Efficient Backbone Construction Methods in MANETs Using Directional Antennas 1 Shuhui Yang, 1 Jie Wu, 2 Fei Dai 1 Department of Computer Science and Engineering Florida Atlantic University 2 Microsoft Corporation

Outline Introduction –Network Backbone ( DS 、 CDS 、 DCDS ) –Antenna Module Goal Backbone Construction Method –Node coverage condition (NCC) –Edge coverage condition (ECC) –Sector optimization (SO) Proof for Directional Connected Dominating Set Simulation Results Conclusions

Introduction - DS Broadcasting is the most frequently used operation for the dissemination of data and control messages in the preliminary stages of some other applications. The Dominating Set (DS) has been widely used in the selection of an efficient virtual network backbone. nodes in the set

Introduction - CDS When a DS is connected, it is called a Connected Dominating Set (CDS). CDS as a connected virtual backbone has been widely used for efficient broadcasting in MANETs. nodes in the set

Introduction - DCDS The use of directional antenna systems helps to –improve channel capacity as well as conserve energy since the signal strength towards the direction of the receiver can be increased. Due to the constraint of the signal coverage area, interference can also be reduced. a b nodes in the set

Introduction - Antenna Module A common directional antenna model involves dividing the transmission range of a node into K identical sectors. All nodes use a directional antenna for transmission and an omnidirectional antenna for reception. a d c b K K-1 a b c d e f

Introduction - Antenna Module Sectors in the antenna model are not necessary aligned. The antenna uses the steerable beam techniques.

Goal - minimum DCDS To find the minimum DCDS in directed network graph. –The problem of finding the smallest connected subgraph (CDS) in terms of number of edges in a given strongly connected graph (G) is NP-complete. –Heuristic localized solutions to find the minimum DCDS in network graph (NP-complete). DCDS is a set of selected nodes and their associated selected edges. nodes in the set

u v Backbone Construction Method Each node has its unique ID. Each node sends out "Hello" messages K times to the K directions and accomplishes the directional neighborhood discovery. Dominating and Absorbant : u’s dominating edge v’s absorbant edge u’s absorbant neighbor v’s dominating neighbor

Backbone Construction Method Authors propose an heuristic localized solutions to select forwarding nodes and edges for the DCDS. The status of each node depends on its h-hop topology only for a small constant h, and is usually determined after h rounds of "Hello" message exchange among neighbors. The given directed graph is strongly connected. –The graph is a directed graph with symmetric connectivity. u v

Backbone Construction Method Using NCC (Node Coverage Conditions) and ECC (Edge Coverage Conditions) to unmark the nodes and directed edges. –unmarked nodes and directed edges : not in the DCDS. –marked nodes and directed edges : in the DCDS. Some node properties can be used as node priority in NCC and ECC. –Energy Level –Node Degree –Node IDs (unique) Author assume that the priority of node u is p(u) based on the alphabetic order, such as p(u) > p(v) > p(w) > p(x).

Backbone Construction Method - NCC A node v is unmarked if, for any two dominating and absorbant neighbors, u and w, a directed replacement path exists connecting u to w such that –(1) each intermediate node on the replacement path has a higher priority than v. –(2) u has a higher priority than v if there is no intermediate node. u v w t u v w p(t) > p(v)p(u) > p(v) a b c d e f g h i j k l m n o p q r s t u v w x y z

Backbone Construction Method - ECC Edge Priority Assignment. –For each edge (v → w), the priority of this edge is p(v → w) = (p(v), p(w)) = p(v) + p(w) a b c d e f g h i j k l m n o p q r s t u v w x y z v w p(v → w) = (p(v), p(w)) = p(v) + p(w) = = 9

Backbone Construction Method - ECC Each marked node uses the edge coverage condition to determine the status of its dominating edges. –Edge (v → w) is unmarked if a directed replacement path exists connecting v to w via several intermediate edges with higher priorities than (v → w). v w u p(v → w) = 9 p(u → w) = 10 p(v → u) = 11 p(v → u) > p(v → w) and p(u → w) > p(v → w) a b c d e f g h i j k l m n o p q r s t u v w x y z

Backbone Construction Method - SO Sector Optimization (SO) –Align the edge of one sector to each selected forwarding edge, and determine the one with the smallest number of switched-on sectors.

Proof for DCDS Before NCC and ECC : G ( V, E ) After NCC and ECC : G’ ( V’, E’ ) Proof : Any two nodes s ∈ V’ and d ∈ V, there is a path S P with all intermediate nodes and edges only from V’ and E’, we prove that (V’, E’) is a DCDS. Prove by contradiction –S P connecting s to d has at least one unmarked edge –S P connecting s to d has at least one unmarked node s d SPSP

Proof for DCDS S P connecting s to d has at least one unmarked edge. After ECC, (u → w) has higher priorities than other paths. If (u → w) is an unmarked edge, it must exists a replacement path R P that several intermediate edges in R P with higher priorities than (u → w). –Contradiction to ECC. s d SPSP RPRP uw u’

Proof for DCDS S P connecting s to d has at least one unmarked node. If u' is unmarked node, it must exists a replacement path R P that –1. several intermediate nodes on the R P has a higher priority than u’. –2. no intermediate nodes on the R P, u has a higher priority than u’. s SPSP RPRP uw u’’ d u’

Proof for DCDS After NCC, u’ has higher priorities than other nodes. If u’ is unmarked node, it must exists a replacement path R P that several intermediate nodes on the R P has a higher priority than u’. –Contradiction to NCC step 1. s SPSP RPRP uw u’’ d u’

Proof for DCDS If u’ is unmarked node, it must exists a replacement path R P that no intermediate nodes on the R P, u has a higher priority than u’. –NCC step 2 already exclude this situation. –Contradiction to NCC step 2. s d SPSP RPRP uw u’

Examples NCC –(10) ： (25) → (07) ， P(25)>P(10) ， 可取代 (25) → (10) → (07) ， (10) unmarked –(07) ： (25) → (10) ， P(25)>P(07) 可取代 (25) → (07) → (10) ， (07) unmarked –(04) ： (25) → (07) ， P(25)>P(04) ， 可取代 (25) → (04) → (07) ， (04) unmarked –(25) ：找不到 優先權更大的路徑可取代， (25) marked – 不考慮 (10) 、 (07) 、 (04) 的 dominating edge

Examples ECC –(25)→(10) ， P(25)+P(10) =35 ， (25)→(07)→(10) 優先權： 32<35 、 17<35 (25)→(10) marked. –(25)→(07) ， P(25)+P(07) =32 ， (25)→(04)→(07) 優先權： 29<32 、 11<32 (25)→(10)→(07) 優先權： 35 、 17<32 (25)→(07) marked. –(25)→(04) ， P(25)+P(07) =29 ， (25)→(07)→(04) 優先權： 32 、 11<29 (25)→(04) marked

Simulation Results Area : 100 x 100 Communication Rang : 30

Simulation Results Area : 100 x 100 Communication Rang : 40 (Larger)

Simulation Results Area : 100 x 100 Communication Range : 30 K=4 K=6 (Rule K 、 Generic) all sectors of each forwarding node are switched- on due to the omnidirectional antenna.

Simulation Results Area : 100 x 100 Communication Range : 40 (Larger) K=4 K=6

Simulation Results Area : 100 x 100 ECC with different h-hop local information.

Conclusions Using directional antennas, constructing a directional network backbone in MANETs further reduces total energy consumption as well as reducing interference in broadcasting applications. A heuristic localized algorithm for constructing a small DCDS is proposed. The sector optimization algorithm is developed for the second phase. Our future work includes some extensions of the ECC algorithm, such as applying ECC to topology control.

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