CN110958051B - Method for improving error rate performance of NOMA VLC system based on parameter adjustment - Google Patents

Method for improving error rate performance of NOMA VLC system based on parameter adjustment Download PDF

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CN110958051B
CN110958051B CN201911209238.4A CN201911209238A CN110958051B CN 110958051 B CN110958051 B CN 110958051B CN 201911209238 A CN201911209238 A CN 201911209238A CN 110958051 B CN110958051 B CN 110958051B
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data
parameters
constellation diagram
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王子雄
任浩
徐义桐
吴彤
韩士莹
陈健
余长源
于晋龙
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Tianjin 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
    • H04B10/11—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
    • 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
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/3405—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power

Abstract

The invention discloses a method for improving the error rate performance of a NOMA VLC system based on parameter adjustment, which relates to three data transmitting terminals, three data receiving terminals and three users; the data transmitting terminal respectively carries out quadrature amplitude modulation on binary data to be transmitted of three users; then, superposition of three user signals is carried out by utilizing a superposition coding technology to obtain a superposition constellation diagram; under the condition of not increasing the total power, adjusting parameters of the superposed constellation diagram through a differential evolution algorithm to obtain an adjusted superposed constellation diagram signal; after channel transmission, the three data receiving ends all receive the superposed signal and obtain data required by three users through a SIC detection algorithm; when SIC decoding is carried out, SIC decoding parameters are adjusted through a differential evolution algorithm. The invention realizes the improvement of the error rate of the NOMA VLC system by adjusting the parameters of the superposed signal constellation diagram of the transmitting terminal and the SIC decoding parameters of the receiving terminal, thereby improving the communication performance of the non-orthogonal multiple access technology.

Description

Method for improving error rate performance of NOMA VLC system based on parameter adjustment
Technical Field
The invention relates to a method for improving the performance of a multi-user visible light communication system, in particular to a method for improving the error rate performance of a non-orthogonal multiple access visible light communication system based on parameter adjustment.
Background
Non-orthogonal multiple access (NOMA) is a new communication technology that has attracted attention in recent years. The NOMA can transmit a plurality of users after superposition according to different power allocations, so that the plurality of users share time domain and frequency domain resources, thereby obtaining high frequency spectrum utilization rate, increasing the connection number of system users and ensuring low transmission delay.
The Visible Light Communication (VLC) technology is a communication method in which light in a visible light band is used as an information carrier, and an optical signal is directly transmitted in the air without a transmission medium such as an optical fiber or a wired channel. The visible light communication technology is green and low-carbon, can realize nearly zero-energy-consumption communication, can effectively avoid the defects of leakage of radio communication electromagnetic signals and the like, and quickly constructs an anti-interference and anti-interception safety information space. The downlink transmission with high throughput can be realized by utilizing visible light communication, and meanwhile, illumination and communication are realized.
Researches show that the total throughput of the multi-user visible light communication system can be further improved by adopting the non-orthogonal multiple access technology. Although the total capacity of a NOMA VLC system increases, the Bit Error Rate (BER) performance of the system decreases. Under the scheme based on the NOMA technology, all users occupy the same frequency spectrum, and orthogonality among different users is not maintained. The NOMA scheme involves two key technologies, which are transmitter superposition coding and receiver Successive Interference Cancellation (SIC) decoding, respectively. Because different users have different power distribution coefficients under the SIC decoding technology, the distances between adjacent points in the superposed constellation are different. Thus, error performance deteriorates.
Disclosure of Invention
Aiming at the prior art, in order to improve the bit error rate performance, a method for further improving the bit error rate performance of the NOMA VLC system by adjusting the superposition constellation diagram and simultaneously adjusting the continuous interference elimination decoding parameter of the receiver and the superposition coding parameter of the transmitter is provided.
In order to solve the technical problems, the invention provides a method for improving the error rate performance of a NOMA VLC system based on parameter adjustment, which relates to three data transmitting ends and three data receiving ends; the three data transmitting terminals simultaneously transmit data to three users, the three users are respectively marked as a user 1, a user 2 and a user 3, and the user 1, the user 2 and the user 3 respectively correspond to the three data receiving terminals; the method comprises the following steps:
a data transmitting terminal respectively carries out quadrature amplitude modulation on binary data to be transmitted of a user 1, a user 2 and a user 3;
then, overlapping the three user signals by using an overlapping coding technology to obtain an overlapping constellation diagram;
under the condition of not increasing the total power, obtaining the adjusted parameters of the superposition constellation diagram through a differential evolution algorithm, thereby obtaining the adjusted superposition constellation diagram;
after channel transmission, the three data receiving ends all receive the adjusted superposed constellation diagram, and obtain data required by three users through a serial interference elimination detection algorithm; when SIC decoding is carried out, the SIC decoding parameters obtained through a differential evolution algorithm are used for adjusting the parameters of the superposed constellation map, so that the error rate performance is further improved.
Further, the method for improving the error rate performance of the NOMA VLC system based on the parameter adjustment, provided by the invention, comprises the following steps: respectively carrying out quadrature amplitude modulation and power normalization on binary data of a user 1, a user 2 and a user 3 to respectively obtain modulated complex data corresponding to three users, and then respectively carrying out three groups of complex data according to a power distribution coefficient alpha1、α2And alpha3Power adjustment is performed, and alpha1+α2+α3＝1，α1＞α2＞α3And respectively obtaining the adjusted power of the complex data of the user 1, the user 2 and the user 3.
In the process of obtaining the parameters for adjusting the superposed constellation diagram through the differential evolution algorithm, the proportion parameters in the horizontal direction and the vertical direction of the constellation diagram are respectively set as
Figure GDA0002703427220000021
Wherein i, j is 1,2,3, 4; the superposition constellation point before adjustment is (x, y), and the superposition constellation point after adjustment is (m)ix,mjy); because the superposed constellation diagram is symmetrical, the superposed constellation diagram is adjusted by using four parameters, and the four parameters are obtained by a differential evolution algorithm and are respectively m1，m2，m3And m4Represents; parameter m1，m2，m3And m4Is a function of the signal-to-noise ratio of the user 1, thereby obtaining four parameters m under the conditions of different signal-to-noise ratios1，m2，m3And m4The optimum value of (c).
In SIC decoding, beta1And beta2Denotes the adaptation parameter of SIC decoding, where1≠α1And beta is2≠α2(ii) a Firstly, the demodulated data of the user 1 with larger transmitting power is detected and obtained, and then the adjustment parameter beta of the SIC decoding is carried out1Detecting and acquiring the demodulated data of the user 2 after parameter adjustment, and finally decoding the demodulated data according to the SIC2The data of the user 3 is detected and acquired, so that the required data of the three users are acquired respectively.
Compared with the prior art, the invention has the beneficial effects that:
the invention improves the performance of the NOMA VLC system by adjusting the superposition constellation diagram parameter of the transmitting end and the SIC decoding parameter of the receiving end. The method realizes the improvement of the error rate of the NOMA VLC system and improves the communication performance of the non-orthogonal multiple access technology.
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Fig. 1 is a block diagram illustrating the performance of improving the error rate of a NOMA VLC system based on parameter adjustment according to the present invention.
Detailed Description
The invention will be further described with reference to the following figures and specific examples, which are not intended to limit the invention in any way.
The method for improving the error rate performance of the NOMA VLC system based on parameter adjustment, disclosed by the invention, comprises three data transmitting ends and three data receiving ends, as shown in figure 1. The data transmitting end simultaneously transmits data to three users, the three users are marked as a user 1, a user 2 and a user 3, and the user 1, the user 2 and the user 3 respectively correspond to three data receiving ends. The data transmitting terminal respectively carries out Quadrature Amplitude Modulation (QAM) on binary data to be transmitted of a user 1, a user 2 and a user 3, then carries out OFDM modulation, and then carries out superposition of three user signals by utilizing a superposition coding technology. BER performance is improved by adjusting the superposition constellation parameters at the transmitter without increasing the total power. And obtaining the adjusted parameters of the superposition constellation diagram through a Differential Evolution (DE) algorithm so as to obtain the adjusted superposition constellation diagram. After channel transmission, the three data receiving ends all receive the superposed constellation diagram, and obtain data required by three users through a Serial Interference Cancellation (SIC) detection algorithm. When SIC decoding is carried out, SIC decoding parameters obtained through a Differential Evolution (DE) algorithm are needed to be used for adjusting the parameters of the superposed constellation map, and therefore the Bit Error Rate (BER) performance is further improved.
The method comprises the following specific steps:
step one, respectively carrying out orthogonal amplitude modulation, OFDM modulation and power normalization on binary data of a user 1, a user 2 and a user 3 so as to respectively obtain modulated complex data corresponding to three users, and then respectively carrying out three groups of complex data according to a power distribution coefficient alpha1、α2And alpha3And adjusting the power, then:
P1＝α1P (1)
P2＝α2P (2)
P3＝α3P (3)
in the formulae (1), (2) and (3), P1Adjusted power, P, for user 1 complex data2Adjusted power, P, for user 2 complex data3The adjusted power of the complex data for user 3, P is the total power of the signal sent by the data transmitting end, and alpha1+α2+α3＝1，α1＞α2＞α3(ii) a The complex data of the three users after power adjustment are respectively recorded as QAM1, QAM2 and QAM 3. And then, overlapping the three user signals by using an overlapping coding technology to obtain a constellation diagram after signal overlapping.
Step two, in the adjustment process of the superposed constellation diagram,
Figure GDA0002703427220000031
means are respectivelyThe scaling parameter in the horizontal and vertical directions of the constellation diagram. If the original superimposed constellation point is (x, y), the adjusted superimposed constellation point is (m)ix,mjy). Since the superposition constellation is symmetric, the superposition constellation is adjusted using four parameters before driving the LEDs. The four optimization parameters respectively use m1,m2,m3,m4It is shown that the four optimization parameters mentioned above will be obtained by the DE algorithm. In the optimization process of the DE algorithm, the population size and the generation number are both 500, the mutation scale factor is 0.5, and the cross probability is 0.2. Thereby obtaining a parameter m1,m2,m3,m4Is a function of the signal-to-noise ratio of user 1. Thereby obtaining four optimized parameters under different signal-to-noise ratios.
Step three, the adjusted superposed constellation diagram is sent by LEDs and respectively passes through a time domain channel h1、h2、h3And receiving by the data receiving end. At a data receiving end, firstly, an optical signal sent by an LED is received through a Photoelectric Detector (PD), the optical signal is converted into an electric signal, then OFDM demodulation is carried out on the electric signal, and data required by three users are obtained through a Serial Interference Cancellation (SIC) detection algorithm. When SIC decoding is carried out, the SIC decoding parameters obtained by a DE algorithm are used for adjusting the parameters. Using beta1And beta2To indicate the adjustment parameter of SIC decoding, where1≠α1And beta is2≠α2. Firstly, the demodulated data of the user 1 with larger transmitting power is detected and obtained, and then the demodulated data is decoded according to a decoding parameter beta1Detecting and acquiring the demodulated data of the user 2 after parameter adjustment, and finally decoding the parameter beta2The data of the user 3 is detected and acquired, so that the required data of the three users are acquired respectively.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.

Claims (4)

1. A method for improving the error rate performance of a NOMA VLC system based on parameter adjustment relates to three data transmitting terminals and three data receiving terminals; the three data transmitting terminals simultaneously transmit data to three users, the three users are respectively marked as a user 1, a user 2 and a user 3, and the user 1, the user 2 and the user 3 respectively correspond to the three data receiving terminals; it is characterized in that the preparation method is characterized in that,
the method comprises the following steps:
a data transmitting terminal respectively carries out quadrature amplitude modulation on binary data to be transmitted of a user 1, a user 2 and a user 3;
then, overlapping the three user signals by using an overlapping coding technology to obtain an overlapping constellation diagram;
under the condition of not increasing the total power, obtaining the adjusted parameters of the superposition constellation diagram through a differential evolution algorithm, thereby obtaining the adjusted superposition constellation diagram;
after channel transmission, the three data receiving ends all receive the adjusted superposed constellation diagram, and obtain data required by three users through a serial interference elimination detection algorithm; when SIC decoding is carried out, the SIC decoding parameters obtained through a differential evolution algorithm are used for adjusting the parameters of the superposed constellation map, so that the error rate performance is further improved.
2. The method of claim 1, wherein the quadrature amplitude modulation is performed by: respectively carrying out quadrature amplitude modulation and power normalization on binary data of a user 1, a user 2 and a user 3 to respectively obtain modulated complex data corresponding to three users, and then respectively carrying out three groups of complex data according to a power distribution coefficient alpha1、α2And alpha3Power adjustment is performed, and alpha1+α2+α3＝1，α1＞α2＞α3And respectively obtaining the adjusted power of the complex data of the user 1, the user 2 and the user 3.
3. The method of claim 2 wherein in obtaining the parameters of the superimposed constellation adjustment through a differential evolution algorithm,
let the ratio parameters in the horizontal and vertical directions of the constellation diagram be
Figure FDA0002703427210000011
Wherein i, j is 1,2,3, 4; the superposition constellation point before adjustment is (x, y), and the superposition constellation point after adjustment is (m)ix,mjy); because the superposed constellation diagram is symmetrical, the superposed constellation diagram is adjusted by using four parameters, and the four parameters are obtained by a differential evolution algorithm and are respectively m1，m2，m3And m4Represents; parameter m1，m2，m3And m4Is a function of the signal-to-noise ratio of the user 1, thereby obtaining four parameters m under the conditions of different signal-to-noise ratios1，m2，m3And m4The optimum value of (c).
4. The method of claim 2, wherein β is β decoded when SIC is performed1And beta2Denotes the adaptation parameter of SIC decoding, where1≠α1And beta is2≠α2(ii) a Firstly, the demodulated data of the user 1 with larger transmitting power is detected and obtained, and then the adjustment parameter beta of the SIC decoding is carried out1Detecting and acquiring the demodulated data of the user 2 after parameter adjustment, and finally decoding the demodulated data according to the SIC2The data of the user 3 is detected and acquired, so that the required data of the three users are acquired respectively.
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