In a wireless sensor network, the network lifetime is an important issue when the size of the network is large. In order to make the network scalable, it is divided into a number of clusters. In each cluster, a set of nodes is grouped and coordinated by a cluster-head. Due to high computations and data forwarding tasks at the cluster-heads, cluster-heads get drained out sooner. Hence, high power nodes are used as cluster- heads. Cluster-heads that are far away from the sink transmit their data packets via intermediate cluster-heads in a multi-hop fashion to the sink. Thus the cluster-heads that are near to the sink get overloaded and drained out sooner due to which the network lifetime decreases. In order to balance the lifetime of the cluster-heads, the existing works try to find either the optimum density or the optimum transmission range for the cluster-heads. The cluster-head placement algorithms should consider the fact that the node density and their transmission ranges are related parameters. In order to balance the lifetime of the cluster- head nodes and achieve the maximum network lifetime with the minimum network cost, we propose a novel optimal placement of cluster-heads (OPC) algorithm. We formulate an optimization problem and find the optimum number of cluster-heads to be deployed and their optimum transmission ranges for the given network parameters. In addition, we show that our algorithm performs better than the existing algorithm, in terms of network lifetime and network cost through the simulation results.

In wireless sensor networks, efficient usage of energy helps in improving the network lifetime. As the battery of a sensor node, in most cases, cannot be recharged or replaced after the deployment of the sensors, energy management becomes a critical issue in such networks. In order to detect an event, a sensor network spends majority of the time in monitoring its environment, during which a significant amount of energy can be saved by placing the radio in the low-power sleep mode. This can be achieved by using a dual frequency radio setup. However, such energy saving protocols increase the latency encountered in setting up a multihop path. We, in this paper, propose a reservation scheme, latency minimized energy efficient MAC protocol (LEEM), which is a novel hop-ahead reservation scheme in a dual frequency radio to minimize the latency in the multihop path data transmission by reserving the next hop's channel a priori. Thus, in a multihop sensor network, a packet can be forwarded to the next hop, as soon as it is received by a sensor node, which helps in eliminating the delay incurred for setting up the path. Simulation results show that LEEM consumes lesser power and reduces end-to-end latency by around 50% than that of the existing schemes