Adaptive Latency Reduction in LoRa for Mission Critical Communications in Mines

Reliable communication is essential to alleviate incidents and escalate rescue operations. However, wireless communication is very challenging in underground mine due to irregular confined shapes and rough environments. A recent wireless standard LoRa (Long Range) is promising in mine environments because of its ultralow power consumption, long range, and deep penetration capabilities. In underground mine, sensors are deployed for continuous monitoring the working environments as well as tracking objects and miners. Therefore, different types of traffic are generated with different QoS requirements. LoRaWAN, the standardized medium access control (MAC) protocol is based on pure ALOHA that can not meet the requirements of mission-critical communications. The mission-critical applications require very low latency and high reliability. In this paper, we evaluate the performance of LoRa and LoRaWAN technologies in an underground mine in the presence of different kinds of traffic; and subsequently we propose redundant retransmission aided adaptive latency reduction protocol for low latency communication. In this protocol the ACK-TIMEOUT is adjusted based on the air time of the previous uplink transmission and the contention stage. Simulation results demonstrate that the proposed protocol significantly improves the performance of the system and outperforms LoRaWAN in terms of data extraction ratio (DER) and average transmission delay.