Symmetry Chirp Modulation Waveform Design for LEO Satellite IoT Communication

Interconnectivity between systems through Internet of Things (IoT) is gaining popularity around the world. Application of chirp signal modulation, a key technique for enabling the LoRa (Long Range) communication, for low-earth-orbit (LEO) satellite IoT communication application has been explored recently where symmetry chirp (SC) type waveforms are used for low data rate communication. In this letter, we analyze the cross-correlation performance of SC waveforms for applications in multiuser systems. To improve the overall cross-correlation level between SC waveforms, we propose a new chirp design, namely symmetry chirp with multiple chirp rates (SC-MCR) for LEO satellite communication. Analytical expressions of cross-correlation and autocorrelation for the proposed SC-MCR waveforms are derived. In addition, the design of time domain multiplexed SC-MCR waveforms is presented to improve the system data rate. Symbol error rate of an M-ary system using SC-MCR waveforms in a multiuser scenario is evaluated considering a Rice-lognormal satellite channel model and the results indicate improved multiple access interference performance of SC-MCR waveforms as compared to SC waveforms.