Maintaining Constructive Interference Using Well-Synchronized Sensor Nodes

Traditionally, achieving constructive interference (CI) required specialized timekeeping hardware. Recently, the ability and interest to employ CI distributedly at any time using groups of ordinary single antenna wireless sensor nodes have grown. In this paper, we investigate achieving CI on sensor nodes. We consider the commonly employed IEEE 802.15.4 wireless standard, which uses a chip frequency of 1 MHz. This means signals need to be synchronized with an error below 0.5 microseconds to allow for CI. Hence, excellent clock synchronization between nodes as well as precise transmission timing are required. We implemented and tested a prototype addressing the implementation challenges of synchronizing the nodes' clocks up to a precision of a few hundred nanoseconds and of timing transmissions as accurately as possible. Our results show that, even after multiple minutes of sleep, our approach is able to achieve CI in over 30% of cases, in scenarios in which any influence from the capture effect can be ruled out. This leads to an increase in a packet's chance of arrival to 30-65%, compared to 0-30% when transmitting with either less synchrony or different data payload. Further, we find that 2 senders generally increase the signal power by 2-3 dB and can double the packet reception ratio of weak links.