Correlation-based communication in wireless multimedia sensor networks

Wireless multimedia sensor networks (WMSNs) are networks of wirelessly interconnected devices that are able to retrieve multimedia content such as video and audio streams, still images, and scalar data from the environment. Most applications of WMSNs require the delivery of multimedia information with a certain level of quality of service (QoS). This is a challenging task because sensors are constrained in battery and processing capabilities, while the delivery of multimedia flows is a resource-intensive task. In a densely deployed sensor network, there exists correlation among the observations of camera sensors with overlapped coverage areas, which could be exploited to remove data redundancy in the network.;The objective of this thesis is to design efficient communication protocols for WM-SNs by leveraging the correlation of visual information of camera sensors. First, the spatial correlation of visual information in WMSNs is studied. By studying the sensing model and deployments of cameras in a WMSN, a spatial correlation coefficient is derived to describe the degree of correlation of visual information observed by cameras with overlapped field of views. The joint effect of multiple correlated cameras is also studied. An entropy-based analytical framework is developed to measure the amount of visual information provided by multiple correlated cameras.;The compression performance of correlated visual information is then studied. A collaborative clustered compression framework is proposed with an objective to maximize the overall compression gain of the visual information gathered in WMSNs. To achieve this, an Entropy-based Divergence Measure (EDM) scheme is proposed to predict the compression efficiency of performing joint coding on the images collected by spatially correlated cameras. Utilizing the predicted results from EDM, a Distributed Multi-cluster Coding Protocol (DMCP) is proposed to construct a compression-oriented coding hierarchy.;The correlation of visual information is then utilized to design a network scheduling scheme to maximize the lifetime of WMSNs. The scheduling scheme consists of three components including MinMax Degree Hub Location (MDHL), Minimum Sumentropy Camera Assignment (MSCA), and Maximum Lifetime Scheduling (MLS). The MDHL problem finds the optimal locations to place the multimedia processing hubs such that the number of channels required for frequency reuse is minimized. The MSCA problem assigns each camera sensor to a hub in such a way that the global compression gain is maximized by jointly encoding the correlated images gathered by each hub. At last, the MLS problem finds a schedule for the cameras to maximize the network lifetime by letting highly correlated cameras perform differential coding.;Furthermore, a correlation-aware QoS routing algorithm is designed to efficiently deliver visual information under QoS constraints. A correlation-aware inter-node differential coding scheme is introduced to remove traffic redundancy along routing paths, and a correlation-aware load balancing scheme is proposed to prevent network congestion by splitting the correlated flows that cannot be reduced to different paths. These correlation-aware operations are integrated into an optimization QoS routing framework that minimizes energy consumption subject to delay and reliability constraints.