M-Ary Aggregate Spread Pulse Modulation With Pulse-Shaping Power Control for Highly Scalable LPWANs

Abstract

M-ary Aggregate Spread Pulse Modulation (M-ASPM) is the physical layer (PHY) modulation technique that is well suited for use in low-power wide-area networks (LPWANs). Notably, M-ASPM combines high energy-per-bit efficiency, robustness, resistance to interference, and a number of other favorable technical characteristics, with the spread-spectrum ability to maintain the capacity of an uplink-focused network while extending its range. However, when all M-ASPM nodes transmit with the same average power, implementation of such capacity-preserving range extension may become impractical in complicated propagation environments with greatly varying path losses. Favorably, the efficiency of M-ASPM with constant-envelope pulses can be maintained effectively the same as the efficiency of transmitting a continuous constant-envelope waveform. Then the transmit power of different nodes can be adjusted, without sacrificing the transmission efficiency, to compensate for differences in the path attenuation. This enables us to significantly simplify planning and management of the network. In addition, such a variable-power approach generally increases the network capacity and the average energy efficiency of the nodes, as compared with the arrangement of the nodes with a constant transmit power. In this paper, we outline a practical approach to implementing such an energy-efficient M-ASPM power control, that can be used for scaling LPWANs with realistic desired and/or actual areal distributions of the uplink nodes under diverse propagation conditions.