CN115865775B

CN115865775B - Unmanned aerial vehicle network rapid route recovery method based on OLSR

Info

Publication number: CN115865775B
Application number: CN202211512148.4A
Authority: CN
Inventors: 董超; 刘青昕; 朱小军; 张磊; 吴启晖
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2022-11-29
Filing date: 2022-11-29
Publication date: 2024-01-05
Anticipated expiration: 2042-11-29
Also published as: CN115865775A

Abstract

The invention discloses an unmanned aerial vehicle network rapid route recovery method based on OLSR, which relates to the technical field of wireless communication and comprises the following steps: each node in the unmanned aerial vehicle network periodically generates and transmits HELLO information, and performs neighbor detection and MPR selection signaling tasks; the method newly defines a link type and updates a corresponding mechanism, and after receiving HELLO information, the node updates a neighbor table, a 2-hop neighbor table and an MPR selection table based on the corresponding mechanism; each MPR node in the network also periodically transmits TC messages, which contain a complete MPR selection table; the node updates the topology table according to the MPR selection table in the received TC message; each node in the network updates the routing table according to the local neighbor table, the 2-hop neighbor table, the topology table and different link weights, and when the neighbor table, the 2-hop neighbor table or the topology table changes, the routing table is also recalculated. The invention can well cope with the situation that the network topology is frequently transformed or the links and nodes are suddenly interrupted.

Description

Unmanned aerial vehicle network rapid route recovery method based on OLSR

Technical Field

The invention relates to the technical field of wireless communication, in particular to an unmanned aerial vehicle network rapid route recovery method based on OLSR.

Background

Along with the development of science and technology, unmanned aerial vehicles become more and more miniaturized, and cost is also lower and lower, and application in various fields is also more popular. Compared with a single unmanned aerial vehicle, the unmanned aerial vehicle group can be combined more efficiently and rapidly to complete more complex tasks.

FANET expands the application of the mobile ad hoc network into the air, and provides a feasible solution for reliable communication of the unmanned aerial vehicle group, so that the unmanned aerial vehicle group can cooperatively complete various tasks. However, unmanned aerial vehicles have the characteristic of high mobility, and modern electromagnetic spectrum environments are increasingly complex, and unmanned aerial vehicle groups are also more and more susceptible to interference. Therefore, compared with the mobile ad hoc network, the FANET has the characteristics of frequent network topology change, easy interference of communication links and the like, so that the routing protocol designed for the mobile ad hoc network cannot be directly applied to the unmanned aerial vehicle network.

OLSR is an optimization of classical link state algorithms formed for mobile radio network requirements, and is one of the protocols widely used in ad hoc networks. The protocol uses a Multi-Point Relay (MPR) technique to forward TC messages, thereby reducing the overhead of transmitting link state information. Each node periodically sends HELLO and TC (Topology Control) messages to establish its own network topology map in a distributed manner, and periodically deletes expired entries to ensure real-time performance of the information used. However, this mechanism results in the protocol being less sensitive to networks with frequent topology changes, which may take a long time to identify when the link suddenly breaks.

The following parameters have a major impact on the network running OLSR: 1) Transmission Interval (HI) of HELLO message; 2) TC message transmission interval (TCI). In the default setting, hi=2s, tci=5s, and the neighbor hold time NHT and the topology hold time THT are set to 3 times of HI and TCI, respectively. At each interface of the nodes in the network, the nodes periodically broadcast HELLO messages to maintain neighbor tables and MPR selection tables. The entry in the neighbor table is considered valid for the time the HELLO message + NHT is received. The HELLO message propagates only within one hop and is not forwarded by other nodes. In addition, each node selected as MPR broadcasts TC message to update the route. The TC message contains all addresses that select this node as MPR node and propagates throughout the network. The node establishes and maintains a topology table according to the received TC message, and sets the expiration time of an entry in the topology table to be the current time +THT.

Although there have been studies to improve OLSR for use in unmanned aerial vehicle networks, the current studies have focused mainly on improvements in load, throughput and end-to-end latency, with less research on rapidly changing network topologies and suddenly disconnected communication links in unmanned aerial vehicle networks. Whereas OLSR has difficulty in coping with the above problems due to its timeout management mechanism, a solution is urgently needed.

Disclosure of Invention

The invention aims to provide an unmanned aerial vehicle network rapid route recovery method based on OLSR (on-line distributed routing) aiming at the defects or problems of the prior art.

In order to achieve the technical purpose, the invention adopts the following technical scheme:

an unmanned aerial vehicle network rapid route recovery method based on OLSR is characterized by comprising the following steps:

periodically generating and sending HELLO information by each node in the unmanned aerial vehicle network, and carrying out neighbor detection and MPR (message passing) selection signaling tasks;

step two, after the node receives the HELLO message, updating a neighbor table, a 2-hop neighbor table and an MPR selection table according to neighbor entries in the HELLO message, wherein the MPR selection table contains all addresses for selecting the node as an MPR node;

step three, each MPR node in the network also periodically transmits TC messages, which include a complete MPR selection table; the node updates the topology table according to the MPR selection table in the received TC message;

and step four, each node in the network updates the routing table according to the local neighbor table, the 2-hop neighbor table and the topology table, and when the neighbor table, the 2-hop neighbor table or the topology table is changed, the routing table is also recalculated, so that the unmanned plane network can be quickly recovered when the network topology is frequently changed or the links and the nodes are suddenly interrupted.

In order to optimize the technical scheme, the specific measures adopted further comprise:

in the first step, the specific steps of performing neighbor detection and MPR selection signaling tasks include: through exchanging HELLO messages, the nodes establish a neighbor table, a 2-hop neighbor table and an MPR selection table; the node updates the neighbor table and the 2-hop neighbor table through periodically exchanging HELLO messages and a 3-way handshake mechanism; the HELLO message is only broadcast in a one-hop range and cannot be forwarded, and the transmission period is HI; after receiving the HELLO message, the node regards the information as valid in NHT time, and periodically updates and calculates a neighbor table and a 2-hop neighbor table, and deletes the expired entry; after receiving the HELLO message, if detecting that the HELLO message generating node is selected as an MPR node, the node adds the generating node into an MPR selection table.

Defining 5 link types and 3 neighbor types for the node to maintain a neighbor table,

the 5 link types are respectively: 1) UNSPEC_LINK: no specific information about the LINK is provided, 2) aspm_link: asymmetric LINK, 3) sym_link: symmetrical LINKs, 4) ESYM_LINK: symmetric LINKs about to expire, 5) lost_link: the link has been lost;

the 3 neighbor types are respectively: 1): sym_neigh: the neighbor node has at least one SYM_LINK or ESYM_LINK, 2) MPR_NEIGH with the node: the neighbor node has at least one sym_link with the node, and the node has been selected by the neighbor node as MPR, 3) not_network: the neighbor node and the node are no longer or are not symmetrical neighbors;

the link type is related to the parameters L_SYM_time, L_ESYM_time and L_ASYM_time, and the specific setting rules comprise:

if l_sym_time > = current time, LINK type = sym_link;

if l_sym_time < current time and l_esym_time > =current time, LINK type=esym_link;

if l_sym_time < current time, l_esym_time < current time, and l_asym_time > = current time, LINK type = asym_link;

if l_sym_time < current time, l_esym_time < current time, l_asym_time < current time, LINK type = lost_link;

if no record of the relevant LINK can be found, LINK type = unspec_link.

In the second step, the neighbor table parameters are updated according to the following rules after the node receives the HELLO message:

1) If the IP address of the HELLO message sending node cannot be found in the neighbor table of the node, adding the address to the neighbor table, and setting L_SYM_time = current time-1, L_ESYM_time = current time-1 and L_ASYM_time = current time + effective time;

2) If the IP address of the HELLO message sending node is found in the node's neighbor table, L _ ASYM _ time = current time + active time,

2.1 If the LINK type of the transmitting node and the local node, i.e., the receiving node, is displayed in the HELLO message is low_link, l_sym_time=current time-1, l_esym_time=current time-1 is set;

2.2 If the LINK type between the sending node and the local node is sym_link, esym_link or asym_link, setting l_sym_time=current time+valid time K, L _esym_time=current time+valid time, where K is a time factor, 0<K is less than or equal to 1, and the time factor of each node is set by the node and is included in the generated HELLO message and sent together.

In the second step, after the node receives the HELLO message, the 2-hop neighbor table is updated according to the following rules:

after receiving the HELLO message of the symmetrical neighbor, for the entry in which each LINK type is sym_link or esym_link, updating the entry in the 2-hop neighbor table, setting the neighbor node as a HELLO message sending node, setting the 2-hop neighbor node as a corresponding node of the sym_link or esym_link LINK in the HELLO message, and setting n_time=current time+valid time,

1) If the LINK type is sym_link, setting n_sym_time=current time+valid time;

2) If the LINK type is esym_link, n_sym_time=current time-1 is set;

in the 2-hop neighbor table, the link type judgment rule is as follows:

1) If n_sym_time > = current time, LINK type = sym_link;

2) If n_sym_time < current time and n_time > =current time, LINK type=esym_link.

The TC message is broadcast to the whole network by taking TCI as a period, and is used for informing the network that the node can reach the node, and the node regards the message as effective and updates the topology table in THT time after receiving the TC message.

In the fourth step, the calculation method of the routing table is as follows:

1) Adding a neighbor table and a 2-hop neighbor table into a topological graph, setting SYM_LINK LINK weight as 1, and ESYM_LINK LINK weight as f (x), wherein a function f (x) is predefined by a node;

2) Adding a topology table into a topology graph, and setting the weight of a link to be 1;

3) Routes from the local node to other nodes are calculated using the dijkstra algorithm and added to the routing table.

The node selects a plurality of neighbor nodes as MPR nodes to cover all 2-hop neighbor nodes, and if the neighbor nodes and the local node have no sym_link in the MPR selection process, the node cannot be selected as MPR node.

The technical scheme provided by the invention has the following beneficial effects:

according to the unmanned aerial vehicle network rapid route recovery method based on the OLSR, a link state and a related mechanism are newly added on the basis of the OLSR protocol, and an improved route calculation method is realized on the basis of the link state and a punishment function. Through the improvement, the overtime management mechanism of the OLSR protocol can be well optimized, and when the links in the network suddenly change, the nodes can quickly react, so that the communication quality of the network is improved, and the service requirements of actual scenes are better met.

Drawings

FIG. 1 is a schematic diagram of a topology used in the simulation of the present invention;

FIG. 2 is a diagram showing the comparison of the simulation results of the recovery time of each protocol route;

fig. 3 is a comparison chart of the simulation results of the packet loss rate of each protocol.

Detailed Description

Embodiments of the present invention are described in further detail below with reference to the accompanying drawings.

The OLSR protocol maintains a neighbor table, a 2-hop neighbor table and a topology table by periodically broadcasting HELLO messages and TC messages, and further calculates according to each table entry when a route needs to be calculated. Based on the AFR-OLSR, a link state and a related mechanism are newly added, and an improved route calculation method is realized based on the link states and penalty functions.

The following examples are given to illustrate in detail:

using the network topology shown in fig. 1, a 14-node drone network, each node runs the AFR-OLSR protocol and can only communicate with neighboring nodes (i.e., the dashed portion of the figure). When each node in the network establishes a complete network topology by broadcasting HELLO messages and TC messages periodically, we use the hop count to measure and set a penalty function f (x) =4x, considering the transmission of data from the source node a to the destination node D. Initially, a→b→c→d was used as the transmission path. Then we set node B to be suddenly offline, then after a certain time node a will set the LINK between AB to ESYM-LINK and select LINK a→e→f→g→h→d as the new transmission path (if we set F (x) =2x, we will still use path a→b→c→d). On this basis, we continue to set node E to be suddenly offline, node a will set the LINK with node E as ESYM-LINK after a while, and generate a new TC message to broadcast its new MPR set, and set paths a→i→j→k→l→m→n→d as new transmission paths.

The AFR-OLSR protocol of the present invention was simulated using the topology diagram shown in FIG. 1. The software used was EXata 5.4 and the parameters are shown in Table 1.

TABLE 1

A simple Constant Bit Rate (CBR) program was used to simulate traffic in a network running on 1 node and measure the performance of data transmission. The node running the CBR program will send packets of a fixed size at fixed intervals to the destination node.

The comparative protocols used for the simulation were OLSRv1, OLSRv2 and OLSR-Improved (OLSR-I), wherein OLSRv1 and OLSRv2 are different versions of the OLSR protocol, and OLSR-I is implemented based on OLSRv1, with the following modifications:

and detecting whether a link state of the HELLO message, which is symmetrical with a neighbor type or an MPR node, is lost or not in each time the node generates the HELLO message. If yes, after the HELLO message is sent, updating the neighbor table and the routing table, and generating and sending a new TC message. And detecting whether the link state of the HELLO message with the neighbor type being a symmetrical node or an MPR node is lost or not in the HELLO message every time the node receives the HELLO message. If yes, the current moment is recorded, and the neighbor table and the routing table are updated after NHT.

The parameters used for each protocol are shown in table 2:

TABLE 2

Parameter	Values
		TC Interval	5s
HELLO Interval	2s
		Refresh Timeout Interval	1s
NeighBor hold time（NHT）	6s
		Topology hold time（THT）	15s
Duplicate hold time	30s
		K of AFR-OLSR	0.5
f(x) of AFR-OLSR	f(x) = 4x

The simulation continues for 60s, and between 20s and 40s, node a runs the CBR program to send data to node D, at a time before which each node in the network is able to form a complete network topology. While we tested the routing performance in 2 cases. In scenario a, node a's neighbor node B fails and goes offline at 20 s. While in scenario B, non-neighbor node C would go offline at 20 s.

Two metrics are used to measure the performance of a routing protocol: 1) Route recovery time: the time taken for the destination node to re-receive the data packet after the node or link suddenly goes offline; 2) Packet loss rate: the rate of packet failure to deliver to the destination.

The route restoration time in both scenarios is shown in fig. 2. It can be seen that the AFR-OLSR route recovery time is reduced by 50% or even 70% compared to OLSR, while the OLSR-I route recovery time is somewhat reduced, but this introduces additional control overhead. Fig. 3 shows packet loss ratio comparisons of several protocols, with the lowest packet loss ratio apparent due to the fastest recovery of AFR-OLSR.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.

Claims

1. An unmanned aerial vehicle network rapid route recovery method based on OLSR is characterized by comprising the following steps:

step four, each node in the network updates the routing table according to the local neighbor table, the 2-hop neighbor table and the topology table, and when the neighbor table, the 2-hop neighbor table or the topology table changes, the routing table is also recalculated, so that the unmanned plane network can be quickly restored when the network topology changes frequently or links and nodes are suddenly interrupted;

if l_sym_time > = current time, LINK type = sym_link;

if no record of the relevant LINK can be found, LINK type = unspec_link;

2.2 If the LINK type between the sending node and the local node is SYM_LINK, ESYM_LINK or ASYM_LINK, setting L_SYM_time=current time+effective time K, L _ESYM_time=current time+effective time, wherein K is a time factor, 0<K is less than or equal to 1, and the node sets the time factor by itself, and the time factors of each node are contained in the generated HELLO message and sent together;

if the LINK type is sym_link, setting n_sym_time=current time+valid time;

if the LINK type is esym_link, n_sym_time=current time-1 is set;

in the 2-hop neighbor table, the link type judgment rule is as follows:

if n_sym_time > = current time, LINK type = sym_link;

if n_sym_time < current time and n_time > =current time, LINK type=esym_link.

2. The method for recovering fast routing of an unmanned aerial vehicle network based on OLSR according to claim 1, wherein in the first step, the specific steps of performing neighbor detection and MPR selection signaling tasks include: through exchanging HELLO messages, the nodes establish a neighbor table, a 2-hop neighbor table and an MPR selection table; the node updates the neighbor table and the 2-hop neighbor table through periodically exchanging HELLO messages and a 3-way handshake mechanism; the HELLO message is only broadcast in a one-hop range and cannot be forwarded, and the transmission period is HI; after receiving the HELLO message, the node regards the information as valid in NHT time, and periodically updates and calculates a neighbor table and a 2-hop neighbor table, and deletes the expired entry; after receiving the HELLO message, if detecting that the HELLO message generating node is selected as an MPR node, the node adds the generating node into an MPR selection table.

3. The method for recovering the fast route of the unmanned aerial vehicle network based on the OLSR according to claim 2, wherein the TC message is broadcast to the whole network with TCI as a period, so as to inform the network that the node can reach itself, and the node considers the message as valid and updates the topology table within THT time after receiving the TC message.

4. The method for recovering fast routing of an unmanned aerial vehicle network based on OLSR according to claim 3, wherein in the fourth step, the method for calculating the routing table is as follows:

adding a neighbor table and a 2-hop neighbor table into a topological graph, setting SYM_LINK LINK weight as 1, and ESYM_LINK LINK weight as f (x), wherein a function f (x) is predefined by a node;

adding a topology table into a topology graph, and setting the weight of a link to be 1;

routes from the local node to other nodes are calculated using the dijkstra algorithm and added to the routing table.

5. The method for fast route restoration of an unmanned aerial vehicle network based on OLSR according to claim 4, wherein the node selects a plurality of neighbor nodes as MPR nodes to cover all 2-hop neighbor nodes, and in the MPR selection process, if there is no sym_link between the neighbor nodes and the local node, the node cannot be selected as MPR node.