Frequency hopping based satellite communication robust access method and system

Abstract

The application provides a satellite communication robust access method based on frequency hopping, wherein a terminal identifies an interfered frequency point through an outlier detection algorithm, assigns a giving-up probability to the interfered frequency point, and screens a frequency hopping frequency set; a frequency hopping interval is calculated according to the number of users, the interference intensity and the channel coherence bandwidth; LT code is used to encode the data to be transmitted to generate an LT encoded data packet; the terminal sends an uplink access request to a satellite, if the access fails, the priority optimization load threshold and the backoff time are optimized, and the terminal re-sends after waiting for the backoff time; the LT encoded data packet is sent based on the optimized frequency hopping frequency set and the frequency hopping interval; and the satellite receives and analyzes the LT encoded data packet. Therefore, the application can consider reliability and spectrum efficiency, can be self-adaptive according to external environment, and can meet different user service requirements.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and in particular to a robust satellite communication access method and system based on frequency hopping. Background Technology

[0002] Satellite communication, with its global coverage, has become an important strategic communication resource. However, satellites are exposed to an open electromagnetic environment and are easily subject to external interference. Frequency hopping communication is an important means of anti-jamming in satellite communication. In frequency hopping satellite communication systems, terminals are assigned a pseudo-random (PN) frequency hopping sequence. By continuously and randomly hopping the carrier frequency over a wide frequency band, it is difficult for external parties to track and predict its changes, thus achieving good anti-jamming performance. Therefore, frequency hopping communication has good anti-jamming capabilities and communication concealment against eavesdropping.

[0003] Frequency hopping schemes were initially designed based on high-bandwidth time-frequency diversity, possessing inherent security and reliability in harsh application environments. Currently, much work is dedicated to improving the spectral efficiency of frequency hopping systems by applying high-dimensional modulation schemes. However, existing work still falls far short of meeting the growing demand for intrinsically secure high-speed wireless communication and access.

[0004] Traditional frequency hopping systems have several major limitations:

[0005] 1) Low spectral efficiency under large bandwidth. This is mainly due to the small carrier bandwidth under large frequency hopping bandwidth, as well as the collision effect when users access the system. If different users use the same frequency in the same time slot when accessing the system, they will interfere with each other, which will reduce the reliability and spectral efficiency of traditional frequency hopping communication systems.

[0006] 2) Weak robustness. It has a weak ability to perceive and adapt to external environments such as noise, interference, and channel quality. It cannot adjust and adapt to the external environment in a timely manner. The frequency bands with good channel conditions and those with poor channel conditions have the same probability of being used, which leads to a decrease in system throughput.

[0007] 3) Lack of differentiation in user services. There is no systematic consideration of the QoS requirements of different users and services, as well as user and service priorities. Different access strategies cannot be adopted based on requirements and priorities when users access services.

[0008] Therefore, there is an urgent need for an access method for frequency-hopping satellite communication systems that can improve the reliability of frequency-hopping communication systems, adjust according to the external environment, and adopt different access strategies for different users and service needs, so as to better meet user access requirements. Summary of the Invention

[0009] To address the aforementioned shortcomings, the present invention aims to provide a robust satellite communication access method and system that balances reliability and spectral efficiency, adapts to external environments, and meets the diverse service needs of users.

[0010] To achieve the above-mentioned technical effects, on the one hand, the present invention provides a robust satellite communication access method based on frequency hopping, comprising the following steps:

[0011] The terminal identifies the interfered frequency points through an outlier detection algorithm, assigns a drop probability to the interfered frequency points, and filters the frequency hopping frequency set based on the drop probability;

[0012] The system monitors the number of users, interference intensity, and channel coherence bandwidth in real time, and optimizes the frequency hopping interval based on these parameters.

[0013] The data to be transmitted is encoded using LT (Luby Transform Code, a fountain code based on random graph theory) to generate LT encoded data packets;

[0014] The terminal sends an uplink access request to the satellite. If the access fails, the load threshold and backoff time are optimized according to the priority, and the terminal waits for the backoff time before retransmitting.

[0015] The LT-coded data packets are transmitted based on the optimized frequency hopping set and frequency hopping interval;

[0016] The satellite receives and parses the LT-encoded data packets.

[0017] Optionally, encoding the data to be transmitted using LT codes includes:

[0018] The coding degree d is determined based on the degree distribution function; wherein, the degree distribution function includes an ideal soliton distribution or a robust soliton distribution;

[0019] Randomly select d packets from the k raw data packets to be transmitted and perform an XOR operation to generate an encoded packet.

[0020] Optionally, the retreat time is calculated as follows:

[0021]

[0022] in, T is the backoff time, n is the data priority number, and T is the time to avoid the backoff. update For the channel load statistics period, L s For satellite payload, L n Let n be the load threshold for the current service priority n, and Random(x,y) represent generating a random number in the interval (x,y). This means that data with priority n will not be backed up.

[0023] Optionally, the load threshold L of the current service priority n. n The settings satisfy:

[0024]

[0025] Among them, the proportion of each priority n service in the total service is r. n (n = 1, 2, ..., N-1).

[0026] Optionally, the outlier detection algorithm is the K-means algorithm, and the terminal identifies the interfered frequency points using the outlier detection algorithm, including:

[0027] Set an outlier threshold and randomly select several cluster centers;

[0028] K-means clustering is used to assign data points whose edge weights are greater than the outlier threshold to the corresponding cluster centers;

[0029] After iteratively updating the cluster centers, re-cluster the clusters and determine whether the clustering results have changed.

[0030] If the clustering results remain unchanged, the unclassified data points are marked as disturbed frequency points.

[0031] Optionally, the optimized calculation formula for the frequency hopping interval is:

[0032]

[0033] Where Δf is the frequency hopping interval, N u For the number of users, B c Let I be the channel coherence bandwidth, I be the interference intensity, and α, β, and γ be the values ​​corresponding to N. u B c The relevant proportional index of I.

[0034] Optionally, in satellite handover scenarios, the following are also included:

[0035] The terminal continuously sends the LT-encoded data packets to the source satellite and the target satellite;

[0036] The source satellite forwards the received encoded packets to the target satellite via an inter-satellite link;

[0037] The target satellite aggregates dual-channel encoded packets and decodes them to obtain the original data; wherein, the dual-channel encoded packets are encoded packets received from the terminal and the source satellite respectively.

[0038] Optionally, transmitting the LT-coded data packet based on the optimized frequency hopping set and frequency hopping interval specifically includes:

[0039] The terminal selects a carrier frequency according to the optimized frequency hopping set, switches the carrier frequency in each time slot according to the optimized frequency hopping interval, and sends the LT-coded data packet to the satellite through the switched carrier frequency, while continuously avoiding the detected and determined interference frequency during the transmission process.

[0040] Optionally, the satellite receiving and parsing the LT-encoded data packets includes:

[0041] After receiving the LT-encoded data, the satellite parses the LT-encoded data packet through message passing decoding or Gaussian elimination decoding.

[0042] On the other hand, the present invention also provides a frequency-hopping-based robust satellite communication access system for implementing the above-described method.

[0043] The frequency-hopping-based robust satellite communication access method provided by this invention employs LT codes to enhance the robustness of uplink data transmission and reduce data retransmissions; it optimizes the access mechanism through load thresholds and backoff time to improve the probability of successful access; and it enhances the anti-interference performance during frequency-hopping access through frequency-hopping interval interference detection and frequency-hopping interval optimization. These optimization measures are used to establish a more complete and robust frequency-hopping-based satellite communication access mechanism. Attached Figure Description

[0044] Figure 1 A flowchart illustrating the steps of the frequency-hopping-based robust satellite communication access method according to an embodiment of the present invention;

[0045] Figure 2 A diagram illustrating a frequency-hopping-based satellite communication access mechanism according to an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of LT code encoding for the frequency-hopping-based robust satellite communication access method provided in an embodiment of the present invention;

[0047] Figure 4 A schematic diagram of the LT code bipartite graph structure of the frequency-hopping-based robust access method for satellite communication provided in an embodiment of the present invention;

[0048] Figure 5 A schematic diagram of the LT code transmission process in a satellite handover scenario for the frequency-hopping-based robust access method for satellite communication provided in an embodiment of the present invention;

[0049] Figure 6A flowchart illustrating the terminal access process based on a responsible threshold and backoff time in the frequency-hopping-based robust satellite communication access method provided in an embodiment of the present invention.

[0050] Figure 7 This is a schematic diagram of the priority load calculation process of the frequency-hopping-based robust access method for satellite communication provided in an embodiment of the present invention.

[0051] Figure 8 The flowchart of the outlier detection algorithm of the frequency-hopping-based robust access method for satellite communication provided in an embodiment of the present invention is shown below.

[0052] Figure 9 A flowchart illustrating the frequency hopping interval optimization in one embodiment of the frequency hopping-based robust satellite communication access method provided by an embodiment of the present invention;

[0053] Figures 10a-10c The diagram illustrates the results of the frequency-hopping-based robust satellite communication access method provided in an embodiment of the present invention, based on big data methods, distance methods, and outlier detection methods using artificial neural networks.

[0054] Figure 11 This diagram compares the frequency-hopping-based robust satellite communication access method provided in this embodiment of the invention with existing random access backoff access methods. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] It should be noted that references to "an embodiment," "embodiment," "example embodiment," etc., in this specification refer to the described embodiment including specific features, structures, or characteristics, but not every embodiment must include these specific features, structures, or characteristics. Furthermore, such expressions do not refer to the same embodiment. Moreover, when describing specific features, structures, or characteristics in conjunction with embodiments, whether or not explicitly described, it is indicated that incorporating such features, structures, or characteristics into other embodiments is within the knowledge of those skilled in the art.

[0057] Furthermore, certain terms are used in the specification and subsequent claims to refer to specific components or parts. Those skilled in the art will understand that manufacturers may use different names or terms to refer to the same component or part. This specification and subsequent claims do not distinguish components or parts by differences in name, but rather by differences in function. The terms "comprising" and "including" used throughout the specification and subsequent claims are open-ended and should be interpreted as "including but not limited to." Additionally, the term "connection" here includes any direct and indirect electrical connection means. Indirect electrical connection means include connections made through other means.

[0058] In frequency-hopping-based satellite communication systems, the factors affecting system performance include:

[0059] 1) Lack of robust transmission methods. Frequency hopping communication has only tens of microseconds per time slot, which is often insufficient for the complete transmission time of a data packet or frame for high-reliability command and control communication. Collisions between different user frequencies can lead to unsuccessful data transmission at some frequencies, resulting in the loss of entire packets or frames of data, thus reducing transmission reliability and spectral efficiency. Therefore, more robust transmission methods are needed.

[0060] 2) Poor environmental adaptability. Current methods require both the user and the satellite to pre-configure frequency hopping patterns before the user connects to the satellite, selecting the carrier frequency for each time slot based on these patterns. While simple, this method cannot adjust in real-time to external interference and changes in channel conditions. The two parties will still communicate in frequency bands subject to interference or with poor channel quality, leading to decreased communication reliability and spectral efficiency.

[0061] 3) Difficulty in meeting diverse needs. In satellite communication systems, satellite coverage is wide, and there are many types of users with varying priorities and service QoS requirements. However, traditional frequency-hopping-based satellite communication systems rarely consider user priorities and service QoS requirements. Each user uses frequency resources equally, and there are insufficient measures to guarantee user priority and QoS requirements such as bit error rate, packet loss rate, and latency.

[0062] To address the issues of reliability, external interference, lack of priority, and limited user numbers in existing frequency-hopping communication systems, this invention employs the following four optimization measures: Figure 2 As shown.

[0063] 1) By using LT codes, transmission reliability and interruption performance can be improved;

[0064] 2) Improve support for high-priority and time-sensitive users through load threshold and rollback time optimization;

[0065] 3) Improve the ability to resist interference and adapt to complex external environments through spectrum sensing and frequency hopping sequence optimization;

[0066] 4) Improve adaptability to different numbers of users and noise levels by optimizing the frequency hopping interval.

[0067] The specific principles of the frequency-hopping-based robust satellite communication access method of this application will be described below with reference to specific embodiments.

[0068] Figure 1 This invention illustrates a frequency-hopping-based robust satellite communication access method according to an embodiment of the present invention, comprising the following steps:

[0069] S101: The terminal identifies interfered frequency points using an outlier detection algorithm, assigns abandonment probabilities to the interfered frequency points, and filters the frequency hopping set based on the abandonment probabilities. Step S101 is a frequency hopping sequence optimization measure based on interference detection, which can be used to improve anti-interference and adaptability to complex external environments. Specifically, the terminal detects interference signals and interference frequencies based on the outlier detection algorithm, determines the interfered frequency points based on the interference signal detection results, and then only initiates a probability avoidance mechanism to filter the frequency hopping set for the confirmed interfered frequency points, avoiding misoperation of normal frequency points.

[0070] To achieve effective analysis of large-scale spectral data and improve analysis efficiency and accuracy, a multi-channel fast adaptive clustering algorithm is employed. A coarse scan with larger granularity is used in the scanning channels to obtain the overall data outline, followed by a residing channel to acquire finer spectral data information. By dividing the spectral data into multiple blocks for real-time high-precision scanning monitoring and analysis, the impact of data noise on data analysis performance is reduced, enabling high-speed and high-precision analysis and detection of large datasets. To detect interference sources, outliers in the spectral data need to be detected, and an outlier detection algorithm is used for this purpose.

[0071] Outlier detection, also known as heterogeneity analysis or isolated point analysis, is a technique used in most data mining algorithms. Outliers are typically treated as noise that affects model performance and are removed during preprocessing. However, these outliers often contain very important information, such as interfering information.

[0072] In specific implementation, the outlier detection algorithm used in this embodiment is the K-means algorithm. The terminal identifies the interfered frequency points through the outlier detection algorithm, including:

[0073] Set an outlier threshold and randomly select several cluster centers; use K-means clustering to assign data points whose edge weights are greater than the outlier threshold to the corresponding cluster centers; iteratively update the cluster centers and re-cluster, then determine whether the clustering results have changed; if the clustering results have not changed, mark the unclassified data points as interference frequency points.

[0074] See Figure 8 The steps of the outlier detection algorithm based on the K-means algorithm are as follows:

[0075] 1) An outlier threshold D needs to be set according to the requirements of hierarchical clustering and outlier point calculation. That is, when the weight value of the edge between any two data elements is less than D, these two points cannot be classified into the same class.

[0076] 2) Randomly select k data elements as the centers of k classes in the clustering algorithm.

[0077] 3) Distribute other data elements into the class with the highest weight value of the edge between the k centers, and the weight value of the edge between the data element and the center point is greater than D.

[0078] 4) Recalculate the center of each class of k.

[0079] 5) Re-cluster the other elements according to the new center, and ensure that the weight of the edge between each data element and the center point is greater than D.

[0080] 6) Check if the clustering results have changed. If they have changed, proceed to step 4) to continue; if they have not changed, proceed to step 7).

[0081] 7) Examine the clustering results and find the data that were not classified into any class. These data elements are the outliers we are looking for.

[0082] Outlier detection algorithms based on K-means clustering are consistent with clustering algorithms. When performing data clustering calculations, only an outlier threshold judgment needs to be added to detect outliers simultaneously, thereby reducing the computational load of the entire system's data analysis and calculation and improving analysis efficiency.

[0083] After detecting interfering frequencies, the frequency hopping sequence, based on the original pseudo-random sequence, needs to avoid channels with poor channel conditions. In this embodiment, the probability of selecting a frequency is set according to the channel conditions. Let the abandonment probability be p. Then, when an interfering frequency is selected, that frequency is abandoned with probability p. The greater the degree of interference, the larger p becomes.

[0084] Figures 10a-10c The charts show a comparison of outlier detection algorithms based on big data, distance, and artificial neural networks. The dashed lines represent outliers. The charts demonstrate that the big data-based method has a higher probability of detecting outliers.

[0085] S102: Monitor the number of users, interference intensity, and channel coherence bandwidth in real time, and optimize the frequency hopping interval based on the number of users, interference intensity, and channel coherence bandwidth. This step is a frequency hopping interval optimization based on the number of users and interference statistics, which can be used to improve the adaptability to different numbers of users and noise levels.

[0086] In frequency-hopping communication systems, with a fixed frequency-hopping bandwidth, a smaller frequency-hopping interval allows for a wider selection of frequency hopping frequencies, making external tracking difficult. However, interference between users using adjacent frequencies also becomes increasingly severe. Therefore, as the number of users increases, it is necessary to reduce the frequency-hopping interval and increase the number of channels to improve user capacity. However, the interval between adjacent frequencies needs to be greater than the coherence bandwidth; otherwise, it will cause severe interference between users. Furthermore, in cases of strong interference or poor channel characteristics, the frequency interval needs to be appropriately increased to reduce the impact of co-channel interference and multipath fading.

[0087] See Figure 9 In an optional implementation, frequency hopping interval optimization based on the number of users and interference statistics can be achieved using a dynamic monitoring module, a frequency hopping interval calculation module, a frequency hopping sequence generation module, and a feedback modulation module, wherein:

[0088] Dynamic monitoring module: Used for real-time monitoring of parameters such as the number of user terminals in the system, the strength and distribution of interference signals in the communication environment, and the relevant bandwidth of the channel. It receives and analyzes signals from the communication environment to monitor the strength and distribution of interference signals and the relevant bandwidth of the channel in real time. These parameters can be obtained through specialized sensors or signal processing algorithms.

[0089] Frequency hopping interval calculation module: Based on the parameters obtained from the dynamic monitoring module and the preset frequency hopping interval optimization algorithm, the optimal frequency hopping interval is calculated. This algorithm can be based on machine learning, neural networks, and other technologies, and through training and learning, it can gradually optimize the calculation accuracy and efficiency of the frequency hopping interval.

[0090] Frequency hopping sequence generation module: Based on the calculated frequency hopping interval, it generates the corresponding frequency hopping sequence to control the hopping of the carrier frequency.

[0091] Feedback Adjustment Module: During communication, the module receives and analyzes feedback information from the receiver, such as bit error rate and signal-to-noise ratio, to adjust the frequency hopping interval. If communication performance is poor or interference worsens, the frequency hopping interval can be dynamically adjusted to optimize frequency hopping performance.

[0092] The optimization of the frequency hopping interval is related to three parameters: the number of users in the system, the interference intensity within the frequency hopping bandwidth, and the channel-dependent bandwidth. Depending on the specific conditions of each system, the optimization formula for the frequency hopping interval can be expressed as:

[0093]

[0094] Where Δf is the frequency hopping interval, N u For the number of users, B c Let I be the channel coherence bandwidth, I be the interference intensity, and α, β, and γ be the values ​​corresponding to N. u B c The relevant proportional index of I.

[0095] S103: Encode the data to be transmitted using LT code to generate LT-encoded data packets.

[0096] Fountain codes, as an intra-stream network coding method, have received widespread attention and research. Fountain codes can be viewed as a type of low-complexity Long Erasure Codes (LECs), capable of reliable data transmission over paths with arbitrary erasure probabilities. A key advantage of fountain codes lies in their rateless nature: the source node generates any number of encoded data points from k original data points, and the destination node, after receiving a sufficient number of encoded data points, can retrieve the original data through decoding. This invention uses fountain codes in satellite communication systems based on the following characteristics:

[0097] 1. The source node does not need to send any feedback from the receiving node. In satellite communication, large transmission delays result in end-to-end round-trip times (RTTs) ranging from minutes to hours, making traditional ARQ schemes unusable in satellite communication systems. However, in communication systems using fountain codes, as long as a sufficient amount of encoded data is received, the receiving node can decode all the original data without sending ACK / NACK messages to the source node as in ARQ schemes. Therefore, fountain codes are particularly suitable for use in environments like satellite communication systems where delays are high and closed-loop control is not feasible.

[0098] 2. Encoded data can be generated "online" through XOR encoding. XOR encoding and decoding operations have low complexity, making them ideal for nodes in satellite networks with limited data processing capabilities.

[0099] 3. Continuous transmission of encoded data is not required. This feature is well-suited for the intermittent connectivity issues in satellite communication systems caused by users switching between beams and satellites.

[0100] LT codes were the first fountain codes to be implemented in a practical system. In LT codes, each encoded data is a linear combination of randomly selected raw data.

[0101] This embodiment uses LT codes to encode the data to be transmitted, including: determining the coding degree d according to the degree distribution function; wherein the degree distribution function includes an ideal soliton distribution or a robust soliton distribution; and randomly selecting d packets from the k original data packets to be transmitted and performing an XOR operation to generate coded packets.

[0102] In practice, assuming there are k raw data items to be transmitted, see [link / reference]. Figure 3 The LT encoding process in this embodiment is as follows:

[0103] 1) Select a degree distribution function based on system requirements. Degree distributions include ideal soliton degree distribution, robust soliton degree distribution, etc.

[0104] 2) Select a number d (the degree of the encoding) from all integers from 1 to k according to the degree distribution function;

[0105] 3) Select d different data packets with equal probability from k original data packets and perform XOR encoding to generate encoded data. The selected d original data packets constitute the neighbors of the encoded data.

[0106] 4) Repeating the above steps can continuously generate n (n>k) coded data.

[0107] LT codes are a type of sparse graph coding with a removed channel, similar to LDPC codes, where the original data and the encoded data form a bipartite graph structure. i Represents the original data, x i This represents encoded data; the original data for each concatenated encoded data is called x. i Each encoded data is generated by XORing all its neighbors. Figure 4 As shown, x2 is generated by XOR encoding of m1 and m2, while x i By m n-2 m i Generated by XOR encoding. i The number of neighbors is called x. i The degree, for example, x n-1 The degree is equal to 3. The degree and neighbor set of each encoded data are sent to the destination node along with the encoded data.

[0108] In the satellite handover scenario, this embodiment further includes: the terminal continuously sending LT-encoded data packets to the source satellite and the target satellite; the source satellite forwarding the received encoded packets to the target satellite via an inter-satellite link; and the target satellite aggregating the dual-encoded packets and decoding the original data; wherein the dual-encoded packets are encoded packets received from the terminal and the source satellite respectively.

[0109] For example, Figure 5This embodiment illustrates the reliable transmission process based on LT codes when a terminal user switches between two satellites, S1 and S2. As the terminal moves from the coverage area of ​​satellite S1 to satellite S2, it sends LT-coded data to the satellites before and after the inter-satellite handover. During the handover, S1 sends previously received coded data from the terminal to S2 via the inter-satellite link (ISL). In this way, satellite S2 can simultaneously receive both the coded data before and after the handover. As long as S2 receives sufficient coded data, it can decode the original data. In extreme cases, even if there is no ISL between satellites S1 and S2, satellite S2 can still decode the original data after receiving sufficient coded data. Furthermore, the LT code-based technology is highly robust to data transmission from the terminal to the satellite. Even if some coded data is lost during transmission, the original data can still be decoded as long as the satellite receives sufficient coded data, thus greatly improving the reliability of access.

[0110] S104: The terminal sends an uplink access request to the satellite. If the access fails, the terminal optimizes the load threshold and backoff time according to its priority, and resends after waiting for the backoff time. That is, the terminal sends an uplink access request message to the satellite, and based on the satellite's feedback, determines whether the access is successful. If successful, it proceeds to step S105; otherwise, the terminal optimizes the load threshold and backoff time according to its priority, obtains the backoff time, and resends the access request after the backoff time, re-determining whether the access is successful. This process is repeated until the access is successful and the process returns to step S105.

[0111] Load threshold and backoff time are two important parameters for users accessing satellite services. The load threshold and backoff time differ for different priorities. Assume that network services are prioritized into levels 0 to N-1, where priority 0 is the highest and priority N-1 is the lowest, and the proportion of services of each priority n in the total services is r. n (n = 1, 2, ..., N-1), the corresponding load threshold is L. n (n = 1, 2, ..., N-1), where L0 ≥ L1 ≥ L2 ≥ ... ≥ L N-1 The satellite's real-time load is L. During the backoff process, services of different priorities back off starting with those of lower priority. For a service with priority n, backoff only occurs when L... n <L≤L n-1 When this priority level is reached, the business needs to be backed off, and the backing-off time is based on the backing-off time for that priority level.

[0112] The basic idea of ​​the backoff algorithm in this embodiment is: during the process of terminal data transmission, if the satellite load is greater than its corresponding priority threshold, backoff is performed; the backoff time corresponding to data with higher priority is relatively shorter, and the backoff time should be greater than the channel load statistical period.

[0113] In practice, the terminal access process based on load threshold and fallback time is as follows: Figure 6 As shown, the specific steps are as follows:

[0114] 1) A service with terminal priority n arrives;

[0115] 2) Data enters the terminal's priority queue with priority n;

[0116] 3) The terminal receives satellite broadcast messages and extracts satellite payload information from them;

[0117] 4) Check if the satellite load is less than the service threshold L for priority n. n ;

[0118] 5) If the value is less than the threshold, the terminal sends data, and the access process for this service ends; otherwise, the terminal backs off the service and waits for the rollback time T. backoff Then, return to step 2), and the business data re-enters the queue with priority n.

[0119] The threshold setting must ensure that a traffic flow will not be retransmitted for a short period after backoff, meaning the channel load is still greater than the threshold corresponding to that traffic flow. Therefore, the priority threshold setting must satisfy the following:

[0120]

[0121] As can be seen from the above formula, the load threshold L for higher priority services... n-1 The minimum value is The higher the load threshold, the lower the probability of backoff, but the greater the probability of access collisions. As the number of users increases, the probability of collisions rises rapidly, causing a sharp drop in the access capacity of the access network.

[0122] Therefore, this embodiment selects the minimum priority threshold to avoid capacity degradation when the number of users increases, that is, the load threshold L of the current service priority n. n The settings satisfy:

[0123]

[0124] Among them, the proportion of each priority n service in the total service is r. n (n = 1, 2, ..., N-1).

[0125] Thus, assuming the load threshold for the lowest priority service is L n-1 Once determined, the load threshold for each priority service can be obtained step by step using the above formula, where the load threshold for a service with priority 0 is 1. The calculation process is as follows: Figure 7 As shown in the figure, the preset formula is the formula mentioned above.

[0126] In addition to calculating the load thresholds for each priority according to the load calculation process, this embodiment also needs to calculate the backoff time based on the priority, satellite load, and the load thresholds for each priority.

[0127] Specifically, the retreat time is calculated as follows:

[0128]

[0129] in, T is the backoff time, n is the data priority number, and T is the time to avoid the backoff. update For the channel load statistics period, L s For satellite payload, L n Let n be the load threshold for the current service priority n, and Random(x,y) represent generating a random number in the interval (x,y). This means that data with priority n will not be backed up.

[0130] S105: Transmit LT-coded data packets based on the optimized frequency hopping set and frequency hopping interval.

[0131] In specific implementation, step S105 includes: the terminal selects a carrier frequency according to the optimized frequency hopping set, switches the carrier frequency in each time slot according to the optimized frequency hopping interval, and sends LT-coded data packets to the satellite through the switched carrier frequency, while continuously avoiding the detected and determined interference frequencies during the transmission process.

[0132] S106: The satellite receives and parses the LT-encoded data packet. Specifically, after receiving the LT-encoded data, the satellite parses the LT-encoded data packet through message passing decoding or Gaussian elimination decoding.

[0133] There are two methods for decoding LT codes:

[0134] I. Message Passing (MP) Decoding.

[0135] Given n encoded data, the decoder, based on a bipartite graph, recursively decodes all the original data, starting with the encoded data of degree "1". The specific steps are as follows:

[0136] 1) Release all encoded data with a degree of "1" and recover the original data they correspond to. The set of these original data is called the preprocessing set (Ripple).

[0137] 2) Select a raw data from the preprocessing set, perform an XOR operation on the data and the adjacent encoded data, reduce the degree of all encoded data participating in the XOR operation by 1, and remove the data from the preprocessing set.

[0138] 3) Encoded data whose degree becomes "1" after XOR operation is released, the corresponding original data is restored, and these original data are added to the preprocessing set; if the degree after XOR is greater than "1", the degree of the encoded data is reduced by 1 accordingly.

[0139] 4) After processing all elements in the preprocessing set, check if there is any encoded data with a degree of "1". If so, recover the corresponding original data and add the data to the preprocessing set for further processing.

[0140] 5) Repeat the above steps until all the encoded data has been processed or all the original data has been recovered.

[0141] Decoding failure means that after all the encoded data has been processed, the original data still cannot be recovered.

[0142] II. Gaussian Elimination (GE) Decoding.

[0143] The steps of GE decoding are as follows:

[0144] 1) Determine whether the generating matrix G is invertible. If it is, decoding can proceed; otherwise, decoding stops.

[0145] 2) If G is invertible, the block matrix [G,C] composed of the generator matrix G and the encoded data C is transformed into [I,A], and then part A is the translated original data.

[0146] Figure 11 The paper presents a comparison of the success probability of user access as the number of users in the system varies. The number of users ranges from 100 to 300, service arrival follows a Poisson distribution, and service priority is randomly selected from 0 to 9. This embodiment of the invention uses LT codes to optimize load threshold, backoff time, frequency hopping sequence, and frequency hopping interval. As can be seen from the figure, the solution in this embodiment of the invention has a significantly higher success probability of access than random access and backoff schemes when the number of users is the same, especially when the number of users is less than 200.

[0147] In another embodiment, the present invention also provides a frequency-hopping-based robust satellite communication access system for implementing the methods described in the above embodiments.

[0148] The system may consist of multiple functional modules, which work together to implement the steps of the method as described in the above embodiments; the functions to be implemented by the system are described in the above embodiments and will not be repeated here.

[0149] In summary, the frequency-hopping-based robust satellite communication access method provided by this invention employs LT codes to enhance the robustness of uplink data transmission and reduce data retransmissions; optimizes the access mechanism through load thresholds and backoff time to improve the probability of successful access; and enhances the anti-interference performance during frequency-hopping access through frequency-hopping interval interference detection and frequency-hopping interval optimization. These optimization measures are used to establish a more complete and robust frequency-hopping-based satellite communication access mechanism.

[0150] It should be noted that the present invention can be implemented in software and / or a combination of software and hardware, for example, using an application-specific integrated circuit (ASIC), a general-purpose computer, or any other similar hardware device. In one embodiment, the software program of the present invention can be executed by a processor to implement the steps or functions described above. Similarly, the software program of the present invention (including associated data structures) can be stored in a computer-readable recording medium, such as RAM memory, a magnetic or optical drive, a floppy disk, or similar devices. Furthermore, some steps or functions of the present invention can be implemented in hardware, for example, as circuitry that works with a processor to perform the various steps or functions.

[0151] This invention can be implemented on a computer as a computer-based method, or in dedicated hardware, or a combination of both. Executable code or portions thereof for the method according to the invention can be stored on a computer program product. Examples of computer program products include memory devices, optical storage devices, integrated circuits, servers, online software, etc. Optionally, the computer program product includes non-transitory program code components stored on a computer-readable medium so as to execute the method according to the invention when the program product is executed on a computer.

[0152] In an optional embodiment, the computer program includes computer program code components adapted to perform all the steps of the method according to the invention when the computer program is run on a computer. Optionally, the computer program is embodied on a computer-readable medium.

[0153] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0154] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A robust satellite communication access method based on frequency hopping, characterized in that, Including the following steps: The terminal identifies the interfered frequency points through an outlier detection algorithm, assigns a drop probability to the interfered frequency points, and filters the frequency hopping frequency set based on the drop probability; The system monitors the number of users, interference intensity, and channel coherence bandwidth in real time, and optimizes the frequency hopping interval based on these parameters. The data to be transmitted is encoded using LT code to generate LT-encoded data packets; The terminal sends an uplink access request to the satellite. If the access fails, the load threshold and backoff time are optimized according to the priority, and the terminal waits for the backoff time before retransmitting. The retreat time is calculated as follows: ； in, To avoid delay, n This is the priority number of the data. For channel load statistics period, For satellite payload, Prioritize current business operations n The load threshold, This indicates the generation of a random number in the interval (x, y), and Indicates priority as n The data will not be backed up; Current business priority n load threshold The settings satisfy: ； Among them, each priority n The proportion of this business in the total business is ; The LT-coded data packets are transmitted based on the optimized frequency hopping set and frequency hopping interval; The satellite receives and parses the LT-encoded data packets; The optimized calculation formula for the frequency hopping interval is as follows: ； in, The frequency hopping interval is... For the number of users, The channel coherence bandwidth is [value missing]. The interference intensity is... They correspond to The relevant proportional index.

2. The robust satellite communication access method based on frequency hopping according to claim 1, characterized in that, Encoding the data to be transmitted using LT codes includes: Determine the coding degree based on the degree distribution function. d The degree distribution function includes an ideal soliton distribution or a robust soliton distribution. From the data to be transmitted k Randomly selected from the original data packets d Each packet is XORed to generate an encoded packet.

3. The robust satellite communication access method based on frequency hopping according to claim 1, characterized in that, The outlier detection algorithm is the K-means algorithm, and the terminal identifies the interfered frequency points using the outlier detection algorithm, including: Set an outlier threshold and randomly select several cluster centers; K-means clustering is used to assign data points whose edge weights are greater than the outlier threshold to the corresponding cluster centers; After iteratively updating the cluster centers, re-cluster the clusters and determine whether the clustering results have changed. If the clustering results remain unchanged, the unclassified data points are marked as disturbed frequency points.

4. The robust satellite communication access method based on frequency hopping according to claim 1, characterized in that, In satellite handover scenarios, the following are also included: The terminal continuously sends the LT-encoded data packets to the source satellite and the target satellite; The source satellite forwards the received encoded packets to the target satellite via an inter-satellite link; The target satellite aggregates dual-channel encoded packets and decodes them to obtain the original data; wherein, the dual-channel encoded packets are encoded packets received from the terminal and the source satellite respectively.

5. The robust satellite communication access method based on frequency hopping according to claim 1, characterized in that, The transmission of the LT-coded data packet based on the optimized frequency hopping set and frequency hopping interval specifically includes: The terminal selects a carrier frequency according to the optimized frequency hopping set, switches the carrier frequency in each time slot according to the optimized frequency hopping interval, and simultaneously sends the LT-coded data packet to the satellite through the switched carrier frequency, while continuously avoiding the detected and determined interference frequency points during the transmission process.

6. The robust satellite communication access method based on frequency hopping according to claim 1, characterized in that, The satellite receives and parses the LT-encoded data packets, including: After receiving the LT-encoded data, the satellite parses the LT-encoded data packet through message passing decoding or Gaussian elimination decoding.

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