Afdm multi-domain index transmission system and method for optical transport network

Abstract

The application discloses an AFDM multi-domain index transmission system and method for an optical front transmission network, and the system comprises: a control center side which is used for splitting a to-be-transmitted original bit stream to form a low-frequency control signal and a high-frequency service signal, and forming a mixed AFDM front transmission signal after frequency division multiplexing; an RRU side which is used for converting the mixed AFDM front transmission signal into a mixed electrical signal; a low-frequency control frame processing branch which extracts a low-frequency AFDM control frame; a high-frequency radio frequency forwarding branch which retains a mixed radio frequency signal containing a low-frequency reference component and a high-frequency service component, and sequentially selects corresponding antenna emission in a high-frequency service time slot; and a target user side which is used for restoring a communication signal from the received high-frequency AFDM-IM service signal. The application realizes the unified organization of space control, service transmission and local echo perception on the premise of maintaining the low complexity of the remote radio frequency unit.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and in particular to an AFDM multi-domain indexed transmission system and method for optical fronthaul networks. Background Technology

[0002] In Centralized Radio Access Networks (C-RAN), the optical fronthaul link handles signal distribution between the centralized processing unit and remote radio units. With the continuous increase in access density and antenna size, the number and distribution of remote nodes are large. If the traditional remote architecture, which includes heavy baseband processing, numerous radio links, and complex control modules, is still used, hardware stacking, energy consumption growth, and operational pressure will rapidly increase. Analog Radio over Fiber (A-RoF) technology can retain more signal generation, beam control, and resource scheduling processes at the central side, thus having a natural advantage in low-latency, low-complexity fronthaul scenarios. Existing technologies, with the aid of A-RoF-assisted optical domain Multiple-Input Multiple-Output (MIMO) signal processing, can significantly reduce the structural and processing burden of remote access units, providing a clear direction for building lightweight remote systems.

[0003] On the other hand, under high-speed mobile and time-frequency channel conditions, Orthogonal Frequency Division Multiplexing (OFDM) is susceptible to inter-carrier interference caused by Doppler spread, making it difficult to balance transmission reliability with subsequent sensing processing. Affine Frequency Division Multiplexing (AFDM), relying on Discrete Affine Fourier Transform (DAFT) to establish the modulation and demodulation process, can improve path separation capabilities under dual-channel conditions through parameter design and has good adaptability in high-mobility and integrated sensing and communications (ISAC) scenarios.

[0004] Building upon AFDM, research on index modulation continues to advance. Existing technologies have proposed a basic Affine Frequency Division Multiplexing with Index Modulation (AFDM-IM) framework, which carries additional information through subcarrier activation modes, improving the flexibility of resource utilization. Further, existing technologies have proposed pre-modulation parameter domain indexing schemes for AFDM, mapping some information to a pre-modulation parameter set. Existing technologies have also combined parameter configuration with subcarrier activation to carry control information, forming a dual-index modulation scheme. Further, existing technologies have combined the spatial domain and DAFT domain to study MIMO-AFDM multi-domain generalized index modulation. These works have demonstrated that the parameter domain and subcarrier domain of AFDM can be used to expand the information carrying dimension, but the focus remains primarily on the wireless link itself, especially receiver joint detection, bit error rate analysis, and spectral efficiency improvement.

[0005] Meanwhile, AFDM has also begun to be used in ISAC scenarios. Existing research shows that, under the condition that the sensing reference is known and remains stable within the processing window, AFDM can obtain sensing information such as target distance and velocity through correlation processing or transform domain processing. However, this precisely exposes a key contradiction in further system integration. For sensing, the reference template needs to be stable. For index extension, the parameter domain and resource domain often need to change dynamically. For A-RoF fronthaul, the remote end must avoid undertaking complex time-slot-by-time detection and control recovery tasks as much as possible. In other words, although existing technologies have solved some problems in remote end simplification, high-mobility transmission, index extension, and sensory processing respectively, when these capabilities need to be implemented simultaneously in the same optical fronthaul system, a situation arises where three goals are difficult to achieve simultaneously: first, remote end lightweighting requires the control recovery process to be as simple as possible; second, multi-domain index extension requires the control dimensions to be as rich as possible; and third, sensory integration requires maintaining a stable reference within the processing window.

[0006] In other words, the existing technology still has the following shortcomings: The conflict between sensing reference stability and dynamic index changes: Existing AFDM integrated communication and sensing schemes typically use a fixed sensing reference or a known probe waveform for sensing processing. That is, within a sensing processing window, the reference signal generally remains unchanged to facilitate correlation calculations and parameter estimation at the receiver. However, if dynamically changing AFDM-IM waveforms are directly used as the sensing reference, their parameter configuration and subcarrier activation mode will change along with the index bits, thereby disrupting the stable reference conditions required for sensing and creating a conflict between communication index expansion and sensing reference maintenance.

[0007] The contradiction between time-slot-by-time control delivery and remote simplification: In existing space control schemes, if control commands are delivered sequentially according to each high-frequency transmission time slot, the remote RF unit needs to repeatedly perform control detection and switching decisions in each time slot. This approach increases control overhead and the burden on remote control, which is detrimental to maintaining the remote simplification advantage emphasized by A-RoF fronthaul.

[0008] The lack of multi-functional collaborative solutions in optical fronthaul architecture: Existing spatial modulation, multi-domain indexed modulation, and AFDM integrated communication and sensing solutions mostly focus on a single function in the wireless link, with little consideration given to the relationship between co-transmission of control and communication services, maintenance of fixed sensing references, and low complexity at the remote end in optical fronthaul scenarios. Therefore, existing technologies often struggle to simultaneously meet the requirements of control signal transmission, stable sensing references, and simplification at the remote end.

[0009] In other words, most existing technical solutions can only compromise between two of the objectives, and there is still a lack of a unified system solution that can simultaneously achieve low-complexity remote execution, multi-domain index control, and stable awareness reference in an optical fronthaul architecture. This is precisely the core problem that this invention aims to solve. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention proposes an AFDM multi-domain indexed transmission system and method for optical fronthaul networks, which achieves unified organization of spatial control, service transmission, and local echo sensing while maintaining low-complexity execution of remote radio frequency units.

[0011] Specifically, this is achieved through the following technical solution: In a first aspect, the present invention proposes an AFDM multi-domain indexed transmission system for optical fronthaul networks, comprising: The control center side includes a bit splitting and function mapping module, a low-frequency control signal forming module, a high-frequency service signal forming module, a frequency division multiplexer, and an MZM fiber optic fronthaul link. The control center side is used to split the original bit stream to be transmitted into low-frequency control signals and high-frequency service signals, which are then frequency-division multiplexed to form a hybrid AFDM fronthaul signal, which is then sent to the RRU side through the MZM fiber optic fronthaul link. On the RRU side, there are photodetectors, power dividers, low-frequency control frame processing branches, high-frequency radio frequency forwarding branches, space switches and transmitting antennas, and echo processing branches. The RRU side converts the hybrid AFDM fronthaul signal into a hybrid electrical signal, which is then divided into low-frequency control frame processing branches and high-frequency radio frequency forwarding branches. The low-frequency control frame processing branch extracts the low-frequency AFDM control frame for fixed reference buffering and control word recovery. The high-frequency radio frequency forwarding branch retains the hybrid radio frequency signal containing low-frequency reference components and high-frequency service components, and sequentially selects the corresponding antenna in the high-frequency service time slot to transmit the hybrid radio frequency signal to the target user side. After the target echo returns, the RRU side extracts the low-frequency component corresponding to the low-frequency fixed reference block from the echo, performs correlation processing with the fixed reference copy in the local buffer, obtains sensing information, and transmits it back to the control center side. On the target user side, it is used to recover the communication signal from the received high-frequency AFDM-IM service signal, and it carries parameter field index, subcarrier field index and modulation communication bits.

[0012] Secondly, this invention also proposes an AFDM multi-domain indexed transmission method for optical fronthaul networks, which includes the following steps: On the control center side, the original bit stream to be transmitted is split into bits and mapped to functions. A portion of the bits is used to form low-frequency control signals, and another portion of the bits is used to form high-frequency service signals. The low-frequency control signals and high-frequency service signals are frequency-division multiplexed to form a hybrid AFDM fronthaul signal, which is sent to the RRU side through the MZM fiber optic fronthaul link. On the RRU side, the photodetector converts the hybrid AFDM fronthaul signal into a hybrid electrical signal, which is divided into a low-frequency control frame processing branch and a high-frequency radio frequency forwarding branch. The low-frequency control frame processing branch extracts the low-frequency AFDM control frame from near the zero frequency and is used for fixing the reference buffer and control word recovery. The high-frequency radio frequency forwarding branch retains the hybrid radio frequency signal containing the low-frequency reference component and the high-frequency service component, and sequentially selects the corresponding antenna in the high-frequency service time slot to transmit the hybrid radio frequency signal to the target user side. On the target user side, the received high-frequency AFDM-IM service signal is recovered into a communication signal, which carries parameter field index, subcarrier field index and modulation communication bits; After the target echo returns, the RRU side extracts the low-frequency component corresponding to the low-frequency fixed reference block from the echo, performs related processing with the local cached fixed reference copy, obtains sensing information, and transmits it back to the control center.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes an AFDM multi-domain indexed transmission system and method for optical fronthaul networks. It constructs low-frequency AFDM control frames and high-frequency AFDM-IM service windows within the same fronthaul link, achieving coordination between low-frequency control, low-frequency reference sensing, and high-frequency service transmission. Based on this, the system can simultaneously support service transmission, spatial control, and local sensing within the same optical fronthaul link, avoiding the structural complexity of building separate communication, control, and sensing links. This facilitates the formation of a more compact integrated communication and sensing system and is suitable for high mobility, dual-selection channels, and centralized optical fronthaul access scenarios. While retaining AFDM's adaptability to high mobility environments, it also addresses the needs of simplified remote optical fronthaul and integrated communication and sensing.

[0014] Building upon this, a low-frequency AFDM control frame structure consisting of a fixed reference block and a control block is proposed. The fixed reference block remains unchanged across multiple control frames and participates in radiation as a low-frequency reference component in the actual transmitted signal. The control block independently carries the space control word, used to recover the antenna switching sequence for subsequent service windows. Furthermore, this low-frequency fixed reference block is used for local echo correlation sensing. It serves both as a stable reference resource in the control frame and as a low-frequency reference component in the mixed RF transmitted signal, participating in spatial radiation. This allows the RRU side to perform correlation processing using a local cache copy and the corresponding low-frequency component in the echo. Thus, while maintaining a stable sensing reference, dynamic control and service transmission are supported, avoiding the reference template change problem caused by directly using the dynamic AFDM-IM service waveform as the sensing reference, and improving the stability of echo correlation processing.

[0015] To achieve efficient spatial scheduling, a mapping mechanism from control words to multi-timeslot antenna switching sequences is proposed. This ensures that the low-frequency control block recovers not a single instantaneous antenna number, but a spatial scheduling plan for a subsequent service window. This allows for the management of antenna switching for multiple subsequent high-frequency service time slots through a single control recovery, reducing the redundant processing and control overhead caused by time-slot-by-slot control detection, and contributing to improved remote execution efficiency.

[0016] In receiving processing, a small-scale DAFT candidate detection plus lookup table approach is proposed on the RRU side to recover the control word and antenna sequence, while the recovery of parameter domain index and subcarrier domain index is retained on the target user side, thus separating the responsibilities of control execution on the RRU side from those of service demodulation on the user side. This significantly reduces the processing burden on the RRU side, which mainly performs low-frequency control recovery, antenna switching execution, and local echo correlation processing, without having to undertake the complete user-side service demodulation task, which is more in line with the design goal of lightweight remote end in A-RoF fronthaul. This architecture clearly defines the functional boundaries of control, sensing, and service recovery, making the tasks of the RRU side and the target user side clearer, reducing the possibility of mutual interference between different processing links, and facilitating subsequent engineering implementation and system expansion. Attached Figure Description

[0017] To more clearly illustrate the solutions in this invention, the accompanying drawings used in the description of the embodiments of this invention will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a general block diagram of the AFDM multi-domain indexed transmission system for optical fronthaul networks according to the present invention. Figure 2 This is a schematic diagram of the low-frequency control and high-frequency service frame structure of the present invention; Figure 3 This is a schematic diagram of the spectrum evolution of the present invention; Figure 4 This is a flowchart illustrating the AFDM multi-domain indexed transmission method for optical fronthaul networks according to the present invention. Detailed Implementation

[0019] The technical solutions of this invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are all within the scope of protection of this invention.

[0020] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0023] The following description, in conjunction with the system block diagram and frame structure diagram, explains the structural composition, signal construction, RRU-side processing flow, and target user-side communication recovery process of the present invention.

[0024] like Figure 1 As shown, the present invention provides an AFDM multi-domain indexed transmission system for optical fronthaul networks, comprising: On the control center side, the original bit stream to be transmitted is split into bits and mapped to functions. A portion of the bits is used to form low-frequency control signals, and another portion of the bits is used to form high-frequency service signals. The low-frequency AFDM control frame and the high-frequency AFDM-IM service waveform are frequency-division multiplexed to form a hybrid AFDM fronthaul signal, which is then transmitted to the remote radio unit (RRU) side through a Mach-Zehnder modulator (MZM) fiber optic fronthaul link. On the RRU side, the photodetector converts the hybrid AFDM fronthaul signal into a hybrid electrical signal, which is then split into a low-frequency control frame processing branch and a high-frequency radio frequency forwarding branch by a power divider. The low-frequency control frame processing branch extracts the low-frequency AFDM control frame from near zero frequency for fixed reference buffering and control word recovery. The high-frequency radio frequency forwarding branch retains the hybrid radio frequency signal containing low-frequency reference components and high-frequency service components, and radiates the hybrid radio frequency signal to the target user side through a 1×N switch, a radio frequency (RF) circulator (RF circulator for short) and a transmitting antenna. After the target echo returns, the RRU side extracts the low-frequency component corresponding to the low-frequency fixed reference block from the echo and performs correlation processing with the fixed reference copy in the local buffer to obtain the perceived information of time delay, Doppler, distance and speed. The time delay and Doppler information are then transmitted back to the control center side. On the target user side, the received high-frequency AFDM-IM service signal is sequentially processed through carrier demodulation, serial-to-parallel conversion, DAFT processing, data demodulation, and parallel-to-serial conversion to recover the communication signal. The recovered communication signal carries parameter field indexes, subcarrier field indexes, and modulated communication bits.

[0025] The control center side includes a bit splitting and function mapping module, a low-frequency control signal forming module, a high-frequency service signal forming module, a frequency division multiplexer, and an MZM fiber optic fronthaul link. At the control center, the original bit stream to be transmitted first enters the control center for bit splitting and function mapping. A portion of the bits is used to form the low-frequency control signal, and another portion is used to form the high-frequency service signal. The low-frequency control signal forming module includes a fixed reference block and a control block. The fixed reference block is a predefined known reference signal, and the control block carries spatial control information, which can be mapped to an antenna index or antenna switching sequence through preset parameter combinations and subcarrier modes. In the low-frequency control signal forming module, after the bits are mapped onto the AFDM waveform, they pass through a digital-to-analog converter (DAC) and a low-pass filter (LPF) to form a low-frequency control signal that is a hybrid AFDM fronthaul signal. In the high-frequency service signal formation module, after bits are mapped onto the AFDM-IM waveform, they are up-converted to the selected band by a digital-to-analog converter (DAC), and then pass through a bandpass filter (BPF) to form a high-frequency service signal that is a hybrid AFDM fronthaul signal. This signal carries service transmission information and includes parameter field indexes, subcarrier field indexes, and modulated communication bits. The low-frequency control signal and the high-frequency service signal are frequency-division multiplexed to form a hybrid AFDM fronthaul signal, which is used as the driving signal for the MZM and modulated onto the optical carrier. This signal is then transmitted to the RRU side via the optical fiber fronthaul link. This achieves coordinated transmission of spatial control information and service information within the same fronthaul link, avoiding the additional signaling overhead and complex multi-point coordination introduced by separate transmission, maintaining the simplicity of the optical fronthaul structure, and improving fronthaul resource utilization.

[0026] The RRU side includes a photodetector, a power divider, a low-frequency control frame processing branch, a high-frequency RF repeater branch, a space switch and transmitting antenna, and an echo processing branch. On the RRU side, the photodetector converts the hybrid AFDM fronthaul signal into a hybrid electrical signal, which is then split into a low-frequency branch and a high-frequency branch by the power divider. In the low-frequency control frame processing branch, the low-frequency branch extracts the low-frequency AFDM control frame through a low-pass filter and enters the low-frequency synchronization and segmentation module. This module synchronizes the entire low-frequency control block content according to the preset frame structure and the known fixed reference block content, then extracts the known fixed reference block portion, dividing the low-frequency AFDM control frame into a fixed reference block and a control block. The extracted fixed reference block is sent to the local reference buffer module as a local known reference for subsequent echo correlation processing; the extracted control block is sent to the control recovery module to recover the corresponding antenna control command or antenna switching sequence. The high-frequency radio frequency forwarding branch retains the mixed radio frequency signal containing low-frequency reference components and high-frequency service components, which is then amplified by the radio frequency amplifier and sent to the RF circulator through a 1×N switch and radio frequency forwarding link. Under the action of the space control command recovered by the low-frequency branch, the corresponding transmitting antenna is selected sequentially in the transmitting antenna array for space transmission in multiple subsequent transmission time slots.

[0027] During the sensing process, the mixed signal radiated by the transmitting antenna illuminates the sensing target and generates a sensing echo. The sensing echo enters the echo processing branch through the receiving antenna and RF circulator, and is then converted to the corresponding processing frequency band by the echo down-conversion module. The digital correlator uses a copy of the fixed reference block stored in the local reference buffer module to perform correlation processing with the corresponding components in the echo, thereby estimating sensing parameters such as distance and velocity, and obtaining sensing information such as time delay, Doppler, distance and velocity. The time delay and Doppler information are then transmitted back to the control center for analysis.

[0028] The target user-side communication recovery is mainly performed on the high-frequency AFDM-IM service waveform, while the RRU side does not undertake the complete user service demodulation task, but is only responsible for low-frequency control recovery, high-frequency radio frequency forwarding and local echo-related processing.

[0029] The spectral evolution of the AFDM multi-domain indexed transmission system for optical fronthaul networks, as described in this invention, is as follows: Figure 3As shown. On the control center side, the low-frequency AFDM control / reference subband and the high-frequency AFDM-IM service subband are first frequency-division multiplexed in the electrical domain to form a hybrid fronthaul electrical signal. The low-frequency AFDM subband is located near the zero frequency in the electrical domain and contains a fixed reference block and a control block; the high-frequency AFDM-IM subband is located at a higher radio frequency position and carries parameter domain indexes, subcarrier domain indexes, and modulated communication bits. After this hybrid electrical signal drives the MZM, both the low-frequency AFDM subband and the high-frequency AFDM-IM subband are modulated near the optical carrier, appearing as electro-optical modulation sidebands on both sides of the optical carrier. After fiber fronthaul and photodetection on the RRU side, the optical domain sidebands are restored to a hybrid radio frequency signal in the electrical domain, where the low-frequency AFDM control / reference component remains near the zero frequency, and the high-frequency AFDM-IM service component remains in the radio frequency service subband. The local low-frequency processing branch on the RRU side extracts low-frequency AFDM control frames from near the zero frequency for fixed reference buffering and control word recovery. The RF transmission branch retains a mixed RF signal containing low-frequency reference components and high-frequency service components, and radiates the mixed RF signal to the target user side through a 1×N switch, an RF circulator, and a transmit antenna. After the target echo returns, the RRU side extracts the low-frequency component corresponding to the low-frequency fixed reference block from the echo and performs correlation processing with the fixed reference copy in the local buffer to obtain sensing information such as time delay, Doppler, range, and velocity.

[0030] In this invention, both low-frequency control signals and high-frequency service signals can be generated using AFDM modulation. Let... The length of the AFDM discrete transform. Input symbols for the DAFT field. Given the time-domain AFDM signal obtained by IDAFT transformation, the AFDM modulation process can be expressed as follows: in, , and Here are two chirp parameters in AFDM modulation; m is the subcarrier index where the input symbol is located, which is also the input symbol index. The formula means that for each n, m is traversed and summed; s[i] is the i-th input symbol in the DAFT field, and j is the imaginary unit. Subsequent low-frequency control blocks and high-frequency service blocks are generated based on the above AFDM modulation formula, the difference being the different DAFT field input vectors and parameter selection methods.

[0031] The construction of low-frequency AFDM control frames, such as Figure 2As shown, the low-frequency AFDM control frame adopts a two-layer structure, including a fixed reference block and a control block. The fixed reference block consists of one or more preset digital AFDM reference symbols. Its AFDM parameters, active resources, and symbol content remain unchanged across multiple control frames. It is used to extract local references on the RRU side and participate in subsequent echo correlation processing. The control block is used to carry spatial control information. The RRU side detects this control block, recovers the corresponding control word, and further generates the antenna switching sequence in the subsequent high-frequency AFDM-IM service window.

[0032] Let a set of control bits to be transmitted be... To balance control flexibility and detection complexity, this set of control bits is divided into two parts: parameter selection bits and subcarrier selection bits. The parameter selection bits are used to select a set of control parameters from a finite number of AFDM parameter combinations, for example... , Or a preset combination of the two. The subcarrier selection bit is used to select an activation position or combination from a finite number of control subcarrier activation schemes. The two are combined to form a control word number. , can be represented as:

[0033]

[0034] in, Indicates the parameter selection bit. Indicates the subcarrier selection bit. This represents the control word mapping function. The control word here... It does not directly represent a specific instantaneous antenna number, but rather corresponds to the antenna switching plan within a subsequent high-frequency AFDM-IM service window. In its specific construction, a set of control resources is first reserved in the DAFT domain. Subsequently, according to the control word The corresponding AFDM parameter combinations and control subcarrier activation schemes generate sparse control vectors in the DAFT domain. This vector takes a non-zero value only at the selected control subcarrier positions, and is set to zero at all other positions. Then, an IDAFT operation is performed on this control vector to obtain the time-domain control waveform. , can be represented as: In the formula, Indicates the length of the AFDM discrete transform. and This indicates the AFDM parameters of the control block, determined by the parameter selection bits. This represents the DAFT domain sparse control vector determined by the subcarrier selection bits; m is the subcarrier index where the input symbol is located, which is also the input symbol index. The formula means that for each n, m is traversed and summed. That is, the i-th input symbol of the sparse control vector, where j is the imaginary unit.

[0035] In the digital baseband, a low-frequency AFDM control frame is formed by splicing a fixed reference block and a control block end-to-end. If the fixed reference block is denoted as... The time-domain waveform corresponding to the control block is denoted as The low-frequency AFDM control frame can then be simplified as:

[0036] After being converted into a continuous-time low-frequency electrical signal by a DAC, the low-frequency AFDM control frame occupies the low-frequency control sub-band in the hybrid drive signal. Therefore, from a temporal perspective, the low-frequency AFDM control frame has a block structure consisting of a fixed reference block and a control block; from a spectral perspective, it manifests as a control sub-band located in the low-frequency region and is transmitted together with the high-frequency AFDM-IM service signal via frequency division.

[0037] The construction of a high-frequency AFDM-IM service window, such as... Figure 2 As shown, a low-frequency AFDM control frame is used to control subsequent... Each high-frequency service time slot. The low-frequency AFDM control frame includes a fixed reference block and a control block. The fixed reference block remains unchanged across multiple low-frequency AFDM control frames and participates in space radiation as a low-frequency reference component in the actual transmitted signal; the control block is used to carry space control information and restores the antenna switching sequence for subsequent high-frequency AFDM-IM service windows on the RRU side.

[0038] Let the control word recovered by the low-frequency control block be The corresponding antenna switching sequence can be represented as: in, Indicates the first Each high-frequency service time slot corresponds to a transmit antenna number. In other words, the RRU side does not need to re-recover control information for each high-frequency time slot; instead, it recovers the information through a single low-frequency AFDM control frame to obtain subsequent... Antenna switching plan for each high-frequency service time slot.

[0039] The high-frequency AFDM-IM service window is provided by It consists of several high-frequency service time slots. Each high-frequency service time slot primarily carries AFDM-IM data sub-blocks. This data sub-block is used for communication recovery on the target user side. The low-frequency fixed reference block mainly serves local echo sensing, the low-frequency control block mainly serves antenna switching control, and the high-frequency AFDM-IM data sub-block mainly serves user-side service transmission. All three are transmitted in the same optical fronthaul link, but they are distinguished in terms of frequency location and functional division.

[0040] For the One high-frequency service time slot, DAFT domain input symbol Replaced with AFDM-IM service vector This service vector is generated jointly by parameter field index bits, subcarrier field index bits, and modulation communication bits. Specifically, the parameter field index bits are used to select the AFDM parameters of the service block, the subcarrier field index bits are used to select the active subcarrier mode, and the modulation communication bits are mapped to constellation symbols. The time-domain AFDM-IM service waveform for each service time slot is generated by the above AFDM modulation formula, denoted as . .

[0041] in, In the formula, Indicates the length of the AFDM discrete transform. Indicates the first AFDM-IM service vectors of high-frequency service time slots in the DAFT domain Preset business parameters can be used. Can be selected from the candidate set by parameter field index. The corresponding parameter can be denoted as... and superscript Indicates a business block. Indicates the business parameter index number.

[0042] On the control center side, low-frequency AFDM control frames and high-frequency AFDM-IM service windows are combined into a hybrid AFDM fronthaul signal using frequency division multiplexing. The low-frequency AFDM control frame is converted into a low-frequency electrical control signal after passing through a digital-to-analog converter (DAC), while the high-frequency AFDM-IM service waveform is shifted to the high-frequency service subband via an RF link. The combined signal is then modulated onto the optical carrier as the driving signal for the MZM and transmitted to the RRU side via the fiber optic fronthaul link.

[0043] On the RRU side, the hybrid electrical signal after photodetection is filtered by a low-pass filter to extract the low-frequency AFDM control frame, and then filtered by a wideband band-pass filter to extract the hybrid radio frequency signal containing the low-frequency fixed reference component and the high-frequency AFDM-IM service component. The fixed reference block in the low-frequency AFDM control frame is cached as a local reference copy and used for correlation processing with the corresponding low-frequency component in the echo to estimate the time delay and Doppler information. The control block in the low-frequency AFDM control frame is used to recover the control word. And further obtain the antenna switching sequence. The high-frequency AFDM-IM service signal then follows this antenna switching sequence in subsequent... The signal is sequentially transmitted to the corresponding antenna in each high-frequency service time slot. Thus, the signal actually radiated by the antenna simultaneously contains low-frequency fixed reference components and high-frequency AFDM-IM service components. The low-frequency fixed reference components are used to form a stable echo sensing reference, while the high-frequency AFDM-IM service components are used for communication recovery on the target user side. After the echo returns, the RRU extracts the low-frequency component corresponding to the low-frequency fixed reference block from the echo and performs correlation processing with a locally cached fixed reference copy to estimate the time delay and Doppler information.

[0044] On the RRU side, low-frequency control recovery and antenna scheduling are implemented. After photoelectric detection, the recovered hybrid electrical signal is divided into a local low-frequency processing branch and an RF transmission branch. The local low-frequency processing branch extracts the low-frequency AFDM control frame using a low-pass filter (LPF). This control frame includes a fixed reference block and a control block. The RRU side first uses the fixed reference block to synchronize the control frame and caches this fixed reference block as a local reference copy for subsequent echo-related processing. Subsequently, the RRU side performs low-complexity detection on the control block to recover the control word. .

[0045] To reduce the processing complexity on the RRU side, this invention preferably employs small-scale DAFT candidate detection. Let the received control block be... The system pre-sets a finite number of AFDM control parameter combinations and a finite number of control subcarrier activation schemes. For the first... Group candidate control parameters, RRU side Perform the DAFT transform with the corresponding parameters to obtain in, Indicates the use of the first The candidate AFDM control parameters are processed using DAFT. This indicates the corresponding DAFT field output.

[0046] Subsequently, the RRU side uses the preset control resource set. The energy of each candidate subcarrier activation scheme is measured. Let the first... The activation set corresponding to the control subcarrier activation scheme is: Then the following metric function can be used: The first term represents the energy at the candidate activation site, and the second term represents the leakage energy at the inactive site. This is used for leakage suppression weights. This metric considers both the energy concentration at active positions of the control subcarrier and the suppression of residual energy at inactive positions, thereby improving the reliability of control word decisions.

[0047] The RRU side searches for the maximum metric value among all candidate parameter combinations and candidate subcarrier activation schemes to obtain the estimation result: Furthermore, according to Obtain control word estimates in, This represents the control word mapping function. Control word It doesn't simply correspond to a single instantaneous antenna number, but rather to the spatial scheduling plan within a subsequent high-frequency AFDM-IM service window. The RRU side obtains the antenna switching sequence corresponding to this control word through a table lookup: in, For length is Antenna switching sequence, Indicates the first The transmit antenna number that should be connected to each high-frequency service time slot.

[0048] Therefore, the RRU side does not need to re-perform control detection in every high-frequency service time slot. Instead, it only needs to recover the control word once at the low-frequency AFDM control frame level and execute the switching actions of subsequent high-frequency service time slots according to the lookup table results. This approach improves the effective control capability of the low-frequency AFDM control frame and reduces the control update frequency on the RRU side without introducing a complete user-side baseband demodulation chain.

[0049] The remote radio frequency unit only needs to complete control recovery, radio frequency forwarding and local related processing, without the need to deploy a complete user-side baseband demodulation chain, which significantly reduces the processing complexity, hardware cost and power consumption of the remote end, and is conducive to large-scale, high-density deployment of lightweight remote nodes; By mapping low-frequency control to a multi-slot antenna switching sequence, a single control recovery can drive the execution of antennas in multiple subsequent high-frequency transmission slots, significantly reducing the remote control signaling reception frequency and processing burden. While ensuring the real-time performance of spatial control, this further enhances the lightweight execution capability of the remote end.

[0050] The RRU side is also used for fixed reference buffering and echo-related sensing. On the RRU side, the fixed reference block is extracted by the low-frequency processing branch and buffered as a local reference copy. At the same time, the RF transmit branch retains a mixed RF signal containing low-frequency fixed reference components and high-frequency AFDM-IM service components, and transmits it from the designated antenna according to the recovered antenna switching sequence. Therefore, the actual radiated signal contains low-frequency fixed reference components, and its echo can be used for subsequent related sensing processing.

[0051] Since the low-frequency fixed reference block is also part of the actual transmitted signal, the echo reflected back from the target or environment will contain a low-frequency echo component corresponding to that fixed reference block. After the echo returns via the receiving antenna and RF circulator, it enters the echo processing branch. The echo processing branch first performs down-conversion and low-frequency component extraction on the echo to obtain the echo segment corresponding to the fixed reference block, denoted as... .

[0052] Let the fixed reference block copy of the local cache on the RRU side be... Then it can be obtained through numerical correlation. in, Indicates the relevant output, Represents discrete delay variables, This represents the conjugate delay form of the local reference copy. The location of the correlation peak is used to estimate the target echo delay. If the delay sampling point corresponding to the correlation peak is... The sampling period is The target distance can be estimated using the following formula: In the formula, This indicates the speed of electromagnetic wave propagation.

[0053] Furthermore, if correlation outputs are obtained continuously in adjacent control frames or adjacent sensing processing windows, the Doppler frequency shift can be estimated using the phase change at the correlation peak. Let the phase difference between two adjacent correlation peaks be... The time interval between the two observations is Then the Doppler frequency shift can be expressed as The corresponding speed can be expressed as In the formula, This represents the wavelength corresponding to the transmitted signal. The above-described distance and velocity estimation method is only a preferred embodiment, and the present invention is not limited to specific distance and velocity calculation formulas. In actual systems, multi-frame accumulation, peak search, or other Doppler estimation methods can also be used depending on the echo processing accuracy requirements.

[0054] It should be noted that the fixed sensing reference in this invention does not require the entire low-frequency AFDM control frame to remain unchanged, but only requires that the fixed reference block used for sensing remain stable within the processing window. The control block can change with spatial control information, and the high-frequency AFDM-IM service signal can also change with service data, but these changes do not affect the correlation between the fixed reference block and its echo components. Therefore, this method can maintain the stable reference conditions required for echo-correlated sensing while preserving dynamic control and service transmission capabilities.

[0055] The sensing results such as time delay, Doppler, distance, or speed obtained from the RRU side do not need to be transmitted back to the control center in the form of raw echo waveforms. Instead, they can be fed back to the control center as low-speed status information through the uplink control channel of the fiber optic fronthaul link. This uplink control channel can be implemented using a shared fiber transmission method with the downlink fronthaul, for example, by different wavelengths, different time slots, or different low-frequency control subbands; alternatively, it can use a separate fiber or other low-speed control interface depending on the system deployment conditions. The above-described feedback method does not limit the scope of protection of this invention.

[0056] By employing a stable sensing reference retention mechanism, the reference required for sensing processing is ensured to remain undistorted within the processing window during dynamic mapping of control information and service transmission. This guarantees the stability and accuracy of echo sensing without affecting the normal operation of control and services, thus achieving reliable integration of communication and sensing.

[0057] The division of labor between low-frequency control, sensing reference, and high-frequency services: In this invention, the low-frequency AFDM control frame performs two functions. First, it provides a stable reference through a fixed reference block and serves as a low-frequency reference component in the actual transmitted signal for spatial radiation, used in subsequent echo correlation sensing. Second, it recovers the spatial control word through the control block and generates the antenna switching sequence for subsequent service windows. The high-frequency AFDM-IM service window primarily undertakes the AFDM-IM communication bearer function, where service data is represented by parameter field index, subcarrier field index, and modulation communication bits, and is recovered by the target user side.

[0058] Therefore, the fixed reference buffer, spatial control recovery, antenna switching execution, and echo correlation in the system are mainly completed by the RRU side, while the parameter domain indexing, subcarrier domain indexing, and modulation communication bit recovery are assigned to the target user side. This division of labor avoids placing all index recovery and sensing tasks on the RRU side simultaneously, and also avoids directly using dynamically changing high-frequency AFDM-IM service waveforms as sensing references. This makes the boundaries between control, sensing, and service transmission clearer and more conducive to engineering implementation.

[0059] The target user side is used for communication recovery. On the target user side, the receiver receives the high-frequency AFDM-IM service signal radiated by the currently selected antenna. This signal, after carrier demodulation, synchronization, and serial-to-parallel conversion, yields the [missing information - likely a specific signal or component]. The data sub-block observation sequence for each service time slot. It should be noted that the parameter field index, subcarrier field index, and modulation communication bits are all recovered by the target user side, not by the low-frequency control branch on the RRU side. The RRU side mainly performs fixed reference buffering, spatial control recovery, antenna switching execution, and local echo correlation processing.

[0060] Let the target user side be in the first... The discrete sequence of data sub-blocks received in each service time slot is as follows: To recover the parameter field index, the receiver first assigns a number to each candidate service parameter. ,right Perform the DAFT transform with the corresponding parameters to obtain the candidate transform domain output: in, Indicates the use of the first The candidate AFDM service parameters are processed using DAFT. This indicates the corresponding transform domain output.

[0061] Subsequently, the receiver uses a predefined set of service resources. The above steps involve detecting the activation modes of each legitimate subcarrier. Let the first... The service subcarrier activation mode is Then the following metric function can be constructed: The first term represents the energy at the candidate active subcarrier position, and the second term represents the leakage energy at the inactive position. This is the leakage suppression coefficient. This metric function is used to measure the leakage suppression coefficient in the first... Group business parameters and the first The degree of energy concentration of the received signal in the DAFT domain under each activation mode.

[0062] By searching for the maximum metric value among all candidate service parameters and all activation modes, the joint estimation results of the parameter domain index and subcarrier domain index can be obtained: in, This indicates the decision result for the parameter field index. This indicates the decision result for the subcarrier domain index. According to... It is possible to determine the actual set of activated service subcarriers. .

[0063] After obtaining the set of active subcarriers, the receiver further recovers the modulated communication symbols. Let the decision be... The positions of the active subcarriers are: Its corresponding effective equivalent channel gain is The business constellation set is Then the modulation symbol at that position can be determined according to the minimum distance criterion as follows: In the formula, For the first The decision symbol on each active subcarrier, where 'a' represents a possible candidate value for the modulation order, such as ±1 in Binary Phase Shift Keying (BPSK). If the system has dedicated pilots or known training blocks, the target user side can first estimate the order. Then, the minimum distance decision is made again.

[0064] Therefore, the communication recovery process on the target user side can be summarized as follows: (1) For the received data sub-blocks Each candidate service parameter is used to perform DAFT transformation, resulting in multiple sets of candidate transform domain outputs; (2) Under each set of candidate outputs, traverse all legal service subcarrier activation modes and construct a decision metric based on the energy concentration degree and leakage suppression results; (3) Perform a joint search on the candidate service parameter set and the subcarrier activation mode set to obtain the parameter domain index estimate. and subcarrier domain index estimate ; (4) At the determined active subcarrier position, the modulation symbol decision is completed by combining the equivalent channel gain and the constellation set; (5) The parameter number, activation mode number and constellation symbol obtained from the decision are restored to parameter field index bit, subcarrier field index bit and modulation communication bit respectively through the inverse mapping table.

[0065] The above process can also be implemented using a layered detection method. For example, the receiver can first make a coarse decision on the candidate service parameters, and then narrow down the search range of the subcarrier activation mode near the coarse decision result to reduce the detection complexity on the user side. This invention is not limited to a specific maximum likelihood detection or minimum distance detection form; any method that can complete the parameter domain indexing, subcarrier domain indexing, and modulation communication bit recovery can be used as an implementation of this invention.

[0066] The target user can recover the parameter domain index, subcarrier domain index and modulated communication bits from the high-frequency AFDMIM service signal, making full use of the high spectral efficiency brought by multi-domain index modulation, and improving the service transmission capacity and demodulation flexibility.

[0067] This invention also provides an AFDM multi-domain indexed transmission method for optical fronthaul networks, which includes the following steps: On the control center side, the original bit stream to be transmitted is split into bits and mapped to functions. A portion of the bits is used to form low-frequency control signals, and another portion is used to form high-frequency service signals. The low-frequency control signals and high-frequency service signals are frequency-division multiplexed to form a hybrid AFDM fronthaul signal, which is then transmitted to the RRU side via an MZM fiber optic fronthaul link. Specifically, the information to be transmitted is split into low-frequency control information and high-frequency service information. The low-frequency control information forms a digital AFDM control frame, in which the fixed reference block remains preset and serves as the low-frequency reference component in the actual transmitted signal. The control block is mapped from control bits to control words. The corresponding AFDM control waveform; high-frequency service information forms the AFDM-IM service window, and each service time slot mainly includes a data sub-block. It is used to carry parameter domain index, subcarrier domain index and modulated communication bits; after the low-frequency AFDM control frame and the high-frequency AFDM-IM service window are frequency-division multiplexed on the control center side, they form a hybrid AFDM fronthaul signal. This hybrid signal is modulated onto the optical carrier as an MZM drive signal and transmitted to the RRU side through optical fiber.

[0068] On the RRU side, the photodetector converts the hybrid AFDM fronthaul signal into a hybrid electrical signal, which is divided into a low-frequency control frame processing branch and a high-frequency radio frequency forwarding branch. The low-frequency control frame processing branch extracts low-frequency AFDM control frames from near zero frequency for fixed reference buffering and control word recovery. The high-frequency radio frequency forwarding branch retains the hybrid radio frequency signal containing low-frequency reference components and high-frequency service components, and radiates the hybrid radio frequency signal to the target user side through a 1×N switch, an RF circulator, and a transmit antenna. Specifically, after photoelectric conversion, one path extracts low-frequency AFDM control frames through the LPF, completes synchronization and reference buffering using a fixed reference block, and recovers the control word from the control block. Antenna switching sequence The RF transmit branch retains a mixed RF signal containing low-frequency fixed reference components and high-frequency AFDM-IM service components. After broadband filtering, amplification, or amplitude shaping, it is then processed according to... Controlling 1×N switches, in the subsequent In each high-frequency service time slot, the corresponding antenna is selected sequentially for transmission.

[0069] On the target user side, the received high-frequency AFDM-IM service signal is sequentially processed by carrier demodulation, serial-to-parallel conversion, DAFT processing, data demodulation, and parallel-to-serial conversion to recover the communication signal. The recovered communication signal carries parameter field index, subcarrier field index, and modulated communication bits. Meanwhile, after the target echo returns, the RRU extracts the low-frequency component corresponding to the low-frequency fixed reference block from the echo and performs correlation processing with the locally cached fixed reference copy to obtain sensing information such as time delay, Doppler, range, and velocity. The low-frequency fixed reference component in the mixed radio frequency signal forms a corresponding echo after reflection from the target or environment. The RRU extracts the low-frequency echo component from the echo and performs correlation processing using the cached fixed reference copy to obtain sensing parameters such as target range and velocity.

[0070] In actual transmission, such as Figure 4 As shown, for example, the RRU side is configured with 4 candidate transmit antennas, and one low-frequency AFDM control frame is used to control the subsequent 4 high-frequency service time slots. Let the original bit stream to be transmitted on the control center side be... The control center first performs functional splitting on the original bitstream, with the first 5 bits... It is divided into low-frequency control bits for generating low-frequency control blocks. ; Subsequent bits These are divided into high-frequency service bits for generating high-frequency AFDM-IM service signals. Simultaneously, a preset fixed reference block is inserted into each low-frequency AFDM control frame at the control center. The fixed reference block It does not carry the service bits to be transmitted. Its AFDM parameters, active resources and symbol content remain unchanged between multiple control frames and are used for local reference buffering and echo correlation processing on the RRU side.

[0071] For low-frequency control bits The system splits it into two parts according to preset rules. The first two digits... The last 3 bits are used as parameters to select bits. As subcarrier selection bits. Parameter selection bits are used to select a set of parameters from a finite number of AFDM control parameter combinations, and subcarrier selection bits are used to select an activation mode from a finite number of control subcarrier activation schemes.

[0072] In this embodiment, the system pre-sets four sets of AFDM control parameter combinations. For example, parameter selection bits. Corresponding to the first group of control parameters, Corresponding to the second group of control parameters, Corresponding to the third group of control parameters. This corresponds to the 4th group of control parameters. Therefore, the current parameter selection bit... The corresponding control parameter in group 3 is denoted as .

[0073] Meanwhile, the system reserves 8 control subcarrier positions in the DAFT domain, denoted as... And it uses an 8-to-1 activation method. For example, the subcarrier selection bit correspond , correspond , correspond , correspond And so on. Therefore, the current subcarrier selection bit Corresponding to the 4th control subcarrier Therefore, the low-frequency control bit Two things were actually determined: First, the control block uses the third group of AFDM control parameters. Secondly, activate the fourth control subcarrier in the DAFT domain. Based on this, the control center constructs sparse control vectors in the DAFT domain. So that it can be in The position is set to a non-zero value, while the positions of the other control subcarriers are set to zero. Subsequently, the control center uses the third set of control parameters to perform IDAFT modulation on the control vector to obtain the low-frequency AFDM control block. .

[0074] The parameter selection result and the subcarrier selection result together correspond to a single control word. This control word is not a specific instantaneous antenna number, but rather a spatial control number. The system pre-stores a mapping table between control words and antenna switching sequences on the RRU side. For example, the current control word... The corresponding antenna switching sequence is This indicates that the subsequent four high-frequency service time slots will be transmitted sequentially by antenna 1, antenna 3, antenna 1, and antenna 3.

[0075] Therefore, the complete mapping relationship of the low-frequency control bits in this embodiment can be summarized as follows:

[0076] On the control center side, a low-frequency control block is generated. With fixed reference block Forming low-frequency AFDM control frames, i.e.

[0077] Simultaneously, high-frequency service bits are mapped to high-frequency AFDM-IM service windows, with some service bits used to select service AFDM parameters, some used to select service subcarrier activation modes, and the remaining service bits mapped to constellation modulation symbols. Subsequently, the low-frequency AFDM control frame and the high-frequency AFDM-IM service signal are frequency-division multiplexed at the control center side to form a hybrid AFDM fronthaul electrical signal, which is then modulated onto the optical carrier as the MZM drive signal and transmitted to the RRU side via the optical fiber fronthaul link.

[0078] On the RRU side, the mixed electrical signal after photodetection is divided into a low-frequency processing branch and an RF transmission branch. The low-frequency processing branch extracts the low-frequency AFDM control frame and buffers the fixed reference block from it. and from the control block Recovery control word Then, the antenna switching sequence is obtained by looking up a table. The radio frequency transmit branch retains a mixed radio frequency signal containing low-frequency fixed reference components and high-frequency AFDM-IM service components, and transmits it sequentially by antenna 1, antenna 3, antenna 1, and antenna 3 in the subsequent four high-frequency service time slots according to the antenna switching sequence.

[0079] After receiving the high-frequency AFDM-IM service signal, the target user side completes parameter domain indexing, subcarrier domain indexing, and modulation communication bit recovery. Simultaneously, the RRU side receives the echo generated by the low-frequency fixed reference component and utilizes the locally buffered fixed reference block. The relevant processing is performed to obtain the target's time delay, Doppler, distance, or speed perception results.

[0080] In summary, the AFDM multi-domain indexed transmission system and method for optical fronthaul networks proposed in this invention have the following advantages compared with existing transmission systems and methods: Integrated communication and sensing with simplified structure: Based on the system framework of constructing low-frequency AFDM control frames and high-frequency AFDM-IM service windows in the same optical fronthaul link, it can simultaneously support service transmission, spatial control and local sensing, avoiding the structural complexity caused by building communication links, control links and sensing links separately, and is conducive to forming a more compact integrated communication and sensing system.

[0081] Stable sensing reference and improved echo processing performance: By adopting a low-frequency AFDM control frame structure with a fixed reference block and a control block, the fixed reference block remains unchanged across multiple control frames and serves as the low-frequency reference component for actual radiation. The RRU side uses a locally cached copy of the fixed reference block to perform correlation processing with the corresponding low-frequency component in the echo, avoiding the reference template change problem introduced when the dynamic AFDM-IM service waveform is directly used as the sensing reference, thereby significantly improving the stability of echo correlation processing and achieving stable coexistence of spatial control and echo sensing.

[0082] Reduced remote processing burden and separation of responsibilities: On the RRU side, a small-scale DAFT candidate detection plus lookup table method is used to recover the control word and antenna sequence, while the recovery of parameter domain index and subcarrier domain index is retained on the target user side. This allows the RRU side to only be responsible for low-frequency control recovery, antenna switching execution and local echo related processing, without having to complete the complete user-side service demodulation task, which is more in line with the design goal of lightweight remote processing in A-RoF fronthaul.

[0083] Improved spatial control efficiency and reduced control overhead: The introduction of a mapping mechanism from control words to multi-slot antenna switching sequences enables the management of antenna switching processes for multiple subsequent high-frequency service slots with a single control recovery. This reduces the repetitive processing and control overhead caused by slot-by-slot control detection, effectively improving remote execution efficiency.

[0084] Clear functional boundaries and system scalability: By clearly defining the functional boundaries of control, perception and service recovery, the tasks on the RRU side and the target user side are clearer, reducing the possibility of mutual interference between different processing links and facilitating subsequent engineering implementation and system expansion.

[0085] High adaptability to high mobility scenarios: It is suitable for high mobility, dual-channel and centralized optical fronthaul access scenarios. While fully retaining the adaptability of AFDM to high mobility environments, it also takes into account the actual needs of optical fronthaul remote simplification and communication sensing integration, and has broad application prospects.

[0086] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An AFDM multi-domain indexed transmission system for optical fronthaul networks, characterized in that, It includes: The control center side includes a bit splitting and function mapping module, a low-frequency control signal forming module, a high-frequency service signal forming module, a frequency division multiplexer, and an MZM fiber optic fronthaul link. The control center side is used to split the original bit stream to be transmitted into low-frequency control signals and high-frequency service signals, which are then frequency-division multiplexed to form a hybrid AFDM fronthaul signal, which is then sent to the RRU side through the MZM fiber optic fronthaul link. On the RRU side, there are photodetectors, power dividers, low-frequency control frame processing branches, high-frequency radio frequency forwarding branches, space switches and transmitting antennas, and echo processing branches. The RRU side is used to convert the hybrid AFDM fronthaul signal into a hybrid electrical signal, which is then divided into low-frequency control frame processing branches and high-frequency radio frequency forwarding branches. The low-frequency control frame processing branch extracts the low-frequency AFDM control frame for fixing the reference buffer and control word recovery. The high-frequency radio frequency forwarding branch retains the hybrid radio frequency signal containing low-frequency reference components and high-frequency service components, and sequentially selects the corresponding antenna in the high-frequency service time slot to transmit the hybrid radio frequency signal to the target user side. After the target echo returns, the RRU side extracts the low-frequency component corresponding to the low-frequency fixed reference block from the echo, performs related processing with the local cached fixed reference copy, obtains sensing information, and transmits it back to the control center. On the target user side, it is used to recover the communication signal from the received high-frequency AFDM-IM service signal, and it carries parameter field index, subcarrier field index and modulation communication bits; The low-frequency control frame processing branch includes: a low-pass filter and a low-frequency synchronization and segmentation module; one signal after the power divider is filtered by the low-pass filter to extract the low-frequency AFDM control frame, which then enters the low-frequency synchronization and segmentation module; the low-frequency synchronization and segmentation module divides the low-frequency AFDM control frame into a fixed reference block and a control block according to a preset frame structure, wherein the fixed reference block is extracted and sent to the local reference buffer module for use as a local known reference for subsequent echo correlation processing; the control block is extracted and sent to the control recovery module for recovering the corresponding antenna control command or antenna switching sequence.

2. The AFDM multi-domain indexed transmission system for optical fronthaul networks according to claim 1, characterized in that, The low-frequency control signal forming module includes a fixed reference block and a control block. The fixed reference block is a predefined known reference signal, and the control block is used to carry space control information. It is mapped to the antenna index or antenna switching sequence through preset parameter combinations and subcarrier modes. The high-frequency service signal forming module uses a high-frequency AFDM-IM service waveform to carry service transmission information. It includes parameter domain index, subcarrier domain index, and modulation communication bits.

3. The AFDM multi-domain indexed transmission system for optical fronthaul networks according to claim 1, characterized in that, The high-frequency radio frequency forwarding branch retains a mixed radio frequency signal containing low-frequency reference components and high-frequency service components. This signal is sent to the RF circulator through a 1×N switch and a radio frequency forwarding link. Under the spatial control command recovered by the low-frequency control frame processing branch, the corresponding transmitting antenna is selected sequentially in multiple subsequent transmission time slots for spatial transmission. During the sensing process, the mixed signal radiated by the transmitting antenna illuminates the sensing target and generates a sensing echo. The sensing echo enters the echo processing branch through the receiving antenna and the RF circulator, and is then converted to the corresponding processing frequency band by the echo down-conversion module. The digital correlator uses a copy of a fixed reference block stored in the local reference cache module to perform correlation processing with the corresponding components in the echo, thereby realizing the sensing parameter information of distance and velocity, which is then transmitted back to the control center for analysis.

4. The AFDM multi-domain indexed transmission system for optical fronthaul networks according to claim 1, characterized in that, On the control center side, the low-frequency AFDM control / reference subband and the high-frequency AFDM-IM service subband are first frequency-division multiplexed in the electrical domain to form a hybrid fronthaul electrical signal. The low-frequency AFDM subband is located near the zero frequency in the electrical domain and contains a fixed reference block and a control block. The high-frequency AFDM-IM subband is located at a higher radio frequency position and carries parameter domain index, subcarrier domain index and modulation communication bits.

5. The AFDM multi-domain indexed transmission system for optical fronthaul networks according to claim 1, characterized in that, The signal actually radiated by the antenna contains both low-frequency fixed reference components and high-frequency AFDM-IM service components. The low-frequency fixed reference components are used to form a stable echo sensing reference, while the high-frequency AFDM-IM service components are used for communication recovery on the target user side.

6. The AFDM multi-domain indexed transmission system for optical fronthaul networks according to claim 1, characterized in that, In digital baseband, a low-frequency AFDM control frame is formed by splicing a fixed reference block and a control block end-to-end; one low-frequency AFDM control frame is used to control subsequent... High-frequency service time slots.

7. The AFDM multi-domain indexed transmission system for optical fronthaul networks according to claim 6, characterized in that, Depend on A high-frequency service time slot constitutes a high-frequency AFDM-IM service window, the first Each high-frequency service time slot carries an AFDM-IM data sub-block, which is used for communication recovery on the target user side.

8. An AFDM multi-domain indexed transmission method for optical fronthaul networks, characterized in that, It is implemented based on the AFDM multi-domain indexed transmission system for optical fronthaul networks as described in claim 1, and the transmission method includes the following steps: On the control center side, the original bit stream to be transmitted is split into bits and mapped to functions. A portion of the bits is used to form low-frequency control signals, and another portion of the bits is used to form high-frequency service signals. The low-frequency control signals and high-frequency service signals are frequency-division multiplexed to form a hybrid AFDM fronthaul signal, which is sent to the RRU side through the MZM fiber optic fronthaul link. On the RRU side, the photodetector converts the hybrid AFDM fronthaul signal into a hybrid electrical signal, which is divided into a low-frequency control frame processing branch and a high-frequency radio frequency forwarding branch. The low-frequency control frame processing branch extracts the low-frequency AFDM control frame from near the zero frequency and is used for fixing the reference buffer and control word recovery. The high-frequency radio frequency forwarding branch retains the hybrid radio frequency signal containing the low-frequency reference component and the high-frequency service component, and sequentially selects the corresponding antenna in the high-frequency service time slot to transmit the hybrid radio frequency signal to the target user side. On the target user side, the received high-frequency AFDM-IM service signal is recovered into a communication signal, which carries parameter field index, subcarrier field index and modulation communication bits; After the target echo returns, the RRU side extracts the low-frequency component corresponding to the low-frequency fixed reference block from the echo, performs related processing with the local cached fixed reference copy, obtains sensing information, and transmits it back to the control center.

9. The AFDM multi-domain indexed transmission method for optical fronthaul networks according to claim 8, characterized in that, The communication recovery process on the target user side includes the following steps: (1) Perform DAFT transformation on the received data sub-blocks using each candidate service parameter to obtain multiple sets of candidate transform domain outputs; (2) Under each set of candidate outputs, traverse all legal service subcarrier activation modes and construct a decision metric based on the energy concentration degree and leakage suppression results; (3) Perform a joint search on the candidate service parameter set and the subcarrier activation mode set to obtain the parameter domain index estimate and the subcarrier domain index estimate; (4) At the determined active subcarrier position, the modulation symbol decision is completed by combining the equivalent channel gain and the constellation set; (5) The parameter number, activation mode number and constellation symbol obtained from the decision are restored to parameter field index bit, subcarrier field index bit and modulation communication bit respectively through the inverse mapping table.

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