OQAM-based multi-band modulation signal generation method, spectrum wireless transmission method and system

Abstract

The invention discloses a multi-band modulation signal generation method based on OQAM, and a frequency spectrum wireless transmission method and system. The method comprises the following steps: a transmitting end performs OQAM preprocessing and modulation on original data flow to realize subcarrier multiplexing; and the receiving end is used for sampling the received signal, and down-conversion, demodulation and original data recovery of the signal are completed through a DSP (Digital Signal Processor) processing module. The multi-subcarrier staggered orthogonal amplitude modulation technology is combined, the spectrum efficiency is effectively improved, interference among subcarriers is avoided, and efficient spectrum utilization, low-cost transmission and multi-user access are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless transmission, and particularly relates to a method for generating a multi-band modulation signal based on OQAM, a spectrum wireless transmission method and system. Background Art

[0002] With the rapid development of B5G / 6G communication technologies, the demand for high-speed, low-latency, and large-capacity transmission in communication services is increasing day by day, driving the evolution of communication systems to higher frequency bands, which also poses higher requirements for key indicators such as signal bit error rate, spectral efficiency, and device bandwidth. Sub-carrier multiplexing (SCM) technology has been widely used in the field of optical fiber communication due to its advantages such as easy implementation, low cost, good compatibility, and strong flexibility, and has received extensive attention from scholars in the field of optical communication at home and abroad. In addition, the independence between sub-carrier channels reduces the requirement for the bandwidth of the receiving device and supports the simultaneous transmission of multiple types of signals and flexible access of multiple users. However, due to the use of RRC / SRRC filters and strict orthogonality requirements in traditional SCM technology, interference inevitably exists between sub-carriers. Although it can be mitigated by adding a guard interval, it will reduce the spectral efficiency and cause waste of spectral resources.

[0003] The new generation of integrated space-air-ground-sea network requires a larger transmission capacity, a higher transmission rate, and a farther transmission distance, and the existing single microwave wireless communication architecture is difficult to meet. Space laser communication technology has the advantages of high communication rate and convenient band selection, but it is easily affected by smoke, atmospheric turbulence, and beam alignment. At the same time, the emerging photon terahertz wireless communication technology route has the advantages of ultra-large bandwidth spectral resources, easy seamless integration with fiber optic networks, and strong stability, but it is severely affected by rain and snow weather. Summary of the Invention

[0004] Object of the Invention: To solve the problems existing in the above-mentioned prior art, the present invention provides a method for generating a multi-band modulation signal based on OQAM, a spectrum wireless transmission method and system.

[0005] Technical Solution: The present invention provides a method for generating a multi-band modulation signal based on OQAM, specifically including the following steps:

[0006] Step 1: Allocate sub-bands for each user's data, and perform amplitude modulation on each user's data based on QAM constellation mapping to obtain a complex symbol sequence;

[0007] Step 2: Separate the real and imaginary parts of the complex symbols of the subcarriers, upsample the real and imaginary parts, and introduce a time delay of half a symbol period alternately between the two paths of the real and imaginary parts according to whether the subcarrier index is odd or even. Specifically: for the complex symbols of the subcarriers with odd index values, introduce a time delay of T / 2 to the real part branch; for the complex symbols of the subcarriers with even index values, introduce a time delay of T / 2 to the imaginary part branch. Add the real and imaginary sequences of the m-th subcarrier and multiply the result by the phase factor of the m-th subcarrier to obtain the m-th signal, where m = 1, 2, …, M; M represents the number of subcarriers.

[0008] Step 3: Perform pulse shaping and up-conversion on the m-th signal obtained in Step 2 to obtain the m-th sub-band modulated signal.

[0009] Step 4: Based on the sub-band modulated signals, obtain a multi-band modulated signal, and perform digital-to-analog conversion on the multi-band modulated signal to obtain an analog multi-band modulated signal.

[0010] Further, it specifically includes the following steps: Step 1 is specifically: convert the original high-speed data stream into M low-speed sub-data streams through serial-to-parallel conversion, then convert the M low-speed sub-data streams into an M-QAM complex symbol sequence through QAM constellation mapping, and simultaneously upsample the mapped M-QAM complex symbol sequence.

[0011] A wireless transmission method for a multi-band modulated signal

[0012] Separate the real and imaginary parts of the multi-band modulated signal, use the real part as the driving signal for the I path of the IQ modulator, and use the imaginary part as the driving signal for the Q path of the IQ modulator. Use the IQ modulator to perform IQ modulation on the first optical carrier with the first frequency to obtain an optical signal.

[0013] Wirelessly transmit the optical signal through a terahertz link and a free-space laser link.

[0014] When using the terahertz link for wireless transmission, use a terahertz-band receiving antenna to receive the transmission signal. When using the free-space laser link for wireless transmission, use a laser-band to receive the transmission signal.

[0015] Demodulate the received signal into user data.

[0016] Further, the terahertz link couples the optical signal with the second optical carrier with the second frequency to generate an optical coupling signal, performs beat frequency processing on the optical coupling signal to generate a photon terahertz signal with a preset frequency, and emits the photon terahertz signal in a wireless transmission manner.

[0017] Further, the free-space laser link amplifies the optical signal and emits it in a wireless transmission manner.

[0018] Further, when receiving a transmission signal using a terahertz band receiving antenna, demodulation is performed in an heterodyne coherent or direct detection manner to obtain an intermediate frequency / baseband analog modulation signal. The intermediate frequency / baseband analog modulation signal is sampled using an oscilloscope, and then the sampled signal is subjected to impairment compensation, noise removal, and offset recovery.

[0019] A wireless transmission system for a spectrum includes a data processing device, a baseband unit, a receiving unit, and a signal demodulation unit;

[0020] The data processing device includes a multi-band signal generation module and a waveform generator; the multi-band signal generation module includes: a QAM mapping module, an upsampling module, an OQAM preprocessing module, a shaping filter module, a first laser, an IQ modulator, and a separation module;

[0021] The QAM mapping module maps to obtain a complex symbol sequence based on a QAM constellation diagram;

[0022] The upsampling module performs upsampling on the complex symbol sequence;

[0023] The OQAM preprocessing module separates the real and imaginary parts of the symbol in complex form and then performs upsampling, and then alternately introduces a half-symbol period time delay between the real and imaginary part paths according to the parity of the subcarrier index;

[0024] The shaping filter module performs pulse shaping and upconversion on the signal to obtain sub-band modulation signals, and then generates a multi-band modulation signal based on the sub-band modulation signals;

[0025] The waveform generator performs digital-to-analog conversion on the multi-band modulation signal to obtain an analog multi-band modulation signal;

[0026] The first laser generates a first optical carrier and transmits it to the IQ modulator;

[0027] The separation module separates the real and imaginary parts of the analog multi-band modulation signal. The real part serves as the I-channel drive signal of the IQ modulator, and the imaginary part serves as the Q-channel drive signal of the IQ modulator; the IQ modulator is used to modulate the first optical carrier to obtain an optical signal;

[0028] The baseband unit is used to receive the optical signal and transmit the optical signal to a terahertz link and a free space laser link for wireless transmission;

[0029] The receiving unit receives the signal sent by the baseband unit; and transmits it to the signal demodulation unit for demodulation.

[0030] Further, when transmitting the optical signal to the terahertz link for wireless transmission, the baseband unit includes a first optical coupler, a first receiving module, a second laser, a second optical coupler, a photodetector; a first low-noise amplifier; a first transmitting module;

[0031] The first optical coupler receives an optical signal and transmits the optical signal to a first receiving module respectively;

[0032] A second laser generates a second optical carrier with a second frequency;

[0033] The first receiving module transmits the received optical signal to a second optical coupler; the second optical coupler couples the optical signal with the second optical carrier to generate an optical coupling signal;

[0034] A photodetector performs beat frequency processing on the optical coupling signal to generate a photon terahertz signal with a preset frequency;

[0035] A first low-noise amplifier is used to amplify the photon terahertz signal;

[0036] A first transmitting module is used to transmit the amplified photon terahertz signal;

[0037] When the optical signal is transmitted to a free-space laser link for wireless transmission, the baseband unit includes a first erbium-doped fiber amplifier and a second transmitting module;

[0038] The first erbium-doped fiber amplifier is used to compensate for fiber loss and amplify the optical signal, and transmits the amplified optical signal to the second transmitting module; the second transmitting module transmits the amplified optical signal.

[0039] Further, when the optical signal is transmitted to a terahertz link for wireless transmission, the receiving unit includes a second receiving module, a second low-noise amplifier, a mixer, and a radio frequency local oscillator source;

[0040] The second receiving module receives the photon terahertz signal transmitted by the terahertz link,

[0041] The second low-noise amplifier is used to amplify the received photon terahertz signal;

[0042] The radio frequency local oscillator source generates a local oscillator signal;

[0043] The mixer is used to mix the local oscillator signal with the photon terahertz signal and then transmit it to a demodulation unit;

[0044] When the optical signal is transmitted to a free-space laser link for wireless transmission, the receiving unit includes a second erbium-doped fiber amplifier, a third receiving module, and an optical receiver;

[0045] The third receiving module is used to receive the optical signal transmitted by the free-space laser link;

[0046] The second erbium-doped fiber amplifier is used to perform optical compensation and amplification on the received optical signal;

[0047] The optical receiver transmits the optical signal to the demodulation unit.

[0048] Furthermore, the demodulation unit includes an analog-to-digital conversion module and a demodulation module. The demodulation module includes a digital down-conversion module, a matched filter module, an IQ imbalance compensation and orthonormalization module, a clock synchronization module, a down-sampling module, a fast Fourier transform module, a channel equalization module, a carrier recovery module, an OQAM post-processing module, and a QAM demapping module;

[0049] The analog-to-digital conversion module is used to perform analog-to-digital conversion on the received signal;

[0050] The digital down-conversion module is used to down-convert the multi-band modulated signal output by the analog-to-digital conversion module to the baseband and filter out redundant high-frequency components to obtain a baseband signal;

[0051] The matched filter module is used to separate the baseband signal into branch signals;

[0052] The IQ imbalance compensation and orthonormalization module uses the Schmidt orthogonal method to eliminate IQ imbalance and non-orthogonal interference in the IQ modulation of the branch signals;

[0053] The clock synchronization module is used to eliminate clock offset and jitter caused by link loss of the signal;

[0054] The down-sampling module is used to perform down-sampling on each branch signal to match the sampling rate of the oscilloscope;

[0055] The fast Fourier transform module is used to perform a fast Fourier transform on each branch signal, thereby converting the signal from the time domain back to the frequency domain to obtain a frequency-domain signal;

[0056] The channel equalization module is used to equalize the frequency-domain signal;

[0057] The carrier recovery module uses the FOE algorithm based on the fourth power and the blind phase recovery algorithm to obtain the branch signals processed by DSP technology;

[0058] The OQAM post-processing module is used to multiply each branch signal processed by DSP technology by a phase factor, take the real part to obtain real symbols, and then separate every two consecutive real symbols and introduce time delays respectively. One of them is multiplied by the imaginary unit and recombined into a complex symbol;

[0059] The QAM demapping module 3 restores the obtained complex symbols to the original binary data sequence.

[0060] Beneficial effects: The present invention combines sub-band allocation and amplitude modulation. On the one hand, it can perform data transmission for multiple users, enabling multiple users' data to be transmitted at different rates in the same channel, improving spectral efficiency and transmission capacity, avoiding interference between sub-carriers, and making the multi-user data allocation more flexible. On the other hand, it reduces the difficulty of signal modulation and the system cost. Brief Description of the Drawings

[0061] Figure 1 It is a flowchart for generating a multi-band modulation signal.

[0062] Figure 2 It is a flowchart for transmitting an analog multi-band modulation signal.

[0063] Figure 3 It is a flowchart for signal reception.

[0064] Figure 4 It is a block diagram of the spectrum transmission system in Embodiment 4.

[0065] Figure 5 It is a block diagram of the data processing device in Embodiment 5.

[0066] Figure 6 It is a block diagram of the signal generation module in Embodiment 6.

[0067] Figure 7 It is a block diagram of the data processing device in Embodiment 7.

[0068] Figure 8 It is a block diagram of the data processing device in Embodiment 8.

[0069] Figure 9 It is a block diagram of the wireless transmission system in Embodiment 9.

[0070] Figure 10 It is a block diagram of the wireless reception system in Embodiment 10.

[0071] Figure 11 It is a block diagram of the demodulation module in Embodiment 11.

[0072] Figure 12 It is a block diagram of the overall wireless transmission system.

[0073] Figure 13 It is a schematic diagram of the transmission process of user data in a multi-user-oriented spectrum-efficient wireless transmission system based on OQAM. Detailed Embodiments

[0074] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0075] As Figure 1 shown, the present invention provides a method for generating a multi-band modulation signal, specifically:

[0076] S11: Allocate sub-bands for each user data, and map each user data to obtain M-QAM complex symbols.

[0077] Wherein, the user data refers to the data to be transmitted corresponding to each user.

[0078] Specifically, the original high-speed data stream is converted into M low-speed sub-data streams through serial-to-parallel conversion, and then the M sub-data streams are mapped to an M-QAM complex symbol sequence (M is the order) through constellation mapping. At the same time, the mapped M-QAM complex symbols are upsampled to match the sampling rate of the subsequent shaping filter. The number of zero-value samples inserted in the upsampling process is determined by the ratio of the filter sampling frequency to the symbol rate and the number of subcarriers.

[0079] S12: Separate the real part (in-phase component) and the imaginary part (quadrature component) of the M-QAM complex symbols, and introduce a delay of half of the initial QAM symbol period for the in-phase component on the odd subcarriers and the quadrature component on the even subcarriers respectively according to the parity of the subcarrier index value to complete OQAM preprocessing.

[0080] Specifically, use s m (k) represents the k-th complex symbol on the m-th subcarrier after QAM constellation mapping. Separate the real part (in-phase component) and the imaginary part (quadrature component) of the complex symbol, and take their real parts and imaginary parts respectively, and then perform 2-fold upsampling. Then, according to the parity of the subcarrier index m, alternately introduce a delay of half of the initial QAM symbol period between the two paths of the real part and the imaginary part. Let the initial QAM complex symbol period be T. For the symbols on the even subcarriers, introduce a delay of T / 2 for the imaginary part branch; for the symbols on the odd subcarriers, introduce a delay of T / 2 for the real part branch. Finally, after adding the real and imaginary two-path sequences, multiply by the phase factor θ m (k), θ m (k) = j ((m-1)+2k) , and the k complex symbols of each subcarrier are combined after OQAM preprocessing to obtain the signal after OQAM preprocessing.

[0081] S13: Obtain the sub-band modulation signal based on each signal after OQAM preprocessing.

[0082] Specifically, perform an inverse fast Fourier transform on each signal after OQAM preprocessing. After transforming each signal from the frequency domain to the time domain, perform pulse shaping and upconversion on each signal respectively to obtain the sub-band modulation signal.

[0083] S14: Obtain a multi-band modulation signal from each of the sub-band modulation signals.

[0084] Specifically, add the sub-band modulation signals to obtain the multi-band modulation signal. The above modulation process introduces the OQAM modulation technology in a multi-subcarrier system, performs data transmission in the form of alternating virtual and real intervals, and adopts the mapping method with opposite virtual and real parts, which can achieve spectrum-efficient ICI / ISI-free transmission with a carrier interval equal to the symbol rate.

[0085] Convert the multi-band modulation signal into an analog multi-band modulation signal, specifically:

[0086] S15: Perform digital signal processing operations on the multi-band modulation signal to obtain a digital multi-band modulation signal.

[0087] Specifically, performing digital signal processing operations on the multi-band modulation signal includes resampling and / or normalization operations to obtain a digital multi-band modulation signal, which is convenient for subsequent digital-to-analog conversion processing.

[0088] S16: Perform digital-to-analog conversion on the digital multi-band modulation signal to obtain an analog multi-band modulation signal.

[0089] In this embodiment, an arbitrary waveform generator can be used to perform digital-to-analog conversion on the digital multi-band modulation signal to generate an analog multi-band modulation signal. Optionally, after generating the analog multi-band modulation signal, an electrical amplifier can also be used to amplify the analog multi-band modulation signal.

[0090] Embodiment 2 provides a spectrum-efficient wireless transmission method based on OQAM for multiple users, as Figure 2 shown. The spectrum-efficient wireless transmission method based on OQAM for multiple users includes:

[0091] S21: Generate an analog multi-band modulation signal based on each user data;

[0092] S22: Apply the analog multi-band modulation signal to a first optical carrier with a first frequency to generate an optical signal.

[0093] Specifically, a semiconductor laser generates a stable continuous light as the optical carrier and sends it into an IQ modulator for modulation to obtain an optical signal. Among them, the real part and the imaginary part of the analog multi-band modulation signal are respectively used as the driving signals of the I channel and the Q channel of the IQ modulator to achieve IQ modulation of the first optical carrier, thereby obtaining an optical signal.

[0094] S23: For the terahertz link, couple the optical signal with a second optical carrier having a second frequency to generate an optical coupling signal, perform beat frequency processing on the optical coupling signal to generate a photon terahertz signal having a preset frequency, and transmit the transmission signal by wireless transmission; for the free space laser link, amplify the optical signal and then transmit it by wireless transmission.

[0095] In this embodiment, an optoelectronic coupler such as a digital signal optoelectronic coupler is used to couple the optical signal with a second optical carrier having a preset frequency.

[0096] Specifically, heterodyne technology can be used to perform beat frequency on the optical signal to obtain a transmission signal with a terahertz carrier frequency. The transmission signal is sent to the transmitting antenna for wireless transmission. Among them, the principle of heterodyne technology is to generate a new frequency by mixing two signals with different frequencies in wireless signal processing.

[0097] As an example, a terahertz wireless signal can be obtained through beat frequency processing by a photodiode (abbreviated as PD). The optical frequency of the terahertz wireless signal is the difference between the optical frequencies of the second optical signal and the third optical signal with a preset frequency.

[0098] Embodiment 3 also provides a spectrum-efficient wireless transmission method based on OQAM for multiple users, as Figure 3 shown. The spectrum-efficient wireless transmission method based on OQAM for multiple users includes:

[0099] S31: Receive the transmission signal. For the terahertz link, the transmission signal is transmitted by the terahertz link of the spectrum-efficient wireless transmission method based on OQAM for multiple users in the foregoing embodiment; for the free space laser link, the transmission signal is transmitted by the free space laser link of the spectrum-efficient wireless transmission method based on OQAM for multiple users in the foregoing embodiment.

[0100] As an example, for the terahertz link, the user terminal can receive the transmission signal using a terahertz band receiving antenna; for the free laser link, the user terminal can receive the transmission signal using a laser band receiving antenna.

[0101] S32: Demodulate the transmission signal into user data.

[0102] Specifically, the received terahertz wireless signal is demodulated by heterodyne coherent or direct detection to obtain an intermediate frequency / baseband analog modulation signal. The oscilloscope samples the analog signal to complete analog-to-digital conversion, and finally sends it to the receiving end DSP module for subsequent operations such as impairment compensation, noise removal, and offset recovery until the initial information signal is restored.

[0103] Heterodyne coherent detection is a form of coherent detection. After down-converting the terahertz signal to an intermediate-frequency signal through a radio-frequency local oscillator (LO) and a mixer, it is then processed. This scheme has relaxed requirements for the radio-frequency local oscillator frequency used. At the same time, it has high receiving sensitivity, advantages such as high conversion gain, strong detection ability, and high signal-to-noise ratio, and is widely used in the field of optical wireless communication.

[0104] Embodiment 4, as Figure 4 shown, the spectrum-efficient wireless transmission system based on OQAM for multiple users includes: a data processing device 1 and a baseband unit 2. Among them, the data processing device 1 allocates sub-bands for each user's data and performs amplitude modulation on each user's data to obtain complex symbols; separates the real and imaginary parts of the complex symbols and transmits them in an alternating real and imaginary manner with the opposite real and imaginary mappings at a T / 2 symbol period to obtain a sub-band modulated signal; obtains a multi-band modulated signal according to each of the sub-band modulated signals; loads the multi-band modulated signal onto a first optical carrier to obtain an optical signal, and transmits the optical signal through a wired transmission method; the baseband unit 2 is connected to the data processing device in a wired manner, and the baseband unit is used to receive the optical signal and distribute the signal to a terahertz link and a free-space laser link; for the terahertz link, performs a beat-frequency process on the optical signal to obtain a transmission signal with a terahertz carrier frequency, and transmits the transmission signal through a wireless transmission method; for the free-space laser link, directly transmits the first optical signal output by the signal modulation end through a lens antenna.

[0105] Embodiment 5, as Figure 5 shown, the data processing device 1 includes a multi-band signal generation module 11 and a waveform generator 12. Among them, the multi-band signal generation module 11 is used to generate a multi-band modulated signal, and the waveform generator 12 is used to perform digital-to-analog conversion on the multi-band modulated signal. As an example, the waveform generator 12 can be an arbitrary waveform generator. Specifically, after receiving several user data, the multi-band signal generation module 11 allocates sub-bands for each user's data and generates an analog multi-band modulated signal. Among them, user data refers to the data to be transmitted corresponding to each user.

[0106] Embodiment 6, as Figure 6As shown in the figure, the multi-band signal generation module 11 may include a QAM mapping module 111, an upsampling module 112, an OQAM preprocessing module 113, and a shaping filter module 114. Among them, the QAM mapping module 111 maps the binary data of each sub-data stream into an M-QAM complex symbol sequence (M is the order). The upsampling module 112 upsamples the mapped M-QAM signal. The number of zero-valued samples inserted during the upsampling process is determined by the ratio of the sampling frequency of the waveform generator 12 to the symbol rate and the number of subcarriers. The OQAM preprocessing module 113 separates the real part (in-phase component) and the imaginary part (quadrature component) of the complex symbol and then performs 2-fold upsampling. According to whether the subcarrier index value is odd or even, a delay of half of the initial QAM symbol period is introduced to the in-phase component on the odd subcarriers and the quadrature component on the even subcarriers respectively. Finally, after adding the real and imaginary two paths of sequences, it is multiplied by the phase factor θ m (k), where θ m (k) = j ((m-1)+2k) . The shaping filter module 113 performs pulse shaping and upconversion on the signal to obtain each sub-band modulated signal. Finally, adding each sub-band modulated signal can obtain the multi-band modulated signal.

[0107] After obtaining the multi-band modulated signal, the multi-band modulated signal is input into the waveform generator 12 for digital-to-analog conversion to obtain an analog multi-band modulated signal, so as to load the analog multi-band modulated signal onto the carrier for data transmission.

[0108] Embodiment 7, as Figure 7 shown, the data processing device 1 further includes an electrical amplifier 13, and the electrical amplifier 13 is connected to the waveform generator 12 for amplifying the analog multi-band modulated signal.

[0109] Embodiment 8, as Figure 8 shown, the data processing device 1 further includes a first laser 14 and an IQ modulator 15. Among them, the first laser 14 is used to generate the first optical carrier, and the frequency of the first optical carrier is the first frequency; the IQ modulator 15 is used to modulate the subcarrier multiplexing signal onto the first optical carrier to generate the optical signal.

[0110] Specifically, after the analog multi-band modulated signal is amplified, the real part and the imaginary part of the signal are respectively used as the I-channel and Q-channel drive signals of the IQ modulator to achieve IQ modulation of the first optical carrier.

[0111] Embodiment 9, as Figure 9As shown in the figure, the baseband unit 2 includes: an optical coupler 21, configured to receive the optical signal and divide the optical signal into two paths and send them to the terahertz link and the free-space laser link respectively. For the terahertz link, a first receiving module 22 is configured to receive the optical signal; a second laser 23 is configured to generate a second optical carrier, and the frequency of the second optical carrier is a second frequency; an optical coupler 24 is configured to couple the second optical carrier and the optical signal to generate an optical coupling signal; a photodetector 25 is configured to perform a beat frequency process on the optical coupling signal to generate a terahertz signal with a preset frequency, and the preset frequency is the difference between the first frequency and the second frequency; a low-noise amplifier 26 is configured to amplify the terahertz signal; a first transmitting module 27 is configured to transmit the transmission signal. For the free-space laser link, an erbium-doped fiber amplifier 28 is connected to the optical coupler 21 and is configured to compensate for fiber loss; a second transmitting module 29 is configured to transmit the transmission signal. As an example, the transmission signal of the terahertz link may be a terahertz wave signal with a terahertz carrier frequency, and the transmission signal of the free-space laser link may be emitted through a laser beam.

[0112] Specifically, after the optical signal is transmitted from the data processing device 1 to the baseband unit 2 by the optical fiber, it is received by the optical coupler 21. As an example, for the terahertz link, the first receiving module 22 may be a variable optical attenuator. After receiving the optical signal, the variable optical attenuator adjusts its power to achieve sensitivity measurement. Then, the optical signal with adjusted power is input to the first input terminal of the optical coupler 24. A second laser 23 independent of the first laser 14 generates a second optical carrier with a second frequency and inputs it to the second input terminal of the optical coupler 24. The second optical carrier and the adjusted optical signal are coupled in the optical coupler 24 and then sent to the photodetector 25 for beat frequency. The frequency difference between the two optical carriers is terahertz, so as to achieve wireless transmission of the signal. As an example, the first transmitting module 24 may be a terahertz-band transmitting antenna. For the free-space laser link, the optical signal is amplified in the erbium-doped fiber amplifier 28 through optical fiber transmission. The output terminal of the erbium-doped fiber amplifier 28 is connected to the input terminal of the second transmitting module 29, and free laser emission is achieved in the second transmitting module 29. As an example, the second transmitting module 29 may be a lens antenna.

[0113] Embodiment 10, as Figure 10 As shown in the figure, a spectrum-efficient wireless transmission system further includes a terminal 3, and the terminal 3 is configured to receive the transmission signal and demodulate the transmission signal to obtain user data; wherein, the transmission signal is transmitted by the spectrum-efficient wireless transmission system for multiple users based on OQAM described in any of the foregoing embodiments.

[0114] Specifically, the terminal 3 may include: a second receiving module 31 for receiving the transmission signal; a low-noise amplifier 32 for amplifying the signal; a radio frequency local oscillator source 33 for generating a local oscillator signal; a mixer 34 for mixing the local oscillator signal with the terahertz signal; a third receiving module 35 for receiving the transmission signal; an erbium-doped fiber amplifier 36 for compensating for fiber loss; an optical receiver 37 for receiving the transmission signal and converting it into an electrical signal; an analog-to-digital conversion module 38 for performing analog-to-digital conversion on the multi-band modulation signal to obtain a digital multi-band modulation signal; and a demodulation module 39 for demodulating and restoring the digital multi-band modulation signal to the user data.

[0115] Specifically, for the terahertz link, as an example, the second receiving module 31 may be a terahertz-band receiving antenna. After the second receiving module 31 receives the terahertz wave signal from the baseband unit 2, the terahertz wireless signal is amplified by the low-noise amplifier 32 and then sent to the first input terminal of the mixer 34. The radio frequency local oscillator source 33 generates a local oscillator signal and inputs it to the second input terminal of the mixer 34. The local oscillator signal and the terahertz signal are mixed in the mixer 34 and low-pass filtered to obtain an intermediate frequency / baseband analog modulation signal. Since the upper limit frequency of the radio frequency local oscillator is relatively low, the frequency doubling process of the local oscillator is usually also involved. The intermediate frequency / baseband analog modulation signal is amplified by the erbium-doped fiber amplifier and then transmitted to the analog-to-digital conversion module 38 to perform analog-to-digital conversion on the multi-band modulation signal to obtain a digital multi-band modulation signal. As an example, the analog-to-digital conversion module 38 may be a real-time digital storage oscilloscope, and the demodulation module 38 may be a multi-band signal demodulation module. The demodulation module 39 is connected to the analog-to-digital conversion module 38 to demodulate the digital multi-band modulation signal and obtain the original data stream. For the free space optical link, as an example, the third receiving module 35 may be a lens antenna. The third receiving module 35 receives the optical link signal, amplifies it by the erbium-doped fiber amplifier 36, and then transmits it to the optical receiver 37. The optical receiver 37 converts the optical signal into an electrical signal and transmits it to the analog-to-digital conversion module 38 to perform analog-to-digital conversion on the multi-band modulation signal to obtain a digital multi-band modulation signal. As an example, the analog-to-digital conversion module 38 may be a real-time digital storage oscilloscope, and the demodulation module 38 may be a multi-band signal demodulation module. The demodulation module 39 is connected to the analog-to-digital conversion module 38 to demodulate the digital multi-band modulation signal and obtain the original data stream.

[0116] Implementation 11, such as Figure 11As shown, the demodulation module 39 includes: a digital down-conversion module 391, a matched filter module 392, an IQ imbalance compensation and orthogonal normalization module 393, a clock synchronization module 394, a down-sampling module 395, a fast Fourier transform module 396, a channel equalization module 397, a carrier recovery module 398, an OQAM post-processing module 399, and a QAM demapping module 3910. The digital down-conversion module 391 down-converts the multi-band modulation signal output by the analog-to-digital conversion module 38 to the baseband, and filters out the redundant high-frequency components to obtain the baseband signal, and transmits it to the matched filter module 392 to separate the baseband signal into each branch signal; the IQ imbalance compensation and orthogonal normalization module 393 uses the Schmidt orthogonal method to eliminate the IQ imbalance and non-orthogonal interference of each branch signal in the IQ modulation due to the defects of the modulator manufacturing process, the instability of EA or the unsatisfactory working state of the device; the clock synchronization module 394 is used to eliminate the clock offset and jitter caused by the link loss of the signal ; The downsampling module 395 is used to downsample each branch signal to match the oscilloscope sampling rate; After the fast Fourier transform module 396 performs fast Fourier transform on each sub-band signal processed as above, the signal is converted from the time domain back to the frequency domain to obtain the frequency domain signal, and is transmitted to the channel equalization module 397 to equalize the frequency domain signal. In particular, due to the half-symbol period delay between the IQ channels during equalization, the traditional CMA and CMMA equalization algorithms based on the signal modulus value are not applicable. Here, a blind equalization algorithm based on LMS and training sequence is adopted and further optimized in combination with DD-LMS. The carrier recovery module 398 includes frequency offset estimation and phase recovery. In the coherent detection scheme, two local oscillator sources (LO) are involved, namely the laser LO in the RBU and the RF LO in the EU. However, in practice, the frequency difference between the LO and the corresponding carrier is not completely locked, and the random frequency deviation will cause a large phase rotation of the signal light, and even submerge the phase information it carries. In addition, the laser line width introduces randomly changing phase noise, which will cause the constellation diagram to tail, extend and alias, aggravating the deterioration of signal quality. Therefore, the carrier recovery algorithm is the key to eliminating phase noise, including frequency offset estimation (FOE) and phase recovery (CPE). Here, the FOE algorithm based on the fourth power and the blind phase recovery (BPS) algorithm are selected to obtain the branch signals processed by DSP technology. The OQAM post-processing module 399 multiplies the branch signals processed by DSP technology by the phase factor The real part is taken to obtain a real symbol, and then every two consecutive real symbols are separated and a time delay is introduced respectively, one of which is multiplied by j and recombined into a complex symbol. The QAM demapping module 3910 restores the obtained complex symbols to the original binary data sequence.

[0117] Figure 9 and Figure 10The multi-user OQAM-based spectrum-efficient wireless transmission systems in the illustrated embodiments together form a new multi-user OQAM-based spectrum-efficient wireless transmission system, as Figure 12 illustrated. For the specific definitions of each sub-module, reference may be made to the descriptions of the Figure 9 and Figure 10 illustrated embodiments above, which will not be elaborated here.

[0118] Embodiment 12, the transmission process of user data in a multi-user OQAM-based spectrum-efficient wireless transmission system is as Figure 13 illustrated. The multi-user OQAM-based spectrum-efficient wireless transmission system in this embodiment specifically includes: a data processing device 1, an optical fiber 17, a baseband unit 2, and a terminal 3. Specifically, the data processing device 1 may be a central station, the optical fiber 17 may be a single-mode optical fiber, and the terminal 3 may be a user terminal.

[0119] In this embodiment, the central station includes: a multi-band signal generation module 11, a waveform generator 12, an electrical amplifier 13, a first laser 14, an I / Q modulator 15, and an erbium-doped fiber amplifier 16. Among them, the waveform generator 12 is an arbitrary waveform generator, and the first laser 14 is an external cavity semiconductor laser.

[0120] Specifically, the first laser 14 is connected to the input end of the I / Q modulator 15, the output end of the I / Q modulator 15 is connected to the erbium-doped fiber amplifier 16, and the erbium-doped fiber amplifier 16 is connected to the baseband unit 2 through the optical fiber 17. The multi-band signal generation module 11, the waveform generator 12, and the electrical amplifier 13 are sequentially connected to the drive signal input end of the I / Q modulator 15.

[0121] Specifically, at the central station, after the user data is input into the multi-band signal generation module 11 to obtain a multi-band modulation signal, the multi-band modulation signal is input into the waveform generator 12 for digital-to-analog conversion to obtain an analog multi-band modulation signal, so as to load the analog multi-band modulation signal onto a carrier for data transmission. After the analog multi-band modulation signal is amplified by the electrical amplifier 13, the real part and the imaginary part of the signal are respectively used as the I-channel and Q-channel drive signals of the IQ modulator 15. The first laser 14 is used to generate a first optical carrier with a first frequency, which is input into the IQ modulator 15 for modulation to generate the optical signal. The optical signal is amplified by the erbium-doped fiber amplifier 16 and then transmitted to the baseband unit 2 through the optical fiber 17.

[0122] In this embodiment, the baseband unit 2 includes: an optical coupler 21 for receiving the optical signal and splitting the optical signal into two paths for transmission to a terahertz link and a free-space laser link respectively. For the terahertz link, a first receiving module 22 is used to receive the optical signal; a second laser 23 is used to generate a second optical carrier, and the frequency of the second optical carrier is the second frequency; an optical coupler 24 is used to couple the second optical carrier and the optical signal to generate an optical coupling signal; a photodetector 25 is used to perform beat frequency processing on the optical coupling signal to generate a terahertz signal with a preset frequency, and the preset frequency is the difference between the first frequency and the second frequency; a low-noise amplifier 26 is used to amplify the terahertz signal; a first transmitting module 27 is used to transmit the transmission signal. For the free-space laser link, an erbium-doped fiber amplifier 28 is connected to the optical coupler 21 for compensating for fiber loss; a second transmitting module 29 is used to transmit the transmission signal. As an example, the transmission signal of the terahertz link can be a terahertz wave signal with a carrier frequency of terahertz, and the transmission signal of the free-space laser link can be transmitted through a laser beam.

[0123] Among them, the first receiving module 22 is a variable optical attenuator, the first transmitting module 24 is a terahertz-band transmitting antenna, and the second transmitting module 29 is a lens antenna.

[0124] Specifically, in the base unit 2, the optical coupler 21 is used to receive the optical signal and split the optical signal into two paths for transmission to the terahertz link and the free-space laser link respectively. For the terahertz link, after the variable optical attenuator receives the optical signal, it adjusts its power to achieve sensitivity measurement. Then, the optical signal with adjusted power is input to the first input end of the optical coupler 24. A second laser 23 independent of the first laser 14 generates a second optical carrier with a second frequency and inputs it to the second input end of the optical coupler 24. The second optical carrier and the adjusted optical signal are coupled in the optical coupler 24 and then sent to the photodetector 25 for beat frequency. The frequency difference between the two optical carriers is terahertz to achieve wireless transmission of the signal. For the free-space laser link, the optical signal is amplified in the erbium-doped fiber amplifier 28 after being transmitted through the optical fiber and then sent to the lens antenna 29 to achieve the emission of free laser.

[0125] In this embodiment, the terminal 3 includes: a second receiving module 31 for receiving the transmission signal; a low-noise amplifier 32 for amplifying the signal; a radio frequency local oscillator source 33 for generating a local oscillator signal; a mixer 34 for mixing the local oscillator signal with the terahertz signal; a third receiving module 35 for receiving the transmission signal; an erbium-doped fiber amplifier 36 for compensating for fiber loss; an optical receiver 37 for receiving the transmission signal and converting it into an electrical signal; an analog-to-digital conversion module 38 for performing analog-to-digital conversion on the multi-band modulation signal to obtain a digital multi-band modulation signal; and a demodulation module 39 for demodulating the digital multi-band modulation signal to restore the user data.

[0126] Among them, the second receiving module 31 is a terahertz band receiving antenna, the analog-to-digital conversion module 38 is a real-time digital storage oscilloscope, and the demodulation module 39 is a multi-band signal demodulation module.

[0127] Specifically, in the user terminal, for the terahertz link, the terahertz wireless signal detected by the terahertz band receiving antenna is amplified by the low-noise amplifier 32 and down-converted to an intermediate frequency signal through heterodyne coherent detection. This is specifically achieved by mixing the local oscillator signal generated by the radio frequency local oscillator source with the terahertz signal in the mixer and performing low-pass filtering. Since the upper limit frequency of the radio frequency local oscillator is relatively low, a frequency doubling process of the local oscillator is usually also involved. The intermediate frequency signal is amplified by the erbium-doped fiber amplifier 36, and data capture and analog-to-digital conversion are performed by the real-time digital storage oscilloscope. After demodulation by the multi-band signal demodulation module, the original data stream is restored, and multi-user data transmission is completed.

[0128] The steps of the method or algorithm described in combination with the disclosed content of this application can be implemented in a hardware manner or by a processor executing software instructions. The software instructions can be composed of corresponding software modules, and the software modules can be stored in a random access memory (RAM), flash memory, read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), register, hard disk, removable hard disk, compact disc read-only memory (CD-ROM), or any other form of storage medium well-known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be a component of the processor.

[0129] Those skilled in the art should be able to realize that in one or more of the above examples, the functions described in this application can be implemented by hardware, software, firmware, or any combination thereof. When implemented using software, these functions can be stored in a computer-readable medium or transmitted as one or more instructions or codes on a computer-readable medium. A computer-readable medium includes a computer storage medium and a communication medium, where the communication medium includes any medium that facilitates the transfer of a computer program from one place to another. The storage medium can be any available medium that can be accessed by a general-purpose or special-purpose computer.

[0130] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0131] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. Method for generating multi-band modulation signals based on OQAM, characterized in that, Specifically, the following steps are included: Step 1: Allocate sub-bands for each user data, and perform amplitude modulation on each user data based on QAM constellation mapping to obtain a complex symbol sequence; Step 2: Separate the real part and the imaginary part of the complex symbol of the sub-carrier, and perform up-sampling on the real part and the imaginary part. According to the parity of the sub-carrier index, introduce a time delay of half a symbol period alternately between the two paths of the real part and the imaginary part. Specifically, for the complex symbol of the sub-carrier with an odd index value, introduce a time delay of T / 2 to its real part branch; for the complex symbol of the sub-carrier with an even index value, introduce a time delay of T / 2 to its imaginary part branch. Add the real and imaginary part sequences of the m-th sub-carrier and multiply by the phase factor of the m-th sub-carrier to obtain the m-th signal; m = 1, 2, …, M; M represents the number of sub-carriers; Step 3: Perform pulse shaping and up-conversion on the m-th signal obtained in Step 2 to obtain the m-th sub-band modulation signal; Step 4: Based on each sub-band modulation signal, obtain a multi-band modulation signal, and perform digital-to-analog conversion on the multi-band modulation signal to obtain an analog multi-band modulation signal.

2. The method for generating a multi-band modulation signal based on OQAM according to claim 1, wherein Specifically, the following steps are included: Step 1 is specifically: Convert the original high-speed data stream into M low-speed sub-data streams through serial-to-parallel conversion, and then convert the M low-speed sub-data streams into an M-QAM complex symbol sequence through QAM constellation mapping. At the same time, perform up-sampling on the mapped M-QAM complex symbol sequence.

3. A wireless transmission method for a multi-band modulation signal, characterized in that: Separate the real part and the imaginary part of the multi-band modulation signal in any one of Claims 1 or 2. The real part is used as the driving signal of the I path of the IQ modulator, and the imaginary part is used as the driving signal of the Q path of the IQ modulator. Use the IQ modulator to perform IQ modulation on the first optical carrier with the first frequency to obtain an optical signal; Wirelessly transmit the optical signal through a terahertz link and a free space laser link; When using the terahertz link for wireless transmission, use a terahertz band receiving antenna to receive the transmission signal. When using the free space laser link for wireless transmission, use a laser band to receive the transmission signal; Demodulate the received signal into user data.

4. A wireless transmission method for a spectrum according to claim 3, characterized in that: The terahertz link couples the optical signal with the second optical carrier with the second frequency to generate an optical coupling signal, performs beat frequency processing on the optical coupling signal to generate a photon terahertz signal with a preset frequency, and emits the photon terahertz signal by means of wireless transmission.

5. A wireless transmission method of a spectrum according to claim 3, characterized in that: The free space laser link amplifies the optical signal and emits it by means of wireless transmission.

6. According to a wireless transmission method for a spectrum as claimed in Claim 3, characterized in that: When using a terahertz band receiving antenna to receive the transmission signal, perform demodulation in the way of heterodyne coherence or direct detection to obtain an intermediate frequency / baseband analog modulation signal. Use an oscilloscope to sample the intermediate frequency / baseband analog modulation signal, and then perform damage compensation, noise removal and offset recovery on the sampled signal.

7. A wireless transmission system for a spectrum, characterized in that: It includes a data processing device, a baseband unit, a receiving unit and a signal demodulation unit; The data processing device includes a multi-band signal generation module and a waveform generator; the multi-band signal generation module includes: a QAM mapping module, an upsampling module, an OQAM preprocessing module, a shaping filter module, a first laser, an IQ modulator, and a separation module; The QAM mapping module maps to obtain a complex symbol sequence based on the QAM constellation diagram; The upsampling module upsamples the complex symbol sequence; The OQAM preprocessing module separates the real and imaginary parts of the symbols in complex form and then upsamples them, and then alternately introduces a half-symbol period time delay between the two paths of the real and imaginary parts according to the parity of the subcarrier index; The shaping filter module performs pulse shaping and upconversion on the signal to obtain sub-band modulation signals, and then generates a multi-band modulation signal based on the sub-band modulation signals; The waveform generator performs digital-to-analog conversion on the multi-band modulation signal to obtain an analog multi-band modulation signal; The first laser generates a first optical carrier and transmits it to the IQ modulator; The separation module separates the real and imaginary parts of the analog multi-band modulation signal. The real part serves as the I-channel drive signal of the IQ modulator, and the imaginary part serves as the Q-channel drive signal of the IQ modulator; the IQ modulator modulates the first optical carrier to obtain an optical signal; The baseband unit is used to receive the optical signal and transmit the optical signal to the terahertz link and the free-space laser link for wireless transmission; The receiving unit receives the signal sent by the baseband unit; and transmits it to the signal demodulation unit for demodulation.

8. The wireless transmission system of a spectrum according to claim 7, characterized in that: When transmitting the optical signal to the terahertz link for wireless transmission, the baseband unit includes a first optical coupler, a first receiving module, a second laser, a second optical coupler, a photodetector; a first low-noise amplifier; A first transmitting module; The first optical coupler receives the optical signal; and transmits the optical signal to the first receiving module respectively; The second laser generates a second optical carrier with a second frequency; The first receiving module transmits the received optical signal to the second optical coupler; the second optical coupler couples the optical signal with the second optical carrier to generate an optical coupling signal; The photodetector performs beat frequency processing on the optical coupling signal to generate a photon terahertz signal with a preset frequency; The first low-noise amplifier is used to amplify the photon terahertz signal; The first transmitting module is used to transmit the amplified photon terahertz signal; When transmitting the optical signal to the free-space laser link for wireless transmission, the baseband unit includes a first erbium-doped fiber amplifier, a second transmitting module; The first erbium-doped fiber amplifier is used to compensate for the fiber loss and amplify the optical signal, and transmits the amplified optical signal to the second transmitting module; the second transmitting module transmits the amplified optical signal.

9. A wireless transmission system for a spectrum according to claim 7, characterized in that: When transmitting the optical signal to the terahertz link for wireless transmission, the receiving unit includes a second receiving module, a second low-noise amplifier, a mixer, and a radio frequency local oscillator; The second receiving module receives the photon terahertz signal transmitted by the terahertz link, The second low-noise amplifier is used to amplify the received photon terahertz signal; The radio frequency local oscillator generates a local oscillator signal; The mixer is used to mix the local oscillator signal with the photon terahertz signal and then transmit it to the demodulation unit; When transmitting an optical signal to a free-space laser link for wireless transmission, the receiving unit includes a second erbium-doped fiber amplifier, a third receiving module, and an optical receiver; The third receiving module is used to receive the optical signal transmitted by the free-space laser link; The second erbium-doped fiber amplifier is used to perform optical compensation and amplification on the received optical signal; The optical receiver transmits the optical signal to the demodulation unit.

10. A wireless transmission system for a spectrum according to claim 7, characterized in that: The demodulation unit includes an analog-to-digital conversion module and a demodulation module. The demodulation module includes a digital down-conversion module, a matched filter module, an IQ imbalance compensation and orthogonal normalization module, a clock synchronization module, a down-sampling module, a fast Fourier transform module, a channel equalization module, a carrier recovery module, an OQAM post-processing module, and a QAM demapping module; The analog-to-digital conversion module is used to perform analog-to-digital conversion on the received signal; The digital down-conversion module is used to down-convert the multi-band modulated signal output by the analog-to-digital conversion module to the baseband and filter out redundant high-frequency components to obtain a baseband signal; The matched filter module is used to separate the baseband signal into branch signals; The IQ imbalance compensation and orthogonal normalization module uses the Schmidt orthogonal method to eliminate IQ imbalance and non-orthogonal interference in the IQ modulation of the branch signals; The clock synchronization module is used to eliminate clock offset and jitter caused by link loss of the signal; The down-sampling module is used to down-sample each branch signal to match the sampling rate of the oscilloscope; The fast Fourier transform module is used to perform a fast Fourier transform on each branch signal, thereby converting the signal from the time domain back to the frequency domain to obtain a frequency-domain signal; The channel equalization module is used to equalize the frequency-domain signal; The carrier recovery module is used to obtain the branch signal processed by DSP technology based on the fourth-power FOE algorithm and the blind phase recovery algorithm; The OQAM post-processing module is used to multiply each branch signal processed by DSP technology by a phase factor, take the real part to obtain a real symbol, and then separate every two consecutive real symbols and introduce time delays respectively. One of them is multiplied by the imaginary unit and recombined into a complex symbol; The QAM demapping module 3 restores the obtained complex symbol to the original binary data sequence.

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