## 1 Context and Motivations
Figure 1 depicts the distribution of node energy consumption in each radio state, assuming that nodes are not allowed to sleep: they are in the idle state when they have nothing to transmit and nothing to receive. The OLSR routing protocol is used. A network of 100 nodes with a density of 10 is considered. The density denotes the average number of neighbor per node + 1. Each result depicted in Figure 1 corresponds to the average of 10 simulations. We notice that the highest part of node energy is wasted in useless states (states that do not correspond to user data reception or transmission). That is why, in this paper, we will focus on energy efficient routing and node activity scheduling to reduce the energy lost in the interference and idle states. In this paper, we focus on an energy efficient solution for wireless sensor networks integrating an energy efficient routing and a node activity scheduling. For energy efficient routing, we have proposed EOLSR in [1, 2]. The idea consists in reducing the energy consumed in an end-to-end transmission while avoiding nodes with low residual energy. New simulation results compared to [3] show that the increase in network lifetime is accompanied by an increase in the amount of data delivered to the user. In this paper, we show how the use of cross-layering between EOLSR and the application layer considerably reduces the routing overhead. For node activity scheduling, we use SchEduling RoutEr Nodes Activity (SERENA) based on node coloring. SERENA assigns a color to each node while using a small number of colors and ensuring that two nodes with the same color can transmit without interfering. SERENA has been presented as a two-hop coloring algorithm in [4, 5, 6]. In this paper, SERENA is generalized to support different application requirements (e.g., broadcast, data gathering applications, immediate acknowledgement). We evaluate the cost to support such application requirements. This cost is expressed in terms of additional colors required as well as additional messages needed in the coloring process. Another new contribution of this paper is the comparison between SERENA and TDMA-ASAP, evaluating the end-to-end delays and the potential color conflicts. Concerning the integration of EOLSR and SERENA, we evaluate in this paper, the amount of data delivered using EOLSR and/or SERENA (three-hop coloring). We also show that node energy is used more efficiently. For instance, no energy is lost in interferences, the energy lost in idle state is considerably limited. This integration is used in the OCARI project focusing on wireless sensor networks in industrial environment. We provide a refined version of the OCARI stack, initially presented in [7] and describe the strong interaction of EOLSR and SERENA with the MAC layer. The remaining of this paper is organized as follows. In Section 2, we present a state of the art dealing with energy efficient techniques in wireless sensor networks, energy efficient routing, node activity scheduling, and cross layering. In Section 3, we give the principles of EOLSR and report its performance evaluation results. We also explain how cross-layering with both the application layer and the MAC layer can improve benefits obtained from EOLSR. In Section 4, we describe SERENA and evaluate its performance compared to existing solutions like TDMA and TDMA-ASAP. We then quantify the benefits brought by cross-layering to improve SERENA. In Section 5, we first present the benefits of the integration of SERENA and EOLSR regarding the amount of data delivered for the end user and the network lifetime. Second, we describe how SERENA and EOLSR are used in an industrial environment, that is the OCARI project. Finally, we conclude in Section 6.