Laser communication modulation method and system

Abstract

The embodiment of the invention provides a laser communication modulation method and system, which can solve the technical problem of poor free space laser communication sensitivity under the condition of extremely low signal-to-noise ratio. The method comprises the following steps: performing polarization selection modulation on a coding sequence to obtain multiple groups of linearly polarized light pulses; and sending each group of linearly polarized light pulses to different photon detectors through different channels to obtain a first photon count and a second photon count. And obtaining a log-likelihood ratio through soft decision according to the first photon count and the second photon count of all groups of linearly polarized light pulses. And an original information prediction value is obtained through channel decoding. Thus, compared with PPM-PC, better communication sensitivity and stronger background noise resistance can be obtained by performing polarization selection pulse position modulation and a corresponding demodulation mode. And the optical signals in different polarization states respectively bear different data, and then are respectively transmitted in sequence, so that the transmission rate is high.

Description

Technical Field

[0001] The present application relates to the technical field of space laser communication, and in particular, to a laser communication modulation method and system thereof. Background Art

[0002] Free space laser communication is a technology that uses laser beams to transmit information in free space (such as the atmosphere, deep space), and has the advantages of high transmission rate, strong anti-interference ability, good confidentiality, etc. This technology is widely used in ultra-long-distance communication scenarios, such as deep space exploration, satellite communication, etc. In deep space laser communication, due to the extremely long transmission distance and severe signal attenuation, the optical signal intensity at the receiving end is extremely weak, so extremely high requirements are imposed on the sensitivity of the communication system. In order to achieve reliable communication under the premise of meeting the target transmission rate and bit error rate, it is necessary to adopt a signal modulation method with high energy efficiency and a receiver technology with high sensitivity.

[0003] Currently, deep space laser communication systems usually adopt a communication system that combines pulse position modulation (PPM) signals with single-photon detectors, abbreviated as the PPM-PC system. In this system, data is encoded to generate a coded sequence, and the information is mapped to the positions of optical pulses through PPM modulation. The receiving end uses a single-photon detector to detect the number of photons in each time slot, generates a photon counting sequence, and calculates the log-likelihood ratio (LLR) of each PPM symbol based on the photon count. Finally, the original data is recovered by decoding using the LLR. The Poisson channel is a commonly used channel model in deep space laser communication, which can effectively describe the statistical characteristics of photon counting.

[0004] However, the existing PPM-PC system still has certain limitations in deep space laser communication. Due to the extremely long communication distance and extremely low received signal intensity in deep space, the detection efficiency and noise characteristics of single-photon detectors have a significant impact on the system performance. In addition, although PPM modulation has high energy efficiency, its spectral utilization rate is low, which limits the further improvement of the communication rate. Summary of the Invention

[0005] The embodiments of the present application provide a laser communication modulation method and system thereof, which can solve the technical problem of poor sensitivity of free space laser communication under extremely low signal-to-noise ratio conditions.

[0006] To achieve the above object, the embodiments of the present application adopt the following technical solutions:

[0007] In a first aspect, an embodiment of the present application provides a laser communication modulation method, which includes: performing channel coding on original information to obtain a coding sequence; the coding sequence includes polarization angle information and polarization position information; performing polarization selection modulation on the coding sequence to obtain multiple groups of linearly polarized light pulses; when the polarization angle information is a first eigenvalue, the linearly polarized light pulses include a first pulse polarization; when the polarization angle information is a second eigenvalue, the linearly polarized light pulses include a second pulse polarization; the first pulse polarization and the second pulse polarization are orthogonal; the linearly polarized light pulses further include a light pulse position; the light pulse position is determined by the polarization position information; simultaneously sending each group of linearly polarized light pulses to a first photon detector and a second photon detector to obtain a first photon count and a second photon count; the first photon count is obtained when the linearly polarized light pulses pass through the first photon detector; the second photon count is obtained when the linearly polarized light pulses pass through the second photon detector; according to the first photon count and the second photon count of multiple groups of linearly polarized light pulses, a log-likelihood ratio is obtained through soft decision; according to the log-likelihood ratio, an original information prediction value is obtained through channel decoding.

[0008] Based on the above description of the laser communication modulation method provided by the embodiment of the present application, it can be seen that the laser communication modulation method includes performing polarization selection modulation on the coding sequence to obtain multiple groups of linearly polarized light pulses. Sending each group of linearly polarized light pulses through different channels to different photon detectors to obtain a first photon count and a second photon count. According to the first photon count and the second photon count of all groups of linearly polarized light pulses, a log-likelihood ratio is obtained through soft decision. Then, an original information prediction value is obtained through channel decoding. In this way, by performing polarization selection pulse position modulation and its corresponding demodulation method, compared with PPM-PC, better communication sensitivity and stronger anti-background noise ability can be obtained.

[0009] Moreover, optical signals with different polarization states carry different data respectively and are then transmitted sequentially, with a high transmission rate.

[0010] In a feasible implementation manner of the first aspect, when performing the step of simultaneously sending each group of linearly polarized light pulses to a first photon detector and a second photon detector to obtain a first photon count and a second photon count, the multiple groups of linearly polarized light pulses include a first linearly polarized light pulse and a second linearly polarized light pulse, and the laser communication modulation method further includes: at a first moment, only sending the first linearly polarized light pulse to the first photon detector and the second photon detector to obtain the first photon count and the second photon count at the first moment; at a second moment, only sending the second linearly polarized light pulse to the first photon detector and the second photon detector to obtain the first photon count and the second photon count at the second moment; where the first moment and the second moment occur successively, the first moment is the previous moment, and the second moment is the subsequent moment.

[0011] In a feasible implementation of the first aspect, the laser communication modulation method further includes: simultaneously sending each group of linearly polarized light pulses to a first photon detector and a second photon detector through a polarization beam splitter.

[0012] In a feasible implementation of the first aspect, the transmission model of the linearly polarized light pulse is a Poisson channel model.

[0013] In a feasible implementation of the first aspect, the polarization selection modulation is serial concatenated pulse position modulation.

[0014] In a feasible implementation of the first aspect, the first eigenvalue is 0 bit; the second eigenvalue is 1 bit.

[0015] In a feasible implementation of the first aspect, when performing the step of obtaining the log-likelihood ratio through soft decision according to the first photon count and the second photon count; the laser communication modulation method further includes: obtaining a photon sequence according to the first photon count and the second photon count; confirming each symbol value of the coding sequence; calculating the log-likelihood ratio of each symbol value according to the photon sequence.

[0016] In a feasible implementation of the first aspect, the first photon count includes multiple elements; the second photon count includes multiple elements; each element of the first photon count in the photon sequence is located before each element of the second photon count; or, each element of the first photon count in the photon sequence is located after each element of the second photon count; or, the photon sequence is an interleaved sequence formed by alternately arranging each element of the first photon count and each element of the second photon count in turn.

[0017] In a feasible implementation of the first aspect, when the bit value of the coding sequence is m, the symbol length of the polarization selection modulation is 2 m then the total number of decoder time slots for channel decoding is 2 m+1 ; where m is a positive integer.

[0018] In a second aspect, an embodiment of the present application provides a laser communication modulation system, which includes: at least one processor; a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the method provided in the first aspect.

[0019] The laser communication modulation system performs polarization - selective modulation on the encoded sequence by implementing the method provided in the first aspect. The linearly - polarized light pulses corresponding to different pulse polarizations are sent through different channels to different photon detectors, obtaining the first photon count and the second photon count. According to the first photon count and the second photon count, through soft decision, the log - likelihood ratio is obtained. Then, through channel decoding, the predicted value of the original information is obtained. In this way, by performing polarization - selective pulse - position modulation and its corresponding demodulation method, compared with PPM - PC, better communication sensitivity and stronger anti - background - noise ability can be obtained.

[0020] In a third aspect, an embodiment of the present application provides a computer - readable medium, on which computer program instructions are stored. The computer program instructions can be executed by a processor to implement the method provided in the first aspect.

[0021] The computer program instructions in the computer - readable medium perform polarization - selective modulation on the encoded sequence by implementing the method provided in the first aspect. The linearly - polarized light pulses corresponding to different pulse polarizations are sent through different channels to different photon detectors, obtaining the first photon count and the second photon count. According to the first photon count and the second photon count, through soft decision, the log - likelihood ratio is obtained. Then, through channel decoding, the predicted value of the original information is obtained. In this way, by performing polarization - selective pulse - position modulation and its corresponding demodulation method, compared with PPM - PC, better communication sensitivity and stronger anti - background - noise ability can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of a laser communication modulation system provided by an embodiment of the present application;

[0023] Figure 2 It is a schematic flowchart of a laser communication modulation method provided by an embodiment of the present application;

[0024] Figure 3a It is a schematic flowchart of a laser communication modulation method in the related art;

[0025] Figure 3b It is a program block of a laser communication modulation method provided by an embodiment of the present application Figure 1 ;

[0026] Figure 4 It is a program block of a laser communication modulation method provided by an embodiment of the present application Figure 2 ;

[0027] Figure 5 It is the third program block diagram of a laser communication modulation method provided by an embodiment of the present application;

[0028] Figure 6Schematic diagram of the comparison of the bit error rates between the PPM-PC modulation method in the related art and the laser communication modulation method provided in the embodiments of the present application. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be described with reference to the accompanying drawings in the embodiments of the present invention. Among them, in the description of the embodiments of the present invention, unless otherwise specified, "a plurality of" means two or more than two. "At least one (piece)" or a similar expression thereof refers to any combination of these items, including any combination of a single item (piece) or a plurality of items (pieces). For example, at least one (piece) of a, b, or c may represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, c may be single or multiple.

[0030] In addition, in order to clearly describe the technical solutions in the embodiments of the present invention, in the embodiments of the present invention, terms such as "first" and "second" are used to distinguish identical or similar items with basically the same functions and roles. Those skilled in the art can understand that terms such as "first" and "second" do not limit the quantity and execution order, and "first" and "second" do not necessarily mean different. At the same time, in the embodiments of the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present invention should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, using words such as "exemplary" or "for example" is intended to present relevant concepts in a specific way for easy understanding.

[0031] The principles and features of the present application are described below. The examples given are only used to explain the present application and are not used to limit the scope of the present application.

[0032] Pulse Position Modulation (PPM) uses the relative position of a single pulse within a period of time to transmit information. In an M-bit PPM (i.e., M-PPM) modulation system, also known as m-order PPM, m = log2M > 1. Every m-bit information c = [c1, c2,..., c m , is mapped to a PPM symbol x. The transmission of a PPM symbol requires M time slots (unit time). In each time slot of each symbol, only one time slot transmits an optical pulse. The position where the optical pulse appears represents the value of c. Therefore, x can be written as an M-bit pulse sequence x = [x1, x2,..., x M . Among them, x i={0, 1}, where 0 represents no optical signal in the i-th time slot of the symbol, and 1 represents an optical signal in the i-th time slot of the symbol. For the one-to-one mapping relationship between the value of c and the optical pulse position, multiple mapping schemes can be used, such as natural order mapping, Gray mapping, and anti-Gray mapping.

[0033] Linearly polarized light, also known as plane polarized light, refers to light in which the orientation of the light vector (electric field strength vector) in space remains fixed, and the locus traced by its endpoint in space is a straight line. Its light vector vibrates only along a specific direction (polarization angle) and has no vibration component in the direction perpendicular to it.

[0034] The embodiment of the present application provides a laser communication modulation method, which is applicable to various free-space laser communication scenarios, especially free-space laser communication over ultra-long distances. For example, deep space laser communication. In this scenario, there is an extremely high demand for the sensitivity of communication, that is, under the premise of meeting the target transmission rate and bit error rate, the lower the required received signal strength, the better.

[0035] It can be understood that in the laser communication modulation method provided by the embodiment of the present application, the polarization selection PPM modulation can use any channel coding and decoding scheme designed for PPM modulation.

[0036] Taking the application of the serial concatenated pulse position modulation (SCPPM) coding scheme in the CCSDS (Consultative Committee for Space Data Systems) standard in the polarization selection PPM modulation as an example, the following is a detailed description.

[0037] The embodiment of the present application provides a laser communication modulation system capable of executing the laser communication modulation method provided by the embodiment of the present application. Figure 1 It is a schematic structural diagram of a laser communication modulation system provided by the embodiment of the present application.

[0038] As Figure 1 shown, the laser communication modulation system 001 includes at least one processor 011 and a memory 012 communicatively connected to the at least one processor; wherein, the memory 012 stores instructions executable by the at least one processor 011, and the instructions are executed by the at least one processor 011 so that the at least one processor 011 can execute the laser communication modulation method provided by the embodiment of the present application.

[0039] Figure 2 It is a schematic flowchart of a laser communication modulation method provided by the embodiment of the present application. As Figure 2 shown, in some embodiments, the laser communication modulation method includes the following steps:

[0040] S1. Channel-encode the original information to obtain a coded sequence.

[0041] The original information u is encoded to obtain a coded sequence c. As Figure 4 shown, at the transmitting end, the data u undergoes CRC encoding, convolutional encoding, interleaving, and accumulator encoding to obtain the coded sequence c. Exemplarily, when the original information is 100 bits, the coded sequence obtained through channel encoding can be 200 bits.

[0042] The coded sequence includes polarization angle information and polarization position information.

[0043] S2. Perform polarization selection modulation on the coded sequence to obtain multiple groups of linearly polarized light pulses.

[0044] In some embodiments, according to a preset number of bits, for example, it can be 5 bits, perform polarization selection modulation on the coded sequence to obtain multiple groups of linearly polarized light pulses. Exemplarily, when the coded sequence is 200 bits, 40 groups of linearly polarized light pulses are obtained according to the preset number of bits 5.

[0045] The polarization selection modulation will be described in detail below.

[0046] One polarization selection PPM symbol is modulated by m + 1 bits. Among them, m bits determine the position of the linearly polarized light pulse (the same as the method for determining the pulse position in PPM modulation), and the other 1 bit determines the polarization angle of the linearly polarized light pulse. The total length of one polarization selection PPM symbol is M = 2 m time slots.

[0047] Exemplarily, the modulation input bits are c = [c0, c1, …, c m . If c0 = 0, the polarization of the linearly polarized light pulse is 0°. If c0 = 1, the polarization of the linearly polarized light pulse is 90°. The position of the linearly polarized light pulse is determined by [c1, …, c m , and its mapping relationship is the same as the mapping relationship of M-PPM.

[0048] When the polarization angle information is the first eigenvalue, the linearly polarized light pulse includes the first pulse polarization. In some embodiments, the first eigenvalue is 0 bit.

[0049] When the polarization angle information is the second eigenvalue, the linearly polarized light pulse includes the second pulse polarization. In some embodiments, the second eigenvalue is 1 bit.

[0050] Among them, the polarization of the first pulse and the polarization of the second pulse are orthogonal. There are various ways to implement the polarization of the first pulse and the polarization of the second pulse. For example, in some embodiments, the polarization of the first pulse is 0°, and the polarization of the second pulse is 90°. For another example, in some other embodiments, the polarization of the first pulse is 45°, and the polarization of the second pulse is 135°. In this way, the polarization state (polarization angle) of a pair of orthogonal linearly polarized lasers is used to modulate information, ensuring high confidentiality of communication.

[0051] Taking the polarization of the first pulse as 0° and the polarization of the second pulse as 90° as an example, a detailed description will be given below.

[0052] The linearly polarized light pulse also includes the position of the optical pulse. The position of the optical pulse is determined by the polarization position information.

[0053] In some embodiments, PPM uses natural order mapping.

[0054] S3. Simultaneously send each group of linearly polarized light pulses to the first photon detector and the second photon detector to obtain the first photon count and the second photon count.

[0055] As Figure 3b shown, the first photon count is obtained when the linearly polarized light pulse passes through the first photon detector. In some embodiments, the first photon detector detects the linearly polarized light pulse with a polarization of 0°, and obtains the first photon count y0 = [y1, y2, …, y M . Among them, M = 2 m .

[0056] The second photon count is obtained when the linearly polarized light pulse passes through the second photon detector. In some embodiments, the second photon detector detects the linearly polarized light pulse with a polarization of 90°, and obtains the second photon count y1 = [y M+1 , y M+2 , …, y 2M . Among them, M = 2 m .

[0057] In some embodiments, when performing step S3, the laser communication modulation method further includes the following steps:

[0058] S301. At the first moment, send a linearly polarized light pulse to the receiving end to obtain the first photon count and the second photon count at the first moment.

[0059] S302. At the second moment, send another linearly polarized light pulse other than the linearly polarized light pulse sent in step S301 to the receiving end to obtain the first photon count and the second photon count at the second moment.

[0060] S303. At the third moment, send linearly polarized light pulses other than those sent in steps S301 and S302 to the receiving end to obtain the first photon count and the second photon count at the third moment.

[0061] Among them, the first moment and the second moment occur successively, the first moment is the previous moment, and the second moment is the subsequent moment; the second moment and the third moment occur successively, the second moment is the previous moment, and the third moment is the subsequent moment.

[0062] And so on, to complete the transmission of multiple groups of linearly polarized light pulses. It can be understood that there is only one polarization angle for the linearly polarized light pulses sent at each moment, and this polarization angle is only determined by the information sent at the current moment and has nothing to do with the information sent at other moments.

[0063] In one implementation, when performing step S3, the linearly polarized light pulses include the first linearly polarized light pulse and the second linearly polarized light pulse, and the laser communication modulation method further includes the following steps:

[0064] S311. At the first moment, only send the first linearly polarized light pulse to the first photon detector and the second photon detector to obtain the first photon count and the second photon count at the first moment.

[0065] S312. At the second moment, only send the second linearly polarized light pulse to the first photon detector and the second photon detector to obtain the first photon count and the second photon count at the second moment.

[0066] Among them, the first moment and the second moment occur successively, the first moment is the previous moment, and the second moment is the subsequent moment.

[0067] In some embodiments, when performing step S3, the laser communication modulation method further includes the following steps: Through a polarization beam splitter, simultaneously send each group of linearly polarized light pulses to the first photon detector and the second photon detector. The polarization beam splitter decomposes the incident light into different output channels according to its polarization direction. For an ideal 0° and 90° polarization beam splitter, it will output the horizontally polarized (0°) light along one output channel and the vertically polarized (90°) light along another output channel. For light with other polarization states, it will be decomposed according to its components in the horizontal and vertical directions. That is, the probability that a photon with a polarization of φ degrees is recognized as 0° polarized is cos 2 (φ), and the probability that it is recognized as 90° polarized is sin 2(φ). The probability that an actual 0° / 90° polarization beam splitter misidentifies a photon polarized at 0° as a photon polarized at 90° (or vice versa) can be made much less than 0.001 and can be neglected. For natural light (assuming the background noise in the deep space communication scenario is natural light), the probability that photons enter the 0° channel and the 90° channel is both 1 / 2.

[0068] Thus, at the receiving end, the optical signal is first input into the polarization beam splitter, and the two output channels of the polarization beam splitter will respectively output linearly polarized light pulses polarized at 0° and linearly polarized light pulses polarized at 90°.

[0069] In some embodiments, the transmission model of the linearly polarized light pulse can be a Poisson channel model.

[0070] It can be understood that the transmission model of the linearly polarized light pulse can also be other models, which are not limited in this application.

[0071] S4. According to the first photon count and the second photon count of multiple groups of linearly polarized light pulses, through soft decision, the log-likelihood ratio is obtained.

[0072] Calculate the log-likelihood ratio (LLR) of each symbol according to y = [y0 y1]. It can be understood that at each moment, the process from the polarization selection modulation at the transmitting end to the LLR calculation at the receiving end is related to the m + 1 encoded bits transmitted at this moment and is independent of the encoded bits transmitted at other moments.

[0073] In some embodiments, when performing step S4, the laser communication modulation method further includes:

[0074] S41. According to the first photon count and the second photon count, a photon sequence is obtained.

[0075] In some embodiments, the first photon count includes multiple elements. The second photon count includes multiple elements. Each element of the first photon count in the photon sequence is located before each element of the second photon count. Exemplarily, y = [y0 y1] = [y1, y2, …, y 2M .

[0076] In other embodiments, the first photon count includes multiple elements. The second photon count includes multiple elements. Each element of the first photon count in the photon sequence is located after each element of the second photon count. Exemplarily, y = [y0 y1] = [y M+1 , y M+2 , y 2M , …, y1, y2, …, y M .

[0077] In still other embodiments, the first photon count includes a plurality of elements. The second photon count includes a plurality of elements. The photon sequence is an interleaved sequence formed by alternately arranging each element of the first photon count and each element of the second photon count in sequence. Exemplarily, y = [y0 y1] = [y1, y M+1 , y2, y M+2 , …, y M , y 2M .

[0078] S42. Confirm the symbol values of each symbol in the coding sequence.

[0079] Exemplarily, for the input bits c = [c0, c1, …, c m , the calculation formula for the corresponding symbol value is:

[0080]

[0081] It can be understood that this formula obtains the decimal value corresponding to each of c0, c1, …, c m in the sequence.

[0082] S43. Calculate the log-likelihood ratio of each symbol value according to the photon sequence.

[0083] Calculate the log-likelihood ratio (LLR) of each symbol according to the photon sequence y = [y0 y1].[[]END]]

[0084] Exemplarily, according to the photon count sequences y = [y1, y2, …, y 2M of two channels, calculate the symbol log-likelihood ratio when the transmitted symbols C are 0, 1, …, 2M - 1 respectively, that is, the symbol LLR.

[0085] Among them, the symbol LLR is defined as:

[0086]

[0087] Considering the Poisson channel model, let n s represent the normalized intensity of the optical pulse (the average number of signal photons per pulse time slot), and n b represent the normalized intensity of the background noise (the average number of noise photons per time slot).

[0088] In some embodiments, the symbol LLR of the polarization-selective PPM modulation signal can be calculated using Γ C (y) = Y c+1 · log(1 + 2n s / n b ).

[0089] It can be understood that the calculation formula of the symbol LLR in the actual system may be different. For example, it may directly use ΓC Γ(y) = y c+1 or Γ C Γ(y)=(y C+1 - y0)·log(1 + 2n s / n b ) is calculated.

[0090] It can be understood that after the receiving end receives multiple groups of linearly polarized light pulses, LLR (log-likelihood ratio) calculation is performed according to the receiving order, so as to obtain the corresponding LLR calculation results. It can be understood that no matter in what order these 40 groups of pulses are sent, they must be input in the order of 1 to 40 in this step of channel decoding. The order of LLR calculation has no influence on the system and can be the same as or different from the sending order.

[0091] S5. According to the log-likelihood ratio, the predicted value of the original information is obtained through channel decoding.

[0092] In some embodiments, when the bit value of the coding sequence is m, the symbol length of polarization selection modulation is 2 m , then the total number of decoder time slots for channel decoding is 2 m+1 . Where m is a positive integer.

[0093] Exemplarily, for a polarization selection PPM modulation communication system with a symbol length of M = 2 m time slots, a coding and decoding scheme designed for 2M-PPM modulation needs to be used. Assume that the symbol length of the polarization selection PPM modulation system is 16, then the receiving end needs to use an SCPPM decoder designed for 32-PPM instead of a decoder designed for 16-PPM. It can be understood that no adjustment is required to the internal structure of the coding and decoder.

[0094] As Figure 5 shown, every m + 1 bits in the coding sequence c are modulated onto a polarization selection PPM symbol. At the receiving end, the symbol LLR is input into the SCPPM decoder, and the decoder obtains the final decoding result through iterative decoding between the convolutional code decoder and the APPM decoder.

[0095] It can be understood that there are various different decoding algorithms for SCPPM. Only one algorithm is given here as an example, which does not constitute a limitation on the decoding algorithm.

[0096] In the embodiments of the present application, the coding sequence is subjected to polarization selection modulation to obtain multiple groups of linearly polarized light pulses. Each group of linearly polarized light pulses is sent to different photon detectors through different channels to obtain the first photon count and the second photon count. According to the first photon count and the second photon count of all groups of linearly polarized light pulses, the log-likelihood ratio is obtained through soft decision. Then, through channel decoding, the predicted value of the original information is obtained. In this way, by performing polarization selection pulse position modulation and its corresponding demodulation method, compared with Figure 3a the PPM-PC shown, better communication sensitivity and stronger anti-background noise ability can be obtained.

[0097] As Figure 6 shown, when the SCPPM coding scheme is also adopted and the symbol length M = 2 m is the same, the laser communication modulation method provided by the embodiments of the present application enables a higher transmission rate through polarization selection PPM modulation than that through PPM-PC system modulation in the related art. Exemplarily, the transmission efficiency of the polarization selection PPM provided by the embodiments of the present application is (m + 1) / M bits per symbol, and the transmission rate of PPM-PC is m / M bits per symbol. In addition, in terms of the system bit error rate, the receiving sensitivity of the polarization selection PPM modulation provided by the embodiments of the present application has increased significantly. Exemplarily, the polarization selection PPM modulation requires a lower signal intensity to achieve a -6 bit error rate below 10

[0098] Based on the same inventive concept, in the embodiments of the present application, a laser communication modulation system is further provided. The method corresponding to the laser communication modulation system may be the laser communication modulation method in the foregoing embodiments, and the principle of solving problems is similar to that of the method. The laser communication modulation system provided by the embodiments of the present application includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the methods and / or technical solutions of multiple foregoing embodiments of the present application.

[0099] Another embodiment of the present application further provides a computer-readable storage medium, on which computer program instructions are stored, and the computer program instructions can be executed by a processor to implement the methods and / or technical solutions of any one or more foregoing embodiments of the present application.

[0100] Specifically, this embodiment may employ any combination of one or more computer-readable media. The computer-readable media can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the above. More specific examples (a non-exhaustive list) of the computer-readable storage medium include: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this document, the computer-readable storage medium can be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0101] The computer-readable signal medium can include a data signal propagated in a baseband or as part of a carrier wave, which carries computer-readable program code. Such a propagated data signal can take various forms, including - but not limited to - an electromagnetic signal, an optical signal, or any suitable combination of the above. The computer-readable signal medium can also be any computer-readable medium other than the computer-readable storage medium, which can send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, apparatus, or device.

[0102] The program code contained on the computer-readable medium can be transmitted using any appropriate medium, including - but not limited to - wireless, wire, optical fiber cable, RF, etc., or any suitable combination of the above.

[0103] The computer program code for performing the operations of this application can be written in one or more programming languages or combinations thereof. The programming languages include object-oriented programming languages such as Java, Smalltalk, C++, and also include conventional procedural programming languages such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, executed as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or can be connected to an external computer (e.g., by using an Internet service provider to connect through the Internet).

[0104] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of devices, methods, and computer program products according to various embodiments of the present application. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a portion of code that contains one or more executable instructions for implementing a specified logical function. It should also be noted that, in some alternative implementations, the functions noted in the blocks may occur in a different order than that noted in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, as well as combinations of blocks in the block diagram and / or flowchart, may be implemented by a dedicated hardware-based system that performs the specified functions or operations, or by a combination of dedicated hardware and computer instructions.

[0105] Those skilled in the art can clearly understand that, for the sake of convenience and brevity of description, the specific working processes of the systems, devices, and units described above can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0106] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units or page components may be combined or integrated into another system, or some features may be ignored or not executed. Another point is that the couplings or direct couplings or communication connections shown or discussed among each other may be through some interfaces, and the indirect couplings or communication connections of devices or units may be in electrical, mechanical, or other forms.

[0107] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0108] In addition, the functional units in the various embodiments of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated units may be implemented in the form of hardware, or in the form of a combination of hardware and software functional units.

[0109] The integrated unit implemented in the form of software functional units can be stored in a computer-readable storage medium. The above software functional units are stored in a storage medium and include several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) or a processor to execute some steps of the methods described in various embodiments of the present application. The foregoing storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of various embodiments of the present application.

[0111] In addition, it is obvious that the word "including" does not exclude other units or steps, and the singular does not exclude the plural. The multiple units or devices stated in the apparatus claims can also be implemented by one unit or device through software or hardware. The terms first, second, etc. are used to denote names and do not denote any particular order.

Claims

1. A laser communication modulation method, characterized in that, Including: Performing channel coding on the original information to obtain a coded sequence; the coded sequence includes polarization angle information and polarization position information; Performing polarization selection modulation on the coded sequence to obtain multiple groups of linearly polarized light pulses; when the polarization angle information is a first eigenvalue, the linearly polarized light pulses include a first pulse polarization; When the polarization angle information is a second eigenvalue, the linearly polarized light pulses include a second pulse polarization; the first pulse polarization and the second pulse polarization are orthogonal; the linearly polarized light pulses further include a light pulse position; the light pulse position is determined by the polarization position information; Simultaneously sending each group of the linearly polarized light pulses to a first photon detector and a second photon detector to obtain a first photon count and a second photon count; the first photon count is obtained when the linearly polarized light pulses pass through the first photon detector; the second photon count is obtained when the linearly polarized light pulses pass through the second photon detector; Obtaining a log-likelihood ratio through soft decision according to the first photon count and the second photon count of the multiple groups of linearly polarized light pulses; Obtaining a predicted value of the original information through channel decoding according to the log-likelihood ratio.

2. The laser communication modulation method according to claim 1, wherein When performing the step of simultaneously sending each group of the linearly polarized light pulses to the first photon detector and the second photon detector to obtain the first photon count and the second photon count, the multiple groups of linearly polarized light pulses include a first linearly polarized light pulse and a second linearly polarized light pulse, and the laser communication modulation method further includes: At a first moment, only sending the first linearly polarized light pulse to the first photon detector and the second photon detector to obtain the first photon count and the second photon count at the first moment; At a second moment, only sending the second linearly polarized light pulse to the first photon detector and the second photon detector to obtain the first photon count and the second photon count at the second moment; wherein, the first moment and the second moment occur successively, the first moment is the previous moment, and the second moment is the subsequent moment.

3. The laser communication modulation method according to claim 1 or 2, characterized in that, The laser communication modulation method further includes: Simultaneously sending each group of the linearly polarized light pulses to the first photon detector and the second photon detector through a polarization beam splitter.

4. The laser communication modulation method according to claim 1 or 2, characterized in that The polarization selection modulation is serial concatenated pulse position modulation.

5. The laser communication modulation method according to claim 1 or 2, characterized in that, The first eigenvalue is 0 bit; the second eigenvalue is 1 bit.

6. The laser communication modulation method according to claim 1 or 2, characterized in that, When performing the step of obtaining the log-likelihood ratio through soft decision according to the first photon count and the second photon count; the laser communication modulation method further includes: Obtaining a photon sequence according to the first photon count and the second photon count; Confirming each symbol value of the coded sequence; Calculating the log-likelihood ratio of each symbol value according to the photon sequence.

7. The laser communication modulation method according to claim 6, characterized in that The first photon count includes a plurality of elements; the second photon count includes a plurality of elements; each element of the first photon count in the photon sequence is located before each element of the second photon count; or, each element of the first photon count in the photon sequence is located after each element of the second photon count; or, the photon sequence is an interleaved sequence formed by alternately arranging each element of the first photon count and each element of the second photon count in sequence.

8. The laser communication modulation method according to claim 1 or 2, characterized in that When the bit value of the coding sequence is m, the symbol length of the polarization selection modulation is 2 m , then the total number of decoder time slots for the channel decoding is 2 m+1 ; where m is a positive integer.

9. A laser communication modulation system, characterized in that, Comprising: At least one processor; A memory communicatively connected to the at least one processor; Wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the method according to any one of claims 1 to 8.

10. A computer-readable medium having computer program instructions stored thereon, the computer program instructions being executable by a processor to implement the method according to any one of claims 1 to 8.

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