Chitchat: Efficient and Reliable Decoding of Two-Transmitter Superimposed Signals for IoT

The need for wireless communication is growing at an unprecedented pace, making the wireless spectrum at a premium. To use the spectrum more efficiently, a promising solution was proposed to enable two concurrent users to transmit their signals in the same frequency at the same time, and then decode the superimposed signal. In current systems, the superimposed signal is decoded by successive interference cancellation (SIC) that requires strict power control upon each individual user. However, this requirement is infeasible for many IoT devices that are heterogeneous and often low cost. For other superimposed signal decoding technologies that require no power control, a reliable performance can be only achieved by introducing repetitive information in each transmission, which, in turn, reduces the spectrum efficiency. In this article, we introduce Chitchat, a new solution to decode the superimposed signal from two concurrent transmitters without any power control nor repetitive transmissions. Chitchat presents a rotation-code-based idea to provide both the diversity gain and the coding gain, so that it can achieve high reliability while preserving the spectrum efficiency. We implement Chitchat on a software-defined radio platform, and evaluate its performance in various scenarios.