Non-Linear Far Field RF Harvesting in Wireless Communications

A linear radio frequency (RF) harvesting model is commonly assumed in recent simultaneous wireless information and power transfer (SWIPT) research, i.e., RF harvested power is assumed a scaled version of the input (received) power. However, rectifiers typically used in the microwave and radio frequency identification (RFID) industry are non-linear devices; thus, RF harvesting efficiency is not constant but depends on the input power. This work first reviews far field RF harvesting and then models RF harvested power as an arbitrary non-linear, continuous, and non-decreasing function of received power, taking into account sensitivity and saturation effects. Given such model, probability density and cumulative distribution functions of the harvested RF power are offered, based on a piece-wise linear approximation, in conjunction with accuracy analysis. Three example scenarios are considered, including duty-cycled (non-continuous), as well as continuous SWIPT, comparing linear with industry-level nonlinear RF harvesting. It is demonstrated that the proposed methodology, even though simple, offers exact performance for all studied metrics. On the other hand, linear harvesting modeling results deviate from reality, and in some cases are off by one order of magnitude. The proposed modeling and methodology can be utilized in current and future SWIPT research.