CN110445737A - OFDM peak-to-average power ratio based on two stages index modulation reduces method and system - Google Patents

Abstract

The invention discloses a method and system for reducing the peak-to-average power ratio of OFDM based on two-stage index modulation. In the first stage of index modulation, each OFDM signal subframe activates some subcarriers for data transmission according to the index bit information, and in the second stage of index modulation, according to more index bit information Part of the subcarriers are again selected for activation and data transmission. The main purpose of the second stage index modulation is to reduce the peak-to-average power ratio and improve the spectral efficiency of the two-stage index modulation OFDM system. At the same time, a simple method is used to reduce the peak-average A power ratio search algorithm is employed. The receiving end adopts maximum likelihood detection, which will comprehensively consider the index pattern and the mapped signal for detection and recovery of bit information. The proposed method and system can effectively reduce the peak-to-average power ratio performance of two-stage index modulation OFDM, and the spectral efficiency, power efficiency and bit error rate performance of the system are all improved.

Description

OFDM peak-to-average power ratio reduction method and system based on two-stage index modulation

technical field

The present invention relates to the technical field of wireless communication, in particular to a method and system for reducing peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) based on two-stage index modulation.

Background technique

In the field of wireless communication, due to the advantages of high spectrum utilization, effective anti-multipath and anti-frequency selective fading, OFDM technology based on index modulation is being widely researched and applied, even for the fifth generation (5G) mobile communication. A favorable technical candidate. The index modulation OFDM technology can effectively improve the system frequency band utilization and the power efficiency of the signal at the transmitting end. Because an OFDM signal based on index modulation only has some subcarriers activated for information transmission, the other subcarriers are 0, and more transmission The bit information is implicit in the index information, that is, the transmitted bit information is used to determine the activation pattern of the subcarrier. In order to further improve the spectral efficiency of the system, dual-mode index modulation OFDM technology is proposed, which uses two kinds of constellation diagrams for mapping data, and the active subcarriers selected by index information use constellation diagram A to realize the mapping process, while the remaining subcarriers The carrier uses the constellation diagram B to implement the mapping process, and the signal points in the two constellation diagrams here are mutually disjoint.

However, the OFDM system based on index modulation inherits the disadvantage of high PAPR of the traditional OFDM system. High PAPR requires the power amplifier at the transmitting end of the system to have a large linear range, so as to avoid signal distortion caused by the transmitted OFDM signal exceeding the maximum linear range. distortion, and increasing the linear range of the PA is cost-prohibitive. Some commonly used OFDM system PAPR reduction methods include clipping technology, selective mapping, partial transmission sequence and virtual sequence insertion technology, etc. A PAPR reduction method suitable for OFDM systems based on index modulation is yet to be developed.

Contents of the invention

The technical problem to be solved by the present invention is to reduce the PAPR of the index modulation OFDM system, improve the frequency band utilization of the traditional index modulation OFDM system, improve the power efficiency of the dual-mode index modulation OFDM system and improve the bit error rate performance of the index modulation OFDM system, An OFDM based on two-stage index modulation and its PAPR reduction method and system are provided.

According to an aspect of the technical problem solved by the present invention, a method for reducing peak-to-average power ratio of OFDM based on two-stage index modulation comprises the following steps:

(1) Serial-to-parallel conversion and bit grouping: convert the binary sequence to be sent through serial-to-parallel conversion, and convert the serial bit data stream into a parallel data stream, where each p bit is a group input to a sub-frame of OFDM signal frame, where a frame of OFDM signals containing N subcarriers is divided into G=N/n subframes, G _g =[X _g,1 X _g,2 ... X _g,n ] means the gth subframe, 1≤g ≤G, n is the number of subcarriers contained in each subframe, and X represents the subcarriers in one frame of OFDM signal.

(2) The first stage index modulation: input the first p ₁ bits in each group of p bits in step (1) to the first stage index selector, and select the active subcarrier in each subframe of the OFDM signal, that is, p ₁ bits determine the activation pattern of subcarriers in G _g , and then p ₂ bits in each group of p bits in step (1) are input to mapper A for mapping.

(3) Second-stage index modulation: input p ₃ bits in each group of p bits in step (1) to the second-stage index selector, and select again from the inactive subcarriers in G _g in step (2) The subcarriers are activated, and then the p ₄ bits in each group of p bits in step (1) are input to the mapper B for mapping.

(4) Frequency-domain OFDM signal generation, according to the subcarrier activation patterns in steps (2) and (3), pass the p ₂ + p ₄ bits in each group of p bits in step (1) through mapper A and mapper B is mapped to corresponding activated subcarriers.

(5) The frequency-domain OFDM signal obtained in step (4) is transformed into the time domain through an N-point inverse discrete Fourier transform (IDFT).

(6) Input the time-domain OFDM signal obtained in step (5) into the peak-to-average power ratio comparator, and find the best combination of signal mapping in the second stage through a search algorithm to minimize PAPR.

(7) The PAPR-minimized time-domain OFDM signal obtained in step (6) is sent to the channel for transmission after parallel-to-serial conversion, cyclic prefix addition, digital-to-analog conversion and up-conversion processing.

(8) At the receiving end, the received OFDM signal is subjected to down-conversion, analog-to-digital conversion, cyclic prefix removal and serial-to-parallel conversion.

(9) Discrete Fourier transform (DFT) is performed on the output signal of step (8), and the time-domain OFDM signal is converted into the frequency domain.

(10) The output signal of step (9) is subjected to maximum likelihood detection, de-indexing and de-mapping processing, and is restored to binary information.

(11) Perform parallel-to-serial conversion on the output signal of step (10) to obtain the original sent binary sequence.

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, in step (1), the number of bits contained in each subframe of a frame OFDM signal p=p ₁ +p ₂ +p ₃ + p ₄ , where the first p ₁ bits and p ₃ bits are respectively input to the first-stage index selector and the second-stage index selector to select the activation pattern of subcarriers in each subframe of the OFDM signal, p ₂ bits and p ₄ bits are respectively input to mapper A and mapper B for signal mapping, and bit information corresponding to p ₁ , p ₂ , p ₃ and p ₄ are arranged in sequence.

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, the index modulation in the first stage of step (2) is to select k subcarriers from n subcarriers in each subframe for Map bits information, so:

p ₂ =klog ₂ M _A

In the formula Represents the platform function, that is, rounded down, C(n,k) represents the binomial coefficient, that is, the number of combinations of k taken from n, and satisfies k<n at the same time, M _A represents the constellation diagram used in mapper A size. The index information determined by p ₁ -bit information is I _A =[IA _,1 I _A,2 ... I _A,k ], and the signal determined by p ₂ -bit information is S _A =[S(IA _,1 )S(I _A,2 )...S(I _A,k )].

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, the second-stage index modulation of step (3) is n-k subcarriers that are not activated in step (2) Then select k' subcarriers for mapping bit information, so:

p ₄ =k'log ₂ (M _B /u)

In the formula, M _B represents the size of the constellation diagram used in the mapper B, and each u signal point in the constellation diagram B represents the same bit information, which is used to reduce the PAPR of the system, and is randomly selected during the first mapping. The signal points in the constellation diagram B and the constellation diagram A are mutually disjoint, and satisfy k+k'<n at the same time, ensuring that there are 0 carriers, that is, non-activated subcarriers, so as to improve the power efficiency of the system. The index information I _B determined by p ₃ bits of information =[ _IB,1 I _B,2 ... I _B,k' ], the signal S _B determined by p ₄ bits of information =[S( _IB,1 ) S(I _B,2 )...S(I _B,k' )].

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, the frequency-domain OFDM signal generator in step (4) is based on the subcarrier activation pattern in steps (2) and (3), and the step S _A and S _B in (2) and (3) are mapped to corresponding activated subcarriers I _A and I _B through mapper A and mapper B.

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, the time-domain OFDM signal output in step (5) can be expressed as:

x _T ＝[x ₀ x ₁ ... x _N-1 ]＝IDFT{X _T }＝IDFT{[X ₀ X ₁ ... X _N-1 ]}

In the formula, IDFT{} represents the inverse discrete Fourier transform operation, and X _T =[X ₀ X ₁ …X _N-1 ] represents the transmitted frequency-domain OFDM signal, including signal points from constellation diagram A and constellation diagram B and 0 carrier.

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, step (6) is the process of minimizing the PAPR of the time-domain OFDM signal sent, including the following steps:

(61) Calculate initial PAPR value papr, set variable i=1, ii=1, g=1;

(62) Use S _i,g ( _IB,ii ) to replace the signal on the original corresponding subcarrier, and then recalculate the new PAPR value, if the PAPR decreases, replace the original signal point with S _i,g ( _IB,ii ) , and assign the new PAPR value to papr, otherwise the signal point remains unchanged, S _i,g (I _B,ii ) represents one of the optional signals mapped by mapper B in each subframe in the second stage index modulation;

(63) i=i+1, return to step (62), until i=u ends, 1≤i≤u, indicating the optional signal index mapped on the active subcarrier of each subframe in the second stage;

(64) ii=ii+1, return to step (62), until ii=k' ends, 1≤ii≤k', indicating the active subcarrier index of each subframe in the second stage;

(65) g=g+1, return to step (62), until g=G ends, 1≤g≤G, indicating the subframe index of a frame of OFDM signal.

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, the calculation formula of the PAPR value in step (61) is:

In the formula, E{} means to seek expectation, and max{} means to seek the maximum value.

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, maximum likelihood detection is adopted in step (10), and according to step (2) and step (3), the detection process will comprehensively consider each frame For all possible subcarrier activation patterns and mapped signals of OFDM signal subframes, the specific detection process can be expressed as:

In the formula, X _R represents the received frequency domain subcarrier signal, H represents the channel attenuation coefficient in the frequency domain, and the superscript g represents the gth subframe of each OFDM signal, Respectively represent the index information of each subframe at the receiving end and the estimated value of the mapped signal, and then perform de-indexing and de-mapping through the table look-up method according to the detected index information and signals, and restore the binary information.

Further, in the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, through the two-stage index modulation process from step (1) to step (7), the proposed OFDM frequency band utilization can be expressed as:

In the formula, L _CP represents the length of the added cyclic prefix, and G represents the number of subframes of each OFDM signal.

According to another aspect of the technical problem solved by the present invention, a system for reducing peak-to-average power ratio of OFDM based on two-stage index modulation is also provided, and the main modules and functions included are described as follows:

The serial-to-parallel conversion and bit grouping module at the sending end is used to convert the binary sequence to be sent through serial-to-parallel conversion, and convert the serial bit data stream into a parallel data stream, wherein each p bit is a group of input to a frame of OFDM signal A subframe, where an OFDM signal containing N subcarriers is divided into G=N/n subframes, G _g =[X _g,1 X _g,2 ... X _g,n ] means the gth subframe, 1 ≤g≤G, n is the number of subcarriers contained in each subframe, and X represents the subcarriers in one frame of OFDM signal.

The first-stage index selector module is used to select the subcarrier activation pattern in each subframe of the OFDM signal according to the first p ₁ bits in each group of p bits.

A mapper A module, configured to map p ₂ bits in each group of p bits to signal points in the constellation diagram A through the A mapper.

The index selector module in the second stage is configured to reselect the activation pattern of the subcarriers from the inactive subcarriers in each subframe in the first stage according to p ₃ bits in each group of p bits.

The mapper B module is used to map p ₄ bits in each group of p bits to signal points in the constellation diagram B through the B mapper, and the signal points in the constellation diagram B and the signal points in the constellation diagram A are mutually disjoint .

The frequency-domain OFDM signal generator module is used to map the signal to the active subcarrier of the OFDM signal through mapper A and mapper B respectively through the active subcarrier selected according to the index of the first stage and the index of the second stage.

The N-point IDFT module is used to convert the frequency-domain OFDM signal obtained through the two-stage index modulation into the time domain through the IDFT module.

The peak-to-average power ratio comparator module is used to select the signal point mapped by the mapper B through a search algorithm to minimize the PAPR of the OFDM signal.

Parallel-to-serial conversion, cyclic prefix addition, digital-to-analog conversion and up-conversion module at the sending end, used for parallel-serial conversion, adding cyclic prefix, digital signal to analog signal conversion and up-conversion processing on the time-domain OFDM signal generated at the sending end.

The down-conversion, analog-to-digital conversion, cyclic prefix removal, and serial-to-parallel conversion module at the receiving end is used for down-converting, analog-to-digital signal conversion, cyclic prefix removal, and serial-to-parallel conversion of the received time-domain OFDM signal.

The N-point DFT module is used to convert the received OFDM signal in the time domain to the frequency domain.

The maximum likelihood detection, de-indexing and de-mapping modules are used to comprehensively consider all possible subcarrier activation patterns and mapped signals in each OFDM signal subframe by using maximum likelihood detection, and search for all possible cases to detect subcarrier activation patterns And the signal mapped to each active subcarrier, and then recover the binary information through de-indexing and de-mapping processing.

The parallel-to-serial conversion module at the receiving end is used to perform parallel-to-serial conversion on the restored binary information, and restore the original sent binary sequence.

The present invention proposes a method and system for reducing peak-to-average power ratio of OFDM based on two-stage index modulation, which is consistent with traditional index modulation OFDM in the first stage, and uses search algorithm to find the best signal through index modulation in the second stage Mapping minimizes the PAPR value of the transmitted OFDM signal, and increases the transmission bit information, including the index bit and signal bit of the second stage, thereby increasing the spectrum frequency of the system without changing the number of subcarriers of the OFDM signal. At the same time, in the second stage, not all the subcarriers of each subframe of the OFDM signal are activated for data transmission, but some subcarriers are reserved as 0, so as to improve the power efficiency of sending OFDM signals.

Description of drawings

Fig. 1 is a block diagram of the sending end of the OFDM peak-to-average power ratio reduction system based on two-stage index modulation in the present invention.

Fig. 2 is a block diagram of the receiving end of the OFDM peak-to-average power ratio reduction system based on the two-stage index modulation of the present invention.

Fig. 3 is a constellation diagram A and a constellation diagram B in an embodiment of the present invention.

Fig. 4 is a schematic diagram of a bit error rate performance curve of a two-stage index modulation OFDM peak-to-average power ratio reduction system according to an embodiment of the present invention.

FIG. 5 is a schematic diagram of a PAPR performance curve of a two-stage index modulation OFDM peak-to-average power ratio reduction system according to an embodiment of the present invention.

Detailed ways

In order to have a clearer recognition and understanding of the technical features, purposes and effects of the present invention, the specific implementation manners of the present invention will now be described in detail with reference to the accompanying drawings.

Please refer to Fig. 1 and Fig. 2, Fig. 1 shows the block diagram of the transmitting end of the OFDM peak-to-average power ratio reduction system based on two-stage index modulation proposed by the present invention, including serial-to-parallel conversion and bit grouping modules, and a first-stage index selector module , the second stage index selector module, mapper A module, mapper B module, frequency domain OFDM signal generator module, N-point IDFT module, peak-to-average power ratio comparator module, parallel-to-serial conversion, cyclic prefix, digital-to-analog conversion and upconversion modules. Fig. 2 shows the block diagram of the receiving end of the OFDM peak-to-average power ratio reduction system based on two-stage index modulation proposed by the present invention, including down-conversion, analog-to-digital conversion, decyclic prefix and serial-to-parallel conversion modules, N-point DFT modules, and maximum likelihood Ran detection, de-indexing and de-mapping modules, and a parallel-to-serial conversion module.

Set the number of subcarriers of an OFDM signal as N, such a transmitted frequency domain OFDM signal can be expressed as X _T =[X ₀ X ₁ ... X _N-1 ], each OFDM signal subcarrier is divided into G=N/ n subgroups, each subgroup is an OFDM signal subframe, n is the number of subcarriers contained in each subframe, and each OFDM signal subframe carries information of p=p ₁ +p ₂ +p ₃ +p ₄ bits, The bit information corresponding to p ₁ , p ₂ , p ₃ and p ₄ is arranged in sequence, where each OFDM signal contains m=pG bit information in total, and p ₁ , p ₂ , p ₃ and p ₄ are all positive integers.

In the OFDM peak-to-average power ratio reduction method based on two-stage index modulation of the present invention, comprise the following steps:

(1) Serial-to-parallel conversion and bit grouping: convert the binary sequence to be sent through serial-to-parallel conversion, and convert the serial bit data stream into a parallel data stream, wherein each p bit is a group of subframes input to the OFDM signal, A frame of OFDM signal is divided into G subframes, G _g = [X _{g, 1} X _{g, 2} ... X _{g, n} ] (1≤g≤G) represents the gth subframe of the OFDM signal, and X represents a frame of OFDM Subcarriers in the signal, n is the number of subcarriers included in the subframe. For the p bits of information contained in each subframe, the first p ₁ bits and p ₃ bits are respectively input to the index selector of the first stage and the index selector of the second stage, which are used to select the subframe in each subframe of the OFDM signal The activation pattern of the carrier, p ₂ bits and p ₄ bits, are respectively input to mapper A and mapper B for signal mapping.

(2) The first stage index modulation: input the first p ₁ bits in each group of p bits in step (1) to the first stage index selector, and select the active subcarrier in each subframe of the OFDM signal, that is, p ₁ bits determine the activation pattern of subcarriers in G _g , the activated subcarrier index is represented by I _A , and then p ₂ bits in each group of p bits in step (1) are input into mapper A for mapping, for _The mapped signal is denoted by SA. The first stage of index modulation is to select k subcarriers from n subcarriers in each subframe for mapping bit information, p ₁ and p ₂ can be calculated as:

p ₂ =k log ₂ M _A

In the formula Represents the platform function, that is, rounded down, C(n,k) represents the binomial coefficient, that is, the number of combinations of k taken from n, and satisfies k<n at the same time, M _A represents the constellation diagram used in mapper A Size, here mapper A can adopt BPSK constellation diagram, QPSK constellation diagram and so on. The index information determined by p ₁ -bit information is I _A =[IA _,1 I _A,2 ... I _A,k ], and the signal determined by p ₂ -bit information is S _A =[S(IA _,1 )S(I _A,2 )...S(I _A,k )]. When n=4, k=1, and p ₁ =2, the corresponding relationship between index bits and active subcarriers in a subframe can be represented by Table 1.

Table 1

index bit index subframe 0 0 1 [S_A 0 0 0] 0 1 2 [0 S_A 0 0] 1 0 3 [0 0 S_A 0] 1 1 4 [0 0 0 S_A]

(3) Second-stage index modulation: input p ₃ bits in each group of p bits in step (1) to the second-stage index selector, and select again from the inactive subcarriers in G _g in step (2) The subcarrier is activated, and the activated subcarrier index is represented by I _B , and then p ₄ bits in each group of p bits in step (1) are input into mapper B for mapping, and the signal used for mapping is represented by S _B express. The second stage of index modulation is to select k' subcarriers from the n–k unactivated subcarriers in step (2) for mapping bit information, and p ₃ and p ₄ can be calculated as:

p ₄ =k'log ₂ (M _B /u)

In the formula, M _B represents the size of the constellation diagram used in the mapper B, and each u signal point in the constellation diagram B represents the same bit information, which is used to reduce the PAPR of the system, and is randomly selected during the first mapping. The signal points in the constellation diagram B and the constellation diagram A are mutually disjoint, and satisfy k+k'<n at the same time, ensuring that there are 0 carriers, that is, non-activated subcarriers, so as to improve the power efficiency of the system. The index information I _B determined by p ₃ bits of information =[ _IB,1 I _B,2 ... I _B,k' ], the signal S _B determined by p ₄ bits of information =[S( _IB,1 ) S(I _B,2 )...S(I _B,k' )]. Mapper B can use QPSK constellation diagram, 8PSK constellation diagram, etc. In order not to reduce the spectral efficiency of the system and reduce PAPR, the size of constellation diagram B can be larger than constellation diagram A. On the basis of index modulation in the first stage, when k'=1 and p ₃ =1, the corresponding relationship between index bits and active subcarriers in a subframe can be expressed in Table 2.

Table 2

If QPSK constellation diagram is used for data mapping in mapper B, signal points (d, d) and (-d, -d) represent the same bit information, (-d, d) and (d, -d) represent The same bit information is used to reduce the PAPR of the index-modulated OFDM system, as shown in FIG. 3 , where the hollow signal represents constellation diagram A, and the solid signal represents constellation diagram B.

(4) Frequency-domain OFDM signal generation, the frequency-domain OFDM signal generator is based on the subcarrier activation patterns in steps (2) and (3), and S _A and S _B in steps (2) and (3) are mapped Mapper A and mapper B are mapped to corresponding active subcarriers I _A and I _B.

(5) Convert the frequency-domain OFDM signal obtained in step (4) to the time domain through the inverse discrete Fourier transform (IDFT) of N points, and the output time-domain OFDM signal can be expressed as:

x _T ＝[x ₀ x ₁ ... x _N-1 ]＝IDFT{X _T }＝IDFT{[X ₀ X ₁ ... X _N-1 ]}

In the formula, IDFT{} represents the inverse discrete Fourier transform operation, and X _T includes signal points and zero carriers from constellation diagram A and constellation diagram B.

(6) Input the time-domain OFDM signal obtained in step (5) into the peak-to-average power ratio comparator, and find the best combination of signal mapping in the second stage through a search algorithm to minimize PAPR. The PAPR minimization process of sending OFDM signal comprises the following steps:

(61) Calculate the initial PAPR value papr, the calculation formula is:

In the formula, E{} means to seek expectation, max{} means to seek the maximum value, and set variables i=1, ii=1, g=1;

(62) Use S _i,g ( _IB,ii ) to replace the signal on the original corresponding subcarrier, and then recalculate the new PAPR value, if the PAPR decreases, replace the original signal point with S _i,g ( _IB,ii ) , and assign the new PAPR value to papr, otherwise the signal point remains unchanged, S _i,g (I _B,ii ) represents one of the optional signals mapped by mapper B in each subframe in the second stage index modulation;

(63) i=i+1, return to step (62), until i=u ends, 1≤i≤u, indicating the optional signal index mapped on the active subcarrier of each subframe in the second stage;

(64) ii=ii+1, return to step (62), until ii=k' ends, 1≤ii≤k', indicating the active subcarrier index of each subframe in the second stage;

(65) g=g+1, return to step (62), until g=G ends, 1≤g≤G, indicating the subframe index of a frame of OFDM signal.

(7) The PAPR-minimized time-domain OFDM signal obtained in step (6) is sent to the channel for transmission after parallel-to-serial conversion, cyclic prefix addition, digital-to-analog conversion and up-conversion processing. Through the two-stage index modulation process from step (1) to step (7), the proposed OFDM frequency band utilization can be expressed as:

In the formula, L _CP represents the length of the added cyclic prefix, and G represents the number of subframes of each OFDM signal.

(8) At the receiving end, the received OFDM signal is subjected to down-conversion, analog-to-digital conversion, cyclic prefix removal and serial-to-parallel conversion.

(9) Discrete Fourier transform (DFT) is performed on the output signal of step (8), and the time-domain OFDM signal is converted into the frequency domain.

(10) The output signal of step (9) is subjected to maximum likelihood detection, de-indexing and de-mapping processing, and is restored to binary information. According to step (2) and step (3), the maximum likelihood detection process will comprehensively consider all possible subcarrier activation patterns and mapped signals of each OFDM signal subframe, and the specific detection process can be expressed as:

In the formula, X _R represents the received frequency domain subcarrier signal, H represents the channel attenuation coefficient in the frequency domain, and the superscript g represents the gth subframe of each OFDM signal, Respectively represent the index information of each subframe at the receiving end and the estimated value of the mapped signal, and then perform de-indexing and de-mapping through the table look-up method according to the detected index information and signals, and restore the binary information.

(11) Perform parallel-to-serial conversion on the output signal of step (10) to obtain the original sent binary sequence.

Example:

Specific parameter scheme: the number of subcarriers of an OFDM signal N=128, the number of subframes of each OFDM signal G=32, the number of subcarriers in each subframe n=4, the number of subcarriers activated in the first stage k=1, the number of subcarriers activated in the second stage k'=1, the mapper A uses the BPSK constellation diagram, that is, M _A =2, and the mapper B uses the QPSK constellation diagram, that is, M _B =4, u=2 It means that the two signal points on the diagonal in the QPSK constellation diagram represent the same bit information, as shown in Figure 3, which is used to reduce the PAPR of the OFDM signal through the search algorithm, and the adjacent signals in constellation diagram B and constellation diagram A The point distance is d, and the length of the cyclic prefix L _CP =16. Without considering the reduction of PAPR, each subframe can contain 6 bits of information, and the spectral efficiency of the system can be calculated as 1.3333 bits/second/Hz. In the case of considering the reduction of PAPR, each subframe contains 5 bits of information, and the system’s The spectral efficiency can be calculated to be 1.1111 bits/second/Hz. The channel adopts frequency selective Rayleigh fading channel, and the channel impulse response length of Rayleigh channel is 10.

The simulation results are shown in Figure 4 and Figure 5. The horizontal axis of Figure 4 represents the signal-to-noise ratio, that is, the power per bit of the signal to the noise power, and the vertical axis represents the bit error rate. In order to prove the advantages of the present invention, under the same spectral efficiency conditions, Fig. 4 also provides the simulation results of traditional index modulation OFDM and dual-mode index modulation OFDM, the number of subcarriers in each subframe is 4, and the traditional index modulation OFDM system 16QAM is used for signal mapping, and k=1 subcarriers are activated in each subframe; in the dual-mode index modulation OFDM system, mode A adopts BPSK constellation diagram, mode B adopts BPSK constellation diagram perpendicular to A, and its signal power Greater than the signal in mode A, where k=2 subcarriers are mapped with mode A, and the other two subcarriers are mapped with mode B. It can be seen from the simulation results that under the same spectral efficiency condition, the bit error rate performance of the OFDM system based on two-stage index modulation proposed by the present invention is better than that of the traditional OFDM system based on index modulation. In the case of considering the PAPR reduction algorithm, the OFDM peak-to-average power ratio reduction system of the two-stage index modulation proposed by the present invention can also provide better bit error rate performance, but the spectral efficiency of the system is slightly reduced, but the PAPR performance is similar to that of the classic Compared with the OFDM system, it can improve about 5dB.

Compared with the prior art, the present invention has the following effect gains: in terms of peak-to-average power ratio reduction, the OFDM peak-to-average power ratio reduction system based on two-stage index modulation proposed by the present invention can effectively improve system PAPR performance; In terms of utilization rate, the OFDM peak-to-average power ratio reduction system based on the two-stage index modulation proposed by the present invention is consistent with the traditional index modulation OFDM in the first stage, and the transmission bit information is increased through the index modulation in the second stage, including the second The index bits and signal bits of the stage, thereby improving the spectrum frequency of the system without changing the number of OFDM signal subcarriers, and at the same time achieving the function of improving the PAPR of the system through the search algorithm; In the OFDM peak-to-average power ratio reduction system based on two-stage index modulation, in the second stage, all subcarriers that were not activated in the first stage of each subframe of the OFDM signal are not activated for data transmission, but some subcarriers are reserved as 0, compared with the traditional dual-mode index modulation OFDM technology, it can improve the power efficiency of sending OFDM signals. Simultaneously, under the same condition of spectral efficiency, or consider the situation that PAPR reduces (at the expense of reducing spectral efficiency a little), the system that the present invention proposes has better performance than traditional index modulation OFDM and dual-mode index modulation OFDM system. bit error rate performance.

Embodiments of the present invention have been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementations, and the above-mentioned specific implementations are only illustrative, rather than restrictive, and those of ordinary skill in the art will Under the enlightenment of the present invention, many forms can also be made without departing from the gist of the present invention and the protection scope of the claims, and these all belong to the protection of the present invention.

Claims (10)

1. a method for reducing the peak-to-average power ratio of OFDM based on two-stage index modulation, is characterized in that, comprises the steps: (1) Serial-to-parallel conversion and bit grouping: convert the binary sequence to be sent through serial-to-parallel conversion, and convert the serial bit data stream into a parallel data stream, where each p bit is a group input to a sub-frame of OFDM signal frame, where a frame of OFDM signals containing N subcarriers is divided into G=N/n subframes, G _g =[X _g,1 X _g,2 ... X _g,n ] means the gth subframe, 1≤g ≤G, n is the number of subcarriers contained in each subframe, and X represents the subcarriers in a frame of OFDM signal; (2) The first stage index modulation: input the first p ₁ bits in each group of p bits in step (1) to the first stage index selector, and select the active subcarrier in each subframe of the OFDM signal, that is, p ₁ Bits determine the activation pattern of subcarriers in G _g , and then p ₂ bits in each group of p bits in step (1) are input into mapper A for mapping; (3) Second-stage index modulation: input p ₃ bits in each group of p bits in step (1) to the second-stage index selector, and select again from the inactive subcarriers in G _g in step (2) The subcarrier is activated, and then p ₄ bits in each group of p bits in step (1) are input into mapper B for mapping; (4) Frequency-domain OFDM signal generation, according to the subcarrier activation patterns in steps (2) and (3), pass the p ₂ + p ₄ bits in each group of p bits in step (1) through mapper A and mapper B is mapped to the corresponding activated subcarrier; (5) the frequency-domain OFDM signal obtained by step (4) is converted to the time domain by the inverse discrete Fourier transform of N points; (6) The time-domain OFDM signal that step (5) obtains is input into the peak-to-average power ratio comparator, and finds the best combination of the second-stage signal mapping by a search algorithm, so that PAPR is minimized; (7) the time-domain OFDM signal of the minimum PAPR obtained by step (6) is sent into the channel after parallel-serial conversion, adding cyclic prefix, digital-to-analog conversion and up-conversion processing for transmission; (8) At the receiving end, the received OFDM signal is subjected to down-conversion, analog-to-digital conversion, cyclic prefix removal and serial-to-parallel conversion processing; (9) Discrete Fourier Transform is carried out to the output signal of step (8), and the time domain OFDM signal is converted to the frequency domain; (10) The output signal of step (9) is carried out maximum likelihood detection, deindexing and demapping processing, recovers as binary information; (11) Perform parallel-to-serial conversion on the output signal of step (10) to obtain the original sent binary sequence. 2. the OFDM peak-to-average power ratio reduction method based on two-stage index modulation according to claim 1, is characterized in that, the number of bits p=p contained in each subframe of a frame OFDM signal in step ( ₁ ) p ₂ +p ₃ +p ₄ , where the first p ₁ bits and p ₃ bits are respectively input to the first-stage index selector and the second-stage index selector for selecting the activation of subcarriers in each subframe of the OFDM signal pattern, p ₂ bits and p ₄ bits are respectively input to mapper A and mapper B for signal mapping, and bit information corresponding to p ₁ , p ₂ , p ₃ and p ₄ are arranged in sequence. 3. the OFDM peak-to-average power ratio reduction method based on two-stage index modulation according to claim 1, is characterized in that, the first-stage index modulation of step (2) is selected from n subcarriers of each subframe k subcarriers are used to map bit information, so: p ₂ =k log ₂ M _A In the formula Represents the platform function, that is, rounded down, C(n,k) represents the binomial coefficient, that is, the number of combinations of k taken from n, and satisfies k<n at the same time, M _A represents the constellation diagram used in mapper A size, the index information determined by p ₁ -bit information is I _A =[IA _,1 I _A,2 ... I _A,k ], and the signal determined by p ₂ -bit information is S _A =[S(I _{A ,1} ) S(I _A,2 ) … S(I _A,k )]. 4. the OFDM peak-to-average power ratio reduction method based on two-stage index modulation according to claim 1, is characterized in that, the second stage index modulation of step (3) is n-k in step (2) Select k' subcarriers from the unactivated subcarriers for mapping bit information, so: p ₄ =k'log ₂ (M _B /u) In the formula, M _B represents the size of the constellation diagram used in the mapper B. Each u signal point in the constellation diagram B represents the same bit information, which is used to reduce the PAPR of the system. It is randomly selected during the first mapping, and the constellation diagram B and the constellation diagram The signal points in Figure A are mutually disjoint, satisfying k+k'<n at the same time, ensuring that there are 0 carriers, that is, inactive subcarriers, in order to improve the power efficiency of the system, and the index information I _B determined by p ₃ bits of information =[I _B,1 I _B,2 ... I _B,k' ], the signal S _B determined by p ₄ bits of information =[S(I _B,1 ) S( _IB,2 ) ... S(I _{B ,k'} )]. 5. the OFDM peak-to-average power ratio reduction method based on two-stage index modulation according to claim 1, is characterized in that, step (4) frequency domain OFDM signal generator is according to the subclass in step (2) and (3) The carrier activation pattern maps SA and S _B in steps (2) and (3) to corresponding activated subcarriers I _A and I _B through mapper A and mapper _B. 6. the OFDM peak-to-average power ratio reduction method based on two-stage index modulation according to claim 1, is characterized in that, the time-domain OFDM signal that step (5) outputs is: x _T ＝[x ₀ x ₁ ... x _N-1 ]＝IDFT{X _T }＝IDFT{[X ₀ X ₁ ... X _N-1 ]} In the formula, IDFT{} represents the inverse discrete Fourier transform operation, and X _T =[X ₀ X ₁ … X _N-1 ] represents the transmitted frequency-domain OFDM signal, including signal points from constellation diagram A and constellation diagram B and 0 carrier. 7. OFDM peak-to-average power ratio reduction method according to claim 1, is characterized in that, step (6) is the PAPR minimization process that sends OFDM signal, comprises the steps: (61) Calculate initial PAPR value papr, set variables i=1, ii=1, g=1, the calculation formula of PAPR value is: In the formula, E{} means to seek expectation, and max{} means to seek the maximum value; (62) Use S _i,g ( _IB,ii ) to replace the signal on the original corresponding subcarrier, and then recalculate the new PAPR value, if the PAPR decreases, replace the original signal point with S _i,g ( _IB,ii ) , and assign the new PAPR value to papr, otherwise the signal point remains unchanged, S _i,g (I _B,ii ) represents one of the optional signals mapped by mapper B in each subframe in the second stage index modulation; (63) i=i+1, return to step (62), until i=u ends, 1≤i≤u, indicating the optional signal index mapped on the active subcarrier of each subframe in the second stage; (64) ii=ii+1, return to step (62), until ii=k' ends, 1≤ii≤k', indicating the active subcarrier index of each subframe in the second stage; (65) g=g+1, return to step (62), until g=G ends, 1≤g≤G, indicating the subframe index of a frame of OFDM signal. 8. the OFDM peak-to-average power ratio reduction method based on two-stage index modulation according to claim 1, is characterized in that, adopts maximum likelihood detection in step (10), according to step (2) and step (3), detects The process will comprehensively consider all possible subcarrier activation patterns and mapped signals of each OFDM signal subframe. The specific detection process is expressed as: In the formula, X _R represents the received frequency domain subcarrier signal, H represents the channel attenuation coefficient in the frequency domain, and the superscript g represents the gth subframe of each OFDM signal, Respectively represent the index information of each subframe at the receiving end and the estimated value of the mapped signal, and then perform de-indexing and de-mapping through the table look-up method according to the detected index information and signals, and restore the binary information. 9. the OFDM peak-to-average power ratio reduction method based on two-stage index modulation according to claim 1, is characterized in that, by the index modulation process of two stages of step (1) to step (7), the proposed OFDM frequency band Utilization is: In the formula, L _CP represents the length of the added cyclic prefix, and G represents the number of subframes of each OFDM signal. 10. A system for reducing the peak-to-average power ratio of OFDM based on two-stage index modulation, characterized in that it comprises the following modules: The serial-to-parallel conversion and bit grouping module at the sending end is used to convert the binary sequence to be sent through serial-to-parallel conversion, and convert the serial bit data stream into a parallel data stream, wherein each p bit is a group of input to a frame of OFDM signal A subframe, where an OFDM signal containing N subcarriers is divided into G=N/n subframes, G _g =[X _g,1 X _g,2 ... X _g,n ] means the gth subframe, 1 ≤g≤G, n is the number of subcarriers contained in each subframe, and X represents the subcarriers in a frame of OFDM signal; The first stage index selector module is used to select the subcarrier activation pattern in each subframe of the OFDM signal according to the first p ₁ bits in each group of p bits; The mapper A module is used to map p ₂ bits in each group of p bits to signal points in the constellation diagram A through the A mapper; The second stage index selector module is used to select the activation pattern of the subcarrier again from the subcarriers that are not activated in each subframe in the first stage according to p ₃ bits in each group of p bits; The mapper B module is used to map p ₄ bits in each group of p bits to signal points in the constellation diagram B through the B mapper, and the signal points in the constellation diagram B and the signal points in the constellation diagram A are mutually disjoint ; The frequency domain OFDM signal generator module is used to map the signal to the active subcarrier of the OFDM signal through the mapper A and the mapper B respectively according to the active subcarriers selected by the index of the first stage and the index of the second stage; The N-point IDFT module is used to convert the frequency-domain OFDM signal obtained through the two-stage index modulation to the time domain through the IDFT module; The peak-to-average power ratio comparator module is used to select the signal point mapped by the mapper B through a search algorithm, so that the PAPR of the OFDM signal is minimized; Parallel-to-serial conversion, adding cyclic prefix, digital-to-analog conversion and up-conversion module at the sending end, used for parallel-serial conversion, adding cyclic prefix, converting digital signal to analog signal and up-converting the time-domain OFDM signal generated at the sending end; The down-conversion, analog-to-digital conversion, cyclic prefix removal and serial-to-parallel conversion module at the receiving end is used to perform down-conversion, analog-to-digital signal conversion, cyclic prefix removal and serial-to-parallel conversion processing on the received time-domain OFDM signal; The N-point DFT module is used to convert the received OFDM signal in the time domain to the frequency domain; The maximum likelihood detection, de-indexing and de-mapping modules are used to comprehensively consider all possible subcarrier activation patterns and mapped signals in each OFDM signal subframe by using maximum likelihood detection, and search for all possible cases to detect subcarrier activation patterns And the signal mapped to each active subcarrier, and then restore the binary information through de-indexing and de-mapping processing; The parallel-to-serial conversion module at the receiving end is used to perform parallel-to-serial conversion on the restored binary information, and restore the original sent binary sequence.