FREE - Fine-grained Scheduling for Reliable and Energy Efficient Data Collection in LoRaWAN
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Collecting data from remote sensor devices with limited infrastructure is still considered a challenging task. Here, LoRa radios and LoRaWAN networks represent an appealing option due to their inexpensively, high link budgets, low energy consumption and one-hop system architecture. However, LoRaWAN suffers from a scalability issue due to its Aloha-like MAC layer. Additionally, the duty cycle restriction at the gateway limits the acknowledgment handling even in medium size networks. Therefore, we propose FREE as a fine-grained scheduling scheme for reliable and energy-efficient data collection in LoRaWAN. FREE schedules spreading factors, transmission powers, frequency channels, timeslots, and slot numbers in frames for LoRa end-devices. As a result, FREE overcomes the scalability issue of LoRaWAN by eliminating collisions and grouping acknowledgments. We propose two objective functions for FREE to either optimize the energy consumption or the data collection time. Their choice depends on gateway availability. We evaluate the performance of FREE for different LoRaWAN configurations. The numerical results show that FREE scales well for unconfirmable and confirmable transmissions. Furthermore, FREE achieves almost 100 over 10 years regardless of the running application and the network size
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