Dual-Use Chirp Spread Spectrum Waveform With Ranging Capability

Chirp Spread Spectrum (CSS) is modeled after frequency-hopping spread spectrum and adopted by the LPWAN (Low Power Wide Area Network) standard. Designated as IEEE 802.15.4a, it is suited to applications requiring low power and low data rates. The use of chirps as the basic building blocks provides opportunities to adapt the waveform to radar applications. The information bearing signal in each hop is encoded as the sum of overlapping, orthogonal and circularly shifted chirps. Each chirp carries one bit with each hop carrying multiple chirps simultaneously. The composite waveform is detected by the receiver using a bank of dechirpers, each tuned to a separate chirp. The orthogonality property of the dechirping detector is used to allow the receiver to detect and decode the embedded chirps without crossterm interference. Target returns are detected by an adaptive dechirp detector, allowing dual-use.