Device and method for generating W-band vector QPSK millimeter wave signal
Technical Field
The invention belongs to the technical field of radio over fiber communication, and particularly relates to a device and a method for generating W-band vector QPSK millimeter wave signals.
Background
The explosive growth of mobile data service demands forces future 5G network communications to move towards more spectrally efficient transmission. The high-order modulation signal has high frequency spectrum utilization rate, is beneficial to further expanding transmission capacity, reducing transmission baud rate and reducing the transmission bandwidth requirement of the electronic device. Millimeter wave (mm-wave) generation based on photon-assisted technology is a key technology in fiber-optic wireless networks, and it effectively overcomes the bandwidth bottleneck of electronic devices. At present, there are two main methods for millimeter wave generation, including optical heterodyne and optical frequency doubling methods. Compared with the traditional optical heterodyne beat frequency method, the optical frequency doubling method based on the external modulator can effectively avoid phase noise due to the frequency and phase-locking characteristics of the optical frequency doubling method, so that the optical frequency doubling method has more application prospects in an actual 5G communication system. However, the currently used photodetector has a beat-square rate detection principle, and a vector millimeter wave generation scheme based on an external modulator must perform precoding processing on Amplitude and phase information of a transmitted multi-order Quadrature Amplitude Modulation (QAM), which greatly increases the system complexity. In addition, in the millimeter wave generation scheme using optical frequency doubling, an optical filter is an essential device, such as a Wavelength Selective Switch (WSS) or an interleaver, and needs to filter out a required target subcarrier, which also increases the cost and complexity of a Radio Over Fiber (ROF) system.
In addition, in the conventional photon-assisted millimeter wave generation scheme, a high-performance Arbitrary Waveform Generator (AWG) or a Digital-to-Analog Converter (DAC) is usually required to convert the Digital signal into an Analog signal, and most of these devices are expensive and consume more power, thereby greatly increasing the transmission cost of the system. In addition, one of the major obstacles of such digital-to-analog converters is the limited 3dB electronic bandwidth, and the number of effective bits of the current commercial DACs is less than 6 bits, which all limit the development of high-speed 5G and beyond 5G, and even 6G mobile communications in the future. Therefore, the digital transmission of millimeter wave signals is realized by avoiding the adoption of a digital-to-analog converter, and the problem of DAC bandwidth limitation can be effectively solved. Digital modulation is currently used primarily in digital data transmission because it has greater noise immunity and robustness to channel impairments.
Therefore, the invention provides a W-band vector QPSK millimeter wave generation device and method without a digital-to-analog converter, which simplify the structure of a transmitting end, avoid the adoption of an optical filter and realize that the phase difference between two binary signals is 90 by adjusting an optical delay lineoThe method realizes the generation of QPSK signals, improves the frequency spectrum utilization rate by times, reduces the bandwidth requirement, effectively reduces the system cost, and has important application significance for the development of high-speed and large-capacity 5G or even 6G mobile communication networks in the future.
Disclosure of Invention
The invention aims to provide a generating device and a generating method of W-band vector QPSK millimeter wave signals, which have the advantages of simplified structure and reduced cost.
The invention provides a W-band vector QPSK millimeter wave signal generating device, which comprises:
the distributed feedback laser is used for generating laser of the W-waveband millimeter wave signal;
a binary pseudo-random sequence generator for generating a binary signal to be transmitted;
a radio frequency source for generating a radio frequency signal;
two intensity modulators for generating a target photon carrier carrying a binary modulation signal;
two electrical amplifiers for amplifying the optical signal;
the polarization beam splitter is used for splitting the modulated continuous light wave into two paths of polarized light;
the optical attenuator is used for adjusting the gain difference of the two paths of optical signals;
the optical delay line is used for adjusting the phase difference of the two optical signals;
the light polarization coupler is used for coupling two paths of polarized light;
and the photoelectric detector is used for generating a vector millimeter wave signal of a W waveband in a beat frequency mode.
Wherein:
laser of a W-waveband millimeter wave signal is generated by a distributed feedback laser and input to a first intensity modulator; a binary pseudo-random sequence generator generates a binary signal, the binary signal passes through a first electric amplifier and directly drives a first intensity modulator, and an optical signal is modulated and then further sent to a second intensity modulator;
the radio frequency signal generated by the radio frequency source passes through a second electric amplifier to drive a second intensity modulator, and the direct current bias voltage applied to the intensity modulator is adjusted to enable the intensity modulator to work at the maximum transmission point;
the continuous light wave modulated by the first intensity modulator and the second intensity modulator only generates even-order photon carriers; adjusting the radio frequency driving voltage to enable the light power of two sub-carriers of +/-2 orders to be larger; the polarized light is divided into upper and lower paths of transmitted polarized light after passing through a polarization beam splitter; one path of light is transmitted through the first optical attenuator and the optical delay line, and the other path of light is transmitted through the second optical attenuator; adjusting the first and second optical attenuators to equalize output optical powers of the two paths, and adjusting the optical delay line to equalize the phase difference of the two paths of light waves to 90o;
The optical signal is coupled into a path of optical signal by an optical polarization coupler, is adjusted by a third optical attenuator and then passes through a photoelectric detector to obtain a W-band vector QPSK millimeter wave signal.
The invention provides a W-band vector QPSK millimeter wave signal generation method, which comprises the following specific steps:
(1) laser of a W-band millimeter wave signal generated by a distributed feedback laser is input to a first intensity modulator 1; a binary pseudo-random sequence generator generates a binary signal, the binary signal passes through a first electric amplifier and directly drives a first intensity modulator 1, and an optical signal is modulated and then further sent to a second intensity modulator 2;
(2) frequency generation from a radio frequency sourcef s A radio frequency signal of 20GHz passes through a second electric amplifier to drive a second intensity modulator 2, and the direct current bias voltage applied to the intensity modulator 2 is adjusted to enable the intensity modulator to work at the maximum transmission point;
(3) the continuous light wave modulated by the first intensity modulator 1 and the second intensity modulator 2 only generates even-order photon carriers; adjusting the radio frequency driving voltage to enable the light power of two sub-carriers of +/-2 orders to be larger; the polarized light is divided into upper and lower paths of transmitted polarized light after passing through a polarization beam splitter; wherein one path of signal passing through the first optical attenuator and the optical delay line isdata 1The other signal transmitted by the second optical attenuator isdata 2(ii) a The first and second optical attenuators are adjusted to make the output light powers of the two paths equal toG 0And adjusting the optical delay line to make the phase difference of the two light waves equal to 90o;
(4) Then the optical signal is coupled into a path of optical signal by an optical polarization coupler, and the optical signal is adjusted by an optical attenuator 13 and sent to a photoelectric detector to obtain the optical signal with the frequency of 80GHz (4 GHz)f s ) The W-band vector QPSK millimeter wave signal can be expressed as:
wherein R is the sensitivity of the photodetector,J -2 (k)andJ 2 (k)respectively, the values of the first-class bessel function of order ± 2.
The invention utilizes the optical delay line to accurately control the phase difference between two paths of binary optical signals to be equal to 90oTherefore, the orthogonal phase distribution of two paths of digital binary signals is realized, the 4-frequency-doubled W-band QPSK vector millimeter wave signal is realized by performing beat frequency on two second-order subcarriers in the photoelectric detector, a digital-to-analog converter and an optical filter are not needed, the structure of a millimeter wave generator is simplified, the cost is effectively reduced, the frequency spectrum utilization rate is improved in a multiplied manner, and the bandwidth requirement on electronic devices in a system is reduced.
Drawings
FIG. 1 is a schematic diagram of a device for generating a multilevel optical signal based on a single modulator according to the present invention.
Reference numbers in the figures: the distributed feedback type laser device comprises a distributed feedback type laser device 1, a first electric amplifier 2, a binary pseudorandom sequence generator 3, a second electric amplifier 4, a radio frequency source 5, a first intensity modulator 6, a second intensity modulator 7, a polarization beam splitter 8, a first optical attenuator 9, an optical delay line 10, a second optical attenuator 11, a polarization coupler 12, an optical attenuator 13 and a photoelectric detector 14.
Detailed Description
The present invention will be further described with reference to the following specific experimental examples and the accompanying drawings.
As shown in fig. 1, the components and functions of a W-band vector QPSK millimeter wave signal generating apparatus without a digital-to-analog converter are respectively described as follows:
continuous laser output by a distributed feedback laser 1 is incident to an intensity modulator 6, a signal emitted by a binary pseudorandom signal generator 3 is amplified by an electric amplifier 2 and then drives the modulator 6, the continuous laser is modulated by the modulator 6 and then is incident to the intensity modulator 7 for modulation, and the frequency isf s The radio frequency signal 5 is amplified by the electric amplifier 4 and then drives the intensity modulator 7, the direct current bias of the intensity modulator 7 is controlled, so that the continuous light wave only keeps +/-2-order optical subcarriers, the modulated continuous light is divided into two beams of polarized light through the polarization beam splitter 8, and one path of polarized light isThe other path passes through an optical attenuator 11 only, passing through an optical attenuator 9 and an optical delay line 10. The two optical attenuators adjust the gain difference of the two optical signals, and the optical delay line adjusts the phase difference of the two optical signals, so that the two optical signals have equal gains and the phase difference is 90o. The two optical signals are combined into one optical signal by the polarization coupler 12, the optical power entering the photodetector 14 is adjusted by the optical attenuator 13, and finally, the quadruple frequency 80GHz W band QPSK vector millimeter wave signal generated by the photodetector 14 is:
where R is the sensitivity of the photodetector,J -2 (k)andJ 2 (k)respectively, the values of the first-class bessel function of order ± 2.
The phase difference of two paths of binary signals is accurately controlled by using a single optical delay line, so that the phase quadrature distribution is met, the generation of quadruple frequency W-band QPSK vector millimeter wave signals is realized, the structure is simple, the complexity is low, and the method is very suitable for the development of high-speed and high-capacity super-5G and even 6G mobile communication networks.