SEA-MAC: A Simple Energy Aware MAC Protocol for Wireless Sensor Networks for Environmental Monitoring Applications By: Miguel A. Erazo and Yi Qian International Symposium on Wireless Pervasive Computing – ISWPC 2007 San Juan, Puerto Rico 2007

February ISWPC 2007 Outline Introduction Related work S-MAC design overview Experimental results Conclusions Q & A

February ISWPC 2007 What are wireless sensor networks? Introduction Related work SEA-MAC design overview Experimental results Conclusions o A sensor network is a group of specialized transducers with a communications infrastructure intended to monitor and record conditions at diverse locations. o A sensor network consists of multiple detection stations called sensor nodes, each of which is small, lightweight and portable. Every sensor node is equipped with a transducer, microcomputer, transceiver and power source.

February ISWPC 2007 Functionalities of a MAC protocol Introduction Related work SEA-MAC design overview Experimental results Conclusions Creation of a network infrastructure. Establish communication links for data transfer. Fairly and efficiently share communication resources between sensor nodes.

February ISWPC 2007 Contributions of this paper Design of a simple listen - sleep schedule. Propose a unique synchronization in the network. Comparison of the SEA-MAC performance with that of S-MAC and SCP-MAC in terms of energy consumption in both simulations in ns-2 and implementation in mica2 motes. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 S-MAC Ye et al. proposed S-MAC, a medium access control (MAC) protocol designed for wireless sensor networks.  Nodes form virtual clusters based on common sleep schedules to reduce control overhead and enable traffic-adaptive wakeup.  S-MAC uses in-channel signaling to avoid overhearing unnecessary traffic.  S-MAC applies message passing to reduce contention latency. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 SCP-MAC Ye et al. introduced SCP-MAC, a protocol which uses Scheduled Channel Polling (SCP) to achieve more energy savings than those of protocols that use coordinated transmissions and listen periods. The contributions of SCP-MAC are the ultra low duty cycles it achieves and its capacity to adapt to variable traffic loads. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 T-MAC / D-MAC Dam et al. proposed T-MAC, a contention-based Medium Access Control protocol for wireless sensor networks designed to lower energy consumption. Lu et al. proposed D-MAC, a protocol whose objective is to achieve very low latency. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 Objectives First, to provide a way to achieve low duty cycle for periodic traffic e.g. sampling solar radiation or humidity. Second, to make synchronization simpler and unique in the whole network. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 Time schedule SEA-MAC attempts to make use of the advantage that the entire traffic of environmental monitoring applications is periodic. It creates a schedule in which nodes only wake up when a sample from environment is taken. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 Time schedule cont. Introduction Related work SEA-MAC design overview Experimental results Conclusions Fig. 1. Time schedule in SEA-MAC

February ISWPC 2007 The synchronization Nodes running SEA-MAC, upon being turned on, turn on their radios to listen for synchronization (SYNC) packets from the BS. BS is the only node that can start and maintain synchronization while the other nodes only disseminate synchronization in a multihop environment. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 The synchronization cont. Introduction Related work SEA-MAC design overview Experimental results Conclusions Fig. 2. SEA-MAC synchronization.

February ISWPC 2007 Table of terms for energy analysis Introduction Related work SEA-MAC design overview Experimental results Conclusions TABLE 1 List of symbols used in energy consumption Symbol Meaning P tx Power in transmitting P rx Power in receiving P listen Power in sleep P sleep Power in sleeping t csl Average carrier sense time tBtB Time to Tx/Rx a byte T data Data packet period T sync Synchronization packet period r data Data packet rate (1/T data ) r sync Synchronization packet rate (1/T sync ) L data Data packet length L sync Synchronization packet length t tx Average time a node is transmitting t rx Average time a node is receiving t cs Average time a node is on carrier sense t sleep Average time a node is sleeping

February ISWPC 2007 How to compute energy consumption Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 Comparing S-MAC vs. SCP-MAC Introduction Related work SEA-MAC design overview Experimental results Conclusions Esnp = P listen t cs1 (r data +r sync ) + (P tx +nP rx )(t tone +L data t B )r data + (P tx +nP rx )(t tone +L sync t B )r sync + P poll t p1 /T p + P sleep [1−t cs1 (r data +r sync ) − (n+1)(t tone +L data t B )r data − (n+1)(t tone +L sync t B )r sync − t p1 /T p ]

February ISWPC 2007 Simulation Introduction Related work SEA-MAC design overview Experimental results Conclusions Fig 3. Network configuration used for simulations.

February ISWPC 2007 Simulation results Introduction Related work SEA-MAC design overview Experimental results Conclusions Fig. 4. Energy consumption of SEA-MAC and S-MAC Fig. 5. Energy consumption as a function of the rate of transmission.

February ISWPC 2007 Experiments Introduction Related work SEA-MAC design overview Experimental results Conclusions Fig. 6. Network configuration for implementation.

February ISWPC 2007 Results of experiments Introduction Related work SEA-MAC design overview Experimental results Conclusions Fig. 7. Voltage drop in 48 hours of test

February ISWPC 2007 Voltage drop TABLE 2 Voltage drop PROTOCOL NodeVoltag e Drop [mV] SEA-MAC2102 SEA-MAC3108 Average=105 S-MAC at 10% DC2155 S-MAC at 10% DC3198 Average=176.5 SCP-MAC at 1 [s] polling interval2164 SCP-MAC at 1 [s] polling interval3190 Average=177 S-MAC at 25% DC2182 S-MAC at 25% DC3213 Average=197.5 S-MAC at 50% DC2228 S-MAC at 50% DC3206 Average=217 Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 Conclusions This paper proposes SEA-MAC, a new MAC protocol whose objective is to reduce energy consumption for environmental monitoring applications. SEA-MAC reduces drastically the DC by making that nodes wake up only when a sample is taken from the environment. In this way, idle listening is reduced. Also, synchronization has been made unique in the whole network in order to save energy by making nodes to follow only one time schedule. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 Conclusions Simulation results in ns-2 have shown that SEA-MAC achieves better energy performance that S-MAC at different DC’s. Furthermore, tests on mica2 motes have shown that SEA-MAC outperforms S-MAC and SCP-MAC achieving the least voltage drop on the batteries of the motes in tests of 48 hours. SCP-MAC and S-MAC achieved similar results in energy performance even though SCP-MAC has much lower DC’s than S-MAC. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 Future work Future work will include an analysis of SEA-MAC performance in multi-hop configurations as well as an analysis of the optimal values of its parameters for minimum consumption of energy. Introduction Related work SEA-MAC design overview Experimental results Conclusions

February ISWPC 2007 QUESTIONS