Demodulator design for collaborative signal reinforcement in sensor networks

Nodes in sensor fields and in autonomous swarms of mobile robots need to communicate; this usually requires individual nodes to either consume a significant amount of energy, carefully position themselves, precisely align carrier phase, or use complex coding. The paper proposes allowing multiple independent and mobile wireless transmitters to share the power-consumption burden by combining low-power transmissions into a unified higher-power transmission. This is not a distributed beamforming or space-time coding approach. Instead, all nodes simultaneously broadcast the same symbol on the same channel without using different code books and without aligning carriers. This paper briefly describes a modulation scheme (random-phase frequency shift keying, RPFSK), a synchronization scheme (Ensemble), and a node selection scheme which make this possible. It then describes an RPFSK demodulator design in detail for Ensemble nodes. It also covers both baseband and over-the-air test results.