CN103916356A - Low-peak-to-average-ratio wireless optical transmission method based on dynamic scalar regulation - Google Patents

Abstract

The invention discloses a low-peak-to-average-ratio wireless optical transmission method based on dynamic scalar regulation. The low-peak-to-average-ratio wireless optical transmission method based on dynamic scalar regulation comprises the steps that different scalar regulation coefficients are selected according to time domain peak values of all OFDM symbols, the symbols with extremely large peak values are compressed to a certain extent, in this way, the PAPR of signals of a whole frame is lowered, and therefore the transmission performance is improved; a user just needs to measure the average power of the received symbols at the receiving end so as to estimate the multiplied regulation coefficient, and the method is easy to realize; requirements of a system for power amplifiers and the degree of linearity of LED lamps are lowered due to the fact that the PAPR is lowered, nonlinear distortion of signals in an electric and optical domain is reduced, and the receiving performance of the system is improved; the direct-current bias needing to be added at the transmitting end is reduced due to the fact that the PAPR is lowered, and power consumption of the system is reduced.

Description

A kind of low peak average ratio wireless optical transmission method regulating based on dynamic scalar

Technical field

The present invention relates to a kind of low peak average ratio wireless optical transmission method regulating based on dynamic scalar, belong to wireless light communication technology.

Background technology

Wireless light communication, due to advantages such as its frequency spectrum resource are abundant, communications security is good, transmitting power is large, electromagnetic radiation is few, had become the focus of communications field research in the last few years.In order to realize the high speed data transfer of wireless light communication, reduce intersymbol interference (ISI), in wireless light communication, introduce OFDM modulation, by the symbol parallel modulating is sent on orthogonal subcarrier, can provide high speed data transfer, antagonism multipath effect.

Normal working strength modulation/direct-detection (IM/DD) in wireless light communication, therefore the time domain after OFDM modulation transmits and need to ensure the positive signal into real-valued.Have at present two kinds of more conventional optical communication OFDM methods, direct current biasing light OFDM(DCO-OFDM) and asymmetric peak clipping light OFDM(ACO-OFDM).ACO-OFDM only transmits modulation symbol in odd subcarriers, and even subcarriers does not send symbol, and the negative part of the time-domain signal obtaining through IFFT is abandoned, and only retains on the occasion of part.Can ensure that like this time-domain signal sending is positive real signal, can reduce again transmitting power, economize on resources, but frequency efficiency be lower, N subcarrier can only send N/4 symbol, and this method has avoided adding the power loss of direct current biasing taking sacrifice data rate as cost.DCO-OFDM is adding direct current biasing on the signal after OFDM modulation, make signal become on the occasion of, this method realizes simple, frequency efficiency is high, but has increased DC power.

Similar with the ofdm system in radio communication, the ofdm system in wireless light communication also exists the too high problem of signal peak-to-average power power ratio.The higher meeting of PAPR proposes very high requirement to the linearity of transmitter terminal power amplifier, in optical OFDM system, PAPR is too high except to power amplifier, also the linearity of LED lamp is proposed to higher requirement, because power amplifier and LED lamp nonlinear characteristic can cause nonlinear distortion, thereby seriously reduce the overall performance of system.Meanwhile, in wireless light communication DCO-OFDM system, high PAPR also can cause the direct current biasing of needs to increase, thereby increases system power consumption.

The method of a variety of reduction ofdm system PAPR is proposed in twireless radio-frequency communication, as amplitude limit, dynamic constellation extension (ACE), coding, partial transmission sequence (PTS), selectivity mapping (SLM), preserved sub-carrier (TR) etc.

Summary of the invention

Goal of the invention: in order to overcome the deficiencies in the prior art, the invention provides a kind of low peak average ratio wireless optical transmission method regulating based on dynamic scalar, it is a kind of method that very simply reduces wireless light communication PAPR that realizes, its time domain peak value according to each OFDM symbol is selected different scalar adjustment factors, thereby the king-sized symbol of peak value is carried out to compression to a certain degree, thereby reduce the PAPR of whole frame signal, thereby improve transmission performance; Also only need to estimate the scalar factor being multiplied by transmitting terminal by the average power of measuring receiving symbol at receiving terminal, realize simple; The improvement of PAPR has reduced the requirement of system to power amplifier and LED lamp linear degree, has reduced the nonlinear distortion of signal in electricity, light territory, has improved system receptivity; The decline of PAPR has also reduced the direct current biasing that transmitting terminal need to increase, and has reduced system power dissipation.

Technical scheme: for achieving the above object, the technical solution used in the present invention is:

The low peak average ratio wireless optical transmission method regulating based on dynamic scalar,

At transmitting terminal, first, system produces bit information flow needs transmitting frequency domain symbol through constellation point mapping modulation; Secondly, frequency-region signal conjugation is mapped on system subcarrier symmetrically, and produces real-valued base band time domain orthogonal frequency division multiplexing (OFDM) by inverse fast Fourier transform (IFFT) and transmit; Then,, according to the time domain peak value of each OFDM symbol, each symbol is multiplied by corresponding scalar adjustment factor; Finally, time domain transmits and adds that direct current biasing rear drive light-emitting diode (LED) launches;

At receiving terminal, first, the light signal receiving is converted into the signal of telecommunication by photodiode, and receiver estimates according to each the OFDM Symbol average power receiving the scalar adjustment factor that signal is multiplied by transmitting terminal; Then, the time domain OFDM symbol receiving is done to fast Fourier transform (FFT) after divided by the adjustment factor estimating and be converted to frequency domain symbol, and remove conjugation symmetric part; Finally, obtain receiving symbol through demodulation.The present invention realizes simply, can effectively reduce the peak-to-average power ratio of wireless light communication ofdm system, reduce system power dissipation, and by reducing the requirement to power amplifier and LED lamp linear degree, reduce the nonlinear distortion of signal in electricity, light territory, thereby improved system receptivity.

Said method specifically comprises the steps:

Transmitting terminal:

(11) at transmitting terminal, the sub-carrier number of setting wireless optical communication ofdm system is N, and every frame transmitted signal has M OFDM symbol; The binary data source that information source produces, through M-ary orthogonal amplitude modulation(PAM) (M-QAM), forms frequency-region signal to be sent m=1,2 ..., M;

(12) be real-valued in order to meet wireless optical signal, OFDM sub-carriers mapping is carried out according to formula below, meets conjugate symmetry: (not causing obscure in the situation that, be simplified illustration, subscript (m) omits)

$X_k=\left\{\begin{array}{cc}0,& k=0,\frac{N}{2}\\ X_k,& k=1,...,\frac{N}{2}\\ X_{N-k}^{*},& k=\frac{N}{2}+1,...,N-1\end{array},-1\right.$

Wherein, () ^*represent to get complex conjugate;

(13) after N point IFFT, to transfer real-valued time domain OFDM signal to as follows for frequency-region signal:

$x_n=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}{X}_k{e}^{j2\mathrm{\πkn}/N}$

Wherein, n=0,1 ..., N-1, is time domain OFDM symbol sebolic addressing;

(14), according to the peak value of each time domain OFDM symbol, in { 1, α }, select suitable adjustment factor, wherein 0< α <1, be the scalar adjustment factor of the OFDM symbol excessive for compression peaks, span 0.5～0.9, generally desirable conventionally have $y_n^{\left(m\right)}=c^{\left(m\right)}{x}_n^{\left(m\right)},$ Wherein adjustment factor meets $c^m=\left\{\begin{array}{cc}1,& \underset{n}{\max }\left\{\right|x_n^{\left(m\right)}\left|\right\}\&le;T\\ \mathrm{\&alpha;},& \underset{n}{\max \left\{\right|x_n^{\left(m\right)}\left|\right\}}>T\end{array}\right.,$ T is positive threshold value, can be according to the different values of the distribution of the peak value that transmits and the characteristic of channel, as for adopting 16-QAM modulation, the optical OFDM system of sub-carrier number N=128, while getting thresholding T=3.1, there is 10% OFDM symbol peaks to exceed thresholding and will be conditioned compression;

(15) signal after adjusting $y^{\left(m\right)}=\left[\begin{array}{ccc}{y}_0^{\left(m\right)}& ...& y_{N-1}^{\left(m\right)}\end{array}\right],$ M=1 ..., M is sent to optical communication transmitter module, adds the transmitting of direct current biasing rear drive LED lamp;

Receiving terminal:

(21) at receiving terminal, light signal is converted to the time domain signal of telecommunication by photodiode, the OFDM symbol receiving by calculating each average power adopt maximum a posteriori (MAP) criterion to estimate the index of modulation of this symbol according to the adjustment factor of estimating, detect and receive signal ? wherein ${\hat{X}}^{\left(m\right)}=\left[\begin{array}{ccc}{\hat{x}}_0^{\left(m\right)}& ...& {\hat{x}}_{N-1}^{\left(m\right)}\end{array}\right]$ For the time domain OFDM that receiving terminal is estimated is launched symbol;

(22) right do to obtain frequency domain reception signal after N point FFT conversion ${\hat{X}}^{\left(m\right)}=\left[\begin{array}{ccc}{\hat{x}}_0^{\left(m\right)}& ...& {\hat{x}}_{N-1}^{\left(m\right)}\end{array}\right],$ Demodulation obtains final receiving symbol.

Beneficial effect: the low peak average ratio wireless optical transmission method regulating based on dynamic scalar provided by the invention, tool has the following advantages: 1, do not need to transmit extra side information, do not waste frequency resource and can effectively reduce system peak-to-average power ratio; 2, be that transmitter or the realization of receiver are all very simple; 3, low PAPR can reduce the requirement of system to power amplifier and LED lamp linear degree, and that reduces transmitter realizes difficulty, and reduces the nonlinear distortion causing due to power amplifier and LED lamp nonlinear characteristic, improves the receptivity of system; 4, low PAPR has also reduced the DC component size that transmitting must add, and has reduced system power dissipation.

Brief description of the drawings

Fig. 1 is the system block diagram of the low peak average ratio wireless optical transmission method regulating based on dynamic scalar that proposes of the present invention;

Fig. 2 is without scalar factor adjusting and the wireless light communication time domain OFDM schematic symbol diagram after regulating;

Fig. 3 is the complementary accumulated probability scatter chart of the PAPR of the present invention and general unadjusted optical communication OFDM.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further described.

Be illustrated in figure 1 a kind of low peak average ratio wireless optical transmission method regulating based on dynamic scalar, carry out as follows: at transmitting terminal, first, system produces bit information flow, and mapping is modulated to the frequency domain symbol that needs transmitting through constellation point; Secondly, frequency-region signal conjugation is mapped on system subcarrier symmetrically, and produces real-valued base band time domain by inverse fast Fourier transform and transmit; Then,, according to the time domain peak value of each OFDM symbol, each symbol is multiplied by corresponding scalar adjustment factor; Finally, time domain transmits and adds that direct current biasing drives light-emitting diode to launch.At receiving terminal, first, the light signal receiving is converted into the signal of telecommunication by photodiode, the scalar adjustment factor being multiplied by transmitting terminal according to each the OFDM Symbol average power estimated signal receiving; Then, the time domain OFDM symbol receiving is done to fast Fourier transform after divided by the adjustment factor estimating and be converted to frequency domain symbol, and remove conjugation symmetric part; Finally, obtain receiving symbol through demodulation.

Said method specific implementation process is as follows:

Transmitting terminal:

(11) at transmitting terminal, the sub-carrier number of setting wireless optical communication ofdm system is N, and every frame transmitted signal has M OFDM symbol; The binary data source that information source produces, through M-ary orthogonal amplitude modulation(PAM) (M-QAM), forms frequency-region signal to be sent m=1,2 ..., M;

(12) be real-valued in order to meet wireless optical signal, OFDM sub-carriers mapping is carried out according to formula below, meets conjugate symmetry: (not causing obscure in the situation that, be simplified illustration, subscript (m) omits)

$X_k=\left\{\begin{array}{cc}0,& k=0,\frac{N}{2}\\ X_k,& k=1,...,\frac{N}{2}\\ X_{N-k}^{*},& k=\frac{N}{2}+1,...,N-1\end{array},-1\right.$

Wherein, () ^*represent to get complex conjugate;

(13) after N point IFFT, to transfer real-valued time domain OFDM signal to as follows for frequency-region signal:

$x_n=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_k{e}^{j2\mathrm{\&pi;kn}/N}$

Wherein, n=0,1 ..., N-1, is time domain OFDM symbol sebolic addressing;

(14), according to the peak value of each time domain OFDM symbol, in { 1, α }, select suitable adjustment factor, wherein 0< α <1, be the scalar adjustment factor of the OFDM symbol excessive for compression peaks, span 0.5～0.9, generally desirable conventionally have $y_n^{\left(m\right)}=c^{\left(m\right)}{x}_n^{\left(m\right)},$ Wherein adjustment factor meets $c^m=\left\{\begin{array}{cc}1,& \underset{n}{\max }\left\{\right|x_n^{\left(m\right)}\left|\right\}\&le;T\\ \mathrm{\&alpha;},& \underset{n}{\max \left\{\right|x_n^{\left(m\right)}\left|\right\}}>T\end{array}\right.,$ T is positive threshold value, can be according to the different values of the distribution of the peak value that transmits and the characteristic of channel, as for adopting 16-QAM modulation, the optical OFDM system of sub-carrier number N=128, while getting thresholding T=3.1, there is 10% OFDM symbol peaks to exceed thresholding and will be conditioned compression;

(15) signal after adjusting $y^{\left(m\right)}=\left[\begin{array}{ccc}{y}_0^{\left(m\right)}& ...& y_{N-1}^{\left(m\right)}\end{array}\right],$ M=1 ..., M is sent to optical communication transmitter module, adds the transmitting of direct current biasing rear drive LED lamp;

Receiving terminal:

(21) at receiving terminal, light signal is converted to the time domain signal of telecommunication by photodiode, the OFDM symbol receiving by calculating each average power adopt maximum a posteriori (MAP) criterion to estimate the index of modulation of this symbol according to the adjustment factor of estimating, detect and receive signal ? wherein ${\hat{X}}^{\left(m\right)}=\left[\begin{array}{ccc}{\hat{x}}_0^{\left(m\right)}& ...& {\hat{x}}_{N-1}^{\left(m\right)}\end{array}\right]$ For the time domain OFDM that receiving terminal is estimated is launched symbol;

(22) right do to obtain frequency domain reception signal after N point FFT conversion ${\hat{X}}^{\left(m\right)}=\left[\begin{array}{ccc}{\hat{x}}_0^{\left(m\right)}& ...& {\hat{x}}_{N-1}^{\left(m\right)}\end{array}\right],$ Demodulation obtains final receiving symbol.

As shown in Figure 2, according to the time domain peak value of each OFDM, each symbol is multiplied by corresponding scalar adjustment factor, be multiplied by adjustment factor α (α <1) for the excessive symbol of peak value, by whole OFDM sign compression, thereby reduce the PAPR of whole frame signal.

Fig. 3 has provided not the complementary integral distribution curve of PAPR of the system through the optical communication ofdm system of coefficient adjustment and after using this method.System all adopts 16-QAM modulation, when sub-carrier number N=128, gets thresholding T=3.1, adjustment factor in the time of sub-carrier number N=1024, get thresholding T=3.8, adjustment factor statistical system PAPR frame by frame, that is:

${\mathrm{PAPR}}_f=\frac{\underset{m,n}{\max }\left\{{\left|y_n^{\left(m\right)}\right|}^2\right\}}{\frac{1}{\mathrm{MN}}\underset{m}{\mathrm{\&Sigma;}}\underset{n}{\mathrm{\&Sigma;}}{\left(y_n^{\left(m\right)}\right)}^2}$

Adopt as can be observed from Figure this method can effectively reduce the PAPR of system, thereby reduce the linearity of transmitting terminal device, reduce the nonlinear distortion of signal in electricity, light territory, improve overall system receptivity.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (2)

1. the low peak average ratio wireless optical transmission method regulating based on dynamic scalar, is characterized in that:

At transmitting terminal, first, system produces bit information flow, and through constellation point, mapping is modulated to the frequency domain symbol that needs transmitting; Secondly, frequency-region signal conjugation is mapped on system subcarrier symmetrically, and produces real-valued base band time domain by inverse fast Fourier transform and transmit; Then,, according to the time domain peak value of each OFDM symbol, each symbol is multiplied by corresponding scalar adjustment factor; Finally, time domain transmits and adds that direct current biasing drives light-emitting diode to launch;

At receiving terminal, first, the light signal receiving is converted into the signal of telecommunication by photodiode, the scalar adjustment factor being multiplied by transmitting terminal according to each the OFDM Symbol average power estimated signal receiving; Then, the time domain OFDM symbol receiving is done to fast Fourier transform after divided by the adjustment factor estimating and be converted to frequency domain symbol, and remove conjugation symmetric part; Finally, obtain receiving symbol through demodulation.

2. the low peak average ratio wireless optical transmission method regulating based on dynamic scalar according to claim 1, is characterized in that: comprise the steps:

Transmitting terminal:

(11) at transmitting terminal, the sub-carrier number of setting wireless optical communication ofdm system is N, and every frame transmitted signal has M OFDM symbol; The binary data source that information source produces, through M-ary orthogonal amplitude modulation(PAM), forms frequency-region signal to be sent m=1,2 ..., M;

(12) OFDM sub-carriers mapping is carried out according to formula below, meets conjugate symmetry:

$X_k=\left\{\begin{array}{cc}0,& k=0,\frac{N}{2}\\ X_k,& k=1,...,\frac{N}{2}\\ X_{N-k}^{*},& k=\frac{N}{2}+1,...,N-1\end{array},-1\right.$

Wherein, () ^*represent to get complex conjugate;

(13) after N point IFFT, to transfer real-valued time domain OFDM signal to as follows for frequency-region signal:

$x_n=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_k{e}^{j2\mathrm{\&pi;kn}/N}$

Wherein, n=0,1 ..., N-1, is time domain OFDM symbol sebolic addressing;

(14) according to the peak value of each time domain OFDM symbol, select suitable adjustment factor in { 1, α }, wherein 0< α <1, is the scalar adjustment factor of the OFDM symbol excessive for compression peaks; Have wherein adjustment factor meets $c^m=\left\{\begin{array}{cc}1,& \underset{n}{\max }\left\{\right|x_n^{\left(m\right)}\left|\right\}\&le;T\\ \mathrm{\&alpha;},& \underset{n}{\max \left\{\right|x_n^{\left(m\right)}\left|\right\}}>T\end{array}\right.,$ T is positive threshold value;

(15) signal after adjusting $y^{\left(m\right)}=\left[\begin{array}{ccc}{y}_0^{\left(m\right)}& ...& y_{N-1}^{\left(m\right)}\end{array}\right],$ M=1 ..., M is sent to optical communication transmitter module, adds the transmitting of direct current biasing rear drive LED lamp;

Receiving terminal:

(21) at receiving terminal, light signal is converted to the time domain signal of telecommunication by photodiode, the OFDM symbol receiving by calculating each average power adopt maximum a posteriori criterion to estimate the index of modulation of this symbol according to the adjustment factor of estimating, detect and receive signal ? wherein ${\hat{X}}^{\left(m\right)}=\left[\begin{array}{ccc}{\hat{x}}_0^{\left(m\right)}& ...& {\hat{x}}_{N-1}^{\left(m\right)}\end{array}\right]$ For the time domain OFDM that receiving terminal is estimated is launched symbol;

(22) right do to obtain frequency domain reception signal after N point FFT conversion ${\hat{X}}^{\left(m\right)}=\left[\begin{array}{ccc}{\hat{x}}_0^{\left(m\right)}& ...& {\hat{x}}_{N-1}^{\left(m\right)}\end{array}\right],$ Demodulation obtains final receiving symbol.