CN103441981A - Method for inhibiting peak-to-average power ratio of OFDM (orthogonal frequency division multiplexing) signals of carrier injection based on cut noise - Google Patents

Abstract

The invention discloses a method for inhibiting the peak-to-average power ratio of wireless OFDM (orthogonal frequency division multiplexing) signals of a carrier injection technology based on cut noise, and mainly aims to solve the problems of high complexity and poor capability of inhibiting the peak-to-average power ratio of signals in the prior art. The method specifically comprises the implementation steps of: (1) performing orthogonal amplitude constellation mapping on input bit streams; (2) performing OFDM modulation on orthogonal amplitude modulation symbols; (3) calculating cut noise projection and acquiring the optimal step size of the cut noise projection according to the size of the original signal peak-to-average power ratio, and then performing carrier injection selection; and (4) transmitting output signals which satisfies peak-to-average power ratio restriction into a D/A (digital/analog) converter and a radio frequency amplifier, and then transmitting out the output signals through an antenna. According to the method, a good peak-to-average power ratio improvement performance can be obtained through relatively low calculation complexity, and no extra sideband information needs to be transmitted to the receiving end, so that a wireless OFDM system using the method can be directly compatible with the existing standard.

Description

Carrier signal injection ofdm signal method for inhibiting peak-to-average ratio based on shearing noise

Technical field

The invention belongs to wireless communication technology field, relate to (the orthogonal frequency division multiplexing of OFDM in the LTE system, OFDM) peak-to-average ratio (the peak-to-average power ratio of modulation wireless signal transmission, PAPR) inhibition method, can be widely used in the ratio of the signal peak-to-average in the wideband OFDM wireless communication system in all kinds of LTE systems and suppress.

Background technology

The modulating in OFDM technology has good ability of anti-multipath, efficient band efficiency, has become one of key technology of future broadband wireless communication systems.The OFDM modulation technique has been widely used in high definition TV (High Definition Television at present, HDTV), the Equations of The Second Kind HiperLAN of Europe and north America region (High-Performance LAN type2, HIPERLAN/2), ADSL (Asymmetric Digital Subscriber Line) (Asymmetric Digital Subscriber Line, ADSL) and the standard such as 3GPP (The3rd Generation Partnership Pfoject) Long Term Evolution (Long Term Evolution, LTE).

Yet the OFDM modulation technique still exists some major issues not to be well solved in its application, and one of them crucial technological difficulties is exactly the high peak-to-average ratio problem of its signal.Therefore because the OFDM transmitted signal is to be formed by stacking by a plurality of sub-carrier signals, when the phase place of a plurality of sub-carrier signals is close, the signal transient power produced will be far above average power signal, thus the higher peak-to-average ratio of appearance.Higher peak-to-average ratio requires the power amplifier of transmitting terminal must have the larger range of linearity.Otherwise bring larger nonlinear distortion will to the signal after amplifying, thereby make systematic function sharply descend.Therefore, how effectively reducing the peak-to-average ratio of ofdm signal to improve efficiency of transmission, is a Major Difficulties in current Wireless OFDM System application.

So far, both at home and abroad the researcher has proposed the solution of many reduction ofdm signal peak-to-average ratios, comprising: signal limiter, companding, carrier wave are reserved, partial transmission sequence and select mapping etc.But they all can't obtain performance preferably because of its intrinsic defect in existing ofdm system.Such as, signal limiter and companding can produce larger out-of-band radiation and inband distortion, therefore can't obtain good bit error rate performance; Carrier wave is reserved is to have reserved a part of subcarrier to be specifically designed to the Inhibitory signal peak-to-average ratio, has therefore reduced channel efficiency; Partial transmission sequence and selection mapping must take some subcarriers and send special side information, thereby have also lost efficiency of transmission.

In order to improve signal peak-to-average than inhibition ability, the patent application that Xian Electronics Science and Technology University proposes " the ofdm signal method for inhibiting peak-to-average ratio based on hyperbolic companding and associating the amplitude limit " (applying date: on 09 19th, 2011, application number: 201110276782.8, publication number: CN102325118A) with " the wireless OFDM signal peak-to-average based on the segmentation distribution optimization is than inhibition method " (applying date: on 04 23rd, 2012, application number: 201210118320.8, publication number: disclose two kinds of methods of utilizing hyperbolic companding and sectional companding restricting signal peak-to-average ratio CN102664853A), the method of these two parts of patent applications can both effectively reduce the signal peak-to-average ratio.But the deficiency existed in their methods is: these two kinds of methods error rate to received signal produce larger impact, and can cause larger out of band spectrum to reveal, thereby make systematic function sharply descend.

Summary of the invention

The object of the invention is to overcome the deficiency of above-mentioned prior art, a kind of carrier signal injection wireless OFDM signal peak-to-average based on shearing noise is proposed than inhibition method, this method does not need transmitted sideband information, also can not produce the inside and outside distortion of band, so this method can meet the demand of Modern Communication System.

Technical scheme of the present invention is: embed the OFDM frequency domain symbol and select module before the inverse discrete fourier transform module of original ofdm system, carry out the carrier signal injection selection by shearing noise, obtain optimum alternative constellation point and using it as new OFDM frequency domain symbol, thereby reduce the peak-to-average ratio of OFDM emission system.The specific implementation step is as follows:

(1) initialization: peak-to-average ratio thresholding A and maximum iteration time T are set;

(2) original input signal is carried out to serial to parallel conversion and quadrature amplitude modulation, will input data-mapping is quadrature amplitude modulation signal X=[X ₀, X ₁..., X _k..., X _n-1], N means the subcarrier number of ofdm system;

(3) the quadrature amplitude-modulated signal is carried out after OFDM modulation and parallel serial conversion calculating the peak-to-average ratio of gained signal, then take out in signal higher than the signal component of peak-to-average ratio thresholding A, shear noise f _n;

(4) will shear noise f _nprojection is in quadrature amplitude modulation signal X _kand carry out the FFT computing and obtain new time-domain signal f ' _n;

(5) try to achieve time-domain signal f ' by minimizing the signal power that exceeds the peak-to-average ratio thresholding _noptimal step size β;

(6) by comparing the relation between primary signal and carrier signal injection signal, try to achieve the position of carrier signal injection signal;

(7) calculate the transmitted signal x ' suppressed through peak-to-average ratio _n;

(8) calculate transmitted signal x ' _npeak-to-average ratio, if be greater than A, return to step 3; Otherwise enter step 9;

(9) x ' step 8 obtained _nprocess D/A converter and radio frequency amplifier are by being gone out by antenna transmission.

The present invention compared with prior art has the following advantages:

The first, the present invention can obtain with lower computation complexity good peak-to-average ratio and improve, and therefore can reduce the linearity of signal to power amplifier, thus the operating efficiency of effective boost amplifier;

The second, the signal that the present invention processes gained can not produce out-of-band radiation, can not affect the bit error rate performance of ofdm system receiving terminal yet;

The 3rd, realization of the present invention and receiving terminal normal operation are irrelevant, so do not need extra transmitted sideband information to receiving terminal, therefore applying Wireless OFDM System of the present invention can be directly compatible with existing standard.

Simulation result shows, the present invention can obtain good peak-to-average ratio inhibition with utmost point lowland complexity, and simultaneously because the present invention can not change the minimum range between each constellation point, so it can not affect the bit error rate performance of system receiving terminal.

The accompanying drawing explanation

Fig. 1 is realization flow block diagram of the present invention;

Fig. 2 is the present invention and existing methodical peak-to-average ratio performance comparison diagram;

Fig. 3 is the present invention and existing methodical complexity performance comparison diagram.

Embodiment

With reference to accompanying drawing 1, specific implementation step of the present invention is as follows:

(1) initialization: peak-to-average ratio thresholding A and algorithm maximum iteration time T are set;

(2) original input signal is carried out to serial to parallel conversion and quadrature amplitude modulation, will input data-mapping is quadrature amplitude modulation signal X=[X ₀, X ₁..., X _k..., X _n-1], wherein, N means the subcarrier number that ofdm system comprises;

(3) after the quadrature amplitude-modulated signal is carried out to OFDM modulation and parallel serial conversion, calculate the peak-to-average ratio of gained signal, and then take out in signal higher than the signal component of peak-to-average ratio thresholding A, shear noise f _n, carry out in accordance with the following steps:

(3a) the quadrature amplitude-modulated signal is carried out to OFDM modulation and parallel serial conversion, carries out according to following formula:

$x_n=\frac{1}{\sqrt{N}}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}{X}_{\mathrm{<figure-callout\; id="2"\; label="k\; e\; j"\; filenames="HDA0000383179650000012.png"\; state="\{\{state\}\}">k</figure-callout>}}{e}^j{\frac{2\mathrm{\&pi;}}{\mathrm{JN}}\mathrm{nk}}^{},0\&le;k\&le;N-1---\left(1\right);$

Wherein j is imaginary unit, and J is oversample factor, and N is the subcarrier number, and n is the symbol following table;

(3b) calculate and take out input signal x _nin higher than the signal component of peak-to-average ratio thresholding A, shear noise f _n, according to following formula, carry out:

$f_n=\left\{\begin{array}{cc}{x}_n-{\mathrm{Ae}}^{\mathrm{j\&phi;}}& \left|x_n\right|>A\\ 0& \left|x_n\right|\&le;A\end{array}\right.---\left(2\right);$

Wherein φ is signal x _nphase place, | x _n| be the mould value of signal;

(4) will shear noise f _nprojection is in original signal X _kand carry out the FFT computing and obtain new time-domain signal f ' _n, carry out in accordance with the following steps:

(4a) will shear noise f _ncarry out the FFT computing and obtain frequency-region signal F _k, according to following formula, carry out:

$F_k=\frac{1}{\sqrt{N}}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}{f}_n{e}^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000383179650000012.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{\mathrm{JN}}\mathrm{nk}}---\left(3\right);$

Wherein 0≤k≤N-1 is real number;

(4b) by frequency-region signal F _kprojection is in X _k, according to following formula, carry out:

$P_k=\frac{\mathrm{Re}\left[F_k{X_k}^{*}\right]}{{\left|X_k\right|}^2}---\left(4\right);$

Re[wherein] for getting the real part operation, * is for getting conjugate operation;

(4c) to frequency-region signal F _kthe P of projection signal _kcarry out the IFFT computing and obtain new time-domain signal f ' _n, according to following formula, carry out:

$f_n^{\&prime;}=\frac{1}{\sqrt{N}}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}{P}_k{X}_{\mathrm{<figure-callout\; id="2"\; label="k\; e\; j"\; filenames="HDA0000383179650000012.png"\; state="\{\{state\}\}">k</figure-callout>}}{e}^j{\frac{2\mathrm{\&pi;}}{\mathrm{JN}}\mathrm{nk}}^{}---\left(5\right);$

(5) by minimizing the transmitted signal x ' that exceeds the peak-to-average ratio thresholding _npower try to achieve time-domain signal f ' _noptimal step size β, according to following formula, carry out:

$\underset{\mathrm{\&beta;}}{\min }\underset{\left|x_n^{\&prime;}\right|>A}{\mathrm{\&Sigma;}}{\left(\right|x_n^{\&prime;}|-A)}^2---\left(6\right);$

Solve this model, can obtain optimal step size:

Wherein * is for getting conjugate operation;

(6) by comparing the relation between primary signal and carrier signal injection signal, try to achieve the position of carrier signal injection signal, carry out according to following formula:

$\begin{array}{c}\mathrm{\&epsiv;}=E\left\{{|x_n-x_n^{\&prime;}|}^2\right\}\\ =\frac{1}{\mathrm{LN}}\underset{n}{\mathrm{\&Sigma;}}{|\frac{1}{\sqrt{N}}\underset{k\&Element;S}{\mathrm{\&Sigma;}}(2X_k-\mathrm{\&beta;}\&CenterDot;P_k{X}_k+{\mathrm{\&Delta;}}_k){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HDA0000383179650000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^j-\frac{1}{\sqrt{N}}\underset{k\&NotElement;S}{\mathrm{\&Sigma;}}\mathrm{\&beta;}\&CenterDot;P_k{X}_{\mathrm{<figure-callout\; id="2"\; label="k\; e\; j"\; filenames="HDA0000383179650000012.png"\; state="\{\{state\}\}">k</figure-callout>}}{e}^j{2\mathrm{\&pi;}(\mathrm{nk}/\mathrm{LN})}^{}|}^2\\ \&le;\frac{1}{N}\left\{\underset{k\&Element;S}{\mathrm{\&Sigma;}}\right[|{2X}_k-{\mathrm{\&beta;P}}_k{X}_k|+\left|{\mathrm{\&Delta;}}_k\right|]+\underset{k\&NotElement;S}{\mathrm{\&Sigma;}}|{\mathrm{\&beta;P}}_k{X}_k\left|\right\}\end{array}---\left(7\right);$

Wherein ε is the difference between primary signal and carrier signal injection signal,

for the equivalent locations of carrier signal injection signal, d is the minimum range between constellation point, and M is order of modulation, and S is the carrier signal injection set;

(7) calculate the transmitted signal x ' suppressed through peak-to-average ratio _n, according to following formula, carry out:

x′ _n＝x _n-βf′ _n (8)；

, for Max{} gets maxima operation, be wherein E[] get equal Value Operations, log ₁₀() is the operation of taking the logarithm;

(8) calculate x ' _npeak-to-average ratio, according to following formula, carry out:

$\mathrm{PAPR}=10\&CenterDot;\mathrm{lo}{g}_{10}\frac{\mathrm{Max}\left\{{\left|x_n^{\&prime;}\right|}^2\right\}}{E\left[{\left|x_n^{\&prime;}\right|}^2\right]}\left(\mathrm{dB}\right),---\left(9\right);$

Wherein Max{} is for getting maxima operation, E[] for getting equal Value Operations, log ₁₀() is the operation of taking the logarithm; If its peak-to-average ratio is greater than A, return to step 3; Otherwise enter step 9;

(9) X ' step 8 obtained _nthrough adding after Cyclic Prefix, D/A conversion and radio frequency amplify, by antenna transmission, gone out successively.

Effect of the present invention can further illustrate by following simulation example.

One, simulated conditions:

The subcarrier number that ofdm system comprises is 256, and modulation system is orthogonal amplitude 16QAM modulation, not coded system; Channel is the position additive white Gaussian noise channel.Simulate signal at transmitting terminal by solid-state power amplifier by being sent by antenna, its amplitude distortion expression formula is

$\mathrm{SSPA}\left(x\right)=\frac{x}{{(1+{\left(\frac{\left|x\right|}{C}\right)}^{2P})}^{\frac{1}{2p}}}---\left(10\right);$

Wherein C=6dB is saturation threshold, and p=3 is power amplifier smoothness parameter.

Two, emulation content and result:

Fig. 2 has provided the present invention and existing methodical peak-to-average ratio performance curve, with partial transmission sequence, with selection sequence of mapping method, compares, and the inventive method has larger lifting to the effect of improving of peak-to-average ratio performance; Fig. 3 has provided the complexity performance curve of several different methods, with additive method, compares, and is reaching under the condition that peak-to-average ratio is 6.5dB, and the method that the present invention carries only needs 24 FFT computings, and other method needs the FFT computing of up to a hundred times.

The above, it is only preferred embodiment of the present invention, not the present invention is done to any pro forma restriction, although the present invention discloses as above with preferred embodiment, yet not in order to limit the present invention, any those skilled in the art, within not breaking away from the technical solution of the present invention scope, when the method that can utilize above-mentioned announcement and technology contents are made a little change or be modified to the equivalent embodiment of equivalent variations, in every case be the content that does not break away from technical solution of the present invention, any simple modification of above embodiment being done according to technical spirit of the present invention, equivalent variations and modification, still belong in the scope of technical solution of the present invention.

Claims (4)

1. the carrier signal injection wireless OFDM signal peak-to-average based on shearing noise, than inhibition method, comprises the steps:

(1) initialization: peak-to-average ratio thresholding A and maximum iteration time T are set;

(2) original input signal is carried out to serial to parallel conversion and quadrature amplitude modulation, will input data-mapping is quadrature amplitude modulation signal X=[X ₀, X ₁..., X _k..., X _n-1], N means the subcarrier number of ofdm system;

(3) the quadrature amplitude-modulated signal is carried out after OFDM modulation and parallel serial conversion calculating the peak-to-average ratio of gained signal, then take out in the gained signal higher than the signal component of peak-to-average ratio thresholding A, shear noise f _n;

(4) will shear noise f _nprojection is in quadrature amplitude modulation signal X _kand carry out the FFT computing and obtain new time-domain signal f ' _n;

(5) try to achieve time-domain signal f ' by minimizing the signal power that exceeds the peak-to-average ratio thresholding _noptimal step size β;

(6) by comparing the relation between primary signal and carrier signal injection signal, try to achieve the position of carrier signal injection signal;

(7) calculate the transmitted signal x ' suppressed through peak-to-average ratio _n;

(8) calculate transmitted signal x ' _npeak-to-average ratio, if be greater than A, return to step 3; Otherwise enter step 9;

(9) the transmitted signal x ' step 8 obtained _nprocess D/A converter and radio frequency amplifier are by being gone out by antenna transmission.

2. the carrier signal injection wireless OFDM signal peak-to-average based on shearing noise according to claim 1, than inhibition method, is characterized in that, in described step 4, by shearing noise f _nprojection is in quadrature amplitude modulation signal X _k, and the gained signal is carried out to the FFT computing obtain new time-domain signal f ' _n.

3. the carrier signal injection wireless OFDM signal peak-to-average based on shearing noise according to claim 1, than inhibition method, is characterized in that, in described step 5, by minimizing the signal power that exceeds the peak-to-average ratio thresholding, optimizes time-domain signal f ' _n, and try to achieve optimal step size β.

4. the carrier signal injection wireless OFDM signal peak-to-average based on shearing noise according to claim 1, than inhibition method, is characterized in that, in described step 6, by comparing the relation between primary signal and carrier signal injection signal, utilizes the time-domain signal f ' of step 5 gained _ntry to achieve the position of carrier signal injection signal.

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