Joint Channel, Carrier Frequency Offset and I/Q Imbalance Estimation in Ambient Backscatter Communication Systems

Ambient backscatter communication systems (ABCSs) have been gaining popularity as a green alternative to conventional communication systems. To deploy such systems, it is important to acquire the channel state information (CSI) and to account for hardware imperfections such as carrier-frequency offsets (CFOs) and inphase/quadrature (I/Q) imbalance. In this work, we present two algorithms for the joint estimation of the channel, CFO and I/Q imbalance at the receivers of ABSCs. The first algorithm is the pilot-based maximum-likelihood estimator, while the second is a semi-blind estimator based on the expectation maximization (EM) framework. While both estimators converge to their respective Cramer-Rao bounds, the EM algorithm provides significantly higher estimation accuracy, leading to better bandwidth utilization.