CN113595650B - Ultra-narrow-band communication transmission system and transmission method for orbital angular momentum microwave quantum - Google Patents
Ultra-narrow-band communication transmission system and transmission method for orbital angular momentum microwave quantum Download PDFInfo
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Abstract
The invention discloses an ultra-narrow band transmission system and a transmission method of orbital angular momentum microwave quanta.A ultra-narrow band signal source generates OAM microwave quanta with different modes in the system, a mode combination selection unit determines the mode form, an information key control unit switches the OAM microwave quanta with the mode corresponding to the current information in the mode key control form, and loads the original information on the OAM microwave quanta with different modes; the phase synchronization unit reduces the phase difference value when the OAM microwave quantum mode number is switched; the method comprises the following steps that an ultra-narrow band signal receiving module receives an OAM microwave quantum carrying an ultra-narrow band signal and converts the OAM microwave quantum into a signal of which an OAM mode can be identified or sorted; and the ultra-narrow band signal recovery and analysis module determines a corresponding OAM mode through identifying and sorting the received signals and recovers the original information. The invention can realize ultra-narrow band information transmission based on vortex OAM microwave quanta without complex devices, can reduce the occupancy rate of traditional frequency domain resources, and improves the frequency band utilization rate and the channel capacity.
Description
Technical Field
The invention relates to the technical field of electromagnetic wave Orbital Angular Momentum (OAM) quantum states, in particular to an ultra-narrow band information transmission system and a transmission method based on Orbital Angular Momentum microwave quanta.
Background
According to classical electrodynamic theory, electromagnetic radiation carries both linear and Angular Momentum, wherein Angular Momentum is composed of Spin Angular Momentum (SAM) and Orbital Angular Momentum (OAM). In 1909, Poynting theoretically predicts the mechanical effect of electromagnetic field angular momentum; in 1992, Allen et al verified the existence of electromagnetic wave Orbital Angular Momentum (OAM) in lightwave band experiments. In the radio band, s.m. mohammadi et al propose to generate electromagnetic waves with orbital angular momentum using a circular array antenna and to propose a corresponding detection method. In 2004, Gibson et al proposed that independent modulation and transmission of information could be made using different modes of light. In 2011, two paths of signals with different OAM modes in the same frequency band are successfully received outside 442m, and the feasibility of increasing the channel capacity by OAM is verified. With the increasing maturity of OAM in optical communication and the gradual saturation of radio frequency spectrum resources, this technology starts to gradually turn to the quantum information layer, photons as basic particles constituting electromagnetic waves can also carry OAM, which means that new information dimensions appear, and the detection of the angular momentum of photons can complete the detection of the orbital angular momentum of electromagnetic waves. By utilizing the characteristic that photons can carry OAM, the ultra-narrow band signal can be constructed under the condition of occupying very narrow bandwidth in a frequency domain according to a keying mode. The photon carrying OAM is characterized in that the concept of a modal domain can be generated on the resource different from the traditional frequency domain, so that information is transmitted by using different modes, the application of electromagnetic waves based on an ultra-narrow band technology in the aspects of communication, navigation and detection is further developed, and the channel capacity and the transmission performance are improved.
The frequency spectrum is a very important communication resource in the information transmission process, the communication technology for realizing the Ultra Narrow Band (UNB) by using the unconventional modulation mode is firstly proposed by an American electronic engineer Walker HR, in 1993 and 1999, H.R. Walker respectively proposes an improved VPSK method and a famous VMSK (very Minimum Shifting keying) method, and in 2002, a PRK (phase reverse keying) method with a cleaner frequency spectrum is mainly proposed. In 2000, Walker HR transmitted data at a rate of 1.544Mb/s in a 30kHz bandwidth slot, while power consumption was below-60 dBm [2 ]. Ultra-narrow bands are attracting more and more attention in next-generation communication systems as a concept capable of transmitting more information with limited spectrum resources and ultra-narrow band bandwidths.
In summary, the existing methods for implementing ultra-narrow band are implemented by changing the modulation method of information, and it is very likely that useful information is submerged in the carrier signal with very high frequency, even if the information implements ultra-narrow band transmission, the effective information cannot be received and recovered, so a method for fundamentally implementing an "ultra-narrow band" communication transmission system is needed. Until now, there has been no better method.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides an ultra-narrow band communication transmission system based on orbital angular momentum microwave quanta, the system introduces OAM microwave quanta in the whole communication process, adopts the switching of the OAM microwave quanta with controllable modes, which can be single modes or mixed modes, to transmit ultra-narrow band information, and recovers ultra-narrow band signals by using diffraction patterns. Compared with the traditional electromagnetic wave communication, the OAM microwave quantum can transmit information through the value of the self modal number, and when the modal number of the OAM microwave quantum is directly detected through a diffraction pattern or a modal classifier, the operation is directly carried out in an angular momentum domain, and the traditional frequency domain resources are not occupied. And the problem of phase asynchronism among different OAM modes is solved, so that extremely narrow bandwidth is occupied in a frequency domain, and the method has extremely high frequency band utilization rate. The technical scheme adopted by the invention is as follows:
an ultra-narrow-band communication transmission system of orbital angular momentum microwave quanta comprises a transmitting end and a receiving end,
the transmitting end includes:
the ultra-narrow band signal source comprises a signal excitation source and an OAM microwave quantum generation unit, wherein the signal excitation source is used for providing original excitation for the OAM microwave quantum generation unit;
the OAM microwave quantum generating unit is used for generating OAM microwave quanta in different modes;
the ultra-narrow band signal generation module comprises a mode combination selection unit, an OAM microwave quantum information keying unit and a mode switching position phase alignment unit, wherein the mode combination selection unit determines the mode form of an OAM microwave quantum in the transmission time of transmitting each code element;
the OAM microwave quantum information keying unit switches the OAM microwave quantum corresponding to the current information in a mode form in a mode keying mode, and loads the original information to the OAM microwave quantum in different mode forms;
the mode switching position phase alignment unit is used for reducing a phase difference value during OAM microwave quantum mode switching to form an ultra-narrow band signal;
the receiving end includes:
the receiving module of the ultra-narrow band signal, is used for receiving and carrying the ultra-narrow band signal of the information in the form of OAM microwave quantum, and realize the signal phase synchronization at the receiving end;
and the ultra-narrow band signal recovery and analysis module is used for detecting the OAM microwave quantum received by the ultra-narrow band signal receiving module, determining an OAM mode corresponding to each ultra-narrow band signal and demodulating the signal to recover original information.
Optionally, the OAM microwave quanta of different modes generated by the OAM microwave quantum generating unit are transmitted through the same waveguide antenna, or are transmitted separately through a plurality of waveguide antennas.
Optionally, the OAM microwave quantum is an OAM microwave quantum within a full frequency band.
Optionally, the modality forms include a single modality and a plurality of modality combinations, which refers to a combination of at least two modalities.
Optionally, determining the corresponding OAM mode form of each ultra-narrow band signal by adopting an identification or sorting method, wherein identification refers to identifying the diffraction pattern of the OAM microwave quantum carrying the ultra-narrow band signal, determining the mode of the OAM microwave quantum,
sorting is the mode of determining OAM microwave quanta by an OAM sorter.
Optionally, the ultra-narrow band signal recovery and analysis module further includes a spectrum analysis unit, and the spectrum analysis unit analyzes the received original information in a frequency domain to obtain the occupation condition of the signal on the spectrum resource.
Optionally, in the communication transmission system, there are M transmitting ends, and a received signal of an OAM transmission process of G receiving ends is represented as:
y＝H OAM x+n
wherein,
g is more than or equal to 1 and less than or equal to G;
a set of representative signal vectors;
g represents the g-th transmitting end;
m represents the mth receiving end;
Optionally, the transmitting end transmits a symbol information by using a period of a sinusoidal signal, and the receiving end receives a total signal S r Comprises the following steps:
wherein the mathematical form of g (t) is represented as follows:
A n is the amplitude value of the signal for each time length;
t represents the total transmission time;
n represents an nth OAM modality;
ω 0 frequency of the OAM microwave quantum;
t is the time length occupied by transmitting each code element information;
Optionally, the transmitting end generates different-mode OAM microwave quanta by using a method of generating different-mode OAM by using homologous excitation, generates the same-phase OAM microwave quanta in different modes and transmits the same-phase OAM microwave quanta with original information, calculates the placement position of the OAM microwave quantum generating unit when the modes are switched to meet the condition of phase alignment, places the OAM microwave quantum generating unit at the transmitting end according to the calculation result, and finally achieves phase alignment;
after the receiving end receives the signal, the bit synchronization method is adopted to realize the bit synchronization of the ultra-narrow band signal of the receiving end.
Optionally, the initial phase of the sinusoid for each symbol of information
In response to the signal having been received,
represents the initial phase of the nth symbol information in the received signal, at this time
Is a determined value, S r Becomes a deterministic signal S q For deterministic signals S q Fourier transform is carried out, and the expression of the Fourier transform in a frequency domain is obtained as follows:
F q (ω) is the frequency spectrum of the deterministic signal;
n is the nth symbol information of the transmission;
j is an imaginary symbol;
ω 0 is the frequency of the OAM microwave quantum;
ω represents a signal frequency variable;
the Sa function is a non-normalized sampling function;
the delta function is an impact function;
t is the time length occupied by transmitting each code element information;
n denotes the transmitted N symbol information.
The invention also provides an ultra-narrow band communication information transmission method of the orbital angular momentum microwave quantum, which comprises the following steps:
OAM microwave quanta with the same phase and different modes are generated in a homologous excitation mode;
selecting a mode form to transmit information by using a mode combination selection unit, wherein the mode form comprises a single mode and a plurality of modes in a mode combination, and the mode combination refers to a combination of at least two modes;
switching the OAM microwave quanta of the current information corresponding to the mode in a mode keying mode, and loading the original information to the OAM microwave quanta in different mode forms so as to form an ultra-narrow band signal;
after an OAM microwave quantum carrying an ultra-narrow band signal irradiates an OAM microwave quantum receiving device, the microwave quantum becomes a signal form capable of identifying an OAM microwave quantum mode through a diffraction pattern or an OAM sorter under the combined action of an auxiliary facility of the receiving device and the OAM microwave quantum receiving device;
determining the modal form of the OAM microwave quantum by adopting a recognition diffraction pattern or an OAM sorter;
and placing the transmitting end according to the calculation of the positions of different OAM microwave quantum generating units, further aligning the phases of different modes of OAM microwave quantum switching positions, and demodulating signals after carrying out bit synchronization on the receiving end so as to recover original information.
Compared with the prior art, the invention has the beneficial effects that: the ultra-narrow band communication transmission system of the orbital angular momentum microwave quantum realizes that the frequency band utilization rate is greatly improved, namely the information transmission rate in a unit frequency band is greatly improved under the condition of very narrow bandwidth on a relatively simple physical device, occupies few frequency domain resources, completes a large amount of information transmission, and can be used in numerous application scenes such as quantum state OAM information large-capacity transmission and the like.
Drawings
The above features and technical advantages of the present invention will become more apparent and readily appreciated from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.
Fig. 1 is a schematic structural diagram of an ultra-narrow-band communication transmission system of orbital angular momentum microwave quanta according to an embodiment of the invention;
FIG. 2 is a diagram of a system hardware architecture according to one embodiment of the present invention;
fig. 3 is a schematic diagram of keyed loading of encoded symbol information into different mode OAM microwave quanta according to one embodiment of the present invention;
fig. 4 is a signal waveform diagram of an ultra-narrow band signal constructed based on OAM microwave quanta in a time domain according to an embodiment of the present invention;
fig. 5 is a graph showing the spectral density in the frequency domain of an ultra-narrow band signal composed of ═ pi/2, pi/10, pi/100, pi/1000 with different variances, where the phase difference of the transmitted signals between the transmitting terminals obeys a mean value of zero at a specific frequency of 50Hz, and the abscissa in fig. 5 is a frequency value and the ordinate represents the spectral density, according to an embodiment of the present invention;
fig. 6 is a power spectral density curve in the frequency domain of an ultra-narrow band signal composed of σ ═ pi/2, pi/10, pi/100, pi/1000 with different variances, where the phase difference of the transmitted signal between the transmitting ends obeys a mean value of zero at a specific frequency of 50Hz, and the abscissa in fig. 6 is a frequency value and the ordinate represents the power spectral density according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a situation that an ultra-narrow band signal with a phase difference Δ Φ ═ pi/1000, pi/500, 3 pi/1000, pi/100, pi/10, pi/2 } under different amplitude ratio levels (k ═ {1,2,3,4}) between front and back signals occupies a bandwidth of a frequency band compared to a conventional modulation mode after normalization according to an embodiment of the present invention;
FIG. 8 is a graph of signal bandwidth versus phase variance in inter-symbol error according to one embodiment of the present invention;
fig. 9 is a plot of channel capacity as a function of signal-to-noise ratio, SNR, according to one embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
As shown in fig. 1, an ultra-narrow band communication transmission system 10 of orbital angular momentum microwave quanta includes an ultra-narrow band signal source 100, an ultra-narrow band signal generating module 200, an ultra-narrow band signal receiving module 300, and an ultra-narrow band signal recovering and analyzing module 400.
The ultra-narrow band signal source 100 includes a signal excitation source 101 and an OAM microwave quantum generating unit 102, which are used for generating OAM microwave quanta of different modes. The signal excitation source 101 is positioned outside the OAM microwave quantum generating unit 102 and provides original excitation for generating OAM microwave quanta; the OAM microwave quantum generating unit 102 mainly radiates OAM microwave quanta of different modes to the external space through the transformation of the signal excitation source.
For example, the signal excitation source 101 may be a combination of a cathode at the front end of an electronic gyrotron and a large magnet coil outside the gyrotron, and the OAM microwave quantum generating unit 102 may be an electronic gyrotron. The cathode at the front end of the electronic gyrotron provides electrons for the gyrotron, and the large-scale magnet coil is positioned outside the electronic gyrotron and provides a specific magnetic field for the electrons to rotate in the electronic gyrotron; the electron gyrotron provides an environment that electrons do gyrotron motion in a strong magnetic field, the electrons perform high-speed gyrotron motion under the action of the magnetic field, and the electrons moving at high speed in the electron gyrotron radiate OAM microwave quanta to an external space. The OAM microwave quanta are transmitted through the waveguide antenna, and the OAM microwave quanta in different modes can be transmitted by the same waveguide antenna or can be transmitted through a plurality of waveguide antennas respectively.
The ultra-narrow band signal generation module 200 is configured to selectively transmit OAM microwave quanta of different modes in a keying manner and align phases between them, so as to generate an ultra-narrow band signal. The different modality forms may be a single modality or any of several combined modalities of multiple modalities. The device comprises a mode combination selection unit 201, an OAM microwave quantum information keying unit 202 and a mode switching position phase alignment unit 203. The mode combination selection unit 201 determines whether the OAM combination mode information transmission in a single OAM mode or a mixed form of multiple modes is in one symbol transmission time, and determines a specific combination form of different modes OAM; the OAM microwave quantum information keying unit 202 switches the OAM microwave quantum of the current information corresponding mode in a keying manner, loads the original information onto the OAM microwave quantum of different state, and realizes information loading; the mode switching position phase alignment module 203 is used for reducing a phase difference value generated by incomplete synchronization between signals when OAM microwave quantum mode numbers are switched, so that the phase difference is as small as possible, the bandwidth is as narrow as possible, and an ultra-narrow band signal is generated.
In the ultra-narrow band signal receiving module of the receiving part, the receiving of the OAM microwave quantum can be regarded as the inverse process of the OAM microwave quantum transmitting. After the OAM microwave quantum propagated in free space is irradiated to the OAM microwave quantum receiving device 302, it becomes a signal form that can be identified or sorted after passing through the receiving device auxiliary facility 301 and the receiving end bit synchronization module 303.
For example, the OAM microwave quantum receiving device 302 may be an electronic gyrotron with a large magnet coil outside, OAM microwave quanta carrying ultra-narrow band signals interact with gyrotron moving at high speed in a magnetic field electronic gyrotron, and the microwave quanta couple the ultra-narrow band signals carried by the microwave quanta to the gyrotron through OAM, that is, generate eddy electron beams of OAM, and complete the reception of the ultra-narrow band signals. The auxiliary facilities 301 of the receiving device can be a water cooling system and a high-voltage power supply to create conditions for receiving the OAM microwave quantum, while the receiving end phase synchronization module refers to the communication principle, and the receiving end bit synchronization module 303 can be a bit synchronization module in the traditional communication system and is realized by means of a gardner algorithm.
The ultra-narrow band signal recovery and analysis module 400 is a device for receiving and analyzing an OAM ultra-narrow band signal according to the idea of discrimination and sorting (i.e., by discriminating diffraction patterns or sorting a mode of determining OAM microwave quanta by a sorter), and includes the following units: signal demodulation recovery section 401, OAM microwave quantum detection section 402, and spectrum analysis section 403. The signal demodulation and recovery unit 401 demodulates the transmission information after the mode form is identified by the OAM microwave quantum detection unit 402, and the OAM microwave quantum detection unit 402 identifies the OAM mode in the signal by adopting an identification or sorting idea, so as to recover the transmission information. The spectrum analysis unit 403 is used to quantitatively measure the bandwidth of the frequency band occupied by the transmitted ultra-narrow band signal, and analyzes the acquired ultra-narrow band signal in the frequency domain to obtain the spectrum resource occupation of the signal. The position relationship of each module in the system is shown in the system hardware structure diagram of fig. 2.
The system can be used as a wireless transmission system for constructing ultra-narrow band information transmission, an ultra-narrow band signal source 100 and an ultra-narrow band signal generating module 200 jointly form a transmitting end, OAM microwave quanta in different modal forms are switched through a keying form to transmit information in an ultra-narrow band signal form, and a receiving end converts the OAM microwave quantum form of the received OAM ultra-narrow band signal into a signal form which can be identified and sorted through the system, so that the identification of an OAM mode can be realized, and the transmitted original information can be recovered. The values of the relevant parameters related to the system in the embodiment are shown in table 1.
Table 1: list of relevant parameters
| Ultra-narrow band signal frequency omega 0 ＝50Hz | Phase difference phi-N (0, sigma) between transmitting ends |
| The number M of transmitting terminals is 2 | Number of transmission symbols N1001 |
In this embodiment, an information receiving end of the OAM ultra-narrowband communication system receives an OAM microwave quantum, which is different from a mode in which a conventional antenna receives an OAM beam. Assuming that the OAM microwave quantum detection unit 402 can detect the electric field strength of an OAM microwave quantum and can also detect the value of the mode number through a diffraction pattern, the channel formula of the entire communication system can be represented by two parts, which are electric field strength expression and mode number expression, respectively.
For the detection of the electric field intensity, for a single traditional antenna which can only detect the electric field intensity of the electromagnetic wave, the OAM cannot be directly identified, so that only a single-frequency carrier signal with continuous phase can be detected. The received signal of the OAM transmission process with M transmitting ends and G receiving ends may be represented as:
y＝H OAM x+n
wherein,
g is more than or equal to 1 and less than or equal to G;
Constructing a symbol vector x ' according to the mode keying method shown in fig. 3, (the OAM mode of transmitting information, the number of elements in the symbol vector x ' is set to 1), and multiplying the symbol vector x ' by the OAM carrier signal to obtain a transmitted signal vector
ω＝[ω 1 ,...,ω m ,...ω M ] T Which represents an M-way OAM carrier signal,
representing the hadamard product of the matrix elements. The channel matrix is modeled by the spatial energy distribution characteristics of OAM waves and is directly contained in the channel matrix H OAM In (1).
In the value part of the diffraction pattern detection mode number, the channel form can be written as:
L＝f(l)
l is a value of a modal number generated by the OAM microwave quantum generating module 100, and L is a modal value detected after the OAM microwave quantum generated by the transmitting end passes through the transmission channel and is received by the OAM receiving end without error. f represents the action relation, which comprises the crosstalk of the transmission process to the transmission mode value and the influence of the diffraction pattern on the mode discrimination error after receiving the signal.
Conventional wireless communication systems use antennas to detect the electric field strength of electromagnetic waves and increase the capacity of the communication system using frequency, time, code, space (number of antennas) and other degrees of freedom. But the whole OAM ultra-narrowband communication system is completed by the mode keying mode, and the mode keying mode is as shown in fig. 3. For a frequency of ω 0 The monochromatic sine wave of (2) is represented as a sine signal with continuous phase in a time domain, and is represented as single impact in a frequency domain, the signal bandwidth is infinitely close to 0, and when an OAM microwave quantum transmits information in a mode of mode keying, because strict phase synchronization cannot be achieved among different transmitting ends, the form of a receiving end signal y is changed into a sine signal with abrupt phase change.
As shown in fig. 4, for a binary digital signal, "1" is transmitted by using one OAM mode generated by one transmitting end, and "0" is transmitted by using another OAM mode generated by another transmitting end, carrier signals carrying OAM information generated by the two transmitting ends are combined into a sinusoidal signal with continuous phase in the time domain, however, the phases of the two transmitting ends are not synchronized, which results in that the form of a signal y at a receiving end is changed into a sinusoidal signal with abrupt phase, so that the frequency spectrum occupied by a signal with an infinite bandwidth close to 0 in the frequency domain is also broadened, which results in broadening of the frequency bandwidth.
The detailed analysis of the specific mathematical form and spectrum of the signal will be described herein below.
Assuming that each symbol is transmittedThe information occupies a time length of T, and there is a random deviation of the phase of T between each coded symbol information. At this time, the receiving end receives the total signal S r Can be written as:
wherein the mathematical form of g (t) is represented as follows:
A n is the amplitude value of the signal for each time length;
t represents the total transmission time;
n represents an nth OAM modality;
ω 0 frequency of the OAM microwave quantum;
When the phases of the OAM microwave quantum generating module 100 from the first generating module to the mth generating module are perfectly synchronized, the frequency spectrum is an impulse in the frequency domain, and at this time, no frequency spectrum resource is occupied. In an actual situation, the phases of signals generated by the two OAM microwave quantum generating units are not perfectly synchronized, at this time, a staggered sine wave appears, the phase transmitted by the transmitting end has a deviation, and the distances between the transmitting end and the receiving end are different, which also causes a deviation. In order to synchronize signals as much as possible, a method of generating different modes of OAM by using homologous excitation may be used, microwave quanta of different modes are radiated from the same signal source, the sources are the same, the transmitting end may generate signals of the same phase and different modes to be transmitted by using this method, so that the factors affecting the phase difference between the two signals are only the distance from the OAM microwave quantum generating unit of the transmitting end to the transmitting antenna (the OAM microwave quanta of different modes may be transmitted by using the same waveguide antenna or by using multiple waveguide antennas, but the distances between the waveguide antennas and the receiving end are the same, so that the distances between the transmitting end and the receiving end are only reflected in the distance from the OAM microwave quantum generating unit to the transmitting antenna), at this time, the placing position of each OAM microwave quantum generating unit is accurately calculated at the receiving end, so that the distances from the OAM microwave quantum generating units to the transmitting antenna are the same, therefore, the phases of the OAM microwave quanta in different modes are further aligned, and the effect of phase synchronization is achieved as far as possible. In practice perfect synchronization is not possible and thus the signal is transmitted as an ultra narrow band signal. As shown in fig. 5.
The transmitting end transmits deterministic signals in a mode keying mode (M OAM modes are used in the embodiment in total), when N code element information is transmitted, one code element information is transmitted by using the period of one sinusoidal signal, and the initial phase of the sine of each code element information
Is a constant value, and for the purpose of facilitating the spectrum analysis, it is assumed that the amplitude value of the signal in each time span is a normalized constant value, i.e., A n When 1, the signal S is received r (t) can be further simplified as:
ω 0 the frequency of the OAM microwave quantum. Sinusoidal initial phase of each symbol information
In response to the signal having been received,
represents the initial phase of the nth symbol information in the received signal, at this time
Is a determined value, S r Becomes a deterministic signal S q . For certaintySignal S q Fourier transform is carried out, and the expression of the Fourier transform in a frequency domain is obtained as follows:
F q (ω) is the frequency spectrum of the deterministic signal;
n is the number of transmitted symbol information;
j is an imaginary symbol;
ω 0 is the frequency of the OAM microwave quantum;
ω represents a signal frequency variable;
the Sa function is a non-normalized sampling function;
the delta function is an impact function;
t is the length of time taken to transmit each symbol of information.
Given a particular set of sinusoidal initial phases, the deterministic signal spectrum is now as shown in fig. 6.
The spectral energy of the determined signal in the case of phase discontinuity is shown in fig. 6. As the variance of the difference in phase between each symbol becomes smaller (synchronicity becomes stronger), the spectral bandwidth at the full spectral energy maximum minus the 3dB difference also becomes smaller.
During actual transmission, the phase change is random,
for random variables, the power spectral density of the random signal is studied at this time.
The autocorrelation function of the signal received at the receiving end is:
R r (τ) represents the autocorrelation function of the received signal, T 1 For the duration of an ultra-narrow band signal, S r (t) is a received signal with time t as variable, and τ is a determination signal S r (t) and time-shifted copy S r (t-τ) of the time difference.
Fourier transforming the autocorrelation function to the power spectral density of the signal,
f r (omega) power spectral density, R, of the received signal r (τ) autocorrelation function of the received signal.
The power spectral density of the random signal in the case of phase discontinuity is shown in fig. 7. As the variance of the difference in phase between each symbol becomes smaller (synchronization becomes stronger), the bandwidth of the power spectral density of the entire power spectral density maximum point minus the 3dB difference becomes smaller.
When the total power is constant, assuming that the entire signal is a periodically repeated signal having two symbols and the amplitude ratio of the former symbol and the latter symbol is k, the relationship between the signal bandwidth and the variance of the difference in phase between the symbols is as shown in fig. 8. It can be seen that the larger the phase deviation, the larger the frequency bandwidth, and that as the phase deviation increases to some extent, the frequency bandwidths caused by different amplitude ratios k do not differ much.
To show the variation of channel capacity of ultra-narrowband communication systems compared to conventional communication systems. The channel capacity of the ultra-narrow band communication system varies with the signal-to-noise ratio when different phase offsets are given as shown in fig. 9, and it can be seen from fig. 9 that the smaller the phase offset, the faster the channel capacity increases with the increase of the signal-to-noise ratio. When σ is pi/2, it is a curve of channel capacity along with the variation of signal-to-noise ratio in QPSK modulation in conventional communication system, and when σ is pi/500, the channel capacity is obviously faster than σ 3 pi/1000, σ pi/100, σ pi/10, and σ pi/2, and the channel capacity increases with the increase of signal-to-noise ratio.
Although a specific embodiment of the present invention has been described above, it should be understood that the above-described embodiment is illustrative, and not restrictive, and that various changes, modifications, substitutions, and alterations can be made herein by those skilled in the art without departing from the scope of the invention.
Claims (9)
1. An ultra-narrow-band communication transmission system of orbital angular momentum microwave quanta comprises a transmitting end and a receiving end, and is characterized in that,
the transmitting end includes:
the ultra-narrow band signal source comprises a signal excitation source and an OAM microwave quantum generation unit, wherein the signal excitation source is used for providing original excitation for the OAM microwave quantum generation unit;
the OAM microwave quantum generating unit is used for generating OAM microwave quanta in different modes;
the ultra-narrow band signal generation module comprises a mode combination selection unit, an OAM microwave quantum information keying unit and a mode switching position phase alignment unit, wherein the mode combination selection unit determines the mode form of an OAM microwave quantum in the transmission time of transmitting each code element;
the OAM microwave quantum information keying unit switches the OAM microwave quantum corresponding to the current information in a mode form in a mode keying mode, and loads the original information to the OAM microwave quantum in different mode forms;
the mode switching position phase alignment unit is used for reducing a phase difference value during OAM microwave quantum mode switching to form an ultra-narrow band signal;
the receiving end includes:
the system comprises an ultra-narrow band signal receiving module, a receiving end bit synchronization module and a data processing module, wherein the ultra-narrow band signal receiving module is used for receiving an ultra-narrow band signal carrying information in an OAM microwave quantum form and realizing signal phase synchronization at the receiving end, the ultra-narrow band signal receiving module comprises an OAM microwave quantum receiving device and the receiving end bit synchronization module, the OAM microwave quantum receiving device is used for receiving the ultra-narrow band signal carrying information in the OAM microwave quantum form, the received OAM microwave quantum passes through the receiving end bit synchronization module and then becomes a signal form which can be identified or sorted, the identification refers to identifying diffraction patterns of the OAM microwave quantum carrying the ultra-narrow band signal and determining the mode of the OAM microwave quantum, and the sorting is to determine the mode of the OAM microwave quantum through an OAM sorter;
the ultra-narrow band signal recovery and analysis module is used for detecting the OAM microwave quantum received by the ultra-narrow band signal receiving module, determining the OAM mode corresponding to each ultra-narrow band signal and demodulating the signal to recover the original information,
the ultra-narrow band signal recovery and analysis module comprises a signal demodulation recovery unit, an OAM microwave quantum detection unit and a spectrum analysis unit, wherein the OAM microwave quantum detection unit adopts an identification or sorting thought to identify an OAM mode in a signal so as to recover transmission information, the signal demodulation recovery unit is used for demodulating the information subjected to identification or sorting mode form by the OAM microwave quantum detection unit so as to recover original information, and the spectrum analysis unit is used for analyzing the received original information in a frequency domain so as to obtain the occupation condition of the signal on spectrum resources.
2. The ultra-narrow band communication transmission system of orbital angular momentum microwave quanta according to claim 1,
the OAM microwave quanta of different modes generated by the OAM microwave quanta generating unit are sent by the same waveguide antenna or are respectively transmitted by a plurality of waveguide antennas.
3. The ultra-narrow band communication transmission system of orbital angular momentum microwave quanta according to claim 2,
the OAM microwave quanta are all-band OAM microwave quanta.
4. The ultra-narrow band communication transmission system of orbital angular momentum microwave quanta according to claim 2, wherein the modal forms include a single mode and a plurality of modes in a mode combination, the mode combination being a combination of at least two modes.
5. The ultra-narrow band communication transmission system of orbital angular momentum microwave quanta according to claim 1,
in the communication transmission system, there are M transmitting terminals, and the received signals of the OAM transmission process of G receiving terminals are represented as:
y＝H OAM x+n
wherein,
g is more than or equal to 1 and less than or equal to G;
a set of representative signal vectors;
g represents the g-th transmitting terminal;
m represents the mth receiving end;
6. The ultra-narrow band communication transmission system of orbital angular momentum microwave quanta according to claim 1,
the transmitting end transmits a code element information by using the period of a sine signal, and the receiving end receives a total signal S r Comprises the following steps:
wherein the mathematical form of g (t) is represented as follows:
A n is the amplitude value of the signal for each time length;
t represents the total transmission time;
n represents an nth OAM modality;
ω 0 frequency of the OAM microwave quantum;
t is the time length occupied by transmitting each symbol information;
7. The ultra-narrow band communication transmission system of orbital angular momentum microwave quanta according to claim 1,
the transmitting terminal generates OAM microwave quanta with the same phase and different modes by using a method of generating OAM with different modes by using homologous excitation, transmits the OAM microwave quanta with original information, and calculates the placement position of each OAM microwave quantum generating unit to ensure that the distances from each OAM microwave quantum generating unit to the transmitting antenna are equal, so that the phases of the OAM microwave quanta with different modes are aligned;
after the receiving end receives the signal, the bit synchronization method is adopted to realize the bit synchronization of the ultra-narrow band signal of the receiving end.
8. The ultra-narrow band communication transmission system of orbital angular momentum microwave quanta according to claim 5,
sinusoidal initial phase of each symbol information
In response to the signal having been received,
represents the initial phase of the nth symbol information in the received signal, at this time
Is a determined value, S r Becomes a deterministic signal S q For deterministic signals S q Performing Fourier transform to obtain an expression of the Fourier transform in a frequency domain as follows:
F q (ω) is the frequency spectrum of the deterministic signal;
n is the nth symbol information of the transmission;
j is an imaginary symbol;
ω 0 is the frequency of the OAM microwave quantum;
ω represents a signal frequency variable;
the Sa function is a non-normalized sampling function;
the delta function is an impact function;
t is the time length occupied by transmitting each code element information;
n denotes the transmitted N symbol information.
9. An ultra-narrow band communication information transmission method of orbital angular momentum microwave quanta is characterized by comprising the following steps:
OAM microwave quanta with the same phase and different modes are generated in a homologous excitation mode;
selecting a mode form to transmit information by using a mode combination selection unit, wherein the mode form comprises a single mode and a plurality of modes in a mode combination, and the mode combination refers to a combination of at least two modes;
switching the OAM microwave quanta of the current information corresponding to the mode in a mode keying mode, and loading the original information to the OAM microwave quanta in different mode forms so as to form an ultra-narrow band signal;
after an OAM microwave quantum carrying an ultra-narrow band signal irradiates an OAM microwave quantum receiving device, the microwave quantum becomes a signal form capable of identifying an OAM microwave quantum mode through a diffraction pattern or an OAM sorter under the combined action of an auxiliary facility of the receiving device and a receiving end bit synchronization module;
determining the modal form of the OAM microwave quantum by adopting a diffraction pattern recognition or OAM sorter;
and placing the transmitting end according to the calculation of the positions of different OAM microwave quantum generating units, further aligning the phases of different modes of OAM microwave quantum switching positions, and demodulating signals after carrying out bit synchronization on the receiving end so as to recover original information.
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