CN110071890B

CN110071890B - Low peak-to-average power ratio FBMC-OQAM signal processing method and system

Info

Publication number: CN110071890B
Application number: CN201910335891.9A
Authority: CN
Inventors: 汪洋; 李黎明; 丁丽琴; 张珊
Original assignee: Shenzhen Graduate School Harbin Institute of Technology
Current assignee: Shenzhen Graduate School Harbin Institute of Technology
Priority date: 2019-04-24
Filing date: 2019-04-24
Publication date: 2021-11-02
Anticipated expiration: 2039-04-24
Also published as: CN110071890A

Abstract

A low peak-to-average ratio FBMC-OQAM signal processing method and system are a baseband signal processing method and system for reducing the peak-to-average ratio of FBMC-OQAM signals based on DFT precoding. The grouped pre-transmission data is mapped into a data sequence meeting specific conjugate symmetry characteristics, and then the conjugate symmetric data sequence obtained by mapping can be converted into a real and virtual alternately arranged data sequence meeting the OQAM real quadrature modulation requirement by adopting DFT for pre-coding, so that the pre-coded data sequence can be directly mapped onto a corresponding subcarrier for IFFT subcarrier modulation and filtering. By the system and the signal processing method, the additional OQAM preprocessing operation of separating real and imaginary parts of complex numbers between DFT precoding and subcarrier modulation IFFT is avoided. Therefore, the system and the signal processing method can recover the single carrier characteristic of the transmitting signal of the FBMC-OQAM system by means of DFT precoding, and further can remarkably reduce the peak-to-average ratio of the FBMC-OQAM transmitting signal.

Description

Low peak-to-average power ratio FBMC-OQAM signal processing method and system

Technical Field

The invention relates to the technical field of communication, in particular to a low peak-to-average ratio FBMC-OQAM signal processing method and system.

Background

Multicarrier modulation has been widely used in various communication systems as a communication waveform technology, and its basic idea is to divide a transmission bit stream into a plurality of sub-bit streams and then modulate the sub-bit streams onto different subcarriers for transmission. Among many multicarrier modulation techniques, Orthogonal Frequency Division Multiplexing (OFDM) is widely used, for example, Digital television broadcasting (DVB) in europe and Wireless Local Area Networks (WLAN) due to its advantages of high spectrum efficiency, low transceiver complexity, simple equalization, and easy use in combination with the multi-antenna technique. With the isomerization and asynchronization Of future communication networks, OFDM has some disadvantages such as higher Out Of Band (OOB) radiation and sensitivity to synchronization errors, and the like. For example, mass wireless access of the internet of things, multipoint cooperative transmission, direct communication between devices, and the like all need to reduce the requirement of modulation waveforms for accurate synchronization, so as to meet the requirements of low cost and low signaling overhead while ensuring communication performance. In addition, cognitive radio, carrier aggregation, and other technologies also require that the signal modulation waveform have lower out-of-band leakage, so as to utilize the fragmented spectrum more efficiently.

To address these challenges, Filter Bank Multi-Carrier (FBMC) is considered a promising waveform technology due to its advantages of extremely low OOB radiation. In the FBMC system, OOB radiation is greatly reduced due to the introduction of a Prototype Filter (PF) having a good Time-Frequency focusing (TFL), so that Inter-Carrier Interference (ICI) can be effectively controlled, thereby flexibly and effectively utilizing Frequency spectrum resources and reducing synchronization requirements. Meanwhile, in order to improve the spectrum utilization and cope with the non-orthogonality caused by the introduction of the prototype filter, the FBMC system usually adopts Offset Quadrature Amplitude Modulation (OQAM) instead of the conventional Quadrature Amplitude Modulation (QAM). In OQAM modulation, the complex data symbols transmitted by the original QAM modulation can be approximately equivalent to transmitting two real symbols in the same time, thereby keeping the spectral efficiency unchanged. That is, in the FBMC-OQAM system, the complex orthogonal property in the conventional OFDM needs to be relaxed to be the real number domain orthogonal, thereby providing a compromise solution of the spectrum efficiency, the OOB radiation and the orthogonality. FBMC has great advantages in asynchronous communication networks because it modulates very low OOB radiation. For example, in a massive internet of things, due to the number of numerous terminals, synchronization between devices needs to consume a large amount of signaling resources, and the FBMC system can use good protection subcarriers to greatly reduce interference between asynchronous users, so that the signaling resources and the power consumption of terminal devices can be greatly saved.

As a multi-carrier waveform technology, like OFDM, FBMC also faces a relatively serious Peak-to-Average Power Ratio (PAPR) problem, where an FBMC-OQAM symbol is formed by adding signals modulated by a plurality of independent subcarriers with equal bandwidths, and when the phases of the signals on the subcarriers are the same, they are added to generate a larger Peak Power, which results in a larger Ratio of the Peak Power to the Average Power of the signals, and this Ratio is called the PAPR for short. In order to avoid the influence of power amplifier nonlinearity, the amplifying circuit needs an increased power back-off value, which will seriously increase the power consumption of the terminal device and reduce the battery life cycle, which has a particularly serious influence on the nonlinear satellite communication system and the low-cost internet of things communication. In order to reduce the PAPR of the FBMC system, a technique conventionally used for reducing the PAPR of the OFDM system is also studied to be applied to the FBMC system, such as a selective mapping method or a partial transmit sequence method. But these methods are difficult to apply in the FBMC-OQAM system due to high computational complexity.

Disclosure of Invention

The invention mainly solves the technical problem of designing an FBMC-OQAM system which can obviously reduce the PAPR.

According to a first aspect, an embodiment provides a data processing method for FBMC-OQAM, comprising:

grouping the pre-transmitted original data, and performing serial-parallel conversion on each group of original data;

mapping each group of original data after serial-parallel conversion into a data sequence meeting specific conjugate symmetry characteristics;

and respectively carrying out DFT precoding on each group of mapped data sequences to obtain real and virtual alternative arranged pre-transmission data meeting the real and orthogonal requirements of the FBMC-OQAM system.

Furthermore, the length of each group of original data is M/2, wherein M is the number of subcarriers of the FBMC-OQAM system and conjugate pairsThe length of the mapped data sequence is called M, and M is 2^LThe value range of L is a natural number of 2 or more.

Further, the data sequence satisfying the specific conjugate symmetry property is a data sequence satisfying the following formula:

where b (k) is the kth data in a data sequence, the sequence length is M, λ ═ j or ± 1 is a constant factor,

to take the imaginary part.

According to a second aspect, an embodiment provides a data processing method of low peak-to-average ratio FBMC-OQAM, including:

a receiving end of the FBMC-OQAM system carries out polyphase filtering, FFT subcarrier demodulation, equalization and OQAM demodulation operation on a received baseband signal to obtain demodulated real data;

adding a phase factor to each real number data in the same symbol period of the FBMC-OQAM system, and performing IFFT conversion to obtain a receiving end conjugate symmetric data sequence meeting specific conjugate symmetric characteristics;

performing demapping operation on the receiving end conjugate symmetric data sequence to obtain an estimated value of original data;

and outputting the estimated value of the original data after parallel-serial conversion.

Further, real data demodulated by m-th subcarrier in n-th symbol of FBMC-OQAM system is multiplied by phase factor j^mConverting real data received in each symbol period of the FBMC-OQAM system into a group of data sequences alternately arranged in real and imaginary; wherein the value range of n is a natural number, and the value range of M is 0, 1, 2, …, M; m is the number of working subcarriers of the FBMC-OQAM system.

Furthermore, the real data added with the phase factor in each symbol period is subjected to IFFT conversion to obtain a receiving-end conjugate symmetric data sequence satisfying a specific conjugate symmetric characteristic.

Furthermore, the vector for the receiving end conjugate symmetric data sequence in any nth symbol period

Indicates, a data sequence within the symbol period

Vector for estimated value of n-th group of raw data obtained by demapping operation

Represents;

data sequence in the nth symbol period

Demapping to estimated value of n-th group of original data according to the following formula

Wherein the value range of n is a non-negative integer;

expressed as estimated value of n-th set of raw data

The kth data of (1);

is represented as a data sequence in the nth symbol period

The kth data of (1); conjugates of the representatives marked with indicesThe value is obtained.

Operating for a solid part;

to take the imaginary part.

According to a third aspect, an embodiment provides a low peak-to-average ratio FBMC-OQAM system, comprising:

a preprocessing module for preprocessing the pre-transmitted original data to obtain the data satisfying FBMC-

Pre-transmission data which are required by real orthogonality of the OQAM system and are alternately arranged in real and virtual;

the transmission module is used for carrying out baseband signal processing operations of the FBMC system such as subcarrier modulation and polyphase filtering on the preprocessed pre-transmission data, and finishing carrier frequency modulation, filtering, amplification and the like and transmitting the data to a channel;

the preprocessing module comprises:

the front serial-parallel conversion module is used for grouping the pre-transmitted original data and performing serial-parallel conversion on each group of original data;

the conjugate symmetry mapping module is used for respectively mapping each group of original data after serial-parallel conversion into a data sequence meeting specific conjugate symmetry characteristics;

and the front FFT module is used for respectively carrying out DFT precoding on each group of mapped data sequences so as to obtain pre-transmission data which meets the real-virtual alternative arrangement of the real-quadrature requirement of the FBMC-OQAM system.

According to a fourth aspect, an embodiment provides a low peak-to-average ratio FBMC-OQAM system, comprising:

a receiving module, configured to perform polyphase filtering, FFT subcarrier demodulation, equalization, and OQAM demodulation on a baseband signal received from a channel to obtain real data;

the post-processing module is used for adding a phase factor, IFFT conversion, demapping and serial-parallel conversion operations to the real data obtained by the receiving module to obtain the real data which is used as the final demodulation output data of the FBMC-OQAM system;

the post-processing module comprises:

the phase factor adding module is used for adding a phase factor to each real demodulation data in the same symbol period of the FBMC-OQAM system;

the back IFFT module is used for carrying out IFFT conversion on the real data added with the phase factor so as to obtain a receiving end data sequence meeting the specific conjugate symmetry characteristic;

the de-mapping module is used for performing de-mapping operation on the receiving end data sequence to obtain an estimated value of original data;

and the post serial-to-parallel conversion module is used for performing parallel-to-serial conversion on the estimated value of the original data to obtain the final demodulation output data of the FBMC-OQAM system.

According to the data processing method for the FBMC-OQAM and the FBMC-OQAM system in the embodiment, the grouped pre-transmission data is mapped into the data sequence meeting the specific conjugate symmetry characteristic, and then the data sequence is converted into the pre-transmission data alternately arranged in real and virtual by adopting DFT precoding, so that the pre-transmission data can be directly transmitted by the transmitting end of the FBMC-OQAM system, the modulation of the FBMC-OQAM system recovers the single carrier characteristic, and the PAPR of the FBMC-OQAM system can be remarkably reduced.

Drawings

FIG. 1 is a schematic diagram of an OFDM system model based on DFT precoding;

FIG. 2 is a diagram illustrating a model structure of a baseband system of an FBMC-OQAM system in an embodiment;

fig. 3 is a schematic structural diagram of an OQAM pre-processing module of the FBMC-OQAM system in an embodiment;

fig. 4 is a schematic structural diagram of an OQAM pre-processing module of an FBMC-OQAM system in another embodiment;

fig. 5 is a schematic structural diagram of an OQAM post-processing module of the FBMC-OQAM system in an embodiment;

FIG. 6 is a schematic structural diagram of an FBMC-OQAM system with direct DFT precoding in one embodiment;

FIG. 7 is a flow chart of a method for processing a signal at a transmitting end of a FBMC-OQAM system in accordance with an embodiment;

FIG. 8 is a diagram illustrating a data sequence mapped to satisfy a specific conjugate symmetry property for each set of original data length 4 in one embodiment;

FIG. 9 is a diagram illustrating a data sequence mapped to satisfy a specific conjugate symmetry property for each set of original data length 8 in one embodiment;

FIG. 10 is a diagram illustrating a data sequence in which each set of original data has a length M/2 mapped to satisfy a specific conjugate symmetry property according to an embodiment;

fig. 11 is a flowchart of a signal processing method for a receiving end of an FBMC-OQAM system in another embodiment;

FIG. 12 is a data sequence diagram illustrating certain conjugate symmetry properties in one implementation;

FIG. 13 is a diagram of a low peak-to-average ratio FBMC-OQAM system in another embodiment;

FIG. 14 is a diagram illustrating a simulation of PAPR performance of an FBMC-OQAM system in an embodiment;

fig. 15 is a schematic diagram of bit error rate BER simulation of the FBMC-OQAM system in an embodiment.

Detailed Description

The present invention will be described in further detail with reference to the following detailed description and accompanying drawings. Wherein like elements in different embodiments are numbered with like associated elements. In the following description, numerous details are set forth in order to provide a better understanding of the present application. However, those skilled in the art will readily recognize that some of the features may be omitted or replaced with other elements, materials, methods in different instances. In some instances, certain operations related to the present application have not been shown or described in detail in order to avoid obscuring the core of the present application from excessive description, and it is not necessary for those skilled in the art to describe these operations in detail, so that they may be fully understood from the description in the specification and the general knowledge in the art.

Furthermore, the features, operations, or characteristics described in the specification may be combined in any suitable manner to form various embodiments. Also, the various steps or actions in the method descriptions may be transposed or transposed in order, as will be apparent to one of ordinary skill in the art. Thus, the various sequences in the specification and drawings are for the purpose of describing certain embodiments only and are not intended to imply a required sequence unless otherwise indicated where such sequence must be followed.

The numbering of the components as such, e.g., "first", "second", etc., is used herein only to distinguish the objects as described, and does not have any sequential or technical meaning. The term "connected" and "coupled" when used in this application, unless otherwise indicated, includes both direct and indirect connections (couplings).

The terms used in this application define: c. C

Bold lowercase letters, representing row vectors, e.g., a;

bold capital letters, representing a matrix, e.g., a;

superscript T, representing the transpose of the matrix;

superscript H, which represents the conjugate transpose of the matrix;

lower case letters, without bolder, represent scalar values, e.g., a;

superscript, representing conjugate value;

j, an imaginary unit;

operating for a solid part;

to take the imaginary part.

The OFDM technology is one of multicarrier modulation, can greatly improve the spectrum utilization rate, and can effectively combat frequency selective fading, and is particularly suitable for high-speed transmission of data. Among various techniques for reducing the peak-to-average ratio of the OFDM system, the precoding technique has attracted much attention. At present, in an actual OFDM system, better precoding matrices include a DHT matrix, a WHT matrix, and a DFT matrix, which can effectively reduce the peak-to-average ratio of the OFDM system, wherein DFT precoding is adopted with the best effect. For example, in the uplink of LTE (Long Term Evolution), an OFDM system based on Discrete Fourier Transform (DFT) coding, namely DFT-s-OFDM (also referred to as SC-FDMA), becomes an effective means for reducing PAPR.

Referring to fig. 1, a schematic diagram of an OFDM system model based on DFT precoding is shown, which includes a transmitting end and a receiving end. The transmitting end comprises serial-to-parallel conversion, precoding, IFFT and signal transmitting parallel-to-serial conversion. The receiving end comprises serial-parallel conversion, FFT, demodulation, de-precoding and parallel-serial conversion of signal receiving. The number of subcarriers of the OFDM system is set to be M, and a precoding matrix is adopted to reduce the peak-to-average ratio of the system before IFFT. Considering DFT and IFFT as a whole, DFT-s-OFDM is considered to be a single carrier because it performs sampling rate conversion on input single carrier modulation symbols, thereby reducing PAPR. However, simply combining a DFT with an FBMC system is very limited in its effectiveness.

Fig. 2 is a schematic diagram of a baseband system model structure of an FBMC-OQAM system in an embodiment, which includes a transmitting end and a receiving end. The sending end comprises a serial-parallel conversion module, an OQAM preprocessing module, an IFFT module and a multiphase filter module, and the receiving end comprises a multiphase filter module, an FFT module, an OQAM post-processing module and a parallel-serial conversion module. Because the pre-transmitted data is complex data, the pre-transmitted data is subjected to series-parallel conversion and then passes through an OQAM preprocessing module, and the OQAM preprocessing module is used for separating the input complex data into two real data which are arranged in different sub-carrier waves or symbol periods. The method aims to separate the real part and the imaginary part of the modulation data into two real numbers so as to meet the requirement of OQAM modulation real number orthogonality, then the real part and the imaginary part are alternately arranged in two adjacent symbol periods in time and multiplied by a phase modulation factor j corresponding to the nth symbol period and the mth subcarrier^m+nData which is virtually alternated on subcarrier and symbol arrangement is generated, and finally IFFT subcarrier modulation is carried out. That is, OQAM modulation needs to separate real and imaginary parts of input complex data and arrange the real and imaginary parts at different symbolsWithin the number period. Referring to fig. 3, a schematic structural diagram of an OQAM pre-processing module of an FBMC-OQAM system in an embodiment is shown, where the number of subcarriers of the FBMC-OQAM system is set to M, and since the pre-transmitted data is modulated complex data, when the mth path of input data enters the OQAM pre-processing module, 2 times of a real part of the input data is up-sampled (zero-inserted), 2 times of an imaginary part of the input data is up-sampled (zero-inserted) and delayed by 1 data point, and then multiplied by a phase modulation factor j on the nth symbol period and the mth subcarrier respectively^m+nAnd real virtual alternate data is realized on subcarrier and symbol arrangement. Referring to fig. 4, which is a schematic structural diagram of an OQAM pre-processing module of an FBMC-OQAM system in another embodiment, the OQAM pre-processing module may further multiply a real part of input data of an nth symbol period by a phase modulation factor j^2m+nThen mapped to the 2 m-th sub-carrier, and the imaginary part of the input data is multiplied by a phase modulation factor j^2m+1+nAnd then mapping to the 2m +1 path of subcarriers to realize that data which is virtually alternated appears on subcarrier and symbol arrangement. Referring to fig. 5, a schematic structural diagram of an OQAM post-processing module of an FBMC-OQAM system in an embodiment is shown, where the OQAM post-processing module at a receiving end of the FBMC-OQAM system corresponds to the aforementioned first OQAM pre-processing method, and is configured to down-sample (extract) received real part data by 2 times, delay a data point, down-sample (extract) received imaginary part data by 2 times, multiply j, and sum the real part and the imaginary part to recover complex data to be pre-transmitted.

In order to reduce the PAPR of the FBMC-OQAM system, a conventional technique for reducing the PAPR of the OFDM system is applied to the FBMC system, for example, a precoding matrix is applied to the FBMC-OQAM system, please refer to fig. 6, which is a schematic structural diagram of the FBMC-OQAM system with direct DFT precoding in an embodiment, and the system includes a transmitting end and a receiving end, wherein the transmitting end includes a front FFT module, an OQAM preprocessing module, a front IFFT module and a polyphase filtering module, and the receiving end includes a polyphase filtering module, a rear FFT module, a demodulation output module, an OQAM post-processing module and a rear IFFT module. The transmitting end groups the original data to be transmitted and carries out serial-parallel conversion on each group of original data. After M point modulation is carried out on each group of original data after serial-parallel conversionPre-coding is carried out by a front FFT module, and then processing is carried out by a traditional OQAM preprocessing module. The OQAM preprocessing module is used for processing the original data into real and virtual alternately arranged pre-transmission data meeting the real and quadrature requirements of the FBMC-OQAM system. Since OQAM modulation requires input data to be pure real number, after the output of the pre-coding DFT is sent to OQAM modulation in the direct DFT pre-coding FBMC-OQAM scheme, the real part and the imaginary part can be placed on different subcarriers or FBMC symbols, and therefore DFT pre-coding cannot completely recover the single-carrier characteristic of the OQAM signal. The specific process is to carry out serial-parallel conversion modulation on the preprocessed data, set M-point modulation data input, send M-point complex data coded by DFT into OQAM preprocessing after M input complex signals pass through M-point Fast Fourier Transform (FFT), respectively place the real part and the imaginary part of the input complex data in two symbol periods (or two subcarriers) in an OQAM preprocessing module, and add a phase factor item j^m+nGenerating M-point output data with alternating real and virtual, then sending the M-point output data with alternating real and virtual into an IFFT module for subcarrier modulation, generating a base band transmitting signal of FBMC-OQAM after polyphase filtering, and then carrying out corresponding inverse operation at a receiving end to demodulate data information. However, even if DFT precoding is adopted, the subsequent OQAM precoding separates real and imaginary parts of DFT output data, that is, data modulated on subcarriers are real and imaginary alternating data, not direct output values of DFT, and thus an inverse transformation relation cannot be formed with a subsequent IFFT subcarrier modulation module, and thus, adding direct DFT precoding to the FBMC-OQAM system cannot completely recover single carrier characteristics.

In the embodiment of the invention, the pre-transmitted original data is grouped, each group of original data is subjected to serial-parallel conversion, each group of original data subjected to serial-parallel conversion is mapped into a data sequence meeting specific conjugate symmetry characteristics, and then each group of mapped data sequences is subjected to DFT pre-coding, so as to obtain the pre-transmitted data which meets the real-virtual alternative arrangement requirement of the FBMC-OQAM system.

The first embodiment is as follows:

referring to fig. 7, a flow chart of an embodiment of a method for processing a low peak-to-average ratio FBMC-OQAM signal, the method includes:

the method comprises the steps of firstly, grouping pre-transmitted original data, and performing serial-parallel conversion on each group of original data.

In one embodiment, the length of each set of original data is set to M/2, where M is the number of subcarriers of the FBMC-OQAM system, and M is 2^LThe value range of L is a natural number of 2 or more.

And step two, mapping each group of original data after serial-parallel conversion into a data sequence meeting specific conjugate symmetry characteristics.

The data sequence satisfying the specific conjugate symmetry characteristic is a data sequence satisfying the following formula:

to take the imaginary part.

Respectively mapping each group of original data after serial-parallel conversion into a data sequence meeting specific conjugate symmetry characteristics, wherein the mapping comprises the following steps:

vector x for any nth set of raw data_nRepresents the set of raw data x_nVector b for mapped nth data sequence_nRepresents;

the nth set of raw data x_nMapping the data sequence b as the nth group of data sequences satisfying specific conjugate symmetry characteristics according to the following formula_n：

Wherein the value range of n is a non-negative integer; x is the number of_n(k) Denoted as n-th set of raw data x_nThe kth data of (1); b_n(k) Expressed as the nth data sequenceColumn b_nThe kth data of (1); the conjugate value marked with the superscript;

operating for a solid part;

to take the imaginary part.

As shown in fig. 8, a schematic diagram of a data sequence mapped to satisfy a specific conjugate symmetry property in which each group of original data length is 4, in an embodiment, when each group of original data length is 4, the number of subcarriers of the FBMC-OQAM system is 8, in this embodiment, j in the b (k) value is omitted for convenience of understandingⁿAn item. Assume that each set of raw data sequences is x ═ x (0), x (1), x (2), x (3)]^TThen the mapped data sequence of the specific conjugate symmetry property is b ═ b (0), b (1), …, b (7)]^T. Wherein the values of b (0) to b (7) in the data sequence b are x (0), x (1) and,

x^*(1)、x^*(0)、x(3)、

And x^*(3). b (2) and b (6) are singularities of the set of data sequences of the specific conjugate symmetry property, the values of which are respectively

And

b (1) and b (3) are conjugate symmetric with respect to the singularity b (2), and the values of b (5) and b (7) are conjugate symmetric with respect to the singularity b (6).

As shown in fig. 9, a schematic diagram of a data sequence mapped to satisfy a specific conjugate symmetry characteristic in which each group of original data length is 8, in an embodiment, when each group of original data length is 8, the number of subcarriers of the FBMC-OQAM system is 16, and in this embodiment, b is omitted for ease of understanding_n(k) J in the value associated with nⁿAn item. Assume that each set of raw data sequences is x ═ x (0), x (1),.., x (7)]^TThen, the mapped data sequence with the specific conjugate symmetry property is b ═ b (0), b (1), b (2),.. multidot.b (15)]^T. Wherein the values of b (0) to b (15) in the data sequence b are x (0), x (1), x (2), x (3), respectively,

x^*(3)、x^*(2)、x^*(1)、x^*(0)、x(5)、x(6)、x(7)、

x^*(7)、x^*(6) And x^*(5). b (0), b (1), b (2) and b (3) are conjugate symmetric with b (5), b (6) and b (7), b (8) with respect to the singularity b (4), and b (9), b (10) and b (11) are conjugate symmetric with b (13), b (14) and b (15) with respect to the singularity b (12).

As shown in fig. 10, which is a schematic diagram of a data sequence mapped to satisfy a specific conjugate symmetry property with each group of original data length being M/2, when each group of original data length is M/2, the number of subcarriers of the FBMC-0QAM system is M, and then the group of data sequence of the specific conjugate symmetry property includes 2 singular points, which are b (M/4) and b (3M/4), respectively. Besides the 2 singularities, the data on both sides of b (M/4) and b (3M/4) are respectively in conjugate symmetry with respect to the center positions of b (M/4) and b (3M/4), and positive and negative slashes represent two pairs of conjugate symmetric data blocks, wherein b (0) and b (M/4) are also in conjugate symmetry with each other.

And step three, respectively carrying out DFT precoding on each group of mapped data sequences.

And respectively carrying out DFT pre-coding on each group of mapped data sequences to obtain real and virtual alternately arranged pre-transmission data meeting the real and quadrature requirements of the FBMC-OQAM system. In one embodiment, each set of data sequences satisfying a particular conjugate symmetry property is separately FFT transformed. The data sequence after DFT pre-coding can meet the real-virtual alternate arrangement of the real-quadrature requirement of the FBMC-OQAM system, namely the pre-processing process of pre-transmission data of the FBMC-OQAM system is completed.

In one embodiment, the method further comprises the steps of:

and step four, taking each group of data sequences after DFT precoding as modulation data of one symbol period of the FBMC-OQAM system for IFFT conversion so as to complete subcarrier modulation. In one embodiment, one symbol period of the FBMC-OQAM system is T, where T is 1/2F, where F is the subcarrier bandwidth.

And step five, passing each group of data sequences after subcarrier modulation through a polyphase filter, and then sending the data sequences as baseband transmitting signals.

Referring to fig. 11, a flowchart of a signal processing method for a receiving end of an FBMC-OQAM system in another embodiment is shown, and in an embodiment, a signal processing method for a receiving end of an FBMC-OQAM system is further disclosed, which includes:

step 1, a receiving end of the FBMC-OQAM system performs polyphase filtering, FFT subcarrier demodulation, equalization and OQAM demodulation operation on a received baseband signal to obtain real data.

And 2, adding a phase factor.

After the OQAM real data is demodulated, a phase factor is further added to each real data in the same symbol period of the FBMC-OQAM system, and in an embodiment, the real data demodulated by the m-th subcarrier in the nth symbol of the FBMC-OQAM system is multiplied by the phase factor j^mConverting real data received in each symbol period of the FBMC-OQAM system into a data sequence alternately arranged in real and imaginary; wherein, the value range of M is 0, 1, 2, …, M. M is the number of working subcarriers of the FBMC-OQAM system.

Step 3, performing IFFT (inverse fast Fourier transform) transcoding on the real number received data added with the phase factors to obtain a data sequence meeting the specific conjugate symmetry characteristic

Step 4, receiving end data sequence

A demapping operation is performed to obtain an estimate of the raw data.

In one embodiment, the vector for the receiving end conjugate symmetric data sequence in any nth symbol period

Indicates, a data sequence within the symbol period

Represents;

the receiving end in the nth symbol period is conjugated with the symmetric data sequence

Wherein the value range of n is a non-negative integer; data sequence

A length of M;

expressed as estimated value of n-th set of raw data

The kth data of (1);

is represented as a data sequence in the nth symbol period

The kth data of (1); the conjugate value marked with the superscript;

operating for a solid part;

to take the imaginary part.

And 5, outputting the estimated value of the original data after parallel-serial conversion.

And after the estimated value of the nth group of original data is obtained, performing serial-parallel conversion on the estimated value of the nth group of original data to output the estimated value of the original data.

In the embodiment of the application, the single carrier low PAPR characteristic of the FBMC-OQAM system is realized by DFT coding, the original M/2 complex data is mapped into M-point complex signals with conjugate symmetry according to the time-frequency dual relation of Fourier transform, and the signals can directly generate M-point real and imaginary alternating signals after DFT precoding, so that the IFFT conversion can be directly carried out by the subcarrier modulation of the FBMC-OQAM system without carrying out OQAM preprocessing and keeping the same spectrum efficiency, and the scheme can completely recover the modulation characteristic of the FBMC-OQAM system, the peak-to-average ratio of the FBMC-OQAM system signal can be obviously reduced.

Example two

The present embodiment explains the implementation idea of the patent scheme based on the principle of FBMC multi-carrier modulation baseband processing system. The FBMC-OQAM baseband transmission signal is formed by overlapping M subcarrier signals, so that the PAPR is high. To reduce PAPR, DFT precoding may be employed in an OFDM system, and the baseband transmit signal may be restored to a single carrier form. Similar ideas can also be applied to the FBMC-OQAM system, for example, the baseband transmission signal s (t) of the FBMC-OQAM containing M subcarriers can be expressed as:

where (m, n) represents the mth subcarrier and the nth symbol period,

for real data symbols, j, sent on corresponding sub-carriers and symbol periods^m+nFor the OQAM modulation phase factor term, p (T) is the prototype filter, T is the symbol period, F is the subcarrier spacing, and TF 1/2 is satisfied.

If with T_s＝f_sSampling the baseband transmit signal s (t) for a period, where f_sFor the sampling rate, in the present embodiment, assume f_sAs MF, the discrete baseband transmit signal s (k) may be expressed as:

wherein k is a discrete sampling number.

According to the formulas (4) and (5), the input real and imaginary alternative data vector entering the IFFT module after the OQAM preprocessing can be expressed as

Wherein:

depending on the nature of the fourier transform,

result of inverse Fourier transform of (a)_nWith conjugate symmetry properties, please refer to fig. 12, which is a data sequence diagram of a specific conjugate symmetry property in an implementation.

In particular, the output sequence a of the inverse Fourier transform is observed_nThe kth element a (k) in (a), which is obtained from the fourier transform equation:

if it is

Then it is first

An element can be represented as

In the same way, for

The M-k th element can be represented as

That is, the IFFT output sequence an contains two sections of conjugate symmetric sequences, and the two sections of conjugate symmetric sequences are respectively

And

is conjugate and symmetrical about the central point. While

And

the values of the two points can be obtained as a phase factor j according to a Fourier transform formulaⁿThe product of a real number.

In order to enable DFT precoding to counteract the subsequent IFFT subcarrier modulation operation, an embodiment proposes an improved DFT precoding FBMC-OQAM system by mapping the input data to a data sequence of a specific conjugate symmetry characteristic as shown in fig. 12 and multiplying by a phase factor item jⁿThe time-frequency dual relation of Fourier transform can be found, and b is_nAfter FFT, the original is obtained

The output data is preprocessed by the form of real-virtual alternate OQAM, so that the data can be recovered to be b after the IFFT modulation by subcarriers_nThe sequence is a single carrier modulation signal of data, that is, the conjugate symmetric mapping mode proposed by the patent can be similar to SC-FDMA or DFT-s-OFDM, and the FBMC-OQAM transmission signal is also restored to be a single carrier signal, so that the PAPR of the FBMC-OQAM signal is obviously reduced. The original sending data x can be demodulated by carrying out corresponding OQAM demodulation, phase factor addition, IFFT decoding and corresponding demapping operation at the receiving end_n。

Fig. 13 is a schematic structural diagram of an FBMC-OQAM system with low peak-to-average power ratio in another embodiment, which includes a transmitting end and a receiving end.

The transmitting end of the FBMC-OQAM system comprises a preprocessing module and a transmitting module. The preprocessing module is used for preprocessing the pre-transmitted original data to obtain the pre-transmitted data which meets the real-virtual alternate arrangement of the real-quadrature requirement of the FBMC-OQAM system. The transmitting module is used for transmitting the preprocessed pre-transmission data from the transmitting end, only the processing of a baseband system is described in the patent, and intermediate frequency and radio frequency processing units such as analog-to-digital/digital-to-analog conversion, an amplifier, a mixer, a radio frequency filter, an antenna and the like are omitted. The preprocessing module comprises a front serial-to-parallel conversion module 21, a conjugate symmetric mapping module 22, a front FFT module 23, a front IFFT module 24 and a front polyphase filtering module 25. The front serial-to-parallel conversion module 21 is configured to group pre-transmitted original data and perform serial-to-parallel conversion on each group of original data. In one embodiment, the length of each set of original data is set to be M/2, where M is the number of subcarriers of the FBMC-OQAM system,M＝2^Land the value range of L is a natural number larger than 2.

The conjugate symmetry mapping module 22 is configured to map each group of serial-to-parallel converted original data into a data sequence satisfying a specific conjugate symmetry characteristic, where the length of the mapped data sequence is M. The data sequence satisfying the specific conjugate symmetry characteristic is a data sequence satisfying the following formula:

where b (k) is the kth data in the data sequence, and λ ═ j or ± 1 is a constant factor.

n-th set of raw data x_nMapping the data sequence b as the nth group of data sequences satisfying specific conjugate symmetry characteristics according to the following formula_n：

Wherein the value range of n is a non-negative integer; x is the number of_n(k) Denoted as n-th set of raw data x_nThe kth data of (1); b_n(k) Represented as the nth data sequence b_nThe kth data of (1);

the front FFT module 23 is configured to perform DFT precoding on each group of mapped data sequences, respectively, to obtain pre-transmission data that is alternately arranged in real and imaginary and meets the real-quadrature requirement of the FBMC-OQAM system. The pre-IFFT module 24 is configured to perform IFFT conversion on the DFT precoded data sequence, that is, perform subcarrier modulation of the FBMC-OQAM system. The pre-polyphase filter module 25 is configured to perform polyphase filtering on the data sequence signal modulated by the subcarrier, output a baseband transmit signal, perform carrier frequency modulation by the intermediate frequency and radio frequency processing unit, and send the baseband transmit signal to the channel 26.

The receiving end of the FBMC-OQAM system comprises a receiving module and a post-processing module, wherein the receiving module is used for carrying out polyphase filtering, FFT subcarrier demodulation, equalization and OQAM demodulation operation on a received baseband signal to obtain real data, and the post-processing module is used for adding a phase factor, IFFT conversion, demapping and serial-parallel conversion operation on the real data obtained by the receiving module to obtain output data of the FBMC-OQAM system.

The receiving module includes a post-polyphase filtering module 31, a post-FFT module 32, and a demodulation output module 33, and the post-polyphase filtering module 31, the post-FFT module 32, and the demodulation output module 33 are respectively configured to perform polyphase filtering, FFT subcarrier demodulation, equalization, and OQAM demodulation operations on the signal received from the channel 26. In one embodiment, the demodulation output module 33 employs an OQAM post-processing module of a conventional FBMC-OQAM system, as shown in fig. 5, to down-sample (extract) the received real part data by 2 times and delay one data point, to down-sample (extract) the received imaginary part data by 2 times and multiply by j, and to sum the real part and the imaginary part, thereby recovering the complex data to be transmitted.

The post-processing modules include an add phase factor module 34, a post IFFT module 35, a demapping module 36 and a post parallel to serial conversion module 37. And a phase factor adding module 34 for adding a phase factor to each real data in the same symbol period of the FBMC-OQAM system. In an embodiment, the adding phase factor module 34 is configured to perform an operation of adding a phase factor to a data sequence at a receiving end after an OQAM demodulation operation, and multiplies real data demodulated by a M-th subcarrier in an nth symbol of the FBMC-OQAM system by the phase factor jm, so that the real data received in each symbol period of the FBMC-OQAM system is converted into a set of data sequences alternately arranged in real and imaginary states, where a value range of n is a natural number, and a value range of M is 0, 1, 2.

The post IFFT module 35 is configured to perform IFFT conversion on the real data added with the phase factor to obtain a receiving end data sequence satisfying a specific conjugate symmetry characteristic. The demapping module 36 is configured to perform demapping operation on the data sequence at the receiving end to obtain an estimated value of the original data. In one embodiment, the vector is used for the data sequence in any nth symbol period

Indicates, a data sequence within the symbol period

Represents;

then, the data sequence in the nth symbol period

Wherein the value range of n is a natural number;

expressed as estimated value of n-th set of raw data

The kth data of (1);

is represented as a data sequence in the nth symbol period

The kth data of (1);

sequence ofA length of M;

the sequence length is M/2.

The post serial-parallel conversion module 37 is configured to perform parallel-serial conversion on the estimated value of the original data to obtain output data of the FBMC-OQAM system. In one embodiment, after obtaining n sets of estimated values of the raw data, the estimated values of the raw data are output by performing serial conversion on the n sets of estimated values of the raw data.

Please refer to fig. 14 and fig. 15, which are a schematic diagram illustrating PAPR performance simulation and BER simulation in an embodiment of an FBMC-OQAM system, respectively, wherein taking a system with a subcarrier number M of 64, a subcarrier bandwidth of 15KHz and 4QAM constellation modulation as an example, fig. 14 and fig. 15 respectively illustrate PAPR performance and BER (Bit Error Ratio) of an example signal. As can be seen from the cumulative distribution function curve of the peak-to-average power ratios of the signals in fig. 14, the probability distribution function values of the DFT-spread coded DFT-s-FBMC signal in the embodiment of the present application at most of the decibel (dB) values of the peak-to-average power ratio are significantly smaller than those of the non-spread coded FBMC-OQAM signal, and also smaller than those of the conventional direct DFT-s-FBMC and optimum-phase DFT-s-FBMC system, which indicates that the DFT coded FBMC-OQAM signal in the present application has a lower peak-to-average power ratio than the other three systems. The bit error rate performance of 16QAM modulation in ITU vehicular-a channel is shown in fig. 15, and since the spread code signal has diversity effect in frequency, it can be shown that the bit error rate curve of the DFT spread coding FBMC-OQAM (DFT-s-OFDM) system proposed in this application is close to the bit error rate curve of SC-FDMA, and lower than that of the uncoded FBMC-OQAM system at the same signal-to-noise ratio, which proves the validity and correctness of the technical solution of this application.

The present invention has been described in terms of specific examples, which are provided to aid understanding of the invention and are not intended to be limiting. For a person skilled in the art to which the invention pertains, several simple deductions, modifications or substitutions may be made according to the idea of the invention.

Claims

1. A low peak-to-average ratio FBMC-OQAM signal processing method is characterized by comprising the following steps:

respectively carrying out DFT precoding on each group of mapped data sequences to obtain real and virtual alternative arranged pre-transmission data meeting real and orthogonal requirements of an FBMC-OQAM system;

the length of each group of original data is M/2, wherein M is the number of subcarriers of an FBMC-OQAM system, the length of a data sequence subjected to conjugate symmetric mapping is M, and M is 2^LThe value range of L is a natural number more than or equal to 2;

to take the imaginary part.

2. The method of claim 1, wherein the mapping each set of serial-to-parallel converted raw data into a data sequence satisfying a specific conjugate symmetry property comprises:

Wherein the value range of n is a non-negative integer; x is the number of_n(k) Denoted as n-th set of raw data x_nThe kth data of (1); b_n(k) Represented as the nth data sequence b_nThe kth data of (1); the conjugate value marked with the superscript;

operating for a solid part;

to take the imaginary part.

3. The method of claim 1, further comprising:

taking each group of data sequences after DFT precoding as modulation data of one symbol period of the FBMC-OQAM system to perform IFFT conversion so as to complete subcarrier modulation; one symbol period of the FBMC-OQAM system is T, where T is 1/(2F), where F is a subcarrier bandwidth;

and outputting each group of data sequences after completing subcarrier modulation as baseband sending signals after passing through a polyphase filter.

4. A data processing method of low peak-to-average power ratio FBMC-OQAM is characterized by comprising the following steps:

the estimated value of the original data is output after parallel-serial conversion;

the adding of the phase factor to each real data in the same symbol period of the FBMC-OQAM system includes:

multiplying real data demodulated by m-th subcarrier in nth symbol of FBMC-OQAM system by phase factor j^mConverting real data received in each symbol period of the FBMC-OQAM system into a group of data sequences alternately arranged in real and imaginary; wherein the value range of n is a natural number, and the value range of M is 0, 1, 2. M is the number of working subcarriers of the FBMC-OQAM system;

the demapping operation of the receiving end conjugate symmetric data sequence to obtain an estimated value of original data includes:

vector for receiving end conjugate symmetric data sequence in arbitrary nth symbol period

Indicates, a data sequence within the symbol period

Represents;

the receiving end conjugate symmetric data sequence in the nth symbol period

Wherein the data sequence

A length of M; the value range of n is a non-negative integer;

expressed as estimated value of n-th set of raw data

The kth data of (1);

is represented as a data sequence in the nth symbol period

The kth data of (1); the conjugate value marked with the superscript;

operating for a solid part;

to take the imaginary part.

5. A low peak-to-average ratio FBMC-OQAM system, comprising:

the preprocessing module is used for preprocessing the pre-transmitted original data to obtain real and virtual alternately arranged pre-transmitted data meeting the real and quadrature requirements of the FBMC-OQAM system;

the preprocessing module comprises:

a conjugate symmetry mapping module, which is used for respectively mapping each group of original data after serial-parallel conversion into data sequences meeting specific conjugate symmetry characteristics by adopting the low peak-to-average ratio FBMC-OQAM signal processing method as claimed in claim 1;

6. A low peak-to-average ratio FBMC-OQAM system, comprising:

a post-processing module, configured to add a phase factor, IFFT conversion, demapping, and serial-parallel conversion operations to real data obtained by the receiving module by using the data processing method of FBMC-OQAM with low peak-to-average ratio as claimed in claim 4, and then use the real data as final demodulated output data of the FBMC-OQAM system;

the post-processing module comprises: