An Energy-Efficient and Low-Latency Routing Protocol for Wireless Sensor Networks Antonio G. Ruzzelli, Richard Tynan and G.M.P. O’Hare Adaptive Information Cluster, Smart Media Institute Department of Computer Science University College Dublin Proceedings of the 2005 Systems Communications (ICW’05) Chien-Ku Lai

Outline Introduction Related Work Scheduling in Merlin Experimentation and Results Conclusions and Future Work

Introduction - Wireless Sensor Networks (WSNs) Components:  One or more base-stations  Many sensor nodes Constraints on sensor nodes:  Energy  Storage capacities  Data processing

Introduction - Wireless Sensor Networks (WSNs) (cont.) Applications:  Ecosystem monitoring  Emergency operation  Intelligence detection of ambient conditions  Intrusion detection  Localization of objects or animals  Medical monitoring  Structural monitoring  Surveillance

Introduction - Wireless Sensor Networks (WSNs) (cont.) Major form of energy wastage:  Idle listening  Collision  Transmissions overhead  Overhearing

Introduction - about this paper MERLIN is presented  Mac Energy efficient, Routing and Localization INtegrated  Combination of TDMA and CSMA

Related Work SMAC TMAC DMAC

SMAC Uses a coordinated adaptive sleeping mechanism The main drawbacks:  Latency RTS/CTS mechanism  The increase of energy consumption when some nodes join the network

TMAC An improvement to the SMAC protocol Uses an overhearing mechanism  RTS/CTS collisions are very high  Latency is still present

DMAC Incorporates a data gathering tree to reduce the latency The main drawback:  It is suitable only for unidirectional communication flow to a single gateway

Scheduling in Merlin

The purpose of MERLIN scheduling is to allocate time-zone slots Nodes in the same time-zone use the same slot to transmit The timing of the slots prevents most collisions

Scheduling in Merlin V-table X-table

Scheduling in Merlin - V-scheduling Gateway

Scheduling in Merlin - X-scheduling Gateway

Experimentation and Results 1. Network setup time 2. Network lifetime 3. Latency of messages

Simulation environment OmNet++ EYES WSNs testbed Number slot /frame = 4 DataRate = bits/sec Contention period = 30ms DataSize = 16+8 Bytes (data + 3 bytes preamble + starting code)

Simulation environment (cont.) Nodes with the same colors are in the same zone (same hop count number)

Network setup time

Network lifetime

Latency of messages (1/4) X-scheduling V-scheduling

Latency of messages (2/4) X-scheduling V-scheduling

Latency of messages (3/4) X-scheduling V-scheduling

Latency of messages (4/4) X-scheduling V-scheduling

Latency of messages - Comparison

Conclusions and Future Work

Conclusions The absence of handshake mechanisms like RTS/CTS can considerably reduce the latency of messages Idle listening is reduced by the TDMA approach CSMA technique increases the scalability

Conclusions (cont.) X scheduling  is suitable for applications in which latency is a tighter constraint V-scheduling  performs better than the X-scheduling in terms of percentage of collisions and network lifetime

Future Work Perform more experimentation to compare MERLIN scheduling with other WSN protocols Clarify the impact of our design decisions with mobile nodes

Questions? Thank you.