Multi-Hop LoRa Networks Enabled by Concurrent Transmission

In this paper, we strive to construct an efficient multi-hop network based on the sub-GHz low-power wide-area technology. Specifically, we investigate the combination of LoRa, a physical-layer standard that can provide several-kilometer outdoor coverage, and concurrent transmission (CT), a recently proposed multi-hop protocol that can significantly improve the network efficiency. The main contributions of this paper are threefold. 1) Since the CT enhances the network efficiency by allowing synchronized packet collisions, the performance of the physical-layer receiver under such packet collisions needs to be carefully examined to ensure the network reliability. We first extensively evaluate the LoRa receiver performance under CT to verify that LoRa is compatible to CT. Specifically, we find that, due to the time-domain and frequency-domain energy spreading effect, LoRa is robust to the packet collisions resulting from CT. 2) We further find the receiver performance under CT can be further improved by introducing timing offsets between the relaying packets. In view of this, we propose a timing delay insertion method, the offset-CT method, that adds random timing delay before the packets while preventing the timing offset from diverging over the multi-hop network. 3) We conduct proof-of-concept experiments to demonstrate the feasibility of CT-based LoRa multi-hop network and the performance improvement brought by the proposed offset-CT method.