CN117915427B - Space perception routing method for aviation self-organizing network based on position prediction - Google Patents
Space perception routing method for aviation self-organizing network based on position prediction Download PDFInfo
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Abstract
The world air transportation industry is rapidly evolving and there is an increasing demand for civilian air communication systems, but their capacities are approaching a limit. This problem becomes more pronounced in the context of transoceanic flight. The invention provides an aviation self-organizing network space perception routing protocol based on position prediction, which is used for realizing efficient and reliable communication between civil aviation aircrafts in transoceanic flight scenes. The routing protocol combines the time required for packet transmission with neighbor location prediction, filtering out neighbor nodes that may experience communication disruption during transmission. And the routing process considers the airplane node position, airplane flight path and node congestion situation obtained by position prediction, and ensures stable and efficient communication in the civil aviation communication network. In addition, the invention also provides an adaptive beacon interval mechanism for reducing the routing overhead.
Description
Technical Field
The invention belongs to the technical field of civil aviation communication systems, and particularly relates to an aviation self-organizing network space perception routing protocol based on position prediction.
Background
With the development of global economy and science and technology, the air transportation industry is rapidly developing, the performance and the number of aircrafts are continuously improved, and the air transportation amount is continuously increased. Current civilian aviation communication systems face tremendous pressures with capacities approaching saturation. In recent years, there has been a significant change in the needs of passengers who wish to maintain an uninterrupted internet connection during travel. The results of the holmivir survey indicate that approximately 75% of the airline passengers are willing to replace airlines to obtain more reliable, faster internet service, and more than 20% of the airline passengers have replaced airlines to enjoy a better internet experience. The international civil aviation organization introduced the concept of free flight and accepted it as a recommended method for future air traffic management. This concept aims at reducing the length of the flight path, reducing the operating costs, reducing environmental pollution, allowing pilots to modify the flight trajectory with the aid of ground stations and air traffic control. These requirements place higher demands on existing civilian aviation communication systems.
The capacity of the existing civil aviation communication system is gradually approaching the limit, and the introduction of aviation self-organizing networks provides a new solution. The aviation self-organizing network enables direct communication between adjacent airplanes through airborne wireless communication equipment. Each aircraft acts as a network node capable of sending, receiving and forwarding messages. Routing protocols are a key element in aviation ad hoc networks, which require finding the optimal path from a source node to a destination node through intermediate nodes, playing an important role in determining overall network performance. But at the same time, because of the special civil aviation application scene, the routing protocol of the routing protocol also faces a plurality of challenges, and the existing self-organizing network routing protocol cannot be directly applied to the aviation self-organizing network.
In the prior study, the routing protocol based on the service life of the link is used for predicting the service life of the link by using the position, the speed and the signal-to-noise ratio of signals received from nearby airplanes, so that the cost is greatly reduced, and the stability of the link is improved. The multipath doppler routing protocol uses doppler shift to estimate the relative velocity between nodes. The mechanism determines whether two nodes are near or far from each other. MUDOR selects the path with the minimum Doppler frequency shift value to construct a route, thereby constructing a longer-service-life and more stable route and reducing the extra network overhead caused by route switching. However, this protocol does not take into account load balancing and QoS issues, making it susceptible to local network congestion. Delay-aware multipath doppler routing uses a combined measure of relative velocity and expected node delay to select the next hop. The link-duration-based AODV makes a routing decision using the remaining path duration, establishing a relatively persistent route. The geographic load sharing routing algorithm considers the geographic location and the load of the next hop node when forwarding the data packet. AeroRP uses the disconnect time for routing. However, the protocol has the problems of unreliable network delay, easiness in network congestion and the like, and cannot meet the real-time requirements of large data volume communication and partial services in the civil aviation self-organizing network.
While many experiments have demonstrated the effectiveness of the routing protocols described above, they still have significant limitations. Many of these protocols are primarily designed for specific applications and scenarios, with network requirements that are quite different from those of civilian aviation. In addition, they were originally designed without a comprehensive understanding of the characteristics of civil aviation scenes. Nor do they fully exploit the conditions available in civil aviation scenarios. Therefore, these protocols cannot be directly applied to civil aviation communication systems.
Disclosure of Invention
In view of this, the present invention aims to overcome the shortcomings of the prior art, and proposes an aviation ad hoc network space aware routing protocol based on position prediction to achieve efficient and reliable communication between civil aircraft in transoceanic flight scenarios. The routing protocol combines the time required for packet transmission with neighbor location prediction, filtering out neighbor nodes that may experience communication disruption during transmission. And the routing process considers the airplane node position, airplane flight path and node congestion situation obtained by position prediction, and ensures stable and efficient communication in the civil aviation communication network.
In order to achieve the above purpose, the technical scheme of the invention is realized as follows:
The space perception routing protocol of the aviation self-organizing network based on the position prediction comprises the following specific implementation steps:
Step 1: node information acquisition and neighbor table establishment: each plane in the network acquires own position and speed information through a satellite positioning system, when nodes in the network need to send data packets to a target node, real-time information of the target node is acquired through a position service algorithm, and a neighbor table is acquired through a beacon mechanism;
Step 2: calculating an interval of broadcasting the beacon message next time according to the node information stored in the neighbor table and the link duration calculated by the beacon message;
step 3: when a data packet arrives at a node and needs to be forwarded, predicting the position of the neighbor node and the transmission time of the data packet according to the information in the neighbor table, and carrying out preliminary screening according to the position and the transmission time of the data packet, so as to screen the neighbor node which is possibly disconnected in the transmission process;
Step 4: calculating a routing parameter P for other neighbor nodes, and selecting the neighbor node with the largest routing parameter P as a forwarding node;
step 5: the above steps are repeatedly executed until successful transmission of each data packet is completed.
Further, in the step 2, calculating the interval of broadcasting the beacon message next time according to the node information stored in the neighbor table and the link duration calculated by the beacon message includes:
Let the communication distance between nodes i and j be R, and the node i receives the beacon packet of the neighboring node j at time t, at this time, the geographic position coordinates of the two nodes are respectively expressed as (X i,Yi),(Xj,Yj), the speed is expressed as V i,Vj, the included angle between the movement direction of the nodes and the horizontal position is expressed as theta i and theta j, and the link survival time between the nodes is deduced by Pythagorean theorem to be
；
Wherein,；
Calculating the link duration time between each node and each neighbor node when the node receives the beacon message of the neighbor node, maintaining the link duration time of each neighbor node in the neighbor table to remove the neighbor table after the expiration of the beacon message, setting a preset beacon transmission interval T every time the beacon transmission moment is reached, setting the neighbor nodes with the link duration time in the range of (0, T) as the easy-to-break connection nodes, setting the total number k of the neighbor nodes and the number s of the easy-to-break connection nodes, and setting the interval of the next beacon transmission of the node as Tx (1-s/k); if k=s or k=0, the beacon message is transmitted using the minimum transmission interval T min.
Further, in the step3, predicting the location of the neighbor node according to the information in the neighbor table specifically includes:
Assuming that the node obtains the position of the neighbor node (X t, Yt) through the beacon message at the time t, the speed V t and the course angle theta, predicting the position of the neighbor node to be at the time t+delta t
。
Further, in the step 2, the step of screening out the neighbor nodes that may be disconnected during the transmission process specifically includes:
Setting the communication distance R of the node i, when a data packet with the size of S pkt arrives at the moment t and needs to be forwarded, storing the position and speed information contained in the beacon message of the neighbor node j received at the moment t 0 in a neighbor table, wherein the residual available bandwidth B s at the node i is as follows
；
Where μ is the channel maximum capacity, T idle（s） is the total idle period during node i measurement time T s;
calculating time t required by node i to send data packet transmitting
；
Then predicting the positions of the node i and the node j at the predicted data packet transmission completion time by using the position and the speed information at the time t 0 in the neighbor table to respectively obtain predicted positions (X i_p,Yi_p）,(Xj_p,Yj_p), defining delta as a parameter for judging whether to screen the neighbor node as the possibility of the next-hop node, d ij represents the distance between the node i and the node j at the time t+t transmitting, epsilon represents redundancy for compensating the addition of a prediction error,
；
Wherein,；
If delta is more than 0, in the process of data packet transmission, the neighbor and the current node keep continuous communication links, uninterrupted connection is ensured, the node is selected as a next-hop node for message forwarding, and if delta is less than or equal to 0, the node is filtered in the process of routing and cannot be selected as the next-hop node.
Further, in the step 4, the routing parameter P includes a distance D from the neighboring node to the destination node, a beacon message delay L, and a distance C from the destination node to the neighboring node route,
The calculation formula of the distance D from the neighbor node to the destination node is as follows:
；
Wherein X d、Yd is the abscissa of the position of the destination node obtained through global position service, and X j_p、Yj_p is the abscissa of the predicted position of the neighbor node at the current moment;
the beacon message delay L is calculated as follows:
；
Wherein t Send represents the time when the transmitting node transmits the beacon message, and t Receive represents the time when the receiving node receives the beacon message from the transmitting node;
the calculation formula of the distance C from the destination node to the neighbor node route is as follows:
；
Wherein X d,Yd is the abscissa of the position of the destination node, X a、Ya is the abscissa of the neighbor node a, and θ is the course angle of the neighbor node;
Weights are assigned to the three parameters, and the calculation formula is as follows:
；
Wherein D min,Lmin,Cmin is the minimum value obtained by calculating the information of all the screened neighbor nodes, α, β and γ are weights corresponding to three parameters, and α+β+γ=1, and the values of α, β and γ are between 0 and 1.
Compared with the prior art, the space-aware routing protocol of the aviation self-organizing network based on the position prediction has the following advantages:
When selecting a forwarding node, the routing protocol of the invention firstly screens nodes which are possibly interrupted in the transmission process through the position prediction of the neighbor nodes and the transmission time prediction of the data packet, then selects the optimal next-hop node from other neighbor nodes through a plurality of parameters, comprehensively considers the effective transmission distance of each hop, considers the possibility of the neighbor nodes for transmitting the data packet along the route and the congestion degree of the link according to the characteristics of civil aviation scenes, and improves the communication performance of the whole network. Meanwhile, the self-adaptive beacon interval is used, the beacon sending period is adjusted according to the topological structure, and the routing overhead is reduced.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
FIG. 1 is a general flow chart of an aviation ad hoc network space aware routing protocol based on location prediction of the present invention;
FIG. 2 is a schematic diagram of an unstable communication example of a communication edge node according to the present invention;
FIG. 3 is a schematic diagram illustrating the transmission of data packets along a route according to the present invention;
FIG. 4 is a schematic diagram of a simulation scenario of a transoceanic civil aviation communication network of the present invention;
FIG. 5 is a graph showing the variation of packet transfer rate with node density according to the present invention;
FIG. 6 is a graph showing the packet transfer rate as the traffic increases according to the present invention;
FIG. 7 is a graph showing the variation of end-to-end delay with increasing node density according to the present invention;
FIG. 8 is a graph showing the variation of end-to-end delay with increasing traffic volume according to the present invention;
fig. 9 is a schematic diagram of the routing overhead of the present invention as node density increases.
Detailed Description
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first", "a second", etc. may explicitly or implicitly include one or more such feature. In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art in a specific case.
The invention will be described in detail below with reference to the drawings in connection with embodiments.
The invention provides an aviation self-organizing network space perception routing protocol (SPRLP) based on position prediction so as to realize efficient and reliable communication between airplanes in transoceanic flight scenes. The routing protocol combines a position prediction algorithm and a data packet transmission time prediction algorithm, and effectively solves the problem that the neighbor table loses effectiveness and accuracy. In the forwarding strategy, the routing protocol firstly performs preliminary screening to screen out the communication edge nodes, and then performs routing decision by considering the distance from the neighbor to the destination node, the distance from the destination node to the neighbor flight path and the beacon message delay so as to establish a stable communication path. Furthermore, the protocol incorporates an adaptive beacon interval mechanism based on link duration prediction to reduce routing overhead. The general flow is shown in fig. 1, and the specific implementation steps are as follows:
1. Node information acquisition and neighbor table establishment: each aircraft in the network obtains its position and velocity information via GPS, beidou or other satellite positioning systems. The destination node location is obtained by a location services algorithm and the neighbor table is obtained using a beacon mechanism.
2. The interval of next broadcasting the beacon message is calculated according to the node information stored in the neighbor table and the link duration calculated by the beacon message.
3. When a data packet arrives at a node and needs to be forwarded, the position of the neighbor node and the transmission time of the data packet are predicted according to the information in the neighbor table, and preliminary screening is carried out according to the position and the transmission time of the data packet, so that the neighbor node which is possibly disconnected in the transmission process is screened out.
4. And calculating a routing parameter P for the rest neighbor nodes, and selecting the neighbor node with the maximum P as a forwarding node.
5. The above steps are repeatedly executed until successful transmission of each data packet is completed.
The routing protocol of the invention utilizes the nodes to create the neighbor list and broadcast the beacon information containing the position and speed information to all neighbor nodes in the communication range at certain intervals, and the nodes can acquire the distribution condition of the neighbor nodes and route according to the one-hop neighbor information. The content of the beacon message includes node location, speed, transmission time stamp. And after receiving the beacon message, the neighbor node updates the neighbor table and records the information of the sending node. And establishing a timer, and if the beacon message of the designated node is not received within the set time, identifying that the node is invalid and removing the invalid neighbor node. However, the airplane node moves fast, beacon information is easy to be outdated, and one-hop range neighbor node information maintained by the node is easy to be invalid. Meanwhile, the aircraft nodes in the aviation self-organizing network do not do random motion, but fly along the airlines, the change of the flight state is slow, and short-term position prediction is feasible, so that the accuracy of node position sensing is improved by using the position prediction of the neighbor nodes.
In the cruising stage, the flight speed and direction of the airplane are relatively stable, and no large acceleration or steering action exists, so that the position and track of the neighbor node are predicted by using a uniform linear motion model. Assuming that the node obtains the position of the neighbor node (X t, Yt) through the beacon message at the time t, the speed V t and the course angle theta, predicting the position of the neighbor node at the time t+delta t
。
Although aircraft may be subject to some external factors (e.g., wind speed, air density, etc.) affecting the state of motion, these effects are relatively small and do not result in significant speed or direction changes of the aircraft in a short period of time. Meanwhile, the neighbor table is updated through a series of beacon messages, so that errors between the prediction model and the real motion state can be corrected in a short time, and the influence on routing is reduced.
Because the motion rate of the aircraft node in the aviation environment is very high, the network topology structure is changed rapidly, and the adjacent node is likely to move out of the wireless coverage range of the node, so that the path is interrupted, as shown in fig. 2, the node j at the current moment is a one-hop adjacent node of the node i and serves as a next-hop forwarding node. However, since the node speed is fast, after the time interval t 1, the node j moves out of the one-hop wireless coverage of the node i, and if the transmission of the data packet is not completed at this time, the routing is invalid. Thereby causing a series of defects such as reduced data packet transmission rate, increased time delay, resource waste and the like.
To avoid this, when there is a packet to be forwarded, we first predict the time required to transmit the packet and screen the neighbor nodes at the communication edge, except for the neighbor nodes that may have a communication disruption due to movement outside the communication range during transmission. Assuming that the node i has a communication distance R, a data packet with a size of S pkt arrives at time t and needs to be forwarded, and the neighbor table stores position and speed information contained in the beacon message of the neighbor node j received at time t 0. In a shared wireless medium, any mobile node can monitor the idle time of the channel, with the remaining available bandwidth B s at node i being
；
Where μ is the channel maximum capacity and T idle（s） is the total idle period during node i measurement time T s. Now, the time t required for node i to send a packet is calculated transmitting
；
And predicting the positions of the node i and the node j at the predicted data packet transmission completion time by using the position and the speed information at the time t 0 in the neighbor table and the position prediction method, respectively obtaining predicted positions (X i_p,Yi_p）,(Xj_p,Yj_p), defining delta as a parameter for judging whether to screen the neighbor node as the possibility of the next-hop node, d ij represents the distance between the node i and the node j at the time t+t transmitting, and epsilon represents redundancy for compensating the addition of a prediction error.
；
Wherein,；
If delta > 0, the neighbor can keep a continuous communication link with the current node during the transmission of the data packet, thereby ensuring uninterrupted connection. The node may be selected as the next hop node for message forwarding. If delta is less than or equal to 0, the node is filtered out in the process of routing, and cannot be selected as a next-hop node.
The routing parameters of the invention comprise three components, namely the distance from the neighbor node to the destination node, the beacon message delay and the distance from the destination node to the neighbor node route. Weights are assigned to these three parameters, as follows:
(1) Distance from neighbor node to destination node
We use the distance of the neighbor node to the destination node as one of the metrics of the routing based on the idea of greedy forwarding. Definition D is the distance from the neighbor node to the destination node
；
Wherein, X d,Yd is the abscissa of the position of the destination node obtained by the global position service, and X j_p,Yj_p is the abscissa of the predicted position of the neighbor node at the current time. The smaller D is, the longer the effective distance of one-hop transmission is, the data packet is transmitted to the area closer to the target, the fewer forwarding nodes can reach the target node, the data packet collision and the collision in the network are reduced, and the data transmission efficiency is improved.
(2) Beacon message delay
The beacon message delay refers to the time required in the process of sending the beacon message from the source node to the destination node, and mainly comprises node processing delay, queuing delay, transmission delay and signal propagation delay, wherein the beacon message delay reflects the response time of service processing in a network, and whether the network is smooth or not can be judged. When channel resources are tense or the network is severely congested, transmission delay is increased, and the performance parameter can be used as a measure of system instantaneity and congestion condition. The beacon message delay is fully utilized for routing, so that local network congestion caused by overload of the selected link can be avoided, and the overall performance of the network is improved. Beacon message delay L between node m and node n mn
；
Where t Send represents the time when node n sends a beacon message, and t Receive represents the time when node m receives a beacon message from node n. If L mn is large, it means that the more easily the link between nodes m and n is congested, the lower the transmission quality, and the longer the data packet of node n may need to be queued for transmission, node n is unsuitable as a next-hop node.
(3) Distance from destination node to neighbor node route
Because of the special application scene of civil aviation, the airplane nodes approximately do uniform linear motion in the cruising stage, and the airplane motion direction can be approximately regarded as the route direction. Most of civil aviation aircrafts are distributed along the airlines, and certain density of aircrafts on the airlines is required in order to ensure networking feasibility. Therefore, we approximately consider that data packets can be communicated more stably between planes distributed on the same route. The closer the distance from the destination node to the neighbor node route is, the easier the data packet is to be forwarded along other aircraft on the neighbor node route, and finally the data packet is successfully transmitted to the destination node, so the distance from the destination node to the neighbor node route is used for measuring the capability of the neighbor node to transmit the data packet to the destination node hop by hop along the aircraft on the route. Defining the distance from the destination node to the route of the neighbor node as C
；
Wherein, X d,Yd is the abscissa of the destination node position, X a,Ya is the abscissa of the neighbor node a, θ is the heading angle of the neighbor node, and can also be considered as the route direction. As can be seen from fig. 3, when node i has a data packet with a destination address of node d to be forwarded, if node b is selected as the next-hop node, the data packet is easy to be lost. If the node a is selected as the next hop, the destination node is closer to the route where the node a is located, and the data packet can be transmitted hop by hop along the aircraft on the route, and finally is successfully transmitted to the destination node.
(4) Joint selection index
Based on the previous discussion, comprehensively considering the distance from the neighbor node to the destination node, the end-to-end time delay and the distance from the destination node to the route of the neighbor node, the joint index P j of the neighbor node j is calculated as
；
Wherein D min,Lmin,Cmin is the minimum value obtained by calculating the information of all the screened neighbor nodes, α, β and γ are weights corresponding to three parameters in the joint index, and α+β+γ=1, and the values of α, β and γ are between 0 and 1. For application scenes with different characteristics, different weights can be set for three parameters to achieve the best network performance. Meanwhile, the characteristics (such as route distribution, moving speed, number of flights and the like) of the network under the same civil aviation scene are relatively fixed in most cases, so that in the routing protocol, the fixed weights are set for three parameters according to the characteristics of the civil aviation scene of a specific area, and the protocol can exert stable performance in the aviation self-organizing network.
In the aeronautical ad hoc network AANET, bandwidth resources of links are very tight, so that it is necessary to reasonably utilize the bandwidth resources. To maintain the node neighbor table, the beacon message periodically sent between node one-hop neighbors is a main source of routing overhead in SPRLP protocol, while ADS-B data can provide location and status information between aircrafts and update and maintain the neighbor table, maintaining the neighbor table only using ADS-B message may reduce the accuracy of node to sensing neighbor node status because the identification range of ADS-B is not completely consistent with the communication range of A2A communication system (such as an on-board collision avoidance system (ACAS), an on-board separation assurance system (ASAS), an L-DACS1 A2A mode, and Free Space Optical (FSO) communication) that may be supported by the routing protocol. Therefore, the data provided by ADS-B cannot completely replace the beacon message in the routing protocol. In the routing protocol, the adaptive beacon transmission interval is used to reduce routing overhead with less bandwidth resources.
The link duration represents the period of time that the wireless link remains active between two nodes, i.e., the time that one node is present within the signal radiation range of the other node, and is a parameter that measures the path stability. The longer the link duration of the neighbor node, the more stable the link with the node, and the beacon transmission interval can be increased without high-frequency beacon exchange between nodes, so as to reduce the communication overhead caused by transmitting the beacon while ensuring the communication performance. Assuming that the communication distance between the nodes i and j is R, the node i receives the beacon packet of the neighbor node j at the moment t. At this time, the geographical position coordinates of the two nodes are respectively expressed as (X i,Yi),(Xj,Yj), the speed is expressed as V i,Vj, the included angles between the movement direction of the nodes and the horizontal position are expressed as theta i and theta j, and the link survival time between the nodes is deduced from the Pythagorean theorem
；
Wherein,；
The node calculates the link duration with the node each time it receives a beacon message of a neighbor node, and maintains the link duration of each neighbor node in the neighbor table to remove the neighbor table after the beacon message expires. And assuming a preset beacon transmission interval T when the beacon transmission moment is reached, setting neighbor nodes with the link duration in the range of (0, T) as the easy-to-break connection nodes, wherein the total number k of the neighbor nodes and the number s of the easy-to-break connection nodes are the same, and the interval of the next beacon transmission of the node is Tx (1-s/k). If k=s or k=0, the beacon message is transmitted using the minimum transmission interval T min. And setting node beacon transmission intervals in a self-adaptive mode according to the number of the easily-broken nodes, and using smaller beacon intervals when the number of the easily-broken nodes is large. When the frangible connection node is smaller, a larger beacon interval is used. Routing overhead is reduced while guaranteeing the role of beacon messages.
In the invention, we propose a routing protocol, when selecting the forwarding node, the protocol screens nodes which are possibly interrupted in the transmission process through the position prediction of the neighbor nodes and the transmission time prediction of the data packet, then selects the optimal next-hop node from other neighbor nodes through a plurality of parameters, comprehensively considers the effective transmission distance of each hop, considers the possibility of the neighbor nodes for transmitting the data packet along the route and the congestion degree of the link according to the civil aviation scene characteristics, and improves the communication performance of the whole network. Meanwhile, the self-adaptive beacon interval is used, the beacon sending period is adjusted according to the topological structure, and the routing overhead is reduced.
In order to evaluate the performance of the routing protocol, the present invention uses the north atlantic corridor as the background of the transoceanic civil aviation communication network, and the simulation scenario of the transoceanic civil aviation communication network established by using the simulation software OMNeT++ and INET framework is shown in FIG. 4 based on all airlines passing through the area in the global airport and airlines database. We set 12 routes (including forward and reverse routes) and 5 base stations. This scenario mainly simulates the directionality, parallel course and cross course characteristics of the transoceanic flights. And compares the calculation result with the conventional routing protocol AODV and GPSR protocol.
We set parameters for three selection weights in the routing protocol. We empirically set α=0.8, β=0.15, γ=0.05 as an optimal combination for this scenario, the maximum beacon interval T in the routing protocol SPRLP of the present invention is equal to the beacon transmission interval of the GPSR, and the main simulation parameters are shown in table 1.
TABLE 1
| Parameter | Parameter Value |
| Simulation scene scale | 2500km * 1000km |
| Antenna type | Omnidirectional antenna |
| Signal propagation model | Free space propagation model |
| MAC protocol | TDMA |
| Space-space communication distance | 222km |
| Air-ground communication distance | 370km |
| Bandwidth of a communication device | 2Mbps |
| Simulation time | 3600s |
1. Data packet transfer rate (PDR) simulation results
Fig. 5 shows the change in packet transfer rate as node density increases. As can be seen from the figure, when the number of the simulation nodes is set to 50, the node density in the network is sparse, a stable network topology cannot be established, the probability of link failure or interruption is high, and it is difficult to establish an effective and long-lasting communication path, so that the PDR of three routing protocols is lower, but the routing protocol SPRLP of the present invention considers the capability of the forwarding node to transmit the data packet to the destination node along the route by considering the neighboring node, so that the PDR is higher than the other two protocols. As the number of nodes increases from 50 to 75, PDR for the 3 routing protocols increases to varying degrees due to the increased connectivity of the overall network. In the 50 and 75 node scenario, we propose a 14.3% and 15.1% improvement in PDR compared to GPSR, respectively. PDR was also increased by 17.4% and 33.4%, respectively, compared to AODV. However, as the number of nodes further increases, network overhead increases rapidly, so that network load increases, part of paths are congested, and node buffers overflow, so that although the connectivity of the whole network is further improved, the PDR of three protocols is reduced to different degrees. The routing protocol of the invention considers the congestion degree of the path with the neighbor node and screens out the nodes which may be disconnected in the communication transmission process when the routing protocol is used for routing, and meanwhile, the self-adaptive beacon interval and the ADS-B message are used for replacing part of beacons, so that the overall overhead is lower, and the PDR can still keep higher level compared with other two protocols along with the further increase of the number of the nodes. In the 150-node and 175-node scenario, we propose a method that shows an average improvement in PDR of more than 15% compared to GPSR. The PDR is increased by more than 25% compared to AODV.
Fig. 6 shows the packet transfer rate as a function of increasing traffic. Overall, with increasing network load, the PDR of all three protocols is greatly reduced. Analysis of the reason why data delivery performance is affected by network load is that, on the one hand, a larger network load causes local network congestion, resulting in a large number of data packets being lost. On the other hand, due to the limited processing capacity of the nodes, the busy channel prolongs the queuing time delay of the data, and finally, the data is lost due to the overflow of the queues. Compared with GPSR and AODV, the routing protocol SPRLP of the invention is designed aiming at the environment of aviation communication, the base number of PDR is larger, meanwhile, the congestion degree of the path with the neighbor node is considered in the process of routing, and the lower routing cost does not further aggravate the load of the whole network, so the PDR has relatively better performance. We propose a method that increases PDR by 6.8% compared to GPSR at a traffic load of 150 kb/s. Compared with AODV, PDR is improved by 40%. As the traffic load increases, the PDR of all three protocols decreases dramatically. However, SPRLP still has significant advantages over the other two protocols under larger traffic loads.
2. End-to-end delay simulation results
Fig. 7 shows the variation of end-to-end delay with increasing node density. It can be obtained from the experimental results that the delay performance of the routing protocol based on the geographical location information and the GPSR protocol is better than that of the protocol AODV based on the topology structure, because AODV is an on-demand routing protocol, the routing is established only when communication is needed, and the routing table needs to be maintained and updated, and the delay is increased when various control messages are sent. When the number of nodes is small, the delay performance of the routing protocol SPRLP of the present invention is slightly better than GPSR because the network is relatively smooth and the number of hops is a major factor affecting the delay. The GPSR uses a greedy algorithm to maximize the distance per transmission, thereby reducing the number of hops across the transmission path. However, GPSR relies only on the distance between the neighbor and the destination node as a routing metric, resulting in a lower PDR. The routing protocol of the present invention considers the ability of neighbors to forward messages to destination nodes when selecting the next hop node. The inventive routing protocol significantly enhances the PDR, although the number of hops in the transmission path is increased. In addition, the routing protocol of the present invention takes the beacon message delay as a routing parameter, alleviating some of the delay due to the increase in hop count. Congestion in a network becomes an important source of delay as the number of nodes increases. Furthermore, the routing protocol of the present invention exhibits lower end-to-end delay due to reduced overhead and consideration of the congestion level of the neighbors.
Fig. 8 shows the end-to-end delay as traffic increases. It can be derived from the experimental results that the routing protocol of the present invention can keep lower end-to-end delay with increased traffic in the network compared to AODV and GPSR. This is because the channel is prone to congestion under high network load conditions. The queuing delay caused by congestion becomes a major factor of the increase in end-to-end delay compared to the increase in the number of transmission path hops. The routing protocol of the invention considers the congestion degree of the link when selecting the next hop node, and the beacon message delay is taken as one of the routing parameters, so that the routing protocol has better performance in end-to-end delay. At loads of 250 and 300kb/s, we propose a method that shows an average reduction of about 0.06 seconds and 0.26 seconds from end-to-end delay compared to GPSR. The end-to-end delay is reduced by 0.37 seconds and 0.47 seconds, respectively, compared to AODV.
3. Routing overhead simulation results
Fig. 9 shows the change of routing overhead with increasing node density, and to ensure fairness we replace part of the beacon messages in the GPSR with ADS-B messages for performance comparison of the routing overhead. The average routing overhead for all three protocols increases with the number of nodes. Because of the route discovery and maintenance mechanism in AODV, a larger number of nodes means that the same packet is forwarded more times, and meanwhile, the control packet is easy to cause local network congestion, and the network congestion generates more control packets for the route maintenance process, so that the cost of the control packet increases in a near-exponential trend along with the increase of the number of nodes. Both the routing protocol SPRLP and the GPSR of the present invention periodically send beacon messages to update the location information of neighboring nodes. When the node density in the network is lower, the number of times of the control packet being forwarded is less, so the cost of the protocol is lower, and when the number of nodes in the network is increased, the routing protocol and the GPSR protocol of the invention can generate more control packets, so the routing cost is increased along with the increase of the number of nodes. In the case where ADS-B messages are used in place of a portion of the beacon message, the routing protocol of the present invention has lower overall routing overhead than GPSR due to its adaptive beacon interval mechanism.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (4)
1. The space-aware routing method of the aviation self-organizing network based on the position prediction is characterized by comprising the following steps of: the specific implementation steps are as follows:
Step 1: node information acquisition and neighbor table establishment: each plane in the network acquires own position and speed information through a satellite positioning system, when nodes in the network need to send data packets to a target node, real-time information of the target node is acquired through a position service algorithm, and a neighbor table is acquired through a beacon mechanism;
Step 2: calculating an interval of broadcasting the beacon message next time according to the node information stored in the neighbor table and the link duration calculated by the beacon message;
Step 3: when a data packet arrives at a node and needs to be forwarded, predicting the position of the neighbor node and the transmission time of the data packet according to the information in the neighbor table, and carrying out preliminary screening according to the position and the transmission time of the data packet, so as to screen the neighbor node which is possibly disconnected in the transmission process; the screening out neighbor nodes that may be disconnected during transmission specifically includes:
Setting the communication distance R of the node i, when a data packet with the size of S pkt arrives at the moment t and needs to be forwarded, storing the position and speed information contained in the beacon message of the neighbor node j received at the moment t 0 in a neighbor table, wherein the residual available bandwidth B s at the node i is as follows
；
Where μ is the channel maximum capacity, T idle（s） is the total idle period during node i measurement time T s;
calculating time t required by node i to send data packet transmitting
；
Then predicting the positions of the node i and the node j at the predicted data packet transmission completion time by using the position and the speed information at the time t 0 in the neighbor table to respectively obtain predicted positions (X i_p,Yi_p）,(Xj_p,Yj_p), defining delta as a parameter for judging whether to screen the neighbor node as the possibility of the next-hop node, d ij represents the distance between the node i and the node j at the time t+t transmitting, epsilon represents redundancy for compensating the addition of a prediction error,
；
Wherein,；
If delta is more than 0, in the data packet transmission process, the neighbor and the current node keep continuous communication links, uninterrupted connection is ensured, the node is selected as a next-hop node for message forwarding, and if delta is less than or equal to 0, the node is filtered in the routing process and cannot be selected as the next-hop node;
Step 4: calculating a routing parameter P for other neighbor nodes, and selecting the neighbor node with the largest routing parameter P as a forwarding node;
step 5: the above steps are repeatedly executed until successful transmission of each data packet is completed.
2. The location prediction based aviation ad hoc network space aware routing method of claim 1, wherein: in the step 2, calculating the interval of broadcasting the beacon message next time according to the node information stored in the neighbor table and the link duration calculated by the beacon message includes:
Let the communication distance between nodes i and j be R, and the node i receives the beacon packet of the neighboring node j at time t, at this time, the geographic position coordinates of the two nodes are respectively expressed as (X i,Yi),(Xj,Yj), the speed is expressed as V i,Vj, the included angle between the movement direction of the nodes and the horizontal position is expressed as theta i and theta j, and the link survival time between the nodes is deduced by Pythagorean theorem to be
；
Wherein,；
Calculating the link duration time of each node when the node receives the beacon message of the neighbor node, maintaining the link duration time of each neighbor node in the neighbor table to remove the neighbor node from the neighbor table after the expiration of the beacon message, setting a preset beacon transmission interval T every time the beacon transmission moment is reached, setting the neighbor nodes with the link duration time in the range of (0, T) as the easy-to-break connection nodes, setting the total number k of the neighbor nodes and the number s of the easy-to-break connection nodes, and setting the interval of the next beacon transmission of the node as T× (1-s/k); if k=s or k=0, the beacon message is transmitted using the minimum transmission interval T min.
3. The location prediction based aviation ad hoc network space aware routing method of claim 1, wherein: in the step 3, predicting the position of the neighbor node according to the information in the neighbor table specifically includes:
Assuming that the node obtains the position of the neighbor node (X t, Yt) through the beacon message at the time t, the speed V t and the course angle theta, predicting the position of the neighbor node to be at the time t+delta t
。
4. The location prediction based aviation ad hoc network space aware routing method of claim 1, wherein: in said step 4, the routing parameters P include the distance D from the neighboring node to the destination node, the beacon message delay L and the distance C from the destination node to the neighboring node route,
The calculation formula of the distance D from the neighbor node to the destination node is as follows:
；
Wherein X d、Yd is the abscissa of the position of the destination node obtained through global position service, and X j_p、Yj_p is the abscissa of the predicted position of the neighbor node at the current moment;
the beacon message delay L is calculated as follows:
；
Wherein t Send represents the time when the transmitting node transmits the beacon message, and t Receive represents the time when the receiving node receives the beacon message from the transmitting node;
the calculation formula of the distance C from the destination node to the neighbor node route is as follows:
；
Wherein X d,Yd is the abscissa of the position of the destination node, X a、Ya is the abscissa of the neighbor node a, and θ is the course angle of the neighbor node;
Weights are assigned to the three parameters, and the calculation formula is as follows:
；
Wherein D min,Lmin,Cmin is the minimum value obtained by calculating the information of all the screened neighbor nodes, α, β and γ are weights corresponding to three parameters, and α+β+γ=1, and the values of α, β and γ are between 0 and 1.
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