Energy Efficient Transmission Scheme For Wireless Sensor Networks

Wireless sensor networks bridge the gap between physical world information and digital world, enhance the data collection ability of computer, and open up a broad application prospect for the fields of military, medicine, environment moni-toring, intelligent home system and so on, and cause wide concern. The sensors in the sensor networks are connected wirelessly with ad hoc mode. Efficient communi-cation supports are needed to build network. The researches on traditional ad hoc networks focus on better service quality and higher throughput. The key issue of wireless sensor networks is energy efficiency. So, efficient communication strategies with low energy consumption are required. We design transmission scheme for MAC layer, cross-layer between MAC and route layer, and special scenario in structural health monitoring. In this paper, we make the following contributions to energy efficient communication for wireless sensor networks:(1) We have designed an asynchronous duty cycle based MAC layer broadcast protocol for wireless sensor networks. The sender repeats the broadcast packets with dynamic interval. The repeated transmissions would make the period sleeping neighbors receive the packet when they wake up. The dynamic interval would reduce the packets collision caused by hidden nodes problem. We implement our scheme in MICAz motes to validate the applicability. We also have performed further experi-ments with NS-2simulation environment. The results show that our protocol could deal with packet collision well. The extra power consumption caused by collision is reduced and the data reception ratio is enhanced.(2) We have proposed a cross layer designed communication protocol for data collection in wireless sensor networks. In the MAC layer, we inherit the low power listening approach to save the power consumption. Instead of single target adopted in traditional MAC protocol, the sender could select multi-nodes to be the candidate targets and transmit the data to the node that wakes up first. In the route layer, we evaluate the latency from each node to sink and select the nodes with low latency to be the next hop targets. The sleeping based energy efficient protocol trades high latency for low energy consumption. Our work could achieve lower energy consumption with much less latency introduced. The experiments shows the energy consumption and latency are lower than state of art sleeping based energy efficient protocols. Our protocol is much efficient in large scale network.(3) We have introduced a novel scheme of using the elevators to assist data collection for wireless sensor networks used in structural health monitoring applica-tion. A base station is attached to an elevator. A representative node on each floor collects and transmits the data to the base station using short range communication when the elevator stops at or passes by this floor. We formulate the problem as an optimization problem where the data traffic should be transmitted on time and the lifetime of the sensors should be maximized. We show that if we know the movement pattern of the elevator in advance, this problem can be solved optimally. We then study the online version of the problem and show that no online algorithm has a constant competitive ratio against the offline algorithm. We show that knowledge of the future elevator movement will intrinsically improve the data collection per-formance. We discuss how the information could be collected and develop online algorithms based on different level of knowledge of the elevator movement patterns. A comprehensive set of simulations and MICAz testbed experiments have demon-strated that our algorithm substantially outperforms conventional multi-hop routing and naive waiting for elevator scheme.