  To enhance the reliability of LoRa sensor networks, we propose two
opportunistic forwarding protocols in which relays overhear sensor-to-gateway
messages and periodically forward them to a gateway. To reduce the number of
transmissions, the relays forward XOR sums of the overheard messages. One
protocol employs a single relay node, while two relays cooperate in the other.
With a single relay, our proposed protocol requires fewer relay transmissions
to achieve similar loss rates as conventional uncoded forwarding in which every
received message is immediately forwarded. We demonstrate up to 55% reduction
in relay transmission time relative to uncoded forwarding. The cooperative
protocol provides better loss and delay performance than the single-relay
protocol, and we demonstrate up to 16% reduction in the message-loss rate along
with 33% reduction in relay transmission times compared to conventional
forwarding.
