CN102244636A - Partial transmit sequence method - Google Patents

Abstract

The invention belongs to the field of mobile communication systems, and discloses a partial transmit sequence method, which aims to solve the problem of relatively higher complexity of a conventional random partial transmit sequence. In the method provided by the invention, phase factor sequences are sequenced from low correlation to high correlation, and alternative signals with relatively lower peak-to-average power ratios are searched only by the searching of a part of first alternative signals with relatively lower correlation rather than conventional random partial transmit sequence (PTS) traversing searching, so that optimal signal searching times is reduced and performance approximate to that of the conventional PTS can be achieved by operations with relatively lower complexity; moreover, the correlation of each alternative signal of an interleaved PTS is determined only by phase factors and independent from specific signal data, so that the sequencing can be stored only by once computation without increasing of system complexity.

Description

A kind of partial transmission sequence method

Technical field

The invention belongs to the mobile communication system field, be specifically related to a kind of partial transmission sequence method.

Background technology

OFDM (OFDM, Orthogonal Frequency Division Multiple) technology declines and interference free performance with its very high availability of frequency spectrum, good anti-multipath, becomes new generation of wireless communication core technology.One of major defect of ofdm system is that the ratio (PAPR, Peak-to-average Power Ratio) of signal peak power and average power is higher.Here PAPR is formulated as: Wherein, x _nThe output signal of expression through obtaining after the IFFT computing, max{} represents maximum, E{} represents mean value.And when high peak valve signal enters the power amplifier saturation region of system's transmitting terminal, can produce very big inband distortion and out-of-band radiation, cause the interference of distorted signals and adjacent band to cause system performance degradation.For undistorted transmission OFDM signal, require the very big range of linearity that has of transmitting terminal, the cost that this has just improved system design has limited the OFDM broad application.

Partial transmission sequence (PTS, Partial Transmit Sequence) then is a kind of common method that reduces the PAPR of ofdm signal, it represents that by a plurality of sequences same group of transmission of Information is to reduce the probability that high-power signal occurs, its method is described specifically can list of references: Muller.S.H., Huber.J.B, A novel peak power reduction scheme forOFDM.The 8th IEEE International Symposium on Personal, Indoor and Mobile RadioCommunications, 1997,1090-1094.Be specially: N subcarrier is divided into the V group by certain packet mode, and every group is carried out the IFFT computing respectively and obtains x _v=IFFT{X _V, be multiplied by different phase factor b again _v, the signal of respectively organizing after will multiplying each other then superposes, by selecting different phase factor { b _v, v=1,2 ..., the V} combination obtains a plurality of alternative signal At last therefrom select the signal of PAPR minimum to transmit.Here phase factor b _vAbsolute value is 1 complex factor,

φ _v∈ [0,2 π], theoretically, b _vPhase _vGenerally choose in P phase factor value, be without loss of generality, the phase factor of fixing first grouping usually is 1, then the alternative signal number U=P of PTS generation ^V-1Common phase factor b _vFrom+1 ,-1 ,+j ,-j} or+1, choose among-the 1}, expression is to the rotation of the phase place of signal.Concrete operation principle as shown in Figure 1, idiographic flow is as shown in Figure 2.

But its shortcoming is the complexity of algorithm and is exponential increasing along with the increase of grouping number and phase rotation coefficient number.This is for ofdm system, and computation complexity is higher, and system burden is bigger.

Summary of the invention

The objective of the invention is to have proposed a kind of partial transmission sequence method in order to solve existing P TS method complexity problem of higher.

Technical scheme of the present invention is: a kind of partial transmission sequence method comprises the steps:

Step 1. is divided into the individual subvector of V (V 〉=2) with the N point frequency domain data vector X that desire in the block of sub-carriers sends, and each subvector has N data, and wherein, N/V data are identical with the data of relevant position among the X, and other data are zero, and satisfy

X _V(v=0 ..., V-1) subvector for cutting apart;

Step 2. is carried out the IFFT computing to each subvector;

(u, size i) is according to deterministic for the cross-correlation function variable variance Δ of any two-way alternative signal of step 3. basis

All U road pairing phase factor sequence of alternative signal are carried out correlation ordering from low to high, the judgment condition when wherein the argmin{} representative function is obtained minimum value, U=P ^V-1, P is the phase factor number, all phase factors of at first setting the 1 tunnel phase factor sequence are all identical; From remaining U-1 road phase factor sequence, select then to make with the minimum Ω (2) of the 1 tunnel phase factor sequence correlation as the 2nd optimum angle sequence; From remaining U-k (k=2 ..., U-1) choose in the phase factor sequence of road make with the minimum Ω (k+1) of preceding k road phase factor sequence average correlation be k+1 road optimum angle factor sequence; Obtain correlation phase factor sequence from low to high at last;

The correlation phase factor sequence from low to high that step 4. utilizes step 3 to obtain produces correlation U road alternative signal from low to high successively;

L lower alternative signal of front correlation calculated its PAPR value respectively in the U road alternative signal that step 5. selection step 4 produces, and therefrom selects the minimum alternative signal of PAPR and exports as optimum alternative signal.

Beneficial effect of the present invention: method of the present invention is by sorting phase factor sequence from low to high according to correlation, when seeking the lower alternative signal of PAPR, only need to search the lower a part of alternative signal of front correlation, and the traversal search of non-traditional PTS at random, reduced the Optimal Signals searching times, so just can reach the performance close by lower complexity computing with conventional P TS; And the correlation of each alternative signal of PTS that interweaves is irrelevant with concrete signal data only by the phase factor decision, and therefore ordering only needs once to calculate to store to get final product, and does not improve system complexity.

Description of drawings

Fig. 1 is the transmitter fundamental diagram of PTS.

Fig. 2 searches for the schematic flow sheet of optimum alternative signal with traditional PTS method at random.

Fig. 3 is the fundamental diagram of PTS, the PTS that interweaves at random.

Fig. 4 is the schematic flow sheet with the inventive method.

Embodiment

Below in conjunction with accompanying drawing, provide specific embodiments of the invention.Need to prove: the parameter among the embodiment does not influence generality of the present invention.

For the ease of the understanding of the present invention, before setting forth specific embodiment, at first introduce wherein used term:

PTS at random: each subcarrier is randomized to either in V the PTS, and concrete operation principle as shown in Figure 3.

PTS interweaves: the subcarrier allocation that is V to separation is within a PTS, and concrete operation principle as shown in Figure 3.

Alternative signal correlation analysis: establish x ^uAnd x ⁱBe interweave u road and i road alternative signal among the PTS,

Represent in the alternative signal of u road on k the subcarrier the phase factor of corresponding grouping, wherein When k subcarrier v the grouping in, N is a sub-carrier number.Therefore arbitrarily the two-way alternative signal (be designated as u, i) at any time point (be designated as m, n) cross-correlation function between is defined as:

$R_{u,i}(m,n)=E\left[x^u\left(m\right)x^{i*}\left(n\right)\right]$

$=\frac{1}{N}E\left(\right[\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}{b}_k^u{X}_u\exp \left(j\frac{2\mathrm{\πkm}}{N}\right)\left]\right)\left({\left[\underset{y=0}{\overset{N-1}{\mathrm{\Σ}}}{b}_y^i{X}_i\exp \left(j\frac{2\mathrm{\πyn}}{N}\right)\right]}^{*}\right)$

$=\frac{1}{N}E\left[\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}\underset{y=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{b}_k^u{b}_y^{i*}{X}_u{X_i}^{*}\exp \left(j\frac{2\mathrm{\&pi;}(\mathrm{km}-\mathrm{yn})}{N}\right)\right],0\&le;m,n<N$

The system input data of setting up departments X _nBe that average power is 1 independent identically distributed stochastic variable, definition τ=m-n, following formula can be reduced to:

$R_{u,i}\left(\mathrm{\&tau;}\right)=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{b}_k^u{b}_y^{i*}\exp \left(j\frac{2\mathrm{\&pi;k\&tau;}}{N}\right),-N<\mathrm{\&tau;}<N$

Because R _{U, i}(τ) about the τ symmetry, be positive part so only need to analyze the τ value, therefore:

$R_{u,i}\left(\mathrm{\&tau;}\right)=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{b}_k^u{b}_y^{i*}\exp \left(j\frac{2\mathrm{\&pi;k\&tau;}}{N}\right)=\mathrm{IFFT}\left\{b_k^u{b}_y^{i*}\right\},0\&le;\mathrm{\&tau;}<N$

Definition cross-correlation function variable

The variance Δ (u, i):

$\mathrm{\&Delta;}(u,i)=\frac{1}{N}\underset{\mathrm{\&tau;}=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{({\left|R_{u,i}\left(\mathrm{\&tau;}\right)\right|}^2-\mathrm{\&eta;}(u,i))}^2$

Wherein,

For

Average.Cross-correlation function stochastic variable in all alternative signal

The arithmetic mean of variance is low more, and the degree of correlation between each alternative signal is just low more, and it is just good more that the PAPR of system suppresses effect, simultaneously also as can be seen the correlation of each alternative signal only by the phase factor decision, irrelevant with concrete signal data.

Method flow schematic diagram of the present invention as shown in Figure 4, concrete steps are as follows:

Step 1. is divided into the individual subvector of V (V 〉=2) with the N point frequency domain data vector X that desire in the block of sub-carriers sends, and each subvector has N data, and wherein, N/V data are identical with the data of relevant position among the X, and other data are zero, and satisfy

X _V(v=0 ..., V-1) subvector for cutting apart;

Step 2. is carried out the IFFT computing to each subvector;

(u, size i) is according to deterministic for the cross-correlation function variable variance Δ of any two-way alternative signal of step 3. basis

All U road pairing phase factor sequence of alternative signal are carried out correlation ordering from low to high, judgment condition when wherein the argmin{} representative function is obtained minimum value, when being sequencing selection k road phase factor sequence, calculate u (the average cross correlation value of road phase factor sequence of k≤u＜U) and k-1 road, front phase factor sequence, selection makes the original u road phase factor sequence of deterministic minimum as the k road phase factor sequence after sorting, U=P ^V-1, P is the phase factor number, is specially: all phase factors of at first setting the 1 tunnel phase factor sequence are all identical, and can select phase factor here all is complete 1 sequence; From remaining U-1 road phase factor sequence, select then to make with the minimum Ω (2) of the 1 tunnel phase factor sequence correlation as the 2nd optimum angle sequence; From remaining U-k (k=2 ..., U-1) choose in the phase factor sequence of road make with the minimum Ω (k+1) of preceding k road phase factor sequence average correlation be k+1 road optimum angle factor sequence; Obtain correlation phase factor sequence from low to high at last.

The correlation phase factor sequence from low to high that step 4. utilizes step 3 to obtain produces correlation U road alternative signal from low to high successively.

L lower alternative signal of front correlation calculated its PAPR value respectively in the U road alternative signal that step 5. selection step 4 produces, and therefrom selects the minimum alternative signal of PAPR and exports as optimum alternative signal.

In the present embodiment, sub-carrier number N=256, b _vFrom+1, and choose among-the 1}, promptly phase factor number P=2 is cut apart several V=8, and U=P is arranged ^V-1=128 groups of alternative signal produce.For traditional PTS at random, the complex multiplication number of times that the IFFT computing of V grouping needs is Complex addition is Nlog ₂N.Be equivalent to 18 real number additions according to 1 complex multiplication, 1 complex addition is equivalent to 2 real number additions, can draw that the total real number addition complexity of equal value of IFFT computing is among the PTS at random that V cuts apart: 11VNlog ₂N.

Here in step 1, adopt to interweave and cut apart.For the PTS that interweaves, here adopt the employing Cooley-Tukey fft algorithm of proposition in " An algorithm for the machine calculation of complex Fourier series; in Math.Comput.; vol.19; no.90; pp.296-301,1965 ", the complexity of complex multiplication can be reduced to based on J.W.Cooley and J.W.Tukey

Complex addition is reduced to

Entire I FFT process need carries out

Individual real number addition.If L alternative signal arranged, the PTS phase factor is in conjunction with NL complex addition of needs (V-1), and the minimum alternative signal of search PAPR needs 2NL real multiplications and NL real number addition.The equivalent real number addition number of times of the total complexity of the whole algorithm of PTS at random is C _R-PTS=11Nlog ₂N+ (2V+7) NU, the equivalent real number addition number of times of the total complexity of PTS algorithm that interweaves is

For the method for the present invention's proposition, if there be L=64 alternative signal from the U=128 alternative signal of all generations, to select, total calculating complexity C of the PTS that interweaves _I-PTS=526336, the complexity of this moment only is the total complexity C of PTS at random _R-PTS=933888 53.4%.By analysis of complexity, the complexity of the PTS that interweaves as can be seen is than PTS is much lower at random.Under same computation complexity, the PTS that interweaves compares with PTS at random, can adopt more sub-piecemeal V and alternative signal L to reach better PAPR rejection.

Above example only is a preferred example of the present invention, and use of the present invention is not limited to this example, and is within the spirit and principles in the present invention all, any modification of being made, is equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (4)

1. a partial transmission sequence method is characterized in that, comprises the steps:

Step 1. is divided into the individual subvector of V (V 〉=2) with the N point frequency domain data vector X that desire in the block of sub-carriers sends, and each subvector has N data, and wherein, N/V data are identical with the data of relevant position among the X, and other data are zero, and satisfy

X _V(v=0 ..., V-1) subvector for cutting apart;

Step 2. is carried out the IFFT computing to each subvector;

(u, size i) is according to deterministic for the cross-correlation function variable variance Δ of any two-way alternative signal of step 3. basis

All U road pairing phase factor sequence of alternative signal are carried out correlation ordering from low to high, the judgment condition when wherein the argmin{} representative function is obtained minimum value, U=P ^V-1, P is the phase factor number, all phase factors of at first setting the 1 tunnel phase factor sequence are all identical; From remaining U-1 road phase factor sequence, select then to make with the minimum Ω (2) of the 1 tunnel phase factor sequence correlation as the 2nd optimum angle sequence; From remaining U-k (k=2 ..., U-1) choose in the phase factor sequence of road make with the minimum Ω (k+1) of preceding k road phase factor sequence average correlation be k+1 road optimum angle factor sequence; Obtain correlation phase factor sequence from low to high at last;

The correlation phase factor sequence from low to high that step 4. utilizes step 3 to obtain produces correlation U road alternative signal from low to high successively;

L lower alternative signal of front correlation calculated its PAPR value respectively in the U road alternative signal that step 5. selection step 4 produces, and therefrom selects the minimum alternative signal of PAPR and exports as optimum alternative signal.

2. partial transmission sequence method according to claim 1 is characterized in that, step 1 is described to be divided into to interweave and to cut apart.

3. partial transmission sequence method according to claim 1 and 2 is characterized in that, what the described IFFT computing of step 2 was adopted is the Cooley-Tukey fft algorithm.

4. partial transmission sequence method according to claim 3 is characterized in that, described phase factor from+1, choose among-the 1}.

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