LoRaWANs, a widely accepted IoT connectivity solution, adopt a simple (ALOHA-like) MAC layer, enabling low-power communication at the cost of scalability due to packet collisions. Hence, current studies on LoRaWAN conclude that the network does not support dense deployments. Several alternative MACs are proposed but they stumble upon well-known limitations: time division eliminates the asynchrony of LoRa nodes but requires feedback from the gateways; carrier-sensing-based protocols are heavily constrained by the reduced sensing ranges of the devices, thus creating a large number of hidden terminals, leading to collisions. To enhance LoRaWAN to cater to both low- and high-density deployments, in this paper, we propose Spreading Factor MAC (SFMAC), a novel, practical, distributed, and energy-efficient MAC protocol. SFMAC, a channel-sensing-based MAC, takes an unconventional approach to eliminate hidden terminals - by operating with pairs of SFs, wherein the higher SF is used for channel sensing and the lower for data transmission. Bleeps are transmitted in the higher SF as they can be sensed at longer ranges. SFMAC does not require any change in hardware or the LoRaWAN protocol. We demonstrate that the fundamental tradeoff made by SFMAC - utilizing two SFs per data transmission instead of using all for data - works extremely well due to the elimination of hidden terminals. Through real-world experiments on 30 SX1261 devices and data-driven ns-3 simulations, we showcase that SFMAC increases goodput and channel utilization by manifolds over state-of-the-art protocols such as p-CARMA, np-CECADA, and LMAC. ... Read more

Long Range Wide Area Networks (LoRaWAN) offer easy deployment, robustness against interference, and operational longevity to energy constrained IoTdevices which communicate in a best-e_ort fashion in extended ranges. However, the simple (ALOHA-like) design of the MAC layer leads to packet collisions in dense LoRaWAN deployments with high traffic loads. To achieve scalability above a few hundreds of devices, time division is not an option, since LoRaWAN is asynchronous regarding communication. Further, feedback mechanisms are discouraged due to duty cycle limitations. In this document, we propose Spreading Factor MAC (SFMAC); a distributed and energy efficient MAC protocol for LoRaWAN, wherein {for the _rst time to the best of our knowledge{ high-SF channels are dedicated strictly to Channel Sensing (CS), while low-SF channels are focused on data-transmission. The Capture E_ect (CE) phenomena that is manifested in the PHY layer is extensively evaluated on-_eld and embodied in the SFMAC operating principle. The dedicated high-SF sensing allows e_ective revealing of hidden devices' transmissions without a_ecting the low-SF tra_c. We showcase the impact of SFMAC in scalability by designing a realistic implementation of the mechanism in ns-3. We report a x2.08 improvement in channel utilization and x2 goodput compared to LoRaWAN, without substantially increasing complexity. ... Read more