CN101631103A - Method and system for reducing peak value average power rate of orthometric frequency division multiplexing mark - Google Patents

Abstract

The invention discloses a method for reducing a peak value average power ratio of an orthometric frequency division multiplexing mark, comprising the following steps: adopting a standard window function to carry out the window treatment on a part of orthometric frequency division multiplexing OFDM marks obtained after finishing inverse fast Fourier transform IFFT; and adopting a rectangular window function to carry out the window treatment on the other part of the OFDM marks. The invention adopts a frequency domain windowing method at a transmitting end to reduce a peak-to-average ratio of the OFDM mark, improves the window function to reduce the peak-to-average ratio of an OFDM transmitting signal so as to achieve a more ideal frequency domain characteristic, and the power consumption of a transmitter can be greatly reduced. The invention only relates to the change of the transmitter without changing a receiver, thereby being simple to realize and easy to operate and having lower cost.

Description

Reduce the method and system of the peak-to-average power ratio of OFDM symbol

Technical field

The present invention relates to the orthogonal frequency division multiplexi field, relate in particular to a kind of method and system that reduce the peak-to-average power ratio of OFDM symbol.

Background technology

OFDM (Orthogonal Frequency Division Multiplexing,, OFDM) be a kind of multi-carrier transmission technology.OFDM is a kind of transmission technology that has potentiality in military wideband data chain, WLAN (WLAN (wireless local area network)), 4G (the 4th third-generation mobile communication technology), CMMB broadband communication systems such as (China Mobile multimedia broadcasting) in the application of field of wireless transmission more and more widely.OFDM has good anti-arrowband and multipath interference capability, and can change transfer rate and received signal to noise ratio (SNR) thresholding by independent modulation system and the parameter of adjusting subcarrier.Therefore, OFDM can greatly improve the data transmission efficiency and the interference free performance of communication equipment, satisfies transmission of Information demands such as a large amount of speeches, data and image.

OFDM comes modulating data with one group of mutually orthogonal carrier wave, the information of modulating on each subcarrier is separate, for certain subchannel, can regard flat decline as in the decline of the frequency domain selectivity in the entire belt, but when these subcarriers of OFDM superpose on time domain, can cancel out each other or produce very big peak value, be that peak-to-average power is more higher than (PAPR), peak-to-average power is than being called for short: peak-to-average ratio.The signal of too high peak-to-average ratio can cause slicing during by nonlinear amplifier, causes the distortion of serious distortion and signal spectra, thereby causes error code to rise even normally demodulation.Particularly along with the increase of the modulation level number on number of subcarriers and the subcarrier, the too high problem of PAPR can be more serious.

At present, the problem high to peak-to-average ratio proposed some solutions, such as, distorted signals technology, coding techniques and phase optimization technology etc. are arranged on time domain.The windowing method is arranged on frequency domain, but, existing window function can make the amplitude of the beginning and end of each OFDM symbol on the time domain reduce brokenly, and at receiving terminal, need to adopt this two parts decision signal original position of beginning and end of OFDM symbol, therefore, the amplitude of the beginning and end of OFDM symbol reduces brokenly, will influence the judgement of whole burst, reduce the quality of reception.

Summary of the invention

The technical problem to be solved in the present invention provides a kind of method and system that reduce the peak-to-average power ratio of OFDM symbol, realizes reducing peak-to-average ratio, guarantees good frequency domain and the time domain specification of signal, optimizes the signal emission characteristics, improves systematic function.

For solving the problems of the technologies described above, a kind of method that reduces the peak-to-average power ratio of OFDM symbol of the present invention comprises:

Adopt the standard window function to carry out window to a part of finishing the orthogonal frequency division multiplex OFDM symbol that inverse fast Fourier transform IFFI obtains and handle, adopt rectangular window function to carry out window to another part of OFDM symbol and handle.

Further, to carry out the part that window handles be [N to the employing standard window function of OFDM symbol _g, (N _Fft-N _g)], the employing rectangular window function of OFDM symbol carry out part that window handles for [0, N _g] and [(N _Fft-N _g), N _Fft], wherein, N _FftCount N for IFFT or fast Fourier transform FFT _gBe α N _Fft, $0<\mathrm{\&alpha;}\&le;1.$

Further, rectangular window function is α, 0≤t≤N _gAnd N _Fft-N _g≤ t＜N _Fft

Further, the process that adopts the standard window function to carry out the window processing comprises:

In the OFDM symbol, at [N _g, (N _Fft-N _g)] between each road serial signal, according to each self-corresponding window function coefficient of each road serial signal, multiply by corresponding standard window function respectively.

Further, the process that adopts rectangular window function to carry out the window processing comprises:

In the OFDM symbol, [0, N _g] and [(N _Fft-N _g), N _Fft] between each road serial signal, multiply by rectangular window function respectively.

Further, a kind of system that reduces the peak-to-average power ratio of OFDM symbol comprises: window added device, wherein:

Window added device is used for adopting the standard window function to carry out window to a part of finishing the OFDM symbol that IFFI obtains and handles, and adopts rectangular window function to carry out window to another part of OFDM symbol and handles.

Further, the employing standard window function of OFDM symbol is carried out the part that window handles is [N to window added device _g, (N _Fft-N _g)], the employing rectangular window function of OFDM symbol carry out part that window handles for [0, N _g] and [(N _Fft-N _g), N _Fft], wherein, N _FftCount N for IFFT or fast Fourier transform FFT _gBe α N _Fft, $0<\mathrm{\&alpha;}\&le;1..$

Further, the rectangular window function that window added device adopts is α, 0≤t≤N _gAndN _Fft-N _g≤ t＜N _Fft

Further, window added device adopts the standard window function to carry out the process that window handles to comprise:

In the OFDM symbol, at [N _g, (N _Fft-N _g)] between each road serial signal, according to each self-corresponding window function coefficient of each road serial signal, multiply by corresponding standard window function respectively.

Further, window added device adopts rectangular window function to carry out the process that window handles to comprise:

In the OFDM symbol, [0, N _g] and [(N _Fft-N _g), N _Fft] between each road serial signal, multiply by rectangular window function respectively.

In sum, the present invention reduces the peak-to-average ratio of OFDM symbol by adopt the method for frequency domain windowing at transmitting terminal, by window function is improved, the peak-to-average ratio that makes OFDM send signal reduces, and reaches more desirable frequency domain characteristic, and the transmitter power consumption also can significantly reduce, the present invention only relates to the change of transmitter, then do not have any change for receiver, therefore, realize simple, easy operating, cost is lower.

Description of drawings

Fig. 1 is the Organization Chart of system of the present invention;

Fig. 2 is the flow chart of the inventive method;

Fig. 3 is the schematic diagram of window processing procedure of the present invention.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described.

Fig. 1 is the system of Modulation OFDM symbol, through coding, interweave QAM (quadrature amplitude modulation) mapping at the transmitting terminal binary code, pilot tone is inserted, carry out serial/parallel processing then to prepare to carry out IFFT (inverse fast Fourier transform) conversion, the parallel signal to through the IFFT conversion carries out windowing process, be processed into serial signal again, then carry out digital-to-analogue conversion, baseband signal is modulated on the intermediate frequency, secondary modulation is launched to radio frequency again.

Consider that the OFDM symbol is f by frequency interval _SubN subcarrier constitute, promptly channel width B is divided into N equidistant subchannel.Each subcarrier is by complex symbol a _nSeparate modulation, the IFFT of being ordered by N realizes the modulation of orthogonal sub-carriers.The OFDM symbol can be expressed as:

$s\left(t\right)=\frac{1}{\sqrt{N}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{a}_{\mathrm{<figure-callout\; id="2"\; label="n\; e\; j"\; filenames="A2009101615910010H3.png"\; state="\{\{state\}\}">n</figure-callout>}}{e}^j{2\mathrm{\&pi;tn}/T}^{}=h\left(n\right)e^{-\mathrm{j\&phi;}\left(t\right)},0\&le;t\&le;T---\left(1\right)$

The power spectral density of OFDM symbol is:

$s\left(f\right)={(T+T_g)}^2\underset{n}{\mathrm{\&Sigma;}}{s}_a^2\left[\mathrm{\&pi;}(T+T_g)(f-\mathrm{n\&Delta;f})\right]---\left(2\right)$

By (2) formula as can be known, the outer power spectral density of OFDM symbol band descends slow, that is to say that the out-of-band noise power ratio is bigger.In order to make the outer power spectral density of band descend sooner, need adopt windowing (windowing) technology to the OFDM symbol, carry out windowing process.Each OFDM symbol is carried out windowing process, can make the range value at OFDM symbol period edge carry out the transition to zero gradually, window function comprises: rectangular window function, hamming window function, hanning window function and kaiser window function etc., above-mentioned window function all can reach the range value that makes OFDM symbol period edge and carry out the transition to zero purpose gradually.

Rectangular window is used in suggestion in the IEEE 802.11a agreement, but when adopting rectangular window, the frequency spectrum that sends signal is having higher energy on frequency band.At present, using more window function is raised cosine window function (standard window function), and the raised cosine window function can reduce the outer energy of band, and it is defined as follows:

$w\left(t\right)=\left\{\begin{array}{c}0.5+0.5\cos (\mathrm{\&pi;}+\mathrm{t\&pi;}/\left(\mathrm{\&beta;}{T}_s\right)),0\&le;t\&le;\mathrm{\&beta;}{T}_s\\ 1.0,\mathrm{\&beta;}{T}_s\&le;t\&le;T_s\\ 0.5+0.5\cos ((t-T_s)\mathrm{\&pi;}/\left(\mathrm{\&beta;}{T}_s\right)),T_s\&le;t\&le;(1+\mathrm{\&beta;})T_s\end{array}\right.---\left(3\right)$

(3) the standard window function represented of formula can make the OFDM symbol be subjected to a certain degree destruction, so that influences the performance of receiver.

For the adverse effect that reduces to cause receiver, consider [N at an OFDM symbol _g, (N _Fft-N _g)] part adopts the standard window function, [0, N _g] and [(N _Fft-N _g), N _Fft] part adopts rectangular window function.Wherein, N _FftBe counting of IFFT or FFT, N _gBe counting of protection section, the α that counts that elects FFT (fast Fourier transform) or IFFT as doubly, i.e. α N _Fft, $0<\mathrm{\&alpha;}\&le;1.$ Window function after the improvement is defined as follows:

$w_{\mathrm{new}}\left(t\right)=\left\{\begin{array}{cc}w\left(t\right),& N_g<t<N_{\mathrm{fft}}-N_g\\ \mathrm{\&alpha;},& 0\&le;t\&le;N_g\mathrm{and}{N}_{\mathrm{fft}}-N_g\&le;t\&le;N_{\mathrm{fft}}\end{array}\right.---\left(4\right)$

Simulation result shows the window function after the improvement, and promptly formula (4) can reduce out of band spectrum preferably, and plays the effect of level and smooth sign mutation, and since it to symbol [0, N _g] and [N _Fft, N _Fft-N _g] influence of section is identical, therefore, will reduce the adverse effect that may cause receiver performance.

Figure 2 shows that the present invention reduces the method for the peak-to-average ratio of OFDM symbol, comprising:

201: to finishing coding, interweave, the binary signal of QAM mapping, pilot tone insertion and serial/parallel conversion carries out the IFFT conversion;

202: after finishing the IFFT conversion, the window function of employing formula (4) adopts the standard window function to carry out window to the part of OFDM symbol and handles, and adopts rectangular window function to carry out window to another part of OFDM symbol and handles and carry out window and handle;

As shown in Figure 3, carrying out the process that window handles is: to carrying out each the group parallel signal after the IFFT conversion, multiply by the window function of the different coefficients of parallel signal correspondence respectively, comprise the multi-path serial signal in each group parallel signal, the corresponding window function coefficient of each road serial signal can obtain window function according to the window function coefficient, as, the window function coefficient is 1, and then window function is w _New(1).To in the OFDM symbol at [N _g, (N _Fft-N _g)] between each road serial signal, according to the window function coefficient of each road serial signal correspondence, multiply by corresponding standard window function respectively.In the OFDM symbol, [0, N _g] and [(N _Fft-N _g), N _Fft] between each road serial signal, multiply by rectangular window function respectively.

203: the OFDM symbol transition that will finish the window processing is a serial signal, conversion of the line number of going forward side by side mould and intermediate frequency Modulation, and secondary modulation is launched to radio frequency again.

Please referring again to Fig. 1, the system of the peak-to-average power ratio of reduction orthogonal frequency-division multiplex singal of the present invention, comprise: encoder, interleaver, QAM mapper, pilot tone inserter, serial/parallel converter, IFFT transducer, window added device, parallel/serial converter, D/A converter, intermediate frequency modulator and radiofrequency launcher, wherein:

Described window added device is used for adopting the standard window function to carry out window to a part of finishing the OFDM symbol that IFFI obtains and handles, and adopts rectangular window function to carry out window to another part of OFDM symbol and handles.It is [N that the employing standard window function of OFDM symbol is carried out the part that window handles _g, (N _Fft-N _g)], the employing rectangular window function of OFDM symbol carry out part that window handles for [0, N _g] and [(N _Fft-N _g), N _Fft], wherein, N _FftBe counting of IFFT or FFT, described N _gBe α N _Fft, $0<\mathrm{\&alpha;}\&le;1.$ The rectangular window function that window added device adopts is α, 0≤t≤N _gAnd N _Fft-N _g≤ t＜N _FftThe process that window added device adopts the standard window function to carry out the window processing comprises: in the OFDM symbol, at [N _g, (N _Fft-N _g)] between each road serial signal, according to each self-corresponding window function coefficient of each road serial signal, multiply by corresponding standard window function respectively.The process that window added device adopts rectangular window function to carry out the window processing comprises: in the OFDM symbol, [0, N _g] and [(N _Fft-N _g), N _Fft] between each road serial signal, multiply by described rectangular window function respectively.

The function of other parts please refer to relevant references in the system.

The above is the preferred embodiments of the present invention only, is not limited to the present invention, and for a person skilled in the art, the present invention can have various changes and variation.Within the spirit and principles in the present invention all, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (10)

1, a kind of method that reduces the peak-to-average power ratio of OFDM symbol comprises:

Adopt the standard window function to carry out window to a part of finishing the orthogonal frequency division multiplex OFDM symbol that inverse fast Fourier transform IFFI obtains and handle, adopt rectangular window function to carry out window to another part of described OFDM symbol and handle.

2, the method for claim 1 is characterized in that,

The part that the employing standard window function of described OFDM symbol carries out the window processing is [N _g, (N _Fft-N _g)], the employing rectangular window function of described OFDM symbol carry out part that window handles for [0, N _g] and [(N _Fft-N _g), N _Fft], wherein, described N _FftBe counting of IFFT or fast Fourier transform FFT, described N _gBe α N _Fft, 0＜α≤1.

3, method as claimed in claim 2 is characterized in that,

Described rectangular window function is α, 0≤t≤N _gAnd N _Fft-N _g≤ t＜N _Fft

4, method as claimed in claim 3 is characterized in that, the process that described employing standard window function carries out the window processing comprises:

In described OFDM symbol, at [N _g, (N _Fft-N _g)] between each road serial signal, according to each self-corresponding window function coefficient of each road serial signal, multiply by corresponding standard window function respectively.

5, method as claimed in claim 3 is characterized in that, the process that described employing rectangular window function carries out the window processing comprises:

In described OFDM symbol, [0, N _g] and [(N _Fft-N _g), N _Fft] between each road serial signal, multiply by described rectangular window function respectively.

6, a kind of system that reduces the peak-to-average power ratio of OFDM symbol comprises: window added device, wherein:

Described window added device is used for adopting the standard window function to carry out window to a part of finishing the OFDM symbol that IFFI obtains and handles, and adopts rectangular window function to carry out window to another part of described OFDM symbol and handles.

7, system as claimed in claim 6 is characterized in that,

It is [N that described window added device carries out the part that window handles to the employing standard window function of described OFDM symbol _g, (N _Fft-N _g)], the employing rectangular window function of described OFDM symbol carry out part that window handles for [0, N _g] and [(N _Fft-N _g), N _Fft], wherein, described N _FftBe counting of IFFT or fast Fourier transform FFT, described N _gBe α N _Fft, 0＜α≤1.。

8, system as claimed in claim 7 is characterized in that,

The rectangular window function that described window added device adopts is α, 0≤t≤N _gAndN _Fft-N _g≤ t＜N _Fft

9, system as claimed in claim 8 is characterized in that, the process that described window added device adopts the standard window function to carry out the window processing comprises:

In described OFDM symbol, at [N _g, (N _Fft-N _g)] between each road serial signal, according to each self-corresponding window function coefficient of each road serial signal, multiply by corresponding standard window function respectively.

10, system as claimed in claim 8 is characterized in that, the process that described window added device adopts rectangular window function to carry out the window processing comprises:

In described OFDM symbol, [0, N _g] and [(N _Fft-N _g), N _Fft] between each road serial signal, multiply by described rectangular window function respectively.

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