CN107425919B - QAM (quadrature amplitude modulation) -based modulation and demodulation method and device - Google Patents
QAM (quadrature amplitude modulation) -based modulation and demodulation method and device Download PDFInfo
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Abstract
The invention discloses a modulation and demodulation method and a device based on QAM, wherein the method comprises the following steps: performing serial-parallel conversion on one path of digital signals to be transmitted to obtain N paths of digital signals to be modulated, wherein N is a positive integer; respectively generating N paths of carriers related to the carrier frequency according to a preset carrier frequency, wherein any two carriers in the N paths of carriers are orthogonal to each other, and N is more than or equal to 3; multiplying the N paths of digital signals to be modulated with the N paths of carriers respectively to obtain N paths of modulated analog signals; the N paths of modulated analog signals are linearly superposed and then output through an antenna, so that the problem that the modulation rate of the conventional digital modulation and demodulation mode cannot meet the requirement of a 5G communication system is solved.
Description
Technical Field
The present invention relates to the field of communications, and in particular, to a method and an apparatus for modulation and demodulation based on QAM.
Background
The baseband data modem technology is a very important technology in digital communication, and directly determines the transmission rate of the following channel data. There are many digital Modulation and demodulation methods applied in the communication field, such as one-dimensional degree-of-freedom Modulation methods such as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK), and two-dimensional degree-of-freedom Modulation methods such as Quadrature Amplitude Modulation (QAM).
The QAM is a high-order modulation method combining amplitude and phase, and has a high frequency band utilization rate and a good power utilization rate. The quadrature amplitude modulation is that two independent baseband waveforms are used to perform double-sideband modulation of restraining carrier waves on two mutually orthogonal co-frequency carrier waves, so that the orthogonality of frequency spectrums of modulated signals in the same bandwidth is utilized to realize two-way parallel digital information transmission.
Because QAM is a quadrature amplitude modulation technique based on two-dimensional modulation variables, the adjustment rate is twice that of the one-dimensional modulation method, but the modulation accuracy still depends on the order of amplitude shift. For example: the quality of a wireless channel is poor, and the highest order of a baseband modulation and demodulation technology applied to a 4G LTE (long term Evolution, universal mobile telecommunications technology) system is 64 QAM; the cable channel quality is good, and the highest level of the baseband modulation and demodulation technology applied to the high-definition cable television system is 256QAM and 512 QAM. At present, the high-order modems in application are all two-dimensional modulation and demodulation technologies, and the highest order is 1024 QAM. However, with the continuous development of 5G communication systems in communication technologies, the modulation rate of the current digital modulation and demodulation scheme cannot meet the requirement of the 5G communication system, so a digital modulation and demodulation scheme is urgently needed to improve the modulation rate while ensuring the modulation and demodulation effect.
Disclosure of Invention
The embodiment of the invention provides a QAM (quadrature amplitude modulation) -based modulation and demodulation method and device, which are used for solving the problem that the modulation rate of the conventional digital modulation and demodulation mode cannot meet the requirement of a 5G communication system.
The method comprises the following steps: a QAM-based modulation method, the method comprising: performing serial-parallel conversion on one path of digital signals to be transmitted to obtain N paths of digital signals to be modulated, wherein N is a positive integer; respectively generating N paths of carriers related to the carrier frequency according to a preset carrier frequency, wherein any two carriers in the N paths of carriers are orthogonal to each other, and N is more than or equal to 3;
multiplying the N paths of digital signals to be modulated with the N paths of carriers respectively to obtain N paths of modulated analog signals; and linearly superposing the N paths of modulated analog signals and outputting the signals through an antenna.
Corresponding to the modulation method, the embodiment of the invention further provides a demodulation method based on QAM, which comprises the following steps: respectively multiplying analog signals received by an antenna with N paths of carriers to obtain N paths of demodulated digital signals, wherein the analog signals are signals modulated by the N paths of carriers, the N paths of carriers are generated according to a preset carrier frequency, any two carriers in the N paths of carriers are orthogonal to each other, and N is greater than or equal to 3;
and performing parallel-serial conversion on the N paths of demodulated digital signals to obtain a path of demodulated digital signal.
Based on the same inventive concept, the embodiment of the present invention further provides a QAM-based modulation apparatus, which includes:
the serial-parallel conversion unit is used for performing serial-parallel conversion on one path of digital signals to be transmitted to obtain N paths of digital signals to be modulated, wherein N is a positive integer;
the carrier generation unit is used for respectively generating N paths of carriers related to the carrier frequency according to a preset carrier frequency, wherein any two carriers in the N paths of carriers are orthogonal with each other, and N is more than or equal to 3;
the modulation unit is used for multiplying the N paths of digital signals to be modulated with the N paths of carriers respectively to obtain N paths of modulated analog signals;
and the linear superposition unit is used for linearly superposing the N paths of modulated analog signals and outputting the superposed analog signals through an antenna.
Corresponding to the modulation device, the embodiment of the invention further provides a QAM based demodulation device, which comprises:
the demodulation unit is used for multiplying analog signals received by an antenna with N paths of carriers respectively to obtain N paths of demodulated digital signals, wherein the analog signals are signals modulated by the N paths of carriers, the N paths of carriers are generated according to a preset carrier frequency, any two carriers in the N paths of carriers are orthogonal to each other, and N is greater than or equal to 3;
and the parallel-serial conversion unit is used for performing parallel-serial conversion on the N paths of demodulated digital signals to obtain a path of demodulated digital signal.
The embodiment of the invention is based on the mature QAM technology at present, and obtains other carriers by the product deformation of two original orthogonal carriers of QAM, thereby changing the traditional two-dimensional QAM method into a multi-dimensional amplitude modem, namely, one path of digital signal to be sent is subjected to serial-parallel conversion to obtain N paths of digital signals to be modulated, wherein N is more than or equal to 3; and multiplying the N paths of digital signals to be modulated with two orthogonal carriers and other carriers respectively to obtain N paths of modulated analog signals, and then linearly superposing the N paths of modulated analog signals and outputting the N paths of modulated analog signals through an antenna.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a schematic flowchart of a modulation method based on QAM according to an embodiment of the present invention;
FIG. 2 is a first schematic diagram of the basic working principle of three-dimensional modulation and demodulation according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a basic working principle of three-dimensional modulation and demodulation according to an embodiment of the present invention;
fig. 4 is a flowchart illustrating a QAM-based demodulation method according to an embodiment of the present invention;
fig. 5 is a signal spectrogram in a three-dimensional 64-TDAM modulation and demodulation process according to an embodiment of the present invention;
fig. 6 is a three-dimensional constellation diagram of a three-dimensional 64TDAM before and after noise addition according to an embodiment of the present invention;
FIG. 7 is a bit error rate curve according to an embodiment of the present invention;
fig. 8 provides a QAM based modulation apparatus for an embodiment of the present invention;
fig. 9 provides a QAM based demodulation apparatus for an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail with reference to the accompanying drawings, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, an embodiment of the present invention provides a schematic flowchart of a modulation method based on QAM, and a specific implementation method includes:
step S101, performing serial-to-parallel conversion on one path of digital signal to be transmitted to obtain N paths of digital signals to be modulated, wherein N is a positive integer.
Step S102, respectively generating N paths of carriers related to the carrier frequency according to a preset carrier frequency, wherein any two carriers in the N paths of carriers are mutually orthogonal, and N is more than or equal to 3.
Step S103, multiplying the N paths of digital signals to be modulated with the N paths of carriers respectively to obtain N paths of modulated analog signals.
And step S104, carrying out linear superposition on the N paths of modulated analog signals and outputting the signals through an antenna.
In step S102, a plurality of carriers associated with w, such as cos (wt), sin (wt), cos (wt), sin (wt), are generated according to a predetermined frequency w2cos(wt)、sin(wt)cos(wt)2These carriers, except for cos (wt), sin (wt), are essentially harmonics generated after the product of cos (wt) and sin (wt).
Assuming that when N is equal to 3, N carriers related to the carrier frequency are a sine wave, a cosine wave and a third carrier obtained by multiplying the sine wave and the cosine wave, respectively, then multiplying N digital signals to be modulated by the N carriers, respectively, including:
the N paths of digital signals to be modulated are respectively a first path of digital signal to be modulated, a second path of digital signal to be modulated and a third path of digital signal to be modulated;
multiplying the first path of digital signal to be modulated by a sine wave through a first multiplier;
multiplying the second path of digital signal to be modulated by a cosine wave through a second multiplier;
and multiplying the third path of digital signal to be modulated with the third carrier wave through a third multiplier.
As shown in fig. 2, the embodiment of the present invention provides a schematic diagram of the basic operation principle of three-dimensional modulation and demodulation. The modulation process at the left-hand side of FIG. 2 is a binary data stream { a }nIs converted into a three-way binary data stream a1n}、{a2nAnd { a } and3nthen modulate these three signals with three preset carriers sin (wt), cos (wt) and sin (wt) cos (wt) to become the carrier modulated data stream { c }1n}、{c2nAnd { c }and3nAnd finally, linearly superposing the three paths of modulation data streams into { c }nAnd is sent out from the antenna.
In order to make the modulation effect better, the embodiment of the present invention further adds a step of level conversion after the serial-parallel conversion, specifically, waits for the N channelsAnd carrying out level conversion on the modulated digital signals to obtain N paths of digital signals to be modulated with a plurality of amplitudes. As shown in FIG. 3, when the binary data stream { a }nIs converted into a three-way binary data stream a1n}、{a2nAnd { a } and3nafter that, the three data streams are distributed with 4 level values according to 2 bits, and 2-4 level conversion is realized to become a new data stream { b }1n}、{b2nAnd { b }and3nAnd modulating the three signals by using three carriers, namely cos (wt), sin (wt) and sin (wt) cos (wt), wherein in actual operation, level conversion of other modes can be used for replacing 2-4 level conversion, and experimental analysis can conclude that the effect of the 2-4 level conversion is relatively low in error rate.
It is understood that when N is greater than 3, for example, N is equal to 4, for example, a carrier sin (wt) is added2cos (wt), then equals binary data stream { a }nIs converted into a four-way binary data stream { a }1n}、{a2n}、{a3nAnd { a } and4nwhen binary data stream { a }nIs converted into a four-way binary data stream { a }1n}、{a2nAnd { a } and3nand { a } and4nfourthly, then four carriers are used, cos (wt), sin (wt) cos (wt) and sin (wt)2cos (wt) modulates the four signals, and the modulation method for other value conditions of N is similar, and is not described herein again.
Corresponding to the modulation method, an embodiment of the present invention provides a schematic flowchart of a demodulation method based on QAM, as shown in fig. 4, and the specific implementation method includes:
step S201, multiplying analog signals received by an antenna by N channels of carriers respectively to obtain N channels of demodulated digital signals, where the analog signals are signals modulated by the N channels of carriers, the N channels of carriers are generated according to a preset carrier frequency, any two carriers in the N channels of carriers are orthogonal to each other, and N is greater than or equal to 3.
Step S202, the N paths of demodulated digital signals are subjected to parallel-serial conversion to obtain a path of demodulated digital signal.
In step S201, the N carriers are identical to the N carriers in the modulation method, i.e. if the modulation method uses cos (wt), sin (wt) cos (wt), then the demodulation is also cos (wt), sin (wt) cos (wt).
Assuming that N is equal to 3, and the N carriers are a sine wave, a cosine wave, and a third carrier obtained by multiplying the sine wave and the cosine wave, respectively, then the multiplying the analog signal received by the antenna by the N carriers respectively includes:
multiplying the analog signal received by the antenna with the sine wave to obtain a first path of demodulated digital signal; multiplying the analog signal received by the antenna with the cosine wave to obtain a second path of demodulated digital signal; and multiplying the analog signal received by the antenna with the third carrier to obtain a third path of demodulated digital signal.
Specifically, as shown in fig. 2, the demodulation method at the receiving end on the right side of the figure is as follows: the signal received by the receiving antenna is transmitted by a wireless channel and added with noise { dnThe receiving system also uses the carriers cos (ω t), sin (ω t) and sin (wt) cos (wt) for { d }nDemodulating to re-separate three signals { e }1n}、{e2nAnd { e } and3nand finally, carrying out parallel-to-serial conversion to synthesize a path of data signal { g }nAnd outputting, in order to make a demodulation result more accurate, in the embodiment of the present invention, after demodulation, each path of demodulated digital signals is further subjected to low-pass filtering processing, sampling processing, and level conversion, as shown in fig. 3, three paths of data signals { g1N }, { g2N }, and { g3N } are obtained, and finally, the three paths of data signals are synthesized into one path of data signal { gn } through parallel-to-serial conversion, and for convenience of description, a Modulation and demodulation method corresponding to N being equal to 3 is named as three-dimensional Amplitude Modulation (TDAM).
In order to prove the effect of high modulation rate of modulation and demodulation in the embodiment of the present invention, the embodiment of the present invention proves through an experimental process of performing simulation analysis, and the specific process is as follows.
Fig. 5 shows a signal spectrum in the three-dimensional 64TDAM modulation and demodulation process, and the embodiment of the present invention is in actual simulation60 binary code elements are taken, the sampling value of each code element is 90, the carrier frequency is 20Hz, and the signal-to-noise ratio of the wireless channel is 5 dB. In the signal spectrum, the baseband data stream { anThe binary pulse signal is converted into three data streams in series-parallel mode, and then the data streams are converted into data streams with 4 amplitude changes { b } by 2-4 level conversion1n}、{b2nAnd { b }and3nThen modulated by the carriers cos (wt), sin (wt) and cos (ω t) sin (ω t) to become three modulation signals { c }1n}、{c2nAnd { c }and3nAnd the combined signals are transmitted to a wireless channel to form a noise signal dn}; the receiving end, after receiving the signal, the receiving system passes through the pairs { d) of the carriers cos (wt), sin (wt) and cos (ω t) × sin (ω t)nDemodulating to separate three-way signal { e }1n}、{e2nAnd { e } and3nfinally, the low-pass, sampling, judging, 4-2 level conversion and combination are carried out to restore the output signal { g }n}. It can be seen that { gnAnd { a } andnthe signal spectrums of the three-dimensional 64TDAM are the same, which shows that the modulation and demodulation performance of the three-dimensional 64TDAM is high, and the method is simple and easy to implement.
Fig. 6 is a schematic representation of a three-dimensional 64TDAM constellation corresponding to fig. 5 before and after addition of noise. Since each degree of freedom of the 64TDAM also supports 2-bit binary data, each modulation symbol of the 64TDAM contains 6-bit binary data, and 64 modulation states, or 64 stereo constellation points, can be supported. Before noise is added, because the binary data code elements corresponding to 64 modulation states are not interfered, the positions after level conversion are matched with the constellation positions, thereby completing the mapping of all the binary data and the constellation points, and the whole mapping data is stacked on 64 three-dimensional constellation points. After the noise is added, because the mapping data corresponding to 64 modulation states are influenced by the noise of a wireless channel, all the mapping data originally matched with the constellation points are deviated from the actual positions of the constellation points to a greater or lesser extent, but can still be randomly distributed around the original positions of the constellation points to form a clustered constellation cloud corresponding to 64 states, which indicates that the received signals contain a great deal of interference, and the system can possibly recover the original signals only through means of low pass, judgment, level inversion and the like.
Further, in the embodiment of the present invention, an error rate curve is obtained by calculating two-dimensional 4QAM, 16QAM, and 64QAM and three-dimensional 8TDAM, 64TDAM, and 512TDAM by using simulation and theoretical formulas, as shown in fig. 7. In the two-dimensional 4QAM, 16QAM, and 64QAM and the three-dimensional 8TDAM, 64TDAM, and 512TDAM modes, the number of modulation bits per degree of freedom is 1, 2, and 3, respectively, so that the two-dimensional and three-dimensional three modulation modes are respectively in one-to-one correspondence. Because of limited computer computing power, for convenient uniform analysis and comparison, the parameters of transmission bit number, code element sampling number and carrier frequency, etc. of 6 simulation processes are completely the same, and the signal level error rate is still 10-6Reference is made to. It can be seen that if the signal-to-noise ratio of 8TDAM is 0dB, 64TDAM is about 8dB, 512TDAM is about 15dB, and the variation span between the curves is also 7-8 dB. Compared with the bit error rate curve of two-dimensional QAM, the curve change is basically consistent, and only the position is advanced by 1-2 dB, so that the requirement of the TDAM modem on the environment is slightly higher than that of the QAM modem, but the TDAM has more one-dimensional modulation freedom, and the modulation data rate is half of that of the QAM. Therefore, the modulation and demodulation method of the embodiment of the invention not only ensures the accuracy of modulation and demodulation, but also improves the modulation rate, and if the original two-way modulation is changed into three-way modulation, the modulation rate is improved by 50 percent, so that the modulation rate is greatly improved, and the requirement of a 5G communication system is met. .
Based on the same technical concept, an embodiment of the present invention further provides a QAM-based modulation and demodulation apparatus, where the modulation apparatus is shown in fig. 8, and includes: a serial-to-parallel conversion unit 401, a carrier generation unit 402, a modulation unit 403, and a linear superposition unit 404, wherein:
a serial-to-parallel conversion unit 401, configured to perform serial-to-parallel conversion on one path of digital signals to be transmitted to obtain N paths of digital signals to be modulated, where N is a positive integer;
a carrier generation unit 402, configured to generate N carriers related to a preset carrier frequency according to the preset carrier frequency, where any two carriers in the N carriers are orthogonal to each other, and N is greater than or equal to 3;
a modulation unit 403, configured to multiply the N paths of digital signals to be modulated with the N paths of carriers, respectively, to obtain N paths of modulated analog signals;
and a linear superposition unit 404, configured to linearly superpose the N channels of modulated analog signals and output the superposed analog signals through an antenna.
Preferably, N is equal to 3, and the N carriers related to the carrier frequency are a sine wave, a cosine wave, and a third carrier obtained by multiplying the sine wave and the cosine wave, respectively; the N paths of digital signals to be modulated are respectively a first path of digital signal to be modulated, a second path of digital signal to be modulated and a third path of digital signal to be modulated.
Further, the modulation unit 403 is specifically configured to: multiplying the first path of digital signal to be modulated by a sine wave through a first multiplier; multiplying the second path of digital signal to be modulated by a cosine wave through a second multiplier; and multiplying the third path of digital signal to be modulated with the third carrier wave through a third multiplier.
Further, still include: a level converting unit 405, configured to perform level conversion on the N channels of digital signals to be modulated, so as to obtain N channels of digital signals to be modulated with multiple amplitudes.
Based on the same inventive concept as the demodulation method, an embodiment of the present invention further provides a QAM-based demodulation apparatus, as shown in fig. 9, including: a demodulation unit 501 and a parallel-serial conversion unit 502, wherein:
a demodulation unit 501, configured to multiply an analog signal received by an antenna with N channels of carriers, respectively, to obtain N channels of demodulated digital signals, where the analog signal is a signal modulated by the N channels of carriers, the N channels of carriers are generated according to a preset carrier frequency, any two carriers in the N channels of carriers are orthogonal to each other, and N is greater than or equal to 3;
a parallel-to-serial conversion unit 502, configured to perform parallel-to-serial conversion on the N demodulated digital signals to obtain a demodulated digital signal.
Preferably, N is equal to 3, and the N carriers are a sine wave, a cosine wave, and a third carrier obtained by multiplying the sine wave and the cosine wave, respectively.
Further, the demodulation unit 501 is specifically configured to: multiplying the analog signal received by the antenna with the sine wave to obtain a first path of demodulated digital signal; multiplying the analog signal received by the antenna with the cosine wave to obtain a second path of demodulated digital signal; and multiplying the analog signal received by the antenna with the third carrier to obtain a third path of demodulated digital signal.
Further, still include: a processing unit 503, configured to perform low-pass filtering, sampling, and level conversion on each demodulated digital signal.
In summary, the embodiments of the present invention are based on the current mature QAM technology, and use the original two orthogonal carriers of QAM to multiply and deform to obtain other carriers, so that the traditional two-dimensional QAM method becomes a multi-dimensional amplitude modem, that is, one path of digital signal to be transmitted is serial-parallel converted to obtain N paths of digital signals to be modulated, where N is greater than or equal to 3; and multiplying the N paths of digital signals to be modulated with two orthogonal carriers and other carriers respectively to obtain N paths of modulated analog signals, and then linearly superposing the N paths of modulated analog signals and outputting the N paths of modulated analog signals through an antenna.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (8)
1. A QAM-based modulation method, comprising:
performing serial-parallel conversion on one path of digital signals to be transmitted to obtain N paths of digital signals to be modulated;
respectively generating N paths of carriers related to the carrier frequency according to a preset carrier frequency, wherein any two carriers in the N paths of carriers are orthogonal to each other, and N is more than or equal to 3;
multiplying the N paths of digital signals to be modulated with the N paths of carriers respectively to obtain N paths of modulated analog signals;
linearly superposing the N paths of modulated analog signals and outputting the signals through an antenna;
after performing serial-to-parallel conversion on one path of digital signals to be transmitted to obtain N paths of digital signals to be modulated, before multiplying the N paths of digital signals to be modulated with the N paths of carriers respectively, the method includes:
and carrying out level conversion on the N paths of digital signals to be modulated to obtain N paths of digital signals to be modulated with a plurality of amplitudes.
2. The method of claim 1, wherein N is equal to 3, and the N carriers associated with the carrier frequency are a sine wave, a cosine wave, and a third carrier resulting from a product of the sine wave and the cosine wave, respectively;
the multiplying the N paths of digital signals to be modulated by the N paths of carriers respectively comprises:
the N paths of digital signals to be modulated are respectively a first path of digital signal to be modulated, a second path of digital signal to be modulated and a third path of digital signal to be modulated;
multiplying the first path of digital signal to be modulated by a sine wave through a first multiplier;
multiplying the second path of digital signal to be modulated by a cosine wave through a second multiplier;
and multiplying the third path of digital signal to be modulated with the third carrier wave through a third multiplier.
3. A QAM-based demodulation method, comprising:
respectively multiplying analog signals received by an antenna with N paths of carriers to obtain N paths of demodulated digital signals, wherein the analog signals are signals modulated by the N paths of carriers, the N paths of carriers are generated according to a preset carrier frequency, any two carriers in the N paths of carriers are orthogonal to each other, and N is greater than or equal to 3;
performing parallel-serial conversion on the N paths of demodulated digital signals to obtain a path of demodulated digital signal;
after obtaining the N demodulated digital signals and before performing parallel-to-serial conversion on the N demodulated digital signals to obtain a demodulated digital signal, the method includes:
and performing low-pass filtering processing, sampling processing and level conversion on each path of demodulated digital signals respectively.
4. The method of claim 3 wherein N is equal to 3, and wherein the N carriers are a sine wave, a cosine wave, and a third carrier resulting from the multiplication of the sine wave and the cosine wave, respectively;
the multiplying the analog signals received by the antenna by the N channels of carriers respectively includes:
multiplying the analog signal received by the antenna with the sine wave to obtain a first path of demodulated digital signal;
multiplying the analog signal received by the antenna with the cosine wave to obtain a second path of demodulated digital signal;
and multiplying the analog signal received by the antenna with the third carrier to obtain a third path of demodulated digital signal.
5. A QAM-based modulation apparatus, comprising:
the serial-parallel conversion unit is used for performing serial-parallel conversion on one path of digital signals to be transmitted to obtain N paths of digital signals to be modulated, wherein N is a positive integer;
the carrier generation unit is used for respectively generating N paths of carriers related to the carrier frequency according to a preset carrier frequency, wherein any two carriers in the N paths of carriers are orthogonal with each other, and N is more than or equal to 3;
the modulation unit is used for multiplying the N paths of digital signals to be modulated with the N paths of carriers respectively to obtain N paths of modulated analog signals;
the linear superposition unit is used for linearly superposing the N paths of modulated analog signals and outputting the superposed analog signals through an antenna;
further comprising:
and the level conversion unit is used for carrying out level conversion on the N paths of digital signals to be modulated to obtain N paths of digital signals to be modulated with a plurality of amplitudes.
6. The apparatus of claim 5, wherein N is equal to 3, and the N carriers associated with the carrier frequency are a sine wave, a cosine wave, and a third carrier resulting from a product of the sine wave and the cosine wave, respectively;
the N paths of digital signals to be modulated are respectively a first path of digital signal to be modulated, a second path of digital signal to be modulated and a third path of digital signal to be modulated;
the modulation unit is specifically configured to: multiplying the first path of digital signal to be modulated by a sine wave through a first multiplier; multiplying the second path of digital signal to be modulated by a cosine wave through a second multiplier; and multiplying the third path of digital signal to be modulated with the third carrier wave through a third multiplier.
7. A QAM-based demodulation apparatus, comprising:
the demodulation unit is used for multiplying analog signals received by an antenna with N paths of carriers respectively to obtain N paths of demodulated digital signals, wherein the analog signals are signals modulated by the N paths of carriers, the N paths of carriers are generated according to a preset carrier frequency, any two carriers in the N paths of carriers are orthogonal to each other, and N is greater than or equal to 3;
the parallel-serial conversion unit is used for carrying out parallel-serial conversion on the N paths of demodulated digital signals to obtain a path of demodulated digital signal;
and the processing unit is used for respectively carrying out low-pass filtering processing, sampling processing and level conversion on each path of demodulated digital signals.
8. The apparatus of claim 7, wherein N equals 3, the N carriers being a sine wave, a cosine wave, and a third carrier resulting from a product of the sine wave and the cosine wave, respectively;
the demodulation unit is specifically configured to: multiplying the analog signal received by the antenna with the sine wave to obtain a first path of demodulated digital signal; multiplying the analog signal received by the antenna with the cosine wave to obtain a second path of demodulated digital signal; and multiplying the analog signal received by the antenna with the third carrier to obtain a third path of demodulated digital signal.
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