阅读说明：本技术 一种vlc混合调制系统的点对点光功率分配算法 (Point-to-point optical power distribution algorithm of VLC hybrid modulation system ) 是由 张天 王宏旭 党甜甜 周倩 漆益红 李金泽 宋丁 乔双 于 2021-07-12 设计创作，主要内容包括：本发明公开了一种VLC混合调制系统的点对点光功率分配算法。引入了星座组合和噪声功率谱密度的联合推导,避免了由于分配给每个分支的功率导致不同的误码率性能,并用迭代收敛算法实现。仿真结果表明,在理想的线性传输模型下,与传统方案相比,本发明所提出的点对点光功率分配方法能进一步提高基于PHO-OFDM调制的可见光通信系统的误码率性能。(The invention discloses a point-to-point light power distribution algorithm of a VLC hybrid modulation system. The joint derivation of constellation combination and noise power spectral density is introduced, so that different error rate performances caused by the power distributed to each branch are avoided, and the iterative convergence algorithm is used for realizing the performance. Simulation results show that under an ideal linear transmission model, compared with the traditional scheme, the point-to-point optical power distribution method provided by the invention can further improve the bit error rate performance of a visible light communication system based on PHO-OFDM modulation.)

1. A point-to-point optical power allocation algorithm for a VLC hybrid modulation system, comprising:

(1) in the hybrid modulation system, under the condition of optical power normalization, assuming that the optical power distribution coefficient of the PAM branch is α, the optical power distribution coefficient of the QAM branch is (1- α);

and deducing the optical power distribution coefficient under the minimum bit error rate through a bit error rate formula:

（12）

with regard to the above-mentioned formula,andrespectively representing the modulation order of PAM and QAM,kindicating the degree of dc offset.

(2) The signal-to-noise ratio SNR is defined as:

（13）

wherein the content of the first and second substances,the electric power of the time domain signal of PHO-OFDM can be expressed as:

（15）

giving M₁、M₂DC bias levelkAnd SNR value, may be set to 0.5; the values can then be iterated in accordance with equations (12) (13) and (15), i.e.(ii) a Each iterationiThe value is incremented by 1 until the value converges.

2. The point-to-point optical power distribution algorithm of a VLC hybrid modulation system as claimed in claim 1, wherein said iterative convergence algorithm is:

。

3. a point-to-point optical power allocation algorithm for VLC hybrid modulation systems as claimed in claim 1 or 2, wherein: the iterative convergence algorithm, namely the point-to-point optical power distribution scheme, is also applicable to other hybrid modulation systems. The present invention is only to show the scheme and algorithm by taking the PHO-OFDM system as an example.

4. The point-to-point optical power allocation algorithm for VLC hybrid modulation system as claimed in claim 3, wherein: the PHO-OFDM hybrid modulation system comprises:

(1) inputting data of data to be transmitted to a mapping module, and respectively generating PAM (pulse amplitude modulation) and QAM (quadrature amplitude modulation) symbols according to odd and even carriers;

(2) then respectively modulating PAM and QAM symbols onto corresponding carriers according to the modulation format of the PHO-OFDM system;

(3) after a modulated frequency domain symbol is obtained by adopting a Hermite symmetrical module, the modulated frequency domain symbol is input into an IFFT module to obtain a time domain symbol;

(4) the time domain symbols on the odd carriers adopt negative clipping operation to achieve the unipolar property of the transmission signals, and the time domain symbols on the even carriers achieve the unipolar property requirement by adding direct current offset.

Technical Field

The invention belongs to the technical field of visible light transmission communication, and particularly relates to a point-to-point light power distribution algorithm of a VLC hybrid modulation system.

Background

In recent years, Visible Light Communication (VLC) technology has become one of potential candidate means for future 6G Communication due to advantages such as electromagnetic interference resistance, lighting and Communication compatibility, and unlicensed spectrum of hundreds of terahertz. To compensate for the limited bandwidth of the visible light communication transmitter LED, a spectrally efficient hybrid modulation technique has received much attention. Because the Pulse-amplitude multi-audio modulation-Based Hybrid Optical orthogonal frequency division multiplexing (PHO-OFDM) technology adopts two paths of OFDM branch signals to carry out time domain superposition transmission.

Therefore, the design of power allocation at the transmitting end becomes one of the key factors affecting the performance of the visible light communication system based on the PHO-OFDM modulation. It is worth mentioning that most hybrid modulation schemes use a constant power allocation factor for a given constellation combination. In practice, this factor is also affected by the real-time signal-to-noise ratio of the communication system receiver.

Disclosure of Invention

In order to solve the above problems, the present invention provides a point-to-point optical power allocation algorithm for VLC hybrid modulation system, and for convenience of description, the present invention describes the PHO-OFDM hybrid modulation system as an example;

a point-to-point optical power allocation algorithm for a VLC hybrid modulation system, comprising:

(1) in a PHO-OFDM hybrid modulation system, under the condition of optical power normalization, assuming that the optical power distribution coefficient of a PAM branch is alpha, the optical power distribution coefficient of a QAM branch is (1-alpha);

and deducing the optical power distribution coefficient under the minimum bit error rate through a bit error rate formula:

（12）

with regard to the above-mentioned formula,andrespectively representing the modulation order of PAM and QAM,kindicating the degree of dc offset.Representing the noise power;。

(2) the signal-to-noise ratio is defined as:

（13）

wherein the content of the first and second substances,the electric power of the time domain signal of PHO-OFDM can be expressed as:

（15）

according to the proposed iterative convergence algorithmDC bias levelkAnd SNR value, may be set to 0.5. The values can then be iterated in accordance with equations (12) (13) and (15), i.e.. Each iterationiThe value is added by 1 until the values converge, and the optical power distribution value under the specific constellation combination and the signal-to-noise ratio, namely the point-to-point optical power distribution, can be obtained. While the threshold value isThe rate of convergence can be determined, typically by takingOnly 3 iterations are required to converge. The iterative convergence algorithm is as follows:

the hybrid modulation system is a PHO-OFDM hybrid modulation system;

the PHO-OFDM hybrid modulation system comprises:

(1) inputting data of data to be transmitted to a mapping module, and respectively generating PAM (pulse amplitude modulation) and QAM (quadrature amplitude modulation) symbols according to odd and even carriers;

(2) then respectively modulating PAM and QAM symbols onto corresponding carriers according to the modulation format of the PHO-OFDM system;

(3) after a modulated frequency domain symbol is obtained by adopting a Hermite symmetrical module, the modulated frequency domain symbol is input into an IFFT module to obtain a time domain symbol;

(4) the time domain symbols on the odd carriers adopt negative clipping operation to achieve the unipolar property of the transmission signals, and the time domain symbols on the even carriers achieve the unipolar property requirement by adding direct current offset.

The invention provides a point-to-point optical power distribution algorithm of a VLC hybrid modulation system. Since the power allocated to each branch can cause different bit error rate performances, joint derivation of constellation combination and noise power spectral density is introduced and is realized by an iterative convergence algorithm. Simulation results show that under an ideal linear transmission model, compared with the traditional scheme, the point-to-point optical power distribution method provided by the invention can further improve the bit error rate performance of a visible light communication system based on PHO-OFDM modulation.

Drawings

FIG. 1 is a block diagram of a point-to-point optical power distribution algorithm and apparatus structure for a PHO-OFDM modulation system according to the present invention;

FIG. 2 is a comparison graph of bit error rate curves for the present invention;

fig. 3 is a diagram of the performance of the error rate under different optical power allocations in the technical solution of the present invention.

Detailed Description

Embodiment 1 a point-to-point optical power distribution algorithm for a PHO-OFDM modulation system

(1) In the case of optical power normalization, the optical power of the PAM branch is assumed to beThe optical power of the QAM branch is. For this purpose, it is necessary to multiply one companding factor on both branchesAndexpressed as follows:

（1）

(2) firstly, an error rate calculation formula of two branches of the PHO-OFDM system is given.

（2）

（3）

Wherein the content of the first and second substances,andrespectively representing modulation orders of PAM and QAM;andrespectively representing the electrical power of the PAM branch and the QAM branch,representing the noise power;。

then, the overall bit error rate of the PHO-OFDM system is further deduced to be approximately:

（4）

whereinNIs the number of subcarriers. When in useNWhen the size of the particles is large enough,1 can be approximately regarded as。

The optical and electrical power of the PAM branch is given below:

（5）

（6）

substituting (1), (5) and (6) into equation (2) yields:

（7）

one point to note for the QAM branch is that it adds oneThe DC bias ensures the non-negativity of the time domain signal, so the DC bias level can be defined as. The optical and electrical power of the QAM branch is given by:

（8）

（9）

substituting (1), (8) and (9) into equation (3) can be approximated as:

（10）

and finally, substituting the simplified formulas (7) and (10) into the formula (4) to obtain the bit error rate formula of the PHO-OFDM. And solving the second derivative to obtain:

（11）

in the above formulaWhen at the same time. So as to. This is illustrated inA minimum value may be taken. So that corresponding at minimum bit error rateThe value may be expressed as:

（12）

and (3) performing iterative convergence algorithm and point-to-point optical power distribution based on a PHO-OFDM hybrid modulation system.

In equation (12), the only amount of uncertainty is the noise powerThe value of (c). Therefore, an iterative convergence algorithm is proposed for calculating the signal-to-noise ratio of each signalThe value is obtained.

First, a Signal-to-noise Ratio (SNR) is defined as:

（13）

wherein the content of the first and second substances,the electric power of the time domain signal of PHO-OFDM can be expressed as:

（14）

wherein the content of the first and second substances,is the power of the light, and is,i.e. electrical power. Equation (14) can be further reduced by substituting equations (1) (5) (6) (8) and (9) therein:

（15）

the iterative convergence algorithm is proposed as follows:

according to the proposed iterative convergence algorithm, M is given₁、M₂DC bias levelkAnd SNR value, may be set to 0.5. The values can then be iterated in accordance with equations (12) (13) and (15), i.e.. Each iterationiThe value is added by 1 until the values converge, and the optical power distribution value under the specific constellation combination and the signal-to-noise ratio, namely the point-to-point optical power distribution, can be obtained. The threshold value may determine the convergence speed, and generally, if the threshold value is selected, only 3 iterations are needed to converge.

The iterative convergence algorithm presented is also applicable to other hybrid modulation systems. The present invention is only to show the scheme and algorithm by taking the PHO-OFDM system as an example.

Embodiment 2 a data processing procedure of a PHO-OFDM hybrid modulation system

The invention aims at the improvement of optical power distribution performed by a sending end, so that a receiving end is consistent with a traditional receiving end on the premise of knowing an optical power distribution coefficient. As shown in fig. 1, the data processing steps are as follows:

(1) and inputting data of the data to be transmitted to a mapping module, and respectively generating PAM (pulse amplitude modulation) and QAM (quadrature amplitude modulation) symbols according to the odd-even carriers.

(2) And then respectively modulating PAM and QAM symbols onto corresponding carriers according to the modulation format of the PHO-OFDM system, wherein an Hermite symmetrical module is also necessary for ensuring the real value of a transmission signal.

(3) After the modulated frequency domain symbol is obtained, the modulated frequency domain symbol is input to an IFFT module to obtain a time domain symbol.

(4) The time domain symbols on the odd carriers adopt negative clipping operation to achieve the unipolar property of the transmission signals, and the time domain symbols on the even carriers achieve the unipolar property requirement by adding direct current offset.

(5) Due to the optical power distribution idea added thereto, the transmission signal can not be obtained by only time-domain superposition of two layers of signals as in the conventional scheme, but should be multiplied by coefficients respectivelyAnd。

point-to-point optical power distribution scheme:

it should be noted that the iterative convergence algorithm, i.e., the point-to-point optical power allocation scheme, is also applicable to other hybrid modulation systems. The present invention is only to show the scheme and algorithm by taking the PHO-OFDM system as an example.

According to the iterative convergence algorithm above, the power allocation values under two parameter combinations (case 1 and case 2) are given, as shown in table 1.

Under the above optical power distribution, an error rate curve under the corresponding modulation format is given, and it can be seen from fig. 2 that the proposed optical power distribution scheme can obtain better signal-to-noise ratio gain under different modulation orders. It can be seen from fig. 3 that the bit error rate performance obtained by the proposed optical power allocation scheme is indeed better.