Opportunistic Routing in LoRa-based Wireless Mesh Networks

Abstract

The recent move of the LoRa wireless technology towards the wider 2.4 GHz ISM spectrum band creates multiple opportunities for its broader usage in new IoT applications requiring larger data rates. However, this ISM band is already crowded with other wireless technologies like WiFi or Bluetooth, and cross-technology interference issues need to be considered. Moreover, the less favorable radio propagation properties in the 2.4 GHz band shorten the communication distance of LoRa transmissions and therefore make relaying necessary. Unfortunately, the direct usage of LoRa technology in a wireless mesh network is challenging due to the non-existent generic frame preamble and header, i.e. LoRa frames are not self-contained. This makes the dynamic adaptation of the modulation used by LoRa per link or even packet transmission challenging. We show in this paper that such limitation can be partially overcome by utilizing the macro spacial diversity provided by opportunistic routing (OR) protocols. In contrast to traditional routing OR selects a candidate set of nodes per hop along the path in the mesh network. Thus any temporal channel fading and local interference conditions will not result in a failed transmissions due to utilization of the spatial diversity provided by OR. The usage of OR achieves a much higher E2E packet delivery rate as well as lower E2E delay as compared to traditional routing while the overhead is reasonable. Moreover, with OR the same signal modulation can be used network-wide and its adjustment can be made on a long-term basis.