Free space light and millimeter wave / terahertz fusion transmission system and working method

Abstract

The invention relates to the technical field of wireless communication, and discloses a free space light and millimeter wave / terahertz fusion transmission system and a working method. The system comprises a transmitter, a base station and a central office, a millimeter wave / terahertz signal is generated at a transmitting end by adopting an all-optical up-conversion architecture, a received millimeter wave / terahertz electric signal is converted into an optical domain signal at the base station to be fused with a free space optical signal, and a fused optical signal is received and processed by utilizing a single optical coherent receiver at the central office. The system enables two types of heterogeneous signals to fall into a receiving bandwidth of a single coherent receiver through accurately designing an optical frequency relation, thereby achieving the receiving of the single receiver. Two working modes of high capacity and high reliability are supported, an adaptive demodulation or hybrid automatic repeat request mechanism based on maximum ratio combination is adopted under severe weather conditions, the transmission reliability is improved, and the technical effects of reducing the system complexity, improving the spectrum utilization efficiency, enhancing the communication reliability and supporting flexible deployment are achieved.

Description

Technical Field

[0001] This application relates to the field of wireless communication technology, and in particular to a free-space light and millimeter-wave / terahertz fusion transmission technology based on all-optical assistance and a single receiver. Background Technology

[0002] With the rapid development of mobile communication services and the continuous advancement of integrated space-air-ground networks, the demand for higher bandwidth and reliability in communication systems is increasing daily. To meet the needs of next-generation wireless communication systems, there is an urgent need to develop new communication methods with wider spectrum. Millimeter-wave and terahertz communication technologies, with their ultra-high bandwidth and abundant spectrum resources, have shown broad application prospects. Meanwhile, free-space optical communication, with its higher data transmission rates and flexible deployment advantages, is highly favored in scenarios such as high-speed link connections between low-Earth orbit satellites and the ground.

[0003] In recent years, although millimeter-wave / terahertz communication systems have gradually evolved from electrical domain architectures to all-optical architectures, achieving significant progress in system bandwidth and transmission distance, they still face challenges such as poor environmental adaptability. While free-space optical communication systems can provide ultra-high data rates, their transmission quality is susceptible to the effects of haze and atmospheric turbulence. Therefore, existing technologies have proposed a fusion approach between free-space optical and millimeter-wave / terahertz technologies, aiming to leverage the complementarity of the two technologies in channel characteristics to construct a hybrid communication system that combines high bandwidth and high reliability.

[0004] However, most current free-space optical and millimeter-wave / terahertz fusion systems still suffer from the following problems: First, the use of separate receivers and electrical down-conversion processing methods leads to high system complexity and limitations in broadband signal processing; second, the fusion schemes often employ hard handover strategies, affecting the overall system throughput. These problems result in existing fusion systems being significantly insufficient to meet future high-capacity, high-reliability communication requirements. Furthermore, the compatibility of existing fusion systems with fiber optic communication networks needs further improvement, making them difficult to deploy flexibly in diverse application scenarios.

[0005] Based on the above analysis, there is an urgent need for a novel free-space optical and millimeter-wave / terahertz integrated transmission system. This system should significantly reduce receiver complexity while fully leveraging the advantages of both technologies to provide ultra-high-speed, highly reliable transmission services. Furthermore, the system should possess good networking flexibility, suitable for both terrestrial communication and more complex applications such as space-to-ground interconnection. Such an integrated transmission system will play a crucial role in future high-speed integrated space-air-ground communication networks. Summary of the Invention

[0006] The purpose of this application is to provide a free-space light and millimeter-wave / terahertz fusion transmission system and its operating method to solve the problems mentioned in the background art.

[0007] This application proposes a free-space optical and millimeter-wave / terahertz integrated transmission system based on all-optical assistance and a single receiver, aiming to meet the requirements of next-generation integrated air-space-ground communication networks for ultra-high speed, high reliability, and flexible deployment capabilities. The system integrates the high capacity of free-space optical communication and the strong environmental adaptability of millimeter-wave communication, employing an all-optical architecture design. This overcomes the structural complexity and bandwidth limitations caused by the separate configuration of receivers and electrically down-converting modules required in existing free-space optical and millimeter-wave / terahertz integrated systems.

[0008] Specifically, in this application's system, millimeter-wave signals are up-converted and down-converted in the optical domain using an all-optical beat frequency method, ensuring seamless compatibility between millimeter-wave links and fiber optic and free-space optical communication systems. Simultaneously, by aligning the center frequencies of the free-space optical signal and the millimeter-wave signal in the optical domain, only one optical coherent receiver is needed to simultaneously receive both types of signals. This unified reception scheme significantly simplifies the receiver structure and reduces system deployment complexity.

[0009] This application further integrates joint digital signal processing (DSP) technology to perform collaborative demodulation and fusion processing of free-space light and millimeter-wave / terahertz signals, fully utilizing the complementarity of the two types of channels in transmission characteristics. In the system, the millimeter-wave link not only serves as a supplementary path to the free-space light link but also provides a stable redundant transmission path when the free-space light link's performance degrades due to fog, turbulence, etc., thereby effectively improving the overall system throughput and reducing the probability of outages. To enhance the system's robustness, this application also introduces adaptive diversity combining (ADCT) technology based on maximum ratio combining (MRC) and hybrid automatic repeat request (ccHARQ) technology to achieve efficient resource scheduling and error recovery among multiple paths.

[0010] The converged architecture described in this application is adaptable to various application scenarios with high capacity and high reliability requirements, such as ground-to-ground and low-Earth orbit satellite-to-ground communication. Furthermore, the system is highly compatible with existing fiber optic communication networks and can achieve distributed deployment of ground receiving stations through flexible configuration, providing a promising technical solution for future 6G and higher-generation integrated space-air-ground high-speed communication networks.

[0011] This application discloses a free-space light and millimeter-wave / terahertz fusion transmission system, comprising:

[0012] The transmitter includes a fusion signal generation module (101), an electro-optical conversion modulation module (102), an optical-electrical conversion millimeter-wave / terahertz generation module (103), and a fusion transmitting antenna module (104); wherein: the fusion signal generation module (101) is used to generate an electrical signal to be transmitted according to the application scenario requirements; the electro-optical conversion modulation module (102) is used to modulate the electrical signal to be transmitted onto the corresponding laser carrier to generate a free-space optical modulation signal and a millimeter-wave / terahertz modulation optical signal; the optical-electrical conversion millimeter-wave / terahertz generation module (103) is used to generate a millimeter-wave / terahertz electrical signal from the millimeter-wave / terahertz modulation optical signal through photoelectric beat frequency conversion; and the fusion transmitting antenna module (104) is used to simultaneously transmit the millimeter-wave / terahertz electrical signal and the free-space optical modulation signal.

[0013] The base station includes a fusion receiving antenna module (105) and an electro-optical conversion millimeter-wave / terahertz signal receiving module (106); wherein: the fusion receiving antenna module (105) is used to receive the millimeter-wave / terahertz electrical signal and the free-space optical modulation signal; the electro-optical conversion millimeter-wave / terahertz signal receiving module (106) is used to convert the received millimeter-wave / terahertz electrical signal into an optical signal, and fuse it with the received free-space optical modulation signal to form a fusion optical signal, which is then transmitted to the central office via optical fiber;

[0014] The central office includes an optical coherent receiving module (107) and a fusion signal processing module (108); wherein: the optical coherent receiving module (107) is used to receive the fused optical signal through a single optical coherent receiver and perform photoelectric conversion; the fusion signal processing module (108) is used to demodulate and fuse the photoelectric converted signal to restore the original transmission information.

[0015] In a preferred embodiment, the fusion signal generation module (101) can generate a free-space optical signal and a millimeter-wave / terahertz signal according to the channel environment. The free-space optical signal and the millimeter-wave / terahertz signal have the same or different bandwidths to adapt to the inconsistent channel bandwidths supported by the two in actual communication. The bandwidth of the free-space optical signal is B. FSO The bandwidth of millimeter-wave / terahertz signals is B. RF ;

[0016] The millimeter-wave / terahertz signal can transmit signals that are unrelated to or related to free-space optical signals according to different operating modes, so as to improve the overall capacity or reliability of the system.

[0017] When improving reliability, the millimeter-wave / terahertz signal is a sampled portion of the free-space optical signal. If the sampling rate is x, then the bandwidth of the millimeter-wave / terahertz signal satisfies B.RF =B FSO / x; where B FSO B represents the bandwidth of the free-space optical signal. RF This represents the bandwidth of the millimeter-wave / terahertz signal, and x represents the sampling rate.

[0018] The fusion signal processing module (108) selects the corresponding fusion processing mode according to the system's operating status.

[0019] In a preferred embodiment, the optical / electric conversion millimeter-wave / terahertz generation module (103) includes a first laser, a first coherent modulator, a third laser, a first optical coupler, and an emission optical / electric converter;

[0020] The center frequency of the first laser output is f c1 The optical signal, after being modulated by the first coherent modulator, is transmitted through the first optical coupler to the third laser, which emits a center frequency of f. c3 Local oscillator optical coupling, where f c3 =f c1 +f RF ;

[0021] After the coupled optical signal undergoes the transmitted light-to-electrical conversion, a frequency of f is generated. c3 -f c1 =f RF Millimeter-wave / terahertz signals; where f c1 f represents the center frequency of the first laser. c3 f represents the center frequency of the third laser. RF Indicates the frequency of the millimeter-wave / terahertz signal;

[0022] The millimeter-wave / terahertz signal is transmitted into free space through the millimeter-wave / terahertz antenna in the fused transmit antenna module (104).

[0023] In a preferred embodiment, the electro-optical conversion millimeter-wave / terahertz signal receiving module (106) includes a fourth laser and a receiving electro-optical conversion module;

[0024] The millimeter-wave / terahertz electrical signal received by the fusion receiving antenna module (105) is modulated onto the optical signal of the fourth laser through the ultra-high bandwidth thin-film lithium phosphate MZM in the receiving electro-optical conversion module. The center frequency of the fourth laser is f. c4 The MZM operates at the carrier suppression point;

[0025] The modulated optical signal is coupled with the free-space optical signal received by the fusion receiving antenna module (105) and transmitted to the central office via a single-mode optical fiber.

[0026] In a preferred embodiment, the signal light frequency f of the fourth laser of the base station c4 and the local oscillator frequency f of the fifth laser of the central office c5 The design ensures that both the upper sideband of the electro-optically converted millimeter-wave / terahertz signal and the free-space optical signal fall within the bandwidth of the coherent receiver at the central office.

[0027] The center frequency of the upper sideband of the millimeter-wave / terahertz signal is f. c4 +f RF The bandwidth is B RF ;

[0028] The center frequency of the free-space optical signal is f. c2 Maximum bandwidth is

[0029] The guard interval between the millimeter-wave / terahertz signal and the free-space optical signal in the receiver is f. guard ;

[0030] The f c4 Satisfying Relationship:

[0031] The maximum bandwidth of the coherent receiver is B. Rx ;

[0032] The f c5 Satisfying Relationship:

[0033] Among them, f c2 f represents the center frequency of a free-space optical signal. c4 f represents the center frequency of the fourth laser. c5 f represents the center frequency of the fifth laser. RF B represents the frequency of millimeter-wave / terahertz signals. RF Indicates the bandwidth of millimeter-wave / terahertz signals. f represents the maximum bandwidth of a free-space optical signal. guard B represents the guard interval frequency. Rx This indicates the maximum bandwidth of the coherent receiver.

[0034] In a preferred embodiment, the fusion signal processing module (108) performs down-conversion and matched filtering on the fusion signal to filter out out-of-band signals and obtain signals from the respective links of millimeter wave / terahertz and free space light.

[0035] The fusion signal processing module (108) directly obtains the communication information and calculates the bit error rate, or introduces adaptive diversity combination technology (ADCT) based on maximum ratio combining and cascaded hybrid automatic repeat request mechanism (ccHARQ) for subsequent optional fusion signal processing.

[0036] In a preferred embodiment, a method for operating the above-described free-space light and millimeter-wave / terahertz fusion transmission system is also proposed, comprising the following steps:

[0037] The fusion signal generation module (101) in the transmitter generates a corresponding fusion signal according to the application scenario requirements;

[0038] The millimeter-wave / terahertz signal and the free-space optical signal are modulated onto the laser by the electro / optical conversion modulation module (102) in the transmitter, respectively;

[0039] The transmitter generates a millimeter-wave / terahertz signal through the optical / electric conversion millimeter-wave / terahertz generation module (103), and transmits the millimeter-wave / terahertz signal and the free-space light signal through the fusion transmitting antenna module (104).

[0040] The millimeter-wave / terahertz signal and the free-space optical signal are fused and received in the optical domain through the fusion receiving antenna module (105) and the electro-optical conversion millimeter-wave / terahertz signal receiving module (106) of the base station, and then transmitted to the central office through optical fiber.

[0041] The fused signal is received by optical-to-electric conversion through the optical coherent receiving module (107) in the central office, and then processed by the fused signal processing module (108).

[0042] This application proposes a free-space light and millimeter-wave / terahertz fusion transmission system, which has the following advantages and technical effects:

[0043] First, an all-optical up-conversion architecture is adopted to achieve efficient generation and reception of broadband millimeter-wave / terahertz signals. Specifically, unlike most existing millimeter-wave / terahertz communication systems that use electrical up-conversion modules, this application utilizes an optical / electrical conversion millimeter-wave / terahertz generation module 103 and an electrical / optical conversion millimeter-wave / terahertz signal receiving module 106 to fully leverage the ultra-high bandwidth characteristics of photons and achieve efficient generation and reception of broadband millimeter-wave / terahertz signals through photoelectric conversion. Specifically, the optical / electrical conversion millimeter-wave / terahertz generation module 103 uses optical beat frequency conversion to convert millimeter-wave / terahertz modulated optical signals into high-frequency electrical signals; the electrical / optical conversion millimeter-wave / terahertz signal receiving module 106 uses ultra-high bandwidth MZM to remodulate the received high-frequency electrical signals onto an optical carrier, achieving all-optical up-conversion processing.

[0044] Secondly, by designing the signal frequencies in the optical domain, the two signals can be received by a single receiver, reducing the complexity of the receiver. Specifically, unlike existing free-space light and millimeter-wave / terahertz fusion systems that mostly rely on independent receivers, this application rationally designs the frequencies of the free-space light signal and the millimeter-wave / terahertz signal in the optical domain. This allows the two signals, after being processed by the electro-optical conversion millimeter-wave / terahertz signal receiving module 106, to be uniformly received by a single optical coherent receiver in the optical coherent receiving module 107. According to claim 5, by rationally setting the laser frequencies fc4 and fc5, both the upper sideband of the electro-optical converted millimeter-wave / terahertz signal and the free-space light signal can fall within the bandwidth of the coherent receiver, achieving simultaneous reception of the two signals by a single receiver. This scheme significantly reduces the system complexity of the receiver, reduces the number of devices, and also improves the utilization efficiency of the coherent receiver bandwidth.

[0045] Furthermore, independent or joint processing can be flexibly selected based on channel conditions to improve transmission reliability in harsh environments. Specifically, unlike existing systems that mostly employ independent processing procedures such as hard handover, the fusion signal processing module 108 in this application can flexibly choose to use independent or joint processing based on channel conditions. In joint processing, the fusion signal processing module 108 introduces adaptive diversity combining technology (ADCT) based on maximum ratio combining (MRC) and hybrid automatic repeat request (HARQ) technology, fully leveraging the large bandwidth of free-space light and the strong environmental robustness of millimeter-wave / terahertz waves. Under harsh conditions such as fog or turbulence, the millimeter-wave / terahertz link can serve as a reliable backup channel, effectively reducing the probability of communication interruption. Claim 2 further specifies that the correlation between the free-space light signal and the millimeter-wave / terahertz signal is controlled by the fusion signal generation module 101, and claim 6 clarifies several optional processing mechanisms of the fusion signal processing module 108, demonstrating the advantages of this system in improving reliability.

[0046] Furthermore, the system adopts an all-optical link design, is compatible with fiber optic communication networks, and supports flexible and diverse deployment scenarios. Specifically, the integrated transmission system of this application adopts an all-optical link design, which has natural compatibility with existing fiber optic communication networks and is suitable for flexible deployment in different application scenarios. For example, in terrestrial communication, this system can be used to build a distributed fiber optic transmission network; in air-to-ground communication, this system can also be used to connect ground stations and low-orbit satellites to build a high-speed, low-latency integrated air-space-ground network. Claim 7 summarizes the workflow of this system at the transmitter, base station, and central office nodes from a methodological perspective, reflecting the all-optical link end-to-end design concept.

[0047] In summary, this application overcomes the bottlenecks of traditional free-space optical and millimeter-wave / terahertz fusion systems in terms of reception complexity and transmission bandwidth, providing a highly reliable, high-capacity, low-complexity, and flexible fusion transmission solution. The system employs all-optical frequency conversion at the transmitting end to generate broadband millimeter-wave / terahertz signals, and at the receiving end, it achieves fusion reception of the two signals using a single-optical coherent receiver, supporting adaptive independent / joint processing. It can balance transmission reliability and spectral efficiency under different channel conditions. Furthermore, the all-optical link design endows the system with flexible networking capabilities, allowing deployment in various terrestrial or air-to-ground communication scenarios, contributing to the construction of next-generation integrated high-speed air-space-ground communication networks.

[0048] The specification of this application contains numerous technical features distributed across various technical solutions. Listing all possible combinations of these technical features (i.e., technical solutions) would make the specification excessively lengthy. To avoid this problem, the various technical features disclosed in the above-described invention, the various technical features disclosed in the following embodiments and examples, and the various technical features disclosed in the accompanying drawings can be freely combined to form various new technical solutions (all of which are considered to have been described in this specification), unless such a combination of technical features is technically infeasible. For example, one example discloses feature A+B+C, and another example discloses feature A+B+D+E. Features C and D are equivalent technical means that serve the same function, and technically only one needs to be used; they cannot be used simultaneously. Feature E can technically be combined with feature C. Therefore, the solution A+B+C+D should not be considered as described because it is technically infeasible, while the solution A+B+C+E should be considered as described. Attached Figure Description

[0049] Figure 1 This is a structural block diagram of a free-space light and millimeter-wave / terahertz fusion transmission system according to an embodiment of this application.

[0050] Figure 2This is a signal processing flowchart of a free-space light and millimeter-wave / terahertz fusion communication system according to an embodiment of this application.

[0051] Figure 3 The above are the signal spectrum diagrams after optical-to-electrical conversion of the central office optical coherent receiving module according to the embodiments of this application, wherein: (a) is the spectrum when both the free space optical channel and the millimeter wave / terahertz channel transmit 10-Gbaud 16QAM; (b) is the spectrum when the free space optical channel transmits 20-Gbaud 16QAM and the millimeter wave / terahertz channel transmits 10-Gbaud 16QAM; and (c) is the spectrum when the free space optical channel transmits 40-Gbaud 16QAM and the millimeter wave / terahertz channel transmits 10-Gbaud 16QAM.

[0052] Figure 4 The diagram shows the signal processing flow and performance of the fused transmission system according to the embodiments of this application when the maximum ratio combining (MRC) mechanism is used, wherein: (a) is a schematic diagram of the MRC signal processing flow; and (b) is the real-time test performance of the system when the MRC mechanism is used.

[0053] Figure 5 The diagram shows the signal processing flow and performance of the converged transmission system according to the embodiments of this application when the Hybrid Automatic Repeat Request (HARQ) mechanism is adopted, wherein: (a) is a schematic diagram of the HARQ signal processing flow; and (b) is the real-time test performance of the system when the HARQ mechanism is adopted.

[0054] Explanation of the labels in the diagram:

[0055] 101-Fusion Signal Generation Module

[0056] 102-Electro-optical conversion modulation module

[0057] 103-Optical / Electrical Conversion Millimeter Wave / Terahertz Generation Module

[0058] 104-Integrated Transmit Antenna Module

[0059] 105-Fusion Receiver Antenna Module

[0060] 106-Electro-optical conversion millimeter-wave / terahertz signal receiving module

[0061] 107-Optical Coherent Receiver Module

[0062] 108-Fusion Signal Processing Module Detailed Implementation

[0063] In the following description, many technical details are presented to help the reader better understand this application. However, those skilled in the art will understand that the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0064] Explanation of some concepts:

[0065] Free-space optical communication (FSO) refers to optical communication technology that uses lasers to transmit data in free space (such as the atmosphere or vacuum). It has advantages such as ultra-high bandwidth, resistance to electromagnetic interference, and strong security, but its transmission performance is easily affected by weather conditions such as fog and atmospheric turbulence.

[0066] Millimeter wave / terahertz (MMW / THz) refers to electromagnetic waves with frequencies ranging from 30 to 300 GHz, while terahertz refers to electromagnetic waves with frequencies ranging from 0.1 to 10 THz. These frequency bands have abundant spectrum resources and ultra-high bandwidth potential, are mainly affected by humidity, and exhibit relatively stable performance under smog conditions.

[0067] All-optical assistance refers to the use of optical devices and methods throughout the generation, transmission, and reception of millimeter-wave / terahertz signals. This includes photoelectric beat frequency upconversion, optical domain transmission, and photoelectric conversion downconversion, thus avoiding the bandwidth limitations of traditional electrical domain processing.

[0068] A single optical coherent receiver refers to a receiver that simultaneously receives and processes free-space optical signals and millimeter-wave / terahertz converted optical signals. It achieves unified reception through optical domain frequency design, simplifying the system structure and reducing costs.

[0069] Photoelectric beat frequency refers to the physical phenomenon in which two laser signals of different frequencies interact in a photodetector to generate an electrical signal with a frequency equal to the difference in frequency between the two laser signals. It is often used for all-optical generation of millimeter-wave / terahertz signals.

[0070] A Mach-Zehnder modulator (MZM) is an optical modulator based on the electro-optic effect. It modulates the amplitude or phase of an optical signal by applying an electrical signal to change the phase of the light wave. Thin-film lithium phosphate MZMs exhibit ultra-high bandwidth characteristics.

[0071] The carrier suppression point refers to the operating state of the MZM, in which the original carrier signal is suppressed and the upper and lower sideband signals are mainly output. It is often used in optical carrier modulation to reduce carrier power loss.

[0072] Maximum Ratio Combining (MRC) is a combination merging technique that assigns weight coefficients to each signal based on its signal-to-noise ratio (SNR), maximizing the SNR of the combined signal and improving reception performance and system reliability.

[0073] Adaptive diversity combining technique (ADCT) dynamically adjusts the weights of each received signal according to channel conditions and system requirements, adaptively combining multiple signals to maximize the quality of the received signal and the reliability of the system.

[0074] Concatenated Hybrid Automatic Repeat Request (ccHARQ) combines forward error correction coding and automatic repeat mechanism error control technology to improve transmission reliability through intelligent retransmission strategy while maintaining system throughput.

[0075] Fusion optical signal refers to a composite optical signal formed by converting millimeter-wave / terahertz electrical signals into optical signals and merging them with free-space optical signals in the optical domain. This composite optical signal can be transmitted to the central office through a single optical fiber.

[0076] The guard interval, in the frequency domain, is a frequency spacing set to avoid mutual interference between different signals, ensuring that each signal can be effectively separated and demodulated within the receiver bandwidth.

[0077] Optical coherent reception, which utilizes the optical receiving technology of coherently mixing the local oscillator light with the received signal light, can achieve complete recovery of the amplitude and phase information of the optical signal and has high receiving sensitivity.

[0078] Downsampling refers to a signal processing technique that extracts a portion of the sample from the original signal according to a certain ratio. In this application, it is used to extract part of the information from the free space optical signal and transmit it through a millimeter-wave / terahertz link when the bandwidth is mismatched.

[0079] The integrated air-space-ground communication network is a three-dimensional communication network architecture that integrates satellite communication, aviation communication and terrestrial communication, providing a technological foundation for achieving seamless global coverage and highly reliable communication services.

[0080] The following is a brief summary of some of the innovative aspects of this application:

[0081] This application proposes a free-space optical and millimeter-wave / terahertz fusion transmission system based on all-optical assistance and a single receiver. This system can be applied to future high-speed integrated air-space-ground communication scenarios, utilizing the ultra-wideband characteristics of photons to achieve all-optical generation and reception of broadband millimeter-wave / terahertz signals, thereby improving system speed. Through optical domain frequency design, the system enables both types of signals to be received by the same optical coherent receiver, reducing equipment complexity and improving spectrum utilization efficiency. It supports adaptive independent or cooperative signal processing, integrating the advantages of both types of links to improve transmission reliability in harsh environments. The system architecture is compatible with fiber optic networks and is suitable for terrestrial or space-to-ground high-speed communication scenarios.

[0082] More specifically, this application proposes a free-space optical and millimeter-wave / terahertz fusion transmission system based on all-optical assistance and a single receiver, aiming to overcome the shortcomings of existing solutions, such as complex receiver structure and limited link bandwidth. The system includes a fusion signal generation module 101, an electro-optical conversion modulation module 102, an optical-to-electrical conversion millimeter-wave / terahertz generation module 103, and a fusion transmitting antenna module 104 at the transmitter, achieving seamless conversion and fusion of signals from the electrical domain to the optical and millimeter-wave / terahertz domains. Specifically, the fusion signal generation module 101 generates an electrical signal to be transmitted according to the application scenario requirements. The electro-optical conversion modulation module 102 modulates the electrical signal onto a free-space optical carrier and a millimeter-wave / terahertz optical carrier, respectively, thereby obtaining two modulated optical signals. Then, the optical-electrical conversion millimeter-wave / terahertz generation module 103 efficiently converts the millimeter-wave / terahertz modulated optical signal into a millimeter-wave / terahertz electrical signal through an optoelectronic beat frequency unit. The fusion transmitting antenna module 104 then simultaneously transmits the free-space optical modulation signal and the millimeter-wave / terahertz electrical signal to the base station.

[0083] At the base station, the fusion receiving antenna module 105 receives free-space light and millimeter-wave / terahertz signals from the transmitter. The electro-optical conversion millimeter-wave / terahertz signal receiving module 106 uses ultra-high bandwidth thin-film lithium phosphate (MZM) to remodulate the received millimeter-wave / terahertz electrical signals into optical signals, and after fusion with the free-space light modulation signal in the optical domain, transmits them to the central office via optical fiber. The optical coherent receiving module 107 in the central office uses a single optical coherent receiver to perform unified demodulation and photoelectric conversion on the fused optical signal, eliminating the need for multiple receivers to process both signals simultaneously, thus significantly simplifying the receiver hardware and improving spectrum utilization efficiency.

[0084] The fusion signal processing module 108 flexibly selects independent or joint processing strategies based on channel conditions. In joint processing mode, the fusion signal processing module 108 introduces adaptive modulation-demodulation switching (ADCT) and hybrid automatic repeat request (ccHARQ) technology based on maximum ratio combining (MRC), taking into account the large bandwidth advantage of free space light and the environmental robustness of millimeter wave / terahertz links, thereby effectively reducing the probability of link interruption and improving the overall reliability of the system under harsh conditions such as fog and turbulence.

[0085] This system adopts an end-to-end all-optical link design, which is naturally compatible with existing high-speed fiber optic communication networks. It can be deployed in terrestrial communication networks and applied to integrated space-air-ground connections between ground stations and low-Earth orbit satellites, meeting the comprehensive communication requirements of high speed, low latency, and high reliability. In summary, this application provides a simplified, bandwidth-extended, robust, and flexible converged transmission solution suitable for the construction and application of future integrated space-air-ground communication networks.

[0086] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0087] Reference Figure 1 This embodiment proposes a free-space light and millimeter-wave / terahertz fusion transmission system, comprising three main parts: a transmitter, a base station, and a central office. The transmitter includes a fusion signal generation module 101, an electro-optical conversion modulation module 102, an optical-to-electrical conversion millimeter-wave / terahertz generation module 103, and a fusion transmitting antenna module 104. The base station includes a fusion receiving antenna module 105 and an electro-optical conversion millimeter-wave / terahertz signal receiving module 106. The central office includes an optical coherent receiving module 107 and a fusion signal processing module 108.

[0088] This system can be applied to future high-speed integrated air-space-ground communication scenarios. It utilizes the ultra-wideband characteristics of photons to achieve all-optical generation and reception of broadband millimeter-wave / terahertz signals, thereby improving system speed. Through optical domain frequency design, both types of signals can be received by the same optical coherent receiver, reducing equipment complexity and improving spectrum utilization efficiency. It supports adaptive independent or cooperative signal processing, integrates the advantages of both types of links, and improves transmission reliability in harsh environments. The system architecture is compatible with fiber optic networks and is suitable for high-speed terrestrial or space-to-ground communication scenarios.

[0089] The transmitter structure and working principle will be described in detail below.

[0090] The fusion signal generation module 101 is used to generate the electrical signal to be transmitted according to the application scenario requirements. This module can generate free-space optical signals and millimeter-wave / terahertz signals based on the channel environment. These two signals can have the same or different bandwidths to adapt to the inconsistent channel bandwidths supported by the two signals in actual communication. The bandwidth of the free-space optical signal is B. FSO The bandwidth of millimeter-wave / terahertz signals is B. RF .

[0091] Furthermore, millimeter-wave / terahertz signals can transmit signals independent of or related to free-space optical signals, depending on the operating mode, thereby improving the overall capacity or reliability of the system. Depending on the specific application scenario, the system can select the following operating modes:

[0092] (1) When the free-space optical link is stable and the system pursues high capacity, the free-space optical link and the millimeter-wave / terahertz link transmit two sets of unrelated information to be transmitted, with bandwidths of B respectively. FSO B RF In this embodiment, B RF Fixed at 10GHz, B FSO 10GHz, 20GHz and 40GHz can be selected respectively;

[0093] (2) When the free-space optical link is significantly affected by weather and its bandwidth is comparable to that of a millimeter-wave / terahertz link, both paths transmit the same information to be transmitted. In this embodiment, B FSO and B RF Both are 10GHz;

[0094] (3) When the free-space optical link is significantly affected by weather and its bandwidth is greater than that of the millimeter-wave / terahertz link, the information to be transmitted is downsampled at the symbol level. Based on the downsampling factor x, the millimeter-wave / terahertz link transmits a portion of the information, and its bandwidth is 1 / x of that of the free-space optical link. When improving reliability, the millimeter-wave / terahertz signal is a sampled portion of the free-space optical signal, satisfying B. RF =B FSO / x. In this embodiment, B FSO 20GHz, x is 2, B RF It is 10GHz.

[0095] In this embodiment, the modulation format for both free-space light and millimeter-wave / terahertz signals is 16QAM.

[0096] The electro-optical conversion modulation module 102 is used to modulate the electrical signal to be transmitted onto the corresponding laser carrier to generate free space light modulation signal and millimeter wave / terahertz modulation light signal.

[0097] In the transmitter, the fused communication signal obtained by the fused signal generation module 101 includes a millimeter-wave / terahertz signal that is modulated onto a first laser via a first coherent modulator. The center frequency of the first laser is f. c1 The free-space optical signal is modulated onto a second laser by a second coherent modulator. The center frequency of the second laser is f. c2 In this embodiment, f c1 and f c2 Both are 192.2 THz. A schematic diagram of free-space optical signals can be seen... Figure 1 Point C in the middle.

[0098] The optical-to-electric conversion millimeter-wave / terahertz generation module 103 is used to generate millimeter-wave / terahertz electrical signals from millimeter-wave / terahertz modulated optical signals through photoelectric beat frequency conversion. This module includes a first laser, a first coherent modulator, a third laser, a first optical coupler, and an emission optical-to-electric converter.

[0099] The center frequency of the first laser output is f. c1 The optical signal, modulated by the first coherent modulator, is transmitted through the first optical coupler to the third laser, where the center frequency is f. c3 Local oscillator optical coupling, where f c3 =f c1 +f RF After coupling, the optical signal undergoes photoelectric conversion to generate a frequency of f. c3 -f c1 =f RF Millimeter-wave / terahertz signals. Schematic diagrams of the signals before and after photoelectric conversion are shown. Figure 1 Points A and B in the diagram.

[0100] In this embodiment, f c1 192.2 THz, f c3 The frequency is 192.2779 THz, and the center frequency of the generated millimeter-wave signal is 77.9 GHz (E / W band).

[0101] The fusion transmit antenna module 104 is used to simultaneously transmit millimeter-wave / terahertz electrical signals and free-space optical modulation signals. This module includes a millimeter-wave / terahertz antenna and an optical antenna, which transmit the two signals into free space respectively.

[0102] The base station structure and working principle will be described in detail below.

[0103] The fusion receiving antenna module 105 is used to receive millimeter-wave / terahertz electrical signals and free-space optical modulation signals. In this embodiment, the free-space transmission distance is 4.3 km.

[0104] The electro-optical conversion millimeter-wave / terahertz signal receiving module 106 is used to convert the received millimeter-wave / terahertz electrical signal into an optical signal, and fuse it with the received free-space optical modulation signal to form a fused optical signal, which is then transmitted to the central office via optical fiber.

[0105] This module includes a fourth laser and a receiving electro-optical conversion module. The millimeter-wave / terahertz signal received by the fused receiving antenna module 105 is modulated to a center frequency of f by the ultra-high bandwidth thin-film lithium phosphate MZM in the receiving electro-optical conversion module. c4 The fourth laser is used, and the MZM operates at the carrier suppression point. The modulated optical signal is coupled with the free-space optical signal received by the fusion receiving antenna module 105, and then sent to the central office through a single-mode fiber.

[0106] In this embodiment, f ca The Hz frequency is 192.096 THz, and the fiber optic cable is 10 km long.

[0107] The structure and working principle of the central bureau will be described in detail below.

[0108] The optical coherent receiver module 107 is used to receive the fused optical signal and perform photoelectric conversion via a single optical coherent receiver. The central office receives the fused optical signal from the base station, and the fifth laser at the central office serves as the local oscillator frequency f for coherent reception. c5 Through design, the upper sideband of the millimeter-wave / terahertz signal after electro-optic conversion and the free-space optical signal fall within the bandwidth of the coherent receiver at the central office.

[0109] The signal light frequency f of the fourth laser in the base station c4 The local oscillator frequency f of the fifth laser at the central station c5 The design ensures that both the upper sideband of the electro-optically converted millimeter-wave / terahertz signal and the free-space optical signal fall within the bandwidth of the coherent receiver at the central office. Specifically, the center frequency of the upper sideband of the millimeter-wave / terahertz signal is f. c4 +f RF The bandwidth is B RF The center frequency of the free-space optical signal is f. c2 Maximum bandwidth is The guard interval between the millimeter-wave / terahertz signal and the free-space optical signal in the receiver is f. guard .

[0110] In this configuration, f ca Relationships must be satisfied:

[0111]

[0112] The maximum bandwidth of the coherent receiver is B Rx Then f c5 Relationships must be satisfied:

[0113]

[0114] The designed optical frequency can meet the requirements for single-receiver reception and maximize the receiver's bandwidth utilization.

[0115] In this embodiment, f c4 192.096 THz, f guard For 2GHz, B RF Fixed at 10GHz For 40GHz, f c5 It is 192.194 THz.

[0116] Figure 3 The signal spectrum after optical-to-electrical conversion by the central office's optical coherent receiving module is displayed. Figure 3 (a) The received spectrum of the fused signal when transmitting 10-Gbaud 16QAM in free space optical channel and 10-Gbaud 16QAM in millimeter wave / terahertz channel; Figure 3 (b) The received spectrum of the fused signal when transmitting 20-Gbaud 16QAM in a free-space optical channel and 10-Gbaud 16QAM in a millimeter-wave / terahertz channel; Figure 3 (c) The received spectrum of the fused signal when transmitting 40-Gbaud 16QAM via a free-space optical channel and 10-Gbaud 16QAM via a millimeter-wave / terahertz channel. It can be seen that the received signal utilizes the full bandwidth of the receiver and can be flexibly allocated. The maximum bandwidth of the free-space optical link transmission is 40 GHz, maintaining the system's high throughput.

[0117] The fusion signal processing module 108 is used to demodulate and fuse the photoelectric converted signal to restore the original transmission information. This module performs down-conversion and matched filtering on the fused signal, filtering out out-of-band signals to obtain the signals of the millimeter-wave / terahertz and free-space light links respectively.

[0118] Depending on the system's operating state, the fusion signal processing module 108 selects different fusion processing modes:

[0119] (1) When the free-space optical link is stable and the system pursues high capacity (the free-space optical link and the millimeter-wave / terahertz link in the fusion signal generation module transmit two sets of unrelated information to be transmitted), the transmission information of the two channels is recovered separately, and the total communication rate of the system is B. FSO +B RF In this embodiment, B RF Fixed at 10GHz, B FSOWith 10GHz, 20GHz, and 40GHz respectively, and both modulation formats being 16QAM, the highest speed achieved by this link is 200Gbps.

[0120] (2) When the free-space optical link is significantly affected by weather and its bandwidth is comparable to that of a millimeter-wave / terahertz link (both channels transmit the same information to be transmitted), after the transmission information of the two channels is recovered, the recovered symbol sequence S of the free-space light will be... FSO and the recovery symbol sequence S of millimeter wave / terahertz RFn Perform MRC merging. Assume symbol sequence S. FSO and S RFn The normalized signal-to-noise ratios are SNR and SNR respectively. FSO Given SNR_RF, for MRC, the normalized combining gain coefficients for free-space optical links and millimeter-wave / terahertz are α and 1-α, respectively. The combined sequence can then be expressed as:

[0121] S MRC =αS FSO +(1-α)S RFn

[0122] According to MRC, by selecting the optimal combining gain for each channel, the signal-to-noise ratio (SNR) of the combined output signal is the sum of the SNRs of each sub-link. Therefore, α must satisfy:

[0123]

[0124] The symbol sequence following MRC is then demapped to obtain the original transmission information. In this embodiment, MRC is performed on two signals with a bandwidth of 10 GHz, improving the system's reliability.

[0125] (3) When the free-space optical link is significantly affected by weather and its bandwidth is greater than that of the millimeter-wave / terahertz link (the millimeter-wave / terahertz link transmits some information), the fusion processing module combines MRC and HARQ technologies. Figure 5 It is a fusion signal processing flow based on the cCHARQ architecture.

[0126] Specifically, the fusion processing module first demodulates the free-space optical signal and the millimeter-wave / terahertz signal to obtain the symbol sequence S. FSO and S RFn During the first transmission, the millimeter-wave / terahertz link transmits the first set of free-space light samples, i.e., S. RFn =S FSO[n], where n is the sampling index. The system then calculates the bit error rate (BER) of the free-space optical link and the millimeter-wave / terahertz link. If the BER exceeds a threshold, a retransmission is triggered; during the second transmission, the millimeter-wave / terahertz link transmits the second set of free-space light samples, i.e., S. RF (n+1)=S FSO [n+1], while the free-space optical link continues to transmit the next frame of data, keeping the system throughput constant.

[0127] After two transmissions, the fusion signal processing module will convert the free space light S FSO [n] and millimeter wave / terahertz S RFn MRC consolidation is performed, and the consolidation factor is the same as in case (2), that is:

[0128]

[0129] The merged output is:

[0130] S MRC =αS FsO +(1-α)S RFn

[0131] Subsequently, constellation demapping was performed on the merged symbol sequence of MRC to obtain the original information.

[0132] In this embodiment, the free-space optical bandwidth is 20 GHz, the sampling rate x is 2, and the millimeter-wave / terahertz bandwidth is 10 GHz. Retransmission is triggered when the BER exceeds a set threshold of 2E-2. This processing mechanism ensures communication reliability even under adverse weather conditions.

[0133] The system workflow will be described in detail below.

[0134] Figure 2 The system's workflow is demonstrated, including the following steps:

[0135] The fusion signal generation module 101 in the transmitter generates the corresponding fusion signal according to the application scenario requirements;

[0136] The millimeter-wave / terahertz signal and the free-space optical signal are modulated onto the laser by the electro-optical conversion modulation module 102 in the transmitter, respectively.

[0137] Millimeter-wave / terahertz signals are generated by the optical / electric conversion millimeter-wave / terahertz generation module 103 in the transmitter, and the millimeter-wave / terahertz signals and free-space light signals are transmitted through the fusion transmitting antenna module 104.

[0138] The base station uses a fusion receiving antenna module 105 and an electro-optical conversion millimeter-wave / terahertz signal receiving module 106 to fuse and receive millimeter-wave / terahertz signals and free-space optical signals in the optical domain, and then transmits them to the central office via optical fiber.

[0139] The fused signal is received by optical-to-electric conversion through the optical coherent receiving module 107 in the central office, and then processed by the fused signal processing module 108.

[0140] The all-optical free-space light and millimeter-wave / terahertz fusion transmission system of this embodiment has been verified in a 4.3km wireless communication scenario. Figure 4 The system performance test results were presented. Figure 4 (a) shows a comparison of 16QAM constellation diagrams under different signal-to-noise ratios (SNR). Figure 4 (b) shows the comparison results of bit error rate performance.

[0141] As can be seen, in high-capacity mode, the system can achieve a clear constellation diagram and a maximum transmission rate of 200Gbps under high SNR conditions; in high-reliability mode, through MRC or HARQ mechanisms, the system can keep the BER below the threshold value under severe weather conditions. This fully demonstrates the superior performance of the system in this embodiment in improving transmission capacity and reliability.

[0142] This embodiment has the following technical effects:

[0143] First, an all-optical up-conversion architecture is adopted to achieve efficient generation and reception of broadband millimeter-wave / terahertz signals. Specifically, unlike most existing millimeter-wave / terahertz communication systems that use electrical up-conversion modules, this embodiment utilizes an optical / electrical conversion millimeter-wave / terahertz generation module 103 and an electrical / optical conversion millimeter-wave / terahertz signal receiving module 106 to fully leverage the ultra-high bandwidth characteristics of photons and achieve efficient generation and reception of broadband millimeter-wave / terahertz signals through photoelectric conversion. Specifically, the optical / electrical conversion millimeter-wave / terahertz generation module 103 uses optical beat frequency conversion to convert millimeter-wave / terahertz modulated optical signals into high-frequency electrical signals; the electrical / optical conversion millimeter-wave / terahertz signal receiving module 106 uses ultra-high bandwidth MZM to remodulate the received high-frequency electrical signals onto an optical carrier, achieving all-optical domain up-conversion processing.

[0144] Secondly, by designing the signal frequency in the optical domain, both signals can be received by a single receiver, reducing the complexity of the receiver. Specifically, unlike existing free-space light and millimeter-wave / terahertz fusion systems that mostly rely on independent receivers, this embodiment rationally designs the frequencies of the free-space light signal and the millimeter-wave / terahertz signal in the optical domain. This allows the two signals, after being processed by the electro-optical conversion millimeter-wave / terahertz signal receiving module 106, to be uniformly received by a single optical coherent receiver in the optical coherent receiving module 107. This is achieved by rationally setting the laser frequency f. c4 and f c5 This approach allows both the upper sideband of the electro-optically converted millimeter-wave / terahertz signal and the free-space optical signal to fall within the bandwidth of the coherent receiver, enabling a single receiver to simultaneously receive both signals. This scheme significantly reduces the system complexity at the receiver end, decreases the number of devices, and also improves the utilization efficiency of the coherent receiver's bandwidth.

[0145] Furthermore, by flexibly selecting independent or joint processing based on channel conditions, transmission reliability in harsh environments is improved. Specifically, unlike existing systems that mostly employ independent processing procedures such as hard handover, the fusion signal processing module 108 in this embodiment can flexibly choose between independent or joint processing based on channel conditions. During joint processing, the fusion signal processing module 108 introduces Adaptive Diversity Combining (ADCT) technology based on Maximum Ratio Combining (MRC) and Hybrid Automatic Repeat Request (HARQ) technology, fully leveraging the large bandwidth of free-space light and the strong environmental robustness of millimeter-wave / terahertz waves. Under harsh conditions such as fog or turbulence, the millimeter-wave / terahertz link can serve as a reliable backup channel, effectively reducing the probability of communication interruption. By controlling the correlation between the free-space light signal and the millimeter-wave / terahertz signal through the fusion signal generation module 101, the fusion signal processing module 108 employs different fusion processing mechanisms, demonstrating the system's advantages in improving reliability.

[0146] Furthermore, the system adopts an all-optical link design, ensuring compatibility with fiber optic communication networks and supporting flexible and diverse deployment scenarios. Specifically, the converged transmission system in this embodiment employs an all-optical link design, possessing inherent compatibility with existing fiber optic communication networks and suitable for flexible deployment in various application scenarios. For example, in terrestrial communication, this system can be used to construct a distributed fiber optic transmission network; in air-to-ground communication, this system can also be used to connect ground stations with low-Earth orbit satellites, building a high-speed, low-latency integrated air-space-ground network. The system's workflow demonstrates the end-to-end design concept of an all-optical link.

[0147] In summary, this embodiment overcomes the bottlenecks of traditional free-space optical and millimeter-wave / terahertz fusion systems in terms of reception complexity and transmission bandwidth, providing a highly reliable, high-capacity, low-complexity, and flexible fusion transmission solution. The system employs all-optical frequency conversion at the transmitting end to generate broadband millimeter-wave / terahertz signals, and at the receiving end, it achieves fusion reception of the two signals using a single-optical coherent receiver, supporting adaptive independent / joint processing. It can balance transmission reliability and spectrum utilization under different channel conditions. Furthermore, the all-optical link design gives the system flexible networking capabilities, allowing deployment in various terrestrial or air-to-ground communication scenarios, contributing to the construction of next-generation integrated high-speed air-space-ground communication networks.

[0148] To better understand the technical solution of this application, specific examples are provided below. The details listed in these examples are for ease of understanding and are not intended to limit the scope of protection of this application.

[0149] In this example, a free-space light and millimeter-wave / terahertz fusion transmission system based on all-optical assistance and a single receiver is proposed, such as... Figure 1 As shown, it includes a fusion signal generation module 101, an electro-optical conversion modulation module 102, an optical-electrical conversion millimeter-wave / terahertz generation module 103, and a fusion transmitting antenna module 104 in the transmitter; a fusion receiving antenna module 105 and an electro-optical conversion millimeter-wave / terahertz signal receiving module 106 in the base station; and an optical coherent receiving module 107 and a fusion signal processing module 108 in the central office; wherein:

[0150] The fusion signal generation module 101 in the transmitter generates corresponding fusion communication signals according to the application scenario requirements;

[0151] The electro-optic conversion modulation module 102 in the transmitter modulates the free space light and the millimeter-wave / terahertz fused signal onto their respective signal lasers to complete the electro-optic conversion.

[0152] The optical / electric conversion millimeter-wave / terahertz generation module 103 in the transmitter generates a millimeter-wave / terahertz signal from the optical signal modulated by the millimeter-wave / terahertz link of the electrical / optical conversion modulation module, and transmits the millimeter-wave / terahertz and free-space optical signals through the millimeter-wave / terahertz antenna and optical antenna in the fusion transmitting antenna module 104.

[0153] The fusion receiving antenna module 105 in the base station receives millimeter-wave / terahertz signals and free-space optical signals transmitted by the transmitter, and converts the millimeter-wave / terahertz signals into optical signals through the electro-optical conversion millimeter-wave / terahertz signal receiving module 106 via the electro-optical conversion of ultra-high bandwidth thin-film lithium phosphate MZM (also referred to as "ultra-high bandwidth thin-film lithium phosphate MZM" in this document), and couples them with the received free-space optical signals, and transmits them to the central office via optical fiber;

[0154] The optical coherent receiving module 107 in the central office receives the fused optical signal sent from the base station, and after optical-to-electrical conversion, it is centrally processed by the fused signal processing module 108.

[0155] The specific steps for implementing the all-optical-assisted and single-receiver free-space light and millimeter-wave / terahertz fusion transmission system proposed in this example are as follows:

[0156] Step 1: The fusion signal generation module 101 generates the corresponding fusion communication signal according to the application scenario requirements;

[0157] Depending on the specific application scenario, millimeter-wave / terahertz links can choose to transmit two types of signals. When the free-space optical link is stable and the system prioritizes high capacity, the free-space optical link and the millimeter-wave / terahertz link transmit two unrelated sets of information to be transmitted, with bandwidths of B respectively. FSO B RF In the example B RF Fixed at 10GHz, B FSO The GHz frequencies are 10GHz, 20GHz, and 40GHz respectively. When the free-space optical link is significantly affected by weather and its bandwidth is comparable to that of a millimeter-wave / terahertz link, both paths transmit the same information to be transmitted. In the example, B... FSO B RF Both are 10GHz; when the free-space optical link is significantly affected by weather and its bandwidth is greater than that of the millimeter-wave / terahertz link, the information to be transmitted is downsampled at the symbol level. Based on the downsampling factor x, the millimeter-wave / terahertz link transmits part of the information, and its bandwidth is 1 / x of that of the free-space optical link. In the example, B FSo 20GHz, x is 2, B RF The frequency is 10 GHz. In this embodiment, both the free space light and the millimeter-wave / terahertz signal modulation format are 16QAM.

[0158] Step 2: The electro-optical conversion modulation module 102 in the transmitter modulates the free space light and the millimeter-wave / terahertz fused signal onto their respective signal lasers to complete the electro-optical conversion;

[0159] In the transmitter, the fused communication signal obtained in step one, wherein the millimeter-wave / terahertz signal is modulated onto the first laser by the first coherent modulator, the center frequency of the first laser being f. c1 In the embodiment, f c1 The frequency is 192.2 THz; the free-space optical signal is modulated onto the second laser by the second coherent modulator, and the center frequency of the second laser is f. c2 In the embodiment, f c2 The frequency is 192.2 THz; a schematic diagram of the free-space optical signal can be seen. Figure 1Point C in the middle.

[0160] Step 3: The optical / electric conversion millimeter-wave / terahertz generation module 103 in the transmitter generates a millimeter-wave / terahertz signal from the optical signal modulated by the millimeter-wave / terahertz link of the electrical / optical conversion modulation module, and transmits the millimeter-wave / terahertz and free-space optical signals through the millimeter-wave / terahertz antenna and optical antenna in the fusion transmitting antenna module 104.

[0161] In the transmitter, the millimeter-wave / terahertz emitted optical signal obtained in step two passes through the first optical coupler and is coupled with the local oscillator light f emitted by the third laser. c3 After coupling and passing through the optical-to-electrical conversion module, a frequency of f can be obtained. c3 -f c2 The millimeter-wave / terahertz signal, and the signal diagrams before and after photoelectric conversion are shown. Figure 1 Points A and B in the example; in the embodiment, f c3 The frequency is 192.2779 THz, meaning the center frequency of the generated E / W band millimeter-wave signal is 77.9 GHz. The millimeter-wave / terahertz signal and the free-space optical signal are transmitted into free space via a fused transmitting antenna.

[0162] Step 4: The fusion receiving antenna module 105 in the base station receives the millimeter-wave / terahertz signal and free-space optical signal transmitted by the transmitter, and converts the millimeter-wave / terahertz signal into an optical signal after electro-optical conversion by the ultra-high bandwidth thin-film lithium phosphate MZM through the electro-optical conversion of the millimeter-wave / terahertz signal receiving module 106, and couples it with the received free-space optical signal, and transmits it to the central office through optical fiber.

[0163] The millimeter-wave / terahertz signal and free-space optical signal obtained in step three are transmitted via a fused transmitting antenna and transmitted through free space. In this implementation example, the free-space transmission distance is 4.3 km. At the base station, the signal is received by a fused receiving antenna module and converted into an optical signal by an ultra-high bandwidth thin-film lithium phosphate MZM in an electro-optical conversion millimeter-wave / terahertz signal receiving module. The MZM operates at the carrier suppression point, and the base station's fourth laser serves as the frequency f of the signal light. c4 In the embodiment f c4 The frequency is 192.096 THz. After the millimeter-wave / terahertz optical signal is coupled with the received free-space optical signal, it is transmitted to the central office through an optical fiber. In this embodiment, the length of the optical fiber is 10 km.

[0164] Step 5: The optical coherent receiving module 107 in the central office receives the fused optical signal sent from the base station, and after optical-to-electrical conversion, it is centrally processed by the fused signal processing module 108.

[0165] The central office receives the fused optical signal obtained in step four, and the fifth laser at the central office serves as the local oscillator frequency f for coherent reception. c5 Through design, the upper sideband of the electro-optically converted millimeter-wave / terahertz signal and the free-space optical signal fall within the bandwidth of the coherent receiver at the central office. Specifically, the center frequency of the upper sideband of the millimeter-wave / terahertz signal is f. c3 +f RF The bandwidth is B RF The center frequency of the free-space optical signal is f. c2 Maximum bandwidth is The guard interval between the millimeter-wave / terahertz signal and the free-space optical signal in the receiver is required to be f. guard Then f c4 Relationships must be satisfied:

[0166]

[0167] The total maximum bandwidth of the signal considering the guard interval is Then f c5 Relationships must be satisfied:

[0168]

[0169] The designed optical frequency can meet the requirements for single-receiver reception and maximize receiver bandwidth utilization. In the embodiment f c4 192.096 THz, f guard For 2GHz, B RF Fixed at 10GHz For 40GHz, f c5 It is 192.194 THz.

[0170] After optical-to-electrical conversion by an optical coherent receiver, the corresponding signal undergoes down-conversion and matched filtering to obtain free-space light and millimeter-wave / terahertz signals. Different signal processing procedures can be implemented depending on the specific application scenario.

[0171] When the free-space optical link is stable and the system aims for high capacity, the two sets of information to be transmitted in step one are unrelated, namely, the free-space optical link and the millimeter-wave / terahertz link. Therefore, the transmission information of the two channels is recovered separately, and the total communication rate of the system is B. FSO +B RF In the embodiment, B RF Fixed at 10GHz, B FSO With 10GHz, 20GHz, and 40GHz respectively, and both modulation formats being 16QAM, the highest speed achieved by this link is 200Gbps.

[0172] When a free-space optical link is significantly affected by weather and its bandwidth is comparable to that of a millimeter-wave / terahertz link, both transmissions carry the same information. Therefore, after the transmission information from both channels is recovered, the recovered symbol sequence S of the free-space light is... FSO and the recovery symbol sequence S of millimeter wave / terahertz RFn Perform MRC merging. Assume symbol sequence S. FSO and S RFn The normalized signal-to-noise ratios are SNR and SNR respectively. FSO and SNR RF For MRC, the normalized combining gain coefficients for free-space optical links and millimeter-wave / terahertz are α and 1-α, respectively. The combined sequence can then be expressed as:

[0173] S MRC =αS FSO +(1-α)S RFn

[0174] According to MRC, by selecting the optimal combining gain for each channel, the signal-to-noise ratio (SNR) of the combined output signal is the sum of the SNRs of each sub-link. Therefore, α must satisfy...

[0175]

[0176] The symbol sequence following MRC is then demapped to obtain the transmission information from step one. In this embodiment, MRC is performed on two signals, each with a bandwidth of 10 GHz, which improves the reliability of the system.

[0177] When a free-space optical link is significantly affected by weather and its bandwidth is greater than that of a millimeter-wave / terahertz link, the information to be transmitted is downsampled at the symbol level. Based on the downsampling factor x, the millimeter-wave / terahertz link transmits a portion of the information, while the bandwidth of the free-space optical link is [missing information]. Example B FSO 20GHz, x is 2, B RF The frequency is 10 GHz. During the first transmission, the free-space optical link transmits symbol S. FSO Millimeter-wave / terahertz links, on the other hand, originate from S... FSO Starting with the first bit, downsampling is performed every other symbol, and the final transmitted symbol is S. RF1 During the second transmission, the millimeter-wave / terahertz link then... FSO Starting from the second bit, downsampling is performed every symbol interval, and the final transmitted symbol is S. RF2 Upon first reception, sequence S FSO Starting from the first symbol, each symbol interval corresponds to the sequence S. RF1 Corresponding to S RFn The corresponding SFSO The sampling sequence is represented as Therefore, it can be With S RF1 MRC is performed, and the merged sequence is represented as S. MRC1 The merged sequence is then subjected to constellation point mapping, followed by a bit error rate (BER) check. If the BER threshold of 2E-2 is not met, a retransmission command is sent to the transmit buffer via HARQ control. At this point, the free-space optical link at the transmitting end continues transmitting the next frame, maintaining system throughput, while the millimeter-wave / terahertz link transmits the next sampled data S. RF2 Upon receiving its corresponding S FSO Sampling sequence MRC is performed, and the merged sequence is represented as S. MRC2 In the embodiment, the retransmitted signals all meet the requirement of a bit error rate threshold of 2E-2, which greatly improves the system reliability.

[0178] This concludes the implementation method of a free-space optical and millimeter-wave / terahertz fusion transmission system with all-optical assistance and a single receiver.

[0179] The following section describes the verification steps and results of the all-optical-assisted and single-receiver free-space optical and millimeter-wave / terahertz fusion transmission system in this example, applied to an outdoor 4.3km wireless communication system.

[0180] The specific steps of a fully optical-assisted, single-receiver free-space optical and millimeter-wave / terahertz fusion transmission system in an outdoor 4.3km wireless communication system are as follows:

[0181] The experimental framework for the free-space light and millimeter-wave / terahertz fusion communication system in this example can also be used... Figure 1 Obtained from Figure 1 Number 101 is the fusion signal generation module in the transmitter; number 102 is the electro-optical conversion modulation module in the transmitter; number 103 is the optical-electrical conversion millimeter-wave / terahertz generation module in the transmitter; number 104 is the fusion transmitting antenna module in the transmitter; number 105 is the fusion receiving antenna module in the base station; number 106 is the electro-optical conversion millimeter-wave / terahertz signal receiving module in the base station; number 107 is the optical coherent receiving module in the central office; and number 108 is the fusion signal processing module in the central office.

[0182] Figure 2 The paper demonstrates the signal processing flow of free-space light and millimeter-wave / terahertz integrated communication. Figure 2The details of the fusion signal generation module in the transmitter are shown in section 101, and the details of the fusion signal processing module in the central office are shown in section 102. It can be seen that the millimeter-wave / terahertz link can choose to transmit downsampled signals related to the free-space optical link signal or independent signals. The receiver can also process the signals in conjunction with the free-space optical received signals or process them independently, thereby adapting to the requirements of high throughput and high reliability under different channel conditions.

[0183] Figure 3 This is the signal spectrum after optical-to-electrical conversion by the optical coherent receiving module of the central office of this application, wherein... Figure 3 (a)- Figure 3 (c) shows the spectra of the fused signal under different bandwidth ratios. Figure 3 (a) The received spectrum of the fused signal when transmitting 10-Gbaud 16QAM in free space optical channel and 10-Gbaud 16QAM in millimeter wave / terahertz channel; Figure 3 (b) The received spectrum of the fused signal when transmitting 20-Gbaud 16QAM in a free-space optical channel and 10-Gbaud 16QAM in a millimeter-wave / terahertz channel; Figure 3 (c) The received spectrum of the fused signal when transmitting 40-Gbaud 16QAM via a free-space optical channel and 10-Gbaud 16QAM via a millimeter-wave / terahertz channel. It can be seen that the received signal utilizes the full bandwidth of the receiver and can be flexibly allocated, and the maximum bandwidth of the free-space optical link transmission is 40 GHz, maintaining the system's high throughput.

[0184] Figure 4 The middle section details the signal processing flow and performance of the all-optical-assisted and single-receiver free-space optical and millimeter-wave / terahertz fusion transmission system using MRC. Figure 4 (a) details the specific signal processing flow. Figure 4 The details of transmitter fusion signal generation are shown in section 101. The free-space light and millimeter-wave / terahertz channels transmit the same 10-Gbaud 16QAM signal. Figure 4 Number 102 details the central office's fusion signal processing. After frequency conversion and matched filtering, the free space light and millimeter wave / terahertz signals are recovered respectively. After performing their respective coherent demodulation operations, the signal-to-noise ratio is calculated, the merging coefficients are derived, symbol-level MRC merging is performed, and finally constellation demapping is performed to recover the transmitted information. Figure 4 (b) shows the performance of the converged communication system under this working mode. It can be seen that turbulence causes large performance fluctuations in the single free space optical link, while the millimeter wave link fluctuates relatively less. After MRC merging, the performance is below the 2E-2 bit error rate threshold, maintaining the high reliability of the system.

[0185] Figure 5 This section details the signal processing flow and performance of the all-optical-assisted and single-receiver free-space optical and millimeter-wave / terahertz fusion transmission system using HARQ in this example. Figure 5 (a) details the specific signal processing flow. Figure 5 Number 101 is the signal downsampling process in the transmitter fusion signal generation. The free space optical transmission is 20-Gbaud 16QAM, and the millimeter wave / terahertz will sample the transmitted signal every 2 symbols to form two sets of bandwidth 10-Gbaud 16QAM signals. Figure 5 Number 102 in the middle section describes the details of the central office's fusion signal set-up. After the free-space optical signal and the first set of millimeter-wave / terahertz signals are fused, frequency-converted, and matched-filtered, they are combined at the corresponding symbol level using MRC. Finally, constellation demapping is performed to recover the transmitted information. If the bit error rate check does not meet the threshold requirements, the HARQ control will instruct the transmitter to retransmit the next set of sampled signals for the millimeter-wave / terahertz signal, while the free-space optical signal continues to transmit the next frame of signal, maintaining the system's throughput. Figure 5 (b) shows the performance of the converged communication system under this working mode. It can be seen that turbulence causes the single free space optical link to exceed the bit error rate threshold at some sampling points. At this time, the retransmission mechanism is triggered. After two retransmissions and the combination of the diffractometers, the performance is below the 2E-2 bit error rate threshold, maintaining the high reliability of the system.

[0186] In summary, through innovations in structural design, signal processing mechanisms, and system compatibility, the above-described implementation methods demonstrate, through experimental results, the superior performance advantages of the proposed all-optical-assisted, single-receiver-based free-space light and millimeter-wave / terahertz fusion transmission system. The system fully utilizes the large bandwidth characteristics of photons to achieve efficient all-optical generation and reception of broadband millimeter-wave / terahertz signals, overcoming the bandwidth and complexity bottlenecks of traditional systems in electrical up-conversion and multi-receiver architectures. Simultaneously, by leveraging the coordinated design of the optical domain center frequency, unified reception of free-space light and millimeter-wave / terahertz signals is achieved, significantly simplifying the receiving structure and improving system resource utilization.

[0187] Furthermore, this application constructs a signal fusion mechanism with adaptive joint processing capabilities, which can dynamically select independent or joint processing strategies based on channel conditions. Combined with ADCT and HARQ mechanisms, it enhances the system's robustness and reliability in complex environments. The system architecture is inherently compatible with existing fiber optic communication networks and can be flexibly deployed in diverse scenarios such as ground-to-ground or low-Earth orbit satellite-to-ground communication, contributing to the construction of a highly reliable, high-capacity, and low-complexity next-generation integrated space-air-ground communication infrastructure. This fusion system provides a practical solution for future high-frequency, high-bandwidth communication, possessing broad application prospects and promotional value.

[0188] It should be noted that in this patent application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this patent application, if it refers to performing an action according to an element, it means performing the action at least according to that element, including two cases: performing the action only according to that element, and performing the action according to that element and other elements. Expressions such as "multiple," "repeatedly," and "various" include two, two times, two kinds, and more than two, more than two times, and more than two kinds.

[0189] All documents mentioned in this application are considered to be incorporated in their entirety into the disclosure of this application so that they can serve as a basis for modifications if necessary. Furthermore, it should be understood that after reading the foregoing disclosure of this application, those skilled in the art can make various alterations or modifications to this application, and these equivalent forms also fall within the scope of protection claimed in this application.

Claims

1. A free-space light and millimeter-wave / terahertz fusion transmission system, characterized in that, include: The transmitter includes a fusion signal generation module (101), an electro-optical conversion modulation module (102), an optical-electrical conversion millimeter-wave / terahertz generation module (103), and a fusion transmitting antenna module (104); wherein: the fusion signal generation module (101) is used to generate an electrical signal to be transmitted according to the application scenario requirements; the electro-optical conversion modulation module (102) is used to modulate the electrical signal to be transmitted onto the corresponding laser carrier to generate a free-space optical modulation signal and a millimeter-wave / terahertz modulation optical signal; the optical-electrical conversion millimeter-wave / terahertz generation module (103) is used to generate a millimeter-wave / terahertz electrical signal from the millimeter-wave / terahertz modulation optical signal through photoelectric beat frequency conversion; and the fusion transmitting antenna module (104) is used to simultaneously transmit the millimeter-wave / terahertz electrical signal and the free-space optical modulation signal. The base station includes a fusion receiving antenna module (105) and an electro-optical conversion millimeter-wave / terahertz signal receiving module (106); wherein: the fusion receiving antenna module (105) is used to receive the millimeter-wave / terahertz electrical signal and the free-space optical modulation signal; the electro-optical conversion millimeter-wave / terahertz signal receiving module (106) is used to convert the received millimeter-wave / terahertz electrical signal into an optical signal, and fuse it with the received free-space optical modulation signal to form a fusion optical signal, which is then transmitted to the central office via optical fiber; The central office includes an optical coherent receiving module (107) and a fusion signal processing module (108); wherein: the optical coherent receiving module (107) is used to receive the fused optical signal through a single optical coherent receiver and perform photoelectric conversion; the fusion signal processing module (108) is used to demodulate and fuse the photoelectric converted signal to restore the original transmission information.

2. The free-space light and millimeter-wave / terahertz fusion transmission system according to claim 1, characterized in that, The fusion signal generation module (101) can generate free-space optical signals and millimeter-wave / terahertz signals according to the channel environment. The free-space optical signals and the millimeter-wave / terahertz signals have the same or different bandwidths to adapt to the inconsistent channel bandwidths supported by the two in actual communication. The bandwidth of the free-space optical signal is B. FSO The bandwidth of millimeter-wave / terahertz signals is B. RF ; The millimeter-wave / terahertz signal can transmit signals that are unrelated to or related to free-space optical signals according to different operating modes, so as to improve the overall capacity or reliability of the system. When improving reliability, the millimeter-wave / terahertz signal is a sampled portion of the free-space optical signal. If the sampling rate is x, then the bandwidth of the millimeter-wave / terahertz signal satisfies B. RF =B FSo / x; where B FSO B represents the bandwidth of the free-space optical signal. RF This represents the bandwidth of the millimeter-wave / terahertz signal, and x represents the sampling rate. The fusion signal processing module (108) selects the corresponding fusion processing mode according to the system's operating status.

3. The free-space light and millimeter-wave / terahertz fusion transmission system according to claim 1, characterized in that, The optical / electric conversion millimeter-wave / terahertz generation module (103) includes a first laser, a first coherent modulator, a third laser, a first optical coupler, and an emission optical / electric converter; The center frequency of the first laser output is f c1 The optical signal, after being modulated by the first coherent modulator, is transmitted through the first optical coupler to the third laser, which emits a center frequency of f. c3 Local oscillator optical coupling, where f c3 =f c1 +f RF ; After the coupled optical signal undergoes the transmitted light-to-electrical conversion, a frequency of f is generated. c3 -f c1 =f RF Millimeter-wave / terahertz signals; where f c1 f represents the center frequency of the first laser. c3 f represents the center frequency of the third laser. RF Indicates the frequency of the millimeter-wave / terahertz signal; The millimeter-wave / terahertz signal is transmitted into free space through the millimeter-wave / terahertz antenna in the fused transmit antenna module (104).

4. The free-space light and millimeter-wave / terahertz fusion transmission system according to claim 1, characterized in that, The electro-optical conversion millimeter-wave / terahertz signal receiving module (106) includes a fourth laser and a receiving electro-optical conversion module; The millimeter-wave / terahertz electrical signal received by the fusion receiving antenna module (105) is modulated onto the optical signal of the fourth laser through the ultra-high bandwidth thin-film lithium phosphate MZM in the receiving electro-optical conversion module. The center frequency of the fourth laser is f. c4 The MZM operates at the carrier suppression point; The modulated optical signal is coupled with the free-space optical signal received by the fusion receiving antenna module (105) and transmitted to the central office via a single-mode optical fiber.

5. The free-space light and millimeter-wave / terahertz fusion transmission system according to claim 1, characterized in that, The signal light frequency f of the fourth laser of the base station c4 and the local oscillator frequency f of the fifth laser in the central office c5 The design ensures that both the upper sideband of the electro-optically converted millimeter-wave / terahertz signal and the free-space optical signal fall within the bandwidth of the coherent receiver at the central office. The center frequency of the upper sideband of the millimeter-wave / terahertz signal is f. c4 +f RF The bandwidth is B RF ; The center frequency of the free-space optical signal is f. c2 Maximum bandwidth is The guard interval between the millimeter-wave / terahertz signal and the free-space optical signal in the receiver is f. guard ; The f c4 Satisfying Relationship: The maximum bandwidth of the coherent receiver is B. Rx ; The f c5 Satisfying Relationship: Among them, f c2 f represents the center frequency of a free-space optical signal. c4 f represents the center frequency of the fourth laser. c5 f represents the center frequency of the fifth laser. RF B represents the frequency of millimeter-wave / terahertz signals. RF Indicates the bandwidth of millimeter-wave / terahertz signals. f represents the maximum bandwidth of a free-space optical signal. guard B represents the guard interval frequency. Rx This indicates the maximum bandwidth of the coherent receiver.

6. The free-space light and millimeter-wave / terahertz fusion transmission system according to claim 1, characterized in that, The fusion signal processing module (108) performs down-conversion and matched filtering on the fusion signal, and after filtering out out-of-band signals, obtains the signals of the millimeter wave / terahertz and free space light links respectively. The fusion signal processing module (108) directly obtains the communication information and calculates the bit error rate, or introduces adaptive diversity combination technology (ADCT) based on maximum ratio combining and cascaded hybrid automatic repeat request mechanism (ccHARQ) for subsequent optional fusion signal processing.

7. A method for operating the free-space light and millimeter-wave / terahertz fusion transmission system according to claim 1, characterized in that, Includes the following steps: The fusion signal generation module (101) in the transmitter generates a corresponding fusion signal according to the application scenario requirements; The millimeter-wave / terahertz signal and the free-space optical signal are modulated onto the laser by the electro / optical conversion modulation module (102) in the transmitter, respectively; The transmitter generates millimeter-wave / terahertz signals through the optical / electric conversion millimeter-wave / terahertz generation module (103), and transmits the millimeter-wave / terahertz signals and the free-space light signals through the fusion transmitting antenna module (104). The millimeter-wave / terahertz signal and the free-space optical signal are fused and received in the optical domain through the fusion receiving antenna module (105) and the electro-optical conversion millimeter-wave / terahertz signal receiving module (106) of the base station, and then transmitted to the central office through optical fiber. The fused signal is received by optical-to-electric conversion through the optical coherent receiving module (107) in the central office, and then processed by the fused signal processing module (108).

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