CN112803988B - Hybrid contact graph routing method based on link error rate prediction - Google Patents
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- H04B7/00—Radio transmission systems, i.e. using radiation field
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- H—ELECTRICITY
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- H04B7/00—Radio transmission systems, i.e. using radiation field
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- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/18578—Satellite systems for providing broadband data service to individual earth stations
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Abstract
The invention discloses a hybrid contact map routing method based on link error rate prediction in a satellite internet scene, which combines the characteristics of inter-satellite links in the satellite internet and the problems in a contact map routing algorithm, provides a dynamic contact map routing algorithm DCGR-CFD based on contact failure detection, improves the accuracy of a contact plan, improves the delivery success rate, but has lower delivery success rate in an environment with poorer channel quality of the inter-satellite links, therefore, the invention is provided for the problems in path selection on the basis of the DCGR-CFD algorithm, adopts a CGR-DSR improved algorithm based on the error rate for satellite nodes with better channel quality, adopts a Prophet algorithm of multi-copy transmission only for satellite nodes with stronger signal interference of the inter-satellite links, improves the delivery success rate of data packets, and can effectively control the number of backup data packets, the probability of occurrence of network congestion is reduced.
Description
Technical Field
The invention relates to the technical field of satellite communication, in particular to a hybrid contact map routing method based on link error rate prediction and suitable for a satellite internet scene.
Background
With the improvement of satellite on-board processing capability, the maturity of inter-satellite link communication technology and the reduction of satellite manufacturing and launching costs, satellite communication is advancing to a new era of space network communication dominated by satellite internet. The satellite internet is used for global networking of a large-scale low-orbit satellite constellation by utilizing a one-rocket multi-satellite launching technology and a rocket recovery technology, a space network information exchange infrastructure is constructed, and global seamless coverage of satellite mobile communication services is realized by integrating advanced technologies such as atmospheric laser communication, edge calculation and phased array antennas. The satellite internet is widely applied to scenes such as weather forecast, agricultural production, disaster prevention and relief, satellite navigation and the like by virtue of the global coverage capability of the satellite internet, and is incorporated into a new infrastructure strategy of China. The inter-satellite link has the characteristics of long time delay, high error code, intermittent interruption and the like, and is an important factor for restricting the improvement of the network performance of the satellite internet. Based on a five-layer protocol architecture, a DTN (delay Tolerant network) network introduces a bundle layer between an application layer and a transmission layer, and can effectively adapt to the characteristics of inter-satellite links by virtue of a storage-carrying-forwarding mechanism and a hosting transmission mechanism, so that the DTN (delay Tolerant network) network becomes one of the most promising directions in the current satellite internet network architecture research, and a CGR (Carrier-grade-Transponder) algorithm becomes a research hotspot of the current DTN network routing algorithm by virtue of the advantages of less occupied storage and calculation resources. Under the influence of poor channel quality of inter-satellite links, a large number of inter-satellite links with contact failure occur in a DTN, so that the data packet delivery success rate of the CGR algorithm is rapidly reduced, and therefore, the improvement of the data packet delivery success rate of the CGR algorithm under the interference of a complex electromagnetic environment is an important link for enhancing the anti-interference capability of the satellite Internet.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.
Therefore, the invention aims to provide a hybrid contact graph routing method based on link error rate prediction, which is suitable for satellite internet scenes.
In order to achieve the above object, an embodiment of the present invention provides a hybrid contact graph routing method based on link error rate prediction in a satellite internet scenario, including the following steps: step S1, establishing a dynamic contact graph routing algorithm based on contact failure detection, and calculating a next hop alternative node set in a route module through the dynamic contact graph routing algorithm based on contact failure detection; step S2, calculating the link error rate of the inter-satellite link corresponding to each next hop candidate node in the next hop candidate node set, and constructing an error rate prediction value set; step S3, screening the minimum bit error rate in the bit error rate prediction value set, judging whether the minimum bit error rate is smaller than a preset threshold value, if not, adopting a Prophet algorithm based on encounter probability to judge whether a next hop node met by a target node exists in the next hop candidate node set, if not, storing the beam in a permanent storage space, and waiting for a proper path; if yes, executing step S4 for all next hop candidate nodes meeting the condition respectively; if the error rate is less than the threshold value, a CGR-DSR improved algorithm based on the error rate is adopted, and the step S4 is executed; step S4, setting ICI interface control information, binding the ICI interface control information with a data packet and transmitting the ICI interface control information to a mac module; step S5, after the mac module receives the packet, the bundle with the same next hop node is aggregated and segmented, the data segment is forwarded to the next hop node, whether the data segment receives a confirmation packet before the timer is overtime is judged, if yes, the session resource is released, the route module is notified to update the local contact plan information, and the transmission of the bundle is completed; if not, the mac module determines whether the retransmission times of the data segment are less than the maximum retransmission times, if so, the mac module retransmits the data segment overtime, and the step S5 is repeated; if not, judging that the contact is invalid, releasing session resources, informing the route module of the contact failure, adopting a broadcast to inform all satellite nodes of updating a contact plan by the route module, carrying out rerouting calculation on a beam failed in transmission, and executing step S6; step S6, the satellite node which detects the contact failure of the inter-satellite link sends an inter-satellite link detection packet, starts a contact failure recovery algorithm, judges whether a receiving confirmation packet is received before the time-out of the timer, if so, judges whether the random sending sequence number in the receiving confirmation packet is equal to the sending random sequence number, if so, judges that the contact failure is recovered to be normal, the route module notifies all the satellite nodes to update the contact plan, if not, the inter-satellite link detection is carried out again, and the step S6 is repeated; if not, the mac module judges whether the current time is greater than the latest sending time, if not, the inter-satellite link detection packet is sent again, the step S6 is repeated, and if so, the session resource is released to wait for the next detection period.
According to the hybrid contact graph routing method based on the link error rate prediction in the satellite internet scene, the CGR-DSR improved algorithm based on the error rate is adopted for the satellite nodes with better channel quality, the Prophet algorithm of multi-copy transmission is adopted only for the satellite nodes with stronger signal interference of inter-satellite links, and the Prophet algorithm is only used in local nodes, so that the delivery success rate of data packets is improved, the number of backup data packets can be effectively controlled, the occurrence probability of network congestion is reduced, the advantage complementation of the CGR-DSR algorithm and the Prophet algorithm is realized, and the DTN can obtain higher delivery success rate in different channel environments.
In addition, the hybrid contact map routing method based on link error rate prediction in the satellite internet scene according to the above embodiment of the present invention may further have the following additional technical features:
further, in an embodiment of the present invention, the dynamic contact map routing algorithm based on contact failure detection established in step S1 includes a static contact planning self-updating strategy based on visibility analysis and a dynamic contact planning external trigger updating strategy based on contact failure detection.
Further, in one embodiment of the present invention, the visibility analysis-based static contact planning self-updating strategy is composed of visibility analysis-based inter-satellite contact information acquisition and segment fitting-based inter-satellite distance variation function acquisition.
Further, in an embodiment of the present invention, the process of acquiring the contact information between satellites based on the visibility analysis includes: and carrying out visibility analysis on a preset satellite constellation by using STK simulation software to generate a visibility analysis report, wherein the visibility analysis report comprises encounter information in a preset time period among any satellites, carrying out downward rounding and segmentation operation on the encounter information to obtain an initial encounter state among the satellites and an encounter state in one period, and then triggering local update of contact starting time and contact finishing time by the satellite node only by setting a timer.
Further, in an embodiment of the present invention, the process of obtaining the distance variation function between satellites based on the piecewise fitting is as follows: utilizing a plurality of inter-satellite distance change data acquired by STK simulation software, and importing the plurality of inter-satellite distance change data into MATLAB for piecewise curve fitting to obtain an inter-satellite distance change function; based on the inter-satellite distance change function, the accurate inter-satellite distance can be obtained only by inputting the current time, and the round trip delay of data packet transmission is estimated.
Further, in an embodiment of the present invention, the dynamic contact plan external trigger updating strategy based on contact failure detection adopts a contact failure detection algorithm based on an LTP beam retransmission method, specifically: s101, when a contact failure occurs in an inter-satellite link, detecting a failure contact position by using a contact failure detection algorithm based on an LTP beam retransmission method; step S102, starting a contact failure recovery algorithm at the satellite node of the failure contact position, and periodically sending an inter-satellite link detection packet to check whether the failure contact is recovered; step S103, if the contact is recovered, the satellite node broadcasts the contact failure recovery message again to notify all satellite nodes, the contact plan is triggered to be updated, the normal transmission of the failure contact is recovered, and the satellite nodes are switched to a contact failure detection state from the contact failure recovery state.
Further, in an embodiment of the present invention, the step S101 further includes: and when the satellite nodes are switched from the contact failure detection state to the contact failure recovery state, broadcasting contact failure information notice to all the satellite nodes, and triggering all the satellite nodes to update the local contact plan.
Further, in an embodiment of the present invention, the step S102 further includes: if the detection node of the inter-satellite link detection packet receives the confirmation packet, comparing whether the random sending sequence number of the confirmation packet is equal to the sending random sequence number or not, if so, judging that the invalid contact is recovered to be normal, entering step S203, if not, performing inter-satellite link detection again, if not, judging whether the current time is greater than the latest sending time corresponding to the contact, if so, releasing session resources, and waiting for the next inter-satellite link detection period; if not, the inter-satellite link detection packet is sent again, and the operation of the step is repeated.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a flow chart of a hybrid contact graph routing method based on link error rate prediction in a satellite Internet scenario according to an embodiment of the present invention;
FIG. 2 is a flow chart of the characteristics of inter-satellite links in the existing satellite Internet and a contact graph routing algorithm according to one embodiment of the invention;
fig. 3 is a flowchart of a LTP beam retransmission protocol-based contact failure handling algorithm according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a satellite node model based on the HCGR-LBERP algorithm according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The hybrid contact graph routing method based on link error rate prediction in a satellite internet scenario proposed by the embodiment of the invention is described below with reference to the accompanying drawings.
Fig. 1 is a flowchart of a hybrid contact graph routing method based on link error rate prediction in a satellite internet scenario according to an embodiment of the present invention.
As shown in fig. 1, the hybrid contact graph routing method based on link error rate prediction in a satellite internet scenario includes the following steps:
in step S1, a dynamic contact graph routing algorithm based on contact failure detection is established, and a next-hop candidate node set is calculated by the route module through the dynamic contact graph routing algorithm based on contact failure detection.
It should be noted that, as shown in fig. 2, a Contact Graph Routing algorithm (CGR) in the prior art generates a Contact Graph through a complete Contact plan, and eliminates invalid paths by using a Contact checking process to obtain an alternative path set, thereby completing path selection and bundle forwarding, where the Contact Graph includes all transmission paths from a source node to a destination node, and therefore the accuracy of the Contact plan directly affects the performance of the DTN network. In the traditional CGR algorithm, a contact plan needs to be periodically updated by depending on a ground measurement and control center, but due to the large satellite-to-ground round-trip delay and the intermittent interruption of an inter-satellite link, the update mechanism of the contact plan has the problem of inconsistent update. If there is a failed contact or an error in the contact checking process caused by inaccurate contact information in the contact plan, the phenomenon that the data packet is sent along an invalid path is caused, so that frequent overtime retransmission of the data packet occurs at the failed contact, which undoubtedly reduces the delivery success rate of the data packet and increases the average end-to-end transmission delay. And the CGR algorithm is lack of a contact failure detection mechanism and cannot deal with the sudden inter-satellite link contact failure problem.
Therefore, the invention provides a Dynamic Contact Graph Routing algorithm (DCGR-CFD) based on Contact Failure Detection aiming at the problems of the Contact plan updating mechanism of the CGR algorithm, and the Dynamic Contact Graph Routing algorithm based on Contact Failure Detection comprises a static Contact plan self-updating strategy based on visibility analysis and a Dynamic Contact plan external triggering updating strategy based on Contact Failure Detection.
The static contact plan self-updating strategy based on the visibility analysis is adopted to realize the local updating and maintenance of the contact plan, the mode of relying on the periodic updating of a ground measurement and control center in the past is abandoned, the accuracy of the contact plan can be effectively improved, and the accuracy of the contact inspection process is ensured. By adopting a dynamic contact plan external trigger updating strategy based on contact failure detection and a contact failure detection algorithm based on an LTP beam retransmission protocol, the problem of failure contact detection is solved, dynamic maintenance of a static contact plan is realized, millisecond-level detection efficiency of failure contact can be realized, contact plan updating is triggered, follow-up data packets are prevented from being continuously transmitted along a failure path, and the delivery success rate of the data packets is improved.
Further, the static contact plan self-updating strategy based on the inter-satellite visibility analysis specifically comprises the following steps:
the contact plan is composed of contact information including a transmitting node, a receiving node, a contact start time, a contact end time, and an expected data transmission rate, and distance information including a transmitting node, a receiving node, a contact start time, a contact end time, and an expected inter-node distance. The sending node, the receiving node and the expected data sending rate are fixed, so in order to obtain a complete contact plan, the algorithm only needs to obtain information such as contact starting time, contact ending time and expected distance between nodes of any satellite. The static contact planning self-updating strategy based on the inter-satellite visibility analysis comprises the acquisition of inter-satellite contact information based on the visibility analysis and the acquisition of an inter-satellite distance change function based on the piecewise fitting.
Although each satellite in the satellite constellation is in a fast moving state at the moment, each satellite periodically moves around the earth on a fixed satellite orbit, so that unlike a mobile ad hoc network, the topology of the satellite network is not randomly changed, but periodically changes with time, and the encounters between the satellites are periodic. The method comprises the following steps of (1) obtaining contact information between satellites based on visibility analysis: for a given satellite constellation, a visibility analysis function in stk (satellite Tool kits) simulation software can analyze the on-off condition of satellite nodes by superposing factors such as transmission power, modulation mode, channel noise and interference on the basis of a line-of-sight transmission model to generate a visibility analysis report, wherein the visibility analysis report comprises the encounter condition of any satellite within a long time, the initial encounter state and the encounter condition within a period between satellites are obtained by performing downward rounding and dividing operations on encounter information, and then the satellite nodes only need to set a timer to trigger local update of the contact start time and the contact end time. Because the encounter between the satellites is periodic, the data update can be completed only by overlapping the encounter period on the basis of the original contact start time and contact end time.
Because the network topology of the satellite network is periodically and repeatedly changed, the distances between the satellite nodes are also periodically changed. The implementation process of obtaining the distance change function between the satellites based on the piecewise fitting comprises the following steps: the invention utilizes a large amount of distance change data between satellites acquired by STK simulation software. Due to intermittent interruption of the inter-satellite link, the distance information between the satellite nodes is also data which is acquired in a time discontinuous section. The invention leads the data into MATLAB to carry out piecewise curve fitting to obtain the function of the change of the distance between the satellites. In the future simulation, only the current moment needs to be input, the accurate distance between the satellites can be obtained, the round-trip delay of data packet transmission is accurately estimated, the accuracy of information in a contact plan is improved, and the accuracy of a contact checking process is improved.
Further, the dynamic contact plan external update strategy based on contact failure detection specifically includes:
the static contact plan self-updating strategy based on visibility analysis realizes local updating of the contact plan at the satellite node, but the static contact plan is obtained through the strategy, and due to the fact that the static contact plan is inevitably influenced by noise and interference in the space, failure contact can occur in the network. In order to ensure the timeliness and the accuracy of the contact plan, the DCGR-CFD algorithm adds a contact failure detection algorithm based on the LTP beam retransmission protocol on the basis of the CGR algorithm. In the LTP bundle retransmission protocol, if the number of data segments exceeds the maximum retransmission number, the data segments are recovered to be bundled and then subjected to rerouting calculation, but under normal conditions, the probability of retransmission of the bundle is extremely low unless the inter-satellite link fails, so that the detection algorithm regards the retransmission of the bundle as a sign of contact failure of the inter-satellite link. As shown in fig. 3, the implementation flow of the dynamic contact plan external update strategy based on contact failure detection is as follows:
step one, when the inter-satellite link is in contact failure, detecting failure contact by a contact failure detection algorithm based on an LTP (low temperature resistant packet) bundle retransmission protocol. The satellite nodes are switched from a contact failure detection state to a contact failure recovery state, contact failure information is sent to all the satellite nodes in a broadcasting mode, all the satellite nodes are triggered to update a local contact plan, and subsequent beams are prevented from being continuously transmitted along failure contact positions;
and step two, at the failure contact position, the satellite node starts a contact failure recovery algorithm, and periodically sends an inter-satellite link detection packet to check whether the failure contact is recovered. And if the detection node receives the confirmation message fed back by the opposite node, comparing whether the random sending sequence number in the receiving confirmation packet is equal to the sending random sequence number or not. And if the two are completely consistent, judging that the failure contact is recovered to be normal, and entering the third step. And if the two signals are not consistent, performing inter-satellite link detection again. If the confirmation message fed back by the opposite end node is not received all the time, the contact failure recovery algorithm judges whether the current time is greater than the latest sending time corresponding to the contact, if the current time is greater than the latest sending time, the session resources are released, and the arrival of the next inter-satellite link detection period is waited. And if the current time is less than or equal to the latest sending time, sending the inter-satellite link detection packet again, and repeating the operation in the second step.
And step three, after the failure contact is recovered, the satellite node broadcasts the contact failure recovery message again to inform all the satellite nodes, the contact plan is triggered to be updated, the normal transmission of the failure contact is recovered, and the satellite nodes are switched to a contact failure detection state from a contact failure recovery state.
A contact failure detection algorithm based on an LTP (low-temperature peer-to-peer) bundle retransmission protocol runs through the whole transmission process, failure contact can be effectively avoided, and the delivery success rate of data packets is improved. Compared with an inter-satellite link fault Detection algorithm based on the Hello message, the Detection algorithm has higher Detection efficiency and stronger applicability, does not depend on a routing protocol, and is compared with a Bidirectional Forwarding Detection (BFD) algorithm, no extra session needs to be established for inter-satellite link fault Detection, and the implementation mode is simpler and more convenient.
Although the DCGR-CFD algorithm improves the contact mode of the CGR algorithm, improves the accuracy of the contact plan and improves the delivery success rate, the DCGR-CFD algorithm has lower delivery success rate in the environment with poor channel quality of the inter-satellite link. The DCGR-CFD algorithm is only improved on a contact plan updating mechanism, the earliest arrival time is still adopted as a routing basis in the aspect of routing selection, the influence on the transmission quality caused by the quality of an inter-satellite link is lacked, and the contact failure is easy to occur under the condition of serious channel interference, so that the delivery success rate is reduced. The CGR algorithm (CGR-DSR) based on Delivery Success Rate obtains historical Delivery Success Rate statistics of all channels by means of mathematical statistics, and then selects a path with the highest Delivery Success Rate as an optimal transmission path, but the algorithm cannot timely cope with channel quality changes of inter-satellite links, has serious hysteresis, and obviously reduces the Delivery Success Rate under the condition that the channel quality is generally poor. The Prophet algorithm adopts a multi-copy transmission strategy based on the encounter probability, can improve the delivery success rate of a data packet to a certain extent, but has the problem of network congestion, so the invention provides a hybrid contact graph routing method HCGR-LBERP based on link error rate prediction aiming at the problem of path selection on the basis of a DCGR-CFD algorithm.
Furthermore, frequent cross-layer information interaction exists between a binding layer and a network layer in the DTN, and the operation efficiency of the system is reduced. As shown in fig. 4, the present invention fuses the binding layer in the bundle layer with the network layer based on the DTN network architecture, and implements the routing calculation of the bundle in the binding layer, thereby simplifying the satellite node model and improving the execution efficiency of the satellite node.
Therefore, the present invention calculates the next-hop candidate node set by a dynamic contact graph routing algorithm based on contact failure detection in step S1.
In step S2, a link error rate of the inter-satellite link corresponding to each next-hop candidate node in the next-hop candidate node set is calculated, and an error rate prediction value set is constructed.
Specifically, as shown in fig. 1, a set of candidate nodes is calculated through a contact plan, then data such as transmission power and inter-satellite distance prediction of a channel corresponding to the nodes are acquired, the data are transmitted to an inter-satellite link error rate prediction model based on a long-short term memory network in an MATLAB through an OPNET and MATLAB joint simulation interface, prediction of inter-satellite link error rates is achieved, and finally an error rate prediction value is transmitted to a satellite node in the OPNET through a third-party application program interface of the MATLAB, so that an error rate prediction value set is obtained.
The Ka-band inter-satellite link is a non-frequency selective fading channel, and the channel approximation can be regarded as the superposition of an additive white Gaussian noise channel and a slowly-changing multiplicative fading channel. The received power of the signal may be expressed as:
wherein, P r To receive power, P t To transmit power, G t For transmitting antenna gain, G r For the gain of the receiving antenna, L s Is the propagation loss of the signal in free space.
Wherein, the gain of the transmitting antenna is:
the gain of the receiving antenna is:
wherein f is the carrier frequency, c is the speed of light, S t For the effective area of the transmitting antenna, S r Is the effective area of the receive antenna.
Free space transmission loss is the main energy consumption of signals in the space transmission, and the free space loss is:
wherein d is the transmission distance between satellites.
Substituting equations (2), (3) and (4) into (1), the signal received power S is:
the relationship between the BER and the snr is:
wherein k is 1 And k 2 For the influencing factor, N is the noise power and M is the modulation polyphase coefficient.
As can be known from the formula (5), the receiving power of the satellite node is mainly influenced by the transmitting power and the distance of the signal, and according to the relation between the error rate and the signal-to-noise ratio, when the space interference changes not severely, the error rate is mainly influenced by the receiving power of the signal, therefore, under the condition that the inter-satellite link interference changes little, the error rate is mainly influenced by the transmitting power and the distance of the signal, and the current error rate can be predicted by using the information of the transmitting power and the inter-satellite distance through an inter-satellite link error rate prediction model based on a long and short term memory network.
In step S3, screening the minimum bit error rate in the bit error rate prediction value set, and determining whether the minimum bit error rate is smaller than a preset threshold;
if not, judging whether a next hop node met by the target node exists in the next hop candidate node set or not by adopting a Prophet algorithm based on the meeting probability, if not, storing the bundle in a permanent storage space, and waiting for a proper path; if yes, executing step S4 for all next hop candidate nodes meeting the condition respectively;
if so, a CGR-DSR improvement algorithm based on the bit error rate is used to perform step S4.
Specifically, as shown in fig. 1, a minimum value of the error rate prediction value set is calculated, if the minimum value of the error rate is smaller than a preset threshold, a CGR-DSR improved algorithm based on the error rate is adopted, and if the minimum value of the error rate is greater than or equal to the preset threshold, a Prophet algorithm based on the encounter probability is adopted, so that the delivery success rate of the data packet is improved through multi-copy transmission.
The meeting probability of the next hop node and the destination node can be directly calculated by using a complete contact plan. If the next hop node does not contact the destination node, the encounter probability is 0, and if the next hop node contacts the destination node, the encounter probability is 1. If there are a plurality of transmission paths with an encounter probability of 1, then a plurality of copies of these paths are transmitted. If no path with an encounter probability of 1 exists, the bundle is stored in a permanent storage space, the occurrence of a proper path is waited, and the operations of the steps S1-S3 are repeated.
In step S4, ICI interface control information is set and bound with the packet and transferred to the mac module. Wherein the ICI interface control information includes round trip delay and latest transmission time of the bundle.
Specifically, when the mac module receives the bundle with the ICI interface control information, the round-trip time and the latest transmission time are extracted first, the round-trip time delay is used as the duration of the transmission timer, the time interval of the timeout retransmission of the data segment is controlled, and the latest transmission time limits the number of retransmissions of the data segment.
In step S5, when the mac module receives the packet, it aggregates and segments the bundle with the same next hop node, forwards the data segment to the next hop node, determines whether the data segment receives an acknowledgement packet before the timer expires,
if so, releasing session resources, notifying a route module to update local contact plan information, and finishing bundle transmission;
if not, the mac module determines whether the retransmission times of the data segment are less than the maximum retransmission times, if so, the mac module retransmits the data segment overtime, and the step S5 is repeated;
if not, judging that the contact is invalid, releasing session resources, informing the route module of the contact invalidation, adopting a broadcast to inform all satellite nodes of updating the contact plan by the route module, carrying out rerouting calculation on the beams failed in transmission, and executing step S6.
Specifically, as shown in fig. 1, the mac module aggregates and segments the bundles having the same next hop forwarding node, reduces the number of received acknowledgement packets, relieves network congestion, and finally forwards the data segment to the next hop node. If the receiving confirmation message of the data segment is received before the timer is overtime, the session resource is released, and the route module is notified to update the local contact plan information, so that the transmission of the bundle is completed, and the operation of the following steps is not executed. If the timer is overtime and still does not receive the receiving confirmation packet, the mac module determines whether the retransmission times of the data segment is less than the maximum retransmission times, if so, the mac module retransmits the data segment overtime, and the step S5 is repeated. If the number of times of retransmission is less than the maximum number of times of retransmission, the contact is judged to be invalid, session resources are released, contact failure information is informed to the route module, then the route module informs all satellite nodes of updating a contact plan in a broadcasting mode, rerouting calculation is carried out on a beam with transmission failure, and step S6 is executed.
In step S6, the satellite node that detects the inter-satellite link contact failure sends an inter-satellite link probing packet, starts a contact failure recovery algorithm, determines whether a reception acknowledgement packet is received before the timer expires,
if yes, judging whether the random sending sequence number in the receiving confirmation packet is equal to the sending random sequence number or not, if yes, judging that the invalid contact is recovered to be normal, informing all satellite nodes to update the contact plan by the route module, if not, performing inter-satellite link detection again, and repeating the step S6;
if not, the mac module judges whether the current time is greater than the latest sending time, if not, the inter-satellite link detection packet is sent again, the step S6 is repeated, and if so, the session resource is released to wait for the next detection period.
Specifically, as shown in fig. 1, an inter-satellite link probing packet is sent, and a contact failure recovery algorithm is started. If the receiving confirmation packet is received before the timer is overtime, comparing whether the random sending sequence number in the receiving confirmation packet is equal to the sending random sequence number or not. If the two are completely consistent, the failure contact is judged to be recovered to be normal, and the route module informs all satellite nodes of updating the contact plan. And if not, detecting the link between the satellites again, and repeating the operation of the fifth step. If the receiving confirmation packet is not received within the set time of the detection timer, the mac module firstly judges whether the current time is greater than the latest sending time, if the current time is less than or equal to the latest sending time, the inter-satellite link detection packet is sent again, and the operation of the fifth step is repeated. If the current time is larger than the latest sending time, the session resource needs to be released, and the arrival of the next detection period is waited.
A satellite constellation is built in an STK, then a satellite orbit file is led into an OPNET (optimized Network Engineering tool) Network simulator, an HCGR-LBERP algorithm is designed and realized according to the modeling concept of a process layer, a node layer and a Network layer from bottom to top, and finally the routing performance of the HCGR-LBERP algorithm provided by the invention is verified by comparing the performance with other routing protocols.
The method adopts an LSTM prediction model for predicting the bit error rate of the inter-satellite link, and uses the acquired distance and the acquired transmitting power information as two inputs of the LSTM prediction model to predict the bit error rate of the inter-satellite link. The LSTM prediction model consists of a sequence Input Layer (sequence Input Layer), an LSTM Layer, a Fully Connected Layer (full Connected Layer), and a Regression Layer (Regression Layer), wherein the LSTM Layer contains 250 hidden units and requires 300 rounds of training. The initial threshold of the gradient of this model training is set to 1, the initial learning rate is 0.005, and after 150 rounds of training, the learning rate is reduced to 0.25 times of the original learning rate. In order to prevent the predicted error rate from generating a negative value, a sigmoid activation function with the addition range of 0-1 is output at the predicted value of the LSTM. The simulation experiment of the invention sets the receiving of the data packets to satisfy the Poisson distribution with the mathematical expectation of 1.0, receives 100 data packets per second, sets the queue storage space of the satellite node to 5000 data packets, and sets the specified threshold of the inter-satellite link error rate to 0.4. In order to simulate the actual transmission channel environment, a Corazza satellite channel model is adopted in the experiment, an interference machine is arranged in a network, and an interference signal in a space is simulated. And two groups of comparison experiments with the average interference power of the jammer of 10W and 100W are set in the model simulation experiment, the change conditions that the delivery success rate and the transmission delay of the DCGR-LBERP are reduced along with the average occurrence time interval of the interference under different channel interference intensities are compared, and the DCGR-CFD algorithm, the DCGR-DSR algorithm and the Prophet algorithm are subjected to simulation comparison to obtain a comparison result.
In the simulation experiment, two indexes of the delivery success rate of the data packet and the average end-to-end transmission delay are adopted to measure the routing method:
the success rate of data packet delivery reflects the reliability of data transmission of a routing protocol. In the simulation of the invention, the ratio of the total number of the data packet packets successfully received by all target nodes in the network to the total number of the data packet packets sent by all source nodes in unit time in the simulation process is defined as the data delivery success rate. The higher the delivery success rate DSR value of the data packet is, the better the transmission reliability of the representative routing protocol is, and the stronger the channel interference resistance is.
The average end-to-end transmission delay reflects the transmission efficiency, i.e. the effectiveness, of a routing protocol. In the simulation of the invention, the ratio of the accumulated sum of the time intervals of the receiving time and the sending time of all data packet packets in the network in the simulation process to the number of the packets is defined as the average end-to-end transmission delay. The smaller the average end-to-end transmission delay, the higher the efficiency of the data packet transmission process, and the better the performance of the routing protocol.
To sum up, the hybrid contact graph routing protocol based on link error rate prediction in the satellite internet scenario proposed by the embodiment of the present invention adopts the CGR-DSR improved algorithm based on the error rate for the satellite nodes with better channel quality, and adopts the Prophet algorithm of multiple copies transmission only for the satellite nodes with stronger signal interference on the inter-satellite links.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (8)
1. A hybrid contact graph routing method based on link error rate prediction in a satellite Internet scene is characterized by comprising the following steps:
step S1, establishing a dynamic contact graph routing algorithm based on contact failure detection, and calculating a next hop alternative node set in a route module through the dynamic contact graph routing algorithm based on contact failure detection;
step S2, calculating the link error rate of the inter-satellite link corresponding to each next hop candidate node in the next hop candidate node set, and constructing an error rate prediction value set;
step S3, screening the minimum bit error rate in the bit error rate prediction value set, judging whether the minimum bit error rate is less than a preset threshold value,
if not, judging whether a next hop node met by the target node exists in the next hop candidate node set or not by adopting a Prophet algorithm based on the meeting probability, if not, storing the bundle in a permanent storage space, and waiting for a proper path; if yes, executing step S4 for all next hop candidate nodes meeting the condition respectively;
if the answer is less than the answer, a CGR algorithm (CGR-DSR) based on the Delivery Success Rate is adopted to execute the step S4;
step S4, setting ICI interface control information, binding the ICI interface control information with a data packet and transmitting the ICI interface control information to a mac module;
step S5, after the mac module receives the packet, it aggregates and segments the beam with the same next hop node, forwards the data segment to the next hop node, judges whether the data segment receives the acknowledgement packet before the timer is overtime,
if so, releasing session resources, notifying the route module to update local contact plan information, and completing bundle transmission;
if not, the mac module determines whether the retransmission times of the data segment are less than the maximum retransmission times, if so, the mac module retransmits the data segment overtime, and the step S5 is repeated;
if not, judging that the contact is invalid, releasing session resources, informing the route module of the contact failure, adopting a broadcast to inform all satellite nodes of updating a contact plan by the route module, carrying out rerouting calculation on a beam failed in transmission, and executing step S6;
step S6, the satellite node which detects the inter-satellite link contact failure sends the inter-satellite link detection packet, starts the contact failure recovery algorithm, judges whether receives the receiving confirmation packet before the timer is overtime,
if yes, judging whether the random sending sequence number in the receiving confirmation packet is equal to the sending random sequence number or not, if yes, judging that the invalid contact is recovered to be normal, informing all satellite nodes to update the contact plan by the route module, if not, detecting the inter-satellite link again, and repeating the step S6;
if not, the mac module judges whether the current time is greater than the latest sending time, if not, the inter-satellite link detection packet is sent again, the step S6 is repeated, and if so, the session resource is released to wait for the next detection period.
2. The hybrid contact map routing method based on link error rate prediction in satellite internet scenario as claimed in claim 1, wherein the dynamic contact map routing algorithm based on contact failure detection established in step S1 includes a static contact plan self-updating strategy based on visibility analysis and a dynamic contact plan external trigger updating strategy based on contact failure detection.
3. The method for routing a hybrid contact map based on link error rate prediction in a satellite internet scenario as claimed in claim 2, wherein the static contact plan self-updating strategy based on visibility analysis is composed of inter-satellite contact information acquisition based on visibility analysis and inter-satellite distance variation function acquisition based on piecewise fitting.
4. The method for routing a hybrid contact map based on link error rate prediction in a satellite internet scenario as claimed in claim 3, wherein the process of obtaining contact information between satellites based on visibility analysis comprises:
and carrying out visibility analysis on a preset satellite constellation by using STK simulation software to generate a visibility analysis report, wherein the visibility analysis report comprises encounter information in a preset time period among any satellites, carrying out downward rounding and segmentation operation on the encounter information to obtain an initial encounter state among the satellites and an encounter state in one period, and then triggering local update of contact starting time and contact finishing time by the satellite node only by setting a timer.
5. The method for routing a hybrid contact map based on link error rate prediction in a satellite internet scenario as claimed in claim 3, wherein the step of obtaining the function of distance change between satellites based on piecewise fitting comprises:
utilizing a plurality of inter-satellite distance change data acquired by STK simulation software, and importing the plurality of inter-satellite distance change data into MATLAB for piecewise curve fitting to obtain an inter-satellite distance change function;
based on the inter-satellite distance change function, the accurate inter-satellite distance can be obtained only by inputting the current time, and the round trip delay of data packet transmission is estimated.
6. The hybrid contact map routing method based on link error rate prediction in the satellite internet scenario as claimed in claim 2, wherein the dynamic contact plan external trigger update strategy based on contact failure detection adopts a contact failure detection algorithm based on LTP beam retransmission method, specifically:
s101, when a contact failure occurs in an inter-satellite link, detecting a failure contact position by using a contact failure detection algorithm based on an LTP beam retransmission method;
step S102, starting a contact failure recovery algorithm at the satellite node of the failure contact position, and periodically sending an inter-satellite link detection packet to check whether the failure contact is recovered;
step S103, if the contact is recovered, the satellite node broadcasts the contact failure recovery message again to notify all satellite nodes, the contact plan is triggered to be updated, the normal transmission of the failure contact is recovered, and the satellite nodes are switched to a contact failure detection state from the contact failure recovery state.
7. The method for routing a hybrid contact graph based on link error rate prediction in a satellite internet scenario as claimed in claim 6, wherein the step S101 further comprises:
and when the satellite nodes are switched from the contact failure detection state to the contact failure recovery state, broadcasting contact failure information notice to all the satellite nodes, and triggering all the satellite nodes to update the local contact plan.
8. The method for routing a hybrid contact map based on link error rate prediction in a satellite internet scenario as claimed in claim 6, wherein the step S102 further comprises:
if the detection node of the inter-satellite link detection packet receives the confirmation packet, comparing whether the random sending sequence number of the confirmation packet is equal to the sending random sequence number or not, if so, judging that the invalid contact is recovered to be normal, entering step S103, if not, performing inter-satellite link detection again, if not, judging whether the current time is greater than the latest sending time corresponding to the contact, if so, releasing session resources, and waiting for the next inter-satellite link detection period; if not, the inter-satellite link detection packet is sent again, and the operation of the step is repeated.
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| CN115276756B (en) * | 2022-06-21 | 2023-09-26 | 重庆邮电大学 | Low orbit satellite constellation optimization design method for guaranteeing service quality |
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