Interference Analysis for LoRa Chirp Spread Spectrum Signals

LoRa modulation is a modulation scheme patented by SemTech that uses chirp spread spectrum (CSS) signals to modulate data. This paper analyzes the interference between those signals for different spreading factors (SFs) and bandwidths (BWs). First, principles and properties of LoRa modulation and demodulation in discrete-time domain are presented, followed by theoretical analysis of the interference. Extensive simulation was performed to characterize the effect of interference on both detection signal-to-interference ratio (SIR) and the bit-error rate (BER) performance of the desired signals. Results demonstrate that the effect of interference is very serious if the desired and interfering signals have the same chirp rate (even though they might have different spreading factors and bandwidths), while it can be practically ignored for all other cases.