On prolonging network lifetime by adjusting sleep/awake cycles in wireless sensor networks

To save their energy, sensors spent most of their life in sleeping mode waking up for short intervals to achieve any required tasks. While performing their sensing and communicational obligations to the network and due to the random nature of sleep and awake cycles, sensors are usually assigned different workloads which in turn consume their energy unevenly. Eventually, the energy of those heavily loaded sensors will be totally depleted. This results in reducing network density around those sensors and creates energy holes that isolate the network into disconnected islands. These problems have their negative impacts on network durability and reliability. To avoid these problems, we propose and evaluate a distributed protocol that adjusts sensor sleep and wake up times based on the relative differences between sensor energy and the energy of surrounding sensors. Using simulation, we first show that during network lifetime, variations in sensors energy can be very large compared to what can be achieved using our proposed protocol. In addition to this, we show the impact of these variations on the network lifetime measured in terms of the number of tasks the network can perform till the network density goes below certain threshold.