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Wireless sensor network is attractive to researcher and commercial users. It provides several usages in different areas, but it also has a weakness. Energy restriction of sensor network leads to several research outputs. In this paper, we consider cluster header selection mechanism with routing tree to the sink node. We select cluster head as small as possible and it also provides connectivity to the sink node with routing tree.

In a wireless sensor networks, many topics have been studied in several filed. Most of them are concentrated on efficient use of energy to prolong the network lifetime. In a special environment like as remote battlefield, desert, forest, it is more difficult to recharging the battery of sensor. In this paper, we propose a density control method in a dense wireless sensor. We prolong the lifetime of network by selecting small set of active sensor nodes. Hopbased disjoint wakeup method is used and calculates the hop count with adjustment of communication radius. We analyzed the number of active sensor node and compared with other method with simulation.

Wireless sensor network can be applied in several part of real world. For efficient use of energy, we propose hop by hop routing method with cluster heads. Cluster head is selected distributed manner in a same hop count. For high probability of upstream cluster head within transmission range, we use reduced transmission range to calculate hop count.

Energy efficiency is essential factor in a wireless sensor network. We propose topology control method with small set of active sensor nodes. In this paper we use hop-based disjoint wake-up scheduling with adjusted hop-radius.

Wireless sensor networks consist of many nodes with sensing, computation, and wireless communications capabilities. Due to difficulty of recharging battery, energy efficiency is essential problem in wireless sensor network. We propose a density control scheme based on disjoint wakeup scheduling which can provide a full connectivity to sink node with a minimum set of active nodes in a highly dense network to prolong the network lifetime.

Since sensor nodes have limited battery power, it is desirable to select a minimum set of working sensor nodes which should be involved in sensing and forwarding data to the sink. In this paper, we propose a topology scheme which selects a minimum set of working nodes in the sensor network field to avoid wasting excessive energy by turning off too many redundant nodes. Our scheme offers a solution for configuring network topology with a minimal number of working nodes. Simulations show that our scheme extends the lifetime of the dense sensor networks, and achieves the desired robust coverage as well as satisfactory connectivity to the sink in an energy efficient fashion.

Since it is difficult to replace batteries of the sensor nodes that are once deployed in the field, energy saving is one of the most critical issues for object tracking in wireless sensor networks. It is desirable that only the nodes surrounding the mobile target should be responsible for observing the target to save the energy consumption and extend the network lifetime as well by reducing the number of participating nodes. The number of nodes participating in object tracking can be reduced by an accurate estimation of the target location. In this paper, we propose a tracking method that can reduce the number of participating sensor nodes for target tracking. We show that our tracking method performs well in terms of energy saving regardless of mobility pattern of the mobile target.