VSAT master and small station data clock alignment method

Abstract

The invention discloses a VSAT master and small station data clock alignment method, which comprises the following steps: S1, receiving a master station DVB signal and a small station TDMA signal, and demodulating and decoding the signals; s2, the master station decoding data and the small station decoding data are sent to a data processing module, and the data processing module receives and caches the data in real time and analyzes the data; s3, accumulating a plurality of continuous overclocking time slot allocation plans and burst data frames; and S4, traversing the time slot allocation plans cached in the step S2 in sequence, and obtaining an alignment result of the main small station clocks according to a matching result of the free time slot and the empty burst. The method has the beneficial effects that the main station decoding data and the small station decoding data are received and processed in real time, lost time slot distribution and empty burst are detected and inserted and are marked, and the preprocessed idle time slot and empty burst are matched, so that the clock alignment of the main station data and the small station data is efficiently completed in real time, and the accuracy of the data alignment is improved. And the timeliness of clock alignment is improved.

Description

Technical Field

[0001] The invention relates to the technical field of satellite communication, in particular to a VSAT master station data clock alignment method. Background Art

[0002] VSAT (Very Small Aperture Terminal) communication is a satellite communication technology that uses very small (generally with a diameter of 0.3m to 1.4m) aperture antennas and terminals for two-way communication. Compared with traditional satellite communication networks, it has higher satellite channel resource utilization, more flexible channel allocation, lower communication costs, more convenient system installation and use, and easier expansion. It is very suitable for news, finance, ocean, emergency, military and other industries. 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 small stations. The master station, also known as the central station, is mainly responsible for the allocation of channel resources (including frequency resources and time slot resources) and the management of the communication network; the small station, also known as the remote station, is mainly used to establish communication links between the master station and other small stations through satellites, encode / decode and modulate / demodulate carrier signals, and send and receive user communication payload data. The current mainstream VSAT master stations all use DVB-S2 / S2X signals (hereinafter referred to as DVB signals), and small stations use TDMA signals of different specifications. In the non-cooperative satellite communication scenario, the receiver acts as a hidden third party to independently receive, demodulate, decode, align clocks, restore payloads, and conduct statistical analysis on the target VSAT master station and small station carrier signals. Generally speaking, the receiver's processing process mainly includes the following five steps:

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

[0005] Secondly, according to the analyzed small station carrier parameters, the small station carrier signal is channelized and demodulated and decoded, and burst data is extracted from the small station decoded data;

[0006] Third, since neither the master station nor the small station of the target VSAT will synchronize the clock with the receiver, and the master station signal and the small station signal are two carrier signals received independently, the receiver must first perform the master station time slot allocation plan and the small station burst data clock alignment;

[0007] Fourth, based on the master station time slot allocation plan and the small station burst data clock alignment, 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 load is achieved;

[0008] Fifth, statistics are collected on the reception completeness rate of the burst data frames of the small station (the number of burst data frames of the small station that are received and decoded and verified / the number of time slots actually allocated to the small station in the time slot allocation plan), as well as the activity patterns of the users of the small station (including online time, offline time, communication duration, communication data volume, communication traffic, etc.).

[0009] In the above steps, the third step of master station time slot allocation plan and clock alignment of small station burst data is the key to correct payload data restoration in non-cooperative satellite communication scenarios. Figure 1 As shown in the figure, the existing master station time slot allocation plan and the clock alignment technology route for small station burst data are:

[0010] First, demodulate and decode the main station DVB signal and the small station TDMA signal (you can choose FPGA, CPU, GPU and other implementation methods), and output the main station decoding data and the small station decoding data to different files respectively;

[0011] Secondly, the data processing software is used to read and parse the data in the two types of files in batches, and the time matching counts between the master station time slot allocation plan and the time slot where the burst data of the small station is located are accumulated;

[0012] Finally, when the matching count between the master station's time slot allocation plan and the time slot where the burst data of the small station is located exceeds the preset threshold value, it is considered that the master small station clock is aligned.

[0013] Specific implementation process, such as Figure 2 As shown, it mainly includes the following steps:

[0014] 1. Perform channelized reception, demodulation and decoding of the main station DVB signal and the small station TDMA signal respectively, and add a timestamp to the output decoded data (the absolute time of demodulation processing, with an accuracy of ≥100ns, the same below);

[0015] 2. For the master station decoding data, a data header is added to the head of each BBF (Base Band Frame); for the small station decoding data, a data header is added to the head of each burst data frame; the main information elements included in the data header are: synchronization flag, timestamp, decoding check pass flag, etc.;

[0016] 3. Output and store the master station decoding data and the small station decoding data as files for analysis by data processing software;

[0017] 4. Synchronously read the contents of the master station decoding data file and the small 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 TS stream / GS stream, parse the signaling in the stream data, and obtain the time slot allocation plan;

[0019] 6. Calculate the time (absolute time) of each allocated time slot based on the superframe period, burst period, and the timestamp of the BBF where the time slot allocation plan signaling is located;

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

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

[0022] 9. If the time matching count is greater than the preset threshold value, it is considered that the master station clock has been aligned, and subsequent burst data frame extraction, rearrangement and splicing operations can be performed according to the station terminal / communication link / user;

[0023] 10. Otherwise, the time matching count is cleared and step 8 is performed again starting from the next burst data frame;

[0024] 11. When the burst data of the small station in step 7 does not meet the quantity requirement of the time matching, restart from step 5.

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

[0026] 1. The decoding data of the main station is processed in a non-real-time manner in the form of files, which is not very real-time;

[0027] 2. The threshold value for matching the time slot allocated by the master station with the burst data of the small station is generally taken from the experience value and is related to the VSAT type and signal-to-noise ratio: the threshold value is different for different types of VSAT; 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 the threshold value does not have universality or generalization ability;

[0028] 3. When the BBF in the DVB signal of the master station loses frames (and the signaling therein is also lost) or the signaling parsing error occurs, the superframe time slot allocation plan will be lost (i.e., the time slot allocation plan of one or more superframes is lost, hereinafter referred to as superframe loss). The time slot allocation plan cannot match the burst data moment, and can only wait for the next batch of data that has not been lost. The clock alignment of the master station is delayed or even cannot be aligned, resulting in the inability to extract the burst data that should have been extracted;

[0029] 4. Due to the precise control of transmission power (Transmission Level Contriol, TLC), the TDMA signal of the small cell is often weak for non-cooperative parties. When the signal-to-noise ratio is low, it is easy to cause burst data frame loss (hereinafter referred to as burst loss) due to frame loss in demodulation and decoding, which will affect the matching result of the master station's allocated time slot and the small cell's burst data time, resulting in false alignment of the master cell clock, and then causing burst data extraction and splicing errors;

[0030] 5. Since the time slot allocation algorithm (also known as time slot allocation pattern) of each type of VSAT is different, each burst data frame extracted from the decoded data of the slave station through the synchronization mark sequence corresponds to which allocated time slot of which superframe of the master station. The calculation is relatively complicated, resulting in low algorithm performance, and it is difficult to implement, debug and troubleshoot. Summary of the invention

[0031] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a VSAT master station data clock alignment method.

[0032] The purpose of the present invention is achieved through the following technical solutions: A VSAT master station data clock alignment method comprises the following steps:

[0033] S1: Receives the main station DVB signal and the small station TDMA signal, and demodulates and decodes them;

[0034] 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;

[0035] S3: accumulating multiple consecutive overclocked time slot allocation plans and burst data frames;

[0036] S4: traverse the 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.

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

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

[0039] 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;

[0040] A23: caching the pre-processed superframe time slot allocation plan;

[0041] A24: Calculate the absolute time at which each allocated time slot occurs.

[0042] Preferably, in step S2, the parsing steps of the small station decoding data 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 time difference between the burst period and the timestamps of adjacent burst data frames, and insert the corresponding number of empty bursts and their timestamps for marking;

[0045] B23: Cache the pre-processed burst data frames and their timestamps.

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

[0047] Preferably, 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 time slot allocation plan,

[0048] 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;

[0049] 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 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, 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 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. The present invention receives and processes the master station decoding data and the small station decoding data in real time, thereby performing the master small station clock alignment in real time, thereby improving the timeliness of the clock alignment.

[0054] 2. The present invention fills lost superframes and lost bursts, and fills empty bursts in idle time slots, so that the time slot allocation plan and burst data frames involved in the matching are completely consistent in number. The clock alignment position can be quickly found through shift positioning and flag screening, which greatly improves the efficiency of the clock alignment of the main station, while reducing the complexity of the algorithm, improving the algorithm performance, and simplifying software debugging and fault location.

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

[0056] 4. The present invention adopts an idle time slot matching algorithm to realize the clock alignment of the main station, which greatly improves the adaptability and generalization ability of the algorithm for different types of VSAT. It is not only more accurate and efficient, but also ensures that it will not be affected by the superframe loss of the main station or the burst loss of the small station from the implementation mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0058] Figure 2 A schematic diagram of the process of the existing master station clock alignment method based on in-use time slot matching;

[0059] Figure 3 A schematic diagram of real-time output of main station decoding data and small station decoding data;

[0060] Figure 4 The figure is a schematic diagram of the process of the master station clock alignment method based on idle time slot matching. DETAILED DESCRIPTION

[0061] In order to make the purpose, 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 drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown 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 accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0064] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0065] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use, or the positions or positional relationships commonly understood by those skilled in the art, which are only for the convenience of describing the present invention and simplifying the description, and do 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 cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0066] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" 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 a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0067] In this embodiment, if Figure 3 and Figure 4 As shown, a VSAT master station data clock alignment method includes the following steps:

[0068] S1: Receives the main station DVB signal and the small station TDMA signal, and demodulates and decodes them;

[0069] S2: Send the main station decoding data and the small station decoding data to the data processing module, the data processing module receives and caches the data in real time, and parses it; specifically, by receiving and processing the main station decoding data and the small station decoding data in real time, the main station clock is aligned in real time, thereby improving the timeliness of the clock alignment. That is to say, the prior art adopts a forward matching algorithm between the in-use time slot and the burst data frame, and superframe loss and burst loss are inevitable, so the main station clock alignment often needs to be completed based on multiple batches of data (until there is data without superframe and burst loss), and realignment is required when false alignment occurs. Therefore, the requirement for the amount of cached data is relatively large, so it is processed in the form of a file. The data required for the main station clock alignment of the present invention is no longer read from a file, but is based on real-time data output from the network, thereby improving the real-time processing and no longer occupying disk storage space.

[0070] S3: accumulating a plurality of consecutive overclocked time slot allocation plans and burst data frames; preferably, accumulating more than three consecutive overclocked time slot allocation plans and burst data frames.

[0071] S4: Traverse the time slot allocation plan cached in step S2 in sequence, and obtain the alignment result of the main station clock according to the matching result of the idle time slot and the empty burst. The present invention adopts an idle time slot matching algorithm to realize the clock alignment of the main station, which greatly improves the adaptability and generalization ability of the algorithm for different types of VSAT, that is, the matching threshold value and standard are based on the superframe period, and no fixed parameters or ratios are set according to empirical values, so it can be applied to VSATs of different types or different regions. Moreover, it is guaranteed from the implementation mechanism that it will not be affected by the superframe loss of the main station or the burst loss of the small station. In this embodiment, step S1 is implemented using the existing method, which is not improved here and will not be described in detail.

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

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

[0074] 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;

[0075] A23: caching the pre-processed 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 decoding 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: According to the time difference between the burst period and the timestamps of adjacent burst data frames, the number of idle time slots and lost burst data frames is calculated, and the corresponding number of empty bursts and their timestamps are inserted for marking; specifically, there are two sources of empty bursts: the first is that the idle time slots cause the small station to not generate burst data; the second is that the small station generates burst data in the allocated time slot, but due to the burst loss, the third party does not receive the burst data in the time slot. To facilitate the subsequent matching operation, empty bursts are filled in both cases. Here, the meaning of empty bursts is only a placeholder for burst data frames, without data payload.

[0079] B23: Cache the pre-processed burst data frames and their timestamps. Specifically, by filling the lost superframes and lost bursts, and filling the empty bursts in the idle time slots, the time slot allocation plan and burst data frames participating in the matching are completely consistent in number, and the clock alignment position can be quickly found through shift positioning and mark screening, which greatly improves the efficiency of the clock alignment of the master station, while reducing the complexity of the algorithm, improving the algorithm performance, simplifying software debugging and fault location, that is, when looking for the clock alignment position, first, the idle time slots and empty bursts are quickly screened by using the mark filtering method, and second, the position offset is calculated first (through the superframe period, burst period and timestamp), and then the idle time slots and burst data frames to be compared are quickly located by direct shifting. The combination of the two avoids multiple traversals of the two queues to be compared, eliminates the original time matching performance bottleneck, greatly improves the efficiency of the clock alignment of the master station, and reduces the complexity of the algorithm. The lost superframe and lost burst detection algorithm is used to measure the number of lost superframes and the number of lost bursts to ensure the correctness and robustness of the time matching between the time slot allocation plan and the burst data. That is to say, for the allocated time slot, superframes or bursts may be lost due to reasons such as poor signal-to-noise ratio, demodulation frame loss, decoding errors and signaling parsing errors. Therefore, the existing technology is easily affected by burst loss. However, in non-cooperative satellite communication scenarios, it is common that the received TDMA signal quality of the small station is poor and the signal-to-noise ratio is low. Demodulation frame loss and decoding errors as well as signaling parsing errors caused by the former two are inevitable. Therefore, the present invention adopts an idle time slot matching algorithm to significantly improve the versatility and robustness of the main station clock alignment.

[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 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 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 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; S3: accumulating multiple consecutive overclocked time slot allocation plans and burst data frames; S4: traverse the 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 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 / GS stream, parse the signaling in the stream data, and obtain the 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; A23: caching the pre-processed superframe time slot allocation plan; A24: Calculate the absolute time at which each allocated time slot occurs.

3. The VSAT master station data clock alignment method according to claim 2, characterized in that: 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 period and the timestamps of adjacent burst data frames, and insert the corresponding number of empty bursts and their timestamps for marking; B23: Cache the pre-processed burst data frames and their timestamps.

4. The VSAT master station data clock alignment method according to claim 3, characterized in that: In the step S3, more than three consecutive overclocked time slot allocation plans and burst data frames are accumulated.

5. The VSAT master station data clock alignment method according to claim 4, 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 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 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 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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