CN110290087B

CN110290087B - Method and device for modulating and demodulating GFDM signal

Info

Publication number: CN110290087B
Application number: CN201910605925.1A
Authority: CN
Inventors: 杨阳; 朱立东; 毛兴; 谭琪; 张海鹏; 卢宁宁; 宋瑞良
Original assignee: University of Electronic Science and Technology of China; CETC 54 Research Institute
Current assignee: University of Electronic Science and Technology of China; CETC 54 Research Institute
Priority date: 2019-07-05
Filing date: 2019-07-05
Publication date: 2021-10-15
Anticipated expiration: 2039-07-05
Also published as: CN110290087A

Abstract

The invention discloses a method and a device for modulating and demodulating a GFDM signal. The modulation method comprises the following steps: carrying out channel coding on binary signals to be transmitted, and mapping the binary signals into multilevel symbols in groups; according to the multi-system symbol, generating a corresponding ZC cyclic shift keying sequence after the original ZC sequence is cyclically shifted; the ZC cyclic shift keying sequence is used as a spread spectrum code string, and CCSK is adopted to spread spectrum on binary data; performing serial-parallel conversion on the spread data to generate data blocks, wherein column vectors of the data blocks are ZC cyclic shift keying sequences in a column; taking the column vector of the data block as a subsymbol of the GFDM; obtaining an IDFT form of the subsymbol according to the original ZC sequence and the corresponding cyclic shift value; and performing cyclic shift filtering on the IDFT form of each sub-symbol, and then superposing to generate a baseband signal waveform. The invention reduces the PAPR of the transmission signal and improves the anti-interference performance aiming at the characteristics of low signal-to-noise ratio of the channel, large signal path fading, sensitivity to the signal peak-to-average power ratio and the like in satellite communication.

Description

Method and device for modulating and demodulating GFDM signal

Technical Field

The invention belongs to the field of communication, and particularly relates to a modulation and demodulation method and device for a GFDM signal.

Background

Satellite communication has been an important means of communication due to its wide area coverage advantages, however its limited transmission rate has once limited its development in public communications. For this reason, the satellite communication system is a power-limited system due to the limitation of the size of the platform and the terminal. Orthogonal Frequency Division Multiplexing (OFDM) is one of the key technologies in 4G LTE and 5G NR, and as a multi-carrier waveform technology, it greatly improves the spectrum utilization rate, thereby increasing the data transmission rate of the network and meeting the requirements of people on high-speed personal communication. However, when OFDM is applied to satellite communication, the Power backoff problem of the non-linear Power amplifier on the satellite due to the excessively high PAPR of the OFDM Peak-to-average Power Ratio has to be faced.

Currently, various OFDM improvement techniques are proposed in the industry, and one of them is the Generalized Frequency Division Multiplexing (GFDM). GFDM was developed on the basis of OFDM to improve spectral efficiency by introducing multiple sub-symbols per sub-carrier. The GFDM is a multi-carrier modulation system adopting non-rectangular pulse forming, and a DFT filter bank structure is realized on a frequency domain by using cyclic convolution. The symbol blocks on M time slots and K subcarriers are regarded as a frame, a cyclic prefix does not need to be added in front of each symbol, and only the cyclic prefix needs to be added in front of the frame, so that interframe interference is avoided, and the frequency spectrum utilization rate is improved. The GFDM may select different pulse shaping filters and insert different length CPs depending on the different types of services and the requirements of the application on the air interface. Because the GFDM prototype filter has sparsity in the frequency domain, a lower complexity transmitting and receiving algorithm can be designed. The conventional GFDM generally employs a frequency domain linear receiving algorithm, typically a Matched Filtering (MF)/Zero Forcing (ZF)/Minimum Mean Square Error (MMSE) algorithm, etc. In addition, the GFDM is based on independent block modulation, and different subcarriers and sub-symbols are configured, so that the GFDM has a flexible frame structure and can be suitable for different service types. The sub-carrier of the GFDM is filtered by an effective prototype filter and is circularly shifted in a time domain and a frequency domain, and the process reduces out-of-band leakage and is beneficial to reducing interference among multiple users and multiple systems. It is because of these advantages of GFDM that we consider the application of this multi-carrier technique to satellite communication links. However, the peak-to-average power ratio of conventional GFDM is even higher than OFDM and needs to be improved to be more suitable for satellite communications.

In the PRACH channel of the terrestrial LTE system, a transmitting end selects a special zero autocorrelation constant envelope (CAZAC) -ZC sequence, which has many good characteristics. The amplitude of a ZC sequence of any length is constant with a constant envelope characteristic. After any ZC sequence is shifted by n bits, when n is not an integral multiple of the period of the ZC sequence, the shifted sequence is not related to the original sequence and has ideal periodic auto-correlation/cross-correlation characteristics. The good autocorrelation property and cross-correlation property make the ZC sequence an ideal spreading sequence. The ratio of the peak value to the average value of a signal composed of any ZC sequence is very low. Furthermore, the DFT/IDFT transform of the ZC sequence is still a ZC sequence. In summary, we consider that each sub-symbol of GFDM is spread by ZC sequence and then transmitted, and design a low PAPR multi-carrier waveform technique suitable for satellite communication link.

Disclosure of Invention

In order to meet the requirement of a satellite communication system link on low PAPR waveform, the invention provides a GFDM signal modulation and demodulation method and a device.

A modulation method of a GFDM signal is applied to a transmitting end, and comprises the following steps:

the method comprises the following steps: carrying out channel coding on binary data to be transmitted, and mapping the binary data into multi-system symbols in groups;

step two: according to the multi-system symbol, generating a corresponding ZC cyclic shift keying sequence after the original ZC sequence is cyclically shifted; the ZC cyclic shift keying sequence is used as a spread spectrum code string, and CCSK is adopted to spread spectrum on binary data;

step three: performing serial-parallel conversion on the spread data to generate data blocks, wherein column vectors of the data blocks are ZC cyclic shift keying sequences in a column; taking the column vector of the data block as a subsymbol of the GFDM; obtaining an IDFT form of the subsymbol according to the original ZC sequence and the corresponding cyclic shift value; and performing cyclic shift filtering on the IDFT form of each sub-symbol, and then superposing to generate a baseband signal waveform.

Preferably, in the third step, after performing periodic extension on the IDFT format of each sub-symbol, performing cyclic shift filtering respectively, and then performing superposition; and adding CP to the superposed signals, and performing molding filtering to generate baseband signal waveforms.

Preferably, the method further comprises the following step four: up-converting the baseband signal into a transmission signal.

Preferably, the binary signal packet is mapped into M K-ary symbols; the root index of the original ZC sequence is u, and the length of the original ZC sequence is K; the data block is K × M dimensional.

A demodulation method of GFDM signal is applied to a receiving end, and the method comprises the following steps:

s1, solving a baseband signal according to the received transmission signal;

s2, carrying out GFDM demodulation on the baseband signal to obtain a sub-symbol;

s3, performing cyclic convolution on the subsymbols and the local ZC sequence to obtain a cyclic shift value of the local ZC sequence; and demapping the cyclic shift value of the local ZC sequence to obtain transmitted binary information.

Preferably, the GFDM demodulation method includes performing demodulation by using a matched filter algorithm, a zero-forcing algorithm, or a minimum mean square error algorithm.

Preferably, in step S3, different users are distinguished according to different root indexes of the local ZC sequence, and the cyclic shift value of the local ZC sequence is demapped to obtain the transmitted binary information.

A device for modulating a GFDM signal for use at a transmitting end, the device comprising: the mapping module is a CCSK-GFDM combined modulation module;

the mapping module is used for carrying out channel coding on the binary signals to be transmitted and mapping the binary signals into multi-system symbols in groups;

the CCSK-GFDM joint modulation module,

according to the multi-system symbol, generating a corresponding ZC cyclic shift keying sequence after the original ZC sequence is cyclically shifted; the ZC cyclic shift keying sequence is used as a spread spectrum code string, and CCSK is adopted to spread spectrum on binary data; performing serial-parallel conversion on the spread data to generate data blocks, wherein column vectors of the data blocks are ZC cyclic shift keying sequences in a column; taking the column vector of the data block as a subsymbol of the GFDM; obtaining an IDFT form of the subsymbol according to the original ZC sequence and the corresponding cyclic shift value; and performing cyclic shift filtering on the IDFT form of each sub-symbol, and then superposing to generate a baseband signal waveform.

A demodulation apparatus for GFDM signals, applied to a receiving end, the apparatus comprising: the device comprises a GFDM demodulator, a CCSK dispreading module and a demapping module;

a GFDM demodulator for GFDM demodulating the baseband signal to obtain subsymbols;

the CCSK de-spreading module is used for performing cyclic convolution on the subsymbols and the local ZC sequence to obtain a cyclic shift value of the local ZC sequence;

and the demapping module is used for demapping the cyclic shift value of the local ZC sequence to obtain a binary symbol.

According to another aspect of the present invention, there is provided an electronic device, comprising at least one processor, and a memory communicatively coupled to the at least one processor; the memory stores instructions executable by the at least one processor to enable the at least one processor to perform any of the methods described above.

Compared with the prior art, the invention has the beneficial effects that:

aiming at the characteristics of low channel signal-to-noise ratio, large signal path fading, sensitivity to signal peak-to-average power ratio and the like in satellite communication, the CCSK-GFDM combined modulator is designed by adopting a method of combining CCSK soft spreading and GFDM in order to meet the requirements of a system on PAPR and anti-interference performance of a transmission signal. The method fully utilizes the characteristics of stronger anti-interference performance of spread spectrum communication technology, low sidelobe and high spectral efficiency of GFDM, adopts a sub-symbol soft spreading method on a GFDM data block, distributes a ZC sequence with constant amplitude characteristic to each subcarrier, avoids the high PAPR characteristic after time domain spread spectrum signals are superposed, ensures that the modulated transmitting signal not only completely retains the advantages of GFDM, but also greatly improves the PAPR performance compared with OFDM signals and traditional GFDM signals. Compared with OFDM and GFDM which are not spread, the soft spread spectrum technology adopted by the invention improves the information transmission rate of the traditional direct sequence spread spectrum on the premise of keeping the anti-interference performance of spread spectrum communication, and can obtain better error rate performance under the environment of low signal-to-noise ratio of satellite communication. In addition, in the random access process, the invention expands GFDM signals from the traditional time-frequency structure to the time-frequency code structure, so that the access resources which can be selected by the user are increased, thereby greatly improving the access success rate of the user and increasing the access capacity of the system.

Description of the drawings:

fig. 1 is a schematic flow chart of a method for modulating and demodulating a GFDM signal according to the present invention.

Fig. 2 is a schematic structural diagram of a GFDM signal modulation apparatus according to the present invention.

Fig. 3 is a schematic structural diagram of a demodulation apparatus for a GFDM signal according to the present invention.

Fig. 4 is a schematic structural diagram of an electronic device provided in the present invention.

Fig. 5 is a schematic diagram of GFDM data block spreading according to the method of the present invention.

Fig. 6 is a diagram showing PAPR comparison between GFDM based on CCSK cyclic spreading and conventional OFDM/GFDM.

Detailed Description

The present invention will be described in further detail with reference to test examples and specific embodiments. It should be understood that the scope of the above-described subject matter is not limited to the following examples, and any techniques implemented based on the disclosure of the present invention are within the scope of the present invention.

Referring to fig. 1, the present invention uses soft spreading cyclic Code Shift keying (ccsk) and GFDM special time-frequency block structure, and uses ZC sequence to soft-spread the sub-symbols of GFDM, so that the soft-spread sub-symbols with constant envelope are allocated to each sub-carrier, thereby obtaining GFDM waveform with lower PAPR. The GFDM waveform acquires corresponding binary transmission information by utilizing the relevant peak position of the spread spectrum code, and can resist noise interference under a low signal-to-noise ratio channel environment. Meanwhile, the GFDM waveform designed by the invention integrates code domain resources, so that a plurality of user information can be transmitted on the same subcarrier and the same subsymbol in an overlapping way. The invention fully utilizes the constant modulus zero autocorrelation characteristic of the spread spectrum sequence and the special time-frequency block structure of the GFDM, solves the problem of higher PAPR of the traditional OFDM/GFDM waveform under the condition of low signal-to-noise ratio of satellite communication, improves the high error rate characteristic of the traditional GFDM under the environment of low signal-to-noise ratio, and greatly improves the system capacity.

The method for modulating the GFDM signal is applied to a transmitting end and comprises the following steps:

carrying out channel coding on binary signals to be transmitted, and mapping the binary signals into M K-ary symbols in groups;

spreading binary data by adopting a spreading Code string (ZC cyclic Shift keying sequence) generated by cyclic Shift of an original ZC sequence with the root index of u and the length of K and adopting a CCSK (cyclic Code Shift keying) cyclic spreading modulation scheme. The ZC sequence can generate ZC cyclic shift keying sequences with K different cyclic shift states after cyclic shift, and the K states can represent log₂K bits of binary information. The spreading factor is defined as the ratio of the spreading code length to the number of bits, so that the spreading factor of CCSK is K/log₂K。

After generating the spread signal, serial-to-parallel converting the spread data to form a GFDM data block with dimension K × M, as shown in fig. 5, where the number of subcarriers is K, the number of subsymbols included in each subcarrier is M, and the total number of symbols N is K × M. Column vectors of the data blocks are ZC cyclic shift keying sequences in a column; taking the column vector of the data block as a subsymbol of the GFDM; obtaining an IDFT form of the subsymbol according to the original ZC sequence and the corresponding cyclic shift value; after the IDFT form of each sub-symbol is subjected to period prolongation, cyclic shift filtering is respectively carried out, and then superposition is carried out; and adding CP to the superposed signals, and performing molding filtering to generate baseband signal waveforms.

The data block is subjected to GFDM modulation, including time-frequency conversion, forming filtering, data block adding CP and the like. The prototype filter is proposed to adopt an RC root raised cosine filter, the larger the roll-off coefficient is, the better the PAPR performance is, and when the roll-off coefficient is 1, the PAPR performance is optimal. In addition, the GFDM modulation operation may be implemented in the frequency domain or in the time domain. When frequency domain modulation is adopted, the sampling value of the prototype filter is sparse in the frequency domain, and the memory resource can be saved by adopting the frequency domain modulation. When time domain modulation is adopted, the ZC sequence is still the ZC sequence after IFFT, and the cyclic shift number is unchanged, so that an IFFT conversion signal corresponding to the ZC sequence can be obtained by directly looking up a table according to the cyclic shift number, CCSK-GFDM combined modulation is realized, IFFT operation times of a transmitting end are reduced, and complexity is remarkably reduced.

The modulated baseband signal is up-converted into a transmission signal, and enters a satellite channel environment.

Then, a demodulation method of a GFDM signal is applied to a receiving end, the method includes:

after the received transmission signal is subjected to time-frequency synchronization, down-conversion and channel equalization, a baseband signal is solved;

carrying out GFDM demodulation on the baseband signal to obtain a CCSK symbol carried on the subsymbol; the GFDM demodulation method comprises the step of demodulating by adopting a matched filtering algorithm or a zero forcing algorithm or a minimum mean square error algorithm.

After each sub-symbol is demodulated by the GFDM, the sub-symbol data and the local ZC sequence are subjected to cyclic cross-correlation, and the correlation peak value is the cyclic shift value of the ZC sequence. And distinguishing different users according to different root indexes u of the ZC sequence, and demapping the cyclic shift value of the ZC sequence to obtain transmitted binary information.

Corresponding to the modulation method, the embodiment of the invention also provides a modulation device of the GFDM signal. The following describes a modulation apparatus for a GFDM signal according to an embodiment of the present invention.

Referring to fig. 2, a GFDM signal modulation apparatus applied to a transmitting end, the apparatus comprising: the mapping module is a CCSK-GFDM combined modulation module;

the CCSK-GFDM joint modulation module comprises: generating a corresponding ZC cyclic shift keying sequence from the multilevel symbols; the ZC cyclic shift keying sequence is used as a spread spectrum code string, and CCSK is adopted to spread spectrum on binary data; performing serial-parallel conversion on the spread binary data to generate a data block; taking a ZC cyclic shift keying sequence as a sub-symbol of the GFDM to obtain an IDFT form of the sub-symbol; and performing cyclic shift filtering on the IDFT form of each sub-symbol, and then superposing to generate a baseband signal waveform.

Corresponding to the demodulation method, the embodiment of the invention also provides a demodulation device of the GFDM signal. The following describes a demodulation apparatus for GFDM signals according to an embodiment of the present invention.

As shown in fig. 3, a demodulation apparatus for GFDM signal, applied to a receiving end, comprises: the device comprises a GFDM demodulator, a CCSK dispreading module and a demapping module;

the CCSK de-spreading module is used for performing cyclic convolution on the subsymbols and the local ZC sequence to obtain a cyclic shift value of the ZC sequence;

and the demapping module is used for demapping the cyclic shift value of the ZC sequence to obtain a binary symbol.

FIG. 4 illustrates an electronic device (e.g., a computer server with program execution functionality) including at least one processor, a power source, and a memory and input-output interface communicatively coupled to the at least one processor, according to an exemplary embodiment of the invention; the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method disclosed in any one of the preceding embodiments; the input and output interface can comprise a display, a keyboard, a mouse and a USB interface and is used for inputting and outputting data; the power supply is used for supplying electric energy to the electronic equipment.

Those skilled in the art will understand that: all or part of the steps for realizing the method embodiments can be completed by hardware related to program instructions, the program can be stored in a computer readable storage medium, and the program executes the steps comprising the method embodiments when executed; and the aforementioned storage medium includes: various media that can store program codes, such as a removable Memory device, a Read Only Memory (ROM), a magnetic disk, or an optical disk.

When the integrated unit of the present invention is implemented in the form of a software functional unit and sold or used as a separate product, it may also be stored in a computer-readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present invention may be essentially implemented or a part contributing to the prior art may be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the methods described in the embodiments of the present invention. And the aforementioned storage medium includes: a removable storage device, a ROM, a magnetic or optical disk, or other various media that can store program code.

Example 1

The length of binary data is set to be 64 bits, every 4 bits are mapped into 16-system symbols through Gray coding, and 16 symbols are totally to be transmitted. The CCSK cyclic spread spectrum modulation scheme is adopted to spread the binary data, a ZC sequence with the index of 3 and the length of 16 is selected as a spread spectrum sequence, and the cyclic shift number is determined by a 16-system symbol. The data length after spreading is 256 symbols. The data is serial-to-parallel converted to form a 16 x 16 data matrix, i.e., 16 rows of subcarriers and 16 columns of subsymbols. When a GFDM time domain modulation mode is adopted, each column of ZC sequences of data can be converted into a corresponding IFFT conversion form through table lookup or pre-calculation, and the complexity of the system is reduced. Multiplying each line of data by a raised cosine filter time domain waveform sequence with a roll-off coefficient of 0.9, and finally, circulating each line of data to the right in sequence for 16 bits and then superposing to obtain a GFDM waveform with low PAPR. The demodulation process can adopt the traditional GFDM frequency domain demodulation, the spread spectrum data is solved and then the cyclic cross correlation is carried out with the local ZC sequence, and the position of the related peak value represents the value of the transmission symbol. In contrast, we analyze the PAPR of the GFDM signal and the OFDM signal without sub-symbol spreading when the number of subcarriers K is 16. As shown in FIG. 6, the improved GFDM waveform design proposed by the present patent is 5-8 dB higher than the conventional OFDM/GFDM waveform under the simulation conditions.

The foregoing is merely a detailed description of specific embodiments of the invention and is not intended to limit the invention. Various alterations, modifications and improvements will occur to those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A method for modulating a GFDM signal, for use at a transmitting end, the method comprising:

step two: according to the multi-system symbol, after the ZC sequence is circularly shifted, generating a corresponding ZC circularly shifted keying sequence; the ZC cyclic shift keying sequence is used as a spread spectrum code string, and CCSK is adopted to spread spectrum on the binary data;

step three: performing serial-parallel conversion on the spread data to generate data blocks, wherein column vectors of the data blocks are a column of ZC cyclic shift keying sequences; taking the column vector of the data block as a sub-symbol of the GFDM; obtaining the IDFT form of the subsymbol according to the ZC sequence and the corresponding cyclic shift value; and performing cyclic shift filtering on the IDFT form of each sub-symbol, and then performing superposition to generate a baseband signal.

2. The method according to claim 1, wherein in the third step, after the periodic extension of the IDFT form of each of the sub-symbols, the cyclic shift filtering is performed separately, and then the sub-symbols are superimposed; and adding CP to the superposed signals, and performing shaping filtering to generate the baseband signals.

3. The method of modulating a GFDM signal as defined in claim 1, further comprising the steps of: and up-converting the baseband signal into a transmission signal.

4. The method of modulating a GFDM signal as claimed in claim 1, wherein in step one, said binary data packets are mapped into M K-ary symbols; the root index of the ZC sequence is u, and the length of the ZC sequence is K; the data block is of dimension K × M.

5. A demodulation method of a GFDM signal, applied to a receiving end, the method comprising:

s1, solving a baseband signal according to the received transmission signal;

6. The method for demodulating a GFDM signal as claimed in claim 5, wherein in step S2, the GFDM demodulation comprises demodulation using a matched filter algorithm or a zero-forcing algorithm or a minimum mean square error algorithm.

7. The method of claim 6, wherein in step S3, different users are distinguished according to different root indexes of the local ZC sequences, and the cyclic shift values of the local ZC sequences are demapped to obtain binary information for transmission.

8. An apparatus for modulating a GFDM signal, for use at a transmitting end, the apparatus comprising: the mapping module is a CCSK-GFDM combined modulation module;

the CCSK-GFDM joint modulation module,

according to the multi-system symbol, after the ZC sequence is circularly shifted, generating a corresponding ZC circularly shifted keying sequence; the ZC cyclic shift keying sequence is used as a spread spectrum code string, and CCSK is adopted to spread spectrum on binary data; performing serial-parallel conversion on the spread data to generate data blocks, wherein column vectors of the data blocks are a column of ZC cyclic shift keying sequences; taking the column vector of the data block as a sub-symbol of the GFDM; obtaining the IDFT form of the subsymbol according to the ZC sequence and the corresponding cyclic shift value; and performing cyclic shift filtering on the IDFT form of each sub-symbol, and then superposing to generate a baseband signal waveform.

9. A demodulation apparatus for GFDM signals, for use at a receiving end, comprising: the device comprises a GFDM demodulator, a CCSK dispreading module and a demapping module;

the GFDM demodulator is used for carrying out GFDM demodulation on the baseband signal to obtain a subsymbol;

the demapping module demaps the cyclic shift value of the local ZC sequence to obtain a binary symbol.

10. An electronic device for GFDM signal processing comprising at least one processor and a memory communicatively coupled to the at least one processor; the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method of any one of claims 1 to 9.