Hybrid modulation transmission method, transmitter and system for indoor visible light communication

Abstract

This invention discloses a hybrid modulation transmission method, transmitter, and system for indoor visible light communication, relating to the field of visible light communication transmission technology. It includes receiving external commands and parsing mode bits and data bits; constructing a transmission frame, with a fixed frame header and a data area length determined by the modulation order; selecting a frame header from a set of valid dynamic frame headers based on the mode bits; constructing the data area using positive pulse position modulation in dark mode and inverse pulse position modulation in bright mode; sequentially concatenating the frame header and data area to form a complete transmission frame and converting it into a time-domain driving waveform; writing the transmission frame into a transmission buffer and setting an update flag; scheduling a timer slot-by-slot according to the symbol period and updating the active buffer at the boundary of the transmission period; and outputting the driving waveform slot-by-slot according to the active buffer to control the LED array's illumination. This invention unifies synchronization prefix, brightness adjustment, and data mapping within the frame structure, balancing communication and dimming, and is suitable for integrated indoor lighting and communication systems.

Description

Technical Field

[0001] This invention relates to the field of visible light communication transmission technology, and more particularly to a hybrid modulation transmission method, transmitter, and system for indoor visible light communication. More specifically, this invention relates to a transmitter implementation mechanism that combines dynamic frame headers, positive pulse position modulation, inverse pulse position modulation, buffered double-buffering scheduling, and LED array driving light emission, suitable for integrated indoor lighting communication systems that simultaneously require data communication transmission and brightness adjustment. Background Technology

[0002] In indoor visible light communication systems, the transmitting end not only undertakes the function of transmitting data information, but also needs to meet multiple requirements such as lighting, dimming, stable driving timing, and compatibility with the synchronization mechanism of the receiving end. Although traditional single OOK or PPM transmission methods are relatively simple to implement, they often suffer from problems such as limited dimming capability, low utilization of synchronization prefix, and insufficient flexibility of frame structure in practical applications. When the system needs to complete information transmission and brightness adjustment simultaneously within a fixed time slot period, if the transmission frame structure is not designed properly, it is very easy to encounter a situation where synchronization performance and transmission efficiency cannot be balanced.

[0003] Furthermore, in microcontroller-based hardware deployments, the transmitting end must also address issues such as input command buffering and verification, frame construction, precise control of buffer update timing, timer slot-by-slot scheduling, and the actual driving of the LED array. If the transmitting end updates data midway through a single transmission cycle, it can easily cause output waveform tearing, frame boundary chaos, and optical signal flicker, severely impacting the receiver's synchronization performance and decision-making results. Simultaneously, the layout of the LED array directly affects the power distribution and signal-to-noise ratio (SNR) fluctuations on the indoor receiving surface, thus affecting the overall system performance. Currently, there is a lack of a unified system architecture that integrates a fixed 4-bit dynamic frame header, a dual-mode transmission mechanism, seamless updates via shadow / active double buffering, and the driving of arrayed LEDs (such as a 23×8 square array).

[0004] Therefore, there is an urgent need to propose a new transmission method and system architecture that can uniformly map external input commands into transmission frames containing dynamic frame headers and data payloads under fixed time slots, and complete a stable, flexible and highly reliable indoor visible light communication transmission process through precise timing double buffer scheduling and LED array driving mechanism. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, the present invention aims to provide a hybrid modulation transmission method, transmitter, and system for indoor visible light communication. The invention aims to achieve the joint expression of synchronization prefix, brightness adjustment, and data position mapping by constructing a unified transmission frame structure comprising a fixed 4-bit dynamic frame header area and a positive / inverse pulse position modulation (PPM) data area. Simultaneously, by employing a shadow / active double buffer mechanism and a timer-based slot-by-slot scheduling strategy, the absolute stability of the transmission timing is ensured. Thus, under a fixed slot period, the system balances synchronization robustness, data transmission efficiency, dimming flexibility, and ease of embedded hardware implementation.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: First, the present invention provides a hybrid modulation transmission method for indoor visible light communication, comprising the following steps: Step 1: Receive external input instructions, cache, format-check, and determine the validity of the input instructions. When the input instructions meet the predetermined rules, parse out the mode bits and data bits. Step 1 constitutes the preprocessing stage of the sending end control logic, ensuring the reliability of subsequent frame construction and sending processes.

[0007] Step 2: Construct a transmission frame, which includes a frame header area and a data area. The frame header area has a fixed length of 4 bits, and the length of the data area is determined by the modulation order. Step 3: Select the corresponding 4-bit dynamic frame header from the set of valid dynamic frame headers based on the mode bit; when the transmission mode is dark mode, select from the set of valid dark mode frame headers. H dark ={0001, 0011}; when the sending mode is bright mode, select from the set of valid bright mode frame headers. H bright Select from {1100, 1110}; that is, the set of legal dynamic frame headers. H ={0001, 0011, 1100, 1110}; Step 4: Construct a data area based on the data bits; in dark mode, positive pulse position modulation is used to construct the data area, and in bright mode, inverse pulse position modulation is used to construct the data area. Step 5: Concatenate the dynamic frame header and the data area in time sequence to form a complete transmission frame; Step 6: Convert the complete transmitted frame into a time-domain driven waveform; Step 7: Write the complete transmission frame into the transmission buffer and set the buffer update flag; Step 8: The timer schedules the output slot by slot according to the symbol period, and checks the validity of the buffer update flag only at the boundary of the complete transmission period. If it is valid, the entire transmission frame in the buffer is updated to the active buffer. If it is invalid, the current active buffer content remains unchanged. Step 9: Based on the current time slot level state in the active buffer, output the driving waveform time slot by time slot to control the LED array to emit light and output indoor visible light communication signals.

[0008] In a preferred embodiment of the present invention, in step 2, the total length of the transmitted frame satisfies L frame = L header + L data The length of the frame header area is fixed as follows: L header =4, the data area length is defined as: L data =2 (m-2) , m This represents the modulation order.

[0009] Specifically, when the modulation order m When the value is 4, the transmitted frame consists of a dynamic frame header of 4 bits and a data area of ​​4 bits.

[0010] In another preferred embodiment of the present invention, in step 4, the length of the data area is set to... M = L data =2 (m-2) The position index obtained by bit mapping the input data is p Therefore, in dark mode, the positive pulse position modulation data region satisfies: That is, in length of M In the data area, only the first p One time slot is high level, and the rest are low level; in bright mode, the inverse pulse position modulation data area satisfies: That is, in length of M In the data area, only the first p One time slot is low level, and the rest of the time slots are high level.

[0011] As another preferred embodiment of the present invention, in step 5, the dark mode transmission frame is represented as: x dark =[ h dark , d p ],in h dark For dark mode dynamic frame headers, hdark ∈{0001,0011}; the bright mode transmission frame is represented as: ,in h bright For bright mode dynamic frame header, h bright ∈{1100,1110}. In this way, the sending end can map the input command into a fixed-length, synchronously recognizable time-slot sequence with brightness adjustment capability.

[0012] As another preferred embodiment of the present invention, in step 6, the width of a single time slot is set to... T s The first frame sent k The corresponding level for each time slot is x k If ∈{0,1}, then the baseband drive waveform output by the transmitter satisfies: ; in, p ( t ( ) represents the basis function of a unit time-slot pulse; considering the LED driving bias, the actual light intensity modulation signal satisfies: I ( t )= I bias + A · s ( t );in, I bias This is the DC bias light intensity. A This refers to the modulation amplitude.

[0013] In another preferred embodiment of the present invention, in steps 7 and 8, the transmitting end adopts a double-buffered structure of shadow buffer and active buffer. A new transmitted frame is first written to the shadow buffer and a buffer update flag is set. The timer advances slot by slot according to the symbol period, and the output is controlled by the current slot level of the active buffer. Specifically, the transmitting end adopts a double-buffered structure of shadow buffer and active buffer to avoid directly overwriting the current transmitted frame during the output process.

[0014] Secondly, the present invention provides a hybrid modulation transmitter for indoor visible light communication, used to execute the hybrid modulation transmission method for indoor visible light communication; specifically including: an instruction input and buffer module, a format verification and legality judgment module, a parameter parsing module, a dynamic frame header generation module, a data area construction module, a transmission frame splicing module, a waveform generation module, a transmission buffer module, a timing scheduling module, a drive output module, and an LED array transmission module; The instruction input and buffering module is used to receive external input instructions and buffer them. The format validation and legality judgment module is used to perform format validation and legality judgment on the external input instructions; The parameter parsing module is used to parse the mode bits and data bits from valid instructions; The dynamic frame header generation module is used to select a corresponding 4-bit dynamic frame header from the set of legal dynamic frame headers based on the mode bit. A data area construction module is used to generate a positive pulse position modulation data area or an inverse pulse position modulation data area based on the data bits; The frame splicing module is used to splice the dynamic frame header and the data area in a time sequence to form a complete transmission frame. A waveform generation module is used to convert the complete transmission frame into a time-domain driven waveform; A sending buffer module is used to store frames to be sent. The sending buffer module adopts a double buffer structure of shadow buffer and active buffer. The timed scheduling module is used to schedule the cached content on a time-slot basis according to the symbol period, and control the cache update at the boundary of the complete sending cycle; The driver output module is used to output LED driving waveforms; The LED array emitting module is used to emit indoor visible light communication optical signals according to the driving waveform.

[0015] Furthermore, the set of legal dynamic frame headers is as follows: H ={0001, 0011, 1100, 1110}, where the set of valid dark mode frame headers is: H dark ={0001, 0011}, the set of valid frame headers in bright mode is: H bright ={1100, 1110}.

[0016] Furthermore, the LED array emitting module adopts a 23×8 square array structure of LED array.

[0017] Finally, the present invention provides a hybrid modulation transmission system for indoor visible light communication, comprising: an external control terminal, a microcontroller transmission control module, a driving circuit module, and an LED array transmission module; External control terminal, used to input and send commands; The microcontroller transmit control module is used to execute the hybrid modulation transmit method for indoor visible light communication. The driving circuit module is used to convert the time-slot-by-time driving waveform output by the microcontroller's transmission control module into a driving signal suitable for the operation of the LED array; The LED array emitting module is used to emit indoor visible light communication optical signals according to the driving signal.

[0018] Furthermore, in this invention, the dynamic frame header not only serves as a synchronization prefix but also participates in the formation of the average duty cycle of the entire frame. Therefore, the dynamic frame header simultaneously possesses both synchronization and dimming functions. Let the average brightness coefficient of the entire frame be... ζ Then we have: ; Therefore, it can be seen that the dimming mechanism of this invention does not rely solely on the data area, but is composed of both the frame header area and the data area. If the number of "1"s in the frame header in dark mode is denoted as... w (h dark If the average brightness of the dark mode is: ; If the number of "1"s in the frame header is recorded as follows in bright mode: w (h bright If the average brightness in bright mode is: ; Furthermore, under the AWGN approximation, the theoretical processing gain of frame header correlation detection approximately satisfies the following relationship with the frame header length: ; At the same time, the effective transmission efficiency meets the following requirements: ; When the frame header length is 4 bits and m When the value is 4, the system can achieve a better engineering trade-off between synchronization gain and transmission efficiency.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Improve frame utilization: Unify synchronization prefix, brightness adjustment and data mapping in the same frame structure to effectively reduce protocol overhead; (2) Balancing communication and dimming: Constructing a dual-branch system for dark mode (frame header + positive PPM) and bright mode (frame header + reverse PPM) to flexibly adapt to different brightness requirements; (3) Enhanced synchronization robustness: A fixed 4-bit dynamic frame header is adopted, which makes it easy for the receiver to quickly achieve accurate synchronization and identification through multi-template correlation detection; (4) Ensure waveform stability: Introduce a double buffer architecture and a periodic boundary update mechanism to effectively avoid waveform tearing caused by mid-frame refresh; (5) Fits hardware timing: This invention enables the transmitter to be highly adapted to the microcontroller timer scheduling mechanism through fixed time slot division and unified frame beat design, reducing the complexity of the underlying driver logic, ensuring the stability of the LED array output timing, and improving the reliability of the system implementation on the embedded platform. (6) Optimize power distribution: Use a 23×8 square LED array to improve the uniformity of light power coverage on the indoor receiving surface and the system signal-to-noise ratio. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the transmitting end of the present invention; Figure 2 A comparison of the normalized cross-correlation outputs of a traditional 3-bit fixed frame header and a 4-bit dynamic frame header under the combined effects of additive white Gaussian noise and bandwidth-limited distortion. Figure 3 Engineering game theory analysis diagram for frame header length design in visible light communication (VLC) systems; Figure 4 A comparison of the false synchronization probability of different coded frame headers under low signal-to-noise ratio conditions in indoor visible light communication (VLC); Figure 5 The graph shows the relationship between the total slot bit error rate and the signal-to-noise ratio for three modulation schemes under different modulation orders. Figure 6 A comparison chart of the dimming flexibility of the three modulation methods; Figure 7 This is a comparison chart of the original received waveform and the restored waveform of the measured command Cmd1; Figure 8 This is a comparison chart of the original received waveform and the restored waveform of the measured command Cmd11; Figure 9 This is a comprehensive performance comparison chart of different LED layout schemes for indoor visible light communication (VLC) systems. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0022] This embodiment addresses the challenge of integrating information transmission, brightness adjustment, and timing control in indoor visible light communication systems. It proposes a hybrid modulation transmission method for indoor visible light communication. This method uses a fixed-length dynamic frame header as a protocol prefix and employs both positive pulse position modulation and inverse pulse position modulation as data payload representations. Within a unified time slot period, it completes frame construction, buffer updates, and LED array driving. Based on this method, the overall workflow of the transmitter in this embodiment mainly includes three stages: instruction input and frame parameter analysis, frame construction and waveform generation, and buffer scheduling and LED array transmission.

[0023] 1. Overall workflow of the sending end like Figure 1 As shown, the specific workflow of the sending end in this embodiment is as follows: First, in the instruction input and frame parameter analysis stage, the sending end receives external control instructions and sequentially performs instruction buffering, format verification, and legality judgment. If the input is determined to be illegal, the system directly discards the instruction to block the abnormal state; if the input is determined to be legal, the system further parses and extracts the mode bits and data bits from the instruction, and then enters the transmission frame construction and waveform generation stage.

[0024] Secondly, during the frame construction and waveform generation stage, the system executes a dual-branch scheduling strategy based on the mode bits: if the system is determined to be in dark mode, the corresponding dynamic frame header is selected from the preset set of legal dynamic frame headers, and positive pulse position modulation mapping is performed based on the data bits to construct a "frame header + positive PPM" transmission branch; if the system is determined to be in bright mode, the corresponding dynamic frame header is selected from the corresponding set of legal dynamic frame headers, and inverse pulse position modulation mapping is performed based on the data bits to construct a "frame header + inverse PPM" transmission branch. Subsequently, the system sequentially concatenates the selected dynamic frame header area with the modulated data area according to the timing sequence to form a complete transmission frame, and writes it into the shadow buffer.

[0025] Finally, during the buffer scheduling and LED array transmission phase, the underlying timer strictly advances slot by slot according to the symbol period. When a complete transmission cycle boundary is detected, the system determines whether the buffer update flag is valid: if the flag is valid, the entire transmission frame in the shadow buffer is seamlessly updated to the active buffer; if invalid, the current active buffer content remains unchanged. Based on this, the driver circuit outputs the corresponding drive waveform slot by slot according to the current time slot level in the active buffer, and further controls the LED array to emit light, thereby stably outputting visible light communication transmission signals in indoor free space.

[0026] 2. Relevant characteristics and synchronization advantages of dynamic frame headers like Figure 2 The diagram shown is a comparison of the normalized cross-correlation outputs of a traditional 3-bit fixed frame header and a 4-bit dynamic frame header of this invention under the combined effects of additive white Gaussian noise and bandwidth-limited distortion. Figure 2 It is known that the traditional 3-bit fixed frame header, limited by its short correlation length, has insufficient identification of the correlation peak, making it prone to false alarms in complex noise environments. In contrast, the 4-bit dynamic frame header (containing 0001, 0011, 1100, and 1110) used in this invention can form clear and sharp correlation peaks under complex channel conditions. This comparative result shows that the 4-bit dynamic frame header design at the transmitting end of this invention significantly enhances the signal's anti-interference capability and is more conducive to achieving high-precision time slot synchronization detection and frame header identification at the receiving end.

[0027] Furthermore, when the receiving end performs sliding cross-correlation detection, let the received discrete signal be... r (n The local template signal is s ( n The template length is... L Then the normalized sliding cross-correlation function can be expressed as: ; in, τ This represents the sliding window offset. When the received signal and the template reach optimal alignment at a certain position, the correlation output achieves its maximum peak value, corresponding to the optimal synchronization position of the frame header. Since the transmitter of this invention uses a 4-bit dynamic frame header, it is more advantageous for the receiver to obtain a clear main peak using multi-template normalized correlation detection.

[0028] 3. Engineering trade-offs in frame header length design like Figure 3 The figure shows the engineering game analysis results of the frame header length design in this embodiment. As can be seen from the figure, with the increase of the frame header length, the system's related processing gain gradually increases, but the effective transmission efficiency decreases accordingly. Therefore, setting the frame header length to 4 bits achieves an ideal balance between synchronization performance and transmission efficiency. Specifically, when both the frame header length and the data area length are 4 bits, the theoretical processing gain of the system is approximately 6 dB, and the transmission efficiency is approximately 50%. This design achieves a good engineering trade-off between the transmitter's synchronization support capability, frame protocol overhead, and the convenience of microcontroller-level hardware implementation.

[0029] 4. False synchronization performance under low signal-to-noise ratio conditions like Figure 4 The diagram shown illustrates a comparison of false synchronization probabilities in different coded frame headers under low signal-to-noise ratio conditions in indoor visible light communication (VLC) in this embodiment. Figure 4 It can be seen that, under the same received signal-to-noise ratio, the frame header false synchronization probability of the hybrid coding scheme of this invention is significantly lower than that of traditional PPM and traditional MPPM; especially in low-light edge scenarios, the probability reduction trend is more significant. This result shows that the frame header structure constructed at the transmitting end of this invention, combined with template matching detection at the receiving end, has superior synchronization anti-interference capability.

[0030] 5. Total time slot error performance at different orders like Figure 5 The diagram shown illustrates the relationship between the total slot bit error rate and signal-to-noise ratio for three modulation schemes under different modulation orders in this embodiment. Figure 5It can be seen that as the received signal-to-noise ratio increases, the bit error rate of all three modulation methods decreases. Compared with the traditional MPPM, the hybrid coding proposed in this invention exhibits superior overall anti-interference performance under multiple order conditions; compared with the traditional PPM, this invention, by introducing a dynamic frame header and a dual-mode transmission mechanism, enriches the frame structure while maintaining excellent overall communication performance.

[0031] 6. Dimming flexibility analysis: like Figure 6 The diagram shown is a comparison of the dimming flexibility of the three modulation methods in this embodiment. Figure 6 It is known that traditional PPM has a low average duty cycle and a limited range of variation; while traditional MPPM expands the duty cycle range to some extent, it is still mainly limited to the medium brightness region. In contrast, the hybrid coding mechanism proposed in this invention introduces a dual-mode structure of "dark mode and bright mode," enabling the system to effectively cover both low and high brightness regions simultaneously. This results in a wider dimming range under the conditions of fixed frame length and fixed time slot period. This demonstrates that this invention successfully achieves a high degree of integration between data communication and flexible dimming while maintaining a fixed time slot period.

[0032] 7. Verification of transmitted and received waveforms by actual measurement: like Figure 7 The image shows a comparison between the original received waveform and the restored waveform of the measured command Cmd1. Figure 7 It can be seen that, despite the influence of channel attenuation and noise on the original received waveform, the receiver can still stably recover the corresponding transmitted frame based on the frame header and data area structure constructed by the transmitter of this invention. This indicates that the "frame header + positive PPM" structure in the dark mode branch of this invention has good signal recoverability.

[0033] like Figure 8 The figure shows a comparison between the original received waveform and the restored waveform of the measured command Cmd11. This figure further demonstrates that in the bright mode branch, the "frame header + inverse PPM" transmission mechanism adopted in this invention can also generate a transmitted frame that can be stably recovered by the receiving end, fully verifying the effectiveness of the dual-mode transmission structure.

[0034] 8. Buffer scheduling and LED array transmission: In this embodiment, after the complete transmission frame is constructed, it is first written to the shadow buffer, and the buffer update flag is set. The timer advances slot by slot according to a fixed symbol period. When the boundary of the complete frame period is detected, if the buffer update flag is valid, the entire transmission frame in the shadow buffer is seamlessly updated to the active buffer; otherwise, the active buffer remains unchanged. The LED driving logic always outputs the driving waveform according to the current slot level in the active buffer. This double-buffered scheduling mechanism effectively avoids the waveform tearing problem caused by the transmission frame being refreshed midway.

[0035] Furthermore, the driving waveform is amplified by the driving circuit and then drives the LED array to emit light. For example... Figure 9 As shown, this embodiment preferably uses a 23×8 square array of LEDs, which significantly improves the uniformity of light power distribution on the indoor receiving surface and the stability of system transmission while maintaining the total light emission scale constraint.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the protection scope defined by the claims of the present invention.

Claims

1. A hybrid modulation transmission method for indoor visible light communication, characterized in that, Includes the following steps: Step 1: Receive external input instructions, cache, format-check, and determine the validity of the input instructions. When the input instructions meet the predetermined rules, parse out the mode bits and data bits. Step 2: Construct a transmission frame, which includes a frame header area and a data area. The frame header area has a fixed length of 4 bits, and the length of the data area is determined by the modulation order. Step 3: Select the corresponding 4-bit dynamic frame header from the set of valid dynamic frame headers according to the mode bit; when the sending mode is dark mode, select from the set of valid dark mode frame headers {0001, 0011}; when the sending mode is bright mode, select from the set of valid bright mode frame headers {1100, 1110}. Step 4: Construct a data area based on the data bits; in dark mode, positive pulse position modulation is used to construct the data area, and in bright mode, inverse pulse position modulation is used to construct the data area. Step 5: Concatenate the dynamic frame header and the data area in time sequence to form a complete transmission frame; Step 6: Convert the complete transmitted frame into a time-domain driven waveform; Step 7: Write the complete transmission frame into the transmission buffer and set the buffer update flag; Step 8: The timer schedules the output slot by slot according to the symbol period, and checks the validity of the buffer update flag only at the boundary of the complete transmission period. If it is valid, the entire transmission frame in the buffer is updated to the active buffer. If it is invalid, the current active buffer content remains unchanged. Step 9: Based on the current time slot level state in the active buffer, output the driving waveform time slot by time slot to control the LED array to emit light and output indoor visible light communication signals.

2. The hybrid modulation transmission method for indoor visible light communication according to claim 1, characterized in that, In step 2, the total length of the transmitted frame satisfies L frame = L header + L data The length of the frame header area is fixed as follows: L header =4, the data area length is defined as: L data =2 (m-2) , m This represents the modulation order.

3. The hybrid modulation transmission method for indoor visible light communication according to claim 2, characterized in that, In step 4, the length of the data area is set to be... M = L data =2 (m-2) The position index obtained by bit mapping the input data is p ; but: In dark mode, the positive pulse position modulation data region satisfies: ; In bright mode, the inverse pulse position modulation data area satisfies: .

4. The hybrid modulation transmission method for indoor visible light communication according to claim 3, characterized in that, In step 5, the dark mode transmission frame is represented as follows: x dark =[ h dark , d p ],in h dark For dark mode dynamic frame headers, h dark ∈{0001,0011}; the bright mode transmission frame is represented as: ,in h bright For bright mode dynamic frame header, h bright ∈{1100,1110}.

5. A hybrid modulation transmission method for indoor visible light communication according to claim 4, characterized in that, In step 6, the width of a single time slot is set to be... T s The first frame sent k The corresponding level for each time slot is x k If ∈{0,1}, then the baseband drive waveform output by the transmitter satisfies: ； in, p ( t ( ) represents the basis function of a unit time-slot pulse; considering the LED driving bias, the actual light intensity modulation signal satisfies: I ( t )= I bias + A · s ( t );in, I bias This is the DC bias light intensity. A This refers to the modulation amplitude.

6. The hybrid modulation transmission method for indoor visible light communication according to claim 1, characterized in that, In steps 7 and 8, the transmitting end adopts a double-buffered structure of shadow buffer and active buffer. The new frame to be transmitted is first written into the shadow buffer and the buffer update flag is set. The timer advances one time slot at a time according to the symbol period and is controlled by the current time slot level of the active buffer to output one time slot at a time.

7. A hybrid modulation transmitter for indoor visible light communication, used to execute the hybrid modulation transmission method for indoor visible light communication according to any one of claims 1 to 6, characterized in that, include: The module includes: instruction input and buffer module, format verification and legality judgment module, parameter parsing module, dynamic frame header generation module, data area construction module, transmission frame splicing module, waveform generation module, transmission buffer module, timing scheduling module, drive output module, and LED array transmission module. The instruction input and buffering module is used to receive external input instructions and buffer them. The format validation and legality judgment module is used to perform format validation and legality judgment on the external input instructions; The parameter parsing module is used to parse the mode bits and data bits from valid instructions; The dynamic frame header generation module is used to select a corresponding 4-bit dynamic frame header from the set of legal dynamic frame headers based on the mode bit. A data area construction module is used to generate a positive pulse position modulation data area or an inverse pulse position modulation data area based on the data bits; The frame splicing module is used to splice the dynamic frame header and the data area in a time sequence to form a complete transmission frame. A waveform generation module is used to convert the complete transmission frame into a time-domain driven waveform; A sending buffer module is used to store frames to be sent. The sending buffer module adopts a double buffer structure of shadow buffer and active buffer. The timed scheduling module is used to schedule the cached content on a time-slot basis according to the symbol period, and control the cache update at the boundary of the complete sending cycle; The driver output module is used to output LED driving waveforms; The LED array emitting module is used to emit indoor visible light communication optical signals according to the driving waveform.

8. A hybrid modulation transmitter for indoor visible light communication according to claim 7, characterized in that, The set of legal dynamic frame headers is as follows: H ={0001, 0011, 1100, 1110}, where the set of valid dark mode frame headers is: H dark ={0001, 0011}, the set of valid frame headers in bright mode is: H bright ={1100, 1110}.

9. A hybrid modulation transmitter for indoor visible light communication according to claim 7, characterized in that, The LED array emitting module adopts a 23×8 square array structure.

10. A hybrid modulation and transmission system for indoor visible light communication, characterized in that, include: External control terminal, microcontroller transmitting control module, driver circuit module and LED array transmitting module; External control terminal, used to input and send commands; A microcontroller transmission control module is used to execute a hybrid modulation transmission method for indoor visible light communication as described in any one of claims 1 to 6; The driving circuit module is used to convert the time-slot-by-time driving waveform output by the microcontroller's transmission control module into a driving signal suitable for the operation of the LED array; The LED array emitting module is used to emit indoor visible light communication optical signals according to the driving signal.

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