1. KAIS T Location-Aided Flooding: An Energy-Efficient Data Dissemination Protocol for Wireless Sensor Networks Harshavardhan Sabbineni and Krishnendu Chakrabarty IEEE transactions on computer 2005 2006. 11. 28 Hanjin Lee

2. 2 컴퓨터구조특강 Introduction Wireless sensor networks Applications Remote monitoring, surveillance, tracking, feature extraction Characteristics Limited battery power A small amount of memory Connected to the outside world with base stations or access points Base stations send periodic control signals to all the sensor nodes Such dissemination of information is a challenging problem in sensor network because of resource constraints

3. 3 컴퓨터구조특강 Introduction Dissemination of information Application-specific requests Link state information needs to be distributed for routing Classical flooding Broadcast storm problem Redundancy Contention Collision In this paper Location aided flooding (LAF) Energy efficiency Self-configuration Scalable

4. 4 컴퓨터구조특강 Introduction LAF (Location-aided flooding) Virtual grids Partition the set of nodes into groups of gateway nodes and internal nodes Gateway nodes Forward the packet s across virtual girds Internal nodes Forward the packets with a virtual grid Reduce the number of redundant transmission Store a small amount of state information in a packet Infer the information about nodes that already have the packet from the modified packet header

5. 5 컴퓨터구조특강 Related prior works Classical flooding protocol The source node starts by sending the packet that needs to be flooded to all of its neighbors Each recipient node stores a copy of the packet and rebroadcasts the packet exactly once Neighborhood knowledge Location information Virtual grids Multiaccess signaling protocol

6. 6 컴퓨터구조특강 Location-aided flooding Modified flooding Use node ids to improve the energy efficiency of information dissemination Each packet includes a special field in the packet header called the Node List The Node List contains the ids of all the nodes that already have the packet When a node receives a packet If all its neighbors are already in the Node List The node does not broadcast the packet If its own ID is in the Node List The node does not process the packet and simply drops it Energy efficient, but longer packet length due to the Node List

7. 7 컴퓨터구조특강 Location-aided flooding Location information LAF uses location information to divide the sensor network into virtual grids GPS (Global positioning system) High cost Less precise location RSSI (received signal strength information) Acoustic time of flight (TOF) Time of arrival

8. 8 컴퓨터구조특강 Location-aided flooding Virtual grids Divides the monitored area (sensor field) into “virtual grids” Each node associates itself with a virtual grid depending on its physical location

9. 9 컴퓨터구조특강 Location-aided flooding Packet header format Variable length Contains the list of the nodes that have already received the packet The ID of the grid in which the sender of the packet is currently in Whether the node is a gateway node or an internal node

10. 10 컴퓨터구조특강 Location-aided flooding LAF Node Types Gateway nodes If any of the neighbors of a node A belong to a different virtual grid than that of A, then A becomes a gateway node Forward the data across virtual grids Internal nodes If all the neighbors of a node A belong to the same virtual grid as that of A, then A becomes an internal node Forward the data within a virtual grid Nodes determine their virtual grid and status (gateway or internal node) autonomously

11. 11 컴퓨터구조특강 Location-aided flooding Information dissemination using LAF Data forwarding by gateway nodes When a gateway node receives a packet from within its virtual grid Check if any of its neighbors within the same virtual grid have not yet received the packet If such nodes exist, the gateway node appends the ids of those nodes to the Node List of the packet and forwards it When a gateway node receives a packet from another gateway node Strips the packet of its Node List Adds its own id and all its neighbors’ ids Forwards the packet Data forwarding by internal nodes Modifies the Node List of the packet Includes the ids of all its neighbors in the Node List Forwards it

12. 12 컴퓨터구조특강 Location-aided flooding Grid maintenance costs : The total number of nodes : The number of beacon messages needed to know the position of a sensor node : The energy needed to receive each beacon message : Processing cycles to calculate grid association : The amount of energy needed for a single processing cycle The grid maintenance cost grows only linearly with the size of network

13. 13 컴퓨터구조특강 Location-aided flooding Completeness of the data dissemination procedure

14. 14 컴퓨터구조특강 Location-aided flooding Errors in location estimates The inaccuracies in position estimation do not affect the performance of LAF Even if the error in location estimate causes the node to assume a different location in the same grid Even if the error in location estimate causes the node to assume a different virtual gird than the virtual grid it really belongs to Even if a large correlated error causes a group of nodes belonging to a single virtual grid to be shifted to a different physical location

15. 15 컴퓨터구조특강 Performance evaluation Simulation model Implemented in C++ 50 nodes in 200x200m Monitored area is divided into 4 virtual grids Processing delay for transmitting a packet : 0~5ms A randomly selected node floods the network with a 64byte-packet Radio range : 20m Bandwidth of the radio : 20Kbps Energy model Specifications for the TR1000 radio

16. 16 컴퓨터구조특강 Performance evaluation

17. 17 컴퓨터구조특강 Performance evaluation N=1 N=4 N=8 N=50 Packet length is limited State information is not utilized

18. 18 컴퓨터구조특강 Performance evaluation

19. 19 컴퓨터구조특강 Conclusions LAF (location-aided flooding) Energy-efficient flooding algorithm Virtual grids Gateway nodes Internal nodes Location information Future work Adaptation of the size of the virtual grid Reconfiguration of the virtual grid in a distributed manner after node failures, wearout and battery depletion Evaluation of energy savings on physical hardware