A full-duplex visible light backscattering communication transmission optimization method and device

Abstract

The application discloses a full-duplex visible light backscattering communication transmission optimization method and relates to the technical fields of visible light communication and Internet of Things. A hardware link containing a coaxial transmitting and receiving light path of a reader end and double-unit liquid crystal shutters of a tag end is built; a constant envelope binary frequency shift keying modulation mode is used as a downlink optical carrier at the reader end, so that multiplicative self-interference of the downlink is eliminated and available energy of the tag end is maximized; the double-unit liquid crystal shutters are cooperatively driven by two independent signals at the tag end, a light transmission falling edge is forced to block light by an active electric field to cover a slow natural relaxation process of liquid crystal molecules; at a reader receiving end, a discrete baseband envelope signal of an echo is extracted, and a double-threshold finite state machine based on relative trend detection is used for post-equalization processing, so that a digital logic level is reconstructed. The application further discloses a full-duplex visible light backscattering communication transmission optimization device, which realizes full-duplex communication and greatly improves transmission rate and reliability of an uplink.

Description

Technical Field

[0001] This invention relates to the fields of visible light communication and Internet of Things (IoT) technology, and in particular to a method and apparatus for optimizing full-duplex visible light backscatter communication transmission. Background Technology

[0002] With the rapid development of 6G mobile communication and the Internet of Things (IoT), the connection of massive IoT devices has placed extremely stringent demands on energy efficiency. Traditional visible light communication (VLC) and radio frequency (RF) technologies typically rely on active light-emitting devices (such as LEDs) or RF transmitter modules in the uplink. Their milliwatt-level or even watt-level power consumption places a heavy burden on the battery maintenance of edge IoT nodes, making it difficult to meet the development needs of the future low-power or even net-zero energy IoT ecosystem.

[0003] To overcome this energy consumption bottleneck, visible light backscatter communication (VLBC) has emerged as an ultra-low-power alternative. VLBC tags passively modulate and reflect incident light using a liquid crystal shutter (LCS) and corner reflectors, rather than actively transmitting signals, thus successfully reducing power consumption to the microwatt level. However, in practical applications, achieving a robust VLBC system faces two major challenges.

[0004] First, in full-duplex communication scenarios, there is a serious downlink multiplicative self-interference problem. Most existing VLBC research is often limited to isolated uplink analysis or assumes that the downlink light source is ideal constant DC light (i.e., half-duplex mode). However, in actual bidirectional full-duplex scenarios, the reader needs to transmit modulated downlink waveforms (such as traditional on / off keyed OOK modulation). Due to the multiplicative nature of backscattered signals, drastic fluctuations in the downlink optical carrier amplitude (such as the logic '0' level period in OOK modulation) are directly transferred to the uplink signal, leading to severe communication interruptions or extreme deterioration of the signal-to-noise ratio in the uplink.

[0005] Secondly, the core modulation device, the liquid crystal shutter, suffers from a strict physical bandwidth limitation. Due to the slow physical relaxation characteristics of liquid crystal molecules, as the uplink modulation frequency increases, the signal exhibits severe "fin-like" waveform distortion and severe inter-symbol interference (ISI). This results in the transmission rate of traditional VLBC systems typically being strictly limited to an extremely low range of 0.5 to 1 kbps. To overcome this bandwidth bottleneck, current cutting-edge research (such as delay-superimposed modulation or multi-user MIMO architectures) often employs hardware optimization, using complex multi-pixel array spatial multiplexing techniques to improve the rate. However, these methods inevitably increase system hardware complexity and cost, while also increasing dynamic power consumption, contradicting the original intention of low-power IoT design. Furthermore, traditional decision mechanisms based on absolute voltage thresholds often fail directly when faced with the aforementioned severe waveform distortion and extreme attenuation caused by the spatial optical path.

[0006] Therefore, there is an urgent need for a transmission optimization method for full-duplex visible light backscatter communication systems that can effectively suppress downlink multiplicative self-interference in full-duplex communication without relying on complex multi-pixel hardware arrays, and use signal processing techniques to overcome the physical bandwidth bottleneck of liquid crystal devices, thereby achieving high-reliability, high-data-rate, low-power uplink transmission. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a full-duplex visible light backscatter communication transmission optimization method and device to solve the serious downlink multiplicative self-interference problem in the existing full-duplex visible light backscatter communication, as well as the technical problems of low uplink transmission rate and serious signal distortion caused by slow physical relaxation of liquid crystal shutter, so as to achieve low power consumption, high reliability and high data rate visible light uplink transmission.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A full-duplex visible light backscatter communication transmission optimization method proposed according to the present invention includes:

[0010] A hardware transceiver link for a full-duplex visible light backscatter communication system is constructed, comprising a reader end and a tag end; among which...

[0011] At the reader end, it is used to generate downlink optical carrier signals using a constant envelope binary frequency shift keying modulation method;

[0012] The tag receives downlink optical carrier signals and backscatters them, then outputs the modulated light as echo data backscattered to the reader. The reader extracts the discrete baseband envelope signal of the echo data and uses a dual-threshold finite state machine based on relative trend detection to perform post-equalization on the discrete baseband envelope signal to recover the uplink data, which is the echo data.

[0013] As a further optimization of the full-duplex visible light backscatter communication transmission optimization method described in this invention, the reader end includes a host computer, a downlink transmitting module, an uplink receiving and decoding module, a beam splitter, and a converging lens. The downlink transmitting module includes a signal generator and a light-emitting device, and the uplink receiving and decoding module includes a photodetector and an oscilloscope.

[0014] The host computer is used to generate downlink data and output the downlink data to the signal generator; the downlink data is a downlink optical carrier signal.

[0015] It is also used to receive discrete-time received signals from oscilloscopes, and to perform post-equalization processing on the discrete-time received signals to recover the uplink data, which is the echo data.

[0016] The signal generator is used to receive downlink data output from the host computer, convert the downlink data into analog drive signals and output them to the light-emitting device;

[0017] The light-emitting device is used to convert the analog driving signal into a downlink optical carrier signal. The downlink optical carrier signal is collimated by a converging lens and then output to the beam splitter.

[0018] A beam splitter is used to transmit the received downlink optical carrier signal and output the downlink optical carrier signal to the tag.

[0019] It is also used to reflect the received echo data from the tag and guide the echo data to the converging lens;

[0020] A converging lens is used to converge the echo data reflected by the beam splitter and output it to a photodetector;

[0021] A photodetector is used to receive the echo data output from the converging lens, convert the echo data into an electrical signal, and output it to an oscilloscope.

[0022] An oscilloscope is used to sample and digitize electrical signals to obtain discrete-time received signals and transmit them back to a host computer.

[0023] As a further optimization of the full-duplex visible light backscatter communication transmission optimization method described in this invention, the tag end includes a modulation and reflection module. The modulation and reflection module includes a controller, a dual-channel digital-to-analog converter, a dual-channel drive amplifier, a dual-unit cascaded liquid crystal shutter, and a corner reflector. The dual-unit cascaded liquid crystal shutter includes a first liquid crystal unit and a second liquid crystal unit, and the dual-unit cascaded liquid crystal shutter is tightly mounted on the light-incident side of the corner reflector.

[0024] The controller is used to generate two independent digital drive signals based on the uplink data to be sent, and output the two digital drive signals to the dual-channel digital-to-analog converter respectively.

[0025] A dual-channel digital-to-analog converter is used to convert two digital drive signals into analog signals, which are then output to a dual-channel drive amplifier.

[0026] A dual-channel drive amplifier is used to amplify two analog drive signals and output the amplified two drive signals to the first and second liquid crystal units of the dual-unit cascaded liquid crystal shutter, respectively.

[0027] A dual-unit tandem liquid crystal shutter is used to backscatter and modulate the incident downlink optical carrier signal under the coordinated drive of two driving signals. During the falling edge of light transmission, the drive of the first liquid crystal unit is canceled and a driving pulse is actively applied to the second liquid crystal unit. The overall light transmission state is changed through the coordinated action of the first and second liquid crystal units.

[0028] A corner reflector is used to backscatter the light signal modulated by the dual-unit cascaded liquid crystal shutter to the reader. The light signal backscattered to the reader is the echo data.

[0029] As a further optimization scheme of the full-duplex visible light backscatter communication transmission optimization method described in this invention, the controller is an FPGA controller.

[0030] As a further optimization scheme for the full-duplex visible light backscatter communication transmission optimization method described in this invention, the specific details are as follows:

[0031] Step S1: Construct the hardware transceiver link of the full-duplex visible light backscatter communication system. The hardware transceiver link includes a reader end and a tag end. At the reader end, a beam splitter is used to construct a coaxial transmission and reception optical path. At the tag end, a dual-unit series liquid crystal shutter is tightly mounted on the light-incident side of the corner reflector to construct a passive backscatter modulation module.

[0032] Step S2: The host computer at the reader end generates downlink data, uses binary frequency shift keying to obtain downlink digital waveforms from the downlink data, transmits the downlink digital waveforms to the signal generator and is controlled by the host computer, and the signal generator outputs analog drive signals corresponding to the downlink digital waveforms to drive the light-emitting device to emit downlink optical carrier signals.

[0033] Step S3: The first and second liquid crystal units in the dual-unit tandem liquid crystal shutter at the tag end are driven by an amplifier after being amplified by an independent signal output from the FPGA controller. The dual-unit tandem liquid crystal shutter switches its light transmission state in coordination according to the uplink data, performs backscatter modulation on the incident downlink optical carrier signal to obtain the modulated light signal, and backscatters the modulated light signal back to the reader end through the corner reflector. The modulated light signal is the echo data.

[0034] Step S4: The photodetector at the reader end receives the backscattered echo data and converts it into an electrical signal. The electrical signal is sampled and digitized using an oscilloscope to obtain the digitized signal. The digitized signal is then transmitted to the host computer and the discrete baseband envelope signal is extracted from it.

[0035] Step S5: The reader performs offline digital processing on the baseband envelope signal in the host computer, and reconstructs the digital logic level of the uplink data using a dual-threshold finite state machine based on relative trend detection to obtain the uplink data with distortion eliminated.

[0036] As a further optimization scheme of the full-duplex visible light backscatter communication transmission optimization method described in this invention, step S3 includes:

[0037] S301, the FPGA controller generates two independent digital drive signals based on the uplink data to be transmitted;

[0038] S302. The two digital drive signals are converted from digital to analog by a dual-channel digital-to-analog converter, and then amplified by an amplifier before being input as drive signals to the first and second liquid crystal units of the dual-unit cascaded liquid crystal shutter.

[0039] S303. During the falling edge of the uplink data state switching from logic 1 to logic 0, the preset compensation waveform logic output by the FPGA controller is as follows: stop applying the driving voltage to the first liquid crystal cell that is currently in the excited light-transmitting state, so that the first liquid crystal cell enters the physical natural relaxation stage of the liquid crystal molecules; at the same time, actively apply the electric field driving pulse to the second liquid crystal cell that is in the unexcited state, so that the second liquid crystal cell flips to the light-blocking state under the action of the electric field.

[0040] S304. By coordinating the two independent driving signals in time, and utilizing the light-blocking response of the second liquid crystal unit under the active electric field, the physical natural relaxation process of the first liquid crystal unit is superimposed in series on the physical optical path, thereby realizing the switching of the decrease in backscattering transmittance at the label end.

[0041] As a further optimization scheme of the full-duplex visible light backscatter communication transmission optimization method described in this invention, step S4 involves extracting the discrete baseband envelope signal, including:

[0042] S401. The host computer sends instructions to the oscilloscope through the communication interface, controlling the oscilloscope to perform analog-to-digital conversion on the electrical signal output by the photodetector at a preset sampling rate, and then transmits the collected discrete-time received signal back to the host computer.

[0043] S402. In the host computer, perform incoherent demodulation on the discrete-time received signal, calculate the amplitude of the approximate analytic signal using a sliding integral window, and extract the baseband envelope. The specific formula is as follows:

[0044]

[0045] in, Indicated by sampling frequency Sampling discrete-time received signals; This represents the extracted baseband envelope; Indicates the size of the sliding integral window. The value is approximately: , For carrier frequency; This represents the maximum-minimum normalization operator;

[0046] S403, Using the max-min normalization operator The baseband envelope signal is mapped to the [0,1] interval to decouple the power fluctuations caused by the detection logic and the optical path geometry loss;

[0047] S404, Calculate the baseband envelope The cross-correlation function between the data and the known preamble reference sequence; frame synchronization of uplink data frames is achieved by maximizing the cross-correlation function.

[0048] As a further optimization scheme of the full-duplex visible light backscatter communication transmission optimization method described in this invention, in step S5, the digital logic level of the uplink data is reconstructed using a dual-threshold finite state machine based on relative trend detection. The specific content is as follows:

[0049] S501. Dynamically track and update the local historical extreme values ​​of the baseband envelope signal: While the dual-threshold finite state machine is in state 0, track the current local minimum value. ; Track the current local maximum value while the finite state machine is in state 1. ;

[0050] S502. Constructing an asymmetric dual-threshold judgment logic to identify trends: A relative valley decision criterion is used to identify the upward trend of the baseband envelope, and a relative peak decision criterion is used to identify the downward trend of the baseband envelope. The output state is based on the dual-threshold finite state machine. Reconstruct the digital logic level of the uplink data.

[0051] As a further optimization scheme for the full-duplex visible light backscatter communication transmission optimization method described in this invention, in step S502, the state transition equation of the asymmetric dual threshold judgment logic is:

[0052]

[0053] in, This represents the current output logic state. This represents the logical state at the previous moment. This is the baseband envelope signal at the current moment. This is the local minimum value recorded at the previous time step. This is the local maximum value recorded at the previous time step. The preset upward trend trigger threshold, The preset threshold for triggering a downward trend.

[0054] A full-duplex visible light backscatter communication transmission optimization device includes a reader end and a tag end. The reader end includes a host computer, a downlink transmitting module, an uplink receiving and decoding module, a beam splitter, and a converging lens. The downlink transmitting module includes a signal generator and a light-emitting device. The uplink receiving and decoding module includes a photodetector and an oscilloscope.

[0055] The host computer is used to generate downlink data and output the downlink data to the signal generator; the downlink data is a downlink optical carrier signal.

[0056] It is also used to receive discrete-time received signals from oscilloscopes, and to perform post-equalization processing on the discrete-time received signals to recover the uplink data, which is the echo data.

[0057] The signal generator is used to receive downlink data output from the host computer, convert the downlink data into analog drive signals and output them to the light-emitting device;

[0058] The light-emitting device is used to convert the analog driving signal into a downlink optical carrier signal. The downlink optical carrier signal is collimated by a converging lens and then output to the beam splitter.

[0059] A beam splitter is used to transmit the received downlink optical carrier signal and output the downlink optical carrier signal to the tag.

[0060] It is also used to reflect the received echo data from the tag and guide the echo data to the converging lens;

[0061] A converging lens is used to converge the echo data reflected by the beam splitter and output it to a photodetector;

[0062] A photodetector is used to receive the echo data output from the converging lens, convert the echo data into an electrical signal, and output it to an oscilloscope.

[0063] An oscilloscope is used to sample and digitize electrical signals to obtain discrete-time received signals and transmit them back to a host computer.

[0064] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0065] (1) The problem of multiplicative self-interference in full-duplex mode has been solved. This invention innovatively uses 2FSK as the downlink optical carrier in the physical layer waveform design, and realizes high-precision waveform generation through upper computer program control. By utilizing its constant envelope characteristic, not only can the LED always work at the maximum average emission power state, maximizing the backscattered light energy that can be obtained at the passive tag end, but it also fundamentally eliminates the severe fluctuations in downlink light intensity caused by traditional modulation methods such as OOK, ensuring that the uplink is not affected by communication interruptions caused by self-interference.

[0066] (2) Hardware and software collaboration breaks through the physical relaxation bottleneck of core components. At the hardware modulation end, the present invention innovatively adopts a dual-unit series liquid crystal shutter and an asymmetric driving strategy. During the falling edge, the active electric field is used to force the shutdown, which perfectly masks the slow natural relaxation of liquid crystal molecules. At the software receiving end, a dedicated liquid crystal shutter sensing post-equalizer is designed. The easily failed absolute voltage threshold decision mechanism is abandoned. Through dynamic extreme value tracking and asymmetric dual threshold relative trend detection, the digital logic that is severely distorted due to physical bandwidth limitation is accurately reconstructed.

[0067] (3) It achieves efficient automated verification and performance leap. With the help of the high-speed sampling of the programmable instrument and the powerful numerical calculation capability of the host computer, this system has successfully increased the maximum achievable data rate that meets the forward error correction threshold without the need to introduce additional complex multi-pixel spatial multiplexing array hardware, demonstrating excellent error correction and signal recovery capabilities.

[0068] (4) It has excellent system robustness and broad prospects for Internet of Things (IoT) applications. The solution of this invention utilizes a beam splitter to construct a precise coaxial optical transmission path, which effectively overcomes severe geometric optical path attenuation and provides a highly reliable transmission path with extremely low dynamic power consumption for edge IoT nodes. It fills the huge gap between weak ambient light energy harvesting and uplink communication energy consumption, and has outstanding engineering value for promoting the implementation of a net-zero energy consumption massive IoT ecosystem in future 6G networks. Attached Figure Description

[0069] Figure 1 This is a general flowchart of a transmission optimization method for a full-duplex visible light backscatter communication system provided in an embodiment of the present invention;

[0070] Figure 2 A schematic diagram of the hardware transceiver link and coaxial optical path structure of the system provided in the embodiments of the present invention;

[0071] Figure 3 This is a timing diagram of the asymmetric compensation drive waveform during the falling edge of a dual-unit tandem liquid crystal shutter provided in an embodiment of the present invention;

[0072] Figure 4 This is a schematic diagram of the state transition of a dual-threshold finite state machine based on relative trend detection, provided in an embodiment of the present invention.

[0073] Figure 5 This invention provides a performance comparison curve of the system uplink bit error rate as a function of received optical power under different downlink modulation schemes in an embodiment of the invention.

[0074] Figure 6 This is a schematic diagram comparing the waveform and eye diagram of the baseband signal before and after processing by the liquid crystal shutter sensing post-equalizer, provided in an embodiment of the present invention; wherein, (a) is the waveform diagram of the original received signal before equalization processing, (b) is the eye diagram of the original received signal before equalization processing, (c) is the waveform diagram of the signal after equalization processing, and (d) is the eye diagram of the signal after equalization processing.

[0075] Figure 7 The graph shows a performance comparison of the uplink bit error rate of the system with the transmission rate under different shutter modulation rates, as provided in this embodiment of the invention. Detailed Implementation

[0076] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0077] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0078] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0079] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0080] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0081] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0082] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0083] Figure 1 The diagram shows a schematic flowchart of a transmission optimization method for a full-duplex visible light backscatter communication system provided in an embodiment of this application.

[0084] like Figure 1 As shown, the transmission optimization method for this full-duplex visible light backscatter communication system includes the following steps:

[0085] S1. Construct the hardware transceiver link of a full-duplex visible light backscatter communication system, comprising a reader end and a tag end; wherein, at the reader end, a beam splitter is used to construct a coaxial transmit and receive optical path; at the tag end, a dual-unit cascaded liquid crystal shutter is tightly mounted on the light-incident side of a corner reflector to construct a passive backscatter modulation module. The hardware transceiver link and coaxial optical path structure of the system are as follows: Figure 2 As shown, it includes the following:

[0086] S101. The reader is equipped with a host computer, a programmable arbitrary waveform generator, a light-emitting device, a beam splitter, a converging lens, a photodetector, and a programmable oscilloscope. The downward beam emitted by the light-emitting device is collimated by the converging lens, transmitted through the beam splitter, and projected onto the tag end at a preset distance.

[0087] S102. An FPGA controller, a dual-channel digital-to-analog converter, a dual-channel drive amplifier circuit, a dual-unit cascaded LCD shutter, and a corner reflector are configured at the tag end. The dual-unit cascaded LCD shutter is mounted flush against the light-incident side of the corner reflector. When the downlink beam reaches the tag end, the uplink digital sequence generated by the FPGA controller, after digital-to-analog conversion and high-voltage amplification, drives the two LCD units to switch transmittance, achieving backscatter modulation.

[0088] S103. The backscattered light modulated at the tag end is transmitted in the reverse direction along the original optical path to the reader end. At this time, the backscattered light is reflected by the beam splitter and focused onto the photosensitive surface of the photodetector by the converging lens. This optical path design achieves coaxial isolation between the transmitter and receiver in full-duplex mode at the physical level, reduces the geometric alignment difficulty of system deployment, and ensures that the weak uplink echo signal is effectively captured by the photodetector.

[0089] S2. The reader uses a host computer to generate downlink data, employs a binary frequency shift keying (2FSK) modulation strategy to generate downlink digital waveforms, and controls an arbitrary waveform generator to output corresponding analog drive signals by sending programmable commands to drive the light-emitting device to transmit downlink optical carrier signals, including the following:

[0090] S201. In the host computer, a digital waveform sequence containing a 2FSK modulated signal is generated using preset numerical calculation software. The 2FSK signal carries downlink binary information by switching between two different discrete frequency points.

[0091] S202. The host computer sends program control commands to the arbitrary waveform generator through the communication interface, loads the generated digital waveform sequence into the memory of the arbitrary waveform generator, performs digital-to-analog conversion at a preset sampling rate, and outputs analog drive voltage.

[0092] S203. The analog voltage is used to drive the light-emitting device. Because the 2FSK signal has a strictly constant envelope characteristic in the time domain, the light-emitting device can maintain a maximum and constant average emitted light power while transmitting downlink data. This design not only maximizes the backscattered light energy available at the tag end, but also completely avoids, from a physical mechanism, the multiplicative self-interference caused by the drastic fluctuations in the downlink waveform amplitude due to traditional duty cycle modulation (such as on / off keying modulation) on the backscattered uplink, ensuring that the uplink communication link will not be interrupted due to downlink light source flicker.

[0093] S3. The dual-unit cascaded liquid crystal shutter and corner reflector at the tag end receive the downlink optical carrier signal. Each liquid crystal unit in the dual-unit cascaded liquid crystal shutter is driven by an independent signal output from the FPGA, amplified by an amplifier. The dual-unit cascaded liquid crystal shutter coordinates to switch its light transmission state according to the uplink data sequence, performs backscatter modulation on the incident downlink optical carrier signal, and backscatters the modulated light signal back to the reader end through the corner reflector. The specific driving process includes the following:

[0094] S301, the FPGA controller generates two independent digital drive signals based on the uplink data sequence to be sent.

[0095] S302. These two digital drive signals are converted from digital to analog by a dual-channel digital-to-analog converter, and then amplified by an amplifier before being input as high-voltage drive signals to the two independent liquid crystal units in front and behind the dual-unit cascaded liquid crystal shutter.

[0096] S303. During the falling edge of the uplink data state switching from logic '1' to logic '0', the FPGA outputs a preset compensation waveform. The timing of the asymmetric compensation drive waveform of the dual-unit cascaded LCD shutter during the falling edge is as follows: Figure 3 As shown, Figure 3 This is a timing diagram of the asymmetric compensation driving waveform during the falling edge of the dual-unit tandem liquid crystal shutter provided in this embodiment of the invention. The specific logic is as follows: immediately stop applying the driving voltage to the first liquid crystal unit that is currently in the excited and transparent state, so that it enters the physical natural relaxation stage of the liquid crystal molecules; at the same time, actively apply an electric field driving pulse to the second liquid crystal unit that is in the unexcited state, so that it is quickly forced to flip to the light-blocking state under the action of the electric field.

[0097] S304. Since the optical path is physically connected in series, the overall transmittance of the system depends on the product of the transmittances of the two liquid crystal cells. By coordinating the two independent driving signals in time, and utilizing the rapid light-blocking response of the second liquid crystal cell under the active electric field, the slow natural relaxation process of the first liquid crystal cell is superimposed and masked in series on the physical optical path, thereby forcing a high-speed decrease in the backscatter transmittance of the system, breaking through the inherent physical bandwidth limit of a single liquid crystal device.

[0098] S4. The photodetector at the reader end receives the backscattered echo signal and converts it into an electrical signal. A programmable oscilloscope is used to perform high-speed sampling and digitization of the electrical signal. The digitized signal is then transmitted to the host computer, from which discrete baseband envelope signals are extracted, including the following:

[0099] S401. The host computer sends a command to the programmable oscilloscope through the communication interface, controls the programmable oscilloscope to perform analog-to-digital conversion on the electrical signal output by the photodetector at a preset sampling rate, and transmits the collected discrete-time received signal back to the host computer.

[0100] S402. In the host computer, the discrete-time received signal is noncoherently demodulated. The amplitude of the approximate analytic signal is calculated using a sliding integral window, and the baseband envelope is extracted. The specific formula is as follows:

[0101]

[0102] in, Indicated by sampling frequency Sampling discrete-time received signals; This represents the extracted baseband envelope; This represents the size of the sliding integral window, and its value is approximately... , For carrier frequency; This represents the maximum-minimum normalization operator;

[0103] S403, Using the max-min normalization operator The baseband envelope signal is mapped to the [0,1] interval to decouple the power fluctuations caused by the detection logic and the optical path geometry loss.

[0104] S404, Calculate the baseband envelope A cross-correlation function between the cross-correlation function and a known preamble reference sequence; frame synchronization of uplink data frames is achieved by maximizing the cross-correlation function.

[0105] S5. The reader terminal performs offline digital processing on the baseband envelope signal in the host computer using a preset LCD shutter sensing post-equalizer. It then reconstructs the digital logic level of the uplink data using a dual-threshold finite state machine based on relative trend detection, obtaining an uplink data sequence with distortion eliminated. The state transition process of this finite state machine is as follows: Figure 4 As shown, Figure 4 This is a schematic diagram of the state transition of a dual-threshold finite state machine based on relative trend detection provided in an embodiment of the present invention; the specific process includes the following:

[0106] S501. Dynamically track and update the local historical extreme values ​​of the baseband envelope signal: While the finite state machine is in state '0', track the current local minimum value. While the finite state machine is in state '1', track the current local maximum value. ;

[0107] S502. Constructing an asymmetric dual-threshold judgment logic to identify effective trends: A relative valley decision criterion is used to identify upward trends, and a relative peak decision criterion is used to identify downward trends, in order to suppress noise fluctuations and tolerate signal amplitude attenuation and fin-like distortion caused by the physical relaxation of the liquid crystal shutter. Combined with... Figure 4 The specific mathematical state transition equation for the asymmetric double threshold judgment logic is as follows:

[0108]

[0109] in, This represents the current output logic state. This represents the logical state at the previous moment. This is the baseband envelope signal at the current moment. This is the local minimum value recorded at the previous time step. This is the local maximum value recorded at the previous time step. The preset upward trend trigger threshold, The preset threshold for triggering a downward trend.

[0110] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0111] In one embodiment, the transmission optimization method proposed in this application is compared with a traditional unbalanced transmission link in terms of accuracy and transmission rate. The comparison indicators are bit error rate (BER) and the maximum achievable data rate that meets the forward error correction (FEC) threshold. The performance of different configuration schemes under different downlink modulation methods is also compared. The performance of different communication models is evaluated, and the comparison curves of simulation and measured results are shown below. Figures 5 to 7As shown:

[0112] Performance comparison curves for different downlink modulation methods are as follows: Figure 5 As shown, Figure 5 This is a performance comparison curve of the uplink bit error rate as a function of received optical power under different downlink modulation methods provided in this embodiment of the invention. Comparative experiments show that when using multi-carrier modulation methods such as Orthogonal Frequency Division Multiplexing (OFDM), due to its inherent peak-to-average power ratio (PAPR), the downlink drive signal experiences severe amplitude fluctuations. This not only easily leads to nonlinear distortion and signal clipping in the light-emitting device, but also the extremely unstable instantaneous light intensity severely disrupts the weak uplink in the form of multiplicative interference. When using traditional on-off keying (OOK) modulation, although simple to implement, its waveform suffers from approximately 50% duty cycle loss, significantly reducing the average backscattered light energy obtainable at the tag end and severely deteriorating the uplink signal-to-noise ratio. In contrast, when using 2FSK as the downlink carrier in this invention, its strict time-domain constant envelope characteristic allows the light-emitting device to continuously maintain its maximum average transmit power point. This design maximizes the reflected energy at the tag end and completely eliminates the multiplicative self-interference caused by downlink light intensity fluctuations from a physical mechanism. This makes the required received power the minimum when meeting the FEC threshold, and the performance closest to the ideal DC baseline without downlink interference.

[0113] A schematic diagram comparing the waveforms and eye diagrams before and after baseband signal processing is shown below. Figure 6 As shown, Figure 6 This is a schematic diagram comparing the waveform and eye diagram of the baseband signal before and after processing by the liquid crystal shutter sensing post-equalizer, provided in an embodiment of the present invention; wherein, Figure 6 (a) in the diagram is the original received signal waveform before equalization processing. Figure 6 (b) in the diagram is the original received signal eye diagram before equalization processing. Figure 6 (c) in the diagram is the signal waveform after equalization. Figure 6 In the diagram, (d) represents the signal eye diagram after equalization. For example... Figure 6 As shown in (a) and (b), due to the slow physical relaxation of liquid crystal molecules, the unbalanced original received signal suffers from severe inter-symbol interference, making it difficult for digital logic to make decisions, resulting in a completely closed eye diagram. And as... Figure 6 As shown in (c) and (d) in the figure, after the state machine post-equalization processing designed in this invention, the distorted signal logic is successfully and accurately restored, the eye diagram is clearly opened, and the signal reconstruction capability of the equalizer is demonstrated.

[0114] Performance comparison curves at different shutter modulation rates are as follows: Figure 7 As shown, Figure 7This is a performance comparison curve showing the uplink bit error rate as a function of transmission rate under different shutter configurations provided in this embodiment of the invention. The comparative test results show that the traditional single-unit system, limited by physical relaxation constraints, has a maximum achievable data rate of only 1.0 kbps; while the present invention, employing a dual-unit cascaded asymmetric drive combined with a state machine post-equalizer, successfully increases the maximum achievable data rate to approximately 5.7 kbps, satisfying the FEC threshold. This system maintains high-precision and reliable transmission performance, demonstrating a significant performance improvement.

[0115] Secondly, embodiments of this application provide a transmission optimization device for a full-duplex visible light backscatter communication system, comprising: a reader end and a tag end. The reader end includes a host computer, a downlink transmission module, and an uplink reception decoding module; the host computer is used to run numerical calculation software to realize instrument programmable control and offline digital signal processing; the downlink transmission module includes a programmable arbitrary waveform generator and a light-emitting device, used to generate and transmit downlink optical carrier signals using a binary frequency shift keying modulation strategy; the uplink reception decoding module includes a photodetector and a programmable oscilloscope, used to receive echo signals, extract the baseband envelope using a sliding window, and perform post-equalization using a dual-threshold finite state machine based on relative trend detection to recover uplink data. The tag includes a modulation and reflection module, which is equipped with an FPGA, a dual-channel digital-to-analog converter, a dual-channel drive amplifier, a dual-unit cascaded liquid crystal shutter, and a corner reflector. The FPGA is used to generate two independent digital drive signals based on the uplink data to be transmitted. After conversion and amplification, these signals drive the first and second liquid crystal units of the dual-unit cascaded liquid crystal shutter, respectively. During the falling edge of the light transmission, the drive to the first liquid crystal unit is deactivated, and a drive pulse is actively applied to the second liquid crystal unit. Through the synergistic effect of the two units, the overall light transmission state is changed, and the downlink optical carrier signal is modulated and backscattered to the reader end through the corner reflector.

[0116] Thirdly, embodiments of this application provide a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the transmission optimization method for a full-duplex visible light backscatter communication system as described above.

[0117] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for optimizing full-duplex visible light backscatter communication transmission, characterized in that, include: A hardware transceiver link for a full-duplex visible light backscatter communication system is constructed, comprising a reader end and a tag end; among which... At the reader end, it is used to generate downlink optical carrier signals using a constant envelope binary frequency shift keying modulation method; The tag end is used to receive downlink optical carrier signals and backscatter them, and output the modulated light as echo data backscattered to the reader end; The reader extracts the discrete baseband envelope signal of the echo data and uses a dual-threshold finite state machine based on relative trend detection to perform post-equalization on the discrete baseband envelope signal to recover the uplink data, which is the echo data.

2. The full-duplex visible light backscatter communication transmission optimization method according to claim 1, characterized in that, The reader includes a host computer, a downlink transmitting module, an uplink receiving and decoding module, a beam splitter, and a converging lens. The downlink transmitting module includes a signal generator and a light-emitting device, and the uplink receiving and decoding module includes a photodetector and an oscilloscope. The host computer is used to generate downlink data and output the downlink data to the signal generator; the downlink data is a downlink optical carrier signal. It is also used to receive discrete-time received signals from oscilloscopes, and to perform post-equalization processing on the discrete-time received signals to recover the uplink data, which is the echo data. The signal generator is used to receive downlink data output from the host computer, convert the downlink data into analog drive signals, and output them to the light-emitting device. The light-emitting device is used to convert the analog driving signal into a downlink optical carrier signal. The downlink optical carrier signal is collimated by a converging lens and then output to the beam splitter. A beam splitter is used to transmit the received downlink optical carrier signal and output the downlink optical carrier signal to the tag. It is also used to reflect the received echo data from the tag and guide the echo data to the converging lens; A converging lens is used to converge the echo data reflected from the beam splitter and output it to a photodetector; A photodetector is used to receive the echo data output from the converging lens, convert the echo data into an electrical signal, and output it to an oscilloscope. An oscilloscope is used to sample and digitize electrical signals to obtain discrete-time received signals and transmit them back to a host computer.

3. The full-duplex visible light backscatter communication transmission optimization method according to claim 2, characterized in that, The tag end includes a modulation and reflection module, which comprises a controller, a dual-channel digital-to-analog converter, a dual-channel drive amplifier, a dual-unit cascaded liquid crystal shutter, and a corner reflector. The dual-unit cascaded liquid crystal shutter includes a first liquid crystal unit and a second liquid crystal unit, and is mounted tightly on the light-incident side of the corner reflector. The controller is used to generate two independent digital drive signals based on the uplink data to be sent, and output the two digital drive signals to the dual-channel digital-to-analog converter respectively. A dual-channel digital-to-analog converter is used to convert two digital drive signals into two analog drive signals, which are then output to a dual-channel drive amplifier. A dual-channel drive amplifier is used to amplify two analog drive signals and output the amplified two drive signals to the first and second liquid crystal units of the dual-unit cascaded liquid crystal shutter, respectively. A dual-unit tandem liquid crystal shutter is used to backscatter and modulate the incident downlink optical carrier signal under the coordinated drive of two driving signals. During the falling edge of light transmission, the drive of the first liquid crystal unit is canceled and a driving pulse is actively applied to the second liquid crystal unit. The overall light transmission state is changed through the coordinated action of the first and second liquid crystal units. A corner reflector is used to backscatter the light signal modulated by the dual-unit cascaded liquid crystal shutter to the reader. The light signal backscattered to the reader is the echo data.

4. The full-duplex visible light backscatter communication transmission optimization method according to claim 3, characterized in that, The controller is an FPGA controller.

5. The full-duplex visible light backscatter communication transmission optimization method according to claim 2, characterized in that, Specifically as follows: Step S1: Construct the hardware transceiver link of the full-duplex visible light backscatter communication system. The hardware transceiver link includes a reader end and a tag end. At the reader end, a beam splitter is used to construct a coaxial transmission and reception optical path. At the tag end, a dual-unit series liquid crystal shutter is tightly mounted on the light-incident side of the corner reflector to construct a passive backscatter modulation module. Step S2: The host computer at the reader end generates downlink data, uses binary frequency shift keying to obtain downlink digital waveforms from the downlink data, transmits the downlink digital waveforms to the signal generator and is controlled by the host computer, and the signal generator outputs analog drive signals corresponding to the downlink digital waveforms to drive the light-emitting device to emit downlink optical carrier signals. Step S3: The first and second liquid crystal units in the dual-unit tandem liquid crystal shutter at the tag end are driven by an amplifier after being amplified by an independent signal output from the FPGA controller. The dual-unit tandem liquid crystal shutter switches its light transmission state in coordination according to the uplink data, performs backscatter modulation on the incident downlink optical carrier signal to obtain the modulated light signal, and backscatters the modulated light signal back to the reader end through the corner reflector. The modulated light signal is the echo data. Step S4: The photodetector at the reader end receives the backscattered echo data and converts it into an electrical signal. The electrical signal is sampled and digitized using an oscilloscope to obtain the digitized signal. The digitized signal is then transmitted to the host computer and the discrete baseband envelope signal is extracted from it. Step S5: The reader performs offline digital processing on the baseband envelope signal in the host computer, and reconstructs the digital logic level of the uplink data using a dual-threshold finite state machine based on relative trend detection to obtain the uplink data with distortion eliminated.

6. The full-duplex visible light backscatter communication transmission optimization method according to claim 5, characterized in that, Step S3 includes: S301, the FPGA controller generates two independent digital drive signals based on the uplink data to be transmitted; S302. The two digital drive signals are converted from digital to analog by a dual-channel digital-to-analog converter, and then amplified by an amplifier before being input as drive signals to the first and second liquid crystal units of the dual-unit cascaded liquid crystal shutter. S303. During the falling edge of the uplink data state switching from logic 1 to logic 0, the preset compensation waveform logic output by the FPGA controller is as follows: stop applying the driving voltage to the first liquid crystal cell that is currently in the excited light-transmitting state, so that the first liquid crystal cell enters the physical natural relaxation stage of the liquid crystal molecules; at the same time, actively apply the electric field driving pulse to the second liquid crystal cell that is in the unexcited state, so that the second liquid crystal cell flips to the light-blocking state under the action of the electric field. S304. By coordinating the two independent driving signals in time, and utilizing the light-blocking response of the second liquid crystal unit under the active electric field, the physical natural relaxation process of the first liquid crystal unit is superimposed in series on the physical optical path, thereby realizing the switching of the decrease in backscattering transmittance at the label end.

7. The full-duplex visible light backscatter communication transmission optimization method according to claim 5, characterized in that, In step S4, the discrete baseband envelope signal is extracted, including: S401. The host computer sends instructions to the oscilloscope through the communication interface, controlling the oscilloscope to perform analog-to-digital conversion on the electrical signal output by the photodetector at a preset sampling rate, and then transmits the collected discrete-time received signal back to the host computer. S402. In the host computer, perform incoherent demodulation on the discrete-time received signal, calculate the amplitude of the approximate analytic signal using a sliding integral window, and extract the baseband envelope. The specific formula is as follows: ； in, Indicated by sampling frequency Sampling discrete-time received signals; This represents the extracted baseband envelope; Indicates the size of the sliding integral window. The value is approximately: , For carrier frequency; This represents the maximum-minimum normalization operator; S403, Using the max-min normalization operator The baseband envelope signal is mapped to the [0,1] interval to decouple the power fluctuations caused by the detection logic and the optical path geometry loss; S404, Calculate the baseband envelope The cross-correlation function between the data and the known preamble reference sequence; frame synchronization of uplink data frames is achieved by maximizing the cross-correlation function.

8. The full-duplex visible light backscatter communication transmission optimization method according to claim 5, characterized in that, In step S5, the digital logic level of the uplink data is reconstructed using a dual-threshold finite state machine based on relative trend detection. Specifically: S501. Dynamically track and update the local historical extreme values ​​of the baseband envelope signal: While the dual-threshold finite state machine is in state 0, track the current local minimum value. ; Track the current local maximum value while the finite state machine is in state 1. ; S502. Constructing an asymmetric dual-threshold judgment logic to identify trends: A relative valley decision criterion is used to identify the upward trend of the baseband envelope, and a relative peak decision criterion is used to identify the downward trend of the baseband envelope. The output state is based on the dual-threshold finite state machine. Reconstruct the digital logic level of the uplink data.

9. The full-duplex visible light backscatter communication transmission optimization method according to claim 8, characterized in that, In step S502, the state transition equation for the asymmetric dual-threshold judgment logic is: ； in, This represents the current output logic state. This represents the logical state at the previous moment. This is the baseband envelope signal at the current moment. This is the local minimum value recorded at the previous time step. This is the local maximum value recorded at the previous time step. The preset upward trend trigger threshold, The preset threshold for triggering a downward trend.

10. A full-duplex visible light backscatter communication transmission optimization device, characterized in that, The system includes a reader and a tag. The reader includes a host computer, a downlink transmitting module, an uplink receiving and decoding module, a beam splitter, and a converging lens. The downlink transmitting module includes a signal generator and a light-emitting device. The uplink receiving and decoding module includes a photodetector and an oscilloscope. The host computer is used to generate downlink data and output the downlink data to the signal generator; the downlink data is a downlink optical carrier signal. It is also used to receive discrete-time received signals from oscilloscopes, and to perform post-equalization processing on the discrete-time received signals to recover the uplink data, which is the echo data. The signal generator is used to receive downlink data output from the host computer, convert the downlink data into analog drive signals, and output them to the light-emitting device. The light-emitting device is used to convert the analog driving signal into a downlink optical carrier signal. The downlink optical carrier signal is collimated by a converging lens and then output to the beam splitter. A beam splitter is used to transmit the received downlink optical carrier signal and output the downlink optical carrier signal to the tag. It is also used to reflect the received echo data from the tag and guide the echo data to the converging lens; A converging lens is used to converge the echo data reflected from the beam splitter and output it to a photodetector; A photodetector is used to receive the echo data output from the converging lens, convert the echo data into an electrical signal, and output it to an oscilloscope. An oscilloscope is used to sample and digitize electrical signals to obtain discrete-time received signals and transmit them back to a host computer.

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