A Method for Aligning Data Clocks of VSAT Master Remote Terminals

Abstract

The present invention discloses a method for data clock alignment of a VSAT master and slave stations, comprising the following steps: S1: Receive the master station DVB signal and the slave station TDMA signal, and demodulate and decode them; S2: Send the master station decoded data and the slave station decoded data to the data processing module, which receives and caches the data in real time and performs parsing; S3: Accumulate consecutive multiple overclocked time slot allocation plans and burst data frames; S4: Traverse the time slot allocation plans cached in step S2 in sequence, and obtain the clock alignment result of the master and slave stations according to the matching result of the idle time slots and empty bursts. The beneficial effects of the present invention are: By receiving and processing the master station decoded data and the slave station decoded data in real time, detecting and inserting lost time slot allocations and empty bursts and marking them, and matching the preprocessed idle time slots and empty bursts, the clock alignment of the master and slave station data is completed in real time and efficiently, improving the timeliness of clock alignment.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite communication, and particularly to a method for aligning the data clocks of a VSAT master station and slave stations. Background Art

[0002] VSAT (Very Small Aperture Terminal) communication is a satellite communication technology that uses very small (generally with a diameter between 0.3 m and 1.4 m) aperture antennas and terminals to conduct two-way communication with each other. Compared with traditional satellite communication networks, it has higher utilization rate of satellite channel resources, more flexible channel allocation, lower communication costs, more convenient system installation and use, and is easier to expand. It is very suitable for multiple industries such as news, finance, ocean, emergency, and military. In addition to fixed stations, it is also widely used in mobile platforms such as vehicles, ships, warships, and aircraft.

[0003] Generally speaking, a VSAT communication system consists of a master station and multiple slave stations. The master station is also called the central station, which is mainly responsible for the allocation of channel resources (including frequency resources and time slot resources) and the management of the communication network; the slave stations are also called remote stations, which are mainly used to establish communication links with the master station and other slave stations through satellites, encode / decrypt and modulate / demodulate carrier signals, and send and receive communication payload data of users. Currently, the mainstream VSAT master stations all adopt DVB-S2 / S2X signals (hereinafter simply referred to as DVB signals), and the slave stations adopt TDMA signals of different specifications. In a non-cooperative satellite communication scenario, the receiving party, as a hidden third party, independently receives, demodulates and decodes, aligns the clocks, restores the payloads, and statistically analyzes the carrier signals of the target VSAT master station and slave stations. Generally speaking, the processing process of the receiving party mainly includes the following five steps:

[0004] First, parse various network control signaling from the decoded data of the master station to obtain network parameters (including superframe period, number of slave station terminals / communication links / users, number of single-carrier time slots, etc.), slave station carrier parameters (including carrier frequency, symbol rate, modulation method, code rate, code length / information length, etc.), and superframe time slot allocation plan (which slave station terminals / communication links / users are allocated to several time slots on each carrier);

[0005] Second, according to the parsed slave station carrier parameters, conduct channelized reception and demodulation and decoding of the slave station carrier signals, and extract burst data from the decoded data of the slave stations;

[0006] Third, since neither the target VSAT master station nor the slave stations will perform clock synchronization with the receiving party, and the master station signal and the slave station signals are two independently received carrier signals, the receiving party must first align the superframe time slot allocation plan of the master station and the burst data of the slave stations;

[0007] Fourth, based on the clock alignment of the main station superframe time slot allocation plan and the small station burst data, the burst data is extracted, rearranged, and spliced according to the small station terminal / communication link / user, and finally the purpose of restoring the communication payload is achieved;

[0008] Fifth, the reception completion rate of the small station burst data frames is statistically calculated (the number of small station burst data frames received and decoded successfully / the number of time slots actually allocated to this small station in the superframe time slot allocation plan), as well as the activity patterns of small station users (including online time, offline time, communication duration, communication data volume, communication traffic, etc.).

[0009] In the above steps, the clock alignment of the main station superframe time slot allocation plan and the small station burst data in the third step is the key to correctly restoring the payload data in the non-cooperative satellite communication scenario. As Figure 1 shown, the existing technical route for the clock alignment of the main station superframe time slot allocation plan and the small station burst data is as follows:

[0010] First, demodulate and decode the main station DVB signal and the small station TDMA signal (multiple implementation methods such as FPGA, CPU, GPU can be selected), and output and store the decoded data of the main station and the small station in different files respectively;

[0011] Second, batch read and parse the data in the two types of files through data processing software, and accumulate the matching count of the moments of the main station superframe time slot allocation plan and the time slot where the small station burst data is located;

[0012] Finally, when the matching count of the moments of the main station superframe time slot allocation plan and the time slot where the small station burst data is located exceeds the preset threshold, it is considered that the main and small station clocks are aligned.

[0013] The specific implementation process, as Figure 2 shown, mainly includes the following steps:

[0014] 1. Respectively perform channelized reception, demodulation, and decoding on the main station DVB signal and the small station TDMA signal, and add a timestamp (the absolute time of the demodulation process, with a precision of ≥100 ns, the same below) to the output decoded data;

[0015] 2. For the main station decoded data, add a data header to the head of each BBF (Base Band Frame, baseband frame); for the small station decoded data, add a data header to the head of each burst data frame; the main information elements included in the data header part are: synchronization flag, timestamp, decoded verification passed flag, etc.;

[0016] 3. Output and store the main station decoded data and the small station decoded data as files respectively for the data processing software to parse;

[0017] 4. Synchronously read the content in the master station decoding data file and the slave station decoding data file, and perform corresponding processing;

[0018] 5. Read and parse a batch of master station BBF data from the master station decoding data file, extract the TS stream or GS stream, parse the signaling in the stream data, and obtain the superframe time slot allocation plan;

[0019] 6. Calculate the moment (absolute time) of each allocated time slot according to elements such as the superframe period, burst period, and the timestamp of the BBF where the superframe time slot allocation plan signaling is located;

[0020] 7. Read and parse a batch of burst data (the burst data frames of multiple different users are connected together irregularly) from the slave station decoding data file. According to the synchronization flag in the data header, extract the burst data into multiple burst data frames and their timestamps;

[0021] 8. Accumulate the matching count of the allocated time slots in step 6) and the moments of the burst data frames in step 7). The matching condition is generally: the time difference between the two ≤ the fixed time deviation of the master-slave station demodulation and decoding clocks ± 2 superframe periods;

[0022] 9. If the moment matching count > the preset threshold value, it is considered that the master-slave station clocks are already aligned, and subsequent processing operations such as extracting, rearranging, and splicing the burst data frames according to the slave station terminal / communication link / user can be performed;

[0023] 10. Otherwise, clear the moment matching count, and start to re-execute the operation in step 8 from the next burst data frame;

[0024] 11. When the number of slave station burst data in step 7) does not meet the moment matching quantity requirement, re-execute from step 5.

[0025] However, the above method has the following defects:

[0026] 1. The non-real-time post-processing of the master-slave station decoding data in the form of files has low real-time performance;

[0027] 2. The moment matching threshold value between the master station allocated time slot and the slave station burst data is generally taken from empirical values and is related to the VSAT type and signal-to-noise ratio: for different types of VSAT, the threshold value is different; even for the same type of VSAT with different signal-to-noise ratios, the threshold value is not exactly the same; that is, the setting of this threshold value does not have universality or generalization ability;

[0028] 3. When there is a frame loss in the BBF of the main station DVB signal (along with the loss of the signaling), or when there is an error in signaling parsing, a situation of lost superframe time slot allocation plan will occur (that is, one or several superframe time slot allocation plans are lost, hereinafter referred to as superframe loss). The superframe time slot allocation plan cannot be matched with the burst data time, and one can only wait to process the next batch of data without loss. The clock alignment between the main and slave stations lags behind or even cannot be aligned, resulting in the inability to extract the burst data that should have been extractable.

[0029] 4. Due to the precise control of the transmission power (Transmission Level Contriol, TLC) of the slave station TDMA signal, it is often weak for non-cooperating parties. When the signal-to-noise ratio is low, it is prone to frame loss during demodulation and decoding, resulting in the problem of lost burst data frames (hereinafter referred to as burst loss), which will affect the matching result between the time slots allocated by the main station and the burst data time of the slave station, leading to false clock alignment between the main and slave stations, and further resulting in errors in burst data extraction and splicing.

[0030] 5. Since the time slot allocation algorithms (also known as time slot allocation patterns) for each type of VSAT are different, it is relatively complex to calculate which allocation time slot of which superframe of the main station each burst data frame sequentially extracted from the decoded data of the slave station corresponds to, resulting in low algorithm performance and difficulties in implementation, debugging, and troubleshooting. Summary of the Invention

[0031] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for aligning the data clocks of the VSAT main and slave stations.

[0032] The purpose of the present invention is achieved through the following technical solutions: A method for aligning the data clocks of the VSAT main and slave stations includes the following steps:

[0033] S1: Receive the main station DVB signal and the slave station TDMA signal, and demodulate and decode them.

[0034] S2: Send the decoded data of the main station and the decoded data of the slave station to the data processing module. The data processing module receives and caches the data in real time and performs parsing.

[0035] S3: Accumulate multiple consecutive superframe time slot allocation plans and burst data frames.

[0036] S4: Sequentially traverse the superframe time slot allocation plans cached in step S2, and obtain the alignment result of the main and slave station clocks according to the matching result between the idle time slots and the empty bursts.

[0037] Preferably, in step S2, the parsing steps of the decoded data of the main station are as follows:

[0038] A21: Read the BBF data of the master station, extract the TS stream or GS stream, parse the signaling in the stream data, and obtain the superframe time slot allocation plan;

[0039] A22: Detect whether there is any loss in the superframe time slot allocation plan in the signaling. If there is a loss, insert the corresponding number of empty superframe time slot allocation plans according to the superframe period, the timestamp of the previous superframe, and the timestamp of the new superframe, and mark them;

[0040] A23: Cache the preprocessed superframe time slot allocation plan;

[0041] A24: Calculate the absolute time of each allocated time slot.

[0042] Preferably, in step S2, the parsing steps of the decoding data of the slave station are as follows:

[0043] B21: Read and parse the burst data, and extract the burst data into multiple burst data frames and their timestamps according to the synchronization flag in the data header;

[0044] B22: Calculate the number of idle time slots and lost burst data frames according to the burst period and the time difference between the timestamps of adjacent burst data frames, insert the corresponding number of empty bursts and their timestamps, and mark them;

[0045] B23: Cache the preprocessed burst data frames and their timestamps.

[0046] Preferably, in step S3, accumulate more than three consecutive superframe time slot allocation plans and burst data frames.

[0047] Preferably, in step S4, sequentially traverse the superframe time slot allocation plan cached in step A23. For all the idle time slots in the superframe time slot allocation plan,

[0048] If all the burst data frames cached in step B23 can find corresponding empty bursts, and the time difference between each pair of matching idle time slots and empty bursts does not exceed one superframe period, then the master and slave station clocks are aligned;

[0049] If the current burst data frame is not an empty burst, then the master and slave station clocks are not aligned, the matching count of the idle time slot and the empty burst is cleared, and it is shifted backward by one burst data frame to re-match the idle time slot with the superframe time slot allocation plan cached in step A23;

[0050] If the current burst data frame is an empty burst, but the time difference between the idle time slot and the empty burst exceeds one superframe period, then the master and slave station clocks are falsely aligned, the matching count of the idle time slot and the empty burst is cleared, and it is shifted backward by one burst data frame to re-match the idle time slot with the superframe time slot allocation plan cached in step A23;

[0051] When the burst data of the small station in step B21 does not meet the matching quantity requirement, step A21 is executed again.

[0052] The present invention has the following advantages:

[0053] 1. By receiving and processing the master station decoding data and the small station decoding data in real time, the present invention aligns the master and small station clocks in real time, improving the timeliness of clock alignment.

[0054] 2. By filling the missing superframes and missing bursts, and filling empty bursts at the positions of idle time slots, the present invention makes the superframe time slot allocation plan and the burst data frames participating in the matching exactly the same in quantity. The clock alignment position can be quickly found through shift positioning and flag screening, greatly improving the efficiency of master and small station clock alignment, reducing the complexity of the algorithm, improving the algorithm performance, and simplifying software debugging and fault location.

[0055] 3. The present invention adopts a missing superframe and missing burst detection algorithm to calculate the number of missing superframes and the number of missing bursts, ensuring the correctness and robustness of the matching between the superframe time slot allocation plan and the burst data moment.

[0056] 4. The present invention adopts an idle time slot matching algorithm to achieve the clock alignment of the master and small stations, greatly improving the adaptability and generalization ability of the algorithm for different types of VSATs. It is not only more accurate and efficient, but also ensures from the implementation mechanism that it will not be affected by the loss of master station superframes or the loss of small station bursts. Description of the Drawings

[0057] Figure 1 It is a schematic diagram of the output of the existing master station decoding data and small station decoding data into two types of files;

[0058] Figure 2 It is a schematic diagram of the process flow of the existing master and small station clock alignment method based on the matching of used time slots;

[0059] Figure 3 It is a schematic diagram of the real-time output of the master station decoding data and the small station decoding data;

[0060] Figure 4 It is a schematic diagram of the process flow of the master and small station clock alignment method based on the matching of idle time slots. Detailed Embodiments

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention usually described and illustrated in the drawings here can be arranged and designed in various different configurations.

[0062] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0063] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0064] It should be noted that: Similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0065] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive distinction and cannot be understood as indicating or implying relative importance.

[0066] In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0067] In this embodiment, as Figure 3 and Figure 4As shown in the figure, a method for aligning the data clock of a VSAT master sub-station includes the following steps:

[0068] S1: Receive the DVB signal of the master station and the TDMA signal of the sub-station, and demodulate and decode them;

[0069] S2: Send the decoded data of the master station and the decoded data of the sub-station to the data processing module. The data processing module receives and caches the data in real time and performs parsing. Specifically, by receiving and processing the decoded data of the master station and the decoded data of the sub-station in real time, the clock alignment of the master sub-station is performed in real time, improving the timeliness of clock alignment. That is to say, the existing technology uses the forward matching algorithm of the used time slot and the burst data frame with existence. However, the loss of super-frames and bursts is inevitable. Therefore, the clock alignment of the master sub-station often needs to be completed based on multiple batches of data (until the data without loss of super-frames and bursts is encountered), and when false alignment occurs, realignment is required. Therefore, a large amount of cached data is required, so it is processed in the form of a file. However, the data required for the clock alignment of the master sub-station in the present invention is no longer read from the file, but is based on the real-time data output by the network, improving the real-time performance of processing and no longer occupying disk storage space.

[0070] S3: Accumulate the slot allocation plans of multiple consecutive super-frames and burst data frames; preferably, accumulate the slot allocation plans of three or more consecutive super-frames and burst data frames.

[0071] S4: Traverse the slot allocation plans of the super-frames cached in step S2 in sequence, and obtain the alignment result of the master sub-station clock according to the matching result of the idle time slot and the empty burst. The present invention adopts the idle time slot matching algorithm to realize the clock alignment of the master sub-station, greatly improving the adaptability and generalization ability of the algorithm for different types of VSAT. That is, the matching threshold and standard are based on the super-frame period, and no fixed parameters or ratios are set according to empirical values. Therefore, it can be applied to different types or different regions of VSAT. Moreover, from the implementation mechanism, it is ensured that it will not be affected by the loss of super-frames of the master station or the loss of bursts of the sub-station. In this embodiment, step S1 is implemented by the existing method and is not improved here, so it will not be elaborated.

[0072] Further, in step S2, the parsing steps of the decoded data of the master station are as follows:

[0073] A21: Read the BBF data of the master station, extract the TS stream or GS stream, parse the signaling in the stream data, and obtain the slot allocation plan of the super-frame;

[0074] A22: Detect whether there is a loss in the slot allocation plan of the super-frame in the signaling. If there is a loss, insert the corresponding number of empty super-frame slot allocation plans according to the super-frame period, the time stamp of the previous super-frame, and the time stamp of the new super-frame, and mark them;

[0075] A23: Cache the preprocessed superframe time slot allocation plan;

[0076] A24: Calculate the absolute time of each allocated time slot. Further, in step S2, the parsing steps of the small station decoded data are as follows:

[0077] B21: Read and parse the burst data, and extract the burst data into multiple burst data frames and their timestamps according to the synchronization flag in the data header;

[0078] B22: Calculate the number of idle time slots and lost burst data frames according to the burst period and the time difference between adjacent burst data frame timestamps, and insert the corresponding number of empty bursts and their timestamps for marking; specifically, there are two sources of empty bursts: the first is that the idle time slot causes the small station not to generate burst data; the second is that the small station generates burst data in the allocated time slot, but due to burst loss, the third party does not receive the burst data in this time slot. For the convenience of subsequent matching operations, empty bursts are filled in both cases. Here, the meaning of an empty burst is that there is only a placeholder for the burst data frame and no data payload.

[0079] B23: Cache the preprocessed burst data frames and their timestamps. Specifically, by filling the lost superframes and lost bursts, and filling empty bursts at the positions of idle time slots, the superframe time slot allocation plan and burst data frames participating in the matching are made exactly the same in quantity. The clock alignment position can be quickly found through shift positioning and flag screening, which greatly improves the clock alignment efficiency of the master small station, reduces the algorithm complexity, improves the algorithm performance, simplifies software debugging and fault location. That is, when looking for the clock alignment position, one is to quickly screen the idle time slots and empty bursts by using the method of marker filtering, and the other is to first calculate the position offset (through the superframe period, burst period and timestamp), and then directly shift to quickly locate the idle time slots and burst data frames to be compared. The combination of the two avoids the multiple traversals of the two queues to be compared, eliminates the original time matching performance bottleneck, greatly improves the clock alignment efficiency of the master small station, and reduces the algorithm complexity at the same time. The lost superframe and lost burst detection algorithm is adopted to measure the number of lost superframes and the number of lost bursts, ensuring the correctness and robustness of the matching between the superframe time slot allocation plan and the burst data time. That is to say, for the allocated time slots, lost superframes or bursts may occur due to reasons such as poor signal-to-noise ratio, demodulation frame loss, decoding error and signaling parsing error. Therefore, the existing technology is easily affected by burst loss. However, in the non-cooperative satellite communication scenario, the TDMA signal quality received by the small station is poor and the signal-to-noise ratio is low, which is a common situation. Demodulation frame loss, decoding error and signaling parsing error caused by the former two are inevitable. Therefore, the idle time slot matching algorithm adopted by the present invention can significantly improve the generality and robustness of the clock alignment of the master small station.

[0080] In this embodiment, in step S4, the superframe time slot allocation plan cached in step A23 is traversed in sequence, and for all idle time slots in the superframe time slot allocation plan,

[0081] If the corresponding empty bursts can be found for all the burst data frames cached in step B23, and the time difference between each pair of matching idle time slots and the empty burst does not exceed one superframe period, the clock of the master station is aligned;

[0082] If the current burst data frame is not an empty burst, the master station clock is not aligned, the matching count between the idle time slot and the empty burst is reset, and one burst data frame is shifted backward to rematch the idle time slot with the superframe time slot allocation plan cached in step A23;

[0083] If the current burst data frame is an empty burst, but the time difference between the idle time slot and the empty burst exceeds one superframe period, the master station clock is falsely aligned, the matching count between the idle time slot and the empty burst is reset, and one burst data frame is shifted backward to rematch the idle time slot with the superframe time slot allocation plan cached in step A23;

[0084] When the burst data of the small station in step B21 does not meet the matching quantity requirement, step A21 is executed again.

[0085] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A VSAT master station data clock alignment method, characterized in that: The following steps are involved: S1: Receives the main station DVB signal and the small station TDMA signal, and demodulates and decodes them; S2: Send the decoded data of the main station and the decoded data of the small station to the data processing module, which receives and caches the data in real time and performs analysis; In step S2, the parsing steps of the master station decoding data are as follows: A21: read the BBF data of the master station, extract the TS stream or GS stream, parse the signaling in the stream data, and obtain the superframe time slot allocation plan; A22: Detect whether the superframe time slot allocation plan in the signaling is lost. If there is a loss, insert a corresponding number of empty superframe time slot allocation plans according to the superframe period, the timestamp of the previous superframe and the timestamp of the new superframe, and mark them to form a pre-processed superframe time slot allocation plan; A23: caching the pre-processed superframe time slot allocation plan; A24: Calculate the absolute time of each allocated time slot; In step S2, the parsing steps of the small station decoding data are as follows: B21: read and parse the burst data, and extract the burst data into multiple burst data frames and their timestamps according to the synchronization flag in the data header; B22: Calculate the number of idle time slots and lost burst data frames according to the time difference between the burst cycle and the timestamps of adjacent burst data frames, and insert the corresponding number of empty bursts and their timestamps for marking to form pre-processed burst data frames; B23: Cache the pre-processed burst data frames and their timestamps; S3: Accumulate multiple consecutive superframe time slot allocation plans and burst data frames; S4: traverse the superframe time slot allocation plan cached in step S2 in sequence, and obtain the alignment result of the master station clock according to the matching result of the idle time slot and the empty burst.

2. The VSAT master station data clock alignment method according to claim 1, characterized in that: In the step S3, more than three consecutive superframe time slot allocation plans and burst data frames are accumulated.

3. The VSAT master station data clock alignment method according to claim 2, characterized in that: In step S4, the superframe time slot allocation plan cached in step A23 is traversed in sequence, and for all idle time slots in the superframe time slot allocation plan, If the corresponding empty bursts can be found for all the burst data frames cached in step B23, and the time difference between each pair of matching idle time slots and the empty burst does not exceed one superframe period, the clock of the master station is aligned; If the current burst data frame is not an empty burst, the master station clock is not aligned, the matching count between the idle time slot and the empty burst is reset, and one burst data frame is shifted backward to rematch the idle time slot with the superframe time slot allocation plan cached in step A23; If the current burst data frame is an empty burst, but the time difference between the idle time slot and the empty burst exceeds one superframe period, the master station clock is falsely aligned, the matching count between the idle time slot and the empty burst is reset, and one burst data frame is shifted backward to rematch the idle time slot with the superframe time slot allocation plan cached in step A23; When the burst data of the small station in step B21 does not meet the matching quantity requirement, step A21 is executed again.

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