Effect of opportunistic scheduling on the efficiency of wireless power transfer

Far-field wireless power transfer (WPT) is a promising technique to resolve the painstaking power-charging of wireless user terminals (UTs). However, the main issue hindering the implementation of this technique in practice is its limited efficiency. This paper aims to improve WPT efficiency in terms of the time-average direct current (DC) output power at UTs in support of simultaneous data and power transfer. In particular, the power scaling law when opportunistic scheduling strategy is performed among N UTs is analytically attained, by using the extreme value theory. Our results reveal that, the opportunistic technique has a scheduling gain of N times that of the round-robin scheduling policy, thereby improving the power transfer efficiency significantly.