In wireless sensor networks (WSNs) having a high density of sensor nodes, transmitted measurements are spatially correlated, often redundantly whenever an event of interest is detected. In this work, the authors propose a correlation model to enable energy-efficient methodologies that exploit the spatial correlation at the network and medium access control (MAC) layers. At the network layer, the authors first demonstrate how, through proper tuning of both the sensing range and correlation threshold, WSNs can be partitioned into disjoint correlated clusters without degrading the information reliability, thus enabling significant energy saving. On the other hand, as another contribution, the authors investigate the impacts of correlation between nodes on achieved distortion in the event estimation at the sink. The interactions among various parameters such as distortion constraints, spatial node density, node selection, sensing range and their impacts on the reconstruction performance are quantitatively studied. The authors demonstrate that the same level of distortion constraint can be achieved by selecting fewer nodes. The nodes can be still fewer if they are less spatially correlated. However, the MAC protocols which show distributive effect of this selection needs more study.
Cognitive Radio Networks (CRN) have enabled us to efficiently reuse the underutilized radio spectrum. The MAC protocol in CRN defines the spectrum usage by sharing the channels efficiently among users. In this paper we propose a novel TDMA based MAC protocol with dynamically allocated slots. Most of the MAC protocols proposed in the literature employ Common Control Channel (CCC) to manage the resources among Cognitive Radio (CR) users. Control channel saturation in case of large number of CR users is one of the main drawbacks of the CCC based MAC protocols. In contrast with CCC based MAC protcols, DSAT-MAC protocol is based on the TDMA mechanism, without using any CCC for control information exchange. The channels are divided into time slots and CR users send their control or data packets over their designated slot. The protocol ensures that no slot is left vacant. This guarantees full use of the available spectrum. The protocol includes the provision for Quality of Service, where real-time and safety critical data is transmitted with highest priority and least delay. The protocol also ensures a fair sharing of available spectrum among the CR users, with the mechanism to regulate the transmission of malicious nodes. Energy saving techniques are also presented for longer life of battery operated CR nodes. Theoretical analysis and simulations over ns-2 of the proposed protocol reveal that the protocol performs better in various CR adhoc network applications.
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