CN107347044B - Multi-carrier modulation and demodulation method in VDES system - Google Patents
Multi-carrier modulation and demodulation method in VDES system Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1851—Systems using a satellite or space-based relay
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2668—Details of algorithms
- H04L27/2681—Details of algorithms characterised by constraints
- H04L27/2688—Resistance to perturbation, e.g. noise, interference or fading
Abstract
The invention relates to the field of satellite communication, in particular to a multi-carrier modulation and demodulation method in a VDES system, which divides non-orthogonal subcarriers into cosine frequency point components and sine frequency point components, correspondingly modulates real parts and imaginary parts of subcarrier signals, transforms the non-orthogonal subcarrier matrixes into standard orthogonal bases, and modulates and demodulates the subcarrier signals together before the non-orthogonal subcarrier matrixes are combined, so that a NOMM algorithm is reasonably applied to the VDES multi-carrier system, the aim of effectively inhibiting the inter-subcarrier interference caused by the non-orthogonal subcarriers is achieved, the target bit error rate condition of data transmission in the VDES system is met, and the aim of high-speed transmission is fulfilled.
Description
Technical Field
The invention relates to the field of satellite communication, in particular to a multi-carrier modulation and demodulation method in a VDES system.
Background
An Automatic Identification System (AIS) for ships has been widely used in the fields of water traffic management, navigation assistance, ship approach, and the like as a marine communication means. However, as the number of AIS users continues to increase, existing AIS communication links have become overloaded. In order to effectively relieve the pressure of AIS Data communication and ensure the performance of AIS systems, very high frequency Data Exchange systems (VDES) have been developed since 2013.
In China, the research on the VDES technology is still in the initial stage, and the research and experimental verification of the VDES key technology have been started by the domestic research institutes and related enterprises under the traction of IALA.
Disclosure of Invention
In order to realize the data transmission with higher speed between ships and ships, ships and shore, and between ships and satellites, the invention provides a multi-carrier modulation and demodulation method in a VDES system, thereby improving the transmission speed of the VDES system.
In order to solve the technical problems, the invention adopts the following technical scheme:
a multi-carrier modulation and demodulation method in a VDES system specifically comprises the following steps:
s1, receiving data, constructing a non-orthogonal subcarrier matrix G and a K-dimensional subcarrier signal x, wherein each row vector of the K-dimensional subcarrier signal x represents a subcarrier signal, each column vector of the non-orthogonal subcarrier matrix G represents a channel of subcarrier frequency point, and mapping a data bit stream into a plurality of subcarrier signals to enable each subcarrier signal to respectively correspond to one channel of subcarrier in a modulated multicarrier;
s2, dividing column vectors of the non-orthogonal subcarrier matrix G into cosine frequency point components and sine frequency point components, multiplying a real part of a K-dimensional subcarrier signal x by the cosine frequency point components of the column vectors of the non-orthogonal subcarrier matrix G, and multiplying an imaginary part of the K-dimensional subcarrier signal x by the sine frequency point components of the column vectors of the non-orthogonal subcarrier matrix G;
s3, increasing the number of column vectors of the non-orthogonal subcarrier matrix G according to multiple, and correspondingly increasing the number of row vectors of the K-dimensional subcarrier signal x;
s4, calculating a matrix R corresponding to cosine frequency point components and a matrix P corresponding to sine frequency point components according to the increased non-orthogonal subcarrier matrix G, and converting the non-orthogonal subcarrier matrix G into a standard orthogonal base;
s5, modulating and demodulating the real part and the imaginary part of the K-dimensional subcarrier signal x according to the matrix R and the matrix P;
and S6, combining the non-orthogonal subcarrier matrix G of the matrix R divided into cosine frequency point components and the matrix P divided into sine frequency point components, and synthesizing and adding the demodulated subcarrier signals to form a multicarrier signal.
In some embodiments of the present invention, in step S1, the process of mapping the plurality of subcarrier signals is specifically:
y＝Gx，
wherein x is a K-dimensional subcarrier signal, x ═ x0,x1,…,xK-1]TG is a non-orthogonal subcarrier matrix, G ═ G0,g1,…,gK-1]The column vectors of x and G are linearly independent, y is x to L2(R) linear mapping of the space.
In some embodiments of the invention, in step S2, the column vector of the non-orthogonal subcarrier matrix G is divided into cosine frequency point components Gk＝cos(2πfmt) and sinusoidal frequency point components gk＝sin(2πfmt) wherein fmRepresenting subcarrier frequency points and t time.
In some embodiments of the present invention, the time t is within a symbol period time.
In some embodiments of the present invention, the non-orthogonal subcarrier matrix G is linearly transformed by the matrix P at the signal transmitting end and the signal receiving end of the VDES system, respectively.
In some embodiments of the present invention, 32 multi-carriers are used for modulation in the channel of the VDE system.
In some embodiments of the present invention, the carrier frequency points of the subcarriers in the 32-channel multicarrier are respectively:
fm＝(0.5625-(M/2-m)×1.125)/T
where M denotes the number of subcarriers, M is 0,1,2, …, M-1, and T denotes a symbol period.
In some embodiments of the present invention, after increasing the number of column vectors of the non-orthogonal subcarrier matrix G, the non-orthogonal subcarrier matrix G is divided into:
due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects:
the multi-carrier modulation and demodulation method reasonably applies the NOMM algorithm to the VDES multi-carrier system, achieves the aim of effectively inhibiting the inter-carrier interference caused by the non-orthogonal sub-carriers, and meets the target bit error rate condition of data transmission in the VDES system, thereby achieving the aim of high-speed transmission.
Drawings
FIG. 1 is a schematic diagram of a multi-carrier modem process according to the present invention;
fig. 2 is a signal constellation diagram obtained by modulating 32 paths of non-orthogonal subcarriers, demodulating the modulated subcarriers, and performing parallel-to-serial conversion in embodiment 2 of the present invention without adding noise;
fig. 3 is a signal constellation diagram obtained by modulating 32 paths of non-orthogonal subcarriers, demodulating the signals, and performing parallel-to-serial conversion in embodiment 2 of the present invention under the condition of adding noise and when the signal-to-noise ratio is 10 dB;
FIG. 4 shows the bit error rate and E of the VDES multi-carrier system in embodiment 2 of the present inventionb/N0The corresponding relationship of (1).
Detailed Description
The technical solution proposed by the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims. It is noted that the drawings are in greatly simplified form and that non-precision ratios are used for convenience and clarity only to aid in the description of the embodiments of the invention.
The invention designs a modulation and demodulation method of multi-carrier in VDES system aiming at the requirements of VDES related protocol proposed by ITU, based on the given non-orthogonal sub-carrier frequency point, by dividing the non-orthogonal sub-carrier into cosine frequency point component and sine frequency point component, correspondingly modulating the real part and imaginary part of sub-carrier signal, and transforming the non-orthogonal sub-carrier matrix into standard orthogonal base, before the non-orthogonal sub-carrier matrix is combined, the sub-carrier signal is modulated and demodulated together, thereby the NOMM algorithm can be reasonably applied to VDES multi-carrier system, and the multi-carrier modulation of VDES under 100kHz channel is realized.
Referring to fig. 1, the modulation and demodulation method of the present invention specifically includes:
s1, receiving data, constructing a non-orthogonal subcarrier matrix G and a K-dimensional subcarrier signal x, wherein each row vector of the K-dimensional subcarrier signal x represents a subcarrier signal, each column vector of the non-orthogonal subcarrier matrix G represents a channel of subcarrier frequency point, and mapping a data bit stream into a plurality of subcarrier signals to enable each subcarrier signal to respectively correspond to one channel of subcarrier in a modulated multicarrier;
s2, dividing column vectors of the non-orthogonal subcarrier matrix G into cosine frequency point components and sine frequency point components, multiplying a real part of a K-dimensional subcarrier signal x by the cosine frequency point components of the column vectors of the non-orthogonal subcarrier matrix G, and multiplying an imaginary part of the K-dimensional subcarrier signal x by the sine frequency point components of the column vectors of the non-orthogonal subcarrier matrix G;
s3, increasing the number of column vectors of the non-orthogonal subcarrier matrix G according to multiple, and correspondingly increasing the number of row vectors of the K-dimensional subcarrier signal x;
s4, calculating a matrix R corresponding to cosine frequency point components and a matrix P corresponding to sine frequency point components according to the increased non-orthogonal subcarrier matrix G, and converting the non-orthogonal subcarrier matrix G into a standard orthogonal base;
s5, modulating and demodulating the real part and the imaginary part of the K-dimensional subcarrier signal x according to the matrix R and the matrix P;
and S6, combining the non-orthogonal subcarrier matrix G of the matrix R divided into cosine frequency point components and the matrix P divided into sine frequency point components, and synthesizing and adding the demodulated subcarrier signals to form a multicarrier signal.
Specifically, in step S1, the process of mapping the plurality of subcarrier signals specifically includes:
y＝Gx，
wherein x is a K-dimensional subcarrier signal, x ═ x0,x1,…,xK-1]TG is a non-orthogonal subcarrier matrix, G ═ G0,g1,…,gK-1]The column vectors of x and G are linearly independent, y is x to L2(R) linear mapping of the space.
For the decomposition process of step S2, the column vectors of the non-orthogonal subcarrier matrix G in the present invention are divided into cosine frequency point components and sine frequency point components, and the cosine frequency point components are denoted as Gk＝cos(2πfmt) and sinusoidal frequency components are denoted as gk＝sin(2πfmt) wherein fmRepresenting the frequency point of the subcarrier, and t represents time, wherein the value range of the time t is within the symbol period time.
And carrying out linear transformation on the non-orthogonal subcarrier matrix G by using the matrix P at a signal transmitting end and a signal receiving end of the VDES system respectively, and further effectively eliminating crosstalk or interference between different symbols.
Example 1
The design concept and process of the present invention will be further described by taking 32 multi-carriers as an example for modulation in the channel of the VDE system, so as to describe the technical solution of the present invention in more detail.
The invention adopts 32 paths of multi-carrier modulation in a 100kHz channel of a VDE system, and modulates each path of subcarrier by using a 16QAM modulation mode, wherein the symbol rate of each path of subcarrier is 2400symbol/s/carrier, the carrier interval delta f is 2.7kHz, the frequency points of a plurality of subcarriers are not mutually orthogonal, the reason is that the carrier interval specified in the standard is 2.7kHz and is more than 2.4kHz required by the orthogonal frequency point, therefore, the carrier frequency points of each subcarrier in the 32 paths of multi-carrier are respectively:
fm＝(0.5625-(M/2-m)×1.125)/T
wherein M represents the number of subcarriers, that is, 32 channels selected by the present invention, M is 0,1,2, …, M-1; t then represents the symbol period, so the spacing of the center frequency bins of each subcarrier is 2.7 kHz.
Since a plurality of subcarrier frequency points in the VDES system are non-orthogonal, the inter-subcarrier interference caused by the non-orthogonal subcarriers needs to be solved. The invention adopts a Non-orthogonal multi-modulation (NOMM) algorithm to realize Non-orthogonal multi-carrier modulation.
According to the principle of NOMM, a non-orthogonal subcarrier matrix G and a K-dimensional subcarrier signal x are constructed, a plurality of subcarrier signals are mapped, and the following expression is formed:
y＝Gx，
wherein x is a K-dimensional subcarrier signal, x ═ x0,x1,…,xK-1]TG is a non-orthogonal subcarrier matrix, G ═ G0,g1,…,gK-1]The column vectors of x and G are linearly independent, y is x to L2(R) linear mapping of the space.
Applying the NOMM algorithm in the multi-carrier modulation technique of VDES systems requires solving two main problems. First, the specific form of the non-orthogonal subcarrier matrix G needs to be determined.
Referring to the basic principle of OFDM modulation and demodulation, a serial bit stream is mapped to serial symbols after passing through a data encoder, and each symbol modulates one subcarrier therein. Then, with respect to the VDES system, each sub-carrier is modulated by the 16QAM signal, that is, the real part and imaginary part of the 16QAM equivalent baseband signal are multiplied by the cos component and sin component of the corresponding non-orthogonal sub-carrier, respectively, and the modulated sub-carriers are added and combined to form the multi-carrier symbol.
It can be known from the above-mentioned idea that the row vector of x represents one path of subcarrier signal in the 16QAM signal, the column vector of G corresponds to one path of subcarrier frequency point, and since the 16QAM signal is a complex signal and contains real part and imaginary part, the real part and imaginary part of the 16QAM signal, i.e. the K-dimensional subcarrier signal x, are extracted during processing, respectively, the real part of the K-dimensional subcarrier signal x and cos (2 pi f) of the non-orthogonal subcarrier matrixmt) component multiplication, imaginary part of the K-dimensional subcarrier signal x and non-orthogonal subcarrier matrix sin (2 π f)mt) component multiplication.
Thus, let the column vector G of the G matrixk＝cos(2πfmt) and gk＝sin(2πfmt), the representation of the G matrix column vector is thus preliminarily determined.
However, from this, two G matrices are generated, namely from cos (2 π f)mt) matrix of frequency point components and sum of sin (2 π f)mt) a matrix of frequency bin components,therefore, the two G matrices are merged.
Before G matrix combination, if the sum of cos (2 pi f)mt) frequency point components and sin (2 π f)mt) respectively calculating a G matrix formed by frequency point components to obtain a corresponding R matrix and a corresponding P matrix, correspondingly and respectively modulating a real part and an imaginary part of a K-dimensional subcarrier signal x, and adding modulated subcarriers, so that the signals are transmitted in a channel without noise, and after corresponding demodulation is carried out at a receiving end, the situation that error-free demodulation cannot be realized is found.
For the first sub-carrier, cos (2 π f)1t) and sin (2 π f)1t) is in [0,1/f1]Upper quadrature, i.e.:
and the symbol period T is 1/2400, f11350Hz so cos (2 π f)1t) and sin (2 π f)1T) in one symbol period [0, T ]]The inner parts are not orthogonal, so that the real part and the imaginary part of the K-dimensional subcarrier signal x respectively modulate the subcarriers and then are combined and added to interfere with each other.
Therefore, the number of column vectors of the non-orthogonal subcarrier matrix G is increased by multiple, and in this embodiment, the number of column vectors is increased by one time, namely, increased from 32 to 64.
According to the idea, the first 32 column vectors of the non-orthogonal subcarrier matrix G can be made to be cos (2 π f)mt) frequency components, followed by 32 column vectors of sin (2 π f)mt) frequency components, i.e.:
correspondingly, the number of the row vectors of the K-dimensional subcarrier signal x is doubled, the first 32 row vectors are the real part of the 16QAM signal, the second 32 row vectors are the imaginary part of the 16QAM signal, an R matrix and a P matrix are calculated according to a newly defined non-orthogonal subcarrier matrix G, the real part and the imaginary part of the K-dimensional subcarrier signal x are modulated and demodulated together according to the matrix R and the matrix P, finally, the matrix R divided into cosine frequency point components and the non-orthogonal subcarrier matrix G of the matrix P divided into sine frequency point components are combined, and the demodulated subcarrier signals are synthesized and added to form a multicarrier signal, so that the modulation and demodulation process of the multicarrier signal is completed. Simulation results show that the receiving end can realize error-free demodulation under the condition of not adding noise, so that the interference between subcarriers can be effectively inhibited.
In addition, before G matrix combination, in order to make the algorithm proceed normally, it is also necessary to determine the value range of time t, and the reason why t needs to take one symbol time is the relationship between the subcarrier frequency point and the symbol period.
Since the symbol rate of a 100kHz channel in a VDES system is 2400symbol/s/carrier, that is, 2400 symbols are transmitted per subcarrier in one second. According to the frequency point values of the subcarriers in the VDES, the minimum frequency point value is 1350Hz, and the frequency point values of the rest subcarriers are all odd multiples of the minimum frequency point value.
Setting the period of the subcarrier with the minimum frequency point value as T0I.e. T 01/1350, however, the symbol period specified in the VDES system is T1/2400, and the two have the following relationship:
16T＝9T0
that is to say, exactly 9 first-path subcarriers are transmitted in a time period of 16 symbol periods, so that each 16 symbol periods can be regarded as orthogonal, and when t is taken according to a time range of one second, that is, 2400symbol times are taken, since 2400 is an integer multiple of 16, 2400 symbols are orthogonal, so that the obtained R matrix is a diagonal matrix. Therefore, the value of time t in the modulation and demodulation calculation process is limited to one symbol period time.
Example 2
In this embodiment, a simulation experiment is performed by using the multi-carrier modulation and demodulation method of the present invention, the simulation observation time is 100s, the modulated multi-carrier symbol is transmitted through an AWGN channel, and the value range of the simulation selected signal-to-noise ratio is between 0dB and 16 dB.
Under the condition of no noise, a signal constellation diagram obtained by modulating 32 paths of non-orthogonal subcarriers, demodulating the modulated subcarriers and carrying out parallel-to-serial conversion is shown in fig. 2, and as can be seen from fig. 2, under the condition of transmission in a channel without noise, although 32 paths of subcarriers are non-orthogonal, the non-orthogonality does not affect the performance of the system, so that the multi-carrier modulation and demodulation method in the invention can effectively eliminate the inter-subcarrier interference caused by the non-orthogonality of the subcarriers, thereby obtaining the performance in the orthogonal state.
Under the condition of adding noise, when the signal-to-noise ratio is 10dB, 32 paths of non-orthogonal subcarriers are modulated, and a signal constellation diagram obtained by demodulating and performing parallel-serial conversion on the signals is shown in fig. 3.
Bit error rate and E of VDES multi-carrier systemb/N0The corresponding relation is shown in fig. 4, and the theoretical bit error rate curve is referred and compared, as can be seen from fig. 4, the bit error rate of the multi-carrier modulation and demodulation method of the present invention follows Eb/N0The bit error rate of the target bit error rate index is increased and decreased, and the bit error rate of the target bit error rate index is close to a theoretical curve and can meet the target bit error rate index requirement.
Simulation results show that: the multi-carrier modulation and demodulation method provided by the invention has good performance, can meet the performance requirement of the target bit error rate, not only can meet the requirement in a protocol, but also overcomes the interference caused by the non-orthogonality of the sub-carriers, thereby achieving the purpose of high-speed transmission.
It should be understood by those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention, and that the foregoing disclosure is only illustrative of the preferred embodiments of the invention. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents, and one skilled in the art can make variations and modifications within the spirit and scope of the invention as defined by the appended claims.
Claims (8)
1. A multi-carrier modulation and demodulation method in a VDES system is characterized in that the modulation and demodulation method specifically comprises the following steps:
s1, receiving data, constructing a non-orthogonal subcarrier matrix G and a K-dimensional subcarrier signal x, wherein each row vector of the K-dimensional subcarrier signal x represents a subcarrier signal, each column vector of the non-orthogonal subcarrier matrix G represents a channel of subcarrier frequency point, and mapping a data bit stream into a plurality of subcarrier signals to enable each subcarrier signal to respectively correspond to one channel of subcarrier in a modulated multicarrier;
s2, dividing column vectors of the non-orthogonal subcarrier matrix G into cosine frequency point components and sine frequency point components, multiplying a real part of a K-dimensional subcarrier signal x by the cosine frequency point components of the column vectors of the non-orthogonal subcarrier matrix G, and multiplying an imaginary part of the K-dimensional subcarrier signal x by the sine frequency point components of the column vectors of the non-orthogonal subcarrier matrix G;
s3, increasing the number of column vectors of the non-orthogonal subcarrier matrix G according to multiple, and correspondingly increasing the number of row vectors of the K-dimensional subcarrier signal x;
s4, calculating a matrix R corresponding to cosine frequency point components and a matrix P corresponding to sine frequency point components according to the increased non-orthogonal subcarrier matrix G, and converting the non-orthogonal subcarrier matrix G into a standard orthogonal base;
s5, modulating and demodulating the real part and the imaginary part of the K-dimensional subcarrier signal x according to the matrix R and the matrix P;
and S6, combining the non-orthogonal subcarrier matrix G of the matrix R divided into cosine frequency point components and the matrix P divided into sine frequency point components, and synthesizing and adding the demodulated subcarrier signals to form a multicarrier signal.
2. The method as claimed in claim 1, wherein in step S1, the process of mapping the plurality of sub-carrier signals comprises:
y＝Gx，
wherein x is a K-dimensional subcarrierSignal, x ═ x0,x1,…,xK-1]TG is a non-orthogonal subcarrier matrix, G ═ G0,g1,…,gK-1]The column vectors of x and G are linearly independent, y is x to L2(R) linear mapping of the space.
3. The method as claimed in claim 1, wherein in step S2, the column vector of the non-orthogonal sub-carrier matrix G is divided into cosine frequency point components Gk＝cos(2πfmt) and sinusoidal frequency point components gk＝sin(2πfmt) wherein fmRepresenting subcarrier frequency points and t time.
4. The method as claimed in claim 3, wherein the time t is within a symbol period time.
5. The method as claimed in claim 1, wherein the matrix P is used to perform linear transformation on the non-orthogonal sub-carrier matrix G at the signal transmitting end and the signal receiving end of the VDES system.
6. The method as claimed in claim 1, wherein the modulation and demodulation of the multiple carriers in the VDES system is performed by using 32 channels of the multiple carriers in the channel of the VDE system.
7. The method according to claim 6, wherein the carrier frequencies of the subcarriers in the 32-channel multicarrier are respectively as follows:
fm＝(0.5625-(M/2-m)×1.125)/T
where M denotes the number of subcarriers, M is 0,1,2, …, M-1, and T denotes a symbol period.
8. The method as claimed in claim 7, wherein after increasing the number of column vectors of the non-orthogonal sub-carrier matrix G, the non-orthogonal sub-carrier matrix G is divided into:
wherein f ismIs the carrier frequency point, g, of each subcarrierkIs the column vector of the G matrix.
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