As a compelling wireless networking technology for the Internet of Things, long-range wide area network (Lo-RaWAN) has been newly designed to exploit the 2.4 GHz unlicensed band instead of the traditional sub-GHz bands. However, this makes LoRaWAN frequently suffer from communication failures caused by the signal interference from coexisting Wi-Fi networks using the same 2.4 GHz band. To mitigate this problem, this paper presents a physical-layer solution to directly extract LoRaWAN data out of Wi-Fi interference. This is achieved by exploiting the correlation of the signal demodulation results between the preamble and the payload of a LoRa (the physical layer of LoRaWAN) signal. Experimental results show that in comparison with existing approaches, our proposed technique can achieve up to 83% reduction of LoRa packet error rate.