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Generally, routing techniques are essential for Wireless Sensor Networks (WSNs) to deliver data packets to their destinations (also known as sinks). For a practical application, sensors are deployed to monitor environmental changes and events. Most WSNs detect specific events in their specific environments. But, different WSNs may monitor different events with different sensors in the same area. For example, a smart-home WSN deploys thermal sensors/meters to measure indoor and outdoor temperatures, bodytemperature sensors to detect thief intrusion, etc. Also, in the underlying house, there is a health WSN which utilizes physiological sensors to monitor patients' health condition. In other words, several WSNs of different purposes co-exist in the same geographical area. Currently, each WSN's data delivery is independent from others'. Basically, if all sensors in such a multi-WSNs environment can share their routing paths/nodes and relay event packets for other WSNs, the delivery efficiency can be enhanced since many more sensors can be found there for packet relay. Consequently, the transmission energy can be reduced since energy consumed for wireless transmission is proportional to d 2 where d is the transmission distance between sender and receiver. Therefore, in this study, we propose an energy saving routing mechanism, named Energy-Efficient Cooperative Routing Scheme for Heterogeneous Wireless Sensor Networks (EERH for short), in which several WSNs deployed in the same geographical environment form a heterogeneous sensor network and sensors relay packets for its own WSN and also for other WSNs. Routing paths are dynamically established according to the transmission directions of event packets and the residual energy of the underlying sensors and their neighbors. In addition, the packets routed to the same direction by the same sensors are aggregated to save delivering energy. Moreover, the network parameters of the EERH, like propagation delay of an event packet and the transmission distance of a sensor, are adjustable so as to satisfy the practical environment needs. Simulation results show that the EERH efficiently extends the lifetime of a heterogeneous WSN. INDEX TERMS Wireless sensor networks, heterogeneous wireless sensor networks, energy efficient, cooperative routing.

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In recent years, the Internet of Things (IoT) has significantly increased the number of Internet connections to a large number of objects in different domains, including industry, homes and transportation. The LoRaWAN developed by the LoRa Alliance is a long-range wide area network specification suitable for an IoT environment due to its low-power communication. It provides a star-of-stars topology, welldefined MAC layer protocol and three communication modes to further lower its power consumption and employs the Advanced Encryption Standard (AES) cryptography and several session keys to increase its network security. However, for battery powered IoT end nodes, the AES encryption process consumes some amounts of power owing to involving multiple cycles of repetition. To solve this problem, in this study, we propose a low power consumed AES encryption architecture, named Low-Power AES Data Encryption Architecture (LPADA), which reduces the power consumed by the AES for data encryption by using low power SBox, power gating technique and power management method. A key updating procedure is also proposed to increase the security of the session-key renewal. The system is simulated using the Synopsys library with five different supply voltages. The experimental results show that 62.0% of dynamic power reduction and 88.5% of leakage power lowering have been achieved compared to the power consumed by traditional AES data encryption. The security analysis also shows that the key updating procedure for the LPADA enables mutual authentication between end nodes and application servers, and resists replay attacks and eavesdropping attacks from hackers.

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