CN106059983A - OFDM (Orthogonal Frequency Division Multiplexing) signal peak-to-average power ratio suppression method based on asymmetric window functions - Google Patents

Abstract

The invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) signal peak-to-average power ratio suppression method based on asymmetric window functions. The method comprises the following steps: modulating and converting original input signals in sequence to obtain OFDM modulated signals x<n>; calculating peak-to-average power ratios of the x<n>, and selecting signals of which the peak-to-average power ratios are greater than a threshold as peak value reduction signals; determining a right half window length n<r>(m) of an mth peak value reduction signal and a left half window length n<l>(m+1) of an (m+1)th peak value reduction signal by calculating distances between adjacent peak value reduction signals; and performing window function processing on a current peak value reduction signal to obtain a signal x'<n>, replacing signals of which the peak-to-average power ratios are greater than a peak-to-average power ratio threshold A in the x<n> with the signal x'<n>, and transmitting obtained signals. In the method, the peak value reduction signals in transmitted signals are selected; the lengths of the window functions are determined according to the distances between adjacent peak value reduction signals; the signals are reduced; the reduced signals are combined with the signals of which the peak-to-average power ratios are lower than the threshold in the original transmitted signals; and the combined signals are transmitted as new signals. Thus, the peak-to-average power ratios of OFDM transmitted signals are lowered.

Description

Ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function

[technical field]

The invention belongs to wireless communication technology field, be specifically related to ofdm signal peak-to-average ratio based on asymmetric window function and press down Method processed.

[background technology]

OFDM (orthogonal frequency division multiplexing, OFDM) modulation technique There is good ability of anti-multipath, efficient band efficiency, it has also become one of key technology of future broadband wireless communication systems.Mesh Front OFDM modulation technique is widely used to high-definition television (High Definition Television, HDTV), Europe With the Equations of The Second Kind HiperLAN of north America region (High-Performance LAN type 2, HIPERLAN/2), asymmetric DSL (Asymmetric Digital Subscriber Line, ADSL) and 3GPP (The 3rd Generation Partnership Project) standard such as Long Term Evolution (Long Term Evolution, LTE).

But OFDM modulation technique yet suffers from some major issues and is not well solved, wherein in it is applied One crucial technological difficulties is exactly the peak-to-average ratio problem of its signal.It is by multiple sub-carrier signals owing to OFDM sends signal Being formed by stacking, therefore when the phase place of multiple sub-carrier signals is close, produced signal transient power will be far above signal Mean power, thus higher peak-to-average ratio (peak-to-average power ratio, PAPR) occurs.Higher peak-to-average ratio The power amplifier requiring transmitting terminal must have the bigger range of linearity.Bring bigger otherwise will to the signal after amplifying Nonlinear distortion, so that systematic function drastically declines.Therefore, the peak-to-average ratio of ofdm signal how is effectively reduced to improve Efficiency of transmission, is a Major Difficulties in the application of current Wireless OFDM System.

So far, domestic and international researcher has been proposed for the solution of many reduction ofdm signal peak-to-average ratios, including: signal Amplitude limit, companding, Tone reservation, partial transmission sequence and Choose for user etc..But they all because of its intrinsic defect existing Ofdm system in cannot obtain preferable performance.Such as, in signal limiter and companding can produce bigger out-of-band radiation and carry Distortion, therefore cannot obtain good bit error rate performance；Tone reservation is to have reserved a part of subcarrier to be specifically designed to suppression letter Number peak-to-average ratio, therefore reduces channel efficiency；Partial transmission sequence and Choose for user must tie up some subcarriers and send specially The side information of door, thus also have lost efficiency of transmission.

In order to improve signal peak-to-average than rejection ability, the patent application that Xian Electronics Science and Technology University proposes is " based on hyperbolic pressure Extend to the ofdm signal method for inhibiting peak-to-average ratio of associating amplitude limit " (applying date: on 09 19th, 2011, application number: 201110276782.8, publication number: CN 102325118A) with " wireless OFDM signals peak-to-average ratio based on segmentation distribution optimization presses down Method processed " public in (applying date: on 04 23rd, 2012, application number: 201210118320.8, publication number: CN 102664853A) Having opened two kinds of methods utilizing hyperbolic companding to limit signal peak-to-average ratio with sectional companding, the method for these two parts of patent applications can Effectively reduce signal peak-to-average ratio.But, present in they methods, deficiency is: the bit error rate of received signal can be produced by both approaches Raw large effect, and bigger out of band spectrum can be caused to reveal, so that systematic function drastically declines.

[summary of the invention]

It is an object of the invention to overcome above-mentioned the deficiencies in the prior art, propose a kind of OFDM based on asymmetric window function Signal peak-to-average compares suppressing method, it is not necessary to transmitted sideband information, also will not introduce the inside and outside distortion of band, and suppress signal peak-to-average ratio.

In order to achieve the above object, the present invention is by the following technical solutions:

Comprise the following steps:

(1) initialize: set peak-to-average ratio thresholding A, maximum iteration time T, the long L of maximal window_max, Caesar's window parameter beta and work as Front iterations t=1；

(2) original input signal is carried out serial to parallel conversion and quadrature amplitude modulation, obtain quadrature amplitude modulation signal X= [X₀,X₁,...,X_k,...,X_N-1], N represents the subcarrier number of ofdm system；

(3) orthogonal amplitude-modulated signal is carried out OFDM modulation and parallel serial conversion, obtain OFDM modulated signal x_n；

(4) OFDM modulated signal x is calculated_nPeak-to-average ratio, choose peak-to-average ratio more than the signal of peak-to-average ratio thresholding A as peak value Cut down signal, and try to achieve its amplitude a_mWith number M；

(5) by calculating the distance between present peak value reduction signal and next peak value reduction signal, n is determined_r(m) and n_l (m+1) size, wherein n_rM () represents that m-th peak value cuts down the right half-window length of signal, n_l(m+1) the m+1 peak value is represented Cut down the left half-window length of signal；

(6) the window function length L that present peak value reduction signal is processed is determined_m；

(7) present peak value is cut down signal and carry out the abatement operation of window function peak value；

(8) make m=m+1, if m=M, then forward step (9) to；Otherwise return to step (5), continue cycling through；

(9) make t=t+1, if t=T, then loop ends, obtain signal x '_n, forward step (10) to；Otherwise return to step (4), continue cycling through；

(10) by OFDM modulated signal x_nThe middle peak-to-average ratio signal more than peak-to-average ratio thresholding A replaces with step (9) circulation knot The signal x ' that bundle obtains_n, together with x_nIn remaining signal launch together.

Further, in step (3),

Wherein X_kFor quadrature amplitude modulation signal, j is imaginary unit, and J is oversample factor, and 0≤k≤N-1 and k is real Number.

Further, step also includes in (4): initializes peak value simultaneously and cuts down signal traversal parameter m=1, n_l(1)= (L_max-1)/2, wherein n_l(1) represent that first peak value cuts down the left half-window length of signal.

Further, in step (5):

$n_r\left(m\right)=\left\{\begin{array}{cc}\frac{L_{max}-1}{2}& d(m,m+1)\&GreaterEqual;L_{max}\\ \frac{d(m,m+1)}{2}& \frac{L_{max}-1}{2}\&le;d(m,m+1)<L_{max}\\ \frac{a_m}{a_m+a_{m+1}}d(m,m+1)& d(m,m+1)<\frac{L_{max}-1}{2}\end{array}\right.---\left(2\right)$

$n_l(m+1)=\left\{\begin{array}{cc}\frac{L_{\max }-1}{2}& d(m,m+1)\&GreaterEqual;L_{\max }\\ \frac{d(m,m+1)}{2}& \frac{L_{\max }-1}{2}\&le;d(m,m+1)<L_{\max }\\ \frac{a_{m+1}}{a_m+a_{m+1}}d(m,m+1)& d(m,m+1)<\frac{L_{\max }-1}{2}\end{array}\right.---\left(3\right)$

Wherein, d (m, m+1) represents that m-th peak value cuts down signal and the m+1 peak value cuts down the distance between signal.

Further, in step (6), window function length L_m=n_l(m)+n_r(m)+1。

Further, step (7) is specifically carried out according to equation below:

x′_n=c_n·x_n (4)

In formula (4),

Wherein, a_iIt is the amplitude of i-th peak value reduction signal, 1≤i≤M；w_n-iFor window function.

Further, window function is Caesar's window function, Gauss function or Hamming window function, wherein the table of Caesar's window function Reaching formula is:I₀() is 0 rank Bessel function.

Further, the signal in step (10) is launched by antenna after sequentially passing through D/A conversion and radio frequency amplification.

Compared with prior art, the present invention has a following useful technique effect:

The present invention embeds peak signal window function Leveling Block after ofdm system carries out inverse discrete fourier transform, takes Send the signal more than pre-determined threshold of peak-to-average ratio in signal as peak value eliminating tolerancing signal, according between adjacent peak eliminating tolerancing signal away from From determining the length of window function, and by selected window function, this signal is smoothed, and will smooth after signal with original In the number of delivering letters, peak-to-average ratio is incorporated as new ofdm signal in thresholding signal below and is transmitted, thus reduces OFDM transmission letter Number peak-to-average ratio.It also have the advantage that

First, the present invention can obtain good peak-to-average ratio with relatively low computation complexity and improve, and therefore can reduce signal Linearity to power amplifier, thus the work efficiency of effective boost amplifier；

Second, the present invention processes the signal of gained will not produce out-of-band radiation, does not also interfere with ofdm system receiving terminal Bit error rate performance；

3rd, the realization of the present invention normally works unrelated with receiving terminal, so need not extra transmitted sideband information to connecing Receiving end, therefore applies the Wireless OFDM System of the present invention can be directly compatible with existing standard.

4th, compared with additive method, the present invention, without transmitted sideband information, also will not introduce the inside and outside distortion of band, therefore This method disclosure satisfy that the demand of Modern Communication System.And simulation result shows, the present invention can obtain with extremely low ground complexity Good peak-to-average ratio inhibition, the present invention is obtained in that good system receiving terminal bit error rate performance simultaneously.

5th, the present invention is the method for inhibiting peak-to-average ratio of a kind of OFDM modulation wireless signal transmission, can be extensive The signal peak-to-average being applied in all kinds of wideband OFDM wireless communication system is than suppression.

[accompanying drawing explanation]

Fig. 1 be the present invention realize FB(flow block)；

Fig. 2 is the present invention and existing methodical peak-to-average ratio Performance comparision figure；

Fig. 3 is the present invention and existing methodical bit error rate performance comparison diagram.

[detailed description of the invention]

Referring to the drawings 1, the present invention to implement step as follows:

(1) initialize: set peak-to-average ratio thresholding A, maximum iteration time T, the long L of maximal window_max, Caesar's window parameter beta and work as Front iterations t=1；

(2) original input signal is carried out serial to parallel conversion and quadrature amplitude modulation, input data are mapped as orthogonal amplitude Modulated signal X=[X₀,X₁,...,X_k,...,X_N-1], wherein N represents the subcarrier number of ofdm system；

(3) orthogonal amplitude-modulated signal is carried out OFDM modulation and parallel serial conversion, obtain OFDM modulated signal x_n, according to such as Lower formula is carried out:

$x_n=\frac{1}{\sqrt{N}}\underset{n=1}{\overset{N}{\&Sigma;}}{X}_k{e}^{j\frac{2\mathrm{\&pi;}}{JN}nk}---\left(1\right)$

Wherein x_nFor OFDM modulated signal, X_kFor quadrature amplitude modulation signal, j is imaginary unit, and J is oversample factor, 0 ≤ k≤N-1 and k is real number；

(4) signal calculated x_nPeak-to-average ratio PARP, choose PARP more than peak-to-average ratio thresholding A signal as peak value cut down letter Number and try to achieve its amplitude a_mWith number M, initialize peak value simultaneously and cut down signal traversal parameter m=1, n_l(1)=(L_max-1)/2, its Middle n_l(1) represent that first peak value cuts down the left half-window length of signal；

(5) by calculating the distance between present peak value reduction signal and next peak value reduction signal, n is determined_r(m) and n_l (m+1) size, wherein n_r(m) and n_l(m+1) represent that m-th peak value cuts down the right half-window length of signal and the m+1 peak respectively Value cuts down the left half-window length of signal.For avoiding present peak value to cut down right half-window and the left side half for next peak value reduction signal of signal Window is overlapped, is given and is defined below:

$n_r\left(m\right)=\left\{\begin{array}{cc}\frac{L_{max}-1}{2}& d(m,m+1)\&GreaterEqual;L_{max}\\ \frac{d(m,m+1)}{2}& \frac{L_{max}-1}{2}\&le;d(m,m+1)<L_{max}\\ \frac{a_m}{a_m+a_{m+1}}d(m,m+1)& d(m,m+1)<\frac{L_{max}-1}{2}\end{array}\right.---\left(2\right)$

$n_l(m+1)=\left\{\begin{array}{cc}\frac{L_{\max }-1}{2}& d(m,m+1)\&GreaterEqual;L_{\max }\\ \frac{d(m,m+1)}{2}& \frac{L_{\max }-1}{2}\&le;d(m,m+1)<L_{\max }\\ \frac{a_{m+1}}{a_m+a_{m+1}}d(m,m+1)& d(m,m+1)<\frac{L_{\max }-1}{2}\end{array}\right.---\left(3\right)$

Wherein, d (m, m+1) represents that m-th peak value cuts down signal and the m+1 peak value cuts down the distance between signal；False If it is x that m-th peak value cuts down signal_a, it is x that the m+1 peak value cuts down signal_b, then this adjacent peak value cuts down signal x_bWith x_aIt Between distance be b-a.

(6) the window function length L that present peak value reduction signal is processed is determined according to the result in step (5)_m=n_l (m)+n_r(m)+1；

(7) present peak value is cut down signal and carries out the abatement operation of window function peak value, carry out according to equation below:

x′_n=c_n·x_n (4)

In formula,

$c_n=1-\underset{i=-\mathrm{\&infin;}}{\overset{\mathrm{\&infin;}}{\&Sigma;}}{a}_i\&CenterDot;w_{n-i}---\left(5\right)$

A in formula_iIt is the amplitude of i-th peak value reduction signal, 1≤i≤M.And

$w_{n-i}=\frac{I_0\left(\mathrm{\&beta;}\sqrt{1-{(\frac{2(n-i)}{L_m+1}-1)}^2}\right)}{I_0\left(\mathrm{\&beta;}\right)}---\left(6\right)$

I₀() is 0 rank Bessel function, w_n-iFor Caesar's window function, window function here not only can choose Caesar's window letter Number, it is possible to arbitrarily replaced with window function such as Gauss function or the Hamming window function etc. of type by other.

(8) make m=m+1, if m=M, then forward step (9) to；Otherwise return to step (5), continue cycling through；

(9) make t=t+1, if t=T, then loop ends, obtain signal x '_n, forward step (10) to；Otherwise return to step (4), continue cycling through.

(10) by OFDM modulated signal x_nThe middle peak-to-average ratio signal more than peak-to-average ratio thresholding A replaces with step (9) circulation knot The x ' that bundle obtains_n, x_nIn remaining signal constant, sequentially pass through the most together D/A conversion and radio frequency amplify after launched by antenna Go.

The effect of the present invention can be further illustrated by simulations below example.

One, simulated conditions:

In emulation, ofdm system subcarrier number is 256, and modulation system is orthogonal amplitude 64QAM modulation, uncoded system； Channel is additive white Gaussian noise channel.Emulation signal warp after transmitting terminal is by solid-state power amplifier is sent by antenna, Gu The amplitude distortion expression formula of state power amplifier is

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

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

Two, emulation content and result:

Fig. 2 gives the present invention and existing methodical peak-to-average ratio performance curve, and peak-to-average ratio performance is changed by the inventive method Kind effect has bigger lifting, after partial transmission sequence and Choose for user sequence the peak-to-average ratio of signal be 6.5dB with 7.5dB, and this method peak-to-average ratio is only 5dB, inhibition improves 1.5dB and 2.5dB；Fig. 3 gives the mistake of multiple method Code performance curve, compared with additive method, the method error performance that the present invention is carried is better than other algorithms, reaches at error code 10^-3During platform, the present invention is better than partial transmission sequence and Choose for user sequence 1dB and 2dB.

The present invention is by the following step that mainly realizes: (1) carries out quadrature amplitude modulation to incoming bit stream；(2) to orthogonal Modulation and Amplitude Modulation symbol carries out OFDM modulation；(3) take out transmission signal peak-to-average to cut down as peak value than the signal more than pre-determined threshold Signal；(4) by calculating the distance between present peak value eliminating tolerancing signal and next peak value eliminating tolerancing signal, the length of window function is determined Degree；(5) long based on selected window, present peak value eliminating tolerancing signal is carried out window function and processes operation；(5) will meet what peak-to-average ratio limited After output signal sends into D/A converter and radio frequency amplifier, launch via antenna.The present invention can be complicated with relatively low calculating Degree obtains good peak-to-average ratio and improves performance, and the present invention need not extra transmitted sideband information to receiving terminal, therefore applies The Wireless OFDM System of the present invention can be directly compatible with existing standard, and the present invention is strong to the rejection ability of signal peak-to-average ratio, energy Enough effectively reduce the bit error rate.

Claims (8)

1. ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function, it is characterised in that comprise the following steps:

(1) initialize: set peak-to-average ratio thresholding A, maximum iteration time T, the long L of maximal window_max, Caesar's window parameter beta and currently changing Generation number t=1；

(2) original input signal is carried out serial to parallel conversion and quadrature amplitude modulation, obtain quadrature amplitude modulation signal X=[X₀, X₁,...,X_k,...,X_N-1], N represents the subcarrier number of ofdm system；

(3) orthogonal amplitude-modulated signal is carried out OFDM modulation and parallel serial conversion, obtain OFDM modulated signal x_n；

(4) OFDM modulated signal x is calculated_nPeak-to-average ratio, choose peak-to-average ratio more than peak-to-average ratio thresholding A signal as peak value cut down Signal, and try to achieve its amplitude a_mWith number M；

(5) by calculating the distance between present peak value reduction signal and next peak value reduction signal, n is determined_r(m) and n_l(m+1) Size, wherein n_rM () represents that m-th peak value cuts down the right half-window length of signal, n_l(m+1) represent that the m+1 peak value cuts down letter Number left half-window length；

(6) the window function length L that present peak value reduction signal is processed is determined_m；

(7) present peak value is cut down signal and carry out the abatement operation of window function peak value；

(8) make m=m+1, if m=M, then forward step (9) to；Otherwise return to step (5), continue cycling through；

(9) make t=t+1, if t=T, then loop ends, obtain signal x '_n, forward step (10) to；Otherwise return to step (4), continue Continuous circulation；

(10) by OFDM modulated signal x_nThe middle peak-to-average ratio signal more than peak-to-average ratio thresholding A replaces with step (9) loop ends and obtains Signal x '_n, together with x_nIn remaining signal launch together.

Ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function the most according to claim 1, it is characterised in that In step (3),

Wherein X_kFor quadrature amplitude modulation signal, j is imaginary unit, and J is oversample factor, and 0≤k≤N-1 and k is real number.

Ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function the most according to claim 1, it is characterised in that Step also includes in (4): initializes peak value simultaneously and cuts down signal traversal parameter m=1, n_l(1)=(L_max-1)/2, wherein n_l(1) Represent that first peak value cuts down the left half-window length of signal.

Ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function the most according to claim 1, it is characterised in that In step (5):

$n_r\left(m\right)=\left\{\begin{array}{cc}\frac{L_{\max }-1}{2}& d\left(m,m+1\right)\&GreaterEqual;L_{\max }\\ \frac{d\left(m,m+1\right)}{2}& \frac{L_{\max }-1}{2}\&le;d\left(m,m+1\right)<L_{\max }\\ \frac{a_m}{a_m+a_{m+1}}d\left(m,m+1\right)& d\left(m,m+1\right)<\frac{L_{\max }-1}{2}\end{array}\right.---\left(2\right)$

$n_l\left(m+1\right)=\left\{\begin{array}{cc}\frac{L_{\max }-1}{2}& d\left(m,m+1\right)\&GreaterEqual;L_{\max }\\ \frac{d\left(m,m+1\right)}{2}& \frac{L_{\max }-1}{2}\&le;d\left(m,m+1\right)<L_{\max }\\ \frac{a_{m+1}}{a_m+a_{m+1}}d\left(m,m+1\right)& d\left(m,m+1\right)<\frac{L_{\max }-1}{2}\end{array}\right.---\left(3\right)$

Wherein, d (m, m+1) represents that m-th peak value cuts down signal and the m+1 peak value cuts down the distance between signal.

Ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function the most according to claim 1, it is characterised in that In step (6), window function length L_m=n_l(m)+n_r(m)+1。

Ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function the most according to claim 1, it is characterised in that Step is specifically carried out according to equation below in (7):

x′_n=c_n·x_n (4)

In formula (4),

Wherein, a_iIt is the amplitude of i-th peak value reduction signal, 1≤i≤M；w_n-iFor window function.

Ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function the most according to claim 6, it is characterised in that Window function is Caesar's window function, Gauss function or Hamming window function, and wherein the expression formula of Caesar's window function is:

I₀() is 0 rank Bessel function.

Ofdm signal method for inhibiting peak-to-average ratio based on asymmetric window function the most according to claim 1, it is characterised in that Signal in step (10) is launched by antenna after sequentially passing through D/A conversion and radio frequency amplification.