Performance Analysis of Simultaneous Wireless Information and Power Transfer in MISO Systems

A scenario in which a multi-antenna access point (AP) transfers both information and power to a single-antenna user terminal (UT) is considered. The UT harvests energy from the received signals to perform operations such as channel estimation, uplink signaling, and data decoding. Differently from most state-of-the-art works on this subject, a non-zero power consumption for data decoding at the UT is considered. Three cases of practical interest are studied: 1) time-division duplex (TDD) communications, and imperfect channel state information (CSI) at the AP, 2) frequency-division duplex (FDD) communications, and imperfect CSI at the AP, 3) no explicit duplexing scheme and absence of CSI at the AP. Closed-form representations of the ergodic downlink rate, and analytic approximations of the optimal durations of power transfer and channel estimation/feedback phases are derived for the three cases. Numerical findings confirm the accuracy of the analytic results. The presence of CSI at the AP for both considered duplexing schemes, albeit imperfect and resource-demanding, brings significant performance enhancements in simultaneous wireless information and power transfer (SWIPT) systems. Furthermore, the TDD scheme consistently outperforms FDD scheme over practical signal-to-noise ratio (SNR) range, confirming the potential of this duplexing scheme for future energy efficient networks.