CN112688896A

CN112688896A - Orthogonal frequency division multiplexing modulation system and frequency domain spreading non-orthogonal active interference cancellation method

Info

Publication number: CN112688896A
Application number: CN202011528279.2A
Authority: CN
Inventors: 代光发; 陈少平; 饶文贵; 王勤; 杨杨
Original assignee: South Central University for Nationalities
Current assignee: South Central Minzu University
Priority date: 2020-12-22
Filing date: 2020-12-22
Publication date: 2021-04-20
Anticipated expiration: 2040-12-22
Also published as: CN112688896B

Abstract

The invention belongs to the technical field of wireless communication, and discloses an orthogonal frequency division multiplexing modulation system and a non-orthogonal active interference cancellation method for frequency domain expansion, which convert serial sending data into parallel data; mapping the binary information into a multilevel communication constellation symbol; allocating data symbols to appropriate subcarriers; modulating a symbol from a frequency domain to a time domain; converting the parallel signal into a serial signal; adding a time domain cyclic prefix; windowing and forming time domain signals; suppressing the frequency spectrum leakage of the transmitted signal by adopting a frequency domain spreading non-orthogonal active interference cancellation method; the signal is converted from a baseband signal to a frequency band signal. The invention greatly reduces the frequency spectrum leakage of the orthogonal frequency division multiplexing signal, and leads the frequency spectrum leakage to be lower than-80 dB; the interference of the interference cancellation signal to data is reduced and is lower than-80 dB; the energy of interference cancellation subcarriers is reduced, and the energy efficiency of the system is improved; while maintaining the symbol waveform compatible with the CP-OFDM symbol format.

Description

Orthogonal frequency division multiplexing modulation system and frequency domain spreading non-orthogonal active interference cancellation method

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to an orthogonal frequency division multiplexing modulation system and a frequency domain spreading non-orthogonal active interference cancellation method.

Background

At present, bandwidth wireless communication faces a serious problem of insufficient spectrum resources, and an orthogonal frequency division multiplexing modulation system widely adopted in the bandwidth wireless communication has serious spectrum leakage and reduces spectrum efficiency. The method and the device have the advantages that the frequency spectrum side lobe of the orthogonal frequency division multiplexing signal is suppressed, and the method and the device are of great significance for improving the frequency spectrum efficiency and relieving the insufficiency of wireless frequency spectrum resources.

The main methods for suppressing the spectrum leakage of the OFDM signal include a windowing method and an active interference cancellation method (AIC), and they may also be used in combination. The non-orthogonal active interference cancellation sidelobe suppression effect is good, but the defect that the data subcarrier of the system is interfered exists.

The method comprises the following steps: (1) the energy of the CC inserted into the transition protective belt is too large, so that the energy efficiency of the system is reduced, and the energy efficiency of the system is possibly lower than 50%; (2) the non-orthogonal CC causes larger inter-subcarrier interference to data subcarriers, and the system error rate is deteriorated; (3) the existing method of windowing combined with active interference cancellation leads to problems of symbol time length and incompatibility of CP-OFDM symbol formats.

In the prior art, an OFDM cognitive radio system and a non-orthogonal active side lobe suppression method) are reported, but the requirements of symbol length and structure after windowing and CP-OFDM before windowing are not guaranteed. The Windowing method adopted by the document CPW-OFDM (cyclic post transmit OFDM) for the B5G (Beyond 5th Generation) Waveform does not change the symbol length and structure of CP-OFDM, but does not consider the organic combination with active interference cancellation, so the spectrum leakage is still large.

The frequency distribution of the interference cancellation subcarrier (CC) of the conventional non-orthogonal interference cancellation method is simply set in a target side lobe suppression area and a transition guard band area, which fails to suppress the frequency spectrum leakage of the orthogonal frequency division multiplexing most effectively and is also not beneficial to reducing the interference of the non-orthogonal CC to the data subcarrier in the system.

Through the above analysis, the problems and defects of the prior art are as follows:

(1) the existing non-orthogonal interference cancellation method cannot inhibit the frequency spectrum leakage of orthogonal frequency division multiplexing most effectively, and is also not beneficial to reducing the interference of non-orthogonal CC to data subcarriers in the system.

(2) The existing non-orthogonal interference cancellation method reduces the energy efficiency of the system;

(3) the existing method of windowing combined with active interference cancellation leads to problems of symbol time length and incompatibility of CP-OFDM symbol formats.

The difficulty and solution to the above problems and disadvantages are:

the inserted non-orthogonal active interference cancellation sub-carrier can cause interference to the data sub-carrier while canceling the spectrum leakage of the OFDM, and the system error rate is increased. Extending the interference cancellation subcarriers to more efficient frequency band locations, such as the data subcarrier frequency bands, reduces the interference caused to the data subcarriers by the non-orthogonal subcarriers.

The goal of OFDM spectral sidelobe leakage suppression is to create a signal with a strictly limited bandwidth of the band, which would be in contrast to an OFDM signal that is rectangular in shape in the time domain, i.e., a signal with a strictly limited bandwidth must be windowed (or bandpass filtered) like. However, windowing typically destroys the format of the CP-OFDM signal waveform. Therefore, the invention utilizes the window function of a very small roll-off factor to be matched with a non-orthogonal active interference cancellation method, can bring about great reduction of side lobe leakage, simultaneously improves the Gibbs effect, reduces the CC energy of a transition zone and improves the energy efficiency of a system.

The significance of solving the problems and the defects is as follows:

a more effective frequency band for setting the non-orthogonal interference cancellation sub-carrier is found, so that the frequency spectrum leakage and the self-interference are greatly reduced, and the utilization rate of wireless frequency spectrum resources is improved; a small part of CP is used for windowing, so that the structure of the OFDM symbol and the existing CP-OFDM window are kept, the design of a receiver is not changed, the serious Gibbs effect possibly occurring in the frequency domain of the OFDM symbol is effectively avoided, and the energy efficiency of the system is improved.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides an orthogonal frequency division multiplexing modulation system and a non-orthogonal active interference cancellation method for frequency domain expansion.

The present invention is achieved as such, an orthogonal frequency division multiplexing modulation system comprising: a transmitter and a receiver;

the transmitter includes:

the serial-parallel conversion module is used for converting serial data into parallel data;

the symbol mapping module is used for mapping the binary information into a multi-system communication constellation symbol;

the subcarrier mapping module is used for distributing the data symbols to proper subcarriers and setting the unused subcarriers to zero;

the multi-carrier modulation module is used for modulating and converting the symbols from a frequency domain to a time domain;

the parallel-serial conversion module is used for converting the parallel signals into serial signals;

the cyclic prefix adding module is used for adding cyclic prefixes to serial OFDM time domain symbols one by one in a time domain;

the windowing module is used for windowing and forming the time domain signals;

the frequency spectrum leakage cancellation module is used for suppressing the frequency spectrum leakage of the transmission signal by adopting a non-orthogonal active interference cancellation method; simultaneously, the method is used for counteracting the spectrum leakage of a plurality of sidelobe suppression areas;

and the up-conversion module is used for converting the signal from the baseband signal into a frequency band signal.

Another object of the present invention is to provide a frequency domain extended non-orthogonal active interference cancellation method applied to the ofdm modulation system, where the frequency domain extended non-orthogonal active interference cancellation method includes:

and a part of the cyclic prefix is utilized to carry out windowing without changing the time length of the CP-OFDM symbol, and meanwhile, the frequency domain expansion is combined with the frequency domain expansion active interference cancellation to carry out the non-orthogonal active interference cancellation method of the frequency domain expansion.

The orthogonal frequency division multiplexing system and the inserted active interference cancellation subcarriers are both time domain oversampled. Meanwhile, the sidelobe canceling signal inserted by the spectrum sidelobe canceling module is frequency domain extended, namely, the spectrum sidelobe canceling subcarrier (CC) is partially arranged in a transition guard band position where data is not sent and a frequency band area to be suppressed, and particularly, part of the CC is arranged in a data subcarrier area of the system for enhancing the sidelobe canceling effect and reducing the inter-subcarrier interference which is possibly introduced.

Further, the frequency domain extended non-orthogonal active interference cancellation method comprises the following steps:

firstly, windowing processing is carried out, and the frequency spectrum leakage of the orthogonal frequency division multiplexing signals of time domain windowing and frequency domain expansion is calculated;

step two, calculating interference cancellation signals of time domain windowing and frequency domain expansion; the interference cancellation is performed on the transmitted signal in the time domain.

Further, in step one, the windowing includes: windowing is performed using a raised cosine window, or other window function having smaller spectral sidelobes than a rectangular window.

Further, in the step one, the calculating the spectrum leakage of the time-domain windowed and frequency-domain spread orthogonal frequency division multiplexing signal includes:

obtaining a windowed time-domain CP-OFDM signal s_wObtaining a time domain CP-OFDM signal s through v times oversampling DFT analysis_wOf the spectrum

s_w＝GF_dx；

Wherein G is a linear sum of 2(M + L)_cpThe window function of + δ) -1 constitutes the diagonal matrix of its diagonal elements, 2L_cpIs the CP length, 2 δ is the length of the roll-off region of the window function; multiple 2 is the complement of the symbol in the frequency domainA multiple of zero of 2;

the elements are defined as:

-2L_cpn is less than or equal to 2(M + delta) -1, M is less than or equal to 0 and less than or equal to 2M-1, wherein n and M respectively represent the time normalized to the sampling interval and the frequency normalized to the carrier interval, and the units are T/(2M) and 1/(2T) respectively.

Represents a v-fold oversampled DFT analysis matrix whose elements are defined as:

representing and taking matrix

The submatrix is positioned in the row corresponding to the frequency spectrum suppression area; l_puBy 1 or more suppression zone (PU) frequency band sets

The union of (1);

further, in step two, the calculating the interference cancellation signal of the time domain windowing and the frequency domain spreading includes:

the interference cancellation signal may be expressed as:

c＝GBw；

wherein, B represents a basis function matrix of which the columns are formed by all the interference cancellation subcarriers; w represents a weighting coefficient;

the elements of B are defined as:

wherein l_ccRepresents the frequency set of all CCs with the frequency interval of 1/u, wherein u is an integer greater than 1;

then, the frequency spectrum of the interference cancellation signal is:

wherein

The sidelobe of the interference suppression zone (PU frequency band) is as follows:

wherein

By taking P_cIn_puThe row in (1) is obtained.

Further, in step three, the performing interference cancellation on the transmission signal in the time domain includes:

calculating a weight coefficient w of the active interference cancellation signal by using the following formula to perform spectrum leakage cancellation;

wherein the content of the first and second substances,

upper label

Representing a Mohr-Pentos generalized inverse matrix, i.e.

The matrix P is a matrix composed of

A CC subcarrier frequency spectrum observation matrix formed by stacking the CC subcarrier frequency spectrum observation matrix and the inter-carrier interference coefficient matrix; q is composed of

And the data subcarrier spectrum observation matrix is formed by stacking the data subcarrier spectrum observation matrix and the 0 matrix.

It is a further object of the invention to provide a computer device comprising a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to perform the steps of:

performing windowing processing, and calculating the frequency spectrum leakage of the orthogonal frequency division multiplexing signals subjected to time domain windowing and frequency domain expansion;

calculating interference cancellation signals of time domain windowing and frequency domain expansion; and carrying out non-orthogonal active interference cancellation on the transmission signals in a time domain.

It is another object of the present invention to provide a computer-readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the steps of:

Another object of the present invention is to provide an information data processing terminal, wherein the information data processing terminal is configured to implement the frequency domain spreading non-orthogonal active interference cancellation method.

Another object of the present invention is to provide an application of the frequency domain spreading non-orthogonal active interference cancellation method in bandwidth wireless communication.

By combining all the technical schemes, the invention has the advantages and positive effects that: the invention expands the frequency band distributed by the interference cancellation subcarrier, so that the frequency band is positioned at a position where OFDM frequency spectrum leakage is more effectively cancelled, the frequency spectrum leakage suppression effect is greatly improved, and the self-interference caused by the interference cancellation signal is reduced. For example, the frequency spectrum leakage is reduced to-80 to-100 dB from about-60 dB of the traditional method (of the EAIC-CP method), and the performance is improved by 20 to 40 dB. Moreover, the interference of the CC subcarrier to the data subcarrier in the system is reduced to-80 dB or even lower, and the improvement of the method compared with the traditional method (the interference is-30 dB to-40 dB) reaches more than 40dB, so that the system error rate performance is greatly improved.

And a small part of the CP is utilized to realize windowing, the symbol time length and the waveform format of the OFDM are not changed at all, the Gibbs effect is improved, the CC energy of a transition zone is reduced, and the energy efficiency of a system is improved. For example, reducing the CC energy from the conventional about 20dB to below 3dB greatly improves the energy efficiency of the system.

The combination of windowing and non-orthogonal active interference cancellation keeps the waveform structure of system symbols compatible with the traditional CP-OFDM system, and brings convenience to the upgrading of a future wireless communication system.

Technical effect or experimental effect of comparison. The method comprises the following steps:

table 1 compares the performance of several conventional OFDM sidelobe suppression methods with the active interference cancellation methods WFE-NAIC-i and WFE-NAIC-ii proposed by the present invention, and takes the multi-carrier number N as 128 as an example. Therefore, when no sidelobe suppression technology is adopted, the frequency spectrum leakage of the OFDM signal is up to-17 to-25 dB; when the windowing method is independently adopted, the frequency spectrum leakage is about-43 to-25 dB; when non-orthogonal active interference cancellation is used alone, the spectrum leakage is about-60 dB, but the CC power is significantly too high, up to 15dB or more. The WFE-NAIC-i and WFE-NAIC-ii greatly reduce the frequency spectrum leakage, and the residual frequency spectrum leakage can be as low as-80 dB or less; the caused interference to the sub-carriers in the system is lower than-80 dB; and the power of the CC is also lower, which is reduced to below 3dB from about 15dB of the traditional non-orthogonal active interference cancellation, and the energy efficiency of the system is improved.

TABLE 1 Performance vs. cost comparison of several different OFDM sidelobe suppression techniques

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained from the drawings without creative efforts.

Fig. 1 is a schematic structural diagram of an ofdm modulation system according to an embodiment of the present invention;

in the figure: 1. a transmitter; 2. a receiver; 11. a serial-to-parallel conversion module; 12. a symbol mapping module; 13. a subcarrier mapping module; 14. a multi-carrier modulation module; 15. a parallel-to-serial conversion module; 16. a cyclic prefix adding module; 17. a windowing module; 18. a spectrum leakage cancellation module; 19. and an up-conversion module.

Fig. 2 is a schematic diagram of an ofdm modulation system transmitter according to an embodiment of the present invention.

Fig. 3 is a flowchart of a frequency domain spread non-orthogonal active interference cancellation method according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of WFE-NAIC data subcarrier and CC subcarrier distribution provided by an embodiment of the present invention.

Fig. 5 is a schematic diagram of the WFE-NAIC waveform shaping procedure provided by the embodiment of the present invention being compatible with CP-OFDM symbols.

Fig. 6 is a schematic diagram illustrating that the average time length of the symbols is still T + Δ when the windowed symbols are transmitted after overlapping the end and the end according to the embodiment of the present invention.

FIG. 7 is a schematic diagram of the spectrum leakage suppression effect of WFE-NAIC-i provided by the embodiment of the present invention.

FIG. 8 is a diagram illustrating the spectrum leakage suppression effect (number of CC per edge of the suppression area is 24) of WFE-NAIC-ii provided by the embodiment of the present invention.

FIG. 9 is a diagram illustrating the spectrum leakage suppression effect (number of CC per edge of the suppression area is 48) of WFE-NAIC-ii provided by the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In view of the problems in the prior art, the present invention provides an ofdm modulation system and a frequency domain spreading non-orthogonal active interference cancellation method, and the following describes the present invention in detail with reference to the accompanying drawings.

As shown in fig. 1-2, an ofdm modulation system according to an embodiment of the present invention includes: a transmitter 1 and a receiver 2;

the transmitter 1 includes:

a serial-to-parallel conversion module 11 for converting serial data into parallel data;

a symbol mapping module 12, configured to map binary information into a multilevel communication constellation symbol;

a subcarrier mapping module 13, configured to allocate data symbols to appropriate subcarriers and set unused subcarriers to zero;

a multi-carrier modulation module 14, configured to convert the modulation of the symbol from the frequency domain to the time domain;

a parallel-to-serial conversion module 15 for converting the parallel signal into a serial signal;

an add cyclic prefix module 16, configured to add cyclic prefixes to serial OFDM time-domain symbols one by one in the time domain;

a windowing module 17, configured to perform windowing on the time domain signal;

a spectrum leakage cancellation module 18, configured to suppress spectrum leakage of the transmission signal by using a non-orthogonal active interference cancellation method; simultaneously, the method is used for counteracting the spectrum leakage of a plurality of sidelobe suppression areas;

and an up-conversion module 19, configured to convert the signal from the baseband signal to a frequency band signal.

The frequency domain extended non-orthogonal active interference cancellation method provided by the embodiment of the invention comprises the following steps:

As shown in fig. 3, the frequency domain extended non-orthogonal active interference cancellation method provided in the embodiment of the present invention includes the following steps:

s101, performing windowing processing, and calculating the frequency spectrum leakage of the orthogonal frequency division multiplexing signal subjected to time domain windowing and frequency domain expansion;

s102, calculating interference cancellation signals of time domain windowing and frequency domain expansion; the interference cancellation is performed on the transmitted signal in the time domain.

In step S101, the windowing provided in the embodiment of the present invention includes: windowing is performed using a raised cosine window, or other window function having smaller spectral sidelobes than a rectangular window.

In step S101, the calculating of the frequency spectrum leakage of the orthogonal frequency division multiplexing signal with time domain windowing and frequency domain spreading provided by the embodiment of the present invention includes:

s_w＝GF_dx；

Wherein G is a linear sum of 2(M + L)_cpThe window function of + δ) -1 constitutes the diagonal matrix of its diagonal elements, 2L_cpIs the CP length, 2 delta is the window functionThe length of the roll-off zone; multiple 2 is the multiple 2 of zero padding of the symbol in the frequency domain;

the elements are defined as:

-2L_cp≤n≤2(M+δ)-1,0≤m≤2vM-1；

representing and taking matrix

The union of (a).

In the second step, the calculating the interference cancellation signal of the time domain windowing and the frequency domain spreading includes:

the interference cancellation signal may be expressed as:

c＝GBw；

the elements of B are defined as:

then, the frequency spectrum of the interference cancellation signal is:

wherein

wherein

By taking P_cIn_puThe row in (1) is obtained.

In step S103, the interference cancellation of the transmission signal in the time domain according to the embodiment of the present invention includes:

wherein the content of the first and second substances,

upper label

Representing a Mohr-Pentos generalized inverse matrix, i.e.

The matrix P is a matrix composed of

The technical effects of the present invention will be further described with reference to specific embodiments.

Example 1:

fig. 2 shows a block diagram of an OFDM system transmitter for suppressing spectrum leakage by using a windowing and frequency domain spreading orthogonal frequency division multiplexing modulation system and an active interference cancellation method (WFE-NAIC) according to the present invention. Comprising a transmitter and a receiver, the transmitter comprising: a serial-to-parallel conversion module for converting serial data into parallel data; the symbol mapping module is used for mapping the binary information into a multi-system communication constellation symbol; the subcarrier mapping module is used for distributing the data symbols to proper subcarriers and setting the subcarriers which are not used to zero; the multi-carrier modulation module is used for completing modulation conversion from a frequency domain to a time domain; parallel-to-serial conversion, converting parallel signals into serial signals; the cyclic prefix adding module is used for adding cyclic prefixes to serial OFDM time domain symbols one by one in a time domain; the windowing module is used for windowing and forming the time domain signals; the frequency spectrum leakage counteracting module counteracts frequency spectrum leakage of the sending signal; the up-conversion module converts the signal from a baseband signal into a frequency band signal; the method is characterized in that: the side lobe canceling signal inserted by the spectral side lobe canceling module is spectrally spread. The spectral side lobe canceling subcarriers (CC) are located in a frequency band of not only a frequency band inserted in which useful data is not transmitted but also a part of data subcarriers. Meanwhile, the interference cancellation signal realizes oversampling in the frequency domain by zero padding.

Fig. 4 is a WFE-NAIC data subcarrier and CC subcarrier distribution. At a sending end, data to be sent is converted into a complex-valued frequency domain symbol vector x through serial-to-parallel conversion and symbol mapping. Because the OFDM is intended to share the spectrum with other communication systems, its own frequency is generally discontinuous, i.e., NC-OFDM systems. Of course, WFE-NAIC may also be used for only one spectral suppressionContinuous spectrum OFDM spectral sidelobe leakage suppression of bins (two edges of a continuous band). The sub-carrier not transmitting data in the NC-OFDM system maps a value of 0 to avoid interfering with other users, such as the frequency band where PU1 and PU2 are located as shown in fig. 2. PU1 is located within M subcarriers of the OFDM signal, and PU2 is located outside (on both sides) of the M subcarriers of the OFDM signal, i.e., M e S_pTime symbol x_m0, wherein S_pThe index sets corresponding to the non-data subcarriers (corresponding to PU1 frequency band and PU2 frequency band). Although NC-OFDM turns off subcarriers for which data is not transmitted, NC-OFDM causes spectrum leakage interference to PU1 region and PU2 region because the spectral sidelobes of its subcarriers decay very slowly.

Fig. 4 also shows a frequency domain spreading method for data subcarriers, which is characterized in that: the OFDM signal itself is zero-padded in the frequency domain to spread the frequency band before multi-carrier modulation. For example, in the sub-carrier mapping module, M/2 symbols 0 are inserted into both ends of a data symbol (including a sub-carrier with zero inserted therein) with a length of M, respectively, to obtain an OFDM symbol with a length of 2M

OFDM modulation is next implemented with a 2M point IFFT, where M is an integer. If the calculation amount is saved, the number of the actual data in the symbol x can be properly increased, and the number of 0 complementing at two ends of the frequency domain is correspondingly reduced, so that the number of zero complementing in the middle is not influenced. For simplicity of description, the present invention assumes that the length of data after zero padding at both ends is 2 times the length before zero padding. While edge subcarriers are also nulled in some OFDM systems, spectral leakage interference to other bands is reduced by increasing the inter-band spacing, but spectral efficiency is reduced. The invention obtains equivalent oversampling under the condition of not losing the spectrum efficiency by frequency domain zero filling, and makes it possible to utilize active interference cancellation to restrain the out-of-band spectrum in the spread spectrum region (PU 2).

Performing 2M-point IFFT on the symbol x after frequency domain expansion to obtain a time domain OFDM symbol s which is 2 times of oversampling,

then do it with sParallel-to-serial conversion and the addition of a Cyclic Prefix (CP) to combat inter-symbol interference (ISI) that may be caused by a multipath channel environment. CP Length 2L_cpSample value, 2L_cpNot less than the maximum delay spread of the channel. Note that the number of discrete time samples of the OFDM symbol is 2M and the CP length is 2L_cpAll by a factor of 2. This is because time domain 2-fold oversampling means that the sample point time interval is halved, while the time domain actual length of the OFDM symbol remains substantially unchanged.

Fig. 4 also shows a frequency domain spreading method for interference Cancellation Subcarriers (CCs), which is characterized in that: the side lobe canceling signal inserted by the spectral side lobe canceling module is spectrally spread. The spectral side lobe canceling subcarriers (CC) are located in a frequency band of not only a frequency band inserted in which useful data is not transmitted but also a part of data subcarriers. In fig. 2 (D), CC subcarriers are spread to a wider band on both sides (PU2 region), and this method is denoted WFE-NAIC-i. Fig. 2 (E) shows a further improvement of the present invention, namely, reducing the CC subcarriers in the PU1 region, and adding CC subcarriers in the data subcarrier edge band of the present system, which is denoted as WFE-NAIC-ii. The expansion and optimization of the distribution positions of the CC subcarriers are beneficial to inhibiting the frequency spectrum leakage and reducing the interference introduced to the data subcarriers of the system.

FIG. 5 shows the WFE-NAIC time-domain waveform shaping process. The windowing process enhances the effect of active side lobe cancellation on the premise of ensuring that the symbol length after windowing is not changed with the CP-OFDM symbol before windowing. In the extended mode in the LTE standard, the CP length of an OFDM signal is Δ ═ T/4, where T is the OFDM symbol length when no CP is present. The invention is characterized in that: the windowing compatible with CP-OFDM is realized by only using a part of delta (such as delta is delta/8, delta/4, delta/2, wherein delta is the length of a windowing roll-off region), so that the influence on a data protection interval is reduced as much as possible, and meanwhile, the negative Gibbs effect and the enhanced sidelobe suppression effect generated by active interference cancellation can be improved to the maximum extent. Firstly, time domain cyclic extension is carried out on time domain OFDM, namely, a part with the length delta of the head of an OFDM symbol is copied to the tail of the OFDM symbol to be used as a cyclic suffix, and a part with the length delta of the tail of the OFDM symbol is copied to the head of the OFDM symbol to obtain a cyclic prefix. The total length of the OFDM symbol after the front and rear cyclic extensions is T + Δ + δ. Then, the sign of the cyclic extension is multiplied by the same length, and the length of the roll-off region is a delta window function, so that the windowing process is completed.

Fig. 6 shows the method of overlapping the windowed symbols. In order to save transmission time and improve the time efficiency of the OFDM system, two consecutive windowed CP-OFDM symbols are overlapped end to end in the time domain when being transmitted into a channel. Therefore, the average time domain length of the OFDM symbol after windowing is identical to that of CP-OFDM without windowing, and is T + delta, and the compatibility with the CP-OFDM symbol is maintained. As can be seen from fig. 6, even if the roll-off region length of the window function varies, the average symbol time length after windowing does not change accordingly. In addition, although the windowing and overlapping processing is performed at the transmitting end, the symbol recovery is only required to be performed at the receiving end after the guard interval is removed as in the conventional CP-OFDM system, so that the design of the receiver is not affected, and the interference caused to the data symbols is very small.

Thus, the time domain CP-OFDM signal after windowing can be written as: s_w＝GF_dx, wherein G is a linear chain of length 2(M + L)_cpThe raised cosine window function of + δ) -1 constitutes the diagonal matrix of its diagonal elements, 2 δ being the length of the roll-off region;

is the OFDM modulation matrix and 2M is the total number of subcarriers. F_dThe elements of (a) are defined as:

-2L_cpn is less than or equal to 2(M + delta) -1, M is less than or equal to 0 and less than or equal to 2M-1, wherein n and M respectively represent the time normalized for the sampling interval and the frequency normalized for the carrier interval, and the units are T/(2M) and 1/(2T) respectively. Signal s_wThe spectrum of (2) can be obtained by v times oversampling DFT analysis, and the spectrum is:

wherein

Is a v-fold oversampled DFT analysis matrix, whichThe elements are defined as:

-2L_cpn is not less than 2(M + delta) -1, M is not less than 0 and not more than 2 vM-1. Will s_wSubstitution into

Obtaining the frequency spectrum of the windowed OFDM signal:

thus, the spectral leakage to be suppressed can be written as:

wherein

Finger-taking matrix

Is located in the corresponding row (marked as l) of the frequency spectrum inhibition zone_pu) The resulting sub-matrix. l_puFrequency aggregation by 1 or more in-band or out-of-band suppression zones (e.g., corresponding to PU1, PU2, PU3)

The union of (a).

It is assumed that all CC and data subcarriers use the same raised cosine window function. And the frequency domain interval of the CC subcarriers is set to 1/u subcarrier interval, where u is an integer greater than 1, and generally 2 is taken. Thus, the interference cancellation signal can be expressed as: GBw where B is the basis function matrix whose columns are composed of all interference cancellation subcarriers (CC) and w is the weighting coefficient. The elements of B are defined as:

-2L_cp≤n≤2M+2δ-1,l∈l_ccwherein l is_ccIs of all CCsAnd frequency sets with frequency intervals of 1/u. The frequency spectrum of the interference cancellation signal is then:

wherein

The side lobes in the PU band are:

wherein

Is obtained by taking P_cIn_puThe row in (1) is obtained. For WFE-NAIC, the objective of active sidelobe cancellation is to use the spectrum of the interference cancellation signal CC

Canceling leakage of NC-OFDM signal in PU frequency band

Namely, the optimization objective function is:

limiting inter-subcarrier interference and inter-symbol interference. The interference cancellation signal (CC) contains a component that is not orthogonal to the data subcarrier, and therefore causes a certain inter-subcarrier interference (ICI) to the data subcarrier. Even the insertion of the CC in the extension band of the present invention increases ICI. The present invention contemplates that the inserted CC, in addition to canceling the spectral leakage of the OFDM signal to the maximum extent, also needs to limit the ICI it may generate on the data. Note that WFE-NAIC does not cause inter-symbol interference because the CC length is controlled within one symbol, even in the case of channel multipath, the inter-symbol interference is small. After the protection prefix is removed at the receiving end, the frequency domain signal which is still interfered by CC is obtained through DFT demodulation:

wherein

The interference cancellation signal with the length of 2M of the prefix and suffix removed;

is a standard Fourier analysis matrix whose elements are defined as

0≤n,m≤2M-1。

The submatrix is obtained by removing the corresponding row after the postfix and the postfix of the CC subcarrier basis function matrix B are circulated. Thus, ICI interference caused by CC on data can be expressed as:

wherein M is₀Is the number of data sub-carriers,

by removing from the Fourier analysis matrix

And the row corresponding to the non-data subcarrier.

The WFE-NAIC sidelobe suppression problem is summarized as minimizing the NC-OFDM spectral leakage under the condition that the introduced ICI is smaller than a given threshold λ, i.e.:

the optimization problem is a quadratic minimization problem of quadratic constraint, so that the optimization problem can be solved directly or by adopting an indirect solution with smaller calculation amount. To save complexity in the communication transmitter, the present invention contemplates converting the optimization problem into solving the following unconstrained quadratic minimization problemTitle:

mu is a compromise factor between the sidelobe suppression performance and data inter-subcarrier interference (ICI) allowed to be introduced, and the larger mu is, the stronger the limit on the ICI is, and the worse the sidelobe suppression effect is; otherwise, the sidelobe suppression effect is better. The specific value of μ can be determined by simulation experiments. Thus, the original optimization problem is equivalent to a least squares solution of the following equation:

thus, the least squares solution for WFE-NAIC can be written as:

wherein

Upper label

Representing a Mohr-Pentos generalized inverse matrix, i.e.

FIG. 7 shows the results of simulation experiments on the sidelobe suppression effect of WFE-NAIC-i, compared with other conventional methods. Wherein the OFDM system has 128 sub-carriers in total, the sub-carriers being numbered from 0. Assuming that there are 3 spectral suppression zones, wherein PU1 is located in the interval of 64-96 subcarriers and represents a medium-bandwidth spectral suppression zone; PU2 represents the frequency interval below the NC-OFDM lowest frequency (normalized frequency less than 0) and above the highest frequency (normalized frequency higher than 128), which is equivalent to the sidelobe leakage interval outside the OFDM whole band (i.e. the two leftmost and rightmost regions of the spectrogram); PU3 is located in the interval of 32-40 subcarriers and represents a narrow-band spectrum suppression interval. All passband edges use 2 subcarrier widths as transition guard bands. The total symbol time guard interval delta is 1/4 OFDM symbol lengths for both WFE-NAIC method and EAIC-CP method, with the same time efficiency. For WFE-NAIC, the window function roll-off region length to protection prefix overall ratios δ/Δ are 1/8,1/4, and 1/2, respectively. The CC subcarrier spacing is 1/2T. For fairness, ICI was defined to be less than-80 dB for both EAIC-CP and WFE-NAIC-i schemes.

It can be seen that: first WFE-NAIC-i provides better spectral sidelobe suppression than other methods. WFE-NAIC-i reduces the residual sidelobe leakage to-80 dB, even-100 dB, in each sidelobe suppression zone, regardless of its bandwidth (e.g., PU2) or its narrowness (e.g., PU3), far superior to other approaches such as EAIC-CP, Windows, etc. The wider the sidelobe suppression area (e.g., PU2 area), or the longer the roll-off area of the window function (larger value of δ/Δ), the stronger the sidelobe suppression effect of WFE-NAIC-I. Where FE-NAIC is a simplified version of WFE-NAIC-i without windowing (δ/Δ ═ 0), i.e., only the OFDM signal and CC subcarrier bands are extended without windowing. It can be seen that the frequency domain spreading of the data subcarrier and the interference cancellation subcarrier solves the out-of-band (PU2 region) spectrum leakage problem, and simultaneously brings about the enhancement of the sidelobe suppression effect of the other two sidelobe suppression regions (PU 1 and PU3), which has about 10dB performance gain. The sidelobe suppression effect of WFE-NAIC-i is further improved compared with that of FE-NAIC without a window, and the effect is more obvious when the delta/delta is larger. For example, the WFE-NAIC approach enhanced the sidelobe suppression effect by about 10dB as the delta/delta value increased from 1/8 to 1/2. And meanwhile, the CC energy is slightly reduced, so that the energy efficiency is improved. This demonstrates that windowing and increasing the roll-off factor can act to enhance sidelobe suppression. Secondly, the CC energy inserted into the transition guard band by WFE-NAIC-i is obviously lower than that of the EAIC-CP method, and the energy efficiency of the system is greatly improved. This can be seen mainly from the CC power of the guard band amplified in the upper left sub of fig. 7. The power of CC with WFE-NAIC-i inserted on the transition guard band is lower than that of EAIC-CP, and the larger the windowing roll-off factor is, the more the energy efficiency is improved.

FIGS. 8 and 9 show the results of simulation experiments of the side lobe suppressing effect of WFE-NAIC-ii, and the experimental conditions were kept the same as for WFE-NAIC-I. The main difference between WFE-NAIC-ii and WFE-NAIC-i is that the distribution bits of CCs are different, each interference suppression zone inserts an equal number of non-orthogonal interference cancellation signals in the experiment, and CCs are arranged near the edge of each data subcarrier and span the width of 24 subcarriers (corresponding to fig. 6) or 48 subcarriers (corresponding to fig. 7), respectively, and are symmetrically distributed by taking the transition zone as the center. In practice, the number and distribution of the sub-carriers may be slightly adjusted, and obviously fall within the protection scope of the present application. It can be seen that the method provided by the invention reduces the frequency spectrum leakage of the orthogonal frequency division multiplexing modulation system from about-60 dB to below-80 to-100 dB when the EAIC-CP is adopted, and the performance is improved by 20-40 dB. And secondly, the power of the CC is greatly reduced from the traditional 15dB to below 3dB, and the energy efficiency of the system is greatly improved. Finally, because of more reasonable distribution position of CC and reduction of power, the interference of CC subcarrier to data subcarrier in the system is greatly reduced, which is lower than-80 dB and far lower than EAIC-CP method (about-30 to-40 dB) under the same condition. Meanwhile, as can be seen from comparison between fig. 8 and fig. 9, for WFE-NAIC-ii, the greater the number of CCs, the better the side lobe suppression effect and the higher the energy efficiency. However, increasing the number of CCs increases the calculation amount of WFE-NAIC-ii proportionally, so that the side lobe suppression effect and the calculation amount are balanced.

Example 2:

the invention provides a windowed orthogonal frequency division multiplexing system, which comprises a transmitter and a receiver, wherein the transmitter comprises: a serial-to-parallel conversion module for converting serial data into parallel data; the symbol mapping module is used for mapping the binary information into a multi-system communication constellation symbol; the subcarrier mapping module is used for distributing the data symbols to proper subcarriers and setting the subcarriers which are not used to zero; the multi-carrier modulation module is used for completing modulation conversion from a frequency domain to a time domain; parallel-to-serial conversion, converting parallel signals into serial signals; the cyclic prefix adding module is used for adding cyclic prefixes to serial OFDM time domain symbols one by one in a time domain; the windowing module is used for windowing and forming the time domain signals; the frequency spectrum leakage cancellation module is used for suppressing the frequency spectrum leakage of the transmission signal by adopting a non-orthogonal active interference cancellation method; the up-conversion module converts the signal from a baseband signal into a frequency band signal; the method is characterized in that: the orthogonal frequency division multiplexing system and the inserted active interference cancellation sub-carrier realize oversampling through frequency domain zero padding. Meanwhile, the sidelobe canceling signal inserted by the frequency spectrum sidelobe canceling module is frequency domain extended, namely, a frequency spectrum sidelobe canceling subcarrier (CC) is overlapped with a data subcarrier region of the system except for a transition guard band position where data is not transmitted and a frequency band region to be suppressed so as to enhance the sidelobe canceling effect and reduce the inter-subcarrier interference which is possibly introduced.

The invention also provides a method for combining windowing and active interference cancellation, which comprises the steps of windowing and active interference cancellation. The method is characterized in that: the windowing process does not change the actual length of the symbols. And (3) utilizing a part of delta in the CP to realize windowing, wherein the symbols after windowing are sent after being overlapped end to end before being sent, and the overlapping length is delta, so that the time length of the symbols of the OFDM is not changed at all. In the existing method of combining windowing and active interference cancellation, the windowed symbols are longer than the CP-OFDM symbols (the literature is supplemented), destroying the compatibility with the existing system. The invention uses part of the cyclic prefix for windowing, achieves the purpose of not changing the CP-OFDM symbol time structure, and can do so because the active interference cancellation effect after the oversampling and the spectrum expansion are applied is good, and the requirement for windowing is reduced. The invention combines the windowing method without changing the time length of the CP-OFDM symbol with the frequency domain expansion active interference cancellation provided by the invention, which is another improvement provided by the invention.

When the windowing is implemented, a raised cosine window can be adopted, and other window functions with smaller spectrum sidelobes than those of the rectangular window can also be adopted.

The invention also provides a non-orthogonal active interference cancellation method, which comprises the following steps: calculating the frequency spectrum leakage of the orthogonal frequency division multiplexing signals of time domain windowing and frequency domain expansion; calculating interference cancellation signals (CC) of time domain windowing and frequency domain spreading; performing interference cancellation on the transmission signal in a time domain;

(1) calculating the frequency spectrum leakage of the orthogonal frequency division multiplexing signals of time domain windowing and frequency domain spreading: supposing that the data subcarrier is zero-filled in a frequency domain by 2 times of the original length to obtain a frequency domain symbol vector x with the length of 2M; the definition symbol G is composed of a length of 2(M + L)_cpThe window function of + δ) -1 constitutes the diagonal matrix of its diagonal elements, 2L_cpIs the CP length, 2 δ is the length of the roll-off region; the multiple of 2 is due to zero padding being 2 times the length. Defining an OFDM modulation matrix

The elements are defined as:

-2L_cpn is less than or equal to 2(M + delta) -1, M is less than or equal to 0 and less than or equal to 2M-1, wherein n and M respectively represent the time normalized to the sampling interval and the frequency normalized to the carrier interval, and the units are T/(2M) and 1/(2T) respectively. The time domain CP-OFDM signal after windowing can be written as: s_w＝GF_dx. Signal s_wThe spectrum of (2) can be obtained by v times oversampling DFT analysis, and the spectrum is:

wherein

Is a v-fold oversampled DFT analysis matrix whose elements are defined as:

-2L_cpn is not less than 2(M + delta) -1, M is not less than 0 and not more than 2vM-1_wSubstitution into

Obtaining the frequency spectrum of the windowed OFDM signal:

thus, the spectral leakage to be suppressed can be written as:

wherein

Finger-taking matrix

The frequency domain symbol zero padding is adopted, the related calculation matrix becomes an equivalent oversampling form, and the estimated value of the frequency spectrum leakage is more approximate to the continuous signal; the OFDM time domain signal is windowed by applying a raised cosine window function of CP-OFDM, and the symbol time length and the format of the OFDM time domain signal are kept compatible with a CP-OFDM system; the frequency-domain suppression region includes the frequency band over which the frequency-domain zero padding extends, such as the PU3 region.

As an improvement of the present invention, the number of zero padding for the frequency domain data symbols may be less than 2 times the length of the symbols before zero padding, or the ratio of the number of data subcarriers to the total number of subcarriers after zero padding may be increased, thereby increasing the calculation efficiency.

(2) And calculating the interference cancellation signals of time domain windowing and frequency domain expansion. The interference cancellation signal may be expressed as: GBw where B is the basis function matrix whose columns are composed of all interference cancellation subcarriers (CC) and w is the weighting coefficient. The elements of B are defined as:

-2L_cp≤n≤2M+2δ-1,l∈l_ccwherein l is_ccIs the frequency set of all CCs, and the frequency interval is 1/u, wherein u is an integer greater than 1, and generally 2. The frequency spectrum of the interference cancellation signal is then:

wherein

The side lobes in the PU band are:

wherein

Is obtained by taking P_cIn_puThe row in (1) is obtained. The goal of active side lobe cancellation is to use the spectrum of the interference cancellation signal CC

Canceling leakage of NC-OFDM signal in PU frequency band

The sidelobe canceling signal is frequency domain extended, that is, the spectrum sidelobe canceling subcarrier (CC) is overlapped with the data subcarrier area of the system except the position of the transition guard band where no data is sent and the frequency band area to be suppressed, so as to enhance the sidelobe canceling effect and reduce the inter-subcarrier interference which may be introduced.

As a further improvement of the present invention, the number of CCs in the data subcarrier region or the spectrum suppression region may be increased or decreased according to different conditions such as a limitation of side lobe leakage, a limitation of introduced inter-subcarrier interference, and a limitation of a calculation amount of the system.

(3) And solving the weight coefficient w of the active interference cancellation signal, and finishing the frequency spectrum leakage cancellation. After the protection prefix is removed at the receiving end, the frequency domain signal which is still interfered by CC is obtained through DFT demodulation:

wherein

is a standard Fourier analysis matrix whose elements are defined as

0≤n,m≤2M-1。

wherein M is₀Is the number of data sub-carriers,

by removing from the Fourier analysis matrix

And the row corresponding to the non-data subcarrier. Minimizing the spectrum leakage of NC-OFDM on condition that the introduced ICI is smaller than a given threshold λ, namely:

the optimization problem is transformed to solve the following unconstrained quadratic minimization problem:

where μ is a compromise between sidelobe suppression performance and allowable introduced inter-data-subcarrier interference (ICI), the least squares solution of the equivalent equation below is:

thus, the least squares solution for WFE-NAIC can be written as:

wherein

Upper label

Representing a Mohr-Pentos generalized inverse matrix, i.e.

The various computation matrices are time oversampled; the interference cancellation sub-carrier part overlaps with the data sub-carrier; the spectral leakage suppression zone includes a band spread by oversampling.

As another improvement of the present invention, the position and order of the spectral sidelobe suppression module in the system may be changed, for example, the subtraction operation of cancellation is performed in the frequency domain, and then the result of the frequency domain cancellation is multi-carrier modulated.

Effectiveness analysis

The frequency distribution of the interference cancellation subcarrier (CC) of the conventional non-orthogonal interference cancellation method is simply set in a target side lobe suppression area and a transition guard band area, which fails to suppress the frequency spectrum leakage of the orthogonal frequency division multiplexing most effectively and is also not beneficial to reducing the interference of the non-orthogonal CC to the data subcarrier in the system. The frequency band of the interference cancellation subcarrier expanded by the invention is distributed at a wider and more effective position, and the frequency spectrum leakage suppression effect of the non-orthogonal active interference is greatly improved. For example, the frequency spectrum leakage is reduced to-80 to-100 dB from about-60 dB of the existing EAIC-CP method, and the performance is improved by 20 to 40 dB. Due to the effectiveness of spectrum spreading, the power of the CC is greatly reduced from the traditional more than 15dB to less than 3dB, and the energy efficiency of the system is greatly improved. Meanwhile, due to the more reasonable distribution position of the CC and the reduction of the power, the interference of the CC subcarriers to the data subcarriers in the system is also greatly reduced, and the other interference is lower than-80 dB.

The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A frequency domain extended non-orthogonal active interference cancellation method is characterized in that the frequency domain extended non-orthogonal active interference cancellation method comprises the following steps:

2. The frequency domain spread non-orthogonal active interference cancellation method of claim 1, wherein the windowing comprises: windowing is performed using a raised cosine window, or other window function having smaller spectral sidelobes than a rectangular window.

3. The frequency domain spread non-orthogonal active interference cancellation method of claim 1, wherein the calculating the spectral leakage of the time domain windowed and frequency domain spread orthogonal frequency division multiplexed signal comprises:

obtaining a windowed time-domain OFDM signal s_wObtaining a time domain OFDM signal s through v times oversampling DFT analysis_wOf the spectrum

s_w＝GF_dx；

Wherein G is a linear sum of 2(M + L)_cpThe window function of + δ) -1 constitutes the diagonal matrix of its diagonal elements, 2L_cpIs the CP length, 2 δ is the length of the roll-off region of the window function; multiple 2 is the multiple 2 of zero padding of the symbol in the frequency domain;

the elements are defined as:

where n and m represent the sampling intervalThe normalized time and the normalized frequency for the carrier spacing are in units of T/(2M) and 1/(2T), respectively;

representing and taking matrix

The union of (a).

4. The frequency domain spread non-orthogonal active interference cancellation method of claim 1, wherein the computing the time domain windowed and frequency domain spread interference cancellation signal comprises:

the interference cancellation signal is represented as:

c＝GBw；

the elements of B are defined as:

then, the frequency spectrum of the interference cancellation signal is:

wherein

wherein

By taking P_cIn_puThe row in (1) is obtained.

5. The frequency domain spread non-orthogonal active interference cancellation method of claim 1, wherein the non-orthogonal active interference cancellation of the transmission signal in the time domain comprises:

wherein the content of the first and second substances,

upper label

Representing a Mohr-Pentos generalized inverse matrix, i.e.

The matrix P is a matrix composed of

6. An orthogonal frequency division multiplexing modulation system for implementing the frequency domain spreading non-orthogonal active interference cancellation method according to any one of claims 1 to 5, wherein the orthogonal frequency division multiplexing modulation system comprises: a transmitter and a receiver;

the transmitter includes:

the windowing module is used for windowing and forming the time domain signals;

7. The orthogonal frequency division multiplexing modulation system of claim 6 wherein the orthogonal frequency division multiplexing system and the inserted active interference cancellation subcarriers are both time domain oversampled; meanwhile, the sidelobe canceling signal inserted by the spectrum sidelobe canceling module is frequency domain extended, namely, a part of the spectrum sidelobe canceling subcarrier is arranged in a transition guard band position where data is not sent and a frequency band area to be suppressed, and a part of CC is arranged in a data subcarrier area of the system and is used for enhancing the sidelobe canceling effect and reducing the inter-subcarrier interference which is possibly introduced.

8. A computer device, characterized in that the computer device comprises a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to carry out the steps of:

9. A computer-readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the steps of:

10. An information data processing terminal, characterized in that the information data processing terminal is configured to implement the frequency domain extended non-orthogonal active interference cancellation method of any one of claims 1 to 5.