ELORA: Even Longer Range Sensor Networking Through Modulated Concurrent LoRa Transmissions.

LoRa is a widely used physical layer for Low Power Wide Area Networks (LPWANs). Its comparably low data rates still suffice for many IoT applications, while communication ranges of several kilometers can be accomplished. Due to their wireless nature, LoRa data transmissions become unreliable when the distance between sender and receiver approaches the limit at which the signal-to-noise ratio falls below the receiver's sensitivity. Furthermore, reliability can also be hampered by rough environmental conditions, like heavy rain or high humidity levels, both of which can have attenuating effects on the wireless signal propagation. While the Forward Error Correction in LoRa can compensate for sporadic bit errors, its overall efficacy is limited. To prevent data loss even in adverse weather conditions, alternative methods need to be found to maintain the reliability of communications. One such approach is the use of Constructive Interference, i.e., the concurrent transmission of identical LoRa packets by multiple transmitting stations. As the required clock synchronization is hard to accomplish, however, fully constructive LoRa data transmissions are virtually impossible in practice. In this paper, we hence present two modulation techniques (based on On-Off Keying and Pulse Width Modulation) that take advantage of constructive interference periods occurring in concurrent transmissions to increase the range and thus make a Wireless Sensor Network better usable in emergency scenarios. We present their implementation on actual LoRa transceivers and analyze the resulting signal's characteristics. Our first experimental results prove the viability of our concept, and show that data can be modulated and demodulated without the knowledge of the actual LoRa message.