In this paper, we study THz simultaneous wireless information and power transfer (SWIPT) systems. Since coherent information detection is challenging at THz frequencies and Schottky diodes may not be efficient for THz energy harvesting (EH) and information detection, we employ unipolar amplitude shift keying (ASK) modulation at the transmitter (TX) and a resonant tunnelling diode (RTD)-based EH circuit at the receiver (RX) to extract both information and power from the RX signal. We model the dependence of the instantaneous output power at the RX on the instantaneous received power by a non-linear piecewise function, whose parameters are adjusted to fit circuit simulation results. To determine the rate-power tradeoff in THz SWIPT systems, we derive the distribution of the TX signal that maximizes the mutual information between the TX and RX signals subject to constraints on the required average harvested power at the RX and the peak signal amplitude at the TX. Since the computational complexity of maximizing the mutual information may be too high for real-time THz SWIPT systems, for high and low required average harvested powers, we also obtain the suboptimal input signal distribution that maximizes the achievable information rate numerically and in closed form, respectively. Furthermore, based on the obtained results, we propose a suboptimal closed-form TX distribution which also achieves a desired harvested power at the RX. Our simulation results show that a lower reverse current flow and a higher breakdown voltage of the employed RTD are preferable when the input signal power at the RX is low and high, respectively. Finally, we demonstrate that for low and high received signal powers, the rate-power tradeoff of THz SWIPT systems is determined by the peak amplitude of the TX signal and the maximum instantaneous harvested power, respectively.

翻译：本文研究太赫兹同时无线信息与功率传输(SWIPT)系统。由于太赫兹频段下相干信息检测具有挑战性，且肖特基二极管在太赫兹能量收集(EH)与信息检测中效率有限，我们采用发射端(TX)单极性幅移键控(ASK)调制与接收端(RX)基于共振隧穿二极管(RTD)的能量收集电路，从接收信号中同时提取信息与功率。通过非线性分段函数建模接收端瞬时输出功率对瞬时接收功率的依赖关系，并调整函数参数以拟合电路仿真结果。为确定太赫兹SWIPT系统的速率-功率权衡，我们推导了在满足接收端所需平均收集功率与发射端峰值信号幅度约束条件下，最大化发射端与接收端信号互信息的发射信号分布。考虑到互信息最大化的计算复杂度对实时太赫兹SWIPT系统可能过高，针对高、低所需平均收集功率场景，我们分别通过数值计算与闭式解析形式获得可达到信息速率次优的输入信号分布。基于所得结果进一步提出一种次优闭式发射分布，该分布同样能实现接收端的目标收集功率。仿真结果表明：当接收端输入信号功率较低时，优先选用反向漏电流较小的RTD；当输入信号功率较高时，优先选用击穿电压更高的RTD。最后证明：在低接收信号功率与高接收信号功率场景下，太赫兹SWIPT系统的速率-功率权衡分别由发射端峰值幅度与最大瞬时收集功率主导。