Simple and Efficient LoRa Receiver Scheme for Multipath Channel

This article presents a novel long-range (LoRa) receiver operating in the frequency selective multipath channel (MPC). The dechirped received LoRa waveforms under MPC allows us to derive a simple and efficient LoRa receiver scheme by using a matched filter (MF) approach that aims to maximize the signal-to-noise ratio (SNR) at the symbol index frequency of the discrete Fourier transform (DFT) output. We show that the MF receiver can be seen as a RAKE structure where interference peaks related to multipath, exhibited at DFT output, are recombined in a constructive way. Detection performance is driven by channel energy and the benefit of this novel MF/RAKE receiver over original coherent and noncoherent receiver appears only for MPC that exhibits significant paths energy. These two MF and RAKE receivers have however different implementation complexities that are studied in detail. We provide in that sense recommendations on which receiver variant to use for real operations, depending on complexity constraints. Finally, the proposed MF/RAKE receiver outperforms previous results on time-delay estimation LoRa (TDEL) receiver over MPC, especially at low SNR and higher LoRa spreading factor (SF) parameter, at the cost of higher but reasonable complexity.