Abstract—Deployment of wireless sensor networks always faces the issue of energy limitation. Without appropriate control policy, data messages might be routed over already- exhausted routes, quickly disrupting network connectivity. If a node transmits data at an excessively high power level, it not only depletes its own energy budget wastefully, but also interferes in other parallel transmissions. In this study, we introduce a cooperative power control strategy in which nodes of routes jointly tune their transmit power regularly over time and upon route setup. Tuning is made under hints of surrounding nodes. Routes are selected based on link metrics that is a function of signal strength, remaining energy, and path loss. To keep balancing power consumption among nodes, energy-aware established routes are considered re-routing periodically. Transmit power of each node is set at a level is just high enough under the hint of its adjacent downstream node. Simulation outputs do demonstrate the soundness of our proposals with respect to connectivity and throughput. Keywords: WSN, routing, power control, link quality. I. INTRODUCTION Energy consumption is a critical issue in any wireless sensor network (WSN), given that nodes operate solely on their battery. Power spent on communication always accounts for major proportion of the total consumption [1][2][4][5]. To reduce the consumption, there are two main approaches that the research community has been following: • Minimizing data amount exchanged among sensor nodes, in term of message count and length [1][2][5]; • Controlling transmission to let nodes transmit data at appropriate power level, avoiding excessive power setting [3][4][6]. Most of studies in literature mainly aim at how to minimize consumption for individual nodes [2][4][5][7], while only a few papers address the connectivity of the whole network system. For the latter purpose, data flows need to be shaped taking into account load balance among nodes. Specifically, remaining energy of nodes should be considered a variable of link metrics, which considerably influences route selection. In such a way, nodes with less energy reserve are unlikely forced to relay data for others. In this study, we introduce a fine-grained cooperative power control policy in combination with route maintaining strategy for saving energy while keeping sufficient signal quality. The setup is made adaptively considering channel conditions. Specifically, link metrics is formulated as a function of LQI (link quality indicator) [7] – a factor that reflects how good the signal transmitted along the link is. Our contribution does not concentrate on routing, but in the model of cooperation between routing and power control policies, and regular power tuning. This brings the adaptability of power control to the current channel status. The rest of this paper is organized as follows. The next section proposes the communication architecture. Section III subsequently describes how link metrics is estimated and how routing table are constructed. The strategy of cooperative power control is then presented in Section IV. Section V demonstrates how the designed protocol behaves by reporting simulation results. Finally, Section VI concludes the paper and anticipates future work. II. COMMUNICATION DESCRIPTION This section describes the overview of communication architecture. Figure 1 illustrates the cross-layer design that we propose. At the physical layer, upon receiving messages, the node infers the LQI value from the experienced RSSI (received signal strength indicator). At the same time, the layer also reports the currently set transmit power and remaining energy to routing functions. Based on these statistics, the link metrics is estimated, providing necessary inputs for route calculation in the upper layer. This means that route is determined accordance with channel goodness and available resource (including transmit power and battery reserve). Without loss of generality, let’s assume that routing protocol used is the well-known reactive AODV scheme. As presented later, our proposed design can in principle come together with any routing protocol. Figure 1 – Cross-layer interaction Adaptive Combined Power Control and Routing for Lengthening Connectivity in WSNs Pham Van Tien, Tran Huu Cuong, Nguyen Tien Dung, and Trinh Phuong Dung Department of Communications Engineering, School of Electronics and Telecommunications Hanoi university of Science and Technology, Vietnam Email: tienpv-fet@mail.hut.edu.vn