A fundamental evolution is witnessed in recent research and development of wireless sensor networks (WSNs): the capabilities of the sensor nodes are strong enough to support more and more comprehensive applications. At the same time, more and more unique challenges have been introduced. In this thesis, we present our current research status on two different topics: a novel energy-efficient event collection scheme, and a measurement study focusing on non-orthogonal multi-channel design of WSNs....[ Read more ]

A fundamental evolution is witnessed in recent research and development of wireless sensor networks (WSNs): the capabilities of the sensor nodes are strong enough to support more and more comprehensive applications. At the same time, more and more unique challenges have been introduced. In this thesis, we present our current research status on two different topics: a novel energy-efficient event collection scheme, and a measurement study focusing on non-orthogonal multi-channel design of WSNs.

We consider an event collection scenario in a 2D region. Using traditional multihop routing to report events to a sink node or base station, will result in severe imbalanced energy consumption of static sensors. In addition, full connectivity among all the static sensors may not be possible in some cases. Therefore, we exploit a mobile sensor as the sink node to assist the event collection by controlling the movement of the mobile sink to collect static sensor readings. A key observation of our work is that an event has spatial-temporal correlation. Specifically, the same event can be detected by multiple nearby sensors within a period of time. Thus, it is more energy-efficient if the mobile sink can selectively communicate with only a portion of static sensors, while still collecting all the interested events. We discuss the event collection problem by leveraging the mobility of the sink node and the spatial-temporal correlation of the event, in favor of maximizing the network lifetime with a guaranteed event collection rate.

In addition, another critical issue in WSNs is represented by the network throughput. To meet the throughput requirement, researchers propose multi-channel design in 802.15.4 networks to better utilize the wireless medium and avoid the co-channel interference. We argue that the orthogonality is not necessary for multi-channel design in WSNs and investigate the feasibility of non-orthogonal channel design. In our experiment, we observe that with non-orthogonal transmission, the effect of interference comes from co-channel and inter-channel is different, i.e., the inter-channel interference is more tolerable. Based on that, we propose a novel scheme DCN (Dynamic CCA-threshold for Non-orthogonal transmission) which adjusts the CCA-threshold to enable the concurrent transmissions on adjacent non-orthogonal channels and thus improve the overall network throughput performance.