Combating interference for long range LoRa sensing

Wireless sensing has become a hot research topic recently, enabling a large range of applications. However, due to the intrinsic nature of employing weak target-reflection signal for sensing, the sensing range is limited. Another issue is the strong interference from surroundings and therefore a lot of wireless sensing systems assume there is no interferer in the environment. One recent work explored the possibility of employing LoRa signal for long range sensing which is a favorable step in addressing the first issue. However, the interference issue becomes even more severe with LoRa due to its larger sensing range. In this paper, we propose Sen-fence - a LoRa-based sensing system - to significantly increase the sensing range and at the same time mitigate the interference. With careful signal processing, Sen-fence is able to maximize the movement-induced signal variation in software to increase the sensing range. To address the interference issue, we propose the concept of "virtual fence" to constrain sensing only within the area of interest. The location and size of virtual fence can be flexibly controlled in software to meet the requirements of different applications. Sen-fence is able to (i) achieve a 50 m sensing range for fine-grained human respiration, which is twice the state-of-the-art; and (ii) efficiently mitigate the interference to make LoRa sensing work in practice.