CN111181596B - Modulation-demodulation method and system - Google Patents
Modulation-demodulation method and system Download PDFInfo
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- CN111181596B CN111181596B CN201911423106.1A CN201911423106A CN111181596B CN 111181596 B CN111181596 B CN 111181596B CN 201911423106 A CN201911423106 A CN 201911423106A CN 111181596 B CN111181596 B CN 111181596B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B2001/6912—Spread spectrum techniques using chirp
Abstract
The present invention relates to the field of wireless communication technologies, and in particular, to a modulation and demodulation method and system. The modulation and demodulation system comprises a radio frequency module, a baseband modulation module and a baseband demodulation module, wherein the radio frequency module comprises a radio frequency transmitting module and a radio frequency receiving module, and the baseband modulation module comprises a chirp generator, a frame header generator, a data modulation module and a frame composition module. The invention combines the direct sequence spread spectrum and the chirp spread spectrum, integrates the advantages of the direct sequence spread spectrum and the chirp spread spectrum, ensures that the demodulation algorithm is simple and easy to realize, simultaneously ensures that the realization structure of a modulation-demodulation system is simpler, and greatly reduces the cost and the failure rate.
Description
Technical Field
The present invention relates to the field of wireless communication technologies, and in particular, to a modulation and demodulation method and system.
Background
Modulation in wireless communication is to use baseband signal to control the change of some parameter or parameters of carrier signal, and load information on it to form modulated signal transmission, while demodulation is the inverse process of modulation, and the original baseband signal is recovered from the parameter change of modulated signal by a specific method. Spread spectrum communications are characterized by the fact that the bandwidth used to transmit the information is much greater than the bandwidth of the information itself. The spread spectrum communication technology uses spread spectrum coding to perform spread spectrum modulation at a transmitting end and uses related demodulation technology to receive information at a receiving end, and the process makes the communication technology have a plurality of excellent characteristics. Spread spectrum communication technology is an information transmission mode, and the frequency bandwidth occupied by signals is far larger than the minimum bandwidth necessary for the transmitted information; the frequency band is spread by an independent code sequence, and the spreading is realized by a coding and modulation method and is independent of the information data; at the receiving end, the same code is used for carrying out related synchronous receiving, despreading and recovering the transmitted information data.
The spread spectrum communication technology has remarkable anti-interference and anti-fading characteristics, low power consumption and low detection probability, so that the spread spectrum communication technology is widely applied to civil and military communication. There are three main types of spread spectrum communication techniques in common use: direct sequence spread spectrum, frequency hopping and chirp spread spectrum techniques.
Direct Sequence Spread Spectrum (DSSS) techniques encode a single bit of data into a multi-bit Sequence, called a "chip". For example, data "0" is encoded with chip "00100111000", data "1" is encoded with chip "11011000111", and data string "010" is encoded as "00100111000", "11011000111", "00100111000". Apparently, the use of direct sequence spread spectrum techniques requires higher bandwidth, but this cost is worthwhile.
The chip is reasonably selected, which is beneficial to improving the processing gain and enhancing the anti-interference capability of the channel so as to deal with the noisy wireless network environment. If orthogonal chip sets are selected, multiple data can be transmitted simultaneously using the same frequency. In the DSSS system, Differential Binary Phase Shift Keying (DBPSK) and Differential Quadrature Phase Shift Keying (DQPSK) modulation techniques are used to support 1Mb/s and 2Mb/s data transmission rates, respectively, and 14 channels can be provided, but there are only three non-overlapping channels that can be used simultaneously, so when there are multiple BSS overlapping areas, each BSS should select the operating frequency band that does not interfere with each other as much as possible.
The Chirp Spread Spectrum (CSS) technique uses Chirp pulse modulation of Chirp to transmit information to achieve a Spread Spectrum effect. A Chirp pulse is a sinusoidal signal whose frequency increases or decreases linearly with time over a period of time. Like DSSS, FHSS, CSS utilizes its entire bandwidth to despread the spectrum of the signal, except that CSS does not require the addition of any pseudo-random sequence, it utilizes the frequency linearity characteristic of the Chirp pulse itself, which is continuously variable in frequency.
The spread spectrum technology, the demodulation algorithm and the system structure used in the prior art are complex, and the cost and the failure rate are increased.
Disclosure of Invention
The present invention provides a modulation and demodulation method and system for solving the problems in the prior art.
In one aspect, the present invention provides a modulation and demodulation method applied to a modulation and demodulation system, where the method includes:
the modulation and demodulation system generates a chirp signal; the modulation and demodulation system utilizes chirp signals to combine a frame header; the modulation and demodulation system sequentially passes through direct sequence spread spectrum and chirp spread spectrum on an original signal to generate modulation data; the modulation and demodulation system combines the frame header data and the modulation data to generate complete modulated data information; the modulation and demodulation system receives the modulated data information and sends out the modulated data information; the modulation and demodulation system receives the modulated radio frequency signal and converts the radio frequency signal into a baseband signal; the modulation and demodulation system receives baseband signals, and performs chirp despreading and direct sequence despreading on the received baseband signals in sequence to finally obtain despread original signals.
Optionally, the modem system sequentially performs direct sequence spreading and chirp spreading on the original signal to generate modulated data, including: the modulation and demodulation system carries out channel coding on original data;
the modulation and demodulation system whitens the data after channel coding; the modulation and demodulation system interweaves the whitened data; the modulation and demodulation system carries out direct sequence spread spectrum on the interleaved data to generate a QPSK signal; the modulation and demodulation system multiplies the QPSK signal by the upchirp signal to generate modulation data.
Optionally, the modem system performs direct sequence spreading on the interleaved data to generate a QPSK signal, including: the modulation and demodulation system carries out serial-to-parallel conversion on the interleaved data and divides the data into an I path and a Q path; the modulation and demodulation system carries out direct sequence spread spectrum processing on signals on each branch of the data after serial-parallel conversion by using a pseudo-random code generated by a pseudo-random code generator, and converts a symbol after spread spectrum into a bipolar symbol; the modulation and demodulation system carries out inverse transformation of series-parallel transformation on the I path data and the Q path data after transformation to generate QPSK signals.
Optionally, the receiving, by the modem system, a baseband signal, and sequentially performing chirp despreading and direct sequence despreading on the received baseband signal to obtain a despread original signal, where the despreading original signal includes: the modulation and demodulation system carries out symbol synchronization on the received baseband signal and determines the initial position of the modulation signal; the modulation and demodulation system carries out time offset and frequency offset correction on the signals after symbol synchronization; the modulation and demodulation system multiplies the signals after time offset and frequency offset correction by the downlink chirp signals generated by the modulation and demodulation system to complete chirp de-spreading of the signals; the modulation and demodulation system performs direct sequence despreading on the signals after chirp despreading to obtain demodulated data; the modulation and demodulation system de-interleaves the demodulated data; the modulation and demodulation system carries out de-whitening on the de-interleaved data; and the modulation and demodulation system decodes the de-whitened data to obtain original information.
Optionally, the performing, by the modem system, direct sequence despreading on the signal after completing chirp despreading to obtain demodulated data includes: the modulation and demodulation system judges the signals after chirp despreading according to the phase, and then carries out series-parallel conversion on the judged signals to be distributed to an I path and a Q path; the modulation and demodulation system carries out conversion from bipolar codes to unipolar codes on the data after serial-to-parallel conversion, and de-spreads the direct sequence spread spectrum by using the pseudo-random code which is the same as the transmitting end; and the modulation and demodulation system performs parallel-to-serial conversion on the despread I path data and Q path data to obtain demodulated data.
On the other hand, the invention provides a modulation and demodulation system, which comprises a radio frequency module, a baseband modulation module and a baseband demodulation module, wherein the radio frequency module comprises a radio frequency transmitting module and a radio frequency receiving module, and the baseband modulation module comprises a chirp generator, a frame header generator, a data modulation module and a frame composition module;
the chirp generator is used for generating a chirp signal; the frame header generator is used for combining a frame header by using a chirp signal; the data modulation module is used for sequentially passing the original signal through direct sequence spread spectrum and chirp spread spectrum to generate modulation data; the frame composition module is used for combining the frame header data and the modulation data to generate complete modulated data information; the radio frequency transmitting module is used for receiving the modulated data information and sending out the modulated data information; the radio frequency receiving module is used for receiving the modulated radio frequency signal and converting the radio frequency signal into a baseband signal; the baseband demodulation module is used for receiving baseband signals, and sequentially performing chirp despreading and direct sequence despreading on the received baseband signals to finally obtain despread original signals.
Optionally, the data modulation module includes a coding module, a whitening module, an interleaving module, a QPSK modulation module, and a first calculation module;
the encoding module is used for carrying out channel encoding on the original data; the whitening module is used for whitening the data subjected to the channel coding by the coding module; the interleaving module is used for interleaving the data whitened by the whitening module; the QPSK modulation module is used for performing direct sequence spread spectrum on the data interleaved by the interleaving module to generate a QPSK signal; and the first calculating module is used for multiplying the QPSK signal and the upchirp signal to generate modulation data.
Optionally, the QPSK modulation module includes a first serial-to-parallel conversion module, a first symbol conversion module, and a first parallel-to-serial conversion module;
the first serial-parallel conversion module is used for performing serial-parallel conversion on the interleaved data and dividing the data into an I path and a Q path; the first symbol conversion module is used for performing direct sequence spread spectrum processing on a signal on each branch of the serial-parallel converted data by using a pseudo-random code generated by a pseudo-random code generator and converting a spread symbol into a bipolar symbol; and the first parallel-serial conversion module is used for performing inverse conversion of serial-parallel conversion on the I path data and the Q path data after conversion to generate QPSK signals.
Optionally, the baseband demodulation module includes a symbol synchronization module, a time-frequency correction module, a second calculation module, a QPSK demodulation module, a de-interleaving module, a de-whitening module, and a decoding module;
the symbol synchronization module is used for carrying out symbol synchronization on the received baseband signal and determining the initial position of the modulation signal; the time-frequency correction module is used for correcting time offset and frequency offset of the signals subjected to symbol synchronization; the second calculating module is used for multiplying the signal after time offset and frequency offset correction with a down chirp signal generated by the modulation and demodulation system to complete chirp de-spreading of the signal; the QPSK demodulation module is used for performing direct sequence despreading on the signals after chirp despreading to obtain demodulated data; the de-interleaving module is used for de-interleaving the data demodulated by the QPSK demodulation module; the de-whitening module is used for de-whitening the data de-interleaved by the de-interleaving module; and the decoding module is used for decoding the data subjected to the de-whitening by the de-whitening module to obtain the original information.
Optionally, the QPSK demodulation module includes a second serial-to-parallel conversion module, a second symbol conversion module, and a second parallel-to-serial conversion module;
the second serial-parallel conversion module is used for judging the signals after chirp despreading according to the phase, and then performing serial-parallel conversion on the judged signals to distribute the signals to an I path and a Q path; the second symbol conversion module is used for converting the data after the serial-parallel conversion from a bipolar code to a unipolar code and performing despreading of direct sequence spread spectrum by using a pseudo-random code which is the same as that of the transmitting end; and the second parallel-serial conversion module is used for performing parallel-serial conversion on the despread I-path data and Q-path data to obtain demodulated data.
The invention has the following beneficial effects:
the invention combines the direct sequence spread spectrum and the chirp spread spectrum, integrates the advantages of the direct sequence spread spectrum and the chirp spread spectrum, ensures that the demodulation algorithm is simple and easy to realize, simultaneously ensures that the realization structure of a modulation-demodulation system is simpler, and greatly reduces the cost and the failure rate.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a flow chart of a modulation and demodulation method according to an embodiment of the present invention;
fig. 2 is a schematic flow chart of a method for generating modulated data by sequentially performing direct sequence spreading and chirp spreading on an original signal according to an embodiment of the present invention;
fig. 3 is a flowchart illustrating a method for generating a QPSK signal by performing direct sequence spreading on interleaved data according to an embodiment of the present invention;
fig. 4 is a schematic flow chart of a method for receiving a baseband signal, sequentially performing chirp despreading and direct sequence despreading on the received baseband signal, and finally obtaining a despread original signal according to an embodiment of the present invention;
fig. 5 is a schematic flowchart of a method for performing direct sequence despreading on a signal subjected to chirp despreading to obtain demodulated data according to an embodiment of the present invention;
fig. 6 is a block diagram of the modem system according to the embodiment of the present invention.
The labels in the figure are: 1. a radio frequency module; 2. a baseband modulation module; 3. a baseband demodulation module; 11. a radio frequency transmission module; 12. a radio frequency receiving module; 21. a chirp generator; 22. a frame header generation module; 23. a data modulation module; 24. a frame composition module; 31. a symbol synchronization module; 32. a time-frequency correction module; 33. a second calculation module; 34. a QPSK demodulation module; 35. a de-interleaving module; 36. a de-whitening module; 37. a decoding module; 231. an encoding module; 232. a whitening module; 233. an interleaving module; 234. a QPSK modulation module; 235. a first calculation module; 341. a second serial-to-parallel conversion module; 342. a second symbol conversion module; 343. a second parallel-to-serial conversion module; 2341. a first serial-to-parallel conversion module; 2342. a first symbol conversion module; 2343. and the first parallel-serial conversion module.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. 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.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures. Meanwhile, in the description of the present invention, the terms "first", "second", and the like are used only for distinguishing the description, and are not to be construed as indicating or implying relative importance.
Embodiments provided in embodiments of the present invention will be described in detail below with reference to specific examples and the accompanying drawings.
As shown in fig. 1, an embodiment of the present application provides a modulation and demodulation method applied to a modulation and demodulation system, where the method may include: step S10, step S20, step S30, step S40, step S50, step S60, and step S70.
Step S10: the modem system generates a ch i rp signal.
Step S20: and the modulation and demodulation system utilizes the ch i rp signals to combine into a frame header.
Step S30: the modulation and demodulation system sequentially passes through direct sequence spread spectrum and ch irp spread spectrum to generate modulation data.
Step S40: and the modulation and demodulation system combines the frame header data and the modulation data to generate complete modulated data information.
Step S50: and the modulation and demodulation system receives the modulated data information and sends out the modulated data information.
Step S60: and the modulation and demodulation system receives the modulated radio frequency signal and converts the radio frequency signal into a baseband signal.
Step S70: and the modulation and demodulation system receives the baseband signals, and sequentially performs ch i rp despreading and direct sequence despreading on the received baseband signals to finally obtain despread original signals.
Alternatively, as shown in fig. 2, step S30 may include: step S301, step S302, step S303, step S304, and step S305.
Step S301: the modulation and demodulation system carries out channel coding on the original data.
Step S302: and the modulation and demodulation system whitens the data after the channel coding.
Step S303: and the modulation and demodulation system interweaves the whitened data.
Step S304: and the modulation and demodulation system carries out direct sequence spread spectrum on the interleaved data to generate a QPSK signal.
Step S305: the modulation and demodulation system multiplies the QPSK signal by the upch irp signal to generate modulation data.
Alternatively, as shown in fig. 3, step S304 may include: step S3041, step S3042, and step S3043.
Step S3041: the modulation and demodulation system carries out serial-to-parallel conversion on the interleaved data and divides the data into an I path and a Q path.
Step S3042: the modulation and demodulation system carries out direct sequence spread spectrum processing on signals on each branch of the data after serial-parallel conversion by using a pseudo random code generated by a pseudo random code generator, and converts a symbol after spread spectrum into a bipolar symbol.
Step S3043: the modulation and demodulation system carries out inverse transformation of series-parallel transformation on the I path data and the Q path data after transformation to generate QPSK signals.
Alternatively, as shown in fig. 4, step S70 may include: step S701, step S702, step S703, step S704, step S705, step S706, and step S707.
Step S701: and the modulation and demodulation system carries out symbol synchronization on the received baseband signal and determines the initial position of the modulation signal.
Step S702: and the modulation and demodulation system carries out time offset and frequency offset correction on the signals after symbol synchronization.
Step S703: and the modulation and demodulation system multiplies the signals after time offset and frequency offset correction by the downlink chirp signals generated by the modulation and demodulation system to complete the despreading of the chirp signals.
Step S704: and the modulation and demodulation system performs direct sequence despreading on the signals subjected to the despreading of the ch i rp to obtain demodulated data.
Step S705: and the modulation and demodulation system performs de-interleaving on the demodulated data.
Step S706: and the modulation and demodulation system carries out de-whitening on the de-interleaved data.
Step S707: and the modulation and demodulation system decodes the de-whitened data to obtain original information.
Alternatively, as shown in fig. 5, the step S704 may include: step S7041, step S7042, and step S7043.
Step S7041: and the modulation and demodulation system judges the signals after completing the de-spreading of the ch irp according to the phase, and then carries out series-parallel conversion on the judged signals and distributes the signals to an I path and a Q path.
Step S7042: the modulation and demodulation system carries out conversion from bipolar codes to unipolar codes on the data after serial-to-parallel conversion, and despreads direct sequence spread spectrum by using a pseudo-random code which is the same as that of a transmitting end.
Step S7043: and the modulation and demodulation system performs parallel-to-serial conversion on the despread I path data and Q path data to obtain demodulated data.
As shown in fig. 6, an embodiment of the present invention provides a modulation and demodulation system, where the modulation and demodulation system includes a radio frequency module 1, a baseband modulation module 2, and a baseband demodulation module 3, the radio frequency module 1 includes a radio frequency transmitting module 11 and a radio frequency receiving module 12, and the baseband modulation module 2 includes a cirp generator 21, a frame header generator, a data modulation module 23, and a frame formation module 24.
The ch i rp generator 21 is configured to generate a ch i rp signal.
And the frame header generator is used for combining the frame headers by using the ch i rp signals.
The data modulation module 23 is configured to sequentially perform direct sequence spreading and chirp spreading on the original signal to generate modulation data.
The frame composition module 24 is configured to combine the frame header data and the modulation data to generate complete modulated data information.
And the radio frequency transmitting module 11 is configured to receive the modulated data information and send the modulated data information.
The rf receiving module 12 is configured to receive the modulated rf signal and convert the rf signal into a baseband signal.
And the baseband demodulation module 3 is configured to receive a baseband signal, and sequentially perform ch i rp despreading and direct sequence despreading on the received baseband signal to finally obtain a despread original signal.
The chirp generator 21 generates a chirp signal of a fixed length according to the parameter configuration. The chirp signal may be divided into an upchirp (linearly increasing frequency) signal and a downchirp (linearly decreasing frequency) signal, which are conjugate to each other.
The frame header generating module 22 combines the chirp signals generated by the chirp generator 21 into a frame header, which mainly plays a role in symbol synchronization and frequency offset estimation. In the system, symbol synchronization is carried out by using the downlink signals, the number of the downlink signals can be configured according to the system requirements, and is generally not less than 2. The down-chirp signal is followed by two up-chirp signals conjugated thereto for frequency offset estimation.
Optionally, the data modulation module 23 includes an encoding module 231, a whitening module 232, an interleaving module 233, a QPSK modulation module 234, and a first calculation module 235.
The encoding module 231 is configured to perform channel encoding on the original data.
The whitening module 232 is configured to whiten the data subjected to channel coding by the coding module 231.
The interleaving module 233 is configured to interleave the data whitened by the whitening module 232.
The QPSK modulation module 234 is configured to perform direct sequence spreading on the data interleaved by the interleaving module 233 to generate a QPSK signal.
The first calculating module 235 is configured to multiply the QPSK signal and the upchirp signal to generate modulation data.
The data modulation module 23 mainly converts a binary data stream to be transmitted into a modulation signal. The original information to be transmitted includes Header information (Header), device information (Addr), packet data (payload), and CRC check information (optional, configured according to parameters). The original information firstly enters a coding module 231 for channel coding, then enters a whitening module 232 for whitening, then enters an interleaving module 233 for interleaving, the data after interleaving is sent to a direct sequence spread spectrum QPSK modulation module 234 for generating a QPSK signal, and finally the QPSK signal is multiplied by an upchirp signal generated by a chirp generator 21 to realize chirp spread spectrum.
Optionally, the QPSK modulation module 234 may include a first serial-to-parallel conversion module 2341, a first symbol conversion module 2342, and a first parallel-to-serial conversion module 2343;
the first serial-parallel conversion module 2341 is configured to perform serial-parallel conversion on the interleaved data, and divide the data into an I path and a Q path;
the first symbol conversion module 2342 is configured to perform direct sequence spreading processing on a signal on each branch of the serial-to-parallel converted data by using a pseudo random code generated by a pseudo random code generator, and change a symbol after spreading into a bipolar symbol;
the first parallel-to-serial conversion module 2343 is configured to perform inverse serial-to-parallel conversion on the I-path data and the Q-path data after conversion, and generate a QPSK signal.
The QPSK modulation module 234 is a direct sequence spread spectrum, the direct sequence spread spectrum QPSK modulation module 234 firstly sends the input signal to a serial-parallel conversion module for serial-parallel conversion, i.e. the input binary stream is divided into two paths I and Q, and is basically distributed according to bit-by-bit interleaving: the first bit is input to the I-path and the second bit is input to the Q-path (other interleaving schemes may be used here). The signals on each branch are subjected to direct sequence spread spectrum processing by utilizing pseudo random codes generated by a pseudo random code generator. And the spread symbols are changed into bipolar symbols, i.e. bit 0 is represented by 1 and bit 1 is represented by-1. The transformed I and Q paths of data are sent to a parallel-to-serial conversion module for inverse conversion of serial-to-parallel conversion, and finally QPSK signals are generated.
The pseudo-random code generator can select different primitive polynomials according to the system parameter setting so as to generate pseudo-random codes with different lengths and different code words. For example, when the primitive polynomial is f (x) ═ x4When + x +1, 2 can be obtained4-spreading code of order 1-15.
Because the data of the paths I and Q adopt a bipolar representation mode, namely each path only has data of 1 and 1 types, the QPSK signal has the following four expression modes, namely: 1+ j, -1+ j, -1-j, 1-j. The corresponding phases are pi/4, 3 pi/4, 5 pi/4 and 7 pi/4 respectively. If expressed in complex form as
Where N is the QPSK chip sequence number, θNIs the corresponding phase.
The frame composing module 24 combines the frame header data generated by the frame header generating module 22 and the modulation data generated by the data modulation module 23 to generate complete data information, and then sends the complete data information to the radio frequency transmitting module 11, and sends the information through a series of processing of the radio frequency module 1.
The rf receiving module 12 receives the modulated rf signal, and then converts the modulated rf signal into a baseband signal through a series of processes and sends the baseband signal to the baseband demodulating module 3.
Optionally, the baseband demodulation module 3 may include a symbol synchronization module 31, a time-frequency correction module 32, a second calculation module 33, a QPSK demodulation module 34, a de-interleaving module 35, a de-whitening module 36, and a decoding module 37.
The symbol synchronization module 31 is configured to perform symbol synchronization on the received baseband signal, and determine an initial position of the modulation signal;
the time-frequency correction module 32 is configured to perform time-offset and frequency-offset correction on the signal after symbol synchronization;
the second calculating module 33 is configured to multiply the time-offset and frequency-offset corrected signal with the down chirp signal generated by the modulation and demodulation system, so as to complete chirp despreading of the signal;
the QPSK demodulation module 34 is configured to perform direct sequence despreading on the signal after chirp despreading is completed, so as to obtain demodulated data;
the deinterleaving module 35 is configured to deinterleave the data demodulated by the QPSK demodulation module 34;
the de-whitening module 36 is configured to de-whiten the data de-interleaved by the de-interleaving module 35;
the decoding module 37 is configured to decode the data that is subjected to whitening removal by the whitening removal module 36, so as to obtain original information.
The baseband demodulation module 3 firstly sends the input signal to the symbol synchronization module 31 for symbol synchronization, and further performs fine time offset and frequency offset estimation, according to the estimation result, the signal is subjected to time offset and frequency offset correction by the time-frequency correction module 32, and the accurate initial position of the modulation signal is determined. Then, the signal is multiplied by the down chirp signal generated by the chirp generator 21, and the chirp despreading process of the signal is completed. The chirp despread signal sequentially passes through a QPSK demodulation module 34, a de-interleaving module 35, a de-whitening module 36 and a decoding module 37, and finally the original transmission signal is restored.
Optionally, the QPSK demodulation module 34 may include a second serial-to-parallel conversion module 341, a second symbol conversion module 342, and a second parallel-to-serial conversion module 343;
the second serial-parallel conversion module 341 is configured to determine a signal after chirp despreading is completed according to a phase, and then perform serial-parallel conversion on the determined signal to distribute the determined signal to an I path and a Q path;
the second symbol transformation module 342 is configured to perform conversion from a bipolar code to a unipolar code on the data after serial-to-parallel conversion, and perform despreading of direct sequence spread spectrum by using a pseudo-random code that is the same as that of the transmitting end;
the second parallel-to-serial conversion module 343 is configured to perform parallel-to-serial conversion on the despread I-path data and Q-path data, so as to obtain demodulated data.
The QPSK demodulation module 34 is completely an inverse process of the QPSK modulation module 234, and firstly determines an input signal after chirp despreading according to phases, the determined phases conform to four phase conditions of a QPSK signal, then performs serial-to-parallel conversion on the determined signal and distributes the determined signal to I and Q paths, and completes conversion from a bipolar code to a unipolar code, then completes a despreading process of direct sequence spreading by using a pseudorandom sequence identical to a transmitting end, and finally performs parallel-to-serial conversion on despread data of the I and Q paths to obtain demodulated data.
In the embodiments provided in the present application, it should be understood that the disclosed apparatus and method can be implemented in other ways. The apparatus embodiments described above are merely illustrative, and for example, the flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (8)
1. A modulation and demodulation method applied to a modulation and demodulation system, the method comprising:
the modulation and demodulation system generates a chirp signal;
the modulation and demodulation system utilizes chirp signals to combine a frame header;
the modulation and demodulation system sequentially passes through direct sequence spread spectrum and chirp spread spectrum on an original signal to generate modulation data;
the modulation and demodulation system combines the frame header data and the modulation data to generate complete modulated data information;
the modulation and demodulation system receives the modulated data information and sends out the modulated data information;
the modulation and demodulation system receives the modulated radio frequency signal and converts the radio frequency signal into a baseband signal;
the modulation and demodulation system receives baseband signals, and performs chirp despreading and direct sequence despreading on the received baseband signals in sequence to finally obtain despread original signals;
the modulation and demodulation system generates modulation data by sequentially passing an original signal through direct sequence spread spectrum and chirp spread spectrum, and comprises:
the modulation and demodulation system carries out channel coding on original data;
the modulation and demodulation system whitens the data after channel coding;
the modulation and demodulation system interweaves the whitened data;
the modulation and demodulation system carries out direct sequence spread spectrum on the interleaved data to generate a QPSK signal;
the modulation and demodulation system multiplies the QPSK signal by the upchirp signal to generate modulation data;
the method for receiving baseband signals by the modulation and demodulation system includes the following steps of:
the modulation and demodulation system carries out symbol synchronization on the received baseband signal and determines the initial position of the modulation signal;
the modulation and demodulation system carries out time offset and frequency offset correction on the signals after symbol synchronization;
and the modulation and demodulation system multiplies the signals after time offset and frequency offset correction by the downlink chirp signals generated by the modulation and demodulation system to complete chirp de-spreading of the signals.
2. The modem method according to claim 1, wherein the modem system performs direct sequence spread spectrum on the interleaved data to generate a QPSK signal, and the method comprises:
the modulation and demodulation system carries out serial-to-parallel conversion on the interleaved data and divides the data into an I path and a Q path;
the modulation and demodulation system carries out direct sequence spread spectrum processing on signals on each branch of the data after serial-parallel conversion by using a pseudo-random code generated by a pseudo-random code generator, and converts a symbol after spread spectrum into a bipolar symbol;
the modulation and demodulation system carries out inverse transformation of series-parallel transformation on the I path data and the Q path data after transformation to generate QPSK signals.
3. The modem method according to claim 1, wherein the modem system receives a baseband signal, and sequentially performs chirp despreading and direct sequence despreading on the received baseband signal to obtain a despread original signal, and the method comprises:
the modulation and demodulation system performs direct sequence despreading on the signals after chirp despreading to obtain demodulated data;
the modulation and demodulation system de-interleaves the demodulated data;
the modulation and demodulation system carries out de-whitening on the de-interleaved data;
and the modulation and demodulation system decodes the de-whitened data to obtain original information.
4. The method according to claim 3, wherein the modem system performs direct sequence despreading on the chirp-despread signal to obtain demodulated data, and comprises:
the modulation and demodulation system judges the signals after chirp despreading according to the phase, and then carries out series-parallel conversion on the judged signals to be distributed to an I path and a Q path;
the modulation and demodulation system carries out conversion from bipolar codes to unipolar codes on the data after serial-to-parallel conversion, and de-spreads the direct sequence spread spectrum by using the pseudo-random code which is the same as the transmitting end;
and the modulation and demodulation system performs parallel-to-serial conversion on the despread I path data and Q path data to obtain demodulated data.
5. A modem system, characterized by: the modulation and demodulation system comprises a radio frequency module, a baseband modulation module and a baseband demodulation module, wherein the radio frequency module comprises a radio frequency transmitting module and a radio frequency receiving module, and the baseband modulation module comprises a chirp generator, a frame header generator, a data modulation module and a frame composition module;
the chirp generator is used for generating a chirp signal;
the frame header generator is used for combining a frame header by using a chirp signal;
the data modulation module is used for sequentially passing the original signal through direct sequence spread spectrum and chirp spread spectrum to generate modulation data;
the frame composition module is used for combining the frame header data and the modulation data to generate complete modulated data information;
the radio frequency transmitting module is used for receiving the modulated data information and sending out the modulated data information;
the radio frequency receiving module is used for receiving the modulated radio frequency signal and converting the radio frequency signal into a baseband signal;
the baseband demodulation module is used for receiving baseband signals, sequentially performing chirp despreading and direct sequence despreading on the received baseband signals and finally obtaining despread original signals;
the data modulation module comprises a coding module, a whitening module, an interleaving module, a QPSK modulation module and a first calculation module;
the encoding module is used for carrying out channel encoding on the original data;
the whitening module is used for whitening the data subjected to the channel coding by the coding module;
the interleaving module is used for interleaving the data whitened by the whitening module;
the QPSK modulation module is used for performing direct sequence spread spectrum on the data interleaved by the interleaving module to generate a QPSK signal;
the first calculation module is used for multiplying the QPSK signal and the upchirp signal to generate modulation data;
the baseband demodulation module comprises a symbol synchronization module, a time-frequency correction module and a second calculation module:
the symbol synchronization module is used for carrying out symbol synchronization on the received baseband signal and determining the initial position of the modulation signal;
the time-frequency correction module is used for correcting time offset and frequency offset of the signals subjected to symbol synchronization;
and the second calculating module is used for multiplying the signal after time offset and frequency offset correction with the downlink chirp signal generated by the modulation and demodulation system to complete chirp de-spreading of the signal.
6. The modem system of claim 5, wherein: the QPSK modulation module comprises a first serial-parallel conversion module, a first symbol conversion module and a first parallel-serial conversion module;
the first serial-parallel conversion module is used for performing serial-parallel conversion on the interleaved data and dividing the data into an I path and a Q path;
the first symbol conversion module is used for performing direct sequence spread spectrum processing on a signal on each branch of the serial-parallel converted data by using a pseudo-random code generated by a pseudo-random code generator and converting a spread symbol into a bipolar symbol;
and the first parallel-serial conversion module is used for performing inverse conversion of serial-parallel conversion on the I path data and the Q path data after conversion to generate QPSK signals.
7. The modem system of claim 5, wherein: the baseband demodulation module comprises a QPSK demodulation module, a de-interleaving module, a de-whitening module and a decoding module;
the QPSK demodulation module is used for performing direct sequence despreading on the signals after chirp despreading to obtain demodulated data;
the de-interleaving module is used for de-interleaving the data demodulated by the QPSK demodulation module;
the de-whitening module is used for de-whitening the data de-interleaved by the de-interleaving module;
and the decoding module is used for decoding the data subjected to the de-whitening by the de-whitening module to obtain the original information.
8. The modem system of claim 7, wherein: the QPSK demodulation module comprises a second serial-parallel conversion module, a second symbol conversion module and a second parallel-serial conversion module;
the second serial-parallel conversion module is used for judging the signals after chirp despreading according to the phase, and then performing serial-parallel conversion on the judged signals to distribute the signals to an I path and a Q path;
the second symbol conversion module is used for converting the data after the serial-parallel conversion from a bipolar code to a unipolar code and performing despreading of direct sequence spread spectrum by using a pseudo-random code which is the same as that of the transmitting end;
and the second parallel-serial conversion module is used for performing parallel-serial conversion on the despread I-path data and Q-path data to obtain demodulated data.
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| CN113141195B (en) * | 2021-04-06 | 2022-08-23 | 重庆邮电大学 | Demodulation method for dispreading in direct sequence spread spectrum system and storage medium |
| CN115149978B (en) * | 2022-09-05 | 2022-11-11 | 中国人民解放军国防科技大学 | Chirp spread spectrum modulation method, system and medium with anti-interception function |
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