BROADCASTING TECHNIQUES IN AD-HOC NETWORKS

1. A survey on BROADCASTING TECHNIQUES IN AD-HOC NETWORKS by Shubham Bhat (skb25@drexel.edu) Surendra Shenoy (svs25@drexel.edu) References: • “ Broadcasting in Ad-hoc networks based on Self-Pruning” • Jie Wu and Fei Dai , INFOCOM 2003,Twenty-Second Annual Conference of the IEEE Computer and Communication society. • 2. “ Localized Minimum-energy broadcasting in ad-hoc networks” • Julien Cartigny, David Simplot , Ivan Stojmenovic, INFOCOM 2003,Twenty-Second Annual Conference of the IEEE Computer and Communication society.

2. Ad-hoc networks Non restricted mobility Broadcasting: Basic vehicle for on demand routing Available resources for node mobility

3. Broadcasting in Ad hoc networks Types of Broadcasting • Flooding • Probabilistic based Methods • Area based methods • Neighbor Knowledge Methods

4. Globalized Vs Localized Protocols Globalized • Require knowledge of the whole network. • Mobility of nodes and changes in node’s activity status cause global changes in any MST structure. • Extreme and unacceptable communication overhead Localized • Based only on the information from all nodes within a constant hop distance. • Distances can be measured using signal strength, time delay or more sophisticated techniques like microwave distance .

5. Broadcasting in Ad hoc networks • Neighbor Knowledge methods • Connected Dominating Set( CDS) • Neighbor Designating method (Dominant Pruning) • Self Pruning

6. The node decides for itself whether it is a forwarding or a non-forwarding node, based on neighborhood coverage condition. This paper provides a general framework based on which other specific algorithms can be developed. Self pruning

7. Self pruning Assumptions Moderate mobility Near to accurate K-hop information (for small K)

8. Basics • Forwarding or non-forwarding status Before a broadcast packet is received After the first copy is received After many copies of the packet are received. • Static approach ( “up to date”) CDS based on network topology • Dynamic approach ( “On the fly” ) Dependent on the location of the source and progress of the broadcast process

9. Neighbor Set Coverage • On arrival at node v , the packet contains Information D(v) : this is the information about the “h” most recently visited nodes.

10. Coverage Condition 1 ( static) “Node v has a non-forward node status if for any two neighbors u and w, a replacement path exists that connects u and w via several intermediate nodes (if any) with higher priority values than the priority value of v.” In other words, assume that v is a non-forward node. Let N(v) be the neighbor set of node v, then for any u, w N(v), a replacement path (u, u1, u2, ..., ul, w) exists such that id(ui) > id(v) for 1 ≤i ≤ l.

11. Replacement paths Max-min node for (u, w, v): A minimum node in a path is a node with the lowest priority. Assume {Pi} is the set of replacement paths for node v that connect u and w. A max-min node in {Pi} is a node with the highest priority among all the minimum nodes in {Pi}. Next we define a procedure called MAXMIN to construct a maximal replacement path for v that connects u and w. MAXMIN(u,w, v): 1: if u and w are directly connected then return . 2: Find the max-min node x for (u, w, v). 3: return path (MAXMIN (u, x, v), x, MAXMIN (x, w, v)).

12. Maximal replacement path 6 8 4 Node 4 is the Max-Min node. 7 5 w u Sample Maximal replacement path The priority can be based on a priori definition or it may be based on various metrics such as node degree 3 v

13. Coverage Condition I (dynamic) “Node v has a non-forward node status if for any two neighbors u and w, a replacement path exists that connects u and w via several intermediate nodes (if any) with either higher priority values than the priority value of v or with visited node status.” A Because node 3 is a visited node, node 5 can conclude that it should be a non-forward node since any two neighbors can be connected using nodes 3 and 8. B D C

14. Coverage Condition II ( dynamic) A set C (v) is called a coverage set of v if the neighbor set of v can be “covered” by nodes in C (v). In addition, nodes in C (v) are either visited nodes or nodes with higher priorities than v’ s priority. Clearly, all nodes in C (v) are within two hops of v. Note that C (v) may include some neighbors of v. Node v has a non-forward node status if it has a coverage set. In addition, the coverage set belongs to a connected component of the sub-graph induced from visited nodes and nodes with higher priority values than the priority value of v.

15. Neighborhood information Generalizing for k-hop approximation Coverage Condition I :Node v has a non-forward node status if for any two neighbors u and w, a replacement path exists that connects u and w via several intermediate nodes (if any) in Nk (v) with either higher priorities than the priority of v or with the visited node status. Coverage Condition II: Node v has a non-forward node status if it has a coverage set. In addition, the coverage set belongs to a connected component of the sub-graph induced from visited nodes and nodes with higher priorities than v’ s priority in Nk (v). where D is the density of the network; that is, maximum number of nodes per unit area.

16. Special cases • Flooding A special case where no neighborhood information is available. • Wu and Li’s algorithm: U U W W V X V V is non forward because U. W are directly connected. V is non forward because X “covers” U and W This is a special case of the algorithm with 2 or 3 hop neighborhood information and no routing history.

17. Special cases continued… • Stojmenovic’s Algorithm: Improvement on the Wu and Li algorithm • Each node only maintains a list of its neighbors and their geographic positions. • The number of forward nodes are further reduced by a neighbor elimination algorithm • When a forward node v receives a broadcast packet, instead of forwarding the packet immediately, v will wait for a back off delay and monitor the forwarding activities of its neighbors. For each neighbor u that has forwarded the broadcast packet, node v removes N(u) from N(v). If N(v) is not empty after the delay period, node v forwards the broadcast packet; otherwise, node v becomes a non-forward node. U V W

18. Simulation Results Comparisons for k-hop information Small neighborhood Large neighborhood

19. Simulation Results Comparison of different coverage conditions Small neighborhood Large neighborhood

20. Conclusion • This general framework to reduce number of forward nodes, is more efficient than existing ones. • It gives a perception on the mechanisms such as neighborhood information, routing history , coverage conditions and priority functions. • Simulation shows that 1,2-hop routing history and coverage condition 2 are appropriate configuration parameters.

21. “ Localized Minimum-energy broadcasting in ad-hoc networks”

22. Topology Control Oriented Vs Broadcast Oriented Protocols Topology Control Oriented • Independently of broadcast utilization. • All nodes can be a source of a broadcast. • Minimizing the total transmission power. Broadcast Oriented • Broadcast process from a given source node. • Broadcasting incremental power. • The sub graph introduced by the minimum energy broadcast does not need to be strongly connected.

23. Various Communication Models • One –to-all • Mobile nodes use omni directional antennas • One –to-one • Nodes are equipped with directional antennas with small angles that can provide more energy savings • Variable angular range • The nodes can choose direction and width of the beam that allows to target several neighbor with one transmission. This paper discusses localized broadcast oriented protocols in one-to-all communication models in wireless ad-hoc networks.

24. Energy Model Where is a real constant greater than 2 and r (u) is the range of the transmitting node. In reality, The constant c is added in order to take into account the overhead due to signal processing, minimum energy needed for successful reception and MAC control messages.

25. Energy Model(Contd.) S D S D (a) (c) (b) S D Transmissions in all figures cost the same energy by using Pythagoras theorem and induction. Total Power Consumption Each node has to reduce its transmission range while maintaining the connectivity of the graph.

26. Minimum Energy Broadcasting Protocols GLOBALIZED LOCALIZED MINIMUM SPANNING TREE (MTCP) RNG TOPOLOGY CONTROL PROTOCOL (RTCP) TOPOLOGY ORIENTED RNG BROADCAST ORIENTED PROTOCOL (RBOP) BROADCAST INCREMENTAL POWER (BIP) BROADCAST ORIENTED

27. Minimum Spanning Tree Algorithm Average degree is 8 Average degree is 2 Prim’s Algorithm

28. Broadcast Incremental Power (BIP) 2 Node 10 is the source 4 2 4 10 8 8 9 10 9 6 6 1 1 1 7 5 7 5 3 3 Wieselthier et al.

29. RNG Topology Control Protocol Substitute MST by the relative neighborhood graph (RNG) • RNG can be deduced locally using the distance with its neighbors. • With positioning system , nodes need only 1-hop information. • Without positioning system ,nodes can achieve RNG using 2-hop distance information.

30. G A F E C S B D RNG Broadcast Oriented Protocol ( RBOP) Sis the source Node S emits its message with the range d (S,A), and A, B and C receive the message. The node C resends the message with range d (C,D). F applies neighbor elimination and eliminates E. At the same time, E decides not to send the message since all its RNG-neighbors are eliminated with the message from C. Finally when A forwards the message , F and G eliminate A from their respective neighborhood list and terminate the protocol for this broadcast since their lists are empty.

31. RNG Broadcast Oriented Protocol ( RBOP) G G A A F F E E C C S S B D B D The Broadcast is accomplished in 3 transmissions

32. RBOP Algorithm When receiving a new broadcast message: If the emitter is a RNG-neighbor; the node calculates the furthest of its RNG-neighbors that did not receive this message. The node resends the message according to this range or ignores the message if all of its RNG-neighbors have received the message. Otherwise, the node generates, for this broadcast , the list of RNG-neighbors that have not received this message. After a given timeout, if the neighbor list is not empty, the node retransmits the message with a range allowing to reach furthest neighbor in the associated list. When receiving an already received message: The node ignores the message if it has already forwarded it. The node removes the nodes that received this message from the associated neighborhood list. The message is ignored if the associated list is empty. Otherwise , if the message arrives on a RNG-edge send the message with range allowing to reach furthest neighbor in the list of non-eliminated RNG neighbors.

33. Comparison of Different Protocols = 2 , c = 0, no. of nodes=n=100, maximum communication radius = R =250 m

34. Inference from the Graph • Localized RBOP has quite close performance globalized MTCP protocol. • BIP spends 50% less energy than RBOP in average case. • This overhead compensates the network load which is needed for full knowledge of network in globalized solutions. • EER of RBOP decreased with and c.

35. Conclusion • A localized RNG based minimum energy broadcast RBOP that’s competes with globalized BIP protocol. • MST structure does not necessarily capture the structural properties in case of broadcasting. • Increased transmission radius beyond the value of the furthest uncovered neighbor in any MST does not necessarily increase the overall energy consumption. • MPR (Multipoint relaying) broadcast and stochastic flooding and combination of both between RBOP may lead to improvement in the current results.

36. Summary Both the papers discuss broadcasting techniques in ad-hoc networks using neighborhood information. In the first case, algorithm prunes the number of nodes it needs to forward to. In the second paper, a decision is made whether a node should forward the packet or not. These two papers underscore two diverse ways to use metrics of k-hop neighborhood information for moderate values of k.