Method and System for High-Power LED Visible Light Signal Transmission without DC Bias

Abstract

This invention discloses a method and system for transmitting high-power LED visible light signals without DC bias, relating to the field of optical communication technology. The method includes: modulating the raw audio and video data using 64QAM-OFDM and IQ modulation; extracting the peak-to-peak value of the AC-coupled signal and filtering out the DC component; then performing single-supply amplification and pre-equalization to generate a positive driving voltage signal to drive a high-power LED diode to emit light, thus generating an optical communication signal. By using a low-loss AC-coupled transmission method, the peak-to-peak value of the modulated real signal is coupled and transmitted, and amplified by a single positive supply to convert it into a positive voltage to control the LED light intensity, forming an LED optical communication signal. This eliminates the need to introduce DC voltage into the digital domain, avoiding bandwidth reduction issues and ensuring that the LED's own DC bias voltage remains stable and operates in the linear modulation region. Furthermore, the bandwidth is extended through a pre-equalization circuit, thus accommodating both LED lighting and high-speed communication functions.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a method and system for transmitting high-power LED visible light signals without DC bias. Background Technology

[0002] LED visible light communication combines lighting and communication, providing a green and secure information exchange channel, especially in environments where wireless communication is restricted due to electromagnetic sensitivity. This is because in the complex electromagnetic environment of information technology, traditional radio frequency-based wireless communication is not only prone to interference with other wireless devices on the same frequency band, but also susceptible to eavesdropping or interception, leading to information leakage, crosstalk, and other security problems. In contrast, LED-based optical communication occupies the visible light frequency band, does not interfere with other wireless devices, and emits highly focused and directional light signals. It possesses numerous advantages, including inherent confidentiality, abundant spectral resources, security, anti-interference capabilities, high energy efficiency, environmental friendliness, multifunctionality, and cost-effectiveness, making it particularly suitable for complex information technology scenarios.

[0003] Currently, in LED visible light communication systems, intensity modulation and direct detection (IM / DD) are often used to complete data transmission and reception. However, the baseband signal of traditional OFDM communication systems is a bipolar complex signal, which cannot be directly applied to IM / DD systems. This can be addressed by adding DC bias (DCO-OFDM) or by using only odd subcarriers and limiting them to generate non-complex signals (ACO-OFDM). However, both methods sacrifice system performance. DCO-OFDM uses Hermitian symmetry to obtain the baseband real signal, resulting in half the number of effective subcarriers and a 50% loss in spectral efficiency. ACO-OFDM further reduces its spectral efficiency to 25% by using only odd subcarriers. Since the signal after OFDM modulation is a dual-channel complex signal, and a single LED light source cannot simultaneously propagate dual complex signals, to avoid problems such as signal asynchrony and high bit error rate caused by the two light sources, IQ modulation is performed in the digital domain using digital quadrature modulation technology to serially output the dual complex signals to a single LED light source. The unidirectional conductivity of diodes in LED light sources means they can only transmit positive real-valued signals. The complex signal after IQ modulation combines the real and imaginary parts. Therefore, the analog signal output by the DAC will have a negative real-valued voltage in the time domain. If a DC bias voltage is introduced in the digital domain to raise the negative real-valued signal above 0, the introduced DC signal will increase the DC power of the device, resulting in a significant reduction in the bandwidth of the analog domain (hardware circuit). Examples include operational amplifier chips in RF power devices, and ADC / DAC chips for analog-to-digital and digital-to-analog conversion. This will hinder the bandwidth rate of the communication system, especially in modern information technology scenarios, and will not be able to meet the high demand for transmission rates. Summary of the Invention

[0004] This invention provides a method and system for transmitting high-power LED visible light signals without DC bias, in order to solve the technical problem that DC bias affects the bandwidth rate of LED visible light communication.

[0005] In a first aspect, embodiments of the present invention provide a method for transmitting high-power LED visible light signals without DC bias, comprising:

[0006] S101 performs Orthogonal Frequency Division Multiplexing (OFDM) modulation and high-order Orthogonal Amplitude (QAM) modulation on the original audio and video data to generate a complex baseband signal;

[0007] S102 performs quadrature IQ modulation on the complex baseband signal to generate a single real baseband signal;

[0008] S103 performs peak-to-peak extraction and AC coupling processing on a single real baseband signal to obtain an AC peak-to-peak signal with DC components removed.

[0009] S104 performs single positive power supply differential amplification and pre-equalization on the AC peak-to-peak signal to generate a driving positive voltage signal.

[0010] S105 uses a positive driving voltage signal to drive a high-power LED diode to emit light, generating an LED optical communication signal.

[0011] Furthermore, S101 includes:

[0012] The audio and video sources are processed by channel coding and data framing in the host computer (PC).

[0013] Perform constellation mapping on the data after frame processing;

[0014] OFDM subcarriers are assigned to the constellation-mapped data, and a cyclic prefix is ​​added to form a complex baseband signal.

[0015] Furthermore, S102 includes:

[0016] The complex baseband signal is subjected to quadrature carrier IQ modulation to generate a single real optical intensity signal;

[0017] A single real optical intensity signal is converted into an analog electrical signal to obtain a single real baseband signal.

[0018] Furthermore, S103 includes:

[0019] A single real baseband signal is input to the primary coil of the RF power divider. The output voltage of the secondary coil of the RF power divider changes according to the peak-to-peak value of the input voltage of the primary coil. The center tap of the secondary coil is grounded, thus obtaining an AC peak-to-peak signal with the DC component filtered out.

[0020] Furthermore, S104 includes:

[0021] The AC peak-to-peak signal is input into a differential amplifier powered by a single positive power supply to generate a non-negative voltage signal;

[0022] A non-negative voltage signal is input into an active pre-equalization circuit based on a fourth-order high-pass RC bypass, which generates a stable positive driving voltage signal within a -3dB bandwidth. The -3dB bandwidth is the basis for measuring the operating bandwidth of a communication system in communication engineering.

[0023] Secondly, embodiments of the present invention provide a high-power LED visible light signal transmission system without DC bias, comprising:

[0024] The source modulation module is used to perform orthogonal frequency division multiplexing (OFDM) modulation and high-order orthogonal amplitude (QAM) modulation on the raw audio and video data to generate complex baseband signals;

[0025] The carrier modulation module is used to perform quadrature carrier IQ modulation and digital-to-analog conversion on complex baseband signals to generate a single real baseband signal.

[0026] The radio frequency power divider coupling module is used to extract the peak-to-peak value of a single real baseband signal to obtain an AC peak-to-peak value signal with the DC component removed.

[0027] The signal amplification and pre-equalization module is used to perform single-supply differential amplification and pre-equalization processing on AC peak-to-peak signals, and can generate a stable driving positive voltage signal within a -3dB bandwidth.

[0028] The optical signal output module is used to drive LEDs to emit light using a positive driving voltage signal, thereby generating LED optical communication signals.

[0029] Furthermore, the source modulation module includes:

[0030] The channel coding and framing submodule is used to perform channel coding and data framing processing on audio and video sources;

[0031] The constellation mapping submodule is used to perform constellation mapping on the data after frame processing;

[0032] The subcarrier allocation submodule is used to allocate OFDM subcarriers to the constellation-mapped data and add a cyclic prefix to form a complex baseband signal.

[0033] Furthermore, the carrier modulation module includes:

[0034] The quadrature carrier modulation submodule is used to perform quadrature carrier IQ modulation on complex baseband signals to generate a single real optical intensity signal.

[0035] The digital-to-analog conversion submodule is used to convert a single real-valued optical intensity signal into an analog electrical signal to obtain a single real-valued baseband signal.

[0036] Furthermore, the radio frequency power splitting coupling module includes: a radio frequency power splitting coupling submodule and a DC blocking capacitor submodule.

[0037] Furthermore, the signal amplification and pre-equalization module includes:

[0038] The differential amplifier submodule is used to amplify the AC peak-to-peak signal, reduce electrical noise, improve the signal-to-noise ratio, and generate a non-negative voltage signal.

[0039] The active pre-equalization submodule is used to extend the bandwidth of non-negative voltage signals and generate a stable positive drive voltage signal within a -3dB passband bandwidth.

[0040] This invention provides a method and system for transmitting high-power LED visible light signals without DC bias. The method involves QAM-OFDM modulation of the original audio and video data in a host computer, followed by quadrature IQ modulation of the resulting complex baseband signal to convert it into a single real baseband signal. This signal is then subjected to AC coupling and DC filtering to obtain a non-negative voltage signal without a DC component. The signal is then amplified and pre-equalized to extend its transmission bandwidth, forming a voltage signal for driving LED light emission. The LED diode adjusts its luminous intensity based on the peak-to-peak value variation, thus achieving signal transmission. By using a low-loss AC coupling transmission method, the peak-to-peak values ​​of the real signals after QAM-OFDM and IQ quadrature modulation are coupled and transmitted, and then amplified by a single positive power supply to convert them into a positive voltage to control the LED light intensity, forming an LED optical communication signal. This eliminates the need to introduce DC voltage in the digital domain, avoiding the bandwidth reduction problem of DAC devices and power devices, and does not affect the DC operating conditions of the LED itself. This allows the LED's own DC bias voltage to remain stable, thus ensuring stable operation in the linear modulation region. Combined with a pre-equalization circuit to extend the bandwidth, it can transmit audio and video signals without distortion, thus combining the functions of LED lighting and high-speed communication. Attached Figure Description

[0041] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0042] Figure 1 This is a flowchart of a high-power LED visible light signal transmission method without DC bias, as described in Embodiment 1 of the present invention.

[0043] Figure 2This is a waveform diagram of the time-domain signal after IQ modulation as described in Embodiment 1 of the present invention;

[0044] Figure 3 This is a schematic diagram of the signal modulation process at the transmitting end and the signal demodulation process at the receiving end as described in Embodiment 1 of the present invention;

[0045] Figure 4 This is a spectrum diagram of the transmitter as described in Embodiment 1 of the present invention;

[0046] Figure 5 This is the signal constellation diagram received by the receiving end as described in Embodiment 1 of the present invention;

[0047] Figure 6 The bit error rate at a rate of 1 Mbps as described in Embodiment 1 of the present invention;

[0048] Figure 7 The bit error rate at a rate of 500 Mbps as described in Embodiment 1 of the present invention;

[0049] Figure 8 This is a flowchart of a high-power LED visible light signal transmission method without DC bias, as described in Embodiment 2 of the present invention.

[0050] Figure 9 This is a schematic diagram of the time-domain signal waveform after coupling via the radio frequency power divider as described in Embodiment 2 of the present invention;

[0051] Figure 10 This is a circuit diagram of the active pre-equalization circuit described in Embodiment 2 of the present invention;

[0052] Figure 11 This is a schematic diagram of the structure of a high-power LED visible light signal transmission device without DC bias as described in Embodiment 3 of the present invention;

[0053] Figure 12 This is a schematic diagram of the composition structure of the transmitting end according to Embodiment 3 of the present invention;

[0054] Figure 13 This is a circuit diagram of the high-power LED driving circuit described in Embodiment 3 of the present invention. Detailed Implementation

[0055] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0056] In LED visible light communication systems, to cope with the bipolar complex baseband signal generated by OFDM modulation, and to ensure signal integrity, reduce bit error rate, and ensure signal synchronization, a single LED light source is used. Improving the transmission rate of LED visible light communication without adding a DC bias is affected by various factors. For example, the complex signal after IQ modulation combines the real and imaginary parts, and the analog signal output by the DAC has a negative voltage value in the time domain. Introducing a DC bias would raise the negative real level too high, above 0, reducing the analog domain bandwidth of the hardware circuit and hindering the expansion of the transmission rate. Therefore, a method is needed to improve the transmission rate of LED visible light communication without adding a DC bias, as follows:

[0057] Example 1

[0058] Figure 1 This is a flowchart of a high-power LED visible light signal transmission method without DC bias according to Embodiment 1 of the present invention. This embodiment modulates the original audio and video signal using QAM-OFDM, then obtains a single-channel real-valued baseband signal through IQ modulation and digital-to-analog conversion. After filtering out DC and extracting the AC peak-to-peak value, differential amplification and pre-equalization bandwidth expansion are performed to obtain the communication signal driving the LED to emit light. Specifically, the method includes the following steps:

[0059] S101 performs Orthogonal Frequency Division Multiplexing (OFDM) modulation and high-order Quadrature Amplitude (QAM) modulation on the original audio and video data to generate a complex baseband signal.

[0060] The raw audio and video data for LED optical communication needs to be modulated by a host computer before being transmitted through the circuit. During modulation, the modulation software in the host computer allocates subcarriers to the audio and video data signals to form digital signals. After converting the digital signals according to the corresponding signal transmission rules, they can be transmitted to the LED visible light communication system.

[0061] Specifically, S101 includes:

[0062] The audio and video sources are channel-coded and data framing processed in the host PC.

[0063] The audio and video signal sources in the host computer are first processed by channel coding and data framing according to the corresponding channels and rules. For example, the modulation software in the host PC can use GNU Radio, utilizing its FileSource as the audio and video source. The channel coding method is RS coding to form a parallel bit stream. After encoding, Streamto-tagged Stream is used to mark the encoded data stream, forming data packets. Subsequently, the data is framed by adding a frame header to the beginning of the valid data stream and a 32-bit Cyclic Redundancy Check (CRC) to the end. The valid data in the resulting data stream is the audio and video data sent by the source. Information is added to the frame header, which mainly includes the data packet length, source address, and destination address. Checksum information is added to the end, forming the frame header and checksum information for the receiving end to parse. The frame header information provides the parsing rules for the valid data, and the checksum information is used to verify whether errors exist during transmission. Channel coding and data framing, by introducing redundancy information, can effectively reduce the bit error rate, improve communication quality, reduce the error rate when the signal is affected by noise, improve the signal's anti-interference capability, and ensure the reliability of the communication system.

[0064] Constellation mapping is performed on the data after frame processing.

[0065] For the framed data, constellation mapping is performed on both the frame header and the effective data portion. The frame header undergoes BPSK constellation mapping, while the effective data portion undergoes QAM64 constellation mapping, forming a 6-bit / symbol complex symbol. Then, a Tagged Stream Mux is used to merge the two constellation-mapped signals to obtain the complete symbol data. Phase modulation of the carrier using BPSK constellation mapping in the frame header maximizes the accuracy of the smaller frame header data, reduces computational load, and ensures the stability of digital communication for LED visible light. To meet the demands of high-speed communication, the larger effective data portion is modulated using QAM64 constellation mapping.

[0066] OFDM subcarriers are assigned to the constellation-mapped data, and a cyclic prefix is ​​added to form a complex baseband signal.

[0067] The constellation-mapped data is allocated subcarriers via an OFDM Carrier Allocator to achieve serial-to-parallel conversion. For example, complex symbols are loaded into 59 effective subcarriers according to the IEEE 802.11a subcarrier allocation rules, for a total of 64 subcarriers, including 4 pilot subcarriers and 1 DC subcarrier. The number of effective subcarriers used for data transmission is 59. The pilot subcarrier is used for channel estimation and equalization at the receiver, compensating for the effects of signal transmission. The DC subcarrier is used to reduce the peak-to-average power ratio (PAPR) of OFDM and avoid IQ imbalance. Afterwards, serial-to-parallel conversion and IFFT-64-point operations are performed. IFFT (Inverse Fourier Transform) converts data from the frequency domain to the time domain, forming a time-domain signal for real-time transmission in the communication system. Simultaneously, to reduce multipath interference and improve communication quality, a 16-sample cyclic prefix with a length of 4 (equivalent to 1 / 16 of the IFFT length) is added using an OFDM Cyclic Prefixer, ultimately forming a complex baseband signal. Furthermore, serial audio and video signals encoded by RS can be divided into parallel data streams according to the number of subcarriers through serial-to-parallel conversion, facilitating multi-channel parallel transmission. LED visible light communication uses visible light as a carrier, eliminating the need for spectrum shifting and transmitting antennas. Combined with OFDM modulation, it can fully utilize the limited bandwidth of LED light sources, especially enabling multi-channel parallel communication within a 3dB bandwidth.

[0068] S102 performs quadrature IQ modulation on the complex baseband signal to generate a single real baseband signal.

[0069] Since a single LED light source can only transmit a single signal, the complex baseband signal needs to be converted into a single real baseband signal using quadrature carrier modulation (IQ modulation). After receiving the signal at the receiving end, the original information can be recovered through demodulation. The signal modulation method in this embodiment first orthogonally modulates the complex baseband signal to form positive and negative real baseband signals, and then converts these signals back into positive real signals for transmission to the LED. No DC bias voltage is required, and this can be achieved using the FPGA and DAC sections of the subsequent USRP, combined with an RF power divider coupler.

[0070] Specifically, S102 includes:

[0071] The complex baseband signal is subjected to quadrature carrier IQ modulation to generate a single real optical intensity signal.

[0072] The complex baseband signal is converted into a real signal, i.e., a single-channel real optical intensity signal, within the FPGA (USRP's processor) using digital up-conversion (DUC). The formula is as follows:

[0073]

[0074] in, The signal is a real number signal after digital up-conversion. This represents the real part of the baseband signal. This represents the imaginary part of the baseband signal. The center frequency is t, and time is t, such as Figure 2 The figure shows the waveform of the modulated time-domain signal. The blue waveform represents the real part of the signal, and the red waveform represents the imaginary part. The photodetector at the receiving end converts the captured light intensity signal into an electrical signal. After sampling by the ADC, it undergoes quadrature demodulation via digital down-conversion. The demodulation method is as follows:

[0075]

[0076]

[0077] in, and These represent the real and imaginary parts of the demodulated baseband signal, respectively. This represents the electrical signal converted from a photodetector. This represents a digital low-pass filter. It's important to note that when a photodetector converts a light intensity signal into an electrical signal, although the absolute phase of the optical carrier cannot be preserved due to the direct detection mechanism, the real and imaginary parts of the signal can be re-separated using a locally generated carrier of the same frequency, as described above. However, phase errors will affect signal recovery. Phase shifts can be suppressed using pilot symbols and the high-precision numerically controlled oscillator in the USRP X310 hardware, thereby allowing for complete reconstruction of the original OFDM complex baseband signal. For example... Figure 3 The diagram shows the signal modulation process at the transmitting end and the signal demodulation process at the receiving end. After the receiving end receives and demodulates the optical signal, it uses VLC mediaplayer (the video player that comes with GNU Radio software) at the application layer to play the received data. The application layer exchanges data with GNU Radio through the UDP (User Datagram Protocol) interface.

[0078] A single real optical intensity signal is converted into an analog electrical signal to obtain a single real baseband signal.

[0079] The real signal obtained after digital up-conversion A digital-to-analog converter (DAC) is used to convert the digital signal into an analog signal using a 16-bit DAC at a sampling rate of ≥200 MSa / s, forming a single-channel real-valued baseband signal. Based on the peak-to-peak value of this single-channel real-valued baseband signal, the amplitude changes of the electrical signal are mapped to changes in the light intensity of the LED through optical intensity modulation for optical communication. However, a DC component still exists in the signal at this stage, requiring DC filtering to improve the transmission rate. At the receiving end, the light intensity signal is captured by a photodetector, converted back into an electrical signal, and then demodulated to recover the transmitted signal, forming a closed loop in the optical communication link.

[0080] S103 performs peak-to-peak extraction and AC coupling processing on a single real baseband signal to obtain an AC peak-to-peak signal with DC components removed.

[0081] To ensure that the operating bandwidth of power devices is not reduced during the digital-to-analog converter (DAC) and after the DAC converts digital signals to analog signals, thus guaranteeing the transmission rate of LED optical communication, an AC-coupled transmission method is used. Peak-to-peak value extraction is performed on the single-channel real baseband signal, eliminating the introduction of DC bias current. Simultaneously, the DC component in the analog signal is filtered out, resulting in an AC peak-to-peak signal with the DC component removed. An RF power divider is used, with its primary coil connected to the output of the DAC. This ensures that even with a negative voltage in the primary coil, the output voltage signal of the transformer's secondary coil will not be affected. Furthermore, the secondary voltage constantly follows the change in the primary voltage, converting the time-domain signal waveform into a positive real number signal. Finally, the signals output from the two terminals of the RF power divider are connected to subsequent circuits, such as signal amplifiers, to amplify the output signals so that they can be used to drive LEDs. This solves the problem that negative real numbers cannot be directly used for LED transmission and eliminates the need for adding DC bias, thus removing some obstacles affecting the transmission rate.

[0082] S104 performs single positive power supply differential amplification and pre-equalization on the AC peak-to-peak signal to generate a driving positive voltage signal.

[0083] A differential amplifier is used to amplify the signal output from the RF power divider. For example, the two outputs of the RF power divider are connected to the input of a differential amplifier powered by a single positive power supply. The input non-negative voltage signal is amplified by the differential amplifier and then processed by an active pre-equalization circuit to extend the bandwidth and form a driving positive voltage signal. Since the output of the RF power divider is a dual-channel inverted AC signal, it can be connected through the dual inputs of the differential amplifier. By controlling the single positive power supply of the differential amplifier, the negative real part can be eliminated without losing the effective information carried in the AC peak-to-peak signal. Simultaneously, the differential amplifier also reduces electrical noise, effectively improving the signal-to-noise ratio and thus increasing the system's operating bandwidth. For example, the active pre-equalization circuit can be formed by connecting a fourth-order high-pass RC bypass in parallel with an integrated operational amplifier chip. Its amplitude-frequency response curve has negative gain at low frequencies and positive gain at high frequencies, and changes with frequency according to the negative slope of the LED's own frequency response, thus extending the LED's bandwidth to 100MHz as needed.

[0084] S105 uses a positive driving voltage signal to drive a high-power LED diode to emit light, generating an LED optical communication signal.

[0085] After the pre-equalized positive voltage signal is input to the high-power LED driver circuit, the circuit drives the LED diode to emit light, generating an LED optical communication signal. When driving the LED, the light intensity is adjusted based on the peak-to-peak value variation trend to ensure stable light emission and signal transmission within the bandwidth required by the user. For the LED diode itself, the input signal is similar to a pulsating positive DC signal; the effective information is hidden in the peak-to-peak value of the pulsating signal. High-speed information transmission is achieved by controlling the LED's luminous power, and the information is effectively detected by the receiver.

[0086] This embodiment modulates the original audio and video data using QAM-OFDM in the host computer, then performs quadrature IQ modulation on the resulting complex baseband signal, converting it into a single real baseband signal. This signal is then AC-coupled and DC-filtered to obtain a non-negative voltage signal without DC components. After signal amplification and pre-equalization, its transmission bandwidth is expanded to form a voltage signal for driving LED illumination. The LED diode adjusts its luminous intensity based on the peak-to-peak value variation, thus transmitting the signal. By using a low-loss AC-coupled transmission method, the peak-to-peak values ​​of the real signals obtained from QAM-OFDM and IQ quadrature modulation are coupled and transmitted, and then amplified by a single positive power supply to convert it into a positive voltage to control the LED light intensity, forming an LED optical communication signal. This eliminates the need to introduce DC voltage into the digital domain, avoiding the bandwidth reduction issues of DAC and power devices, and does not affect the LED's DC operating conditions. This ensures the LED's DC bias voltage remains stable, allowing it to operate stably in the linear modulation region. Combined with the pre-equalization circuit to expand the bandwidth, it enables distortion-free transmission of audio and video signals, balancing LED lighting and high-speed communication functions.

[0087] For example, using the QT GUI Time Sink, QT GUI Frequency Sink, and QT GUI Constellation Sink in GNU Radio, one can observe the time-domain waveform, frequency-domain waveform, and constellation diagram of a signal in real time, such as... Figure 4 , 5 As shown, Figure 4 This is the spectrum diagram of the transmitter. Figure 5 This is a constellation diagram of the signal received at the receiving end. During actual testing, the frequency coverage of the 64QAM-OFDM modulated video signal in this embodiment was within the range of 0MHz-100MHz, the test system bandwidth reached 100MHz, and the signal quality was close to the OFDM signal required in engineering. During the test, the transmitting end used File Source in GNU Radio to select the desired video file for transmission. The video file format was MPEG2-TS. The receiving end used File Sink to save the received video file to the local computer and named it rx.ts. The video file was played using VLCmedia player software. By observing and comparing the quality of the source video at the transmitting end and the video file at the receiving end, the real-time video transmission function was verified, and the bit error rate and maximum communication rate of the communication system were jointly tested. The test results show that within a communication distance of 0-110 meters, with a communication rate of 1Mbps and video file transmission, the transmission rate and bit error rate of the source video at the transmitting end and the video file at the receiving end were calculated in MATLAB. The lowest system bit error rate was found to be 0.1×10⁻⁶.-5 ,like Figure 6 As shown; subsequently, a high-speed test experiment was conducted. Within a communication distance of 1-10 meters, with a communication rate set at 500 Mbps, the calculated minimum system bit error rate was 0.1 × 10⁻⁶. -4 ,like Figure 7 As shown.

[0088] Example 2

[0089] Figure 8 This is a flowchart of a high-power LED visible light signal transmission method without DC bias according to Embodiment 2 of the present invention. This embodiment is based on the above embodiment and optimized. In this embodiment, S104 is specifically optimized as follows:

[0090] The AC peak-to-peak signal is input into a differential amplifier powered by a single positive power supply to generate a non-negative voltage signal;

[0091] A non-negative voltage signal is input into an active pre-equalization circuit based on a fourth-order high-pass RC bypass, which generates a stable positive driving voltage signal within a -3dB bandwidth. The -3dB bandwidth is the basis for measuring the operating bandwidth of a communication system in communication engineering.

[0092] Accordingly, the high-power LED visible light signal transmission method without DC bias provided in this embodiment specifically includes:

[0093] S201 performs Orthogonal Frequency Division Multiplexing (OFDM) modulation and high-order Quadrature Amplitude (QAM) modulation on the original audio and video data to generate a complex baseband signal.

[0094] S202 performs quadrature IQ modulation on the complex baseband signal to generate a single real baseband signal.

[0095] S203 performs peak-to-peak extraction and AC coupling processing on a single real baseband signal to obtain an AC peak-to-peak signal with DC components removed.

[0096] In one optional implementation of this embodiment, a single real baseband signal is input into the primary coil of an RF power divider. The output voltage of the secondary coil of the RF power divider varies with the peak-to-peak value of the input voltage of the primary coil, and the center tap of the secondary coil is grounded to obtain an AC peak-to-peak signal with DC components filtered out.

[0097] A low-insertion-loss RF power divider is used to reduce power attenuation caused by heat loss after signal insertion into the coupler. For example, an ADT1:1WT RF transformer (1:1 RF transformer) is used, with a 10µF DC blocking capacitor connected in series at its output. This forms an RF power divider that can AC couple a single real-valued baseband signal and filter out the DC component, allowing bidirectional coupling of the single real-valued baseband signal to extract positive and negative peak-to-peak values. The input of this RF power divider receives the output from a DAC. The output of the DAC is connected to the primary coil, and the center tap of the secondary coil is connected to the simulated ground of the subsequent amplifier circuit. This converts the input signal containing negative voltage components into an AC peak-to-peak signal with ground level as a reference, containing positive and negative variations. The two outputs of the secondary coil of the RF power divider are connected to the subsequent amplifier circuit, serving as the output of the RF power divider and the input of the subsequent amplifier circuit, resulting in an AC peak-to-peak signal with the DC component filtered out. Figure 9 As shown, the waveform of the single-channel output time-domain signal after coupling by the RF power divider has become a positive real number signal, but the peak-to-peak value variation pattern is still the same as the original baseband signal. After passing through a single positive power supply differential amplifier circuit, the two are cascaded, and the middle tap of the secondary coil of the RF power divider is connected to the analog ground of the input terminal of the differential amplifier. At this time, the dual-channel signal output by the secondary coil of the RF power divider is equivalent to positive for the differential amplifier. After controlling the differential amplifier to be powered by a single positive power supply, the negative real number part can be eliminated without losing the effective information carried in the AC peak-to-peak value signal, forming a positive voltage signal (non-negative voltage signal).

[0098] S204 inputs the AC peak-to-peak signal into a single-supply differential amplifier to generate a non-negative voltage signal.

[0099] The AC peak-to-peak signal, after the DC component has been filtered out from the RF power divider, is amplified using a differential amplifier circuit. For example, a differential amplifier circuit powered by a single positive power supply is used, employing dual-ended differential inputs for single-ended to differential conversion. This allows for effective interface with the RF power divider and also effectively reduces electrical noise interference, improving the signal-to-noise ratio. The amplified signal generates a non-negative voltage signal, which is then input to the LED circuit to drive the LED to emit light.

[0100] S205 inputs a non-negative voltage signal into an active pre-equalization circuit based on a 4th-order high-pass RC bypass to generate a driving positive voltage signal. The -3dB bandwidth is the basis for measuring the operating bandwidth of a communication system in communication engineering.

[0101] To extend the bandwidth of LED optical communication and achieve the desired target bandwidth, a pre-equalization circuit is used to adjust the signal response slope. This ensures that the amplitude-frequency response function curve of the pre-equalization circuit is within the target bandwidth range, enabling stable signal transmission with a low bit error rate. Only then can the target bandwidth communication be considered achieved. For example, an active pre-equalization circuit is formed by connecting a fourth-order high-pass RC bypass in parallel with an integrated operational amplifier chip. Figure 10 The diagram shows the circuit diagram of an active pre-equalizer circuit. The differential signal is fed into a 4th-order active high-pass pre-equalizer circuit. Its amplitude-frequency response curve exhibits negative gain at low frequencies and positive gain at high frequencies, and its frequency response varies with the LED's own negative slope. By adjusting its amplitude-frequency response value, the LED's transmission bandwidth can be extended to the desired target bandwidth, such as 100MHz. After pre-equalization, the signal is amplified to 0V–+5V via a single power supply, serving as the final positive driving voltage signal. The transfer function of this active pre-equalizer circuit is:

[0102]

[0103] in, Indicates the gain resistor. This represents the feedback resistance, and s represents the S-parameter. , , , Indicates resistance. , , , This represents capacitance. Its transfer function... The circuit exhibits a positive slope of +0.7 dB / dec to +1.2 dB / dec within the 1 MHz–100 MHz frequency band to compensate for the negative slope of -0.8 dB / dec in the LED frequency response, thus extending the system's 3 dB bandwidth from ≤20 MHz to ≥100 MHz. By adjusting the RC parameters (resistance and capacitance parameters) of the RC network, the circuit achieves amplitude-frequency characteristics that suppress low frequencies and enhance high frequencies, compensating for the bandwidth attenuation of the LED light source and achieving stable transmission within the desired target bandwidth range. Based on the Laplace transform principle, a frequency domain transformation is performed on the above transfer function to form the amplitude-frequency response function of the active pre-equalization circuit:

[0104]

[0105] Among them, gain resistor The value is 52k ohms, and the feedback resistor is... The value is 453 ohms. Therefore, the capacitor... Make the molecules follow the angular frequency The capacitance increases with the increase of [something]. , , Make the denominator change with angular frequency The amplitude-frequency response increases with increasing frequency, and thus decreases as the frequency increases. This can be achieved by adjusting... , , , , , , The parameter values ​​are adjusted to change the amplitude-frequency response curve so that it has negative gain at low frequencies and positive gain at high frequencies, and changes with frequency according to a certain slope. This allows the equalization circuit to increase the high-frequency response and suppress the low-frequency response, thereby expanding the bandwidth of the LED light source.

[0106] S206 uses a positive driving voltage signal to drive a high-power LED diode to emit light, generating an LED optical communication signal.

[0107] This embodiment uses an RF power divider to directly couple the peak-to-peak value of the USRP's baseband signal to the input of a differential amplifier. This performs AC coupling processing to extract the peak-to-peak value of the single-channel real baseband signal, and filters out the DC component using a DC blocking capacitor. The resulting AC peak-to-peak value signal, after removing the DC component, eliminates the need for DC bias current and removes the influence of DC on power devices, thus avoiding obstacles to bandwidth expansion. A differential amplifier with a single positive power supply and an active pre-equalization circuit amplify the peak-to-peak value of the input baseband signal using the DC-free AC peak-to-peak value signal. The pre-equalization circuit then performs equalization processing, increasing high frequencies and attenuating low frequencies, enabling the LED circuit driven by it to transmit signals stably within the required target bandwidth range, thus achieving the transmission bandwidth actually needed by the user.

[0108] Example 3

[0109] Figure 11 This is a schematic diagram of a high-power LED visible light signal transmission system without DC bias according to Embodiment 3 of the present invention. In this embodiment, the high-power LED visible light signal transmission system without DC bias includes:

[0110] The signal source modulation module 810 is used to perform orthogonal frequency division multiplexing (OFDM) modulation and high-order orthogonal amplitude (QAM) modulation on the original audio and video data to generate complex baseband signals;

[0111] The carrier modulation module 820 is used to perform quadrature carrier IQ modulation and digital-to-analog conversion on complex baseband signals to generate a single real baseband signal.

[0112] The RF power divider coupling module 830 is used to extract the peak-to-peak value of a single real baseband signal to obtain an AC peak-to-peak value signal with the DC component removed.

[0113] The signal amplification and pre-equalization module 840 is used to perform single-supply differential amplification and pre-equalization processing on AC peak-to-peak signals, and can generate a stable power drive positive voltage signal within a -3dB bandwidth.

[0114] The optical signal output module 850 is used to drive an LED to emit light using a positive driving voltage signal, thereby generating an LED optical communication signal.

[0115] For example, the high-power white LED light source module in this embodiment adopts a 3*2 array structure, using a total of 6 3-watt white LEDs, arranged in a 3x2 layout, where each column consists of 3 LEDs connected in series and then in parallel. The center wavelength of the light source is 450 nanometers, and the modulation bandwidth can reach 100MHz after pre-equalization. Figure 12 The diagram shows the structural composition of the transmitter. Its high-power LED driver circuit is composed of an integrated operational amplifier circuit based on the LD5530, a 2SK3476 high-power MOSFET, a passive LC impedance matching network, and a BT circuit cascaded together. Figure 13 The diagram shows the circuit diagram of a high-power LED driver circuit. The Bias-T circuit mainly consists of one inductor and one capacitor. The inductor is made of 0.1 cm pure copper enameled wire wound with a high-frequency ferrite core, with a winding spacing of 0.05 mm. The 2SK3476 high-power MOSFET has its source (S) directly grounded, its gate (G) bias voltage of 1.76V, and its drain (D) voltage of 5V, with an AC output power of 30dBm. The output signal is coupled through a capacitor. The impedance matching network uses an LC series structure connected in parallel at the input of the 2SK3476 high-power MOSFET. To achieve output impedance matching, a 1:4 transmission line transformer is added to the output of the MOSFET, made of 0.05 cm diameter enameled wire wound on a high-frequency ferrite core. An LED driver stage is constructed using an LD5530 controller and 2SK3476 power MOSFETs. The MOSFET gate is biased at 1.76 V, the drain voltage is +5 V, and the AC output power is ≥30 dBm. A 1:4 transmission line transformer and an LC matching network are connected in parallel at the output of the MOSFET to transform the output impedance of the MOSFET from 12.5Ω to 50Ω, thereby driving a 3×2 array of high-power white LEDs. The LED center wavelength is 450 nm, the total optical power is ≥3 W, and the optical signal waveform is linearly proportional to the driving positive voltage signal, achieving 500 Mb / s visible light communication.

[0116] This embodiment uses a source modulation module to perform 64QAM-OFDM modulation on the original audio and video signals, a carrier modulation module to perform quadrature carrier modulation and digital-to-analog conversion on the complex baseband signal, an RF power divider / coupler module to extract peak-to-peak values ​​and filter out DC components, a signal amplification and pre-equalization module to amplify and expand the bandwidth of the AC peak-to-peak signal, and an optical signal output module to drive LED diodes to emit light and output optical communication signals. By using a low-loss AC coupling transmission method, the peak-to-peak values ​​of the real signals after QAM-OFDM and IQ quadrature modulation are coupled and transmitted, and then amplified by a single positive power supply to convert them into a positive voltage to control the LED light intensity, forming an LED optical communication signal. This eliminates the need to introduce DC voltage into the digital domain, avoiding the bandwidth reduction problems of DAC and power devices, and does not affect the DC operating conditions of the LED itself, allowing the LED's DC bias voltage to remain stable, thus ensuring stable operation in the linear modulation region. Combined with the pre-equalization circuit to expand the bandwidth, it can transmit audio and video signals without distortion, thus balancing the functions of LED lighting and high-speed communication.

[0117] Optionally, the source modulation module includes:

[0118] The channel coding and framing submodule is used to perform channel coding and data framing processing on audio and video sources.

[0119] The constellation mapping submodule is used to perform constellation mapping on the data after frame processing.

[0120] The subcarrier allocation submodule is used to allocate OFDM subcarriers to the constellation-mapped data and add a cyclic prefix to form a complex baseband signal.

[0121] For example, GNU Radio (software version 3.10.11.0, processor speed 2.30 GHz, operating system Linux) is used in the host computer to perform channel coding, data framing, constellation mapping and subcarrier allocation on the raw audio and video signals.

[0122] Optionally, the carrier modulation module includes:

[0123] The quadrature carrier modulation submodule is used to perform quadrature carrier IQ modulation on complex baseband signals to generate a single real optical intensity signal. For example, GNU Radio is used in the host computer to perform quadrature carrier IQ modulation on a negative baseband signal.

[0124] The digital-to-analog converter (DAC) submodule is used to convert a single real-valued optical intensity signal into an analog electrical signal, resulting in a single real-valued baseband signal. For example, the DAC submodule can utilize the DAC unit in the USRP modulation board, specifically the USRP X310, and communicate with GNURadio via UHD (USRP Hardware Driver, the official USRP driver, version 4.7).

[0125] Optionally, the RF power divider coupling module includes: an RF power divider coupling submodule and a DC blocking capacitor submodule. The RF power divider coupler uses a 1:1 RF transformer (ADT1:1WT), connected in series with the DC blocking capacitor at the output end. The capacitance value C of the DC blocking capacitor is set to satisfy C≥1 / (2πf) min R), where R is typically taken as 50Ω in the radio frequency field. f min The lowest subcarrier frequency of the OFDM signal is used to completely filter out the DC component and maintain a 3 dB bandwidth ≥ 100 MHz.

[0126] Optionally, the signal amplification and pre-equalization module includes:

[0127] The differential amplifier submodule is used to amplify the AC peak-to-peak signal, reduce electrical noise, improve the signal-to-noise ratio, and generate a non-negative voltage signal. For example, the differential amplifier uses the integrated operational amplifier chip AD8130, with a working bandwidth of 270MHz, a supply voltage of 5V, and a gain of 8dB.

[0128] The active pre-equalization submodule is used to extend the bandwidth of non-negative voltage signals, generating a stable positive drive voltage signal within a -3dB passband. For example, the pre-equalization circuit employs a 4th-order high-pass RC bypass active integrated operational amplifier circuit, formed by connecting the integrated operational amplifier VCA824 in parallel with a 4th-order RC bypass network.

[0129] The DC-bias-free high-power LED visible light signal transmission method provided in the embodiments of the present invention can execute the DC-bias-free high-power LED visible light signal transmission method provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method.

[0130] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for transmitting a high-power LED visible light signal without DC bias, characterized in that, The method comprises the following steps: S101, orthogonal frequency division multiplexing (OFDM) modulation and high-order quadrature amplitude modulation (QAM) modulation are performed on original audio and video data to generate a complex baseband signal; S102, the complex baseband signal is subjected to orthogonal IQ modulation to generate a single real baseband signal; S103, the single real baseband signal is input into a primary coil of a radio frequency power division coupler, and the output voltage of a secondary coil of the radio frequency power division coupler changes with the peak-to-peak value of the input voltage of the primary coil, and the center tap of the secondary coil is grounded to extract the peak-to-peak value of the single real baseband signal and filter out the direct current component to obtain an alternating peak-to-peak value signal with the direct current component filtered out; S104, the alternating peak-to-peak value signal is subjected to single positive power supply differential amplification and pre-equalization processing to generate a driving positive voltage signal; The S104 comprises: The alternating peak-to-peak value signal is input into a single positive power supply differential amplifier to generate a non-negative voltage signal; The non-negative voltage signal is input into an active pre-equalization circuit based on a fourth-order high-pass resistance-capacitance bypass to generate a driving positive voltage signal with stable power within a -3dB passband width, which is a basis for measuring the working bandwidth of a communication system in communication engineering; S105, the driving positive voltage signal is used to drive a high-power LED diode to emit light to generate an LED optical communication signal.

2. The method of claim 1, wherein, The S101 comprises: Channel coding and data framing processing are performed on an audio and video source in a host computer PC; Constellation mapping is performed on the data after framing processing; OFDM subcarriers are allocated to the data after constellation mapping, and a cyclic prefix is added to form a complex baseband signal.

3. The method of claim 1, wherein, The S102 comprises: The complex baseband signal is subjected to orthogonal carrier IQ modulation to generate a single real light intensity signal; Analog electrical signal conversion is performed on the single real light intensity signal to obtain a single real baseband signal.

4. A DC-bias-free high-power LED visible light signal transmission system for implementing the DC-bias-free high-power LED visible light signal transmission method according to any one of claims 1-3, characterized in that, The method comprises the following steps: A source modulation module is configured to perform orthogonal frequency division multiplexing (OFDM) modulation and high-order quadrature amplitude modulation (QAM) modulation on original audio and video data to generate a complex baseband signal; A carrier modulation module is configured to perform orthogonal carrier IQ modulation and digital-to-analog conversion on the complex baseband signal to generate a single real baseband signal; A radio frequency power division coupling module is configured to extract the peak-to-peak value of the single real baseband signal to obtain an alternating peak-to-peak value signal with the direct current component filtered out; A signal amplification and pre-equalization module is configured to perform single positive power supply differential amplification and pre-equalization processing on the alternating peak-to-peak value signal to generate a driving positive voltage signal with stable power within a -3dB passband width; An optical signal output module is configured to use the driving positive voltage signal to drive an LED to emit light to generate an LED optical communication signal.

5. The system of claim 4, wherein, The source modulation module comprises: A channel coding and framing sub-module is configured to perform channel coding and data framing processing on an audio and video source; A constellation mapping sub-module is configured to perform constellation mapping on the data after framing processing; A subcarrier allocation sub-module is configured to allocate OFDM subcarriers to the data after constellation mapping and add a cyclic prefix to form a complex baseband signal.

6. The system of claim 4, wherein, The carrier modulation module comprises: An orthogonal carrier modulation sub-module is configured to perform orthogonal carrier IQ modulation on the complex baseband signal to generate a single real light intensity signal; Analog-to-digital conversion sub-module, configured to convert the single-channel real light intensity signal into an analog electrical signal to obtain a single-channel real baseband signal.

7. The system of claim 4, wherein, The radio frequency power division coupling module comprises a radio frequency power division coupling sub-module and a direct current blocking capacitor sub-module.

8. The system of claim 4, wherein, The signal amplification pre-equalization module comprises: A differential amplification sub-module, configured to amplify the AC peak-to-peak value signal, reduce electrical noise, improve signal-to-noise ratio, and generate a non-negative voltage signal; An active pre-equalization sub-module, configured to expand the bandwidth of the non-negative voltage signal and generate a stable driving positive voltage signal within a-3dB passband.

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