  Future 5G and Internet of Things (IoT) applications will heavily rely on
long-range communication technologies such as low-power wireless area networks
(LPWANs). In particular, LoRaWAN built on LoRa physical layer is gathering
increasing interests, both from academia and industries, for enabling low-cost
energy efficient IoT wireless sensor networks for, e.g., environmental
monitoring over wide areas. While its communication range may go up to 20
kilometers, the achievable bit rates in LoRaWAN are limited to a few kilobits
per second. In the event of collisions, the perceived rate is further reduced
due to packet loss and retransmissions. Firstly, to alleviate the harmful
impacts of collisions, we propose a decoding algorithm that enables to resolve
several superposed LoRa signals. Our proposed method exploits the slight
desynchronization of superposed signals and specific features of LoRa physical
layer. Secondly, we design a full MAC protocol enabling collision resolution.
The simulation results demonstrate that the proposed method outperforms
conventional LoRaWAN jointly in terms of system throughput, energy efficiency
as well as delay. These results show that our scheme is well suited for 5G and
IoT systems, as one of their major goals is to provide the best trade-off among
these performance objectives.
