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We propose a dual-mode (DM) time domain multiplexed (TDM) chirp spreadspectrum (CSS) modulation for spectral and energy-efficient low-power wide-areanetworks (LPWANs). DM-CSS modulation that uses both the even and odd cyclictime shifts has been proposed for LPWANs to achieve noteworthy performanceimprovement over classical counterparts. However, its spectral efficiency (SE)is half of the in-phase and quadrature (IQ)-TDM-CSS scheme that employs IQcomponents with both up and down chirps, resulting in a SE that is four timesrelative to Long Range (LoRa) modulation. Nevertheless, the IQ-TDM-CSS schemeonly allows coherent detection. Furthermore, it is also sensitive to carrierfrequency and phase offsets, making it less practical for low-costbattery-powered LPWANs for Internet-of-Things (IoT) applications. DM-CSS useseither an up-chirp or a down-chirp. DM-TDM-CSS consists of two chirped symbolsthat are multiplexed in the time domain. One of these symbols consisting ofeven and odd frequency shifts (FSs) is chirped using an up-chirp. The secondchirped symbol also consists of even and odd FSs, but they are chirped using adown-chirp. It shall be demonstrated that DM-TDM-CSS attains a maximumachievable SE close to IQ-TDM-CSS while also allowing both coherent andnon-coherent detection. Additionally, unlike IQ-TDM-CSS, DM-TDM-CSS is robustagainst carrier frequency and phase offsets.

Dual-Mode Time Domain Multiplexed Chirp Spread Spectrum