Channel Estimation for Ambient Backscatter Systems over Frequency-Selective Channels

Recently, ambient backscatter has attracted much attention since it enables battery-free devices to communicate with other devices by utilizing environmental radio frequency signals. Existing studies about ambient backscatter often assume flat fading channels. In fact, most practical channels are frequency-selective. Thus, in this paper, we consider the ambient backscatter communication systems over frequency-selective channels and focus on the problem of channel estimation. Specifically, we first adopt the least square (LS) algorithm to obtain the estimates of channel parameters when the tag is in different states. Next, an iterative estimator is proposed to improve the estimation performance. In addition, the Cramér-Rao Lower Bounds (CRLBs) for different channel parameters are derived to evaluate the mean square error (MSE) performance. Finally, simulation results are provided to corroborate the proposed studies.