Exact Performance of Wireless-Powered Communications with Maximum Ratio Combining

We consider a single-antenna power transmitter (PT), a single-antenna information transmitter (IT) and a multiple-antenna information receiver (IR). The IT is autonomous without an energy source, and thus uses harvest-and-transmit protocol. It first harvests energy from the signals of the PT, and then uses all harvested energy for information transmission to the IR. For Nakagami-m fading channels, we analyze the system performance rigorously. In particular, we derive the exact probability density function of the end-to-end signal-to-noise-ratio (SNR), outage probability, bit error rate and ergodic channel capacity. Moreover, asymptotic ergodic capacity results are also provided at the high SNR regime. We find that the performance of a WPT link falls far short of that of one with a power supply. However, this gap can be narrowed by employing the spatial diversity at the receiver. Additionally, findings showed that the existence of a line-of-sight link between the power transmitter and the energy-harvesting unit increases the amount of harvested energy significantly.