FRFT-Based Interference Suppression for OFDM Systems in IoT Environment

The OFDM technology has been widely used in 4G, 5G, and other wireless communication systems for its anti-frequency selective fading and high spectral efficiency. However, OFDM systems are very sensitive to narrowband interference (NBI). There are many existing NBI suppression algorithms for OFDM systems. Unfortunately, in these existing algorithms, the NBI is typically modeled as a sinusoidal signal. With the widespread use of LoRa, which is one of the most imposing IoT technologies, the sinusoidal interference model is unreasonable since LoRa adopts non-stationary chirp signals. Toward this end, we study LoRa interference suppression for OFDM Systems (IEEE 802.11ah). First, we derive the analytical expression of LoRa signal in the fractional Fourier transform (FRFT) domain. Then, we present the principle and procedure of the proposed FRFT-domain interference suppression algorithm for OFDM systems interfered by LoRa. Simulation results show that the proposed FRFT-domain algorithm can significantly improve the BER performance of OFDM systems interfered by LoRa at different signal to interference ratios, compared with the frequency-domain algorithm.