CN109120347B - Multi-frequency multi-probability optical carrier millimeter wave generation method with time-frequency dynamic change - Google Patents
Multi-frequency multi-probability optical carrier millimeter wave generation method with time-frequency dynamic change Download PDFInfo
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Abstract
The invention discloses a multi-frequency multi-probability optical carrier millimeter wave generation method with time-frequency dynamic change, which comprises the following steps: preparing an optical millimeter wave generation system; generating optical multi-carriers, using a crystal oscillator as a clock source, outputting adjustable local oscillator signals by radio frequency, and modulating the local oscillator signals and pulse optical signals emitted by a pulse light source in a circulating frequency shifter; grouping the optical multi-carriers; and respectively carrying out different probability mappings on the grouped optical multi-carriers. The invention can obtain better spectrum efficiency and better anti-noise performance under the condition of unchanged transmitting power.
Description
Technical Field
The invention relates to a method for generating optical millimeter waves, in particular to a method for generating multi-frequency multi-probability optical millimeter waves with dynamically-changed time frequency.
Background
In recent years, with the rapid development of networks, the demand of people for network bandwidth increases day by day, and communication networks require larger bandwidth and better spectral efficiency, so that the demand for multi-rate and multi-carrier frequency is more and more increased. Broadband and wireless technologies are the hot research focus for communication today. With the increasingly mature optical fiber research and manufacturing technology, optical fiber communication with the advantages of large communication capacity, long transmission distance, low loss and the like is distinguished, matured gradually and widely applied. Meanwhile, flexibility and mobility of wireless communication are favored by users, and the problem of bandwidth limitation in wireless communication is well solved by the increasingly mature optical Fiber communication, so that mutual convergence of optical Fiber communication and wireless communication opens a path for development of Radio-over-Fiber (RoF) technologies. In the coming fifth generation mobile communication (5G) era, RoF technology will become a 5G transmission core technology due to its characteristics of large capacity, low cost, low energy consumption, etc. The optical radio frequency system simply means that the advantages of large optical communication capacity, long transmission distance and low loss are utilized, a base band signal is modulated onto laser at a central station, the modulated optical wave with the signal is transmitted through an optical fiber link, and after receiving the optical signal, a base station carries out photoelectric conversion to convert the optical signal into an electric signal and transmits the electric signal through an antenna for a user to use. The RoF can realize the transmission of microwave signals with large bandwidth and low distortion, compared with coaxial cables, the radio frequency over fiber technology well solves the problems of low transmission rate, limited bandwidth and the like, and has great research value.
One of the core technologies of RoF is a photo-generated millimeter wave technology, and the conventional photo-generated millimeter wave technology adopts a modulator to perform sideband modulation, utilizes a cyclic frequency shifter to generate multiple carriers, and uses pulsed light and photonic crystal fiber to perform parameter processes, but the technologies all have the common disadvantage that the generated multiple carriers are fixed and cannot dynamically change along with time and frequency, so that the system cannot flexibly generate dynamically-changing electric millimeter waves. This makes it impossible to meet the requirements for bandwidth differences between different users.
Disclosure of Invention
The invention aims to solve the technical problem of providing a multi-frequency multi-probability optical carrier millimeter wave generation method with dynamically-changed time frequency, so that the frequency band utilization rate and the power benefit of a system are improved.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a multi-frequency multi-probability optical carrier millimeter wave generation method with dynamically changed time frequency is characterized by comprising the following steps:
the method comprises the following steps: preparing an optical millimeter wave generation system;
step two: generating optical multi-carriers, using a crystal oscillator as a clock source, outputting adjustable local oscillator signals by radio frequency, and modulating the local oscillator signals and pulse optical signals emitted by a pulse light source in a circulating frequency shifter;
step three: grouping the optical multi-carriers;
step four: and respectively carrying out different probability mappings on the grouped optical multi-carriers.
Further, the optical millimeter wave generation system in the first step includes a pulsed light source, an adjustable radio frequency source, a cyclic frequency shifter, spectrum processing, multi-probability mapping coding, dynamic optical switch selection, and photoelectric conversion.
Furthermore, the work flow of the optical carrier millimeter wave generation system is that pulsed light emitted by a pulsed light source and radio frequency signals emitted by a radio frequency source with specified frequencies are modulated in a cyclic frequency shifter to generate optical multiple carriers with radio frequency difference, then a plurality of groups of optical multiple carriers with different frequency difference are obtained through frequency spectrum processing, different probability mapping is carried out on the multiple carrier groups, and therefore the system obtains better spectrum efficiency and anti-noise performance under the condition that the emission power is not changed, and finally, the optical multiple carriers are converted into electric millimeter waves to be output through photoelectric conversion after selection of an optical switch.
Further, the second step is to set the frequency to f0The continuous light enters the I/Q modulator after passing through the coupler, and the frequency of the radio frequency is fsIn the I path of the modulatorAnd respectively inputs V on the Q pathsm sin(2πfst) and Vm cos(2πfst), a modulation parameter cos (2 π f) is added to the optical field output by the modulator after modulationst)+jsin(2πfst)＝exp(j2πfst) and a corresponding frequency shift of f1＝f0+fsAmplified by the EDFA and re-entered in the I/Q modulator via the coupler to generate a second carrier wave of frequency f2＝f1+fsThe carrier wave of (2). Thus, multiple cycles in a frequency shifting system can produce a frequency f0、f1、f2…fNA plurality of carriers of which intervals are all fs. We can also use a band pass filter to control the number of sub-carriers to obtain a number and frequency locked optical multi-carrier.
Further, the third step is to use the LCOS filter to arbitrarily screen out two subcarriers in the multicarrier, since the frequency between any two same subcarriers is fsThen the frequency difference between the two screened subcarriers may be fs、2fs…nfsThus obtaining a plurality of groups of multi-carrier groups.
Further, the fourth step is specifically
The Gaussian beam emitted by the pulse light source conforms to the Gaussian distribution and follows the probability density distribution formula of the Gaussian distribution
Wherein x is the distance from the constellation point to the origin, mu is the mean value of the random variables obeying Gaussian distribution, and sigma is the standard deviation of the random variables, and the shape of the Gaussian distribution can be changed by changing the value of mu in the formula to obtain different Gaussian distributions;
the method for setting the mu value comprises the steps of extracting sub-symbol blocks from a transmitted symbol string to form a sub-symbol string, then carrying out probability setting on the sub-symbol string, and setting different probability values mu on the sub-symbol blocks through time and frequency to ensure that the mu value of each symbol block is different;
in the link of grouping the multiple carriers, the frequency of the electric millimeter waves obtained through photoelectric conversion is different due to different subcarrier frequency intervals of each group of multiple carriers, and in the link of mapping and coding, a multi-probability method is adopted, so that the multi-frequency multi-probability electric millimeter waves with time-frequency change are finally obtained through the photoelectric conversion.
Compared with the prior art, the invention has the following advantages and effects: the invention generates multi-frequency multi-probability optical carrier millimeter waves with dynamically changed time frequency through the cyclic frequency shifter and multi-probability mapping coding. Through the cyclic frequency shifter and the fine frequency spectrum processing, a plurality of groups of optical multi-carriers with different frequency differences can be obtained, and the frequency spectrum utilization rate is high and the frequency is stable. And multi-probability mapping is carried out on the grouped optical multi-carriers, a constellation diagram with non-uniform distribution can be obtained, probability distribution parameters of the constellation diagram are adjusted, and better spectrum efficiency and better anti-noise performance can be obtained under the condition that the transmitting power is not changed.
Drawings
Fig. 1 is a schematic diagram of an optical millimeter wave generation system of the present invention.
Fig. 2 is a block diagram of the cyclic frequency shifter of the present invention to produce optical multiple carriers.
Fig. 3 is a schematic diagram of an LCOS filter of the present invention in a multi-carrier packet.
Fig. 4 is a diagram of a multi-carrier packet multi-probability map of the present invention.
Fig. 5 is a constellation diagram received at the receiving end.
Detailed Description
The present invention will be described in further detail below by way of examples, which are illustrative of the present invention and are not limited to the following examples, in conjunction with the accompanying drawings.
In the conventional constellation mapping, each symbol point represented by the same bit number in the constellation map is transmitted with the same probability, and because constellation points at different positions have different euclidean distances, the energy required for transmitting them is different, and the energy required for the points closer to the inner circle is smaller. If the mapping probability of different position points is optimized, the inner circle point with lower emission energy can be mapped with higher probability, and the outer circle point with higher emission energy is mapped with lower probability, so that the emission power of the whole system can be effectively reduced. This technique is called probabilistic Profiling (PS).
The method for generating the multi-frequency multi-probability optical carrier millimeter waves with time-frequency change is a time, frequency and rate multi-dimensional dynamically-changing RoF system, and achieves frequency self-adaption and rate dynamically-changing RoF systems by endowing different probability distributions to optical carriers with different time and different frequency intervals. The method has the advantages of high flexibility, high frequency spectrum utilization rate, low cost and the like, and can be fully suitable for the coming 5G era and the future development of over 5G.
The invention discloses a method for generating multi-frequency multi-probability optical carrier millimeter waves with dynamically changed time frequency, which is characterized by comprising the following steps of:
the method comprises the following steps: preparing an optical millimeter wave generation system; the system mainly comprises modules of a pulse light source, an adjustable radio frequency source, a cyclic frequency shifter, frequency spectrum processing, multi-probability mapping coding, dynamic optical switch light selection and photoelectric conversion.
The work flow is roughly as follows:
pulse light emitted by a pulse light source and radio frequency signals emitted by a radio frequency source and having specified frequencies are modulated in a cyclic frequency shifter to generate optical multiple carriers with the frequency difference of radio frequency, then a plurality of groups of optical multiple carriers with different frequency differences are obtained through frequency spectrum processing, and different probability mapping is carried out on the multiple carrier groups, so that the system can obtain better spectrum efficiency and anti-noise performance under the condition of unchanged emission power. And finally, after the selection of the optical switch, performing photoelectric conversion to convert the optical multi-carrier into electric millimeter waves to be output.
Step two: generating optical multi-carriers, using a crystal oscillator as a clock source, outputting adjustable local oscillator signals by radio frequency, and modulating the local oscillator signals and pulse optical signals emitted by a pulse light source in a circulating frequency shifter;
as shown in fig. 2, the frequency is f0The continuous light enters the I/Q modulator after passing through the coupler, and the frequency of the radio frequency is fsIn the meantime ofV is respectively input on the I path and the Q path of the systemm sin(2πfst) and Vm cos(2πfst), a modulation parameter cos (2 π f) is added to the optical field output by the modulator after modulationst)+jsin(2πfst)＝exp(j2πfst) and a corresponding frequency shift of f1＝f0+fsAmplified by the EDFA and re-entered in the I/Q modulator via the coupler to generate a second carrier wave of frequency f2＝f1+fsThe carrier wave of (2). Thus, multiple cycles in a frequency shifting system can produce a frequency f0、f1、f2…fNA plurality of carriers of which intervals are all fs. We can also use a band pass filter to control the number of sub-carriers to obtain a number and frequency locked optical multi-carrier.
Step three: grouping the optical multi-carriers;
a specified number of multiple carriers are available through the cyclic frequency shifter and the frequencies between its subcarriers are all locked. Grouping of multiple carriers is achieved in this patent using LCOS filters. As shown in fig. 4, two subcarriers are arbitrarily selected from the multicarrier by using the LCOS filter, since the frequency between any two same subcarriers is fsThen the frequency difference between the two screened subcarriers may be fs、2fs…nfsThus obtaining a plurality of groups of multi-carrier groups.
Step four: and respectively carrying out different probability mappings on the grouped optical multi-carriers.
The optical multi-carriers obtained by the cyclic frequency shifter are grouped by an LCOS optical filter, and the frequency difference between the carriers is fs、2fs…nfsMultiple groups of multiple carriers. The multi-probability mapping coding is to perform different probability mappings on the multi-carrier groups respectively.
Taking 16QAM as an example, because the Gaussian beam emitted by the pulse light source conforms to the Gaussian distribution, the probability density distribution formula of the Gaussian distribution is obeyed
Where x is the distance from the constellation point to the origin, μ is the mean of the random variables that obey the gaussian distribution, σ is the standard deviation of the random variables, the image of the gaussian distribution is symmetric about μ, and takes the maximum value at μ, takes the value of 0 at positive (negative) infinity, and has an inflection point at μ ± σ. Changing the value of μ in the formula can change the shape of the gaussian distribution to obtain a different gaussian distribution.
The method for setting the mu value comprises the following steps: extracting sub-symbol blocks from the transmitted symbol string to form a sub-symbol string, then setting the probability of the sub-symbol string, and setting different probability values mu on the sub-symbol blocks through time and frequency, so that the mu value of each symbol block is different. As shown in fig. 4, the multi-probability distribution scheduling is performed on different subcarrier groups a-D, and the obtained constellation mapping is shown as a-D, which shows that the constellation mapping is non-uniformly distributed, and when a signal point with lower energy has a higher transmission frequency than a signal point with higher energy, better spectrum efficiency can be obtained under the condition that the transmission power is not changed.
In the link of grouping the multiple carriers, the frequency of the electric millimeter waves obtained through photoelectric conversion is different due to different subcarrier frequency intervals of each group of multiple carriers, and in the link of mapping and coding, a multi-probability method is adopted, so that the multi-frequency multi-probability electric millimeter waves with time-frequency change are finally obtained through the photoelectric conversion.
Fig. 5 is two received constellations, where a in fig. 5 is a constellation of a conventional 16QAM signal, and b in fig. 5 is a 16QAM constellation after multi-probability mapping, which proves the feasibility of the system proposed by this patent, and can achieve the purpose of improving the efficiency of the frequency spectrum without changing the transmission power.
The invention generates multi-frequency multi-probability optical carrier millimeter waves with dynamically changed time frequency through the cyclic frequency shifter and multi-probability mapping coding. Through the cyclic frequency shifter and the fine frequency spectrum processing, a plurality of groups of optical multi-carriers with different frequency differences can be obtained, and the frequency spectrum utilization rate is high and the frequency is stable. And multi-probability mapping is carried out on the grouped optical multi-carriers, a constellation diagram with non-uniform distribution can be obtained, probability distribution parameters of the constellation diagram are adjusted, and better spectrum efficiency and better anti-noise performance can be obtained under the condition that the transmitting power is not changed.
The above description of the present invention is intended to be illustrative. Various modifications, additions and substitutions for the specific embodiments described may be made by those skilled in the art without departing from the scope of the invention as defined in the accompanying claims.
Claims (3)
1. A multi-frequency multi-probability optical carrier millimeter wave generation method with dynamically changed time frequency is characterized by comprising the following steps:
the method comprises the following steps: preparing an optical millimeter wave generation system;
the optical millimeter wave generation system comprises a pulse light source, an adjustable radio frequency source, a cyclic frequency shifter, frequency spectrum processing, multi-probability mapping coding, dynamic optical switch light selection and photoelectric conversion; the working process of the optical millimeter wave generation system comprises the steps that pulse light emitted by a pulse light source and radio-frequency signals emitted by a radio-frequency source and having specified frequencies are modulated in a cyclic frequency shifter to generate optical multiple carriers with radio-frequency difference, then multiple groups of optical multiple carriers with different frequency differences are obtained through frequency spectrum processing, different probability mapping is carried out on the multiple carrier groups, and therefore the system can obtain better spectral efficiency and anti-noise performance under the condition that the emission power is not changed, and finally, photoelectric conversion is carried out after selection of an optical switch to convert the optical multiple carriers into electric millimeter waves to be output;
step two: generating optical multi-carriers, using a crystal oscillator as a clock source, outputting adjustable local oscillator signals by radio frequency, and modulating the local oscillator signals and pulse optical signals emitted by a pulse light source in a circulating frequency shifter;
step three: grouping the optical multi-carriers;
step four: respectively carrying out different probability mappings on the grouped optical multi-carriers;
the fourth step is specifically that
Gaussian beam emitted by pulse light sourceConforming to a Gaussian distribution, subject to a formula for probability density distribution of the Gaussian distribution
Wherein x is the distance from the constellation point to the origin, mu is the mean value of the random variables obeying Gaussian distribution, and sigma is the standard deviation of the random variables, and the shape of the Gaussian distribution can be changed by changing the value of mu in the formula to obtain different Gaussian distributions;
the method for setting the mu value comprises the steps of extracting sub-symbol blocks from a transmitted symbol string to form a sub-symbol string, then carrying out probability setting on the sub-symbol string, and setting different probability values mu on the sub-symbol blocks through time and frequency to ensure that the mu value of each symbol block is different;
in the link of grouping the multiple carriers, the frequency of the electric millimeter waves obtained through photoelectric conversion is different due to different subcarrier frequency intervals of each group of multiple carriers, and in the link of mapping and coding, a multi-probability method is adopted, so that the multi-frequency multi-probability electric millimeter waves with time-frequency change are finally obtained through the photoelectric conversion.
2. The method for generating multi-frequency multi-probability optical carrier millimeter waves with dynamically changed time and frequency according to claim 1, wherein: the second step is to set the frequency as f0The continuous light enters the I/Q modulator after passing through the coupler, and the frequency of the radio frequency is fsV is input on the I path and Q path of the modulator respectivelymsin(2πfst) and Vmcos(2πfst), a modulation parameter cos (2 π f) is added to the optical field output by the modulator after modulationst)+jsin(2πfst)＝exp(j2πfst) and a corresponding frequency shift of f1＝f0+fsAmplified by the EDFA and re-entered in the I/Q modulator via the coupler to generate a second carrier wave of frequency f2＝f1+fsThe carrier wave of (2); thus, multiple cycles in a frequency shifting system can produce a frequency f0、f1、f2…fNA plurality of carriers of which intervals are all fs(ii) a The number of sub-carriers is controlled by means of a band-pass filter resulting in a number and frequency locked optical multi-carrier.
3. The method for generating multi-frequency multi-probability optical carrier millimeter waves with dynamically changed time and frequency according to claim 1, wherein: step three is specifically to utilize the LCOS filter to randomly screen out two subcarriers in the multicarrier, and the frequency between any two same subcarriers is fsThen the frequency difference between the two screened subcarriers may be fs、2fs…nfsThus obtaining a plurality of groups of multi-carrier groups.
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