Trong Nhan Le

A Joint Duty-Cycle and Transmission Power Management for Energy Harvesting WSN

In this paper, we propose a global power management approach for energy harvesting sensor nodes. Our approach is based on a joint duty-cycle optimization and transmission power control. By simultaneously adapting both parameters, the node can maximize the number of transmitted packets while respecting the limited and time-varying amount of available energy. We obtain a high-packet delivery by using an original predictive transmission power control that can efficiently adapt the transmission power to the wireless channel conditions. To accurately model the wireless channel and the node communication hardware, a waveform-level radio frequency simulator has been developed. Simulation results show 6.5 times improvement in energy efficiency and a packet reception ratio which is 9 times more efficient than a recently published technique. A 15% increase in energy efficiency, with respect to a fixed transmission power configuration, has also been observed. Finally, the global power management strategy has been validated on a real wireless sensor networks platform. Experimental results are very similar to those obtained in simulations, and thus confirm the efficiency of our power management approach.

Ultra low power asynchronous MAC protocol using wake-up radio for energy neutral WSN

To extend the system lifetime of WSN, energy harvesting techniques have been considered as potential solutions for long-term operations. Instead of minimizing the consumed energy as for the case of battery-powered systems, the harvesting node is adapted to Energy Neutral Operation (ENO) to achieve a theoretically infinite lifetime. Therefore, consumed energy due to communications is the critical issue to increase the system performance. In this paper, a nano-watt wake-up radio receiver (WUR) is used cooperatively with the main transceiver in order to reduce the wasted energy of idle listening in asynchronous MAC protocols where the node is waiting for potential messages, while still maintaining the same reactivity. Simulation results show that the throughput can be improve up to 82% with 53% energy saving compared to non-WUR approach of the TICER protocol. Our simulations are performed on OMNET++ with three different widely radio chips CC2420, CC2500 and CC1100 using models with measured data.

Duty-cycle power manager for thermal-powered Wireless Sensor Networks

Exploiting energy from the environment to extend the system lifetime of Wireless Sensor Network (WSN), especially thermal energy, is considered as a promising approach. When considering self-powered systems, the Power Manager (PM) plays an important role in energy harvesting WSNs. Instead of minimizing the consumed energy as in the case of battery-powered systems, it causes the harvesting node to converge to Energy Neutral Operation (ENO) in order to achieve a theoretically infinite lifetime. In this paper, a low complexity PM for a thermal-powered WSN is presented. Our PM adapts the duty cycle of the node according to the estimation of harvested energy and the consumed energy provided by a simple energy monitor for a super capacitor based WSN to achieve the ENO. Experiments are performed on a real WSN platform where harvested energy is extracted from the wasted heat of a PC adapter by two thermoelectric generators.

Energy-Efficient Power Manager and MAC Protocol for Multi-Hop Wireless Sensor Networks Powered by Periodic Energy Harvesting Sources

To overcome the limited energy in battery-powered wireless sensor networks (WSNs), harvested energy is considered as a potential solution to achieve autonomous systems. A power manager (PM) is usually embedded in wireless nodes to adapt the computation load by changing their wake-up interval according to the harvested energy. In order to prolong the network lifetime, the PM must ensure that every node satisfies the energy neutral operation (ENO) condition. However, when a multi-hop network is considered, changing the wake-up interval regularly may cripple the synchronization among nodes and, therefore, degrade the global system quality of service. In this paper, a wake-up variation reduction PM is proposed to solve this issue. This PM is applied for wireless nodes powered by a periodic energy source (e.g., light energy in an office) over a constant cycle of 24 h. Our PM not only follows the ENO condition, but also reduces the wake-up interval variations of WSN nodes. Based on this PM, an energy-efficient protocol, named synchronized wake-up interval MAC, is also proposed. OMNET++ simulation results using three different harvested profiles show that the data rate of a WSN node can be increased up to 65% and the latency reduced down to 57% compared with state-of-the-art PMs. Validations on a real WSN platform have also been performed and confirmed the efficiency of our approach.

Power Manager with PID Controller in Energy Harvesting Wireless Sensor Networks

System lifetime is the crucial problem of Wireless Sensor Networks (WSNs), and exploiting environmental energy provides a potential solution for this problem. When considering self-powered systems, the Power Manager (PM) plays an important role in energy harvesting WSNs. Instead of minimizing the consumption energy as in the case of battery powered systems, it makes the harvesting node converge to Energy Neutral Operation (ENO) to achieve a theoretically infinite lifetime and maximize the system performance. In this paper, a low complexity PM with a Proportional Integral Derivative (PID) controller is introduced. This PM monitors the buffered energy in the storage device and performs adaptation by changing the wake-up period of the wireless node. This shows the interest of our approach since the impractical monitoring harvested energy as well as consumed energy is not required as it is the case in other previously proposed techniques. Experimental results are performed on a real WSN platform with two solar cells in an indoor environment. The PID controller provides a practical strategy for long-term operations of the node in various environmental conditions.

Improving Energy Efficiency of Mobile WSN Using Reconfigurable Directional Antennas

Reconfigurable directional antennas (RDA) bring new opportunities to reduce data collision in wireless sensor networks (WSN). In this letter, a new reconfigurable directional antenna-based receiver-Initiated cycled receiver (RDA-RICER) medium access control (MAC) protocol is proposed for WSN nodes equipped with switched antennas. A low complexity and energy efficient scanning process is embedded in RDA-RICER to identify the direction providing the highest received signal strength Indicator between two nodes. OMNeT++ simulation results for a single hop network show that data collision rate can be drastically reduced compared with related MAC protocols, leading to a significant decrease in energy consumption. Our approach is also validated in the field using WSN platforms equipped with a four-direction RDA, and powered by solar cells.

Energy-Neutral Design Framework for Supercapacitor-Based Autonomous Wireless Sensor Networks

To design autonomous wireless sensor networks (WSNs) with a theoretical infinite lifetime, energy harvesting (EH) techniques have been recently considered as promising approaches. Ambient sources can provide everlasting additional energy for WSN nodes and exclude their dependence on battery. In this article, an efficient energy harvesting system which is compatible with various environmental sources, such as light, heat, or wind energy, is proposed. Our platform takes advantage of double-level capacitors not only to prolong system lifetime but also to enable robust booting from the exhausting energy of the system. Simulations and experiments show that our multiple-energy-sources converter (MESC) can achive booting time in order of seconds. Although capacitors have virtual recharge cycles, they suffer higher leakage compared to rechargeable batteries. Increasing their size can decrease the system performance due to leakage energy. Therefore, an energy-neutral design framework providing a methodology to determine the minimum size of those storage devices satisfying energy-neutral operation (ENO) and maximizing system quality-of-service (QoS) in EH nodes, when using a given energy source, is proposed. Experiments validating this framework are performed on a real WSN platform with both photovoltaic cells and thermal generators in an indoor environment. Moreover, simulations on OMNET++ show that the energy storage optimized from our design framework is utilized up to 93.86%.

Asynchronous on demand MAC protocol using wake-up radio in wireless body area network

A fast growing class of sensing technology is wearable, where network nodes are tightly coupled with the human body. Wireless body area networks (WBAN) technology has gained popularity over the last few years, with a wide range of applications covered, in particular in health and rehabilitation. Wearable and pervasive computing are able to sense, monitor and process the data to provide smart assistance and context-aware ambient intelligence environments. However present-day WBAN devices are mainly battery-powered and due to energy issue they need to be recharged every day or even hours and thus they miss the expectations for a truly unobtrusive user experience. This work presents a novel energy-efficient asynchronous MAC protocol using a nano-watt wake up radio with addressing capabilities to reduce the energy consumption of the communication and then extend the WBAN life time. We present the benefits of the wake up radio in a star topology widely used in WBAN where the number of the node is around 5 to 10. The implemented protocol exploiting the low power consumption of the wake up radio, the low latency and the addressing capabilities can increase significantly the energy efficiency of the single node and entire network reducing both idle listening and data collisions. Result based on measured power consumption and OMNET++ simulation demonstrate that by using the wake up radio it is possible to reduce the power consumption up to 150 times compared to related protocols and the lifetime can be significantly increased in a real world scenario.

A power manager with balanced quality of service for energy-harvesting wireless sensor nodes

Future Internet of Things is paving the way for the proliferation of Wireless Sensor Networks (WSNs). To overcome the limited energy in batteries, WSN nodes are relying on everlasting environmental energy. Moreover, a Power Manager (PM) is also embedded in each WSN node to guarantees that the total consumed energy is equal to the harvested energy for a long period, leading to Energy Neutral Operation (ENO) with a theoretically infinite lifetime. In this paper, a new PM for WSN nodes powered by periodic sources (e.g. ambient energy is not available during the full harvesting cycle) is proposed. Not only respecting the ENO condition, our PM is able to balance the Quality of Service (QoS) during the whole cycle to provide regular data tracking, which is essential for WSN applications like monitoring. Simulations on OMNET++ show that our PM can improve the QoS during the absence of energy by a factor up to 84% compared to state-of-the-art PMs, while guaranteeing the same global QoS.

Multi-source power manager for super-capacitor based energy harvesting WSN

In this paper, a multi-source power manager (PM) is applied using different types of energy harvesting WSN. Specifically, this PM is embedded in both thermal and solar-powered WSN in order to adapt the consumed energy of the node by changing its wake-up period according to the harvested energy. Experimental results performed on real WSN platforms show that our PM is able to make harvesting nodes converge to Energy Neutral Operation (ENO) with a theoretically infinite system lifetime.