## 2 Related Work  
In OppNets, the nodes opportunistically exchange their information when they encounter each other. In order to enable such information exchanging process, the nodes must probe the environment to discover their neighbors. If the nodes keep contact probing frequently, it will consume large amounts of energy. [PERSON] et al. [19] made measurements on a Nokia mobile phone and concluded that the neighbor discovery process was as energy-intensive as making a phone call. Hence, for limited power supply, the nodes should have their energy saved in contact probing.  
In previous research, many works have been done to reduce energy consumption in the contact probing. [PERSON] et al. [20] investigated the impact of contact-probing schedule on link duration and the transmission capacity of DTNs, and proposed a model for calculating the optimal contact-probing rate with limited energy. In [21], the authors proposed two adaptive algorithms for dynamically adjusting the Bluetooth parameters based on past perceived activity in the ad-hoc network. Their experiments showed that the proposed adaptive algorithms can reduce energy consumption by 50% and have up to 8% better performance than a static power-conserving scheme. In addition, there are some works [22; 23] that have dealt with the energy conservation issue in DTN routing, which paid attention to the extra energy consumption due to more packet copies used in routing, and thus, the energy constraint was expressed as the limitation on the number of duplicate packet copies.  
The studies mentioned above focused on the conservation of energy related with contact-probing and packet copies [22; 23; 24]. However, the energy wasted in the idle listening state is much more than that used in contact-probing. To this end, some studies have investigated how to decrease the energy consumption in idle listening state. [PERSON] et al. [PERSON] et al. (2013) proposed the Power Saving Management (PSM) techniques, which enabled the lifetime of the nodes to be extended and showed the conditions in which a node can be in sleeping state with no impact on the contact processing. The simulation results showed that the mathematical model was accurate and the contact rates in DTNs can be quite low, and the wireless radio can be turned off for energy conservation according to the operation regions. In [PERSON] et al. (2016), the authors introduced a technique of increasing the battery lifetime for a PDA-based phone by reducing its idle power, in which the wireless interfaces of the devices would be shut down when they were not being used. In [PERSON] et al. (2017), the authors proposed the cooperative duty cycling (CDC) base on a mobility pattern in which several nodes periodically encountered at certain hot spots and they would be well-connected. From theoretical analyses and simulations, CDC had a good performance in terms of energy conservation with no decline of data delivery performance.  
In contrast to the above existing studies, we pay attention to the self-similarity feature in opportunistic mobile networks. Making use of the predictability of self-similarity, we propose an adaptive scheduling mechanism to switch the states of each node between sleeping and listening states for energy conservation.