the signal to the central unit / distributed unit after electric / optical conversion by a thin film lithium niobate Mach-Zehnder modulator (MZM); The optical / electric conversion and digital signal processing module in the central unit / distributed unit receives the optical signal sent back by the active antenna unit, and performs digital signal processing on the uplink signal after optical / electric conversion.

[0008] In the application, the electric / optical conversion module in the central unit / distributed unit comprises a downlink signal generation module, an IQ modulator, a first laser, a second laser and a first optical coupler. In the downlink signal generation module, the downlink communication data is subjected to constellation mapping, up-sampling and shaping by a root-raised cosine filter. The generated downlink signal is modulated onto the light emitted by the first laser by the IQ modulator, and the center frequency of the first laser is The modulated optical signal is combined with the local oscillator light emitted by the second laser through the first optical coupler, and the combined signal is sent to the active antenna unit through a single-mode optical fiber.

[0009] In the application, the downlink millimeter wave / terahertz generation module in the active antenna unit comprises a second optical coupler and a first optical / electric conversion module. The combined optical signal is divided into two paths after passing through the second optical coupler. One of the two paths of the combined optical signal is converted into a downlink millimeter wave / terahertz signal with a frequency of after passing through the first optical / electric conversion module, and the downlink millimeter wave / terahertz signal is transmitted to the free space through an antenna.

[0010] In the application, the downlink receiving and digital signal processing module in the user terminal comprises an electronic down-conversion module and a downlink digital signal processing module. The downlink millimeter wave / terahertz signal is converted to the baseband after passing through the antenna and the down-conversion operation of the electronic down-conversion module. After demodulation of the baseband signal, the downlink communication information is obtained and the bit error rate is calculated.

[0011] In the application, the uplink millimeter wave / terahertz generation module in the user terminal comprises an uplink signal generation module and an electronic up-conversion module. The uplink communication data is subjected to constellation mapping, up-sampling, shaping filtering and up-conversion to generate an uplink communication signal. The uplink communication signal is subjected to the up-conversion operation of the electronic up-conversion module to obtain the uplink millimeter wave / terahertz signal, and the uplink millimeter wave / terahertz signal is transmitted to the free space through an antenna.

[0012] In the application, the uplink receiving and electric / optical conversion module in the active antenna unit comprises a thin film lithium niobate MZM. The uplink millimeter wave / terahertz signal is received by an antenna. The thin film lithium niobate MZM works at zero point. The input of the thin film lithium niobate MZM comprises the uplink millimeter wave / terahertz signal and another of the two optical signals after the second optical coupler. In the thin film lithium niobate MZM of the active antenna unit, the uplink millimeter wave / terahertz signal is modulated to the local oscillator light of the downlink signal, the millimeter wave / terahertz is converted to light, and the optical signal is sent to the central unit / distributed unit through a single-mode optical fiber.

[0013] In the application, the optical / electric conversion and digital signal processing module in the central unit / distributed unit comprises a third laser, a second optical / electric conversion module and an uplink digital signal processing module. The input of the second optical / electric conversion module comprises the optical signal sent back by the active antenna unit and the optical signal emitted by the third laser. After the two optical signals pass through the down-conversion operation of the second optical / electric conversion module, they are converted to intermediate frequency. The intermediate frequency signal is down-converted to baseband, and the baseband signal is demodulated to obtain the uplink communication information and calculate the bit error rate.

[0014] The bidirectional millimeter wave / terahertz seamless optical fiber wireless integrated system provided by the application has the following working process: The working process is as follows: (1) The electric / optical conversion module in the central unit / distributed unit generates a communication signal for downlink transmission, modulates the downlink communication signal to a laser to complete electric / optical conversion and sends the downlink communication signal to a base station through an optical fiber; (2) The downlink millimeter wave / terahertz generation module in the active antenna unit generates a millimeter wave / terahertz signal and transmits the downlink millimeter wave / terahertz signal through an antenna; (3) The downlink receiving and digital signal processing module in the user terminal receives the millimeter wave / terahertz signal transmitted by the active antenna unit, performs down-conversion and downlink signal digital signal processing; (4) The uplink millimeter wave / terahertz generation module in the user terminal generates a communication signal for uplink transmission, generates a millimeter wave / terahertz signal by using electronic up-conversion of the communication signal, and transmits the uplink millimeter wave / terahertz signal through an antenna; (5) The uplink receiving and electric / optical conversion module in the active antenna unit receives the uplink millimeter wave / terahertz signal, and sends the uplink millimeter wave / terahertz signal to the central unit / distributed unit after electric / optical conversion of the thin film lithium niobate MZM; (6) The optical / electric conversion and digital signal processing module in the central unit / distributed unit receives the optical signal sent back by the active antenna unit, and performs uplink signal digital signal processing after optical / electric conversion.

[0015] The bidirectional millimeter wave terahertz seamless optical fiber wireless integrated system has the core that full optical sub- and down-conversion technologies are used on the optical fiber network side, millimeter wave / terahertz and optical signals are directly converted at the optical fiber end, seamless integration of millimeter wave / terahertz and optical fiber networks is achieved, and specifically: In the downlink (DL) direction, after a data sequence is generated at the central unit / distributed unit (CU / DU), the data sequence is output by an arbitrary waveform generator (downlink signal generation), is modulated to light emitted by an external cavity laser (first laser) by using an IQ modulator, is combined with local light emitted by another external cavity laser (second laser), is transmitted to an AAU (active antenna unit) through a single-mode optical fiber, at the AAU, the optical signal is amplified and divided into two paths, one path provides a light source for an uplink (UL) signal, and the other path generates a downlink millimeter wave / terahertz signal through a photodiode (first optical / electric conversion), the signal is emitted to free space by a horn antenna, is transmitted through a wireless link, is received by an antenna at a user end (UE), is mixed with local signal generated by a frequency multiplier (electronic down-conversion) to be down-converted to a baseband, is collected by an oscilloscope, and is reconstructed into original data through offline digital signal processing (DSP).

[0016] In the uplink (UL) direction, a transmission signal is generated at the UE, a DSP processing process is similar to that in the DL, except that the signal is up-converted after pulse shaping, the UL intermediate frequency signal is up-converted to a millimeter wave / terahertz band by a frequency mixer (electronic up-conversion) and is emitted by an antenna, is transmitted through a wireless link, is received by an antenna at the AAU, is then modulated to local light of the DL signal by a thin film lithium niobate MZM, to achieve conversion of the millimeter wave / terahertz to light, the signal is returned to the CU / DU through the same single-mode optical fiber, is combined with light emitted by another external cavity laser at the CU / DU, and is down-converted by a balanced photodiode (second optical / electric conversion). The generated intermediate frequency signal is amplified by an electric amplifier, is collected by an oscilloscope, and is reconstructed into original data through DSP.

[0017] The application has the following advantages by using full optical sub- and down-conversion to achieve seamless integration of optical fiber and wireless: (1) The application uses full optical sub- and down-conversion technologies on the optical fiber network side, directly converts millimeter wave / terahertz and optical signals at the optical fiber end (including conversion of millimeter wave / terahertz to light and conversion of light to millimeter wave / terahertz), breaks through the limitation of traditional technologies, eliminates the obstacle of integration of millimeter wave / terahertz and optical fiber networks, and achieves seamless integration of optical fiber and wireless; (2) The local light used in the DL can directly receive the UL millimeter wave / terahertz, the same light source is used to realize bidirectional communication, the optical path design of the system is simplified, and the integration of the system is improved. At the same time, with the large bandwidth characteristics of the photonic device, the complexity of the AAU is significantly reduced; (3) Compared with other fiber wireless systems, the application supports simultaneous transmission of uplink and downlink, data can flow in two directions at the same time, which greatly increases the overall data throughput of the system.

[0018] The proposed millimeter wave / terahertz seamless fiber wireless integrated system of the application can perfectly adapt to the future 6G fiber-wireless integrated network demand. The system adopts all-optical up-conversion and down-conversion technology on the fiber network side, realizes direct conversion of millimeter wave / terahertz and optical signals, achieves seamless integration of fiber and wireless, and greatly reduces the complexity of the active antenna unit; at the same time, its distributed architecture relieves the equipment load of the central unit / distributed unit; the bidirectional millimeter wave / terahertz system proposed by the application has high-efficiency bidirectional transmission capability, supports simultaneous transmission of uplink and downlink, and significantly improves the data transmission rate. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The figure is a block diagram of the fiber wireless integrated system based on photon up-conversion and down-conversion of the application.

[0020] Figure 2 The figure is a schematic diagram of the uplink transmitting end DSP and the receiving end DSP of the application.

[0021] Figure 3 The figure is a relationship diagram of the BER of the uplink / downlink millimeter wave / terahertz signal and the carrier frequency.

[0022] Figure 4 The figure is a relationship diagram of the baud rate and the BER of the uplink / downlink.

[0023] In the figure, 101 is an electrical / optical conversion module in the central unit / distributed unit, 102 is a downlink millimeter wave / terahertz generation module in the active antenna unit, 103 is a downlink receiving and digital signal processing module in the user end, 104 is an uplink millimeter wave / terahertz generation module in the user end, 105 is an uplink receiving and electrical / optical conversion module in the active antenna unit, and 106 is an optical / electrical conversion and digital signal processing module in the central unit / distributed unit. DETAILED DESCRIPTION

[0024] To make the purpose, technical solutions and advantages of the application clearer, the embodiments of the application will be described in detail below with reference to the drawings. However, those skilled in the art can understand that in the embodiments of the application, many technical details are proposed in order to make the readers better understand the application. However, the technical solutions claimed by the claims of the application can be realized even without these technical details and various changes and modifications based on the following embodiments.

[0025] The bidirectional millimeter wave terahertz seamless fiber wireless integrated system provided by the application can be applied to a high-speed fiber-wireless integrated network. On the fiber side, the mutual conversion of millimeter wave / terahertz and optical signals (including conversion of millimeter wave / terahertz into light and conversion of light into millimeter wave / terahertz) is successfully realized by virtue of all-optical up-conversion and down-conversion technology, and then seamless fiber-wireless integration is achieved. The local oscillator light used in the downlink process can also be used for direct reception of the uplink millimeter wave / terahertz, and the complexity of the active antenna unit is significantly reduced by virtue of the large bandwidth characteristics of the photonic device.

[0026] The bidirectional millimeter wave terahertz seamless fiber wireless integrated system provided by the application, as shown in Figure 1 the figure, includes an electrical / optical conversion module 101 in the central unit / distributed unit, a downlink millimeter wave / terahertz generation module 102 in the active antenna unit, a downlink reception and digital signal processing module 103 in the user terminal, an uplink millimeter wave / terahertz generation module 104 in the user terminal, an uplink reception and electrical / optical conversion module 105 in the active antenna unit, and an optical / electrical conversion and digital signal processing module 106 in the central unit / distributed unit. The electrical / optical conversion module 101 in the central unit / distributed unit is configured to generate a downlink transmission communication signal, modulate the downlink communication signal onto a laser to complete electrical / optical conversion, and send the downlink communication signal to the active antenna unit through an optical fiber. The electrical / optical conversion module 101 includes a downlink signal generation module, an IQ modulator, a first laser, a second laser, and a first optical coupler. The downlink millimeter wave / terahertz generation module 102 in the active antenna unit is configured to generate a millimeter wave / terahertz signal from the optical signal modulated by the electrical / optical conversion module in the central unit / distributed unit, and emit the downlink millimeter wave / terahertz signal through an antenna. The downlink millimeter wave / terahertz generation module 102 includes a second optical coupler and a first optical / electrical conversion module. The downlink reception and digital signal processing module 103 in the user terminal is configured to receive the millimeter wave / terahertz signal emitted by the active antenna unit, perform communication signal processing after down-conversion, and includes an electronic down-conversion module and a downlink digital signal processing module. The uplink millimeter wave / terahertz generation module 104 in the user terminal is configured to generate a communication signal for uplink transmission, generate a millimeter wave / terahertz signal from the communication signal by using electronic up-conversion, and emit the uplink millimeter wave / terahertz signal through an antenna. The uplink millimeter wave / terahertz generation module 104 includes an uplink signal generation module and an electronic up-conversion module. The uplink reception and electrical / optical conversion module 105 in the active antenna unit is configured to receive the uplink millimeter wave / terahertz signal, and send the uplink millimeter wave / terahertz signal to the central unit / distributed unit after electrical / optical conversion by a thin-film lithium niobate MZM. The uplink reception and electrical / optical conversion module 105 includes a thin-film lithium niobate MZM.

[0027] The optical / electric conversion and digital signal processing module 106 in the central unit / distributed unit receives the optical signal sent back by the active antenna unit, and performs digital signal processing on the uplink signal through optical / electric conversion. It includes a third laser, a second optical / electric conversion module and an uplink digital signal processing module.

[0028] The working process of the bidirectional millimeter wave terahertz seamless optical wireless integrated system is as follows: (1) The electric / optical conversion module 101 in the central unit / distributed unit generates a communication signal for downlink transmission, modulates the downlink communication signal onto a laser to complete electric / optical conversion and sends it to the base station through an optical fiber; In the central unit / distributed unit, a downlink signal generation module is used to generate a downlink communication signal. In the embodiment, the modulation format of the downlink data sequence is 16QAM. Then, the signal is up-sampled and shaped using a root-raised cosine filter with a roll-off factor of 0.1. The signal obtained by the downlink signal generation module is modulated onto a first laser by an IQ modulator, and the center frequency of the first laser is . The obtained modulated optical signal passes through a first optical coupler and is coupled with the local oscillator light emitted by a second laser, and the synthesized optical signal is sent to the active antenna unit through a single-mode optical fiber. In the embodiment, the length of the single-mode optical fiber is 10 km.

[0029] (2) The downlink millimeter wave / terahertz generation module 102 in the active antenna unit generates a millimeter wave / terahertz signal and transmits the downlink millimeter wave / terahertz signal through an antenna; In the active antenna unit, the synthesized optical signal obtained in step one passes through a second optical coupler. One output of the second optical coupler is used as the input of a thin-film lithium niobate modulator for receiving an uplink millimeter wave / terahertz signal, and the other output passes through a first optical / electric conversion module to obtain a millimeter wave / terahertz signal with a frequency of . The millimeter wave / terahertz signal is transmitted to the free space through an antenna. By adjusting the frequency difference between the first laser and the second laser, the carrier frequency of the downlink millimeter wave / terahertz signal can be controlled. In the embodiment, is 193.1 THz, is 193.19 THz, and the frequency of the generated millimeter wave / terahertz signal is 90 GHz. The relationship between the BER of the downlink signal and the carrier frequency can be seen from Figure 3 .

[0030] (3) Step three: The downlink receiving and digital signal processing module 103 in the user terminal receives the millimeter wave / terahertz signal transmitted by the active antenna unit and performs communication signal processing after down-conversion; The millimeter wave / terahertz signal obtained in step (2) is transmitted by an antenna and transmitted through free space. At the user end, the signal is received by an antenna and down-converted by a mixer. After the down-conversion operation, the signal is converted to a baseband. In an embodiment, the distance of the downlink wireless communication is 0.8 m. At the user end, the baseband signal after the down-conversion needs to undergo a series of signal processing. In an embodiment, the downlink digital signal processing flow at the user end includes resampling, coherent DSP, demapping, and error rate calculation. (4) The uplink communication signal is generated by the uplink millimeter wave / terahertz generation module 104 in the user end. The communication signal is converted to a millimeter wave / terahertz signal by electronic up-conversion, and the uplink millimeter wave / terahertz signal is transmitted by an antenna. At the user end, the uplink signal is first generated by the uplink signal generation module. In an embodiment, the modulation format of the uplink data sequence is 16QAM. Then, the signal is up-sampled and shaped. Unlike the downlink signal generation, the uplink signal is up-converted after the pulse shaping. The uplink signal is converted to a millimeter wave / terahertz signal by a mixer, and the signal is transmitted by an antenna and transmitted through free space. The millimeter wave / terahertz carrier frequency is controlled by adjusting the local oscillator signal at the user end. In an embodiment, the frequency of the generated uplink millimeter wave / terahertz signal is 89 GHz. The schematic diagram of the uplink transmission end DSP can be seen from Figure 2 . The relationship between the BER of the uplink signal and the carrier frequency can be seen from Figure 3 .

[0031] (5) The uplink millimeter wave / terahertz signal is received by the uplink receiving and electric / optical conversion module 105 in the active antenna unit, and sent to the central unit / distributed unit after electric / optical conversion by the thin-film lithium niobate MZM. The millimeter wave / terahertz signal obtained in step (4) is transmitted by an antenna and transmitted through free space. At the user end, the signal is received by an antenna and down-converted by a mixer. After the down-conversion operation, the signal is converted to a baseband. In an embodiment, the distance of the downlink wireless communication is 0.8 m. At the user end, the baseband signal after the down-conversion needs to undergo a series of signal processing. In an embodiment, the downlink digital signal processing flow at the user end includes resampling, coherent DSP, demapping, and error rate calculation.

[0032] (6) The optical signal sent back by the active antenna unit is received by the optical / electric conversion and digital signal processing module in the central unit / distributed unit, and the digital signal processing of the uplink signal is performed after the optical / electric conversion.

[0033] In the central unit / distributed unit, the optical signal transmitted back in step five is sent into the second optical / electric conversion module, and the light emitted by the third laser is also sent into the second optical / electric conversion module. After passing through the second optical / electric conversion module, the signal is down-converted to an intermediate frequency. The intermediate frequency signal after down-conversion needs to pass through a series of signal processing. In the embodiment, the working frequency of the third laser is 193.303 THz, and the uplink digital signal processing process includes down-conversion, resampling, coherent DSP, demapping, and error rate calculation. The uplink receiving end DSP schematic diagram can be seen from Figure 2 .

[0034] The experimental situation of the bidirectional millimeter wave terahertz seamless optical wireless integrated system is further introduced below. The specific steps are as follows: In the experimental example, the optical wireless integrated system framework of photon up-conversion and down-conversion can be obtained in Figure 1 , including: Figure 1 The number 101 in the table is the electric / optical conversion module in the central unit / distributed unit, the number 102 is the downlink millimeter wave / terahertz generation module in the active antenna unit, the number 103 is the downlink receiving and digital signal processing module in the user end, the number 104 is the uplink millimeter wave / terahertz generation module in the user end, the number 105 is the uplink receiving and electric / optical conversion module in the active antenna unit, and the number 106 is the optical / electric conversion and digital signal processing module in the central unit / distributed unit.

[0035] Figure 2 The uplink signal transmitting end DSP and receiving end DSP are shown in the table. The transmitting end DSP steps include constellation mapping, up-sampling, shaping filtering, and up-conversion. The receiving end DSP includes down-conversion, resampling, coherent DSP, demapping, and error rate calculation. The coherent DSP includes IQ imbalance correction, clock recovery, dispersion compensation, frequency offset correction, phase offset correction, and equalization. The transmitting end DSP and receiving end DSP of the downlink signal are similar to the transmitting end DSP and receiving end DSP of the uplink signal, but the downlink signal does not contain the process of up-conversion from baseband to intermediate frequency and down-conversion from intermediate frequency to baseband.

[0036] Figure 3 is a relationship diagram of the uplink / downlink carrier frequency and BER. By adjusting the frequency difference of the first laser and the second laser, the carrier frequency control of the downlink millimeter wave / terahertz signal can be realized. For the uplink, the electric local oscillator signal of the user end needs to be adjusted to control the millimeter wave / terahertz carrier frequency. It can be observed from Figure 3 that for the uplink, the optimal carrier frequency is 89 GHz, and for the downlink, the optimal carrier frequency is 95 GHz. By increasing the bandwidth of the device, a higher working frequency can be supported. At the optimal center frequency, the frequency spectrum of the received baseband signal is shown in Figure 3 (i) and Figure 3(ii) in the middle.

[0037] Figure 4 The figure in the middle is the BER and baud rate relationship of the uplink / downlink signal. In order to determine the maximum capacity of the uplink / downlink, the BER of the signal at different baud rates is quantified. For the uplink, its capacity is mainly limited by the intermediate frequency input of the user end mixer. With a soft decision forward error correction mechanism with an overhead of 15%, the acceptable BER threshold is , and through testing, it is found that the maximum baud rate of the uplink is 11.3 GBaud, and the corresponding data rate is 45.2 Gbps. For the downlink, with the same BER threshold, a baud rate as high as 32 GBaud can be achieved, and the corresponding data rate is 128 Gbps.

[0038] Through multi-dimensional experimental analysis, the experimental results show that the bidirectional millimeter wave terahertz seamless optical wireless integrated system proposed by the application has the potential to be applied to high-speed optical wireless integrated networks. On the optical fiber side, the application successfully realizes the mutual conversion of millimeter wave / terahertz and optical signals by virtue of all-optical upconversion and downconversion technology, thereby achieving seamless optical wireless integration; the local oscillator light used in the downlink process can also be used for direct reception of the uplink millimeter wave / terahertz, and with the help of the large bandwidth characteristics of the photonic device, the complexity of the active antenna unit is significantly reduced.

[0039] Those skilled in the art can understand that the above-mentioned embodiments are specific examples for implementing the application, and in actual application, various changes can be made in form and details without departing from the spirit and scope of the application.

Claims

1. A bidirectional millimeter-wave terahertz seamless fiber wireless integrated system, characterized by, The optical fiber network side adopts all-optical up-conversion and down-conversion technology to realize direct conversion of millimeter wave / terahertz and optical signals at the end of the optical fiber, and achieve seamless integration of millimeter wave / terahertz and optical fiber network; it includes an electrical / optical conversion module in the central unit / distributed unit, a downlink millimeter wave / terahertz generation module in the active antenna unit, a downlink receiving and digital signal processing module in the user terminal, an uplink millimeter wave / terahertz generation module in the user terminal, an uplink receiving and electrical / optical conversion module in the active antenna unit, an optical / electrical conversion and digital signal processing module in the central unit / distributed unit; wherein: The electrical / optical conversion module in the central unit / distributed unit generates a communication signal for downlink transmission, modulates the downlink communication signal onto a laser to complete electrical / optical conversion, and sends it to the active antenna unit through a single-mode optical fiber; The downlink millimeter wave / terahertz generation module in the active antenna unit generates a millimeter wave / terahertz signal from the optical signal modulated by the electrical / optical conversion module in the central unit / distributed unit, and transmits the downlink millimeter wave / terahertz signal through an antenna; The downlink receiving and digital signal processing module in the user terminal receives the millimeter wave / terahertz signal transmitted by the active antenna unit, performs digital signal processing on the downlink signal after down-conversion; The uplink millimeter wave / terahertz generation module in the user terminal generates a communication signal for uplink transmission, generates a millimeter wave / terahertz signal from the communication signal using electronic up-conversion, and transmits the uplink millimeter wave / terahertz signal through an antenna; The uplink receiving and electrical / optical conversion module in the active antenna unit receives the uplink millimeter wave / terahertz signal, and sends it to the central unit / distributed unit after electrical / optical conversion by a thin-film lithium niobate Mach-Zehnder modulator (MZM); The optical / electrical conversion and digital signal processing module in the central unit / distributed unit receives the optical signal sent back by the active antenna unit, and performs digital signal processing on the uplink signal after optical / electrical conversion.

2. The bidirectional millimeter-wave terahertz seamless fiber wireless integrated system of claim 1, wherein, The electric / optical conversion module comprises a downlink signal generation module, an IQ modulator, a first laser, a second laser and a first optical coupler; downlink communication data is subjected to constellation mapping, up-sampling and shaping using a root-raised cosine filter; the generated downlink signal is modulated onto light emitted by the first laser through the IQ modulator, the center frequency of the first laser is , and the modulated optical signal is combined with local light emitted by the second laser through the first optical coupler, and the combined signal is sent to an active antenna unit through a single-mode optical fiber.

3. The bidirectional millimeter-wave terahertz seamless fiber wireless integrated system of claim 2, wherein, The downlink millimeter wave / terahertz generation module comprises a second optical coupler and a first optical / electric conversion module, and the synthetic optical signal is divided into two paths after passing through the second optical coupler, wherein one of the two paths of the synthetic optical signal, after passing through the first optical / electric conversion module, obtains the downlink millimeter wave / terahertz signal with a frequency of , and the downlink millimeter wave / terahertz signal is transmitted to the free space through the antenna.

4. The bidirectional millimeter-wave terahertz seamless fiber wireless integrated system of claim 3, wherein, The downlink receiving and digital signal processing module includes an electronic down-conversion module and a downlink digital signal processing module. The downlink millimeter wave / terahertz signal is converted to baseband after down-conversion by the antenna and the electronic down-conversion module. After demodulation of the baseband signal, the downlink communication information is obtained and the bit error rate is calculated.

5. The bidirectional millimeter-wave terahertz seamless fiber wireless integrated system of claim 1, wherein, The uplink millimeter wave / terahertz generation module includes an uplink signal generation module and an electronic up-conversion module; uplink communication data is mapped, up-sampled, shaped filtered and up-converted to generate an uplink communication signal; The uplink communication signal is up-converted by the electronic up-conversion module to obtain the uplink millimeter wave / terahertz signal, which is transmitted to the free space through the antenna.

6. The bidirectional millimeter-wave terahertz seamless fiber wireless integrated system of claim 5, wherein, The uplink receiving and electric / optical conversion module comprises a thin film lithium niobate MZM; the uplink millimeter wave / terahertz signal is received through an antenna; the thin film lithium niobate MZM works at zero point; the input of the thin film lithium niobate MZM comprises another one of two light signals after the uplink millimeter wave / terahertz signal and the synthesized light signal pass through a second optical coupler; in the thin film lithium niobate MZM of the active antenna unit, the uplink millimeter wave / terahertz signal is modulated to the local oscillator light of the downlink signal, the millimeter wave / terahertz is converted to light, and the light signal is sent to the central unit / distributed unit through a single-mode optical fiber.

7. The bidirectional millimeter-wave terahertz seamless fiber wireless integrated system of claim 6, wherein, The optical / electric conversion and digital signal processing module comprises a third laser, a second optical / electric conversion module and an uplink digital signal processing module; the input of the second optical / electric conversion module comprises the light signal sent back by the active antenna unit and the light signal emitted by the third laser, the two light signals are converted to intermediate frequency after the down-conversion operation of the second optical / electric conversion module, the intermediate frequency signal is down-converted to baseband, and the baseband signal is demodulated to obtain the uplink communication information and calculate the bit error rate.

8. The bidirectional millimeter-wave terahertz seamless fiber wireless integrated system according to one of claims 1-7, characterized in that, The working process is as follows: (1) the communication signal for downlink transmission is generated through the electric / optical conversion module in the central unit / distributed unit, the downlink communication signal is modulated to the laser to complete the electric / optical conversion and is sent to the base station through the optical fiber; (2) the millimeter wave / terahertz signal is generated through the downlink millimeter wave / terahertz generation module in the active antenna unit, and the downlink millimeter wave / terahertz signal is emitted through the antenna; (3) the millimeter wave / terahertz signal emitted by the active antenna unit is received through the downlink receiving and digital signal processing module in the user end, and the downlink signal is processed after down-conversion; (4) the communication signal for uplink transmission is generated through the uplink millimeter wave / terahertz generation module in the user end, the communication signal is used for electronic up-conversion to generate the millimeter wave / terahertz signal, and the uplink millimeter wave / terahertz signal is emitted through the antenna; (5) the uplink millimeter wave / terahertz signal is received through the uplink receiving and electric / optical conversion module in the active antenna unit, and is sent to the central unit / distributed unit after the electric / optical conversion of the thin film lithium niobate MZM; (6) the light signal sent back by the active antenna unit is received through the optical / electric conversion and digital signal processing module in the central unit / distributed unit, and the uplink signal is processed after the optical / electric conversion.

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