Distributed Location-aware Transmission for Ad-Hoc Networks

Bey-Ling Su1/29/2004

Features for Ad-Hoc NetworksNode Location Collection by Single-FloodingThe Modified Dijkstra AlgorithmEfficient Unicast ,Multicast , and BroadcastTransmission Handling for Node Re-organizationConclusion

Outline

Features for Ad-Hoc Networks

Wireless network has seen a rapid expansion of visibility due to the proliferation of inexpensive, widely available wireless devices and the network community's interest in mobile computing.No fixed infrastructure available, and have no predetermined organization of available links. Ad hoc is a multi–layer networking (physical, mac, network, transportation…)

Features for Ad-Hoc Networks

The networking layer needs to calculate paths in a way that maintains efficiency when links change and bandwidth is at a premium.A key assumption is that not all nodes can directly communicate with each otherRapid changes in connectivity and link characteristics are introduced due to node mobility and power control practicesApplications need to be designed to handle frequent disconnection and reconnection with peer applications

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Fig. 1: A sample graph (ad hoc network)

Node Location Collection by Single-Flooding

Assume there are n nodes in a wireless ad-hoc network and the location of each node is located by a GPS initiallyThe traditional localization method needs to flood n times (one for each node) to let every node to get the location information of all n nodesOur single-flooding algorithm reduces the flooding times from n to 1

Node Location Collection by Single-Flooding (cont.)

The Single-Flooding AlgorithmInput: The location info of each nodeOutput: The root node builds up a location

table and a distance table1. Initially, arbitrarily select a node as the

root-node in the network, and broadcast RREQ including the root id to other n-1 nodes

2. Each of the n-1 nodes follows the previous broadcasting path to send its id and GPS location back to the root-node

Node Location Collection

by Single-Flooding (cont.)

The Single-Flooding Algorithm

3. Once the root-node receives the ids and GPS location info from all the other n-1 nodes, it creates a location table (see Table 1)

4. Using the position table to calculate a distance table (see Table 2) to represent the network as a graph

5. Root node sends the position table and distance table to all other n-1 nodes by using the shortest paths which were calculated by the following Modified Dijkstra Algorithm

Node id Position

Node 1 (x1,y1)

Node 2 (x2,y2)

Node 3 (x3,y3)

Node 4 (x4,y4)

Node 5 (x5,y5)

Node 6 (x6,y6)

Node 7 (x7,y7)

Node 8 (x8,y8)

Table 1. Position table

Table 2. Distance table

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5 6 3 5 8

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Fig. 2. The root node sends Position Table and Distance Table to all the other n-1 nodes by following the shortest path table.

(Position Table & Distance Table)

The Modified Dijkstra AlgorithmInitially, root node uses the modified Dijkstra algorithm to find the shortest paths to all the other n-1 nodes rather than flooding.The shortest path means that a source node transmits packages to a destination node will choose the furthest node within its transmission range to transfer packages and skip other intermediate nodes (see Fig. 3)The root node will go through the least-hop path to reach the destination node and to avoid unnecessary package passing in a network.

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Fig. 3. Node 1 transmits the packages to node 7, by using the modified Dijkstra algorithm, will take the furthest path from node 1 to node 6 rather than from node 1 to node 3.

transmissionRange k

The Modified Dijkstra AlgorithmFor i=1 to n do S(i)=0 ; If Cost (v, i) > K then Dist (i) <- Cost (v, i) else Dist(i) <- ∞ (* distance longer than the transmission range k, see Table 3 *) End (* If *) S(v) <- 1 ; Dist(v) <- 0 ; num <- 2 While num<n do Choose u : Dist(u)= Min{Dist (w)} at s(w)=0 S(u) <- 1 ; num <- num + 1 For all w with s(w) =0 do Dist(w) <- Min{ Dist(w) , Dist(u) + Cost (u,w)} End (* of For all *) End (* of While loop *)End (* of Algorithm *)

Table 3. Assume the transmission range is 5

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2 4

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5 ∞ 3 3 ∞6 5 4 3 ∞ 1

7 ∞ 5 5 ∞ 2 3

8 ∞ ∞ ∞ ∞ 4 5 5

The Efficient Unicast, Multicast & Broadcast

Table 4. Broadcast: Assume the transmission radius k=5. Initially, node 1 sends packets to all other n-1 nodes according to the following shortest-path table after executed the Modified Dijkstra Algorithm.

Node 2

1->2

Node 3

1->3

Node 4

1->3->4

Node 5

1->3->5

Node 6

1->3->6

Node 7

1->3->6->7

Node 8

1->3->6->8

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Fig. 4. Broadcast: assume node 1 sends packets to all other n-1 nodes according to the following shortest-path table after ran the modified Dijkstra algorithm.

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Fig. 5. Unicast: From the above path table, node 1 can send packets to any other node easily. Assume node 1 sends packets to node 8.

The Efficient Unicast, Multicast & Broadcast (cont.)

After executed the Dijkstra algorithm to get the shortest path from one node to all other n-1 nodes.We can simultaneous to unicast, multicast and broadcast efficiently on demand.For multicast and broadcast, we take the repetition paths only once.

Table 5. Multicast: Assume the source node is node 1 and the multicast nodes are node 4, 6, 7, and 8

Multicast node Efficient path

Node 4 1->3->4

Node 6 1->3->6

Node 7 1->3->6->7

Node 8 1->3->6->8

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Fig. 6. Multicast: From above table, we get the following graph

The Efficient Way to Pass Packets

Originally, each node in the network receives the position table and distance table from root node through the shortest paths rather than flooding.

In this method, it only needs one flooding. Afterward all nodes transmitting packets are not necessary to use flooding.

The Efficient Way to Pass Packets (cont.)

At beginning, a node does nothing unless it wants to transmit the packets to other nodes. Only in this case, it needs to execute the Modified Dijkstra Algorithm to get the shortest-path table. Each node in the network is easy to unicast, multicast and broadcast simultaneously, according to the shortest-path table.

Transmission Handling for Node Re-organization

Each node has an Added List and a Removed List for handling the changes in the network.If one node added, it sends RREQ to its neighbors for requesting the Position Table and Distance Table.After getting the two Tables, the added node executes the Modified Dijkstra Algorithm to send its position to other n-1 nodes by using the shortest-path table rather than flooding.A node receives the added node information, then appends the node’s info to the Added List.

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Fig. 6. An added node 9

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Node 9 get position table and distance table and two listsFrom neighbor nodes

Node 9 sends itsPosition to all otherN-1 nodes by running MDA.

Other n-1 nodesAdd node 9 into Their Added list

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Fig. 7. Node 3 moves : node 3 informs the other n-1 nodes through the shortest-path table

Transmission Handling for Node Re-organization (cont.)

If one node removed, it will inform other nodes by using the shortest-path table. If the other node receives the removed node info, then it appends the info to the removed node list. If any node wants to send packets to other nodes, it has to check its transmission path including any removed node. If yes, it needs to execute the Modified Dijkstra Algorithm. Otherwise, it uses its previous shortest-path table.If any node wants to send packets to a node in the added list, it needs to execute the Modified Dijkstra Algorithm. Otherwise, it uses its previous shortest-path table.

Using single-flooding approach to collect node locations and to create the position table and distance table of the ad-hoc network.Using the modified Dijkstra algorithm to distribute the position table and distance table to each node in the ad-hoc network efficiently instead of the traditional n-flooding strategy.

Conclusion – contributions of this paper

Conclusion – contributions of this paper (cont.)

Using a shortest path table for each node to transmit packets with less hops.Each node could execute unicast, multicast and broadcast simultaneously according to the shortest path table.Handling moving-nodes easily by using the shortest-path table instead of flooding.