KR100278304B1 - Call Rerouting in Low Orbit Satellite Systems - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a call rerouting method in a low orbit satellite system.

2. The technical problem to be solved by the invention

The present invention is to solve the problem of increasing the probability of call failure due to traffic concentration in a low-orbit satellite system and to provide a call rerouting method for resetting the call path for more stable service and provision.

3. Summary of the Solution of the Invention

The present invention includes a first step of checking whether an available bandwidth of a destination path is smaller than a predetermined threshold and calculating an average available bandwidth of alternate paths for the destination path and the destination path if it is smaller than the predetermined threshold; Calculating a weight of each alternate path for the destination path and calculating a distributable bandwidth excess for the destination path; And a third step of calculating the bandwidth assigned to the alternate path via the given satellite during the excess bandwidth of the destination path and distributing the corresponding traffic to each alternate path.

4. Important uses of the invention

The present invention is used in a low orbit satellite system.

Description

Call Rerouting in Low Orbit Satellite Systems

The present invention relates to a method for resetting a call in a low orbit satellite system and a computer readable recording medium having recorded thereon a program for realizing the same.

In the conventional call rerouting method, there is a method for adapting to a network topology that changes with time in an asynchronous transmission mode based low-orbit satellite network operating in a connected mode.

Conventional methods, as described above, have re-established fixed paths for each of the expected environments in order to respond to environments that change over time. However, previous studies have not considered the uneven concentration of traffic distribution, or the characteristic that the traffic distribution continues to change with time was not reflected in the routing, and there was a problem that it could not variably cope with the changing environment.

Therefore, the present invention devised to solve the above problems, the call rerouting method for resolving the problem of increasing the call failure probability due to traffic concentration in the low-orbit satellite system and resetting the call path for more stable service and provision And a computer readable recording medium having recorded thereon a program for realizing the same.

1 is a configuration example of a low orbit satellite system to which the present invention is applied.

2 is an explanatory diagram of call rerouting in which bandwidth excess is distributed to alternative paths of neighboring satellites.

3 is a flowchart of an embodiment of a call rerouting method according to the present invention;

In the method of the present invention for achieving the above object, in the call rerouting method applied to the low-orbit satellite system, it is confirmed whether the available bandwidth of the destination path is smaller than the predetermined threshold, if the target path and the target path is smaller than the predetermined threshold; Calculating a mean available bandwidth of alternate paths for; Calculating a weight of each alternate path for the destination path and calculating a distributable bandwidth excess for the destination path; And a third step of calculating the bandwidth assigned to the alternate path via the given satellite during the excess bandwidth of the destination path and distributing the corresponding traffic to each alternate path.

In addition, the present invention is to determine whether the available bandwidth of the target path is less than the predetermined threshold in the low-orbit satellite system having a large capacity processor, and if it is less than the predetermined threshold, calculate the average available bandwidth of the alternative path for the target path and the destination path A first function of doing; A second function of calculating a weight of each alternate path for the destination path and calculating a distributable bandwidth excess for the destination path; And a computer-readable recording medium having recorded thereon a program for realizing a third function of distributing the corresponding traffic to each alternative path by calculating the bandwidth assigned to the alternative path via the predetermined satellite during the excess bandwidth of the destination path. .

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an exemplary configuration diagram of a low-orbit satellite system to which the present invention is applied.

As shown in the figure, low-orbit satellite systems can provide optical communication-class communication services anywhere on the earth. Low-orbit satellite systems provide optical communication-class digitized broadband transmission capabilities that are not limited to areas that traditional communication systems could not provide.

Many low-orbit satellite systems, such as iridium and TELEDESIC, have been proposed to provide communication that is not limited by the global region. Low orbit satellites are generally satellites with orbits 500 km to 2000 km above the Earth's surface. This low altitude allows for short end-to-end delays and enables low power communication between satellites and terrestrial terminals. In the low-orbit satellite system, an intersatellite link can be used to directly connect to a satellite network without passing through a terrestrial network.

While there are these advantages, there are also new problems that do not exist in geostationary satellite systems. Low orbit satellites travel in orbit relative to the earth at a substantially constant speed. Because of this mobility, the service area of the low orbit satellite is not constant, and the overall service provision is obtained by using several orbits and several satellites for each orbit.

The Iridium low orbit satellite system has six pole orbits and eleven satellites in each orbit, as shown in FIG. 1. As the service areas of each satellite continue to change, ground terminals may need to use services from satellites other than the one from which they first communicated. Therefore, the satellites need to pass the serving ground terminal after some time to another satellite closer to the ground terminal. This is called handoff in low orbit satellite systems. Inter-satellite links in low-orbit satellite networks allow hand off between satellites. Each satellite has an inter-satellite link with these satellites, and these interconnected networks form a non-hierarchical mesh network.

As the orbiting satellites continue to move in orbit and at the same time rotate the earth, the traffic distribution of the orbiting satellite system changes over time. The service area of a low orbit satellite may be one with few users, such as a desert or the ocean, or a densely populated area such as a city. If the service area is a densely populated area, the satellite's traffic load will be much higher than the satellites floating on neighboring oceans. Also, the traffic load of the inter-satellite link between two satellites floating on the city will be much higher than the traffic load of the inter-satellite link connecting two adjacent satellites floating on the sea. The service area may correspond to the bright side of the earth during daytime, or to the dark side of the night. This non-uniform traffic distribution is one of the traffic distribution characteristics in the low-orbit satellite system. This characteristic causes a problem of increasing call blocking probability due to traffic concentration in a low-orbit satellite system.

To solve these problems and provide better service, low-orbit satellite networks must adapt to changing environments. In order to solve these problems, there is a need for a distributed and local method of distributing the load of a satellite under load to neighboring satellites with a low load by using traffic load information of neighboring satellites.

The overall traffic load balance is obtained by distributing calls via satellites in a congested overloaded domain to alternate paths in low traffic domains. By applying the proposed method, it is possible to cope with the failure of the node or link of the network in real time.

In the present invention, only the system supporting the inter-satellite link is considered. The traffic load balancing through call rerouting proposed here is based on a low-orbit satellite network using a variable inter-satellite link such as in iridium or TELEDESIC.

2 is an explanatory diagram of a call rerouting in which the bandwidth excess is distributed to alternative paths of neighboring satellites.

As shown in the figure, the number of satellites in a low-orbit satellite network is fixed at n, providing a link between nodes. In addition, it is assumed that a low orbit satellite network is a network based on a fast switching technology such as asynchronous transfer mode (ATM), and provides a connectivity service. A low orbit satellite network can be modeled with the following directional graph:

G = (V, E), V = {v ₁ , v ₂ , v ₃ , v ₄ , ......, v _n }, ｜ V | = n

E⊆ {{v _i , v _j } | v _i , v _j ∈ V and i ≠ j}

f: E → φ, φ≥0

V is a set of vertices and E is a set of edges. In low-orbit satellite systems, satellites correspond to peaks, and inter-satellite links correspond to edges. Thus, the number of adjacent edges for a vertex v is equal to the number of inter-satellite links in a low orbit satellite system.

φ value is a characteristic value for each trunk line. Since each link has two connections that transmit data in the opposite direction, each edge {i, j} ∈E consists of two directional arcs of (i, j) and (j, i). In the present invention, two characteristic values are considered for each arc, the distance and the available bandwidth. It is assumed in the network model that all arcs have the same distance d. The available bandwidth r of the arc is the difference between the maximum bandwidth capacity and the sum of the bandwidths used by the calls transmitted through the arc. In general, the two arcs have different available bandwidth values r ((i, j)) and r ((j, i)) because the arcs transmitted through arcs (i, j) and (j, i) are different.

The loop can be avoided by limiting the distance of the bypass path during rerouting or by using an absolute address. The call rerouting decision process determines whether to perform call rerouting. Since the probability of call failure is minimized by increasing the efficiency of network resources, the determination of call reestablishment is determined by the available bandwidth R (t) for each direction of the inter-satellite link at time t. In Equation 1 below, R (t) is defined as the difference between the maximum capacity, B _max, and the bandwidth B _current in use at the current time t.

R (t) = B _max -B _current

Call rerouting is determined by comparing the R (t) value with the available bandwidth threshold R _threshold in Equation 2 below. Call rerouting is performed when the available bandwidth is less than the threshold.

R (t) <R _threshold

Call rerouting can be performed by dividing the low orbit satellite system into independent groups called rerouting domains, and enabling rerouting if congestion occurs independently in each group. The size of the domain can range from several satellites to the entire system.

Decisions for call rerouting are made only based on the information held by the nodes in each domain. Rerouting can be done distributedly through the rerouting domain. In addition, by reducing the number of paths to be considered in rerouting, it is possible to reduce the time and cost required to determine whether to reestablish call rerouting and call rerouting. In a rerouting domain, if congestion occurs on a path through one central node, a call corresponding to excess bandwidth is sent to another alternate path in the domain. Thus, the number of domains is equal to the number of satellites in the system. At this time, one node in the center is called a destination node and is represented by α.

The rerouting domain Φ consists of a destination node and neighboring nodes close to the destination node. Define the partial graph rerouting domain Φ of graph G.

Φ⊆G

Θ represents a set of nodes other than the destination node in the domain Φ, where | Φ | = K.

For each call, we denote the source node in the domain as ζ and the destination node in the domain as μ. The paths through the destination nodes distinguished by ζ and μ are called destination paths. If the set of target nodes is P _α , then P _α | = k (k−1). P _β is defined as the set of all paths through node β, distinguished by ζ and μ.

Here, a path with ζ = s and μ = d is represented by p (s, d) and P _β (s, d) when the path passes through the node β∈Φ. For any path p (v ₁ , v _k ) = {v ₁ , v ₂ , v ₃ , v ₄ , ......, v _k }, the distance value of path p (v ₁ , v _k ) is It is expressed as d (p) and is defined as Equation 3 below.

In addition, the available bandwidth of the path is represented by r (p) and is defined as Equation 4 below.

r (p (v ₁ , v _k )) = min (r ((v ₁ , v ₂ )), r ((v ₂ , v ₃ )), ....., r ((v _k-1 , v _k ))]

An alternative route for one destination route may be bypassed through a route having a ζ and μ equal to the destination route and having a distance value equal to or less than the distance of the target route. The distance limit for the alternate path is to prevent the deterioration of service quality and to prevent loops from being included in the path.

The role of the call rerouting step is to first determine the destination and alternate paths to be distributed and to distribute the excess bandwidth between them, in order to distribute excess traffic in case of congestion on the destination path in each domain. You must decide which calls to make. Second, if congestion occurs in alternate paths in the domain, the excess bandwidth must be distributed over the entire network.

The reroute domain concept reduces the time and cost of rerouting, but uses a nested domain as a reroute domain that causes bandwidth distribution from congested domains to neighboring domains for load balancing across the entire system. do.

In the call rerouting method according to the present invention, each individual satellite operates independently and distributes the excess bandwidth to alternate paths through neighboring satellites that do not have congestion. Each satellite relies solely on information from satellites in its domain, and all satellites manage their R (t) values for all inter-satellite links. Satellites send their R (t) level information to neighboring satellites and update this information periodically.

If the available bandwidth of the destination path is less than the threshold R _threshold value, calls connected using that path can be redirected to an alternate path.

As shown in Equation 5 below, the determination of whether to perform the rerouting is performed when the available bandwidth of one of the target paths passing through each satellite becomes less than the predetermined threshold R _threshold .

r _α ^p <R _threshold

Where r _α ^p represents the available bandwidth of the destination path p.

Call rerouting begins with calculating the average available bandwidth of the destination path and alternate paths for that destination path. The average bandwidth of the domain for the destination path p is expressed by Equation 6 below.

Where r _k ^p is the available bandwidth of the alternate path of the destination path p via satellite k∈Θ.

Call rerouting is accomplished by sending traffic excess on the congested destination path to an alternate path with less traffic. weight of the alternate path for the purpose of passing a path p k∈Θ χ _k ^p is determined according to Eq. (7) below.

These weights are added together to determine the distributable bandwidth excess, X ^P , for the destination path p, as shown in Equation 8 below.

Finally, the bandwidth δ _k ^p assigned to the alternate path via k during the bandwidth excess of the destination path p is defined as Equation (9).

Once the amount of bandwidth to distribute from the destination path to the alternate path is determined, the corresponding calls are rerouted. The rerouting will continue to be performed whenever the condition to determine whether to perform a call rerouting is true.

Referring to FIG. 2, the number of inter-satellite links is 8, K = 8, | P _a | = K (K-1) = 56, and σ = 0. In the example, the target node is satellite S _{i, i} , and the call path reconfiguration is performed when the available bandwidth of the target path P (S _{i, i-1} , _{Si, i + 1} ) is less than or equal to the R _threshold . The average available bandwidth of the destination path p (S _{i, i-1} , S _{i, i + 1} ) and its alternative paths, E [R _Φ ^{p (s i-1, s i + 1 )} ] = 20 to be. Destination path p _{s i, i} (S _{i, i-1} , S _{i, i + 1} ) Is available bandwidth r _{S i, i} ^{p (s i, i-1, s i, i + 1 )} = 10 Have an alternative path p _{s i + 1, i} (S _{i, i-1} , S _{i, i + 1} ) Is r _{S i + 1, i} ^{p (s i, i-1, s i, i + 1 )} = 28 And alternative paths p _{s i-1, i} (S _{i, i-1} , S _{i, i + 1} ) Is r _{S i-1, i} ^{p (s i, i-1, s i, i + 1 )} = 22 Has the available bandwidth of. The bandwidth excess for the destination path is X _Φ ^{p (s i, i-1, s i, i + 1 )} = 10 to be. The bandwidth excess distributed over each alternate path δ _{S i + 1, i} ^{p (s i, i-1, s i, i + 1 )} = 8 and δ _{S i + 1, i} ^{p (s i-1, i, s i, i + 1 )} = 2 to be. The available bandwidth of the resulting destination path is r _{S i, i} ^{p (s i, i-1 , s i, i + 1 )} = 20 Becomes

In order to avoid the problem that the call already in service by call rerouting is affected, if the available bandwidth of the destination path satisfies (Equation 5), use the alternate path only for resource reservation requests for routing through the new destination path. You can also set the path. At this time, the probability that each alternative path is selected is determined according to the ratio of δ values according to Equation (9). That is, the probability that the call requesting the path setting using the destination path p is assigned to the alternative path via satellite k λ _k ^p Is defined as (Equation 10).

On the other hand, one of the important considerations in regional call rerouting is that the traffic load information update method for calculating the available bandwidth for paths via other satellites in the domain is based on the traffic load information for a part of the network. Make a call rerouting decision.

This part can be one neighboring satellite or all satellites in the network. The accuracy of the information determines the performance of call rerouting. In general, the accuracy of the information is determined by the available bandwidth assessment of the satellite's inter-satellite links, the inaccuracy of the information due to communication delays, and the frequency of transmission of traffic load update messages.

The factor of available bandwidth evaluation is related to the trade-off between the complexity of the evaluation task and the accuracy of the evaluated information, and the factor of inaccuracy of information due to communication delay is determined by the call rerouting method.

For call rerouting, each satellite manages the available bandwidth of its own path. Therefore, the information update message from one satellite contains available bandwidth information for each path via it.

By using a variable update period, which is calculated as a function of the available bandwidth value, it provides a fixed error rate for the available bandwidth and at the same time reduces the number of messages required. Define the variable u as an information update determinant that causes an update to occur when the available bandwidth r increases or decreases by ur. For example, if u = 0.5, the satellite should send an update message if the last available bandwidth increased or decreased by (1/2) r. Each satellite will have to send a message the number of times log (r) is in order, with the maximum error being ur. In this case, the update message transmission frequency will be increased to reduce the available bandwidth of the satellite. Therefore, the higher the probability that call rerouting will occur, the higher the accuracy of the information.

3 is a flowchart illustrating an embodiment of a call rerouting method according to the present invention.

As shown in the figure, it is determined whether the available bandwidth of the destination path is smaller than the predetermined threshold (301) and if it is less than the predetermined threshold, the average available bandwidth of the destination path and the alternative paths for that destination path is calculated (302). In operation 303, a weight of each alternate path with respect to the destination path is calculated.

Then, calculate a distributable bandwidth excess for the destination path (304), calculate the bandwidth assigned to the alternate path via k during the bandwidth excess of the destination path (305), and as many as corresponding to each alternative path from the destination path. Move traffic (306).

On the other hand, the average available bandwidth of alternate paths for the destination path is Where K represents a given satellite, r _α ^p Represents the available bandwidth of the destination path p, r _k ^p Denotes the available bandwidth of the alternate path of the destination path p via the given satellite K.

Also, the weight of each alternate path for the destination path r _k ^p ＞ E [R _Φ ^p ] If χ _k ^p = r _k ^p -E [R _Φ ^p ] , Where r _k ^p Denotes the available bandwidth of the alternate path of the destination path p via the given satellite K, E [R _Φ ^p ] Denotes the average available bandwidth of alternate paths for the destination path p.

In addition, the distributable bandwidth excess for the destination path , Where x _k ^p Denotes the weight of each alternate path with respect to the destination path p.

In addition, the bandwidth specified in the alternate path , Where E [R _Φ ^p ] Denotes the average available bandwidth of alternate paths for the destination path p, r _a ^p Represents the available bandwidth of the destination path p, x _k ^p Denotes the weight of each alternate path for the destination path p, X ^p Denotes the distributable bandwidth excess for the destination path p.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains, and the above-described embodiments and accompanying It is not limited to the drawing.

As described above, the present invention reconfigures a call path by using path bypass between satellites, and when the available bandwidth of the path via the target satellite falls below a certain level, the traffic load is reset by using another alternative path in the domain. By distributing to satellite networks, local congestion can be prevented, which increases the throughput of the system for the overall traffic load, thereby reducing the probability of call failure and providing stable services.

Claims (6)

In the call rerouting method applied to a low orbit satellite system, A first step of checking whether the available bandwidth of the destination path is smaller than a predetermined threshold and calculating an average available bandwidth of replacement paths for the destination path and the destination path if it is smaller than the predetermined threshold; Calculating a weight of each alternate path for the destination path and calculating a distributable bandwidth excess for the destination path; And A third step of distributing the corresponding traffic to each alternative path by calculating the bandwidth assigned to the alternative path via the predetermined satellite during the excess bandwidth of the destination path; Call rerouting method in a low-orbit satellite system comprising a. The method of claim 1, The average available bandwidth of alternate paths for the destination path of the first step is Where K represents a given satellite, r _α ^p Represents the available bandwidth of the destination path p, r _k ^p Is a usable bandwidth of an alternate path of the destination path p via a given satellite K. The method according to claim 1 or 2, The weight of each alternative path to the destination path of the second step is r _k ^p ＞ E [R _Φ ^p ] If χ _k ^p = r _k ^p -E [R _Φ ^p ] , Where r _k ^p Denotes the available bandwidth of the alternate path of the destination path p via the given satellite K, E [R _Φ ^p ] Is an average available bandwidth of alternate paths for a destination path p. The method of claim 3, wherein The distributable bandwidth excess for the destination path of the second stage is , Where x _k ^p The call rerouting method of the low-orbit satellite system, characterized in that the weight represents the weight of each alternative path to the destination path p. The method of claim 4, wherein The bandwidth specified in the alternate path via the predetermined satellite of the third stage is , Where E [R _Φ ^p ] Denotes the average available bandwidth of alternate paths for the destination path p, r _a ^p Represents the available bandwidth of the destination path p, x _k ^p Denotes the weight of each alternate path for the destination path p, X ^p Is a scatterable bandwidth excess for the target path p. In a low orbit satellite system with a large processor, A first function of determining whether the available bandwidth of the destination path is less than a predetermined threshold and calculating an average available bandwidth of the alternative path for the destination path and the destination path if it is less than the predetermined threshold; A second function of calculating a weight of each alternate path for the destination path and calculating a distributable bandwidth excess for the destination path; And A third function of calculating a bandwidth assigned to an alternate path via a predetermined satellite during the excess bandwidth of the destination path and distributing corresponding traffic to each alternative path; A computer-readable recording medium having recorded thereon a program for realizing this.