Channel capacity and lower bound for ambient backscatter communication systems

Ambient backscatter is an emerging technology that utilizes the surrounding radio frequency (RF) signals such as digital digital television (TV) broadcasting, cellular or Wireless-Fidelity (Wi-Fi) to enable batteryless devices to communicate with each other. One open problem for ambient backscatter is channel capacity. In this paper, we investigate the capacity problem of an ambient backscatter communication system with a passive tag and a reader. Based on the Gaussian channel model, we design a method to determine channel capacity for the ambient backscatter communication system. The channel capacity is the maximal value of the derived mutual information. Interestingly, we find that the capacity for the ambient backscatter communication system is obtained when the input signals are not equiprobable. Finally, numerical results are provided to corroborate our theoretical analysis.