What is CSS (chirp spread spectrum)?

Chirp spread spectrum (CSS) utilizes wideband linear frequency modulated chirp pulses to encode data. A chirp is a sinusoidal signal whose frequency increments or diminishes over time. Chirp spread spectrum was initially intended to compete with ultra-wideband for precision ranging and low-rate wireless networks in the 2.45 GHz band. Chip spread is required for low power usage and low data rate applications.