Ambient backscatter communication (AmBC) enables a passive backscatter deviceto transmit information to a reader using ambient RF signals, and has emergedas a promising solution to green Internet-of-Things (IoT). Conventional AmBCreceivers are interested in recovering the information from the ambientbackscatter device (A-BD) only. In this paper, we propose a cooperative AmBC(CABC) system in which the reader recovers information not only from the A-BD,but also from the RF source. We first establish the system model for the CABCsystem from spread spectrum and spectrum sharing perspectives. Then, for flatfading channels, we derive the optimal maximum-likelihood (ML) detector,suboptimal linear detectors as well as successive interference-cancellation(SIC) based detectors. For frequency-selective fading channels, the systemmodel for the CABC system over ambient orthogonal frequency divisionmultiplexing (OFDM) carriers is proposed, upon which a low-complexity optimalML detector is derived. For both kinds of channels, the bit-error-rate (BER)expressions for the proposed detectors are derived in closed forms. Finally,extensive numerical results have shown that, when the A-BD signal and theRF-source signal have equal symbol period, the proposed SIC-based detectors canachieve near-ML detection performance for typical application scenarios, andwhen the A-BD symbol period is longer than the RF-source symbol period, theexistence of backscattered signal in the CABC system can enhance the MLdetection performance of the RF-source signal, thanks to the beneficial effectof the backscatter link when the A-BD transmits at a lower rate than the RFsource.
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