WiChronos: energy-efficient modulation for long-range, large-scale wireless networks

Wireless communication over long distances has become the bottleneck for battery-powered, large-scale deployments. Currently used low-power protocols such as Zigbee and Bluetooth Low Energy have limited communication range, whereas long-range communication strategies used in cellular and satellite networks are heavy on energy consumption. Methods that use narrow-band communication such as LoRa, SigFox, and NB-IoT have low spectral efficiency, leading to scalability issues. The goal of this work is to develop a communication framework that can satisfy the following requirements: (1) Increased battery life, (2) Longer communication range, (3) Scalability in a wireless network. In this work, we propose, design, and prototype WiChronos, a communication paradigm that encodes information in the time interval between two narrowband symbols in order to drastically reduce the energy consumption in a wide area network with a large number of senders. We leverage the low data-rate and relaxed latency requirements of such applications to achieve the desired features identified above. Based on our prototype using off-the-shelf components, WiChronos achieves an impressive 60% improvement in battery life compared to state-of-the-art LPWAN technologies at distances of over 800 meters. We also show that more than 1000 WiChronos senders can co-exist with less than 5% probability of collisions under low traffic conditions.