CN109905344B - OFDM signal peak-to-average ratio suppression method based on partial transmission sequence - Google Patents
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Abstract
The invention provides a method for inhibiting a peak-to-average power ratio based on an OFDM signal of a partial transmission sequence, which mainly solves the problem that the peak-to-average power ratio performance of an OFDM system in the prior art is low. The implementation scheme is as follows: firstly, collecting OFDM signals and grouping the signal subcarriers, and calculating the peak-to-average ratio of the original signals; then, the peak-to-average ratio value of the system is calculated from the phase inversion of the first group, the sub-blocks behind the descending direction are subjected to grouping iterative search through judgment, if the calculated peak-to-average ratio value is smaller than the original peak-to-average ratio, the following groups are regrouped, phase iterative search is carried out on each new sub-block, and if not, the peak-to-average ratio of the following groups is calculated, and the judgment is carried out again; and finally, finding an optimal phase factor to obtain the minimum peak-to-average ratio value. The invention can obtain better phase factor and smaller peak-to-average ratio, improves the system peak-to-average ratio performance, can be applied to broadband wireless communication, and plays an important role in 5G.
Description
Technical Field
The invention belongs to the technical field of communication, and particularly relates to an OFDM signal peak-to-average power ratio suppression method which can be used for broadband wireless communication and OFDM signal transmission of a wireless local area network.
Background
With the continuous development of communication technology, the requirement on communication rate is higher and higher, and the OFDM system is concerned because of its unique slow anti-multipath interference capability. However, the peak-to-average power ratio PAPR is high due to the multi-carrier structure of the OFDM system. Since a general power amplifier is not linear, its linear range is limited. Therefore, when such a signal with a large variation range in the OFDM system enters a nonlinear operation region of an amplifier, nonlinear distortion is generated in the signal, harmonics are generated, and relatively significant spectrum spreading interference and in-band signal distortion are generated, so that the performance of the whole OFDM system is reduced. Therefore, it is imperative to reduce PAPR of OFDM systems.
At present, a typical representation in probability theory technology is a partial transmission sequence technology, because the partial transmission sequence has very high search complexity at the transmitting end and the receiving end. Two researchers, l.j.cimini and n.r.sollenberger, proposed an iterative flipping algorithm based on partial transmission sequences. The algorithm complexity of the technology is greatly reduced compared with the original partial transmission sequence, and the low-complexity iterative flipping technology in the partial transmission sequence is used for carrying out peak-to-average ratio suppression on the OFDM signal in practical application. The basic principle of the existing iterative inversion technology is to group OFDM signals, then invert and change the phase of each group only between +1 and-1, then perform phase iterative search, and finally find a local minimum. The search complexity is reduced much with respect to the original partial transmission sequence, but the reduction in peak-to-average performance is much greater. This reduction of the peak-to-average ratio using the iterative flipping technique is not satisfactory if the peak-to-average ratio performance is more demanding in some systems.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an OFDM signal peak-to-average ratio inhibition method based on a partial transmission sequence, so as to further reduce the peak-to-average ratio of the OFDM signal and improve the peak-to-average ratio inhibition performance of the OFDM signal.
The core idea for realizing the purpose of the invention is that when grouping iteration, a direction of peak-to-average ratio reduction is found first, and after the direction is found, the subsequent groups are combined into a group every q to carry out iterative search on the phase inside. This time corresponds to an increase in the range of phase combining because the phases of each group are independent before the re-grouping, but the phases of q groups are combined after the re-grouping, but because q is chosen to be 2, the number of searches is not increased, thereby achieving better performance than in the prior art. The method comprises the following specific steps:
(1) dividing N subcarriers in an OFDM frequency domain signal X into V subblocks X(s) by adopting an interleaving and dividing mode, wherein s is 1, 2.
(2) Performing fast fourier transform on each sub data block to obtain a time domain signal t(s), wherein s is 1, 2.
(3) Assuming that the initial value b(s) of the phase rotation factor is 1, and the index of the first sub-block is 1, then combining the results of (1) and (2) to calculate the PAPR0 of the OFDM frequency domain signal;
(4) changing the phase factor in the sub-block marked as index from +1 to-1, namely b _ index to-1, and calculating the PAPR of the OFDM signal at the moment;
(5) and performing grouping iterative search on the sub-blocks behind the descending direction:
(5a) determination of PAPR and PAPR0 size: if PAPR < PAPR0, perform (5b), otherwise b _ index is 1;
(5b) starting from the subblock marked by the index, performing q phase factor grouping iterative searches on the following subblocks, determining a phase rotation factor for each iterative search, calculating to obtain the minimum PAPR1 of the OFDM signal, determining the final phase rotation factor b(s), and making PAPR0 be PAPR1 and index be V;
(6) adding one to the search index, namely, the index is equal to index +1, judging whether the index is satisfied with the value of V +1, if so, returning to the step (4), and if not, executing the step (7);
(7) calculating the minimum peak-to-average ratio (PAPR) 0 according to the final phase rotation factor b(s) obtained in the step (5), and calculating to obtain a final OFDM transmission signal:
compared with the prior art, the invention has the following advantages:
because the grouping iteration is added in the process of searching the minimum phase, more phase combinations can be combined, and compared with the prior iterative inversion algorithm which only has single phase change in the process of searching the minimum phase and has no more phase combinations, the reduced peak-to-average power ratio is lower.
The experimental simulation result shows that: compared with the existing iterative inversion algorithm, the method can reduce the peak-to-average ratio to 9.0dB on the premise of the same complexity, and the performance of the peak-to-average ratio is improved by 0.2dB compared with the iterative inversion algorithm.
Drawings
FIG. 1 is a schematic diagram of a system model for partial transmission sequences in accordance with the present invention;
FIG. 2 is a flow chart of an implementation of the present invention;
FIG. 3 is a graph showing the comparison result of the peak-to-average ratio performance simulation of the present invention and the prior art.
Detailed Description
The following detailed description of specific embodiments and technical effects of the present invention will be made with reference to the accompanying drawings.
Referring to fig. 1, a partial transmission sequence system model suitable for the present invention includes an OFDM frequency domain signal X, a subcarrier X(s), a time domain signal t(s), a phase factor b(s) to be optimized, and a processed transmission signal y, where s is 1, 2.
Referring to fig. 2, the method for suppressing the peak-to-average power ratio of the OFDM signal based on the partial transmission sequence of the present invention includes the following steps:
The existing dividing modes of the OFDM frequency domain signal include a random dividing mode, an interleaving dividing mode and an adjacent dividing mode, wherein the random dividing mode is to divide the signal randomly by using a random function, the interleaving dividing mode is to sample the signal for a plurality of times at a certain distance, and the adjacent dividing mode is to directly divide the signal into a certain number of groups in an adjacent manner.
The invention adopts but not limited to an interleaving division mode to divide N subcarriers in an OFDM frequency domain signal X into V subblocks X(s) at intervals of N/V, wherein s is 1, 2.
And 2, performing fast Fourier transform processing on the sub-data block to obtain a time domain signal t(s).
Performing fast fourier transform on each sub data block x(s) to obtain a time domain signal t(s) as:
where b(s) is the rotational phase factor to be optimized, s 1, 2.
And 3, calculating an initial signal peak-to-average ratio.
Let the phase rotation factor initial value b(s) be 1, and index of the first sub-block be 1;
combining the results of step 1 and step 2 to obtainComputing peak-to-average ratio of OFDM frequency domain signal
And 4, calculating the peak-to-average ratio at the mark index.
Assuming that V is 4 at the beginning, b(s) { (1, 1,1,1}, the phase factor in the sub-block marked as index is changed from +1 to-1, and b _ index { -1, when b(s) { -1,1,1,1} is calculated to obtain the phase factor
Calculating the peak-to-average ratio of the OFDM signal at the moment
And 5, performing grouping iterative search on the sub-blocks behind the descending direction.
(5a) Determine PAPR < size of PAPR 0: if the PAPR is less than the PAPR0, entering packet iteration, otherwise b _ index is 1;
(5b) taking the iterative phase factor q as 2, each iteration searches the total q 24 phase combinations, which are respectively: (1, 1), (1, -1), (-1, 1), (-1, -1), in which case the four cases of b(s) are { -1,1,1,1}, -1,1, -1,1}, -1, -1,1 };
(5c) in 4 phase combinations, one phase combination at a time is changed, calculated
Obtaining the peak-to-average ratio of the OFDM signal
Each time, a comparison is made, if PAPR2<PAPR, PAPR2, PAPR1 PAPR,
(5d) and repeating the loop (5b) and the loop (5c) for four times to obtain a final phase rotation factor b(s), and jumping out the loop to make the PAPR0 equal to PAPR1 and index equal to V.
And 6, circularly judging.
Adding one to the search index, namely index is equal to index + 1;
judging index<Whether V +1 is true or not, if so, returning to the step 4, otherwise, obtaining the optimal phase rotation factor b(s), and calculating to obtain the minimum peak-to-average ratio
And step 7 is performed.
And 7, obtaining a final sending signal y.
According to the b(s) obtained in the step 6, calculating to obtain a processed sending signal
The technical effects of the invention are explained in combination with simulation experiments as follows:
1. simulation conditions
The simulation experiment is carried out on a hardware platform of which the running system is an Intel (R) core (TM) i3CPU 380@2.53GHz 64-bit Windows operating system, and simulation software adopts MATLAB.
A partial transmission sequence system model used in simulation is shown in fig. 1, where X is an original OFDM frequency domain signal, b(s) ═ 1(s ═ 1, 2., V) is a phase rotation factor to be optimized, X adopts a QPSK modulation method, an oversampling rate is 4, the number of phase rotation factors is 2, the number of iterative phase factors q is 2, the number of subcarriers in X is 256, and y is a signal after X is processed.
2. Emulated content
The invention and the existing iterative inversion technology are applied to carry out phase factor optimization on part of the transmission sequence system model shown in the figure 1 respectively, and a peak-to-average ratio performance comparison diagram of the two methods is simulated, and the result is shown in figure 3. Where the abscissa represents the peak-to-average ratio (PAPR) of the signal in dB and the ordinate represents the standard Complementary Cumulative Distribution Function (CCDF) for peak-to-average ratio performance. The curve marked by triangles represents the peak-to-average ratio value of the improved iterative inversion algorithm obtained by using the method, the curve marked by cross indicates the peak-to-average ratio obtained by using the iterative inversion algorithm, and the curve marked by solid lines indicates the peak-to-average ratio of the original OFDM signal which is not processed.
As can be seen from FIG. 3, the prior art and the prior art have the prior probability Pr (PAPR > PAPR)0)＝10-4And compared with the prior art, the peak-to-average power ratio performance of the invention is improved by 0.2dB, thereby more reducing the peak-to-average power ratio of the system.
The foregoing description is only an example of the present invention, and it will be apparent to those skilled in the art that various modifications and variations in form and detail can be made without departing from the principle and structure of the invention, but these modifications and variations are within the scope of the invention as defined in the appended claims. The invention has not been described in detail in part of the common general knowledge of those skilled in the art.
Claims (4)
1. The OFDM signal peak-to-average power ratio suppression method based on partial transmission sequences is characterized by comprising the following steps:
(1) dividing N subcarriers in an OFDM frequency domain signal X into V subblocks X(s) by adopting an interleaving and dividing mode, wherein s is 1, 2.
(2) Performing fast fourier transform on each sub data block to obtain a time domain signal t(s), wherein s is 1, 2. The formula is as follows:
(3) assuming that the initial value b(s) of the phase rotation factor is 1, and the index of the first sub-block is 1, then combining the results of (1) and (2) to calculate the PAPR0 of the OFDM frequency domain signal; the formula is as follows:
wherein E [ | t(s) | ] is the mean of the absolute values of t(s);
(4) changing the phase factor in the sub-block marked as index from +1 to-1, namely b _ index to-1, and calculating the PAPR of the OFDM signal at the moment;
(5) and performing grouping iterative search on the sub-blocks behind the descending direction:
(5a) determination of PAPR and PAPR0 size: if PAPR < PAPR0, perform (5b), otherwise b _ index is 1;
(5b) starting from the subblock marked by the index, performing grouping iterative search on every q phase factors of the following subblocks, determining a phase rotation factor for each iterative search, calculating to obtain the minimum PAPR1 of the OFDM signal, determining the final phase rotation factor b(s), and making the PAPR0 be PAPR1 and the index be V;
(6) adding one to the search index, namely, the index is equal to index +1, judging whether the index is satisfied with the value of V +1, if so, returning to the step (4), and if not, executing the step (7);
(7) calculating the minimum peak-to-average ratio (PAPR) 1 according to the final phase rotation factor b(s) obtained in the step (5), and calculating to obtain a final OFDM transmission signal:
2. the method of claim 1, wherein the dividing of the N subcarriers of the OFDM frequency domain signal X in (1) by interleaving division is performed by taking signal values of the OFDM signal every N/V distances, and taking V signals in total to obtain V subblocks X(s).
3. The method of claim 1, wherein (5b), starting from the sub-block marked with index, the following sub-blocks are searched iteratively for each q phase factors in a packet, and wherein the search is performed as follows:
(5b1) taking the iterative phase factor q as 2, each iteration searches the total q24 phase combinations, which are respectively: (+1, +1), (+1, -1), (-1, +1), (-1, -1);
(5b2) and in 4 phase combinations, the peak-to-average ratio (PAPR) 2 of the OFDM signal is calculated once by changing one phase combination, comparison judgment is carried out once each time, if the PAPR2 is less than the PAPR1, the PAPR1 is equal to the PAPR2, and the phase rotation factor b(s) is finally determined by circulating four times.
4. The method according to claim 1, wherein the minimum PAPR1 in (7) is calculated as follows:
where E [ | t(s) | ] is the mean of the absolute values of t(s).
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| CN106506431A (en) * | 2016-12-27 | 2017-03-15 | 哈尔滨工业大学 | The method that joint peak-to-average force ratio suppresses the ofdm system pulse interference suppression extinguished with pulse |
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