CN102244636B - A kind of partial transmission sequence method - Google Patents

Abstract

The invention belongs to mobile communication system field, discloses a kind of partial transmission sequence method.The higher problem of sequence complexity is transmitted for traditional random partial, the method of the present invention is by phase factor sequence is ranked up from low to high according to dependency, in the relatively low alternative signals of searching PAPR, only need to search above dependency lower part alternative signal, and the traversal search of non-traditional random PTS, Optimal Signals searching times are reduced, so just the performance close with traditional PTS can be reached by relatively low complexity computing；It is and the dependency of each alternative signal of intertexture PTS is only determined by phase factor, unrelated with specific signal data, thus sequence only need once to calculate to store, be not improved system complexity.

Description

Partial transmission sequence method

Technical Field

The invention belongs to the field of mobile communication systems, and particularly relates to a partial transmission sequence method.

Background

Orthogonal Frequency Division Multiplexing (OFDM) technology is a new generation of wireless communication core technology due to its high spectrum utilization rate, good multipath fading resistance and interference resistance. One of the main disadvantages of the OFDM system is that the ratio of the Peak-to-average power (PAPR) of the signal is high. The PAPR here is formulated as:wherein x is_nDenotes an output signal obtained by IFFT operation, max {. cndot.represents a maximum value, and E {. cndot.represents an average value. When a high peak signal enters a power amplifier saturation region at a system transmitting end, great in-band distortion and out-of-band radiation are generated, signal distortion and adjacent-band interference are caused, and system performance is deteriorated. In order to transmit OFDM signals without distortion, a large linear range is required at the transmitting end, which increases the cost of system design and limits the wide application of OFDM technology.

Partial Transmit Sequence (PTS) is a common method for reducing PAPR of OFDM signal, and it represents transmission of the same set of information by multiple sequences to reduce the probability of occurrence of high power signal, and its method description can refer to documents: Muller.S.H., Huber.J.B, A novel peak power reduction scheme for OFDM.the 8th IEEE International Symposium on Personal, inor and Mobile radio communications, 1997, 1090-1094. The method specifically comprises the following steps: dividing N sub-carriers into V groups according to a certain grouping mode, and performing IFFT operation on each group to obtain x_v＝IFFT{X_VMultiplied by different phase factors b_vThe multiplied sets of signals are then superimposed by selecting different phase factors b_vV1, 2.. V } are combined to obtain a plurality of candidate signalsNumber (C)And finally, selecting the signal with the minimum PAPR from the signals for transmission. Here the phase factor b_vA complex factor having an absolute value of 1,φ_v∈[0，2π]theoretically, b_vPhase phi of_vGenerally, the phase factor of the first packet is fixed to 1, and the number of candidate signals U generated by PTS is P without loss of generality^V-1. Phase factor b in general_vIs selected from { +1, -1, + j, -j } or { +1, -1} and represents a phase rotation on the signal. The specific working principle is shown in fig. 1, and the specific flow is shown in fig. 2.

But has the disadvantage that the complexity of the algorithm increases exponentially as the number of packets and the number of phase rotation factors increase. For the OFDM system, the computation complexity is high, and the system load is large.

Disclosure of Invention

The invention aims to solve the problem of higher complexity of the existing PTS method and provides a partial transmission sequence method.

The technical scheme of the invention is as follows: a partial transmission sequence method, comprising the steps of:

step 1, dividing N point frequency domain data vectors X to be transmitted in a subcarrier block into V (V is more than or equal to 2) sub-vectors, wherein each sub-vector has N data, N/V data are the same as data at corresponding positions in X, and other data are zero and meet the requirement that the N/V data are the same as the data at corresponding positions in XX_V(V-0, …, V-1) is a segmented subvector;

step 2, performing IFFT operation on each subvector;

step 3, according to the magnitude of the cross-correlation function variable variance delta (u, i) of any two paths of alternative signals, according to a decision formulaSorting the phase factor sequences corresponding to all the U-path alternative signals from low correlation to high correlation, wherein argmin {. cndot } represents a judgment condition when the function obtains the minimum value, and U ═ P { } represents a judgment condition when the function obtains the minimum value^V-1And P is the number of phase factors, firstly setting all the phase factors of the 1 st path of phase factor sequence to be the same; then selecting omega (2) with the lowest correlation with the 1 st path phase factor sequence from the rest U-1 path phase factor sequences as a 2 nd optimal phase sequence; selecting an optimal phase factor sequence with k +1 paths of omega (k +1) which has the lowest average correlation with the phase factor sequence of the previous k paths from the rest U-k (k 2.., U-1) path phase factor sequences; finally, a phase factor sequence with the correlation from low to high is obtained;

step 4, sequentially generating U-path alternative signals with the correlation from low to high by using the phase factor sequence with the correlation from low to high obtained in the step 3;

and 5, selecting the L alternative signals with lower correlation in the front among the U-path alternative signals generated in the step 4, respectively calculating the PAPR values of the L alternative signals, and selecting the alternative signal with the lowest PAPR from the L alternative signals as the optimal alternative signal to be output.

The invention has the beneficial effects that: the method of the invention sorts the phase factor sequence from low to high according to the relevance, when searching the alternative signal with lower PAPR, only a part of the alternative signal with lower relevance is needed to be searched, instead of the traversal search of the traditional random PTS, so that the optimal signal search frequency is reduced, and the performance similar to the traditional PTS can be achieved through the operation with lower complexity; and the correlation of each alternative signal of the interleaved PTS is only determined by a phase factor and is irrelevant to specific signal data, so that the sorting only needs to be calculated and stored once, and the complexity of the system is not improved.

Drawings

Fig. 1 is a transmitter operation schematic diagram of PTS.

Fig. 2 is a flowchart illustrating a process of searching for an optimal candidate signal using a conventional random PTS method.

Fig. 3 is a diagram illustrating the operation of the random PTS and the interleaved PTS.

FIG. 4 is a schematic flow diagram of a process using the present invention.

Detailed Description

Specific embodiments of the present invention will be given below with reference to the accompanying drawings. It should be noted that: the parameters in the examples do not affect the generality of the invention.

To facilitate an understanding of the invention, before setting forth specific embodiments, the terms used therein are first introduced:

random PTS: each sub-carrier is randomly allocated within V PTSs, and the specific operation principle is shown in fig. 3.

And (3) interweaving PTS: the sub-carriers with a distance V are allocated within a PTS, and the specific operation principle is shown in fig. 3.

Alternative signal correlation analysis: let x^uAnd xⁱThe u-th path and the i-th path of the alternative signal in the interleaved PTS,representing a phase factor of a corresponding packet on a k-th subcarrier in the u-th candidate signal, whereinWhen the kth subcarrier is in the vth packet, N is the number of subcarriers. Therefore, the cross-correlation function between any two candidate signals (denoted as u, i) at any time point (denoted as m, n) is defined as:

input data X of system_nIs an independent and equally distributed random variable with average power of 1, and defines τ ═ m-n, and the above formula can be simplified as:

due to R_u，i(τ) is symmetric about τ, so only the portion where τ is positive needs to be analyzed, thus:

defining variables of a cross-correlation functionVariance Δ (u, i) of (a):

wherein,is composed ofIs measured. Random variation of cross-correlation function in all candidate signalsThe lower the arithmetic mean of the variance, the lower the correlation between the candidate signals, and the better the PAPR suppression effect of the system, and it can be seen that the correlation of the candidate signals is determined only by the phase factor and is independent of the specific signal data.

The method of the invention has a flow diagram as shown in fig. 4, and comprises the following steps:

step 1, dividing N point frequency domain data vectors X to be transmitted in a subcarrier block into V (V is more than or equal to 2) sub-vectors, wherein each sub-vector has N data, N/V data are the same as data at corresponding positions in X, and other data are zero and meet the requirement that the N/V data are the same as the data at corresponding positions in XX_V(V-0, …, V-1) is a segmented subvector;

step 2, performing IFFT operation on each subvector;

step 3, according to the magnitude of the cross-correlation function variable variance delta (u, i) of any two paths of alternative signals, according to a decision formulaSorting the phase factor sequences corresponding to all the U-path alternative signals from low correlation to high correlation, wherein argmin {. DEG } represents a judgment condition when a function obtains a minimum value, namely when a k-path phase factor sequence is selected for sorting, calculating an average cross correlation value between the U-path phase factor sequence (k is less than or equal to U and less than U) and the k-1-path phase factor sequence, selecting an original U-path phase factor sequence which minimizes a judgment formula as the k-path phase factor sequence after sorting, and taking U as P^V-1P is the number of phase factors, specifically: firstly, setting all phase factors of the 1 st path phase factor sequence to be the same, wherein the sequence with all the phase factors being 1 can be selected; then from the remaining U-1 pathSelecting omega (2) with the lowest correlation with the 1 st path phase factor sequence from the phase factor sequences as a 2 nd optimal phase sequence; selecting an optimal phase factor sequence with k +1 paths of omega (k +1) which has the lowest average correlation with the phase factor sequence of the previous k paths from the rest U-k (k 2.., U-1) path phase factor sequences; finally, a phase factor sequence with the correlation from low to high is obtained.

And 4, sequentially generating U-path alternative signals with the correlation from low to high by using the phase factor sequence with the correlation from low to high obtained in the step 3.

And 5, selecting the L alternative signals with lower correlation in the front among the U-path alternative signals generated in the step 4, respectively calculating the PAPR values of the L alternative signals, and selecting the alternative signal with the lowest PAPR from the L alternative signals as the optimal alternative signal to be output.

In this embodiment, the number of subcarriers N is 256, b_vSelected from { +1, -1}, i.e. the number of phase factors P is 2, the number of divisions V is 8, and U is P^V-1128 sets of candidate signals are generated. For a conventional random PTS, the IFFT operation of V packets requires a complex multiplication number of V packetsAdding complex numbers to Nlog₂And N is added. According to 1 complex multiplication is equivalent to 18 real addition, and 1 complex addition is equivalent to 2 real addition, the total equivalent real addition complexity of IFFT operation in V divided random PTS can be obtained as follows: 11VNlog₂N。

Here interleaved partitioning is used in step 1. For interleaved PTS, the complexity of complex multiplication can be reduced to that of complex multiplication by applying Cooley-TukeyFFT algorithm based on J.W.Cooley and J.W.Tukey as proposed in "A algorithm for the machine calculation of complex Fourier series, in Math.Compout., vol.19, No.90, pp.296-301, 1965Complex addition down toThe whole IFFT process needs to be carried outThe real number addition. If there are L candidates, the PTS phase factor combination requires (V-1) NL complex additions, and searching for the candidate with the lowest PAPR requires 2NL real multiplications and NL real additions. The addition frequency of equivalent real number of the total complexity of the whole random PTS algorithm is C_R-PTS＝11Nlog₂N + (2V +7) NU, the number of times of adding equivalent real numbers of the total complexity of the interweaving PTS algorithm is

For the method proposed by the present invention, the total computational complexity C of the interleaved PTS is selected from all generated U-128 candidates if there are L-64 candidates_I-PTSAt 526336, the complexity at this time is only the random PTS total complexity C_R-PTS53.4% of 933888. From the complexity analysis, it can be seen that the complexity of the interleaved PTS is much lower than the random PTS. Under the same computational complexity, the interleaved PTS can adopt more sub-blocks V and alternative signals L to achieve better PAPR suppression performance than the random PTS.

The above examples are only preferred examples of the present invention, and the use of the present invention is not limited to the examples, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. A partial transmission sequence method, comprising the steps of:

step 1, dividing N point frequency domain data vectors X to be sent in a subcarrier block into V sub-vectors, wherein V is larger than or equal to 2, each sub-vector has N data, wherein N/V data are the same as data of corresponding positions in X, other data are zero, and the requirement of meeting the requirement of the condition that the N/V data are the same as the data of corresponding positions in X is metX_VIs a divided sub-vector, V is 0, …, V-1;

step 2, performing IFFT operation on each subvector;

step 3, according to the magnitude of the cross-correlation function variable variance delta (u, i) of any two paths of alternative signals, according to a decision formulaSorting the phase factor sequences corresponding to all the U-path alternative signals from low correlation to high correlation, wherein a cross-correlation function variable is definedVariance Δ (u, i) of (a):

$\mathrm{\Δ}(u,i)=\frac{1}{N}\underset{\mathrm{\τ}=0}{\overset{N-1}{\Σ}}{\left(\right|R_{u,i}\left(\mathrm{\τ}\right){|}^2-\mathrm{\η}\left(u,i\right))}^2$

wherein,is composed ofThe mean value of (a);

argmin {. cndot } represents a decision condition when the function takes a minimum value, U ═ P^V-1And P is the number of phase factors, firstly setting all the phase factors of the 1 st path of phase factor sequence to be the same; then selecting omega (2) with the lowest correlation with the 1 st path phase factor sequence from the rest U-1 path phase factor sequences as a 2 nd optimal phase sequence; selecting omega (k +1) with the lowest average correlation with the former k paths of phase factor sequences from the rest U-k paths of phase factor sequences as k +1 paths of optimal phase factor sequences, wherein k is 2, … and U-1; finally, a phase factor sequence with the correlation from low to high is obtained;

step 4, sequentially generating U-path alternative signals with the correlation from low to high by using the phase factor sequence with the correlation from low to high obtained in the step 3;

and 5, selecting the L alternative signals with lower correlation in the front among the U-path alternative signals generated in the step 4, respectively calculating the PAPR values of the L alternative signals, and selecting the alternative signal with the lowest PAPR from the L alternative signals as the optimal alternative signal to be output.

2. The method of claim 1, wherein the partitioning of step 1 is an interleaved partitioning.

3. The method according to claim 1 or 2, wherein the IFFT operation in step 2 is performed by using Cooley-Tukey FFT algorithm.

4. The method of claim 3 wherein the phase factor is selected from { +1, -1 }.