Method for increasing throughput of a laser communication system

Abstract

The application provides a throughput improvement method of a laser communication system, wherein a first step is to encode the information to be transmitted by using a unique decodable code word set at a transmitting end, and then to transmit; a second step is to complete non-orthogonal superposition in a power domain to obtain a superposition signal after the transmitted symbol passes through a channel; and a third step is to demodulate the superposition signal by using a noiseless superposition pattern set to map into a code word at a receiving end, so as to obtain complete and accurate transmission information. The application uses the non-orthogonal characteristics of the unique decodable code word, effectively improves the throughput of the multi-antenna laser communication system, that is, the number of bits correctly transmitted per unit time, and the way of mapping into a code word by using a noiseless superposition pattern set also provides a new idea for demodulating the transmission information. Meanwhile, the application can also be combined with other multiplexing technologies, such as multi-level modulation, angular momentum multiplexing and wavelength division multiplexing, so as to further improve the throughput of the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser communication technology, and particularly provides a throughput improvement method of a laser communication system. BACKGROUND

[0002] Free space optical communication has the advantages of large capacity, strong anti-electromagnetic interference ability, and no need for frequency authorization. The intensity modulation direct detection system is easy to apply to various scenes due to its simple structure, low cost, and easy coupling. In order to overcome the poor channel conditions, researchers have proposed diversity technology to overcome channel fading. The common diversity technology is spatial diversity. Spatial diversity can resist channel fading, but cannot improve the system throughput. Therefore, the present application focuses on improving the throughput of the multi-transmit-single-receive laser communication system of the intensity modulation direct detection system.

[0003] Unlike radio frequency communication, the non-negativity of light intensity in laser communication makes the mature space-time coding in radio frequency communication cannot be directly used in laser communication system. In addition, the space-time coding mode itself does not improve the information rate. Especially for high-dimensional space-time coding, it will also reduce the amount of information per unit time. In existing research, the coding applied in the multi-antenna laser communication system is orthogonal coding. This makes it impossible to obtain the degree of freedom gain in the case of a single receiver without introducing other dimension multiplexing mode. Therefore, it is necessary to study the throughput improvement method of the multi-antenna laser communication system based on non-orthogonal code words. SUMMARY

[0004] To solve the above problems, the present application provides a throughput improvement method of a laser communication system, which mainly encodes the information to be transmitted by using a unique decodable code word set at the transmitting end, and then transmits. The code word set is subjected to power non-orthogonal superposition in the channel to obtain a superimposed signal. The receiving end demodulates the superimposed signal by mapping it into a code word through a noiseless superposition pattern set, and obtains complete and accurate transmission information.

[0005] The throughput improvement method of the laser communication system provided by the present application comprises the following steps:

[0006] S1, at any k time, the information to be transmitted by the transmitter is encoded by using a unique decodable code word and transmitted to the receiver. The unique decodable code word set of the mth transmitter is represented as wherein m represents the serial number of the transmitter, 1≤m≤M, and M represents the total number of transmitters; represents the unique decodable code word transmitted by the mth transmitter at the k time,

[0007] S2, at the k time, the code word is subjected to non-orthogonal superposition in the power domain when passing through the channel to obtain a superimposed signal yk ;

[0008] S3, demodulating the information to be transmitted at the kth moment;

[0009] Step S31, determining the noiseless superposition pattern set at the kth moment according to the channel information at the kth moment and the unique decodable code word set of all M transmitters

[0010] Step S32, judging the noiseless superposition pattern at the kth moment according to the minimum Euclidean distance criterion

[0011] Step S33, using the operation of mapping the noiseless superposition pattern to the code word, mapping the noiseless superposition pattern to the code word transmitted by all M transmitters and further solving the information to be transmitted, wherein, represents the unique decodable code word transmitted by the mth (1≤m≤M) transmitter at the kth moment determined by the receiver.

[0012] Preferably, in numerical value, the power non-orthogonal superposition of the code word set is equivalent to the power superposition of the optical signal, and the calculation formula of the superposition signal y k is as follows:

[0013]

[0014] wherein n k is the equivalent Gaussian noise after photoelectric conversion of the receiving end at the kth moment, represents the channel information between the mth transmitter at the kth moment and the receiver, and η represents the photoelectric conversion coefficient of the optical signal converted into the electrical signal in the receiver.

[0015] Preferably, in step S31, the noiseless superposition pattern set at the kth moment is determined as:

[0016]

[0017] wherein c m represents any code word in the code word set .

[0018] Preferably, in step S32, the function of the noiseless superposition pattern at the kth moment is as follows:

[0019]

[0020] wherein ψ p represents any element in the noiseless superposition pattern set , and p represents the noiseless superposition pattern set​ the order of the middle element, argmin() represents a function that filters out the value of the independent variable when the objective function is minimum, represents a set of noiseless superimposed patterns the number of elements, is equal to the product of the number of code words of each code word set.

[0021] Preferably, in step S33, the mapping function of the noiseless superimposed pattern to the code word is as follows:

[0022]

[0023] wherein, represents a function of the noiseless superimposed pattern to the code word mapping.

[0024] Compared with the prior art, the present application can achieve the following beneficial effects:

[0025] The present application effectively improves the throughput of the multi-antenna laser communication system, i.e., the number of bits correctly transmitted per unit time, by utilizing the non-orthogonal characteristics of the uniquely decodable code word, and provides a new idea for demodulating and transmitting information by mapping the set of noiseless superimposed patterns into code words. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a multi-antenna laser communication system of intensity modulation direct detection system of M transmitters according to an embodiment of the present application;

[0027] Figure 2 is a flowchart of a throughput improvement method of a multi-antenna laser communication system according to an embodiment of the present application;

[0028] Figure 3 is a data graph of the noiseless superimposed pattern to the code word mapping according to an embodiment of the present application;

[0029] Figure 4 is a comparison graph of the throughput improvement effect of a multi-antenna laser communication system according to an embodiment of the present application.

[0030] The reference signs in the drawings include: transmitter 1, receiver 2, channel 21, back-end processing module 22, receiving lens 23, system throughput curve a using the method of the present application, system throughput curve a' not using the method of the present application. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. In the following description, the same modules are denoted by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0032] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not constitute a limitation on the present application.

[0033] It should be noted that in this embodiment, the throughput is the number of bits correctly transmitted per unit time, i.e. the amount of information correctly transmitted per unit time. Therefore, in a noise-free environment, the throughput of the system is In a noisy environment, the throughput of the system is R 有噪 = R 无噪 × (1-BER), where BER represents the bit error rate.

[0034] Figure 1 The structure of a multi-antenna laser communication system of an intensity modulation direct detection system of M transmitters is shown according to an embodiment of the present application.

[0035] As shown in Figure 1 , the multi-antenna laser communication system of the intensity modulation direct detection system of M transmitters includes a transmitter 1 and a receiver 2, the transmitter 1 is used to transmit information and encode information, and the receiver 2 is used to receive the information transmitted by the transmitter 1 and demodulate the encoded information, the receiver 2 includes a channel 21, a back-end processing module 22 and a receiving lens 23, and there are the same number of receiving lenses 23 as the total number of transmitters 1 and one back-end processing module 22 in the receiver 2. Each receiving lens 23 of the receiver 2 is fiber-coupled, and the multiplexed optical signals coupled into the optical fiber are combined and superimposed to form one optical signal. The superimposed optical signal is demodulated in the back-end processing module 22 of the receiver 2 to obtain the signal information of each transmitter 1.

[0036] In this embodiment, the multiplexing of non-orthogonal transmission is realized by using the non-orthogonal characteristics of the unique decodable code word set of the M transmitters 1, and the code word superposition has mathematical equivalence with the power superposition of the optical signal. For the mth transmitter 1, the unique decodable code word set used is Code word set contains different code words, the length of each code word is the same, M represents the total number of transmitters 1, and m represents the serial number of the transmitter 1, 1≤m≤M. At each time, each transmitter 1 can complete the transmission of one code word.

[0037] Figure 2A method for improving throughput of a multi-antenna laser communication system is shown.

[0038] As shown in Figure 1 and Figure 2 , the information transmission process of the laser communication system applying the method of the present application at the kth moment is as follows:

[0039] S1, at any kth moment, the mth optical transmitter 1 encodes the information to be transmitted using the unique decodable code and transmits it to the receiver 2, and the set of encoded code words is represented as The encoded code word is represented as and is transmitted.

[0040] S2, the encoded code word in the receiver 2 is subjected to non-orthogonal superposition in the power domain when passing through the channel 21, and the superimposed optical signal is obtained after photoelectric conversion to obtain the superimposed signal y k , and the calculation formula of the superimposed signal y k is as follows:

[0041]

[0042] where n k is the equivalent Gaussian noise after photoelectric conversion in the receiver 2 at the kth moment, represents the information of the channel 21 between the mth transmitter 1 and the receiver 2 at the kth moment.

[0043] S3, the receiver 2 knows all the information of the channel 21, and the noiseless superposition pattern set can be determined according to the information of the channel 21 and the M code word sets. Due to the unique decodable characteristic of the code word, the number of elements of the noiseless superposition pattern set is equal to the product of the number of code words of each code word set, i.e. The elements of the noiseless superposition pattern set are one-to-one mapped with the different code words sent by the M transmitters 1. Therefore, the process of demodulating the information sent by the M transmitters 1 at the kth moment in the receiver 2 mainly includes three steps:

[0044] Step S31, according to the information of the channel 21 and the code word sets of the unique decodable code of all M transmitters, the noiseless superposition pattern set at the kth moment is determined as:

[0045]

[0046] where c m represents any one code word in the code word set , and in the process of determining the noiseless superposition pattern set at the kth moment , c m is replaced with the code word set ​η represents the photoelectric conversion coefficient of the optical signal converted into the electrical signal in the receiver 2.

[0047] Step S32, judging the noiseless superposition pattern at the kth moment according to the minimum Euclidean distance criterion judging the noiseless superposition pattern at the kth moment according to the minimum Euclidean distance criterion The function is as follows:

[0048]

[0049] wherein ψ p represents any element in the noiseless superposition pattern set p represents the serial number of the element in the noiseless superposition pattern set argmin() represents a function, i.e. filtering out the value of the independent variable when the minimum value of the objective function, represents the element number of the noiseless superposition pattern set is equal to the product of the code word number of each code word set.

[0050] Step S33, using the operation of mapping the noiseless superposition pattern to the code word, mapping the noiseless superposition pattern to the code word transmitted by all the M transmitters 1 and further calculating the transmitted information, the mapping function of mapping the noiseless superposition pattern to the code word is as follows:

[0051]

[0052] wherein, represents the unique decodable code word transmitted by the mth (1≤m≤M) transmitter 1 at the kth moment judged by the receiver 2, represents all the transmitted code words of the M transmitters 1 demodulated by the receiver 2, represents the noiseless superposition pattern mapped to the code word.

[0053] Figure 3 The process data of mapping the noiseless superposition pattern to the code word provided by the embodiment of the present application is shown.

[0054] As shown in Figure 3 , taking the total number of the transmitters 1 M=2 as an example, the code word sets of the two transmitters 1 are respectively:

[0055] The information of the channels 21 of the two transmitters 1 and the receiver 2 at the kth moment is respectively and

[0056] ​At the kth moment, then the noiseless superposition pattern set is:

[0057] {[0, 0.5], [0.8, 1.3], [0.5, 0], [1.3, 0.8], [0, 0], [0.8, 0.8]}.

[0058] The noiseless superposition pattern set Each element in the set is different from each other, and there are elements, and the six elements are combined with different code words of the code word set of the two transmitters 1 to generate a one-to-one mapping.

[0059] The mapping process is as shown in Figure 3 : each row in the figure represents the mapping relationship between the code word set of the noiseless superposition pattern and the transmission code word of the transmitter 1. The code word is mapped to the noiseless superposition pattern [0, 0.5]. The noiseless superposition pattern [0, 0.5] can also be mapped back to the code word

[0060] Figure 4 The comparison of the throughput improvement effect of the multi-antenna laser communication system provided by the embodiment of the present application is shown.

[0061] Taking the total number of transmitters 1 as an example, the code word set of the two transmitters 1 is respectively

[0062] After applying the method of the present application, the normalized throughput data of the laser communication system is compared as shown in Figure 4 :

[0063] The vertical axis in the figure is the throughput, the horizontal axis is the signal-to-noise ratio, that is, SNR, a is the system throughput curve using the method of the present application; a' is the system throughput curve a' without using the method of the present application. Through data comparison, it can be seen that the throughput of the system using the method of the present application is better than that of the system without using the method of the present application. In the system without using the method of the present application, since the receiver 2 has only one backend processing module 22, the system cannot distinguish the information transmitted by different transmitters, so it cannot have the degree of freedom gain. Therefore, the normalized throughput is close to 1 bit / s / Hz at high signal-to-noise ratio. The degree of freedom gain of the system using the method of the present application benefits from the non-orthogonal characteristic of the unique decodable code word, so it has a throughput greater than 1, and at high signal-to-noise ratio, the throughput is close to:

[0064]

[0065] The present application can also be combined with other multiplexing techniques, such as multi-ary modulation, angular momentum multiplexing, wavelength division multiplexing, to further improve the throughput of the system.

[0066] Although the embodiments of the present application have been shown and described above, it should be understood by those having ordinary skill in the art that the above embodiments are exemplary and are not to be construed as limiting the present application. Those having ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present application.

[0067] The above detailed description of the application is not intended to limit the scope of the present application. Various other changes and modifications can be made to the above-described embodiments according to the technical concept of the present application, and all such changes and modifications are included within the scope of the present application claimed.

Claims

1. A method for throughput enhancement of a laser communication system, the method comprising: A multi-antenna laser communication system for intensity modulation direct detection scheme of M transmitters, the method comprises the following steps: S1, at any k moment, the transmitter's information to be transmitted is encoded using unique decodable code and transmitted to the receiver, the code word set of the unique decodable code of the mth transmitter is represented as wherein m represents the serial number of the transmitter, M represents the total number of the transmitter; represents the code word of the unique decodable code transmitted by the mth transmitter at the k moment, ; S2, at the kth moment, the code word is subjected to non-orthogonal superposition in the power domain when passing through the channel to obtain a superimposed signal In numerical terms, the power non-orthogonal superposition of the code word set is equivalent to the power superposition of the optical signal, and the superimposed signal The calculation formula is as follows: ； wherein, is an equivalent Gaussian noise after photoelectric conversion of the received end at the kth moment, represents channel information between the kth moment and the mth transmitter and receiver, represents a photoelectric conversion coefficient of the optical signal converted into an electrical signal in the receiver; S3, demodulate the information to be transmitted at the k moment; Step S31, according to the channel information of the kth moment and the unique decodable codeword set of all M transmitters, determine the noiseless superposition pattern set of the kth moment ; In step S31, the noise-free superposition pattern set at the kth moment is determined is: ； wherein represents any one of the code word set in the code word set Step S32, judging the noise-free superimposed pattern of the kth moment according to the minimum Euclidean distance criterion ; in step S32, judging the noise-free superimposed pattern of the kth moment The function is as follows: ； wherein, denotes the set of noiseless superposition patterns denotes any element in the set of noiseless superposition patterns denotes the index of the element in the set of noiseless superposition patterns denotes the set of noiseless superposition patterns denotes the number of elements in the set of noiseless superposition patterns is equal to the product of the number of codewords in each of the set of codewords Step S33: Using the operation of mapping the noiseless superimposed pattern to codewords, the noiseless superimposed pattern is... Mapped to codewords transmitted by all M transmitters. This allows us to calculate the information to be transmitted, including... The receiver's decision at time k represents the... Each transmitter transmits a uniquely decodable codeword; in step S33, the mapping function for mapping the noiseless superposition pattern to the codeword is as follows: ； wherein, denotes the noise-free superposition pattern a function mapping to a code word.

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