CN115549805A - Adaptive equalization method based on POE-VLC system and VLC receiver - Google Patents

Adaptive equalization method based on POE-VLC system and VLC receiver Download PDF

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CN115549805A
CN115549805A CN202210976503.7A CN202210976503A CN115549805A CN 115549805 A CN115549805 A CN 115549805A CN 202210976503 A CN202210976503 A CN 202210976503A CN 115549805 A CN115549805 A CN 115549805A
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signal
equalizer
channel
vlc
optimal weight
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王玉皞
菅杰
陈煊邦
许林
陈俊源
洪子伟
刘超良
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Nanchang University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/66—Non-coherent receivers, e.g. using direct detection
    • H04B10/69—Electrical arrangements in the receiver
    • H04B10/697—Arrangements for reducing noise and distortion
    • H04B10/6971—Arrangements for reducing noise and distortion using equalisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114—Indoor or close-range type systems
    • H04B10/116—Visible light communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/02—Details
    • H04L12/10—Current supply arrangements

Abstract

The invention provides a self-adaptive equalization method based on a POE-VLC system and a VLC receiver, wherein the method comprises the following steps: acquiring the average power of the transmission of the received signals in the Ethernet channel and the visible light channel, acquiring the average power of the noise received by the Ethernet channel and the visible light channel integrally, and calculating the average signal-to-noise ratio according to the average power of the received signals and the average power of the noise; establishing an optimal weight coefficient iterative formula of the equalizer coefficient through a variable step LMS algorithm, establishing a variable step updating function according to the average signal-to-noise ratio, and performing iterative updating on the optimal weight coefficient iterative formula according to the variable step updating function; and outputting the optimal weight coefficient of the equalizer after iterative updating. According to the adaptive equalization method based on the POE-VLC system and the VLC receiver, iterative updating is carried out on the variable step length LMS algorithm by introducing the signal-to-noise ratio function, so that the updated equalizer coefficient is more adaptive to the signal-to-noise ratio change of the system.

Description

Adaptive equalization method based on POE-VLC system and VLC receiver
Technical Field
The invention relates to the technical field of visible light communication, in particular to a POE-VLC system-based adaptive equalization method and a VLC receiver.
Background
In recent years, 5G and Internet of things technologies rise, wireless connection intelligent terminal equipment is increased explosively, and a traditional radio frequency wireless access mode has a risk of serious data rate competition among users due to limited frequency spectrum resources. With the rapid development of lighting technology and optical wireless Communication technology, visible Light Communication (VLC) has a very broad application prospect due to the advantages of abundant spectrum resources, communication and lighting, no electromagnetic interference and the like.
Ethernet is a widely used and most excellent communication standard at present, and has been fully integrated into the lives of people. The Power Over Ethernet (POE) technology integrating data communication and Power supply functions through the Ethernet cable is a revolutionary new technology, and can ensure the safety of structured wiring without interfering concurrent network operation. The POE technology-based visible light communication illumination integrated system (POE-VLC system) utilizes the advantages of the POE-VLC system and the POE-VLC system, saves the cost of traditional wiring, and integrates the advantages of high safety factor, adaptability to traditional LAN networks, high data rate and the like.
In the prior art, aiming at the problem of slow convergence speed in an equalization algorithm used by a POE-VLC system, and because environmental factors of the POE-VLC system are complex and changeable, the existing equalization method mostly only considers a single environmental factor, and cannot take account of the influence of the signal-to-noise ratio of the whole system, so that the equalization effect is poor.
Disclosure of Invention
Based on this, the present invention aims to provide a POE-VLC system-based adaptive equalization method and a VLC receiver, which solve the problem in the background art that the equalization effect is poor due to the fact that the environmental factors of the POE-VLC system are complex and changeable, and the existing equalization method cannot take into account the influence of the signal-to-noise ratio of the whole system.
The invention provides a POE-VLC system self-adapting method, which is applied to a VLC receiver and comprises the following steps:
acquiring a receiving signal, wherein the receiving signal is generated after an electric signal is transmitted in an Ethernet channel and a visible light channel, acquiring the average power of the receiving signal transmitted in the Ethernet channel and the visible light channel, acquiring the average noise power received by the Ethernet channel and the visible light channel, and calculating the average signal-to-noise ratio according to the average power of the receiving signal and the average noise power;
establishing an optimal weight coefficient iterative formula of the equalizer coefficient through a variable step LMS algorithm, establishing a variable step updating function according to the average signal-to-noise ratio, and iteratively updating the optimal weight coefficient iterative formula according to the variable step updating function;
judging whether the optimal weight coefficient iterative formula is converged;
if yes, outputting the equalizer optimal weight coefficient after iterative updating, namely the equalizer coefficient after adaptive equalization.
According to the POE-VLC system self-adaptive method, the average signal-to-noise ratio of the whole system of an Ethernet channel and a visible light channel is calculated, the equalization coefficient is iteratively updated through a variable step LMS algorithm, and the variable step factor of the variable step LMS algorithm is updated by introducing an average signal-to-noise ratio function, so that the signal-to-noise ratio influence of the whole system is fully considered, the equalizer is enabled to adapt to different channel environment changes of different systems, the self-adaptive equalization effect of the equalizer is improved, and the problem that the equalization effect is poor due to the fact that environmental factors of the POE-VLC system are complex and changeable in the background technology and the signal-to-noise ratio influence of the whole system cannot be considered by the existing equalization method is solved.
Further, the step of obtaining the average power of the received signal transmitted in the ethernet channel and the visible light channel includes:
and acquiring the integral channel transmission function of the received signal in the Ethernet channel and the visible light channel, and calculating the average power of the received signal according to the integral channel transmission function.
Further, the step of obtaining the overall channel transfer function of the received signal in the ethernet channel and the visible light channel includes:
establishing an Ethernet total transmission characteristic function according to the transmission characteristic of the Ethernet channel, and establishing a frequency domain formula of visible light channel response according to a visible light channel model;
and establishing an integral channel transmission function corresponding to the Ethernet channel and the visible light channel according to the transmission characteristics of the Ethernet channel and the frequency domain of the visible light channel.
Further, the overall channel transfer function of the ethernet channel and the visible light channel is:
Figure 416320DEST_PATH_IMAGE001
in the formula (I), the compound is shown in the specification,
Figure 768279DEST_PATH_IMAGE002
as a function of the total transmission characteristics of the ethernet,
Figure 205077DEST_PATH_IMAGE003
for the frequency domain formulation of the visible light channel response,
Figure 160263DEST_PATH_IMAGE004
for VLC transmitter preamplifier voltage gain, α is the conversion coefficient of the LED driver, β is the LED model light gain conversion coefficient,
Figure 340709DEST_PATH_IMAGE005
is the frequency response of the VLC channel and,
Figure 940318DEST_PATH_IMAGE006
is a high pass filter frequency response for rejecting ambient light,
Figure 688962DEST_PATH_IMAGE007
is the gain of the trans-impedance amplifier,kis a receiverThe gain of the pre-amplifier is increased,fis the frequency.
Further, the step of establishing an optimal weight coefficient iterative formula of the equalizer coefficient by the variable step length LMS algorithm comprises:
controlling the equalizer coefficient to carry out initialization state, sending a known sequence to the equalizer in sequence for training and sending an actual signal for decision to obtain an error signal corresponding to the known sequence and the actual signal, and establishing an optimal weight coefficient iterative formula of the equalizer coefficient corresponding to the error signal of the known sequence and the actual signal through a variable step length LMS algorithm.
Further, the step of sequentially sending the known sequence to the equalizer for training and sending the actual signal for decision to obtain the error signal corresponding to the known sequence and the actual signal includes:
acquiring a known sequence and an actual signal, and obtaining a receiving sequence corresponding to the known sequence and a receiving sequence corresponding to the actual signal after the known sequence and the actual signal pass through a POE-VLC system;
inputting the received sequence corresponding to the known sequence into an equalizer to obtain an equalizer output signal of the known sequence, and performing difference on the equalizer output signal of the known sequence and the known sequence to obtain an error signal corresponding to the known sequence;
and inputting the receiving sequence corresponding to the actual signal into an equalizer to obtain an equalizer output signal and a decision device output signal of the actual signal, and subtracting the equalizer output signal and the decision device output signal of the actual signal to obtain an error signal corresponding to the actual signal.
Further, the variable step update function is:
Figure 741232DEST_PATH_IMAGE008
in the formula
Figure 725368DEST_PATH_IMAGE009
，
Figure 304117DEST_PATH_IMAGE010
In the form of a variable step-size,εis an index ofThe factor of the decay constant is a function of,F(n)as a function of the signal to noise ratio.
Further, the variable step updating function comprises an exponential decay term and a signal-to-noise ratio function term established according to the average signal-to-noise ratio, and the step of iteratively updating the optimal weight coefficient iterative formula according to the variable step updating function comprises the following steps:
performing initial iterative update on an optimal weight coefficient iterative formula of a known sequence according to an exponential decay term;
and after the optimal weight coefficient iterative formula is converged, iteratively updating the optimal weight coefficient iterative formula of the actual signal according to the signal-to-noise ratio function term.
Further, the step of outputting the iteratively updated optimal weight coefficients of the equalizer, that is, the adaptively equalized equalizer coefficients, includes:
and acquiring an input signal received by the equalizer, and processing the input signal according to the optimal weight coefficient of the equalizer to obtain output data after adaptive equalization.
Another aspect of the present invention provides a VLC receiver, comprising:
the signal-to-noise ratio calculation module is used for acquiring a received signal, transmitting the received signal to a visible light channel through an Ethernet channel, acquiring the average power of the received signal transmitted in the Ethernet channel and the visible light channel, acquiring the average noise power of the Ethernet channel and the visible light channel, and calculating the average signal-to-noise ratio according to the average power of the received signal and the average noise power;
the equalizer coefficient updating module is used for establishing an optimal weight coefficient iterative formula of the equalizer coefficient through a variable step LMS algorithm, establishing a variable step updating function according to the average signal-to-noise ratio and iteratively updating the optimal weight coefficient iterative formula according to the variable step updating function;
the judging module is used for judging whether the optimal weight coefficient iterative formula is converged;
and the first execution module is used for outputting the equalizer optimal weight coefficient after iterative updating if the optimal weight coefficient iterative formula is converged, wherein the equalizer optimal weight coefficient is the equalizer coefficient after adaptive equalization.
Drawings
Fig. 1 is a flowchart of a POE-VLC system adaptation method in a first embodiment of the present invention;
fig. 2 is a flowchart illustrating a POE-VLC system adaptive method in a second embodiment of the present invention;
fig. 3 is a system block diagram of an adaptive method of a POE-VLC system in a third embodiment of the present invention;
fig. 4 is a block diagram of a POE-VLC integrated communication system according to an embodiment of the present invention;
FIG. 5 is a flowchart of a decision feedback-based variable step LMS equalization algorithm according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a variable step size update according to an embodiment of the present invention;
the following detailed description will further illustrate the invention in conjunction with the above-described figures.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully hereinafter with reference to the accompanying drawings. Several embodiments of the invention are presented in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like are used herein for purposes of illustration only.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The invention obtains the channel characteristics and noise of the system by integrally modeling the Ethernet wired channel and the visible light communication wireless channel related to the POE-VLC system, and evaluates the signal-to-noise ratio. And (3) comprehensively considering factors such as the length of an Ethernet cable, the distance between a transmitter and a receiver in a visible light communication channel and the like, and designing a suitable self-adaptive equalization method. As shown in fig. 4, the technical solution of the present invention mainly includes three modules to implement adaptive equalization.
A PSE module: comprises a coding and modulation unit. The embodiment of the invention mainly aims at the 100Base-TX Ethernet standard. The binary data stream is coded and modulated at the Ethernet physical layer, and a 4B/5B coding method is adopted to ensure that the transmission code stream has enough jump level. The modulation may use a multilevel transmission code (Multi-level Transmit-3, MLT-3). The code is characterized in that the code jumps along with the 1, keeps unchanged along with the 0, is a bipolar code and has three levels of '-1', '0' and '1'.
The electrical signal is then transmitted to the VLC transmitter over a conventional Cat5 unshielded twisted pair cable, while power is simultaneously injected into the same cable.
VLC transmitter & PD module: the PD herein refers to a powered device in the POE concept. The RJ45 receives a data stream which is separated from a power supply, the data stream is amplified through an amplifier in a voltage signal form, the voltage signal is converted into driving current through an analog front-end LED driving circuit, the LED luminous intensity is enabled to avoid negative values by means of Bias-Tee, and finally LED intensity modulation is conducted.
A VLC receiver module: the photoelectric detector converts a received optical signal into an electric signal, the transimpedance amplifier converts a current signal into a voltage signal, and the modules for filtering, amplifying, balancing, decoding and the like recover original data.
The POE-VLC system involves intermediate links represented by an ethernet wired channel and a visible light communication wireless channel, respectively a Cat5 cable link between the VLC transmitter to the PSE power supply and a VLC link to the VLC receiver. The POE-VLC overall system is subject to various influences of devices and noise, and can restore an original signal through channel compensation and reduce interference of random noise using equalization.
In the embodiment of the invention, the adaptive equalization in the VLC receiver module is to perform adaptive equalization on the POE-VLC system through an adaptive equalizer. The adaptive equalizer is an equalizer device based on an adaptive equalization algorithm, and can adjust its coefficient at any time based on the measurement of the system channel characteristics to adapt to the change of the channel characteristics and eliminate the intersymbol interference. The adaptive equalizer includes two filters, a forward filter (FFF) and a backward filter (FBF), and the filter coefficients of the two filters in the adaptive equalizer affect the adaptive equalization effect.
In an actual system, a receiving end cannot know the dynamic change of a channel in advance, so that the channel characteristics need to be accurately estimated, and an adaptive equalizer capable of automatically adjusting to adapt to different channel conditions needs to be designed. The self-adaptation is to automatically adjust the filter coefficients, and may consider to continuously adjust the coefficients according to the continuously changing channel conditions, specifically, training is performed by periodically sending training signals during data transmission, and after the training is finished, the equalizer parameters are basically close to the optimal values, so as to ensure accurate reception of user data, and the training process of the equalizer is also successful, which is called the convergence of the equalizer. Once the channel response is adapted, the equalizer can evaluate the slight change of the channel, and continuously change the equalizer parameters along with the change of the channel characteristic when receiving the user data.
Various algorithms can be used to find the optimal filter coefficient combination, for example, the LMS algorithm is used in the embodiment of the present invention, that is, the filter coefficient is adjusted by using the difference between the decision output and the actual output, and then the convergence speed and stability of the algorithm are controlled by the step length μ.
Example one
Referring to fig. 1, a POE-VLC system adaptive method in a first embodiment of the present invention includes steps S11 to S14.
S11, receiving signals are obtained, the receiving signals are generated after electric signals are transmitted in an Ethernet channel and a visible light channel, the average power of the receiving signals transmitted in the Ethernet channel and the visible light channel is obtained, the average power of noise received by the Ethernet channel and the visible light channel is obtained, and the average signal-to-noise ratio is calculated according to the average power of the receiving signals and the average power of the noise.
And transmitting the coded and modulated signal electric signal to an Ethernet channel, transmitting the electric signal to a visible light channel through an Ethernet cable wired channel, and converting the electric signal into a receiving signal through a VLC receiver. The received signal now passes through the dual effects of the ethernet channel and the visible light channel.
Firstly, establishing a channel model simultaneously having an Ethernet wired channel and a visible light communication wireless channel:
the ethernet signal is affected by channel attenuation, crosstalk, return loss, noise, baseband drift, etc. during the transmission process, and thus, serious distortion is generated. An ethernet total transmission characteristic function is established according to the transmission characteristics of the ethernet channel, and in an embodiment, the total transmission characteristics of a Cat5 ethernet cable with a unit length can be simply expressed as:
Figure 348296DEST_PATH_IMAGE011
Figure 763228DEST_PATH_IMAGE012
transfer functions representing waveform overshoot, baseline drift, cat5 cable attenuation, flat attenuation, and return loss, respectively.
Secondly, the VLC channel, which is assumed to be invariant in a static environment, since the position of the luminaire is determined at the time of installation and the receiver is substantially fixed. Even if the user moves within a range of tens of centimeters per second of the receiver, it can be considered slow in the context of high data rates of VLC channels. We consider a Line of sight (LOS) indoor channel model, assuming no occlusion between the transmitting end and the receiving end of the VLC, and do not consider reflected and refracted light. The VLC channel model can be simply expressed as:
Figure 551056DEST_PATH_IMAGE013
lambert radiation order
Figure 859677DEST_PATH_IMAGE014
，
Concentrator gain
Figure 199392DEST_PATH_IMAGE015
D is the distance between the transmitting end and the receiving end of VLC, A is the receiving area of the photoelectric detector, and the unit is m 2 ，
Figure 960674DEST_PATH_IMAGE016
Is the angle of the irradiation angle,
Figure 552193DEST_PATH_IMAGE017
is the angle of incidence and is,
Figure 590687DEST_PATH_IMAGE018
is the signal transmission of an optical band-pass filter,
Figure 976669DEST_PATH_IMAGE019
is the receiver viewing angle, n is the refractive index,
Figure 756406DEST_PATH_IMAGE020
is the half power emission angle.
Calculating a frequency domain of the visible light channel according to the light channel model, wherein the frequency domain of the VLC channel is represented as
Figure 745091DEST_PATH_IMAGE021
C is the speed of light and j is the unit of imaginary number.
Assuming that each component of the system can be considered linear, the links are also time invariant.
The VLC receiving end captures an optical signal using a conventional photodetector, and after the optical detection, a frequency domain received signal may be represented as:
Figure 28305DEST_PATH_IMAGE022
Figure 451765DEST_PATH_IMAGE023
respectively, a received signal, an MLT-3 voltage input signal, and an overall channel transfer function.
Figure 453219DEST_PATH_IMAGE024
Figure 855381DEST_PATH_IMAGE025
For VLC transmitter preamplifier voltage gain, α is the conversion coefficient of the LED driver, β is the LED model light gain conversion coefficient,
Figure 383315DEST_PATH_IMAGE005
is the frequency response of the VLC channel and,
Figure 111099DEST_PATH_IMAGE006
is a high pass filter frequency response for rejecting ambient light,
Figure 334270DEST_PATH_IMAGE007
is the gain of the trans-impedance amplifier,kis the gain of the receiver pre-amplifier,fis the frequency.
The average power of the received signal is approximately:
Figure 946648DEST_PATH_IMAGE026
in the formula (I), the compound is shown in the specification,
Figure 938875DEST_PATH_IMAGE027
is the average power of the received signal and,
Figure 696616DEST_PATH_IMAGE028
for receiving signals
Figure 672662DEST_PATH_IMAGE029
Is measured.
The ethernet cable background white noise and transmitter thermal noise are negligible compared to the total noise power output by the receiver, where the receiver noise is mainly composed of VLC shot noise, transimpedance amplifier thermal noise and low noise amplifier noise.
The average power of the total noise is calculated as:
Figure 682206DEST_PATH_IMAGE030
in the formula (I), the compound is shown in the specification,
Figure 669885DEST_PATH_IMAGE031
is the average power of the total noise,
Figure 5051DEST_PATH_IMAGE032
in order for the VLC to loose noise,
Figure 937235DEST_PATH_IMAGE033
in order for the transimpedance amplifier to be thermally noisy,
Figure 140683DEST_PATH_IMAGE034
is the variance of the thermal noise voltage of the low noise amplifier.
The calculation formula of the average signal-to-noise ratio of the POE-VLC system is as follows:
Figure 107502DEST_PATH_IMAGE035
in the formula (I), the compound is shown in the specification,
Figure 957778DEST_PATH_IMAGE036
is the average signal-to-noise ratio of the POE-VLC system. S12, establishing an optimal weight coefficient iterative formula of the equalizer coefficient through a variable step LMS algorithm, establishing a variable step updating function according to the average signal-to-noise ratio, and performing iterative updating on the optimal weight coefficient iterative formula according to the variable step updating function.
After analyzing the comprehensive channel characteristics of the Ethernet cable and VLC channel, the characteristics of the comprehensive channel are estimated in real time by using a least mean square error algorithm (LMS) and a method of sending a known sequence at fixed time, and each tap coefficient of the decision equalizer is adjusted at any time.
The working process of the self-adaptive equalizer is divided into two stages of training and judging, the coefficients of two filters of the equalizer are initialized to be zero, the training stage is carried out when the switch S is at 1, and the equalizer output signal output by the equalizer is outputr(n)With the desired signald (n)Difference is made to obtain an error signale(n)And initially adjusting the coefficients of the decision feedback equalizer. After the self-adaptive algorithm is converged, the equalizer enters a decision feedback stage, and the switch S is turned to 2 to execute the function of the conventional decision feedback equalizer.
The optimal weight coefficient iterative formula of the equalizer coefficient established by the variable step LMS algorithm aiming at the error signals in the training and judging stages is as follows:
Figure 908416DEST_PATH_IMAGE037
in the formula (I), the compound is shown in the specification,
Figure 525342DEST_PATH_IMAGE010
is a variable step size.
Whereinx(n)For received signals received by POE-VLC systemx r (f)Time domain signal after Fourier inverse transformationx r (f)The known sequence and the actual signal of the two phases of training and decision are included.
The contradiction exists between the convergence rate and the steady-state error of the variable step length LMS algorithm, and the purpose of providing the variable step length LMS algorithm is to use a large step length factor when the error is largeμ(n)The convergence rate of the algorithm is accelerated, the steady-state error is gradually reduced along with the increase of the iteration times of the algorithm, and the step size factor is reduced along with the reduction, so that the steady-state mean square error of the system is correspondingly reduced.
In order to make the equalizer more adaptive to the change of the signal-to-noise ratio of the system, average is introduced in the iterative updating process of the coefficient of the equalizerSignal-to-noise ratio update step size factorμ(n)。
The updating formula of the variable step length is as follows:
Figure 471302DEST_PATH_IMAGE038
in the formula
Figure 882692DEST_PATH_IMAGE009
，εThe method is characterized in that an exponential decay constant factor is selected, and a proper exponential decay constant factor is selected according to the state of an actual system, so that the variable-step-size self-adaptive equalizer achieves rapid convergence on the premise of ensuring the precision of a weight coefficient.F (n)Is a linear function of the signal-to-noise ratio, expressed as
Figure 789468DEST_PATH_IMAGE039
In the formula, the selection principle of the gamma and delta coefficients is that under the conditions of low signal-to-noise ratio and high signal-to-noise ratio, the selected large step size does not cause extra error codes or the error codes caused by the large step size do not influence the decoding accuracy of a receiving end.
And S13, judging whether the optimal weight coefficient iterative formula is converged.
If yes, go to step S14.
And S14, outputting the equalizer optimal weight coefficient after iterative updating, wherein the equalizer optimal weight coefficient is the equalizer coefficient after adaptive equalization.
The method comprises the steps of presetting iteration times of an equalization coefficient in a training stage and presetting the BER (bit error rate) of a system, wherein the preset iteration times comprise the sum of the iteration times of the training stage and a judging stage, and the preset BER is mainly to obtain an error code threshold to obtain an optimal coefficient in a time period.
During a training stage, judging whether the system bit error rate BER is smaller than a preset bit error rate threshold value in the iterative updating process of the algorithm, if so, judging that the algorithm is basically converged, entering a judging stage after the basic convergence, performing coefficient updating on the variable-step LMS algorithm according to a signal-to-noise ratio function term, judging whether the optimal weight coefficient iterative formula is converged, and outputting to obtain the optimal coefficient of the equalizer when the iteration times of two times reach the preset iteration times or the system bit error rate BER is smaller than the preset bit error rate threshold value, wherein the optimal weight coefficient of the equalizer is the coefficient of the equalizer after self-adaptation is completed.
In summary, in the adaptive method for a POE-VLC system in the above embodiments of the present invention, the average signal-to-noise ratio of the entire system of the ethernet channel and the visible light channel is calculated, the equalization coefficient is iteratively updated by using the variable-step-size LMS algorithm, and the variable-step-size factor is updated by introducing the average signal-to-noise ratio function to the variable-step-size LMS algorithm, so that the influence of the signal-to-noise ratio of the entire system is fully considered, so that the equalizer adapts to different channel environment changes of different systems, the adaptive equalization effect of the equalizer is improved, and the problem of poor equalization effect due to the fact that the influence of the signal-to-noise ratio of the entire system cannot be considered in the conventional equalization method is solved.
Example two
Referring to fig. 2, a POE-VLC system adaptive method in a second embodiment of the present invention is shown, including steps S21-S27.
S21, obtaining a receiving signal, wherein the receiving signal is generated after the electric signal is transmitted in an Ethernet channel and a visible light channel, obtaining the average power of the receiving signal transmitted in the Ethernet channel and the visible light channel, obtaining the average power of noise received by the Ethernet channel and the visible light channel integrally, and calculating the average signal-to-noise ratio according to the average power of the receiving signal and the average power of the noise.
And transmitting the coded and modulated signal electric signal to an Ethernet channel, transmitting the electric signal to a visible light channel through an Ethernet cable wired channel, and converting the electric signal into a receiving signal through a VLC receiver. The received signal now passes through the dual effects of the ethernet channel and the visible light channel.
Firstly, establishing a channel model simultaneously having an Ethernet wired channel and a visible light communication wireless channel:
the ethernet signal is affected by channel attenuation, crosstalk, return loss, noise, and baseband drift during the transmission process, thereby causing severe distortion. An ethernet total transmission characteristic function is established according to the transmission characteristics of the ethernet channel, and in an embodiment, the total transmission characteristics of a Cat5 ethernet cable with a unit length can be simply expressed as:
Figure 816942DEST_PATH_IMAGE040
Figure 758353DEST_PATH_IMAGE041
transfer functions representing waveform overshoot, baseline drift, cat5 cable attenuation, flat attenuation, and return loss, respectively.
Secondly, the VLC channel, which is assumed to be invariant in a static environment, since the position of the luminaire is determined at the time of installation and the receiver is substantially fixed. Even if the user moves within a range of tens of centimeters per second of the receiver, it can be considered slow in the context of high data rates of VLC channels. We consider a Line of sight (LOS) indoor channel model, assuming no occlusion between the transmitting end and the receiving end of the VLC, and do not consider reflected and refracted light. The VLC channel model can be simply expressed as:
Figure 465278DEST_PATH_IMAGE042
lambert radiation order
Figure 124929DEST_PATH_IMAGE014
，
Concentrator gain
Figure 83658DEST_PATH_IMAGE015
D is the distance between the transmitting end and the receiving end of the VLC, A is the receiving area of the photoelectric detector, and the unit is m 2 ，
Figure 754942DEST_PATH_IMAGE016
Is the angle of the irradiation angle,
Figure 773714DEST_PATH_IMAGE017
is the angle of incidence and is,
Figure 389503DEST_PATH_IMAGE018
is the signal transmission of an optical band-pass filter,
Figure 276556DEST_PATH_IMAGE019
is the receiver field angle, n is the refractive index,
Figure 926980DEST_PATH_IMAGE020
is the half power emission angle.
Calculating a frequency domain of the visible light channel from the light channel model, wherein the frequency domain of the VLC channel is represented as
Figure 116653DEST_PATH_IMAGE021
C is the speed of light, and j is the unit of imaginary number.
Assuming that each component of the system can be considered linear, the links are also time-invariant.
The VLC receiving end captures an optical signal using a conventional photodetector, and after the optical detection, a frequency domain received signal may be represented as:
Figure 360684DEST_PATH_IMAGE022
Figure 661215DEST_PATH_IMAGE023
respectively, a received signal, an MLT-3 voltage input signal, and an overall channel transfer function.
Figure 290780DEST_PATH_IMAGE001
Figure 385775DEST_PATH_IMAGE004
Is the VLC transmitter preamplifier voltage gain, alpha is the conversion coefficient of the LED driver, beta is the LED model light gain conversion coefficient,
Figure 241735DEST_PATH_IMAGE005
is the frequency response of the VLC channel and,
Figure 955745DEST_PATH_IMAGE006
is a high pass filter frequency response for rejecting ambient light,
Figure 846340DEST_PATH_IMAGE007
is the gain of the transimpedance amplifier and,kis the gain of the receiver pre-amplifier,fis the frequency.
The average power of the received signal is calculated as:
Figure 377816DEST_PATH_IMAGE026
in the formula (I), the compound is shown in the specification,
Figure 580127DEST_PATH_IMAGE027
is the average power of the received signal and,
Figure 222461DEST_PATH_IMAGE028
for receiving signals
Figure 580280DEST_PATH_IMAGE029
Is measured.
The ethernet cable background white noise and transmitter thermal noise are negligible compared to the total noise power output by the receiver, where the receiver noise is mainly composed of VLC shot noise, transimpedance amplifier thermal noise and low noise amplifier noise.
The average power of the total noise is calculated as:
Figure 282656DEST_PATH_IMAGE043
in the formula (I), the compound is shown in the specification,
Figure 847630DEST_PATH_IMAGE031
as an average of the total noiseThe power of the electric motor is controlled by the power controller,
Figure 418288DEST_PATH_IMAGE032
in order to achieve VLC shot noise,
Figure 283476DEST_PATH_IMAGE033
in order for the transimpedance amplifier to be thermally noisy,
Figure 891175DEST_PATH_IMAGE034
is the variance of the thermal noise voltage of the low noise amplifier.
The calculation formula of the average signal-to-noise ratio of the POE-VLC system is as follows:
Figure 818811DEST_PATH_IMAGE035
in the formula (I), the compound is shown in the specification,
Figure 802948DEST_PATH_IMAGE036
is the average signal-to-noise ratio of the POE-VLC system.
S22, initializing the coefficient of the equalizer, sequentially sending a known sequence and an actual signal to the equalizer for training and judging to obtain an error signal corresponding to the known sequence and the actual signal, and establishing an optimal weight coefficient iterative formula of the coefficient of the equalizer according to the error signal corresponding to the known sequence and the actual signal by a variable step length LMS algorithm.
After the comprehensive channel characteristics of the Ethernet cable and the VLC channel are analyzed, a variable step length self-adaptive POE-VLC comprehensive channel equalization method based on a decision feedback equalization DFE is adopted, the characteristics of the comprehensive channel are estimated in real time by utilizing a least mean square error algorithm (LMS) and a method for sending a known sequence at fixed time, and each tap coefficient of a decision equalizer is adjusted at any time, so that the purposes of Ethernet cable loss and self-adaptive equalization of an indoor visible light communication dynamic channel are met.
As shown in fig. 5, the working process of the adaptive equalizer is divided into two stages of training and decision:
the adaptive equalizer comprises two filters, a forward filter (FFF) and a backward filter (FBF), which will first be bothCoefficients of two filters of weighing apparatus
Figure 381696DEST_PATH_IMAGE044
And
Figure 425876DEST_PATH_IMAGE045
initialise to zero, and j =0.
The first stage is as follows: when the equalizer switch S is in 1, the training stage is adopted, and the known sequence is sent to obtain a receiving sequence after passing through a POE-VLC systemx(n)Then, the output signal of the equalizer corresponding to the known sequence is obtained through the equalizerr(n)The known sequence transmitted is taken as the expected signal at this staged(n)，To equalizer output signalr(n)And a desired signald(n)Differencing to obtain an error signal corresponding to the known sequencee(n)Based on the error signale(n)And establishing an optimal weight coefficient iterative formula of the equalizer, and performing initial updating adjustment on the coefficient of the equalizer.
And a second stage: after the adaptive algorithm converges, the equalizer enters a decision feedback stage, the equalizer switch S is switched to 2, and the function of the conventional decision feedback equalizer is executed. After actual signals are sent to pass through a POE-VLC system, a receiving sequence of the stage is obtainedx (n)，Obtaining equalizer output signal corresponding to actual signal by equalizerr(n)And the decision device output signal
Figure 699862DEST_PATH_IMAGE046
And will then
Figure 363056DEST_PATH_IMAGE046
As the desired signal at this stage, the desired signal is selected
Figure 937257DEST_PATH_IMAGE046
And equalizer output signalr(n)Differencing to obtain an error signal corresponding to the received sequencee(n)，Error signal according to this stagee(n)And establishing an optimal weight coefficient iterative formula of the equalizer, and updating and adjusting the coefficient of the equalizer.
In two stagesr(n)Andx(n)different, corresponding computing stationObtaining an error signale(n)And also different. The equalizer input-output relationship is defined as:
Figure 886758DEST_PATH_IMAGE047
in the formula
Figure 303833DEST_PATH_IMAGE044
And
Figure 364193DEST_PATH_IMAGE045
respectively the adjustable coefficients of the forward filter FFF and the backward filter FPF,d(n)for the desired signal, M is the order of the FFF of the forward filter and N is the order of the FPF of the backward filter.
The error signal for the known sequence and the actual signal is calculated as:
Figure 58479DEST_PATH_IMAGE048
synthetic weight vector of adaptive filter
Figure 54248DEST_PATH_IMAGE049
Is defined as two sets of coefficients
Figure 568406DEST_PATH_IMAGE050
And
Figure 557091DEST_PATH_IMAGE051
the vectors that are composed together, that is,
Figure 105884DEST_PATH_IMAGE052
. The iterative formula of the optimal weight coefficient of the equalizer of the variable step length LMS algorithm obtained according to the gradient descent method is as follows:
Figure 397188DEST_PATH_IMAGE037
in the formula (I), the compound is shown in the specification,
Figure 271079DEST_PATH_IMAGE010
is a variable step size.
And S23, establishing a variable step size updating function according to the average signal-to-noise ratio.
The convergence rate of the LMS algorithm and the steady-state error are contradictory, and the purpose of proposing the variable step size algorithm is to use a large step size factor to accelerate the convergence rate of the algorithm when the error is larger, the steady-state error is gradually reduced along with the increase of the iteration times of the algorithm, and the step size factor is reduced along with the reduction, so that the steady-state mean square error of the system is correspondingly reduced.
The updating formula of the variable step length is as follows:
Figure 938820DEST_PATH_IMAGE038
in the formula (I), the compound is shown in the specification,εthe method is characterized in that the method is an exponential decay constant factor, and a proper exponential decay constant factor is selected according to the state of an actual system, so that the variable-step-size self-adaptive equalizer achieves rapid convergence on the premise of ensuring the precision of a weight coefficient.F(n)Is a linear function of the signal-to-noise ratio, expressed as
Figure 342120DEST_PATH_IMAGE039
In the formula, the selection principle of the gamma and delta coefficients is that under the conditions of low signal-to-noise ratio and high signal-to-noise ratio, the large step size is selected without
Figure 194538DEST_PATH_IMAGE009
Extra errors or errors caused by large step length can not influence the decoding accuracy of the receiving end.
S24, performing initial iterative update on the optimal weight coefficient iterative formula of the known sequence according to the exponential decay term;
and judging whether the system error rate is smaller than a preset error rate threshold value, and if so, executing a step S26.
Variable step lengthμ(n)Is determined by the exponential decay term plus the signal-to-noise ratio function term. When S is placed in the training stage of 1, the exponential decay term plays a main role, and the coefficient of the equalizer is updated according to the exponential decay term, so that the equalizer is quickly decayed. When the algorithm is judged to be basically converged, S is entered and is put into 2 judgmentStage(s) at this timeF(n)The signal-to-noise ratio function plays a main role, the equalizer coefficient is updated according to different signal-to-noise ratios in the environment, and the optimal weight coefficient of the equalizer in the signal-to-noise ratio environment is obtained, so that the equalizer can adapt to various signal-to-noise ratio environments.
The method comprises the steps of presetting iteration times of an equalization coefficient in a training stage and presetting the BER (bit error rate) of a system, wherein the preset iteration times comprise the sum of the iteration times of the training stage and a judging stage, and the preset BER is mainly to obtain an error code threshold to obtain an optimal coefficient in a time period.
As shown in fig. 6, assuming that the preset iteration number is 2000, the exponential term plays a main role in the training phase for fast convergence; and then, according to the actual signal and channel change, the signal-to-noise ratio item mainly influencing the step length at the moment, and different step lengths are adopted to update the coefficients corresponding to different signal-to-noise ratios.
The first stage is as follows: and in the training stage, judging whether the BER of the system in the iterative updating process of the algorithm is smaller than a preset BER threshold value, if so, judging that the algorithm is basically converged.
And S25, iteratively updating the optimal weight coefficient iterative formula of the actual signal according to the signal-to-noise ratio function term.
And judging whether the optimal weight coefficient iterative formula is converged.
If yes, go to step S26.
And S26, outputting the equalizer optimal weight coefficient after iterative updating, wherein the equalizer optimal weight coefficient is the equalizer coefficient after adaptive equalization.
And a second stage: after the algorithm is basically converged, the method enters a decision stage S arranged in 2, when the coefficient of the variable step length LMS algorithm is updated according to the signal-to-noise ratio function term, whether the optimal weight coefficient iteration formula is converged is judged, when the iteration times of two times reach the preset iteration times or the system bit error rate BER is smaller than the preset bit error rate threshold value, the optimal weight coefficient of the equalizer is output, and the optimal weight coefficient of the equalizer is the equalizer coefficient after the self-adaption is completed. And obtaining the output data after equalization according to the data signal received by the system and the obtained optimal coefficient of the equalizer.
Optionally, the system environment is variable, and therefore, the sequence signal is periodically sent to the equalizer to train and adjust the coefficient of the equalizer, so that the equalizer can continuously adapt to the variable channel environment.
And S27, acquiring the input signal received by the equalizer, and processing the input signal according to the optimal weight coefficient of the equalizer to obtain output data after adaptive equalization.
And inputting signals to the equalizer after the adaptive equalization, wherein the equalizer processes the input signals through the adjusted equalizer coefficient, eliminates the influence of loss, noise and the like of the input signals on an Ethernet channel and a visible light signal, and outputs calculated data, wherein the output data is effective data after effective equalization compensation.
The invention can be applied to a POE-VLC system, simultaneously considers the factors influencing the transmission performance in the transmission process, evaluates the comprehensive link, and effectively performs balanced compensation on the loss and distortion of the communication signal in the transmission process.
In summary, in the adaptive method for a POE-VLC system in the above embodiments of the present invention, the average signal-to-noise ratio of the entire system of the ethernet channel and the visible light channel is calculated, the equalization coefficient is iteratively updated by using the variable-step LMS algorithm, and the variable-step factor of the variable-step LMS algorithm is updated by introducing the average signal-to-noise ratio function, so that the influence of the signal-to-noise ratio of the entire system is fully considered, the equalizer adapts to different channel environment changes of different systems, the adaptive equalization effect of the equalizer is improved, and the problem of poor equalization effect caused by the fact that the existing equalization method cannot give consideration to the influence of the signal-to-noise ratio of the entire system due to the fact that the environmental factors of the POE-VLC system are complex and changeable in the background art is solved.
EXAMPLE III
Referring to fig. 3, the VLC receiver in the present embodiment includes:
the signal-to-noise ratio calculation module is used for acquiring a received signal, generating the received signal after an electric signal is transmitted in an Ethernet channel and a visible light channel, acquiring the average power of the received signal transmitted in the Ethernet channel and the visible light channel, acquiring the average power of noise received by the Ethernet channel and the visible light channel integrally, and calculating the average signal-to-noise ratio according to the average power of the received signal and the average power of the noise;
the equalizer coefficient updating module is used for establishing an optimal weight coefficient iterative formula of the equalizer coefficient through a variable step LMS algorithm, establishing a variable step updating function according to the average signal-to-noise ratio and performing iterative updating on the optimal weight coefficient iterative formula according to the variable step updating function;
the judging module is used for judging whether the optimal weight coefficient iterative formula is converged;
and the first execution module is used for outputting the equalizer optimal weight coefficient after iterative update if the optimal weight coefficient iterative formula is converged, wherein the equalizer optimal weight coefficient is the equalizer coefficient after adaptive equalization.
Further, the signal-to-noise ratio calculating module includes:
and the received signal average power calculation unit is used for acquiring the overall channel transmission function of the received signal in the Ethernet channel and the visible light channel and calculating the average power of the received signal according to the overall channel transmission function.
Further, the received signal average power calculating unit includes:
the channel transmission characteristic calculation subunit is used for establishing an Ethernet total transmission characteristic function according to the transmission characteristic of the Ethernet channel and establishing a frequency domain formula of visible light channel response according to a visible light channel model;
and establishing an overall channel transmission function corresponding to the Ethernet channel and the visible light channel according to the transmission characteristics of the Ethernet channel and the frequency domain of the visible light channel.
Wherein the overall channel transfer function of the ethernet channel and the visible light channel is:
Figure 417709DEST_PATH_IMAGE053
in the formula (I), the compound is shown in the specification,
Figure 154721DEST_PATH_IMAGE002
as a function of the total transmission characteristics of the ethernet,
Figure 22314DEST_PATH_IMAGE003
which is a frequency domain formula of the visible light channel response,
Figure 921000DEST_PATH_IMAGE004
is the VLC transmitter preamplifier voltage gain, alpha is the conversion coefficient of the LED driver, beta is the LED model light gain conversion coefficient,
Figure 756101DEST_PATH_IMAGE005
is the frequency response of the VLC channel and,
Figure 31224DEST_PATH_IMAGE006
is a high pass filter frequency response for rejecting ambient light,
Figure 143537DEST_PATH_IMAGE007
is the gain of the transimpedance amplifier and,kis the gain of the receiver pre-amplifier,fis the frequency.
Further, the equalizer coefficient update module comprises:
and the error signal calculation unit is used for controlling the equalizer coefficient to carry out an initialization state, sequentially sending a known sequence to the equalizer for training and sending an actual signal for judgment to obtain an error signal corresponding to the known sequence and the actual signal, and establishing an optimal weight coefficient iterative formula of the equalizer coefficient corresponding to the known sequence and the error signal of the actual signal through a variable step length LMS algorithm.
Further, the error signal calculation unit includes:
the receiving sequence subunit is configured to obtain a known sequence and an actual signal, and obtain a receiving sequence corresponding to the known sequence and a receiving sequence corresponding to the actual signal after the known sequence and the actual signal pass through a POE-VLC system;
a training subunit, configured to input the received sequence corresponding to the known sequence into an equalizer to obtain an equalizer output signal of the known sequence, and perform a difference between the equalizer output signal of the known sequence and the known sequence to obtain an error signal corresponding to the known sequence;
and the decision subunit is used for inputting the receiving sequence corresponding to the actual signal into an equalizer to obtain an equalizer output signal and a decision device output signal of the actual signal, and performing difference on the equalizer output signal and the decision device output signal of the actual signal to obtain an error signal corresponding to the actual signal.
Further, in the equalizer coefficient update module, the variable step update function is:
Figure 88490DEST_PATH_IMAGE054
in the formula
Figure 286253DEST_PATH_IMAGE009
，εIs a factor of the constant of the exponential decay,F(n)as a function of the signal to noise ratio.
Further, the variable step update function includes an exponential decay term and a signal-to-noise ratio function term established according to the average signal-to-noise ratio, and the equalizer coefficient update module includes:
the first iteration updating unit is used for carrying out initial iteration updating on the optimal weight coefficient iteration formula of the known sequence according to an exponential decay term;
and the second iteration updating unit is used for performing iteration updating on the optimal weight coefficient iteration formula of the actual signal according to the signal-to-noise ratio function term after the optimal weight coefficient iteration formula is converged.
Further, the VLC receiver further includes:
and the decision equalization module is used for acquiring the input signal received by the equalizer, and processing the input signal according to the optimal weight coefficient of the equalizer to obtain output data after adaptive equalization.
The functions or operation steps of the modules and units when executed are substantially the same as those of the method embodiments, and are not described herein again.
In summary, in the VLC receiver in the above embodiment of the present invention, the average signal-to-noise ratio of the entire system of the ethernet channel and the visible light channel is calculated, the equalization coefficient is iteratively updated by using the variable-step-size LMS algorithm, and the variable-step-size factor of the variable-step-size LMS algorithm is updated by introducing the average signal-to-noise ratio function, so that the influence of the signal-to-noise ratio of the entire system is fully considered, so that the equalizer adapts to different channel environment changes of different systems, the adaptive equalization effect of the equalizer is improved, and the problem of poor equalization effect due to the fact that the environmental factors of the POE-VLC system are complicated and changeable in the background art and the influence of the signal-to-noise ratio of the entire system cannot be considered in the existing equalization method is solved.
An embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the POE-VLC system adaptive method in the above embodiment.
An embodiment of the present invention further provides a data processing apparatus, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and when the processor executes the computer program, the steps of the method in the foregoing embodiments are implemented.
The logic and/or steps represented in the flowcharts or otherwise described herein, such as an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, various steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
In the description of the specification, reference to the description of "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A POE-VLC system adaptive method is applied to a VLC receiver, and is characterized by comprising the following steps:
acquiring a receiving signal, wherein the receiving signal is generated after an electric signal is transmitted in an Ethernet channel and a visible light channel, acquiring the average power of the receiving signal transmitted in the Ethernet channel and the visible light channel, acquiring the average power of noise received by the Ethernet channel and the visible light channel, and calculating the average signal-to-noise ratio according to the average power of the receiving signal and the average power of the noise;
establishing an optimal weight coefficient iterative formula of the equalizer coefficient through a variable step LMS algorithm, establishing a variable step updating function according to the average signal-to-noise ratio, and performing iterative updating on the optimal weight coefficient iterative formula according to the variable step updating function;
judging whether the optimal weight coefficient iterative formula is converged;
if yes, outputting the equalizer optimal weight coefficient after iterative updating, wherein the equalizer optimal weight coefficient is the equalizer coefficient after adaptive equalization.
2. The adaptive method for POE-VLC system of claim 1, wherein the step of obtaining the average power of the received signal transmitted in the ethernet channel and the visible light channel comprises:
and acquiring the integral channel transmission function of the received signal in the Ethernet channel and the visible light channel, and calculating the average power of the received signal according to the integral channel transmission function.
3. The adaptive method for POE-VLC system of claim 2, wherein the step of obtaining the overall channel transfer function of the received signal in the ethernet channel and the visible light channel comprises:
establishing an Ethernet total transmission characteristic function according to the transmission characteristic of the Ethernet channel, and establishing a frequency domain formula of visible light channel response according to a visible light channel model;
and establishing an overall channel transmission function corresponding to the Ethernet channel and the visible light channel according to the transmission characteristics of the Ethernet channel and the frequency domain of the visible light channel.
4. The adaptive method for POE-VLC system of claim 2, wherein the overall channel transfer function of the ethernet channel and the visible light channel is:
Figure 227444DEST_PATH_IMAGE001
in the formula (I), the compound is shown in the specification,
Figure 720742DEST_PATH_IMAGE002
as a function of the total transmission characteristics of the ethernet,
Figure 755694DEST_PATH_IMAGE003
for the frequency domain formulation of the visible light channel response,
Figure 398640DEST_PATH_IMAGE004
is the VLC transmitter preamplifier voltage gain, alpha is the conversion coefficient of the LED driver, beta is the LED model light gain conversion coefficient,
Figure 493635DEST_PATH_IMAGE005
is the frequency response of the VLC channel and,
Figure 615175DEST_PATH_IMAGE006
is a high pass filter frequency response for rejecting ambient light,
Figure 312873DEST_PATH_IMAGE007
is the gain of the transimpedance amplifier and,kis the gain of the receiver pre-amplifier,fis the frequency.
5. The adaptive method for POE-VLC system according to claim 1, wherein the step of establishing an optimal weight coefficient iterative formula for the equalizer coefficients by using a variable step LMS algorithm comprises:
controlling the equalizer coefficient to carry out initialization state, sending a known sequence to the equalizer in sequence for training and sending an actual signal for decision to obtain an error signal corresponding to the known sequence and the actual signal, and establishing an optimal weight coefficient iterative formula of the equalizer coefficient corresponding to the error signal of the known sequence and the actual signal through a variable step length LMS algorithm.
6. The POE-VLC system adaptation method of claim 5, wherein the step of sequentially sending a known sequence to the equalizer for training and sending an actual signal for decision to obtain an error signal corresponding to the known sequence and the actual signal comprises:
acquiring a known sequence and an actual signal, wherein the known sequence and the actual signal pass through a POE-VLC system to obtain a receiving sequence corresponding to the known sequence and a receiving sequence corresponding to the actual signal;
inputting the received sequence corresponding to the known sequence into an equalizer to obtain an equalizer output signal of the known sequence, and subtracting the equalizer output signal of the known sequence from the known sequence to obtain an error signal corresponding to the known sequence;
and inputting the receiving sequence corresponding to the actual signal into an equalizer to obtain an equalizer output signal and a decision device output signal of the actual signal, and performing difference on the equalizer output signal and the decision device output signal of the actual signal to obtain an error signal corresponding to the actual signal.
7. The adaptive method for POE-VLC system of claim 5, wherein the variable step size update function is:
Figure 203468DEST_PATH_IMAGE008
in the formula
Figure 344731DEST_PATH_IMAGE009
，
Figure 687987DEST_PATH_IMAGE010
In the form of a variable step-size,εis a factor of the exponential decay constant of,F(n)as a function of the signal to noise ratio.
8. The adaptive method for POE-VLC system of claim 7, wherein the variable step size update function comprises an exponential decay term and a signal-to-noise ratio function term established according to the average signal-to-noise ratio, and the step of iteratively updating the optimal weight coefficient iterative formula according to the variable step size update function comprises:
performing initial iterative update on the optimal weight coefficient iterative formula of the known sequence according to an exponential decay term;
and after the optimal weight coefficient iterative formula is converged, iteratively updating the optimal weight coefficient iterative formula of the actual signal according to the signal-to-noise ratio function term.
9. The adaptive method for POE-VLC system according to claim 1, wherein the step of outputting iteratively updated equalizer optimal weight coefficients, namely adaptive equalized equalizer coefficients, comprises:
and acquiring an input signal received by the equalizer, and processing the input signal according to the optimal weight coefficient of the equalizer to obtain output data after adaptive equalization.
10. A VLC receiver, characterized in that the VLC receiver comprises:
the signal-to-noise ratio calculation module is used for acquiring a received signal, wherein the received signal is transmitted to a visible light channel through an Ethernet channel, acquiring the average power of the received signal transmitted in the Ethernet channel and the visible light channel, acquiring the average power of noise received by the Ethernet channel and the visible light channel integrally, and calculating the average signal-to-noise ratio according to the average power of the received signal and the average power of the noise;
the equalizer coefficient updating module is used for establishing an optimal weight coefficient iterative formula of the equalizer coefficient through a variable step LMS algorithm, establishing a variable step updating function according to the average signal-to-noise ratio and performing iterative updating on the optimal weight coefficient iterative formula according to the variable step updating function;
the judging module is used for judging whether the optimal weight coefficient iterative formula is converged;
and the first execution module is used for outputting the equalizer optimal weight coefficient after iterative updating if the optimal weight coefficient iterative formula is converged, wherein the equalizer optimal weight coefficient is the equalizer coefficient after adaptive equalization.
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* Cited by examiner, † Cited by third party
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CN115987727A (en) * 2023-03-21 2023-04-18 荣耀终端有限公司 Signal transmission method and device
CN116054960A (en) * 2023-04-03 2023-05-02 南昌大学 PoE power supply-based visible light communication system power control method and system

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115987727A (en) * 2023-03-21 2023-04-18 荣耀终端有限公司 Signal transmission method and device
CN115987727B (en) * 2023-03-21 2023-09-26 荣耀终端有限公司 Signal transmission method and device
CN116054960A (en) * 2023-04-03 2023-05-02 南昌大学 PoE power supply-based visible light communication system power control method and system

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