CN106850056A - A kind of method of assessment PAM OFDM visible light communication system signal peak-to-average ratios - Google Patents

Abstract

The invention discloses a kind of method of assessment PAM OFDM visible light communication system signal peak-to-average ratios, the peak-to-average force ratio that the present invention is drawn has high degree of accuracy, the calculated value obtained with the present invention by system emulation is mutually verified, and the calculated value that the present invention is obtained has at a relatively high accuracy when number of sub carrier wave is sufficiently large；The peak-to-average force ratio of signal has the simple easily property calculated after the slicing that the present invention is drawn, the PAM DMT sufficiently large for number of sub carrier wave, only it is to be understood that after modulation on each subcarrier time-domain signal power and the bound of slicing, you can the quick peak-to-average force ratio for drawing signal after slicing, and without actual hardware measurement.

Description

A kind of method of assessment PAM-OFDM visible light communication system signal peak-to-average ratios

Technical field

Wireless light communication technical field of the present invention, especially a kind of assessment PAM-OFDM visible light communication system signal peak-to-average powers The method of ratio.

Background technology

Many advantages, such as LED has long service life, energy-conservation, luminous efficiency high, is widely used in room lighting, not Traditional fluorescent lamp and incandescent lamp etc., the indoor lighting device as main flow can progressively be replaced.Recently research have indicated that, LED devices Part is while illumination, it is also possible to carry out the digital communication of high speed, and LED-based indoor visible light communication system has cost Low, transmission rate is high, good confidentiality the advantages of, therefore, it is considered to be a kind of important indoor wireless communication technology.It is indoor visible Optic communication, with environmental protection, does not have an electromagnetic radiation compared with existing radio communication, the advantage such as frequency spectrum resource is abundant, this Outward, indoor visible light communication is particularly suitable for applications in the occasion that some wireless devices are prohibitted the use of, such as aircraft, hospital.

Different from traditional twireless radio-frequency communication system, intensity modulated is generally used in visible light communication system straight Detection technique is connect, because in visible light communication system, generally uses luminous intensity to carry information, and LED Luminous intensity can only be nonnegative real number, therefore complex signal can not be used as in conventional radio frequency field.Therefore in visible ray The signal to be transmitted in communication system will all experience the process that optical signal is converted into by electric signal, i.e., signal is converted at information source Non-negative electric signal drives LED.In order to solve the problems, such as the intersymbol interference that multipath effect causes, orthogonal frequency division multiplexi is in tradition Furtherd investigate already and widely used in RF communication system, the technology has the advantages that some are unique, for example：Spectrum utilization Rate is high, mitigating frequency-selective fading, anti-ISI, and modulation /demodulation is simple and is easily achieved, and receiving terminal is without complicated balanced The advantages of technology.Just because of this, orthogonal frequency division multiplexi is also widely used in indoor visible light communication system.But no The OFDM technology of the conventional radio frequency communications field is same as, is needed in the visible light communication technology using intensity modulated Direct Inspection Technology Slicing treatment is carried out to signal.A kind of conventional modulation system is PAM-DMT.A big difficult point in OFDM technology is transmission signal The excessive problem of peak-to-average force ratio is still suffered from PAM-DMT, therefore influence tool of the slicing to peak-to-average force ratio is assessed in PAM-DMT technologies It is significant.

The content of the invention

The technical problems to be solved by the invention are, there is provided one kind assessment PAM-OFDM visible light communication system signal peaks Than method, can quickly draw the peak-to-average force ratio of signal after slicing, and without actual hardware measurement.

In order to solve the above technical problems, the present invention provides a kind of assessment PAM-OFDM visible light communication system signal peak-to-average ratios Method, comprise the following steps：

(1) it is the system architecture of the PAM-DMT of N according to sub-carrier number, calculates the time domain of Fast Fourier Transform Inverse output Signal

(2) due to frequency-region signal A_kIt is zero-mean and is independent identically distributed, according to central-limit theorem, works as sub-carrier number When mesh N is enough, the time-domain signal s that will be obtained by Fast Fourier Transform Inverse_nBeing approximately obedience zero-mean variance is's Gaussian Profile, i.e.,

(3) because it has odd symmetry：

Taking it zero passage slicing will not lose any information, and the process for carrying out slicing to time-domain signal is as follows：

(4) standardization processing is carried out to upper slicing degree, obtaining the slicing upper bound is：

(5) it is hereby achieved that the probability density function of signal is after slicing：

(6) mean power that can obtain signal after slicing by probability density function is：

Wherein, c (l, u) is power factor, c (l, u)=(l²-1)Φ(l)-(u²-1)Φ(u)+u²+lg(l)-ug(u).；

(7) when number of sub carrier wave is enough, when frequency domain symbol is that PAM is modulated, same PAM-DMT symbols sub-carriersIt is separate, therefore by the definition of peak-to-average force ratio：

The CCDF that the peak-to-average force ratio of the PAM-DMT symbols after bilateral slicing can be released is：

Wherein, θ_0,U=u²/c(0,u)。

Beneficial effects of the present invention are：The peak-to-average force ratio that is drawn of the present invention has high degree of accuracy, by system emulation with The calculated value that the present invention is obtained mutually is verified, and the calculated value that the present invention is obtained has phase when number of sub carrier wave is sufficiently large When accuracy high；The peak-to-average force ratio of signal has the simple easily property calculated after the slicing that the present invention is drawn, for number of sub carrier wave foot Enough big PAM-DMT, only it is to be understood that after modulation on each subcarrier time-domain signal power and the bound of slicing, you can it is quick Go out the peak-to-average force ratio of signal after slicing, and without actual hardware measurement.

Brief description of the drawings

Fig. 1 is method of the present invention schematic flow sheet.

Fig. 2 is of the invention based on PAM-DMT indoor visible light communication system transmitting terminal schematic diagrames.

Fig. 3 be maximum peak-to-average force ratio in PAM-DMT of the invention after upper slicing with standardization after upper slicing border relation Schematic diagram.

Fig. 4 is the peak-to-average force ratio distribution assessed value that the present invention is calculated under different sub-carrier number of the invention and actual imitative True value schematic diagram.

Fig. 5 is present invention PAM-DMT peak-to-average force ratio distribution curve schematic diagrames in all cases in 1024 subcarrier.

Specific embodiment

As illustrated in fig. 1 and 2, a string of bit streams of high-speed parallel pass through the low rate data streams for going here and there and turning multidiameter delay, then The data flow of parallel low speed is by pulse amplitude modulation (PAM) and adds the symbol after modulating to be the as the imaginary part of signal to be transmitted Signal on k subcarriers is S_k=jA_k, each sub-carrier frequency domain signal of PAM-DMT meets conjugate symmetry, its frequency domain frame knot Structure is：

By after IFFT, time-domain signal s_nCan be expressed as

Noticing the time-domain signal of PAM-DMT has odd symmetry, i.e.,：

Therefore, taking the IFFT output signals of PAM-DMT zero passage slicing will not lose any information.So to PAM- Slicing is all zero passage slicing under the signal of DMT, and upper slicing then depends on the circumstances, and clipping procedure is：

Due to being zero passage slicing, s_clip,nIt has been nonnegative real number, thus without adding direct current biasing again.After having cut ripple Time-domain signal drives LED to send visible optical information by being converted to time domain continuous signal by DAC.

Fig. 3 show maximum distribution of the peak-to-average force ratio on u after slicing.It can be seen that having the PAM-DMT of upper slicing in itself It is the lower slicing that there is zero passage, therefore after its slicing there is maximum in peak-to-average force ratio, and the value of this maximum peak-to-average force ratio is the list of u Increasing function is adjusted, that is, more (u is smaller) cut, the maximum peak-to-average force ratio of residual signal is smaller.

Peak-to-average force ratio distribution assessed value and actual emulation value that Fig. 4 is calculated for this method under different sub-carrier number.Can The distribution of this method is calculated during seeing number of sub carrier wave smaller (128 subcarrier) peak-to-average force ratio and actual emulation out point Cloth slightly has difference, because the approximate condition of central-limit theorem is not enough, there is some difference.And it is enough to work as number of sub carrier wave When many, the system that the peak-to-average force ratio that this method is calculated is distributed the actual emulation that can coincide well.

Fig. 5 is the CCDF curve of the PAM-DMT peak-to-average force ratios in all cases in 1024 subcarrier. As a comparison, not taking the CCDF curves of the signal of slicing under giving the same terms simultaneously.It can be seen that to PAM-DMT signals After carrying out slicing there is a Greatest lower bound value in its peak-to-average force ratio, and maximum peak-to-average ratio slicing degree u upper with standardization is single Adjust what is be incremented by, that is, more (u is smaller) cut, maximum peak-to-average ratio is smaller.And examine and can obtain, with regard to a certain specific peak Than for, slicing extent index u is smaller in its specification, and its CCDF value is bigger, and this just embodies slicing Double action.

Although the present invention is illustrated and has been described with regard to preferred embodiment, it is understood by those skilled in the art that Without departing from scope defined by the claims of the present invention, variations and modifications can be carried out to the present invention.

Claims (1)

1. a kind of method of assessment PAM-OFDM visible light communication system signal peak-to-average ratios, it is characterised in that comprise the following steps：

(1) it is the system architecture of the PAM-DMT of N according to sub-carrier number, calculates the time-domain signal of Fast Fourier Transform Inverse output

$s_n=-\frac{2}{\sqrt{N}}\underset{k=1}{\overset{\frac{N}{2}-1}{\Σ}}{A}_k\sin \frac{2\mathrm{\π}kn}{N};$

(2) due to frequency-region signal A_kIt is zero-mean and is independent identically distributed, according to central-limit theorem, when number of sub carrier wave N foot When more than enough, the time-domain signal s that will be obtained by Fast Fourier Transform Inverse_nBeing approximately obedience zero-mean variance isGauss point Cloth, i.e.,

(3) because it has odd symmetry：

$s_{N-n}=-\frac{2}{\sqrt{N}}\underset{k=1}{\overset{\frac{N}{2}-1}{\Σ}}{A}_{k}sin\frac{2\mathrm{\π}k(N-n)}{N}=-s_n,n=1,...,\frac{N}{2}-1$

Taking it zero passage slicing will not lose any information, and the process for carrying out slicing to time-domain signal is as follows：

$s_{clip,n}=Clip\&lsqb;s_n\&rsqb;=\left\{\begin{array}{cc}{B}_U,& s_n\&GreaterEqual;B_U\\ s_n,& 0<s_n<B_U\\ 0,& s_n\&le;0.\end{array}\right.;$

(4) standardization processing is carried out to upper slicing degree, obtaining the slicing upper bound is：

$u=\frac{B_U}{{\mathrm{\&sigma;}}_s};$

(5) it is hereby achieved that the probability density function of signal is after slicing：

$f_{pam}\left(w\right)=\frac{1}{2}\mathrm{\&delta;}\left(w\right)+\frac{1}{\sqrt{2\mathrm{\&pi;}}{\mathrm{\&sigma;}}_s}{e}^{-\frac{w^2}{2{\mathrm{\&sigma;}}_s^2}}\&lsqb;u\left(w\right)-u(w-B_U)\&rsqb;+\&lsqb;1-\mathrm{\&Phi;}\left(u\right)\&rsqb;\mathrm{\&delta;}(w-B_U);$

(6) mean power that can obtain signal after slicing by probability density function is：

$P_{pam}={\mathrm{\&sigma;}}_s^{2}c(0,u)$

Wherein, c (l, u) is power factor, c (l, u)=(l²-1)Φ(l)-(u²-1)Φ(u)+u²+lg(l)-ug(u).；

(7) when number of sub carrier wave is enough, when frequency domain symbol is that PAM is modulated, same PAM-DMT symbols sub-carriersIt is separate, therefore by the definition of peak-to-average force ratio：

$PAPR=\frac{\underset{0\&le;n\&le;N-1}{max}|s_{clip,n}{|}^2}{E\&lsqb;|s_{clip,n}{|}^2\&rsqb;}$

The CCDF that the peak-to-average force ratio of the PAM-DMT symbols after bilateral slicing can be released is：

$F_{pam}\left(x\right)=P(PAPR>x)=\left\{\begin{array}{cc}1-{\&lsqb;2\mathrm{\&Phi;}\left(\sqrt{c(0,u)x}\right)-1\&rsqb;}^{\frac{N}{2}-1},& 0\&le;x<{\mathrm{\&theta;}}_{0,U}\\ 0,& x\&GreaterEqual;{\mathrm{\&theta;}}_{0,U}\end{array}\right.$

Wherein, θ_0,U=u²/c(0,u)。