text: In LoRa (Long Range), when a collision occurs in the network, each end-device has to retransmit its colliding frame, which reduces the throughput, and increases the energy consumption of the end-devices and the delay of the frames. In this paper, we propose an algorithm to decode colliding synchronized LoRa signals and thus improve the overall performance of the network. Indeed, we use successive transmissions of bitmaps by the end-devices to determine the correct symbols of each colliding frame, instead of retransmitting the whole frames. Simulation results show that our algorithm is able to significantly improve the overall throughput of LoRaWAN, and to decrease the energy consumption and the delay of the transmitters.
  @cite_4: Long range low power is a family of technologies promising to connect thousands of sensors to the future internet of things. Within this family of possible technology choices, two different branches have emerged: the standards based on spreaded wideband communication and the standards based on narrowband communication, both promising to reach long range connectivity at very low power. More specifically, this paper focuses on chirp spread spectrum (CSS). This paper presents a detailed model of CSS, showing that the symbols are not perfectly orthogonal. The results show the potential communication ranges are close to narrowband networks and the robustness against interfering signals is 22 dB better for spreading factor 10 than BPSK. Although wideband communication is robust to interference, in long range communication, this robustness is insufficient due to the long range and the larger footprint. The large propagation losses due to the long range and the larger footprint make CSS prone to collisions with other noise sources, possibly larger than the coding gain.
summary: In @cite_4 , the authors made a study regarding the CSS modulation technique. They show that some CSS symbols are not orthogonal. Their simulations show that the achievable range of the CSS technique is lower than an ultra-narrowband solution, but the robustness against interference is higher.