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Although the idea of using wireless links for covering large areas is not new, the advent of low-power wide-area networks (LPWANs) has recently started by changing the game. Simple, robust, and narrowband modulation schemes permit the implementation of low-cost radio devices offering high receiver sensitivity, thus improving the overall link budget. The several technologies belonging to the LPWAN family, including the well-known LoRaWAN solution, provide a cost-effective answer to many Internet-of-Things (IoT) applications, requiring wireless communication capable of supporting large networks of many devices (e.g., smart metering). Generally, the adopted medium access control (MAC) strategy is based on pure ALOHA, which, among other things, allows to minimize the traffic overhead under constrained duty-cycle limitations of the unlicensed bands. Unfortunately, ALOHA suffers from poor scalability …