Environmental Monitoring

We focus on the design and implementation of the monitoring WSN system, especially when facing harsher communication and deployment environment. We plan to provide hybrid hierarchical network architecture with access control protocol and power-aware cross-layer scheme to adjust the lifetime of the system adaptively. We also care about the device cost of real system. To achieve low cost, a deployment optimization technology is proposed. Test-bed experiments are used to validate these designs before the real system deployment. Our prototype system has been built in the YanXi, Wumen, Wuyingdian Palace of the Forbidden City for more three years. The performance analysis showed that our strategy has achieved a significant extension of the network lifetime and a major improvement on the effectiveness of the packet delivery.

Approach

We first proposed a three-tiered architecture for environmental monitoring applications. The nodes in sensing layer directly communicate with at least one of the routing nodes to build the routing backbone. Gateways receive data from routing layer and send data to the remote server. Then we propose a deployment technology based on the ant colony optimization algorithm. The constraints of communication and deployment can be modeled as special limit parameters in DT-ACO. With these limits, the candidate deployment solutions are constructed with the optimizing objective of minimizing the number of nodes. We also provide a novel power-aware cross-layer scheme (PACS) to guarantee the different requirements on lifetime and surveillance accuracy.

Systems/Experiments

We employ indoor test-bed to validate the tied architecture and the novel power-aware cross-layer scheme. The test-bed is set up with nine EASI210 sensing nodes and one EASI500 gateway which are randomly distributed in a room. The default data transmission power is set to -10dBm. The packet size is fixed to 36 bytes.

In Yanxi Palace of the Forbidden City on December 4, 2005, we deployed the prototype system for the first phase. The system contained eight sensing nodes and one gateway. The second phase of deployment began on March 7, 2006, in which the hybrid hierarchical network architecture and the power-aware cross-layer scheme were adopted. The third phase of deployment began on July 25, 2007 in Wumen Palace with 32 nodes. This system keeps alive till now. We extended this system to another palace, Wuying Palace , on March, 2008 with another 26 nodes. The performance is evaluated on three metrics: the lifetime, the mean retransmission times and the packet loss rate of the whole system. Analysis showed that the system packet loss rate of our network is largely reduced and the maximum lifetime of nodes is significant extended in comparison with the traditional modules in TinyOS.

Accomplishments

1. Dong Li, Wei Liu, Ze Zhao and Li Cui. Demonstration of a WSN Application in Relic Protection and an Optimized System Deployment Tool. ACM/IEEE International Conference on Information Processing in Sensor Networks (IPSN 2008), demo paper, Page 541-542, St. Louis, Missouri, USA, April 22-24, 2008.
2. Dong Li, Wei Liu, Chunli Hui, ChangCheng Huang andLi Cui. Wireless Sensor Networks in Relics Protection: Deployment Methodology and Cross-layer Design. Accepted to appear at High Technology Letters.

Future Directions

In future, we will employ the DTN (delay tolerant network) characters in the real environmental monitoring applications and try to increase the scale of our network while maintaining good system performance.