Loading in 2 Seconds...
Loading in 2 Seconds...
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
Paper By: Ram Ramanathan, Regina Resales-Hain
Instructor: Dr Yingshu Li
Presented By: R. Jayampathi Sampath
STATIC NETWORKS: OPTIMUM CENTRALIZED ALGORITHMS
Separation Edges and Vertices
MOBILE NETWORKS : DISTRIBUTED HEURISTICS
“Multihop wireless network”
a packet may have to traverse multiple consecutive wireless links to reach its destination.
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.
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
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.
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.
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
Separation edges and vertices represent single points of failure in a network and are critical to the operation of the network
3, 5 and 6 are separation vertices
(3,5) is a separation edge
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
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.
40 nodes spread out with a density of 2 nodes/sq mile
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
Uses locally available information colleted by a routing protocol
Attempt to keep degree of each node bounded.
reduce transmit power
increase transmit power
dh High threshold on the node degree
dl Low threshold on the node degree
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)
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.
BICONN uses more power
LINT is better
No significant changes