An Enhanced Cross-Layer Protocol for Energy Efficiency in Wireless Sensor Networks

1. An Enhanced Cross-Layer Protocol for Energy Efficiency in Wireless Sensor Networks Jaehyun Kim, Dept. of Electrical & Electronic Eng., Yonsei University; Seoul, Korea Jaiyong Lee, Dept. of Electrical & Electronic Eng., Yonsei University; Seoul, Korea Seoggyu Kim, Dept. Information & Computer Eng., Andong National University; Andong, Korea Presented by: Jordan Templeton EEL 6935G Fall 2011

2. Introduction • Wireless sensor networks are severely limited in system resources. • Bandwidth requirements are generally very low compared to traditional networks. • These factors require significantly different network management techniques.

3. Objectives • Most important goal is to maximize the lifetime of the network. • Integrity of transmitted data is a priority. • Throughput is not as critical as latency due to low bandwidth requirements.

4. Influential Work • S-MAC • T-MAC • AODV • DSR • AD-MAC

5. Enhanced Cross-Layer Protocol • Tree-based routing algorithm • Improves upon S-MAC and T-MAC • Major difference is the addition of the SYNCreply packet • SYNCreply packet is used to convey information about energy cost for a given link.

6. SYNC packet • Exclusively for synchronization in S-MAC and T-MAC. • ECLP also uses for routing management. • ECLP adds SYNCreply for network configuration.

7. SYNC packet • Used primarily to configure routing tree. • Similar to implementation in S-MAC and T-MAC. • Five additional fields for ECLP. • r_lth: routing length. • r_cost: routing cost in terms of energy. • thresholds: relative to remaining energy. • parents: parent nodes in branch tree. • status: intermediate, leaf, danger, or emergency.

8. SYNCreply packet • Unique to ECLP. • Modified from SYNC packet . • Two packets are replaced, r_lth and parent. • r_lthtotal: used to track hop count. • sink: identification of root node in branch.

9. Establishing Routing Tree • Initial setup starts at the sink node. • The SYNC packet is transmitted from the sink node to its neighbors, then to their neighbors, and so on. • Initially, r_lth and r_cost for all sensor nodes are set to maximum value of 255; single byte parameter. • Initially for sink node, r_lth=0 and r_cost=255. • r_lth is incremented by 1 at each stage and r_cost is calculated locally by each node. • Each node chooses parent nodes based on lowest received r_lth and r_cost values and creates a list of neighbors. • SYNCreply packet is used as a confirmation and to return r_lthtotal value for determining a hop count.

10. Link Failure Detection Method • WSNs are susceptible to interruptions. • ECLP incorporates a method to reestablish a communication link between nodes in the event of a failure. • Link failures must first be detected; ECLP uses RTS and CTS messages. • Data transmission is preceded by an RTS message and a failure is assumed if no CTS message is received after sending 3 RTS messages.

11. Link Failure Recovery Method • The first step is for a node to check its neighbor list for an alternate parent node. • The r_lth value is set to 255 for the original parent node to signify that the node is disabled. • The PERR (Path ERRor) packet is used when no alternate parent node was part of the neighbor list. • This packet is similar to the SYNC packet but contains an identification field to indicate that its sender needs a new parent node.

12. Adaptive Duty Cycling for Energy Efficiency • Allows nodes to utilize sleep mode in order to avoid energy waste from overhearing. • Variable time-out period to initiate sleep period if no communication is necessary. • RRTS (Reservation Ready-to-Send) packet used to limit overhearing by allowing unintended nodes to sleep.

13. Evaluation Method and Parameters • ECLP was compared to IEEE 802.11 with AODV and with DSR, and to S-MAC with AODV and with DSR. • The evaluation was performed via ns-2 which is a network simulation tool. • The simulations were configured with 20 and 50 nodes. • Each simulation randomly chose one node to move away from its original location.

14. Average Energy Consumption (20 nodes) • E802_11 = Etrans + Erecv + Eidle • ESMAC/ECLP = Etrans + Erecv + Eidle + Esleep

15. Average Energy Consumption (50 nodes) • E802_11 = Etrans + Erecv + Eidle • ESMAC/ECLP = Etrans + Erecv + Eidle + Esleep

16. Average End-to-End Delay (20 nodes)

17. Average End-to-End Delay (50 nodes)

18. Control Overhead • Simulation only performed with 20 nodes

19. Conclusion • Average energy consumption appears to be primarily dependent upon node quantity and relatively constant relative to data rate. • ECLP had the lowest average energy consumption while IEEE 802.11 was highest. The differences between DSR and AODV were negligible. • Average end-to-end delay was lowest for IEEE 802.11 and was relatively unaffected whether DSR or AODV were chosen. The highest delay occurred with S-MAC and, again, was relatively unaffected by the choice of AODV or DSR. ECLP was consistently in the mid range. Average delay scaled with node quantity and had very little dependence on actual data rate. • Energy consumption from network control was much more significant at for all of the protocols. ECLP had much lower control related energy consumption compared to IEEE 802.11. Again, the difference between AODV and DSR was negligible.

20. References • Jaehyun Kim; Jaiyong Lee; Seoggyu Kim; , "An Enhanced Cross-Layer Protocol for Energy Efficiency in Wireless Sensor Networks," Sensor Technologies and Applications, 2009. SENSORCOMM '09. Third International Conference on , vol., no., pp.657-664, 18-23 June 2009