LoRa is popular for internet of things applications as this communication technology offers both a long range and a low power consumption. However, LoRaWAN, the standard MAC protocol that uses LoRa as physical layer, has the bottleneck of a high downlink latency to achieve energy efficiency. To overcome this drawback we explore the use of wake-up radio combined with LoRa, and propose an adequate MAC protocol that takes profit of both these heterogeneous and complementary technologies. This protocol allows an opportunistic selection of a cluster head that forwards commands from the gateway to the nodes in the same cluster. Furthermore, to achieve self-sustainability, sensor nodes might include an energy harvesting sub-system, for instance to scavenge energy from the light, and their quality of service can be tuned, according to their available energy. To have an effective self-sustaining LoRa system, we propose a new energy manager that allows less fluctuations of the quality of service between days and nights. Latency and energy are modeled in a hybrid manner, i.e., leveraging microbenchmarks on real hardware platforms, to explore the influence of the energy harvesting conditions on the quality of service of this heterogeneous network. It is clearly demonstrated that the cooperation of nodes within a cluster drastically reduces the latency of LoRa base station commands, e.g., by almost 90% compared to traditional LoRa scheme for a 10 nodes cluster.

Energy management is a perennial issue in the design of wireless sensor networks that require long-term sustainability. Radio transmissions being the main energy consuming tasks, adaptive transmission power and relaying protocols represent promising solutions to increase network lifetime. In this work, a novel MAC protocol leveraging emerging wake up receivers is proposed for multihop wireless sensor networks. It uses energy-based back-off mechanism to allow nodes to choose the best transmission schemes (relay or not) and corresponding transmission powers. The proposed approach has been implemented on a real hardware platform. Performance evaluation combining analytical models and microbenchmarks demonstrates a potential lifetime gain up to 1.7 when two relays are used.

One of the main challenges of wireless sensor networks is to maintain sensor nodes alive as long as possible, and a lot of efforts are dedicated to enable energy efficient communications. Wake-Up Receivers (WuRs) represent a promising solution for reducing the power consumption of nodes by enabling asynchronous communications. However, to achieve an ultra-low power consumption, WuRs circuits are kept as simple as possible, inducing a low sensitivity and thus a short range communication. As channel coding improves sensitivity, we propose to take advantage of the computing capability of the WuRs to apply a specific channel coding. The novelty resides in applying Minimum Energy coding with an Early Shutdown (MEES) of WuRs based on On-Off Keying (OOK) detectors. Both theoretical derivations and Monte-Carlo simulations show that the proposed coding scheme improves the reliability. Moreover, Moreover, MEES has been implemented on a non-coherent WuR prototype, and it is shown through experimentation that WuR reliability can be raised up to 22% compared to uncoded communications. Moreover, both the energy consumption and the latency can be significantly decreased thanks to the shutdown mechanism of MEES.