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Topology Control of Multihop Wireless Networks Using Transmit Power Adjustment. Paper By: Ram Ramanathan, Regina Resales-Hain Instructor: Dr Yingshu Li Presented By: R. Jayampathi Sampath. Outline . lNTRODUCTION PROBLEM STATEMENT STATIC NETWORKS: OPTIMUM CENTRALIZED ALGORITHMS CONNECT

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topology control of multihop wireless networks using transmit power adjustment

Topology Control of Multihop Wireless Networks Using Transmit Power Adjustment

Paper By: Ram Ramanathan, Regina Resales-Hain

Instructor: Dr Yingshu Li

Presented By: R. Jayampathi Sampath

outline
Outline

lNTRODUCTION

PROBLEM STATEMENT

STATIC NETWORKS: OPTIMUM CENTRALIZED ALGORITHMS

CONNECT

Separation Edges and Vertices

Biconnected Graph

BICONN-AUGMENT

MOBILE NETWORKS : DISTRIBUTED HEURISTICS

LINT Description

LILT Description

EXPERIMENTAL RESULTS

lntroduction
lNTRODUCTION

“Multihop wireless network”

a packet may have to traverse multiple consecutive wireless links to reach its destination.

“Topology”

set of communication links between node pairs used explicitly or implicitly by a routing mechanism.

uncontrollable factors: mobility, weather, noise

controllable factors: transmit power, antenna direction

This paper addresses the problem of controlling the topology of the network by changing the transmit powers of the nodes.

Controlling the set of neighbors to which a node talks to is the basic approach.

lntroduction contd
lNTRODUCTION(Contd.)

Why do we need to control the topology?

Draw back of a wrong topology

Reduce the capacity

Increase the end-to-end packet delay

Decrease the robustness to node failures

Example 1 – Too sparse network

A danger of network partitioning

High end to end delays

Example 2 – Dense network

Many nodes interfere with each other

Recompute routes even if small node movements

problem statement
PROBLEM STATEMENT

Definition 1:A multihop wireless network is represented as M = (N, L), where N is a set of nodes and L is a set of coordinates on the plane denoting the locations of the nodes.

Definition 4:The least-power function gives the minimum power needed to communicate a distance of d.

Definition 6:Problem Connected MinMax Power (CMP). Given an M = (N, L), and a least-power function find a per-node minimal assignment of transmit powers such that the induced graph of (M, p) is connected, and is a minimum.

problem statement contd
PROBLEM STATEMENT (Contd.)

Definition 7:Problem Biconnectivity Augmentation with MinMax Power (BAMP). Given a multihop wireless net M = (N, L), a least-power function and an initial assignment of transmit powers such that the induced graph of (M, p) is connected, find a pernode minimal set of power increases such that the induced graph of is biconnected, and is a minimum.

static networks optimum centralized algorithms
STATIC NETWORKS: OPTIMUM CENTRALIZED ALGORITHMS

s-p

step number

power assigned

d(s)

distance

step number

algorithm connect contd
Algorithm CONNECT (Contd.)

side-effect edge

  • A side effect edge may form a loop with other edges and may allow the lowering of some power levels and the elimination of some edges added previously.
separation edges and vertices
Separation Edges and Vertices

Definitions

Let G be a connected graph

A separation edge of G is an edge whose removal disconnects G

A separation vertex of G is a vertex whose removal disconnects G

Applications

Separation edges and vertices represent single points of failure in a network and are critical to the operation of the network

Example

3, 5 and 6 are separation vertices

(3,5) is a separation edge

4

7

1

6

2

5

3

8

biconnected graph
Biconnected Graph

Equivalent definitions of a bi-connected graph G

Graph G has no separation edges and no separation vertices

For any two vertices u and v of G, there are two disjoint simple paths between u and v (i.e., two simple paths between u and v that share no other vertices or edges)

For any two vertices u and v of G, there is a simple cycle containing u and v

Example

4

7

1

6

2

5

3

8

algorithm biconn augment
Algorithm BICONN-AUGMENT
  • Identify the bi-connected components in the graph induced by the power assignment from algorithm CONNET
  • This is done using method based on depth-first search
  • Node pairs are selected in non-decreasing order of their mutual distance and joined only if they are in different bi- connected components
  • This is continued until the network is biconnectd.
static networks optimum centralized algorithms contd
STATIC NETWORKS: OPTIMUM CENTRALIZED ALGORITHMS (Contd.)

Theorem 1:Algorithm CONNECT is an optimum solution to the CMP problem.

Proof: Lines 4, 5 create an edge between two nodes if they are in different clusters. Line 7 ensures that if we end then the graph is connected and line 3 ensures that if we end then all node pairs have been considered. Thus, the algorithm is correct.

Theorem 2: Algorithm BICONN-AUGMENT produces an optimum solution to the BAMP problem.

Proof: The correctness of BICONN-AUGMENT follows from lines 3 and 4 which force nodes to be in the same bi-connected component. The proofs for optimality and per-node minimality are similar to that for theorem 1.

implementation
Implementation

40 nodes spread out with a density of 2 nodes/sq mile

mobile networks distributed heuristics
MOBILE NETWORKS : DISTRIBUTED HEURISTICS

The topology is continually changing

Solution: continually readjust the transmit powers of the nodes to maintain the desired topology.

The solution must use only local or already available information. Eg. Positions

Centralized solutions not available in a mobile context.

Present two distributed heuristics

Local Information No Topology (LINT)

Local Information Link-State Topology (LILT)

Zero overhead protocols; they do not use any special control messages for their operation

slide15
LINT

Uses locally available information colleted by a routing protocol

Attempt to keep degree of each node bounded.

if d(Ni)>dh

reduce transmit power

if d(Ni)<dl

increase transmit power

dh High threshold on the node degree

dl Low threshold on the node degree

New power

slide16
LILT

significant shortcomings of LINT

Unaware of network connectivity

Danger of a network partitioning

LILT uses global information available in locally to recognize and repair network partitions

Two main parts

Neighbor reduction protocol (NRP)

LINT mechanism

Neighbor addition protocol (NAP)

Triggered whenever an event driven or periodic link-state updates arrives

The purpose triggering is to override the high threshold bounds and increase the power if the topology change indicated by the routing update results in undesirable connectivity.

experimental results
EXPERIMENTAL RESULTS

BICONN better

BICONN uses more power

experimental results cont
EXPERIMENTAL RESULTS (Cont.)

LINT is better

No significant changes