## 4 Cross Layer Adaptation of Check Intervals
### Tree-Based Topologies
A good synchronization strategy is essential to saving the node resources. In this paper we propose an approach to deal with communication delays which occur in preamble sampling-based protocols in order to improve the synchronization of the nodes. Our approach, called Cross Layer Adaptation of Check intervals (CLAC), allows to precisely update the check interval at each hop based on estimating the delay that a packet traveling along a multi-hop path introduces at each hop within the path. CLAC successfully synchronizes the sender and the receiver by delaying the check interval to match the expected packet arrival time. To estimate the check interval, CLAC uses information provided by the routing and MAC layers. We have shown by simulation that for the linear and tree topologies, CLAC improves the synchronization between the nodes and contributes to finding a good balance between connectivity and energy saving at no additional packet loss. CLAC increases the network lifetime, maintains the connectivity and reduces the packet loss as compared to CTP/BoX-MAC. Thus, we demonstrate that for dealing with network latencies, it is not necessary to increase the duty cycle and the radio activation in the nodes can be adapted to suit this need. Ongoing work includes the extension of CLAC to other LPL protocols beyond BoX-MAC. We also plan to analyze the behavior of CLAC on different network topologies (for example grids) in order to study the delays that the packets traveling from the sender to the sink introduce and how they are propagated. Finally, we also plan to compare CLAC with other approaches that adjust the duty cycle in order to find a good balance between high packet delivery and energy savings. ## Acknowledgments

This work has been partially funded by the Spanish Ministry of Science and Technology under the grant TIN2010-16497 \"Tecnicas Escalables de Entrada/Salida en Entornos Distribuidos y de Computacion de Altas Prestaciones\". ## References

* _[PERSON] et al. (2007)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Wireless sensor networks: A survey on the state of the art and the 802.15.4 and ZigBee standards. _Comput. Commun._**2007**, _30_, 1655-1695. * _[PERSON] et al. (2009)_ [PERSON]; [PERSON]; [PERSON] [PERSON] Application-driven, energy-efficient communication in wireless sensor networks. _Comput. Commun._**2009**, _32_, 896-906. * _[PERSON] et al. (2002)_ [PERSON]; [PERSON]; [PERSON]; [PERSON] Wireless sensor networks: A survey. _Comput. Netw._**2002**, _38_, 393-422. * [4] [PERSON] System architecture for wireless sensor networks. Ph.D. thesis, University of California, Berkeley, CA, USA, 2003. * [5] [PERSON] [PERSON] Aloha with Preamble Sampling for Sporadic Traffic in Ad Hoc Wireless Sensor Networks. In _Proceedings of the IEEE International Conference on Communications, 2002. ICC 2002_, New York, NY, USA, 28 April-2 May 2002; Volume 5, pp. 3418-3423. * [6] [PERSON]; [PERSON] [PERSON] WiseMAC: An Ultra Low Power MAC protocol for the Downlink of Infrastructure Wireless Sensor Networks. In _Proceedings of the Ninth International Symposium on Computers and Communications 2004_, Alexandria, Egypt, 28 June-1 July 2004; Volume 2, pp. 244-251. * [7] [PERSON]; [PERSON]; [PERSON] Versatile Low Power Media Access for Wireless Sensor Networks. In _Proceedings of the 2 nd International Conference on Embedded Networked Sensor Systems_, Baltimore, MD, USA, November 2004; pp. 95-107. * [8] [PERSON]; [PERSON] BoX-MACs: Exploiting Physical and Link Layer Boundaries in Low-Power Networking. Technical report, Stanford University, Stanford, CA, USA, 2008. * [9] [PERSON]; [PERSON] Medium access control in wireless sensor networks. _Comput. Netw._**2007**, _51_, 961-994. * [10] [PERSON] Medium Access Control in Wireless Sensor Networks. In _Medium Access Control in Wireless Networks_; [PERSON], [PERSON], Eds. ; Nova Science Publishers, Inc.: New York, NY, USA, 2008; pp. 535-560. * [11] [PERSON]; [PERSON]; [PERSON] MAC protocols for wireless sensor networks: A survey. _IEEE Commun. Mag._ **2006**, _44_, 115-121.