阅读说明：本技术 一种实部虚部零填充三模ofdm索引调制算法及系统 (Real part and imaginary part zero filling three-mode OFDM index modulation algorithm and system ) 是由 王孟依 于 2020-12-28 设计创作，主要内容包括：本发明涉及子载波索引调制领域,具体涉及一种实部虚部零填充三模OFDM索引调制算法及系统,该算法将高阶星座图中的符号点的实部和虚部分量分别看成两个PAM调制,通过对PAM调制星座图进行设计,从同向分量和正交分量两个方面进行零填充三模索引调制,从而将索引比特扩充了一倍。在接收端,采用一种改进的两级LLR解调器,其将检测出活跃子载波的激活样式,以便恢复出原始的比特信息。仿真结果表明,在几乎没有信噪比损失的情况下,实部虚部零填充三模OFDM索引调制系统较原系统获得了频谱增益。(The invention relates to the field of subcarrier index modulation, in particular to a real part and imaginary part zero filling three-mode OFDM index modulation algorithm and a system. At the receiving end, an improved two-stage LLR demodulator is employed that will detect the active pattern of active subcarriers to recover the original bit information. Simulation results show that the real part and the imaginary part zero-filling three-mode OFDM index modulation system obtains spectrum gain compared with the original system under the condition of almost no loss of signal-to-noise ratio.)

1. A real part and imaginary part zero filling three-mode OFDM index modulation algorithm is characterized by comprising the following steps:

step 1, serial-parallel conversion and bit separation: the binary serial bit stream with the length of B is converted into a parallel data stream through serial-parallel conversion;

each P_IQ-ZTMInputting bits into an index modulation module to obtain a subframe of a frame of OFDM signals, wherein one frame of OFDM signals comprises N subcarriers; the system has G ═ N/N subframes in total, and N is the number of subcarriers contained in each subframe; p_IQ-ZTM＝P₁+P₂，P₁To index a bit, P₂Is a sign bit;

step 2, P_IQ-ZTMBit input sub-module bit separator, which is divided into two bit streams with equal length and respectively carries out zero-padding three-mode index modulation on the same-direction component and the orthogonal component;

step 2.1, aiming at the equidirectional component;

step 2.1.1, P₁The/2 bit enters an index selector to select k active subcarriers from n subcarriers to obtain a constellation diagram M_ASymbol point S of_AConstellation diagram M_BSymbol point S of_BIndex of modulated active subcarriersThe number of which is respectively k₁And k₂And k is₁+k₂K is; the output of the index selector is: j. the design is a square_β,I＝[J_β,I(1) J_β,I(2)...J_β,I(k₁)...J_β,I(k)](ii) a Beta is a beta (beta is more than or equal to 1 and less than or equal to G) sub-frame;

step 2.1.2, P₂/2 bit input M_AAnd M_BA joint mapper for the sum of the two combined constellations, mapping into symbol points on the joint constellation; combining the output of the index selector in step 2.1.1, modulating the corresponding active sub-carriers by using the symbol points, and the output of the joint mapper is as follows: x_β,I＝[X_β,I(1) X_β,I(2)...X_β,I(k₁)...X_β,I(k)]β ═ 1,2,. gtg; wherein, X_β,I(γ), γ ═ 1, 2.., n, with the value S_AOr S_B；

Step 2.2, for the orthogonal component, the modulation of the index selector and the joint mapper repeats step 2.1.1 and step 2.1.2, with the output J respectively_β,QAnd X_β,Q；

Wherein, P₁The first half and the second half of the bits are respectively input into the index selectors of the same-direction component and the orthogonal component to generate a subcarrier arrangement pattern, P, of each subframe₂The first half and the second half of the bit are respectively input into a joint mapper of the same direction component and the orthogonal component for signal mapping; therefore, the following steps are carried out:

in the above formulaDenotes rounding down, C_n ^kRepresenting binomial coefficients, i.e. k from n sub-carriers, satisfying k<n; taking 2 in the above formula is to consider the homodromous component and the orthogonal component to carry out index modulation simultaneously;

and 3, according to the output signals of the step 2.1 and the step 2.2, respectively taking the same-direction component and the orthogonal component as a real part and an imaginary part of a subframe, and obtaining a beta-th subframe as: x_β＝X_β,I+jX_β,Q(ii) a The output of each index modulation module is:X_i＝X_i,I+jX_i,Q1,2, ·, G; the OFDM block generator arranges the outputs of the G index modulation modules, and obtains a frame of OFDM signal on the frequency domain as: x ═ X (1) X (2).. X (n)](ii) a Considering the presence of inactive subcarriers, there are: x (α), α ═ 1, 2.. the real and imaginary parts of N take on the value S_A、S_BOr {0 };

step 4, performing Inverse Fast Fourier Transform (IFFT) of N points on the frequency domain OFDM signal obtained in the step 3 to convert the frequency domain OFDM signal into a time domain;

step 5, inputting the time domain OFDM signal of the step 4 into a Rayleigh frequency selective fading channel after parallel-serial conversion, cyclic prefix addition, digital-to-analog conversion and up-conversion;

step 6, at the receiving end, carrying out down-conversion, analog-to-digital conversion, cyclic prefix removal and serial-parallel conversion on the OFDM signal;

and 7, performing Fast Fourier Transform (FFT) of N points on the output signal of the step 6 to obtain an OFDM receiving signal on a frequency domain: y ═ Y (1) Y (2.. Y (n))]Wherein the beta group submodule is: y is_β＝[Y_β(1) Y_β(2)...Y_β(n)]；

Step 8, carrying out improved two-stage log-likelihood ratio LLR detection on the output signal of the step 7 to obtain a result S_AAnd S_BAn index of the modulated active subcarriers;

step 9, carrying out index bit estimation and symbol bit estimation on the output signal of the step 8 to recover a binary data stream;

and step 10, inputting the output signal of the step 8 into a parallel-serial converter and comparing the output signal with the original binary information to obtain the bit error rate of the system.

2. The real-imaginary zero-padding three-mode OFDM index modulation algorithm of claim 1 wherein the improved two-stage log-likelihood ratio LLR detection of step 8 comprises:

step 8.1, detecting by sub-modules one by one; firstly, carrying out single-key zero-forcing equalization on an output signal of the beta submodule;

step 8.2, taking a real part from the output signal of the step 8.1 and carrying out first-stage LLR detection to obtain an index of the active subcarrier;

step 8.3, according to the detection result in the step 8.2, taking a real part from the output signal of the step 8.1 and carrying out second-stage LLR detection to obtain a second-stage LLR signal_AAnd S_BA modulated subcarrier index;

and 8.4, repeating the step 8.2 and the step 8.3 in the two-stage LLR detection process of the orthogonal component.

3. The real-imaginary zero-padding three-mode OFDM index modulation algorithm of claim 2 wherein the zero-forcing equalization of step 8.1 is expressed as:

4. the real-imaginary zero-padding three-mode OFDM index modulation algorithm of claim 2, wherein the first-stage LLR detection of step 8.2 is expressed as:

where α ═ 1, 2., n, δ_C,i＝M_A∪M_BThe ith symbol point, Re (.) on the joint constellation represents the real part operation.

5. The real-imaginary zero-padding three-mode OFDM index modulation algorithm of claim 2, wherein the second-stage LLR detection of step 8.3 is expressed as:

in the formula S_A,iAnd S_B,iRespectively representing the ith symbol point on constellation a and constellation B.

6. The real-imaginary zero-padding three-mode OFDM index modulation algorithm of claim 2, wherein the two-stage LLR detection of the orthogonal components of step 8.4 is represented as:

and Im (.) in the formula represents the operation of taking an imaginary part.

7. System for the real-imaginary zero-padding three-modulus OFDM index modulation algorithm according to any of claims 1-6, characterized by comprising a transmitting-side serial-to-parallel conversion and bit separation module for converting a binary serial bit stream of length B into a parallel data stream, where each P is P_IQ-ZTMInputting bits into an index modulation module to obtain a subframe of a frame of OFDM signals, wherein one frame of OFDM signals comprises N subcarriers; the whole system has G-N/N subframes, wherein N is the number of subcarriers contained in each subframe;

sub-module bit separator module for separating P_IQ-ZTMThe bit is averagely divided into two bit streams which are respectively distributed to a same-direction component and an orthogonal component for zero padding three-mode index modulation;

index selector module according to P₁The/2 bit determines the subcarrier activation pattern for each subframe, determines S_AAnd S_BModulated subcarrier index, the number of which is k respectively₁And k₂And both satisfy the constraint condition: k is a radical of₁+k₂＝k；

A joint mapper module for mapping according to P₂The/2 bit selects a symbol point from the joint constellation diagram to modulate the corresponding active subcarrier;

the adding module is used for adding the same-direction component and the orthogonal component which are respectively used as a real part and an imaginary part to obtain a subframe of the OFDM signal;

the OFDM signal generator module is used for arranging the OFDM signals of each subframe to obtain a frame of OFDM signals on a frequency domain;

the N-point IFFT module converts a frame of OFDM signals of the index modulation system from a frequency domain to a time domain through IFFT operation of N points;

the transmitting terminal serial-parallel conversion, cyclic prefix adding, digital-to-analog conversion and up-conversion module is used for performing serial-parallel conversion, cyclic prefix adding and digital signal conversion on a frame of time domain OFDM signal of the transmitting terminal to obtain an analog signal and a baseband signal, and modulating the analog signal and the baseband signal into a band-pass signal for processing;

the receiving end down-conversion module, the analog-to-digital conversion module, the cyclic prefix removal module and the serial-to-parallel conversion module are used for carrying out band-pass signal modulation on a frame of time domain OFDM signals of the receiving end into baseband signals, converting the analog signals into digital signals, and removing the cyclic prefix and the serial-to-parallel conversion processing;

the N-point FFT module converts a frame of OFDM signal of the receiving end from a time domain to a frequency domain through FFT operation of N points;

a two-stage log-likelihood ratio detection module for detecting the activation pattern of the sub-carrier by using two-stage LLR demodulation algorithm and detecting the S_AAnd S_BA modulated subcarrier index;

the de-indexing and de-symbolizing module is used for comparing the lookup table with the joint constellation diagram according to the detected subcarrier activation mode and restoring an index bit and a symbolic bit;

and the parallel-serial conversion and bit error rate calculation module is used for converting the recovered parallel binary bit stream into a serial data stream and comparing the serial data stream with the original index bit and the symbol bit to obtain the bit error rate of the system.

Technical Field

The invention belongs to the field of subcarrier index modulation, and particularly relates to a real part and imaginary part zero filling three-mode OFDM index modulation algorithm and system.

Background

The orthogonal frequency division multiplexing technology based on subcarrier index modulation, which utilizes on-off keying modulation to transmit information, is considered as one of the candidate technologies for the 5G wireless communication system. In order to further increase the data transmission rate of the system, an OFDM-IM (OFDM-IM) system based on index modulation is proposed. In the system, information is not only represented by symbol points on a constellation diagram, but also represented by indexes of subcarriers, and the breakthrough of the system from two dimensions to three dimensions is realized. The OFDM-IM system obtains the index of the active subcarrier by using a table look-up method or a combined number method, thereby improving the frequency spectrum efficiency and the energy efficiency of the system. To further improve the system's ability to transmit index bits and symbol bits, a zero-padding three-mode OFDM index modulation (ZTM-OFDM-IM) system modulates active subcarriers using two mutually exclusive constellations. In this system, the subcarriers can be modulated by symbol points or {0} on constellation a, constellation B, adding to the permutation pattern of the subcarrier indices. The system takes advantage of both high spectral efficiency and energy efficiency by allowing the presence of inactive subcarriers.

Recently, in order to further improve the spectrum efficiency of the ZTM-OFDM-IM system, some researchers have proposed a generalized ZTM-OFDM-IM (GZTM-OFDM-IM) system in which the number and allocation pattern of active subcarriers are made variable, thereby enriching the arrangement pattern of subcarrier indexes. However, under the condition of a high-order constellation diagram (M >2), the spectrum gains of the two index modulation systems can be ignored due to the inactive subcarriers, and the application of the system is limited. Therefore, a zero padding three-mode OFDM system suitable for high-order constellations is yet to be developed.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a real part and imaginary part zero filling three-mode OFDM index modulation (RI-ZTM-OFDM-IM) algorithm and a system.

In order to solve the technical problems, the invention adopts the following technical scheme: a real part and imaginary part zero filling three-mode OFDM index modulation algorithm comprises the following steps:

step 1, serial-parallel conversion and bit separation: the binary serial bit stream with the length of B is converted into a parallel data stream through serial-parallel conversion;

each P_IQ-ZTMInputting bits into an index modulation module to obtain a subframe of a frame of OFDM signals, wherein one frame of OFDM signals comprises N subcarriers; the system has G ═ N/N subframes in total, and N is the number of subcarriers contained in each subframe; p_IQ-ZTM＝P₁+P₂，P₁To index a bit, P₂Is a sign bit;

step 2, P_IQ-ZTMBit input sub-module bit separator, which is divided into two bit streams with equal length and respectively carries out zero-padding three-mode index modulation on the same-direction component and the orthogonal component;

step 2.1, aiming at the equidirectional component;

step 2.1.1, P₁Ratio of 2 toThe special entry index selector selects k active subcarriers from n subcarriers to obtain a constellation diagram M_ASymbol point S of_AConstellation diagram M_BSymbol point S of_BIndex of modulated active subcarriersThe number of which is respectively k₁And k₂And k is₁+k₂K is; the output of the index selector is: j. the design is a square_β,I＝[J_β,I(1)J_β,I(2)...J_β,I(k₁)...J_β,I(k)](ii) a Beta is a beta (beta is more than or equal to 1 and less than or equal to G) sub-frame;

step 2.1.2, P₂/2 bit input M_AAnd M_BA joint mapper for the sum of the two combined constellations, mapping into symbol points on the joint constellation; combining the output of the index selector in step 2.1.1, modulating the corresponding active sub-carriers by using the symbol points, and the output of the joint mapper is as follows: x_β,I＝[X_β,I(1)X_β,I(2)...X_β,I(k₁)...X_β,I(k)]β ═ 1,2,. gtg; wherein, X_β,I(γ), γ ═ 1, 2.., n, with the value S_AOr S_B；

Step 2.2, for the orthogonal component, the modulation of the index selector and the joint mapper repeats step 2.1.1 and step 2.1.2, with the output J respectively_β,QAnd X_β,Q；

Wherein, P₁The first half and the second half of the bits are respectively input into the index selectors of the same-direction component and the orthogonal component to generate a subcarrier arrangement pattern, P, of each subframe₂The first half and the second half of the bit are respectively input into a joint mapper of the same direction component and the orthogonal component for signal mapping; therefore, the following steps are carried out:

c represents downward rounding of the middle ++, of the above formula_n ^kRepresenting binomial coefficients, i.e. k from n sub-carriers, satisfying k<n; on the upper partTaking 2 as index modulation by considering the same-direction component and the orthogonal component;

and 3, according to the output signals of the step 2.1 and the step 2.2, respectively taking the same-direction component and the orthogonal component as a real part and an imaginary part of a subframe, and obtaining a beta-th subframe as: x_β＝X_β,I+jX_β,Q(ii) a The output of each index modulation module is: x_i＝X_i,I+jX_i,Q1,2, ·, G; the OFDM block generator arranges the outputs of the G index modulation modules, and obtains a frame of OFDM signal on the frequency domain as: x ═ X (1) X (2).. X (n)](ii) a Considering the presence of inactive subcarriers, there are: x (α), α ═ 1, 2.. the real and imaginary parts of N take on the value S_A、S_BOr {0 };

step 4, performing Inverse Fast Fourier Transform (IFFT) of N points on the frequency domain OFDM signal obtained in the step 3 to convert the frequency domain OFDM signal into a time domain;

step 5, inputting the time domain OFDM signal of the step 4 into a Rayleigh frequency selective fading channel after parallel-serial conversion, cyclic prefix addition, digital-to-analog conversion and up-conversion;

step 6, at the receiving end, carrying out down-conversion, analog-to-digital conversion, cyclic prefix removal and serial-parallel conversion on the OFDM signal;

and 7, performing Fast Fourier Transform (FFT) of N points on the output signal of the step 6 to obtain an OFDM receiving signal on a frequency domain: y ═ Y (1) Y (2.. Y (n))]Wherein the beta group submodule is: y is_β＝[Y_β(1)Y_β(2)...Y_β(n)]；

Step 8, carrying out improved two-stage log-likelihood ratio LLR detection on the output signal of the step 7 to obtain a result S_AAnd S_BAn index of the modulated active subcarriers;

step 9, carrying out index bit estimation and symbol bit estimation on the output signal of the step 8 to recover a binary data stream;

and step 10, inputting the output signal of the step 8 into a parallel-serial converter and comparing the output signal with the original binary information to obtain the bit error rate of the system.

In the above real-part and imaginary-part zero-padding three-mode OFDM index modulation algorithm, the improved two-stage log-likelihood ratio LLR detection in step 8 comprises:

step 8.1, detecting by sub-modules one by one; firstly, carrying out single-key zero-forcing equalization on an output signal of the beta submodule;

step 8.2, taking a real part from the output signal of the step 8.1 and carrying out first-stage LLR detection to obtain an index of the active subcarrier;

step 8.3, according to the detection result in the step 8.2, taking a real part from the output signal of the step 8.1 and carrying out second-stage LLR detection to obtain a second-stage LLR signal_AAnd S_BA modulated subcarrier index;

and 8.4, repeating the step 8.2 and the step 8.3 in the two-stage LLR detection process of the orthogonal component.

In the real part and imaginary part zero padding three-mode OFDM index modulation algorithm, the zero-forcing equalization in step 8.1 is expressed as:

in the real part and imaginary part zero padding three-mode OFDM index modulation algorithm, the first-stage LLR detection in step 8.2 is expressed as:

where α ═ 1, 2., n, δ_C,i＝M_A∪M_BThe ith symbol point, Re (.) on the joint constellation represents the real part operation.

In the real part and imaginary part zero padding three-mode OFDM index modulation algorithm, the second-stage LLR detection in step 8.3 is expressed as:

in the formula S_A,iAnd S_B,iRespectively representing the ith symbol point on constellation a and constellation B.

In the real part and imaginary part zero padding three-mode OFDM index modulation algorithm, the two-stage LLR detection of the orthogonal component in step 8.4 is expressed as:

and Im (.) in the formula represents the operation of taking an imaginary part.

A system for a real-imaginary zero-padding three-mode OFDM index modulation algorithm comprises a transmitting-end serial-to-parallel conversion and bit separation module for converting a binary serial bit stream of length B into a parallel data stream, wherein each P_IQ-ZTMInputting bits into an index modulation module to obtain a subframe of a frame of OFDM signals, wherein one frame of OFDM signals comprises N subcarriers; the whole system has G-N/N subframes, wherein N is the number of subcarriers contained in each subframe;

sub-module bit separator module for separating P_IQ-ZTMThe bit is averagely divided into two bit streams which are respectively distributed to a same-direction component and an orthogonal component for zero padding three-mode index modulation;

index selector module according to P₁The/2 bit determines the subcarrier activation pattern for each subframe, determines S_AAnd S_BModulated subcarrier index, the number of which is k respectively₁And k₂And both satisfy the constraint condition: k is a radical of₁+k₂＝k；

A joint mapper module for mapping according to P₂The/2 bit selects a symbol point from the joint constellation diagram to modulate the corresponding active subcarrier;

the adding module is used for adding the same-direction component and the orthogonal component which are respectively used as a real part and an imaginary part to obtain a subframe of the OFDM signal;

the OFDM signal generator module is used for arranging the OFDM signals of each subframe to obtain a frame of OFDM signals on a frequency domain;

the N-point IFFT module converts a frame of OFDM signals of the index modulation system from a frequency domain to a time domain through IFFT operation of N points;

the transmitting terminal serial-parallel conversion, cyclic prefix adding, digital-to-analog conversion and up-conversion module is used for performing serial-parallel conversion, cyclic prefix adding and digital signal conversion on a frame of time domain OFDM signal of the transmitting terminal to obtain an analog signal and a baseband signal, and modulating the analog signal and the baseband signal into a band-pass signal for processing;

the receiving end down-conversion module, the analog-to-digital conversion module, the cyclic prefix removal module and the serial-to-parallel conversion module are used for carrying out band-pass signal modulation on a frame of time domain OFDM signals of the receiving end into baseband signals, converting the analog signals into digital signals, and removing the cyclic prefix and the serial-to-parallel conversion processing;

the N-point FFT module converts a frame of OFDM signal of the receiving end from a time domain to a frequency domain through FFT operation of N points;

a two-stage log-likelihood ratio detection module for detecting the activation pattern of the sub-carrier by using two-stage LLR demodulation algorithm and detecting the S_AAnd S_BA modulated subcarrier index;

the de-indexing and de-symbolizing module is used for comparing the lookup table with the joint constellation diagram according to the detected subcarrier activation mode and restoring an index bit and a symbolic bit;

and the parallel-serial conversion and bit error rate calculation module is used for converting the recovered parallel binary bit stream into a serial data stream and comparing the serial data stream with the original index bit and the symbol bit to obtain the bit error rate of the system.

Compared with the prior art, the invention has the beneficial effects that: in the aspect of spectrum gain, the high-order constellation diagram is mapped on a real part and an imaginary part, and the invention simultaneously carries out zero filling three-mode index modulation based on PAM modulation on the same-direction component and the orthogonal component of a frame of OFDM signals, thereby doubling the transmission capability of a system to index bits and improving the spectrum efficiency.

Drawings

FIG. 1 is a block diagram of a transmitting end of a real-imaginary part zero-padding three-mode OFDM index modulation system according to an embodiment of the present invention;

FIG. 2 is a block diagram of an index modulation module of a real-imaginary part zero-padding three-mode OFDM index modulation system according to an embodiment of the present invention;

FIG. 3 is a block diagram of a receiving end of a real-imaginary part zero-padding three-mode OFDM index modulation system according to an embodiment of the present invention;

fig. 4 is a diagram illustrating a QPSK modulation decomposition into two PAM modulations in an embodiment of the present invention;

fig. 5 is a constellation a and a constellation B of the same directional component in the embodiment of the present invention;

FIG. 6 is a constellation A and a constellation B of quadrature components in an embodiment of the present invention;

fig. 7 is a schematic diagram of a bit error rate performance curve of a real-part and imaginary-part zero-padding three-mode OFDM index modulation system in an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention.

In order to improve the spectrum efficiency of the ZTM-OFDM-IM system in the high-order constellation, the embodiment provides a real part and imaginary part zero padding three-mode OFDM index modulation (RI-ZTM-OFDM-IM) algorithm and system. The real part and the imaginary part of the symbol point in the high-order constellation diagram are respectively regarded as two PAM modulations, and by designing the PAM modulation constellation diagram, the embodiment performs zero padding three-mode index modulation from two aspects of the same-direction component and the orthogonal component, thereby doubling the index bit. At the receiving end, an improved two-stage LLR demodulator is employed. Simulation results show that under the condition of almost no loss of signal-to-noise ratio, the spectrum gain is obtained compared with a ZTM-OFDM-IM system.

A real part and imaginary part zero filling three-mode OFDM index modulation algorithm comprises the following steps:

s1, serial-to-parallel conversion and bit separation: the binary serial bit stream of length B is converted from serial to parallel into a parallel data stream, where each P_IQ-ZTMThe bits are input into an index modulation module to obtain a sub-frame of a frame of OFDM signals, wherein the frame is the OFDM signals comprising N sub-carriers. Considering the whole system, there are N/N subframes, and N subcarriers included in each subframe.

S2, take β (1 ≦ β ≦ G) sub-frame as an example without loss of generality. P_IQ-ZTMAnd the bit is input into a sub-module bit separator, is equally divided into two bit streams with equal length, and simultaneously carries out zero padding three-mode index modulation on the same-direction component and the orthogonal component respectively. Taking the homodromous component as an example, P₁The/2 bit enters an index selector to select k active subcarriers from n subcarriers, and further a constellation diagram A (M) is obtained_A) Symbol point (S) of_A) Constellation diagram B (M)_B) Symbol point (S) of_B) Index of modulated active subcarriersThe number of which is respectively k₁And k₂And both satisfy the constraint condition: k is a radical of₁+k₂K. Thus, the output of the index selector can be expressed as: j. the design is a square_β,I＝[J_β,I(1)J_β,I(2)...J_β,I(k₁)...J_β,I(k)]。

S3，P₂The/2 bit input is formed by M_AAnd M_BThe combined joint mapper (with the size of the sum of the two constellations) maps to the symbol points on the joint constellation. Combining the output of the index selector in S2, modulating the corresponding active sub-carriers with the symbol points, and the output of the joint mapper is: x_β,I＝[X_β,I(1)X_β,I(2)...X_β,I(k₁)...X_β,I(k)]1,2, G wherein X_β,I(γ), γ ═ 1, 2.., n may be taken as S_A、S_B。

S4, for the orthogonal component, index selectorAnd the joint mapper operates on the same principle as S2 and S3, the outputs of which are denoted J_β,QAnd X_β,Q。

S5, the system respectively uses the homodromous component and the quadrature component as the real part and the imaginary part of a sub-frame according to the output signals of S3 and S4, and the obtained β -th sub-frame can be expressed as: x_β＝X_β,I+jX_β,Q. Similarly, the output of each index modulation block in the system can be expressed as: x_i＝X_i,I+jX_i,Q1, 2. The OFDM block generator arranges the outputs of the G index modulation modules, and obtains a frame of OFDM signal on the frequency domain as: x ═ X (1) X (2).. X (n)]Since the presence of inactive subcarriers is allowed, X (α), α, 1,2_A、S_BOr 0.

S6, the frequency domain OFDM signal obtained in S5 is subjected to an N-point Inverse Fast Fourier Transform (IFFT) and converted into a time domain.

And S7, the time domain OFDM signal of S7 is input into a Rayleigh frequency selective fading channel after parallel-serial conversion, cyclic prefix addition, digital-to-analog conversion and up-conversion.

S8, at the receiving end, down-conversion, analog-to-digital conversion, cyclic prefix removal, and serial-to-parallel conversion are performed on the OFDM signal.

S9, performing N-point Fast Fourier Transform (FFT) on the output signal of S8 to obtain an OFDM received signal in the frequency domain, which is represented as: y ═ Y (1) Y (2.. Y (n))]. Wherein, the β -th group of sub-modules can be expressed as: y is_β＝[Y_β(1)Y_β(2)...Y_β(n)]。

S10, the output signal of S9 is processed with improved two-stage Log Likelihood Ratio (LLR) detection to obtain the result S_AAnd S_BIndex of the modulated active sub-carriers.

And S11, performing index bit estimation and symbol bit estimation on the output signal of S10 to recover the binary data stream.

And S12, inputting the output signal of S10 into a parallel-serial converter and comparing the output signal with the original binary information to obtain the bit error rate of the system.

And, P in S1_IQ-ZTM＝P₁+P₂In which P is₁To index a bit, P₂Are sign bits. In S2, P₁The first half and the second half of the bits are respectively input into the index selectors of the same-direction component and the orthogonal component to generate a subcarrier arrangement pattern, P, of each subframe₂The first half and the second half of the bit are respectively input into a joint mapper of the same direction component and the orthogonal component for signal mapping. The analysis shows that:

whereinDenotes rounding down, C_n ^kRepresenting binomial coefficients, i.e. k from n sub-carriers, satisfying k<n is the same as the formula (I). The 2 in the equation is because the same directional component and the orthogonal component are index-modulated at the same time. In other words, the two components are considered to be independent from each other, and the active modes of the same directional component and the orthogonal component of the same subcarrier can be different in a certain transmission, so that a zero padding three-mode OFDM index modulation (ZTM-OFDM-IM) system can be considered as a special case. Taking QPSK modulation as an example, each symbol point thereof is mapped onto the real axis and the imaginary axis, and the resulting in-directional component and quadrature component can be regarded as two PAM modulations.

Assume that size N of constellation diagram A before split in S3_AThe size of the constellation B before being split is N_BThen P is₂The bits may be represented as:

1/2 in the equation is because the equivalent constellation size of the in-direction component and the quadrature component is 1/2 th power of the original constellation size.

The spectral efficiency of this embodiment is:

wherein L is_CPG is the number of subframes of one frame of OFDM signal, which is the length of the cyclic prefix. While the spectrum efficiency of the ZTM-OFDM-IM system is:

therefore, compared with the ZTM-OFDM-IM system, the embodiment doubles the index bit, thereby improving the spectrum efficiency of the system.

When the system adopts QPSK modulation and n is 4, k₁＝2，k₂When the frequency spectrum efficiency is 1, the frequency spectrum efficiency of the original system is 2bits/s/Hz, and the frequency spectrum efficiency of the embodiment is 2.67bits/s/Hz, and the frequency spectrum gain of 33.3 percent is obtained.

The unit impulse response coefficient of the beta group Rayleigh type frequency selective fading channel in S7 is H_βAnd the length is nu. In connection with S9, the relationship between the symbol points of the two transceivers can be expressed as:

Y_β＝diag(X_β)H_β+Z_β,β＝1,2,...,g

wherein diag { X_βDenotes the element on the diagonal as X_βDiagonal matrix of, Z_βIs beta-group additive white Gaussian noise in the frequency domain, and the energy is N₀。

The improved two-stage LLR detection process in S10, comprising the steps of:

s10.1, detection is carried out by one submodule and one submodule. Taking the beta-th submodule as an example, the output signal of S10.1 is firstly subjected to zero-forcing equalization of a single key;

s10.2, taking the same-direction component as an example, taking a real part of the output signal of the S10.1 and carrying out first-stage LLR detection to obtain an index of an active subcarrier;

s10.3, according to the detection result in S10.2, the output result of S10.1 is taken out and the second-stage LLR detection is carried out to obtain the result of S_AAnd S_BThe modulated subcarrier index.

S10.4, the two-stage LLR detection process for the quadrature component is exactly the same as S10.2 and S10.3.

The equalization process in S10.1 can be expressed as:

the first stage detection process in S10.2 can be expressed as:

where α ═ 1, 2., n, δ_C,i＝M_A∪M_BThe ith symbol point, Re (.) on the joint constellation represents the real part operation. Gamma ray_αThe larger the probability that a subcarrier is active, and conversely, γ_αThe smaller the subcarrier, the greater the probability that the subcarrier is more inactive. Since the zero-forcing equalization in S10.1 amplifies the energy of the noise, a factor | H is introduced in the above equation_β(α)|²And H does not need to be considered in the calculation of Euclidean distance_β(α) influence of the reaction.

The second stage detection process in S10.3 can be expressed as:

in the formula S_A,iAnd S_B,iRespectively representing the ith symbol point on constellation a and constellation B. Gamma ray_α ^*The larger the subcarrier is, the more S_AThe greater the probability of modulation, and vice versa, γ_α ^*The smaller the subcarrier is, the less S_BThe greater the probability of modulation. The process of two-stage LLR detection for the quadrature component in S10.4 can be expressed as:

and Im (.) in the formula represents the operation of taking an imaginary part.

A real imaginary zero-padding three-mode OFDM index modulation system, comprising the following modules:

a transmitting side serial-to-parallel conversion and bit separation module for converting a binary serial bit stream of length B into a parallel data stream, wherein each P_IQ-ZTMThe bits are input into an index modulation module to obtain a sub-frame of a frame of OFDM signals, wherein the frame is the OFDM signals comprising N sub-carriers. Considering the whole system, there are N/N subframes, where N is the number of subcarriers included in each subframe.

Sub-module bit separator module for separating P_IQ-ZTMThe bit is averagely divided into two bit streams which are respectively distributed to the same-direction component and the orthogonal component to carry out zero padding three-mode index modulation.

Index selector module according to P₁The/2 bit determines the subcarrier activation pattern for each subframe, i.e. by S_AAnd S_BModulated subcarrier index, the number of which is k respectively₁And k₂And both satisfy the constraint condition: k is a radical of₁+k₂＝k。

A joint mapper module for mapping according to P₂The/2 bits select symbol points from the joint constellation to modulate the corresponding active subcarriers. The symbol point sets in constellation A and constellation B are not intersected with each other.

And the addition module is used for adding the homodromous component and the orthogonal component which are respectively used as a real part and an imaginary part to obtain a subframe of the OFDM signal.

And the OFDM signal generator module is used for arranging the OFDM signals of each sub-frame to obtain a frame of OFDM signals on the frequency domain.

And the N-point IFFT module converts a frame of OFDM signals of the index modulation system from a frequency domain to a time domain through the IFFT operation of the N points.

And the sending end serial-parallel conversion, cyclic prefix adding, digital-to-analog conversion and up-conversion module is used for performing serial-parallel conversion, cyclic prefix adding and digital signal conversion on a frame of time domain OFDM signal of the sending end to obtain an analog signal and a baseband signal, and modulating the analog signal and the baseband signal into a band-pass signal for processing.

And the receiving end down-conversion module, the analog-to-digital conversion module, the cyclic prefix removal module and the serial-to-parallel conversion module are used for performing band-pass signal modulation on a frame of time domain OFDM signal of the receiving end into a baseband signal, converting the analog signal into a digital signal, and removing the cyclic prefix and the serial-to-parallel conversion processing.

And the N-point FFT module converts a frame of OFDM signal of the receiving end from a time domain to a frequency domain through the FFT operation of the N points.

A two-stage log-likelihood ratio detection module for detecting the activation pattern of the sub-carrier by using two-stage LLR demodulation algorithm, i.e. detecting the S_AAnd S_BThe modulated subcarrier index.

And the de-indexing and de-symbolizing module is used for comparing the lookup table with the joint constellation diagram according to the detected subcarrier activation mode and restoring the index bit and the symbolic bit.

And the parallel-serial conversion and bit error rate calculation module is used for converting the recovered parallel binary bit stream into a serial data stream and comparing the serial data stream with the original index bit and the symbol bit to obtain the bit error rate of the system.

In specific implementation, as shown in fig. 1, a block diagram of a transmitting end of the real part and imaginary part zero-padding three-mode OFDM index modulation system of this embodiment includes a serial-to-parallel conversion and bit separation module, an index modulation module, an OFDM signal generator module, an N-point IFFT module, and a serial-to-parallel conversion, cyclic prefix adding, digital-to-analog conversion and up-conversion module of the transmitting end. Fig. 2 is a block diagram of an index modulation module of a real-part and imaginary-part zero-padding three-mode OFDM index modulation system according to this embodiment, which includes an index selector module, a joint mapper module and an addition module. Fig. 3 is a block diagram of a receiving end of the real part and imaginary part zero-padding three-mode OFDM index modulation system according to this embodiment, which includes a down-conversion module, an analog-to-digital conversion module, a cyclic prefix removal module, a serial-to-parallel conversion module, an N-point FFT module, a two-stage LLR demodulation module, an index and de-sign module, and a parallel-to-serial conversion and bit error rate calculation module.

Assuming a real part and imaginary part zero filling three-mode OFDM index modulation systemThe number of the systematic subcarriers is N, and the signal sent by the sending end can be represented as: x ═ X (1) X (2).. X (n)]. Each frame of the OFDM signal is divided into G subframes, each of which includes N-N/G subcarriers. Further, assume that one frame OFDM signal carries P_IQ-ZTMBit, wherein the index bit is P₁The sign bit is P₂. It can be known by analysis that a frame of OFDM signal can carry m ═ P in total_IQ-ZTMG bits, P_IQ-ZTM、P₁、P₂Are all positive integers.

The real part and imaginary part zero padding three-mode OFDM index modulation algorithm of the embodiment comprises the following steps:

step 01, serial-parallel conversion and bit separation: the binary serial bit stream of length B is converted from serial to parallel into a parallel data stream, where each P_IQ-ZTMThe bits are input into an index modulation module to obtain a sub-frame of a frame of OFDM signals, wherein the frame is the OFDM signals comprising N sub-carriers. Considering the whole system, there are N/N subframes, and N subcarriers included in each subframe. Each subframe containing P_IQ-ZTMBit in which P₁A bit input index selector for determining a subcarrier activation pattern, P₂The bits are input into a joint mapper for signal mapping.

Step 02, taking the β (β is more than or equal to 1 and less than or equal to G) th subframe as an example without loss of generality. P_IQ-ZTMAnd the bit is input into a sub-module bit separator, is equally divided into two bit streams with equal length, and simultaneously carries out zero padding three-mode index modulation on the same-direction component and the orthogonal component respectively. Taking the homodromous component as an example, P₁The/2 bit enters an index selector to select k active subcarriers from n subcarriers, and further a constellation diagram A (M) is obtained_A) Symbol point (S) of_A) Constellation diagram B (M)_B) Symbol point (S) of_B) Index of modulated active subcarriersThe number of which is respectively k₁And k₂And both satisfy the constraint condition: k is a radical of₁+k₂K. Thus, the output of the index selector, i.e. active in every subframeThe index of the subcarrier can be expressed as: j. the design is a square_β,I＝[J_β,I(1)J_β,I(2)...J_β,I(k₁)...J_β,I(k)]. As can be seen from the analysis, considering both the homodromous component and the orthogonal component, the index bits can be expressed as:

wherein + -. represents rounding down, C_n ^kRepresenting binomial coefficients, i.e. k from n sub-carriers, satisfying k<n is the same as the formula (I). The 2 in the equation is because the same directional component and the orthogonal component are index-modulated at the same time. Taking the same direction component as an example, in each subframe, when n is 4, k₁＝2，k₂The relationship between the index bits and the subcarrier activation pattern is shown in table 1 (look-up table) when 1.

TABLE 1

The look-up table for the quadrature component is exactly the same as table 1. The two components can be regarded as independent, and the activation modes of the same directional component and the orthogonal component of the same subcarrier can be different in a certain transmission, so that the index bit in the embodiment is expanded by one time compared with the ZTM-OFDM-IM system. The ZTM-OFDM-IM system is a special case of the present embodiment. As shown in fig. 4, each symbol point of QPSK modulation is mapped onto the real axis and the imaginary axis, and the obtained homodyne component and quadrature component can be regarded as two PAM modulations.

Step 03, P₂The/2 bit input is formed by M_AAnd M_BThe combined joint mapper (with the size of the sum of two constellations) selects the corresponding symbol point to modulate the active sub-carrier. In conjunction with the output of the index selector in step 02,the corresponding active sub-carriers are modulated with the symbol points, and the output of the joint mapper is: x_β,I＝[X_β,I(1)X_β,I(2)...X_β,I(k₁)...X_β,I(k)]1,2, G wherein X_β,I(γ), γ ═ 1, 2.., n may be taken as S_A、S_BAnd {0 }. Assume that the size of the constellation diagram A before being split in step 03 is N_AThe size of the constellation B before being split is N_BThen P is₂The bits may be represented as:

1/2 is the equivalent constellation size of the same direction component and the orthogonal component is 1/2 power, k of the original constellation size₁And k₂Respectively represent by S_AAnd S_BThe number of active subcarriers modulated. The joint constellations for the in-direction and quadrature components are shown in fig. 5 and 6, respectively.

To sum up, the spectral efficiency of this embodiment is:

wherein L is_CPG is the number of subframes of one frame of OFDM signal, which is the length of the cyclic prefix. While the spectrum efficiency of the ZTM-OFDM-IM system is:

therefore, compared with the ZTM-OFDM-IM system, the embodiment doubles the index bit, thereby improving the spectrum efficiency of the system. When the system adopts QPSK modulation and n is 4, k₁＝2，k₂When the frequency spectrum efficiency is 1, the frequency spectrum efficiency of the original system is 2bits/s/Hz, and the frequency spectrum efficiency of the embodiment is 2.67bits/s/Hz, and the frequency spectrum gain of 33.3 percent is obtained.

Step 04, for the orthogonal component, index selector andthe working principle of the joint mapper is the same as that of step 02 and step 03, and the output is denoted as J_β,QAnd X_β,Q。

Step 05, the system uses the homodromous component and the orthogonal component as the real part and the imaginary part of a subframe respectively according to the output signals of step 03 and step 04, and the obtained beta-th subframe can be expressed as: x_β＝X_β,I+jX_β,Q. Similarly, the output of each index modulation block in the system can be expressed as: x_i＝X_i,I+jX_i,Q1, 2. The OFDM block generator arranges the outputs of the G index modulation modules, and obtains a frame of OFDM signal on the frequency domain as: x ═ X (1) X (2).. X (n)]Since the presence of inactive subcarriers is allowed, X (α), α, 1,2_A、S_BOr 0.

Step 06, performing an Inverse Fast Fourier Transform (IFFT) of N points on the frequency domain OFDM signal obtained in step 05 to convert into a time domain, which may be represented as:

x＝[x(1)x(2)...x(N)]＝IFFT{X}＝IFFT([X(1)X(2)...X(N)])

and step 07, inputting the time domain OFDM signal of step 06 into a Rayleigh frequency selective fading channel after parallel-serial conversion, cyclic prefix addition, digital-to-analog conversion and up-conversion.

And step 08, performing down-conversion, analog-to-digital conversion, cyclic prefix removal and serial-to-parallel conversion on the OFDM signal at a receiving end.

Step 09, performing Fast Fourier Transform (FFT) of N points on the output signal of step 08 to obtain an OFDM received signal in the frequency domain, which is represented as: y ═ Y (1) Y (2.. Y (n))]. The β th set of sub-modules may be represented as: y is_β＝[Y_β(1)Y_β(2)...Y_β(n)]. Let the unit impulse response coefficient of the beta group Rayleigh type frequency selective fading channel be H_βAnd the length is nu. In conjunction with step 09, the relationship between the symbol points of the two transceivers can be expressed as:

Y_β＝diag(X_β)H_β+Z_β,β＝1,2,...,g

wherein diag { X_βDenotes the diagonal lineThe element above is X_βDiagonal matrix of, Z_βIs beta-group additive white Gaussian noise in the frequency domain, and the energy is N₀。

Step 010, performing improved two-stage LLR detection on the output signal of step 09 to obtain a result S_AAnd S_BIndex of the modulated active sub-carriers. This process comprises the following steps:

0101, detection is performed one sub-module by one sub-module. Without loss of generality, taking the β -th sub-module as an example, the output signal of step 09 is first subjected to zero-forcing equalization by a single key. This process can be expressed as:

(2) taking the same-direction component as an example, the real part of the output signal of step 0101 is taken and the first-stage LLR detection is performed to obtain the index of the active subcarrier. This process can be expressed as:

where α ═ 1, 2., n, δ_C,i＝M_A∪M_BThe ith symbol point, Re (.) on the joint constellation represents the real part operation. Gamma ray_αThe larger the probability that a subcarrier is active, and conversely, γ_αThe smaller the subcarrier, the greater the probability that the subcarrier is more inactive. Since the zero-forcing equalization in step 0101 amplifies the energy of the noise, a factor | H is introduced in the above equation_β(α)|²And H does not need to be considered in the calculation of Euclidean distance_β(α) influence of the reaction.

0103, according to the detection result in 0102, the output result real part of 0101 is processed with second-level LLR detection to obtain respective result from M_AAnd M_BThe modulated subcarrier index. This process can be expressed as:

in the formula S_A,iAnd S_B,iRespectively representing the ith symbol point on constellation a and constellation B. Gamma ray_α ^*The larger the subcarrier is, the more S_AThe greater the probability of modulation, and vice versa, γ_α ^*The smaller the subcarrier is, the less S_BThe greater the probability of modulation.

In step 0104, the two-stage LLR detection process of the orthogonal component is completely the same as in steps 0102 and 0103, and can be expressed as:

and Im (.) in the formula represents the operation of taking an imaginary part.

And 011, performing index bit estimation and symbol bit estimation on the output signal of 010 by using a table look-up method and a method for calculating Euclidean distance, and recovering the binary data stream.

And a step 012, in which the output signal of the step 011 is input into the parallel-serial converter and compared with the original binary information to obtain the bit error rate of the system.

Example 1

One frame of OFDM signal comprises 128 sub-carriers; n is 4, k₁＝2，k₂1, the number n of subcarriers of each subframe is 4; total G ═ 32 subframes; s_ANumber k of modulated active subcarriers₁＝2；S_BNumber k of modulated active subcarriers₂1 is ═ 1; k is total₁+k₂3 active subcarriers; the ZTM-OFDM-IM system adopts two QPSK and 8QAM joint constellation diagrams without intersection; the same-direction component and the orthogonal component of the real part and the imaginary part of the zero-padding three-mode OFDM index modulation system of the embodiment respectively adopt the constellation diagrams as shown in the figure 5 and the figure 6; cyclic prefix length L_CP16; the system adopts Rayleigh type frequency selectionSelective fading channel, channel length v 10 (satisfying L)_CP>V is a condition); the system can send B bit once; the energy of the noise is N₀(ii) a Channel estimation is error-free; frequency offsets of the transmitting end and the receiving end are not considered. Analysis shows that, in the example, each subframe carries 12 bits of information, and the spectrum efficiency is 2.67 bits/s/Hz.

The simulation results are shown in fig. 7, where the horizontal axis in fig. 7 represents the signal-to-noise ratio, i.e., the ratio of power per bit of information to noise power. The vertical axis is the bit error rate, i.e. the ratio of the number of erroneous decisions to the total number of bits. To demonstrate the advantages of this example, fig. 7 also provides simulation results of OFDM index modulation and zero-padding three-mode OFDM index modulation under conditions where bit error rate performance is very close. Each subframe comprises 4 subcarriers, an OFDM index modulation system adopts 8QAM to modulate, and each subframe comprises 2 active subcarriers; there is k in each sub-frame of the zero-padding three-mode OFDM index modulation system₁QPSK modulation for 2 active subcarriers, k₂8QAM modulation is used for 1 active subcarrier. Analysis shows that in the OFDM index modulation system, each subframe carries 8bits of information, and the spectral efficiency is 1.78 bits/s/Hz; in a zero padding three-mode OFDM index modulation system, each subframe carries 10 bits of information, and the spectral efficiency is 2.22 bits/s/Hz. Thus, the present example achieves spectral gains of 0.89bits/s/Hz and 0.45bits/s/Hz, i.e., 50% and 20%, respectively, as compared to the first two systems with little loss of signal-to-noise ratio.

Meanwhile, analysis shows that the ZTM-OFDM-IM system can be regarded as a special case of the embodiment. Simulation results show that the embodiment obtains higher spectral gain than the prior art under the condition of almost no loss of signal-to-noise ratio.

In the embodiment, the homodromous component and the orthogonal component of the OFDM signal are subjected to zero padding three-mode index modulation simultaneously, so that the original system is expanded, and the capability of the system for transmitting index bits is enhanced. The receiving end employs a modified two-stage LLR demodulator that will detect the active pattern of active subcarriers to recover the original bit information. Simulation results show that the real part and the imaginary part zero-filling three-mode OFDM index modulation system obtains spectrum gain compared with the original system under the condition of almost no loss of signal-to-noise ratio.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.