GPS-less Localization Protocol for Underwater Acoustic Networks

1. GPS-less Localization Protocol for Underwater Acoustic Networks • Othman, A.K;Wireless and Optical Communications Networks, 2008. WOCN '08. 5th IFIP International Conference on • Slides by Alex Papadimitriou

2. GPS-less Localization Protocol for Underwater Acoustic Networks • Limitations: • Propagation Delays are very long with limited bandwidth. • Incapability of modems to transmit and receive signals at the same time. • Scheduled transmission is required. • Connectivity depends upon factors such as relative node orientation, noise level, propagation losses, fading, relative movement of nodes, node and link failures, addition of new nodes. • Measurement Type: Ranging • Timing, Signal Strength • Deployment Techniques: • Anchor-based: Fraction of nodes somehow know their position. • Anchor-free: Uses local distance information.

3. GPS-less Localization Protocol for Underwater Acoustic Networks • Discovery and localization protocol can be divided into two parts: • Stage 1: Building up the relative co-ordinate system using the information gained from the first three seed node discoveries. • Stage 2: Further node discovery by selected seed nodes.

4. GPS-less Localization Protocol for Underwater Acoustic Networks • S1 is the first seed node. It broadcasts DISC_COMM packet and awaits for replies. • S1 discovers IDs and distances of neighbors but not locations. • Set a second seed node for further discovery. Propose that it is the furthest node from S1, so that a larger area can be covered quicker. • A1 is the information set of a discovery sequence, containing the distance measurements and IDs of those nodes replied. S1 broadcasts A1 and MORE_DISC to its neighbors. • If a node in the S1 region receives this command and the ID is equal to its own, then it recognizes that it is the next seed, S2 and it proceeds in the same manner. • And so on… • In the end, using triangulation each node finds its relative position to the initial seed.

5. GPS-less Localization Protocol for Underwater Acoustic Networks • Algorithms for selecting further seed nodes. • The Farthest/Farthest algorithm uses the farthest undefined node from a previous seed node, and the node with the maximum summation distance from this node and the previous seed node. Each remote node in the seed nodes region of the first stage of discovery will independently compute the relative location of all other nodes.

6. GPS-less Localization Protocol for Underwater Acoustic Networks • Farthest/Nearest Algorithm A different approach can be taken in order to gain the relative coordinates of nodes. The Farthest/Nearest algorithm uses the farthest undefined node from a previous seed node and the node with minimum summation distance from this node and the previous seed node. • Nearest/Farthest Algorithm Alternatively, the Nearest/Farthest algorithm can use the nearest undefined node from a previous seed node and the node with maximum summation distance from this node and the previous seed node. • Nearest/Nearest Algorithm The Nearest/Nearest algorithm uses the nearest undefined node from a previous seed node and the node with minimum summation distance from this node and the previous seed node.