Satellite communication robust access method and system based on frequency hopping

Abstract

The invention provides a satellite communication robust access method based on frequency hopping, and the method comprises the steps: a terminal recognizes interfered frequency points through an outlier detection algorithm, distributes an abandoning probability for the interfered frequency points, and screens a frequency hopping frequency set; calculating a frequency hopping interval according to the number of the users, the interference intensity and channel coherent bandwidth optimization; encoding data to be transmitted by adopting an LT code to generate an LT encoded data packet; the terminal sends an uplink access request to the satellite, if the access fails, the load threshold and the backoff time are optimized according to the priority, and the uplink access request is sent again after waiting for the backoff time; transmitting an LT coded data packet based on the optimized frequency hopping frequency set and the optimized frequency hopping interval; and the satellite receives and analyzes the LT coded data packet. Therefore, reliability and spectrum efficiency can be taken into consideration, meanwhile, self-adaption can be carried out according to the external environment, and the service requirements of different users can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite communications, and in particular to a frequency hopping-based satellite communication robust access method and system. Background Art

[0002] Satellite communications, with their global coverage, have become a vital strategic communications resource. However, satellites are exposed to an open electromagnetic environment and are susceptible to external interference. Frequency-hopping (FH) communications are a key anti-interference measure for satellite communications. In a FH satellite communication system, terminals are assigned a pseudo-random (PN) hopping frequency sequence. By continuously and randomly hopping the carrier frequency across a wide frequency band, these changes are difficult to track and predict, resulting in excellent anti-interference performance. Therefore, FH communications offer excellent anti-interference capabilities and concealed communication capabilities against eavesdropping.

[0003] Frequency-hopping schemes were originally designed based on wide-bandwidth time-frequency diversity, offering inherent security and reliability in harsh environments. Currently, extensive research is dedicated to improving the spectral efficiency of frequency-hopping systems by applying high-dimensional modulation schemes. However, existing work falls far short of meeting the growing demand for intrinsically safe high-speed wireless communications and access.

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

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

[0006] 2) Weak robustness. The system has weak perception and self-adaptation capabilities to external environments such as noise, interference, and channel quality, and cannot adjust and adapt to the external environment in a timely manner. Frequency bands with good and poor channel conditions are used with equal probability, resulting in reduced system throughput.

[0007] 3) No differentiation between user and service services. There is no systematic consideration of the QoS requirements and user and service priorities of different users and services, and different access policies cannot be adopted based on user service access needs and priorities.

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

[0009] In view of the above-mentioned defects, the object of the present invention is to provide a satellite communication robust access method and system that takes into account both reliability and spectrum efficiency, can adapt to the external environment, and can meet the business needs of different users.

[0010] In order to achieve the above technical effects, on the one hand, the present invention provides a method for robust access to satellite communications based on frequency hopping, comprising the steps of:

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

[0012] Real-time monitoring of the number of users, interference intensity, and channel coherence bandwidth, and optimizing and calculating the frequency hopping interval based on the number of users, interference intensity, and channel coherence bandwidth;

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

[0014] 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 the priority, and waits for the backoff time to resend;

[0015] Sending the LT coded data packet based on the optimized frequency hopping frequency set and frequency hopping interval;

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

[0017] Optionally, using LT code to encode the data to be transmitted includes:

[0018] Determining a coding degree d according to a 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 original data packets to be transmitted and perform XOR operation to generate encoded packets.

[0020] Optionally, the backoff time is calculated as:

[0021]

[0022] in, is the backoff time, n is the priority number of the data, T update is the channel load statistics period, L s is the satellite payload, L n is the load threshold of the current service priority n, Random(x,y) represents the generation of a random number in the interval (x, y), and Indicates that data with priority n will not be backed off.

[0023] Optional, the load threshold L for the current service priority n n The settings satisfy:

[0024]

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

[0026] Optionally, the outlier detection algorithm is a K-means algorithm, and the terminal identifying the interfered frequency point by using the outlier detection algorithm includes:

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

[0028] Using K-means clustering, data points whose edge weights are greater than the outlier threshold are classified into the corresponding cluster centers;

[0029] Iteratively updating the cluster centers and then re-clustering to determine whether the clustering results have changed;

[0030] If the clustering result does not change, the unclassified data points are marked as disturbed frequency points.

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

[0032]

[0033] Wherein, Δf is the frequency hopping interval, N u is the number of users, B c is the channel coherence bandwidth, I is the interference intensity, α, β, γ are the values ​​corresponding to N u 、B c , the relevant proportion index of I.

[0034] Optionally, in a satellite handover scenario, it also includes:

[0035] The terminal continuously sends the LT coded data packet to the source satellite and the target satellite;

[0036] The source satellite forwards the received coded packet to the target satellite via an intersatellite link;

[0037] The target satellite aggregates two-way coded packets and decodes them to obtain original data; wherein the two-way coded packets are coded packets received from the terminal and the source satellite respectively.

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

[0039] The terminal selects a carrier frequency according to the optimized frequency hopping frequency set, switches the carrier frequency according to the optimized frequency hopping interval in each time slot, and simultaneously sends the LT encoded data packet to the satellite through the switched carrier frequency, and continuously avoids the interfered frequency determined by detection during the sending process.

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

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

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

[0043] The frequency-hopping-based robust satellite communication access method provided by this invention uses LT codes to enhance the robustness of uplink data transmission and reduce data retransmissions. It optimizes the access mechanism through load thresholds and backoff times to increase the probability of successful access. Furthermore, it enhances the anti-interference performance of frequency-hopping access through frequency-hopping interval interference detection and optimization. These optimization measures contribute to the establishment of a more complete and robust frequency-hopping-based satellite communication access mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flowchart of the steps of the frequency hopping-based satellite communication robust access method provided in one embodiment of the present invention;

[0045] Figure 2 A diagram of a satellite communication access mechanism based on frequency hopping provided in one embodiment of the present invention;

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

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

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

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

[0050] Figure 7 A schematic diagram of a flow chart showing the calculation of loads at each priority level for the frequency hopping-based satellite communication robust access method provided in one embodiment of the present invention;

[0051] Figure 8 A flow chart of an outlier detection algorithm for the frequency hopping-based satellite communication robust access method provided in one embodiment of the present invention;

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

[0053] Figures 10a to 10c Schematic diagram of the results of the frequency hopping-based satellite communication robust access method provided in one embodiment of the present invention based on the big data method, distance and artificial neural network outlier detection methods;

[0054] Figure 11 The figure is a comparison between the frequency hopping-based satellite communication robust access method provided by an embodiment of the present invention and the existing random access and back-off access method. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present 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 only used to explain the present invention and are not intended to limit the present invention.

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

[0057] In addition, certain words are used in the specification and subsequent claims to refer to specific components or parts. It should be understood by those with ordinary knowledge in the relevant field that manufacturers may use different nouns or terms to refer to the same component or part. This specification and subsequent claims do not use differences in names as a way to distinguish components or parts, but rather use differences in the functions of components or parts as the criteria for distinction. The words "including" and "comprising" mentioned throughout the specification and subsequent claims are open-ended terms and should be interpreted as "including but not limited to". In addition, the word "connect" here includes any direct and indirect electrical connection means. Indirect electrical connection means include connection through other devices.

[0058] In a frequency hopping satellite communication system, the factors that affect system performance are:

[0059] 1) Lack of robust transmission methods. Each time slot in frequency-hopping communication is only tens of microseconds long, often insufficient to fully transmit a data packet or frame for highly reliable command and control communications. Furthermore, frequency collisions between different users can lead to unsuccessful data transmission on some frequencies, resulting in the loss of entire packets or frames, reducing transmission reliability and spectral efficiency. This necessitates the use of more robust transmission methods.

[0060] 2) Poor environmental adaptability. Existing methods pre-set a frequency hopping pattern for both the user and the satellite before accessing the satellite. The carrier frequency for each time slot is selected based on the frequency hopping pattern. This method is simple, but it cannot adapt in real time to external interference and changes in channel conditions. Therefore, both parties will still communicate in frequency bands subject to interference or poor channel quality, reducing communication reliability and spectrum efficiency.

[0061] 3) Difficulty meeting diverse needs. Satellite communication systems offer wide coverage, diverse user types, and varying priorities and QoS requirements. However, traditional frequency-hopping satellite communication systems rarely consider user priorities and QoS requirements. Each user has equal access to frequency resources, and there are no adequate measures to ensure user priority and QoS requirements such as bit error rate, packet loss rate, and latency.

[0062] In view of the problems of reliability, external interference, lack of priority and number of users in the existing frequency hopping communication system, the present invention adopts the following four optimization measures: Figure 2 shown.

[0063] 1) Improve transmission reliability and interruption performance through the use of LT code;

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

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

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

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

[0068] Figure 1 A frequency hopping-based robust access method for satellite communication provided by an embodiment of the present invention is shown, comprising the following steps:

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

[0070] To effectively analyze spectrum data and improve efficiency and accuracy, a multi-channel fast adaptive clustering algorithm is employed. A scanning channel is used for a coarse scan with a large granularity to obtain the overall data outline, followed by a resident channel to obtain detailed spectrum data information. By dividing spectrum 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, high-precision analysis and detection of big data. To detect interference sources, outliers in the spectrum data must be detected, and this outlier detection employs an outlier detection algorithm.

[0071] Outlier detection is also known as heterogeneous analysis, isolated point analysis, etc. In most data mining algorithms, outliers are usually treated as noise that affects the model performance and are cleaned up in the preprocessing stage. However, in fact, these outliers often contain very important information, such as interference information.

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

[0073] An outlier threshold is set and several cluster centers are randomly selected. Data points with edge weights greater than the outlier threshold are classified into corresponding cluster centers through K-means clustering. After iteratively updating the cluster centers, the data are re-clustered to determine whether the clustering results have changed. If the clustering results have not changed, the unclassified data points are marked as interfered frequency points.

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

[0075] 1) According to the system clustering and outlier calculation, it is necessary to set the outlier threshold D. That is, when the weight value of the edge between any two data elements is less than D, the two points will not 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 centers of k categories.

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

[0080] 6) Check whether the clustering results have changed. If so, go to step 4) and continue; if not, go to step 7).

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

[0082] The outlier detection algorithm based on the K-means clustering algorithm is in the same vein as the clustering algorithm. When performing data clustering calculations, it is only necessary to add the judgment of the outlier threshold to detect the outliers at the same time, thereby reducing the amount of data analysis and calculation of the entire system and improving the analysis efficiency.

[0083] After detecting an interfering frequency, the frequency hopping sequence, based on the original pseudo-random sequence, needs to avoid channels with poor channel conditions. This embodiment sets the probability of selecting a frequency based on the channel conditions. Let the abandonment probability be p. Once an interfered frequency is selected, it is abandoned with probability p. The greater the interference, the greater the probability of abandoning it.

[0084] Figures 10a to 10c The following charts compare the results of outlier detection algorithms based on big data, distance, and artificial neural networks. The dashed lines correspond to outliers. As can be seen from the chart, the big data-based method has a higher probability of detecting outliers.

[0085] S102: Real-time monitoring of the number of users, interference intensity, and channel coherence bandwidth, and optimization and calculation of the frequency hopping interval based on the number of users, interference intensity, and channel coherence bandwidth. This step optimizes the frequency hopping interval based on the number of users and interference statistics, and can be used to improve adaptability to different numbers of users and noise levels.

[0086] In a frequency-hopping communication system, given a fixed hopping bandwidth, a smaller hopping interval increases the number of selectable hopping frequencies, making them difficult to predict and track. However, interference between users using adjacent frequencies also becomes increasingly severe. Therefore, as the number of users increases, it's necessary to reduce the hopping interval and increase the number of channels to increase user capacity. However, the spacing between adjacent frequencies must be greater than the coherence bandwidth, otherwise severe interference between users will occur. In cases of strong interference or poor channel characteristics, the frequency spacing should be appropriately increased to reduce the effects of co-channel interference and multipath fading.

[0087] See also Figure 9 In an optional embodiment, the frequency hopping interval optimization based on the number of users and interference statistics can be implemented 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: This module monitors the number of user terminals in the system, the strength and distribution of interference signals in the communication environment, and other parameters such as the channel bandwidth in real time. By receiving and analyzing signals from the communication environment, it monitors the strength and distribution of interference signals, as well as other parameters such as the channel bandwidth, in real time. These parameters can be obtained through specialized sensors or signal processing algorithms.

[0089] Frequency Hopping Interval Calculation Module: This module calculates the optimal frequency hopping interval based on the parameters obtained by the dynamic monitoring module and a preset frequency hopping interval optimization algorithm. This algorithm, based on machine learning and neural network technologies, gradually optimizes the accuracy and efficiency of frequency hopping interval calculation through training and learning.

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

[0091] Feedback Adjustment Module: During communication, this module receives and analyzes feedback from the receiver, such as bit error rate (BER) and signal-to-noise ratio (SNR), to adjust the frequency hopping interval. If communication performance is poor or interference worsens, the frequency hopping interval can be dynamically adjusted to optimize 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 correlation bandwidth. According to the different conditions of each system, the optimization calculation formula of the frequency hopping interval can be expressed as:

[0093]

[0094] Wherein, Δf is the frequency hopping interval, N u is the number of users, B c is the channel coherence bandwidth, I is the interference intensity, α, β, γ are the values ​​corresponding to N u 、B c , the relevant proportion index of I.

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

[0096] Fountain codes, as a method for intra-stream network coding, have garnered extensive attention and research. Fountain codes can be viewed as low-complexity long erasure codes (LECs) that can be used for reliable data transmission over paths with arbitrary erasure probabilities. The key advantage of fountain codes lies in their rate-free nature: a source node generates any number of encoded data from k original data, and the destination node, after receiving a sufficient amount of encoded data, can decode and retrieve the original data. The present invention utilizes fountain codes in satellite communication systems based on their following properties:

[0097] 1. The source node does not require any feedback from the receiving node. In satellite communications, long transmission delays result in end-to-end round-trip times (RTTs) of several minutes to hours, making traditional ARQ schemes unusable in satellite communication systems. In contrast, in a communication system using fountain codes, as long as a sufficient amount of encoded data is received, the receiving node can decode all the original data, eliminating the need to send ACK / NACK information to the source node as in ARQ schemes. Therefore, fountain codes are particularly suitable for use in satellite communication systems, where high latency and closed-loop control are unavailable.

[0098] 2. XOR encoding (exclusive OR encoding) can generate encoded data "online". XOR encoding and decoding operations are low in complexity and are well suited for nodes in satellite networks with limited data processing capabilities.

[0099] 3. Continuous transmission of coded data is not required. This feature is very suitable for the intermittent connection characteristics of satellite communication systems caused by users switching between beams and satellites.

[0100] LT codes are the first fountain codes implemented in practical systems. In LT codes, each coded data is a linear combination of randomly selected original data.

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

[0102] In the specific implementation, it is assumed that there are k original data to be transmitted, see Figure 3 , the LT encoding process of this embodiment is as follows:

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

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

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

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

[0107] LT code is a sparse graph coding similar to LDPC code with deletion channel as the background, and the original data and the encoded data form a bipartite graph structure. i Represents the original data, x i Represents the encoded data, and the original data of each connected encoded data is called x i neighbors, and each coded data is generated by XOR encoding of all its neighbors. Figure 4 As shown, x2 is generated by XOR encoding of m1 and m2, and x i By m n-2 、m i XOR code is generated. i The number of neighbors is called x i The degree, for example, x n-1 The degree of is equal to 3. The degree and neighbor set of each coded data are sent to the destination node along with the coded data.

[0108] In the satellite switching scenario, this embodiment also includes: the terminal continuously sends LT coded data packets to the source satellite and the target satellite; the source satellite forwards the received coded packets to the target satellite via an inter-satellite link; the target satellite aggregates the two-way coded packets and decodes the original data; wherein the two-way coded packets are coded 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 gradually moves from the coverage area of ​​satellite S1 to that of satellite S2, it transmits LT-coded data to the satellites before and after the handoff. During the handoff, S1 transmits the previously received coded data from the terminal to S2 via the intersatellite link (ISL). This allows satellite S2 to receive both the coded data before and after the handoff. As long as S2 receives sufficient coded data, it can decipher the original data. In extreme cases, if there is no ISL between satellites S1 and S2, satellite S2 can still decipher the original data after receiving sufficient coded data. Furthermore, LT code-based technology offers strong robustness during data transmission from the terminal to the satellite. Even if some coded data is lost during transmission, the satellite can still decipher the original data as long as it receives sufficient coded data, significantly improving access reliability.

[0110] S104: The terminal sends an uplink access request to the satellite. If access fails, the load threshold and backoff time are optimized based on the priority, and the request is resent after the backoff time has expired. Specifically, the terminal sends an uplink access request message to the satellite and, based on the satellite's feedback, determines whether access is successful. If so, the process proceeds to step S105. Otherwise, the terminal optimizes the load threshold and backoff time based on its priority. After the backoff time has expired, the terminal resends the access request and re-determines whether access is successful. This process repeats until access is successful and the process proceeds to step S105.

[0111] Load threshold and backoff time (i.e., backoff time) are two important parameters for users to access satellites. For different priorities, the load threshold and backoff time are different. Assume that the priorities of services in the network are divided into levels 0 to N-1, where 0 is the highest priority and N-1 is the lowest priority. 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 real-time load is L. During the backoff process, the services of different levels of priority start to backoff from the low priority services. For the service with priority n, only when L n <L≤L n-1 When the priority service needs to be backed off, the backoff time is based on the backoff time of the priority service.

[0112] The basic idea of ​​the backoff algorithm in this embodiment is: when the terminal data is being sent, if the satellite load is greater than the corresponding priority threshold, a backoff is performed; the higher the priority level of the data, the shorter the backoff time corresponding to it, and the backoff time should be greater than the channel load statistical period.

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

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

[0115] 2) The data enters the queue of terminal priority n;

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

[0117] 4) Check whether the satellite load is less than the service threshold L of priority n n ;

[0118] 5) If it is less than, the terminal sends the data and the access process of the service ends; otherwise, the terminal backs off the service and waits for the backoff 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 the service flow will not be sent again within a short period of time after the backoff occurs, that is, the channel load is still greater than the threshold corresponding to this service flow. Therefore, the setting of the priority threshold must meet the following requirements:

[0120]

[0121] From the above formula, we can see that the load threshold L of the service with higher priority is n-1 The minimum value of The higher the load threshold, the smaller the backoff probability, and the greater the probability of access collision. When the number of users increases, the collision probability will rise rapidly, causing the access capacity of the access network to drop sharply.

[0122] Therefore, this embodiment selects the priority as the minimum threshold to avoid the problem of capacity reduction 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 business in the total business is r n (n=1,2,…,N-1).

[0125] So, assuming the load threshold of the lowest priority service is L n-1 Determine, and then gradually obtain the load threshold of each priority service through the above formula, where the load threshold of the service with priority 0 is 1. The calculation process is as follows: Figure 7 As shown in the figure, the preset formula referred to in the figure is the above formula.

[0126] In addition to calculating the load threshold of each priority level according to the load calculation process, this embodiment also needs to calculate the backoff time according to the priority level, satellite load, and the load threshold of each priority level.

[0127] Specifically, the backoff time is calculated as:

[0128]

[0129] in, is the backoff time, n is the priority number of the data, T update is the channel load statistics period, L s is the satellite payload, L n is the load threshold of the current service priority n, Random(x,y) represents the generation of a random number in the interval (x, y), and Indicates that data with priority n will not be backed off.

[0130] S105: Sending an LT coded data packet based on the optimized frequency hopping frequency set and frequency hopping interval.

[0131] In specific implementation, step S105 includes: the terminal selects a carrier frequency according to the optimized frequency hopping frequency set, switches the carrier frequency according to the optimized frequency hopping interval in each time slot, and sends the LT encoded data packet to the satellite through the switched carrier frequency, and continuously avoids the interfered frequency determined by detection during the sending process.

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

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

[0134] 1. Message Passing (MP) decoding

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

[0136] 1) Release all the coded data with a degree of "1" and restore the original data corresponding to them. The set of these original data is called the preprocessing set (Ripple).

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

[0138] 3) The coded data whose degree becomes "1" after the 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 operation is greater than "1", the degree of the coded data is reduced by 1 accordingly.

[0139] 4) After processing all elements in the preprocessing set, determine whether there is coded data with a degree of "1". If so, restore 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 restored.

[0141] Decoding failure means that after all the encoded data have been processed, all the original data have not been restored.

[0142] 2. Gaussian Elimination (GE) decoding.

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

[0144] 1) Determine whether the generator matrix G is reversible. If so, decoding can be performed; if not, decoding stops.

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

[0146] Figure 11 This figure compares the probability of successful user access as the number of system users changes. The number of users ranges from 100 to 300, service arrival follows a Poisson distribution, and service priorities are randomly selected from 0 to 9. This embodiment of the present invention uses LT codes and optimizes load thresholds, backoff time, hopping sequence, and hopping interval. As can be seen from the figure, the embodiment of the present invention significantly outperforms the random access and backoff schemes when the number of users is the same. This performance is particularly pronounced when the number of users is under 200.

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

[0148] The system may be composed of multiple functional modules, and the functional modules work together to implement the various steps of the method described in the above embodiment; the functions to be implemented by the system can be found in the above embodiment and will not be repeated here.

[0149] In summary, the robust access method for frequency hopping-based satellite communications provided by this invention uses LT codes to enhance the robustness of uplink data transmission and reduce data retransmissions. It optimizes the access mechanism through load thresholds and backoff times to increase the probability of successful access. Furthermore, it enhances the anti-interference performance of frequency hopping access through frequency hopping interval interference detection and optimization. These optimization measures establish a more complete and robust frequency hopping-based satellite communications 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, can be implemented 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 above steps or functions. Similarly, the software program of the present invention (including related data structures) can be stored in a computer-readable recording medium, for example, a RAM memory, a magnetic or optical drive or a floppy disk and similar devices. In addition, some steps or functions of the present invention can be implemented using hardware, for example, as a circuit that cooperates with a processor to perform each step or function.

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

[0152] In an alternative embodiment, the computer program comprises computer program code means adapted to perform all the steps of the method according to the invention when the computer program is run on a computer.Alternatively, the computer program is embodied on a computer readable medium.

[0153] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

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

Claims

1. A robust access method for satellite communication based on frequency hopping, characterized in that: Including steps: The terminal identifies the interfered frequency point through an outlier detection algorithm, assigns a abandonment probability to the interfered frequency point, and selects a frequency hopping frequency set based on the abandonment probability; Real-time monitoring of the number of users, interference intensity, and channel coherence bandwidth, and optimizing and calculating the frequency hopping interval based on the number of users, interference intensity, and channel coherence bandwidth; Use LT code to encode the data to be transmitted and generate LT encoded data packets; 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 the priority, and waits for the backoff time to pass before resending. Sending the LT coded data packet based on the optimized frequency hopping frequency set and frequency hopping interval; The satellite receives and parses the LT encoded data packet.

2. The frequency hopping-based robust access method for satellite communication according to claim 1, characterized in that: The LT code is used to encode the data to be transmitted, including: Determining a coding degree d according to a degree distribution function; wherein the degree distribution function includes an ideal soliton distribution or a robust soliton distribution; Randomly select d packets from the k original data packets to be transmitted and perform XOR operation to generate encoded packets.

3. The frequency hopping-based robust access method for satellite communication according to claim 1, wherein: The backoff time is calculated as: in, is the backoff time, n is the priority number of the data, T update is the channel load statistics period, L s is the satellite payload, L n is the load threshold of the current service priority n, Random(x,y) represents the generation of a random number in the interval (x, y), and Indicates that data with priority n will not be backed off.

4. The method for robust access to satellite communication based on frequency hopping according to claim 1, wherein: Load threshold L of current service priority n n The settings satisfy: Among them, the proportion of each priority n business in the total business is r n (n=1,2,…,N-1).

5. The method for robust access to satellite communication based on frequency hopping according to claim 1, wherein: The outlier detection algorithm is a K-means algorithm, and the terminal identifies the interfered frequency point by using the outlier detection algorithm, including: Set the outlier threshold and randomly select several cluster centers; Using K-means clustering, data points whose edge weights are greater than the outlier threshold are classified into the corresponding cluster centers; Iteratively updating the cluster centers and then re-clustering to determine whether the clustering results have changed; If the clustering result does not change, the unclassified data points are marked as disturbed frequency points.

6. The frequency hopping-based robust access method for satellite communication according to claim 1, wherein: The optimization calculation formula of the frequency hopping interval is: Wherein, Δf is the frequency hopping interval, N u is the number of users, B c is the channel coherence bandwidth, I is the interference intensity, α, β, γ are the values ​​corresponding to N u 、B c , the relevant proportion index of I.

7. The frequency hopping-based robust access method for satellite communication according to claim 1, wherein: In the satellite handover scenario, it also includes: The terminal continuously sends the LT coded data packet to the source satellite and the target satellite; The source satellite forwards the received coded packet to the target satellite via an intersatellite link; The target satellite aggregates two-way coded packets and decodes them to obtain original data; wherein the two-way coded packets are coded packets received from the terminal and the source satellite respectively.

8. The frequency hopping-based robust access method for satellite communication according to claim 1, wherein: The sending of the LT coded data packet based on the optimized frequency hopping frequency set and frequency hopping interval specifically includes: The terminal selects a carrier frequency according to the optimized frequency hopping frequency set, switches the carrier frequency according to the optimized frequency hopping interval in each time slot, and simultaneously sends the LT encoded data packet to the satellite through the switched carrier frequency, and continuously avoids the interfered frequency determined by detection during the sending process.

9. The frequency hopping-based robust access method for satellite communication according to claim 1, wherein: The satellite receives and parses the LT coded data packet, comprising: After receiving the LT coded data, the satellite parses the LT coded data packet through message passing decoding or Gaussian elimination decoding.

10. A frequency hopping-based satellite communication robust access system for implementing the method according to any one of claims 1 to 9.

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