CN101232488B - Communication method capable of reducing peak average power ratio of OFDM system - Google Patents

Abstract

The invention relates to a communication method which can reduce the peak-to-average power ratio of orthogonal frequency division multiplexing communication systems and overcomes the shortcoming of signal distortion caused by signal correction technology and complex process of probability technology. The method includes the following steps: the multi-decimal baseband modulating signal is inverse discrete Fourier transformed after being series-parallel conversed at the transmitter end to get an orthogonal frequency division multiplexing signal which is sent to a forward transformation module; the data is carrier modulated after being four weighted fractal Fourier transformed under the control of parameter Alpha, and then is sent to the channel for transmission after being D/A and up converted; the data is sent to an anti-transformation module for digital carrier coherent demodulation after being down-converted and A/D sampled at the transmitter end, and then go through the tetrachoric weighing fractal Fourier transformation under the control of parameter Alpha to get an orthogonal frequency division multiplexing signal; the carrier demodulation is completed after the signal is forward discrete Fourier transformed.

Description

Can reduce the communication means of ofdm system peak-to-average power ratio

Technical field

The invention belongs to communication technical field, relate to the communication means of the peak-to-average power ratio that can reduce orthogonal FDM communication system.

Background technology

OFDM (OFDM), has obtained people and has paid close attention to widely with its availability of frequency spectrum, good anti-multipath fading characteristic efficiently as the core technology of the 4th third-generation mobile communication.

Ofdm system belongs to multicarrier system, and the peak-to-average power ratio problem is a common problem in the multicarrier system.The amplitude of ofdm signal is relevant with the phase place of each subcarrier, so-called peak-to-average power ratio problem, at a time promptly, each subcarrier in the multicarrier system can produce very big peak value when adding up with identical phase place, thereby requires power amplifier to have the very big range of linearity.Otherwise, when signal peak enters the amplifier nonlinearity zone, will make signal produce distortion, thereby produce Intermodulation Interference and out-of-band radiation between subcarrier, destroy the orthogonality between subcarrier, reduce systematic function.

Time domain sample sequence { the x of the ofdm system of power normalization _nAs follows:

$x\left(n\right)=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}X\left(k\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="S2008100640290E00021.png,S2008100640290E00031.png"\; state="\{\{state\}\}">e</figure-callout>}}^j,n=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,N-1$

Wherein N is a sub-carrier number, X _kRepresent k the modulation symbol on the subcarrier.The modulated process of ofdm system can have inverse discrete Fourier transformer inverse-discrete to realize that demodulating process can be realized by the discrete Fourier direct transform.Peak-to-average power ratio can be defined as:

$\mathrm{PAPR}\left(\mathrm{dB}\right)=10\lg \frac{\underset{n}{\max }\left\{{\left|x_n\right|}^2\right\}}{E\left\{{\left|x_n\right|}^2\right\}}$

The typical method that reduces peak-to-average power ratio (PAPR:Peak-to-Average Power Ratio) influence is to increase the power amplifier linearity zone, but this can increase system cost, reduces power amplification efficient.The effective means of taking at present that reduces the PAPR influence mainly is the PAPR that reduces the signal of input power amplifier by the whole bag of tricks.The existing method that reduces PAPR can roughly be divided into following type: 1. signal correction class technology, also claim amplitude limit class technology, by directly the signal after the modulation being carried out the amplitude limit correction to reduce the amplitude of peak value, comprise limit filtration, peak window and peak value offset, this class technology belongs to nonlinear operation, can cause the distortion of signal; 2. probability class technology, this class technology is not conceived to reduce the maximum of signal amplitude, but reduce the probability that peak value occurs, owing to introduce new component usually, inject the class technology so be also referred to as new component, comprise that selecting mapping (SLM:Selected Mapping), partial transmission sequence (PTS:PartialTransmit Sequence), impact forging (PS:Pulse Shaping), carrier wave to insert (TI:Tone Injection), carrier suppressed or carrier wave reserves (TR:Tone Rejection) and coding class technology, its implementation procedure is loaded down with trivial details; 3. operation rule change class technology comprises wavelet transformation and C conversion (compression expansion).

Summary of the invention

The purpose of this invention is to provide a kind of communication means that can reduce the ofdm system peak-to-average power ratio, to overcome defective and the loaded down with trivial details defective of existing probability class technology implementation procedure that existing signal correction class technology can cause signal distortion.

Method of the present invention realizes by following step: at transmitter terminal, multi-system baseband modulation signal after string and the conversion obtains orthogonal frequency-division multiplex singal through after the inverse discrete Fourier transformer inverse-discrete, this signal is sent to the direct transform module again, the direct transform module is carried out four-item weight score Fourier conversion to data under the control of parameter alpha, then finish the digital carrier modulation, data are sent into the channel transmission again after D/A conversion and up-conversion then; At receiver end, be sent to inverse transform block through the data after down-conversion and the A/D sampling, in inverse transform block, at first carry out digital carrier coherent demodulation, then the four-item weight score Fourier conversion of controlling through parameter-α more afterwards obtains containing the orthogonal frequency-division multiplex singal of carrier wave, then through finishing carrier wave demodulation work after the discrete Fourier direct transform.

Compare with the conventional orthogonal Frequency Division Multiplexing system, the present invention respectively increases a four-item weight score Fourier conversion module after the transmitting terminal inverse discrete Fourier transformer inverse-discrete He before the direct transform of receiving terminal discrete Fourier.At transmitting terminal, after orthogonal frequency-division multiplex singal is the four-item weight score Fourier conversion module of α through parameter, finished the process of inhibition of peak-to-average power ratio; At receiving terminal, can reply former orthogonal frequency-division multiplex singal for the four-item weight score Fourier conversion of-α through parameter.

Method of the present invention is not carried out nonlinear operation to signal, therefore can not cause the distortion of signal.Method of the present invention can be to realizing reducing the purpose of ofdm system PAPR under the condition of occupying volume external spectrum resource not; The complexity and the fourier transform algorithm of its realization are suitable, and it is less to take system hardware resources, are easy to realize; Transmitter is identical with the core cell of receiver, all is the four-item weight score Fourier conversion module, and one of them gets final product only to need the positive and negative conversion of fast Flourier, so multiplexing when being easy to duplex communication; Can select parameter alpha according to actual conditions, realize dynamically adjusting flexibly, can make system works under the condition of best performance.

Description of drawings

Fig. 1 is based on the ofdm communication apparatus structure schematic diagram of four-item weight score Fourier conversion, Fig. 2 is a transmitting terminal direct transform module diagram, Fig. 3 is a receiving terminal inverse transform block structural representation, Fig. 4 is the counter-rotating modular structure schematic diagram of serial process mode, Fig. 5 is the counter-rotating modular structure schematic diagram of parallel processing mode, Fig. 6 is the ofdm system of 512 subcarriers carries out 200 tests under the QPSK modulation system PAPR (peak-to-average power ratio), and Fig. 7 is the ofdm system based on the four-item weight score Fourier conversion of parameter alpha=0.5 of 512 subcarriers carries out 200 tests under the QPSK modulation system PAPR.

Embodiment

Embodiment one: specify present embodiment below in conjunction with Fig. 1.The method of present embodiment realizes by following step: at transmitter terminal, multi-system baseband modulation signal after string and the conversion obtains orthogonal frequency-division multiplex singal through after the inverse discrete Fourier transformer inverse-discrete, this signal is sent to the direct transform module again, the direct transform module is carried out four-item weight score Fourier conversion to data under the control of parameter alpha, then finish the digital carrier modulation, data are sent into the channel transmission again after D/A conversion and up-conversion then; At receiver end, be sent to inverse transform block through the data after down-conversion and the A/D sampling, in inverse transform block, at first carry out digital carrier coherent demodulation, then the four-item weight score Fourier conversion of controlling through parameter-α more afterwards obtains containing the orthogonal frequency-division multiplex singal of carrier wave, then through finishing carrier wave demodulation work after the discrete Fourier direct transform.

The direct transform concrete steps of carrying out in the direct transform module are: one, give the direct transform module through the ofdm signal after the inverse discrete Fourier transformer inverse-discrete, wherein the form of signal is a plural number.Two, direct transform module is carried out conversion to data frame by frame, and frame length is the length of discrete Fourier transform (DFT), chooses 2 integral number power usually, and the user can select flexibly according to actual conditions.Data after the conversion have promptly been finished the inhibition work of PAPR.The core of conversion is that the data sequence is weighted summation, and four sequences that are weighted are followed successively by: the sequence after the sequence after the OFDM data sequence of input, the OFDM data sequence process discrete Fourier transform (DFT), the OFDM data sequence process counter-rotating module, OFDM data sequence are successively through the sequence after discrete Fourier transform (DFT) and the counter-rotating module.User's Dynamic Selection parameter alpha, and by coefficient generation module generation weight coefficient a ₀, a ₁, a ₂, a ₃Be weighted summation to being weighted sequence.Three, the sequence of complex numbers after the weighting is carried out digital carrier modulation back output.

The inverse transformation concrete steps of carrying out in inverse transform block are: the coherent demodulation that the data after, sampling through A/D are at first carried out digital carrier obtains in-phase component and quadrature component, and carrying out the Synchronous Processing of sequence after as the corresponding addition of imaginary part as real part, quadrature component with in-phase component, output sequence is sequence of complex numbers to be transformed synchronously.Two, sequence of complex numbers to be transformed is done the four-item weight score Fourier conversion of parameter for-α, detailed process is identical with the direct transform process.Sequence after the conversion is the ofdm signal to be demodulated that contains carrier wave, can transfer to discrete Fourier direct transform module and carry out carrier wave demodulation work.

The direct transform module of present embodiment and inverse transform block all can be realized by DSP, FPGA or FPGA+DSP.

The direct transform module of present embodiment and inverse transform block can adopt the system configuration of parallel or serial, and wherein parallel organization is more suitable in FPGA, and serial structure is more suitable in DSP; If adopt FPGA+DSP or other hardware structures, then can be according to the suitable Adjustment System structure of actual conditions.

Fractional Fourier transform is a kind of new mathematical tool that time-frequency domain is effectively integrated, and four-item weight score Fourier conversion is again the mathematic(al) manipulation method that is different from a kind of renewal of classical fractional Fourier transformation.

Four-item weight score Fourier conversion is defined as:

F ^α[f](t)＝a ₀(α)f(t)+a ₁(α)F(t)+a ₂(α)f(-t)+a ₃(α)F(-t)

A wherein ₀～a ₃Be the weight coefficient by parameter alpha control, the form of embodying is:

$a_l\left(\mathrm{\&alpha;}\right)=\cos \left(\frac{(\mathrm{\&alpha;}-l)\mathrm{\&pi;}}{4}\right)\cos \left(\frac{2(\mathrm{\&alpha;}-l)\mathrm{\&pi;}}{4}\right)\exp \left(\frac{3(\mathrm{\&alpha;}-l)\mathrm{\&pi;i}}{4}\right),(l=\mathrm{0,1,2,3})$

The value cycle of parameter alpha is 4, and the span of setting α here is any real number between [0,4] or [2,2], for the real number outside the span, and weight coefficient a _l(l=0,1,2,3) will present cyclic variation along with α.The result of four-item weight score Fourier conversion is f (t) when α=0; The result of four-item weight score Fourier conversion is F (t) when α=1, is the result of f (t) through 1 Fourier transform or 3 inverse fourier transforms; The result of four-item weight score Fourier conversion is that (t), be the result of f (t) through 2 Fourier transforms or 2 inverse fourier transforms, be the counter-rotating function at center with the initial point for f (t) to f when α=2; The result of four-item weight score Fourier conversion is that (t), be the result of f (t) through 3 Fourier transforms or 1 inverse fourier transform, be the counter-rotating function at center with the initial point for F (t) to F when α=3.Wherein Fourier transform adopts following definition:

$X\left(\mathrm{\&omega;}\right)=\frac{1}{\sqrt{2\mathrm{\&pi;}}}\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}x\left(t\right)e^{-\mathrm{j\&omega;t}}\mathrm{dt},-\&infin;<\mathrm{\&omega;}<\&infin;$

Inverse fourier transform adopts following definition:

$x\left(t\right)=\frac{1}{\sqrt{2\mathrm{\&pi;}}}\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}X\left(\mathrm{\&omega;}\right)e^{\mathrm{j\&omega;t}}\mathrm{dt},-\&infin;<t<\&infin;$

For digital system, can adopt the fast algorithm (FFT) of discrete Fourier transform (DFT) to realize Fourier transform.

Following definition is adopted in the discrete Fourier direct transform:

$X\left(k\right)=\frac{1}{\sqrt{N}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}x\left(n\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="S2008100640290E00021.png,S2008100640290E00031.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\mathrm{kn}},k=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,N-1$

Inverse discrete Fourier transformer inverse-discrete adopts following definition:

$x\left(n\right)=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}X\left(k\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="S2008100640290E00021.png,S2008100640290E00031.png"\; state="\{\{state\}\}">e</figure-callout>}}^j,n=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,N-1$

If sequence S (n) carries out the result that parameter is the four-item weight score Fourier conversion of α for sequence x (n), then sequence S (n) is carried out parameter and can obtain sequence x (n) for the four-item weight score Fourier conversion of-α.Be of the choose embodiment of the invertibity of four-item weight score Fourier conversion by parameter alpha, and with conversion process in choose the Fourier direct transform or inverse transformation does not have positive connection, only need satisfy positive inverse transformation and take identical Fourier transform form to get final product (be all direct transform or be all inverse transformation).

The following describes the basic principle that the ofdm system that adopts four-item weight score Fourier conversion can reduce the PAPR of system.If M, N, P and Q are the integer greater than 1, wherein M＞N, P＞Q, and satisfy

$\frac{M}{N}>\frac{P}{Q}>1\&DoubleRightArrow;\mathrm{MQ}-\mathrm{NP}>0$

The PAPR that carries out the information before the OFDM modulation in the real system is less than the PAPR after the modulation usually, so can establish the PAPR of the preceding ofdm signal of modulation is:

The PAPR of the ofdm signal after the modulation can be expressed as

Then adopt the PAPR of the ofdm system modulation back signal of four-item weight score Fourier conversion approximate representation to be: ${\mathrm{PAPR}}_{\mathrm{FrFT}}\&ap;\frac{M+P}{N+Q}>1,$ α is not an odd number

Be PAPR _FrFT＜PAPR _{Behind the OFDM}, α is not an odd number

Because the result of four-item weight score Fourier conversion is relevant with parameter alpha, so also relevant with parameter alpha through the PAPR of signal behind the four-item weight score Fourier conversion:

For the QPSK signal, the ofdm system of 512 subcarriers, the employing parameter is that the four-item weight score Fourier conversion of α=0.5 is handled, PAPR on average can reduce 0.76dB, can reduce more than the 5dB the most for a long time.

Embodiment two: specify present embodiment below in conjunction with Fig. 2.The difference of present embodiment and execution mode one is: the direct transform module comprises counter-rotating module 2 No. one, Fourier transform module 3, coefficient generation module 4, No. two counter-rotating modules 5, parallel serial conversion module 7, summation module or adder 6 and digital carrier modulation module 8, orthogonal frequency-division multiplex singal is transported to the input of a counter-rotating module 2 respectively, an input of the input of Fourier transform module 3 and coefficient generation module 4, another input of the output coefficient of connection generation module 4 of a counter-rotating module 2, the input of another input of the output coefficient of connection generation module 4 of Fourier transform module 3 and No. two counter-rotating modules 5, another input of the output coefficient of connection generation module 4 of No. two counter-rotating modules 5, parameter alpha are input in the coefficient generation module 4 to produce weight coefficient a ₀, a ₁, a ₂, a ₃Four outputs of coefficient generation module 4 connect an input of summation module or adder 6 respectively, the output of summation module or adder 6 connects the input of digital carrier modulation module 8, the output of digital carrier modulation module 8 connects the input of parallel serial conversion module 7, and parallel serial conversion module 7 is finished serial data stream output.

The direct transform module is used for producing the fractional Fourier transform signal based on four-item weight, and wherein Fourier transform module 3 is used the fast algorithm implementation of discrete Fourier transform (DFT).Wherein discrete Fourier transform (DFT) adopts as gives a definition:

$X\left(k\right)=\frac{1}{\sqrt{N}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}x\left(n\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="S2008100640290E00021.png,S2008100640290E00031.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\mathrm{kn}}$

Inverse transform block is compared with the direct transform module, has replaced the central digital carrier modulation module of direct transform module with digital carrier coherent demodulation module, and has increased the sequence synchronization module in order to carry out the synchronous of information sequence, and all the other modules are all identical.As Fig. 3.

A counter-rotating module 2 and No. two counter-rotating modules 5 are used for realizing handling the time reversal of list entries.Detailed process is: first element position of list entries is constant, other elements according to from back to front order rearrange the back as output sequence second to last element.As Fig. 4 and Fig. 5.

The base band data of input direct transform module can be digital modulation signals such as MPSK or MQAM.Baseband modulation/demodulation module can with just/inverse transform block is integrated in simultaneously in a DSP or the fpga chip and realizes.

Embodiment three: specify present embodiment below in conjunction with Fig. 3.The difference of present embodiment and execution mode one is: inverse transform block comprises string and modular converter 1, digital carrier coherent demodulation module 18, a counter-rotating module 2, Fourier transform module 3, coefficient generation module 4, No. two counter-rotating modules 5, sequence synchronization module 11 and summation module or adder 6, serial data stream is input to the input of string and modular converter 1, the output of string and modular converter 1 connects the input of digital carrier coherent demodulating module 18, the input of the output catenation sequence synchronization module 11 of digital carrier coherent demodulation module 18, the output of sequence synchronization module 11 connects the input of Fourier transform module 3, the input of a counter-rotating module 2 and an input of coefficient generation module 4, another input of the output coefficient of connection generation module 4 of a counter-rotating module 2, the input of another input of the output coefficient of connection generation module 4 of Fourier transform module 3 and No. two counter-rotating modules 5, another input of the output coefficient of connection generation module 4 of No. two counter-rotating modules 5, parameter-α are input in the coefficient generation module 4 to produce weight coefficient a ₀, a ₁, a ₂, a ₃, four outputs of coefficient generation module 4 connect the input of summation module or adder 6 respectively, and the output of summation module or adder 6 connects the input of parallel serial conversion module 7, and the output of parallel serial conversion module 7 is finished serial data stream output.

Claims (5)

1. can reduce the communication means of ofdm system peak-to-average power ratio, it is characterized in that it realizes by following step: at transmitter terminal, multi-system baseband modulation signal after string and the conversion obtains orthogonal frequency-division multiplex singal through after the inverse discrete Fourier transformer inverse-discrete, this signal is sent to the direct transform module again, the direct transform module is carried out four-item weight score Fourier conversion to data under the control of parameter alpha, then finish the digital carrier modulation, data are sent into the channel transmission again after D/A conversion and up-conversion then; At receiver end, be sent to inverse transform block through the data after down-conversion and the A/D sampling, in inverse transform block, at first carry out digital carrier coherent demodulation, then the four-item weight score Fourier conversion of controlling through parameter-α more afterwards obtains containing the orthogonal frequency-division multiplex singal of carrier wave, then through finishing carrier wave demodulation work after the discrete Fourier direct transform.

2. the communication means that can reduce the ofdm system peak-to-average power ratio according to claim 1, it is characterized in that the direct transform concrete steps of carrying out in the direct transform module are: one, give the direct transform module through the ofdm signal after the inverse discrete Fourier transformer inverse-discrete, wherein the form of signal is a plural number; Two, direct transform module is carried out conversion to data frame by frame, and frame length is the length of discrete Fourier transform (DFT), and the core of conversion promptly is weighted summation to the data sequence; Four sequences that are weighted are followed successively by: the sequence after the sequence after the OFDM data sequence of input, the OFDM data sequence process discrete Fourier transform (DFT), the OFDM data sequence process counter-rotating module, OFDM data sequence are successively through the sequence after discrete Fourier transform (DFT) and the counter-rotating module; User's Dynamic Selection parameter alpha, and by coefficient generation module generation weight coefficient a ₀, a ₁, a ₂Or a ₃Be weighted summation to being weighted sequence; Three, the sequence of complex numbers after the weighting is carried out digital carrier modulation back output.

3. the communication means that can reduce the ofdm system peak-to-average power ratio according to claim 1, it is characterized in that the inverse transformation concrete steps of carrying out in inverse transform block are: the coherent demodulation that the data after, sampling through A/D are at first carried out digital carrier obtains in-phase component and quadrature component, and carrying out the Synchronous Processing of sequence after as the corresponding addition of imaginary part as real part, quadrature component with in-phase component, gained is a sequence of complex numbers to be transformed; Two, sequence of complex numbers to be transformed is done the four-item weight score Fourier conversion of parameter for-α, the sequence after the conversion is the ofdm signal to be demodulated that contains carrier wave, transfers to discrete Fourier direct transform module and carries out carrier wave demodulation work.

4. the communication means that can reduce the ofdm system peak-to-average power ratio according to claim 1, it is characterized in that the direct transform module comprises counter-rotating module (2) No. one, Fourier transform module (3), coefficient generation module (4), No. two counter-rotating modules (5), parallel serial conversion module (7), summation module or adder (6) and digital carrier modulation module (8), orthogonal frequency-division multiplex singal is transported to the input of a counter-rotating module (2) respectively, an input of the input of Fourier transform module (3) and coefficient generation module (4), another input of the output coefficient of connection generation module (4) of a counter-rotating module (2), the input of another input of the output coefficient of connection generation module (4) of Fourier transform module (3) and No. two counter-rotating modules (5), another input of the output coefficient of connection generation module (4) of No. two counter-rotating modules (5), parameter alpha are input in the coefficient generation module (4) to produce weight coefficient a ₀, a ₁, a ₂Or a ₃Four outputs of coefficient generation module (4) connect an input of summation module or adder (6) respectively, the output of summation module or adder (6) connects the input of digital carrier modulation module (8), the output of digital carrier modulation module (8) connects the input of parallel serial conversion module (7), and parallel serial conversion module (7) is finished serial data stream output.

5. the communication means that can reduce the ofdm system peak-to-average power ratio according to claim 1, it is characterized in that inverse transform block comprises string and modular converter (1), digital carrier coherent demodulation module (18), a counter-rotating module (2), Fourier transform module (3), coefficient generation module (4), No. two counter-rotating modules (5), sequence synchronization module (11) and summation module or adder (6), serial data stream is input to the input of string and modular converter (1), the output of string and modular converter (1) connects the input of digital carrier coherent demodulating module (18), the input of the output catenation sequence synchronization module (11) of digital carrier coherent demodulation module (18), the output of sequence synchronization module (11) connects the input of Fourier transform module (3), the input of a counter-rotating module (2) and an input of coefficient generation module (4), another input of the output coefficient of connection generation module (4) of a counter-rotating module (2), the input of another input of the output coefficient of connection generation module (4) of Fourier transform module (3) and No. two counter-rotating modules (5), another input of the output coefficient of connection generation module (4) of No. two counter-rotating modules (5), parameter-α are input in the coefficient generation module (4) to produce weight coefficient a ₀, a ₁, a ₂Or a ₃Four outputs of coefficient generation module (4) connect the input of summation module or adder (6) respectively, the output of summation module or adder (6) connects the input of parallel serial conversion module (7), and the output of parallel serial conversion module (7) is finished serial data stream output.

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