Class-Based Data Reporting Scheme in Heterogeneous Wireless Sensor Networks

Data reporting strategy in heterogeneous wireless sensor networks can be differentiated based on task-specific requirements. In this paper, we propose a novel two-phase data reporting (TDR) scheme that supports class-based QoS to sensor nodes in different priority classes. In the first phase, time slots are divided into separate data reporting round defined for each class, while in the second phase, the sensor nodes in the same class are scheduled to particular time slots depending on the given number of slots calculated in the first phase. In TDR, sensor nodes compete with other nodes in the same class only, while nodes in different classes have differentiated channel access opportunity. TDR is performed in a single-hop cluster-based topology, and a cluster head acts as a node assignment manager (NAM). Sensor nodes wake up for their scheduled time slots; otherwise, they go into sleep mode to save energy. TDR supports both schedule- based and contention-based channel access mechanisms and is scalable due to its distributed nature. Wireless sensor networks (WSNs) consist of several dozens, hundreds or even thousands of wireless sensor nodes that have sensing, processing, and communication capabilities (1)-(3). A sensor monitors the targeted phenomena in its sensing range and reports the results to its data sink in a single or multi- hop manner. Compared to traditional networks, WSNs face challenges related to the network lifetime, the wide range of network densities, and scalability that have originated from the underlying network characteristics. The definition of quality of service (QoS) and the metrics to evaluate the network performance are also different from that of traditional net- works, which are usually related to multimedia applications. In WSNs, the QoS attributes highly depend on the different types of sensing tasks. The end system, indeed, has task-specific data collecting demands, and the sensor nodes are required to operate for the specific task in order to successfully accomplish the goal of the task. In WSNs, the efficient management of limited resources is important (4). Data reporting using an adaptive media (chan- nel) control mechanisms serve an important role in deciding the performance of the entire network as well as that of a sensor device by ensuring energy efficient operations such as sleep/wake-up mode and adaptive listening (5). A low-energy adaptive clustering hierarchy (LEACH) pro- tocol has been proposed in (6), (7) for a dense wireless sensor network. LEACH forms clusters and the cluster heads maintain a TDMA schedule for the other members to communicate with cluster heads. During the setup phase, the nodes compete using the CSMA protocol. The role of a cluster head is rotated due to the energy consuming role of the cluster heads such as the long-range transmissions. Each cluster head broadcasts a random CDMA code to its members to avoid collisions with other nodes in different clusters. After gathering data from the members, a cluster head performs data aggregation and sends the results to the sink. Our scheme borrows the basic system model of LEACH but a cluster head can reach to the sink in a single-hop or multi-hop manner excluding a scalability