阅读说明：本技术 一种haco-ofdm调制系统的零值回归算法及装置 (Zero value regression algorithm and device of HACO-OFDM modulation system ) 是由 张天 王宏旭 孙龙飞 于 2021-05-31 设计创作，主要内容包括：本发明公开了一种HACO-OFDM混合调制系统的零值回归算法,在HACO-OFDM混合调制系统中,对拥有N个子载波的HACO-OFDM混合调制系统的时域接收信号进行理论零值的抓取,并将其数值尽数归零；HACO-OFDM混合调制系统的零值回归解调装置,它包括：光电探测单元、信号零值回归单元、信号处理单元；接收LED可见光信号依次通过上述单元进行数据处理后传输出进制数据；信号零值回归单元采用前述的零值回归算法对光电探测单元接收到的信号进行噪声抑制；降低基于HACO-OFDM调制的可见光接收装置接收、处理信号过程中解调信号的误码率。(The invention discloses a zero value regression algorithm of an HACO-OFDM hybrid modulation system, in the HACO-OFDM hybrid modulation system, a time domain received signal of the HACO-OFDM hybrid modulation system with N subcarriers is subjected to theoretical zero value grabbing, and the number of the time domain received signal is reset to zero; a null regression demodulation device of HACO-OFDM hybrid modulation system comprises: the device comprises a photoelectric detection unit, a signal zero value regression unit and a signal processing unit; receiving LED visible light signals, performing data processing through the units in sequence, and transmitting binary data; the signal zero value regression unit adopts the zero value regression algorithm to carry out noise suppression on the signal received by the photoelectric detection unit; the error rate of the demodulated signal in the process of receiving and processing the signal by the visible light receiving device based on HACO-OFDM modulation is reduced.)

1. A zero-value regression algorithm of a HACO-OFDM modulation system comprises the following steps:

(1) in the HACO-OFDM hybrid modulation system, the ACO-OFDM branch and the PAM-DMT branch are respectively mapped in the following frequency domains:

（1）

and

（2）

(2) performing IFFT operation and negative cutting operation on the frequency domain signals to obtain two branched time domain signals; the probability density function is respectively expressed as:

（3）

and

（4）

wherein the content of the first and second substances,andrespectively representing the root mean square before the time domain signals of the first branch and the second branch are clipped,the unit of a step function is represented,expressing a unit impulse function; after the two branch signals are superposed in the time domain, a time domain signal of the HACO-OFDM is formed, and the probability density function of the two branch signals can be derived as follows:

（5）

wherein the content of the first and second substances,，，，

according to the HACO-OFDM signal probability density function of the formula, the zero-value occurrence probability of the HACO-OFDM time domain signal generated theoretically is 25%;

according to the statistical characteristics in the formula (5), for the HACO-OFDM (N is larger than or equal to 64) with N subcarriers, N/4 theoretical zero values of the directly received signals are captured, the numerical value of the zero values is reset to zero, and the suppression of the channel noise, the interlayer noise and the constellation point noise of the mixed signals can be realized without separating the mixed signals.

2. A null regression apparatus for a HACO-OFDM modulation system, comprising: the device comprises a photoelectric detection unit, a signal zero value regression unit and a signal processing unit; receiving LED visible light signals, sequentially performing data processing through the units, and transmitting the LED visible light signals to the incoming system number;

the signal zero value regression unit adopts a zero value regression algorithm to carry out noise suppression on the signal received by the photoelectric detection unit;

the signal processing unit comprises a photoelectric conversion module, an A/D module, a zero value regression module, an FFT module, a constellation point restoration module and a de-mapping module in sequence;

the null regression algorithm is the null regression algorithm of the HACO-OFDM modulation system as claimed in claim 1.

3. The apparatus of claim 2, wherein the apparatus comprises: the data processing steps for receiving the LED visible light signals are as follows:

(1) the photoelectric detection unit receives the LED optical signal and performs photoelectric conversion on the optical signal;

(2) performing analog-to-digital conversion and median downsampling on the converted electric signals, sequencing N time domain discrete HACO-OFDM data after downsampling from small to large, performing 0 setting processing on the first N/4 numerical points in the small to large direction, and finally putting the data after null regression back to the corresponding position before sequencing to realize the noise suppression processing for suppressing channel noise, interlayer noise and constellation point noise from the angle of directly receiving signals, namely a null regression module;

(3) performing FFT (fast Fourier transform) on the discrete time domain signal after the zero value regression processing to obtain a frequency domain symbol of the discrete time domain signal, separating the ACO-OFDM and PAM-DMT branch signals from the frequency domain angle of the HACO-OFDM signal, and further performing suppression processing on interlayer noise and constellation point noise of the branch signals by using the time-frequency domain symmetry of the ACO-OFDM and PAM-DMT signals;

(4) utilizing a maximum likelihood estimation method to respectively carry out constellation point restoration processing on the separated and denoised branch ACO-OFDM and PAM-DMT signals;

(5) and the demapping module demodulates the binary data carried by the ACO-OFDM and PAM-DMT branches in sequence.

4. The HACO-OFDM visible light communication system includes: the device comprises an upper computer, a transmitting device and a receiving device; a null regression means of a HACO-OFDM modulation system as claimed in claim 2; the transmitter is a device for realizing normal light emission and data transmission of the LED, and the data processing steps are as follows:

(1) the upper computer software generates binary code data to be transmitted, and the binary code data is fed to a mapper to be changed into frequency domain symbols of a corresponding modulation format according to the requirement of the HACO-OFDM system;

(2) the data is processed through an IFFT module, a D/A module and negative cutting to obtain a time domain sending signal;

(3) the time domain signal is matched with a Bias-tee circuit to drive the light modulator LED through direct current coupling;

(4) the LED sends out visible light signals to realize HACO-OFDM signal transmission.

Technical Field

The invention belongs to the technical field of visible light transmission communication, and particularly relates to a zero value regression algorithm and a zero value regression device for an HACO-OFDM modulation system.

Background

High-speed Visible Light Communication (VLC), as a high-speed Communication mode without spectrum authorization, is a powerful complementary Communication means for traditional Radio Frequency (RF) Communication, and its THz spectrum is one of potential candidates for future B5G and 6G Communication. In a visible light communication system using LEDs as light emitting devices, how to further increase the communication speed under the bottleneck of communication bandwidth is one of the key problems in the current high-speed visible light communication system. The conventional single carrier modulation techniques, such as OOK, PPM, ASK, etc., are limited in their applications in ultra-high speed communication scenarios due to their low spectral efficiency. Multi-carrier modulation techniques such as Orthogonal Frequency Division Multiplexing (OFDM) techniques are preferred modulation and demodulation techniques for high-speed visible light communication because they have higher spectrum utilization than single carrier modulation.

However, the conventional optical OFDM Modulation technique is limited by the Intensity Modulation and Direct Detection (IM/DD) model of the optical communication system, and half of the frequency domain subcarriers of the conventional optical OFDM Modulation technique need to satisfy hermitian mirror symmetry, so that the spectral efficiency of the conventional optical OFDM Modulation technique is halved. In order to better improve the spectral efficiency of a visible light communication system, a Hybrid modulation technique based on a time domain superposition principle has been proposed in recent years and has gained wide attention, such as a Hybrid asymmetric clipping Optical Orthogonal Frequency Division Multiplexing (HACO-OFDM) modulation technique, which realizes the significant improvement of the spectral efficiency under an effective bandwidth by modulating only a QAM symbol of an odd carrier and a PAM symbol on an imaginary part of an even carrier on two frames of parallel OFDM respectively and combining two paths of branch signals of a time domain for synchronous superposition; meanwhile, because the output signals of the ACO-OFDM and PAM-DMT branches after IFFT have time domain antisymmetry, unipolar output of mixed signals can be realized without information loss through negative clipping, and the mixed signals have good power efficiency and are considered as an optical communication mixed modulation scheme with extremely excellent overall performance; however, due to the multilayer superposition mechanism of the hybrid modulation scheme, when a transmission signal is interfered by channel and environmental noise in the transmission process, extra interlayer interference is inevitably generated, and the error rate of the system is reduced. Therefore, how to effectively remove the noise interference from the received signal becomes a key for improving the performance of the HACO-OFDM-based hybrid modulation system.

Disclosure of Invention

The invention provides a zero regression algorithm and a device aiming at the HACO-OFDM modulation system in order to solve the problems;

1. a zero-value regression algorithm of a HACO-OFDM modulation system comprises the following steps:

(1) in the HACO-OFDM hybrid modulation system, the ACO-OFDM branch and the PAM-DMT branch are respectively mapped in the following frequency domains:

（1）

and（2）

(2) performing IFFT operation and negative cutting operation on the frequency domain signals to obtain two branched time domain signals; the probability density function is respectively expressed as:

（3）

and（4）

wherein the content of the first and second substances,andrespectively representing the root mean square before the time domain signals of the first branch and the second branch are clipped,unit of expressionThe number of steps in the function of a step,expressing a unit impulse function; after the two branch signals are superposed in the time domain, a time domain signal of the HACO-OFDM is formed, and the probability density function of the two branch signals can be derived as follows:

（5）

wherein，，，，

According to the HACO-OFDM signal probability density function of the formula, the zero-value occurrence probability of the HACO-OFDM time domain signal generated theoretically is 25%. In addition, the presented HACO-OFDM probability distribution function curve also demonstrates the scientificity of this conclusion.

According to the statistical characteristics in the above formula (5); for HACO-OFDM (N is larger than or equal to 64) with N subcarriers, capturing N/4 theoretical zero values of directly received signals, and enabling the numerical value to be zero, so that the suppression of channel noise, interlayer noise and constellation point noise of mixed signals can be realized without separating the mixed signals.

2. A null regression apparatus for a HACO-OFDM modulation system, comprising: the device comprises a photoelectric detection unit, a signal zero value regression unit and a signal processing unit; receiving LED visible light signals, sequentially performing data processing through the units, and transmitting the LED visible light signals to the incoming system number;

the signal zero value regression unit adopts a zero value regression algorithm to carry out noise suppression on the signal received by the photoelectric detection unit;

the signal processing unit comprises a photoelectric conversion module, an A/D module, a zero value regression module, an FFT module, a constellation point restoration module and a de-mapping module in sequence;

the zero value regression algorithm of the HACO-OFDM modulation system is described.

3. The zero value regression device of the HACO-OFDM modulation system;

the data processing steps for receiving the LED visible light signals are as follows:

(1) the photoelectric detection unit receives the LED optical signal and performs photoelectric conversion on the optical signal;

(2) performing analog-to-digital conversion and median downsampling on the converted electric signals, sequencing N time domain discrete HACO-OFDM data after downsampling from small to large, performing zero setting processing on the first N/4 numerical points in the small to large direction, and finally putting the data after zero value regression back to the corresponding position before sequencing to realize the noise suppression processing for suppressing channel noise, interlayer noise and constellation point noise from the angle of directly receiving the signals, namely a zero value regression module;

(3) performing FFT (fast Fourier transform) on the discrete time domain signal after the zero value regression processing to obtain a frequency domain symbol of the discrete time domain signal, separating the ACO-OFDM and PAM-DMT branch signals from the frequency domain angle of the HACO-OFDM signal, and further performing suppression processing on interlayer noise and constellation point noise of the branch signals by using the time-frequency domain symmetry of the ACO-OFDM and PAM-DMT signals;

(4) utilizing a maximum likelihood estimation method to respectively carry out constellation point restoration processing on the separated and denoised branch ACO-OFDM and PAM-DMT signals;

(5) and the demapping module demodulates the binary data carried by the ACO-OFDM and PAM-DMT branches in sequence.

4. The HACO-OFDM visible light communication system includes: the device comprises an upper computer, a transmitting device and a receiving device; the receiving device is; a zero-value regression device of a HACO-OFDM modulation system; the transmitter is a device for realizing normal light emission and data transmission of the LED, and the data processing steps are as follows:

(1) the upper computer software generates binary code data to be transmitted, and the binary code data is fed to a mapper to be changed into frequency domain symbols of a corresponding modulation format according to the requirement of the HACO-OFDM system;

(2) the data is processed through an IFFT module, a D/A module and negative cutting to obtain a time domain sending signal;

(3) the time domain signal is matched with a Bias-tee circuit to drive the light modulator LED through direct current coupling;

(4) the LED sends out visible light signals to realize HACO-OFDM signal transmission.

The invention provides a zero-value regression algorithm of an HACO-OFDM modulation system, in the HACO-OFDM hybrid modulation system, ACO-OFDM branches and PAM-DMT branches are respectively subjected to frequency domain mapping; after performing the IFFT operation on the frequency domain signal, two branched time domain signals are obtained. For HACO-OFDM with N subcarriers, capturing about N/4 theoretical zero values of received signals of the HACO-OFDM, and enabling the numerical value of the HACO-OFDM to be zero; a null regression apparatus using HACO-OFDM modulation system, comprising: the device comprises a photoelectric detection unit, a signal zero value regression unit and a signal processing unit; receiving LED visible light signals, processing data through the units in sequence, and transmitting binary data; the signal zero value regression unit denoises the optical signal received by the photoelectric detection unit by adopting the zero value regression algorithm; the error rate of the demodulated signal in the process of receiving and processing the signal by the visible light receiving device is reduced.

Drawings

FIG. 1 is a schematic diagram of the principle of an upper computer and a transmitter of a null regression algorithm of a HACO-OFDM modulation system of the present invention;

FIG. 2 is a schematic diagram of the principle of an upper computer and a receiving device of a zero value regression algorithm of the HACO-OFDM modulation system of the invention;

FIG. 3 is a graph of the HACO-OFDM probability distribution function of the present invention.

Detailed Description

Referring to fig. 1, the HACO-OFDM communication system includes: the device comprises an upper computer, a transmitting device (transmitter) and a receiving device; the upper computer transmits the signal to the transmitter, the transmitter converts the received signal into a visible light signal to be sent out, the receiving device receives the visible light signal through the receiving device, and a processor in the receiving device carries out signal noise reduction on the visible light signal through an HACO-OFDM zero value regression algorithm;

the upper computer is specially provided with equipment for changing random data into a binary code, and the binary code is a binary code.

Embodiment 1 a transmitting apparatus of a HACO-OFDM modulation system

The transmitter is a device for realizing normal light emission and data transmission of the LED, and the data processing steps are as follows:

(1) the upper computer software generates binary code data to be transmitted, and the binary code data is fed to a mapper to be changed into frequency domain symbols of a corresponding modulation format according to the requirement of the HACO-OFDM system;

(2) the data is processed through an IFFT module, a D/A module and negative cutting to obtain a time domain sending signal;

(3) the time domain signal is matched with a Bias-tee circuit to drive the light modulator LED through direct current coupling;

(4) the LED sends out visible light signals to realize HACO-OFDM signal transmission.

Embodiment 2 a receiving apparatus of HACO-OFDM modulation system

A receiving apparatus of a HACO-OFDM modulation system, comprising: the device comprises a photoelectric detection unit, a signal zero value regression unit and a signal processing unit; receiving LED visible light signals, processing data through the units in sequence, and transmitting binary values;

the signal zero value regression unit adopts a zero value regression algorithm to carry out noise suppression on the signal received by the photoelectric detection unit;

the signal processing unit comprises a photoelectric conversion module, an A/D module, a zero value regression module, an FFT module, a constellation point restoration module and a de-mapping module in sequence;

the data processing steps for receiving the LED visible light signals are as follows:

(1) the photoelectric detection unit adopts a PD photoelectric detector, receives an optical signal sent by the LED and performs photoelectric conversion on the optical signal; i.e. the visible light is received by the photodetector through the spatial channel to realize communication after providing the illumination requirement;

a condenser lens is arranged at the front end of the photoelectric detector to increase the signal-to-noise ratio of the receiving device, and in application, the integrated design of the lens can be carried out at the two ends of the transceiver to further improve the communication distance according to the focal length parameters of the lens;

(2) performing analog-to-digital conversion and median downsampling on the electric signal subjected to photoelectric conversion, sequencing N time domain discrete HACO-OFDM data subjected to downsampling from small to large, performing zero setting processing on the first N/4 numerical points in the small to large direction, and finally putting the data subjected to zero value regression back to the corresponding position before sequencing to realize noise suppression processing for suppressing channel noise, interlayer noise and constellation point noise from the angle of directly receiving the signal, namely a zero value regression module;

(3) performing FFT (fast Fourier transform) on the discrete time domain signal after the zero value regression processing to obtain a frequency domain symbol of the discrete time domain signal, separating the ACO-OFDM and PAM-DMT branch signals from the frequency domain angle of the HACO-OFDM signal, and further performing suppression processing on interlayer noise and constellation point noise of the branch signals by using the time-frequency domain symmetry of the ACO-OFDM and PAM-DMT signals;

(4) restoring the constellation points by utilizing maximum likelihood estimation; visible light communications typically employ maximum likelihood detection algorithms for symbol recovery. Noise introduced in a time domain is represented as position deviation relative to a standard constellation point in a frequency domain, the maximum likelihood detection means that the Euclidean distance between a constellation point to be detected and the standard constellation point is calculated, and the position with the closest distance is regarded as the position before the constellation point to be detected is interfered. Therefore, the symbol recovery is realized, and the specific algorithm is as follows:

（6）

(5) the restored signal is fed to a de-mapping module to demodulate the transmitted binary data.

And (3) a zero value regression algorithm:

in the HACO-OFDM hybrid modulation system, the ACO-OFDM branch and the PAM-DMT branch are respectively mapped in the following frequency domains:

（7）

and

（8）

performing IFFT operation and negative cutting operation on the frequency domain signals to obtain two branched time domain signals; the probability density function is respectively expressed as:

（9）

and

（10）

wherein the content of the first and second substances,andrespectively representing the root mean square before the time domain signals of the first branch and the second branch are clipped,the unit of a step function is represented,a unit impulse function is represented. After the two branch signals are superposed in the time domain, a time domain signal of the HACO-OFDM is formed, and the probability density function of the two branch signals can be derived as follows:

（11）

wherein the content of the first and second substances,，，，

for HACO-OFDM with N subcarriers according to the statistical properties in the above equation (N ≧ 64) whose time-domain signal has approximately N/4 zeros, the remainder being positive values. However, these data points that are supposed to be zero values are affected by noise during transmission and show a phenomenon of fluctuating around the zero value. Therefore, noise can be removed from the directly received signal in the time domain in one step only by finding out the minimum N/4 points and then zeroing the best number of the points, and the demodulation performance of the receiving device is improved. In practical application, the visible light communication system generally works under the condition of high signal-to-noise ratio, that is, the root mean square of noise is far smaller than the fluctuation degree of the OFDM signal, so that the zero value regression operation is more accurate in capturing the zero value.

By utilizing the time domain statistical characteristic of the HACO-OFDM signal, zero regression operation is further added on the basis of the traditional receiving device, and the time domain signal directly received by the receiving device is corrected to reduce the error rate of the demodulated signal; because the operation does not need to carry out time domain separation and extraction on the two branch signals, the increase of the original complexity of the system is almost negligible while the error rate performance of the system is improved.