Contender waveforms for Low-Power Wide-Area networks in a scheduled 4G OFDM framework

When designing new solutions for Low-Power Wide-Area (LPWA) networks, coexistence and integration into existing 4G frameworks should be considered to ease the deployment procedure and reduce costs. In a previous work, Turbo-FSK was proposed as a potential physical layer for LPWA networks. With its constant envelope and high energy efficiency, the scheme is a serious contender for this type of networks. We propose to study the system in the Orthogonal Frequency Division Multiplexing (OFDM) framework, currently used by existing cellular networks and also considered for the recently standardized Narrow-Band IoT (NB-IoT). Several extensions of the Turbo-FSK scheme are presented. A hybrid modulation alphabet, combining orthogonal with linear modulations, is introduced, and the substitution of Frequency Shift Keying (FSK) modulation for another orthogonal modulation based on Zadoff-Chu (ZC) sequences is considered. Simulations are run under various conditions including Rayleigh fading channel with mobility, demonstrating that the Turbo-FSK scheme is able to achieve performance close to the Turbo Coded Orthogonal Frequency Division Multiplexing (TC-OFDM) when a low rate is considered. When considering hybridation of the alphabet, limitations appear for higher data rate, which can be overcome by changing the orthogonal alphabet. The study of the variation of the envelope of the compared solutions emphasizes the crucial trade-off between performance and efficiency of the power amplifier (PA), a main concern for low-power applications. While using the proposed solutions, we demonstrate that energy consumption can be reduced by up to a factor of 2.5.