  To improve the data rate in differential chaos shift keying (DCSK) based
ambient backscatter communication (AmBC) system, we propose a new AmBC system
based on code index modulation (CIM), referred to as CIM-DCSK-AmBC system. In
the proposed system, the CIM-DCSK signal transmitted in the direct link is used
as the radio frequency source of the backscatter link. The signal format in the
backscatter link is designed to increase the data rate as well as eliminate the
interference of the direct link signal. As such, the direct link signal and the
backscatter link signal can be received and demodulated simultaneously.
Moreover, we derive and validate the theoretical bit error rate (BER)
expressions of the CIM-DCSK-AmBC system over multipath Rayleigh fading
channels. Regarding the short reference DCSK-based AmBC (SR-DCSK-AmBC) system
as a benchmark system, numerical results reveal that the CIM-DCSK-AmBC system
can achieve better BER performance in the direct link and higher throughput in
the backscatter link than the benchmark system.
