CN109194400B - Compensation method and device based on visible light communication system - Google Patents

Compensation method and device based on visible light communication system Download PDF

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CN109194400B
CN109194400B CN201811029928.7A CN201811029928A CN109194400B CN 109194400 B CN109194400 B CN 109194400B CN 201811029928 A CN201811029928 A CN 201811029928A CN 109194400 B CN109194400 B CN 109194400B
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compensation
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phase
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quadrature
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CN109194400A (en
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刘鹏
郭亚榕
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Yangzhong Intelligent Electrical Institute North China Electric Power 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
    • 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
    • H04B10/548—Phase or frequency 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

Abstract

The invention discloses a compensation method based on a visible light communication system, which comprises the following steps: calculating the average value of the in-phase component and the quadrature component of four areas in the constellation diagram; calculating a compensation angle through a specific formula according to the average value of the in-phase component and the orthogonal component; calculating the rotated in-phase component and the rotated quadrature component through a specific algorithm; and adjusting the compensation times according to the nonlinear degree of the LED and the modulation order adopted by the system to compensate the error code caused by the nonlinearity. The invention compensates the error code caused by LED nonlinearity in a Visble Light Communication (VLC) system, and well compensates the advantage of phase-quadrature (IQ) imbalance caused by LED nonlinearity through the rotation of the phase of the received signal.

Description

Compensation method and device based on visible light communication system
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a compensation method and apparatus based on a visible light communication system.
Background
The ISI phenomenon in the OFDM optical fiber communication system is mainly caused by IQ imbalance, and there are two solutions proposed for the ISI phenomenon. In 2008, Irshaad Fatadin et al used GSOP (Gram-Schmidt orthogonality Procedure) algorithm to perform Schmidt Orthogonalization on non-orthogonal signals for IQ imbalance problem in QPSK (quadrature phase shift keying) modulated coherent optical system. A 10.7Gb/s NRZ (non-return to zero) transmission system was established, and the method is also applicable to polarization multiplexing systems.
In 2010, W Shieh et al proposed a time-frequency domain hybrid compensation method for IQ imbalance at both transmit and receive ends.
The IQ imbalance of the receiving end is compensated on a time domain by using the training symbols, and IQ imbalance factors and channel imbalance of the transmitting end are compensated on a frequency domain. The system adopts 16QAM modulation, and the line widths of the lasers are all 100 kHz.
Patents related to IQ compensation in coherent optical communication systems are now focused on dedicated areas. A non-iterative blind phase noise compensation method (application number: 201510611860.3) suitable for a CO-OFDM (coherent light OFDM system) system is characterized in that non-iterative operation is carried out through an approximate cost function to calculate the approximate estimated value of CPE (user terminal equipment) of each OFDM symbol, a decision-oriented phase equalization algorithm (DDPE) is used to calculate the residual CPE estimated value, and finally phase noise compensation is completed. The invention discloses a method for compensating sampling clock frequency deviation of a low-complexity OFDM-PON system (application number: 201610966929.9). A phase rotation factor caused by sampling clock frequency deviation is eliminated by utilizing subcarrier sampling frequency deviation rotation increment, symbol synchronization is carried out on data collected by an ADC (analog-to-digital converter) at a receiving end, the position of an FFT (fast Fourier transform) window is found, a training sequence and a data symbol are respectively extracted, a training sequence frequency domain value and a local training sequence frequency domain value are obtained by utilizing the extracted training sequence frequency domain value, a channel response initial value of the system is estimated, a channel response more positive value at each symbol is obtained by utilizing the channel response initial value of the system through a recursion and feedback system, and phase rotation caused by the sampling clock frequency deviation of the system is compensated according to the updated channel response coefficient of the system. The disadvantage is obvious, and the error code caused by the LED nonlinearity in the Visible Light Communication (VLC) system is compensated, so that the phase-quadrature (iq) imbalance caused by the LED nonlinearity cannot be compensated.
Disclosure of Invention
The technical problem to be solved by the present invention is to overcome the above drawbacks of the prior art, and to provide a compensation method based on a visible light communication system, the method comprising:
calculating the average value of the in-phase component and the quadrature component of four areas in the constellation diagram;
calculating a compensation angle through a specific formula according to the average value of the in-phase component and the orthogonal component;
calculating the rotated in-phase component and the rotated quadrature component through a specific algorithm;
and adjusting the compensation times according to the nonlinear degree of the LED and the modulation order adopted by the system to compensate the error code caused by the nonlinearity.
Preferably, the specific formula is:
Figure BDA0001789458390000021
E(x1)，E(x2) The energy mean value of the in-phase component in the first and second quadrants, E (y)1)，E(y2) The energy mean value of the orthogonal component in the first quadrant and the second quadrant respectively, and phi is a compensation angle.
Preferably, the specific algorithm is a coordinate rotation numerical calculation algorithm.
Preferably, the modulation is quadrature phase shift keying and quadrature amplitude modulation.
A compensation apparatus based on a visible light communication system, the apparatus comprising:
the front calculation module is used for calculating the average value of in-phase components and orthogonal components of four areas in a constellation diagram;
the compensation angle calculation module is used for calculating a compensation angle through a specific formula according to the average value of the in-phase component and the orthogonal component;
the post-calculation module is used for calculating the rotated in-phase component and the rotated quadrature component through a specific algorithm;
and the compensation module is used for adjusting the compensation times according to the LED nonlinearity degree and the modulation order adopted by the system and compensating the error code caused by nonlinearity.
Preferably, the specific formula is:
Figure BDA0001789458390000031
E(x1)，E(x2) The energy mean value of the in-phase component in the first and second quadrants, E (y)1)，E(y2) The energy mean value of the orthogonal component in the first quadrant and the second quadrant respectively, and phi is a compensation angle.
Preferably, the specific algorithm is a coordinate rotation numerical calculation algorithm.
Preferably, the modulation is quadrature phase shift keying and quadrature amplitude modulation.
Compared with the prior art, the compensation method and the compensation device based on the visible light communication system have the following advantages that:
1. IQ imbalance in a VLC-OFDM system is analyzed, and the influence of LED nonlinearity on signal distortion is considered.
2. The CORDIC algorithm is applied to a VLC-OFDM system, and the received signal is compensated by calculating the rotation angle. Monte Carlo simulation experiments prove that the blind compensation mode is suitable for VLC systems.
3. The invention compensates the error code caused by LED nonlinearity in a Visble Light Communication (VLC) system, and well compensates the advantage of phase-quadrature (IQ) imbalance caused by LED nonlinearity through the rotation of the phase of the received signal.
Drawings
Figure 1 is a flow chart of the operation of the present invention,
figure 2 is a basic model of the CORDIC,
fig. 3 is a block diagram of the present invention.
Detailed Description
For the purpose of clearly illustrating the aspects of the present invention, preferred embodiments are given below in conjunction with the accompanying drawings. The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
As shown in fig. 1. A compensation method based on a visible light communication system, the method comprising:
s101, calculating the average value of in-phase components and orthogonal components of four areas in a constellation diagram;
s102, calculating a compensation angle through a specific formula according to the average value of the in-phase component and the orthogonal component; the specific formula is:
Figure BDA0001789458390000041
E(x1)，E(x2) The energy mean value of the in-phase component in the first and second quadrants, E (y)1)，E(y2) The energy mean value of the orthogonal component in the first quadrant and the second quadrant respectively, and phi is a compensation angle.
S103, calculating the rotated in-phase component and the rotated quadrature component through a specific algorithm; the specific algorithm is a coordinate rotation numerical calculation algorithm. In VLC-OFDM system, the initial signal is represented as:
x(t)＝cos(wLOt)+jsin(wLOt) (1)
wherein wLOAt the transmitting end, the signal is distorted in amplitude and phase by LED nonlinearity and Inter-Carrier Interference (ICI) in OFDM. For the sake of analysis, we consider only the distortion of the quadrature component Q, let kqAnd
Figure BDA0001789458390000042
the amplitude and phase distortion of the Q component, respectively. So the signal of the transmitting end can be expressed as:
Figure BDA0001789458390000043
the signal is modulated to an LED optical carrier to enter a channel for transmission, and the influence of the amplitude and the phase caused by the nonlinearity of the LED on the signal is respectively set as klAnd
Figure BDA0001789458390000044
expressed as:
Figure BDA0001789458390000045
the system channel Noise is Additive White Gaussian Noise (AWGN) n (t), and the signal transmitted through the channel can be represented as:
Figure BDA0001789458390000051
the matrix is represented as:
Figure BDA0001789458390000052
likewise, the receive-side imbalance can be expressed as:
Figure BDA0001789458390000053
wherein k and phirRepresenting amplitude and phase distortions at the receiving end, theoretically, to be recoveredThe original signal is simply multiplied by the inverse matrix of the expressions (5) and (6) with respect to the received signal. The compensation inverse matrix is:
Figure BDA0001789458390000054
it should be noted that channel noise may also be affected by the compensation matrix when recovering the signal. However, it is more complicated to measure the angle and amplitude distortion in the system, and with respect to the angle measurement, a phase-locked loop can be introduced for phase estimation, but the complexity of the system is increased. Therefore, we introduce a blind compensation method based on the CORDIC algorithm to estimate the parameters.
As shown in fig. 2. In the figure, the rotation of a can be decomposed into angular rotation and amplitude addition and subtraction, and the following equation needs to be satisfied:
xA'＝xAcos(θ)-yAsin(θ)＝cos(θ)(xA-yAtan(θ)) (8)
yA'＝yAcos(θ)+xAsin(θ)＝cos(θ)(yA+xAtan(θ)) (9)
let the tangent of the angle of rotation at each time be
Figure BDA0001789458390000055
The angle superposition is:
Figure BDA0001789458390000056
wherein d isiAnd + -1 is an operation decision symbol used for deciding the rotation direction. When the number of iterations reaches a certain level, the value of cos (θ) approaches 0.607, then the above can be expressed as:
x(i+1)＝0.607(x(i)-diy(i)(2-i)) (10)
y(i+1)＝0.607(y(i)-dix(i)(2-i)) (11)
and S104, adjusting the compensation times according to the LED nonlinearity degree and the modulation order adopted by the system, and compensating the error code caused by nonlinearity. The modulation is quadrature phase shift keying and quadrature amplitude modulation.
In the invention, a blind compensation method based on a CORDIC algorithm is applied to a VLC-OFDM system, and the effectiveness of the blind compensation method is proved through a Monte Carlo simulation experiment. IQ distortion caused by LED nonlinearity is compensated by calculating the angular distortion of the received signal in the constellation diagram. Taking QPSK modulation as an example, the BER of the system is affected differently by the nonlinear performance of the LED, so the number of compensation times needs to be adjusted according to the nonlinear performance of the LED, and the BER is obviously reduced after compensation.
As shown in fig. 3, a compensation apparatus based on a visible light communication system, the apparatus includes:
a pre-calculation module 201, configured to calculate an average value of in-phase components and quadrature components of four regions in a constellation diagram;
a compensation angle calculation module 202, configured to calculate a compensation angle according to an average value of the in-phase component and the quadrature component by using a specific formula; the specific formula is:
Figure BDA0001789458390000061
E(x1)，E(x2) The energy mean value of the in-phase component in the first and second quadrants, E (y)1)，E(y2) The energy mean value of the orthogonal component in the first quadrant and the second quadrant respectively, and phi is a compensation angle.
A post-calculation module 203, configured to calculate the rotated in-phase component and quadrature component through a specific algorithm; the specific algorithm is a coordinate rotation numerical calculation algorithm.
And the compensation module 204 is configured to adjust the compensation times according to the LED nonlinearity degree and the modulation order adopted by the system, so as to compensate for the error code caused by the nonlinearity. The modulation is quadrature phase shift keying and quadrature amplitude modulation.
In summary, the above descriptions are only examples of the present invention, and are only used for illustrating the principle of the present invention, and not for limiting the protection scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. A compensation method based on a visible light communication system, the method comprising:
calculating the average value of the in-phase component and the quadrature component of four areas in the constellation diagram;
calculating a compensation angle through a specific formula according to the average value of the in-phase component and the orthogonal component;
calculating the rotated in-phase component and the rotated quadrature component through a specific algorithm;
adjusting the compensation times according to the nonlinear degree of the LED and the modulation order adopted by the system to compensate the error code caused by the nonlinearity;
wherein the specific formula is:
Figure FDA0002441718390000011
E(x1)，E(x2) The energy mean value of the in-phase component in the first and second quadrants, E (y)1)，E(y2) The energy mean values of orthogonal components in a first quadrant and a second quadrant are respectively, and phi is a compensation angle;
wherein the specific algorithm is a coordinate rotation numerical calculation algorithm.
2. The visible light communication system-based compensation method of claim 1, wherein: the modulation is quadrature phase shift keying and quadrature amplitude modulation.
3. A compensation device based on a visible light communication system is characterized in that: the device includes:
the front calculation module is used for calculating the average value of in-phase components and orthogonal components of four areas in a constellation diagram;
the compensation angle calculation module is used for calculating a compensation angle through a specific formula according to the average value of the in-phase component and the orthogonal component;
the post-calculation module is used for calculating the rotated in-phase component and the rotated quadrature component through a specific algorithm;
the compensation module is used for adjusting the compensation times according to the LED nonlinear degree and the modulation order adopted by the system and compensating the error code caused by the nonlinearity;
wherein the specific formula is:
Figure FDA0002441718390000012
E(x1)，E(x2) The energy mean value of the in-phase component in the first and second quadrants, E (y)1)，E(y2) The energy mean values of orthogonal components in a first quadrant and a second quadrant are respectively, and phi is a compensation angle;
wherein the specific algorithm is a coordinate rotation numerical calculation algorithm.
4. The visible light communication system-based compensation apparatus of claim 3, wherein: the modulation is quadrature phase shift keying and quadrature amplitude modulation.
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CN103595688A (en) * 2013-11-04 2014-02-19 复旦大学 Visible light communication multiple access method and system based on carrierless amplitude/phase modulation
CN103888398A (en) * 2008-07-31 2014-06-25 爱立信电话股份有限公司 Optical signal modulation

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CN103888398A (en) * 2008-07-31 2014-06-25 爱立信电话股份有限公司 Optical signal modulation
CN103595688A (en) * 2013-11-04 2014-02-19 复旦大学 Visible light communication multiple access method and system based on carrierless amplitude/phase modulation

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