SWIPT Schemes for Carrier Index Differential Chaos Shift Keying Modulation: A New Look at the Inactive Carriers

In this paper, two carrier index differential chaos shift keying (CI-DCSK) with simultaneous wireless information and power transfer schemes, which integrate CI-DCSK modulation with wireless power transfer, are proposed. In the proposed schemes, based on the transmission characteristics of index modulation, the inactive carriers of CI-DCSK are exploited to deliver energy by transmitting random noise-like signals subjected to normal distribution. By applying time switching (TS) at the receiver, each frame time of the proposed schemes is divided into two intervals. Unlike usual TS-based systems, two intervals of the proposed schemes are related, where energy harvesting and decoding of the modulated bits are both operated in the second interval. Analytical bit error rate (BER) expressions over additive white Gaussian noise and multipath Rayleigh fading channels of the two schemes are derived. The expression for the parameter $\xi$ is also derived that measures the probability of self-sufficiency of these schemes. The impact of the dividing point of two intervals on BER performance of systems is also analyzed and optimized. Since the energy on the inactive carriers is adjustable, the schemes are always self-sustainable in energy supply. To provide the best performance, the ratio of energy on the inactive carriers to that on the active carriers is optimized. Simulation results show that though performances of the proposed schemes are a little worse than CI-DCSK with the same spectral efficiency, the proposed schemes are all self-sustainable.