Laser communication modulation method and system

Abstract

The embodiment of the present application provides 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. The method includes performing polarization-selective modulation on a coding sequence 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 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, the original information prediction value is obtained through channel decoding. In this way, polarization-selective pulse position modulation and its corresponding demodulation method can obtain better communication sensitivity and stronger resistance to background noise compared to PPM‑PC. In addition, optical signals in different polarization states carry different data respectively, and are then transmitted in sequence, with a high transmission rate.

Description

Technical Field

[0001] The present application relates to the field of space laser communication technology, 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 and deep space). It offers advantages such as high transmission rates, strong anti-interference capabilities, and excellent confidentiality. This technology is widely used in ultra-long-distance communication scenarios, such as deep space exploration and satellite communications. In deep-space laser communication, due to the extremely long transmission distances, severe signal attenuation, and extremely weak optical signal strength at the receiving end, extremely high requirements are placed on the sensitivity of the communication system. To achieve reliable communication while meeting the target transmission rate and bit error rate, highly energy-efficient signal modulation methods and highly sensitive receiver technologies are required.

[0003] Currently, deep-space laser communication systems typically employ a pulse position modulation (PPM) signal combined with a single-photon detector (SPD), often referred to as a PPM-PC system. In this system, data is encoded to generate a coded sequence, which is then mapped to the position of the optical pulse using PPM modulation. At the receiver, a SPD detects the number of photons per time slot, generating a photon count sequence. The log-log likelihood ratio (LLR) of each PPM symbol is calculated based on the photon counts, and the LLR is used for decoding to recover the original data. The Poisson channel is a commonly used channel model in deep-space laser communication and effectively describes the statistical characteristics of photon counting.

[0004] However, the existing PPM-PC system still has certain limitations in deep-space laser communications. Due to the extremely long distances and low received signal strength of deep-space communications, the detection efficiency and noise characteristics of single-photon detectors significantly impact system performance. Furthermore, while PPM modulation offers high energy efficiency, its spectrum utilization is low, limiting further increases in communication rates. 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 objectives, 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: channel encoding the original information to obtain a coding sequence; the coding sequence includes polarization angle information and polarization position information; polarization-selective modulation of 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 pulse includes a first pulse polarization; when the polarization angle information is a second eigenvalue, the linearly polarized light pulse includes a second pulse polarization; the first pulse polarization and the second pulse polarization are orthogonal; the linearly polarized light pulse also includes a light pulse position; the light pulse position is determined by the polarization position information; each group of linearly polarized light pulses is simultaneously sent 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 pulse passes through the first photon detector; the second photon count is obtained when the linearly polarized light pulse passes through the second photon detector; based on the first photon count and the second photon count of the multiple groups of linearly polarized light pulses, a log-likelihood ratio is obtained through soft decision; based on the log-likelihood ratio, a prediction value of the original information is obtained through channel decoding.

[0008] Based on the above description of the laser communication modulation method provided in the embodiment of the present application, it can be seen that the laser communication modulation method includes polarization-selective modulation of the coding sequence 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 a first photon count and a second photon count. Based on 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, the original information prediction value is obtained through channel decoding. In this way, polarization-selective pulse position modulation and its corresponding demodulation method can achieve better communication sensitivity and stronger resistance to background noise compared to PPM-PC.

[0009] Furthermore, optical signals in different polarization states carry different data respectively, and are then transmitted in sequence, resulting in a high transmission rate.

[0010] In a feasible implementation of the first aspect, when executing the step of simultaneously sending 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, the multiple groups of 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: 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 latter moment.

[0011] In a feasible implementation of the first aspect, the laser communication modulation method further includes: sending each group of linearly polarized light pulses to the first photon detector and the second photon detector simultaneously 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 manner of the first aspect, the polarization selective modulation is serial cascade 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 executing the step of obtaining a log-likelihood ratio through soft decision based on the first photon count and the second photon count; the laser communication modulation method also includes: obtaining a photon sequence based on the first photon count and the second photon count; confirming each symbol value of the coding sequence; and calculating the log-likelihood ratio of each symbol value based on 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 interspersed sequence formed by alternating the elements of the first photon count and the elements of the second photon count in sequence.

[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 selective 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 that can be executed 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 coding sequence by executing the method provided in the first aspect. Linearly polarized light pulses corresponding to different pulse polarizations are sent to different photon detectors through different channels to obtain a first photon count and a second photon count. A soft decision is made based on the first and second photon counts to obtain a log-likelihood ratio. Channel decoding is then performed to obtain a predicted value of the original information. In this way, polarization-selective pulse position modulation and its corresponding demodulation method can achieve better communication sensitivity and stronger resistance to background noise than PPM-PC.

[0020] In a third aspect, an embodiment of the present application provides a computer-readable medium having computer program instructions stored thereon, and 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 implement the method provided in the first aspect to perform polarization-selective modulation on the coding sequence. Linearly polarized light pulses corresponding to different pulse polarizations are sent to different photon detectors through different channels to obtain a first photon count and a second photon count. A log-likelihood ratio is obtained through soft decision making based on the first photon count and the second photon count. Channel decoding is then performed to obtain a predicted value of the original information. In this way, polarization-selective pulse position modulation and its corresponding demodulation method can achieve better communication sensitivity and stronger resistance to background noise than PPM-PC. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the structure of a laser communication modulation system provided in an embodiment of the present application;

[0023] Figure 2 A schematic diagram of a laser communication modulation method according to an embodiment of the present application;

[0024] Figure 3a Schematic diagram of the process of laser communication modulation method in related art;

[0025] Figure 3b A program block diagram of a laser communication modulation method provided in an embodiment of the present application Figure 1 ;

[0026] Figure 4 A program block diagram of a laser communication modulation method provided in an embodiment of the present application Figure 2 ;

[0027] Figure 5 A flowchart of a laser communication modulation method according to an embodiment of the present application is provided in FIG3;

[0028] Figure 6Schematic diagram comparing the bit error rates of the PPM-PC modulation method in the related art and the laser communication modulation method provided in the embodiment of the present application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described below in conjunction with the accompanying drawings in the embodiments of the present invention. In the description of the embodiments of the present invention, unless otherwise specified, "multiple" refers to two or more than two. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0030] In addition, in order to facilitate the clear description of the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, words such as "first" and "second" are used to distinguish between identical or similar items with substantially the same functions and effects. Those skilled in the art will understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit differences. 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 scheme described as "exemplary" or "for example" in the embodiments of the present invention should not be interpreted as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a concrete 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 over 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. Each m bit of 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 symbol's time slot, 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 the absence of an optical signal in the i-th time slot of the symbol, and 1 represents the presence of an optical signal in the i-th time slot of the symbol. The one-to-one mapping relationship between the value of c and the position of the optical pulse can be achieved using various mapping schemes, 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 light vector (electric field intensity vector) has a fixed orientation in space, with its endpoints describing a straight line in space. Its light vector vibrates only in a specific direction (polarization angle) and has no vibration component in the perpendicular direction.

[0034] The present invention provides a laser communication modulation method suitable for various free-space laser communication scenarios, particularly ultra-long-distance free-space laser communication, such as deep-space laser communication. In these scenarios, extremely high communication sensitivity is required, meaning that the lower the received signal strength, the better, while still meeting the target transmission rate and bit error rate.

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

[0036] The following describes in detail the application of the serial concatenated pulse position modulation (SCPPM) coding scheme in the Consultative Committee for Space Data Systems (CCSDS) standard to polarization-selective PPM modulation as an example.

[0037] An embodiment of the present application provides a laser communication modulation system capable of executing the laser communication modulation method provided in an embodiment of the present application. Figure 1 A schematic structural diagram of a laser communication modulation system provided in an embodiment of the present application.

[0038] like Figure 1 As 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 that can be executed 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 in the embodiment of the present application.

[0039] Figure 2 This is a flow chart of a laser communication modulation method provided in an embodiment of the present application. Figure 2 As 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 the encoded sequence c. Figure 4 As shown, at the transmitting end, data u is CRC-encoded, convolutionally encoded, interleaved, and accumulator-encoded to obtain a coded sequence c. For example, when the original information is 100 bits, the coded sequence obtained by channel coding may be 200 bits.

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

[0043] S2, performing polarization selective modulation on the coding sequence to obtain multiple groups of linearly polarized light pulses.

[0044] In some embodiments, the coding sequence is subjected to polarization selective modulation according to a preset number of bits, such as 5 bits, to obtain multiple sets of linearly polarized light pulses. For example, when the coding sequence is 200 bits, 40 sets of linearly polarized light pulses are obtained according to the preset number of bits 5.

[0045] Polarization selective modulation is described in detail below.

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

[0047] For example, the modulated 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 given by [c1,…,c m ] is determined, and its mapping relationship is equivalent to the mapping relationship of M-PPM.

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

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

[0050] The polarization of the first pulse and the polarization of the second pulse are orthogonal. The polarization of the first pulse and the polarization of the second pulse can be implemented in a variety of ways. 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, information is modulated using the polarization states (polarization angles) of a pair of orthogonal linearly polarized laser beams, ensuring high confidentiality in communications.

[0051] The following describes in detail the case where the first pulse polarization is 0° and the second pulse polarization is 90° as an example.

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

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

[0054] S3, sending each group of linearly polarized light pulses to the first photon detector and the second photon detector simultaneously to obtain a first photon count and a second photon count.

[0055] like Figure 3b As shown, the first photon count is obtained by the linear polarized light pulse passing through the first photon detector. In some embodiments, the first photon detector detects the linear polarized light pulse with 0° polarization and obtains the first photon count y0=[y1, y2, ..., y M ], where M = 2 m .

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

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

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

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

[0060] S303 , at a third moment, sending a linearly polarized light pulse other than the linearly polarized light pulses sent in step S301 and step S302 to the receiving end, to obtain a first photon count and a 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 next moment; the second moment and the third moment occur successively, the second moment is the previous moment, and the third moment is the next moment.

[0062] It is understood that each linearly polarized light pulse sent at a given moment has only one polarization angle, and this polarization angle is determined only by the information sent at the current moment and has nothing to do with information sent at other moments.

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

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

[0065] S312 , at the 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.

[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 next moment.

[0067] In some embodiments, when executing step S3, the laser communication modulation method further includes the following steps: each group of linearly polarized light pulses is sent to the first photon detector and the second photon detector simultaneously through a polarization beam splitter. 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 horizontally polarized (0°) light along one output channel and vertically polarized (90°) light along another output channel, while for light in other polarization states, it will be decomposed according to its components in the horizontal and vertical directions. That is, the probability that a φ-degree polarized photon is identified as 0° polarization is cos 2 (φ), the probability of being identified as 90° polarization is sin 2(φ). The probability of a practical 0° / 90° polarization beam splitter misclassifying a 0° polarized photon as a 90° polarized photon (or vice versa) is far less than 0.001, which is negligible. The probability of a photon from natural light (assuming the background noise in deep space communication scenarios is natural light) entering either the 0° or 90° channel is 1 / 2.

[0068] In this way, 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 a linearly polarized light pulse with a 0° polarization and a linearly polarized light pulse with a 90° polarization.

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

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

[0071] S4, obtaining a log-likelihood ratio through soft decision according to the first photon count and the second photon count of the plurality of groups of linearly polarized light pulses.

[0072] The log-likelihood ratio (LLR) of each symbol is calculated according to y = [y0y1]. It can be understood that at each moment, the process from polarization-selective modulation at the transmitter to LLR calculation at the receiver is related to the m+1 coded bits sent at that moment and is independent of the coded bits sent at other moments.

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

[0074] S41 , obtaining a photon sequence according to the first photon count and the second photon count.

[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. For example, y = [y0y1] = [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. For example, y = [y0y1] = [y M+1 ,y M+2 ,y 2M ,…,y1,y2,…,y M ].

[0077] In some other embodiments, the first photon count includes multiple elements. The second photon count includes multiple elements. The photon sequence is an interlaced sequence formed by alternating the elements of the first photon count and the elements of the second photon count. For example, y = [y0y1] = [y1, y M+1 ,y2,y M+2 ,…,y M ,y 2M ].

[0078] S42, confirming the symbol values ​​of the coding sequence.

[0079] For example, the input bits c=[c0,c1,…,c m ]The calculation formula of the symbol value corresponding to is:

[0080]

[0081] It can be understood that this formula gives c0,c1,…,c m Each of the corresponding decimal values.

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

[0083] The log-log likelihood ratio (LLR) of each symbol is calculated based on the photon sequence y=[y0y1].

[0084] For example, according to the photon counting sequence y=[y1, y2, ..., y 2M ]Calculate the symbol log-log likelihood ratio, i.e. symbol LLR, when the transmitted symbol C is 0, 1,…, 2M-1 respectively.

[0085] Wherein, the symbol LLR is defined as:

[0086]

[0087] Consider the Poisson channel model, let n s represents the normalized intensity of the optical pulse (the average number of signal photons per pulse time slot), n b represents 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 modulated signal can be expressed as Γ C (y) = Y c+1 ·log(1+2n s / n b )calculate.

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

[0090] It is understood that after receiving multiple sets of linearly polarized light pulses, the receiver calculates LLRs (Log-Likelihood Ratios) based on the order in which they are received, thereby obtaining the corresponding LLR calculation results. It is also understood that regardless of the order in which these 40 sets of pulses are transmitted, they must be input in the order 1 to 40 during the channel decoding step. The order of LLR calculation has no effect on the system and can be consistent with the transmission order or not.

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

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

[0093] For example, for a symbol length of M=2 m A polarization-selective PPM modulation communication system with 100 timeslots requires a codec designed for 2M-PPM modulation. Assuming a symbol length of 16, the receiver must use an SCPPM decoder designed for 32-PPM, rather than a decoder designed for 16-PPM. As you can see, no adjustments to the internal structure of the codec are required.

[0094] like Figure 5 As shown, every m+1 bits in the code sequence c are modulated onto a polarization-selective PPM symbol. At the receiver, the symbol LLRs are input into the SCPPM decoder, which performs iterative decoding between the convolutional code decoder and the APPM decoder to obtain the final decoding result.

[0095] It is understandable that SCPPM has a variety of different decoding algorithms. Here, only one algorithm is given as an example and does not constitute a limitation on the decoding algorithm.

[0096] In the embodiment of the present application, the coding sequence is subjected to polarization selective 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. Based on 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, the original information prediction value is obtained through channel decoding. In this way, polarization selective pulse position modulation and its corresponding demodulation method are compared with the following methods: Figure 3a The PPM-PC shown can achieve better communication sensitivity and stronger resistance to background noise.

[0097] like Figure 6 As shown, the SCPPM coding scheme is also used, and the symbol length M=2 m When consistent, the laser communication modulation method provided in the embodiment of the present application uses polarization-selective PPM modulation to make the transmission rate higher than that of the PPM-PC system modulation in the related art. Exemplarily, the transmission efficiency of the polarization-selective PPM provided in the embodiment 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 system bit error rate, the receiving sensitivity of the polarization-selective PPM modulation provided in the embodiment of the present application is greatly improved. Exemplarily, the polarization-selective PPM modulation requires a lower signal strength to reach 10 -6 The following bit error rate (sensitivity improvement of more than 0.4dB).

[0098] Based on the same application concept, an embodiment of the present application also provides a laser communication modulation system. The corresponding method of the laser communication modulation system can be the laser communication modulation method in the aforementioned embodiment, and its principle of solving the problem is similar to that of the method. The laser communication modulation system provided in the embodiment 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 the aforementioned multiple embodiments of the present application.

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

[0100] Specifically, the present embodiment can adopt any combination of one or more computer-readable media. The computer-readable medium 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, device or component, or any combination thereof. More specific examples (non-exhaustive list) of computer-readable storage media 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 thereof. In this document, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system, device or device.

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

[0102] Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

[0103] Computer program code for performing the operations of the present application can be written in one or more programming languages, or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, 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 cases involving 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., through the Internet using an Internet service provider).

[0104] The flow chart or block diagram in the accompanying drawings illustrate the possible architecture, functions and operations of the equipment, methods and computer program products according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, program segment or a part of code, and the module, program segment or a part of code include one or more executable instructions for realizing the logical function of the specification. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a sequence different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented with a dedicated system for hardware that performs the function or operation of the specification, or can be implemented with a combination of dedicated hardware and computer instructions.

[0105] Those skilled in the art will clearly understand that, for the 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 aforementioned method embodiments and will not be repeated here.

[0106] In the several embodiments provided in this 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 only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or page components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

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

[0108] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0109] The above-mentioned integrated unit implemented in the form of a software functional unit can be stored in a computer-readable storage medium. The above-mentioned software functional unit is stored in a storage medium and includes a number of instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) or a processor to execute some steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and other media that can store program code.

[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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

[0111] Furthermore, it is clear that the word "comprising" does not exclude other units or steps, and the singular does not exclude the plural. Multiple units or devices recited in a device claim may also be implemented by a single unit or device through software or hardware. Terms such as "first" and "second" are used to indicate names and do not imply any particular order.

Claims

1. A laser communication modulation method, characterized in that: include: Channel-encoding the original information to obtain a coding sequence; the coding sequence includes polarization angle information and polarization position information; Performing polarization selective modulation on the coding sequence to obtain a plurality of 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 pulse includes a second pulse polarization; the first pulse polarization and the second pulse polarization are orthogonal; the linearly polarized light pulse also includes a light pulse position; and the light pulse position is determined by the polarization position information; Sending each group of the linearly polarized light pulses to a first photon detector and a second photon detector simultaneously 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 by soft decision based on the first photon count and the second photon count of the multiple groups of linearly polarized light pulses; According to the log-likelihood ratio, the original information prediction value is obtained through channel decoding.

2. The laser communication modulation method according to claim 1, characterized in that: When executing the step of simultaneously sending 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, the multiple groups of 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: At a first moment, only the first linearly polarized light pulse is sent 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 the second linearly polarized light pulse is sent 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 next moment.

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

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

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

6. The laser communication modulation method according to claim 1 or 2, characterized in that: When executing the step of obtaining a log-likelihood ratio by soft decision based on 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 the values ​​of each symbol of the coding sequence; The log-likelihood ratio of each of the symbol values ​​is calculated based on the photon sequence.

7. The laser communication modulation method according to claim 6, characterized in that: 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 interspersed sequence formed by alternating the elements of the first photon count and the elements of the second photon count.

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 selective 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.

9. A laser communication modulation system, characterized in that: include: at least one processor; a memory communicatively coupled to the at least one processor; The memory stores instructions that can be executed 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 perform the method according to any one of claims 1 to 8.

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

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