KAIS T Using Mobile Relays to Prolong the Lifetime of Wireless Sensor Networks Wei Wang, Vikram Srinivasan, Kee-Chaing Chua MobiCom ‘05 Presentation by Mrinalini Sawhney Network & Security Lab (Dept of Computer Science, KAIST)

2 Using mobile relays to prolong the lifetime of WSNs Contents Introduction & Motivation Use of mobile nodes as relays or sinks Related works Energy conservation methods with mobile relay Static routing Dynamic routing Network lifetime comparison Lifetime upper bounds using Mobile relay Proposed algorithms Aggregation Routing Algorithm (ARA) Aggregation Routing Algorithm with Limited Nodes (ARALAN) Performance Evaluations Conclusions

3 Using mobile relays to prolong the lifetime of WSNs Introduction [1/4] [1] – Yang et al, How to prolong the lifetime of Wireless Sensor Network. Investigate the benefits of a heterogeneous architecture for WSN composed of a few resource rich mobile nodes and a large number of simple static nodes and a large number of simple static nodes Mobile Relays or Mobile Sinks

4 Using mobile relays to prolong the lifetime of WSNs Motivation [1/2] Scenario 2 -> very economical What about performance improvement from mobile node and the tradeoffs associated ?? Scenario 1 Deploy a million static nodes 15 cents per node Total deployment cost = $150,000 Scenario 2 Few expensive resource rich mobile nodes and many simple static nodes 10 $100 each 100,000 static 15 cents/node Total deployment cost = $16,000 VS

5 Using mobile relays to prolong the lifetime of WSNs Introduction [3/4] Sample network Two components are connected via sensor nodes A & B Lifetime of these two nodes is T Both A & B are the critical bottleneck nodes in the network Use of a mobile node doubles network lifetime Shuttles between node A & B Inherits the responsibility of the node with which its co-located

6 Using mobile relays to prolong the lifetime of WSNs Introduction [4/4] Mobile Node could be either Mobile relay or, Mobile Sink Analyze the lifetime for 3 different cases using different routing algorithms When the network is all static When there is one mobile sink When there is one mobile relay

7 Using mobile relays to prolong the lifetime of WSNs Related Works Shah et al., “Data Mules: Modeling a three-tier architecture for sparse sensor networks”, in proceedings of the IEEE Wkshp, on Sensor network Protocols and Applications (SNPA) 2003 Charkabarti et al., “Using Predictable Observer Mobility for Power Efficient Design of Sensor Network” The 2 nd Int’l Wkshp on Information Processing in Sensor Networks (IPSN), 2003 Gandham et al., “Energy Efficient schemes for wireless sensor networks with multiple mobile base stations” in proceedings of IEEE GLOBECOM, DEC 2003 Shankar et al., “Maximum lifetime routing in in wireless ad-hoc networks,”, in proceedings of 23 rd IEEE INFOCOM, Mar 2004 ….. Disadvantages Mobile sink needs to roam around the network All nodes in the network need to be aware of the current location of the mobile sink

8 Using mobile relays to prolong the lifetime of WSNs Energy Conservation Methods with Mobile Relays Static Routing Sensors know the location of mobile relays and redirect their packets through them Lifetime extended by u i time units Sort the original lifetime of static nodes in increasing order {( l 1, u 1 ), ( l 2, u 2 ), …., ( l n, u n )} Stays in a sleep mode for duration u i

9 Using mobile relays to prolong the lifetime of WSNs Energy Conservation Methods with Mobile Relays Dynamic Routing Routes to the sink depend upon the position of the mobile relay Focus of this paper S S

10 Using mobile relays to prolong the lifetime of WSNs Lifetime Improvement by using a Mobile Relay

11 Using mobile relays to prolong the lifetime of WSNs Lifetime Upper Bounds Without mobile relay, the lifetime upper bound is in the network With one mobile relay, the lifetime upper bound is With m mobile relays, the lifetime upper bound is A mobile relay needs to stay only within a two hop radius of the sink in order to maximize the lifetime

12 Using mobile relays to prolong the lifetime of WSNs Aggregation Routing Algorithm (ARA) [1/2] Routing Algorithm -> set of all nodes which can reach the sink with 2 hops -> set of all nodes outside the range Q2 O M

13 Using mobile relays to prolong the lifetime of WSNs Aggregation Routing Algorithm (ARA) [2/2] The # of nodes in a 3 is always greater than the sum of that in area a 1 and a 2 There are 4ρ candidates for aggregate node

14 Using mobile relays to prolong the lifetime of WSNs Another Proposed Algorithm Merits of ARA Efficient upper bound of Drawbacks of ARA algorithm Every node needs to know the position of the mobile This is a huge overhead Aggregation Routing Algorithm with Limited Nodes (ARALAN) Only a limited number of nodes in the network need to know the location of the mobile relay The upper bound is maintained

15 Using mobile relays to prolong the lifetime of WSNs Aggregation Routing Algorithm with Limited Nodes (ARALAN) Use of shortest path routing Once the information reaches Ps Relay it to the aggregation ring – Ring s,r Information reaches aggregation rings Travels through a series of aggregation rings before it reaches the aggregation node When the traffic reaches OM, its routed hop by hop

16 Using mobile relays to prolong the lifetime of WSNs Performance Performance of Mobile Sink Approach Lifetime would be atleast O(R) times better than static approach Mobile relay Approach Need to use O(R) nodes to achieve the same performance

17 Using mobile relays to prolong the lifetime of WSNs Performance Evaluations With one mobile relay Scenario Radius = 4 density = 4 # of nodes = % improvement

18 Using mobile relays to prolong the lifetime of WSNs Performance Evaluations

19 Using mobile relays to prolong the lifetime of WSNs Conclusions Investigates the possibility of Using the mobile node as a relay Using the mobile node as a sink Mobile sink always beneficial but application scenario is not feasible With one mobile relay lifetime improvement of up to four times over the static approach One static rich resource can improve the lifetime by 60% One mobile relay can increase by almost 300%