Recently, a number of experimental studies showed that concurrent transmissions can boost wireless network performance, despite collisions. While these practical works provide evidence that concurrent transmissions may be received reliably, the underlying mechanisms are not fully understood. This work studies packet collisions starting with their mathematical representations to analyze the effect of factors like power ratio, timing offset, and carrier phase offset. Our results show that the capture effect alone can result in poor reception performance. We extend our model to study the effect of direct sequence spread spectrum (DSSS) with IEEE 802.15.4 as an example. With DSSS, we observe a reception ratio of over 90% in the model, complying with existing studies. We further experimentally validate our model on two widely used receivers (CC2420, AT86RF230), observing a good fit between analysis and experiments. Our model provides insights that help to improve existing and future protocols exploiting concurrent transmissions.
The code for simulations and some figures is available at GitHub: github.com/mwil/collision