M based on ODL 2 QAM quadrupling millimeter wave signal generation and transmission system

Abstract

The application belongs to the technical field of optical fiber wireless network communication, and particularly relates to an M 2 -QAM four times frequency millimeter wave signal generation and transmission system. In the system, the sending end comprises an input module, an optical modulator, an optical coupler, an optical delay line, a polarization beam combiner, an optical fiber transmission module and a photodiode; the input module generates a binary message; the optical modulator modulates the binary message and a clock signal onto an optical carrier; the optical coupler and the optical delay line divide the signal into two orthogonal signals; the optical fiber transmission module transmits the synthesized optical signal; the photodiode square detects the signal and outputs a vector M 2 -QAM millimeter wave signal; the receiving end comprises a radio frequency source and a signal recovery module; the radio frequency source provides a local oscillation signal for mixing with a received signal to complete down-conversion of the signal; and the signal recovery module recovers the signal received by the oscilloscope. The system does not use DAC and optical filters, and can simultaneously realize vector M 2 -QAM millimeter wave signal and optical fiber wireless communication.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber wireless network communication technology, specifically relating to a vector M based on the ODL modulation format. 2 -QAM quadruple frequency millimeter wave signal generation and transmission system. Background Technology

[0002] With the development of 5G networks, the demand for mobile data services has greatly driven research into advanced modulation formats with high spectral efficiency. This is in order to meet the future access network's requirements for high speed, large bandwidth, and wide coverage.

[0003] The development of new next-generation optical access network technologies and fiber-optic wireless convergence technologies is imperative. Photon-assisted millimeter wave generation is a key technology for fiber-optic wireless networks, effectively overcoming the bottlenecks of current electrical equipment. Currently, there are two main methods for millimeter wave generation: optical heterodyne and optical frequency doubling. Comparatively, optical frequency doubling, based on external modulation, is more practical for 5G applications due to its frequency-locked and phase-locked characteristics, as well as its ability to effectively avoid phase noise. However, optical filters, wavelength selection switches, or splitters are indispensable in the optical frequency doubling communication framework, increasing the cost and complexity of the optical wireless communication network. Furthermore, due to the squared monitoring rule of the photodiode (PD) at the receiver, the amplitude and phase information of the transmitted QAM signal must be pre-encoded, significantly increasing the computational burden at the receiver. In addition, the method of generating millimeter waves based on optical frequency doubling typically requires a complex transceiver and an expensive digital-to-analog converter, which also greatly increases the system cost. Moreover, the limited 3-dB bandwidth and effective bit limit of commercial DACs pose a potential constraint on the future development of high-speed communication. One effective way to address the DAC bandwidth issue is to use digital signal transmission, as digital signals have greater noise tolerance and robustness to channel impairments. 【1-4】 .

[0004] Currently, research on digitally modulated optical vector millimeter wave generation methods is limited. In 2014, Zhang et al. proposed a system for generating QPSK signals without a DAC; however, due to the superposition of the OOK branches in free space, it was impossible to precisely control the phase difference between the two branches. 【5】 Therefore, this invention proposes a system that uses ODL (optical delay line) to adjust the phase difference between two modulated branches, and then generates and transmits an M2-QAM millimeter-wave signal via heterodyne beat frequency. Summary of the Invention

[0005] The purpose of this invention is to provide an M-type converter based on the ODL modulation conversion format, which does not employ a digital-to-analog converter (DAC) and optical filters.2 -QAM millimeter-wave signal generation and transmission system, which can generate high-order vector QAM signals while achieving high-speed and high-reliability communication.

[0006] The present invention provides an ODL-based M 2 The QAM quadruple frequency millimeter-wave signal generation and transmission system consists of a signal transmitter and a signal receiver, wherein:

[0007] (a) The signal transmitting end includes:

[0008] A distributed feedback semiconductor laser (DFB-LD) is used to output continuous light waves as a light source and then modulate them;

[0009] A pseudo-random code (PRBS) generator is used to generate binary signals;

[0010] A radio frequency source (RF1) is used to generate a clock signal;

[0011] Two electronic amplifiers (EA), wherein the first electronic amplifier (EA1) is used to amplify binary signals and the second electronic amplifier (EA2) is used to amplify clock signals;

[0012] Two cascaded optical modulators (MZMs) are used. The first optical modulator (MZM1) modulates the amplified binary signal onto the optical carrier. The second optical modulator (MZM2) modulates the output signal of the first optical modulator (MZM1) with the amplified clock signal as the driving voltage. By controlling the modulation index, a large optical power is ensured on the ±2nd order subcarrier.

[0013] An optical coupler (PM-OC) is used to split the cascaded modulated signal into two identical upper and lower paths;

[0014] Two attenuators (ATT1 and ATT2) are used to match the amplitude gain of the upper and lower optical signals, respectively.

[0015] An optical extension line (ODL) is used to change the phase of one of the upper and lower optical signals so that the upper and lower optical signals are orthogonal;

[0016] A polarization beam combiner (PBC) is used to combine optical signals from two branches;

[0017] A dispersion-shifted fiber (DSF) transmits the optical signal output from the polarization combiner (PBC) to the next part of the system;

[0018] An erbium-doped fiber amplifier (EDFA) is used to enhance the signal after transmission through the optical fiber;

[0019] An attenuator (ATT3) is used to adjust the power of the optical signal to avoid the saturation effect of the photodiode;

[0020] A photodiode (PD) generates M using square law detection. 2 -QAM millimeter-wave signal;

[0021] An electronic amplifier (EA) is used to increase M. 2 - The power of the QAM millimeter-wave signal;

[0022] A transmitting antenna will receive M 2 -QAM millimeter wave signals are transmitted;

[0023] A lens is used to focus the optical signal power between the antennas;

[0024] (ii) The signal receiving end includes:

[0025] A receiving antenna for receiving M 2 -QAM millimeter-wave signal;

[0026] A radio frequency source (RF2) provides a local oscillation source;

[0027] A mixer down-converts the signal received by the antenna.

[0028] An oscilloscope (OSC) is used to capture the amplified signal and observe its time and frequency domain plots.

[0029] The workflow of the sending end is as follows:

[0030] First, a laser source generates a center frequency of f. c A continuous light wave passes through two cascaded intensity modulators, MZM1 and MZM2. MZM1 is driven by a digital signal data amplified by EA, which modulates the light to obtain an optical baseband signal, which is then input to MZM2. The DC bias point of MZM2 is set at zero bias and controlled by a clock signal f. s Driven. At the same time, the output voltage of the clock source input to MZM2 is adjusted via EA to ensure that the ±2nd order subcarriers have large optical power after modulation.

[0031] The MZM2 modulated optical signal is then split into upper and lower branches by an optical coupler, and amplitude matching is achieved by adjusting the optical signal amplitude through attenuators ATT1 and ATT2 in the upper and lower branches respectively. At the same time, the phase information of the upper branch optical signal is changed by ODL to achieve phase orthogonality between the two signals.

[0032] The two signals are then combined using a polarization combiner and transmitted through a dispersion-shifted fiber. The signal power is then adjusted using an erbium-doped fiber amplifier and an attenuator.

[0033] Finally, the optical signal transmitted through the optical fiber is passed through the PD to generate vector M. 2 -QAM fourth-harmonic millimeter-wave signal. After adjusting the power using an amplifier, the millimeter-wave signal can be transmitted through an antenna. Here, the millimeter-wave signal after passing through the PD is:

[0034]

[0035] κ=πV drive / V pp (2).

[0036] Where R is the sensitivity of the photodiode; κ is the modulation index; G0 is the power gain of the upper and lower optical signals; and φ is the phase delay. -2 J(κ), J2(κ) are second-order Bessel functions, data upper , data lower These are the signals to be modulated in the upper and lower branches, respectively. V drive It is the MZM driving voltage amplitude, V pp It is the MZM half-wave voltage. As can be seen from the output signal expression, the frequency of the obtained millimeter-wave signal is 4 times the clock frequency, and quadrature phase modulation is achieved.

[0037] The receiver's workflow is as follows: after 1m of wireless transmission, the signal is received through the antenna. First, the received signal is down-converted, then collected by an analog-to-digital converter such as an oscilloscope, and finally the modulated signal can be recovered by offline DSP processing.

[0038] At this point, the system has completed vector M. 2 -QAM is a function for generating and communicating quadruple frequency millimeter-wave signals.

[0039] The millimeter-wave signal generation method proposed in this invention has a simpler structure compared to existing technologies, consisting of only two MZMs, one ODL, and one PD, without a DAC or optical filter. This reduces both system cost and structural complexity. It effectively avoids the bandwidth limitations and other constraints associated with using a DAC, providing a feasible solution for future high-speed optical communication. Attached Figure Description

[0040] Figure 1 This invention proposes a method for generating M based on ODL. 2 - A schematic diagram of the QAM millimeter-wave signal and communication system architecture. The solid lines in the diagram represent the optical path, and the dashed lines represent the circuitry.

[0041] Figure 2This is a graph of the first type of Bessel function. Only the curves of even-order (J0, J2, J4, J6) as a function of the modulation index κ are shown in the graph. When κ is 2.4048, J2 is significantly larger than J0, J4, and J6.

[0042] The diagram is labeled as follows: 1 is the distributed feedback semiconductor laser (DFB-LD); 2 is the optical modulator (MZM1); 3, 6, 17, and 23 are the first to fourth electronic amplifiers (EA1, EA2, EA3, and EA4), respectively; 4 is the signal source; 5 is the first radio frequency source (RF1); 7 is the optical modulator (MZM2); 8 is the optical coupler (PM-OC); 9, 10, and 15 are the first to third attenuators (ATT1, ATT2, and ATT3), respectively; 11 is the optical delay line (ODL); 12 is the polarization combiner (PBC); 13 is the dispersion-shifting fiber (DSF); 14 is the erbium-doped fiber amplifier (EDFA); 16 is the photodiode (PD); 18 is the transmitting antenna (HA1); 19 is the lens; 20 is the receiving antenna (HA2); 21 is the mixer; 22 is the second radio frequency source (RF2); 24 is the oscilloscope (OSC); and 25 is the offline digital signal processing unit. Detailed Implementation

[0043] The following is in conjunction with the appendix Figure 1 The present invention will be further described below.

[0044] At the signal transmitting end, DFB-LD(1) generates a continuous light wave as the light source input MZM1(2). MZM1(2) is composed of:

[0045] The amplified signal source (4) of EA1 (3) drives the modulation to obtain the optical baseband signal. Then, it is input to MZM2 (7), driven by the first radio frequency source (5) of MZM2. The amplitude of the input clock signal is modulated by EA2 to achieve odd-order carrier suppression and ensure that the ±2nd order carrier has a large power. Then, the optical signal is split into upper and lower paths by an optical splitter PM-OC (8), and the amplitudes of the two signals are matched by attenuators AAT1 (9) and ATT2 (10). The upper branch uses ODL (11) as a phase shifter to adjust the phase so that the phases of the two signals are orthogonal. Then, the upper and lower optical signals are combined by PBC (12) and transmitted through a 1km dispersion-shifted fiber DSF (13). The power of the signal after fiber transmission is adjusted by erbium-doped fiber amplifier EDFA (14) and ATT3 (15), and then the M signal is detected by photodiode PD (16). 2 -QAM millimeter-wave signal. After being amplified by EA3 (17), it is transmitted through antenna HA1 (18). During wireless transmission, the wireless signal power between the transmitting and receiving antennas is focused by lens (19) to improve the signal transmission effect.

[0046] At the signal receiving end, the signal is received using antenna HA2 (20). Then, using an RF source (22) as a local oscillator, the received signal is down-converted via a mixer (21) to obtain an intermediate frequency (IF) signal. The IF signal is then adjusted in power using EA4 (23) and amplified by an oscilloscope OSC (24). Finally, the received M signal is recovered via an offline DSP (25). 2 -QAM millimeter wave signal.

[0047] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes can be made in form and detail without departing from the spirit and scope of the present invention.

[0048] [1] PSMundra, TLSingal, R.Kapur. "The choice of a digital modulationscheme in a mobile radio system," in Proc.IEEE 43rd Vehicular Technology Conference, 1993, pp.1-4.

[0049] [2] M.Barnela, DSKumar. "Digital modulation schemes employed inwireless communication: A literature review," International Journal of Wiredand WirelessCommunications, 2014, vol.2, no.2, pp.15-21

[0050] [3] S.Kharbech, I.Dayoub, M.Zwingelstein-Colin, et al. "Blind digitalmodulation identification for MIMO systems in railway environments with high-speed channels and impulsive noise," IEEE Transactions on VehicularTechnology, 2018, vol.67, no.8, pp.7370-7379

[0051] [4]C.U.Ndujiuba,O.Oni,A.E.Ibhaze.“Comparative analysis of digitalmodulation techniques in LTE 4G systems,”Journal of Wireless Networking andCommunications,2015,vol.5,no.2,pp.60-66

[0052] [5]Q.Zhang,J.Yu,X.Li,et al.“Adaptive photonic-assisted M 2-QAMmillimeter-wavesynthesis in multi-antenna radio-over-fiber system using M-ASKmodulation,”Opt.Lett.,2014,,vol.39,no.21,pp.6106-6109。

Claims

1. An ODL-based M 2 -QAM fourth-harmonic millimeter-wave signal generation and transmission system, characterized in that... The structure is divided into a signal transmitting end and a signal receiving end, wherein: (a) The signal transmitting end includes: A distributed feedback semiconductor laser (DFB-LD) is used to output continuous light waves as a light source and then modulate them. A pseudo-random code (PRBS) generator is used to generate binary signals; An RF source RF1 is used to generate a clock signal; Two electronic amplifiers EA, wherein the first electronic amplifier EA1 is used to amplify binary signals and the second electronic amplifier EA2 is used to amplify clock signals; Two cascaded optical modulators MZMs are used. The first optical modulator MZM1 is used to modulate the amplified binary signal onto the optical carrier. The second optical modulator MZM2 uses the amplified clock signal as the driving voltage to modulate the output signal of the first optical modulator MZM1. By controlling the modulation index, a large optical power is ensured on the ±2nd order subcarrier. An optical coupler PM-OC is used to split the cascaded modulated signal into two identical upper and lower paths; The first attenuator ATT1 and the second attenuator ATT2 are used to match the amplitude gain of the upper and lower optical signals, respectively. An optical extension line (ODL) is used to change the phase of one of the upper and lower optical signals, making the upper and lower optical signals orthogonal. A polarization beam combiner (PBC) is used to combine the optical signals from two branches; A dispersion-shifted fiber (DSF) transmits the optical signal output from the polarization combiner (PBC) to the next part of the system. An erbium-doped fiber amplifier (EDFA) is used to enhance the signal after transmission through the fiber optic cable. An attenuator ATT3 is used to adjust the power of the optical signal and avoid the saturation effect of the photodiode; A photodiode (PD) generates M using square law detection. 2 -QAM millimeter-wave signal; An electronic amplifier EA is used to improve M 2 - The power of the QAM millimeter-wave signal; A transmitting antenna will receive M 2 -QAM millimeter-wave signals are transmitted; A lens is used to focus the optical signal power between the antennas; (ii) The signal receiving end includes: A receiving antenna for receiving M 2 -QAM millimeter-wave signal; One radio frequency source RF2 provides a local oscillation source; A mixer down-converts the signal received by the antenna. An oscilloscope (OSC) is used to capture the amplified signal and observe its time and frequency domain plots. The workflow of the sending end is as follows: First, a laser source generates a center frequency of... A continuous light wave is passed through two cascaded optical modulators, MZM1 and MZM2; MZM1 is powered by a digital signal amplified by EA. data The optical baseband signal is obtained after driving and modulation and input to MZM2; the DC bias point of MZM2 is set at zero bias point and controlled by clock signal. Drive; at the same time, adjust the output voltage of the clock source input to MZM2 through EA to ensure that the modulated ±2nd order subcarrier has a large optical power; The optical signal modulated by MZM2 is then split into upper and lower branches by an optical coupler, and the amplitude of the optical signal is adjusted by attenuators ATT1 and ATT2 in the upper and lower branches respectively to achieve amplitude matching; at the same time, the phase information of the upper branch optical signal is changed by ODL to achieve phase orthogonality between the two signals. Then, the two signals are combined using a polarization combiner and transmitted through a dispersion-shifted fiber. The signal power is adjusted using an erbium-doped fiber amplifier and an attenuator. Finally, the optical signal transmitted through the optical fiber is passed through the PD to generate vector M. 2 -QAM fourth-harmonic millimeter-wave signal; after power adjustment using an amplifier, the millimeter-wave signal is transmitted through an antenna; here, the millimeter-wave signal after passing through the PD is: ,（1） , （2） Where R is the sensitivity of the photodiode; The modulation index; This represents the power gain of the upper and lower optical signals; For phase delay; It is a second-order Bessel function. data upper , data lower These are the signals to be modulated in the upper and lower branches, respectively; V drive It is the MZM drive voltage amplitude. V pp It is an MZM half-wave voltage; the frequency of the resulting millimeter-wave signal is 4 times the clock frequency, and quadrature phase modulation is achieved.

2. The M based on ODL according to claim 1 2 -QAM fourth-harmonic millimeter-wave signal generation and transmission system, characterized in that... The receiving end's workflow is as follows: After a 1-meter wireless transmission, the signal is received via an antenna. The received signal is first down-converted, then collected by an analog-to-digital converter, and finally processed by an offline DSP to recover the modulated signal.

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