A synchronization method for a photon counting type underwater wireless optical OOK communication system

Abstract

A synchronization method for a photon counting type underwater wireless optical OOK communication system, including the design of a transmission data structure and a synchronization method. The design of the data structure includes the design of the sending frame structure and the division of the received signal. The data is transmitted in the form of continuous frames, and the synchronization sequence is periodically embedded in the transmitted data. Before synchronization, the received signal is divided into slices of the same length; during synchronization, based on a frame-long received signal, the maximum likelihood joint estimation method is used to establish the corresponding optimization problem to find the synchronization sequence position, and some simplification is used to reduce the complexity of solving the original optimization problem. The present application solves the problem of poor transmission performance of the underwater wireless optical OOK communication system from the perspective of signal synchronization. The synchronization method is simple in form, and the complexity of the method is reduced by simplification, which is more suitable for the photon counting type underwater wireless optical OOK communication system. The present application can improve the synchronization performance with low complexity and improve the reliability of the photon counting type underwater wireless optical OOK communication system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of underwater wireless optical communication and signal synchronization, and particularly relates to a synchronization method for a photon counting type underwater wireless optical OOK communication system. BACKGROUND

[0002] With the increasingly serious problems of global warming and resource depletion, people's interest in comprehensive exploration of the ocean is growing. As an important information transmission link in the development of ocean exploration, underwater communication plays an important role in underwater autonomous machines, underwater sensor networks, and underwater reconnaissance and detection. Underwater communication technology mainly includes wired communication and wireless communication. Wired communication generally communicates through underwater cables. This communication method is not sensitive to water quality and has a high communication rate, but laying cables is costly, and communication cables can be eroded and damaged, so it is not suitable for underwater mobile operations. Common underwater wireless communication includes radio frequency communication, acoustic communication and wireless optical communication. Among them, radio frequency communication has achieved great success in land commercial use. However, in underwater scenarios, due to the good conductor properties of seawater, radio frequency signals will quickly attenuate in water due to the skin effect, greatly limiting the transmission distance of underwater radio frequency communication. Generally speaking, the communication distance of radio frequency communication under water is only ten meters, which is not very practical. For underwater acoustic communication, although it can achieve long-distance underwater communication, acoustic communication devices are often large in size and high in power consumption. At the same time, due to the low frequency and slow propagation of sound waves, acoustic communication is usually unsatisfactory in terms of transmission rate and transmission delay. In addition, underwater acoustic communication may also have some adverse effects on the marine ecosystem. Compared with the first two, underwater wireless optical communication has the advantages of high speed and low delay, and can achieve a communication distance of hundreds of meters. At the same time, due to the high directionality of the light beam and the low diffraction and low diffraction ability of the short wavelength, underwater wireless optical communication has stronger security. In addition, underwater wireless optical communication devices also have the advantages of small size, low power consumption and low cost. Therefore, underwater wireless optical communication is often considered as a promising transmission scheme in underwater wireless communication.

[0003] In the underwater wireless optical communication system, synchronization is an indispensable part, and accurate synchronization is the premise to ensure the receiving end to accurately recover the transmitted data. The underwater wireless optical communication transmission environment is complex, and many unfavorable factors may affect the communication performance. First, due to the influence of absorption and scattering, the light wave in the water body will experience a large attenuation, and the long-distance transmission light signal will become very weak. Second, the water body in the ocean is constantly circulating, causing uneven distribution of temperature and humidity in the seawater, which will lead to uneven refraction of light by the water body, thereby forming turbulence to affect the propagation of the light signal. In addition, ship wake, marine biological activity, underwater gas, underwater operation, raindrops and waves may introduce bubbles underwater, and the wireless optical signal may be attenuated or deviated from the direction aligned by the transmitting and receiving ends. In summary, the complex underwater environment brings many difficulties to underwater wireless optical communication, and also brings many challenges to the synchronization problem. In the weak light scene (corresponding to low power or long distance transmission), the photon counting receiver is often used, and the number of photons detected in a symbol period is generally modeled as a Poisson distribution. The existing photon counting type underwater wireless optical OOK communication system generally uses a sliding correlation method for synchronization, which fails to fully utilize the information of the complete received signal. In view of the important role of synchronization in the communication system, it is of great significance to study an efficient synchronization method for the photon counting type underwater wireless optical OOK communication system. Therefore, we will combine the dynamic characteristics of the underwater channel to study the synchronization problem of the photon counting type underwater wireless optical OOK communication system. SUMMARY

[0004] Therefore, the main purpose of the present application is to provide a synchronization method for a photon counting type underwater wireless optical OOK communication system, in order to partially solve at least one of the above technical problems.

[0005] In order to achieve the above purpose, as one aspect of the present application, a synchronization method for a photon counting type underwater wireless optical OOK communication system is provided, including the design of transmission data structure and synchronization method. The design of data structure includes the design of sending frame structure and the division of received signal, and the data is transmitted in the form of continuous frames, and the synchronization sequence is periodically embedded in the data sequence, and the received signal is divided into slices with the same length before synchronization; based on a frame long received signal, the maximum likelihood joint estimation method is used to establish the corresponding optimization problem to find the synchronization sequence position, and some simplifications are used to reduce the complexity of solving the original optimization problem.

[0006] A synchronization method for a photon counting type underwater wireless optical OOK communication system, comprising the following steps:

[0007] (1) transmitting data in the form of continuous frames, and periodically embedding a synchronization sequence into the data sequence; dividing the received signal into slices with the same length.

[0008] (2) Based on a frame length of the received signal, the number of photons in each symbol interval in the frame is counted, and based on the Poisson distribution model of the number of photons in each symbol interval, the vector composed of the number of photons is used to jointly estimate the synchronization sequence position, data, timing signal strength parameter and background intensity parameter to realize synchronization; maximum likelihood detection is equivalent to threshold detection, and based on the sorting result of the received data signal from large to small, the estimation of data is equivalent to the estimation of the number of symbols "1" in the data, and finally the synchronization sequence position is found by using the traversal search method to complete synchronization.

[0009] Further, the step (1) specifically comprises:

[0010] (1.1) The data is transmitted in the form of continuous frames, each frame has a length of N symbol periods, and a synchronization sequence containing L symbols is periodically embedded in the transmitted data, and a frame length of the received signal contains the synchronization sequence.

[0011] (1.2) The duration of a frame of signals is ensured to be less than the coherence time of the channel, and the channel state is considered to remain unchanged within a frame of time.

[0012] (1.3) Each symbol period in the received signal is divided into K slices of the same length, and a frame length of the received signal is divided into N·K slices of the same length.

[0013] Further, the step (2) specifically comprises:

[0014] (2.1) Starting from the kth (1≤k≤NK) slice, the number of photons in each symbol interval is counted. Let r k represent the vector composed of the detected number of photons in each symbol interval in the received signal frame starting from the kth (1≤k≤NK) slice.

[0015] (2.2) Based on the Poisson distribution model of the number of photons in each symbol interval, r k is used to jointly estimate the synchronization sequence position k, data d, timing signal strength parameter λ s and background intensity parameter λ b to realize synchronization. Let Pr(r k |k,λ s ,λ b ,d) represent the conditional probability function of r k given k, λ s , λ b , d; the optimal estimate of (k, λ L , λ N-L , d) can be obtained by using joint maximum likelihood estimation.

[0016]

[0017] in,

[0018]

[0019] In the above formula {s1,s2,…,s L} represents a known synchronization sequence symbol, {d1,d2,…,d N-L} represents the data sequence symbol to be estimated.

[0020] (2.3) Using the synchronization sequence position k and data d to give the signal strength parameter λ s and background intensity parameter λ b The estimated expression of , the original synchronous optimization formula (1) is equivalently transformed into:

[0021]

[0022] in,

[0023]

[0024] (2.4) Using maximum likelihood detection is equivalent to threshold detection, based on the sorting results of the received data signals from large to small The estimation of data d is equivalent to the number of symbols "1" in data d Δ d The estimation of , formula (2) is equivalently transformed into:

[0025]

[0026] in,

[0027]

[0028] Traverse the integer k between 1 and N·K and the integer Δ between 0 and NL d , find F2(k,Δ d )The largest Select the corresponding As the starting position of the synchronization sequence, synchronization is completed.

[0029] The present invention discloses a synchronization system for a photon counting underwater wireless optical OOK communication system, specifically comprising:

[0030] The data regularization module transmits data in the form of continuous frames and periodically embeds the synchronization sequence into the data sequence. The received signal is divided into slices of equal length. Specifically, it includes:

[0031] The data frame packaging block transmits data in the form of continuous frames, each frame having a length of N symbol periods, and a synchronization sequence of L symbols being periodically embedded in the transmitted data.

[0032] The duration of a frame of signals is ensured to be less than the coherence time of the channel, and the channel state is considered to remain unchanged within a frame of time.

[0033] The received signal slicing module divides each symbol period in the received signal into K slices of equal length, and divides a frame of received signals into N·K slices of equal length.

[0034] The synchronization sequence positioning module is used to find the position of the synchronization sequence based on a frame of received signals, and uses a maximum likelihood joint estimation method to reduce the computational complexity. Specifically, it includes:

[0035] The photon counting module is used to count the number of photons in each symbol interval from the k-th (1≤k≤NK) slice. Let r k denote the vector composed of the number of photons detected in each symbol interval in the frame of received signals from the k-th (1≤k≤NK) slice.

[0036] The joint estimation module is used to use the Poisson distribution model of the number of photons in each symbol interval to estimate r k The joint estimation of the synchronization sequence position k, the data d, and the timing signal intensity parameter λ s and the background intensity parameter λ b is used to achieve synchronization. Let Pr(r k |k,λ s ,λ b ,d) denote the conditional probability function of r s given k, λ b , λ k , and d; the optimal estimate of (k, λ s , λ b , d) can be obtained by using joint maximum likelihood estimation.

[0037]

[0038] wherein,

[0039]

[0040] In the above formula, {s1, s2, …, s L} represents the known synchronization sequence symbols, and {d1, d2, …, d N-L} represents the data sequence symbols to be estimated.

[0041] The equivalent conversion module is used to use the synchronization sequence position k and the data d to give the signal strength parameter λ s and background intensity parameter λ b The estimated expression of , the original synchronous optimization formula (1) is equivalently transformed into:

[0042]

[0043] in,

[0044]

[0045] The traversal search module is used to use the maximum likelihood detection equivalent to the threshold detection, based on the sorting results of the received data signal from large to small The estimation of data d is equivalent to the number of symbols "1" in data d Δ d The estimation of , formula (2) is equivalently transformed into:

[0046]

[0047] in,

[0048]

[0049] Traverse the integer k between 1 and N·K and the integer Δ between 0 and NL d , find F2(k,Δ d )The largest Select the corresponding As the starting position of the synchronization sequence, synchronization is completed.

[0050] An embodiment of the present application also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, each process of each embodiment of the above-mentioned synchronization method for a photon counting underwater wireless optical OOK communication system is implemented, and the same technical effect can be achieved. To avoid repetition, it will not be repeated here.

[0051] Based on the above technical methods, it can be seen that the synchronization method for a photon counting underwater wireless optical OOK communication system of the present invention has at least one or part of the following beneficial effects compared to the prior art:

[0052] (1) The present invention solves the problem of poor transmission performance of photon counting underwater wireless optical OOK communication system from the perspective of signal synchronization. The synchronization method is simple in form and reduces the complexity of solving the original optimization problem through some simplifications. It is suitable for photon counting underwater wireless optical OOK communication system.

[0053] (2) The present invention provides a synchronization method that does not require channel information, which can improve the synchronization performance with lower complexity and enhance the reliability of the photon counting underwater wireless optical OOK communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Schematic diagram of the frame structure;

[0055] Figure 2 Schematic diagram of the synchronization process;

[0056] Figure 3 A block diagram of an underwater wireless optical communication system provided as a preferred embodiment of the present invention;

[0057] Figure 4 A block diagram of a synchronization system provided for a preferred embodiment of the present invention;

[0058] Figure 5 is the cumulative distribution function of synchronization timing error of underwater wireless optical communication system;

[0059] Figure 6 This is the curve showing the bit error rate of the underwater wireless optical communication system changing with the transmitted optical power. DETAILED DESCRIPTION

[0060] The primary objective of this invention is to provide a synchronization method for a photon-counting underwater wireless optical OOK communication system. This method is simple and, through simplifications, reduces the complexity of the original optimization problem. This method can improve the synchronization performance of photon-counting receivers and enhance the reliability of underwater wireless optical OOK communication systems.

[0061] Specifically, the present invention discloses a synchronization method for a photon-counting underwater wireless optical OOK communication system, including the design of a transmission data structure and a synchronization method. The data structure design includes the design of a transmission frame structure and the division of the received signal. Data is transmitted as continuous frames, and a synchronization sequence is periodically embedded in the transmitted data. Before synchronization, the received signal is divided into slices of equal length. During synchronization, a maximum likelihood joint estimation method is used to establish an optimization problem based on a frame-long received signal to locate the synchronization sequence. The complexity of solving the original optimization problem is reduced through simplification.

[0062] In order to make the objectives, technical methods and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0063] The synchronization method of the present invention adopts the following data transmission format: Figure 1The shown frame structure, data frames are transmitted continuously, and synchronization sequences are periodically embedded into data, which guarantees that a frame length of data is collected, and a synchronization sequence is necessarily contained in the frame length of data. The underwater channel is often dynamic due to reasons such as turbulence, bubbles and shaking of the transceiver, and therefore short frames are adopted for data transmission, so that the time of a frame length is less than the coherence time of the channel, and the channel information is guaranteed to remain unchanged within a frame length of time.

[0064] For a photon counting type underwater wireless optical OOK communication system, the received signal appears in the form of pulses, and pulse detection is first performed, and synchronization is performed based on the number of detected pulses. In order to realize synchronization, the received signal is divided into slices of the same length. The position of the synchronization sequence is found based on a frame length of received data, and a joint maximum likelihood estimation method is adopted to simultaneously estimate the position of the synchronization sequence, the data sequence and the channel parameters. A synchronization optimization problem is established based on the Poisson distribution model of the number of photons in each symbol interval, and some simplifications are adopted to reduce the computational complexity of the original optimization problem. During synchronization, integers k between 1 and N·K and integers Δ d between 0 and N-L are traversed to find the maximum d The corresponding is selected as the starting position of the synchronization sequence, and synchronization is completed, and the synchronization process is as shown in Figure 2 .

[0065] The application discloses a synchronization method for a photon counting type underwater wireless optical OOK communication system, and specifically comprises the following steps:

[0066] (1) Data is transmitted in the form of continuous frames, and a synchronization sequence is periodically embedded into the data sequence. The received signal is divided into slices of the same length. The method comprises the following steps:

[0067] Step 1: Data is transmitted in the form of continuous frames, and a synchronization sequence containing L symbols is periodically embedded into the transmitted data, and a frame length of signal is received, and the synchronization sequence is necessarily contained in the frame length of signal.

[0068] Step 2: The duration of a frame length of signal is guaranteed to be less than the coherence time of the channel, and the channel state is considered to remain unchanged within a frame length of time.

[0069] Step 3: Each symbol period in the received signal is divided into K slices of the same length, and a frame length of received signal is divided into N·K slices of the same length.

[0070] (2) During synchronization, the position of the synchronization sequence is found based on a frame length of received signal by using a maximum likelihood joint estimation method, and the computational complexity is reduced through some simplifications, and synchronization is completed. The method comprises the following steps:

[0071] ​Step 1: Starting from the kth (1≤k≤NK) slice, count the number of photons in each symbol interval. Let r k It represents a vector consisting of the number of photons detected in each symbol interval within the received signal frame starting from the kth (1≤k≤NK) slice.

[0072] Step 2: Based on the Poisson distribution model of the number of photons in each symbol interval, use r k Jointly estimate the synchronization sequence position k, data d, and timing signal strength parameter λ s and background intensity parameter λ b To achieve synchronization. Let Pr(r k |k,λ s ,λ b ,d) indicates that given k,λ s ,λ b ,d when r k The conditional probability function of (k,λ) can be obtained by using joint maximum likelihood estimation. s ,λ b ,d) is the optimal estimate

[0073]

[0074] in,

[0075]

[0076] In the above formula {s1,s2,…,s L} represents a known synchronization sequence symbol, {d1,d2,…,d N-L} represents the data sequence symbol to be estimated.

[0077] Step 3: Use the synchronization sequence position k and data d to give the signal strength parameter λ s and background intensity parameter λ b The estimated expression of , the original synchronization optimization problem (1) is equivalently transformed into:

[0078]

[0079] in,

[0080]

[0081] Step 4: Using maximum likelihood detection, which is equivalent to threshold detection, sort the received data signals from large to small. The estimation of data d is equivalent to the number of symbols "1" in data d Δ d The estimation of , formula (2) is equivalently transformed into:

[0082]

[0083] wherein,

[0084]

[0085] traversing integers k between 1 and N*K and integers Delta between 0 and N-L d , find the maximum F2(k, Delta d ) select the corresponding as the starting position of the synchronization sequence, and complete synchronization.

[0086] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below in combination with specific embodiments and with reference to the drawings.

[0087] Figure 3 The communication block diagram shown is a schematic diagram of a preferred embodiment. Specifically, the transceiver is placed in a 0.7m underwater environment, the transmitting end uses a green LED, the receiving end uses a photomultiplier tube, an attenuator and a filter are placed in front of the receiving end for attenuating the signal and filtering out noise, and the received signal is in the photon counting area. In order to simulate the dynamic underwater environment, a wave generator is placed in the underwater channel to make the channel dynamic. The system performance is tested in this environment.

[0088] Figure 4 The synchronization system block diagram shown is a schematic diagram of the synchronization system of the present application. Specifically, the data is first regularized to transmit the data in the form of continuous frames, and the synchronization sequence period is embedded into the transmitted data; the received signal is divided into N*K pieces of the same length at the receiving end. Then, based on a frame-long received signal, the maximum likelihood joint estimation method is used to locate the position of the synchronization sequence, and the calculation complexity is reduced through some simplifications, including the following: photon counting, joint estimation, equivalent transformation, and traversal search. The traversal search can obtain the position of the synchronization sequence, and complete synchronization.

[0089] The present application discloses a synchronization system for a photon counting type underwater wireless optical OOK communication system, specifically comprising:

[0090] The data regularization module transmits the data in the form of continuous frames, and periodically embeds the synchronization sequence period into the data sequence. The received signal is divided into pieces of the same length. Specifically, it comprises:

[0091] The data frame packaging module transmits the data in the form of continuous frames, and each frame has a length of N symbol periods. A synchronization sequence containing L symbols is periodically embedded into the transmitted data, and a frame-long signal is received, which must contain the synchronization sequence.

[0092] The duration of one frame signal is ensured to be less than the coherence time of the channel, and the channel state is considered to be unchanged within one frame time.

[0093] The received signal slicing module divides each symbol period in the received signal into K slices of the same length, and divides a received frame-long signal into N·K slices of the same length.

[0094] The synchronization sequence positioning module, based on a frame-long received signal, counts the number of photons in each symbol interval in the received signal frame, and based on a Poisson distribution model of the number of photons in each symbol interval, jointly estimates the synchronization sequence position, data, timing signal intensity parameter and background intensity parameter by using a vector composed of the photons to achieve synchronization; maximum likelihood detection is equivalent to threshold detection, and based on the descending order of the received data signal, the estimation of the data is equivalent to the estimation of the number of symbol "1"s in the data, and finally the traversal search method is used to find the synchronization sequence position to complete the synchronization. Specifically, it includes:

[0095] The photon counting module is used to count the number of photons in each symbol interval from the kth (1≤k≤NK) slice. Let r k represent a vector composed of the detected photons in each symbol interval in the received signal frame from the kth (1≤k≤NK) slice.

[0096] The joint estimation module is used to jointly estimate the synchronization sequence position k, data d, timing signal intensity parameter λ k and background intensity parameter λ s based on a Poisson distribution model of the number of photons in each symbol interval by using r b to achieve synchronization. Let Pr(r k |k,λ s ,λ b ,d) represent the conditional probability function of r s given k, λ b , λ k and d; the joint maximum likelihood estimation can obtain the optimal estimation s of (k, λ b , λ L and d).

[0097]

[0098] wherein,

[0099]

[0100] In the above formula, {s1, s2,..., s L} represents the known synchronization sequence symbol, and {d1, d2,..., d N-L} represents the data sequence symbol to be estimated.

[0101] The equivalent conversion module is used to use the synchronization sequence position k and the data d to give the signal strength parameter λ s and background intensity parameter λ b The estimated expression of , the original synchronous optimization formula (1) is equivalently transformed into:

[0102]

[0103] in,

[0104]

[0105] The traversal search module is used to use the maximum likelihood detection equivalent to the threshold detection, based on the sorting results of the received data signal from large to small The estimation of data d is equivalent to the number of symbols "1" in data d Δ d The estimation of , formula (2) is equivalently transformed into:

[0106]

[0107] in,

[0108]

[0109] Traverse the integer k between 1 and N·K and the integer Δ between 0 and NL d , find F2(k,Δ d )The largest Select the corresponding As the starting position of the synchronization sequence, synchronization is completed.

[0110] Figure 5 The cumulative distribution functions of the synchronization timing errors for the proposed method (Proposed) and the traditional synchronization method (Correlation) are shown. As can be seen, the synchronization effect of both methods improves with increasing optical power. Furthermore, compared to the traditional method, the timing error of this method is closer to zero.

[0111] Figure 6 The BER performance of different synchronization methods is shown. It can be seen that the proposed method has an optical power gain of about 1dB compared to the traditional method. Specifically, when the BER is 10 -3 When the optical power required by this method is -0.4dBm and the traditional method is 0.9dBm, respectively. This shows that this method can improve synchronization performance with low complexity and enhance the reliability of photon-counting underwater wireless optical OOK communication systems. Therefore, the synchronization method proposed in this invention is more suitable for photon-counting underwater wireless optical OOK communication systems.

[0112] The computer readable storage medium stores a computer program. The computer program is executed by a processor to implement each process of each embodiment of the synchronization method for the photon counting type underwater wireless optical OOK communication system, and the same technical effects can be achieved. To avoid repetition, details are not described herein.

[0113] Each embodiment in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between each embodiment can be referred to each other.

[0114] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, device, or computer storage medium. Therefore, the embodiments of the present application can be in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the embodiments of the present application can be in the form of a computer program product implemented on one or more computer usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer usable program code.

[0115] The embodiments of the present application are described with reference to flowcharts and / or block diagrams of the method, system, and computer program product according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing terminal equipment to produce a machine, so that the instructions executed by the computer or other programmable data processing terminal equipment produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one flow or multiple flows and / or blocks Figure 1 The device that implements the functions specified in one block or multiple blocks.

[0116] These computer program instructions can also be stored in a computer readable storage medium that can guide the computer or other programmable data processing terminal equipment to work in a specific way, so that the instructions stored in the computer readable storage medium produce a product including instruction devices that implement the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one flow or multiple flows and / or blocks Figure 1 The device that implements the functions specified in one block or multiple blocks.

[0117] These computer program instructions can also be loaded into a computer or other programmable data processing terminal device, so that a series of operational steps are performed on the computer or other programmable terminal device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable terminal device provide steps for implementing the function specified in the flowchart Figure 1 one flow or multiple flows and / or the function specified in the block Figure 1 one block or multiple blocks.

[0118] The principles and implementation modes of the present application are described herein by applying specific examples, and the above example descriptions are only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in specific implementation modes and application ranges, and the above description should not be understood as limiting the present application.

[0119] The above specific examples further describe the purpose, technical method and beneficial effects of the present application, and it should be understood that the above description is only for specific embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A synchronization method for a photon counting type underwater wireless optical OOK communication system, characterized by, The method comprises the following steps: (1) transmitting data in the form of continuous frames and periodically embedding a synchronization sequence into the data sequence; The received signal is divided into slices of the same length; (2) based on a frame-long received signal, counting the number of photons in each symbol interval in the frame of the received signal, based on the Poisson distribution model of the number of photons in each symbol interval, jointly estimating the position of the synchronization sequence, data, timing signal intensity parameters and background intensity parameters by using a vector composed of photons to realize synchronization; using maximum likelihood detection equivalent to threshold detection, based on the sorting results of the received data signal from large to small, equivalent conversion of the estimation of data into the estimation of the number of symbols "1" in the data, and finally using the traversal search method to find the position of the synchronization sequence to complete synchronization.

2. The synchronization method for a photon-counting type underwater wireless optical OOK communication system according to claim 1, characterized in that, The step (1) specifically comprises: (1.1) transmitting data in the form of continuous frames, the length of each frame is N symbol periods, a synchronization sequence containing L symbols is periodically embedded into the transmitted data, and a frame-long signal is received, which must contain the synchronization sequence; (1.2) ensuring that the duration of a frame of signals is less than the coherence time of the channel, and the channel state is considered to remain unchanged within a frame of time; (1.3) dividing each symbol period in the received signal into K slices of the same length, and dividing the received frame-long signal into N·K slices of the same length.

3. The method of synchronizing a photon-counting type underwater wireless optical OOK communication system according to claim 2, wherein, The step (2) specifically comprises: (2.1) From the kth (1≤k≤NK) slice, count the number of photons in each symbol interval; let r k denote the vector consisting of the number of photons detected in each symbol interval in the received signal frame starting from the kth (1≤k≤NK) slice; (2.2) Based on the Poisson distribution model of the photon number in each symbol interval, r k Jointly estimate the synchronization sequence position k, data d, timing signal intensity parameter λ s and background intensity parameter λ b to achieve synchronization; let Pr(r k |k, λ s , λ b , d) represent the conditional probability function of r k given k, λ s , λ b , d; using joint maximum likelihood estimation, the optimal estimate of (k, λ s , λ b , d) can be obtained wherein, {s1, s2,..., s L} denotes known synchronization sequence symbols, {d1, d2,..., d N-L} denotes data sequence symbols to be estimated; (2.3) The timing signal strength parameter λ is given by the synchronization sequence position k and data d s and the background intensity parameter λ b The original synchronization optimization formula (1) is equivalently transformed into: wherein, (2.4) Using maximum likelihood detection is equivalent to threshold detection, based on the ordering of the received data signals from large to small Converting the equivalent estimate of the data d into an estimate of the number of symbols "1" in the data d d Converting the equivalent estimate of the data d into an estimate of the number of symbols "1" in the data d wherein, traversing integers k between 1 and N-K and integers Δ between 0 and N-L d , finding the maximum of F2(k,Δ d ) selecting the corresponding as the starting position of the synchronization sequence, completing synchronization.

4. A synchronization system for a photon counting type underwater wireless optical OOK communication system, characterized in that, Specifically comprising: a data regularization module, configured to transmit data in the form of continuous frames and periodically embed a synchronization sequence into the data sequence, and divide the received signal into slices of the same length; a synchronization sequence positioning module, configured to, based on a frame-long received signal, count the number of photons in each symbol interval in the frame of the received signal, based on the Poisson distribution model of the number of photons in each symbol interval, jointly estimate the position of the synchronization sequence, data, timing signal intensity parameters and background intensity parameters by using a vector composed of photons to realize synchronization; using maximum likelihood detection equivalent to threshold detection, based on the sorting results of the received data signal from large to small, equivalent conversion of the estimation of data into the estimation of the number of symbols "1" in the data, and finally using the traversal search method to find the position of the synchronization sequence to complete synchronization.

5. The synchronization system for a photon counting underwater wireless optical OOK communication system according to claim 4, characterized in that: The data regularization module specifically comprises: a data frame packaging module, configured to transmit data in the form of continuous frames, the length of each frame is N symbol periods, a synchronization sequence containing L symbols is periodically embedded into the transmitted data, and a frame-long signal is received, which must contain the synchronization sequence; ensuring that the duration of a frame of signals is less than the coherence time of the channel, and the channel state is considered to remain unchanged within a frame of time; a received signal slicing module, configured to divide each symbol period in the received signal into K slices of the same length, and divide the received frame-long signal into N·K slices of the same length.

6. The synchronization system for a photon-counting type underwater wireless optical OOK communication system according to claim 5, characterized in that, The synchronization sequence positioning module specifically comprises: a photon counting module for counting the number of photons in each symbol interval from the kth (1≤k≤NK) slice; let r k denote a vector consisting of the number of photons detected in each symbol interval in the signal frame received from the kth (1≤k≤NK) slice; a joint estimation module for estimating the synchronization sequence position k, the data d, the timing signal intensity parameter λ k and the background intensity parameter λ s to achieve synchronization; let Pr(r b |k, λ k , λ s , d) denote the conditional probability function of r b given k, λ s , λ b , d; using joint maximum likelihood estimation, the optimal estimate of (k, λ k , λ s , d) can be obtained by solving the following optimization problem b ​ wherein, {s1, s2,..., s L} denotes known synchronization sequence symbols, {d1, d2,..., d N-L} denotes data sequence symbols to be estimated; An equivalent transformation module for transforming the original synchronization optimization formula (1) into an equivalent form using the estimated expressions of the timing signal strength parameter λ with the synchronization sequence position k and the data d s and the background intensity parameter λ b ​ wherein, The traversal search module is configured to utilize maximum likelihood detection equivalent to threshold detection to sort the received data signals from large to small based on a result of the sorting The estimation of the data d is equivalent to the estimation of the number of symbols "1" Δ in the data d d The formula (2) is equivalent to: wherein, traversing integers k between 1 and N-K and integers Δ between 0 and N-L d , finding the maximum of F2(k, Δ d ) selecting the corresponding as the starting position of the synchronization sequence, completing synchronization.

7. A computer-readable storage medium, a computer program is stored on the computer-readable storage medium, and the computer program is executed by a processor to implement the synchronization method of the photon counting type underwater wireless optical OOK communication system according to any one of claims 1-3.

Images