CN115766363A - Frequency offset estimation method based on multi-path selection and spatial coherent laser communication system - Google Patents
Frequency offset estimation method based on multi-path selection and spatial coherent laser communication system Download PDFInfo
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Abstract
The invention belongs to a frequency offset estimation method, which aims to solve the technical problems that when the frequency offset estimation method based on FFT is adopted for frequency offset estimation at present, the estimation precision is improved by increasing the number of FFT points, the processing time delay and the calculation complexity are increased, and the real-time performance and the dynamic adaptability of frequency compensation are reduced, and simultaneously, in order to solve the problem that different degrees of deviation occur in the frequency offset estimation due to different sampling moments of chips, the invention provides a frequency offset estimation method based on multi-path selection and a spatial coherent laser communication system.
Description
Technical Field
The invention belongs to the field of spatial laser communication, and particularly relates to a frequency offset estimation method based on multi-path selection and a spatial coherent laser communication system.
Background
With the advent of the information age, it has become difficult for conventional wireless communication systems to meet the current increasing high speed and large capacity demands for communication systems due to limited bandwidth and transmission speed. Therefore, a laser communication system using laser light as a carrier wave has been developed.
The laser communication systems are of various types, wherein coherent optical communication mainly utilizes coherent modulation, and has the advantages of high sensitivity, long relay distance, large communication capacity and the like.
Compared with the traditional radio communication, the difficulty of carrier time domain synchronization is obviously increased for space optical communication such as satellite-borne communication. In addition, because the carrier frequency of the optical signal is high, the carrier search in a large range and the frequency offset estimation in high precision need to be completed before demodulation. At present, under the condition that signals are weak and modulation bit information cannot be accurately predicted, the stability of a frequency offset estimation result is reduced. The estimation accuracy of the traditional frequency offset estimation method based on FFT is related to the number of FFT calculation points, and the number of FFT points must be increased to improve the estimation accuracy, so that the processing time delay and the calculation complexity are increased, and the real-time performance and the dynamic adaptability of frequency compensation are reduced. In addition, due to the difference of sampling time, the difference is inevitably generated when the frequency offset estimation is performed on the captured data.
Disclosure of Invention
The invention provides a frequency offset estimation method based on multipath selection and a spatial coherent laser communication system, aiming at solving the technical problems that when the frequency offset estimation method based on FFT is adopted for frequency offset estimation at present, the estimation precision is improved by increasing the number of FFT points, the processing time delay and the calculation complexity can be increased, the real-time performance and the dynamic adaptability of frequency compensation are reduced, and different degrees of deviation occurs in the frequency offset estimation due to different sampling moments of chips.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
a frequency offset estimation method based on multi-path selection is characterized by comprising the following steps:
s1, carrying out optical mixing on signal light emitted by a transmitting communication terminal and local oscillator light of a receiving communication terminal, and converting the signal light and the local oscillator light into intermediate-frequency analog electric signals through a photoelectric conversion device;
s2, converting the intermediate-frequency analog electric signal into n paths of sampling intermediate-frequency digital signals, wherein n is an integer greater than 1;
s3, dividing the n paths of sampled intermediate frequency digital signals into m groups of data, wherein each group of k paths of data has n = m x k, m is an integer larger than 1, and k is an integer larger than or equal to 1; respectively eliminating the modulation signals in the m groups of data to obtain m groups of digital recovery carrier data after the modulation signals are eliminated;
s4, respectively calculating m frequency offset estimation values of the digital recovery carrier data after the m groups of modulation signals are eliminated;
and S5, determining a final frequency deviation estimation value according to the m groups of frequency deviation estimation values obtained in the step S4, and taking the final frequency deviation estimation value as a frequency deviation reference for subsequent digital signal processing demodulation processing and simultaneously as a correction value for local oscillator optical frequency deviation control of the receiving communication terminal.
Further, in step S5, the determining a final frequency offset estimation value according to the m groups of frequency offset estimation values obtained in step S4 specifically includes selecting a frequency offset estimation value a with the closest deviation value from the frequency offset estimation values obtained in step S4, and calculating an average value of the frequency offset estimation values of the group a as the final frequency offset estimation value, where a is an integer greater than or equal to 2.
Further, step S3 specifically includes: dividing n paths of sampling intermediate-frequency digital signals into m groups of data, averaging each path of sampling intermediate-frequency digital signals of each group in the m groups respectively, then synthesizing one path of data, then carrying out arctan angle conversion operation on the path of data, multiplying the path of data by a high-order modulation order to obtain the phase of a digital recovery carrier signal recovered after the modulation signal is eliminated, and then generating a signal waveform of a digital recovery carrier according to the phase to obtain m groups of digital recovery carrier data after the modulation signal is eliminated.
Further, step S4 specifically includes: and respectively carrying out averaging operation on the m groups of digital recovery carrier data subjected to modulation signal elimination through a sliding window method, and multiplying by a unit conversion coefficient to respectively obtain frequency offset estimation values corresponding to the m groups of data.
Further, step S4 specifically includes: and preferentially grabbing partial data from each group of digital recovery carrier data after modulation signal elimination to obtain an average value, wherein the data volume of the partial data is equal to the length of a sliding window, then, when one data is sent, under the condition of ensuring that the length of the sliding window is not changed, the first data of the sliding window is omitted, and the average value of the data contained in the current sliding window is calculated, so that the corresponding frequency deviation estimation value can be calculated in real time to obtain a real-time frequency deviation estimation value which is used as the frequency deviation estimation value of each group of digital recovery carrier data after modulation signal elimination.
A space coherent laser communication system can realize the frequency offset estimation method based on multi-path selection, and comprises a transmitting communication terminal and a receiving communication terminal, wherein the receiving communication terminal comprises a receiving antenna and a local oscillator laser; the receiving communication terminal is characterized by further comprising a 90-degree mixer, a balanced detector, an ADC and a data processing unit;
the input end of the 90-degree frequency mixer is respectively connected with the receiving antenna and the local oscillator laser, and the output end of the 90-degree frequency mixer is connected with the input end of the balance detector; the output end of the balance detector is respectively connected with the input end of the ADC, n paths of output data of the ADC are respectively connected with the input end of the data processing unit, and the output end of the data processing unit is connected with the input end of the control unit of the local oscillator laser;
the signal light and the local oscillation light emitted by the local oscillation laser are subjected to optical frequency mixing through a 90-degree frequency mixer, then are converted into intermediate-frequency analog electric signals through a balance detector, are converted into n paths of sampling intermediate-frequency digital signals through an ADC (analog to digital converter), and are divided into m groups of data, wherein k paths of data in each group are n = m x k, m is an integer larger than 1, and k is an integer larger than or equal to 1;
the data processing unit is used for eliminating the modulation signal in the m groups of data, calculating the frequency offset estimation value of the m groups of data of the digitally restored carrier after the modulation signal is eliminated, selecting the frequency offset value meeting the requirement according to the m groups of frequency offset estimation values, averaging to obtain the final frequency offset estimation value, and performing frequency offset reference of subsequent digital signal processing demodulation processing according to the final frequency offset estimation value and simultaneously serving as the correction value of local oscillator optical frequency offset control of the receiving communication terminal.
Further, said m is determined by:
m＝x/(y*c)
where c is an integer greater than 1, x is the sampling rate of the ADC, and y is the data bit rate loaded on the signal light.
Further, the transmitting communication terminal comprises a signal laser, an electro-optical modulator, a modulator driver and a transmitting antenna;
the output end of the signal laser is sequentially connected with the electro-optical modulator and the transmitting antenna; the output end of the modulator drive is connected with the electro-optical modulator and used for amplifying the signal of the modulation information and then loading the amplified signal to the laser in the electro-optical modulator; the electro-optical modulator is used for receiving laser emitted by the signal laser, and transmitting modulation information to a receiving antenna of a receiving communication terminal through the transmitting antenna after the modulation information is loaded.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention provides a frequency offset estimation method based on multi-path selection, which comprises the steps of carrying out optical frequency mixing on signal light and local oscillator light, converting the signal light and the local oscillator light into intermediate-frequency analog electric signals, dividing the signals into m groups of data through analog-to-digital conversion, eliminating modulation signals, calculating a frequency offset estimation value of each group, selecting a number a of data with the closest deviation value to average to serve as a final frequency offset estimation value, and using the frequency offset estimation value as a correction value of local oscillator light frequency offset control, so that the problem that individual data in m frequency offset estimation values calculated by m paths of data have larger difference compared with other data due to different sampling moments, and the final frequency offset estimation value is inaccurate if the data are averaged together is solved. In addition, compared with the traditional optical fiber communication bit synchronization before carrier synchronization, the bit synchronization output and the received data rate are in positive correlation, when the data rate is reduced, the traditional frequency offset estimation range is reduced, and the invention places the bit synchronization after the carrier synchronization, thereby overcoming the problems and improving the stability of frequency offset estimation.
2. The frequency offset estimation method can be used as a reference value for local oscillator optical frequency offset control in real time according to the frequency offset estimation value, so that the real-time property and the dynamic adaptability of frequency compensation are ensured, meanwhile, the requirement of the system on the clock precision is reduced, and the adaptability of the system in operation is improved.
3. When the frequency offset estimation value is calculated, the sliding window method is adopted for calculation, so that the frequency of frequency compensation is improved, the real-time performance and the dynamic adaptability of the frequency offset compensation are further improved, the residual error of the frequency is reduced, and the precision of the frequency offset compensation is further improved.
4. The invention correspondingly provides a spatial coherent laser communication system adopting the frequency offset estimation method, which has the effect of the frequency offset estimation method, has higher stability in the communication process and can compensate the frequency offset in real time.
Drawings
FIG. 1 is a schematic diagram of an embodiment of a spatially coherent laser communication system of the present invention;
fig. 2 is a schematic view of a processing flow of n-way sampling of the if digital signal according to the embodiment of the present invention.
Wherein: the system comprises a receiving antenna 1, a local oscillator laser 2, a frequency mixer 3-90 degrees, a balance detector 4, a data processing unit 5, an ADC6, a signal laser 7, an electro-optical modulator 8, a modulator driver 9 and a transmitting antenna 10.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
As shown in fig. 1, in order to solve the problem of poor real-time performance and dynamic adaptability of frequency compensation in the existing laser communication system, the present invention provides a frequency offset estimation method based on multiple path selection, which specifically includes the following steps:
s1, carrying out optical frequency mixing on signal light emitted by a transmitting communication terminal and local oscillator light of a receiving communication terminal, and converting the signal light and the local oscillator light into intermediate-frequency analog electric signals through a photoelectric converter;
s2, converting the intermediate-frequency analog electric signal into n paths of sampled intermediate-frequency digital signals through an ADC (analog to digital converter), wherein n is an integer greater than 1, and the specific value can be determined according to the processing capacity of the analog-to-digital conversion device when the intermediate-frequency analog electric signal is converted into n paths of sampled intermediate-frequency digital signals;
s3, converting the n paths of sampling intermediate frequency digital signals into m groups of data, wherein each group of k paths of data has n = m x k, m is an integer larger than 1, k is an integer larger than or equal to 1, and the specific value of m is determined according to the bit rate of data loaded on the signal light and the sampling rate of an analog-digital conversion device;
s4, respectively eliminating the modulation signals in the m groups of data to obtain m groups of data with the modulation signals eliminated; when the modulation signal is eliminated, the k paths in each group of m groups can be averaged and then synthesized into 1 path, then the arctan angle conversion operation is carried out on the data, the data is multiplied by the order of high-order modulation, the phase of a digital recovery carrier signal recovered after the modulation signal is eliminated is obtained, then the signal waveform of the digital recovery carrier is generated according to the phase, and then the digital recovery carrier data after the modulation signal is eliminated in the m groups are obtained, wherein the order of the high-order modulation can be determined according to the modulation type of the laser in the laser communication;
s5, respectively calculating m groups of data after modulation signals are eliminated, and obtaining frequency offset estimation values through averaging; the specific method for calculating the average value can adopt a sliding window method to carry out averaging operation, and the specific method how to carry out the operation by the sliding window method is to preferentially grab partial data from each group of data after modulation signals are eliminated to obtain the average value, wherein the data quantity of the partial data is equal to the length i of the sliding window, then every time one data is sent, under the condition of ensuring that the length i of the sliding window is not changed, the first data of the sliding window is discarded, the average value of the data contained in the current sliding window is calculated, and then the average value is multiplied by a unit conversion coefficient, so that the corresponding frequency deviation estimated value can be calculated in real time.
And S6, according to the m groups of frequency offset estimation values obtained in the step S5, selecting the group a values with the closest difference as a final frequency offset estimation value. Wherein a is an integer greater than or equal to 2, and the specific numerical value of a can be adjusted according to actual conditions.
And S7, according to the final frequency deviation estimated value obtained in the step S6, the final frequency deviation estimated value is used as a frequency deviation estimated value of digital demodulation and is also used as a correction value of local oscillation optical frequency deviation control of the receiving communication terminal.
As shown in fig. 1, the present invention further provides a spatial coherent laser communication system, in which the frequency offset estimation in the spatial coherent laser communication system adopts the frequency offset estimation method, and similar to the existing spatial coherent laser communication system, the spatial coherent laser communication system includes a transmitting communication terminal and a receiving communication terminal. The transmitting communication terminal comprises a signal laser 7, an electro-optical modulator 8, a modulator driver 9 and a transmitting antenna 10, wherein the output end of the signal laser 7 is sequentially connected with the electro-optical modulator 8 and the transmitting antenna 10, the output end of the modulator driver 9 is connected with the electro-optical modulator 8 and used for amplifying a signal of modulation information and then loading the amplified signal to laser in the electro-optical modulator 8, the electro-optical modulator 8 is used for receiving the laser emitted by the signal laser 7, and the loaded modulation information is sent to a receiving antenna 1 of the receiving communication terminal through the transmitting antenna 10. The receiving communication terminal comprises a receiving antenna 1, a local oscillator laser 2, a 90-degree frequency mixer 3, a balance detector 4, an ADC6 and a data processing unit 5, the input end of the 90-degree frequency mixer 3 is respectively connected with the receiving antenna 1 and the local oscillator laser 2, the output end of the balance detector 4 is connected with the input end of the balance detector 4, the output end of the balance detector 4 is respectively connected with the input end of the ADC6, the output end of the ADC6 is respectively connected with the input end of the data processing unit 5, and the output end of the data processing unit 5 is connected with the input end of the local oscillator laser 2.
The transmitting communication terminal sends out signal light loaded with modulation information through a transmitting antenna 10, the receiving communication terminal receives the signal light transmitted by the transmitting communication terminal, the signal light and local oscillator light of the receiving communication terminal enter a 90-degree optical mixer 3 simultaneously to be subjected to optical frequency mixing, the signal light and the local oscillator light are converted into intermediate-frequency analog electric signals after passing through a balance detector 4, the intermediate-frequency analog electric signals are converted into n-path sampling intermediate-frequency digital signals through an ADC6, and n is determined by the processing capacity of the ADC 6. Dividing n paths of intermediate frequency digital signals into m groups of data according to the sampling rate x of the ADC6 and the bit rate y of the modulation data:
m＝x/(y*c)
wherein c is an integer greater than 1, and the value of c is such that the calculation result of m is a positive integer.
For example: a chip with the sampling rate of 10G S/S is used in the ADC6, the modulation data bit rate is 2.5Gbps, and at the moment, the modulation data bit rate can be divided into 4 groups of data for subsequent data analysis and processing; the data rate is 1.25Gbps, and the data can be divided into 8 groups or 4 groups for analysis processing.
As shown in fig. 2, n channels of sampled intermediate frequency digital signals S1, S2 \8230 \ 8230, sn, ADC6 output is n =64 channels of data, the chip sampling rate of ADC6 is 10 gs S/S, the modulation data bit rate is 2.5Gbps, before entering the data processing unit 5, the data is divided into m groups of data, which are S1', S2'... Sm ' respectively, and in this embodiment, the data is specifically 4 groups, and each group of k channels of data, namely k = n/m =16, is processed for 4 groups of data respectively. After each group of data is respectively converted into an angle domain, 16 paths of summation and averaging are carried out to obtain corresponding Arg (×), the corresponding Arg (×) is obtained after the Arg (× 4) is multiplied by the order M =4 of high order modulation, the demodulation information processing is carried out to obtain Arg (× 4), the phases of the digital recovery carrier signals recovered after the modulation signals are eliminated are respectively Phs1', phs2'... Phsm ', and then M groups of orthogonal I and Q digital recovery carrier signal waveform data are generated according to the phases, wherein the I and Q digital recovery carrier signal waveform data are respectively the signal waveform data of the I and Q digital recovery carrier wavesI1', I2'. Im 'and Q1', Q2'. Qm'. Then, averaging N =256 data in the signal waveform data of each group of digital recovery carriers in a sliding window mode to obtain frequency offset estimation values delta f1, delta f2,. Delta fm of each group of data, and finally selecting 2 frequency offset estimation values with the minimum frequency offset estimation value difference from the frequency offset estimation values to average to obtain a final frequency offset estimation value
As the frequency deviation estimated value of digital demodulation, and returns to the local oscillator laser as the reference value of frequency deviation control. In other embodiments of the present invention, three frequency offset estimation values with the closest deviations or more frequency offset estimation values with the closest deviations may be selected according to actual needs to calculate the average.
In this embodiment, due to different sampling times, the difference between one or two frequency offsets of the four groups of frequency offset estimation values is much larger than that of the other two frequency offsets, for example, the four groups of frequency offset estimation values are 60mhz,50mhz,21.5MHz, and 22mhz, and finally, the average value 21.75MHz of 21.5MHz and 22MHz is selected as the final frequency offset estimation value.
In addition, in this embodiment, the signal laser 7 adopts a narrow linewidth laser, the generated laser is used as a carrier, the modulator driver 9 amplifies modulation information and loads the amplified modulation information to the electro-optical modulator 8, the electro-optical modulator 8 is an IQ modulator and modulates the carrier into a QPSK signal, the modulated optical signal is transmitted by the transmitting antenna 10, after transmission, the modulated optical signal is received by the receiving antenna 1 at the receiving communication terminal, after being mixed with local oscillator light in the 90 ° frequency mixer 3, the modulated optical signal is converted into I-path and Q-path electrical signals by the balance detector 4, after analog-to-digital conversion is performed on the two electrical signals by the ADC6, n groups of data are output and sent to the data processing unit 5, in the data processing unit 5, frequency offset estimation is performed on the data, and the local oscillator light emitted by the local oscillator laser 2 is compensated, specifically, the frequency offset estimation method is adopted.
The above embodiment selects QPSK modulation, and in other embodiments of the present invention, the present invention is also applicable to other high-order modulations such as MPSK.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A frequency offset estimation method based on multi-path selection is characterized by comprising the following steps:
s1, carrying out optical mixing on signal light emitted by a transmitting communication terminal and local oscillator light of a receiving communication terminal, and converting the signal light and the local oscillator light into intermediate-frequency analog electric signals;
s2, converting the intermediate frequency analog electric signal into n paths of sampling intermediate frequency digital signals, wherein n is an integer greater than 1;
s3, dividing the n paths of sampling intermediate frequency digital signals into m groups of data, wherein m is an integer greater than 1; respectively eliminating the modulation signals in the m groups of data to obtain m groups of digital recovery carrier data after the modulation signals are eliminated;
s4, respectively calculating frequency offset estimation values of the m groups of digital recovery carrier data after modulation signals are eliminated;
and S5, determining a final frequency offset estimation value according to the m groups of frequency offset estimation values obtained in the step S4, and taking the final frequency offset estimation value as a frequency offset reference for subsequent digital signal processing demodulation processing and simultaneously as a correction value for local oscillator optical frequency offset control of the receiving communication terminal.
2. The method of frequency offset estimation based on multiple paths selection according to claim 1, wherein: in step S5, the step of determining the final frequency offset estimation value according to the m groups of frequency offset estimation values obtained in step S4 specifically includes selecting a group a frequency offset estimation value with the closest deviation from the m groups of frequency offset estimation values obtained in step S4, and calculating an average value of the group a frequency offset estimation values as the final frequency offset estimation value, where a is an integer greater than or equal to 2.
3. The frequency offset estimation method based on multi-path selection according to claim 1 or 2, wherein the step S3 is specifically: dividing n paths of sampled intermediate frequency digital signals into m groups of data, averaging each path of sampled intermediate frequency digital signals of each group in the m groups respectively, then synthesizing one path of data, then carrying out arctan angle conversion operation on the path of data, multiplying the result by the order of high-order modulation to obtain the phase of a digital recovery carrier signal recovered after the modulation signal is eliminated, and then generating the signal waveform of the digital recovery carrier according to the phase to obtain m groups of digital recovery carrier data after the modulation signal is eliminated.
4. The frequency offset estimation method based on multiple paths selection according to claim 3, wherein step S4 specifically comprises: and respectively carrying out averaging operation on the m groups of digital recovery carrier data subjected to modulation signal elimination through a sliding window method, and multiplying by a unit conversion coefficient to obtain corresponding frequency deviation estimated values.
5. The frequency offset estimation method based on multiple paths selection according to claim 4, wherein step S4 specifically comprises: and respectively grabbing partial data from each group of digital recovery carrier data after the modulation signal is eliminated to obtain an average value, wherein the data volume of the partial data is equal to the length of the sliding window, continuing to send the residual data, and when one data is sent, under the condition of ensuring that the length of the sliding window is not changed, omitting the first data of the sliding window, calculating the average value of the data contained in the current sliding window to obtain a real-time frequency deviation estimation value which is used as the frequency deviation estimation value of each group of digital recovery carrier data after the modulation signal is eliminated.
6. A space coherent laser communication system, which can realize the frequency offset estimation method based on multi-path selection as claimed in any one of claims 1 to 5, comprises a transmitting communication terminal and a receiving communication terminal, wherein the receiving communication terminal comprises a receiving antenna (1) and a local oscillator laser (2); the method is characterized in that: the receiving communication terminal also comprises a 90-degree mixer (3), a balance detector (4), an ADC (analog to digital converter) unit (6) and a data processing unit (5);
the input end of the 90-degree frequency mixer (3) is respectively connected with the receiving antenna (1) and the local oscillator laser (2), and the output end of the 90-degree frequency mixer is connected with the input end of the balance detector (4); the output end of the balance detector (4) is connected with the input end of the ADC (6), n paths of digital signals output by the ADC (6) are all connected with the input end of the digital signal processing unit (5), and the output end of the data processing unit (5) is connected with the input end of the local oscillator laser (2);
the signal light and the local oscillation light emitted by the local oscillation laser (2) are subjected to optical frequency mixing through a 90-degree frequency mixer (3), then are converted into intermediate-frequency analog electric signals through a balance detector (4), are converted into n paths of sampling intermediate-frequency digital signals through an ADC (6), and then the n paths of digital signals are uniformly divided into m groups of data, wherein m is an integer greater than 1;
the data processing unit (5) is used for eliminating the modulation signals in the m groups of data, so as to calculate the frequency deviation estimated value of the digital recovery carrier data after the m groups of data are subjected to modulation signal elimination, select the frequency deviation value meeting the requirement according to the m groups of frequency deviation estimated values, obtain the final frequency deviation estimated value after averaging, perform frequency deviation reference of subsequent digital signal processing demodulation processing according to the final frequency deviation estimated value, and simultaneously serve as the correction value of local oscillator optical frequency deviation control of the receiving communication terminal.
7. The spatially coherent laser communication system of claim 6, wherein: the m is determined by the following formula:
m＝x/(y*c)
where c is an integer greater than 1, x is the sampling rate of the ADC (6), y is the data bit rate loaded on the signal light, and finally m is an integer greater than 1.
8. The spatially coherent laser communication system according to claim 6 or 7, wherein: the transmitting communication terminal comprises a signal laser (7), an electro-optical modulator (8), a modulator driver (9) and a transmitting antenna (10);
the output end of the signal laser (7) is sequentially connected with an electro-optical modulator (8) and a transmitting antenna (10); the output end of the modulator driver (9) is connected with the electro-optical modulator (8) and is used for amplifying the signal of the modulation information and then loading the amplified signal to the laser in the electro-optical modulator (8); the electro-optical modulator (8) is used for receiving laser emitted by the signal laser (7), loading modulation information and then sending the modulation information to a receiving antenna (1) of a receiving communication terminal through a transmitting antenna (10).
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| CN115987742A (en) * | 2023-03-20 | 2023-04-18 | 四川创智联恒科技有限公司 | Frequency domain Doppler frequency offset resistant extension method based on OFDM communication system |
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| CN115987742A (en) * | 2023-03-20 | 2023-04-18 | 四川创智联恒科技有限公司 | Frequency domain Doppler frequency offset resistant extension method based on OFDM communication system |
| CN115987742B (en) * | 2023-03-20 | 2023-06-16 | 四川创智联恒科技有限公司 | OFDM communication system-based frequency domain Doppler frequency offset expansion resisting method |
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